There are 3 main steps to the heat treatment process for these hand-made knives.
Normalizing (a/k/a Thermocycling). Forging the blade from the original stock involves heating the metal repeatedly in a forge until it is bright orange in color and hitting it with a hammer on the anvil. This process builds up stresses within the metal that can interfere with the effectiveness of next heat treatment steps and cause the blade to warp or bend. Normalizing brings everything inside the steel back to a normal or equalized state and relieves the chaos inflicted by the hammer.
Hardening. To harden, the steel is heated to its critical temperature and then rapidly cooled (i.e., “quenched”), which causes a microstructure to form within the steel called “martensite.” At this point the steel is very hard and very brittle.
Tempering. In order to decrease brittleness and increase toughness, the steel is heated at 450 degrees for 2 hours. Tempering not only increases toughness and ductility, it also reduces the chance of distortion or cracking from the hardening process.