The effects of test temperature and thermal aging on impact toughness and dynamic fracture toughness of Incoloy 800 H alloy were studied by means of scanning electron microscope(SEM)

energy dispersive spectrometer(EDS) and instrumented impact test. The results show that

the total impact energy(Et) and dynamic fracture toughness of solution treated Incoloy 800 H alloy at 675 ℃ were about 30% lower than that at room temperature

and the main reason was that the strength of the alloy decreased with the increase of temperature. After thermal aged for 300 h

the Et of Incoloy 800 H alloy at room temperature and 675 ℃ decreased by 68.8% and 55.4% respectively. With the extension of the thermal aging time

the impact energy decreased slowly. After thermal aging for 3 000 h

the impact energy at room temperature and 675 ℃ decreased by 74.1% and 60.3% compared with the solid-solution state

and the dynamic fracture toughness at room temperature and 675 ℃ decreased by about 70%. The reason for the decrease of the impact toughness of aged samples was the plastic decrease of material caused by the precipitation of carbides on grain boundary

twin boundary and in the grain. It is concluded that Incoloy 800 H alloy shows good toughness after 3 000 h of thermal aging according to the total impact energy

the dynamic load-displacement curve type and the ductile section ratio of the fracture.