Porosity forming mechanism and numerical simulation of casting process optimization of nickel-based heat-resistant alloy electrode ingot with large height to diameter ratio

Abstract

Based on the simulation results of ProCAST software for the filling and solidification process, the formation mechanism of the VIM electrode ingot's pipe and porosities and the influence of the casting process on the formation of electrode shrinkage were studied in detail. The research results indicate that the critical condition for the formation of 200 kg grade C650R heat-resistant alloy is verified to be G/R≤5.0 (K·s)0.5/cm. In addition to the alloy's inherent characteristics, the substantial height to diameter ratio (H/D) of the VIM electrode ingot is the primary factor contributing to the formation of deep pipe and severe porosities. Simply adjusting the casting time or casting speed alone does not significantly improve the solidification quality of the ingot. While the use of a hot top can eliminate pipe, its effectiveness is limited, as the alloy melt at the hot top location has minimal influence on the solidification process in the lower regions of the electrode ingot, thereby failing to effectively reduce the formation of porosities. Properly reducing the casting speed and casting superheat lead to the formation of a V-shaped melt at localized positions during the final stage of solidification. This enhances the ability of the liquid phase for further feeding, ultimately significantly decreasing both the depth of pipe and the porosity rate. The optimal casting process optimization solution for C650R alloy electrode ingot with a size of Φ130 mm × 1240 mm is the casting speed of 60 kg/min and the superheat of 40 °C.