Stainless Steel Rust Problem 1

[MManufacturing]

Thanks in advance to those willing to lend a hand with this project....

Our company (a custom machine shop) is trying to develop a salt water product. Since we're in the middle of South Dakota, we don't really deal with saltwater anything. hahahah

Basically, we've silver soldered a stainless steel wire (about .08" thick) to a brass plate. The product is then sent to a plater for a special saltwater finish.

When we sent out the product for testing, we found that directly AFTER the soldered joint area, there was a spot of rust forming all around the wire. But.... AFTER the little rust spot, the wire is fine, with no signs of corrosion.

Now, I've read somewhere that this could be caused by us heating the stainless steel too high, causing some sort of carbon problem. Is this correct?

Would someone be able to offer some solutions?

Again, thanks in advance....

 

[unclesyd]

Your problem is probably stemming from the flux used during the process of soldering the SS wire to the plate. A flux will activate the surface of the SS that will cause the SS to rust very quickly. Another possibility is that during the soldering process some flux is being left on the SS wire, again with the same result.

I would look at selecting the least reactive flux that will do the job. Make sure all the flux is cleaned from the wire prior to testing.
Is this going to be a production process?

The reason for asking is that an additional step might have to be accomplished to prevent the rusting.

 

[MManufacturing]

Thanks for all the help bud....

Just to clarify things - The rust is happening only AFTER its been in saltwater. Didn't know if that would make any difference in your answer.

Ok, if it's the flux, then would you be able to recommend a superior flux product to use?

Also, yes... this will be a production process. If we can nail down the formula, then what we'll end up doing is making some sort of jig system for the guy doing the welding. Then he can just 'tap and go' so to speak.

Once the products are complete, we'll then send off to the plater for it's special salt water plating. Is there something that we need to do BEFORE it gets to the plater?

Thanks for the help!

 

[kenvlach]

Maybe some galvanic corrosion of the stainless, as the fluxed area is directly adjacent to the very noble silver solder.

Monel wire or nickel-plated stainless wire will be easier to flux & solder and should minimize the galvanic corrosion potential.

What is the "special salt water plating?"

 

[MManufacturing]

Not sure what the special salt water plating is. We happen to have other products that are plated by the same company, but nothing is plated specifically for salt water..... except for this particular project.

I 'think' that they plate it in chrome first, then something after that. I guess I'd have to speak with them to get specific details.

I've read on the internet here -

http://www.mcnallyinstitute.com/04-html/4-1.html

- that it looks like it could be due to the heat in the process. My boss agree's. Other than that, the article is full of mumbo jumbo that I don't understand. hahahahha

Anyone have any other solutions??

 

[metrat]

Another consideration may be the effects that heating can have on the stainless. What alloy stainless are you dealing with? Sensativing the material can caould a reduction in the corrosion resistance of some mateirals. If this is the casue you may need to consider a therrmal treatment after the welding to accomadate the effects.

One thing to consider at least.

 

[MManufacturing]

Thanks for the reply.

A thermal treatment AFTER it's welded?

How hot do we need to get it? And... do we need to control the cool down rate?

 

[kenvlach]

Silver soldering at ~1300 ^oF [≠] welding of SS.

Use a low carbon SS not susceptible to sensitization, such as 316L. Also, buy the 316L wire in the bright annealed condition (easier to solder & plate and avoids SCC in seawater).

You may still have a problem if the brazer is slow & uses a carbon-rich reducing flame. Using Monel or nickel-plated stainless wire would minimize any pickup of carbon. As would a oxy-hydrogen flame.

The 'saltwater plating' maybe is electroless nickel?
It surely isn't chrome plated first; chromium is so difficult to properly plate over that chrome plating is stripped before replating. Perhaps, a Wood's nickel strike followed by either electroless nickel or duplex electrolytic nickel, then chromium plating. The corrosion resistance comes mostly from the nickel, not the chromium.

 

[MManufacturing]

I see, thanks for the input.

I was hoping to avoid using a better grade stainless steel, as these are parts ordered in from somewhere else. There is a minimum order for special orders, and we probably wouldn't see the return for about 10 years (sales volume just won't be high enough).

But it is something to keep in mind, and I'll let the boss know.

Thanks guys, everyone has been a big help.