Abstract
For instrumentals used at high temperature for long term, such as steam turbine of thermal power plant, it is indispensable to grasp these deterioration states, since a material deterioration of softening, causes strength reduction and embrittlement leads to a falloff of tolerance crack length, etc., advances gradually, even when the creep or creep fatigue are not actualized, in order to prevent a destruction. Although it has been reported, at the hot section with the operating temperature higher than 500 ℃, tensile and creep strength fall together with softening, the knowledge which is needed for future operation management, whether deterioration state will advance with increasing speed or saturate etc., is not acquired. In this study, for the reheat stop valve scrap wood used for more than 300,000 hours, we carried out a hardness testing, charpy impact test, etc., and investigated the deterioration and embrittlement status.
