PSI - Issue 68

Ema Kukuljan et al. / Procedia Structural Integrity 68 (2025) 822–827 E. Kukuljan et al. / Structural Integrity Procedia 00 (2025) 000–000

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7. Discussion and conclusions The developed transient thermal numerical model enables simulation and estimation of the hardness after the quenching process i.e., rapid cooling of the steel specimen in the quenching medium. Relevant variables in heat transfer during quenching 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 conductivity coefficients, the 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, a particularly high influence of the heat transfer coefficient and to a somewhat lesser degree that of heat conduction coefficient and their significant temperature dependence were observed. Iterative calibration procedure that considers the non-stationarity of these coefficients was performed. Based on the cooling curves obtained for each node of the model, values t 8/5 representing the time required for cooling from 800°C to 500°C were determined and used for the analytical determination of resulting hardness using Jominy diagram and related values. The validity of the developed numerical model was confirmed by comparing the obtained hardness values with experimentally determined hardness values of quenched steel specimens. Acknowledgements This research has been supported by Croatian Science Foundation under the project IP-2020-02-5764 and by the University of Rijeka under the project number uniri-tehnic-18-116. The work of doctoral student Ela Marković has been fully supported by the „Young researchers’ career development project – training of doctoral students” of the Croatian Science Foundation. References Ansys Inc., 2010. ANSYS Mechanical APDL Command Reference. Liščić, B., Singer, S., Smoljan, B., 2010. Prediction of quench-hardness within the whole volume of axially symmetric workpieces of any shape. ASTM Special Technical Publication, 1523, STP, 467–488. Max Planck Institute, 1954. Atlas zur Wärmebehandlung der Stähle. Verlag Stahleisen. Smoljan, B., Iljkić, D., Totten, G. E., 2015. Mathematical Modelling and Simulation of Hardness of Quenched and Tempered Steel. Metallurgical and materials transactions B, Process metallurgy and materials processing science, 46, 6, 2666-2673. Smoljan, B., Liščić, B., 1999. Computer simulation of quenching of steel workpieces with complex shape. 7th International Seminar of IFTH. Budapest.