Control of Carbides and Graphite in Cast Irons Type Alloy’s Microstructures for Hot Strip Mills

Abstract

The carbide and graphite formation and redistribution of alloy elements during solidification were investigated on high-speed steel (HS) and Ni-hard type cast irons with Nb and V. The crystallization of hypereutectic HSS proceeds in the order of primary MC, γ + MC, γ + M 6 C, γ + M 7 C 3 , and γ + graphite eutectic, in hypoeutectic alloys proceeds in the order of primary γ, γ + MC, γ + graphite, γ + M 6 C, and γ + M 7 C 3 eutectic, and in Ni-hard proceeds in the order of primary γ, γ + MC, γ + M 3 C, and γ + graphite eutectic. The γ + graphite eutectic solidifies with the decrease of V, Nb, and Cr and the increase of Si and C contents in residual liquid during solidification. The behavior in graphite forming tendency in the residual liquid is estimated by the parameter ∑ C L i m i ′ . The eutectic graphite crystallizes at the solid fraction when ∑ C L i m i ′ takes a minimum value. The amount of graphite increases with the decrease in ∑ C L i m i ′ of initial alloy content in both specimens. Inoculation with ferrosilicon effectively increases the graphite content in both specimens.