热镀锌钢材在海洋大气中的氢渗透行为及脆化研究

【作者】 张大磊；

【导师】 李焰；

【作者基本信息】 中国科学院研究生院（海洋研究所） ， 海洋化学， 2010， 博士

【摘要】 由于镀层对钢材基体具有良好的防腐作用,热浸镀钢材在各种腐蚀环境中均获得了广泛的研究和应用；然而,当镀层出现破损时,镀锌层在对基体提供阴极保护的同时,很可能会导致碳钢表面因保护电位过负而有氢析出。考虑到海洋大气是钢材发生氢致延迟断裂的敏感介质,热镀锌钢材在此环境中应用时存在的安全隐患应引起足够重视。本文以目前广泛使用的热镀锌钢材为研究对象,首次采用混合丝束电极技术证实了海洋大气环境中镀锌层出现破损或存在缺陷时,钢材基体表面会析氢,并以此建立了一种用以检测析氢电流密度的方法；制备了用于研究海洋大气环境中氢渗透行为的双面电解池,研究了气氛温度、湿度、试样表面亚硫酸盐沉积量以及镀层缺陷比例等因素对热镀锌钢材氢渗透行为的影响,得到了用以推测最大氢渗透电流和氢渗透总量的数学模型：通过慢应变速率拉伸试验(SSRT)配合断口形貌分析,探讨了不同环境因素对钢材基体力学性能的影响,结果表明：(1)海洋大气环境中,热镀锌钢材缺陷处的基体表面会有氢析出,且随钢材基体暴露面积的增加,析氢电流先增大后减小,干湿交替的大气环境条件对钢材表面的氢析出有促进作用。(2)气氛温度、湿度、试样表面的亚硫酸盐沉积量及镀层缺陷比例对热镀锌钢材的氢渗透行为影响显著。随着海洋大气环境的气氛温度、湿度的升高,试样的氢渗透行为被加速,并且温度与湿度之间存在明显的协同效应；亚硫酸盐在试样表面的沉积进一步促进了热镀锌钢材的氢渗透行为；而随镀层缺陷面积的增大,热镀锌钢材的渗氢电流逐渐减小：干湿交替循环的海洋大气环境对热镀锌钢材的氢渗透行为存在明显的加速作用,干、湿时间在每个循环中所占的比例对其氢渗透行为影响显著。(3)热镀锌钢材在海洋大气中的氢渗透能降低材料的强度,增大其氢脆敏感性,其断口形貌随着暴露时间的延长由韧性断裂变为脆性断裂；高温、高湿且干湿循环交替的大气环境对其氢脆敏感性提高最大。更多还原

【Abstract】 As an effective protection measure, zinc coating prevents corrosion of steel through a barrier effect and a galvanic effect. On the other hand, it also acts as a barrier for hydrogen entry into steel substrate because the reduction of water on zinc coating is more hardly than that on iron and the diffusivity of hydrogen in zinc is also smaller compared with iron. However, if zinc coating was damaged and exposed to corrosive environment, such as marine atmosphere, the exposed steel substrate would act as cathodic sites where hydrogen was generated by the reduction of water molecule. For engineering purpose, therefore, it is necessary to estimate the amount of hydrogen absorbed by galvanized steel into the substrate steel when exposed to marine atmospheric environment. In this article, a new technology, which was called hybrid wire beam electrode (WBE), was used to prove that hydrogen must generate on the steel surface if zinc coating damaged. Hydrogen permeation current curve of hot-dip galvanized steels in marine atmosphere was also measured using a modified Devanathan-Stachurski cell. Influences of temperature, humidity, coating defect and amount of sulphite on samples’surface were also investigated. The stress-strain curves of galvanized steel with different hydrogen charging conditions were obtained by SSRT, and their mechanical properties was compared. Fractography were also carried out to investigate the effect of hydrogen permeation zinc coating with defect in seawater on the mechanical properties of steel substrate. The results as follows:(1) The hybrid-WBE was developed and measured the hydrogen generation current density. The results showed that the hydrogen generation current became larger firstly and then reduced as follows as the surface of steel increasing. The wet-dry marine atmosphere can accelerate the hydrogen generation.(2)The atmospheric environment at elevated temperature and humidity accelerates the hydrogen permeation process; meanwhile, cathodic protection of zinc coating to the exposed steel surface promotes the hydrogen absorption of the defective coated steels; the deposition of sulphite can also accelerates the hydrogen permeation process.(3) Self hydrogen permeation behavior of Galvanized coating in marine atmosphere can reduce their percentage elongation after fracture. With longer hydrogen charging time, the materials showed higher susceptibility to hydrogen embrittlement.更多还原