油气管道用双相不锈钢CMT-P复合焊接熔滴过渡行为与组织调控机制研究

Deep-water oil and gas development in the South China Sea is an important strategic measure for the sustainable development of oil and gas resources in our country. Due to the harsh deep-water oil and gas environment, duplex stainless steel (DSS) pipeline welded joints face enormous challenges for long-life service. As a unsolved key scientific problem, the traditional welding technology cannot suppress harmful secondary phase precipitation in the DSS welded joint to improve its localized corrosion resistance, and never satisfy good welding quality, high efficiency, and low cost simultaneously. Therefore, a new cold metal transition and pulse (CMT-P) hybrid welding technology is introduced to join DSS for oil and gas pipeline. Based on multidisciplinary theories of materials science, interface science, and thermodynamics, the droplet transition behavior and microstructure evolution rules during the CMT-P hybrid welding process are investigated by incorporating the experimental research, theoretical analysis, and numerical simulation. The inherent relationships between welding process parameters and droplet transition behavior and microstructure at the different zones of welded joint are explored. Then the models of unsteady diffusion kinetics and boundary migration rate were established. Finally, the secondary phase precipitation mechanism during the CMT-P hybrid welding process is revealed. All these investigations provide scientific evidence and theoretical supporting for microstructure control and performance optimization of the CMT-P hybrid welded joint of DSS, which are of great significance both in scientific investigation and industrial application for enhancing the safe transportation capacity of deep-sea oil and gas.

南海深水油气开发是我国油气资源可持续发展的重大战略举措，但苛刻的深水油气环境使双相不锈钢管道焊接接头面临长寿命安全服役的巨大挑战。传统的焊接技术无法抑制有害的二次相析出以改善双相不锈钢焊接接头的耐局部腐蚀性能，且难以兼顾焊接质量、效率和成本，这是目前尚未解决的关键科学问题。本项目拟以油气管道用双相不锈钢为研究对象，引入新型的冷金属过渡与脉冲（CMT-P）复合焊接技术，融合材料学、界面科学、热动力学等多学科理论，运用实验、理论分析和数值模拟方法，围绕CMT-P复合焊接熔滴过渡行为和组织演化规律展开研究，探究焊接工艺参数与熔滴过渡行为和焊接微区组织的内在关联性，建立非稳态扩散动力学和边界迁移速率模型，揭示CMT-P复合焊接过程中二次相析出机制，旨在为双相不锈钢CMT-P复合焊接接头组织控制、性能优化等方面提供科学依据与理论支撑，对提升我国深海油气安全输送能力具有重要的科学与工程应用价值。

南海深水油气开发是我国油气资源可持续发展的重大战略举措，但苛刻的深水油气环境使双相不锈钢管道焊接接头面临长寿命安全服役的巨大挑战。本项目以油气管道用双相不锈钢为研究对象，引入新型的冷金属过渡与脉冲（CMT-P）复合焊接技术，融合材料学、界面科学、热动力学等多学科理论，运用实验、理论分析和数值模拟方法，围绕CMT-P复合焊接熔滴过渡行为和组织演化规律展开研究。综合考虑CMT-P复合焊接接头的宏观形貌、成形系数及铁素体/奥氏体两相比例等因素，揭示了保护气、焊接速度、送丝速度、CMT/P比值等工艺参数对焊缝成形质量的影响规律；运用高速摄像和电信号同步采集技术阐明了双相不锈钢CMT-P复合焊接熔滴过渡行为；运用多物理场耦合仿真的方法，建立了CMT-P复合焊接电磁热耦合模型，揭示了CMT与脉冲不同阶段的熔滴过渡演变机理；阐明了双相不锈钢CMT-P复合焊接接头各微区的微观组织特征；揭示了保护气中添加不同比例的N2对双相不锈钢焊接接头各微区微观组织、力学和耐点蚀性能的影响规律；充分考虑高温铁素体化和后续焊道的多次再加热等复杂的焊接热循环历程，阐明了多层多道焊接过程中热影响区的微观组织演变规律，揭示了Cr2N和γ2的析出机制；研究了CMT-P复合焊接热循环过程对热影响区的力学和耐点蚀性能的影响机理。本项目研究为双相不锈钢CMT-P复合焊接接头组织控制、性能优化等方面提供科学依据与理论支撑，对提升我国深海油气安全输送能力具有重要的科学与工程应用价值。