Numerical Simulation of the Influence of Electrode Shrinkage Cavity on ESR Process of IN718 Alloy

Numerical simulation and analysis of the influence of electrode shrinkage cavity on electroslag remelting (ESR) process of IN718 alloy ingot with a diameter of 430 mm were carried out using the self-developed ESR process model. Electromagnetic fields of ESR system were simulated by a specially designed shrinkage cavity with different shapes and sizes in the electrode. The results show that the contacting area changes between the electrode and the slag owing to the cavity, which plays a predominant role in the distribution of the Joule heat and electromagnetic force in the slag, while the effect of axial dimension change of the shrinkage cavity is negligible. Constant melt rate ESR processes were simulated for different radius cavity situations. It is shown that, at a constant melt rate, the shrinkage cavity has no effect on the ESR process as its radius is less than 0.025 m, and only a small influence on the slag flow when the radius reaches 0.05 m. As the radius increases over 0.05 m, an increasingly evident influence on the slag zone appears via the weakened center downward flow and the increased temperature. Nevertheless, the cavity has no obvious influence on the ingot including the melt pool and mush zone. There is a nonlinear relation between the shrinkage cavity radius and the ESR melting parameters such as current and power, and the critical value of the radius is approximately 0.05 m. Below the critical value, faint or even no change in the parameters appears, while, above the value, the parameters of power and current increase rapidly in an approximately linear manner. From the standpoint of process control stability, the shrinkage cavity radius should be controlled below 0.05 m.