Soldering on stainless steel

[Vindhyachal.takniki]

I have small strips of stainless steel 202 grade (5cmx2cm) , thcinkess is 0.4mm of sheet.
I tried to do direct tinning of it on small area so that i can direct solder wire on it for use. Tempearture of iron is 425C.

Sometimes tinning happens and sometimes not? whats the right way to do it?

[viperidae]

At the very least you'll need an acid flux to get through the oxide layer.

[Zoli]

Kester 817 is the answer; unfortunately, the smallest amount is one gallon.

[Ian.M]

At the very least you'll need an acid flux to get through the oxide layer.

Maybe not.  Copper sulphate solution and a Q-tip may be sufficient to flash plate the area you want to solder to with enough copper for it to 'take' solder.  See my comments here: https://www.eevblog.com/forum/beginners/soldering-to-strange-metal-contacts/msg3315024/#msg3315024 + later in the same topic.

[Raj]

I have small strips of stainless steel 202 grade (5cmx2cm) , thcinkess is 0.4mm of sheet.
I tried to do direct tinning of it on small area so that i can direct solder wire on it for use. Tempearture of iron is 425C.

Sometimes tinning happens and sometimes not? whats the right way to do it?

experiment with braising some other metal onto it. Handling Oxy Acetylene or propane is easier than using chemicals.
Get a brass brush and heat your steel part until rubbing that brush there, will turn it yellowish.

btw. flux for stainless steel usually have HCL (very dangerous)

[Raj]

https://youtu.be/hz6wdvraC-g?t=68

[gcewing]

experiment with braising some other metal onto it.

I think you mean brazing. 

You could try braising, but I don't think it would work very well on stainless steel...

[BrokenYugo]

Since you're already getting intermittent results, maybe try adding some RA flux?

[bobbydazzler]

sand the surface down a little?

[RoV]

I confirm brazing with silver-loaded material (Castolin or similar) allows using tin over it, but requires a flame.
Another technique that I found useful is attaching a small patch of Nickel with the spot welder (same material and technique used for connecting 18650 batteries). Nickel patches attach very strongly to stainless steel and then are easily tinnable.

[Doctorandus_P]

The problem with stainless steel is that it has a thin oxide skin (Just like Aluminimum) and the solder does not adhere to this oxide.

There are fluxes specifically designed for use on stainless steel. These are usually quite agressive acids, that dissolve the oxide.

It also helps if you use sandpaper just before soldering, and do this under an protective atmosphere.
For example, fist use dry sand paper, then apply some "regular" flux just to form an air tight layer, and then scrub again with a glass fiber pencil through the flux.

[wizard69]

It might help to say why you are doing this.  Also what are you trying to solder to that stainless.   There are a range of soldering and brazing solutions that might apply.  Then there is welding. 

[Raj]

It might help to say why you are doing this.  Also what are you trying to solder to that stainless.   There are a range of soldering and brazing solutions that might apply.  Then there is welding.

He's gonna need high temp gases or argon for welding such thin metal. But ones he has that, brazing with TIG is pretty easy.