Effect Of Solution Treatment Temperature On The Corrosion Behavior And Hydrogen Embrritlement Of Duplex Stainless Steel

2205 Duplex stainless steel(DSS) which is composed of ferrite(?) and austenite(?) phases exhibits well-balanced characteristics of favorable mechanical strength of the ? phase and the high corrosion resistance of the ? phase. DSS2205 is widely used in marine constructions, acid storage containers, and oil and gas pipeline because of these well-balanced characteristics. However, during the service of DSS2205, since service condition contains large amounts of impurity ions, combined with artificial protection measures, such as cathodic protection, causing hydrogen ions et al get into the interior of DSS much more easier. Combination of applied stress and hydrogen, promote the embrittlement fracture of DSS2205. This could have grave consequences. The microstructure of the material determines its properties. Therefore,it has a certain theoretical and practical significance to investigate the effect of microstructure on the corrosion behavior and hydrogen embrittlement of DSS2205.In this paper, different solution treatment temperatures were used in order to change the phase structure of DSS2205. The effect of microstructure on the corrosion behavior and hydrogen embrittlement of DSS2205 was investigated by microstructure and microhardness analysis, electrochemical tests(polarization curves,electrochemical impedance spectroscopy), slow strain rate test, hydrogen permeation experiment and scanning electron microscope test.The results of microstructure analysis showed that the second phase such as sigma phase and chromium nitride phase dissolved when the DSS2205 was treated at solution treatment temperatures in the range of 1000? to 1200?, the phase ratio of ferrite showed a linear growth and the austenite ratio showed a linear decrease with the increase of solution treatment temperatures. The proportion of ferrite phase and austenite phase was about 1:1 at 1050 ?. The microhardness of DSS2205 was minimum at 1050?, and then it increased with the increasing of solution treatment temperature. The electrochemical tests in 0.5M sulfuric acid solution showed that the DSS2205 has a obvious passivation interval, and the corrosion resistance and thedensity and stability of passivision films of DSS2205 were the best at 1050?. Stress corrosion cracking was not happened at an applied anodic potential in 0.5M sulfuric acid solution. The slow strain rate test combined with electrochemical impedance spectroscopy test during stress corrosion test showed the consequence that the impedance of DSS2205 decreased and the hydrogen embrittlement susceptibility increased significantly after hydrogen charge. It was also showed that a finer microstructure(1050 ?) is assumed to enhance the resistance of hydrogen embrittlement, and the increasing of solution treatment temperature drastically increased hydrogen embrittlement susceptibility of DSS2205. When the crack initialed during the tests after hydrogen charge it was soon passived in 0.5M sulfuric acid solution. The electrochemical experiments of single phase in 3.5%NaCl and0.5M sulfuric acid solution showed that the corrosion resistance of ferrite phase was best at 1050?, and it decreased with the increasing of solution treatment temperature.The similar phenomenon was also observed for austenite phase. In 3.5%NaCl the corrosion resistance of ferrite was phase better than austenite phase, and the selective corrosion occurred in austenite phase. But in 0.5M sulfuric acid solution the difference of corrosion resistance were not obvious, and uniform corrosion was happened. Hydrogen permeation results showed that the diffusion coefficient of hydrogen increased with the increasing of solution treatment temperature. The hydrogen embrittlment sensitivity increase with the increasing of phase ratio and diffusion coefficient of the single ferrite phase.