The growth kinetics of the iron-nitride compound layer during nitriding and nitrocarburizing of pure iron has been investigated for various temperatures and various combinations of imposed nitrogen and carbon activities. The results indicate that no local equilibrium occurs at the gas/solid interface during nitriding/nitrocarburizing, due to the slow kinetics of ammonia dissociation, the development and subsequent desorption of molecular nitrogen gas at the surface and, for the case of nitrocarburizing, the fast initial carbon uptake. The kinetics of gaseous nitriding of pure iron can be adequately described by a model that adopts local equilibrium at the solid/solid interfaces and a composition-weighted intrinsic diffusion coefficient of nitrogen in the Fe-N phases. For nitrocarburizing modeling appears not possible yet, due to compositions at gas/solid and solid/solid interfaces which change with treatment time and the lack of accurate thermodynamic and kinetic data for Fe-N-C phases.
|Title of host publication||17th Heat Treating Society Conference Proceedings|
|Place of Publication||Metals Park|
|Publication status||Published - 1998|
|Event||ASM heat treating society conference - Indianapolis|
Duration: 1 Jan 1997 → …
|Conference||ASM heat treating society conference|
|Period||01/01/1997 → …|