Abstract
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 °C for 100-5000 hours, the M₂₃C₆, Laves and MX secondary phases were identified. The M₂₃C₆ 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 °C; at 650 °C it was found after 5000 hours of annealing only.

Key words
ferritic steel, secondary phase precipitation, phase analysis, thermodynamic calculations

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