Influence of DIT Parameters on the Cementite Spheroidization in a Low-Alloy Medium Carbon Steel

The influence of strain, strain rate, and temperature on deformation-induced transformation (DIT) in a low-alloy medium carbon steel is studied. The strain promotes the nucleation of ferrite (deformation-induced ferrite) and also pearlite (deformation-induced pearlite), this last being characterized by a fine interlamellar spacing and morphological instability. At strains ε > 0.5, intragranular nucleation activates and further ferrite nucleation over the newly created α/γ interface takes place, which gives rise to the precipitation of cementite (deformation-induced cementite) at the ferrite boundaries. Soft annealing treatments have been performed on the microstructures obtained by DIT, and the degree of spheroidization has been quantified by image analysis techniques. In comparison to non-deformed conditions, the application of DIT results in a higher degree of spheroidization after soft annealing. Moreover, the EBSD analysis denotes that ferrite grain size refinement is achieved with respect to non-deformed conditions. The degree of spheroidization is highly influenced by the applied strain level and subsequent holding temperature.