Improvement of stretch flangeability of ultra high strength steel sheet by smoothing of sheared edge

Stretch flangeability of an ultra high strength steel sheet having small ductility was increased by improving quality Of a sheared edge The effect of the quality of the sheared edge oil the stretch flangeability of the high strength steel sheets was examined from expansion of a sheared hole with a conical punch. The quality of the sheared edge varied with the clearance between the punch and the quality Influenced the limiting expansion ratio It was shown from measurement Of Surface of the sheared edge that the limiting expansion ratio of the sheared ultra high strength steel sheet is dependent oil the Macroscopic unevenness and hardness of the sheared edge and not on the microscopic toughness The macroscopic unevenness of the sheared edge was eliminated by smoothing the edge with a conical punch It was found that the smoothing of the sheared edge is effective in improving the stretch flangeability of the ultra high strength steel sheet (C) 2009 Elsevier B.V. All rights reserved