[JoshEarl]

Normalizing
I start the heat-treatment process with a step that I didn't mention in my previous post. All the heating and cooling during the forging process, plus the heat and strain of the grinding, leave the blade blank with some internal stresses. To get rid of those stresses and set up the internal structure of the steel to respond to the heat-treatment, I do a step called "normalizing."

Normalizing involves heating the steel up past its critical temperature, then allowing it to cool slowly in still air. It's not annealing, which involves slowly cooling the blade over a period of hours. Normalizing takes less than 20 minutes, start to finish.

I stand the blade on its spine in the forge, inside the pipe. The temperature probe sits near the edge, allowing me to keep close tabs on how hot the steel is getting. When the steel first goes into the forge, the readout on the thermometer drops quickly—it’s like putting an ice cube in water. When the temperature reaches its previous level and stabilizes, the steel is the same temperature as the inside of the pipe.

This is where I run into a problem. My forge doesn’t heat very evenly right now. Even with the pipe, there is still a hot spot in the middle. I have to compensate for this by keeping it a little hotter than I really want to and moving the blade into and out of the hot spot. Overheating slightly gives me a little leeway to play with. If the tip gets 50 degrees hotter than I want, it’ll cool a bit when I shift the blade to heat the heel. I don’t like having to do this, and my next forge will be much more even.

Because of that, don’t take the temperatures I’m listing here too seriously. They’re working pretty well for me right now in my setup, but they may be off base with better equipment.

To normalize, I heat the steel to 1450 F, hold it there for a couple of minutes, then take it out of the forge and allow it to cool until it’s black again. This takes about two or three minutes. The color is all gone by the time the steel reaches about 800 F or so, and then it’s back into the forge again. I normalize three times.

By heating above critical and then cooling, I’m allowing the steel to recrystalize with each cycle. This refines the internal structure of the steel and relieves any residual stresses from the hammering and grinding. Normalizing helps prevent warping and cracking, and it allows the steel to harden more fully when it’s quenched.