VTN Advantage:

Austempering

1. The process
The conventional method of increasing hardness or strength is the hardening and tempering process. A second, somewhat more specialised method, is austempering.

This heat treatment method involves austenitizing the component in the same way as with hardening, i.e. heat treatments are performed at temperatures of 800-1,050°C, depending on the material.

Quenching is performed in a hot salt bath. The bath temperature depends on the material and is somewhere between 250°C and 450°C. The component remains in the salt bath at constant temperature (isothermal) until the structural transformation of austenite to bainite is complete. No martensite is formed in the process. Depending on the material, the transformation may be complete in a few minutes but it can also sometimes take several hours. The component is then cooled in the air and normally not subjected to tempering.

Bainite microstructures have very specific characteristics that comprise high strengths (hardnesses), maximum toughnesses, and usually relatively low distortions. Not every component and not every material is suitable for austempering. The positive characteristics described above can only be achieved if no other microstructure is formed during cooling, such as ferrite, perlite or upper bainite. Thin-walled components or alloy steels with high hardnesses are particularly well suited to this process.

2. Suitable materials
Typically, components made of steels such as C45, C75, C67E, 42CrMo4, 65Cr3, or 67SiCr5, as well as alloy cast iron can be austempered (ADI Material).

3. Benefits of this heat treatment
The advantage of this method is that it creates the best possible toughness with a high hardness level. At the same time, it offers very favourable conditions for minimizing hardening distortion. Typical example applications for austempering include safety-belt fixtures in automobile construction, springs, nails and special blades, as well as crankshafts made of alloy cast iron.

4. Customer information required for heat treatment

  • Material
  • Material analysis
  • Target hardness with plus tolerance