稀土对A572 Gr.65钢电化学腐蚀行为的影响

Influence of Rare Earth on Electrochemical Corrosion Behavior of A572 Gr.65 Steel

目的提高A572 Gr.65钢的耐蚀性能。方法通过向A572 Gr.65钢中添加La和Ce的混合稀土,得到不同稀土含量的A572 Gr.65钢。以3.5%NaCl溶液为腐蚀介质,借助电化学工作站、XRD和SEM等手段分析表征了不同稀土含量的A572 Gr.65钢的电化学腐蚀行为。结果稀土能使A572 Gr.65钢腐蚀电位正移,腐蚀电流减小。当稀土质量分数为0.0047%时,腐蚀电位最正,为−0.50 V,腐蚀电流密度最小,为2.77×10^−6 A/cm^2,极化曲线的阳极部分存在明显的活化-钝化过渡区,有明显的钝化过程。不同稀土含量的A572 Gr.65钢的阻抗谱均由单一的容抗弧组成,容抗弧半径代表着对电荷传输的阻碍能力,稀土质量分数为0.0047%时,容抗弧半径最大,对电荷传输的阻碍能力最大。稀土可以使钢中的夹杂物变性,使夹杂物由CaS和Al2O3-CaO变为稀土的氧硫化物,夹杂物尺寸由5μm变为2μm,减小腐蚀发生的活性区。此外,稀土离子可以提高阴极极化率,使腐蚀产物中不稳定的γ-FeOOH含量减少,增强锈层的稳定性、致密性和附着能力,增大电荷转移的阻力,有效阻碍侵蚀性Cl^−的侵入。结论稀土的添加能有效提高A572 Gr.65钢的耐蚀性,稀土质量分数为0.0047%时,试验钢的耐蚀性最好。腐蚀过程中,由点蚀逐渐转变为均匀腐蚀,活性点的形成和阳极溶解速度为整个腐蚀过程中的限制性环节。

The work aims to improve the corrosion resistance of A572 Gr.65 steel.A572 Gr.65 steel with different RE contents was obtained by adding mixture rare earths with La and Ce.The electrochemical corrosion behavior of A572 Gr.65 steel with different rare earth contents was analyzed by electrochemical workstation,XRD and SEM with 3.5%NaCl solution corrosion medium.The rare earth made the corrosion potential shift positively and decreased the corrosion current.When the rare earth content was 0.0047%,the corrosion potential was the most positive of−0.50 V and the corrosion current was the minimum of 2.77×10^−6 A/cm^2.The anode part of the polarization curve had obvious transition zone of activation-passivation and passivation process.The impedance spectroscopies of A572 Gr.65 steel with different RE contents were composed of single capacitive reactance arc.The radius of the capacitive reactance arc represented the ability to hinder the transfer of charge.When the rare earth content was 0.0047%,the radius of the capacitive reactance arc was the largest and had maximum ability to hinder the transfer of charge.The rare earth could change the property of the inclusions in the steel.RE transformed inclusions from CaS and Al2O3-CaO to RE2O2S and the size of inclusions changed from 5μm to 2μm,so the active area of corrosion decreased.The rare earth ions improved the polarization rate of cathode and made the content of unstableγ-FeOOH decrease,so the stability,density and adhesive ability of the rust layer increased.The charge transfer resistance was raised,thus effectively preventing the invasion of the corrosive Cl^–.The rare earth can effectively improve the corrosion resistance of A572 Gr.65 steel.When the rare earth content is 0.0047%,the experiment steel has the best corrosion resistance.In the process of corrosion,corrosion changes from pitting corrosion to uniform corrosion,so the formation of active point and the rate of anodic dissolution are the restrictive links.