Formation of Manganese Sulfide in Steel

Abstract

Manganese sulfides in low carbon steel were grouped into a colony type (type II according to Sims' classification) and non-colony type (type I, type III and type X). The formation mechanisms of both types were investigated on the basis of the experimental results with the effects of sulfur content and cooling rate on the morphology of sulfides, the relation between the solidification structure and the distribution of sulfides, and the observation of formation process of sulfides in steels quenched from various temperatures.
Though the colony type sulfide was increased with the sulfur content and cooling rate, the non-colony type sulfide was hardly affected by the sulfur content but decreased with an increase of cooling rate. The former was observed mostly in interdendritic space and formed in contact with a melt at a final period of solidification, while the latter was observed mainly around a dendrite and increased remarkably after solidification.
These results can rationally be explained by the mechanisms that the colony type sulfide is formed by the eutectic reaction and the non-colony type sulfide is formed as a precipitate from the solid steel.