Hastelloy Xの高温低サイクル疲労特性に関する研究

抄録

Isothermal low-cycle fatigue tests including both load controlled and strain controlled tests were conducted on Hastelloy X, one of the materials for VHTR (Very High Temperature Gas Cooled Reactor). The effects of temperature, atmosphere, strain rate and hold time were studied. Special attention was given to the creep-fatigue criteria. The results are summarized as follows.
(1) In the simulated VHTR He gas, the fatigue life increases as compared with that in air for the test without any strain hold time, but remains almost unchanged for the test with a long strain hold time.
(2) In the temperature range from 800 to 1000°C, the Coffin-Manson relationship holds between plastic strain range and fatigue life, but it does not agree well with the result estimated from the tensile test.
(3) The relationships between plastic strain range and fatigue life obtained from the strain controlled test under different strain rates and strain hold times are almost equal. The fatigue life under the strain controlled test can be estimated using these relationships.
(4) The result of the load controlled test agrees well with that obtained by applying the linear damage rule on the assumption that the total damage consists of the two kinds of damages caused by cyclic plastic strain and by accumulation of creep strain on one side. The both damages can be calculated by applying the life fraction rule to the relationship between plastic strain range and fatigue life and to that between stress and creep rupture ductility, respectively.