Differential hot stamping of USIBOR® 1500 steel: effect of partial tool heating on phase transformation, hardness and springback

Abstract This study investigates the thermo-mechanical response of USIBOR ® 1500 steel subjected to differential hot stamping using partial tool heating. Real-time temperature measurements, cooling rate analysis, microhardness mapping, and optical microscopy were employed to establish process–structure–property relationships under non-isothermal conditions. Increasing tool temperature (100–300 °C) reduces local cooling rates in the heated regions, promoting a transition from predominantly martensitic to mixed martensitic–bainitic and bainitic-dominated microstructures. This transition is accompanied by a decrease in hardness from approximately 470 HV 0.2 to 326 HV 0.2 . Partial tool heating also affects springback behavior, inducing a mensurable shift toward negative springback due to asymmetric thermal contraction and phase transformation-induced strains. The results demonstrate that partial tool heating provides an effective and controllable strategy for tailoring local mechanical properties and springback response in press-hardened steel components.