3: Heat Treatments

Question 1

Hardening - Process (3)

Answer 1

• Heat material to a specific temperature above its critical point.
• Hold at that temperature to ensure uniform heating.
• Rapidly cool (quench) in water, oil, or air to form a hard, crystalline structure known as martensite.

Question 2

Tempering - Process (3)

Answer 2

• Reheat hardened material to a temperature below its critical point.
• Hold at that temperature to reduce brittleness.
• Cool slowly in air to achieve the desired balance of hardness and toughness.

Question 3

Case Hardening - Process (3)

Answer 3

• Heat material to a cherry red colour and introduce carbon (carburizing) to the surface.
• Hold at that temperature to allow diffusion into the surface layer.
• Rapidly cool (quench) to harden the surface layer.

Question 4

Annealing - Process (3)

Answer 4

• Heat material to a specific temperature above its critical point.
• Hold at that temperature to allow recrystallization.
• Cool slowly in a furnace or controlled environment to relieve internal stresses and increase ductility.

Question 5

Normalising - Process (3)

Answer 5

• Heat material to a specific temperature above its critical point.
• Hold at that temperature to refine the grain structure.
• Cool in still air to enhance uniformity and mechanical properties