【作者】 郭晓军；

【导师】 李铸国；

【作者基本信息】 上海交通大学 ， 材料学， 2012， 硕士

【摘要】 本文以船舶轻量化发展中的先进结构材料的应用研究为主要背景,以激光穿透焊接低合金高强钢T型搭接接头为主要研究对象,结合国内外关于激光焊接三明治结构夹芯板的研究现状,系统研究了高功率CO2激光穿透焊接低合金高强钢T型搭接接头时焊接工艺参数对焊缝成形影响的规律,且对T型接头的显微组织和力学性能进行了测试与分析,并重点研究了装配间隙对焊缝成形及焊后接头扭转性能的影响。NbV微合金化10CrNiMnMoV钢的激光焊接工艺参数试验表明,适宜的激光功率与线能量的匹配可以获得成形良好、截面特征尺寸合适的焊缝;增大激光功率有利于增加熔深,且在确定的激光功率下,线能量略高于深熔焊阈值2.4 kJ/cm时会取得合适的结合区宽度,继续增大线能量对提高结合区宽度收效甚微;离焦量对截面形貌尤其是熔深有较大影响,试验根据试样熔深实际需求选取离焦量为负2 mm;此外,面腹板间的配合间隙会影响激光焊接过程中热输入的传递,进而影响熔池的稳定流动,不利于获得稳定的焊缝尺寸。间隙过大时由于熔池的流动失稳并填充面腹板处间隙,造成焊缝表面塌陷与结合区气孔等缺陷。显微组织分析表明,NbV微合金化10CrNiMnMoV钢T型搭接接头焊缝中心为典型的柱状晶,组织为过冷奥氏体转变得到的低碳马氏体,且细小的晶粒组织有利于提高焊缝的强度。热影响区从熔合线起至母材处,依次是粗晶区、细晶区和两相区。热影响区宽度约为1 mm,相比接头尺寸而言较窄,有利于获得良好的接头性能。T型搭接接头的显微硬度测试表明,典型焊接工艺下低合金高强钢激光穿透焊接T型搭接接头的显微硬度水平分布呈马鞍形,焊缝中心的硬度由于细小板条状马氏体的出现达320 HV左右,较母材硬度约180 HV有大幅提高。热影响区尺寸较窄,因而硬度在热影响区域出现突变。焊接线能量在不同优化工艺参数下区间内的变化对焊缝组织的影响有限,因而相同显微硬度测试位置的硬度值变化很小。T型搭接接头扭转试验表明,结合区宽度对接头抗扭转性能的有重要影响,结合区宽度越宽时T型接头所能承受扭矩也越大。结合区宽度达到2 mm时,所承受最大扭矩约100 N·m。当接头存在间隙时,虽然结合区宽度稍有增加,但不利于抗扭转性能的提升及稳定焊缝尺寸的获得,因而焊接时尽力避免配合间隙的存在。更多还原

【Abstract】 The main application backgrounds of this paper are the development of advanced lightweight structural materials in the shipbuilding industry, and its research subjects are laser welding T-lap joint of high strength low alloy steel. Combined with the advanced manufacturing methods of laser welded sandwich structure panels abroad, the influence of laser welding parameters were studied under high power CO2 laser to achieve proper dimensions, then microstructure and mechanical properties of T-lap joints were also analyzed. Root gap’s influence on section dimensions and torsion performance were especially researched.The laser penetration welding experiment of 10CrNiMnMoV steel shows that appropriate macrograph and section dimensions can be achieved under matching parameters between laser power and heat input; the increasing of laser power is conducive to increase laser penetration. After the laser power is selected, appropriate root width could be obtained where the heat input slightly higher than the deep penetration threshold: 2.4 kJ / cm, and the root width maintain stable even if heat input keeps increasing; defocus amount of -2 mm is selected cause it has important influence on weld penetration and section morphology. In addition, root gap between the web plate and core will affect the stability of welding pool, which is not conducive to stable section dimensions, and may lead to other defects like surface collapsing and porosity etc.Microstructure analysis showed that, seam center of 10CrNiMnMoV steel consists of typical columnar grain, low-carbon martensitic is form the transformation of austenite due to rapid cooling process, and fine grain organization will help improve the joint strength. Joint area is consists of coarse grain zone, fine grain zone, and mushy zone. Width of heat-affected zone is about 1 mm, which is narrow comparing to the joint size, and it is conductive to good application performance.Microhardness test of T-lap joint under optimized parameter indicates that horizontal T-lap joint hardness distribution was saddle-shaped under optimized welding parameters. The hardness of seam is about 320 HV due to appearance of fine martensite, which is largely improved compared with 180 HV of raw materials. The width of heat-affected zone is narrow, where hardness appears sudden drawdown in this area. Heat input of experimental parameters have limited impact on microstructure, then microhardness of same testing spots have little changes.T-lap joint torsion tests show that root width plays critical role when joint are under torsional loading, T-lap joints can withstand greater torque with wider root width. Torque reaches 100 N·m when root width increasing to 1 mm. Root gap have negative effect on torsion performance and section dimensions, although it may slightly increase root width, thus root gap should be avoided during welding process.更多还原