Engineering Materials and Their Properties
This section covers Engineering Materials and Their Properties. The exam tests whether you can classify ferrous and non-ferrous metals, match properties such as strength, hardness, toughness and ductility to service needs, and justify a material choice without confusing one property with another.
Core concepts
- Ferrous metals contain iron; mild steel has about 0.05–0.25% carbon, is ductile and weldable; high-carbon steel has roughly 0.6–1.5% carbon and takes a hard, wear-resistant edge; cast iron has about 2–4% carbon and is brittle in tension but strong in compression.
- Non-ferrous examples: aluminium is light and corrosion-resistant; copper conducts electricity well; brass is copper-zinc; bronze is copper-tin.
- Strength resists stress; hardness resists indentation or scratching; toughness absorbs shock without fracture; ductility allows drawing into wire; malleability allows hammering into sheets; brittleness fractures with little deformation; elasticity returns to shape after load removal.
- Heat treatment can alter properties: hardening and tempering trade some hardness for toughness.
Worked example
A cold chisel must cut mild steel yet survive hammer blows. Cast iron is hard and cheap but brittle, so its edge may chip. Aluminium is too soft. High-carbon steel, hardened and tempered, gives a hard cutting edge with enough toughness to resist shock. The reasoning is to match both hardness at the edge and shock resistance in the body, not just pick the hardest material.
Traps that cost marks
Do not say hardness and toughness are the same; a hard tool can still be brittle. Do not call stainless steel completely corrosion-proof. Do not assume higher carbon always means better for every job: weldability and toughness usually fall as carbon rises.