How to Make Steel Hard
Ideally, steel should be in its softest form when being machined. This state, known as the annealed state, shortens the time required to machine the steel while reducing the amount of wear on the cutting blade. Once machined, most applications require steel to be hardened to make it useful. Hardening steels locks in a predetermined crystalline structure making the steel much harder. Tempering steel after it is hardened reduces the stress produced during the hardening process. Just as various steel differs in its chemical composition, the temperatures at which they are hardened differ as well but the all follow a similar process.
Place the steel in the forge or furnace and slowly raise the temperature to the reference heat. The reference heat is generally the point at which steel loses its magnetic properties. This heating creates a homogeneous crystalline composition suspended in the heated steel.
Remove the steel and quench in the appropriate liquid. Some steels can be quenched in water or even air cooled to harden while others require oil or other medium to properly quench. The quench locks the crystalline structure but introduces stress within the steel, which can make it brittle.
Reheat the steel to the requisite tempering temperature. This temperature is much lower than the hardening temperature and can be achieved by monitoring the subtle color changes in the steel as it heats. Once tempered remove the steel and allow to cool to room temperature.
Things You Will Need
- Forge or furnace
- Quenching vessel
- Quenching liquid
- Most steel has heat treatment references available through various standardization organizations such as the American Iron and Steel Institute, the American Society for Testing and Materials, or the Society of Automotive Engineers.
- Heat treatment requires extremely high heat. Proper safety equipment is needed to prevent severe burns.