| 引用本文: | 赵志博,朱加雷,李桂新,李松钊,赵友亮,赵亮.304L不锈钢局部干法水下激光填丝角焊接头的组织及性能[J].中国表面工程,2024,37(5):384~392 |
| ZHAO Zhibo,ZHU Jialei,LI Guixin,LI Songzhao,ZHAO Youliang,ZHAO Liang.Microstructure and Properties of 304L Stainless Steel Local Dry Underwater Laser Welding Joint with Filler Wire[J].China Surface Engineering,2024,37(5):384~392 |
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| 摘要: |
| 核电乏燃料池在长期的服役过程中不可避免会出现缺陷，目前针对核电站乏燃料池底面和壁面交界处 L 型拐角位置存在的裂纹缺陷修复研究还鲜有报道。自主设计一款局部干法水下角焊排水罩，并以第二代核电站乏燃料池覆板用的 304L 不锈钢为研究对象，开展局部干法水下激光填丝角焊试验。通过光学显微镜分析多层多道角焊缝的显微组织；用 DPT-5 着色渗透探伤剂对焊缝表面及其横截面进行渗透检测；采用显微硬度计测试不同区域的显微硬度分布情况；使用 VersaSTAT 3F 电化学工作站测定 3.5%NaCl 溶液中不同区域的极化曲线和 Nyquist 图谱。结果表明：焊缝的成型质量高，宏观和微观均无明显缺陷，显微组织主要由奥氏体和铁素体组成；焊缝区域层与层之间有明显的分界，热影响区不明显；搭接区由于多次热积累， 铁素体含量减少，奥氏体晶粒变大；各区域晶粒尺寸大小的不同，致使硬度呈近似“M”形分布；极化曲线和 Nyquist 图谱结果均表明不同区域抗电化学腐蚀能力的顺序为 BM＞WM＞HAZ。利用自主设计的角焊排水罩进行了水下激光填丝角焊修复试验，获得良好的角焊接头工艺性能，可为乏燃料池的裂纹修复提供技术参考。 |
| 关键词: 局部干法水下激光焊接 乏燃料池 拐角修复 显微组织 电化学腐蚀 |
| DOI：10.11933/j.issn.1007-9289.20230919001 |
| 分类号:TG456 |
| 基金项目:北京市科技计划重点项目（KZ202210017023）；国家自然科学基金联合基金重点支持项目（U22B20127）；北京市属高等学校高水平科研创新团队建设支持计划（BPHR20220110） |
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| Microstructure and Properties of 304L Stainless Steel Local Dry Underwater Laser Welding Joint with Filler Wire |
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ZHAO Zhibo，ZHU Jialei，LI Guixin，LI Songzhao，ZHAO Youliang，ZHAO Liang
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School of Mechanical Engineering, Beijing Institute of Petrochemical Technology, Beijing 102617 , China
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| Abstract: |
| At the 75th United Nations General Assembly, China announced that its carbon dioxide emissions would peak before 2030, and the nation will achieve carbon neutrality before 2060. In this context, nuclear power, as a clean, safe, efficient, and stable green and low-carbon energy source that can be developed on a large scale, can play a significant role in promoting green development and helping to achieve the “dual carbon” goals. During the long-term service of nuclear power plants, the stainless steel cladding of the spent fuel pool experiences aging effects, and its failure mechanisms primarily include mechanical impact, uniform corrosion, stress corrosion cracking, and pitting corrosion. Reliable underwater maintenance technology is crucial to ensure the safe operation and smooth life extension of nuclear power plants. Underwater laser welding, a relatively efficient in-situ repair technology, has the advantages of accurate heat input, low residual stress, high welding quality, and fully automated welding process, in addition to being less affected by water pressure. It has received widespread attention for underwater operations. Currently, there are few reports on the repair of crack defects at the L-shaped corner position at the junction between the bottom and wall of spent fuel pools in nuclear power plants. Therefore, a local dry underwater corner welding drainage cover was independently designed, and a local dry underwater laser wire-filling corner welding test was conducted on the 304 L stainless steel used for second-generation spent fuel pool cladding in nuclear power plants. The microstructures of the multi-layer and multi-pass fillet welds were analyzed using an optical microscope. Penetration testing was performed on the surface and cross-section of the weld using a DPT-5 dye penetrant. The micro-hardness distribution in different areas was tested using a micro-hardness tester. The polarization curves and Nyquist spectra of different regions in a 3.5% NaCl solution were measured using a VersaSTAT 3F electrochemical workstation. The results demonstrate that the forming quality of the fillet weld is high, and the metallurgical bonding is tight, with no obvious defects at both macro and micro levels. Owing to the protection of the pure argon gas environment, the surface of the fillet weld inside the underwater drainage hood presents a silver white fish scale as a delicate ripple. The penetration results revealed no obvious defects on the cross-section and surface of the weld seam. The microstructure is mainly composed of austenite and ferrite, and there is a clear boundary between the layers in the weld seam area. The heat-affected zone is not clearly displayed owing to the rapid cooling effect of water. The center structure of the fillet weld is mainly composed of vermicular ferrite, γ Austenite, and lath ferrite, and the crystal morphology is mainly equiaxed crystal. The fusion zone is mainly composed of vermicular ferrite and γ Austenite, with a small amount of feathery ferrite. The crystalline form is mainly columnar crystals, which grow perpendicular to the fusion line toward the center of the weld seam. The overlapping area is mainly composed of vermicular ferrite and γ Austenite. Owing to multiple heat accumulations in the overlap zone, it is equivalent to solid solution treatment on the surface of the weld, resulting in a decrease in the ferrite content and an increase in the austenite grains. The average micro-hardness values of BM, HAZ, and WM for multi-layer and multi-pass corner welding joints are 209 HV, 226 HV, and 234 HV, respectively, with uneven distribution and an approximate M-shaped distribution. The polarization curve and Nyquist spectrum results indicate that the order of resistance to electrochemical corrosion in different regions is BM＞WM＞HAZ. Underwater laser wire-filling corner welding repair experiments were conducted using a self-designed corner welding drainage cover. A good process performance of the corner welding joints was obtained, which can provide a technical reference for the crack repair of spent fuel pools. |
| Key words: local dry underwater laser welding spent fuel pool corner repair microstructure electrochemical corrosion |
