タービン用12%Cr耐熱鋼の時効およびクリープに伴うスモールパンチ試験特性の変化

抄録

In order to examine the adaptability of small punch (SP) test to the evaluation of aging degradation of 12%Cr heat resistant steels used for the USC steam turbine, the rotor and casing steels, which had been thermally aged and stress aged at 610, 630 and 650°C, were subjected to the SP test at the temperature range from -196°C to 80°C. The changes in tensile and ductile-brittle transition properties due to aging were investigated based on the SP test results. Experimental results revealed that the tensile strength decreased with increasing aging temperature and aging time, and this decrease in strength level (softening) was more pronounced in the rotor steel. It was also found that the ductile-brittle transition region shifted to higher temperature side and the upper shelf energy decreased with aging at 610°C. This embrittlement tended to recover by the higher temperature aging at 630 and 650°C. There was no significant influence of stress aging (creep) on the abovementioned material deteriorations, that is, softening and embrittlement.