STUDY ON THICKNESS EFFECTS OF LOW CARBON STEEL IN ...
Transcript of STUDY ON THICKNESS EFFECTS OF LOW CARBON STEEL IN ...
STUDY ON THICKNESS EFFECTS OF LOW CARBON STEEL IN RAPID
COOLING PROCESS
NUR ADJLA BINTI MOHAMAD HAFIZIN
This thesis is submitted as a partial fulfillment of the requirements for the award of the
Bachelor of Mechanical Engineering with Manufacturing Engineering
Faculty of Mechanical Engineering
UNIVERSITI MALAYSIA PAHANG
JUNE 2012
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ABSTRACT
Hot stamping is among the latest technology applied in sheet metal manufacturing. It is
a combination of a forming and rapid cooling to produce stronger products with the
creation of martensite inside the sheet metal components. To cope with a huge range of
sheet metal that suitably used for hot forming process, this research investigates
microstructure changes during the rapid cooling process of three different sheet metal
thicknesses. The Low Carbon Steel specimens of 2, 4 and 6mm thick were heated in a
furnace to austenite region before immediately quenched in water and normalized in air.
During the process, cooling rates were measured with acquisition system. The quenched
specimens were observed using metallurgical microscope. The results show that water
quench produced martensite structures while air quench produced pearlite and ferrite
structures. The 2mm specimen of water quench formed a higher percentage of
martensite and compactly bonded structure compared to 4mm and 6 mm specimens’
structure. For the air quench, 2mm specimen formed finely dispersed pearlite and
ferrite. However, the microstructure of 4mm and 6mm specimens’ shows coarse pearlite
and ferrite with lower hardness surface.
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ABSTRAK
Proses pembuatan bersuhu panas ke atas logam adalah antara teknologi terkini yang
digunakan dalam industri pembuatan. Ia adalah gabungan pembentukan dan proses
penyejukan pantas untuk menghasilkan produk lebih kukuh dengan penciptaan
martensit di dalam komponen yang dihasilkan dari lembaran logam. Untuk berhadapan
dengan pelbagai besar kepingan logam yang sesuai digunakan untuk proses
pembentukan panas, kajian ini mengkaji perubahan mikrostruktur semasa proses
penyejukan pada tiga kepingan logam yang berlainan ketebalan. Spesimen keluli carbon
rendah daripada ketebalan 2, 4 dan 6mm telah dipanaskan dalam relau sehingga
mencapai fasa austenit sebelum segera disejukkan dalam media penyejukan iaitu air dan
udara. Semasa proses penyejukan, kadar penyejukkan setiap specimen telah diukur
dengan sistem pemerolehan data. Mikrostruktur dalam spesimen telah di analisis
menggunakan mikroskop metalurgi. Keputusan menunjukkan bahawa air lindap kejut
menghasilkan struktur martensit manakala udara lindap kejut menghasilkan struktur
pearlit dan ferit. Spesimen berketebalan 2mm pada proses air lindap kejut membentuk
peratusan martensit yang lebih tinggi dan struktur yang kemas terikat dengan kekerasan
permukaan yang tinggi berbanding mikrostuktur yang dihasilkan oleh specimen 4mm
dan 6mm. Bagi lindap kejut udara, spesimen 2mm membentuk taburan halus pearlit dan
ferit. Walau bagaimanapun, mikrostruktur 4mm dan 6mm spesimen menghasilkan
pearlit dan ferit yang kasar dengan kekerasan permukaan yang lebih rendah.
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TABLE OF CONTENTS
TITLE PAGE Page
SUPERVISOR’S DECLARATION i
STUDENT’S DECLARATION iii
DEDICATION iv
ACKNOWLEDGEMENTS v
ABSTRACT vi
ABSTRAK viii
TABLE OF CONTENTS ix
LIST OF FIGURES xii
LIST OF TABLES xv
LIST OF SYMBOLS xvi
LIST OF ABBREVIATIONS xviii
CHAPTER 1 INTRODUCTION
1.1 Introduction 1
1.2 Problem Statement 3
1.3 Objectives 3
1.4 Background of Project 3
1.5 Scope of Project 4
CHAPTER 2 LITERATURE REVIEW
2.1 Introduction 5
2.2 Material 5
2.3 Heat Treatment 7
2.4 Internal Structure After Heat treatment 7
2.4.1 Austenite 7
2.4.2 Ferrite 8
2.4.3 Carbon 8
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2.4.4 Cementite 8
2.4.5 Pearlite 8
2.4.6 Martensite 8
2.5 Normalizing process 9
2.6 Quenching Process 10
2.7 Slow cooling of Hypotectoid Steel 11
2.8 Continuous-Cooling Transformation Diagram For
Carbon Steel
14
2.9 Time-Temperature Transformation Diagram 17
2.9.1 Austenite to Pearlite Transformation 18
2.9.2 Austenite to Bainite Transformation 19
2.9.3 Austenite to martensite transformation 19
2.10 Microstructure Theory 20
2.11 Testing On Mechanical Properties 20
2.11.1 Hardness Test 20
2.11.2 Rockwell Hardness Tests 21
2.12 Heat Treatment Effects of Low Carbon Steel 23
2.13 Effect Of Cooling Rate On Hardness And
Microstructure
25
2.14 Heat Treatment In Industry 27
2.14.1 Thermocouple 27
CHAPTER 3 METHODOLOGY
3.1 Introduction 29
3.2 Specimen Preparation 31
3.2.1 Design of specimen 31
3.2.2 Milling 32
3.2.3 EDM Wire cut 33
3.2.4 Material composition test for specimens 34
3.3 Heat Treatment 35
3.3.1 Thermocouple 35
3.3.2 Data Logger 35
3.3.3 National Instrument, NI 9213 36
3.3.4 Heat treatment Setup 37
3.3.5 Air Cooling Process 38
3.3.6 Water Quenching Process 39
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3.4 Microstructure Analysis 39
3.4.1 Sectional cut 39
3.4.2 Mounting 41
3.4.3 Grinding 42
3.4.4 Final Polishing 43
3.4.5 Etching 44
3.4.6 Microstructure and composition analysis 45
3.5 Hardness Test 46
CHAPTER 4 RESULT AND DISCUSSION
4.1 Introduction 48
4.2 Material Composition 48
4.3 Heat Treatment 50
4.4 Microstructure Analysis 54
4.4.1 AISI 1023 57
4.4.2 Air cooling process 58
4.4.3 Water Quenching 65
4.4 Hardness Test 70
4.4.1 Surface Hardness for Air Cooled
Specimens
70
4.4.2 Surface Hardness for Water Quenched
Specimens
72
4.5 Comparison Between Normalizing And Water
Quenching With Different Thickness
74
4.6 Conclusion 75
CHAPTER 5 CONCLUSION AND RECOMMENDATION
5.1 Introduction
5.2 Conclusion 76
5.3 Recommendation 78
REFERENCES 77
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APPENDICES 80
A1 Digimizer Software results of Pearlite area
measurement for AISI 1023 untreated specimen
81
A2 Digimizer Software results of Pearlite area
measurement for AISI 1023 6mm specimen after Air
Cooling process
82
A3 Digimizer Software results of Pearlite area
measurement for AISI 1023 4mm specimen after Air
Cooling process
85
A4 Digimizer Software results of Pearlite area
measurement for AISI 1023 2mm specimen after Air
Cooling process
87
B Chemical composition results of Low carbon Steel 89
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LIST OF FIGURES
Figure
No. Title Page
2.1 Carbon Steel Classification 6
2.2 The microstructure of 0.2% carbon steel after air cooled. Fine
dispersed Pearlite (black) and Ferrite (white)
10
2.3 Transformation of 0.4% carbon Hypoeuctectoid steel 12
2.4 Microstructure of a 0.38 wt% C steel having a microstructure
consisting of pearlite (dark region) and proeutectoid ferrite
(white region)
14
2.5 Continuous-cooling diagram for a plain-carbon eutectoid steel 15
2.6 Variation in the microstructure of a eutectoid plain-carbon steel
by continuously cooling at different rates
16
2.7 Time-temperature diagram for carbon steel 17
2.8 Summary of basic thermocouple properties 28
3.1 Flow of methodology process 30
3.2 Low carbon steel blocks 31
3.3 Microstructure and hardness test specimen 31
3.4 Milling machine Partner VMM3917 32
3.5 Face milling process 33
3.6 EDM Wire Cut Machine 33
3.7 Cutting wire 33
3.8 Arc Spark Spectrometer for testing the metal composition 34
3.9 Cutting wire 34
3.10 Thermocouple wire type K 35
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3.11 Tested specimen with 4 testing sparks 36
3.12 Furnace 37
3.13 National instrument NI 9123 37
3.14 Data logger set up 38
3.15 Sectional Cut off Machine MSX200M 40
3.16 Cutting section of specimen 40
3.17 Mounted specimens 42
3.18 HandiMet 2Roll Grinder frames 42
3.19 Grinding process using HandiMet 2Roll Grinder 43
3.20 Metken Forcipol 2V Grinding/Polishing M/C 43
3.21 Polycrystalline solution 6 µm, 1 µm and 0.05 µm 44
3.22 Fume hood 44
3.23 Metallurgical Microscope 45
3.24 Metallurgical analysis process 45
3.25 Matsuzawa Digital Rockwell Hardness Tester 46
3.26 Scale table of Rockwell testing test 47
4.1 Tested specimen with 4 tested sparks 49
4.2 Experiment equipment and setup 50
4.3 Heat treatment experiment setup 51
4.4 Cooling curve of water quenching 52
4.5 Cooling curve for air cooling specimen 53
4.6 Specific part of specimen for microstructure analysis 54
4.7 Microstructure analysis using Digimizer software 55
4.8
(a) The microstructure of AISI 1023 steel without heat
treatment
56
(b) Inverted image of microstructure of AISI 1023 untreated 56
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specimen using Digimizer software
4.9 (a) Microstructure of 2mm specimen after normalizing
process
59
(b) Inverted image of microstructure 2mm specimen of
normalizing using Digimizer software
60
4.10 (a) Microstructure of 4mm specimen after normalizing
process
61
(b) Inverted image of microstructure 4mm specimen of
normalizing using Digimizer software
61
4.11 (a) Microstructure of 6mm specimen after normalizing
process
61
(b) Inverted image of microstructure 6mm specimen of
normalizing using Digimizer software
61
4.12 Influence of thickness on Pearlite structure area 64
4.13 (a) Microstructure of 2mm specimen after water quenching
process
65
(b) The inverted image of 2mm specimen by Digimizer
software
66
4.14 (a) Microstructure of 4mm specimen after water quenching
process
67
(b) The inverted image of 4mm specimen by Digimizer
software
67
4.15 (a) Microstructure of 6mm specimen after water quenching
process
68
(b) The inverted image of 6mm specimen by Digimizer
software
69
4.16 Graph effect of thickness of Air cooled specimen 71
4.17 Graph of Rockwell Hardness of Water quenched specimens 73
4.18 Cooling rate and thickness effect on hardness 74
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LIST OF TABLES
Table
No.
Title Page
2.1 Application of Low Carbon Steel based on carbon contain 7
2.2 Hardness Testing Techniques 22
2.3 Rockwell Hardness Scale 23
2.4 The percentage of phases after heat treatment of AISI 1020 steel 26
3.1 Geometry dimension for microstructure and hardness test
specimen
32
4.1 Average composition of material for the specimen 49
4.2 Classification of specimen 51
4.3 Microstructures of Air Cooled and Water quenched Specimens 55
4.4 The total value of pearlite measurement of untreated specimen 58
4.5 Total measurement of pearlitic phase of 2mm air cooled
specimen
60
4.6 Total measurement of pearlitic phase of 4mm air cooled
specimen
62
4.7 Total measurement of pearlitic phase of 6mm air cooled
specimen
63
4.8 Summarization of Resulted Pearlitic area of 2mm, 4mm and
6mm Air Cooled Specimen
64
4.9 Rockwell hardness (60kgf) of AISI 1023 at the surface of
specimens with Air Cooling Process
70
4.10 Rockwell hardness (60kgf) of AISI 1023 at the surface of
specimens with Water Quenching Process
72
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LIST OF SYMBOLS
𝛾 Austenite Phase
𝛼 Ferrite Phase
Te Eutectoid Temperature
Ms Martensite Start
Mf Martensite Finish
C Carbon
Fe Ferrous
Si Silicon
Mn Manganese
P Phosphorus
S Sulphur
Cr Chromium
Mo Molybdenum
Ni Nickel
Al Aluminum
Co Cobalt
Cu Copper
Nb Niobium
Ti Titanium
V Vanadium
Pb Plumbum
Sn Stannum
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B Boron
Ca Calcium
Zr Zirconium
As Arsenic
Bi Bismuth
Fe3C Cementite
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LIST OF ABBREVIATIONS
AISI American Iron and Steel Institute
BCC Body-centered Cubic
BCT Body-centered Cubic
CCT Continuous-cooling Time
EDM Electric-discharged Machine
FCC Face-centered Cubic
ISA Instrument Society of America
NI National Instrument
CHAPTER 1
INTRODUCTION
1.1 INTRODUCTION
Process of manufacturing activities can be improved by the understanding of
microstructure characteristic of the used material. In this case, the most useful material
is metals where their material properties are usually determined by tests. As a
mechanical engineer, it is necessary to engage in testing work to have a general
understanding of the common methods of properties test of metals. From an engineering
point of view, the mechanical properties are the most important requirement in selecting
material for design purpose. Mechanical properties and microstructure of metals
describes their behavior under mechanical and physical usage.
Generally, the applications of metals have been studied a long time ago. Since
the Iron Age, metal have been practically used in daily life and become very important
in the development of industry. The ability to withstand service for higher loadings
without permanently deforms and ruptures. In the other hand, the ability of metal
undergoes large permanent deformation, thus permitting the formation of different
shapes under the application of proper forces [Izabel, 2005]. Plenty of studies have been
done on metal, so the microstructures of most metals are well identified as well as the
effects of heat treatment in altering their mechanical properties.
The most popular metal is known as carbon steel. Carbon steel is being divided
as low carbon steel, medium carbon steel and high carbon steel which based on the
carbon content. Normally carbon steel is not enough hard to use in certain
manufacturing. Therefore heat treatment is important process to improve the mechanical
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properties of the carbon steel. The common forms of heat treatment for steels are
hardening, tempering, annealing, normalizing and case hardening [Krauss, 1989].
The different mechanical properties of carbon steels will be resulted as different
microstructures formed during cooling. Furthermore, the diffusionless transformations
obtain the martensite formation which is the highest hardness in iron-carbon system and
the lowest hardness is obtained due to a diffusion transformation, which cause the
ferrite and/or pearlite formation by a eutectoid reaction. Martensite is obtained during
rapid cooling while ferrite and pearlite obtained from austenite during slow cooling near
the equilibrium. Therefore, both steel microstructure and mechanical properties are
related to steel thermal history [W. Wen, 2005]. Pressure also has an influence on
stability of phase of equilibrium. However, this parameter is not usually taken in
account, mainly in solid state reaction. It is because the influence of pressure is limited
[Jokhio et al., 2000].
Low carbon steel as one of engineering material that has been selected in this
project is to investigate the comparison of the effects on thickness of material of rapid
cooling process and develop a mechanical data of low carbon steel after the heat
treatment. This material have been chosen because this type of steel is mostly used for
deep drawing of motor car bodies, motor cycle parts, and other domestic applications
where it is must involved the desired mechanical properties processes.
From the engineering material theory, the required properties of material can be
changed by manufacturing process and heat treatment process method. Therefore the
present work was planned to investigate the relationship between thickness,
microstructure, mechanical properties, and heat treatment for intelligent selection of
manufacturing process, properties, and application for particular purpose [Sim et al,.
2004].
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1.2 PROBLEM STATEMENT
This project is being undertaken to compare microstructure effects of different
thickness on metal in rapid cooling process. In present day, new approaches of
manufacturing process have been introduced. For example, the application of hot
stamping technique is used to form many types of car component. This process involves
thermo mechanical effects where the sheet metal parts are quenched after forming
process to improve the mechanical properties. It is important to investigate the thickness
effects on microstructure development.
1.3 OBJECTIVES
The aim of this research is to understand the mechanism of investigation
microstructures changes during rapid cooling process of different sheet metal
thicknesses. In order to achieve the objectives, the approach to the research has been
determined as listed below:
1) To conduct experiment of rapid cooling process on low carbon steel
2) To identify the material composition of low carbon steel
3) To investigate the microstructure effect after water quenching and air cooling
process with different thickness
4) To determine the effect of material thickness on surface hardness
1.4 PROJECT BACKGROUND
Quenching is common process to harden the steel. This process are widely used
in industry which to obtain the required properties of any application. From this study,
the mechanical properties of the specimen from in-received after quenching process
with different material thickness can be differentiate. The formation of martensite and
pearlite can be analyzed and the investigation of influences of thickness effecting the
microstructure and hardness of material.
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1.5 PROJECT SCOPE
1.5.1 Literature Reviews
i. Researching and surveying on the paper work that have been made by the
previous researcher.
ii. Collect the information related to the project’s objectives.
1.5.2 Experiment
i. Planning the methodology flow of experiment.
ii. Specimen preparation of experiment.
iii. Do the experiment to compares the effects of different thickness in two types of
different process which are normalizing and quenching
iv. Apply two types of test on the low carbon steel after heat treatment
(Microstructure test and Rockwell hardness test).
1.5.3 Analysis of the Experiment
i. Analyze the experiments result and do a comparison related of the experiment.
ii. Summarize the assumption from the research.
1.5.4 Thesis Writing
i. Transfer all the experiment data and results into a form of thesis report including
the conclusion of project.
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CHAPTER 2
LITERATURE REVIEW
2.1 INTRODUCTION
Rapid cooling is a process purpose to harden the metals by immersion in oil or
water, of a metal object from the high temperature at which it has been shaped. This
usually is undertaken to maintain mechanical properties associated with a crystalline
structure or phase distribution that would be lost upon slow cooling. The technique is
commonly applied to steel objects, to which it imparts hardness. On the other hand,
copper objects that have become hardened by hammering or other deformation at
ordinary temperatures can be restored to the malleable state by heating and quenching.
2.2 MATERIAL
In this project, low carbon steel has been chosen to serve as experimental
material. Low carbon steel is a type of metal that has an alloying element made up of a
relatively low amount of carbon. Typically, it has a carbon content that ranges between
0.05% and 0.20% and a manganese content that falls between 0.40 and
1.5%. According to Figure 2.1, Low Carbon Steel can be classified into hypoeutectoid
steel based on its carbon content range.
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Figure 2.1: Carbon Steel Classification
Source: Ginzel (1995)
Low carbon steel is known as low carbon steel is one of the most common types
of steel used for general purposes, in part because it is often less expensive than other
types of steel. While the steel contains properties that work well in manufacturing a
variety of goods, it is most frequently made into flat-rolled sheet or strips of steel.
Steel with low carbon content has the same properties as iron, soft but easily
formed. As carbon content rises the metal becomes harder and stronger but less ductile
and more difficult to weld. Higher carbon content lowers steel's melting point and its
temperature resistance in general. Carbon content influences the yield strength of steel
because they fit into the interstices crystal lattice sites of the body-centered cubic (BCT)
arrangement of the iron molecules [Merbaki et al., 2004].
Steel can be heat-treated which allows parts to be fabricated in an easily
formable soft state. If enough carbon is present, the alloy can be hardened to increase
strength, wear, and impact resistance. Steels are often wrought by cold-working
methods, which is the shaping of metal through deformation at a low equilibrium or met
a stable temperature.
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Table 2.1: Application of Low Carbon Steel based on carbon contain
Carbon Percentage (%) Applications
0.1-0.2 Chain, stamps, rivets, nails, wire, pipe and where
very soft, plastic steel is needed
0.2 – 0.3 Structural steels, machine parts, soft and tough steels
and use of case hardened machine part and screw
2.3 HEAT TREATMENT
A combination of times heating and cooling operations which applied to the
solid state metal or alloy is called as heat treatment. This method is often used to modify
or alter the microstructure and properties of steels. The various types of heat-treating
processes are similar because they all involve the heating and cooling of metals.
However, they differ in the heating temperatures and the cooling rates used. The final
results of each method are different. The usual methods of heat-treating ferrous metals
(metals with iron) are annealing, normalizing, hardening, and tempering. Most
nonferrous metals can be annealed, but never tempered, normalized, or case-hardened.
According to [Jokio et al., 2005], heat treatment is defined as physical process
which entails the controlled heating and cooling of material, such as metal or alloys to
obtain desired properties. Heat treating is an energy intensive process that is carried out
in different furnaces such as electric and gas. Shortening heat treatment cycles can
provide great environment and financial benefits through energy saving. Many texture
detail furnace equipment and its design but little to no literature can be found in furnace
temperature method [Qiao et al., 2009].
2.4 INTERNAL STRUCTURE AFTER HEAT TREATMENT
2.4.1 Austenite
This phase is only possible in carbon steel at high temperature. It has a Face
Center Cubic (FCC) atomic structure which can contain up to 2% carbon in solution.
8
2.4.2 Ferrite
This phase has a Body Centre Cubic structure (BCC) which can hold very little
carbon. Typically 0.0001% at room temperature and can exist as either alpha or delta
ferrite.
2.4.3 Carbon
A very small interstitial atom that tends to fit into a cluster of iron atoms. It
strengthens steel and gives it the ability to harden by treatment.
2.4.4 Cementite
A very hard intermetallic compound which consisting of 6.7% carbon and the
remainder iron. Its chemical symbol is Fe3C. However, when it is mixed with soft ferrite
layers, the average hardness is reduced considerably. Slow cooling gives course
pearlite; soft and easy to machine but poor toughness. Faster cooling gives very fine
layers of ferrite and cementite which is harder and tougher.
2.4.5 Pearlite
Pearlite is a mixture of alternate strips of ferrite and cementite in single grain.
The distance between the plates and their thickness is depending on the cooling rate of
the material. Fast cooling will creates thin plates that are close together and slow
cooling creates a much coarser structure possessing less toughness. A fully pearlitic
structure occurs at 0.8% carbon. Further increases in carbon will create cementite at the
grain boundaries, which will start to weaken the steel.
2.4.6 Martensite
Body centered tetragonal (BCT) structure occur when steel is cooled rapidly
from austenite, the FCC structure rapidly changes to BCC leaving insufficient time for
the carbon to form pearlite. This results in a distorted structure that has the appearance
9
of fine needles. There is no partial transformation associated with martensite, it either
form or it doesn’t. However, only the part of the section that cool fast enough will form
martensite. In the thick section it will only form to a certain depth, and if the shape is
complex it may only form in small pockets. The hardness of martensite is solely
dependent on carbon content; it is normally very high, unless the carbon content is
exceptionally low.
2.5 NORMALIZING PROCESS
This process can be done by heating the steel to austenite phase and cooling it in
the air. In industry, normalizing is applied to eliminate coarse-grained structures
obtained in previous working operations such as rolling and forging. Besides,
normalizing is purpose to modify and improve the cast dendritic structures and reduce
segregation by homogenizing the microstructure. The desired microstructure and
mechanical properties can be obtain and improve the machinability of low carbon steel.
In normalizing steel is uniformly heated to a temperature which causes complete
transformation to austenite. The steel is held at this temperature for sufficient time for
the formation of homogeneous structure throughout its mass. Then, it is allowed to cool
in air. Furthermore, normalizing results in the formation of ferrite, cementite and
lamellar pearlite. Due to the higher cooling rate in this process, the transformation of
austenite is occurring at a lower temperature than in annealing process. Therefore, the
transformation of pearlite is finer where having lower interlamellar spacing between the
two neighboring of cementite plates compared to anneled steel compared to coarse
pearlite [Izabel, 2005].
The amount of pearlite will affect the hardness and strength of steel. The
normalized steels are harder and stronger than annealed steels due to the amount of
pearlite in normalized steel is more despite having the same carbon content [Saquet et
al., 1999]. This differences value of pearlite occurs due to the shifting of eutectoid
composition to a lower value. The microstructure of 0.2% carbon steel in normalized
condition is shown in Figure 2.2 refers to the researched of the Effect of Cooling Rate
on Hardness and Microstructure of AISI 1020 Steels [Adnan C., 2009].
10
In normalizing, the mass of metal has an influence on the cooling rate and on the
resulting structure. Thin pieces cool faster and are harder after normalizing than thick
ones. In annealing (furnace cooling), the hardness of the two are about the same [Holzcr
et al., 1991].
Figure 2.2: The microstructure of 0.2% carbon steel after air cooled. Fine dispersed
pearlite (black) and ferrite (white)
Source: Adnan C. (2009)
Since normalizing is a much more economical process, this type of method is
extensively used in industry as cooling take place in the air. Some typical examples of
normalizing in commercial practice are homogenization of cast and wrought structures,
improvement of machinability, grain size refinement of cast structures and stress
relieving of castings [Monsanto, 1992].
2.6 QUENCHING PROCESS
Quenching is one of the hardening processes of steel that may be defined as
rapid cooling from the austenite phase. The rapid cooling is obtained by immersion of
steel in a liquid bath such as water or oil. The rapid cooling of steel from austenite
phase results in the formation of meta-stable phase called martensite. The main
objective of this process is to increase hardness, strength and wear resistance. Besides,