In this investigation, an electron beam hardening (EBH) procedure was applied to heat-treatable steel 51CrV4 coated with Ti(1-x)AlxN hard coatings, where x ranged from 0.3 to 0.6. The coatings with variable composition and mechanical properties were deposited by reactive magnetron sputtering. For electron beam surface hardening following hard coating deposition, the energy distribution within the energy transfer field caused a nearly constant hardening temperature on the treated material surface. Morphology, composition, and mechanical properties of the coatings remained mostly unchanged, whereas the coating-substrate interface and the steel surface region were highly modified. Diffusion of the near-interface coating elements into the substrate occurred, and the corresponding region of the substrate showed clear changes in morphology and composition. These changes can be correlated with substantial improvements of the coating adhesion properties. Based on temperature measurements and calculations of electron penetration depths, a plausible description of the observed effects was derived. The EBH caused a significant improvement of delamination resistance, especially for coatings with insufficient adhesion properties.