Analysis of corrosion action of liquid heat-carrier Pb–Bi eutectic on stainless steel

The corrosion behavior of 316L, 15–15Ti and T91 steel samples exposed to the lead-bismuth liquid-metal heat carrier Pb–Bi eutectic (Pb–Bie) was studied under static conditions at 500 °C for 200, 300 and 400 h. The authors evaluated thickness and morphology of the diffusion zone at the steel/Pb–Bie interface, oxide-layer structure, Pb and Bi penetration depth, and signs of intergranular melt penetration. Steel class affects the physicochemical parameters of corrosion. Austenitic steels 316L and 15–15Ti undergo local intergranular corrosion and Pb–Bie penetration along grain boundaries to a depth of about 5·10 –5 m after 300 h of contact, which can be considered a prerequisite for liquid-metal embrittlement. Martensitic T91 steel is affected by corrosion associated with dissolution, mutual diffusion of elements. All studied samples showed signs of oxidation during contact with the melt. An external Fe 3 O 4 oxide layer (≈10 –5 m) and an internal (Fe,Cr) 3 O 4 layer (≈5·10 –5 m thick) were observed. As contact time increased, Pb and Bi penetration in steel increased from nearly zero after 200 h to about 10 –4 m after 400 h. A difference was found between austenitic and martensitic steels not only in the depth of melt penetration, but also in the localization of damage. A theoretical assessment of the liquid-metal embrittlement conditions of 316L steel samples exposed to Pb–Bie melt is presented using the Griffiths and Robertson models. Using the lattice mean-field theory, the authors theoretically studied the relationship between surface wetting and the steel crystal lattice type. The interaction energy between the steel surface and Pb–Bie decreases more rapidly with increasing temperature for austenitic steel than for martensitic one.