熔焊接头组织耐高速流液态金属腐蚀机制研究

For future nuclear reactor loops, the corrosion behavior of welded joints in high-speed liquid Pb-Bi alloy, which were obtained under the conditions such as different welding heat input and filler material chemical composition, will be studied in this research. Dissolving erosion, cavitation erosion, friction and wear, and their combined damage effect were the problems appeared on the surface of corroded materials in liquid Pb-Bi alloy. To research on these problems, the morphology on corroded surface was compared before and after corrosion, elements and compounds on the corroded surface were detected, mechanism of phase transitions, which was induced when alloying elements had dissolved and migrated, was analyzed and studied. Corrosion and penetration of liquid Pb-Bi alloy were detected on the section, so that the law of intergranular corrosion, which was caused by penetration of liquid Pb-Bi alloy along the grain boundaries of base material and welded joints, could be concluded. The flowing state of the high-speed liquid Pb-Bi alloy was characterized by the hydrodynamic parameters. To reveal the effect of flowing state of the liquid Pb-Bi alloy on cavitation erosion, friction and wear, the interaction between liquid alloy and solid component material was studied. A kind of protection material will be researched and developed to prevent liquid alloy corrosion in nuclear engineering. This project aims at revealing the corrosion mechanism of dissolving erosion, cavitation erosion, friction and wear, and their combined damage, which were appeared on the corroded surface of component materials and their welded joints in high-speed liquid Pb-Bi alloy, and provide a theoretical basis and effective protection measurement to enhance the corrosion resistance and service life of nuclear engineering structural materials.

针对未来核反应堆液态金属循环回路中，不同参数下（焊接热输入量、填充材料化学成分）获得的熔焊接头组织受高速流液态Pb-Bi溶解腐蚀、空泡腐蚀、摩擦磨损的作用机理进行研究。对比熔焊接头组织在液态Pb-Bi合金腐蚀前后的表面形貌、受腐蚀表面组成元素及化合物的变化，研究熔焊接头受腐蚀表面合金元素溶解、迁移并诱发组织相变的机理；分析熔焊接头截面上液态金属元素的腐蚀渗透情况，揭示液态Pb-Bi沿晶界渗透导致晶间腐蚀的规律；对比分析熔焊接头表面状态和硬度不同时，受液态Pb-Bi冲刷过程中的摩擦磨损情况，对高速流液态金属摩擦磨损机理进行研究；采用流动参数表征高速流液态Pb-Bi合金的流动状态，研究液固两相的相互作用情况，揭示液态Pb-Bi流动状态对于空泡腐蚀和摩擦磨损的影响规律。本项目旨在揭示熔焊组织在高速流液态Pb-Bi合金中的腐蚀机制，为提高核反应堆过流部件的耐腐蚀性能及服役寿命提供理论依据。

加速器驱动次临界系统和铅冷快堆中的包层结构材料长期暴露在液态LBE中会发生溶解腐蚀、氧化腐蚀和空泡腐蚀，而焊接技术广泛应用于这些包层结构材料中，因此研究熔焊接头在液态LBE中的腐蚀行为意义重大，可以为进一步优化熔焊接头耐腐蚀性能方面提供理论和试验依据。.本项目设计制造出一套耐高速流液态LBE腐蚀的试验装置，和一套液态金属空泡腐蚀装置，并申请了专利。.动静态LBE腐蚀试验装置主要用于研究溶解腐蚀情况，针对流速、钢种、热处理工艺、焊接参数、表面熔敷等进行了试验研究，研究表明：无论静态还是动态腐蚀，CLAM钢、316L钢等钢的TIG焊接接头均发生明显的氧化腐蚀，表面都形成了具有保护作用的双氧化层，外氧化层主要为疏松多孔的Fe3O4，内氧化层主要为致密FeCr2O4，热影响区的耐腐蚀性高于焊缝区，液态铅铋的相对速度越大，氧化腐蚀和磨损腐蚀越严重。在相应的试验条件下，304钢焊接接头耐蚀性最好，CLAM钢其次，Q235B钢最差；含较少Cr的304L钢焊接接头比316L焊接接头更耐腐蚀；760℃回火热处理能显著改善CLAM钢焊接接头耐高速流液态铅铋的腐蚀性能；热输入为7.6KJ/cm时316L钢焊件的腐蚀失重速度最小，耐蚀性达到最佳；WC添加量在3.73~5.33%时CrWMn铁基合金熔敷层耐蚀性能和耐磨性能最佳。.液态金属空泡腐蚀装置主要用于研究空泡腐蚀情况，针对时间、热处理工艺、钢种等不同参数进行试验研究，研究表明：液态金属中的空泡腐蚀过程包括孕育期、加速期，存在空泡腐蚀与溶解氧化腐蚀的联合腐蚀机制，时间越长，空泡腐蚀越严重，母材的耐蚀性优于焊缝区域。在相应的试验条件下，调质处理后的CLAM钢焊缝耐蚀性能最好；固溶处理后的316L钢焊缝的耐空蚀性得到改善；50℃/30min热处理后的钴基合金焊缝耐蚀性最好。.本项目揭示了高速流动态腐蚀机理和空泡联合腐蚀机制，为熔焊接头耐高速流液态金属腐蚀和空泡腐蚀的性能提供了理论基础和技术依据，对提高原子能装置部件的使用寿命以及各种包层结构材料在核工业中的实际应用具有重要的理论意义和实际应用价值。