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: 2021
• 资助国家: 加拿大
• 起止时间: 2021-01-01 至 2022-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=739752
• 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.

该项目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材焊接的物理冶金技术。短期研究目标是建立X70管道钢热循环至较低或较高临界温度的非平衡相变理论，并通过控制多道焊缝热影响区显微组织来优化其低温韧性。焊接会产生热影响区，其中最关键的是粗晶区，由于韧性差，该区域一直被认为是“局部脆性区”的位置。最近，临界间热影响区，即焊接过程中的峰值温度落在奥氏体形成的较低临界温度（Ac1）和较高临界温度（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效应。然而，对于焊接加热速率、峰值温度和各种启动组织的影响，无法定量预测相变。提出了以下研究主题：主题1：多道焊热历史进行焊接试验，表征弧焊临界间热影响区的典型热循环。将进行数值热模拟，以了解受焊缝几何形状和热输入影响的温度场。主题2：使用Gleeble和淬火膨胀仪再现X70钢的热循环。模拟和测量预先存在的微观组织、加热/冷却速率、奥氏体晶粒尺寸、碳化物溶解和均匀化对随后的非冷却转变的影响。主题3:通过表征Gleeble试样的微观结构，颗粒溶解时贝氏体峰的出现，颗粒未完全溶解时异晶铁素体峰的出现，我们将通过量化奥氏体形成和碳氮化物溶解（加热）的峰值温度，建立一个微观结构演变模型，以优化冲击韧性。和铁素体型转变（on- cooling）。这些科学发现将为微合金钢的高级焊接提供有关微观结构-加工-性能关系的新知识，有助于材料工程和物理冶金。首次系统、定量地研究了多道次焊缝复杂热影响区组织形成的机理。该研究项目也为培养大量高质量的物理冶金研究生提供了理想的平台，以促进他们的学术或职业前景。