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To further investigate the relationship between fracture toughness of M2B and wear resistance of Fe–3.0 wt% B cast alloy, the taper-section and worn surface after mild etching have been observed. Fig. 13 exhibits the mild etching worn surfaces of A0 and A3. As shown in Fig. 13a, a large number of cracks and broken borides arise on M2B for A0 specimen after micro cutting by SiC abrasive. By contrast, there is nearly no crack existing on the mild etching of the worn surfaces of A3 specimen. Fig. 14 exhibits the micrographs of the taper-sections through the worn surfaces of A0 and A3 specimens. In Fig. 14a and b, the lower left parts show the etched section of substrate and the upper right parts show the abraded surface. By observing the scratched grooves on the upper right worn surfaces, it can be concluded that the main wear mechanism of Fe–3.0 wt% B cast alloys is micro cutting. During the process of abrasive wear, SiC abrasive will shovel off the matrix and boride together under certain load. From Fig. 14a, it can be seen that lots of cracks distribute on boride in the subsurface after plowing by abrasive particles. In Fig. 14b, there is hardly crack coming into being on M2B. To explain the phenomena in Figs. 13 and 14, a corresponding physical model is established (Fig. 15). As shown in Fig. 15a, when abrasive particle impresses into M2B, cracks will occur on boride under external pressure if fracture toughness of the boride is too poor. Moreover, when abrasive particle scratches the specimen surface under high load, cracks will also come into being in M2B grains due to friction force and extrusion force from abrasive particles (Fig. 15a). On the other hand, if the boride possesses a better fracture toughness, nearly no crack will appear on M2B grains during the processes of indentation and micro cutting by abrasive particles, as shown in Fig. 15b.