Heat treatment

Question 1

What is cold working

Answer 1

• When material is cold worked, faults known as dislocations are formed within the structure
• Causes it to harden and eventually fracture

Question 2

What is work hardening

Answer 2

• When metal is worked through processes of hammering, rolling and bending
• Causes it to become brittle

Question 3

Annealing (‘normalising’ for ferrous metals)

Answer 3

• Application of heat to relieve internal stress
• Causes the metal to become malleable

Question 4

Annealing of ferrous metals (normalising)

Answer 4

• Heated to 725ºC - a cherry red colour
• Allowed to cool slowly

Question 5

Annealing of aluminium

Answer 5

• Heated to 350-400ºC
• Allowed to cool

Question 6

Annealing of copper and brass

Answer 6

• Heated to a dull red

Question 7

What is case hardening

Answer 7

• Increases wear resistance of mild steel
• Introduces a surface layer of carbon into the steel

Question 8

How is case hardening achieved

Answer 8

• Heated to red heat
• Dipped into carbon compound
• May be repeated

Question 9

What is hardening and how is it achieved

Answer 9

• Heated to a red heat and is quenched in water
• Makes the steel hard but brittle

Question 10

What is tempering and how is it achieved

Answer 10

• Raising of metal to 230-300ºC and quenched in water
• Causes the metal to be more tough