CORROSION AND MECHANICAL-PROPERTIES OF THE MARTENSITIC STEEL X18CRMOVNB 12 1 IN FLOWING PB-17LI

Corrosion, creep-rupture and low-cycle fatigue tests were performed with specimens fabricated of the martensitic steel X18CrMoVNb 12 1 (MANET) in liquid Pb-17Li medium at temperatures in the range 500 to 550-degrees-C. The corrosion behaviour was studied in the pumped Pb-17Li loop "PICOLO" at the two temperatures and a flow velocity of 0.30 m/s. A steady state corrosion rate was observed after an initial period of 1000-2000 hours. The corrosion did not show a uniform distribution over the surface of the specimens. The mechanical tests were made in stagnant liquid Pb-17Li. Creep-rupture tests showed an influence of the liquid metal in long lasting tests only. The ductile behaviour of the steel and the metallurgical examinations as well indicated that the effect of Pb-17Li was a corrosion phenomenon. Low-cycle fatigue tests in Pb-17Li resulted in longer fatigue life than in air. However, a pre-exposure of the specimens in Pb-17Li changed this beneficial effect. Thus, corrosion may also influence the fatigue life of the steel in Pb-17Li, if the contact of the specimens with the liquid alloy lasts long enough. Wetting by the liquid metal is a necessary condition for its corrosive action and its influence on the mechanical properties.