Applied Mechanics Lab.: Metallography and Hardness Test

University of Baghdad Al Khwarizmi engineering college Automated Manufacturing Eng. Dept.

Applied Mechanics Lab.: Metallography and Hardness Test

By: Ahmed N. Abdul Razaq

Date: 15-5-2016

E-mail: ahmednajah5049@gmail.com

Metallography and Hardness Test Abstract The purpose of this document is demonstrate the importance of the metallographic protocols that helps to reveal the microstructures of different metals and to clear the way for measuring the microhardness of the metals. Its shown how they were accomplished step by step, and with several photos to illustrate the processes. A brief description about each tool that has been used and some additional work has been discussed with the final results for the microstructure and microhardness for the different metals are tabulated and compared to the standard values and calculations along with the standard micrographic evidences.

Contents

Introduction

3

Procedure

4

Metallography

5

Microstructure

8

Chemical Composition

9

Hardness Test

9

Additional Work: Heat Treatment

10

Results and Discussion

11

Table 1: Austenitic Stainless Steel 303 chemical composition

14

Table 2: Tool Steel D2 chemical composition

14

Table 3: Naval Brass chemical composition

15

Table 4: Austenitic Stainless Steel 303 hardness values

15

Table 5: Tool Steel D2 hardness values

16

Table 6: Naval Brass (Tin-Brass) CDA 482 hardness values

16

The Used Samples

17

References

18

Introduction Metallography is the study of the physical structure and components of metals, typically using microscopy. Ceramic and polymeric materials may also be prepared using metallographic techniques, hence the terms ceramography, plastography and, collectively, materialography [1].

To identify any material properties and behavior, one need to study the microstructure of that material. The microstructure of the metals provides insights to the mechanical properties of the metal. In some cases, the structure is large enough to be seen with the unaided eye fig. 1. In other cases, where the structure cannot be seen, metallographic techniques are used to reveal the structure after a few steps of preparation for the metal. Eventually when the preparation is done some tests are performed that predicts the metal properties.

Purpose In our case, the goal test after this preparation was the hardness test so the surface needed to be as flat and clean as possible.

Hardness is a measure of how resistant solid matter is to various kinds of permanent shape change when a compressive force is applied, and it’s one of the mechanical properties of the materials.

Fig. 1 Bronze bell with visible material structure.

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Procedure Before we started the metallographic procedure, we needed to prepare the samples for the work:

1. A saw cutter fig. 2 was used to cut a small piece from each metal and a grinder fig. 3 was utilized to remove the unwanted parts from the sectioned piece to make the surface as flat as possible without unequal areas to get it ready for mounting and later work.

Fig. 2 Saw cutter.

Fig. 3 Grinder.

2. For mounting purposes, we used an acrylic powder (copolymer MMA + MA) mixed with its liquid (methylmethacrylate, dimethyl-paratoluidine, ethylene glycoldimethacrylate) fig. 4, after mixing them we used a small wooden stick to stir the mixture for a (4-7 seconds) to turn them into a thick solution. Then we poured it over the sectioned piece that is placed in the center of the cylindrical mould fig.5, which is consist of a hollow tube with a (ID = 30 mm, OD = 32 mm) and a (30 mm) diameter punch to push the sample after the solution has completely dried which is after 5-10 minutes.

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Fig. 4 Acrylic powder and its liquid.

Fig. 5 A cylindrical mould.

Metallography After the samples were prepared we were finally ready to start the metallographic protocols step by step:

1. Grinding The first step was to even out the sides of the sample, making the surfaces smoother to be able to place it on the translation table (Vickers microhardness tester table) in a steady position. So we used a (SAD – 11 Belt Surfaces Grinder) fig.

6 to grind it. After grinding it for several minutes, the sides were finally evened out and it was time to switch to the other machine to grind the small scratches off the metal surface with abrasive papers fig. 7.

We used the (MP-1S Metallurgical Preparation Grinder/Polisher) fig. 8 that consist of a rotating disc with a 230mm diameter, and after cutting the papers to a circled shape we started with a 400 grit size papers for about 15 to 20 minutes with the machine running at 400 rpm speed by pressing firmly on the sample against the rotating disc with the paper fixed on it to remove the scratches making the surface evened. The pressing was continuous till the there 5|Page

Fig. 6 SAD – 11 Belt Surfaces Grinder.

Fig. 7 Abrasive papers. were no any noticeable changes on the surface, and during this grinding operation a water was continuously pouring on the rotating disc in a medium flow speed so the removed particles from the metal wont stick on the papers and also so the metal wont be heated from friction.

Fig. 8 MP-1S Metallurgical Preparation Grinder/Polisher.

The next paper grit sizes were 600,800,1000 and 2000, the pressing intensity on the sample was decreased when changing to a smoother paper because pressing harder may create scratches again. After using the last paper (2000 grit size) the metal finally started to look shiny because most of the scratches were removed and the sample was ready for the next step.

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2. Polishing Another grinder/polisher (MP-200) fig. 9 was used for this purpose but instead of the abrasive papers we used a red colored cloth that is pasted to the rotating disc.

While pressing the sample gently onto the rotating cloth, a mixture of alumina (Al2O3) powder fig. 10 and water was being poured out over the cloth with small amounts which polishes the surface.

The pressing was continuous for about 8-12 minutes. After the polishing was over, we gently whipped the metal part of the sample with a soft cloth while washing it with water for about 1 minute.

Fig. 9 MP-200 Grinder/Polisher.

Fig. 10 Alumina Al2O3.

Finally, we used Ethyl alcohol to also wash the sample for a couple of seconds and dried it with a hair dryer. After this step the sample was finally ready for the etching process.

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3. Etching since we had three different metals (Stainless Steel, Tool Steel and Brass) different etchants were used:

Metal

Etchant

Nital Austenitic Stainless Steel 303

[2]

Conc.

Condition

Nitric Acid (10 ml) Ethanol (100 ml)

Immersed for 3-5 seconds.

Nitric Acid (10 ml) Ethanol (100 ml) Naval brass CDA Distilled Water 50 ml 482 Nitric Acid 50 ml

Immersed for 15 minutes.

Immersed for 3-5 seconds.

Tool Steel D2

Nital

Table 1 Used etchants After immersing the sample in the etchant, we washed it with water and then with Ethyl alcohol and dried it with the hair dryer. And finally after repeating each step for each sample, the samples were ready for the microscopic test to reveal the microstructure and then measure the microhardness for the metal.

Microstructure To reveal the microstructure, we used a MEIJITM microscope fig. 11, which consist of 3 magnification lenses (100x,400x and 600x), a table for placing the samples, two lenses to view the magnified part and a camera placed above the microscope and attached to the computer to show the microstructure on the screen and take photos to it.

Fig. 11 MEIJITM Microscope.

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Chemical Composition Since the metals were unknown, we had to do a test that helps to reveal the chemical composition to identify the metal. And for that purpose we used (X-MET3000TX) fig. 12 device that uses spectrum to identify the chemical composition using X-ray which is a non-destructive test.

Fig. 12 X-MET3000TX Testing device.

Hardness Test To measure the microhardness for the samples, TH715 Micro Vickers Hardness Tester fig. 13 was utilized to do the test. It consists of two small cameras, a diamond shaped indenter with different loads to apply, a small monitor to reveal the surface 9|Page

and a translation table to place the samples on. After placing the samples, we started to apply the loads which were (9.8 N for Steels and 1.96 N for Brass) after this process was finished which lasts about 15 sec. we measured the diagonal of the pyramid shaped spot fig. 14 that was created on the surface after the indentation and the hardness value was calculated.

Fig. 13 TH715 Micro Vickers Hardness Tester.

Fig. 14 Indentation spot.

Additional Work Heat Treatment We tried to harden the Tool Steel D2 sample but we failed because the required quenching temperature is 982-1024 oC and our furnace only reaches 560 oC as it needs some maintenance, but we put it in there to see if anything would change but nothing happened. The quenching medium was the air.

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Results and Conclusions Microstructures 1. Austenitic Stainless Steel 303

Fig. 15 Lab. result.

Fig. 16 Standard microstructure [3].

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2. Tool Steel D2

Fig. 17 Lab. result.

Fig. 18 Standard microstructure [4].

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3. Naval brass (Tin-brasses) CDA 482

Fig. 19 Lab. result.

Fig. 20 Standard microstructure [5].

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Chemical Composition 1. Austenitic Stainless Steel 303 Lab. Results Component Wt. % Cr 18.18 Mn 1.76 Fe 71.68 Mo 0.42 Ni 7.51 V 0.12 Co 0.08 Cu 0.53 W 0.07 Nb 0.08 Si --------S --------P ---------

Standard Composition [6] Component Wt. % Cr 18 Mn Max. 2 Fe 69 Mo Max. 0.6 Ni 9 V --------Co --------Cu --------W --------Nb --------Si 1 S 0.03 P 0.04

Table 1 Austenitic Stainless Steel 303 chemical composition.

2. Tool Steel D2 Lab. Results Component Cr Mn Fe Mo Ni V Co Cu W Si

Wt. % 11.43 0.33 84.42 0.97 0.24 1.11 ------0.09 0.52 -------

Standard Composition [7] Component Wt. % Cr 11-13 Mn Max. 0.6 Fe 84.79 Mo 0.7-1.2 Ni Max. 0.3 V Max. 1.1 Co Max. 1 Cu ------W ------Si Max. 0.6 14 | P a g e

Ti

2.17

Ti

-------

Table 2 Tool Steel D2 chemical composition.

3. Naval Brass (Tin-Brass) CDA 482 Lab. Results Component Pb Mn Fe Sn Ni Zn Cu Ti

Standard Composition Component Wt. % Pb 0.2 Mn ------Fe 0.1 Sn 0.5-1 Ni ------Zn 36.7-40 Cu 59-62 Ti -------

Wt. % 2.38 0.03 0.12 0.4 0.09 39.37 57.98 2.17

Table 3 Naval Brass chemical composition.

Hardness Test 1. Austenitic Stainless Steel 303 Taking the average of three test results yields to: HV = (264.8 + 251.8 + 232.5)/3 = 249.7 HV Lab. results Vickers

Brinell

249.7

238

Standard values

Rockwell Rockwell Knoop B C

99.5

22.2

262

Vickers

Brinell

240

228

Rockwell Rockwell Knoop B C

96

19

251

Table 4 Austenitic Stainless Steel 303 hardness values. .

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2.

A. Tool Steel D2 (Before the failed hardening) Taking the average of five test results yields to: HV = (251.5 + 264.4 + 252.2 + 248.2 + 258.2)/5 = 254.9 HV

B. Tool Steel D2 (After the failed hardening) Taking the average of five test results yields to: HV = (251.1 + 253.3 + 245.3 + 249.3 + 258.2)/5 = 251.44 HV Since there weren’t any noticeable changes with the hardness value, the quenching process was definitely a failure.

Lab. results Vickers

Brinell

254.9 251.44

243

Standard values

Rockwell Rockwell Knoop B C

99

23.1

Vickers

Brinell

760

710

267

Rockwell Rockwell Knoop B C

160

62.5

788

Table 5 Tool Steel D2 hardness values.

3. Naval Brass (Tin-Brass) CDA 482 Taking the average of three test results yields to: HV = (114.9 + 111.4 + 111.2)/3 = 112.5 HV Lab. results Vickers

Brinell

112.5

106.9

Standard values

Rockwell Rockwell Knoop B C

64

9.9

128

Vickers

Brinell

110

105

Rockwell Rockwell Knoop B C

62.3

9.68

123

Table 6 Naval Brass (Tin-Brass) CDA 482 hardness values.

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The Used Samples

Fig. 21 Austenitic Stainless Steel 303 sample.

Fig. 23 Naval Brass CDA 482 sample.

Fig. 22 Tool Steel D2 (Hardened) sample.

Fig. 24 Tool Steel D2 (NonHardened) sample

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References 1. "Metallographic and Materialographic Specimen Preparation, Light Microscopy, Image Analysis and Hardness Testing".

2. http://www.metallographic.com/Etchants/Copper%20alloy%20etchants.ht m.

3. http://vacaero.com/information-resources/metallography-with-georgevander-voort/894-microstructure-of-ferrous-alloys.html.

4. http://www.britishblades.com/forums/showthread.php?156551-12-C-27is-no-more/page2.

5. http://www.copper.org/resources/properties/microstructure/tin_brasses.h tml.

6. http://www.espimetals.com/index.php/technical-data/199-stainless-steel303-alloy-composition.

7. http://www.globalmetals.com.au/_pdf/Tool_Steel/Tool_Steel_D2.pdf.

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