Destabilization Treatment and Its Influence on Microstructure and Matrix Hardness of High-Cr Cast Iron

High-chromium cast irons are an essential class of wear-resistant materials commonly used for wear-resistant applications in the mining and steel industries. There is ongoing debate on the secondary carbide types and their formation sequences during heat treatment. This work examines the microstructural evolution during destabilization treatment of a hypoeutectic high-chromium cast iron containing 2.2 wt pct C and 16.5 wt pct Cr. Starting from an inhomogeneous as-cast microstructure consisting of ~ 28 pct M7C3 eutectic carbide and a mixed matrix of martensite and retained austenite, destabilization treatments resulted in the establishment of near homogeneous structure with a near equilibrium level of carbon concentration in the matrix, which fully transformed to martensite upon cooling. Homogeneously distributed M23C6 secondary carbides with a square-shaped morphology and 100 to 500 nm in size precipitated during heating up to the destabilization temperature. For higher destabilization temperatures (1000 °C), M7C3 secondary carbides formed together with M23C6 and were identifiable by a distinctly different morphology (elongated). It was found that the carbon content of the matrix, a function of the destabilization temperature and subsequent eutectic carbide dissolution, controls the martensite start temperature and has a dominating influence on bulk-hardness.