JP2011143440A - Method of manufacturing grain oriented silicon steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an advantageous method of manufacturing a grain oriented silicon steel sheet excellent in core loss properties. <P>SOLUTION: In the method of manufacturing the grain oriented silicon steel sheet, which includes a series of processes in which a hot-rolled steel sheet is made into a cold-rolled steel sheet having the final sheet thickness by one time or two or more times of the cold rolling holding intermediate annealing between the cold rolling processes, after that, primary recrystallization annealing is performed and secondary recrystallization annealing is performed, in one or more passes in the final cold rolling, rolling is performed by using work rolls having a crossed grinding mark which is composed of a grinding mark inclined at ≥2° to <90° with respect to a roll peripheral direction and a grinding mark inclined at ≥2° to <90° in the opposite direction of the above grinding mark. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing a grain-oriented electrical steel sheet having excellent iron loss characteristics.

  The grain-oriented electrical steel sheet is mainly used as a core material of a transformer, and is required to have excellent magnetic properties, particularly iron loss properties (low iron loss).

  Generally, the iron loss characteristics of grain-oriented electrical steel sheets become better as the surface roughness of the product is smaller, the degree of integration of the crystal orientation of the product in the Goth orientation is higher, and the crystal grain size of the product is smaller. It is known. It is also known that the above characteristics are greatly affected by a work roll in final cold rolling that is cold-rolled to a product plate thickness (final plate thickness).

  For example, if the work roll diameter in the final cold rolling is small, the contact surface pressure between the work roll and the material to be rolled increases, and the rolling friction coefficient also increases. Deformation increases. As a result, since the number of goth-oriented grains in the texture after primary recrystallization annealing increases, the degree of accumulation in the goth orientation of the texture obtained by secondary recrystallization annealing increases, and the crystal grain size of the product plate Becomes smaller.

  In addition, if the surface roughness of the work roll in the final cold rolling is small, the amount of rolling oil taken in between the roll and the material to be rolled during rolling is reduced and the oil film thickness is reduced. It becomes easy to be transferred to the surface of the rolled material, and the roughness of the steel plate surface is also reduced.

  For the reasons described above, final cold rolling of grain-oriented electrical steel sheets is generally performed using a Sendzimir mill or a cluster mill having a small-diameter work roll having a diameter of about 80 mmφ and mirror-polished. However, the Sendzimir mill and the cluster mill have problems that the rolling speed is low and the reverse rolling is performed, so that the productivity is low and the manufacturing cost is high.

  Therefore, in order to increase productivity and reduce manufacturing costs, it has been attempted to perform final cold rolling using a large-diameter roll tandem rolling mill. However, in tandem rolling with large-diameter rolls, the rolling speed is large and productivity is improved, while the amount of rolling oil taken up between the roll and the material to be rolled (steel plate) increases, and the rolling friction coefficient decreases. The problem is that good iron loss characteristics cannot be obtained because the amount of shear deformation in plastic deformation received by rolling is reduced or the surface roughness of the steel sheet surface called oil pits increases and the surface roughness increases. I have it.

  Several improvement techniques have been proposed for the above problem in the tandem rolling method. For example, in Patent Document 1, when producing a grain-oriented electrical steel sheet by a two-time cold rolling method, a roll provided with scratch ridges extending in the roll circumferential direction in the previous stage including at least the first stand in the second cold rolling. A technique for improving the magnetic properties by reducing the surface roughness of the final cold rolled sheet by cold rolling using a scratch dull roll having an axial surface roughness Ra of 0.3 μm or more is disclosed.

  Patent Document 2 discloses a work roll having a surface roughness Ra of 1.0 to 3.0 μm as a first stand in the second cold rolling when a grain-oriented electrical steel sheet is produced by a two-time cold rolling method. , Using a slanted abrasive work roll with a surface roughness Ra of 0.05 to 0.5 μm to one or more stands after the second stand to reduce the surface roughness and improve the iron loss characteristics Techniques to do this are disclosed.

Japanese Patent Laid-Open No. 02-175010 JP-A-11-199933

  However, in the rolling method of Patent Document 1, although a certain effect is recognized in reducing the surface roughness, the effect of improving the friction coefficient during rolling is small, so the iron loss improvement effect is only at an insufficient level. Moreover, in the rolling method of Patent Document 2, although a certain effect is recognized for reducing the surface roughness and increasing the friction coefficient during rolling, the iron loss improvement effect is still at an insufficient level. Furthermore, in the rolling method of Patent Document 2, the friction coefficient decreases with wear of the work roll polishing eyes, and the iron loss improvement effect decreases rapidly. Therefore, it is necessary to frequently replace the roll, and the roll basic unit is There was a problem that it was expensive.

  Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art and to propose an advantageous method for producing a grain-oriented electrical steel sheet having excellent iron loss characteristics.

  In order to solve the above-mentioned problems, the inventors have made extensive studies on the influence of the difference in rolling method and the roughness characteristics of the rolling roll on the iron loss characteristics. As a result, in at least one pass of multi-pass rolling performed by a tandem cold rolling mill or the like, rolling is performed using a work roll provided with a cross-grind, thereby increasing the rolling friction coefficient and the steel sheet surface roughness. Therefore, the present inventors have found that the iron loss characteristics of the grain-oriented electrical steel sheet can be greatly improved, and have completed the present invention.

  That is, in the present invention, a hot-rolled steel sheet for grain-oriented electrical steel sheet is made into a cold-rolled steel sheet having a final thickness by one or more cold rollings sandwiching intermediate annealing, followed by primary recrystallization annealing, In the method for producing a grain-oriented electrical steel sheet comprising a series of steps for recrystallization annealing, the polishing marks inclined at least 2 ° and less than 90 ° with respect to the roll circumferential direction at least one pass in the final cold rolling; Is a method for producing a grain-oriented electrical steel sheet, characterized in that rolling is performed using a work roll having a cross-grind having a slant of 0 ° or more and less than 90 °.

  The method for producing a grain-oriented electrical steel sheet according to the present invention includes, as the work roll, a polishing eye inclined at 10 ° or more and less than 90 ° with respect to the roll circumferential direction, and an inclination of 0 ° or more and less than 90 ° opposite to the polishing eye. It is characterized by using a work roll having a cross-polishing eye consisting of the polished eye.

  The surface roughness of the work roll in the method for producing a grain-oriented electrical steel sheet according to the present invention is characterized in that an arithmetic average roughness Ra is 0.05 to 1.5 μm.

  Moreover, the manufacturing method of the grain-oriented electrical steel sheet according to the present invention is characterized in that the final cold rolling is performed using a tandem rolling mill.

  According to the present invention, since the final cold rolling is performed using a work roll provided with a cross-grind, the rolling friction coefficient can be increased as compared with the prior art, and the steel sheet surface after rolling As a result, the roughness of the product surface can be reduced, so that the iron loss characteristics of the grain-oriented electrical steel sheet can be greatly improved. In addition, according to the present invention, since the final cold rolling can be performed using a tandem rolling mill, in addition to the improvement of iron loss characteristics, it greatly contributes to the improvement of productivity and the reduction of manufacturing cost. be able to. In addition, since the work roll provided with the cross-abrasion according to the present invention has a small decrease in the friction coefficient due to the abrasion of the abrasion, the roll basic unit can be reduced, which greatly contributes to an improvement in productivity and a reduction in manufacturing cost. be able to.

It is a figure explaining the grinding eye direction of the conventional cold rolling roll. It is a figure explaining the inclination grinding eye roll disclosed by patent document 2. FIG. It is a figure explaining the cloth polishing eye roll of the present invention.

  In the present invention, a hot-rolled steel sheet for grain-oriented electrical steel sheets is subjected to cold rolling of a final thickness by one or two or more cold rolling sandwiching intermediate annealing, followed by primary recrystallization annealing and secondary recrystallization. In the method for producing a grain-oriented electrical steel sheet comprising a series of annealing steps, one or more passes in cold rolling (final cold rolling) with a final thickness is inclined by 2 ° or more and less than 90 ° with respect to the roll circumferential direction. A grain-oriented electrical steel sheet having excellent iron loss characteristics is obtained by rolling using a work roll having a cross-grinding eye composed of a grinding eye and a polishing eye inclined at an angle of 0 ° or more and less than 90 ° in the opposite direction to the polishing eye. It is a technology to manufacture.

  Here, the hot-rolled steel sheet as a raw material used for manufacturing the grain-oriented electrical steel sheet of the present invention is a steel material (slab) having a conventionally known component composition for the grain-oriented electrical steel sheet, and is hot-rolled under a generally known condition. Thus, any steel type can be used, and therefore, it can be used in the present invention regardless of the presence or type of the inhibitor component. For example, as the component system to which the inhibitor component is added, S: 0.01 to 0.03 mass% and / or Se: 0.01 to 0.03 mass%, Al: 0.01 to 0.04 mass%, N: The component system containing at least one of 0.0050 to 0.0200 mass%, and the component system not containing the inhibitor component is S: less than 0.0050 mass%, Se: less than 0.0050 mass%, Al: 0. Any material containing less than 01 mass% and N: less than 0.0050 mass% can be suitably used.

  Further, the hot-rolled steel sheet may be subjected to hot-rolled sheet annealing as necessary, and the annealing conditions may be applied under generally known conditions, and there is no particular limitation.

  Next, the hot-rolled steel sheet is descaled by pickling or the like as necessary, and then cold-rolled to obtain a cold-rolled sheet having a final thickness. In this cold rolling, the final plate thickness may be obtained once, or the final plate thickness may be obtained by cold rolling two or more times with intermediate annealing. Here, in the present invention, rolling immediately before the primary recrystallization annealing with the final plate thickness is referred to as final cold rolling, and the rolling reduction in this final cold rolling is generally performed in the range of 50 to 95%. In the present invention, it is preferable to carry out within the above range.

  In general, the work roll used in the cold rolling is a bright roll (hereinafter, referred to as “bright roll”) having polishing eyes in the circumferential direction of the roll as shown in FIG. 1 from the viewpoint of reducing the friction coefficient and improving the rollability. Also called “normal roll”). However, when rolling using the above normal roll, as described above, the surface roughness of the material to be rolled is increased, and the rolling friction coefficient is reduced, so that the goth orientation in the secondary recrystallized structure is reduced. The degree of integration is reduced, and excellent iron loss characteristics cannot be obtained.

  FIG. 2 schematically shows an inclined abrasive roll provided with a 45 ° abrasive in the roll circumferential direction, which is disclosed in Patent Document 2. However, when rolling is performed using this inclined abrasive roll, the rolling oil taken into the roll bite between the roll and the material to be rolled (steel plate) cannot be completely discharged, so the friction coefficient The amount of increase was small and insufficient to improve the iron loss characteristics. In addition, as the abrasive eyes wear, it becomes increasingly difficult to discharge the rolling oil. As the rolling amount increases, the friction coefficient decreases, and the iron loss improvement effect decreases rapidly.

Therefore, in the present invention, a polishing eye inclined at an inclination angle θ ₁ of 2 ° or more and less than 90 ° with respect to the roll circumferential direction in one or more passes in the final cold rolling, and 0 ° in the opposite direction to the polishing eye. It was decided to use a work roll having cross polishing eyes composed of polishing eyes inclined at an inclination angle θ ₂ of less than 90 °. By using a work roll with this cross-grind, it is possible to sufficiently discharge the rolling oil taken into the roll bite, so that the rolling friction coefficient can be increased and the steel sheet surface roughness can be reduced. As a result, iron loss characteristics can be reliably improved. In addition, since the rolling oil can be discharged even if the abrasive eyes are worn somewhat, a high friction coefficient can be secured over a long period of time, so that even if the rolling amount increases, a high iron loss improvement effect can be maintained. it can.

FIG. 3 shows an example of a cross polishing eye roll according to the present invention. FIG. 3A shows a case where the absolute values of the inclination angle θ ₁ and the inclination angle θ ₂ are equal, that is, the cross polishing eye roll. If There is symmetrical with respect to the roll circumferential direction, FIG. 3 (b), when the absolute value of the inclination angle theta ₁ and the inclination angle theta ₂ are not equal, i.e., left and right cross polishing marks are relative to the roll circumferential direction This is the case when it is asymmetric.

Here, the inclination angle θ ₁ of _one polishing eye in the cross polishing eye roll of the present invention needs to be 2 ° or more and less than 90 ° with respect to the circumferential direction of the roll. If the inclination angle θ ₁ is less than 2 °, the effect of reducing the surface roughness of the product is small, and the effect of increasing the friction coefficient during rolling is small, so that the effect of improving the iron loss characteristics cannot be obtained. Furthermore, if θ ₁ is 10 ° or more, the effect of increasing the friction coefficient during rolling can be further enhanced, and the iron loss characteristics can be greatly improved. Therefore, θ ₁ is preferably 10 ° or more and less than 90 °. Note that the relationship between θ ₁ and θ ₂ does not have to be as shown in FIG. 3, and it is needless to say that θ ₁ and θ ₂ may be reversed.

In addition, the inclination angle θ ₂ of the other polishing eye needs to be 0 ° or more and less than 90 ° opposite to θ ₁ with respect to the circumferential direction of the roll. In addition to the polishing eyes having the inclination angle θ ₁ , by applying the polishing marks, the rolling oil is discharged without being enclosed in the roll bite, so that the friction coefficient during rolling can be reliably increased. The steel plate surface roughness can be further reduced.

  Moreover, it is preferable that the surface roughness of the work roll used for the said final cold rolling is the range of 0.05-1.5 micrometers in arithmetic mean roughness Ra prescribed | regulated by JISB0601 (2001). If Ra is less than 0.05 μm, the effect of cross polishing is not obtained. On the other hand, if it exceeds 1.5 μm, the surface roughness of the roll is too large and the surface roughness of the product is increased. It is because it deteriorates. Here, the Ra is a value measured in the axial direction of the work roll in accordance with JIS B0601 (2001), and the reference value described in the JIS is used for the evaluation length and the cut-off value at the time of Ra measurement.

  In addition, the said grinding | polishing eyes provided to a work roll do not necessarily need to be continuous, and when grinding | polishing a work roll, it is rather preferable that it is intermittent. Further, any method may be used to apply the polishing marks to the surface of the work roll. For example, the work roll surface may be provided by polishing with a rotating grindstone or loose abrasive grains, polishing with a grinding bit or etching.

  Further, in the final cold rolling, it is not necessary to use the cross polishing rolls in all rolling passes, and it is sufficient to use at least one pass or more. However, in order to reliably obtain the effect of the cross polishing roll, it is preferable to use two or more passes rather than one pass.

  The final cold rolling mill may be a tandem cold rolling mill, a sendzimir mill, a planetary mill, or the like. From the viewpoint of improving productivity and reducing manufacturing costs, a tandem cold rolling mill may be used. A rolling mill is preferable.

  Next, in the method for producing a grain-oriented electrical steel sheet according to the present invention, the cold-rolled steel sheet that has been finally cold-rolled under the above-described conditions is subjected to primary recrystallization annealing, then secondary recrystallization annealing, and further, if necessary. It is preferable to form a product (oriented electrical steel sheet) by depositing a generally known insulating coating.

  The primary recrystallization annealing may be performed under generally known conditions. For example, annealing conditions that also serve as decarburization annealing at 800 ° C. for 2 minutes in a wet hydrogen atmosphere are suitable. Also, the secondary recrystallization annealing may be performed under generally known conditions. For example, annealing conditions in which secondary recrystallization and purification are performed by annealing at 1200 ° C. for 5 hours in a hydrogen atmosphere are preferably suitable. Note that nitriding treatment may be performed between the primary recrystallization annealing and the secondary recrystallization annealing.

Further, after the primary recrystallization annealing, the secondary recrystallization annealing may be performed after applying the annealing separator. In this case, as the annealing separator, any conventionally known ones mainly composed of MgO, Al ₂ O _{3 and the} like can be used. After the secondary recrystallization annealing, a forsterite film is applied to the steel sheet surface. Regardless of forming or not.

C: 0.07 mass%, Si: 3.2 mass%, Mn: 0.07 mass%, Al: 0.02 mass%, N: 0.01 mass%, S: 0.02 mass%, the balance from Fe and inevitable impurities After subjecting the hot rolled sheet for directional electrical steel sheet having a thickness of 2.8 mm to a hot rolled sheet for 900 ° C. × 3 minutes, an intermediate sheet thickness of 2.0 mm is obtained by the first cold rolling, Intermediate annealing at 1050 ° C. for 3 minutes was performed. Next, the second cold rolling (final cold rolling) was performed using a tandem cold rolling mill consisting of 4 stands and a work roll diameter of # 3 and # 4 stands of 300 mmφ. A 3 mm cold-rolled steel sheet was used.
For the # 1 and # 2 stands of the rolling mill, a normal work roll (Ra: 1.0 μm bright roll) having abrasive eyes in the circumferential direction is used, and for the # 3 and # 4 stands, Using a work roll having various polishing marks and surface roughness shown in No. 1, rolling was performed for 500 tons or more under each condition.
Next, the cold-rolled steel sheet having a final thickness is subjected to primary recrystallization annealing also serving as decarburization annealing at 800 ° C. for 2 minutes in a wet hydrogen atmosphere, and after applying and drying MgO slurry as an annealing separator, A secondary recrystallization annealing was performed at 1200 ° C. for 5 hours to obtain a grain-oriented electrical steel sheet.
A specimen parallel to the rolling direction was collected from the position of the grain-oriented electrical steel sheet thus obtained immediately after the roll change in each roll condition and the position after 500 ton rolling, and subjected to 800 ° C. × 3 hr strain relief annealing. After that, the iron loss W _17/50 was measured according to JIS C2550 (2000) and the iron loss at both positions was compared to evaluate the improvement effect of the iron loss property and the life of the work roll.

The results are shown together in Table 1. Here, No. 1 shown in Table 1 was used. No. 1 is an example in which a normal roll having polishing eyes (θ ₁ = 0 °) in the circumferential direction is used for the # 3 and # 4 stands. The comparative example of No. 2 is an example in which the inclined abrasive roll disclosed in Patent Document 2 is used for # 3 and # 4 stands, The comparative example 3 is an example in which a roll having an inclination angle θ ₁ outside the present invention is used for the # 3 and # 4 stands, although it is a cross-polishing eye. In addition, No. 1 shown in Table 1. Examples 4 to 15 are examples in which various cross polishing rolls suitable for the present invention are used for the # 3 and # 4 stands.
From the results shown in Table 1, in the inventive examples using the cross polishing rolls suitable for the present invention, a grain-oriented electrical steel sheet having excellent iron loss characteristics as compared with the comparative examples is obtained, and the rolling amount is increased. Even when the effect of improving the iron loss was decreased, the No. It is smaller than the comparative example 2 and it can be seen that the work roll life is also excellent.

C: 0.01 mass%, Si: 3.4 mass%, Mn: 0.05 mass%, Al: 0.0025 mass%, N: 0.0035 mass%, S: 0.0010 mass%, Se: 0.0002 mass%, balance After subjecting a hot rolled sheet for a directional electrical steel sheet with a thickness of 1.8 mm having a component composition consisting of Fe and unavoidable impurities to hot rolled sheet annealing at 1000 ° C. for 30 seconds, it consists of 4 stands, Using a tandem cold rolling mill with a work roll diameter of 300 mmφ, a cold rolled steel sheet having a final sheet thickness of 0.20 mm was obtained by one cold rolling.
In addition, for each stand of the rolling mill, a work roll having the types of polishing marks shown in Table 2 was used, and rolling was performed for 500 tons or more under each condition. Further, the surface roughness Ra of the work roll of each stand was adjusted to 1.0 μm for the # 1 stand and 0.3 μm for the # 2 to # 4 stands regardless of the normal roll and the cross polishing roll.
Next, the cold-rolled steel sheet having a final thickness is subjected to primary recrystallization annealing also serving as decarburization annealing at 850 ° C. for 1 minute in a wet hydrogen atmosphere, and after applying and drying MgO slurry as an annealing separator, A secondary recrystallization annealing at 1250 ° C. for 12 hours was performed to obtain a grain-oriented electrical steel sheet.
A test piece parallel to the rolling direction was collected from a position corresponding to 500 ton of the rolling amount under each roll condition of the grain-oriented electrical steel sheet thus obtained, and subjected to strain relief annealing at 800 ° C. × 3 hr. The iron loss W _17/50 was measured in accordance with C2550 (2000), and the iron loss characteristics were evaluated.

The results are shown together in Table 2. Here, No. 1 shown in Table 2 was used. The comparative example of No. 1 is an example in which a normal roll having circumferential polishing eyes (θ ₁ = 0 °) is used for all the stands. In the invention examples 2 to 8, work rolls having cross polishing eyes (θ ₁ = 30 °, θ ₂ = 45 °) suitable for the present invention in any one or more of the # 1 to # 4 stands were used. It is an example.
From the results in Table 2, it is possible to obtain a grain-oriented electrical steel sheet having excellent iron loss characteristics by performing cold rolling using a work roll having a cross-grind suitable for the present invention in any one or more stands. Recognize.

Claims (4)

A series of hot-rolled steel sheets for grain-oriented electrical steel sheets, which are cold-rolled steel sheets having a final thickness by one or more cold rollings with intermediate annealing, followed by primary recrystallization annealing and secondary recrystallization annealing. In the method for producing a grain-oriented electrical steel sheet comprising the steps, a polishing eye inclined at least 2 ° and less than 90 ° with respect to the roll circumferential direction for at least one pass in the final cold rolling, and 0 ° in the opposite direction to the polishing eye A method for producing a grain-oriented electrical steel sheet, characterized by rolling using a work roll having a cross-grid having an abrasive grain inclined by less than 90 °. As the work roll, a work having a cross polishing eye composed of a polishing eye inclined at 10 ° or more and less than 90 ° with respect to the roll circumferential direction and a polishing eye inclined at an angle of 0 ° or more and less than 90 ° in the opposite direction to the polishing eye. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein a roll is used. The method for producing a grain-oriented electrical steel sheet according to claim 1 or 2, wherein the surface roughness of the work roll has an arithmetic average roughness Ra of 0.05 to 1.5 µm. The method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 3, wherein the final cold rolling is performed using a tandem rolling mill.

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