In the automotive industry, the heat treatment of strip steel safety components is a crucial and highly responsible process in terms of quality. The growing demand for passenger car safety makes heat treatment highly important in qualified engineering. This study is focused on the part austenitization in the industrial furnace. The study includes testing with a laboratory furnace and an industrial test on a continuous austempering line. The purpose of this work is to find the basis for selecting optimal furnace parameters for the heat treatment line furnace without affecting the final quality of treated parts. For this study, the safety belt tongue, as the main product of the involved company, was chosen. Seatbelt tongues are fineblanked from steel grade C60E, which is preferred for austempering, to gain the desired lower bainitic structure. The results of the study show that the austenitization of the parts depends on the furnace temperature, heating time, layer thickness and the geometry of parts. All these variables affect the final quality of the tongue.