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Forge welding is the core technique involved in creating Damascus steels. It is a solid-phase bonding technique that uses heat and pressure to make the weld. To make Damascus steels the current method is to stack alternating pieces of steel, each with a contrasting composition, heat the billet in a fire and at the proper temperature apply pressure to make the weld.
It is possible to weld at a dull red heat, what is required for a good weld is that the metal be clean of oxides and contaminants and that the surfaces be mated. Perfectly polished and mated surfaces will have a natural affinity for each other and under ideal conditions can be welded cold, sticking gauge blocks are an example of this. When the metal is heated the outer electrons become excited and begin to lose their attraction to the nucleus, at the right temperature if pressure is applied they will cross boundaries and attach themselves to the adjacent materials and a solid bond is made.
I use to give a demonstration for the welding class at a local tech school where I would forge weld a stack of eight layers of alternating high and low carbons steels. After the weld was made, I would stand the billet on its edge and draw it out flattening it on the edge of the weld. If the weld was good there would be no cracks or breaks in the seams between the layers, just straight lines running down the steel from the different layers. It had become one solid piece of steel.
I will run through the process of welding up a billet as I do it. There are as many ways as there are makers and if it works it is right, but the method I use works and should be a good starting point.
I usually like to weld thicker pieces rather than thin. The reason for this is that thicker pieces hold the heat longer and lessen the chance of getting a cold shut. Also thin pieces have a tendency to bow when heated and can create trapped pockets of gas making blisters that show as bubbles on the surface of the billet. My normal billet would be comprised of five pieces of 1095, alternating with four pieces of L-6, each piece being 1/4x11/2x5 inches. I cut the pieces and stack them. Then I run a bead of weld along each end seam with the arc welder. I do this on both ends. Then I weld the billet to a handle. Since I work off a handle and because the billet is suspended in a vertical propane forge, I use two 3/8x11/2x6 inch pieces of low carbon steel which are then welded to a handle long enough to remain cool during the welding and allow easy handling of the weight. The handle should be forged to a thinner cross section just after it joins the end pieces. This change in cross section will keep the shock of the hammer from traveling up the handle and causing discomfort.
I like to work hot! and have had my welding forge clocked with an optical pyrometer at 3000F. At those temperatures the inside of the forge is white and can not be looked into without dark glasses. There are many ideas about what is the ideal colored lens to use to look into the fire, I use a dark green lens suitable for oxyacetylene welding. There are some neat gold coated lens on the market that are suppose to offer complete protection. The fire gives off both ultra violet and infrared radiation and if you might consider wear a sun block if you are fair skinned.
The fire should be adjusted so that it is slightly rich. A flame will come out the door a bit when the burner is adjusted properly. Another way to adjust the burner is to stick a piece of ceramic wool on the wall opposite the burner port. The fibers on the wool will burn brightest when the flame is neutral and will drop off either side depending on whether the flame is rich or lean. Adjust until it is burning brightest and then add a little more gas. Each forge has a particular sound and you should remember the sound of the forge when it running right, it will help you dial it in too.
When the fire is at temp, slide the billet in and let it warm up. As soon as it begins to show color, I remove the billet and sprinkle it with flux. The most common flux used is borax. The purpose of the flux is to melt and coat the billet protecting it from oxidization. It also helps to lower the melting point of the scale making it liquid and enabling it to squirt contaminants out with the flux. Because I weld hot, I have run into problems with the nickel in the L-6 creating nickel oxides. Borax is not aggressive enough to deal with the nickel oxides and the surface of the billet will appear gummy instead of liquid. To correct for this I have gone to mixing florspar in with my anhydrous borax. Florspar is a very aggressive flux and you should only use as much as necessary to wet out the surface of the billet. Al Pendray tells a story about over doing the florspar in one of his wootz melts and cutting a silicon carbide crucible in half. I use a couple of tablespoons in a coffee can and mix well. I have also taken to adding carbon black to cut down on the silver decarb line you get between the layers.
The billet is put back in the fire and brought up to welding heat. You have to use visual clues to judge when the billet is at welding heat. In a really hot fire it is necessary to soak at temperature for a bit because the surface of the billet will be ready while the interior is still cool. The flux is a good indicator of the heat of the billet. Bill Moran says the billet is ready when the surface looks like butter melted in the hot sun. The flux has wet out and will drip freely off the end of the billet when it is tipped down. Little bubbles will dance around on the surface. Look the whole billet over and make sure that the heat has equalized through out. When the billet is the same color as the background of the forge you are at temp and you will not get it any hotter. Remove the billet and strike with a hammer.
If you are welding with a hand hammer, run a series of light blows from the far end to the handle end directly up the middle of the billet and then with quick light blows go around the outside edges of the billet. If you are welding under a power hammer, use light blows and start at the far end and rapidly move to the handle end of the billet. The idea behind this is to squirt out the flux and molten slag so it won't be trapped in between the layers. This is very viscous and very hot. I recommend a leather apron, and gauntlet style leather gloves. The gloves should be loose so you can shake them off in case molten material gets down inside. You will get burned. Check the forearms of the Damascus makers and you will see that they are speckled with white spots. These are burns, you get use to it. For press welding, it is good if you can get the whole billet between the dies and weld in one squeeze, but it can be done in multiple bites. Care should be taken to lightly squeeze the billet together and not over do it. You can tear the welds if you are too aggressive. The press will spit the flux out like a redneck with chew, so don't get your face in line with the billet.
After the first welding heat and while there is still a fair amount of heat in the billet, I reflux and return it to the fire. Flux is not glue and you should use it sparing. It is also messy. I have a deep metal baking pan that I use for fluxing. I keep my flux in coffee cans inside the pan and use a long handle spoon that I made to apply it. Some folks like using a salt shaker.
The second welding heat, you start at the handle end and go in the opposite direction then the first heat. Most flaws occur at the ends of the billet. Unfortunately, these get worked into the middle of the piece during the folding and welding. If you are in doubt about a weld taking, forge lightly on the edges and see if it opens up. If it does, reflux while it slightly open and reweld. Periodically while I am welding up billet I allow it to cool for what I call a grind and check. I grind the edges of the billet looking for flaws and inclusions.
The end of the second heat is used for drawing the billet out prior to folding and for squaring and flattening. It is helpful to maintain even width and thickness so that when you fold the billet it lines up evenly on the sides. I use the last of the heat to mark the piece for cutting. I added a stick-on tape measure to the edge of my anvil so I can accurately mark the center of the billet. On the first cut, I mark the exact middle of the billet. I want to fold the far end so that the weld filler is brought back to the handle and out of the way. The second fold is short and this will keep the filler from migrating into the billet. Accurate measurement will prevent pulling thicker lines and filler material into the billet and keep the layers of constant thickness.
The billet is cut using a hot cutter. This is a hand held tool that has a face for striking on one side of its handle and a long tapered chisel on the other. The tool is designed to be struck, driving the chisel through the hot metal. This usually done on the anvil while the piece is held in place by a hold down tool. If you are unfamiliar with these tools, I would recommend buying a basic blacksmithing book. The Edge of the Anvil by Jack Andrews is an excellent choice. This and many other books can be purchased from Centaur Forge Ltd. 1-414-763-9175 for a catalog.
Hot cutting is another excellent use for the hydraulic forging press. I made a hot cutter using a short piece of rail road rail. I cut off a five inch length of heavy rail on the bandsaw. Standing it on its edge, I profiled the webbing between the top of the rail and the base into a chisel edge. It sits on my large press dies and the flats serve as a stop and the cutter quickly cuts through hot steel.
When you hot cut the billet, you leave a small amount of metal at the end of the cut to serve as a hinge. While the billet is still hot, I take it to the belt sander and quickly grind off any scale. Then while there is still heat left, I fold it over using a hand hammer and get it lined up on itself and close it together. Reflux and put it back in the fire. You may vary the way you fold the billet. The Japanese method of making sword steel involves forging the billet wide and cutting down the middle and folding side to side. Any change will affect the look of the steel and may yield some interesting patterns.
Making Damascus is a repetitive task and it is easy to get lost in the process. I keep a notebook right by the forge and write down each fold and its subsequent layer count. I also note anything that is unusual about the billet or any inspired changes I make to the process. You would be amazed how quickly you forget that great idea. I also number the billet, writing on the handle with a grease marker. All work on the billet is noted in the log under that number.
Also, again because of the repetition of the work it is helpful to establish a routine to your tasks and to do them in sequence each time. It is easy to notice your concentration wandering when you have a ritualized routine because anything out of normal will alert you. If you find you are not focused, take a short break to gather or if you are tired and it is the end of the day, better shut it down before you ruin the work you have already done or worse. You are working in a very dangerous environment, extremely hot fire, extremely hot metal, powerful equipment can be a bad combination if you are not awake.
Don Fogg Custom Knives
Copyright © 1997 Don Fogg Custom Knives. All rights reserved.
Revised: October 18, 2003.