低合金鋼の高温低サイクル疲労特性に及ぼす経年材質劣化の影響

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"Low cycle fatigue (LCF) tests were carried out at 839K on Cr-Mo-V forgings and castings taken from various power plant components after long-term service. Δε_e-N_c and Δε_p-N_c properties of the used and artificially deteriorated materials were compared with the virgin material. The effect of deterioration on mechanical properties and its correlation with LCF properties were examined. The results obtained are summarized as follows. (1) Cr-Mo-V forging and casting became soft and/or brittle through long-term heat. Material deterioration (softening and embrittlement) changed LCF properties of these steels as follows. i)Δε_e-N_c relationship shifted downward by softening. ii) Δε_p-N_c relationship shifted downward when embrittlement became dominant. (2) Vickers hardness had good correlation with Δε_e-N_c coefficient C_1, as long as hardness took the value from 200 to 260, while Δε_e-N_c, expenent α_1, Δε_p-N_c coefficient C_2 and exponent α_2 were insensitive to the change of hardness. (3) True fracture strain had no clear correlation with C_1, α_1, C_2 and α_2. (4) FATT (50% fracture appearence transition temperature) bad good correlation with C_2 of casting. Embrittled casting had relatively high FATT and low C_2. De-embrittled casting decreased FATT remarkably and increased C_2 to some extent. By fractographic observation the former showed intergranular cracking, and the latter showed ductile striation pattern. The values of α_2, C_1 and α_1 were insensitive to the change of FATT. As the effect of deterioration on LCF properties is complicated, further investigation is necessary.
社団法人日本材料学会の論文
1984-06-15

低合金鋼の高温低サイクル疲労特性に及ぼす経年材質劣化の影響

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