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Analysis of the microstructural evolution of a intercritically deformed NbV microalloyed steel

Thursday (27.09.2018)
12:15 - 12:30 S1/01 - A4
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Many structural steels in conjunction with advanced rolling strategies are being developed in order to fulfill increasing mechanical property requirements. In the last decades, intercritical rolling has been extensively employed in the production of heavy gauge structural plates, especially to achieve strength requirements. Unfortunately, the mechanical properties of toughness and strength are usually contradictory. In this sense, a deeper understanding of the microstructural evolution under intercritical conditions is required. Rolling in the austenite/ferrite two-phase region has already been explored for plain carbon steels. However, the effect of intercritical rolling for microalloyed steels is less investigated. It is well known that the addition of Nb as an alloying element can retard or inhibit recrystallization of austenite and ferrite due to two mechanisms: the solute drag effect owed to Nb atoms in solid solution and the pinning effect caused by strain-induced precipitation. The current work shows the complex interaction between austenite/ferrite content prior to deformation, microalloying elements, austenite condition (recrystallized and deformed austenite) and microstructural evolution during intercritical rolling. For that purpose, intercritical deformation simulations were performed in a deformation dilatometer for a NbV microalloyed steel. In addition to conventional characterization techniques (optical and electron microscopy), EBSD characterization technique was used to distinguish the intercritically deformed ferrite from non-deformed ferrite transformed during final air cooling step. Given that more bainitic phases, such as quasipolygonal ferrite, are formed when microalloying elements are added, the differentiation of the non-deformed and deformed ferrite grains is more complex. The results suggest that the transformation of ferrite from recrystallized and deformed austenite infers modifications in the intercritically deformed ferrite.

Additional Authors:
  • Unai Mayo Ijurra
    Ceit and Universidad de Navarra (Tecnun)
  • Dr. Pello Uranga Zuaznabar
    Ceit and Universidad de Navarra (Tecnun)
  • Prof. Dr. Jose María Rodriguez Ibabe
    Ceit and Universidad de Navarra (Tecnun)