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

Abstract

Cylindrical samples of iron, austenitic steel 1.4571, and nickel‐based alloy 2.4663 were tested in liquid tin (Sn) at 500 and 700 °C. The exposure times ranged from 3 to 100 h. During exposure the oxygen content of the melt was measured online. In case the oxygen content is higher than the oxide threshold, even Fe‐oxides, which were not specifically created before exposure, are capable of reducing liquid Sn corrosion. In case of lower oxygen contents more stable oxides, like Cr‐oxides, fail locally leading to corrosion pits. The influence of saturation with the parent element of the tested alloy on material consumption and morphology of corrosion scales was also investigated. Saturation reduces material consumption and promotes formation of intermetallic compounds of the respective parent element and Sn. The capacity of liquid Sn for taking up nickel leads predominantly to selective removal of nickel from the corrosion scale on austenitic steel and nickel‐based alloy samples, whereas the less soluble elements remain. Finally, typical rate laws were tested for expressing the observed material consumption as a function of time.

Dissimilar Metal Solution from Solid Alloys as Observed for Steels and Nickel‐Based Alloys in the Presence of Lead‐Based Liquid Alloys or Liquid Tin

“…Interference of solid oxide formation with element solution is also possible for steels and Ni-based alloys in contact with liquid tin. 23…”

“…Element transfer from the steel to the intermetallic layers is largely in proportion to the original steel composition. 21,22 Under conditions that result in local initiation of enhanced degradation, pits formed in the steel surface exhibit FeSn 2 dispersed in a network of ferrite or another phase that is rich in Cr and Mo, 23 suggesting that the percolation mechanism was active, at least temporarily. In the center of the pits, it rather is Sn that penetrates this network, unless FeSn 2 formation is not particularly favored, i.e., for liquid Sn not pre-saturated with Fe.…”

“…In the center of the pits, it rather is Sn that penetrates this network, unless FeSn 2 formation is not particularly favored, i.e., for liquid Sn not pre-saturated with Fe. 23 At 700°C, FeSn gains in importance for the intermetallic layers that now form along with columnar ferrite. 21,22 From this ferrite, particles pinch off, similar to the situation depicted in Fig.…”

“…22 Locally enhanced interaction between austenitic steel and liquid Sn again results in Fe-Sn intermetallics dispersed in a network of Ni-and Fe-depleted steel. 23 Due to the high solubility of Ni in liquid Sn, Ni-Sn intermetallics tend to form in a later stage of interaction with the liquid metal than, e.g., Fecontaining intermetallics. Accordingly, they are likely to influence aging rather than early development of a depletion zone that results from dissimilar metal solution in the form of selective leaching.…”

“…The influence of oxygen dissolved in the liquid metal as well as the formation of intermetallic compounds is discussed. The observations evaluated with respect to dissimilar metal solution stem from experiments in Pb-based alloys 1,3,[8][9][10][11][12][13][14][15][16][17][18][19] and liquid Sn [20][21][22][23] at 400-750 and 500-1000°C, respectively.…”