不同焊接方法的纯镍直缝焊管焊接接头组织和性能研究

发布时间：2018-06-30 05:19

本文选题：纯镍直缝焊管 + PAW焊接　；参考：《兰州理工大学》2017年硕士论文

【摘要】：镍及镍合金具有较高的强度、塑性以及可锻性,在冷、热状态下均具有良好的机械加工性能,因此可以通过各种冷热加工制成板材、箔材、线棒材以及管状等各类产品。镍及镍合金管常应用于制碱、氯碱化工、有机氯化物和食品加工等行业,尤其在各种耐强碱的设备中的应用广泛。等离子弧焊(PAW)能量密度高、穿透力强,能够实现板厚6mm以下镍及镍合金单面焊双面成形,用于镍及镍合金管的焊接具有较大的优势;钨极氩弧焊(TIG)可靠性高、易操作、电弧稳定,具有良好的覆盖能力,焊缝成形美观,性能良好,在镍及镍合金的焊接方面也得到了大量应用。本课题分别采用PAW焊以及PAW+TIG焊两种不同的焊接方法,不添加填充材料,实现尺寸规格为Ф112mm×3.5mm×6500mm纯镍直缝焊管的焊接,对获得的焊接接头组织和性能进行对比分析和研究。从纯镍直缝焊管接头宏观形貌分析可知,两种焊接方法均能够实现板厚为3.5mm纯镍直缝焊管单面焊双面成形,与此同时,PAW+TIG焊能够有效避免PAW焊接接头咬边、凹陷、气孔等缺陷,获得了成形均匀、美观的鱼鳞纹状焊缝表面形貌;焊接接头显微组织观察结果表明,纯镍母材为均匀细小的单相奥氏体等轴晶组织,平均晶粒尺寸为47.32μm,PAW焊接接头热影响区为等轴晶组织,平均晶粒尺寸为96.43μm,焊缝区域形成了柱状晶组织,平均晶粒尺寸为463.57μm;PAW+TIG焊接接头各区域由于受到TIG电弧的二次加热作用,较PAW接头组织出现长大现象,热影响区为等轴晶组织,平均晶粒尺寸为103.75μm,焊缝区域形成了粗大的柱状晶组织,平均晶粒尺寸为547.32μm;焊接接头XRD物相分析表明,两种焊接方法所获得的焊缝中物相组成与母材相同,基体均为奥氏体组织;焊接接头力学性能测试结果表明,PAW+TIG接头抗拉强度达到母材的85.60%,冲击功为母材的61.58%,较PAW接头力学性能虽有所降低,但均能满足镍管接头力学性能要求,均为韧性断裂;采用盲孔法测量镍管PAW焊接接头以及PAW+TIG焊接接头残余应力,结果表明:由于TIG电弧对焊接接头的二次加热作用对焊缝具有重熔和热处理作用,与PAW焊相比较,PAW+TIG焊可以显著降低镍管焊缝的轴向残余应力σ_x以及周向残余应力σ_y。室温浸泡试验与电化学试验结果均表明,纯镍母材、镍管PAW焊缝以及镍管PAW+TIG焊缝在不同腐蚀溶液中耐蚀性均呈现相同的变化趋势,但耐蚀性由强到弱顺序为:母材,PAW+TIG焊缝,PAW焊缝。综合可见,PAW+TIG焊满足了镍管接头力学性能要求的同时,有效避免了接头咬边、气孔等缺陷,获得了成形均匀、美观的鱼鳞纹状焊缝表面形貌,成材率高,生产成本低,显著降低了镍管焊接接头的残余应力以及在腐蚀溶液中较PAW焊缝具有更好的耐蚀性,是纯镍N6直缝焊管焊接的理想方法。
[Abstract]:Nickel and nickel alloys have high strength, plasticity and forgability, and have good mechanical properties in cold and hot state, so they can be made into sheet, foil, wire bar and tube by various kinds of cold and hot processing. Nickel and nickel alloy tubes are widely used in alkali making, chlor-alkali chemical industry, organic chlorides and food processing, especially in various equipment with strong alkali resistance. Plasma arc welding (paw) has the advantages of high energy density and strong penetration, it can realize the forming of nickel and nickel alloy single side welding under plate thickness 6mm, and it has great advantages in the welding of nickel and nickel alloy tubes, and tungsten electrode argon arc welding (TIG) has high reliability and is easy to operate. The arc is stable, has good covering ability, the weld seam is beautiful, the performance is good, also has obtained the massive application in the nickel and the nickel alloy welding. In this paper, two different welding methods, PAW welding and PAW TIG welding, are used to realize the welding of 112mm 脳 3.5mm 脳 6500mm pure nickel straight seam welded pipe without adding filling material. The microstructure and properties of the welded joints obtained are compared and studied. From the macroscopic morphology analysis of straight welded pipe joints of pure nickel, it can be seen that both of the two welding methods can realize single side welding and double side forming of straight nickel straight welded pipe with plate thickness, and at the same time, it can effectively avoid defects such as edge bite, depression, porosity and so on. The microstructure of the welded joint shows that the pure nickel base metal is a uniform and fine single phase austenite equiaxed structure. The average grain size is 47.32 渭 m and the average grain size is 96.43 渭 m. The columnar grain structure is formed in the weld zone, and the average grain size is 463.57 渭 m. Compared with the PAW joints, the microstructure of the joints grew up, the HAZ was equiaxed crystal structure, the average grain size was 103.75 渭 m, and the coarse columnar grain structure was formed in the weld zone, the average grain size was 547.32 渭 m. The phase composition of the weld obtained by the two welding methods is the same as that of the base metal, and the matrix is austenitic structure. The test results of mechanical properties of welded joints show that the tensile strength of the welded joints reaches 85.60 of the base metal and the impact energy of the joints is 61.58, which is lower than that of the PAW joints, but all of them can meet the requirements of the mechanical properties of the nickel pipe joints and are all ductile fracture. The residual stresses of nickel tube PAW welded joints and PAW TIG welded joints were measured by blind hole method. The results show that the secondary heating of the welded joints by TIG arc has remelting and heat treatment effects on the weld. Compared with PAW welding, PAW TIG welding can significantly reduce the axial residual stress 蟽 x and circumferential residual stress 蟽 Y of nickel pipe weld. The results of immersion test at room temperature and electrochemical test showed that the corrosion resistance of pure nickel base metal, nickel tube PAW weld and nickel tube PAW TIG weld showed the same trend in different corrosion solutions. However, the order of corrosion resistance from strong to weak is as follows: the base metal is PAW TIG weld and PAW weld. Comprehensive visible PAW TIG welding can meet the requirements of mechanical properties of nickel pipe joints, effectively avoid defects such as edge cutting and porosity of joints, obtain uniform and beautiful surface morphology of fish-scale welds, high yield of finished materials and low production cost. The residual stress of the welded joint of nickel tube is significantly reduced and the corrosion resistance of the welded joint is better than that of PAW weld in corrosion solution. It is an ideal method for welding pure nickel N6 straight seam welded pipe.
【学位授予单位】：兰州理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG407

【参考文献】