EARLY STAGES OF DECOMPOSITION IN IRON-CARBON AND IRON-NITROGEN MARTENSITES - DIFFRACTION ANALYSIS USING SYNCHROTRON-RADIATION

The early stages of decomposition of iron-carbon and iron-nitrogen mar tensites were studied by means of diffraction analysis. After aging at room temperature (RT) for 3.5 years and after tempering at 405 K for 1 hour, epsilon/eta transition carbide reflections but no alpha''-type (superstructure) reflections were detected for FeC martensites. Howev er, for FeN martensites, the alpha'' superstructure reflections were o bserved on aging at RT for 3.5 years and on tempering at 405 K for 1.5 hour. For short aging times at RT (up to 60 hours), alpha'' reflectio ns (not of the superstructure type) were observed for FeN martensites. Upon tempering, changes in the alpha'' crystal structure occur, which were discussed in terms of annihilation of structural vacancies on th e nitrogen sublattice and stress relaxation. In the diffraction patter n recorded from FeC martensite (for short aging times at RT), weak ref lections occurred which could not be identified conclusively yet and w hich disappeared after tempering for 1 hour at 405 K.