Cast iron is the most numerous group of foundry iron alloys (Fe). These are, to be more precise, alloys of iron and carbon, in which the carbon content is above 2%, with a maximum content ranging from 3.8% to 6.7%. Today we will discuss another type of cast iron: a gray cast iron.
If you want to learn more about cast iron in general, its properties and applications, check out our article What are the differences between cast iron and cast steel?
Gray cast iron is an alloy of iron with lamellar graphite (EN-GJL). This alloy owes its name to the dark gray color occurring in the fracture, caused by the presence of graphite.
It is considered to be of higher quality than white cast iron, because it is more ductile, easier to machine, has good castability and has lower casting shrinkage (around 1.0%) than white cast iron.
A particular advantage of it is its economic nature: namely the low cost of production.
Gray cast iron is an alloy in which carbon is present in the so-called free form. Graphite, metallic matrix and added elements containing phosphorus and sulfur are the main components of the structure of gray cast irons.
The properties of gray cast irons are distinguished not only by the structure of the metallic matrix, but also by the form of graphite itself. We wrote about it in the article Ductile iron - properties, features and application.
Depending on the amount of bound carbon in gray cast iron, we divide them into:
Within the group of this alloys, its different grades are distinguished, being classified on the basis of tensile strength and ability to elongate, for example:
The basis for dividing cast irons into different classifications is their tensile strength. The compressive strength of this type of cast iron is about 4 times greater than the tensile strength, and the elongation does not exceed over 1%.
Good machinability and workability of this alloy allows it to be used for the production of castings with thin-walled contours, often distinguished by a complicated form.
Its greatest advantages are:
However, it has lower resistance to corrosion and abrasion than, for example, ductile iron.
We have summarized the advantages and disadvantages of this alloy in the following table:
advantages | disadvantages |
good machinability | it is not very plastic, has low bending and tensile strength |
helps dampen vibrations | low strength |
it increases sliding properties | low resistance to abrasion and corrosion in chemical enviroment |
improves fatigue strength | worse mechanical properties than ductile iron |
has good compressive strength | |
low production cost |
It is used in various environments, which are amongst others:
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