How to Case Harden Steel


Pure steel is somewhat soft and malleable. In many situations it is important that the steel have a tough, hard coating. Adding that hard coating to steel is what case hardening is all about.In order to case harden steel you will need to heat the steal in the presence of carbon. It is the infusion of carbon into the outer layer of the steel which hardens it.

Things You'll Need

  • Steel
  • Forge or furnace
  • Carbon (powdered charcoal)
  • Metal container
  • Tongs
  • Heavy gloves
  • Protective clothing
  • Eye protection
  • Crush several dozen charcoal briquettes, enough to more than cover the item you wish to case harden.

  • Prepare a metal container with a metal lid. The container should be slightly larger than the item you wish to case harden. Place a 2-inch layer of crushed charcoal into the bottom of the container.

  • Heat the steel you wish to case harden until it glows red hot. This can be done in a furnace or it can be done using a torch with a rich fuel mixture.

  • Using tongs remove the red hot steel and place it in the metal container on the bed of crushed charcoal. Immediately pour additional crushed charcoal over the red hot steel until it is completely covered. Put the lid on the metal container and leave your steel to cool for at least 1 hour.

  • Remove your steel from the charcoal and reheat it until it glows red hot. Using tongs dump it into a container of room-temperature water. Your item is now case hardened.

Tips & Warnings

  • If you want to add a second layer a carbon to your steel in order to increase the depth of the hardening, reheat the item to red hot and place it back into the crush charcoal and leave it covered for another hour. Then reheat to red hot and plunge into water.
  • Use extreme caution when handling red hot steel. When you cover your steel with the crush charcoal it is likely the charcoal will catch fire. Simply place the metal cover on the box and allow the fire to extinguish itself.
  • Always wear heavy gloves when working with hot steel.

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