高氮奥氏体不锈钢光纤激光焊接工艺试验研究

发布时间：2018-01-18 12:16

本文关键词：高氮奥氏体不锈钢光纤激光焊接工艺试验研究　出处：《南京理工大学》2015年硕士论文　论文类型：学位论文

【摘要】：激光焊能量密度高,焊接速度快,焊缝深宽比大、热影响区窄、焊接热变形小,且无需真空。光纤激光焊接更是具有柔性化的光纤传输优势,正成为研究和应用的热点。高氮钢利用氮元素替代镍,在室温甚至低温下获得单相奥氏体组织,具有高强、高韧、高耐蚀性的特点。针对高氮钢在普通熔焊过程中易产生的氮损失等焊接问题,本文对12mm厚的高氮奥氏体不锈钢进行了光纤激光焊接工艺试验的研究,成果如下：探究了影响高氮钢焊接质量的主要工艺参数,发现激光功率是最主要的影响因素,决定了焊缝的熔透状态；其次是焊接速度,当焊接速度过快时,焊缝表面产生焊瘤缺陷,且内部气孔严重；离焦量是第三大影响因素,直接决定了热影响区的宽窄；最后是保护气的种类,当使用N：保护时,焊接表面鱼鳞纹形貌明显,焊缝内部气孔有所改善。通过单因素控制变量的试验方法,总结出最佳焊接工艺参数：激光功率8kW,离焦量+2mm,焊接速度0.84m/min,保护气为20L/min的N2。此时焊缝氮含量高达0.556%,约达母材的90%；在此基础上,适当进行激光束的倾斜,能更进一步增加焊缝中的氮含量,使氮含量增加至0.564%,但增加量微小。根据激光深熔焊的机理,探究了高氮钢厚板光纤激光焊接过程中的气孔问题,分析了其产生机理、模型特征以及影响因素,在保证小孔熔透的前提下,选择较小的激光功率与焊接速度,改变激光束的倾角,前倾10。-30。,选择N2保护,能有效减少焊缝内部气孔。对最佳工艺参数下的焊接接头组织与性能进行研究,结果表明高氮钢光纤激光焊焊缝组织为树枝晶状的单相奥氏体,晶粒沿着极大的温度梯度方向垂直向焊缝中心生长,方向性显著。焊缝晶粒尺寸相当小,基本没有氮化物析出。焊接热影响区非常窄,约为50μm。焊缝硬度较母材有所降低,约为320HV；热影响区硬度高于焊缝,但略低于母材。焊接接头发生韧性断裂,抗拉强度略低于母材,约为1064MPa。
[Abstract]:Laser welding has high energy density, fast welding speed, large depth to width ratio, narrow heat affected zone, small thermal deformation and no vacuum. Fiber laser welding has the advantage of flexible optical fiber transmission. High nitrogen steel replaces nickel with nitrogen element to obtain single-phase austenitic structure at room temperature or even at low temperature, which has high strength and toughness. The characteristics of high corrosion resistance. In view of the welding problems such as loss of nitrogen and so on in the common welding process of high nitrogen steel, the experiment of optical fiber laser welding of 12mm thick high nitrogen austenitic stainless steel was carried out in this paper. The results are as follows: the main technological parameters which affect the welding quality of high nitrogen steel are investigated. It is found that laser power is the most important factor, which determines the penetration status of the weld. The second is welding speed, when the welding speed is too fast, the weld surface has weld defects, and the internal blowhole is serious. The defocus is the third most important factor, which directly determines the width of the heat affected zone. Finally, the types of protective gas, when the use of N: protection, the surface of the weld surface, the shape of the obvious, weld internal porosity improved, through the single factor control variables of the test method. The optimum welding parameters are as follows: laser power 8kW, defocus 2mm, welding speed 0.84m / min. The nitrogen content of weld is as high as 0.556, about 90% of the base metal. On this basis, the proper tilt of the laser beam can further increase the nitrogen content in the weld, and increase the nitrogen content to 0.5644.According to the mechanism of laser deep penetration welding, the increase is small. This paper probes into the blowhole problem in the process of laser welding of high nitrogen steel thick plate fiber, analyzes its mechanism, model characteristics and influencing factors, and chooses the smaller laser power and welding speed under the premise of ensuring the penetration of the small hole. Changing the inclination of laser beam, tilting forward 10.-30.and selecting N2 protection can effectively reduce the internal porosity of weld seam. The microstructure and properties of welded joints under the optimum process parameters are studied. The results show that the microstructure of high nitrogen steel fiber laser welding weld is dendritic single-phase austenite, the grain grows vertically along the maximum temperature gradient to the center of the weld, and the directivity is obvious. The grain size of the weld is quite small. There is no nitride precipitation. The HAZ is very narrow, about 50 渭 m. The hardness of weld is lower than that of base metal (about 320HVV). The hardness of the HAZ is higher than that of the weld, but slightly lower than that of the base metal. The toughness fracture and tensile strength of the welded joint are slightly lower than that of the base metal, about 1064MPa.
【学位授予单位】：南京理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG457.11;TN249

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