Heat Treatment and Phase Transformation
How time, temperature and cooling rate control microstructure and properties.
Heat treatment is not heating alone
A heat-treatment cycle combines heating rate, soak temperature, hold time, atmosphere, cooling path and component geometry. Each variable changes transformation and residual stress.
Common objectives
Annealing can reduce hardness, relieve stress or recrystallise cold-worked structures. Quenching suppresses equilibrium products and may form martensite. Tempering balances strength and toughness. Solution treatment dissolves selected phases; ageing then precipitates a controlled distribution of strengthening particles.
Section size matters
A laboratory coupon and a thick industrial component do not cool at the same rate. Hardenability describes the ability to form hardness through a section; it is not the same as maximum hardness.
Failure modes
Distortion, cracking, decarburisation, grain growth and non-uniform properties commonly arise from poor cycle design or inadequate atmosphere and quench control.
Takeaway
Specify the desired microstructure first. The furnace schedule is only the route used to produce it.