Ferrous alloys are widely used due to their abundant natural resources, economical production processes, and versatility. There are several types of ferrous alloys including iron, steels, and cast irons. Cast irons contain 2.14-4.5% carbon and exist in gray, ductile, white, malleable, chilled, and alloyed forms depending on composition and microstructure. Impurities like carbon, silicon, sulfur, and phosphorus influence the properties and microstructure of cast iron.

1. C.Karthika
AP/Physics
Kongu Engineering Collecge
Types of cast iron &
Effect of impurities

2. Why ferrous alloys are widely used in large
amount?
Answer:
(1) iron-containing compounds exist in abundant quantities within the
earth’s crust
(2) produced using relatively economical extraction, refining, alloying, and
fabrication techniques
(3) ferrous alloys are extremely versatile- tailored to have a wide range of
mechanical and physical properties.
It is capable of creating any desired property by altering the microstructure
through surface hardening, heat treatment and deformation processing,
combined with other elemental alloying additions.

3. Types of ferrous alloys
1. Iron: less than 0.008 wt% C in α ferrite
at room temperature
2. Steels: 0.008 – 2.14 wt% C in α ferrite
and Fe3C at room temperature
3. Cast Iron: 2.14 – 4.5 wt % C

4. Cast Irons (C-2.1 - 4.5 %)
❖Generically, carbon content is above 2.14 wt%; in
practice, however, most cast irons contain between
3.0 and 4.5 wt% C and, in addition, other alloying
elements
❖Low melting pt -1150 and 1300ºC –
due to the presence of eutectic point.
❖Easily melted, good fluidity, low
shrinkage, very brittle and amenable
to casting

5. Types of cast iron
Classification based on- microstructure and heat treatment

6. Gray iron
❖ Typical composition
C - 2.5 -4.0 wt%
Si - 1.0 - 3.0 wt%
Mn – 0.4 – 1 wt %
S - 0.02 – 0.15 %
P – 0.15 -1 %
❖ mostly, the graphite exists in the form of flakes (similar to corn flakes),
which are normally surrounded by an ferrite or pearlite matrix.
❖ Because of these graphite flakes -gray appearance

7. ❖ Under tensile stress- weak and brittle in tension (the tips
of the graphite flakes are points of stress concentration)
❖ Under compressive load - high Strength and ductility
❖ High fluidity -easy to cast complex shapes
❖ Good thermal conductivity-cookware and brake rotors
❖ High resistance to wear
❖ Least expensive
❖ Low casting shrinkage
Gray iron -Property
❖ Effective in damping vibrational
energy-base structures for machines and
heavy equipment that are exposed to
vibrations are frequently constructed of this
material

8. ❖ pressure valve
❖ coupling plates
❖ break wheels
❖ gear,
❖ cams, crankshaft,
❖ flywheel
❖bushing, pipes,
❖cylinders
❖cookwares
Applications-Gray

9. Ductile (or Nodular) Iron
❖ Typical composition
C – 2.3 -3.4 wt%
Si – 0.6 wt%
Mg – 0.03 – 0.06 wt %
Mn – 0.4 wt%
P – 0.03 wt%
❖ Addition of small amount of Mg and/or cerium to the gray iron converts
graphite flakes to nodules or sphere like particles.
❖ The matrix phase surrounding these particles is either pearlite or ferrite,
depending on heat treatment, it is normally pearlite for an as cast piece.
However, a heat treatment for several hours at about 700ºC will yield a
ferrite matrix

10. ❖It has high strength, ductility and impact
strength (like steel) than gray iron – as
stress concentration flake tips are
eliminated.
❖It has high yield point.
❖It can be easily welded and galvanized.
Ductile iron -Property

11. Ductile iron- application
❖automotive industry
parts- crankshafts,
spindle, knuckles,
disc brake callipers,
gear, valves
❖ hydraulic cylinders
❖pump bodies
❖water pipe,
❖pipe fittings

12. White Iron
❖ Typical composition
C – 1.8 -3.6 wt%
Si - 0.5 – 2.0 wt%
Mn – 0.2 – 0.8 wt %
S - 0.06 – 0.2 %
P – 0.05 -0.2 %
❖ White cast typically has a lower carbon and silicon content, allowing for a
hard brittle carbide to form with no free graphite (Carbon exists as cementite
instead of graphite)
❖ Sudden cooling of molted cast iron produces white cast iron.
❖ A fracture surface of this alloy has a white appearance, and thus it is termed
white cast iron

13. ❖Due to of large amounts of the cementite
phase -Very hard and brittle- un machinable
(not used for structural materials)
❖High compressive strength but low resistance
to impact.
❖Use as intermediate to produce malleable cast
iron.
White iron -Property

14. White iron- application
❖ Very limited applications- Used only where wear resistance is
desirable, such as on the teeth of excavators, rollers in rolling mills.

15. Malleable cast iron
❖Malleable cast iron is white cast iron that has
been annealed - Heating white iron at temperatures between 800
and 900ºC for a prolonged time period and in a neutral atmosphere (to
prevent oxidation) causes a decomposition of the cementite, forming
graphite, which exists in the form of clusters or rosettes surrounded by
a ferrite or pearlite matrix, depending on cooling rate.
❖ Therefore, its composition is very similar to that of white
cast iron, with slightly higher amounts of carbon and
silicon

16. ❖The microstructure is similar to that of nodular iron
which accounts for relatively high strength and
appreciable ductility or malleability, less brittle, shock
resistant.
❖Applications include connecting rods, transmission
gears, and differential cases for the automotive
industry, and also flanges, pipe fittings, and valve parts
for railroad, marine, and other heavy-duty services

17. Chilled cast iron
❖Chilling- quick cooling
❖Outer surface of castings are chilled by
bringing them in contact with the cool sand.
❖So, it has a surface layer of white iron (hard
wear resistant) that was “chilled” during the
casting process; gray iron at interior regions,
which cool more slowly.
❖Used in making hard the
running surface of wheel
of a railway carriage and
casting of rolls.

18. Mottled cast iron
❖Intermediate between (mixture) gray and
white cast iron-shows mottled surface on
fracture.
❖Mottled structures should
be avoided –by increasing
(yields gray cast iron) or
decreasing (yields gray
cast iron) Carbon & Si
content because of bad
properties.

19. Alloy cast iron
❖Obtained by adding varying amount of -
Ni, Cr & Si
❖Ex:
Nickel cast iron – C-3.2%, Ni-1.5%, Si-
1.25%, Mn-0.7% -resistant to caustic
corrosion-used in making caustic pots, pipes

20. Effect of impurities on cast iron
⚫ Carbon (2-4%) – Exist in 2 forms
◦ Free form – Graphite (C) -Easily machineable, brittle & weak
◦ Combined form - Cementite (Fe3C) - hard
⚫ Silicon
Below 2.5% it promotes the formation of f graphite -
cast iron becomes soft.
Above 2.5% makes cast iron hard
⚫ Sulphur (0.02-0.15 % )
Promotes the formation of Fe3C – makes cast iron hard 7
brittle.
Accelerates the rate of solidification -defect blow hole
⚫ Manganese (0.5 – 1%)
minimize the effect of sulphur.
⚫ Phosphorus (1% max)
Promotes the formation of f graphite
Imparts the fluidity to molten cast iron.

21. Thank you………..