1
SPECIFICATION
W TITLE OF INVENTION
ENVIRONMENTALLY FRIENDLY FLUX FOR MOLTEN STEEL
DESULFURIZATION
5
Field of the Invention
[0001]
The present invention relates to a flux used during refining of highly clean steel.
The invention particularly relates to a flux that is used to perform desulfurization in a
10 secondary refining process after a converter process or in a refining process inside or
outside an electric furnace during steel making. Here, the flux is a collective term of
various compounds which react with molten iron so as to have a function of removing
impurities.
Priority is claimed on Japanese Patent Application No. 2011-79113, filed March
15 31, 2011, the content of which is incorporated herein by reference.
Description of Related Art
[0002]
For high-tensile steel having favorable formability, high-strength line pipes,
20 high-strength steel plates, and the like, there is a demand for an extreme decrease in the
amount of S which is an impurity of steel. Therefore, desulfurization of molten steel is
performed in a secondary refining process after a converter process or in a reduction
stage of an electric furnace process during steel making. For desulfurization of molten
steel, a CaO-based desulfurization flux is mainly used, and there are frequent cases in
25 which a flux including CaF2 having a high desulfurization ability is used to decrease the
2
S content within a short period of time.
W [0003]
However, since the desulfurization flux including CaF2 is highly reactive, and
easily erodes away refractories in a refining reactor, there is a problem in that the service
5 life of the refractories is shortened. In addition, slag discharged after refining is
generally used for roadbed materials and the like; however, when a large amount of CaF2
is present in slag which is formed during desulfurization using a flux including CaF2,
there is a concern that F eluted from CaF2 may have an adverse influence on the
environment. Therefore, in this case, it is necessary to perform stricter management of
10 slag components or further limit the use of slag.
[0004]
As a molten steel desulfurization flux which does not include CaF2, but has a
high desulfurization ability, for example, Patent Citation 1 discloses a desulfurization
flux including Na20. However, Patent Citation 1 does not disclose the Na20 content
15 (mass%) in the desulfurization flux.
[0005]
Patent Citation 2 discloses a desulfurization flux including K2O. Patent
Citation 3 discloses a desulfurization flux including Na20 or K2O. However, those
desulfurization fluxes are for hot metal desulfurization. In addition, the Na20 and K2O
20 contents in the desulfurization flux are 15 mass% or more. Thus, when large amounts
of Na20 and K2O are present in the desulfurization flux, there is a problem in that Na20
and K2O evaporate during a desulfurization treatment. In addition, there is a concern
that large amounts of Na20 and K2O may be present in slag after desulfurization
treatment.
25 [0006]
3
Patent Citation 4 discloses a method in which a desulfurizing agent containing
!Pfa2C03 is used. However, the desulfurizing agent is a flux for hot metal desulfurization,
and, in Patent Citation 4, since the Na2C03 content is high, there is a problem in that
Na20 evaporates or remains in slag.
5 [0007]
Patent Citations 5 to 8 disclose methods in which NaiO is used, but all the
methods are targeted at hot metal desulfurization. In the hot metal desulfurization, the
treatment temperature or the C and O contents in hot metal are significantly different
from those in molten steel desulfurization. Therefore, when the methods of Patent
10 Citations 5 to 8 are applied to molten steel desulfurization with no change, there is a
concern that the problem of evaporation of Na20 may become significant, or a large
amount of Na20 may remain in slag after desulfurization treatment.
[0008]
As described above, for high-tensile steel having favorable workability,
15 high-strength line pipes, high-strength steel plates, and the like, there is a demand for a
decrease in S which is an impurity of steel as much as possible, and desulfurization of
molten steel is performed in a secondary refining process (a refining process after a
converter process or an electric furnace process) during steel making. At this time,
there are frequent cases in which a flux including CaF2 having a high desulfurization
20 ability is used to decrease S within a short period of time.
[0009]
However, as described above, since the desulfurization flux including CaF2 is
highly reactive, there is a problem in that refractories in a refining reactor are easily
melted away, and the service life of the refractories is shortened. In addition, slag
25 discharged after refining is generally used for roadbed materials and the like; however,
4
since slag includes CaF2 when a desulfiirization flux including CaF2 is used for
^Pesulfurization, and there is a problem of elution of F, and therefore the use of slag is
significantly limited.
[0010]
5 Therefore, with regard to hot metal desulfiirization, a number of techniques in
which a desulfiirization flux including Na20 or K2O instead of CaF2 is used are proposed.
However, as described above, since the conditions of hot metal desulfiirization are
significantly different from the conditions of molten steel desulfiirization, it is not
possible to apply the hot metal desulfiirization techniques to molten steel desulfiirization
10 with no change.
[0011]
In a case where the Na20 content (mass%) or the K2O content (mass%) is high,
there is a concern that a problem may occur in which easily evaporating Na20 or K2O
attaches to the exhaust duct in a secondary refining facility, or the Na20 or K2O content
15 in slag becomes high after desulfiirization such that recycled slag has an adverse
influence on the environment.
Patent Citation
[0012]
20 [Patent Citation IJ Japanese Unexamined Patent Application, First Publication
No. H03-264624
[Patent Citation 2] Japanese Unexamined Patent Application, First Publication
No. 2000-226284
[Patent Citation 3] Japanese Unexamined Patent Application, First Publication
25 No. H06-235011
5
[Patent Citation 4] Japanese Unexamined Patent Application, First Publication
f l o . 2002-241823
[Patent Citation 5] Japanese Unexamined Patent Application, First Publication
No. H08-209212
5 [Patent Citation 6] Japanese Unexamined Patent Application, First Publication
No. 2001-335819
[Patent Citation 7] Japanese Unexamined Patent Application, First Publication
No. 2001-335820
[Patent Citation 8] Japanese Unexamined Patent Application, First Publication
10 No. 2003-253315
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0013]
15 Therefore, the present invention has been made in consideration of the above
problems, and an objective of the present invention is to provide an environmentally
friendly desulfurization flux for molten steel desulfurization which has a high
desulfurization ability even when not including CaF2.
20 Methods for Solving the Problem
[0014]
The present invention has been made to solve the above problems, and the
purports thereof are as follows.
[0015]
25 (1) An environmentally friendly flux for molten steel desulfurization according
6
to an aspect of the present invention includes CaO and AI2O3 so that [CaO]/[Al203] is
iRithin a range of 1.6 to 3.0, and includes one or more alkali metal oxides of Na20, K2O,
and U2O, and Si02 so that [Si02]/[R20] is within a range of 0.1 to 3, [R2O] is within a
range of 0.5 mass% to 5 mass%, and [SiCy is within a range of 0.05 mass% to 15
5 mass% in a case in which the [CaO], the [AI2O3], the [Si02], and the [R2O] represent the
mass% of CaO, the mass% of AI2O3, the mass% of S1O2, and the total amount of the
mass% of Na20, the mass% of K2O, and the mass% of L12O respectively.
[0016]
(2) The environmentally friendly flux for molten steel desulfurization according
10 to the above (1) may further include 1 mass% to 10 mass% of MgO.
[0017]
(3) In the environmentally friendly flux for molten steel desulfurization
according to the above (1) or (2), the [Si02] may be 0.05 mass% to 9.3 mass%.
[0018]
15 (4) In the environmentally friendly flux for molten steel desulfurization
according to any one of the above (1) to (3), the [Si02] may be 0.05 mass% to 8.0
mass%.
[0019]
(5) In the environmentally friendly flux for molten steel desulfurization
20 according to any one of the above (1) to (4), the [Si02]/[R20] may be 0.1 to 2.
[0020]
(6) In the environmentally friendly flux for molten steel desulfurization
according to any one of the above (1) to (5), some or all of the alkali metal oxides may
have a chemical bond with the Si02.
25 [0021]
7
(7) In the environmentally friendly flux for molten steel desulfurization
^pccording to any one of the above (1) to (6), the alkali metal oxides may be Na20.
[0022]
(8) In a molten steel desulfurization method according to an aspect of the
5 present invention, the environmentally friendly flux for molten steel desulfurization
according to any one of the above (1) to (9) is supplied to molten steel.
[0023]
(9) In a molten steel desulfurization method according to an aspect of the
present invention, slag including one or more of Na20, K2O, and L12O, as well as CaO,
10 AI2O3, and SiC>2 is formed on the surface of molten steel so that [CaO]/[Ai203] is within
a range of 1.6 to 3.0, [Si02]/[R20] is within a range of 0.1 to 3, [R2O] is within a range of
0.5 mass% to 5 mass%, and [SiCh] is within a range of 0.05 mass% to 15 mass% in a
case in which the [CaO], the [AI2O3], the [SiC^], and the [R2O] represent the mass% of
CaO, the mass% of AI2O3, the mass% of Si02, and the total amount of the mass% of
15 Na20, the mass% of K2O, and the mass% of L12O respectively.
Effects of the Invention
[0024]
According to the aspects of the present invention, it is possible to manufacture
20 high-grade steel having an extremely small amount of S without the occurrence of
problems of elution of F from slag after desulfurization, attachment of Na20 or K2O to a
facility due to evaporation, a decrease in productivity due to a decrease in desulfurization
efficiency, an increase in desulfurization costs, and the adverse influence of slag
including a large amount of Na20 or K2O after desulfurization on the environment.
25
8
BRIEF DESCRIPTION OF THE DRAWINGS
W [0025]
FIG. 1 is a view showing the relationship between the desulfurization efficiency
parameter and the amount (mass%) of R2O (one or more of Na20, K2O, and Li20).
5 FIG. 2 is a view showing the relationship between the desulfurization efficiency
parameter and the Na20 content (mass%) with respect to a variety of [Si02]/[Na20]s.
FIG. 3 is a view showing the relationship between the desulfurization rate
constant and [Ca0]/[A1203].
FIG. 4 is a view showing the relationship between [Si02]/[Na20] and the
10 desulfurization rate constant in a case in which [CaO]/[Ai203] is 2.
DETAILED DESCRIPTION OF THE INVENTION
[0026]
Hereinafter, [CaO], [A1203], [Si02], [MgO], and [R20] represent the mass% of
15 CaO, the mass% of AI2O3, the mass% of Si02, the mass% of MgO, and the mass% of
R2O. Meanwhile, hereinafter, there are cases in which the amounts (mass%) of the
various components are represented by [chemical formula of component]. In addition,
in a case in which a compound from which a metallic oxide such as CaO (including
complex oxides thereof) is obtained through thermal decomposition is included, the mass
20 percentage of a metal oxide in the compound is evaluated using the mass of the thermally
decomposed compound, and byproducts such as CO2 or H2O which are generated due to
thermal decomposition are not included in the mass percentage of a flux. Herein, the
R2O corresponds to Na20, K2O, and Li20, and the [R2O] represents the total amount of
Na20, K2O, and Li20. Among Na20, K2O, and Li20, the amount of components not
25 included in a flux is evaluated to be zero.
9
[0027]
W The inventors firstly studied use of oxides of alkali metals such as Na20, K2O,
and U2O instead of CaF2. As described above, a flux including Na20 or K2O has a high
desulfurization ability. In addition, L12O is also an oxide of an alkali metal, similarly to
5 the case of Na20 or K2O, Li20 is expected to have a high desulfurization ability.
[0028]
However, as described above, the oxides (R2O) of the alkali metals such as
Na20, K2O, and O2O have a characteristics of being easily evaporated at a high
temperature. Since ease of evaporation is dependent on [R2O], the amount of R2O in a
10 flux is preferably as small as possible, but the desulfurization ability of a flux enhances
as [R2O] increases.
[0029]
Therefore, in a case in which R2O is added to a desulfurization flux in order to
enhance the desulfurization ability, to what extent the amount of [R2O] in the
15 desulfurization flux can be decreased while a desulfurization ability necessary for a
desulfurization flux is secured becomes a key to the solution to the problems. In order
to suppress [R2O] to a low level while a desulfurization ability is secured, the
composition of main components that compose a flux is important.
[0030]
20 The inventors used a CaO-AkC^-based desulfurization flux which is generally
used as a base component in a desulfurization flux, and investigated the desulfurization
ability by changing [Na20], [K2O], and [Li20] in the desulfurization flux through
laboratory scale experiments.
[0031]
25 The chemical compositions of molten steel used in the experiments are shown in
10
Table 1.
V [0032]
[Table 1]
(mass%)
G
0.05
Si
0.2
Mn
1.0
P
0.005
S
0.004
Al
0.03
N
0.03
0
0.0015
5 [0033]
The experimental conditions are as follows.
Melting furnace: resistance melting furnace, amount of molten steel: 10 kg,
temperature of molten steel: 1600°C
Experimental procedure: melting - composition adjustment - Al deoxidization -
10 desulfurization - cooling
Desulfurization method: a desulfurization flux is injected into the molten steel
using a refractory pipe.
Desulfurization flux composition: '
CaO-Al203-R20
15 [CaO]/[Al2O3]=2.0
Na20, K20, or Li20: 0 mass% to 10 mass%
[0034]
The experimental results are shown in FIG. 1. The desulfurization efficiency
parameter (the vertical axes in FIGS. 1 and 2) and the desulfurization rate constant (the
20 vertical axis in FIG. 3) are defined as follows.
Desulfurization efficiency parameter = (desulfurization rate constant)/(amount
of R20 evaporated)
Desulfurization rate constant = -ln(final [S]/initial [S])/time, time=15 minutes
11
Amount evaporated: (initial [R20]-fmal [R20])/(initial [R20])
W [0035]
Since desulfurization is performed within as short a time as possible in the
industrial process from the viewpoint of productivity improvement, in the experiments,
5 values at 15 minutes after the initiation of desulfurization were used as the
desulfurization rate constant. It is found from FIG. 1 that, in the case of Na20, the
desulfurization efficiency parameter becomes the maximum at an initial content of "2
mass%." Similarly, in the case of K20 or Li20, the desulfurization efficiency parameter
becomes the maximum at an initial content of "2 mass%."
10 [0036]
As such, a high desulfurization efficiency parameter means that "the amount of
R20 evaporated is small, and the desulfurization rate constant is large", that is, a
desulfurization reaction proceeds favorably. From this fact, it can be said that it is not
necessary to add a large amount of R20 (Na20, K20, and/or Li20) to a desulfurization
15 flux in order to supply a high desulfurization ability. That is, even when [R20] is
simply increased, the amount evaporated increases, and the majority of R20 is simply
wasted.
[0037]
Actually, in a case in which a large amount of a desulfurization flux is produced,
20 it is difficult to control the R20 content to be 2 mass% because of content fluctuation.
However, the factor that significantly influences desulfurization reaction or evaporation
is not the component content, but the component activity, that is, the lability in
consideration of the influence of coexisting components. From this fact, the inventors
obtained an idea of controlling the activity of components that compose a desulfurization
25 flux.
12
[0038]
W Since SiC>2 is firstly considered as a component that has a large influence on the
activity of Na20, K2O, or U2O, the inventors investigated the influence of [SiCy on the
activity of Na20 through similar laboratory scale desulfurization experiments. The
5 chemical compositions of molten steel used in the experiments are shown in Table 1, and
the experimental conditions are as follows.
[0039]
Melting furnace: resistance melting furnace, amount of molten steel: 10 kg,
temperature of molten steel: 1600°C
10 Experimental procedure: melting - composition adjustment - Al deoxidization -
desulfurization - cooling
Desulfurization method: a desulfurization flux is injected into the molten steel
using a refractory pipe.
Desulfurization flux composition:
15 CaO-Al203- Si02-Na20
[CaO]/[Al2O3]=2.0
[SiO2]/[Na2O]=0 to 5
Na20: 0 mass% to 10 mass%
[0040]
20 The experimental results are shown in FIG. 2. The vertical axis in FIG. 2
indicates the desulfurization efficiency parameter similarly to the vertical axis in FIG. 1.
It is found from FIG. 2 that [Na20] at which the desulfurization efficiency parameter
becomes the maximum increases as [SiC>2]/[Na20], which is a mass% ratio, increases.
[0041]
25 [Na20] at which [Si02]/[Na20]=3, and the desulfurization efficiency parameter
13
becomes the maximum is 5 mass%. When [SiC^] is increased with the above
i02]/[Na20] as a criterion, the [Na20] at which the desulfurization efficiency parameter
becomes the maximum also increases. However, when [Na20] increased to more than
the criterion, the manufacturing costs of a desulfurization flux increases, and,
5 furthermore, [Na20] in slag also increases after desulfurization.
[0042]
Generally, when [Na20] in slag exceeds 2 mass% after desulfurization, the slag
becomes inappropriate for civil engineering aggregate or cement aggregate. Therefore,
the inventors separately analyzed the relationship between [Na20] in slag after
10 desulfurization and [Na20] in a desulfurization flux, and obtained the maximum
acceptable amount of [Na20] in the desulfurization flux. As a result of the analysis, it
was found that the maximum acceptable amount of [Na20] is approximately 5 mass%.
Therefore, [Na20] in a desulfurization flux is preferably 5 mass% or less. Similarly,
[K2O] and [Li20] in a desulfurization flux are also preferably 5 mass% or less. It is
15 preferable that the [Na20], [K2O], and [Li20] are as small as possible.
[0043]
The inventors further investigated [CaO]/[ AI2O3] regarding CaO and AI2O3
which were main components of a desulfurization flux. Desulfurization experiments
were performed by making the desulfurization flux contain 2.5 mass% of Na20 and 5
20 mass% of SiC>2 as other components, and changing [CaO]/[Ai203]. The chemical
compositions of molten steel used for the experiments are shown in Table 1, and the
experimental conditions are as follows.
[0044]
Melting furnace: resistance melting furnace, amount of molten steel: 10 kg,
25 temperature of molten steel: 1600°C
# S
14
Experimental procedure: melting - composition adjustment - Al deoxidization -
TPiesulfurization - cooling
Desulfurization method: a desulfurization flux is injected into the molten steel
using a refractory pipe.
5 Desulfurization flux composition:
CaO-Al203- Si02-Na20
[CaO]/[Al2O3]=1.0to4.0
Si02: 5 mass%, Na20: 2.5 mass%
[0045]
10 The experimental results are shown in FIG. 3. The vertical axis in FIG. 3
indicates the desulfurization rate constant. It is found from FIG. 3 that the
desulfurization rate constant becomes a high value of 0.10 or more in a range of
[CaO]/[Al2O3]=1.6to3.0.
[0046]
15 For desulfurization of molten steel, CaO-based fluxes are generally used, and,
among them, a CaO- Al203-based flux is frequently used. In a case in which the CaOAl203-
based flux is used, the composition region appropriate for desulfurization is
generally a region of [CaO]/[Al203] of 1.0 to 2.33 in a CaO- Al203 binary phase diagram.
[0047]
20 This region is a region in which a liquid phase is present in a flux at the
desulfurization temperature (approximately 1600°C) of molten steel, and some
solid-phase CaO is generated. When the flux is in a liquid phase, desulfurization
rapidly proceeds, and, when solid-phase CaO is present in the liquid phase even at a
small amount, the activity of CaO in the liquid phase becomes 1, and a desulfurization
25 reaction can easily proceed.
15
[0048]
w However, in a case in which Na20 and SiC>2 are present in a desulfurization flux,
there is a possibility of a change in the desulfurization ability due to the composition
conditions. Therefore, the inventors found from the results shown in FIG. 3 obtained
5 through the molten steel desulfurization experiments that the optimal [CaOJ/fAbOa] for
desulfurization was 1.6 to 3.0.
[0049]
Similarly to SiC>2, AI2O3 is also an oxide having an influence on the reactivity of
R2O, and, when AI2O3 is excessively present in a desulfurization flux, the reactivity of
10 R2O degrades. This fact is also reflected in the desulfurization experimental results
shown in FIG. 3.
[0050]
Hereinafter, a molten steel desulfurization flux according to an aspect of the
present invention will be described. Except in a case in which CaF2 is inevitably
15 included in the starting materials of a flux, the molten steel desulfurization flux according
to the embodiment basically does not include CaF2. Even in a case in which CaF2 is
inevitably included, CaF2 may be limited to 1 mass% or less and preferably 0.1 mass% or
less in terms of outer percentage.
[0051]
20 The environmentally friendly flux for molten steel desulfurization according to
the embodiment (hereinafter sometimes referred to as the "present flux") substantially
does not include CaF2,
(i) includes CaO and AI2O3 as main components so that [CaO]/[Al203] becomes
within a range of 1.6 to 3.0,
25 (ii) includes 0.5 mass% to 5 mass% of one or more of Na20, K2O, and Li20
16
(R20), and 0.05 mass% to 15 mass% of Si02 so that [Si02]/[R20] becomes within a
ge of 0.1 to 3, and, furthermore, includes 10 mass% or less of MgO according to
necessity.
[0052]
5 In the present flux, the reason why [CaOJ/fAbOa] is set to 1.6 to 3.0 is to secure
a sufficient desulfurization rate as described above. In order to obtain a higher
desulfurization rate, [CaOJ/fAbC^] is preferably 1.6 to 2.8.
[0053]
In the present flux, the reason why [R2O] is set to 0.5 mass% to 5 mass% is as
10 follows.
[0054]
Based on the experimental results shown in FIGS. 1 and 2, the minimum Na20
content (mass%) at which the effect of addition of Na20 sufficiently develops is set to 0.5
mass% at which the desulfurization efficiency parameter exceeds 0.60. The maximum
15 content of 5 mass% is a threshold limit value in order to prevent [Na20] in slag from
exceeding 2 mass% after desulfurization in consideration of the amount of Na20 reduced
during a desulfurization treatment.
[0055]
Since the effects of K2O, or Li20 are the same as the effects of Na20, similarly
20 to Na20, [K2O] was set to 0.5 mass% to 5 mass%, and [L12O] was set to 0.5 mass% to 5
mass%.
[0056]
Since the effects of K2O, Li20, and Na20 are the same, two or more of Na20,
K2O, and IJ2O may be additively used. The combinations are Na20+K20, Na20+Li20,
25 K2O+IJ2O, and Na20+K20+Li20. In conclusion, the total of the amounts of one or
Hfcn
17
more of Na20, K2O, and Li20, that is, [R2O] is set to 0.5 mass% to 5 mass%.
© [0057]
Na20, K2O, and Li20 are expensive, and there are cases in which Na20, K2O,
and Li20 evaporate so as to attach to and deposit on a facility, or melt away refractories
5 in a refining reactor. Particularly, the amount of R2O in slag is preferably as small as
possible after desulfurization treatment from the viewpoint of the recycling of the slag.
Therefore, the R2O content ([R2O]) in a desulfurization flux is preferably as small as
possible. From such a viewpoint, the upper limit of [R2O] is preferably 3 mass% or less.
In addition, in a case in which the effect of R2O is obtained more sufficiently, [R2O] is
10 preferably 1 mass% or more.
[0058]
In the present flux, the reason why [SiC^/tR^O] is set to 0.1 to 3 is as follows.
[0059]
As shown in FIG. 2, in a case in which [SiC^] (that is, herein, [Si02]/[Na20]) is
15 zero, the Na20 content at which the desulfurization efficiency parameter becomes
maximum is 2 mass%. Therefore, even when [SiC^] is zero, the effect (improvement of
the desulfurization ability) of Na20 develops. However, in order to stabilize Na20 and
suppress evaporation as much as possible, SiC>2 is preferably present in the flux even at a
small amount. Therefore, the lower limit of [Si02]/[Na20] was set to 0.1.
20 [0060]
The upper limit of [Si02]/[Na20] of 3 is a condition under which the maximum
value of the desulfurization efficiency parameter shown in FIG. 2 is obtained at the
maximum acceptable value of [Na20] of 5 mass%. In this case, the desulfurization
efficiency parameter exceeds 0.6 throughout the entire range in which [Na20] is 0.5
25 mass% to 5 mass%. Definitely, in FIG. 2, even when [Si02]/[Na20] is 4 or more, there
18
is a range of [Na20] in which the desulfurization efficiency parameter exceeds 0.6, but
e range is narrow. In addition, in the range, while evaporation of Na20 can be
sufficiently suppressed, the desulfurization ability per the unit amount of Na20
significantly degrades, and therefore [Si02]/[Na20] of 4 or more is not preferable from
5 the viewpoint of securing the effects of Na20.
[0061]
For K20 and Li20 as well, [Si02]/[K20] was set to 0.1 to 3, and [Si02]/[Li20]
was set to 0.1 to 3 respectively for the same reason. Even a case in which two or more
of Na20, K20, and Li20 are additively used in combination is the same as the above case.
10 That is, in the present flux, [Si02]/[R20] is set to 0.1 to 3. [Si02]/[R20] is preferably
0.1 to 2, more preferably 0.5 to 2, and still more preferably 1 to 2.
FIG. 4 shows the relationship between [Si02]/[Na20] and the desulfurization rate
constant in a case in which [CaO]/[Al203] is 2. It is found from FIG. 4 that the
desulfurization rate constant is maximized at [Si02]/[Na20] of 1.5. In addition, when
15 [Si02]/[Na20] is 2 or less, in a case in which [Si02]/[Na20] is sufficiently small (for
example, 0.1), a similar desulfurization rate constant is obtained. Therefore, in a case in
which a sufficient desulfurization efficiency parameter is secured, and a processing time
is shortened, [Si02]/[R20] may be 0.1 to 2. In this case, the intensity of the bond
between Si02 and R2O can be appropriately controlled, and the desulfurization effect of
20 R2O can be further enhanced while suppressing evaporation of R2O.
[0062]
From the viewpoint of the desulfurization efficiency (per the unit amount of
R20), environmental protection through resource saving, and cost reduction, among R20
(alkali metal oxides), Na20 has higher performance. Therefore, R20 may be Na20.
25 That is, in a case in which R20 is used at a high temperature and a low oxygen partial
m
19
pressure or a case in which R2O is used in combination with a deoxidizing material such
s Al, it is possible to suppress the loss of R2O due to evaporation using Na20 or L12O
compared to K2O since the boiling point of K is relatively low. In addition, since Li20
is a rare oxide, Na20 helps resource saving and cost reduction compared to L12O.
5 [0063]
Furthermore, in a case in which R2O is introduced into the network of SiC>2 so as
to further suppress the evaporation of R2O, some or all of R2O may have a chemical bond
with SiC>2. In this case, for example, 10% or more of R2O with respect to the total
amount of R2O preferably has a bond with SiC>2. Particularly, in a case in which the
10 evaporation suppression effect of R2O is secured using the chemical bond, the present
flux may include waste material such as soda-lime glass, glass cullet, and slag including
R2O or Si02. In this case, environmental protection or cost reduction through recycling
and stabilization can be achieved at the same time. For example, the present flux may
include a hybrid oxide in which some or all of R2O has a chemical bond with SiCh, and
15 the [Si02]/[R20] of the oxide is not particularly limited, and may be 0.01 or more.
[0064]
[SiC^] in the present flux is naturally determined from [R2O] (0.5 mass% to 5
mass%) and [Si02]/[R20] (=0.1 to 3), and is 0.05 mass% to 15 mass%. When
[SiC>2]/[R20] increases through evaporation of R2O during a desulfurization reaction, the
20 desulfurization efficiency is degraded. In a case in which the degradation of the
desulfurization efficiency is suppressed, the [SiC>2] is preferably 0.05 mass% to 9.3
mass%, and more preferably 0.05 mass% to 8.0 mass%. Here, inclusion of SiC>2 in the
flux is important in order to suppress evaporation of R2O; however, in a case in which the
basicity of slag is adjusted more flexibly, [SiCy may be limited to, for example, 0.6
25 mass% or 0.45 mass% or less.
20
[0065]
^ P In the present flux, 10 mass% or less of MgO is desirably added to the flux.
The reason why the amount of MgO added is set to 10 mass% or less as an optional
component is as follows.
5 [0066]
MgO is generally a component that composes a refractory, and is added to a
desulfurization flux for the purpose of suppressing the melting-away of refractories due
to the desulfurization flux. In a case in which the effect of suppressing the melting
away of refractories is sufficiently secured, 1 mass% or more of MgO is preferably added.
10 However, when the amount of MgO ([MgO]) exceeds 10 mass%, the melting point of a
desulfurization flux increases, and the desulfurization effect of a flux does not develop.
Therefore, the amount of MgO is limited to 10 mass% or less.
[0067]
The composition of the present flux is determined, for example, as follows.
15 Firstly, the types of R2O (at least one) in the flux are determined, and [Na20], [K2O], and
[L12O] which correspond to the types of R2O are set so as to satisfy [R2O] of 0.5 mass%
to 5 mass%. Next, [Si02] is set so as to satisfy a predetermined range of the ratio of
[Si02] to [R2O]. After that, [MgO] is set according to necessity, and the total of [R2O],
[Si02], and [MgO] is subtracted from 100, thereby obtaining [CaO]+[Al203].
20 [0068]
After [CaO]+[Al203] is obtained, [CaO] and [AI2O3] are set so as to satisfy a
predetermined range of [CaO]/[Al203]. Thereby, the amounts (mass%) of all the
components of the flux are determined. Meanwhile, starting materials used to
manufacture the flux (flux starting materials) contain impurities inevitably, and the
25 impurities are inevitably introduced into the desulfurization flux, but the amounts of the
21
inevitably contained components (inevitable impurities) are excluded from the above
^content calculation.
[0069]
Next, a method of manufacturing the present flux will be described. A
5 desulfurization flux is generally a mixture of oxide powder. A desulfurization flux can
be used in a mixture form in which the powder is mixed; however, when the
desulfurization flux is used after all or some of the oxide powder is mixed, fused or
sintered, cooled, and crushed in advance, the desulfurization effect can be obtained more
reliably.
10 [0070]
In a case in which R2O is stabilized by suppressing evaporation of R2O, since
the above fusing or sintering accelerates the bond between R2O, and Si02 or AI2O3, and
contributes to the stabilization of R2O, the manufacturing method preferably includes a
process in which a mixture including R2O for which [SiC^] or [AI2O3] is adjusted is
15 fused or sintered. Particularly, the desulfurization effect is improved simply by fusing
or sintering the powder mixture (mixed powder) of R2O and SiC>2, and then mixing in
other starting materials (for example, starting materials including other components).
[0071]
In soda-lime glass, glass cullet, used slag after refining, and the like, since waste
20 material mainly including Na20 or SiC>2 includes Na20 and S1O2, Na20 is stabilized, and
the waste material is a preferable material of the present flux. In a case in which the
waste material is used, Na20 or SiC>2 is added as necessary to the waste material or other
starting materials, and the composition is adjusted so that [Si02]/[Na20] becomes within
a range of 0.1 to 3.
25 [0072]
22
Since CaO, Na20, K2O, and Li20 are often present in a carbonate form, a
orresponding carbonate powder may be blended in the flux as CaO, Na20, K2O, and
IJ2O. In this case, it is necessary to estimate the mass of CO2 generated during a
decomposition reaction at a high temperature in advance and blend the carbonates.
5 [0073]
For example, the present flux may include 43 mass% to 75 mass% of CaO, 17.5
mass% to 38.5 mass% of AI2O3, 0.05 mass% to 15 mass% of Si02, and 0.5 mass% to 5
mass% of R2O. In addition, the present flux may include 10% or less of MgO
according to necessity. For example, in a case in which the present flux does not
10 include MgO, the present flux may include 20 mass% to 38.5 mass% of AI2O3, 0.05
mass% to 15 mass% of Si02, and 0.5 mass% to 5 mass% of R2O with the remainder
composed of CaO and inevitable impurities (outer percentage). In addition, for example,
in a case in which the present flux includes MgO, the present flux may include 17.5
mass% to 38.5 mass% of AI2O3, 0.05 mass% to 15 mass% of Si02, 0.5 mass% to 5
15 mass% of R2O, and 10 mass% or less of MgO (preferably 1 mass% to 10 mass%) with
the remainder composed of CaO and inevitable impurities (outer percentage).
Additionally, in the present flux, as described above, [CaO]/[Al203] is in a range of 1.6 to
3.0, and [Si02]/[R20] is in a range of 0.1 to 3.
[0074]
20 When molten steel desulfurization is performed using the present flux, it is
possible to manufacture high-grade steel having an extremely small S content without
occurrence of an environmental issue due to elution of F from slag after desulfurization,
attachment of a large amount of evaporated Na20, K2O, and L12O to a facility, a decrease
in productivity due to a decrease in desulfurization efficiency, and an increase in
25 desulfurization costs.
e
23
[0075]
The present flux can be used for molten steel desulfurization in a secondary
refining process after a converter process, ladle refining in which an electrode heating
method such as a ladle furnace (LF) is used, molten steel desulfurization in a reduction
5 period of an electric furnace process, secondary refining after electric furnace process,
and the like.
[0076]
Hereinafter, molten steel desulfurization methods according to first and second
embodiments of the present invention will be described. In the molten steel
10 desulfurization method according to the first embodiment, the environmentally friendly
flux for molten steel desulfurization according to the above embodiment is supplied to
molten steel (into molten steel or onto the surface of molten steel).
[0077]
A method of adding the desulfurization flux to molten steel (supply method) is
15 not particularly limited. Examples of the addition method that can be used include an
injection method in which the flux is blown into molten steel through a nozzle immersed
in the molten steel, a method in which a lumpy flux is added to the surface of molten
steel from the above, a method in which flux powder is sprayed together with gas, and
the like. The desulfurization treatment time is preferably 30 minutes to 40 minutes.
20 The specific consumption of flux is preferably 3 kg/t to 4 kg/t (per ton of molten steel).
In addition, other starting materials such as calcined lime may be supplied to molten steel
separate. Even in this case, since a local reaction (a decrease in the evaporation rate of
R2O in the flux, acceleration of a slagging reaction between the flux and slag on the
surface of the molten steel, and acceleration of a desulfurization reaction between the
25 flux and molten steel) is important, the effect of the environmentally friendly flux for
24
molten steel of the embodiment can be sufficiently obtained.
W [0078]
In the molten steel desulfurization method according to the second embodiment,
a plurality of types of oxides are supplied to the surface of molten steel so that slag
5 (including a solid-liquid mixture of slag and a flux) having the same composition as the
environmentally friendly flux for molten steel desulfurization according to the above
embodiment is formed.
[0079]
The environmentally friendly flux for molten steel desulfurization according to
10 the above embodiment is supplied from the outside of a reactor (a variety of furnaces and
the like), and is, for example, powder or lump; however, in the molten steel
desulfurization method according to the present embodiment, slag may be formed on the
surface of molten steel so that the composition becomes the same as the composition of
the flux.
15 On the surface of molten steel before initiation of desulfurization, there are cases
in which slag generated in the prior process (residual slag) is somewhat present. In this
case, since a desulfurization reaction proceeds in a state in which a desulfurization flux
supplied from the outside of the reactor and the residual slag are mixed, the composition
of the slag (slag during desulfurization) on the molten steel may be in a state in which the
20 desulfurization flux supplied from the outside of the reactor and the existing slag are
mixed.
[0080]
Furthermore, the composition of the slag during desulfurization does not only
mean the composition of the slag on the molten steel immediately after initiation of
25 desulfurization.
25
[0081]
Since Na20, K2O, and Li20 easily evaporate, the composition of the slag on the
molten steel immediately after initiation of desulfurization need not satisfy the
composition of the environmentally friendly flux for molten steel desulfurization of the
5 embodiment. That is, in addition to the fact that the composition of the residual slag is
basically different from the composition of the environmentally friendly flux for molten
steel desulfurization of the embodiment, R2O (Na20, K2O, and L12O) evaporate in a
process in which a desulfurization reaction proceeds, and the composition of
desulfurization slag present on the surface of the molten steel may satisfy the
10 composition of the environmentally friendly flux for molten steel desulfurization of the
embodiment.
[0082]
When the rate of the desulfurization reaction is taken into account, the
composition of the slag present on the surface of the molten steel may satisfy the
15 composition of the environmentally friendly flux for molten steel desulfurization of the
embodiment until at least the first half (at a point in time at the half of the desulfurization
treatment time) of the desulfurization treatment time. In this case, the second half of the
desulfurization time can be effectively used for the desulfurization reaction, and a more
favorable desulfurization effect can be obtained compared to a case in which the slag on
20 the surface of the molten steel is adjusted in the second half of the desulfurization
treatment time.
[0083]
In the molten steel desulfurization method according to the second embodiment,
when a desulfurization flux comes into contact with molten steel, the composition may
25 be adjusted so as to become the composition of the environmentally friendly flux for
26
molten steel desulfurization flux of the embodiment. For example, instead of mixing
me of the components of a desulfurization flux and other components, some of the
components and other components may be separately added (supplied) using, for
example, different supply mechanisms or supply apparatuses. That is, as long as the
5 composition is adjusted to the composition of the environmentally friendly flux for
molten steel desulfurization of the embodiment on the molten steel, the addition method
(supply method) is not limited to a specific method.
[0084]
Therefore, in the molten steel desulfurization method according to the second
10 embodiment, slag including one or more alkali metal oxides of Na20, K2O, and Li20,
CaO, AI2O3, and SiC>2 wherein [CaO]/[Al203] is within a range of 1.6 to 3.0,
[Si02]/[R.20] is within a range of 0.1 to 3, [R2O] is within a range of 0.5 mass% to 5
mass%, and [Si02] is within a range of 0.05 mass% to 15 mass%, is formed on the
surface of molten steel. Meanwhile, a desulfurization flux in which some or all of R2O
15 has a chemical bond with SiC>2 may be used. Here, since the composition of the slag
formed on the surface of the molten steel is the same as the composition of the
environmentally friendly flux for molten steel desulfurization of the above-mentioned
embodiment, the amounts of each component will not be described here.
Meanwhile, evaporation of R2O can be suppressed more in the molten steel
20 desulfurization method according to the first embodiment than in the molten steel
desulfurization method according to the second embodiment.
[Examples]
[0085]
Next, examples of the present invention will be described, but the conditions in
25 the examples are simply an example of conditions employed to confirm the feasibility
Wo
10
15
27
and effects of the present invention, and the present invention is not limited to the
Wxample of conditions. The present invention can employ a variety of conditions within
the scope of the purport of the present invention as long as the objective of the present
invention can be achieved.
[0086]
(Example)
Molten steel prepared using a 400 t-capacity converter was desulfurized in an
RH vacuum degasser. After desulfurization, a sample was taken from the molten steel,
and the S content in the sample (molten steel) was analyzed. The chemical
compositions of the molten steels used in the actual tests are shown in Table 2. The
conditions in the actual tests are as follows.
Desulfurization process: RH vacuum degasser, ladle capacity: 4001, molten steel
temperature: 1620°C
Desulfurization method: blowing of powder into the molten steel using an
injection lance or onto the surface of the molten steel using a lance
Desulfurization time: 35 minutes
Specific consumption of flux (per ton of molten steel): 3.5 kg/t
[0087]
[Table 2]
(mass%)
20
GRADE
A
B
C
C
0.05
0.08
0.16
Si
0.2
0.8
1.0
Mn
1.0
1.5
1.3
P
0.005
0.004
0.003
Al
0.03
0.04
0.035
Ti
0.05
0.13
0.15
Nb
0.02
0.04
0.08
N
0.003
0.0035
0.003
O
0.0015
0.0020
0.0022
[0088]
The condition Nos. of the actual tests are shown in Table 3.
NO.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
STEEL
GRADE
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
[CaO]
61
59
62
62
66
60
62
64
66
60
56
52
55
55
63
63
59
55
53
71
64
60
COMPOSITION OF OESULFURIZATION FLUX (mass%)
[Si02]
0.4
0.3
3.6
4.0
0.5
15.0
1.2
9.4
7.4
10.0
2.0
16.0
22.1
4.1
5.4
0.8
14.9
0
16.5
4.8
4.0
[AI.OJ
38.1
34.7
34.4
31.0
30.0
25.0
25.8
24.6
23.6
20.0
35.0
26.0
22.9
37.9
30.0
26.3
21.1
32.4
26.5
22.2
32.0
[Na20]
0.5
0
0
2.0
0
0
0.5
0
2.0
3.0
7.0
0
0
3.0
0
0.2
3.0
2.0
0
2.0
0
EK20]
0
1.0
0
0
3.5
0
0.5
2.0
1.0
0
0
6.0
0
0
1.65
0.1
2.0
0
4.0
0
0
[U20]
0
0
2.0
0
0
5.0
0
2.0
1.0
2.0
0
0
8.0
0
0
0
2.0
3.0
0
0
0
[MgO]
0
5.0
0
1.0
0
0
10.0
0
0
7.0
0
0
0
0
0
0
0
12.0
0
0
0
40CaF2
[CaO]/
[AIM
(-)
1.6
1.7
1.8
2.0
2.2
2.4
2.4
2.6
2.8
3.0
1.6
2.0
2.4
1.45
2.1
2.4
2.8
1.7
2.0
3.2
2.0
-
[Si02]/([Na20]+
[K20]+[Li20])
(-)
0.8
0.3
1.8
2.0
0.1
3.0
1.2
2.3
1.9
2.0
0.3
2.7
2.8
1.4
3.3
2.7
2.1
0
4.1
2.4
-
-
NOTE
MIXED POWDER
PARTIALLY-FUSED PRODUCT
PARTIALLY-FUSED PRODUCT
USE OF SODA-LIME GLASS
MIXED POWDER
MIXED POWDER
PARTIALLY-FUSED PRODUCT
MIXED POWDER
MIXED POWDER
USE OF GLASS CULLET
MIXED POWDER
PARTIALLY-FUSED PRODUCT
PARTIALLY-FUSED PRODUCT
USE OF SODA-LIME GLASS
PARTIALLY-FUSED PRODUCT
MIXED POWDER
USE OF GLASS CULLET
MIXED POWDER
MIXED POWDER
MIXED POWDER
MIXED POWDER
PARTIALLY-SINTERED PRODUCT
[0090]
Wr The note column in Table 3 will be described as follows.
MIXED POWDER: a flux of a powder mixture of the oxides
PARTIALLY-FUSED PRODUCT: a flux obtained by melting, cooling, and
5 crushing a powder mixture of R2O and Si02 in advance, and then mixing the obtained
pre-melted powder with powder of other components
PARTIALLY-SINTERED PRODUCT: a flux obtained by sintering, cooling, and
crushing a powder mixture of R2O and Si02 in advance, and then mixing the obtained
sintered powder with powder of other components
10 USE OF SODA-LIME GLASS: a flux obtained by crushing soda-lime glass and
mixing the obtained glass powder with powder of the oxides
USE OF GLASS CULLET: a flux obtained by crushing glass cullet and mixing
the obtained glass powder with powder of the oxides
[0091]
15 The results of the actual tests are shown in Table 4. The desulfurization ratio is
defined to be ((the S content before desulfurization-the S content after
desulfurization)/the S content before desulfurization)xl00.
[0092]
[Table 4]
30
NO.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
INITIAL S
CONTENT
(ppm)
47
40
44
36
50
42
36
38
44
49
50
48
44
50
53
50
45
52
50
52
50
40
FINAL S
CONTENT
(ppm)
8
6
7
5
8
7
6
7
8
9
12
11
11
11
14
15
13
14
15
13
17
8
DESULFURIZATION
RATIO
(96)
83
85
84
86
84
83
83
82
82
82
76
77
75
78
74
70
71
73
70
75
66
80
NOTE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE
[0093]
[Table 5]
(mass%)
SODA-LIME GLASS
GLASS GULLET
CONVERTER SLAG
[CaO]
9.5
0.2
48
[Si02]
75
64
14
DMA]
—.
0.6
16
[MnO]
—
—
4.3
[MgO]
—
0.2
7.1
[P20J
—
—
3
[Na20]
15.5
35
0
CFeO]
—'
—
12
[Fe2Cy
—
—
10
3*
Nos. 1 to 10 are examples that satisfy the conditions of the present invention.
the examples, the S content is sufficiently decreased, and a high desulfurization ratio
of 82% or more is obtained. In addition, Na-based compounds, K-based compounds,
and Li-based compounds are not attached to the inside of the exhaust duct, and [Na20],
5 [K2O], and [Li20] in slag were 2 mass% or less after desulfurization. Therefore, under
the conditions of Nos. 1 to 10, Na2<3, K2O, and Li20 (R2O) can be efficiently used, and
the obtained slag can be sufficiently used for a variety of uses.
[0095]
Meanwhile, in Nos. 6, 8, and 10, since the existing slag is mixed in the
10 desulfurization flux, the composition of the desulfurization flux is a composition after
mixing of the slag. In addition, in No. 10, the composition of the slag during
desulfurization reaches a composition shown in Table 3 when the desulfurization reaction
process proceeds, and the composition of the slag is a composition of the second half of
the desulfurization (20 minutes/35 minutes of the desulfurization treatment time).
15 Additionally, in No. 10, even in a case in which a flux having a composition shown in
Table 3 was used, the same desulfurization ratio (84%) was obtained.
Here, the chemical compositions of soda-lime glass used in Nos. 4 and 14, slag
(converter slag) used in Nos. 6, 8, and 10, and glass cullet used in Nos. 10 and 17 are
shown in Table 5.
20 [0096]
Nos. 11 to 22 are comparative examples that do not satisfy the conditions of the
present invention. Among the comparative examples, the maximum desulfurization
ratio was 80% which was obtained in No. 22 in which CaF2 was used, and the
desulfurization ratio was as low as 68% to 78% in other Nos.
25 [0097]
*
35
The amount of Na20 was excessive in No. 11, the amount of K2O was excessive
No. 12, and the amount of Li20 was excessive in No. 13. Therefore, in Nos. 11 to 13,
the desulfurization ratios were low, and the amounts of R2O attached to the facility due to
evaporation were large. In addition, large amounts of Na20, K2O, and Li20 were
5 included in slag after desulfurization, and recycling of the slag was not possible.
[0098]
Since the content ratio [CaO]/[Al203] is too low in No 14, and the content ratio
[Si02]/[K20] is too high in No. 15, the desulfurization ratios were low in Nos. 14 and 15.
Since the total amount of Na20 and K2O is small in No. 16, and the total amount of Na20,
10 K2O, and Li20 is too large in No. 17, the target desulfurization ratio of 82% or more was
not achieved in Nos. 16 and 17.
[0099]
The amount of MgO was large, and the amount of SiC>2 was small in No. 18, the
amount of Si02 was large in No. 19, and the content ratio [CaOJ/fAkOa] was too high in
15 No. 20. Therefore, the target desulfurization ratio of 82% or more was not achieved in
Nos. 18 to 20. In addition, in No. 21, since the flux did not include any of Na2<3, K2O,
and Li20, the target desulfurization ratio of 82% or more was not achieved.
[0100]
In No. 22, since the flux contained CaF2, a relatively high desulfurization ratio
20 was obtained compared to other comparative examples, but the desulfurization ratio
failed to exceed 82%). Furthermore, in No. 22, the obtained slag had a high content of F,
and could not be recycled.
Industrial Applicability
25 [0101]
*
3%
As described above, according to the present invention, it is possible to
anufacture high-grade steel having an extremely small amount of S without occurrence
of problems of elution of F from slag after desulfurization, attachment of Na20 or K2O to
a facility due to evaporation, a decrease in productivity due to a decrease in
5 desulfurization efficiency, an increase in desulfiirization costs, and the adverse influence
of slag including a large amount of Na20 or K2O after desulfurization on the
environment. Therefore, the present invention is highly available in steel-making
techniques of steel industry.
URI

3f
What is claimed is:
1. An environmentally friendly flux for molten steel desulfurization comprising:
CaO and AI2O3 so that [CaO]/[Al203] is within a range of 1.6 to 3.0; and
5 one or more alkali metal oxides of Na20, K2O, and Li20, and SiC-2 so that
[Si02]/[R20] is within a range of 0.1 to 3, [R2O] is within a range of 0.5 mass% to 5
mass%, and [SiCy is within a range of 0.05 mass% to 15 mass%,
in a case in which the [CaO], the [AI2O3], the [Si02], and the [R2O] represent
mass% of CaO, mass% of AI2O3, mass% of Si02, and a total amount of mass% of Na20,
10 mass% of K2O, and mass% of L12O respectively.
2. The environmentally friendly flux for molten steel desulfurization according to
Claim 1, further comprising 1 mass% to 10 mass% of MgO.
15 3. The environmentally friendly flux for molten steel desulfurization according to
Claim 1 or 2,
wherein the [Si02] is 0.05 mass% to 9.3 mass%.
4. The environmentally friendly flux for molten steel desulfurization according to
20 Claim 1 or 2,
wherein the [Si02] is 0.05 mass% to 8.0 mass%.
5. The environmentally friendly flux for molten steel desulfurization according to
Claim 1 or 2,
25 wherein the [Si02]/[R20] is 0.1 to 2.
3*
• "o. The environmentally friendly flux for molten steel desulfurization according to
Claim 1 or 2,
wherein some or all of the alkali metal oxides have a chemical bond with the
5 Si02.
7. The environmentally friendly flux for molten steel desulfurization according to
Claim 1 or 2,
wherein the alkali metal oxides are Na20.
10
8. A molten steel desulfurization method comprising
supplying the environmentally friendly flux for molten steel desulfurization
according to Claim 1 or 2 to a molten steel.
15 9. A molten steel desulfurization method comprising
forming a slag on a surface of a molten steel, the slag including one or more of
Na20, K20, and Li20, as well as CaO, A1203, and Si02 so that [Ca0]/[Al203] is within a
range of 1.6 to 3.0, [Si02]/[R20] is within a range of 0.1 to 3, [R2O] is within a range of
0.5 mass% to 5 mass%, and [Si02] is within a range of 0.05 mass% to 15 mass%,
20 in a case in which the [CaO], the [AI2O3], the [Si02], and the [R2O] represent
mass% of CaO, mass% of AI2O3, mass% of Si02, and a total amount of mass% of Na20,
mass% of K2O, and mass% of LJ2O respectively.