2013 Volume 99 Issue 2 Pages 87-93
Influence of cooling rate on the development of solidification structure and microsegregation of multi-component white cast iron was investigated by using Fe-2mass%C-5mass%Cr-5mass%Mo-5.5mass%V alloy.
Primary austenite(γ), MC and M2C carbides were crystallized at the cooling rates obtained by this experiment and the solidification process and structure were unchanged within the cooling rate of 5K/min to 351K/min. The amount of M2C carbide decreased with an increase in the cooling rate, while that of MC carbide was almost same level.
Concentrations of alloying elements in the residual liquid during solidification varied greatly in line with the progress of crystallizing each phase. As the primary γ continued to crystallize, Cr, Mo and V contents in the residual liquid were increased. According to the crystallization of (γ+MC) eutectic, the V content decreased and both the Cr and Mo contents increased more in the residual liquid. In the final liquid highly concentrated with Mo, (γ+M2C) eutectic started to crystallize. The microsegregation can be estimated using the partition coefficient of elements to each phase and the diffusivity of alloying elements. The estimated results showed relatively good accordance with the experimental results.
Since the apparent partition coefficient of alloying element in the residual liquid is varied by the cooling rate, the amount of M2C carbide crystallized in the final liquid enriched with Mo was changed.
The estimated amount of M2C carbide decreased from 6.8% in volume at 5K/min to 5.2% at 20K/min, and the estimated and the experimental results were close each other.
