V. KURKA et al.: INCREASING MICRO-PURITY AND DETERMINING THE EFFECTS OF THE PRODUCTION ...
419–426
INCREASING MICRO-PURITY AND DETERMINING THE
EFFECTS OF THE PRODUCTION WITH AND WITHOUT
VACUUM REFINING ON THE QUALITATIVE PARAMETERS OF
FORGED-STEEL PIECES WITH A HIGH ALUMINIUM CONTENT
POVE^ANJE MIKRO^ISTO^E IN DOLO^ITEV U^INKA
PROIZVODNJE, Z VAKUUMSKIM RAFINIRANJEM ALI BREZ, NA
KVALITATIVNE PARAMETRE KOVANEGA JEKLA Z VISOKO
VSEBNOSTJO ALUMINIJA
Vladislav Kurka1, Jaroslav Pindor1, Jana Kosòovská1, Zdenìk Adolf2
1Material and metallurgical research, Ltd, Pohranicni 693/31, 703 00 Ostrava-Vítkovice, Czech Republic
2V[B – Technical University of Ostrava, 17. listopadu 15/2172, 708 33 Ostrava-Poruba, Czech Republic
vladislav.kurka@mmvyzkum.cz
Prejem rokopisa – received: 2014-10-13; sprejem za objavo – accepted for publication: 2015-03-24
doi:10.17222/mit.2014.258
The quality production technology for the WNr. 1.8504 steel was developed. The aim of the work was to achieve the required
internal micro-purity and determine the effects of different production technologies on the qualitative parameters of forged-steel
pieces. Firstly, polygonal ingots weighing 1600 kg were produced, using the metallurgical units, in a controlled-atmosphere
induction-melting furnace (IF) without vacuum treatment, and in a vacuum and pressurized induction-melting furnace (VPIM)
with vacuum treatment. The ingots were subsequently reshaped by open-die forging into bars with a rectangular cross-section.
The effect of the ingot-production technology was evaluated by comparing the forged-steel pieces in terms of their purity,
macrostructure and microstructure.
Keywords: vacuum, inclusion, aluminium, steel
Izvr{en je bil razvoj kakovostne proizvodne tehnologije jekla W.Nr. 1.8504. Namen je bil dose~i `eleno notranjo mikro~isto~o in
ugotoviti vpliv razli~nih tehnologij proizvodnje na kvalitativne parametre odkovkov. Najprej so bili izdelani poligonalni kovani
ingoti z maso 1600 kg, z uporabo naslednjih metalur{kih agregatov: v indukcijski talilni pe~i s kontrolirano atmosfero (IF) brez
vakuumskega rafiniranja in v vakuumski ter indukcijski talilni pe~i (VPIM) s povi{anim tlakom in z vakuumskim rafiniranjem.
Nato so bili ingoti s prostim kovanjem preoblikovani v palice s pravokotnim prerezom. Vpliv tehnologije proizvodnje ingotov je
bil ocenjen s primerjavo odkovkov z vidika ~istosti, makro in mikrostrukture.
Klju~ne besede: vakuum, vklju~ki, aluminij, jeklo
1 INTRODUCTION
Aluminium is primarily used in steel as a deoxidising
agent as well as an alloying element. In a melt, alumi-
nium occurs in the dissolved form, in a solid solution as
aluminium metal, aluminium oxide Al2O3 and, in an
interaction with nitrogen, also as aluminium nitride
AlN.1 An increased aluminium content in steel reduces
its formability due to the mechanical effect of its pre-
cipitates, and alternatively also due to its local ferrite
affecting the structural state. An increased concentration
of strongly ferrite generating aluminium may occur in
the vicinity of dissolved AlN particles. AlN is separated
in steel in the form of acicular crystals, usually on the
grain borders. The quality of WNr1.8504 (hereinafter
referred to as the "steel") is, with regard to its chemical
composition, intended for surface nitration. Nitration is a
saturation of the steel surface with nitrogen that creates
hard nitrides with the alloying elements Al, Cr, Ti and V.
Figure 1 shows an example of a nitrated steel layer. The
process of nitration takes place at temperatures of 500 °C
– 540 °C for about 50 h,2 when the nitrated steel layer
achieves a 0.3 mm thickness in 30 h, and a 0.5 mm thick-
ness in 50 h. The process depends on the temperature,
pressure, chemical composition of the steel and atmo-
spheric composition.
Materiali in tehnologije / Materials and technology 50 (2016) 3, 419–426 419
UDK 669.18:669.178.52:621.77 ISSN 1580-2949
Professional article/Strokovni ~lanek MTAEC9, 50(3)419(2016)
Figure 1: Example of a nitrated steel layer2
Slika 1: Primer nitrirane plasti na jeklu2
Nitrogen is thus an element that creates AlN nitrides
with Al in steel, which are very hard and non-malleable.
On the steel surface, it creates a hard, abrasion-resistant
area. AlN nitrades inside the steel are non-malleable
inclusions that impair the micro-purity of the steel. This
work is concerned with the elimination of AlN inclu-
sions from the WNr1.8504 quality steel with 0.8 % – 1.1
% of mass fractions of high Al.
An important step in the elimination of the AlN-type
inclusions with a high aluminium content from steel is
the reduction of the nitrogen content to the minimum
level.
1.1 Nitrogen in steel
Nitrogen in steel not only reacts with iron but also
with other dissolved elements, forming a wide variety of
compounds. These are dominated by nitrides, but carbo-
nitrides, oxynitrides, cyanonitrides, complex binary
nitrides and other phases of variable compositions can
occur as well. Their existence depends on a number of
factors, such as the composition of the steel, the melting
method, the temperature, the pressure, the thermal treat-
ment, etc.4 In our case, aluminium nitrides form under
the liquidus temperature and re-dissolve in the steel at
temperatures of 900 °C – 1100 °C, where the dissolution
rate is a function of the material temperature and struc-
ture.5 Increased frequency and size of, for example, the
AlN particles may lead to the generation of inter-
crystalline steel fractures. The effects of the elements on
the solubility of nitrogen in molten iron at a temperature
of 1600 °C and a nitrogen pressure of 100 kPa are pre-
sented in Figure 2.4
Surface-active elements such as sulphur and oxygen
hinder the removal of nitrogen from the molten steel
during vacuuming (nitrogen diffusion in argon bubbles
during bubbling) and from the vacuum above the steel
surface. If reducing the nitrogen content, e.g., to a
required value below 0,004 % of mass fractions, very
low values of sulphur and oxygen need to be ensured at
the same time. See Figures 3 and 4 for a graphic illustra-
tion of this dependence.6
1.2 Solubility of nitrogen in steel
The solubility of nitrogen in steel and the effects of
individual elements are described in detail in a previous
paper.7 The transition of nitrogen in steel is governed by
Sievert’s law, which presupposes its atomic dissolution.
The dependence of the nitrogen content in an iron melt at
pressure is described with relationship (1):
[ ] { }%N Fe N
N
N
rel.
= ⋅
K
f
p
2
(1)
where:
V. KURKA et al.: INCREASING MICRO-PURITY AND DETERMINING THE EFFECTS OF THE PRODUCTION ...
420 Materiali in tehnologije / Materials and technology 50 (2016) 3, 419–426
Figure 4: Nitrogen removal by tank degassing as a function of sulphur
content6
Slika 4: Zmanj{anje vsebnosti du{ika pri odstranjevanju plina v ko-
mori, kot funkcija skupne vsebnosti `vepla6
Figure 2: Effects of elements on the solubility of nitrogen in molten
iron at a temperature of 1600 °C and a pressure of 100 kPa4
Slika 2: Vpliv elementov na topnost du{ika v staljenem `elezu pri
1600 °C in tlaku 100 kPa4
Figure 3: Nitrogen removal by tank degassing as a function of the
total oxygen content6
Slika 3: Zmanj{anje vsebnosti du{ika pri odstranjevanju plina v ko-
mori, kot funkcija skupne vsebnosti kisika6
KN is the equilibrium constant of the dissolution process
(in mass fractions, (w/%)) maximum,
fN is the nitrogen activity coefficient in iron melt,1
{ }pN
rel.2
is the relative partial nitrogen pressure above
iron melt.1
The equilibrium constant KN expresses the nitrogen
solubility in iron under standard conditions, i.e., its
maximum content under a pressure of 0.1 MPa{ }pN
rel.2
= 1 a fN = 1. The temperature dependence of nitrogen
solubility is expressed with Equation (2):
[ ]lg . lg %K
TN Fe
N= − − =
188
1246 (2)
and the adequate dependence of the reaction-free en-
thalpy on the temperature is expressed with relationship,
Equation (3):
ΔG T0 3600 2386= + . (J) (3)
As it is clear from Equation (2), the solubility of ni-
trogen at a temperature of 1600 °C is 0.045 % of mass
fractions, but it drops significantly when the melt
solidifies. It slightly increases in iron 
, and then drops in
iron  to approximately 0.0015 % of mass fractions at
600 °C.
The nitrogen solubility in steel is significantly
affected by the presence of alloying elements, parti-
cularly in highly alloyed corrosion-resistant steels. The
effect of alloying elements is manifested in the value of
active coefficient fN:
[ ]lg %f eN N
X N= ∑ (4)
This effect can be expressed by means of interaction
coefficients eN(1873K)
X . The temperature dependence of the
interaction coefficients expressing the effects of elements
on the nitrogen activity was described by Chipman and,
according to the author8, it is expressed with Equation
(5):
e
T
eTN( , K)
X
N(1873K)
X= −⎛⎝
⎜ ⎞
⎠
⎟ ⋅
3280
0 75. (5)
Therefore, the dependence of the nitrogen solubility
on the temperature can be expressed with Equations (6)
and (7):
[ ] { }lg % lg lg lgN steel N N N
rel.
= − +K f p
1
2 2
(6)
[ ]lg % .
.
N steel
N(
= − −⎛⎝
⎜ ⎞
⎠
⎟ −
− −⎛⎝
⎜ ⎞
⎠
⎟ ⋅∑
188
1246
3280
0 75
T
T
e { }1873K)X N
rel.
+
1
2 2
lg p
(7)
An improvement of the calculation is, especially for
highly alloyed steels (e.g. CrNi steels) conditioned not
only by the knowledge of the first values of the inte-
raction coefficients but also of the second values and the
cross-interaction coefficients, Equation (8):
[ ] [ ] [ ]
[ ] [ ] [ ]
lg % lg % %
% % %
N N X
X X Y
steel Fe N
X
N
X 2
N
X, Y
= − ⋅ −
− ⋅ −− ⋅ ⋅
∑
∑ ∑
e
r r
2
(8)
For significantly corrosion-resistant steel alloys,
these values are quoted by, e.g., Z. Buzek8 in Table 1.
Table 1: Values of interaction coefficients 1, 2, and cross-interaction
coefficients8
Tabela 1: Vrednosti interakcijskih koeficientov 1, 2 in navzkri`nih
koeficientov8
X (in mass
fractions, (w/%))
eN(1873K)
X
rN(1873K)
X rN(1873K)
X, Y
Cr –0.0468 +0.00034 –
Nb –0.0667 +0.00019 +0.00136 (Cr-Nb)
Mo –0.0106 – +0.00002 (Cr-Mo)
Ni +0.0107 – –0.00041 (Cr-Ni)
Si +0.047 – –0.00149 (Cr-Si)
1.3 Elimination of AlN from WNr1.8504 quality steel
Elimination of the AlN inclusions from steel
commenced with the evaluation of standardly produced
steel with production-technology adjustments. The ob-
jective of the work was a reduction of the nitrogen con-
tent and thus the occurrence of AlN in the final product.
In MMR, ingots were produced in an atmospheric
induction-melting furnace (hereinafter referred to as the
IF) with a nominal batch weight of 1750 kg, and in a
vacuum and pressurized induction-melting furnace
(hereinafter referred to as the VPIM), in which vacuum
degassing (VD) at a minimum pressure of 40 Pa (a), or
vacuum oxygen decarburisation (VOD) can be carried
out by using of an oxygen-argon nozzle.
One polygonal ingot for forging, V2A, was produced
from each melt, weighing approximately 1650 kg. With
every melt, the ingot was filled from the bottom through
the casting system. The ingots were forged by open-die
forging into bars of the following dimensions: 140–160
mm × 90–110 mm.
The melts were produced and found as follows:
Melt 1 – Production of the melt in the IF with casting on
an atmospheric casting bed under a protective argon
atmosphere.
Melt 2 – Production of the melt in the VPIM, vacuum
refined with VD, with casting on an atmospheric
casting bed under a protective argon atmosphere.
Melt 3 – Production of the melt in the VPIM, vacuum
refined with VD, with casting under a protective
argon atmosphere in a cofferdam.
The chemical composition of the steel according to
the standard3 and the chemical compositions of the
monitored and evaluated melts and forged pieces are
shown in Table 2. All the melts and forged pieces
featured the required standardised chemical composition.
The content of nitrogen in the forged piece from Melt 1
was 0,0132 % of mass fractions. This amount was
reduced to the value of 0.0108 % of mass fractions,
V. KURKA et al.: INCREASING MICRO-PURITY AND DETERMINING THE EFFECTS OF THE PRODUCTION ...
Materiali in tehnologije / Materials and technology 50 (2016) 3, 419–426 421
through the VD process, in the pieces forged from Melts
2 and 3.
Elements of C, S, N were determined with the ther-
mochemical method using equipment LECO CS 230 and
LECO TCH 600. Metal samples were melted in an
induction (for C and S) or resistor (for N) furnace in a
gas stream. The gas was analysed for the absorption of
infrared radiation (for SO2 and CO2) and the change in
the thermal conductivity was measured (for N2). Ele-
ments Si, Mn, P, S, Cr were determined with an X-ray
spectrometry apparatus, ARL ADVANT’X IntelliPower
THERMOFISHER SCIENTIFIC. The method of seque-
ntial X-ray fluorescence spectrometry is based on the
excitation of characteristic X-rays of the elements pre-
sent in a sample using an X-ray lamp. The Al element
was determined on Optima 3000SC PERKIN ELMER.
The analysed sample was dissolved in acids and
transferred into the solution, and then it was measured
using optical emission spectrometry with inductively
bounded plasma.
The pieces forged from all the melts were subjected
to non-destructive ultrasound testing according to SEP
1921/84 Group 3, Class C/c. All the forged pieces fully
conformed to the evaluation.
The work further presents an evaluation of the
micro-purity of the pieces forged from Melts 1 to 3,
according to ASTM E45-10, method A. This method
classifies the inclusions by their shape and light reflec-
tivity only, so their chemical composition plays no role.
For the above reason, a spectral microanalysis was also
performed with a scanning electron microscope JEOL
JSM-5510, equipped with an energy-dispersive analyser
from Oxford Instruments, with which the chemical
compositions of the inclusions were determined. Last but
not least, the work presents an evaluation of the forged
pieces’ macrostructures.
1.4 Micro-purity of the pieces forged from Melt 1 in
the IF
First of all, micro-purity was evaluated on the pieces
forged from Melt 1 in the IF. Very coarse inclusions, spot
D (oxidic inclusions), were observed in the specimens
that often exceeded the allowed limit of 12 μm, specified
in the classification of these inclusions. The biggest
inclusion achieved the size of 49 μm; the spot-D (oxidic)
inclusions were not quite standard, i.e., globular. They
featured a rather sharp-edged shape with s variable size.
Then there was a smaller quantity of specimens with the
inclusions arranged in lines, often in combination with
sulphides that were, using the relevant standard etalon,
evaluated as the B type – line Al2O3. A very low number
of slightly shaped A-type inclusions were then observed
in some places, exceeding the thickness of 6 μm that is
specified for the coarse A-type inclusions. Examples of
non-metallic inclusions are shown in Figures 5 and 6;
V. KURKA et al.: INCREASING MICRO-PURITY AND DETERMINING THE EFFECTS OF THE PRODUCTION ...
422 Materiali in tehnologije / Materials and technology 50 (2016) 3, 419–426
Table 2: Chemical compositions of standardised3 WNr1.8504, the melts and forged pieces (in mass fractions (w/%))
Tabela 2: Kemijska sestava normiranega3 jekla WNr1.8504, taline in odkovkov (v masnih dele`ih (w/%))
1.8504 C Si Mn P S Cr Aldiss. Albound Altotal N
Standard
min 0.30 0.15 0.60 – – 1.20 – – 0.800 –
max 0.37 0.35 0.90 0.035 0.035 1.50 – – 1.100 –
Melt 1
melt 0.33 0.30 0.81 0.017 0.006 1.39 – – 1.20 –
forged piece 0.33 0.30 0.82 0.012 0.007 1.42 1.08 0.02 1.10 0.0132
Melt 2
melt 0.33 0.27 0.70 0.015 0.007 1.44 – – 1.11 –
forged piece 0.34 0.26 0.73 0.011 0.008 1.45 1.07 0.02 1.09 0.0108
Melt 3
melt 0.35 0.24 0.76 0.018 0.007 1.47 – – 0.97 –
forged piece 0.35 0.23 0.77 0.010 0.007 1.48 0.94 0.02 0.96 0.0108
Figure 6: Non-metallic inclusions in the piece forged from Melt 1.
Magnified 330×.
Slika 6: Nekovinski vklju~ki v odkovku iz taline1. Pove~ava 65×.
Figure 5: Non-metallic inclusions in the piece forged from Melt 1.
Magnified 65×.
Slika 5: Nekovinski vklju~ki v odkovku iz taline 1. Pove~ava 65×.
see Figures 7 and 8 for the chemical compositions of the
most frequent inclusions.
Table 3 shows the results of the micro-purity eva-
luation; the table also includes the largest inclusion
found in the tested metal specimens.
1.5 Micro-purity of the pieces forged from Melt 2 in
the VPIM through the VD process and casting
under Ar atmosphere
During the examination of the polished state, most
often non-metallic inclusions of D- and A-type com-
plexes were observed in the tested chains, as shown in
Figures 9 and 10. Oval inclusion particles were often
locally dispersed in the metallic matrix in the forged
pieces, sometimes achieving a diameter of 48 μm. The
results of the micro-purity evaluation of Melt 2 are
shown in Table 3.
Locally occurring complex non-metallic particles on
the tested specimen surfaces were classified into groups
with the closest shape similarity. The majority of the
tested inclusions were observed to be globular particles
(D type) or elongated sulphides (A type). Small-scale
tiny lines of B-type inclusions were observed in the
forged-piece matrix as well.
The microanalysis detected the chemical composi-
tions of the most frequent inclusions of the AlN type
V. KURKA et al.: INCREASING MICRO-PURITY AND DETERMINING THE EFFECTS OF THE PRODUCTION ...
Materiali in tehnologije / Materials and technology 50 (2016) 3, 419–426 423
Figure 8: EDX spectrum of non-metallic Al2O3 particles in the piece
forged from Melt 1
Slika 8: EDX-spekter nekovinskih delcev Al2O3, v odkovku iz 1.
taljenja
Figure 7: EDX spectrum of non-metallic AlN particles in the piece
forged from Melt 1
Slika 7: EDX-spekter nekovinskih delcev AlN, v odkovku iz 1.
taljenja
Figure 11: EDX spectrum of non-metallic AlN particles in the piece
forged from Melt 2
Slika 11: EDX spekter nekovinskih delcev AlN, v odkovku iz taline 2
Figure 10: Non-metallic inclusions in the piece forged from Melt 2.
Magnified 330×.
Slika 10: Nekovinski vklju~ki v odkovku iz taline 2. Pove~ava 330×.
Figure 9: Non-metallic inclusions in the piece forged from Melt 2.
Magnified 65×.
Slika 9: Nekovinski vklju~ki v odkovku iz taline 2. Pove~ava 65×.
(Figure 11), the MnS type (Figure 12), or the complex
AlN-MnS type inclusions (Figure 13).
1.6 Micro-purity of the piece forged from Melt 3 in
VPIM through the VD process and casting in the
cofferdam under Ar
As in the previous cases, the presence of a high
amount of coarse inclusions was detected in this forged
piece; due to their shape, these inclusions were classified
as D-type inclusions (oxidic inclusions). Their size
significantly exceeded the admissible diameter of up to
12 μm specified for the D-type inclusions. The occur-
rence of these inclusions was frequent and they achieved
the size of up to 50 μm; however, their shape was not
typically globular but rather angular, as shown in
Figures 14 and 15. The occurrence of oxidic inclusions
in a line arrangement was less frequent.
Besides the oxidic inclusions, A-type inclusions were
observed in the specimen, or complexes of these inclu-
sions, the occurrence of which was relatively frequent.
The results of the non-metallic inclusion evaluation are
listed in Table 3. The microanalysis revealed that, unlike
in Melt 2, AlN-type inclusions were the most frequent in
Melt 3, as shown in Figures 16, 17 and 18.
V. KURKA et al.: INCREASING MICRO-PURITY AND DETERMINING THE EFFECTS OF THE PRODUCTION ...
424 Materiali in tehnologije / Materials and technology 50 (2016) 3, 419–426
Figure 14: Non-metallic inclusions in the piece forged from Melt 3.
Magnified 65×.
Slika 14: Nekovinski vklju~ki v odkovku iz taline 3. Pove~ava 65×.
Figure 15: Non-metallic inclusions in the forged piece in Melt 3.
Magnified 330×.
Slika 15: Nekovinski vklju~ki v odkovku iz taline 3. Pove~ava 330×.
Figure 16: EDX spectrum of non-metallic AlN particles in the piece
forged from Melt 3
Slika 16: EDX-spekter nekovinskih delcev AIN, v odkovku iz taline 3
Figure 13: EDX spectrum of non-metallic AlN-MnS particles in the
piece forged from Melt 2
Slika 13: EDX-spekter nekovinskih delcev AlN-MnS, v odkovku iz
taline 2
Figure 12: EDX spectrum of non-metallic MnS particles in the piece
forged from Melt 2
Slika 12: EDX-spekter nekovinskih delcev MnS, v odkovku iz taline 2
1.7 Macrostructure evaluation
The macrostructures of the forged pieces were
revealed by etching in 10 % HNO3. Unequally distributed
insignificant segregations of a darker contrast were
revealed in the specimen of the piece forged from Melt
1, as shown in Figure 19. More or less uniform macro-
structures of the surfaces were observed for the spe-
cimens forged from Melts 2 and 3, as shown in Figures
20 and 21.
V. KURKA et al.: INCREASING MICRO-PURITY AND DETERMINING THE EFFECTS OF THE PRODUCTION ...
Materiali in tehnologije / Materials and technology 50 (2016) 3, 419–426 425
Table 3: Micro-purity evaluation according to the ASTM E45-10 standard, method A, and the largest D-type inclusions found in the pieces
forged from Melts 1 to 3
Tabela 3: Vrednotenje mikro~isto~e po standardu ASTM E45-10, metoda A in najve~ji najdeni vklju~ki vrste D v vzorcih iz odkovkov iz taline 1
do 3
Specimen
Maximum contamination, method A Maximum
dimension of
D-type inclusionType A sulphides Type B aluminates Type C silicates Type D oxides
Fine Coarse Fine Coarse Fine Coarse Fine Coarse μm
Melt 1 1 1 2 2 2 2 49
Melt 2 2 2 2 1 – – 2 2 48
Melt 3 2 1 2 – – – 2 2 50
Figure 18: EDX spectrum of non-metallic AlN particles in the piece
forged from Melt 3
Slika 18: EDX-spekter nekovinskih delcev AlN, v odkovku iz taline 3
Figure 17: EDX spectrum of non-metallic AlN particles in the piece
forged from Melt 3
Slika 17: EDX-spekter nekovinskih delcev AIN, v odkovku iz taline 3
Figure 21: Macrostructure of the piece forged from Melt 3
Slika 21: Makrostruktura odkovkov iz taline 3
Figure 20: Macrostructure of the piece forged from Melt 2
Slika 20: Makrostruktura odkovkov iz taline 2
Figure 19: Macrostructure of the piece forged from Melt 1
Slika 19: Makrostruktura odkovkov iz taline 1
2 CONCLUSION
The objective of the presented work was to increase
the inner purity of a WNr1.8504 high-quality forged
piece. For this reason, three production technologies
(melts) were evaluated in this work.
As the performed analysis of the chemical com-
positions and non-destructive ultrasound tests indicate,
the atmospheric induction furnace and the vacuum and
pressurized induction-melting furnace with casting out-
side and inside the cofferdam are suitable for the produc-
tion of this material.
However, from the macrostructural point of view, the
production of melt in the atmospheric induction-melting
furnace proved to be unsuitable.
With respect to the micro-purity determined with the
microanalysis of the detected particles and nitrogen
content in the forged pieces, none of the three techno-
logies can be applied to achieve a reduced content of
mostly AlN inclusions. The production technology for
Melt 3 in the VPIM, with the VD process and the casting
in the cofferdam under a protective argon atmosphere,
eliminated the portion of oxidic and complex inclusions
but not the AlN inclusions.
The experiments showed that vacuum degassing
(VD) helps to reduce the Al content. The content of
nitrogen was reduced by 0.0024 % of mass fractions,
from 0.0132 % of mass fractions (the steel made in the
IF) to 0.0108 % of mass fractions (the steel made in the
VPIM). Based on this fact, the authors are preparing
another experiment that will eliminate the nitrogen
content using vacuum oxygen decarburization (VOD)
because the melt is mixed better with VOD than with
VD. VOD includes a more efficient degassing process
because, generally, a high oxygen content in a melt
decreases the solubility of nitrogen. For this process, a
newly manufactured oxygen-argon nozzle will be used.
Acknowledgement
This paper was created within Project No. LO1203
"Regional Materials Science and Technology Centre –
Feasibility Program" funded by the Ministry of Edu-
cation, Youth and Sports of the Czech Republic.
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