ME-SAW焊接X120级管线钢熔池形态与HAZ热循环特性研究

The application of grade X120 ultra-high-strength low-alloy pipeline steel is beneficial to further cost-cutting of long-distance transmission of oil and natural gas and enhancement of transmission security. Welding process is key forming technology to assemble plates to tubes and tubes to pipelines of grade X120 pipeline steel. In this study, four-wire tandem submerged arc welding of grade X120 pipeline steel with thickness 16 mm is investigated by employing numerical simulation, welding test, physical simulation and microstructure & property measurement. Through selecting adaptive heat source mode under multi-arc synergy action and accurate calibrating the distribution parameters of the heat source, the fluid flow and heat transfer model is developed for the larger & longer weld pool corresponding to the four-wire tandem submerged arc welding. The groove filling and weld reinforcement are processes by combining the free surface equation of the weld pool and the model of molten pool dynamics. Based on the systemic analysis of the welding thermal field, weld pool behaviors, weld morphology evolution and thermal cycle characteristics in heat affected zone (HAZ), the quantitative correlation of the welding process parameters-weld pool behaviors-thermal cycle characteristics in HAZ-grain sizes in HAZ-properties in HAZ is established. The influencing mechanism of the welding process parameters on the grain coarsening and property worsening in HAZ of grade X120 pipeline steel is revealed. It will lay solid foundation for the optimization and match of the welding process parameters as well as the process management of the microstructure & property in HAZ when the grade X120 pipeline steel is welded by four-wire tandem submerged arc welding.

X120级超高强度低合金管线钢的应用，可显著降低油气资源远程输送成本和提高输送安全性，而焊接成形是X120钢从板材到管材、从筒体到管道的关键环节。本项目将数值分析与焊接试验、物理模拟、组织与性能分析测试相结合，研究16 mm厚X120钢串列4丝埋弧焊接工艺。通过设计多电弧多熔滴协同作用下的焊接热源模式及准确标定热源分布参数，结合熔池自由表面变形方程处理坡口填充和焊缝余高，建立X120钢串列4丝埋弧焊接产生的大而长熔池的流体动力学状态及其热过程数值分析模型。系统分析多电弧、多熔滴热-力耦合作用下的焊接温度场、熔池行为、焊缝形貌演变和HAZ热循环特性，研究"焊接工艺参数-熔池形态-HAZ热循环特征-HAZ晶粒尺寸-HAZ力学性能"之间的定量关系，揭示焊接工艺参数对HAZ晶粒粗化和接头性能劣化的影响机制。为实现X120钢串列4丝埋弧焊接工艺参数的优化匹配、HAZ组织与性能的工艺调控奠定坚实基础。

X120级管线钢中涉及到三类焊缝：从板材加工成筒体的纵向直焊缝；从卷板加工成筒体的螺旋焊缝；钢管与钢管间的环形焊缝。X120钢采用了特殊的合金化方案和更为严格的控轧控冷技术，以细小弥散的下贝氏体为基体、少量的马氏体及其衍生物组成的显微组织，具有超高强度和良好的低温韧性，但可焊性较差，冷裂敏感指数偏高。采用常规熔化焊工艺，HAZ组织极易粗大化，导致接头强度和韧性变差，成为制约X120钢走向工程应用的技术瓶颈。.项目设计了X120级钢管环形焊缝、内外直缝4丝串列埋弧焊和螺旋缝内2丝外3丝埋弧焊的工艺方案并成功开展了焊接试验，建立了多丝串列直缝埋弧焊、多丝串列螺旋缝埋弧焊和环形焊缝单丝多层焊接的数值分析模型，定量研究了焊接电流、电弧电压、送丝速度、焊接热输入量对焊接温度场分布、HAZ焊接热循环特性、HAZ组成相与晶粒度的影响规律，定量分析了电磁力、表面张力、电弧压力和浮力对熔池流体流动行为、熔池几何形状、焊缝成形的影响规律，揭示了HAZ晶粒粗化和焊接接头软化的产生机制及影响规律，为X120级管线钢纵向直焊缝、纵向螺旋焊缝和环形焊缝的焊接工艺参数优化匹配和HAZ组织与性能的调控奠定了坚实基础。.项目成功开发了2套焊接工艺方案。16 mm厚X120级钢管环形焊缝，采用焊接热输入量更易于调控的P-GMAW和窄间隙复合双V型坡口，焊接5层就可获得成形良好且接头组织和性能满足要求。对于18.4 mm厚X80级钢管环缝，采用复合双V型坡口，仅需一套双丝自动焊系统，根焊层采用前丝焊，热焊层采用后丝焊，2道填充层和1道盖面层采用双丝焊，就可获得成形好、质量优的接头。相比于包括西二线等工程建设中广泛采用的环缝7层焊道+两套焊接设备的工艺方案，可使焊接效率提高30%左右。.电磁力和表面张力驱动液态金属流动能力最强，电磁力主要影响熔深，表面张力主要影响熔宽；电弧压力对熔池自由表面变形影响最大。焊接热输入量对HAZ的晶粒度有明显影响，脉冲焊是X120钢的可选方案，而常规埋弧焊，无论是单丝还是多丝，都很容易导致HAZ晶粒明显长大，难于满足对X120钢焊接接头的力学性能指标要求。.