Abstract The nitriding performance of low power electron beam excited plasma is investigated by characterizing the surface of nitrided low alloy Cr–Mo steels. In this research, a particular attention was given to the effect of the acceleration voltage and processing time on the composition and hardness of the processed samples. In an attempt to maximize the dissociation of N 2, the acceleration voltages applied in our experiments were set within a range that corresponds to the maximum dissociation cross-section of N 2. The results show that the peak intensity of the alpha Fe observed for the unprocessed sample decreases as the acceleration voltage increases. Moreover, the peak intensities depicting the formation of the nitride compound layers, Fe 4N and Fe 3N phases, increases with the acceleration voltage of the electron beam. Consequently, the surface hardness of the treated low alloy steel was increased by more than two times that of the unprocessed specimen.