超耐熱Ni基合金U-520の熱間加工性

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The hot workability of U-520 was studied by means of Gleeble ductility test and tensile test in the temperature range from 925°C to 1240°C at various strain rates.Hot ductility, measured as reduction of area at fracture, was increased with increasing strain rate below 1025°C and also with decreasing strain rate above 1130°C.Fractographs and microstructures of such ductile fracture showed typical dimple pattern and recrystallization. Ductility falls abruptly at high strain rate above 1130°C and fractographs of the fracture surface showed local melting similar to that observed at high temperature above 1180°C. Hot ductility depends on the morphology of grain boundary carbide and intergranular γ precipitates: ductility of the furnace-cooled material which contained coarse precipitates of grain boundary carbide and γ is superior below 1025°C but inferior above 1075°C to the air-cooled material which contained no grain boundary carbide and γ.
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