摘 要

本文主要阐述了正交异性钢桥U肋与面板焊接接头处易出现各种焊接缺陷，接头性能差，易出现疲劳裂纹，导致桥梁寿命降低的问题。

论文主要研究了在合适的焊接工艺参数下单面焊接，双面焊接，单面焊双面成型三种焊接方法的焊接接头，进行金相观察，得到焊接接头不同位置的金相照片，通过观察金相照片中的组织结构，晶粒大小形态等，得到焊接接头组织性能，并对三种焊接方法，工艺及过程进行了对比与研究。

研究结果表明：单面焊焊接热输入较小，焊接速度快，效率较高。焊接接头在U肋上达到75%熔深，焊缝成型良好，呈凸圆弧状，整体平滑美观。在焊根处存在未熔合缺陷，在U肋上的热影响区较宽，在底板上的热影响区较窄。焊缝整体组织分布均匀，晶粒生长大小及方向合理。在焊趾部位，组织分布不均匀。在焊根处存在未熔合缺陷。单面焊双面成型焊接焊接电流较大，热输入较大。在焊接过程中需要使用软衬垫、金属衬垫、衬垫支撑工具等，焊接方法的过程较为复杂，焊接效率较低。焊接接头实现了U肋的全熔透焊接，焊缝成型良好，焊缝两侧都呈凹圆弧状，晶粒以汇聚式从焊缝两侧向焊缝中心和焊缝表面生长，晶粒生长方向合理。接头的热影响区较宽，接头无明显焊接缺陷。双面焊焊接方法焊接电流较小，热输入较小，内部焊接与外部焊接达到了U肋的全熔透焊接。焊缝成型美观，内部焊焊缝为凸圆弧状，外部焊焊缝为凹圆弧状。焊接接头中组织分布均匀，晶粒较小，内部与外部焊接焊缝中晶粒都以汇聚式从焊缝两侧向焊缝中心和焊缝表面生长，热影响区窄。

本文的特色：通过三种焊接接头的组织研究来比较焊接接头的性能区别，得到了三种焊接方法的差别与特点。

关键词：焊接方法；U肋；全熔透；组织性能

Abstract

This paper mainly expounds the problems that the welded joints between U-ribs and panels of orthotropic steel bridges are prone to various welding defects, poor joint performance and fatigue cracks, which lead to the reduction of bridge life.

This paper mainly studies the welded joint of three welding methods: single-sided welding, double-sided welding and single-sided welding and double-sided forming under appropriate welding process parameters. Metallographic observation is carried out to obtain metallographic photos of different positions of the welded joint. Microstructure and grain size morphology in the metallographic photos are observed to obtain the microstructure and properties of the welded joint. Three welding methods, processes and processes are compared and studied.

The results show that single-sided welding has lower heat input, faster welding speed and higher efficiency. The welded joint reaches 75% penetration depth on the U-rib, and the weld seam is well formed, with convex arc shape, smooth and beautiful overall. Incomplete fusion defects exist at the weld root, the heat affected zone on the U rib is wider, and the heat affected zone on the bottom plate is narrower. The overall structure of the weld is evenly distributed, and the grain growth size and direction are reasonable. At the welding toe, the microstructure is not evenly distributed. Incomplete fusion defect exists at the weld root. Single-sided welding and double-sided forming welding have higher welding current and heat input. In the welding process, soft gaskets, metal gaskets, gasket support tools, etc. are required. The welding process is relatively complicated and the welding efficiency is relatively low. The welded joint realizes full penetration welding of U-rib, the weld is well formed, both sides of the weld are concave arc-shaped, crystal grains grow from both sides of the weld to the center of the weld and the surface of the weld in a convergent manner, and the growth direction of crystal grains is reasonable. The heat affected zone of the joint is wide, and the joint has no obvious welding defects. The welding method of double-sided welding has small welding current and heat input, and the internal welding and the external welding reach the full penetration welding of U rib. The weld formation is beautiful, the internal weld is convex arc, and the external weld is concave arc. The microstructure in the welded joint is evenly distributed and the grains are small. The grains in the internal and external welded seams grow from both sides of the weld seam to the center of the weld seam and the surface of the weld seam in a convergent manner, and the heat affected zone is narrow.

The characteristics of this paper: through the study of the structure of three kinds of welded joints to compare the performance differences of welded joints, the differences and characteristics of three kinds of welding methods are obtained.

Key words：Welding method; U rib；Full penetration; Organizational performance

目 录

第1章 绪论 1

1.1正交异性钢桥与U肋 1

1.2 U肋焊接发展现状 1

1.3 研究内容及意义 2

1.4 研究的社会影响 2

第2章 钢桥U肋的焊接 3

第3章 焊接接头组织 4

第4章 焊接与金相实验 5

4.1 焊接实验 5

4.1.1 实验材料及设备 5

4.1.2 焊接工艺及参数 6

4.2 金相实验 6

4.2.1 实验材料及设备 6

4.2.2 金相试样制作 6

4.2.3 金相试样的观察 6

第5章 接头组织性能分析 7

5.1 焊接接头的宏观形貌 7

5.2 焊接接头的微观组织 8

5.2.1 母材组织 8

5.2.2 单面焊焊接接头组织 9

5.2.3 单面焊双面成型焊接接头组织 10

5.2.4 双面焊焊接接头组织 12

5.2.5 焊接接头组织性能分析 14

第6章 结论 16

参考文献 17

致谢 18

第1章 绪论

1.1 正交异性钢桥与U肋

近年来， 桥梁交通建设对于经济发展的作用越来越大， 材料科学技术、 焊接工艺技术、 桥梁设计技术以及架设施工技术等也在不断发展进步，大跨径钢桥以其新型性、质量轻、外观美丽、 轻质和跨度大等优势，在世界范围内得到了越来越广泛的使用，发展极其迅速。^[1] 正交异性钢桥面板是用纵横向互相垂直的加劲肋和连同面板盖所组成的共同承受车轮荷载的结构。这种结构由于其刚度在互相垂直的二个方向上有所不同，造成构造上的各向异性。正交异性板板已经成为正交异性钢桥的标准组件，与常规钢筋混凝土甲板相比，他们重量轻，耗材少，载重能力强，安装时间短。因此，正交异性钢桥在钢桥梁建设中得到广泛应用。^[2]

钢桥面板是由面板、纵肋和横助三种薄板件焊接而成，在焊缝交叉处设弧形缺口，其构造细节很复杂。当车辆通过时，轮载在各部件上产生的应力，以及在各部件交叉处产生的局部应力和变形也非常复杂，所以钢桥面板的疲劳问题是设计考虑的重点之一。在日本，甲板到U肋和U肋对底部连接处的这些疲劳裂纹约占正交异性钢桥面疲劳裂纹的58%。这些接头通常是在底板部分角焊缝熔透性焊接。U 肋是钢桥面板中的重要受力构件， 其结构具有封闭、狭窄细长的特点，内部空间狭小，难以实现焊接。因此，U肋与顶板焊接常采用单面焊接的方式。受限于目前的焊接工艺及U 肋工件的特点，这些接头在底板只能实现很低的熔透率，在U肋上往往也只能达到 80%熔透。根据疲劳设计的建议，焊接过程中的技术上的条例和标准是不同的。例如，日本道路协会规定的最低贯入率和美国国家公路运输官员协会分别为75%和80%。^[3]