ABSTRACTThe development of accurate constitutive equations is important for the success of computer simulations of high temperature forming operations. Often, these simulations must be made on alloys that have not been completely characterized. For that reason physically-based constitutive equations taking the chemical composition into consideration, involving deformation mechanisms and characteristic properties of the material are necessary. The influence that exerts the solute elements to an alloy on the mechanisms of diffusion on deformation processes at high temperatures is not an easy subject and the available information in literature is scarce.This study examines that influence working on the basis of eight structural plain carbon steels with the chemical composition ranging between 0.15-0.45%C, 0.2-0.4%Si and 0.6-1.6%Mn produced by Electro-Slag Remelting ESR process and tested by isothermal uniaxial compression technique. The studied deformation conditions include strain rates ranging between 5·10−4 to 1·10−1 s−1 and temperatures between 0.6-0.75Tm, with Tm the melting temperature.A constitutive expression for the hot working behavior is proposed, it includes the variation of the diffusion parameters with the chemical composition. To such aim the effect of the chemical composition of the alloy on the pre-exponential factor D0 of the gamma iron self-diffusion coefficient Dsd is included. Finally, a comparison of the experimental and predicted results shows the good agreement of the model with experimental flow data.