Early Stages of Decomposition in Iron-Carbon and Iron-Nitrogen Martensites: Diffraction Analysis Using Synchrotron Radiation

Abstract

The early stages of decomposition of iron-carbon and iron-nitrogen martensites 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,ε/η transition carbide reflections but noα′-type (superstructure) reflections were detected for FeC martensites. However, for FeN martensites, theα′ superstructure reflections were observed 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),α′ reflections (not of the superstructure type) were observed for FeN martensites. Upon tempering, changes in theα′ crystal structure occur, which were discussed in terms of annihilation of structural vacancies on the nitrogen sublattice and stress relaxation. In the diffraction pattern recorded from FeC martensite (for short aging times at RT), weak reflections occurred which could not be identified conclusively yet and which disappeared after tempering for 1 hour at 405 K.