Effect Of S^2-?HSO₃^- And Cathodic Polarization On Corrosion Behavior Of A710 Steel In NaCl Solution

A710 steel,a new type of high strength marine engineering steels,will suffer corrosion in marine environment in the presence of anions and cathodic polarization during its service process.In this study,weightlessness method,electrochemical methods,combined with morphological observation and phase analysis were employed to investigated the corrosion behavior of A710 steel in 3.5%NaCl solution with different S^2-and HSO₃^-concentration or under cathodic polarization potentials.The effect of S^2-and HSO₃^-on corrosion behavior,as well as the influence of cathodic polarization on SCC mechanism were also discussed.The main research progress and results are as follows:?1?The presence of S^2-accelerated the corrosion of A710 steel metal and has an important influence on its electrochemical behavior and corrosion products.The addition of S^2-increased the electrochemical activity of A710 steel in NaCl solution,narrowed the stable passivation zone of the anode section in the polarization curve,and the blunt current was higher than that of the NaCl solution without S^2-,with the soaking time.Extend,the blunt current increases gradually.Moreover,the generated corrosion products contain FeS which are loose and have weak binding ability to the matrix,which weakens the protective properties of the corrosion products and leads to the occurrence of pitting corrosion under the film.With the prolongation of the soaking time,the number of pitting points gradually increases.Increase in size,and gradually merge into larger etch pits.?2?The concentration of HSO₃^-has great influence on the cathode process in the corrosion process of A710 steel,which increased its corrosion rate.The corrosion current was 15.6 times than in the NaCl solution.Moreover,in the coexistence of S^2-and HSO₃^-,two ions was involved in the reaction process,and changed the composition and morphology of corrosion products could accelerate the corrosion of A710 steel in NaCl solution.When the concentrations of S^2-and HSO₃^-were1000ppm and 0.1mol/L respectively,the corrosion current was 10.6 times than in NaCl solution,which accelerated the corrosion.?3?The SCC sensitivity of A710 steel in 3.5%NaCl solution is related to the cathodic polarization potential.With the decrease of the polarization potential,the fracture life and the area shrinkage of A710 steel in NaCl solution first increased and then decreased.The sensitivity of SCC at-800 and-900 mV was lower than under the open circuit potential.The sensitivity of SCC increased significantly under potentials of 1100 and-1200 mV,and there was a negative effect of overprotection.Under open circuit potential,the SCC followed the anodic dissolution mechanism;Under-800 and-900 mV,the mixing mechanism of anodic dissolution and hydrogen embrittlement;Under-1100 and-1200 mV,the SCC followed hydrogen embrittlement mechanism.