Research On Corrosion Resistance Enhancement Of AISI430 Ferritic Stainless Steel By Laser Shock Peening

Ferritic stainless steel has been widely used in many fields such as automobile manufacturing,home appliance industry and construction industry due to its advantages of nickel-free,low price,good oxidation resistance,stress corrosion resistance and high thermal conductivity.Because it is often in corrosive places,it has higher requirements for the localized corrosion resistance of ferritic stainless steel.As a new surface modification technology,laser shock peening(LSP)uses high strain rate shock waves to act on the surface of the material,resulting in grain refinement and residual compressive stress to improve the mechanical properties and corrosion resistance of the sample.In thist thesis,AISI430 ferritic stainless steel was used as the research object.Through the electrochemical experiments such as polarization curve and electrochemical impedance spectroscopy(EIS),combined with mechanical properties and surface morphology,the corrosion resistance of laser shock process to AISI430 ferritic stainless steel was studied.The main research contents and results of this thesis are as follows:(1)The strengthening mechanism of LSP on AISI430 ferritic stainless steel was analyzed theoretically.The optimum experimental parameters of LSP on AISI430 ferritic stainless steel were obtained through analysis and calculation.The change of mechanical properties of AISI430 ferritic stainless steel after LSP was studied.The three-dimensional morphology and micro-morphology of the sample after LSP were observed and analyzed.The results show that the surface of AISI430 ferritic stainless steel after LSP has plastic deformation and grain refinement,and the micro-hardness of the material surface has been improved obviously after LSP.After impact,the residual compressive stress layer appears on the surface of AISI430 ferritic stainless steel.(2)Electrochemical experiments were carried out on AISI430 ferritic stainless steel before and after LSP in 0.1mol/L HCl solution.The experimental results show that the selfcorrosion potential of the sample is positively shifted after LSP,and the corrosion current density is reduced.The capacitive reactance arc of EIS is increased,and the corrosion resistance of the materials is enhanced.Microscopically,the resistance of AISI430 ferritic stainless steel in an acidic environment was improved.Combined with residual stress and grain refinement,the reasons are theoretically summarized.The results show that the residual compressive stress can make the oxide film on the surface of the material more compact,inhibit the peeling of corrosion products on the surface of the material,and reduce the further development of corrosion.The grain refinement improves the mechanical properties of the sample,and the structure of the material is more dense,which makes the corrosion difficult.Grain refinement enriches the Cr element on the surface of the material to enhance corrosion resistance.(3)The electrochemical experiments of AISI430 ferritic stainless steel before and after LSP were carried out in 3.5% NaCl solution.The experimental results show that LSP can positively shift the self-corrosion potential of AISI430 stainless steel in 3.5% NaCl solution,reduce the corrosion current density of materials,reduce the corrosion pits and strip corrosion on the corroded surface of materials,enhance the corrosion resistance of AISI430 stainless steel in neutral solution.