Analysis of Cooling Regimes as a Function of Biot Number During Quenching by Immersion

ABSTRACT This paper analyses the transition temperature and duration of the cooling regimes (film boiling, transition boiling, nucleate boiling, and convection) during quenching by immersion of specimens covering a range of Biot numbers from 0.70 to 1.32. Test data were acquired under an industrial environment, thus capturing the in situ conditions, information that is rarely available in the literature. The experimentally acquired cooling curves were processed to determine characteristic points, in the form of time, temperature, and cooling rate, representing the transition between cooling regimes. These points were precisely identified as per the peaks of the cooling curve derivatives with respect to time. The results show that transition temperatures tend to decrease with the number following a linear behavior. Correlation models between the duration of each regime and the number were developed following the nonlinear behavior of the regimes. The duration of boiling phases and convection evolve inversely; the former prevails as the number decreases, while the latter drives the cooling time for larger numbers. The models provide reference points for time and temperature that constitute the basis for a more comprehensive thermal modeling of immersion quenching.