Inferring the specific heat of an ultra high strength steel during the heating stage of hot forming die quenching, through inverse analysis

In hot forming die quenching, furnaces are used to austenitize ultra high strength steel blanks. In the case of coated steels, like Usibor® 1500 P, furnace heating also transforms a protective Al-Si layer into a permanent Al-Si-Fe coating. Modeling this process requires knowledge of how the sensible energy and latent heat of austenitization change with blank temperature; while the former is known, there is considerable uncertainty regarding the latter. In this work the effective specific heat of Usibor® 1500 P is inferred through inverse analysis of temperature data collected on coupons heated in a muffle furnace. This technique is first used to validate the heat transfer model, and then used to investigate austenitization at higher temperatures. Finally, the methodology is applied to analyze temperature data collected from an instrumented blank heated in a roller hearth furnace.