炭素鋼溶接金属の水素脆化割れに及ぼす微小欠陥の影響,2

Effect of defect contained within weld metal on susceptibility of hydrogen embrittlement of carbon steel weld joint, 2

小林 正人*; 高橋 里栄子*; 朝野 英一*; 谷口 直樹 ; 藤田 朝雄 

Kobayashi, Masato*; Takahashi, Rieko*; Asano, Hidekazu*; Taniguchi, Naoki; Fujita, Tomoo

溶接時に生じた球状欠陥が水素脆化感受性に及ぼす影響を定電流SSRTにより評価した。溶接組織の影響を取り除くため、焼ならし処理を施した試験片を使用した。試験後の破面観察、及び鋼中水素濃度分析の結果、ある水素濃度以上で欠陥を起点とした割れが生じた。この現象は破断ひずみ量を低下させるが、水素濃度の影響と比較した場合に有意性は認められず、脆化感受性を顕著に高めるものではないと推察される。

Susceptibility of hydrogen embrittlement of carbon steel weld joint was evaluated by slow strain rate testing (SSRT) in consideration of a diffusive hydrogen concentration and a presence of a fine flaw which is hard to detect by ultrasonic testing due to the dimension. In order to avoid an effect of metallurgical micro structure, normalized specimens were prepared to the SSRT. The results of SSRT showed the rupture elongation decreases with an increase in hydrogen concentration. And observation of the fracture surface and measurement of the hydrogen concentration in the specimens showed a generation of a crack initiated from fine flaw at up to a certain value of hydrogen concentration. Although decreasing of fracture strain was observed on the specimens fracture morphology, it was evaluated as no significant effect in comparison with the effect of the concentration of the diffusive hydrogen in the specimens. These results suggest that a presence of a fine flaw has a small impact on the hydrogen embrittlement of weld joint.