Study on Influence of heat treatment on Tribological properties of mild steel

IDL - International Digital Library Of Technology & Research Volume 1, Issue 3, Apr 2017

Available at: www.dbpublications.org

International e-Journal For Technology And Research-2017

Study on Influence of heat treatment on Tribological properties of mild steel Mr. SriramMukunda1, AmanSuryan2, Hareesh Nair2, Sanjeev Kumar2, Siddharth sanu2 1 Asst. Professor, Dept. Of Mechanical engineering, NitteMeenakshi institute of technology 2 BE students, Dept. of Mechanical engineering, NitteMeenakshi institute of technology Bangalore, India

Keywords: heat treatment, microstructure, wear, hardness, tensile strength

Abstract:A study was made on the effect of heat treatment upon the mild steel. Total six samples were prepared for each test (hardness test, tensile test, microstructure test and wear test) from those two was tested as received and rest four were subjected to different heat treatment that are annealing and normalizing (heated on a temperature of 850 degree Celsius). The hardness of all sample was measured

by Rockwell hardness testing machine. Wear measurement was done on pin-on disc wear machine.

Tensometer was used to find out the ultimate stress and strain of the sample. The result of tensile test showed that the strength is decreased by heat treating and the surface hardness is also decreased by heat treatment. Microstructure of the mild steel specimens shows the grain boundary of the particles and the content of % of carbon present. It justifies the experimental results of tensile test and hardness test.

Surface Hardness is the measure of resistance that any material applies. As the specimen gets soft on treating the hardness also gets decreased. Tensile strength of any specimen is specified as how much stress the material can withstand before breaking. As the metal gets soft after heat treatment the load required for breaking goes on decreasing. Wear test is carried out to see the variation in wear measurement and coefficient of friction as the mesh size of paper are varied. More soft the surface of material is more wear is seen and vice-versa.

IDL - International Digital Library

1. INTRODUCTION Sliding, Over 500 million tonnes of low carbon steels are produced yearly around the world; they are used for most of the engineering applications. Low carbon steels are utilized to produce cars body panels, tubes, domestic appliance side panels and other engineering applications because they are readily available, workable and weldable [1]. Furthermore, low carbon steel also called mild steel have carbon content below 0.2 per cent, and manganese content below 0.7 per cent, with maximum values for silicon, phosphorus and sulphur at 0.6, 0.05 and 0.05 per cent respectively.

The performance of low carbon steel in service depends on inherent factors which include its grain size, presence of defects, its chemical composition, ultimate Tensile strength, etc. as well as extrinsic factors. Studies have also shown that failure of carbon steels can result from production methods, use of substandard material, poor design, manufacturing errors due to poor machining, or failure from a phenomenon called fatigue [2, 3].

Sequentially, to forestall these failures, the mechanical properties can be changed as desired by heat treatment [4]

1 |P a g e

Copyright@IDL-2017

IDL - International Digital Library Of Technology & Research Volume 1, Issue 3, Apr 2017

Available at: www.dbpublications.org

International e-Journal For Technology And Research-2017 Heat treatment is a combination of timed heating and cooling applied to a particular metal or alloy in the solid state in such ways as to produce certain microstructure and desired mechanical properties (hardness, toughness, yield strength, ultimate tensile strength, Young’s modulus, percentage elongation and percentage reduction) [5,6]. Annealing, normalizing, hardening and tempering are the most important heat treatments often used to modify the microstructure and mechanical properties of engineering materials particularly steels [7]. Metallic materials consist of a microstructureof small crystalscalled "grains" or crystallites. The nature of the grains (i.e. grain size and composition) is one of the most effective factors that can determine the overall mechanical behavior of the metal [8].

Heat treatment provides an efficient way to manipulate the properties of the metal by controlling the rate of diffusionand the rate of cooling within the microstructure [9].Annealing, in metallurgy and materials science, is a heat treatment that alters the physical and sometimes chemical properties of a material to increase its ductilityand reduce its hardness, making it more workable. It involves heating a material to above its recrystallization, maintaining a suitable temperature, and then cooling. In annealing, atoms migrate in the crystal lattice and the number of dislocations decreases, leading to the change in ductility and hardness. Normalizing is a technique used to provide uniformity in grain size and composition throughout an alloy. The term is often used for ferrous alloys that have been austenitized and then cooled in open air [10]. Normalizing not only producespearlite, but also martensite and sometimes bainite, which gives harder and stronger steel, but with less ductility for the same composition than full annealing.After the heat treatment process we prepare specific specimen for different testing like hardness test, microstructure test, tensile test and wear test. We did hardness test using Rockwell hardness tester as this machine can be used to test the surface harness of material of any composition, any IDL - International Digital Library

structure and shape. Coming on to microstructure test we prepared the sample using different sizes of mesh paper and got a flat mirror shape structure. Lapping was used to give the final finishing to the specimens.

Microstructure of as received sample showed differed result then the other two sample that are annealed, and normalized ones. The tensile test was done using tensometer at a reference speed of 0.4mm/min and a load cell of 20030N. The standard ASTM E8 specimen was prepared in considerable number and test was conducted to get a better view of the variation of mechanical properties of different specimen. Wear test was conducted by taking a reference and constant speed of 400rpm and a load of 20N. The pin-on-disc machine as used to conduct the test showing results of the value of wear in micron meter and the graph of coefficient of friction. These different results are found by using 3 sizes of mesh paper that are 220, 600 & 1500. 600 being the standard 220 and 1500 mesh are used to clearly compare the variation in values.

2. OBJECTIVE Conclusions from the literature review encouraged for the need of a systematic study of various tribological properties of Mild Steel. This study can lead one to investigate the possibility of identifying the use of these mild steel for commercial applications like in the aerospace and automotive industries. Therefore the work taken up had the following objectives: To perform heat treatment on mild steel material as per industrial applications. To observe the changes in the microstructure of mild steel after subjected to heat treatment and comparing the same with the as-received material. To perform Pin-on-disk wear test and wear measurement on Mild steel specimens. To determine the effect of heat-treatment on the mechanical properties of Mild Steel such as hardness, wear, tensile strength

3. METHODOLOGY Microstructure study

2 |P a g e

Copyright@IDL-2017

IDL - International Digital Library Of Technology & Research Volume 1, Issue 3, Apr 2017

Available at: www.dbpublications.org

International e-Journal For Technology And Research-2017 The specimens for microstructure will be prepared as per standard metallurgical procedures, etched in etchant prepared using 90 ml water, 4 ml HF, 4 ml H2S04 and 2g Cr03 (Keller’s Reagent), Using Optical Microscope.The specimens for microstructure are prepared by heat treatment (Annealed, Normalized) and an as received specimen of length 4-5mm and same thickness. The specimens are properly grinded, filed with filling, polished, and lapped to obtain a mirror surface.

temperature using Pin-on-Disc apparatus for 2kgf loads and sliding distances.

4.IMPLEMENTATION Microstructure study Polishing of specimen is done using sandpapers.

Sandpapers are made from garnet, aluminum oxide or silicon carbide. They are available in different grit sizes in the market. The grit sizes we have used are 220, 400, 600 and size 1,2,3,4 and 5 subsequently. A particular to and fro motion is repeated on the sandpaper. While changing the grit size of the emery paper, the specimen is rotated by 90°. Lapping is a machining process, in which two surfaces are rubbed together with an abrasive between them, by hand movement or using a lapping machine. The abrasive used here is alumina, and its solution is prepared by dilution with water. Alumina solution is added drop by drop while the circular platform is rotated and specimen is rubbed against the cloth. In this way, the surface of the specimen is mirror finished.

Hardness test The hardness tests will be conducted norms using Rockwell Hardness Testing Machine, where the tests will be performed at randomly selected points on the polished surface of samples by providing sufficient space between indentations and distance from the edges.Specification of the Rockwell hardness machine are as follows: Indentation used is 1/4˝ ball diamond indenter, Load applied is 60 kg, Dial used isBlack and Scale used is L.

Tensile test

Hardness study

Tensile properties of materials will be tested in Tensometer. UTS and percentage Elongation are obtained by carrying out an average of 2 trails each of heat treated and untreated specimen and tabulated.

The specimens are prepared taking ASTM E8 as the reference and each specimen was individually tested in the machine by using a suitable holder to hold the specimen. The test is programmed using software and the results are displayed on the computer screen.

Hardness test is done on the flat surface of the specimen prepared using Rockwell hardness tester.

A grade testing is done for soft mild steel where ¼ diamond indenter is used for indentation and for testing and readings are taken from the black dial of the tester. A load of 60kg is used for this process.

The specimens after harness test is done is shown below.

Wear test

Tensile test

Wear is a process of removal of material from one or both of two solid surfaces come in solid state contact.Wear is correlated to interactions between surfaces and more precisely, the removal and deformation of a material on a surface as a result of the mechanical action of the opposite surface. Dry sliding Wear tests are carried out at room

Tensile test is done to carry out the result about the tensile strength of the specimen before and after heat treatment. Tensometer is used to conduct this test which has holder of standard sizes and the specimen has to be prepared according to these standards. For mild steel we take ASTM E8 as the reference and few samples of each type of specimen is prepared.

The gauge length of the specimen must be 12mm

IDL - International Digital Library

3 |P a g e

Copyright@IDL-2017

IDL - International Digital Library Of Technology & Research Volume 1, Issue 3, Apr 2017

Available at: www.dbpublications.org

International e-Journal For Technology And Research-2017 and the outer diameter along this 12mm length must be 2.5mm. The total length of specimen is 24mm and outer most diameter is 6mm.this is the reference for the holder used. A constant speed of 0.4mm/min is maintained to carry out the test to get a comparable results. The standard specimen is shown below. The breaking of the specimen is the completion of the test. Digital results in the form of mathematical values and graphs are shown in the computer screen.

Frictional force and coefficient of friction data are measured as a function of time.

5. OUTCOMES Microstructure study The distribution of carbon particles in the mild steel material was checked before checking the microstructure of the specimen. A specimen without any treatment along with two other heat treated specimen (one annealed and one normalized) was taken on the testing slide and was observed under the microscope. The particle sizes were measured and it was found correct as the particles were resting on their maximum surface area (a stable condition).

Wear test Pin-on-disc:Wear test was carried out on Pin-OnDisc experimental set up. The samples were 10 mm in length and 5 mm in diameter. The surfaces of the pin samples were slides using emery paper (220,600 and 1500 grit size) prior to test in order to ensure effective contact of fresh and flat surface with the steel disc. The surface of the specimen is rigidly held against the rotating disc and the wear of the specimen takes place. The rotation speed of the disc, track radius, time duration of test, etc. can be varied according to the requirements. The pin was held against the counter face of a rotating disc (steel disc) with wear track diameter 100 mm. The pin was loaded against the disc through a dead weight loading system. The specimen was pressed against the disc at a specified load by means of an arm and attached weights. The wear test for all specimens was conducted under the normal load of 20N. The samples and wear track were subjected to emery paper polishing prior to and after each test.The measurement in reduction of height of the specimen due to wear and coefficient of friction will be measured continuously by electronic sensors. The LVDT which is used, is capable of measuring a maximum displacement of + 2 mm and the measuring range of wear is + 2000 micron with an accuracy of + 1Âľm. A load cell is used to measure frictional force. The data acquired will be processed in the controller and transmitted to the PC using Winducom 2006 software. Wear is measured as reduction in specimen (pin) length in microns.

IDL - International Digital Library

The microstructure of mild steel shows the distribution of ferrite which is indicated by bright spots and pearlite which can be seen as black dots in the grain structure of the specimen being tested. The specimen were prepared using different size of mesh papers along with lapping process for finishing and finally etching was done just before the experiment.

The specimen who was tested as received from casting (untreated) shows a large fraction of pearlite (black dots) which is all over the ferrite region. This shows the higher percentage of carbon content in the untreated specimen. Whereas the pearlite distribution is smaller in normalized specimen and is least among all three in annealed specimen. This shows that the carbon content is decreased in normalized specimen and is least in annealed test specimen. This very well explains the trend of surface hardness and tensile characters of the specimen.

The grain size of the tested specimen is also measure and found out to be as expected. The grain size of untreated test specimen was found to be least and that of annealed test specimen was largest among all three specimens. The image of all three specimen with their grain sizes are shown below.

Hardness test

4 |P a g e

Copyright@IDL-2017

IDL - International Digital Library Of Technology & Research Volume 1, Issue 3, Apr 2017

Available at: www.dbpublications.org

International e-Journal For Technology And Research-2017 The below bar chart shows the result of hardness test.

As we see untreated specimen has the highest value of RHN and annealed specimens has the lowest value of RHN we can easily conclude that untreated specimen is having more surface hardness than normalized specimen and annealed specimen having the least surface hardness among these three.

The test result of wear test shows approximately the expected trend. Untreated specimen being the hardest tends to lesser wear compare to heat treated samples whereas annealed sample is least hard among these three and so is more affected by wear. Also as the mesh size used to prepare the sample goes from fine to coarse the wear of the specimen decreases from the result. The comparison of all the wear values of all specimen under different meshes are shown through a bar chart and it concludes that the wear value is maximum in case of annealed specimen under 1500 mesh and it is minimum in case of normalized specimen under 220 mesh.

Variation of RHN 100 0 Annealed

Normalized Mean

As received

RHN

The wear value, coefficient of friction and frictional force of all the specimen is graphically shown below:-

Tensile test

50 40 30 20 10 0

The tensile test was carried out on the following specimen. The results obtained have been plotted in the below bar graph from the test results generated by the system software.From the results we concluded that the untreated specimen had the maximum engineering ultimate tensile stress and had the maximum true ultimate tensile stress, whereas normalized specimen had a lesser value and annealed specimen had the minimum value of the engineering UTS and true UTS.We also concluded that the load required to break the specimen is maximum in untreated specimen and least in annealed specimen.

The graph between load v/s displacement of all the heat treated and untreated was obtained and analyzed.

Normalized

Engg. UTS

CONCLUSION The comparison of the microstructures of untreated and annealed samples revealed that the grains have begun to grow larger in the heat-treated samples due to stress relief. Also there is more presence of Pearlite seen in the heat-treated samples.The comparison of microstructure of untreated and normalized samples revealed that the grains have begun to grow larger but not large as annealed samples. There is more presence of Pearlite than untreated sample.There is also a marked change found in the mechanical properties in terms of increased ductility found by tensile testing.The wear is clearly seen to increase in all the samples with increase in the surface roughness. The wear is seen to go up with heat-treatment possibly due to relieving of

As received

Break load

Wear test IDL - International Digital Library

600 Mesh 220 Mesh

2000 1500 1000 500 0 Annealed

1500 Mesh

5 |P a g e

Copyright@IDL-2017

IDL - International Digital Library Of Technology & Research Volume 1, Issue 3, Apr 2017

Available at: www.dbpublications.org

International e-Journal For Technology And Research-2017 the internal stresses in the material, which needs to be confirmed by further examinations such as Scanning Electron Microscopy.

REFERENCES [1]Fish P.M, Woodhead Pub. Ltd., Cambridge, (1995) [2] Ajayi J. A.,Joseph O. O., Oloruntoba D.T., Joseph O.O.Int. J. Metal & Mat. Eng. Lett. 3 (2013) 85 [3] Joseph O. O., Abidakun O. A., Aniyikaye A. O., Folorunsho O. O. Industry. Engg.Lett.3 (2013) 46 [4] Singh D. K., Ane Books, Pvt. Ltd., India (2011) [5] Kempester M.H.A., 1984, Materialfor Engineers, 3rd Edition. Hodder and Stonghton.

[6] Raymond A., Higgins B., 1985, Properties of Engineering Materials. Hoodder and Stonghton.

[7]Jutta Rohde, Anders Jeppsson,Heat Treatment Simulations with respect to Phase Transformation, Residual stresses and Distortion (2000).

[8] O.O. Joseph, O.O. Joseph2 , R.O. Leramo , O.S. Ojudun,Effect of Heat Treatment on Microstructure and Mechanical Properties of SAE 1025 Steel (2014).

[9] Mohd marhan bin asari, A Studyon heat treatment of carburizing carbon steel (2010).

[10] Min Shan Htun, Si Thu Kyaw, Effect of Heat treatment on Micro structure and Mechanical Properties of Spring Steel.

IDL - International Digital Library

6 |P a g e

Copyright@IDL-2017