Changshuai Wang

Ni-Fe Based Alloy GH984G Used for 700 °C Coal-Fired Power Plants

To meet the requirements of 700 °C ultra-supercritical (USC) coal-fired power plants, a new Ni-Fe based alloy (GH984G) has been developed. GH984G has excellent creep strength, thermal stability and resistance to oxidation/corrosion. Harmful phases were not observed even if after thermal exposure at 650–750 °C for 35,000 h. After exposure at 700 °C for 30,000 h, the yield strength has no obvious change. Its 105 h creep strength at 700 °C is up to 137 MPa and comparable to the level of 617B. The oxidation/corrosion evaluate at 700–800 °C up to 2000 h shows that it can meet the requirements of 700 °C USC coal-fired power plants. Currently, the pipes and tubes with different sizes have been manufactured. Moreover, it is an economic alloy due to the elimination of Co and containing more than 20% Fe. This makes it an interesting alternative for 700 °C USC coal-fired power plants and is now being evaluated at test platform for key components of China.

Precipitation Behaviors of M 23 C 6 Carbides and γʹ Phase in Cast IN617B Alloy During Long-Term Aging

The precipitation behaviors of M23C6 carbides and γʹ phase in cast IN617B alloy during long-term aging was systematically investigated by comparison with previous studying results about wrought IN617B alloy. The results showed that the morphology of M23C6 carbides and the nucleation location of γʹ particles in cast IN617B alloy were distinctly different from those of wrought IN617B alloy due to the difference of processing method. The microstructure observation revealed that the morphology of M23C6 carbides at grain boundaries (GBs) transformed from film-like shape into cellular shape owing to the reduction in the interfacial energy of GBs. Within the grains the bar-like M23C6 carbides and spherical γʹ phase directly precipitated from the γ matrix. Moreover, the growth of M23C6 facilitated the formation of γʹ phase by enriching γʹ-formation elements, and conversely, dense γʹ phase inhibited the coarsening and decomposition of M23C6 by constraining the diffusion of M23C6-formation elements. In addition, the mechanism of inhibiting effect of γʹ phase on the coarsening of bar-shaped M23C6 was discussed.