Effects of heat treatment on the creep properties of alloy 800H possessing long service history

Alloy 800H is extensively used for high-temperature service in such items as pressure turbines and heating tubes of steam-raising boilers in atomic power plants, catalyst regenerators and expansion bellows of chemical plants, and so on. However, it is known that hardening occurs due to a finely distributed uniform precipitation of y′-phase Ni3(Al, Ti) in the grains when this material is used for long periods in the temperature range of 550-750°C, which is slightly lower than its normal service temperature range (800°C and over). Consequently, in the current research, the effects of heat treatment on the creep properties of the material were clarified by using as the test material Alloy 800H, which had been utilized in actual equipment for a period of 72,000 h at temperatures of around 650°C, with greatly increased hardness compared to its initial state.