Prediction Of Macrosegregation Of Fe-C-Cr Alloy Ingot By Coupling Solidification Path

The micro-solidification path is the bridge between the macroscopic transmission process and macroscopic nucleation.In order to close the macroscopic transport equation,a micro-solidification solidification path is required.In the past,for binary alloys,the solidification path used the analytical expression of the Lever Rule to express the transition between a single solid phase and a liquid phase.The solute partition coefficient is fixed,and the relationship between phase fraction,average enthalpy and temperature is simplified.However,during the solidification of the actual alloy,multiple solid phases(FCC,BCC,Cementite)may exist at the same time,and the solute partition coefficient also changes instantaneously with the solid and liquid solute concentration.Especially for multicomponent alloys,with two or more solute elements,the analytical formula cannot completely reflect the change of the solidification path,and the phase information is not completely provided by the phase diagram.Therefore,the thermodynamic equilibrium calculation(TEC)must be coupled to obtain the solidification path of the multicomponent and multiphase alloy to calculate the macrosegregation.Aiming at the composition of Fe-C alloy,this paper uses the combination of thermodynamic solidification path prediction and macro-transmission continuum model to predict the macrosegregation formation process of Fe-C-based multiple alloy solidification.The main findings are as follows:1.Prediction of the full solidification path of ternary(Fe-C-Cr)and seven-element(Fe-C-Mn-Si-S-P-Al)alloys by Partical Equilibrium approximation combined with Para-Equilibrium pproximation(PE+PA)models.(1)PE+PA undergoes a temperature interval during the peritectic reaction at high temperature.The solid-solid eutectoid transformation below the solidus line is completed in a larger temperature interval,which is consistent with the solidification process of the actual alloy.(2)The results of predicting the solidification path of the ternary alloy are consistent with the results of experimental measurements and model predictions in the literature.This verifies the accuracy of the PE+PA model in this study.2.Combining the predicted solidification path with multivariate interpolation and the macro-transmission continuum model to predict the macro-segregation of Fe-C based multicomponent alloys.(1)Binary alloy system.1)Numerical simulations of typical experiments and simulation results of Sn-5wt%Pb alloy composition verify the accuracy of simulating the macroscopic solidification process of the alloy by solidification path coupled macroscopic transmission.2)The solidification path adopts the law of leverage combined with thermodynamic equilibrium calculation to obtain the instantaneous changes in the solid and liquid concentration,which is more in line with the actual solidification path than the fixed value distribution coefficient in the analytical formula of Lever Rule.At the same time,it can reflect the influence of multi-solid phase precipitation on macrosegregation during solidification.3)As the heat transfer coefficient becomes smaller and smaller,the degree of segregation becomes more and more serious,so a higher cooling rate is conducive to a more uniform solute distribution;If the solute buoyancy greatly exceeds the thermal buoyancy,significant channel segregation is formed.(2)Ternary alloy system.The macrosegregation results of the ternary alloy show that there is a significant positive segregation in the lower right part of the ingot,and a lack of solutes in the upper right part,showing negative segregation.(1)After adding Cr,the segregation of solute C weakens.The degree of segregation of C in the ternary alloy is less than that in the binary alloy.(2)The segregation of solute C is more serious than that of solute Cr.This is because the average distribution coefficient of C is higher than that of Cr.(3)The segregation result of Partical Equilibrium approximation combined with Para-Equilibrium pproximation coupling macro transmission is more serious than the Lever Rule.