Change of Microstructure Evaluation during Fatigue of Stainless Steel in Power Plants

The microstructural change into an austenitic stainless steel (SUS316L) by low-cycle fatigue was measured with two measurement methods: the positron annihilation method and electron backscatter diffraction (EBSD) technique. Samples of various degrees of low-cycle fatigue with strain control in room temperature were prepared for the above measurement methods. The cyclic strain was caused crystal misorientation at the micro level and the change was quantified by a parameter called local misorientation by KAM (Kernel Average Misorientation). The average of misorientation obtained by KAM showed a proportional increase with the fatigue damage to cycle to fatigue, Nf. Positron annihilation lifetime measurements showed an increase in the positron lifetime for fatigued SUS316L samples compared to the as-received sample.