In the hot stamping process, the temperature evolution drives the metallurgy, as well as the metallurgical transformation influences the temperature evolution through the exothermic nature of the austenite to martensite transformation. This heat release has already been highlighted by previous experimental work. This heat release leads to a source term in the heat equation in the blank. This source term must be quantified in order to accurately predict blank temperature evolution. Moreover, the end of the heat release corresponds to the end of the metallurgical transformation. It allows the determination of the minimum quenching time, relevant information for industry to minimize the process time.
This paper presents a method to quantify the heat released by the metallurgical transformation during the hot stamping of Usibor 1500P® ArcelorMittal steel, solving inverse conduction problems. It allows the determination of this heat release as a function of temperature or time. Then, integrating it, the latent heat of the transformation can be estimated. This can be done for different contact pressures between tool and blank. Finally, it can be linked to the martensite proportion to estimate it as a function of time or temperature and determine the Koistinen-Marburger model parameters. These results should improve the accuracy of numerical simulations of the hot stamping process.
