Effect of Strain Hold Time on Fatigue Life of Alloy 800H at High Temperatures.

Axial strain-controlled fatigue tests and tensile peak strain hold fatigue tests were conducted on alloy 800H in 850°C∼950°C air to investigate the effect of the stress relaxation process on the fatigue life of the material. Subsequently, it was noted that the fatigue lives were only slightly affected by temperature in this high temperature region. It was also recognized that fatigue life decreased with the introduction of tensile strain hold time, but the effect of strain hold time on fatigue life saturated in a rather short strain hold period due to the rapid stress relaxation behavior of the material in these temperatures. These results were investigated from the viewpoint of microstructural changes and fractographic features of specimens. Finally, creep-fatigue damage interaction values were calculated and D=0.4 was found to be the optimum minimum damage value of this material.