【Technical Field】
The present disclosure relates to a method of
producing manganese-containing steel, and more particularly,
to a method of producing high-quality molten manganesecontaining
steel without additional processes or problems
such as a temperature decrease in molten steel and high
manufacturing costs that may be caused by the use of large
amounts of alloying elements when high manganese steel is
produced using a basic oxygen furnace. Also, the present
disclosure relates to a holding furnace for the method, and
an apparatus including the holding furnace for producing
molten manganese-containing steel.
In addition, the present disclosure relates to a
method of producing molten manganese-containing steel
without deteriorating the quality of the molten manganesecontaining
steel even though molten metals prepared in
different amounts and at different production times are
poured (mixed) together to form a product of the molten
3
manganese-containing steel, and a holding furnace for the
method, and an apparatus including the holding furnace for
producing molten manganese-containing steel.
【Background Art】
In general, high manganese (Mn) steels have an Mn
content of about 1 wt% to about 5 wt%, and some stainless
steels have an Mn content of 10 wt% or less. In addition,
some recent steels having a high degree of strength and a
high degree of formability for use in automobiles have an
Mn content of 15 wt% to 25 wt%. Generally, in a high
manganese steel producing process using a basic oxygen
furnace, molten iron having a carbon content of about 4.5
wt% is decarbonized in the basic oxygen furnace to produce
molten steel having a carbon content of 0.2 wt% to 0.4 wt%,
and when drawing the molten steel out of the basic oxygen
furnace, a solid Mn-containing ferroalloy produced through
a melting process and a refining process is supplied to the
molten steel so as to control the Mn content of the molten
steel.
In such a process, the supply of an Mn-containing
ferroalloy increases in proportion to a required Mn content
of molten steel. However, if the supply of an Mn-containing
ferroalloy increases, the temperature of molten steel
decreases, and thus a method of preventing or compensating
4
for a temperature decrease is necessary.
For example, a method of increasing the temperature
of molten steel in a final stage of a basic oxygen furnace
process or increasing the temperature of molten steel in a
secondary refining process is used when producing molten
steel having an Mn content of 1 wt% to 5 wt%, so as to
compensate for a temperature decrease in the molten steel
caused by the supply of a ferroalloy. However, in a process
of manufacturing high manganese steel having an Mn content
of 10 wt% or greater, molten steel contained in a basic
oxygen furnace has to be maintained at a high temperature
so as to prepare for a temperature decrease when a
ferroalloy is supplied to the molten steel. In this case,
the temperature of the molten steel is maintained at a
temperature higher than a normal process temperature by
about 150°C or greater, thereby causing excessive oxidation
of the molten steel and increasing the amount of oxygen
dissolved in the molten steel. As a result, when a
ferroalloy is supplied to the molten steel, the ferroalloy
may be easily oxidized, and thus large amounts of effective
metal elements contained in the ferroalloy may be wasted.
Therefore, in another method for solving the abovementioned
problems, only a portion of the necessary amount
of a ferroalloy is supplied to molten steel when the molten
5
steel is drawn out of a basic oxygen furnace, and then the
remaining portion of the necessary amount of the ferroalloy
is supplied to the molten steel in a secondary refining
process while increasing the temperature of the molten
steel using oxidation energy or electrical energy. However,
the method of increasing the temperature of molten steel in
a secondary refining process requires a large amount of
energy, as compared to the case of increasing the
temperature of molten steel in a basic oxygen furnace. In
addition, the method has low efficiency with an increased
process time and higher manufacturing costs.
In a method disclosed in Korean Patent Application
Laid-open Publication No. 2008-0072786, molten
ferromanganese (FeMn) having a carbon content of about 6%,
molten steel having a carbon content of about 0.1%, and a
necessary amount of a slag forming agent are supplied to a
FeMn-refining basic oxygen furnace. However, the disclosed
method requires additional processes such as a refining
process for obtaining necessary impurity contents in a
final steel product, thereby increasing the costs and
process time of a manufacturing process. In addition, when
steel is produced by the disclosed method, it is difficult
to adjust impurity contents in molten FeMn according to a
required composition of molten steel.
6
In another method disclosed in Korean Patent No.
1047912, refined molten steel is supplied to a molten
ferroalloy, or vice versa, and the content of at least one
of carbon, phosphorus, and nitrogen in the molten
ferroalloy is controlled according to the state or kind of
the molten steel by taking into account the impurity
contents of the molten steel at the end of a molten steel
basic oxygen furnace, the amount of the molten ferroalloy,
and design specifications and weight values set according
to types of steel.
However, according to the disclosed method, since
molten steel and a molten ferroalloy are supplied through
different processes, it is necessary to supply the molten
steel and the molten ferroalloy on time in spite of
differences in production amounts and process times.
Particularly, manganese has a high vapor pressure and a
high degree of affinity with oxygen and nitrogen and so may
be easily combined therewith. Therefore, when storing a
molten metal including manganese, manganese may be wasted,
or additional processes may be necessary, thereby causing
problems related to costs and processes.
【Disclosure】
【Technical Problem】
Aspects of the present disclosure may provide a
7
method of rapidly producing molten manganese-containing
steel according to the production of molten steel by
preparing a high-quality molten ferroalloy or nonferrous
metal on time in spite of differences between processes, a
holding furnace for the method, and an apparatus including
the holding furnace for producing molten manganesecontaining
steel.
Aspects of the present disclosure may also provide a
method of producing molten manganese-containing steel by
adjusting the state of a molten ferroalloy or molten
nonferrous metal according to the state of molten steel
produced using a basic oxygen furnace, a holding furnace
for the method, and an apparatus including the holding
furnace for producing molten manganese-containing steel.
In addition, according to the present disclosure,
when storing a molten ferroalloy or molten nonferrous metal,
the molten ferroalloy or molten nonferrous metal is
denitrified or prevented from absorbing nitrogen, and thus
post processing such as a denitrification process may not
be performed.
【Technical Solution】
Accordingly, the present disclosure provides a method
of producing molten manganese-containing steel.
For example, according to an aspect of the present
8
disclosure, a method of producing molten manganesecontaining
steel may include: preparing a molten ferroalloy
or a molten nonferrous metal; maintaining the molten
ferroalloy or the molten nonferrous metal at a temperature
equal to or higher than a melting point thereof; and
pouring the molten ferroalloy or the molten nonferrous
metal into prepared molten steel, wherein in the
maintaining of the molten ferroalloy or the molten
nonferrous metal, the molten ferroalloy or the molten
nonferrous metal is subjected to a nitrogen-absorption
prevention process or a denitrification process.
The maintaining of the molten ferroalloy or the
molten nonferrous metal may be carried out in a holding
furnace together with the nitrogen-absorption prevention
process or the denitrification process, and the nitrogenabsorption
prevention process or the denitrification
process may include supplying argon (Ar) gas to the holding
furnace as an atmospheric gas to maintain an interior of
the holding furnace at a positive pressure.
The maintaining of the molten ferroalloy or the
molten nonferrous metal may be carried out in a holding
furnace together with the nitrogen-absorption prevention
process or the denitrification process, and the nitrogenabsorption
prevention process or the denitrification
9
process may include agitating the molten ferroalloy or the
molten nonferrous metal in at least one of upper and lower
regions of the holding furnace using argon (Ar) gas.
The nitrogen-absorption prevention process or the
denitrification process may include adding silicon (Si) to
the molten ferroalloy such that the molten ferroalloy may
have a silicon (Si) content of 1.5 wt% or greater.
The holding furnace may include: a case; an
accommodation unit disposed in the case and including an
internal space to accommodate a molten or solid ferroalloy
or nonferrous metal; a heating unit configured to heat the
ferroalloy or nonferrous metal contained in the
accommodation unit; and a cover disposed on an upper side
of the accommodation unit to close the internal space of
the accommodation unit, wherein the cover may include an
atmospheric gas supply unit connected to an inert gas
supply unit and supplying an atmospheric gas to the
accommodation unit so that the ferroalloy or the nonferrous
metal melted in the accommodation unit may be denitrified
or prevented from absorbing nitrogen.
The preparing of the molten ferroalloy or the molten
nonferrous metal may be performed in the holding furnace.
The molten ferroalloy or the molten nonferrous metal
may be prepared in an amount greater than a required amount
10
in the pouring of the molten ferroalloy or the molten
nonferrous metal, and after the required amount of the
molten ferroalloy or the molten nonferrous metal is poured
into the molten steel, a remaining amount of the molten
ferroalloy or the molten nonferrous metal may be
continuously maintained at a temperature equal to or
greater than the melting point thereof.
The preparing of the molten ferroalloy or the molten
nonferrous metal may include melting solid FeMN or a solid
Mn metal having a manganese (Mn) content and a phosphorus
(P) content according to the following formula:
P content (wt%) < -0.026 x (target Mn content (wt%)
of Mn-containing molten steel + (4.72 x 10-4) x (target Mn
content (wt%) of Mn-containing molten steel)2.
The heating unit of the holding furnace may include
an induction coil, and the preparing of the molten
ferroalloy or the molten nonferrous metal may include
induction heating using the induction coil.
The pouring of the molten ferroalloy or the molten
nonferrous metal may include: pouring the molten ferroalloy
or the molten nonferrous metal into a ladle in which the
molten steel is contained; and agitating the molten steel
together with the molten ferroalloy or the molten
nonferrous metal, wherein the agitating may be performed by
11
supplying an inert gas through a lower side of the ladle.
The pouring of the molten ferroalloy or the molten
nonferrous metal may include: pouring the molten ferroalloy
or the molten nonferrous metal into a ladle in which the
molten steel is contained; and agitating the molten steel
together with the molten ferroalloy or the molten
nonferrous metal, wherein the agitating may be performed
using an agitator inserted through an upper side of the
ladle into the molten steel and the molten ferroalloy or
the molten nonferrous metal.
In the maintaining of the molten ferroalloy or the
molten nonferrous metal, the molten ferroalloy or the
molten nonferrous metal may be maintained at a temperature
of 1300°C to 1500°C, and immediately prior to the pouring
of the molten ferroalloy or the molten nonferrous metal,
the method may further include heating the molten
ferroalloy or the molten nonferrous metal in consideration
of states of the molten steel and target states of high
manganese molten steel.
After the pouring of the molten ferroalloy or the
molten nonferrous metal, the method may further include
performing an RH vacuum refining process or a ladle furnace
(LF) refining process in which at least one of Al, C, Cu, W,
Ti, Nb, Sn, Sb, Cr, B, Ca, Si, and Ni is supplied to the
12
molten steel and the molten ferroalloy or the molten
nonferrous metal, and the RH vacuum refining process may be
performed together with a dehydrogenation process.
In addition, the present disclosure provides a
holding furnace.
For example, according to another aspect of the
present disclosure, a holding furnace may include: a case;
an accommodation unit disposed in the case and including an
internal space to accommodate a solid or molten ferroalloy
or a solid or molten nonferrous metal; a heating unit
configured to heat the ferroalloy or nonferrous metal
contained in the accommodation unit; and a cover disposed
on an upper side of the accommodation unit to close the
internal space of the accommodation unit, wherein the cover
includes an atmospheric gas supply unit connected to an
inert gas supply unit and supplying an atmospheric gas to
the accommodation unit so that the ferroalloy or the molten
nonferrous metal melted in the accommodation unit is
denitrified or prevented from absorbing nitrogen.
The heating unit may include at least one of: an
induction coil wound around the accommodation unit; an
electrode bar disposed in the cover; and a plasma disposed
in the cover.
The holding furnace may further include a control
13
unit connected to the heating unit, wherein the molten
ferroalloy or the molten nonferrous metal may be maintained
at a temperature of 1300°C to 1500°C under the control of
the control unit, and immediately prior to the molten
ferroalloy or the molten nonferrous metal being poured into
molten steel, the molten ferroalloy or the molten
nonferrous metal may be heated under the control of the
control unit.
An atmospheric gas supply tube may be disposed in the
cover disposed on the upper side of the accommodation unit,
and the cover may include a vent to maintain an interior of
the holding furnace at a constant positive pressure when an
atmospheric gas is supplied to the interior of the holding
furnace.
The holding furnace may further include: a siphon
structure including a suction part inserted through the
cover into the molten ferroalloy or the molten nonferrous
metal contained in the accommodation unit, a discharge part
connected to the suction unit so as to discharge the molten
ferroalloy or the molten nonferrous metal drawn through the
suction part to a ladle, a transfer part connected between
the suction part and the discharge part to transfer the
molten ferroalloy or the molten nonferrous metal, and an
initial pressure port connected to the transfer part for
14
creating an initial pressure difference; and a driving unit
connected to a lower side of the case to assist operations
of the siphon structure by lifting or lowering the case.
The holding furnace may further include: a driving
unit connected to the case for lifting or lowering the case
and the accommodation unit; a first guide disposed on an
outer surface of the case; and a guide frame disposed at an
outer side of the case and including a guide roller, the
guide roller blocking an upward movement of the first guide
by engaging with the first guide when the first guide is
moved upwardly, wherein a connection point at which the
driving unit is connected to the case may be located behind
the guide roller when viewed on a horizontal plane, and
when the case is moved upwardly by the driving unit, the
first guide may be hooked on the guide roller and then the
case is tilted.
In addition, the present disclosure provides an
apparatus for producing molten manganese-containing steel.
For example, according to another aspect of the
present disclosure, an apparatus for producing molten
manganese-containing steel may include: an Mn supply unit
supplying a molten metal having a high manganese content;
a molten steel supply unit supplying molten steel;
and a ladle configured to move between the molten steel
15
supply unit and the Mn supply unit to receive the molten
metal having a high Mn content from the Mn supply unit and
the molten steel from the molten steel supply unit, wherein
the Mn supply unit includes the holding furnace.
An inert gas supply tube may be disposed on a lower
side of the ladle, and the ladle may be connected to an
inert gas supply unit at a position at which the ladle
receives the molten metal from the Mn supply unit or the
molten steel from the molten steel supply unit, and the
molten metal and the molten steel poured into the ladle may
be agitated using an inert gas.
【Advantageous Effects】
According to the above-described aspects of the
present disclosure, the following effects may be provided.
Embodiments of the present disclosure provide a
method of immediately producing molten manganese-containing
steel by preparing a high-quality molten ferroalloy or
nonferrous metal on time according to the production of
molten steel in spite of differences between processes, a
holding furnace for the method, and an apparatus including
the holding furnace for producing molten manganesecontaining
steel. Particularly, according to the present
disclosure, a molten ferroalloy or molten nonferrous metal
is refined (denitrified or prevented from absorbing
16
nitrogen) while being maintained within a constant
temperature range. That is, the temperature of a refining
process which is one of important conditions for refining
may be maintained at a constant level, thereby guaranteeing
high refining efficiency. In addition, a production rate
difference between processes may be properly handled
without having to perform post processing, thereby
improving the efficiency of processes.
In addition, embodiments of the present disclosure
provide a method of producing molten manganese-containing
steel by adjusting the state of a molten ferroalloy or
molten nonferrous metal according to the state of molten
steel produced using a basic oxygen furnace, a holding
furnace for the method, and an apparatus including the
holding furnace for producing molten manganese-containing
steel.
Furthermore, according to the present disclosure,
when storing a molten ferroalloy or molten nonferrous metal,
the molten ferroalloy or molten nonferrous metal is
denitrified or prevented from absorbing nitrogen, and thus
post processing such as a denitrification process may not
be performed.
【Description of Drawings】
FIG. 1 is a flowchart illustrating a method of
17
producing manganese-containing steel in the related art.
FIG. 2 is a flowchart illustrating a method of
producing molten manganese-containing steel according to an
embodiment of the present disclosure.
FIG. 3 is a flowchart illustrating a method of
producing molten manganese-containing steel according to
another embodiment of the present disclosure.
FIGS. 4A to 4C are schematic views illustrating an
apparatus for producing molten manganese-containing steel
according to an embodiment of the present disclosure.
FIG. 5 is a schematic cross-sectional view
illustrating a holding furnace of the molten manganesecontaining
steel production apparatus.
FIG. 6 is a plan view illustrating the holding
furnace of the molten manganese-containing steel production
apparatus.
FIG. 7 is a partial cut-away view illustrating the
holding furnace of the molten manganese-containing steel
production apparatus.
FIGS. 8A and 8B are schematic cross-sectional views
examples of the holding furnace of the molten manganesecontaining
steel production apparatus according to
embodiments of the present disclosure.
FIGS. 9 and 10 are schematic cross-sectional views
18
illustrating other examples of the holding furnace of the
molten manganese-containing steel production apparatus
according to embodiments of the present disclosure.
FIGS. 11 and FIGS. 12A to 12C are a cross-sectional
view and operational views illustrating the holding furnace
of the molten manganese-containing steel production
apparatus according to embodiments of the present
disclosure.
FIG. 13 is a cross-sectional view illustrating
another example of the holding furnace of the molten
manganese-containing steel production apparatus according
to an embodiment of the present disclosure.
FIG. 14 is a graph illustrating the content of
nitrogen over time in Example 1, and FIG. 15 is an image of
a molten metal surface in Example 1.
FIG. 16 is a graph illustrating the content of
nitrogen over time in Comparative Example 1, and FIG. 17 is
an image of a molten metal surface in Comparative Example 1.
FIG. 18 is a graph illustrating the content of
nitrogen over time in Example 2.
FIG. 19 is a graph illustrating the content of
nitrogen over time in Example 3.
FIG. 20 is a graph illustrating the content of
nitrogen over time in Example 4.
19
FIG. 21 is a graph illustrating the content of
nitrogen in Example 2 and Comparative Example 2.
【Best Mode】
Hereinafter, methods of producing manganese (Mn)-
containing steel will be described in detail according to
embodiments of the present disclosure with reference to the
accompanying drawings. The disclosure may, however, be
exemplified in many different forms and should not be
construed as being limited to the specific embodiments set
forth herein. Rather, these embodiments are provided so
that this disclosure will be thorough and complete, and
will fully convey the scope of the present invention to
those skilled in the art.
In a basic oxygen furnace process for producing high
manganese steel, a manganese-containing ferroalloy may be
supplied to low manganese steel. In this case, although
varying according to the content of manganese in a final
product, 45 tons to 63 tons of a ferroalloy may have to be
supplied to every 280 tons of molten steel so as to produce
a steel having an Mn content of 15 wt% or greater, and as a
result, the temperature of the molten steel may be
decreased by about 250°C to about 350°C. Theoretically,
when molten steel is drawn out of a basic oxygen furnace,
the temperature of the molten steel has to be about 1900°C
20
so as to compensate for such a decrease in the temperature
of the molten steel caused by the supply of a ferroalloy.
However, this temperature is outside the temperature range
controllable by currently available refining equipment.
Even through a temperature increasing apparatus such as a
ladle furnace is used, it takes 100 or more minutes to
increase the temperature of molten steel for preparing for
a temperature decrease, thereby excessively increasing the
process time. In addition, when manganese is melted in an
electric furnace, the nitrogen content of molten steel may
increase to about 300 ppm or greater.
Thus, as shown in FIG. 1, a method of supplying a
molten manganese ferroalloy to molten steel produced
through a blowing process in a basic oxygen furnace has
been proposed. Referring to FIG. 1, after a melting process
(high carbon FeMn), a refining process (medium/low carbon
FeMn), or a dephosphorization process (low phosphorus (P)
FeMn), a molten manganese ferroalloy is directly supplied
to molten steel drawn out of a basic oxygen furnace. In
this case, however, a process of producing molten steel and
a process of producing a molten ferroalloy are required,
and then the molten metals (molten steel and molten
ferroalloy) are poured (mixed) together. Therefore, if the
amount of final molten manganese-containing steel is
21
excessive or insufficient, the amount of one of the molten
metals may have to be adjusted based on the amount of the
other of the molten metals, and this may result in
unnecessary waste of molten steel. Thus, another method of
storing a molten metal in a container has been proposed.
However, a molten metal such as a molten ferroalloy or
particularly a molten manganese-containing ferroalloy may
be oxidized or nitrided in a container, and post processing
may be necessary to process the molten metal.
Thus, the embodiments of the present disclosure
provide methods of producing molten manganese-containing
steel that do not have the above-mentioned problems.
According to the embodiments of the present disclosure, a
refining process (such as a denitrification process or a
process for preventing nitrogen absorption) is performed in
a holding furnace so as to prevent the loss of manganese,
omit post processing, and increase the efficiency of the
refining process.
FIG. 2 is a schematic flowchart illustrating a method
of producing molten manganese-containing steel according to
an embodiment of the present disclosure. As shown in FIG. 2,
molten steel may be produced in the same manner as that
used in the related art. Molten steel produced in a blast
furnace may be supplied to a basic oxygen furnace and may
22
then be subjected to a process such as a blowing process or
a dephosphorization process according to necessary
properties (S100). Thereafter, the molten steel is drawn of
the basic oxygen furnace (S110). Meanwhile, FeMn
(hereinafter referred to as a ferroalloy) such as an Mncontaining
ferroalloy or an Mn metal is supplied to a
ferroalloy melting furnace (S120) and is melted (S130).
Thereafter, the molten ferroalloy is poured into a holding
furnace 100 (described with reference to FIG. 5) (S140).
Before the molten ferroalloy is poured into the holding
furnace 100, the molten ferroalloy may be dephosphorized or
refined by a well-known method if necessary.
The molten ferroalloy is stored in the holding
furnace 100 and maintained at a temperature equal to or
higher than the melting point of the molten ferroalloy
(S150), and then the molten ferroalloy is poured into
(mixed with) the molten steel (S160). Herein, expressions
such as "temperature maintaining" or "being maintained at a
temperature" refer to maintaining the temperature of the
molten ferroalloy by heating the molten ferroalloy in the
case of heat loss as well as referring to simply preventing
a temperature decrease of the molten ferroalloy. The molten
ferroalloy is maintained within the temperature range of
about 1300°C to 1500°C.
23
An induction heating method using an induction coil
may be used for temperature maintaining, and in this case,
an induction agitating effect may also be obtained owing to
a magnetic field induced during induction heating. Owning
to the induction agitating effect, the temperature and
components of the molten ferroalloy may be uniformly
distributed. In addition, owing to a molten ferroalloy
(FeMn) agitating effect induced by the induction agitating
effect, the efficiency of a denitrification refining
process may be improved.
According to the embodiment of the present disclosure,
while the molten ferroalloy is stored in the holding
furnace 100 and maintained at a temperature equal to or
higher than the melting point of the molten ferroalloy
(S150), an inert gas (such as argon (Ar) gas) is used to
prevent the molten ferroalloy from absorbing nitrogen, or
the molten ferroalloy is refined. That is, according to the
embodiment of the present disclosure, a refining process is
performed while the molten ferroalloy is stored in the
holding furnace 100 at a temperature equal to or higher
than the melting point of the molten ferroalloy.
Since temperature maintaining and refining are
simultaneously performed, time loss may be prevented
compared to the case that temperature maintaining and
24
refining are performed separately. In addition, if a
refining process is individually performed, a temperature
decrease may occur, and thus an additional temperature
maintaining process may have to be performed. This may
cause heat loss. However, according to the embodiment of
the present disclosure, energy may be saved because
refining and temperature maintaining are simultaneously
performed.
Moreover, since one of basic conditions affecting the
efficiency of a refining process is a temperature condition,
if a refining process is individually performed, the
efficiency of the refining process may be lowered due to a
temperature variation caused by heat loss. However,
according to the embodiment of the present disclosure, a
refining process is performed while continuously
maintaining the temperature of a molten ferroalloy, thereby
increasing the efficiency of the refining process and
minimizing heat and time loss that may occur if the
refining process is individually performed.
After the molten ferroalloy and the molten steel are
poured (mixed) together to obtain molten manganesecontaining
steel, the molten manganese-containing steel may
be subjected to an RH vacuum refining process (S170) or a
ladle furnace (LH) refining process in which at least one
25
of Al, C, Cu, W, Ti, Nb, Sn, Sb, Cr, B, Ca, Si, and Ni is
supplied to the molten manganese-containing steel.
Alternatively, while performing a RH vacuum refining
process in which at least one of Al, C, Cu, W, Ti, Nb, Sn,
Sb, Cr, B, Ca, Si, and Ni is supplied to the molten
manganese-containing steel, a dehydrogenation process may
be performed.
Thereafter, a continuous casting process may be
performed to produce slabs or steel sheets (S180).
FIG. 3 is a schematic flowchart illustrating a method
of producing molten manganese-containing steel according to
another embodiment of the present disclosure. Referring to
FIG. according to the other embodiment, FeMn is melted in a
melting furnace (S200) and is subjected to a process such
as a dephosphorization process (S210) to produce to a
product having a desired composition (S220).
The product may have a phosphorus (P) content of 0.03
wt% or less because the upper limit of the phosphorus (P)
content of molten manganese-containing steel is generally
0.03 wt% for a continuous casting process. If manganesecontaining
steel, in particular, high manganese steel
having a phosphorus (P) content of 0.03 wt% or greater, is
processed through a continuous casting process, surface
defects may be formed due to phosphorus (P).
26
Therefore, when high Mn steel is produced, the
phosphorus (P) content of solid FeMn or a solid Mn metal
that will be supplied to the holding furnace 100 may be
limited according to the Mn content of the high Mn steel as
expressed by the following Formula 1. That is, as the Mn
content of high Mn steel increases, the phosphorus (P)
content of a molten metal supplied to the melting furnace
decreases. In addition, when molten FeMn or a molten Mn
metal is supplied instead of supplying solid FeMn or a
solid Mn Metal, the phosphorus (P) content of the molten
FeMn or the molten Mn metal may be adjusted according to
the following Formula 1.
[Formula 1]
P content (wt%) of molten metal in holding furnace <
-0.026 x (Mn content (wt%) of high Mn steel + (4.72 x 10-4)
x (Mn content (wt%) of high Mn steel)2
A solid ferroalloy is supplied to the holding furnace
100 and is melted in the holding furnace 100 (S240). The
temperature of the molten ferroalloy is maintained (S250)
until a pouring (mixing) process S270 is performed. While
the temperature of the molten ferroalloy is maintained, a
process of preventing nitrogen absorption or a refining
(denitrification) process is performed (S250).
In the temperature maintaining process S250, the
27
temperature of the molten ferroalloy is maintained within
the temperature range of 1300°C to 1500°C, and the interior
of the holding furnace 100 is maintained at a positive
pressure by blowing argon (Ar) gas to an upper internal
region of the holding furnace 100 through a lance or
blowing argon (Ar) gas directly into the molten ferroalloy
through a lower gas tube so as to denitrify the molten
ferroalloy or prevent the molten ferroalloy from absorbing
nitrogen. While or after the argon (Ar) gas is supplied to
the holding furnace 100, silicon (Si) may be supplied to
the holding furnace 100.
Meanwhile, molten steel is prepared through a
separate process S270, and the molten steel is mixed with
the molten ferroalloy in the pouring (mixing) process S280.
In the embodiment illustrated in FIG. 3, the molten
ferroalloy contained in the holding furnace 100 is heated
(S260) according to the state of the molten steel before
pouring (mixing) or a desired state after pouring (mixing).
To this end, the temperature of the molten steel may be
checked immediately prior to or after pouring (mixing), so
as to control the temperature of the holding furnace 100.
In temperature control, the final temperature of the
holding furnace 100 may be controlled as follows: the
temperature of the molten metal (molten ferroalloy) in the
28
holding furnace 100 may be calculated by the following
Formula 2 using the temperature of the molten steel (S270)
to be mixed with the molten metal of the holding furnace
100 and a target temperature after the molten steel and the
molten metal are mixed, and the temperature of the molten
metal contained in the holding furnace 100 may be
controlled based on the calculated temperature.
[Formula 2]
[(molten steel amount x molten steel temperature
(°C)) + (molten metal amount in holding furnace × molten
metal temperature (°C) in holding furnace)] / (final amount
of Mn-containing molten steel) = temperature (°C) after
pouring (mixing) (°C)
That is, the temperature of the molten manganesecontaining
steel may be controlled by adjusting the
temperature of the holding furnace 100 according to the
temperature of the molten steel supplied through the
process S270 after pouring (mixing). For example, when the
molten manganese-containing steel is initially produced,
the temperature of the molten steel may be lower than a
target temperature set for the molten steel and may be
different from the temperature of the molten ferroalloy
drawn out of the holding furnace 100, and thus the
temperature of the molten manganese-containing steel may be
29
lower than a desired temperature after pouring (mixing). In
this case, according to the embodiment of the present
disclosure, the temperature of the molten ferroalloy
contained in the holding furnace 100 may be increased in
the heating process S260 so as to compensate for the low
temperature of the molten steel, and thus the temperature
of the molten manganese-containing steel may be adjusted to
a desired temperature after pouring (mixing).
During pouring (mixing), the content of manganese
(Mn) may vary in a vertical direction due to a density
difference between the molten steel and the molten
ferroalloy, and thus the molten steel and the molten
ferroalloy may be agitated using a mechanical tool or gas.
FIGS. 4A to 4C are views schematically illustrating
an apparatus for producing molten manganese-containing
steel according to an embodiment of the present disclosure.
FIGS. 4A to 4C illustrate the apparatus according to
processes.
Referring to FIG. 4A, molten steel is produced using
a basic oxygen furnace 10, and a molten ferroalloy is
produced using a ferroalloy melting furnace 20. The molten
ferroalloy produced using the ferroalloy melting furnace 20
is poured into a holding furnace 100. A process for
preventing nitrogen absorption and a denitrification
30
process are performed on the molten ferroalloy contained in
the holding furnace 100. The volume of the holding furnace
100 is sufficiently large, such that the molten ferroalloy
contained in the holding furnace 100 may be supplied to the
molten steel at least once.
In the embodiment of the present disclosure, since
molten ferroalloy is stored in the holding furnace 100,
even though the volume of the ferroalloy melting furnace 20
is smaller than the volume of the basic oxygen furnace 10,
molten steel produced a plurality of times using the
ferroalloy melting furnace 20 may be stored in the holding
furnace 100. That is, even though the production rates of
the ferroalloy melting furnace 20 and the basic oxygen
furnace 10 are different, problems related with the
different production rates may be solved using the the
holding furnace 100. On the contrary, even though the
volume of the ferroalloy melting furnace 20 is greater than
the volume of the basic oxygen furnace 10, after a proper
amount of a molten ferroalloy is supplied according to the
amount of molten steel produced using the basic oxygen
furnace 10, the remaining amount of the molten ferroalloy
may be stored in the holding furnace 100. That is, each
process may be freely operated.
Referring to FIG. 4B, the molten steel produced using
31
the basic oxygen furnace 10 is poured into a ladle 30, and
the ladle 30 is moved toward the holding furnace 100 using
a ladle transfer car 50.
Referring to FIG. 4C, the molten ferroalloy is poured
from the holding furnace 100 into the ladle 30 in which the
molten steel is contained. At this time, a gas supply tube
31 disposed at a lower side of the ladle 30 is connected to
a gas supply unit 40 located adjacent to the holding
furnace 100 so as to supply an inert gas a molten metal
mixture of the molten steel and the molten ferroalloy
through the lower side of the ladle 30 and thus agitate the
molten metal mixture.
FIG. 5 is a cross-sectional view illustrating the
holding furnace 100 according to an embodiment of the
present disclosure, and FIG. 6 is a plan view illustrating
the holding furnace 100 according to the embodiment of the
present disclosure. FIG. 7 is an enlarged view illustrating
an upper cover 140 of the holding furnace 100.
According to the embodiment of the present disclosure,
the holding furnace 100 includes: a case 110 forming the
exterior of the holding furnace 100; an accommodation unit
120 disposed in the case 110 and formed of a refractory
material to accommodate a molten or solid ferroalloy; a
heating unit 130 (refer to FIGS. 8 and 9) connected to the
32
accommodation unit 120 to heat a ferroalloy or a nonferrous
metal accommodated in the accommodation unit 120; and the
upper cover 140 disposed on an upper side of the
accommodation unit 120 to close an internal space of the
accommodation unit 120. A molten steel outlet 160 is formed
in an upper lateral side of the holding furnace 100.
The case 110 may be a steel shell surrounding and
protecting the accommodation unit 120 and the heating unit
130, and first guides 111 (refer to FIGS. 12A to 12C) or
driving units 190 (refer to FIG. 11) may be connected to
the case 110 to move and tilt the case 110 for pouring a
molten ferroalloy from the accommodation unit 120 to the
ladle 30 (refer to FIGS. 4A to 4C).
The accommodation unit 120 is formed of a refractory
material to contain a solid or molten ferroalloy, and the
upper side of the accommodation unit 120 may be closed with
the upper cover 140.
The upper cover 140 includes: a refractory material
141 disposed on a surface facing the accommodation unit
120; a window 142 through which a molten ferroalloy
contained in the accommodation unit 120 can be seen or
sampled; and a connection part 145 disposed on an outer
side of the upper cover 140 and connected to a rotating
unit 147 and a vertical actuator 146 that move the upper
33
cover 140. When a solid or molten ferroalloy is initially
supplied to the accommodation unit 120, the upper cover 140
is opened and moved and rotated away from the accommodation
unit 120, and after the solid or molten ferroalloy is
completely supplied, the upper cover 140 closes the
accommodation unit 120.
Referring to FIG. 6, the molten steel outlet 160 is
formed in an upper lateral side of the accommodation unit
120, and if the case 110 is tilted, the molten ferroalloy
flows out of the accommodation unit 120 through the molten
steel outlet 160. The molten steel outlet 160 is closed
with a molten steel outlet cover 164, and the molten steel
outlet cover 164 is opened by a molten steel outlet driving
unit 165 only when a molten ferroalloy is drawn out of the
accommodation unit 120.
Referring to FIG. 7, an atmospheric gas supply unit
150 is disposed in the upper cover 140. The atmospheric gas
supply unit 150 includes: an atmospheric gas supply valve
152 configured to control the flow rate of an atmospheric
gas supplied from an atmospheric gas supply source (not
shown); and an atmospheric gas supply tube 151 connected to
the atmospheric gas supply valve 152 and extending into the
upper cover 140.
An inert atmospheric gas may be supplied through the
34
atmospheric gas supply tube 151, and a vent 172 may be
provided to maintain the interior of the holding furnace
100 at a constant positive pressure when an atmospheric gas
is supplied to the holding furnace 100. If the interior
pressure of the holding furnace 100 becomes greater than a
certain level, the vent 172 is opened to discharge an inert
gas such as argon (Ar) gas from the interior of the holding
furnace 100.
The upper cover 140 includes an opening to receive a
lance 170, and the lance 170 may be insert into a molten
ferroalloy isothermally contained in the holding furnace
100 through the opening of the upper cover 140 so as to
denitrify the molten ferroalloy by blowing an inert gas
therein.
Alternatively, a gas supply unit (not shown) may be
disposed at a lower side of the holding furnace 100 instead
of the lance 170, so as to supply an inert gas through the
lower side of the holding furnace 100 and denitrify the
molten ferroalloy contained in the holding furnace 100.
FIGS. 8A and 8B illustrate examples of the heating
unit 130 including induction coils 131 according to
embodiments of the present disclosure. Referring to FIG. 8A,
the induction coil 131 is wound around the accommodation
unit 120 formed of a refractory material to melt a solid
35
ferroalloy contained in the accommodation unit 120 or
maintain the temperature of a molten ferroalloy contained
in the accommodation unit 120. If an induction heating
method is used as illustrated in FIG. 8A, since the
induction coil 131 is disposed outside the refractory
material of the accommodation unit 120, the interior of the
holding furnace 100 may be easily sealed. In addition,
since the molten ferroalloy is agitated by a magnetic field
induced for induction heating, the temperature and
composition of the molten ferroalloy may be uniformized,
and the efficiency of a denitrification refining process
may also be improved.
Referring to FIG. 8B, a path 132 is formed along a
bottom side of the accommodation unit 120, and the
induction coil 131 is wound around the path 132. In the
embodiment illustrated in FIG. 8B, a molten ferroalloy
introduced into the path 132 is heated by the induction
coil 131 wound around the path 132, and then the heated
molten ferroalloy flows to the interior of the
accommodation unit 120. In this manner, the molten
ferroalloy may be maintained at a constant temperature.
FIGS. 9 and 10 illustrate other examples of the
heating unit 130 including electrode bars 133 or a plasma
generator 135. Referring to FIGS. 9 and 10, the electrode
36
bars 133 are inserted into the accommodation unit 120
through penetration holes 143 formed in the upper cover 140,
or the plasma generator 135 is inserted into the
accommodation unit 120 through a penetration hole 143
formed in the upper cover 140. Sealing members 133 are used
to prevent leakage of an insert inert gas through the
penetration holes 143.
FIGS. 11 and FIGS. 12A to 12C illustrate the driving
units 190 and a guide frame 180 for tilting the holding
furnace 100, according to an embodiment of the present
disclosure. Referring to FIGS. 11 and FIGS. 12A to 12C, the
driving units 190 are connected to a lower side of the case
110 of the holding furnace 100, and the guide frame 180 is
disposed on a lateral side of the case 110.
The first guides 111 formed on the lateral side of
the case 110 facing the guide frame 180. The first guides
111 (only one shown in FIGS. 12A to 12C) include: first
members 111a extending on a horizontal plane forward in a
tilting direction from connection points at which the case
110 and the driving units 190 are connected; second members
111b extending from the first members 111a and configured
to receive guide rollers 181 for controlling tilting; and
third members 111c extending from the second members 111b
and sloped upwardly for guiding descending of the case 110.
37
The guide frame 180 is disposed on both sides of the
case 110. The guide frame 180 includes the guide rollers
181 disposed at a predetermined height for coupling with
the first members 111a.
In operation, if the case 110 is moved upwardly by
the driving units 190, the first guides 111 are brought
into contact with the guide rollers 181 of the guide frame
180. Then, the case 110 is no longer lifted but rotated by
lifting force. That is, as the guide rollers 181 engage
with the first guides 111, the case 110 starts to rotate,
and the amount of rotation of the case 110 is determined by
the amount of engagement between the guide rollers 181 and
the first guides 111.
FIG. 13 illustrates another structure for tapping a
molten metal according to another embodiment of the present
disclosure. In the embodiment illustrated in FIG. 13,
driving units 190 are connected to a lower side of a case
110 as in the embodiment shown in FIGS. 11 and FIGS. 12A to
12C. However, a siphon structure 200 is used instead of the
molten steel outlet 160. The siphon structure 200 has a
pipe shape including: a suction part 220 for suctioning a
molten ferroalloy containing in a holding furnace 100; a
discharge part 230 for discharging the molten ferroalloy to
molten steel contained in a ladle 30; and a transfer part
38
240 through which the molten ferroalloy is transferred. An
initial pressure port 210 is connected to the siphon
structure 200 to generate an initial pressure difference.
The surface of the molten steel contained in the
ladle 30 is lower than the surface of the molten ferroalloy
contained in the holding furnace 100 so that a sufficient
pressure differential may be generated to allow for
siphonic free falling. At this time, if an initial pressure
difference is created using a decompressing device (not
shown) connected to an rear end of the initial pressure
port 210, the molten ferroalloy contained in the holding
furnace 100 is drawn into the transfer part 240 through the
suction part 220, and thus if the molten ferroalloy drawn
into the transfer part 240 starts to undergo free falling,
the initial pressure port 210 is closed using a value 211.
Then, the molten ferroalloy containing in the holding
furnace 100 is forced to flow to the molten steel contained
in the ladle 30 by a natural pressure difference.
As the molten ferroalloy is transferred from the
holding furnace 100 to the ladle 30, the height difference
between the surface of the molten steel contained in the
holding furnace 100 and the molten steel contained in the
ladle 30 is decreased, and thus negative pressure generated
by free falling of the molten ferroalloy and acting on the
39
suction part 220 is decreased. That is, the siphonic effect
is lowered. In this case, the holding furnace 100 may be
lifted using the driving units 190 to increase the height
difference between the surface of the molten ferroalloy and
the surface of the molten steel and maintain the siphonic
effect.
If the siphon structure 200 is used, when a molten
ferroalloy and molten steel are poured (mixed) together, it
may not be necessary to tilt the holding furnace 100, and
the molten ferroalloy may not absorb nitrogen from the air
because the molten ferroalloy is not exposed to the air.
【Mode for Invention】
Hereinafter, the embodiments of the present
disclosure will be explained more specifically through
examples.
Table 1 illustrates results of Examples 1 to 4 and
Comparative Examples 1 and 2.
[Table 1]
Conditions FeMn Composition N variation
C
(wt%)
Mn
(wt%)
Si
(wt%)
Example 1 Ar positive
pressure
1.5 71.2 0.6 Maintain
Example 2 Ar lance
injection
1.5 70.7 0.5 0.002 wt%
decrease
for 370 min
Example 3 Ar positive 1.5 67.9 2.7 0.013 wt%
40
pressure + Si
addition
decrease
for 380 min
Example 4 Ar lance
injection + Si
addition
1.3 69.8 3.1 0.091 wt%
decrease
for 190 min
Comparative
Example 1
- 1.48 70.9 0.6 Increase
Comparative
Example 2
Si addition in
small amounts
0.2 70 1.5 Slight
decrease
Example 1
1.5 tons of FeMn were melted in the holding furnace
100, and after closing the holding furnace 100 with the
upper cover 140, the interior of the holding furnace 100
was controlled using an argon (Ar) atmosphere. While
maintaining the interior of the holding furnace 100 at
1500°C, temperature measurement, sampling, and molten FeMn
surface observation were performed at regular time
intervals. At that time, the main components of the molten
FeMn were 1.5 wt% carbon (C), 71.2 wt% manganese (Mn), and
0.6 wt% silicon (Si).
As shown in FIG. 15, since the interior of the
holding furnace 100 was controlled using an argon (Ar)
atmosphere, the nitrogen (N) content of the molten FeMn was
maintained substantially at a constant level. That is,
since the interior of the holding furnace 100 was filled
with argon (Ar), the molten FeMn was not exposed to the air,
41
and thus the absorption of nitrogen (N) was prevented.
FIG. 15 is an image of the surface of the molten FeMn.
Referring to FIG. 15, the molten FeMn was maintained in an
exposed state. Since the upper cover 140 was not closed and
the interior of the holding furnace 100 was not maintained
in an argon (Ar) atmosphere when the FeMn was initially
melted and the surface of the molten FeMn was initially
observed, Mn oxides were formed along a wall of the
refractory material 120 around the center of the holding
furnace 100. However, after the upper cover 140 is closed
and the interior of the holding furnace 100 is filled with
argon (Ar), Mn oxides were not formed any more. As shown in
FIG. 15, the Mn oxides initially formed before the interior
of the holding furnace 100 were maintained in an argon (Ar)
atmosphere were moved toward the refractory material by
agitation caused by an induced magnetic field, and the
surface of the molten FeMn was exposed in a central region
of the holding furnace 100 as described above.
Since the interior of the holding furnace 100 was
maintained in an argon (Ar) atmosphere, the permeation of
air and nitrogen was blocked, and thus the formation of Mn
oxides was prevented. However, as shown in FIG. 14, the
high nitrogen (N) content of the molten FeMn was also not
decreased. That is, the molten FeMn was not denitrified
42
only by maintaining the interior of the holding furnace 100
in an argon (Ar) atmosphere.
Comparative Example 1
1.7 tons of FeMn was melted in the same holding
furnace 100 as that used in Example 1, and the surface and
nitrogen (N) content of the molten FeMn were observed or
measured while maintaining the holding furnace 100 at
1500°C without filling the interior of the holding furnace
100 with argon (Ar) and closing the holding furnace 100
with the upper cover 140. The FeMn included 1.48 wt% carbon
(C), 70.9 wt% manganese (Mn), and 0.6 wt% silicon (Si).
FIG. 16 illustrates the nitrogen (N) content of the
molten FeMn of Comparative Example 1 over time when the
molten FeMn was maintained at a temperature of 1500°C.
Initially, the surface of the molten FeMn was maintained
and exposed to the air, and thus nitrogen (N) was
introduced into the molten FeMn. However, after the molten
FeMn was maintained at 1500°C for 50 minutes, nitrogen (N)
was not introduced into the molten FeMn. As shown in FIG.16,
the reason for this was that Mn oxides were formed by a
reaction between manganese (Mn) and oxygen at the surface
of the molten FeMn exposed to the air, and thus air was
blocked by the Mn oxides as if air was blocked by argon
43
(Ar). Although the Mn oxides had the same effect of
blocking air as the effect of blocking air by argon (Ar),
manganese (Mn) was wasted by being oxidized, and if molten
FeMn is additionally supplied, nitriding could occur again.
FIG. 17 illustrates slag formed on the molten FeMn.
Since the interior of the holding furnace 100 was not
filled with argon (Ar) and the upper cover 140 was opened,
the molten FeMn was exposed to the air, and manganese (Mn)
of the molten FeMn reacted with oxygen and formed Mn oxides.
When the surface of the molten FeMn started to make
contact with nitrogen (N), the nitrogen (N) content of the
molten FeMn increased. However, as the surface of the
molten FeMn was covered with Mn oxides, the surface of the
molten FeMn was restricted from making contact with the air,
and thus the introduction of nitrogen (N) into the molten
FeMn was blocked. However, after the introduction of
nitrogen (N) was blocked, manganese (Mn) was continuously
oxidized and wasted.
Example 2
In Example 2, 1.4 tons of molten FeMn was stored at
temperature of 1500°C in the same holding furnace 100 as
that used in Comparative Example 1. The interior of the
holding furnace 100 was filled with argon (Ar) as in
44
Example 1. For filling the interior of the holding furnace
100 with argon (Ar) and obtaining an agitating effect by
the argon (Ar), the lance 170 was inserted through an upper
side of the holding furnace 100 into the molten FeMn to a
depth of 200 mm from the surface of the molten FeMn, and
argon (Ar) was blown into the molten FeMn through the lance
170 at a rate of 20 Nl/min. The FeMn included 1.5 wt%
carbon (C), 70.7 wt% manganese (Mn), and 0.5 wt% silicon
(Si). FIG. 18 illustrates the nitrogen (N) content of the
molten FeMn over time. The nitrogen (N) content of the
molten FeMn was decreased over time.
Example 3
In Example 3, 1.4 tons of molten FeMn was stored at
1500°C in the same holding furnace 100 as that used in
Comparative Example 1. The holding furnace 100 was closed
with the upper cover 140 and filled with argon (Ar) gas.
The molten FeMn included 1.5 wt% carbon (C), 67.9 wt%
manganese (Mn), and 2.7 wt% silicon (Si), and variations of
the molten FeMn caused by the increased content of silicon
(Si) were observed. As shown in FIG. 19, the nitrogen (N)
content of the molten FeMn was gradually decreased over
time.
45
Example 4
In Example 4, 1.4 tons of molten FeMn, as in Example
2, was stored at a temperature of 1500°C in the same
holding furnace 100 as that used in Comparative Example 1.
Argon (Ar) gas was blown into the molten FeMn as in Example
2, and the silicon (Si) content of the molten FeMn was
increased as in Comparative Example 3. Effects of the argon
(Ar) gas and the increased content of silicon (Si) were
checked. The molten FeMn included 1.3 wt% carbon (C), 69.8
wt% manganese (Mn), and 3.1 wt% silicon (Si). As in Example
2, the lance 170 was inserted from the upper side of the
holding furnace 100 into the molten FeMn to a depth of 200
mm from the surface of the molten FeMn, from argon (Ar) gas
was blown through the lance 170. As shown in FIG. 20, the
nitrogen (N) content of the molten FeMn was gradually
decreased over time. The reduced amount of nitrogen was
0.091 wt% for 190 minutes. In Example 2, the reduced amount
of nitrogen was 0.002 wt% for 370 minutes, and in Example 3,
the reduced amount of nitrogen was 0.013 wt% for 380
minutes. That is, the rate of denitrification was not
simply in linear proportion to the flow rate of argon (Ar)
gas and the content of silicon (Si) but was in exponential
proportion to the flow rate of argon (Ar) gas and the
content of silicon (Si) owing to the synergy effect.
46
Comparative Example 2
In Comparative Example 2, the effects of argon (Ar)
gas blown into molten FeMn and an increased content of
silicon (Si) in the molten FeMn were checked as in Example
4. Unlike in Example 4, the molten FeMn included 1.5 wt%
silicon (Si), 70 wt% manganese (Mn), and 0.2 wt% carbon (C).
1.4 tons of the molten FeMn was stored at 1500°C in the
same holding furnace 100 as that used in Example 4, and the
interior of the holding furnace 100 was filled with argon
(Ar) gas. The lance 170 was inserted from the upper side of
the holding furnace 100 into the molten FeMn to a depth of
200 mm from the surface of the molten FeMn, and argon (Ar)
gas was blown through the lance 170 at a flow rate of 20
Nl/min. Results are shown in FIG. 21.
The nitrogen (N) content of the molten FeMn was
decreased over time. As shown in FIG. 21, the rate of
denitrification was slightly improved in Comparative
Example 2 when compared to Example 2 in which the content
of silicon (Si) was 0.8 wt%. However, this improvement was
meaningless if factors such as an error range were
considered. That is, it is preferable that the content of
silicon (Si) is 1.5 wt% or greater, so as to obtain an
meaningful improvement by only the addition of silicon (Si)
47
or in combination with agitation by argon (Ar) gas.
Comparative Example 3
Molten FeMn was maintained at 1500°C in the holding
furnace 100, and 0.35 tons of the molten FeMn was poured to
1.3 tons of molten steel contained in the ladle 30. For
pouring (mixing) the molten FeMn and the molten steel
together, the ladle 30 in which the molten steel was
contained was moved to a position under the holding furnace
100, and the holding furnace 100 was tilted to pour the
molten FeMn to the ladle 30. While mixing the molten FeMn
and the molten steel, gas or mechanical agitation was not
performed.
The molten FeMn included 70 wt% manganese (Mn), and
the molten steel included 0.6 wt% manganese (Mn). A high Mn
steel obtained by pouring (mixing) the molten FeMn and the
molten steel together was expected to include 15.3 wt%
manganese (Mn). However, the manganese (Mn) content of the
high Mn steel was 46.7 wt% after 10 minutes from the
pouring (mixing). That is, the molten FeMn was not
uniformly mixed with the molten steel but stayed above the
molten steel, and thus a sample taken at a position near
the surface of the mixture had a high manganese (Mn)
content.
48
Example 5
As in Comparative Example 3, high Mn steel was
produced by mixing molten FeMn and molten steel. As in
Comparative Example 3, 0.47 tons of molten FeMn contained
at 1497°C in the holding furnace 100 was poured into 1.4
tons of molten steel contained in the ladle 30.
However, unlike in Comparative Example 3, when the
molten FeMn and the molten steel was poured (mixed), argon
(Ar) gas was blown at a flow rate of 10 Nl/min (10.9 Nl/min
for each ton of high Mn steel) into the ladle 30 through a
gas supply tube 31 located on a lower side of the ladle 30
to agitate the molten FeMn and the molten steel. The molten
FeMn included 70.6 wt% manganese (Mn), and the molten steel
included 0.6 wt% manganese (Mn). The manganese (Mn) content
of high Mn steel produced by pouring (mixing) together the
molten FeMn and the molten steel was expected to be 18.2
wt%. A sample of the high Mn steel taken immediately after
the mixing was analyzed to have a manganese (Mn) content of
18.9 wt%, and a sample of the high Mn steel taken after 20
minutes from the start of pouring (mixing) was analyzed to
have a manganese (Mn) content of 18.7 wt%. That is,
agitation by the argon (Ar) gas blown from the lower side
of the ladle 30 was effective in uniformizing the
49
distribution of manganese (Mn) after the pouring (mixing).
Example 6
High Mn steel was produced under the same conditions
as in Example 5 except for the use of an impeller instead
of using gas agitation. The impeller was rotated at a speed
of 30 rpm. In the same sequence as in Comparative Example 3
and Example 5, 0.52 tons of molten FeMn was poured into 1.1
tons of molten steel contained in the ladle 30, and the
mixture of molten FeMn and molten steel was agitated using
the impeller. The molten steel included 0.07 wt% manganese
(Mn), and the molten FeMn included 67.9 wt% manganese (Mn).
The high Mn steel produced by pouring (mixing) the molten
FeMn and the molten steel together was expected to have a
manganese (Mn) content of 21.8 wt%. A sample taken from the
mixture (high Mn steel) after 2 minutes from the end of
mechanical agitation by the impeller had a manganese (Mn)
content of 21.6 wt%, and a sample taken from the mixture
after 20 minutes from the end of mechanical agitation by
the impeller had a manganese (Mn) content of 21.4 wt%. That
is, the agitation by the impeller was effective in
uniformizing the composition of the high Mn steel.
Example 7
50
0.34 tons of molten FeMn contained in a holding
furnace was poured into 1.3 tons of molten FeMn contained
in the ladle 30. If the temperature of the molten steel is
required to be 1671°C when the molten steel is moved toward
the holding furnace, and the temperature of molten high Mn
steel is required to be 1590°C after the pouring (mixing),
the temperature of the molten FeMn contained in the holding
furnace may have to be adjusted to be 1483°C based on
Formula 2 explained above. Therefore, after the holding
furnace was maintained at 1450°C for 3 hours, the
temperature of the holding furnace was increased 30 minutes
before pouring (mixing), and the molten FeMn was drawn out
of the holding furnace at a final temperature of 1477°C and
poured into the molten steel contained in the ladle 30. The
temperature of the mixture immediately after the pouring
(mixing) was 1589°C. That is, high manganese molten steel
having a temperature close to a desire temperature could be
obtained.

We Claim:
【Claim 1】
A method of producing molten manganese-containing
steel, the method comprising:
preparing a molten ferroalloy or a molten nonferrous
metal;
maintaining the molten ferroalloy or the molten
nonferrous metal at a temperature equal to or higher than a
melting point thereof; and
pouring the molten ferroalloy or the molten
nonferrous metal into prepared molten steel,
wherein in the maintaining of the molten ferroalloy
or the molten nonferrous metal, the molten ferroalloy or
the molten nonferrous metal is subjected to a nitrogenabsorption
prevention process or a denitrification process.
【Claim 2】
The method of claim 1, wherein the maintaining of the
molten ferroalloy or the molten nonferrous metal is carried
out in a holding furnace together with the nitrogenabsorption
prevention process or the denitrification
process, and
the nitrogen-absorption prevention process or the
denitrification process comprises supplying argon (Ar) gas
to the holding furnace as an atmospheric gas to maintain an
52
interior of the holding furnace at a positive pressure.
【Claim 3】
The method of claim 1, wherein the maintaining of the
molten ferroalloy or the molten nonferrous metal is carried
out in a holding furnace together with the nitrogenabsorption
prevention process or the denitrification
process, and
the nitrogen-absorption prevention process or the
denitrification process comprises agitating the molten
ferroalloy or the molten nonferrous metal in at least one
of upper and lower regions of the holding furnace using
argon (Ar) gas.
【Claim 4】
The method of any one of claims 1 to 3, wherein the
nitrogen-absorption prevention process or the
denitrification process comprises adding silicon (Si) to
the molten ferroalloy such that the molten ferroalloy has a
silicon (Si) content of 1.5 wt% or greater.
【Claim 5】
The method of claim 2, wherein the holding furnace
comprises:
a case;
an accommodation unit disposed in the case and
comprising an internal space to accommodate a molten or
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solid ferroalloy or nonferrous metal;
a heating unit configured to heat the ferroalloy or
nonferrous metal contained in the accommodation unit; and
a cover disposed on an upper side of the
accommodation unit to close the internal space of the
accommodation unit,
wherein the cover comprises an atmospheric gas supply
unit connected to an inert gas supply unit and supplying an
atmospheric gas to the accommodation unit so that the
ferroalloy or the nonferrous metal melted in the
accommodation unit is denitrified or prevented from
absorbing nitrogen.
【Claim 6】
The method of claim 5, wherein the preparing of the
molten ferroalloy or the molten nonferrous metal is
performed in the holding furnace.
【Claim 7】
The method of claim 1, wherein the molten ferroalloy
or the molten nonferrous metal is prepared in an amount
greater than a required amount in the pouring of the molten
ferroalloy or the molten nonferrous metal, and
after the required amount of the molten ferroalloy or
the molten nonferrous metal is poured into the molten steel,
a remaining amount of the molten ferroalloy or the molten
54
nonferrous metal is continuously maintained at a
temperature equal to or greater than the melting point.
【Claim 8】
The method of claim 2 or 3, wherein the preparing of
the molten ferroalloy or the molten nonferrous metal
comprises melting solid FeMN or a solid Mn metal having a
manganese (Mn) content and a phosphorus (P) content
according to the following formula:
P content (wt%) < -0.026 x (target Mn content (wt%)
of Mn-containing molten steel + (4.72 x 10-4) x (target Mn
content (wt%) of Mn-containing molten steel)2.
【Claim 9】
The method of claim 6, wherein the heating unit of
the holding furnace comprises an induction coil, and
the preparing of the molten ferroalloy or the molten
nonferrous metal comprises induction heating using the
induction coil.
【Claim 10】
The method of claim 1, wherein the pouring of the
molten ferroalloy or the molten nonferrous metal comprises:
pouring the molten ferroalloy or the molten
nonferrous metal into a ladle in which the molten steel is
contained; and
agitating the molten steel together with the molten
55
ferroalloy or the molten nonferrous metal,
wherein the agitating is performed by supplying an
inert gas through a lower side of the ladle.
【Claim 11】
The method of claim 1, wherein the pouring of the
molten ferroalloy or the molten nonferrous metal comprises:
pouring the molten ferroalloy or the molten
nonferrous metal into a ladle in which the molten steel is
contained; and
agitating the molten steel together with the molten
ferroalloy or the molten nonferrous metal,
wherein the agitating is performed using an agitator
inserted through an upper side of the ladle into the molten
steel and the molten ferroalloy or the molten nonferrous
metal.
【Claim 12】
The method of claim 1, wherein in the maintaining of
the molten ferroalloy or the molten nonferrous metal, the
molten ferroalloy or the molten nonferrous metal is
maintained at a temperature of 1300°C to 1500°C, and
immediately prior to the pouring of the molten
ferroalloy or the molten nonferrous metal, the method
further comprises heating the molten ferroalloy or the
molten nonferrous metal in consideration of states of the
56
molten steel and target states of high manganese molten
steel.
【Claim 13】
The method of claim 1, wherein after the pouring of
the molten ferroalloy or the molten nonferrous metal, the
method further comprises performing an RH vacuum refining
process or a ladle furnace (LF) refining process in which
at least one of Al, C, Cu, W, Ti, Nb, Sn, Sb, Cr, B, Ca, Si,
and Ni is supplied to the molten steel and the molten
ferroalloy or the molten nonferrous metal.
【Claim 14】
The method of claim 13, wherein the RH vacuum
refining process is performed together with a
dehydrogenation process.
【Claim 15】
A holding furnace comprising:
a case;
an accommodation unit disposed in the case and
comprising an internal space to accommodate a solid or
molten ferroalloy or a solid or molten nonferrous metal;
a heating unit configured to heat the ferroalloy or
nonferrous metal contained in the accommodation unit; and
a cover disposed on an upper side of the
accommodation unit to close the internal space of the
57
accommodation unit,
wherein the cover comprises an atmospheric gas supply
unit connected to an inert gas supply unit and supplying an
atmospheric gas to the accommodation unit so that the
ferroalloy or the molten nonferrous metal melted in the
accommodation unit is denitrified or prevented from
absorbing nitrogen.
【Claim 16】
The holding furnace of claim 15, wherein the heating
unit comprises at least one of:
an induction coil wound around the accommodation
unit;
an electrode bar disposed in the cover; and
a plasma disposed in the cover.
【Claim 17】
The holding furnace of claim 16, further comprising a
control unit connected to the heating unit,
wherein the molten ferroalloy or the molten
nonferrous metal is maintained at a temperature of 1300°C
to 1500°C under the control of the control unit, and
immediately prior to the molten ferroalloy or the molten
nonferrous metal is poured into molten steel, the molten
ferroalloy or the molten nonferrous metal is heated under
the control of the control unit.
58
【Claim 18】
The holding furnace of claim 15, wherein an
atmospheric gas supply tube is disposed in the cover
disposed on the upper side of the accommodation unit, and
the cover comprises a vent to maintain an interior of the
holding furnace at a constant positive pressure when an
atmospheric gas is supplied to the interior of the holding
furnace.
【Claim 19】
The holding furnace of claim 15, further comprising:
a siphon structure comprising a suction part inserted
through the cover into the molten ferroalloy or the molten
nonferrous metal contained in the accommodation unit, a
discharge part connected to the suction unit so as to
discharge the molten ferroalloy or the molten nonferrous
metal drawn through the suction part to a ladle, a transfer
part connected between the suction part and the discharge
part to transfer the molten ferroalloy or the molten
nonferrous metal, and an initial pressure port connected to
the transfer part for creating an initial pressure
difference; and
a driving unit connected to a lower side of the case
to assist operations of the siphon structure by lifting or
lowering the case.
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【Claim 20】
The holding furnace of claim 15, further comprising:
a driving unit connected to the case for lifting or
lowering the case and the accommodation unit;
a first guide disposed on an outer surface of the
case; and
a guide frame disposed at an outer side of the case
and comprising a guide roller, the guide roller blocking an
upward movement of the first guide by engaging with the
first guide when the first guide is moved upwardly,
wherein a connection point at which the driving unit
is connected to the case is located behind the guide roller
when viewed on a horizontal plane, and when the case is
moved upwardly by the driving unit, the first guide is
hooked on the guide roller and then the case is tilted.
【Claim 21】
An apparatus for producing molten manganesecontaining
steel, the apparatus comprising:
an Mn supply unit supplying a molten metal having a
high manganese content;
a molten steel supply unit supplying molten steel;
and
a ladle configured to move between the molten steel
supply unit and the Mn supply unit to receive the molten
60
metal having a high Mn content from the Mn supply unit and
the molten steel from the molten steel supply unit,
wherein the Mn supply unit comprises the holding
furnace of any one of claims 15 to 20.
【Claim 22】
The apparatus of claim 21, wherein an inert gas
supply tube is disposed in a lower side of the ladle, and
the ladle is connected to an inert gas supply unit at
a position at which the ladle receives the molten metal
from the Mn supply unit or the molten steel from the molten
steel supply unit, and the molten metal and the molten
steel poured into the ladle is agitated using an inert gas.