High chromium cast irons show superior abrasion resistance due to their chromium carbides. Their abrasion resistance is improved by insert casting with cemented carbide. The effects of high temperature exposure during insert casting on the microstructures of cemented carbide were investigated in this research. A high chromium cast iron (2.7%C-27%Cr) and cemented carbide (WC-13.7%Co) round bars were prepared. The cemented carbide round bars were dipped in molten high chromium cast iron at 1596 K. The dipped round bars were pulled up after the elapse of 30 to 180 s. Microstructures of dipped cemented carbide round bars were changed from homogeneous sinter structure to three-layer structure, cemented carbide, diffusion layer and reaction layer. The thicknesses of the diffusion layer and the reaction layer were increased with increase of dipping time. FE-EPMA analysis revealed that the diffusion layer was formed by the elution of Co from the cemented carbide and diffusion of Fe and Cr from the molten high chromium cast iron into the cemented carbide round bar. In addition, rectangle particles were randomly distributed in the diffusion layer. The equivalent circular diameter of the rectangle particle was increased with increasing dipping time. The vickers hardness of the diffusion layer decreased about 30% relative to the cemented carbide but higher than that of high chromium cast irons. The inserted cemented carbide is thought to have contributed to improving abrasion resistance. I was suggested that thin diffusion layers are more effective for improving abrasion resistance.

  Continuous cooling transformation of plain high chromium cast iron with Cr/C value from 2 to 15 was investigated using a transformation measuring apparatus with subzero function, and the transformation behavior was clarified. Both A_C1 and nose temperature of pearlite transformation (T_P-n) rose slightly and its nose time (t_P-n) shifted to long time side with an increase in Cr/C value. When the austenitizing temperature was increased, T_P-n did not change but t_P-n moved to the long time side regardless of the Cr/C value. The relationship between t_P-n and Cr/C value can be expressed by the following equations (1). M_s and M_f temperatures rise with increasing Cr/C value and the relations can be expressed by the equations below (2). As Cr/C value increased, the maximum hardness after finishing transformation increased to the highest at 6 of Cr/C value, and then decreased in spite of subzero treatment.

  t_P-n (s) (1273Kγ) ＝ 43exp (0.3 (Cr/C))    }

  t_P-n (s) (1323Kγ) ＝ 79exp (0.3 (Cr/C))    } ― (1)

  M_s (K) (1273Kγ) ＝ 342 ＋ 8.5 (Cr/C)    }

  M_f (K) (1273Kγ) ＝ 150 ＋ 6.8 (Cr/C)     }

  M_s (K) (1323Kγ) ＝ 262 ＋ 8.0 (Cr/C)    }

  M_f (K) (1323Kγ) ＝ 143 ＋ 4.0 (Cr/C)     } ― (2)