Development of Low Silicon Carbide Free Bainitic Steel for Automotive Industry

The main objective of this work is to design a cold rolled Advanced High Strength Steel (AHSS) for the automotive industry with a carbide-free bainite microstructure. Three experimental grades with three Chromium contents were obtained at a pilot plant scale. For this purpose, dilatometry experiments were performed in a Bahr 850 A/D dilatometer on cold rolled material in order to define the optimum annealing cycle. Afterwards, simulations of continuous annealing were carried out to achieve carbide free bainitic microstructures with an optimum combination of in-use properties. Finally, the materials were subjected to an advanced microstructure characterization. The desired microstructure consisting of mainly fine lath-shaped bainitic ferrite and thin retained austenite was obtained in the specimens submitted to a simulated industrial continuous annealing cycle and accordingly, an excellent combination of elongation to fracture tensile strength was achieved.