Physical Metallurgy for Superior Toughness of Pipeline Welds - Intercritical phase transformations in microalloyed high-strength steels

***该项目的长期目标是开发用于安全运输化石燃料和可再生能源的下一代钢管的焊接冶金。短期研究目标是建立X70管道钢在上下临界温度之间热循环的非平衡转变理论，并通过控制多道焊缝组织来优化低温韧性。该专业的教育目标是培养铁合金物理冶金、先进的机械测试方法以及异质材料性能分析和数值模拟方面的高素质人才。******先进的钢具有卓越的强度和延展性，含有少量元素，分别为0.01至0.10 wt%的Nb， V， Cr和Mo，广泛用于从汽车到天然气和石油管道的关键结构。焊接作为一种不可缺少的制造工艺，往往会破坏原有管线钢的优化组织和性能。如何正确焊接这些管道钢以获得优异的性能，不仅在技术上，而且在经济上都是“圣杯”。申请人提出以下研究任务进行定量调查：******对X70管线钢进行了焊接试验，表征了金属气弧焊和埋弧焊临界间热影响区的典型热循环。在-20℃至-60℃的温度范围内测量焊缝结合线和热影响区的冲击韧性。* * * * * * 2。通过数值模拟来了解焊接几何形状和热输入对温度场的影响。用Gleeble和淬火膨胀计重现测试合金的热循环。* * * * * * 3。通过量化奥氏体形成和碳氮化物溶解（加热）以及铁素体型转变（冷却）的峰值温度，发展微观组织演化理论，以优化冲击韧性。该理论将应用于3D打印工具钢零件的多道次沉积。******拟议计划的经济影响将非常大。该技术成果将直接提高石油化工和发电行业焊接钢结构的性能和安全性。这将对加拿大的金属和钢铁、制造业、石化和能源部门产生直接影响。这一科学发现将为一类重要的工程合金提供有关显微组织-加工-性能关系的新知识，有助于材料工程和物理冶金。为了培养高素质的人才，本研究项目为物理冶金研究生和本科生提供了一个理想的教育平台。*****

***The long-term objective of this program is to develop the welding metallurgy for next generation steel linepipe for safe transportation of fossil-fuel and renewable energy. The short-term research objectives are to develop a theory for non-equilibrium transformations in X70 pipeline steel thermally cycled between lower and upper critical temperatures, and to optimize the low-temperature toughness by controlling the multipass weld microstructure. The educational objective of this program is to train highly qualified personnel in physical metallurgy of ferrous alloys, advanced mechanical testing methods, and analytical and numerical modeling of heterogeneous material performance.******Possessing exceptional strength and ductility, advanced steels alloyed with small amounts of elements, 0.01 to 0.10 wt% of Nb, V, Cr, and Mo each, find widespread use in critical structures from automotive to gas and petroleum pipelines. As an indispensable fabrication process, welding usually damages the optimized microstructure and properties of the original pipeline steels. How to properly weld these pipeline steels for superior performance has been the “holy grail” not only technologically, but also economically. The applicant proposes the following research tasks to quantitatively investigate:******1. Conduct welding tests on X70 pipeline steel, and characterize the thermal cycles typical for the intercritical heat-affected zone for gas-metal arc welding and submerged arc welding. Measure the impact toughness of the weld bondline and the heat-affected zone for the temperature range of -20 to -60C. ******2. Numerical simulations will be conducted to understand the temperature fields as influenced by the weld geometry and heat input. Reproduce the thermal cycles on the test alloys using the Gleeble and a quench dilatometer. ******3. Develop a microstructural evolution theory for optimizing the impact toughness by quantifying the peak temperatures on austenite formation and carbonitride dissolution (on-heating), and ferritic-type transformations (on-cooling). This theory will be applied to multipass deposits of 3D printed tool steel parts.******The economic impact of the proposed program promises to be very large. The technical findings will directly enhance the performance and safety of welded steel structures in petrochemical and power generating industries. There will be direct impact on Canadian metals and steels, manufacturing, petrochemical, and energy sectors. The scientific findings will contribute to materials engineering and physical metallurgy by providing new knowledge on microstructure-processing-properties relationship for an important class of engineering alloys. For training of highly qualified personnel, this research program serves as an ideal platform to educate graduate and undergraduate students in physical metallurgy.*****