In the paper a flow stress model based on internal variables is shortly presented. The multiplicative model contains three parts. In the model, the normalized dislocation density ρm was considered, as a strain function only, independently to the strain rate and the temperature. Influence of varying processing conditions (the strain rate and the temperature) is introduced as a factor. The first one is a model of so called master curve. It is an internal variable model based on dislocation density and its output value strongly depends on strain and very weakly on temperature and strain rate. The second factor introduces varying deformation conditions. Changes of flow stress do not occur instantly with the change of deformation conditions, but it requires some strain for transition. The third part considers influence of recrystallization. The results of the model parameters identification and verification in varying deformation conditions are presented in this paper.