梯度结构相变诱导塑性钢的组织演变和增塑机制的定量研究

The application project will take the conventional TRIP steel and medium Mn TRIP steel with gradient structure as the research subject, on the basis of quantitative research, the similarity and difference of microstructural evolution and mechanism of ductility enhancement(MDE) during deformation for the two kinds of steels are systematically studied. By the step-wise experiment of stresss load program control, the MDE caused by deformation induced transformation of austenite to martensite under single stress or single strain is confirmed, the influence rule of the original microstructure on the stress, strain, transformation of gradient structural austenite and the MDE could be clarified. A study of quantitative strain under dynamic deformation could be achieved by changing the V-shaped opening extent of a specimen, using the method combining of quantitative experimental research and theoretical analysis, deformation induced the variation of dislocation density, the mode of transformation and crack propagation and their MDE will be demonstrated. The constitutive model contained microstructural evolution on the TRIP steel with gradient structure is established, the micro-deformation behavior of constituent phases under constant stress and dynamic deformation is quantitativly described. Based on the above research, the essence of deformation induced ductility enhancement is futher revealed, the theoretical basis and consultation of microstructural design and fabrication will be provided for the development of a new generation automotive steel plate with excellent combination of strength, ductility and toughness.

本项目以梯度结构的常规TRIP钢和中锰TRIP钢为研究对象，以定量研究为基点，系统研究两种钢变形过程中的组织演变和增塑机制的异同性。通过阶段式力保载程序控制实验，确认单一应力或应变作用下的奥氏体向马氏体相变的形变诱导机制，明确原始组织对应力、应变、梯度结构奥氏体的相变和增塑机制的影响规律。通过改变试样的V型开口度实现动态变形的定应变研究，从定量实验和理论分析两方面论证形变诱导位错密度的变化、相变和裂纹扩展的方式及其增塑机制。建立包含组织变化的梯度结构相变诱导钢的本构方程，定量描述恒定应力和动态变形条件下各组成相的微观变形行为。基于上述的研究，深化对梯度结构相变诱导塑性钢的形变诱导塑性本质的认识，为新一代汽车用的强度、塑性和韧性同步提高的梯度结构相变诱导塑性钢提供组织设计及制备的依据和理论基础。

针对传统高强度钢存在难以解决的强度与塑性同步提高的科学和技术难题，本项目通过梯度结构和形变诱导相变增塑效应相结合的方法，为金属材料强度与塑性、韧性同步的提高提供了新途径。制备了出不同组织分布、晶粒尺寸和相比例的梯度结构相变诱导塑性钢，获得了强塑积36GPa•％以上的梯度结构低碳Si-Mn钢和50GPa•％以上的梯度结构Fe-15Mn-3Al钢的制备工艺；研究了动态变形条件下的组织演变和变形行为，随着应变速率从7/s增加到70/s，Goss {110} < 001 > 和Brass {110} < 112 > 织构减弱，Copper {112} < 111 > 织构增强，形变孪晶逐渐增加，并出现多个方向的孪生系统相互交割。当应变速率达到700/s时，Copper {112} < 111 > 织构减弱，形变孪晶减少。动态变形过程中，TRIP效应、TWIP效应及绝热温升效应共存。对于Fe-15Mn-3Al钢，在不同应变速率的动态变形过程中，TWIP效应占据主导地位，应变速率对TRIP效应的影响不大；研究了在应力加载阶段和恒应力阶段的组织演变和变形行为，明确TRIP效应、TWIP效应和其它效应发生的条件、顺序和比例，确认形变诱导增塑的本质；构建了实验钢的计算模型并编写了马氏体相变方程子程序，构建了静态和动态变形条件下的基于微观组织演变的本构方程模型；在ABAQUS有限元软件中模拟了中锰TRIP钢在不同变形条件下的TRIP效应及应力应变分布状况。本项目的研究为梯度结构和形变诱导相变增塑效应的良好匹配、实现先进高强塑性钢组织性能的控制及优化提供了依据。在应用上为潜在的新一代高安全性、重量轻的经济型汽车用先进高强度钢板的生产奠定了理论基础。