Fretting fatigue strength of materials for hydrogen utilization machines in hydrogen gas environment

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  • 水素利用機器用材料の水素ガス環境中フレッティング疲労強度
  • スイソ リヨウ キキヨウ ザイリョウ ノ スイソ ガス カンキョウチュウ フレッティング ヒロウ キョウド

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Abstract

Fretting fatigue is one of the major failure modes at the joint or contact part between components in machines and structures. To clarify the effect of hydrogen gas environment, fretting fatigue tests were performed. Fretting fatigue strengths at 3×107 cycles obtained in air and hydrogen gas were compared. The test materials were low alloy steel SCM435H, heat resisting alloy SUH660 and two kinds of austenitic stainless steels SUS304 and SUS316L. Stainless steels were hardened by giving 30% strain under monotonic tension. Nitrided material was also used in the experiment to investigate prevention of fretting in hydrogen gas environment. The pressure of hydrogen gas was 0. 12MPa in absolute pressure. Fretting fatigue life in hydrogen gas rather increased in the short-life region. It was found that the extension of fatigue life was caused by the delay of start of stable crack propagation. In air, there was no decrease of fretting fatigue strengths between 1×107 and 3×107 cycles. In hydrogen gas environment, fretting fatigue strengths continued to decrease exceeding 107 cycles. As the results, fretting fatigue strengths at 3×107 cycles were lower in hydrogen gas environment than in air. The reduction was 12% for SCM435H, 18% for SUH660, 7% for SUS316L and 24% for SUS304. Nitriding was effective for the improvement of fretting fatigue strength not only in air but also in hydrogen gas environment. The tangential force coefficient in hydrogen gas environment increased. Detail observations of fretted surface and initiation and early propagation of fretting fatigue crack in hydrogen gas environment showed that adhesion between contact surfaces might have an effect of crack initiation at the stress level which is lower than fretting fatigue limit in air. The effect of absorbed hydrogen and high-pressurized hydrogen gas environment are the problems that remain to be solved.

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