Industry hot deformation processes such as hot rolling are complex in nature. Setting up a rolling mill requires precise knowledge of the loads needed to shape the metal. This in turn, demands the ability to predict the strength of the material when deformed to a value of strain and strain rate at a given temperature. On and off-line models need, however, to be fed with constitutive equations relating the stresses required to deform a certain metal under the usual process variables. This paper shows how a set of stress-strain curves can be modeled so that both hardening and softening mechanisms commonly present during hot deformation are taken into account. The model predictions are compared to a set of literature data in order to be validated. Reasonable agreement between published results and predicted values were obtained indicating how efficiently the model can assess values of stresses under hot working conditions.