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Boron-based diffusion layers and coatings are capable to provide enhanced mechanical properties of machine elements and tools. Several methods of surface engineering result in the synthesis of such coatings and layers. In the present work, electron-beam alloying (EBA) and thermal-chemical treatment (TCT) of L6 and H21 tool steels were studied. Boron carbide and aluminum powders as alloying components were pre-mixed with ethanol to obtain a paste-like composition and applied to the treated surface. After drying, the samples were heated in two ways, by the continuous electron beam in a vacuum for 0.5-5 min or in a muffle furnace at the temperature of 1050 °C for 120 min. Metallographic analysis showed that the layer thickness on L6 steel was 1.1-1.2 mm after TCT and 0.3-0.35 mm after EBA; the layer thickness on H21 steel was 0.5-0.6 mm and 0.3-0.32 mm after TCT and EBA respectively. Both TCT and EBA processes resulted in complex structure formation on the surface of the tool steels. For example, the cellular structure was obtained on L6 steel after TCT, where coarse cellular dendrites were visible. As for H21 steel, several sublayers were distinguished after TCT. Both types of steels after EBA had a similar structure with light crystals embedded in the matrix. The maximum microhardness was measured in the upper layer on both types of steels, where boron-rich phases usually concentrate. It was determined that microhardness distribution over the layer thickness on H21 steel had a more favorable profile without significant fluctuations after EBA compared to the TCT process. On the contrary, a better microhardness distribution on L6 steel was observed after TCT rather than after EBA. However, the maximum microhardness after the first process was much lower than after the latter, corresponding to 1100 HV and 2100 HV respectively.