Interdendritic MnS Precipitation And Dendrite Growth Under Forced Convection During Steel Solidification

For describing the evolution of MnS morphology directly during steel solidification and revealing the mechanism of interdendritic MnS precipitation,two cellular automaton(CA)modules with different grid sizes are coupled to be a polydimensional model in order to simulate MnS precipitation accompanied by the matrix growth of dendrites during the solidification of a Fe-C-Mn-S steel,where the dendrite matrix growth is calculated using CA module with large grids based on the solute conservation as well as the undercooling of curvature,thermal and solutal,and the precipitation of MnS is synchronously solved by CA module in combination with the transient thermodynamic equilibrium on small grids of local remeshing once MnS precipitation is formed.Polydimensional model can not only solve the problem of ununified scale of MnS and dendrite but also effectively save the computational cost,where the simulation results obtained well agree with the experimental case in published work.For describing the dendrite growth under fluid molten steel,the efficient fluid computational model of lattice Boltzmann method is coupled into CA method to simulate dendritic growth and distribution of solutes under forced convection during solidification of Fe-C-Mn-S steel.The results showed that:(1)With the simulation of equiaxed dendrite during alloy Fe-0.6%C-1.0%Mn-0.3%S solidification,it is found that the solute concentration gradually decreases from the frontier of dendrite to liquid phase,and the diffusion zone of element C is larger than that of Mn and S.The modeling dendrite tip velocity is verified with prediction of LGK model(2)The polydimensional model is applied to simulate MnS precipitation during alloy Fe-0.6%C-1.0%Mn-0.3%S solidification,showing the MnS nucleation and growth.It is revealed that the ultimate morphology of MnS in matrix is greatly affected by MnS nucleation site,and the Mn concentration in liquid phase apparently decreases after MnS precipitation.(3)The polydimensional model is applied to simulate MnS precipitation during solidification of alloys Fe-0.6%C-0.2%Mn-0.02%S(Alloy 1)and Fe-0.6%C-0.8%Mn-0.005%S(Alloy 2)with the same initial concentration products of S and Mn.It is shown that the MnS is generated under lower solid fraction with less volume fraction in solidified matrix in Alloy 1.The re-precipitation is observed in Alloy 2.(4)The polydimensional model is applied to simulate Fe-0.6%C-0.8%Mn-0.005%S under various cooling rate.It is found that the MnS is generated in higher solidification with lower volume fraction in solidified matrix.Meanwhile,the MnS inclusions are in spot-like distributed inside a belt along the cooling direction,where the width of inclusion belt become narrower under higher cooling rate.(5)The equiaxed dendrite growth of alloy Fe-0.6%C-0.6%Mn-0.005%S under fluid filed is simulated in the paper.It is revealed that upstream arm is more developed than downstream arm of dendrite,and the enriched solute segregates more at the downstream side than that at upstream side of the dendrite.With the fluid velocity increasing,the length of dendritic upstream arm increases firstly and then be stable,where the dendrite necking is restrained,and the upstream arm of dendrite become longer.