Creep-to-rupture of the steel P92 at 650 °C in oxygen-controlled stagnant lead in comparison to air

Creep-to-rupture experiments were performed on 9%-Cr ferritic-martensitic steel P92 in the CRISLA facility. The specimens of P92 were examined at 650 °C and static tensile stress between 75 and 325 MPa in both stagnant lead with 10−6 mass% dissolved oxygen and air. The steel showed an insignificant difference in time-to-rupture, tR, and ductile fracture in both environments at >100 MPa, corresponding to tR < 3,442 h. At 75 MPa in Pb (tR = 13,090 h), the steel, however, featured purely brittle fracture pointing to liquid metal embrittlement. Structural changes in the steel and surface oxidation in the different environments were studied using metallographic techniques. The Laves phase that forms during thermal aging at 650 °C was found along prior austenite grain boundaries and martensite laths already after relatively short testing time, along with chromium carbides that are already present in the as-received condition of the steel.