Microstructure and homogenization of as-cast 617B alloy for 700℃ ultra-supercritical boilers

The microstructure and microsegregation of nickel-based superalloy Inconel 617B ingots produced by vacuum induction melting and electroslag remelting were studied by optical microscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy. Their kinetic homogenization curves were calculated by Dictra software through the residual segregation parameter model. Based on the theoretical results, seven homogenizing treatments were tested. Microstructure analysis and thermal compression test with a Gleeble 1500 machine were used to verify the effect of homogenizing treatment. It is found that dendrites and element segregation exist in the ingots, and Mo and Ti are the principal segregated elements. The main precipitated phases in the ingots are different kinds of primary carbides which tend to symbiotic growth. After homogenization at 1210℃ for 48 h, this segregation can almost be eliminated, the phase of intragranular carbides dissolves to the matrix, and the ingots exhibit excellent workability.