Study on the Molten Pool Behavior, Solidification Structure, and Inclusion Distribution in an Industrial Vacuum Arc Remelted Nickel-Based Superalloy

In this work, an industrial vacuum arc remelting (VAR) trial was conducted in a nickel-based superalloy with 508 mm diameter. And the molten pool behavior, solidification structure, and inclusion distribution of the VAR ingot were investigated by optical microscopy (OM), scanning electron microscopy (SEM), electro probe micro-analysis (EPMA), and computational fluid dynamics (CFD) simulations. Results demonstrated that numerical calculations are well in agreement with the experimental observation. Columnar grains are well developed during the ramp-up and steady-stage region, while typical equiaxed grains layer and shrinkage hole was presented at the hot-top region. The molten pool profile varies with the melting time, from a shallow flat shape to a stable U shape in 355 minutes, and finally shrinks after the end of melting, wherein the maximum depth and average temperature are 240 +/- 5 mm and 1753 K, respectively. Solidification parameters show the continuous variation characteristics in the solidified ingot from the center to the surface, in which PDAS is reduced from 714.76 to 212.34 mu m, SDAS is reduced from 142.32 to 62.26 mu m, and W and Ti elements severe segregated between the dendrites. The major inclusion particles in the VAR ingot are complex inclusions with a multi-layer structure, consisting of an MgO center dot Al2O3 spinel core surrounded by an inner layer with Ti-rich and N-rich carbonitrides Ti(NC) or outer TiC layer. Optimizing the molten pool by adjusting the process parameters may help to get lower segregation and cleaner ingots.