Beneficial Effects of the Core-Shell Structure of Primary Carbides in High-Cr (45 wt%) White Cast Irons on Their Mechanical Behavior and Wear Resistance

High-chromium cast irons (HCCIs) are widely used in many industrial processes involving wear and corrosion, such as oil sands mining and slurry handling in the oil sands industry. In very harsh mining environment and severe working conditions, conventional HCCIs, however, often exhibit a short service life. Great efforts have been made to improve the performance of HCCIs. One of the trials is to extend the chromium content to a higher level, e.g., 45 wt%, and widen the carbon content to a range of 1-6 wt%. In this study, we investigated the wear behavior of 45-series (Fe-45 wt% Cr with 1-6 wt% C) and observed that 45-4 HCCI (Fe-45 wt% Cr-4 wt% C) had the highest hardness and exhibited remarkably high resistance to abrasion and erosion. Microstructure analysis showed that the primary carbides in 45-4 had a core-shell structure. The outer shell was M23C6, while the inner core was harder M7C3, confirmed by the EBSD technique. The ferrous matrix was eutectic colony with martensite and fine M23C6 carbides. Micro-mechanical probing in combination with finite element analysis demonstrated that the core-shell structure helped reduce the interfacial stress, thus enhancing the hardness and overall wear resistance of the material.