Abstract: Densely distributed coherent nanoparticles (DCN) in steel matrix can enhance the work-hardening ability and ductility of steel simultaneously. All the routes to this end can be generally classified into the liquid–solid route and the solid–solid route. However, the formation of DCN structures in steel requires long processes and complex steps. So far, obtaining steel with coherent particle enhancement in a short time remains a bottleneck, and some necessary steps remain unavoidable. Here, we show a high-efficiency liquid-phase refining process reinforced by a dynamic magnetic field. Ti–Y–Mn–O particles had an average size of around (3.53 ± 1.21) nm and can be obtained in just around 180 s. These small nanoparticles were coherent with the matrix, implying no accumulated dislocations between the particles and the steel matrix. Our findings have a potential application for improving material machining capacity, creep resistance, and radiation resistance.