Formation of MnS-type Inclusion in Steel

Abstract

The formation mechanism of MnS-type inclusion in steel was investigated on the basis of the experimental results with the effects of sulfur content and cooling rate on the morphology of sulfide, the relation between the solidification structure and the distribution of sulfides, and the observation of formation process of sulfide in steel quenched from various temperatures.
As the result, it became clear that the sulfide which formed an eutectic colony (type II according to SIMS' classification) was increased with the sulfur content in steel and the cooling rate, observed mostly in the region solidified lastly and formed in contact with the melt at the final period of solidification, and also that the non-colony type sulfide (type I, type III and so on) was hardly affected with the sulfur content in steel, decreased as an increase of cooling rate, observed mainly around a dendrite and increased remarkably after the finish of solidification.
These results can be explained rationally by an idea that the colony type sulfide is formed by the eutectic reaction while the non-colony type sulfide is formed as the precipitate from the solid steel.