Analysis of Microcracks Formed during Strip Casting of AISI 304 Stainless Steels

摘要

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