节约型TRIP双相不锈钢的宏微观耦合循环塑性本构模型研究

The lean duplex stainless steel with TRIP（transformation-induced plasticity）effect has a prospective application in rail transit field. At present studies on the microstructure characterization and performance evaluation under unidirectional loading condition are popular. However, the relation among deformation-microstructure-property under cyclic loading is unclear. Owning to the lack of cyclic constitutive model considering TRIP effect, the forming process simulation is inaccurate, then the development cycle of the forming process is lengthened, and it has become the bottleneck problem for the industrial application of this high-performance material. In this project, theoretical analysis, cyclic loading test and microstructure characterization are synthetically utilized. The strain distribution law of constituent phase under cyclic deformation, the evolution of strain-induced martensitic transformation and mechanical properties characteristics are investigated. The martensitic transformation kinetic model considering deformation inhomogeneity of constituent phase is built, and the inherent relation among deformation-microstructure-property under cyclic loading is clarified，and the microscopic mechanism of cyclic deformation characteristics is revealed. The relation between martensitic transformation and macroscopic mechanical property parameters is proposed, so as to realize macro-micro coupling, and a cyclic plasticity constitutive model is established which can describe the deformation inhomogeneity of constituent phase and the strain-induced transformation. The constitutive model can be used in the simulation of the forming process for lean TRIP duplex stainless steel to improve the accuracy. The expected results of this project can enrich the theory of strain-induced transformation and provide reference for the research on constitutive theory of other multiphase metastable materials.

具有TRIP效应的节约型双相不锈钢在轨道交通领域具有良好的应用前景。目前该材料的研究集中在单向加载下组织表征与性能评价，而其循环加载时的变形-组织-性能的关联规律欠明确，尤其缺少考虑TRIP效应的循环本构模型，导致成形过程的预测能力不足，工艺开发周期长，已成为该高性能材料工业化应用的瓶颈问题。本项目综合理论分析、循环加载试验、微观组织表征，研究循环变形下组元相间的应变配分规律、形变诱导马氏体演变及力学性能响应特性，构建考虑相间变形不均匀特征的马氏体相变动力学模型，阐明循环加载时变形-组织-性能间的关联关系，揭示循环变形特性的微观机理；搭建马氏体转变量与宏观力学性能参量间的映射关系，实现宏微观耦合，建立可综合描述相间变形不均匀性和形变诱导相变特征的循环塑性本构模型，形成节约型TRIP双相不锈钢材料成形过程的仿真能力。研究结果可丰富形变诱导相变理论，并为其它复相亚稳材料的本构理论研究提供借鉴。

TRIP双相不锈钢因其优异的力学性能，在汽车及轨道交通领域具有巨大的应用潜力，然而目前对该材料在循环加载时的变形-组织-性能关系欠明确，阻碍了其工业化应用。本项目研究了循环加载条件下TRIP双相不锈钢的马氏体相变转变及力学性能响应特性，揭示了循环变形特性的微观机理，建立了循环塑性本构模型，形成了节约型TRIP双相不锈钢成形过程的仿真能力。具体包括，搭建了循环加载条件下马氏体转变量原位测量试验平台，对马氏体转变特征和演化规律进行了研究，建立了“表观”马氏体相变动力学模型。通过EBSD中的GOS分析技术，研究了微观晶粒取向，揭示了组元相间应变配分规律，引入应变比，建立了应变配分模型。结合应变配分模型和“表观”相变动力学模型，建立了 “真实”循环马氏体相变动力学模型，并进行了验证。另外，测得了应变幅0.5%、0.7%、0.9%、1.1%和1.3%下的迟滞回线。在较低应变水平下，试验钢表现为初始循环硬化-循环软化-循环稳定；在较高应变水平下，出现了二次循环硬化。通过TEM微观结构分析发现，位错的缠结是发生初始循环硬化的主要原因；在循环软化阶段，形成位错墙、位错胞的过程导致的应力降低，大于ε马氏体和α´马氏体对材料的强化；二次循环硬化主要由ε马氏体和α´马氏体主导。最后，基于纳米压痕试验结果，通过理论推导，构建了各组元相本构模型；通过混合法则，将微观相变和宏观力学性能参量相联系，结合马氏体相变动力学模型和各组元相本构模型，构建了宏微观耦合本构模型。利用 ABAQUS 有限元软件的二次开发功能，编写了上述本构模型的有限元程序。将所建立的本构模型，应用于板料拉深成形模拟，并进行了物理实验验证。研究结果丰富了形变诱导相变理论，并可为其它复相亚稳材料的本构理论研究提供借鉴。所建立的本构模型，可对TRIP双相不锈钢的成形过程进行可靠预测，可缩短工艺开发周期，有利促进该类高性能钢铁的工业化应用。