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Formation of Internal Defects in S.G. Cast Irons in Relation to the Solidification Process

Published online by Cambridge University Press:  21 February 2011

G. Lesoult ,
P. Dietrich ,
F. Arnould  and
J. M. Theret
G. Lesoult
Affiliation:
Formely with the Centre des Matériaux de l'Ecole des Mines de Paris, now with the Ecole des Mines de Nancy, Parc de Saurupt, 54042 Nancy Cedex, France
P. Dietrich
Affiliation:
Ecole des Mines de Nancy
F. Arnould
Affiliation:
Formely with the Ecole des Mines de Nancy, now with the Centre de Recherches de Pont-à-Mousson, B.P. 28, 54703 Pont-à-Mousson Cedex, France
J. M. Theret
Affiliation:
Formely with the Centre des Matériaux de l'Ecole des Mines de Paris, now with SNECMA, B.P.48, 92234 Gennevilliers Cedex, France.
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Abstract

It is well known that ductile iron is more prone to the formation of internal defects and to the swelling-out of the mold than grey iron. This is likely related to differences in the way the volume changes due to solidification and graphitization occur for these two cast irons. Direct study of these phenomena is difficult because interdendritic feeding and graphite expansion are intimately related.

A simple physical model is proposed to simulate the effects of a few variables on the tendency for a S.G. cast iron to lead to a casting with internal defects: its chemical composition, inoculation and the rate of heat extraction.

The aim of the model is to calculate the pressure of the residual liquid at any point of the casting during its solidification. A special attention is payed to the pressure drop due to the movement of the residual liquid in the mushy zone. Therefore the evolution of the fractions of liquid, austenite and graphite are taken into account for calculating the local volume changes which are assumed to be the main driving forces for the liquid flow. In the same time, the evolution of the permeability of the mushy zone is estimated for calculating the liquid flow pattern and the pressure drop pattern.

The numerical values for the quantities which describe the solidification of the cast iron are issued from quantitative image analysis of samples quenched during directional solidification (Q.D.S.).

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 34: Symposium – Physical Metallurgy of Cast Iron , 1984 , 223
Copyright
Copyright © Materials Research Society 1985

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References

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