Research on the regulation of welding residual stress in 316L austenitic stainless steel thick-section based on ultrasonic impact and vibration

In nuclear fusion engineering, high residual tensile stresses post-weld critically undermine structural integrity by reducing fatigue strength, accelerating crack propagation, and increasing the risk of failure. Alleviating residual tensile stresses in thick-section 316L austenitic stainless steel continues to be a significant scientific and engineering issue. This study investigated the effects of ultrasonic vibratory stress relief (UVSR) and ultrasonic impact treatment (UIT) through 4 customized process schemes: layer-by-layer UVSR, post-weld UVSR, and the UIT-UVSR composite process. The distribution of residual stress, microstructure, and mechanical properties of welded joints in fusion reactor vacuum vessel components were thoroughly assessed. All four schemes diminished welding residual stresses, enhanced the microstructure, and elevated local mechanical characteristics. Significantly, post-weld UVSR attained optimal stress relief, diminishing longitudinal and transverse residual stresses by 51.2 % and 25 %, respectively, while facilitating a more uniform stress distribution. The UIT-UVSR composite processes could not demonstrate synergy beyond individual UVSR, and layer-by-layer UVSR proved less effective than post-weld UVSR. In summary, post-weld UVSR is an efficient technique for regulating residual stresses in thick-section 316L welds, offering practical insights for components of fusion-reactor vacuum vessels.