Transient Cooling of Metallic Piece during a Quenching Process: Effect of Bath Agitation

Abstract During the quenching process, metallurgical transformations and residual stress fields are controlled by the metallic piece cooling speed. It is a fact that the agitation of the bath matters, and this is why all the industrial processes use agitated baths in the quenching process. The first role of agitation is to remove the vacuum film from the vicinity of the metallic piece. This agitation should contribute to the enhancement of convective heat coefficient, but the effect of such an increase of the convection heat transfer depends on the size and properties of the metallic piece. It was shown that the cooling process is predominated by convection in the cases of massive, resistive, or massive and resistive metallic pieces (mean Biot number higher than 10). In contrast, in the cases of thin, very conductive, or thin and very conductive pieces, boiling is the main cooling phenomenon. This study will focus on the characterization of the fluid flow depending on the agitation system—a pump or a turbine. It has been observed that the flows are dramatically different in terms of velocity field and energy dissipated. The results of this study could help in the design of an agitation system, considering the metallic piece to be treated.