Age Softening Characteristics of Annealed 2-1/4Cr-1Mo Steel in the Temperature Range 424 to 704°C

The short-term age softening characteristics of isothermal annealed and post weld heat treated 2-1/4Cr-1Mo steel have been investigated over the temperature range 454 to 727°C (850 to 1340°F). Significant degradation in flow strength is observed for times and temperatures within the current service regime of the commercial alloy. Age softening is atypical: flow strength degradation is most rapid at some intermediate temperature. The reduction in flow strength is greatest, and occurs most rapidly, at 575°C (1067°F). The strength degradation is attributed to time-dependent redistribution of molybdenum within the proeutectoid ferrite. It is predicted that thermal aging in the temperature range 427 to 593°C (800 to 1000°F) will result in similar strength decrements for annealed 2-1/4Cr-1Mo steel regardless of prior thermal history above 704°C (1300°F).