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用于安全运输化石燃料和可再生能源的下一代钢质管道的焊接冶金技术。短期的研究目标是发展X70管线钢在上下临界温度之间热循环的非平衡相变理论，并通过控制多道焊组织来优化低温韧性。该计划的教育目标是培养高素质的黑色金属合金物理冶金、先进的机械测试方法以及非均质材料性能的分析和数值模拟方面的人才。*先进钢具有优异的强度和延展性，含有0.01至0.10wt%的Nb、V、Cr和Mo元素，广泛应用于从汽车到天然气和石油管道的关键结构中。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。如何正确地焊接这些管线钢，以获得优异的性能，不仅在技术上，而且在经济上都是“圣杯”。申请人提出了以下研究任务以进行定量研究：*1.对X70管线钢进行焊接试验，并表征气体-金属弧焊和埋弧焊的临界热影响区的典型热循环。在-20到-60摄氏度的温度范围内测量焊接熔合线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和淬火膨胀仪在测试合金上重现热循环。*3.通过量化奥氏体形成和碳氮化物溶解(加热)和铁素体类型转变(冷却)的峰值温度，发展了优化冲击韧性的微观组织演变理论。这一理论将应用于3D打印工具钢零件的多道沉积。*拟议计划的经济影响有望非常大。这些技术成果将直接提高石化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、石化和能源行业产生直接影响。这些科学发现将有助于材料工程和物理冶金，为一类重要的工程合金的微观结构-加工-性能关系提供新的知识。为了培养高素质的人才，该研究项目是培养物理冶金专业研究生和本科生的理想平台。

***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.*****