Abstract
Abstract Formation of the shrinkage defects in ductile iron castings is far more complicated phenomenon than in other casting alloys. In the paper one of the aspects of formation of porosity in this alloy was considered - changes in cast iron's density during crystallization caused by varying temperature, phase fractions and phase's composition. Computer model, using cellular automata method, for determination of changes in density of ductile iron during crystallization was applied. Simulation of solidification was conducted for 5 Fe-C binarie alloys with ES from 0.9 to 1.1 for the estimation of the eutectic saturation influence on the ductile iron shrinkage and expansion. As a result of calculations it was stated that after undercooling ductile iron below liquidus temperature volumetric changes proceed in three stages: preeutectic shrinkage (minimal in eutectic cast iron), eutectic expansion (maximum value equals to about 1.5% for ES = 1.05) and last shrinkage (about 0.4% in all alloys regardless of ES).
Highlights
Density of the majority of known substances is increased during transition from liquid to solid state
Castings made of ductile iron (DI) in Odlewnie Polskie S.A. are characterized by the same, known from literature, shrinkage defects typical for this alloy [4]: 1) the mechanism of feeders performance is far more complicated than in alloys which has no expansion; sometimes by elimination of the feeders causes decrease in porosity; 2) minimal porosity occurs in eutectic alloys, wherein an increase in carbon concentration in eutectic has positive effect; 3) porosity of grey iron castings is considerably smaller than that of DI
This paper presents assessments of change in specific volume of DI during crystallization using cellular automata method
Summary
Density of the majority of known substances is increased during transition from liquid to solid state. To water and bismuth cast iron with high carbon concentration behaves The reason for this increase in the volume during crystallization is participating of graphite, which density is almost three times smaller than other phases. Castings made of DI in Odlewnie Polskie S.A. are characterized by the same, known from literature, shrinkage defects typical for this alloy [4]: 1) the mechanism of feeders performance is far more complicated than in alloys which has no expansion; sometimes by elimination of the feeders causes decrease in porosity; 2) minimal porosity occurs in eutectic alloys, wherein an increase in carbon concentration in eutectic (having conserved ES = 1.0) has positive effect; 3) porosity of grey iron castings is considerably smaller than that of DI. Experience dictates that it doesn't always lead to reduction of shrinkage defects level in casting itself
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