基于形变储能的薄带连铸4.5wt.%Si高硅钢再结晶形核机制及调控理论

Thin gauge, high silicon content and strong easily-magnetized texture give the developing direction for medium and high frequency non-oriented silicon steel. In the preliminary study, short process and highly efficient preparation of high silicon steel were realized by the idea of “twin roll strip casting + moderate silicon content design (4.5wt.%Si)”. It is found that the induced formation of strong easily-magnetized texture is an effective way to further enhance the soft magnetic properties. The project intends to proceed from the perspective of deformation stored energy. Based on the thermodynamics and kinetic theories of recrystallization, the sub-structure evolution and stored deformation energy characteristics of the experimental steel will be systematically studied during recovery and nucleation stage after large deformation, clarifying the mechanism of priority nucleation for specific orientation, revealing the conditions of stored deformation energy to avoid orientation pinning, and establishing integrated regulation and control guidelines of the sub-structure and stored energy during recovery. The aim of this project is to find the control theory and technology of preferred orientation “appropriate nucleation” based on the stored deformation energy, to solve the key scientific issues about the mechanism and control theory of recrystallization nucleation, and to provide theoretical support to develop high quality high silicon steel ultra-thin strip.

薄规格、高硅元素含量和强易磁化织构是中、高频用无取向硅钢的发展方向。前期研究通过“薄带连铸+适度硅元素含量设计(4.5wt.%Si)”的思路，实现了高硅钢超薄带材的短流程高效制备。研究发现诱导形成强易磁化织构是进一步提升其软磁性能的有效途径。本项目拟从形变储能角度出发，以再结晶热力学和动力学理论为基础，系统研究大变形条件下实验钢在回复和形核阶段的亚结构演化及形变储能特征，明确特定取向晶粒的优先形核机制，揭示避免取向钉扎的形变储能临界条件，建立回复过程中亚结构与形变储能的一体化调控准则。项目研究旨在发现基于形变储能的择优取向“适度形核”控制理论与技术，解决再结晶形核机制及调控理论中的关键科学问题，为高品质高硅钢超薄带材开发提供基础理论支撑。

为满足电机小型化和高效化的发展需求，大幅提高了电机的工作频率，当前常规无取向硅钢在中、高频环境下铁芯损耗严重。高硅元素含量、强易磁化织构以及更薄厚度规格的无取向硅钢将是中、高频电机铁芯材料的发展方向。本项目采用短流程薄带连铸技术与适度硅元素含量设计（4.5wt.%Si）相结合，通过减薄成品厚度及形成强{100}织构，开发高品质高硅钢超薄带材。基于形变储能对再结晶行为的作用，开展了铸带组织结构、轧制路线、预退火工艺对再结晶形核、成品织构以及性能水平的影响研究。再此基础上，通过合金成分及浇铸工艺优化，获得了强{100}<013>织构的4.5wt.%Si钢，并对回复阶段亚结构演变以及{100}<013>织构形成机制进行了分析研究。另外，通过调整铸带组织及设计轧制压下率配比，制备了4.5wt.%Si钢超薄带材。研究发现连铸薄带经一步冷轧和短时退火后抗拉强度达到719MPa，铁损P10/400为35.66W/kg。两步冷轧工艺能有效提高成品磁性能，尤其第二阶段采用小变形冷轧，铁损P10/400低至21.43W/kg，基体以强Cube ({100}<001>)和Goss ({110}<001>)织构为主，{111}织构几乎完全消失，但抗拉强度降低至605MPa。晶粒尺寸能显著影响冷轧组织结构及形变储能，进而改变再结晶织构，通过晶粒尺寸优化，制备了一种含较强{100}织构的无取向硅钢薄带，相同厚度条件下铁损值进一步降低，P10/400为17.69W/kg。与普通规格无取向硅钢相比，冷轧超薄带中原始晶界处形变剧烈、形变储能高，大量晶核优先在原始晶界处形成。利用强{100}织构的等轴晶铸带组织，获得了强{100}<013>再结晶织构的硅钢薄带。研究发现回复过程中位错通过滑移、攀移实现对消、重排，生成无畸变亚晶，{100}<013>取向晶粒在剪切带位置优先形核，并保持数量和尺寸优势，定向形核机制是终形成强{100}<013>织构的主要原因。低温预退火通过改变基体形变储能和微观亚结构直接影响随后高温退火薄带的织构组分同时不改变基体组织的晶粒尺寸，为织构优化提供了一种新思路。本项目对4.5wt.%Si钢再结晶形核及织构优化进行了较细致的研究工作，相关成果可为短流程制备中、高频用无取向硅钢带材提供参考和理论基础。