【作者】 张波；

【导师】 黄坚；

【作者基本信息】 上海交通大学 ， 材料科学与工程， 2016， 硕士

【摘要】 本文主要研究了厚板低合金高强钢Q345D在窄间隙激光填丝焊接中出现的焊接缺陷问题,主要从焊接工艺方面研究了高强钢窄间隙激光焊中存在的未熔合缺陷和气孔缺陷,对窄间隙焊接中缺陷行为进行控制。首先研究不同的离焦量、激光功率、送丝速度和焊接速度对未熔合缺陷的影响规律。研究发现增加离焦量有利于减轻侧壁未熔合缺陷,在本次试验中取+20 mm的离焦量合适;调节激光功率、送丝速度和焊接速度三者的比例有利于消除窄间隙中的未熔合缺陷,当焊接速度为0.42m/min时,激光功率与送丝速度的比值在0.89~1.33时未熔合缺陷得到抑制。其次研究了激光功率、送丝速度和焊接速度对多层焊气孔缺陷的影响规律。多层焊气孔主要出现在每层的底部和中间区域,气孔为工艺性气孔。增加激光功率,降低送丝速度和焊接速度,会导致匙孔前后壁的所受压力失去平衡,小孔失稳,从而导致气孔倾向增加。高功率、低送丝速度和焊接速度,容易形成深熔焊缝,导致气泡逸出路径增加,来不及逸出的气泡留在焊缝中形成气孔。最后通过优化工艺参数对40 mm厚Q345D低合金高强钢进行了多层填丝焊接。填丝焊缝组织主要为铁素体和粒状贝氏体,焊缝中心冲击韧性良好。热影响区主要为马氏体组织,填丝焊的最高硬度值均出现在焊缝热影响区,随着热输入的增加,HAZ最高硬度增加。拉伸试样均断于母材,焊接接头具有良好的力学性能。更多还原

【Abstract】 Weld defects and its control behavior in narrow gap laser wire multilayer welding of thick high strength steel plates are mainly studied.Especially,lack of fusion and porosity in narrow gap laser welding with filler wire have been researched in the way of welding procedure.Control on the defects have been made by the research.Firstly,effects on lack of fusion with different defocus distances,laser power,feeding wire speed and welding speed have been studied.The study turned out increasing the defocus distance can improve the side wall fusion in the narrow gap and +20 mm is suitable for this study.Adjusting the ratio among the laser power,feeding wire speed and welding speed can largely remove the defects about the lack of fusion.When the welding speed is 0.42 m/min,the ratio between laser power and feeding wire speed ranging from 0.89 to 1.33 can eliminate incomplete fusion.Then,how welding parameters such as laser power,feeding wire speed and welding speed affected the porosity in the narrow gap has been studied.Pore in multilayer laser welding mainly appeared in the zone of bottom and center and it belonged to craft blowhole.Balance between the front wall of t and rear wall in the keyhole broke down by high laser power,low feeding speed and welding speed,which made keyhole unstable,causing many pores.What’s more,increased depth of joint made the pore through more distances away from the joint and some of pores stayed in the weld because of long distance.Finally,thick plates with optimized parameters in the narrow gap laser wire multilayer welding have been well welded.The weld with filler wire consists of a mass of acicular ferrite and a few of granular bainite and it shows good impact toughness.The martensite mainly makes of the HAZ of weld.The highest value of hardness is obtained in the HAZ,and the value increases as the heat input increases.The fractures occur on the base metal of tensile test specimens.The weld has fine mechanical properties.更多还原