Simple Instructions for Air Hardening Tool Steel
Tool steel is used by woodworkers and metal machinists to make tools with sharp edges such as knives and razors, and tools for low-speed machine operations. The steel is first annealed, or heated up to its hardening temperature, and slowly cooled. Once the annealed tool steel has cooled it is shaped into a tool. The shaped steel tool is hardened by sitting for a period of time in a furnace that is heated up to its hardening temperature. The steel is then removed from the furnace and air quenched or cooled down at room temperature to harden it. Does this Spark an idea?
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Things You'll Need
- High alloy annealed tool steel
- Metal file
- Vacuum furnace or furnace with controlled protective gas atmosphere
- Stainless steel foil
- Forge tongs
- Heat-resistant gloves
- Heat-resistant surface
Instructions
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File the annealed steel to the shape of your tool. If the tool is going to have sharp edges, don't sharpen them at this time, just shape the tool's point or blade edge and leave the edge blunt. The tool is sharpened after it is hardened.
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Turn on the furnace to preheat it. Wrap the tool steel with stainless steel foil to protect it from oxidation and decarburization. Once the furnace has finished preheating, put on your heat-resistant gloves and insert the tool steel into the furnace with a pair of tongs.
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Slowly raise the temperature of the furnace to 1450 degrees Fahrenheit, at a rate of 3/4 hour per inch of steel thickness, allowing the steel tool to gradually rise in temperature.
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Raise the temperature of the furnace up to 1700 degrees Fahrenheit or 1800 degrees Fahrenheit, depending on what tool steel alloy you are using. Let the tool steel sit in this temperature for 30 minutes. Remove the tool steel and allow it to sit exposed to the air in a safe location, on a heat-resistant surface so that it can harden as it cools down.
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Wait two hours for the tool steel to cool down to 150 degrees to 125 degrees Fahrenheit. Temper the tool steel by raising its temperature back up to 390 degrees Fahrenheit in the forge. Remove the steel from the heat. Wait another two hours for it to cool down to 150 degrees and raise its temperature back up to 390 degrees to temper it twice. This allows the steel to harden uniformly.
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Tips & Warnings
If you are using an electric muffler furnace, pack the tool in used charcoal or cast iron chips to protect it.
