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How to Heat Treat 41L40 Steel

Heat treating any steel will allow you to alter the density and hardness of it through controlling the time and method of cooling. When steel is heated to its malleable temperature, rapidly cooling it will harden it. Slowly cooling it will force it to become slightly softer. You can do this with relatively small pieces of steel in the comfort of your own home and with some common metalworking tools. 41L40 steel responds well to heat treatment and hardness can be adjusted many times.

Things You'll Need

Safety goggles and gloves
Oxy-acetylene torch
Magnet
Tongs
Oven
Peanut oil
Bucket

Instructions

- 1
  Put on your safety goggles and gloves. Light your oxy-acetylene torch.
- 2
  Heat the piece of steel you wish to temper by evenly fanning the white tip inside the blue flame from the torch nozzle over the 41L40 steel. You must get the steel to its critical temperature before continuing.
- 3
  Place a magnet to the surface of the steel. When critical temperature has been attained, the magnet will no longer be attracted to it. If you wish to soften the steel, allow it to cool at room temperature without the addition of water, airflow or other cooling sources. If you wish to harden the steel, proceed to the next step.
- 4
  Plunge the steel, held with your tongs, evenly and uniformly into a bucket filled with a sufficient amount of peanut oil to completely submerge the steel. Peanut oil should be used as it has a high flash point, reducing the risk of fire.
- 5
  Remove the steel from the peanut oil once it has cooled to the temperature of the oil. It will now be very brittle and will require tempering if you plan to use the 41L40 steel for tool making.
- 6
  Bake the piece of steel in an electric oven for 15 minutes at 325 degrees Fahrenheit. Place the steel on a baking sheet and allow to cool naturally once removed. The steel can now be filed, cut and ground as you like.

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