以(84 - X)FeXCr15Co1Si (X = 20、25、30、35，质量分数，%)合金为研究对象，利用具有原子分辨率的扫描透射电子显微镜(STEM)研究了Cr元素对热处理后合金中α ₁和α ₂相形态、体积分数、尺寸分布、相成分、合金磁性能和硬度的影响。STEM分析结果表明，随着Cr含量由20%增加到35%，α ₁相的平均尺寸由26 nm逐渐增加到55 nm；随着Cr含量由20%增加到25%，α ₁相的体积分数增加了12%，但Cr含量的继续增加不能进一步改变体积分数。EDS结果表明，随着Cr含量的增加，富Fe-Co α ₁相里的Fe含量逐渐降低，而Cr和Co含量逐渐增加；同时，富Cr α ₂相里的Fe和Co含量逐渐降低，而Cr的含量逐渐增加。调幅分解过程可促使试样的硬度显著上升，且Cr含量的增加也可提升合金硬度。合金的剩磁、矫顽力和磁能积均随Cr含量的增加而逐渐增大，3者在Cr含量为25%时均达到最大值，并随Cr含量的继续增加而降低。分析了磁性能与α ₁相的尺寸、体积分数、成分以及与α ₁和α ₂相成分差之间的关系，讨论了调幅分解硬化合金的机理，并分析了Cr含量影响硬度的原因。

FeCrCo permanent magnet alloys draw wide attention because of their excellent machinability. These alloys can be deformed and extruded into thin wires or sheets for various applications, such as electric motors, telephone receivers, printers, and stereo cartridges. In these alloys, the content and distribution of Cr play an important role in improving their magnetic and hardness properties. To optimize both properties of these alloys, the effect of Cr must be studied. This study describes the effect of Cr content on microstructure, i.e., volume fraction, size, and composition of α ₁ and α ₂ phases in (84 - X)FeXCr15Co1Si (X = 20, 25, 30, 35, mass fraction, %) samples using atomic-resolution STEM. The effect of microstructure parameters on both Vickers hardness and magnetic properties was evaluated. STEM images showed that the average size of the α ₁ phase increased from 26 nm to 55 nm with an increase in Cr content from 20% to 35%. When the content of Cr increased from 20% to 25%, the volume fraction of the α ₁ phase increased by 12%, and when the content of Cr increased beyond 25%, the volume fraction remained the same. EDS results showed that with the increase of Cr content, in the (Fe-Co)-rich α ₁ phase, the content of Fe decreased, whereas the contents of Cr and Co increased. By contrast, in the Cr-rich α ₂ phase, the contents of Fe and Co decreased but the content of Cr increased. After step aging, hardness increased because of spinodal decomposition and continued to increase with an increase in Cr content. Remanence, coercivity, and magnetic energy product reached their maximum values when the content of Cr was at 25% and decreased as the content of Cr increased. The dependence of magnetic properties on the size, volume fraction, composition of α ₁ phase, and difference in composition between α ₁ and α ₂ phases was discussed. The mechanism for hardening was also discussed, which increased with the Cr content.