Heat Treatment — Hardening, Tempering & Case Hardening

What it is and when to specify it

Heat treatment is a family of controlled heating and cooling cycles that change the mechanical properties of a metal part without changing its shape. The same alloy can be supplied soft and easy to machine, then hardened and tempered to a working condition, then stress relieved so it stays stable. Each cycle is defined by temperature, hold time and cooling rate, and the exact recipe is chosen per material and per drawing requirement.

You specify heat treatment when a part must resist wear, carry load, or hold its shape after machining. The most common reasons are: hardening and tempering to raise strength and wear resistance, stress relief to remove the internal tension left by machining or forming, annealing to soften and homogenise the material, normalising to refine the grain, and case hardening or nitriding to produce a hard, wear-resistant skin over a tougher core.

Heat treatment is arranged through our vetted partner network, managed under one quality process. We stay your single point of contact, and the treatment requirement is taken from your drawing rather than assumed.

Specifications

The primary specification is the treatment cycle and the resulting property, which is set by your drawing. We do not invent a hardness target; we read what the drawing calls for — such as harden and temper, stress relieve, case harden or nitride — and route the part to the correct partner furnace with the alloy and the target clearly stated. Where the drawing gives a hardness value, that value is met to the drawing specification, and the material certificate (MTR) confirms the incoming alloy.

The common processes we specify at a general level:

• Stress relief: a lower-temperature soak that relaxes internal stress without a major property change.
• Hardening and tempering: heat to austenitise, quench, then temper to balance hardness against toughness.
• Annealing: a slow-cooling cycle that softens the material and removes work hardening.
• Normalising: air cooling from an elevated temperature to refine the grain and even out the structure.
• Case hardening and nitriding: surface treatments that build a hard outer layer over a tougher core.

Because heating and quenching move metal, we review the dimensional impact on a drawing before quoting and build any allowance into the machining plan.

Which materials and parts it suits

Heat treatment matters mostly for steels. Our carbon and alloy steels — 1045, 1095, 1215, 4130, 4140 and the tool steels D2 and O1 — respond well to hardening, tempering, annealing and normalising, and 4140 is the workhorse for hardened shafts, pins and structural parts. The 300-series stainless grades (301, 303, 304, 304L, 316, 316L) are generally supplied in their solution-annealed state and are chosen for corrosion resistance rather than high hardness, though they can be stress relieved; the hardenable stainless grades 410, 416 and 17-4PH are the ones that take a real through-hardness or precipitation-hardening cycle. Aluminium 2024, 6061 and 7075 use their own ageing treatments, and brass, copper, bronze and titanium have their own specific cycles. Grade detail lives on our materials index, then steel parts, stainless steel parts and aluminum parts pages.

Typical heat treated parts include custom shafts, pins, gears, bushings and sleeves and wear components that must hold a load over many cycles. A part that carries a running surface or a contact face is the classic candidate for hardening or case treatment.

Corrosion, wear and dimensional impact

The main benefit is wear and strength. Hardening, case hardening and nitriding raise surface hardness and resistance to abrasive wear, which is why they are specified on gears, shafts, cams and sliding parts. The trade-off is dimensional: heating and quenching can move a part, so features that carry tight tolerances are either machined after treatment or given a machining allowance.

Stress relief before final machining matters for exactly this reason. A part that carries internal stress will shift when the last few tenths are cut, so we stress relieve, then finish to size. The requirement is always set by the drawing: we never quote a hardness figure as a promise that is not on the drawing, and we do not treat a cosmetic finish the same as a load-bearing case. If the drawing names a process and a target, we meet it; if it only names the process, we confirm the target with you before cutting.