Influence of temperature on the oxidation/corrosion process of F82Hmod. martensitic steel in lead–bismuth

A F82Hmod. martensitic steel has been tested in lead–bismuth under a gas atmosphere with a H2/H2O equilibrium of 0.3 to examine the influence of temperature on the oxidation/corrosion process. The temperature range studied was 535–550 °C, temperatures just below the temperature transformation of magnetite into wustite. The durations of the tests were 500 and 1000 h and the oxygen concentration in lead–bismuth was between 3×10−7 and 4×10−7 wt%. The results point out the existence of a threshold temperature, around 550 °C, above which corrosion occurs and the formation of a protective oxide layer is not possible. Two approaches have been considered to explain this behaviour: (a) a kinetic mechanism more than thermodynamic considerations as the driving force of the oxidation/corrosion in lead–bismuth under low oxygen potential, (b) the possible transformation of magnetite into wustite.