=Paper=
{{Paper
|id=Vol-2485/paper54
|storemode=property
|title=Visualization of the Phase Volume Distribution in Alloys
|pdfUrl=https://ceur-ws.org/Vol-2485/paper54.pdf
|volume=Vol-2485
|authors=Konstantin Makarenko,Sergey Kuzovov,Alexander Nikitin
}}
==Visualization of the Phase Volume Distribution in Alloys ==
https://ceur-ws.org/Vol-2485/paper54.pdf
Visualization of the Phase Volume Distribution in Alloys
Makarenko K.V., Kuzovov S.S., Nikitin A.A.
makkon1@yandex.ru| kss41188@inbox.ru|zzzalexzzz95@gmail.com
BSTU, Bryansk, Russian Federation
The method of obtaining the volume distribution of phases in structural materials is considered. The technique is based on the layer-
by-layer grinding of metallographic samples with photo fixation of microstructure images and the subsequent computer processing of
these images. An example of using the developed methodology to study the features of the volumetric distribution of graphite inclusions
in high-strength cast irons is presented. The classification of graphite inclusions depending on the shape, size and distribution features
is given. The study of the features of the distribution of graphite inclusions led to the conclusion about the patterns and mechanisms of
formation graphite phase in cast iron.
Keywords: visualization, tomography, volume distribution, phase, materials, cast iron, graphite.
investigated cast iron, % mass: 3.17 C; 3.3 S; 0.76 Mn, 0.06 P;
1. Introduction 0.03S; 0.05 Mg.
Cast iron was cast into sand and loam moulds for making
The methods of obtaining the idea about the volume
the castings of different shapes and blanks in the form of the
distribution of phases in different structural materials have
block of size 500x500x1000. From the blanks were obtained the
undergone considerable evolutionary development in recent
specimens for metallographic investigations, in the castings were
decades. Basic principles and approaches were laid down in
investigated the microstructure of special boss specimens and
the works by S.A.Saltykov [9]. The methods which were used
elements of pouring gate systems.
by stereometric metallography were characterized by high
Subsequent investigations of the volume distribution of
labor intensity and required from the researcher special
graphite inclusions were carried out on one specimen cut out
preparation and thorough execution of the developed methods.
from the blank, with the use of methods of optical tomography
However, the results which were obtained in the course of
(fig.1)
present investigation, widened considerably the idea
(conception) about the processes going in the materials, and
allowed to maintain important relations between their
structure and properties. For example, the works by K.P.Bunin
with his pupils [1], allowed to get the idea about morphology
of graphite inclusions in grey cast irons.
The wide introduction of computer methods of a) b) c)
processing the images simplified considerably the methods Fig.1. Stages of processing the images of the
and visualizations of phase volume distribution in alloys. microstructure of the high-strength cast iron:
However, the approaches remained the same. a) – initial image of microstructure x80;
At the present time an individual direction named as a b) – transformation to binary image of graphite
three-dimensional one [5,12,6] is developing intensely in the inclusions distribution in the plane of the metallographic
material science. As follows from the name, with such an specimen;
approach the structures of the described materials have a 3- c) – summation of binary images
dimensional (volume) image. Undoubtedly, such an approach
allows to obtain a more integral and realistic idea about the As reference points served the imprints of introduction of
structure of the materials and processes going in them the hardness tester indenter TK-2M in the surface layers of the
[11,3,4,2,8]. metallographic specimen. For obtaining the idea about volume
The main method which is used by the new direction in location of the graphite phase the layered machining was made
the material science is a computer computational tomography on the grinding-and-polishing machine-tool TIME PG-1000.
[7]. Tomography used in the material science, uses different The calculation of the depth of grinding was determined by the
physical processes and methods for investigation of internal change of the diameter of the harness tester indenter imprint
structure of materials: X-ray, magnetic-resonance, acoustic (fig.2). The diameter of the imprint was determined by means of
ones and a traditional one based on the mechanical layered the special eyepiece with the scale, for the graduation of which a
grinding the material with obtaining 2-dimensional images of reference object (micrometer) was used.
the structure and their subsequent summation and transition
to the volume representation [9].
In the present article the methods is presented based on the
latter approach of computer tomography. The developed
methods was used for the study of peculiarities of distribution
of the graphite phase in high-strength cast irons.
a) b) c)
2. Methods of Holding the Investigation Fig. 2. Methods of determination of the grinding depth:
a) – diagram of introduction of hardness tester
For the study of volume distribution of graphite phase in indenter and obtaining the imprint;
cast irons the cast iron was made in the production conditions of b) – photo of initial imprint of indenter on the surface
the cast iron workshop of the CJSC «UK BMZ». The specimens
of the investigated specimen;
were investigated from the cast iron which was produced by
means of induction melting in the furnace PVK-NK, based on c) – geometric diagram of determination of depth at
the remelting of conversion pig iron PVK-NK and steel С245. successive grinding of the specimen along the change of
As a carburizer, the graphitized coke breeze was used. indenter imprint diameter.
Inoculation was made in the ladle by the sandwich process, the
inoculant FeSiMg-7. The average chemical composition of the
Copyright © 2019 for this paper by its authors. Use permitted under Creative Commons License Attribution 4.0 International (CC BY 4.0).
Distribution of graphite was studied on the non-etched simultaneously and crystallized in the same conditions. In the cast
metallographic specimen with the help of the inverted iron structure the chains occur which are represented only by
metallographic microscope Nikon ECLIPSE MA 200 with small inclusions, or small inclusions are at the beginning (at the
magnification x80. The observed microstructure was fixed end) of the chain. It is explained by the fact that on the
with the help of the digital camera built into the microscope. metallographic specimens at the layered grinding the complete
The next processing of the obtained photos was made with the inclusion is not present wholly, but only the projections of the cut
help of program Above Photoshop and Image J. For obtaining (section) corresponding to the upper or lower part of the graphite
the image of volume distribution of graphite inclusions in the spheroid, cut by the plane of the metallographic specimen during
matrix of the cast iron was used the program module Image J, investigation. The observed chains do not have any generalizing
for rendering the volume images – the module Volume J. regularities in structure. By topological structure they form nuclear
complexes passing into each other which bifurcate and inosculate,
or grow (swell) in layers. Under the cell in this case the eutectic
3. Results of Investigations cell is meant.
Besides the spheroidal graphite, in the cast iron
The results of computer processing of the
microstructure are present inclusions of irregular compact shape.
microstructure are presented in fig.3. Unfortunately, such an
They have comparatively big sizes. It means that in the process of
image does not allow to evaluate fully the picture of volume
growth they do not lack in carbon. Such graphite, as a rule, is not
distribution of the graphite phase in cast irons, because
included into chains and is located in the microstructure apart
graphite inclusions on different levels obstruct each other.
(fig.4, a and b).
Location and shape of graphite inclusions of non-
spheroidal shape show that they appear at the final stage of
hardening the cast iron, in the conditions not allowing their
spheroidizing because of the lack of Mg.
Besides the above-mentioned graphite forms, in the cast
iron microstructure the areas occur with especially big inclusions,
fig. 4, a and b. The prevailing size shows that graphite spheroids
are initial. The composition of the investigated cast iron is eutectic
one , however, the elements of structure of hypereutectic cast iron
are present. Formation of excessive, even for layers of eutectic
composition, primary phases was also observed earlier, in
particular, in systems Al-Si, Pb-Bi and Zn-Gd [10]. The arisen
contradiction is explained by a considerable deviation in the
processes of hardening of real production alloys from balanced
conditions of crystallization of eutectic alloys. The main reason
which results in appearing the primary crystals of phases is
fluctuation of chemical composition. For cast irons the increase of
stability of chemical composition fluctuations is conditioned by
Fig.3. Volume distribution of graphite inclusions in high- additional inoculation. Initially in the melt Fe-C-Si there are areas
strength cast iron with spheroidal graphite with different content of carbon and silicon, hereby the areas
enriched with silicon are depleted with carbon, and vice versa; this
is connected with influence of silicon on thermodynamic activity
The next analysis was carried out on separate levels of carbon. At inoculation with silicon-containing spheroidizating
with division of initial mass into 2 separate layers. The results alloying compositions to which also refers the inoculant FeSiMg-
of the analysis in the form of projections of isolines of graphite 7, the process of heterogenisation increases. In the areas with
inclusions are presented in fig.4, a and b. increased concentration of carbon graphite inclusions start
forming, as the concentration of carbon in these areas exceed
ultimate solubility in the iron melt at this temperature. Fluctuations
of the content result in arising not only individual inclusions of
primary graphite (fig.4 , a), but also in formation of spheroidal
cluster consisting of several primary inclusions (fig.4, b). The
structure of the cluster presented by the chains of graphite
inclusions, shows the unified mechanism of distribution of
inclusions of primary and eutectic graphite.
Thus, graphite inclusions observed in the cast iron
microstructure can be classified by the following kinds: I - cluster
a) b)
and individual inclusions of primary graphite of spheroidal shape;
Fig.4. Layered distribution of graphite inclusions in high-
II – spheroidal inclusions of eutectic graphite and III –large
strength cast iron:
compact inclusions of non-spheroidal shape.
a) – layer consists of 10 images;
Based on classification of graphite inclusions, the
b) – layer consists of 8 images pattern of distribution of graphite phase in the high-strength cast
iron is developed. Morphological peculiarities of the structure of
graphite inclusions, observed on metallographic specimens, can be
explained by the fact that graphite in the cast iron forms in several
4. Discussion of Results stages.
During the analysis of images (fig.4) the fact draws At the initial stage of crystallization after inoculation
attention that the chains of inclusions are represented by graphite occurs heterogenization of the melt by silicon and carbon.
spheroids of approximately the same size. Apparently, such Heterogenization of the melt results in its separation into layers. In
graphite inclusions making the chain, were nucleated the areas with increased concentration of carbon the centres of
crystallization of graphite start to arise. The subsequent
overcooling, which arises at the inoculation of the melt with The structures of chains of graphite inclusions, formed
magnesium-containing alloying compositions, stabilize the nuclei in the process of crystallization of the high-strength cast iron, are,
of graphite inclusions. The nuclei of graphite phase grow with big by themselves, fractal clusters, which can be described with the
speeds on account of accelerated diffusion of carbon and get big help of the CCA pattern (Cluster-Cluster Aggregation). In this
sizes. Graphite inclusions arising in the melt volume, limited by pattern the particles colliding with each other, form originally
fluctuation, during the contact which is caused by their growth and simple clusters, which later unite in the clusters of big sizes. The
the size of fluctuation, form spherical cluster at the moment clusters arising in the melt, consisting in eutectic nuclei, manifest
preceding formation of the austenite shells. In case when sizes themselves most clearly in the flaws of shrink origin. In shrink
of arising fluctuation are comparatively small, a single inclusion cavities, at the condition when the mother liquor, enriched with
of primary graphite forms in it. Hereby, in case of formation of segregated materials and carbon, is removed in the process of
several centres of crystallization of graphite in a small area of the shrinkage, the crystallized welded cluster chains of eutectic grains
melt, occurs their accretion into one big inclusion in accordance are found in the shrink porosity. This is the proof of the suggested
with the mechanism of overcondensation. cluster pattern of distribution of graphite inclusions in high-
At the next stage in the areas of the melt with chemical strength iron.
composition corresponding to eutectic content of the alloy Big graphite of irregular compact shape is crystallized at
components, eutectic cells start to form, which present by the last stage from the mother melt, in the areas stuck by growing
themselves graphite of spheroidal shape covered with shells of austenite-and-graphite eutectic aggregates. The proof of
crystallizing austenite. Graphite nuclei in the melt areas arise crystallization of graphite from the mother liquor are the fringes
evenly, the process of coalescence, which aligns average sizes of graphite observed in shrink cavities. Graphite crystallizing at
of centres of graphite crystallization, prevents them from the last stage, is surrounded, as a rule, by the pearlite structure and
segregation. does not have any ferrite fringes of the “bull’s eye” type. The
In case of arising, beside the growing graphite nucleus, conditions of formation of graphite inclusions do not contribute to
of another smaller one, a gradual enlargement of the smaller one spheroidization of graphite, and it degenerates into the compact,
is observed, on account of diffusion of carbon from small nuclei close to vermicular, X-shape. Apparently, the last portions of
to big ones, which arose earlier. Graphite inclusions form at the metal crystallize without concentration of residual magnesium,
big rates of overcooling and are covered with austenite shell earlier required for spheroidization of graphite.
than primary graphite, which slows down their subsequent growth.
Chemical composition of austenite surrounding graphite 5. Conclusion
inclusions, has the increased concentration of silicon, which
Methods of visualization of phase volume distribution in
confirms the fact of formation of ferrite areas around graphite, the
alloys is developed. The suggested method is used for the
so-called “ a bull’s eye “ structure. The growth and formation of
analysis of peculiarities of graphite phase distribution in high-
graphite inclusions at this stage occurs in the areas of the melt with
strength cast irons and for the study of crystallization process.
the increased content of silicon.
The processes of primary structure formation of graphite phase
The organization of the chains of eutectic graphite,
in high-strength cast irons are investigated. At the use of
observed on the metallographic specimen is caused by weldability
methods of stereology and digital metallography was obtained
of austenite shells and their subsequent joint growth during
crystallization. At this stage, due to the shortfall of carbon 3D-distribution of graphite inclusions in the cast iron. The
classification of graphite inclusions dependent on the shape,
duffusing through austenite shells, the neighbouring (competitive)
sizes and peculiarities of their distribution, is stated. The
graphite inclusions can get the shape of ellipsoids and form the
hypothesis is proposed about the fact that structures of chains of
necks uniting them (fig.5).
graphite inclusions forming in the process of crystallization of
the high-strength cast iron, are actually fractal clusters which
can be described with the help of the CCA pattern (Cluster-
Cluster Aggregation).
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