Study On Corrosion Behavior Of Weathering Steel In Marine Atmospheric Environment

China is a development country with land and sea,improving the development of marine resources,developing the marine economy,and building a powerful marine country have been upgraded to unprecedented strategic heights in China.With the continuous development and utilization of marine resources,more and more structural equipment will be served in the marine atmosphere.In addition,China's coastline is long,the number of coastal projects,sea-crossing bridges,etc.is growing rapidly,and weathering steel is also being more and more widely used in railways,bridges,towers,containers and other engineering equipment.At present,there have been a lot of researches on the corrosion regular pattern of weathering steel under the industrial atmosphere environment,but the corrosion problem of the weathering steel in the marine atmospheric environment has not been deeply studied at present.Due to the large amount of Cl-,high temperature and humidity in the marine atmospheric environment,facing this harsh corrosion environment,to study the initial corrosion behavior and corrosion regular pattern of weathering steel has great significance to improve the corrosion resistance of weathering steel,enhance the durability and safety of steel structures,prolong the service life,reduce the occurrence of accidents and develop weathering steel under high humidity and heat environment.In this paper,the pitting corrosion behavior of Q345GNHL weathering steel in C1-environment was studied.The initial corrosion behavior of Q345GNHL weathering steel was studied by changing the temperature and Cl-concentration of the experiment to simulation different marine atmospheric environments through the periodic infiltration accelerated corrosion test chamber.The stabilization of rust layer was studied by spraying different formulations rust layer stabilizers on the surface of weathering steel.The corrosion kinetics of the sample,the morphology,composition of the phase of the rust layer and the influencing factors of corrosion resistance were analyzed,the results show that:In the environment containing Cl-,the pitting corrosion of weathering steel will also occur at the initial stage of corrosion,and the pitting corrosion mainly begins with the inclusions and then induces comprehensive corrosion.The induced pitting ability of different inclusions is different,because the electrode potential of MnS inclusion in Q345GNHL weathering steel is higher and the thermodynamic stability is poor,the induced pitting corrosion is more serious,meanwhile,the expansion of pitting corrosion is influenced by the temp erature and the concentration of Cl-of the environment.With the temperature and C1-concentration increase,the pitting sensitivity of steel increases,the pitting potential decreases,the number of pitting pits increases.the area of pitting pits increases.and the resistance to pitting corrosion decreases.The effect of temperature on pitting corro sion is greater than that of Cl-concentration.In the marine atmosphere environment,humidity and Cl-concentration have a great influence on the corrosion behavior of the weathering steel.When the humidity increases from 40%to 80%,the corrosion weight loss rate of weathering steel increases obviously.When the humidity is low,the drying time of the steel substrate surface is longer,the liquid film formed on the substrate surface is relatively thin,and the oxygen supply is sufficient,thus accelerating the stabilization process of the rust layer,at the same time,meanwhile,because the humidity is lower,the adsorption capacity of Cl-in the liquid film decreased,the conductivity of media decreased,the dissolved amount of the matrix decreased,the rust layer particles were smaller,the rust layer was denser,and the protective ability was enhanced.With the increase of Cl-concentration,the corrosion weight loss rate of weathering steel increases,the thickness of rust layer increases at high Cl-concentration in the same corrosion time,but the density of rust layer decreases,the grain size of rust layer increases,and the cracks increase.Furthermore,the protective performance of the rust layer is reduced,and the stable rust layer is difficult to form.In marine atmosphere environment,the phase structure of rust layer changes with the extension of corrosion time.In the initial stage of corrosion,the corrosion product in the rust layer is spherical corrosion product Fe(OH)3 with whisker,and the rust layer is looser.With the increase of corrosion time,the structure of rust layer changes to lamellae,and y-FeOOH is formed.With the further corrosion,the lamellar structure grows continuously,the lamellar layer thickens,they interlaced arrangement forms reticular structure or reunited into spherical structure,forming a more stable ?-FeOOH,the rust layer particles are refined continuously,the density of rust layer is improved,and the protection is enhanced.The phase composition of the inner rust layer is obviously different from that of the outer rust layer.The outer rust layer is mainly composed of a large amount of Fe3O4/?-Fe2O3,?-FeOOH and a small amount of ?-FeOOH,while the inner rust layer is mainly composed of Fe3O4/?-Fe2O3,?-FeOOH,?-FeOOH,in which the highest content is Fe3O4/?-Fe2O3,the second is ?-FeOOH,the lowest is ?-FeOOH.The corrosion rate of weathering steel after spraying with rust layer stabilizer decreased rapidly in a short corrosion time.Compared with the samples without spray treatment,the dissolution of matrix was accelerated and the formation of rust layer was promoted by spraying with rust layer stabilizer.the corrosion potential of the rust-bearing specimen after peri-immersion corrosion is significantly higher than that of the rust-bearing sample without treatment,and the corrosion current density is also lower.However,there is no difference in phase composition between spraying treatment specimens and non-spraying treatment specimens,both of which are composed of Fe3O4/?-Fe2O3.?-FeOOH and ?-FeOOH.However.the content of ?-FeOOH in the rust layer formed by the former methods increase.indicating that the rust layer stabilizer promotes the formation of the stable phase ?-FeOOH.