ELEVATED-TEMPERATURE LOW-CYCLE FATIGUE BEHAVIOR OF HK40 ALLOY

By conducting creep tests and creep-fatigue tests at temperatures of 8 00-degrees-C, 900-degrees-C and 1000-degrees-C, on centrifugal cast HK 40 alloy (which is used for example for the steam reformer tubes of fu el cell plants) and varying the strain rate during the loading and unl oading process, the influence of strain history on the life of the mat erial has been clarified. Furthermore, the data obtained from these te sts were subjected to analyses by means of life evaluation methods uti lizing the life fraction rule, strain range partitioning method, and d amage rate approach, and comparative studies were conducted on each li fe evaluation method, As a result, problematic points concerning the a pplication of the life fraction rule, strain range partitioning method , and damage rate approach have been clarified and data which would be useful in establishing design guidelines for structures to be used un der conditions such as involves the interaction of creep and fatigue h ave been obtained.