Prediction method of voids distribution in the punched surface of the spheroidizing annealed medium carbon steel sheet by the scrap

Several studies have reported that voids near punched surface decrease stretch flange formability. However, non-destructive observation of voids near punched surface before hole expanding is difficult. Therefore, the authors assumed that the voids distribution in a thickness direction of blank (holder side) is point symmetrical with that of scrap (hole side). The objective of this study was to investigate validity of the assumption and establishing the prediction method of voids distribution near punched surface. After punching a spheroidizing annealed medium carbon steel sheet, voids near punched surface were measured. The distribution of the number density of voids in a thickness direction between scrap and blank had slight deviation in a thickness direction. The area fraction of voids of the scrap was higher than that of the blank. However, as these differences showed systematic tendencies, the voids distribution in a blank can be predicted through evaluation of its corresponding scrap.