Corrosion behavior and corrosion products of a low-alloy weathering steel in Qingdao and Wanning

A newly developed low-alloy weathering steel has been exposed in two coastal sites （Qingdao in the north, Wanning in the south） in China for one year. The samples in Wanning corroded far more seriously than those in Qingdao. The rust layer formed on the steel was analyzed by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, N2 adsorption approach, polarization curves, and electrochemical impedance spectroscopy （EIS）. The rust formed in Qingdao contains more X-ray amorphous compounds and is more compact than that formed in Wanning. Cr and Cu are enriched in the rust layer near the steel matrix, and the phenomenon is more obvious in Qingdao than in Wanning. The rust layer formed in Qingdao suppresses the anodic and cathodic reaction more remarkably than that formed in Wanning does. The rust layer formed in Qingdao possesses a higher ability to block the permeation of chloride ions than that formed in Wanning does.

Some Advances in the Application of Weathering and Cold-Formed Steel in Transmission Tower

Application of weathering and cold-formed steel in transmission lines can reduce steel consumption and environmental pollution. Some advances in the studies on the weathering and cold-formed steel in transmission tower are introduced. Firstly, corrosion-resistant tests of weathering steel samples under different simulating technical atmospheres were carried out separately for 240 hours. It shows that the corrosion degree of joint samples is higher than that of single chip samples, and the corrosion-resistant performance of weathering steel is superior to common carbon steel. The corrosion-resistance of weathering steel meets with the requirement of transmission tower. Secondly, experiments and finite element analysis for cold-formed angles and a 220kV prototype tower were completed, and the stability coeffi-cient fitting curves as well as the modification formulas of slenderness ratio for cold-formed members were determined. According to the structural characteristics of transmission towers, four sections of cold-formed angles with different sections and slenderness ratios were selected in this study. The finite element model well predicted the buckling behav-iour of the cold-formed members. Ultimate loads calculating by the fitting curve were well agreed to the experimental values, especially for the members with small slenderness ratios. Weight of the cold-formed steel tower can be reduced by more than 5 percent after considering the strength enhancement. Cost of the weathering and cold-formed steel transmission tower is nearly equivalent to that of hot-rolled steel tower with hot galvanizing.

CORROSION BEHAVIORS OF THE EXPOSED SIDE AND UNDERSIDE OF LOW ALLOY WEATHERING STEEL IN QINGDAO AND WANNING FOR 18 MONTHS

For 18 months, a newly developed low alloy weathering steel has been exposed in two coastal sites （Qingdao in the north China, Wanning in the south China）. The different corrosion behaviors of the exposed side and the underside of the samples were characterized by X-ray diffraetion （XRD）, polarization curve, electrochemical impedance spectroscopy （EIS）, scanning electron microscopy （SEM）, and N2 adsorption approach. It was found that the samples exhibited higher corrosion rate in Wanning than that in Qingdao. The underside of the samples corrodes more seriously than the exposed side in Qingdao, whereas the result in Wanning is just the reverse. The protection performance of rust layers mainly depends on its compactness and the enrichment of Cu and Cr is a secondary causation. The different compactness of rust layers in the exposed side and the underside originates from different corrosion conditions of the two sides.

Industrial trial of strip-casting weathering steel

Baostrip has chosen a steel-grade weathering steel for industrial trial. By carefully designing the composition and manufacturing process,qualified weathering-steel products have been successfully produced on the Ningbosteel-Baosteel strip casting industrialization demo project( NBS) production line. The industrialized practice of Baostrip shows the following: The surface microstructure of weathering-steel products is polygonal ferrite +pearlite,and that of the center is acicular ferrite. After single-stand on-line hot rolling at a 26% low pressure rate,the thickness tolerance ratio controlled within ± 25 μm reaches 99. 6%. The surface convexity and the wedge can be controlled to | C40 |< 50 μm and | W40 |< 30 μm,respectively. The mechanical properties of the strip are superior,exhibiting a yield strength range of( 430 ± 50) MPa,a tensile strength range of( 550 ± 50) MPa,and an elongation range of( 27 ± 5)%. The corrosion resistance is equivalent to that of current commercial atmospheric corrosion-resistant steels,with a relative corrosion rate of 43%. When used,the weathering steel produced by the strip-casting process meets the strict quality and usage requirements of container steel sheets.

Characteristics of Corrosion Product Layer Formed on Weathering Steel Exposed to the Tropical Climate of Vietnam

The weathering steel (Corten B) was exposed to out-door atmosphere of Hanoi (urban site) and Donghoi (marine site). The results showed the protective ability of corrosion product layer formed on weathering steel in the initial stage. The SEM-EDX analysis detected the presence of chromium and copper in the inner layers of corrosion product formed on weathering steel. These elements improved corrosion resistance of corrosion product layers. In addition, the dense α-FeOOH phase were appeared early in corrosion product which is detected by X-ray diffraction and Micro Raman investigations. The results of polarization and EIS measurements also demonstrated the protectiveness of the corrosion product of weathering steel.

Stress-assisted corrosion mechanism of 3Ni steel by using gradient boosting decision tree machining learning method

Traditional 3Ni weathering steel cannot completely meet the requirements for offshore engineering development,resulting in the design of novel 3Ni steel with the addition of microalloy elements such as Mn or Nb for strength enhancement becoming a trend.The stress-assisted corrosion behavior of a novel designed high-strength 3Ni steel was investigated in the current study using the corrosion big data method.The information on the corrosion process was recorded using the galvanic corrosion current monitoring method.The gradi-ent boosting decision tree(GBDT)machine learning method was used to mine the corrosion mechanism,and the importance of the struc-ture factor was investigated.Field exposure tests were conducted to verify the calculated results using the GBDT method.Results indic-ated that the GBDT method can be effectively used to study the influence of structural factors on the corrosion process of 3Ni steel.Dif-ferent mechanisms for the addition of Mn and Cu to the stress-assisted corrosion of 3Ni steel suggested that Mn and Cu have no obvious effect on the corrosion rate of non-stressed 3Ni steel during the early stage of corrosion.When the corrosion reached a stable state,the in-crease in Mn element content increased the corrosion rate of 3Ni steel,while Cu reduced this rate.In the presence of stress,the increase in Mn element content and Cu addition can inhibit the corrosion process.The corrosion law of outdoor-exposed 3Ni steel is consistent with the law based on corrosion big data technology,verifying the reliability of the big data evaluation method and data prediction model selection.

Atmospheric corrosion of carbon steel in acid rain by accelerated weathering test

In this work, the accelerated weathering test of immersion-wet-dry combined cycles was carried ont. The artificial acid rain of NaHSO3-(NH4)2SO4-H2SO4 solution system was selected as immersion solution. Acidity of artificial acid rain affected corrossion weight loss of carbon steel, and pH 4.1 was found to be a critical point. Anodic reaction resistance of the samples during accelerated weathering test increased with exposed time by electrochemical measurement.

Electrochemical Performance Study of Rust Layer on Cu-P-RE Weathering Steel

Corrosion rates of 10PCuRE steels with different rate earth contents and plain carbon steel were studied by dry-wet cycle immersion test. The corrosion resistance of rust layer on rare earths weathering steel and carbon steel was studied through the electrochemical means of polarization test and electrochemical impedance spectra. The difference of corrosion resistance of testing steels was analyzed through electrochemical means. The 10PCuRE steels whose rare earths content is smaller than 0.016% have good performance of corrosion resistance because corrosion potential of the steel is positive and resistance of rust layer is large. The results showed that rare earths of proper content could diminish corrosion tendency and promote the formation of the steady and compact rust layer.

Anticorrosive Properties of Hot-Dip Galvanized Weathering Steel in Atmospheric Exposure

Hot-dip galvanized steel is one of the most used materials in equipment and metallic structures of the Brazilian electric sector. Although carbon steel is the main substrate in the galvanizing hot-dip process, recently, weathering steel has been used as an alternative material to be galvanized. In the transmission line segment of the Brazilian electric sector, for instance, compact towers made of galvanized weathering steel have been installed to conduct energy through urban sites. It is well known that weathering steel, depending on wet and dry cycles and on the pollutants present in the atmosphere, develops a protective patina made of its corrosion products. The patina is dense and strongly adhered to the substrate, blocking the active surface and, thus, reducing the corrosion rate of the base metal. However, when the weathering steel is galvanized, the substrate surface has a layer of zinc and zinc-iron intermetallic alloys. When the sacrificial layer is consumed by atmospheric corrosion, critical questions remain to be answered regarding the underlying substrate. Will the patina of weathering steel be formed? In what condition? Does the hot-dip galvanizing process modify the weathering steel microstructure? The present work carried out an experimental research to shed light on the anticorrosive behavior of hot-dip galvanized weathering steel, after the zinc layer is corroded. This was done by a controlled pickling process, where the zinc layer was removed simulating its consumption during real corrosion processes. The results, obtained through electrochemical techniques and different accelerated corrosion tests, showed that galvanizing weathering steel is a promising technology to enhance the lifetime of structures used in the Brazilian electric sector.

SPA-H耐候钢表面氧化铁皮缺陷原因分析及措施

采用LEICA DIM5000M光学显微镜、ZEISS SUPRA 55场发射扫描电镜和OXFORD能谱仪,检测SPA-H耐候钢表面氧化铁皮缺陷并分析了产生原因,采取降低加热段和均热段加热温度、RDT温度,缩短板坯在炉时间,提高上线轧辊辊面质量,合理控制炉后除鳞和机架间除鳞水压力和喷嘴安装角度等措施后,SPA-H耐候钢表面氧化铁皮缺陷率由0.83%降至0.07%,约降低91.6%。

Design and evaluation of UHPP steel bridge deck pavement for high-temperature and rainy regions

To enhance the serviceability of steel bridge deck pavement(SBDP)in high-temperature and rainy regions,a concept of rigid bottom and flexible top was summarized using engineering practices,which led to the proposal of a three-layer ultra-high-performance pavement(UHPP).The high-temperature rutting resistance and wet-weather skid resistance of UHPP were evaluated through composite structure tests.The internal temperature distribution within the pavement under typical high-temperature conditions was analyzed using a temperature field model.Additionally,a temperature-stress coupling model was employed to investigate the key load positions and stress response characteristics of the UHPP.The results indicate that compared with the traditional guss asphalt+stone mastic asphalt structure,the dynamic stability of the UHPP composite structure can be improved by up to 20.4%.Even under cyclic loading,UHPP still exhibits superior surface skid resistance compared to two traditional SBDPs.The thickness composition of UHPP significantly impacts its rutting resistance and skid resistance.UHPP exhibits relatively low tensile stress but higher shear stress levels,with the highest shear stress occurring between the UHPP and the steel plate.This suggests that the potential risk of damage for UHPP primarily lies within the interlayer of the pavement.Based on engineering examples,introducing interlayer gravel and optimizing the amount of bonding layer are advised to ensure that UHPP possesses sufficient interlayer shear resistance.

连铸连轧过程中SPA-H钢板表面的氧化锈蚀

利用光学显微镜、扫描电镜、能谱和XRD衍射物相分析等手段,研究了SPA-H钢经连铸连轧后表面黄色锈斑的形成原因。结果表明,黄色锈斑的外层主要由Fe2O3、里层由FeO组成,在钢板表面呈条带状分布;而无黄色锈斑的钢板表面主要是由FeO组成。黄色锈斑是由于在轧制过程中,钢表面的高温氧化产物(FeO)破裂,在随后的冷却过程中破裂处特别是裂纹的尖端形成大量的Fe2O3所致,高温氧化产物FeO的应变速率和该氧化膜的横向生长比较高,高温氧化膜开裂后,裂纹不能自愈,较低温度时合金表面发生了线性氧化。

合金元素对SPA-H耐候钢显微组织和低温冲击韧性的影响

通过L9(34)正交实验设计,在实验室轧制了9种铜、硅、镍含量不同的SPA-H耐候钢,研究了合金元素对试验钢显微组织、夹杂物和低温冲击韧性的影响以及对低温冲击韧性的影响机理。结果表明:试验钢中的夹杂物均为Al2O3脆性夹杂物;合金元素对试验钢晶粒度和珠光体含量的影响不大,但对低温冲击韧性有明显影响,三种合金元素对低温冲击韧性的影响从大到小的顺序为硅、镍、铜;试验钢冲击韧性的变化是显微组织和夹杂物综合作用的结果。

川威SPA-H耐候用热轧带钢研制开发

本文介绍了耐候钢(SPA-H)在我公司的成分设计及轧制工艺特点,并根据川威集团的实际制定了相应的冶炼以及轧制工艺方案;同时根据6万多吨的生产实践表明,该工艺措施能很好的满足该钢种的需要。

SPA-H耐候钢边部裂纹缺陷的原因分析及改进措施

针对SPA—H耐候钢边部裂纹缺陷的宏观特征和微观特征进行了分析。结果表明，带钢边部裂纹缺陷表面主要是由氧化铁皮构成，截面带有一定的延伸裂纹，且裂纹附近有一定的氧化质点。通过排查轧制温度、加热制度和板坯质量等因素，最终确定SPA-H耐候钢边部裂纹缺陷是由板坯裂纹遗传所致。通过采取板坯停止热送、定期标定结晶器锥度、定期检查板坯断面情况以及提高出钢温度等措施后，有效控制了SPA—H耐候钢边部裂纹缺陷。

耐候钢SPA-H和09CuPTiRE大气腐蚀性能试验

对武钢生产的SPA-H和09CuPTiRE耐候钢在青岛、琼海和江津3个大气暴露试验点,暴露5年的腐蚀数据进行了分析。结果表明,SPA-H和09CuPTiRE钢的耐蚀性在各试验站均优于Q345钢,是一种优良的耐大气腐蚀用钢。大气暴露5年带锈样的极化曲线测试结果表明,耐候钢的锈层致密,防护性能就好。

轧制工艺对集装箱用SPA-H耐候钢耐蚀性能的影响

采用CSP连铸连轧工艺与传统热轧工艺生产的SPA-H耐候钢,在3.5%NaCl(质量分数)溶液模拟的海洋大气环境中进行周期浸润腐蚀试验,分别采用扫描电子显微镜和电化学交流阻抗谱法(EIS)对比研究了两种工艺轧制钢试样锈层的形貌和耐腐蚀性能。结果表明:采用连铸连轧工艺生产的SPA-H耐候钢的显微组织要比传统热轧工艺生产的耐候钢的更为细小均匀;有Cl-存在的环境下,连铸连轧工艺生产的SPA-H耐候钢的耐蚀性能优于传统工艺生产的。

耐候钢SPA-H的耐腐蚀性能研究

采用加速腐蚀试验方法研究了珠钢生产的耐候钢SPA-H的耐腐蚀性能。结果表明:在72h的加速腐蚀条件下,珠钢生产的耐候钢SPA-H的耐腐蚀性能优于国内A厂和B厂生产的同类钢种;高钙、低硫、高钛、少量珠光体组织,有利于提高钢的耐腐蚀性能。

Surface grain refinement mechanism of SMA490BW steel cross joints by ultrasonic impact treatment

Ultrasonic impact treatment (UIT) is a postweld technique for improving the fatigue strength of welded joints. This technique makes use of ultrasonic vibration to impact and plastically deform a weld toe and can achieve surface grain refinement of the weld toe, which is considered as the main reason for the improvement of fatigue strength. In this paper, the microstructure of the surface of a treated weld toe was observed by metallographic microscopy and transmission electron microscopy (TEM). The results show that UIT could produce severe plastic deformation on the surface layer of the weld toe and the maximum depth of plastic deformation extended to approximately 260 μm beneath the treated surface. Repeated processing could exacerbate the plastic deformation on the surface layer, resulting in finer grains. We can conclude that the surface grain refinement mechanism of SMA490BW welded joints is related to the high density of dislocation tangles and dislocation walls. © 2017, University of Science and Technology Beijing and Springer-Verlag Berlin Heidelberg.

高强度耐候钢SPA-H的试制

南钢采用100t电弧炉-钢包炉-连铸-轧制工艺路线试制了成分（％）为：C≤0．12，Mn0．20～0．50。Si0.25～0.75，P0．07～0．15，s≤0．04，Cu0．25～0．60，Cr0．30～1．25，Ni≤0．65低合金高强度耐候钢SPA-H钢带。检验和使用结果表明，该钢组织为铁素体＋珠光体，有较高洁净度，钢的屈服强度345～435MPa，抗拉强度480～570MPa，延伸率23％～43％，并具有良好的焊接性能。