Making a hot cut chisel involves a three-step process: first is the normalizing of the steel to a critical temperature, the second step is hardening it through oil or water, and lastly, tempering it.
The first step involves hardening the flat end by first heating it up to a critical temperature. Critical temperature has to be achieved gradually. When critical temperature is achieved, the material will not stick to any magnet. Hardening it must be quick to not let the steel go below the critical temperature.
Next, it is dipped into the quenching material (either oil or water) to harden it. Sizzling will stop once it’s properly hardened. Finally, polish, sharpen and temper it by using angle grinders, a stone of some sort, sandpapers, or a sharp file.
This DIY process may be used for tempering other hand tools that are similarly made of oil or water hardening material.
source: Christ Centered Ironworks
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