The Investigation Of Local Corrosion And Passive Properties Of 2205 Duplex Stainless Steel

Duplex stainless steel(DSS)is composed of ferrite and austenite phases,possessing the characteristics of both ferrite and austenite stainless steel,and is widely used in harsh environments such as petroleum,chemical engineering,and bridges.Although a passive film may form on the surface of DSS during service,hindering material exchange between the substrate and corrosive media,corrosion reactions still occur slowly,which can cause serious harm to the constitute phases of DSS and affect the service life of DSS.Therefore,the investigation of the local corrosion and passive properties of DSS is of great significance for guiding production practice and optimizing process parameters.In this work,KEYENCE VHX-5000 ultra depth of field microscope,scanning electron microscope with energy spectrum(SEM-EDS),Thermo calc calculation software,electron backscatter diffraction(EBSD),X-ray photoelectron spectroscopy(XPS)and X-ray diffractometer(XRD)are used for this investigation.Moreover,scanning vibration electrode technology(SVET),zero resistance ammeter(ZRA),open circuit potential(OCP)measurement,dynamic potential polarization test,constant potential polarization test,Electrochemical impedance spectroscopy(EIS)and Mott-Schottky are used to investigate the factors affecting the local corrosion and passive properties of DSS.In addition,a numerical simulation model is used to study the corrosion potential distribution,local current density,and corrosion morphology of DSS due to the random occurrence and difficulty in detecting local corrosion.The effects of solution treatment temperature and immersion time on the micro-galvanic corrosion of DSS are investigated,and then study the effect of solution treatment time on the passive properties of DSS and its constituent phases.Finally,cold-rolling and annealing is used to refine the grain size of DSS to improve its resistance to local corrosion and passive properties,and the mechanism of grain refinement on the local corrosion and passive propertises of DSS is explored.The main conclusions are as follows:(1)As the solution treatment temperature increases,the micro-galvanic corrosion resistance of DSS shows a trend of first increasing and then decreasing,and the resistance to micro-galvanic corrosion of DSS is the best at 1100℃.The micro-galvanic corrosion of DSS is influenced by both phase ratio and the electrochemical properties of the constituent phases.(2)In 1 M H2SO4+1 M NaCl solution,the micro-galvanic corrosion depth,local current density and corrosion rate of DSS increase gradually with the increase of immersion time.The function relationship between galvanic corrosion depth and time is deduced by mathematical method:h=3.22×[(6.52×10-2t+1)1.85-1](3)With the extension of solution treatment time,the grains of ferrite and austenite phases coarsen,and the grain boundary density and the proportion of low angle grain boundaries decrease.The corrosion resistance of DSS decreases with the increase of solution treatment time.The corrosion resistance of ferrite phase decreases with the increase of solution treatment time.The corrosion resistance of austenite phase increases first and then decreases with the extension of annealing time.(4)After cold-rolling and annealing,the grain size of DSS decreases,the proportion of low angle grain boundaries of ferrite and austenite phases decreases,but the density of low angle grain boundaries increases.After grain refinement,the corrosion resistance of ferrite and austenite phases is improved,and the corrosion resistance of DSS is also improved.The results of scanning vibrating electrode technology and numerical simulation show that the potential difference of the constituent phases of the fine-grained DSS sample is reduced,and its microgalvanic corrosion resistance is enhanced.