On 19 Aug 2016 01:30:46 GMT, "DoN. Nichols" <
BPdnic...@d-and-d.com>
wrote:
Different Types Of Cast Iron
Cast iron is a ferrous alloy that is made by re-melting pig iron in a
capola furnace until it liquefies. The molten iron is poured into
molds or casts to produce casting iron products of the required
dimensions. Based on the application of cast iron, the alloying
elements added to the furnace differ. The commonly added alloy
elements are carbon followed by silicon. The other alloying elements
added are chromium, molybdenum, copper, titanium, vanadium, etc.
How is cast iron classified?
Based on the alloying elements added, the variation in the
solidification of the cast iron and heat treatment used, the
microstructure of the cast iron can vary. Depending upon the
application and the preferred mechanical properties, iron castings can
be classified into the following.
Types of cast iron
White cast iron
When the white cast iron is fractured, white coloured cracks are seen
throughout because of the presence of carbide impurities. White cast
iron is hard but brittle. It has lower silicon content and low melting
point. The carbon present in the white cast iron precipitates and
forms large particles that increase the hardness of the cast iron. It
is abrasive resistant as well as cost-effective making them useful in
various applications like lifter bars and shell liners in grinding
mills, wear surfaces of pumps, balls and rings of coal pulverisers,
etc.
Grey cast iron
Grey is the most versatile and widely used cast iron. The presence of
carbon leads to formation of graphite flakes that does not allow
cracks to pass through, when the material breaks. Instead, as the
material breaks the graphite initiates numerous new cracks. The
fractured cast iron is greyish in colour, which also gives it the
name. The graphite flakes make the grey cast iron exhibit low shock
resistance. They also lack elasticity and have low tensile strength.
However, the graphite fakes gives the cast iron excellent
machinability, damping features as well as good lubricating properties
making them useful in many industrial applications. The graphite
microstructure of the cast iron has a matrix that consists of ferrite,
pearlite or a combination of two. The molten grey iron has greater
fluidity and they expand well during the solidification or freezing of
cast iron. This has made them useful in industries like agriculture,
automobile, textile mills, etc.
Malleable cast iron
Malleable cast iron is basically white iron that undergoes heat
treatment to convert the carbide into graphite. The resultant cast
iron has properties that vary from both grey and white cast iron. In
case of malleable cast iron, the graphite structure is formed into
irregularly shaped spheroidal particles rather than flakes that are
usually present in gray cast iron. This make the malleable cast iron
behave like low-carbon steel. There is considerable shrinkage that
results in reduced production of cast iron as well increased costs.
Malleable cast iron can be identified easily by the blunt boundaries.
Ductile cast iron
Ductile cast iron is yet another type of ferrous alloy that is used as
an engineering material in many applications. To produce ductile iron,
small amount of magnesium is added to the molten iron, which alters
the graphite structure that is formed. The magnesium reacts with
oxygen and sulphur in the molten iron leading to nodule shaped
graphite that has earned them the name-nodular cast iron. Like
malleable iron, ductile iron is flexible and exhibits a linear stress
strain relation. It can be casted in varied sizes and into varying
thickness.