COMPARATIVE STUDY OF THE MICRO-STRUCTURE OF QUENCHED, SELF-TEMPERED AND ORDINARY STEEL

Micro-structural study of two different grade-60 steel samples, the ordinary and Quenched and selftempered steel (QST) has been carried out. Ordinary steel is cooled in air right after it comes out of final pass or finishing stand while QST steel is quenched by intensely spraying water for very short time span after the final pass. Consequently a thin martensitic layer is formed on the surface while the core remains hot and austenitic. After this, the exterior is self-tempered by the heat flow from the interior. Thus the micro-structure of QST and ordinary steel is same in the interior while it is different in the exterior region. Interior of both steel bars comprise ferrite-pearlite, but exterior of QST steel is tempered martensite and ferrite-pearlite for ordinary steel bar.