铁素体/马氏体钢在液态铅铋环境中的腐蚀机理研究进展

Research Progress on Corrosion Mechanism of Ferritic/Martensitic Steel in LBE Environment

摘要:

液态铅铋共晶合金（Liquid lead-bismuth eutectic, LBE）具有优良的热工水力和中子学性能，是第四代先进快中子堆的冷却剂和加速器驱动次临界核能系统(Accelerator driven sub-critical system, ADS)的散裂靶最重要的材料之一。然而，LBE与金属结构材料之间的相容性问题是阻碍液态重金属快中子堆发展的主要瓶颈。由于铁素体/马氏体钢（F/M钢）具有良好的力学性能且导热性好、热膨胀系数低及抗辐照性能优异，已成为液态重金属快中子堆主要的候选材料，其腐蚀问题对于液态重金属快中子堆的材料选型和结构设计尤为重要。LBE腐蚀受多种因素（温度、流速、氧浓度和材料组分等）影响，从而导致腐蚀过程较为复杂。因此，对F/M钢在不同LBE环境中的腐蚀行为、规律、机理和相关模型进行分析总结十分重要。可用空间模型理论是最受广泛认同及应用于解释LBE腐蚀行为的理论，几乎所有腐蚀机理模型均建立在该理论的基础上。F/M钢与LBE腐蚀环境之间的元素扩散运动与腐蚀产物生长密切关联，Fe离子向外扩散留下空位，空位累积形成空穴，O扩散到空穴后大部分发生氧化生成Fe-Cr尖晶石，部分O沿着晶界和马氏体板条边界扩散，选择性优先氧化Cr生成Cr₂O₃。对于添加Si的F/M钢，沿着位错优先生成SiO₂，降低了富Cr氧化物的成核势垒，从而促进了Cr₂O₃和Fe-Cr尖晶石的形成。在实验研究和机理研究的基础上，建立预测F/M钢长期腐蚀性能的模型，常用的有热工水力模型（MATLIM）和CEA提出的机理模型。通过对F/M钢在LBE环境中腐蚀的机理研究，研发出更快形成保护性氧化层（Fe-Cr尖晶石层）和增加 Fe-Cr尖晶石层致密度的有效方法，从而提高材料的抗LBE腐蚀性能。（专精特新·特殊环境材料服役行为专辑十五之三）

Abstract:

Liquid lead bismuth eutectic （LBE） is one of the most important materials for the coolant of the fourth-generation advanced fast neutron reactor and the scattering target of the accelerator driven subcritical nuclear energy system， owing to its excellent thermal-hydraulic and neutron properties. However， the compatibility issue between LBE and metal structural materials is the main bottleneck hindering the development of liquid heavy metal fast neutron reactor. Ferritic/Martensitic steel （F/M steel） has become a major candidate material for liquid heavy metal fast neutron reactor， due to its excellent mechanical properties and thermal conductivity， low coefficient of thermal expansion， and outstanding radiation resistance. Thus， its corrosion resistanceis particularly important for material selection and structural design of liquid heavy metal fast neutron reactor. The corrosion process of F/M steel in LBE is intrinsically complex， influenced by a multitude of factors including temperature， flow rate， oxygen concentration， and material composition. Therefore， it is important to analyze and summarize the corrosion behavior， laws， mechanisms， and related models of F/M steel in different LBE environments. The “available space model” theory is the most widely recognized and applied theory for explaining LBE corrosion behavior， and almost all corrosion mechanism models are based on this theory. The element diffusion movement between F/M steel and LBE corrosion environment is closely related to the growth of corrosion products. The vacancies left by the outward diffusion of Fe ions accumulate to form holes. When O diffuses into the holes， most of it will be oxidized to form FeCr spinel， and a part will diffuse along the grain boundaries and martensite lath boundaries to selectively oxidize Cr to form Cr₂O₃. For F/M steel with Si adding， SiO₂ is preferentially generated along dislocations， reducing the nucleation barrier of Cr rich oxides and promoting the formation of Cr₂O₃ and Fe Cr spinel. Based on experimental and mechanistic studies， a model for predicting the long-term corrosion performance of F/M steel is established. Commonly used models include the Thermal Hydraulic Model （MATLIM） and the mechanistic model proposed by CEA. By studying the corrosion mechanism of F/M steel in LBE environment， effective methods have been developed to form a protective oxide layer （Fe-Cr spinel layer） and increase its density， thereby improving the material's resistance to LBE corrosion.