Study On Stress Corrosion Sensitivity Of Cold Deformed 316L Austenitic Stainless Steel In H₂S Environment

316L austenitic stainless steel is excellent in corrosion resistance and is widely used in the petrochemical industry.With the development of H₂S-rich oil and gas fields,316L austenitic stainless steel is prone to stress corrosion cracking in a composite environment composed of H₂S and Cl_-solution,causing economic losses and casualties.In addition,316L austenitic stainless steel has low strength and can meet the mechanical requirements and can be strengthened by cold deformation.This paper mainly studies the stress corrosion mechanism of cold deformed 316L in Cl^-/H₂S environment.Firstly,the stress corrosion sensitivity of solid solution state and cold deformation316L in Cl^-/H₂S environment at different temperatures was studied by SSRT.The results show that the cold deformation improves the stress corrosion sensitivity of 316L,but does not change the stress corrosion sensitivity of 316L:from 30?to 200?,the stress corrosion sensitivity of 316L increases with the increase of temperature,at 200?stress corrosion sensitivity is the highest;from 200 to 300?,the stress corrosion sensitivity of 316L decreases with increasing temperature.The morphology of SSRT fractures in solid solution and cold deformation 316L in Cl^-/H₂S environment was observed by SEM.The results show that the cold deformation and solid solution 316L have the same fracture mode:30?,150?and 300?,316L The fracture mode is transgranular fracture.At 200?and 250?,the fracture mode of 316L is intergranular fracture.The difference in the microstructure between solid solution and cold deformation 316L was analyzed by metallographic microscope and XRD.It was found that after cold deformation,no martensitic transformation occurred in 316L,but the dislocation density increased,and a large number of slip bands and twins were generated.The entanglement of dislocations hindered plastic deformation,so 316L was strengthened.The cold deformation increased the tensile strength of 316L from 600MPa to 860 MPa,but the elongation decreased from 73.72%to 17.62%.Secondly,the stress corrosion susceptibility of cold deformed 316L in single Cl-or H2S environment at 30?,150?,200?and 250?was studied by SSRT.The fracture morphology of cold deformed 316L SSRT was observed by SEM.The results show that the cold-deformed 316L has no stress corrosion resistance in the Cl-environment at200?,and no stress corrosion occurs in the other Cl^-or H₂S environment at other temperatures,only in the environment where Cl^-and H₂S coexist.Stress corrosion will occur.Then,the stress corrosion sensitivity of cold deformed 316L in Cl^-environment of different poisoning agents was studied by SSRT,and the fracture morphology of SSRT was observed by SEM.The results show that the cold deformation 316L undergoes ductile fracture in Cl^-/H⁺environment.After adding poisoning agent KSCN in Cl^-/H⁺environment,the fracture mode of cold deformation 316L is changed into brittle fracture,and cold deformation 316L is in Cl^-/H₂S.The fractures in the environment are the same.The hydrogen content of the cold-deformed 316L after electrochemical hydrogen charging was measured by a diffusion hydrogen meter.The results show that the poisoning agent can increase the hydrogen content into the interior of 316L.Finally,SSRT was used to study the stress corrosion sensitivity of cold deformed316L in Cl^-and S^2-solutions containing H₂S,and the fracture morphology was observed by SEM.The results show that the cold-deformed 316L does not undergo stress corrosion in the S^2-solution containing H₂S,stress corrosion occurs in the Cl^-solution containing H₂S,and the stress corrosion sensitivity of cold-deformed 316L increases with the increase of Cl^-concentration..The polarization curves of cold deformed 316L in different concentrations of Cl^-solution indicate that the pitting potential of cold deformed 316L decreases with increasing Cl^-concentration.The hydrogen content of the cold-deformed 316L after electrochemical hydrogenation was measured by a diffusion hydrogen meter.The results show that the hydrogen content entering the cold-deformed 316L is increased in the case of a little etching.The stress corrosion of cold deformation 316L is the result of the interaction of Cl^-and H₂S:Cl^-destructive cold deformation 316 surface passivation film produces pitting corrosion and causes crack initiation.Due to the existence of pitting corrosion,hydrogen entering the cold deformation 316 The content increases;the poisoning agent formed by the dissolution of H₂S in water further increases the hydrogen content into the cold deformed 316L,resulting in hydrogen induced martensite transformation,cold brittleness,local brittleness,and brittle fracture of cold deformation 316L.