Design Engineering Theory Topics - Home Page



1 Key terms



  • The ability of a material to deform by bending, twisting or stretching (stretching to wire).
  • The ability to be drawn out without breaking.
  • The ductility in metals increases with temperature.


  • The ability of a material (metal) to be permanently deformed in all directions without fracture (beating to sheet).
  • This ability also increases with temperature.


  • The ability of a material to resist deformation, indentation or penetration.
  • Hard materials can resist abrasion, drilling, impact, scratching and wear and tear.


  • An alloy is a mixture of 2 or more metals or elements.
  • This mixture is used to improve the properties and characteristics.

2 Ferrous Metals

  • Ferrous metals are metals that contain Iron (ferrite). This makes most of them have magnetic properties.
  • Because ferrous metal contain Iron, they are prone to corrosion (rust) when exposed to moisture, the only 2 exceptions are, stainless steel and wrought iron.
  • Materials properties.

Mild Steel

  • Properties - Tough, ductile, malleable, magnetic, high tensile strength, easily joined, poor corrosion resistance.
  • Composition - Iron + 0.1 - 0.3% carbon.
  • Melting point - 1400 degrees celsius.
  • Example uses - Screws, nails, bolts, girders and car body panels.

Stainless Steel

  • Properties - Corrosion resistant, hard, tough, sometimes magnetic, resists wear, difficult to cut. Specific properties can be altered by varying the alloy metals.
  • Composition - Carbon steel(which contains Iron) + 10.5 - 18% chromium + 8% nickel + 8% manganese.
  • Melting point - 1400 degrees celsius.
  • Example uses - Kitchenware, sinks, cutlery, medical equipment.

Cast iron

  • Properties - Hard skin, brittle, soft core, good compressive strength, self lubricating, magnetic.
  • Composition - Iron + 2-6% carbon.
  • Melting point - 1200 degrees celsius.
  • Example uses - Machine parts, vices, brake discs and manhole covers.

3 Non Ferrous Metals

  • These metals do not contain Iron.
  • This means that they are not magnetic.
  • They are also very resistant to corrosion (rust).
  • As they do not contain Iron, they are softer and are therefore more malleable (easy to shape and bend).


  • Properties - Greyish white, corrosion resistant, malleable, ductile, easily machined, good heat/electrical conductor, excellent strength to weight ratio and polishes well.
  • Composition - Pure metal.
  • Melting point - 660 degrees celsius.
  • Example uses - Aircraft parts, foil, window frames, engine parts, and drinks cans.


  • Properties - Reddish brown, corrosion resistant, malleable, ductile, tough, easily machined, good heat/electrical conductor, good hot or cold working and polishes well.
  • Composition - Pure metal.
  • Melting point - 1100 degrees celsius.
  • Example uses - Electrical wire, gas and water pipes, printed circuit board (PCB) tracks and roofing.


  • Properties - Yellow, corrosion resistant, easily machined, good heat/electrical conductor, casts well, harder than copper and polishes well.
  • Composition - Alloy, 65% copper and 35% zinc
  • Melting point - 900-940 degrees celsius.
  • Example uses - Plumbing fittings, door fittings, locks and musical instruments.

4 Mechanical Properties

  • The mechanical properties of metals define how they react to forces. A large force, when applied, will deform metal.
  • A temporary change is called 'elastic' deformation (it will spring back into its original shape).
  • A permanent change is called 'plastic' deformation.
  • Three properties of materials are ductility, malleability and hardness.
  • All ductile materials are malleable, but not all malleable materials are ductile.
  • Hard materials are often brittle (crack easily), with a low resistance to impact, and break easily.
  • This property is important for cutting tools such as saws, drills and files.
  • Diamond is the hardest naturally occurring materials and is measured at 10 on the Mohs scale (the scales that measures hardness).
    • An example of this is: Mineral talc is 1 on the scale, aluminium is 2-2.9 and steels are 5-8.5.

5 Sample questions

  • Explain 2 reasons why stainless steel may be suitable for the roof of a building.
  • Name the elements that are added to iron to make stainless steel.
  • Explain what is meant by the term 'Ductility'.
  • Cast iron has 2-6% carbon. Describe what would happen when you decrease the carbon content (HINT: Diamonds are made from carbon, which is a 10 on the Mohs scale).
  • Explain 2 reasons why stainless steel would be used for motorcycle nuts and bolts.
  • Summarise what makes metal an alloy. Identify 2 further alloys and explain why the 'new' metal is suitable to a particular application.