JP2592740C - - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grain-oriented electrical steel sheet having extremely low iron loss and a method for producing the same. [0002] In the production of grain-oriented electrical steel sheets, it is important to reduce iron loss from the viewpoint of energy saving. Methods for reducing iron loss include increasing the magnetic east density, increasing the specific resistance,
In addition to conventionally known metallurgical methods such as thinning, magnetic domain segmentation techniques disclosed in JP-A-55-18566 and JP-A-61-117218, or JP-A-49-117218. No. 96920, JP-A-53-144419 and the like. In addition, Japanese Patent Application Laid-Open No.
There is a method disclosed in Japanese Patent Application Laid-Open No. 4-43115, in which a steel sheet having a mirror surface is given a small strain to subdivide magnetic domains. However, this method has a drawback that it is not useful as a material for a wound iron core transformer requiring strain relief annealing because the magnetic domain segmentation effect is lost by annealing. [0003] The present invention has a large iron loss reducing effect as compared with the above-described method, and can obtain an unprecedented ultra-low iron loss material. An object of the present invention is to provide a grain-oriented electrical steel sheet which has a high value of use as a material for a wound iron core transformer requiring strain relief annealing and has extremely low iron loss, and a method for producing the same. Means for Solving the Problems The present invention removes the surface coating of a finish-annealed unidirectional magnetic steel sheet having a linear or dot-like groove having a certain depth and width, and removing the surface coating. After forming the above-mentioned grooves on the surface of the finished grain-finished magnetic steel sheet having a roughness of 0.4 μm or less in average roughness or finish annealing having a mirror surface with an average roughness of 0.4 μm or less, The purpose of the present invention is to obtain a grain-oriented electrical steel sheet having extremely low iron loss by applying a tension insulating film. Therefore, the application is not limited to the wound iron core transformer, and a sufficient effect can be expected with a stacked iron core transformer. That is, the present invention aims to obtain an unusually low-loss iron-oriented unidirectional magnetic steel sheet by the synergistic effect of the reduction of the surface roughness and the magnetic domain control by the formation of the grooves. Hereinafter, the present invention will be described in detail. The material used in the present invention has a Goss orientation developed by a secondary recrystallization method, and there is no particular restriction on the manufacturing method. The general process is smelting and refining in a converter, electric furnace, vacuum melting furnace, etc., adjusting the components, adding a small amount of inhibitor-forming elements, etc., and then casting it continuously or casting it into a normal mold, then sizing. A slab is formed by rolling. The slab is formed into a coil having a thickness of usually 3.0 mm or less by hot rolling under known conditions. Alternatively, the molten steel is directly quenched and solidified to form a thin plate, which does not change the essence of the present invention. Thereafter, the hot-rolled sheet is annealed or pickled without annealing. In the case of a single cold rolling step, rolling is performed to the final thickness as it is. In the case of the twice cold rolling step, the final thickness is obtained by rolling twice with a known intermediate annealing. Thereafter, decarburization annealing is performed, nitriding treatment is performed as required, an annealing separator is applied, and finish annealing is performed. MgO is usually used as an annealing separating agent, and TiO ₂ or the like may be added to the MgO to help form a forsterite film. Further, a B-based compound, an Sb-based compound, Na,
The proper addition of a K-based compound or the like does not affect the essence of the present invention. Also, Al
An annealing separator such as ₂ O ₃ or SiO ₂ may be used. In the present invention, it is convenient not to form a forsterite film, but in the present invention, it does not matter whether a forsterite film is present. In the grain-oriented electrical steel sheet, it is important that the secondary recrystallized grains have high orientation.
The finish annealing for the secondary recrystallization is performed under known conditions, for example, at a temperature of 1200 ° C. for about 20 hours. In the production of ordinary grain-oriented electrical steel sheets, there are a product in which after finishing annealing, an annealing separating agent is washed off to obtain a product, and a product in which a coating is applied on this forsterite film and shape correction annealing is performed. [0007] The steel sheet treated in such a process is subjected to magnetic domain control to withstand strain relief annealing by a known method. As a method of controlling the magnetic domain, there is, for example, a groove forming method by a mechanical method disclosed in Japanese Patent Application Laid-Open No. 61-117218, and an insulating film is locally formed by laser irradiation described in Japanese Patent Application Laid-Open No. 60-255926. After the removal, there is a method of dissolving the base iron with an acid to form a groove. In addition, a method of forming a concave portion having a constant depth by laser irradiation may be used, or a known method may be used as long as it is a magnetic domain control method that can withstand strain relief annealing. [0008] A feature of the present invention is that the surface of a steel sheet grooved by the above-described method has a mirror surface with a roughness less than a certain critical value, and furthermore, imparts a specific range of tension thereto. The point is to apply. Here, the mirror surface means one having a roughness average roughness of 0.4 μm or less. One known method for obtaining a mirror surface is electrolytic polishing. This can be obtained by removing the insulating film or oxide on the surface of the steel sheet with an acid or the like and then electrically polishing in an electrolytic solution of phosphoric acid and chromic anhydride, for example. A method of chemically obtaining a mirror surface is also known. For example, there is a method of using a liquid obtained by adding a small amount of hydrofluoric acid to a hydrogen peroxide solution. In addition, when using dilute sulfuric acid, dilute nitric acid, or dilute hydrochloric acid, a surface with low roughness can be obtained. In addition, it can also be obtained by an annealing separator applied before the finish annealing or the finish annealing atmosphere conditions. In the present invention, a similar effect can be obtained by forming the above-described groove after obtaining a mirror surface by the above method. Next, a method for imparting tension to a steel sheet will be described. It is well known that applying tension in the rolling direction of a grain-oriented electrical steel sheet reduces iron loss. Currently commercial products are provided by the tension created by the difference in the expansion coefficients of the steel sheet and the surface coating. In the present invention, as a tension coating solution, for example, a solution containing chromic anhydride-aluminum phosphate as a main component described in JP-B-53-28375, or a chromic anhydride-magnesium phosphate described in JP-B-56-52117. By applying and baking a liquid containing as a main component a steel plate, tension can be imparted. This tension was further increased by repeating the number of times of coating and baking, and a new finding was obtained that iron loss characteristics were significantly improved.
This will be further described below based on experimental results. FIG. 1 shows a unidirectional magnetic steel sheet containing 3.2% of Si and having a thickness of 0.16 mm and a magnetic flux density B _{8 of} 1.94T, which is disclosed in Japanese Patent Application Laid-Open No. 61-117218, 90-220 k.
The magnetic domain was controlled by forming a groove in the steel sheet with a load of g / m ² and heat-treating the steel sheet at a temperature of 750 ° C. or more (in this experiment, the groove depth was 13 μm, the width was 50 μm, and the rolling direction was 7 μm).
5 mm groove spacing in the 5 ° direction, strain relief annealing at 850 ° C. for 2 hours), removing the surface coating, adjusting the smoothness of the steel sheet surface by chemical polishing, and then coating liquid mainly composed of chromic anhydride-aluminum phosphate 1 shows iron loss characteristics after baking at 820 ° C. From the figure, it can be seen that a very low iron loss can be obtained when the average roughness is 0.4 μm or less. FIG. 2 shows the relationship between the number of application and baking of the coating liquid and the iron loss. The material used was one subjected to magnetic domain control under the same conditions as in FIG. The average roughness of the steel sheet surface after the removal of the coating was adjusted to 0.1 μm or less by chemical polishing. This steel sheet was dipped in 10% diluted sulfuric acid aqueous solution for a short time, washed with water and dried, and then applied with a liquid containing chromic anhydride-aluminum phosphate as a main component at a rate of 3 g / m ² per side, and then dried. Was annealed and then magnetically measured. Next, the coating and the heat treatment were further repeated, and a magnetic measurement was performed. From the figure, it can be seen that the iron loss is further improved by repeating the coating baking treatment. FIG. 3 shows the relationship between the number of times of the coating baking process and the tension applied to the steel sheet. The tension was obtained by calculating the bending amount of the steel sheet after removing the insulating coating on one side of the steel sheet with acid. It can be seen that the tension increases as the number of printing operations increases. It can be said that this tension brings about a further improvement in iron loss and achieves ultra-low iron loss. As the coating liquid, a known liquid such as a liquid mainly containing chromic anhydride-aluminum phosphate or a liquid mainly containing chromic anhydride-magnesium phosphate can be used. A thin metal plating may be applied to the steel sheet in order to enhance the adhesion to the steel sheet. Next, the reasons for limitation of the present invention will be described. Si is an element effective in reducing iron loss, and its upper limit is 4.5%. 4.5%
If the ratio exceeds, there are problems such as brittleness in the ordinary secondary recrystallization method, and the production becomes difficult. As shown in FIG. 1, an extremely low iron loss cannot be obtained unless the surface roughness of the steel sheet is 0.4 μm or less. Regarding the depth, width and spacing of the grooves formed in the steel plate, see JP-B-62-53579.
No. in the official gazette. According to this, when the depth of the groove formed in the steel plate exceeds 5 μm, there is an effect of magnetic domain control, and when the width of the groove exceeds 300 μm, the margin of improvement in iron loss is reduced. The interval between the grooves is 2 to 15 mm, preferably 3 to 8 mm, and is 45 to 90 °, preferably 70 to 90 ° with respect to the rolling direction. FIG. 5 shows the results of searching for the baking temperature of the tensile insulating film (sheet thickness 0.15 mm, adhesion amount 3 g / m ² , baking process twice). According to this, it is found that the temperature is higher than 750 ° C. to 950 ° C., preferably 800 to 900 ° C. If the temperature is lower than 750 ° C. or higher than 950 ° C., sufficient tension cannot be obtained. When the number of times of coating baking is repeated two or more times, the tension increases, and the effect of reducing iron loss is large. However, if the tension is more than 1.0 kg / mm ² , a considerable effect can be expected even once. EXAMPLES Examples will be described below. Example 1 Si: 3.2% in which dot-like grooves having a depth of 12 μm, a diameter of 50 μm, and a point-to-point distance of 0.2 mm were formed at intervals of 5 mm in the direction of 90 ° with respect to the rolling direction on the surface of the steel plate of the steel sheet. , High magnetic flux density unidirectional magnetic steel sheets (A) and (B) having a thickness of 0.15 mm were prepared. In the sample (A), the surface film was removed with hydrofluoric acid, and Ra was 0.1 μm by electrolytic polishing.
Adjusted below. Next, after immersion in 5% diluted sulfuric acid, a coating solution containing chromic anhydride + aluminum phosphate + colloidal silica as a main component is applied, and 800 ° C. ×
Annealing was performed for 30 seconds. Then, coating under the same conditions and annealing at 820 ° C. for 30 seconds were repeated twice. For sample B, coating and annealing at 820 ° C. × 30 seconds were performed once. FIG. 4 shows cross-sectional photographs of the coatings of the samples (A) and (B). The boundary between the ground iron and the coating of the sample (A) is smoother than that of the sample (B). The magnetic properties are as follows. Sample (A) showed an extremely low iron loss value. Example 2 C: 0.054%, Si: 3.3%, Mn: 0.14%, S: 0.007%,
Acid-soluble Al: 0.030%, N: 0.0075%, Cr: 0.10%, Sn:
After heating a steel ingot consisting of 0.05% and the balance of Fe and unavoidable impurities to 1150 ° C., it was hot-rolled to a sheet thickness of 1.6 mm. This hot rolled sheet was annealed at 1100 ° C., and then pickled,
. It was cold rolled to a thickness of 16 mm. Next, after decarburizing annealing was performed at 830 ° C. in a wet hydrogen nitrogen atmosphere, nitriding was performed at 750 ° C. in a mixed gas of hydrogen, nitrogen, and ammonia. Next, an annealing separator MgO was applied and finish annealing was performed at 1200 ° C. to complete secondary recrystallization. Samples A and B having substantially uniform magnetic properties were selected from the obtained samples, and a groove having a depth of 14 μm and a width of 50 μm was formed in the direction of 75 ° with respect to the rolling direction by 5 mm using a toothed roll.
Formed at intervals. Next, annealing was performed at 850 ° C. × 2 hours. Next, after removing the surface film of the sample A with an acid, Ra was adjusted to 0.1 μm (a thickness reduction of 10 μm) with a mixed solution of a hydrogen peroxide solution and hydrofluoric acid.
) The following mirror surface. Next, a coating solution containing chromic anhydride, aluminum phosphate, and colloidal silica as the main components was applied to each of Samples A and B at a rate of 3 g / m ² per side, and 8
Tensile coating was performed at 20 ° C. for 30 seconds, and the magnetism was measured. Further, the same tension coating was repeated, and the magnetic measurement was performed. Table 1 shows the results. [Table 1] Sample A had extremely low iron loss compared to Sample B. Example 3 C: 0.056%, Si: 3.6%, Mn: 0.09%, S: 0.007%,
Acid-soluble Al: 0.029%, N: 0.0078%, Cr: 0.08%, Sn:
A steel ingot consisting of 0.04%, the balance being Fe and unavoidable impurities, was heated to 1150 ° C., and then hot-rolled to a thickness of 1.4 mm. After annealing this hot rolled sheet at 1100 ° C., it was pickled and cold rolled to a thickness of 0.14 mm. Next, after decarburizing annealing was performed at 830 ° C. in a wet hydrogen nitrogen atmosphere, nitriding was performed at 750 ° C. in a mixed gas of hydrogen, nitrogen, and ammonia, and the [N] amount of the steel sheet was set to 200 ppm. Next, Al ₂ O ₃ as an annealing separating agent is dissolved in alcohol and applied, and then 1200 ° C. ×
Finish annealing was performed for 20 hours. Then, in the state of washing and drying, no forsterite was formed on the surface of the steel sheet, and the surface roughness was Ra = 0.3 μm. Next, a groove having a depth of 12 μm and a width of 50 μm was formed in the same state as in Example 2 using a toothed roll. Then, it is rinsed with 10% dilute sulfuric acid for a short time, washed with water and dried, and coated with a coating solution mainly composed of chromic anhydride, aluminum phosphate and colloidal silica at a rate of 3 g / m ² on one side, and annealed at 880 ° C. for 30 seconds. Was performed and the magnetism was measured. Further, the same coating baking treatment was repeated, and the magnetism was measured. Table 2 shows the results. [Table 2] Example 4 C: 0.080%, Si: 3.5%, Mn: 0.075%, S: 0.025%
, Acid-soluble Al: 0.035%, N: 0.0080%, Sn: 0.13%, Cu
: A steel ingot consisting of 0.07%, the balance being Fe and unavoidable impurities was heated to 1350 ° C. and then hot-rolled to a thickness of 2.3 mm. Then, after hot-rolled sheet annealing was performed at 1000 ° C., it was pickled and cold-rolled to 1.35 mm. Next, annealing was carried out at a temperature of 1120 ° C. in the former stage and 900 ° C. in the latter stage, and then poured into hot water at 100 ° C., cooled, then pickled, and cold rolled to 0.17 mm. Next, the cold-rolled sheet was degreased, and a 2% aqueous sodium hydroxide solution was applied thereto.
Decarburization annealing was performed at 50 ° C. Next, a MgO slurry was applied and finish annealing was performed at a temperature of 1200 ° C. Next, after washing and drying, grooves having a depth of 15 μm and a width of 50 μm were formed at intervals of 5 mm in the direction of 75 ° with respect to the rolling direction using a toothed roll. Then after annealing at 800 ° C,
The average roughness of the surface after immersion in a 5% aqueous sulfuric acid solution was approximately 0.2 μm. Next, after applying a coating solution containing chromic anhydride, aluminum phosphate, and colloidal silica as main components at a coating amount of 3 g / m ² per side and annealing conditions of 820 ° C. for 30 seconds, application and annealing under the same conditions are performed. Was repeated. Magnetic properties are iron loss W _13/5
0 = 0.28 w / kg, indicating a very low iron loss value. According to the present invention, there is a wide range of uses as various iron core materials, and in particular, it is highly useful as a material for wound iron core transformers that require strain relief annealing, and is one-way with extremely low iron loss. An electrical magnetic steel sheet is provided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing the relationship between the average roughness of a steel sheet surface and iron loss. FIG. 2 is a diagram showing a relationship between the number of times of coating and baking of a coating liquid and iron loss. FIG. 3 is a diagram showing the relationship between the number of times of coating and baking of a coating liquid and the film tension. FIG. 4 is a photograph showing a cross section of a coating before removing the coating and a cross section of the coating after coating after removing the coating. FIG. 5 is a diagram showing a relationship between coating baking temperature and film tension.

Claims (1)

Claims: 1. A steel plate having a surface iron surface having a Ra of 0.4 μm or less and a linear or dot-like groove having a depth of more than 5 μm and a width of 300 μm or less in the plate surface in the rolling direction. 45 to
In the direction of 90 ° forms the 2~15mm spacing, tension coating on the surface of the steel sheet
The iron loss with a tension insulating coating obtained by applying and baking the solution is W13 / 50: 0.3
An ultra-low iron loss unidirectional electrical steel sheet having a sheet thickness of 0.17 mm or less containing 4 w / kg or less of Si 4.5% or less. 2. A linear or dot-like groove having a surface iron surface Ra of 0.4 μm or less and a depth of more than 5 μm and a width of 300 μm or less in the steel sheet having a diameter of 45 to 45 μm.
Si4 characterized by being subjected to a tension coating treatment of applying and coating a tension coating solution in a temperature range of more than 750 ° C to 950 ° C on finish-annealed unidirectional magnetic steel sheets formed at intervals of 2 to 15 mm in a direction of 90 °. 0.17mm or less including 5% or less
The method of manufacturing the ultra-low iron loss unidirectional electrical steel sheet below . 3. A tension coating process in a temperature range of more than 750 ° C. to 950 ° C.
The method for producing an ultra-low iron loss unidirectional magnetic steel sheet having a sheet thickness of 0.17 mm or less according to claim 2, wherein the method is repeated at least once. 4. A tension coating treatment in a temperature range of more than 750 ° C. to 950 ° C.
. 3. The sheet thickness according to claim ^{2, wherein} a tension of more than 0 kg / mm ^{2 is applied} .
A method for manufacturing an ultra-low iron loss unidirectional magnetic steel sheet of 17 mm or less . 5. A plate thickness of 0.17 mm according to claim 2, wherein a liquid mainly composed of chromic anhydride-aluminum phosphate-colloidal silica is used as the tension coating liquid. The following method for producing an ultra-low iron loss unidirectional electrical steel sheet.