Investigation of the tribological behaviour of hot stamping steel in a bending-under-tension test

Hot stamping is an industrially established process to form critical, safety-relevant components in the car body-in-white. This is enabled by martensitic hardening from high cooling rates between water-cooled tools and the austenitic workpiece. Austenitisation temperatures above 850 °C, prolonged furnace dwell times, and elevated forming temperatures prevent the use of lubricants, causing high friction and wear, impairing tool lifetime and part quality. To characterise tribological behaviour under these conditions, several laboratory-scale tests adapted from cold forming are used; however, these are limited in accurately reproducing hot stamping contact conditions. In this work, a modified strip-drawing rig adapted for bending-under-tension under hot stamping conditions is presented. The approach includes a breakdown of drawing-force components and a method to determine friction coefficients using an inverse approach and the Euler–Eytelwein formula. The study investigates radii (7.5, 10, 12.5 mm) and drawing temperatures (530, 600, 700 °C) for two Al-Si coating thicknesses 80 and 150 g/m 2 at 100 mm/s. The main experimental outcomes are summarised: friction coefficients differ between coatings; parameters significantly affect the 150 g/m 2 coating, while the 80 g/m 2 variant behaves similarly only at 700 °C. This is attributed to wear, which becomes comparable at 700 °C. The main mechanism behind tool-sided adhesive wear was workpiece-sided crack formation—perpendicular to the drawing direction—at lower temperatures due to limited coating formability. The new method enables the characterisation of the thinner coating. The results are compared with the previous setup to demonstrate the improved capability to assess friction and wear under hot stamping conditions.