Can Stainless Steel be Soldered?
Soldering stainless steel is not as easy as soldering Copper or even mild steel, but it can be done. Many of the commonly-used stainless steels can be soldered. They key to successful soldering of stainless steel lies in three key areas: the flux, the solder, and the heat source.
Choosing the Right Flux for Stainless Steel
When it comes to soldering stainless steel, it is crucial that you choose the right flux. When we say “the right flux” we mean an active flux, like our No. 71 Stainless Steel Soldering Flux. The kind of fluxes you use for plumbing, for example, are generally not strong enough to solder stainless steel (though they’ll do fine for soldering Copper). However, a flux like No. 71 has the strong ingredients that are needed for soldering stainless steel.
No. 71 is a liquid flux, which is great for many applications. However, if you need a paste flux, try our No. 144, which has the activity of No. 71 but in a paste form. Examples of where a paste form is advantageous can include working with a vertically oriented piece or when you want to apply a lot of flux at one location. We also have a gel flux, called No. 78, that works well with soldering stainless steel.
Choosing the Right Solder for Stainless Steel
Choosing the right solder is as important as choosing the right flux. The key word when it comes to “the right solder” for stainless steel is “Silver.” Solders that have some Silver do a better job with soldering stainless steel. This may be a Lead-Free solder, like a Sn96/Ag4 (96% Tin & 4% Silver). Or where you can use a Lead-bearing solder, it may be the Sn45/Pb54/Ag1 (45% Tin, 54% Lead & 1% Silver). Yes, the addition of Silver increases the cost of the solder, but it makes a difference when it comes to soldering stainless steel.
Turning on the Heat
You need to turn on the heat when soldering Stainless Steel. It’s not like soldering Copper, where all you need to do is melt the solder and soldering happens. You need to heat up the surface of the stainless steel so that you activate the flux and the surface of the stainless steel can accept the solder. This means that, unless the parts you’re soldering have a small mass, a standard soldering iron won’t be hot enough. You need to use a torch (Oxy-Acetylene or Map gas, for example) or the kind of heavy-duty soldering irons that roofers like to use. When soldering stainless steel, don’t be stingy with heat.
Putting it all Together
Once you have the three ingredients, the right flux, the right solder, and the right heating tool, you’re ready to solder stainless steel. But don’t start before considering safety. As with all soldering, make sure you work in a well-ventilated area with full respiratory protection. Strong fluxes, like our No. 71, give off strong fumes that you are harmful to breath in. Also, wear the necessary safety gloves, respiratory protection, and eye protection, as specified in the SDS (safety data sheet).
Clean Up after Soldering
One important point to stress when soldering stainless steel: the fluxes you’ll need, like our No. 71, leave a strong residue after soldering. These residues, if left on the part, can cause corrosion of the parts down the line. Therefore, make sure to clean off flux residues with warm water after soldering. Wash off flux residues off well, otherwise, they might come back to haunt you in the form of corrosion.
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How about Brazing?
Soldering stainless steel is a great option for creating strong joints without exposing the parts to higher heats. But sometimes soldering is not enough. Sometimes you need an even stronger joint, and you don’t mind exposing the parts to higher temperatures than soldering. If this is the case, then brazing the stainless steel with a flux like our No. 601B/3411 and the appropriate braze alloy is an option. But that’s for another post!
Be in Touch
We are always happy to field your questions about soldering stainless steel or any other matter pertaining to flux, metal joining and the like. Contact Us!