Effect of Destabilization Heat Treatments on the Microstructure of High-Chromium Cast Iron: A Microscopy Examination Approach

A 18.22 wt.% Cr white iron has been subjected to various destabilization heat treatments. Destabilization at 800 °C caused gradual precipitation of M₂₃C₆ secondary carbide particles with time leading to a gradual increase in the bulk hardness. At 900, 1000, and 1100 °C, an initial sharp increase in bulk hardness with time occurred, reaching a plateau that was followed by a slightly decreasing trend. The combination of martensite formed, stoichiometry, and morphology of the secondary carbides present (mostly M₇C₃) are responsible for the obtained values of hardness. At 1100 °C, severe dissolution of the secondary carbides and consequent stabilization of the austenitic phase took place. Maximum hardness values were obtained for destabilization at 1000 °C. The correlation between bulk hardness and microstructural features was elaborated.