Forge welding

Forge welding is a welding process of heating two or more pieces metal and then hammering them together. The process has been used since ancient times, being one of the simplest methods of joining metals. Forge welding is versatile, being able to join a host of similar and dissimilar metals. With the invention of electrical and gas welding methods during the Industrial Revolution forge welding has been largely replaced.

Forge welding between similar materials is caused by solid-state diffusion. This results in a weld that only consists of the materials without any fillers or bridging materials.

Forge welding between dissimilar materials is caused by the formation of a lower melting temperature eutectic between the materials. Due to this the weld is often stronger than the individual metals.

This ancient form of welding was one of the first methods used to join metals by heating two or more pieces metal and then hammering them together. Initially used on wrought iron and steel, but is now used to join a wide array of similar and dissimilar metals. forge welding has taken the back seat with the invention of electical and gas welding methods during the Industrial Revolution.

A simple flux can be made from borax, sometimes with the addition of iron filings. Since the welding temperature is above the forging temperature, typically 50-90% of the melting temperature care must be taken to avoid 'burning' the metal, which is overheating to the point that it gives off sparks from rapid oxidation. For example Steel welds at a lower temperature than iron. The metal may take on a glossy, or wet, appearance at the welding temperature. One of the most famous applications of forge welding is in the production of Japanese katana blades. During the process a billet of steel is repeatedly drawn out, folded back and welded upon itself. The katana, kris, and other Damascus steel products are fine examples of pattern welded objects.

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.

Applications

One of the most famous applications of forge welding is in the production of pattern-welded blades. During the process a billet of steel is repeatedly drawn out, folded back and welded upon itself. Another lesser known application was the manufacture of shotgun barrels. Metal wire was spooled onto a mandrel, and then forged into a barrel that was thin, uniform, and strong. Often such objects are acid etched to expose the underlying pattern of metal which is unique to each item and adds to their aesthetic appeal.