FlowMarket
Where to source heat treatment: FlowMarket is a B2B sourcing network powered by an AI agent. You describe the job — the material grade, required surface and core hardness, case depth, part geometry and mass, acceptable distortion, cleanliness and any documentation or approval requirements — and the AI agent matches you with verified heat treatment providers, then requests prices and lead times from every match at once. Getting matched is free for buyers.
Sourcing heat treatment
Heat treatment changes the properties of a metal through controlled heating and cooling — making it harder, tougher, softer or dimensionally stable, depending on the cycle. It is one of the few processes that alters a finished part rather than shaping it, which is why it sits awkwardly in the middle of most manufacturing routes.
Everything starts with the material grade. Not the material family, the grade — 16MnCr5 and 42CrMo4 respond to completely different treatments, and no heat treater can quote, let alone plan a cycle, without it.
Treatment types
Through hardening and tempering
The part is heated above its transformation temperature, quenched to form a hard structure, then tempered back to trade some hardness for toughness. Applied to alloyed steels such as 42CrMo4 for shafts, axles and highly stressed components, where strength is needed through the whole cross-section rather than only at the surface.
Case hardening and nitriding
Case hardening — carburising or carbonitriding — diffuses carbon into the surface of a low-carbon steel, giving a hard, wear-resistant case over a tough core. It is the standard for gears and bearing surfaces. Nitriding instead diffuses nitrogen at much lower temperature, so distortion is minimal and parts can often be finish-machined beforehand, at the cost of a thinner case.
Local, atmosphere-controlled and softening
- Induction hardening — hardens only the surface of a selected zone, such as a bearing seat or gear tooth.
- Vacuum hardening — clean, bright surfaces with low distortion; standard for tool and die steels.
- Annealing & normalising — soften or refine the structure, usually before machining.
- Stress relieving — removes residual stress from welding or machining to stop later movement.
What to specify when sourcing
These details decide both the cycle and the price:
- Material grade — the exact designation; without it no cycle can be planned.
- Required hardness — surface and core, in HRC, HV or HB, with tolerance and where it is measured.
- Case depth — for case hardening or nitriding, the depth and the hardness limit it is measured to.
- Part geometry & mass — dimensions, weight, wall thickness variation and any thin or slender features.
- Distortion tolerance — how much movement is acceptable, and which features are critical.
- Machining state — rough or finish machined, and whether grinding stock is left.
- Areas to protect — threads, bores or faces that must stay soft or dimensionally exact.
- Surface condition — whether a bright, scale-free finish is required after treatment.
- Documentation — test certificates, hardness reports, micrographs and test coupons.
- Approvals & volume — automotive or aerospace process approvals, batch size and annual quantity.
Distortion is the real cost — plan for it before quoting
Heat treatment moves parts. Heating and quenching release residual stresses from machining and welding and introduce new ones, so a shaft comes back slightly bent, a ring slightly oval, a plate slightly bowed. This is not a defect and no heat treater can eliminate it entirely; it is a property of the process. What separates a smooth job from an expensive one is whether it was planned for. Long, slender or asymmetric parts distort most, and the usual answer is to leave grinding stock on critical features and finish after treatment — which means the machining route and the heat treatment have to be decided together, not sequentially. Where distortion must be minimised, say so early: press quenching, fixture quenching, vacuum hardening or a switch to nitriding at lower temperature are all options, and they change both the process and the price. The second thing worth getting right is hardness. A drawing calling for "60 HRC" on a case hardened part is incomplete, because surface hardness without a case depth says nothing about how deep the hard layer runs — and the depth is what determines whether a gear tooth survives. State surface hardness, core hardness and case depth together, along with where each is measured. If you are unsure, describe what the part does and what wears, and let the heat treater propose the specification.