Microstructure and Typical Mechanical Properties of Overheated K424 Superalloy

The stress rupture test at 975 degrees C/196 MPa and room temperature tensile test were performed on K424 alloys which were standard heat-treated and overheated under different conditions (1050 similar to 1150 degrees C/2 h, air cooling), and then the microstructure and fracture features were investigated. The results show that the mechanical properties of the standard heat-treated K424 alloy are only slightly decreased after overheating at 1050 similar to 1150 degrees C for 2 h, while its mechanical property indexes are obviously higher than the standard values. Microstructure characterization indicates that the grain morphology, grain boundary morphology and gamma' phase of the interdendritic region do not show significant changes after overheating under different conditions. The more cuboidal primary gamma' phase and the precipitation of secondary gamma' phase in gamma channel are responsible for the slightly reduced mechanical properties after overheating. In addition, the high temperature and room temperature fracture mechanism of the overheated K424 alloy was also discussed.