Decarburization during plasma nitriding

This work reports on the decarburization of steel surfaces nitrided in d.c. plasma discharges. Mass spectrometry was used to detect the presence of ch emical species, such as C and CH3, in plasma atmospheres containing hydroge n, and CO2 in those containing oxygen. The active species of gaseous mixtur es containing hydrogen react with superficial carbon to form CH3 radicals, thus enabling decarburization. Conversely, although CO2-forming reactions t aking place in the presence of oxygen drive early decarburization, at highe r oxygen concentrations, an oxide coating layer is formed and acts as a red ucing agent for the process. (C) 1999 Published by Elsevier Science S.A. Al l rights reserved.