Gaseous Nitriding Iron -— Evaluation of Diffusion Data of N ın γ' and ε Phases

Experimental information on the growth rate of γ' and e layers formed during gaseous nitriding iron is assessed applying the most recent thermodynamic description of the Fe-N system. The atomic mobility of N in γ' was found approximately independent of composition yielding a concentration independent self-diffusivity of N in γ' obtained as D N *(γ') = 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 e was assumed to be independent of concentration and evaluated as M N e = 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. Furthermore, the evaluated data were compared with the previous evaluations.