Stress corrosion behavior of T91 steel in static lead–bismuth eutectic at 480 °C

• The stress corrosion test of T91 stressed C-rings in LBE with the constant strain technology was conducted.
• Cracks were not found on the T91 in oxygen saturated LBE due to the oxide prevents the contact between the matrix and LBE.
• The growth of the oxide layer was accelerated by stress, especially for the outer layer.

The corrosion behavior of stressed C-rings made of martensitic steel T91 was investigated through constant strain tests. The specimens with different initial hoop stresses (0 MPa, 150 MPa and 300 MPa) were exposed to static oxygen saturated lead–bismuth eutectic (LBE) at 480 °C for 500 h, 1000 h and 1500 h, respectively. The results showed that no crack was found on the outer surface of all the specimens after exposure; and the microscopic analysis showed that the specimens were covered with two oxide layers, which included a magnetite outer layer and a Fe–Cr spinel inner layer. The transformation of spinel into magnetite at the spinel/magnetite interface might be promoted by stress, which increased the difference between the thickness of the inner and outer layers. Moreover, the steel loss was estimated by the observed oxide layers; it increased rapidly when the stress was above 300 MPa, and was about 1.3 times of when the stress was absent.