What does Quenching mean?

Quenching is a stage of material processing through which a metal is quickly brought down to room temperature from a high temperature by rapid cooling. Quench hardening is a mechanical process in which steel and cast-iron alloys are strengthened and hardened. Quenching and tempering provides steel with high strength and ductility.

During quenching, the following media are used to rapidly cool material:

  • Air/argon/nitrogen
  • Liquid polymers
  • Oil
  • Water

The slower the quench rate, the longer thermodynamic forces have to alter the microstructure, which is in some cases desirable, hence the use of different media. Sometimes multiple media are used. For example, metal may be air cooled and then dipped in a water bath to complete the quenching process.
Quenching can lead to warping/cracking and other issues with the material, even when it is done properly. Using water as a quench media, for instance, can cause the material to warp as it cools. It is crucial to control the environment in which the quenching is done to minimize the risk of damage to the material. When done properly, the material is harder and more durable, making it suitable for a wide range of uses. Extremely rapid cooling can prevent the formation of a crystal structure, resulting in amorphous metal or “metallic glass.”

Four types of furnaces are commonly used in quench hardening:

  • Salt bath furnace
  • Continuous furnace
  • Box furnace
  • Vacuum furnace

The type of furnace used depends on what other processes or types of quench hardening are being done on the different materials.

The quenchant is determined by the steel

In tool steels we have a letter prefix .A-2 is an Air hardening steel, O-1 is an Oil hardening steel and W-1 is a Water hardening steel !! A quenchant for a steel should be fast enough to fully harden the steel but no faster. A faster quench will produce unnecessary stresses in the steel and may lead to things like quench cracks.You can edge quench in oil, this is common for knives.Or you can fully quench in oil. You can edge quench in water which is usually done with clay or you can fully quench in water. It all depends on the steel and what you want to achieve.

The more complex the alloy the more care needs to be taken with the specific quenchant. Simple steels are more foregiveing and different quenchants can be used. A certain amount of expermentation may be required to attain the best mixture of hard, tough, edge retention etc IMHO. The 10XX series is about as simple as you can get and can be quenched in oil or water as needed for the specif blade configuration.