Enhancement of the stretch-flangeability of a cold-rolled dual phase steel intercritically annealed

Abstract

The application of advanced high-strength steels (AHSS) by automakers is now a consolidated reality. In this scenario, Dual Phase (DP) steels deserve special mention due to their versatility in a vast range of applications, since they present an excellent combination between high mechanical strength and high ductility. On the other hand, applying a classical DP steel, with microstructure formed essentially by ferrite and martensite, shear fracture and edge cracking, have regularly been observed in die-bending and flanging operations. In this work the improvement of stretch-flangeability, while still keeping an appropriate ductility, of a classical 980 MPa DP steel was pursued by testing different intercritical annealing conditions in a dilatometer and a Gleeble thermomechanical simulator. According to the results obtained in this study, the stretch-flangeability improvement of a cold-rolled dual phase steel intercritically annealed can be obtained by increasing the soaking and austempering temperatures.

Keywords

• Dual phase steel
• Stretch-flangeability
• Hole expansion ratio (HER)
• Automotive application