【作者】 高超；

【导师】 杨春利；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2009， 硕士

【摘要】 船舶耐压壳体是具有特殊性能的焊接结构,其主要连接方法为焊接。由于窄间隙焊具有热输入量低、生产效率高等诸多技术与经济的优越性,在厚板船用钢焊接中得到广泛应用。船舶制造中通常会遇到横向焊接,在横向焊接中由于熔化金属受重力作用向下流动,使焊缝厚度不均匀。当下塌严重时会在上部形成咬边,下部形成焊瘤。由于旋转电弧焊接方法可以消除上述缺陷,因而被应用在厚板窄间隙横向焊接中。本文以厚板12Ni3CrMoV钢为对象,进行了旋转电弧窄间隙MAG横向焊接工艺的研究,消除了窄间隙横向焊接中的各种缺陷,得到了优质的焊接接头。确定了合适的焊接工艺参数,得到了外观成形良好,内部无缺陷的焊接接头。研究了旋转电弧窄间隙横向焊接中所出现焊接缺陷的特点,分析了其产生原因和消除措施。在窄间隙横向焊接中容易产生下塌和未熔合缺陷。为了消除这些缺陷,一方面需要减少热输入,防止由于热输入过大导致熔池下塌;另一方面,还需要保持一定水平的热输入,以保证足够的侧壁熔深,防止产生层间未熔合。通过旋转电弧焊接工艺可以扩大电弧作用区域,改善焊缝侧壁熔透,实现了在较低水平热输入条件下层间未熔合的消除。采用高速摄像对窄间隙坡口中旋转电弧的熔滴过渡行为和电弧形态进行了观测。结果表明:由于侧壁和熔池表面的影响,旋转过程中弧长变化,引起焊接电流波动,导致熔滴过渡形式发生变化。熔滴过渡形式随着电弧的旋转发生周期性的变化,在一个旋转周期内分别呈现出射流过渡、滴状过渡等不同的熔滴过渡形式,熔滴过渡过程稳定,这对于实现良好的焊缝成形是有利的。研究12Ni3CrMoV钢横向焊接接头的微观组织及力学性能。从焊缝中心向外分四个区,即焊缝区、熔合区、热影响区和母材区。热影响区又分为四个区,即淬火粗晶区、淬火细晶区、不完全淬火区和回火区。由于各区在焊接过程中受焊接热循环影响程度不同,所以呈现出不同的微观组织。焊接接头整体和局部的拉伸结果完全相同,所有接头均断裂在母材区。这表明焊缝和热影响区的强度大于母材,焊接接头的硬度分布也证实了这一点。0℃试验温度下焊缝金属、热影响区和母材的平均冲击功分别为115.4J、212.2J和236J。更多还原

【Abstract】 Pressure shell of ship is the welding structure with special properties which is connected mainly by welding. Because of narrow-gap welding with the technical and economic superiority such as low heat input, high production efficiency, it has been widely used in thick ship steel plate welding. The manufacture of ships often encounters problems in the horizontal welding because the liquid molten metal is sagged by its gravity. It resulted in the uneven weld thickness. When the pool collapses it can cause defects such as undercut, overlap and incomplete fusion. As the rotating arc welding method could eliminate the above-mentioned defects, it has been applied in thick horizontal narrow gap welding. This paper investigates the process of rotating arc horizontal narrow gap welding on 12Ni3CrMoV steel. The defects are eliminated and high-quality welding joints are gained.Through the pre-test and analysis, the appropriate welding parameters have been determined and the shapely and internal non-defective multilayer single pass horizontal joint could be obtained. The characteristic of the defect in the rotating arc horizontal welding is studied. The reason of these defects and the measure to eliminate them is analyzed.In the horizontal narrow gap welding, collapse and incomplete fusion usually appear. In order to eliminate these defects, on the one hand, it needs to reduce the heat input to prevent pool to collapse result from excessive heat input; On the other hand, it need to maintain a certain level of heat input to ensure adequate penetration of the sidewall in order to prevent the inter-layer incomplete fusion. The rotating arc welding process can expand the region to arc and improve the sidewall penetration. It achieved the elimination of non-fusion at a relatively low level heat input conditions.The transitional characteristics of droplets and the shape of rotating arc in narrow gap are observed with the help of high-speed camera. Results show that fluctuation of welding current will appear with the variation of arc length and the external shape of the welding pool, and this will lead to variation of droplet transitional form. The droplet transitional form changes periodically with the rotation of arc. In a rotational cycle, the droplet transitional form presents globular transfer or spray transfer. The process of droplet transfer is stable, which is beneficial to achieve good weld. The joint can be divided into three zones: base material zone, heat affected zone and welding zone. HAZ could be divided into four parts: coarse-grained HAZ, fine-grained HAZ, incomplete normalized zone and tempering zone. Different zone is characterized by different microstructure because of the affected level by the welding thermal circle. The mechanical properties of the rotating arc horizontal narrow gap welds are studied. The TSE of both integral and local joints is equal to 100%. All the joints are fractured in the BM. It indicates that the tensile properties of WZ and HAZ are larger than that of BM. This can be improved by the result of the Vickers hardness distribution of the joint. The impact toughness in WZ, HAZ and BM at 0℃is equal to 115.4, 212.2 and 236J respectively.更多还原