Corrosion Behavior Of Super Duplex Stainless Steel In Typical Service Environment

Super duplex stainless steel is one of the important development directions of high-quality stainless steel. High Cr, high Mo, high N and ultra low carbon duplex stainless steel has the characteristics of austenitic stainless steel and ferrite stainless steel. Compared with the austenitic stainless steel, it has high strength and intergranular corrosion resistance and resistance to chloride stress corrosion properties are significantly improved; and compared with ferrite stainless steel, the plasticity and toughness are higher, no room temperature brittleness, intergranular corrosion resistance and welding performances are significantly improved; it has excellent resistance to pitting corrosion and local corrosion, seawater corrosion resistance, resistance to organic acid and other special medium are fine. Therefore, studying the main factors on the super duplex stainless steel in typical corrosive environment effects about failure regularity and mechanism, establish and perfect the related experimental database can provide theoretical guidance for the production enterprises to select reasonable material, and then accelerates the development of related industries healthily.This article mainly focuses on the corrosion behavior of super duplex stainless steel S32750in two typical service environments. The corrosion behavior of super duplex stainless steel S32750in simulated sea water and paper white liquor is investigated by five electrochemical detection methods of tentiodynamic polarization, potentiostatic polarization, cyclic polarization, electrochemical impedance (EIS) and Mott-Schottky with electrochemical workstation Gamry Reference600. Using scanning electron microscopy (SEM) to observe the pitting morphology of super duplex stainless steel S32750in simulated seawater and paper white liquid. The structure of the passive film of duplex stainless steel S32750in simulated sea water and paper white liquid is analysed by XPS analysis tools.In simulated seawater desalination environment, potentiodynamic polarisation study shows that with the seawater temperature and concentration increasing, current density increases gradually, the pitting potential decreases significantly; constant potential polarization study shows that with the seawater temperature and concentration increasing, current density increases gradually, pitting index n decreases gradually, with the seawater temperature and concentration increasing, growth rate of passivation film decreases, reduce the protection performance of matrix; Cyclic polarization method showes that, with sea water temperature and concentration increasing, the area of hysteresis loop increases, the self repair ability of passivation film is weakened, pitting sensitivity increases; EIS study shows that, with the sea temperature and concentration increasing, super duplex stainless steel S32750polarization impedance decreases, which shows that the stability of the passive film variation, the corrosion rate increased; M-S results showed, membrane protective effects of passivation decreases with the seawater temperature and concentration increasing, pitting corrosion resistance decreases. At the same time, the study find that super duplex stainless steel S32750pitting resistance in seawater can be better than the super austenitic stainless steel S31254, ordinary duplex stainless steel S32205and316L steel.In the simulated white liquid environment, potentiodynamic polarisation study showes, with the white liquid temperature increasing, current density increases gradually, the pitting potential decreased significantly; polarization method of constant potential shows that, with the white liquid temperature increasing, current density increases, pitting index n decreases gradually, with the increase of temperature, the growth rate of passivation membrane decreases, reducing the protection performance of matrix; EIS shows that, with the white liquid temperature increasing, polarization resistance of super duplex stainless steel S32750decreases, that the stability of the passive film variation, the corrosion rate increases; M-S results showed, membrane protective effects of passivation decreases with the white liquid temperature increasing, resistance pitting corrosion decreases. In addition, corrosion performance of super duplex stainless steel S32750in white liquor is better than the ordinary S32205duplex stainless steel. In addition, the observed pitting morphology of super duplex stainless steel S32750in simulated seawater desalination and white solution by using scanning electron microscopy shows that pitting occurs preferentially from the inclusion of steel surface produces, main composition of inclusions for Al2O3.Crevice corrosion behaviors of super duplex stainless steel S32750are studied in seawater and paper white liquor using potentiodynamic polarization. Studies show that with the seawater and paper white liquor temperature increasing, crevice corrosion resistances of super duplex stainless steel S32750reduce.The structure of polarized passivation film of super duplex stainless steel S32750in seawater are detected by XPS analysis method, the study finds that layer is mainly composed of Fe2O5, Cr(OH)3, Cr2O3, Fe3O4, Cr2N and other components. The existence of Mo4+and NH4+between the membrane and the solution has a good protective effect on the passive film. Polarized oxide layer of the passivation film of super duplex stainless steel S32750is mainly composed of Cr(OH)3, Cr2O3, Fe3O4, Fe2O3and other components.