The effect of graphite flake morphology on the thermal diffusivity of gray cast irons used for automotive brake discs

摘要

Thermal diffusivity of automotive grade SAEG3000(d) gray cast iron has been measured as a function ofgraphite flake morphology, chemical composition and temperatue.Cast iron samples used for this investigation were cut from "stepblock" castings designed to produce iron with different graphiteflake morphologies resulting from different cooling rates, sampleswere also machined from prototype and commercial brake rotors,as well as from a series of cast iron slugs with slightly varyingcompositions. Thermal diffusivity ws measured at room andelevated temperatures via the flash technique. Graphite flakemorphology of the various cast iron samples was quantifiedstereologically with image analysis techniques. Several geometricfeatures of the graphite flake morphology were quantified. It wasfound that the thermal diffusivity of these gray cast irons increaseswith carbon equivalent and has a strong linear correlation tographite flake length. For gray iron with the same chemicalcomposition, a four fold increase in the graphite flake size resultsin a 50% increase in thermal diffusivity. Amongst the commercialrotors, room temeprature thermal diffusivity varied from 0.156 to 0.200 cm2/s.