Effect of destabilization heat treatment on the microstructure and wear properties of ASTM A532 high-chromium white cast iron
Abstract
This study investigates the effect of molybdenum (Mo) content on the microstructure, hardness, and wear resistance of ASTM A532 eutectic high-chromium white cast iron (HCCI) subjected to destabilization heat treatment with different cooling paths. Three alloys containing 1.23%, 1.395%, and 1.86% Mo were destabilized at 995°C and held for sufficient soaking time to promote secondary carbide precipitation and matrix transformation. After heat treatment, the specimens were subjected to several cooling routes, including still-air cooling, furnace cooling, oil quenching, and water quenching, to evaluate the influence of cooling rate on the resulting microstructure and wear behavior. Following cooling, all specimens were tempered at 400°C to relieve residual stresses and stabilize the martensitic matrix. Microstructural analysis revealed that increasing Mo content promoted fine secondary carbide precipitation and improved matrix hardenability, while the cooling path significantly affected carbide distribution and martensite formation. Faster cooling paths such as oil and water quenching enhanced martensitic transformation and hardness, whereas slower cooling produced comparatively softer matrices with coarser carbides. Excessive Mo addition increased the fraction of primary \mathrm{M_7C_3} carbides at the expense of martensite formation. Abrasion testing according to ASTM G65-16 demonstrated that the alloy containing 1.86% Mo exhibited the best wear resistance, with a minimum volume loss of 9.03 mm³, due to the combined effect of a high primary carbide fraction (40.72%) and dense secondary carbide precipitation. In contrast, the medium-Mo alloy (1.395%) showed higher wear loss (29.69 mm³) because of its lower carbide content and reduced hardness. The study confirms that both Mo content and cooling path during destabilization heat treatment play critical roles in controlling carbide morphology, martensite stability, hardness, and ultimately the abrasive wear performance of HCCI alloys.