Steel Fundamentals: Carbon, Phases and Heat Treatment
The essential logic connecting carbon content, ferrite, austenite, cementite, martensite and practical steel processing.
Why steel is versatile
Small changes in carbon, alloying and thermal history produce large changes in phase balance and mechanical behaviour. This tunability explains steel’s enormous industrial range.
Core phases and constituents
Ferrite is relatively soft and ductile; cementite is hard and brittle; austenite is the high-temperature face-centred cubic phase; martensite is a supersaturated transformation product formed by rapid cooling. Pearlite and bainite are structured transformation products.
Carbon controls transformation
Carbon stabilises austenite and increases hardenability and achievable martensitic hardness, but can reduce weldability and toughness. Alloying elements modify transformation rates, corrosion resistance and tempering response.
Heat-treatment logic
Normalising, annealing, quenching and tempering are routes to control phase, grain size, residual stress and carbide distribution. Section size and cooling severity matter.
Working rule
Specify steel by composition, processing condition and required properties. A grade designation without heat-treatment state is incomplete.