Development of a numerical model for estimating the hardness of steel after quenching

For estimation of hardness of steel after quenching, the transient thermal numerical model was developed enabling simulation of the quenching process i.e., rapid cooling of the steel specimen in the quenching medium. Relevant variables in heat transfer during quenching process are geometry of the specimen, temperatures of quenchant and specimen and related material and heat transfer coefficients. Due to the unknown values of the heat transfer and heat conduction coefficients, numerical model and corresponding parameters were calibrated based on simulated cooling curves and reference cooling curves for both the surface and the core of the specimens obtained from the literature. During the development of the numerical model, particularly high influence of the heat transfer coefficient and to a somewhat lesser degree that of heat conduction coefficient and their significant dependence on temperature was observed. Iterative calibration procedure that considers the non-stationarity of these coefficients was performed. For model validation, the obtained hardness values were compared with experimental results from literature.