During the past ten years, considerable interest has developed in the use of the HP-45 alloy for high-temperature furnace components, and this alloy has replaced the conventionally used HK-40 alloy in some critical applications. The wide use of the HP-45 alloy, however, has been retarded by the scarcity of long-time creep-rupture data.

This paper presents the results of different research programs conducted at Battelle over the past several years and compares the properties of the HP-45 and HK-40 alloys. Included are comparisons of the short-time tensile and long-time creep-rupture properties, the effects of long-time exposure on the tensile and impact properties, the elastic properties, and the surface and microstructural stability of the two alloys. Creep-rupture comparisons are based upon the results of tests of up to 10 000-h duration at 871, 982, and 1093°C (1600, 1800, and 2000°F) on three commercially produced heats of each alloy.