<b>Abstract</b>— <p>The structure, mechanical, and tribological properties of the surface of the plasma-sprayed deposited layer in a nitrogen environment of high-speed molybdenum steel on a substrate of medium-carbon steel 30KhGSA were studied using methods of modern physical materials science. It was found that the deposited layer has a polycrystalline structure and contains eutectic interlayers. The eutectic grains are formed by alternating layers of carbide of the Me₂₃C₆ or Me₆C type and layers of the α-phase. Less often, monolithic inclusions of carbides of the Me₂₃C₆ or Me₆C type are found along the grain boundaries of the α-phase. The multiphase structure of the deposited layer is represented by the α-phase (solid solution based on the bcc crystal lattice of Fe), γ-phase (solid solution based on the fcc crystal lattice of Fe), carbides of complex composition Me₂₃C₆ and Me₆C, and iron carbide of the Fe₂C composition. The formation of the deposited layer is accompanied by martensitic γ → α transformation with the formation of a lamellar martensite structure. The revealed regularities of the change in nanohardness and Young’s modulus with the distance to the irradiation surface confirm the developed ideas about the nature of hardening of the plasma-deposited layer of high-speed molybdenum steel due to the formation of a martensitic structure and the presence of eutectic grains.</p>