Abstract：Abstract: The present work aims to investigate microstructural evolution of shot peened 316L austenitic stainless steel during strain-controlled low-cycle fatigue test. The investigated specimen is first mechanically and electrolytically polished, then the interrupted fatigue testing is carried out until crack initiation stage. The microstructure is subsequently examined and characterized using multi-instrumental techniques such as scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and atomic force microscope (AFM). Shot peening produces a surface treated austenitic steel with gradient microstructure, thus the surface region divides into 2 layers: highly deformed layer and bulk material. Result shows that at the crack initiation stage, the surface is roughened, the height of extrusion is increased, the grain average misorientation is augmented in both the two layers. The extrusion height in bulk material layer is higher, which means it favoring the crack nucleation process, hence the crack is found to be more likely to occur along slip band in the core material rather than at the near surface region.
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2020, Vol. 27 