Study on the Corrosion Resistance of 304L Stainless Steel

304L is an austenitic stainless steel with very low carbon content, and is served as the application to the oxidizing media, however, its corrosion resistance is not satisfactory in reducing media. For example, the pitting corrosion occurred on 304L stainless steel tube, which had been mounted for one year, somewhere at the power station in die seashore of China. For this reason we have studied the corrosion behavior of 304L in some media and invented a novel surface treatment technique of stainless steel for extremely improving the corrosion resistance of 304L. The characteristics of the modified passive film on the steel were examined in this paper, and the corrosion resistance of treated 304L stainless steel was tested in our laboratory and the testing ground. The results are satisfactory.     

不锈钢点腐蚀发生的早期过程 Ⅰ. 扫描微参比电极法研究

本文应用扫描微参比电极联机测量系统对18-8型不锈钢在含Cl~-介质中点腐蚀发生的早期过程进行研究。结果表明, 在点腐蚀发生的早期阶段, 可用特征电位E_r表征表面钝化膜的局部破坏和微点腐蚀的发生, E_r电位与传统的E_P电位不同, E_r电位通常比E_p, 电位更负100—400 mV, E_r电位值与钝化膜的表面状态直接有关, 且随介质Cl~-浓度的增加和pH的降低而负移。在E_r电位附近, 微点腐蚀开始发生, 但一般不能稳定发展, 电位越接近于E_p, 则已发生的微点腐蚀越容易扩展为宏观点腐蚀, 由此, 作者提出“不稳定微点腐蚀”的新概念, 并对不锈钢点腐蚀发生的早期过程机理加以讨论。     

Characterization of the Passive Film and Corrosion of Martensitic AM355 Stainless Steel

Electrochemistry methods were used to investigate the influence of pH on the passive film and corrosion behavior of ultrahigh strength AM355 stainless steel in chloride-containing media. Analysis of the Pourbaix diagram indicates that AM355 stainless steel exhibits higher corrosion resistance in natural and near-natural environments than that in acidic and alkaline conditions. Electrochemistry measurements and composition analysis of the passive film show that pitting potential increased due to the enhanced repassivation capacity of AM355 stainless steel with increasing pH. The mixed MnS/oxide inclusions are the main pitting sensitive locations under all conditions. Morphological observations and energy-dispersive spectroscopy showed that the influence of the gap between the martensitic laths is significant with increasing pH. The inclusions, element concentrations, and microstructures weaken the resistance of ultrahigh-strength martensitic AM355 stainless steel against corrosion.     

抗菌处理含铜铁素体不锈钢的耐微生物腐蚀性能

采用电化学测试技术及微生物学方法, 研究了抗菌处理含铜铁素体不锈钢在含有培养基的异养菌溶液中的耐蚀性能. 结果表明, 不锈钢的腐蚀电位随异养菌的新陈代谢呈现规律性变化, 抗菌处理使不锈钢在菌液中钝化膜的稳定性得到改善, 点蚀敏感性降低; 抗菌不锈钢表面弥散分布的ε-Cu析出相的杀菌作用, 降低了异养菌的活性, 减缓了异养菌对抗菌不锈钢的腐蚀, 提高了抗菌不锈钢耐微生物腐蚀性能.     

基于电化学噪声研究模拟海洋大气环境下304不锈钢的点蚀行为

基于电化学噪声技术建立了不锈钢海洋大气点蚀监测系统,利用该系统对处于干湿循环环境下不锈钢的点蚀行为进行监测. 使用时域谱图、时域统计、频域谱图和散粒噪声理论等分析方法对采集到的电化学噪声数据进行处理分析,并结合动电位极化法,形貌分析法共同研究不锈钢的点蚀行为. 研究结果表明,304不锈钢在模拟海洋大气环境下的点蚀行为分为钝化、亚稳态点蚀和稳态点蚀三个阶段. 在钝化阶段,电位电流噪声信号出现少量的同步异向波动,腐蚀事件发生频率高,平均电量低;在亚稳态点蚀阶段,电位电流噪声信号出现大量的同步同向波动,腐蚀事件发生频率降低,平均电量上升,通过扫描电镜观察蚀点;在稳态点蚀阶段,电位电流噪声信号不仅存在大量的同步同向波动,还出现了同步异向波动,腐蚀事件发生频率较低,平均电量大幅度上升,通过扫描电镜观察到电极表面出现小而浅的蚀点. 而动电位极化法可以证实304不锈钢点蚀的发生. 两种分析方法所得结果具有较好的一致性,证明该监测系统很好地实现了对模拟海洋大气环境下304不锈钢点蚀行为的连续监测,并能判断点蚀的发生.     

磁场对316L不锈钢微生物腐蚀行为的影响

采用循环极化、微生物分析法、扫描电镜及表面能谱分析等方法,研究了磁场对316L不锈钢在含硫酸盐还原菌(SRB)的土壤模拟溶液中的腐蚀行为。结果表明,磁场可以抑制SRB的生长;未外加磁场时316L不锈钢表面膜层以局部堆积为主,加有磁场时,局部堆积明显减小,膜层均匀致密的排列于基体表面;无论有或没有外加磁场,316L不锈钢表面均发生钝化膜破裂型点蚀,未外加磁场时的点蚀电位低于加有磁场时的。在相同的浸泡时间,未外加磁场时循环极化滞后环面积明显比加有磁场时的大,说明磁场可以有效抑制316L不锈钢点蚀的形成与发展,降低316L不锈钢的点蚀诱发能力。     

A zirconia-polyester glycol coating on differently pretreated AISI 316L stainless steel: corrosion behavior in chloride solution

The effect of zirconia and zirconia-polyester glycol hybrid coatings on the corrosion resistance of mechanically polished or anodized AISI 316 stainless steel (316L), was studied by potentiodynamic polarization and electrochemical impedance spectroscopy in 0.1 M NaCl and scanning electron microscope and atomic force microscopy examinations. The deposition of zirconia coatings was achieved by the sol–gel technique by immersing the samples in either the inorganic polymer or the organic–inorganic polymer mixture. From potentiodynamic and impedance measurements, the grade of protection is reduced with the exposure time to the electrolyte, which is mainly associated with lost of film adhesion and, consequently, detachment from the metal substrate. However, the uncoated anodized sample revealed an unexpected corrosion behavior; the anodic film formed during anodizing readily increased the corrosion resistance of the 316L stainless steel in 0.1 M NaCl, revealing a considerable reduction in the corrosion current density and an increase in the pitting potential.     

Improvement of pitting corrosion resistance of a biomedical grade 316LVM stainless steel by electrochemical modification of the passive film semiconducting properties

In the present paper we show that a significant improvement in pitting corrosion resistance of a biomedical grade stainless steel, 316LVM, can be achieved by the formation of a surface passive oxide film under cyclic potentiodyanamic polarization (passivation) conditions. A complete absence of pitting in physiological simulating solutions was demonstrated, while the electrochemically formed passive film maintained its very high pitting resistance even at higher chloride concentrations in the bulk solution. The improvement in the film’s pitting corrosion resistance was correlated with its semiconducting properties.     

Pitting inhibition of stainless steel by surfactants: an electrochemical and surface chemical approach

Pitting corrosion of stainless steels causes tremendous damage in terms of material loss and resulting accidents. Organic surfactants have been tried as pitting inhibitors but the understanding of the inhibition mechanisms is mainly speculative. In the present study the inhibition of the pitting corrosion of 304 stainless steel by N-lauroylsarcosine sodium salt (NLS) in 0.1 M NaCl solutions at neutral pH was studied using an approach that combines surface chemical techniques with electrochemical ones. It was found that NLS increases the pitting resistance of 304 stainless steel, with possible complete inhibition at high NLS concentration (30 mM). Adsorption of NLS on 304 stainless steel particles was directly measured. NLS adsorbs significantly on 304 stainless steel with maximum adsorption density close to bilayer coverage. Electrophoretic mobility data for 304 stainless steel particles show that the surface of 304 stainless steel is negative in NaCl solution at neutral pH. The adsorption of NLS makes the interfacial charge even more negative. The relationship between pitting inhibition and adsorption density of NLS suggests that NLS does not adsorb preferentially on the pit nucleation sites and complete inhibition requires that the whole surface be covered completely by NLS. The inhibition mechanism of NLS is proposed to be due mainly to the blocking effect of a negatively charged NLS adsorption layer. This study shows that in addition to the adsorption amount of surfactant, interfacial charge also plays an important role in pitting inhibition.     

双相不锈钢的选择性腐蚀研究(英文)

双相不锈钢中的铁素体(α相)和奥氏体(γ相)具有不同的晶体结构和化学成分,使之在水溶液环境中表现不同的耐蚀特征.本文应用空间分辨电化学技术测量2205双相不锈钢中铁素体和奥氏体的电位差异,并用电镜技术分析了α相和γ相的选择性腐蚀形态.结果表明,在0.01mol/LNaCl溶液中,铁素体的腐蚀电位比奥氏体高,而在2mol/LH2SO4+xmol/LHCl溶液中,双相不锈钢在活化＿钝化电位区出现两个明显的阳极电流峰.铁素体相的选择性腐蚀发生在较负的阳极峰电位,而奥氏体则在较正的阳极电位峰发生选择性腐蚀.     

Electrochemical and XPS studies on corrosion behaviours of AISI 304 and AISI 316 stainless steels under plastic deformation in sulphuric acid solution

The corrosion behaviours of austenitic stainless steels were investigated by electrochemical methods under plastic deformation with constant strain in the naturally aerated 0.5 M H₂SO₄ + 0.2 M KCl solution at room temperature. The work addresses the influence of plastic deformation and molybdenum element on the corrosion resistance of austenitic stainless steels in the test solution. Electrochemical impedance spectroscopy presents the decreasing charge transfer resistance (R_t) and polarization resistance (R_p) values with the immersion time for AISI 304 stainless steel under constant strain deformation, and the increasing R_t and R_p values with the immersion time for AISI 316 stainless steel. The analysis of the chemical composition of the corrosion products was carried out by XPS. Molybdenum addition in AISI 316 stainless steel affects significantly the corrosion resistance because of its high ability to form Mo (VI) and MoCl₅ insoluble compounds in acid medium. Copyright © 2011 John Wiley & Sons, Ltd.     

Dynamic electrochemical impedance spectroscopy measurements of passive layer cracking under static tensile stresses

Electrochemical impedance spectroscopy allows the examination of corrosion susceptibility and resistance for different construction materials, in particular the determination of the properties of their passive films. This technique makes possible the analysis of electrochemical processes in time domain, including rapid phenomena such as changes in the properties of passive films, but it has never been used for passive layer cracking examination. In many cases, fracture of the passive film under tensile stresses leads to stress corrosion cracking. Therefore, investigations of passive layer cracking on austenitic stainless steels under tensile stresses facilitate the understanding of the mechanism of stress corrosion cracking in these common engineering materials. The effect of static tensile stresses on the passive film cracking behaviour of type 304L stainless steel immersed in 0.5 M NaCl solution at room temperature has been investigated. This paper presents the impedance spectra obtained for 304L stainless steel samples at different potential values.Contribution to the 3rd Baltic Conference on Electrochemistry, Gdansk-Sobieszewo, Poland, 23–26 April 2003Dedicated to the memory of Harry B. Mark, Jr. (28 February 1934–3 March 2003)     

Interfacial Behavior of beta-Lactoglobulin at a Stainless Steel Surface: An Electrochemical Impedance Spectroscopy Study

The electrochemical impedance spectroscopy technique was used to investigate the interfacial behavior of beta-lactoglobulin at an austenitic stainless steel surface over the temperature range 299 to 343 K at an open circuit potential. The electrode/electrolyte interface and corresponding surface processes were successfully modeled by applying an equivalent-electrical-circuit approach. A charge-transfer resistance value was found to be very sensitive to the amount of adsorbed protein (surface concentration), thus indicating that the adsorption of the protein (i) was accompanied by the transfer of the charge, via chemisorption, and (ii) influenced the mechanism and kinetics of the corrosion reaction. This was also apparent from the large decrease in the corrosion activation energy (16 kJ mol(-1)) caused by the adsorption of the protein. Adsorption of beta-lactoglobulin onto the stainless steel surface at an open circuit potential resulted in a unimodal isotherm at all the temperatures studied and the adsorption process was described with a Langmuir adsorption isotherm. From the calculated Gibbs free energies of adsorption it was confirmed that beta-lactoglobulin molecules adsorb strongly onto the stainless steel surface. The enthalpy and entropy values indicated that the molecule partially unfolds at the surface upon adsorption. The adsorption process was found to be entirely governed by the change in entropy. Copyright 2000 Academic Press.     

Stressed Corrosion of an Austenitic Stainless Steel Studied by Scanning Kelvin Probe Force Microscopy

Under the ambient temperature (25°C) and pressure (one Standard Atmospheric Pressure) conditions, surface Volta potential of an austenitic stainless steel was measured using the Scanning Kelvin Probe Force Microscopy (SKPFM) to study its stressed-related corrosion behavior in a 0.5 M chloride solution. In an oxygen and water regulated environment (using a glovebox), the steel shows a map of Volta potentials with high contrasts among the different grains and grain boundaries, which was then linked to the actual corrosion potential (w.r.t. a saturated calomel electrode) based on a rigorous calibration procedure. Corrosion behavior of the steel under tensile stress was then compared to that of the same sample under no tensile stress in light of the measured Volta potential, which was found to be sensitive to the level of applied tensile stress, although the tested stainless steel in general is known for its high corrosion-resident capability. According to this study, surface Volta potential measured by SKPFM can be used as a high-accuracy indicator for localized corrosion of steels.     

Electrochemical behavior of Ni-Al-Fe alloys in simulated human body solution

An investigation about the corrosion resistance of Ni-Al-Fe intermetallic alloys in simulated human body fluid environments has been carried out using electrochemical techniques. Tested alloys included 57 (wt%) Ni-(20 to 30) Al-(12 to 23) Fe using the Hank's solution because the high corrosion resistance provided by protective Al₂O₃ external layer. For comparison, AISI 316L type stainless steel has also been used. Electrochemical techniques included potentiodynamic polarization curves, electrochemical impedance spectroscopy, and electrochemical noise measurements. The different techniques have shown that these alloys showed a similar or higher corrosion resistance than conventional AISI 316L type stainless steel, and this corrosion resistance decreased as the Al content in the alloy increased. The alloys were susceptible to pitting type of corrosion on the interdendritic Ni-rich phases.     

合金元素及模拟热处理对2205双相不锈钢之孔蚀性质影响

本文研究了Ｎｉ元素及不同模拟焊后热影响区（ＨＡＺ）组织对２２０５双相不锈钢孔蚀性质之影响。结果发现：在研究成分范围内，不同Ｎｉ含量对于底材电化学极化曲线之影响不大，其Ｅｎｐ和Ｅｎｐ均在１１００￣１２００ｍＶ之间。     

Surface remelting of 316 L + 434 L sintered steel: microstructure and corrosion resistance

This study presents arc surface remelting of three types of sintered stainless steels carried out in order to constitute a homogeneous microstructure in the surface layer which is free from open and interconnected porosity. The main aim of this treatment was to improve functional properties of the sinters analysed, especially their resistance to pitting corrosion. The sinters were obtained from powders of 316 L and 434 L steels. The PM austenitic-ferritic stainless steels are used mainly in the automotive industry, but their general application is still limited due to relatively poor corrosion properties when compared to casts or wrought components. This study used the gas tungsten arc welding (GTAW) process as a method of economical surface treatment. The effect of surface treatment was evaluated based on macro- and microstructural observations, energy-dispersive X-ray spectroscopy (EDX) analysis, X-ray phase analysis, measurements of surface roughness and electrochemical examinations. It was found that a cellular or mixed cellular and dendritic structure was formed in the remelted zone of the sinters after remelting. X-ray analysis demonstrated that application of remelting contributes to formation of the austenitic phase in the surface layer. The corrosion resistance of the remelted surface layers was evaluated using polarization tests in 0.5 M NaCl solution. It was found that arc surface remelted layers exhibit much better anticorrosive properties than sinters without surface treatment. Microstructural observations of the surface of specimens after electrochemical tests showed only a few single pits in the remelted layer, while the surface of initial sinters was much more corroded.     

Synthesis and Properties of Cerium and Titanium Oxide Thin Coatings for Corrosion Protection of 304 Stainless Steel

Powders and thin coatings of ceria and titania were synthesized from aqueous and solvent-based precursors. Thin coatings were deposited on polished 304 stainless steel coupons by dipping them in the appropriate sol-gel oxide precursors. The coatings were subsequently densified and crystallized at several hundreds of degrees. It was possible to obtain dense titania coatings by applying thin coatings of cerium dioxide prior to titania on stainless steel substrates. Underlayer ceria coatings proved to be pivotal in obtaining dense titania coatings and preserving the integrity of the stainless steel while going through the high temperature treatments. The effect of processing parameters such as the atmosphere of heat-treatment, and temperature on the microstructure and crystal structure of the films and powders of ceria and titania was investigated. X-ray diffraction was used to identify the crystal structure of films and powders upon heat-treatment. Electrochemical measurements in NaCl, and analytical techniques such as SEM and EDX were used to evaluate the corrosion performance and pitting morphology of coated samples. A composite coating of ceria and titania was able to prevent crevice corrosion and increase the pitting resistance of the 304 stainless steel relative to the uncoated substrate.     

18／8型不锈钢在受力形变条件下腐蚀电化学行为的研究

应用电化学稳态技术、电化交流阻、抗微区电化学技术及扫描电等方法，研究１８／８型不锈钢在Ｎａ２Ｓ２Ｏ３稀溶液中，受外力形变条件下，的腐蚀电化学行为，结果表明，力学因素可使表面腐蚀电化学活性增加，表面微裂纹的发生、消失和再钝化的动态过程，同时受电位和拉应力的影响；点腐蚀可优先发生在应力集中位置，点蚀的发展可能诱导不锈钢的应力腐蚀开裂。     

Evaluation of passive film behaviour of super austenitic stainless steels at different potential regions using dynamic electrochemical impedance spectroscopy

Potentiodynamic anodic polarisation and dynamic electrochemical impedance spectroscopic (DEIS) measurements were carried out on 316L stainless steel and alloys 926 and 31 in natural seawater in order to assess the crevice corrosion resistance. DEIS measurements were performed over a wide range of potentials covering the corrosion potential, passive region, breakdown region and dissolution region. The impedance measurements in potentiodynamic conditions clearly reveal the changes that occur in the passive layer with change in potential. The impedance spectra at different potential regions were also discussed elaborately. The surface morphology of the alloy after crevice corrosion was studied using optical microscope and atomic force microscopy.