Author(s)

L. Xu, F. Barlat, M. G. Lee, K. S. Choi & X. Sun

Abstract

In this work, the stretch-flangeability of dual phase (DP) steels was investigated through hole expansion (HE) tests for three DP980 steel sheet samples. In order to understand the effect of hole surface quality on the HE results, the specimens were prepared with three hole machining methods, namely, electrical discharge machining (EDM), punching and laser cutting. The HE results were discussed in terms of the hole surface quality before and after testing. Moreover, the failure behaviour was analyzed based on the observations of the fracture surfaces using optical microscopy (OM) and scanning electron microscopy (SEM). Keywords: dual phase steel, hole expansion, hole surface quality, failure. 1 Introduction Advanced high strength steels (AHSS) have been continuously improved to meet the various requirements of the automotive industry, such as vehicle weight reduction, crash performance improvement, energy saving considerations and environmental protection. For example, dual phase (DP) steels have increasingly been used in various vehicle components. Typical DP steel sheets have an excellent combination of high strength and elongation, but poor stretchflangeability. The hole expansion (HE) test has been recognized as a discriminating method to characterize stretch-flangeability. Moreover, it is well known that the hole surface quality has a significant effect on the HE results. Although many papers have focused on the HE tests of DP steel sheets [1–5], only a few of them investigated the effect of hole surface quality on the HE results and failure behaviour [6, 7]. In this work, the stretch-flangeability for three DP980 steel sheet samples, denoted materials A, B and C, and provided by different steel producers, was

Keywords

dual phase steel, hole expansion, hole surface quality, failure.