How to harden mild steel with salt water

Written by h.c. hisel
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How to harden mild steel with salt water

Hardening mild steel with salt water is an old-time method not used so often anymore in the welding community, although using salt water is a great way to keep everything easy, and it's readily available to anyone. The greatest benefit to this method is that it's completely non-toxic.

Skill level:

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Things you need

  • Wholemeal flour
  • Salt
  • Water

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  1. 1

    Mix the hardening paste. In a glass bowl, add a spoonful of wholemeal flour and 2 spoonfuls of salt. Slowly add water while mixing until it becomes a smooth paste. How much steel surface you will be hardening will determine how much hardening paste you will need. Repeat these directions until you have produced an amount that seems sufficient.

  2. 2

    Coat the steel with hardening paste in the areas you'd like hardened. You do this by first evenly heating the area. Heat the object slowly so that the hardening paste will securely stick to the surface. Since the temperature to achieve this task varies with item size and your location, it is very important to heat slowly. Check often how well the paste is sticking. Immediately after the temperature reaches a degree where the paste will stick, evenly cover all the areas you'd like hardened. How the paste lays on the surface is the shape the object will harden to, so make sure to take care when applying the hardening paste.

  3. 3

    Heat the areas covered in paste to a bright red colour, about 1,500 degrees C. This heating process can take up to several hours. Once the appropriate temperature and colour is reached, immediately quench the steel: Plunge the item into cold, clean water. Almost instantly the steel will become harder. Make sure to let the item remain sitting in the cold water for several minutes to make sure the hardening process is fully completed.

  4. 4

    Temper the steel after the hardening process. The extreme rapid change in temperature when heating and quenching steel is what makes steel harden, but it also causes the steel to become very brittle. So after hardening steel it is very important to temper it. Simply heat the already hardened steel until a visible blue heat appears around the object. This means you have reached the appropriate temperature. Let the object sit and cool at room temperature.

Tips and warnings

  • The provided instructions and guidelines are only to be considered when working with "mild" steel.

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