The effect of mechanical loading on residual stress induced by laser peening

The stress corrosion cracking(SCC) of austenitic stainless steel and nickel-based alloy is a primary concern for stable operation in Boiling Water Reactors(BWRs) and Pressurized Water Reactors (PWRs). Laser peening is one of the promising technologies for prevention of SCC initiation to induce compressive residual stress near the surface region. However, the compressive residual stress by laser peening is likely affected due to applied stress. In this study, the effect of mechanical loading on the compressive residual stress by laser peening was investigated. The specimens of low carbon austenitic stainless steel (Type316L), nickel-based alloy (Alloy600) and their weldments were prepared, and several levels of cyclic loading were applied to their specimens. The surface residual stress at surface was measured by X-ray diffraction method before and after loading. The relaxation behaviour of the compressive surface residual stress by laser peening was evaluated at the base metal and heat affected zone (HAZ) of the weldment. It was confirmed that compressive surface residual stress remained after stress loading which corresponds to 0.2% proof stress, and that the relaxation of the surface residual stress remarkably observed after initial loading during cyclic loading test. These relaxation behaviour were similar in Type316L, Alloy600 and their HAZ. (author)