Research And Application Of Solidification Structure And Composition Homogeneity Of Continuous Casting Bloom For Heavy Rail Steel

Rail steel is the important backbone of high-speed train and its quality seriously affects the development of high-speed train.Promoting the homogenization of solidification structure and composition is beneficial to stabilize the mechanical property of rail steel.In order to achieve the high even solidification structure and composition in rail steel,laboratory tests,numerical simulation and industrial test were performed in a native factory.The solification structure detection,three-dimensional MnS inclusions morphology testing,numerical simulation of solidification structure,numerical simulation of micro solute segregation and MnS inclusions precipitation behavior were investigated.Industrial experiments,such as cooling water flowrate of mold,M-EMS and water flowrate of secondary cooling were carried out.The MnS inclusions precipitation behavior was detailed analyzed and the key control measures of MnS inclusions in rail steel were proposed.Solidification structures of blooms in rail steel U75V were analyzed by dendritic structures corrosion technology.Also a mathematical model was established to predict the solidification structure of rail steel.The influences factors on solidification structures of bloom,such as superheat,casting speed,water flowrate of secondary cooling and cooling water flowrate of mold were calculated using the model and the solidification behavior was obtained on the condition of different influence factors.The temperature field,secondary dendritic arm spacing and CET position were obtained.The MnS inclusions precipitation model was established.The influence factors on MnS size,such as different sulfur content,different solidification structures and different cooling speed were calculated using the model.When the sulfur content was less than 0.003wt%,MnS inclusions could not precipitate during the solidification process of rail steel U75V.When the sulfur content changed from 0.003wt%to 0.010wt%,precipitation amount of sulfur changed from 8.6%to 51.9%.When the sulfur content was 0.20wt%,precipitation amount of sulfur was up to 70.1%.The level of MnS inclusions could satisfy the requirement less than 1.5 levels when the sulfur content was not more than 0.008wt%.When the solidification structure was small,the secondary dendritic arm spacing was small with less precipitation amount of MnS inclusions.The calcium carbide was suggested to use in ladle slag in rail steel melting process.Tests results show the ratio of sulfur contents in rail steel with less than 0.008wt%was 92.54%.It was improved by 8.29%with the comparison with previous technology that is only 84.25%.The average of desulfurization rate from converter end to RH refining end was 39.78%and it was improved by 19.17%with the comparison with previous technology that is only 20.62%.The oxidability of slag at LF refining end was 1.19%in average.The basicity of slag at LF refining end was 2.94 in average.The industrial experiments with different continuous casting parameters were carried out.The relation between precipitation ratio of MnS inclusions and water flowrate in mold,M-EMS and t water flowrate in secondary cooling were analyzed.The relation between homogenization of solidification structures and casting parameters were analyzed too.It can be obtain bigger the equiaxed crystal area with 350A current strength of M-EMS.The High water flowrate in mold and in secondary cooling were benefit to reduce the segregation of bloom.The little size MnS inclusions precipitation(diametere not more than 4um)was promoted but the big size MnS inclusions precipitation(diametere more than 10um)was inhibited through the above mentioned technology.Finally,the MnS inclusions levels can be decreased.