SUS304鋼の疲労挙動に及ぼす加工誘起マルテンサイト変態量の影響とEBSDによる相変態解析

概要

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The effects of the strain-induced martensitic transformation on the fatigue behavior of type 304 stainless steel were studied. Rotating bending fatigue tests have been performed in laboratory air and in 3%NaCl solution using specimens subjected to tensile-prestrains at ambient temperature and -25°C. Martensitic transformation occurred more remarkably at -25°C than at ambient temperature. In laboratory air, the fatigue strengths of the prestrained specimens increased with increasing prestrain and the specimens subjected to the same prestrains at each temperature exhibited similar fatigue strength in spite of the different amount of martensitic phase. This indicated that the increase in fatigue strength of the prestrained specimens was primarily attributed to work hardening. In 3%NaCl solution, the fatigue strengths of the prestrained specimens at -25°C decreased significantly compared with those in laboratory air. EBSD analysis revealed that the strain-induced martensitic transformation took place within slip bands and corrosion pits were observed at the crack initiation site in the large prestrained specimens. Based on these results, it was confirmed that the strain-induced martensitic transformation exerted large influence on the fatigue behavior in 3%NaCl solution.