What is austempering?

Austempering is an isothermal heat treatment that, when applied to ferrous materials, produces a structure that is stronger and tougher than comparable structures produced with conventional heat treatments used for treating thin sections of certain medium or high carbon steels or some alloy-containing steels of thicker section. These items are typically small springs or steel pressings. Its aim is to produce this tough and ductile structure with the minimum of distortion.

This structure is preferable to the less ductile, oil-hardened structure, and has the added benefit of producing less distortion. It achieves this by utilising a high temperature quench and then being held in a molten salt bath whilst the steel undergoes its hardening process. No subsequent tempering is required.

The parts are heated above the austenitising temperature in a controlled atmosphere then are quenched in a bath of molten salt between 240 - 380 degrees centigrade. The part is held at this temperature for the required time to transform the austenite into bainite. The part is then removed from the salt quench rinsed free of salt and cooled to room temperature.

Advantages of Austempering

  • Less distortion and cracking than other hardening routes
  • Improved ductility
  • Higher impact and fatigue strengths
  • Improvement of toughness and increased wear resistance
  • Parts are "plating friendly" due to the clean surface from the salt quench
  • Resistance to hydrogen embrittlement
  • No need for final tempering

Recommend austemper for

We recommend using the austemper process if the components are:

  • Distortion prone
  • Material thickness between 0.2 and 3mm
  • Material uses: medium carbon steels e.g. SAE1060, CS67, CS70
  • Hardness requirements typically 400 - 550 VPN (Austempering at 430/480 is often considered the perfect spring condition)

The salt used gives a small amount of surface protection. We also offer a dewatering oil which will give good protection against surface rust for several months in warehouse conditions.