JP2017222898A - Production method of grain oriented magnetic steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for stably producing a grain oriented magnetic steel sheet having excellent magnetic property at an industrial scale.SOLUTION: A production method of a grain oriented magnetic steel sheet is provided that is composed of a series of steps including: heating a slab containing, by mass%, C:0.02 to 0.10%, Si:2.5 to 4.5%, Mn:0.06 to 0.15%, S+0.405Se:0.02 to 0.050%, acid soluble Al:0.01 to 0.05%, N:0.002 to 0.015%, P:0.01 to 0.09% and the balance Fe with impurities to more than 1300°C and 1400°C or less; hot- rolling the heated slab; then performing hot rolled sheet annealing on the hot rolled slab; performing one cold rolling or two or more cold rolling sandwiching process annealing on the steel sheet to prepare a cold rolled sheet; then performing decarbonization annealing; applying an annealing separation agent onto a steel sheet surface; and performing final annealing. Heating to a temperature of 800°C or more is performed at a heating rate of 650°C/sec. or more and just before the decarbonization annealing or in a temperature rising process of the decarbonization annealing.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a grain-oriented electrical steel sheet. In particular, the present invention relates to a method for stably producing a grain-oriented electrical steel sheet having excellent magnetic properties on an industrial scale.

  A grain-oriented electrical steel sheet is a steel sheet containing about 2 to 5% of Si and having a crystal grain orientation highly integrated in the {110} <001> orientation, and is mainly used as a core material for stationary machines such as transformers. Used as Control to the {110} <001> orientation is achieved by suppressing normal grain growth in primary recrystallization and utilizing the subsequent grain growth phenomenon called secondary recrystallization. For this purpose, it is indispensable to precisely control fine precipitates and grain boundary segregation elements in steel called inhibitors.

  As a control method of the secondary recrystallization, there is a method in which a precipitate acting as an inhibitor is completely dissolved at the time of heating a steel slab before hot rolling, and then finely precipitated in hot rolling and subsequent annealing steps. For example, MnS and AlN as shown in Patent Document 1 are used as inhibitors and rolling at a rolling reduction exceeding 80% in the final cold rolling process, and MnS and MnSe as shown in Patent Document 2 are used as inhibitors. A method of performing the cold rolling process twice has been industrially implemented. In these methods, the steel slab before hot rolling is heated at a high temperature of 1280 ° C. or higher in order to completely dissolve the precipitate.

  As another control method for secondary recrystallization, for example, as shown in Patent Documents 3 and 4, heating of a steel piece before hot rolling is performed at a temperature of less than 1280 ° C., and nitriding after cold rolling is performed. A method of using AlN formed by treatment as an inhibitor has been industrially implemented.

  In the production of the grain-oriented electrical steel sheet as described above, in order to obtain more excellent magnetic properties, it is effective to improve the orientation in the {110} <001> orientation, and Bi that is considered to strengthen the action of the inhibitor. Means for inclusion is disclosed (Patent Documents 5 and 6). However, when Bi is contained in the steel, it becomes difficult to form a primary film, and there arises a problem that the adhesion deteriorates when an insulating film having a film tension is applied, which is a problem for stable production on an industrial scale. There is. Patent Documents 5 to 8 disclose that a method of rapid heating at the time of decarburization annealing and a rapid heat treatment performed immediately before decarburization annealing to improve the primary recrystallization texture to improve magnetic properties. However, as described above, when Bi is contained, the adhesiveness of the coating is deteriorated, so that there is a problem in stable production on an industrial scale while improving magnetic properties by rapid heating.

Japanese Patent Publication No. 40-15644 Japanese Patent Publication No. 51-13469 Japanese Examined Patent Publication No. 62-45285 Japanese Patent Laid-Open No. 2-77525 JP-A-8-188824 JP 2003-96520 A JP-A-8-295937 JP 2014-91855 A

  An object of the present invention is to provide a method for stably producing a grain-oriented electrical steel sheet having excellent magnetic properties on an industrial scale.

  The inventors of the present invention conducted intensive research on a method capable of stably obtaining a suitable effect on magnetic characteristics obtained by increasing the heating rate during decarburization annealing. As a result, it was found that a grain-oriented electrical steel sheet having excellent magnetic properties can be stably obtained by containing an appropriate amount of P and controlling the heating rate during decarburization annealing according to the P content. . The gist of the present invention based on such new findings is as follows.

That is, the method for producing a grain-oriented electrical steel sheet according to the present invention is mass%, C: 0.02 to 0.10%, Si: 2.5 to 4.5%, Mn: 0.06 to 0.15. %, S + 0.405Se: 0.02-0.050%, acid-soluble Al: 0.01-0.05%, N: 0.002-0.015%, P: 0.01-0.09% The slab containing the remaining Fe and impurities is heated to more than 1300 ° C. and not more than 1400 ° C., hot-rolled, then subjected to hot-rolled sheet annealing, and sandwiched once by cold rolling or intermediate annealing. This is a method for producing a grain-oriented electrical steel sheet comprising a series of steps in which cold rolling is performed to obtain a cold-rolled steel sheet, decarburization annealing is performed, an annealing separator is applied to the steel sheet surface, and then finish annealing is performed. And
Heating is performed at a heating rate of 650 ° C./sec or more and a temperature of 800 ° C. or more immediately before the decarburization annealing or in the temperature raising process of the decarburization annealing.

  In the method for producing a grain-oriented electrical steel sheet according to the present invention, the slab further contains Bi: 0.0005 to 0.0200%, and thus the grain-oriented electrical steel sheet having excellent magnetic properties is stably produced. It is preferable from the point which can be performed.

  Moreover, in the manufacturing method of the grain-oriented electrical steel sheet of this invention, the said slab is further Ni: 0.01-1.50%, Cr: 0.01-0.50%, Cu: 0.01-0. A grain-oriented electrical steel sheet having excellent magnetic properties by containing one or more selected from 50%, Sb: 0.005-0.50%, and Sn: 0.005-0.50% Is preferable because it can be stably produced.

  The present invention can provide a method for stably producing a grain-oriented electrical steel sheet having excellent magnetic properties on an industrial scale. The grain-oriented electrical steel sheet obtained by the present invention is a functional material that supports the increase in global power generation demand, and its industrial value is extremely high.

Hereafter, the manufacturing method of the grain-oriented electrical steel sheet of this invention based on such new knowledge is demonstrated in detail.
In the present invention, “%” represents “% by mass” unless otherwise specified.

The manufacturing method of the grain-oriented electrical steel sheet according to the present invention is, in mass%, C: 0.02-0.10%, Si: 2.5-4.5%, Mn: 0.06-0.15%, S + 0.405Se: 0.02-0.050%, acid-soluble Al: 0.01-0.05%, N: 0.002-0.015%, P: 0.01-0.09% The slab composed of the remaining Fe and impurities is heated to more than 1300 ° C. and not more than 1400 ° C., hot-rolled, then subjected to hot-rolled sheet annealing, and two or more times sandwiching one cold rolling or intermediate annealing. After cold rolling and making a cold-rolled steel sheet, it is a method for producing a grain-oriented electrical steel sheet comprising a series of steps in which decarburization annealing is performed, and an annealing separator is applied to the steel sheet surface and then finish annealing is performed.
Heating is performed at a heating rate of 650 ° C./sec or more and a temperature of 800 ° C. or more immediately before the decarburization annealing or in the temperature raising process of the decarburization annealing.

  According to the method for producing a grain-oriented electrical steel sheet of the present invention, a grain-oriented electrical steel sheet having excellent magnetic properties can be stably produced on an industrial scale.

About the effect | action which said effect can be acquired by the manufacturing method of the said invention, although there is an unclear part, it estimates as follows.
It has been known that magnetic properties are improved by rapid heating during decarburization annealing or rapid heat treatment immediately before decarburization annealing to improve the primary recrystallization texture (for example, Patent Documents 5 to 8). ). However, the conventional method sometimes causes variations in magnetic characteristics.
The present inventors diligently studied to improve magnetic properties by increasing the heating rate during decarburization annealing. As a result, when P is contained, the magnetic characteristics can be improved without excessively increasing the heating rate, and the knowledge that the variation in magnetic characteristics is reduced even when the heating rate is increased. Got. As a result of further studies, the inventors have obtained a grain-oriented electrical steel sheet having excellent magnetic properties and suppressed variation by setting the P content in the slab to 0.01% or more. I found out.
The reason why the magnetic properties have been improved without excessively increasing the heating rate when P is contained in the slab is not clear, but the texture after decarburization annealing, so-called primary recrystallization texture, is not limited to the heating rate. It is presumed that the content is also affected, and a steel having a higher P content can obtain a primary recrystallized texture preferable for improving magnetic properties even if the heating rate is low. Moreover, it is thought that the dispersion | variation in the magnetic characteristic when heating rate is increased excessively originates in the increase in the temperature distribution in a sample, or the change of the progress form of surface layer oxidation at the time of decarburization annealing. P, which has a strong tendency to segregate to grain boundaries, tends to concentrate in the surface layer of the steel sheet, and it is speculated that the inclusion of P in the steel sheet will change the progress of surface oxidation during decarburization annealing. It is considered that the preferable range of the heating rate during the decarburization annealing changed according to the P content through changes in both the form of surface oxidation and the surface layer oxidation, and excellent magnetic properties were stably obtained.
On the other hand, when the P content in the slab exceeds 0.09%, the rolling processability deteriorates and sometimes breaks during production.
From the above, in the method for producing a grain-oriented electrical steel sheet according to the present invention, using a slab having a P content of 0.01 to 0.09%, immediately before decarburization annealing or in the temperature raising process of decarburization annealing, By heating at a heating rate of 650 ° C./sec or more to a temperature of 800 ° C. or more, a grain-oriented electrical steel sheet having excellent magnetic properties and suppressing variations in the magnetic properties can be manufactured.
In addition, according to the present invention, it is possible to reduce the content ratio of Bi, and it is also possible to produce a grain-oriented electrical steel sheet having excellent magnetic properties and excellent film adhesion.
Hereinafter, each process of the manufacturing method of the grain-oriented electrical steel sheet according to the present invention will be described in more detail.

[Slab (steel ingot)]
In the manufacturing method of the grain-oriented electrical steel sheet of the present invention, in mass%, C: 0.02 to 0.10%, Si: 2.5 to 4.5%, Mn: 0.06 to 0.15%, S + 0.405Se: 0.02-0.050%, acid-soluble Al: 0.01-0.05%, N: 0.002-0.015%, P: 0.01-0.09% A slab composed of the remaining Fe and impurities is used.
By using the slab, a grain-oriented electrical steel sheet having excellent magnetic characteristics and suppressed variation can be obtained.

  In the present invention, the slab is at least one of C (carbon), Si (silicon), Mn (manganese), S (sulfur) and Se (selenium), acid-soluble Al (aluminum), N (nitrogen), and It contains P (phosphorus) and may contain Bi (bismuth), Ni (nickel), Cr (chromium), Cu (copper), Sb (antimony), and Sn (tin). The composition may contain impurities as long as they are not damaged, and the balance is composed of Fe (iron).

(C: 0.02-0.10%)
In the present invention, the slab contains 0.02 to 0.10% of C. By setting the C content to 0.02% or more, it is possible to suppress excessively coarsening of crystal grains in slab heating prior to hot rolling, and secondary recrystallization failure can be suppressed. In addition, by making the C content 0.10% or less, decarburization proceeds sufficiently even if the decarburization time in decarburization annealing after cold rolling is short, and suppresses magnetic property defects called magnetic aging. can do.

(Si: 2.5-4.5%)
In the present invention, the slab contains 2.5 to 4.5% of Si. By containing Si, the electrical resistance of steel in the grain-oriented electrical steel sheet can be increased, and eddy current loss constituting a part of iron loss can be reduced. From the viewpoint of reducing eddy current loss, the Si content is 2.5% or more, and preferably 3.0% or more. On the other hand, from the viewpoint of improving the magnetic flux density of the grain-oriented electrical steel sheet and workability at the time of rolling, the Si content is 4.5% or less, preferably 3.4% or less.

(Mn: 0.06 to 0.15%)
In the present invention, the slab contains 0.06 to 0.15% of Mn. Mn combines with S or Se described later to form MnS or MnSe, and acts as an inhibitor of secondary recrystallization. If the Mn content is 0.06% or more, sufficient MnS or MnSe can be obtained. On the other hand, when the Mn content is 0.15% or less, Mn can be easily dissolved during slab heating, and MnS or MnSe having an appropriate particle size as an inhibitor can be obtained during hot rolling. From such a viewpoint, the Mn content is preferably 0.09% or less.

(S + 0.405Se: 0.02-0.050%)
In the present invention, the slab contains 0.02 to 0.050% of S + 0.405Se (that is, the sum of the mass of S and 0.405 times the mass of Se). S and Se form MnS or MnSe in combination with Mn. In the present invention, only one of S and Se may be contained, or both S and Se may be contained. From the viewpoint of obtaining a sufficient effect as an inhibitor, the content of S + 0.405Se may be 0.01% or more, preferably 0.022% or more. Moreover, the upper limit of S + 0.405Se is 0.050%, and preferably 0.030% or less.

(Acid-soluble Al: 0.01 to 0.05%)
In the present invention, the slab contains 0.01 to 0.05% of acid-soluble Al. Acid-soluble Al combines with N described later to form AlN and acts as an inhibitor. By containing 0.01% or more of acid-soluble Al, the magnetic flux density of the grain-oriented electrical steel sheet can be improved. In addition, by setting the content of acid-soluble Al to 0.05% or less, AlN deposited as an inhibitor can suppress coarsening, suppress a decrease in inhibitor strength, and reduce the magnetic flux density of the grain-oriented electrical steel sheet. Can be improved. From such a viewpoint, the content of acid-soluble Al is 0.01 to 0.05%, and preferably 0.02% or more and 0.03% or less.

(N: 0.002 to 0.015%)
In the present invention, the slab contains 0.002 to 0.015% of N. N forms AlN in combination with the acid-soluble Al, and acts as an inhibitor. Among these, the N content is preferably 0.005% or more and 0.012% or less.

(P: 0.01-0.09%)
In the present invention, the slab contains 0.01 to 0.09% of P. By containing 0.01% or more of P, a grain-oriented electrical steel sheet having excellent magnetic properties and suppressed variation can be obtained. In the present invention, it is preferable to contain 0.02% or more of P, more preferably 0.025% or more, and even more preferably 0.03% or more.
On the other hand, when the content of P in the slab is set to 0.09% or less, it is possible to suppress the rolling processability from being excessively reduced, and it is possible to suppress breakage during manufacturing. From such a viewpoint, the P content is more preferably 0.08% or less.

(Bi)
In the present invention, the slab may further contain Bi. By containing Bi, the magnetic properties can be improved. In the method for producing a grain-oriented electrical steel sheet according to the present invention, since the slab contains 0.01% or more of P, if the Bi content is 0.0005% or more, the magnetic properties can be obtained by combining with P. It can be improved further. Moreover, in this invention, the content rate of Bi shall be 0.0200% or less, and the reduction | decrease of the film | membrane adhesiveness by containing Bi can be suppressed, improving a magnetic characteristic.
For these reasons, when the slab contains Bi in the present invention, the content is 0.0005 to 0.0200% from the viewpoint of improving the magnetic properties and suppressing the reduction of the film adhesion. It is preferable that it is 0.0007% or more and 0.0100% or less.

  In the present invention, the slab is an element that stabilizes secondary recrystallization. Ni: 0.01 to 1.50%, Cr: 0.01 to 0.50%, Cu: 0.01 to 0.50 %, Sb: 0.005 to 0.50% and Sn: 0.005 to 0.50% may be included.

Furthermore, in the present invention, the slab may contain various elements (impurities) that are inevitably mixed within a range that does not impair the effects of the present invention. Examples of such elements include Ti (titanium), Nb (niobium), and Mo (molybdenum) in addition to C, N, and S.
In the present invention, the content of impurities in the slab is preferably 0.15% or less, and more preferably 0.10% or less.

The content ratio of each element in the slab used in the present invention can be measured by known methods under the following method according to the kind of element.
Si, Mn, Se, Al, Bi, Ni, Cr, Cu, Sb, and Sn can be measured by inductively coupled plasma mass spectrometry (ICP-MS method).
C, S, and P can be measured by a combustion infrared absorption method.
Further, N can be measured by a heat melting-heat conduction method.
In addition, the ratio of each element may change in the decarburization annealing process and finish annealing process which will be described later. Therefore, the chemical composition of the slab may differ from the chemical composition of the grain-oriented electrical steel sheet obtained by the production method of the present invention. However, since the content ratios of P, Si, and Mn contained in the grain-oriented electrical steel sheet are substantially equal to the content ratio in the slab, these elements are contained in the slab from the obtained grain-oriented electrical steel sheet. The percentage can be determined.

Next, the manufacturing process will be described.
First, molten steel for producing grain-oriented electrical steel sheets having an appropriate chemical composition is cast to obtain a slab (steel ingot) having the above composition. The casting method is not particularly limited, and a conventionally known method can be appropriately selected and used.
Next, hot rolling is performed on the obtained slab. In this invention, it heats so that the surface temperature of the slab at the time of hot rolling may become 1400 degreeC or more exceeding 1300 degreeC. By setting the surface temperature of the slab to above 1300 ° C., the inhibitor is sufficiently solid-solved, so that a grain-oriented electrical steel sheet having excellent magnetic properties and suppressed variation can be obtained. On the other hand, a surface temperature of 1400 ° C. or lower is sufficient from the viewpoint of magnetic properties, and by setting it to 1400 ° C. or lower, manufacturing costs can be suppressed without using special equipment.
In the present invention, the holding time of the surface temperature of the slab may be adjusted as appropriate. In view of obtaining a grain-oriented electrical steel sheet having excellent magnetic characteristics and suppressed variation, it is preferably set to 5 minutes or more. On the other hand, 60 minutes or less is sufficient from the viewpoint of magnetic characteristics, and 60 minutes or less is preferable from the viewpoint of improving productivity and suppressing manufacturing costs.
Although the thickness of the steel plate after hot rolling is not specifically limited, For example, it can be set as 1.8-3.5 mm. Other conditions related to hot rolling are not particularly limited, and may be adjusted as appropriate.

  After hot rolling, hot-rolled sheet annealing is performed for the purpose of improving magnetic properties. Hot-rolled sheet annealing is not particularly limited, and a known method may be selected as appropriate. For example, the hot-rolled sheet annealing can be performed in a temperature range of 750 to 1200 ° C. for 30 seconds to 10 minutes. The steel sheet after hot-rolled sheet annealing may be pickled as necessary.

Next, the cold rolled steel sheet is formed by performing one cold rolling or two or more cold rolling sandwiching the intermediate annealing. One cold rolling means finishing to a desired plate thickness by letting the rolling mill pass once or a plurality of times without intermediate annealing. Moreover, intermediate annealing is an annealing process performed after making it into an intermediate thickness by letting a rolling mill pass once or a plurality of times, and after the intermediate annealing, by passing the rolling mill once or a plurality of times. Finish to desired thickness. The cold rolling twice or more including intermediate annealing means cold rolling in which the intermediate annealing is performed once or more.
The intermediate annealing conditions are not particularly limited, and may be selected as appropriate, for example, in a temperature range of 750 to 1200 ° C. for 30 seconds to 10 minutes. Here, when letting a rolling mill pass a plurality of times, it is preferable to carry out rolling after heating the steel plate to about 300 ° C. or less between rollings to improve magnetic properties.

Next, the obtained cold-rolled steel sheet is subjected to decarburization annealing. In the method for producing a grain-oriented electrical steel sheet according to the present invention, heating is performed at a heating rate of 650 ° C./sec or more and a temperature of 800 ° C. or more immediately before decarburization annealing or in a temperature raising process of decarburization annealing. And In the present invention, since the slab contains 0.01% or more of P, by heating to a temperature of 650 ° C./sec or more and 800 ° C. or more, it has excellent magnetic properties and suppresses variation. The obtained grain-oriented electrical steel sheet is obtained.
The upper limit of the heating rate is not particularly limited, but it is usually preferably 1500 ° C./sec or less from the viewpoint of device restrictions and the like. In the present invention, the heating rate is an average heating rate from 300 ° C. to the ultimate temperature. In order to obtain such a high heating rate, it is preferable to employ induction heating or electric heating as a heating method. In order to achieve a sufficient heating rate for obtaining the effects of the present invention, an induction heating method is preferred. From the viewpoint of process simplification, it is desirable to incorporate the above heat treatment at the time of heating in the decarburization annealing process.
The upper limit of the reached temperature is not particularly limited, but is preferably 1000 ° C. or lower.

Furthermore, as a result of intensive studies, when the content ratio of P in the slab and the heating rate satisfy the following relational expression (1), the directional electromagnetic wave having particularly excellent magnetic characteristics and suppressed variation. It became clear that a steel plate was obtained.
Formula (1): [Heating rate] ≧ 930-12000 × [% P]
(Here, [% P] represents the content (mass%) of P in the slab. The unit of [heating rate] is (° C./sec).)
According to the above formula (1), it can be seen that increasing the P content in the slab can improve the magnetic properties without excessively increasing the heating rate.

After decarburization annealing, an annealing separator is applied and dried on the steel sheet surface, and then finish annealing is performed. Finish annealing is a step of secondary recrystallization of {110} <001> oriented grains, and is extremely important for improving the magnetic properties of the steel sheet. The finish annealing method is not particularly limited. For example, after the secondary recrystallization is developed in the process of raising the temperature to 1100 to 1200 ° C. in a nitrogen-hydrogen mixed atmosphere, the hydrogen annealing atmosphere is changed to 1100 to 1200 ° C. By performing annealing for about 20 hours at a temperature, N, S, Se, etc. can be diffused and removed out of the steel sheet, and the magnetic properties of the product plate can be improved.
As said annealing separation agent, it can select suitably from conventionally well-known things and can use it. In the present invention, an annealing separator containing MgO (magnesium oxide) is preferable from the viewpoint of improving magnetic properties, and an annealing separator containing MgO as a main component is more preferable.

In the manufacturing method of the grain-oriented electrical steel sheet according to the present invention, other steps may be included as long as the effects of the present invention are not impaired.
For example, after finish annealing, an insulating coating may be further applied on the primary coating of the steel plate. In particular, an insulating coating obtained by baking a coating solution mainly composed of phosphate and colloidal silica has a large tension applied to the steel sheet, and is effective in improving iron loss.
Further, the grain-oriented electrical steel sheet may be subjected to a so-called magnetic domain refinement process by laser irradiation, plasma irradiation, tooth roll, etching or the like.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

Hereinafter, the present invention will be described specifically by way of examples and comparative examples.
[Example 1]
C: 0.08%, Si: 3.2%, Mn: 0.08%, S: 0.025%, acid-soluble Al: 0.024%, N: 0.008%, Bi: 0.0035% , P: 0.008% to 0.10%, the remainder of Fe and impurities slab is heated to 1350 ° C. and held for 30 minutes, then hot-rolled to a 2.3 mm thick hot rolled A coil was used. The hot-rolled coil was subjected to hot-rolled sheet annealing that was held at 1120 ° C. for 120 seconds, then pickled, and cold-rolled to a thickness of 0.22 mm. The obtained cold-rolled steel sheet was subjected to decarburization annealing in wet hydrogen at 850 ° C. for 120 seconds. In the heating process of the decarburization annealing, the ultimate temperature was 850 ° C., and the heating rate was changed in the range of 20 ° C./second to 1000 ° C./second. After the decarburization annealing, an annealing separator containing MgO as a main component was applied to the steel sheet surface and subjected to a final annealing at 1150 ° C. for 20 hours. After the finish annealing, excess MgO of the steel sheet was removed and sheared into a single-plate magnetic measurement test piece to form an insulating film composed mainly of colloidal silica and aluminum phosphate. About the obtained steel plate, while measuring magnetic flux density B8 (magnetic flux density at the time of magnetizing by 800 A / m) by single plate magnetic measurement (SST), the primary film was evaluated.

  Table 1 shows the evaluation results of B8 and the primary coating, together with the P content and the heating rate. The coating evaluation was performed by bending a test piece along a 10φ cylinder and expressing the peeling state of the coating by internal bending, with A being the best and then B, C, and D. Scores A and B were accepted. The magnetic characteristics improved with an increase in the heating rate. However, when the conditions for the P content and the heating rate of the present invention were not satisfied, the evaluation of the film was C or D. Although the magnetic properties increase with increasing heating rate, the adhesion of the coating was inferior for steels with P content below the scope of the present invention. In addition, steel with a P content exceeding the scope of the present invention could not be subjected to subsequent steps because it broke during cold rolling. Under conditions where the P content and the heating rate satisfy the scope of the present invention, both the magnetic properties and the film evaluation were excellent.

[Example 2]
The steel composition slabs shown in Table 2 were held at various temperatures for 50 minutes and then finished to a thickness of 2.0 mm to 2.5 mm by hot rolling. These hot-rolled sheets were subjected to hot-rolled sheet annealing at 1100 ° C. for 100 seconds, and finished to a sheet thickness of 0.22 mm by cold rolling after pickling. About the steel plates of test numbers 2-1 and 2-3, after finishing by cold rolling to an intermediate thickness, intermediate annealing was performed at 1050 ° C. for 100 seconds, and finished to a thickness of 0.22 mm by cold rolling. The obtained cold-rolled steel sheet was subjected to decarburization annealing in wet hydrogen at 850 ° C. for 120 seconds. In the heating process of decarburization annealing, the ultimate temperature was 850 ° C., and the heating rate was 900 ° C./second. After the decarburization annealing, an annealing separator containing MgO as a main component was applied to the steel sheet surface and subjected to a final annealing at 1150 ° C. for 20 hours. After the finish annealing, excess MgO of the steel sheet was removed and sheared into a single-plate magnetic measurement test piece to form an insulating film composed mainly of colloidal silica and aluminum phosphate. About the obtained steel plate, while measuring magnetic flux density B8 similarly to Example 1, the primary film was evaluated. Table 3 shows the evaluation results together with the slab heating temperature, hot-rolled plate thickness, and intermediate plate thickness.

  In Test No. 2-9, the slab heating temperature was below the range limited by the present invention, and the magnetic properties were particularly inferior. In Test No. 2-10, the steel composition limited in the present invention, particularly the element acting as an inhibitor was outside the scope of the present invention, and the magnetic properties were particularly inferior. On the other hand, test numbers 2-1 to 2-8 and 2-11 satisfied the conditions limited in the present invention, and desired magnetic characteristics were obtained and the film evaluation was excellent.

Claims (3)

In mass%, C: 0.02-0.10%, Si: 2.5-4.5%, Mn: 0.06-0.15%, S + 0.405Se: 0.02-0.050%, A slab containing acid-soluble Al: 0.01 to 0.05%, N: 0.002 to 0.015%, P: 0.01 to 0.09%, and remaining Fe and impurities exceeding 1300 ° C After heating to 1400 ° C. or less and hot rolling, hot-rolled sheet annealing is performed, and after cold rolling or intermediate cold annealing is performed twice or more to form a cold-rolled steel sheet, It is a method for producing a grain-oriented electrical steel sheet comprising a series of steps of performing decarburization annealing, applying an annealing separator to the steel sheet surface, and then performing finish annealing,
A method for producing a grain-oriented electrical steel sheet, wherein heating is performed at a heating rate of 650 ° C./sec or more and a temperature of 800 ° C. or more immediately before the decarburization annealing or in the temperature raising process of the decarburization annealing.   The method for manufacturing a grain-oriented electrical steel sheet according to claim 1, wherein the slab further contains Bi: 0.0005 to 0.0200%.   The slab further contains Ni: 0.01 to 1.50%, Cr: 0.01 to 0.50%, Cu: 0.01 to 0.50%, Sb: 0.005 to 0.50%, and Sn. The method for producing a grain-oriented electrical steel sheet according to claim 1, comprising one or more selected from 0.005 to 0.50%.