Brittle fracture of T91 steel in liquid lead–bismuth eutectic alloy

Environmental degradation of structural materials in liquid lead- and lead-bismuth eutectic-cooled reactors

“…This obviously cannot explain the fast crack propagation of several tens of micrometres per second reported in Ref. [527] and shown in Fig. 4.38, as diffusion is a quite time-consuming process.…”

“…(4-12), which is the mathematical formulation of this model, and concluded that, if the stress-assisted dissolution model described accurately LME crack propagation, the crack propagation rate would only be 2.4 × 10 − 4 μm/s. This value is far smaller than the experimentally observed crack propagation rates, which can actually reach values as high as 100 μm/s [473,520,527]. Ersoy et al [532] The cyclic stress response under low-cycle fatigue showed a predominant cyclic softening behaviour for T91 F/M steels [500,502,509].…”

“…Such a mechanism operates in neutron-irradiated materials as well, where abundant irradiationinduced defects tend to localise plastic deformation, thus favouring crack initiation. Both cases promote the occurrence of LME [45,457,471,493,[496][497][498]519,527].…”

“…Increasing the hardness of T91 F/M steels by tempering at relatively low temperatures, e.g., 500 • C or 600 • C, instead of the standard tempering at ~760 • C, has been shown to strongly promote the steel LME susceptibility to liquid Pb/LBE, particularly in the presence of stress concentrators, such as notches [456,457,471,506,519,526,527]. During steel tempering, interstitial atoms, such as carbon, precipitate from the supersaturated matrix to form carbides at the martensitic lath boundaries.…”

“…The parametric studies reviewed in Section 4.6 demonstrate that T91 and similar F/M steels are susceptible to liquid Pb/LBEinduced embrittlement. The magnitude of LME susceptibility is crack initiation-controlled, considering that once cracks are initiated, they will propagate into the steel bulk as fast as several tens of micrometres per second [473,520,527]. However, crack initiation takes place at a microscopic length, making it difficult to properly understand the LME mechanism.…”