Influence of Heat Treatment System on Microstructure and Creep Properties of GH4698 Alloy Disk

The effect of heat treatment on microstructure and creep properties of GH4698 disc and its all-phase creep behavior after standard heat treatment under 750 ℃ were studied. The results show that GH4698 plate microstructure after standard heat treatment is composed of globular gamma prime phase and carbides within grains. After the fourth stage heat treatment, the microstructure changed. Small gamma prime phase grew up, gamma prime phase dilution zone width along the grain boundary significantly reduced, and carbide precipitation along the grain boundary granular was more perfect. The fourth stage heat treatment is favorable to the creep limit at 750 ℃/382 MPa, and the process stability is better. The complete creep curves of GH4698 alloy at 750 ℃ show that the steady-state creep stage of GH4698 alloy at 750 ℃ is relatively short. The non-uniformity of microstructure and grain size would cause greater fluctuation of the creep properties. The reasonable acceptance condition for creep properties is σ_p≤0.2% at 700 ℃/412 MPa/100 h.