DESCRIPTION
TITLE OF INVENTION: METHOD OF CHANGING PICKLING
SOLUTION AND METHOD OF MANUFACTURING ELECTRICAL STEEL
SHEET
TECHNICAL FIELD
[0001] The present invention relates to a method of
changing a pickling solution used in pickling of a
steel sheet and a method of manufacturing an
electrical steel sheet.
BACKGROUND ART
[0002] Conventionally, in manufacturing process of
an electrical steel sheet, pickling of the steel
sheet is performed before cold rolling. On the
surface of the steel sheet after hot rolling or hot
band annealing when necessary is performed, an
adhered matter called scale made of components such
as iron-based oxide, Si02, AI2O3 is formed. If the
cold rolling is performed on the steel sheet with the
scale remaining on the surface thereof, Si02 and AI2O3
which are particularly hard partially grind the
surface of a work roll of the cold rolling to
extraordinarily degrade the shape of the steel sheet.
The steel sheet having a poor shape is corrected in
shape to some extent by recrystallization annealing
at the next process but sometimes deteriorates in
magnetic property because of residual stress
remaining therein. For this reason, a work of
- 1 -
removing the scale is performed by pickling. A
technique of performing the pickling under the
conditions that the concentration of hydrochloric
acid is 3% or higher, the solution temperature is 7 0°C
or higher, the immersion time is 5 seconds or longer
as the pickling conditions is disclosed, for example,
in Patent Literature 1.
[0003] Further, in a pickling line, the pickling
solution deteriorates every time when the steel sheet
passes through the picking line. Conventionally,
when the pickling solution deteriorates, the
concentration of hydrochloric acid is increased by
replenishing with hydrochloric acid, the solution
temperature is increased as high as possible, or a
pickling accelerator is added to prevent a reduction
in pickling property.
[0004] However, if the above-described work is
excessively repeated to prevent a reduction in
pickling property, the effect of improving the
pickling property is reduced. For example, there is
a problem that when the pickling property has
degraded and the work of replenishing with
hydrochloric acid is repeated in order to increase
the concentration of hydrochloric acid, the pickling
property is not sufficiently improved any longer even
when hydrochloric acid is replenished and the
solution temperature is sufficiently increased.
CITATION LIST
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PATENT LITERATURE
[0005] Patent Literature 1: Japanese Laid-open
Patent Publication No. 11-350033
Patent Literature 2: Japanese Laid-open Patent
Publication No. 2-129400
Patent Literature 3: Japanese Laid-open Patent
Publication No. 9-13183
SUMMARY OF INVENTION
TECHNICAL PROBLEM
[0006] In consideration of the above-described
problems, it is an object of the present invention to
provide a method of changing a pickling solution and
a method of manufacturing an electrical steel sheet
capable of efficiently and surely ensuring a pickling
property in a pickling process.
SOLUTION TO PROBLEM
[0007] The summary of the present invention to solve
the problem is as follows.
(1) A method of changing a pickling solution,
including: pickling a hot-rolled sheet containing Si:
0.3 mass% to 4.0 mass%, Al: 0.001 mass% to 2.0 mass%,
and Mn: 0.05 mass% to 2,0 mass% and the balance being
Fe and inevitable impurities, wherein the pickling
solution satisfies conditions of a concentration of
hydrochloric acid: 3% to 20% and a solution
temperature: 70°C to 98°C, and when a concentration of
iron ions Fe^"^ in the pickling solution is higher than
- 3 -
180 g/1, the pickling solution is adjusted to satisfy
the conditions and have the concentration of iron
ions Fe^"^ falling within a range of 3 g/1 to 180 g/1,
(2) The method of changing a pickling solution
described in (1) wherein when the concentration of
iron ions Fe^"*" in the pickling solution is higher than
180 g/1, the pickling solution is changed while a
part of the pickling solution is left, to satisfy the
conditions and have the concentration of iron ions
Fe^"" falling within 3 g/1 to 180 g/1.
(3) The method of changing a pickling solution
described in (1) wherein the hot-rolled sheet is a
steel sheet made by performing annealing after hot
rolling.
(4) A method of manufacturing an electrical steel
sheet, including:
obtaining, by hot rolling, a hot-rolled sheet
containing Si: 0.3 mass% to 4.0 mass%, Al: 0.001
mass% to 2.0 mass%, and Mn: 0,05 mass% to 2.0 mass%
and the balance being Fe and inevitable impurities;
pickling the hot-rolled sheet with a pickling
solution satisfying conditions of a concentration of
hydrochloric acid: 3% to 20% and a solution
temperature: 70°C to 98°C;
cold-rolling the pickled hot-rolled sheet to
obtain a cold-rolled sheet;
annealing the cold-rolled sheet; and
adjusting, when a concentration of iron ions Fe^"^
in the pickling solution is higher than 180 g/1, the
- 4 -
pickling solution to satisfy the conditions and have
the concentration of iron ions Fe^"^ falling within a
range of 3 g/1 to 180 g/1.
ADVANTAGEOUS EFFECTS OF INVENTION
[0008] According to the present invention, even in a
case where a pickling solution deteriorates, its
pickling property can be efficiently and surely
ensured in a pickling process.
DESCRIPTION OF EMBODIMENTS
[0009] Hereinafter, an embodiment of the present
invention will be described.
[0010] Conventionally, in manufacturing process of a
grain-oriented electrical steel sheet and a nonoriented
electrical steel sheet, increasing the
concentration of hydrochloric acid, increasing the
solution temperature as high as possible, or adding a
pickling accelerator is performed as a method of
adjusting the pickling property of a pickling
solution in pickling performed before cold rolling.
However, after the pickling is repeated several times,
the pickling property cannot be sufficiently improved
any longer because old pickling solution is left.
[0011] After investigation of the reason why the
pickling property is not improved, the present
inventor found that the concentration of iron ions
Fe^"^ more seriously affects the pickling property than
does the concentration of hydrochloric acid. When
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pickling is performed, scale formed on the surface of
a steel sheet due to hot rolling is dissolved and the
iron ions Fe^"^ mix into the pickling solution. It was
found that when the concentration of iron ions Fe^"^ in
the pickling solution exceeds the limit value due to
repetition of pickling, the pickling property is not
improved any longer even by replenishing with
hydrochloric acid and increasing the solution
temperature.
[0012] Hence, a finding was obtained that it is
effective, when the concentration of iron ions Fe^"^
reaches the limit value, not to replenish with
hydrochloric acid but change the pickling solution
filled in a tank to reduce the concentration of iron
ions Fe^"^.
[0013] Hereinafter, conditions of a pickling
solution and a method of changing a pickling solution
for pickling a hot-rolled sheet containing Si: 0.3
mass% to 4.0 mass%, Al: 0.001 mass% to 2.0 mass%, and
Mn: 0.05 mass% to 2.0 mass% and the balance being Fe
and inevitable impurities, as a steel sheet after hot
rolling (hereinafter, a hot-rolled sheet) that is an
intermediate product of a grain-oriented electrical
steel sheet and a non-oriented electrical steel sheet,
will be described. Note that the hot-rolled sheet
may be subjected to hot band annealing before
pickling according to its object.
[0014] As a method of manufacturing an electrical
steel sheet, heating and hot rolling are performed on
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a slab having a predetermined composition so as to
obtain a hot-rolled sheet having the aforementioned
composition. Then, hot band annealing is performed
as necessary, and pickling and cold rolling are
performed on the hot-rolled sheet to obtain a coldrolled
steel sheet. Then, finish annealing is
performed to obtain an electrical steel sheet.
[0015] As the hot-rolled sheet that is the object of
pickling in this embodiment, the one having the
aforementioned composition is used. Si has an effect
of reducing core loss. When the Si content is less
than 0.3 mass%, this effect becomes insufficient. On
the other hand, when the Si content exceeds 4.0 mass%,
the cold rolling after pickling becomes difficult.
[0016] Al has an effect of reducing core loss as
with Si. When the Al content is less than 0.001
mass%, this effect becomes insufficient. On the
other hand, the Al content exceeding 2.0 mass%
decreases magnetic flux density and leads to
disadvantage in terms of its addition cost.
[0017] Mn also has an effect of reducing core loss
as with Si and Al. When the Mn content is less 0.05
mass%, this effect becomes insufficient. Further,
demanganization-refining to make the Mn amount equal
to or less than 0.05 mass% in steel manufacturing
process is industrially difficult. On the other hand,
when the Mn content exceeds 2.0 mass%, magnetic flux
density decreases.
[0018] Scale is formed on the surface of the hot-
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rolled sheet having the aforementioned composition
due to the hot rolling. This scale is made of an
iron-based oxide, Si02, AI2O3 or the like and removed
in a pickling process described below.
[0019] The conditions of the pickling solution when
pickling the hot-rolled steel sheet having the
aforementioned composition are as follows.
[0020] As the acid of the pickling solution,
hydrochloric acid is used, and the concentration of
hydrochloric acid is set to 3% to 20%. When the
concentration of hydrochloric acid is less than 3%,
the scale cannot be sufficiently removed. On the
other hand, when the concentration of hydrochloric
acid exceeds 20%, not only the scale but also the
surface of the steel sheet under the scale can be
dissolved. Note that when the concentration of
hydrochloric acid is decreased by repeated pickling,
the concentration is adjusted to a range of 3% to 20%
by replenishing with hydrochloric acid.
[0021] The solution temperature of the pickling
solution is set to 70°C to 98°C. When the solution
temperature is lower than 70°C, the reaction to
dissolve the scale does not sufficiently proceed and
accordingly requires a longer immersion time,
resulting in low productive efficiency. Further,
when the solution temperature exceeds 98°C, water
(H2O) in the pickling solution vaporizes, whereby the
concentration of hydrochloric acid relatively becomes
too high and highly toxic hydrogen chloride becomes
- 8 -
more likely to vaporize.
[0022] Further, when the hot-rolled sheet having the
aforementioned composition is pickled with the abovedescribed
pickling solution, the pickling solution is
changed when the following conditions are satisfied
accompanying the deterioration of the pickling
solution,
[0023] The timing to change the pickling solution is
when the concentration of iron ions Fe^"^ exceeds 180
g/1. When the concentration exceeds this value, the
reaction between the iron ions Fe^"^ existing in the
pickling solution and Cl' in hydrochloric acid tends
to occur, so that an iron-based oxide and the like
forming the scale on the steel sheet cannot be
dissolved any longer.
[0024] Further, when changing the pickling solution,
new pickling solution is supplied while a small
amount of old pickling solution filled in the tank is
left. The concentration of iron ions Fe^"^ is made
equal to or higher than 3 g/1. When the
concentration of iron ions Fe^"^ is less than 3 g/1,
the pickling property significantly degrades. The
reason is not clear yet at present, but it is
presumed that iron ions Fe^"^ equal to or higher than 3
g/1 take catalytic action to the pickling property.
Accordingly, when performing pickling, the
concentration of iron ions Fe^"^ is set to 3 g/1 to 180
g/1.
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EXAMPLE
[0025] Next, experiments carried out by the present
inventors will be described. The conditions in the
experiments are examples employed for confirming the
operability and effects of the present invention, and
the present invention is not limited to those
examples.
[0026] First, the Si amount, the Al amount, and the
Mn amount were adjusted to 3.0 mass%, 0.5 mass%, 0.2
mass% respectively in the steel manufacturing process,
steel was continuously casted to obtain a slab with a
thickness of 250 mm. The slab was then heated at
1150°C and a hot-rolled coil with a thickness of 2.2
mm was obtained. The hot-rolled coil was then
continuously annealed at 1000°C for 100 seconds in a
nitrogen atmosphere. Test pieces were cut out of the
hot-rolled coil and employed as samples for pickling
experiments.
[0027] Then, the samples were immersed in the
pickling solutions for 20 seconds under the
conditions that the concentration of hydrochloric
acid was set to 15% and the solution temperature was
set to 90°C with only the concentration of iron ions
Fe^"^ different. Then, the samples after pickling were
observed and the pickling properties were evaluated.
Note that visual determination was performed as the
evaluation of the pickling property, and O was given
in the case where the area of brown scale was less
than 5% and X was given in the case where the area
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was equal or greater than 5%. The results are
presented in the following Table 1. Note that the "*
" mark indicates that the area falls out of the range
of the present invention.
[0028] [Table 1]
Table 1
HCL Solution Fe^* Immersion „. ,,.
HiCKiins Sample NO. Concentration Temperature Concentration Time „ Note
(%) (°C) (g/l) (s) P'-^P^'^y
1 15 90 0* 20 X Comparative
Example
2 15 90 2* 20 X Comparative
Example
3 15 90 3 20 O Present Invention
Example
4 15 90 45 20 O Present Invention
Example
5 15 90 175 20 O Present Invention
Example
6 15 90 183* 20 X Comparative
Example
7 15 90 240* 20 x Comparative
I I I \ I I I Example
[0029] As presented in Table 1, in No. 1 and No.2
with low concentrations of iron ions Fe^"^ in the
pickling solution, the scale remained on the surface
of steel sheets at a rate of 5% or higher, and also
in No.6 and No.7 with high concentrations of iron
ions Fe^"^ in the pickling solution, the scale remained
on the surface of steel sheets at a rate of 5% or
higher.
INDUSTRIAL APPLICABILITY
[0030] According to the present invention, an
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electrical steel sheet excellent in core loss can be
manufactured and used as a core material of a
transformer, a rotary machine, and a small
transformer.

CLAIMS
[Claim 1] A method of changing a pickling solution,
comprising:
pickling a hot-rolled sheet containing Si: 0.3
mass% to 4.0 mass%, Al: 0.001 mass% to 2.0 mass%, and
Mn: 0.05 mass% to 2.0 mass% and the balance being Fe
and inevitable impurities, wherein the pickling
solution satisfies conditions of a concentration of
hydrochloric acid: 3% to 20% and a solution
temperature: 70°C to 98°C, and when a concentration of
iron ions Fe^"^ in the pickling solution is higher than
180 g/1, the pickling solution is adjusted to satisfy
the conditions and have the concentration of iron
ions Fe^"^ falling within a range of 3 g/1 to 180 g/1.
[Claim 2] The method of changing a pickling solution
according to claim 1,
wherein when the concentration of iron ions Fe^"^
in the pickling solution is higher than 180 g/1, the
pickling solution is changed while a part of the
pickling solution is left, to satisfy the conditions
and have the concentration of iron ions Fe^"^ falling
within 3 g/1 to 180 g/1.
[Claim 3] The method of changing a pickling solution
according to claim 1,
wherein the hot-rolled sheet is a steel sheet
made by performing annealing after hot rolling.
[Claim 4] A method of manufacturing an electrical
steel sheet, comprising:
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obtaining, by hot rolling, a hot-rolled sheet
containing Si: 0.3 mass% to 4.0 mass%, Al: 0.001
mass% to 2.0 mass%, and Mn: 0.05 mass% to 2.0 mass%
and the balance being Fe and inevitable impurities;
pickling the hot-rolled sheet with a pickling
solution satisfying conditions of a concentration of
hydrochloric acid: 3% to 20% and a solution
temperature: 7 0°C to 98°C;
cold-rolling the pickled hot-rolled sheet to
obtain a cold-rolled sheet;
annealing the cold-rolled sheet; and
adjusting, when a concentration of iron ions Fe^"^
in the pickling solution is higher than 180 g/1, the
pickling solution to satisfy the conditions and have
the concentration of iron ions Fe^"^ falling within a
range of 3 g/1 to 180 g/1.