JP5228563B2 - Method for producing grain-oriented electrical steel sheet - Google Patents

Description

  The present invention relates to a method for producing a grain-oriented electrical steel sheet that is suitable for use as a core material of a transformer.

Directional electrical steel sheets are used for large voltage transformers and pole transformers to reduce energy loss. The grain-oriented electrical steel sheet orients the <001> orientation, which is the easy axis of iron, in one direction by selectively growing only grains having the {110} <001> orientation called the Goss orientation. Energy loss called loss is reduced.
Since the iron loss is preferably as low as possible, it not only improves the degree of orientation in the <001> orientation, but also reduces the magnetic domain width by, for example, applying a treatment called magnetic domain refinement to the steel sheet, and moves the domain wall during excitation. Low iron loss has been achieved by shortening the distance.

As a method for subdividing the magnetic domain, a method of introducing physical grooves and strains almost perpendicular to the rolling direction oriented in the <001> direction is generally used. A method of reducing (Patent Document 1), a method of introducing thermal strain by plasma irradiation (Patent Document 2), a method of introducing thermal strain by laser irradiation (Patent Document 3), and a method of chemically etching (Patent Document 4) Etc. have been developed.
JP 60-96719 Japanese Patent Publication No. 7-72300 Japanese Patent Publication No.58-26405 Japanese Patent Publication No. 6-57857

In addition, a method is also known in which the surface of a steel plate is smoothed like a mirror surface to remove obstacles during domain wall movement, thereby smoothing the movement and reducing iron loss. As a mirror surface method, various additives are added to MgO used as an annealing separator to weaken the bond at the interface between forsterite and ground iron, and then peel off after forsterite formation ( Patent Documents 5 and 6), a method of physically or chemically removing a forsterite film after it has been formed (Patent Document 7), and a method of using an oxide or inorganic material that does not form forsterite as an annealing separator (patent Documents 8, 9) have been proposed.
Japanese Patent Laid-Open No. 2-228481 JP 7-173642 A Japanese Patent Publication No. 3-74488 JP-A-5-156362 JP-A-5-43943

Among the conventional methods described above, in order to prevent the formation of a forsterite film, a method of using alumina as an annealing separator has been actively studied.
Since alumina is inexpensive and has various particle sizes, it is easy to change the applicability and the adhesion to the steel sheet by adjusting the particle size. In addition, since alumina is a very stable substance, for example, oxygen of alumina is released, and there is no possibility that Si and oxides in steel are formed to deteriorate characteristics.

However, when considering the reduction of iron loss by surface mirroring without forming a forsterite film, it was found that if final finish annealing was performed at a high temperature such as 1200 ° C, the magnetic properties deteriorated. .
Such a phenomenon is a phenomenon that did not occur in the case of a normal method of manufacturing a grain-oriented electrical steel sheet for forming a forsterite film.

  The present invention advantageously solves the above-described problem, and is a grain-oriented electrical steel sheet that does not cause deterioration of magnetic properties even in the final finish annealing of a material having a mirror-finished surface (hereinafter referred to as a mirror-finished material). The purpose is to propose a new manufacturing method.

Now, the inventors to solve the deterioration of the magnetic properties of concern during the final finish annealing of mirror-material, a result of intensive studies, the final Finish sintered blunt surface before the steel sheet is smoothed, and the final It has been found that magnetic property deterioration can be advantageously avoided by lowering the finish annealing temperature.
The present invention is based on the above findings.

That is, the gist configuration of the present invention is as follows.
1. Hot rolling a steel slab containing, by mass%, C: 0.10% or less, Si: 2.0-8.0%, Mn: 0.005-1.0% and S: 0.0005-0.0026% , the balance being Fe and inevitable impurities Then, after performing hot-rolled sheet annealing as necessary, it is cold-rolled at least once with one or two intermediate sandwiches to make the final cold-rolled sheet, and then applied with an annealing separator after primary recrystallization annealing Then, in producing a grain-oriented electrical steel sheet through a series of manufacturing processes for final finishing annealing,
The surface roughness of the steel sheet before the final finish annealing should be 0.3 μm or less in arithmetic mean roughness Ra, and the final finish annealing should be performed at a temperature of 1100 ° C. or lower using an alumina-based separator as the annealing separator. A method for producing a grain-oriented electrical steel sheet that does not have a forsterite coating.

2. The steel slab is further mass%, Ni: 0.010-1.50%, Cr: 0.01-0.50%, Cu: 0.01-0.50%, P: 0.005-0.50%, Nb: 0.003-0.050%, Sn: 0.005-0.50. %, Sb: 0.005 to 0.50%, Bi: 0.005 to 0.50%, Mo: 0.005 to 0.10%, Al: 0.0010 to 0.0097 %, and N: 0.0005 to 0.0036%. 2. The method for producing a grain-oriented electrical steel sheet according to 1 above, wherein the composition is a composition.

In accordance with the present invention, the final Finish sintered blunt surface before the steel sheet is smoothed, and the final annealing temperature by low temperature, can be obtained oriented electrical steel sheet having no excellent forsterite film on the magnetic properties .

Hereinafter, the present invention will be specifically described.
First, an experiment that is the basis of the present invention will be described. Unless otherwise specified, “%” in relation to ingredients means mass%.

<Experiment 1>
Steel slab containing C: 600ppm, Si: 3.28%, Mn: 0.07%, S: 0.0020%, Se: 0.0035%, Cr: 0.02% and Sb: 0.050%, with the balance being Fe and inevitable impurities Is manufactured by continuous casting, heated to slab at 1250 ° C, hot rolled to 2.5 mm thickness, then annealed at 1000 ° C for 60 seconds and then rolled to a thickness of 0.60 mm by the first cold rolling. Say it. Then, after intermediate annealing at 1000 ° C. for 60 seconds, a cold rolled sheet having a thickness of 0.23 mm was finished by the second cold rolling (final cold rolling). Thereafter, after decarburization annealing was performed at 820 ° C. for 90 seconds, slurry-like alumina suspended in water was applied to the surface of the steel plate and baked at 200 ° C. Furthermore, after final holding at 850 ° C. for 20 hours, final finish annealing was performed by raising the temperature to the final temperature and holding for 10 hours. At this time, the experiment was performed with various changes in the final temperature.
A sample is taken from the obtained _grain- oriented electrical steel sheet, and the result of measuring the iron loss W _{17/50 of the} sample by the method described in JIS C 2550 is shown in FIG.
As shown in the figure, it was found that the iron loss deteriorates when the final final annealing temperature reached 1100 ° C.

However, even at temperatures below 1100 ° C., the obtained iron loss values were somewhat worse than expected.
Therefore, analysis of trace elements in the railway was conducted. As a result, it was found that the amount of S in the ground iron had an adverse effect on iron loss.

  That is, in the conventional grain-oriented electrical steel sheet, since S in the ground iron is less than 5 ppm (analysis limit), this S did not adversely affect the iron loss. It was found that 10 to 17 ppm of S remained in the ground iron when the final reached temperature of 1125 ° C. or higher, and 6 to 11 ppm of S remained in the ground iron even when it was less than 1125 ° C. It is presumed that S in the ground iron deteriorates magnetism.

As a result of further studies, it was found that the surface roughness of the steel sheet before final finish annealing is strongly involved in the purification of S.
<Experiment 2>
Using a steel slab with the same composition as in Experiment 1, after heating the slab at 1250 ° C to a thickness of 2.5 mm by hot rolling, then annealing at 1000 ° C for 60 seconds, followed by the first cold rolling The thickness was 0.60 mm. Then, after intermediate annealing at 1000 ° C. for 60 seconds, a cold rolled sheet having a thickness of 0.23 mm was finished by the second cold rolling (final cold rolling). Thereafter, after decarburization annealing was performed at 820 ° C. for 90 seconds, the surface roughness of the steel sheet was variously changed by treatment with an acid obtained by adding 5% hydrofluoric acid to hydrogen peroxide. Thereafter, slurry-like alumina suspended in water was applied to the surface of the steel sheet and baked at 200 ° C. Further, after final holding at 850 ° C. for 20 hours, final finish annealing was performed in which the temperature was raised to 1100 ° C. and held for 10 hours.
A sample is taken from the obtained _grain- oriented electrical steel sheet, and the result of measuring the iron loss W _{17/50 of the} sample by the method described in JIS C 2550 is shown in FIG.

As shown in the figure, the iron loss is improved by setting the surface roughness of the steel sheet before final finish annealing to an arithmetic average roughness Ra of 0.3 or less.
Further, when the amount of S in the ground iron was investigated, it was found that the amount of S was reduced to less than 5 ppm (analysis limit) in a sample with low surface roughness Ra and good iron loss.

The reason why the magnetic properties are improved by setting the final finish annealing temperature to 1100 ° C. or less and reducing the surface roughness is not necessarily clear, but the inventors consider as follows.
When a forsterite film is formed on the surface like a normal grain-oriented electrical steel sheet, impurities such as S in the steel are considered to be trapped in the forsterite film by purification annealing. However, in a mirror-finishing material using a substance that does not form a surface film as an annealing separator (for example, alumina), there is no place where impurities are trapped. At this time, it is considered that S in the ground iron reacts with hydrogen to be separated as hydrogen sulfide. Since the standard free energy of formation of gas is generally higher at higher temperatures, in this experiment, the standard free energy of formation changes from a negative value to a positive value when the final temperature exceeds 1100 ° C. It is presumed that the reaction became so high that it did not react, that is, hydrogen sulfide was no longer produced. Furthermore, since the final finish annealing is usually applied to the steel sheet wound in a coil shape, the steel sheet surfaces are in contact with each other through an annealing separator. . At this time, when the surface roughness of the steel sheet is large and uneven, a part of the hydrogen sulfide that has become a gas stops in the recess, and under some circumstances, S returns to the ground iron again, deteriorating the magnetic properties. It is estimated that

Hereinafter, the reason why the component composition of the steel slab is limited to the above range in the present invention will be described.
C: 0.10% or less C is a useful element that homogenizes the structure after hot rolling by improving the γ transformation and improves the magnetic properties, but if the content exceeds 0.10%, 50 ppm or less where magnetic aging does not occur Therefore, the amount of C is limited to 0.10% or less.

Si: 2.0-8.0%
Si is an element necessary to increase the specific resistance of steel and improve iron loss, but if the content is less than 2.0%, it is difficult to obtain a sufficient effect, while if it exceeds 8.0%, the workability of steel deteriorates. However, since rolling becomes difficult, the Si content is limited to a range of 2.0 to 8.0%.

Mn: 0.005 to 1.0%
Mn is an element necessary for improving the hot workability, but if the content is not less than 0.005%, the effect of addition is poor, while if it exceeds 1.0%, the magnetic flux density of the product plate decreases. The amount of Mn was limited to a range of 0.005 to 1.0%.

S: 0.0005 to 0.0026 %
S is considered to be the main cause of deterioration of magnetic characteristics. According to the present invention, the adverse effect of S can be effectively eliminated even in the mirror- finished material, but if the content exceeds 0.0026 %, it is difficult to avoid deterioration of the magnetic properties even with the present invention. The upper limit was set to 0.0026 %. On the other hand, when the S amount is less than 0.0005% at the material stage, it is not necessary to apply the present invention, so the lower limit of the S amount is set to 0.0005%.

As described above, the essential component and the suppressing component have been described. In addition, in the present invention, the following elements can be appropriately contained from the viewpoint of improving the texture by improving the texture.
Ni: 0.010 to 1.50%
Ni is an element useful for improving the magnetic properties by improving the hot-rolled sheet structure. However, if the content is less than 0.010%, the improvement in magnetic properties is small. On the other hand, if it exceeds 1.50%, secondary recrystallization becomes unstable and the magnetic properties deteriorate, so Ni is contained in the range of 0.010 to 1.50%. It is preferable.

Cr: 0.01 to 0.50%, Cu: 0.01 to 0.50%, P: 0.005 to 0.50%
Cr, Cu, and P are all useful elements for improving iron loss. However, if the content is less than the lower limit, the effect of addition is poor. On the other hand, the growth of secondary recrystallized grains is suppressed when the upper limit is exceeded. Since the magnetic properties are deteriorated, each of them is included in the above range.

Nb: 0.003-0.050%, Sn: 0.005-0.50%, Sb: 0.005-0.50%, Bi: 0.005-0.50%, Mo: 0.005-0.10%, Al: 0.0010-0.0097 %, N: 0.0005-0.0036%
Nb, Sn, Sb, Bi, Mo, Al, and N are all useful elements for improving the magnetic flux density. However, if the content is less than the lower limit, the addition effect is poor, while if the upper limit is exceeded, the secondary is secondary. Since the development of recrystallized grains is suppressed and the magnetic properties are deteriorated, each of them is included in the above range.

  In addition, the above-mentioned selective component may be added either alone or in combination.

Next, the manufacturing method of this invention is demonstrated.
The slab adjusted to the above suitable component composition range is produced by a normal ingot-making method and a continuous casting method. Further, a thin cast piece having a thickness of 100 mm or less may be manufactured by a direct casting method.
Next, the slab is usually heated and subjected to hot rolling, but may be immediately subjected to hot rolling without being heated after casting. In the case of a thin slab, hot rolling may be performed, or the hot rolling may be omitted and the subsequent process may be performed as it is. The slab heating temperature prior to hot rolling does not require high-temperature annealing to dissolve the inhibitor, which was essential in the past, in the case of a component system that does not contain an inhibitor component with reduced Al, N, S, and Se. Therefore, a low temperature of 1250 ° C. or lower is desirable in terms of cost .

  Next, hot-rolled sheet annealing is performed as necessary. In order to obtain good magnetism, the hot-rolled sheet annealing temperature is preferably 800 ° C or higher and 1150 ° C or lower. When the hot-rolled sheet annealing temperature is less than 800 ° C., a band structure in hot rolling remains, and it becomes difficult to realize a primary recrystallized structure of sized particles, thereby inhibiting the development of secondary recrystallization. On the other hand, when the hot-rolled sheet annealing temperature exceeds 1150 ° C., the grain size after the hot-rolled sheet annealing is excessively coarsened, which is extremely disadvantageous in realizing the primary recrystallized structure of sized particles.

  After hot-rolled sheet annealing, after finishing to the final sheet thickness by one or more cold rolling processes including intermediate annealing, primary recrystallization annealing is performed. In the cold rolling process, increasing the temperature to 100 to 300 ° C, or performing aging treatment in the range of 100 to 300 ° C one or more times during the cold rolling improves the magnetic properties. It is effective on The primary recrystallization annealing is performed in a wet atmosphere when decarburization is required, but may be performed in a dry atmosphere when decarburization is not required. After the primary recrystallization annealing, a technique for increasing the Si amount by a siliconization method may be used in combination.

Thereafter, an alumina-based separating agent is applied in the form of a slurry as an annealing separator. Here, the alumina-based separating agent means that alumina is contained in an amount of mass% exceeding at least 50% of the annealing separating agent component. In addition to alumina, there is no problem if a conventionally known component such as CaO or SiO ₂ is contained, but from the viewpoint of magnetic properties, it is desirable to contain 90% or more of alumina.

After applying the annealing separator, a final finish annealing is performed. As described above, it is important that the surface roughness of the steel sheet before the final finish annealing is 0.3 μm or less in terms of arithmetic average roughness Ra.
Here, as a means for reducing the surface roughness of the steel sheet before final finish annealing, a pickling method, a method of mechanically polishing the surface, and the like can be considered. Particularly preferred is a method of adjusting the surface roughness by immersing in a mixed solution of hydrogen water and hydrofluoric acid for 5 seconds or more and changing the concentration of hydrofluoric acid and the immersion time.

  The final finish annealing needs to be performed at 750 ° C. or higher for secondary recrystallization, but it is desirable to hold at a temperature of 800 ° C. or higher for 5 hours or longer in order to complete the secondary recrystallization. Moreover, in order to purify impurities in the steel, it is desirable to hold at 1000 ° C. or higher for 1 hour or longer. However, if the temperature exceeds 1100 ° C, the magnetic properties deteriorate due to the reasons described above, so the maximum temperature reached is limited to 1100 ° C or less. Since the optimal temperature for secondary recrystallization and the optimal temperature for purification are often different, it is desirable to first hold at the optimal temperature for secondary recrystallization and then raise the temperature to the optimal temperature for purification. .

After final finish annealing, it is useful to perform water washing, brushing, and pickling to remove the adhered alumina. After that, correcting the shape by flattening annealing is effective for reducing iron loss.
Moreover, when using it, laminating | stacking a steel plate, in order to improve an iron loss, it is effective to give an insulating coating to the steel plate surface before or after planarization annealing. In order to reduce iron loss, it is desirable to provide a tension coating. Since the steel plate surface is smoothed, the coating method with excellent adhesion can be obtained and the iron loss can be reduced by applying the coating method by tension coating via binder or by depositing inorganic material on the steel plate surface by CVD and PVD. Since the effect is also remarkable, it is particularly suitable.

Example 1
Steel slab containing C: 220ppm, Si: 3.20%, Mn: 0.068%, S: 0.0026%, Sn: 0.059%, Al: 0.0085% and N: 0.0035%, with the balance being Fe and inevitable impurities Is manufactured by continuous casting, heated to 1200 ° C, slab heated to 2.5 mm thick by hot rolling, and then annealed at 1000 ° C for 45 seconds by hot rolling and then cold rolled to a thickness of 0.23 mm Finished on a board. Thereafter, after decarburization annealing was performed at 850 ° C. for 90 seconds under a soaking condition, Ra on the steel sheet surface was variously changed as shown in Table 1 by pickling. At this time, the surface roughness Ra was adjusted by polishing the surface using No. 600 emery paper to increase Ra, or by immersing in 5% hydrofluoric acid-hydrogen peroxide solution to decrease Ra. .

Then, an alumina: 100 mass% annealing separator was applied in the form of a slurry to the surface of the steel sheet and baked at 200.degree. Thereafter, after holding at 850 ° C. for 20 hours, as shown in Table 1, final finishing annealing was performed in which the maximum temperature reached was variously changed and held for 10 hours. Thereafter, the adhering alumina was removed by washing with water, and TiN was deposited on the surface layer of the steel sheet by a CVD method to form a coating.
A sample for magnetic measurement was taken from the _grain- oriented electrical steel sheet thus obtained, and the magnetic properties (iron loss W _17/50 ) were measured according to the method described in JIS C 2550.
The obtained results are also shown in Table 1.

  As is clear from the table, according to the present invention, the surface roughness of the steel sheet before final finish annealing is 0.3 μm or less in Ra, and the final finish annealing temperature is applied under the condition that the maximum temperature is 1100 ° C. or less. In this case, good magnetic properties could be obtained.

Example 2
Steel slabs with the composition shown in Table 2 were manufactured by continuous casting, heated to 1400 ° C, slab heated to 2.2 mm thick, then annealed at 1100 ° C for 20 seconds for 20 seconds, first time The sheet thickness was set to an intermediate thickness of 0.60 mm by cold rolling. Then, after intermediate annealing at 950 ° C. for 60 seconds, a cold rolled sheet having a thickness of 0.20 mm was finished by the second cold rolling. Thereafter, after decarburization annealing was performed at 820 ° C. for 90 seconds, the surface roughness of the steel sheet was adjusted to 0.22 to 0.29 μm in Ra by pickling. Here, the surface roughness was adjusted by dipping in a 5% hydrofluoric acid-hydrogen peroxide aqueous solution.

Next, an alumina annealing separator having a composition of alumina: 98% by mass and silica: 2% by mass was applied in the form of a slurry to the surface of the steel sheet and baked at 200 ° C. Then, after hold | maintaining at 900 degreeC for 30 hours, the final finishing annealing which hold | maintains at 1100 degreeC for 5 hours was performed. Thereafter, the adhering alumina was removed by washing with water, and TiN was deposited on the surface layer of the steel sheet by a CVD method to form a coating.
A sample for magnetic measurement was taken from the _grain- oriented electrical steel sheet thus obtained, and the magnetic properties (iron loss W _17/50 ) were measured according to the method described in JIS C 2550.
The obtained results are also shown in Table 2.

  As is clear from the table, according to the present invention, it is set as an appropriate component, the surface roughness of the steel plate before final finish annealing is set to 0.3 μm or less with Ra, and the final achieved temperature is 1100 ° C. or less. It can be seen that good magnetic properties are obtained when the finish annealing temperature is applied. In all of the comparative examples of Nos. 2 to 4, secondary recrystallized grains did not appear.

It is the figure which showed the relationship between the final ultimate temperature at the time of final finishing annealing, and an iron loss. It is the figure which showed the relationship between the steel sheet surface roughness Ra before final finishing annealing, and an iron loss.

Claims (2)

Hot rolling a steel slab containing, by mass%, C: 0.10% or less, Si: 2.0-8.0%, Mn: 0.005-1.0% and S: 0.0005-0.0026% , the balance being Fe and inevitable impurities Then, after performing hot-rolled sheet annealing as necessary, it is cold-rolled at least once with one or two intermediate sandwiches to make the final cold-rolled sheet, and then applied with an annealing separator after primary recrystallization annealing Then, in producing a grain-oriented electrical steel sheet through a series of manufacturing processes for final finishing annealing,
The surface roughness of the steel sheet before the final finish annealing should be 0.3 μm or less in arithmetic mean roughness Ra, and the final finish annealing should be performed at a temperature of 1100 ° C. or lower using an alumina-based separator as the annealing separator. A method for producing a grain-oriented electrical steel sheet that does not have a forsterite coating. The steel slab is further mass%, Ni: 0.010-1.50%, Cr: 0.01-0.50%, Cu: 0.01-0.50%, P: 0.005-0.50%, Nb: 0.003-0.050%, Sn: 0.005-0.50. %, Sb: 0.005 to 0.50%, Bi: 0.005 to 0.50%, Mo: 0.005 to 0.10%, Al: 0.0010 to 0.0097 %, and N: 0.0005 to 0.0036%. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the composition has a composition.

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