Title of invention: Method for manufacturing grain-oriented electrical steel sheet
Technical field
[0001]
The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet.
Background technology
[0002]
The grain-oriented electrical steel sheet has a high degree of crystal grains accumulated in the {110} <001> orientation (such crystal grains are also referred to as Goth orientation grains), and Si is approximately 7% or less in mass%. It is a steel plate including. Control of crystal orientation in the production of such grain-oriented electrical steel sheets is achieved by utilizing a catastrophic grain growth phenomenon called secondary recrystallization.
[0003]
One method for controlling this secondary recrystallization is to completely dissolve the inhibitor during heating of the steel slab before hot rolling, and then finely deposit it in the hot rolling and subsequent hot rolling plate annealing steps. It is carried out industrially. In this method, the steel slab needs to be heated at 1350 to 1400 ° C. in order to completely dissolve the inhibitor during heating of the steel slab before hot rolling. However, since this heating temperature is about 200 ° C. higher than the heating temperature when manufacturing ordinary steel, there is a problem that a heating furnace dedicated to the manufacture of grain-oriented electrical steel sheets is required. Further, since it is necessary to heat the steel slab to a very high temperature, there is a problem that the amount of molten scale increases.
[0004]
Therefore, research and development is underway on a technique for heating steel slabs at a low temperature before hot rolling. As such a technique, for example, Patent Document 1 discloses a method of using (Al, Si) N formed by nitriding treatment as an inhibitor. Further, Patent Document 2 discloses, as a specific method of nitriding treatment, a method of stripping a steel sheet after decarburization annealing into a strip shape and nitriding it. Non-Patent Document 1 discloses the behavior of a nitride when a steel sheet is nitrided in strip form.
[0005]
Here, in the technique of heating the steel slab at a low temperature before hot rolling, the adjustment of the primary recrystallized grain texture during decarburization annealing is important for controlling the secondary recrystallization. However, in this technique, the inhibitor may not be sufficiently formed during decarburization annealing. In this case, according to Patent Document 3, the coefficient of variation of the particle size distribution of the primary recrystallized grain texture becomes larger than 0.6, so that the primary recrystallized grain texture becomes non-uniform. As a result, there is a problem that the secondary recrystallized grain structure becomes non-uniform and unstable.
[0006]
Therefore, research on the primary recrystallization grain texture, which is a control factor for secondary recrystallization, is being enthusiastically pursued. In such studies, it was found that the {411} oriented grains in the primary recrystallized grain texture affect the preferential growth of {110} <001> secondary recrystallized grains. For example, in Patent Document 4, the ratio of I {111} / I {411} of the primary recrystallized grain texture after decarburization annealing is adjusted to 3.0 or less, and then the steel sheet is subjected to nitriding treatment. Techniques for enhancing inhibitors are disclosed. Patent Document 4 discloses that a grain-oriented electrical steel sheet having a high magnetic flux density can be industrially and stably manufactured by strengthening an inhibitor. Here, I {111} and I {411} are the abundance ratios of grains whose {111} and {411} planes are parallel to the plate surface, respectively, and are measured by X-ray diffraction measurement in the plate thickness 1/10 layer. It represents the diffraction intensity value.
[0007]
After that, while research on the primary recrystallized grain texture was advanced, it was found that controlling the heating temperature during decarburization annealing was an effective method for controlling the grain structure after the primary recrystallization. For example, in the technique disclosed in Patent Document 5, in the heating step (heating process) of the decarburization annealing step, the steel sheet temperature reaches the reached temperature within the range of 750 to 900 ° C. from the inlet temperature of 600 ° C. or lower. Rapidly heat the steel sheet at a heating rate of 40 ° C./sec or higher. Thereby, the ratio of I {111} / I {411} is controlled to 3 or less in the temporarily recrystallized grain aggregate structure after decarburization annealing. Further, by subsequent annealing, the oxygen content of the oxide layer of the steel sheet is adjusted to 2.3 g / m 2 or less. Patent Document 5 discloses that the secondary recrystallization is stabilized by the above technique.
[0008]
Further, Patent Document 6 discloses a technique in which the heating rate in the temperature range where the temperature of the steel sheet is 200 ° C. to 700 ° C. is 50 ° C./sec or more. Further, in the technique disclosed in Patent Document 6, the retention treatment with a treatment time of 0.5 to 10 seconds is performed 1 to 4 times at any temperature of 250 ° C. or higher and lower than 500 ° C., and any of 500 ° C. or higher and 700 ° C. or lower. At that temperature, the retention treatment with a treatment time of 0.5 to 3 seconds is performed once or twice. Patent Document 6 discloses that a grain-oriented electrical steel sheet having a small variation in iron loss can be manufactured by such a treatment.
[0009]
Here, as a device for rapidly heating a steel sheet in the heating step during decarburization and quenching, a device using a radiant heat source such as a radiant tube, a device using a high energy heat source such as a laser, an induction heating device, and an energization heating device. The device and the like are exemplified in Patent Document 5. Of these, the induction heating device is particularly advantageous in that it has a high degree of freedom in heating rate, can be heated in a non-contact manner with a steel plate, and is relatively easy to install in a decarburization annealing furnace. Patent Document 7 discloses a technique for heating at the time of decarburization annealing using an induction heating device.
[0010]
However, when decarburizing and annealing a steel plate with a relatively thin plate thickness using an induction heating device, the current penetration depth of the eddy current becomes deep when the temperature is near the Curie point because the plate thickness of the steel plate is thin. Therefore, the front and back cancellation of the eddy current that goes around the surface layer portion of the cross section in the plate width direction occurs, and the eddy current does not flow. Therefore, it becomes difficult to heat the steel sheet to a temperature higher than the Curie point. Here, the Curie point of the steel sheet is about 750 ° C. Therefore, rapid heating using an induction heating device can only be performed up to 750 ° C. Therefore, when it is desired to heat the steel sheet to a higher temperature, it is not possible to use an induction heating device, and it is necessary to use another heating device in combination.
[0011]
However, when other heating devices are used together, various problems occur. For example, since the energization heating device or the like comes into contact with the steel sheet, in addition to the problem that the steel sheet is scratched, the equipment advantage of the induction heating device is lost.
[0012]
Therefore, in the technique disclosed in Patent Document 7, the lamella spacing is controlled to 20 μm or more in the grain structure after the hot-rolled plate annealing step by controlling the annealing conditions in the hot-rolled plate annealing step. Patent Document 7 states that such a technique can reduce the rapid heating temperature range (temperature range from the entry side temperature to the ultimate temperature) in the heating process during decarburization annealing to a temperature at which an induction heating device can be used. Is disclosed. Specifically, in Patent Document 7, in the heating process during decarburization annealing, the heating rate from the inlet temperature to the reaching temperature of 550 to 720 ° C. is set to 40 ° C./sec or more, and then averaged. The heating rate up to the thermal temperature range is 10 to 15 ° C./sec.
Prior art literature
Patent documents
[0013]
Patent Document 1: Japanese Patent Publication No. 62-45285
Patent Document 2: Japanese Patent Application Laid-Open No. 2-77525
Patent Document 3: Japanese Patent Publication No. 8-322929
Patent Document 4: Japanese Unexamined Patent Publication No. 9-256051
Patent Document 5: Japanese Unexamined Patent Publication No. 2002-60842
Patent Document 6: Japanese Patent Application Laid-Open No. 2015-193921
Patent Document 7: Japanese Unexamined Patent Publication No. 2008-1983
Non-patent literature
[0014]
Non-Patent Document 1: "Materials Science Forum" 204-206 (1996), pp593-598
Outline of the invention
Problems to be solved by the invention
[0015]
However, the technique disclosed in Patent Document 7 has an effect of improving the magnetic characteristics as compared with the technique of performing rapid heating up to about 750 to 900 ° C. by an apparatus regardless of the heating method as shown in Patent Documents 5 and 6. The problem of not being fully enjoyed still remains. More specifically, according to the technique disclosed in Patent Document 7, the magnetic flux density is improved, but the crystal grain size of the steel sheet after the secondary recrystallization grain (hereinafter, also referred to as “secondary recrystallized grain size”). Since the diameter of (referred to as) is increased, there is a problem that the improvement cost of iron loss is small.
[0016]
On the other hand, the techniques disclosed in Patent Documents 1 to 3 have a problem that the primary recrystallized grain aggregate structure becomes non-uniform and unstable as described above. Therefore, the iron loss characteristic was not sufficient. According to the techniques disclosed in Patent Documents 4 to 6, improvement of iron loss characteristics can be expected, but further improvement of iron loss characteristics is required for grain-oriented electrical steel sheets.
[0017]
The iron loss of the grain-oriented electrical steel sheet can be improved by applying magnetic domain control such as laser thermal strain, addition of mechanical grooves, and addition of etching grooves to the grain-oriented electrical steel sheet, but in order to realize higher iron loss. Is required to further improve the iron loss before magnetic domain control.
[0018]
The present invention has been developed in view of the above circumstances, and an object of the present invention is to provide a method for manufacturing grain-oriented electrical steel sheets capable of stably producing grain-oriented electrical steel sheets having further improved iron loss characteristics. It is a thing.
Means to solve problems
[0019]
The present inventor has made extensive studies to solve the above problems. As a result, the present inventor has found that when the steel sheet is rapidly heated by using an induction heating device in the heating process of decarburization annealing, the secondary recrystallization particle size is low when the heating rate from the reached temperature to the soaking temperature is slow. It was found that the diameter of the steel increased and the iron loss worsened. Further, the present inventor controls the heating rate in the rapid heating temperature range (temperature range from the entry side temperature to the ultimate temperature) and the heating rate from the ultimate temperature to the soaking temperature under appropriate conditions to perform secondary operations. It has been found that the grain size of recrystallized particles can be reduced to stably produce grain-oriented electrical steel sheets having excellent iron loss characteristics. That is, the gist of the present invention is as follows.
[0020]
According to a certain aspect of the present invention, as a chemical component, Si: 2.00 to 4.00%, C: 0.085% or less, Al: 0.01 to 0.065%, N: 0 in mass%. A steel slab containing .004 to 0.012%, Mn: 0.05 to 1.00%, S: 0.003 to 0.015% and composed of the balance Fe and impurities is heated at a temperature of 1280 ° C. or lower. A reheating step for hot rolling, a hot rolling step for hot rolling the heated steel slab, a hot rolling plate annealing step for annealing the hot rolled plate obtained by the hot rolling step, and a hot rolling plate annealing step are performed. After that, a cold rolling step of cold rolling the hot rolled sheet, a decarburizing and annealing step of decarburizing and annealing the cold rolled sheet obtained by the cold rolling step, and a cold rolling after performing a decarburized and annealed step. The decarburized rolling step includes a finish annealing step of finishing and annealing the plate, in which the decarburized and rolled plate is heated from an inlet temperature T0 ° C. of 600 ° C. or lower to a soaking temperature T2 ° C. higher than the inlet temperature T0 ° C. In the heating step of the decarburization and annealing step, which includes a step and a soaking step of maintaining the temperature of the cold rolled plate at the soaking temperature T2 ° C., the temperature of the cold rolled plate is 700 to 900 ° C. from the entry side temperature T0 ° C. The heating rate HR1 until the reaching temperature T1 ° C., which is within the range of and lower than the soaking temperature T2 ° C., is set to 40 ° C./sec or more, and the temperature of the cold rolled plate changes from the reached temperature T1 ° C. to the soaking temperature T2 ° C. Provided is a method for manufacturing a directional electromagnetic steel plate, characterized in that the heating rate HR2 until reaching is set to more than 15 ° C./sec to 30 ° C./sec.
[0021]
Here, the heating rate HR1 may be 75 to 125 ° C./sec.
[0022]
Further, as a chemical component, the steel slab further contains, in terms of mass%, B: 0.0100% or less, Cr: 0.30% or less, Cu: 0.40% or less, P: 0.50% or less, Sn: Even if it contains one or more of 0.30% or less, Sb: 0.30% or less, Ni: 1.00% or less, Mo: 0.1% or less, Bi: 0.01% or less. good.
Effect of the invention
[0023]
According to the above viewpoint of the present invention, the heating rate in the rapid heating temperature range in the heating (heating) step of decarburization and quenching is controlled, and the heating rate from the reached temperature to the soaking temperature is controlled under appropriate conditions. As a result, the grain size of the secondary recrystallization can be reduced, and the grain-oriented electrical steel sheet having further improved iron loss characteristics can be stably manufactured. Further, it is possible to manufacture grain-oriented electrical steel sheets having further improved magnetic properties and the like according to further added elements.
A brief description of the drawing
[0024]
FIG. 1 is a graph illustrating a temperature rise pattern in decarburization annealing of the present embodiment.
[Fig. 2] Fig. 2 is a graph showing the correlation between secondary recrystallization grain size and iron loss.
[Fig. 3] A diagram schematically showing how an aggregate is formed.Is.
Embodiment for carrying out the invention
[0025]
<1. Examination by the present inventor>
The present inventor first investigated the reason why the technique disclosed in Patent Document 7 could not sufficiently obtain the iron loss improving effect of the grain-oriented electrical steel sheet. As a result, the present inventor has found that some grain-oriented electrical steel sheets manufactured by the technique disclosed in Patent Document 7 have a high magnetic flux density but an inferior iron loss. Therefore, when the present inventor investigated the characteristics of the inferior iron loss, it became clear that the secondary recrystallization grain size tended to be larger. That is, as the magnetic flux density increases, the hysteresis loss is reduced. However, when the secondary recrystallization grain size is increased, the eddy current loss increases. Therefore, in the technique disclosed in Patent Document 7, it was found that the reduction of the hysteresis loss is offset by the increase of the eddy current loss, and the iron loss becomes worse.
[0026]
As a result of investigating a method for solving this problem, the present inventor appropriately controls the heating rate from the inlet temperature to the soaking temperature in decarburization annealing, thereby causing {111} in the primary recrystallized grain aggregate structure. It has been found that the frequencies of azimuth grains, {411} azimuth grains, and goth azimuth grains can be appropriately controlled. Furthermore, the present inventor has found that the diameter of the secondary recrystallized grains can be reduced by finishing and annealing the steel sheet whose primary recrystallized grain texture is controlled as described above. Hereinafter, the method for manufacturing the grain-oriented electrical steel sheet according to the present embodiment will be described in detail. Regarding each temperature during decarburization and quenching, the inlet temperature is the temperature of the steel plate when it is introduced into the quenching furnace, the soaking temperature is the temperature when the steel plate is maintained at a constant temperature, and the ultimate temperature is the inlet temperature. It shall mean a temperature higher and lower than the soaking temperature. The specific range of each temperature will be described later.
[0027]
<2. Manufacturing method of grain-oriented electrical steel sheet ＞
(2-1. Outline of manufacturing method)
Next, a method for manufacturing the grain-oriented electrical steel sheet according to the present embodiment will be described. The method for manufacturing the directional electromagnetic steel plate according to the present embodiment includes a steel slab preparation step, a reheating step, a hot rolling step, a hot rolled plate annealing step, a cold rolling step, a decarburization annealing step, a nitrided treatment step, and a quench separation. Includes agent application step, finish quenching step, purification annealing step, and cooling step. Hereinafter, each step will be described in detail.
[0028]
(2-2. Steel slab preparation process)
In this process, prepare a steel slab. Specifically, steel is melted by, for example, a converter or an electric furnace. The molten steel thus obtained is vacuum degassed as necessary, and then continuously cast or ingot-rolled in chunks. This gives a steel slab. The thickness of the steel slab is not particularly limited, but is usually cast in the range of 150 to 350 mm, preferably 220 to 280 mm. However, the steel slab may be a so-called thin slab having a thickness range of 30 to 70 mm. When a thin slab is used, there is an advantage that it is not necessary to roughen the intermediate thickness when manufacturing the hot-rolled plate.
[0029]
(2-2-1. Component composition of steel slab)
The chemical composition of the steel slab is Si: 2.00 to 4.00%, C: 0.085% or less, Al: 0.01 to 0.065%, N: 0.004 to 0. It contains 012%, Mn: 0.05 to 1.00%, S: 0.003 to 0.015%, and is composed of the balance Fe and impurities. Hereinafter,% related to the component composition shall mean mass% with respect to the total mass of the steel slab.
[0030]
(Si: 2.00-4.00%)
Si is an element that increases the electrical resistance of steel sheets and improves iron loss characteristics. If the Si concentration is less than 2.00%, γ transformation of the iron structure occurs during finish baking and the crystal orientation of the steel sheet is impaired. Therefore, the Si concentration is set to 2.00% or more. The Si concentration is preferably 2.50% or more, more preferably 3.00% or more. On the other hand, if the Si concentration exceeds 4.00%, the workability of the grain-oriented electrical steel sheet deteriorates and cracks occur during rolling, so the Si concentration is set to 4.00% or less. The Si concentration is preferably 3.50% or less.
[0031]
(C: 0.085% or less)
C is an element that is effective in controlling the primary recrystallization structure, but it adversely affects the magnetic properties, so it is an element that is removed by decarburization annealing before finish annealing. If the C concentration exceeds 0.085%, the decarburization annealing time becomes long and the productivity decreases, so the C concentration is set to 0.085% or less. The C concentration is preferably 0.070% or less, more preferably 0.050% or less. The lower limit of the C concentration includes 0%, but if the C concentration is reduced to less than 0.0001%, the manufacturing cost will increase significantly, so 0.0001% is a practical lower limit on the practical steel sheet. In grain-oriented electrical steel sheets, the C concentration is usually reduced to about 0.001% or less by decarburization annealing.
[0032]
(Al: 0.010-0.065%)
Al is an element that binds to N to form (Al, Si) N or AlN that functions as an inhibitor. If the Al concentration is less than 0.010%, the effect of adding Al is not sufficiently exhibited and secondary recrystallization does not proceed sufficiently, so the Al concentration is set to 0.010% or more. The Al concentration is preferably 0.015% or more, more preferably 0.020% or more. On the other hand, when the Al concentration exceeds 0.065%, the precipitation and dispersion of the inhibitor become non-uniform, the required secondary recrystallization structure cannot be obtained, and the magnetic flux density decreases, so that the Al concentration is 0.065% or less. And. The Al concentration is preferably 0.050% or less, more preferably 0.040% or less.
[0033]
(N: 0.004 to 0.012%)
N is an element that binds to Al to form AlN that functions as an inhibitor. However, N is also an element that forms blister (vacancy) in the steel sheet during cold rolling. If the mass% of N is less than 0.004%, the formation of AlN is insufficient, so the N concentration is set to 0.004% or more. It is preferably 0.006% or more, more preferably 0.007% or more. If the N concentration exceeds 0.012%, many blister may be formed in the steel sheet during cold rolling, so the N concentration should be 0.012% or less.
[0034]
(Mn: 0.05 to 1.00%)
Mn is an element that prevents cracking during hot rolling and combines with S to form an Mn compound that functions as an inhibitor, that is, MnS. If the Mn concentration is less than 0.05%, the effect of adding Mn is not sufficiently exhibited, so the Mn concentration is set to 0.05% or more. The Mn concentration is preferably 0.07% or more, more preferably 0.09% or more. On the other hand, when the Mn concentration exceeds 1.00%, the precipitation and dispersion of the Mn compound become non-uniform, the required secondary recrystallization structure cannot be obtained, and the magnetic flux density decreases, so that the Mn concentration is 1.00%. It shall be as follows. The Mn concentration is preferably 0.80% or less, more preferably 0.60% or less.
[0035]
(S: 0.003 to 0.015%)
S is an element that binds to Mn to form MnS that functions as an inhibitor. If the S concentration is less than 0.003%, the effect of adding S is not sufficiently exhibited, so the S concentration is set to 0.003% or more. The S concentration is preferably 0.005% or more, more preferably 0.007% or more. On the other hand, when the S concentration exceeds 0.015%, the precipitation and dispersion of MnS become non-uniform, the required secondary recrystallization structure cannot be obtained, and the magnetic flux density decreases, so that the S concentration is 0.015%. do. The S concentration is preferably 0.013% or less, more preferably 0.011% or less.
[0036]
In the components of the steel slab, the rest excluding the above elements are Fe and impurities. Impurities are basically unavoidable impurities, but when the steel slab contains optional additive elements described later, the impurities are composed of these optional additive elements in addition to the unavoidable impurities. The unavoidable impurities are elements that are inevitably mixed in both the steel raw material and the steelmaking process, and are permissible elements as long as they do not impair the characteristics of the grain-oriented electrical steel sheet according to the present embodiment.
[0037]
Further, for the purpose of not impairing the magnetic properties of the steel slab and enhancing other properties, B: 0.0100% or less, B: 0.0100% or less, Cr: 0.30% or less. , Cu: 0.40% or less, P: 0.50% or less, Sn: 0.30% or less, Sb: 0.30% or less, Ni: 1.00% or less, Mo: 0.1% or less, Bi : One or more of 0.01% or less may be added as an optional additive element. Since these elements are optional additives, the lower limit of the concentration may be 0%.
[0038]
(B: 0.0100% or less)
B is an element that binds to N in the base steel sheet and complex-precipitates with MnS to form BN that functions as an inhibitor. The lower limit of the B concentration is not particularly limited, and may be 0% as described above. However, in order to fully exert the effect of adding B, the lower limit of the B concentration is preferably 0.0005%. The B concentration is preferably 0.001% or more, more preferably 0.0015% or more. On the other hand, when the B concentration exceeds 0.0100%, the precipitation and dispersion of BN become non-uniform, the required secondary recrystallization structure cannot be obtained, and the magnetic flux density decreases. Therefore, the B concentration is preferably 0.0100% or less. The B concentration is preferably 0.0080% or less, more preferably 0.0060% or less, and more preferably 0.0040% or less.
[0039]
(Cr: 0.30% or less)
Cr is an element that improves the internal oxide layer formed during decarburization annealing and is effective in forming a glass film. Therefore, Cr may be added to the steel slab in the range of 0.30% or less. If the Cr concentration exceeds 0.30%, the decarburization property is significantly inhibited. Therefore, the upper limit of the Cr concentration is preferably 0.30%.
[0040]
(Cu: 0.40% or less)
Cu is an element effective in increasing the specific resistance of grain-oriented electrical steel sheets and reducing iron loss. If the C concentration exceeds 0.40%, the iron loss reducing effect is saturated and it causes a surface defect called "copper hegging" during hot rolling. Therefore, the upper limit of the C concentration is preferably 0.40%.
[0041]
(P: 0.50% or less)
P is an element effective in increasing the specific resistance of grain-oriented electrical steel sheets and reducing iron loss. If the P concentration exceeds 0.50%, a problem may occur in rollability. Therefore, the upper limit of the P concentration is preferably 0.50%.
[0042]
(Sn: 0.30% or less, Sb: 0.30% or less)
Sn and Sb are well-known grain boundary segregation elements. Since the steel slab according to the present embodiment contains Al, Al may be oxidized by the water released from the annealing separator depending on the conditions of finish annealing, and the inhibitor strength may fluctuate at the coil position. As a result, the magnetic characteristics may fluctuate depending on the coil position. As one of the countermeasures, there is a method of preventing the oxidation of Al by adding these grain boundary segregating elements, and for that purpose, Sn and Sb may be added to the base steel sheet at a concentration of 0.30% or less, respectively. .. On the other hand, when the concentration of these elements exceeds 0.30%, Si is less likely to be oxidized during decarburization annealing, the formation of a glass film becomes insufficient, and the decarburization annealing is significantly impaired. Therefore, the upper limit of the concentration of these elements is preferably 0.30%.
[0043]
(Ni: 1.00% or less)
Ni is an element effective in increasing the specific resistance of grain-oriented electrical steel sheets and reducing iron loss. Ni is also an effective element for controlling the iron structure of the hot-rolled sheet and improving the magnetic properties. However, if the Ni concentration exceeds 1.00%, secondary recrystallization becomes unstable, so the upper limit of the Ni concentration is preferably 1.00%.
[0044]
(Mo: 0.1% or less)
Mo is an element effective for improving the surface texture during hot spreading. However, if the Mo concentration exceeds 0.1%, the Mo addition effect is saturated, so the upper limit of the Mo concentration is preferably 0.1%.
[0045]
(Bi: 0.01% or less)
Bi has the effect of stabilizing precipitates such as sulfides and strengthening the function as an inhibitor. However, if the Bi concentration exceeds 0.01%, Bi adversely affects the formation of the glass film, so the upper limit of the Bi concentration is preferably 0.01%.
[0046]
(2-3. Reheating process)
In this process, the steel slab is reheated. The reheating temperature of the steel slab is 1280 ° C or lower is preferable. When the reheating temperature exceeds 1280 ° C., the amount of melt scale increases. Further, since MnS is completely dissolved in the steel slab and finely precipitated in the subsequent steps, it is necessary to set the decarburization annealing temperature to more than 900 ° C. in order to obtain the desired primary recrystallization grain size. Therefore, in this embodiment, it is preferable to reheat the steel slab at 1280 ° C. or lower. The lower limit of the reheating temperature is not particularly limited, but may be, for example, 1100 ° C. In this embodiment, the temperature of the steel slab or the steel plate can be measured by, for example, a radiation thermometer.
[0047]
(2-4. Hot rolling process, hot rolled sheet annealing process)
In the hot rolling (hot rolling) process, the steel slab after reheating is hot rolled. In the hot-rolled plate annealing step, the iron structure is recrystallized by heating the hot-rolled plate obtained by the hot rolling step to the first stage temperature of 1000 to 1150 ° C. Then, the hot-rolled plate is annealed at 850 to 1100 ° C. and at a second stage temperature lower than the first stage temperature. This hot-rolled plate annealing step is mainly performed for the purpose of homogenizing the non-uniform structure generated during hot rolling.
[0048]
That is, in order to make the non-uniform iron structure (history) generated during hot rolling uniform before the final cold rolling, it is preferable to perform annealing once or more in this embodiment. The upper limit of the first stage temperature in this case has a great influence on the inhibitor. For example, if the temperature of the first stage exceeds 1150 ° C., the inhibitor may be finely precipitated in the subsequent steps. Therefore, it is preferable to set the upper limit of the first stage temperature to 1150 ° C. On the other hand, if the temperature of the first stage is less than 1000 ° C., recrystallization may be insufficient and the iron structure after hot rolling may not be uniform. Therefore, it is preferable to set the lower limit of the first stage temperature to 1000 ° C. The upper limit of the second stage temperature also has a great effect on the inhibitor. For example, when the temperature of the second stage exceeds 1100 ° C., the inhibitor may be finely precipitated in the subsequent step. Therefore, it is preferable to set the upper limit of the second stage temperature to 1100 ° C. When the temperature of the second stage is less than 850 ° C., the γ phase does not occur and the iron structure may not be uniformized. Therefore, it is preferable to set the lower limit of the second stage temperature to 850 ° C. Further, it is preferable to control the temperature of the second stage to a value lower than the temperature of the first stage.
[0049]
(2-5. Cold rolling process)
After performing the hot-rolled sheet annealing step, the hot-rolled plate is subjected to one cold rolling or two or more cold rollings (cold rolling) sandwiching intermediate annealing. As a result, the final cold-rolled plate is produced. Each cold rolling may be performed at room temperature, or may be hot rolling in which the temperature of the steel sheet is raised to a temperature higher than normal temperature, for example, about 200 ° C.
[0050]
(2-6. Decarburization annealing process)
The decarburization annealing step is a heating step of heating the steel plate (cold-rolled plate) after the cold-rolling process from the inlet temperature T0 ° C to a soaking temperature T2 ° C higher than the inlet temperature, and a heating step of soaking the temperature of the cold-rolled plate. It includes a soaking step in which the temperature is set to T2 ° C. for a predetermined time. The decarburization annealing process is performed in a moist atmosphere. Here, the inlet temperature T0 ° C. is the temperature at which the cold rolled sheet is introduced into the annealing furnace, and is generally 600 ° C. or lower. The soaking temperature is a temperature in the range of 700 to 900 ° C.
[0051]
The decarburization annealing soaking step is performed for the purpose of removing carbon in steel and controlling the primary recrystallization grain size to a desired grain size. The heat equalizing step is preferably performed at a soaking temperature of T2 ° C. in a temperature range of 700 ° C. to 900 ° C. and a time such that the primary recrystallization particle size is 15 μm or more. If the soaking temperature T2 ° C. is less than 700 ° C., the desired primary recrystallization grain size cannot be achieved, and if the soaking temperature T2 ° C. exceeds 900 ° C., the primary recrystallization exceeds the desired grain size.
[0052]
In the heating step, as shown in FIG. 1, until the temperature of the cold rolled plate reaches the ultimate temperature T1 ° C. within the range of the inlet temperature T0 ° C. to 700 to 900 ° C. and lower than the soaking temperature T2 ° C. (that is, The heating rate HR1 in the rapid heating temperature range) is set to 40 ° C./sec or more. Further, the heating rate HR2 from the ultimate temperature T1 ° C. to the soaking temperature T2 ° C. is set to more than 15 ° C./sec to 30 ° C./sec. The ultimate temperature T1 ° C. may be arbitrarily set within the range in which the above conditions are satisfied, but by setting the ultimate temperature T1 ° C. to be equal to or lower than the Curie point (750 ° C.) of the steel sheet, the inlet temperature T0 ° C. to the ultimate temperature T1 Heating in the temperature range of ° C. (rapid heating temperature range) can be performed by an induction heating device.
[0053]
As described above, in the heating step according to the present embodiment, the frequency of {111} oriented grains, {411} oriented grains, and Goth oriented grains in the primary recrystallized grain aggregate structure is appropriately controlled by controlling the heating rate. do. Specifically, in the primary recrystallized grain aggregate structure, it is preferable to reduce the number of {111} oriented grains and increase the number of {411} oriented grains and Goth oriented grains. The ease of recrystallization differs depending on the crystal orientation, and {411} oriented grains are most likely to recrystallize at a heating rate of around 100 ° C./sec, and Goth oriented grains are more likely to recrystallize in proportion to the heating rate. .. Therefore, in the present embodiment, the heating rate HR1 from the inlet temperature T0 ° C. to the soaking heat T1 ° C. is set to 40 ° C./sec or more. This makes it possible to reduce {111} azimuth grains and increase {411} azimuth grains and Goth azimuth grains. The heating rate HR1 is preferably 75 ° C./sec or higher, more preferably 75-125 ° C./sec.
[0054]
Further, in the present embodiment, the heating rate HR2 from the ultimate temperature T1 ° C. to the soaking temperature T2 ° C. is set to more than 15 ° C./sec to 30 ° C./sec. The lower limit of the heating rate HR2 is preferably 16 ° C./sec. As described above, in the present embodiment, the heating rate HR2 after the temperature of the cold rolled plate reaches the ultimate temperature T1 ° C. is set to a relatively high value of more than 15 ° C./sec to 30 ° C./sec. This makes it possible to obtain a primary recrystallized grain aggregate structure in which the frequency of {411} azimuth grains and Goth azimuth grains is high and the crystal grain size of the Goth azimuth grains is increased. As a result, the grain size of the secondary recrystallization is reduced in the subsequent secondary recrystallization of finish annealing, so that a grain-oriented electrical steel sheet having good iron loss can be obtained.
[0055]
Here, the reason why the above effect is obtained when the heating rate HR2 is controlled to more than 15 ° C./sec to 30 ° C./sec is not clear, but the present inventor considers the reason as follows. .. That is, in the temperature range from the ultimate temperature T1 ° C. of rapid heating to the soaking temperature T2 ° C. at 700 to 900 ° C., recrystallization of unrecrystallized grains and grain growth of crystal grains that have already been recrystallized occur. At the soaking temperature of T2 ° C., all the unrecrystallized grains are recrystallized grains. After that, in the soaking step (soaking annealing) at the soaking temperature T2 ° C., the recrystallized grains enter the grain growth mode, the azimuth grains having a small crystal grain size are eclipsed, and the azimuth grains having a large crystal grain size have a large diameter. To become. Here, the Goth azimuth grain has completed recrystallization at an ultimate temperature of T1 ° C. or lower. Goss that has already completed recrystallization by controlling the heating rate HR2 from the ultimate temperature T1 ° C to the soaking temperature T2 ° C to more than 15 ° C / sec to 30 ° C, preferably 16 ° C / sec or more and 30 ° C / sec or less. Grain growth of oriented grains is promoted. That is, since the Goth azimuth grains are already large-diameter crystal grains at the start of the heat soaking step, they can exist without being eaten by other azimuth grains in the heat soaking step.
[0056]
Here, when the heating rate HR2 is 15 ° C./sec or less, the growth of the crystal grains in the orientation of recrystallization after the reaching temperature T1 ° C. and the growth of the Goth-oriented grains compete with each other, and the Goth-oriented grains cannot be sufficiently grown. .. As a result, the frequency of Goth orientation grains decreases in the primary recrystallized grain aggregate structure, and an electromagnetic steel sheet having good iron loss characteristics cannot be obtained. On the other hand, when the heating rate HR2 is more than 30 ° C./sec, the frequency and crystal grain size of Goth oriented grains become extremely large in the primary recrystallized grain aggregate structure, and the grain size (uniformity) of the entire structure is significantly impaired. It will be lost. Therefore, stable secondary recrystallization cannot be obtained, and as a result, the iron loss characteristics deteriorate. Further, the upper limit of HR2 may be 25 ° C. or lower or less than 25 ° C. The range of HR2 can be heated by various heating devices as described in detail later, but if HR2 becomes large and overshoots the soaking temperature T2, it may lead to subsequent secondary recrystallization failure. Therefore, it is preferable that the upper limit of HR2 is 25 ° C. or lower or less than 25 ° C., because it is possible to prevent overshoot of the soaking temperature T2.
[0057]
By the decarburization annealing step, an internal oxide layer containing a large amount of SiO 2 is formed on the surface layer of the cold-rolled sheet.
[0058]
(2-6-1. Heating method in decarburization annealing process)
The cold rolled plate may be heated by an induction heating device in the heating step. In this case, the degree of freedom in the heating rate is high, the steel sheet can be heated in a non-contact manner, and the effect of being relatively easy to install in the decarburization annealing furnace can be obtained. In particular, when the ultimate temperature T1 ° C. is 750 ° C. or lower, which is the Curie point of the steel sheet, the cold-rolled sheet can be rapidly heated from the inlet temperature T0 ° C. to the ultimate temperature T1 ° C. only by the induction heating device.
[0059]
On the other hand, heating from the ultimate temperature T1 ° C. to the soaking temperature T2 ° C. and the soaking heat treatment in the subsequent soaking step may be performed using a heating device using a radiant heat source such as a radiant tube. It is difficult to heat after the Curie point with an induction heating device, but a heating device using a radiant heat source can stably heat the cold-rolled sheet even in such a temperature range. Further, heating by radiant heat has an advantage that it is easy to control within the range of the heating rate HR2 (within the range slower than the heating rate HR1).
[0060]
Of course, the heating method is not particularly limited. In addition to the above-mentioned method, the heating method may be a method using a new high-energy heat source such as a laser or plasma, a method using an energization heating device, or the like. It is also possible to combine these as appropriate. However, by using an induction heating device or a heating device using a radiant heat source, there is an advantage that the cold-rolled plate can be heated without the heating device coming into direct contact with the cold-rolled plate.
[0061]
(2-7. Nitriding process)
After decarburization annealing, the steel sheet is nitrided so that the nitrogen concentration of the steel sheet is 40 ppm or more and 1000 ppm or less. If the nitrogen concentration of the steel sheet after the nitriding treatment is less than 40 ppm, AlN does not sufficiently precipitate in the steel sheet, and AlN does not function as an inhibitor. Therefore, the nitrogen concentration of the steel sheet is set to 40 ppm or more. On the other hand, when the nitrogen concentration of the steel sheet exceeds 1000 ppm, AlN is excessively present in the steel sheet even after the completion of the secondary recrystallization in the finish annealing. Such AlN causes deterioration of iron loss. Therefore, the nitrogen concentration of the steel sheet is set to 1000 ppm or less.
[0062]
(2-8. Annealing separator application process)
After the nitriding process, apply an annealing separator to the surface of the steel sheet. Finish annealing, which will be described later, may be performed in a state where the steel sheet is wound into a coil. When finish annealing is performed in such a state, the coil may be seized and it may be difficult to unwind the coil. Therefore, in the present embodiment, an annealing separator is applied so that the coil can be unwound after finish annealing. Here, the main component of the annealing separator is MgO, and MgO in the annealing separator undergoes a solid phase reaction with SiO 2 in the internal oxide layer during finish annealing to form a glass film.
[0063]
(2-9. Finish annealing process)
The finish annealing step is an annealing, which is also called a secondary recrystallization annealing step, and is a process for promoting secondary recrystallization of the iron structure. In the finish annealing step, the cold-rolled plate (steel plate) is heated to about 1200 ° C., which will be described later. Here, in the heating process, it is preferable that the heating rate HR3 is 15 ° C./h or less in the temperature range of at least 1000 ° C. to 1100 ° C. Further, instead of controlling the heating rate, it is also effective to keep the temperature within the temperature range of 1000 ° C. to 1100 ° C. for 10 hours or more. That is, the heating rate in this temperature range is extremely slowed down. This can promote preferential growth (secondary recrystallization) of Goth oriented grains. If the heating rate HR3 is too fast (more than 15 ° C./h), crystal grains in crystal orientations other than the Goth orientation will grow. The heating rate in other temperature ranges is not particularly limited and may be about the same as that of the conventional finish annealing. The finish annealing atmosphere is not particularly limited, and may be the same as that of the conventional finish annealing. For example, the finish annealing atmosphere may be a mixed atmosphere of nitrogen and hydrogen.[0064]
In particular, in the present embodiment, the frequency of {411} oriented grains and Goth oriented grains in the primary recrystallized grain aggregate structure before finish annealing is high, and the crystal grain size of the Goth oriented grains is (in the temporary recrystallized grain aggregate structure). The diameter is increased (relatively). For this reason, the secondary recrystallized grain aggregate structure is a structure in which the Goth azimuth grains with smaller diameters are highly aligned. That is, the frequency of Goth-oriented grains is extremely high (relative to the secondary recrystallized grain texture obtained by the prior art), and the particle size of the Goth-oriented grains is small. This is considered to be due to the following reasons.
[0065]
That is, the frequency of {411} oriented grains and Goth oriented grains in the primary recrystallized grain aggregate structure before finish annealing is high, and the crystal grain size of the Goth oriented grains is (relatively in the temporary recrystallized grain aggregate structure). Due to the large diameter, Goth azimuth grains grow in preference to other azimuth grains during finish annealing. Therefore, the frequency of Goth orientation grains is high (in other words, there are many growth nuclei), and the diameter of each Goth orientation grain is preferentially increased, so that many Goth orientation grains are growing after secondary recrystallization. Since the plurality of grown Goth azimuth grains have a slight azimuth difference, they do not coalesce, so that the region occupied by the individual Goth azimuth grains after the secondary recrystallization, that is, the particle size becomes smaller.
[0066]
FIG. 3 is a diagram schematically showing how the texture of the present embodiment is formed, and also shows how the texture of the prior art is formed for reference. ..
[0067]
As described above, in the present embodiment, the heating rate HR1 in the rapid heating temperature range in the heating (heating) step of decarburization annealing and the heating rate HR2 from the reached temperature to the soaking temperature are controlled under appropriate conditions. As a result, the grain size of the secondary recrystallization can be reduced, and a grain-oriented electrical steel sheet having further improved iron loss characteristics can be stably manufactured. Further, it is possible to manufacture grain-oriented electrical steel sheets having further improved magnetic properties and the like according to further added elements.
[0068]
Here, the measuring method of HR1 and HR2 is not particularly limited, but can be calculated by measuring the temperature of the steel sheet using, for example, a radiation thermometer or the like. However, if it is difficult to measure the steel plate temperatures T0, T1 and T2, and it is difficult to estimate the exact locations of the start and end points of HR1 and HR2, by analogizing each heat pattern in the temperature rise process. , These locations may be estimated.
[0069]
The present inventor prepared grain-oriented electrical steel sheets manufactured under various manufacturing conditions. Then, the particle size (particle size after secondary recrystallization) of these Goth azimuth grains was measured. Specifically, the glass film is removed by pickling, the crystal grains are exposed, the number of crystal grains in the range of 180 cm 2 is measured, and the area per secondary recrystallized grain (= 180 / number). ), The particle size (diameter equivalent to a circle) was calculated. Further, the iron loss W 17/50 of these grain-oriented electrical steel sheets was measured. The result is shown in FIG. The horizontal axis of FIG. 2 shows the particle size after the secondary recrystallization, and the vertical axis shows the iron loss. Plot P1 shows the measurement results of each grain-oriented electrical steel sheet, and straight line L1 is an approximate straight line of plot P1. According to FIG. 2, there is a high correlation between the particle size after the secondary recrystallization and the iron loss, and it can be seen that the smaller the particle size after the secondary recrystallization, the smaller the iron loss. Further, as will be described in detail later, the grain-oriented electrical steel sheet manufactured by the method for manufacturing grain-oriented electrical steel sheet according to the present embodiment has an iron loss of approximately 0.85 (W / kg) or less. The following steps may be further performed after the finish annealing step.
[0070]
(2-10. Purification annealing process)
In the purification annealing step following the finish annealing step, the precipitates (AlN, MnS, etc.) used as inhibitors are detoxified by performing purification after the completion of secondary recrystallization. This makes it possible to reduce the hysteresis loss in the final magnetic characteristics. In the purification annealing step, for example, it is preferable to retain the steel sheet at 1200 ° C. for 10 hours or more in a hydrogen atmosphere. After purification annealing, the cold rolled plate (steel plate) is cooled.
[0071]
(2-11. Insulation film coating)
Apply an insulating film coating to the surface of the steel sheet after the cooling process and bake it. The type of the insulating film is not particularly limited, and any conventionally known insulating film is suitable for the grain-oriented electrical steel sheet of the present embodiment. Examples of the insulating film include a film formed by applying an aqueous coating solution containing a phosphate and colloidal silica. In this case, examples of the phosphate include phosphates such as Ca, Al, and Sr. Of these, the aluminum phosphate salt is more preferable. Colloidal silica is not particularly limited, and its particle size can be used as appropriate. A particularly preferable particle size (average particle size) is 200 nm or less. Even if the particle size is less than 100 nm, there is no problem in dispersion, but the manufacturing cost becomes high and it may not be realistic. If the particle size exceeds 200 nm, it may settle in the treatment liquid.
[0072]
It is preferable to apply the insulating film coating liquid to the surface of the steel sheet by a wet coating method such as a roll coater and bake it in an air atmosphere at a temperature of 800 to 900 ° C. for 10 to 60 seconds to form a tension insulating film. ..
[0073]
(2-12. Magnetic domain control process)
The specific processing method of the magnetic domain control process is not particularly limited, and lower iron loss can be obtained by performing magnetic domain control by, for example, laser irradiation, electron beam, etching, or a groove forming method using gears. As described above, the iron loss is greatly improved in the grain-oriented electrical steel sheet according to the present embodiment even before the magnetic domain control.
Example
[0074]
Next, an embodiment of the present invention will be described. The conditions in the examples are one condition example adopted for confirming the feasibility and effect of the present invention, and the present invention is not limited to this one condition example. The present invention can adopt various conditions as long as the gist of the present invention is not deviated and the object of the present invention is achieved.
[0075]
<1. Example 1>
In Example 1, a steel slab having the composition shown in Table 1 was heated to 1150 ° C. and then subjected to hot rolling to obtain a hot-rolled plate having a plate thickness of 2.6 mm. Then, the hot-rolled plate was annealed by setting the temperature of the first stage to 1100 ° C. and the temperature of the second stage to 900 ° C. Then, the hot-rolled plate was subjected to one cold-rolling or a plurality of cold-rolling with intermediate annealing sandwiched between them to prepare a cold-rolled plate having a final plate thickness of 0.23 mm.
[0076]
[table 1]

[0077]
Then, the cold-rolled sheet having a final thickness of 0.23 mm was subjected to decarburization annealing and nitriding treatment (annealing to increase the nitrogen content of the steel sheet). The heating rates HR1 and HR2, the ultimate temperature T1 ° C., and the soaking temperature T2 ° C. in decarburization annealing were as shown in Table 2. The heating method was a radiant tube method. Here, the inlet temperature T0 ° C. was set to 550 ° C. Further, in the heat soaking step, the soaking temperature T2 was maintained for 100 seconds.
[0078]
After that, an annealing separator containing magnesia (MgO) as a main component was applied to the surface of the steel sheet, and finish annealing was performed. Then, in the finish annealing step, the steel sheet was heated to 1200 ° C. Here, the heating temperature in the temperature range of 1000 to 1100 ° C. was set to 10 ° C./h. Then, a water-based coating liquid composed of phosphate and colloidal silica was applied to the steel sheet, and the steel sheet was baked in air at 800 ° C. for 60 seconds. As a result, a tension insulating film was formed on the surface of the steel sheet (more specifically, the surface of the glass film). Then, the iron loss W 17/50 (energy loss measured under the excitation conditions of 1.7 T and 50 Hz) of the grain-oriented electrical steel sheet to which the tension insulating film was applied was measured. The measurement was carried out based on JIS C 2550. The results are shown in Table 2.
[0079]
[Table 2]

[0080] [0080]
In Invention Examples B1 to B17 that satisfy all the conditions (component composition, temperature control in the decarburization annealing step) of the method for manufacturing grain-oriented electrical steel sheets according to the present embodiment, the iron loss W 17/50 is 0.85 W / kg or less. Good iron loss is obtained. In Invention Examples B1 to B17, the heating rate HR1 from the entry side temperature T0 ° C. (550 ° C.) to the ultimate temperature T1 ° C. is set to 40 ° C./sec, and the heating rate HR2 from the ultimate temperature T1 ° C. to the soaking temperature T2 ° C. Was set to more than 15 ° C./sec to 30 ° C./sec.
[0081]
In B18 to B21, the iron loss W 17/50 is 0.85 W / kg or less, which is a good iron loss. In the invention examples B18 to B21, the heating speed HR1 from the entry side temperature T0 ° C. (550 ° C.) to the ultimate temperature T1 ° C. is set to 100, 400, 1000, 1200 ° C./sec, respectively, and the heat is equalized from the ultimate temperature T1 ° C. The heating rate HR2 up to the temperature T2 ° C. was set to more than 15 ° C./sec to 30 ° C./sec.
[0082]
On the other hand, in Comparative Examples b2, b4, b6, b7, b9, and b11, steel slabs in which the mass% of a part of the component composition was out of the range of the present embodiment were used, so that secondary recrystallization did not occur and iron loss W. 17/50 was 1.00 W / kg or more, which was significantly inferior. Further, Comparative Example b1 had poor decarburization, Comparative Examples b3 and b5 had low intrinsic resistance, and Comparative Example b10 had an inferior iron loss of 0.9 W / kg or more due to residual sulfide. In Comparative Example b8, although the iron loss was good, blisters frequently occurred on the product board, which was unsuitable as a commercial product. In Comparative Examples b12 to b18, although the mass% of the component composition is within the range of the present invention, the heating conditions for decarburization annealing are outside the range of the present invention. Therefore, the iron loss W 17/50 remained at 0.89 W / kg or more. Specifically, in Comparative Example b12, since the heating rate HR2 was high, the frequency of Goth azimuth grains became too high, and secondary recrystallization over the entire coil length could not be obtained after finish annealing. In Comparative Examples b13 and b14, the heating rate HR1 or the heating rate HR2 was slow, respectively, so that the number of Goth-oriented grains was reduced in the primary recrystallized grain aggregate structure. Therefore, good iron loss could not be obtained. In Comparative Examples b15 and b18, the soaking temperature T2 ° C. exceeded 900 ° C., and therefore overshooted. Therefore, the primary recrystallization grain size became too large, and the secondary recrystallization did not occur due to finish annealing. In Comparative Examples b16 and b17, since the heating rate HR1 was slow, Goth-oriented grains did not develop in the primary recrystallized grain aggregate structure, and good iron loss could not be obtained.
[0083]
For b19 to b21, the heating rate HR1 from the entry side temperature T0 ° C. (550 ° C.) to the ultimate temperature T1 ° C. is set to 40, 100, and 300 ° C./sec, respectively, and the heating rate from the ultimate temperature T1 ° C. to the soaking temperature T2 ° C. HR2 was set to 15 ° C./sec. The iron loss W 17/50 was 0.85 W / kg or more, which was not a good iron loss. This is because the Goth orientation grains in the primary recrystallized texture did not develop.
[0084]
For b22 to b24, the heating rate HR1 from the entry side temperature T0 ° C. (550 ° C.) to the ultimate temperature T1 ° C. is set to 100, 350, 1000 ° C./sec, respectively, and the heating rate from the ultimate temperature T1 ° C. to the soaking temperature T2 ° C. The HR2 was set to 26 ° C./sec, and the desired soaking temperature T2 was set to 840, 850, and 830 ° C., respectively. The iron loss W 17/50 greatly exceeded 1.00 W / kg, and a secondary recrystallization failure occurred. This is because the heating rate was too high and T2 was too high above the desired temperature (overshoot).
[0085]
<2. Example 2>
In Example 2, the steel slab having the composition shown in Table 1 was heated to 1150 ° C. and then subjected to hot rolling to obtain a hot-rolled steel sheet having a plate thickness of 2.6 mm. Then, the hot-rolled plate was annealed by setting the temperature of the first stage to 1100 ° C. and the temperature of the second stage to 900 ° C. Then, the hot-rolled plate was subjected to one cold-rolling or a plurality of cold-rolling with intermediate annealing sandwiched between them to prepare a cold-rolled plate having a final plate thickness of 0.23 mm.
[0086]
Then, the cold-rolled sheet having a final thickness of 0.23 mm was subjected to decarburization annealing and nitriding treatment (annealing to increase the nitrogen content of the steel sheet). The heating rates HR1 and HR2, the ultimate temperature T1 ° C., and the soaking temperature T2 ° C. in decarburization annealing were as shown in Table 2. The heating method was a radiant tube method. Here, the inlet temperature T0 ° C. was set to 550 ° C. Further, in the heat soaking step, the soaking temperature T2 was maintained for 120 seconds.
[0087]
After that, an annealing separator containing magnesia (MgO) as a main component was applied to the surface of the steel sheet, and finish annealing was performed. Then, in the finish annealing step, the steel sheet was heated to 1200 ° C. Here, the heating temperature in the temperature range of 1000 to 1100 ° C. was set to 10 ° C./h. After that, a water-based coating liquid consisting of phosphate and colloidal silica is applied to the steel sheet, and it is baked in air at 800 ° C. for 60 seconds.I tightened it. As a result, a tension insulating film was formed on the surface of the steel sheet (more specifically, the surface of the glass film). Then, the iron loss W 17/50 (energy loss measured under the excitation conditions of 1.7 T and 50 Hz) of the grain-oriented electrical steel sheet to which the tension insulating film was applied was measured. The measurement was carried out based on JIS C 2550. The results are shown in Table 3.
[0088]
[Table 3]

[0089]
Inventive Examples C1 to C9 all satisfy the conditions (component composition, temperature control in the decarburization annealing step) of the method for manufacturing grain-oriented electrical steel sheets according to the present embodiment, so that the iron loss W 17/50 is 0. Good iron loss of 85 W / kg or less is obtained. In particular, in the invention examples C5 to C9, the heating rate HR1 from the entry side temperature T0 ° C. (550 ° C.) to the ultimate temperature T1 ° C. is set to 100 ° C./sec, and the heating rate HR2 from the ultimate temperature T1 ° C. to the soaking temperature T2 ° C. Was set to more than 15 ° C./sec to 30 ° C./sec. That is, the heating rate HR1 was increased. As a result, in the examples C5 to C9 of the invention, the iron loss W 17/50 is 0.80 W / kg or less, which is a particularly good iron loss.
[0090]
Although the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that any person having ordinary knowledge in the field of the art to which the present invention belongs can come up with various modifications or modifications within the scope of the technical ideas described in the claims. , These are also naturally understood to belong to the technical scope of the present invention.
Code description
[0091]
P1: Plot showing measured values ​​of particle size and iron loss after secondary recrystallization
L1: Approximate straight line of plot P1
The scope of the claims
[Claim 1]
As chemical components, in terms of mass%, Si: 2.00 to 4.00%, C: 0.085% or less, Al: 0.01 to 0.065%, N: 0.004 to 0.012%, Mn. A reheating step of heating a steel slab containing 0.05 to 1.00% and S: 0.003 to 0.015% and composed of the balance Fe and impurities at a temperature of 1280 ° C. or lower, and
The hot rolling process of hot rolling the steel slab after heating and
The hot-rolled plate annealing step of annealing the hot-rolled plate obtained by the hot rolling process, and
After performing the hot-rolled plate annealing step, the cold-rolling step of cold-rolling the hot-rolled plate and
The decarburization annealing step of decarburizing and annealing the cold rolled plate obtained by the cold rolling step,
Includes a finish annealing step of finishing and annealing the cold rolled plate after performing the decarburization annealing step.
The decarburization annealing step includes a heating step of heating the cold-rolled plate from an inlet temperature T0 ° C. of 600 ° C. or lower to a soaking temperature T2 ° C. higher than the inlet temperature T0 ° C., and the temperature of the cold-rolled plate. Including the soaking step of maintaining the soaking temperature T2 ° C.
In the heating step of the decarburization annealing step, until the temperature of the cold-rolled plate reaches the ultimate temperature T1 ° C. within the range of the inlet temperature T0 ° C. to 700 to 900 ° C. and lower than the soaking temperature T2 ° C. The heating rate HR1 is set to 40 ° C./sec or higher, and the heating rate HR2 from the reached temperature T1 ° C. to the soaking temperature T2 ° C. is set to more than 15 ° C./sec to 30 ° C./sec. A method for manufacturing a directional electromagnetic steel plate, characterized in that.
[Claim 2]
The method for manufacturing a grain-oriented electrical steel sheet according to claim 1, wherein the heating rate HR1 is 75 to 125 ° C./sec.
[Claim 3]
As a chemical component, the steel slab further contains, in terms of mass%, B: 0.0100% or less, Cr: 0.30% or less, Cu: 0.40% or less, P: 0.50% or less, Sn: 0. It is characterized by containing one or more of 30% or less, Sb: 0.30% or less, Ni: 1.00% or less, Mo: 0.1% or less, Bi: 0.01% or less. The method for manufacturing a directional electromagnetic steel sheet according to claim 1 or 2.