Austempered Ductile Iron (ADI) / Isothermal Heat Treatment

  • ADI is a material produced through a specialised heat treatment process applied to a base ductile iron.
  • The ADI process involves high temperature homogenisation of components followed by isothermal quenching into molten salt baths at elevated temperatures, typically 240°C to 400°C.
  • The completed process results in isothermal transformation – Ausferrite in Austempered Ductile Iron and Austempered Grey Iron;   Bainite in steels.
  • ADI offers dimensional predictability and components can be cast near nett shape, offering a lower machining cost, lower heat treatment cost (than carburising or induction hardening), a higher degree of uniformity.
  • ADI is stronger per unit weight than aluminium, allowing economic material selection.
  • ADI offers twice the strength of many conventional ductile irons which can be achieved with similar levels of ductility.
  • At a given hardness level, ADI can achieve tensile strengths approaching those of steels.
  • ADI offers excellent damping capacity, up to five times that of steel.
  • ADI offers toughness and fatigue strengths that may equal or better cast or forged steels.
  • Unlike carburised steels that lose wear resistance as the carburised case is worn away, the wear resistance of austempered ductile iron materials improves in service due to unique work hardening characteristics.
  • To maximise the unique combination of properties, it is important that a nodular iron of good commercial quality is used.  We can advise on suitable base irons during design stage.
  • Recent improvements in wear resistance have been seen with the introduction of Carbidic Austempered Ductile Iron (CADI), requiring a special base iron, and by selectively induction hardening already Austempered irons.
  • Typical materials processed include SG cast iron, ASTM A897M and BS EN 1564.
  • Components up to 680mm in diameter and 1200mm long can be treated vertically using special jigging.
  • Weight up to 400Kg

James Menzies


Leonard Powell

Technical Planner

David Wright

Production Director

Mark Barron

Business Development Manager

Keighley Laboratories Ltd
Registered Office:
Croft House
South Street
West Yorkshire
BD21 1EG
Registered in England 164811
UK Tel: +44 (0)1535 664211

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