A macroscopic constitutive model for a metastable austenitic stainless steel

The constitutive behaviour of a metastable austenitic stainless steel during metal forming and hardening is described with a macroscopic model. The steel undergoes a strain-induced transformation during forming. Depending on the annealing conditions, the steel also transforms isothermally as opposed to athermal martensite. This transformation can also take place immediately after plastic deformation, as a result of the residual stresses. The martensite phase of this steel shows a substantial ageing response, about 1000 N/mm(2). A constitutive model based on the data from literature as well as on measurements is presented which describes the stress-strain behaviour along with the phase transformation. The work hardening is based on dislocation density as internal state variable. With this information, a new model is constructed that describes the isothermal or stress-assisted transformation, the strain-induced transformation, the work hardening as well as the ageing behaviour of the steel. The model can be implemented in a FEM code. (C) 2007 Elsevier B.V. All rights reserved.