Effects of V and Nb additions on high temperature deformation properties of low alloy martensites

Abstract

The effects of microalloying elements such as V and Nb on the high temperature deformation properties of low alloy martensites have been investigated by means of slow strain rate tensile tests at various temperatures. It was confirmed that the precipitations of fine carbonitrides, such as V(C.N) and NbC, are quite effective in reducing the high temperature ductilities. In particular, it has been concluded that the most detrimental effects on ductility arise from the dynamic trapping of the mobile dislocations generated at prior austenite grain boundaries by the simultaneous precipitation of V(C.N) or NbC. The cyclic repetition of such a process would result in strain concentration in the vicinity of prior austenite grain boundaries, and microvoids would form at the cementite/matrix interfaces on these boundaries, leading to intergranular ductile fracture.