多道次成形是制造汽车零件重要的冷冲压工艺，高强高塑的大奥氏体量中锰钢在多道次成形时易发生破裂，未能体现高塑性优势。由于成形过程对组织演变的影响作用尚不明晰，无法揭示破裂机制，影响工业应用。本项目从分析多道次成形的应变历史特征出发，探讨在该特征下成形的材料科学与力学问题。基于马氏体相变理论，阐明考虑应变历史的奥氏体转变条件、马氏体与基体相的协同变形机制、以及各相界面形态对破裂失效的影响，并建立马氏体相变动力学模型；结合塑性力学理论，建立耦合相变因素的本构模型和破裂预测模型，进行仿真与零件对标，准确描述成形的应变历史和破裂状态。基于零件成形特性，掌握“应变历史-微观结构-力学行为”的多维规律，为组织调控技术提供新的思路，提升中锰钢成形能力。项目以应用为导向，提出的基于应变历史的组织演变、本构模型和力学行为研究的全新课题，拓展对含大量奥氏体汽车钢多道次成形特性的理解，为新材料的应用夯实理论基础。

The multi-step forming is an important cold-stamping process for manufacturing the automotive parts. The high-strength and high-plasticity medium-Mn steel with large-fractioned austenite be easy to crack during multi-step forming, and consequently the advantage of high-plasticity cannot be realized in parts. The cracking mechanism has not been revealed because the effect of forming procedure on microstructural evolution is unclear, which affects the industrial application of medium-Mn steel. This project is to investigate the problem of materials science and mechanics on forming by considering the strain history of multi-step forming process. Based on the theory of martensitic transformation, the transforming condition from austenite to martensite is studied. The cooperative deformation mechanism between the martensite and the austensite matrix is analyzed. The influences of interfacial morphology between martensite and austenite phases on cracking are discussed. Furthermore, the kinetics model for martensitic transformation of medium-Mn steel are established. Based on the theory of plastic mechanics, the constructive model and crack predictive model coupling martensitic transformation are built to accurately describe the strain history and cracking status during multi-step forming. As a result, the relation of strain history, microstructures and mechanical behavior during forming the parts is obtained, which provides a new idea for the control technology of microstructural organization and helps to enhance the formability of medium-Mn steel. This project is application-oriented. The new topics, such as microstructural evolution, constructive model and mechanical behavior based on the strain history, are proposed. The research results will help to understand the multi-step forming characteristics for the medium-Mn steel with large-fractioned austenite, and further promote its application in automotive industry.