DP grades with improved formability
High strength steel grades with excellent formability make a remarkable contribution to the reduction of the mass of the body-in-white and, additionally, an increased crash safety for cars. The most important steel grades which fulfil these requirements are DP steels with tensile strength levels up to 1 000 MPa. For their further improvement, the fundamental understanding of the impact of microstructure on formability is essential. In the present project, different microstructures processed industrially and also in the lab are correlated with the mechanical properties, mainly yield and tensile strength, uniform and total elongation, and additionally with bendability and hole expansion behaviour. The most relevant microstructure constituents determining the formability were identified based on an accurate investigation of the microstructure and the damage during straining. These investigations were supported using basic modelling with finite element calculations. Based on the experimental work and the finite element modelling, the strength (hardness) of the inclusion was identified as the most important parameter. Generally, a higher hardness difference between matrix and inclusion resulted in high work hardening and therefore a higher uniform and total elongation; however, in only moderate bendability and moderate hole expansion values. Based on the reduction of the hardness of the inclusion, the hole expansion values and bendability could be improved remarkably. Generally, the impact of the abovementioned parameters and the arrangement of the phases were found to be more pronounced for grades with a larger fraction of the second phase.
Bibliographic Reference: EUR 23862 EN (2009), 149 pp. Euro: 20
Availability: http://bookshop.europa.eu/is-bin/INTERSHOP.enfinity/WFS/EU-Bookshop-Site/en_GB/-/EUR/ViewPublication-Start?PublicationKey=KINA23862 (Catalogue Number: KI-NA-23862-EN-S)
ISBN: ISBN: 978-92-79-11322-2
Record Number: 200910479 / Last updated on: 2009-10-12
Original language: en
Available languages: en