X70钢高压干法GMAW直流正接焊接工艺研究

发布时间：2018-11-19 11:01

【摘要】：我国拥有丰富的海上石油和天然气资源,包括240亿吨近海石油和140万亿立方米天然气资源,开发利用好这些资源对我国经济的可持续发展具有特别重要的意义。大量的海洋工程建设及海底管道建设对海底管道钢的性能提出了更高的要求。近年来X70高强钢广泛应用于国内海底管道建设,而对在役X70海底管道钢的维护、修复技术研究较少。水下高压干法GMAW焊接技术是船舶、海洋平台、海底管道等水下设备维修的关键技术。本课题将对X70钢高压GMAW焊接工艺进行研究,通过高压舱模拟0.8-2MPa环境压力,进行X70钢高压GMAW焊接工艺研究。结合已有的高压GMAW焊接特性,设计合理的工艺实验并在平板上进行堆焊实验,研究电源极性、环境压力和焊接工艺参数对焊接过程稳定性、熔滴过渡和焊缝成形的影响。得出不同环境压力下能确保焊接过程稳定的大致工艺参数范围,并总结环境压力和工艺参数对焊接过程的影响,为X70钢高压GMAW焊接提供指导。考虑X70海底管道钢的实际使用场景,结合常压下X70管线钢焊接和多层多道焊特点,对X70钢多层多道焊工艺进行实验和研究。计算出合理的工艺参数范围,并在此基础上,结合堆焊上得出的高压GMAW焊接规律,进行X70钢高压GMAW多层多道焊接试验。对焊接接头的宏观金相、微观组织、硬度、冲击功和抗拉强度进行分析和总结,得出符合要求的X70钢高压GMAW焊接工艺,并对已有的焊接工艺进行优化。实验结果表明,与常压下X70钢GMAW焊接不同,高压下维持焊接过程稳定的工艺参数范围变窄。随着环境压力的增加,熔滴过渡形式由短路过渡逐渐转变为排斥过渡,飞溅逐渐增多。增加焊枪摆动能有效的减少焊接过程中焊漏、咬边的情况。X70钢高压GMAW焊接接头的焊缝的主要组织为针状铁素体、先共析铁素体以及少量上贝氏体,硬度值变化不大;热影响区尤其过热区组织和力学性能差异较大,过热区为粗大的马氏体组织或细小均匀的珠光体和贝氏体。高压下,焊缝熔宽变窄,熔深变深,热影响区粗大马氏体数量增加,冲击功下降。适当的增加焊接电压、送丝速度和降低焊接速度能有效的提高焊接接头的抗拉强度、冲击功和降低焊接接头的硬度。
[Abstract]:China has abundant offshore oil and natural gas resources, including 24 billion tons of offshore oil and 140 trillion cubic meters of natural gas resources. A large number of offshore engineering and submarine pipeline construction put forward higher requirements for the performance of submarine pipeline steel. In recent years, X70 high strength steel has been widely used in domestic submarine pipeline construction, but little research has been done on the maintenance and repair of existing X70 submarine pipeline steel. Underwater high pressure dry GMAW welding technology is the key technology of underwater equipment maintenance, such as ship, offshore platform, submarine pipeline and so on. The high pressure GMAW welding technology of X70 steel will be studied in this paper. The high pressure chamber simulation 0.8-2MPa environment pressure, the X70 steel high pressure GMAW welding process will be studied. Combined with the existing high pressure GMAW welding characteristics, reasonable process experiments were designed and surfacing experiments were carried out on the flat plate to study the effects of power polarity, environmental pressure and welding process parameters on the stability, droplet transfer and weld formation of the welding process. The general range of process parameters which can ensure the stability of welding process under different ambient pressures is obtained. The influence of environmental pressure and process parameters on welding process is summarized, which provides guidance for high pressure GMAW welding of X70 steel. Considering the practical application scenario of X70 submarine pipeline steel, combined with the characteristics of X70 pipeline steel welding and multi-layer multi-pass welding under atmospheric pressure, the multi-layer and multi-pass welding process of X70 steel was studied and tested. The reasonable range of process parameters was calculated. On the basis of this, combined with the rules of high pressure GMAW welding obtained from surfacing welding, the multi-layer and multi-pass welding test of X70 steel was carried out. The macroscopic metallography, microstructure, hardness, impact energy and tensile strength of welded joints were analyzed and summarized. The high pressure GMAW welding process of X70 steel was obtained, and the existing welding process was optimized. The experimental results show that, unlike GMAW welding of X70 steel under atmospheric pressure, the range of process parameters for maintaining the stability of welding process at high pressure becomes narrower. With the increase of environmental pressure, droplet transfer form gradually changed from short-circuit transition to repellent transition, and spatter gradually increased. Increasing welding torch swing can effectively reduce welding leakage and edge cutting. The main microstructure of high pressure GMAW welded joint of X70 steel is acicular ferrite, preeutectoid ferrite and a small amount of upper bainite. The hardness of X70 steel high pressure GMAW welding joint has little change. The microstructure and mechanical properties of the heat affected zone, especially the superheated zone, differ greatly. The superheated zone is composed of coarse martensite structure or fine and uniform pearlite and bainite. Under high pressure, the weld width becomes narrower, the penetration depth becomes deeper, the amount of coarse martensite in the heat affected zone increases and the impact energy decreases. Properly increasing the welding voltage, feeding wire speed and reducing welding speed can effectively increase the tensile strength, impact power and reduce the hardness of the welded joint.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG457.11

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