Hardening

Metallurgy (Heat Treatment): This involves heating steel or aluminum to specific temperatures, followed by rapid cooling (quenching) in oil, water, or gas to increase strength.

Tempering: Often, hardened metal is too brittle, requiring a second, lower-temperature heating process (tempering) to improve toughness.

Case Hardening: A technique that hardens only the surface of a metal component, such as gears or shafts, leaving a tougher core.