Experimental and thermodynamic studies of phase transformations in Cr–V low alloy steels

Phase transformations in three Cr–V low alloy steels at 773 and 853 K were studied experimentally in a transmission electron microscope (TEM). The theoretical calculations were carried out for ternary Fe–Cr–C and quaternary Fe–Cr–V–C systems corresponding to the investigated steels. The calculations of phase equilibria were performed using the thermodynamic database program thermo-calc. M3C in 1Cr and 1Cr–0.3V steels, M7C3 in 1Cr–0.3V steel, and MC in 1Cr–0.3V and 1Cr–0.5V steels were identified. The formation M3C precedes the formation of M7C3. The M7C3 carbide in all investigated steels and the MC carbide in steels containing vanadium were determined by thermo-calc as equilibrium phases. The comparison of experimental and computational results indicates that the investigated steels have not achieved equilibrium even after aging for 5000 h at 773 and 853 K.