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

Results are presented of SANS and TEM experimental investigations of t he 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 an d with theoretical models. Combined use of these techniques provides v aluable diagnostic data for quantifying the development of microstruct ures in this class of steels. It is found that the observed precipitat ion behaviour is consistent with the theory of precipitation at high s upersaturations, but includes a surprising secondary burst of nucleati on at precipitation half completion.