極軟鋼の静引張性質ならびに繰返し応力下の応力-ひずみ挙動に及ぼすひずみ時効の影響

概要

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For the purpose of explaining the mechanism of so-called "fatigue hardening", the static tension tests and the fatigue tests under pulsating tension with a constant stress amplitude were performed on a extremely low cabon steel and the relations among its yield strength, grain size, strain hardening exponent and strain ageing capacity were studied. The effects of decarburizing and denitriding on the mechanical properties were also investigated. From the fatigue experiments, the static tension properties during fatigue stressing and the variation of plastic strain amplitude under constant stress amplitude were clarified. Several significant results were obtained as follows: The values of the constants in the Petch relation on yield stress increase with strain ageing capacity. The strain hardening exponent does not depend on decarburizing and denitriding but its value increases with grain size. It is found that denitriding is much more effective than decarburizing to eliminate strain ageing. Three stages are recognized in the fatigue process of unnotched material. The hardening in STAGE I results mainly from strain hardening, while strain ageing seems to be the dominant factor of fatigue hardening in STAGE II.
1974-10-15