铈改善无取向硅钢磁性能机理研究

It is important and necessary for saving energy to develop the high magnetic induction and low iron loss non-oriented silicon steels. Magnetic properties of non-oriented silicon steels are mainly affected by grain size, textures and inclusions, which could be influenced significantly by addition of rare earth. However, on one hand, the present works mostly focus on the misch metals. The mechanism of modifying magnetic properties by single rare earth is still lacking understanding. On the other hand, the effect of rare earth on modifying texture of non-oriented silicon steels isn’t also researched in depth, moreover, there are few attempts to discuss the relationship among modifying inclusions, affecting grain size and ameliorating texture which are important for elucidating the mechanism of Ce addition in non-oriented silicon steels. Therefore, the effect of Ce on the magnetic properties of non-oriented silicon steels will be investigated in the project. Firstly, some non-oriented silicon steels with different Ce content are manufactured by the same technology, including vacuum melting, casting, hot rolling, cold rolling, normalizing, etc. The relationship between Ce content and magnetic properties of non-oriented silicon steels will be obtained. Secondly, the effect of Ce on the modifying inclusions, affecting grain size and ameliorating texture in non-oriented silicon steels will be investigated by using OM, SEM/EDS, TEM and EBSD etc. Then, on the basis of above works, the effect of Ce on the evolution of recrystallized texture and possible coupling effect of above three aspects will be discussed detailedly. Finally, theoretical model of coupling effect will be achieved and mechanism of magnetic properties improvement by addition Ce in non-oriented silicon steels will be revealed. It will be helpful for the research and development of high efficiency silicon steels.

高磁感、低铁损无取向硅钢对于节能降耗意义显著。影响磁性能的因素主要有晶粒尺寸、织构组分及夹杂物性质等，研究表明稀土在这三方面均发挥着明显作用，对改善磁性能有益。但目前的工作，一方面研究对象大多为混合稀土，单一元素改善磁性能的机理尚不明确；另一方面并未深入探讨稀土对再结晶织构的影响机理，且关于变质夹杂、调控晶粒尺寸、改善织构三者之间的相互影响关系研究也不充分。本项目针对上述问题拟开展铈对无取向硅钢磁性能影响机理研究。首先，采用统一的工艺制得不同铈含量的无取向硅钢成品，测量其磁性能，获得铈含量与成品磁性能的关系；其次，利用OM、SEM/EDS、TEM、EBSD等技术研究铈在改善织构、变质夹杂、调控晶粒尺寸等方面的作用；然后，在此基础上重点研究铈对再结晶织构演变规律的影响，探讨三者可能的耦合效应，建立相关的理论模型，揭示铈改善无取向硅钢磁性能的机理，为高性能无取硅钢研发提供理论指导。

无取向硅钢是电机中应用最广泛的软磁材料，是构成电机核心部件的关键材料之一，其磁性能优劣直接影响着电机效率，开发高效无取向硅钢具有显著的节能降耗意义。无取向硅钢磁性能决定于铁损和磁感两方面，高磁感、低铁损是良好磁性能的保证。然而，这两者往往不能兼顾，很难同时趋优。因此，同时提高磁感和降低铁损是高效无取向硅钢开发过程中面临的关键问题。本项目主要针对目前无取向硅钢研究中同时提高磁感和降低铁损存在的困难，对单一稀土元素铈在无取向硅钢中变质夹杂、调控组织及改善织构等方面的作用进行了较系统的研究，揭示了铈改善磁性能的机理。结果显示，无取向硅钢铁损随铈含量的增加先降低后升高，磁感应强度则先升高然后降低。合适的铈含量时铁损值最低，磁感应强度值最高，磁性能达到最佳。随着铈含量的增加，无取向硅钢的平均晶粒尺寸以及有利织构组分所占比例（织构因子{100}/{111}和{100}+{110}/{111}）均先增大后减小，适量的铈能使有利织构组分所占比例和平均晶粒尺寸达到最大值。适量的铈显著降低了无取向硅钢中微细夹杂物（尺寸<1μm）的数量，增加了粗大夹杂物（尺寸：2~5μm）数量；铈使AlN、Al2O3等夹杂物变性为球状的CeO2S2+AlN、CeS+CeAlO3和CeS+Al2O3等复合夹杂，有效抑制了钢中MnS的析出。一方面，细小夹杂物数量降低使得晶粒长大的钉扎阻力变小，可以一定程度上充分长大，减小晶界数量从而降低磁畴转动阻力；另一方面，球状夹杂物与基体的界面应力集中程度小，对于磁畴转动的阻力小，有利于磁感的提高；再一方面， MnS析出受抑制并且AlN、Al2O3等夹杂有效被变质，可促进{100}和{110}位向的晶粒长大，阻碍退火时{111}和{112}位向的晶粒在AlN、MnS等夹杂物附近优先形核，使得再结晶形核织构和长大过程中晶粒织构中有利织构所占的比例更高，而对磁性能不利的{111}面织构所占的比例更低，提高磁性能。而过量的铈会生成过多的Ce2O2S和CeS夹杂，不但增强了晶界钉扎力，阻碍了退火时晶粒长大，而且还促使对磁性能有害的{111}位向的晶粒在其周围优先形核，恶化了磁性能。