Empirical and physically based flow rules relevant to high speed processing of 304L steel

Thermomechanical processing of metals involves severe plastic deformation at strain rates up to 104 s-1, and temperatures up to the melting point. On the other hand, areas far from the tools may be much less or not affected by strain or temperature. A constitutive equation valid for quasi-static to 104–105 s-1, for temperatures ranging from room temperature to the melting point, and up to strains about 10 is required to predict accurate results. To fit the experimental data, the proposed models tend to a steady state limit with increasing strain, whereas this fundamental characteristic is not reproduced by the most used Johnson-Cook model. Moreover, two distinct types of behaviour are observed according to whether dynamic recrystallization occurs or not. A first empirical model derived from the classical Voce equation is proposed. The second model is physically based on the mechanisms involved during discontinuous dynamic recrystallization. Coefficients are fitted for the case of 304L stainless steel.