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

* 该计划的长期目标是开发下一代钢制管线管的焊接冶金技术，以安全运输化石燃料和可再生能源。短期研究目标是建立X70管线钢在上下临界温度之间热循环的非平衡相变理论，并通过控制多道焊缝组织来优化低温韧性。该计划的教育目标是培养高素质的人才在铁合金的物理冶金，先进的机械测试方法，以及非均质材料性能的分析和数值建模。具有优异的强度和延展性，与少量元素（0.01至0.10重量%的Nb、V、Cr和Mo）合金化的先进钢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，往往会破坏原始管线钢的优化组织和性能。如何正确焊接这些管线钢以获得上级性能，不仅在技术上，而且在经济上一直是“圣杯”。申请人提出以下研究任务进行定量研究：**1.对X70管线钢进行焊接试验，并对气体保护金属极电弧焊和埋弧焊的临界区热影响区的典型热循环进行表征。在-20 ℃至-60 ℃的温度范围内，测量焊缝和热影响区的冲击韧性。2.将进行数值模拟，以了解焊接几何形状和热输入对温度场的影响。使用Gleeble和淬火温度计再现试验合金的热循环。3.通过量化奥氏体形成和碳氮化物溶解（加热时）以及铁素体型转变（冷却时）的峰值温度，开发用于优化冲击韧性的显微组织演变理论。该理论将应用于3D打印工具钢零件的多道次沉积。拟议中的计划的经济影响有望非常大。这些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。这一研究成果将为材料工程和物理冶金学的发展提供新的理论依据，为这类重要的工程合金的组织-工艺-性能关系提供新的认识。为了培养高素质的人才，该研究计划作为一个理想的平台，教育研究生和本科生在物理冶金。

***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.*****