Sheared edge formability of multi-phase steels under in- and out-of-plane deformation

Abstract

Multi-phase advanced high strength steels can exhibit significant sheared edge sensitivity due to their microstructures and alloying elements. Processing defects such as centerline segregation of martensite or Ti-based inclusions can affect edge formability depending upon the applied deformation such as in-plane stretching versus out-of-plane hole extrusion. This study investigates the influence of punching clearance and deformation mode on the sheared edge formability of two hot-rolled MP800 steels, MP800-V1 and MP800-V2, which differ in local ductility and severity of centerline segregation. Hole punching was performed at clearances ranging from 5% to 20%, followed by hardness mapping in the shear affected zone (SAZ), conical hole expansion (HX), and in-plane bending tests. The MP800-V1 steel exhibited negligible sensitivity to the punch-die gap, while MP800-V2, which had centerline segregation, achieved the highest edge formability for clearances of 12% and 20% during HX. Additionally, MP800-V1 exhibited a strong sensitivity to the applied loading for clearances of 5% and 8% , with fracture strains from in-plane bending lower than HX by 0.20 at 5% and 8% clearance. In contrast, MP800-V2 showed minimal variation in fracture strains between bending and HX, except at 8% clearance, highlighting the importance of boundary conditions on the sheared edge stretchability.

Keywords

• sheared edge
• in-plane bending
• fracture strain
• conical hole expansion