Austempering is a specialized heat treatment process used to fortify metals. It amplifies several of the desirable properties ductile iron castings already possess — including strength, abrasion resistance, and toughness. Austempered ductile iron (ADI) castings — aka ausferritic ductile castings — are often employed in mission-critical, high-demand applications, for parts that must withstand extreme stresses — in particular the construction and mining, agriculture, automotive, heavy truck, and railroad industries.
Exceptional ADI castings start with exceptional ductile iron. Urick Foundry's castings are among the industry's highest in graphite nodularity and nodule count, key factors in maximizing the austempered ductile iron properties. Applied Process, a world-class expert in metal heat treatments, recognizes this consistency and is proud to work with us as our exclusive austempering partner.
Like other heat treatments for metals, austempering begins by heating a ductile iron part to a temperature of between 1550° and 1700° F, which loosens the molecular structure and allows for increased carbon absorption. Where it differs is the salt quench — immersion of the part in a bath of molten salt (between 450° F to 750° F), rather than oil or water. Because the temperature of the salt bath is held constant over a longer period of time, carbon absorption and structural consistency are improved as the part cools, resulting in a stronger near-net shape product.
ADI is up to three times stronger than aluminum, and up to 2.3 times as stiff. This means more resilient parts can be achieved with less material, trimming weight from the final product.
Other heat treatments can leave metals prone to distortion or cracking as part surfaces and interiors cool at different rates. As an isothermal process, austempering avoids this pitfall.
Per pound, austempered ductile iron parts offer a similar tensile strength to steel with superior yield strength — all in one piece. No additional forging, welding, or fabrication is required.
Urick is capable of providing various grades of austempered ductile iron (ADI) castings through a trusted partner, in accordance with the latest standards set forth by ASTM International.
Tensile Strength (MPa/KSI)
Yield Strength (MPa/KSI)
Impact Energy (J/Lb-Ft.)
|Typical Hardness BHN|
When is it necessary to austemper ductile iron?
It's necessary to austemper ductile iron for extreme applications wherein only the strong survive. ADI is often used in construction and mining, agriculture, automotive, heavy truck, and railroad applications.
What am I getting with a higher grade of austempered ductile iron?
With a higher grade of austempered ductile iron, you're getting more strength and hardness at the expense of elongation. As such, the higher grades of ADI are less ductile.
How long does the austempering process take?
Depending on the ductile iron casting's size and weight, the austempering process could take several minutes or several hours, as the desirable austenitic microstructure forms uniformly throughout the casting in the temperature-controlled molten salt bath.
Can I machine an austempered ductile iron part?
Because austempered ductile iron parts are significantly harder and stiffer than regular ductile iron, we recommend machining prior to austempering.
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