Influence of Thermal Treatment on Microstructure and Hardness of Niobium Alloyed PM-Tool Steel.

This work describes carbides present in the tool steel containing 2.5% C, 3.3% Si, 6.2% Cr, 2.2% Mo, 2.6% V, 2.6% Nb, 1.0% W, prepared by the powder metallurgy (PM) process. The influence of thermal treatment conditions on carbide behavior is investigated. During austenitization, some dissolution of M7C3 occurs, while MC carbides are thermally stable. So, the quenched steel is composed of two types of carbides: chromium rich M7C3 and niobium rich MC, besides martensite and retained austenite. During tempering of the hardened steel at the temperatures above 480°C, the precipitation of very fine carbides and martensite recovery occur, which results in secondary hardening. Precipitated particles are predominantly vanadium and molybdenum rich MC, M2C, and M6C carbides. [ABSTRACT FROM AUTHOR]