Key factors in quality control of a high Cr content cast Ni-base superalloy K4648

Abstract

K4648 possesses the highest Cr content in applied cast Ni-base superalloys and has been applied to manufacture the integral castings of advanced gas turbines in China. However, the large blocky primary α phase in alloy had detrimental effect on the impact ductility, and the alloy severely reacted with the silica-based ceramic core during the solidification process. The investigation results indicate that the primary α phase precipitated in the late solidification at 1190 °C. The Vickers microhardness value of α phase is 6.3 GPa at the load of 0.2 N. The primary α phase transforms to M23C6 carbides after solid solution treatment at 1180 °C. The cracked α or transformed M23C6 can be observed at the fracture surface and longitudinal section of the impact specimens. Moreover, the severe reaction exists in the metal/ceramic interface. The reaction products consist mainly of the oxides which elements come from both alloy and silica-based ceramic core. For high Cr content superalloys, the solidified parameters should be controlled properly to inhibit primary α phase precipitation and more stable alumina-based core is recommended.