2007 Volume 79 Issue 12 Pages 726-731
In (Fe, Ni)-Cr-C alloys which are substituted by 25massNi% to 70mass%Ni for Fe in high chromium cast irons, the effect of Ni content on the solidification structure, solidification sequence and liquidus surface diagram was investigated.
It was found that the microstructures of alloys consist of matrix and M7C3 carbides precipitated as primary and/or eutectic crystals, and that they are similar to general high chromium cast irons except for mostly austenitic matrix. According to the EDS analysis of alloy content in each phase of the specimens, Cr content in M7C3 carbide increases by increasing the Ni content but that in γ has almost no change.
Solidification begins by crystallization of primary austenite (γ) in hypoeutectic alloy and that of primary M7C3 carbide in hypereutectic alloy, and is followed by the precipitation of (γ+M7C3) eutectic in both cases. However, graphite precipitates from melt in alloys with high C or high Ni content and its precipitation region shifts to the low C-high Cr side as Ni content increases. The (γ-M7C3) eutectic line on the liquidus surface diagram moves considerably to the low C side with an increase in the Ni content, but it returns to the high C side when the Ni content exceeds 50mass%. The diagrams obtained by the Thermo-Calc software are found to be close to those constructed using experimental results.
