Austempering

Austempering is heat treatment that is applied to ferrous metals, most notably steel and ductile iron. 

In steel, it produces a bainite microstructure whereas in cast irons it produces a structure of acicular ferrite and high carbon, stabilized austenite known as ausferrite. It is primarily used to improve mechanical properties or reduce/eliminate distortion.  Austempering is defined by both the process and the resultant microstructure.  Typical austempering process parameters applied to an unsuitable material will not result in the formation of bainite or ausferrite and thus the final product will not be called austempered. Both microstructures may also be produced via other methods, but these materials are also not referred to as austempered.

Austempering consists of rapidly cooling the metal part from the austenitizing temperature to about 440 °F to 750 °F and holding at a constant temperature to allow isothermal transformation.

Because Austempering is an isothermal process, components will grow the same way every time.

From one lot to another and one part to another, your components will grow in a predictable manner when Austempered.

The most notable difference between austempering and conventional quenching and tempering is that it involves holding the workpiece at the quenching temperature for an extended period.

Austempering offers many manufacturing and performance advantages over conventional material/process combinations.  

One of the advantages that is common to all austempered materials is a lower rate of distortion than for quenching and tempering. This can be translated into cost savings by adjustment of the entire manufacturing process. The most immediate cost savings are realized by machining before heat treatment.

Performance improvements of austempered materials, compared to conventionally quench-and-tempered materials with a tempered Martensite microstructure, in steels above 40.0 HRC include:

• Higher ductility, impact strength and wear resistance for a given hardness.
• A low-distortion, repeatable dimensional response.
• Increased fatigue strength.
• Resistance to hydrogen and environmental embrittlement.

 In cast irons (from 250-550 HBW) these improvements include:

• Higher ductility and impact resistance for a given hardness.
• A low-distortion, repeatable dimensional response.
• Increased fatigue strength.
• Increased wear resistance for a given hardness.