To realize a balance between strength,elongation as well as stretch flangeability, a 780 MPa class high strength hot rolled sheet has recently been developed. This has been possible by applying a new (PDF) Hole Expansion Characteristics of Ultra High The stretch flangeability of an ultra-high strength steel sheet having low ductility was improved by smoothing the sheared edge of the sheet.
Abstract. Complex phase (CP) concept is justified based on the improvement of stretch flangeability (hole expansion) due to replacement of martensite, at least partially, by bainite. Relationship between microstructure and mechanical properties of CP steels is presented as well as recommended for processing parameters to obtain bainite fraction Education system in Japan Development of Japanese Improvement of springback in bending of ultra-high strength steel sheets using servo press Prevention of fracture in stretch flanging of ultra-high strength steel sheets Prevention of wrinkling in shrinkage flanging of ultra-high strength steel sheets Improvement of quality of sheared edge in punching of ultra-high strength steel sheets Effect of YAG Laser Cutting on Stretch-flangeability of Furthermore, the strengthstretch-flangeability balance (TS×) of TBF steel sheet austempered at 375°C showed the highest value after laser cutting at 100 W. Compared to mechanical punching, YAG laser cutting contributed to the improvement of the TS× to 1100 MPa with TBF steel sheet possessing fine bainitic ferrite matrix.
 Mori, K., Abe, Y., Suzui, Y., Improvement of stretch flangeability of ultra-high strength steel sheet by smoothing of sheared edge, Journal of Materials Processing Technology 210(4) (2010) 653659. Improvement of Fatigue Strength of Hole Edge of Ultra-High The effect of the hole edge shape formed by a punching process including thickening on the fatigue strength of the hole of ultra-high strength steel sheets was investigated. The bending and tensile fatigue tests of the thickened hole edge were performed. For the bending fatigue strength, the high height of hole edge was effective because of high bending stiffness. Study for Sheared Edge Quality of High Strength Steel  Mori K., Abe Y., Suzui Y. Improvement of stretch flangeability of ultra high strength steel sheet by smoothing of sheared edge. J. of Materials Processing Technology 210 (2010) 653659. DOI:10.1016/j.jmatprotec.2009.11.014
In automotive body designing, high strength steels are applied in order to achieveweight reduction and high crashworthiness. 980MPa class ultra-high strength steelis recently applied to seat parts. However, it has less formability than that of conven-tional high strength steels. To meet this demand, three types of 980MPa ultra-highstrength steels are developed, which are good elongation type, high stretchflangeability UDC 699 . 14 . 018. 295 - 415 :629 . 11 . 011 is the most common index of press formability of high strength steels. Since the ductility is known to decrease with increasing the strength, stretchability generally decreases with increasing the strength of steels. Stretch flangeability indicates the formability of the edges, par-ticularly cutting edges. It is typically evaluated by the hole expand- Yohei AbeTOYOHASHI UNIVERSITY of TECHNOLOGY K. Mori, Y. Abe, K. Norita, Improvement of stretch flangeability of ultra-high strength sheets by gradually contacting punch, Proceedings of 11th International Conference on Numerical Methods in Industrial Forming Processes, AIP Conf. Proc. 1532, (2013), 122-127.
Jan 01, 2020 · Jewoong Lee et al. investigated the relationship between micro-alloying additions and the stretch-flangeability of DP steels by means of microstructural analysis and mechanical testing, it was concluded that the increased amount of inter-critical ferrite formed at higher annealing temperature resulted in an improved stretch-flangeability, and the addition of 200ppm Nb was beneficial for stretch-flangeability while the addition of 400ppm Nb had a detrimental effect