Studying the Fatigue Properties Of Hardened For Carbon Steel

ISSN (e): 2250 – 3005 || Volume, 06 || Issue, 08|| August – 2016 || International Journal of Computational Engineering Research (IJCER)

Studying the Fatigue Properties Of Hardened For Carbon Steel Dr. Mohammed Abdulraoof Abdulrazzaq Materials Eng. Dept. /University of Mustansiriyah, Baghdad, Iraq mohammedraof415@yahoo.com

ABSTRACT In this study, Medium carbon steel is one of the most important materials used in industrial applications especially it is used in applications exposed to fatigue stresses such as airplanes, automotive components and electrical engines industries. Medium carbon steels were prepared and the effect of hardening on hardening strength of medium carbon steel was studied, the flame hardening method was used at different speeds then fatigue test was done. The following results were obtained, first sample (none), second sample (3.5 mm/s), and third sample (1.75 mm /s) and forth sample (1.165 mm/s). It has been found that as the flaming speed increases, the fatigue strength of the material decreases.

The fatigue test result at stress (407.44 N/mm2) was as follow: for the first sample the no. of cycles to failure was at (67511 rpm), for the second sample (95832 rpm), for the third sample (122565rpm) and for the fourth sample it was (134585 rpm).

Keywords: Medium carbon steel, flame hardening, fatigue test.

I.

INTRODUCTION

The medium carbon steels have a normal content of carbon carbon (0.45 – 0.8)that means that they are not as hard as high carbon steel neither are as strong as the Mild carbon steel. The mechanical properties of medium carbon steel were investigated in two different quenching media (water and palm oil). The properties are hardness, impact and strength of the material. Result indicated that water quenched steel produce best properties in strength and hardness; while palm oil quenched steel has its best properties in impact strength [1-3]. Some mechanical properties of medium carbon steel [4]: (1) Machinability is 60%-70%; therefore cut slightly better than low carbon steels. It is less machinable than high carbon steel since that is very hard steel. (2) Good toughness and ductility. Enough carbon to be quenched to form martensite and bainite (if the section size is small). (3) Responds to heat treatment but is often used in the natural condition. (4) The hardenability is low. (5) The loss of strength and embrittlement are decreased by both low and high temperature. (6) Subject to corrosion in most environments. All heat treating operators consist of subjecting a metal or steel to a definite timetemperature cycle which may be divided into three parts: (1) Heating the metal or alloy. (2) Holding at certain temperature (soaking). (3) Cooling [5-6]. Medium carbon steel is steel where the major interstitial alloying component is carbon. It is usually treated by using high temperatures so as to enhance ductility and strength. A 0.8% carbon steel (medium carbon steel) will begin to solidify at approximately 1470 0C. And when solidification is complete, the structure will consist of crystals of austenite of composition 0.8% carbon. As the steel cools slowly, the structure becomes uniform and no further structural change will take place. The upper and lower critical temperatures coincide and the austenitic structure transform at this temperature to pearlite.

The treatment of medium carbon steel with heat significantly changes the mechanical properties, such as ductility, hardness and strength. Heat treatment of steel slightly affects other properties such as its ability to conduct heat and electricity as well. A variety of methods exist for treating steel with heat [7].

The uses for medium-carbon steel are defined by the requirement for a high tensile strength and ductility that, despite its brittleness when compared to other forms of steel, make it the preferred choice.

Medium carbon steels is used for making car components such as crankshafts, gears, axles, tool shanks and heat treated machine elements. it is also used to make lead screws bright drawn bar , railway wheels , tracks , turbine discs , connecting rods , tram axles , gun parts shells rifle barrels , forging dies and spindles . Medium-carbon steels have good wear resistance, so they are often used for automobile parts and similar applications. They are also used in forging and for large parts [8]. Surface hardening is a process which is used to improve the wear resistance of parts without affecting the softer, tough interior of the part. This combination of hard surface and resistance and breakage upon impact is useful in parts such as a cam or ring gear, bearing or shafts, turbine applications. Most surface treatments result in compressive residual stresses at the surface that reduce the www.ijceronline.com

Open Access Journal

Page 9

Studying The Fatigue Properties Of Hardened For Carbon Steel probability of crack initiation. Further, the surface hardening of steels has an advantage over through hardening because less expensive low-carbon and medium-carbon steels can be surface hardened without the problems of distortion and cracking associated with the through hardening of thick sections [9]. Plain- carbon and low alloy steels are used for surface hardening. Manganese may be present in amounts up to 1.4% since it stabilizes cementite and increases the depth of hardening .unfortunately it increases the tendency of steel to crack during quenching [10].

Types of surface hardening (thermal treatments) are Flame hardening, Induction hardening, Electron beam hardening. Flame hardening is a method for hardening of surfaces of components, usually in selected areas by a short time application of heating followed by quenching. Flame hardening rely on the presence of an adequate carbon content in the material to achieve the hardness level required .Flame hardening is the process of selective hardening with a combustible gas flame as the source of heat. The heating media may be oxygen-acetylene, propane or any other combination of fuel gases that will allow reasonable heating rates .the hardening temperatures are the same as those required for furnace hardening [11, 12]. Flame hardening is a heat treating process in which a thin surface shell of a steel part is heated rapidly to a temp., above the critical point of the steel. After the grain structure has become austenitic the part is quickly quenched, transforming the austenite to martensite. Flame hardening is mainly used to develop high levels of hardness for wear resistance. The process also improves bending and torsional strength and fatigue life [13, 14]. The success of many flame hardening applications depends largely on the skill of the operator. This is especially true when the volume of work is so small. The principle operating variables are distance from inner core of oxy-fuel gas flame to work surface, flame velocities and oxygen to fuel ratios, rate of travel of flame head or work and type of quenching [15].

Flame hardenings have the following benefits: (1) Flame hardening imparts a hard, wear resistance surface to the component improving its fatigue strength, (2) Flame hardening offer options for the treatment of exceptionally large components, where only localized surface hardening is required, (3) Flame hardening can be automated for reproducible results once the process parameters have been set [4].

S.K. Akay et al.(2008) presented the effect of heat treatment on the fatigue life of low carbon steel sheet with dual-phase microstructure. The steel sheets were heat treated with two different procedures; intermediate quenching, intermediate quenching and tempering. The properties of tensile strength, fatigue life, hardness, micro hardness and microstructure were evaluated by the mechanical tests and metallographic analysis, respectively. The results showed that dual-phase steel (DPS) microstructures, composed by ferrite and martensite had higher fully reversed plane bending fatigue strength when compared with as-received steel and tempered martensite (TM) steel. The experimental results showed that fatigue life of the heat-treated steel sheets enhanced with increasing amount of martensite in the microstructure. The highest fatigue strength was observed on the intermediately annealed steel sheets at 870 ◦C. internal microstructures, fatigue crack initiation and propagation of the heat-treated steel were analyzed by scanning electron microscopy (SEM) [16]. Vytautas et al.

(2010) investigated the influence of various kinds of surface treatments (hardening with high frequency electric current, rolling by rollers, tempering) on fatigue strength of carbon steel specimens. Analyzed technology of surface hardening greatly increases the fatigue strength and durability of specimens. They estimated that hardening effect depends on the residual stresses introduced applying deformation and thermal treatment regimes. The optimal treatment of the analyzed carbon steel is deformation up to 1 mm depth, hardening with high-frequency electric current and tempering for 2 hours at 200 ºC. Conditions of machine elements during exploitation, also durability and security of all construction depends a lot on the state of metals surface layer.

Hardening of metals surface allows changing expensive metals to cheap ones. Improvement of surface quality allows increasing the durability of all construction [17]. Sweta Rani Biswal (2013) studied fatigue of medium carbon steel (EN9 grade) and investigated the effect of various heat treatment operations (like annealing, normalizing, tempering) on fatigue life since the mechanical properties are greatly influenced by heat-treatment techniques. He also studied The change in the value of endurance limit of the material concerned as a result of various heat-treatment operations and found that the specimens tempered at low temperature (2000C) exhibits the best results as far as fatigue strength is concerned [18].

II.

EXPERIMENTAL WORK

Substrate material used in this study was medium carbon steel which contains (0.390) %C, with chemical composition illustrate in table (1). The specimen as shown in figure (1) according ASTM G99. Figure (1) explains the experimental for this research.

Table (1) Chemical composition of specimen used in research Element wt % Standard: 1039 ASTM value Measured value

www.ijceronline.com

C 0.36-0.44 0.39

Si 0.4 0.173

S ≤ 0.05 0.022

P ≤ 0.04 0.009

Open Access Journal

Mn 0.7-1 0.796

Fe 0.057 remain

Page 10

Studying The Fatigue Properties Of Hardened For Carbon Steel

Fig. (1) Fatigue sample with dimensions Flame hardenings processes were used in this research which consists of the following steps: Step1: examine the chemical composition of the metal used in the test conclusion in State Company for Inspection and Engineering Rehabilitation (SIER). Step2: five samples of medium carbon steel are prepared according to standard specifications for fatigue testing using turning machine. This step was done in Public Company for Electrical Industry. Step3: sample no.2 was hardened by oxy acetylene torch (in the Mechanical workshop, College of Engineering, Al-Mustansiriya University). This process is called flame hardening, the sample is first subjected to heat of the torch for certain time and then is cooled directly by water after hardening. The heat used was at temperature (7500C) and hardening time was (5sec.) this means that the hardening speed was (3.5mm/sec).

Sample number 2 after being hardened by oxy acetylene torch is shown in figure (2).

Fig.(2): Sample number 2 after hardening Step4: sample no.3 is hardened by oxy acetylene torch (in the Mechanical workshop, College of Engineering, Al-Mustansiriya University). For hardening the sample by flame hardening method, then direct cooling by water. The heat of the torch was at (7500C) and hardening time (10sec). The hardening speed was at (1.75mm/s). Step5: sample no.4 is hardened by oxy acetylene torch (in the Mechanical workshop, College of Engineering, Al-Mustansiriya University). For hardening the sample by flame hardening method , then direct cooling by water. The heat of the torch was at (750 0C) and hardening time (15sec.). The hardening speed was at (1.165mm/s). Step 6: A sample was tested in material testing laboratory (in the Department of Production and Metallurgy, Engineering University of technology). In this test, the ultimate strength was at 1000 Maps. Step7: fatigue test is achieved in material testing laboratory in material engineering, college of engineering, AlMustansiriya University. Sample No.1 was not hardened by flame hardening method. All the samples were fatigue tested. In this test, the applied stress was constant at (407.44N/mm2 ) and the applied load was at (20N) and the number of cycles at which the samples failed was calculated.

III.

RESULTS AND DISCUSSION

Table (2) explains the relationship between the flame hardening speed and the number of samples.

Table (2) Relationship between hardening speed and number of samples.

No. of Sample 1 2 3 4

www.ijceronline.com

Time of Flame Hardening (sec) non 5 10 15

Hardening Speed (mm/s) non 3.5 1.75 1.165

Open Access Journal

Page 11

Studying The Fatigue Properties Of Hardened For Carbon Steel Table (3) explains the relationship between the flame hardening speed and number of cycles to failure.

Table (3): Relationship between flame hardening speed and number of cycles.

No. of Samples 1 2 3 4

Applied Load (N) 20 20 20 20

Applied Bending Stress (N/mm2) 407.44 407.44 407.44 407.44

Number of Test Cycles (rpm) 67511 95832 122565 134585

Flame Hardening speed (mm/s) non 3.5 1.75 1.165

Figure (3) shows the relationship between No. of samples and flame hardening speed

Fig.(3): Relationship between No. of samples and flame hardening speed.

Figure (4) shows the relationship between the No. of samples and number of cycles:

Fig.(4) relationship between the No. of samples and number of cycles Figure (5) shows stress and strain of a tensile test sample.

Fig.(5): stress-strain curve of a tensile test sample www.ijceronline.com

Open Access Journal

Page 12

Studying The Fatigue Properties Of Hardened For Carbon Steel Flame hardening process didn't do on sample no.1 to compare it with other samples that have been hardened by oxy acetylene torch in order to understand the effect of flame hardening speed on fatigue strength of the material. From table (2) it is clear that sample no.2 was subjected to oxy acetylene torch for (5 sec.) at flame hardening speed of (3.5mm/s), sample no. 3 subjected to oxy acetylene torch for (10 sec.) at speed of (1.75 mm/s) and sample no. 4 was subjected to oxy acetylene torch for (15 sec.) at speed of (1.165 mm/s), so in this case flame hardening speed decreases as the no. of samples increases.

Table (3) shows the relationship between flame hardening speed and no. of cycles. Sample no.1 failed at no. of cycles (67511 rpm), sample no.2 failed at (95832 rpm) at flame hardening speed of (3.5 mm/s), sample no.3 failed at (122565 rpm) at flame speed of (1.75 mm/s) and finally sample no.4 failed at (134585rpm) at flame speed of 1.165 mm/s).

From information above we notice that there is a reverse relationship between flame hardening speed and no. of cycles. With increasing no. of samples, no. of cycle's increases and flame hardening speed decreases. As the no. of cycle's increases and flame hardening speed decreases, the fatigue strength of the material increases. So the fatigue strength of sample no.4 is more than sample no.3 and fatigue strength of sample no.3 is more than sample no.2 and fatigue strength of sample no.2 is more than sample no.1 because the no. of cycles to failure is more and flame hardening speed is less.

IV.

CONCLUSIONS

Regarding the effect of hardening speed by oxy acetylene torch on medium carbon steel we can conclude that as the flame hardening speed increases, the fatigue strength of the material decreases. Tables (2) and (3) from chapter four shows the effect of flame hardening speed and no. of cycles to failure on fatigue strength. Conclude that as the no. of cycle's increases and flame hardening speed decreases, the fatigue strength of the material increases. So there is a straight relationship between the no. of cycles to failure and fatigue strength and there is a reverse relationship between flame hardening speed and fatigue strength.

In order to enhance the capability of medium carbon steel to withstand the fatigue crack the following recommendations can be suggested: 1- Increasing the number of the samples in order to get more precise result.

2- Changing the value of the stress greater or less than the stress used.

3- Apply other methods of surface hardening such as carburizing, coating and nitriding in order to know which method is the best.

4- It is possible to use flat samples instead of circular samples which were used in this project so that to know the difference between them.

REFERENCES [1].

[2].

[3].

[4].

[5].

[6].

[7].

[8].

[9].

[10].

[11].

[12].

[13].

[14].

[15].

[16].

[17].

[18].

John.V.B., Introduction to Engineering materials , Higher and Further Education Division, London, 1985.

Higgins.R.A, Materials for Engineering and technicians, Linacre House, Jordan Hill, 2006.

Callister,W.D.J., Materials science and engineering, John Wiley & Sons, 2003.

Lakhtin.Y.M., Engineering Physical metallurgy and heat treatment, Mir Publ., Allin and Bacon, Boston, MD, USA, 1977.

Bhadesha H.K.D.H. and Honeycombe, steels microstructure and properties, Burlington, USA, Elsevier Itd. R.M. Brick and Arthur Phillips, Structures and properties of alloys, New York, 1949.

M.B.Ndaliman, An Assessment of Mechanical Properties of Medium Carbon Steel, Department of Mechanical Engineering , Federal university of technology , Minna , Nigeria , 2006.

R.K.RAJPUT, Engineering Materials and Metallurgy, New Delhi, India, 2006.

Budinski.K.G., Surface Engineering for Wear Resistance", Prentice-Hall, 1988.

Fulco.N.J., Flame Hardening Heat Treatment"p 14-17, Aug , 1974.

Budinski.K.G.,E gineering Materials Properties and selection, Engineering Materials: Properties and selection,9 th ed., New Jersey,U.S.A.,2010.

Chawla K.K, Mechanical Behavior of Materials, Prentic- Hall Inc., 1998.

H.O.Fuchs and R.I.Stephens, Metal fatigue in ingineering, John Wiley and Sons ,1980.

Terentjev,V.F, Fatigue of Metallic Materials, Moscow, Russian, 2002.

Norman E. Dowling, Mechanical Behavior of Materials, Prentice-Hall International, 1993.

Akay S.K., Bayran A., Fatigue Life Behavior of the Duel-Phase Low Carbon Steel Sheets, Bursa, Turkey, 2008.

Vaytautas et al., Increasing of Carbon Steel Durability by Surface Hardening", Kaunas, Lithuania, 2010.

Sweto Rani Biswal, Fatigue Behavior Analysis Differently Heat Treated Medium Carbon Steel, Rourkela, 2013.

www.ijceronline.com

Open Access Journal

Page 13