In this study, the AISI 440C steel was plasma paste borided in a gas mixture of 70 %H2–30 %Ar using borax paste as a boron source. This thermochemical treatment was carried out at three temperatures of 700, 750 and 800 °C for 3, 5 and 7 h. The morphology of the formed boride layers was studied by scanning electron microscope. An identification of iron borides was performed using an X-ray microanalyzer, equipped with energy dispersive X-ray spectroscopy. The phases present in the boride layer were identified by means of X-ray diffraction analysis. In addition, the glow discharge optical spectroscopy analysis was performed in order to determine the concentration profiles of elements. The wear resistance of plasma paste borided AISI 440 C steel (at 800 °C for 3 h) was also investigated. As a result, the value of boron activation energy for the AISI 440C steel was found to be equal to 134.62 kJ mol−1 on the basis of our experimental results. Finally, this value of boron activation energy was compared to the literature data.