Recent lightweight body engineering makes massive use of modern high strength steel. This approach simultaneously enables moderate weight and cost reduction and nevertheless meeting the targets of emission control, safety, driving performance and lifetime. The different classes of high strength steel for automotive applications are primarily defined by the constitution of phases being ferrite, pearlite, martensite, bainite and retained austenite. The deliberate mixture of two or more phases is used to achieve a particular property profile of the steel. Microstructural control by niobium microalloying is demonstrated in this paper to be a powerful tool for optimization of the property profile of such steels. The fundamental effect of niobium is that of grain refinement increasing the strength without deteriorating the ductility. This mechanism allows a leaner alloying concept to reach the specified strength level. A leaner alloy concept is beneficial with regard to welding operations. Grain refinement also brings about a more homogeneous microstructure improving the forming behavior particularly when highly localized strains are being induced such as in bending and stretch flanging. Multiphase steels have gained a significant share in vehicle bodies reaching about 20% in the currently most advanced body structures. The best-established multiphase material is dual phase steel. The majority of the material is produced using the hot dip continuous galvanizing process. Compared to microalloyed HSLA steel the availability of multiphase steel is limited to fewer steelmakers operating specialized equipment and having considerable experience in automotive strip production. The cost of niobium as a ferroalloy has been kept nearly stable on a moderate level since many years as compared to other microalloying elements such as titanium, vanadium or molybdenum. Since the amount of niobium needed to achieve the desired effect in terms of strength enhancement and property improvement is also comparably low, niobium microalloying is a very cost attractive way of producing automotive high strength steel.
Niobium microalloyed automotive sheet steel - a cost effective solution to the challenges of modern body engineering
Nb-mikrolegierter Stahl für Automobilbleche - eine kostengünstige Lösung für die Herausforderungen der modernen Karosseriekonstruktion
2006
23 Seiten, 18 Bilder, 1 Tabelle, 40 Quellen
Conference paper
English
Karosseriebau , Karosseriekomponente , Anwendung im Fahrzeugbau , mikrolegierter Stahl , hochfester niedrig legierter Stahl , Niobzusatz , Mikrostruktur , Trend (Entwicklung) , Kaltumformbarkeit , Kostensenkung , Schweißbarkeit , Feinblech , Leichtbauweise , Gewichtsverringerung , Dualphasenstahl , TRIP-Stahl , Mehrphasenstahl
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