=Paper=
{{Paper
|id=Vol-2744/short38
|storemode=property
|title=Using Computer Microscopy Methods to Control the Microstructure of Malleable Cast Iron Product with Spherical Graphite (short paper)
|pdfUrl=https://ceur-ws.org/Vol-2744/short38.pdf
|volume=Vol-2744
|authors=Konstantin Makarenko,Alexander Nikitin,Alexander Vdovin,Ekaterina Zentsova
}}
==Using Computer Microscopy Methods to Control the Microstructure of Malleable Cast Iron Product with Spherical Graphite (short paper)==
https://ceur-ws.org/Vol-2744/short38.pdf
Using Computer Microscopy Methods to Control the
Microstructure of Malleable Cast Iron Product with
Spherical Graphite*
Konstantin Makarenko[0000-0002-7195-0500], Alexander Nikitin[0000-0003-1891-5033],
Alexander Vdovin[0000-0002-6014-0043], and Ekaterina Zentsova[0000-0003-1513-3271]
Bryansk State Technical University, Bryansk, Russian Federation1
makkon1@yandex.ru
zzzalexzzz95@gmail.com
vdovin.alexander.v@yandex.ru
kopilka.32@mail.ru
Abstract. The method of identification of objects on images of the microstruc-
ture of cast iron with spherical graphite of the correct shape with uniform distri-
bution is presented. Morphological analysis techniques were used to identify
shrinkage pores and graphite inclusions in microstructure images. Geometric fea-
tures of the shape of graphite inclusions were used as methods for identifying
graphite, in particular, particle size analysis, which is widely used to identify var-
ious objects in computer microscopy. The computer analysis of the image was
performed with the program ImageJ. To determine the pores against the back-
ground of graphite inclusions, two characteristics were used - the shape and size
of the objects themselves. The pores, presented on the image, differ from graphite
inclusions by a complex, fractal border and comparatively large areas. For the
visualization of the research results, the combination of the graphite part with the
calculation and analytical part was used. Such presentation of the results is the
most significant and allows to perform the most correct evaluation of the graph-
itized cast iron microstructure in accordance with GOST 3443-87.
Keywords: Computer Microscopy, Microstructure, Metallography, Image, Cast
Iron, Graphite, Pores.
Copyright © 2020 for this paper by its authors. Use permitted under Creative Commons License
Attribution 4.0 International (CC BY 4.0).
* Publication financially supported by RFBR grant №20-01-00547
2 K.Makarenko, A.Nikitin, A.Vdovin, E.Zentsova
1 Introduction
The modern methods of computer microscopy allow you with a high degree of ade-
quacy, mathematically, to describe the main dimensional and topological characteris-
tics of the structure of constructional materials. The data, obtained in the result of such
analysis can be used for the description and construction of mathematical models, eval-
uating the relationship “structure-properties”. Using the modern methods for pro-
cessing large data arrays, accumulated in the course of numerous researches, it becomes
possible to create the predictive models of managing the technology for obtaining prod-
ucts, in order to ensure the presence of the specified properties in them, directly from
the cast state [1, 2].
The modern methods of the identification of graphitized cast iron structure use dif-
ferent approaches to identify dimensional and topological parameters of the structure.
The significant influence on the properties of graphitized cast irons comes from such
parameters as distribution and shape of graphite inclusions. These characteristics are
difficult to describe objects and different researchers use different methods of their
identification. For example, in the work [3], the method of the study of graphite phase
distribution in the amount of cast iron is presented, it uses the most accurate technique
of synchrotron mathematical tomography. The method allows you to visualize the dis-
tribution of the basic phases, particularly, graphite inclusions in the amount of cast iron.
Such method, however, in spite of high adequacy of the obtained results, was not widely
used due to the limited usage of this class research equipment in the world practice.
Most frequently used methods of the study of dimensional and topological characteris-
tics of cast irons are the methods of computer microscopy for structure images, obtained
on modern digital optical microscopes [4-9]. It is connected with a wide introduction
into the production of digital microscopes, allowing not only to perform photo- and
video-fixation of the studied materials’ structures, but also to describe mathematically
the studied objects.
The purpose of this work is to develop the technique of identification for objects of
the types of pores and gas inclusions for the development of the technology, managing
cast iron structure and for the obtaining products with the specified properties from cast
irons.
2 The Technique of the Conducting Research
As initial samples for the research, the cylindrical cast billets were taken, these pieces
are used in the production of the samples, designed to identify the cast iron mechanical
properties. Metallographic slots for the microscopic researches were obtained from the
upper parts of the billets. That is why, in the structure of cast iron, except the graphite
inclusions that are identified on the non-etched thin sections, there were the shrinkage
pores. The initial image of the microstructure of the studied cast iron is presented in the
Fig. 1.
To obtain the image of the cast iron microstructure, the digital complex, created on
the base of the inverted metallographic microscope Leica DM IRM, was used. As it
Using Computer Microscopy Methods to Control the Microstructure of Malleable… 3
was mentioned above, the study of the cast iron microstructure was performed on the
non-etched thin section.
On the microstructure image, there are two objects to be studied. The first one – the
pores, representing internal cavities that break the continuity of the material. The object
is referred to casting defects and is an undesirable artifact. The second object – the
graphite inclusions that are an indispensable part of the ductile cast iron structure. The
majority of mechanical properties of the product material depend on the graphite inclu-
sions’ shape, size and distribution.
Fig. 1. The image of the initial microstructure of cast iron samples, 100 (non-etched)
In metallography there is a problem of identification of such objects. Very often, even
experienced metallographs, not knowing the samples’ prehistory, cannot identify pores
and distinguish them on the studied thin section. The problem is compounded by the
fact that the graphite inclusions’ shape is a changeable and the main controlled param-
eter in graphitized cast irons. The ideal structure of ductile cast iron contains graphite
inclusions of a globular (it is more correctly, spherical) shape. But any deviation in the
modification technology and the chemical composition leads to degradation of the
graphite phase morphology and it degenerates into a vermicular graphite shape. A per-
functory study of the structure, presented in the Fig. 1, may give the wrong idea and the
pores can be identified in correctly as a degenerated, vermicular graphite shape.
Meanwhile, on the presented microstructure image, a number of features can be
identified, helping to perform the correct identification of objects. Firstly, it is a colour
4 K.Makarenko, A.Nikitin, A.Vdovin, E.Zentsova
scheme (or highlight the brightness level), the pores on the image have a darker (black)
tint than a graphite phase, characterized by a grey,” graphite” colour. This difference is
due to the peculiarities of getting images in the optical reflecting metallographic micro-
scope. When reflected from the pores, having a certain depth, the light beam is scat-
tered, that is the light rays, having got in this area, do not return to the microscope lens,
so the area containing the pores will be of a black colour. In the computer analysis of
the image, using a grey palette with the brightness gradations, you can select such color
range that will match the pores. As it follows from the previously presented explana-
tion, its values will adjoin the values of completely black colour. Secondly, you can use
the geometrical peculiarities of the graphite inclusions’ shapes in ductile cast irons. For
these purposes, you can use the granulometric analysis, widely applied for the identifi-
cation of different objects in the computer microscopy. To identify the pores on the
graphite inclusions’ background, two features are used – directly a shape and sizes of
the objects. The pores, presented on the image, differ from graphite inclusions by a
complex, fractal border and comparatively large areas.
It was the second approach that was used in this work to identify the undesirable
artifacts on the image of the ductile cast iron microstructure.
The computer analysis of the image was performed with the program ImageJ.
3 The Research Results
In this part, the separate stages of the analysis of the initial image of the ductile cast
iron microstructure, made to identify the shrinkage pores on the graphite phase back-
ground, are presented. Taking into account the fact that the image quality was good, the
noise elimination was not performed. That is why, the first stage of the image pro-
cessing was the operation of the binarization. With this representation of the image, it
can be easily analyzed on the basis of counting pixels, occupied by certain objects. The
results of the image binarization are presented in the Fig. 2.
The following stage of the analysis included the segmentation of inclusions. The
segmentation allows to identify different objects on the basis of different distinctive
stereological and planar parameters. Given the fact that in ductile cast iron, in the thin
section plane, the graphite inclusions are in the shape of a circle, their identification on
the image simplifies. The Fig. 3 shows the results of selection of the graphite inclusions
of a circular shape on the background of the pores of much larger sizes and more com-
plex geometrical border morphology.
To identify an average area, occupied by the graphite phase, the previously seg-
mented image was divided into four identical parts (Fig. 4). Within each separate part,
the analysis of the area, occupied by graphite inclusions, to the area of the metal matrix,
was performed. The results of the researches are presented in the Fig.5 and in the Fig. 6.
Using Computer Microscopy Methods to Control the Microstructure of Malleable… 5
Fig. 2. The binary image of the studied cast iron microstructure
Fig. 3. The inclusions’ segmentation of the graphite inclusions (green colour)
and the shrinkage pores (lilac colour)
6 K.Makarenko, A.Nikitin, A.Vdovin, E.Zentsova
Fig. 4. The division of the image into four parts
Fig. 5. The ratio of the area, occupied by graphite, to the total area of the matrix material
The analysis of the graphite phase distribution on separate sections of the micro-
structure image allowed to identify the normal distribution of graphite inclusions in
ductile cast iron. The prevailing size of graphite inclusions for all parts of the image, in
pixels is in the range from 300 to 700 units.
Using Computer Microscopy Methods to Control the Microstructure of Malleable… 7
At the final stage, the results of the identification of the dimensional and topological
characteristics in the studied cast iron microstructure, were summarized. For the visu-
alization of the research results, the combination of the graphite part with the calcula-
tion and analytical part was used (Fig. 7). Such presentation of the results is the most
significant and allows to perform the most correct evaluation of the graphitized cast
iron microstructure in accordance with GOST 3443-87.
4 Conclusion
The presented method of the analysis of the graphitized cast iron images is available
for use only with the identification of the microstructure where the spherical graphite
inclusions are prevailed. In case of the simultaneous presence of the spherical and ver-
micular inclusions in the cast iron structure, their identification becomes difficult. In
this situation, it is necessary to use the method, based on the selecting the objects by
brightness (colour).
Fig. 6. The inclusions’ distribution by sizes in four studied frequent images
8 K.Makarenko, A.Nikitin, A.Vdovin, E.Zentsova
Fig. 7. The results of the analysis of the microstructure of the ductile cast iron sample with the
selection of the graphite inclusions and the shrinkage pores
However, from our point of view, the best results of the objects’ identification in the
graphitized cast irons, you can obtain, using the integrated approach, combining two
methods simultaneously
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