Thermophysical properties of Alloy 709

Alloy 709 (UNS S31025) has shown enhanced performance, particularly in creep strength, over current generation high temperature structural materials, specifically Type 316 stainless steel and Grade 91. Accurate knowledge of the thermal properties of the material is important to design efficient systems and to allow calculation of thermally induced stresses and stress gradients. Thermal diffusivity, thermal conductivity, specific heat capacity, and coefficients of thermal expansion have been determined for Alloy 709 as a function of temperature in the range of 20-850 °C. The results do not vary significantly for the three heats of Alloy 709 tested, and compare well with those reported for other high Cr, high Ni austenitic stainless steels. Deviations from monotonic behavior have been observed for the specific heat capacity and to a lesser degree for the thermal conductivity, while the thermal expansion and thermal diffusivity increase nearly linearly with increasing temperature.