CN1054885C - Method for producing grain-oriented electrical steel sheet having mirror surface and improved iron loss - Google Patents

Abstract

Disclosed is a method of producing a grain oriented electrical steel sheet having a mirror surface in the form of a strip containing 0.8-4.8% Si and having been subjected to a series of conventional procedures including hot rolling with or without annealing , one or at least two cold rollings with intermediate annealing to obtain the final gauge, decarburization annealing with or without nitriding, coating with an annealing spacer mainly containing non-hydrated oxides, followed by final annealing, which Improvements include:

Satisfy the relation

[A]>0.2×[O]

Where [A] is the total concentration (% by weight) of alkali metal impurities in the annealed spacer,

And [O] is the amount of oxygen (g/m ² ) contained in the steel sheet immediately before final annealing.

Description

Method for producing a grain oriented electrical steel sheet having a mirror surface and improved iron loss

The present invention relates to a method of producing grain oriented electrical steel sheets for use as iron cores for transformers or other electrical appliances. More precisely, the present invention relates to a method of producing a grain-oriented electrical steel sheet in which iron loss is reduced by making the sheet mirror-like and free of precipitates in the surface region.

Grain-oriented electrical steel sheets for different types of electrical equipment, mainly transformers, contain 0.8-4.8% Si and have a crystal structure preferentially arranged in {110}<001> orientation. The characteristics required for grain-oriented electrical steel sheets are high magnetic flux density and low iron loss, which are represented by B ₈ and W _17/50 respectively. A core material exhibiting low power loss, that is, a grain-oriented electrical steel sheet having low iron loss, is strongly demanded from the viewpoint of environmental protection and energy saving.

Iron loss can be subdivided into eddy current loss and hysteresis loop loss. The former is reduced in proportion to the reduction of the magnetic domain width of the steel plate, while the latter can be reduced by removing the obstacles to the domain wall motion. The main causes of the trouble are the uneven or rough surface of the steel plate and the presence of precipitates near the surface of the steel plate.

In the industrial production of grain-oriented electrical steel sheets with low iron loss, priority has been given to the development of magnetic domain improvement technology. For example, in Japanese Unexamined Patent Publication (Kokai) No. 55-18566, it is disclosed that partial or linear microstrain is applied to a finish-annealed steel sheet by laser beam irradiation in the case of a laminated core material. Also, as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 61-117218, in the case of a core material used for winding, stress relief annealing is applied to the manufactured core without causing magnetic domain improvement Effect. According to the above method, since the eddy current loss is greatly reduced, the total iron loss is reduced.

On the other hand, various methods of producing grain-oriented electrical steel sheets with low hysteresis loop loss at low cost have been proposed. These methods are aimed at obtaining a uniform and smooth, or mirror-like steel surface (hereinafter referred to as "mirror steel surface"). However, industrial production using these methods has not yet been achieved.

The following presents various conventional solutions for reducing hysteresis loop losses and explains how these solutions cannot be commercialized.

On the surface of the grain-oriented electrical steel sheet produced by the current production process, there is an inner oxide layer mainly composed of SiO ₂ and a glass film mainly composed of forsterite (Mg ₂ SiO ₂ ). The inner oxide layer is formed on the steel surface by decarburization annealing. In addition, the above-mentioned glass film is formed on the above-mentioned inner oxide layer during the final annealing, which reacts _SiO2 with MgO, in order to prevent the coil windings from sticking to each other.

Since the glass film is formed on the basis of the above-mentioned internal oxide layer, the interface between the glass film and the steel plate is not smooth due to the presence of precipitates. As a result, these precipitates become obstacles to the movement of magnetic domains. This phenomenon is known from various reports, for example by S.D. Washko, T.H. Shen and W.G. Morris in Journal of Applied Physics., vol.53, pp8296-8298. Accordingly, various different methods of dealing with this phenomenon have been suggested. For example, one of these methods is to prevent the formation of a glass film during final annealing, and the other is to obtain a uniform and smooth surface by chemical and mechanical polishing after removal of the glass film. When coarse and high-purity alumina, which is a non-hydrated oxide, is used as an annealing spacer in the final annealing, no glass film is formed on the steel surface of the resulting product. This method is disclosed in US Patent No. 3,785,882.

However, the iron loss improvement shown is at most 2% due to the presence of residual deposits just below the steel surface as well as the residual inhomogeneous surface after final annealing.

In order to form a mirror surface by eliminating residual deposits present just below the steel surface, it is known to use a chemical or electrolytic polishing process as disclosed in Japanese Unexamined Patent Publication Nos. 49-96920 and 60-39123. These above-mentioned methods are suitable for processing small samples in the laboratory, but have not been practically used in industrial scale production. This is due to the difficulty of controlling chemical concentrations and the need for waste disposal facilities.

In terms of producing a precipitate-free grain-oriented electrical steel sheet having a specular-finish steel surface, the present inventors have previously proposed a method for preventing the The process by which precipitates are formed just below the steel surface by the application of an annealing spacer consisting mainly of aluminum oxide after the oxide layer formed on the decarburized steel sheet has been removed by pickling. According to this method, the iron loss can be reduced by 0.1w/kg at W _17/50 compared with the case where the oxide layer is not eliminated. Although pickling can be carried out on an industrial scale according to the method described above, this method requires additional investment in a pickling plant thereby increasing production costs. Therefore, there is a strong demand for the development of a grain-oriented electrical steel sheet having a mirror surface to reduce iron loss through a simple process and at a low production cost.

The main object of the present invention is to provide a grain-oriented electrical steel sheet having a mirror surface, reduced iron loss, and no precipitates directly below the surface. Another object of the present invention is to provide a simple process which reduces production costs by eliminating the pickling step.

The present inventors conducted a series of experiments aimed at overcoming the disadvantages of the conventional technology and achieving the above-mentioned purpose in order to develop a more efficient production method for obtaining a mirror-like steel surface without precipitates directly below the surface of the grain-oriented electrical steel sheet product.

In this study, the present inventors found that the amount of impurities contained in the oxide used as an annealing spacer, especially the concentration of alkali metals, was obtained in accordance with the amount of oxygen contained in the steel sheet at the time of decarburization annealing. Controlled, the formation of precipitates that increase iron loss can be prevented from the start, and in addition, the formation of mirror surfaces can be promoted in the final annealing step.

According to the present invention, reduction of iron loss is achieved by using an annealing spacer mainly composed of non-hydrated oxides and controlling the concentration of alkali metal impurities in the annealing spacer and the amount of oxygen in the steel sheet prior to final annealing. Provided is a grain-oriented electrical steel sheet with a low iron loss mirror surface. More specifically, according to the present invention, the mirror surface is obtained by satisfying the following relationship:

[A]>0.2×[O],

Where [A] is the total concentration (% by weight) of alkali metal impurities in the annealed spacer,

And [O] is the oxygen content (g/m ² ) in the steel sheet immediately before final annealing.

Furthermore, the present invention provides a non-hydrated oxide mainly composed of alumina contained in the annealing spacer to obtain a mirror steel surface and reduced iron loss.

In addition, the above-mentioned alkali metal impurity is composed of at least one of Li, Na and K. The annealed spacer additionally contains at least one of Li, Na or K hydroxides, nitrates, sulfates, chlorides or acetates.

Thus, a mirror steel surface free of precipitates directly below the surface can be easily obtained by a simple method in order to reduce iron loss, especially hysteresis loop loss.

Figure 1 shows the results of X-ray diffraction (CuKα) microscopy of a grain oriented electrical steel sheet coated with alumina as an annealing spacer followed by final annealing. (a) shows an example of the results of X-ray diffraction analysis (CuKα) in the case of using high-purity alumina. (b) shows an example of the results of X-ray diffraction analysis (CuKα) in the case of using alumina containing 0.2 (wt%) Na as an impurity.

Figure 2 is a graph illustrating the relationship between the amount of sodium in the alumina as an annealing barrier and the oxygen content in the steel sheet during decarburization annealing and the formation of precipitates just below the steel surface. "0" represents the absence of precipitates, and "·" represents the presence of precipitates.

Figure 3 is a photomicrograph showing a cross-sectional view of a grain oriented electrical steel sheet coated with alumina as an annealing spacer and then subjected to a final anneal. (a) shows an example in the case of using high-purity alumina. (b) shows an example in the case of using alumina containing 0.2 (wt%) Na as an impurity.

The present inventors have used various kinds of alumina - usually oxides used as an annealing spacer - and found that sodium, which is an impurity contained in the alumina, affects the formation of precipitates and the specular condition of the steel surface. This is because when there is a large amount of Na, a mirror surface can be obtained even if an oxide film exists. Furthermore, while the steel surface exhibited a mirror-like condition, no deposits were observed beneath the steel surface. The present inventors have not found out the reason for this. It is thought that the reduction of _SiO2 formed upon decarburization annealing may be promoted during the final annealing step due to the presence of Na. If the reduction of _SiO2 tends to occur in the final annealing step, the precipitates once formed that are under the surface of the steel are reduced and disappear. Otherwise they would not have formed in the first place. As a result, mirror steel surfaces can be easily obtained.

In the production of grain-oriented electrical steel sheets, carbon is an essential element to obtain the desired crystal structure in the intermediate product, so as to preferentially promote the {110}<001> crystal orientation in the final product. Although carbon must be included in the desired amount at an early stage of production, carbon remaining in the final product increases iron loss. Therefore, a recrystallization annealing is performed in a wet hydrogen/nitrogen mixed atmosphere for decarburization. This primary recrystallization annealing is usually called decarburization annealing. The concentration of residual carbon in the final product must be limited to less than 30 ppm.

In general, the speed of the decarburization reaction depends on the reaction potential of oxygen in the decarburization atmosphere. When the reaction potential of oxygen becomes lower, the decarburization reaction slows down. On the other hand, the oxygen potential of the reaction can be increased, forming an inner oxide layer mainly composed of SiO ₂ on the surface of the electrical steel sheet. At present, there has not been found a condition under which the decarburization and the formation of the inner oxide layer can be simultaneously completed during the decarburization period without lowering the productivity.

Therefore, decarburized annealed steel sheets processed under normal conditions necessarily include an inner oxide layer mainly composed of _SiO2 . As described above, if a coarse and high-purity alumina coating is applied to a decarburized steel sheet having an inner oxide layer, followed by final annealing, a grain-oriented electrical steel sheet having no oxide film on the surface can be obtained. However, the steel sheet thus obtained not only exhibited a mirror steel surface but also had precipitates under the steel surface. These precipitates were clearly observed in the micro-sectional view of the steel sheet surface shown in Fig. 3(a).

The chemical structure of these precipitates that are forming below the steel surface depends on whether or not acid-soluble Al was present in the steel sheet prior to final annealing. When acid-soluble aluminum is contained in the steel sheet prior to final annealing, it is observed by X-ray diffraction (CuKα) microscopy that the formed precipitates consist mainly of mullite (3Al ₂ O ₃ ·2SiO ₂ ). On the other hand, when no acid-soluble Al was contained in the steel sheet before final annealing, observation of the residue by infrared spectroscopy showed that the formed precipitates were mainly composed of _SiO2 .

Since the amount of precipitates being formed below the steel surface increases with increasing dew point during decarburization annealing, the origin of the SiO ₂ contained in these precipitates is considered to be the SiO ₂ -containing interior formed during decarburization annealing. oxide layer. On the other hand, the origin of Al ₂ O ₃ contained in the precipitates is presumed to be acid-soluble Al contained in the steel sheet to control secondary recrystallization, and alumina used as an annealing spacer. This is because these precipitates are not exposed on the steel surface. Starting from the above facts, it will be understood that the _SiO2 inner oxide layer formed during the decarburization annealing remains just below the steel surface and thus this _SiO2 cannot be reduced by the reducing atmosphere of the final annealing. In particular, when the steel sheet contains acid-soluble Al, this acid-soluble Al can react with _SiO2 and form mullite just below the steel surface. Since these precipitates exist within the steel sheet, they cannot be reduced under the reducing atmosphere conditions at high temperature in the second half of final annealing. If these precipitates are not present on the steel surface, atomic diffusion is strongly promoted, thus accelerating the formation of the mirror finish. On the other hand, if these precipitates are present just below the steel surface, the facilitation of atomic diffusion and thus the formation of a mirror finish during final annealing is prevented.

Considering the above-mentioned mechanism regarding the formation of precipitates under the surface of the steel during final annealing, problems always arise in the production of grain-oriented electrical steel sheets under the following conditions: (1) when the steel contains absorbing Si, (2) when When decarburization annealing is necessary, and (3) when a mirror surface is formed during final annealing without forming a glass film containing forsterite. Thus, the present invention can basically be applied to the production of all kinds of grain-oriented electrical steel sheets in accordance with the above-mentioned conditions (1)-(3).

The present inventors have used various types of alumina, which are commonly used as annealing separators, containing varying amounts of impurities such as Na, K or Li and/or other compounds, and found that , when Na is contained in alumina as an impurity, even if there is an oxide film, it will affect the formation of precipitates and the condition of the mirror brightness. Furthermore, this phenomenon depends on the amount of Na. Therefore, when alumina containing a large amount of Na is used as the annealing spacer, no precipitates are found just below the surface of the steel and a mirror-like surface is obtained. This phenomenon is clearly observed in the micrographs of Fig. 3(a) and Fig. 1(b). The inventors of the present invention have not yet understood the reason for this phenomenon. It was hypothesized that the reduction of _SiO2 formed upon decarburization annealing could be accelerated in the final annealing step because of the presence of Na. If the reduction of _SiO2 is prone to occur in the final annealing step, the precipitates formed under the surface of the steel are reduced and disappear, or are not formed at all. As a result, if alumina containing a large amount of Na is used as an annealing spacer. A mirror surface can be easily obtained.

According to further research on the Na concentration in alumina required to prevent precipitates from forming below the steel surface, it was found that the presence of precipitates depends on the oxygen content in the decarburization anneal. Figure 2 shows the Na concentration in the alumina and the precipitation state of the precipitates just below the steel surface. When the oxygen content in the decarburized steel sheet is small, the required amount of Na is also small. This leads to the following relation:

[A]>0.2×[O] where [A] is the Na concentration (% by weight) in the alumina used as an annealing spacer, and [O] is the oxygen content per surface of the decarburized steel sheet (g/m ² ). Therefore, when the decarburized steel sheet and the annealed spacer satisfy the above relationship, the final product is free of precipitates and has a mirror surface.

In order to satisfy the above-mentioned relationship of Na contained in alumina used as an annealing spacer, it is preferable to lower the dew point of the decarburization annealing atmosphere, or to remove the oxide film by light pickling after the decarburization annealing. In addition, in order to satisfy the above-mentioned relationship under the oxygen content of the decarburized steel sheet, it is preferable to select alumina containing an appropriate amount of Na as an impurity, or to arbitrarily different sodium compounds such as sodium oxide, hydroxide Compounds, chlorides, sulfates or nitrates are added to alumina. In each of the above cases, a mirror surface can be obtained. As for impurities other than Na contained in alumina, alkali metals such as Li and K etc. show the same effect as Na. Therefore, a lithium compound or a potassium compound may be added to alumina.

When the present invention is applicable to the actual production of grain-oriented electrical steel sheets, typical conventional processes can be used. These methods include the method of N.P. Goss et al. using MnS as the main inhibitor disclosed in U.S. Patent No. 1,965,559, Taguchi, Sakakura et al. using AlN and MnS as the main inhibitors disclosed in U.S. Patent No. 3,287,183 and the method of Komatsu et al. using (Al,Si)N as the main inhibitor disclosed in Japanese Patent Publication No. Sho 60-45285 (publication). The components of the steel of the present invention and the amounts used are explained below.

Carbon is an element necessary for the formation of the gamma phase and for controlling the primary recrystallization structure prior to final annealing to ensure proper secondary recrystallization. Therefore, the carbon contained in the cold-rolled steel sheet must be in the range of 0.02-0.1%. If the carbon content is more than 0.1%, the primary recrystallization structure deteriorates and a long period is required for decarburization.

Silicon is an important element for increasing resistance and reducing iron loss. If the silicon content is less than 0.8%, alpha to gamma transformation occurs during final annealing and damages the crystal structure and orientation, while if the silicon content is greater than 4.8%, cold rolling becomes difficult because of cracks. The preferred silicon content is 0.8%-4.8%.

Manganese and sulfur form inhibitors that suppress the generation of primary grains. In order to ensure stable secondary recrystallization, the contents of manganese and sulfur must be limited to the ranges of 0.02-0.3% and 0.005-0.40%, respectively.

Acid-soluble aluminum is a basic element, which combines with nitrogen to form AlN or (Al, Si)N as an inhibitor to obtain high magnetic flux density. The preferred content of acid-soluble aluminum is 0.012-0.05%.

Nitrogen is also an essential element that combines with acid-soluble aluminum to form an inhibitor. If the nitrogen content is greater than 0.01%, scabs form undesirably in the final product. The preferred nitrogen content is not more than 0.01%.

In addition to acid-soluble aluminum, other elements such as B, Bi, Pb, S, Se, Sn or Ti can also be used to form the inhibitor.

The hot-rolled strip adjusted to the above-mentioned composition range by known methods is directly cold-rolled or short-time hot-rolled strip annealed. The hot strip annealing is effective to improve the magnetic energy of the final product and is performed at a temperature between 750°C and 1200°C for 30 seconds to 30 minutes. The annealing conditions are determined according to the desired product quality or cost.

In the case of using AlN or (Al, Si)N as an inhibitor, with the known cold rolling method disclosed in Japanese Patent Publication (Gazette) No. Sho 40-15644, at a reduction ratio of more than 8 to the final thickness % under the conditions of cold rolling. Of course, cold rolling conditions may be varied depending on the inhibitor used.

The cold-rolled strip is then decarburized annealed at a temperature between 750°C and 900°C in a wet atmosphere to effect primary recrystallization and remove carbon from the cold-rolled strip. In the case of using (Al,Si)N as the main inhibitor, nitriding treatment is performed after decarburization annealing. The nitriding treatment is carried out in an atmosphere gas containing NH ₃ with nitriding ability. The amount of nitriding is more than 0.005% of the total amount of nitrogen contained in the steel plate, preferably greater than the aluminum equivalent of the steel plate.

Subsequently, an annealing spacer is applied to the decarburized or nitrided steel strip to form a glass film and prevent sticking during the final anneal. The annealed spacer useful in the present invention is a poorly hydratable oxide. If an oxide that is easily hydrated, such as MgO, is used, a peroxidation reaction occurs on the steel surface during final annealing or an oxide layer is formed on the steel surface due to the reaction with the oxide film formed by decarburization, resulting in less than the mirror.

If the annealed spacer is a stable oxide with non-hydratable properties, it is not limited to a particular oxide. Oxides like ZrO ₂ or Y ₂ O ₃ can be used.

Alumina is a suitable oxide for the present invention due to its non-hydratable nature and low cost. Alumina, which is inexpensive, is suitable because it contains a lot of sodium. This annealed spacer is applied as a slurry by conventional means or by electrostatic coating. When the annealed spacer is suspended in water, it is desirable to add a resist to the suspension to prevent rusting of the steel surface when coated. In the case of using coarser oxide particles suspended in water, a binder such as methyl cellulose is added to improve coatability and adhesion.

The specified requirement for obtaining the mirror surface of the present invention is that the conditions specified below must be satisfied during the decarburization annealing and the coating of the annealing spacer. The stated condition is the relationship: [A]>0.2×[O], where [O] is the amount of oxygen (g/m ² ) in the steel sheet immediately before final annealing, and [A] is the amount of oxygen in the annealed spacer Total concentration (% by weight) of alkali metal impurities.

The above conditions can be achieved by the following means. When an oxide containing low concentration of alkali metal impurities is used as an annealing spacer, the oxygen content in the steel sheet can be reduced by light pickling treatment after decarburization annealing. However, this method is not recommendable from a production cost point of view since it requires an extra step. In the decarburization annealing process, a non-hydrated oxide containing alkali metal impurities can be used as an annealing separator according to the amount of oxygen generated contained in the steel plate when decarburization is almost completed, and one that can avoid oxidation of the steel plate can be selected. Appropriate atmosphere and annealing cycle.

The following measures can be taken to ensure the necessary concentration of alkali metal impurities in the non-hydrated oxide as an annealing spacer. Inexpensive commercially available alumina, which is commonly used, naturally contains the impurity Na in an amount of about 0.2% due to its production method. Therefore, this low-cost, commercially available alumina is very useful as an annealing spacer for the purposes of the present invention. When the amount of Na impurity contained in the alumina is not enough to match the oxidation amount of the steel plate, or when a non-hydrated oxide without alkali metal impurities is used as an annealing spacer, an alkali metal chloride (or salt) is added to this Oxide powder or an alkali metal chloride (or salt) is dissolved in the necessary amount in the slurry for preparing the annealed spacer. For this alkali metal chloride (or salt), it is feasible to use a water-soluble salt selected from hydroxides, nitrates, sulfates, chlorides or acetates of Na, K or Li, etc. group of objects.

Finally, after applying the annealing spacer, a final anneal is performed for secondary recrystallization and cleanup. As disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2-258929, a prescribed heating period in which a constant temperature is maintained in the heating step to promote secondary recrystallization is effective for increasing the magnetic flux density.

After the secondary recrystallization is completed in the final annealing, when the temperature is higher than 100°C, the heated steel strip is kept in a 100% hydrogen atmosphere to purify nitrides and adjust the mirror surface of the steel surface.

An insulating coating is applied to the strip to create tension and reduce iron losses. In addition, a magnetic domain improvement process by laser irradiation may be applied to further reduce iron loss.

The present invention will now be described in detail with reference to the following examples, which are not meant to limit the scope of the present invention. The present invention will be applicable to other steel compositions or other production processes that have been disclosed so far, either individually or in combination: (1) the steel contains Si, (2) decarburization annealing is necessary, and (3) In grain-oriented electrical steel sheets, a mirror surface is formed during final annealing without a forsterite-containing glass film. Example 1

A compound containing 0.05% (weight) C, 3.3% (weight) Si, 0.1% (weight) Mn, 0.007% (weight) S, 0.03% (weight) acid-soluble Al, 0.008% (weight) N, and 0.05 % (weight) Sn, the remainder including Fe and unavoidable impurities in the grain-oriented electrical steel for processing, the method used is the usual production steps, namely hot rolling to a thickness of 2.3mm, annealing the hot-rolled strip at a temperature of 1100°C for 2 Minutes, then cold rolled to a final thickness of 0.23 mm and pickled at the same time. The cold-rolled strip thus obtained was then treated by decarburization annealing in different atmospheres for different annealing times. Table 1 shows the oxygen content in the steel sheet. Then, nitriding treatment is carried out in _NH3 atmosphere gas, so that the nitrogen content in the steel plate reaches 0.025% to strengthen the inhibitor. Subsequently, an annealed spacer is applied to the nitrided steel sheet. Conventional MgO was coated on some steel sheets, and alumina of different concentrations in the form of a slurry containing different kinds of alkali metals as impurities was coated on the remaining steel sheets. Then, final annealing was carried out by heating the steel sheet to 1200°C in 100% nitrogen at a constant heating rate of 10°C/hour and maintaining it at 1200°C in 100% hydrogen for 20 hours. At 1200°C the atmosphere gas was switched from nitrogen to hydrogen. Finally, an insulating coating and a magnetic domain modification treatment by laser radiation are imposed on the final annealed steel sheet. The obtained product had the magnetic properties shown in Table 1.

Table 1 Oxygen amount/unit surface (g/m ² ) Types of Annealing Spacers Concentration of impurity Na in the annealing spacer (weight %) The amount of alkali metal added to the annealing spacer (wt%) Alkali metal addition method condition of the steel surface Is there any precipitate under the surface Magnetic properties B ₈ (T) W _17/50 (w/kg) Comparative example 1 0.7 MgO - - - glass film - 1.91 0.80 Comparative example 2 0.7 Al ₂ O ₃ 0.12 - - Non-specular have 1.92 0.81 The present invention 1 0.7 Al ₂ O ₃ 0.20 - - mirror none 1.94 0.63 Invention 2 0.5 Al ₂ O ₃ 0.05 0.10 Add NaOH mirror none 1.94 0.63 Comparative example 3 0.3 Al ₂ O ₃ 0.03 - - Non-specular have 1.95 0.79 Invention 3 0.3 Al ₂ O ₃ 0.03 - - mirror none 1.95 0.62 Invention 4 0.3 Al ₂ O ₃ 0.03 0.05 Join KOH mirror none 1.96 0.61 Invention 5 0.3 Al ₂ O ₃ 0.03 0.05 Add LiOH mirror none 1.96 0.62 Comparative example 4 0.2 Al ₂ O ₃ 0.015 - - Non-specular have 1.94 0.80 The present invention 6 0.2 Al ₂ O ₃ 0.08 - - mirror none 1.97 0.58 The present invention 7 0.2 Al ₂ O ₃ 0.015 0.05 Add NaCl environment none 1.96 0.61 Invention 8 0.2 Al ₂ O ₃ 0.015 0.05 Add NaNH ₃ mirror none 1.96 0.60 The present invention 9 0.2 Al ₂ O ₃ 0.015 0.05 Add potassium acetate environment none 1.95 0.62 Example 2

Will contain 0.07% (weight) C, 3.3% (weight) Si, 0.07% (weight) Mn, 0.025% (weight) S, 0.026% (weight) acid-soluble Al, 0.008% (weight) N, and 0.1% ( Weight) Sn, the balance including Fe and unavoidable impurities of grain-oriented electrical steel sheet for processing, the method used is the usual production steps, that is, hot rolling to a thickness of 2.3mm, the hot rolled strip is not annealed at a temperature of 1100 ℃ 2 minutes, then cold rolled to a final thickness of 0.23mm, pickling at the same time. The cold-rolled strip thus obtained is then treated by decarburization annealing in different atmospheres for different annealing times. Table 2 shows the oxygen content in the steel sheet.

Subsequently, an annealing spacer is applied to the decarburized steel strip. Conventional MgO was coated on some steel sheets, while alumina containing different kinds of alkali metals as impurities and slurries of different concentrations were coated on the remaining steel sheets. Then, final annealing is carried out by heating the steel plate to 1200°C at a constant heating rate of 15°C/hour in a mixed atmosphere containing 15% nitrogen and 85% hydrogen, and then further heating the steel plate at a temperature of 1200°C. 20 hours in 100% hydrogen. Finally the gas of the atmosphere was switched from nitrogen to hydrogen at 1200°C. Finally, an insulating coating and a magnetic domain modification treatment by laser radiation are applied to the final annealed strip. The obtained product has the magnetic properties shown in Table 2.

Table 2 Oxygen amount/unit surface (g/m ² ) Types of Annealing Spacers Concentration of impurity Na in the annealing spacer (weight %) The amount of alkali metal added to the annealing spacer (wt%) Alkali metal addition method condition of the steel surface Is there any precipitate under the surface Magnetic properties B ₃ (T) W _17/50 (w/kg) Comparative example 1 0.7 MgO - - - glass film - 1.90 0.81 Comparative example 2 0.7 Al ₂ O ₃ 0.12 - - Non-specular have 1.92 0.80 The present invention 1 0.7 Al ₂ O ₃ 0.20 - - mirror none 1.93 0.65 Invention 2 0.5 Al ₂ O ₃ 0.05 0.10 Add NaOH mirror none 1.93 0.66 Comparative example 3 0.3 Al ₂ O ₃ 0.03 - - Non-specular none 1.94 0.78 Invention 3 0.3 Al ₂ O ₃ 0.08 - - mirror none 1.96 0.60 Invention 4 0.3 Al ₂ O ₃ 0.03 0.05 Join KOH mirror none 1.95 0.61 Invention 5 0.3 Al ₂ O ₃ 0.03 0.05 Add LiOH mirror none 1.95 0.62 Comparative example 4 0.2 Al ₂ O ₃ 0.015 - - Non-specular have 1.94 0.80 The present invention 6 0.2 Al ₂ O ₃ 0.08 - - mirror none 1.95 0.60 The present invention 7 0.2 Al ₂ O ₃ 0.015 0.05 Join NaCI mirror none 1.96 0.60 Invention 8 0.2 Al ₂ O ₃ 0.015 0.05 Add NaNH ₃ mirror none 1.95 0.61 The present invention 9 0.2 Al ₂ O ₃ 0.015 0.05 Add potassium acetate mirror none 1.96 0.62 Example 3

The grain-oriented electrical steel material containing 0.05% (weight) C, 3.3% (weight) Si, 0.07% (weight) Mn, and 0.025% (weight) S, the balance including Fe and unavoidable impurities is processed, and the used The method is a common production step, that is, hot rolling to a thickness of 2.5mm, pickling at the same time, and then cold rolling to a final thickness of 0.30mm, while performing intermediate annealing at a temperature of 900°C for 2 minutes. Then, the cold-rolled strip thus obtained is subjected to decarburization annealing treatment in different atmospheres and different annealing times. Table 3 shows the amount of oxygen in this steel sheet. Subsequently, an annealing spacer is applied to the decarburized steel strip.

Commonly used MgO was coated on some steel sheets, while alumina containing different kinds of alkali metals as impurities was coated on the remaining steel sheets in different concentrations of slurry. Then, final annealing is carried out by heating the sodium plates to 1200°C at a constant heating rate of 15°C/hour in a mixed atmosphere containing 15% nitrogen and 85% hydrogen and heating the steel plates at a temperature of 1200°C Keep under 100% hydrogen atmosphere for 20 hours. The gas of the atmosphere was switched from nitrogen to hydrogen at 1200°C. Finally, an insulating coating and a magnetic domain modification treatment by laser radiation are applied to the final annealed steel sheet. The obtained product had the magnetic properties shown in Table 3.

table 3 Oxygen amount/unit surface (g/m ² ) Types of Annealing Spacers Concentration of impurity Na in the annealing spacer (weight %) The amount of alkali metal added to the annealing spacer (wt%) Alkali metal addition method condition of the steel surface Is there any precipitate under the surface Magnetic properties B ₃ (T) W _17/50 (w/kg) Comparative example 1 0.7 MgO - - - glass film - 1.85 1.21 Comparative example 2 0.7 Al ₂ O ₃ 0.12 - - Non-specular have 1.87 1.17 The present invention 1 0.7 Al ₂ O ₃ 0.20 - - mirror none 1.87 1.07 Invention 2 0.5 Al ₂ O ₃ 0.05 0.10 Add NaOH environment none 1.86 1.06 Comparative example 3 0.3 Al ₂ O ₃ 0.03 - - Non-specular have 1.87 1.17 Invention 3 0.3 Al ₂ O ₃ 0.08 - - environment none 1.87 1.07 Invention 4 0.3 Al ₂ O ₃ 0.03 0.05 Join KOH mirror none 1.86 1.07 Invention 5 0.3 Al ₂ O ₃ 0.03 0.05 Add LiOH mirror none 1.86 1.07 Comparative example 4 0.2 Al ₂ O ₃ 0.015 - - Non-specular have 1.86 1.18 The present invention 6 0.2 Al ₂ O ₃ 0.08 - - mirror none 1.87 1.06 The present invention 7 0.2 Al ₂ O ₃ 0.015 0.05 Join NaCI mirror none 1.87 1.07 Invention 8 0.2 Al ₂ O ₃ 0.015 0.05 Add NaNH ₃ mirror none 1.86 1.07 The present invention 9 0.2 Al ₂ O ₃ 0.015 0.05 Add potassium acetate mirror none 1.86 1.07

Claims (7)

1. A method of producing a grain-oriented electrical steel sheet having a mirror surface, said steel sheet being in the form of a strip containing 0.02-0.1% C and 0.8-4.8% Si and having been subjected to a series of conventional processes, the method comprising with or without hot rolling with annealing, one or at least two cold rolling with intermediate annealing to obtain the final gauge, decarburization annealing with or without nitriding, coating with an annealing spacer mainly containing non-hydrated oxides, then Final annealing, whose improvements include: Satisfy the relation [A]>0.2×[O] where [A] is the total concentration (% by weight) of alkali metal impurities in the annealed spacer, and [O] is the amount of oxygen (g/m ² ) contained in the steel sheet just before final annealing. 2. A method of producing a grain-oriented electrical steel sheet having a mirror surface, said steel sheet being in the form of a strip containing 0.02-0.1% C, 0.8-4.8% Si, 0.012-0.05% acid-soluble Al, less than 0.01% N and 0.02-0.3% Mn and have been subjected to a series of conventional procedures including hot rolling with or without annealing, one or at least two cold rollings with intermediate annealing to obtain final thickness, decarburization annealing with nitriding, coating An annealed spacer comprising primarily non-hydrated oxides and a final anneal, the improvements comprising: Satisfy the relation [A]>0.2×[O] where [A] is the total concentration (% by weight) of alkali metal impurities in the annealed spacer, and [O] is the amount of oxygen (g/m ² ) contained in the steel sheet just before final annealing. 3. A method of producing a grain-oriented electrical steel sheet with a mirror surface, said steel sheet being in the form of a strip containing 0.02-0.1% C, 0.8-4.8% Si, 0.012-0.05% acid-soluble Al, less than 0.01% N , 0.02-0.3% Mn, and 0.005-0.040% S and has been subjected to a series of conventional procedures including hot rolling with or without annealing, one or at least two cold rollings with intermediate annealing to obtain the final thickness, Decarburization annealing, coating with an annealing spacer mainly containing non-hydrated oxides followed by final annealing, modifications include: Satisfy the relation [A]>0.2×[O] where [A] is the total concentration (% by weight) of alkali metal impurities in the annealed spacer, and [O] is the amount of oxygen (g/m ² ) contained in the steel sheet just before final annealing. 4. A method of producing a grain-oriented electrical steel sheet having a mirror surface, said steel sheet being in the form of a strip containing 0.02-0.1% C, 0.8-4.8% Si, less than 0.01% N, 0.02-0.3% Mn, and 0.005-0.040% S and has been subjected to a series of conventional procedures including hot rolling with or without annealing, one or at least two cold rollings with intermediate annealing to obtain final thickness, decarburization annealing, coating with a Annealed spacers containing primarily non-hydrated oxides, followed by final annealing, modifications include: Satisfy the relation [A]>0.2×[O] where [A] is the total concentration (% by weight) of alkali metal impurities in the annealed spacer, and [O] is the amount of oxygen (g/m ² ) contained in the steel sheet just before final annealing. 5. The method of claim 1, wherein the non-hydrated oxide consists essentially of alumina. 6. The method of claim 1, wherein the alkali metal impurities in the annealed spacer consist essentially of one or more metals selected from the group consisting of Li, Na or K. 7. The method of claim 1, wherein the annealing spacer contains one or more selected from the group consisting of Li, Na or K hydroxide, nitrate, sulfate, chloride or acetate compound.

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