双相不锈钢温度与应力协同作用下再钝化机理的显色研究

Understanding on the repassivation mechanism of duplex stainless steel subject to sever environment of temperature and stress, is one of the scientific issues to achieve advanced corrosion protection of vital stainless steel facilities and surface quality evaluation techniques. The integrity of passive film and its evolution is a key point in exploring the repassivation mechanism. Considering the disability of conventional electrochemical technique during the characterization on the integrity of passive film, this project proposes a color-change indicator to research on the repassivation behavior of 2205 and 2507 duplex stainless steel under the effect of solution temperature and stress. Based on the color change regulation on passive film integrity, characteristic current density parameters and morphology analysis, the electrochemical critical conditions and kinetics characteristics during the metastable pitting growth and repassivation is hoped to be realized. Also the effect of stress on key electrochemical parameters such as critical repassivation temperature and critical pitting temperature will be investigated. The synergistic mechanism of temperature and stress on electrochemical corrosion will be explored. The boundary condition and influence factors on local corrosion is thus desired and the relationship between pitting and repassivation-color change values-corrosion resistance will be established. Based on the researches as mentioned above, the theoretical model of repassivation under the synergistic effect of temperature and stress will be summarized. It hopes that the study achievement can supply the theoretical and technology support for facility corrosion protection made of stainless steel and inspection techniques of surface passive film quality.

温度和应力作用下双相不锈钢的再钝化机理研究，是提升关键不锈钢装备腐蚀防护性能、发展表面质检技术的科学问题。钝化膜特征及完整性演化规律是认识双相钢再钝化机理的关键环节。本项目拟以2205和2507双相不锈钢为对象，针对常规电化学方法在钝化膜完整性表征中的不足，系统研究亚稳态点蚀发展与再钝化过程中钝化膜完整性的显色演变规律，探索应力对临界再钝化温度、临界点蚀温度等特征参量的影响及作用机理，阐明温度与应力影响耐蚀性的协同效应；结合微电极电化学噪声与金属元素溶出分析，深入刻画亚稳态点蚀发展与再钝化动力学特征；通过多场耦合数值模拟结果，探讨温度与应力对蚀坑微区电化学与介质环境影响规律；探明温度与应力作用下影响双相钢局部腐蚀的主要因素与临界条件，建立双相钢亚稳态点蚀与再钝化特征—显色值—耐蚀性关联模型，为关键不锈钢装备制造中的腐蚀防护及工程现场钝化膜监检提供理论和技术支持。

温度和应力作用下双相不锈钢点蚀及再钝化机理研究，是提升关键不锈钢装备腐蚀防护性能、发展表面质检技术的科学问题。本课题以2205双相不锈钢为对象，研究了应力与温度对双相不锈钢点蚀及亚稳态点蚀过程中的再钝化特性，并提出了邻菲啰啉显色评价钝化膜损伤的方法，其主要内容如下：.（1）利用Ag丝伪参比电极电位监测技术，研究了变形对双相钢液滴干湿循环点蚀和再钝化影响；比较了热轧和冷轧态钢的点蚀和再钝化临界相对湿度，揭示了拉伸和压缩变形均增大临界相对湿度，且对再钝化临界相对湿度影响较大的规律特征；形貌分析发现了冷轧钢在拉伸变形下有成微裂纹；铁素体相以及奥氏体变形滑移区成为点蚀优先溶解区域。不同钢种比较可知，在25oC下随PREN值增大，点蚀概率降低；在50oC下，点蚀概率增大，但PREN值对点蚀概率影响不大；随PREN值增大，点蚀和再钝化临界氯离子浓度均增加，且对再钝化临界氯离子浓度影响更大。.（2）研究了温度和应力作用下双相钢亚稳态点蚀特征，发现了U形弯曲拉伸和压缩状态下亚稳态点蚀出现了新型态峰，相比于常规的态峰中电流缓升陡降类型，该新型态峰具有钝化膜快速击破的电流快升以及再钝化弱的电流缓降特征；亚稳态点蚀频率增多，其形核位置从PREN值低的奥氏体区向相对高的铁素体区迁移，结合组织观察以及阻抗等分析技术，揭示了变形过程中夹杂破碎的缝隙腐蚀和钝化膜缺陷增多是暂态峰演化和形核迁移的关键；并从点蚀形核概率和稳态生长概率角度分析了变形对双相不锈钢从亚稳态点蚀向稳态点蚀转变的影响。.（3）基于应力及温度作用下不锈钢点蚀中表面损伤演化特征，发展了邻菲啰啉显色法评价不锈钢表面钝化膜损伤的技术，分析了不锈钢疲劳过程中均匀变形及开裂的显色特征；揭示了液滴干湿循环过程中，点蚀萌生形成红色色、点蚀生长红色程度增大、再钝化过程红色程度降低的显色演化规律，相关检测方法在核电站工程现场得到应用，为核电装备制造质检评估提供支持。