Study On Accelerated Stabilization Technology And Long-term Weatherability Evaluation Of The Rust Layer For Weathering Steel

This study aims to solve the rust layer serving long period in the atmospheric environment,early rust liquid hanging,generation of the nonuniform rust layer without painting application.In this study,Q420q ENH weathering steel is used as the basic test steel to explore the evolution mechanism of the rust layer structure,phase and electrochemical properties for the weathering steel in the typical atmosphere,and then to analyze the applicability of uncoating service.It reveals the three different mechanism of rust layer stabilization technology;Based on the exposure data for the weathering steel in typical industrial atmospheric environment,it is established the rust layer stability detection technology and then evaluates the correlation between three different rust layer stabilization treatment processes and exposure test.Hence,it is predicted and established the evaluation model of long-term corrosion resistance for rust layer stabilization treatment.At last,it sets the technology for rust layer acceleration stabilization and rust layer stability detection for weathering steel.In the coastal atmospheric conditions,the corrosion process of WS in presence of Cl^-1≤0.05 mol/L can be divided into three stages:i)at the first stage,the corrosion rate sharply increases;ii)at the second stage,the corrosion rate rapidly decreases;iii)at the third stage,the corrosion rate tends to be stable.However,0.50 mol/L<Cl^-1<0.10 mol/L can be divided into two stages:i)sharp rise at the first stage and ii)slightly decrease at the second stage.At the initial corrosion stage,different Cl^-1 concentrations lead to ion electromigration in the electrolyte,resulting in uneven oxygen distribution and formation of oxygen-poor and oxygen-rich regions.It leads to anisotropy of electrode potential and promote the occurrence of corrosion reaction.As the corrosion process prolonging,the increase ofα-Fe OOH content in the condition of Cl^-1≤0.05 mol/L promots the positive electrode potential shift,inhibites the occurrence of electrochemical reaction,and reduces the corrosion rate.Under the condition of 0.05 mol/L<Cl^-1<0.10 mol/L,excessiveγ-Fe OOH andβ-Fe OOH lead to negative electrode potential shift,which promotes the electrochemical reaction and improves the corrosion rate.In the industrial atmospheric conditions,the corrosion process of WS in presence of SO₄^2-≤0.01 mol/L can be divided into two stages:i)sharp rise at the first stage and ii)slightly decrease at the second stage.However,SO₄^2->0.01 mol/L can be divided into three stages:i)at the first stage,the corrosion rate sharply increases;ii)at the second stage,the corrosion rate rapidly decreases;iii)at the third stage,the corrosion rate tends to be stable.At the initial corrosion stage,different SO₄^2-concentrations lead to uneven distribution of anode current density and cathode current density,which promotes corrosion reaction.With the corrosion process prolonging,the acid regeneration reaction continues to occur under the condition of SO₄^2-≤0.01 mol/L,which promotes the corrosion reaction and increased the corrosion rate.Under the condition of 0.01 mol/L<SO₄^2-<0.10mol/L,SO₄^2-promotes the transformation ofγ-Fe OOH toα-Fe OOH,promotes the increase ofα-Fe OOH content and makes the electrode potential shift,inhibites the electrochemical reaction and reduces the corrosion rate.In view of the treatment process of rust layer stabilization stabilizer,the optimal treatment process of rust layer stabilization is determined by orthogonal test:Na F 0.25 g/L,Tannic acid 0.75 g/L,Se O₂ 0.75 g/L,Mg SO₄ 0.50 g/L and treatment time 5 days.The weathering steel stabilized by rust layer forms a"dry riverbed"coating which are composed of organic chelates and Fe oxides（Fe OOH,Fe₂O₃,Fe₃O₄）and fluoride（Na₃Fe F₆）,which significantly improves the corrosion resistance;The corrosion behavior of weathering steel was changed by regulating direct current field in order to accelerate rust stabilization.At the initial corrosion stage,the direct current electric field is added to make the self-corrosion potential of the weathering steel move positively,and dissolved oxygen is enriched on the surface of the weathering steel,which inhibits the transformation ofγ-Fe OOH toα-Fe OOH,promots the corrosion reaction,accumulats a large amount ofγ-Fe OOH,and mades the corrosion rate rises sharply.In the later corrosion stage,the direct current electric field is removed,and the transformation rate of unstable phase to stable phase is accelerated.The corrosion rate of weathering steel is accelerated from the rising stage to the falling stage,and the physical barrier is formed to accelerate the stabilization of the rust layer;In view of the characteristics of atmospheric corrosion environment in China,three typical rust-layer stabilized water treatment environment characteristics can be divided into high relative humidity sites,low relative humidity sites and coastal sites.After sandblasting treatment,it can be obtained the rust layer with uniform color,sufficient thickness,compact structure and basically stable properties by water treatment for 4-6 weeks.The relationship between the bonding strength and corrosion resistance was established for weathering steel via adhesion test.When the adhesion strength of the rust layer is greater than 1700N,it indicates that the rust layer equips with a certain protection ability.Meanwhile,based on the exposure test data and three different stabilization treatment of rust layer corrosion kinetics data,the model of corrosion prediction is established through polynomial fitting model.The stabilizer processing technology,field synergy stabilizing treatment technology and water treatment technology consumes by cycle sequence is:stabilizer processing technology<field synergy stabilizing treatment technology<water treatment technology.At last,it can be selected different rust layer stabilization techniques according to specific industrial needs.