Metal

There are three main types of metal, ferrous, non-ferrous and alloy.

Ferrous Metals
Contains iron and therefore rusts and is magnetic. Examples are Cast Iron and Steel.

Non-Ferrous Metals
These metals do not contain iron and are usally more expensive, and they dont rust. Examples are Aliminum and Copper.

Alloys
Alloys are a mixture of two or more materials. They are mixed so that the properties of two materials can be combined. By combining them you can change the:
-Resistance to corrosion
-Melting Point
-Colour
-Strength
-Electrical properties
-Thermal properties
-Flow of the melted metal

Examples of Non-Ferrous Alloys are Brass and Bronze. Examples of Ferrous Alloys are Stainless steel and High speed steel.

Work Hardening and Heat-Treating Metals

Annealing
The metal is heated and cooled slowly, so that is becomes soft and relieves stress. This make it less brittle and more ductile, so it is easier to work.

Hardening
Carbon steel is heated, until the carbon crystals move out of position. The material is then quenched so the crystals cannot move back into place. This causes internal stress which hardens and strengthens the metal.

Tempering
Tempering removes the stress from a harden piece of steel. this makes it less brittle but still hard. the metal is polished until you can see the surface of the metal and then heat is applied. When the metal reaches the desired colour, it is quenched.
As the tempering temperature rises, the materials hardness is reduced but its toughness is increased.