车用先进超高强度钢板光纤激光焊接接头的显微组织和力学性能的研究

发布时间：2018-01-13 20:01

本文关键词：车用先进超高强度钢板光纤激光焊接接头的显微组织和力学性能的研究　出处：《上海工程技术大学》2015年硕士论文　论文类型：学位论文

【摘要】：节能、环保、安全是当今汽车制造业的三大主题,而汽车轻量化是各大汽车公司实现汽车低油耗、少废气排放的主要措施之一。先进超高强度钢以其抗拉强度高、能量吸收率高和碰撞后不易发生变形等优势,迅速发展成为重要的汽车轻量化材料。目前激光焊接技术作为一种新型的高能、快速、精确的焊接工艺,在汽车工业中的应用越来越广泛。结合激光焊接与先进高强钢以满足汽车对轻量化与安全性的要求已经引起了许多厂家和研究机构的兴趣。本文采用光纤激光器对超高强度钢22Mn B5进行搭接和对接深熔焊的研究。另外,22Mn B5钢分别与车用双相高强钢DP980、DP590和传统高强钢Q235进行了激光拼焊试验。焊后研究了焊接接头接头微观组织形貌和硬度、拉伸、疲劳等性能特点。22Mn B5钢激光搭接研究表明,接头宽度随着焊接速度的增加而减小,当焊接速度增加到一定值时,搭接钢板未能焊透。焊缝微观组织主要为板条马氏体,硬度值比母材稍高,热影响区发生了明显的软化现象。接头剪切强度随着焊接速度的增加而减小,在焊接速度为1.5m/min时具有最大值。断口表面的微观形貌主要为韧窝,这说明断裂过程是以微孔聚集的形式进行的,但从宏观来看其断裂方式依然很“脆”。22Mn B5钢激光对接焊研究表明,焊缝及其邻近的热影响区组织仍然为板条马氏体,接头硬度的分布情况与搭接焊基本一致,热影响区有明显的软化现象。其热影响区可以分成:淬火区、不完全淬火区和回火区。在回火区,马氏体由于回火转变为回火马氏体。当焊接速度增加时,焊缝组织变得更细小,马氏体含量增多,回火区的宽度变窄,焊接接头硬度升高。在垂直于焊缝的负载下,3-5m/min焊接速度的22Mn B5拉伸试样均断在热影响区,塑性较差,断后延伸率仅为2%左右。断口表面的微观形貌为韧窝和解理小平面,还有一些撕裂棱清晰可见,呈现明显的准解理断裂特征。22Mn B5钢的激光拼焊研究表明,异种钢焊接接头的成形良好,无裂纹气孔等缺陷产生。焊接接头最大硬度依然在焊缝,然而焊缝却呈现由低到高增长的两部分,在双相钢和Q235一侧焊缝的硬度明显低于22Mn B5一侧焊缝的硬度。双相钢热影响区与22Mn B5一样存在软化区,且随着钢材等级的增加,软化区区的软化程度也相应增加,由于Q235钢板母材为正火态,所以该钢热影响区不存在软化区。22Mn B5-22Mn B5、22Mn B5-DP980的拉伸试验均断在热影响区,而22Mn B5-DP590、22Mn B5-Q235均断在低强度钢板的母材。在相同试验参数下,22Mn B5母材拥有最高疲劳寿命,22Mn B5-22Mn B5疲劳试样依然断在热影响区,而22Mn B5-DP980的疲劳试样均断在DP980的母材。典型的疲劳断口分为三部分:裂纹萌生区,裂纹扩展区,瞬断区。萌生区往往出现在试样表面,而扩展区会出现疲劳条带和二次裂纹,瞬断区与拉伸断口很相似。
[Abstract]:Energy saving, environmental protection, safety is the three major themes in today's automobile manufacturing industry, and the automotive lightweight is the major car companies realize low fuel consumption, one of the main measures to reduce the exhaust emissions. The advanced ultra high strength steel with high tensile strength, high energy absorption rate and after the collision is not easy to deform and other advantages, the rapid development of become important automotive lightweight materials. At present, the laser welding technology as a new type of high energy, fast, precise welding process, the application in the auto industry is more and more widely in. Combined with laser welding and advanced high strength steel to meet the requirements of automotive lightweight and safety has attracted many manufacturers and research institutions of interest. Study on fiber laser lap and butt welding of ultra high strength steel 22Mn B5 in this paper. In addition, 22Mn and B5 steel respectively car with dual phase high strength steel DP980 were studied by DP590 and conventional high strength steel Q235 Laser welding after welding on the tensile test. The microstructure and hardness of joints, welded joints, fatigue properties of.22Mn steel laser lap B5 research shows that the joint width decreases with the increase of welding speed, when the welding speed increases to a certain value, the plate can not lap welding. The microstructure of the weld is mainly lath martensite, hardness is slightly higher than the parent material, has an obvious softening of heat affected zone. The shear strength of joint decreases with the increase of welding speed, the maximum value in the welding speed is 1.5m/min. The micro morphology of the fracture surface is mainly dimple, it indicated that the rupture process is carried out in the form of microporous gathering from a macro point of view, but the fracture is still "brittle".22Mn B5 steel butt laser welding research shows that the weld heat affected zone and its adjacent tissue is lath martensite, hardness distribution of joint Consistent with the overlap welding heat affected zone has obvious softening phenomenon. The heat affected zone can be divided into: quenching zone, incomplete quenched zone and tempering zone. In the tempering zone, the martensite tempering is tempering martensite. When the welding speed increases, the weld microstructure become finer, more martensite content. Tempering zone width of welded joints, hardness increased. In the direction perpendicular to the weld load, 22Mn B5 specimens of 3-5m/min welding speed were broken in the heat affected zone, poor plasticity, the elongation is only about 2%. The morphology of the fracture surface dimple and cleavage planes, and some clear tear ridge therefore, the laser show quasi cleavage fracture characteristics of.22Mn steel B5 was welded research shows that the forming of dissimilar weld joints, no crack defects such as pores. The maximum hardness of welded joints in the weld seam is still, however, presented by Low to high growth in the two part, one side of the Q235 dual phase steel and the hardness of the weld was significantly lower than that of 22Mn B5 on one side of the hardness of the weld. Dual phase steel heat affected zone and 22Mn B5 as the softening zone, and with the increase of steel grade, softening also increased softening degree only, because of the Q235 steel base metal for normalizing state, so the steel heat affected zone does not exist.22Mn B5-22Mn B5,22Mn tensile softening zone B5-DP980 were broken in the heat affected zone, and the 22Mn B5-DP590,22Mn B5-Q235 parent material are broken in low strength steel. Under the same experimental conditions, 22Mn B5 parent material has the highest fatigue life, 22Mn B5-22Mn B5 is still broken in thermal fatigue specimen the affected area, and fatigue specimens of 22Mn B5-DP980 were broken in base metal DP980. Typical fatigue fracture is divided into three parts: crack initiation, crack propagation and fracture zone. The initiation region often appear in the surface of the sample, and the exhibition will be expanded The fatigue strip and two cracks are present, and the instantaneous fracture zone is similar to the tensile fracture.

【学位授予单位】：上海工程技术大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG456.7

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