A Study On Strengthening Effects Of Laser Peening On Stress Corrosion Cracking Resistance Of Stainless Steel Welded Joints

Tensile welding residual stress existing in stainless steel weldment is the essential factor resulting in stress corrosion cracking (SCC). For this reason, a residual stress improvement technique using high energy laser beam which is usually so-called laser peening (LP, also known as laser shock processing) has been developed as a preventive maintenance technique to suppress SCC. This surface treatment technology is similar to traditional shot peening, in which significant compressive residual stresses are mechanically introduced into welded joints. In this thesis, based on finite element analysis and experimental studies, the influence of laser peening processing on SCC resistance of type 304 stainless steel welded joints in acidic chloride solutions is studied and evaluated. Main research works and conclusions are summarized as follows:(1) On the basis of analyzing the physical process of laser–matter interaction with high power density (in order of GW/cm2 range) and short duration (tens of nanoseconds) laser beam, the influence of energy transfer medium including absorbent coating and confined layer on laser-induced shock wave pressures amplitude and evolution was discussed. The experimental studies were carried out and it is observed that thickness and uniformity of absorbent sacrificial coating are influential factors relating to surface quality of laser-peened 304 stainless steel specimen. The shock wave pressure-time evolution generated by laser heated plasma was measured by PVDF transducer. As expected, pressure profile is a Gaussian temporal shape with a full width at half maximum (FWHM) of 80 ns which is approximately three times of laser pulse duration.(2) The surface residual stresses distributions of type 304 stainless steel specimens induced by laser peening were measured using X-ray diffraction technique. The measurement results show that LP processing produces compressive residual stress on the surface of impact zone which is extending to the periphery of processed zone, and the amplitude of compressive residual stress is improved as a result of an increase in laser pulse energy. But, at the same time, the"surface stress hole", which means the surface...