Metal Enhancement Methods

Question 1

Work hardening

Answer 1

Cold worked
Bending rolling hammering
Crystals become distorted
Improved tensile strength and hardness
Crystals can’t move freely less ductile cracking or damage

Question 2

Anealing

Answer 2

Makes work hardened metal easier to work by making it less brittle and more ductile
Heated then cooled slowly
Crystals grow and move slowly into place

Question 3

Case hardening

Answer 3

Hardens surface of steels less that 0.4% carbon content
Produces outer casing
Wear resistant
Inner core retains original softer properties
Two stages:
Carburising changes chemical composition so it can absorb more carbon to increase hardness
Placed in ceramic box with carbon
Box heated
Carbon atoms diffuse into material
The longer exposed the thicker the layer

Quenching
Hot material quenched into water to cool without changing properties

Question 4

Hardening

Answer 4

Medium and high carbon content steels
Heated to alter their crystalline structure
Hold for given time then quenched in water oil salt water baths
Increases hardness and brittleness

Question 5

Tempering

Answer 5

Heat treatment
Reduces some excess hardness and brittleness
Increases ductility and toughness
Metal heated below critical point for given time then slowly air cooled
Temp determines amount of hardness removed
Tempering colour on the metal indicates temperature to which brittleness is removed