Method of and apparatus for hardening workpieces in a liquid hardening agent

In hardening by cooling in a positively circulated liquid hardening agent, in order to prevent a distortion of the workpieces leading to stresses and crack formations the cooling is such that after the first film vaporisation phase of the cooling operation, effected with positive circulation, and during the subsequent second boiling phase the flow through the quench shaft (3) is interrupted or reversed and the speed of flow of the hardening agent (2) on the workpiece surface (at grid 4) is brought at least nearly to a halt, whereafter, after the transition from the boiling phase into the subsequent third convection phase, the flow through the quench shaft is recommenced with positive circulation (5) of the hardening agent.