Initiation and growth of edge cracks after shear cutting of dual-phase steel

Abstract

Dual-phase steels suffer from low edge ductility, which limits their formability. In this study, an in-plane bending test is used to investigate the initiation and evolution of edge cracks. The edges of samples were prepared by shear cutting and afterwards further deformed by the in-plane bending test. Void distribution and non-uniform plastic deformation were explored with the help of scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) analysis and microhardness measurement in different regions of the material edge. The extent of micro-cracks was revealed by microcomputed tomography (µCT) scan. The result shows that the blanking process creates inhomogeneous void distribution in the thickness direction. As the deformation increases during the subsequent in-plane bending test, the micro-cracks initiate at the burr region and grow towards the rollover region. Once they entirely pass the thickness of the material, they grow further, away from the edge. High roughness, plastic deformation, and void volume fraction were observed at the burr region, triggering crack initiation. The in-plane bending test successfully distinguished the dominant mechanism behind edge cracking.