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.

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.

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.

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.

卷取温度对铁道车辆用高耐候钢显微组织和力学性能影响

通过中试热轧试验、拉伸试验机、维氏硬度计、光学显微镜(OM)、扫描电镜(SEM)、能谱仪(EDS)研究了卷取温度对高耐候钢显微组织和力学性能的影响。研究结果表明:卷取温度显著影响高耐候钢的显微组织和力学性能。卷取温度由540℃提高到700℃,屈服强度下降189 MPa,抗拉强度下降228 MPa,延伸率提高9.5%,HV_(0.5)降低57。卷取温度为540℃和620℃时,显微组织均为准多边形铁素体和粒状贝氏体,粒状贝氏体体积分数分别为42.7%和26%。随着粒状贝氏体体积分数增加,高耐候钢的强度显著提高,延伸率大幅下降。在卷取温度为700℃时,显微组织为准多边形铁素体和沿晶界弥散分布的颗粒状碳化物,试验钢板具有优异的强塑性匹配。

坡口角度对K形对接接头组织与疲劳性能的影响

为解决Q450NQR1耐候钢K形坡口对接接头的坡口角度选择问题,以45°、50°、60°K形坡口对接接头为研究对象,对三种坡口角度的对接接头进行了金相、疲劳试验,分析阐述了坡口角度对接头金相组织分布与疲劳性能的影响;此外,通过对疲劳断口的扫描观察,分析了其断裂特征与机理。试验结果表明:各坡口角度对接接头各区域的组织成分相近,焊缝柱状晶粒宽度及粗晶区晶粒尺寸与坡口角度成正比;45°、50°、60°K形坡口对接接头的疲劳极限依次为151 MPa、147.5 MPa、135 MPa,疲劳极限与坡口角度成反比;疲劳试件断口启裂区和扩展区具有典型的疲劳断裂特征,扩展区存在较为明显的疲劳弧线,终断区可观察到典型的韧窝组织;坡口角度越大,扩展区疲劳弧线与终断区韧窝组织越稀疏。

Effect of La on the Corrosion Behavior and Mechanism of 3Ni Weathering Steel in a Simulated Marine Atmospheric Environment

The corrosion behavior and mechanism of 3Ni weathering steel in a simulated oceanic atmospheric environment are investigated in order to comprehend the impacts of La,as determined through electrochemical analysis and rust layer characterization.The results of this study demonstrate that the addition of La enhances the corrosion resistance of 3Ni weathering steel in the marine atmospheric environment,thereby reducing the corrosion rate and improving the protection of the rust layer.The influence of La on corrosion resistance can be attributed to two primary factors.Firstly,La functions as a grain refiner,minimizing the potential difference of the micro-regions on the substrate surface,thereby significantly reducing the corrosion of bare steel in the marine environment.Secondly,La inhibits the process of Fe_(3)O_(4) oxidation back toγ-FeOOH during corrosion at the local site,thus decreasing the formation ofγ-FeOOH and enhancing the charge transfer resistance.This research work may serve as a reference for expanding the application of rare earth elements in the field of weathering steel.

Q450NQR1耐候钢激光填丝焊与MAG焊接头组织与性能对比

通过对Q450NQR1高强度耐候钢进行激光填丝焊和MAG焊对接工艺试验,研究了两种焊接方法下焊接接头微观组织及力学性能,并对拉伸试件断口进行扫描分析。研究表明,激光填丝焊和MAG焊接头焊缝区微观组织以粒状贝氏体为基体,伴有先共析铁素体及少量的珠光体。两种焊接方法的接头显微硬度从焊缝到母材整体呈下降趋势,激光填丝焊接头热影响区宽度较窄,熔合线是硬度最高位置,其硬化区平均硬度整体高于MAG焊接头同区域。两种焊接方法下试件弯曲性能良好,拉伸试件断裂位置均在母材,激光填丝焊接头具有更高的强度承载。拉伸断口扫描发现,断口均呈现典型的微孔聚集型韧性断裂特征。

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.

Pitting corrosion behavior of Cu-P-RE weathering steels

The weathering steels are prone to pitting corrosion in an environment containing chloride ions.The pitting behavior of Cu-P-RE weathering steels and its effect on the corrosion resistance of steels were investigated by multifarious analytical techniques,such as field emission-scanning electron microscopy(FE-SEM),electron probe microanalysis(EPMA),scanning Kelvin probe force microscopy(SKPFM),electrochemical workstation and a series of immersion tests.The results show that the original stripshaped MnS inclusions and Al_(2)O_(3)inclusions with sharp angles are modified into the fine spherical rare earth(RE)inclusions with small average size,which are mainly RE oxysulfides after adding appropriate amount of mischmetal(48.9 wt%Ce-42 wt%La-5 wt%Nd-Fe)into the Cu-P weathering steel.In the environment containing Cl^(-),the pitting corrosion in RE weathering steel is induced by the preferential dissolution of RE inclusions in that the RE inclusions have a more negative potential than steel matrix at the initial corrosion stage.With the increase of corrosion time,the driving force of pitting expansion is weakened as a re sult of the continuous dissolution of RE inclusions,which makes the pitting tend to propagate horizontally around the RE inclusions.Once the RE inclusions completely dissolve,the open corrosion pits with shallow depth are formed in steel.The dispersed pitting pits with small size and shallow depth induced by RE inclusions are conducive to the formation of uniform and dense corrosion products layer on the steel surface,which reveals that the addition of RE can improve the corrosion resistance of weathering steels.

Characterization of Compactness of Rust Layers on Weathering Steels by an Adsorption/Dehydration Test of Ethanol

A new method for evaluating the compactness of rust layers on steels has been proposed in the present study. The method includes adsorption and dehydration process of anhydrous ethanol. The protective ability of rust layers can be qualitatively reflected by the adsorption/dehydration rates. The specific surface area and porosity of rust layers can be calculated by a quantitative model. The results from the present method are consistent with electrochemical tests, N2 adsorption and X-ray diffraction analysis. The method characterizes the compactness of rust layers rather than that of corrosion products removed from the metal surfaces, which is generally practiced in classic N2 adsorption method. Furthermore, the method can reflect the compactness of inner rust layers, to which N2 adsorption is unavailable. The method provides a new approach for the study of rust layers.

Abnormal relationship between rust particles size and rust layer compactness of weathering steels

In order to reveal evolution of the rust layer during atmospheric corrosion, commercial weathering steel （WS） 09CuPCrNi and a recently developed bainite WS were subjected to a salt fog test. The protection and compactness of the rust layer were evaluated by electrochemical analysis, absorption-desorption test, etc. The experimental results indicate that more compact rust layer could be derived from the rust particles with larger size. The well-established notion that the rust particle growth can induce the decrement of corrosion resistance of WS. However, the present investigation shows that the notion might not be universally accurate. The unusual result means that the rust particles might grow anisotropically during corrosion.

Influence of N/C ratio on microstructure and properties of new highstrength weathering steels

Influence of the N/C ratio on the microstructure and properties of new-generation high-strength weathering steels was investigated using calculation of phase diagram(CALPHAD)and experiments.The microstructures of weathering steels containing different N/C ratios were predicted by a CALPHAD approach,and only three phases were predicted in these steels within the rolling temperature range of 850-1050℃.The precipitation fraction of VN/V(C,N)in creases with increasing N/C ratio.Microstructures of the four tested steels were all experimentally determined to contain bainite,ferrite,and VN precipitates after air cooling to room temperature.The bainite fraction increases with in creasing N/C ratio,and it is 85%in the steel containing 0.038% N and 0.032% C,The results of the tensile tests and impact tests demonstrated that the yield strength and tensile strength of the steel containing 0.038%N and 0.032%C are greater than 550 and 650 MPa,respectively,and the elongation is greater than 24%,which satisfies the design objectives for mechanical properties.The impact toughness values of the four steels at 0,-20,and-40℃ are all greater than 24 J.With increasing N/C ratio,the bainite fraction and the precipitation fraction of VN/V(C,N)increase,resulting in increasing yield strength and tensile strength.

古金赤水河大桥主桥总体设计

古金赤水河大桥主桥为(83.5+173.5+575+173.5+83.5)m半飘浮体系双塔双索面斜拉桥。主梁采用双边主梁断面钢-混组合梁,由工字钢主梁和混凝土桥面板组成,全宽43.8 m,设置裙板抑制主梁涡振。桥塔为下塔柱内收的A形塔,南、北塔塔高分别为217 m和261 m。由于山区超高桥塔塔墩景观效果欠佳,采用超高塔柱无塔墩方案,桥塔采用嵌岩群桩基础;针对山区桥梁养护不便的情况,索塔锚固采用耐候钢钢锚梁;针对剪力钉在拉拔力作用下承载能力降低问题,采用以开孔板连接件为主的钢-混结合构造实现锚梁牛腿壁板与塔壁连接。斜拉索采用公称直径15.20 mm、标准抗拉强度1860 MPa的钢绞线拉索,全桥共4×23对(184根),空间双索面扇形布置。由于斜拉索锚拉板+外置减振阻尼器景观效果不佳,选用全内置减振阻尼器方案。