UNIVERSITI TEKNIKAL MALAYSIA MELAKA
EFFECT OF CHROMIUM CARBIDE (Cr23C6) FORMATION ON
MICROSTRUCTURE AND CORROSION PASSIVITY
BEHAVIOR OF AISI 304 STAINLESS STEEL
This report submitted in accordance with requirement of the Universiti Teknikal
Malaysia Melaka (UTeM) for the Bachelor Degree of Manufacturing Engineering
(Engineering Materials) with Honours.
By
SITI FAIZAH BINTI MAD ASASAARI
FACULTY OF MANUFACTURING ENGINEERING
2010
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
BORANG PENGESAHAN STATUS TESIS*
TAJUK: EFFECT OF CHROMIUM CARBIDE (Cr23C6) FORMATION ON
MICROSTRUCTURE AND CORROSION PASSIVITY BEHAVIOR OF AISI 304 STAINLESS STEEL
SESI PENGAJIAN: 2009/2010
Saya SITI F AIZAH BINTI MAD ASASAARI mengaku membenarkan tesis (PSM/Sarjana/Doktor Falsafah) ini disimpan di Perpustakaan Universiti Teknikal Malaysia Melaka (UTeM) dengan syarat-syarat kegunaan seperti berikut:
1. Tesis adalah hak milik Universiti Teknikal Malaysia Melaka . 2. Perpustakaan Universiti Teknikal Malaysia Melaka dibenarkan membuat salinan
untuk tujuan pengajian sahaja. 3. Perpustakaan dibenarkan membuat salinan tesis ini sebagai bahan pertukaran
antara institusi pengajian tinggi. 4. **Sila tandakan (-1)
D SULIT
TERHAD
TIDAK TERHAD
(Mengandungi maklumat yang berdarjah keselamatan atau kepentingan Malaysia yang termaktub di dalam AKTA RAHSIA RASMI 1972)
(Mengandungi maklumat TERHAD yang telah ditentukan oleh organisasi /badan di mana penyelidikan dijalankan)
Disa;Jleh: (SIT I FAIZAH MAD ASASAARI) (DR. MOHD WARIKH B. ABD RASHID)
Alamat Tetap: B3, Kompleks Niaga Parit Raja, 86400 Parit Raja, Batu Pahat, Johor.
Tarikh: 20 May 2010
OR. MOHO WARIKH BIN ABO. JlltASHI Cop Rasmi 7imNlan De/can (Penvelidik:fn & Pengajlan Siswa ah)
Fakultf KeJuruteraan Pembuatan Universiti Teknikal Malaysia Melaka
Tarikh:
* Tesis dimaksudkan sebagai tesis bagi ljazah Doktor Falsafah dan Sarjana secara penyelidikan, atau disertasi bagi pengajian secara kerja kursus dan penyelidikan, atau Laporan Projek Sarjana Muda (PSM) ** Jika tesis ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/organisasi berkenaan dengan menyatakan sekali sebab dan tempoh tesis ini perlu dikelaskan sebagai SULIT atau TERHAD.
DECLARATION
I hereby, declared this report entitled “Effect of Chromium Carbide (Cr23C6)
Formation on Microstructure and Corrosion Passivity Behavior of AISI 304 Stainless
Steel” is the results of my own research except as cited in references.
Signature :
Author’s Name : SITI FAIZAH BINTI MAD ASASAARI
Date : 16th
April 2010
APPROVAL
This report is submitted to the Faculty of Manufacturing Engineering of UTeM as a
partial fulfillment of the requirements for the degree of Bachelor of Manufacturing
Engineering (Engineering Materials) with Honours. The member of the supervisory
committee is as follow:
………………..………………………………
(DR. MOHD WARIKH BIN ABD. RASHID)
i
ABSTRACT
This project aimed to study the effect of chromium carbide, Cr23C6 formation on the
microstructure and corrosion resistance behavior of AISI 304 stainless steels in 3.5 %
NaCl solution. Five specimens of AISI 304, 15 mm x 15 mm x 2 mm each size with
various heating time, 5 seconds, 10 seconds, 20 seconds, 40 seconds, and 60 seconds
respectively are used. All specimens are immersed in 3.5 % NaCl solution, for cyclic
potentiodynamic polarization technique with a scan rate of 0.5 mV/s, then, the
corrosion behavior of AISI 304 was analyzed. The Cr23C6 formation on the
microstructure of AISI 304 to resist pitting corrosion is studied by exposed the
specimens to the heating time and five different pH solutions which is pH 3, pH 5,
pH 7, pH 9, and pH 12. The number of Cr23C6 formation is high at 60 s of heating
time by observing on the optical microscope. X-ray diffraction (XRD) analysis is
used to study the Cr23C6 formation that presence on the structure of AISI 304. The
increase in number and size of Cr23C6 performed in the structure of AISI 304, the
corrosion resistance of the specimens decrease. At high heating time and more acidic
solution, the pitting corrosion attack is increased. Based on the cyclic polarization
scan, it is clear that at 60 s, the value of high potential stress is 0.325 V, decreases
from 0.420 V as performed by 5 s heating time. While for the effect of pH solution,
specimen immersed in pH 3 shows the lowest potential, 0.32 V as performed by
specimen number one.
ii
ABSTRAK
Projek ini bertujuan untuk mempelajari pengaruh pembentukan kromium karbida,
Cr23C6 terhadap mikrostruktur dan perilaku rintangan pengaratan bagi keluli tahan
karat AISI 304 dalam larutan 3.5 % NaCl. Lima spesimen AISI 304 bersaiz 15 mm x
15 mm x 2 mm dipanaskan pada pelbagai masa pemanasan iaitu 5 saat, 10 saat, 20
saat, 40 saat, dan 60 saat. Kesemua spesimen telah direndam dalam larutan 3.5 %
NaCl dengan kadar imbasan sebanyak 0.5 mV/s bagi teknik kitaran potentiodinamik
polarisasi. Dengan itu, perilaku pengaratan bagi AISI 304 dianalisis. Pembentukan
Cr23C6 pada mikrostruktur AISI 304 dipelajari untuk menangani pengaratan bopeng
yang terdedah pada spesimen apabila didedahkan dengan masa pemanasan yang
berbeza dan lima larutan pH yang berbeza iaitu pH 3, pH 5, pH 7, pH 9 dan pH
12. Jumlah pembentukan Cr23C6 adalah tinggi pada masa 60 saat dengan mengamati
pembentukannya pada mikroskop optik. Analisis pembelauan X-ray (XRD)
digunakan untuk mengkaji pembentukan Cr23C6 yang hadir pada struktur AISI 304.
Peningkatan jumlah dan saiz Cr23C6 pada struktur AISI 304 menunjukkan rintangan
pengaratan semakin menurun. Pada masa pemanasan yang tinggi dan keadaan
berasid, serangan pengaratan bopeng meningkat. Berdasarkan imbasan kitaran
polarisasi, jelas menunjukkan bahawa pada masa pemanasan 60 saat, nilai potensi
stres menurun sebanyak 0.325 V dari 0.420 V iaitu ketika 5 saat masa
pemanasan. Manakala, untuk pengaruh larutan pH, spesimen yang direndam pada pH
3 menunjukkan potensi terendah iaitu 0.32 V untuk spesimen nombor satu.
iii
DEDICATION
Dedicated to my beloved family and friend
iv
ACKNOWLEDGEMENT
Alhamdulillah, thank to Allah for giving me a chance to complete this report with
successfully.
First and foremost I offer my sincerest gratitude to my supervisor, Dr. Mohd Warikh
Bin Abd Rashid, who has supported me throughout my final year project and report
writing with his patience and knowledge that he give to me in this research. Thank
you to the other lecturers, technicians, and staff that help me in fulfilling this final
year project and conducted me during the experimental process in the laboratory.
My colleagues from Bachelor Degree of Manufacturing in Engineering Materials,
Mohd Ashaari Omar, Nur Farizan Ayoob, Nikmah Abd. Muin, Nurhashima Shafiee,
Nur Rifhan Rosli, and Nurul Aina Abd Talib to help me in giving a lot of idea and
information about this research.
I would also like to say thanks to my beloved parent for supporting me and providing
a space for me in which to complete my writing up.
v
TABLE OF CONTENT
Abstract
i
Abstrak
ii
Dedication
iii
Acknowledgement
iv
Table of Content
v
List of Tables
ix
List of Figures
x
List of Abbreviations
xii
List of Symbol
xiii
1.0 INTRODUCTION
1
1.1 Background of Study
1
1.2 Problem Statement
2
1.3 Objectives
2
1.4 Scope of Study
3
2.0 LITERATURE REVIEW
4
2.1
Stainless Steel 4
2.1.1 AISI 304 Stainless Steel 5
2.1.1.1 Mechanical, Thermal and Electrical Properties of
AISI 304
5
2.1.1.2 Effect of Alloying Compositions
6
vi
2.2
Passivity 8
2.2.1 Corrosion Phenomena on Passivated Metal Surfaces 9
2.2.2 Passivity Breakdown 9
2.3
Corrosion Behavior 9
2.4
Optical Microscope 10
2.4.1 Chemical and Microstructure Analysis 10
2.5
Previous Study on Corrosion Behavior of AISI 304 11
2.6 Corrosion of Stainless Steel
14
2.6.1 Types of Corrosion 15
2.6.1.1 Pitting Corrosion 15
2.6.1.2 Intergranular Corrosion 15
2.6.1.3 Galvanic Corrosion 16
2.6.1.4 Crevice Corrosion 17
2.6.1.5 Stress Corrosion Cracking 17
2.6.1.6 Erosion Corrosion 17
2.6.1.7 Selective Leaching Corrosion 18
2.6.1.8 Uniform Corrosion 19
2.6.2 Factors Affecting Corrosion
19
2.6.2.1 Effect of Temperature
19
2.6.2.2 Effect of pH
19
2.6.3 Effect of Chloride Environments
20
2.7 Corrosion Tests
21
2.7.1 Electrochemical Methods
21
2.7.2 Corrosion Rates
24
2.7.3 Cyclic Potentiodynamic Polarization Technique 25
vii
3.0
METHODOLOGY 28
3.1
Introduction 28
3.2
Specimens Size Preparation 28
3.3
Sample Preparation 30
3.3.1 Grinding and Polishing Method 34
3.4
Corrosion Test 35
3.4.1 Electrochemical Test 36
3.4.1.1 Conducting the Electrochemical Test Experiment
37
3.4.1.2 Sample and Solution Preparation 37
3.4.1.3 Experimental Analysis of Electrochemical Test 38
4.0
RESULTS AND DISCUSSION 39
4.1
Introduction 39
4.2 Electrochemical Results
39
4.2.1 Effect of Temperature on Corrosion Behavior of AISI 304
40
4.2.2 Effect of pH Solution on Corrosion Behavior of AISI 304
44
4.3
Characterization of Corrosion Attack 46
4.4 Microstructural Analysis
49
4.5
X-ray Diffraction Analysis 50
4.6 Hardness of Tested Specimen
53
5.0 CONCLUSION AND RECOMMENDATION
55
5.1 Conclusion and Finding
55
5.2
Recommendation 56
viii
REFERENCES
57
APPENDICES
A Gantt Chart PSM 1
B Gantt Chart PSM 2
C Cyclic Polarization Scan for Temperature Effect
D Cyclic Polarization Scan for pH Effect
ix
LIST OF TABLES
Table 2.1 Chemical composition of stainless steels 5
Table 2.2 Mechanical properties of AISI 304 6
Table 2.3 Chemical composition (in weight percent) of AISI 304 SS 6
Table 3.1 Summary of sample preparation for temperature and pH effect 31
Table 3.2 Preparation Method (ASTM E3) 33
Table 3.3 Sample Preparation of pH Effect at specific aqueous solution and
condition
38
Table 3.4 Temperature Effect on Aqueous Solution 38
Table 4.1 The electrochemical parameters where Ecorr, icorr, and Epit collected
in the cyclic potentiodynamic polarization curves
43
Table 4.2 Vickers Hardness value for AISI 304 after exposed to the heat 53
x
LIST OF FIGURES
Figure 2.1 Anodic polarization and overvoltage curve in H2SO4 8
Figure 2.2 (A) and (B) shows the backscattered SEM images of AISI 304
stainless steel before electrochemical test
(C) and (D) shows the backscattered SEM images of AISI 304
stainless steel after electrochemical test
11
Figure 2.3 SEM analysis of pit formed around MnS inclusions of AISI 304
specimen after electrochemical polarization test
12
Figure 2.4 SEM analysis of a pit formed in stainless steel after polarized
close to Epit
13
Figure 2.5 Typical corrosion morphology of as-received samples 14
Figure 2.6 Effect of pH on the corrosion rate 20
Figure 2.7 Potentiodynamic polarization behavior of the three alloys in
deaerated 0.5 M NaCl solution at 80°C using scan rate 0.5 mV/s
21
Figure 2.8 Wiring diagram for potentiostatic experiments 22
Figure 2.9 Overvoltage curves and corresponding polarization curves 23
Figure 2.10 Polarization curves in non carbonated saturated Ca(OH)2
solutions with 0.5 % NaCl of AISI 304 stainless steel before and
after welding as respect to heating exposure
26
Figure 2.11 Cyclic Polarization Curves for AISI 304 after expose in 3.5 %
NaCl solution
27
Figure 3.1 Flowchart of research study on AISI 304 29
Figure 3.2 Illustration of AISI 304 specimens’ size in 3D view 30
Figure 3.3 (a) Side view of AISI 304 specimen
(b) and (c) Actual length and width of AISI 304 specimen which
indicate (15 mm x 15 mm) respectively
30
xi
Figure 3.4 (a) The grinding machine used in the laboratory testing
(b) The sand paper grit used in this practice expressed in the
ANSI system units
33
Figure 3.5 Grinding process performed on the rotating wheels 34
Figure 3.6 Polishing process with diamond powder 35
Figure 3.7 Process Flow of Corrosion Test 36
Figure 3.8 Electrochemical Polarization Test Setup 36
Figure 3.9 Instrumentation setup 37
Figure 4.1 Corrosion attack of AISI 304 stainless steel at various heating
temperatures
41
Figure 4.2 Analysis of high potential stress for AISI 304 specimens 42
Figure 4.3 Polarization scan of AISI 304 in various pH solutions 46
Figure 4.4 Effect of pH on the potential value of AISI 304 47
Figure 4.5 Microstructure of AISI 304 appears on optical microscope
(a) As-received specimen after exposed to oxalic acid
(b) 20 seconds after exposed to heat of oxy acetylene
48
Figure 4.6 Microstructure of AISI 304 after exposed to heat for 60 seconds 48
Figure 4.7 Microstructure of welded AISI 304 stainless steel
(a) Heat affected zone
(b) Weld Metal as refer to exposed area
50
Figure 4.8 Identification of Cr23C6 presence in the structure of AISI 52
Figure 4.9 The Vickers Hardness value for six specimens of AISI 304 53
xii
LIST OF ABBREVIATIONS
AISI - American Iron and Steel Institute
ANSI - American National and Standard Institute
ASTM - American Society for Testing and Materials
SAE - Society for Automotive Engineers
UNS - Unified Numbering System
SEM - Scanning Electron Microscopy
OM - Optical Microscope
EDS - Energy Dispersive X-Ray Spectroscopy
XRD - X-ray Diffraction
EBDS - Electron Backscatter Diffraction
DC - Direct Current
CR - Corrosion Rate
xiii
LIST OF SYMBOLS
Ecorr - corrosion potential
Epit - pitting potential
Erep - repassivation potential
iapp - applied current density
icorr - current density
βa - anodic Tafel slope
βc - cathodic Tafel slope
iox - oxidation current density
Iox - oxidation current
F - Faraday’s constant (96,487 C/gram)
n - number of electrons
A - surface area
I - circuit current
t - time in Coulombs (C)
d - metal or alloy density
ni - number of electron of component ith
element of alloy
fi - mass fraction of component ith
of alloy
Mi - atomic weight of element ith
of alloy
EW - equivalent weight
pH - - log a (H+)
HCl - hydrochloric acid
H2SO4 - sulfuric acid
NaCl - sodium chloride
SiC - silicon carbide
S1 - specimen one
C - capacitance
V - voltage
T - temperature (oC)
M - molar
wt % - weight percent
1
CHAPTER 1
INTRODUCTION
1.1 Background of Study
Stainless steels are an important class of alloys. Their importance is revealed in a
wide range of applications that rely on their use. From low end applications, like
cooking utensils and furniture, to very sophisticated ones, such as space vehicles (Lo,
K.H., et al., 2009), the use of stainless steels is crucible. Stainless steels are used for
consumer products, machinery, architectural and military applications, and for
equipment in the petroleum, chemical, aerospace, power, and process industries. In
fact, the omnipresence of stainless steels in our daily life makes it impossible to
specify their applications. In order to impart stainlessness to steels, chromium (Cr)
must be added to at least about 11 wt% (Lo, K.H., et al., 2009). At this Cr level, an
adherent, self-healing chromium oxide can form on the steel surface in relatively
benign environments. Stainless steel type 304 containing 18 % chromium, 8 % nickel
and also known by the UNS Number S30400 (Schweitzer, P.H., 2007), they do in
fact suffer from certain types of corrosion. Corrosion can cause a variety of
problems, depending on the applications (Steinberg, A.M., 2008). Corrosion is an
expensive process which leads to enormous damage for modern industrial societies.
The serious consequences of the corrosion process have become a problem of
worldwide significance where due to this problem, more cost had been use for
research and development of corrosion engineering as to control corrosion on the
material. Hence, this study will introduce the fundamentals and the electrochemical
basis of the corrosion of metals in an aqueous environment and the corrosion
passivity behavior on AISI 304.
2
1.2 Problem Statement
A lot of stainless steel components are used at elevated temperatures. Upon high-
temperature exposure, a numerous of phases may precipitate in the various classes of
stainless steels especially AISI 304. Some of these phases, like the Cr23C6, may be
common to all classes, but some of them are not. High corrosion resistance of AISI
304 is primarily attributed to the passive oxide film formed on its surface that
exposed to an aqueous solution and chromium oxide enrichment at the metal film
interface (Marcus, P., 2002). Formation of grain boundary carbides, with an attendant
decrease in Cr content in their regions, degrades corrosion resistance and is known to
be the main culprit for causing sensitization. Susceptibility of the heat applied on
stainless steels to intergranular corrosion has been known for a long time (Kokawa,
H. and Kuwana, T., 1992), and is principally caused by the diffusion of carbon in the
steel to the grain boundaries in the sensitized region. The interrelationship between
Cr23C6 and grain boundary irregularity has been studied in detail in several recent
works. Hong and Nam (2002) have discovered that grain boundary irregularity
occurs before Cr23C6 precipitation and exerts a dramatic effect on its formation in
austenitic stainless steels. Based on the previous research, the presents of Cr23C6 in
the microstructure of AISI 304 have been affecting the corrosion behavior of this
material, which by means, the number of Cr23C6 present will tend to localize
corrosion. This occurs at a short distance from the base metal. Chromium carbide
precipitates form at the boundaries with the result that regions adjacent to the grain
boundaries are depleted of the chromium necessary for passivity. However, the
resistance of this passive film is determined by the environmental effects which
exposed to the stainless steel. In this study, AISI 304 will be exposed to heat of oxy
acetylene at various times and the corrosion resistance of AISI 304 is analyzed as to
study the effect of temperature by using electrochemical test. It becomes clear that
the best methods to study susceptibilities to this form of corrosion are the
electrochemical techniques.
3
1.3 Objectives
(1) To study the effect of chromium carbide (Cr23C6) formation at the grain
boundaries of AISI 304 stainless steel.
(2) To study the corrosion behavior of AISI 304 from electrochemical technique
due to the temperature effect and pH effect.
1.4 Scope of Study
The scope of this project is to study the corrosion passivity behavior of AISI 304
towards electrochemical technique in an aqueous environment. The purpose of
electrochemical technique is to investigate corrosion properties of AISI 304 due to
the temperature effect and pH effect. Five samples of various pH values are exposed
to 3.5 % NaCl solution to study the corrosion behavior of AISI 304 in an acidic,
neutral, and alkali solution. The as-received specimens of AISI 304 is exposed to
heat of oxyacetylene gas welding and another five specimens ranging from 5
seconds, 10 seconds, 20 seconds, 40 seconds, and 60 seconds also exposed to the
same heat of oxyacetylene gas welding to investigate the effect of temperature on
microstructure and corrosion properties of this materials. The study will focused on
the microstructure of AISI 304 such the present of Cr23C6 formation by using optical
microscope (OM) and X-ray diffraction analysis (XRD) is used to determine the peak
corresponding to the presence of Cr23C6.
4
CHAPTER 2
LITERATURE REVIEW
This section will reviewed the study of AISI 304 stainless steel properties and the
application of electrochemical technique to corrosion research. This literature survey
provides information related to corrosion phenomena on passivated metal surfaces
and its finding on AISI 304 stainless steel corrosion behavior.
2.1 Stainless Steels
The main reason for existence of the stainless steels is their resistance to corrosion.
Chromium (Cr) is the main alloying element, and the steel should contain at least 11
percent (Fontana, M.G., 1987). Cr is a reactive element, but it passivates and exhibit
excellent resistance to many environments. Stainless steels are characterized by their
corrosion resistance, high strength and ductility referred to mechanical properties,
and high Cr content. They are called stainless because in the presence of oxygen,
they develop a thin, hard, adherent film of chromium oxide that protects the metal
from passivation corrosion. Stainless steels generally are divided into five types
decomposed of austenitic stainless steel, ferritic stainless steel, martensitic stainless
steel, precipitation-hardening, and duplex structure (Kalpakjian, S., 2006). Table 2.1
lists the compositions of stainless steels. The American Iron and Steel Institute
(AISI) type numbers shown designate wrought compositions. A recent study by the
Society for Automotive Engineers (SAE) and the American Society for Testing
Materials (ASTM) resulted in the Unified Numbering System (UNS). UNS numbers
are also listed in the Table 2.1 where the letter S identifies stainless steels.
5
Table 2.1: Chemical compositions of stainless steels (Fontana, M.G., 1987)
AISI
Type
UNS
Number
Carbon Content
(%)
Chromium
Content (%)
304 S 30400 0.08 maximum 18 - 20
316 S 31600 0.10 maximum 16 - 18
2.1.1 AISI 304 Stainless Steel
The most common stainless steel used in industries is AISI 304 stainless steel. Type
304 stainless steel is a T 300 series stainless steel austenitic. AISI 304 stainless steel
is the most common austenitic grades, containing approximately 18 percent
chromium and eight percent nickel. It is used for chemical processing equipment, for
food, dairy, and beverage industries, for heat exchangers, and for the milder
chemicals. It has high corrosion or oxidation resistance due to the chromium content,
it has a deep drawing quality, excellent toughness, low temperature properties
responding well to hardening by cold working and it is easy to clean, fabrication and
has a beauty appearance.
2.1.1.1 Mechanical, Thermal and Electrical Properties of AISI 304
Table 2.2 lists mechanical properties of AISI 304. The high strength materials exhibit
good strength. High hardness is desirable for wear and some applications where
resistance to corrosion is required. The austenitic steels retain good ductility and
impact resistance at very low temperatures. Stainless steel, an alloy of Cr, nickel (Ni)
and iron (Fe), requires at least 12 % Cr for passivity. If stainless steel is heated to a
high temperature such as 425 degree celcius (oC), chromium carbide precipitates will
start to form along grain boundaries, leaving a zone depleted of Cr. The precipitates
will dissolve back into the grain structure when heated above 850 oC and fast cooled
to room temperature.
6
Table 2.2: Mechanical properties of AISI 304 (Fontana, M.G., 1987)
2.1.1.2 Effect of Alloying Compositions
Table 2.3 shows the chemical composition of AISI 304 which decomposed of
chromium, manganese, silicon, carbon, and nickel. The element that can influence
the corrosion behavior and properties of AISI 304 is discussed.
Table 2.3: Chemical composition of AISI 304 stainless steels (Schweitzer, P.A., 2006)
Element Carbon Manganese Silicon Chromium Nickel
Weight
%
0.08
maximum
2.00
maximum
1.00
maximum 18 - 20 8 - 10
Chromium
Chromium is commonly added to steel to increase corrosion resistance and oxidation
resistance or to improve high temperature strength. It is added for wear resistance
and most importantly for corrosion resistance of AISI 304. Chromium has a tendency
to increase hardness penetration. When five percent chromium or more is used in
conjunction with manganese, the critical quenching speed is reduced to the point that
the steel becomes air hardening. Chromium can also increase the toughness of steel,
as well as the wear resistance.
Material Condition
Tensile
strength,
lb/in.2
Yield point,
lb/in.2
0.2 % offset
Elongation,
% in 2 in.
Hardness
Rockwell Brinell
Type 304
Annealed 85,000 35,000 55 B80 150
7
Nickel
Nickel is used as alloying compositions in AISI 304 to improve low-temperature
toughness and to increase hardenability. It appears to reduce the sensitivity of a
stainless steel to variations in heat treatment and to distortion and cracking during
quenching. Nickel is particularly effective when used in combination with chromium
and molybdenum in producing AISI 304 that has high strength, toughness and
hardenability.
Manganese
Manganese always present in steels to reduce the negative effects of impurities
carried out forward from the production process for example sulfur embrittlement
(Schweitzer, P.A., 2006). Manganese combines with sulfur to form manganese
sulfides stringers. It considered having a detrimental effect on the general corrosion
resistance of stainless steels. Manganese also used in stainless steels in order to
improve hot ductility and increase the solubility of nitrogen and is used to obtain
high nitrogen contents in austenitic stainless steels.
Carbon
Carbon is the most important single alloying element in steel. Toughness and
ductility are reduced by increases in carbon content. The hardness of AISI 304
stainless steel is increased by raising the carbon content of stainless steel.
