热输入及处理工艺对316L焊接接头在液态铅铋中空泡腐蚀行为的影响

发布时间：2018-05-03 06:29

  本文选题：Pb-Bi共晶合金 + 空泡腐蚀　； 参考：《江苏大学》2017年硕士论文

【摘要】：能源是决定当前社会能否得到可持续发展的最重要因素,而核能的使用有助于缓解当前能源困境。液态铅铋共晶合金(LBE)的抗辐射性强,导热性和安全性好,并且其中子学性能优异,因此被广泛用作核动力加速器、次临界驱动系统(ADS)和铅冷快堆的冷却剂(LFR),但流动的液态铅铋会对循环回路中的管道、储存箱以及主泵叶轮材料造成严重的冲刷磨损腐蚀和空泡腐蚀。结构钢焊接接头属于铸造组织,其内部粗大的晶粒和焊后残余应力会进一步加剧其在液态LBE中的空泡腐蚀。316L不锈钢是奥氏体不锈钢,拥有优异的综合力学性能是核反应堆中应用最广泛的结构材料,因此研究其耐空泡腐蚀性能有助于提高核反应堆过流部件的耐腐蚀性能及为其服役寿命提供理论依据。本课题组自主设计了一套空泡腐蚀实验装置,其中超声波变幅杆的功率为3kw,频率是19.2kHz,振幅为50μm。通过该空泡腐蚀装置,对不同热输入的焊接接头、预腐蚀后的焊接接头、不同焊材的焊接接头的空泡腐蚀行为进行了研究。对不同热输入下的316L焊接接头和其母材进行80h的空泡腐蚀,结果显示316L焊接接头的耐空蚀性与焊接热输入的关系为焊接热输入越大,焊接接头耐空蚀性越差。316L焊接接头的耐空蚀性主要受奥氏体晶粒尺寸的影响,当焊接热输入增大时,焊缝区的奥氏体晶粒发生长大,其抗空蚀能力较差。母材的耐空蚀性能普遍优于焊缝,母材是锻态组织,而焊缝是铸态组织,其凝固模式是F-A型:铁素体+奥氏体结晶,焊缝内部形成了蠕虫状的铁素体和粗大的奥氏体晶粒。316L焊接接头在550℃液态LBE中进行空泡腐蚀时,试样表面会生成双氧化层,外氧化层为Fe_3O_4,内氧化层为FeCr2O4,内氧化的致密性高于外氧化层。外氧化层随焊接热输入的增加而变厚,内氧化层的厚度变化受热输入影响不大。探索空泡时间对316L焊接接头空泡腐蚀行为的影响规律。在550℃液态LBE中对316L焊接接头进行不同时间的空泡腐蚀,观测分析其空蚀后的表面SEM形貌和AFM形貌,结果显示316L焊接接头的表面粗糙度和腐蚀坑深度会随着空蚀时间的增加而增加。空泡腐蚀过程中,316L焊接接头受空化应力的作用,其表面会发生加工硬化,由于变形的晶粒迅速堆积在晶界处,相互之间的位错进行了交割,空蚀后材料的表面硬度高于空蚀前材料的表面硬度。研究Ni元素对316L焊接接头在550℃液态LBE中的空泡腐蚀的影响。结果表明焊接接头中的Ni颗粒会弥散分布在晶粒内,与基体相的结合强度高,因此能够显著提升焊接接头的耐空蚀能力。研究了预腐蚀对316L焊接接头耐空泡腐蚀行为的影响。在200℃液态LBE预腐蚀80h后316L焊接接头,其表面会形成一层薄的Fe_3O_4氧化层,在孕育期内能有效抵挡空化应力的冲击作用,进入上升期阶段时反而降低了基体材料的抗空蚀能力。
[Abstract]:Energy is the most important factor to determine the sustainable development of the current society, and the use of nuclear energy can help alleviate the current energy predicament. Liquid lead-bismuth eutectic alloy (LBE) is widely used as a nuclear power accelerator because of its strong radiation resistance, good thermal conductivity and safety, and excellent subproperties. The subcritical drive system ADS) and the lead cooled fast reactor coolant LFRN, but the flowing liquid lead bismuth will cause serious erosion and cavitation corrosion on the pipes, storage tanks and impeller materials of the main pump. The welded joints of structural steel belong to cast structure, and the coarse grains inside them and the residual stress after welding will further aggravate the cavitation corrosion in liquid LBE. 316L stainless steel is austenitic stainless steel. Having excellent comprehensive mechanical properties is the most widely used structural material in nuclear reactors. Therefore, studying its cavitation corrosion resistance is helpful to improve the corrosion resistance of nuclear reactor overflowing components and provide theoretical basis for its service life. A cavitation corrosion experimental device was designed by our team, in which the power of ultrasonic horn is 3 kwk, the frequency is 19.2 kHz, and the amplitude is 50 渭 m. The cavitation corrosion behavior of welded joints with different heat input, pre-corroded joints and welded joints of different welding materials was studied by using the cavitation corrosion device. The cavitation corrosion of 316L welded joint and its base metal under different heat input was carried out for 80 h. The results showed that the relationship between cavitation corrosion resistance of 316L welded joint and welding heat input was the greater the welding heat input was. The cavitation corrosion resistance of welded joints is mainly affected by austenite grain size. When the welding heat input increases, the austenite grains in weld zone grow up, and the cavitation corrosion resistance of welded joints is poor. The cavitation corrosion resistance of the base metal is generally superior to that of the weld metal. The base metal is a forged structure, while the weld metal is a cast structure, and its solidification mode is F-A: ferrite austenite crystallization. When worm-like ferrite and coarse austenitic grain .316L welded joints are formed inside the weld, when cavitation corrosion is carried out in liquid LBE at 550 鈩，

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