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Blade Induction Hardening (Knives and Saws)

Blade hardening

  Blade hardening is a crucial step in the heat treatment of knives and saws, as it significantly enhances the quality and durability of the blade. The process involves several key steps and considerations:

  • Heating to Critical Temperature: The steel is heated until it becomes non-magnetic, which indicates the start of the austenite phase. It’s essential not to overheat the steel as it can cause the grain to grow, making the steel less flexible and more prone to cracking during quenching.
  • Quenching: This step involves rapidly cooling the steel from the critical temperature to form martensite, which is very hard but also brittle. The quenching medium can be oil, water, or a specialized solution.
  • Tempering: After quenching, the blade is tempered to reduce brittleness. This usually involves heating the steel to a lower temperature, such as 400℉, and then cooling it, which can be done in an oven for knives.
  • Normalizing: For forged blades, normalizing is done to relieve stress and reset the steel’s crystalline structure. The steel is heated to a non-magnetic state and then allowed to air cool slowly without quenching.
  • Annealing: If the steel has been previously hardened, annealing softens it by heating it to critical temperature and then cooling it very slowly, often done by leaving the steel in the forge after it’s been turned off.

  Each type of steel and blade shape may require specific adjustments to these steps. For example, differential heat treating can be used to produce a blade with a very hard edge and a softer spine. It’s important to follow the appropriate heat-treating process for the specific type of steel and blade characteristics to achieve the desired properties such as edge retention, toughness, and corrosion resistance.

  Remember, safety is paramount when performing heat treatments, so always use personal protective equipment and follow safety guidelines.

Knives and Saws Blade Hardening by Induction Heating

  Induction heating is a highly efficient method for the hardening of blades for knives and saws. Here’s a brief overview of how the process works:

  • Induction Heating: The blade is exposed to an alternating magnetic field, which generates heat within the metal due to the metal’s resistance to the flow of eddy currents. This method allows for precise control of the temperature and the area being heated.
  • Critical Temperature: For high-speed tool steel, the critical temperature is around 2375°F. The induction heating process heats the teeth of the blade to this critical temperature without affecting the rest of the blade.

  • Quenching: Once the critical temperature is reached, the heated part of the blade is rapidly cooled, usually by a spray of water or oil. This rapid cooling transforms the structure of the steel, creating martensite, which is hard and wear-resistant.

  • Tempering: After quenching, the blade is often tempered to reduce brittleness. This involves heating the blade to a lower temperature and then cooling it, which adjusts the hardness and toughness to a more balanced state.
  • Induction hardening is particularly beneficial for saw blades and knives because it can selectively harden specific areas, such as the teeth of a saw blade while leaving the rest of the blade less brittle. This selective hardening process ensures that the cutting edges are wear-resistant, while the body of the blade retains enough flexibility to resist breaking under stress.
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