AN INVESTIGATION ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF QUENCHED AND TEMPERED SS440C MARTENSITIC STAINLESS STEEL

440C steel is a high- carbon martensitic stainless steel with excellent mechanical properties. This paper describes the relative effect of various austenitizing temperature and tempering temperature on the microstructure and mechanical properties of 440C martensitic stainless steel. Solution treatment was carried out at 1150°C for 1 hr, followed by reheat at 1100°C and 30 minute holding. Then, tempered at various temperatures for 1 hr. In the As-quenched sample the microstructure contains undissolved carbide M7C3 with retained austenite in a matrix of un-tempered martensite while as the austenitizing temperature increase, the size of the austenite grain also increases with decrease in the mechanical properties. Hardness test found out that tempering at 500°C resulted in maximum hardness value of 564HV. However, the hardness of the as-quenched sample was 765HV. Tensile test at 500°C tempering temperature showed Y.S of 2100MPa and UTS of 2178MPa. As comparison, the as-quenched sample showed Y.S of 1300MPa and UTS 1507MPa. It is believed that secondary hardening phenomenon occurred while tempering and influence the value of hardness and tensile strength of the 440C steel