Solidifying shell waviness during continuous casting of AHSS slabs

Abstract

Transverse cracking of continuously cast products has been encountered at almost every caster operation. Enormous efforts have been carried out in the past aiming at identifying the cause and reducing the problem, especially on steel grades with peritectic chemistries. So far, however, there is still no cost-effective solution with good trade-off for internal quality and productivity. In this study, a new cracking formation mechanism is proposed based on observations of equally spaced crack pattern and the undulation (shell thinning pattern) observed on the inside and/or outside (surface depression) of the breakout shell with similar spacing. This wavy solidification shell forms at initial solidification stage and induces the local shell thinning and reheating which in turn causes the local “Blown grains” inside the solidification shell. As observed on slab surfaces, these blown grains are closely related to transverse cracking problem.