不锈钢薄板冷金属过渡焊焊接（CMT）工艺研究

发布时间：2018-04-02 02:20

本文选题：冷金属过渡焊（CMT）　切入点：不锈钢薄板　出处：《吉林大学》2015年硕士论文

【摘要】：不锈钢轨道客车车体搭接焊缝，采用电阻点焊工艺焊接，为了达到整个车体的密封性，还要对焊点间缝隙进行密封处理。传统工艺采用熔化极活性气体保护焊（MetalActive-gas Arc Welding，简称MAG焊）焊接这一纵缝，但焊缝存在过热严重、焊接缺陷多需经常补焊的问题。本文针对搭接焊缝焊接工艺上存在的问题，提出利用冷金属过渡焊接技术（Cold Metal Transfer，简称CMT）代替传统的MAG焊。CMT焊接技术是一种改进型熔化极气体保护焊，与传统的熔化极气体保护焊相比具有热输入低、无飞溅、强搭桥能力的特点。本文以直径Φ=1mmER308L不锈钢焊丝为填充材料，以厚度1.5mm的A304奥氏体不锈钢薄板作为母材，主要研究CMT焊不锈钢薄板焊接参数优化，通过光学显微镜、扫描电子显微镜（SEM）和万能拉伸试验机对不锈钢薄板CMT焊接接头微观组织和性能进行了分析，并研究了焊接送丝速度、弧长修正系数、焊接速度对不锈钢薄板CMT焊接头成型和组织影响。不锈钢薄板CMT焊缝连续平整，没有明显焊接缺陷，整个接头的焊接变形较小。不锈钢CMT焊缝接头组织致密，焊缝区主要由黑色树枝晶的铁素体组织，和白色的奥氏体组织组成。热影响区较窄，组织为粗大的奥氏体组织，有晶粒粗化现象。试验表明，CMT焊不锈钢薄板搭接焊缝取得了较好的成型效果。接头性能方面，不锈钢CMT焊接接头的显微硬度分布不均匀，焊缝硬度低于母材硬度，而HAZ（Heat-affected Zone)硬度最低。拉伸试验结果说明，不锈钢CMT焊接接头的抗拉强度略低于母材的抗拉强度，接头的断裂模式主要为结合面断裂。不锈钢耐腐蚀实验的结果表明，不锈钢CMT焊接接头的腐蚀率大于母材。随着焊接送丝速度的增加，焊缝在宏观形貌上焊道变得愈发宽大，焊缝周围色差范围愈大。焊缝的熔深、熔宽逐渐增大，深宽比有增加的趋势。热影响区范围增大。随着弧长修正系数的增加，焊缝在宏观形貌上焊道变得略微宽大，焊缝周围色差范围愈大。焊缝的熔深、熔宽逐渐增大，深宽比有增加的趋势。热影响区范围增大。随着焊接速度的增加，焊缝在宏观形貌上焊道变的愈发细小，焊缝周围色差范围愈小。焊缝的熔深、熔宽逐渐减小，深宽比有减小的趋势。热影响区范围增小。不锈钢CMT焊接接头疲劳试验表明，疲劳断口主要包括了裂纹源、裂纹扩展区、瞬时断裂区。裂纹扩展区存在疲劳裂纹痕迹、瞬时断裂区存在大量的韧窝。疲劳强度为315.84MPa，约为母材抗拉强度的50%左右。冷金属过渡焊接技术（CMT）代替传统MAG焊可以得到形貌和性能俱佳的不锈钢薄板焊接接头。通过大量试验工作，最终得到适用于本文工艺条件下不锈钢薄板CMT焊接工艺的最优参数：送丝速度为8m/min.、弧长修正系数为5%、焊接速度为540mm/min.。
[Abstract]:In order to achieve the sealing of the whole car body, the welding seam of the car body of stainless steel rail car is welded by resistance spot welding. And seal the gap between the joints. The traditional process is to weld the longitudinal seam in MetalActive-gas Arc welding (MAG welding), but the weld is overheated. Welding defects often need to be repaired. This paper aims at the problems existing in the welding process of lap weld. In this paper, it is proposed that the cold metal transition welding technology (Metal) is an improved type of gas shielded gas welding, which has lower heat input and no spatter than the conventional cold metal transfer welding technology, instead of the traditional MAG welding .CMT welding technology is a kind of improved gas shielded welding. The characteristic of having a strong ability to bypass. In this paper, with diameter 桅 1 mm ER308L stainless steel wire as filler material, A304 austenitic stainless steel sheet with thickness 1.5mm as base material, the welding parameters optimization of CMT welding stainless steel sheet is studied, and the welding parameters of A304 austenitic stainless steel sheet with thickness 1.5mm are studied by optical microscope. Scanning electron microscope (SEM) and universal tensile tester were used to analyze the microstructure and properties of CMT welded joint of stainless steel sheet, and the wire feeding speed and arc length correction coefficient were studied. Effect of welding speed on forming and microstructure of CMT welded joint of stainless steel sheet. The CMT weld of stainless steel sheet is continuous leveling, without obvious welding defects, and the welding deformation of the whole joint is relatively small. The microstructure of the stainless steel CMT weld joint is compact, and the weld zone is mainly composed of ferrite with black dendrite. And white austenite structure. The heat affected zone is narrow, the microstructure is coarse austenitic structure, and there is grain coarsening. The test shows that the welding seam of stainless steel sheet welded by CMT welding has better forming effect. The distribution of microhardness of stainless steel CMT welded joint is uneven, the hardness of weld is lower than that of base metal, while the hardness of HAZ(Heat-affected Zone is the lowest. The tensile test results show that the tensile strength of stainless steel CMT welded joint is slightly lower than that of base metal. The corrosion resistance of stainless steel CMT welded joint is higher than that of base metal. With the increase of wire feeding speed, the weld seam becomes wider and wider in macroscopic morphology, and the wider the range of color difference around the weld is, the deeper the weld seam is, and the wider the weld width is. With the increase of the arc length correction coefficient, the weld seam becomes slightly wider in macroscopic morphology, and the wider the range of color difference around the weld, the deeper the weld, and the wider the weld width. The ratio of depth to width is increasing. The heat affected zone increases. With the increase of welding speed, the weld flux becomes smaller and smaller, and the range of color difference around the weld is smaller. The weld penetration depth and the weld width decrease gradually. The aspect ratio tends to decrease and the range of heat affected zone increases. The fatigue test of stainless steel CMT welded joint shows that the fatigue fracture surface mainly includes the crack source, crack propagation zone, instantaneous fracture zone, and the fatigue crack trace exists in the crack propagation zone. There are a lot of dimples in the instantaneous fracture zone, and the fatigue strength is 315.84 MPA, which is about 50% of the tensile strength of the base metal. Instead of conventional MAG welding, the cold metal transition welding technique can obtain stainless steel sheet welded joints with good morphology and properties. Finally, the optimal parameters for CMT welding of stainless steel sheet are obtained: wire feeding speed is 8 m / min., arc length correction coefficient is 5, welding speed is 540 mm / min.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG457.11

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