In this part of the tutorial we take the knife back out to the forge and harden/temper it.

This is a two step process that we do in order to change the steel into something that is very useful as a knife.

Part 1 of this tutorial is located here

First we Harden the Blade

The first thing we want to do is harden the blade. we do this by heating it to red hot. That will be about 1500 degrees fahrenheit.

We know we have it at the right temperature by using a magnet on it. When it is red hot heck it with a magnet. When it no longer sticks you have reached the right temperature. This is called Curie temperature. The steel has changed its molecular arrangement and is now very hard.

You will get good at finding this temperature just by the color of the steel. I can see that this is not quite hot enough and it needs to glow more red before it is at the right temperature.

Now, to lock those molecules in their hardened configuration you quench the knife in oil. This cools it very quickly not allowing the molecules to go back to their original pattern.

Tempering

But, hardened steel is very brittle! It can easily shatter or crack. So we actually want to soften it up a little bit. This process of softening it is called tempering. We monitor the process of tempering by checking the color of the steel as we heat it.

We know the steel is at the right temperature when it is wheat in color. So.....

So.. clean off the blade of the knife with emory paper. It is very easy to clean at this point. Now we will be able to see the steel as it changes color in the forge.

We want to heat it slowly and only to about 450-500 degrees. To do this you put something over the forge like this that will support the knife blade about six inches from the fire. This way it heats slowly. Rotate and turn the knife over regularly. Monitor it closely.

This is just about right. A little bit more heat and the wheat color will darken more. Just be careful not to overheat it. A blue/plum color will set in. That means it is getting too soft.

Once it gets to that wheat color quench it again. This quench isn't as hot so it won't be as dramatic. Just a little smoke this time.

And that's it. The knife is now hardened and tempered. Which means it has strength. It will keep an edge very well. Yet it has a little flexibility to it so it won't snap easily.

Now we just need to do the final sanding. Use emory paper, starting around 100 grit and work your way up as high as you want. The higher the grit you go the more mirror-like the finish of the blade. You can go as high as 1500 to give you a mirror like finish.

Congratulations! Your Rebar Knife is done!

Make a Karambit Fighting Knife- We use the stock removal method to make this vicious fighting knife. I also have the template for you.

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