Corrosion in austenitic steels and nickel-based alloys caused by liquid tin at high temperature

Aspects of corrosion of iron‐ and nickel‐based materials by liquid tin: Oxygen dissolved in the melt and saturation with the parent element

“…On a binary Fe–Ni alloy, tested at 270 °C in liquid Sn, the stannides were blocky FeSn 2 ‐layers for samples with 40.8 at% Ni‐content, whereas for a Ni‐content of 95 at% massive appearing Ni 3 Sn 4 ‐layer, of which segments spalled off, formed at the instantaneous sample surface . In case of austenitic steels the FeSn 2 depicted generally a blocky shape . Hence, the stannide crystal shape on these tested materials is apparently influenced by the Ni‐content.…”

“…For a constant solubility and material consumption rate, saturation of the liquid metal will be approached the earlier the larger the ratio is. On the other hand, for a constant ratio of exposed surface area to melt volume but increasing solubility the ratio decreases and the melt will be later saturated . Hence, in case of alloys and for a small ratio, the high soluble element, like Ni, will be predominantly solved as long as the melt is not saturated.…”

“…This may even lead to selective leaching of the high soluble elements. Selective leaching is, though, only an intermediate step of consuming the whole alloy . Vice versa, a large ratio, for the same exposed surface area and melt volume, indicates that the melt will be earlier saturated in low soluble elements, like chromium (Cr) and molybdenum (Mo).…”

“…Vice versa, a large ratio, for the same exposed surface area and melt volume, indicates that the melt will be earlier saturated in low soluble elements, like chromium (Cr) and molybdenum (Mo). Saturation will on the one hand end the solution driven corrosion and on the other hand cause re‐precipitation if further alloy material is consumed by the melt . For re‐precipitation there are two possibilities: (1) the element does not form intermetallic compounds with Sn, as in the case of Cr, and re‐precipitates as separate metallic particles; (2) the alloying element, e.g., Fe or Ni, forms intermetallic compounds with Sn .…”

“…These layers do not inhibit corrosion as with increasing exposure time material consumption continues in form of transformation of material into these layers . Furthermore, also through these layers leaching of Ni occurs, causing de‐alloying of the alloy beneath the solid layer . The material loss generally increases with temperature and exposure time .…”