The basics of the austempering process

• Austempering heat treatment
• Austempering systems
• Austempered ductile iron ADI
• Isothermal ductile iron IDI

The heat treatment of austempering makes it possible to obtain different types of austempered materials, of which austempered ductile irons (ADI) are the best-known example. It is possible to perform the process with heat treatment plants able to avoid the formation of martensite and pearlite.

Austempering is a heat treatment applicable to ferrous alloys, characterised by the fact that the material, after being partially or completely austenitized, is quenched in a bath of molten salts to avoid pearlitic transformation and transforming austenite at temperatures higher than martensite start, to obtain bainite in steels and ausferrite in cast irons.

Austempering plants allow a structural transformation of ferrous materials that avoids the formation of martensite and pearlite.

The various plant configurations and their sizing, together with the chemical composition and quality of the base material, have decisive effects on the quality of the material obtained and on the repeatability of the process.

Thanks to the heat treatment of austempering, the rough ferrous as cast matrix, consisting of alpha iron grains (ferrite/pearlite), is transformed into a matrix consisting of alpha iron in acicular form (Widmastätten ferrite) and gamma iron (austenite), obtaining different material properties and advantageous opportunities for use in mechanical components.

Isothermed ductile iron (IDI) is obtained by austenisation in the intercritical interval. This peculiarity causes a transformation of austenite into pearlite, which is characterised by a lower sensitivity to thickness and a favourable interconnection with the ferritic phase, thanks to the reduced mobility of carbon due to the fast cooling.