Fe-C-Mn(-Si)钢预先铁素体/马氏体相变后贝氏体相变行为及动力学理论

Nowadays, particularly for automotive application, the desire for novel advanced high strength steels (AHSS) with high ductility has rapidly intensified. The excellent combination of strength and ductility in AHSS benefits from a multi-phase microstructure consisting of ferrite, bainite and martensite as well as finite amounts of retained austenite, which emphasizes the control of the non-ferrite phases. Recent studies show that the occurrence of pre-ferrite or martensite transformation will seriously affect the formation and evolution of subsequent bainite phase transformation. In present project, bainite transformation after prior ferrite or martensite transformation in the hot-rolled TRIP and Q&P processing of Fe-C-Mn(-Si) steels is the focus. Firstly, the plastic accommodation and self-accommodation (variant selection) of bainite transformation from the mixed prior-ferrite or martensite and austenite matrix is studied. Secondly, the interaction between the kinetic process and the strain accommodation of bainite transformation is analyzed. Finally, kinetic theory of bainite transformation considering the mixed microstructure characteristic variables of pre-existed ferrite or martensite is constructed. The present project will lay a theoretical foundation for process design and microstructure control.

先进高强钢的高强度和高塑性得益于铁素体、贝氏体、马氏体、残余奥氏体等两相或多相组织的合理搭配，强调铁素体以外非平衡相的控制。近来研究发现，预先铁素体/马氏体相变会严重影响后续贝氏体相组织的形成及演化。本项目以Fe-C-Mn(-Si)系高强钢热轧TRIP或Q&P加工路径下预先铁素体/马氏体相变后的贝氏体相变为核心，重点研究预先铁素体/马氏体混合母相组织中贝氏体转变应变的塑性调节与自调节变体选择，以及与相变动力学过程的交互，旨在构建可以耦合预先相变混合组织特征参量的贝氏体相变动力学理论，为实现面向目标性能的先进高强钢微观组织精细化调控奠定理论基础。

钢中相变的经典理论描述往往依赖于经验模型、恒定应变能、忽略非平衡多相交互效应，难以实现复杂加工路径下的微观组织预测。本项目以Fe-C-Mn-Si高强钢特定加工路径下的多相微观组织演变为核心，开展了预先铁素体/马氏体相变对后续贝氏体相变行为的影响研究。实验上，采用热膨胀测量、X射线衍射和透射电镜等技术，研究了Fe-C-Mn-Si钢预先等温铁素体相变对后续等温贝氏体相变动力学及组织演化的影响；采用EBSD分析和奥氏体母相重构技术，研究了Fe-C-Mn-Si钢中不同体积分数预先马氏体对后续贝氏体相变变体选择的影响。理论上，从基于微观结构的铁素体相变理论模型出发，构建了多组元钢中奥氏体逆相变模块化动力学模型，同时考虑扩散所引起的非均匀摩尔体积效应，采用热力学极值原理，构建了修正的奥氏体/铁素体相变理论模型；考虑晶界形核、自催化形核以及碳原子配分，构建了贝氏体相变热-动力学相关性模型；耦合晶体塑性滑移理论以及相场模型分析了贝氏体/马氏体相变转变应变调节与动力学过程的交互效应。为实现面向目标性能的先进高强钢微观组织精细化设计与调控奠定了基础。