| Hydrogen energy has the advantages of rich reserves,renewable,storable,transportable and high conversion utilization,which is considered to be the most promising clean energy in the 21 st century.The safe and efficient storage of hydrogen is the key to large-scale utilization of hydrogen energy.Austenitic stainless steel is widely used in the field of hydrogen energy equipment because of its weak sensitivity to hydrogen embrittlement.However,when austenitic stainless steel is in service in hydrogen-rich environments,hydrogen induced cracking often occurs prematurely due to hydrogen permeation,which greatly reduces its service life.Laser peening(LP),as a novel and highly efficient surface modification technology,can effectively improve the hydrogen embrittlement resistance and service life of key components of hydrogen energy equipment.In this paper,the mechanism of resistance to hydrogen embrittlement of 316 L stainless steel in hydrogen-rich environments strengthened by LP was studied by theoretical analysis,experimental research and numerical simulation.Main tasks as follows:(1)Explore the mechanism of hydrogen permeation,hydrogen diffusion,and hydrogen-induced martensite transformation of austenitic stainless steels in hydrogenrich environments,and elaborate the governing and constitutive equations of hydrogen permeation.The mechanism of resistance to hydrogen embrittlement of 316 L stainless steel in hydrogen-rich environments was revealed from the static and dynamic perspectives.(2)Experiments of LP,electrochemical hydrogen charging and slow stretching on typical 316 L stainless steel samples were carried out to explore the macro and micro evolution characteristics of residual stress,grain size and dislocation configuration induced by laser peening on the surface and analyze their influence on hydrogen atom diffusion,aggregation behavior,hydrogen-induced martensitic transformation,hydrogen induced plastic loss and fracture morphology.Then,reveal the mechanism of hydrogen embrittlement resistance based on the coordination of residual stress,grain size and dislocation configuration.The results show that the compressive residual stress(CRS)and grain refinement induced by LP densified the treated surface,which could hinder the diffusion of external hydrogen into the material.At the same time,highdensity dislocations acted as hydrogen traps to capture invading free hydrogen.In addition,complex grain boundaries formed by grain refinement increased the slip length of hydrogen-carrying dislocations and made their distribution uniform to hinder the polymerization of hydrogen atoms into hydrogen molecules.The stress-strain curve shows that LP improved the tensile strength and elongation of 316 L stainless steel,reduced the degree of hydrogen-induced plastic loss.(3)Based on ABAQUS software,an integrated digital analysis module of LP process parameters,residual stress,hydrogen diffusion and stretching processes was established.The stress-strain results obtained from the numerical simulation of LP were used as the predefined fields for the simulation of hydrogen diffusion and stretching processes.The sequential coupling calculations of residual stress-hydrogen diffusion coupling field and stretching were performed to analyze the effect of CRS distribution on the hydrogen diffusion resistance and tensile behavior.Furthermore,the influence of residual compressive stress and hydrogen permeation behavior on the mechanical properties of 316 L stainless steel was investigated,and the hydrogen embrittlement sensitivity of stainless steel was reasonably predicted.The simulation results show that the simulated values of CRS induced by LP were in agreement with the experimental values,which could effectively inhibit hydrogen permeation.In addition,the tensile strength and elongation of laser peened samples were less affected by hydrogen diffusion,and the loss of hydrogen induced plasticity was not obvious,which was consistent with the change trend of test values. |
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