Comparative investigation on ingot evolution and product quality under different arc distributions during vacuum arc remelting process

Abstract

The arc characteristics especially the arc distribution of the vacuum arc remelting (VAR) process are closely related to the ingot evolution and consequently the final product quality. Taking segregation defects and solidification quality as the indexes to evaluate the final product quality under different arc distributions, a three-dimensional full-scale transient model for predicting segregation defects is developed in this paper. Local solidification time (LST) and secondary dendrite arm spacing (SDAS) are used to characterize the solidification quality. This model is adopted to predict channel segregation (freckle) and macrosegregation defects during VAR process of Ni-5.8 wt.%Al-15.2 wt.%Ta alloy under several typical arc distributions. The results show that the diffuse arc has the shallowest molten pool among several arc distributions. At the early stage of solidification, the solute enrichment channels formed under the Gaussian and diffuse arc are slender and concentrated, while they are relatively sparse and uneven in thickness under the rotating arc. The value of volume-averaged segregation extent is always the smallest under the diffuse arc and the largest under the Gaussian arc, with final values of 67.53% and 69.66%, respectively. The volume-averaged values of LST and SDAS are relatively the largest under the Gaussian arc, about 1599 s and 209 μm, respectively; and they are the smallest under the diffuse arc, about 1520 s and 206 μm, respectively. In the same process conditions, the product quality of VAR ingots prepared under the diffuse arc is the best, followed by the rotating arc, and the worst under the Gaussian arc.

Keywords

• Vacuum arc remelting
• Arc distribution
• Ni-based superalloy
• Segregation defect
• Solidification quality