La Metallurgia Italiana, n.7/8 Luglio-agosto 2022

La

Metallurgia Italiana

International Journal of the Italian Association for Metallurgy

n. 7/8 luglio-agosto 2022 Organo ufficiale dell’Associazione Italiana di Metallurgia.

Rivista fondata nel 1909

La Metallurgia Italiana International Journal of the Italian Association for Metallurgy Organo ufficiale dell’Associazione Italiana di Metallurgia.

House organ of AIM Italian Association for Metallurgy.

Rivista fondata nel 1909

Direttore responsabile/Chief editor: Mario Cusolito Direttore vicario/Deputy director: Gianangelo Camona Comitato scientifico/Editorial panel: Marco Actis Grande, Silvia Barella, Paola Bassani, Christian Bernhard, Massimiliano Bestetti, Wolfgang Bleck, Franco Bonollo, Irene Calliari, Mariano Enrique Castrodeza, Emanuela Cerri, Vlatislav Deev, Andrea Di Schino, Donato Firrao, Bernd Kleimt, Carlo Mapelli, Denis Jean Mithieux, Roberto Montanari, Marco Ormellese, Mariapia Pedeferri, Massimo Pellizzari, Barbara Previtali, Evgeny S. Prusov, Dario Ripamonti, Dieter Senk Segreteria di redazione/Editorial secretary: Marta Verderi Comitato di redazione/Editorial committee: Federica Bassani, Gianangelo Camona, Mario Cusolito, Carlo Mapelli, Federico Mazzolari, Marta Verderi, Silvano Panza Direzione e redazione/Editorial and executive office: AIM - Via F. Turati 8 - 20121 Milano tel. 02 76 02 11 32 - fax 02 76 02 05 51 met@aimnet.it - www.aimnet.it Immagine in copertina: Shutterstock

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La

Metallurgia Italiana

International Journal of the Italian Association for Metallurgy

n. 07 luglio 2022 Organo ufficiale dell’Associazione Italiana di Metallurgia.

Rivista fondata nel 1909

Editoriale / Editorial

Inox e duplex protagonisti a Bardolino

A cura di Ing. Sandro Fraccia.............................................................................................................. pag.04

Memorie scientifiche / Scientific papers Acciai Inossidabili / Stainless Steels

Enhancement of ductility of work hardened strips in AISI 301 austenitic stainless steel

G. Di Egidio.......................................................................................................................................... pag.07

n.7/8 luglio-agosto 2022

Anno 113 - ISSN 0026-0843

The effect of hot rolling and coiling temperature on microstructure and texture of ferritic stainless steel

A. Kisko, A. Kaijalainen, L. Kurtti, S. Kodukula, T. Ylimäinen................................................................ pag.16

Thermodynamic property of hydrogen in molten stainless steel

J.Y. Kim, H.R. Lee, I.H. Kwon, Y. Kang................................................................................................................. pag.24

Selective laser melting manufacturing of stainless steels: heat treatment effect on microstructure and hardness in maraging steels G. Stornelli, D. Gaggia, M. Gaggiotti, M. Rallini, A. Di Schino ........................................................................ pag.28

indice

Laser OES - How an efficient melt shop monitoring tool tackles increasing energy and raw material costs A. Schlemminger................................................................................................................................................... pag.38

Attualità industriale / Industry news Technologies paving the way to carbon neutral stainless steel production

edited by: J. von Schéele, H. Alshawarghi, D. Razzari.................................................................................... pag.49

Atti e notizie / AIM news Eventi AIM / AIM events ....................................................................................... pag.59 Comitati tecnici / Study groups ............................................................................. pag.61 Normativa / Standards ........................................................................................... pag.62

editoriale - editorial

“

“Hanno partecipato più di 120 relatori e delegati da 20 paesi, provenienti dall’industria, dall’università e dalle associazioni europee e mondiali.”

"More than 120 speakers and delegates from 20 countries from industry, academia, and European and world associations participated".

Ing. Sandro Fraccia

INOX E DUPLEX PROTAGONISTI A BARDOLINO

STAINLESS STEELS AND DUPLEX ON STAGE IN BARDOLINO

Cari Lettori,

Dear Readers, edizioni

following the success of the previous Conferences,

precedenti, in particolare dopo l’ultima tenutasi a Vienna

particularly after the last one held in Vienna in 2019, AIM,

nel 2019, è stata organizzata dalla AIM, l’Associazione

the Italian Association for Metallurgy, organised the

Italiana di Metallurgia, l’undicesima European Stainless

eleventh European Stainless Steel Conference Science

Steel Conference Science & Market insieme alla

& Market together with the seventh European Duplex

settima European Duplex Stainless Steel Conference &

Stainless Steel Conference & Exhibition.

A

seguito

del

successo

ottenuto

nelle

Exhibition.

The international event, in which I had the honor and L’evento, di carattere internazionale, al quale ho avuto

pleasure of participating, as Chairman of the Organizing

l’onore e il piacere di partecipare, in qualità di Presidente

Committee, was held, in English, on Lake Garda in

del Comitato Organizzativo, si è svolto, in lingua inglese,

Bardolino at the Hotel Caesius conference center on

sul lago di Garda a Bardolino presso il centro congressi

June 15th,16th and 17th, 2022.

dell’Hotel Caesius In tre giornate 15-16-17 giugno scorsi.

More than 120 speakers and delegates from 20

Hanno partecipato più di 120 relatori e delegati da 20

countries from industry, academia, and European and

paesi, provenienti dall’industria, dall’università e dalle

world associations participated. Over 50 papers were

associazioni europee e mondiali. Sono stati presentati

presented in one session.

La Metallurgia Italiana - Luglio-Agosto 2022

pagina 4

editoriale - editorial

più di 50 lavori in un’unica sessione.

As for contents, various aspects concerning research, development, production, technology and corrosion

Quanto ai contenuti, sono stati esposti e discussi diversi

resistance of stainless and duplex stainless steels were

aspetti riguardanti la ricerca, lo sviluppo, la produzione,

exposed and discussed.

la tecnologia e la resistenza alla corrosione dell’acciaio inossidabile e duplex.

The results arising from this meeting highlighted the existing and potential application aspects of stainless

I risultati derivanti da questo incontro hanno messo

steel and laid out a guide for its future development.

in evidenza gli aspetti applicativi esistenti e potenziali dell’acciaio inossidabile e ne hanno tracciato una guida per lo sviluppo futuro.

The conference also featured an interesting section regarding the current situation of the stainless and

Nel corso della Conferenza ha trovato spazio anche

duplex steel market, possible expectations and future

un’interessante sezione riguardante la situazione attuale

trends, with the participation of Siderweb and Centro

del mercato dell’acciaio inox e duplex, le possibili

Inox.

aspettative e gli andamenti futuri, con la partecipazione di Siderweb e Centro Inox.

In this issue of "La Metallurgia Italiana" you will find available some of the papers presented during the

In questo numero de “La Metallurgia Italiana” trovate

Conference.

disponibile alcuni lavori presentati nel corso della Conferenza.

Enjoy reading

Buona lettura

La Metallurgia Italiana - July-August 2022

pagina 5

Padova, 21-23 settembre 2022 www.aimnet.it/nazionaleaim Manca poco alla 39 a edizione del Convegno Nazionale AIM! Il Convegno, con oltre 170 lavori suddivisi in sessioni tematiche, si conferma la principale iniziativa di riferimento nazionale per le aziende e tutte le figure professionali appartenenti al comparto metallurgico.

Con questa edizione il Convegno acquista un particolare significato alla luce della ripresa post-pandemica e del ruolo sempre più strategico e trasversale che le discipline metallurgiche giocano nell’ambito della transizione ecologica, della mobilità sostenibile, dell’economia circolare, delle performance sempre più elevate richieste a qualsiasi componente meccanico.

Il programma completo e tutte le informazioni per prendere parte all’evento sono disponibili sul sito: www.aimnet.it/nazionaleaim

Organizzato da

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Sponsorizzato da

in collaborazione con

Scientific papers - Stainless Steels

Enhancement of ductility of work hardened strips in AISI 301 austenitic stainless steel D. Montepagano, I. Citi, R. Guerra, P.E. Di Nunzio, F. Ruffini

During plastic deformation metastable austenitic stainless steels undergo a partial transformation from the initial face-centred-cubic austenite phase (γ) to the body-centred-tetragonal martensite (α’), commonly referred to as strain-induced martensite. The martensitic transformation enhances their work hardening capability and allows to obtain engineering materials with high strength and good corrosion resistance (typical of the austenitic stainless steels). These properties make them very attractive for a wide range of applications especially in the automotive and electronic sectors where the components are produced by forming and bending the strips into various shapes. For these specific applications a good ductility is also required besides the high mechanical properties. In this paper, the effect of chemical composition and processing conditions of a work-hardened stainless-steel strip of EN 1.4310 (AISI 301 type) has been studied. Each factor has been analysed both separately and in combination with the others. The role of chemical composition on the formation of strain-induced martensite formation has been evaluated by means of the Md30 temperature. Likewise, the effect of intermediate annealing treatments has been investigated by varying the temperature and the furnace atmosphere (N2 or H2). All the specimens have been qualified by tensile tests, measurement of the volume fraction of strain-induced martensite and bending tests. The most suitable and effective industrial production cycle for obtaining work hardened flat products with an aimed minimum ductility has been defined.

KEYWORDS: AUSTENITIC STAINLESS STEEL, WORK-HARDENED STATE, STRAIN-INDUCED MARTENSITE, DUCTILITY; INTRODUCTION Austenitic stainless steels are widely used in the automotive industry because they provide a combination of high mechanical strength and excellent formability, thus allowing a reduction of vehicle weight and consequently of CO2 emissions.

Flat products made of austenitic steel EN 1.4310 (type AISI 301) are commonly requested in work-hardened condition.

In fact, the chemical composition of this grade promotes the formation of strain-induced martensite during the cold working processes resulting in a consequent high increase of the mechanical properties. Therefore, strips of this material are obtained by a cold rolling process and used in a

D. Montepagano, I. Citi Arinox SpA (Italy)

davide.montepagano@arinox.arvedi.it; iacopo.citi@arinox.arvedi.it

R. Guerra, P.E. Di Nunzio, F. Ruffini Rina Consulting Centro Sviluppo Materiali S.p.A. (Italy)

wide range of industry sectors because of their good corrosion resistance and mechanical characteristics. Most of these applications are related to the production of parts and components which need a high spring effect; for example, in the automotive industry the temper rolled strips are used for producing several items such as strip springs for instru-

La Metallurgia Italiana - July-August 2022

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Memorie scientifiche - Acciai Inossidabili

ments, car lighting components, hose clamps, anti-noise

sly if γSFE lies between 15 and 20 mJ/m2.

shims for the braking system and many others. They are also

For example, Shen et al. have reported that in the austeni-

widely used in the electronic industry (electrical contacts,

tic grades 304 (γSFE=18 mJ/m2) and 301 (γSFE=14.7 mJ/m2),

fine components etc…) as well as in the civil sectors (springs

ε, α’ and twinning operate at different strains. In particuar,

for furniture and windows, kitchen tools, paper clips etc..).

ε martensite and twinning act as intermediate phases in the

However, in some of these cases, the steel strip is pressed

transformation from γ to α’ martensite [1, 2].

and bent in very complicated shapes and its high strength

Besides the enhancement of tensile properties, it has to be

must be combined also with a good ductility. For this rea-

considered that the existence of α’ martensite is closely re-

son, the manufacturers, beside the tensile strength, often

lated to the hydrogen induced embrittlement of metastable

require the bending resistance to avoid the cracks during

CrNi austenitic steels. The formation of α’ martensite is ac-

forming.

companied by a change of the diffusion conditions of hy-

This paper is focused on the production of cold rolled ultra

drogen atoms within the body-centred cubic (bcc) lattice

thin precision strips in the thickness 0.25 mm. The process

structure [3]. Hydrogen embrittlement is a knwown pheno-

flow typically consists of a first rolling to an intermediate

menon in materials with high mechanical properties and can

thickness, a bright annealing treatment and a final rolling to

cause fracture initiation that is responsible of various macro-

achieve the required thickness. The resulting mechanical

scopic consequences and in particular of the reduction of

properties of the work hardened product are affected by the

ductility [4].

chemical composition, as well as by the production process

The tendency towards the formation of the strain induced

conditions: thickness reduction percentage, cold rolling

α’ martensite is mainly dependent on chemical composition

practice and annealing parameters mainly.

and deformation temperature. Other factors that can affect

The aim of this study is to evaluate not only the effect of each

the extent of transformation are plastic strain, strain rate,

factor on the mechanical characteristics but also to define

stress state, and grain size. The transformation results in an

how they can be adjusted to obtain a material with same

increased strength, because martensite is stronger than au-

strength and enhanced ductility and, at the same time, to

stenite and, at the same time, it can increase the ductility if

improve the bending resistance required in the production

it occurs rapidly, just prior to the formation of severe strain

of specific components.

accumulation. Transformation from austenite to martensite

Mechanical properties of austenitic stainless steels depend

can also occur by two other mechanisms such as spontane-

strongly on the stability of the austenite matrix. High stren-

ous transformation at low temperatures and stress-assisted

gth, ductility and toughness can be achieved via the TRIP

nucleation.

(transformation induced plasticity) or TWIP (twinning in-

Spontaneous transformation occurs when the material is

duced plasticity) effects where, respectively, strain induced

cooled below the martensite start temperature (Ms) as in

martensite and mechanical twinning form as a consequen-

conventional steels. Slightly above the Ms, stress-assisted

ce of additional strain. The occurrence of these mechani-

martensite can form in response to an applied elastic stress.

sms depends on the stacking fault energy (γSFE), the initial

The temperature above which strain-induced martensite is

microstructure and the deformation conditions [1,2]. The

not produced by plastic deformation is referred to as Md.

martensitic transformation from austenite (γ) to hexagonal

The susceptibility of an alloy to strain-induced transforma-

ε martensite and/or α’ martensite occurs if γSFE is typically

tion depends on the stability of austenite.

below 20 mJ/m , whereas mechanical twinning is promoted

Nohara et al. (1977) proposed to describe the Md30 tempe-

if the stacking fault energy lies between 15 and 30 mJ/m . It

rature of Cr-Ni steels by the following equation:

2

2

has been reported that these structures form simultaneou-

[1]

La Metallurgia Italiana - Luglio-Agosto 2022

pagina 8

Scientific papers - Stainless Steels

where all the concentrations are expressed in mass percent.

302 are less stable than 304, 305, and 309 [5-9].

The Md30 is defined as the temperature at which an amount of 50% austenite is transformed into martensite by a cold-de-

MATERIAL AND METHODS

formation with true strain equal to 0.30. Equation [1] indica-

In this work, a selected set of specimens of the austenitic

tes that interstitially dissolved elements, such as C and N, are

grade EN 1.4310 (see Tab.1), has been analyzed in order to:

particularly strong austenite stabilizers.

• assess the effect of chemical composition, intermediate

A reduction of the temperature increases the thermodyna-

annealing parameters and final cold rolling reduction on

mic driving force for the martensite formation and leads to

mechanical properties of the steel in the work hardened

a higher martensite transformation rate during shaping. Mo-

state;

reover, as temperature decreases, the stacking fault energy

• define the required conditions for the production of she-

reduces, thus promoting a higher martensite formation.

ets combining a tensile strength complying with the C1300

Generally speaking, the austenitic grades with lower alloy

level (1300 MPa<Rm<1500 MPa) and a good ductility.

content are found to be less stable. For example, 301 and Tab.1 – Chemical composition of the austentic grade EN 1.4310 according to EN 10088-2 standard.

Steel Grade

EN 1.4310

C (%) Min

0.05

Max

0.15

Mn (%)

2.0

Cr (%)

Ni (%)

16.0

6.0

19.0

9.5

N (%)

0.10

The list of the analysed specimens together with the corresponding Md30 temperature and processing conditions is reported in Tab. 2.

Tab. 2 - Analysed specimens.

Specimen ID 1 2 3 4 5 6

Analysed parameter

Chemical composition

Annealing time

Annealing atmosphere

Atmosphere

Temperature (°C)

Time (s)

Cold Rolling reduction (%)

29

N2

1060

39

22

21

N2

1060

39

22

30

N2

1060

26

22

30

N2

1060

39

22

30

N2

1100

39

22

30

N2

1100

39

22

Md30 (°C)

Intermediate annealing treatment

7

Post treatment (after intermediate annealing)

30

N2

1060

39

22

8

Post treatment (after final cold rolling)

30

N2

1060

39

22

30

N2

1060

39

26

28

N2

1060

39

19

30

N2

1040

32

19

30

N2

1040

54

29

9 10 11 12

Cold Reduction

Temperature+Cold Reduction +Annealing time

La Metallurgia Italiana - July-August 2022

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Memorie scientifiche - Acciai Inossidabili

All samples have been analysed in the work-hardened state

rection.

and qualified by means of: • Tensile tests;

Contact bending tests at 180° have been performed on

• Measurement of the volume fraction of martensite (ferri-

specimens taken parallel to the rolling direction. Bent spe-

toscope);

cimens have been observed by a stereomicroscope (50X).

• Bending tests.

The test is considered passed if no heavy cracks are present.

The acceptance criterion is based on the comparison of the

Tensile tests have been carried out according to ISO 6892-

specimen surface after bending with the reference images

1 standard by means of Zwick Roell Z050 testing machine

shown in Fig. 1.

using dog bone specimens, taken parallel to the rolling di-

Fig.1 – Reference images for bending test evaluation (stereomicroscope, 50X magnification).

The volume fraction of strain induced martensite has been

ASTM E3 standard by means of a Nikon Metaphot Optical

evaluated by means of a Helmut-Fischer ferritscope, whi-

Microscope. Specimens have been observed in longitudinal

ch measures the content of magnetic phases (δ‑ferrite and

sections, mechanically polished and electrolytically etched

strain‑induced martensite) in austenitic and duplex steels

in a nitric-hydrochloric acid solution.

according to the magnetic induction method.

RESULTS In order to asses the effectiveness of the intermediate an-

The results of tensile tests, martensite fraction and bending

nealing, selected specimens have been characterised in the

tests of the studied samples are shown in Tab. 3, together

annealed state by optical microscope (OM) analysis. The

with the corresponding values of the calculated Md30 tempe-

microstructure analysis has been carried out according to

rature.

La Metallurgia Italiana - Luglio-Agosto 2022

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Scientific papers - Stainless Steels

Tab. 3 - Mechanical properties, volume fraction of martensite and bending test of the analysed specimens.

Specimen ID

Md30 (°C)

1

Intermediate annealing treatment

Cold Rolling reduction (%)

Rp0.2 (MPa)

Rm (MPa)

Strain induced Martensite (vol.%)

Bending test

1078

1368

5.9

Fine cracks

Atmosphere

Temperature (°C)

Time (s)

29

N2

1060

39

2

21

N2

1060

39

1141

1360

6.4

Heavy cracks

3

30

N2

1060

26

1144

1417

10.1

Heavy cracks

1036

1340

5.2

Heavy cracks

22

22 4

30

N2

1060

39

5

30

N2

1100

39

22

951

1326

4.7

Heavy cracks

6

30

N2

1100

39

22

1037

1383

5.2

No cracks

7

30

N2

1060

39

22

965

1408

8.7

Heavy cracks

8

30

N2

1060

39

22

1073

1379

6.0

Heavy cracks

9

30

N2

1060

39

26

1111

1435

8.0

Heavy cracks

10

28

N2

1060

39

19

1017

1356

5.3

Fine cracks

11

30

N2

1040

32

19

1133

1416

8.8

Heavy cracks

12

30

N2

1040

54

29

1092

1411

5.7

Heavy cracks

It can be observed that all the specimens are compliant

range between about 20 and 30°C (considering that the

by the process parameters.

within a strict range of variation and the tensile strength

with the C1300 level but the bending resistance is affected

Samples 1 and 2, produced with same annealing treatment conditions and cold rolling final reduction percen-

tage, show that the effect of chemical composition on the amount of strain-induced martensite is not of primary importance provided that the M d30 temperature lies in the

strain induced martensite fractions for both samples are values are within the measurement uncertainty).

It is apparent that the yield strength increases as the mar-

tensite fraction increases. In the present case indeed,

sample 1 has passed the bending test (Fig.2), whereas

sample 2, which exhibits a lower bending resistance and a higher yield strength, failed the test (Fig. 3).

Fig.2 – Stereomicroscopic observation of sample 1 after bending test: OK (fine cracks).

La Metallurgia Italiana - July-August 2022

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Memorie scientifiche - Acciai Inossidabili

Fig.3 – Observation at stereomicroscope of sample 2 after bending test: KO (heavy cracks).

Qualification of samples 3, 4 and 5 has shown that, if the

resistance to bending although, in this case, it is shifted

intermediate annealing is performed in hydrogen atmo-

towards the lower limit of acceptance.

sphere, the resistance to bending of the final product is impaired whereas changes in time/temperature are not

The qualification of samples 9 and 10 has shown that a de-

effective. Indeed, only sample 6, annealed in a N2 atmo-

crease of the cold rolling reduction down to 19% enhan-

sphere, has passed the bending test.

ces the resistance to bending but tensile strength is also

Qualification of samples 7 (hydrogen desorption treat-

reduced, although still being within the limits of the C1300

ment after the intermediate annealing) and 8 (hydrogen

level. If the cold rolling rate is increased to 26%, the hi-

desorption treatment after cold rolling) has shown that

ghest tensile strength is achieved but with poor ductili-

this treatment is effective in promoting the hydrogen de-

ty in terms of resistance to bending and a higher volume

sorption since a recovery of the ductility in terms of elon-

fraction of strain induced martensite.

gation to rupture (tab. 4) is observed. On the other hand,

The combination of a lower annealing temperature and

the resistance to bending still remains poor. Moreover, it

cold rolling rate realized on samples 11 and 12 appears to

is noticed that the post treatment is more effective if it is

have detrimental effect on ductility since it induces a poor

carried out on the final product because it improves the

resistance to bending.

Tab. 4 - Comparison of mechanical properties (tensile strength and elongation to rupture) of the specimens annealed in H2 before/after post treatmen(200°C x 2h).

Specimen ID

Intermediate annealing treatment Atmosphere

Temperature (°C)

Time (s)

7 7P (post treatment after intermediate annealing)

N2

1060

N2

La Metallurgia Italiana - Luglio-Agosto 2022

1060

Rm (MPa)

A (%)

Bending test

965

1408

16.4

Heavy cracks

920

1367

18.8

Heavy cracks

1073

1379

16.8

Heavy cracks

1134

1330

22.0

Fine cracks

39

8 8P (post treatment after cold rolling)

Rp0.2 (MPa)

39

pagina 12

Scientific papers - Stainless Steels

DISCUSSION

rolling reduction.

The matrix of experimental tests has been designed in such a way to isolate the effect of a single compositio-

The experimental activity has shown that an intermediate

nal or processing parameter to permit a straightforward

annealing in hydrogen atmosphere impairs the ductility of

analysis of the results.

the material, probably because the strain-induced mar-

Samples 1 and 2 differ for the Md30 temperature and have

tensite interfaces formed during the first cold rolling step

been manufactured with the same processing conditions.

act as trapping sites for hydrogen.

To assess the effect of a single processing parameter such

The bending resistance of specimens annealed in N2 at-

as the annealing atmosphere, the temperature and time

mosphere is shown in the histrogram of Fig. 4 as a fun-

of the intermediate annealing treatment and the final cold

ction of the processing parameters, while the tensile

rolling reduction, specimens having similar M d30 and dif-

strength is represented in Fig. 5. It can be observed that,

ferent process parameters have been selected (samples

if the annealing treatment is carried out at the lowest tem-

3 to 12).

perature 1040°C, a poor resistance to bending is obtained

In particular, samples 3, 4, 5 and 6 differ in the time of

even when a longer annealing time is used (54 s instead of

heat treatment and annealing atmosphere. Samples 7 and

32 s) and the Rm value is close to the upper threshold for

8, annealed in H2 atmosphere, have been submitted to a

the C1300 level. When the annealing treatment is perfor-

heat treatment at 200°C for 2 hours to promote hydrogen

med at 1060°C, the resistance to bending is close to the

desorption. The heat treatment has been performed after

acceptance threshold provided that the cold rolling re-

the intermediate annealing in sample 7 and after the final

duction is in the range between 19% and 22%. In fact, a

cold rolling in sample 8. In case of sample 7 the final cold

poor bending resistance and high Rm value is found when

rolling has been performed in the laboratory.

the cold rolling reduction is raised to 26%. The highest re-

Samples 9 and 10 differ only for the final cold reduction

sistance to bending combined with good tensile strength

rates. Samples 11 and 12 differ from the former ones for

is observed when the annealing treatment is performed at

the temperature and duration of the intermediate anne-

1100°C and the cold rolling rate is 22%.

aling treatment and, among them, also for the final cold

Fig.4 – Resistance to bending as a function of the processing parameters.

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Memorie scientifiche - Acciai Inossidabili

Fig.5 – Tensile strength as a function of the processing parameters.

It has been noticed that the volume fraction of strain-in-

lower average through-thickness hardness of 196 HV than

duced martensite is always higher in all the samples exhi-

specimen 12 annealed at lower temperature (10.5-11.0

biting a poor bending resistance than that formed in those

ASTM) and whose average through-thickness hardness is

passing the test. This is probably due to a low effective-

215 HV. The former has passed the bending test, whereas

ness of the intermediate annealing treatment in reverting

the latter has failed it.

it back to austenite.

This supports the hypothesis that a more effective inter-

Moreover, as shown in Fig. 6, the recrystallised structure

mediate annealing favours the ductility of the material in

of sample 6, annealed at a higher temperature, is characte-

the work hardened state and therefore its ability to resist

rised by a larger average grain size (9.5 ASTM) and by a

bending.

Fig.6 – Microstructure of two specimens annealed at different times/temperatures (Optical Microscope).

La Metallurgia Italiana - Luglio-Agosto 2022

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Scientific papers - Stainless Steels CONCLUSION

ning a good ductility and resistance to bending. It has

Flat products in austenitic steel EN 1.4310 (type AISI 301)

been observed that the annealing in hydrogen atmosphe-

are commonly manufactured in the work hardened condi-

re has a detrimental effect on the bending resistance of

tion because the strain-induced martensite formed during

the final product because the strain-induced martensite

cold working allows to obtain a high increase of the me-

interfaces, formed during the first cold rolling step, act as

chanical properties. They are used in a wide range of indu-

trapping sites for hydrogen thus promoting the formation

stry sectors thanks to the combination of good corrosion

of cracks during bending.

resistance and mechanical strength. Most of the applications are in the automotive industry where the sheets are

In order to obtain a material compliant with the C1300 le-

cold formed in very complex shapes, and this requires

vel while maintaining a good ductility and resistance to

the high mechanical strength to be associated with good

bending test, the following conditions should be fulfilled:

ductility.

• the chemical composition should be balanced so that

In this study, the effect of chemical composition, inter-

an Md30 of 28-30°C is obtained;

mediate annealing and final cold rolling reduction on the

• the intermediate annealing should be carried out in N 2

mechanical properties of this steel in the work hardened

atmosphere;

state have been analysed.

• the minimum recrystallization annealing temperature

Laboratory investigations have shown that the atmosphe-

is 1060°C;

re of the intermediate annealing treatment is of primary

• the final cold rolling reduction should be in the range

importance for the production of material compliant with

between 19% and 22%.

the required high mechanical properties while maintai-

REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9]

P.O. SANTACREU, J.C. GLEZ, N. ROULET,T. FROLICH, Y.GROSBETY. Austenitic Stainless Steel For Automative Structural Parts.

SAE 2006 World Congress & Exhibition; Detroit, Michigan, April 3-6, 2006.

E.I. GALINDO-NAVA, P.E.J. RIVERA-DIAZ-DEL-CASTILLO. Understanding martensite and twin formation in austenitic steels: A model describing TRIP and TWIP effects. Acta Materialia 128 (2017) 120-134.

R. FUSSIK, G. EGELS, W. THEISEN, S. WEBER. Stackling Fault in Relation to Hydrogen Environment Embrittlement of Metastable Austenitic Stainless CrNi-Steels. Metals 2021, 11 (8), 1770.

S.K. DWIVEDI, M. VISHWAKARMA. Hydrogen Embrittlement in different materials: A review. International Journal of Hydrogen Energy 43 (2018), 21603-21616.

H.J. CHRIST, A. GRIGORESCU, C. MULLER-BOLLENHAGEN, M. ZIMMERMANN. Metastable Austenitic Stainless Steels and the Effect of Deformation-Induced Phase Transformation on the Fatigue Properties. Material Science 2014.

J.A. LICHTENFELD, M.C. MATAYA, C.J. VAN TYNE. Effect of Strain Rate on Stress-Strain Behaviour of Alloy 309 and 304L Ausenitic Stainless Steel. Metallurgical and Material Transactions A, vol. 37A (January 2006) 147-161.

T. ANGEL. Formation of Martensite in Austenitic Stainless Steel. J. of the ISI, 5 (1954), 165–174.

P. MARSHALL. Austenitic Stainless Steel Microstructure and Mechanical Properties. Hoepli (1984), 59.

A.DAS, S. SIVAPRASAD, M. GHOSH, P.C. CHAKRABORTI, S.TARAFDER. Morphologies and Characteristics of Deformation Induces Martensite during Tensile Deformation of 304LN Stainless Steel. Material Science Eng. A. 486, 283-86.

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Memorie scientifiche - Acciai Inossidabili

The effect of hot rolling and coiling temperature on microstructure and texture of ferritic stainless steel A. Kisko, A. Kaijalainen, L. Kurtti, S. Kodukula, T. Ylimäinen

The effect of hot rolling and coiling temperature on microstructure and texture of stabilized high-Cr ferritic stainless steel was investigated. The steel sheets were hot-rolled at a hot rolling mill with three finishing rolling and two coiling temperatures. The microstructure and texture of steel were characterized at the surface and centreline using the electron backscatter diffraction technique. Microstructure studies showed that at the surface high finish rolling temperature promoted the formations of substructure (low-angle boundaries) and recrystallized grains instead of deformed grains. At the centreline, the low finishing hot rolling temperature increased the tendency of deformed structure and decreased the tendency of recrystallized structure. Lowering the coiling temperature, promoted substructure and decreased the tendency of deformed grains. It was observed that at the surface layer of the investigated materials contains ~{112}<111>, ~{110}<112> and ~{011}<110> and shear texture components and at the centreline mainly ~{554}<225>, ~{001}<110>, ~{112}<110> and ~{112}<131> texture components. A decrease in finish rolling and coiling temperature strengthens the texture intensities at the subsurface. At the centreline, lower finish rolling and coiling temperatures sharpened the α- and γ- fibres and texture.

KEYWORDS: FERRITIC STAINLESS STEEL, HOT ROLLING, MICROSTRUCTURE, TEXTURE, GRAIN SIZE, ELECTRON BACKSCATTER DIFFRACTION; INTRODUCTION Ferritic stainless steels (FSS), containing over 17% Cr, are very promising steel for several applications. The low Ni and Mo concentrations, together with Cu alloying and high-Cr content ensure good corrosion resistance, even comparable to that of the commonly used austenitic stainless steel grade such as AISI 304, but with much lower alloying costs. Other key properties for high-Cr ferritic stainless steels are heat resistance and good combinations of mechanical properties [1]. Likewise, the high-Cr ferritic stainless steels are used in wide-scale varying from kitchen appliances, building materials, and

Anna Kisko, Antti Kaijalainen University of Oulu, Finland

Lauri Kurtti, Suresh Kodukula, Tapani Ylimäinen Outokumpu Stainless Oy, Finland

different mobile components. Indeed, one of the most demanding components is the exhaust system where high-Cr FSSs have been replacing conventional cast iron as the most commonly used material [2,3]. The processing of those highly demanding applications need often deep drawability. Unfortunately, ferritic stainless steels are prone to the surface defect called ridging [4]. Riding

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Scientific papers - Stainless Steels defects appear as corrugations parallel to the rolling di-

EXPERIMENTAL PROCEDURE

rection as they arise after the deep drawing process to the

The investigated material is EN 1.4509 from Outokumpu

steel sheet. The only way to remove ridges from the ste-

Stainless Oy (Tornio, Finland) production site/pilot sca-

el sheet is by polishing, but the additional process step is

le rolling mill. The chemical composition is Fe-<0.05C-

not desirable. Hence, the prevention of the ridges is ex-

17.6Cr-0.4Si-<0.5(Ti+Nb) (in wt.%). Materials finish rolling

tremely important.

temperature (FRT) and coiling temperature (CT) were varied. Each sample was coded according to its finish rolling

The solidification structure of the ferritic stainless steels

temperature (low, middle or high) and the coiling tempe-

may consist of columnar grains and during re-crystalliza-

rature (low or high). Therefore, six hot band variations of

tion, they will transform into bands or similarly oriented

the 3 mm thickness are investigated.

grains. Orientation of the grains may re-main until the final steel sheet. As these grains have different plastic aniso-

Microstructural examination and microtexture analysis

tropies compared with the ma-trix, ridging may occur sin-

were performed using field emission scanning electron

ce ridging defects are caused by differences in the plastic

microscope (JEOL-JSM-7900F FESEM) together with

anisotropies of grains and heterogeneities in the texture

electron backscatter diffraction (EBSD) device (Oxford In-

structure [5]. The hot rolling stage effects to the texture of

strument HKL, Aztec and Channel5 software). The EBSD

the final steel sheet.

measurements were conducted using accelerating voltage of 20 kV, working distance of 16-21 mm and step size

During cold rolling, the hot band textures might even

of 0.5 μm. The characterization was performed for RD-ND

sharpen slightly as the texture of the final product is inhe-

(rolling-normal directions) at the subsurface and centreli-

rited from the hot band [6,7]. Since stabilized FSS does

ne of 1200 μm x 800 μm area.

not undergo an austenite-ferrite transformation, hot rolling or hot band annealing are the only ways to affect to the formed texture. At the hot rolling stage, the temperature

RESULTS AND DISCUSSION

profile and the strained state varies through-thickness of

Fig. 1 shows the inverse pole figure (IPF) maps obtained

the sheet resulting shear defor-mation at the sub-surfa-

by EBSD for the studied steel samples from the surface

ce and plain strain deformation at the centreline [8]. A hi-

and centreline. The subsurface is located at the top of the

gher amount of stored en-ergy, caused by deformation,

surface of the sample´s images. It is seen that the FRT and

is stored in a colder surface leading to partial recrystal-

CT affect the formed microstructure, sub-boundaries, and

lization, whereas the temperature in centre layer is high

the degree of dynamic restoration. The microstructural

enough for dynamic recovery to occur. This leads to a

variations are visible between the subsurface and centre-

pancake-like mi-crostructure in centreline. The desirable

line samples. At low FRT the microstructure is still most-

texture in stabilized FSS is closely related to the γ-fibre

ly in a deformed state whereas at high FRT the sample is

texture [9]. Hence, the understanding of the evolution of

dynami-cally recovered. The number of low-angle grain

the hot rolling and coiling temperature to the formed mi-

boundaries decreases significantly as the FRT increases.

cro-structure and texture is extremely important.

The corresponding trend is seen with the coiling temperature.

In this study the effect of the hot rolling finishing and coiling temperature to the formed microstructure, grain size

The studied ferritic stainless steels hot bands have quite a

and texture were studied. Also, the changes in the hot

typical hot deformed structure since after hot rolling sta-

rolling finishing and coiling temperatures to the formed

bilized FSSs usually has a strong texture gradient throu-

structure and texture at the subsurface and centreline are

gh the thickness (Fig. 1). From Fig. 1 can be seen that at

discussed.

the subsurface layers tiny grains are recrystallized along RD. The grain size seems to increase gradually trough

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Memorie scientifiche - Acciai Inossidabili the thickness and their shape changes from the equiaxed

boundaries.

towards the pancaked structure. The highly elongated

In the further processing steps, in-grain shear bands of-

grains are visible of about 200-400 μm from the sample’s

fer nucleation sites for static recrystallization. <111>//ND

edge. Hence, highly elongated grains with a length over

grains belonging to γ-fibre nucleates to these in the in-

600 μm along to the rolling direction are seen both at the

grain shear bands. In order to obtain good final product

surface and centreline.

properties, the presence of in-grain shear bands should be promoted. This can be done by decreasing CT.

Generally, the highly deformed i.e. pancaked grains contained different amounts of low-angle grain boundaries.

It is seen that the microstructure of the hot band subsur-

In some of the deformed grains were numerous low-an-

face has the orientations of <001>//ND and <111>//ND as

gle grain boundaries aligned at 35° to the rolling direction.

shown in red and purple (Fig. 1). This so-called shear tex-

These aligned boundaries are also called in the literature

ture is a result of shear deformation at the surface layer

as in-grain shear bands [10,11], which refer to recovered

and consists mainly of Goss texture with the {011} <100>

grains. More in-grain shear bands were detected in the

orientation.

specimens with low or middle than in high FRT samples.

Low CT also increased the amount of in-grain shear bands,

At the centreline, the microstructure is highly pancaked.

which may be due to the slight static recovery taking place

The low-angle grain boundaries are visible, which might

during high CT i.e. slow cooling. Hence, the formation of

refer to the recovered grain structure. The highly elonga-

the in-grain shear band required relatively low tempera-

ted grains with 101 orientations are shown in green (Fig.

tures, which is supported by the literature [10]. Lowering

1). The α-fibre texture is formed due to the strain defor-

the FRT from high, middle to low led to a significant flatte-

mation conditions and is dominated by the {001}<110>

ned structure and increase the number of low-angle grain

orientation.

Fig.1 - Inverse pole figure maps (coloured of RD direction) of RD-ND section of the hot bands obtained by

EBSD. The black-coloured grain boundaries have misorientation higher than 15° and the grey coloured grain boundaries between 2.5 – 15°.

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Scientific papers - Stainless Steels The recrystallized, recovered and deformed structure

4.7% to 19.5% in high CT and from 5.6% to 19.0% in low

fractions for the studied steels obtained from EBSD data

CT. This is due to the heat conductivity during coiling

are shown in Table 1 and Fig. 2. The amount of deformed

which enables faster cooling at the subsurface than in

structure decreases as FRT and CT increase. Low FRT

centreline. The same phenomenon is detected for the

enables higher stored energy in the structure promoting

recovered structure.

further recrystallization during annealing. As FRT and CT increase, recovered and recrystallized fractions of the

The finish hot rolling temperature effects to the stored

samples increase in many samples. As discussed earlier,

energy of the ferritic stainless steels and further

in-grain shear bands refer to the recovered structure,

recrystallization behaviour. Previously Mehtonen et

which fraction is higher at the centreline than in the surface.

al. [10] reported that by lowering the deformation

At the surface, more recrystallized grains are detected as

temperature, the stored energy of the material increased

tiny, recrystallized grains appear near the surface.

due to the less effective dynamic recovery, which further promotes static recrystallization at hot band annealing.

Typically, FRT affects to the recrystallization rate more at

The result is supported by this study, as high FRT and/or

the subsurface than in the centreline as increasing FRT

increased recrystallized fraction of the studied steels.

from low to high, recrystallized fraction increased from Tab.1 - Recrystallized fractions for the studied steels. (Note: in Channel5 analyses following parameters are

used when determinate the recrystallization/recover/deform grain fractions. Minimum angle for low-angle grain boundary (LAGB) was set to 2.5° and minimum angle for high-angle grain boundary (HAGB) to 15°.)

RECRYSTALLIZED FRACTION Deformed [%]

Recovered [%]

Recrystallized [%]

material FRT-CT

subsurface

centreline

subsurface

centreline

subsurface

centreline

low-high

91.0

60.8

4.3

37.2

4.7

2.0

middle-high

68.2

49.9

19.1

45.8

12.7

4.4

high-high

50.8

20.9

29.7

72.3

19.5

6.8

low-low

86.6

23.4

7.9

74.0

5.6

2.6

middle-low

47.4

22.3

36.5

72.1

16.1

5.6

high-low

38.2

7.7

42.7

87.8

19.0

4.6

In order to analyse the evolution of grain size after hot

grain size decreases at both surfaces and centrelines, e.g.

rolling and coiling, the grain sizes of the steels were

at high and low CT (low FRT) the grain size increase from

measured using EBSD data. Fig. 3 shows the grain size

2.4 μm to 3.1 μm at the surface and from 3.7 μm to 6.3 μm

distribution of the studied steel samples. From the Fig. 3 it

at the centreline. The same trend was observed with the

is seen that with increasing FRT low- and high-angle grain

recrystallized fractions (Table 1) as the low CT increased

size increase both at the surfaces and centrelines, since

the percentage of the recrystallized grains.

e.g. at low and high FRT (and high CT) the grain sizes were 2.4 μm and 4.6 μm at the surface and 3.7 μm and 7.5 μm at the centreline, respectively. The increase in grain sizes is due to the re-crystallization following grain growth during hot rolling (see Table 1).

Opposite to FRT, with increasing CT the low and high angle La Metallurgia Italiana - July-August 2022

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Memorie scientifiche - Acciai Inossidabili

Fig.2 - Fraction of deformed, recovered and recrystallized structures of the investigated materials at the centreline.

Effective coarse grain size (d90%), i.e. grain size at 90 %

sizes when FRT is decreased. Typically, coarse grains

in the cumulative grain size distribution, is show-ing the

effect on the mechanical properties such as impact

few biggest grains from the EBSD acquisition. d90% value

energies. However, in this study mechanical properties

is showing, how homogenised grain size is distributed.

were not determined.

In this case, it is behaviour similar to the high-angle grain

Fig.3 - Mean low- (>2.5°) and high-angle (>15) equivalent circle diameter (ECD) grain sizes of the investigated materials at the surface (left) and centreline (right).

EBSD was also utilized to determine the microtexture of the

main texture components are ~{112}<111>, ~{110}<112>,

studied steels. Fig. 4. presents the orientation distribution

and ~{011}<110>. Only slight variation in the individual

functions (ODFs) as φ2=45° cross-sections generally for

maxima along the texture fibres were observed with the

ferritic stainless steels and Fig. 5 for the studied samples.

variation of FRT. However, the high CT sharpened the

It is evident that the texture varies through thickness.

Goss texture as maximum texture intensity changes for

The subsurface texture is affected by the newly formed

the investigated samples were 6 – 12, 10 – 15, and 5 – 12

recrystallized grains together with elongated grains

for the low, middle, and high FRTs. A decrease in FRT and

parallel to the rolling direction. At the surface, shear

CT strengthens the texture intensities at the subsurface.

texture is dominant due to the shear deformation and the

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Scientific papers - Stainless Steels

Fig.4 - Alpha, gamma, and epsilon fibres and the important texture components of the BBC structure in the φ 2=45° section.

Plane strain deformation and dynamic recovery are pre-

of ~{554}<225> was detected. The intensity maximum in-

sent at the centreline. Hence, the sharp α-fibre is evident

creases as FRT increases or CT decreases. Also, a sharp

with the sharp texture components of ~{001}<110> and

α-fibre texture component of ~{001}<110> is observed for

~{112}<110>. The highest texture intensity maximums are

the low-low or low-high sample, being weaker for other

11, 11, and 9 for the low, middle, and high FRT samples

studied samples. The sharp texture may be due to the mi-

with the low CT. With high CT, the texture gradients de-

crostructure as discussed previously. Generally, at the

crease, except in the low FRT sample. According to the

centreline, lower finish rolling and coiling temperatures

microstructural characterization of the low-high sam-

sharpened the α- and γ- fibres and texture.

ple, the grains seemed to be the most pancaked due to the less dynamic recovery. It could be assumed that this

A sharp γ-fibre texture component of ~{001}<110> is

would result in a strong texture. Gao et al. [12] reported

detected especially for low FRT specimens. In the fur-

that the decrease in the hot deformation temperature shi-

ther processing, the presence of ~{001}<110> orientated

fted the orientation maximum from ~{001}<110> towards

grains are challenging since their pronounced tendency

~{111}<110> due to an increase in the lattice rotations,

to recover instead of recrystallizing. In addition, grains

which promoted the development of texture towards

with ~{001}<110> orientation are last to recrystallize and

stable end orientations. In the current study, the orien-

the process is time-consuming. To obtain excellent pro-

tation maximums were shifted from ~{001}<110> towards

perties of the final product, these orientations should be

~{111}<110> by decreasing FRT or CT. However, the dif-

avoided.

ferences were not that significant. Low FRT and/or CT increase intensity towards ~{112}<110> texture component,

Generally, the intensity of the γ-fibre texture correlates

which is known to increase grain rotations and texture

with the normal r-value since good formability requires

towards ~{112}<110> component from ~{001}<110> com-

γ-fibre texture. Hence, by increasing the in-grain shear

ponent enhancing good formability of the final product

band content and optimum texture components the hot

[11].

band structure will recrystallize after further processing.

This kind of structure can be achieved by enhancing the

At the centreline, in the γ-fibre the texture component

La Metallurgia Italiana - July-August 2022

formation of {111} oriented grains, i.e. decreasing the FRT.

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Memorie scientifiche - Acciai Inossidabili

Fig.5 - φ2=45° sections of ODFs at the surface (left) and centreline (right) positions in investigated samples.

SUMMARY The effect of hot rolling and coiling temperature on micro-

ACKNOWLEDGMENTS

structure and texture of stabilized high-Cr ferritic stainless

Financial assistance of the Business Finland, project TO-

steel was investigated. The finish hot rolling temperature

CANEM – Towards Carbon-neutral Metals, is acknowled-

varied from low, middle to high and the coiling tempera-

ged.

ture from low to high. The resultant microstructures, grain sizes, and textures were examined using EBSD. It turned out that by lowering the FRT the stored energy of the material increased by means of deformed and/or recovered grains. This would enhance the static recrystallization in further hot band annealing as the stored energy of the material is increased since dynamic recovery during hot rolling decreased. A sharp α-fibre texture component of ~{001}<110> is detected especially for low FRT specimens.

By decreasing FRT or CT, the orientation maximums were shifted from ~{001}<110> towards ~{111}<110>. Hence, in order to obtain the preferred orientations, lower FRT and/ or CT are recommended.

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Scientific papers - Stainless Steels REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]

[11] [12]

Yazawa Y, Ishii K, Okada S, Ujiro T, Yamasita H. Ni Mo-Free Stainless Steel with High Corrosion Resistance. Corrosion Engineering.

2007;56(10):599-606.

Hua M, Garcia C, DeArdo AJ, Tither G. Dual-stabilized ferritic stainless steels for demanding applications such as automotive exhaust systems. Iron and Steelmaker. 1997;24(4):41-44.

Charles J, Mithieux JD, Santacreu PO, Peguet L. The ferritic stainless steel family: the appropriate answer to nickel volatility? 6th European Stainless Steel Conference Science and Market. 2008 June 10-13; Helsinki, Finland. p. 703-720 Chao HC. The mechanism of ridging in ferritic stainless steels. Trans. ASM. 1967;60(1):37-50.

Shin HJ, An JK, Park SH, Lee DN. The effect of texture on ridging of ferritic stainless steel. Acta Materialia. 2003;51(16):4693-4706.

Available from: https://doi.org/10.1016/S1359-6454(03)00187-3 Raabe D, Lücke K. Influence of particles on recrystallization textures of ferritic stainless steels. Steel Research. 1992;63(10):457-464.

Available from: https://doi.org/10.1002/srin.199201742 Raabe D. Experimental investigation and simulation of crystallographic rolling textures of Fe-11Cr steel. Materials Scinece and Technology. 1995;11(10):985-993. Available from: https://doi.org/10.1179/mst.1995.11.10.985 Raabe D, Lücke K. Textures of ferriti stainless steels. Materials Science and Technilogy. 1993;9(4):302-312. Available from: DOI: 10.1179/mst.1993.9.4.302 Yazawa Y, Muraki M, Kato Y, Furukimi O. Effect of chromium content on relationship between r-value and {111} recrystallization texture in ferritic steel. ISIJ International. 2003;43(10):1647-1651. Available from: https://doi.org/10.2355/isijinternational.43.1647 Mehtonen S, Palmiere E, Misra D, Karjalainen P, Porter D. Microstructrual and texture development during multi-pass hot deformation of a stabilized high chrimium ferritic stainless steel. ISIJ International. 2014;54(6):1406-1415. Available from: https://doi.org/10.2355/ isijinternational.54.1406 Kodukula S. Ridging in stabilized ferritic stainless steels. The effects of casting and hot-rolling parameters. Doctoral Dissertation.

Oulu: Univeristy of Oulu; 2012. 134 p. Available from: http://urn.fi/urn:isbn:9789526231259 Gao F, Liu Z, Liu H, Wang G. Influence of the finish rolling temperatures on the microstructure and texture evolution in the ferritic satinless steels. Acta Metellurgica Sinica (English Letters). 2011;24(5):343-350.

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Thermodynamic property of hydrogen in high nitrogen martensitic stainless steel melts J.Y. Kim, H.R. Lee, I.H. Kwon, Y. Kang

Hydrogen in steel products may cause serious defects such as hydrogen embrittlement and hydrogen flake. Similarly, seasonal pinhole defects of stainless steel have been often considered to be related to excess hydrogen in molten steel. Hence, reliable information on hydrogen in molten steel is extremely important. However, it should be noted that reliable information of hydrogen in stainless steel is not sufficient. Moreover, there has been significant uncertainty in hydrogen content among previously reported data due to difficulty in measurement.

In the present study, it was aimed to determine the hydrogen solubility of molten stainless steel. Particularly, the influence of Cr content on the hydrogen solubility was focused. Metal samples were equilibrated under controlled hydrogen partial pressure at 1823K and quenched by dropping them into liquid nitrogen. Then the activity coefficient of hydrogen in molten stainless steel with varying Cr content could be determined based on following equation.

Additionally, relatively convenient method for estimating H content in molten steel using hydroxyl capacity of slags and the equilibrium relation among gas-slag-metal was also investigated. To verify the tentatively suggested the measurement method, the measurement of diffusional hydrogen at the moderately elevated temperature was attempted using a gas chromatograph.

KEYWORDS: STAINLESS STEEL, HYDROGEN SOLUBILITY, CR CONTENT, ACTIVITY COEFFICIENT;

INTRODUCTION As the conventional structure of global industries quickly shifts towards hydrogen economy, the demands of metallic materials suitable for the storage and the transportation of highly compressed hydrogen or liquid hydrogen are drastically increasing. Since stainless steel can be a good candidate for hydrogen-related applications owing to its superior characteristics and phase stability even in very low temperatures, it is greatly important to understand the properties of hydrogen for its proper control.

Jun Young Kim, Youngjo Kang

Dept. Material Science and Engineering, Dong-A University, Korea

Hye Ran Lee, Ik Hwan Kwon

Dept. Metallurgical Engineering, Dong-A University, Korea

Hydrogen in steel products may cause serious defects such as, hydrogen embrittlement and hydrogen flake.[1] Similarly, seasonal pinhole defects of stainless steel have been often considered to be related to excess hydrogen in molten steel. Typical examples of the pin hole defects La Metallurgia Italiana - Luglio-Agosto 2022

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Scientific papers - Stainless Steels

in stainless steel product are present in Fig. 1. Although

study is to determine the hydrogen solubility of molten

reliable information on of hydrogen in molten steel is ex-

stainless steel with high nitrogen content and propose

tremely important, there has been significant uncertainty

simpler way of estimating hydrogen content of molten

in hydrogen content among previous studies due to diffi-

steel.

culty in measurement. Therefore, the aim of the present

Fig.1 - Photograph of pin-hole defect just under the surface of martensitic stainless steel product.

EXPERIMENTAL

8 hours equilibration at 1823K with Ar+H2 mixture ga-

In order to determine the hydrogen content of molten

ses (3%, 6.5%, 10%H2), the sample was instantaneously

steel, an electric resistance tube furnace, with which a

dropped into liquid nitrogen, which was placed at the bot-

molten steel sample can be quenched, was used. An alu-

tom of the furnace. The experimental apparatus is sche-

mina crucible holding the sample was hanged with Mo or

matically described in Fig. 2.

Pt wire to be located at the even temperature zone. After

Fig.2 - Schematic presentation of experimental apparatus for hydrogen solubility measurements.

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Memorie scientifiche - Acciai Inossidabili

And the dissolution of water vapor into molten stainless

H2 partial pressure increases, hydrogen content increa-

steel was also investigated. Water vapor generated at

ses. A good linearity between the hydrogen content and

303K was introduced into the furnace, in which molten

square root of H2 partial pressure indicates hydrogen in

steel samples were prepared, along with Ar+H2 mixture

stainless steel obeys Sievert’s law. From the value of slo-

gas. After the equilibration with the same conditions to

pe, moreover, the activity coefficient of hydrogen in mol-

those described earlier, the sample was quenched in si-

ten stainless steel could be determined to with respect

milar manner using liquid nitrogen. Hydrogen and oxygen

to infinite dilute solution, in which the activity coefficient

contents in the steel samples for hydrogen solubility and

of hydrogen is unity. It can be inferred that the difference

water vapor dissolution were measured by N/O/H deter-

between the activity coefficient in stainless steel to unity

minator (ONH2000, ELTRA GmbH, Haan, Germany).

is caused by the existence of other elements, such as, Cr, C and Si. This relationship can be expressed as Eq. [1]. Ba-

RESULTS AND DISCUSSION

sed on obtained results about hydrogen dissolution, the

Hydrogen solubility in high nitrogen stainless steel

hydrogen solubility in molten stainless steel was evalua-

The relationship with H2 partial pressure and hydrogen

ted to be 9.7 ppm, which is slightly smaller than that in

content in molten stainless steel is presented in Fig. 3. As

pure Fe. [1]

Fig.3 - Relationship with H2 partial pressure and hydrogen content in molten stainless steel.

Dissolution of water vapor in high nitrogen stainless

hydrogen and oxygen as following reaction [2], the equi-

steel

librium content of hydrogen is supposed to be inversely

Since water vapor dissolves into molten steel as elemental

proportional to that of oxygen at constant temperature.

[2]

Based on the equilibrium contents of hydrogen and oxy-

difference in the equilibrium constant is consistent with

gen at 1823K, the equilibrium constants of water dissolu-

the tendency of the hydrogen solubility of stainless steel

tion into stainless steel could be estimated to be 5.47×10 ,

and pure Fe, as explained the previous section.

-7

which is one order less than the case of pure Fe.[2] This La Metallurgia Italiana - Luglio-Agosto 2022

pagina 26

Scientific papers - Stainless Steels

Estimation method hydrogen content in steel

tent in steel from the direct measurement of the hydrogen

The accurate determination of hydrogen in steel has been

content in the slag, equilibrated with the steel.

known to be extremely difficult, due to its extraordinarily

In order to derive the hydrogen content in steel from

high diffusivity and the readiness of surface adsorption.

that in slag, the partition ratio of hydrogen, which can be

There is also high possibility that hydrogen diffuses out

expressed using hydroxyl capacity of slag and the equili-

during sample preparation and contaminates from envi-

brium constant of water vapor dissolution into steel, are

ronmental moisture. Compared to the case in steel, on

required. Since the activity coefficient of hydrogen and

the other hand, the hydrogen content in slag may be me-

the equilibrium of water dissolution were already discus-

asured more correctly, because hydrogen is more tightly

sed, the hydrogen content in steel can be deduced from

bound to oxygen by covalent bond in slag structure. The-

oxygen activity in steel and hydroxide content in slag

refore, it can be proposed to estimate the hydrogen con-

whose hydroxyl capacity is known, as shown in Eq. [3],

[3]

Here, f H and aOare the activity coefficient of hydrogen and

Finally, useful relationship to predict the hydrogen con-

the activity of oxygen in molten steel, while COH- and KGM

centration in the metal from that in molten slag, using hy-

stand for hydroxyl capacity of the slag and the equilibrium

droxyl capacity of the slag and the activity of oxygen in

constants of water dissolution into steel, respectively.

the steel. Conclusively, relatively convenient method for estimating hydrogen in molten steel could be suggested.

SUMMARY Experimental investigation on the influence of hydrogen

ACKNOWLEDGEMENT

on the pinhole defect in high nitrogen stainless steel was

The authors would like to acknowledge the financial sup-

carried out. The hydrogen solubility and the equilibrium

port from the Ministry of SMEs and Startups through the

constant of the dissolution of water vapor (KGM) in stain-

Human Resource Training Project for Industry Matched

less steel were experimentally determined using liquid

R&D (No. S3282193)

nitrogen quenching. Hydrogen solubility as well as the equilibrium constant of the dissolution of water vapor turned out to be lower in stainless steel than in pure Fe.

REFERENCES [1] [2]

M.R. Louthan Jr., G.R. Caskey Jr., J.A. Donovan and D.E. Rawl Jr., Materials Science and Engineering, 1972, Vol. 10, 357-368.

Sungkoo Jo and Seonhyo Kim, Steel Research, 2000, Vol. 71, 15-21.

TORNA ALL'INDICE >

La Metallurgia Italiana - July-August 2022

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Memorie scientifiche - Acciai Inossidabili

Selective laser melting manufacturing of stainless steels: heat treatment effect on microstructure and hardness of maraging steels G. Stornelli, D. Gaggia, M. Gaggiotti, M. Rallini, A. Di Schino

Laser Powder Bed Fusion (L-PBF) Selective Laser Melting (SLM) is a widespread additive manufacturing technology in industrial applications, for metal components manufacturing. Maraging steel is a special class of Fe-Ni alloys, typically used in the aerospace and tooling sectors due to their good combination of mechanical strength and toughness. This work reports about the heat treatment effect on the microstructure and hardness value of 300-grade maraging steel manufactured by the L-PBF SLM process. The considered heat treatment consists of a solution annealing treatment followed by quenching and ageing hardening treatment. The effect of ageing temperature is reported, in a wide temperature range. Results show that solution annealing treatment fully dissolves the solidification structure caused by the SLM process. Moreover, the ageing hardening treatment has a significant impact on the hardness, hence on strength, of SLM maraging steel. The optimal ageing conditions for the SLM maraging steel are identified and reported: in particular, results show that the hardness of 583 HV is achieved following ageing treatment at 490 °C for 6 hours. A higher treatment temperature leads to over-ageing resulting in a decrease of hardness. Conversely, an excessive ageing time does not seem to affect the hardness value, for the ageing temperature of 490 °C.

KEYWORDS: MARAGING STEEL, 300-GRADE, SELECTIVE LASER MELTING, LASER POWER, SCANNING SPEED, RELATIVE DENSITY, CARBIDES PRECIPITATION; INTRODUCTION Additive Manufacturing (AM), also known as 3D-Printing, is an emerging technology, in the spotlight for its unique capability to produce near-net-shape components, even geometrically complex, without part-specific tooling needed. Moreover, it is particularly suited for small batches production and part-customization: this is why it first emerged as a rapid prototyping technology. The adoption of AM technologies resulted in new production paradigm [1], where the designer can project a new component, or optimize the geometry of an alreadyexisting one, according to its service condition, free from production related constraints (e.g. undercuts, straight cuts, internal ducts

Giulia Stornelli

Università di Roma Tor Vergata,

Dipartimento di Ingegneria Industriale, Roma, Italy giulia.stornelli@students.uniroma2.eu

Damiano Gaggia

Green Tales Srl, Terni, Italy

Marco Rallini

Università degli Studi di Perugia,

Dipartimento di Ingegneria Civile e Ambientale, Perugia, Italy

with sharp edges). At the same time, AM made possible

Matteo Gaggiotti, Andrea Di Schino

to simplify components assembly, merging different parts

Dipartimento di Ingegneria, Perugia, Italy

Università degli Studi di Perugia,

in one single monolith: most emblematic example being the fuel nozzle showed in [2], that passed from being an assembly of 20 parts to a single unit, allowing for a 25% weight reduction [3,4].

La Metallurgia Italiana - Luglio-Agosto 2022

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Scientific papers - Stainless Steels

Today the term Additive Manufacturing refers to a range of

particular, various metal alloys.

technologies, making possible to process several classes

Focusing on metal alloys, it is in principle possible to ma-

of materials – polymers, metals, ceramics, composites and

nufacture every weldable metal alloy, the proper setting of

sand – in different delivery condition – i.e. liquid, powder,

working parameters is required material by material (e.g.

wire or sheets. In particular, a wider AM adoption happened

laser power, layer thickness, gas fluxing). Working para-

thanks to the gained possibility to process metal alloys with

meters identification and validation on manufactured com-

mechanical properties comparable to equivalent wrought

ponents is the real know-how of LPBF systems producers

alloys. Since 2000, the AM technology is assisting to a fast

and technology developers. Today, the most established

acceleration [5] due to the degree of development gained

and LPBF-verified alloys comprehend: Aluminum alloys

in several sectors, the most relevant being lasers, compu-

(AlSi10Mg, AlSi7Mg0.6), Cobalt alloys (CoCrMo), Nickel

ters, CAD technologies, Programmable Logic Controllers

alloys (Haynes HX, Inconel 625, Inconel 718), Iron alloys

(PLCs) and data storage systems [6]. The first commercially

(Maraging steels, AISI 304, AISI 3016L, Tool steels), Tita-

available AM system, back to 1987, is SLA-1 by 3D Systems

nium alloys (Ti6Al4V, Ti6Al4V ELI, CP-Titanium Grade 2).

and it is based on the stereolithography technique: the de-

Stainless Steels are nowadays diffused in almost every ap-

sired piece is obtained through the superimposition of thin

plication field, thanks to their peculiar combination of pro-

layers of ultraviolet light-sensitive liquid polymer solidified

perties namely, strength, corrosion resistance and relative

by a ultraviolet (UV) laser source. Growing interest in the

low cost that made its fortune since its discovery in the

field led several companies and researchers working con-

early 19th century [8,9]. In particular, following their good

temporarily to develop systems capable to handle metal

strength/ductility combination coupled with their excellent

alloys. EOS Gmbh presented its first prototype - EOS M160

corrosion resistance stainless steels are adopted in many

- for metal processing in 1994 and, the following year, EOS

applications including automotive [10], construction and

M250 system was launched on the market. In the meanwhi-

building [11], energy [12,13], aeronautical [14], medical [15]

le, Deckard filed a patent [7] concerning an apparatus ca-

and food [16]. The implementation of stainless steel grades

pable to sinter powders thanks to a laser source. The cited

in LPBF systems, together with a deeper understanding of

manufacturing devices are the precursors of modern La-

the technology, could definitely result in a wide adoption

ser Powder Bed Fusion (LPBF) technology (also known as

of the technology itself. Among stainless steels, maraging

Selective Laser Melting SLM, Direct Metal Laser Sintering

ones are quite promising following their high mechanical

or Laser Cusing) which, among Additive Manufacturing, is

characteristics combined to ductility and toughness. Such

the most relevant for mechanical components production.

combination allows to maraging steels to be widely used

The recent spreading of International Standards regarding

in aerospace and aircraft sectors and in application in whi-

metal alloys LPBF-manufactured reflects this condition.

ch is required high precision, as gears and molds [17-20].

LPBF is a layer-wise production technology accompli-

Maraging steels represents a category of steels [21], with

shing material consolidation through a highly focused la-

a high content of elements as Ni, Mo, Co, Ti and Al [22,23];

ser source: the spot of the laser, impinging on the powder

the low carbon and the high Ni content, combined with a

bed, releases a quantity of energy necessary to melt metal

specific cooling process (from a solid solution of γ-Fe),

particles.

promotes a soft martensite microstructure, highly dislo-

The success of LPBF lies in its:

cated. The combination of strengthening and toughness is

• capability to obtain the best geometrical and dimensio-

allowed by the aging treatment [24], an heat process oc-

nal tolerances among AM

curring in a range temperatures between 400 °C - 700 °C

• capability to obtain near-net-shape components

which allows the precipitation of nano sized intermetallic

• capability to produce components characterized by re-

compounds [25, 26] (such as Fe2Mo, NiAl, Ni3(Ti, Al, Mo),

lative densities, with respect to wrought or forged me-

Ni(Al, Fe), etc.). It is precisely the formation of precipitates,

tals, up to 99.9%

following this heat treatment, which guarantees the inhi-

• possibility to process a wide range of materials, and, in-

bition of the dislocation motion [27] and, consequently,

La Metallurgia Italiana - July-August 2022

pagina 29

Memorie scientifiche - Acciai Inossidabili the improvement of the mechanical characteristics. The

speed and layer thickness on residual stresses, distortions

aging treatment, referring to maraging steels, represents

and achievable density for maraging 300-steel, in order to

the last step of a production process characterized by ca-

achieve the optimum input parameter combinations. Han-

sting, plastic deformation, solution annealing, quenching

zl et al. [42] evaluated no differences between laser power

and machining [28]. Thanks to the low carbon content and

and scanning speed on the impact on the mechanical and

to the characteristic of good ductility, maraging steels can

physical properties of SLM manufactured parts. The aim of

be produced through additive manufacturing (AM) techno-

this work is analyzed the effect of aging heat treatment, in

logies [29] the most widely used method is SLM [30-32].

terms of temperature-time combination, on microstructu-

The low carbon content in maraging steel, allow to this

re and mechanical features of 18Ni 300-grade maraging

class of material to be very usefull, as this characteristic

steel based on the SLM technology. The as-built and the

prevent the formation of cracks during rapid cooling (this

solution annealed sample were also compared with the

allows to avoid carbides or carbon segregation phenome-

material after aging treatment, in order to show the diffe-

na). Many efforts are focused to optimize the parameters of

rences in terms of mechanical behavior.

solution annealing and aging heat treatment [33], with the aim to obtain the best conditions of mechanical properties,

MATERIAL AND METHODS

required by aerospace or tool-manufacturing industries

Test samples were produced through SLM technology

to produce complex geometries by SLM technology [34].

(Model EosM290), with a laser power of 400 W and an high

The maraging steels structure deeply depends on scanning

scanning speed up to 7.0 m/s (23 ft./sec). The layer thick-

strategy and on laser source settings, which affect the rela-

ness was 0.05 mm and the plate form temperature was kept

tive density and the performance of compounds (e.g., [35-

at 40 °C, moreover the machinery was equipped whit a pre-

39]). Yongqiang Yang et al. [40] investigated the effect of

cision optics F-theta lens Yb fibre laser with a nominal dia-

laser powder, scanning speed and scanning space on the

meter of 100 μm (0.004 in). For the manufacturing process

relative density of maraging steel 300; they studied the best

was used a 300-grade maraging steel powder, produced by

configuration in terms of laser power and scanning speed,

gas-atomization and with a nominal chemical composition

to obtain a relative density higher than 99%. Igor Yadroit-

(wt.%) showed in Tab. 1.

sev et al. [41] studied the influence of laser power, scanning

Tab.1 - 300-grade maraging steel powder chemical composition (wt.%).

La Metallurgia Italiana - Luglio-Agosto 2022

Element

Content, wt.%

Fe

To balance

Ni

17.00 – 19.00

Co

8.50 – 9.50

Mo

4.50 – 5.20

Ti

0.60 – 0.80

Al

0.05 – 0.15

Cr

0.50

Cu

0.50

C

0.03

Mn

0.10

Si

0.10

P

0.01

S

0.01

pagina 30

Scientific papers - Stainless Steels The test samples were machined along a plane parallel to

been chosen to obtain the highest homogenization of the

the build direction (BD), polished and etched with a so-

composition and to dissolve the columnar microstructure

lution of 2 % Nital. An optical microscope (OM) (Eclipse

and the micro-segregation, typically induced by AM pro-

LV150NL, Nikon) and a high-resolution scanning electron

cess. The SAT + Q was performed according to the heating

microscope (SEM) (FE-SEM Zeiss, Gemini Supra 25) were

profile showed in Fig. 1; then the effect of aging hardening

used to analyze the microstructure of 300-grade maraging

treatment (AHT) was investigated for temperature between

steel. The solution annealing and quenching treatment

450 °C and 550 °C in a time range of 6 - 24 h (heat treatment

(SAT + Q), follows the manufacturing process of maraging

parameters in Tab. 2).

steel samples and, the time-temperature conditions have

Fig.1 - Heat profile (SAT + Q).

Tab.2 - Heat treatment scheme carried out on 300-grade maraging steel based on L-PBF process.

SAT + Q Experiment No.

AHT

Temperature (°C)

SAT holding time (hours)

Cooling rate (°C/minutes)

Temperature (°C)

Aging time (hours)

1

940

2

16

450

6

2

940

2

16

470

6

3

940

2

16

490

6

4

940

2

16

490

10

5

940

2

16

490

24

6

940

2

16

510

6

7

940

2

16

530

6

8

940

2

16

550

6

The morphology of particle (Fig. 2) was analyzed by the

The microstructural analysis was carried out for different

high-resolution scanning electron microscope. The mor-

states of material, as built, after solution annealing and

phology of the powders was generally spherical and some

quenching and after the various time-temperature com-

particles have satellites; moreover a fraction of elliptic sha-

bination of the aging treatment. During the analysis, were

pe particles can be observed. The average size of maraging

also measured the values of hardness (HV10) to estimate the

steel powders is > 63 μm.

best condition of AHT.

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Memorie scientifiche - Acciai Inossidabili

Fig.2 - SEM image of morphology of 300-grade maraging steel powder.

RESULTS AND DISCUSSION

ples are clearly visible. The cellular structure is dominant

The result of SAT + Q on SLM maraging steel

in morphology, mainly for the fast cooling rate within the

The images in Fig. 3 and Fig. 4 show, respectively, the mi-

melt pool during the SLM process.

crostructure at low and high magnification (OM and SEM

The OM and SEM images after SAT + Q, showed a structure

analysis), of the as-built sample along the vertical plane.

seriously changed (Fig. 5 and Fig. 6) if compared with the

The measured hardness value of the as-built sample is 384

as-built material: the laser traces disappear completely and

HV. The solidified structure is composed by columnar and

the cellular and columnar structure have been replaced by

cellular morphology (red and black arrows respectively),

large lath of martensite. After the solution annealing treat-

and the melt pools are located by red dotted lines. Moreo-

ment and quenching, the hardness of sample results 312

ver through red dotted line, the laser track on etched sam-

HV.

Fig.3 - OM image of 300-grade maraging steel as-built sample. The red dotted lines delimitate the of the melt pools.

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Scientific papers - Stainless Steels

Fig.4 - SEM image of 300-grade maraging steel as-built sample. The columnar and cellular solidification structures are clearly visible.

The effect of AHT on SLM maraging steel

perature of 490 °C and the aging time of 6 hours. For higher

The aging hardness treatment effect have been studied for

temperatures as 550 °C and same aging time (6 h), the har-

six different temperatures (450 °C – 470 °C – 490 °C – 510

dness decreases from 583 HV to 532 HV, compared with

°C – 530 °C – 550 °C) and an aging time of 6 hours; the tre-

490 °C. The best configuration of AHT, corresponding to

atment followed the solution annealing and quenching tre-

the temperature of 490 °C and the aging time of 6 hours.

atment. The Fig. 7 shows clearly the hardness decreasing

This condition has been deeply investigated and the Fig. 8

trend in relation with the increasing of temperature, above

shows that at 490 °C the treatment time is not relevant as

490 °C. For high temperature the over aging phenomena

the heat treatment temperature. The aging time seems to

occurs, and leads to the coarsening of intermetallic com-

not be affective for the characteristic of hardness, in parti-

pounds and the reconversion of the metastable martensite

cular after 24 h of treatment the hardness is 590 HV, against

into austenite being [43]. In addition to this, an excessive

583 HV for 6 h. Fig. 9 and Fig. 10 show, respectively, the

long treatment time leads to the same trend with a decre-

SEM images relating to the best (490 °C, 6 hours) and the

ase of mechanical characteristics, in terms of strength, on

worst (550°C, 6 hours) aging treatment conditions, in terms

maraging steel. The best solution corresponds to the tem-

of hardness.

Fig.5 - OM image of 300-grade maraging steel after SAT + Q heat treatment.

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Memorie scientifiche - Acciai Inossidabili

Fig.6 - SEM image of 300-grade maraging steel after SAT + Q heat treatment.

Fig.7 - Values of hardness (HV10) in relation with temperature (aging time: 6 hours).

Fig.8 - Effect of aging time on hardness (treatment temperature: 490 °C).

La Metallurgia Italiana - Luglio-Agosto 2022

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Scientific papers - Stainless Steels

Fig.9 - SEM image referred to the best condition of AHT (490°C, 6 h).

Fig.10 - SEM image referred to the worst condition of AHT (550 °C, 6 h).

CONCLUSIONS

ser trace boundaries, with lath martensite microstructu-

In this work, the solution annealing treatment at 940 °C for

re. The hardness decreased from 384 HV to 312 HV after

2 hours and quenching effect on 300-grade maraging steel,

solution annealing treatment;

manufactured by SLM process, was investigated. Moreo-

3. The best aging hardness treatment condition was in

ver, the effect of a following aging hardness treatment was

correspondence of temperature of 490 °C and treatment

reported for different times and temperatures conditions,

time of 6 h; the hardness measured was 583 HV. Higher

in the time range of 6 h- 24 h and temperature range of 490

temperatures led to a decrease of hardness, due to physi-

°C - 550 °C.

cal phenomena such as coarsened of intermetallic com-

The main conclusions can be listed:

pounds and reversed austenite. Treatment temperature

1. The original microstructure of 300-grade maraging

of 550 °C led to a hardness value of 530 HV;

steel, manufactured by SLM process, is characterize

4. The aging time seems to be not affective on 300-grade

mainly by cellular and some areas of columnar solidifi-

maraging steel produced with SLM technology. The dif-

cation structure;

ference between 6 hours and 24 hours of treatment was

2. the solution annealing at 940 °C for 6 h and quenching,

about 10 HV.

replace completely the solidification structure and the laLa Metallurgia Italiana - July-August 2022

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Memorie scientifiche - Acciai Inossidabili

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Di Schino A. Analysis of phase transformation in high strenght low alloyed steel. Metalurgija. 2017; 56(3-4): 349-352.

Di Schino A, Alleva L, Guagnelli M. Microstructure evolution during quenching and tempering of martensite in a medium C steel.

Materials Science Forum. 2012; 715-716: 860-865.

Stornelli G, Montanari R, Testani C, Pilloni L, Napoli G, Di Pietro O, Di Schino A. Microstructure Refinement Effect on EUROFER 97 Steel for Nuclear Fusion Application. Materials Science Forum. 2021; 1016: 1392–1397.

Stornelli G, Di Schino A, Mancini S, Montanari R, Testani C, Varone A. Grain refinement and improved mechanical properties of EUROFER97 by thermo-mechanical treatments. Applied sciences. 2021; 11: 10598.

Tan C, Zhou K, Ma W, Zhang P, Liu M, Kuang T. Microstructural evolution, nanoprecipitation behav-ior and mechanical properties of selective laser melted high-performance grade 300 maraging steel. Materials and Design. 2017; 134: 23–34.

Yongqiang Y, Yuchao B, Mingkang W, Di Z. Influence mechanism of parameters process and me-chanical properties evolution mechanism of maraging steel 300 by selective laser melting. Materials Science & Engineering A. 2017; 703: 116-123.

Yadroitsev I, Mugwagwa Y, Matope S. Effect of Process Parameters on Residual Stresses, Distor-tions, and Porosity in Selective Laser Melting of Maraging Steel 300. Metals, 2019, 9: 1042.

Hanzl P, Zetek M, Baksa T, Kroupa T. The Influence of Processing Parameters on the Mechanical Properties of SLM Parts. Procedia Engineering. 2015; 100: 1405-1413.

Viswanathan UK, Dey GK, Sethumadhavan V. Effects of austenite reversion during over-aging on the mechanical properties of 18 Ni (350) maraging steel. Materials Science & Engineering A. 2005; 398(1-2): 367-73.

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Memorie scientifiche - Acciai Inossidabili

Laser OES - How an efficient melt shop monitoring tool tackles increasing energy and raw material costs A. Schlemminger

Winter 2021-2022.

The steel industry faces one of the most significant increases in energy prices in a short period. On the other hand, the shortage of alloying elements makes completely new process designs economically attractive. In this environment, dynamic process control is becoming increasingly important. But the availability of in-situ measurement data from the process is crucial for successful dynamic process control.

Until now, the composition of the slag was missing from this approach. Due to the time-consuming sample homogenization before analysis, the chemical composition of the slag was available post-mortem. But this has changed now, and the extremely fast Laser Optical Emission Spectroscopy (Laser OES) solves that issue. The measurement rate in the kHz range generates such large amounts of data that homogenization of data instead of physical samples is possible from now on. With early-stage deviation detection, the precise adjustment of slag parameters in small steps can tolerate more considerable variations in input materials.

KEYWORDS: LASER OES, LIBS, SLAG ANALYSIS, SAMPLE PREP. FREE ANALYSIS, MELT SHOP MANAGEMENT, LADLE FURNACE OPTIMIZATION, IN SITU PROCESS CONTROL, STEELMAKING EFFICIENCY; TODAYS ANALYSIS OF HETEROGENOUS MATERIALS The simplest and fastest method to analyze heterogeneous materials such as slags, dust, minerals, alloying materials, or others was the measurement with a (handheld) XRF device. After 2-4 repeated measures, an average analysis value was generated. Due to the few measurements, outliers resulting from sample heterogeneity can strongly influence the analysis result. Hence, this approach is considered somewhat unreliable for process control. Nevertheless, handheld XRF instruments are prevalent due to their usability and low investment.

Alexander Schlemminger QuantoLux Innovation GmbH, Germany

alexander.schlemminger@quantolux.de

Until now, the most common way to analyze heterogeneous samples quickly and accurately at the same time relied on X-ray-based technologies in combination with prior sample homogenization. This approach requires a solidified sample, undergoing plenty of preparation steps. The samples are first broken in a crusher within a few seconds and then magnetically demetallized. The subsequent grinding step takes approximately 2-5 minutes before the

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Scientific papers - Stainless Steels

ground material is pressed into a pellet. Even if the final

DISADVANTAGES OF TODAYS ANALYSIS APPROA-

analysis in an XRF laboratory instrument takes less than

CHES

one minute, the overall analysis time is over 10 - 15 minu-

Sample preparation error

tes.

As Fig. 1 displays, the sample preparation risks causing a

Very high analytical needs required even more complex

deviation, the so-called sample preparation error. Gene-

preparation steps. The measured sample reaches the ma-

ral causes for sample preparation errors are e.g., sample

ximum homogeneity in a glass beat or during the ICP-OES

carryovers from the previous to the subsequent samples

analysis. Both methods show even better analytical perfor-

or negative human influence for non-/partially automated

mances, like the pressed pellet XRF. However, they require

systems. For instance, contamination during the transport

considerably more than the 10 - 15 minutes mentioned.

of the sample from one preparation step to the other can reduce representativeness.

Fig.1 - Impact of the individual steps on the measurement error from sampling to analysis.

Particle sizes

faulty weighing of the digestion agent.

A too-short grinding time can lead to too large particle

Each of the deviations described can reduce the represen-

sizes since the material does not pulverize sufficiently. If

tativeness of the sample result and lead to incorrect deci-

the grinding time is too long, agglomeration effects may

sions in process control. Thus, the efficiency is reduced.

arise, causing the particle size to grow again. In both cases, the risk of segregation in the subsequent pressing

High equipment, labor, and maintenance costs

process increases considerably. Beneath the particle size,

To eliminate sample preparation errors and reduce labor

the wrong pressing speed or the pressing force can lead to

costs, laboratories use more and more partial or comple-

segregations within the pressed tablet. The sample is not

te automation. In addition, the use of selected laboratory

compacted sufficiently, and particles segregate inside the

crushers and mills can reduce contamination by sample

pellet.

carryover and presses with controlled lifting speeds to minimize the risk for segregation. Nevertheless, the high

Additives / binders

number of individual, specialized devices results in incre-

Alternatively, samples can be molten down or digested by

ased costs for purchase, maintenance, and servicing. In

liquid for XRF glass beat or ICP-OES measurements. Here

addition, the manual effort and the costs for the required

the risk of segregation is substituted e.g., with the risk of

automation for sample handling are significant. Automated

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Memorie scientifiche - Acciai Inossidabili

sample preparation systems alone easily cost more than

ration, automation, and analytical equipment necessary to

200 k€ plus 5 k€ maintenance per year. Binding materials,

perform the analysis forced an analysis in the main labora-

sample trays, and agents for melting or acid digestion can

tory.

additionally exceed 1€ per sample.

Therefore, (slag-) samples had to be first cooled at the sampling site, then packed and usually sent to the labora-

Remote instead of onsite analysis

tory manually or by pneumatic tube. The disadvantages of

Another disadvantage is that the analyzer and the sample

additional cooling, packaging, transport times and associa-

preparation equipment could hardly find a space close to

ted risk of sample contamination are on hand.

the sampling location. The complexity of sample prepa-

Fig.2 - Impact of the individual steps on the measurement error from sampling to analysis.

Long analysis time

ter nor ladle furnaces can wait that long for results due to

However, as Fig. 2 shows, the most significant disadvan-

throughput and energy efficiency reasons. Production

tage is the long period of 6-30 minutes from sampling to

continues, and as Fig. 3 displays, the analysis results opti-

the availability of reliable results. Usually, neither conver-

mize subsequent batches post-mortem.

Fig.3 - Deviation in steelmaking process due to post-mortem analysis.

In both cases, delayed analysis results can lead to instability

in the process, increased refractory consumption, reduced

La Metallurgia Italiana - Luglio-Agosto 2022

product quality, reduced throughput, higher energy consumption, poor product yield, and many other issues.

pagina 40

Scientific papers - Stainless Steels RAPID, SAMPLE PREP. FREE SLAG ANALYSIS BASED ON

It works equivalently to the established spark optical emis-

Laser OES principle

ser pulse instead of an electric spark generates the plasma.

LASER OES

Laser-based optical emission spectrometry, or Laser OES, can be an alternative to X-ray-based analytical approaches.

sion spectrometry (Spark OES) with the difference that a laTherefore Laser OES analyses metals and non-conductive materials such as slags.

Fig.4 - left: Laser OES principle – right: Laser OES Plasma ignited on slag.

Fig.4 shows that a pulsed laser focusing on the sample rai-

Individual points are analyzed one after the other, and the

ses the surface temperature in a tiny area.

measurement data is then homogenized in a fraction of a second using an appropriate calibration. In this way, a re-

A few micrograms of the sample material convert into pla-

presentative analysis result is generated even for highly he-

sma at up to 20,000 °C. During the regression of this pla-

terogeneous materials.

sma, a spectrometer collects the emitted light, which is specific to the sample's composition in the measurement

Calibration

position. The spectrometer converts the light signal into a

A specific calibration interprets each spectrum alone or a

piece of digital information. A Laser OES analyzer genera-

specific amount of spectra based on various mathematical

tes thousands of analysis values within seconds with a mul-

calculations. The most straightforward approach is to com-

ti-digit kHz measurement frequency. Based on that huge

pare the intensities and compare them with the concentra-

amount of data, the digital homogenization of data replaces

tions of the reference materials.

the physical homogenization of samples.

Fig.5 - Laser OES plasma on medium concentration material.

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Memorie scientifiche - Acciai Inossidabili

Fig.6 - Laser OES plasma on high concentration material.

As can be seen in the metal-making-related spectra shown

Laser OES works with the significant advantage of a main-

in Fig. 5 and Fig. 6, in the simplest case, already the bare eye

tenance-free and highly stable laser. The precise intensity

differentiates concentrations.

of monochromatic light ignites the plasma with a precisely determined amount of energy. Furthermore, the accuracy

Precision and representativeness

of the plasma-excitation position is defined down to a few

Compared to other OES-based analytical approaches, the

micrometers by the focus point of the Laser.

Fig.7 - Reproducibility of a heterogeneous steel making slag sample (measurement in Fig. 4).

Compared to other OES-based analytical approaches, the

ger problematic. The precise intensity of monochromatic

Laser OES works with the significant advantage of a mainte-

light ignites a plasma with a precisely determined amount

nance-free and highly stable laser as an excitation source.

of energy. Furthermore, the accuracy of the plasma-excita-

Laser lifetimes of 100,000 hours and more ensure that the

tion position is defined down to a few micrometers by the

excitation source runs without interruption for at least 10

focus of the Laser. Last but not least, the number of single

years. Deviations caused by maintenance activities, such as

measurements allows a much more comprehensive stati-

the exchange of X-ray tubes in XRF devices, are no lon-

stical evaluation, which also increases reproducibility.

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Scientific papers - Stainless Steels

As displayed in Fig. 7, the Laser OES can translate these

Stability with direct Laser OES analysis

advantages into similar analytical performances at the be-

As Figure 8 shows, the analysis of steel slag is significantly

ginning of its industrial use as XRF-based approaches after

faster with sample preparation-free laser OES.

decades of evolution.

Fig.8 - Laser OES direct slag analysis, sample prep. free and fast.

Results can be used earlier for process control. In addition,

much more closely than before at the same or lower cost.

the analysis becomes more accessible and less expensive.

Laboratory utilization is no longer an obstacle, with analy-

As a result, pyrometallurgical processes can be monitored

sis times well below 1 minute.

Fig.9 - Close-meshed, fast analysis for max. stability.

Figure 9 shows that close-meshed monitoring detects deviations earlier. A narrow process window can operate closer to the desired optimum efficiency.

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Memorie scientifiche - Acciai Inossidabili

BENEFITS

BOF. Therefore, the slag basicity and the MgO saturation

Converter splashing on demand

must meet a value that protects the refractory lining. But

Refractory lifetime is one of the most important KPIs in

to apply the slag on the walls, a specific minimum viscosity

steel making. A splashing of slag residues on the walls can

has to be achieved because it is almost impossible to blow

enhance refractory lifetime in converters, especially in the

semi-liquid up the walls.

Fig.10 - Converter splashing - tapping → slag analysis → splashing decision.

With the existing 15 minutes slag analysis, there is no chan-

Improved foaming = insulation

ce to check the slag composition before analysis.

In the EAF, especially for increasing pyrometallurgical

The new slag splashing on-demand, based on precise

operation due to the rising Phosphorus content in Direct

analysis values, enables to adapt dynamically to the actual

Reduced Iron, sufficient insulation is crucial to reach ener-

slag composition. Deciding pro- or contra slag splashing is

gy efficiency levels.

now possible before each tapping.

Fig.11 - Improved foaming in the EAF. Knowing the slag composition supports adjusting the addi-

use of secondary raw materials with its variations chal-

tives and the treatment time accordingly.

lenges melt shop managers. The close meshed and fast analysis enables to keep a stable process inside the pro-

Reduced slag former consumption and alloy oxidiza-

cess windows. Even if the deviation in incoming material

tion

establishes as day-to-day routine, an increase inefficient

For energy efficiency reasons the process windows are

buffers is avoided.

chosen as narrow as possible. On the other hand the rising La Metallurgia Italiana - Luglio-Agosto 2022

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Scientific papers - Stainless Steels

Fig.12 - Reduced oxidization, less slag former consumption, easy slag disposal.

The CaO consumption is kept on a minimum and still the

and simplifies disposal in byproduct sale instead of landfill.

oxidation of alloys into the slag is safely avoided. That sa-

Precise end-point determination

ves costs during purchase, it reduces the required melting

The availability of the slags' chemical analysis right after

energy and is makes life easy during disposal, since e.g. a

melting is a novel piece of additional information for the

too high Cr content in the slag forces to costly landfill in-

melt shop. Used solely or in combination with other pro-

stead of byproduct sale.

cess information, such as steel composition or temperature in a simulation model. As shown in Fig. 9 melt shop en-

Pinpoint slag former calculation

gineers can precisely determine the processing endpoint

For energy efficiency reasons, the process windows are as

based on that information. Overtreatment is efficiently eli-

narrow as possible. The increasing use of secondary raw

minated, and pyrometallurgical treatment continues exact-

materials with variations in chemical composition is a com-

ly as long as necessary. And no longer.

plex challenge for melt shop managers. The close-meshed and rapid analysis enables a stable process inside the pro-

Reduced refractory and ladle wear

cess windows and extensive and inefficient buffers become

Stable process control and increased production time with

needless. The challenge is to reduce CaO consumption to

optimum basicity can reduce the reactivity between slag

a minimum and, at the same time, to prevent Fe and alloys

and refractory. This is advantageous for refractory lining

from oxidizing into the slag o. This optimization saves co-

and ladle lifetime.

sts during purchase, reduces the required melting energy,

Fig.13 - Precise basicity, reduced refractory & ladle wear, cleaner steel.

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Memorie scientifiche - Acciai Inossidabili

Thus, the extension of the ladle lifetime can also contribute

non-metallic inclusions, which also reduces the arising of

to the increased overall efficiency.

unwanted inclusions.

Clean steel

Easy disposal

The reduced refractory wear, described in the previous

Knowing the slag composition, before tapping the melt

section, has an additional benefit on the cleanliness of the

shop engineer can adjust the slag composition according

steel. Since Fig. 13 shows less refractory material dissol-

to the by-product-sale/disposal strategy. The waste be-

ving in the slag/steel melt, less refractory ends up as an

comes an attractive by-product by further reducing Chro-

inclusion in the product. Furthermore, the increased sta-

mium in the steel. With the rapid slag analysis, Melt shop

bility of the melt enables the targeted reduction of other

engineers can even make more radical decisions.

Fig.14 - – Precise basicity, reduced refractory & ladle wear, cleaner steel.

Based on the composition, they can decide to post-pro-

splashing-on-demand or post-process LF slag optimiza-

cess the slag after steel tapping. The additional heating

tion become a reality.

energy and processing time tackle the overall efficiency,

Laser OES thus represents an essential element for the re-

but in certain circumstances, the advantages of easy slag

source-efficient steel industry.

disposal can compensate for the disadvantages.

CONCLUSION Until now, slags could not be analyzed in-situ. The extensive sample preparation time resulted in the production receiving the slag analysis mostly only post-mortem. As a further development of spark OES, Laser OES now enables direct analysis in well under 1 minute. According to the expression “who knows a lot, can optimize a lot” overall analysis time allows melt store engineers to make in-situ decisions based on actual analysis. The process windows can be smaller, and buffers can be reduced. In addition, previously unthinkable production strategies such as slag-

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Scientific papers - Stainless Steels

REFERENCES [1]

[2]

[3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]

Buckley S., Eloot K., Görner S., Malladi R., and Mori L. McKinsey & Company 2021, "How AI-powered solutions can help optimize smelters", https://www.mckinsey.com/industries/metals-and-mining/our-insights/how-ai-powered-solutions-can-helpoptimize-smelters Bruzenak L., Campbell I. “The Common Sources of Error in Sample Preparation for XRF Analysis andthe Capabilities of Standalone Automation” https://cdn2.hubspot.net/hubfs/494827/AAACaseStoryPDF/Common_sources_of_error_in_sample_preparation_ for_XRF_Analysis_and_the_Capabilities_of_Standalone_Automation.pdf Cremers, David A., Leon J. Radziemski, 2013, Laser-Induced Breakdown Spectroscopy. Chiches-ter: John Wiley & Sons Ltd. Esbensen K.H., Wagner C., "Why We Need the Theory of Sampling” https://theanalyticalscientist.com/techniques-tools/why-weneed-the-theory-of-sampling Kolmhofer, P.; Eschlböck-Fuchs, S.; Huber, N.; Rössler, R.; Heitz, J.; Pedarnig, J.: Calibration-free analysis of steel slag by laserinduced breakdown spectroscopy with combined UV and VIS spec-tra. Spectrochim. Acta Part B At. Spectrosc. 2015, 106, 67–74.

Kolmhofer, B.; Pedarnig, J.; Praher, R.; Huber, N.; Rössler, J.H.: Element analysis of complex ma-terials by calibration-free laserinduced breakdown spectroscopy. Appl. Phys. A 2013, 112, 105–111.

Kraushaar M.; Noll, R.; Schmitz, H.: Multi-elemental analysis of slag from steel production using laser induced breakdown spectroscopy, Int. Meet. Chem. Eng. …, p. 2000, 2000.

Kraushaar M.; Noll, R.; Schmitz, H.: Slag analysis with laser-induced breakdown spectrometry, Appl. Spectrosc., vol. 57, no. 10, pp.

1282–1287, Oct. 2003.

Miziolek M.; Palleschi, V.; Schechter, I.: Laser Induced Breakdown Spectroscopy: Fundamentals and Applications. 2006.

Noll R., 2012 "Laser-Induced Breakdown Spectroscopy - Fundamentals and Applications" pp. 429-235, Springer Verlag: Düsseldorf Steininger V., "Neues Analysesystem für Schmelzrückstand" https://www.voestalpine.com/blog/de/innovation/neuesanalysesystem-fuer-schmelzrueckstand/ Sturm, V.; Noll, R.: Determining the Lime Standard for Liquid Slag with LIBS; https://www.ilt.fraunhofer.de/content/dam/ilt/en/ documents/annual_reports/ar13/AR13_P126.pdf Sturm, V.; Schmitz, H.; Reuter, T.; Fleige, R.; Noll, R. Fast vacuum slag analysis in a steel works by laser-induced breakdown spectroscopy. Spectrochim. Acta Part B At. Spectrosc. 2008, 63, 1167–1170.

Thurston A., 2019, “The Role of X-Ray Fluorescence for In-Process Steel Slag Monitoring” https://www.azom.com/article. aspx?ArticleID=18627 Zhang, T.; Wu, S.; Dong, J.; Wang, K.; Tang, H.; Yang, X.; Li, H. Quantitative and classification analysis of slag samples by laser induced breakdown spectroscopy and partial least square (PLS) methods. J. Anal. At. Spectrom. 2015, 30, 368–374.

TORNA ALL'INDICE >

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Organised by

Six years after the successful first conference on the topic, AIM, in cooperation with its sister society ASMET, organises once again a twoday event focused on the Surface Quality of continuously cast products.

The surface quality of ingots, billets, blooms and slabs is a particularly important issue in order to insure the required surface quality of final rolled and forged products. This aspect is becoming increasingly significant especially nowadays, when a lot of steelmakers are refocusing their activity on the search for better surface quality or new specialty steels requiring high quality surface features. All this lays on a table of new challenges faced by steelmaking industries, when energy efficiency and consequently lower environmental impact are concerned.

This international meeting aims at sharing the knowledge about the improvement of the surface quality of the continuously cast products and this scope will be achieved by clear expositions about: • recent advances on the defect analysis; • the root cause of the defects; • innovative lubricating products; • operations and maintenance; • application of electromagnetic devices; • AI applications, simulation and computing methods.

New call for paper deadline: 26th September, 2022 Prospective authors wishing to present are invited to submit a tentative title and an abstract of maximum 400 words (in English) to the Organising Secretariat (met@aimnet.it).

The abstract should provide sufficient information for a fair assessment.

Two ways to submit papers will be available: • to fill in the form online >> www.aimnet.it/iwsq-2.htm • to send the title and the abstract, together with the requested information (Name and Surname, Affiliation, Mailing Address, Phone, Fax and e-mail) by e-mail to: met@aimnet.it The Conference will be held in Bergamo at the Congress Center Giovanni XXIII, viale Papa Giovanni XXIII, 106 (http://www.congresscenter.bg.it).

Bergamo greets visitors with its Venetian Walls. Surrounded by rivers and lush, verdant valleys, crossed by paths that widen to Parco dei Colli, the area’s largest park, the city looks like a lounge filed with art, culture and nature, with a fascinating and complex history just waiting to be shared with others. The “upper and lower” city reveals a mixture of pleasant surprises and unexpected encounters, such as those with Gaetano Donizetti, the great composer of international renown, Bartolomeo Colleoni, the Bergamo leader who served under the Republic of Venice and Lorenzo Lotto, among the most famous Italian Renaissance artists who lived and worked in Bergamo for over a decade.

www.aimnet.it/iwsq-2.htm

Industry news - Attualità industriale

Technologies paving the way to carbon neutral stainless steel production edited by: J. von Schéele, H. Alshawarghi, D. Razzari

Many steelmakers have set carbon neutral goals over the 2030-2050 timeframe. Naturally near-term approaches are focused on minor alterations and improvements parallel to mapping out longer term options. However, any technology change today should be ready for future use of hydrogen. Increase of the energy-efficiency immediately reduces the carbon footprint, and for most stainless steel producers there are four processes to address: the electric arc furnace (EAF); the AOD converter; ladle preheating; reheating and annealing. This paper discusses how this can take place and how use of hydrogen is considered. CoJet was introduced by Linde 25 years ago, and it has revolutionized EAF operation. Today more than 170 EAFs are using CoJet, yet rather few among stainless steel makers. The energyefficiency of the AOD can be approved by using good performing control systems. An example of the that is AOD-IRS, which is successfully in operation at more than 100 AOD converters. To achieve preheating and reheating with a low carbon footprint – and ultimately bring it to zero – a first step is to increase the energy-efficiency. Flameless Oxyfuel has a demonstrated ability to reduce the fossil fuel consumption in ladle preheating and reheat furnaces by typically 20% to -50%. With more than 200 installations in ladle preheating and 180 in reheating and annealing, it is a wellestablished solution, which already has led to considerable decarbonization, and installations using hydrogen as fuel will be commissioned shortly.

KEYWORDS: STAINLESS STEEL, CARBON FOOTPRINT, AOD, ENERGY EFFICIENCY, OXYFUEL, REHEATING, HYDROGEN; INTRODUCTION From a life-cycle perspective, stainless steel often can be considered as a preferred option compared to competing materials, but there are large opportunities to strengthen this position further, with a focus on improving its production. Many steelmakers have set carbon neutral goals over the 2030-2050 timeframe. On average, considering Scope 1+2, stainless steel producers have a smaller carbon footprint than most carbon steel producers, yet many are investigating various available decarbonization approaches. In stainless production, the importance of Scope 3 emissions is huge. Accordingly, it is vital attention is paid to the carbon footprint when procuring alloys

Joachim von Schéele

Linde Technology, Linde plc, Germany joachim.von.scheele@linde.com

Hamzah Alshawarghi Linde Technology, Linde plc, USA

– alloys could be a large contributor to the final carbon footprint of the stainless steel product. The carbon footprint of, e.g., nickel can make the resulting carbon footprint of the stainless steel product increase several times. [1][2][3]

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Attualità industriale - Industry news

Using Green Power – based on renewable energy sour-

EAFs; the first commercial installation was commissioned

ces – is an obvious step that can be taken wherever possi-

in 1996. In an EAF, the laser-like oxygen jet from a cohe-

ble. The biggest consumer of electricity is the Electric Arc

rent injector travels significantly farther than an oxygen jet

Furnace (EAF). Typically procuring Green Power would

from a conventional supersonic lance. Hence, coherent

decrease CO2 emissions by 50-200 kg per tonne of steel

jet injectors can be positioned well above the bath in the

produced, depending on how the currently used electri-

sidewall of the furnace, and still carry out effective bath

city is produced at the specific location. Green Power

lancing. Also, when the coherent jet of oxygen produced

preferably also should be used to produce the required

by the nozzle impinges and penetrates through the slag

industrial gases (oxygen, argon, nitrogen).

and into the molten steel bath, the concentrated momentum of the oxygen jet dissipates in the steel as fine bub-

Naturally, near-term approaches to decarbonization are

bles, providing deep penetration and effective slag-metal

focused on minor alterations and improvements paral-

mixing. This results in high efficiency lancing and decar-

lel to mapping out longer term options. However, any

burization. [4][5]

technology change today should take the future into account, e.g., being ready for use of hydrogen. Increase of

In addition to lancing, the CoJet injector also provides

the energy-efficiency immediately reduces the carbon

other multiple functions. Each injector, as needed during

footprint. Following the mainly used production route

the heat, functions as a burner to melt scrap and to simul-

for stainless steel, there are four processes to address:

taneously inject supplementary oxygen at subsonic ve-

the EAF; the AOD converter; ladle preheating; reheating

locity to achieve post combustion. The post combustion

and annealing. Here improved control and use of oxyfuel

oxygen is introduced in a controlled fashion at a speci-

combustion can significantly increase the energy-effi-

fic shallow angle and close to the main lance oxygen to

ciency This paper discusses how this can take place and

achieve maximum benefits, not only during scrap melting,

how use of hydrogen is considered. Moreover, oxyfuel

but also during flat bath periods. This results in further re-

combustion, producing a much smaller flue-gas volume

duction in electric power consumption, with concomitant

with a high concentration of CO 2, also supports Carbon

increase in furnace productivity. Finally, included in the

Capture Storage and Use (CCUS).

CoJet injector assembly, is the feature to introduce car-

Linde has a long history working with its customers in

bon. The carbon is injected in a fully automated mode

the stainless steel industry, and development of new te-

through a port specifically located to allow for effective

chnologies and solutions, frequently in cooperation with

slag foaming and reduction. Under proper conditions, this

leading steelmakers, has always been in focus. Naturally,

injected carbon can also provide some recarburisation of

the most famous among them is the AOD process, in-

the bath. The benefits resulting from this efficient mode

vented by Linde already back in 1954 and today used for

of carbon injection is the excellent slag foaming achie-

more than 75% of the world’s stainless steel production.

ved, with significantly reduced quantity of injected carbon

Another example is the REBOX® technology, applying

used.

Flameless Oxyfuel in reheating and annealing, where the first two installations took place at Outokumpu’s mills at

With over 170 installations worldwide, covering all types

Degerfors and Nyby in Sweden in 2003.

of EAFs and all kinds of charge mixes, the successful and energy efficient results of using CoJet has been fully pro-

USE OF COJET SYSTEMS IN THE ELECTRIC ARC FUR-

ven. Stainless steel producers using CoJet include, e.g.,

NACE

Jindal Stainless, Electralloy, and North American Stain-

Since the CoJet® technology was introduced by Linde 25

less, however, there are great opportunities for many

years ago, it has revolutionized the EAF operation. The

more mills to beneficially use CoJet to increase efficiency

concept of coherency was then translated into use in

and reduce carbon footprint. [6]

La Metallurgia Italiana - Luglio-Agosto 2022

pagina 50

Industry news - Attualità industriale

Fig.1 - Four CoJet injectors in operation in an EAF.

CONTROL OF THE AOD PROCESS

heat and automatically controls the continuous ratio pro-

Since bringing the AOD to the market in the 1950s, Lin-

gression of oxygen to inert gas (nitrogen and/or argon),

de has continued to work with the process and support

and the nitrogen-to-argon switch point. When interme-

its customers. Over the past decades, a strong focus has

diate carbon content and temperature are measured, the

been on the process control, and Linde introduced the In-

system automatically updates for the new conditions.

telligent Refining System (IRS), a platform that improves

Once decarburization begins with the IRS, everything

AOD process efficiency and productivity. The IRS models

proceeds automatically. The system calculates the le-

carbon content and temperature during decarburization,

ast-cost additions to achieve the melt’s aim chemistry.

and controls reduction temperature and chemistry. The

The system rotates the AOD vessel to the proper position

system also performs all tasks and calculations, including

for blowing, sampling, charging or making additions, and

automatic vessel positioning, ratio and inert gas selection,

injects the right gases during each of these operations.

and alloying requirements. Computer-controlled, stan-

During decarburization, Linde’s IRS monitors the top and

dardized operating procedures ensure consistency, and

bottom oxygen being blown and determines the metal

allow manual override of the system when necessary. By

chemistry. It can also calculate the amount and types of

interfacing IRS with scales, spectrometers and thermo-

reducing agents and fluxes that must be added. As decar-

couples, the devices themselves directly enter heat wei-

burization is completed, the reduction mix becomes avai-

ght, chemistry, and bath temperature into the system wi-

lable. If the projected temperature after reduction is be-

thout operator input. [7][8]

low the desired tap temperature, the IRS can calculate the fuel, flux and oxygen required for reheating to the desired

The IRS controls the three major steps in AOD process

temperature. At the end of the heat the IRS calculates le-

refining: Decarburization, Reduction, and Final Chemistry

ast-cost additions to meet specified compositions. The

and Temperature trim. On the HMI screen, in the fore-

required calculation inputs, after-reduction chemistry,

ground, the operator works with the program controlling

current weight and grade specifications are all entered or

the metallurgical processing steps, while a background

traced automatically and used to calculate the least-cost

program determines temperature and chemistry. These

additions with available alloying agents. During normal

complex calculations are made exactly the same way each

processing, overriding the automatic values should not

time. During decarburization, IRS dynamically models the

be necessary.

La Metallurgia Italiana - July-August 2022

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Attualità industriale - Industry news

IRS also increases the carbon removal efficiency by op-

with the first installations at stainless steel producer Ou-

timizing the decarburization blow results in less metallic

tokumpu. The feature of reducing NOx emission has been

oxidation and less reduction requirements (silicon and

a proven success, but the large improvement of tempera-

aluminium alloys). Increased oxygen blow rates (when

ture uniformity has also been an important key to its suc-

appropriate) also speed up the heat time and decrea-

cess. Use of Flameless Oxyfuel has demonstrated energy

se heat losses to the environment. The lower total heat

savings of up to 65%; most installations with an operation

losses, in turn, result in less heat to be made up through

fully converted from air-fuel to Flameless Oxyfuel show

oxidation of various elements, which ultimately decre-

fuel and CO2 savings of 20% to 50%. Linde has made more

ases the reduction alloy consumption. The decrease in

than 400 installations of Flameless Oxyfuel in practically

reduction alloys not only has a direct alloy cost, but also

all kinds of steel reheating and annealing furnaces, alu-

decreases slag-making additions (lime, magnesia, and

minium and copper melting furnaces, and ladle and other

dolomitic lime). The slag volume that must be handled

vessel preheating systems. If the full potential of using

is decreased, which lowers the heat load on the system.

Flameless Oxyfuel in the steel production processes were

Thus, there are decreases in consumption of reduction

captured, the global steel industry’s combined carbon fo-

alloy and slag- making additions in addition to those due

otprint would be reduced by 200 million tonnes annually.

directly to improved carbon removal efficiency.

[9]

Since its introduction in 1995, the IRS has been installed in

In Flameless Oxyfuel the mixture of fuel and oxidant re-

more than 100 vessels in more than 12 countries ranging

acts uniformly through the reaction flame volume, with

in size from 3 tonnes to 120 tonnes. IRS customers have

the rate controlled by partial pressures of reactants and

observed decreases in reduction alloy costs, processing

their temperature. In Flameless Oxyfuel, the combustion

time, argon consumption, and refractory consumption.

gases are effectively dispersed throughout the furnace,

Also, the improvement in AOD process efficiency and

ensuring more effective and uniform heating of materials

productivity results in a lower tap to tap time and a lower

even with a limited number of burners installed. Although

carbon footprint.

the first installations took place in reheating and annealing, Flameless Oxyfuel was quickly adopted for preheating of

FLAMELESS OXYFUEL COMBUSTION

ladles and converters where it has demonstrated great re-

To achieve preheating and reheating with a low carbon

sults as well. The next area being exploited, with substan-

footprint – and ultimately bringing it to zero – a first step

tial positive impact, could be the blast furnace hot stoves.

is to increase the energy-efficiency. Flameless Oxyfuel

Another interesting area is use of low calorific fuels, e.g.,

combustion occurs under diluted oxygen concentration

blast furnace top gas; use of oxyfuel strongly supports

as flue gases are mixed into the combustion zone. This

a successful use of low calorific gases. The lower flame

slows down the oxyfuel combustion reactions and results

temperature – same temperature as at traditional air-fuel

in lower flame temperatures, which are below the point

combustion – substantially reduces the NOx formation,

of thermal NOx creation. It reduces flue gas volumes by

which together with the temperature uniformity results in

75-80% due to lower fuel consumption and no nitrogen

NOx emissions substantially lower than with air-fuel com-

in combustion. Low flue gas volumes with very high CO2

bustion. Moreover, the excellent temperature uniformity

concentration are of course favourable for CCUS. The

achieved leads to reduced heating times and, in case of

mixing of flue gases into the flame also disperses the

reheating, to reduced scale losses. [10][11]

energy throughout the entire vessel or furnace for faster and more uniform heating.

Linde started applying Flameless Oxyfuel already 2003

La Metallurgia Italiana - Luglio-Agosto 2022

pagina 52

Industry news - Attualità industriale

Fig.2 - FRound billets for tube production being heated before piercing using Flameless Oxyfuel in a Rotary Hearth Furnace at ArcelorMittal in the USA. Here the conversion from air-fuel resulted in fuel savings of 60%..

LADLE PREHEATING

ted, use of Flameless Oxyfuel is decreasing the NOx emis-

Ladle preheating using Flameless Oxyfuel, like in Linde’s

sions compared to air-fuel. [12]

OXYGON® system, has been demonstrated to typically lead to fuel (and CO 2) savings of 40-60%, shorter heating

Over the past decades more than 200 OXYGON systems

times, lower NOx emissions, more uniformly heated lad-

have been successfully put into operation for vessels

les, longer ladle life, and – if wanted – to higher preheating

from one tonne up to several hundred tonnes. Examples

temperatures. An example of the benefits of the latter, is a

of stainless steel producers using this technology for

recent installation where the steel mill was able to lower

preheating of ladles and converters, include companies

the tapping temperature of the EAF and thereby achieve

like Acerinox, Outokumpu, Sandvik, and Walsin.

electricity savings at more than 20 kWh/t. It should be no-

Fig.3 - OXYGON Flameless Oxyfuel ladle preheating at Taiwanese stainless steel producer Walsin.

La Metallurgia Italiana - July-August 2022

pagina 53

Attualità industriale - Industry news

REHEATING AND ANNEALING

batch furnaces, e.g., soaking pit and chamber furnaces.

Reheat furnaces typically consume 1.2-1.6 GJ/t of steel,

Among prominent users could be mentioned several pro-

and Flameless Oxyfuel solutions can reduce fuel and CO 2

ducers of engineering steel grades, including Ascométal

emissions from reheat furnaces by up to 60%. Linde is

(nowadays a French subsidiary of Swiss Steel), Mahindra

the world-leader in oxyfuel steel reheating; its REBOX®

Sanyo (Indian subsidiary of the Japanese company Sanyo)

Flameless Oxyfuel technology for reheating and anne-

and Ovako (Sweden). But there are also examples of in-

aling was introduced 20 years ago. The total number of

stallations in continuous furnaces like Rotary Hearths and

installations – in all types of furnaces and for all kinds of

Walking Hearths at, e.g., ArcelorMittal (USA) and Sandvik

steel grades – has reach above 180 and at more than 40

(Sweden). Those include final products like seamless pi-

steel mills worldwide. Converting a reheat furnace com-

pes and rock drills. Other examples are found in annealing

pletely into full Flameless Oxyfuel combustion is a rather

of stainless steel, e.g., for production of wire rods at Yon-

big task, particularly if it is a large continuous furnace.

gxing and Dongbei Steel in China and strips at Outokum-

Therefore, most of such conversions has taken place in

pu in Sweden.

Fig.4 - Coiled wire rod entering a REBOX DST line operating 100% with Flameless Oxyfuel at Yongxing, China, providing the world’s lowest fuel consumption for stainless wire rod annealing.

Partial or full conversion of reheat furnaces from air-fuel

The concept to REBOX HLL is an add-on solution where

to Flameless Oxyfuel combustion is not only a relatively

the existing air-fuel burners are kept for fuel supply and a

easy first step to decarbonization, but it also prepares the

partial oxygen (air) supply but with the main oxygen re-

furnace for subsequent hydrogen fuels. Indeed, oxyfuel

quired injected through a high-velocity lance adjacent to

combustion will be necessary with hydrogen fuels. For

the air-fuel burner, is an efficient and flexible solution.

20 years Linde has applied Flameless Oxyfuel to impro-

REBOX HLL provides a semi flameless semi oxyfuel re-

ve temperature uniformity and secure reduction of NOx

gime delivering typically 10% to 30% fuel savings and

emissions, a matter particularly important going forward

throughput increase. This solution, installed in more than

including use of H2. [10][11]

30 furnaces worldwide, is particularly suitable for large continuous furnaces. It is so far in operation at up to

More than 40 installations have taken place at stainless

300 t/h; the largest furnaces using REBOX HLL are found

steel producers, achieving substantial fuels savings. The

at Masteel in China, Outokumpu in Finland, and SSAB in

largest furnace fully converted from air-fuel to 100% Fla-

Sweden. Over the past 12 months REBOX HLL projects

meless Oxyfuel is found at Outokumpu in Sweden, being

have been commissioned at Jindal Stainless in India, Celsa

a 150 t/h catenary furnace with 40 MW all oxyfuel with re-

in Norway, Amsteel in Malaysia, and ArcelorMittal in Ger-

sulting fuel savings at 40%.

many.

La Metallurgia Italiana - Luglio-Agosto 2022

pagina 54

Industry news - Attualità industriale

Despite only being a partial conversion, typically in the

of the system, which can be turned on and off with a re-

pre-heating and/or heating zones, REBOX HLL has de-

sponse time of less than a minute, is that its installation

monstrated great results on increased temperature uni-

and commissioning do not require any furnace down-ti-

formity and reduced scale losses. An additional advantage

me; all can take place during a scheduled stoppage.

Fig.5 - Discharging of a stainless steel ingot from soaking pit furnace at Sandvik, Sweden, operation with 100% Flameless Oxyfuel.

Fig.6 - Installation of a high-velocity lance as part of a REBOX HLL system at Outokumpu’s plant at Tornio, Finland.

HYDROGEN READY OXYFUEL COMBUSTION

otprint, but it has been demonstrated hydrogen is the ide-

Hydrogen combustion results in a 100% H2O as product

al fuel for CoJet! The CoJet injection system with hydrogen

of combustion, thereby no CO2 emissions. Over the past

as fuel is ready for full implementation in operation. [4][6]

years Linde has performed tests at its Technology Centres to develop hydrogen burners and to assess the impact of

Starting in spring 2018 Linde has evaluated combustion

hydrogen combustion.

with Flameless Oxyfuel in up to 1.0 MW scale using hydrogen as fuel partly or fully. The results clearly showed

The CoJet technology has been tested with hydrogen as

the benefits of Flameless Oxyfuel, including temperature

fuel. Previous fuels used in operation include natural gas,

uniformity and low NOx emissions, could be maintained.

LPG, coke oven gas, and fuel oil. It was concluded from

Next step was then to evaluate impact on materials. and

those tests that with hydrogen as fuel the longest jets are

pilot tests were carried out with 10 kg samples together

produced and the scrap melting is enhanced. Accordin-

with steel and aluminium producers for reheating and

gly, using hydrogen does not only reduce the carbon fo-

melting, respectively. Those pilot test were encouraging,

La Metallurgia Italiana - July-August 2022

pagina 55

Attualità industriale - Industry news displaying no negative impact on the materials.

of quality as always. A thorough inspection and analysis of

Based on the positive outcome from the pilot tests, en-

the final bars showed that heating using hydrogen as fuel

gineering steel producer Ovako and Linde decided to

does not impact the quality. Ovako has concluded that

make a full-scale demonstration of hydrogen-hydrogen

they are confident hydrogen can be used simply and flexi-

reheating in a soaking pit furnace at Ovako’s Hofors mill in

bly, with no impact on steel quality, which would mean a

Sweden. This the world’s first heating of steel with 100%

very large reduction in the carbon footprint. A permanent

hydrogen as fuel was carried out in March 2020 with 25 ton-

full-scale installation of REBOX Hyox at Ovako Hofors is

nes of ball-bearing steel ingots. The pit furnace was fired

planned for 2023, where both the oxygen and the hydro-

with hydrogen-oxyfuel using REBOX Hyox. After heating

gen will be produced by using renewable energy. [13][14]

and soaking, the ingots were successfully rolled to bars in

Also for ladle preheating the OXYGON Hyox systems,

the rolling mill. Rolling forces, dimensions, scale losses

operating with 100% hydrogen as fuel, are expected to be

and temperature uniformity were at the same high level

commissioned within the coming 12 months.

Fig.7 - The world’s first full-scale reheating of steel with 100% hydrogen as fuel, using REBOX Hyox Flameless Oxyfuel, at Ovako’s Hofors mill in Sweden in March 2020.

CONCLUSIONS Stainless steel production has great opportunities to re-

Another area to focus on is increased energy efficiency,

ally move ahead towards becoming carbon neutral, whi-

which can take place without cost penalty and alteration

ch, given its advantages in use, would further strengthen

of the existing processes. Use of oxyfuel solutions in the

the sustainability position of stainless steel. At most pla-

EAF, ladle preheating, reheating and annealing processes,

ces, use of hydrogen is yet not viable, however, there are

are well proven solutions. Moreover, further improve-

actions that can be taken immediately to reduce the car-

ments in process control, e.g., in the AOD process, will

bon footprint of stainless steel production. Scope 2 and

also contribute with improved yields and reduced use

Scope 3 play important roles here, including the carbon

of input materials. Not only would oxyfuel decrease the

footprint of, e.g., power and alloys; often there are choi-

fuel consumption today, but also – as these solutions are

ces that could have a large positive impact.

hydrogen-ready – decrease the need for hydrogen going

La Metallurgia Italiana - Luglio-Agosto 2022

pagina 56

Industry news - Attualità industriale forward.

becomes available to achieve full decarbonization in the future.

The economics of oxyfuel combustion are typically dri-

The journey to carbon neutral stainless steel production

ven by fuel price, but as steel mills adopt green hydrogen

does not have to wait for viable supply of hydrogen. The-

fuel to decarbonize their footprint, oxyfuel combustion

re are great options for immediate decarbonization, with

will become economically necessary. This is because

a careful and selective procurement of power and alloys,

hydrogen prices are expected to drop down to around

but not at least for using Flameless Oxyfuel in ladle prehe-

€2/kg, which is equivalent to €15/GJ, i.e., hydrogen will

ating, reheat furnaces and annealing lines to substantially

always be a relatively expensive fuel; accordingly, oxyfuel

reduce the carbon footprint. Those proven technologies

combustion is required to minimize its use. Therefore, the

are hydrogen-ready and the first permanent installations

recommendation to steel mills is to convert to oxyfuel

using hydrogen as fuel are now under way to be installed,

combustion now to achieve 20% to 50% CO2 reduction

to turn them into zero CO2 emissions processes.

and be prepared to start using Green hydrogen when it

REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]

[13] [14]

Mathur PC, von Schéele J. Decarbonizing Solutions for Steel. Steel Times International, Apr, 2021.

Samuelsson P, von Schéele J. Improving Life-Cycle of Stainless Steel: From Start to Finish. Stain-less Steel World Americas, Jun, 2022, p. 10-11.

Wei W, Samuelsson P, Tilliander A, Gyllenram R, Jönsson P. Energy Consumption and Greenhouse Gas Emissions of Nickel Products. Energies 13(6564), Oct, 2020.

Mathur PC, Mahoney WJ, Warty SK, von Schéele J. CoJet® – 25 years of Revolutionizing EAF Steelmaking. Steel Tech, vol. 15, No. 4, Jul, 2021, p. 65-71.

Editorial. Electric steelmaking: 25 years of CoJet technology. Steel Times International, Sep, 2021, p.43-47. von Schéele J, Mathur PC, Bridger W. Hydrogen-Ready Energy-Efficient Technologies for EAF Steelmaking. 12th European Electric Steelmaking Conference, organised by IOM3, Sep 12-14, 2021, Sheffield, UK. Chan AH, Andrew W. Cullen AW, Stambaugh L, Wiencek JP. Operating Experience with Praxair’s AOD Intelligent Refining System.

17th Process Technology Conference, Iron and Steel Society, Or-lando (FL), Nov, 2000.

Chan AH, Alshawarghi H. AOD Process Control: From Slide Rule to Factory Automation AISTech 2019, Pittsburgh (PA), USA, May 6-9, 2019. von Schéele, J. Short-term Possibilities to Decrease CO2 Emissions from the Steel Industry. Inter-national Journal of Green Energy, vol. 3, no. 2, July 2006, p. 139-148.

Blasiak, W, Yang W, Krishnamurthy N, von Schéele, J. Flameless Oxyfuel Combustion for Fuel Consumption and Nitrogen Oxides Emissions Reductions and Productivity Increase. Journal of the Energy Institute, vol. 80, no. 1, Mar, 2007; p. 3-11.

Pfeifer, H., Högner W, Fredriksson P, von Schéele J, Paul R. Energieeffizienz und Minderung des CO2-Ausstoßes durch Sauerstoffverbrennung“, Stahl und Eisen, Aug, 2009.

Nakkhong C, Nutthaphong Tangprasopchot N, Tananiran P, Doijad G, von Schéele J. Successful Results from Improved Sustainability

by Using Flameless Oxyfuel in SYS. 2019 Annual Meeting & Conference of South East Asia Iron and Steel Institute (SEASI), Jun 16-19, 2019, Bangkok, Thailand. von Schéele J. Decarbonizing and Use of Hydrogen in Reheat Furnaces. 3. Aachener Ofenbau- und Thermoprozess-Kolloquium, Oct 7-8, 2021. Aachen, Germany. von Schéele J. Advancing Use of Hydrogen as Fuel in Steelmaking. Millenium Steel, May, 2022, p.20-22.

TORNA ALL'INDICE >

La Metallurgia Italiana - July-August 2022

pagina 57

Organi e Cariche Sociali 2022/2024

Presidente

Sig. Silvano Panza - IPSAI

Vicepresidenti

Dr. Paolo Cattaneo - TenarisDalmine Ing. Maurizio Fusato - Gruppo Feralpi

Past President

Prof. Carlo Mapelli - Politecnico di Milano Ing. Federico Mazzolari - Gruppo Arvedi

Segretaria del Consiglio

Ing. Francesca Maurigh - ABS

Consiglieri

Dr.ssa Paola Artioli - Asonext Spa Dr. Giovanni Banzato - Acciaierie Venete Prof. Franco Bonollo - Università di Padova - DTG Ing. Andrea Colombo - A.C.S.A. Steel Forgings Spa Ing. Uggero De Miranda - ORI Martin Dr. Alessandro Ferraiuolo - Marcegaglia Carbon Steel Sig.ra Alessandra Franchini - Franchini Acciai Sig. Ezio Gianotti - F G Gruppo Spa Dr.ssa Vittoria Gozzi - Duferco Ing. Enrico Malfa - Tenova Dr.ssa Simona Maura Martelli - Fondazione Promozione Acciaio Ing. Matteo Marten-Perolino - Cogne Acciai Speciali Dr. Paolo Morandi - Siderweb Dr.ssa Raffaella Poggio - Pipex Dr.ssa Agnese Sangoi - Sangoi Spa Dr.ssa Cinzia Vezzosi - Assofermet

Tesoriere

Dr. Stefano Vittadini - Co.Re.As.

Revisori dei Conti

Dr. Arrigo Berenghi - Berenghi e Soci Dr.ssa Anna Giacovelli - Studio AGV Dr. Maurizio Perugini - Berenghi e Soci

Segretario Generale

Dr.ssa Federica Bassani

Direttore della rivista La Metallurgia Italiana Ing. Mario Cusolito

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Atti e notizie - AIM news

Comitati tecnici / Study groups CT CORROSIONE (C)

(riunione telematica del 06 maggio 2022) Notizie dal Comitato •

Il Presidente ricorda la scomparsa di Cecilia Monticelli, Professore Associato di “Corrosione e protezione dei materiali metallici” presso il Centro Studi Corrosione e Metallurgia “A. Daccò” dell'Università di Ferrara. La Rivista le ha dedicato una pagina sul numero di febbraio,

mentre il CT Corrosione ha l’intenzione di organizzare una iniziativa in sua memoria, per esempio un premio a un giovane ricercatore, in occasione delle Giornate Nazionali sulla Corrosione e Protezione del 2023.

Manifestazioni in corso di organizzazione •

La 15° edizione delle “Giornate Nazionali sulla Corrosione e Protezione” si svolgerà indicativamente dal 28 al 30 giugno 2023 presso il

•

Il coordinatore Balbo illustra la bozza di programma del Corso sulle “Tecniche elettrochimiche per lo studio della corrosione”, elaborato

Politecnico di Torino. Si comincerà a lavorare a questa iniziativa a settembre.

insieme a Bellezze. Il corso si svilupperà in tre giorni (18 ore totali), e tratterà fondamenti della scienza della corrosione, aspetti cinetici della corrosione e strumentazione, tecniche elettrochimiche tradizionali ed altre tecniche per lo studio della corrosione, teoria dell’im-

pedenza elettrochimica e esempi applicativi, spettroscopia a foto-corrente e tecniche localizzate per lo studio dei fenomeni corrosivi. La scuola potrebbe tenersi tra metà gennaio e metà febbraio 2023 prezzo l’Università di Ferrara, e il corso sarà dedicato a Cecilia Monticelli.

•

Ora si studierà come integrare attività di laboratorio, probabilmente nei pomeriggi o dopo la parte teorica.

L’iniziativa “Verifiche e manutenzione di strutture metalliche storiche”. suggerita dall’IIS – Istituto Italiano della Saldatura – si terrà il 21-23 novembre a Milano. Per il CT Corrosione sono previsti 3 interventi relativi a corrosione atmosferica, protezione mediante rivestimenti metallici o pitture e un caso di studio, forse relativo alla corrosione di un ponte storico.

Iniziative future •

Il “Corso modulare di corrosione” sarà ripreso nell’autunno 2023. Si sta considerando la possibilità di tenere il corso in inglese, in funzione dei partecipanti (provenienza aziendale o dottorandi non solo italiani).

CT MATERIALI PER L’ENERGIA (ME) (riunione telematica del 20 giugno 2022)

Notizie dal Comitato •

Di Gianfrancesco informa sulla situazione del gruppo di lavoro italiano Creep ed ECCC: sta per iniziare la qualificazione del Gr.23 per

applicazioni sopra i 620°C. E’ stato necessario mettere a punto un programma di verifiche a tempi corti perché il prodotto ricevuto non ha le caratteristiche dichiarate e va quindi qualificato prima di procedere con il programma a tempi lunghi.

Manifestazioni in corso di organizzazione •

Gariboldi presenta una bozza di programma per la GdS sul Thermal Storage rielaborato insieme a Paola Bassani. La tematica riguar-

derà i materiali per la gestione del calore ed in risparmio energetico. La successione degli interventi deve essere ancora definita ma si

prevedono presentazioni da parte di Politecnico di Milano, Università di Pisa e R.S.E. La giornata è prevista per ottobre/novembre 2022 in modalità ibrida.

Iniziative future •

Il gruppo di lavoro incaricato di organizzare la GdS sulla stesura delle specifiche non ha fatto passi avanti, ma il tema è decisamente

interessante. Viene dato incarico a Pinciroli di coordinare questo gruppo di lavoro e di presentare una possibile scaletta della manifestazione per la prossima riunione.

La Metallurgia Italiana - July-August 2022

pagina 61

Atti e notizie - AIM news

Normativa / Standards Norme pubblicate e progetti in inchiesta (aggiornamento 27 giugno 2022) Norme UNSIDER pubblicate da UNI nel mese di maggio 2022

Steel and steel products — Vocabulary

Petroleum and natural gas industries -

relating to chemical analysis

Drilling and production equipment - Part 1: Electric submersible pump systems for artificial lift (ISO 15551-1:2022)

ISO 4954:2022 Steels for cold heading and cold extruding

prEN ISO 683-17

Tubazioni per teleriscaldamento - Sistemi di tubazioni flessibili prodotti in fabbrica UNI EN ISO 16808:2022 Materiali metallici - Fogli e nastri della

prEN ISO 15551-1

Heat-treated steels, alloy steels and free-

ISO/TR 4340:2022

UNI EN 15632-1:2022

Determinazione

ISO/TS 6084:2022

curva

biassiale

sforzo-deformazione per mezzo di test di rigonfiamento con sistemi di misurazione ottici UNI EN 15632-2:2022 Tubazioni per teleriscaldamento - Sistemi di tubazioni flessibili prodotti in fabbrica

Water

aggressiveness

evaluation

and

optimized lining choice

bearing steels (ISO/DIS 683-17:2022))

ISO 4298:2022

ISO/DIS

Manganese ores and concentrates —

–

internazionali

progetti

di

norma

Determination of manganese content — ISO/DIS 19901-4

Potentiometric method

Petroleum and natural gas industries ISO 3421:2022

— Specific requirements for offshore

Petroleum and natural gas industries —

structures — Part 4: Geotechnical design

Drilling and production equipment —

considerations

Offshore conductor design, setting depth ISO/DIS 15551

and installation

Petroleum and natural gas industries —

- Parte 2: Sistemi di tubazioni bloccate

Drilling and production equipment —

con tubi di servizio in plastica; requisiti e metodi di prova

cutting steels - Part 17: Ball and roller

Electric submersible pump systems for

Progetti UNSIDER messi allo studio

artificial lift

dal CEN (Stage 10.99) – luglio 2022

ISO/DIS 9649

Norme UNSIDER pubblicate da CEN e ISO nel mese di giugno 2022 ISO 23838:2022 Metallic materials — High strain rate

EN 1515-4:2021/prAC

Metallic materials — Wire — Reverse

Flanges and their joints - Bolting - Part 4:

torsion test

Selection of bolting for equipment subject to the Pressure Equipment Directive

ISO/DIS 6338

2014/68/EU

Method to calculate GHG emissions at LNG plant

torsion test at room temperature ISO/TS 21913:2022 Temperature verification method applied to dynamic fatigue testing ISO 19901-2:2022 Petroleum and natural gas industries — Specific requirements for offshore structures — Part 2: Seismic design procedures and criteria

La Metallurgia Italiana - Luglio-Agosto 2022

Progetti UNSIDER in inchiesta prEN e ISO/DIS – luglio 2022

ISO/DIS 4998 Steel sheet, zinc‐coated and zinc‐iron alloy‐coated by the continuous hot‐dip

prEN – progetti di norma europei

process, of structural quality

prEN ISO 19901-4

ISO/DIS 683-17

Petroleum and natural gas industries

Heat-treatable steels, alloy steels and

-

free-cutting steels — Part 17: Ball and

Specific

requirements

for

offshore

structures - Part 4: Geotechnical design

roller bearing steels

considerations (ISO/DIS 19901-4:2022)

pagina 62

ISO 404:2013/DAmd 1 Steel and steel products — General technical

delivery

requirements

—

Amendment 1

Progetti UNSIDER al voto FprEN e ISO/FDIS – luglio 2022

FprEN – progetti di norma europei FprEN ISO 10113 Metallic materials - Sheet and strip Determination of plastic strain ratio (ISO/ FDIS 10113:2019)

ISO/FDIS

–

internazionali

progetti

di

norma

ISO/FDIS 11531 Metallic materials — Sheet and strip — Earing test

12th International ROLLING Conference | Trieste (Italy), 26-28 October 2022 Organised by

in cooperation with

Thanks to a long and successful series, the ROLLING conferences have become the premier international event for rolling practitioners worldwide. The target audience embraces the whole metals rolling community: flat and long products rolling, hot and cold rolling and ferrous and nonferrous rolling.

The forum will cover product and process topics, encompassing rolled product properties, quality and applications, in addition to the design, control and management of mill assets.

The Conference will bring together rolling practitioners, steel producers, plant designers and researchers and it will provide a forum for best practices and state-of-the-art technology. It will also take a look at developments in the foreseeable future.

BACKGROUND 1985 Tokyo, Japan 1987 Deauville, France 1990 London, UK 1994 Düsseldorf, Germany 1998 Tokyo, Japan 2002 Orlando, USA 2006 Paris, France 2010 Beijing, China 2013 Venice, Italy 2016 Graz, Austria 2019 São Paulo, Brazil CONFERENCE SCHEDULE October 26, 2022: Opening session and opening of the exhibition October 27, 2022: Session + Social event – Cocktail October 28, 2022: Sessions + Plant visit

main sponsor

silver sponsor

CONFERENCE CHAIRMAN Gianpietro Benedetti - DANIELI, Italy INTERNATIONAL SCIENTIFIC & STEERING COMMITTEE Lorenzo Angelini - Feralpi Group, Italy Wolfgang Bleck - Rwth Aachen University, Germany Franco Bonollo - Università di Padova, Italy Alberto Bregante - SMS Group, Italy Jochem Groot - Tata Steel, The Netherlands Gerhard Hirt - Rwth-Aachen, Germany Andreas Kugi - Technische Universität Wien, Austria Carlo Mapelli - Politecnico di Milano, Italy Pierre Montmitonnet - Mines Paris - Cemef, France Heinz Palkowski - Clausthal University of Technology, Germany Rolando Paolone - Danieli, Italy Marco Rinaldi - Danieli, Italy Jose M. Rodriguez-Ibabe - Ceit, Spain Ivo Schindler - Vsb-Technical University of Ostrava, Czech Republic Fulvio Siciliano - Federal Institute of Maranhao, Brazil Jilt Sietsma - Delft University of Technology, The Netherlands John G. Speer - USA Claudio Tomat - Danieli, Italy Giorgio Zuccaro - Acciaierie Venete, Italy ORGANISING SECRETARIAT

Via Filippo Turati 8 – 20121 Milano, Italy Tel. +39 0276021132 – +39 0276397770 E-mail: aim@aimnet.it – http://www.aimnet.it

more info: www.aimnet.it/rolling-12/