Final Report on Low-Cycle Fatigue and Creep-Fatigue Testing of Salt-Filled Alloy 800 Specimens

摘要

Uniaxial low-cycle fatigue and creep-fatigue tests have been carried out on hollow alloy 800 specimens that were either filled with air or with a molten mixture of sodium nitrate, potassium nitrate and an oxidizer. Low-cycle fatigue tests were carried out at 1200 exp 0 F and 650 exp 0 F by cycling the strain continuously between equal mangitude of tensile and compressive values at a rate of 4 x 10 exp -3 sec exp -1 until failure. The creep-fatigue tests were carried out at 1200 exp 0 F. The loading cycle differed from that of low-cycle fatigue testing only in the imposition of a hold at the peak compressive strain in each cycle. Cracks always initiated on the inner surface of the hollow specimen, and therefore, corrosive effects on crack propagation and initiation were controlled by the environment within the specimen cavity. In common with tests carried out earlier on steam-filled alloy 800 specimens, at 1200 exp 0 F in the presence of molten salt the heat of alloy 800 with the lower carbon content had a higher fatigue strength than the heat with the higher carbon content even though different heats were used in the two testing programs. The fatigue strength of the two heats of material in the presence of molten salt at 650 exp 0 F were about the same. Tests with air-filled specimens indicated that the presence of the molten salt degraded the fatigue life at 1200 exp 0 F but did not affect the creep fatigue life, while the presence of steam enhanced both the fatigue life and the creep-fatigue life.