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The influence of graphite shape, pearlite content and chemical composition have been investigated to determine their effect on the machinability of compacted graphite iron (CGI). In the comparison to gray iron, the reduced sulfur content of CGI prevents the beneficial formation of a protective manganese sulfide layer on the cutting insert. This accounts for much of the difference in tool life during high speed continuous cutting. Beyond this critical mechanism, the machinability of CGI can be optimized by providing a consistent, low nodularity microstructure with a minimum of tramp elements such as titanium and chromium that form abrasive inclusions.

The demands for improved fuel economy, performance and emissions continue to pose challenges for engine designers and the materials they choose. The present paper provides a review of the properties of Compacted Graphite Iron (CGI), gray cast iron and aluminum and shows how the superior mechanical properties of CGI can contribute to engine design and performance. Based on production experience in Europe, Asia and the Americas, the application of CGI can provide new opportunities for reductions in engine weight and package size, increased specific performance together with improved durability, and improved NVH. Despite the density difference between CGI and aluminum, the ability to make a more compact cylinder block when using CGI often results in a fully assembled CGI engines that weigh less than an aluminum engines of the same displacement. This design opportunity is illustrated with specific examples of V6 and V8 diesel engines that are currently in production.

In comparison to aluminum, Compacted Graphite Iron (CGI) iron has superior mechanical properties, enables the use of parent bore running surfaces and fracture split main bearings, and provides advantageous NVH, package size, cost, and manufacturing CO2 profiles. Despite these advantages, aluminum blocks have leveraged density, and therefore weight, differentials to make considerable gains in the small, in-line passenger vehicle sector over the last 30 years. In order to demonstrate the potential benefits of CGI for small, in-line spark-ignition engines, the present study converted the cylinder block of a series production 1.2 litre three-cylinder engine from aluminum to CGI. Leveraging a novel design concept, with the running surface and load path constructed from high-strength CGI and the outer crankcase housing fabricated from durable, lightweight plastic, the assembled cylinder block achieved the same weight as the original aluminum block.