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How to Harden a Blade at Home

Humans have made knives for defense and to help acquire food and other resources for a very long time. Early knives were made from flint and other natural materials. Later knives were made from metal, and then the metal blades were tempered to make them even harder so they could withstand heavy use. Today manufacturers and hobbyists use carbon-impregnated stainless steel to make knives for uses ranging from opening boxes to cutting crash victims out of cars.

Things You'll Need

Tongs
High-heat source
Tub (optional)
Oil or water (optional)
Emery cloth or fine-grit sandpaper
Oven

Instructions

- 1
  Hold the blade with tongs, and heat it using a source of high heat. Soft metals may require only the heat from a propane torch while harder steel needs the higher temperatures provided by a furnace or forge.
- 2
  Dip the blade in a tub of oil or water, or quench the blade with air. The method to use depends on the blade's metal. If you use oil, take care to avoid burns if the oil ignites. Tool steel marked with "O-1" requires oil quenching. Use water to quench steel marked with "W-1." Quench steel marked "A-2" with air. Place the blade vertically in the medium to prevent warping. The quenched steel is hardened but brittle. Quenching a blade in water may crack the metal, but it cools the blade faster than other methods.
- 3
  Scrub the black coating off the blade with emery cloth or fine-grit sandpaper. Doing so allows you to see the metal as it is tempered. Wash all oil and/or other debris off the blade.
- 4
  Heat an oven to 350 to 400 degrees Fahrenheit, and place the blade inside the oven. Bake the blade for 20 to 60 minutes until its metal turns a light straw color. Remove the blade from the oven, and allow it to cool or plunge it into water for a fast quench. Tempering the hardened steel reduces stresses introduced by the quench and reduces brittleness.

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