Problems in Solidification Model for Microsegregation Analysis of Fe–Cr–Ni–Mo–Cu Alloys

Abstract

Microsegregation of a Fe–Cr–Ni–Mo–Cu alloy was studied with the calculation model on the basis of two-dimensional concept considering diffusion of solutes during and after solidification. The calculated results were compared with the previous experimental results of the microsegregation profiles obtained by random sampling method. At first, a calculation model was created by applying two database sets of diffusion coefficients reported on Fe(γ)-X binary and Fe–Cr–Ni systems. The results using the database of the Fe–Cr–Ni systems fitted the experimental data better than those using the Fe(γ)-X systems in the region of lower solid fraction (fs). Meanwhile, in the higher fs region, the calculated lines passed below the arranged experimental data plots particularly for Cr and Mo. This inconsistency could be attributed to the following problems:

(a) Diffusion coefficients might be lower at the post solidification temperature.

(b) Partition coefficients might vary with solidification progress.

(c) The ratio of the solid/liquid interfacial area to the solid volume might vary with solidification progress.

Further, Fe contents analyzed in the previous experiments were rearranged as they simply decreased, while Cr, Ni, Mo and Cu were rearranged dependently with the Fe data at each fs point to keep the law of mass conservation. This rearrangement showed that the “slope segment” appearing in the region of fs below 0.1 in random sampling method was attributed to the probable measurement error.