Compound layers developed at 848 K during gaseous nitrocarburizing of iron and iron-carbon specimens were investigated for several combinations of N and C activities imposed at the specimen surface by gas mixtures of NH3, N2, CO2 and CO. The microstructural evolution of the compound layer was studied by light microscopy and by X-ray diffraction analysis. Com-position-depth profiles were determined by electron probe (X-ray) microanalysis. Layer growth kinetics was investigated by layer thickness measurements. The influence of the N and C activities on the microstructural and compositional evolution and the growth kinetics of the compound layers formed is discussed for the iron substrate. The results indicate that the microstructure is governed by a fast C and a slow N absorption at the surface in an early stage of gaseous nitrocarburizing. The influence of carbon in the substrate on the microstructural and compositional evolution and on the growth kinetics was evaluated from comparing the results obtained for a normalised Fe-0.8C alloy with those for iron under identical nitrocar-burizing conditions.
|Journal||Metallurgical and Materials Transactions A|
|Publication status||Published - 2000|