Compacted graphite iron

Cast iron with vermicular graphite also worm ( abgek. CGI ) is an iron -carbon cast material, the graphite formation is predominantly in vermicular form ( vermiculus = worms ). In English usage, the material as a Compacted Graphite Iron ( CGI abgek. ) is called.

General

Compacted graphite iron is used since the 1930s, it is characterized mainly by a favorable combination of tensile strength, toughness, damping, thermal conductivity, thermal shock resistance, machinability and castability. For these reasons, it takes a great proportion in the thermally loaded components of the combustion engine application, but also other applications are known.

Classification of grades

Compacted graphite cast iron according to EN 16079, which is also available as DIN standard and ISO 16112 standardized.

There is also a generally accepted in Germany VDG. Thereafter, the material grades according to the minimum tensile strength of 300, divided 350, 400, 450 and 500 N / mm ². The most often used CGI -300 ( 300 N / mm ² ), which is the only purely ferritic grade.

Properties

In general, one speaks of compacted graphite iron if at least 80 % are vermicular, the rest may be reproduced in ball form, but not present in lamellar form. However, higher ductile parts are perfectly permissible. The mechanical properties of compacted graphite iron lie between the properties of lamellar and nodular graphite.

Strength

Compacted graphite iron has a very marked 0.2 % proof stress. The strength is on average at least 50 % higher than that of cast iron with lamellar graphite, but is dependent on both the wall thickness and the silicon content.

Properties at elevated temperatures

Important application areas for compacted graphite iron are due to increased temperatures and especially by temperature changes stressed components. These fall out, for example, by internal and external oxidation, waxing, cracks and / or delay. Compacted graphite iron is here a favorable compromise between conflicting exposures; The fatigue strength and its ductility give the material is almost the same crack resistance as cast iron with nodular graphite, while it is thanks to lower modulus and higher thermal conductivity less warping.

Use

Compacted graphite iron is used in several areas. The main field of application is the diesel engine is: There is the case of ships, large engines, boats, commercial vehicles and high powered passenger car application. The weight saving to gray cast iron may be due to thinner wall thicknesses up to 15%.