EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Advance High Strength Steels (AHSS) have been widely used in the automobile industry during the last decades due to their excellent combination of strength, ductility and weldability at a competitive cost. In this context, low carbon bainitic steels have proved to be interesting alloys to obtain high strength and toughness microstructures with good formability. However, the final mechanical behavior of bainitic microstructures can vary dramatically depending on the thermal treatment parameters, e.g. the cooling rate. In this work, bainitic microstructures obtained using continuous cooling heat treatments with different cooling rates have been studied in a Ti – Nb – Mo - V low carbon microalloyed steel. Start and end transformation temperatures have been identified using dilatometry. The morphology of bainite has been characterized by performing a stereological quantification of the martensite/austenite constituents (MA) and a crystallographic study has been carried out by using electron backscatter diffraction (EBSD) data. Results show that, as the cooling rate increases, the bainite transformation takes places at lower temperatures, and the MA constituents morphology gradually changes from islands to films, which is directly related to the granular (MA islands) or lath-like (MA films) bainite. Besides, an evolution of the crystallographic features as the transformation temperature changes has also been observed.