酸素飽和の高温水中における炭素鋼の低サイクル疲労強度

抄録

Surface degradations are induced in components of industrial machineries during long period of operation. The integrity assessment for aging component requires the consideration of actual operating conditions. Among those, surface degradation and low strain rate are the major factors to be considered for fatigue assessment in high temperature water. Fatigue tests using notched specimen in oxygenated high temperature water 300°C were performed to establish the assessment criterion for degraded material. It showed that deeper notch caused more reduction of the fatigue strength at long life region and the lower strain rate resulted in shorter fatigue life. The formation of corrosion groove was also investigated using temperature changing test. The formation of corrosion groove was caused by the rupture of oxidation film at the bottom of groove with the aid of mechanical strain cycling. The oxygen concentration cell assisted the corrosion process. This process was accelerated at relatively low temperature, i.e. 150°C. Fatigue life assessment method was proposed for aging component, which incorporated both effects of surface degradation and strain rate.