SANS AND TEM STUDIES OF ISOTHERMAL M2C CARBIDE PRECIPITATION IN ULTRAHIGH STRENGTH AF1410 STEELS

Results are presented of SANS and TEM experimental investigations of the precipitation and growth, as a function of isothermal ageing time, of the main secondary hardening M2C phase in ultrahigh-strength AF1410 steel. The results obtained are compared with APFIM investigations and with theoretical models. Combined use of these techniques provides valuable diagnostic data for quantifying the development of microstructures in this class of steels. It is found that the observed precipitation behaviour is consistent with the theory of precipitation at high supersaturations, but includes a surprising secondary burst of nucleation at precipitation half completion.