Spheroidal-graphite cast iron as an engineering material: Properties and applications

Abstract

Spheroidal-graphite cast iron is a fairly new material characterized by high strength, toughness and good casting and machining qualities. The mechanical properties of the conventional types of cast iron containing flake graphite are considerably improved when the graphite is present in spheroidal form, and spheroidal-graphite cast iron can today be produced with strength figures up to 60 kg/mm² and even over 100 kg/mm² after heat treatment. Quite apart from this gain in strength, the presence of the graphite in spheroidal form also has a favourable influence on other properties, such as elongation, modulus of elasticity, notch toughness, wearing qualities and thermal and chemical resistance. Since the failure of most components in service is due to fatigue, the high endurance strength of S.G. cast iron as compared with ordinary cast iron is particularly important. Its low notch sensitivity also reduces the effect of local stress concentrations.

Because of its comparatively low solidification temperature, S.G. cast iron is likewise very suitable for complicated, thin-walled and highly stressed cast components.

There are hardly any restrictions on the size and weight of S.G.-iron castings, and the Sulzer foundries are able to supply castings of this material weighing anything from a few grams up to about 30 tons.

The addition of alloying constituents has led to the development of new types of S.G. iron with special properties, such as high resistance to corrosion and thermal and volumetric stability, the S.G. irons being much superior in these respects to alloy cast irons containing flake graphite.

The properties of S.G. iron make it extremely versatile, so that it may be regarded as filling the gap between grey cast iron and steel.