进口磁铁芯片的渗氮层组织与热处理工艺分析

Analysis on Microstructure and Heat Treatment Process of Nitriding Layer of the Import Magnetic Chips

对某进口电磁纯铁制成的磁铁芯片的表层和心部组织进行了金相、扫描电镜观察和能谱分析,并检测了显微硬度。实验结果表明,进口磁铁芯片的基体是沿轧制方向伸长的铁素体晶粒,而工作端的局部表面渗层分为两层,最表层是细小片状屈氏体,次表层是铁素体等轴晶粒+针状γ'(Fe4N)氮化物。能谱检测结果表明,渗层中含氮量明显高于含碳量。因此可以认为,进口磁铁芯片的工作端面采用局部软氮化(氮碳共渗)处理之后,再进行工作端面的局部加热和快速冷却热处理工艺。由于经该工艺处理的磁铁芯片心部未受到热损伤,保持了稳定的软磁特性,而局部热处理使工作端面获得较高硬度的软氮化层,提高了其耐磨性,因而进口磁铁芯片的使用寿命明显延长。

In this paper,the surface layer and matrix structures of magnetic chips prepared by import electromagnetic pure iron were observed and analyzed by metallographic,scanning electron microscope and EDS,as well as microhardness was tested. The experimental results show that the matrix is elongated ferrite grain along rolling direction and the local surface layer at working end consists of two layers,in which the surface layer is the fine troostite and the next is the equiaxed ferrite grain with some acicular γ＇（ Fe4N） nitrides. Result of EDS shows that nitrogen content is obviously more than carbon content. So it is considered that the working end of the import magnetic chips is treated by local tufftride（ nitrocarburizing）at first,then by the heat treatment of locally heating and rapidly cooling. Because of no heat damage to the matrix of magnetic chips by that process,the stable soft magnetic property is maintained. The local heat treatment makes the working end get tufftride layer with higher hardness and improve its wear resistance.Therefore,the service life of the import magnetic chips is obviously prolonged.