Numerical Simulation of Columnar Crystal/Equiaxed Crystal Formation Model in a Convection Diffusion-multiphase Transformation System

Abstract

The horizontal rapid solidification of Fe-Bi-Mn free-cutting alloys were simulated by using diffusion-governed phase transformation kinetics. The three-dimensional solidification model for a convection diffusion-multiphase transformation system was built. Effects of alloys solidification on solid, liquid and gas phases flow diffusion transformation were considered. The Bi and MnS (free-cutting phases) of alloy columnar crystal/equiaxed crystal formation process were simulated. The results show that columnar crystal/equiaxed crystal formation model of Bi and MnS in alloy solidification is strongly influenced by convection diffusion and multiphase transformation terms; the large multiphase mass transfer rate and small enrichment degree of species easy to form columnar crystal where the convection diffusion term is positive; the small multiphase mass transfer rate and large enrichment degree of species appear at where the convection diffusion term is negative, the tip of columnar crystal breaking is caused by turbulence from convection diffusion and multiphase transformation when the species enriched to some degree, and which becomes the nucleation center of columnar crystal and the equiaxed crystal continues to grow and tends to be stable.

Keywords

• Fe-Bi-Mn alloy
• solidification
• convection diffusion
• multiphase transformation