Corrosion Behavior Of 2507 Super Duplex Stainless Steel Under AC Interference In Simulated Marine Environment

2507 Super duplex stainless steel has been gradually applied in Marine engineering due to its excellent chlorine corrosion resistance and comprehensive mechanical properties.In addition,AC current is frequently detected in coastal areas near offshore projects and ultra-high voltage transmission lines.The AC interference may threaten the safety service of relevant equipment.At present,there are few reports on the corrosion behavior and mechanism of duplex stainless steel by AC current.Therefore,the corrosion behaviour and mechanism of 2507 SDSS in simulated Marine environment were studied in this article.And main conclusions are as follows:(1)The thickness,composition,structure and electronic properties of the passive film change with the interference of different AC current densities.Under AC interference,the film shows the non-uniform failure characteristics of holes and similar grooves,which makes it easier for corrosion ions to reach the surface of the metal matrix and speeds up the occurrence of corrosion.In addition,with the increase of the AC current density,the sizes of particle increases,this indicates that the AC current promotes the dissolution of the passive film.When the AC current density is less than 100A/m²,pitting corrosion was mainly concentrated on the austenite and the ferrite and austenite boundary.However,when the AC current density reaches 200A/m²,the corrosion driving force is further increased,resulting in a large number of pitting corrosion on the ferrite phase.(2)The 2507SDSS prepared by different cooling methods is studied to simulate the corrosion behavior of welded joints.The results show that the passive films formed on different tissues have different uniformity,stability and protection under the interference of AC.Among them,the passive film on the surface of normalized microstructures has the highest pitting resistance equivalent coefficient(PREN),the least defects,the superior stability and corrosion resistance.Due to the emergence of precipitated phase in annealed microstructures,the protection of passive film is greatly reduced,and the pitting corrosion is mainly distributed in the precipitated phase.In addition,the higher the volt potential difference between ferrite and austenite phases of the quenched microstructures,the greater the driving force of the micro couple corrosion will be,resulting in more serious corrosion than that of the normalized microstructures.(3)With the increase of annealing temperature,the content of austenite decreases and ferrite increases.The corrosion resistance of steel is greatly reduced by precipitation phase and the presence of a large number of ferrite phases.In addition,with the increase of AC current density,the pitting potential of annealing steel at different temperatures shifted negatively,pitting sensitivity and corrosion rate increased.Therefore,the AC corrosion behavior of different annealed tissues is closely related to the structure of the tissues.After aging treatment at 850?,it is found that with the prolongation of aging time,many precipitated phases appeared in the tissues,and the corrosion resistance of the samples decreased successively.The R_ctand R_fof the passive film formed after aging for 1h are the minimum,and possess most defects.When the aging time is 5min,the content of H₂O and Cr₂O₃in the passive film increases,while the content of FeO decreases,which indicates that the precipitated phase seriously reduces the protective ability of the passive film.