Physical Properties and Application of Austempered Gray Iron

By: B.V. Kovacs, J.R. Keough
Publication Date: January 01, 1993
Contact: John Keough
Document Type: White Papers

Mechanical and acoustical properties were determined in Class 20,30 and 40 gray irons in the as-cast condition and as austempered at 500, 600 and 700F (260, 316 and 371C).

The three classes of gray iron were obtained by varying the carbon and silicon content (carbon equivalent) and/or the inoculation. The variation in the other elements was unintentional. The variation of the graphite volume and morphology caused a significant difference in the microstructure, the mechanical properties and the acoustical properties in the tested irons.

Two acoustical paramters were measured: the resonant or natural frequency and the internal damping in the form of the logarithmic decrement. The dynamic (limit) elastic moduli were calculated from the resonant frequency data and were related to the various conditions in the irons.

Tensile strength, impact strength, elongation and hardness were determined as a function of the condition (microstructure and heat treat cycles) in the irons. It was determined that austempered gray iron has a unique combination of high strength and high damping. This combination makes austempered gray iron (AGI) applicable to parts in which high strength, high wear resistance and high vibration and/or sound damping is required.

Both the technical data and potential applications of AGI are discussed in this paper. A very good relationship was established between the acoustical and mechanical properties. Acoustical measurements offer a good technique for quality and/or process control.