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.