高强钢感应传导分区加热热冲压高温变形特性与变强度机理研究

The variable-strength design of body safety parts is crucial to improve crash safety of a car. A heating technique of “induction-conduction” intended for achieving the variable-strength hot stamping of partial heating will be adopted in this project. The project focuses on two problems in the process of “partial heating-forming-quenching”, the deformation characteristics and variable-strength mechanism of high strength steel. The following issues emerging in the process will be addressed through basic experiments, theoretical modeling, numerical simulation and technological testing: the effect of austenization on high temperature deformation behavior and formability of high strength steel, austenitizing process and the effect of austenization on cooling transformation, to establishing a constitutive model of high-strength steel which coupling austenization, to establish a plane stress forming limit prediction model which considering the degree of austenization, to establish a unified multi-scale phase transition model which considering the whole stamping process from heating to cooling, to predict the mechanical properties and microstructure evolution of the part with finite element method and user subroutine development technology. The project will reveal the deformation characteristics and variable-strength mechanism of high strength steel in the process of partial heating variable-strength hot stamping, implement the multi-scale numerical simulation of coupling “deformation-heat transfer-phase transition”, develop scientific theories of material multi-scale modeling, and provide a new idea to the fabrication of variable-strength parts. The realization of trial-producing a variable-strength body will guide the production practice and improve the manufacturing level in the automobile industry of our country.

车身安全结构件变强度设计对提高汽车碰撞安全性非常重要。本项目拟采用感应传导加热实现分区加热变强度热冲压工艺，着眼于“分区加热—成形—淬火”中高强钢高温变形特性和变强度机理两个问题，通过基础实验、理论建模、数值模拟与工艺试验等方法，研究感应传导分区加热中加热规律，研究奥氏体化对高强钢变形行为和成形性能的影响，研究高强钢奥氏体化过程及其对冷却相变的影响；建立耦合奥氏体化本构模型，建立考虑奥氏体化的平面应力成形极限预测模型，建立考虑加热到冷却的统一多尺度相变模型；借助有限元及其二次发开技术，实现分区加热热冲压数值仿真，预测零件力学性能和微观组织演化。本项目揭示了分区加热热冲压中高强钢高温变形特性和变强度机理，实现“变形—传热—相变”耦合多尺度一体化数值仿真，发展材料多尺度建模理论，为变强度零件的制造提供新思路；实现变强度零件试制，为变强度零件生产实践提供指导，提高我国汽车工业的制造工艺水平。

车身安全结构件设计对提高汽车碰撞安全性非常重要，传统热冲压零件通常是等截面力学性能的，但为了更好地满足碰撞吸能要求，汽车关键碰撞结构件需要在不同位置具有不同强度以承受不同碰撞载荷。为了生产变强度汽车零件，本项目采用了成形变强度汽车零件的新方法—“分区加热热冲压工艺”。针对分区加热热冲压工艺的特殊性，本项目主要通过基础实验、理论建模、数值模拟与工艺试验等方法，研究了感应传导分区加热变强度热冲压工艺。通过热膨胀试验，获得了保温温度与饱和奥氏体体积分数的定量关系，揭示了分区加热冲压的变强度机理，通过平板换热试验，发现保温温度和保温时间可以明显改变淬后零件的力学性能，验证了利用分区加热冲压工艺生产变强度零件的可行性；采用Gleeble热模拟试验分析了高强钢高温变形行为，进而建立了一套耦合奥氏体化程度的本构模型；采用刚性凸模胀形试验研究了不同奥氏体化程度对高强钢成形性能的影响，建立考虑奥氏体化的平面应力成形极限预测模型；研究了高强钢奥氏体化过程及其对冷却相变的影响，建立考虑从加热到冷却的统一多尺度相变模型；最后借助有限元及其二次发开技术，实现了分区加热热冲压数值仿真，并能够准确预测零件力学性能和微观组织演化；建立了高温区和低温区加热工艺参数与淬后零件抗拉强度和延伸率之间的响应面模型，分析了加热温度和保温时间对淬后零件力学性能的交互影响。本项目揭示了分区加热热冲压中高强钢高温变形特性和变强度机理，实现“变形—传热—相变”耦合数值仿真，发展材料多尺度建模理论，为变强度零件的制造提供新思路；实现变强度零件试制，为变强度零件生产实践提供指导。