A novel approach to wear testing in hot stamping of high strength boron steel sheets

Abstract

Hot stamping of high strength steel sheets was developed in the automotive industry for the production of components characterized by a high strength-to-weight ratio and an increased resistance to impact. In order to avoid scaling and decarburization, the steel blanks are usually coated with an Al–Si coating that has proved a relevant influence also on their tribological behaviour during the forming stages. However, the knowledge of the influence that this coating may have on the dies wear mechanisms is still inadequate.The paper proposes a novel approach to wear testing, based on a pin-on-disk testing configuration, capable to reproduce in a laboratory environment the conditions arising at the interface between the dies and the blank, by reproducing the sliding velocities at the interface and the cyclic thermal and mechanical stresses on the die material. Investigations were carried out on a hot working tool steel sliding against high strength steel blanks coated with the Al–Si coating under dry reciprocating sliding conditions. Scanning electron microscopy and 3D profilometer analysis were utilized to evaluate the wear mechanisms.The presented results show that the proposed procedure can properly simulate the thermal and mechanical cycles to which the forming dies are subjected during the hot stamping process, allowing to control and vary a number of parameters characterizing the industrial process. The presence of both adhesive and abrasive wear mechanisms is highlighted and a possible explanation of their appearance is given.