目的 阐明Mg处理、Ca处理及Mg-Ca复合处理对高强管线钢在模拟碱性土壤溶液中钝化及点蚀行为的影响。方法 利用动电位扫描、恒电位极化、Mott-Schottky曲线等电化学方法,结合XPS、EDS、点蚀形貌观察等微观分析手段研究了高强管线钢表面钝化膜特性及点蚀行为。结果 Mg处理、Ca处理及Mg-Ca复合处理对高强管线钢的平均晶粒尺寸分别为5.59、9.26和3.81 μm,铁素体相占比分别为74.0%、73.5%、62.3%,夹杂物密度分别为0.098、0.014和0.048个/μm2。在0.01 mol/L NaCl+0.2 mol/L NaHCO3溶液中,3种管线钢表面均生成n型半导体钝化膜,Ca处理试样表面钝化膜具有较正的平带电位（-0.417 V）、较低的施主密度（4.979×1021 cm-3）、最高的钝化膜电阻（27.31 kΩ·cm2）、最高的点蚀电位（-0.082 V）和最低的点蚀密度（734.2 μm-2）。结论 在钝化膜生长阶段,Ca处理试样因其贝氏体组织中均匀分布的空位,加速了钝化膜的生成速率,使其在较短时间内达到稳态电流密度,并形成致密且缺陷较少的钝化膜,表现出较低的施主密度和优异的稳定性。Ca处理试样钝化膜呈现n型半导体特性,具有较正的平带电位、较低的施主密度和较高的钝化膜电阻与电荷转移电阻,表明其钝化膜在较高电位下能保持电荷平衡,耐蚀性最佳。此外,Ca处理试样钝化膜较厚,且夹杂物密度最低,减少了点蚀萌生的可能性,使其具有最高的点蚀电位和最低的点蚀密度,表现出最强的耐点蚀性能。
Abstract
The third-generation oxide metallurgy technology improves the strength, toughness, hydrogen resistance and other properties of high-strength pipeline steel by regulating the microstructure and modifying inclusions, but it also has a significant impact on the formation of passive films, semiconductor properties and pitting corrosion behavior in alkaline soil environments. In this study, the characteristics of passive films and pitting behaviors of X70 grade pipeline steels treated with Mg, Ca, and Mg-Ca in a simulated alkaline soil solution were investigated by electrochemical methods (e.g., potentiodynamic scanning, potentiostatic polarization, and Mott-Schottky curves) combined with microscopic analysis techniques (e.g., XPS, EDS, and pitting morphology observation). The microstructure types, inclusion composition and size in high-strength pipeline steels treated with Mg, Ca and Mg-Ca were characterized, and their correlations with pitting corrosion resistance were discussed, so as to clarify the effects of different treatment methods on the characteristics of passive films and pitting behaviors of high-strength pipeline steels in simulated alkaline soil solutions.
The average grain sizes of the samples treated with Mg, Ca, and Mg-Ca were 5.59, 9.26, and 3.81 μm, respectively. The proportions of the ferrite phase were 74.0%, 73.5%, and 62.3%, and the inclusion densities were 0.098, 0.014, and 0.048 particles μm-2. In a solution of 0.01 mol/L NaCl+0.2 mol/L NaHCO3, n-type semiconductor passive films formed on the surfaces of the Mg-treated, Ca-treated, and Mg-Ca-treated samples. The flat-band potentials (Efb) were -0.519, -0.417, and -0.491 V, respectively, the donor densities were 6.126×1021, 4.979×1021, and 5.889×1021 cm-3, the film resistances (Rf) were 8.14, 27.31, and 14.88 kΩ·cm2. The passivation current of the Mg-Ca-treated sample was the lowest at 0.040 μA/cm2, but its pitting potential was the lowest at -0.128 V, and the hysteresis loop area was the largest, reaching 544 μA·V/cm2. In contrast, the Ca-treated sample had the highest Eb and Ep, with the smallest hysteresis loop area, which were -0.082 V, -0.259 V, and 215 μA·V/cm2, respectively.
Based on nucleation-growth and point defect models, during the nucleation stage of the passive film, ferrite, due to its simple crystal structure and high reactivity, shows a higher nucleation rate, leading to higher initial polarization current density and pseudocapacitance values in Mg-treated samples. In the growth stage of the passive film, the Ca-treated sample, due to uniformly distributed vacancies in its bainitic structure, accelerates the formation rate of the passive film, allowing it to reach a steady-state current density in a shorter time and form a dense passive film with fewer defects, exhibiting lower donor density and excellent stability. The passive films on the surfaces of Mg-treated, Ca-treated, and Mg-Ca-treated samples all exhibit n-type semiconductor characteristics. The passive film on the Ca-treated sample has a more positive flat-band potential, lower donor density, and higher film resistance and charge transfer resistance, indicating that the passive film can maintain charge balance at higher potentials and demonstrates the best corrosion resistance. Additionally, the passive film on the Ca-treated sample is thicker, and its inclusion density is the lowest, reducing the likelihood of pitting initiation, resulting in the highest pitting potential and lowest pitting density, and exhibiting the strongest pitting resistance.
关键词
管线钢 /
钝化膜 /
半导体特性 /
点蚀行为 /
氧化物冶金
Key words
pipeline steel /
passive film /
semiconductor properties /
pitting corrosion behavior /
oxide metallurgy
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基金
湖北省重大科技攻关项目（2023BAA003）
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