The austemper process offers benefits over the more conventional oil quench and temper method of heat treating products that requires the uppermost in distortion control. The process consists of quenching the part from the optimum austenitising temperature directly into a liquid salt bath at a temperature between 310°C to 375°C (above the temperature
Results in properties which exhibit less distortion show consistent hardness, exhibit higher impact and fatigue strengths and in some steels show increased resistance to hydrogen embrittlement.
Typical materials that can be treated:-
Austempering can be applied to thin sections of certain medium or high-carbon steels or to alloy containing steels of thicker section. The selection of the steel is based on the transformation characteristics. Important considerations are: the temperature at which martensite starts and the time required for transformation of austenite to bainite.
Austempered ductile iron (ADI)
ADI is a material produced through a unique heat treatment process. This process involves high temperature homogenisation of components followed by isothermal quenching into molten salt baths at elevated temperatures.
- ADI offers dimensional predictability.
- Components can be cast near nett shape.
- ADI offers a low relative cost per unit of yield strength.
As an alternative to steel castings, forgings, fabrications and even light alloys including aluminium, ADI offers worthwhile cost savings.
ADI is approx 10% lighter than steel.
Properties of ADI
Austemper treated irons combine strength, ductility, toughness and wear resistance. ADI offers such a combination of superior properties because it can be cast like any other member of the Ductile Iron family. The Austemper process produces mechanical properties that are superior to conventional ductile irons, aluminium and many cast and forged steels.
- ADI offers twice the strength of conventional ductile irons which can be achieved with similar levels of ductility.
- At a given hardness level, ADI can achieve equivalent tensile strength to that of steel.
- ADI offers excellent damping capacity, up to five times that of steel.
- ADI offers toughness and fatigue strengths that are equal to or better than cast or forged steels.
Unlike carburised steels that lose wear resistance as the carburised case is worn away, the wear resistance of austempered materials improves in service due to unique work hardening characteristics.
Typical materials which can be treated:-
To maximise the unique combination of properties, it is important that a nodular iron of good commercial quality is used.
Recents improvements in wear resistance have been seen with the introduction of Carbidic Austempered Ductile Iron (CADI) and by selectively induction hardening already Austempered irons.Like this page? Then Share it:
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