Metallography of a common carbon steel sample

University of La Sabana 24/02/2020

Leidy Lorena Bello Forero Felipe Galvis Mora, Javier Andres Lopez Martinez & Diego
Sebastian Varela Rodríguez.

Abstract: either quantitatively or qualitatively,

where it is sought to find the size of
This document provides information ab
the grains and percentages of each of
out the metallography made to a comm
the phases or to observe the
on carbon steelpart for further analysis
microstructure by determining the
through an inverted microscope finding
microconstituintes that compose it
its crystalline structure and mechanical
respectively.
and chemical further such as
conductivity and hardness to determine Materials & methods:
the possible usefulness of this material.
For this process a common carbon steel
Introduction: sheet was obtained (fig. 1), which due
to the way it was found had to be cut
Carbon steels are iron-carbon alloys.
and taken to an embedded (fig. 2) for
There are also simple carbon across,
later use in metallography.
which contain a quantity of carbon in
addition to Magnesium, Silicon, Sulfur
and Phosphorus. Common carbon
steels are classified according to the
amount of carbon you have as follows: Figure 1. Original
A low carbon steel contains amounts common carbón
less than 0.30% carbon, medium steel sheet
carbon steels have a carbon amount
between 0.30% and 0.60%, followed by
these are high carbon steels containing
above 0.60%, and finally those
containing more than 0.77% are called
tool steels, the practice that allows the
analysis of such metals is Figure 2. Embedded
metallography. [1] piece
Metallography is responsible for
studying the structural characteristics
in a microscopic manner of a metal or Later, In order to bring the metal
an alloy, and also for determining sample to its subsequent analysis, the
whether the conditions of such surface to be analyzed must be
material are suitable for the uses with prepared from that sample, this is done
which it was made; this can be done by sanding to the surface with different
sanding grains starting from a grain
larger using a 120 sandpaper rising the
number to a smaller grain 1200, until a
mirror-type surface is found (fig. 3).

Figure3. Embedded
piece with the mirror Figure 3. Microstructure of the carbon steel
sample.

When you have the mirror surface it is

necessary to add the reagent
(hydrochloric acid with nitric acid) to
reveal the structure of the material,
this has to be specific because not any
reagent fulfills the function, and this
process is known as etching.
Microscope analysis: After obtaining Figure 4. Microstructure of the carbon steel
the sample in optimal conditions, an sample zoom 1.
inverted microscope with different
lenses it’s used to reveal the grain
boundaries.

Result analysis:

First, it must be taken into account that

the sanding process was carried out Figure 5. Microstructure of the carbon steel
twice because in the first attempt, the sample zoom 2.
microstructures could not be observed
due to the scratches that appeared.
After sanding and performing the acid
attack for the second time, the
following results were obtained when
analyzed by the microscope. The
images are arranged as the zoom of the
lends used increases.

Figure 6. Microstructure of the carbon steel

sample zoom 3.
Figure 7. Microstructure of the carbon steel Figure 8. Ferrite micrograph. [3]
sample zoom 4.

In Figure 4 we can see a perlite

structure, in which ferrite and
cementite sheets can be identified, the
first being the one that can be
evidenced in greater quantity.
Figure 7 shows a ferrite structure,
which is also known as alpha iron, in
which the body-centered cubic
structure can be seen, although the Figure 9. Perlite micrograph. [4]
color of the polygonal grains is darker
Figures 8 and 9 show the
due to the concentration of cementite
microstructures of the two types of
in this type of steel.
structure found in medium carbon
According to these two types of steel, which we take as a reference in
structures found, the sample can be the literature to compare with those
classified as a medium carbon steel, obtained in our results.
which has an amount of carbon
between 0.2% and 0.5%. This
percentage changes depending on the
amount of ferrite and perlite that the
steel presents, as well as its properties
will be different.
This group of steels are known as
hypoeutectoid, the medium carbon
content refers to most commercial
steel.
Figure 10. Photomicrograph with 0,38%C
with a microstructure of ferrite and perlite.
[5]
In addition, in Figure 10, we find the References:
microstructure of a carbon steel sample
[1] Maldonado. J. (1996) Steels and
with 0,38% C, which we use to compare
their applications. Retrieved from:
with Figure 7 of our sample, in which
http://eprints.uanl.mx/421/1/1020118
we can analyze that we have a carbon
272.PDF
steel with a lower concentration,
because the distance between the [2] Belzunce, F. (2001) Steels and
polygonal grains is smaller. funditions: structures, transformations,
termic treatments and applications.
Among these types of steel we find the
Retrieved from:
references SAE 1020, 1035 and 1045.
https://aceroplatea.es/docs/document
o138.pdf

Conclusions: [3] G. A. Tierra Sani (2015). Automation

of the microstructural analysis of heat
 Based on the references treated steels through the use of
obtained after the analysis and labview, implemented in the heat
the comparisons that were treatment laboratory of the faculty of
taken into account or revision, It mechanics. B.S. thesis. Polytechnic
made possible to deduce the School of Chimborazo.
size and approximate
percentage of carbon present in [4] Microconstituyentes [Online].
our steel sample. Retrieved of:
 It was possible to confirmed the https://es.scribd.com/document/29674
reference an compisition on the 8318/microconstituyentes.
sample comparing with the one [5] Callister, W. (2002). Introduction to
was giving by the supplier. materials science and engineering.
 It was important to use the Reverté, vol. 1.
decoated reagent for the
material, as it allows for [6] Lozano, J. (2018). Metallographic
noticeable change in order to analysis of commercial steels for tools
observe the grains (structure) of in the city of Cuenca. Ecuador.
the material.
Acknownledgements:
With this project we were able to learn
how to determine and observe the
mechanical properties of a material
through metalogracific analasis;
obtaining the type of grain shown
under the inverted microscope. In
addition to this the collaboration by
FabLab staff who were able to help and
explain the different doubts and the
correct use of the equipment when
performing the procedure