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。短期研究目标是为X70管道钢中的非平衡相变的理论开发，热循环至临界温度下部或上部临界温度，并通过控制多层焊接热影响区的微观结构来优化低温韧性。焊接会产生热影响区域，其中最关键的是粗粒区，长期以来，该区域已被确定为“局部脆性区”的位置，以造成较差的韧性。最近，临界热热区域，其中焊接过程中的焊接峰值落在奥氏体形成的下部（AC1）和上部（AC3）临界温度之间，与焊接锅管中IV型损伤的“软区域”有关。通过CCT图已经很好地理解了冷却速率的效果。但是，对于焊接加热速率，峰值温度和各种起始微观结构的影响，相变的定量预测不可用。提出了以下研究主题：主题1：多通焊接进行焊接测试的热历史，并表征了弧形焊接中临界热影响区的典型热周期。将进行数值热模拟，以了解受焊接几何和热输入影响的温度场。主题2：使用Gleeble和Quench缩写仪在X70钢上复制X70钢的热循环。模拟和测量现有的微观结构，加热/冷却速率，奥斯丁晶粒尺寸，碳化物的溶解以及均质化对随后的冷却变换的影响。主题3：多质焊缝和添加剂制造的模型，通过表征gle gle样品的产生的微观结构，如果颗粒溶解的话，贝氏峰的出现，或出现同粒形态的铁氧体峰，如果颗粒峰的峰值，如果颗粒没有完全溶解，我们将通过量化的峰值来量化，以量化峰值的峰值，以量化峰值的峰值，以量化峰值的峰值，以量化的峰值变化，以使跨度的变化构成构成的峰值，以构建峰值的范围，以量化峰值的范围，以量化较高的速度，以构建峰值的范围，以量化较高的峰值，以构建峰值的范围，以量化较高的速度启动，以量化的峰值变化，以量化的峰值变化构成范围（加热）和铁素体类型转换（冷却）。科学发现将通过提供有关微合成钢的高级焊接的微观结构（处理 - 生产关系）的新知识，从而为材料工程和物理冶金。首次将系统地和定量研究复杂的加热影响区微结构的微观结构的机制。该研究计划还可以作为培训众多高质量研究生的理想平台，以促进其学术或职业前景。