Age / Precipitation / Temper

In metallurgy, there is always a trade-off between strength and ductility. This delicate balance highlights many of the subtleties inherent to the tempering process. Precise control of time and temperature during the tempering process are critical to achieve a metal with well-balanced mechanical properties.

After the hardening treatment is applied, steel is often harder than needed and is too brittle for most practical uses. Also, severe internal stresses are set up during the rapid cooling from the hardening temperature. To relieve the internal stresses and reduce brittleness, you should temper the steel after it is hardened. Tempering consists of heating the steel to a specific temperature (below its hardening temperature), holding it at that temperature for the required length of time, and then cooling it, usually in still air. The resultant strength, hardness, and ductility depend on the temperature to which the steel is heated during the tempering process.

Correct tempering which follows hardening of the material allows the choice of steel used to obtain its mechanical properties chosen for the application.

All steels that go through a hardening process, go through a tempering process to stabilize and give mechanical ability. Materials like Precipitating Harden Stainless Steels like 17-4 PH, 630 S/S, 15-5 PH, 13-8 PH and 17-7 PH also go through a tempering process post Solution Annealing but this is normally referred to as an Age.

The size and shape of items that can be tempered depends on the type of equipment operated by the heat treater for hardening the material. For large items, check the availability of suitably-sized facilities at an early stage.

Tempering – because it is often the last heat-treat operation – is considered by most to be relatively simple and straightforward. However we must remember that it is a complex process in which all of the process and equipment variability must be carefully controlled.

Your heat treater will have differing processes for all the various grades of steel they process, to ensure they do not process incorrectly you must provide them with the correct material name and or associated numbers.

All of the following information should be included if possible. If uncertain, ask your heat treater before producing a specification:

  • The process: temper in air or vacuum or protective atmosphere.
  • Material: type, grade, and the standard from which it is drawn, with drawing, composition and mill certificate where available.
  • Any general standards applicable (national, international or company) that contain relevant details which must be adhered to.
  • Existing condition; e.g. details of any prior heat treatment, such as hardening and tempering, solution treatment and ageing, intended to establish mechanical or other properties.
  • The level of mechanical properties required. Generally a hardness range . A maximum hardness level is often requested.
  • The type(s) of testing required; e.g. hardness (Vickers, Brinell), tensile etc. and any special locations for testing or the removal of samples for test pieces.
  • Requirements for any special certificates or data to be provided by your heat treater.

Guidance and information is always available from our experience heat treatment professionals.

Our procedures and work instructions are fully documented under our AS 9100 and ISO 9001 quality management systems.