Analysis and prevention of microcracking phenomenon occurring during strip casting of an AISI 304 stainless steel

Abstract

This study was concerned with the effects of microstructural parameters on the microcracking phenomenon occurring during strip casting of an AISI 304 stainless steel. Detailed microstructural analyses of the microcracked regions showed that microcracks were formed mainly along tortoise-shell-shaped depressions and that their number and size were considerably reduced when strip casting was done right after a shot-blasting or pickling treatment of the casting roll surface. This microcracking phenomenon was closely related to the formation of a black oxide layer, which was mainly composed of manganese-rich oxides, on the roll surface. The black oxide layer acted as a barrier of thermal transfer between the rolls and melt, led to an increased gas gap and inhomogeneous solidification of cast strips, and, thus, played a role in forming both tortoise-shell-shaped depressions and microcracks on the strip surface. The installation of brush rolls behind the casting rolls was suggested as a method to prevent microcracks, because the brush rolls could continuously scrape off the black oxide layer affixed on the roll surface during strip casting.