高强高塑性应变比双相钢γ织构增强机理及物理冶金协调控制

Compared with other automotive high-strength steels, dual phase steel has many advantages, such as low yield ratio, continuous yield, high ductility, non-aging in room temperature, high bake hardening value and good welding property. However, its application was limited by the lack of deep drawing property. Combined with previous works, a design idea of low carbon Cu alloying deep drawing dual phase steel is proposed, about which the strength and drawing property will be improved by controlling the existing form of Cu, rolling method, precipitation and dissolution of the carbides, recrystallization and phase transformation. And the experimental study and theoretical analysis will be carried out aiming at the precipitation behavior of ε-Cu particles and evolution rule of the texture of the low carbon Cu alloying deep drawing dual phase steel. The combination of thermodynamics theory calculation and experiments will be used to discuss the mechanism about the existing form of Cu on the recrystallization and phase transformation and the influence of rolling methods on the recrystallization and α→γ orientation change, to illustrate the dynamic mechanism of the recrystallization nucleation and growth, to reveal the recrystallization kinetics and the corresponding formation mechanism of γ fiber texture in the process of annealing. On the basis, the influence law of martensite phase transformation on the texture evolution will further discussed and a relationship between martensite microscopic characteristics and macro deep drawing properties will be established. The research results of the project will provide theoretical guidance for the development of high performance dual phase steel and have a certain guiding significance for Cu in the application of deep drawing steel.

与其他汽车高强度钢相比，双相钢具有屈强比低、连续屈服、延伸率高、室温无时效、烘烤硬化值高、焊接性能好等一系列优点，但深冲性能不足限制了其应用。结合前期工作积累，本项目提出一种低碳Cu合金化深冲双相钢的设计思路，通过控制Cu的存在形式、轧制方式、碳化物的析出回溶、再结晶及相变过程来提高双相钢的强度与冲压性能；针对Cu合金化深冲双相钢中ε-Cu的析出行为和织构演变规律开展实验研究和理论分析。拟从热力学理论计算与实验相结合的方法，探讨Cu的存在方式对再结晶与相变的作用机制，以及轧制方式对再结晶与α→γ取向转变的影响规律，阐明再结晶形核与长大的动力学机制，揭示退火过程中再结晶动力学规律与相应的γ纤维织构形成机理。在此基础上，进一步探讨马氏体相变对织构发展的影响规律，建立马氏体微观特性与宏观深冲性能的关系。本项目研究结果对高性能双相钢的开发提供理论指导，为Cu在深冲钢的推广应用具有一定的指导意义。

基于碳化物析出回溶、充分再结晶与组织织构遗传耦合作用可实现高塑性应变比冷轧带钢的可控制备和γ纤维织构的有效调控。本项目在Cu-Ni合金体系基础上，开展了5种不同合金体系深冲双相钢的组织织构调控及强塑机制研究。首先研究了深冲试验钢的再结晶与奥氏体转变热力学与动力学机制，探究了合金元素对再结晶与相变的影响规律；其次，从退火温度与退火时间对深冲试验钢的组织性能进行了调控；最后，深入研究了深冲双相钢再结晶与奥氏体相变的交互作用，并对微观组织织构进行调控，探讨了其对织构形成的内在作用机制。结果表明：1）合金元素影响着碳元素的扩散，直接决定着微碳试验钢双相组织的形成，碳化物形成元素与铁素体形成元素有效加速碳元素扩散过程，在较短时间退火即可获得双相组织；然而奥氏体形成元素抑制碳元素的扩散，需较长时间退火才能获得双相组织。2）临界退火奥氏体化程度直接影响微碳试验钢最终组织，高温退火容易形成贝氏体组织，而较低临界退火有利于形成岛状马氏体。3）形变储能与退火温度影响着再结晶与奥氏体化过程，高温与形变组织促进奥氏体过程，抑制再结晶晶粒的形成与长大。4）缓慢加热的预再结晶处理有利于Cu粒子在界面析出形成饼形晶粒与促进γ纤维织构形成，进而改善冲压成形性。通过本项目研究，共发表各类论文21篇(均标注资助号)，其中SCI收录论文10篇，申请发明专利6项，授权5项，培养研究生4名，参加国际会议6人次，参加国际学术合作研究1人次。本研究工作不仅为探索高塑性应变比冷轧带钢可控制备和组织织构调控提供了理论依据，还将为双相钢在覆盖件上的推广应用产生重要启示作用。