Abstract: Continuous thermal treatment for the strengthening of metallic workpieces is carried out by placing a batch of at least two workpieces on a basket hinged on a continuously advancing conveyor chain; introducing said workpieces in said basket through a first instantaneously opening and closing gate into a uniformly heated first thermal treating step wherein the continuously advancing workpieces are heated at a temperature of about 560.degree. C.; introducing the heated workpieces in said basket through a second instantaneously opening and closing gate into a second thermal treatment step placed immediately after the end of the first step and in communication therewith, by lifting a vat containing a cooling fluid to immerse said workpieces in said basket into the cooling fluid of said vat to rapidly cooling said workpieces to a temperature of about 100.degree. C. and thereafter lowering said vat.