Investigation Of Corrosion Behavior Of Low-alloy Steel And Its Welded Joint In Marine Environment

The steel structure and its construction were corroded in marine environment, Whichwas one of the main forms of failure of a metal material. With characteristics such asstrength, plastic,molding, welding and fatigue,09CuPCrNi low alloy steel was applied inMarine atmospheric zone and full immersion zone steel, application to steel sheet pile andoffshore oil platform in ocean engineering. In addition, the welding was used in the modernship and ocean engineering, Which was one of the main forms of material processingmethod.Therefore,the research of corrosion resistant performance and its corrosionmechanism on09CuPCrNi low alloy steel and its welding joint, and the contrast of Q235Bsteel,through the laboratory simulation of Marine atmospheric zone and full immersionzone,had profound significance.In this article, the stress corrosion cracking sensitivity of09CuPCrNi low alloy steeland its welding joint were studied by slow strain stress rate test (SSRT) in differentcorrosion medium. The uniform corrosion mechanism and the influence of alloy elementson corrosion resistance of09CuPCrNi and its welding joint, and compared to steel Q235Bcarbon steel,were studied through laboratory simulation test of marine atmospheric zoneand full immersion corrosion, combined with SEM, XRD, the electrochemical tests, andEPMA.The corrosion rate of09CuPCrNi steel and its welding joint,and Q235B steel,werelarger for days in Marine atmospheric environment.The marine atmospheric corrosionresistance of parent metal was superior to its welded joint for Corrosion cycle (2W to8W),but the corrosion resistance of welded joint was superior to its parent metal on corrosiontime of12W and24W.The atmospheric corrosion resistance of09cupnicr low alloy steelwas better than that carbon steel Q235B.The outer rust layer of test steels was mainlycomposed of α-FeOOH, γ-FeOOH, and Fe3O4.The atmospheric corrosion resistance ofalloy steel was enhanced adding to Cu, Cr, Ni elements.The corrosion rate of09CuPCrNi steel and its welding joint,and Q235Bsteel,decreased for days in marine full immersion zone.The corrosion resistance of09CuPCrNi low alloy steel was superior to its welding joint for corrosion cycle (1W to8W), but the corrosion resistance of welded joint was superior to its parent metal oncorrosion time of12W and24W. The corrosion resistance of09CuPCrNi low alloy steel was better than that carbon steel Q235B during corrosion cycles.The outer rust layer of teststeels was mainly composed of γ-FeOOH, andα-Fe2O3.The local enrichment of alloyingelements Cu，Cr and Ni in rust layer promoted the formation of α-FeOOH phase andtherefore enhancing the corrosion resistance of the steel．In3.5%NaCl and0.052%NaHSO3corrosion medium, stress corrosion resistance of09CuPCrNi low alloy steel was superior to its welding joint.The stress corrosion sensitivityindex of Parent metal and weld metal in3.5%NaCl corrosion medium was higher than in0.052%NaSHO3corrosive medium.The results of stress corrosion test showed that there was a certain tendency of stresscorrosion of09CuPCrNi low alloy steel in3.5%NaCl and0.052%NaHSO3solution, afterwelding,there were more bigger stress corrosion sensitivity.And in0.052%NaHSO3medium, the influence of the welding on stress corrosion sensitivity was bigger than in3.5%NaCl solution.