Annealing
Heat, then cool *very slowly* (often in the furnace) to make steel as soft as possible—lowering hardness, improving machinability/formability and relieving stress.
Useful before further machining or bending, or for steel that is too hard to work.
Normalizing
Heat slightly above the critical range, then cool *in air*—faster than annealing.
The result is a finer, more uniform grain and slightly higher strength than annealed; often done to refine structure before actual hardening.
Tempering
Always done *after* a quench: reheat to 150–650°C to cut brittleness and restore toughness, trading off a little hardness.
Temper temperature sets the final hardness: low temper = very hard/less tough; high temper = tougher.
Quick summary
- Annealing = softest, furnace-cooled.
- Normalizing = grain refinement, air-cooled.
- Tempering = de-brittling after hardening.
FAQ
Annealing vs hardening?+
Annealing softens and relieves stress; hardening makes steel harder. Opposite goals.
Why temper after hardening?+
After a quench the part is hard but very brittle; tempering restores usable toughness.
Is normalizing necessary?+
Not always, but it evens out grain before hardening, making results more consistent.
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