模拟海洋全浸区环境下A517海工钢的腐蚀机理研究

Corrosion Mechanism of A517 Marine Steel in Simulated Marine Immersion Zone

目的 探究 A517 海工钢在海洋全浸区环境下的腐蚀机理。方法 通过模拟海洋全浸区腐蚀环境,利用失重法、SEM、EDS、XRD、电化学等测试技术,分析A517钢的腐蚀行为历程,并探讨其在全浸区的腐蚀机理。结果A517钢在厚度方向上的最大电位差为 13 mV,小于发生电偶腐蚀的最小电位差50mV,说明材料在厚度方向上的腐蚀敏感性一致。随浸泡时间的延长,腐蚀质量损失量逐渐增加,平均腐蚀速率先降低、后升高、最后趋于稳定,腐蚀速率约为 0.127 mm/a。结论 腐蚀动力初期主要是由溶解氧的极限扩散控制,后期则是腐蚀产物的氧化还原电荷转移控制。腐蚀首先在 Al_(2)O_(3)、MgO 等夹杂物处萌生扩展,腐蚀产物出现明显的分层现象,外锈层主要是疏松易脱落的γ-FeOOH,内锈层主要是致密均匀的 Fe_(3)O_(4),同时锈层中还检测到了β-FeOOH和α-FeOOH的存在。锈层中存在大量微裂纹,削弱了产物膜的保护作用,促进了腐蚀的进行。

The work aims to study the corrosion mechanism of A517 marine steel in marine immersion zone. The corrosion environment in the marine immersion zone was simulated. The corrosion behavior of A517 steel was analyzed by weight loss method, SEM, EDS, XRD and electrochemical techniques. Its corrosion mechanism in the full immersion zone was also discussed. The results showed that the maximum potential difference of A517 steel in the thickness direction was 13 mV, which was less than the minimum potential difference of 50 mV in galvanic corrosion, indicating that the corrosion sensitivity of the material in the thickness direction was consistent. With the prolonged immersion time, the corrosion weight loss gradually increased, and the average corrosion rate decreased first and then increased and finally stabilized. The corrosion rate was about0.127 mm/a. The initial stage of corrosion power is mainly controlled by the ultimate diffusion of dissolved oxygen, and later is the redox charge transfer control of corrosion products. Corrosion firstly propagates in the inclusions such as Al_(2)O_(3)and MgO,and the corrosion products show obvious delamination. The outer rust layer is mainly γ-Fe OOH which is loose and easy to fall off. The inner rust layer mainly is dense and uniform Fe_(3)O_(4)β-Fe OOH and α-Fe OOH are also detected in the rust layer. The presence of a large number of microcracks in the rust layer weakens the protective effect of the product film and promotes the corrosion.