Effect of hold-type on cyclic life and microstructural evolution of an austenitic stainless steel

The present work investigates the effect of different type of hold on the change in microstructure and cyclic life. i.e., number of cycles to failure of the 304LN grade austenitic stainless steel at an elevated temperature. The strain-controlled low cycle fatigue and creep-fatigue interaction tests were carried out in air at 540 °C for constant total strain amplitude levels of ± 0.5 % and ± 0.7 %. The duration of hold-time was maintained at a constant level of 600 s at peak tensile, compressive and both peak tensile-compressive strain during different creep-fatigue interaction tests. Due to incorporation of creep damage, the cyclic life of the creep-fatigue interaction-tested samples has been found to be lower than that of the low cycle fatigue-tested samples. The tensile-hold appears to have maximum impact on reduction in cyclic life during creep-fatigue interaction tests followed by tension-compression hold and compressive hold. The scanning electron microscopy and electron back scattered diffraction analyses of creep-fatigue interaction-tested samples have revealed that the grain size coarsening, reduction in twin boundary fraction and increase in average Kernel Average Misorientation are the key factors in reduction of cyclic life.