Crevice corrosion behaviour of superaustenitic stainless steels: Dynamic electrochemical impedance spectroscopy and atomic force microscopy studies

Potentiodynamic anodic polarisation and dynamic electrochemical impedance spectroscopic (DEIS) measurements were carried out for 316L SS, alloy 33 and alloy 24 in natural sea water in order to assess their crevice corrosion resistance. DEIS measurements were performed from open circuit potential to dissolution potential. It was shown that the impedance measurements in potentiodynamic conditions allow simultaneous investigation of changes in passive layer structure. The impedance spectra of various potential regions were also discussed. The surface morphology of the alloys after crevice corrosion studies were studied using optical microscope and atomic force microscopy (AFM).     

Ab initio modelling of localized corrosion: Study of the role of surface steps in the interaction of chlorides with passivated nickel surfaces

Periodic DFT calculations have been performed on a (5 3 3)-oriented hydroxylated NiO surface to model the influence of step edges on the adsorption and sub-surface insertion of Cl at the surface of the passive film on nickel. With increasing Cl coverage, substructures of Ni(OH)₂, Ni(OH)Cl or Ni(Cl)₂ composition are formed and detached from the surface, suggesting a major role of the step edges in the Cl adsorption-induced thinning mechanism of the oxide film. The calculated energies show the promoting effect of the adsorption of Cl on the energy of detachment of the substructures. At surface saturation, sub-surface insertion becomes energetically more favourable than adsorption. The results suggest a possible bifurcation from the Cl adsorption-induced oxide thinning mechanism to the penetration-induced mechanism of passivity breakdown at saturation in adsorbed Cl of the step edges.     

308L不锈钢堆焊试板点腐蚀原因分析

分析和研究了氯离子对308L不锈钢表层钝化膜的破坏机理.对于最大直径为(8～10)μm,深度为( 10～ 12) μm的腐蚀坑,厚度方向上打磨掉0.2 mm后再重新补焊,可彻底杜绝二次点腐蚀的再次发生.     

Corrosion resistance of Mg-5Al-xSr alloys

Four types of Mg-5Al alloy with various weight percentages of Sr ranging from 0 to 1.5 wt% were examined using electrochemical techniques and surface analyses. The electrochemical results indicated that the Mg-5Al alloy containing Sr to have a higher pitting potential and impedance than the Mg-5Al specimen with highest value being observed in the Mg-5Al-1Sr specimen. Sr addition induced the continuous precipitation of Al-Sr phases along with grain refinement and increased the formation of an Al(OH)₃ film on the surface.     

Influence of tempering treatment on microstructure and pitting corrosion resistance of a new super ferritic–martensitic–austenitic stainless steels with 17%Cr

Supermartensitic stainless steels (SMSSs) allow high mechanical strength with better corrosion resistance and toughness than conventional martensitic stainless steels. The SMSS steels with 12–13%Cr have been studied and applied in the oil and gas offshore production. The increase of Cr content, and the addition of Mo and W is now being investigated to increase mechanical and pitting corrosion resistance. In this work, a new 17%Cr steel, with Mo and W additions was studied. Depending on the final tempering treatment, the steel has a complex microstructure of austenite, ferrite, martensite and precipitates. The pitting corrosion resistance also depends on the microstructure produced by tempering. It was found that the pitting potential slightly decreases with the increase of tempering temperature and is further decreased by the double-tempering treatment. The pits initiate and grow preferentially in the martensite or tempered martensite islands, due to the lower Cr, Mo and W contents of these areas.     

利用缓蚀协同效应降低二氧化碳缓蚀剂使用浓度

用失重法及电化学方法研究了抑制碳钢ＣＯ２腐蚀的缓蚀剂的协同效应,得到了低浓度下具有高缓蚀率的复合缓蚀剂,较侍浓度配比时复合缓蚀缓蚀率大于二组分单独作用时慢率之和,优良的缓蚀协同效果归因于复配后对电极过程特别是阳极过程的强烈抑制作用。     

氢对纯镍钝化膜的影响

研究了氢对纯镍阳极极化和钝化膜形成及耐蚀性能的影响。结果表明：预充氢会降低纯镍的自腐蚀电位,使其出现明显的活化区和临界钝化电流,缩短钝化区域;提高钝化电流密度和延长钝化膜的形成时间。固溶氢降低钝化膜的稳定性,增大膜的自活化能力;并导致钝化膜出现明显的孔蚀,膜的孔蚀电位随固溶氢含量的增加而降低。     

Evolution of current transients and morphology of metastable and stable pitting on stainless steel near the critical pitting temperature

Type 904L austenitic stainless steel with a critical pitting temperature (CPT) of 56 °C was polarized at 750 mV (Ag/AgCl) in 1 M NaCl at 45, 49 and 54 °C. Current transients due to metastable pitting were recorded at these three temperatures, and a smaller number of stable pit current transients were recorded at 62 °C. The metastable pit current, I, followed a power law relationship I ∼ tⁿ during initial growth prior to repassivation. The exponent n increased with temperature, from 0.5 to 1.5. To grow at the lower temperatures, the pits need to be more occluded (lower value of n; lower pit current density). The repassivated metastable pits showed two morphologies: small occluded cavities associated with the small transients, and open ones with polished surfaces for large transients recorded close to the CPT. A new type of deterministic repassivation was identified for the latter type of pit. The stable pit currents rose in proportion to t^3/2, just like the faster-growing metastable pits, but only for a few seconds; then there was a drop in current and a further noisy increase occurred with a lower exponent. These pits undercut the metal surface, producing a lacy metal cover. The results are broadly consistent with a model that attributes the CPT to the onset of passivation in the saturated pit solution. A new feature requiring explanation is that, very close to the CPT, pits can precipitate a salt film but fail to undercut the surface. It is hypothesized that since a higher anodic current density is required at the undercutting site than at the pit base, there will be a range of temperatures where the former but not the latter would exceed the critical current density for passivation and is thus disallowed.     

430不锈钢在含Cl^—及CO2体系中的孔蚀行为

用动电位滞后曲线法研究了４３０不锈钢在不同介质条件下的孔蚀特性及行为，并对一些缓蚀剂进行了性能测试。结果表明Ｃｌ＾－浓度升高，能促进４３０不锈钢产生孔蚀；温度也有同样作用。     

316L不锈钢在模拟人体液内腐蚀疲劳裂纹萌生和扩展过程中应力的作用

探讨应力在316L不锈钢腐蚀疲劳过程中的作用。应力降低了不锈钢的点蚀电位,促进了腐蚀疲劳裂纹的萌生和扩展。初始疲劳裂纹在点蚀孔中的晶界上萌生,在应力的作用下,裂纹由沿晶变为穿晶扩展,并在断口上产生二次裂纹和疲劳辉纹。     

氢对310不锈钢钝化膜的影响

采用电化学和ＳＴＭ方法研究了氢对３１０不锈钢阳极极化过程,钝化膜形成过程和表面形貌特征以及膜耐点蚀性能的影响,并进行了相应的理论分析。研究表明：氢会降低不锈钢的自腐蚀电位,缩短钝化区域并使其向低电位方向偏移;降低反应电阻,增大钝化电流工,降低膜在纳米尺度上的结晶度和耐点蚀性能。     

镍对304不锈钢在NaCl溶液中缝隙腐蚀行为的影响

采用化学浸泡实验和电化学测试技术,探讨了Ｎｉ元素对３０４不锈钢在０．３％ＮａＣｌ溶液中缝隙腐蚀行为的影响。结果表明,合金元素Ｎｉ的加入,可提高ＥＲ,抑制不锈钢的活性溶解行为和有效提高抗缝隙腐蚀能力。     

Erosion-enhanced corrosion of carbon steel at passive state

Erosion-enhanced corrosion of carbon steel in passive state during slurry impingement is dominated by the competition between fresh surface generation and repassivation. The presence of chloride retards repassivation. The average corrosion rate is quantitatively predictable when the hydrodynamics of slurry and repassivation kinetics of target material are known. The electrochemical impedance spectroscopy suggests that the corrosion in flowing slurry is under mixed control of interface charge transfer and mass transport. The later becomes the dominative role gradually with increasing generation rate of fresh surface. Slurry impingement may facilitate pit formation and promote repassivation of existing pits simultaneously.     

XPS analysis of the passive film formed on austenitic stainless steel coated with conductive polymer

Improvement of the passivation behavior of Type 304 austenitic stainless steel (SS) by coating with conductive polymers (CPs), like polyaniline (PANI) and poly(o-phenylenediamine) (PoPD), followed by exposure in an acid solution has been demonstrated. The passive films formed on SSs (after peeling off the polymer layer) are compared with those formed during anodic polarization under the same exposure condition. The passive films beneath the CPs are thicker and less hydrated than those formed on uncoated stainless steel. The polymer layer enhances the enrichment of chromium and nickel in the entire passive oxide, forming a more protective film than that formed during anodic polarization. The elemental distribution within the passive film is different in the two modes of passivation. The type of the polymer influences on the composition of the passive film. The best passivation is obtained by PoPD, with the passive film resulting in significant resistance of the SS to pitting corrosion in the 3% NaCl solution. The oxide film of this steel is characterized, in its inner and outer layers, by the highest ratio of Cr(OH)₃/Cr₂O₃ and the lowest content of iron species.     

Influence of pH on the passivation behavior of 254SMO stainless steel in 3.5% NaCl solution

The potentiodynamic polarization measurement of 254SMO stainless steel (UNS 31254) was conducted in 3.5% NaCl solutions with pH ranging from 0.1 to 5. The results indicated that this stainless steel offered excellent pitting corrosion resistance in corrosive environments. Further, it also exhibited various features on the polarization curves in different pH solutions. The electrochemical constant-potential passivation treatment performed at different pH followed by XPS analysis revealed that the primary constituents of the outermost layer of the passive films formed in the weak (pH 5) and strong (pH 0.8) acid solutions are iron oxides and Cr₂O₃ and Cr(OH)₃, respectively. Molybdenum oxides, primarily in the six-valence state, existed in the outermost layer of the passive film. Only very weak signals corresponding to that of nickel oxides were detected in the film formed in the weak acid (pH 5) solution. The ICP-MS analyses indicated selective dissolution of a significant amount of Fe and a few Mo and Ni ions during the passivation treatment in the strong acid (pH 0.8) solution. No Cr dissolution was observed; this indicated that the Cr in the film is relatively stable. XPS depth profiling results showed that a similar bilayer-structured film was formed in both the solutions (pH 0.8 and 5); the outer layer of this film is primarily composed of Cr(OH)₃ and Mo(VI), and the inner layer, Cr₂O₃ and Mo(IV). The results of the examinations of passive film formations and dissolution by XPS and ICP-MS were consistent with the polarization curves.     

马氏体相变对304不锈钢点蚀发展过程的影响

采用模拟闭塞电池法和交流阻抗法研究了奥氏体304不锈钢形变诱发马氏体相变对点蚀发展过程中化学和电化学行为的影响。结果表明，随着马氏体含量的增加，闭塞区溶液pH值下降得更快，Cl^-迁入闭塞区的量更多。马氏体相的存在增强了材料的电化学活性，既减小了点蚀发展过程中钝化膜孔隙内的欧姆电阻，又减小了孔隙内的反应极化电阻，从而促进了点蚀发展。     

W0714己内酰胺薄膜蒸发器下料管管壁腐蚀减薄失效分析

用化学方法、金相显微镜和扫描电镜等对腐蚀减薄失效后的W0714己内酰胺薄膜蒸发器下料管管壁进行了分析,结果表明:此设备用304L不锈钢管壁在非氧化性介质中发生了非敏化态的晶间腐蚀,其腐蚀失效的原因是过钝化电位范围内的电化学溶解所致。     

不锈钢盐酸露点腐蚀行为的原位研究

利用一种新型的露点腐蚀模拟装置结合原位的电化学阻抗谱,电化学噪声等测试手段评价了304和316L两种不锈钢的盐酸露点腐蚀行为.结果表明,316L不锈钢表现出更优异的耐盐酸露点腐蚀性能,主要原因可归结为两点:一是316L不锈钢钝化膜中含有较高的Cr/(Cr+Fe) 比以及较低含量的Fe;二是316L不锈钢钝化膜中含有能改善抗点蚀性能的Mo.