Quenching-Tempering Effects On Hardness And Compression Strength Of Carburized Low Alloy Steel.
I / We* admit that had read this dissertation and in my / our* opinion this dissertation is satisfactory in the aspect of scope and quality for the bestowal of Bachelor of
Mechanical Engineering (Structure and Material)
Signature :……… Name of 1st Supervisor :………....
Date :………
Signature :………. Name of 2nd Supervisor :……….... Date :………
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QUENCHING-TEMPERING EFFECTS ON HARDNESS AND COMPRESSION STRENGTH OF CARBURIZED LOW ALLOY STEEL
NORDIANA BT SIDI
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ii
“I declare that this report is done by my own exclude the citation with the mentioned references for each.”
Signature:………. Author:………... Date:………
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ACKNOWLEDGEMENT
All praises be to Allah S.W.T, The Most Gracious, The Most Merciful for His Guidance and Blessing.
Firstly, I would like to take this opportunity to acknowledge my supervisor, Pn. Rafidah who is very committed to give the best cooperation and also for her guidance in completing this final year project. This appreciation also dedicated to my second supervisor, Mr Hamzah Mat Dom for his time and energy to make sure this project is successfully done.
Secondly, this appreciation goes to the technicians involved; Mr. Mahathir (Material Lab), Mr. Junaidi and Mr Mazlan (Machines Lab), Mr. Rashdan (Solid Lab) and Mr. Azhar (FKP Material Lab). Then, a lot of thanks to the Faculty of Mechanical Engineering UTeM, Faculty of Manufacturing Engineering UTeM, Faculty’s PSM Committee and also to my fellow friends for their helps and supports.
Last but not least, bundle of thanks to my family who is always pray for my success and also to everyone who is involved directly and indirectly, their help and support are highly appreciated.
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ABSTRACT
Nowadays, the major challenge in engineering field is to improve the properties of steels in order to meet the entire engineering requirement. A better toughness, strength and ductility of steels can be achieved by applying several types of heat treatments and surface treatments. In this study, the effects of quenching and tempering of carburized low alloy steel on hardness and compression strength are investigated. There are two conditions of specimens; carburized and uncarburized low alloy steels. The carburized specimens then face different phases of heat treatments. The phases of heat treatments are carburizing and normalizing; carburizing, quenching and normalizing; and carburizing, quenching, tempering and normalizing. Then, the specimens are tested by using Rockwell hardness test and compression test. The data obtained will be analyzed and a comparison will be carried out by using statistical analysis.
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ABSTRAK
Kini, cabaran yang paling utama dalam bidang kejuruteraan adalah untuk meningkatkan sifat-sifat keluli supaya dapat diaplikasikan untuk seluruh keperluan bidang ini. Kekerasan, keliatan dan kemuluran yang lebih baik dapat dicapai dengan menggunakan beberapa jenis rawatan haba dan rawatan permukaan. Dalam kajian ini, kesan-kesan rawatan sepuh lindap dan pembajaan ke atas kekerasan dan kekuatan mampatan keluli beraloi rendah yang ditusukkarbon dikaji. Terdapat dua keadaan spesimen; ditusukkarbon dan tidak ditusukkarbon. Spesimen yang ditusukkarbon kemudiannya melalui rawatan haba yang berlainan fasa. Fasa-fasa rawatan haba adalah penusukkarbonan dan penormalan; penusukkarbonan, sepuh lindap dan penormalan dan penusukkarbonan, sepuh indap, pembajaan dan penormalan. Kemudian, specimen-spesimen tersebut diuji dengan menggunakan ujian kekerasan Rockwell dan ujian kekuatan mampatan. Data yang diperolehi akan dianalisis dan satu perbandingan dapat dilakukan daripada analisis statistik.
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CONTENTS
CHAPTER ITEM PAGE
DECLARATION ii
ACKNOWLEDGEMENT iii
ABSTRACT iv
ABSTRAK v
CONTENTS vi
LIST OF TABLES x
LIST OF FIGURES xii
LIST OF ABBREVIATIONS xvii
LIST OF APPENDICES xviii
CHAPTER 1 INTRODUCTION
1.1 Background 1
1.2 Objectives 2
1.3 Scopes 3
1.4 Problem Statement 3
CHATER 2 LITERATURE REVIEW
2.1 Alloy Steel 4
2.1.1 Low Alloy Steel 6
2.2 Surface Hardening 7
2.2.1 Carburizing 8
2.2.1.1 Pack Carburizing 9
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CHAPTER ITEM PAGE
2.3.1 Quenching 13
2.3.1.1 Quenching Media 15
2.3.2 Tempering 16
2.3.3 Normalizing 19
2.4 Mechanical Test (Destructive Test) 20
2.4.1 Hardness Test 21
2.4.1.1 Rockwell Test 23
2.4.2 Compression Test 25
CHAPTER 3 METHODOLOGY
3.1 Materials 27
3.2 Process Flow 31
3.2.1 Specimens Preparation 32
3.2.2 Carburizing Process 34
3.2.3 Heat Treatment Process 37 3.2.3.1 Phase 1: Carburizing and
Normalizing 38
3.2.3.2 Phase 2: Carburizing, Quenching and Normalizing
Process 39
3.2.3.3 Phase 3: Carburizing, Quenching, Tempering and
Normalizing Process 40
3.2.4 Rockwell Hardness Test 41
3.2.5 Compression test 43
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CHAPTER ITEM PAGE
CHAPTER 4 RESULT AND ANALYSIS
4.1 Hardness Test 47
4.1.1 Result 47
4.1.2 Statistical Analysis 49
4.1.2.1 Comparison between Group
5A and 5B 49
4.1.2.2 Comparison between Group
5C and 5D 52
4.1.2.3 Comparison between Group
5B and 5D 55
4.2 Compression Test 58
4.2.1 Result 58
4.2.2 Statistical Analysis 59
4.2.2.1 Comparison between Group
5A and 5B 59
4.2.2.2 Comparison between Group
5A and 5D 62
4.2.2.3 Comparison between Group
5B and 5D 65
4.2.2.4 Comparison between Group
5A and 5C 68
4.3 Summary of Hardness and Compressive
Strength Comparison by Statistical Analysis 71
CHAPTER 5 DISCUSSION
5.1 Effects On Hardness 72
5.1.1 Hardness comparison between Group
5A and 5B 73
5.1.2 Hardness comparison between Group
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CHAPTER ITEM PAGE
5.1.3 Hardness comparison between Group
5B and 5D 75
5.2 Effects On Compression Strength 76 5.2.1 Comparison of Compressive Strength
between Group 5A and 5B 77 5.2.2 Comparison of Compressive Strength
between Group 5A and 5D 78 5.2.3 Comparison of Compressive Strength
between Group 5B and 5D 79 5.2.4 Comparison of Compressive Strength
between Group 5A and 5C 80
CHAPTER 6 CONCLUSION 81
CHAPTER 7 RECOMMENDATION 82
REFERENCES 83
BIBLIOGRAPHY 85
APPENDIX A 86
APPENDIX B 88
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x
LIST OF TABLES
NO. TITLE PAGE
2.1 Colours formed on steel in the temperingprocess. 18 (Source: Rajput, R.K. 2000)
2.2 The examples of mechanical tests. 20
(Source: Rajput, R.K. 2000)
2.3 General characteristics of hardness testing methods 22 and formulas for calculating hardness.
(Source: Kalpakjian, S. and Schmid, S. 2006)
2.4 Rockwell scales 23
(Source: Horath, L. 2001)
2.5 Equation for converting HRC and HRB to Brinell 24 Hardness.
(Source: Chapman, W.W. 2004)
3.1 Chemical composition of A-2 Low Alloy Steel 28 (Source: Farrar, J.C.M. 2004)
3.2 International standards of A-2 Low Alloy Steel 28 (Source: Farrar, J.C.M. 2004)
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NO. TITLE PAGE
3.3 Specimen distributions 32
4.1 Experimental data for Group 5A and 5B 47
4.2 Experimental data for Group 5C and 5D 48
4.3 Average hardness in Brinell for each group 49
4.4 5A vs 5B 49
4.5 5C vs 5D 52
4.6 5B vs 5D 55
4.7 Experimental data of compressive strength 58
4.8 Average compressive strength for each group 59
4.9 5A vs 5B 60
4.10 5A vs 5D 62
4.11 5B vs 5D 65
4.12 5A vs 5C 68
4.13 Conclusion of hardness compression 71
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LIST OF FIGURES
NO. TITLE PAGE
2.1 The effect of the percentage of alloying elements 5 on the eutectoid temperature of the transformation
of austenite to pearlite in the Fe-Fe3C phase diagram. (Source: Smith, W.F. 2004)
2.2 Hardening effects of alloying elements in solid 5 solution in fully annealed ferrite.
(Source: Internet reference 22th July 2007)
2.3 Carburizing of a low carbon steel to produce a high 8 carbon, resistant surface.
(Source: Askeland, D.R. 1994)
2.4 Carburizing powder. 10
(Source: Internet reference, 11 Sept. 2007)
2.5 Graph of quenching effects on hardness. 14 (Source: Internet reference, 17 August 2007)
2.6 Hardness variation with martensite percentage and 14 carbon content after quenching.
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xiii
NO. TITLE PAGE
2.7 Thermal cycle of quenching and tempering. 16 (Source: Rajput, R.K. 2000)
2.8 The effect of tempering temperature on the 17 mechanical properties of 1050 steel.
(Source: Askeland, D.R. 1994)
2.9 The effect of carbon and heat treatment on the 19 property of carbon steels.
(Source: Askeland, D.R, 1994)
2.10 Column action 25
(Source: Horath, L. 2001)
2.11 Compression specimen specifications 26 (Source: Horath, L. 2001)
3.1 The alloy tree 27
(Source: Farrar, J.C.M. 2004)
3.2 Evaluation of Group A of Low Alloy Steel 30 (Farrar, J.C.M 2004)
3.3 Process flow of project 31
3.4 The dimension of specimen 32
3.5 Low alloy steel specimens 32
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xiv
NO. TITLE PAGE
3.7 The wilcarbo powder was packed at the bottom of the 34 containers.
3.8 The arrangement of specimens in the container 35
3.9 The extra container 35
3.10 The container were taken out from the furnace after 36
6 hours
3.11 The specimens were taken out from the containers 36
3.12 Flow chart of heat treatment processes 37
3.13 Carburizing process 38
3.14 Normalizing process 38
3.15 The schematic diagram of the carburizing-normalizing 38 process
3.16 Carburizing process 39
3.17 Quenching process 39
3.18 Normalizing process 39
3.19 The schematic diagram of the carburizing, quenching 39 and normalizing process
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NO. TITLE PAGE
3.20 Carburizing process 40
3.21 Quenching process 40
3.22 Tempering process 40
3.23 Normalizing process 40
3.24 The schematic diagram of the carburizing, quenching, 40 tempering and normalizing process
3.25 Hardness Test machine 41
3.26 Diamond indenter for HRC scale 41
3.27 Compression test machine 43
3.28 Difference in measurement before and after compression 45 test
3.29 Flow of hypothesis test 46
5.1 Hardness of Group 5A, 5B, 5C and 5D 72
5.2 Hardness comparison between Group 5A and 5B 73
5.3 Hardness comparison between Group 5C and 5D 75
5.4 Hardness comparison between Group 5B and 5D 76
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NO. TITLE PAGE
5.6 Comparison of compressive strength between Group 77 5A and 5B
5.7 Comparison of compressive strength between Group 78 5A and 5D
5.8 Comparison of compressive strength between Group 79 5B and 5D
5.9 Comparison of compressive strength between Group 80 5A and 5C
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LIST OF ABBREVIATIONS
ASTM = American Society of Testing and Material AISI = American Iron and Steel Institute
UNS = Unified Numbering System BHN = Brinell Hardness Number HRB = Rockwell B Hardness HRC = Rockwell C Hardness
EN = Euro Norm
CO = Carbon monoxide
CO2 = Carbon dioxide
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LIST OF APPENDICES
PAGE
APPENDIX A 86
Mitutoyo Conversion Table
APPENDIX B 88
Graphs of compressive strength
APPENDIX C 93
F Distribution table t Distribution table
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CHAPTER 1
INTRODUCTION
1.1 Background
Low alloy steels have been developed to overcome the deficiencies of plain carbon steels that contain alloying elements to improve their properties. The principle alloying elements added to make alloy steel are manganese, nickel, chromium, molybdenum and tungsten. Alloy steels are expensive than plain carbon steel but for many applications, they are the only materials that can be used to meet engineering requirements especially in the manufacture of automobiles and trucks parts. Beside that, low alloy steels also have better combination of strength, toughness and ductility than plain carbon steel. They contain about 0.2 percent C which commonly carburized or surface heat-treated to produce a hard, wear resistance surface while maintaining a tough inner core (Smith, 2004).
Carburizing is a thermal diffusion of an adequate quantity of atomic carbon on to the surface layer of steel and it takes place in its atomic state (Prabhudev, 2000). Basically, there are three most important methods of carburizing; pack carburizing, gas carburizing and liquid carburizing. For this project, pack carburizing method was elected due to simplify of experimental set up. Pack carburizing or powder carburizing process consists of packing the component in a solid carburizing compound in a suitable box and heating it slowly in a furnace to attain a temperature of about 900° to 950°C (Prabhudev, 2000). In this project, three types of heat
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2
treatment processes were carried out in order to compare the effect of quenching, tempering and normalizing after carburizing.
For the experimental set up, the heat treatment were divided into three phases, the first phase consists of carburizing then followed by normalizing, while for the second phase is carburizing, quenching and normalizing and the last phase consists of carburizing, quenching, tempering and normalizing. Quenching is a method of rapid cooling of a metal in a bath of liquid during heat treatment (Rajput, 2000) while the definition of tempering is a reheating of previously quenched alloy to a temperature below the critical range, holding the alloy for a specified time at that temperature, and then cooling it at a controlled rate, usually by immediate rapid quenching, to room temperature (Tomsic and Hodder, 2000). The final treatment is normalizing which it is the term applied to the process of heating the steel approximately 4°C above the critical temperature followed by cooling below this range in still air (Rajput, 2000).
After the heat treatment processes, hardness and compression strength test were carried out to study the effects of those heat treatments on low alloy steel specimens. Hardness is a material’s ability to resist surface abrasion while the compression strength is defined as malleability which it is a measure of the extent to which a material can withstand deformation in compression before failure occurs (Chapman, 2004). The data obtained from these test were compared to each other and the effects on low alloy steel were evaluated and analyzed after the three phases of heat treatments.
1.2 Objective
The objective of this research is to study and discuss the effects of quenching-tempering processes on hardness and compression strength of carburized low alloy steel using statistical analysis.
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1.3 Scopes
The scopes of this study are:
(a) To do literature study on carburizing process.
(b) To carry out carburizing treatment, normalizing, carburizing-quenching-normalizing, carburizing-quenching-tempering-normalizing on low alloy steel.
(c) To carry out hardness and compression test on the material, before and after treatments.
(d) To compare the data using statistical analysis in order to propose a better carburizing treatment process.
1.4 Problem Statement
In advance engineering, low alloy steels are widely used for some applications due to better combination of strength, toughness and ductility than plain carbon steel. In order to obtain the superior strength and toughness properties, there are some heat treatments that should be going through. Low alloy steels are commonly carburized to produce hard, high wear-resistant of the outer surface.
In previous study of FKM student, hardness of carburized low alloy steel was investigated but the result was against the prediction. Supposedly, hardness of carburized low alloy steel should be better than uncarburized low alloy steel. This research is carried out to make some enhancement with further heat treatment processes. After carburizing process, it was followed by other heat treatments like quenching, tempering and normalizing. Each process will presents different effects on the mechanical properties of low alloy steels. These desired properties are depending on how crucial the engineering works are. The effects of these surface hardening and heat treatments on low alloy steels will be investigated.
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CHAPTER 2
LITERATURE REVIEW
2.1 Alloy Steel
Smith (2004), said alloy steels have been developed to overcome the limitations of plain carbon steel which are used widely in engineering application. Some of the limitations of carbon steels are:
(a) Plain carbon steels cannot be strengthened beyond about 100,000 psi (690MPa) without a substantial loss in ductility and impact resistance.
(b) Large-section thickness of plain carbon steels can not be produced with a martensitic structure throughout. That is, they are not deep hardenable.
(c) Plain carbon steels have low corrosion and oxidation resistance.
(d) Medium-carbon plain carbon steels must be quenched rapidly to obtain a fully martensitic structure. Rapid quenching leads to possible distortion and cracking of the heat-treated part.
(e) Plain carbon steels have poor impact resistance at low temperature.
In order to improve the properties of plain carbon steels, alloying elements added such as manganese, nickel, chromium, molybdenum, and tungsten to make alloy steels. Other elements that are added include vanadium, cobalt, boron, copper, aluminum, lead, titanium, and columbium (niobium).
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Figure 2.1:The effect of the percentage of alloying elements on the eutectoid temperature of the transformation of austenite to pearlite in the Fe-Fe3C phase
diagram (Source: Smith, 2004).
Beside that, according to Askeland (1994), the alloying elements are added to steels to provide solution strengthening of ferrite, cause the eutectoid temperature of the Fe-Fe3C phase diagram to be raised or lowered (as shown in Figure 2.1), improve corrosion resistance and other special characteristics of the steel, and improve hardenability. Improving the hardenability is the most important in alloy and tool steels and the general effectiveness is shown in Figure 2.2:
Figure 1.2:Hardening effects of alloying elements in solid solution in fully annealed ferrite (Source: Internet reference 22th July 2007).
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LIST OF APPENDICES
PAGE
APPENDIX A 86
Mitutoyo Conversion Table
APPENDIX B 88
Graphs of compressive strength
APPENDIX C 93
F Distribution table t Distribution table
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CHAPTER 1
INTRODUCTION
1.1 Background
Low alloy steels have been developed to overcome the deficiencies of plain carbon steels that contain alloying elements to improve their properties. The principle alloying elements added to make alloy steel are manganese, nickel, chromium, molybdenum and tungsten. Alloy steels are expensive than plain carbon steel but for many applications, they are the only materials that can be used to meet engineering requirements especially in the manufacture of automobiles and trucks parts. Beside that, low alloy steels also have better combination of strength, toughness and ductility than plain carbon steel. They contain about 0.2 percent C which commonly carburized or surface heat-treated to produce a hard, wear resistance surface while maintaining a tough inner core (Smith, 2004).
Carburizing is a thermal diffusion of an adequate quantity of atomic carbon on to the surface layer of steel and it takes place in its atomic state (Prabhudev, 2000). Basically, there are three most important methods of carburizing; pack carburizing, gas carburizing and liquid carburizing. For this project, pack carburizing method was elected due to simplify of experimental set up. Pack carburizing or powder carburizing process consists of packing the component in a solid carburizing compound in a suitable box and heating it slowly in a furnace to attain a temperature of about 900° to 950°C (Prabhudev, 2000). In this project, three types of heat
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treatment processes were carried out in order to compare the effect of quenching, tempering and normalizing after carburizing.
For the experimental set up, the heat treatment were divided into three phases, the first phase consists of carburizing then followed by normalizing, while for the second phase is carburizing, quenching and normalizing and the last phase consists of carburizing, quenching, tempering and normalizing. Quenching is a method of rapid cooling of a metal in a bath of liquid during heat treatment (Rajput, 2000) while the definition of tempering is a reheating of previously quenched alloy to a temperature below the critical range, holding the alloy for a specified time at that temperature, and then cooling it at a controlled rate, usually by immediate rapid quenching, to room temperature (Tomsic and Hodder, 2000). The final treatment is normalizing which it is the term applied to the process of heating the steel approximately 4°C above the critical temperature followed by cooling below this range in still air (Rajput, 2000).
After the heat treatment processes, hardness and compression strength test were carried out to study the effects of those heat treatments on low alloy steel specimens. Hardness is a material’s ability to resist surface abrasion while the compression strength is defined as malleability which it is a measure of the extent to which a material can withstand deformation in compression before failure occurs (Chapman, 2004). The data obtained from these test were compared to each other and the effects on low alloy steel were evaluated and analyzed after the three phases of heat treatments.
1.2 Objective
The objective of this research is to study and discuss the effects of quenching-tempering processes on hardness and compression strength of carburized low alloy steel using statistical analysis.
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1.3 Scopes
The scopes of this study are:
(a) To do literature study on carburizing process.
(b) To carry out carburizing treatment, normalizing, carburizing-quenching-normalizing, carburizing-quenching-tempering-normalizing on low alloy steel.
(c) To carry out hardness and compression test on the material, before and after treatments.
(d) To compare the data using statistical analysis in order to propose a better carburizing treatment process.
1.4 Problem Statement
In advance engineering, low alloy steels are widely used for some applications due to better combination of strength, toughness and ductility than plain carbon steel. In order to obtain the superior strength and toughness properties, there are some heat treatments that should be going through. Low alloy steels are commonly carburized to produce hard, high wear-resistant of the outer surface.
In previous study of FKM student, hardness of carburized low alloy steel was investigated but the result was against the prediction. Supposedly, hardness of carburized low alloy steel should be better than uncarburized low alloy steel. This research is carried out to make some enhancement with further heat treatment processes. After carburizing process, it was followed by other heat treatments like quenching, tempering and normalizing. Each process will presents different effects on the mechanical properties of low alloy steels. These desired properties are depending on how crucial the engineering works are. The effects of these surface hardening and heat treatments on low alloy steels will be investigated.
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CHAPTER 2
LITERATURE REVIEW
2.1 Alloy Steel
Smith (2004), said alloy steels have been developed to overcome the limitations of plain carbon steel which are used widely in engineering application. Some of the limitations of carbon steels are:
(a) Plain carbon steels cannot be strengthened beyond about 100,000 psi (690MPa) without a substantial loss in ductility and impact resistance.
(b) Large-section thickness of plain carbon steels can not be produced with a martensitic structure throughout. That is, they are not deep hardenable.
(c) Plain carbon steels have low corrosion and oxidation resistance.
(d) Medium-carbon plain carbon steels must be quenched rapidly to obtain a fully martensitic structure. Rapid quenching leads to possible distortion and cracking of the heat-treated part.
(e) Plain carbon steels have poor impact resistance at low temperature.
In order to improve the properties of plain carbon steels, alloying elements added such as manganese, nickel, chromium, molybdenum, and tungsten to make alloy steels. Other elements that are added include vanadium, cobalt, boron, copper, aluminum, lead, titanium, and columbium (niobium).
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Figure 2.1:The effect of the percentage of alloying elements on the eutectoid temperature of the transformation of austenite to pearlite in the Fe-Fe3C phase
diagram (Source: Smith, 2004).
Beside that, according to Askeland (1994), the alloying elements are added to steels to provide solution strengthening of ferrite, cause the eutectoid temperature of the Fe-Fe3C phase diagram to be raised or lowered (as shown in Figure 2.1), improve corrosion resistance and other special characteristics of the steel, and improve hardenability. Improving the hardenability is the most important in alloy and tool steels and the general effectiveness is shown in Figure 2.2:
Figure 1.2:Hardening effects of alloying elements in solid solution in fully annealed ferrite (Source: Internet reference 22th July 2007).