Promoting in situ formation of core‐shell structured carbides in high‐Cr cast irons by boron addition

Abstract

AbstractM7C3 carbide is an important reinforcing phase in high‐Cr cast irons, ferrous alloys, metal‐matrix composites, and hardfacing overlays. However, the mismatch at the carbide/matrix interface due to the differences in structure and mechanical strength between the carbide and metallic matrix may lower the resistance of the material to mechanical attack, such as wear, corresponding to increased risk of interfacial failure or the role of the interfacial mismatch as a stress raiser for crack initiation. Recent studies on high‐Cr cast irons (HCCI; Fe‐45%Cr‐%C series) show that core(M7C3)‐shell(M23C6) structured carbides (CSSCs) help minimize the misfit stress at the interface between carbide and matrix, thus enhancing their resistance to wear. However, such core‐shell structured carbide does not always form. It is of importance to understand the mechanism responsible for the formation of CSSC for maximized benefits. In this study, we conducted thermodynamic analysis to investigate the conditions for in situ forming CSSCs in HCCIs and determine the probability of generating CSSCs through alloying elements. Both thermodynamic analysis and first‐principles calculations demonstrate that the core‐shell structured carbide can be in situ formed in HCCIs by alloying with elements such as boron, which increases the stability of M23C6 with lowered energy. Relevant experiments were performed to verify the theoretical analysis and prediction.