Heat Treatment
Heat treatment heats and cools metal parts under controlled conditions to change their properties, making them harder, tougher, softer or more stable. Processes include hardening, tempering, annealing, normalising, stress relieving, case hardening and nitriding.
What it is
Each process uses a specific temperature, time and cooling method. Hardening heats steel above its transformation temperature and quenches it; tempering then reduces brittleness. Annealing and normalising soften or refine structure; stress relieving removes internal stresses without changing hardness much.
Surface treatments such as carburising, nitriding and induction hardening harden only the surface layer, keeping a tough core for wear-resistant parts.
Typical applications
- Gears, shafts and pins
- Tools, dies and punches
- Springs and fasteners
- Welded and machined structures (stress relief)
- Castings and forgings
Suitable materials
- Carbon steels (EN8, EN9, C45)
- Alloy steels (EN19, EN24, EN31, 42CrMo4)
- Case-hardening steels (EN36, 20MnCr5, 16MnCr5)
- Tool steels (D2, H13, O1)
- Stainless steels (martensitic and PH grades)
Points to consider
- Specify the result needed (for example 55–60 HRC, case depth 0.8–1.2 mm) rather than just "harden".
- Heat treatment can distort parts; leave grinding allowance on precision features.
- Material grade decides achievable hardness; low-carbon steel cannot be through hardened.
- Ask for hardness test reports for critical parts.
Frequently asked questions
What is the purpose of heat treatment?
To change mechanical properties such as hardness, strength, toughness or machinability, or to remove internal stresses.
Will heat treatment change my part dimensions?
It can cause small growth and distortion, so precision features are usually ground after hardening.
How do I specify heat treatment?
State the process and the required result, such as hardness range and case depth, plus the material grade.