Quenching is not necessary when hardening is done by-

Quenching is not necessary when hardening is done by- Correct Answer Nitriding

Explanation:

Case hardening

• Case hardening is a method used to harden the outer surface of low-carbon steel while leaving the center or core soft and ductile.
• Case hardening involves heating the metal to its critical temperature in some carbonaceous material.
• The following methods are commonly used:
  • Pack method
  • Cyaniding
  • Nitriding
  • Induction Hardening
  • Flame hardening

Nitriding:

• Nitriding is a case hardening process in which nitrogen (Ammonia) instead of carbon is added to the surface of the steel. 
• Nitriding heats the steel part to 482-621°C (900-1,150°F) in an atmosphere of ammonia gas and dissociated ammonia.
• The time the part spends in this environment dictates the depth of the case. 
• No quenching is done after nitriding.