Forming carbon from iron

During deformation of austempered ductile iron the carbon can be squeezed out of the material. This carbon is present as nodules of graphite, what is probably happening is that the carbon nodules migrate to the surface, allowing the volume to be reduced in response to the loading.

Another possibility is that carbon is dissolved into the iron and then nucleates and grows sheets on the surface. That seems less likely.

At high temperatures the mostly likely thing to happen would be that carbon on the surface would oxides and form CO gas and be liberated.

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Dyanamic test austempered ductile iron

Drs Dawid Myszka, A. Wieczorek and Tadeusz Cybula from the Warsaw University of Technology, Poland investigated the influence of microstructure on the dynamic mechanical properties of austempered ductile iron using Taylor impact testing. Austempered dictile iron means it’s a cast iron, so has graphite particles in a matrix heat treated to become bainite!. Taylor impact testing means you fire cylinders of the material at an immovable object and see how the material gets squished.

Deforming Austempered Ductile Iron

Shattering Austempered Ductile Iron

The heavily deformed volume which faced the impact has resulted in hardening and in transformation to martensite — both hardness and magnetic measurements have been used. Hardening was due to mostly strain induced austenite-to-martensite transformation, and also due to cold-work.

References
D. Myszka, L. Cybula and A. Wievzorek
Influence of heat treatment conditions on microstructure and mechanical properties of austempered ductile iron after dynamic deformation test
Archives of Metallurgy and Materials
V59, Issue 3, 2014

DOI:10.2478/amm-2014-0204