Early stages of decomposition in iron-carbon and iron-nitrogen martensites: diffraction analysis using synchrotron radiation

After aging at room temp. for 3.5 yr and after tempering at 405 K for 1 h, ε/η transition carbide reflections but no α''-type superstructure reflections were detected for FeC martensites. However, for FeN martensites, the α''- superstructure reflections were obsd. on aging at room temp. for 3.5 yr and on tempering at 405 K for 1.5 h. For short aging times at ≤60 h, α''- reflections not of the superstructure type were obsd. for Fe-N martensites. On tempering, changes in the α''-crystal structure occur and are discussed in terms of annihilation of structural vacancies on the N sublattice and stress relaxation. In the diffraction pattern recorded from Fe-C martensite for short aging times, weak reflections occurred which could not be identified conclusively yet and which disappeared after tempering 1 h at 405 K. [on SciFinder(R)]