70MPa水素ガス中におけるSCM435切欠き材の疲労強度特性評価

抄録

In the present work, smooth and notched rectangular cross-sectional specimens machined from two distinct heat-treated SCM435 steels were employed to carry out fatigue testing in air or in 70 MPa high-pressure hydrogen gas environment. Fracture surfaces of the specimens exposed to hydrogen have revealed intergranular and quasi-cleavage fracture mechanisms, which is a typical effect of the hydrogen embrittlement phenomenon. Evaluation of the hydrostatic stress in notched specimens by an elastoplastic finite element analysis was carried out. A correlation between high hydrostatic stress at the notch vicinity and large fraction of intergranular fracture was found, regardless of the stress concentration factor value induced by the notch. Smooth specimens have highlighted a slight hydrogen gas effect on the fatigue life limited to the high stress region only for low temperature tempered steel. The hydrogen sensitivity for notched specimens tempered at low temperature was also emphasized by a distinct decrease in the fatigue limit, caused by the high triaxial stress state around the notch which enhances the hydrogen accumulation.