The purpose of heat treating is to bring steel to a hardened state. The correct hardness depends on the application of the steel being treated. Knives need to be hard enough to hold an sharp edge through continuous mechanical abrasion, yet be soft (flexible) enough to stand up to forceful use without breaking.
Equipment and tools:
- Visegrip pliers or tongs
- small forge or charcoal fire of sufficient heat (search for forge or smelting instructables)
- fire proof quench container with lid (I used an old cookie tin)
- quenching medium such as used motor oil
- BC fire extinguisher (the kind that puts out grease and oil fires)
- Heat resistant gloves and face shield.
- kitchen oven
- fireproof material for regulator block (I used aluminum tube)
- one mild or high carbon steel knife blank (forged or stock removal)
The quenching method I decided to use for this knife was the “edge quench”. I learned this method from $50 Knife Shop by Wayne Goddard. Instead of dropping the heated knife into the quenching medium tip first, submerging the entire knife, the edge quench involves submerging one third to one half of the blade's width (cutting edge first) into the quenching medium. A regulator block is used to hold the blade at the correct depth. The quenching medium I used was old motor oil. After the blade has been quenched, its hardness is still not suitable for usage. In its hard and brittle state, the quenched blade will shatter like glass if dropped, it must be tempered before it is put to use. Tempering involves heating the blade to a non-critical temperature (350 – 450 F) to slightly soften the steel (I used a kitchen oven). A tempered blade will hold a sharp edge and still retain strength and flexibility.