Thermal fatigue strength of 304 stainless steels

In order to investigate the properties of thermal fatigue strength under creep-fatigue interaction, in-phase and out-of-phase thermal fatigue tests at the temperature ranges of 200 - 550 and 300 - 6000C as well as isothermal low-cycle fatigue tests at 550 and 6000C were carried out on three kinds of 304 stainless steel. Based on the relation between the fatigue life and the failure mode, the time-dependent effect on the fatigue life was discussed. Also, an attempt was made to apply the strain range partitioning method to the thermal fatigue life prediction. As a result, it seemed difficult to evaluate the thermal fatigue life at high temperatures simply from the isothermal fatigue life under the same strain condition. It was also found that an unbalanced creep strain during tensile loading, which increased the number of intergranular cracks. gave the largest damage to the material. By the strain range partitioning method, it was possible to predict the isothermal fatigue and the thermal fatigue at the low temperature range within a factor of 1.5. On the other hand, the thermal fatigue life at the high temperature range could be predicted within a factor of 3. However, further detailed investigations are required on the technique of partitioning the inelastic strain range and the effects of dynamic strain aging and recovery during strain holding for a better prediction. (author)