Ferrous Metals: Mild Steel, Stainless Steel, Cast Iron & HSS

This lesson covers ferrous metals — metals that contain iron as their primary element. Understanding ferrous metals, their properties and applications is essential for AQA GCSE Design and Technology (8552), Section 3.1.6.

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What Are Ferrous Metals?

Ferrous metals contain iron (Fe) as the main element. The word "ferrous" comes from the Latin "ferrum", meaning iron.

Key Characteristics of Ferrous Metals

Characteristic	Detail
Iron content	All ferrous metals contain iron
Magnetic	Most ferrous metals are magnetic (attracted to a magnet)
Corrosion	Most ferrous metals rust when exposed to moisture and oxygen (except stainless steel)
Strength	Generally very strong, especially steel
Cost	Relatively cheap and widely available

AQA Exam Tip: The two defining features of ferrous metals are: (1) they contain iron and (2) they are magnetic. If an exam question asks how to identify a ferrous metal, the answer is to test it with a magnet.

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Mild Steel (Low Carbon Steel)

Mild steel contains approximately 0.1–0.3% carbon with the remainder being iron. It is the most commonly used metal in the world.

Properties

Property	Detail
Carbon content	0.1–0.3%
Strength	Good tensile strength
Hardness	Relatively soft compared to other steels
Ductility	Excellent — can be drawn into wire
Malleability	Excellent — can be hammered and pressed into shape
Weldability	Easy to weld using MIG, TIG or arc welding
Machinability	Easy to cut, drill, file and machine
Corrosion	Rusts easily — requires protective coating (paint, galvanising, plating)
Magnetic	Yes
Cost	Cheap — the most affordable structural metal

Applications of Mild Steel

Application	Why Mild Steel Is Used
Car body panels	Malleable — easily pressed into shape; cheap for mass production
Nuts, bolts, screws	Strong, cheap, easy to thread
Structural steelwork	Beams, columns, girders — high strength at low cost
Wire	Ductile — drawn into wire for fencing, paper clips, staples
Sheet metal products	Cabinets, enclosures, shelving
Garden tools	Spades, rakes, wheelbarrow frames

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Stainless Steel

Stainless steel is an alloy of iron with at least 10.5% chromium (plus varying amounts of nickel and other elements). The chromium forms an invisible, self-healing oxide layer on the surface that prevents rust.

Properties

Property	Detail
Chromium content	≥10.5% (typically 18% in common grades)
Corrosion resistance	Excellent — does not rust under normal conditions
Strength	High tensile strength
Hardness	Harder than mild steel; more difficult to machine
Hygiene	Non-porous surface is easy to clean and sterilise
Appearance	Attractive silver finish; can be polished to a mirror shine
Magnetic	Some grades are magnetic; others (austenitic, e.g. 304/316) are not
Cost	Significantly more expensive than mild steel

Applications of Stainless Steel

Application	Why Stainless Steel Is Used
Kitchen sinks	Corrosion-resistant, hygienic, easy to clean
Cutlery	Food-safe, attractive, durable
Surgical instruments	Sterilisable, corrosion-resistant, hard
Chemical processing equipment	Resists chemical attack
Watch cases	Attractive, durable, hypoallergenic
Outdoor furniture	Will not rust in rain
Food processing machinery	Meets hygiene standards