Have you ever heard someone brag about how sharp their knife is? Or how long it will hold that sharp edge? Well, the ability of a blade to become very sharp and hold an edge is primarily based on the level of hardness the metal is capable of achieving. The carbon within the 5160 steel we use is what gives it hardenability; however, the normalization process also has the effect of annealing, or softening, the metal.
Ok. It's not soft relative to things like wood or feathers, but in a fully annealed state the metal is much softer than it is capable of becoming. And soft metal doesn't make for a sharp or resilient edge...
That being said, it is possible to have too much of a good thing. When metal becomes too hard, it is brittle and can shatter easily. For that reason, we are going to harden just the edge of the blade while leaving the rest of the metal in a softer state. This will leave us with a blade that will hold a razors edge, but at the same time have the flexibility to bend without breaking.
We learned two ways to accomplish this in class. First, you can check out the absurd yet highly amusing saga of Mike Williams hardening and tempering the blade in one step with an oxy-acetalene torch! This method is highly unreliable and you would likely never do this with a blade you just spent a lot of time forging and gringing... But it's amazing to watch anyway!
Now that we've had our fun, let's get back to work. The following steps will get you a hardened hunk of metal:
Seth once again demos the process for us. (Video: 10.1 MB)
More information on Annealing from the 1924 edition of Machinery's Handbook
Beginning - Definitions - Forging - Normalizing - Grinding - Hardening - Tempering - Summary
This page last updated 12/30/2004
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