Improvement of centre segregation in continuous casting bloom and the resulting carbide homogeneity in bearing steel GCr15

Abstract

ABSTRACTIn the present work, solidification structure and centre segregation in continuously cast bearing steel GCr15 blooms with 220mm×260 mm were obtained by different casting conditions (M-EMS, M + F-EMS, M + F-EMS + MSR), which were systematically optimized by numerical simulation and experiments. The relationship between centre segregation in continuously cast GCr15 bloom, heredity in hot-rolled steel and carbide inhomogeneity of hot-rolled steel with was investigated comprehensively. Results showed that compared with M-EMS, centre carbon segregation ratio in the bloom decreased from 1.1∼1.4 to 1.04∼1.22 by M + F-EMS, and could be reduced to 0.96∼1.08 by MSR in combination with M + F-EMS. Moreover, centre segregation in hot-rolled steel decreased with the decrease of centre segregation in bloom. Grade of network and banded carbide in hot-rolled steel decreased accordingly, especially for centre carbon segregation ratio with 0.96∼1.08, grade of network and banded carbide could be significantly reduced to 1. It was important to control centre segregation in as-cast steel to improve the resulting carbide homogeneity of as-rolled steel. According to the experimental results, higher casting speed in bloom with M + F-EMS and MSR integrated process was preferred to effectively reduce centre segregation ratio and further decreased the occurrence of network and banded carbide in as-rolled bearing steel GC15.