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I Forge Iron

Heat Treating in a propane forge.

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Up until today I've been heat treating knife blanks in a simple charcoal forge.
It's not easy to keep the temperature steady and even harder to keep the tip of the blade at the same temp as the rest of the blade.
One trick is to place a piece of steel tubing inside the forge and place the knife blank into that to get a more even temp,
but even this doesn't seem to help much since the tip always seems to get way to hot.
So, I made a propane forge from a can lined with 2 inches of ceramic fibre blanket treated with waterglass and a thin layer of refractory.
The burner is just the burner that came with my propane tank and the 2 bar adjustable pressure regulator.
Rumour has it that its hard to keep a knife blank steady at the desired temp inside a propane forge.
Today I tested with a piece of steel tubing inside the forge.
After ten minutes the steel tubing was glowing along its full length with a color indicating about 800 deg.C (1472F).
Then I inserted the knife blank (1095) and adjusted the gas flow till the knife got to non-magnetic and then some, and then I let it soak for five minutes.
The blade was at a very even temp along its entire length including the very tip.
Quenched in oil and tested with a file. File skated across the edge and then I broke off the tip and examined the grain structure.
The knife blank was glass hard and the grain structure was very even and fine which indicates the temp was high enough to harden the steel
but not so high as to cause grain growth.
So, yes,-it's seems to be possible to control the temp in a propane forge within reasonable limits.


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Yes, that's one way of solving the problem, but I have a small bunch of 1095 equivalent steel and it likes to soak for some time at temp
so the steel tubing method allows the knife blank to lay still in the forge without heating up unevenly.
I do admire japanese sword smiths that manage to heat the whole length of a sword to an even temp in a charcoal forge.
-I'm not quite there yet . . . if ever.

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I don't think heat treating outside of a computer controlled electric oven, is a very smart idea; that said, some heat treating jobs are simpler than others.

So, how to give the best shot at a satisfactory job from a gas forge? The keys, would be even internal temperatures and really good control in lower temperature ranges. Ribbon burners are going to provide both factors better than any other kind of gas burner. Since this work is done at lower temperatures, a hand held pyrometer should work okay for judging forge heat.

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Or you can buy "heat stops / blocks," at a welding supply. There are different kinds some just copper "blocks" you can clamp to the project to prevent heat from getting past. 

A wet rag, straw, etc. works well some folks use a watering can with a single spout to control the heat. You see the later most often when twisting bar.

Frosty The Lucky.

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