Comparison of a dual phase steel with other formable grades

Abstract

The forming properties of an as-rolled dual phase steel were measured and compared with those of three other formable grades of steel sheet. In addition to standard tensile tests, hydraulic bulge, stretch bend, hole expansion and dome stretching tests were performed and forming limit curves and fracture maps obtained. The results show that the strain hardening rate in the dual phase steel is initially higher than in a 50 ksi (350 MPa) HSLA steel but at about 15 pct strain it becomes lower. Fracture strains are similar to those in an 80 ksi (560 MPa) HSLA steel. It is shown that significant strain occurs in the flanks of the stretch bend test piece particularly with the dual phase steel and that the results must be interpreted with care. The hole expansion test indicated that the sheared edged ductility of the dual phase steel was superior to that of an 80 ksi HSLA steel. The discussion includes a correlation of the different mechanical tests and observations on the selection of steels for various types of formed parts.