Abstract
Fully austenitic 15Cr–15Ni titanium modified austenitic stainless steel (alloy D9) is used as fuel clad and wrapper material in fast breeder reactors. The temperature dependence of the low cycle fatigue life of the modified alloy has been evaluated over a temperature range of300–923K employing Ti/C ratios of 4 and 8 at a fixed carbon content of 0.05%. At all temperatures the alloy exhibited cyclic hardening in both conditions. Based on the cyclic stress response and micromechanismsof deformation in the range 300–923 K, for the alloy with a Ti/C ratioof 4 threetemperature domains have been distinguished: the predynamic strain aging regime (300–673 K), the dynamic strain aging regime (673–823 K) and the regime where precipitation processes come into play (> 823 K). In both alloys the temperature dependence of fatigue lifeshowed a peakat ∼573 K, with a rapid decrease in life at higher temperatures. The alloy with a Ti/C ratio of 8 exhibited a lowcycle fatigue life that was longer than that of the alloy with a Ti/C ratio of 4 at temperatures below 748 K. At temperatures higher than 748 K, both alloys exhibitedsimilarfatigue lives. The deformation substructure developed during fatigue deformation in both alloys has been characterised and correlated with the cyclic stress response and low cycle fatigue life.
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