Descalability on Reheated Steel Slabs at High Temperature

Abstract

The mechanism of descaling at high temperature was investigated from the analysis of operation factors in plate rolling shop and the study of scale properties oxidized at high temperature. The descalability of Si-killed steels was inferior to semi-killed steels, because their sensitivity of scale cracking on air cooling was more than on semi-killed steels. The state of cracks in scale on air cooling controlled the descalability of steels. The oxide scale of Si-killed steels including large pores cracked easily but these cracks usually stopped at large pores which were at nearly half thickness of scale. At descaling by the hydraulic scale breaker, the cracks propagated in the scale parallel to the iron substrate and therefore the lower parts of scale thickness remained on the steel slab surface. On Si-killed steels, the fayalite, Fe₂SiO₄, was formed in layers at the interface of scale/iron. Under 1170°C, which was eutectic point of Fe₂SiO₄ and FeO, the fayalite became solid, and then the descalability became worth owing to the increase in adhesion of scale to iron substrate.