Creep-rupture tests of steel AISI 304 at 5500C in liquid sodium

The influence of very pure flowing sodium on the creep-rupture behavior of the austenitic steel AISI 304 is studied in test sections connected to the CREVONA sodium loop in the Kernforschungszentrum Karlsruhe. The position of the test sections causes the super-imposing of sodium corrosion and creep damage. The well known effect of tertiary-creep embrittlement reducing the period of tertiary creep is also observed in these creep-rupture tests. Additionally it was found that under decarburizing sodium conditions the corrosion of the strained specimens dissolves material from grain boundaries. Small cavities of -- 1 μm diameter and up to one grain diameter depth develop in large number along grain boundaries. Surface cracks are generated in these weakened grain boundaries. The growth of such surface cracks reduces the diameter of the bulk material and increases the stress. A small effect on the creep rate results from these effects