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The high carbon steels with bainitic constituents present very interesting mechanical characteristics, such as good ductility, high mechanical resistance to fatigue and high fracture toughness. In this work, two cast and hot-formed alloys were studied, varying the silicon contents (1.5% and 2.0%), to verify their effect on the morphology and kinetics of the bainite transformation during austempering heat treatment at 280 °C wth times varying between 1 min and 839h. Temperatures Bs and Ms were determined from thermodynamic simulations. For the morphological and kinetic characterization, the techniques of optical microscopy (OM) and scanning electron (SEM) were used, the mechanical properties were determined by tensile and hardness tests. A higher bainitic ferrite volume fraction was detected for the alloy with higher Si content. The average ultimate tensile stress (UTS) ranged from 1200 to 1600 MPa and the yield stress ranged from 1000 to 1200 MPa, with a mean hardness of 50 HRC for the samples in the bainitic reaction stage. [ABSTRACT FROM AUTHOR]