Abstract
In (Fe, Ni)-Cr-C alloys, with Fe replaced by 25 mass%Ni–70 mass%Ni in high-chromium cast irons, the effects of Ni content on the solidification structure, solidification sequence, and liquidus surface diagram were investigated.
The microstructures of alloys consist of matrix and M7C3 carbides precipitated as primary and/or eutectic crystals. They resemble general high-chromium cast iron except for mostly austenitic matrix. According to EDS analyses of alloy contents in each phase of specimens, the Cr content in M7C3 carbide increases concomitantly with increasing Ni content, but that in γ exhibits almost no change.
Solidification begins by crystallization of primary austenite (γ) in hypoeutectic alloy and that of primary M7C3 carbide in hypereutectic alloy. Either case is followed by precipitation of (γ+M7C3) eutectic. However, graphite precipitates from melt in the alloys with high-C or high-Ni content and its precipitation region shifts to the low-C–high-Cr side as the Ni content increases. The (γ-M7C3) eutectic line on the liquidus surface diagram moves strongly to the low-C side with increased Ni content, but it returns to the high-C side when Ni contents become greater than 50 mass%. The diagrams produced using thermo-Calc software resemble those constructed based on experimental results.
