无取向硅钢铁芯制造中织构与局部残余应力相互作用机制研究

The development of new energy vehicles puts forward the special performance requirements to the driving motor with small volume, light weight and high power density. This puts forward higher requirements for the magnetic properties of non-oriented silicon steel, which is the key material for the motor core. However, during the manufacturing process of iron core, punching and annealing process always affects the residual stress distribution and texture of non-oriented silicon steel’s cutting edge to weaken its magnetic performance. Therefore, it is urgent to solve the problems of the evolution and interaction mechanism between residual stress and texture in the process of punching and annealing. In response to these problems, we will realize in this project the measurement of local residual stresses in non-oriented silicon steel with the help of X-ray diffraction, and analyze the local residual stresses distribution after punching. The deformation mechanism, recovery/recrystallization mechanism and texture evolution during punching, and annealing processes will also be studied using Electron Backscattered Diffraction (EBSD) technology. On this basis, we plan to define the influence of grain orientation on plastic deformation and local residual stress distribution during deformation process, and reveal the influence of local residual stress distribution on recovery/recrystallization mechanism and texture evolution during annealing process. In order to minimize the influence of manufacturing process on the magnetic properties of motor core, all of these studies will provide theoretical basis for simultaneous control of the texture and residual stress distribution by optimization of manufacturing procedures and parameters.

新能源汽车的发展对驱动电机提出了体积小、质量轻和功率密度高的要求，这就对电机铁芯关键材料无取向硅钢的磁性能提出了更高的要求。然而在铁芯制造过程中，冲裁和退火工艺会对无取向硅钢切割边缘的残余应力分布及局部织构造成影响，降低其磁性能。为此，冲裁和退火过程中材料切割边缘残余应力和局部织构的演变及相互作用机制等问题亟待解决。针对这些问题，本项目将借助X射线衍射法，实现对无取向硅钢局部残余应力的表征，通过分析冲裁过程中局部残余应力的分布情况，借助电子背散射衍射(EBSD)技术，研究冲裁和退火过程中边缘区域的形变机制、回复/再结晶机制及织构演变规律。在此基础上，探讨冲裁过程中织构对塑性形变和局部残余应力分布的影响，以及退火过程中局部残余应力分布对回复/再结晶机制与织构演变的影响，为通过优化工艺参数实现无取向硅钢中织构及残余应力的同步调控，最大限度降低制造工艺对电机铁芯磁性能的影响提供理论依据。

无取向硅钢是车用电机铁芯所需要的重要软磁材料。目前，生产过程中主要借助冲裁工艺制备电机铁芯的叠片。由于冲裁工艺会对无取向硅钢切割边缘织构及残余应力的分布造成影响，降低其磁性能。因此，研究冲裁过程中无取向硅钢切割边缘织构的演变机制及残余应力的产生机制等问题具有一定的科学和应用价值。针对这些问题，该项目执行过程中首先借助电子背散射衍射（EBSD）技术，研究了冲裁后无取向硅钢切割边缘的微观组织及织构的演变。在此基础上，分析了材料切割边缘的塑性形变分布及机制，并揭示了其对材料局部织构演变的影响。研究结果表明，距离切割边缘越近，塑性形变越强，晶粒内部开始出现微观剪切带，从而使得无取向硅钢切割边缘的局部织构发生较大的变化。然而，沿着切割边缘，每个位置所形成的微观剪切带的晶粒取向有所不同。因此，冲裁后的无取向硅钢切割边缘上，每个位置的局部织构分布不尽相同。随后，该项目在塑性形变分布研究的基础上，结合Johnson-Cook（JC）塑性形变准则和JC断裂准则，建立了无取向硅钢冲裁过程的有限元仿真模型。与此同时，借助纳米压痕及有限元仿真，研究了无取向硅钢冲裁边缘残余应力的形成机制。研究结果表明，冲裁模具的钝化程度对切割边缘残余应力的分布具有一定的影响，钝化的模具更有利于在切割边缘形成对材料磁性能影响较小的残余拉应力。