Effect of pre-annealing heat treatment on destabilization behavior of 28 wt. % Cr-2.6 wt. % C high-chromium cast iron

Abstract

In the present work, the effects of pre-annealing heat treatment on microstructure and hardness in destabilized 28 wt. % Cr-2.6 wt. % C high-chromium irons have been investigated by X-ray diffraction, light microscopy, and scanning electron microscopy. As-cast specimens were annealed at 800°C for 4 h, and then furnace cooled. Destabilization after annealing was carried out at 1000°C for 2 and 4 h, followed by forced air-cooling to room temperature. Vickers macro-hardness was measured on specimens from each condition. The results revealed that the as-cast microstructure consisted of primary austenite dendrites with an interdendritic eutectic structure of M7C3 carbide and eutectic austenite. The eutectic austenite had partially transformed to martensite during cooling in the mold. During annealing at 800°C, austenite converted to carbides + ferrite and some pearlite. The hardness decreased from 507 to 425 HV30. Destabilization led to precipitation of secondary carbides and transformation of dendritic and eutectic austenite to martensite with some retained austenite. After destabilization, the macro-hardness increased from 736 HV30 in the iron without prior annealing up to 843 HV30 in the iron with annealing plus destabilization. For maximum hardness, prior annealing reduced the destabilization time from 4 to 2 h.