Cracking and exfoliation behavior of oxide scale on T91 steel under different tensile stresses in oxygen-controlled lead-bismuth eutectic at 550 °C

The effect of different tensile stresses (0−180 MPa) on cracking and exfoliation behavior of oxide scale for T91 steel was studied in lead-bismuth eutectic containing 10−6 wt% oxygen concentration at 550 °C. The results demonstrate that the exfoliation area of magnetite increased with stress. When tensile stress reached about 180 MPa, only a little magnetite remained; the outer sub-layer of spinel began to crack and locally exfoliated, exposing the inner sub-layer of spinel. The cracks with four different morphologies originated at the outer sub-layer of spinel and propagated inward. A model was proposed to explain these phenomena.