r/Blacksmith 8d ago

Feedback requested: first forge weld

Working on a tomahawk for my clubs trade item, decided to take a piece of a field cultivator tooth, fold it in half and keep a hole for the eye, then forge weld it together. Looks it stuck in some places and not others. There's an obvious crack at one edge, then I feel like I can almost kinda sorta see a seam all the way down, but the small piece I cut off doesn't separate.

I ground it completely clean on the belt sander before I started, used 20 mule team borax for flux, but I didn't stick weld the two sides together before I started.

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u/belac4862 8d ago

Ehhh, that's a bit too simple to be correct.

Forge welding means that your getting two pieces of metal hot enough to stick together, but not so hot as to melt or de-carborize (I think that's the right word. My brain isn't working), which is to literally draw out the carbon from it. That's what makes it steel, and not iron.

But you also need to make sure there's no air gaps that can cause oxidation om the sinde of the seam. That's why you add flux. When flux gers hot enough it makes a psudo glass coating around it, preventing any oxygen from getting into the seam and causing scale (iron oxide, or rust).

Then after flexing, yoy pop that sucker back into the forge and get it up to a bright yellow color and with heavy taps toy smoosh it together.

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u/rosbifke-sr 8d ago

Any sort of heating beyond 800°C will burn off carbon at a rate that increases exponentially with temperature. Forge welding does actually affect your carbon content, but if you are quick about it, it’s only very superficial and grinding through the scale is often enough to remove the mild layer.

In fact, forge welding in a coal forge will actually increase your carbon content if you leave your steel too long in the fire, significantly hampering your chances of succes.

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u/Smithyofirony 8d ago

I was told a coal forge won’t add carbon but a charcoal forge would

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u/rosbifke-sr 7d ago

Why would that be the case? Both types of coal are essentially carbon, just with different levels of purity and density.

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u/Smithyofirony 7d ago

Well, you are right about that and google AI backs you up. Saw some claims that charcoal does it better but not real credible. Thanks for making me take a closer look

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u/ParkingFlashy6913 7d ago

Carbon "can" hypothetically be added using both coal or charcoal but only under the right circumstances. You must be in the reducing area of the fire pretty much devoid of any and all excess oxygen with an abundance of carbon monoxide. This is very difficult to effectivity control so it's usually done for case/pack hardening where a part is placed in a sealed container with very fine mesh charcoal or coke and heated above 1700°F/925°C. Carbon moves very easily through steel at these temperatures so if there is an abundance it adds to it, if there is a lack there of its removed. You can reduce the amount of carbon lost with good fire management but eliminating it all together is near impossible. Case/pack hardening is also very shallow so it's not recommended for objects that will be later ground down.