JP2012112006A - Grain-oriented magnetic steel sheet and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a grain-oriented magnetic steel sheet excellent in magnetic properties and a method for producing the same.SOLUTION: The method for producing the grain-oriented magnetic steel sheet includes hot rolling a slab having a component composition comprising, by mass, 0.002 to 0.100% C, 2.0 to 8.0% Si, 0.005 to 1.00% Mn, 0.010% or less Al, 0.005% or less N, 0.005% or less S, 0.005% or less Se, and 0.001 to 0.015% Nb, and the balance consisting of Fe and unavoidable impurities. Then, the hot-rolled steel sheet is subjected to recrystallizing annealing by applying one or two or more cold rolling with intermediate annealing. Then, after finish annealing, the resulting steel sheet is cooled at an average cooling rate of 0.3°C/min or less from the finish annealing temperature to 600°C. The amount of dissolved Nb of the grain-oriented magnetic steel sheet produced in this way will be 0.0006% or less.

Description

  The present invention relates to a grain-oriented electrical steel sheet suitable as a core material of a transformer and a method for manufacturing the same.

With regard to grain-oriented electrical steel sheets, in order to improve magnetic properties, it is a common technique to recrystallize grains having Goss orientation during finish annealing using precipitates called inhibitors. For example, Patent Document 1 discloses a method using AlN and MnS, and Patent Document 2 discloses a method using MnS and MnSe, which are industrially put into practical use. The method using these inhibitors requires slab heating at a high temperature of 1300 ° C. or higher in order to stably develop secondary recrystallized grains.
Furthermore, in order to reinforce the action of these inhibitors, Patent Document 3 discloses a method using Pb, Sb, Nb, and Te, and Patent Document 4 discloses Zr, Ti, B, Nb, Ta, V, Cr. A method of using Mo is disclosed.

  Among them, as described in Patent Document 5, Nb has an effect of effectively reducing the earring of the steel sheet that occurs during hot rolling, and not only improves magnetic properties but also improves product yield. This is a useful technique.

Japanese Patent Publication No.40-15644 Japanese Patent Publication No.51-13469 Japanese Patent Publication No.38-8214 JP-A-52-24116 Japanese Patent Publication No. 6-63031

  In patent document 5, in order to prevent an ear crack, when adding Nb to a grain-oriented electrical steel sheet, the addition amount is regulated within a range in which the magnetic properties do not deteriorate. However, although the magnetic flux density is a relatively good value, the iron loss is not a satisfactory level and remains a problem when adding Nb.

  In view of such circumstances, it is an object of the present invention to provide a grain-oriented electrical steel sheet having excellent magnetic characteristics without deterioration of iron loss and a manufacturing method thereof.

In order to solve the above-mentioned problems, the inventors have conducted intensive research and investigation focusing on the reason for the deterioration of the iron loss characteristics.
As a result, it became clear that precipitates (mainly carbides) were formed after finish annealing, and the precipitates remained in the steel, so that iron loss (hysteresis loss) increased. Furthermore, it was newly found that this iron loss deterioration cannot be evaluated by the total amount of Nb precipitates.

We investigated the correlation between the hysteresis loss and the amount of precipitates before and after applying processing and heat treatment to grain-oriented electrical steel sheets corresponding to product plates produced under various conditions. As a result, it was confirmed that even if the amount of precipitated Nb increased by the same amount by processing or heat treatment, the iron loss might or might not deteriorate.
In addition, as a result of intensive investigation, it was found that the more the fine NbC produced with a precipitate diameter of about 0.1 μm or less, the more the iron loss is deteriorated, and on the contrary, the formation of coarse NbC does not deteriorate the iron loss so much. It was. Furthermore, it has been found that fine Nb precipitates are remarkably increased when the heat treatment is performed after bending the product plate than when only the heat treatment is performed on the product plate. This is considered to be a result of the strain introduced into the steel sheet by processing becoming the nucleus of the Nb precipitate, that is, the increase in the precipitate generation site.

  However, it is difficult for manufacturers to limit the use of product plates after shipment. In particular, it is considered difficult to prevent the iron loss deterioration due to misuse or when the material is deformed without intention of processing. In order to solve the problem of iron loss deterioration before shipment, that is, at the stage of the product plate, the authors conducted intensive studies. As a result, it was found that it is effective to precipitate Nb in steel as much as possible on the product plate. Furthermore, it has been found that the state of Nb in the steel at the product plate stage greatly depends on the average cooling rate in the finish annealing process. In other words, the slower the cooling in the finish annealing process, the easier it is for Nb in the steel to precipitate, and this can be used to prevent iron loss deterioration by allowing Nb in the product plate stage to exist in the precipitated state. It becomes.

This invention is made | formed based on the above knowledge, The summary is as follows.
[1] In mass%, C: 0.002 to 0.100%, Si: 2.0 to 8.0%, Mn: 0.005 to 1.00%, Al: 0.010% or less, N: 0.005% or less, S: 0.005% or less, Se: 0.005% In addition, Nb: 0.001 to 0.015% is included, the remainder is hot-rolled to a slab having a component composition composed of Fe and inevitable impurities, and then one or more times sandwiching intermediate annealing A method for producing a grain-oriented electrical steel sheet, characterized by performing cold rolling, recrystallization annealing, finish annealing, and then cooling from the finish annealing temperature to 600 ° C. at an average cooling rate of 0.3 ° C./min or less.
[2] In the above [1], the component composition is mass%, Ni: 0.01 to 1.50%, Cr: 0.01 to 0.50%, Cu: 0.01 to 0.50%, P: 0.005 to 0.50%, Sb: 0.005 -0.50%, Sn: 0.005-0.50%, Bi: 0.005-0.50%, Mo: 0.005-0.10%, B: 0.0002-0.0025%, V: 0.001-0.010%, Ta: 0.001-0.010% The manufacturing method of the grain-oriented electrical steel sheet characterized by containing 1 type, or 2 or more types.
[3] In mass%, C: less than 0.005%, Si: 2.0 to 8.0%, Mn: 0.005 to 1.00%, Nb: 0.001 to 0.015%, Al: 0.010% or less, N: 0.005% or less, A grain-oriented electrical steel sheet comprising S: 0.005% or less, Se: 0.005% or less, the balance being Fe and inevitable impurities, and a solid solution Nb content of 0.0006% or less.

  In addition, in this specification, all% which shows the component of steel is mass%.

  According to the present invention, it is possible to prevent iron loss deterioration by controlling the existence state of Nb added for reducing the cracking at the product plate stage. As a result, the effect of Nb addition can be utilized to the maximum, and usefulness such as quality stabilization is brought about.

It is a figure which shows the relationship between the average cooling rate of a finish annealing process, and the amount of solid solution Nb in a product board. It is a figure which shows the relationship between the amount of solid solution Nb in a product board, and the deterioration amount of the iron loss by a winding core test.

Details of the present invention will be described below.
The reason for limiting the component composition of the present invention will be described.
C: 0.002 to 0.100%
When C exceeds 0.100%, it becomes difficult to reduce it to less than 0.005%, which is a range in which magnetic aging does not occur after recrystallization annealing (decarburization annealing). On the other hand, if it is less than 0.002%, the inhibitor effect of Nb carbide is not exhibited, and magnetic characteristics are deteriorated. Therefore, C is 0.002% or more and 0.100% or less.

Si: 2.0-8.0%
Si is an element necessary for increasing the specific resistance of steel and improving iron loss. If it is less than 2.0%, sufficient effect cannot be obtained. On the other hand, if it exceeds 8.0%, the workability of steel deteriorates and rolling becomes difficult. Therefore, Si is made 2.0% or more and 8.0% or less.

Mn: 0.005-1.00%
Mn is an element necessary for improving the hot workability. If it is less than 0.005%, a sufficient effect cannot be obtained. On the other hand, if it exceeds 1.00%, the magnetic flux density of the product plate decreases. Therefore, it shall be 0.005% or more and 1.00% or less.

Nb: 0.001 to 0.015%
Nb is an element that forms the basis of the present invention, and the present invention is characterized in that Nb carbide is used as an inhibitor. Therefore, it is essential to add Nb in the range of 0.001% to 0.015%. Since hysteresis loss tends to increase when Nb is large, it is preferably 0.001% or more and 0.005% or less.

Al: 0.010% or less, N: 0.005% or less, S: 0.005% or less, Se: 0.005% or less
Reduction of Al to 0.010% or less, N: 0.005% or less, S: 0.005% or less, and Se: 0.005% or less is essential in order to satisfactorily recrystallize the steel sheet. Al, N, S, and Se are desirably reduced as much as possible from the viewpoint of magnetic properties, but the cost may increase due to the reduction. Considering these, if Al: 0.010% or less, N: 0.005% or less, S: 0.005% or less, Se: 0.005% or less, there is no problem even if it is left in the steel. Therefore, Al: 0.010% or less, N: 0.005% or less, S: 0.005% or less, Se: 0.005% or less. Since Al and Se are elements that are difficult to purify from the steel during finish annealing, Al is preferably 0.008% or less and Se is preferably 0.002% or less. In addition, it is difficult to completely remove N and S light elements at the time of adjusting the components before making the steel slab, and generally 0.002% remains in the steel unless special treatment is performed. It is.

  The balance is Fe and inevitable impurities.

In the present invention, other elements described below can be appropriately contained depending on the purpose.
Ni: 0.01-1.50%, Cr: 0.01-0.50%, Cu: 0.01-0.50%, P: 0.005-0.50%, Sb: 0.005-0.50%, Sn: 0.005-0.50%, Bi: 0.005-0.50%, Mo : 0.005 to 0.10%, B: 0.0002 to 0.0025%, V: 0.001 to 0.010%, Ta: 0.001 to 0.010%, either one or more.
For the purpose of reducing iron loss, one or more of Cr: 0.01 to 0.50%, Cu: 0.01 to 0.50%, and P: 0.005 to 0.50% can be added. In order to improve the magnetic flux density, Ni: 0.01-1.50%, Sb: 0.005-0.50%, Sn: 0.005-0.50%, Bi: 0.005-0.50%, Mo: 0.005-0.10%, B: 0.0002-0.0025% , V: 0.001 to 0.010%, Ta: 0.001 to 0.010%, any one kind or two or more kinds can be added. When the addition amount of each element is less than the lower limit amount, there is no effect of improving the magnetic properties, and when the upper limit amount is exceeded, the development of secondary recrystallized grains is suppressed and the magnetic properties are deteriorated.

Next, the manufacturing method of the grain-oriented electrical steel sheet of this invention is demonstrated.
The slab having the above component composition is hot-rolled, and then subjected to recrystallization annealing by performing cold rolling twice or more with intermediate or intermediate annealing. Next, finish annealing is performed, and subsequently, cooling from the finish annealing temperature to 600 ° C. is performed at an average cooling rate of 0.3 ° C./min or less. If necessary, hot-rolled sheet annealing can be performed after hot rolling. Here, the average cooling rate is a cooling rate per unit time from the holding temperature of the final annealing to a low temperature of around 600 ° C. For example, when the final annealing is performed at 1100 ° C. and the cooling to 600 ° C. is performed in 1 hour, the average cooling rate is (1100 ° C.-600 ° C.) / 60 minutes = 8.3 ° C./minute. When the cooling rate is changed in the middle, the average cooling rate is divided by the total time required for cooling from 1100 ° C to 600 ° C.

  The molten steel having the above components may be produced by a normal ingot-making method or a continuous casting method, or a thin cast piece having a thickness of 100 mm or less may be produced by a direct casting method. The slab is heated and hot-rolled by a normal method, but may be hot-rolled immediately 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 process may proceed as it is. Since the slab heating temperature before hot rolling is a component system in which Al, N, S, and Se are reduced, high temperature annealing is not required. 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. If the annealing temperature of the hot-rolled sheet is lower than 800 ° C, the band structure in the hot-rolling remains, making it difficult to achieve the primary recrystallized structure of sized particles, which may hinder the development of secondary recrystallization. . When the hot-rolled sheet annealing temperature exceeds 1150 ° C., the grain size after the hot-rolled sheet annealing becomes coarse, which may be disadvantageous for realizing a primary recrystallized structure of sized particles.

  After hot-rolled sheet annealing, after performing one or more cold rolling sandwiching the intermediate annealing as necessary, recrystallization annealing that also serves as decarburization is performed. At this time, cold rolling is performed at a temperature of 100 ° C. to 300 ° C., and aging treatment in the range of 100 to 300 ° C. is performed once or a plurality of times during cold rolling. This is effective for improving the magnetic properties by changing the tissue. Since recrystallization annealing requires decarburization, the atmosphere is preferably a wet atmosphere. After recrystallization annealing, a technique for increasing the amount of Si by a silicon immersion method may be used in combination.

Next, finish annealing is performed, and in the subsequent cooling, the average cooling rate is set to 0.3 ° C./min or less.
When forming a forsterite film with emphasis on iron loss, it is possible to develop a secondary recrystallized structure and form a forsterite film by applying a final annealing after applying an annealing separator mainly composed of MgO. Is possible.
If the forsterite film is not required with emphasis on the punching processability, no annealing separator is applied, or even if it is applied, MgO that forms the forsterite film is not used, but silica, alumina, or the like is used.
When applying these annealing separators, it is effective to perform electrostatic application without bringing in moisture. Further, a heat resistant inorganic material sheet (silica, alumina, mica) may be used.
The finish annealing is preferably performed at 800 ° C. or higher for secondary recrystallization. In order to complete the secondary recrystallization, it is desirable to hold at a temperature of 800 ° C. or higher for 20 hours or longer. When the forsterite film is not formed with emphasis on punchability, the secondary recrystallization should be completed. Therefore, the holding temperature is desirably 850 to 950 ° C., and the finish annealing can be completed until the holding. When a forsterite film is formed in order to emphasize iron loss or to reduce the noise of the transformer, it is desirable to raise the temperature to about 1200 ° C.
After the finish annealing, cooling is performed at an average cooling rate of 0.3 ° C./min or less from the finish annealing temperature to 600 ° C.
In the present invention, the addition of Nb is essential for reducing the ear cracks in the middle of the manufacturing process, but after becoming a product plate, it can also be a major cause of iron loss deterioration, so the presence form of Nb in steel and Care must be taken in the manufacturing method. Generally, it is known that iron loss deteriorates when precipitates are formed in steel by processing and heat-treating a product plate after shipment. Many precipitate forming elements are not a problem because they are removed from the steel sheet in the final annealing process, but as a result of investigation, it was found that Nb is an element that is difficult to purify.

  Therefore, the authors examined conditions for preventing iron loss from deteriorating with Nb remaining in the steel. As a result, it has been found that the cooling conditions in the finish annealing process greatly influence the characteristic change (deterioration of iron loss). Specifically, it was concluded that it is important to reduce the solute Nb in the steel at the product plate stage by slowing down the cooling after finish annealing. It is considered that the decrease in the amount of dissolved Nb due to the slow cooling in the finish annealing process reduces the amount of precipitates produced when the product plate is processed and heat-treated after shipment, and suppresses the deterioration of characteristics. The amount of added Nb that is particularly effective for improving properties is 0.001 to 0.005%. In this range, the correlation between the average cooling rate after finish annealing, the amount of solute Nb, and iron loss deterioration was investigated. It was revealed that no deterioration of iron loss was observed under the slow cooling condition where the average cooling rate from 1 to 600 ° C was 0.3 ° C / min or less. From the above, cooling to 600 ° C. after the annealing is performed at an average cooling rate of 0.3 ° C./min or less.

  After finish annealing, it is useful to perform water washing, brushing, and pickling in order to remove the attached annealing separator. After that, it is effective to reduce the iron loss by performing flattening annealing to correct the shape.

  In the case where the steel plates are laminated and used, in order to improve iron loss, it is effective to apply an insulating coating to the steel plate surface before or after the flattening annealing. A coating capable of imparting tension to the steel sheet to reduce iron loss is desirable. Adopting a coating method by depositing an inorganic substance on the steel sheet surface layer by a tension coating application method through a binder, a physical vapor deposition method or a chemical vapor deposition method is desirable because of excellent coating adhesion and a remarkable iron loss reduction effect.

  In order to reduce iron loss, it is desirable to perform magnetic domain fragmentation. As a processing method, a method is generally used, such as grooving the final product plate or introducing thermal strain or impact strain linearly by laser or plasma, or cooling to the final finished plate thickness. A method may be used in which a groove is formed in advance in an intermediate product such as a rolled sheet.

  Thus, the grain-oriented electrical steel sheet (product board) of the present invention is obtained. The grain-oriented electrical steel sheet of the present invention contains C: less than 0.005%, Si: 2.0 to 8.0%, Mn: 0.005 to 1.00%, Nb: 0.001 to 0.015%, and Al: 0.010% or less, N: 0.005% Hereinafter, S: 0.005% or less, Se: 0.005% or less, and remaining Fe and unavoidable impurities. As described above, since the amount of solid solution Nb is reduced by slow cooling in the finish annealing step, the amount of solid solution Nb in the product plate is 0.0006% or less.

In mass%, C: 0.035%, Si: 3.1%, Mn: 0.21%, S: 0.002%, Al: 0.005%, N: 0.002%, Nb: 0.002%, Se: 0.001% or less (showing the detection limit or less) ), And the balance was manufactured by continuous casting of a steel slab composed of Fe and inevitable impurities, heated at 1230 ° C., and then hot rolled to a thickness of 2.6 mm. Thereafter, hot-rolled sheet annealing was performed at 1050 ° C. for 90 seconds, and then the sheet thickness was 0.23 mm by cold rolling. Subsequently, recrystallization annealing was performed in a soaking condition of 840 ° C. for 80 seconds and 50% N ₂ -50% H _{2 in a} humid atmosphere. Next, after applying an annealing separator mainly composed of MgO, finish annealing and cooling were performed at 1200 ° C. for 10 hours. Here, for the purpose of changing the amount of solute Nb in steel after finish annealing, the cooling after finish annealing was performed by changing the average cooling rate in the range of 10 ° C./min to 0.1 ° C./min. Thereafter, flattening annealing was performed at 850 ° C. for 40 seconds under the condition of forming a tension-imparting coating mainly composed of magnesium phosphate and boric acid. The obtained sample corresponding to the product plate was set to Epstein size, and magnetic measurement was performed by the method described in JIS C2550.

  Next, a wound core test was performed as a simulation test assuming processing and heat treatment at the customer site. Specifically, the Epstein sample subjected to magnetic measurement was subjected to bending processing on both the front and back surfaces by bending the plate at an angle of 180 ° so that both ends of the plate were in the same direction around a round bar with a diameter of φ = 40 mm. . Thereafter, the sample was corrected to flattening, and then subjected to strain relief annealing at 800 ° C. for 3 hours in an Ar atmosphere. The magnetic measurement was performed again by the same method as described above, and the amount of iron loss deterioration (ΔW17 / 50) due to bending was evaluated by comparing the magnetic measurement results with a sample corresponding to the product plate.

  FIG. 1 shows the relationship between the average cooling rate after finish annealing and the amount of solute Nb in steel. The composition other than Nb at this time is as follows: C: 0.001 to 0.002%, Si: 3.1%, Mn: 0.21%, Al: 0.001% or less (showing the detection limit or less), N: 0.0005% or less (below the detection limit) S: 0.0005% or less (showing the detection limit or less), Se: 0.001% or less (showing the detection limit or less). As can be seen from FIG. 1, the lower the average cooling rate, the more the Nb precipitate formation in the steel is promoted, and the solute Nb content at the product plate stage decreases. Table 1 shows an example of the relationship between the average cooling rate after finish annealing and the amount of iron loss deterioration. It can be seen that when the average cooling rate is fast, the value of the deterioration amount of iron loss (ΔW17 / 50) increases.

  Next, FIG. 2 shows the relationship between the amount of solute Nb in steel in the product plate and the amount of iron loss deterioration (ΔW17 / 50) in the wound core test. From FIG. 2, it can be seen that the smaller the amount of dissolved Nb in the product plate, the smaller the amount of iron loss deterioration in the wound core test. This is because the greater the amount of dissolved Nb remaining in the steel at the product plate stage, the greater the amount of precipitated Nb that is newly generated at the winding core test stage. It is presumed that the iron loss is degraded by the interaction. Since iron loss deterioration of about 0.05 W / kg can be observed even when Nb is not added, the iron loss deterioration due to Nb addition is substantially reduced by reducing the solid solution Nb content in the steel to about 0.0006% or less from FIG. It is judged that there is almost no. Further, FIG. 1 shows that the average cooling rate after finish annealing should be about 0.3 ° C./min or less as a condition for reducing the solid solution Nb amount to about 0.0006% or less.

A steel slab comprising the composition shown in Table 2 and the balance being Fe and inevitable impurities was manufactured by continuous casting, heated at 1250 ° C., and then hot rolled to a thickness of 2.8 mm. Subsequently, after hot-rolled sheet annealing was performed at 1000 ° C. for 50 seconds, the sheet thickness was 0.30 mm by cold rolling. Subsequently, recrystallization annealing was performed in a soaking condition of 840 ° C. for 80 seconds and 50% N ₂ -50% H _{2 in a} humid atmosphere. Next, after applying an annealing separator mainly composed of MgO, finish annealing was performed by holding at 1200 ° C. for 10 hours, followed by cooling. The average cooling rate after finish annealing is shown in Table 2. Next, planarization annealing was performed at 850 ° C. for 40 seconds under the condition of forming a tension-imparting coating mainly composed of magnesium phosphate and boric acid. The obtained sample corresponding to the product plate was set to Epstein size, and magnetic measurement was performed by the method described in JIS C2550. Further, the amount of solid solution Nb was measured from the sample. The results are also shown in Table 2.

  Next, a wound core test was performed as a simulation test assuming processing and heat treatment at the customer site. Specifically, the Epstein sample subjected to the magnetic measurement was subjected to bending on both the front and back surfaces by bending it at a 180 ° angle with a round bar having a diameter φ = 40 mm. Thereafter, the sample was corrected to flattening and then subjected to strain relief annealing at 800 ° C. for 3 hours in an Ar atmosphere. The magnetic measurement was again performed by the method described in JIS C2550. The difference (ΔW17 / 50) between the obtained iron loss and the iron loss before the wound core test is shown in Table 2 as the amount of iron loss deterioration caused by bending.

  As is apparent from Table 2, in the present invention example, it is understood that the amount of iron loss deterioration (ΔW17 / 50) is small and iron loss deterioration is prevented.

Claims (3)

  In mass%, C: 0.002 to 0.100%, Si: 2.0 to 8.0%, Mn: 0.005 to 1.00%, Al: 0.010% or less, N: 0.005% or less, S: 0.005% or less, Se: 0.005% or less Further, Nb: 0.001 to 0.015% is included, and the balance is hot-rolled to a slab having a composition composed of Fe and inevitable impurities, and then cold-rolled twice or more with one or intermediate annealing in between. A method for producing a grain-oriented electrical steel sheet characterized by subjecting to recrystallization annealing, and after finishing annealing, cooling from the finishing annealing temperature to 600 ° C. at an average cooling rate of 0.3 ° C./min or less.   Furthermore, as a component composition, in mass%, Ni: 0.01 to 1.50%, Cr: 0.01 to 0.50%, Cu: 0.01 to 0.50%, P: 0.005 to 0.50%, Sb: 0.005 to 0.50%, Sn: 0.005 to 0.50 %, Bi: 0.005-0.50%, Mo: 0.005-0.10%, B: 0.0002-0.0025%, V: 0.001-0.010%, Ta: 0.001-0.010% The method for producing a grain-oriented electrical steel sheet according to claim 1.   In mass%, C: less than 0.005%, Si: 2.0 to 8.0%, Mn: 0.005 to 1.00%, Nb: 0.001 to 0.015%, Al: 0.010% or less, N: 0.005% or less, S: 0.005 % Or less, Se: 0.005% or less, the balance Fe and inevitable impurities, and the solid solution Nb content is 0.0006% or less.