Solder Stainless Steel

Stainless Steel comes in pipe, tube, and sheet form. It is usually non-magnetic and often has a silver finish. Stainless Steel alloys with high Nickel or Chromium contents can be very shiny and have a mirror finish. These highly polished alloys are much more difficult to solder due to a very strong oxide layer. They typically require the oxide layer to be physically broken by wire brushing or sanding, and chemically removed by acidic flux. These barriers reform quickly, so agitate, flux and solder in a rapid sequence.

Steps

  1. Prepare the metal to be soldered. Clean the parent metal or metals to be joined. The base metal must be spotlessly clean. Prepare stainless steel surfaces with a stainless steel wire brush, by agitating the surface vigorously. Breaking the tough oxide coating on the parts is crucial to stainless steel soldering.
  2. Apply the Flux. Apply the appropriate stainless steel soldering flux to break the oxide barrier and draw the solder into the joint/repair area. Use the solder wire or rod to move the flux into position if needed.
  3. Heat the metal. Use a soft flame, heat gun, or soldering iron to heat the parent metal adjacent to the repair area, or on the opposite side of the joint. A direct flame on the repair area is likely to overheat the solder and flux. If using a torch, hold the torch tip {{safesubst:#invoke:convert|convert}} away from the parent metal.
  4. Fluxing action begins, apply solder. When the flux bubbles and turns brown, it is time to apply the rod. Drag the rod over the area to be soldered, until it begins to flow. Once the solder starts to flow remove the heat. If additional layers are needed, continue to drag the rod over the area.
  5. Observe the solder deposit. The solder should bond smoothly. If the solder balls up like a bead of water it has not wet to the parent metal. This is likely either due to insufficient breaking of the oxide coating or due to overheating.
  6. Apply additional solder. If you stopped soldering and want to apply more solder or flow out the deposit more, let it cool a little, add more flux and reheat. The flux will help the bonding process, whether adding more solder or just flowing out the previous deposit.
  7. Remove the excess flux with warm water and a wire brush. Flux by its very nature is corrosive and should be removed.

Tips

  • If it is necessary to apply the flame directly to the rod or flux, pull the torch tip back even farther from the work surface and keep it moving. The flux will begin to bubble and turn light brown. Besides preparing the parent metal for the solder, these changes indicate the proper working temperature for the flux. If the flux turns black, let the area cool, clean it & start over.
  • It is important to find the correct stainless steel solder and flux for your application. Some solders do not bond to stainless steel, and due to the tough nature of the oxide coating it is important to have a properly acidic flux.
  • For some difficult to solder very thin wires, and large surface area joints, it may be helpful to pre-tin the joint area on each part with the solder before setting up to join the parts. Simply follow the steps below to coat the joint area of each part with an even coat of solder. Then, after the parts have cooled, follow the steps again to join the parts. Do not pre-tin one day and solder the next. A fresh oxide-free surface is important to soldering success. Pre-tinning your parts with the right solder can greatly improve joints on difficult to solder metals and large surface area parts.

Warnings

  • Do not overheat. The rod will melt if overheated, but will not bond properly.
  • Flux residue is acidic and should always be removed, even for “No Clean” fluxes.
  • Work in a well ventilated area. Fluxes will give off toxic fumes.
  • Wear protective equipment as many solders need to be heated to over 400F.
  • Do not directly heat the solder or flux

Things You'll Need

  • Heat source: Soldering iron, heat gun, or soft flame (propane torch)
  • Stainless Steel Solder: Alloys of tin-silver, tin-lead, tin-copper, tin-copper-silver, cadmium-silver, and cadmium-zinc-silver all wet to stainless steel.
  • Stainless Steel Flux: An activated liquid flux, a mixture of inorganic salts in water. Rosin and other organic fluxes will not consistently break the oxide coating.
  • Stainless Steel brush for removing the oxide coating

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Sources and Citations

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