The microstructural evolution during the hot rolling of coarse grain sized austenite has been modeled taking into consideration all the microstructural mechanisms (dynamic, static and metadynamic recrystallization, strain induced precipitation) that could take place during the industrial TSDR production of a Nb microalloyed. steel. Based on the results obtained from the model, processing maps have been drawn for a 0.035%Nb microalloyed. steel. Optimum processing conditions to exploit all the benefits of Nb microalloying have been defined considering a final gauge thickness range between 1.5 and 12.65 mm.