Corrosion Mechanism Of Sn/Sb-microalloyed 420MPa Low-alloy Steels In Polluted Marine Atmosphere

The study object of this work is the effect and corrosion mechanism of Sn and Sb on 420MPa low-alloy steel in polluted marine atmosphere.Microalloyed low-alloy steels with different Sn and Sb element contents were prepared through vacuum smelting technology,and then the corrosion behaviour of five steels and the synergistic effect of Sn and Sb in a simulated polluted marine atmosphere was studied by using electrochemical technology and wet-dry cycling tests.The influence of Sb on the electrochemical process of low-alloy steel in acid solution was investigated using electrochemical technology and immersion test,and the effect of Sn and Sb on the rust layer of low-alloy steel was explored by outdoor exposure experiment in polluted marine atmosphere.Finally,the impact induced by slight composition deifferences and environment variation was characterized using the big data corrosion monitoring technology.The results showed that the addition of Sn has a considerable impact on the corrosion performance of 420MPa low-alloy steel,especially for 0.05Sn.The addition of Sn caused acidification in the local environment of low alloy steel,accelerating the longitudinal development of pits,and the early corrosion process.As the corrosion progresses,Sn consumes Cl^-at the same time,and an increased ratio of[SO₄^2-]/[Cl^-]of rust layer improved its protection by promoting the conversion of y-FeOOH to α-FeOOH.Sn can also generate the stable SnO₂,which works together with α-FeOOH to improve the stability and compactness of the rust layer,and slow down the corrosion rate of Sn-containing steel in polluted marine atmosphere.Sb microalloying slows down the corrosion rate of low-alloy steel in polluted marine atmosphere.Adding Sb can inhibit the hydrogen evolution reaction,slow down the surface reaction activity,reduce the cathodic current density,inhibit the anodic dissolution process of low-alloy steel,slow down the corrosion rate of the entire corrosion process,and improve the corrosion resistance of low-alloy steel.On the other hand,adding Sb can consume H+,which reduces the acidity of the local microenvironment,promote the conversion of y-FeOOH to Fe₃O₄ in the rust layer,which can block Cl^-.At the same time,Sb can generate a stable product Sb₂O₃,which is precipitated with Fe₃O₄ in the rust layer together,as an anode inhibitor to help the rust layer resist corrosion ions into the matrix,reduce the corrosion rate of Sb-containing steel,and improve the corrosion resistance of Sb-containing steel.Sb and Cu microalloying synergistically improve the corrosion resistance of low-alloy steel in polluted marine atmosphere,while Sn and Cu have no obvious synergistic effect.Sb promotes the enrichment of Cu in the rust layer,enhances the compactness of the rust layer,and reduces the corrosion rate.The addition of Sb and Sn can effectively prevent the development of corrosion pits in the early stage of corrosion and improve the early corrosion resistance of Sn-containing steel.When Cu is present,adding Sb to Sn-containing steel has a little effect on the phase composition of rust layer,and Sn will have a negative effect on the synergistic effect of Sb and Cu,resulting the corrosion resistance of the simultaneous addition of Sn and Sb is not as good as that of low-alloy steel only containing Sb.The influence mechanism of environmental parameters and Sn and Sb microalloying on the corrosion behavior of low-alloy steel in Qingdao was studied using the newly established corrosion big data technology combined with machine learning methods.The linear relationship between the training value and the predicted value was analyzed using machine learning,which accurately and quantitatively characterizes the corrosion resistance influence of the slight changes of Sn and Sb:the impact on the corrosion process is mainly concentrated in two months after corrosion and the third to fifth months.Five months later,with the formation of a stable rust layer,the effects of Sn and Sb on corrosion began to appear insignificant.In addition,experiment showed that the addition of Sn and Sb can improve the corrosion resistance of low-alloy steel in tropical ocean climates.Among them,low-alloy steel containing 0.10%Sb has the best corrosion resistance.