热带海洋大气环境下不锈钢的腐蚀寿命评估

目的 给出一种模拟万宁海洋大气环境的室内加速环境谱并对典型不锈钢材料进行寿命预测。方法 采用失重法对4种不锈钢的耐蚀性进行宏观分析。采用X射线光电子能谱分析仪（XPS）对4种不锈钢的腐蚀产物类型进行分析。采用扫描电子显微镜（SEM）对4种不锈钢的腐蚀产物进行微观分析。采用腐蚀电化学法对4种不锈钢进行宏观电化学分析。采用灰色关联度分析法研究室内加速环境谱与万宁海洋大气环境下户外暴露试验的相关性。结果 4种不锈钢的腐蚀失重速率都随着试验时间的增加而降低,其中430不锈钢腐蚀速率的减小程度最明显。4种不锈钢均在室内加速腐蚀试验中表现出较好的耐蚀性,耐蚀性由好到差依次为2205、316L、304、430不锈钢。XPS结果显示,304不锈钢与316L不锈钢的腐蚀产物主要为Fe₂O₃和Fe₃O₄;2205不锈钢的腐蚀产物主要包括Fe₂O₃以及Fe OOH或FeCr₂O₄;430不锈钢的腐蚀产物属于典型不锈钢的腐蚀产物,主要由...     

0Cr25Ni7Mo4、316与304不锈钢临界点蚀温度研究

采用外加恒定电位下腐蚀电流-温度扫描方法研究了0Cr25Ni7Mo4、304和316不锈钢在1 mol/L NaCl水溶液中的点蚀行为。利用不锈钢临界点蚀温度评价了材料的耐点蚀性能.测得0Cr25Ni7Mo4和316不锈钢的临界点蚀温度分别为79.5 ℃和15 ℃,304不锈钢在0 ℃以下.对0Cr25Ni7Mo4不锈钢材料优良耐点蚀性能的原因进行了分析讨论.     

Electrochemical polishing as a 316L stainless steel surface treatment method: Towards the improvement of biocompatibility

A 316L stainless steel (316L-SS) surface was electrochemically polished (EP) in an electrolyte of a new chemical composition at different cell voltages, with the aim of improving its corrosion resistance and biocompatibility. X-ray photoelectron spectroscopy results revealed that the EP-formed oxide films were characterized by a significantly higher atomic Cr/Fe ratio and film thickness, in comparison to the naturally-grown passive oxide film formed on the untreated (control) 316L-SS surface. As a result of the increase in the oxide film thickness and relative Cr enrichment, the EP-treated 316L-SS surfaces offered a notable improvement in general corrosion resistance and pitting potential. In addition, the attachment of endothelial cells (ECs) and smooth muscle cells (SMCs) to the 316L-SS surfaces revealed a positive effect of electropolishing on the preferential attachment of ECs, thus indicating that the EP surfaces could be endothelialized faster than the control (unmodified) 316L-SS surface. Furthermore, the EP surfaces showed a much lower degree of thrombogenicity in experiments with the platelet-rich plasma. Therefore, the use of the electrochemical polishing technique in treating a 316L-SS surface, under the conditions presented in this paper, indicates a significant improvement in the surface’s performance as an implant material.     

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.     

Corrosion behaviour of Lotus-type porous high nitrogen nickel-free stainless steels

Corrosion behaviour of three austenitic Lotus-type porous high nitrogen Ni-free stainless steels exposed to an acidic chloride solution has been investigated by electrochemical tests and weight loss measurements. Polarization resistance indicates that the corrosion rate of Lotus-type porous high nitrogen Ni-free stainless steels is an order of magnitude lower than that of Lotus-type porous 316L stainless steel in acidic environment. The localised corrosion resistance of the investigated high nitrogen Ni-free stainless steels, measured as pitting potential, E_b, also resulted to be higher than that of type 316L stainless steel. The influences of porous structure, surface finish and nitrogen addition on the corrosion behaviour were discussed.     

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.     

Laser Raman microscopic studies of passive films formed on type 316LN stainless steels during pitting in chloride solution

The surface films formed on type 316LN stainless steels (SS) with different nitrogen contents, during potentiodynamic polarization in acidified 1 M NaCl solution, were characterized by Laser Raman Spectroscopy (LRS). LRS confirmed the presence of oxides and oxychlorides of iron and chromium, hydrated chlorides and nitrates in the film. Raman mapping showed increasing nitrate content in the film with increasing nitrogen content. The film on the uncorroded material showed the presence of chromium and molybdenum oxides. The improvement in pitting corrosion resistance of type 316LN SS with increasing nitrogen content was attributed to increased amount of nitrates in the passive film.     

Pitting corrosion of Type 430 stainless steel under chloride solution droplet

To clarify the critical relative humidity (RH) to initiate pitting corrosion and the rusting mechanism in a marine atmospheric environment, pitting corrosion of Type 430 stainless steels under drops of MgCl₂ solutions were investigated. A pitting corrosion test was performed at different relative humidities under droplets with various diameters and thicknesses. The probability of pitting decreased as the diameter and thickness decreased. Pitting progressed only when the chloride concentration exceeded 4 M, which is the equilibrium concentration at 80% RH. Accordingly, pitting of Type 430 could be initiated when the RH was less than 80%. Additionally, a pitting corrosion mechanism of Type 430 stainless steel under droplets containing chloride ions is proposed.     

Achieving a chromium rich surface upon steels via FBR-CVD chromising treatments

Surface alloying via fluidised bed reactor (FBR) chemical vapour deposition (CVD) can be used to produce adherent and highly corrosion resistant surface layers. In this work, 304, 316, and 409 stainless steels and 1020 steel were chromised, producing distinct surface layers tens of micrometres thick. The composition and surface of these layers was characterised using microscopy, GDOES, and XPS. Surfaces were highly enriched in Cr and displayed improved corrosion resistance as determined by electrochemical evaluations. This work demonstrates that it is possible to form continuous, functional and corrosion resistant Cr-rich surface layers via FBR-CVD on a variety of steels.     

An X-ray photo-electron spectroscopic study of surface treatments of stainless steels

The effects of surface treatments on the surface composition and structure of Type 304 and 316 stainless steels were studied by X-ray photo-electron spectroscopy. The content of chromium and iron in the surface film depends considerably on the surface treatment method, while the nickel content in the film is significantly lowered compared to bulk composition regardless of the method. Some surface treatments which result in a significant enrichment of chromium in the surface film on the steels give the highest pitting potential. When the specimens were left for at least a day in contact with air, a certain amount of a magnetite-like compound was formed in the surface film. This fact is responsible for the ennoblement of the pitting potential by ageing after treatment.     

An X-ray photo-electron spectroscopic study of surface treatments of stainless steels

The effects of surface treatments on the surface composition and structure of Type 304 and 316 stainless steels were studied by X-ray photo-electron spectroscopy. The content of chromium and iron in the surface film depends considerably on the surface treatment method, while the nickel content in the film is significantly lowered compared to bulk composition regardless of the method. Some surface treatments which result in a significant enrichment of chromium in the surface film on the steels give the highest pitting potential. When the specimens were left for at least a day in contact with air, a certain amount of a magnetite-like compound was formed in the surface film. This fact is responsible for the ennoblement of the pitting potential by ageing after treatment.     

ATMOSPHERIC CORROSION OF 304AND 316 STAINLESS STEELS

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Studies of the tensile and corrosion fatigue behaviour of austenitic stainless steels

Corrosion fatigue behaviour of four types of austenitic stainless steels were investigated in boiling 45% magnesium chloride solution at a stress ratio of 0.25 and a frequency of 0.1 Hz. Type 316LN stainless steel possessed the best resistance and type 304 stainless steel had the lowest resistance to corrosion fatigue. XPS studies on the fracture surface indicated that the presence of nitrogen as ion in the surface film of type 316LN stainless steel gave it the highest resistance to corrosion fatigue. Fractographic examination showed wholly transgranular cracking in all cases.     

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.     

Effect of the final annealing of cold rolled stainless steels sheets on the electronic properties and pit nucleation resistance of passive films

Semiconducting properties of passive films formed on AISI 304 stainless steel grade were investigated by capacitances measurements in chloride containing aqueous solutions for different surface finishes: BA (bright annealing in hydrogen containing atmospheres) and 2B (standard annealing in oxidising atmospheres followed by pickling in acid, then water rinsing). Mott-Schottky analysis shows that for high enough electrode potential, and whatever the surface finish, the films behave like n-type semiconductors. 2B passive film appears to be more donor-doped than BA one and the density of donor states increases with chloride concentration. The electron donor levels are assumed to be generated by negatively charged cations vacancies produced by the chloride ions reaction with the outer passive film. This reaction looks easier for 2B than BA condition, which explains why BA resists better than 2B to pit nucleation.     

焊接氧化皮对奥氏体不锈钢孔蚀性能的影响

采用电化学测试技术,在NaCl介质中焊接氧化皮对3种奥氏体不锈钢的耐孔蚀性能进行了探讨.结果表明,有焊接氧化皮部位较比母材更易产生孔蚀,去除氧化皮则改善耐蚀性能.有焊接氧化皮的不锈钢耐孔蚀性能依NK1<316<304次序变劣.通过表面SIMS分析,发现焊接氧化皮合金表面贫乏铬,从而导致耐孔蚀性能下降.有焊接氧化皮NK1不锈钢耐孔蚀性能之所以优于304不锈钢,是由于表面膜中富集铜元素,并参与了成膜过程,改善了表面电化学行为,增强了表面膜抵抗侵蚀性离子破坏的能力.     

Electrochemical reactivation methods applied to PM austenitic stainless steels sintered in nitrogen-hydrogen atmosphere

Exposure methods (ASTM A262 Practice A and Modified Strauss Test) and electrochemical reactivation methods such as EPR and EPRDL was applied to PM 304L and PM 316L stainless and comparisons with wrought stainless steels were made. Sintering in vacuum and nitrogen-hydrogen atmosphere was chosen. The latter was the focus of the work and the former was used on comparative basis. It was seen how nitrogen in PM stainless steels plays a relevant role both when is dissolved and when is in intermetallic precipitates. A set of heat treatments were applied: annealing and sensitizing at 375, 675 and 875 °C. The results indicate that the electrochemical reactivation methods are suitable to evaluate the degree of sensitization of PM austenitic stainless steels.     

Pitting Potential of stainless steels in artificial sweat

The pitting potentials of 12/12, 316 PX, AISI 303, 304, 316F and 316L austenitic stainless steels were determined in artificial sweat (perspiration) at room temperature. Two compositions of sweat were used: the BAM composition which contains two malodorous organic acids and the composition proposed in an ISO standard which does not contain them. The quasi-potentiostatic method (10 mV potential steps per min), potentiodynamic technique (1 V/min linear sweep) and scratch test were used on mechanically polished and HNO₃-passivated surfaces. The aggressivity of the two artificial sweats with respect to stainless steels was found to be practically the same. The pitting potentials and the classification of the stainless steels according to their pitting potential values were found to depend on the surface preparation and, to a lesser extent, on the test method. The experimental techniques were often complementary and a combination of two or three methods in conjunction may increase the confidence with which the conclusions can be applied. The lowest pitting corrosion resistance was found for AISI 303 and the highest for AISI 316L. As expected stainless steels with the lowest concentration of nonmetallic inclusions (sulfides and oxides) exhibited the best pitting corrosion resistance.     

430不锈钢室内加速腐蚀与大气暴露的相关性研究

目的研究室内腐蚀膏试验对430不锈钢的加速性,以及腐蚀膏试验与大气暴露腐蚀试验的相关性。方法采用室内腐蚀膏腐蚀试验对材料进行腐蚀,研究其腐蚀过程的电化学特性和机理,腐蚀产物形貌、组成和结构,以及腐蚀过程的动力学规律,并与材料大气环境暴露试验的结果对比,探讨腐蚀膏试验与大气暴露试验的相关性。最后计算出室内腐蚀膏试验对430不锈钢的加速性。结果 430不锈钢在腐蚀膏腐蚀试验中,腐蚀失重与时间方程为P=0.3998t1.0391,呈幂指数关系,在腐蚀初期腐蚀速度最大。腐蚀机理主要是点蚀。由于腐蚀膏中的Cl-对钝化膜的穿透作用,使得钝化膜在一定点能够维持高的电流密度,并使阳离子杂乱移动而活跃起来,当膜-溶液界面电场达到临界值,点蚀发生。腐蚀表面存在点蚀坑,且随着腐蚀时间的增加,点蚀区域增加,相邻点蚀相互连接,形成腐蚀面。腐蚀面可见红色锈斑,对腐蚀产物进行XPS分析,其主要成分为Fe OOH和Fe3O4。430不锈钢在大气环境的腐蚀过程中,其腐蚀机理也是点蚀,腐蚀失重与时间也呈幂指数关系,腐蚀产物和形貌结构与室内腐蚀膏试验相同。结论腐蚀膏试验对430不锈钢腐蚀具有加速性,且与其大气暴露试验具有相关性,可以作为模拟430不锈钢大气腐蚀的一种加速试验。     

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.