Combined Intercritical Annealing and Q&P Processing of Medium Mn Steel
- PDF / 1,795,637 Bytes
- 7 Pages / 593.972 x 792 pts Page_size
- 71 Downloads / 204 Views
Standardized collision tests such as the National Highway Traffic Safety Administration (NHTSA) New Car Assessment Program (NCAP) convincingly show that increased occupant safety is achieved during collisions when the passenger car has ‘‘crumple zones,’’ i.e., ductile front and rear end structural parts, which allow for a gradual absorption of the impact energy, while protecting the occupants from intrusion into the passenger compartment. The controlled crush of front end structural parts limits the impact force of the collision experienced by the passenger. In side impact conditions, intrusion protection is required to avoid passenger injury. This is achieved by the use of rigid ultra-high strength structural parts which resist the impact, transfer, and
BRUNO C. DE COOMAN, Professor and Director, SEON JONG LEE, Graduate Student, and SUNMI SHIN and EUN JUNG SEO, Post-Doctoral Research Associates, are with the Materials Design Laboratory, Pohang University of Science and Technology, 77 Cheongam-Ro, Nam-Gu, Pohang 37673 South Korea. Contact email: [email protected] JOHN G. SPEER, Professor and Director, is with the Advanced Steel Products and Processing Research Center, Colorado School of Mines, 1500 Illinois StreetHill Hall, Golden, CO 80401. Manuscript submitted August 8, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
spread the load across the car body. Impact beams, roof rails, cross members, sill sections, and pillar reinforcements are usually made of ultra-high strength steel (UHSS) grades (UTS>1 GPa) such as dual-phase (DP) steel grades with a high ‘‘yield ratio,’’ i.e., the ratio of yield strength (YS) to ultimate tensile strength (UTS), or press hardening steel grades with a fully martensitic microstructure.[1–3] An essential feature of these material is their very high YS which provides high levels of passenger safety in cage components. The more limited ductility of UHSS grades usually requires special processing methods such as hot stamping. Medium Mn formable high strength and ultra-high strength steels have been developed recently in order to enable lightweight car body designs that also offer improved passenger safety features. New automotive steel design concepts, such as the medium Mn steels, are often evaluated on the basis of their strength–ductility balance, i.e., the product of the UTS and the total elongation (TE). The strength–ductility balance achievable in medium Mn steels is high, typically >30,000MPa pct.[4–9] The optimization of medium Mn steel has up to now not fully addressed the complexity of their mechanical properties, which are highly dependent on the intercritical annealing (IA) temperature at which they are processed. Figure 1 illustrates that the YS of many different types of medium Mn steels decreases with increasing IA temperature, TIA. The data in the figures, taken from a variety of sources,[10–12] clearly illustrate that in the ultra-high strength conditions, the medium Mn steels normally have a low YS. While their high strength–ductility balance makes these steel grades
Data Loading...
