Controllable heat extraction technology - what it is and what it does

High pressure gas quenching became a modern way of quenching finally machined engineering components, having many advantages compared to quenching in liquid quenchants. The main shortcoming of this technology is the problem of achieving adequate hardness in the core of bigger work-pieces, because of inadequate quenching intensity. Due to the possibility of changing gas pressure and its flow velocity, combined with transient spraying of liquid nitrogen during the quenching process, the intensity of cooling can be instantly increased during selected time intervals. In this way, the heat extraction dynamics can be automatically controlled, and a predetermined path of the heat transfer coefficient can be followed. Preliminary experiments show that using the controllable heat extraction (CHE) technology, the mentioned shortcoming can be eliminated. Theoretical background of the CHE technology is described, with particular attention to the depth of hardening, and to residual stresses. Possibilities and prerequisite conditions for application of the CHE technology in vacuum furnaces, and for automatic heat extraction control, are discussed.