Development And Corrosion Mechanism Of New Seawater Corrosion Resistant Steel

In this paper,corrosion resistance of five experimental steels with different microstructures and compositions was investigated by alternate immersion corrosion test under simulated marine environment.The corrosion mechanism was studied from the composition of rust layer,surface morphology,cross-sectional morphology,element distribution,polarization curve and impedance spectrum.The main work and research results are as follows.(1)Three kinds of seawater corrosion resistant steels were designed.The experiments of alternate immersion corrosion test and rolling and mechanical properties were carried out.The experimental results show that the designed B and C steels all have the seawater corrosion resistance beyond 09CuPV,and the mechanical properties meet the requirements of the relevant domestic supply standard.(2)XRD analysis shows that the rust layer is mainly composed of ?-FeOOH,?-FeOOH,Fe2O3 and Fe3O4 and the addition of corrosion-resistant elements promoted the formation of?-FeOOH,the main protective component of the rust layer.SEM observation shows that the addition of corrosion-resistant elements promotes the formation of dense rust layer in the massive stack.EPMA cross-sectional morphology shows that the dense and uniform rust layer is the key to corrosion resistance,and the loose and cracked rust layer is poorly protective to the substrate.The elemental distribution indicates that the Cl element is the main corrosive element in the substrate and the inner rust layer segregation,Cu element as the main protective element in the rust layer segregation.(3)The polarization curves show that the corrosion current increased with time and then decreased and the corrosion potential increases with the increase of corrosion time.The electrochemical impedance spectroscopy(EIS)showed that the corrosion resistance of samples was controlled by electron transfer and diffusion of reactants.The transfer resistance decreased with time and then increased,and the resistance increased with time.(4)The analysis of weight loss,XRD,SEM,polarization curve and impedance spectrum show that the corrosion of steel in seawater is divided into two stages.At the beginning,the surface of the substrate mainly grows Fe3O4 with good conductivity,and the surface of the sample becomes rough,the corrosion area increases,the current increases,the resistance decreases,and the corrosion rate increases.After 72 hours of corrosion,a protective rust layer mainly composed of oxyhydroxides was formed.And with the increase of corrosion time,the thickness of rust layer increases and the corrosion resistance increases and the corrosion rate decreases.(5)Corrosion resistance elements mainly play a role in promoting the formation of protective ?-FeOOH and increasing the density of the rust layer.