Material characterisation for strength and formability limits of DP 1180 sheet

Abstract

Dual phase steels were specifically developed to address the weight and safety-related problems of the automotive industry. Nevertheless, these steels behave quite differently from conventional high strength steels (single phase) during the stamping processes. The unusual material behaviour limits the application of these steels. This study focuses on the material characterisation of cold rolled and hot dip galvanised dual phase 1180 sheet material. Microstructure and elemental analyses were performed using an optical microscope and a scanning electron microscope with energy dispersive X-ray spectroscopy. Mechanical properties were determined through Rockwell hardness, Vickers hardness, tensile, Nakazima, and hole flanging tests. A digital image correlation system was utilised for Nakazima and hole flanging tests. The average micro hardnesses of the steel and the coating were 341 HV0.5 and 51 HV0.01 respectively. Uniform elongation was similar to 6.6%. The lowest point on the forming limit diagram was similar to 0.1. The average hole expansion ratio was similar to 22%.