A FINAL YEAR PROJECT REPORT ON EFFECT OF HEAT TREATMENT ON MECHANICAL AND CORROSION PROPERTIES OF STAINLESS STEELS

A FINAL YEAR PROJECT REPORT
ON
EFFECT OF HEAT TREATMENT ON MECHANICAL AND CORROSION
PROPERTIES OF STAINLESS STEELS
Submitted in the partial fulfillment of the
Requirements for the course of
Bachelor of Technology
In
Metallurgical and Materials Engineering
By
V. MOUNIKA (N082229)
K. PRIYANKA (N082072)
Ch. NAGARJUN (N082440)
G. ANIL KUMAR (N082422)
A.D.S. ARJUNA RAO (N082350)
Under the Guidance of
Mr. SIVA T M.Tech
Lecturer in Department of Metallurgical & Materials Engineering
Carried out at
Department of Metallurgical and Materials Engineering
Rajiv Gandhi University of Knowledge Technologies
APIIIT-NUZVID, Krishna (Dist), Andhra Pradesh.
May, 2014

RAJIV GANDHI UNIVERSITY OF KNOWLEDGE TECHNOLOGIES
(A.P. Government Act 18 of 2008)
RGUKT-NUZIVID
Nuzvid, Krishna, Andhra Pradesh – 521202.
Ph: 08656 – 235147; Telefax: 08656 – 235150
Mr. SIVA T M.Tech
Department of Metallurgical and Materials Engineering
CERTIFICATE
This is to certify that the project entitled “The Effect of Heat Treatment on Mechanical
and Corrosion Properties of Stainless steel” is a record of bonafide work carried out by
V.Mounika (N082229), K.Priyanka (N082072), Ch.Nagarjun (N082440), G.Anil
Kumar (N082422) ,A.D.S. Arjun Rao(N082350) under my guidance and supervision
for the partial fulfillment for the degree of Bachelor of Technology in Metallurgical and
Materials Engineering during the academic session August 2013 – May 2014 at RGUKT-
Nuzvid.
To the best of my knowledge, the results embodied in this dissertation work have
not been submitted to any university or institute for the award of any degree or diploma.
Mr. SIVA T M.Tech
Department of Metallurgical & Materials
Engineering

RGUKT-NUZIVID
Ph: 08656 – 235147; Telefax: 08656 – 235150
CERTIFICATE OF EXAMINATION
We, V.Mounika, ID No: N082229, K.Priyanka, ID No: N082072, Ch. Nagarjun, ID
No: N082440, G.Anil Kumar, ID No: N082422, A.D.S.Arjuna Rao, ID No:N082350
hereby declare that the project report entitled “Effect of Heat treatment on Mechanical
Properties and Corrosion behaviour of Austenitic Stainless Steels” done by us under
the guidance of Mr.T.Siva is submitted for the partial fulfillment of the requirement for
the award of the degree of Bachelor of Technology in Metallurgical and Material Science
Engineering during the academic session August 2013 – May 2014 at RGUKT – Nuzivid.
We also declare that this project is a result of our own effort and has not been
copied or imitated from any source. Citations from any websites are mentioned in the
references. The results embodied in this project report have not been submitted to any
other university or institute for the award of any degree or diploma.
Ms. Sneha Kandpal, Ms. Dilkush,
Lecturer, Lecturer,
Metallurgical & Materials Engineering, Metallurgical & Materials
Engineering,
RGUKT-IIIT, Nuzivid. RGUKT-IIIT, Nuzivid.

RGUKT-NUZIVID
Ph: 08656 – 235147; Telefax: 08656 – 235150
CERTIFICATE OF PROJECT COMPLETION
This is to certify that the project entitled “The Effect of Heat Treatment on Mechanical
and Corrosion Properties of Austenitic Stainless steel” is a record of bonafide work carried out
by V.Mounika (N082229), K.Priyanka (N082072), Ch.Nagarjun (N082440), G.Anil Kumar
(N082422), A.D.S. Arjun Rao (N082350)” of RGUKT – Nuzvid, submitted to the department
for the partial fulfillment for the degree of Bachelor of Technology in Metallurgical & Materials
Engineering during the academic session August 2013 – May 2014 at RGUKT- Nuzvid.
To the best of my knowledge, the results embodied in this dissertation work have
not been submitted to any university or institute for the award of any degree or diploma.
Head of Department
Dr. VIJAY KUMAR
Lecturer in Metallurgical&
Materials Engineering
RGUKT-NUZIVID

RGUKT-NUZIVID
Ph: 08656 – 235147; Telefax: 08656 – 235150
DECLARATION
We, “The Effect of Heat Treatment on Mechanical and Corrosion Properties
of Stainless steel” is a record of bonafide work carried out by V.Mounika (N082229),
K.Priyanka (N082072), Ch.Nagarjun (N082440), G.Anil Kumar (N082422) , A.D.S.
Arjun Rao (N082350)” hereby declare that the project report entitled “The Effect of
Heat Treatment on Mechanical and Corrosion Properties of Stainless Steel” done by
us under the guidance of Mr. SIVA T M.Tech is submitted for the partial fulfillment for the
degree of Bachelor of Technology in Metallurgical & Materials Engineering during the
academic session August 2013 – May 2014 at RGUKT- Nuzvid.
We also declare that this project is a result of our own effort and has not been
copied or imitated from any source. Citations from any websites are mentioned in the
references.
The results embodied in this project report have not been submitted to any other
university of institute for the award of any degree or diploma.
V.Mounika (N02229)
K.Priyanka (N082072)
Ch.Nagarjun (N082440)
G. Anil Kumar (N082422)
A.D.S. Arjun Rao(N082350)
Place:Nuzvid
Date:

ACKNOWLEDGEMENTS
It gives us immense pleasure to express our deep sense of gratitude to our guide Shri T.
Siva, Lecturer of MME, RGUKT APIIIT-Nuzvid for his valuable guidance, motivation,
and constant inspiration and above all his ever co-operating attitude, that enabled us to
bring this thesis up to this current form.
We would like to take this opportunity to express my profound gratitude to him not only
for academic guidance but also for his personal interest in this project and constant support
coupled with confidence boosting and motivating sessions which proved very fruitful and
were instrumental in infusing self-assurance and trust within us.
We express gratitude to Dr. VIJAY KUMAR (HoD of MME) and other faculty
members for being source of inspiration, and constant encouragement which helped us in
completing the project successfully.
We express our deep sense of gratitude to Prof. R.V.Raja Kumar, Vice-Chancellor,
RGUKT and Prof. Ibrahim Khan, Director, RGUKT-NUZVID and Dr.Vijay N
Nadakuduru, HoD, Dept. of MME, RGUKT-NUZVID for providing us the required
facilities and valuable guidance to carry out the project at RGUKT APIIIT,Nuzvid
successfully.
Finally we are grateful to all our friends whose constant encouragement served to
renew our spirit and constantly encouraged us in carrying out this work.
V. Mounika (N082229)
K. Priyanka (N082072)
CH. Nagarjun (N082440)
G. Anil Kumar (N082422)
A.D.S.Arjuna Rao (N082350)

CONTENTS
Page.
No
ABSTRACT i
LIST OF TABLES ii
LIST OF FIGURES iii
1. Introduction 1
1.1 Introduction 1
1.2 Stainless Steels 2
1.3 Classification of Stainless Steels 3
1.3.1 Austenitic Stainless Steels 3
1.3.2 Ferritic Stainless Steels 4
1.3.3 Martensitic Stainless Steels 5
1.3.4 Duplex Stainless Steels 5
1.3.5 Precipitation Hardening Stainless Steels 6
1.4 Physical Properties of Stainless Steels 7
1.5 Cr-Fe Phase Diagram 10
1.6 Applications 10
1.7 Introduction to Heat Treatment 12
1.7.1 Heat Treatment of Stainless Steel 14
1.8 Mechanical Properties and Testing 17
1.8.1 Brinell Hardness Test 18
1.8.2 Rockwell Hardness Test 18
1.9 Corrosion 19
1.9.1 Corrosion Resistance of Stainless Steel 19
1.9.1 Electrochemical Corrosion 20

2. Literature Review 22
3. at Objective and Scope of The Work 26
3.1 Aim and Scope of the Work 26
3.2 Lay out of Research Work 26
4.
4.1
Experimental Procedure
Weight loss Method
27
28
4.2 Electrochemical Method 28
5. Results and Discussions 30
5.1 Microstructure Results 30
5.1.1 Microstructure of solution treated stainless steels 30
5.1.2 Microstructure of solution treated + aged at 5500
C 31
31
5.1.4. Microstructure of solution treated + aged at 6200
C 32
5.1.5 Microstructure of solution treated stainless steels 33
5.2 Hardness Values 34
5.3 Corrosion Studies Values and Graph 35
6. Conclusions 38
7. Future work
References
39
40

I
ABSTRACT
Stainless Steel used in a wide range of applications including plane, mechanical
equipment and railways. Stainless steel is only uses in major industry but can also be used
in non-major industry such as watch manufacturing that consists of micro size of
elements. Stainless is an iron alloy containing 0.02 to 2.14% of C, Cr content greater than
12% and other alloying elements. Engineering materials, mostly steel, are heat treated
under controlled sequence of heating and cooling to alter their physical and mechanical
properties to meet desired engineering application. In this study, the effect of
solutionization heat treatment on the microstructures, some selected mechanical
properties and corrosion properties of stainless steel were studied. Solutionization is the
process of heating to 10500
c temperature and air cooled to get single phase homogeneous
austenite phase. the microstructure of the sample was examined using metallographic
microscope. The steel samples were heat treated in an electric tubular furnace at different
temperature levels and constant soaking times and then cooled in air cooling. Rockwell
and Brinell hardness values of heat treated and untreated samples were determined using
standard methods. Corrosion studies of heat treated and untreated samples were
determines by using weight loss measurement and potenitiostatic curves and corrosion
rate values are compared.
Key Words: Stainless Steel, Solutionisation Heat treatment, Microstructures, Soaking
time, Mechanical Properties, Corrosion Properties.

II
LIST OF TABLES
Table 1. Physical Properties of Stainless Steels 7
Table 2. Recommended annealing temperatures for austenitic stainlesssteels 8
Table 3. Recommended annealing temperatures for Duplex Stainless Steels 19
Table 4. Different Scales of Rockwell hardness 27
Table 5.Hardness Values at various processing temperatures 34
Table 6.Solutionised Heat Treatment of Stainless Steel Corrosion rate Values
(Weight loss Method) 35
Table 7. Solutionised Heat Treatment of Stainless Steel Corrosion rate Values 36

III
LIST OF FIGURES
Fig. 1 Percentage of stainless steel consumption by Application 2
Fig. 2 Cr-Fe Phase Diagram 10
Fig. 3 Applications of Stainless Steels 11
Fig. 4 Various Parts of Stainless steels 12
Fig. 5 Typical Heat Treatment Cycle 13
Fig. 6 Complete Project Procedure flowchart 26
Fig. 7 Optical micrograph of solution treated 10500
C 30
Fig. 8 Optical micrograph of solution treated+aged
Stainless steel at 5500
C 31
C 32
C 33
Fig. 11Optical micrograph of solution treated+aged
C 33
Fig. 12 Hardness Vs temperature 34
Fig. 13 corrosion rate Vs temperature 35
Fig 14 Potentiodynamic polarization curves of Solutionised samples
And without heat treatment samples
a) Without Heat treatment
b) Solutionized(Cond A)
c) ST+Aged 5500
C
d) ST+Aged 5800
C
e) ST+Aged 6200
C
f) ST+Age6800
C 37

1
CHAPTER: 1.Introduction
1.1 Introduction
In 1913, English metallurgist Harry Brearly, working on a project to improve rifle
barrels, accidentally discovered that adding chromium to low carbon steel gives it stain
resistance. In addition to iron, carbon, and chromium, modern stainless steel may also
contain other elements, such as nickel, niobium, molybdenum, and titanium. Nickel,
molybdenum, niobium, and chromium enhance the corrosion resistance of stainless steel.
It is the addition of a minimum of 12% chromium to the steel that makes it resist rust, or
stain 'less' than other types of steel. The chromium in the steel combines with oxygen in
the atmosphere to form a thin, invisible layer of chrome-containing oxide, called the
passive film. The sizes of chromium atoms and their oxides are similar, so they pack
neatly together on the surface of the metal, forming a stable layer only a few atoms thick.
If the metal is cut or scratched and the passive film is disrupted, more oxide will quickly
form and recover the exposed surface, protecting it from oxidative corrosion. (Iron, on the
other hand, rusts quickly because atomic iron is much smaller than its oxide, so the oxide
forms a loose rather than tightly-packed layer and flakes away. The passive film requires
oxygen to self-repair, so stainless steels have poor corrosion resistance in low-oxygen and
poor circulation environments. In seawater, chlorides from the salt will attack and destroy
the passive film more quickly than it can be repaired in a low oxygen environment. [1]
Stainless steel is an iron-containing alloy, a substance made up of two or more
chemical elements. Stainless steel is characterized by having chromium content greater
than 12 %. Generally stainless steel is an alloy that distributed into four different groups.
The group is Austenitic, Ferritic, Duplex and Martensitic. In treatment of stainless steel,
heat is used as an option to give better structure and strength of its physical properties.
Usually types of heat treatment process depend on the type of alloy and the application.
[2]

2
[3]
Fig 1: Percentage of stainless steel consumption by Application in 2009; includes all
the stainless steel grades.
1.2 Stainless Steels
The stainless steels are branch of the family of ferrous alloys designed for extremely
high levels of corrosion resistance. This effect is achieved byalloying primarily with chromium
but may also enhanced by the addition of elements such as molybdenum and nickel. Moreover,
these alloy elements may significantly alter the phase relationships in the steel and procedure
a wide spectrum of possible microstructures. The range of microstructures serves to qualify
some stainless steels for special types of service beyond their use in corrosion service. 12wt%
of chromium concentration give the stainless character to the steel. To ensure a robust material,
the higher chromium concentration and other solute such as molybdenum, nickel and nitrogen
is needed. [9]
In metallurgy, stainless steel, also known as inox steel or inox from French
"inoxydable", is a steel alloy with a minimum of 10.5% chromium content by mass.
Stainless steel does not readily corrode, rust or stain with water as ordinary steel does,
but despite the name it is not fully stain-proof, most notably under low-oxygen, high-salinity,
or poor-circulation environments. There are different grades and surface finishes of stainless
steel to suit the environment the alloy must endure. Stainless steel is used where both the
properties of steel and resistance to corrosion are required. Stainless steel differs from carbon
steel by the amount of chromium present. Unprotected carbon steel rusts readily when exposed

3
to air and moisture. This iron oxide film (the rust) is active and accelerates corrosion by forming
more iron oxide, and due to the greater volume of the iron oxide this tends to flake and fall
away. Stainless steels contain sufficient chromium to form a passive film of chromium oxide,
which prevents further surface corrosion by blocking oxygen diffusion to the steel surface and
blocks corrosion from spreading into the metal's internal structure, and due to the similar size
of the steel and oxide ions they bond very strongly and remain attached to the surface.[4]
Passivation only occurs if the proportion of chromium is high enough and oxygen is present.
1.3 Classification of Stainless Steels
Stainless steel has different group that have their own properties. There have four type
of stainless steel group which is:
1.3.1 Austenitic Stainless Steels
Austenitic Stainless Steels Having Maximum Composition in the Mainly in range of C
0.15%,Cr 16-18%,Mn 5.5-7.5,Ni 3.5-5.5 and other Elements.
Austenitic Stainless Steels Are Mainly Divided in 5 Groups
 Conventional austenitic, such as types 301, 302, 303, 304, 305, 308, 309, 310, 316,
and 317
 Stabilized compositions, primarily types 321, 347, and 348
 Low-carbon grades, such as types 304L, 316L, and 317L
 High-nitrogen grades, such as AISI types 201, 202, 304N, 316N, and the Nitronic
series of alloys
 Highly alloyed austenitic, such as 317LM, 317LX, JS700, JS777, 904L, AL-4X,
2RK65,
 Carpenter 20Cb-3, Sanicro 28, AL-6X, AL-6XN, and 254 SMO
Compare to a carbon steel, an austenitic stainless steels have high ductility, low yield
stress and relatively high ultimate tensile strength. Mixture of ferrite and cementite is transform
from austenite in cooling stage of carbon steel. With austenitic stainless steel, the high
chromium and nickel content suppress this transformation keeping the material fully austenite
on cooling. Pre-heating is required to austenitic stainless steel because of it is not easy influence
by hydrogen cracking, and except to reduce the risk of shrinkage stresses in thick sections. Post
weld heat treatment is required as this material has a high resistance to brittle fracture;
occasionally stress relief is carried out to reduce the risk of stress corrosion cracking. [23]

4
This material is good in ductility because of the face centered cubic (FCC) of austenitic
steel that provides more plane for the flow of dislocations, combined with the low level of
interstitial elements. This result conclude that this material doesn't have clear defined yield
point. Austenitic steels also have excellent toughness down to 273°C of temperature, with no
steep ductile to brittle transition. Austenitic steels have austenite as their primary phase (face
centered cubic crystal).These are alloys containing chromium and nickel (sometimes
manganese and nitrogen), structured around the Type 302 composition of iron, 18% chromium,
and 8% nickel. [5]. Austenitic steels are not hardenable by heat treatment. The most familiar
stainless steel is probably Type 304, sometimes called T304 or simply 304. Type 304 surgical
stainless steel is an austenitic steel containing 18-20% chromium and 8-10% nickel. [15]
1.3.2 Ferritic Stainless Steels
Ferritic Stainless steels having the maximum composition in the range of C 0.2%,Cr
10.5-27% ,Mn 1.0%,Si 1.5%,Ni 2.0% and other Elements.
The ferritic stainless steels may be divided into two groups:
 Conventional ferritics such as types 405, 409, 430, 434, 439, and 446
 Low-interstitial ferritics such as types 444, E-Brite, Sea-Cure, AL 29-4C, and AL 29-
4-2 [7]
Ferritic stainless steels are highly corrosion-resistant, but less durable than austenitic grades.
They contain between 10.5% and 27% chromium and very little nickel, if any, but some types
can contain lead. Most compositions include molybdenum; some, aluminium or titanium.[6]
Ferritic stainless steel contains more chromium but less carbon than the martensitic
stainless steel. This type of stainless steels cannot be hardened using heat treatment method.
This is because the material changes act towards stabilization of ferrite against austenite so that
ferrite is stable at all temperatures. They have their own physical properties which is they are
ferromagnetic material. They also have good ductility, formability and their toughness is
limited at low temperature and heavy section. Ferritic steels have ferrite (body centered cubic
crystal) as their main phase. These steels contain iron and chromium, based on the Type 430
composition of 17% chromium. Ferritic steel is less ductile than austenitic steel and is not
hardenable by heat treatment. [22]
1.3.3 Martensitic Stainless Steels
The characteristic orthorhombic martensite microstructure was first observed by
German scientist Adolf Martens around 1890. Martensitic steels are low carbon steels built

5
around the Type 410 composition of iron, 12% chromium, and 0.12% carbon Martensitic
stainless steels are not as corrosion-resistant as the other two classes but are extremely strong
and tough, as well as highly machinable, and can be hardened by heat treatment. This type of
stainless steel is typically contains of chromium and carbon that possess the martensitic crystal
structure in hardened condition. This material is a ferromagnetic steel that use for some
application such as knife or blade. It contains chromium about 14%, molybdenum about 1%,
nickel not higher than 2% and carbon on range 0.1% to 1%. This composition making its
physical properties more hardness and bit more brittle. Martensitic stainless steel are suitable
for application that related to wear and corrosion. As an example this material is use in
hydroelectric turbines. They are specified when the application also required good tensile
strength, creep and fatigue strength properties. The heat treating of martensitic stainless steel
is essentially the same as for plain-carbon or low-alloy steels, in that maximum strength and
hardness depend chiefly on carbon content. They may be tempered and hardened. Martensite
gives steel great hardness, but it also reduces its toughness and makes it brittle, so few steels
are fully hardened. [7]
1.3.4 Duplex Stainless Steels
Duplex stainless steels contain 18–29% Cr, 2.5–8.5% Ni, and 1–4% Mo, up to 2.5%
Mn, up to 2% Si, and up to 0.35% N. They possess a mixed structure of ferrite and austenite.
The volume fractions of ferrite and austenite vary between 0.3 and 0.7 in a duplex
structure. The ratio of the ferrite and austenitic determines the properties of duplex stainless
steels. The yield strength increases with increasing ferrite content .Duplex Stainless Steels are
characterized by high chromium (19–32%) and molybdenum (up to 5%) and lower nickel
contents than austenitic stainless steels. Duplex stainless steels have a mixed microstructure of
austenite and ferrite, the aim being to produce a 50/50 mix, although in commercial alloys, the
mix may be 40/60 respectively. Duplex steels have improved strength over austenitic stainless
steels. Duplex stainless steels have a mixed microstructure of austenite and ferrite, the aim
usually being to produce a 50/50 mix, although in commercial alloys the ratio may be 40/60.
Compared with type 316, the annealed duplex alloys provide improved resistance to
chloride stress-corrosion cracking. Duplex stainless steels have roughly twice the strength
compared to austenitic stainless steels and also improved resistance to localized corrosion,
particularly pitting, crevice corrosion and stress corrosion cracking. Duplex stainless steels,
such as SAF 2205, AF 22, DP 3, and Ferralium alloy 255, are alloyed with 0.15 to 0.20% N.
This minimizes alloy element segregation between the ferrite and austenite, thereby improving
the as-welded corrosion resistance compared with the type 329 alloy.

6
There are also other grades of stainless steels, such as precipitation-hardened, duplex,
and cast stainless steels. Stainless steel can be produced in a variety of finishes and textures
and can be tinted over abroad spectrum of colures. [7]
1.3.5 Precipitation Hardening Stainless Steels
Steels of this class have been developed in order to offer high mechanical resistance
and reasonable toughness, with superior corrosion resistance when compared to the martensitic
steels of the Fe–Cr–C system. PH stainless steels may be classified according their
microstructure resulting from the solution-annealing heat treatment into austenitic, semi
austenitic, and martensitic stainless steels Semi austenitic steels will transform into martensite
during subsequent heat treatments. Practically all PH steels have a low-carbon level (0.1 wt%)
with nickel additions. Molybdenum is added to increase mechanical and corrosion resistance.
PH is attained through additions of aluminium, titanium, niobium, or copper Several
precipitates lead to hardening effects, according to the alloy type and the heat treatment
procedure: nickel- and aluminium-rich intermetallic phases such as Ni3 (Al, Ti), Ni3Ti and b-
NiAl, iron-, molybdenum-, and niobium-rich Laves phases such as Fe2 (Mo,Nb), copper-rich
or even nitrides of the Cr2N type, may be formed. Compared to martensitic stainless steels of
the Fe–Cr–C system, PH steels present a superior ductility and toughness. Some alloys have
YS of up to 1700 MPa. Relative to other stainless steel types, PH steels have a moderate-to-
good corrosion resistance.
The A-286 (UNS S66286) alloy is probably the most well-known austenitic PH type.
It is an alloy containing (in wt %): Fe–15% Cr–25 % Ni–1.25% Mo–2% Ti–0.3% Al. [14]
Stainless steels are also classified by their crystalline structure:
 Austenitic, or 200 and 300 series, stainless steels have an austenitic crystalline structure,
which is a face-centered cubic crystal structure. Austenite steels make up over 70% of
total stainless steel production. They contain a maximum of 0.15% carbon, a minimum
of 16% chromium and sufficient nickel and/or manganese to retain an austenitic
structure at all temperatures from the cryogenic region to the melting point of the alloy.

7
 200 Series—austenitic chromium-nickel-manganese alloys. Type 201 is hardenable
through cold working; Type 202 is a general purpose stainless steel. Decreasing nickel
content and increasing manganese results in weak corrosion resistance.
 300 Series—the most widely used austenite steel is the 304, also known as 18/8 for its
composition of 18% chromium and 8% nickel.304 may be referred to as A2 stainless
(not to be confused with A2 grade steel, also named Tool steel, a steel). The second
most common austenite steel is the 316 grade, also called marine grade stainless, used
primarily for its increased resistance to corrosion. A typical composition of 18%
chromium and 10% nickel, commonly known as 18/10 stainless, is often used in cutlery
and high-quality cookware. 18/0 is also available.
1.4 Physical Properties of Stainless Steels
Table 1: Physical Properties of Stainless Steels
Density - 8.0g/cm3
Modulus of Elasticity - 193 Gpa
Melting Point - 14000
C Thermal Conductivity - 16.3 W/m.K
Thermal Expansion - 15.9 x106
/K Electrical Resistivity - 0.0074 x106
Ωm

8
Table 2: Properties of Stainless Steels
Reaction with Acids:-
Stainless steel is generally highly resistant to attack from acids, but this quality depends
on the kind and concentration of the acid, the surrounding temperature, and the type of steel.
Type 304 is resistant to sulphuric acid at room temperature, even in high concentrations, but
type 316 and 317 are only resistant at low concentrations. All types of stainless steel resist
attack from phosphoric acid, 316 and 317 more than 304; and Types 304L and 430 have been
successfully used with nitric acid. Hydrochloric acid will damage any kind of stainless steel,
and should be avoided.
Type Microstructure Mechanical properties Physical
properties
Austenitic Austenitic Tensile strength 490-860 MPa
Yield strength 205-575 MPa
Elongation in 50mm:30-60%
Non heat
treatable
Nonmagnetic
Ferritic Ferritic Tensile strength 415-650 MPa
Non heat
treatable
Non magnetic
Martensitic Martensitic Tensile strength 480-1000 MPa
Hardened by
heat treatments,
high strength
Duplex Austenite & Ferrite Tensile strength 680-900 MPa
Non heat
treatable
Precipitatio
n hardening
Austenite or martenistie Tensile strength 895-1100 MPa
Hardenable by
heat treatment,
very high
strength

9
Reaction with Bases:-
The 300 series of stainless steel grades is unaffected by any of the weak bases such as
ammonium hydroxide, even in high concentrations and at high temperatures. The same grades
of stainless exposed to stronger bases such as sodium hydroxide at high concentrations and
high temperatures will likely experience some etching and cracking, especially with solutions
containing chlorides.
Reaction with Organic acids:-
Types 316 and 317 are both useful for storing and handling acetic acid, especially in
solutions where it is combined with formic acid and when aeration is not present (oxygen helps
protect stainless steel under such conditions), though 317 provides the greatest level of
resistance to corrosion. Type 304 is also commonly used with formic acid though it will tend
to discolour the solution. All grades resist damage from aldehydes and amines, though in the
latter case grade 316 is preferable to 304; cellulose acetate will damage 304 unless the
temperature is kept low. Fats and fatty acids only affect grade 304 at temperatures above 150
°C (302 °F), and grade 316 above 260 °C (500 °F), while 317 is unaffected at all temperatures.
Type 316L is required for processing of urea.
Electricity and magnetism:-
Similarly to steel, stainless steel is a relatively poor conductor of electricity, with a few
percent of the electrical conductivity of copper.
Ferritic and martensitic stainless steels are magnetic. Austenitic stainless steels are non-
magnetic. [5]

10
1.5 Cr-Fe Phase Diagram
Fig 2: Cr-Fe Phase Diagram
In pure iron, the A4 (1394 °C) and A3 (912 °C) transformations take place at constant
temperatures. If an element enters into solid solution in iron forming in that way a binary alloy
each of these transformations are required by the Phase Rule to occur over a range of
temperature. Some elements, such as chromium, lower the A4 and raise the A3 transformation
temperatures, restricting the gamma loop (γ loop) in the iron carbon phase diagram. As the
binary iron-chromium shows, the presence of chromium restricts the gamma loop (Figure
1).Notice that above approximately 13 wt. % Cr, the binary Fe-Cr alloys are ferritic over the
whole temperature range. A narrow (α + γ) range that exists between approximately 12 wt. %
Cr and 13wt% Cr is nothing .The addition of carbon to the Fe-Cr binary system widens the (α
+ γ) field and extends the gamma-loop to higher chromium contents. [19]
1.6 Applications
The alloy is milled into coils, sheets, plates, bars, wire, and tubing to be used in
Cookware, cutlery, household hardware, surgical instruments, major appliances, industrial
equipment (for example, in sugar refineries) and as an automotive and aerospace structural
alloy and construction material in large buildings. Storage tanks and tankers used to transport

11
orange juice and other food are often made of stainless steel, because of its corrosion resistance.
This also influences its use in commercial kitchens and food processing plants, as it can be
steam-cleaned and sterilized and does not need paint or other surface finishes.
Fig 3. Applications of Stainless Steels
Stainless steel is used for jewellery and watches with 316L being the type commonly
used for such applications. It can be re-finished by any jeweller and will not oxidize or turn
black. Some firearms incorporate stainless steel components as an alternative to blued or
parkerized steel. Some handgun models, such as the Smith & Wesson Model 60 and the Colt
M1911 pistol, can be made entirely from stainless steel. This gives a high-luster finish similar
in appearance to nickel plating. Unlike plating, the finish is not subject to flaking, peeling,
wear-off from rubbing (as when repeatedly removed from a holster), or rust when scratched.
Some automotive manufacturers use stainless steel as decorative highlights in their vehicles.
Stainless steel is used for buildings for both practical and aesthetic reasons. Stainless
steel was in vogue during the art deco period. The most famous example of this is the upper
portion of the Chrysler Building (pictured). Some diners and fast-food restaurants use large
ornamental panels and stainless fixtures and furniture. Because of the durability of the material,
many of these buildings retain their original appearance. Type 316 stainless is used on the
exterior of both the PETRONAS Twin Towers and the Jin Mao Building, two of the world's
tallest skyscrapers.
The Parliament House of Australia in Canberra has a stainless steel flagpole weighing
over 220 tonnes (240 short tons).The aeration building in the Edmonton Composting Facility,
the size of 14 hockey rinks, is the largest stainless steel in north America.

12
Fig 4. Various Parts of Stainless Steels
1.7 Introduction to Heat Treatment
Most of the Engineering properties of metals and alloys are relates with atomic structure,
crystal structure and microstructure. Mechanical properties are structure sensitive they depend
on the size, shape and distribution of various micro constituents. Mechanical properties can be
changed by process known as heat treatment. The process consists of heating a metal or alloy
to a specific predetermined temperature, holding at this temperature for required time, and
finally cooling from this temperature. All this processes are carried in solid state. Generally
heat treatment is done for the following purpose.
 Improvement in ductility
 Relieving internal stresses
 Refinement of grain size
 Increasing hardness or tensile strength and achieving changes in chemical composition
of metal surface as in the case of case-hardening.
 Improvement in machinability
 Alteration in magnetic properties
 Modification of electrical conductivity
 Improvement in toughness and development of recrystallized structure in cold worked
metal.
Heat treatment process can be represented by graphically with temperature and time as
coordinates.A typical heat treatment cycle suitable for a precipitation hardenable alloy. In this
the alloy heated and held at predetermined high temperature. This step is solutionizing .The
alloy is heated and held at predetermined high temperature. This step is termed as solutionising.

13
The alloy is then cooled rapidly to room temperature by quenching. The quenched alloy is
heated and held at a moderately high temperature above the room temperature, followed by
slow cooling. The last step is heating to and holding at a moderately high temperature is termed
as ageing or more specifically as artificial aging.it is because some precipitation hardenable
alloys get hardened even at room temperature. Such alloys are known as natural age hardenable
alloys.
Fig5: Typical Heat Treatment Cycle
Heat treatment temperature is governed mainly by chemical composition of the alloy,
prior heat treatment, if any, and the final properties required. The steels are heated above the
austenizing temperature this temperature can be determined for carbon steels by the iron
cementite phase diagram. For carbon steels, this temperature decreases first with increasing
carbon content up to eutectoid composition and again rises with increasing carbon content.
Theoretically at this temperature, steel should be fully austenitic with the smallest grain size
with rapid heating, actual austenizing temperature is raised as compared to the theoretical value
obtained from iron-cementite phase diagram, where as in practice this temperature is lowered
on fast cooling. The austenitic formed on heating near the equilibrium temperature is
inhomogeneous in nature.in the case of alloy steels, some alloying elements or their compounds
do not dissolve or diffuse with ease. Such steels require higher heating temperatures for
homogenization of austenite. Iron carbide, in general, dissolves readily in gamma-iron as
compared to carbides of strong carbide-forming elements. [11]
1.7.1 Heat Treatment of Stainless Steels
HEAT TREATING of stainless steel serves to produce changes in physical condition,
mechanical properties, and residual stress level, and to restore maximum corrosion resistance
when that property has been adversely affected by previous fabrication or heating. [16]

14
Austenitic stainless Steels:
Annealing Of Austenitic Stainless Steels
Conventional austenitic grade like 301,302,304,316 steels cannot be hardened byheat
treatment but will harden as a result of cold working. These steels are usually purchased in an
annealed or cold-worked state. Following welding or thermal processing, a subsequent reanneal
may be required for optimum corrosion resistance, softness, and ductility. During annealing,
chromium carbides, which markedly decrease resistance to intergranular corrosion, are
dissolved.
Based on the Composition we have to choose the annealing temperature.. Time at temperature
and method of cooling depend on thickness. Light sections may be held at temperature for 3 to
5 min per 2.5 mm (0.10 in.) of thickness, followed by rapid air cooling. Thicker sections are
water quenched.
Stress reliving of Austenitic Stainless Steels
Selection of Treatment. Selection of an optimum stress-relieving treatment is difficult
because heat treatments that provide adequate stress relief can impair the corrosion resistance
of stainless steel, and heat treatments that are not harmful to corrosion resistance may not
provide adequate stress relief. To avoid specifying a heat treatment that might prove harmful,
ASME Code neither requires nor prohibits stress relief of austenitic stainless steel.
Mainly Metallurgical Properties affect the selection of temperature for the stress
reliving treatment. Those temperatures are
 Heating in the range from 480 to 815 °C (900 to 1500 °F): Chromium carbides will
precipitate in the grain boundaries of wholly austenitic unstabilized grades. In partially
ferritic cast grades, the carbides will precipitate initially in the discontinuous ferrite
pools rather than in a continuous grain-boundary network. After prolonged heating such
as is necessary for heavy sections, however, grain-boundary carbide precipitation will
occur. For cold-worked stainless, carbide precipitation may occur as low as 425 °C (800
°F); for types 309 and 310, the upper limit for carbide precipitation may be as high as
900 °C (1650 °F). In this condition, the steel is susceptible to intergranular corrosion.
By using stabilized or extra-low-carbon grades, these intergranular precipitates of
chromium carbide can be avoided.
 Heating in the range from 540 to 925 °C: The formation of hard, brittle σ phase may
result, which can decrease both corrosion resistance and ductility. During the times
necessary for stress relief, σ will not form in fully austenitic wrought, cast, or welded

15
stainless. However, if the stainless is partly ferritic, the ferrite may transform to σ during
stress relief. This is generally not a problem in wrought stainless steels because they
are fully austenitic; however, some wrought grades—particularly types 309, 309Cb,
312, and 329 may contain some ferrite. Furthermore, the composition of most austenitic
stainless welds and castings is intentionally adjusted so that ferrite is present as a
deterrent to cracking. The niobium- (columbium)-containing cast grade CF-8C
normally contains 5 to 20% ferrite, which is more likely to transform to σ than the
niobium-free ferrite in the unstabilized CF-8 grade.
 Slow cooling an unstabilized grade (other than an extra-low-carbon grade):
Through either of the above temperature ranges, slow cooling may allow sufficient time
for these detrimental effects to take place.
 Heating at 815 to 925 °C (1500 to 1700 °F):The coalescence of chromium carbide
precipitates or σ phase will occur, resulting in a form less harmful to corrosion
resistance or mechanical properties.
 Heating at 955 to 1120 °C (1750 to 2050 °F):This annealing treatment causes all grain-
boundary chromium carbide precipitates to redissolve and transforms σ back to ferrite,
as well as fully softening the steel. Long heating times (>1 h) may even dissolve some
of the ferrite present and further reduce the probability of σ reforming upon slow
cooling.
 Stress relieving to improve the notch toughness: Unlike carbon and alloy steels,
austenitic steels are not notch sensitive. Consequently, stress relieving to improve notch
toughness would be of no benefit. Notch-impact strength may actually be decreased if
the steel is stress relieved at a temperature at which chromium carbide is precipitated
or σ phase forms.
Although stabilized alloys do not require high-temperature annealing to avoid intergranular
corrosion, the stress-relieving temperature exerts an influence on the general corrosion
resistance of these alloys [7]
Ferritic Stainless Steels:
The ferritic stainless steels are not normally hardened by quenching but rather develop
minimum hardness and maximum ductility, toughness, and corrosion resistance in the annealed
and quenched condition. Therefore, the only heat treatment applied to the ferritics is annealing.

16
This treatment relieves stresses developed during welding or cold working and provides a more
homogeneous structure by dissolving transformation products formed during welding.
Duplex Stainless Steels
Duplex stainless steels consist of a mixed microstructure of austenite and ferrite. So for
this type of stainless also only annealing is suitable.
Ex: for 329 type of steels temperature range is 925-955(0
C)
Martensitic Steels
The heat treating of martensitic stainless steel is essentially the same as for plain-carbon
or low-alloy steels, in that maximum strength and hardness depend chiefly on carbon content.
The principal metallurgical difference is that the high alloy content of the stainless grades
causes the transformation to be so sluggish, and the hardenability to be so high. So Martensitic
Stainless steels can be support to Hardening, Tempering and annealing Treatments. [14]
Precipitation-Hardening Stainless Steels
In the heat treating of precipitation-hardening (PH) stainless steels, areas of primary interest
include:
 Cleaning prior to heat treatment
 Furnace atmospheres
 Time-temperature cycles
 Effect of variations in cycles
 Scale removal after heat treatment
Precipitation-Hardened Type of Steels can be respond to full annealing, austenite conditioning,
transformation cooling, and age tempering or precipitation hardening. [2]
1.8 Mechanical Properties and testing
While selecting materials for engineering purposes, properties such as impact strength,
tensile strength, and hardness indicate the suitability for selection of materials for the desired
applications. In determining the fabrication and possible practical applications, the mechanical
properties of materials, their strength, rigidity and ductility are of vital importance. The
important mechanical properties of materials are: elasticity, plasticity, strength, ductility,
hardness, brittleness, toughness, stiffness, resilience, malleability, fatigue, creep, etc. The
complete specifications of mechanical properties and composition of various materials have
been standardized by BIS.

17
The Mechanical Behavior of Metals and alloys known as the relationship between the
deformations to an applied load. These mechanical properties are determined by performing
various laboratory tests by applying the various loads like tensile, compressive loads by
constantly or fluctuating loads at various temperatures we get the various mechanical properties
like hardness, tensile strength and compressive strength of the alloys. But these temperatures
applied loads and types of loads are mainly based on the application. By conducting these tests
we come to an idea that weather the alloy is suitable to withstand at that particular application
or not. [18]
Stainless steels highly mainly used in the corrosion environments. But based on the application
we use different types of steels. Suppose if we require low corrosion resistance and high
strength use austenitic stainless steels. Like this based on the applications we use suitable
stainless steel type.
1.8.1 Hardness
It is the degree of resistance to indentation or scratching, abrasion and wear. It also the
ease with which atoms move or slip in a metal is an indication of hardness. To determine the
hardness we perform various tests like Brinell hardness test, Vickers hardness test, Rockwell
hardness test etc. Based on the requirement of the application we use this type of tests. There
are several methods of hardness testing, depending either on the direct thrust of some form of
Penetrator into the metal surface, or on the ploughing of the surface as a stylus is drawn across
it under a controlled load, or on the measurement of elastic rebound of an impacting hammer
which possessing known energy. Measurements of hardness are the easiest to make and are
widely used for industrial design and in research.
1.8.1.1 Brinell hardness Tests
Brinell hardness number is the hardness index, calculated by pressing a hardened steel
ball (indenter) into test specimen under standardizes load. Brinell, Rockwell and Vickers
hardness tests are used to determine hardness of metallic materials, to check quality level of
products, for uniformity of samples of metals, for uniformity of results of heat treatment. For
cast iron and steel alloys, a load of 500 kg is applied on 10 mm indenter for at least 30 seconds.
The loads are gradually applied by means of a hydraulic mechanism.[9]. The ball indenters are
made of either high carbon steel or tungsten carbide. After full application of load for the above
times, load is slowly removed. The indenter is taken out and the diameter of the circular

18
impression is measured by a special microscope. This measuring instrument magnifies the
image and with the calibrated grid provided in the eye piece, measurement of diameter is done
with and accuracyof 0.01mm.Byusing the below formula we can calculate the Brinell hardness
number. [13]
=
Load Applied in kg
Area of indentation in square meter
1.8.1.2 Rockwell hardness tests
The Rockwell hardness test is defined in ASTM E 18 and several other standards.
Rockwell hardness testing differs from Brinell testing in that the Rockwell hardness number is
based on the difference of indenter depth from two load applications. Initially a minor load is
applied, and a zero datum is established. A major load is then applied for a specified period of
time, causing an additional penetration depth beyond the zero datum point previously
established by the minor load. After the specified dwell time for the major load, it is removed
while still keeping the minor load applied. The resulting Rockwell number represents the
difference in depth from the zero datum position as a result of the application of the major load.
The entire procedure requires only 5 to 10 s. Here C scale is used here. [4]
Table 3: Different Scale of Rockwell
Scale symbol Indenter Major load, kg Applications of scales
B 1/16”-ball (1.6mm) 100
Brass, low and medium
carbon steels.
C Brale (diamond cone) 150
Hardened steels, hard
cast irons.
A Brale 60
Razor blades, shallow
case hardened steels,
cemented carbides.
[10]

19
1.9 Corrosion
Corrosion is the destructive attack of materials when they react with environment by
chemically or electrochemically. This stainless steel alloys are mainly meant for corrosion
resistance applications. [3]
1.9.1 Corrosion resistance of stainless steels
Stainless Steels having higher corrosion resistance compare to other ferrous alloys.
Because these alloys form passivation layer when react with the atmosphere. Chromium in the
stainless steels react with oxygen and forms thin layer this layer is called as the passivation
layer. This passive layer is strong tight because the same size of atoms of the chromium and
the iron. So tight oxide layer will form.If the metal is cut or scratched and the passive film is
disrupted, more oxide will quickly form and recover the exposed surface, protecting it from
oxidative corrosion. The passive film requires oxygen to self-repair, so stainless steels have
poor corrosion resistance in low-oxygen and poor circulation environments. [5]
High oxidation resistance in air at ambient temperature is normally achieved with
additions of a minimum of 13% (by weight) chromium, and up to 26% is used for harsh
environments. The chromium forms a passivation layer of chromium (III) oxide (Cr2O3) when
exposed to oxygen. The layer is too thin to be visible, and the metal remains lustrous and
smooth. The layer is impervious to water and air, protecting the metal beneath, and this layer
quickly reforms when the surface is scratched. This phenomenon is called passivation and is
seen in other metals, such as aluminium and titanium. Corrosion resistance can be adversely
affected if the component is used in a non-oxygenated environment, a typical example being
underwater keel bolts buried in timber. [17]
1.9.2 Electrochemical Corrosion:
Corrosion of metals and alloys in aqueous environments or other ionically conducting
liquids is almost always electrochemical in nature. It occurs when two or more electrochemical
reactions take place on a metal surface.The products of corrosion may be dissolved species or
solid corrosion products. Because electrochemical reactions are at the origin of corrosion, the
corroding metal surface is considered an electrode.
All corrosion is an electrochemical process of oxidation and reduction reactions. As corrosion
occurs, electrons are released by the metal and gained by elements (reduction) in the corroding
solution. Because there is a flow of electrons (current) in the corrosion reaction, it can be
measured and controlled electronically. [7]

20
In testing practice, a polarization cell is setup consisting of an electrolyte solution, a
reference electrode, a counter electrode(s), and the metal sample of interest connected to a
specimen holder. (The sample is called the working electrode.) The electrodes are connected
to an electronic instrument called a potentiostat. The working, reference, and counting
electrodes are placed in the electrolyte solution, generally a solution that most closely
resembles the actual application environment of the material being tested. In the solution, an
electrochemical potential (voltage) is generated between the various electrodes. The corrosion
potential (ECORR) is measured by the potentiostat as an energy difference between the working
electrode and the reference electrode. In a potentiostatic experiment, the applied potential,
Eappl, is maintained between the Reference Electrode and Working Electrode. The Working
Electrode is at virtual ground. Therefore, the sign of the potential displayed on the potentiostat
is sometimes that of the Reference Electrode to ground and opposite the potential of the
Working Electrode. [8]. Electrochemical corrosion experiments measure and/or control the
potential and current of the oxidation/reduction reactions. Several types of experiments are
possible by manipulating and measuring these two variables. Most experiments impose a
potential on the working electrode and measure the resulting current. A potentiostatic
experiment imposes a constant potential on the working electrode for a specific time period.
The measured current is plotted verses time. For potentiodynamic experiments, the applied
potential is increased with time while the current is constantly monitored. The current (or
current density) is plotted verses the potential. After the potential is scanned to a predetermined
current density or potential, the potential scan may be reversed while the current continues to
be measured. A potentiodynamic scan like this is referred to as reverse polarization or cyclic
polarization. [12]
The basic instrumentation needed for the electrochemical tests includes:
 Test or working electrode (WE)
 One or more counter electrodes (CE)
 Reference electrode (RE)
 Test cell
 Potentiostat
 Recording devices (strip chart or x-y recorders)
 Computer with software program and plotter

21
CHAPTER: 2. Literature Review
French metallurgist Pierre Berthier (1821) the corrosion resistance of iron-
chromium alloys was first recognized in 1821 by French metallurgist Pierre Berthier, who
noted their resistance against attack by some acids and suggested their use in cutlery.
Metallurgists of the 19th century were unable to produce the combination of low carbon and
high chromium found in most modern stainless steels, and the high-chromium alloys they could
produce were too brittle to be practical.
French metallurgist Pierre Berthier (1915) an announcement, as it appeared in the
1915 New York Times, of the development of stainless steel. A few corrosion-resistant iron
artifacts survive from antiquity. A famous example is the Iron Pillar of Delhi, erected by order
of Kumara Gupta I around AD 400. Unlike stainless steel, however, these artifacts owe their
durability not to chromium but to their high phosphorus content, which, together with favorable
local weather conditions, promotes the formation of a solid protective passivation layer of iron
oxides and phosphates, rather than the non-protective cracked rust layer that develops on most
ironwork.
Hans Goldschmidt (1890) in the late of Germany developed an aluminothermic
(thermite) process for producing carbon-free chromium. Between 1904 and 1911 several
researchers, particularly Leon Guillet of France, prepared alloys that would today be
considered stainless steel.Friedrich Krupp Germaniawerft built the 366-ton sailing yacht
Germania featuring a chrome-nickel steel hull in Germany in 1908.In 1911, Philip Monnartz
reported on the relationship between chromium content and corrosion resistance. On 17
October 1912, Krupp engineers Benno Strauss and Eduard Maurer patented austenitic stainless
steel as ThyssenKrupp Nirosta.
Christian Dantsizen and Frederick Becket (1919) Elwood Haynes Similar
developments were taking place contemporaneously in the United States, where Christian
Dantsizen and Frederick Becket were industrializing ferritic stainless steel, applied for a US
patent on a martensitic stainless steel alloy, which was not granted until 1919.

22
Harry Brearley (1912) Also in of the Brown-Firth research laboratory in Sheffield,
England, while seeking a corrosion-resistant alloy for gun barrels, discovered and subsequently
industrialized a martensitic stainless steel alloy. The discovery was announced two years later
in a January 1915 newspaper article in The New York Times. The metal was later marketed
under the 'Staybrite' brand by Firth Vickers in England and was used for the new entrance
canopy for the Savoy Hotel in London in 1929.Brearley applied for a US patent during 1915
only to find that Haynes had already registered a patent. Brearley and Haynes pooled their
funding and with a group of investors formed the American Stainless Steel Corporation, with
headquarters in Pittsburgh, Pennsylvania.
Great Depression (1929) before the Great Depression In the beginning stainless steel
was sold in the US under different brand names like 'Allegheny metal' and 'Nirosta steel'. Even
within the metallurgy industry the eventual name remained unsettled; in 1921one trade journal
was calling it "unstainable steel”. In 1929, before the Great Depression hit, over 25,000 tons of
stainless steel were manufactured and sold in the US.
J.L.Pandy, Inder Singh, M.N. Singh (2002) Attempts to study the effect of heat-
treated AISI 304 stainless steel in a nitrated-sulphuric acid environment. Potentiodynamic
polarization studies of heat-treated AISI 304 SS samples were carried out in 75 per cent
H2SO4 - 25 per cent HNO3 acid environment using a PARC-273 potentiostat/galvanostat.
For comparison, potentiodynamic polarization studies of untreated AISI 304 SS were also
carried out under similar conditions. Potential versus current density were plotted and the
values of Ic were calculated. The curve depicts that the value of Icorr increases with
increasing heat treatment temperature and time of exposure. Abrupt changes in Icorr were
observed in the sample heat-treated at 500°C and 600°C for 120 minutes and 60 minutes
respectively. Infers that heat treatment temperature and time of exposure to heat accelerated
the corrosion in the acid. Attributes this to precipitation of chromium carbide at the grain
boundaries.
Tarun Vabhav Pratap Sikri (2012) Sensitized austenitic microstructures confirm
greater susceptibility to localized attack based on spot tests across 304 Weld and CSS 42L
profiles. Greater amounts of nickel and chromium confirm more noble pitting potentials
based on spot tests across 304 Weld profiles and a comparison of spot tested 304 Weld and
CSS 42L samples. Comparison of bulk and spot test data of 304 Welds demonstrates the

23
utility of the developed microcell by confining electrochemical activity on the metal surface
to areas less than 1 mm2. Spot tests of FSW Al 2195 further demonstrate how the microcell
can be used to determine microstructure-property Relationships for any passive metal surface
susceptible to localized chloride attack. A reduced Scan rate will allow determination of
activation energies and reaction kinetics using Tafel Extrapolations. Adjusting test
parameters so that repassivation potentials can be reached will allow quantitative
comparisons of how charge density for hysteresis loop changes with acidity and chloride
content.
S.Mannesmann,Stott,F.H,G.C.Wood, and J.Stringer, Sedriks A.J(1996)The
chromium content in the alloy is extremely important for improving the oxidation/corrosion
resistance of the steam side of the pipe, bythe formation of a protective, adherent, slow growing
Cr2O3 (chromia) oxide layer. This oxide is slow growing and blocks the outward diffusion of
other alloy elements and the inward diffusion of gaseous impurities as transport processes
through this scale are generally slow. The outward diffusion of chromium (Cr3+
) along grain
boundaries has shown to be faster than the inward diffusion of oxygen by a factor of three and
so the chromia scale usually grows outward and can contain small amounts of iron, nickel and
manganese as seen on high chromium steels such as 310. Chromium content is important in
dictating the oxide formed, lower chromium concentrations e.g. type 304, form the spinel oxide
FeCr2O4 which can be protective to a lesser extent. The greater the chromium content in the
alloy the greater its oxidation resistance. Steels with a chromium content of over 13 wt% show
very low oxidation rates and their scales consist of Cr2O3, (Cr, Fe)2O3 or Cr rich (Cr, Fe
Mn3O4 with an outer layer of Fe2O3 . However, at temperatures exceeding 900o
C, chromia
scales can react further with oxygen to form CrO3 which is a volatile species
Mohd Fahmi, Abdullah Sani (2009) concerned on the effect of heat treatment of
stainless steel for watch manufacturing application which are annealing and water quenching.
Annealing is the process that material is exposing to the standard material temperature in a long
period of time. The purpose of the cooling process is to ensure the material get higher hardness
and to low the temperature of material for use in mechanical testing. Stainless steel needs rapid
cooling in water so that no chemical reaction get involve and affect the physical properties of
stainless steel. The temperature range that use for annealing process is 1010ºC to 1121ºC and
exposed in furnace about 1 hour and 30 minutes. This research also done to investigated the
behaviour of stainless steel after heat treatment process. The suitable mechanical testing and
analysis have been chosen. They are Charpy Impact Test, Rockwell Hardness Test and using

24
Optical Microscope to study the microstructure of stainless steel before and after heat
treatment. This project begins with literature review on subject topic and following by
laboratory work on the material with different annealing temperature and annealing time.
Statistically analysis using F-Test and T-test will be done according to the experiment
parameter on heat treatment process. Finally microstructure observation will be done to predict
the relationship with the heat treatment process.

25
CHAPTER: 3. OBJECTIVE AND SCOPE OF THE WORK
3.1 Aim and Scope of the work:
The aim of the present work is to
(i) Obtaining the effect of heat treatment on Stainless Steel at various
temperatures
(ii) Understanding the phase changes in the heat treated Stainless Steels and
(iii) Studying the corrosion behaviour of the heat treated Stainless Steels in
Hydro Chloric Acid (HCl) solution.
The main scope of the work is to study the changes in behaviour (Mechanical,
Corrosion, and Microstructure) of the Stainless Steel before and after Solutionising and aged
at various temperatures.
3.2 Layout of the research work
Fig 6: Complete Project procedure flow Chart
Observe the
M icrostructure By using
Lica M icroscope
Observe the
microstructure of Oxide
layer
Vickers Hardness Test
Brinell Hardness Test
Mechanical Testing
Electrochemical
Corrosion Studies by
using Potentiostat
Weight Loss M easurement
Corrosion Studies
Observe M icrostructure
by optical Microscopy
Sample Preparation and
polishing and etching
Aged at Various
temperatures
Solutionizing to 10500
C
Austenitic Stainless Steels

26
CHAPTER: 4. Experimental Procedure
Process steps:
Heat treatment, hardness tests, optical microscopy and corrosion studies of the stainless
steel sample were done step wise with illustrations is as follows.
Step 1: Heat treatment of the stainless steel samples at 5500
C, 5800
C, 6200
C and 6800
C were
done in muffle furnace.
Step 2: Rough polishing of the samples using belt grinder.
Step 3: Smooth polishing of the sample using emery papers.
Step 4: Obtaining the mirror image by polishing with diamond paste on a dual disc polisher.
Step 5: Etching of the samples
Step 6: Optical microscopy and image analysis of the samples.
Step 7: Brinell hardness testing of the samples.
Step 8: Potentiodynamic studies of the samples by using electrochemical system.
Heat Treatment
The six stainless steel samples are heat treated to Condition A (heated to 10500
c and air
cooling) in electrical tube furnace. Again those samples are heat treated at different
temperatures and different soaking times and air cooled. The temperatures and soaking time
are as listed in table.
Table 4: Heat Treatment
Solution treated
10500
c and air cool
below (condition A)
Temperature(0
c) Soaking time Type of cooling
550 4hr Air
580 4hr Air
620 4hr Air
680 4hr Air

27
Brinell hardness:
In the Brinell hardness test, a hard spherical indenter is pressed under a fixed
normal load onto the smooth surface of a material. When the equilibrium is reached, the load
and the indenter are withdrawn, and the diameter of the indentation formed on the surface is
measured using a microscope with a built-in millimeter scale. The Brinell hardness is expressed
as the ratio of the indenter load W to the area of the concave (i.e., contact) surface of the
spherical indentation that is assumed to support the load and is given as Brinell hardness
number (BHN).
Brinell hardness Measurements: =
( )
Where, P – Applied Load in kg, D – Diameter of indenter in mm. d – Diameter of indentation
in mm.
Rockwell Hardness: Rockwell Hardness values are taken out by using C Scale.
Metallography:
Metallography is the scientific discipline of examining and determining the
constitution and the underlying structure of (or spatial relationships between) the constituents
in metals, alloys and materials (sometimes called materialography). The most familiar tool of
metallography is the light microscope. Optical (light) characterization of the microstructures
of metals and alloys involves the identification and measurement of phases, precipitates, and
constituents, and the determination of the size and shape of the grains
Corros ion Studies:
Corrosion resistance of Austenitic Stainless Steels were studied by two techniques.
1. Weight loss method
2. Electrochemical method
4.1 Weight Loss Method
In weight loss method can calculate the corrosion rate by deducting the final weight
from the initial weight. Weight loss occur due to the keeping the sample in the 1N HCl solution
for 30mins. The results which are in the below table shown that weight loss and corrosion rate

28
is high for solution treated aged 5800
C sample followed by just solutionised sample at
10500
C.weight loss and corrosion rate is very less for solution treated aged 5200
C sample. The
results shows that we can get less weight loss and corrosion rate only at some optimum aged
temperatures. The corrosion rate was calculated by using the below formula:
( ) =
534
Where, w is the weight loss of the sample (mg), is the density (gcm-3
), A is the surface area
of the sample (in2
) and T is the time (hour).
4.2 Electrochemical Method
To investigate the effect of heat treatment on the corrosion behavior. Electrochemical
tests were conducted on the solutionised and aged samples in 1N HCl. shows a set of potential,
E vs I logarithm plots of the absolute value of the current density, Icorr, for solutinised and aged
samples.In electrochemical method by using electro chemical workstation or potentiostat we
measure the corrosion rate by potentiostat we do the potentiodynamic studies from this we get
Tafel plots which are drawn between log (E) VS log (I).from this we drawn tangents on this
graphs to known the Icorr Values from taking average of 3 Icorr Values. By using this Icorr
values.
We calculate the corrosion rate by using below formula.
( / ) =
( )
CR is given in mm/yr, icorr in µ A/cm2
K=0.00327mm g/ µ A cm yr
ρ= 7.97 density in g/cm3
EW= Equivalent Weight=25.50(for stainless steels)

29
5. RESULTS AND DISCUSSION
5.1 Microstructure results
5.1.1 Microstructure of solution treated stainless steel
In general the austenitic stainless steels are solution treated at 9500
C – 12500
C to
homogenize the microstructure and chemical composition. In addition to homogenization this
treatment removes the residual stresses and to recrystallization. Some alloys due to their low
carbon content do not need a solution treatment due to their carbide formation, but benefit from
a solution treatment to achieve maximum corrosion resistance. The austenitic stainless steels
samples in this study were solution treated at 10500
C and soaking for an hour followed by air
cooled to room temperature. The optical micrograph of solution treated sample at 10500
C
reveals that the homogenized austenite with fine grains containing some small amounts of
carbides along the grain boundaries.
Fig7. Optical micrograph of solution treated stainless steel at 10500
C at 500X

30
C
After solution treatment process a low temperature age hardening stage is employed to
achieve the required properties, as this treatment carried out at low temperatures no distortion
occurs and during the hardening process a slight decrease in size takes place.
The solution treated austenitic stainless steels were subjected to an ageing treatment
with an aim of identifying the effect of ageing temperature on microstructure of homogenized
austenitic stainless steels that would impart a best level of mechanical properties.
In order to achieve the above goal one of the homogenized austenitic stainless steel
samples in this study was aged at 5500
C and soaking for 4 hours followed by air cooled to
room temperature. And this aged treatment sample was examined in optical microscope. The
optical micrograph of this sample is presented in below Fig. The resultant optical micrograph
reveals that the formation of carbides along the grain boundaries without affecting the grain
size.
Fig 8.Optical Micrograph of solution treated + aged at 5500
C at 500X

31
C
The microstructure of austenitic stainless steel which was solution treated + aged at
5800
C and soaking for 4 hours followed by air cooling to room temperature is shown in fig. It
can be seen that the ageing treatment at 5800
C results in slightly coarsened the size of the
carbides while grain size is remains unchanged. The volume fraction of carbides also increases.
Fig 9. Optical micrograph of solution treated + aged stainless steel at 5800
C at 500X
C
6200
C results in significant change in volume fraction
and size of the carbides. It reveals that the volume fraction of carbides decreases by dissolving
the fine carbides and also it is observed that the increasing the grain size of the austenite takes
place.

32
C at 500X
C
6800
C results in optimum grain size of austenite and
it is also observed that the increasing of volume fraction of carbides with optimum size of
carbides along the grain boundaries takes place. [13]
C at 500X

33
5.2 Hardness values
The mechanical properties of stainless steels mainly depends on the microstructure and
heat treatment. Therefore the hardness values are mainly dependent on the heat treatment. Both
Hardness values Rockwell hardness and Brinell hardness values taken at various aged
temperatures are mentioned in the below table. From this values we conclude that hardness
values increasing when increasing the aging temperatures except at 6200
C because of the
dissolution of chromium. But at again increasing the temperatures re appearance of carbides
takes place so that at again when aging at 6800
C.
Table 5: Hardness Values at various processing temperatures
Processing conditions Rockwell hardness Brinell hardness
Solution treated at 10500
C 76.9 477.7
ST + aged at 5500
C 80.6 477.7
ST + aged at 5800
C 82 555.6
ST + aged at 6200
C 79.1 363.4
ST + aged at 6800
C 95.9 653.8
Fig 12: Hardness vs temperature
0
100
200
300
400
500
600
700
ST at 1050 C ST+aged at 550 C ST+Aged 580 C ST+Aged 620 C ST+Aged 680 C
Har
dness
Num
ber
Hardness Values
brinell rockwell

34
5.3 Corrosion Studies Values and Graph
Table 6: Solutionized Heat Treatment of Stainless Steel Corrosion rate Values (weight
loss Method)
Sample
Initial
weight(grms)
Final
weight(grms)
Weight loss
Corrosion
rate(mpy)
Condition A 34.9671 34.9641 0.0030 165.56
ST+ aged 5500
C 37.1328 37.1309 0.0019 99.43
ST+ aged 5800
C 37.3055 37.3020 0.0035 183.5
ST+ aged 6200
C 36.4397 36.4378 0.0019 100.69
ST+ aged 6800
C 37.3975 37.3954 0.0021 110.41
Fig: 13 corrosion rate vs temperature
The corrosion rate values from the electro chemical studies are in this below table. From this
values we observed that corrosion rate is high for solution treated and aged at 5500
C and low
for solution treated + aged 6200
c. From table it is clearly indicating that from aged temperatures
0
20
40
60
80
100
120
140
160
180
200
Solutionise At
1050 C
ST+ Aged 550 C ST+ Aged 580 C ST+ Aged 620 C ST+ Aged 680 C
Corrosion
Rat
e(m
py)
Tempratures(C)
Corrosion rate Values
weight loss method Electrochemical Corrosion

35
5500
C to 6200
C the corrosion rate values are decreasing. The results shows that at some
optimum aged temperature we got less corrosion rate values.
At Temperature 5500
C chromium carbides are formed because of this chromium
content decreases hence corrosion rate is increased where as at 6200
C all chromium carbides
are dissolved. This will give us high chromium content which will form passive layers.
By Comparing these weight loss method and electrochemical method. Both these
values are not comparable.
The corrosion rate calculations at various aged temperatures are below
Table 7: Solutionised Heat Treatment of Stainless Steel Corrosion rate
Values (potentiodynamic studies)
S.NO
Sample(0
c) icorr in A
CR=Corrosion
RateIn10-3
mm/yr
1 Without Heat treatment 1.728868 18.0880
2 Condition A 2.187732 22.8888
3 550 2.23146 23.3463
4 580 2.16380 22.6384
5 620 1.69279 17.7105
6 680 1.841740 19.2689

36
Fig 14: Potentiodynamic polarization curves of Solutionised samples and without heat
treatment samples a) Without Heat treatment b) Solutinised(Cond A) c)ST+Aged 5500
C
d)ST+Aged 5800
C e)ST+Aged 6200
C f)ST+Aged 6800
C

37
6. Conclusions
From the above results and graphs. We Can conclude that the mechanical properties and
corrosion rate values are mainly depends on the heat treatment and at solutionized
temperatures. But in order to get the optimum mechanical properties and corrosion resistance
properties have to choose the optimum temperatures.
1. The solutionized heat treatment of austenitic stainless steels shows microstructure
containing homogenized austenite with fine grains containing some small amounts of
carbides along the grain boundaries.
2. The temperature of ageing treatment affects the volume fraction, grain size of carbides
as well as grain size of austenite.
3. Ageing treatment at 6800
C gives the best microstructure with optimum grain size and
volume fraction of carbides along the grain boundaries.
4. At this temperature uniform distribution of carbides takes place and gives the maximum
Rockwell hardness value as 95.9 and maximum Brinell hardness value as 653.8.
5. In weight loss method at ageing temperatures 5500
C gives the less corrosion rate. This
temperature is optimum for corrosion rate.
6. In potentiodynamic studies at ageing temperature 6200
C gives the less corrosion rate.
This temperature is optimum for corrosion rate because at that temperature the
chromium carbides gets dissolved in the matrix so that it forms a passive layer on the
surface hence corrosion rate is decreased.

38
CHAPTER: 7. FUTURE WORK
1. Using XRD have to investigate the crystal structures of the individual phases with varying
heat treating temperatures.
2. Have to found the suitable inhibitor to stop the corrosion rate of stainless steel in the 1N
HCl Solution.

39
References
1. Beaune, France, October 13, 2010.Environmental Engineering, Georgia Institute of
Technology, Atlanta, GA, 2011.
2. A. J. Sedriks, Corrosion of stainless steels, 2nd ed. New York: Wiley, 1996.
3. e. a. Maloney, "Case Carburized Stainless Steel Alloy for High Temperature
Applications," USA Patent, 1995.
4. R. D. Moser, "High-Strength Stainless Steels for Corrosion Mitigation in
Prestressed Concrete: Development and Evaluation," Ph.D. dissertation, School of
Civil and Material Science
5. M. Genet, Orban, C., "Steel, Alloys and Stainless: Part II," in Stainless Steel
World,
6. ASM INTERNATIONAL, Electronic Materials Handbook, Volume 4
7. ASM INTERNATIONAL, Heat Treating, Volume 4
8. ZAKI AHMAD, Principles of Corrosion Engineering and Corrosion Control
9. S.L.Kakani, Amit Kakani, Material Science
10. CALLISTER (WILEY, 2007), Materials Science and Engineering an Introduction (7
Ed.)
11. Effect of Heat Treatment of Stainless Steels orthodontic wieres, Osmar Aparecido
Cuoghi, Geraldo Francisco Kasbergen,Paulo Henrique dos Santos
12. MARS G.FONTANA, Corrosion Engineering Third Edition
13. H.K.D.H Bhadeshia Steels microstructure and properties by 3rd
edition
14. Glyn Meyrick, Professor Emeritus Physical metallurgy of steel
15. Vijayendra Singh Heat treatment of steels, Heat Treatment of Steels(pg no 450-459)
16. ThomosG.Digges, Samuel J.Rosenberg, and Glenn W.GeilHeat treatment and
properties of Iron and Steel
17. ASM HAND BOOK 13A,Corrosion Fundamentals, Testing and protection
18. ASM HAND BOOK 8,Mechanical Testing And Evolution
19. American Society for Metals, Metals handbook (1948) and Vol. 1 and 2), Am. Soc.
Metals, Metals Park, Ohio.
20. Edgar C. Bain, Functions of the alloying elements in steel, Am. Soc. Metals, Metals
Park, Ohio (1939)(pg no 216-224)
21. R. M. Brick and Arthur Phillips, Structure and properties of alloys (McGraw-Hill
Book Co., Inc., NewYork, N.Y., 1949) (pg no 320-329)

40
22. Malcolm S. Burton, Applied metallurgy for engineers (McGraw-Hill Book Co., Inc.,
New York, N.Y., 1956) (pg no 354-363)
23. J. M. Camp and C. B. Francis, The making, shaping and treating of steel, 7th
edition U.S. Steel Corp., Pittsburgh

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A FINAL YEAR PROJECT REPORT ON EFFECT OF HEAT TREATMENT ON MECHANICAL AND CORROSION PROPERTIES OF STAINLESS STEELS