SELECTION OF EUTECTIC CARBIDES IN MULTI-COMPONENT HIGH SPEED STEEL TYPE CAST IRONS

摘要

High speed steel type cast iron to maintain high wear resistance and fracture toughness is necessary to control eutectic carbides, MC, M_2C, M_7C_3, M_6C and M_3C. To predict carbide formation under certain solidification conditions of multicomponent cast iron, quantitative eutectic selection criterion is needed. Interface undercooling, ΔT, for eutectic growth was given as a function of growth rate, V; ΔT = kV~(1/2) Interface temperature of each eutectic carbide formed in Fe-M-C (M; Cr, V, Mo) systems; γ+M_3C and γ +M_7C_3 eutectics in the Fe-C-C system, γ +VC eutectics in Fe-V-C system and γ+M_6C and γ+M_2C eutectics in Fe-Mo-C system, was measured during unidirectional solidification. The k values of eutectic carbides were then estimated. Relationship between k, carbide spacing and growth rate was discussed. Application of k values obtained in ternary systems to the eutectic selection map and also to more multicomponent systems was discussed.