Electrochemical corrosion behavior of LDX 2101® duplex stainless steel in a fluoride-containing environment

The effect of fluoride on the electrochemical corrosion behavior of an LDX 2101® duplex stainless steel (DSS) was studied. Open-circuit potential (E_OC) and electrochemical impedance spectroscopy (EIS) measurements were carried out in artificial saliva and with the addition of fluoride (1 wt% NaF). The electrochemical corrosion behavior of the AISI 316L austenitic stainless steel (SS) was also evaluated for comparison. Both open-circuit potential and EIS results indicate that DSS and austenitic SS undergo spontaneous passivation due to spontaneously formed oxide film passivating the metallic surface, in the simulated aggressive environments. However, LDX 2101® exhibits superior corrosion resistance as compared with AISI 316L, and this improvement is ascribed to the formation of a passive film which shows a higher protective effect than the one formed on AISI 316L.     

2205和316L不锈钢在氢氟酸中的电化学腐蚀行为

通过动电位极化和电化学阻抗方法考察了2205双相不锈钢和316L不锈钢在5%(体积分数)HF溶液中的电化学行为,借助Mott-Schokkty曲线分析了两种不锈钢表面钝化膜的半导体特性。结果表明：两种不锈钢在氢氟酸溶液中都能发生钝化,且2205双相不锈钢的钝化区间范围更宽,维钝电流密度更低。2205双相不锈钢表面钝化膜表现出更高的钝化膜电阻和电荷转移电阻,其抗氢氟酸腐蚀性能优于316L不锈钢,这主要与2205双相不锈钢中的Mo和Cr含量高、表面钝化膜缺陷少、钝化膜易修复等因素有关。     

恒电位──恒电流瞬态响应技术研究钝化膜多层结构Ⅲ．氯化钠溶液中2205和316L不锈钢钝化膜稳定性的研究

采用恒电位－恒电流（Ｐ－Ｇ）瞬态响应技术研究了２２０５和３１６Ｌ不锈钢在０．５和１．０ｍｏｌ／ＬＮａＣｌ溶液中钝化膜的结构和稳定性．研究结果证实，体系的钝化膜均具有多层结构．讨论了氯离子在钝化膜生长和破坏过程中的作用．并提出可能的作用模式和破坏机制．由Ｐ－Ｇ响应曲线计算得到的各特征参数随极化电位的变化关系表明，２２０５双相钢在ＮａＣｌ介质中的耐蚀性明显高于３１６Ｌ不锈钢．另外，初步探讨了２２０５钢的组织结构与钝化膜稳定性的关系．     

2205双相不锈钢与316L奥氏体不锈钢钝化膜内点缺陷扩散系数的计算分析

应用电容测试法并借助于点缺陷模型（PDM）计算了2205双相不锈钢与316L 奥氏体不锈钢在NaCl溶液中所形成的钝化膜内点缺陷的扩散系数,利用实验测得钝化膜的稳态电流和PDM模型对计算结果进行了验证分析。通过两种计算方法得到点缺陷在2205双相不锈钢与316L奥氏体不锈钢钝化膜内的扩散系数约为10^-23cm²/s~10^-20 cm²/s数量级,并发现在模拟海水溶液中2205钢的扩散系数比316L钢小,氧空位所形成的点缺陷在2205钢的钝化膜内比316L钢扩散困难,从而使得2205不锈钢的钝化膜比316L不锈钢更加致密与完整,保护性能更好。     

Electrochemical and XPS studies of the passive film formed on stainless steels in borate buffer and chloride solutions

The passivity of AISI 304L and AISI 316L stainless steels in a borate buffer solution, with and without the addition of chloride ions, was studied using cyclic voltammetry and potentiodynamic measurements. The passive layers formed by electrochemical oxidation at different passivation potentials on both the stainless steels were studied by X-ray photoelectron spectroscopy, their compositions were analysed as a function of depth, and the cationic fraction of the passive film was determined. The passive films established on the two stainless steels in the borate buffer solution at pH = 9.3 contained the oxides of two main elements, i.e., Fe and Cr. The oxides of the alloying elements Ni and, optionally, Mo, also contribute to the passive layer. In the presence of chloride ions a strong chromium enrichment was observed in the passive layers.     

Changes in the passive layer of corrugated austenitic stainless steel of low nickel content due to exposure to simulated pore solutions

In this work, changes undergone at the passive layer of a new type of corrugated austenitic stainless steel (low Ni, high Mn 204Cu type) when exposed to solutions simulating that contained in the pores of concrete have been studied. Changes in the nature of the passive layer have been characterized by X-ray photoelectronic spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). Particular focus has been put on the influence of the presence of chlorides and/or carbonation in the solution. Changes in the passive layer due to the passivation treatment that is often applied to corrugated stainless steels during manufacturing processes have also been considered. The results obtained on the 204Cu type steel have been compared with those obtained on more traditional, high Ni, austenitic AISI 304 grade and duplex SAF 2205 grade. During the immersion in simulated pore solutions, 204Cu type suffers more intense redox processes than other studied stainless steels. Moreover, it shows less Cr-rich protective passive layers in these media.     

Microbially influenced corrosion on stainless steels in waste water treatment plants: Part 1

Abstract

Field tests on stainless steels have been carried out at five waste water treatment plants for one year. Three grades of stainless steel, i.e. AISI 304 (UNS S30400), AISI 316 (UNS S31600), and duplex 2205 (UNS S31803) were tested in the final settling tank in the plants. The time dependence of the open circuit potential (OCP) was measured for all coupons. Ennoblement of the OCP, similar to that reported from investigations in sea water, was found in one of the plants. Waters from three of the exposure sites, containing dispersed deposits from exposed coupons, were chemically analysed. Pitting corrosion was observed after the field test on steel grade AISI 304 in three of the five plants, and on AISI 316 in one plant. No corrosion was found on 2205 in any of the plants. Laboratory measurements of the OCP were carried out for the AISI 304, AISI 316, and duplex 2205 steels in water collected from one of the plants. Cathodic polarisation curves were recorded in waste water from the same plant. T he cathodic reaction rate increased at the highest OCP. Simulation of the ennoblement was carried out by potentiostatic polarisation in a 600 ppm chloride solution. The current response indicated corrosion of welded AISI 304 material and of AISI 304 and AISI 316 steels in crevice assemblies after a long induction time. Part 2 of this study presents the results of further testing and a risk assessment design.     

High corrosion resistance of austenitic stainless steel alloyed with nitrogen in an acid solution

Passivity of austenitic stainless steel containing nitrogen (ASS N25) was investigated in comparison with AISI 316L in deareated acid solution, pH 0.4. A peculiar nature of the passivation peak in a potentiodynamic curve and the kinetic parameters of formation and growth of the oxide film have been discussed. The electronic-semiconducting properties of the passive films have been correlated with their corrosion resistance. Alloying austenitic stainless steel with nitrogen increases its microstructure homogeneity and decreases the concentration of charge carriers, which beneficially affects the protecting and electronic properties of the passive oxide film.     

Inhibition effect of chromate on the passivation and pitting corrosion of a duplex stainless steel in LiBr solutions using electrochemical techniques

The electrochemical behavior of duplex stainless steel (DSS) in LiBr media was investigated by anodic cyclic polarization curves and AC impedance measurements. The effect of bromide concentration and the presence of chromate in the solutions on the corrosion behavior of AISI 2205 was studied. Cyclic polarization curve analyses showed that there was different pitting susceptibility of passive films depending on the LiBr concentration. Pitting potential decreases with LiBr concentration in a semilogarithmic scale following two different slopes. Chromate presence displaces pitting potentials towards more positive values at low LiBr concentrations but it has no effect when LiBr concentration increases.The comparative analysis carried out in LiBr and LiBr chromate-containing solutions at two different concentrations, 0.016 M and 0.032 M, verifies the assumption that halogen ions facilitate inhibitor adsorption. The addition of halides strongly increased the inhibition efficiency of chromate. The passive film becomes more resistant when bromide concentration increases, although film thickness decreases.     

316L不锈钢、690合金在氢氧化钠溶液中的电化学性能

采用动电位极化、电化学阻抗和电容测量等方法研究了316L、690合金在NaOH溶液中的电化学行为及生成钝化膜的半导体性质.在NaOH溶液中,316L不锈钢存在明显的钝化区间;316L不锈钢、690合金在NaOH溶液中电化学阻抗谱的阻抗模值相近.动电位电化学阻抗谱(DEIS)表明,随扫描电位正移,钝化膜的阻抗在测试溶液中...     

Influence of molybdenum on passivation of polarised stainless steels in a chloride environment

Polarised specimens of AISI 304L and 316L stainless steels (SS) were studied using X-ray photoelectron spectroscopy in conjunction with Ar⁺-ion sputtering. A 5% NaCl test solution was used at room temperature. The polarised passive films formed consist mainly of chromium oxide and hydroxide and a small proportion of iron oxides. The composition of the films depend strongly on the potential. Chloride and molybdenum ions appear when the AISI 316L SS alloy is polarised at a potential close to pitting potential.     

Depassivation-repassivation behavior of type-312L stainless steel in NaCl solution investigated by the micro-indentation

Repassivation behavior of type-312L stainless steel containing 6% of molybdenum was examined in NaCl solution using in situ micro-indentation technique, together with type-304 and 316L stainless steels. High stability of the passive film formed on the type-312L stainless steel was also examined by depth profiling analysis of passive films using glow discharge optical emission spectroscopy (GDOES). In 0.9 mol dm⁻³ NaCl solution at 296 K the type-304 and 316L stainless steels are passive only up to 0.3 V (SHE), above which pitting corrosion occurs. In contrast, no pitting corrosion occurs on type-312L stainless steel. Despite the significant difference of the pitting corrosion resistance, the repassivation kinetics of the three stainless steels, examined by micro-indentation at 0.3 V (SHE), is similar. The presence of molybdenum in the stainless steel does not influence the repassivation kinetics. The charge required to repassivate the ruptured type-312L stainless steel surface increases approximately linearly with the potential, even though the passivity-maintaining current increased markedly at potentials close to the transpassive region. Repassivation occurs without accompanying significant dissolution of steel, regardless of the stability of passive state. Depth profiling analyses of the passive films on the type-312L stainless steels formed at several potentials revealed that molybdenum species enrich in the outer layer of the passive film, below which chromium-enriched layer is present. The permeation of chloride ions may be impeded by the outer layer containing molybdate, enhancing the resistance against the localized corrosion of the type-312L stainless steel.     

Study of the correlation between corrosion resistance and semi‐conducting properties of the passive film of AISI 316L stainless steel in physiological solution

In this work the corrosion resistance of AISI 316L biomedical stainless steel was assessed through electrochemical impedance spectroscopy (EIS) measurements in Hanks' solution at 37 °C. Specimens were immersed in the electrolyte during 21 days. Semi‐conducting properties of the passive film naturally formed on the surface of the metallic material during the test were evaluated through the Mott–Schottky approach. The aim was to investigate the correlation between corrosion resistance and semi‐conducting properties in the physiological solution. The corrosion resistance was found to decrease with the immersion time. The density of defects in the passive film increased accordingly as indicated by the Mott–Schottky plots. The passive film presented a semi‐conducting behavior with a duplex character. Above the flat band potential the behavior was typical of an n‐type semiconductor whilst below such value it was typical of a p‐type semiconductor. The results from EIS measurements and Mott–Schottky were in good agreement, suggesting that the corrosion resistance of biomedical stainless steels may be associated with the semi‐conducting properties of the passive films formed during immersion in physiological medium.     

Electrochemical and XPS studies of AISI 316L stainless steel after electropolishing in a magnetic field

The thermodynamic stability and corrosion resistance of surface oxide layer are the most important features of stainless steels. Electrochemical polishing (EP) is the most extensively used surface technology for austenitic stainless steels. We have modified this surface technology by introducing a magnetic field to the system. With this new process called the magnetoelectropolishing (MEP) we can improve metal surface properties by making the stainless steel more resistant to halides encountered in a variety of environments.In this paper, the corrosion research results are presented on the behaviour of the most commonly used material - medical grade AISI 316L stainless steel. The corrosion investigations have been concerned on the open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and polarisation curves studies in the Ringer’s body fluid under room temperature (25 °C). The X-ray photoelectron spectroscopy (XPS) was performed on 316L samples after three treatments: MP - abrasive polishing (800 grit size), EP - conventional electrolytic polishing, and MEP - magnetoelectropolishing. The comparison of the corrosion behaviour of the stainless steel’s surface after these processes was also carried out. The purpose of XPS studies was to reveal the surface film composition and the reason of this modified corrosion behaviour. It has been found that the proposed MEP process modifies considerably the composition of the surface film and improves the corrosion resistance of the same 316L SS studied.     

Influence of pH on the electrochemical behaviour of a duplex stainless steel in highly concentrated LiBr solutions

The objective is to study the influence of pH on the corrosion and passive behaviour of duplex stainless steels (DSS) using potentiodynamic measurements, potentiostatic tests and electrochemical impedance spectroscopy (EIS).DSS are spontaneously passive in heavy brine LiBr solutions. Under potentiostatic conditions at applied anodic potentials within the passive domain an equivalent circuit with two time constants is the most suitable model to describe the corrosion mechanism in the interface electrolyte/passive film/metal. pH modifies the electrochemical properties of the passivity of the alloy in a 992 g/L LiBr solution reducing its resistance with the applied potential.     

Effects of microplasma arc AISI 316L welds on the corrosion behaviour of pipelines in LiBr cooling systems

The effect of microplasma arc welding (MPAW) on the electrochemical and corrosion behaviour of AISI 316L stainless steel tubes has been studied. Scanning electrochemical measurements were performed in sodium chloride to evaluate the difference in the electrochemical activity of base (non-welded) and welded samples. Oxygen reduction rates increase in AISI 316L due to the heat treatment effect induced by welding, indicating a higher electrochemical activity in the welded samples. Additionally, the use of MPA weldments in lithium bromide (LiBr) absorption machines was also analysed at typical operating temperatures and Reynolds numbers. The welding process increases corrosion rates, hinders passivation and increases the susceptibility to pitting attack in LiBr. However, zero-resistance ammeter and localization index measurements show that the galvanic pair generated between the base and welded alloys is weak, both electrodes being in their passive state. Temperature greatly affects the corrosion process.     

Corrosion behaviour of AISI type 304L stainless steel in nitric acid media containing oxidizing species

The corrosion behaviour of AISI type 304L stainless steel (SS) in different concentration of 0.01 M, 1 M and 5 M HNO₃ in presence of oxidizing ions at different temperatures has been evaluated. The main objective of this study is to assess the corrosion resistance of type 304L SS in non-radioactive conditions encountered during storage of liquid nuclear waste. Electrochemical impedance spectroscopy (EIS) and laser Raman spectroscopy (LRS) has clearly brought out the deleterious effect of oxidizing species on the passive film leading to increased corrosion along with increase in HNO₃ concentration and higher temperature.     

EIS assessment of critical pitting temperature of 2205 duplex stainless steel in acidified ferric chloride solution

In this study, critical pitting temperature (CPT) of 2205 duplex stainless steel (DSS2205) was assessed using electrochemical impedance spectroscopy (EIS) in ferric chloride solution. In order to verify the results other methods such as ASTM G 48, potentiodynamic and potentiostatic polarisation and zero resistance ammeter (ZRA) were also employed. The results show a strong close relation between the results of this method by those of previous methods. CPT of the alloy is 40 °C based on standard method and 44 °C, 49 °C according to the ZRA and potentiostatic methods. Both potentiodynamic and EIS methods give an almost identical CPT value.     

Passivity of 316L stainless steel in borate buffer solution studied by Mott-Schottky analysis, atomic absorption spectrometry and X-ray photoelectron spectroscopy

The passivity of 316L stainless steel in borate buffer solution has been investigated by Mott-Schottky, atomic absorption spectrometry (AAS) and X-ray photoelectron spectroscopy (XPS). The results indicate that the polarization curve in the passive region possesses several turning potentials (0 V_SCE, 0.2 V_SCE, 0.4 V_SCE, 0.6 V_SCE and 0.85 V_SCE). The passive films formed at turning potentials perform different electrochemical and semiconductor properties. Further, the compositions of the passive films formed at turning potentials are investigated. The results reasonably explain why these potentials appear in the passive region and why specimens perform different properties at turning potentials.     

Corrosion performance of HVOF and APS thermally sprayed NiTi intermetallic coatings in 3.5% NaCl solution

Amorphous/nanocrystalline Ni-Ti powders produced by low energy mechanical alloying were used as feedstock to deposit NiTi intermetallic coatings on 316L stainless steel substrate using high velocity oxy-fuel (HVOF) and air plasma spraying (APS) processes. Electrochemical impedance spectroscopy (EIS) and polarization tests indicated that the corrosion performance and passive behaviour of HVOF coating were far better than those of APS coating. The study also showed that the solution had penetrated through the coating microcracks and caused interior corrosion of APS coating, while the HVOF coating was immune from interior corrosion attack and consequently exhibited a good passive behaviour during long-term immersion.