Eliminating corrosive nonmetallic inclusions from pipe steel

Measures to optimize the production of corrosion-resistant steel have been introduced at OAO Severskii Trubnyi Zavod. They ensure that the steel’s content of corrosive nonmetallic inclusions of the first and second type is no more than 2 mm^?2. The measures were developed on the basis of research on the morphology and composition of nonmetallic inclusions and their formation and also current concepts regarding the formation and removal of corrosive nonmetallic inclusions.     

Influence of Trace Alloying Elements on Corrosive Resistance of Cast Stainless Steel

18-8type austenitic stainless steel is a kind ofanti-corrosion material applied extensively.In mostcases,it must be solution-heattreated to gain goodmechanical properties and corrosive resistance.Butfor some castings with complex shape,such as thepropelle…     

Tensile and compressive stress in the metal around a corrosive nonmetallic inclusion,in the presence of an aqueous medium

The formation of a region where corrosive inclusions interact with metal in an aqueous medium is investigated. The inclusion expands as a result of hydration, and corresponding tensile and compressive zones are formed. On the basis of the results, the mechanical-stress distribution around hydrating inclusions is simulated.     

Correlation Between Nonmetallic Inclusions and Localized Corrosion of a Low-Nickel Stainless Steel with Cerium Treatment

The localized corrosion induced by different kinds of inclusions in low-nickel stainless steel is studied through immersion tests and first-principles calculations. The galvanic corrosion between the steel matrix and different kinds of inclusions occurs in the corrosive environment due to the difference in the electron work function of the steel matrix and inclusions. The electron work function of MnS, CeS, and Ce-O-S is smaller than that of the steel matrix, thus, these inclusions first dissolve as the anode. However, the electron work function of cerium-containing oxides is bigger than that of the steel matrix, and the steel matrix dissolves prior to cerium-containing oxides. The order of the volume expansion rate of pits induced by inclusions is CeS > Si-Mn(-Al)-O > MnS > Ce-C-O-S > Ce-Si-Mn(-Al)-O > Ce-O-S. For cerium-containing inclusions, the electron work function of inclusions increases with the increase of the O/Ce ratio and the S/Ce ratio of inclusions. The order of the electron work function of cerium-containing inclusions is cerium oxides > cerium sulfides > cerium oxysulfide.     

Effect of the conditions of REM microalloying of steel on the corrosion activity of nonmetallic inclusions

Experimental heats of low-alloy steel are performed under various conditions of rare-earth metal microalloying and aluminum and calcium deoxidation. Electron-probe microanalysis of nonmetallic inclusions and a metallographic investigation of a metal are used to show that, when interacting with water, nonmetallic cerium oxide inclusions do not form hydrates and, correspondingly, are not aggressive. When aluminum, calcium, and cerium additions are sequentially introduced into a melt, a continuous cerium oxide shell forms on calcium aluminates, protects corrosive nonmetallic inclusions against interaction with water, and weakens local metal corrosion.     

高强度海工钢中腐蚀活性夹杂物与耐海水腐蚀性能研究

利用金相显微镜(OM)和扫描电子显微镜(SEM)观察和分析不同厚度(12和35.5 mm)的EH36钢板中腐蚀活性夹杂物的形貌和尺寸分布;使用X射线能谱仪(EDS)分析腐蚀活性夹杂物的成分;采用电化学腐蚀和室内模拟海水加速腐蚀实验分析EH36钢板的耐腐蚀性能.结果表明:活性夹杂物主要成分为Al、Mg复合氧化物,组成主要...     

Cyclic Tests of Stress-corrosion Cracks in Steel Gas Pipelines with No Corrosive Fluid

Stress-corrosion defects in the output pipeline of a compressor station are subjected to metallographic analysis and mechanical tests. The pipeline consists of pipe imported in the 1980s. Diagnostic data obtained in nondestructive monitoring of such pipelines are analyzed, and the effectiveness of various diagnostic methods in detecting stress-corrosion defects in large-diameter pipe is assessed. The grade of steel in the pipeline is identified. The cracks are identified by type and morphology, and their development is determined. Nonmetallic sulfide inclusions have no influence on pipeline failure in the stress-corrosion conditions considered. The sulfur content in the corrosion products is no more than the sulfur content in the metallic sample. In some samples, the sulfur content may be decreased except for local sections with nonmetallic sulfide inclusions. Electron-microscope images show that such nonmetallic inclusions do not promote failure. The results of cyclic tests of cracked samples cut from the pipeline are presented. The test conditions are selected in accordance with recent operating conditions of the compressor station. According to the results, pipe with defects at the initial stage of development exhibits considerable durability in the tests. In fact, the cracked samples withstand (1.6–7.5) × 10⁶ cycles under transverse cyclic flexure in a single plane, in the absence of corrosive fluid. In practice, the number of such cycles is no more than 120–200 per year, in normal pipeline operation. Hence, a pipeline with stress-corrosion defects in their initial stage of development will last a long time if its metal wall is protected from the action of corrosive fluid.     

碳钢中夹杂物诱发点蚀的规律和特性研究

海洋环境对于金属的腐蚀具有明显的加速作用,尤其在高铁海底隧道环境中,金属比正常的服役时间变短,这种腐蚀情况下会影响高铁的安全和准点运行。基于以上背景,通过夹杂物自动扫描、钢的加速腐蚀及电化学测试对钢中的夹杂物诱发腐蚀行为进行系统分析,重点分析了高铁轨旁信号设备连接金属件（Q235）中夹杂物在盐雾环境下的腐蚀行为。结果表明：钢中主要夹杂物为氧化物、硫化物或者其复合夹杂,而这两类夹杂物对于诱发钢基体点蚀的原因不同。其中数量最多、尺寸小于5 μm类型的夹杂物为硫化物夹杂和氧硫复合类型夹杂物;数量少、尺寸大于5 μm的夹杂物为氧化物夹杂。在服役过程中,钢中硫化物夹杂易溶解脱落形成点蚀坑,而氧化物夹杂周围基体会先溶解引起夹杂物脱落形成点蚀坑,复合类夹杂物也是诱发钢发生腐蚀的因素,不同复合类型的夹杂物腐蚀方式不同,硫化物夹杂和氧硫复合夹杂对碳钢影响较大。电化学测试表明自腐蚀电位约为为−0.1 V,Q235钢本身抗腐蚀能力不强。夹杂物在腐蚀过程中参与了腐蚀,引起阳极极化曲线的波动,加快了Q235钢的腐蚀情况。研究结果对于认识和改善钢的耐腐蚀性能有指导意义。     

Effects of deoxidizing degree on the pitting corrosion behavior of carbon and manganese steels

Nine steels with different deoxidizing degrees and two comparative steels were selected. Their pitting initiation susceptibility was compared by means of potentiodynamic polarization tests in 3wt% NaCl solution. The pit propagation rate was evaluated in artificial sea water and 3wt% sea salt solution by simulating occluded corrosion cell (SOCC) test and hanging plate test, respectively. The composition of inclusions and corrosive feature were studied by scanning electron microscopy (SEM), electron probe micro-analysis (EPMA), and optical microscopy (OM). The results indicate that sulfide inclusions in steel are the sites for pit nucleation. The sulphide inclusions vary in shape from short spindle-like to long strip-like with increasing deoxidizing degree. Under the same conditions, the lower the deoxidizing degree gets, the lower the pitting initiation susceptibility becomes, and the stronger the resistance to pit propagation exhibits. For steels with different deoxidizing degrees, their pitting initiation susceptibility is mainly influenced by thermodynamic stability, while the pit propagation rate is primarily subject to the characteristics ofinclnsions in steel.     

不同脱氧程度锰钢耐点蚀性能比较

选择四种不同脱氧程度的锰钢,在pH10的3%(质量分数)NaCl溶液中进行动电位极化实验,比较钢的点蚀诱发敏感性;在3%(质量分数)海盐水中进行室内间浸挂片实验,评价钢的点蚀扩展速度;利用扫描电镜(SEM)和电子探针(EPMA)分析了钢中夹杂物组成和腐蚀形貌.结果表明,随着脱氧程度的加强,钢中的硫化物夹杂由短棒状变为长条状.脱氧程度越差,钢基体热力学稳定性越强,钢的点蚀诱发敏感性也越弱.室内间浸挂片实验结果表明,脱氧程度较强的锰钢表现出更强的点蚀扩展能力.     

The effect of mean stress and environment on corrosion fatigue behavior of 7075-T6 aluminum

Axial fatigue tests were performed on a 7075-T6 aluminum alloy in tension-compression and under superimposed positive mean stresses in dry air and in aqueous 0.5N NaCl solution. Both corrosive environments and positive mean stresses resulted in lower fatigue lives but no interaction between these variables was observed. Crack initiation in air occurred at electropolish pits at inclusion/alloy interfaces and propagated primarily in a Stage I (crystallographic) mode. Crack initiation in NaCl solutions occurred at heavily corroded regions surrounding non-metallic inclusions and propagated in a cleavage mode normal to the direction of applied stress. The relative number of cycles to crack initiation is shown to be a function of the magnitude of cyclic stress but not of mean stress. Similarly, the percentage of reduction in fatigue life due to corrosive environments is approximately constant at all mean stress levels. These data indicate that fatigue crack initiation is primarily related to mobile dislocations associated with cyclic deformation. Crack propagation on the other hand appears to be controlled by the maximum applied stress. A model for environment assisted cracking is presented which suggests that hydrogen induced cleavage is responsible for the degradation in fatigue properties of this alloy. Formerly Research Assistant, Materials Division, Rensselaer Polytechnic Institute, Troy, N. Y. 12181.     

Origin mechanism of pitting corrosion induced by cerium inclusions

In this paper, the origin mechanism of pitting corrosion induced by Ce₂O₃, Ce₂O₂S, and CeAlO₃ inclusions in a microalloyed steel was investigated by field emission scanning electron microscopy with energy dispersive spectroscopy and electron backscattered diffraction, conductivity atomic force microscopy, immersion test, and first-principles calculation. The results show that the Ce₂O₃, Ce₂O₂S, and CeAlO₃ inclusions are non-conductive, which are impossible to form corrosion couples with the steel matrix. There are no obvious lattice distortion zones in the steel matrix around the Ce₂O₃, Ce₂O₂S, and CeAlO₃ inclusions, so it is difficult to form micro-galvanic corrosion near the Ce inclusion. The order of work functions of the Ce inclusions and the steel matrix from small to large is Ce₂O₂S < Ce₂O₃<CeAlO₃<steel matrix, which is consistent with their dissolution sequence in the immersion test in 3.5 wt% NaCl solution. Consequently, it is effective and reliable to use work function to predict or judge the dissolution behaviors of the Ce inclusions or steel matrix in corrosive solution. The Ce₂O₃, Ce₂O₂S, and CeAlO₃ inclusions have the tendency of self-dissolution and dissolve preferentially to the steel matrix in the solution by the salt effect, which lead to pitting corrosion of Ce-containing microalloyed steel.     

金属铱金相试样的电解腐蚀

探讨了在适当的腐蚀介质中,对粉末冶金铱材样品进行交流电解腐蚀时,腐蚀因素（电流、电压、通电时间等）对腐蚀效果的影响。通过观察比较,找出了最佳电解腐蚀工艺。实验表明,在腐蚀介质中进行交流电解是铱材金相制作的快捷之路。     

提高自蔓延陶瓷内衬钢管耐蚀性研究的进展

广泛应用于石油，化工，能源等领域的钢管，除了要有高强度外，还要有良好的耐蚀性。自蔓延高温合成技术是制备耐蚀钢管的新技术，具有工艺简单，成本低和产品耐蚀性能好等特点。介绍了自蔓延高温合成陶瓷内衬钢管的原理和提高陶瓷内衬钢管耐蚀性的措施，展望了耐蚀陶瓷内衬钢管在工业生产上的应用前景。     

对HIC试验中两种不同腐蚀介质酸碱度的探讨

HIC是腐蚀试验中常用的检测方法,用来测评材料在含硫化氢环境中对氢离子敏感性大小.其包含两种不同的腐蚀介质,不同的腐蚀介质中酸碱度是不一样的,腐蚀介质的酸碱度对试验结果有较大的影响,为此,运用电离平衡理论,计算并分析两种不同腐蚀介质电离平衡前后的氢离子浓度变化,得出动态反应平衡时氢离子浓度的关系式,从而获得介质中精确的氢离子浓度,并对腐蚀介质中相关离子进行了探讨,为进一步探究相关环境中的腐蚀机理提供了依据.     

中碳钙硫易切削钢夹杂物形态控制

在实验室进行了1kg坩埚实验,研究了中碳高硫结构钢钙处理前后夹杂物的形态、尺寸及组成.结果表明:钢钙处理后获得了可以改善钢切削性的纺锤形夹杂物,夹杂物的平均纺锤形率为68.11%,并且随钢中[Ca]/[S]增加夹杂物纺锤形化趋势增加;钙处理后小于2.5μm的夹杂物占夹杂物总量的76.05%,夹杂物细小、弥散分布于钢基体中;夹杂物类型以钙铝酸盐芯硫化物外壳的复合夹杂物、(Mn,Ca)S形式的硫化物为主,有少量的铝酸钙与CaS的复合夹杂物;含钙硫的45钢铸态钢锭比普通45钢铸态钢锭切削性能有所改善.     

Research status of corrosion environment failure and safety assessment of pipeline welded joint

Pipeline transportation is an economical,safe,and efficient transportation method for transporting oil,natural gas,mineral slurry,and other fluids.Welding is the most critical construction process in pipeline engineering and is crucial in the safe operation and service of an entire pipeline system.Theoretically,the girth welded joint is the weakest link in a pipeline system.The unevenness of the structure and performance of the joint caused by welding frequently results in the failure of the welded joint before the failure of the base material of the pipe body,causing the pipeline to leak or even break.For steel pipes used in an acidic corrosive medium environment,the integration of the corrosive medium and mechanical load will accelerate the failure of the welded joint.This article reviews the failure modes of pipeline welded joints in acidic corrosive media,including stress corrosion cracking,hydrogen-induced cracking,and corrosion fracture,and corrosion fatigue considering the diffusion and accumulation of H+at the crack tip.It also reviews service pipelines in acidic corrosive media.The general processing technology of pipe joint engineering critical assessment(ECA)is investigated to provide a reference for the future development of technology in this field.     

总排污水处理后回用于循环冷却水系统的初探

通过现场测试和挂片试验对包钢总排水水质类型及其用于高炉循环冷却系统的现状进行了调查研究.确定了在现有条件下4#高炉循环冷却水系统的水质类型为腐蚀为主,兼有结垢;总排回水为微量结垢和腐蚀型水质,随着浓缩倍数的增加逐步转化为严重结垢型水质.     

72A钢非金属夹杂物行为

采用多种方法对酒钢72A钢中非金属夹杂物进行了调查,对夹杂物的类型、来源、数量及尺寸进行了讨论.实验证明,铸坯中夹杂物有60%外来夹杂物,40%为脱氧产物;引起线材拉拔脆断的主要原因是外来大颗粒脆性夹杂,而控制好脱氧产物和外来夹杂物的组成、形貌、大小及分布,是解决线材拉拔脆断的关键.     

大气环境腐蚀性因素的相关性

通过相关性数据处理和模糊聚类分析,发现影响大气环境腐蚀性的21种环境因素在相关系数大于0.54的情况下,可明显地聚为5类.在此基础上,进一步通过对逐个因素的分类能力的特征评价,选取大气环境腐蚀性的主要因素(RH>80%时数,SO₂沉积速度,水溶性尘降,Cl-沉积速度,NO₂浓度),进而在特征空间中进行镀锌层样本的大气环境腐蚀性预测和考评,为今后实现我国大气环境腐蚀性等级评判提供依据.