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Advances in Electrometallurgy 2014 12 (2) 86–91
86
I.V. Protokovilov, et al.
Advances in Electrometallurgy 2014 12 (2) 86–91
Translated from Sovremennaya Elektrometallurgiya 2014 12 (2) 10–14
The promising direction of increasing the
efficiency of the process of electroslag re-
melting (ESR) is the development of different
methods of influencing heat and mass transfer
and solidification of the metal which make
it possible to control the properties of the
melted alloys already in the stage of melt-
ing the billet. One of these methods is the
pulse power supply to the electroslag process
supplying electric energy. The efficiency of
application of the method for controlling the
process of electroslag melting was described
in [1, 2]. Since the slag and metal pools are
characterised by the high level of thermal
inertia, it is possible to change in a wide
range of the conditions of pulsed supply to
the electroslag process and, consequently,
influence the heat and mass transfer and
solidification of the ingot, whilst retaining
the high-quality of formation of the ingot.
However, the complicated nature of pulsed
supply of high current (tens of kiloamperes)
and expensive equipment greatly restricted the
possibility of application of this method of
influencing the electroslag process.
With the development of the advanced
elemental base, in particular, the powerful
power thyristors with the working current up
to 6 kA and higher [3, 4], the possibilities
of application of the pulsed supply of power
for controlling the process of electroslag
remelting have been greatly expanded. In
addition to reducing the specific consumption
of electric energy, the pulsed power supply
Electroslag melting of titanium billets with
pulsed electric power supply
I.V. Protokovilov1, A.T. Nazarchuk1, V.B. Porokhon'ko1, YU.P. Ivochkin2 and
I.O. Teplyakov2
1E.O. Paton Electric Welding Institute, Kiev;
2Joint Institute of High Temperatures, Russian Academy of Sciences, Moscow
Presented are the results of experiments on electroslag melting of titanium ingots at pulsed
supply of process with electric power. To carry out the experimental melting, the power
transformer TShP-10-1 was subjected to modification, that allowed realizing the electroslag
process at a pulsed mode, adjusting the frequency and amplitude characteristics of pulses
of operating voltage during melting. Experimental investigations were carried out in melt-
ing of 84 mm diameter ingots of titanium of Grade 4. From the experimental results the
stability of electroslag process, its electrical conditions, formation of surface of ingots,
their macrostucture and distribution of hardness in longitudinal section were evaluated.
Two schemes were studied for pulsed supply of electroslag process at different duration of
pulses and pauses of electric supply and voltage level at the pool during the pause. During
experiments the feasibility of electroslag melting of titanium ingots at pulsed mode, keeping
the stability of electroslag process and good formation of lateral surface of ingot, dense mac-
rostructure without metallurgical defects was shown. Possibility of control of solidification of
titanium ingots and refining of their cast structure by pulsed electric supply and appropriate
potion heat input was established. Ref. 9, Table 1, Figures 5.
Key words: electroslag remelting; pulsed electric supply; ingot; macrostructure; portion heat input
Advances in Electrometallurgy 2014 12 (2) 86–91 87
Electroslag melting of titanium billets
makes it possible to influence the formation
and separation of the droplets of electrode
metal, thermal and hydrodynamic processes
in the slag and metal pool, and also control
the solidification of the metal of the billet
[1, 2, 5, 6].
The aim of the present work is the exami-
nation of the technological and metallurgical
special features of the ESR process of tita-
nium in the conditions of the pulsed supply
of electric energy. It was required to develop
equipment for the pulsed power supply in the
electroslag process, and also investigate the
relationships governing the formation of the
ingot and its solidification structure.
In [7, 8] the authors indicated the efficiency
of application of the external electromagnetic
effect for controlling the structure formation
of titanium ingots in the electroslag remelting
process. The experimental results show that of
the pulsed effect of the longitudinal magnetic
Fig. 1. Diagram of electroslag melting of tita-
nium ingots with pulsed electric power supply:
1) the TShP-10-1 power transformer; 2) the thyristor
block; 3) the thyristor control block; 4) the program-
mable logic module.
Fig. 2. Recording of the melting processes with pulsed electric power supply, s: a) tpulse = 7,
tbreak = 1.4 (melt No. 825); b) tpulse = 2, tbreak = 0.5 (melt No. 826).
Advances in Electrometallurgy 2014 12 (2) 86–91
88
I.V. Protokovilov, et al.
field with a sufficiently high induction results
in the spontaneous periodic changes of the
melting current which is caused probably by
the deformation of the surface of the slag
pool and by the increase of the electrical
resistance of the section of the consumable
electrode – metal pool circuit. During the
pulse of the magnetic field, the melting cur-
rent decreases by approximately 30…70%,
and during the break it is restored to the
initial value, i.e., pulsed (discrete-portional)
heat generation takes place in the slag pool.
In the melting of the billets with a diam-
eter of 80–100 mm and the induction of the
external magnetic field of the 0.16–0.24 T,
the best results in the refining of the structure
of the metal and the formation of the surface
of the ingot were obtained in the case of the
pulse and break time of the electromagnetic
effect of respectively 1–2 and 6–15s. This
effect resulted in a reduction of the melting
current during the pulse of the magnetic field
to 70% [7].
Thus, it was interesting to carry out experi-
ments using the Aalst electric power supply,
reproducing the similar nature of variation
of the melting current but in this case as
a result of the change of the voltage of
the power source. Also, to obtain resonance
oscillations, experiments were carried out
with the application of a higher frequency of
current modulation, similar to the frequency
Table 1. Conditions of experimental melts with pulsed power supply
Melt No.
d, mm t, s U, V I, A
electrode ingot pulse break pulse break pulse break
825 3.0...3.5 48 84 7 1.4 28 4 3900....4100 400
826 3.0...3.7 48 84 2 0.5 28 0 4000...4150 0
Fig. 3. External appearance and the side surface of titanium ingots, melted with pulsed electric pass
supply: a) melt No. 825; b) melt No. 826.
Fig. 4. The macrostructure of the titanium ingots,
melted with the electric pass supply: a) melt No.
825; b) melt No. 826.
Comment. Flux AN-T4, the depth of the slag pool 40 mm
Advances in Electrometallurgy 2014 12 (2) 86–91 89
Electroslag melting of titanium billets
of natural oscillations of the metal pool [1].
Experiments with the melting of billets of
titanium of Grade 4 type with the diameter
of 84 mm were carried out in a chamber-
type electroslag furnace (Fig. 1). The power
was supplied to the equipment using the
modernised power transformer TShP-10-1,
fitted with a block of controlling thyristors
connected by the antiparallel connection in
the primary winding circuit. The control
system of the thyristors makes it possible to
control smoothly the voltage during melting
in the range 0–72 V at a current of up to
10 kA and ensure efficient protection against
overloading. To realise the pulsed operating
regime of the transformer, the programmable
logic module SR2 B1218D was connected to
the thyristor control circuit which made it
possible to regulate the duration of the pulses
and breaks of the voltage in the secondary
circuit of the power transformer with a dis-
creteness of 0.1 s in a wide range (0.1…999
s), applying different methods of pulsed power
supply to the ESR process (pulse – breaks, a
group of pulses – breaks with different depth
of modulation, etc).
The conditions of the experimental melts
are presented in Table 1 and Fig. 2. The
experimental results were used with you ear-
lier the stability of the electroslag process,
its electrical parameters, formation of the
surface of the ingots, the macrostructure of
the ingots and the distribution of hardness
in the longitudinal section.
Two methods of pulsed bar supply to the
electroslag process were investigated. In the
first method (melt No. 825), the power was
supply by the pulses of alternating voltage
with the duration of 7 s with a break of 1.5
s during which the voltage was reduced to
4 V (Fig. 2 a). In the second method (melt
No. 826), the duration of the voltage pulses
in the pool was 2 s with a break of 0.5 s
during which the voltage was completely
switched off (Fig. 2b).
In the investigated range of the conditions
of the pulsed power supply the electroslag
process was stable, without any disruption of
stability. In accordance with the variation of
the electrical voltage in the pool, the melt-
ing current was changed cyclically (Fig. 2).
The front of current increase was flatter in
comparison with the front of voltage increase
which is evidently associated with the cool-
ing of the slag pool during the break in the
pulsed supply and the non-linear form of the
electrical resistance of the slag.
The reduction of the supplied power in
the melts produced in the past conditions
resulted in a small (by 3...5%) reduction
of the melting rate of the electrode and the
corresponding increase of the duration of the
process. However, on the whole, the specific
consumption of electric energy, in comparison
with melting in the stationary conditions (with
continuous electric power supply) decreased
Fig. 5. Distribution of hardness HB in the longitudinal section of the ingots: a) melt No. 825; b) melt No.
826, h, r – the height and radius of the ingot, respectively.
Advances in Electrometallurgy 2014 12 (2) 86–91
90
I.V. Protokovilov, et al.
by 7...10%. Evidently, this is associated with
the intensification of droplet formation and
heat and mass processes at the end of the
consumable electrode as a result of the vibra-
tions caused by electrodynamic forces which
in the final analysis increases the thermal
efficiency of melting [6, 9].
The external appearance of the melted bil-
lets it shown in Fig. 3. In both cases, the
billets are characterised by the efficiently
formed side surface. The surface of the ingot
No. 825 showed small corrugations caused by
the pulsed heat input (Fig. 3a). The mechanism
of formation of these corrugations is associ-
ated with the increase of the cooling rate
of the metal during the break-in the electric
power supply and with the appropriate cyclic
variation of the thickness of the slag skull
on the surface of the ingot. The depth of the
corrugations was on average 0.1...0.15 mm,
which did not impair the surface quality of
the ingot. In the case of the duration of the
break of 0.5 s, the surface of the ingot was
almost completely free from corrugations
(Fig. 3b).
The macrostructures of the longitudinal
section of the produced ingots are shown in
Fig. 4. In both cases, the metal is charac-
terised by a dense structure, the absence of
slag inclusions, no lack of fusion defects,
shrinkage porosity and other metallurgical
defects.
The peripheral areas of the ingots (in the
vicinity of the side surface) are characterised
by a fine-grained globular structure, with the
mean size of the globules being 0.5...1.5 mm.
The width of this zone in the ingot No. 825
reached 13 mm, which is slightly greater than
in the ingot No. 826 (11 mm).
The central part of the ingots contained
both globular grains and columnar grains,
elongated in the direction of heat transfer,
with the mean size of 1.87×8.50 mm (ingot
No. 825) and 1.95×10.15 mm (ingot No. 826).
The distinctive ‘weak’ zone was not detected
at the axis of the ingots.
On the whole, analysis of the macrosections
of the produced ingots indicates both refining
and homogenising of the macrostructure of
the ingots, in comparison with the metal of
the titanium ingots melted in the stationary
conditions which are characterised by the
distinctive ‘firtree’ structure of the metal with
the size of the dendrites comparable with the
radius of the ingot.
Evidently, the observed effect is determined
by a number of factors, in particular, the
variation of the temperature gradient at the
solidification from as a result of breaks in
the electric power supply and hydrodynamic
‘impacts’ on the crystals growing in the
two-phase zone during activation and discon-
nection of voltage. The pulsed electric pass
supply also resulted mechanical solutions of
the melt in the metal pool resulting in break-
ing of the dendrites.
The distribution of hardness HB in the
longitudinal section of the ingots (Fig. 5)
indicates the relatively high degree of ho-
mogeneity of the cast metal. The enquiries
of the hardness of the metal of the root
part of the ingot is typical of the majority
of metallurgical processes and is associated
with the higher content of the impurities in
the given zone.
The experiments showed that it is possible
to control the solidification of titanium ingots
in electroslag the melting by the pulsed sup-
ply of electric energy. The further investiga-
tion should be carried out to determine the
relationship between the parameters of the
structure of the cast metal and the influ-
ence conditions, such as the frequency of
the pulses, the on-off ratio of the pulses and
the level of modulation of the voltage four
different standard dimensions of the melted
ingots.
Conclusions
1. The TShP-10-1 power transformer was
modernised for the use in the pulsed supply
for the electroslag process with the possibil-
ity of regulation of frequency and amplitude
characteristics of the pulses of working volt-
age during melting.
2. It has been shown possible to carry out
electroslag melting of titanium ingots with
Advances in Electrometallurgy 2014 12 (2) 86–91 91
Electroslag melting of titanium billets
the pulsed supply of electric energy whilst
retaining the stability of the electroslag pro-
cess ensuring high quality of the formation
of the side surface of the ingot with a dense
structure, without metallurgical defects.
3. The application of the pulsed power
supply has reduced the specific consumption
of electric energy by 7...10% in comparison
with melting in the stationary conditions.
4. New experimental data were obtained
for the special features of the formation of
the macrostructure of the titanium ingots
in the conditions of pulsed electric power
supply. The refining of the structure of the
metal in comparison with the metal of the
ingots produced by conventional electroslag
remelting was observed.
References
1. Control of the process of solidification of the
electroslag ingot, in: Problems of steel ingots,
proceedings of the 5th conference for ingots, Kiev,
September 1974, Metallurgiya, Moscow, 1974,
707–714.
2. Paton, B.E., Medovar, B.I. Electroslag furnaces,
Naukova Dumka, Kiev, 1976.
3. Element-Preobrazovatel': Thyristors, low-fre-
quency tablet design; www.element.zp.ua/prod-
ucts/list.php?category=29.
4. Railton electronics: thyristor disc. www.rail-
tonelectronics.com/powerelectronics.html.
5. Abramov, A.V., et al., Probl. Spets. Elektro-
metall., 1993, No. 4, 10–12.
6. Patent 2337979, RF, MPK S 22 V 9/18; A
method of controlling the operating conditions
of equipment for electroslag remelting and
systems for this purpose, Abramov, A.V., et
al., 10.11.2008, Bull. No. 31.
7. Kompan, Ya.Yu., Sovremen. elektrometallurgiya,
2007, No. 4, 3–7.
8. Nazarchuk, A.T., et al., ibid, 2013, Nol. 4,
21–26.
9. Ivanenko, O.G., et al., Izv. VUZ, Chern. Metall.,
1984, No. 4, 15–18.
Submitted 29.1.2014