The Difference between Cast Iron and Ductile Iron
Some customers of our dandong foundry asked us about the
difference between cast iron and ductile iron, including their
advantages and disadvantages. Herein, we listed their main
properties and hope to give you a reference for material selection.
Actually, before comparison, we need to clarify a definition. The
cast iron is meaning a category of iron material, whose carbon
content is higher than 2.1%. Therefore, it includes many different
types according to different graphite shapes and microstructures,
such as grey iron,
ductile iron, white iron,
vermicular iron, austenitic iron etc.
Therefore, strictly speaking, you can not compare cast iron with
ductile iron, because ductile iron is just a type of cast iron.
However, on the drawings, you may find the material requirements
just written as "Cast Iron", and no other requirements. Under this
circumstances, according to our experience, the designer's meaning
was "grey iron".
Why we say so? Because grey iron is the most common cast iron
material, and its production cost is the lowest one compared with
all other cast iron materials. So, if the customers just required to
use "cast iron", then the grey iron will be the best choice.
Ok, so let us compare ductile iron with all other cast irons.
Ductile iron is also very common and good material worldwide. It has
the following advantages:
1. Mature production technology.
Many iron foundries could produce ductile iron very well, their
physical properties could be controlled strictly. Grey iron also has
this advantages, most of iron foundries could produce grey iron very
well too, but as for other cast iron materials, not many foundries
could produce them.
2. Low prices.
Prices are always an important issues for customers. Ductile iron
just needs some extra nodular agent materials than grey iron, so its
production costs are only some higher than cheapest grey iron, but
far lower than malleable iron and austenitic iron. This is also the
main reason why ductile iron is replacing malleable iron. Refer to
3. Excellent mechanical properties.
Ductile iron has some good mechanical properties than other cast
irons. For example, its highest tensile strength could reach 900 Mpa,
the largest elongation could reach 18%, moreover, its has good
impact property, even good impact property in low temperature
condition. Moreover, after suitable heat treatment, its physical
properties could be improved significantly.
No any material is perfect, ductile iron also has some
1. Comparatively high production costs.
Although we said ductile iron is not expensive, its prices are not
the lowest. It is still more costly compared with grey iron, because
of extra spheroidizing agent alloys, and pig iron of high quality.
So, if grey iron can meet your requirements and application, then
you should not choose ductile iron.
2. Comparatively high requirements to quality control.
As for grey cast iron, the main inspection to material quality is
just tensile strength, only if you have special requirements to the
hardness. So, even the traditional cupola furnace could produce this
material very well.
However, ductile iron needs to inspect tensile strength, yield
strength, elongation, hardness, nodular rate (spheroidization rate).
Therefore, it requires the ductile casting manufacturers to have
enough experience and equipments to produce the castings, and
inspect their quality in-house.
3. Can not meet some special physical requirements.
Although ductile iron has excellent mechanical properties, but it
can not cover all aspects. For example, compared with ductile iron,
grey cast iron has better resistance to deformation during heating,
so most stove and boiler parts were made by grey iron. Moreover, as
for some alloy irons, they will have better properties, such as
anti-heating, wear-resisting, corrosion-resisting. Malleable iron
has better ductility, and austenitic iron has higher tensile
Herein, let us briefly introduce the main differences between
ductile iron and grey iron.
Ductile iron has higher tensile
strength, yield strength and elongation.
Grey iron has lower prices, and
easier to be produced.