austempered
what is austempering?
Austempering is an isothermal process. Unlike other heat treatment processes, the transformation that takes place during austempering happens over many minutes or hours. This means the component transform uniformly to a 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.
austempering process
1. austenitizing
The parts are heated to 1550 °F (843 °C) and 1750 °F (954 °C) 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.
2. quenching / cooling
In conventional heat treatment, parts are heated to a temperature between 1550 °F and 1750 °F and then quenched in a bath of oil or water, typically near room temperature (possibly even as high as a few hundred degrees Fahrenheit). This produces a crystalline structure known as martensite, a hard and brittle phase.
3. tempering
Following that process, parts are then tempered in another furnace at temperatures ranging from 350 °F (177 °C) to 1100 °F (593 °C) to reduce the “brittleness.”
benefits of austempering
Austempered materials have greater strength and toughness due to the unique microstructure gained through the austempering process.
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.
The unique characteristics of an austempered material make it more wear resistant than many competitive materials. The high case hardness of Carbo-Austempered™ 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. Through high strength and toughness of ADI and austempered steel make them more suitable for higher wear applications.
With 3 times the strength of aluminum and 2.3 times the stiffness, ADI can replace aluminum at a weight savings. Increasing the strength of a component by using the austempering process allows for the utilization of thinner sections, effectively reducing the overall weight of products.
Enhancing the strength, durability, lightness, and wear resistance of a component can lead to a reduction in the required material for manufacturing. This, in turn, lowers the raw material costs associated that are needed for the component. Transitioning from expensive forging, welding, or fabricating processes to a more cost-effective casting operation can result in substantial savings in manufacturing expenses. It’s worth noting that irons and steels are considerably less costly materials compared to aluminum, magnesium, and other composite and plastic materials.
suitable steels for austempering
austempered cuctile 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) 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 for weight savings. ADI components are very competitive with steel forgings, castings, weldments, and aluminum forgings and castings.
Furthermore, austempered ductile iron (ADI) has found successful applications across many industries, including construction and mining, agriculture, automotive, heavy truck, and railroad.
- Timing gears
- CV joints
- Steering knuckles
- Sprockets, rollers, idlers
- Suspension housings and brackets
- Wear plates
- Wheel hubs
- Control arms
- Plow points
- Hitches
- Crankshafts
- Flanged shafts
austempered steel
Application of the austempering process to steel provides the user with a tough, high-strength component that resists embrittlement.
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.
- Mower blades
- Clips and clamps
- Cutter and mixer blades
- Transmission gears
- Wave plates
- Turf aeration tines
austempered gray iron (AGI)
AGI offers material with excellent dampening effects, strength, and wear resistance and can be used to make quieter components.
- 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.
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.
- Rasp bars
- Wear plates
- Plow points
- Digger teeth
- Tip holders
- Pump impellors
- Thrashing elements
- Hammers
- Internal tines
- Rollers
Carbo-Austempered™ steel
This process develops a tough, high-carbon, bainitic case on high performance components.
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.
- 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)
- Transmission shafts
- Output Shafts
- Pump Shafts
- Differential Pinions
- Spline Drives
- Parking Pawls.
Locally Austempered Ductile Iron (LADI™)
LADITM 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.
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frequently asked questions - austempering
Austempering is an isothermal heat treatment process that is used for ferrous materials. The precise control of process times and temperatures enables the creation of a microstructure that is stronger and tougher than that achievable with conventional heat treatment processes.
The special properties of an austempered material make it more wear-resistant than many competing materials. With a high surface hardness, the material has a robust wear surface. Embedded carbides and the austempered microstructure of carbide ADI make it a competitive wear material. Due to its high strength and toughness, austempered steels are better suited for applications with higher wear.
By increasing strength through the austempering process, thinner sections can be used in your components, resulting in a reduction in the weight of your products. Increasing the strength, robustness, lightness and higher wear resistance of components can reduce the amount of material required to manufacture products. Less material means lower raw material costs for components.
The process is technically not very difficult and is also economically feasible for large series in automated furnace systems.
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