Abstract
The high-cycle fatigue properties of low carbon 316 stainless steels, 316F with 0.04 mass%C and 316PSI with 0.001 mass%C, were investigated and compared with those of 316(ST-1) with 0.08 mass%C reported previously. Both the fatigue hardening and life decreased with carbon content, especially in 316PSI, indicating that the fatigue induced precipitates suggested for 316(ST-1) were mainly carbide or some complex of carbon-solute atoms. Effects of in situ 20 MeV proton irradiation or thermal-pulse were further investigated for 316F at 333∼573 K. In 316(ST-1), radiation damage, i.e. the effect of irradiation after the subtraction of thermal effect, caused an enhancement of the fatigue hardening at both 333 and 573 K. In contrast, in 316F radiation damage caused a suppression of the fatigue hardening at 333 and 453 which reversed to the enhancement at 403 and 503 K, and again the suppression at 573 K. The suppression can be expected when the effects of dispersion of existing precipitates by irradiation were larger than the other effects of irradiation, and vice versa. Therefore, we consider that the fatigue induced precipitates were smaller in their size in 316F than in 316(ST-1), and in 316F the precipitates of various types probably correspond to the suppressions at 333, 453 and 573 K. The corresponding results for thermal-pulse and the results observed for the effects of in situ irradiation or thermal-pulse on the fatigue life were compatible with the view mentioned above.
