Abstract <p>The structural, phase, and elemental compositions, hardness, and Young’s modulus of transition layer of a “plasma-enhanced molybdenum high-speed steel coating—steel substrate” system subjected to pulsed electron beam irradiation were studied. It was found that coating formation is accompanied by the creation of an extended transition layer containing α- and γ-phases, as well as carbides of complex composition. A lamellar structure with particles of cementite and M₆C-type carbide was revealed within the transition layer volume after irradiation. The substrate contact zone, immediately adjacent to the coating, contains grains of residual austenite strengthened by nanosized M₆C-type carbides. It was revealed that electron beam processing of the “plasma-enhanced molybdenum high-speed steel coating—steel substrate” system leads to a decrease in the hardness and Young’s modulus of transition layer. Physically substantiated ideas are put forward regarding the causes of the decrease in hardness and Young’s modulus of transition layer.</p>