Austempered for iron and steel | isothermal process

what is austempering?

Austempering is an isothermal process. Unlike other heat treat processes, the transformation that takes place during Austempering happens over many minutes or hours. This means the component transforms uniformly to its new microstructure. This means less distortion and no cracking during quenching.

Because Austempering is an isothermal process, components will grow the same way every time. Lot-to-lot and part-to-part, your components will grow in a predictable manner when Austempered. Because of this, it is often possible to design the dimensional change into your component and let it grow to its final dimensions.

The Austempering Process

The parts are heated to 1550 F and 1750 F in a controlled atmosphere (so they don’t oxidize or scale) but then are quenched in a bath of molten salt at 450°F (232°C) to 750°F (399°C). The quench temperature is above the Martensite start temperature and a preferred structure forms. In Austempered Ductile Iron and Austempered Gray Iron, the structure is Ausferrite while Bainite forms in steel.

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. Conventional heat treaters heat the parts to between 1550 F and 1750 F and then quench them in a bath of oil or water that is near room temperature. (Maybe even as high as a few hundred degrees Fahrenheit). This produces a crystalline structure known as Martensite, a hard, brittle phase. The parts are then tempered in another furnace at 350°F (177°C) to 1100°F (593°C) to decrease the “brittleness.”

austempering properties

Higher Strength and Toughness

Austempered materials have greater strength and toughness due to the unique microstructure gained through the Austempering Process.

Improved Damping Capacity

The presence of graphite in cast iron allows for a higher damping capacity than in steel. Austempering further refines the microstructural scale of the matrix and results in additional improvements in the damping capacity for Austempered Ductile Iron and Austempered Gray iron.

Better Wear Resistance

The unique characteristics of an Austempered Material make it more wear resistant than many competitive materials. The high case hardness of Carbo-AustemperedTM steel gives it a tough wear surface. The embedded carbides and Austempered microstructure of Carbidic ADI make it a competitive wear material for ground engaging applications. The high strength and toughness of ADI and Austempered Steel make them more suitable for higher wear applications. Try Austempering today to create components that can handle wear better than conventional materials.

Lighter Components

With 3 times the strength of aluminum and 2.3 times the stiffness, ADI can replace aluminum at a weight savings! When you increase the strength of your component by using the Austempering process, you can use thinner sections in your components, and cut down the weight of your products.

Lower Overall Component Cost

Increasing the strength of your component, making it tougher, lighter and more wear resistant can decrease the amount of material needed to produce your product. Less material means less raw material cost going into your component. Switching from a costly forging, welding or fabricating operation to a lower cost casting operation can also save you many dollars in manufacturing costs; not to mention that irons and steels are significantly less expensive materials that aluminum, magnesium and other composite and plastics materials.

Fields of application of austempering

Austempered Ductile Iron (ADI)

ADI provides a high strength-to-weight material at a component price that is typically 20% less than that of steel.

Austempered Ductile Iron (ADI)

Austempered Ductile Iron (ADI) is a specialty heat treated material that takes advantage of the near-net shape technology and low cost manufacturability of ductile iron castings to make a high strength, low cost, excellent abrasion-resistant material. Six grades of ADI are available to address property combinations of high strength, abrasion resistance and toughness for converting from costly forgings, weldments and assemblies.

It may surprise you to know that in some applications ADI has replaced aluminum as a weight savings. ADI components are very competitive with steel forgings, castings, weldments, and aluminum forgings and castings.

Austempered Ductile Iron (ADI) has found successful applications across many industries, including Construction and Mining, Agriculture, Automotive, Heavy Truck, and Railroad.

Typical applications include

Austempered Steel

Application of the Austempering process to steel provides the user with a tough, high-strength component that resists embrittlement.

Austempered Steel

This dimensionally repeatable process is typically cost competitive with conventional quench and temper processes. Austempering is particularly appropriate for medium and high carbon stampings, forgings, castings, and full density powdered metal parts.

Austempered Steel offers superior toughness at high hardnesses over conventionally quenched and tempered steel. This process exhibits minimal distortion, no cracking during quenching and resistance to hydrogen embrittlement. Austempered Steel (including high-density Austempered Powdered Metals) is superior to conventionally processed steels.

Typical examples of Austempered Steel applications are:

Austempered Gray Iron

Make Quieter Components

AGI offers material with excellent dampening effects, strength, and wear resistance.

Typical applications of AGI include:

Bearing Collars
Light Duty Gears
Cylinder Liners
Machine Parts
Brake Components

Carbidic Austempered Ductile Iron (CADI™)

CADI™ is a new treatment that uses a matrix of ausferrite and carbides to add strength and wear resistance to ductile iron parts.

Carbidic Austempered Ductile Iron (CADI™)

The result is a premium, engineered iron with longer life, and more wear-resistant than Grade 5 ADI. Typical applications for CADI™ will be off-highway vehicles, agricultural equipment, railroad car and track, construction and mining, general industrial, material handling, and ground engaging components.

Carbidic Austempered Ductile Iron (CADI™) is produced by austempering ductile iron that has a controlled volume of carbides present for an even greater abrasion resistant material. The resulting microstructure consists of carbides within an ADI matrix (ausferrite). The amount of carbide in CADI™ is dependent upon the desired abrasion resistance with typical ranges of 10-30% carbide present. The properties of the ADI matrix surrounding the carbide are determined by the selection of the heat treatment parameters.

CADI™ is utilized where abrasion (wear) resistance is of primary concern. It is more wear resistant than Grade 1600 (GR 5) ADI, less expensive and tougher than many abrasion resistant irons and can replace Mn steel at an equal or lower cost.

Typical applications of CADI™ include:

Carbo-Austempered™ Steel

This process develops a tough, high-carbon, bainitic case on high performance components.

Carbo-Austempered

Carbo-Austempered parts have remarkable impact properties that are superior to either neutral hardened or carburized steels. Carbo-Austempering is routinely applied to steel gears, shafts, and power transmission parts that undergo periodic overloading in service.

The Carbo-Austempering™ process is a high performance steel heat treatment that combines a high carbon bainitic case with either a bainitic or tempered martensitic core to produce a component with an exceptional combination of strength and toughness.

Carbo-Austempered ™ steel exhibits:

Higher tensile strength
Increased wear resistance
Greatly improved impact properties
Increased elongation
Lower distortion
No cracking during quenching
Increased fatigue strength (in high load, low cycle fatigue application)

Typical applications of Carbo-Austempered™ Steel include:

Locally Austempered Ductile Iron (LADI™)

LADI^TM is a surface hardening heat treatment process that will produce a localized case depth (3 to 5 mm) of an ausferrite microstructure (ADI) in a desired area of a component. This induction-based technology is unique in that it can be applied to ferritic grades of ductile iron (65-45-12 or 450-12) which are typically not suited for induction hardening.