Effect of cooling rate on microstructure, microsegregation and mechanical properties of cast Ni-based superalloy K417G

The effects of different solidification rates after pouring on the microstructures, microsegregation and mechanical properties of cast superalloy K417G were investigated. Scheil-model was applied to calculate the temperature range of solidification. The casting mould with different casting runners was designed to obtain three different cooling rates. The microstructures were observed and the microsegregation was investigated. Also, high temperature tensile test was performed at 900 °C and stress rupture test was performed at 950 °C with the stress of 235 MPa. The results showed that the secondary dendrite arm spacing, microsegregation, the size and volume fraction of γ′ phase and the size of γ/γ′ eutectic increased with decreasing cooling rate, but the volume fraction of γ/γ′ eutectic decreased. In the cooling rate range of 1.42 °C s−1-0.84 °C s−1, the cast micro-porosities and carbides varied little, while the volume fraction and size of γ′ phase and γ/γ′ eutectic played a decisive role on mechanical properties. The specimen with the slowest cooling rate of 0.84 °C s−1 showed the best comprehensive mechanical properties.