Estimation of hole flangeability for high strength steel plates

Hole flanging experiments are performed on flat circular plates with a hole in the center to investigate the fracture and lip shape behaviors of TRIP steels and ferrite–bainite duplex (F+B) steels. The conventional hole flanging process is limited to a certain limit hole diameter below which failure will ensue during the hole expansion. In the hole flanging, deformation by lip or fracture by petalling may occur when sheets are struck by punches of various shapes and high circumferential strains are induced in the deforming material. Fracture of the plate during hole flanging is mainly caused by lip fracture that results from multiple localized neckings that take place around the hole periphery where straining is most severe. F+B steel has better hole flangeability than TRIP steel in the viewpoint of minimum hole diameter, while in the viewpoint of lip shape accuracy and lip height TRIP steel has better formability than F+B steel. Both criteria are proved to be valuable indices to estimate the hole flangeability of high strength steel.