an investigation on the influence of double heat …eprints.utem.edu.my/15344/1/an investigation on...

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


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


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.


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.


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.


TABLE OF CONTENT

CHAPTER TITLE

DECLARATION

ACKNOWLEDGEMENT

ABSTRAK

ABSTRACT

LIST OF TABLE

LIST OF FIGURE

CHAPTER 1 INTRODUCTION

1.1 Heat Treatment

1.2 Objective

1.3 Scope

1.4 Problem Statement

CHAPTER 2 LITERATURE REVIEW

2.1 Introduction

2.2 Carbon Steel

2.2.1 Low carbon steel

2.2.2 S275JR Steel Plate

2.3 The Background of Mild Steel

2.4 Heat treatment


PAGE

ii

iii

iv

v

vi

vii

2

2

2

3

3

4

4

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

2.5 Hardness Test 22

2.6 Microstructure Analysis 25

CHAPTER3 METHODOLOGY

3.1 Introduction 26

3.2 Material preparation 29

3.3 Equipment 30

3.4 Heat treatment process 32

3.4.l Normalizing 32

3.4.2 Quenching 33

3.4.3 Tempering 33

3.5 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 39 of Mild Steel Plate 4.11 Mechanical 40

Properties 4.12 Microstructure 41

Analysis 4.2 Water Quench Heat 43

Treatment 4.2.1 Mechanical Properties 43 Analysis of Water Quench sample 4.2.2 Microstructure 46


Analysis of Water Quench

sample

4.3 Tempering Heat Treatment 47

4.3 .1 Mechanical Properties 48

Analysis of Tempering

sample


Analysis of Tempering

sample

4.4 Normalizing Heat 51

Treatment

4.4. l Mechanical Properties 51

Analysis of Normalizing

sample


Analysis of Normalizing

sample

CHAPTERS CONCLUSION &

RECOMMENDATION

5.1 Conclusion 56

5.2 Recommendation 58

REFERENCES 59


LIST OF TABLE

NUM. TITLE PAGE

Table 2.1 Properties S275JR mild steel plate 4

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

Normalizing

Table 3.1 Dimension of Specimen AISI I 040 low carbon steel shaped 29 dog bone

Table 4.1 Hardness value of as-received mild steel plate 40

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

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 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 52


LIST OF FIGURE

NUM. TITLE PAGE

Figure 2.1 Variation of hardness and mechanical properties with number 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


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


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


Normalizing Heat Treatment

Figure 4.15 Microstructure of Mild Steel plate after treated with second 54

Normalizing Heat Treatment


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]


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


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.


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% Minimum

Carbon (C) 0.22% Properties

Manganese (Mn) 1.5%

Phosphorus (P) 0.04%

Sulfur (S) 0.04%

4


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

segregat~ . (6)

5


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


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


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 1 O]

800

7()0

6 (-0 Ill

~ 500 t:= GI

e-400 '1..

300

200

100

0

--------

0

• _.,...,---- --------~ ..... u .. mat• lon$il• ~renglh. MPa

- Y-iekl s1nng1h.

~ MP a

* Hardness. HV -'lC.B"n~tion

-~ ---...

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


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


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


Table 2.2: Hardness testing result[ I I]

ROCKWELL(HRA)

As received 53.75

Oil Water

As quenched 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

UTS(N/llllll"2) o/o.Age elongatiun

As received 853.89

Oil Water

UTS(N/mm2) %Age elongation UTS(N/mm2) o/o.Age elongatio:n As quenched 872.75 20.1 As quenched 1096.38 23.6 Tempering Tempering temperature temperature 150°C 629.91 23.7 150 ·c 732.83 23.6 35o·c 618.48 25.7 450 ·c 656.44 25.5 55o·c 579.02 32.2 550 ·c 636.51 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


an investigation on the influence of double heat …eprints.utem.edu.my/15344/1/an investigation on...

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