Basic Process

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Basic Process

Unread post by BlisterBuddy » Thu Jul 06, 2017 10:31 am

With my limited experience I will try and set up a general structure for how this process works and list some key complications that can arise. Correct at will, any adjustment is appreciated.

Many materials can be forge welded, but for the time being lets just stick with ferrous alloys.

1. Clean off the surfaces of the weld layers.
a. Oxide layers (FeO, CO, CO2, MgO, etc.) Can form anchors that block the slip of the lattice in active slip systems.
2. Mechanically fix the weld plains together.
a. The faces tend to be open enough to allow flux to penetrate the gap and protect the weld surface
3. Heat fixture up to whatever temperature your flux will melt and liquefy at.
a. Generally a solid red. (1369 Deg.F or 743 Deg. C) Well into the austenitic range of the metal, if not melting temperature depending on the alloy.
4. Flux the weld seams
a. Coat the weld surfaces with a liquid that will sacrificially oxidize instead of your welding faces.
b. Borax is the most common, but fine sands could also be used (Lodo sand).
c. Check out Non Hydrodizing Borax, really cool stuff because it does not expand and fall off of the piece.
d. Practical Blacksmithing by Richardson has recipes for flux.
5. Bring the assembly up to melting temperature.
a. Depending on your composition this could be at 1600 Deg C or 1150 Deg C.
b. Check out the phase diagrams of your composition you are working with to figure out the lowest melting point.
c. Aim for the high yellow to white hot.
d. If the metal begins to spark you are loosing material and surpassed your melting temp. Don't do this.
6. Join the two welding faces.
a. Start slow, because both of your faces should be liquefied.
b. If to much of an impact is delivered in the early stages of this weld the liquefied metal will eject out and you will need to find a way to bring the seam back up
to that temperature.
c. Repeat two to three heats of light hits at welding temperature, brushing and fluxing after each heat, then go ahead and lay into it.

With any luck your seam will be permanently joined.
Phase diagram for melting/solidification temperatures of Iron alloyed with Carbon
Iron_carbon_phase_diagram.gif (82.69 KiB) Viewed 1984 times
Borax.jpg (29 KiB) Viewed 1984 times

Martin Pansch
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Joined: Thu Feb 14, 2013 10:44 am
Location: Young America, MN

Re: Basic Process

Unread post by Martin Pansch » Mon Jul 17, 2017 4:55 pm

A few comments, though my knowledge is far from exhaustive. Bob Patrick is known to lurk here and would be my go-to authority on forge welding.

Sand for flux: Generally only when you have wrought iron as it has a higher forge welding temp and the sand needs more heat to melt and flow.

Other flux comments: Non Hydrodizing Borax is commonly called anhydrous borax. There are a bunch of other good ones out there too. Fluxes like the old Anti-Borax, and Iron Mountain supposedly have cast iron filings in them to help hold the two pieces you are welding long enough to stick your weld. Many traditions, including most English trained smiths, forge fine without flux as well.

Temperatures: The melting point is too hot. A yellow color is usually what I go for. I have seen those, whom I assume must be stronger with the Force, forge weld at cooler temps then that. Liquefied metal should not be shooting out of your weld, just flux with whatever iron oxide and other forge impurities it is dragging with it.

Don't start slow. Start fast but hit light. The longer you wait the cooler your metal is getting. You only need enough force in you blows to make metal meet metal, and more than that and you are thinning it out more than needed. If you have trouble modulating the strength of your blows get a smaller hammer for welding, this lets you rain blows faster too.

Stop once you no longer have welding heat. Many is the forge weld that was initially stuck only to be broken apart because someone worked it too cold.

Unless you are just forging a billet of Damascus or the like a good scarf is needed to help prevent any inclusions in your weld and to help make the weld disappear when you are done.

Upsetting the areas you plan to weld together is generally a good idea as well as it helps balance out any thinning you are going to encounter by getting it to welding temp and pounding on it multiple times.

The most important thing in forge welding is to get out there and do it. It was once an every day skill for any blacksmiths, a requirement in fact to turn wrought iron from a bloom to a bar. Since the revival of blacksmithing it seems to have gained a mystique that psychs some people out. Get a bunch of 1/2" round rod and make 10' or so of logging chain. Each link lets you practice 2 scarfs, it is easy to position in a coal forge's hot spot and since they are on the same bar no having to worry about drawing two pieces out of a forge and line them up before tapping with the hammer. Once you are done welding the link forge it back into oval link-shape at a dull red heat. If your forge weld isn't solid you should see it then. Having someone show you once or twice what a good scarf and good welding temp looks like is helpful. If you aren't near anyone I suggest several of Mark Asprey's YouTube videos on the subject.

Take care.


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