Shear band development in bending of coarse-grained martensitic steel sheets

抄録

Some investigations on bent sheet metals have reported that the development of shear bands plays an indispensable role in cracking. On the cross-section perpendicular to the bend axis, cracks are observed along the shear bands, which previously developed in the directions of approximately 45° to the sheet surface. In this study, we investigated the microscale surface changes and internal shear band development of coarse-grained martensitic steel sheets using three-point bending tests with a scanning electron microscope (SEM). Shear band formation was confirmed at the small bending strain stage, causing microscopic grooves with localized strain concentration on the surface. The surface grooves subsequently develop with progressive bending deformation, becoming cracks and leading to fracture. Furthermore, cross-sectional microstructure observation indicated that the initiation and development process of shear bands in martensitic steel sheets is largely influenced by finer structures such as packets and blocks rather than by prior austenite grains.