| This study aims at investigating the effect of chromium and molybdenum addition on wear resistance and fracture toughness in duo-cast alloys which consisted of a high-chromium white cast iron and a low-chromium steel as a wear resistant part and a ductile part, respectively. Different shape, size, amount, and distribution of M_7C₃ carbides were employed to the wear resistant part by changing the amount of Cr and Mo. In the alloys containing a large amount of Cr, a number of large hexagonal-shape primary carbides and fine eutectic carbides were formed. These large primary carbides were so hard and brittle that they were easily fractured or fallen off from the matrix, thereby deteriorating wear resistance and fracture toughness. In the alloys containing a smaller amount of Cr, however, a network structure of eutectic carbides having lower hardness than primary carbides was developed well along solidification cell boundaries, and led to the improvement of both wear resistance and toughness. The addition of Mo also helped enhancing wear resistance by forming additional M₂C carbides. Under the duo-casting conditions used in the present study, the appropriate compositions for wear resistance and toughness were 17∼20% of Cr and 2-3% of Mo. |
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