Austempering Ductile Iron for Castings

Austempering is a heat treating process that can be applied to ductile iron castings. The resulting product is referred to as Austempered Ductile Iron (ADI).

It provides superior mechanical properties relative to conventional heat treating processes for cast irons.

In certain applications austempered castings feature superior strength-to-weight ratio when compared to steel parts.



ThermTech has multiple ADI furnaces to meet your heat treating needs.

Furnaces handle dimensions up to 36”W X 72”L X 48”H and 46”W X 46”H X 46”L with a maximum load capacity of 7,000 lbs.

AMS & ASTM Requirements

All austenitizing furnaces meet the military requirements of AMS 2750 Rev E class 5 temperatures of +/-25F. 

Quench tanks are matched to each respective austenitizing furnace and meet the requirements of AMS 2750 Rev E class 2 of +/-10F. 

ASTM A897/897M provides information about the ADI process and mechanical testing requirements.

ThermTech ensures all products meet their necessary requirements before delivery by leveraging close partnerships with several accredited labs.

Our mechanical testing service results in faster testing turnaround, shortened lead times and improved logistics.


When austempering ductile iron for castings the material must be heated to a specified temperature to achieve austenitization.

The ADI process brings the material to a fully austenitic state with typical temperatures ranging from 1575F to 1675F. 

Next, the parts are soaked at a time sufficient to reach complete austenitization.

After soaking, parts are quenched in a molten salt bath at a temperature that minimizes the probability of distortion, which is inherent in all quenching operations.

Quench temperatures range from 450F to 750F.

The temperatures employed are determined as a function of the chemistry of the ductile iron, as well as the required mechanical & hardness requirements specified by the customer.

This quenching allows the material to achieve the specified microstructural, mechanical and hardness requirements.

Other Process Considerations

There are other process considerations that can have a significant impact on austempered castings: Chemistry and Foundry Practices.


When it comes to chemistry, if section size increases, then specific alloying elements must also be increased to achieve desired properties.


Pearlite rating, nodule count, and nodularity rating are critical factors the foundry must control in order to maximize the end properties of austempered castings.


Demanding Specifications

For products that must meet the most demanding specifications, custom heat treating services may be recommended.

ThermTech’s in-house metallurgists & process development team operate in conjunction to coordinate the best heat treating process for your product’s exact needs.


If you are in the alloy consideration stage it may be beneficial to receive support from our metallurgical staff. We recommend obtaining recommendations prior to the quoting process to ensure so you have a full understanding of material options and costs.

Our process development team will read & interpret the specifications you provide to certify that the final product will meet the necessary requirements.

Contact ThermTech to find out how austempering can improve your castings!