Microstructural evolution and control in the directional solidification of Fe-C-Si alloys

166 Pages·2016·2.94 MB·English

Iowa State University Capstones, Theses and
Retrospective Theses and Dissertations
Dissertations
1990
Microstructural evolution and control in the
directional solidification of Fe-C-Si alloys
Jang-Sik Park
Iowa State University
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Recommended Citation
Park, Jang-Sik, "Microstructural evolution and control in the directional solidification of Fe-C-Si alloys " (1990).Retrospective Theses
and Dissertations. 9404.
https://lib.dr.iastate.edu/rtd/9404
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Microstructural evolution and control in the directional
solidification of Fe-C-Si alloys
Park, Jang-Sik, Ph.D.
Iowa State University, 1990
U M I
300N.ZeebRd.
Ann Arbor, MI 48106

Microstructural evolution and control in the directional solidification
of Fe-C-Si alloys
by
Jang-Sik Park
A Dissertation Submitted to the
Graduate Faculty in Partial Fulfillment of the
Requirements for the Degree of
DOCTOR OF PHILOSOPHY
Department : Materials Science and Engineering
Major : Metallurgy
Approved :
Signature was redacted for privacy.
In Charge of Major Work
Signature was redacted for privacy.
'or thy M^0f Department
Signature was redacted for privacy.
tne Graduate CCooll lege
Iowa State University
Ames, Iowa
1990
ii
TABLE OF œNTENTS
Page
GENERAL INTRODUCTION 1
PART I. EFFECT OF S, H AND O ON STRUCTURE CONTROL
IN THE DIRECTIONAL SOLIDIFICATION OF Fe-C-Si
ALLOYS 4
INTRODUCTION 5
EXPERIMENTAL TECHNIQUE 8
RESULTS 12
DISCUSSION 30
CONCLUSIONS 32
REFERENCES 34
PART n. AUGER FRACTURE ANALYSIS ON Fe-3.4C-2Si
ALLOYS WITH AND WITHOUT THE ADDITION
OF 0.02% S 36
INTRODUCTION 37
EXPERIMENTAL TECHNIQUE 40
RESULTS 42
DISCUSSION 76
CONCLUSIONS 81
REFERENCES 82
iii
PART m. GROWTH STRUCTURE OF FLAKE GRAPHITE
(TYPE A AND D) IN Fe-C-Si ALLOYS 83
INTRODUCTION 84
EXPERIMENTAL TECHNIQUE 86
RESULTS 87
DISCUSSION 111
CONCLUSIONS 113
REFERENCES 114
PART IV. EFFECT OF H AND O ON THE POTENCY OF Te
TO PROMOTE WHITE IRON IN THE SOLIDIFICATION
OF Te-DOPED Fe-C-Si ALLOYS 115
INTRODUCTION 116
EXPERIMENTAL TECHNIQUE 117
RESULTS 119
DISCUSSION 124
CONCLUSIONS 127
REFERENCES 129
GENERAL DISCUSSION 130
GENERAL SUMMARY 149
REFERENCES 151
ACKNOWLEDGEMENTS 152
APPENDIX 153
1
GENERAL INTRODUCTION
There are four main types of cast irons each of which is characterized by a
distinctive microstructure; gray, ductile, white and malleable cast iron. Cast irons are
essentially ternary alloys of Fe-C-Si of near eutectic composition. The microstructure of
cast irons, consisting of a carbon-rich phase in an iron-rich phase, isd etermined by the
type of the C-rich phase. The C-rich phase is graphite in all of the cast ironse xcept white
iron, where it is FegC. With the exception of the malleable iron where the graphitei s
formed by heat treatment in the solid state, thes tructure control of cast iron is mostly
accomplished during the solidification. In general, the solidification rate determines the
way the C is precipitated out of the molten cast iron; FegC at high rates and graphitea t low
rates. The transition rate shows a variation depending on the melt chemistiy. For example,
the Si added in cast iron substantially raises the solidification rate required to produce white
iron and encourages the precipitation of graphite over theF egC in solidification. When the
cast iron solidifies by precipitating the Ci n the form of graphite, the graphite phase takes
on various morphologies according to the solidification velocity, temperature gradient and
chemical composition. If the cast iron melt is specially treated by a smalla mount of either
Mg or Ce the graphite is formed in the shape of spheres and the iron so produced is usually
called ductile cast iron. Without such special melt-treatment, the formation of flake graphite
dominates over FegC formation during solidification, thereby producing the gray cast iron.
The flake graphite is precipitated in the formo f either coarse type A at low solidification
rates or fine type D at high rates. When the gray iron contains less impurities such as S and
Te, coral graphite starts to precipitate, replacing the type D graphite which appears in
commercial purity cast irons. The coral graphite has the fine size as typeD but appears as
more of a highly branched rod structure aso pposed to a branched plate structure of type D