薄壁高强度桩管钢的腐蚀性能研究

发布时间：2018-03-23 00:22

  本文选题：薄壁高强度桩管钢　切入点：腐蚀性能　出处：《南京航空航天大学》2015年硕士论文　论文类型：学位论文

【摘要】：随着沿海地区经济开发和滩涂以桥代路工程的迅速发展,高强度桩管钢的研究和应用受到了高度的重视。钢管桩应用过程中损坏失效的最大威胁来自腐蚀,高强度桩管钢的耐蚀性能成为决定高层建筑和桥墩等建筑工程使用寿命的关键,因此低成本耐蚀薄壁高强度桩管钢的研究开发具有重要的理论和应用价值。本文利用光学显微镜(OM)、X射线衍射仪(XRD)、扫描电镜(SEM)及其附带能谱仪(EDS)、拉伸试验、极化曲线测试及电化学阻抗谱测试等多种分析和测试方法,系统研究了Cr、Cu等合金化元素和热处理工艺对低合金高强度桩管钢的组织、性能和在高盐度服役环境下的腐蚀行为的影响规律,为低成本薄壁高强度钢的研究开发和应用发展提供理论指导。结果表明:低碳低合金桩管钢在饱和Na Cl盐水环境下主要发生电化学腐蚀,其中液-气界面区腐蚀最为严重。在普通碳钢基础上添加0.2%Cu(质量分数,下同)和0.2%Cu+0.2%Cr后,其热轧空冷态样品液-气界面区的点蚀坑逐渐细小密集,最大点蚀深度从普通低碳钢的0.44 mm降低到0.2Cu-0.2Cr钢的0.11 mm,腐蚀类型从点蚀向均匀腐蚀转变。与普通低碳钢相比,0.2Cu钢腐蚀速率为0.0388mm/y,降低了71%,0.2Cu-0.2Cr钢腐蚀速率为0.0346 mm/y,降低了74%。对比普通碳钢,加入0.2%Cu、0.2%Cu+0.2%Cr后测试试样的极化阻抗Rp从482.6??cm2分别提高到854.5??cm2、1136??cm2。锈层中Cu、Cr元素的增加抑制了电化学腐蚀反应的阳极过程。Cu、Cr元素富集于锈层与基体的界面处,在基体腐蚀慢的区域锈层中往往伴随着更多的Cu和Cr元素,而腐蚀快的区域则其含量较少。普通低碳钢中添加0.5-2.0%Cr,其控轧控冷态组织由多边形铁素体加少量珠光体转变为贝氏体、铁素体和M-A岛,屈服强度由304MPa提升到503MPa。随着Cr含量的增加,基体电极电位从-0.646V不断升高到-0.544V,但裸钢的极化阻抗值Rp却从1586?·cm2降低到了795.5?·cm2。钢中Cr含量的增加在5个月的半浸泡腐蚀中并未提高其耐腐蚀性,腐蚀速率反而由0.0292mm/y略微增加到0.0304mm/y,其原因在于高的Cr含量导致钢中生成了易腐蚀相贝氏体和M-A岛。在腐蚀产物中发现Cr元素富集于锈层与基体的界面处,随着基体中Cr含量的增高,富集现象越明显,尤其在2.0Cr钢中内锈层Cr含量明显高于基体中的含量,锈层也更加致密。普通低碳钢中添加0.5-2.0%Cr,调质处理后的各试样组织皆为回火索氏体:其中0.5Cr钢中的铁素体充分再结晶转化为多边形铁素体,而1.1Cr和2.0Cr钢中的很多铁素体由于Cr对其回火过程中再结晶的推迟作用使其仍然保持着板条状;屈服强度从0.5Cr钢的391MPa提高到了2.0Cr钢的510MPa。调质态桩管钢试样在3.5%盐溶液中一直处于活化状态,且随着Cr含量增加,试样自腐蚀电位变化不大,皆在-0.57V左右,但腐蚀电流密度icorr从1.657×10-5 A·cm-2降低到了1.391×10-5 A·cm-2,极化阻抗值Rp从1014?·cm2增大到了1611?·cm2。随着Cr含量的增加,钢在液-气界面处腐蚀情况改善明显,与热轧空冷态、控轧控冷态试样相比,其腐蚀程度显著减轻。当Cr含量为2%时,试样耐蚀性最好,年腐蚀速率为0.0234mm/y,比Cr含量为0.5%的试样降低了8.6%。Cr元素在锈层中发现富集现象,在浸泡区主要富集于与基体接触的内锈层区,而在液-气界面区则富集于远离基体的外锈层区。少量合金元素对桩管钢试样腐蚀锈层的物相组成没有明显的影响,锈层均主要由α-Fe OOH、β-Fe OOH、γ-Fe OOH、Fe3O4和Fe2O3等组成。与液-气半浸泡实验相比,液-固腐蚀实验中试样的腐蚀速率普遍极小,皆在0.004 mm/y以下,因此合金元素、热处理方式对钢的腐蚀性影响均不明显,钢的腐蚀速度完全由环境因素,主要是氧含量控制。桩管钢埋在泥土中的部分生成的锈层比浸泡在水溶液中的更加均匀致密。电化学测试表明,桩管钢在饱和水土壤中随时间的推移,极化阻抗Rp不断增大,即表面锈层不断增厚,对基体保护性增强。
[Abstract]:With the rapid development of economic development in coastal areas and beaches to bridge and road engineering, research and application of high strength steel pipe pile is highly emphasized. The biggest threat to the failure damage process of steel pipe pile in the application of high strength pile from corrosion, corrosion resistance of the steel tube decided to become a key service life of high-rise buildings and bridge pier construction therefore, the research and development of low cost and high strength thin-walled steel tube pile corrosion has important theoretical and practical value. In this paper, by using optical microscope (OM), X ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS), tensile test, polarization curves and electrochemical impedance spectroscopy a variety of analysis and testing method, system of Cr, alloying elements and heat treatment process of Cu alloy of high strength low alloy steel pipe pile, performance and corrosion behavior under the environment of service in high salinity influence, To provide theoretical guidance for the development and application of research and development of low cost thin wall and high strength steel. The results showed that the low carbon low alloy Na Cl pile in saturated saline environment mainly electrochemical corrosion of steel tube, the liquid gas interface corrosion is most serious. Add in the ordinary carbon steel on the basis of 0.2%Cu (mass fraction, the same below) and after 0.2%Cu+0.2%Cr, the hot rolling cold pit sample liquid gas interface area gradually dense, maximum pit depth decreases from 0.44 mm to the ordinary low carbon steel 0.2Cu-0.2Cr steel 0.11 mm, change the type of corrosion pitting corrosion from to uniform. Compared with the ordinary low carbon steel, the corrosion rate of 0.2Cu steel is 0.0388mm/y, reduced 71%, the corrosion rate of 0.2Cu-0.2Cr steel is 0.0346 mm/y, reduced 74%. compared with ordinary carbon steel, adding 0.2%Cu, 0.2%Cu+0.2%Cr test Rp samples from the polarization impedance 482.6?? cm2 were increased to 854.5?? cm21136? Cm2.? Cu in the rust layer, Cr elements can inhibit the anodic process of.Cu electrochemical corrosion reaction, Cr elements in the rust layer at the interface of the matrix and the matrix corrosion rust layer in the area of slow often accompanied by more Cu and Cr elements, and the area of the corrosion speed is less content. Addition of 0.5-2.0%Cr low carbon steel, and its control the cold rolling microstructure is composed of polygonal ferrite and pearlite transformation of bainite, ferrite and M-A islands, the yield strength increased from 304MPa to 503MPa. with the increase of Cr content, the matrix electrode potential rising from -0.646V to -0.544V, but the polarization resistance of bare steel anti Rp value from 1586 cm2? Reduced to 795.5? Cr content in cm2. steel increased in semi immersion for 5 months did not improve its corrosion resistance, but the corrosion rate increased slightly by 0.0292mm/y to 0.0304mm/y, the reason is that the high content of Cr in steel is generated in the bainite phase corrosion And the island of M-A. In the corrosion products found in the Cr elements in the rust layer at the interface with the substrate, with the increase of Cr content in the matrix, the enrichment phenomenon is more obvious, especially in 2.0Cr steel inner rust layer Cr content is significantly higher than the content in the matrix, the rust layer became more compact. Adding 0.5-2.0%Cr in low carbon steel after quenching and tempering, their microstructure is tempered sorbite: 0.5Cr steel in ferrite recrystallization fully into polygonal ferrite, and a lot of 1.1Cr and 2.0Cr steel in ferrite due to delayed effect of Cr on recrystallization in the tempering process makes it still keeps the strip; the yield strength of 0.5Cr steel from 391MPa to 2.0Cr steel 510MPa. quenched and tempered steel pipe pile sample in 3.5% salt solution has been in the active state, and with the increase of Cr content, the specimen corrosion potential changed little, all in about -0.57V, but the corrosion current density from icorr 1.657脳10-5 A路cm-2闄嶄綆鍒颁簡1.391脳10-5 A路cm-2,鏋佸寲闃绘姉鍊糝p浠，

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