| Laser peening technology has been proved to be an effective method to increase the fatigue life of components by inducing compressive residual stress as well as refining the surface grain size and influencing the dislocation density. Also it is considered to decrease the susceptibility to stress corrosion cracking of components serving in corrosive environment. It is known that the stress corrosion cracking and the hydrogen embrittlement has the similar phenomenon. Therefore the study of laser peening to increase the anti-hydrogen embrittlement properties of the material is of very important academic value.In this paper, 316 L stainless steel is used for the research. The mechanism and experimental research concerning to the effects of laser peening on the susceptibility to hydrogen embrittlement of 316 L stainless steel are carried out. The principal works are as follows:(1)Based on theories about the plasma shock wave induced by the interaction of nanosecond pulsed laser with material, the strengthening mechanism of material during the loading of high amplitude laser-induced shock wave pressure was theoretically analyzed. Focused on 316 L stainless steel, the microstructure response mechanisms after severe plastic deformation at high strain rates were demonstrated. On the basis of the comprehensive analysis of hydrogen diffusion behavior and the factors that influence the diffusion of hydrogen, the possibility of laser peening to improve the anti-hydrogen embrittlement properties of 316 L stainless steel was demonstrated.(2)The microstructures and surface microhardness of laser peened specimens after hydrogen charging are analyzed by conducting the experimental researches of laser peening strengthening 316 L stainless steel and electrochemical hydrogen charging. The effects of laser peening on the hydrogen diffusion was demonstrated based on the distribution theory of residual stress induced by laser peening. The results showed that: laser peening technology induced a relatively deeper compressive residual stress and grain refinement on the surface of 316 L stainless steel. Afterelectrochemical hydrogen charging, hydrogen blistering was observed on the unpeened samples, as well as some grain boundary segregation, while little hydrogen blistering or grain boundary segregation was found on the laser peened samples surface.Meanwhile the unpeended sample showed higher hydrogen-induced hardening sensibility than the laser peened samples, which meant the anti-hydrogen embrittlement properties of 316 L stainless steel was improved.(3)The unpeened and laser peened samples were both stretched at slow rate before and after hydrogen charging to research the hydrogen embrittlement susceptibility of the samples. The effects of laser peening on the hydrogen induced ductility loss and the fracture morphologies were discussed based on hydrogen diffusion and dislocation migration theory. The results showed that laser peening improved the elongation and tensile strength of 316 L stainless steel and the laser peened specimens after hydrogen charging exhibited lower hydrogen induced ductility loss. However the fracture morphology showed little difference between unpeened and laser peened samples after hydrogen charging, as they were all ductile fracture. |
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