Abstract <p>The features of surface alloying of Hardox 600 steel using B₄C, WC, and Ni powders based on exposure to ytterbium fiber laser radiation are studied. The study of the geometric dimensions, quality, and structure of the surface layers was carried out. The laser-processing modes for steel were selected depending on the power density of the laser radiation of the installation, the linear velocities of the beam, and the diameter of the laser spot. It is shown that the doping process is critical to the regimes of laser action. At a radiation power of ~2 kW, high-quality doping zones can be observed more stably over the entire range of laser beam scanning speeds under study. With an increase in the depth of the alloying zone when using B₄C, the microhardness decreases, which is associated with a decrease in the concentration of introduced alloying elements. The microhardness of the layer can vary in the range of 7300–16 000 MPa.</p>