Hardening

Hardening means making a material, particularly a metal, physically harder, and includes particular cases such as:

• Hardening (metallurgy), the strengthening of metal alloys by heat treatment
• Case hardening, the process of hardening the surface of a metal by infusing elements into the material's surface forming a thin layer of a harder alloy
  • Case hardening of rocks
  • Case hardening (woodworking)
• Air-hardening steel
• Cryogenic hardening
• Differential hardening
• Diffusion hardening
• Fire hardening
• Hardening of the arteries
• Induction hardening
• Laser hardening
• Precipitation hardening
• Quenching#Quench hardening
• a synonym for sclerotization occurring in arthropods
• Shock hardening
• Work hardening, also called strain hardening or cold working
  • Strain hardening exponent, a materials constant used in calculations regarding work hardening

It also has the metaphorical meaning of making something more resistant to some threat:

• Hardening (botany) or cold hardening, the process by which a plant survives freezing temperatures
• Hardening (computing), the process of securing a system
• Intellectual property hardening
• Target hardening, making a military or civilian installation resistant to armed attack
• Radiation hardening, making a component or installation resistant to ionizing radiation
• g-hardening, protection of something against high g-force due to acceleration
• Windows Service Hardening, protection of Microsoft Windows services

It may also mean:

• Absorption hardening, in nuclear engineering, an increase in the average energy of neutrons by absorption of those of lower energy