中高温における低炭素鋼のき裂進展下限界応力拡大係数範囲ΔK_<th>に及ぼす繰返しひずみ時効および高温酸化物の影響

概要

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Fatigue tests of 0.08% C Steel were made on in-plane bending at elevated temperatures up to 450℃ (Room temperature, 200℃, 375℃ and 450℃). the threshold stress intensity factor ΔK_<th> was determined by the critical condition of whether specimens broke or not at 10^7 cycles. The threshold stress intensity factor reached a maximum at 375℃. The value of K_<op>/K_<max> increased with increasing temperature up to 450℃. Both ΔK_<eff th> and ΔK_<eff th>/E showed the same temperature dependence as described above. The oxide at 375℃ was thinner than that at 450℃. The value of ΔK_<th> at 375℃, however, was larger than that at 450℃. It is concluded that the maximum ΔK_<th> is caused by strain aging rather than thick oxide induced closure.
1986-04-25