Effect of molybdenum content on subcritical heat treatment behaviour of hypoeutectic 16 and 26 wt-% chromium cast irons

Hypoeutectic high chromium cast irons containing 16 and 26 wt-% Cr, with and without Mo, were prepared to clarify the variation of hardness and volume fraction of retained austenite (V gamma) during subcritical heat treatment. As cast specimens were held at temperatures between 773 and 973 K for 21.6 ks (6 h) and air cooled with a fan. Hardness and V gamma values were measured in all specimens. In the subcritically heat treated state, secondary hardening similar to hardened tempered alloy cast irons and steels was observed. V gamma decreased gradually with rising temperature. The maximum hardness levels following subcritical heat treatment were obtained at temperatures between 823 and 873 K. The greatest improvement, an increase of 140 HV30, was obtained in 16 wt-% Cr cast iron with 3 wt-% Mo.