GASEOUS NITRIDING IRON - EVALUATION OF DIFFUSION DATA OF N IN GAMMA'-PHASE AND EPSILON-PHASE

Experimental information on the growth rate of gamma' and epsilon laye rs formed during gaseous nitriding iron is assessed applying the most recent thermodynamic description of the Fe-N system. The atomic mobili ty of N in gamma' was found approximately independent of composition y ielding a concentration independent self-diffusivity of N in gamma' ob tained as D-N((gamma')) = 2.7 x 10(-10) exp (-88.3 kJ mol(-1)/RT) m(2 ) s(-1) for 777 K < T < 843 K where R is the gas constant and T is the absolute temperature. The atomic mobility of N in epsilon was assumed to be independent of concentration and evaluated as M(N)(epsilon) = 4 .6 x 10(-13) exp (-80.7 kJ mol(-1)/RT) mol m(2) s(-1) J(-1) for 848 K < T < 1300 K. The result was applied to simulate the nitriding process and reasonably good agreement with the experiments was obtained. Furt hermore, the evaluated data were compared with the previous evaluation s.