On many occasions, it is necessary to reattach silver soldered parts that have broken loose, sweat on sights instead of drilling and tapping the barrel, mend broken parts etc etc.
Silver solder is one way to do that and it works really well if used properly.
Silver solder comes in many different forms, the main difference being how much heat it takes to melt the solder and how strong a joint is needed (and of course, cost which for the higher silver content solders can leave you limping)
I have about 5 flavors of silver solder here at the shop and they each have their own use. The one I seem to end up using the most is Brownells Hi-force 44.
http://www.brownells.com/.aspx/pid=7...4-trade-SOLDER
Its a wonderful solder because it has some of the strength of Silver (about 20,000 PSI), but still melts at a temperature that is low enough that it will not damage the temper of springsteel, but it has a high enough melting temperature that it wont melt in blueing salts (Still, I make a note to be careful to keep the heat down on the tanks).
I repair a lot of firearms, and it has become painfully obvious (to my clients at least) that many gunsmiths out there do not know how to do this. Just last week I had a Mosberg shotgun that had broken forend. The client told me that he had taken this gun to another smith 20 years ago and the smith had soldered the tube back into the block that the carrier arms attach to, it had rebroken 10 years ago and now he wanted it fixed. I took it apart and saw that the "gunsmith" had not even taken the magazine tube out of the action and had merely smeared on some flux and then dobbed on some silver solder. The silver solder had not made any sort of a good bond to the parts and the flux that he left all over the parts had rusted everything. It was just a matter of time before it failed.
I have developed my own method of soldering steel. It may not be the best way but it is a way that might work for you.
I will solder a piece of high carbon steel to a piece of steel scrap (disregaurd my feeble attempts at engraving) to show you how I do this.
The thing is, just like sweating copper pipes together, it is imperative that you get the joint properly tinned before you actually joint the two. Just think of it like contact cement, you have to get both surfaces prepped first. With copper, you can just flux it, dob some solder on there, twist it till it squeaks, and walk away, but steel just aint that way!
First, prep the joint with sand paper to get bare, fresh metal to work with:
http://i1120.photobucket.com/albums/...l/IMG_3645.jpg
http://i1120.photobucket.com/albums/...l/IMG_3647.jpg
Next, apply enough heat to melt the solder and go ahead and dob on a little. It will bead up like a drop of mercury and it will roll right off if you are not careful.
http://i1120.photobucket.com/albums/...l/IMG_3652.jpg
Next, (and here's my trick) take some steel wool and dip it into the flux, and then scrub that ball of solder into the surface of the steel. Just a few strokes and it will stick nicely and wet to the surface like oil.
http://i1120.photobucket.com/albums/...l/IMG_3653.jpg
http://i1120.photobucket.com/albums/...l/IMG_3654.jpg
Its hard to see, but the end of that steel is completely tinned.
http://i1120.photobucket.com/albums/...l/IMG_3655.jpg
Now the other part gets the same treatment (I didn't sweep it clean like I did the other part so you can see the solder.)
http://i1120.photobucket.com/albums/...l/IMG_3656.jpg
Now apply some flux to the joint and clamp the two together (you can use needle nosed vice grips, but I made a special jig to help me hold pieces that I am soldering)
http://i1120.photobucket.com/albums/...l/IMG_3657.jpg
Just apply heat and dob in a little extra solder. You want it to just "lay" in the corners of the joint real pretty like.
http://i1120.photobucket.com/albums/...l/IMG_3659.jpg
Now, test the work to make sure you did it right.
http://i1120.photobucket.com/albums/...l/IMG_3660.jpg
If you do it right, you can get an amazing bond and spring steel will still be spring steel.