316L钢焊接接头在液态铅铋合金中的空泡腐蚀行为研究

发布时间：2018-08-09 07:57

【摘要】：铅铋共晶合金(LBE)具有熔点低,载热能力强,中子特性良好等优良性能,是加速器次临界驱动系统(ADS)的散裂靶和冷却剂的首要候选材料。但是铅铋合金会对暴露于液态金属环境的包层材料造成比较严重的腐蚀。如在核工程冷却循环回路中,核主泵叶轮与液态金属做高速相对运动时使叶轮上的局部区域形成压力突变区,气体析出后在叶轮表面形成气泡,大量的气泡溃灭对金属表面造成空泡腐蚀,导致部件使用寿命的降低和维修成本的提高。316L钢具有优良的力学性能和耐腐蚀性能,常用作ADS冷却循环回路的包层材料与主泵叶轮材料。在核工程中许多结构都使用熔焊的方法进行装配和制造,而焊缝组织一般存在成分偏析、组织粗大等缺陷,是整个冷却循环回路薄弱区域。因此研究316L钢焊接接头在液态铅铋合金中的空泡腐蚀可以为ADS系统及未来聚变示范堆能够更加经济、安全地应用提供理论基础。本文针对316L不锈钢,分别采用316L钢母材和钴基合金作为填充金属进行TIG焊,并进行焊后热处理。自主设计和研发液态金属超声空蚀设备,在550℃液态PbBi中进行316L母材、热处理前后316L焊缝、热处理前后钴基合金焊缝的空泡腐蚀试验。利用SEM与AFM表征不同时间空蚀后各组试样的表面形貌,并研究表面形貌随空蚀时间的变化规律和分析各组试样的空泡腐蚀行为;测量各组试样不同时间空蚀后表面粗糙度与腐蚀坑深度的变化以研究耐空蚀性差异,进而研究不同填充材料和热处理工艺参数对焊缝液态LBE中空泡腐蚀的影响;另外,通过对比静态腐蚀和空泡腐蚀100h后焊缝截面氧化层形貌以及元素的变化,探索熔焊接头表面在液态LBE中产生的溶解与氧化腐蚀和空泡腐蚀的联合作用机制。试验结果表明,316L焊缝与母材试样表面粗糙度和最大腐蚀坑深度随着空蚀试验时间的延长而不断增加,母材表现出的耐空蚀性大大优于焊缝,耐空蚀性差异主要与两者的金相组织有关。将316L钢焊缝进行固溶处理后其耐空蚀性得到改善,但依然没有316L母材耐空蚀性好。另外,通过对比316L钢焊缝静态腐蚀100h和空泡腐蚀100h后焊缝截面的元素变化发现,液态铅铋合金中的溶解与氧化腐蚀和空泡腐蚀会相互促进,它们的联合作用对焊缝造成更加严重的破坏。钴基合金耐腐蚀性很好,因此本文利用钴基合金作为填充材料对316L钢进行TIG对接焊,并将钴基合金焊缝进行不同温度的焊后热处理,之后进行液态铅铋中不同时间的空泡腐蚀试验。试验结果表明钴基合金焊缝的耐空蚀性优于316L钢焊缝,且不同温度焊后热处理后,钴基合金焊缝的耐空蚀性都得到改善,其中750℃热处理后钴基合金焊缝耐空蚀性最优,其次为700℃热处理,800℃热处理后钴基合金耐空蚀性最差。本文所有试样在空蚀试验过程中,316L母材、固溶处理前后316L钢焊缝、未热处理钴基合金焊缝四组试样在空蚀过程中都发生了不同程度的加工硬化,其中316L母材的加工硬化程度最高,钴基合金焊缝加工硬化程度最低;三组温度热处理后的钴基合金焊缝几乎没有发生加工硬化,加工硬化程度在空蚀20h内略微增加,且在20h后表面硬度略微下降。经过综合分析,在本文研究的所有材料中,母材的耐空蚀性能最优,其次是750℃热处理后的钴基合金焊缝,再是固溶处理后的316L焊缝。
[Abstract]:Lead bismuth eutectic alloy (LBE) has good properties such as low melting point, strong heat carrying capacity and good neutron characteristics. It is the primary candidate for the spallation target and coolant of the accelerator subcritical drive system (ADS). But lead bismuth alloy will cause serious corrosion to the cladding material exposed to the liquid metal environment. For example, in the cooling cycle of nuclear engineering. In the road, when the impeller of the nuclear main pump and the liquid metal are moving relative to the liquid metal, the local area on the impeller is formed, the gas bubbles are formed on the surface of the impeller, and a large number of bubbles collapse on the metal surface, resulting in cavitation corrosion on the metal surface, which leads to the improvement of the service life of the components and the improvement of the maintenance cost of the.316L steel with excellent mechanical properties. The cladding material and the main pump impeller are commonly used as the ADS cooling loop. Many structures in the nuclear engineering are assembled and manufactured by the fusion welding method. The weld organization usually has the defects such as composition segregation and coarse organization, which is the weak area of the whole cooling loop. Therefore, the study of 316L steel welded joint is studied. The cavitation corrosion in liquid lead bismuth alloy can provide a theoretical basis for the more economical and safe application of ADS system and future fusion demonstration reactor. In this paper, the TIG welding of 316L stainless steel with 316L steel and cobalt base alloy is used respectively as filled metal, and the post weld heat is carried out. The ultrasonic cavitation of liquid metal is designed and developed independently. The equipment, the 316L parent material, 316L weld before and after heat treatment at 550 C, and the cavitation corrosion test of the cobalt base alloy weld before and after heat treatment. Using SEM and AFM to characterize the surface morphology of each sample after different time cavitation, and study the change rules of surface morphology with the cavitation time and the analysis of the cavitation corrosion behavior of each sample. The changes of surface roughness and corrosion pit depth after different time cavitation were studied to study the difference of cavitation resistance. Then the effects of different filling materials and heat treatment parameters on the corrosion of liquid LBE hollow bubble were studied. In addition, the morphology of the oxidation layer of the weld section and the change of elements after 100h were compared with static corrosion and cavitation corrosion. The joint action mechanism of the dissolving and oxidation corrosion and cavitation corrosion in the liquid LBE is explored. The results show that the surface roughness and the maximum corrosion pit depth of the 316L weld and the parent material increase with the time of cavitation test, and the cavitation resistance of the parent material is much better than that of the weld. The corrosion resistance is mainly related to the metallographic structure of the two. The cavitation resistance of 316L steel welds is improved after solid solution treatment, but still there is no good cavitation resistance of 316L parent material. In addition, the dissolution and oxidation of the liquid lead bismuth alloy is found by the comparison of the element modification of the weld cross section after the static corrosion of the 316L steel weld 100h and the cavitation corrosion 100h. Corrosion and cavitation corrosion will promote each other, their joint effects cause more serious damage to the weld. The corrosion resistance of cobalt base alloys is very good. Therefore, the cobalt base alloy is used as filling material for TIG butt welding of 316L steel, and the cobalt base alloy welds are heat treated at different temperatures after welding, and then the liquid lead bismuth is different. The test results show that the cavitation resistance of the cobalt base alloy welds is better than that of 316L steel, and the cavitation resistance of the cobalt base alloy welds is improved after heat treatment at different temperatures. The corrosion resistance of the cobalt base alloy welds at 750 C is the best, the heat treatment is 700 degrees C, and the cobalt base alloy after heat treatment at 800. In the process of cavitation test, all specimens of this paper in the cavitation test, 316L material, 316L steel weld before and after solution treatment, four groups of cobalt base alloy welds without heat treatment, have different degree of hardening during the cavitation process, of which the working hardening of 316L is the highest, the working hardening of cobalt base alloy welds is the lowest; three groups. The weld seam of cobalt base alloy after temperature and heat treatment has hardly been hardened, and the degree of working hardening is slightly increased in cavitation 20h, and the hardness of the surface decreases slightly after 20h. After comprehensive analysis, the corrosion resistance of the parent material is the best in all the materials studied in this paper, followed by the weld of cobalt base alloy after heat treatment at 750 C, and then solid solution. 316L weld after treatment.
【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG407;TG441.8

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