Influence of the edge conditions on the hole expansion property of dual-phase and complex-phase steels

Hole expansion behavior is one of the most important properties describing the formability of steel sheets, especially those used in automotive industry. In order to determine and emphasize the influence of hole edge conditions and hole surface quality on the results of standardized hole expansion tests, different hole preparation methods such as hole punching, hole drilling and wire cutting were applied on industrially produced dual-phase and complex-phase steel grades covering the tensile strength of approx. 800MPa. The damage characteristics of every procedure were investigated in detail via light optical microscopy (LOM) as well as scanning electron microscopy (SEM). Results of hole expansion testing are compared and discussed with respect to the impact of deformation introduced into the material during the hole preparation and material characteristics determined by microstructure as well as mechanical properties.