Tribological characteristics of high strength steel sheets under hot stamping conditions

Nowadays, the hot stamping of high strength steel sheets is currently utilized to produce automotive components characterized by a high strength-to-weight ratio and an increased resistance to impact. In order to avoid scaling and decarburization during the heating stage, the metal sheets are coated with a specially developed Al-Si coating that have proved a relevant influence also on the tribological behaviour of the metal sheets during the forming stages. The paper presents a fundamental study about the sheet coating characteristics in terms of morphology, surface roughness and tribological behaviour as a function of the process parameters typical of industrial hot stamping processes. The presented results show that the blank heating promotes the iron diffusion into the Al-Si coating giving form to an Al-Fe-Si ternary alloy whose characteristics depend on the thermal cycle parameters; moreover, it is proved that the tribological characteristics of the metal blank surface in terms of friction coefficient depend on the blank temperature and contact pressure.