Introduction of Dendrite Fragmentation to Microstructure Calculation by Cellular Automaton Method

Abstract

Synopsis : Controlofsolidificationmicrostructureisnecessarybecausethemicrostructureaffectsmaterialcharacters.Inordertopredictsolidification microstructure, effect of fragmentation was indirectly introduced to the cellular automaton method using V crit , which is threshold of molten steelflow.CalculationswerecarriedoutwithvariousV crit (200μms-1 V crit 1 mms-1)andtheresultswerecomparedwiththeresultsof castingexperimentusinghighcarbonsteel.Observedspecimenswereextractedfromupperpartandlowerpartofcasting.Equiaxedgrains andbranchedcolumnargrainswereobservedinthemicrostructureofupperspecimenandjustcolumnargrainswereobservedinthemicrostructureoflowerspecimen.CalculationresultswithV crit whichisgreaterthan400μms-1 show good agreement with microstructure of both observedspecimensqualitatively.Themicrostructureswerecalculatedbecauseflowvelocityofmoltensteelaroundupperspecimenwas muchgreaterthanflowvelocityaroundlowerspecimen.Thereisapossibilitythatsolutetransportationwhichinducesthefragmentationoc-cursevenifvelocityofmoltensteelflowwasintheorderof10-4 ms-1 .