How to heat treat & harden small steel parts

Written by don davis
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How to heat treat & harden small steel parts
Steel this hot has a crystalline structure. ( Images)

Steel is "heat treated" in two steps called hardening and tempering. You harden steel by heating the metal to 788 degrees Celsius. Steel crystallises at that temperature, and you preserve that crystalline structure by quickly quenching the steel in oil. But, because hardened steel is often brittle and too hard to machine or grind, you will almost always need to temper it after it has hardened. In tempering, you reheat the steel to 246 degrees Celsius. The reheating relaxes some of the crystalline structure, and after slowly cooling, the steel is less brittle, more dependable and practical to use.

Skill level:

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Things you need

  • Two quarts motor oil
  • 1-gallon pail
  • Block magnet
  • Needle nose vice grips
  • Propane torch
  • Match
  • Gloves
  • Channel lock pliers
  • Anvil
  • Dry rag
  • Emery cloth

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  1. 1

    Pour two quarts of motor oil into a one-gallon pail. Clench a block magnet in needle nose vice grips.

  2. 2

    Set a propane torch on a stable surface and light the torch with a match. Adjust the torch flame until the flame is blue. Put on gloves.

  3. 3

    Hold the part you want to heat treat in a pair of channel lock pliers and hold the part in the propane flame.

  4. 4

    Heat the part in the flame until it glows red. Touch the magnet to the part. The magnet will be attracted to the steel until the steel reaches 1450F.

  5. 5

    Drop the small steel part in the pail of oil when the magnet is no longer attracted to the steel part. Set the channel lock pliers on an anvil. Remove your gloves.

  6. 6

    Agitate the bucket of oil containing the small steel part. Remove the part from the oil when the channel lock pliers on the anvil have cooled.

  7. 7

    Thoroughly clean the hardened part with a dry rag and emery cloth. Clean the part so you will see its colour when you reheat it. Hold the part with the channel lock pliers and reheat the part in the blue, propane flame.

  8. 8

    Heat the part until the part becomes a colour between straw and pale orange. Set the part on the anvil. The mass of the anvil will slowly draw heat from the part. You will be done hardening and tempering the part when it is cool.

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