Influence of thermal exposures on phase evolution in 12Cr-1Mo-0.35V steel

In this work, the effect of time-temperature annealing parameters on phase occurrence and phase chemical composition changes was examined in 12Cr-1Mo-0.35V steel. The phase analysis was carried out by energy dispersive X-ray spectroscopy (EDX) and electron diffraction (SAD). Experimental results of phase occurrence have been compared with their equilibrium data calculated using PD-pp program based on the Hillert-Staffansson model. The same procedure was used for evaluation of chemical composition changes of the phases. After annealing at 500-700 deg C for 100-5000 hours, the M sub 23 C sub 6 , Laves and MX secondary phases were identified. The M sub 23 C sub 6 carbide was found to be the majority phase; together with MX they have been detected in all states. Statistically significant occurrence of Laves phase was found at temperatures up to 620 deg C; at 650 deg C it was found after 5000 hours of annealing only.