经济节铬镍型含锡不锈钢组织演变及局部腐蚀行为研究

As the development of the new tin-addition stainless steel in Japan, resource-saving low-chromium-nickel stainless steels with tin addition have driven more and more attentions at the international level. So it’s important to speed up the process of domestic tin addition stainless steels. A Trace tin addition can improve the formability and corrosion resistance of stainless steels. However some studies need to be done to optimize the microstructure and the element content, in order to improve the mechanism of stainless steels with tin addition. And the mechanism of resistance to pitting and intergranular corrosion is still not clear. The project aims at the corrosion resistance of new economical stainless steels with tin addition, 16Cr-Sn and B316LX, and to study the relevance among the trace elements Sn, environmental factors and microstructure evolution systematacially. In this project, the methods of metastable pitting current fluctuation technique, surface phase analysis and topographic observation, are used to investigate the effects of Sn element on metastable pitting initiation and steady expansion of influence in two steps, and will examine the effects on the progress of growth, dissolution and rupture of the passive film. The intergranular corrosion susceptibility of the stainless steels with tin addition is investigated by double electrochemical potentiodynamic reactivation (DLEPR) technology, in order to clarify the intergranular corrosion mechanism, and to illuminate the internal relations among corrosion resistance, alloying element and microstructure evolution. The effects of environmental factors on corrosion behaviors of the stainless steels with tin addition are analyzed, to further understand the kinetics of corrosion and explore the main influencing factor and the most critical corrosion mechanism. This project can provide a new method and the theoretical basis for the material development and the corrosion resistance improvement of stainless steel with tin addition.

随着新型不锈钢的开发，资源节约型低铬镍含锡不锈钢成为国际学术界的关注热点。微量锡元素能改善不锈钢的成型性和耐蚀性，但是微量元素和组织结构的优化尚需进一步研究，锡元素对耐点蚀和晶间腐蚀性能的改善机理仍不明晰。基于此，本项目针对节铬镍含锡不锈钢16Cr-xSn和B316LX，通过多种电化学测试手段系统研究微量锡元素、组织演变及环境因素对耐蚀性能的影响及电化学机制。明确锡元素在奥氏体和铁素体中的极限溶解度以及析出动力学；研究锡元素对亚稳态点蚀萌生和稳态点蚀扩展两个阶段的影响，尤其是锡元素引发的闭塞区内溶液传质过程的改变对钝化膜的生长、溶解和再钝化的作用。分析新型不锈钢晶界处锡元素的分布，澄清其晶间腐蚀规律和机制。通过探索环境因素对其局部腐蚀行为的影响规律，阐明其耐蚀性和稳定性的主要影响因素和主控机制。此项目为含锡不锈钢的材料设计和耐蚀性能的提高提供新方法和理论依据，为含锡不锈钢国产化奠定基础。

新型经济型不锈钢的研发是我国钢铁领域的重要任务之一。含锡不锈钢通过添加微量锡元素、降低铬和镍元素从而降低成本，同时改善材料耐蚀性。.在硫酸和盐酸环境中，含锡铁素体不锈钢的均匀腐蚀性能均得到明显提高。醋酸溶液中Sn的加入增大了腐蚀速率。奥氏体不锈钢316L，B316LX和317L不锈钢的腐蚀速率随H2SO4浓度的增大而迅速上升；与316L不锈钢相比，含锡量为0.08 wt.%的B316LX不锈钢在H2SO4溶液中的腐蚀速率降低了一个数量级；随Sn含量继续增加，腐蚀速率变化不大，0.06%~0.1 wt.% Sn的添加量即能显著提高材料耐蚀性能。.在氯化钠环境中，随着锡含量的增加，含锡铁素体不锈钢的Eb、Eb-Ecorr和CPT值均随之增长，即耐点蚀性能随之增强。XPS测试结果显示：锡的添加，使得铁素体不锈钢表面生成了一层含有SnO2的保护膜。B316LX不锈钢的亚稳态点蚀萌生的温度降低，同时CPT温度和点蚀电位Eb提高，E(Eb-Ep) 差值变小，稳态点蚀难以扩展。Sn元素提高材料耐蚀性能是抑制了稳态点蚀的发展。Sn的氧化物能减少钝化膜中的缺陷，提高其完整性和致密性，因此提高了B316LX的耐蚀性能。Sn的氧化物和氢氧化物易在点蚀坑内沉积使钝化膜的自修复性能提高。.0.5 Sn 铁素体不锈钢较0 Sn耐晶间腐蚀能力明显提高。含锡铁素体不锈钢的鼻尖温度在650℃附近，在此温度下进行时效处理，Ra值会先增加后减小。这是因为开始时，沉淀析出相会随着时间的增加而累积增多，造成贫铬区的扩大；但随时间的进一步延长，晶粒内的铬能扩散至贫铬区，使样品发生自愈合。B316LX含锡不锈钢的晶间腐蚀性能主要受微观组织演变的影响，热处理之后晶界和晶内可观察到M23C6碳化物和金属间化合物Laves相。M23C6的析出是引起晶间腐蚀敏感性的主要原因。Laves相的析出会引起铬和钼元素的不均匀分布，引起长时间敏化后晶内出现许多点蚀坑。锡元素的添加提高了奥氏体不锈钢的晶间腐蚀敏感性，这是由于锡元素在奥氏体中的固溶度较低，倾向于向晶界偏析。