Effects of Testing Method on Stretch-Flangeability of Dual-Phase 980/1180 Steel Grades

Challenging fuel economy and safety standards in the automotive industry have led to the need for materials with higher strength while maintaining levels of formability that meet component manufacturing requirements. Advanced high-strength steels, such as dual-phase steels with tensile strengths of 980 MPa and 1180 MPa, are of interest to address this need. Increasing the strength of these materials typically comes at the expense of ductility, which may result in problems when stamping parts with trimmed or sheared edges, as cracking at the sheared edge may occur at lower strains. Here, hole expansion tests were performed with different punch geometries (conical and flat-bottom) and different edge conditions (sheared and machined) to understand the effects of testing conditions on performance, and these results are discussed in terms of mechanical properties and microstructures.