| Haynes282 is a wrought,gamma-prime strengthened superalloy,and is selected as one of the leading candidate alloys of turbine application for 700 ℃ Adanced Ultra Supercritical(A-USC) power plant, due to its favorable combination of high creep strength, thermal stability, and excellent processbility. The combination of high strength, oxidation resistance as well as weldability at 700℃ are highly demanded. Therefore, it’s important to investigate the microstructure evolution and mechanical properties during long time aging and creep rupture test.After solution treatment, aging at 700℃and750℃, creep rupture test, impact energy, room temperature and high temperature tensile properties were tested.We also studied the effect of microstructure evolution on mechanical properties.For Haynes282 with solution and double aging heat treatment, the solution treatment was optimized. The content of undissolved carbides and their size are reduced, the strengthen is decreased gradually. The optimal treatment parameters were 1120 ℃/2h/AC+1010 ℃ /2 h/AC+788 ℃/8 h/AC.The M23C6、MC and γ’are precipitated in Haynes282 alloy during aging at 700℃and 750℃. The Cr, Mo-rich carbide,M23C6, mainly precipitate along grain boundary, few distribute on the twin boundary and within the grains. The precipitation along the grain boudary grow up to continuous chain with the increasing aging time, and faster at 750 ℃. The MC phase with large size mainly precipitate inside grains, the key elements are Ti, Mo. MC is relatively stable when aging at 700 ℃, but decomposes at 750 ℃. γ’is the main strengthening phase of the alloy which mainly contain Ni, Al and Ti. The fraction of y’is 18.9% (wt) at 750℃, 5000h. The coarsening of γ’is in line with the Ostwald ripening mechanism. According to the size of the particles, the dynamic growth equation of 700℃ and 750℃ were obtained. It showed that y’coarses slowly at 700℃, but accelerates at 750 ℃.The mechanical properties change the same at 700℃ and 750 ℃. The impact energy decreases rapidly and the hardness increases fast after aging, and finally they tends to be stable. After aging, cracks form between grain boundary carbide and the matrix, which cause the decline of impact energy. The change of hardness is bound up with the evolution of y’phase. When aging at 100h, the hardness increases rapidly due to fine y’phase, after long time aging the strength effect of y’decreases and the hardness changes slowly.Creep strength is an important prameter to decide the alloy whether can be used as steam turbine rotor in 700℃A-USC. Thus, it is necessary to operate the creep strength test. The test results showed that the creep strength of the H282 alloy exhibites relatively high. Its extrapolation valuation of endurance strength is 100MPa at 700℃, 100000h, which meet the design requirements of the alloy. Analysis of the micro structure shows that the effect of stress on the morphology and distribution of y’is indistinctive, but have significant effect on M23C6 phase. The cracks initiated at grain boundaries and propagated along the grain boundary, which finally resulted in failure of the alloy. |
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