Inclusion Characterization in High Strength Low Alloy Steel - T-Space

102 Pages·2009·7.02 MB·English

Inclusion Characterization in High Strength Low
Alloy Steel

by

Chao Peng Paul Wu

A thesis submitted in conformity with the requirements for the degree of
Master of Applied Science
Graduate Department of Materials Science and Engineering
University of Toronto

© Copyright by Chao Peng Paul Wu, 2009
Inclusion Characterization in High Strength Low Alloy
Steel

by
Chao Peng Paul Wu

Master of Applied Science
Department of Materials Science and Engineering
University of Toronto
2009

ABSTRACT

The cleanliness of high strength low alloy (HSLA) steel was assessed qualitatively and
quantitatively. The determination of inclusion type and inclusion morphology were
carried out using Selective Potentiostatic Etching by Electrolytic Dissolution (SPEED)
method allowing in-situ examination of inclusion morphology by analytical techniques
such as SEM/EDS. Inclusion size analysis mainly involved a combination of an
analytical technique to provide images of the sample surface and an image analysis
system to accurately measure the inclusion size. Four analytical methods were compared
in order to evaluate their suitability for subsequent quantitative analysis. It was found that
images taken with backscattered electron imaging mode from the scanning electron
microscope provides the most accurate representation of inclusion distribution. The
various techniques were used to evaluate HSLA steel grades of similar chemistry
produced with and without gas shrouding. The results confirmed that with reoxidation
minimized by gas shrouding between ladle and tundish, the steel cleanliness was
significantly improved.
ii
ACKNOWLEDGEMENTS

I owe my deepest gratitude to my supervisor, Professor A. McLean, whose
encouragement, guidance, and support have motivated and inspired all his students,
myself included.

I would like to express my sincere thanks to my mentors, Dr. Y.D. Yang and Dr. H. Soda
for their constant assistance and encouragement during the term of this project. This
thesis would not have been possible without the helpful discussions. I admire Dr. Yang’s
passion for research and his meticulous approach to questions, which have taught me
much. I am indebted to Dr. Soda, who always manages to make himself available to give
counsel on all aspects.

I would like to extend my thanks to the research group members for the moral support
and friendship. Appreciation is also expressed to the staff of the MSE department for the
technical and administrative support during the course of the project.

Financial support from Natural Sciences and Engineering Council of Canada and
University of Toronto fellowship is greatly appreciated. I would also like to thank Gerdau
Ameristeel Inc. for providing me with the steel samples. I am especially grateful to Mr. S.
Paul at Gerdau Ameristeel Inc. for his helpful advice and assistance.

Finally, I would like to thank my family and friends for their immense support and
encouragement throughout my study.

iii
TABLE OF CONTENTS

ABSTRACT ........................................................................................................................ ii
ACKNOWLEDGEMENTS ............................................................................................... iii
TABLE OF CONTENTS ................................................................................................... iv
LIST OF FIGURES ........................................................................................................... vi
LIST OF TABLES ............................................................................................................. ix
NOMENCLATURE ........................................................................................................... x
CHAPTER ONE: INTRODUCTION ................................................................................. 1
1.1 Introduction and Background ............................................................................... 1
1.2 References ............................................................................................................. 3
CHAPTER TWO: LITERATURE REVIEW ..................................................................... 4
2.1 Melting and Casting Operations ........................................................................... 4
2.2 Steel Deoxidation .................................................................................................. 6
2.2.1 Thermodynamics of deoxidation ............................................................... 6
2.2.2 Single component deoxidation ................................................................... 8
2.2.3 Multi-component deoxidation .................................................................. 12
2.3 Manganese Oxide – Silicon Oxide – Aluminum Oxide System......................... 17
2.4 Classification of Non-Metallic Inclusions .......................................................... 19
2.4.1 Based on inclusion chemistry and composition ....................................... 19
2.4.2 Based on inclusion formation mechanism ............................................... 22
2.5 References ........................................................................................................... 23
CHAPTER THREE: EXPERIMENTAL ASPECTS ........................................................ 24
3.1 Overview ............................................................................................................. 24
3.1.1 Sample preparation .................................................................................. 25
3.2 Qualitative Assessment ....................................................................................... 26
3.2.1 Inclusion morphology examination (SPEED method[1]) ......................... 26
3.2.2 Inclusion species analysis ........................................................................ 28
3.3 Quantitative Assessment ..................................................................................... 29
3.3.1 Image acquisition ..................................................................................... 29
3.3.2 Image analysis .......................................................................................... 31
iv
3.4 References ........................................................................................................... 34
CHAPTER FOUR: RESULTS AND DISCUSSION ....................................................... 35
4.1 Qualitative Assessment ....................................................................................... 35
4.1.1 Al O (Alumina) ...................................................................................... 35
2 3
4.1.2 SiO (Silica) ............................................................................................. 41
2
4.1.3 MnO (Manganosite) ................................................................................. 46
4.1.4 MnO-SiO (Rhodonite) ............................................................................ 47
2
4.1.5 MnO-Al O (Galaxite) ............................................................................. 50
2 3
4.1.6 CaO-Al O (Calcium aluminate) ............................................................. 52
2 3
4.1.7 CaO-SiO (Calcium silicate) .................................................................... 59
2
4.1.8 CaO-Al O -SiO (Calcium aluminosilicate) ............................................ 61
2 3 2
4.1.9 MnS (Manganese sulphide) ..................................................................... 63
4.1.10 Development of inclusion species during steelmaking .......................... 69
4.2 Quantitative Assessment ..................................................................................... 72
4.2.1 Particle size distribution ........................................................................... 73
4.2.2 Maximum particle size ............................................................................. 76
4.2.3 Inclusion area fraction .............................................................................. 78
4.2.3 Backscattered electron image analysis (BSE-IA) in steel cleanliness study
......................................................................................................................... 80
4.3 References ........................................................................................................... 81
CHAPTER FIVE: CONCLUSIONS ................................................................................ 82
5.1 Conclusions ......................................................................................................... 82
5.2 Future Work ........................................................................................................ 83
APPENDICES .................................................................................................................. 84
Appendix A: Inclusion’s Effect on Fatigue Behaviour ............................................. 84
Appendix B: Inclusion Particle Size Distribution of 1018S Samples....................... 85
Appendix C: Inclusion Particle Size Distribution of A529 Samples ........................ 88

v
LIST OF FIGURES

Figure 2-1: Schematic of melting and casting operations in steelmaking[2] ....................... 5
Figure 2-2: Free energy of formation for various oxides. Dash-dot line indicates equal
oxygen pressure in unit of atmosphere[4] .................................................................... 7
Figure 2-3: Deoxidizing power of various elements at 1600°C[5] ...................................... 7
Figure 2-4: a) As-polished (2-dimensional) steel sample showing Al O dendrite b)
2 3
Partial slime extracted (3-dimensional) steel sample showing the same Al O
2 3
dendrite[1] .................................................................................................................. 11
Figure 2-5: Equilibrium relations for manganese-silicon deoxidation of steel at various
temperatures[3] ........................................................................................................... 13
Figure 2-6: The effect of manganese content on stability of oxide phases resulting from
steel deoxidation at 1550ºC (m: mullite; l: liquid manganese silicate)[9] ................. 15
Figure 2-7: CaO-Al O equilibrium phase diagram[10] ..................................................... 16
2 3
Figure 2-8: Schematic representation of MnO-SiO -Al O ternary phase diagram[6] ...... 17
2 2 3
Figure 2-9: Free energy of formation for various sulphides. Dash-dot line indicates equal
sulphur pressure in unit of atmosphere[4] .................................................................. 21
Figure 3-1: Flow chart of the scheme of experiments ...................................................... 24
Figure 3-2: Sampling locations ......................................................................................... 25
Figure 3-3: Schematic of SPEED apparatus [1] ................................................................ 27
Figure 3-4 Anode polarization curve ................................................................................ 28
Figure 3-5: Images acquired using (a) optical microscopy, (b) laser confocal microscopy,
(c) SEM (secondary electron mode) and (d) SEM (backscattered electron mode) .. 32
Figure 3-6: Photograph processed by image analysis showing detected area as inclusions
(a) laser confocal microscopy, (b) SEM (backscattered electron mode) .................. 33
Figure 4-1: Oxide inclusions found in 1018S ladle sample: alumina ............................... 36
Figure 4-2: Oxide inclusion found in A529 billet sample: alumina dendrites .................. 36
Figure 4-3: Oxide inclusions found in A529 ladle sample: a) alumina and galaxite (G) . 37
b) alumina cluster .............................................................................................................. 37
Figure 4-4: Glassy Al O (globular) inclusions found in 1018S furnace tap sample ....... 39
2 3
Figure 4-5: Glassy Al O (plate) inclusions found in 1018S ladle sample ....................... 39
2 3
vi
Figure 4-6: Oxide inclusions in steel: corundum in a) manganese aluminosilicate matrix
[1018S ladle tap sample] b) calcium aluminate matrix [A529 tundish sample] ....... 40
Figure 4-7: Oxide inclusion in A529 billet sample: cristobalite (K) in rhodonite (R) ..... 42
Figure 4-8: Oxide inclusion in A529 billet sample: rhodonite (R), low quartz (Q),
tridymite (T) and glassy silica (A) ............................................................................ 43
Figure 4-9: Oxide inclusion in A529 tundish sample: cristobalite (K) in rhodonite (R)
matrix, and glassy silica (A) ..................................................................................... 44
Figure 4-10: Oxide inclusion in 1018S tundish sample: low quartz (Q) and tridymite (T)
................................................................................................................................... 45
Figure 4-11: Oxide inclusion in 1018S billet sample: low quartz (Q) .............................. 45
Figure 4-12: Oxide inclusion in A529 billet sample: manganosite .................................. 46
Figure 4-13: Oxide inclusions found in A529 ladle tap sample: rhodonite ...................... 47
Figure 4-14: Oxide inclusions found in A529 billet sample: rhodonite (R) and cristobalite
(K) ............................................................................................................................. 48
Figure 4-15: Oxide inclusions found in A529 billet sample: rhodonite (after rolling) ..... 49
Figure 4-16: Oxide inclusions found in 1018S ladle sample: rhodonite .......................... 49
Figure 4-17: Oxide inclusions found in A529 furnace tap sample: galaxite (G) .............. 50
Figure 4-18: Oxide inclusions found in 1018S ladle tap sample: galaxite (G) and
chromium galaxite (Cr G) ......................................................................................... 51
Figure 4-19: Oxide inclusions found in 1018S ladle tap sample: calcium aluminate ...... 52
Figure 4-20: Oxide inclusions found in 1018S furnace tap sample: calcium aluminate
(CA) and galaxite (G) ............................................................................................... 54
Figure 4-21: Oxide inclusions found in A529 ladle sample: calcium aluminate (CA) .... 55
Figure 4-22: Oxide inclusions found in A529 furnace tap sample: calcium aluminate .... 56
Figure 4-23: Oxide inclusions found in 1018S ladle tap sample: calcium aluminate ...... 56
Figure 4-24: Oxide inclusions found in A529 tundish sample: calcium aluminate .......... 57
Figure 4-25: Oxide inclusions found in 1018S ladle sample: calcium aluminate ............ 57
Figure 4-26: Oxide inclusions found in 1018S ladle sample: calcium aluminate ............ 58
Figure 4-27: Oxide inclusions found in 1018S ladle sample: calcium aluminate with high
silica content ............................................................................................................. 58
Figure 4-28: Oxide inclusions found in 1018S billet sample: calcium silicate ................ 59
vii
Figure 4-29: Oxide inclusions found in 1018S furnace tap sample: calcium silicate (CS)
and corundum (C) ..................................................................................................... 60
Figure 4-30: Oxide inclusions found in A529 tundish sample: calcium silicate .............. 61
Figure 4-31: Oxide inclusions found in A529 ladle tap sample: calcium aluminosilicate 62
Figure 4-32: Oxide inclusions found in 1018S ladle sample: calcium aluminosilicate .... 63
Figure 4-33: Sulphide inclusions found in 1018S billet sample: manganese sulphide ..... 64
Figure 4-34: Sulphide inclusions found in 1018S billet sample: manganese sulphide ..... 65
Figure 4-35: Sulphide inclusions found in A529 billet sample: manganese sulphide ...... 66
Figure 4-36: Sulphide inclusions found in A529 billet sample: manganese sulphide ...... 67
Figure 4-37: Sulphide inclusions found in A529 billet sample: manganese sulphide –
additional morphologies ............................................................................................ 67
Figure 4-38: Sulphide inclusions found in 1018S billet sample: manganese sulphide scale
(S) around silicate matrix (M)................................................................................... 68
Figure 4-39: Sulphide inclusions found in 1018S billet sample: manganese sulphide scale
(S) around silicate matrix (M)................................................................................... 69
Figure 4-40: Inclusion size distribution of 1018S............................................................. 74
Figure 4-41: Inclusion size distribution of A529 .............................................................. 74
Figure 4-42: Comparison of total inclusion count ............................................................ 75
Figure 4-43: Maximum particle size plot of 1018S steel samples .................................... 76
Figure 4-44: Maximum particle size plot of A529 steel samples ..................................... 77
Figure 4-45: Comparison of maximum particle size ........................................................ 77
Figure 4-46: Inclusion area fraction of 1018S steel samples ............................................ 78
Figure 4-47: Inclusion area fraction of A529 steel samples ............................................. 79
Figure 4-48: Comparison of inclusion area fraction ......................................................... 79
Figure 5-1: Proposed levitation apparatus ........................................................................ 83

viii
LIST OF TABLES

Table 2-1: Cleanliness requirements for steel products[1] ................................................... 4
Table 2-2: Stoichiometric composition of reported inclusion phases in Figure 2-8[6] ...... 18
Table 2-3: Inclusion phases found in MnO-SiO -Al O , FeO-SiO -Al O , and MnO-SiO -
2 2 3 2 2 3 2
Cr O systems[6] ........................................................................................................ 19
2 3
Table 3-1: Specimen chemical composition ..................................................................... 25
Table 4-1: Summary of inclusion types present in A529 steel ......................................... 70
Table 4-2: Summary of inclusion types present in 1018S steel ........................................ 70
Table A: Coefficient of thermal expansion of various inclusion types[2] ......................... 85

ix
NOMENCLATURE

Symbols Units

a Activity of “x”
x
d Maximum particle size μm
ΔG° Free energy of formation kCal
K Equilibrium constant

T Temperature K
T[O] Total oxygen ppm
λ Wavelength μm
α Coefficient of thermal expansion K-1

Element Abbreviations

Al Aluminum
C Carbon
Ca Calcium
Cu Copper
Cr Chromium
Fe Iron
O Oxygen
P Phosphorus
Pt Platinum
Mg Magnesium
Mn Manganese
N Nitrogen
Ni Nickel
S Sulphur
Si Silicon

x