The use of microalloyed steels for sheet and plates in line pipe, construction and automotive applications has become standard in recent years. Since the end of the 1960's the development of these steel grades has resulted in increasing strength levels combined with excellent toughness and welding properties. However, the potential of microalloyed high strength steel is not used to the same extent in engineering steels. On the other hand customers and steel producers show growing interest in this proven technology that may help to achieve further weight reduction and cost savings. An average passenger car typically contains about 180 kg of long and special steels. On top are stainless components as for the exhaust system. Niobium for example has a threefold influence on the mechanical properties of steel; grain size refinement during thermomechanical hot forming, lowering the to transition temperature (Ar3) and precipitation hardening. Grain refinement is the only mechanism that simultaneously increases strength, toughness and ductility. This makes Nb the most effective microalloying element, even if added in small quantities (1). The grain refining effect of Nb is mainly due to delaying or preventing recrystallisation in the last hot forming steps. Flattened grains and a high dislocation density of the austenite enhance ferrite nucleation. By lowering the to transformation temperature, Nb in solid solution simultaneously enhances the ferrite nucleation rate and reduces the grain growth rate. This combined effect leads to a particularly fine-grained transformation structure. In order to make optimum use of its metallurgical potential microalloying elements have to be in solid solution by heating at an adequate reheating furnace temperature to dissolve precipitates before hot forming, Figure 1. Engineering steels comprise forging steel grades such as for case hardening, quench and tempering (QT) as well as for cold heading, springs and roller bearings. Although engineering steels usually have elevated carbon content, the basic principles of microalloying also apply to this steel group and will be explained using the example of case hardening steel. This paper summarises briefly the metallurgical background of microalloying in medium carbon steels and gives an example for the use of microalloying elements - with focus on Niobium - in automotive applications.


    Zugriff

    Zugriff über TIB

    Verfügbarkeit in meiner Bibliothek prüfen


    Exportieren, teilen und zitieren



    Titel :

    Advanced material and process development for steels for automotive applications


    Weitere Titelangaben:

    Fortschrittliche Werkstoffe und Prozessentwicklungen für Stähle in der Automobilindustrie


    Beteiligte:


    Erscheinungsdatum :

    2006


    Format / Umfang :

    8 Seiten, 10 Bilder, 2 Tabellen, 15 Quellen


    Medientyp :

    Aufsatz (Konferenz)


    Format :

    Print


    Sprache :

    Englisch




    Advanced sheet steels for automotive applications

    Fekete, J.R. / Strugala, D.C. / Zhicong Yao | Tema Archiv | 1992


    Advanced cold rolled steels for automotive applications

    Hofmann, H. / Mattissen, D. / Schaumann, T.W. | Tema Archiv | 2006


    Advanced cold rolled steels for automotive applications

    Hofmann, Harald / Mattissen, Dorothea / Schaumann, Thomas Wilhelm | Tema Archiv | 2009


    Advanced Automotive Steels-Their Development and Application in Australia

    Blatherwick, A. J. / Clarsen, B. J. / White, J. L. | SAE Technical Papers | 1985