Soldering Stainless Steel: Achieving Permanent Connection with Coating & Copper Plate

Hello.

I am looking for a permanent solder connection with stainless steel.

I do not know if it can be done in some way, I would like to apply a coating that can be soldered to stainless steel in some permanent way ... e.g. a copper plate.

I am asking for any ideas what and how to do so that the end result is a solder wire to the stainless steel

greetings

Ultimion

A bit of creativity in searching on the electrode!
Recently, I took part in such a discussion:
https://www.elektroda.pl/rtvforum/topic429151.html
Greetings J.

oh yes, but there is no word about 0H18N9 stainless steel

greetings

Ultimion

Whenever I want to solder something on steel, I first lubricate the surface with acid, take tin, rosin and solder, it always comes out permanent. Greetings

Unfortunately, stainless steel cannot be soldered with tin.
There are three solutions to this.
TIG welding (probably not possible)
Soldering with silver-based binders or special solders (they are expensive, difficult to obtain and usually overlapped -> sheet metal, foil solder, sheet metal. The whole is heated).
Gluing (Alstom glues the car bodies of trams in this way and the connection is stronger than the metal sheet itself, but is not conductive. You can ask at the tram depot)
You can also spray the sheet with copper or apply electroplating copper or silver

You wrote that you want to solder to the sheet ... but what?

Hello, it is possible to cover this plate with brass, but you will not do it with a soldering iron, it has to be done with a torch (I think argon soldering), similar to welding pipes that (Acetylene). Father used to do something like that for me. Disadvantage: the stainless steel plate will color, but it can be removed with some acid or polished with felt.

Hi.
Any stainless steel, even acid-resistant (with a very high content of chromium and nickel), can be soldered with tin (alloy or pure tin - then the weld does not oxidize and looks better). I have done this many times. The trick is to use the right flux. In this case, the flux is phosphoric acid. You can make a solution of rosin in spirit and add about 10% of phosphoric (orthophosphoric) acid. Some of the resin will precipitate, but that's okay. You can also make an acid solution in water (10 - 20%) and solder with tin and rosin. Chrome is also soldered with this flux (e.g. tubes from telescopic antennas). Before brazing, sand the surfaces with 200 to 600 sandpaper so that they are not completely shiny. Any other metal can be soldered to the tin-whitened surface.
A stronger weld is obtained by using a hard solder (brass or silver). Then you have to solder with a burner. Propane-butane is sufficient for small components. The elements need to be heated up to 600 - 900 degrees, depending on the type of solder. The flux is borax or borax with sodium fluoride. The most popular silver solder is LS45 or LS60.
Some types of bronze can also be soldered with phosphoric acid flux (I don't know which ones, but I've met with them). They are light yellow with a greenish tinge and cannot be soldered with commonly available fluxes. After hydrochloric acid or zinc chloride, brown slime forms on the surface and the tin flows like water from butter. The tin also does not catch on rosin. Then only phosphoric acid helps.
I wish you successful attempts.

For brazing stainless steel, I use UREA (artificial fertilizer) as a flux, chemical formula (NH2) 2CO - powder. Urea melts a little faster than tin and is a strong reducer, the tin under such a flux solders everything except chrome coatings and Kanthal resistance wire. He also solders aluminum, although with resistance. After brazing, urea can be removed with water as it can accelerate corrosion.
The more active flux is aniline hydrochloride, here even aluminum can be tinned. I don't know about chrome because I haven't checked it.
One more active flux: acetylsalicylic acid, i.e. POLOPYRINE. It is nice to solder thin winding wires to polopyrin without scraping the enamel, because polopyrin removes it itself: put a polopyrin tablet on the table, then the end of the tinning wire, press the tip with tin and slowly pulls the wire under the tip - it comes out tinned!
ATTENTION! Do not inhale the stench of this soldering with more active fluxes!

I use a simple and reliable method of soldering chromium-nickel with tin: take a copper wire, dip it in concentrated hydrochloric acid and lubricate the soldering surface. It really works.

I would like to add a few words to the topic of stainless steel soldering. Phosphoric acid is safe to use and it works perfectly, which I have checked over and over again. It is a weak acid (in coca cola, cillit and fosol) and safe to use. You can try if the Fosol rust remover, easily available on the market, could be used for soldering (I did not check it myself, because I had access to pure phosphoric acid). Even though it is a weak acid, wash the joint thoroughly with detergent and water after brazing. It is best to tin both the brazed parts with phosphoric acid, wash them and then braze them with rosin.

I personally wanted to solder a copper tube for water with such a stainless steel cup available for food use. I bought silver with flux (it looks like insulated wire) and calmly silver plated it, then with ordinary tin. Of course, a hard solder and a suitable burner, somewhere around 1000 * C, so that it has and can be soldered without any problems.

greetings