Magnetic property based characterization of rust on weathering steels

The characterization of rusts on weathering steels is important in understanding the origin of their corrosion resistance. Rust consists of several phases, e.g. α-, β- and γ-FeOOH, which are anti-ferromagnetic with different Neél temperatures. Rust on so-called advanced weathering steel containing 3 wt.% Ni [H. Kihira, A. Usami, K. Tanabe, M. Ito, G. Shigesato, Y. Tomita, T. Kusunoki, T. Tsuzuki, S. Ito, T. Murata, in: Proc. Symp. on Corrosion and Corrosion Control in Saltwater Environments, Honolulu, 1999, The Electrochemical Soc., pp. 127-136] contains in addition a ferrimagnetic spinel phase [M. Kimura, H. Kihira, Y. Ishii, T. Mizoguchi, in: Proc. 13th Asian-Pacific Corrosion Control Conference, Osaka, 2003; M. Kimura, H. Kihira, N. Ohta, M. Hashimoto, T. Senuma, Corros. Sci., this volume; M. Kimura, N. Ohta, H. Kihira, Mater. Trans. JIM, in press]. The nanostructure of real rust cannot be elucidated satisfactorily only with conventional analytical methods such as X-ray diffraction, because of the complex mixture of phases with fine and imperfect crystallites. Because of the short range of the super-exchange coupling between Fe ions in a solid, the magnetic properties can give information on local configurations even in the absence of perfect crystalline coherence. Therefore, the magnetic properties of rust samples were investigated in detail using a Superconducting Quantum Interference Device (SQUID) magnetometer and Mössbauer spectroscopy. SQUID magnetometry is effective to determine the quantity of the ferrimagnetic phase. The temperature dependence of the Mössbauer spectrum gives information about not only the fractions of the phases but also the distribution of grain volume, V, in each phase according to the super-paramagnetic relaxation effect. This approach has been applied to rust of conventional [T. Okada, Y. Ishii, T. Mizoguchi, I. Tamura, Y. Kobayashi, Y. Takagi, S. Suzuki, H. Kihira, M. Ito, A. Usami, K. Tanabe, K. Masuda, Jpn. J. Appl. Phys. 39 (2003) 3382] and advanced weathering [H. Kihira, A. Usami, K. Tanabe, M. Ito, G. Shigesato, Y. Tomita, T. Kusunoki, T. Tsuzuki, S. Ito, T. Murata, in: Proc. Symp. on Corrosion and Corrosion Control in Saltwater Environments, Honolulu, 1999, The Electrochemical Soc., pp. 127-136] steels.The grains of the rust formed on advanced weathering steel have clearly bimodal Gaussian distributions of volume with peaks at V ≈ 5 × 10⁻²⁴ m³ and V ≈ 16 × 10⁻²⁴ m³ in α-FeOOH and β-FeOOH phases. The outer layer has grains of γ-FeOOH which are an order of magnitude smaller. The inner layer, in contrast, has a continuous distribution of grain volume, consistent with the formation of a continuous densely packed thin protective rust layer which prevents further corrosion.     

Systematic approaches toward minimum maintenance risk management methods for weathering steel infrastructures

Since the revised Japanese Specification for Highway Bridges clearly states that degradation of bridge members to occur in a prolonged period of time must be taken into account as a risk, wide scope of discussion has been carried out in Japan. The final goal of these activities is to realize the ultra long term durability of steel infrastructures with a minimized maintenance cost. To reduce risks for anomalous rusting to occur on weathering steel structures, a computerized corrosion prediction system, visual as well as instrumental rust monitoring methods, repairing or retrofitting methods in case of contingency, etc. have been developed. Unlike organic or inorganic materials, weathering steels do not deteriorate internally. Therefore, all corrosion risks can be monitored by the inspection of steel member surfaces. The present work proposes a systematic management method for Risk Based Minimum Maintenance (RBMM) of weathering steel bridges.     

Corrosion behaviour of friction stir welded AA7108 T79 aluminium alloy

The corrosion behaviour of a friction stir welded AA7108 T79 aluminium alloy has been investigated using accelerated testing (ASTM G34 EXCO) and electrochemical measurements. The welded alloy showed the expected zones associated with friction stir welding, namely nugget, thermomechanically affected zone and heat affected zone. Corrosion testing revealed that the edge regions of the thermomechanically affected zone were most susceptible to corrosion. The localized corrosion occurs intergranularly due to the non-uniform distribution of η/η′ (MgZn₂) precipitates within the thermomechanically affected zone.     

Influence of carbon content and microstructure on corrosion behaviour of low alloy steels in a Cl containing environment

Corrosion behaviour of low alloy steels (A and B) with different carbon content was studied by a salt fog test and an outdoor test. A commercial weathering steel 09CuPCrNi was used for comparison. The corrosion resistance of steels A and B with homogeneous microstructures was better than that of the commercial weathering steel 09CuPCrNi in the salt fog test. Steel A with an ultra-low-carbon content had far less weathering resistance than the other steels in the outdoor test. Selective corrosion of large pearlite produces stress in initial corrosion product films. Uniform corrosion product films with few cracks tend to form on homogeneous microstructures such as ferrite and bainite, and this is advantageous for the formation of a compact rust layer in the initial stage of atmospheric corrosion. However, uniform microstructures will result in over even interfaces between rust layers and bases, which will lead to frequent peeling of rust layers from bases because stress is induced by large temperature fluctuations and wet-dry alternations. Protection of the rust layer on a low alloy steel is dependent on the rust density and the bonding performance of the rust-base rather than the proportion of the rust phase in the initial stage of atmospheric corrosion. These results indicate that homogenous microstructures, proper amounts of carbon content and fine carbon-rich phases that are produced by appropriate processes are beneficial for the corrosion resistance of steels.     

Ni对耐候钢在模拟海洋大气环境下耐蚀性的影响

通过周期浸润加速腐蚀实验,研究了不同Ni含量的耐候钢在模拟海洋大气环境下的腐蚀规律.采用失重法评价耐候钢的耐蚀性,并利用扫描电镜 (SEM),X射线衍射(XRD) 和电化学方法对耐候钢表面生成的锈层进行了分析.结果表明,随着Ni含量的增加实验钢的耐蚀性逐渐增加,当Ni含量超过3%(质量分数) 其耐蚀性较对比钢提高了两倍;Ni的存在能够提高实验钢的自腐蚀电位,并促进保护性腐蚀产物α-FeOOH的形成;电化学阻抗测试结果表明,实验钢中Ni含量越多,实验钢的电阻越大,锈层的保护性越好.     

材料在青岛地区的大气腐蚀及防护对策

在青岛地区对碳钢、低合金钢、不锈钢、铝及铝合金、钛及钛合金以及涂镀层进行了８年大气腐蚀暴露。得到了各种材料在青岛海洋大气中的腐蚀数据及相应的环境数据。８年暴露腐蚀主耐侯钢我为０．０１４６ｍｍ／ａ,碳钢约为０．０６２２ｍｍ／ａ,其腐蚀失重发展符合指数函数规律Ｄ＝ＡＴ＾ｎ。钛合金,高铬不锈钢在大气中完全耐蚀。金属名热喷涂加封闭是保护钢结构最有效的方法。     

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.     

Die Korrosionsbeständigkeit der nichtrostenden Stähle an der Atomosphäre – Auswertung von Versuchen bis zu 10jähriger Auslagerung–

Corrosion resistance of stainless steels at the atmosphere – Evaluation of the results of weathering tests up to 10 years' duration – The evaluation of results obtained in the course of weathering tests up to 10 years' duration has confirmed the conclusions drawn after one year's exposition. A CrNiMo steel (Werkstoff-Nr. 1.4401) can be used even in the most severe conditions; slight corrosions found in marine atmospheres can be attributed to unpolished surfaces. The 17% Cr steel is considerably attacked in industrial and marine atmospheres and should not be used for the external parts of buildings. 18/8 steels are perfectly resistant to urban atmosphere, with the exception of those portions which are not exposed to the cleaning effect of rain waters. In all the cases studied the corrosion resistance of the steels has been improved by electropolishing. Electrochemical studies have further revealed that the pitting corrosion susceptibility decreases in the same order as the atmospheric corrosion resistance.     

二硫化钼固体干膜润滑涂层的性能对比研究

目的为了在产品加工过程中快速选择合适的二硫化钼涂料进行涂覆,对国内目前性能较优异的三种二硫化钼涂料进行相关性能检测。方法依据AS5272C《热固型防腐蚀干膜润滑剂采购规范》中规定的试验项目进行检测,包括附着力、耐铝腐蚀、亚硫酸盐雾、中性盐雾、耐高低温、耐液性、耐磨寿命、承载能力、固体含量。结果 HM-1700二硫化钼涂层除耐磨寿命外,其余性能均符合标准要求,而HD-02和HR-7301C二硫化钼涂层只有耐中性盐雾试验和耐磨寿命不符合标准要求。结论 HD-02和HR-7301C适用于重载、无长时间滑动摩擦的一般腐蚀环境下使用的零件,HM-1700适用于重载、无长时间滑动摩擦的腐蚀较恶劣环境(尤其是海洋大气环境)下使用的零件。     

Spectroscopic identification of protective and non-protective corrosion coatings on steel structures in marine environments

Corrosion research, and the need to fully understand the effects that environmental conditions have on the performance of structural steels, is one area in which Mössbauer spectroscopy has become a required analytical technique. This is in part due to the need to identify and quantify the nanophase iron oxides that form on and protect certain structural steels, and that are nearly transparent to most other spectroscopic techniques. In conjunction with X-ray diffraction and micro-Raman analyses, the iron oxides that form the rusts on steels corroded in different marine and other environments can be completely identified and mapped within the rust coating. The spectroscopic analyses can be used to determine the nature of the environment in which structural steels have been, and these act as a monitor of the corrosion itself. Mössbauer spectroscopy is playing an important role in a new corrosion program in the United States and Japan in which steel bridges, old and new, are being evaluated for corrosion problems that may reduce their serviceable lifetimes. Mössbauer spectroscopy has been used to characterize the corrosion products that form the protective patina on weathering steel, as well those that form in adverse environments in which the oxide coating is not adherent or protective to the steel. Mössbauer spectroscopy has also become an important analytical technique for investigating the corrosion products that have formed on archeological artifacts, and it is providing guidance to aid in the removal of the oxides necessary for their conservation.     

Influence of temperature on the interaction mode of T91 and AISI 316L steels with Pb-Bi melt saturated by oxygen

Corrosion tests of T91 and AISI 316L steels in stagnant Pb-Bi eutectic saturated by oxygen at 500, 520, 540 and 560 °C were carried out. The corrosion mode as a function of temperature was revealed. The oxidation was the main interaction mechanism for both T91 and AISI 316L steels. At 560 °C temperature the interaction mode for AISI 316L was mixed: the oxidation as well as the dissolution of steel components accompanied by the penetration of liquid metal into the solid metal was observed simultaneously. The corrosion rate of AISI 316L steel was less than that of T91 due to higher content of chromium in the austenitic steel. However, the spinel layer containing Ni was more vulnerable to the liquid metal attack. The kinetic model describing nucleation, growth and degradation of double oxide layer on the surface of steels contacting with Pb-Bi melt saturated by oxygen was proposed.     

Electrochemical synthesis of ferritic stainless steels alloyed with 1 wt-%Ti,V and Nb in sulphuric acid solution

Abstract

Corrosion behaviours of stainless steel alloys containing corrosion resistant elements were investigated. Ferritic stainless steel electrodes were synthesised by the application of a scan rate of 1 mV s^–1. Stainless steels were unalloyed and alloyed with approximate 1 wt-% Ti, V and Nb elements. The samples were obtained from casting and forging. The steels were exposed to different heat treatments. Heat treatment was not applied to the first group of samples. The second and the third group of samples were rapidly cooled after annealing at 1100°C for 30 and 180 min respectively. The corrosion performances of ferritic stainless steels were investigated in 0·1 M H₂SO₄ solution, by use of electrochemical impedance spectroscopy. Scanning electron microscopy (SEM) investigations were performed. Scanning electron microscopy micrographs showed generalised pitting on the surface. Corrosion resistance was calculated by Stearn-Geary equation. It was determined that titanium has the best effect on the corrosion resistance of ferritic stainless steels homogenised for 180 min.     

The influence of chromium content on the electrochemical behavior of weathering steels

To investigate the influence of chromium content on corrosion characteristics of weathering steels, the electrochemical measurements were performed on the steels containing 0–9% Cr (wt.%) in NaHSO₃ aqueous solution. The results indicated that the open circuit potential of these steels shifted to the positive direction remarkably, because the additions of Cr improved the passivation capability of the steels. The corrosion current density of the steels containing more than 7% Cr (wt.%) decreased significantly after pre-rusted treatment, implying the corrosion resistance could be enhanced by the formation of protective goethite rust layer.     

Application of High Temperature Corrosion-Resistant Materials and Coatings Under Severe Corrosive Environment in Waste-to-Energy Boilers

Corrosion-resistant materials (CRMs) and coatings are key technologies to increase power generation efficiency and reduce maintenance in waste-to-energy (WTE) plants. Corrosion environment became severe as steam temperatures have increased. The steam condition of more than 400 °C/3.9 MPa became possible in WTE boilers by using highly durable corrosion-resistant coatings, such as thermal spray of Al/80Ni20Cr alloy, HVOF-sprayed NiCrSiB alloy, Alloy 625 weld overlay for waterwall tubes and also superheater tubes. Also, the use of 310S type stainless steels and high Cr-high Mo-Ni base and high Si-Cr-Ni-Fe alloys have progressed because of a better understanding of corrosion mechanisms. Furthermore, high durability coatings using cermet and ceramic materials were applied to high temperature superheaters. This paper describes the major developments and the application of CRMs and coating technologies in the last 30 years in WTE plants, the corrosion mechanisms of alloys, the deterioration mechanisms of spray coating layers, and future subjects for the development of corrosion-resistant materials and coatings.     

Material performance in a solvent extraction Liquefaction plant in Japan

Corrosion behaviour of various steels and alloys in the solvent extraction coal liquefaction process in Japan has been studied by the inplant testing in a 1 ton/ day plant and by the laboratory tests related to it. The severest corrosion was observed in the high pressure separator, corrosion thickness loss and pitting depth being the greatest and stress corrosion cracking being observed for 18–8 series austenitic stainless steels. The cause may be the occurrence of water condensate containing high Cl^? and H₂S. Otherwise corrosion was relatively mild. No obvious symptom of notorious organic-chloride corrosion reported in the U.S. has been observed.     

Outdoor atmospheric corrosion of carbon steel and weathering steel exposed to the tropical-coastal climate of Thailand

This study focuses on atmospheric corrosion of carbon steel and weathering steel exposed at two different locations with dissimilar meteorological parameters and airborne pollutants in Thailand. The samples are subjected to an outdoor atmosphere for up to 36 months at Rayong, close to the Gulf of Thailand, and Phangnga, near the Andaman Sea. Thickness loss (µm), corrosion rate (µm/year) together with corrosion product morphology and composition are systematically analyzed using X-ray diffraction and a scanning electron microscope. Corrosion resistance of the tested steels exposed at both locations is discussed based on the above-mentioned parameters and calculated corrosion kinetics. The results indicate that the total time of wetness, amount of rainfall and chloride deposition rate play an important role in corrosion behavior of the tested steels. Alloying elements, copper, chromium and nickel, are shown to improve corrosion resistance of the samples when exposed at the location with a higher chloride concentration.     

Modelling the relationship between microstructure of Galfan-type coated steel and cut-edge corrosion resistance incorporating diffusion of multiple species

This paper describes a considerable extension to a previously documented [S.G.R. Brown, N.C. Barnard, 3D computer simulation of the influence of microstructure on the cut edge corrosion behaviour of a zinc aluminium alloy galvanized steel, Corrosion Science 48 (2006) 2291-2303], first-order model used to simulate the localized degradation experienced in Zn-4.5 wt% Al steel coatings exposed to 5% NaCl aqueous solution. The temporal localization and intensity of discrete corrosion effects are predicted using established relationships and, in contrast to earlier models, the evolution of multiple concentration fields is included and calculated using straight-forward finite difference techniques. Changes in composition are included in the quantification of both anodic and cathodic processes involved in the corrosion of steel coatings in contact with aerated saline solutions. Reported [J. Elvins, J.A. Spittle, D.A. Worsley, Microstructural changes in zinc aluminium alloy galvanising as a function of processing parameters and their influence on corrosion, Corrosion Science 47 (2005) 2740-2759] and modelled performances of typical Galfan composition coated steels are evaluated for different coating microstructures undergoing so-called cut-edge corrosion. In summary, this latest model successfully matches measured rates of metal loss during localized corrosion. Additionally, the inclusion of multiple species diffusion functionality has greatly improved the simulation of the cathodic reaction in particular and the overall form of the current density distribution near the corroding surface.     

Effect of CO2 on the stability of steels with 1% and 13% Cr in saline water

In engineering storage sites for Carbon Sequestration the CO₂-induced corrosion of injection pipe steels is a relevant safety issue when emission gasses are compressed in deep geological layers. The reliability of the steels suitable for the geological onshore CCS-site (Carbon Capture and Storage) at Ketzin, Germany, is demonstrated in laboratory experiments in equivalent corrosive environment (T = 60 °C, p = 1-60 bar, aquifer water, CO₂-flow rate of 3 L/h, 700-8000 h exposure time). Corrosion kinetics and microstructures were characterized using specimens of the heat treated steel 42CrMo4 (1.7225) used for casing, and specimens of the martensitic stainless injection-pipe steel X46Cr13 (1.4034).     

Steam oxidation resistance of new 12%Cr steels: Comparison with some other ferritic steels

The oxidation resistance in pure steam at the 600-650 °C temperature range of a newly developed 12%Cr steel has been investigated for long-term exposures (224 days = 5,376 h). The laboratory and industrial heats were tested in comparison with other ferritic 9-13% chromium steels. Corrosion rates were determined by direct measurements of mass losses obtained after a reducing descaling process. Weight loss and metallographic results confirm the good corrosion resistance in steam of the new steel and allow classing the tested steels in 2 families: one classical with average oxidation behaviour, “T91-type” and another one with low mass losses, varying very slightly with the temperature and the exposure time increasing. To have a better understanding of the observed phenomena, the possible influences of the main alloying elements (Cr, Si, Mn, Mo, W) of steels mentioned by different authors were reviewed and compared to the results obtained for the ten 9-13%Cr studied steels. It appears that the alloying elements cannot be considered separately: as a matter of fact they have not only a specific influence but also a joint influence on the steam corrosion behaviour of the 9-13%Cr ferritic steels.     

含铬低合金钢在海水中的腐蚀研究

研究了含铬低合金钢在海水中的腐蚀行为 ,分析了其腐蚀率随时间的变化及铬元素对钢海水腐蚀行为的影响 .对铬钢的耐蚀性逆转和铬元素对钢海水腐蚀的影响提出了新的看法 .含铬低合金钢在海水中短期浸泡的耐蚀性比碳钢好 ,长期浸泡的耐蚀性比碳钢差 .碳钢的腐蚀率随时间逐渐下降 ,而含铬低合金钢的腐蚀率随时间逐渐上升 .铬元素使钢在海水中的初始腐蚀率降低 ,但它同时改变了钢的腐蚀率随时间下降的性质 ,使钢的腐蚀率逐渐上升 ,从而导致含铬低合金钢在海水中长期暴露的耐蚀性与碳钢发生逆转 .