冷连轧过程应力波诱导板形演变机理研究

The microcosmic foundation of the sheet flatness problem in cold tandem rolling process of advanced high strength steels (AHSS) is derived from the development and evolution of latent flatness defects (LFD), but now the evolution mechanism of stress wave induced latent flatness is still a difficult problem need to solve. In this project, the strain-hardening characteristics of advanced high strength steels during cold tandem rolling process were revealed intuitively through the study of the microstructure and evolution dynamics of dislocation configuration of materials, and then a high-precision material deformation resistance model was established. On this basis, using Hopkinson pressure bar experiment and high-resolution thermodynamics experiment, the dynamic behaviors characteristics of the stress wave propagation in advanced high strength steels were studied, after that, the propagating characteristics of stress wave were determined, and the experimental model on the stress wave propagation was also established. Meanwhile, the influence law of the stress wave propagation on latent flatness defects and the residual stress field was discussed, to reveal the influence mechanism of evolution of latent flatness defects on residual stress field (RSF); At the same time, based on the experimental data, the finite element simulation method (FEM) was used to construct the stress-temperature field under the condition of stable state and metastable state during plastic deformation process, and the emphasis was on the critical field characteristics of flatness defects and metastable flatness limit law, to establish a critical state physical model and geometric model of flatness defects, which demonstrates the inverse influence mechanism of change of the residual stress field on flatness defects, to further understand the microscopic mechanism of flatness defects. In the end, the theory of stress wave induced flatness evolution was presented, which provides theoretical and experimental support for the development and application of high-precision flatness control technology during cold tandem rolling process.

先进高强钢冷连轧过程板形问题的微观基础源于潜在板形缺陷的发展及演变，而应力波诱导板形演变机理是目前亟待解决的难题。本项目通过对材料微观组织形态和位错组态演变动力学的研究，直观地揭示先进高强钢冷变形过程应变硬化特性，建立高精度材料变形抗力模型。在此基础上，利用霍普金森压杆实验和高分辨率热力学实验，研究应力波在先进高强钢中传播的动态行为特征，确定其传播特性并建立应力波传播实验模型，进而探讨应力波传播对潜在板形缺陷和应力场的影响规律，揭示潜在板形缺陷演变对残余应力场的影响机制；同时，基于实验数据，采用有限元模拟方法构建稳态、亚稳态条件下的塑性变形应力-温度场，重点研究板形缺陷的临界场特性和亚稳态板形极限规律，建立板形缺陷临界态物理模型和几何模型，进而揭示残余应力场变化对潜在板形缺陷的逆影响机制，最终，形成应力波诱导板形演变理论，为冷连轧过程高精度板形控制技术的开发和应用提供理论依据和实验支撑。

先进高强钢冷连轧过程板形问题的微观基础源于潜在板形缺陷的发展及演变，而应力波诱导板形演变机理是目前亟待解决的难题。本项目研究了高强钢中应力波的动态行为特征和几何特征，揭示了应力波对潜在板形缺陷和残余应力场的影响规律，进而明确了板形缺陷演变对应力场的影响机制；解析了临界态板形缺陷的动力学和几何学条件，探索了板形缺陷的临界场特性和亚稳态板形极限规律，明确了应力场变化对潜在板形缺陷的逆影响机制，最终阐明了应力波诱导板形演变机理。研究结果表明：（1）先进高强钢冷变形过程中金属内部位错增殖，位错密度增大，造成位错运动阻力增大，使得变形抗力随着变形程度的增加而增大，但强化强度随变形程度的增加而降低，应变硬化曲线在27.5%~30.8%变形范围内会产生明显的“平台效应”；（2）应力波在超高强钢中随着传播距离的增加，透射波上升时间和持续时间均增加，而振幅减小，呈现显著地衰减效应；相同的传播距离，随着持续时间减小，其衰减率明显减弱。同时应力波传播的阻抗失配效应明显强于碳钢等材料，会产生较大的残余应力，对应力场有显著影响；（3）高速冷连轧极端压力-热力耦合条件下，当应力场中局部域的动力学条件和几何学条件达到板形缺陷的临界态条件，将诱导潜在板形缺陷的发展及演变，进而诱发宏观上的局部高阶浪形，为此提出了比温度法来定量判定潜在板形缺陷的发生；（4）基于应力波诱导潜在板形缺陷演变影响机理，采用非线性锥度结构开发了先进工作辊辊形技术，并采用复合函数模型开发出先进中间辊辊形技术，有效解决了先进高强钢高速冷连轧工艺过程应力波诱导潜在板形演变引起的高阶板形问题，提高了冷连轧机组板形控制能力。实践应用表明：先进高强钢板带的成品综合板形值可有效控制在< 3.0IU，成品带钢边降合格率可进一步提升到> 95.0%。通过本项目的探索工作，建立了应力波诱导板形演变基础理论，为冷连轧过程高精度板形控制提供新的理论指导和实验支撑。