Abstract: Study was made on the swerving of the curves of strength and hardness vs L-M parameter P=T(20+lgt)for steel 20Crl 1MoVNbNB aged at 550.600 and 650℃ for 0—5000 h,T being aging temperature in K and taging time in h.The swerving seems to be due to:(1)the coarsening of the mean size of principal precipitate M_(23)C_6,(2)the precipitation of Laves phase MoFe_2;(3)the decrease of Mo content in matrix and(4)the recovery and recrystallization of the matrix phase.

Key words: L-M parameter, steel 20Cr11MoVNbNB, Lares phase, long-term aging, recovery and recrystallization