Microstructure and properties of high chromium cast irons: effect of heat treatments and alloying additions

Abstract

Different combinations of critical and subcritical heat treatments variously modify the initial as cast microstructure of high chromium white cast irons leading to secondary carbide precipitation of different extent and nature. Destabilisation (critical heat treatment) of austenite at 970°C for 2·5 h followed by annealing (subcritical heat treatment) at 600°C for 13 h results in massive precipitation of M23C6 carbide particles along with spheroidised M7C3. The reversed order of heat treatments leads to extensive precipitation of M7C3 secondary carbide particles. Mo has a favouring effect on the hardness of the microstructures containing pearlite by limiting pearlite formation. The gradual increase in the alloying additions, C and Cr, increases the hardness of the materials at the different treatment states by inducing carbide precipitation. The increase in the Si content leads to the opposite effect by favouring pearlite formation.