The influence of the thermal cycle and austempering treatment on the mechanical behavior of a 0.56C-1.43Si-0.58Mn-0.47Cr (wt%) steel has been investigated. The thermal cycle consisted of heating the steel to 800°C or 900°C, in the intercritical and austenitic region respectively, fast cooling down to 600°C or 400°C, followed by 300 s hold. After austempering the materials were cooled at different rates and then submitted to tensile testing. The total elongation of 15-20 % and tensile strength of 1 300-1 400 MPa were reached after heating to 900°C and transformation at 400°C. The strain-induced austenite transformation to martensite during the plastic deformation (Transformation Induced Plasticity Effect) is responsible for this combination of high strength and ductility. Silicon acts to stabilize the austenite during austempering. However, the stabilized austenite can be transformed and the microstructure modified, resulting in the formation of others constituents such as bainitic ferrite, upper bainite and martensite.