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Inconel 617B is a nickel-base superalloy used for superheater tubes and heater pipes of ultra-supercritical power plants. As the alloy contains many alloy elements, which results in the difficulties in the manufacture process with controlled microstructure, the method of microstructure control during manufacture is described in this paper. Homogenisation, hot extrusion and cold rolling are key parts in the manufacture process. In order to determine the best manufacture parameters, homogenisation tests, annealing and hot compression simulation tests are introduced in the process design. The effects of different manufacture parameters on microstructure are discussed here. The homogenisation treatment is determined as 1180°C for 45-50 h. The recommended extrusion ratio is lower than 4 with the preheating temperature in the range of 1150-1200°C and extrusion speed lower than 125 mm s-1 based on the finite element simulation results. The annealing treatment should be carried out at 1160-1190°C for 1 h and final annealing treatment of four times cold rolled tubes is determined as 1180-1200°C/1·5 h. Guided by the recommended manufacture parameters the first finished Inconel 617B tubes in China has been manufactured successfully. [ABSTRACT FROM AUTHOR]

The oxidation property of powder metallurgy (PM) EP741NP Ni based superalloy in the temperature range of 700-1100°C is investigated by isothermal oxidation test, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. Results show that oxidation kinetics follows a square power law as the time extends. Oxidation layers are composed of Cr2O3 and TiO2 as well as a small amount of NiAl2O4, NiCo2O4 and NiCr2O4. Surface morphologies exhibit that spallation starts to occur at 900°C and becomes severe at 1000 and 1100°C. Cross-sectional morphologies and elemental distributions indicate that the oxidation layer consists of Cr and Ti rich oxide layers. Oxidation kinetics and layer thicknesses confirm that the oxidation activation energy is 164·87 kJ mol-1 and the oxidation process is controlled by diffusions of oxygen, Cr and Ti. A diffusion controlled mechanism is confirmed to understand the oxidation property of PM EP741NP superalloy at elevated temperatures. [ABSTRACT FROM AUTHOR]