Abstract
Ultrasonic shot peening was applied to stainless steel type 304, and rotating bending fatigue tests had been performed at the elevated temperature of 300℃. The shot-peened specimens showed subsurface fatigue crack initiation with typical fish-eye at 300℃ in the high cycle fatigue region (≈10^7 cycles). The crack initiation site was cut by the wire saw method, and observed on the longitudinal section by EBSD technique in detail. Inclusions such as intermetallic compounds were not recognized at the sub-surface crack initiation site, indicating that the crack initiation was due to cyclic slip deformation. Sub-surface crack initiated in the grain with many twins. It was considered that the twining had played important role in the sub-surface crack initiation at the elevated temperature.
