Compacted graphite irons (CGI)

The original morphology of vermicular graphite (GV), derived from the morphology of flake graphite, but without a marked notch effect at the end of the flakes, has been of interest to metallurgists since the 1980s.

This morphology suggests the material's original properties, which, depending on the intended use, can lead to significant advantages:

• tensile properties, modulus of elasticity, fatigue and impact resistance are significantly improved compared with lamellar graphite cast iron (GL);

• compared with spheroidal graphite cast iron (GS), better thermal conductivity and friction resistance, due to the interconnected graphite, are observed.

However, the reproducible production of vermicular graphite is particularly delicate, as it is intermediate between flake graphite and spheroidal graphite, the latter owing its greater ease of reliable industrial production to a fairly wide permitted range of residual magnesium.

What's more, machining has long been a major obstacle to industrialization, particularly in large-scale automotive production.

Today, all the progress we've made enables us to manufacture products in large series:

• control and reproducibility of the structures required for use on raw parts,

• machining under proper industrial conditions, thanks to advances in both tooling and cutting conditions.

The aim of this article is to describe the production and metallurgical properties of vermicular graphite cast iron, as well as its initial industrial applications. The quest for lighter weight in cars and trucks is leading to rapid growth in the use of this cast iron.