Precipitation Behavior of Fine MX Type Carbide in Cr-Mo Steels

Abstract

This study deals with the influence of Ti addition on softening behavior of the martensite structure and precipitation behavior for 2 1/4Cr-1Mo-V steel. The fine MX type (Mo, V) C and (Mo, V, Ti ) C precipitate with heat treatment at from 600 to 700 deg. C after cooling from 1350 deg. C. These fine carbides coarse with the solute and precipitation of V, then the composition of carbides change to V-rich. (Mo, V, Ti) C in Ti-bearing steel keeps fine size even after long time heat treatment at high temperature. It is difficult to understand the retardation of coarsening of (Mo, V, Ti) C by Ostwald ripening theory. We therefore propose a hypothesis that (Mo, V, Ti) C is consequently maintained at fine size without coarsening by Ostwald ripening theory because the fine (Mo, V, Ti) C is practically insoluble due to very low solubility of Ti at heat treat temperature.