Effect of cooling rate on the hot ductility of boron bearing steel during continuous casting (Study for prevention of corner crack on continuous casting slab)

Abstract

During the continuous casting of boron-bearing steel, the corner cracks on the slab are formed by deformation with low strain rate and rapid cooling at the unbending temperature within the range of 800-1,000 degrees C. Especially, the rapid cooling in the corner of slab during the continuous casting leads to as corner cracking. Therefore, in this study, the hot tensile tests applied to the different cooling rates were taken into account in order to study the effect of cooling rate on the hot ductility of boron-bearing steel. The results revealed that increasing cooling rate deteriorate the hot ductility of boron- bearing steel. Rapid decreasing of the hot ductility is caused by formation of a film-like ferrite and precipitate at the austenite grain boundaries. The morphology of the precipitates in the boron-bearing steel was monitored by PTA (Particle Tracking Autoradiography) and TEM, we observed MnS and BN compound and their morphology was quite different depending on the cooling rates. When the cooling rate is increased, rod-shape MnS and BN precipitates can be formed along the austenite grain boundaries. It can cause that weakening the boundary region and decreasing the hot ductility of boron-bearing steel.