Reduced weight and improved crash performance are two important targets for the automotive industry today. More than 50 % of the weight can be taken away by using high strength steel instead of conventional mild steel on single components. Improved crash performance is important in order to produce safer vehicles and to reach five stars in international crash tests, such as the EuroNCAP. With microalloyed high strength steels, these two targets can be achieved simultaneously in a cost effective way compared to other lightweight materials. These steels show good formability, weldability and parts can be manufactured with conventional forming and welding equipment. The main microalloying element used in high strength steels at SSAB is niobium. The range of niobium alloyed steel grades includes precipitation hardened hot-rolled grades, precipitation hardened cold-rolled grades, dual phase cold-rolled grades and martensitic cold rolled grades. Cold-rolled grades are produced uncoated and hot-dip galvanized. This paper shows some examples of how these grades are produced, their properties in forming, welding and design as well as their current applications in the automotive industry. The following conclusions can be drawn: The role of microalloying with Nb in high strength steels includes precipitation hardening and grain refinement. This effect is directly used in the microalloyed grades to increase the yield strength. In dual phase grades microalloying with Nb is used to reduce and control the grain size resulting in a finer dispersion of the martensitic phase, a higher tensile strength and more uniform mechanical properties. In martensitic grades Nb microalloying is mainly used for grain size control. Due to low alloying content in these grades, attractive combinations of formability and weldability can be achieved in the full tensile strength range from 370 to 1400 MPa. The strength increase in these grades can be used for considerable weight reduction and/or improved crash performance when designing car components. Applications include chassis components, body parts, bumper reinforcements, door impact beams and interior parts like seat frames and mechanisms.
Microalloyed high strength steels for reduced weight and improved crash performance in automotive applications
Mikrolegierte hochfeste Stähle für verringertes Gewicht und verbessertes Crashverhalten in Fahrzeuganwendungen
2006
12 Seiten, 12 Bilder, 4 Tabellen, 4 Quellen
Conference paper
English
Anwendung im Fahrzeugbau , mikrolegierter Stahl , hochfester niedrig legierter Stahl , Leichtbauweise , Gewichtseinsparung , Übersicht , Aufprallenergieabsorptionsvermögen , Niobzusatz , warm gewalztes Blech , kalt gewalztes Blech , mechanische Eigenschaft , Mikrostruktur , Grenzformänderungskurve , Schweißbarkeit
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