Quenched and Tempered Steel; Microstructure, Mechanical Properties, Magnetic properties; NonDestructive Evaluation
A TRIP assisted steel was subjected to austenitization above Ac3 at 920°C to generate >98% martensite and inter critical austenization at 810°C to generate about 50% ferrite along with >48% martensite with retained austenite in both the case, tempered in the temperature range between 150 and 650°C. The former hardened and tempered steel show a fully tempered martensite while latter one shows significant ferrite coexisting with tempered martensite. In both conditions, superior mechanical properties (tensile toughness >20 GPa. %) were observed when tempered below 300°C. High Si, shifts the tempered martensite embrittlement to higher temperatures and suppresses the carbide formation and retains austenite laths within the tempered martensite that enhances properties. Magnetic hysteresis loop measurements were carried out at each stage and coercivity showed a strong correlation indicating precise non-destructive magnetic evaluation of tensile strength through a portable magnetic hysteresis loop tester.