Mechanical and physical property tests on annealed 2¼ Cr-1 Mo steel were conducted in an effort to define behavior in support of the design of the Clinch River Breeder Reactor Plant steam generator design. True-stress true-plastic strain tensile data between the 0.2% offset yield stress and the ultimate tensile strength for temperatures between 25 and 593°C and strain rates between 6.7 × 10-6 to 6.7 × 10-3/sec were fit with an equation. Creep data were analyzed and an analytical expression formulated defining strain-time behavior for primary and secondary creep. Similarly, an expression was obtained defining the time to the onset of tertiary creep as a function of stress and temperature. Strain- and load-controlled fatigue data were analyzed and proposed. American Society of Mechanical Engineers (ASME) fatigue design curves were formulated for temperatures ranging from 25 to 593°C. Dynamic strain aging was found to lower the fatigue strength of this material at 371°C, and this was attributed to dynamic strain aging. Results of subcritical crack growth tests are also reported. Comparisons between thermal conductivity and diffusivity values and those found in the ASME Code indicated that the new values were significantly higher than those presently found in the Code.