TEMPERING BEHAVIOR OF A DUAL-PHASE LOW-ALLOY STEEL

The tempering behaviour of a dual phase steel of 0.08% C, 1.21% Mn, 1.00% Si, 0.42% Cr, and 0.41% Mo composition with two different martensite contents of 30 and 52%. (obtained by intercritical treatments at 820 and 860-degrees-C, respectively) has been studied. The ultimate tensile strength decreased and percentage elongation increased continuously with increasing tempering temperature up to 600-degrees-C for both intercritical treatments. The yield strength has, however, increased up to 300-degrees-C, beyond which it decreased for the steel with 30% martensite. In contrast it remained almost constant for 52% martensite up to 300-degrees-C, beyond which it decreased. The martensite of dual-phase steel for both the intercritical treatments has undergone microstructural changes on tempering that are akin to those of fully martensitic low carbon steels. The SEM fractographs from the as-quenched specimens indicate that the tensile specimens failed by microvoid coalescence with the martensite areas appearing facetted and featureless while those for 600-degrees-C tempered condition by the formation of equiaxed dimples.