【作者】 陈闽东；

【导师】 李晓刚；

【作者基本信息】 北京科技大学， 材料科学与工程， 2018， 博士

【摘要】 浪花飞溅区是海洋工程用低合金钢在海洋环境中腐蚀最严重的地方。现有的研究大多关注于低合金钢在飞溅区所产生的腐蚀类型和飞溅区环境影响机制,而对于不同环境的浪花飞溅区和低合金钢在浪花飞溅区腐蚀的行为和演变过程缺乏有效关注。低合金高强钢广泛应用于海洋工程中,我国幅员辽阔,海洋环境南北差异极大,在南北环境下的腐蚀行为有较大差异。同时,研究低合金钢在特定环境下所产生的锈层的耐蚀行为是认清低合金钢腐蚀的控制作用,提高低合金钢耐候性的必要途径。因此,对我国不同海域的浪花飞溅区低合金钢的腐蚀行为进行研究,有着极其重要的意义。本文对海洋工程用E690低合金钢在青岛和三亚浪花飞溅区环境的腐蚀行为、锈层耐蚀行为、合金成分作用、锈层下的阔点蚀发展及离子浓聚作用下应力腐蚀的行为展开了研究。系统阐述了低合金钢在青岛和三亚浪花飞溅区腐蚀的控制因素、腐蚀行为和演变规律,并得到以下结论:(1)E690钢在青岛浪花飞溅区形成不均匀的阳离子选择通过性锈层,抑制阴离子作用随时间增加而降低,腐蚀速率逐渐升高,一年期内幂指数项系数为1.34。在三亚浪花飞溅区形成的锈层有均匀的阳离子选择通过性,抑制阴离子的作用随时间增加而升高,腐蚀速率较为恒定,一年期内幂指数项系数为1.01。(2)干湿交替作用将腐蚀性阴离子克服阳离子选择通过性,从而进入锈层。三亚浪花飞溅区环境低合金钢的锈层中Cl-浓度逐渐升高,青岛浪花飞溅区锈层中Cl-浓度较为稳定,而含S阴离子含量逐渐升高。锈层中的阴离子存在竞争作用,在含SO2环境,含S阴离子主导该过程。(3)低合金钢中的Cr、Ni、Mo和P合金元素在扩散作用控制初期对海水电解质在锈层中的扩散抑制能力较强,Mn、Cu和Ti合金元素在扩散作用控制阶段对海水电解质在锈层中的扩散抑制能力较强。Fe、C和S含量的升高会降低锈层的抑制扩散能力,但合金元素含量总量不宜超过5%。(4)离子浓聚导致低合金钢在青岛和三亚浪花飞溅区都发生严重的阔点蚀行为。三亚环境点蚀状况严重于青岛,但青岛的点蚀越来越严重。三亚环境高Cl-的富集破坏了金属表层锈层,增加了金属表面粗糙度,促进了阳极溶解,进而促进在新的阳极溶解蚀坑内诱发新的点蚀。青岛环境SO2的作用产生的致密锈层使得金属表面有较低粗糙度,但点蚀坑深处硫酸的再生机制促进了点蚀的向深发展。(5)E690钢SCC敏感性受Cl-单一因素影响较小。相对来说,在C1-浓聚的环境中,Cl-浓度为14.5%和饱和时,E690钢SCC敏感性较高。在含工业污染物SO2的离子浓聚的协同作用下,NaHS03浓度在较低情况下,E690钢SCC敏感性最高。更多还原

【Abstract】 Marine splash zone is the place where ocean engineering low-alloy steel corrodes most severly.Research has focused on the corrosion types and environmental impact on the corrosion behavior of low-alloy steel in marine splash zone.Still,there is no effective attention to the typical marine splash zone and the rust layer performance of low-alloy steel in the splash zone.China has a vast territory,and the marine environment is extremely different from north to south.At the same time,rust layer is an important factor in determining the weatherability of low-alloy steel.Therefore,it is of great significance to study the corrosion behavior of low-alloy steels in different marine splash zones in China.In this work,corrosion behavior of E690 low-alloy steel for marine engineering in Qingdao and Sanya marine splash zone,the corrosion behavior of the rust layers,the effect of alloy compositions,the development of broad pitting corrosion under the rust layers and the stress corrosion cracking（SCC）behavior under ion concentration were studied.The control factors,corrosion behavior and evolution of low-alloy steel in the splash zone of Qingdao and Sanya were systematically studied and the following conclusions were obtained:（1）The non-iniform cation selective rust layers were formed in Qingdao marine splash zone.The inhibition effect of the rust layer to anions gradually decreases,and the corrosion rate gradually increases with a power index coefficient of 1.34.Rust layers formed in Sanya have a uniform inhibition to anions which increases with time,and the corrosion rate gradually decreases with a the power index coefficient of 1.01.（2）Dry-wet alternaty drives the anions overcome the cation selective property of the rust layer.The Cl^-concentrated in the rust layer of Sanya.and the concentration gradually increase.Cl^-concentration is constant in Qingdao,while the content of S-containing anions gradually increases.The anions in the rust layer has a competitive mechanism.In the SO₂-containing environment.the S-containing anions dominates the process.（3）The Cr,Ni,Mo and P alloying elements in low-alloy steels achieve good effects on inhibiting the diffusion of seawater electrolytes at the initial stage of diffusion control.The Mn.Cu and Ti alloying elements achieve good effects on inhibiting the diffusion of seawater electrolytes at diffusion control stage.The Fe,C and S contents reduce the ability ofinhibiting diffusion,but the total content of alloying elements should not exceed to 5%.（4）Ion concentration leads to severe pitting corrosion of low-alloy steel in both Qingdao and Sanya marine splash zones.The pitting is more sever in Sanya than Qingdao,but the pitting corrosion in Qingdao is gradually getting worse.The enrichment of Cl^-in Sanya environment destroyed the rust layer of the metal surface,increasing the surface roughness of the metal,promoting the anodic dissolution,and then pittings in anodic dissolution areas are promoted.The dense rust layers are produced in SO₂-containing environment,making the surface of metals have lower roughness.The regeneration mechanism of sulfuric acid promotes the development of pitting corrosion in Qingdao.（5）The SCC susceptibility of E690 low-alloy steel is less affected by Cl^-concentration.The SCC susceptibility of E690 low-alloy steel is higher when the Cl^-concentration is 14.5%or saturated.Under the synergistic effect of Cl^-and SO₂ concentration,the SCC susceptibility of E690 low-alloy steel in the highest when NaHSO3 concentration is low.In the SO₂ and Cl^-containing electrolyte,the low concentration of SO₂ weakens the uniform deformation capability of E690 steel.更多还原