Fe-Ni-Cr-Mo-Cu合金の凝固パス解析

抄録

In this study, the solidification path of a Fe-Ni-Cr-Mo-Cu alloy was investigated to determine the partition coefficient of each alloying element between the solid and liquid phases. The solidification path was confirmed to be single austenite mode whose solidification structure consisted only of austenite phase in the cooling rates from 0.06 to 0.69 K/s. The relation of λ₂=43.6 V^–0.41 between secondary arm spacing (λ₂) and cooling rate (V) was obtained by thermal analyses and microscopic observation.

The content of every alloying element in the primary γ phases was measured by EDS. Random sampling method, as many points were randomly analyzed, was applied to have content distributions of the alloying elements. The randomly measured data were rearranged with an increasing order except for Ni. Reference to Scheil’s equation could give us the partition coefficients (k_R). The k_R values were mostly in accordance to the equilibrium partition coefficients (k_E) obtained after holding a specimen in the solidification temperature for an hour. However, the k_R values tended to be closer to unity than the k_E values implying that segregation was predicted less with the k_R values. This fact leads to the presumption that the k_R values can evaluate the solidification sequence including the other factors such as diffusion of elements during and after solidification. Thus, it can be proposed that the k_R values are useful to predict microscopic segregation of the actual product under a given solidification and cooling condition.