JP6015919B2 - Method for producing grain-oriented electrical steel sheet - Google Patents

Description

  The present invention relates to a method of manufacturing a grain-oriented electrical steel sheet used mainly for iron core materials of transformers and electrical equipment.

  One method for reducing the iron loss of grain-oriented electrical steel sheets is a magnetic domain refinement process. For example, in Patent Document 1, after hot rolling a silicon steel material containing an inhibitor, it is subjected to cold rolling twice or two times sandwiching intermediate annealing to obtain a final product sheet thickness, and then final finishing annealing is performed. In the meantime, a magnetic domain refinement method for a grain-oriented electrical steel sheet is disclosed in which a groove is formed by locally etching the steel sheet surface. As such an etching method, chemical etching and electrolytic etching are known. However, electrolytic etching is advantageous in that the control of the groove depth is easy.

  Further, in Patent Document 2, after the final cold rolling, an etching resist is applied and baked on the surface of the steel sheet, and a continuous or non-continuous linear non-applied portion region is left and subjected to electrolytic etching to form a linear shape on the steel sheet surface A method for forming a groove has been proposed. This electrolytic etching method is generally performed by applying an insulating material such as ink as an etching resist material (etching mask) on the surface of the steel sheet in advance, baking, then performing electrolytic etching, and then removing the insulating material. Already industrialized.

In this method, in order to obtain good magnetic characteristics, it is important to appropriately control the cross-sectional shape (groove width, groove depth) of the groove. When the groove depth is shallow, the magnetic domain fragmentation is performed. effect is insufficient, not the iron loss reducing effect is obtained, conversely, when the groove depth becomes too deep, impeded the flow of the magnetic flux, the magnetic flux density represented by B ₈ is lowered.
Therefore, it is important to appropriately control the groove shape, and several techniques have been proposed so far.

  For example, in Patent Document 3, the electrode in the electrolytic etching tank is divided into multiple parts in the plate width direction, the groove depth in the plate width direction is measured on the exit side of the etching tank, and in the plate width direction based on the measured value. There has been proposed a method of obtaining a uniform groove depth by controlling the value of current applied to each divided electrode so that the groove depth is uniform. Further, in Patent Document 4, in order to reduce variations in the etching groove depth due to changes in the electrical resistance of the steel strip and the electrolytic solution during electrolytic etching, the electrical resistance of the steel strip and the electrical resistance of the electrolytic solution are reduced. Accordingly, there has been proposed a method of performing electrolytic etching by correcting the set voltage.

  However, although the above two methods are effective in reducing variation in the electrolytic etching process, sufficient effects are not always obtained. The reason for this is that the cause of the groove shape defect is not only in the electrolytic etching process, but also the application state in the resist coating process greatly affects. For example, since a rolling strain remains in a normal cold-rolled sheet, the steel sheet shape is not necessarily flat. When resist is applied to such a steel sheet, the wetting and spreading behavior of the resist solution changes, and the resist solution may be applied to the non-application area where the resist solution should not be applied. There arises a problem that the size of the groove changes and the groove size after etching changes.

  As a method for solving such a problem, Patent Document 5 proposes a method in which a steel plate is wound around a roll surface at the time of resist application, and an etching resist is applied in a state where the shape of the steel plate is corrected.

Japanese Unexamined Patent Publication No. 63-042332 Japanese Patent Laid-Open No. 04-088121 JP 07-331332 A JP 09-316698 A Japanese Patent Laid-Open No. 06-108300

  However, even when the etching method using the conventional technique disclosed in Patent Document 5 is used, the variation in the groove shape cannot be completely reduced in the industrial mass production process. For this reason, there has been a problem that the obtained grain-oriented electrical steel sheet (product plate) has a large variation in iron loss and magnetic flux density, and stable quality cannot be ensured.

  The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to propose a method of manufacturing a grain-oriented electrical steel sheet that can stably enjoy the effect of reducing iron loss. .

  The inventors have made extensive studies to solve the above problems, and as a result, found that it is effective to appropriately adjust the surface roughness of the cold rolled plate before electrolytic etching, and developed the present invention. It came to do.

That is, the present invention hot-rolls steel slabs for grain-oriented electrical steel sheets , applies cold resist to the surface of the cold-rolled sheet to obtain the final sheet thickness by cold rolling, and performs an etching treatment to form linear grooves. After forming, in the method of manufacturing a grain-oriented electrical steel sheet that is subjected to resist removal , primary recrystallization annealing, and finish annealing, the surface roughness of the cold rolled sheet before the etching treatment is 0.3 μm or less in terms of arithmetic average roughness Ra It is a manufacturing method of the grain-oriented electrical steel sheet characterized by these.

  The method for producing a grain-oriented electrical steel sheet according to the present invention is characterized in that a roll having a roll surface roughness of arithmetic average roughness Ra of 0.2 μm or less is used for the work roll in the final pass in the cold rolling.

  Moreover, the manufacturing method of the grain-oriented electrical steel sheet according to the present invention is characterized in that an elastic modulus of 300 GPa or more is used for the work roll in the final pass in the cold rolling.

  According to the present invention, a linear groove having a stable width and depth can be formed on the surface of a cold-rolled steel sheet by electrolytic etching treatment, so that the iron loss reduction effect by the magnetic domain refinement treatment is stabilized, and low iron It becomes possible to produce a grain-oriented electrical steel sheet with small loss and small variation.

It is an external appearance photograph of the linear groove | channel formed by the electrolytic etching. It is a figure which shows the three-dimensional roughness measurement result of the linear groove | channel defective part vicinity formed by the electrolytic etching.

  As described above, when the conventional etching method is used, there is a problem that it is difficult to reduce the variation in groove shape (width, depth) in an industrial mass production process. FIG. 1 is an enlarged photograph of the vicinity of a groove forming portion on the surface of a steel plate in which grooves are formed by electrolytic etching after applying an etching resist by gravure printing. In this example, linear grooves are formed at a pitch of 3 mm in the rolling direction and tilted by 10 ° from the sheet width direction to the rolling direction, but the groove width in the rolling direction varies, and depending on the location The part where the groove is broken is also recognized. When such a groove is formed, variations in iron loss and magnetic flux density increase, and it becomes impossible to obtain a grain-oriented electrical steel sheet having stable quality (magnetic characteristics).

  As a result of investigating the cause of the variation in the groove shape as described above, the inventors have found that the surface roughness of the cold-rolled plate to which the etching resist is applied greatly affects the application state of the resist. Fig. 2 shows the distribution of surface irregularities in the vicinity of the part where the groove shape defect occurred using a stylus type three-dimensional roughness meter, and the surface irregularities are shown in a black and white two-color contour diagram (shading diagram). This indicates that the black color is concave. From this figure, it can be seen that the steel plate surface is relatively recessed from the peripheral portion of the portion where the groove is interrupted. Since the applied resist solution flows into the recessed part of the steel plate surface, the cause of the groove shape failure is due to the resist solution flowing in and applied to the place that should be the non-applied part. It was guessed. Therefore, in order to solve such problems, it was considered effective to reduce the unevenness of the steel sheet surface. Based on this result, the inventors have conducted various experiments. As a result, in order to solve the above problems, the roughness in the direction perpendicular to the rolling direction on the steel sheet surface before etching is 0.3 μm or less in terms of Ra. And found that is effective. Here, the Ra is an arithmetic average roughness defined in JIS B0601 (2001). (Hereinafter the same)

  On the other hand, it is known that the surface roughness of the cold rolled sheet is greatly influenced by the final pass in the cold rolling. Therefore, in order to control the surface roughness Ra of the steel sheet to 0.3 μm or less, it is necessary to appropriately manage the final pass condition. Usually, the surface roughness of the cold-rolled sheet is substantially determined by the transfer of the work roll surface roughness during cold rolling and the oil pits. The oil pit is a minute dent formed on the surface of the steel sheet when the lubricating oil used for reducing the load during rolling is sealed in the interface between the work roll and the steel sheet surface. As the amount of lubricating oil introduced into increases, the surface roughness increases. Further, the surface roughness of the work roll of the rolling mill changes due to wear over time, and usually increases gradually as the rolling length increases when the initial roughness is small. Therefore, in order for the surface roughness of the steel sheet after cold rolling to be 0.3 μm or less in Ra, the rolling conditions of the final pass should be set in consideration of changes in the surface roughness of oil pits and work rolls. Must be decided.

  Therefore, the inventors first studied the influence of the change in the surface roughness of the work roll over time by various experiments, and as a result, the initial surface roughness of the work roll in the final pass was expressed by the arithmetic average roughness Ra. It was found that by controlling to 0.2 μm or less, the steel sheet surface roughness after cold rolling can be stably controlled to 0.3 μm or less by Ra. Here, the roughness Ra of the roll surface is a roughness in the roll body length direction.

  In addition, the inventors studied to reduce the adverse effects of oil pits. It is known that the influence of the surface roughness of the work roll on the surface of the steel sheet after rolling, that is, the transfer rate is also affected by the material of the work roll. Therefore, the inventors investigated the influence by using work rolls of various materials. As a result, it was found that it is effective to use a work roll having an elastic modulus of 300 GPa or more.

  The inventors consider the reason as follows. When a work roll having a high elastic modulus is used, the roll flatness due to the rolling load can be reduced, so that the flat roll diameter, which can be said to be the roll diameter during actual rolling, can be reduced. Further, the amount of lubricating oil enclosed in the interface between the roll and the steel plate during rolling decreases as the roll diameter decreases. Therefore, it is considered that the oil pit formation is suppressed as the work roll having a higher elastic modulus is used.

Usually, steel containing about 2 to 10 mass% of Cr is used as a work roll material for cold rolling, and its elastic modulus is only about 205 GPa. On the other hand, as a material having a high elastic modulus that can be used as a work roll for cold rolling, silicon nitride (Si ₃ N ₄ ), sialon (Si—Al—O—N), cemented carbide ( WC-Co) and the like, and their elastic modulus is about 300 to 540 GPa. Therefore, by using work rolls made of these materials, oil pits can be effectively reduced, and the surface roughness of the steel sheet can be stably reduced.
The present invention has been developed based on the above findings.

Next, the manufacturing method of the grain-oriented electrical steel sheet of this invention is demonstrated.
In the grain-oriented electrical steel sheet of the present invention, a steel slab for grain-oriented electrical steel sheet adjusted to a predetermined component composition is hot-rolled, subjected to hot-rolled sheet annealing as necessary, and once or two times between intermediate annealings. After cold rolling as described above, a cold-rolled sheet with the final thickness is formed, grooves are formed on the steel sheet surface, magnetic domain subdivision treatment is performed, and then primary recrystallization annealing (sometimes also decarburization annealing) is performed and annealing separation After the agent is applied to the surface of the steel sheet and subjected to final finish annealing, it can be manufactured by a generally known method of manufacturing through a step of forming a top coating (insulating coating).

  However, the magnetic domain fragmentation process in the manufacturing process described above must be performed while satisfying the following conditions. Usually, the magnetic domain refinement process for a steel sheet after cold rolling is performed by, for example, etching resist containing epoxy resin as a main component by gravure offset printing on the surface of a cold-rolled sheet having a product sheet thickness by final cold rolling. The ink has a pitch of about 3 to 10 mm in the rolling direction, the width in the rolling direction of the non-applied part region is about 0.05 to 0.2 mm, and the inclination is about 0 to 10 ° from the sheet width direction to the rolling direction. After being baked at a temperature of about 200 ° C. for about 30 seconds, electrolytic treatment is performed in a NaCl electrolytic bath to form a linear groove having a predetermined width and depth, and then immersed in an alkaline solution. This is done by removing the etching resist.

Here, what is important in the present invention is to control the roughness of the surface of the steel sheet after rolling to 0.3 μm or less in terms of arithmetic average roughness Ra in the final cold rolling before the magnetic domain refinement treatment. As described above, the surface roughness of the cold-rolled sheet is mainly determined by the surface roughness of the work roll during the final pass rolling and the oil pit. Therefore, in order to control the surface roughness of the steel sheet to 0.3 μm or less with Ra, the surface roughness of the work roll is controlled to Ra with 0.2 μm or less, and silicon nitride (Si ₃ N ₄ ) or sialon ( It is effective to reduce oil pits by using a ceramic work roll having an elastic modulus of 300 GPa or more, such as Si—Al—O—N) or cemented carbide (WC—Co).

  Contains C: 0.06 mass%, Si: 3.1 mass%, Mn: 0.15 mass%, Al: 0.021 mass%, N: 0.007 mass%, S: 0.003 mass% and Se: 0.022 mass% A hot-rolled sheet obtained by hot-rolling a steel slab to be cold-rolled according to a conventional method is subjected to cold-rolling twice (cold-rolled coil) having a final sheet thickness of 0.22 mm and a sheet width of 1160 mm by cold rolling twice with intermediate annealing. ). The cold rolling is performed using a reverse mill having a work roll diameter of 80 mmφ, and the material and the surface roughness of the work roll in the final pass are changed as shown in Table 1 to obtain the final cold rolled sheet. The surface roughness was changed. In addition, the surface roughness of the cold-rolled sheet is obtained by taking samples from three locations of the tip portion, intermediate portion and tail end portion of the coil after cold rolling, and using a stylus roughness meter to determine the rolling direction and The arithmetic mean roughness Ra in the perpendicular direction was measured at 15 points (45 points in total) in the plate width direction, and the variation (standard deviation σ) was obtained.

Then, after applying an etching resist to one surface of the cold-rolled sheet by gravure offset printing, electrolytic etching is performed, and linear grooves having a target width of 0.1 mm and a target depth of 20 μm are spaced at intervals of 3 mm in the rolling direction. And having an inclination of 10 ° with respect to the plate width direction. The etching resist used was an ink mainly composed of an epoxy resin, and the electrolytic etching was performed in a NaCl electrolytic bath under a current density of 10 A / dm ² × 30 seconds. After the cold-rolled plate subjected to the above etching treatment is immersed in an alkaline solution to remove the etching resist, samples are taken again from the tip, middle and tail ends of the coil, and the plate width direction For a total of 15 test pieces divided into 5 pieces at a pitch of about 200 mm, a total of 45 groove shapes (groove width and groove depth) were measured using a stylus roughness meter. The variation (standard deviation σ) was obtained.

  After that, the cold-rolled sheet is subjected to primary recrystallization annealing that also serves as decarburization annealing, applied with an annealing separator mainly composed of MgO, and after final finish annealing, is coated with an insulating film, and is subjected to directional electromagnetic It was set as the product plate (coil) of the steel plate.

Samples were taken from the three positions of the tip, middle and tail ends of the product coil thus obtained, and the width was 30 mm × length from the position (total of 15 positions) divided into five at a pitch of about 200 mm in the plate width direction. A 280 mm Epstein specimen was sampled and subjected to strain relief annealing at 800 ° C. × 5 hr, and then the iron loss W _17/50 was measured to determine the variation (standard deviation σ).
The above results are shown in Table 1 together with the specifications of the work roll used in the final cold rolling pass. From this table, it can be seen that, under conditions suitable for the present invention, the variation in groove shape is reduced and the variation in iron loss is also greatly reduced.

Claims (3)

A steel slab for grain-oriented electrical steel sheets is hot-rolled, cold-rolled to the final cold-rolled sheet surface, coated with a resist, etched to form linear grooves , and then resisted. In the manufacturing method of grain-oriented electrical steel sheet to be removed , primary recrystallization annealing, and finish annealing,
A method for producing a grain-oriented electrical steel sheet, characterized in that the surface roughness of the cold-rolled sheet before the etching treatment is 0.3 μm or less in terms of arithmetic average roughness Ra. 2. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the work roll in the final pass in the cold rolling uses a roll surface roughness having an arithmetic average roughness Ra of 0.2 μm or less. The method for producing a grain-oriented electrical steel sheet according to claim 1 or 2, wherein the work roll in the final pass in the cold rolling uses an elastic modulus of 300 GPa or more.

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