Effect Of Solution Annealing On Microstructure, Corrosion And Mechanical Property Of Sensitized AISI 316.
ABSTRACT
AISI 316 is stainless steels that commonly used in industries. AISI 316 is the most
favored construction material of various components required in chemical,
petrochemical and nuclear industries. It is important to study the corrosion properties
of AISI 316 due to the mechanical properties, microstructure and corrosion attack.
Two types of corrosion attack that commonly found on AISI 316 stainless steels are
intergranular corrosion and pitting corrosion. Intergranular corrosion is occurring
when AISI 316 is sensitized to the heat at temperature 500ºC to 800°C leads to the
grain boundary precipitation of chromium rich carbides (Fe,Cr)23C6 and the
formation of chromium depletion regions (Uhlig, H. H. 2008). The process of
solution annealing followed by rapid quenching can cure the intergranular corrosion
in AISI 316. Pitting corrosion occurs due to the attack of the corrosive environment
to the heterogeneous material composition on the surface of the AISI 316 where at
the surface region, black spot that contain high iron will ease attack by localize
corrosion and form pitting. The formation of respective corrosion is studied by using
electrochemical analysis and the oxalic etch test for classification of etch structures
in determining the suitability of intergranular corrosion. Potentiodynamic Cyclic
Polarization as described in ASTM standard G 61 is applied in order to analyze the
formation of pitting and the behavior of AISI 316 in resisting corrosion. In this study,
intergranular corrosion is investigated by exposing AISI 316 at sensitized
temperature. Based on the experiment, it shows that after AISI 316 exposed to
sensitized temperature, AISI 316 is susceptible to intergranular corrosion attacked.
Solution annealing had been used in order to improve corrosion behavior of AISI 316
for resisting intergranular corrosion. The corrosion product that had been propagates
on surface of AISI 316 was analyzed by Optical Microscope (OM). X-Ray
Diffraction (XRD) Analysis applied to analyze the phase of chromium carbide form
in the structure of AISI 316. This formation had been analyzed that this phases cause
i
susceptibility to intergranular corrosion in AISI 316. Moreover, the effect of solution
annealing and sensitizing of AISI 316 on hardness is evaluated by microhardness
test. Five indentations were taken from each sample to obtain a representative
average. In corrosion studies, when AISI 316 is exposed in 3.5% NaCl solution,
based on hysteresis loop analysis, the corrosion resistance of AISI 316 on the
sensitized is decreased due to the Cr23C6 form.
In morphologies studies, after
solution annealing and quenching by cold water in order to homogenized all austenite
(γ) phase. Further investigation, X-ray diffraction (XRD) analysis is applied to
support the existence Cr23C6 on the sensitized and heat treated sample. Theoretically,
solution annealing process is done to dissolve Cr23C6 as to form homogeneity of alloy
in a sample, leaving on desired phase which in this case involve that austenite.
However, Cr23C6 still present this is due to the time of growth for Cr23C6 has
exceeded the C-shape curve. Furthermore, the present work attempts to provide a
further understanding of the effects of solution annealing of sensitized AISI 316 on
microstructure, corrosion and hardness.
ii
ABSTRAK
AISI 316 adalah keluli tahan karat yang paling biasa digunakan di industri. Keluli
tahan karat jenis AISI 316 adalah dari siri kumpulan T 300 baja keluli. AISI 316
merupakan bahan pembinaan yang paling banyak digunakan dari berbagai-bagai
komponen yang diperlukan dalam indusri kimia, petrokimia dan nuklear. Adalah
penting untuk mempelajari sifat kakisan AISI 316 kerana sifat mekanik,
mikrostruktur dan serangan kakisan. Dua jenis serangan kakisan yang biasa ditemui
pada AISI 316 adalah kakisan intergranular dan kakisan bopeng. Kakisan
intergranular terjadi ketika AISI 316 terdedah panas pada suhu 500ºC hingga 800°C
dan menyebabkan batas butir kaya kromium karbida (Fe,Cr)23C6 dan pembentukan
daerah pengurangan kromium (Uhlig, H. H. 2008). Proses larutan anil diikuti
penyepuh lindapan cepat menggunakan air dapat merawat kakisan intergranular pada
AISI 316. Sementara itu, kakisan bopeng terjadi kerana serangan dari lingkungan
kakisan terhadap komposisi bahan heterogen pada permukaan AISI 316 di mana
permukaan, tompok hitam yang mengandungi kromium (Cr) yang tinggi akan
memudahkan pelokalan serangan kakisan bopeng dan berlaku pada kawasan
setempat. Pembentukan kakisan masing-masing dipelajari dengan menggunakan
analisis elektrokimia, manakala ujian calar oxalic untuk untuk mengklasifikasi
struktur calar dalam menentukan kesesuaiannya dengan kakisan intergranular.
Potensiodinamik Putaran Polarisasi seperti yang dinyatakan dalam standard ASTM G
61 digunakan untuk menganalisis pembentukan kakisan bopeng dan perilaku AISI
316 dalam melawan kakisan. Sementara ASTM A 262-01 amalan A, pemendakan
terhadap serangan kakisan batas butir pada AISI 316 digunakan. Jenis-jenis kakisan
yang telah tersebar pada permukaan AISI 316 dianalisis dengan Mikroskop Optik. XRay Diffraction (XRD). Analisis ini digunakan untuk menganalisa tahap bentuk
pemendakan kromium karbida (Cr23C6) dalam struktur AISI 316. Formasi ini telah
dianalisis bahawa fasa ini menyebabkan pemendakan terhadap kakisan antara butir
iii
AISI 316. Selain itu, Penyepuhlindapan dan pemekaan AISI 316 pada kekerasan
diukur dengan ujian mikrokekerasan. Ujian mikrokekerasan digunakan untuk
menentukan peringkat pembentukan kristal dan memberikan anggaran bahan
ketahanan terhadap deformasi AISI 316. Sebanyak 5 lekukan diambil dari sampel
untuk mendapatkan purata. Dalam kajian ini, ketika AISI 316 direndam dalam 3.5%
larutan NaCl, berdasarkan analisis histeresis loop, rintangan karat AISI 316 pada
peka adalah kerana bentuk Cr23C6 menurun. Dalam kajian morfologi, selepas
penyelesaian pemanasan dan pendinginan segera dengan air sejuk untuk
menyamakan struktur aloi pada fasa austenit (γ). Penyelidikan lebih lanjut dengan Xray pembelauan (XRD) analisis untuk menyokong kewujudan Cr23C6 pada sampel
diperlakukan peka dan panas. Secara teori, penyelesaian proses anil dilakukan untuk
melarutkan Cr23C6 untuk membentuk homogenitas gabungan dalam sampel,
berangkat pada peringkat dikehendaki yang dalam hal ini melibatkan austenit itu.
Namun, Cr23C6 masih ada ini kerana apabila pertumbuhan Cr23C6 telah melebihi
garisan lengkung C. Selain itu, kajian ini untuk memberikan pemahaman lebih lanjut
tentang pengaruh larutan anil yang terdedah pada suhu pemekaan AISI 316 terhadap
mikrostruktur, kakisan dan sifat kekerasan.
iv
DEDICATION
Dedicated to my beloved family and friends
v
ACKNOWLEDGEMENT
Alhamdulillah, thank to ALLAH for HIS blessing, provide me a good health and
thinking during progress this project.
Special thanks to my supervisor Dr. Zulkifli Bin. Rosli, because of his commitment
and supported throughout my final year project and report writing with his patience
and knowledge that he give to me in this research.
I would also like to thanks to the Faculty of Manufacturing labs technicians, Mr.
Azhar, Mr. Farihan, Mr. Hisham and Madam Nurhafizah who encourage me in
laboratory during my PSM project.
Finally, I thank my parent for supporting me throughout all my studies at University.
Thank for being a wonderful parent of mine and thank for providing a space for me
in which to complete my writing up.
I hope, through their guidance will completing my Final Project in my final year
study. These experiences are also made me be more matured than before and
increasing my self-confident.
Thanks to everyone.
vi
TABLE OF CONTENT
Abstract
i
Abstrak
ii
Dedication
v
Acknowledgement
vi
Table of Content
vii
List of Tables
xi
List of Figures
xii
List of Abbreviation
xv
List of Symbol
xvi
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
1.5
Report Organization
3
2.0
LITERATURE REVIEW
6
2.1
Stainless Steel
6
2.1.1
Stainless Steels Classification
7
2.1.1.1
7
2.1.2
Type AISI 316
Effect of Alloying Elements on the Corrosion Behavior of
8
Stainless Steels
2.1.2.1
Chromium (Cr)
vii
9
2.2
2.3
2.4
2.1.2.2
Nickel (Ni)
9
2.1.2.3
Molybdenum (Mo)
9
2.1.2.4
Manganese (Mn)
10
Scanning Electron Microscope
10
2.2.1
11
Chemical and Microstructure Analysis
Corrosion Resistance of Stainless Steels
13
2.3.1
General Corrosion
13
2.3.2
Intergranular Corrosion
14
2.3.3
Pitting Corrosion
15
2.3.4
Stress Corrosion Cracking
15
Corrosion Tests
16
2.4.1
Electrochemical Analysis
16
2.4.2
Cyclic Potentiodynamic Polarization Methods
18
2.5
Previous Studies on the Microstructure of Steel
20
2.6
Microstructure Analysis
21
2.6.1
25
Microstructure of Wrought Stainless Steels
2.7
Hardness Test
27
3.0
METHODOLOGY
28
3.1
Introduction
28
3.2
Raw Material
28
3.3
Sample Size preparation
28
3.3.1
Sample Preparation
30
3.3.2
Metallographic Specimens Preparations
31
viii
3.3.3
Grinding and Polishing Procedure
32
3.4
Morphology Analysis
34
3.5
Corrosion Test
35
3.5.1
35
Electrochemical Test
3.6
Hardness Testing
36
3.7
X-Ray Diffraction (XRD) Analysis
36
4.0
RESULTS AND DISCUSSION
37
4.1
Introduction
37
4.2
Effect of solution annealing of sensitized AISI 316 stainless steels on
37
microstructure
4.2.1
4.3
X-Ray Diffraction (XRD) Analysis and Interpretation
42
4.2.1.1
43
X-Ray Diffraction Pattern for Chromium Carbide
(Cr23C6)
Effect of solution annealing of sensitized AISI 316 stainless steels on
45
corrosion behavior
4.4
4.3.1
Effect of Heat Treatment
45
4.3.2
Result and Discussion of Electrochemical results
46
Effect of solution annealing of sensitized AISI 316 stainless steels on
50
hardness
4.4.1
Hardness Properties
51
5.0
CONCLUSION AND RECOMMENDATION
54
5.1
Conclusion and finding
54
5.2
Recommendation
55
REFERENCES
57
ix
APPENDICES
A
Gantt Chart PSM 1
B
Gantt Chart PSM 2
x
LIST OF TABLES
2.1
Properties of AISI 316 Stainless Steels
8
2.2
Chemical Composition of AISI 316 Stainless Steels
8
3.1
Summary of sample preparation for heat treatment effect
31
3.2
Preparation Method (ASTM E3)
33
4.1
Critical potentials and protection intervals obtained for stainless
47
steels after exposure in 3.5 wt% NaCl solution
4.2
Analysis of Critical potentials and protection intervals obtained for
48
stainless steels after exposure in 3.5 wt% NaCl solution
4.3
List of Result for Hardness Properties of AISI 316
xi
51
LIST OF FIGURES
1.4
Scope of study flowchart
4
1.5
Research flowchart
5
2.1
Effect of Molybdenum content on the anodic polarization curves of Fe 9
18% Cr alloy in H2SO4
2.2
Morphology of AISI 316 before and after electrochemistry test
11
2.3
SEM analysis of a pit formed around a MnS inclusion of AISI 304 12
polarized in 3.5 wt.% NaCl solution until a potential value close to Epit
2.4
Anodic polarization curve of stainless steel in sulphuric acid solution
13
2.5
Schematic diagram of apparatus for the determination of polarization 16
curve of a stainless steel in a solution using a potensiostat
2.6
Tafel extrapolation of measured potential-current density curves.
17
2.7
Schematic diagram of breakdown potential
19
2.8
AISI 304 behavior when polarized in 3.5 % NaCl solution
20
2.9
SEM microstructural (A) austenitic mode contains 0Mo - 18Cr - 17Ni 23
and (B) austenitic-ferritic mode 0Mo - 18Cr - 12Ni
2.10
SEM microstructural (A) ferritic-austenitic mode contains 2Mo - 18Cr 22
- 12Ni (B) ferritic mode contains 2Mo - 17Cr - 8Ni
2.11
Microstructure of the AISI 304 A) after solution annealing – 0% CW, 23
B) after solution annealing – 40% CW, C) after aging at 650 °C/0.5 h,
0% CW, D) after aging at 650 °C/0.5 h, 40% CW
2.12
Example of AISI 304 microstructures obtained after oxalic acid etch 24
test (A) after aging 650°C/10 min. (step),(B) after aging 650°C/30
min., (step) (C) after aging 650°C/5 h (step), (D) after aging
650°C/10h (ditch)
2.13
(A) AISI 304 sensitized 700°C/1 h furnace (B) AISI 304 after Solution 25
Annealing at 1200°C /1 h (water quenching)
xii
2.14
Type 304 stainless steel strip, annealed 5 min at 1065°C (1950°F) and 25
cooled in air
2.15
Type 316stainless steels annealed 30 min at 1080°C (1975°F) and 26
exposed 3000h at 815°
2.16
Type 316 stainless steel, solution annealed at 1035°C (1900 °F) and 26
water quenched
3.1
Flowchart of research study on AISI 316
29
3.2
Project specimen of AISI 316
30
3.3
Flow Chart of preparation metallographic specimens
32
3.4
Mounting machine
32
3.5
Optical microscope provided in UTeM’s laboratory
34
3.6
Gamry Potential Stat
35
4.1
20 X Magnification microstructure, (A) AISI 316 before exposed to
38
heat, (B) AISI 316 after exposed to heat in two hour at temperature
4.2
700 ℃
39
20 X Magnification microstructure, (A, B, C, D) AISI 316 after
40
Microstructure of samples after etched with oxalic acid at 50X
magnification (A) and 100 X magnification (B)
4.3
solution annealing, 1130 ºC (24, 48, 72, 120 minute) and rapidly
quench in cold water
4.4
Reference XRD patterns for Cr23C6 (01-085-1281)
42
4.5
Reference XRD patterns for Martensite (00-044-1290)
42
4.6
Reference XRD patterns for Austenite (00-031-0619)
43
4.7
X-ray diffraction pattern for sample of AISI 316
43
4.8
Cyclic polarization curves obtained as a function of Sensitizing
47
Temperature and Solution Annealing various soaking time after
exposure in 3.5 wt % NaCl solution
4.9
Analysis of high potential stress for AISI 316 specimens with
Sensitizing Temperature and Solution Annealing various soaking time
xiii
49
4.10
The comparison of hardness value between specimens produced by
different process
xiv
53
LIST OF ABBREVIATIONS
A
-
Austenitic
AF
-
Austenitic-Ferritic
AISI
-
American Iron and Steel Institute
ANSI
-
American National and Standard Institute
ASTM
-
American Society for Testing and Materials
CW
-
Cold Working
EBDS
-
Electron Backscatter Diffraction
EDS
-
Energy Dispersive X-Ray Spectroscopy
FCC
-
Face Centre Cubic
F
-
Ferritic
FA
-
Ferritic-Austenitc
GBs
-
Grain Boundaries
HRB
-
Hardness Rockwell B-scale
SAE
-
Society of Automotive Engineers
SEM
-
Scanning Electron Microscope
UNS
-
Unified Numbering System
XRD
-
X-Ray Diffraction
xv
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
HCl
-
Hydrochloric acid
H2SO4
-
Sulfuric acid
NaCl
-
Sodium Chloride
C
-
Capacitance
pH
-
-log a (H+)
V
-
Voltage
T
-
Temperature (oC)
M
-
Molar
wt %
-
weight percent
xvi
CHAPTER 1
INTRODUCTION
1.1
Background of Study
Austenitic stainless steels 300 series contain chromium (Cr) and nickel (Ni) as major
alloying elements. The steels from this group have the highest corrosion resistance,
weldability and ductility. Austenitic stainless steels retain their properties at elevated
temperatures. At the temperatures 500ºC-800ºC chromium carbides (Cr23C6) form
along the austenite grains (Uhlig, H. H. 2008). This causes depletion of chromium
from the grains resulting in decreasing the corrosion protective passive film. This
effect is called sensitization. It is particularly important in welding of austenitic
stainless steels. Stabilization heat treatment of such steels results in preferred
formation of carbides of the stabilizing elements instead of chromium carbides.
These steel are not heat treatable and may be hardened only by cold work.
High corrosion resistance of austenitic stainless steels is primarily attributed to the
passive oxide film formed on its surface when exposed to an aqueous solution.
However, the resistance of this passive film is determined by the environmental
conditions which stainless steel is exposed to, as well as by the alloy composition
(Pardo, A., et al., 2008). Ronald (2007) stated that a very large number of phases
can be present in the microstructure of austenitic stainless steels, mainly carbides
and intermetallic phases. Cr23C6 is carbides that are frequently presence in the
microstructure of austenitic stainless steels and often associated with intergranular
corrosion. It is often associated with intergranular corrosion, as its formation along
the grain boundaries causes a local depletion in chromium and possibly local loss of
the stainless property where the steel is said to be sensitized.
1
1.2
Problem Statement
It is well-known that austenitic stainless steels are the most favored construction
material of various components required in chemical, petrochemical and nuclear
industries. The selection of these is made basically due to a good combination of
mechanical, fabrication and corrosion resistance properties. However, problems
which often arise when welding process applied on stainless steel type AISI 316, it
will cause chromium carbide precipitation at boundary. So, the area of chromium
carbide deflection or is impecunious of chromium, that is less than 12 wt% as steel
condition become to hold up to corrosion. If residing in corrosive environment tend
to happened item boundary corrosion. Seen the problems, hence carbide
precipitation representing cause of failure of function result of steel stainless
welding represent matter which need to be studied by more circumstantial. In this
study, AISI 316 will be sensitized at 700°C temperature for two hours then heat
treated by solution annealing followed by water quench. The corrosion resistance of
AISI 316 is analyzed by study the effect of solution annealing by using
electrochemical test and oxalic acid etch test. Therefore, the present work attempts
to provide a further understanding of the effects of solution annealing of sensitized
AISI 316 on microstructure, corrosion and mechanical properties.
1.3
Objectives
1)
To study the effect of solution annealing of sensitized AISI 316 stainless
steels on microstructure.
2)
To study the effect of solution annealing of sensitized AISI 316 stainless
steels on corrosion behavior.
3)
To study the effect of solution annealing of sensitized AISI 316 stainless
steels on hardness property of material.
2
1.4
Scope of Study
The scope of this project is to study the effect of solution annealing on
microstructure, corrosion behavior and mechanical properties of sensitized AISI 316
as shown in Figure 1.1. The aspects that should be study on this material are
structure and microstructure of AISI 316 such the present of inclusion and formation
of chromium carbide by using optical microscope and X-ray diffraction respectively.
Hardness test is conducted to investigate the hardness of AISI 316 by varying
soaking time use in solution annealing process. Precision Vickers a hardness
measurement with load 0.5 is used to measure the hardness. The corrosion property
of the material is studied by using electrochemical technique and oxalic acids etch.
The purpose of electrochemical technique is to investigate corrosion properties of
AISI 316 due to sensitizing effect and heat treated by solution annealing process.
The oxalic acid etch technique is to investigate susceptibility to intergranular attack
due to heat sensitization effect. The result of the corrosion behavior of AISI 316 in
sensitized conditions analyze as to provide the corrosion control and prevention
method.
1.5
Report Organization
The organization of this report is as follows, chapter 1 as the starting of the report
providing the introduction of the project. The elements that consist in chapter 1 are
background of corrosion environment and application AISI 316, problem statement
of the project study, scope of projects study, objectives of project study and report
organization. Chapter 2 consists of literature review information of AISI 316 on
their mechanical properties, effect of its alloying element in the resistance of
corrosion, morphology analysis, and electrochemical corrosion analysis. Chapter 3
presents the methodology of the project study. This chapter is discussing the
experiment procedure to investigate the corrosion behavior of stainless steel.
Electrochemical test and oxalic acid etch test is conducted to investigate corrosion
behavior and to detecting the susceptibility to intergranular attack of AISI 316.
Chapter 4 present the analysis result based on the conducted experiment and
3
discussion of the investigation on corrosion behavior of AISI 316 based on data
result. Chapter 5 discusses the conclusion and recommendation based on the study
objective and finding the effect of solution annealing on microstructure, corrosion
behavior and mechanical properties of sensitized AISI 316.
Figure 1.1: Flowchart scope of study
4
AISI 316 is stainless steels that commonly used in industries. AISI 316 is the most
favored construction material of various components required in chemical,
petrochemical and nuclear industries. It is important to study the corrosion properties
of AISI 316 due to the mechanical properties, microstructure and corrosion attack.
Two types of corrosion attack that commonly found on AISI 316 stainless steels are
intergranular corrosion and pitting corrosion. Intergranular corrosion is occurring
when AISI 316 is sensitized to the heat at temperature 500ºC to 800°C leads to the
grain boundary precipitation of chromium rich carbides (Fe,Cr)23C6 and the
formation of chromium depletion regions (Uhlig, H. H. 2008). The process of
solution annealing followed by rapid quenching can cure the intergranular corrosion
in AISI 316. Pitting corrosion occurs due to the attack of the corrosive environment
to the heterogeneous material composition on the surface of the AISI 316 where at
the surface region, black spot that contain high iron will ease attack by localize
corrosion and form pitting. The formation of respective corrosion is studied by using
electrochemical analysis and the oxalic etch test for classification of etch structures
in determining the suitability of intergranular corrosion. Potentiodynamic Cyclic
Polarization as described in ASTM standard G 61 is applied in order to analyze the
formation of pitting and the behavior of AISI 316 in resisting corrosion. In this study,
intergranular corrosion is investigated by exposing AISI 316 at sensitized
temperature. Based on the experiment, it shows that after AISI 316 exposed to
sensitized temperature, AISI 316 is susceptible to intergranular corrosion attacked.
Solution annealing had been used in order to improve corrosion behavior of AISI 316
for resisting intergranular corrosion. The corrosion product that had been propagates
on surface of AISI 316 was analyzed by Optical Microscope (OM). X-Ray
Diffraction (XRD) Analysis applied to analyze the phase of chromium carbide form
in the structure of AISI 316. This formation had been analyzed that this phases cause
i
susceptibility to intergranular corrosion in AISI 316. Moreover, the effect of solution
annealing and sensitizing of AISI 316 on hardness is evaluated by microhardness
test. Five indentations were taken from each sample to obtain a representative
average. In corrosion studies, when AISI 316 is exposed in 3.5% NaCl solution,
based on hysteresis loop analysis, the corrosion resistance of AISI 316 on the
sensitized is decreased due to the Cr23C6 form.
In morphologies studies, after
solution annealing and quenching by cold water in order to homogenized all austenite
(γ) phase. Further investigation, X-ray diffraction (XRD) analysis is applied to
support the existence Cr23C6 on the sensitized and heat treated sample. Theoretically,
solution annealing process is done to dissolve Cr23C6 as to form homogeneity of alloy
in a sample, leaving on desired phase which in this case involve that austenite.
However, Cr23C6 still present this is due to the time of growth for Cr23C6 has
exceeded the C-shape curve. Furthermore, the present work attempts to provide a
further understanding of the effects of solution annealing of sensitized AISI 316 on
microstructure, corrosion and hardness.
ii
ABSTRAK
AISI 316 adalah keluli tahan karat yang paling biasa digunakan di industri. Keluli
tahan karat jenis AISI 316 adalah dari siri kumpulan T 300 baja keluli. AISI 316
merupakan bahan pembinaan yang paling banyak digunakan dari berbagai-bagai
komponen yang diperlukan dalam indusri kimia, petrokimia dan nuklear. Adalah
penting untuk mempelajari sifat kakisan AISI 316 kerana sifat mekanik,
mikrostruktur dan serangan kakisan. Dua jenis serangan kakisan yang biasa ditemui
pada AISI 316 adalah kakisan intergranular dan kakisan bopeng. Kakisan
intergranular terjadi ketika AISI 316 terdedah panas pada suhu 500ºC hingga 800°C
dan menyebabkan batas butir kaya kromium karbida (Fe,Cr)23C6 dan pembentukan
daerah pengurangan kromium (Uhlig, H. H. 2008). Proses larutan anil diikuti
penyepuh lindapan cepat menggunakan air dapat merawat kakisan intergranular pada
AISI 316. Sementara itu, kakisan bopeng terjadi kerana serangan dari lingkungan
kakisan terhadap komposisi bahan heterogen pada permukaan AISI 316 di mana
permukaan, tompok hitam yang mengandungi kromium (Cr) yang tinggi akan
memudahkan pelokalan serangan kakisan bopeng dan berlaku pada kawasan
setempat. Pembentukan kakisan masing-masing dipelajari dengan menggunakan
analisis elektrokimia, manakala ujian calar oxalic untuk untuk mengklasifikasi
struktur calar dalam menentukan kesesuaiannya dengan kakisan intergranular.
Potensiodinamik Putaran Polarisasi seperti yang dinyatakan dalam standard ASTM G
61 digunakan untuk menganalisis pembentukan kakisan bopeng dan perilaku AISI
316 dalam melawan kakisan. Sementara ASTM A 262-01 amalan A, pemendakan
terhadap serangan kakisan batas butir pada AISI 316 digunakan. Jenis-jenis kakisan
yang telah tersebar pada permukaan AISI 316 dianalisis dengan Mikroskop Optik. XRay Diffraction (XRD). Analisis ini digunakan untuk menganalisa tahap bentuk
pemendakan kromium karbida (Cr23C6) dalam struktur AISI 316. Formasi ini telah
dianalisis bahawa fasa ini menyebabkan pemendakan terhadap kakisan antara butir
iii
AISI 316. Selain itu, Penyepuhlindapan dan pemekaan AISI 316 pada kekerasan
diukur dengan ujian mikrokekerasan. Ujian mikrokekerasan digunakan untuk
menentukan peringkat pembentukan kristal dan memberikan anggaran bahan
ketahanan terhadap deformasi AISI 316. Sebanyak 5 lekukan diambil dari sampel
untuk mendapatkan purata. Dalam kajian ini, ketika AISI 316 direndam dalam 3.5%
larutan NaCl, berdasarkan analisis histeresis loop, rintangan karat AISI 316 pada
peka adalah kerana bentuk Cr23C6 menurun. Dalam kajian morfologi, selepas
penyelesaian pemanasan dan pendinginan segera dengan air sejuk untuk
menyamakan struktur aloi pada fasa austenit (γ). Penyelidikan lebih lanjut dengan Xray pembelauan (XRD) analisis untuk menyokong kewujudan Cr23C6 pada sampel
diperlakukan peka dan panas. Secara teori, penyelesaian proses anil dilakukan untuk
melarutkan Cr23C6 untuk membentuk homogenitas gabungan dalam sampel,
berangkat pada peringkat dikehendaki yang dalam hal ini melibatkan austenit itu.
Namun, Cr23C6 masih ada ini kerana apabila pertumbuhan Cr23C6 telah melebihi
garisan lengkung C. Selain itu, kajian ini untuk memberikan pemahaman lebih lanjut
tentang pengaruh larutan anil yang terdedah pada suhu pemekaan AISI 316 terhadap
mikrostruktur, kakisan dan sifat kekerasan.
iv
DEDICATION
Dedicated to my beloved family and friends
v
ACKNOWLEDGEMENT
Alhamdulillah, thank to ALLAH for HIS blessing, provide me a good health and
thinking during progress this project.
Special thanks to my supervisor Dr. Zulkifli Bin. Rosli, because of his commitment
and supported throughout my final year project and report writing with his patience
and knowledge that he give to me in this research.
I would also like to thanks to the Faculty of Manufacturing labs technicians, Mr.
Azhar, Mr. Farihan, Mr. Hisham and Madam Nurhafizah who encourage me in
laboratory during my PSM project.
Finally, I thank my parent for supporting me throughout all my studies at University.
Thank for being a wonderful parent of mine and thank for providing a space for me
in which to complete my writing up.
I hope, through their guidance will completing my Final Project in my final year
study. These experiences are also made me be more matured than before and
increasing my self-confident.
Thanks to everyone.
vi
TABLE OF CONTENT
Abstract
i
Abstrak
ii
Dedication
v
Acknowledgement
vi
Table of Content
vii
List of Tables
xi
List of Figures
xii
List of Abbreviation
xv
List of Symbol
xvi
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
1.5
Report Organization
3
2.0
LITERATURE REVIEW
6
2.1
Stainless Steel
6
2.1.1
Stainless Steels Classification
7
2.1.1.1
7
2.1.2
Type AISI 316
Effect of Alloying Elements on the Corrosion Behavior of
8
Stainless Steels
2.1.2.1
Chromium (Cr)
vii
9
2.2
2.3
2.4
2.1.2.2
Nickel (Ni)
9
2.1.2.3
Molybdenum (Mo)
9
2.1.2.4
Manganese (Mn)
10
Scanning Electron Microscope
10
2.2.1
11
Chemical and Microstructure Analysis
Corrosion Resistance of Stainless Steels
13
2.3.1
General Corrosion
13
2.3.2
Intergranular Corrosion
14
2.3.3
Pitting Corrosion
15
2.3.4
Stress Corrosion Cracking
15
Corrosion Tests
16
2.4.1
Electrochemical Analysis
16
2.4.2
Cyclic Potentiodynamic Polarization Methods
18
2.5
Previous Studies on the Microstructure of Steel
20
2.6
Microstructure Analysis
21
2.6.1
25
Microstructure of Wrought Stainless Steels
2.7
Hardness Test
27
3.0
METHODOLOGY
28
3.1
Introduction
28
3.2
Raw Material
28
3.3
Sample Size preparation
28
3.3.1
Sample Preparation
30
3.3.2
Metallographic Specimens Preparations
31
viii
3.3.3
Grinding and Polishing Procedure
32
3.4
Morphology Analysis
34
3.5
Corrosion Test
35
3.5.1
35
Electrochemical Test
3.6
Hardness Testing
36
3.7
X-Ray Diffraction (XRD) Analysis
36
4.0
RESULTS AND DISCUSSION
37
4.1
Introduction
37
4.2
Effect of solution annealing of sensitized AISI 316 stainless steels on
37
microstructure
4.2.1
4.3
X-Ray Diffraction (XRD) Analysis and Interpretation
42
4.2.1.1
43
X-Ray Diffraction Pattern for Chromium Carbide
(Cr23C6)
Effect of solution annealing of sensitized AISI 316 stainless steels on
45
corrosion behavior
4.4
4.3.1
Effect of Heat Treatment
45
4.3.2
Result and Discussion of Electrochemical results
46
Effect of solution annealing of sensitized AISI 316 stainless steels on
50
hardness
4.4.1
Hardness Properties
51
5.0
CONCLUSION AND RECOMMENDATION
54
5.1
Conclusion and finding
54
5.2
Recommendation
55
REFERENCES
57
ix
APPENDICES
A
Gantt Chart PSM 1
B
Gantt Chart PSM 2
x
LIST OF TABLES
2.1
Properties of AISI 316 Stainless Steels
8
2.2
Chemical Composition of AISI 316 Stainless Steels
8
3.1
Summary of sample preparation for heat treatment effect
31
3.2
Preparation Method (ASTM E3)
33
4.1
Critical potentials and protection intervals obtained for stainless
47
steels after exposure in 3.5 wt% NaCl solution
4.2
Analysis of Critical potentials and protection intervals obtained for
48
stainless steels after exposure in 3.5 wt% NaCl solution
4.3
List of Result for Hardness Properties of AISI 316
xi
51
LIST OF FIGURES
1.4
Scope of study flowchart
4
1.5
Research flowchart
5
2.1
Effect of Molybdenum content on the anodic polarization curves of Fe 9
18% Cr alloy in H2SO4
2.2
Morphology of AISI 316 before and after electrochemistry test
11
2.3
SEM analysis of a pit formed around a MnS inclusion of AISI 304 12
polarized in 3.5 wt.% NaCl solution until a potential value close to Epit
2.4
Anodic polarization curve of stainless steel in sulphuric acid solution
13
2.5
Schematic diagram of apparatus for the determination of polarization 16
curve of a stainless steel in a solution using a potensiostat
2.6
Tafel extrapolation of measured potential-current density curves.
17
2.7
Schematic diagram of breakdown potential
19
2.8
AISI 304 behavior when polarized in 3.5 % NaCl solution
20
2.9
SEM microstructural (A) austenitic mode contains 0Mo - 18Cr - 17Ni 23
and (B) austenitic-ferritic mode 0Mo - 18Cr - 12Ni
2.10
SEM microstructural (A) ferritic-austenitic mode contains 2Mo - 18Cr 22
- 12Ni (B) ferritic mode contains 2Mo - 17Cr - 8Ni
2.11
Microstructure of the AISI 304 A) after solution annealing – 0% CW, 23
B) after solution annealing – 40% CW, C) after aging at 650 °C/0.5 h,
0% CW, D) after aging at 650 °C/0.5 h, 40% CW
2.12
Example of AISI 304 microstructures obtained after oxalic acid etch 24
test (A) after aging 650°C/10 min. (step),(B) after aging 650°C/30
min., (step) (C) after aging 650°C/5 h (step), (D) after aging
650°C/10h (ditch)
2.13
(A) AISI 304 sensitized 700°C/1 h furnace (B) AISI 304 after Solution 25
Annealing at 1200°C /1 h (water quenching)
xii
2.14
Type 304 stainless steel strip, annealed 5 min at 1065°C (1950°F) and 25
cooled in air
2.15
Type 316stainless steels annealed 30 min at 1080°C (1975°F) and 26
exposed 3000h at 815°
2.16
Type 316 stainless steel, solution annealed at 1035°C (1900 °F) and 26
water quenched
3.1
Flowchart of research study on AISI 316
29
3.2
Project specimen of AISI 316
30
3.3
Flow Chart of preparation metallographic specimens
32
3.4
Mounting machine
32
3.5
Optical microscope provided in UTeM’s laboratory
34
3.6
Gamry Potential Stat
35
4.1
20 X Magnification microstructure, (A) AISI 316 before exposed to
38
heat, (B) AISI 316 after exposed to heat in two hour at temperature
4.2
700 ℃
39
20 X Magnification microstructure, (A, B, C, D) AISI 316 after
40
Microstructure of samples after etched with oxalic acid at 50X
magnification (A) and 100 X magnification (B)
4.3
solution annealing, 1130 ºC (24, 48, 72, 120 minute) and rapidly
quench in cold water
4.4
Reference XRD patterns for Cr23C6 (01-085-1281)
42
4.5
Reference XRD patterns for Martensite (00-044-1290)
42
4.6
Reference XRD patterns for Austenite (00-031-0619)
43
4.7
X-ray diffraction pattern for sample of AISI 316
43
4.8
Cyclic polarization curves obtained as a function of Sensitizing
47
Temperature and Solution Annealing various soaking time after
exposure in 3.5 wt % NaCl solution
4.9
Analysis of high potential stress for AISI 316 specimens with
Sensitizing Temperature and Solution Annealing various soaking time
xiii
49
4.10
The comparison of hardness value between specimens produced by
different process
xiv
53
LIST OF ABBREVIATIONS
A
-
Austenitic
AF
-
Austenitic-Ferritic
AISI
-
American Iron and Steel Institute
ANSI
-
American National and Standard Institute
ASTM
-
American Society for Testing and Materials
CW
-
Cold Working
EBDS
-
Electron Backscatter Diffraction
EDS
-
Energy Dispersive X-Ray Spectroscopy
FCC
-
Face Centre Cubic
F
-
Ferritic
FA
-
Ferritic-Austenitc
GBs
-
Grain Boundaries
HRB
-
Hardness Rockwell B-scale
SAE
-
Society of Automotive Engineers
SEM
-
Scanning Electron Microscope
UNS
-
Unified Numbering System
XRD
-
X-Ray Diffraction
xv
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
HCl
-
Hydrochloric acid
H2SO4
-
Sulfuric acid
NaCl
-
Sodium Chloride
C
-
Capacitance
pH
-
-log a (H+)
V
-
Voltage
T
-
Temperature (oC)
M
-
Molar
wt %
-
weight percent
xvi
CHAPTER 1
INTRODUCTION
1.1
Background of Study
Austenitic stainless steels 300 series contain chromium (Cr) and nickel (Ni) as major
alloying elements. The steels from this group have the highest corrosion resistance,
weldability and ductility. Austenitic stainless steels retain their properties at elevated
temperatures. At the temperatures 500ºC-800ºC chromium carbides (Cr23C6) form
along the austenite grains (Uhlig, H. H. 2008). This causes depletion of chromium
from the grains resulting in decreasing the corrosion protective passive film. This
effect is called sensitization. It is particularly important in welding of austenitic
stainless steels. Stabilization heat treatment of such steels results in preferred
formation of carbides of the stabilizing elements instead of chromium carbides.
These steel are not heat treatable and may be hardened only by cold work.
High corrosion resistance of austenitic stainless steels is primarily attributed to the
passive oxide film formed on its surface when exposed to an aqueous solution.
However, the resistance of this passive film is determined by the environmental
conditions which stainless steel is exposed to, as well as by the alloy composition
(Pardo, A., et al., 2008). Ronald (2007) stated that a very large number of phases
can be present in the microstructure of austenitic stainless steels, mainly carbides
and intermetallic phases. Cr23C6 is carbides that are frequently presence in the
microstructure of austenitic stainless steels and often associated with intergranular
corrosion. It is often associated with intergranular corrosion, as its formation along
the grain boundaries causes a local depletion in chromium and possibly local loss of
the stainless property where the steel is said to be sensitized.
1
1.2
Problem Statement
It is well-known that austenitic stainless steels are the most favored construction
material of various components required in chemical, petrochemical and nuclear
industries. The selection of these is made basically due to a good combination of
mechanical, fabrication and corrosion resistance properties. However, problems
which often arise when welding process applied on stainless steel type AISI 316, it
will cause chromium carbide precipitation at boundary. So, the area of chromium
carbide deflection or is impecunious of chromium, that is less than 12 wt% as steel
condition become to hold up to corrosion. If residing in corrosive environment tend
to happened item boundary corrosion. Seen the problems, hence carbide
precipitation representing cause of failure of function result of steel stainless
welding represent matter which need to be studied by more circumstantial. In this
study, AISI 316 will be sensitized at 700°C temperature for two hours then heat
treated by solution annealing followed by water quench. The corrosion resistance of
AISI 316 is analyzed by study the effect of solution annealing by using
electrochemical test and oxalic acid etch test. Therefore, the present work attempts
to provide a further understanding of the effects of solution annealing of sensitized
AISI 316 on microstructure, corrosion and mechanical properties.
1.3
Objectives
1)
To study the effect of solution annealing of sensitized AISI 316 stainless
steels on microstructure.
2)
To study the effect of solution annealing of sensitized AISI 316 stainless
steels on corrosion behavior.
3)
To study the effect of solution annealing of sensitized AISI 316 stainless
steels on hardness property of material.
2
1.4
Scope of Study
The scope of this project is to study the effect of solution annealing on
microstructure, corrosion behavior and mechanical properties of sensitized AISI 316
as shown in Figure 1.1. The aspects that should be study on this material are
structure and microstructure of AISI 316 such the present of inclusion and formation
of chromium carbide by using optical microscope and X-ray diffraction respectively.
Hardness test is conducted to investigate the hardness of AISI 316 by varying
soaking time use in solution annealing process. Precision Vickers a hardness
measurement with load 0.5 is used to measure the hardness. The corrosion property
of the material is studied by using electrochemical technique and oxalic acids etch.
The purpose of electrochemical technique is to investigate corrosion properties of
AISI 316 due to sensitizing effect and heat treated by solution annealing process.
The oxalic acid etch technique is to investigate susceptibility to intergranular attack
due to heat sensitization effect. The result of the corrosion behavior of AISI 316 in
sensitized conditions analyze as to provide the corrosion control and prevention
method.
1.5
Report Organization
The organization of this report is as follows, chapter 1 as the starting of the report
providing the introduction of the project. The elements that consist in chapter 1 are
background of corrosion environment and application AISI 316, problem statement
of the project study, scope of projects study, objectives of project study and report
organization. Chapter 2 consists of literature review information of AISI 316 on
their mechanical properties, effect of its alloying element in the resistance of
corrosion, morphology analysis, and electrochemical corrosion analysis. Chapter 3
presents the methodology of the project study. This chapter is discussing the
experiment procedure to investigate the corrosion behavior of stainless steel.
Electrochemical test and oxalic acid etch test is conducted to investigate corrosion
behavior and to detecting the susceptibility to intergranular attack of AISI 316.
Chapter 4 present the analysis result based on the conducted experiment and
3
discussion of the investigation on corrosion behavior of AISI 316 based on data
result. Chapter 5 discusses the conclusion and recommendation based on the study
objective and finding the effect of solution annealing on microstructure, corrosion
behavior and mechanical properties of sensitized AISI 316.
Figure 1.1: Flowchart scope of study
4