Mechanism of Formation of Surface Defects in Continuously Cast Stainless Steel Slabs Containing Titanium

Abstract

An investigation was carried out on surface defects in continuously cast stainless steel slabs containing titanium. Factors affecting the formation of two main surface defects, i.e. crust defects and cluster defects were examined. Furthermore, a study was made on the mechanism of formation of crusts at the meniscus in the mould.
1) Two causes are pointed out for the fact that crusts are apt to form in these steels; a) titanium nitride inclusions in the molten steel act as effective substrates for the nucleation of solidified steel, and b) they react with iron oxide in a mould powder to form nitrogen gas blow holes which lower apparent thermal diffusivity of the molten steel.
2) Cluster defects were formed by two different mechanisms; large size of cluster defects were originated from a piece of build-up in the tundish nozzle, and those of small size are caused by accumulation of the in-clusions at a certain position of the meniscus.