Mechanism of Formation and Method of Detection of Breakout Caused by Sticking between Mould and Slab in Continuous Casting of Steel

Abstract

A sticking type breakout in continuous casting which is distinguished from the ordinary one caused by buldging at the thin shell of slab corner, was investigated in regard to the effect of operation factors, mechanism, and method for detection.
The breakout occurred more frequently after changing the plating material of the mould from Cr to Ni. The breakout frequency decreased by using mould powder with lower viscosity. The thickness of the shell remained in mould after breakout was thicker near meniscus than that at the lower position and then increased downwards. A part with very thin or ruptured shell, which was defined as "constricted line", is formed in an inclination of 30° to 45° downwards to horizontal. The breakout occured at a position where the constricted line crossed the exit line of mould. Ripple marks with narrow pitch formed on the surface of both sides of the constricted line in parallel with the constricted line.
On the basis of the results, a mechanism of this kind of breakout was proposed, that is, the breakout is caused by sticking between mould and slab near meniscus due to lack of mould slag inflow. Two kinds of detection system of the breakout were developed.