Hot cracking behavior of large size GH4742 superalloy vacuum induction melting ingot

The developing of large size superalloy vacuum induction melting (VIM) ingots is limited owing to hot cracking. The hot cracking behavior of the large size GH4742 superalloy VIM ingot was investigated via experiment and simulation. The microstructure was examined by optical microscopy, and element segregation was investigated by electron probe microanalysis. The solidification temperature range and yield strength at high temperature (YSHT) were calculated by JMatPro software. The results show that the variations of microstructure and element segregation in different locations are caused by different cooling rates. Moreover, the larger secondary dendrite arm spacing and serious element segregation of Nb accelerate hot cracking of the VIM ingot. In addition, the solidification temperature range is wider, and YSHT is lower in center than at edge of the ingot. Therefore, the hot cracking susceptibility is the highest in the center of the GH4742 superalloy VIM ingot. The critical criterion of element segregation for hot cracking is that the partition coefficient of Nb should be larger than 0.5.