Si Alloying Enables High Performance in Ce‐Substituted Hot‐Deformed Nd–Fe–B Magnets

High levels of Ce substitution typically degrade the magnetic performance of hot‐deformed Nd–Fe–B magnets, posing challenges for developing resource‐efficient permanent magnets. Here, we demonstrate that minor Si alloying in (Nd 0.6 Ce 0.4 )‐Fe‐B hot‐deformed magnets effectively compensates for this degradation and enables enhanced magnetic performance. It yields a coercivity of 9.5 kOe, a remanence of 13.2 kG, and a maximum energy product of 40.1 MGOe, thereby demonstrating superior magnetic performance compared with previously reported Ce‐ or La/Ce‐substituted magnets at comparable substitution levels. Microstructural analyses reveal that Si effectively refines the grains and generates Si‐rich/Fe‐poor grain–boundary films that weaken intergranular exchange coupling and thereby enhance magnetic performance. These results demonstrate that Si‐driven grain–boundary chemistry engineering offers an effective route to mitigate the magnetic performance degradation of Ce‐rich Nd–Fe–B magnets.