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Solder to stainless steel

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ants

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How should I solder to stainless steel?

I'm finding that the solder just rolls off. My solder contains flux, rosin I presume, but it makes no difference. I'm thinking I need a different type of flux in addition to that already in the solder. What do I need?

Thanks,

Ant.
 

Its impossible to solder Lead to stainless steel. Steel needs temperature more than 1000 degrees to merge any metal which is impossible with a soldering iron. You can simply choose to go for a spot weld instead. Cheers
 

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    ants

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I want to spot solder a wire to a stainless steel disc. The solder I have is lead free, it is tin, silver and copper. I have been looking up a flux 'pen' dispenser, would you recommend that? Thanks.
 

Any flux will not go with SS. The one flux used for led / tin/ copper will not work with SS. You may also have a look at similar thread here.
 


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    ants

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That is a pain. One of the posts mentions using a silver alloy as the brazig agent. I could try to use some silver paint on the stainless steel and then solder to that. Would that work?

Added after 6 minutes:

I have some silver based epoxy on order so I can certainly try that. Thanks.

I just tried putting silver paint on the stainless steel and soldering onto it, but no luck. I will try again but give the paint longer to dry.
 

Silver brazing might work but that needs a torch. Used in
knifemaking to join dissimilar metals including stainless.
You might dig a little and find whether there is an especially
popular flux / braze combo for stainless.

Stainless develops a chromium oxide layer that flux won't
deal with. I have soldered many times to mild steel using
electronics flux-cored solder.

In the plumbing section you can find lead-free tinning flux
that with some surface prep (400-grit, get the oxide off and
flux it right away, then torch from the backside) you might
get a solderable spot.
 

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    ants

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It is a lot more awkward than I thought. I have found a web page that says:

"Special fluxes are needed to eat through these stainless oxides. The silver solder commonly sold for home plumbing with copper pipe will work on stainless, but a different flux is needed. Look for a flux containing hydrochloric acid or one that says it is for fluxing nickel alloys or stainless"

I'd prefer to solder rather than use an epoxy because the nature of where on the stainless steel I need fixed won't lend itself well to the clamping necessary for epoxy resin. (Although it will be possible).

I'm going to have a look for some flux containing hydrochloric acid, but from my school days I quite remember having to be careful with that.

Thanks.
 

Would a "battery tab/tag welder" work for this? I haven't had many dealings attaching things to stainless steel.

Really just a small spot welder. There are some instructions for making hobbyist versions on the 'net.
 

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    ants

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To my knowledge, you can solder stainless steel and other materials using Phosphoric acid; see: **broken link removed**

Please be really careful handling such substances !!!!
 

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    ants

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How many do you need? If just one, then it seems like a lot of work to build some type of spot welder.

What are the mechanical conditions? If the device will be relativlely motionless, then expoxy it.

or

Go to a local weld shop and have them hit it with a Tig.

Unless this is crucial to the design and you are going to do a production run, just get it done and move on in the project.

Red
 

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    ants

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I will be making a few dozen, so while I'd like to build my own spot welder it would take too long in comparison to what I have to do.

It is a vibrating device, I will be using epoxy for another part of the device so I could use that instead of soldering. But its just going to be awkward to clamp.

I'm going to order some acid. I'll just be careful!

Thanks.
 

I will. Thanks all.
 

ants,
You can easily solder stainless steel with ordinary lead-tin solder. However, you need a stainless steel flux. Be warned however, that this is an acid based flux and is highly corrosive. Take extreme care when using it in proximity with electronic equipment. The flux is available from many sources, including Allied Electronics www.AlliedElec.com. Google "Stainless steel" flux. You will get lots of hits.
Regards,
Kral
 

I bought some flux for use in central heating installation (FRYS POWERFLOW FLUX 50GM). It worked no problem. It comes as a paste and doesn't turn acidic until it is heated. Then it bubbles and burns and I'm thinking i'm not going to touch that! The join is rock solid. Thanks.
 

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