Silver solder for SS wire?

[benz]

A friend once made some lengths of SS cable with aircraft eyes, but instead of swaging the cable into the eyes he soldered them with silver. Has anyone looked into doing this for sailboat rigging? It seems the solder would keep water out of the joint, and not having to squash the fitting and the cable during swaging might retain more strength.
Always thinking.....
Ben

[Douglas]

I tried to silver solder small holes in a 304 SS sink once, without successful results. It seemed that the heating temperature of the ss was quite critical, and if only slightly overheated, the silver solder just rolled into balls and didn't flow or stick to the SS.

I was using a propane pencil flame torch, with lots of flux too,,,, disappointing that was !

Douglas

[TomP]

What you may have already discovered is a very tedious and time consuming art...

Soldering anything to stainless steel required a judicious application of high heat. Also, the flux must be correct. One cannot use the paste flux a plumber uses...
Here are some tips:

Both surfaces must be immaculate...sterile would be an understatement. The best way to ensure this is a violent scrub with a Scotch brite green pad and acetone.
Allow the acetone to evaporate (can be accelerated with a heat gun)
Apply flux to both the filler and the surface.
Now this may seem contradictory...but you will want to gradually heat the surface to be soldered, but you also want to get in and out quickly with the torch. Watch the colors of the SS when heating...it will go brown, blue then red quickly...the soldering needs to occur between the blue and red stage...and it happens fast. Also remember that if the flux gets too hot it will loose its binding properties, the metal will oxidize and the solder will just pill.
Two type of solder we use is a pure silver which bonds around 1120*F but only has a 85K psi rating. The one we use most often is a Nickle Bronze alloy which bonds at 1400*F but has a 125K psi rating.
The silver alloy specification is 1210fc and is sold by the ounce
The nickle bronze specification is 528fc and is sold by the pound
The flux is the most important though. The best is Type B1. We get this flux from Rio Grande-a jewelry supply house in New Mexico.

The equipment you use also makes a difference. To get to the heat layer you need quickly enough you should use an oxy/acetylene setup with a slight carborizing flame (no yellow, just a hint of white, mostly blue). You could use a oxy/MAPP gas setup, but it will take considerably longer to get everything properly heated. Remember, the longer it takes to heat, the smaller window of opportunity you will have because the flux will roll off. A propane trigger torch just does not carry enough btu loading to be effective for this application.

We generally avoid soldering when at all possible...GTAW is the far preferred method both in speed and finish.

Hope this helps,
Tom

[Douglas]

Thanks Tom P. , for clairifying what my problem was, when I tried to silver solder ss .

I am not quite sure what GTAW means, could it be Gas Tunstan Arc Welding ?

Have you ever used clay dams to reduce the area of heat spreading through the base metal when soldering or TIG welding ?

Somewhere I think that I read that , even lower elevated temperatures, guessing below 700 degrees F could and can reduce 18-8 ss ability to resist saltwater corrosion, evidenced by pitting and rusting,,,, do you have a comment on that ?

Enquiring minds like to know such trivia,,,, mine included .

Douglas

[TomP]

Douglas,

First off, you are correct...GTAW is gas tungsten arc welding...better known as TIG.
You are also correct that temperatures as low as 700F can, and do, have an effect on the corrosion resistance capability.
Insofaras using clay dams to limit the heat affected area...no. Clay is a natural insulator, and therefor would not proived a "limiter" to the heat affected zone (HAZ). TIG, due to its very nature, is a precise weld. A skilled TIG welder should produce no more than a 1/16 to an 1/8 of an inch on either side of the weldment itself. Thus limiting the HAZ. There are commercially available "heat pastes" for delicate welding. For the most part, they are an amalgam of tin and aluminum powder suspended in a base...designed to act as a heat sink. I do not have first hand experience with these products, but some welders I know use them. Though I personally feel it is to hide their own short comings as a welder and their failure to control the HAZ.

I co-authored a paper on this...it is quite long, so I will just elaborate on the specifics to this conversation:
True, heat does play into the corrosion resistance of materials. However, it is not necessarily the heat that is the culprit in reduced corrosion resistance, but the process in which it was heated. In this case, let us focus on fabrication, i.e soldering and welding. During fabrication, metal products often come in contact with steel components and tools. Transportation, handling, forming, grinding and welding can all result in physical contact with iron-based structures. During such contact, iron may become embedded into the surface of an alloy component. When stainless steels (e.g. austenitic grades such as AISI 316, 317 and 904L) and superaustenitic grades (e.g. INCOLOY alloy 25-6MO) are
exposed to aggressive acid and acid-halide environments, the embedded iron can accelerate localized attack such as crevice and/or pitting corrosion. Embedded iron has not been shown to affect the corrosion resistance of higher alloyed materials, such
as INCONEL alloys 622, 625, C-276 and 686.

So what can be done? One word: Passivation. Passivation is the formation of a thin, protective film on a metal which makes the metal passive (corrosion-resistant).
While stainless steels require an acid treatment to passivate their surface, nickel and the high-nickel alloys become passive upon exposure to air. The film itself is a chromium-nickel-iron-molybdenum oxide for the chromium-bearing nickel alloys. Chromium is the key constituent giving the film its outstanding corrosion resistance. The film formed in air at the mill is stable. However, during fabrication, the film may be damaged locally when
iron, weld spatter, arc strikes and heat tint scale create local defect sites (i.e. local imperfections in an otherwise passive film). The undamaged surface remains passive
throughout fabrication. Removal of defects, by pickling, electropolishing, or mechanical means, immediately restores the film and passivity so passivating by acid washing is not required. Nitric acid cleaning/passivation treatments for stainless steels are described in ASTM A380. It should be noted that these treatments are not suitable for cleaning structures after fabrication. They are applicable only to passivating chromium-nickel stainless steels and are not applicable for cleaning nickel alloys after fabrication. As already stated, such treatments are not required to optimize the corrosion resistance of the nickel-based alloys.

Whichard made a product called Whichinox (sp) and marketed it as a passivation paste. It essentially was a mild phosphoric/nitric acid pasted with some mild abrasives added to the emulsion. It worked quite well, and from a mettalurgical standpoint, it did, to a degree, passivate the metal.

I hope this was not too much of an overload.

Tom

[Douglas]

Tom , that information you just described, tells me that you are knowledgable about ss and monel fabrication.

There is a piece of information on welding ss , that I hope you can clarify .

I have been told that when welding ss, some of the chromium and nickle are boiled away, from the molton puddle, vaporized as it were, and that changes the alloy balance percentage to somewhat less than the mil spec ,,,,, ie 18 - 8 , might be less, of a percentage, at the finished weld.

I have been also told that using a filler rod, higher in content (richer) of chrome and nickle, likely will replace that boiled away "lost" chrome and nickle , thus keeping the alloy percentages more near the mill spec.

Is there any truth to these ideas of enrichening a weld ?

Douglas