抄録
The short time tensile test was conducted on the base metal, TIG weld metal, TIG weld joint and EBW weld joint of Hastelloy X at 700°C, 800°C and 900°C. Their fracture surfaces were observed by means of a scanning electron microscope, and the microstructures by means of both optical and electron microscopes, so as to investigate the relation between the fracture mechanism and microstructure. The results obtained are summarized as follows:
(1) The fracture mode of the base metal changed from dimple fracture to intergranular fracture as the temperature was raised from 700°C to 900°C, though the ductility increased gradually.
(2) TIG weld metal and TIG weld joint showed minima in their ductility near 800°C due to the fracture mode transition from interdendritic fracture to intergranular fracture, while the ductility of EBW joint increased gradually similar to that of the base metal. The fracture surfaces of EBW joint revealed that the fracture type was almost dimple fracture.
(3) Both the dimple fracture of base metal and the interdendritic fracture of TIG weld metal and TIG weld joint were caused by the crack initiation at the precipitated M6C carbide and its propagation.
