MOSSBAUER-SPECTRA AND HYPERFINE PARAMETERS OF IRON CHROMIUM CARBIDES IN FERRITIC STAINLESS-STEELS

Isolated iron-chromium carbides, as well as several mixtures of them extracted from 29% chromium ferritic stainless steels are studied at room temperature by using Mossbauer spectroscopy. The spectra of the hexagonal M7C3 carbide and the M2X carbonitride (M = Fe, Cr; X = C, N) consist both of a quadrupole doublet, while the spectra of the cubic M23C6 carbide consists of two independent,peaks. The spectra of the M7C3 and M23C6 carbides may be interpreted by assuming that chromium atoms enter preferentially the sites that are surrounded by the greatest number of carbon atoms. Using the hyperfine parameters determined from the isolated carbides, it is possible to analyse the spectra of carbide mixtures extracted from stainless steels and thereafter to identify the carbides present in the mixture and to estimate their relative abundance.