Phase transformations in the heat-affected zone of microalloyed steels

微合金钢热影响区的相变

• 批准号: RGPIN-2020-04226
• 负责人: Li, Leijun
• 金额: $ 2.4万
• 依托单位: University of Alberta
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=746875
• 关键词: Phase; transformations; heat; affected; zone

The long-term objective of this program is to develop the physical metallurgy for next generation steel welds for fossil-fuel and renewable energy. The short-term research objectives are to develop a theory for non-equilibrium phase transformations in X70 pipeline steel thermally cycled to lower or upper critical temperatures, and to optimize the low-temperature toughness by controlling the multipass weld heat-affected zone microstructure.   Welding generates the heat- affected zone, the most critical of which is the coarse- grained zone, which has long been identified as the location for "local brittle zone" for poor toughness. More recently the inter-critical heat -affected zone, where the peak temperature during welding falls between the lower (Ac1) and upper (Ac3) critical temperatures for austenite formation, has been correlated with the "soft zone" for Type IV damage in welded boiler tubes. The cooling rate effect has been well understood through the CCT diagrams. However, a quantitative prediction of phase transformations is not available for the effects of weld heating rates, peak temperature, and various starting microstructure. The following research themes are proposed: Theme 1: Thermal History of Multipass Welding  Conduct welding tests, and characterize the thermal cycles typical for the intercritical heat-affected zone for arc welding. Numerical thermal simulations will be conducted to understand the temperature fields as influenced by the weld geometry and heat input. Theme 2: Non-Conventional CCT Diagrams  Reproduce the thermal cycles on X70 steel using the Gleeble and a quench dilatometer. Simulate and measure the effects of pre-existing microstructure, heating/cooling rates, austenite grain sizes, dissolution of carbides, and homogenization on subsequent on-cooling transformations. Theme 3: A Model for Multipass Welds and Additive Manufacturing By characterizing the resulting microstructure of the Gleeble samples, the appearance of bainite peak if particles have dissolved, or the appearance of allotriomorphic ferrite peak if particles have not completely dissolved, we will develop a microstructural evolution model for optimizing the impact toughness by quantifying the peak temperatures on austenite formation and carbonitride dissolution (on--heating), and ferritic- type transformations (on--cooling). The scientific findings will contribute to materials engineering and physical metallurgy by providing new knowledge on microstructure--processing--properties relationship for advanced welding of microalloyed steels. For the first time, the mechanism for the complicated heated-affected zone microstructure of multipass welds will be studied systematically and quantitatively. This research program also serves as an ideal platform to train numerous high -quality graduate students in physical metallurgy to advance their academic or career prospects.

该计划的长期目标是开发用于化石燃料和可再生能源的下一代钢焊缝的物理冶金技术。短期研究目标是建立X70管线钢热循环至下临界温度或上临界温度时的非平衡相变理论，并通过控制多道焊热影响区显微组织来优化低温韧性。   焊接会产生热影响区，其中最关键的是粗晶区，长期以来，粗晶区被认为是韧性差的“局部脆性区”所在。最近，临界间热影响区（焊接期间的峰值温度落在奥氏体形成的下临界温度（Ac1）和上临界温度（Ac3）之间）与焊接锅炉管中 IV 型损伤的“软区”相关。通过 CCT 图可以很好地理解冷却速率的影响。然而，对于焊接加热速率、峰值温度和各种起始微观结构的影响，无法定量预测相变。提出了以下研究主题： 主题 1：多道焊接的热历史 进行焊接测试，并表征电弧焊临界间热影响区的典型热循环。将进行数值热模拟，以了解受焊接几何形状和热输入影响的温度场。主题 2：非常规 CCT 图 使用 Gleeble 和淬火膨胀计重现 X70 钢的热循环。模拟和测量预先存在的微观结构、加热/冷却速率、奥氏体晶粒尺寸、碳化物溶解和均匀化对后续冷却转变的影响。 主题 3：多道焊接和增材制造模型通过表征 Gleeble 样品的最终微观结构、颗粒溶解时贝氏体峰的出现或颗粒未完全溶解时同素异形铁素体峰的出现，我们将开发一个微观结构演化模型，通过量化奥氏体形成和碳氮化物溶解的峰值温度来优化冲击韧性 （加热时）和铁素体型转变（冷却时）。这些科学发现将为先进微合金钢焊接的微观结构-加工-性能关系提供新的知识，从而为材料工程和物理冶金做出贡献。首次系统、定量地研究多道焊缝复杂热影响区显微组织的机理。该研究项目也是培养众多高质量物理冶金研究生的理想平台，以促进他们的学术或职业前景。