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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.
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.
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.
The Austempering Process
Austempering starts the same way. 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 Means Uniform Structure
Martensite forms immediately on quenching when the Martensite Start temperature is reached; resulting in a fully transformed surface while the center of a component is still red hot. At a later time, when the inside transforms to Martensite and wants to expand, the already transformed surface constrains the center. Residual stresses form that are relieved by either a shape distortion or cracking if the stresses exceed the UTS of the material.
In contrast, the Austempering process that produces Ausferrite or Bainite takes place over many minutes or hours. This uniform transformation results in less distortion and no quench cracking.