Effect of Deoxidizing Element on the Hot Ductility of Boron-Containing Steel

Abstract

Improving the surface quality of the casting slab increases the productivity of steel. The slab surface sometimes has transverse cracks along a grain boundary when the slab is bent and/or unbent around the transformation temperature from the austenite to ferrite phases. In particular, for boron-containing steel, the defect is strongly influenced by the precipitation of BN on the grain boundary. In this study, the effect of deoxidizing elements, such as aluminum, calcium, and zirconium, on the hot ductility of boron-containing steel have been investigated fundamentally. The addition of zirconium or calcium improves the hot ductility of boron-containing steel by comparing with that of aluminum. An oxide containing calcium or zirconium acts as a more effective nucleus for BN precipitation than alumina, and the excess precipitation of BN on the grain boundary is suppressed. This improves the hot ductility of boron-containing steel in the region of single-phase austenite. Moreover, the hot ductility of Al+Zr-added steel is the best, even in the region of coexisting austenite and ferrite phases, because the precipitation of ferrite (α-Fe) on the grain boundary is suppressed compared to that of Al+Ca-added steel.