低圧タービンロータ用 3.5%NiCrMoV 鋼の長時間恒温焼戻脆化におよぼす不純物元素および Si, Mn 量の影響

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Isothermal aging tests at 375, 400 and 450℃ for 10000∿20000 hs were performed on 3.5NiCrMoV steel forgings for low pressure turbine rotors with various amount of impruities, Si and Mn, in the Mn range of less than about 0.30 mass %. The results are summarized as follows. 1) The shift in 50% fracture appearance transition temperature by isothermal temper embrittlement at T℃ for t h (ΔFATT_<IT>) decreases with decrease in amount of impurities, defined as X^^-=(10P+5Sb+4Sn+As)×10^2, Si, Mn, cooling rate during quenching and aging temperature. When X^^- is less than 2.1, no temper embrittlement occurs, regardless of Si and Mn contents, but when X^^- is greater than 4.1, embrittlement occurs according to Si and Mn contents. However, with X^^-=10.7, some embrittlement is observed even at 0.02% Si and 0.04% Mn in the aging tests at 450℃ for 10000 hs. Therefore, reduction of amount of impurities is important to reduce susceptibility to temper embrittlement. 2) When X^^- is 4.1 to 7.0, the equation, which can accurately estimate ΔFATT_<IT> from K=(Si+Mn)・X^^-, X^^- and the cooling rate, is derived. 3) When K is less than 0.78 (X^^-≦6.0, Si≦0.05% and Mn≦0.08%), maximum isothermal temper embrittlements at 375∿450℃ for 20 years are calculated to be 24℃ at surface and 16℃ at center of a 1800 mm diameter rotor forging, and the fairly good toughness is estimated to be obtained even after using for a long term.
社団法人日本鉄鋼協会の論文
1993-04-01

低圧タービンロータ用 3.5%NiCrMoV 鋼の長時間恒温焼戻脆化におよぼす不純物元素および Si, Mn 量の影響

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