Modelling And Simulation Of Macrosegregation In Large Steel Ingots By A Multicomponent And Multiphase Model

Many large key forging components of heavy equipment are manufactured by large steel ingots.The quality and production capability of large steel ingots are critical to national economy and security.Macrosegregation,as the main defect of large steel ingots during solidification cannot be alleviated by downstream forging process.Hence it will deteriorate the final mechanical properties of the final components.Therefore,the prediction of macrosegregation during the solidification of large steel ingots based on simulation technology is of great importance in academic significance and engineering application.A multicomponent and multiphase model had been developed to predict macrosegregation in steel ingots.The solid,liquid and air phase are the basic hydrodynamic phase,and the macroscopic mass,heat,momentum and species transfer are coupled with the microscopic descriptions of solid grains nucleation and growth.The thermo-solutal buoyancy,grains sedimentation,and shrinkage-induced flow are taken into account.The interfacial solute constraint relations are derived to close the model by solving the solidification paths in the multicomponent alloy system.The flow prediction accuracy ofnumerical code was validated by the skew lid driven flow and natural convection benchmarks.Besides,the model was applied toan upward unidirectional solidification case of a ternary Al-6.0 wt.%Cu-1.0wt.%Si alloy and a cavity solidification case of Pb-48 wt.%Sn alloy.Comparisons between current predictions and measurements were made,and general good agreements were exhibited.A 36 tons steel ingot was cast and analyzed.Temperature variations at specific positions of mould and ingot were recorded,and the concentration distributions of carbon and sulphur on the ingot longitudinal section were constructed with measurements.The temperature variations were utilized to calibrate the interfacial heat transfer coefficients between the mould and the ingot for the numerical simulations.The concentration measurements had covered the whole longitudinal section of the 36 ton ingots.The multicomponent and multiphase model was applied to predict the macrosegregation of different elements in the 36 tons steel ingot.The effects of shrinkage-induced flow,the thermo-solutal convection and the grains sedimentation were investigated.In order to improve the prediction accuracy,non-orthogonal grids were adopted for the better geometry boundary fitness of ingot.With consideration of the third element(sulphur),the accuracies of predictions along the centerline to the measurements had been improved.Then a three dimensional and ternary alloy macrosegregation simulation had been conducted.Predictions had reproduced the macrosegregation patterns as the measurements.Confidence levels of current predictions by the concentration measurements had been provided.General good agreements were exhibited in quantitative comparisons between measurements and predictions of carbon and sulphur variations along selected positions of ingot.Concentration measurements on the longitudinal section of a 231 tons ingot bottom were analyzed.Predictions by current model were compared with measurements.The results indicated that it is essential to consider the effects of multicomponent elements for improving prediction accuracies.Furthermore,the multicomponent macrosegregation in a 535 tons steel ingot was predicted.