Effect And Mechanism Of Sn On Corrosion Resistance Of New Corrosion Resistant Steel Inner Bottom Plate For Crude Oil Storage Tank

With the continuous development of China’s economy and society,the demand for crude oil reserves was gradually increasing.The corrosion resistance of steel plates used in large crude oil storage tanks needs to be solved urgently.This paper was mainly to optimize the composition of low-alloy steel,developed the inner bottom plate of the coating free crude oil storage tank with excellent corrosion resistance,analyzed the influence of corrosion resistance element Sn on the corrosion resistance of the inner bottom plate and mechanism research,optimized the tempering temperature of industrial trial steel containing Sn to ensure long-term corrosion resistance,analyzed the influence of tempering temperature on the corrosion resistance of industrial trial steel and mechanism research.In this paper,EBSD technology was mainly used to analyze the initial corrosion behavior of Sn-containing test steel,clarified the mechanism of inhibiting the initial corrosion behavior,and Raman spectrum experiment,TEM experiment and SEM+EDS experiment were used to analyze the phase composition and basic structure of the corrosion products formed in the middle and late stage of corrosion of Sn-containing test steel,The effect of Sn on the corrosion resistance of low-alloy steel in the middle and late stage of corrosion and its mechanism analysis were clarified.At the same time,EBSD technology was used to analyze the influence of tempering temperature on the initial corrosion behavior of industrial trial steel,Raman spectrum experiment and SEM experiment were used to analyze the influence of tempering temperature on the corrosion resistance of industrial trial steel in the middle and later stages of corrosion,and electrochemical corrosion test was used to analyze the protective effect of the formed corrosion products on the matrix.Through a series of characterization,it could be seen that the SnO₂ phase formed in the initial corrosion was mainly concentrated in the retained austenite area,grain boundary and the ferrite grain{1,1,1}with high crystal surface energy.With the extension of the initial corrosion cycle,the SnO₂ phase would appeared in the ferrite-retained austenite area and gradually expand from the retained austenite area to the ferrite area,Therefore,the SnO₂ phase formed in the initial corrosion could effectively cover the area prone to corrosion.The addition of Sn could well inhibit the initial corrosion behavior of low-alloy steel.The SnO₂,Fe,α-FeOOH,and graphite（SnO₂-M-G）compound material would be formed in the later stage of corrosion,which could significantly improve the long-term corrosion resistance of low-alloy steel.After tempering treatment,the industrial trial steel containing Sn would reduced the content of the residual austenite,increased the content of SnO₂ formed in the initial stage of corrosion,effectively improved the ratio of the SnO₂/Austenite,promoted the SnO₂phase to effectively cover the residual corrosion prone area,effectively inhibit the initial corrosion behavior,and improved the stability of SnO₂-M-G composite formed in the later stage of corrosion.However,too high tempering temperature would reduced the content of SnO₂ formed in the initial corrosion and SnO₂-M-G composite in the later stage of corrosion,and reduced the overall corrosion resistance.The tempering temperature 620℃was the best tempering temperature to ensure the corrosion resistance of Sn-containing low-alloy,which could improved the long-term corrosion resistance of Sn-containing industrial trial produced steel.