1.Science and Technology on Advanced High Temperature Structural Materials Laboratory, Beijing Institute of Aeronautical Materials, Beijing 100095, China
2.Collaborative Innovation Center of Steel Technology, University of Science and Technology Beijing, Beijing 100083, China
et al.
K4169 samples with grain size of ASTM M9～M7, ASTM M14~M9 and ASTM 3~5 were prepared by conventional casting process, fine grain casting process and micro-grain casting process, respectively. The effects of micro-grain casting process on the microstructures and stress rupture properties of K4169 alloy were analyzed. Results show that micro-grain casting process can significantly refine grains, reduce solidification segregation and the content of Laves phase and large bulk MC carbides, increase the volume fraction of γ″ phase, thus improve the mechanical properties of K4169 alloy. The stress rupture life at 704 ℃/448 MPa of micro-grain K4169 alloy is up to 614.9 h, which is 621% and 44% higher than that of conventional K4169 and finegrain K4169, respectively. The fracture mode transforms from brittle transgranular fracture of conventional K4169 to ductile mixedmode fracture (transgranular fracture and intergranular fracture) of micro-grain K4169. Grain refinement and the increased volume fraction of γ″ effectively strengthen K4169 alloy, while the decreases of Laves phase and large bulk MC carbides reduce the potential crack initiation and propagation locations. The combination of the above two points improves the stress rupture life of K4169 alloy and reduces the dispersion of performance data. The micro-grain casting process can obtain good comprehensive mechanical properties and improve the service performance of K4169 alloy below 700 ℃, which has a good application prospect.