Study On Properties Of 904L Stainless Steel With Different Surface In Fluorine Solution

Austenitic stainless steel has low surface hardness,poor wear resistance,deterioration of corrosion resistance in the presence of defects,etc.In this paper,904L austenitic stainless steel was modified by laser cladding and low-temperature glow ion nitriding.The electrochemical measurement,micro-morphology characterization and finite element simulation were used as the main research methods.The corrosion and mechanical properties of laser cladding and low temperature glow ion nitridation at different pressure were investigated.The corrosion dissolution behavior of 904L austenitic stainless steel after strain concentration on nitrided austenitic stainless steel in acidic solution was studied by simulating the defects caused by the defect of the microstructure surface of the simulated samples in the working environment.Laser cladding results show that After the cladding surface melts and solidifies,the thickness of the cladding layer is about 130μm.New phases such as Cr15Ni4W、γ（Fe,Ni）were precipitated from the cladding layer.The cladding layer forms tetragonal star-shaped grains,fine and dense equiaxed crystals,forming dendrites at the junction of the substrate and the cladding layer.The hardness of the laser cladding coating is improved,and the average hardness is 650 HV.The combination of the cladding layer and the substrate forms planar crystals and dendrites to form a metallurgical bond.The nitriding sample has better self-corrosion potential and transfer charge than the original 904L austenitic stainless steel and laser cladding samples.The corrosion appearance of the three laser corrosion coating samples is severe,and the corrosion of different grain morphology areas inconsistent appearance.The results of different pressure nitridation experiment show that the self-corrosion potential of austenitic stainless steel at 100Pa under low temperature nitriding is-297.03mV,the self-corrosion current density is 15.933 mA·cm^-2,and the corrosion rate is 0.18741 mm·A^-1.The scanning Kelvin probe potential value is 0.7637V.It means that the nitriding at 100Pa can not reduce or slightly improve its corrosion resistance.Its hardness value is as high as 1409 HV.At pressure 100Pa,temperature400℃,glow plasma nitriding can greatly increase the surface hardness value of 904L austenitic stainless steel and slightly increase or not deteriorate its corrosion resistance.Nitrided 904L undergoes a large number of cracks after indentation deformation,and crevice corrosion produces a stepped corrosion morphology.Original 904L corrosion resistance are more sensitive to plastic deformation,which is deeper and wider indentations spread morphology,generating pit bottom.The low sensitivity of nitriding 904L corrosion resistance to plasticity is attributed to the formation of strengthened phaseγN after nitriding,which plays a key role in the mechanical properties and corrosion resistance of 904L Austenite stainless steel.Therefore,there is a certain difference between the original 904L and the nitrided 904lL Austenite stainless steel in the dissolution process.After immersion,the indentation corrosion is closely related to the strain distribution.The square cone indentation strain distribution is concentrated at the apex of the indenter,and the strain distribution is weakened to the periphery.The corrosion dissolution of the original 904L is selective.A large number of cracks produced by nitriding 904L make the corrosion rate larger at the later stage.Strengthened phaseγN has better improvement in corrosion resistance,and the sensitivity of nitriding 904L to plastic deformation is reduced at the same time.