Ordered phases and microhardness of Fe-6.5%Si steel sheet after hot rolling and annealing

Fe-6.5%Si steel was hot rolled and heat treated in the laboratory. The grain interplanar spacing and microhardness of the steel were measured, and the ratio of diffraction peaks intensity of the A2 disordered phase and the DO3 ordered phase was analyzed under different cooling conditions. With the increasing of cooling rate, indentation morphology of Vickers microhardness for the experimental steel was transformed from a sink-in type into a pile-up type, and the strain-hardening exponent decreased. As annealing temperature was decreased below 700 °C, DO3 and B2 ordered phases are formed, resulting in a higher microhardness. When annealing temperature was greater than 800 °C, ordered phase is transformed from B2 to DO3, microhardness of the steel decreased. Indentation morphologies of Vickers microhardness become a sink-in type when annealing temperature was lower than 650 °C. While annealing temperature was 700-900 °C, the surface indentation morphologies of samples was a pile-up type. With the increase of annealing temperature, the amount of DO3 ordered phases and the strain-hardening exponent decreased. The ordered phases in Fe-6.5%Si steel could cause the difficulty of dislocation movement and brittleness at room temperature during plastic deformation.