オーステナイト系ステンレス鋼SUS316の疲労挙動に及ぼす予ひずみの影響

概要

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The fatigue behaviour of prestrained type 316 austenitic stainless steel has been studied. Two types of fatigue tests, conventional S-N tests in laboratory air and in 3%NaCl solution and stress-incremental tests, were performed. Tensile prestrains evaluated are 5%, 15%, 25% and 58%. In laboratory air, fatigue strength increased with increasing prestrain, which was attributed to both work hardening and strain-induced martensitic transformation. In 3%NaCl solution, the fatigue strengths for all specimens decreased compared with those in laboratory air and fatigue strength increased with increasing prestrain up to 15%, but above that prestrain, it decreased significantly. Corrosion pit generation and growth in transformed martensite phase were believed to be primarily responsible for the observed behaviour. Based on stress-incremental test results, the coaxing effect became less pronounced with increasing prestrain, disappeared at 15% and then again appeared at the larger prestrains of 25% and 58%. The observed prestrain dependence in corrosion fatigue behaviour and coaxing effect clearly indicated that different mechanisms had operated below and above the prestrain of approximately 15%. Possible mechanisms such as work hardening and strain-induced martensitic transformation were discussed.
2007-07-25