低炭素綱の水素ガス中疲労におけるぜい性ストライエーション形成機構の検討: 負荷波形と試験環境の制御により破壊過程を可視化した破面の観察

摘要

In order to investigate the brittle-striation formation mechanism of a low carbon steel JIS S10C fatigued in hydrogen gas environment, fractographic observations were conducted on the visualized fracture phenomena at some processes of brittle striation formation. The results showed as follows. A striation line was formed during the loading part of the cycle as a trace of blunting by slip. Then, stable ductile crack growth started. These processes were similar to those in the normal ductile fracture from a crack, that is, ductile tearing process in tension. Based on the experimental results, a brittle striation formation model in which hydrogen only enhances the microscopic ductile tearing process just ahead of a crack tip is proposed. The model rationally explains the peculiar load-frequency effect in quasi-cleavage range on the fatigue crack growth which reveals lower growth rate in spite of lowering the load-frequency.%水素利用機器を長期間安全に使用するためには，金rn属材料の疲労強度に及ぼす水素ガスの影響評価が最rnも重要な課題の一つである．材料としては，低廉な炭rn素鋼や低合金鋼などの用途拡大が期待されている．