Residual stress distribution of austenitic stainless steel 304L with femtosecond laser ablation

Recently a femtosecond laser ablation was proposed as a mitigation method for stress corrosion cracking (SCC). This method cannot only ablate a thin hardened layer of the tensile stress surface, but can also induce a compressive residual stress to the ablated surface. Herein, the effect of different femtosecond laser ablation conditions on the in-depth residual stress profile was investigated for austenitic stainless steel 304L, which is used in core shrouds and recirculation pipes of boiling-water reactors (BWRs). The distribution of the in-plane residual stress was measured by a conventional X-ray method and a strain scanning method with high-energy synchrotron radiation X-rays at SPring-8. It was found that a relationship between the spot diameter and the influenced depth of femtosecond laser ablation exists. A small spot diameter can change the internal residual stress from a tensile stress to a compressive stress, while a large spot diameter can change the tensile residual stress beneath the surface to a compressive stress. Furthermore, the number of scans of the femtosecond laser ablation seems to be crucial in the shift of the tensile stress to a compressive stress in the territory influenced by femtosecond laser ablation. (author)