高窒素オーステナイト系ステンレス鋼SUS304N2の疲労挙動

概要

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This paper presents the fatigue behavior of a high-nitrogen austenitic stainless steel, type 304N2. Rotating bending fatigue tests have been performed in laboratory air and in 3%NaCl solution, and the results obtained were discussed through the comparison with those of type 304. Type 304N2 showed higher static strength and fatigue strength in both environments than those of type 304. Since the crack growth rates in both materials were almost similar, the resistance to crack initiation was the primary cause of the observed higher fatigue strength of type 304N2. In 3%NaCl solution, fatigue strength of both materials increased slightly compared with those in laboratory air due to the cooling effect of the solution. Under stress-incremental tests, failure stress did not increase significantly in type 304N2 compared with type 304, indicating a less pronounced coaxing effect in type 304N2. The difference in the coaxing effect between both materials seemed to be due to strain-induced martensite transformation that occurred significantly in type 304. No strain-induced martensite transformation took place in type 304N2 because of higher stability of austenitic phase, thus the coaxing effect in type 304N2 was attributed to both work hardening and strain aging.