[0001]The present invention relates to a method for producing a grain-oriented
electrical steeL sheet in which a forsterite film is substantialLy absent.
Priority is claimed on Japanese Patent Application No. 2019-005399, filed
January 16, 2019, the content of which is incorporated herein by reference.
10 [Background AI.t]
[0002]
Grain-oriented electrical steel sheets are utilized as magnetic iron core materials
in many cases, and particularly, matetials with a low iron loss are required to reduce
energy loss. It is known that it is effective to provide tension to the smfaces of steel
15 sheets as a means for reducing iron loss.
In order to provide tension to steeL sheets, it is effective to form a coating made
of a material with a coefficient of thermal expansion smaller than those of the steel sheets
at a high temperature. Final-annealing coatings (forsterite films) formed through
reactions between oxides on the surfaces of the steel sheets and annealing separators in
20 the final annealing process can provide tension to the steel sheets and have excellent
coating adhesion.
[0003]
On the other hand, in recent years, it has been clarified that the disordered
interface structures between final-annealing coatings and base steel cancels out the
25 coating tension effect with respe.ct to iron loss. For this reason, a technique for further
1
5
reducing iron loss by obtaining a grain-oriented electrical steel sheet which has been
subjected to milTor finishing during final annealing tln·ough tl1e technique as disclosed in
Patent Document 1 or 2 and then forming a tension coating again has been proposed.
[0004]
Patent document 1 describes that an atmospheric oxidation degree PH2o/PH2 at
the time of heating is set to 0.01 to 0.15 to suppress the formation of an iron-based oxide.
Furthermore, Patent Document 2 describes that effective decarburization can be
performed by setting a heating rate of 770 to 860°C to 9 °C/s or faster.
However, in these patent documents, the sheet thicknesses at the time of
10 decarburization annealing are 0.14 mm and 0.23 mm and a technique applicable to thick
matelials (0.23 mm or more) is not desclibed.
[Prior art document]
[Patent document]
[0005]
15 [Patent document 1]
Japanese Unexamined Patent Application, First Publication No. I-!07-118750
[Patent document 2]
Japanese Unexamined Patent Application, First Publication No. I-!07-278668
[Non-Patent document]
20 [0006]
[Non-Patent document 1]
N. Morito et al.: Scripta METALLURGICA, 10 (1976), 619-622
[Summary of the Invention]
[Problems to be Solved by the Invention]
25 [0007]
2
An object of the present invention is to provide a method for producing a grainotiented
electtical steel sheet in which a forsterite film is substantially absent and which
has excellent magnetic characteristics by achieving both decarburization promotion and
oxidation suppression for a steel sheet in a wide sheet thickness range.
5 [Means for Solving the Problem]
[0008]
[1] A method for producing a grain-oriented electrical steel sheet according to an
aspect of the present invention which has an intem1ediate layer containing silicon oxide
as a main component on a swface of a base steel sheet in which a forsterite film is
10 substantially absent and has an insulation coating on a surface of the intermediate layer
includes: a decarbmization annealing process of obtaining a decarbm·ization-annealed
steel sheet which has an oxygen content of320 ppm or less and a carbon content of25
ppm or less by subjecting a cold-rolled steel she.et containing Si to deca.rburization
annealing; a final annealing process of heating the decarburization-annealed steel sheet in
15 a state in which a swface of the decarburization-annealed steel sheet is coated with an
annealing separator to subject a steel sheet to secondary recrystallization; a removal
process of obtaining a finally-annealed steel sheet by removing the annealing separator
on the steel sheet which has been subjected to the final annealing process; an
intermediate layer f01ming proc.ess of forming the intermediate layer by subjecting the
20 finally-annealed steel sheet to thermal oxidation annealing; and an insulation coating
forming process of forming the insulation coating on the finally-annealed steel sheet
having the intermediate layer formed thereon.
[0009]
[2] A method for producing a grain-oriented electrical steel sheet according to
25 another aspect of the present invention which has an intermediate layer containing silicon
3
oxide as a main component on a surface of a base steel sheet in which a forsterite film is
substantially absent and has an insulation coating on a surface of the intermediate layer
includes: a decarburization annealing process of obtaining a decarburization-annealed
steel sheet which has an oxygen content of 3 20 ppm or less and a carbon content of 25
5 ppm or less by subjecting a cold-rolled steel sheet containing Si to decarburization
annealing; a final annealing process of heating the decarburization-annealed steel sheet in
a state in which a swface of the decarburization-annealed steel sheet is coated with an
annealing separator to subject a steel sheet to secondary recrystallization; a removal
process of obtaining a finally-annealed steel sheet by removing the annealing separator
10 on the steel sheet which has been subjected to the final annealing process; and an
intermediate layer-insulation coating forming process of forming the inte1mediate Layer
and the insulation coating on the finally-annealed steel sheet in one process.
[0010]
[3] In the method for producing a grain-01iented electlical steel sheet according
15 to [1] or [2], in the decarburizalion annealing process, in a soaking area configured to
subject the cold-rolled steel sheet to decarburization annealing, an atmosphere gas may
be introduced from two locations which are an initial part and a latter part of the soaking
20
area.
[0011]
[4] In the method for producing a grain-oriented electlical steel sheet according
to [3], in the decarburization annealing process, a dew point DP1 of the atmosphere gas
introduced from an initial part of the soaking area may be set to 40 to 70°C and a dew
point DP2 of the atmosphere gas introduced from the latter part of the soaking area may
satisfy DP2::;DP1 and 60- DPI::;DP2::;1 00- DPl.
25 [0012]
4
[5] In the method for producing a grain-oriented electrical steel sheet according
to any one of [1] to [4], the cold-rolled steel sheet may contain, as a chemical
component, in terms of mass%, Si; 0.80 to 7 .00%; C: 0.085% or less; acid-soluble AL:
0.010 to 0.065%; N: 0.012% or less; Mn: 1.00% or less; a total amount of Sand Se:
5 0.003 to 0.015%; and the remainder: Fe and impmities.
[Effects of the Invention]
[0013]
According to the above aspect of the present invention, it is possible to provide a
method for producing a grain-oriented electtical steel sheet in which a forsterite fiLm is
lO substantially absent. In the method for producing a grain-oriented electrical steel sheet
according to the above aspect, it is possible to produce a grain-oriented elecuical steel
sheet having Low iron Loss and a high magnetic flux density after magnetic aging by
achieving both decarburization and steel sheet oxidation suppression in a wide sheet
thickness range.
15 [Brief Description of Drawings]
[0014]
20
Fig. 1 is a diagram illustrating a relationship between the oxygen content [0] of
a steel sheet which has been subjected to decarburization annealing and iron loss of a
final product.
Fig. 2 is a relationship between the carbon content [C) of a steel sheet which has
been subjected to decarburization annealing, an aging time of a final product, and a
magnetic flux density (B 8).
Fig. 3 is a diagram for describing an influence of an oxidation degree (PH20IPH2)
of gases on an oxide layer of a steel sheet which has been subjected to decarburization
25 annealing.
5
Fig. 4A is a diagram of a constitution when an atmosphere gas is introduced
only from a latter prui of a soaking area in a decarburization annealing furnace.
Fig. 4B is a diagram of a constitution when an atmosphere gas is introduced
from the two locations of an initial part and a latter part of a soaking area in a
5 decarburization annealing fumace.
Fig. 4C is a diagram for explaining an outline of a dew point distribution of an
atmosphere gas in the furnace when the decarbmization annealing furnace of Fig. 4A or
4B is used.
Fig. 5 is a diagram illustrating a relationship between magnetic characte1istics
10 and dew points (the dew point DPl at the initial part and the dew point DP2 at the latter
paLt).
[Embodiments for implementing the Invention]
[0015]
As desctibed above, a disordered interface stmcture between a forsterite film
15 and base steel cancels out the coating tension effect with respect to iron loss. For this
reason, the inventors of the present invention have proceeded with research concerning a
method for producing a grain-oriented electrical steel sheet in which a forsterite film is
substantially absent. Furthermore, in the grain-oriented electrical steel sheet in which a
forsterite film is substantially absent, in order to ensure the adhesion of the insulation
20 coating, the premise is a method for forming an intermediate layer containing silicon
oxide as a main component on the surface of the base steel sheet and forming an
insulation coating on the surface of the intermediate layer.
As a result of the investigation by the inventors of the present invention, it was
found that, in the method for producing a grain-oriented electrical steel sheet which has
25 an intermediate layer containing silicon oxide as a main component on the surface of a
6
base steel sheet in which a forstetite film is substantially absent and has an insulation
coating on the surface of the intennediate layer, it is possible to obtain a grain-oriented
electrical steel sheet in which both decarburization and steel sheet oxidation can be
achieved in a wide sheet thickness range and which has excellent magnetic
5 characteristics by performing treatment under specific conditions in the decarburization
annealing process and adjusting the oxygen content and the carbon content in a steel
sheet which has been subjected to decarbmization to specific ranges.
[0016]
A method for producing a grain-odented electtical steel sheet according to an
10 embodiment of the present invention (a method for producing a grain-oriented electrical
steel sheet according to this embodiment) and a grain-oriented electrical steel sheet
produced through the method for producing a grain-oriented electrical steel sheet
according to this embodiment will be described in detail below.
In the following description, when a numerical value range is indicated using a
15 "lower limit value to an upper limit value," the numerical value range means a "lower
limit value or more and an upper limit value or less" unless otherwise stated.
[0017]
A. grain-oriented electrical steel sheet
The grain-oriented electrical steel sheet produced through the method for
20 producing a grain-oriented electrical steel sheet according to this embodiment
(hereinafter may be referred to as a "grain-oriented ele.ctrical steel sheet in this
embodiment" in some cases) is a grain-oriented electrical steel sheet which has a threelayer
structure including a base steel sheet, an intermediate layer containing silicon oxide
as a main component, and an insulation coating in this order.
25 A basic structure of three layers of the grain-oriented electdcal steel sheet in this
7
embodiment will be described below.
1-1. Base steel sheet
Although the electrical steel sheet produced through the method for producing a
grain-oriented electricaL steel sheet according to this embodiment (the grain-oriented
5 electrical steeL sheet in this embodiment) has the insulation coating in contact with the
intermediate layer mainly composed of silicon oxide, a constitution such as a chemical
composition and a structure of the base steel sheet in the grain-oriented electrical steel
sheet in this embodiment does not directly relate to a layer constitution of such an
insulation coating except that Si is contained as an essential component. For this
10 reason, the base steel sheet in the grain-oriented electrical steel sheet in this embodiment
is not particularly limited as Long as the actions and effects required in this embodiment
can be obtained. For example, a base steel sheet in a general grain-oriented electtical
steel sheet can be utilized. The base steel sheet in the grain-oriented electrical steel
sheet in this embodiment will be described below.
15 [0018]
(1) Chemical composition
As the chemical composition of the base steel sheet, for example, the chemical
composition of a base steel sheet in a general grain-oriented electrical steel sheet can be
utilized except that Si is contained as an essential component. Since the function of Si
20 is the same as that in a general grain-oriented electrical steel sheet, the content may be
determined within a general range from the characteristics required for the target grainoriented
electrical steel sheet.
In the following description, the amount of each component in the chemical
composition of the base steel sheet is a value in terms of mass%. Furthermore, the
25 chemical composition is a chemical composition at a depth of 50 to 60 ~-tm in which a
8
chemical composition of the grain-oriented electrical steel sheet in this embodiment is
stable.
[0019]
A typical example of the chemical composition of the base steel sheet, in terms
5 of mass%, is an amounts of Si: 0.80% to 7.00% and of Mn: 0.05% to 1.00%, with the
remainder being Fe and impurities. Furthermore, in addition to these chemical
components, a total amount of S and Se which is contained may be 0.003% or more and
0.015% or less. The reason for limiting a typical example of the chemical composition
will be described below.
10 [0020]
''Si": 0.80% or more and 7.00% or less
Si is an essential component which increases electrical resistance and reduces
iron loss. Furthermore, when Si is contained at a high concentration, a strong chemical
affinity develops between the intermediate layer mainly composed of silicon oxide, and
15 the base steel sheet and the intermediate layer and the base steel sheet adhere to e..1.ch
other more firmly. However, if the Si content exceeds 7 .00%, cold rolling is extremely
difficult and cracks are likely to occur during cold rolling. For this reason, the Si
content is preferably 7.00% or less, more preferably 4.50% or less, and even more
preferably 4.00% or less.
20 On the other hand, if the Si content is less than 0.80%, y transformation occurs
during final annealing, which may impair the preferred crystal orientation of the grainoriented
electrical steel sheet in some cases. For this reason, the Si content is preferably
0.80% or more, more preferably 2.00% or more, and even more preferably 2.50% or
more.
25 [0021]
9
"Mn": 0.05% or more and 1.00% or less
"Sand Se": a total amount of0.003% or more and 0.015% or less
Mn generates MnS and MnSe together with S and Se and these composite
compounds function as an inhibitor. When the Mn content is within the range of 0.05%
5 to 1.00%, secondary recrystallization is stable. For this reason, the Mn content is
preferably 0.05% to 1.00%. The Mn content is more preferably 0.08% or more, and
even more preferably 0.09% or more. FUithennore, the Mn content is more preferably
0.50% or less, and even more preferably 0.20% or less.
[0022]
10 "Remainder"
The remainder is composed of Fe and impmities. The "impulities" mean
elements inevitably incorporated from components contained in raw materials when the
base steel sheet is industrially produced or components incorporated in a producing
process.
15 [0023]
1-2. Intermediate layer
The intermediate layer is f01med on the surface of the base steel sheet and
contains silicon oxide as a main component. Since the grain-oriented electrical steel
sheet does not substantially have a forsterite film, the intermediate layer is formed in
20 direct contact with the surface of the base steel sheet. The intermediate layer has a
function of bringing the base steel sheet and the insulation coating to adhere with each
other, in the three-layer structure in this embodiment.
[0024]
In the grain-oriented electrical steel sheet in this embodiment, the intermediate
25 layer means a layer existing between the base steel sheet which will be described later
10
and the insulation coating which will be described Later (a compound layer which will be
described later).
The silicon oxide which is a main component of the intermediate layer is
preferably SiOx (x=l.O to 2.0), and more preferably SiOx (x=1.5 to 2.0). This is
5 because silicon oxide is more stable. If a sufficient heat treatment in which silicon
oxide is formed on the surface of the steel sheet is performed, it is possible to form silica
(Si02).
Containing silicon oxide as main component used means that in a .composition
of the intermediate layer, the Fe content being less than 30 atom%, the P content being
10 less than 5 atom%, the Si content being 20 atom% or more, the 0 content being 50
atom% or more, and the Mg content being 10 atom% or less are satisfied, as will be
described later.
[0025]
If an intetmediate layer is thin, a sufficient them1al stress relaxation effect may
15 not be exhibited. Thus, the coating adhesion cannot be ensured. For this reason, a
thickness of the intermediate layer is preferably 2 nm or more, and more preferably 5 nm
or more. On the other hand, if an inte~mediate layer is thick, there is a concem
conceming a non-uniform thickness and the occurrence of defects such as voids and
cracks in a layer. For this reason, the thickness of the intermediate layer is preferably
20 400 nm or less, and more preferably 300 nm or less. Furthermore, if an intennediate
layer is made thinner within a range in which coating adhesion can be ensured, a
formation time can be shortened, which can contribute to increased productivity and
suppress a decrease in space factor when the intermediate layer is used in an iron core.
The thickness of the intermediate layer is preferably 100 nm or less, and more preferably
25 50 nm or less.
11
[0026]
Although a method for measuring a thickness and a position of the intermediate
layer is not particularly limited, for example, the thickness and the position of the
intermediate layer can be obtained by observing and measuring a cross section of the
5 intermediate layer as follows using a scanning electron microscope (SEM), a
transmission electron microscope (TEM), or the like having a diameter of an electron
beam of 10 nm.
Specifically, a test piece is cut out through focused ion beam (FIB) processing so
that a cut cross section is parallel to a sheet thickness direction and perpendicular to a
10 rolling direction and a cross-sectional structure of this cut cross section is observed (a
blight field image) using a scanning-TEM (STEM) at a magnification at which each layer
is included in an observation field of view. When each Layer is not included in the
observation field of view, a cross-sectional stmcture is observed in multiple continuous
fields of view.
15 [0027]
In order to identify each layer in the cross-sectional structure, quantitative
analysis of a chemical component of each layer is perf01med by performing line analysis
in the sheet thickness direction using energy dispersive X-ray spectroscopy (TEM-EDS).
100 points in an observation cross section of a sampLe are measured at intervaLs of 0.1
20 Jlm in a direction parallel to the surface of the base steel sheet. At this time, quantitative
analysis is performed at 1 nm intervals in the sheet thickness direction using energy
dispersive type X-ray spectroscopy (EDS) having a diameter of an electron beam of 10
nm.
Elements to be quantitatively analy'Zed are 5 eLements such as Fe, P, Si, 0 , and
25 Mg. Furthermore, in order to identify a compound Layer, a crystaL phase is identified
12
through electron beam diffraction together with EDS.
[0028]
A thickness of each layer is measmed by identifying each layer from the abovedescribed
bright field image observation using a TEM, quantitative analysis of a TEM-
5 EDS, and electron beam diffraction result. Subsequent specifically-identification of
each layer and measurement of a thickness are performed all on the same scanning line of
the same sample.
[0029]
A region in which the Fe content is 80 atom% or more is determined to be a base
10 steel sheet. A region in which the Fe content is less than 80 atom%, the P content is 5
atom% or more, the Si content is less than 20 atom%, the 0 content is 50 atom% or
more, and the Mg content is 10 atom% or less is determined to be an insulation coating.
Furthermore, a region in which the Fe content being less than 30 atom%, the P content
being less than 5 atom%, the Si content being 20 atom% or more, the 0 content being 50
15 atom% or more, and the Mg content being 10 atom% or less are satisfied is determined to
be an intermediate layer.
[0030]
If each layer is determined using the components as described above, a region (a
blank region) which does not correspond to any of the compositions in the analysis may
20 occur in some cases. However, in the grain-oriented electrical steel sheet in this
embodiment, each layer is specifically identified so that a three-layer structme such as
the base steel sheet, the intermediate layer, and the insulation coating (including a
composition-variable layer) is obtained. The determination criteria are as follows.
First, in the blank region between the base steel sheet and the intermediate layer,
25 the base steel sheet side is regarded as the base steel sheet and the intermediate layer side
13
is regarded as the intermediate layer using a center of the blank region in a thickness
direction as a boundary. Subsequently, in the blank region between the insulation
coating and the intermediate layer, the insulation coating side is regarded as the
insulation coating and the intermediate layer side is regarded as the intermediate layer
5 using the center of the blank region in the thickness direction as the boundary. Through
this procedure, the base steel sheet, the insulation coating, and the intermediate layer can
be separated.
10
15
[0031]
1-3. Insulation coating
The insulation coating is fo1med on the surface of the inte1mediate layer and has
a function of reducing iron loss as a single steel sheet by providing tension to the steel
she.et and ensuring electrical insulation between grain-oriented electrical steel sheets
when the grain-oriented electtical steel sheets are laminated and utilized.
[0032]
The composition of the insulation coating is not particularly limited, can be
appropriately selected and utilized from known compositions in accordance with the
intended use, and may be either an organic coating or an inorganic coating.
Examples of the organic coating include polyamine-based resins, acrylic resins,
acrylic styrene resins, alkyd resins, polyester resins, silicone resins, fluoro-resins,
20 polyolefin resins, styrene resins, vinyl acetate resins, epoxy resins, phenol resins,
urethane resins, melamine resin, and the like. Ftuthermore, examples of the inorganic
coating include phosphate-based coatings, aluminum phosphate-based coatings, organicinorganic
composite-based coatings containing the above resin. To be more specific,
colloidal silica particles dispersed in a matrix may be baked. Here, the "matrix" is a
25 substrate for an insulation coating, for example, a matrix composed of non-crystalline
14
phosphate. Examples of the non-crystalline phosphate constituting the matrix include
aluminum phosphate, magnesium phosphate, and the like. The insulation coating which
has been subjected to baking is composed of a plurality of compounds containing one or
more of P, 0, and S.
5 [0033]
If an insulation coating is thin, the tension provided to the steel sheet decreases
and the insulating properties also decreases. For this reason, a thickness of the
insulation coating is preferably 0.1 J.lm or more, and more preferably 0.5 J.lm or more.
On the other hand, if the thickness of the insulat.ion coating exceeds 10.0 J.!ffi, there may
10 be a concern concerning cracks occurring on the insulation coating at the stage of
forming the insulation coating. Thus, the thickness of the insulation coating is
preferably 10.0 ~tm or less, and more preferably 5.0 ~tm or less.
The insulation coating may be subjected to a magnetic domain subdivision
treatment in which local micro-strained regions or grooves are formed using laser,
15 plasma, a mechanical method, etching, or other methods.
[0034]
B. Method for producing grain-oriented electlical steel sheet
A method for producing a grain-oriented electrical steel sheet according to this
embodiment will be described beLow.
20 [0035]
The method for producing a grain-oriented electrical steeL sheet according to this
embodiment is the method for producing a grain-oliented electlical steel sheet which has
the intermediate layer containing silicon oxide as a main component on the surface of the
base steel sheet in which the forsterite film is substantially absent described in the item
25 "A grain-oriented electrical steel sheet" described above and has the insulation coating
15
on the surface of the intermediate layer. In other words, the method is the method for
producing a grain-oriented electrical steel sheet which has the base steel sheet, the
intermediate layer fonned on the surface of the base steel sheet, and the insulation
coating formed on the surface of the inte1mediate layer. Since the base steel sheet does
5 not have the forsterite film, the intermediate layer is formed in direct contact with the
base steel sheet.
[0036]
"Producing method in first embodiment"
In the method for producing a grain-oriented electrical steel sheet according to
10 the first embodiment, the inte1mediate layer and the insulation coating are formed in
separate processes. That is to say, the method for producing a grain-oriented electrical
steel sheet according to the first embodiment has the following processes:
(I) a decarburization annealing process of obtaining a decarbmization-annealed steel
sheet which has the oxygen content of 320 ppm or less and the carbon content of 25 ppm
15 or less by subjecting a cold-rolled steel sheet containing Si to decarburization annealing;
(II) a t1nal annealing process of heating the decarbwization-annealed steel sheet in a state
that an annealing separator is applied to a surface of the decarburization-annealed steel
sheet to subject a steel sheet (the decarburization-annealed steel sheet) to cause
secondary recrystallization to oc.cur;
20 (III) a removal process of obtaining a finally-annealed steel sheet by removing the
annealing separator on the steel sheet (the decarburization-annealed steel sheet) which
has been subjected to the final annealing process;
(IV) an intermediate layer forming process of forming the intermediate layer by
subjecting the finally-annealed steel sheet to thermal oxidation annealing; and
25 (V) an insulation coating forming process of forming the insulation coating on the
16
finally-annealed steel sheet having the intermediate layer.
[0037]
"Producing method in second embodiment"
In the method for producing a grain-oriented electricaL steel sheet according to
5 the second embodiment, the intermediate layer and the insulation coating are formed at
the same time in one process. That is to say, the method for producing a grain-oriented
electrical steeL sheet according to the second embodiment has the following processes:
(I) a decarburization annealing process of obtaining a decarbmization-annealed steel
sheet which has the oxygen content of 320 ppm or less and the carbon content of 25 ppm
10 or less by subjecting a cold-rolled steel sheet containing Si to decarburization annealing;
(II) a final annealing process of heating the decarbmization-annealed steel sheet in a state
that an annealing separator is applied to a surface of the decarburization-annealed steel
sheet to subject a steel sheet (the decarbmization-annealed steel sheet) to cause
secondary recrystallization to occur;
15 (III) a removal process of obtaining a finally-annealed steel sheet by removing the
annealing separator on the steel sheet (the decarburization-annealed steel sheet) which
has been subjected to the final annealing process; and
(IV') an intermediate layer-insulation coating forming process of forming the
intermediate Layer and the insulation coating on the finally-annealed steel sheet in one
20 step.
[0038]
In the method for producing a grain-oriented electrical steel sheet according to
this embodiment, it is possible to prevent the effect of reducing iron loss due to the
insulation coating from being hindered due to the interfacial unevenness between the
25 final-annealing coating and the base steel sheet and to secure the adhesion between the
17
insulation coating and the base steel sheet through the intennediate layer.
[0039]
Each process in the method for producing a grain-oriented electrical steel sheet
according to this embodiment will be desclibed below separately for the first
5 embodiment and the second embodiment.
In the following description, the conditions other than above-described
particularly characte1istic processes are shown by taking general conditions as an
example. Thus, it is possible to obtain the effect of this embodiment even if the
conditions are not satisfied.
10 [0040]
15
B-1. First embodiment
1. Cold-rolLed steel sheet for decarburization annealing process
First, a cold-rolled steel sheet used for decarburization annealing which will be
described later will be described.
The cold-rolled steel sheet can have a chemical composition of a base steel sheet
in a general grain-oriented electrical steel sheet except that Si is contained as an essential
component. Since the function of Si contained in the electrical steel sheet is the same as
that of a general grain-oriented electrical steel sheet, the content may be determined
within a general range from the characteristics required for the target electrical steel
20 sheet.
For example, the chemical composition of the cold-rolled steel sheet can be a
chemical composition which contains, in terms of mass%, Si: 0.80 to 7.00%; C: 0.085%
or less; acid-soluble AI: 0.010 to 0.065%; N: 0.012% or less; Mn: 1.00% or less; and a
total amount of Sand Se: 0.003 to 0.015% and the remainder: Fe and impurities as an
25 example.
18
Such a cold-rolled steel sheet can be produced through, for example, a
producing method which includes: a hot rolling process of heating a slab and then
subjecting the slab to hot rolling to obtain a hot-rolled steel sheet; a hot-band allllealing
process of obtaining an annealed steel sheet by subjecting the hot-rolled steel sheet to
5 hot-band annealing; and a cold rolling process of obtaining a cold-rolled steel sheet by
subjecting the annealed steel sheet to one cold rolling or two or more cold rollings having
intermediate annealing pe1formed between the cold rollings.
[0041]
Since the chemical composition does not substantially change through slab
10 heating, hot rolling, hot-band annealing, and cold rolling, the sLab needs to conform to a
known technique in accordance with the chemical composition of the cold-rolled steel
she.et to be required. A typical example of the chemical composition contains, in terms
of mass%, Si: 0.80% to 7.00%; C: 0.085% orless; acid-soluble At: 0.010% to 0.065%;
N: 0.004% to 0.012%; Mn: 0.05% to 1.00%, and a total amount of S and Se: 0.003% to
15 0.015%, and composed of the remainder: Fe and impurities.
20
The reason for limiting typical examples of the chemical compositions of the
slab and the cold-rolled steel sheet obtained using the same will be described below.
[0042]
a. Si: 0.80% to 7.00%
Si is an essential component, which increases electrical resistance and reduces
iron loss. Ftuthermore, when a high concentration of Si is contained, a strong chemical
affinity develops between the intermediate layer mainly composed of silicon oxide and
the base steel sheet and the intermediate layer and the base steel sheet adhere to each
other more firmly. However, if the Si content exceeds 7 .00%, cold rolling is extremely
25 difficult and cracks are likely to occur during cold rolling. For this reason, the Si
19
content is preferably 7.00% or less, more preferably 4.50% or less, and even more
preferably 4.00% or less.
On the other hand, if the Si content is less than 0.80%, y transformation occurs
dming final annealing and the crystal orientation of the grain-oriented electrical steel
5 sheet is impaired. For this reason, the Si content is preferably 0.80% or more, more
preferably 2.00% or more, and even more preferably 2.50% or more.
[0043]
b. C: 0.085% or less
Cis an element effective in controlling a primary recrystallization stmcture, but
10 adversely affects the magnetic characteristics. For this reason, decarbmization
annealing is performed before final annealing. If the C content is more than 0.085%, a
decarburization annealing time increases and the productivity in industrial production
may be impaired in some cases. From these facts , the C content is preferably 0.085% or
less. Although a lower limit value of the C content is not particularly limited, the C
15 content is preferably 0.020% or more, and more preferably 0.050% or more.
[0044]
c. Acid-soluble Al: 0.010% to 0.065%
Acid-soluble Al binds with N to precipitate as (Al, Si)N and functions as an
inhibitor. Secondary recrystallization is stable when the acid-soluble Al content is
20 within the range of 0.010% to 0.065%. For this reason, the acid-soluble Al content is
preferably 0.010% to 0.065%. Furthermore, the acid-soluble Al content is preferably
0.015% or more, and more preferably 0.020% or more from the viewpoint of
concentrating Al on the surface of the steel sheet in final annealing and utilizing AI as AI
among Al and Mg existing on the surface of the steel sheet when forming the
25 intermediate layer in the method for producing a grain-oriented electrical steel sheet of
20
the present invention, as will be described later. Fmthermore, from the viewpoint of
stability of secondary recrystallization, the acid-soluble Al content is more preferably
0.050% or less, and even more preferably 0.035% or less.
[0045]
5 d. N: 0.004% to 0.012%
10
N binds withAl to function as an inhibitor. If theN content is less than
0.004%, a sufficient amount of inhibitor cannot be obtained. For this reason, theN
content is preferably 0.004% or more, more preferably 0.005% or more, and even more
preferably 0.006% or more.
On the other hand, if theN content exceeds 0.012%, defects called blisters are
likely to occur in the steel sheet. For this reason, theN content is preferably 0.012% or
less, more preferably 0.011% or less, and even more preferably 0.010% or less.
[0046]
e. Mn: 0.05% to 1.00%
15 f. TotaL of Sand Se: 0.003% to 0.015%
Mn generates MnS and/or MnSe together with S and/or Se and the complex
compoLmds function as an inhibitor. Secondary recrystallization is stable when the Mn
content is within the range 0.05% to 1.00%. For this reason, the Mn content is
preferably 0.05% to 1.00%. The Mn content is more preferably 0.08% or more, and
20 even more preferably 0.09% or more. Fwthetmore, the Mn content is more preferably
0.50% or Less, and even more preferably 0.20% or less.
[0047]
Secondary recrystallization is stable when a total amount of S and Se contents is
within the range of 0.003% to 0.015%. For this reason, the total of Sand Se contents is
25 preferably 0.003% to 0.015%.
21
[0048]
Here, the expression "the total of Sand Se contents is 0.003% to 0.015%"
means both when the base steel sheet contains only one of S and Se and a total amount of
S or Se content is 0.003% to 0.015% and when the base steel sheet contains both Sand
5 Se and a total amount of S and Se contents is 0.003% to 0.015%.
[0049]
g. Other elements
Various kinds of elements can be contained in place of a part of the remainder:
Fe in accordance with known documents in consideration of the enhancement of an
10 inhibitor function due to fonnation of a compound and the influence on the magnetic
characteristics. The targets of the types and amounts of the elements to be contained in
place of a part of Fe are, for example, "Bi: 0.010% or less," B: 0.080% or less," "Ti:
0.015% or less," "Nb: 0.20% or less," "V: 0.15% or less," "Sn: 0.10% or less," "Sb:
0.10% or less," "Cr: 0.30% or less," "Cu: 0.40% or less;" "P: 0.50% or less," "Ni: 1.00%
15 or less," "Mo: 0.10% or Less," and the like.
[0050]
h. Remainder
The remainder is Fe and impurities. The "impurities" mean elements
incorporated from components contained in raw materials when the base steel sheet is
20 industrially produced of components incorporated in the producing process.
[0051]
The slab is obtained, for example, by melting steel having the above-desclibed
chemical composition in a converter furnace, an electric fuTnace, or the like, subjecting
the steel to vacuum degassing if necessary, and then subjecting the steel to continuous
25 casting or ingot rolling after ingot casting. A thickness of the slab is not particularly
22
limited, but is, for example, 150 mm to 350 mm, and preferably 220 mm to 280 mm.
Furthermore, the slab may be a slab having a thickness of about 10 mm to 70 mm (a socalled
"thin slab"). \Vhen the thin slab is utilized, rough rolling before final rolling can
be omitted in the hot rolling process.
5 [0052]
10

In the hot rolling process, the Si-containing slab as desctibed above is heated
within a temperature range of, for example, 800°C to 1300°C and then is subjected to hot
rolling to obtain a hot-rolled steeL sheet.
When a heating temperature of the slab is 1200°C or lower, for example, it is
preferable to avoid various problems (a dedicated heating furnace is required, a large
amount of melt scale, and the like) when heating is performed at a temperature higher
than 1200°C.
When the heating temperature is too low, hot rolling may be difficult and
15 productivity may decrease in some cases. For this reason, a lower limit value of the
heating temperature of the slab is preferably 950°C. Furthermore, it is also possible to
omit the slab heating process itself and start hot rolling after casting until the temperatLU·e
of the slab decreases.
20
[0053]
In the hot rolling process, the heated slab is subjected to rough rolling and then
to final rolling to obtain a hot-rolled steel sheet having a prescribed thickness. After the
completion of the final rolling, the hot-rolled steel sheet is coiled at a prescribed
temperature.
Also, the sheet thickness of the hot-rolled steel sheet is not particularly limited,
25 but is, for example, 3.5 mm or less.
23
[0054]

In the hot-band annealing process, the hot-rolled steel sheet is subjected to hotband
annealing to obtain an annealed steel sheet. The hot-band annealing conditions
5 may be general conditions, but is held, for example, at a temperature within the range of
750 to 1200°C for 30 seconds to 10 minutes.
[0055]

In the cold rolling process, the annealed steel sheet is subjected to one cold
10 rolling or two or more cold rollings having intennediate annealing performed between
the cold rollings to obtain a cold-rolled steel sheet.
15
20
A cold rolling ratio in final cold rolling (a final cold rolling ratio) is not
particularly limited. but is preferably 80% or more. and more preferably 90% or more
from the viewpoint of crystal orientation controL
Also, the sheet thickness of the cold-rolled steel sheet is not pru1icularly limited,
but, in order to further reduce iron loss, is preferably 0.35 rum or less, and more
preferably 0.30 rum or less.
[0056]
2. Decarburization annealing process
In the d.ecarburization annealing process, the cold-rolled steel sheet is subjected
to decarburization annealing to obtain a decarburization-annealed steel sheet.
To be specific, by performing decarburization annealing, primary
recrystallization occurs in the cold-rolled steel sheet, C contained in the cold-rolled steel
sheet is removed, and the carbon content in the steel sheet which has been subjected to
25 deca.rburization annealing is 25 ppm or Less. It is desirable that the decarburization
24
5
annealing be petfonned in a moist atmosphere to remove C. Furthennore, in the
decarburization annealing process, the oxygen content after decarburization annealing is
controlled to 320 ppm or less by suppressing oxidation.
[0057]
A decarburization annealing method included in the method for producing a
grain-oriented electrical steel sheet according to this embodiment will be described in
detail below.
In the grain-oriented electrical steel sheet, about 500 to 600 ppm of carbon is
contained to obtain a texture for improving magnetic characteristics. However, after the
10 cold rolling process described above, carbon (C) is not required. In the dec.a.rburization
annealing process, it is thus necessary to remove the carbon content after annealing to a
level in which magnetic aging in a final product such as a transformer is not caused. In
the grain-01iented electrical steel sheet having the forsterite film, it is necessary to fonn
an oxide layer having fayalite on a surface layer of the steel sheet. Thus, usually, the
15 cold-rolled steel sheet is annealed at a dew point of 60 to 70°C and a soaldng temperatme
of 800 to 900°C.
[0058]
However, in the grain-oriented electrical steel sheet in which a forsterite film is
substantially absent such as the grain-oriented electrical steel sheet in this embodiment, if
20 annealing is performed under the conditions of a high dew point as described above,
oxides (mullite) are formed dming high-temperature annealing and oxidation of the steel
sheetreduces the smoothness of the surface and reduces the magnetic characteristics.
Furthermore, when a dew point is reduced to avoid this, according to the research of the
inventors of the present invention, it has been found that a decarburization rate decreases,
25 an amount of residual carbon content increases, and magnetic aging occurs. That is to
25
5
say, since decarbmization promotion and oxidation suppression of the steel sheet are
contradictory phenomena in establishing atmosphetic conditions, it is difficult to realize a
dew point at the time of decarburization annealing under certain conditions.
[0059]
The inventors of the present invention considered that it is not possible to
achieve both decarburization and oxidation suppression by first preferentially performing
decarburization at a high dew point and then reducing the dew point to suppress
oxidation after completion of decarburization as a decarburization annealing treatment.
Based on this idea, the inventors of the present invention investigated the influences of
10 dew point control in the first half of the decarburization annealing treatment and of dew
point control in the second half of the decarburization annealing treatment by carrying
out the following tests.
[0060]
These tests were pe1formed using a box -shaped decarburization annealing
15 furnace including a heating furnace 1 and a soaking furnace 2 having the constitutions
illustrated in Figs. 4A and 4B.
As illustrated in Figs. 4A and 4B, the decarburization annealing furnace is a
decarburization annealing furnace in which the inside of the heating furnace l is a
heating area, the inside of the soaking furnace 2 is a soaking area, the steel sheet can be
20 horizontally transported in the rightward direction indicated by the arrows illustrated in
Figs. 4A and 4B from the heating area toward the soaking area, and a decarburization
annealing treatment can be performed on the steel sheet during transportation.
The decarburization annealing furnace illustrated in Fig. 4A is a furnace in
which an atmosphere gas can be supplied from a side wall part (a latter part of the
25 soaking area) near an outlet of the soaking furnace 2 into the inside of the soaking
26
furnace 2 in a direction opposite to a direction in which the steel sheet passes.
The decarburization annealing furnace illustrated in Fig. 4B is a decarburization
annealing furnace in which an atmosphere gas can be suppLied from the side wall part
(the latter part of the soaking m·ea) near the outlet of the soaking furnace 2 into the inside
5 of the soaking f1.unace 2 in the direction opposite to the direction in which the steel sheet
passes and an atmosphere gas can be supplied from a bottom part (an initial part of the
soaking area (a latter part of the heating area)) near an inlet of the soaking furnace 2
toward the heating furnace 1 side in a direction opposite to a direction in which the steel
sheet is transported.
10 h1 this embodiment, the initial part of the soaking m·ea refers to a position closer
to the heating m·ea side (an upstream side) than a center of the soaking m·ea, the latter part
of the soaking area refers to a position closer to a downstream side than center of the
soaking area, and the stages are, for example, the positions illustrated in Fig. 4B. It is
desirable that the position in which an atmosphere gas is introduced be near an inlet of
15 the soaking area (a position in which a temperature reaches the soaldng temperature) if
the position is in the initial part and be near an outlet of the soaking area if the position is
in the latter part.
20
[0061]

In this embodiment, a test in which an atmosphere gas having a dew point (DPI)
of 30 to 70°C was introduced from the initial prut of the soaking area and a dew point
(DP2) of the atmosphere gas introduced from the latter part of the soaking ru·ea was
changed to -20 to 50°C was pelformed, using the decarblu·ization annealing fw·nace
illustrated in Fig. 4B and under the treatment conditions listed in Table 1 below.
25 Subsequently, the obtained decarburization-annealed steel sheet was subjected to a
27
nitriding treatment under the nitriding treatment conditions listed in Table 1 and the
carbon content and the oxygen content of the steel sheet which has been subjected to
decarburization annealing were investigated. The carbon content in the obtained steel
sheet was analyzed using an infrared absorption method by generating CO gas by
5 buming the steel sheet in an oxygen stream. The oxygen content in a sample was
analyzed using an infrared absorption method by burning the sample in a graphite
crucible in an inert gas such as He to generate CO gas.
Although a magnesia water slw1·y may be applied to the obtained
decarbwization-annealed steel sheet as in the related art in some cases, in the case of this
10 example, unevenness of the oxide layer of a surface layer occurs due to reaction with
silica in the final annealing process. Thus, in this test, a water slmTy including an
annealing separator containing alumina as a main component (for example, containing
MgO: about 10 to 50%; and Ah03: 90 to 50%) was applied.
Subsequently, the final annealing was performed, tension coating application
15 was performed, and then magnetic domain subdivision through laser irradiation was
performed to obtain a plurality of grain-oriented electlical steel sheets. The magnetic
characteristics (1.7 T, iron loss Wl7/50 at 50Hz and a magnetic flux density B8 at a
magnetization force of 800 Aim) of these grain-oriented electrical steel sheets were
measured on the basis of the Epstein method described in JISC2550-l: 2011.
20 [0062]
[Table 1]
Purpose of Treatment conditions
treatment
Cold rolling Final thickness (mm) 0.23
Decarbruization Rate of temperature eels) 8
annealing and rise
heating Heating time (sec) 80
Atmosphere H2 (%) 75
28
Dew point DP1 30 to 70
CCC)
Decarburization Soaking (oC) 820
annealing and temperature
soaking Soaking time (sec) 115
Atmosphere H2 (%) 75
Dew point DP2 -20 to 50
CCC)
Nitriding treatment Sheet temperature (oC) 750
at Nitriding
Soaking time (sec) 33
Atmosphere I-b (%) 75
Dew point CCC) 0
NH3 (%) 3
[0063]
Fig. 1 illustrates a relationship between the obtained oxygen content in the steel
sheet and the magnetic characteristics.
It is found from Fig. 1 that the iron loss deteriorates in all of the samples when
5 the oxygen content in the steel sheet is more than 320 ppm. This is because, if an
amount of oxidation in decarburization annealing exceeds 320 ppm, oxides (mullite) are
formed during high-temperature annealing, the smoothness of the steel sheet is lost, and
thus iron Loss is reduced.
Also, Fig. 2 illustrates a relationship among an aging time, the carbon content in
10 the steel sheet, and a magnetic flux density obtained after annealing is pelformed at
150°C for a maximum of 10 days for holding. It is found from Fig. 2 that a coercivity
sharply deteriorates in the sample having the carbon content in the steel sheet of more
than 25 ppm. It is considered that this is because carbides and nitrides precipitate due to
aging, which hinder the movement of a domain waLL
15 [0064]
Subsequently, in this embodiment, a technique for clarifying controlling factors
of decarburization and an oxidation reaction and achieving both decarbmization and
oxidation at the time of low dew point decarburization annealing was examined.
29
It is known that a decarburization reaction rate in the steel sheet is a diffusionrate-
determining rate of carbon in the steel sheet and it is known that a decarbulization
reaction start.s at about 700°C or higher. Thus, it is considered important to improve a
decarbmization temperature, a decarburization time, and a gas oxidation degree of an
5 atmosphere gas at 700°C or higher to improve the decarburization properties.
Non-Patent document 1 describes an influence of a gas oxidation degree
(PH2oiPH2) on oxidation of the steel sheet when 3% Si steel sheet is annealed at 850°C
(refer to Fig. 3). As illustrated in Fig. 3, when the gas oxidation degree (PH2o/PH2) is
0.02 (in the case of a 75% hydrogen atmosphere, a dew point corresponds to that of
10 l8°C) or less, the oxide formed on the surface of the steel sheet is mainly Si02. Since
this Si~ is amorphous, it is known that the extremely small gas pe1meatiou effect is
provided. Furthermore, Si02 is preferentially fonne.d when annealing is performed at a
low dew point in a low temperature part. Thus, it can be seen that, in order to improve
decarbwization, it is important to pelfmm annealing at a relatively high dew point in an
15 early stage of oxidation and suppress the formation of Si02.
[0065]
Fig. 4C illustrates a schematic diagram of an atmosphere gas dew point
distribution (the dotted line) in the decarburization annealing furnace when an
atmosphere gas is introduced from the latter part of the soaking area in the furnace as
20 illustrated in Fig. 4Aand an atmosphere gas dew point distribution (the solid line) in the
furnace when an atmosphere gas is introduced from the two locations which are the
heating area and the soaking area as illustrated in Fig. 4B.
It can be seen that, as illustrated in Fig. 4A, when atmosphere gases are
collectively introduced from the latter part of the soaking area 2, the water vapor in the
25 atmosphere gas is consumed while the atmosphere gas is flowing from the soaking area 2
30
toward the heating area 1 side, and thus a dew point of an atmosphere gas introduced at
the latter part of the soaking area 2 decreases toward a direction of the heating area 1 as
indicated by the dotted line in Fig. 4C. This decrease in dew point promotes the
formation of am01phous Si02, which makes it more difficult to achieve both
5 decarburization and oxidation. Furthermore, since decarbmization is completed when a
temperature reaches the soaking temperature, it is effective to supply an atmosphere gas
having a high dew point before the temperature reaches the soaking temperature to
promote decarbmization.
On the other hand, when an atmosphere gas is introduced from the two locations
10 which are the heating area and the soaking area as illustrated in Fig. 4B, it is possible to
suppress the formation of the amorphous Si02 and to promote the decarbmization
reaction by introducing a high dew point gas at the initial part. On the other hand, it is
possible to suppress excessive oxidation of Si after decarbulization by introducing a low
dew point gas at the latter part.
15 From the above consideration, it is considered in this embodiment that it is
possible to achieve both decarburization and oxidation suppression through introducing
of gases in two stages which are introducing of an atmosphere gas of a high dew point
(DPl) to promote decarburization at an initial part (a point at which a temperature is the
soaking temperature) of the soaking area 2 and introducing of an atmosphere gas of a
20 dew point (DP2) from the latter part of the soaking area 2, as indicated by the solid line
in Fig. 4B, to suppress excessive oxidation.
[0066]

The inventors of the present invention performed a test in which the dew point
25 conditions during decarburization annealing are changed during annealing to promote
31
decarbwization in the heating area 1 and adjust oxidation in the soaking area 2, using a
decarburization annealing furnace 10 illustrated in Fig. 4B under the treatment conditions
listed in Table 2 below. The soaking temperature at the time of decarburization
annealing is determined as a condition in which both decarbmization and an amount of
5 oxidation of the decarbmization-annealed steel sheet are achieved and may be achieved
at 800 to 870°C, preferably 805 to 850°C, and more preferably 820 to 835°C.
[0067]
[Table 2]
Purpose of
Treatment conditions
treatment
Cold rolling
Final (mm) 0.18 0.23 0.35
thickness
Rate of
temperature (°C/s) 13 8 7
Decarburization
rise
Heating
annealing and (sec) 41 80 99 time
heating
Hz(%) 75 75 75
Atmosphere Dew point
30 to 80 30to 80 30 to 80
DP l (°C)
Soaking
temperature CCC) 820 820 820
Decarburi zation Soaking
(sec) 154 115 96
annealing and time
soaking Hz (%) 75 75 75
Atmosphere Dew point
-20 to 50 -20 to 50 - 20to 50
DP2 (°C)
Sheet
temperature (oC) 750 750 750
at Nitriding
Nitriding
Soaking
(sec) 33 33 33
time
treatment
I-h (%) 75 75 75
Atmosphere
Dew point
0 0 0
CC)
NH3 (%) 3 3 3
Magnetic target Iron loss
W17/50
<0.60 <0.70 <0.77
(W/kg)
[0068]
32
The obtained decarbwization-annealed steel sheet was subjected to the nitriding
u·eatment annealing listed in Table 2, subjected to a final annealing after a water slurry
using an annealing separator containing alumina as a main component is applied, coated
with a tension coating, and then subjected to magnetic domain subdivision through laser
5 in·adiation to obtain a plurality of grain-miented electrical steel sheets. Then, the
magnetic charactedstics of the plurality of grain-odented electrical steel sheets were
measw-ed. With regard to the magnetic measurement, the iron loss W 17/50 at 1. 7 T and
50 Hz and the magnetic flux density B8 at the magnetization force of 800 A/m were
evaluated on the basis of the Epstein method described in JISC2550-1: 2011 .
10
15
The test results are shown in Fig. 5. o is an example in which a magnetic
characteristics target is satisfied and x is an example in which a magnetic characteristics
target is not satisfied in Fig. 5. From the test results shown in Fig. 5, it was found that
good magnetic charactedstics can be obtained under the conditions of DPI of 40 to 70°C,
DP2SDP1, and 60-DP1SDP2S100-DP1.
That is to say, when good magnetic characteristics are obtained when the oxygen
content after decarburization annealing is 320 ppm or Less and the carbon content is 25
ppm or less, it is desirable to perform decarburization annealing under the conditions of
DP1 of 40 to 70°C, DP2::SDP1, and 60- DPl:SDP2Sl00- DPl.
When DPl is lower than 40°C, dec.arburizing of thick materials is difficult, and
20 when DPl is higher than 70°C, excessive oxidizing of thin materials occurs. For thick
materials, it is more preferably 50 to 70°C, and for thin materials, it is even more
preferably 40 to 60°C.
[0069]
Also, when DP'2>DP1 is satisfied, oxidation in the soaking area in which a sheet
25 temperature is higher than the heating area proceeds in a state in which the progress of
33
decarbwization in the heating area is delayed, and thus, decarburization is inhibited.
For this reason, it is desirable that DP2~DP1 be satisfied.
Furthermore, when DP2 is lower than (60-DPl), decarburization after
decarbmization annealing is insufficient, and when DP2 is higher than (100-DPl),
5 oxidation of thin materials is excessive. For this reason, it is desirable that DP2 be
within the range of 60-DPl~DP2~100-DPl.
[0070]
3. Final annealing process and removal process
In the final annealing process, the steel sheet is subjected to final annealing.
10 Thus, secondary recrystallization occurs in the steel sheet.
In a n01mal grain-oriented electrical steel sheet, a final-annealing coating
containing forstedte (Mg2Si04) as main component is formed. Thus, generally, the
surface of the decarburization-annealed steel sheet is coated with an annealing separator
having a high magnesia concentration (for example, Mg0~90 mass%) and subjected to a
15 final annealing process.
On the other hand, in the final annealing process in the method for producing a
grain-oriented electrical steel sheet according to this embodiment, the surface of the
decarburization-annealed steel sheet is coated with an annealing separator (for example,
containing MgO: about 10 to 50 mass%; Ah03: about 90 to 50 mass%) containing
20 aluminum oxide having a low magnesia concentration, heated, and subjected to final
annealing (cause secondary recrystallization to occur), and then undergoes the removal of
the excessive annealing separator to obtain a finally-annealed steel sheet. Thus, an
intermediate layer is formed so that a final-annealing coating made of forstelite
(MgzSi04) is not formed.
25 Here, the annealing separator is applied to prevent seizure between steel sheets
34
which have been subjected to final annealing and to form a final-annealing coating mad
of forste1ite (Mg2Si04). In the method for producing a grain-miented electtical steel
sheet according to this embodiment, it is necessary to form an intermediate layer so that a
final-annealing coating made of forste1ite (Mg2Si04) is not formed. Thus, an annealing
5 separator having a low magnesia concentration is utilized.
10
[0071]
The heating conditions for the final annealing may be general conditions, for
example, heating is performed at a heating rate within the range of 5 °C/s to 100 °C/s and
1000°C to 1300°C for 10 hours to 50 homs.
At the time of perf01ming cooling after the heating, it is possible to perform
cooling, for example, from ll00°C to 500°C in an atmosphere of a gas oxidation degree
(PH2o/PH2): 0.0001 to 100000.
To be more specific, in the cooling process after a temperature reaches a
maximum temperatme of the final annealing process, when the maximum temperature is
15 11 00°C or higher, T1 is set to 11 00°C, when the maximum temperature is less than
20
1100°C, T1 is set as the maximum temperature, and a temperature range of T1 to 500°C
can be cooled in an atmosphere of a gas oxidation degree (PH2oiPH2): 0.0001 to 100000.
However, the present invention is not limited by these conditions. The gas oxidation
degree is preferably 0.3 to 100000.
A cooling time at which cooling is performed under the above conditions is not
pruticularly limited, but is preferably 5 to 30 hours.
After cooling, it is possible to obtain a finally-annealed steel sheet by removing
the annealing separator. Although a method for removing the annealing separator is not
particularly limited, the annealing separator can be removed by perf01ming rubbing with
25 a brush on the surface of the base steel sheet.
35
[0072]
4. Intennediate layer fonning process
In the intermediate layer forming process, for example, an intermediate layer
containing silicon oxide as a main component can be formed on the surface of the finally-
5 annealed steel sheet by heating the finally-anneaLed steel sheet to an upper limit
temperature range exceeding 600°C and performing annealing while holding a steel sheet
in an atmosphere of a gas oxidation degree (PH2o/PH2): 0.001 to 0.04 within a temperature
range of higher than 600°C and the upper limit temperature or lower.
It is desirable that the intermediate Layer be formed to the thickness desclibed in
10 the item of "A. Grain-oriented electrical steel sheet 2. Intermediate layer" described
above.
[0073]
Although the heating conditions for the finaLly-annealed steel sheet in the
intermediate layer fonning process are not particularly limited as long as they are heated
15 to a temperature range of higher than 600°C, for example, it is desirable to hold a
temperature within a temperature range of700°C to 1150°C for 10 seconds to 60
seconds. From the viewpoint of a reaction rate, although a temperature needs to exceed
600°C, if the temperature is a high temperature higher than 1150°C, it may be difficult to
keep a formation reaction of the intermediate layer uniform, the severe unevenness of the
20 interface between the intermediate layer and the base steel sheet may be provided, iron
loss may deteliorate, a strength of the steel sheet may decrease, and a treatment in a
continuous annealing furnace may be difficuLt in some cases. Thus, productivity may
decrease in some cases.
A holding time is preferably 10 seconds or longer from the viewpoint of forming
25 the intermediate layer and 60 seconds or shorter from the viewpoint of productivity and
36
avoiding a decrease in the space factor due to an increase in the thickness of the
intermediate layer.
From the viewpoint of forming the intermediate layer to a thickness of 2 to 400
nm, it is desirable to hold the intermediate layer within a temperatlu·e range of 650 to
5 1 000°C for 15 to 60 seconds and it is more desirable to hold the intermediate layer within
a temperature range of 700 to 900°C for 25 to 60 seconds.
[0074]
5. Insulation coating fonning process
In the insulation coating forming process, a coating solution is applied to the
10 surface of the intermediate layer, baked, and then heated, for example, within a
temperature range of 700°C to ll50°C for 5 to 60 seconds in an atmosphere of 100%
nitrogen gas to form an insulation coating on the surface of the intermediate layer.
It is desirable that the insulation coating be formed to have the thickness
described in the term of "A. Grain-Oliented electtical steel sheet 1-3. Insulation coating"
15 descdbed above.
Although the coating solution is not particularly limited, a coating solution
which contains colloidal silica and a coating solution which does not contain colloidal
silica can be utilize.d properly in accordance with the application.
Examples of the coating solution which does not contain colloidal silica include
20 a coating solution containing alumina and boric acid.
Also, examples of the coating solution containing colloidal silica include a
coating solution containing phosphoric acid or phosphate, colloidal silica, and chromic
anhyd1ide or chromate. Examples of the chromate include chromate of Na, K, Ca, Sr,
or the like. Colloidal silica is not particularly limited and a particle size thereof can be
25 appropriately utilized.
37
Furthermore, various elements and components may be further added to the
coating solution to improve various characteristics as long as the desired effect in this
embodiment is not lost.
[0075]
5 In addition, in the insulation coating forming process, heating may be performed
at 650 to 950°C in an atmosphere of a gas oxidation degree (Ptuo/PH2): 0.01 to 0.30 and
then annealing may be petformed. Although the gas may be a generally used gas, for
example, a gas consisting of hydrogen: 25 volume% and the remainder: nitrogen and
impurities can be used.
10 [0076]
If a gas oxidation degree (Pf!2o!Pm) is less than 0.01 during cooling in the
insulation coating forming process, there is a concern that the insulation coating is
decomposed, and if t:he gas oxidation degree (PH2o/PHz) exceeds 0.30, there is a concern
that the oxidation of the base steel sheet is significant and lhe iron loss deteriorates. The
15 gas oxidation degree (Pmo1PH2) is more preferably 0.02 to 0.08, and even more
preferably 0.03 to 0.05.
[0077]
6. Other processes
The method for producing a grain-oriented electrical steeL sheet according to tl1is
20 embodiment may further include processes which are generally performed in the method
for producing a grain-oriented electrical steel sheet. In addition, it is desirable that the
method for producing a grain-oriented electrical steel sheet according to this embodiment
fut1her include a nitriding treatment process of performing nitriding treatment for
increasing theN content in the decarburization-annealed steel sheet between the sta1i of
25 decarburization annealing and the development of secondary recrystallization in final
38
annealing. This is because a magnetic flux density can be stably improved even if a low
temperature gradient provided to the steel sheet at the boundary place between a primary
recrystallization region and a secondary recrystallization region is provided. Although
the nitriding treatment may be a general treatment, examples of the nitriding treatment
5 include a treatment of performing annealing in an atmosphere containing a gas having a
nitriding power such as ammonia, a treatment of subjecting a decarburization-annealed
steel sheet coated with an annealing separator containing powders having a niuiding
effect such as MnN to final annealing, and the like.
[0078]
10 B-2. Second embodiment
Although the processes aimed only at fotming the inte1mediate layer and the
processes aimed only at fmming the insulation coating were performed separately in the
first embodiment, the second embodiment and the first embodiment differ in that, in the
second embodiment, an intermediate layer and an insulation coating are formed at the
15 same time. That is to say, the second embodiment and the first embodiment differ in
that the following intermediate layer-insulation coating forming process is performed
instead of the intermediate layer f01ming process and the insulation coating fmming
process described above.
For this reason, only the intermediate layer-insulation coating forming process
20 will be described below.
[0079]
1. Intermediate layer-insulation coating fonning process
A surface of the finally-annealed steel sheet is coated with a coating solution,
subjected to, for example, annealing within a temperature range of higher than 650°C to
25 950 oc or lower for 5 to 300 seconds in an atmosphere of a gas oxidation degree
39
(PHzoiPHz): 0.01 to 0.30 to form an intennediate Layer and an insulation coating
containing silicon oxide as a main component on the sutface of the finally-annealed steel
sheet at the same time.
If the surface of the finally-annealed steel sheet is coated with the coating
5 solution and subjected to a heat treatment, the intennediate Layer and a metal Fe phase
are formed on the surface of the steel sheet by reducing Fe in a Fe-based oxide, and at the
same time, an insulation coating is fonned on the surface of the intermediate layer by
baking the coating solution.
In order to simultaneously promote the formation of the intermediate layer
10 through themml oxidation and the fonnation of the insulation coating by baking the
coating solution, it is more desirable to set the conditions of a gas oxidation degree
(PHzoiPHz): 0.05 to 0.25 and it is even more desirable to set the conditions of a gas
oxidation degree (PHzoiPHz): 0.10 to 0.20.
15
[0080]
The present invention is not limited to the above-described embodiments. The
above-described embodiments are examples and anything having substantially the same
constitution as the technical idea described in the claims of the present invention and
exhibiting the same action and effect is included in the technical scope of the present
invention.
20 [Examples]
[0081]
The present invention will be described in detail below by with reference to
examples. In the following description, the conditions in the examples e:u·e one
condition example adopted for confirming the feasibility and effect of the present
25 invention and the present invention is not limited to this one condition example. In the
40
5
present invention, various conditions can be adopted as long as the gist of the present
invention is not deviated and the object of the present invention is achieved.
[0082]

"In a case that sheet thickness is 0.18 mm"
A slab having a chemical composition in which Si: 3.45%; C: 0.060%; acidsoluble
Al: 0.030%; N: 0.008%; Mn: 0.10%; a total amount of Sand Se: 0.007%; and the
remainder: Fe and impurities were contained was subjected to soaking at 1150°C for 60
minutes and then the sLab which has been subjected to heating was subjected to hot
10 rolling to obtain a hot-rolled steel sheet having a sheet thickness of 2.8 mm.
Subsequently, the hot-rolled steel sheet was subjected to hot-band annealing in which the
hot-rolled steel sheet was held at 900°C for 120 seconds and then rapidly cooled, to
obtain an annealed steel sheet. Subsequently, the annealed steel sheet was pickled and
then the pickled steel sheet was subjected to one or more cold rollings to obtain a cold-
IS rolled steel sheet having a final sheet thickness of 0.18 mm.
[0083]
As shown in Table 3, decarburization annealing in which a soaking temperature
was set to 820 to 835°C and an atmosphere gas was introduced from two locations which
were an initial part and a latter part in the soaking area was performed using the cold-
20 rolled steel sheet made of this thin material (a sheet thickness of 0.18 mm). At that
time, a dew point DPl of an atmosphere gas introduced from the initial part was changed
to 30 to 80°C and a dew point DP2 of an atmosphere gas introduced from the latter part
was changed to -5 to 55°C. The target carbon content [C] was 25 ppm or less and the
target oxygen content [0] was 320 ppm or less.
25 The carbon content after decarburization annealing was analyzed using an
41
infrared absorption method by burning a sample in an oxygen stream to generate CO gas.
With regard to the oxygen content, a sample in a graphite crucible in an inert gas such as
He was burned to generate CO gas and the CO gas was analyzed using an infrared
absorption methcx:l.
5 [0084]
After decarbmization annealing, an annealing separator containing alumina as a
main component which does not easily react with silica was coated in a water slUITY state
and then subjected to final annealing. The final annealing was perfonued up to 1200°C
in an atmosphere gas of N2: 25%+H2: 75% at a rate of temperature rise of 15 °C/Hr, the
10 atmosphere gas was changed to H2: 100% at 1200°C, and annealing was performed for
20 hom·s. During cooling after the heating, for example, cooling was performed from
ll00°C to 500°C in an atmosphere of a gas oxidation degree (PmoiPHz): 0.0001 to
100000. Furthem1ore, a cooling time at which cooling was perfom1ed under the above
conditions was 5 to 30 hours.
15 The powder of the annealing separator on these steel sheets which has been
subjected to final annealing was removed with a brush and some of the steeL sheets was
annealed at 870°C in an atmosphere in which an atmosphere gas oxidation degree
(PHzo/PH2) was 0.01 for 60 seconds to form an intermediate layer having a thickness of
20 nm. The steel sheets were cooled, coated with a coating solution, and then annealed
20 at 840°C in an atmosphere in which an atmosphere gas oxidation degree (Pmo/PH2) was
0.03 for 60 seconds to form an insulation coating having an amount of adhesion after
baking of 4.5 g/m2 and a thickness of 2 ~tm.
Also, other steel sheets were coated with a coating solution, dried at 450°C, and
then anne.aled at 840°C in an atmosphere in which an atmosphere gas oxidation degree
25 (PHzoiPHz) was 0.10 for 60 seconds to form an intermediate layer having a thickness of
42
20 nm and an insulation coating having an amount of adhesion after baking of 4.5 g/m2
and a thickness of 2 !liD.
Finally, linear grooves extending in a direction intersecting a roLling direction
were subjected to a magnetic domain subdivision treatment using a laser to have
5 prescribed intervals.
After that, the obtained grain-oriented electrical steel sheet was subjected to
magnetic measurement. With regard to the magnetic measurement, the iron loss
Wl7/50 at 1.7 T and 50 Hz and the magnetic flux density B8 at a magnetization force of
800 A/m were evaluated on the basis of the Epstein method described in JISC2550-l:
10 2011. The evaluation of the magnetic characte1istics was determined to be good when
the iron loss Wl7/50 was less than 0.60 W/kg and the magnetic flux density is more than
1.60T.
The test results are shown in Table 3 below.
43
[0085]
[Table 3]
Steel sheet which
Decarburization annealing condition
has been subjected
to decarburization Magnetic
annealing characteristics
Heating Soaking
Oxygen Carbon
content content
Dew Range of dew point DP2 at Remarks
Dew point latter part
B8(T)
Rate of
pointDP
Soaking sheet Soaking DP2
[0 ] [C] W17/50 After
temperature 1 at initial
temperature time at Lower limit Upper limit (ppm) (ppm) (Wikg) IOOHr
rise CC/s) part (0 C) CC) (sec) latter
(60- DP1) (100-DPl) aoino
part ::. <=>
CC)
13.2 30 820 154 15 30 70 25 137 0.53 1.42
Comparative
Example 1
13.2 30 820 154 20 30 70 57 ill 0.55 1.43
Comparative
Example 2
13.2 30 820 154 30 30 70 183 99 0.56 1.45
Comparative
Example 3
13.2 30 820 154 40 30 70 214 80 0.54 1.48
Comparative
Example4
13.2 30 820 154 45 30 70 227 61 0.55 1.51
Comparative
Example 5
13.2 40 820 154 15 20 60 125 42 0.53 1.56
Comparative
Example 6
Present
13.2 40 820 154 20 20 60 157 23 0.56 1.63 Invention
Example 1
Present
13.2 40 820 154 30 20 60 283 19 0.55 1.66 Invention
Example 2
13.2 40 820 154 40 20 60 314 8 0.54 1.65 Present
44
Invention
Example3
13.2 40 820 154 45 20 60 327 4 0.63 1.65
Comparative
Example 7
13.2 50 820 154 5 10 50 275 36 0.55 1.58
Comparative
Example 8
Present
13.2 50 820 154 10 10 50 280 25 0.54 1.62 Invention
Example4
Present
13.2 50 820 154 20 10 50 293 19 0.56 1.65 Invention
Example 5
Present
13.2 50 820 154 30 10 50 304 10 0.55 1.64 Invention
Example6
Present
13.2 50 820 154 40 10 50 313 5 0.56 1.65 Invention
Example 7
Present
13.2 50 820 154 50 10 50 319 0 0.59 1.64 Invention
Example 8
13.2 50 820 154 55 10 50 330 1 0.65 1.65
Comparative
Example 9
13.2 50 835 154 5 10 50 295 26 0.55 1.59
Comparative
Example 10
Present
13.2 so 835 154 10 10 so 300 13 0.56 1.64 Invention
Example 9
Present
13.2 50 835 154 20 10 50 313 7 0.59 1.64 Invention
Example 10
13.2 50 835 154 30 10 50 324 1 0.65 1.65
Comparative
Example 11
13.2 50 835 154 40 10 50 333 0 0.67 1.65
Comparative
Example 12
13.2 50 835 154 50 10 50 339 2 0.69 1.65 Comparative
45
Example 13
13.2 50 835 154 55 10 50 350 0 0.72 1.64
Comparative
Example 14
13.2 60 820 154 - 5 0 40 143 38 0.56 1.57
Comparative
Example 15
Present
13.2 60 820 154 0 0 40 157 24 0.55 1.63 Invention
Example 11
Present
13.2 60 820 154 10 0 40 205 10 0.56 1.64 Invention
Example 12
Present
13.2 60 820 154 20 0 40 250 5 0.54 1.65 Invention
Example 13
Present
13.2 60 820 154 30 0 40 287 2 0.57 1.65 Invention
Example 14
Present
13.2 60 820 154 40 0 40 318 0 0.58 1.65 Invention
Example 15
13.2 60 820 154 45 0 40 330 1 0.68 1.64
Comparative
Example 16
13.2 80 820 154 -5 -20 20 323 0 0.62 1.65
ComparatJ ve
Example 17
13.2 80 820 154 0 - 20 20 337 0 0.68 1.64
Comparative
Example 18
13.2 80 820 154 10 -20 20 351 0 0.72 1.66
Comparative
Example 19
13.2 80 820 154 20 - 20 20 365 0 0.79 1.62
Comparative
Example 20
13.2 80 820 154 30 - 20 20 379 0 0.75 1.63
Comparative
Example 21
13.2 80 820 154 40 -20 20 393 0 0.81 1.64
Comparative
Example 22
13.2 80 820 154 45 - 20 20 407 0 0.86 1.65
Comparative
Example 23
46
[0086]
Although thin materials have better decarburization prope1ties than those of
thick materials and the thin materials have the easy progress of oxidation. Thus, good
magnetic characte1istics could not l1e obtained when the dew point DPl at the initial part
5 was at 30 ac and 80 °C.
Also, as shown in Table 3, in the example of the present invention, in the steel
sheet which has been subjected to decarbmization annealing, a decarbUiization-annealed
steel sheet having the oxygen content of 320 ppm or less and the carbon content of 25
ppm or less could be obtained. Particularly, when the dew point DPl of an atmosphere
10 gas introduced from the initial part in the soaking area was set to 40 to 70 oc and the dew
point DP2 of an atmosphere gas introduced from the latter pru1 in the soaking area
satisfied DP2:SDP1 and 60- DPl:SDP2:S100- DPl, a decarbUiization-annealed. steel sheet
having the oxygen content of 320 ppm or less and the carbon content of 25 ppm or less
could be obtained. Furthe1more, grain-oriented electrical steel sheets obtained by
15 forming an intermediate layer and an insulation layer using these decru·burizationannealed
steel sheets were excellent electrical steel sheets having low iron loss.
Furthermore, in all cases, a sufficient coating adhesion was provided.
20
[0087]

"In a case that sheet thickness is 0.23 mm"
A slab having a chemical composition in which Si: 3.45%; C: 0.060%; acidsoluble
Al: 0.030%; N: 0.008%; Mn: 0.10%; a total amount of Sand Se: 0.007%; and the
remainder: Fe and impurities were contained \.Vas subjected to soaking at 1150°C for 60
minutes and then the slab which has been subjected to heating was subjected to hot
25 rolling to obtain a hot -rolled steeL sheet having a sheet thickness of 2.8 mrn.
47
Subsequently, the hot-rolled steel sheet was subjected to hot-band annealing in
which the hot-rolled steel sheet was held at 900°C for 120 seconds and then rapidly
cooled, to obtain an annealed steel sheet. Subsequently, the annealed steel sheet was
pickled and then the pickled steel sheet was subjected to one or more cold rollings to
5 obtain a cold-rolled steel sheet having a final sheet thickness of 0.23 mm.
[0088]
Decarburization annealing in which a soaking temperature was set to 820 to 840
°C, a dew point DPl at an initial part was changed to 30 to 80°C, and a dew point DP2 at
a latter part was changed to -15 to 55°C was pe1formed using a cold-rolled steel sheet
10 having a thick material of 0.23 mm.
[0089]
After decarburization annealing, an annealing separator containing alumina as a
main component which does not easily react with silica was .coated in a water slun·y state
and then subjected to final annealing. The final annealing was perfonned up to 1200°C
15 in an atmosphere gas of N2: 25%+H2: 75% at a rate of temperature 1ise of 15 °C/Hr, the
atmosphere gas was changed to H2: 100% at 1200°C, and annealing was performed for
20 hours. During cooling after the heating, cooling was pe1formed from ll00°C to
500°C in an atmosphere of a gas oxidation degree (PH2o/PH2): 0.0001 to 100000.
Furthermore, a cooling time at which cooling was performed under the above conditions
20 was 5 to 30 hours.
The powder of the annealing separator on these steel sheets which has been
subjected to final annealing was removed with a bmsh and some of the steel sheets was
annealed at 870°C in an atmosphere in which an atmosphere gas oxidation degree
(PH2oiPH2) was 0.010 for 60 seconds to form an intermediate layer having a thickness of
25 20 nm. The steel sheets were cooled, coated with a coating solution, and then annealed
48
at 840°C in an atmosphere in which an atmosphere gas oxidation degree (PH2o/Pm) was
0.01 for 60 seconds to form an insulation coating having an amount of adhesion after
baking of 4.5 g/m2 and a thickness of 2 ~un. Furthermore, other steel sheets were
annealed at 870°C for 60 seconds in an atmosphere in which an atmosphere gas oxidation
5 degree (PH2o/PH2) was 0.10 to fmm an intermediate layer having a thickness of 20 nm
and an insulation coating having an amount of adhesion after baking of 4.5 g/m2 and a
thickness of 2 !liD·
Finally, linear grooves extending in a direction intersecting a rolling direction
were subjected to a magnetic domain subdivision treatment using a laser to have
10 prescribed intervals.
After that, the obtained grain-oriented electrical steel sheet was subjected to
magnetic measurement. ·with regard to the magnetic measurement, the iron loss
Wl7/50 at 1.7 T and 50 Hz and the magnetic flux density B8 at a magnetization force of
800 Nm were evaluated on the basis of the Epstein method desctibed in JISC2550-1:
15 2011.
The evaluation of the magnetic characteristics was determined to be good when
the iron loss W17/50 was less than 0.70 \V/kg and the magnetic flux density is more than
1.60 T. The test results are shown in Table 4 below.
49
[0090]
[Table 4]
Steel sheet \-Vhich
Decarburization annealing condition
has been subjected
to decarburization Magnetic
armealing characteJ.istics
Heating Soaking
Oxygen Carbon
content content Remarks
Dew Dew Range of dew point DP2 at B8(T)
Rate of
pointDP
Soaking sheet Soaking point latter part
[0 ] [C) Wl7/50
After
temperature
1 at initial
temperature time DP2 at
Lower limit Upper limit (ppm) (ppm) (W/kg)
100
rise CCfs) CC) (sec) latter Hr
patt CC) part(0C) (60-DPl) (100-DPI) aging
8 30 820 154 15 30 70 20 127 0.65 1.43
Comparative
Example24
8 30 820 154 20 30 70 52 110 0.66 1.44
Comparative
Example 25
8 30 820 154 30 30 70 178 93 0.64 1.46
Comparative
Example 26
8 30 820 154 40 30 70 209 76 0.68 1.49
Comparative
Example27
8 30 820 154 45 30 70 222 59 0.65 1.52
Comparative
Example 28
8 40 820 154 15 20 60 120 42 0.65 1.56
Comparative
Example 29
Present
8 40 820 154 20 20 60 152 25 0.64 1.62 Inve:ntion
Example 16
Present
8 40 820 154 30 20 60 278 14 0.66 1.64 Invention
Example 17
Present
8 40 820 154 40 20 60 309 5 0.69 1.64 Invention
Example 18
50
8 40 820 154 45 20 60 322 1 0.74 1.65
Comparative
Example 30
8 50 820 115 5 10 50 163 31 0.64 1.60
Comparative
Example 31
Present
8 50 820 115 10 10 50 195 24 0.63 1.63 Invention
Example 19
Present
8 50 820 115 20 10 50 240 15 0.68 1.65 Invention
Example 20
Present
8 50 820 115 30 10 50 280 8 0.64 1.64 Invention
Example 21
Present
8 50 820 115 40 10 50 310 2 0.69 1.64 Invention
Example 22
Present
8 50 820 115 50 10 50 320 0 0.66 1.65 Invention
Example 23
8 50 820 115 55 10 50 333 0 0.78 1.65
Comparative
Example 32
8 50 840 115 5 10 50 198 26 0.65 1.58
Comparative
Example 33
Present
8 50 840 115 10 10 50 230 19 0.64 1.65 Invention
Example 24
Present
8 50 840 115 20 10 50 275 10 0.67 1.64 Invention
Example 25
Present
8 50 840 115 30 10 50 315 2 0.65 1.65 Invention
Example 26
8 50 840 115 40 10 50 345 1 0.72 1.65
Comparative
Example 34
8 50 840 115 50 10 50 355 0 0.78 1.65
Comparative
Exanlf)le 35_
51
8 50 840 115 55 10 50 368 3 0.78 1.64
Comparative
Example 36
8 60 820 115 -5 0 40 199 32 0.65 1.59
Comparative
Example 37
Present
8 60 820 115 0 0 40 217 24 0.64 1.63 Invention
Example 29
Present
8 60 820 115 10 0 40 250 17 0.65 1.65 Invention
Example 30
Present
8 60 820 115 20 0 40 288 8 0.66 1.64 Invention
Example 31
Present
8 60 820 115 30 0 40 311 3 0.64 1.64 Invention
Example32
Present
8 60 820 115 40 0 40 320 1 0.68 1.64 Invention
Example 33
8 60 820 115 45 0 40 326 0 0.77 1.65
Comparative
Example 38
8 70 820 115 - 15 - 10 30 134 38 0.65 1.57
Comparative
Example39
Present
8 70 820 ll5 - 10 - 10 30 170 25 0.64 1.62 Invention
Example 34
Present
8 70 820 115 0 - 10 30 228 16 0.65 1.65 Invention
Example 35
Present
8 70 820 115 10 -10 30 260 9 0.66 1.65 h1vention
Example36
Present
8 70 820 ll5 20 - 10 30 299 3 0.64 1.64 Invention
Example 37
8 70 820 115 30 -10 30 320 0 0.68 1.65 Present
52
Invention
Example 38
8 70 820 115 35 - 10 30 330 1 0.77 1.64
Comparative
Example 40
8 80 820 115 - 15 -20 20 326 0 0.72 1.65
Comparative
Example41
8 80 820 115 -10 - 20 20 362 0 0.76 1.65
Comparative
Example 42
8 80 820 115 0 -20 20 398 0 0.79 1.64
Comparative
Example 43
8 80 820 115 10 -20 20 434 0 0.77 1.65
Comparative
Example44
8 80 820 115 20 - 20 20 470 0 0.82 1.64
Comparative
Examvle 45
8 80 820 115 30 -20 20 506 0 0.85 1.64
Comparative
Example 46
8 80 820 115 35 -20 20 542 0 0.92 1.64
Comparative
Example 47
53
[0091]
As shown in the test results in Table 4, the conditions for achjeving both
oxidation and decarburization are wider than those of the steel sheets having the sheet
thicknesses listed in Table 3 and there were the conditions in which good magnetic
5 characteristics could be obtained when the dew point DPl at the initial part was set to 40
to 70°C.
As shown in Table 4, in the example of the present invention, in the steel sheet
which has been subjected to decarburization annealing, the decarburization-annealed
steel sheet having the oxygen content of 320 ppm or less and the carbon content of 25
10 ppm or less could be obtained. Fw·thermore, the grain-oliented electlical steel sheet
obtained by forming the intermediate layer and the insulation layer using these
decarburization-annealed steel sheets was an excellent electrical steel sheet having low
iron loss.
Also, it was found that, when a relationship of DP2S:DP1 and
15 60-DPlS:DP2S:l00-DPl is satisfied, an excellent grain-oriented electrical steel sheet
having the oxygen content of 320 ppm or less and the carbon content of 25 ppm or less
and low iron loss could be obtained even with a steel sheet having a thickness of 0.23
mm thicker than 0.18 mrn.
[0092]
20
"In a case that sheet thickness is 0.35 mm"
A slab having a chemical composition in which Si: 3.25%; C: 0.050%; acidsoluble
AI: 0.030%; N: 0.008%; Mn: 0.10%; a total amount ofS and Se: 0.006%; and the
remainder: Fe and impurities were contained was subjected to soaking at 1150°C for 60
25 minutes and then the slab which has been subjected to heating was subjected to hot
54
rolling to obtain a hot-rolled steel sheet having a sheet thickness of 2.8 mm.
Subsequently, the hot-rolled steel sheet was subjected to hot-band annealing in
which the hot-rolled steel sheet was held at 900°C for 120 seconds and then rapidly
cooled, to obtain an annealed steeL sheet. Subsequently, the annealed steel sheet was
5 pickled and then the pickled steel sheet was subjected to one or more cold rollings to
obtain a cold-rolled steel sheet having a final sheet thickness of 0.35 mm.
[0093]
Decarbmization annealing in which a soaking temperature was set to 820 to
840°C, a dew point DP1 at an initial part was changed to 30 to 80°C, and a dew point
10 DP2 at a latter patt was changed to -15 to 55°C was performed using a cold-rolled steel
sheet made of a thick material (a sheet thickness of 0.35 mm).
[0094]
After annealing, an annealing separator containing alumina as a main component
which does not easily react with silica was coated in a water slurry state and then
15 subjected to final annealing. The final annealing was performed up to 1200°C in an
atmosphere gas of N2: 25%+H2: 75% at a rate of temperature rise of 15 °C/Hr, the
atmosphere gas was changed to H2: 100% at 1200°C, and annealing was performed for
20 hours.
During cooling after the heating, for example, cooling was pelformed from
20 11 oooc to 500°C in an atmosphere of a gas oxidation degree (PH2o/PH2): 0.0001 to
100000. Fmthermore, a cooling time at which cooling was performed under the above
conditions was 5 to 30 homs.
The powder of the annealing separator on these samples was removed with a
brush and some of the steel sheets was annealed at 870°C in an atmosphere in which an
25 atmosphere gas oxidation degree (Pmo/Pm) was 0.01 for 60 seconds to form an
55
intermediate layer having a thickness of 20 nm. The steel sheets were cooled, coated
with a coating solution, and then annealed at 840°C in an atmosphere in which an
atmosphere gas oxidation degree (Pmo1PH2) was 0.01 for 60 seconds to form an
insulation coating having an amount of adhesion after baking of 4.5 g/m2 and a thickness
5 of 2 !liD. Furthe1more, other steel sheets were coated with an insulation coating, dlied
10
at 450°C, and then annealed at 840°C in an atmosphere in which an atmosphere gas
oxidation degree (PHzo/Pm) was 0.10 for 60 seconds to form an intermediate layer having
a thickness of 20 nm and an insulation coating having an amount of adhesion after baking
of 4.5 g/m2 and a thickness of 2 !lm at the same time.
Finally, linear grooves extending in a direction intersecting a rolling direction
were subjected to a magnetic domain subdivision treatment using a laser to have
prescribed intervals.
After that, the obtained grain-oriented electrical steel sheet was subjected to
magnetic measurement. The evaluation of the magnetic characteristics was determined
15 to be good when the iron loss W17/50 was less than 0.77 W /kg and the magnetic flux
density is more than 1.60 T.
The test results are shown in Table 5 below.
56
[0095]
[Table 5]
Steel sheet which
Decarburization annealing condition
has been subjected
to decarburization Magnetic
annealing characteristics
Heating Soaking
Oxygen Carbon
content content
Dew Range of dew po:int DP2 at latter
Remarks
Dew point point B8(T)
Rate of
DP 1 at
Soaking sheet Soaking
DP2
part
[0] [C] Wl7/50 After
temperature
initial part
temperature time
(ppm) (_ppm) (\VIkg) 100 I-Ir
rise (°C/s) (OC) (sec)
at (oC) Lower latter
limit
Upper limit aging
part (60- DPl)
(100- DPl)
(OC)
6.7 30 820 96 5 30 70 115 97 0.77 1.46
Comparative
Example48
6.7 30 820 96 10 30 70 119 88 0.79 1.47
Comparative
Example49
6.7 30 820 96 20 30 70 160 7.!l 0.78 1.48
Comparative
Example 50
6.7 30 820 96 30 30 70 190 70 0.75 1.49
Comparative
Example 51
6.7 30 820 96 40 30 70 208 61 0.77 1.51
Comparative
Example 52
6.7 30 820 96 50 30 70 215 52 0.77 1.53
Comparative
Example 53
6.7 30 820 96 55 30 70 219 43 0.78 1.55
Comparative
Example 54
6.7 50 820 96 5 10 50 260 34 0.73 1.58
Comparative
Example62
Present
6.7 50 820 96 10 10 50 290 25 0.76 1.62 Invention
Example 39
57
Present
6.7 50 820 96 20 10 50 308 21 0.74 1.65 Invention
Example40
Present
6.7 50 820 96 30 10 50 315 18 0.75 1.64 Invention
Example 41
Present
6.7 50 820 96 40 10 50 319 15 0.73 1.64 Invention
Example 42
Present
6.7 50 820 96 50 10 50 320 12 0.76 1.65 Invention
Example43
6.7 50 820 96 55 10 50 329 9 0.90 1.64
Comparative
Example63
6.7 50 840 96 5 10 50 292 29 0.73 1.60
Comparative
Example64
6.7 50 840 96 10 10 50 322 20 0.78 1.65
Comparative
Example65
6.7 50 840 96 20 10 50 340 16 0.77 1.65
Comparative
Example66
6.7 50 840 96 30 10 50 347 13 0.79 1.64
Comparative
Example67
6.7 50 840 96 40 10 50 351 10 0.79 1.64
Comparative
Example 68
6.7 50 840 96 50 10 50 352 7 0.81 1.65
Comparative
Example69
6.7 so 840 96 55 10 50 361 4 0.90 1.65
Comparative
Example 70
6.7 60 820 96 - 5 0 40 295 29 0.74 1.58
Comparative
Example 71
Present
6.7 60 820 96 0 0 40 300 24 0.76 1.65 Invention
Example44
Present
6.7 60 820 96 lO 0 40 308 20 0.72 1.65 Invention
Example45
58
Present
6.7 60 820 96 20 0 40 313 16 0.75 1.65 Invention
Example46
Present
6.7 60 820 96 30 0 40 318 13 0.76 1.65 Invention
Example47
Present
6.7 60 820 96 40 0 40 320 11 0.76 1.64 Invention
Example48
6.7 60 820 96 45 0 40 324 8 0.89 1.64
Comparative
Example72
6.7 70 820 96 - 15 - 10 30 278 30 0.76 1.59
Comparative
Example 73
Present
6.7 70 820 96 - 10 -10 30 290 24 0.71 1.64 Invention
Example49
Present
6.7 70 820 96 0 - 10 30 302 19 0.73 1.65 Invention
Example 50
Present
6.7 70 820 96 10 -10 30 310 15 0.72 1.65 Invention
Example 51
Present
6.7 70 820 96 20 -10 30 316 10 0.74 1.63 Invention
Example 52
Present
6.7 70 820 96 25 - 10 30 319 8 0.75 1.64 Invention
Example 53
Present
6.7 70 820 96 30 -10 30 318 5 0.75 1.64 Invention
Example 54
6.7 70 820 96 35 -10 30 324 5 0.87 1.65
Comparative
Example 74
6.7 80 820 96 - 15 - 20 20 321 20 0.88 1.65
Comparative
Example 75
6.7 80 820 96 - 10 -20 20 327 15 0.90 1.64 Comparative
59
Example 76
6.7 80 820 96 0 - 20 20 333 8 0.94 1.65
Comparative
Example 77
6.7 80 820 96 10 -20 20 339 11 0.93 1.65
Comparative
Example 78
6.7 80 820 96 20 - 20 20 345 5 0.98 1.64
Comparative
E.xample 79
6.7 80 820 96 25 - 20 20 351 2 0.93 1.64
Comparative
Example 80
6.7 80 820 96 30 -20 20 357 0 0.96 1.65
Comparative
Example 81
60
[0096]
In the results shown in Table 5, in the example of the present invention, in the
steel sheet which has been subjected to decarburization annealing, a decarburizationannealed
steel sheet having the oxygen content of 320 ppm or less and the carbon content
5 of 25 ppm or less could be obtained. Furthe1more, the grain-oriented electrical steel
sheet obtained by forming the intermediate layer and the insulation layer using these
decarburization-annealed steel sheets was an excellent electrical steel sheet having low
iron loss.
For a thick material, decarbm;zation serves as a bottleneck, which causes
10 deterioration of magnetic aging of a final product. Thus, when a dew point DPl at an
initial part was 30°C and 80°C, in all c.ases, good magnetic characte1istics could not be
obtained.
Also, it was found that, when a relationship of DP1=40 to 70°C and DP2sDPl
and 60-DPlsDP2Sl00-DPl is satisfied, an excellent grain-oriented electrical steel sheet
15 having the oxygen content of 320 ppm or Less and the carbon content of 25 ppm or less
and low iron loss could be obtained even with a thick steel sheet having a thickness of
0.35 mm thicker than 0.23 mm.
20
[Industrial Applicability]
[0097]
According to the present invention, it is possible to provide a method for
producing a grain-oriented electrical steel sheet in which a forsterite film is substantially
absent. In the method for producing a grain-oriented electrical steel sheet according to
the above aspect, when both decarburization and steel sheet oxidation suppression is
achieved in a wide sheet thickness range, it is possible to produce a grain-oriented
25 electrical steel sheet having low iron loss and a high magnetic flux density after magnetic
61
5
aging.
[Reference Signs List]
[0098]
1 Heating furnace
2 Soaking furnace

WE CLAIMS

1. A method for producing a grain-oriented electrical steeL sheet which has an
intermediate layer containing silicon oxide as a main component on a surface of a base
steel sheet in which a forste1ite film is substantially absent and has an insulation coating
5 on a surface of the intermediate layer, comprising:
10
a decarburization annealing process of obtaining a decarburization-annealed
steel sheet which has an oxygen content of 320 ppm or less and a carbon content of 25
ppm or less by subjecting a cold-rolled steel sheet containing Si to decarburization
annealing;
a final annealing process of heating the decarburization-annealed steel sheet in a
state in which a surface of the decarburization-annealed steel sheet is coated with an
annealing separator to cause secondary recrystallization to occur in a steel sheet;
a removal process of obtaining a finally-annealed steel sheet by removing the
annealing separator on the steel sheet which has been subjected to the final annealing
15 process;
an intermediate layer forming process of forming the intermediate layer by
subjecting the finally-annealed steel sheet to thermal oxidation annealing; and
an insulation coating forming process of forming the insulation coating on the
finally-annealed steel sheet having the intermediate layer forme.d thereon.
20 2. A method for producing a grain-oriented electrical steel sheet which has an
intermediate layer containing silicon oxide as a main component on a surface of a base
steel sheet in which a forsterite film is substantially absent and has an insulation coating
on a surface of the intermediate layer, complising:
a decarburization annealing process of obtaining a decarburization-annealed
25 steel sheet which has an oxygen content of 320 ppm or less and a carbon content of 25
63
ppm or less by subjecting a cold-rolled steel sheet containing Si to decarburization
annealing;
a final annealing process of heating the decarburization-annealed steel sheet in a
state in which a surface of the decarburization-annealed steel sheet is coated with an
5 annealing separator to cause secondary recrystallization to occur in a steel sheet;
a removal proc.ess of obtaining a finally-annealed steel sheet by removing the
annealing separator on the steel sheet which has been subjected to the final annealing
process; and
an intermediate layer-insulation coating forming process of forming the
10 intermediate layer and the insulation coating on the finally-annealed steel sheet in one
process.
3. The method for producing a grain-Oiiented electrical steel sheet according to claim 1
or 2, wherein, in the decarburization annealing process, in a soaking area configured to
subject the cold-rolled steel sheet to decarburization annealing, an atmosphere gas is
15 introduced from two Locations which are an initiaL part and a Latter part of the soaking
area
4. The method for producing a grain-miented electrical steel sheet according to claim 3,
wherein, in the decarbudzation annealing process, a dew point DPl of the atmosphere
gas introduced from the initial part of the soaking area is set to 40 to 70°C and a dew
20 point DP2 of the atmosphere gas introduced from the latter part of the soaking area
satisfies DP2::;DP1 and 60-DP1:s;DP2::Sl00-DP1.
25
5. The method for producing a grain-oriented electrical steel sheet according to any one
of claims 1 to 4, wherein the cold-rolLed steel sheet contains, as a chemical composition,
in terms of mass%,
Si: 0.80 to 7 .00%;
64
5
C: 0.085% or less;
acid-soluble Al: 0.010 to 0.065%;
N: 0.012% or less;
Mn: 1.00% or less;
a total amount of S and Se: 0.003 to 0.015%; and
the remainder: Fe and impurities.