Ferrous, non-ferrous and alloys
Ferrous metals contain iron, so unless protected they rust and are usually magnetic — cast iron, mild steel, tool steel, HSS, stainless steel. Non-ferrous metals contain no iron, so resist rusting — aluminium, copper, zinc, lead, tin. An alloy mixes a metal with other elements to improve a property: ferrous (stainless steel = steel + chromium) or non-ferrous (brass = copper + zinc). A ferrous part needs rust protection.
Each metal's signature property
Cambridge wants the specific metal AND its property. Ferrous: mild steel cheap, tough, welds well but rusts; cast iron hard, strong in compression but brittle; tool steel hardens to hold an edge; HSS keeps hardness when hot (drills); stainless steel corrosion-resistant. Non-ferrous: aluminium light, corrosion-resistant; copper excellent conductor; zinc galvanises steel; lead dense, soft; tin coats steel cans.
Four structure-changing heat treatments
Working or heating a metal sets its hardness and toughness. Work hardening: cold bending/hammering makes the area harder, brittle. Annealing reverses it — heat, cool slowly to soften. Hardening and tempering treats tool steel: heat cherry red, quench (hard but brittle), then reheat lower for toughness. Case hardening treats mild steel, too low in carbon to harden through: add carbon to the surface, harden that skin.
Drawn from real examiner reports.
Ferrous = contains iron
Some candidates could not define a ferrous metal. The answer is short: it contains iron, so it rusts in damp air unless protected and is usually magnetic. A non-ferrous metal contains no iron. "A strong metal" earns nothing — that is not what ferrous means. Learn an example each side: ferrous (mild steel), non-ferrous (aluminium).
w23 P32 Q12a — some candidates could not define a ferrous metal
Stainless steel = steel + chromium
Candidates know stainless steel resists rust but cannot say why — the mark is for the added element. Stainless steel is steel with chromium (about 18%) and usually nickel; the chromium forms a self-repairing oxide layer that stops rusting. Still a ferrous metal but corrosion-resistant. "It does not rust" restates the question; the answer is chromium.
w23 P32 Q4b — few named chromium/nickel as the additive that makes steel stainless
Non-ferrous metals under-known
Non-ferrous metals are weakly recalled. Candidates failed to pick aluminium as the light one, and did not know copper (conductor) or lead (heavy, soft). A property headline each: aluminium = light; copper = conducts; zinc = galvanises; lead = heavy, soft; tin = coats steel cans. Picking a ferrous metal for a "non-ferrous" question loses the mark.
s23 P32 Q5/Q7 — aluminium as the non-ferrous metal under-identified; w23 P33 Q9 — copper and lead poorly recalled
Alloy vs pure metal mix-up
Candidates confuse an alloy with a pure metal. A pure metal is a single element — copper, aluminium, lead, tin. An alloy is a base metal mixed with other elements to improve a property: brass (copper + zinc), bronze (copper + tin), stainless steel (steel + chromium). So copper is pure, brass is an alloy. Calling brass "pure" loses the mark.
Hardening vs tempering confused
Hardening and tempering are the two stages of one treatment, easily muddled. Hardening heats tool steel to cherry red then quenches it — very hard but brittle. Tempering comes after: reheat lower and cool to cut brittleness and add toughness. Saying tempering "hardens" the steel is wrong — an un-tempered tool is glass-brittle and can shatter.
Mild steel won't harden through
A common wrong choice is hardening and tempering mild steel. It has too little carbon to harden through — quench it and it stays soft. Only tool (high-carbon) steel hardens and tempers (chisels, files). For a wear-resistant mild-steel part, case harden it: add carbon to the surface, then harden that skin — a hard case over a tough core (gears, cams).
Annealing softens, it doesn't harden
A sharp either/or error: thinking annealing hardens a metal, or that work hardening and annealing do the same job. They are opposites. Work hardening (cold bending, hammering) makes a metal harder and more brittle; annealing heats it then cools it slowly, softening it. The tell is cooling rate — slow cooling softens; quenching hardens tool steel.
Name the metal and the exact property
Metal marks reward precision. Name a specific metal — mild steel, cast iron, HSS, aluminium, copper — never "steel" or "metal". Then add the exact property (tough, corrosion-resistant) or additive (chromium). A vague "strong metal" scores nothing.
Match the command word
Read the command word. State / name wants the fact only. Explain wants the property linked to why it suits the product. Describe a process wants the ordered steps. Answering below the command word leaves marks unclaimed.
Heat treatment: give the effect
Describing a heat treatment, say what it does to the property, not just "it heats the metal". Annealing softens and restores ductility; hardening makes it hard but brittle; tempering trades hardness for toughness; case hardening gives a hard case over a tough core.
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