论文本课题针对雁荡山特大桥的14MnNbq母材的对接、角接接头焊接，采用埋弧焊和CO2气体保护焊进行焊接试验。试验表明：Φ4-5mm埋弧焊时焊接电流550-700A，电压30V左右，焊速400mm/min左右；Φ1.2mmCO2气体保护焊时焊接电流200-300A，电压在28-34V，焊速400mm/min，能获得成形美观、无焊接缺陷的焊接接头。金相试验结果表明：14MnNbq母材金相组织为铁素体加珠光体。焊缝的金相组织为粗大的柱状晶，层间组织经过后道焊的再次热处理，晶粒细化。并且埋弧焊采用的线能量比气体保护焊的线能量大，晶粒要比气保焊的晶粒粗大。力学性能表明：14MnNbq母材焊接接头的平均显微硬度约为220HV，母材的硬度较低，HAZ的硬度相对较高。在焊接接头中，第一道焊一般采用小的热输入，硬度值相对较小，而随着焊接热输入的增加，后面焊道的硬度值也在增加。7246
关键词  14MnNbq  埋弧焊  CO2气体保护焊   焊接接头  金相组织  硬度
毕业设计说明书（论文）外文摘要
Title         Analysis of bridge steel welded joints
Abstract
The research was done for 14MnNbq, which is the parent metal of the Santak bridge with submerged arc welding and CO2 gas shielded welding. Bridge steel 14MnNbq joint forms are butt joint and corner joint. The experiment stated : diameter 4-5mm the submerged arc welding: welding current is in the range of 550-700A,voltage about 30V,welding speed is controlled in 400mm/min. Diameter 1-2mm the CO2 gas shielded welding: welding current is in the range of 200-300A,voltage is 28-34V ,speed is controlled in 400mm/min to get beautiful forming and no welding defect joints. Microstructure results: the microstructure of 14MnNbq is ferrite and pearlite. The microstructure of weld is coarse columnar crystal. Through heat treatment again, the grain of interlayer tissue was refined. The grain of submerged arc welding is coarser than CO2 gas shielded welding. The mechanical properties indicated: the average hardness of parent metal 14MnNbq welding joints is about 220HV.The hardness of 14MnNbq is lower, but HAZ is relatively higher. In welded joints, the first welding generally use small heat input, so the hardness value is relatively low. With the welding heat input increasing, the hardness value of following weldings are on the increase.
Keywords  14MnNbq  Submerged arc welding   CO2 gas shielded welding  Welded joints  Microstructure  Hardness
目 录
1  引言（或绪论）    1
1.1  我国桥梁钢的主要发展历程及现状    1
1.2  本课题研究的主要内容    2
1.3  本课题研究的意义    3
2  雁荡山特大桥桥梁钢焊接接头组织分析    4
2.1  雁荡山特大桥2-90米叠合拱钢梁中的主拱    4
2.2  雁荡山特大桥2-90米叠合拱钢梁中的箱体T型角接    8
2.3  雁荡山特大桥2-90米叠合拱钢梁中的底板对接    11
2.4  雁荡山特大桥桥梁钢中的钢板对接部件1    13
2.5  雁荡山特大桥桥梁钢中的钢板对接部件2    15
3  雁荡山特大桥2-90米叠合拱钢梁底板对接部件力学性能分析    19
3.1  实验设备及实验方法    19
3.2  实验结果及其分析    19
4  分析讨论    21
4.1  焊接方法对焊接接头组织的影响    21
4.2焊接热输入对焊接接头组织的影响    21
结论    23
致谢    24
参考文献    25
1  引言（或绪论） 桥梁钢焊接接头组织分析+文献综述:http://www.751com.cn/cailiao/lunwen_5118.html