The cracking behavior of the new Ni-based superalloy GH4151 in the triple melting process

Abstract

In this paper, the mechanism of crack formation in VIM, ESR, and VAR of GH4151 alloy ingots is discussed. The cracks in VIM ingots are hot tearing, mainly caused by severe segregation of elements such as Nb, Ti, and Al in VIM electrodes, which promotes the precipitation of (γ+γ′) eutectic and Laves phases and thus leads to the formation of hot tearing. On the other hand, cracks in ESR and VAR ingots are cold cracks caused by the uneven distribution of γ′ phases. The temperature range for the precipitation of (γ+γ′) eutectic phases is 1160°C–1148 °C, while that for γ′ phases is 1137°C–1072 °C. At temperatures below 884 °C, the uneven precipitation of γ′ phases results in a maximum internal stress of 1096 MPa at room temperature. Based on computational fluid dynamics (CFD) simulations, to avoid large internal stresses caused by the precipitation of γ′ phase, the ingot should be removed from the water-cooled crystallizer within 57 min. Annealing is an effective measure to improve the quality of electrodes. After annealing treatment, the γ′ phase in the alloy transforms from short rod-shaped to square-shaped, and the decomposition of Laves phase promotes the precipitation of μ phase and σ phase from the matrix, improving the mechanical properties of the alloy.

Keywords

• GH4151 alloy
• Triple melting
• Hot tearing and cold cracking
• CFD simulations
• Annealing treatment