Heat treatment

Heat treatment changes a metal's hardness, strength and toughness by heating and cooling it in a controlled way. Gears, shafts, dies and fasteners usually need it after machining or forging, and the right process depends on the material and how the part is used.

Through hardening and tempering hardens the whole part. Case carburising and induction hardening give a hard surface with a tough core, as gears and shafts need. Nitriding gives a hard, wear-resistant surface with little distortion. Annealing, normalising and stress relieving soften the metal or remove stresses.

Heat treaters use sealed-quench and pit furnaces, induction machines, vacuum furnaces and nitriding furnaces. They check results with hardness tests and, where asked, case-depth and microstructure reports.

Materials commonly used

• Carbon steels such as EN8 and EN9
• Alloy and case-hardening steels such as EN19, EN24, EN353 and 20MnCr5
• Tool and die steels such as D2, H13 and OHNS
• Stainless steels and cast irons for specific treatments

What to send with your requirement

• The material grade of the parts
• The process and the result you need: hardness (for example HRC), case depth, and where
• The size and weight of each part and the quantity per batch
• A drawing marking areas that must not be hardened, if any
• Whether you need a test report with the parts

What affects the cost

• The process: vacuum and nitriding cost more than simple hardening
• The weight of the batch and the furnace load
• Case depth and cycle time
• Masking, straightening and cleaning after treatment
• Testing and reports

Common mistakes to avoid

• Not giving the material grade, so the treater has to guess the cycle
• Asking for a hardness the material cannot reach
• Not allowing for distortion and grinding after hardening
• Mixing different grades in one batch

Frequently asked questions

What information does a heat treater need?

The material grade, the hardness or case depth you need, the part size and weight, and the quantity. A drawing showing any areas to keep soft helps.

Will parts distort?

Some distortion is normal, especially in through hardening. Leave grinding allowance on precision faces, or ask about processes such as nitriding or vacuum hardening that distort less.

Can I get a test report?

Most heat treaters can give a hardness report, and many can report case depth and microstructure. Ask for it in your requirement.