Abstract
Creep-fatigue tests were conducted with 2 1/4Cr-1Mo steel at 550°C in air and vacuums of 0.1 and 100μPa to separate the environmental effect from the pure creep-fatigue behavior. In 0.1μPa vacuum where no environmental effect was detected, creep-fatigue life reduction was observed when the time for tension going stroke exceeded that for compression going stroke. Furthermore, it was observed that a positive mean stress reduced the creep-fatigue life in high vacuum. A good correlation existed between a creep-fatigue life and the fracture mode. No life reduction occurred when the fracture mode was predominantly transgranular. On the contrary, a significant life reduction was observed when it was predominantly intergranular. An environmental effect was also examined qualitatively. The effect of the air environment dependent strongly upon the waveform. The above observations were compared to those obtained with 304 steel in a previous study of one of the authors.
