珠光体钢丝冷拉大变形应变路径效应及微观组织演变机理研究

Pearlitic steel wire drawing is one of metal forming processes, in which the diameter of initial wire rod is reduced progressively in a number of passes accompanying with the change in strain path to produce super high strength wire with fine nano lamellar structures. The urgent requirements for light weight and low-loss products in the steel wire market increase the demand for much higher strength steel wires, hereafter, it is a key and hot topic for both industrial companies and researchers to develop new theories and technologies for producing high strength or super high strength steel wires. In steel wire drawing, the material in the wire core and surface experiencing different strain paths due to the effect of die geometries, will present significant difference in the lamella structure, texture and the mechanical properties. which is named as the strain path effects. As taking strain path as a breakthrough, this project is going to develop an accurate finite element model of multi-pass wire drawing for the strain path analysis; a multi-scale model involving the strain path modeling, the lamella deformation modeling, and the texture modeling; as well as characterizations of the lamellar structure and texture and measurements of the gradient mechanical properties by considering the strain path effects. It aims at study the mechanisms in the strain path evolution, the effects of stain path on lamella structure deformation, texture evolution and mechanical properties between wire core and surface. Based on the new developed strain path effects theory, it will open a new gate to develop super high strength wires with the better control in the strain path and the microstructure evolution.

珠光体钢丝冷拉工艺使钢丝依次通过一系列模具，发生应变路径变化，制备具有极细纳米层片结构的高强度钢丝广泛应用于轮胎钢帘线、切割钢丝和绳缆等。随着钢丝制品市场轻量化和低损耗对钢丝强度要求的不断提升，开发制备高强度或超高强度的钢丝制品的理论与技术已成为企业和学者研究的重点。本项目针对冷拉变形过程钢丝表层和心部材料由于经历不同的应变路径而体现出显著的层片组织结构、晶体学织构和力学性能差异的应变路径效应，拟以应变路径为突破口，分别开发多道次拉拔应变路径全纪录有限元模型、应变路径与层片组织变形和织构演变的多尺度模型、考虑应变路径效应的层片组织和织构实验定量表征方法和力学性能测试方法，研究冷拉过程应变路径变化机理以及应变路径变化对钢丝心部与表层织构演变、层片组织变形和力学性能的影响机理。通过完善钢丝冷拉大变形应变路径效应理论，更好控制应变路径和珠光体层片组织演变开发高强度钢丝开辟一条新思路。

本项目以应变路径为突破口，研究冷拉变形过程钢丝表层和心部材料由于经历不同的应变路径而体现出显著的层片组织结构、晶体学织构和力学性能差异的应变路径效应。首先，开发了多道次拉拔应变路径全纪录网格传递有限元模型，解决了大变形网格畸变难题，预测钢丝强度误差2%以内，拉拔力预测与实测结果吻合，并揭示了心部与表层存在的现在的应变路径差异。其次，开展了由扭转、拉伸和反向扭转组合的简单应变路径的钢丝组织与性能的演变实验和数值模拟研究，揭示了层片间距、取向和形貌在各种复合应变路径下的演变规律，以及对力学性能的影响；再次，开发了应变路径、层片组织变形和织构演变FEM/RVE/VPSC的多尺度模型,结合层片组织SEM/TEM、织构EBSD和电解去除法测定梯度力学性能等实验，揭示了表层与心部珠光体层片组织拉伸、剪切、扭转和卷曲等演变机理以及心部与表层织构的演化规律，预测结果与实测结果吻合。项目完善了钢丝冷拉大变形应变路径效应理论，为更好控制应变路径和珠光体层片组织演变开发高强度钢丝开辟一条新思路。