1.3 Enhancement of Materials - Metal Enhancements

Question 1

How can metals be enhanced

Answer 1

Metals can be enhanced through the controlled application of heating and cooling, known as heat treatment

Question 2

Ways metals are enhanced

Answer 2

• Case hardening
• Hardening
• Tempering

Question 3

Case hardening (3)

Answer 3

• Is used for hardening the surface of steels with less than 0.4 per cent carbon content
• Case hardening produces an outer casing of greater hardness, improved wear resistance and resistance to surface indentation, while the inner core of the metal retains the original ‘softer’ properties
• Has two stages which are: carburising and quenching

Question 4

Carburising - case hardening

Answer 4

The chemical composition changes of the surface of low carbon steel so that it can absorb more carbon to increase surface hardness

Question 5

Quenching - case hardening

Answer 5

The hot metal is quenched in water to fast-cool it and seal the hard surface case while not affecting the properties of the inner core

Question 6

Hardening (2)

Answer 6

• Medium and high carbon steel are heated to alter their crystalline structure, holding them at this temperature for a given time and then quenching them in water, oil or salt-water baths
• The hardening and subsequent quenching increase hardness but also increase brittleness

Question 7

Tempering (4)

Answer 7

• A heat treatment reduces some of the excess hardness and brittleness of a hardened metal, and increases the toughness and ductility
• The metal is heated to below the critical point for a given time then slowly air cooled
• The exact temperature will determine the amount of hardness removed
• Tempering colour on the metal brittleness is removed