An investigation on the influence of double heat treatment process on mild steel plate.
AN INVESTIGATION ON THE INFLUENCE OF DOUBLE HEAT TREATMENT
PROCESS ON MILD STEEL PLATE
RAHFIZAN BIN KHAIRUZZAMAN
This report is submitted In Partially Fulfillment of Requirement for the Bachelor Degree
of Mechanical Engineering (Structure and Material)
Faculty of Mechanical Engineering
Universiti Teknikal Malaysia Melaka
JUNE 2013
© Universiti Teknikal Malaysia Melaka
DECLARATION
"I hereby declare that this report entitled "AN INVETIGATION ON THE
INFLUENCE OF DOUBLE HEAT TREATMENT PROCESS ON MILD STEEL
PLATE" is the result of my own research except as cited in the reference."
Signature:
. .felr . . . . . .
Author:
Rahfizan Bin Khairuzzaman
Date:
25 June 2013
© Universiti Teknikal Malaysia Melaka
SUPERVISOR DECLARATION
"I hereby declare that I have read this thesis and in my opinion this report is
sufficient in term of scope and quality for the award of the degree of Bachelor of
Mechanical Engineering (Structure and Material)."
Signature:
Supervisor:
En. Nazri Huzaimi Bin Zakaria
Date:
25 June 2013
© Universiti Teknikal Malaysia Melaka
ACKNOWLEDGEMENT
First and foremost, I would like express my deepest thanks and appreciation to my
friends for supporting throughout the period of this finaJ year project is conducted. It is a
privilege for me to complete my finaJ year project as to fulfill my degree requirement.
I would like to convey my most heartfelt gratitude to my supervisor, En. Nazri Huzaimi
Bin Zakaria who has graciously offered his precious time, attention, experience and
guidance throughout the completion of the investigation thus far, I appreciate the
opportunities of learning from him.
Lastly, I would thank each and every individual who have either directly or indirectly
help me throughout the effort of this report be it in the form of encouragement, advice
and kind reminder. A special thanks to my beloved family members, I extend my
gratitude for their support and understanding.
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ABSTRACT
This research covered mainly the effect of double heat treatment on mild steel plate.
Three types of heat treatment are quenching, tempering and normalizing were used in
this study. The specimen that used in this study is consisted of square shape mild steel
plate with 250mm x 40 mm x 4 mm dimension. During heat treatment process, specimen
is heated up to 960°C for one hour before taken out from the furnace. Two of the
specimens then are quenched in water at room temperature. For other specimen, it will
cool at room temperature due the normalizing process. One of the specimens from
quenching process will be continued with tempering process, tempering process consist
two level of heating process and temperature will be considered. After the first stage of
the heat treatment process, three types of test will be conducted which are hardness test,
microstructure and tensile testing the specimen. After that, another specimen will
undergo the same heat treatment process for second time. The specimen also will be
tested with three types of testing and the result of single and double heat treatment will
be compared. The expected result for hardness and strength for tempering, quenching
and normalizing is the specimen becomes more increase.
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ABSTRAK
Kajian ini meliputi kesan rawatan haba dua kali terhadap plat keluli lembut. Tiga jenis
rawatan haba yang akan digunakan didalam kajian ini adalah pelindapkejutan,
pembajaan dan penormalan. Dimensi spesimen yang digunakan adalah terdiri daripada
plat keluli berbentuk segiempat dengan ukuran 250mm x 40mm x 4mm. Semasa proses
rawatan haba, spesimen dipanaskan pada suhu 960°C selama satu jam sebelum dibawa
keluar dari relau. Dua daripada spesimen akan disejukkan di dalam air pada suhu bilik.
Bagi spesimen lain, ia akan dibiarkan menyejuk pada suhu bilik untuk proses
penormalan. Salah satu daripada spesimen daripada proses pelindapkejutan akan
diteruskan dengan proses pembajaan, proses pembajaan terdiri dua tahap proses
pemanasan dan suhu akan dipertimbangkan. Selepas peringkat pertama proses rawatan
haba telah selesai, tiga jenis ujian yang akan dijalankan pada specimen adalah ujian
kekerasan, mikrostruktur dan ujian tegangan. Selepas itu, spesimen lain akan menjalani
proses rawatan haba yang sama untuk kali kedua. Spesimen tersebut juga akan diuji
dengan tiga jenis ujian dan hasil rawatan haba pertama dan kedua akan dibandingkan.
Hasil yang dijangkakan untuk kekerasan dan kekuatan untuk pelindap kejutan
pembajaan, dan menormalkan adalah spesimen menjadi lebih k1.1at.
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TABLE OF CONTENT
CHAPTER
CHAPTER 1
CHAPTER 2
TITLE
PAGE
DECLARATION
ii
ACKNOWLEDGEMENT
iii
ABSTRAK
iv
ABSTRACT
v
LIST OF TABLE
vi
LIST OF FIGURE
vii
INTRODUCTION
1.1
Heat Treatment
1.2
Objective
2
1.3
Scope
2
1.4
Problem Statement
2
LITERATURE REVIEW
2.1 Introduction
3
2.2
Carbon Steel
3
2.2.1
Low carbon steel
4
2.2.2
S275JR Steel Plate
4
2.3
2.4
The Background of Mild
Steel
Heat treatment
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5
6
2.4.1
Tempering
9
2.4.2
Normalizing
13
2.4.3
Quenching
17
2.4.3.1 Convection heat
21
transfer model for
liquid quenching
CHAPTER3
2.5
Hardness Test
22
2.6
Microstructure Analysis
25
METHODOLOGY
3.1
Introduction
26
3.2
Material preparation
29
3.3
Equipment
30
3.4
Heat treatment process
32
3.5
3.4.l
Normalizing
32
3.4.2
Quenching
33
3.4.3
Tempering
33
Study of mechanical
33
properties
3.5.1
Tensile test
34
3.5.2
Rockwell Hardness
35
3.5.3
Microstructure
37
Analysis
CHAPTER4
RESULT & DISCUSSION
4.1
Metallurgical Characteristic
of Mild Steel Plate
4.11 Mechanical
Properties
4.12 Microstructure
Analysis
4.2 Water Quench Heat
Treatment
4.2.1 Mechanical Properties
Analysis of Water Quench
sample
4.2.2 Microstructure
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39
40
41
43
43
46
Analysis of Water Quench
sample
4.3 Tempering Heat Treatment
4.3 .1 Mechanical Properties
Analysis of Tempering
sample
4.3.2 Microstructure
Analysis of Tempering
sample
4.4 Normalizing Heat
Treatment
4.4. l Mechanical Properties
Analysis of Normalizing
sample
4.4.2 Microstructure
Analysis of Normalizing
sample
CHAPTERS
47
48
50
51
51
54
CONCLUSION &
RECOMMENDATION
5.1
Conclusion
56
5.2
Recommendation
58
REFERENCES
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59
LIST OF TABLE
NUM.
TITLE
Table 2.1
Properties S275JR mild steel plate
Table 2.2
Hardness testing result
11
Table 2.3
Tensile testing result
11
Table 2.4
Proposed tempering temperature according to application
12
Table 2.5
Summary of changes tempered steel microstructure
13
Table 2.6
Approximate Soaking Period for Hardening, Annealing &
16
PAGE
4
Normalizing
Table 3.1
29
Table 4.1
Dimension of Specimen AISI I 040 low carbon steel shaped
dog bone
Hardness value of as-received mild steel plate
Table 4.2
Ultimate Tensile Strength of as-received mild steel plate
40
Table 4.3
Rockwell Hardness (HRA) for first Water Quench Heat
43
40
Treatment result
Table 4.4
Rockwell Hardness (HRA) for second Water Quench Heat
43
Treatment result
Table 4.5
Ultimate Tensile Test for Water Quench Heat Treatment result
44
Table 4.6
Rockwell Hardness (A) for first Tempering Heat Treatment
48
result
Table 4.7
Rockwell Hardness (A) for second Tempering Heat Treatment
48
result
Table 4.8
Ultimate Tensile Test for Tempering Heat Treatment result
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49
Table 4.9
Rockwell Hardness (A) for first Normalizing Heat Treatment
51
result
Table 4.10
Rockwell Hardness (A) for second Normalizing Heat
51
Treatment result
Table 4.11
Ultimate Tensile Test for Normalizing Heat Treatment result
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52
LIST OF FIGURE
NUM.
TITLE
Figure 2.1
Variation of hardness and mechanical properties with number
PAGE
8
of heat treatment cycles
Figure 2.1
Partial iron-Iron carbide phase diagram, showing typical
13
normalizing range for plain carbon steel
Figure 2.3
Comparison of time-temperature cycles for normalizing and
16
full annealing. The slower cooling of annealing results in
higher temperature transformation to ferrite and pearlite and
coarser microstructures than does normalizing.
Figure 2.4
A quench tank which is used for the uniform quenching of hot
18
steels. It may be used with water, light weight polymer, or oil
Figure 2.5
Temperature gradients and other major factors affecting the
20
quenching of the gear
Figure 2.6
Cooling rate curves for liquid quenching
21
Figure 3.1
Flow Chart of overall process
28
Figure 3.2
Specimen AlSl 1040 low carbon steel shaped dog bone
29
Figure 3.3
Furnace (Nabertherm, High Temperature Stand Alone Type
30
Furnace)
Figure 3.4
Universal Testing Machine (lnstron, 8802)
31
Figure 3.5
Axioskop 2 MAT (Carl Zeiss) equipment
32
Figure 3.6
Rockwell Hardness Test
32
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Figure 3.7
Rockwell hardness measurement showing positions to apply
37
the minor and major loads.
Figure 4.1
Specimen for Tensile Test
41
Figure 4.2
Microstructure observation before heat treatment (1 OOX)
42
Figure 4.3
Specimen after the mounting for microstructure analysis
42
Figure 4.4
Graph result of Water Quench Heat Treatment Hardness
44
Figure 4.5
Graph result of Water Quench Heat Treatment Ultimate Tensile
45
Strength
Figure 4.6
Microstructure of Mild Steel plate after treated with first
46
Water Quench Heat Treatment
Figure 4.7
Microstructure of Mild Steel plate after treated with second
46
Water Quench Heat Treatment
Figure 4.8
Graph result of Tempering Heat Treatment Hardness
48
Figure 4.9
Graph result of Tempering Heat Treatment Ultimate Tensile
49
Strength
Figure 4.10
Microstructure of Mild Steel plate after treated with first
50
Tempering Heat Treatment
Figure 4.l I
Microstructure of Mild Steel plate after treated with second
50
Tempering Heat Treatment
Figure 4.12
Graph result of Normalizing Heat Treatment Hardness
52
Figure 4.13
Graph result of Normalizing Heat Treatment Ultimate Tensile
53
Strength
Figure 4.14
Microstructure of Mild Steel plate after treated with first
54
Normalizing Heat Treatment
Figure 4.15
Microstructure of Mild Steel plate after treated with second
Normalizing Heat Treatment
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54
CHAPTER I
INTRODUCTION
1.1
HEAT TREATMENT
Heat treatment is defined as an operation or combination of operation, involving
heating and cooling of a metal, for this case involving the mild steel in its solid state
with the object of changing the characteristic of the material. For this project, the mild
steel plate will be run with double heat treatment process that is normalizing, quenching
and tempering to investigate the influence of the process to the material. The
characteristic changing can be explored through the microstructure test with applying the
microscope test that was form various characteristics as pearlite, martensite,
tempermartensite and so on. S275JR mild steel plate will we used in this research, this
steel contain the carbon percentage of 0.22%. [I]
Heat treatment is generally employed for following purpose such as to improve
mach inabilility, to change or refine grain size, to improve mechanical properties like
tensile strength and Rockwell hardness test and microstructure test to obtain various
collection data before it can be evaluated to determine the result compare with the
standard data of mild steel as a comparison. [2]
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1.2
OBJECTIVE
a. To investigate the influence of double heat treatment process on mild steel.
b. To observe the change of microstructure and strength of mild steel plate after
subjected to normalizing, tempering and quenching process.
1.3
SCOPE
The scope of this research is:
a. Analyze the strength, hardness and change of microstructure between one and
double heat treatment process on mild steel plate.
b. Specimen preparation for make double heat treatment process.
1.4
PROBLEM STATEMENT
Mild Steel is most common form of steel because its price is low, malleable and
acceptable for many applications. However, the most common problem we are
encountered by mild steel is that it has a relatively low tensile strength. Usage
properties, as well improper heat treatment processes contributes to this problem. In this
research, low carbon steel S275JR has been selected as the material for double heat
treatment process. The hardness and strength of the carbon steel can be analyzed through
Rockwell tester and ultimate tensile testing and the internal structure can be analyzed by
using microscope image analyzer. This research is also to proof that the hardness and
strength of mild steel with double heat treatment is larger compared to the single heat
treatment. [3]
2
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CHAPTER2
LITERATURE RIVEW
2.1
INTRODUCTION
The purpose of literature review is to find out all the necessary information and
unknown knowledge in the research of the effect of double heat treatment towards mild
steel plate strength, hardness and microstructure. The objective of literature review is to
use the source found out to support the research. The sources include books, journals,
articles and internet sources.
2.2
CARBON STEEL
Carbon steel is steel that contain carbon as main alloying element. lt also has up
to 1.5% carbon and other alloying elements like copper, manganese and silicon. As we
can see, nowadays most of the steel produced is plain carbon steel.
Steel with low carbon content has properties similar to iron. As the carbon content
increases the metal becomes harder and stronger but less ductile and more difficult to
weld. Higher carbon content lowers the melting point and its temperature resistance
carbon content cannot alter yield strength of material.
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2.2.1
Low carbon steel
Low carbon steel or mild steel has carbon content of 1.5% to 4.5%. Low carbon
steel is the most common type of steel as its price is relatively low while its provides
material properties that are acceptable for many applications. It is neither externally
brittle nor ductile due to its low carbon content. It has lower tensile strength and
malleable.
2.2.2
S275JR steel plate
The S275JR steel plate has reliable mechanical properties, good formability and
excellent welding performance; it' s also used widely in various industries such as
architecture, bridge construction, marine craft, railway locomotive heavy machine and
other structure parts. Table 2.1 show the properties S275JR mild steel plate.
Table 2.1: Properties S275JR mild steel plate
Source: www.steelnumber.com/en/steel_composition_eu.php?name_id=3
S275JR STEEL
Tensile Strength (1 - lOOmm thickness)
41 OMpa - 560Mpa
Minimum Yield Strength (to 16mm thickness)
275Mpa
Minimum Elongation (3 - 40mm thickness )
23%
Carbon (C)
0.22%
Manganese (Mn)
1.5%
Phosphorus (P)
0.04%
Sulfur (S)
0.04%
Minimum
Properties
4
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2.3
THE BACKGROUND OF MILD STEEL
Mild steel is least expensive of all steel and most common steel used. It is used in
most of product created from steel, mild steel is easy to weld, very hard and very
durable. Mild steel contain less than 2% carbon and it is able to be magnetized. Most of
the object today that are created of steel are made using mild steel, for example,
automobile chassis, motorcycle frame and most cookware are made using mild steel.
Due to the poor corrosion-resistance of mild steel, it must be painted or otherwise
protected and sealed in order to prevent rust from damaging it. The properties of
the steel allow the electrical current to travel through the steel without distorting the
makeup of the material.
Mild steel is one of the least expensive steels used and it' s the most common of
all metal. It is to be found in almost every product created from metal in industry. It is
relatively hard, weldable, easy annealed and very durable.Steel is an alloy of iron
containing a small but definite percentage of Carbon ranges from 0.15-1.5% (4]. Mild
Steel are those containing 0. 1-0.25% carbon, they are soft, malleable and ductile (5). It
has less than 2% carbon and it will magnetize well and being relatively inexpensive, any
project that requiring a lot of steel can used mild steel.
But when it comes to load bearing, its structural strength is not usually sufficient
to be used in structural beam and girders. Carbon is the main element in the formation of
steel causing hardness and strength to be increased with increasing content. Increase in
carbon also lowers the transformation temperature and increase Martensite (brittle
structure). Higher carbon content tends to increase the risk of hydrogen induced cracking
(H.l.C.) due to welding and reduce fracture toughness. Carbons increase strength and
decrease ductility and weld ability. It both controls the maximum attainable hardness
and contributes substantially to hardneability. Carbon has a moderate tendency to
ｳ･ｧｲ｡ｴ
ｾ Ｎ＠
(6)
5
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2.4
HEAT TREATMENT
Heat treatment is defined as a physical process which entails the controlled
heating and cooling of material, such as metal or alloys to obtain desired properties.
Heat treatment is an energy intensive process that is carried out in different furnace such
as electric and gas. Shortening heat treatment cycle 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 on furnace temperature methods. [7]
Heat treatment is an important operation in the manufacturing process of many
machine parts and tools. Only by heat treatment it is possible to impart the high
mechanical properties to steel required for the normal operation of modern machinery
and tools. Heat treatment is usually classified into four typical groups. The first group
comprises first-order or re-crystallization annealing which is employed to relieve
internal stresses, reduce the hardness and to increase the ductility of strained-hardened
metal. It is also known as stress-relieving. At first, upon an increase in the heating
temperature, the elastic distortions of the crystal lattice are eliminated (recovery). At
high temperature, new grains form and begin to grow (re-crystallization). Due to
recovery and re-crystallization, the metals are softened and regain its high ductility. It is
important to point out that the heating temperature for first order annealing is not
associated with phase transformation temperature and only depends upon the recovery or
re-crystallization temperature peculiar to each metal. The second group, second order of
full annealing, which involves phase re-crystallization, consist in heating alloys above
temperature required for phase transformation .
This is followed by sloe cooling. Full annealing substantially changes the
physical and mechanical properties and may refine a coarse-grained structure. In the
third group, hardening, alloys are heated above the phase transformation temperature
and are then rapidly cooled (quenched) to retrain at room temperature, either a phase
stable at high temperatures or various stages of decomposition or transformation of this
6
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phase. Thus, hardening cause the transformation of unstable (non-equilibrium)
structures. The fourth group, tempering, involve the re-heating of a hardened alloy
(steel) to a temperature below that required for phase transformation so as to bring it
nearer to an equilibrium state. [I]
Heat treatment is a collection through many processes such as annealing, stress
relief, quenching, tempering normalizing and ageing. All the different heat treatment
processes consists the following three stages:
1) Heating of the material
2) Holding the temperature for a time.(soaking time)
3) Cooling, usually to room temperature. (normalizing)
However, the temperature and time for the various processes is dependent on the
material mechanism controlling the water effect. For example, if the driving mechanism
is diffusion the time must long enough to allow necessary transformation reaction.
During heating and cooling, there is an existing temperature gradients between the
outside and interior portion of the material; their magnitudes depends on the size and
geometry of the workpiece. If the rate of temperature change in the surrounding in the
surrounding is too high, large temperature gradients may develop in the component. This
creates internal stresses that may lead to the plastic deformation and even to cracking.
[8]
The Korea research institute chemical technology also investigated the effect of
heat treatment on bioactivity and mechanical properties of a poly E-Caprlactore/Silica
hybrid containing calcium. It was conclude from the research that the mechanical
properties of PCL/Silica hybrid could be improved by heat treatment. It was conjectured
to be coursed by the reduction of the low molecule weight PCL phase and the
intensification of silica network by heat treatment. The mechanical properties of the
7
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specimens treated at 150°Cshowed comparable value to those of canceller' s bone and it
mean that its likely to be used for bio-active and degradable bone substitute. [9]Heat
treatment tends to relive internal stresses and remove coarseness of grain and have
significant influence on the properties of welded material. [6]
The hardness and strength properties (yield strength and ultimate tensile
strength) gradually increase up in anexperiment; the experiment is to study the effect of
cyclic heat treatment on microstructure and mechanical properties of 0.6% carbon steel.
Graphical of the result is represent in Figure 2.1 , hardness and strength properties
initially increase due to the finer microstructure (finer pearlite and ferrite) originated
from non-equilibrium forced air cooling in each heat treatment cycle. After 5 heat
treatment cycle, the graph initially increase but after that the graph marginally decrease
until the 8th cycle due to elimination of lamellar pearlite and generation of more
commentate spheroids in the microstructure. However, the steel still possesses much
higher strength than the as-received steel due to extremely fine grain size of ferrite in the
microstructurei 1O]
800
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5
6
7
A
9
Number of heat treatme.nt cycles
Figure 2.1: Variation of hardness and mechanical properties
with number of heat treatment cycles [10]
8
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2.4.1
TEMPERING
Tempering is carried out after quenching to reduce the brittleness of steel. The
steel is heated to below the critical temperature, held, then cooled slowly to provide the
require properties. Tempering is carried out in oil, salt or lead bath and also in furnace
controlled by fans circulating air. The combination of quenching and tempering can
produce the best combination of strength and notch ductility. The purpose is to relive
internal stress, to reduce brittleness and to make steel tough to resist shock and fatigue.
Variable associated with tempering that affect the microstructure and the
mechanical properties of tempered steel include temperature; time at temperature;
cooling rate from the tempering temperature; and composition of the steel; including
carbon content, alloy content and residual elements. In steel, quenched to a
microstructure consisting essentially of martensite, the iron lattice is strained by the
carbon atom, producing the high hardness of quenched steels. On heating, the carbon
atom diffuses and reacts in a series of distinct steps that eventually form Fe3 Cor alloy
carbide in a ferrite matrix of gradually decreasing stress level. The properties of the
tempered steel are determined primarily by the size, shape, composition and distribution
of the carbide that form , with a relatively minor contribution from solid-solution
hardening of the ferrite. These changes in microstructure usually decrease hardness,
tensile strength and yield strength but increase ductility and toughness.
Under certain conditions, hardness may remain unaffected by tempering or may
even be increased as a result of it. For example, tempering of a hardened steel at very
low tempering temperature may cause no change in hardness but may achieve a desired
increase in yield strength. Also, those alloy steels that contain one or more of the
carbide-forming elements (chromium, molybdenum, vanadium and tungsten) and
capable of ' secondary hardening'- that is, they may become somewhat harder as a result
of tempering. The tempered hardness values for several quenched steel are presented. [I]
9
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For heat treatment and subsequent hardness and tensile testing specimen were
obtained from Yi" diameter bar of 0.20%C low carbon steel. Using muffle furnace, the
specimen is heated at 960° C for one hour for austenitizing and then quenched in cold
water and oil. After quenching process is done, hardness and tensile properties were
evaluated and then the specimens were continued with tempering heat treatment in the
temperature range of150 - 550°C. After tempering process is done, the hardness and
tensile properties were again determined. The result from this experiment shown that
2% C low carbon steels that were heated using tempering method showed a reasonable
increase in both hardness and strength during water and oil quenching. Tempering of
both oil and water quench specimen resulted in a decrease in both hardness and strength
in the entire range of tempering temperatures. Effect of tempering on ductility also was
not very clear. [ 11] Table 2.2 and table 2.3 show the hardness testing result and tensile
testing result respectively.
10
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Table 2.2: Hardness testing result[ I I]
ROCKWELL(HRA)
As received
53.75
As quenched
Oil
Water
55.5
68.55
Tempering
temperature °C
150
49.35
56
250
47
49 .5
350
46.4
49
450
46.2
47.4
550
44
45.4
Table 2.3: Tensile testing result [I I]
TENSILE TESTING
o/o.Age elongatiun
UTS(N/llllll"2)
As received
853.89
Water
Oil
As quenched
Tempering
temperature
150°C
35o·c
55o·c
UTS(N/mm2)
872.75
629.91
618.48
579.02
%Age elongation
20.1
Tempering
temperature
23.7
25.7
32.2
As quenched
UTS(N/mm2)
1096.38
o/o.Age elongatio:n
23.6
150 ·c
450 ·c
550 ·c
732.83
656.44
636.51
23.6
25.5
28.4
The objectives during the Tempering process are:
i)
Relieving of internal stress.
ii) Restoration of ductility and toughness
iii) Transformation of retained austenite.
iv) Tempering treatment also lowers hardness, strength and wear resistance of the
hardened steel marginally.
11
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PROCESS ON MILD STEEL PLATE
RAHFIZAN BIN KHAIRUZZAMAN
This report is submitted In Partially Fulfillment of Requirement for the Bachelor Degree
of Mechanical Engineering (Structure and Material)
Faculty of Mechanical Engineering
Universiti Teknikal Malaysia Melaka
JUNE 2013
© Universiti Teknikal Malaysia Melaka
DECLARATION
"I hereby declare that this report entitled "AN INVETIGATION ON THE
INFLUENCE OF DOUBLE HEAT TREATMENT PROCESS ON MILD STEEL
PLATE" is the result of my own research except as cited in the reference."
Signature:
. .felr . . . . . .
Author:
Rahfizan Bin Khairuzzaman
Date:
25 June 2013
© Universiti Teknikal Malaysia Melaka
SUPERVISOR DECLARATION
"I hereby declare that I have read this thesis and in my opinion this report is
sufficient in term of scope and quality for the award of the degree of Bachelor of
Mechanical Engineering (Structure and Material)."
Signature:
Supervisor:
En. Nazri Huzaimi Bin Zakaria
Date:
25 June 2013
© Universiti Teknikal Malaysia Melaka
ACKNOWLEDGEMENT
First and foremost, I would like express my deepest thanks and appreciation to my
friends for supporting throughout the period of this finaJ year project is conducted. It is a
privilege for me to complete my finaJ year project as to fulfill my degree requirement.
I would like to convey my most heartfelt gratitude to my supervisor, En. Nazri Huzaimi
Bin Zakaria who has graciously offered his precious time, attention, experience and
guidance throughout the completion of the investigation thus far, I appreciate the
opportunities of learning from him.
Lastly, I would thank each and every individual who have either directly or indirectly
help me throughout the effort of this report be it in the form of encouragement, advice
and kind reminder. A special thanks to my beloved family members, I extend my
gratitude for their support and understanding.
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ABSTRACT
This research covered mainly the effect of double heat treatment on mild steel plate.
Three types of heat treatment are quenching, tempering and normalizing were used in
this study. The specimen that used in this study is consisted of square shape mild steel
plate with 250mm x 40 mm x 4 mm dimension. During heat treatment process, specimen
is heated up to 960°C for one hour before taken out from the furnace. Two of the
specimens then are quenched in water at room temperature. For other specimen, it will
cool at room temperature due the normalizing process. One of the specimens from
quenching process will be continued with tempering process, tempering process consist
two level of heating process and temperature will be considered. After the first stage of
the heat treatment process, three types of test will be conducted which are hardness test,
microstructure and tensile testing the specimen. After that, another specimen will
undergo the same heat treatment process for second time. The specimen also will be
tested with three types of testing and the result of single and double heat treatment will
be compared. The expected result for hardness and strength for tempering, quenching
and normalizing is the specimen becomes more increase.
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ABSTRAK
Kajian ini meliputi kesan rawatan haba dua kali terhadap plat keluli lembut. Tiga jenis
rawatan haba yang akan digunakan didalam kajian ini adalah pelindapkejutan,
pembajaan dan penormalan. Dimensi spesimen yang digunakan adalah terdiri daripada
plat keluli berbentuk segiempat dengan ukuran 250mm x 40mm x 4mm. Semasa proses
rawatan haba, spesimen dipanaskan pada suhu 960°C selama satu jam sebelum dibawa
keluar dari relau. Dua daripada spesimen akan disejukkan di dalam air pada suhu bilik.
Bagi spesimen lain, ia akan dibiarkan menyejuk pada suhu bilik untuk proses
penormalan. Salah satu daripada spesimen daripada proses pelindapkejutan akan
diteruskan dengan proses pembajaan, proses pembajaan terdiri dua tahap proses
pemanasan dan suhu akan dipertimbangkan. Selepas peringkat pertama proses rawatan
haba telah selesai, tiga jenis ujian yang akan dijalankan pada specimen adalah ujian
kekerasan, mikrostruktur dan ujian tegangan. Selepas itu, spesimen lain akan menjalani
proses rawatan haba yang sama untuk kali kedua. Spesimen tersebut juga akan diuji
dengan tiga jenis ujian dan hasil rawatan haba pertama dan kedua akan dibandingkan.
Hasil yang dijangkakan untuk kekerasan dan kekuatan untuk pelindap kejutan
pembajaan, dan menormalkan adalah spesimen menjadi lebih k1.1at.
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TABLE OF CONTENT
CHAPTER
CHAPTER 1
CHAPTER 2
TITLE
PAGE
DECLARATION
ii
ACKNOWLEDGEMENT
iii
ABSTRAK
iv
ABSTRACT
v
LIST OF TABLE
vi
LIST OF FIGURE
vii
INTRODUCTION
1.1
Heat Treatment
1.2
Objective
2
1.3
Scope
2
1.4
Problem Statement
2
LITERATURE REVIEW
2.1 Introduction
3
2.2
Carbon Steel
3
2.2.1
Low carbon steel
4
2.2.2
S275JR Steel Plate
4
2.3
2.4
The Background of Mild
Steel
Heat treatment
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5
6
2.4.1
Tempering
9
2.4.2
Normalizing
13
2.4.3
Quenching
17
2.4.3.1 Convection heat
21
transfer model for
liquid quenching
CHAPTER3
2.5
Hardness Test
22
2.6
Microstructure Analysis
25
METHODOLOGY
3.1
Introduction
26
3.2
Material preparation
29
3.3
Equipment
30
3.4
Heat treatment process
32
3.5
3.4.l
Normalizing
32
3.4.2
Quenching
33
3.4.3
Tempering
33
Study of mechanical
33
properties
3.5.1
Tensile test
34
3.5.2
Rockwell Hardness
35
3.5.3
Microstructure
37
Analysis
CHAPTER4
RESULT & DISCUSSION
4.1
Metallurgical Characteristic
of Mild Steel Plate
4.11 Mechanical
Properties
4.12 Microstructure
Analysis
4.2 Water Quench Heat
Treatment
4.2.1 Mechanical Properties
Analysis of Water Quench
sample
4.2.2 Microstructure
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39
40
41
43
43
46
Analysis of Water Quench
sample
4.3 Tempering Heat Treatment
4.3 .1 Mechanical Properties
Analysis of Tempering
sample
4.3.2 Microstructure
Analysis of Tempering
sample
4.4 Normalizing Heat
Treatment
4.4. l Mechanical Properties
Analysis of Normalizing
sample
4.4.2 Microstructure
Analysis of Normalizing
sample
CHAPTERS
47
48
50
51
51
54
CONCLUSION &
RECOMMENDATION
5.1
Conclusion
56
5.2
Recommendation
58
REFERENCES
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59
LIST OF TABLE
NUM.
TITLE
Table 2.1
Properties S275JR mild steel plate
Table 2.2
Hardness testing result
11
Table 2.3
Tensile testing result
11
Table 2.4
Proposed tempering temperature according to application
12
Table 2.5
Summary of changes tempered steel microstructure
13
Table 2.6
Approximate Soaking Period for Hardening, Annealing &
16
PAGE
4
Normalizing
Table 3.1
29
Table 4.1
Dimension of Specimen AISI I 040 low carbon steel shaped
dog bone
Hardness value of as-received mild steel plate
Table 4.2
Ultimate Tensile Strength of as-received mild steel plate
40
Table 4.3
Rockwell Hardness (HRA) for first Water Quench Heat
43
40
Treatment result
Table 4.4
Rockwell Hardness (HRA) for second Water Quench Heat
43
Treatment result
Table 4.5
Ultimate Tensile Test for Water Quench Heat Treatment result
44
Table 4.6
Rockwell Hardness (A) for first Tempering Heat Treatment
48
result
Table 4.7
Rockwell Hardness (A) for second Tempering Heat Treatment
48
result
Table 4.8
Ultimate Tensile Test for Tempering Heat Treatment result
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49
Table 4.9
Rockwell Hardness (A) for first Normalizing Heat Treatment
51
result
Table 4.10
Rockwell Hardness (A) for second Normalizing Heat
51
Treatment result
Table 4.11
Ultimate Tensile Test for Normalizing Heat Treatment result
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52
LIST OF FIGURE
NUM.
TITLE
Figure 2.1
Variation of hardness and mechanical properties with number
PAGE
8
of heat treatment cycles
Figure 2.1
Partial iron-Iron carbide phase diagram, showing typical
13
normalizing range for plain carbon steel
Figure 2.3
Comparison of time-temperature cycles for normalizing and
16
full annealing. The slower cooling of annealing results in
higher temperature transformation to ferrite and pearlite and
coarser microstructures than does normalizing.
Figure 2.4
A quench tank which is used for the uniform quenching of hot
18
steels. It may be used with water, light weight polymer, or oil
Figure 2.5
Temperature gradients and other major factors affecting the
20
quenching of the gear
Figure 2.6
Cooling rate curves for liquid quenching
21
Figure 3.1
Flow Chart of overall process
28
Figure 3.2
Specimen AlSl 1040 low carbon steel shaped dog bone
29
Figure 3.3
Furnace (Nabertherm, High Temperature Stand Alone Type
30
Furnace)
Figure 3.4
Universal Testing Machine (lnstron, 8802)
31
Figure 3.5
Axioskop 2 MAT (Carl Zeiss) equipment
32
Figure 3.6
Rockwell Hardness Test
32
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Figure 3.7
Rockwell hardness measurement showing positions to apply
37
the minor and major loads.
Figure 4.1
Specimen for Tensile Test
41
Figure 4.2
Microstructure observation before heat treatment (1 OOX)
42
Figure 4.3
Specimen after the mounting for microstructure analysis
42
Figure 4.4
Graph result of Water Quench Heat Treatment Hardness
44
Figure 4.5
Graph result of Water Quench Heat Treatment Ultimate Tensile
45
Strength
Figure 4.6
Microstructure of Mild Steel plate after treated with first
46
Water Quench Heat Treatment
Figure 4.7
Microstructure of Mild Steel plate after treated with second
46
Water Quench Heat Treatment
Figure 4.8
Graph result of Tempering Heat Treatment Hardness
48
Figure 4.9
Graph result of Tempering Heat Treatment Ultimate Tensile
49
Strength
Figure 4.10
Microstructure of Mild Steel plate after treated with first
50
Tempering Heat Treatment
Figure 4.l I
Microstructure of Mild Steel plate after treated with second
50
Tempering Heat Treatment
Figure 4.12
Graph result of Normalizing Heat Treatment Hardness
52
Figure 4.13
Graph result of Normalizing Heat Treatment Ultimate Tensile
53
Strength
Figure 4.14
Microstructure of Mild Steel plate after treated with first
54
Normalizing Heat Treatment
Figure 4.15
Microstructure of Mild Steel plate after treated with second
Normalizing Heat Treatment
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54
CHAPTER I
INTRODUCTION
1.1
HEAT TREATMENT
Heat treatment is defined as an operation or combination of operation, involving
heating and cooling of a metal, for this case involving the mild steel in its solid state
with the object of changing the characteristic of the material. For this project, the mild
steel plate will be run with double heat treatment process that is normalizing, quenching
and tempering to investigate the influence of the process to the material. The
characteristic changing can be explored through the microstructure test with applying the
microscope test that was form various characteristics as pearlite, martensite,
tempermartensite and so on. S275JR mild steel plate will we used in this research, this
steel contain the carbon percentage of 0.22%. [I]
Heat treatment is generally employed for following purpose such as to improve
mach inabilility, to change or refine grain size, to improve mechanical properties like
tensile strength and Rockwell hardness test and microstructure test to obtain various
collection data before it can be evaluated to determine the result compare with the
standard data of mild steel as a comparison. [2]
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1.2
OBJECTIVE
a. To investigate the influence of double heat treatment process on mild steel.
b. To observe the change of microstructure and strength of mild steel plate after
subjected to normalizing, tempering and quenching process.
1.3
SCOPE
The scope of this research is:
a. Analyze the strength, hardness and change of microstructure between one and
double heat treatment process on mild steel plate.
b. Specimen preparation for make double heat treatment process.
1.4
PROBLEM STATEMENT
Mild Steel is most common form of steel because its price is low, malleable and
acceptable for many applications. However, the most common problem we are
encountered by mild steel is that it has a relatively low tensile strength. Usage
properties, as well improper heat treatment processes contributes to this problem. In this
research, low carbon steel S275JR has been selected as the material for double heat
treatment process. The hardness and strength of the carbon steel can be analyzed through
Rockwell tester and ultimate tensile testing and the internal structure can be analyzed by
using microscope image analyzer. This research is also to proof that the hardness and
strength of mild steel with double heat treatment is larger compared to the single heat
treatment. [3]
2
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CHAPTER2
LITERATURE RIVEW
2.1
INTRODUCTION
The purpose of literature review is to find out all the necessary information and
unknown knowledge in the research of the effect of double heat treatment towards mild
steel plate strength, hardness and microstructure. The objective of literature review is to
use the source found out to support the research. The sources include books, journals,
articles and internet sources.
2.2
CARBON STEEL
Carbon steel is steel that contain carbon as main alloying element. lt also has up
to 1.5% carbon and other alloying elements like copper, manganese and silicon. As we
can see, nowadays most of the steel produced is plain carbon steel.
Steel with low carbon content has properties similar to iron. As the carbon content
increases the metal becomes harder and stronger but less ductile and more difficult to
weld. Higher carbon content lowers the melting point and its temperature resistance
carbon content cannot alter yield strength of material.
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2.2.1
Low carbon steel
Low carbon steel or mild steel has carbon content of 1.5% to 4.5%. Low carbon
steel is the most common type of steel as its price is relatively low while its provides
material properties that are acceptable for many applications. It is neither externally
brittle nor ductile due to its low carbon content. It has lower tensile strength and
malleable.
2.2.2
S275JR steel plate
The S275JR steel plate has reliable mechanical properties, good formability and
excellent welding performance; it' s also used widely in various industries such as
architecture, bridge construction, marine craft, railway locomotive heavy machine and
other structure parts. Table 2.1 show the properties S275JR mild steel plate.
Table 2.1: Properties S275JR mild steel plate
Source: www.steelnumber.com/en/steel_composition_eu.php?name_id=3
S275JR STEEL
Tensile Strength (1 - lOOmm thickness)
41 OMpa - 560Mpa
Minimum Yield Strength (to 16mm thickness)
275Mpa
Minimum Elongation (3 - 40mm thickness )
23%
Carbon (C)
0.22%
Manganese (Mn)
1.5%
Phosphorus (P)
0.04%
Sulfur (S)
0.04%
Minimum
Properties
4
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2.3
THE BACKGROUND OF MILD STEEL
Mild steel is least expensive of all steel and most common steel used. It is used in
most of product created from steel, mild steel is easy to weld, very hard and very
durable. Mild steel contain less than 2% carbon and it is able to be magnetized. Most of
the object today that are created of steel are made using mild steel, for example,
automobile chassis, motorcycle frame and most cookware are made using mild steel.
Due to the poor corrosion-resistance of mild steel, it must be painted or otherwise
protected and sealed in order to prevent rust from damaging it. The properties of
the steel allow the electrical current to travel through the steel without distorting the
makeup of the material.
Mild steel is one of the least expensive steels used and it' s the most common of
all metal. It is to be found in almost every product created from metal in industry. It is
relatively hard, weldable, easy annealed and very durable.Steel is an alloy of iron
containing a small but definite percentage of Carbon ranges from 0.15-1.5% (4]. Mild
Steel are those containing 0. 1-0.25% carbon, they are soft, malleable and ductile (5). It
has less than 2% carbon and it will magnetize well and being relatively inexpensive, any
project that requiring a lot of steel can used mild steel.
But when it comes to load bearing, its structural strength is not usually sufficient
to be used in structural beam and girders. Carbon is the main element in the formation of
steel causing hardness and strength to be increased with increasing content. Increase in
carbon also lowers the transformation temperature and increase Martensite (brittle
structure). Higher carbon content tends to increase the risk of hydrogen induced cracking
(H.l.C.) due to welding and reduce fracture toughness. Carbons increase strength and
decrease ductility and weld ability. It both controls the maximum attainable hardness
and contributes substantially to hardneability. Carbon has a moderate tendency to
ｳ･ｧｲ｡ｴ
ｾ Ｎ＠
(6)
5
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2.4
HEAT TREATMENT
Heat treatment is defined as a physical process which entails the controlled
heating and cooling of material, such as metal or alloys to obtain desired properties.
Heat treatment is an energy intensive process that is carried out in different furnace such
as electric and gas. Shortening heat treatment cycle 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 on furnace temperature methods. [7]
Heat treatment is an important operation in the manufacturing process of many
machine parts and tools. Only by heat treatment it is possible to impart the high
mechanical properties to steel required for the normal operation of modern machinery
and tools. Heat treatment is usually classified into four typical groups. The first group
comprises first-order or re-crystallization annealing which is employed to relieve
internal stresses, reduce the hardness and to increase the ductility of strained-hardened
metal. It is also known as stress-relieving. At first, upon an increase in the heating
temperature, the elastic distortions of the crystal lattice are eliminated (recovery). At
high temperature, new grains form and begin to grow (re-crystallization). Due to
recovery and re-crystallization, the metals are softened and regain its high ductility. It is
important to point out that the heating temperature for first order annealing is not
associated with phase transformation temperature and only depends upon the recovery or
re-crystallization temperature peculiar to each metal. The second group, second order of
full annealing, which involves phase re-crystallization, consist in heating alloys above
temperature required for phase transformation .
This is followed by sloe cooling. Full annealing substantially changes the
physical and mechanical properties and may refine a coarse-grained structure. In the
third group, hardening, alloys are heated above the phase transformation temperature
and are then rapidly cooled (quenched) to retrain at room temperature, either a phase
stable at high temperatures or various stages of decomposition or transformation of this
6
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phase. Thus, hardening cause the transformation of unstable (non-equilibrium)
structures. The fourth group, tempering, involve the re-heating of a hardened alloy
(steel) to a temperature below that required for phase transformation so as to bring it
nearer to an equilibrium state. [I]
Heat treatment is a collection through many processes such as annealing, stress
relief, quenching, tempering normalizing and ageing. All the different heat treatment
processes consists the following three stages:
1) Heating of the material
2) Holding the temperature for a time.(soaking time)
3) Cooling, usually to room temperature. (normalizing)
However, the temperature and time for the various processes is dependent on the
material mechanism controlling the water effect. For example, if the driving mechanism
is diffusion the time must long enough to allow necessary transformation reaction.
During heating and cooling, there is an existing temperature gradients between the
outside and interior portion of the material; their magnitudes depends on the size and
geometry of the workpiece. If the rate of temperature change in the surrounding in the
surrounding is too high, large temperature gradients may develop in the component. This
creates internal stresses that may lead to the plastic deformation and even to cracking.
[8]
The Korea research institute chemical technology also investigated the effect of
heat treatment on bioactivity and mechanical properties of a poly E-Caprlactore/Silica
hybrid containing calcium. It was conclude from the research that the mechanical
properties of PCL/Silica hybrid could be improved by heat treatment. It was conjectured
to be coursed by the reduction of the low molecule weight PCL phase and the
intensification of silica network by heat treatment. The mechanical properties of the
7
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specimens treated at 150°Cshowed comparable value to those of canceller' s bone and it
mean that its likely to be used for bio-active and degradable bone substitute. [9]Heat
treatment tends to relive internal stresses and remove coarseness of grain and have
significant influence on the properties of welded material. [6]
The hardness and strength properties (yield strength and ultimate tensile
strength) gradually increase up in anexperiment; the experiment is to study the effect of
cyclic heat treatment on microstructure and mechanical properties of 0.6% carbon steel.
Graphical of the result is represent in Figure 2.1 , hardness and strength properties
initially increase due to the finer microstructure (finer pearlite and ferrite) originated
from non-equilibrium forced air cooling in each heat treatment cycle. After 5 heat
treatment cycle, the graph initially increase but after that the graph marginally decrease
until the 8th cycle due to elimination of lamellar pearlite and generation of more
commentate spheroids in the microstructure. However, the steel still possesses much
higher strength than the as-received steel due to extremely fine grain size of ferrite in the
microstructurei 1O]
800
6 (-0
ｾ＠
Ill
t:=
500
-----
_.,...,---- •
7()0
--------
Ｍｾ＠
..... u..mat• lon$il•
ｾｲ･ｮｧｬｨＮ＠
ｾ＠
GI
e-400
'1..
300
200
ｾ＠
MPa
-
Y-iekl s1nng1h.
*
Hardness. HV
MPa
ＭＧｬｃＮｂＢｮｾｴｩｯ＠
---...
-
100
0
0
2
5
6
7
A
9
Number of heat treatme.nt cycles
Figure 2.1: Variation of hardness and mechanical properties
with number of heat treatment cycles [10]
8
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2.4.1
TEMPERING
Tempering is carried out after quenching to reduce the brittleness of steel. The
steel is heated to below the critical temperature, held, then cooled slowly to provide the
require properties. Tempering is carried out in oil, salt or lead bath and also in furnace
controlled by fans circulating air. The combination of quenching and tempering can
produce the best combination of strength and notch ductility. The purpose is to relive
internal stress, to reduce brittleness and to make steel tough to resist shock and fatigue.
Variable associated with tempering that affect the microstructure and the
mechanical properties of tempered steel include temperature; time at temperature;
cooling rate from the tempering temperature; and composition of the steel; including
carbon content, alloy content and residual elements. In steel, quenched to a
microstructure consisting essentially of martensite, the iron lattice is strained by the
carbon atom, producing the high hardness of quenched steels. On heating, the carbon
atom diffuses and reacts in a series of distinct steps that eventually form Fe3 Cor alloy
carbide in a ferrite matrix of gradually decreasing stress level. The properties of the
tempered steel are determined primarily by the size, shape, composition and distribution
of the carbide that form , with a relatively minor contribution from solid-solution
hardening of the ferrite. These changes in microstructure usually decrease hardness,
tensile strength and yield strength but increase ductility and toughness.
Under certain conditions, hardness may remain unaffected by tempering or may
even be increased as a result of it. For example, tempering of a hardened steel at very
low tempering temperature may cause no change in hardness but may achieve a desired
increase in yield strength. Also, those alloy steels that contain one or more of the
carbide-forming elements (chromium, molybdenum, vanadium and tungsten) and
capable of ' secondary hardening'- that is, they may become somewhat harder as a result
of tempering. The tempered hardness values for several quenched steel are presented. [I]
9
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For heat treatment and subsequent hardness and tensile testing specimen were
obtained from Yi" diameter bar of 0.20%C low carbon steel. Using muffle furnace, the
specimen is heated at 960° C for one hour for austenitizing and then quenched in cold
water and oil. After quenching process is done, hardness and tensile properties were
evaluated and then the specimens were continued with tempering heat treatment in the
temperature range of150 - 550°C. After tempering process is done, the hardness and
tensile properties were again determined. The result from this experiment shown that
2% C low carbon steels that were heated using tempering method showed a reasonable
increase in both hardness and strength during water and oil quenching. Tempering of
both oil and water quench specimen resulted in a decrease in both hardness and strength
in the entire range of tempering temperatures. Effect of tempering on ductility also was
not very clear. [ 11] Table 2.2 and table 2.3 show the hardness testing result and tensile
testing result respectively.
10
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Table 2.2: Hardness testing result[ I I]
ROCKWELL(HRA)
As received
53.75
As quenched
Oil
Water
55.5
68.55
Tempering
temperature °C
150
49.35
56
250
47
49 .5
350
46.4
49
450
46.2
47.4
550
44
45.4
Table 2.3: Tensile testing result [I I]
TENSILE TESTING
o/o.Age elongatiun
UTS(N/llllll"2)
As received
853.89
Water
Oil
As quenched
Tempering
temperature
150°C
35o·c
55o·c
UTS(N/mm2)
872.75
629.91
618.48
579.02
%Age elongation
20.1
Tempering
temperature
23.7
25.7
32.2
As quenched
UTS(N/mm2)
1096.38
o/o.Age elongatio:n
23.6
150 ·c
450 ·c
550 ·c
732.83
656.44
636.51
23.6
25.5
28.4
The objectives during the Tempering process are:
i)
Relieving of internal stress.
ii) Restoration of ductility and toughness
iii) Transformation of retained austenite.
iv) Tempering treatment also lowers hardness, strength and wear resistance of the
hardened steel marginally.
11
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