In this study solid-gas interactions during sintering of powder metallurgy (PM) irons are simulated by coupling mass, heat, and momentum phenomena in a non-stationary model. The consolidation of a PM compact requires the elimination of the nanometric oxides covering the particles. Theoretically this is achieved by adjusting the inlet atmosphere composition to guarantee thermodynamically reductive values at the processing temperature. That depends on the quotient of hydrogen and water partial pressures when N2/H 2 mixtures are employed. However the actual atmosphere composition inside the porous part is not easy to predict because water produced during reaction can locally increases the pH2O/pH 2 value. This work proposes a methodology to study the effects of local atmosphere degradation on reduction times. The influence of compact temperature and external gas velocities during the processing of the iron/wustite system was evaluated.