铁素体/马氏体不锈钢的电化学腐蚀行为研究

Electrochemical Corrosion Behavior Research of Ferritic/Martensitic Stainless Steel

铁素体/马氏体不锈钢具有较好的机械强度、导热性与耐腐蚀性,被广泛用于反应堆结构材料,而材料腐蚀问题是影响反应堆寿命与安全运行的重要因素。本文利用电化学工作站测量了不锈钢在溶液中的开路电位、极化曲线及电化学阻抗谱,研究了不锈钢在不同条件下的电化学腐蚀行为,并采用数据拟合方法建立了铁素体/马氏体不锈钢的电化学腐蚀模型。试验结果表明:不锈钢浸入液体环境后表面电位升高,形成有减缓腐蚀作用的氧化膜;随着氯离子浓度升高,不锈钢表面腐蚀电位降低,钝化膜稳定性降低;氯离子浓度高于100 ppm时,不锈钢的阻抗明显减小,此时不锈钢表面发生了活跃的腐蚀行为。极化曲线测量结果表明,当温度高于60℃、不锈钢在外加电位时,不锈钢表面的钝化膜会在更低的电位下发生破坏,钝化膜稳定性较低。不锈钢腐蚀的主要原因为表面钝化膜在特定条件下的稳定性降低和阻抗减小。

Ferritic/martensitic stainless steel has a wide range of applications in reactor engineering.During the service phase,reactor materials are required to have good resistance to high temperatures,radiation,and creep.During the retirement phase,it is required that the materials must be kept at a lower temperature in the spent fuel pool and prevent the diffusion of radioactive products.This paper focuses on the alternative material of ferritic/martensitic stainless steel for a specially designed reactor cladding.This paper used electrochemical experimental methods to establish an electrochemical corrosion model to study the corrosion behavior of the material in low-temperature water environments,providing reference for environmental condition control of the material during retirement.The sample was processed by wire cutting method,cleaned with acetone and deionized water,dried,and then connected to the wire by welding.The sample was encapsulated with resin and curing agent.The open circuit potential,polarization curve,and electrochemical impedance spectrum of the sample were measured in aqueous solutions with different chloride ion concentrations and temperatures,and the equivalent circuit fitting of the material was carried out.The experimental results show that stainless steel can generate a protective passivation film in pure water,and the properties of the passivation film change with changes in external conditions.In the early stage of corrosion,a highly corrosive environment has a certain promoting effect on the formation of passivation film.The increase in chloride ion concentration lowers the breakdown potential,impedance,and stability of the passivation film,reduces the solution resistance,and leads to a decrease in the corrosion resistance of the material.The increase in temperature reduces the stability of the passivation film.When the temperature is between 30,40,50℃,the surface properties of the material are relatively stable,and the tendency for severe corrosion is relatively small.The critical pitting temperature of the materials used in the experiment is between 60,70℃.When the temperature exceeds 60℃,the radius of the surface impedance spectrum arc of the material significantly decreases.The activity of electrochemical corrosion is mainly attributed to the decrease in resistance of the passivation film,and this change becomes more pronounced when the temperature exceeds the critical pitting temperature.Therefore,when the chloride ion concentration is less than 10 ppm and the temperature is less than 60℃,the surface passivation film stability of the sample stainless steel is good,and the material has strong corrosion resistance.This condition can be used as a reference condition for the water quality control of the spent fuel pool.