Influence of sodium on the low- and high-cycle fatigue behaviour of type 304 stainless steel

Strain controlled LCF-tests were performed on X 6 CrNi 18 11 steel (Type 304 ss) in air and flowing sodium in a non-isothermal sodium loop. The results measured at 550 0C in an upstream position of the sodium loop show an increase in fatigue life in the strain range from about 1.5 % to 0.4 % for the base material in the as-received condition while the welded joints remain unaffected by the environment. The LCF-behaviour of base material specimens tested at 500 0C in a downstream position after a prior pre-exposure to sodium (4058 h, 500 0C) is also improved in comparison to parallel specimens tested in air with comparable thermal aging. Load controlled HCF-tests performed on X 6 CrNi 18 11 steel at 550 0C show a significant increase in fatigue life in the low cycle region (Nsub(f) < 106 cycles) and a higher endurance limit for the base material in sodium but no influence of the environment is indicated for the welded joints. (author)