Development of mixed (ferrito-ausferritic) structures for spheroidal graphite irons
For years in the automotive industry the objective is to reduce the weight of components for well known car performance and environmental reasons. One way is to use more resistant materials for instance in the area of suspension foundry castings. Austempered Ductile Iron (ADI) is one of the most unique materials due to its particular mechanical properties.
Some tests have been made on chassis parts like front knuckles which have confirmed the good mechanical results obtained about the tensile strength and elongation. Nevertheless, the impact test results can be improved by some metallurgical structure evolution.
The combination of ferritization and ausferritization heat treatments for nodular SG irons should lead to a good compromise of characteristics between yield strength, elongation and impact test. The paper describes some of the works made according to this target acting on chemical and heat treatment parameters. Micrographic structures and mechanical properties obtained are shown. A comparison with existing ADI grades is established. Different structures and associated characteristics are described which allow to imagine a first orientation for chassis applications.
Making use of a dilatometer several tests have been runned to define properly the quality of the structures.