Erosion–Corrosion Behavior of As-cast and Destabilized High Chromium Cast Irons with Mo and W Addition

The relationship between microstructure and erosion-corrosion behavior in 28 wt pct Cr irons with (1 to 6) wt pct Mo and (1 to 4) wt pct W addition was investigated. As-cast irons were destabilized at 1000 °C for 4 hours, and then air-cooled. Microstructural investigation and phase identification were performed by optical microscopy, scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. Vickers macro- and micro-hardness, potentiodynamic testing and erosion–corrosion behavior were investigated. The irons with 1 and 6 wt pct Mo promoted the formation of M₆C and M₂₃C₆, while the irons with 1 and 4 wt pct W caused the chemical composition to be hypereutectic promoting the formation of primary M₇C₃ and eutectic M₆C. After destabilization, the transformation of austenite to secondary carbides and martensite was observed in all the irons, with Mo or W addition promoting finer secondary carbides. During destabilization, the eutectic M₇C₃ carbides changed from M₇C₃ to a duplex M₇C₃–M₂₃C₆, core–shell structure. Vickers macro-hardness and micro-hardness in the as-cast and after-destabilization conditions were increased with increasing Mo or W addition. Secondary passivation was found in the iron with 6 wt pct Mo, suggesting secondary passive film formation. The as-cast iron with 6 wt pct Mo and the destabilized iron with 4 wt pct W exhibited the highest erosion–corrosion resistance.