Achieving optimum properties in ultrahigh-strength low-alloy steel

Abstract

The effects of cyclic austenitization treatments, coupled with intermediate tempering, on the mechanical properties of 300M steel have been studied. The results obtained for these modified heat treatments have been compared with those for the conventional 1143 and 1473 K austenitization treatments. Although cyclic treatment refined the prior austenitic grain size and increased the yield strength, the plane-strain fracture toughness decreased. The introduction of an intermediate tempering treatment between the two-cycle austenitization treatments improved plane-strain fracture toughness as well as the yield strength, while the impact toughness and ductility either remained the same or increased. The improvement in the mechanical properties is attributed to prior austenitic grain-size refinement and to precipitation of carbides during the intermediate tempering stage and the subsequent partial dissolution of these carbides during re-austenitization