Q345qDNH Steel Rapidly Stabilizes The Microstructure And Corrosion Resistance Of The Rust Layer

This article focuses on the two-step fast rust layer stabilization technology of’rust formation’and’post-stabilization’.Firstly,the influence of the oxide layer of Q345qDNH weathering bridge steel on its corrosion resistance was studied.Secondly,the evolution and formation mechanism of rapid stabilization rust layer of Q345qDNH weathering bridge steel under actual industrial atmospheric exposure conditions were clarified.Finally,the intrinsic correlation between the microstructure of the rapidly stabilized rust layer and corrosion resistance was explored,providing theoretical basis and data support for optimizing the formulation of rust layer stabilization treatment for steel samples with different surface conditions,meeting the market promotion of coating-free weather-resistant bridge steel and engineering application requirements of rust layer stabilization technology.The main research progress and conclusions are as follows:（1）In simulated industrial atmosphere,the main components of the rust layer of Q345qDNH weathering bridge steel with or without oxide layer areα-FeOOH,Fe₃O₄,and γ-FeOOH.With the extension of the corrosion time,the rust layer of Q345qDNH samples with oxide layer will become denser due to the enrichment of Cu,Cr,Si elements,showing better corrosion resistance than Q345qDNH bare steel samples with the same corrosion period.In the early stage of corrosion,the better corrosion resistance of Q345qDNH samples with oxide layer is due to the protective effect of surface oxide layer;in the late stage of corrosion,it is mainly due to the enrichment of alloy elements and the denser rust layer and the promotion of α-FeOOH formation in the oxide layer.（2）In the rusting stage,the surface of weathering steel undergoes chemical reactions,accelerating the formation of rust layer to prepare for stabilization;in the stabilization treatment stage,the rust layer is chemically treated to promote dissolution,precipitation,and α-FeOOH formation;in the atmospheric exposure stage,the stabilized rust layer gradually becomes denser,andα-FeOOH gradually grows from the outside to the inside under the promotion of Fe₃O₄,and the enrichment of alloy elements in the rust layer increases and the protective property of rust layer is enhanced.The Fe₃O₄ and Fe₂O₃ bilayer structure of the oxide layer will hinder the progress of chemical reactions in the rusting stage,but promote the formation of α-FeOOH in the stabilization and atmospheric exposure process.（3）There is a certain correlation between the microstructure of the rust layer and the corrosion resistance.From the perspective of physical effects,rust layer with good integrity,good density,and less surface defects has better corrosion resistance;from the perspective of ion selectivity,the enrichment of elements such as Cu and Cr in the rust layer and the formation of a dense and stable protective rust layer rich in α-FeOOH can hinder the entry of corrosive anions,slow down the corrosion of the steel substrate,and thus improve the corrosion resistance.