异种钢TIG-MIG复合窄间隙双层气体保护焊行为研究

发布时间：2018-06-18 16:11

本文选题：异种钢焊接 + TIG-MIG复合焊　；参考：《太原理工大学》2017年硕士论文

【摘要】：304奥氏体不锈钢以其良好的使用性能被广泛应用于生产和生活中,全球镍资源的紧张使其在使用上受到限制。443铁素体不锈钢含有极少量镍,被认为是奥氏体不锈钢的良好替代品。铁素体奥氏体异种不锈钢金属的连接将发挥两种不锈钢金属的各自优势,实现资源的充分利用。TIG-MIG复合焊是一种高效低热输入的新型焊接方法,且焊接成本低,不同于传统电弧焊,TIG-MIG复合焊的电弧形态与熔滴过渡方式及其产生机制尚不明确。根据相关研究,在焊接过程中,双层保护气氛对于电弧稳定性、熔滴过渡以及焊接质量等具有促进作用。氮是一种强奥氏体化形成元素,因此在奥氏体或者双相钢焊接中在保护气中添加一定量的N2可以实现氮向被焊金属的过渡,不仅可以提高焊缝奥氏体相含量,同时对铁素体热影响区的冲击韧性的提高具有促进作用。本文首先借助高速摄像系统和电信号采集系统对焊接电流、电压、钨极-试板高度、钨极-焊丝距离和保护气氛等不同焊接参数下的TIG-MIG复合焊的电弧形态与熔滴过渡方式进行捕捉,并对其导电通道以及熔滴受力进行分析。然后根据焊接稳定性的对比分析,实施不同保护气氛和焊接速度下的异种钢不开坡口对接实验,对其接头形貌、显微组织和力学性能进行分析。研究结果表明,随着焊接电流增大,熔滴过渡周期和尺寸减小,260A电流时出现“流水状”喷涌过渡;电压增大,电弧体积和亮度增加;钨极-试板高度降低,熔滴过渡稳定性差,双电弧耦合性降低,钨极-试板高度增加后熔滴过渡模式表现为混合过渡,熔滴指向性差,钨极-焊丝距离增大后,焊接电弧为单电弧,熔滴过渡频率缓慢;Ar+N2双层保护气氛下,电弧收缩明显。双电弧状态下,焊接电流经过焊丝端一分为二流回焊接电源负极;单电弧时,电流流经熔融焊丝端与母材接触位置后穿过GTA流向钨极,返回焊接电源负极。与传统电弧焊相比,弧根作用在熔滴上的面积增加,并增强其电磁收缩力;双层保护气氛提高等离子流力推动熔化的金属向焊接熔池过渡。滴状细颗粒过渡更有利于促进TIG-MIG复合窄间隙焊异种钢焊接获得良好的焊接接头形貌。接头形貌表明,当试板间隙为1.2mm时,正面与背面焊缝成型差。继续增大试板间隙发现,若试板为1.5mm和1.8mm,焊缝接头形貌均良好。双层保护气氛促进焊接过程中熔池向试板间隙下方流动,促进焊缝成型。双层保护气氛下焊接接头获得更小的焊缝熔宽、余高和更宽的焊缝中部宽度。接头显微组织表明,304热影响区组织未发生明显长大,443热影响区组织晶粒尺寸粗化严重;纯氩气保护气氛下,焊缝组织为奥氏体+骨骼状δ铁素体构成的的双相组织,双层保护气氛下,焊缝组织为奥氏体+蠕虫状δ铁素体双相组织,且奥氏体相比例增加,443热影响区组织晶粒尺寸有一定降低。硬度测试表明,与母材硬度相比,443热影响区显微硬度下降,304一侧变化不大;双层保护气氛下焊缝区硬度下降,443热影响区显微硬度较纯氩单层气氛下略有提高。焊接接头的拉伸试样断裂位置基本位于443铁素体不锈钢母材上。双层保护气氛下所获得的焊接接头焊缝区和443热影响区具有更高的冲击吸收功,304一侧热影响区变化不大。
[Abstract]:304 austenitic stainless steel is widely used in production and life for its good performance. The tension in the global nickel resources makes it restricted to the use of.443 ferritic stainless steel with very small amounts of nickel. It is considered a good substitute for austenitic stainless steel. The connection of Ferritic Austenitic stainless steel metal will play two kinds of rust. The advantages of steel and metal and the full use of resources to make full use of.TIG-MIG composite welding is a new type of welding method with high efficiency and low heat input, and the cost of welding is low. Different from the traditional arc welding, the arc shape and droplet transition mode and its production mechanism of TIG-MIG composite welding are not yet clear. The atmosphere has a promoting effect on arc stability, droplet transition and welding quality. Nitrogen is a strong austenitizing element, so adding a certain amount of N2 in austenite or double phase steel welding can realize the transition of nitrogen to the welded metal. It can not only raise the content of austenite phase in the weld, but also heat the ferrite. The impact toughness of the affected zone is promoted. In this paper, the arc shape and droplet transition mode of TIG-MIG composite welding under different welding parameters such as welding current, voltage, tungsten pole plate height, tungsten electrode wire distance and protective atmosphere are captured with the help of high speed camera system and electrical signal acquisition system. According to the analysis of welding stability, according to the comparison and analysis of the welding stability, the joint experiment of the dissimilar steel with different protective atmosphere and welding speed is carried out. The joint morphology, microstructure and mechanical properties of the joint are analyzed. The results show that the transition period and size of the droplet decrease with the increase of the welding current, 260A The current appears "flowing water" spout transition, the voltage increases, the volume and brightness of the arc increase, the height of the tungsten pole plate decreases, the stability of the droplet transition is poor, the coupling of the double arc is reduced, and the transition mode of the droplet is mixed, the directivity of the droplet is poor, and the welding arc is the single electric arc after the tungsten electrode welding wire is increased. Arc, the transition frequency of droplet is slow; under the double arc condition, the arc contraction is obvious. Under the state of double arc, the welding current passes through the wire end of the welding wire to the negative electrode of the two flow back welding power. In the single arc, the current flows through the contact position of the molten wire end and the parent material to the tungsten pole and return to the anode of the welding power. Compared with the traditional arc welding, the arc is compared with the traditional arc welding. The area of the root effect on the droplet increases and the electromagnetic contraction force is enhanced, and the double-layer protective atmosphere increases the plasma flow force to promote the transition of molten metal to the weld pool. The transition of droplet fine particles is more conducive to the good welding joint appearance of the TIG-MIG composite narrow gap welded steel welding. The joint morphology shows that the gap of the plate is 1.. When 2mm, the front and back weld formation is poor. Continue to increase the gap between the test plate and find that if the test plate is 1.5mm and 1.8mm, the weld joint morphology is good. The double-layer protective atmosphere promotes the flow of the weld pool to the bottom gap in the welding process, and promotes the weld formation. The weld joint under double protective atmosphere obtains smaller weld width, residual height and wider welding. The microstructure of the joint shows that the microstructure of the 304 heat affected zone is not obviously grown, and the microstructure of the 443 heat affected zone is coarsely coarsely coarse-grained. Under the pure argon atmosphere, the weld structure is composed of austenite and skeletal delta ferrite, and the weld structure is austenite + vermicular delta ferrite double phase under the double protective atmosphere. Microstructure, and the proportion of austenite increased, the grain size of the 443 heat affected zone decreased to a certain extent. The hardness test showed that compared with the hardness of the parent material, the microhardness of the 443 heat affected zone decreased and the 304 side changed little. The hardness of the weld zone decreased in the double protective atmosphere, and the microhardness of the 443 heat affected zone was slightly higher than that under the pure argon monolayer atmosphere. The fracture position of the tensile specimen at the head is basically on the 443 ferrite stainless steel parent material. The weld joint zone and the 443 heat affected zone obtained in the double layer protection atmosphere have higher impact absorption work, and the 304 side heat affected zone has little change.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG457.11

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