Creep Properties and Microstructure Evolution of Fe-Ni Based Superalloy under Different Temperatures

High-temperature creep tests at 675 ℃ and 700 ℃ were conducted on Fe-Ni based superalloy under a constant tensile stress of 250 MPa. The creep properties and microstructure after creep fracture of the test alloy at different temperatures were studied. The results show that the creep fracture mode of the test alloy after creep at different temperatures was intergranular fracture. The creep life at 700 ℃ was 7 891 h shorter than that at 675 ℃. The premature fracture at 700 ℃ of the test alloy was related to many unevenly distributed dislocation entanglements formed in the microstructure. The grain size of the test alloy after creep at 675 ℃ was significantly larger than that at 700 ℃, and the grain size distribution was more dispersed. Compared with those after creep at 675 ℃, TiC in the test alloy after creep at 700 ℃ was larger in size and tended to aggregate or be distributed by bands, while the average width of Cr₂₃C₆ was smaller. No obvious continuous network structure of Cr₂₃C₆ was formed after creep at different temperatures. The γ′ phase within the grains after creep at different temperatures was spherical, and the average size of the γ′ phase after creep at 675 ℃ was relatively large. After creep at different temperatures, there were a very small number of precipitation-free zones and discontinuous coarsening zones on grain boundaries of the test alloy.