‌Austempering:‌ ‌heat‌ ‌treatment‌ ‌of‌ ‌ductile iron‌

The Austempering heat treatment, which allows the production of cast parts in austempered ductile iron (ADI), has been our key strength for 30 years. Staff at Zanardi Fonderie performs heat treatments on cast parts in spheroidal graphite iron in a dedicated internal division equipped with hi-tech furnaces for the manufacture of austempered ductile irons ADI, ideal for the manufacture of lightweight, high-performing mechanical parts for use in on-road and off-road vehicles, industrial gear reducers, earth moving machinery and agricultural machinery. Thanks to the austempering heat treatment, it is possible to give the ductile iron mechanical properties comparable or superior to those of quenched and tempered steel, maintaining the typical lightness of ductile iron and its natural capacity to adapt to the manufacture of complex moulds.

Thanks to Zanardi Fonderie’s controlled process and technologically advanced plant, we perform austempering heat treatments in an environment completely isolated from the outside. After loading the treatment baskets and a pre-heating stage, they are inserted into one of our AFC Holcroft UBQA 36″ x 72″ x 36” furnaces. For each austempering heat treatment, our staff defines the times, treatment temperature, number of pieces per basket and their positioning based on the thickness of the casting, chemical analysis and desired ADI grade. Thanks to this procedure, it is possible to achieve and guarantee a constant, high-quality result.

The austempering heat treatment is broken down into two macro stages:

At the end of these two stages, which are strictly controlled, the austempered ductile iron ADI is obtained, a material with an ausferritic matrix. Ausferrite is a structure made up of graphite nodules immersed in a matrix formed by fine-grain acicular ferrite free of carbides and austenite.

Austempered ductile iron is essentially a spheroidal graphite iron enriched with certain alloying elements, mainly copper, nickel and molybdenum. The alloying elements are essential in transforming the matrix and hardenability of the component, which as the thickness increases – in the absence of alloying elements – becomes more and more difficult to harden “to the core”. The temperatures and cycle times are therefore adapted and regulated based on the desired ADI grade, the thickness of the part being treated and alloying element content.

The austempering process applied to a spheroidal graphite iron casting suitably enriched by alloying elements (copper, nickel and molybdenum), therefore leads to the development of a casting in austempered ductile iron, otherwise known as ADI. ADI – which in its various grades maintains the lightness typical of ductile iron and lends to the easy moulding of complex design shapes – is a material with superior mechanical properties with respect to those of classic spheroidal graphite iron, and comparable or superior to those of quenched and tempered steel.