Ferrous & Non-Ferrous Metals
GCSE — 2.1.2 In-depth Knowledge: Product Design
Ferrous metals
Ferrous metals — metals that contain iron and are magnetic. They are prone to rust and require a protective finish to prevent corrosion.
| Metal | Properties | Uses |
|---|---|---|
| Mild steel (low carbon steel) | Ductile, tough, easy to shape/braze/weld, good conductor, corrodes easily | Nuts and bolts, screws, bicycle frames, car parts |
| Medium carbon steel | Stronger and harder than mild steel but less ductile; can be hardened and tempered | Garden tools, springs, hammer heads, gears |
| High carbon steel (tool steel) | Hard, brittle, less malleable than mild steel, good conductor | Tools, screwdrivers, chisels |
| Cast iron | Brittle if thin, strong compressive strength, good conductivity, poor corrosion resistance | Gates, manhole covers, drains, vices |
Carbon content (approximate): mild steel 0.15–0.35%, medium carbon steel 0.35–0.7%, high carbon steel 0.7–1.4%. More carbon makes steel harder but more brittle.
Non-ferrous metals
Non-ferrous metals — metals that do not contain iron and are not magnetic. They do not rust.
| Metal | Properties | Uses |
|---|---|---|
| Aluminium | Lightweight, malleable, strong, good conductor of heat and electricity | Drinks cans, cycle frames, saucepans |
| Copper | Very malleable, excellent conductor of heat and electricity, orange/brown, oxidises green | Plumbing, central heating, electrical wiring |
| Silver | Soft, malleable when hot, highly corrosion-resistant, good conductor | Jewellery |
Alloys
Alloy — a mixture of metals (or a metal with another element) to improve working properties or aesthetics.
| Alloy | Composition | Properties | Uses |
|---|---|---|---|
| Brass | Copper + zinc | Strong, ductile, good heat conductor, golden colour, darkens with age | Taps, door fittings, hinges, locks, musical instruments |
| Bronze | Copper + tin¹ | Hard, corrosion resistant, low friction, reddish-brown | Bearings, outdoor components, monuments, nautical |
| Stainless steel | Iron + chromium + nickel | Hard, tough, good resistance to stains and corrosion, shiny silver | Kitchen sinks, cutlery, hospital equipment, architecture |
| Pewter | Mainly tin with small amounts of copper and antimony | Very low melting point (about 170–230°C), soft, malleable, silvery and polishes well but tarnishes dull grey | Jewellery, tankards, ornaments; ideal for casting in school |
¹ Some bronzes also contain aluminium (aluminium bronze), but the standard answer is copper and tin.
Casting pewter
Because pewter melts at a low temperature, it can be cast in school using a mould cut from MDF (which resists the heat, is easy to cut and has no grain).
Hazards and precautions:
- Molten metal and burns — wear heat-resistant gloves, a leather apron and a face shield.
- Moisture in the mould makes molten metal spit violently — make sure the mould and tools are completely dry.
- Fumes from the mould scorching — work in a well-ventilated area or under extraction.
- Spills — pour over a sand tray and keep the area clear.
Properties of metals
| Property | Definition |
|---|---|
| Hardness | A metal’s ability to withstand friction and abrasion |
| Toughness | How well a metal can resist fracturing when force is applied |
| Elasticity | The ability of a material to bend or stretch under a force and return to its original shape when the force is removed |
| Conductivity | How well a metal allows electricity or heat to flow through it |
| Ductility | The ability of the metal to be drawn or deformed without fracture |
| Tensile strength | The amount of load a metal can withstand before failure |
| Malleability | The metal’s ability to be bent or shaped easily |
| Plasticity | The ability of a material to be permanently changed in shape without cracking, keeping its new shape once the force is removed |
Melting points
| Metal | Melting point |
|---|---|
| Mild steel | about 1450°C |
| Cast iron | 1200°C |
| Copper | 1100°C |
| Brass | 900°C |
| Aluminium | 660°C |
Values are approximate and vary with the exact composition.
Finishing metals
Metal finishing places a coating onto a metal for cleaning, polishing or improving the surface for functional or visual purposes. Finishing is the last step in manufacturing.
Popular finishing processes:
- Powder coating — durable, colourful coating applied as dry powder then cured
- Electroplating — depositing a thin layer of metal onto the surface
- Anodising — electrochemical process creating an oxide layer (common on aluminium)
- Galvanising — coating with zinc to prevent rust
- Enamelling — fusing glass powder to metal surface
- Hot blackening — dark oxide finish for aesthetics and mild protection
- Brushing, sand blasting, buff polishing — mechanical surface preparation and finishing