Heat treatment appts for metal workpieces, - with a molten salt quenching bath, the water content of which is automatically cont

Heat treatment appts. for metal workpieces has an adjustable oven atmosphere which is desirably at overpressure. The preheating chamber has an inlet at the same height or less than the height of the inner base of the chamber oven. A cleansing passage is provided to remove rising vapours from the drop shaft and prevent them from entering the oven chamber, as well as to prevent contaminants from penetrating into the quenching bath. This is effected by passing in gas at overpressure through one opening and sucking it off through a second opening above the first opening. A control mechanism regulates the concn. of the quenching bath and feeds in water from a flushing vessel as a function of the salt concn. in the quenching bath, if this exceeds a predetermined value.