FEM Analysis of Soft Reduction Amount and Its Internal Reduction Efficiency for Continuous Casting Railway Blooms

摘要

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 for a heavy railway bloom casting has been studied in the paper, in which a solidification analysis model and a thermal-mechanical coupled elastic-visco-plastic FEM model were developed to determine the reduction amount based on the local shrinkage in the final solidification and the overall thermal deformation. The volume shrinkage in the centre interdendritic region has been 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 showed 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 oplimum soft reduction has been presented for the bloom casting at various centre solid fraction. Accordingly, an optimized soft reduction practice was determined for high speed railway steel production with improved strand soundness.