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Soft reduction has been proved to be the most promising way to minimize centre segregation together with the strand centre porosity elimination,through which the negative pressure driven residual melt flow could be balanced by a reasonable reduction amount to compensate the centre solidification shrinkage in the crater mushy zone.The optimum soft reduction amount to bloom casting for given heavy railway steel has been studied in the paper,in which a solidification analysis model and a thermal-mechanical coupled FEM model were developed to determine the reduction amount based on the local shrinkage in the final solidification stage,along with the consideration of the deformation state.The volume shrinkage in the centre interdendritic region has been quantitatively calculated through the evaluation to the changing melt density.The squeezing effect of the soft reduction on the centre mushy zone at various solid fractions was revealed quantitatively as well.The results shown that the theoretical soft reduction amount,from the point of view of the volume shrinkage compensation,should decrease from 12.2 mm to 4.0 mm corresponding to the solid fraction from 0.3 to 0.9.A new definition for the calculation of the internal soft reduction efficiency was proposed and compared with the conventional one.The nomogram for the determination of optimum soft reduction has been presented for the bloom casting at various centre solid fraction upon the implementation of soft reduction.Accordingly,an optimized soft reduction practice was determined for quality high speed railway steel production with clearly improved strand soundness.