Forge welding

[Eli Jensen]

Ok I've gone through the search tool but haven't found an answer. It might seem silly, but, how do I forge weld?

I've got a hidden tang knife I'm working on and am making an end piece for it from 416. The problem is the 416 is 1/4" and I want it to be 1/2". I COULD just buy some thicker 416 but for economy sake I want to just combine too pieces. I could solder it but am worried thats not strong enough, as the second piece will not be secured by any mechanical means and is only attached by solder from the first piece. I also want to avoid the silver seam.

I have some borax and my trusty two brick forge. I'm building a new one and already thought I wouldn't need this one anymore so I'm not worried about flux ruining anything. I might set it on a few pieces of firebrick or I've heard cat litter works. Do I just put borax between the pieces and let it sit in my forge until hot enough?

[Doug Lester]

To start with, it will be very difficult to get the stainless steel to forge weld because of all the chromium in it. I know that it can be done because people have made damascus with stainless steel but it's a difficult process that you need to right set up for to eliminate free oxygen from the forge atmosphere.

I also doubt that you will get the temperatures that you need to forge weld even plain steels. And yes, borax will eat up the soft firebrick your forge is made from. When you build your next forge, line it with a high alumina castable refractory like Mizzou or Cast-O-Lite. That stuff is impervious to borax. Also consider a blown burner or at least one of the high power venturi burners because you will need temperatures that you need are around 2200-2300 degrees.

Doug

[Eli Jensen]

My thought was to put the two pieces in my forge where the torch portal is. Maybe use mapp. I figured that would get it hot enough. But if you don't think it will work with stainless, then I probably won't try it.

Do you think silver solder is strong enough? I can get over the silver seam, maybe run with it an put some silver or brass sheet in there to give it a stripe. Hidden pins with the solder maybe?

[Ray Rogers]

What Doug said about there being no chance of welding stainless in a two brick forge, not happening. But, to answer your question about how forge welding is done:

First, understand that I am talking about carbon steel and not stainless which is an entirely different and much more difficult process. You first clean and prepare the pieces you wish to weld. Then, you will usually want to actually use an arc welder (or TIG or whatever you have) to tack weld the pieces together. That block of pieces goes into your forge and heats up. When it is well heated and looking at least reddish the block is pulled out and the edges of the side of the block are sprinkled liberally with flux. Flux is usually anhydrous borax but common drug store borax can be used or so I've heard. You'll notice that the powdery borax has melted a little an sticks to the metal. The block is put back in the forge. You watch the block heat up until the flux starts to bubble - at this point the flux can flow down between the plates that have been tacked together. Give it time to flow as far as it is able. When you think it's ready, pull the block out and flux it again, eventually fluxing from both sides with the object being to make sure that there has been enough flux, heat, and time to get the flux all the way through the block. The flux will flow through the block even though the plates may seem pressed tightly together. Any pieces too tightly together to allow the flux to pass don't need the flux.

Once the block is well fluxed and heated to the point where the flux is bubbling the block can be removed from the forge, placed on your anvil, and tapped very firmly but not smashed with a hammer working from one edge to another with the aim of forcing the flux to flow ahead of the hammer and squeeze out the other side. The light tapping performs the weld where a heavy blow will not and you do not want to trap flux between the layers of steel as this is how inclusions are formed. Once that process is quickly concluded, flux again and put the block back in the forge.

Repeat that whole process until you feel sure that all the flux is squeezed out and the weld has taken. At that point don't flux any more but heat the steel back to temperature. Then, begin hammering the steel into the desired shape and be sure to hammer the edges to see that they don't separate and thus verify the weld.

To accomplish this you will need a proper forge or a heck of a lot of skill working with more primitive processes. A piece of stove pipe, some kaowool, and a good burner can succeed easily at welding and a more elaborately built forge can last longer. But stainless, you don't want to go there right now ....

[Eli Jensen]

So . . . silver solder it is

[Crex]

Braze them together. Much stronger than SS.
However, "for economy sake", by the time you fool around with getting things stuck together, you could go to a local welding shop and have them tack the piece on and come out cheaper and quicker.
Forge welding high carbon as Ray has explained, is tricky enough on that scale. You'll most likely find your newest great misery in trying to forge weld the 416. Stainless requires more heat and a very controlled environment for a solid weld.

[Eli Jensen]

Ok. How do I braze them?

[Eli Jensen]

Is hard jewelers solder the same as silver brazing?

[Ray Rogers]

Hopefully Crex will come back with more detail for you. Until then, I can offer that brazing in it's most common form is done with brass rods, melting them in much the same ways as you would use solder. Since that might make for a strange appearance with stainless steel he may have meant silver brazing which, I'm guessing, is the same process only with silver rods. Don't know about jeweler's solder but it seems unlikely to me that it is the same as silver brazing. Crex might be able to clear that up for us pretty soon....

[Crex]

Eli
Any form of brazing or soldering will leave a visible seam, even welding with the proper rods. Some will obviously be more decernable than others. Brazing is just a step up from soldering on the way to welding and appreciably stronger than soldering. The joint appearance will be similar to the sandwich coins (US Quarter) in appearance depending on the alloy of the brazing rod. If done well, the contrast can be very attractive....or not, a preference thing. You can also "hide" the seam with some embellishment such as engraving or filework.
Note: brazing rod material can be found in many different alloy configurations and can be used for a contrasting seam (higher copper content) to almost undecernable as in the silver braze Ray mentions.

Since you have not done any brazing before, you either need to practice a lot on scrap or have a experienced individual do it for you. It is much the same principle as silver soldering, but a bit harder to learn requiring better and higher heat control.

If you cannot abide by the possibility of a "seam" between the two pieces.......get the thicker piece of 416.

[Eli Jensen]

I've accepted now that there will be a seam. I've mitigated this by including an alternating brass/copper/brass layer in between. I went with 75% silver "hard" solder. I used handy paste flux. I like paste flux much better than liquid like with stay bright. Less messy. I put mapp on my torch and was able to get all 5 pieces up to flowing temp. Takes much more than stay bright, but to be expected. I used a foot of solder, and should have used a little more. There are some minor gaps. I do not believe this was due to poor soldering technique, I have some experience with jewelers solder. Just needed a tad more solder. But the knife is for myself so I am less worried. If it were for a customer I would have to un-solder and clean everything and resolder, or start over. I'll post pics when the knife is finished.

From the research I've done, hard jewelry solder is the same as brazing. I've read it has to do with the silver content, low is solder, high is brazing. I don't know why they call it solder then, even when they sell you brazing flux to go with it. Here is what I read:

http://www.bikeforums.net/archive/in.../t-517692.html

[Ray Rogers]

I think it will probably work fine and interesting looking on top of that. You started this process because you thought it would be more economical that simply buying a larger piece of steel. All things considered, do you still think so?

[Eli Jensen]

$8 for the solder, flux, and non-ferrous. I only used half the non-ferrous and can use the flux in the future. A piece of 1/2" x 3/4" 416 is going to be at LEAST $20-30 before shipping. I learned a new design element. So I would say definitely yes.

A note on the alternating brass/copper/brass. It looks really nice now, the copper is a bit lighter so sort of looks like two brass stripes. We'll see when the copper oxidizes darker. In the future I might do brass/steel/brass or copper/steel/copper to maintain the double stripe look.