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Are 304 stainless steel plates suitable for making a tin/lead melting pot operating at 300 °C or 572 °F?

My concern is that the liquid alloy could form a kind of amalgam on the surface of the steel, therefore not only slowly corroding it, but also contaminating the solder alloy with nickel and chromium from the stainless steel.

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  • $\begingroup$ Note, almalgam is a term to address alloys of mercury. But in your question, mercury does not occur. $\endgroup$
    – Buttonwood
    Commented Mar 2 at 18:11

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TubingChina.com states:

Resistance to molten lead (m.p. 327C)

Lead, in the presence of oxygen, is more aggressive than lead covered with a charcoal layer. At 400C some attack to 1.4301 (304) type can be expected. The 1.4401(316) type and higher alloyed austenitic should be resistant. If temperature are as high as 900C then a charcoal oxidation inhibiting layer is essential if severe corrosion is to be avoided. Any antimony in the lead can increase the risk of corrosion.

Resistance to molten tin (m.p. 232C)

Molten tin should not attack austenitic stainless steel below 400C. At 400C some attack can be expected, which becomes severe at temperature of 500C and above.

In summary, at 300°C, rather than 400°C as in the reference above, I'd expect some slow corrosion to type 304 stainless steel from a $\ce{Pb/Sn}$ solder. This raises two questions:

  • How will the solder be used? In critical aerospace use, for example, with lead-tin solders, extreme care was taken to ensure that the alloy contained no contamination of other materials dissolved from equipment (among other things, it helped prevent tin dendrite growth). For use as a solder pot for commercial lamps, that would not be critical.
  • How thick will the container wall be, and for how long will it be in service? For a few weeks use, with thick metal, there likely would not be an issue. For a year, be prepared for a disaster, when the solder pours through the corroded vessel wall.

The reference also suggests floating charcoal on the solder surface to slow oxidation of the vessel (which should also make the solder itself last longer).

Consider using austenitic 316 stainless steel, which that reference states is more resistant to both molten tin and lead.

Also consider coating the solder pot, as in this study using ceramics. Of course, any coating must be adherent and survive an occasional heating/cooling cycle of the pot. You'd need to do some research on that.

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