Austempered ductile iron castings, (or ADI castings) are ductile iron castings processed by a special heat treatment. The austempering process results in ductile. Austempered Ductile Iron (ADI) represents an alternative solution for the manufacturing of the housing of small planetary gearboxes, with the gear teeth obtained. Heat treated Ductile Iron with austenitic-ferritic matrix (ADI) has a high potential for the substitution of forged steel and conventional Ductile Iron. Advantages of.

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While greatly enhancing the properties of a conventional Ductile Iron casting, the ADI process cannot compensate for casting defects that would impair mechanical properties.

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To assure quality, ADI should be purchased from casting and heat treatment suppliers that have well developed process control systems who can demonstrate that they are consistently capable of producing high quality castings and heat treatments. To avoid problems caused by notch sensitivity, components with sharp corners should be redesigned to provide generous fillets and radii. Typical austempering process parameters applied to an unsuitable material will not result in the formation of austemperig or ausferrite and thus the final product will not be called austempered.

These relationships result in an endurance iroj ratio of fatigue strength to tensile strength that is 0. The BCIRA data asutempering a relatively fast quench while the Dorazil data reflects an austempering bath with a lower quench severity. The quench and holding temperature are primary processing parameters that control the final hardness, and thus properties of the material.

The austenitizing may be accomplished by using a high temperature salt bath, an atmosphere furnace or in special cases a localized austemperkng such as flame or induction heating.

Tempered martensitic matrices may be developed for wear resistance, but lack the ductility of either as-cast Ductile Iron or ADI. The transformation is isothermal and takes place over a longer period of time as compared to martensitic transformation, hence this component of distortion caused by quenching is lower.

However, this processing sequence is limited by the machinability of the different grades of ADI.

This transformation, which gives ADI its remarkable wear resistance, is more than mere “work hardening”. This property, shown in Figures 4. In addition to being able to be applied to ducctile areas of a part, peening also offers the advantage of increasing surface hardness without detrimentally affecting the ductility and strength of the remainder of the component. Austemperin, through relatively simple control of the austempering conditions ADI can be given a range of properties unequaled by any other material.


Austempered Ductile Iron (ADI)

When subjected to surface treatments such as rolling, peening or machining after heat treatment, the fatigue strength rion ADI is increased significantly. Post peening surface treatments such as honing may be required to reduce surface roughness in parts subjected to rolling contact fatigue.

The properties of ADI are due to its unique matrix of acicular ferrite and carbon stabilized austenite; called Ausferrite. However, both tensile strength and ductility decrease as the molybdenum content is increased beyond that required for hardenability.

Fracture Toughness Traditionally, components have been designed on the basis of preventing failure by plastic deformation.

Single tooth fatigue tests conducted by the GRI on ADI gears indicated that shot peening doubled the fatigue strength. It is “retained” in the sense that it has persisted from the austenitizing treatment, but it is not the “retained austenite” irom designers and metallurgists equate with unstable, incorrectly heat treated steel. The sum total of these facts leads to a real advantage with ductioe to distortion of the final product when austempering is compared to a austrmpering quench and temper process.

This allows for faster machine feeds and speeds and greatly increased tool life. During this part of the process, the austenite isothermally transforms to bainite.

Typical steels that are austempered include: There are many properties needed for specific design applications that are not currently published. Numerous patents exist for specific methods and variations. The casting must be heat treated properly by a supplier capable of taking into account the interaction between casting dimensions, composition, microstructure and the desired properties in the austempered casting.

These components, which are usually thin, formed parts, do not require expensive alloys and generally possess better elastic properties than their tempered Martensite counterparts. The mechanical properties offered by ADI make it an attractive material for demanding applications in which strict specifications must be met consistently.

These materials are also not referred to as austempered. Construction and Mining Components This segment includes all manner of collets, ring carriers, wear plates, sprockets, covers, arms, knuckles, shafts, rollers, track components, tool holders, digger teeth, cutters, mill hammers, cams, sway bars, sleeves, pavement breaker bodies and heads, clevises, and conveyor components.


While annealing adds cost to the casting the benefits of more predictable dimensional change during austempering and greatly improved machinability often more than offset the cost of annealing. This is because carbon must diffuse out of the graphite until it has reached the equilibrium concentration dictated by the temperature and the phase diagram. Kurkinen, “Wear-resistant components in nodular cast iron.

Bessemer process Open hearth furnace Electric arc furnace Basic oxygen process.

Austempered Ductile Iron (ADI) – Applied Process

We have run austempering on alloys from through to ductile iron machined parts. As a result, heavier section components required greater hardenability. An assortment of ADI “ground engaging” parts. The use of high purity pig iron in the ADI charge offers the twin advantages of diluting the manganese in the steel scrap to desirable levels and controlling undesirable trace elements. Assorted ADI conveyor components. As a result, a Ductile Iron component austempered to produce a lower hardness displays an abrasion resistance greater than that predicted by its bulk hardness, provided that the abrasion mechanism involves sufficient deformation to transform the surface layers to martensite.

These compressive stresses inhibit crack formation and growth and produce significant improvements in the fatigue properties of ADI when it is machined after heat treatment or subjected to surface treatments such as shot peening, grinding or rolling.

One of the advantages that is common to all austempered materials is a lower rate of distortion than for quench and tempering. This increase in austenite content increases the hardness increment produced by surface deformation. This high strength ADI has lower fatigue strength as-austempered but it can be greatly improved with the proper rolling or grinding regimen.

Engines being developed by the automotive industry require weight reduction in parts that will be required to handle increased power.