This work presents a constitutive model for metastable austenitic steels exhibiting Strain Induced Martensitic Transformation (SIMT). Based on the description of the kinetics of phase transformation proposed by Olson and Cohen [3], and later generalized to 3D by Stringfellow et al. [7] and Papatriantafillou et al. [4], this model includes the effect of temperature increase on the kinetics of SIMT and on the thermal softening of the phases. This allows capturing relevant phenomena exhibited by metastable austenitic steels when subjected to plastic deformation at high strain rates. A systematic procedure for the identification of the constitutive parameters has been proposed. The predictions of the constitutive description are compared with experiments for the austenitic steel AISI 304 provided by Rodríguez-Martínez et al. [6]. Good correlation between experiments and modelling are achieved in terms of macroscopic strain-stress curves and volume fraction of martensite formed during straining