Examination of microstructure of nodular cast iron

Full text

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Khulna University of Engineering and Technology
Department of Materials Science and Engineering
Course Code
MSE 2206
Course Title
Compositional and Microstructure Analysis
Sessional 07
Examination of microstructure of nodular cast iron
Submitted by
Name: Rifat Rafiu
Department: Materials Science and Engineering
Roll: 2027045
Group: B-3
Year: 2nd
Term: 2nd
Date of Performance 10 October, 2023
Date of Submission 17 October, 2023

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Objectives
After performing this experiment, we will be able to learn:
1. Examine the microstructure of nodular cast iron.
2. Investigate different phases present in the microstructure of nodular cast iron.
3. Learn about the properties of these intermetallic phases.
Introduction
Nodular cast iron, also known as ductile iron or nodular iron, is a versatile and widely used
engineering material with remarkable properties that make it an essential component in various
industries. This alloy, characterized by its unique microstructure and mechanical properties, is
the result of a sophisticated metallurgical process that has revolutionized the world of cast iron.
Nodular cast iron is an alloy of iron, carbon, and small amounts of other alloying elements such
as silicon and magnesium. The key features of the microstructure of nodular cast iron include:
1. Spheroidal Graphite: The graphite in nodular cast iron is present in the form of small,
spherical nodules rather than the flake-like graphite found in gray cast iron. This
spherical shape gives the material its improved properties and greater ductility.
2. Ferrite: The matrix of nodular cast iron contains a significant amount of ferrite, which
is a metallic phase with a body-centered cubic crystal structure. Ferrite contributes to
the ductility and toughness of the material.
3. Pearlite: In addition to ferrite, there is often some pearlite in the microstructure. Pearlite
is a lamellar structure composed of alternating layers of cementite (iron carbide) and
ferrite. It provides strength to the material.
One of the most notable advantages of nodular cast iron is its outstanding ductility, making it
highly resistant to fracturing. This characteristic makes it a preferred choice for components
that require a combination of high strength and the ability to withstand impact and shock loads.
Common applications include engine blocks, pipe fittings, hydraulic components, and various
automotive and industrial parts.
Nodular cast iron's excellent resistance to wear and corrosion further enhances its suitability
for various demanding environments. This is particularly important in industries such as
mining, construction, and agriculture, where components are subjected to abrasive forces and
exposure to harsh chemicals. Furthermore, nodular cast iron exhibits good machinability,

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which simplifies the manufacturing process and helps reduce production costs. This material
can be easily cast into complex shapes and precision-machined to meet specific design
requirements, making it a cost-effective solution for a wide range of engineering applications.
Another noteworthy feature is nodular cast iron's thermal conductivity, which is higher than
that of steel. This property makes it an excellent choice for applications where efficient heat
dissipation is crucial, such as in engine cylinder heads and brake components.
In addition to its mechanical and thermal properties, nodular cast iron also offers good vibration
damping characteristics. This feature is particularly valuable in applications where the
reduction of noise and vibration is essential, such as in the automotive and construction
industries.
Experimental equipment
1. Nodular cast iron specimen.
2. Emery papers (Grade-120, Grade-220, Grade-400, Grade-500, Grade-600, Grade-
800, Grade1000, Grade-1200 and Grade-1500)
3. Polishing machine
4. Tissue paper
5. Watch glass
6. Optical microscope
7. Chemical solution:
• Al2O3 powder for polishing
• Distilled water
• Etching reagents: Nital solution (2%HNO3 + 98% C2H5OH)
Experimental procedure
1.Sectioning:
An already sectioned nodular cast iron specimen had been collected from the
laboratory.
2. Grinding:

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a. The sectioned specimen was first cleaned, and emery paper was used to begin the
grinding process.
b. The specimen was forcefully gripped and rubbed on Grade-120 emery paper in a
certain direction.
c. Cleaning was performed, and the process was switched to Grade-220 emery sheets
once the rough surface had become flat.
d. The specimen was rotated 90 degrees from its previous direction above while
switching from Grade-120 to Grade-220 emery paper.
e. This method was continued with Grade-400, Grade-500, Grade-600, Grade-800,
Grade1000, Grade-1200 and Grade-1500 emery paper until a flat, smooth surface was
found
.3. Polishing:
a. After grinding, the specimen was cleaned with distilled water and dried properly.
b. Al2O3 powder was applied on the belt of the wheel and the motor was started at
about 366 rpm.
c. The specimen was placed on the rotating wheel perpendicular to the previous
alignment.
d. After about 20-25 minutes of polishing, unnecessary scratch was removed and finally
a mirror like flat smooth surface was found and then it was ready for etching.
4. Etching:
a. 2% Nital solution was prepared for etching by mixing 2%HNO3 and 98% C2H5OH.
b. The specimen was kept inside the solution for 1-2 sec approximately while dipping
it for 2-3 times.
c. It was cleaned instantly after removing from the etching reagent.
d. To remove extra water acetone was used and the specimen was dried.

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e. It was made ready for revealing the microstructure of the specimen via optical
microscope at 200X zoom
. (a) (b) (c)
Fig 1: Scheme of specimen- (a)before grinding (b)after grinding (c)after polishing
Microscopy
1. The specimen was placed on the optical microscope.
2. The lenses were adjusted to find a clear image.
3. Microstructure of the metal was found.
Graphite
Pearlite
Ferrite
(a)

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(b)
Fig 2: Microstructure of nodular cast iron (a)200x(b)400x[Ferrite- white region, Pearlite-
blackish region, Graphite-spherical black nodule]
Result and Discussion
In this experiment, upon careful microstructural analysis, we have visualized
• The microstructure of nodular cast iron is characterized by the presence of graphite
nodules in a ferrite matrix.
• The graphite in nodular cast iron is present in the form of small, spherical nodules. The
nodules are responsible for its excellent combination of strength, ductility, and
toughness.
• In the microstructure a small amount of pearlite is also observed.The reason behind the
growth of pearlite during isothermal holding after austenitization and quenching to a
temperature where pearlite could nucleate and grow.
Graphite
Ferrite
Pearlite

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Conclusion
In conclusion, the experiment on the microstructure of nodular cast iron provides
• Nodular cast iron's microstructure, characterized by spherical graphite nodules within
an iron matrix, sets it apart as a unique engineering material.
• This microstructure imparts outstanding mechanical properties, including high strength,
ductility, and toughness, while also providing resistance to crack propagation and
excellent thermal conductivity.
• Nodular cast iron finds wide-ranging applications across multiple industries, making it
a vital and versatile material for various engineering needs. Its continued development
and adaptation in response to specific industrial requirements ensure its continued
relevance in modern manufacturing and construction processes.
Reference
[1] Ramesh Singh, "Applied Welding Engineering (Third Edition)" Publisher, 2020
[2] R. B. Johnson and K. L. Martinez, "Advances in Metallographic Techniques," Journal of
Materials Science, vol. 45, no. 7, pp. 1234-1256, Jul. 2018