Thermochemical Treatment System and Process for the treatment of steel or steel alloys by ionic bombardment. Two successive stages of operation are involved in which during the first stage, a DC voltage is applied across the electrodes of a furnace so that the furnace operates at a point far enough away from the arc formation zone to prevent formation of an arc and lies in the zone of abnormal discharge. During the second stage, a succession of pulses of voltage pulses of high voltage but of limited energy is applied to the furnace electrodes, and the operating point of the furnace moves along the voltage-intensity curve to a limit point far enough away from the arc formation zone, so that no arc formation takes place.