CN108431244B - Oriented electrical steel sheet and method for manufacturing the same - Google Patents
Oriented electrical steel sheet and method for manufacturing the same Download PDFInfo
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
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Abstract
The method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention includes the steps of: providing a slab comprising in weight percent: si: more than 0% and 4.0% by weight or less, C: 0.001 to 0.4 wt%, and Mn: 0.001 to 2.0 wt%, the balance consisting of Fe and other impurities that are inevitably mixed in; reheating the slab; hot rolling the slab to manufacture a hot rolled steel sheet; carrying out hot rolled plate annealing on the hot rolled steel plate; performing primary cold rolling on the hot rolled steel plate subjected to annealing of the hot rolled plate; performing decarburization annealing on the cold-rolled steel sheet; carrying out secondary cold rolling on the steel plate subjected to decarburization annealing; and performing final annealing on the cold-rolled steel sheet, wherein the size (2L) of the magnetic domain existing in the crystal grains of the steel sheet subjected to the final annealing is smaller than the thickness (D) of the steel sheet.
Description
Technical Field
The present application relates to a grain-oriented electrical steel sheet and a method for manufacturing the same.
Background
Oriented electrical steel sheets are soft magnetic materials having excellent magnetic properties in the rolling direction, and are composed of crystal grains having a so-called gaussian (Goss) orientation in which the crystal orientation of the steel sheet is {110} <001 >.
Such a grain-oriented electrical steel sheet is manufactured by the steps of: after heating the slab, hot rolling, hot-rolled sheet annealing and cold rolling are performed to a final thickness of usually 0.15mm to 0.35mm, primary recrystallization annealing is performed, and high-temperature annealing is performed to form secondary recrystallization.
In this case, the lower the temperature rise rate is, the higher the aggregation degree of the secondary recrystallized gaussian orientation is, and the more excellent the magnetic properties are. In general, since the rate of temperature rise in high-temperature annealing of a grain-oriented electrical steel sheet is 15 ℃ or less per hour, it takes two or three days, not only for temperature rise, but also for purification annealing for 40 hours or more, and this step is a step with a large energy consumption. In addition, since the conventional final high-temperature annealing process performs Batch (Batch) annealing in a state of a steel coil, the following difficulties are generated in the process. First, since a temperature deviation occurs between the outer winding portion and the inner winding portion of the steel coil due to the heat treatment in the state of the steel coil, the same heat treatment pattern cannot be applied to each portion, and a magnetic deviation occurs between the outer winding portion and the inner winding portion. Second, in the process of coating MgO on the surface after the decarburization annealing and forming the undercoat layer in the high temperature annealing, various surface defects are generated, thereby decreasing the yield. Thirdly, since the decarburized plate after the decarburization annealing is wound into a roll and then subjected to high-temperature annealing, and then subjected to planarization annealing and then to insulation coating, the production process is divided into three steps, which causes a problem of a decrease in yield.
Disclosure of Invention
Technical problem to be solved
An embodiment of the present invention is directed to a method of manufacturing a grain-oriented electrical steel sheet and a grain-oriented electrical steel sheet manufactured by the method.
Technical scheme
The method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention includes the steps of: providing a slab comprising in weight percent: si: more than 0 and 4.0 wt.% or less, C: 0.001 to 0.4 wt% and Mn: 0.001 to 2.0 wt%, the balance consisting of Fe and other impurities that are inevitably mixed in; reheating the slab; hot rolling the slab to manufacture a hot rolled steel sheet; carrying out hot rolled plate annealing on the hot rolled steel plate; performing primary cold rolling on the hot rolled steel plate subjected to hot rolled plate annealing; decarburization annealing the cold-rolled steel sheet; carrying out secondary cold rolling on the steel plate subjected to decarburization annealing; and performing final annealing on the steel plate subjected to the cold rolling, wherein the size 2L of a magnetic domain existing in grains of the steel plate subjected to the final annealing is smaller than the thickness D of the steel plate (2L < D).
The slab may include more than 0 wt% and 1 wt% or less Si.
The slab may further include more than 0 wt% and 0.01 wt% or less of Al.
The slab reheating temperature may be 1050 to 1350 ℃.
The reduction ratios in the step of primary cold rolling and the step of secondary cold rolling may be 50% to 70%, respectively.
The step of decarburization annealing the cold-rolled steel sheet and the step of secondary cold rolling the decarburization annealed steel sheet may be repeated two or more times.
The decarburization annealing step may be performed at a temperature of 800 to 1150 ℃ in an atmosphere containing hydrogen at a dew point temperature of 0 ℃ or higher.
The step of the final annealing may include a first step performed in an atmosphere of 850 to 1150 ℃ with a dew point temperature of 10 to 70 ℃, and a second step performed in an atmosphere of a mixed gas including hydrogen and nitrogen at 900 to 1200 ℃ with a dew point temperature of 10 ℃ or less.
The first step may be performed for 300 seconds or less, and the second step may be performed for 60 seconds to 300 seconds.
The step of final annealing may be continuously performed after the step of cold rolling.
The amount of carbon in the electrical steel sheet after the step of final annealing may be more than 0 wt% and 0.003 wt% or less.
In the finish annealed steel sheet, the volume fraction of crystal grains having an orientation within 15 degrees from the {110} <001> orientation may be 50% or more.
The volume fraction of crystal grains having a grain diameter of 20 to 1000 μm in the steel sheet subjected to the finish annealing may be 50% or more.
The oriented electrical steel sheet according to an embodiment of the present invention includes, in wt%: si: greater than 0 wt% and 4.0 wt% or less, C: greater than 0 wt% and 0.003 wt% or less and Mn: 0.001 to 2.0 wt%, the balance being Fe and other impurities which are inevitably mixed in, and the size 2L of the magnetic domain existing in the grains being smaller than the thickness D of the steel plate.
Si may be included in an amount greater than 0 wt% and 1.0 wt% or less.
More than 0 wt% and 0.01 wt% or less of Al may be further included.
The domain size 2L present within the grain may be 10 μm to 500 μm.
The volume fraction of crystal grains having an orientation within 15 degrees from the {110} <001> orientation may be 50% or more.
The volume fraction of crystal grains having a particle diameter of 20 to 1000 μm may be 50% or more.
Advantageous effects
According to an embodiment of the present invention, it is possible to provide a method for manufacturing a grain-oriented electrical steel sheet capable of performing continuous annealing without performing Batch (Batch) type annealing in a state of a steel coil when performing final annealing.
Further, according to an embodiment of the present invention, the grain-oriented electrical steel sheet can be produced with only short annealing time.
Further, according to an embodiment of the present invention, it is possible to provide a grain-oriented electrical steel sheet without using a grain growth inhibitor.
Furthermore, according to an embodiment of the present invention, nitriding annealing may be omitted.
Drawings
Fig. 1 is a photograph showing the microstructure and magnetic domains of the oriented electrical steel sheet manufactured in example 1.
Detailed Description
The terms first, second, third, etc. are used for describing various parts, components, regions, layers and/or sections, but are not limited thereto. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first part, component, region, layer or section discussed below could be termed a second part, component, region, layer or section without departing from the scope of the present invention.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" include plural forms as well, unless the contrary is expressly stated. The meaning of "comprising" as used in the specification refines particular features, fields, integers, steps, acts, elements and/or components but does not preclude the presence or addition of other particular features, fields, integers, steps, acts, elements, components and/or groups thereof.
When it is referred to a portion being disposed "on" or "over" another portion, it is intended that the portion be formed directly on or over the other portion, or that there may be other portions between the two. In contrast, when a portion is referred to as being disposed directly "over" another portion, it means that there is no other portion between the two.
Although not defined differently, all terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms defined in a commonly used dictionary are additionally interpreted as meanings consistent with those of related art documents and the present disclosure, and are not interpreted as ideal or very formal meanings in the absence of definition.
In addition,% represents% by weight and 1ppm represents 0.0001% by weight unless otherwise specified.
Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art to which the present invention pertains can easily carry out the present invention. The present invention is not limited to the embodiments described herein, but may be embodied in various forms.
Generally, the required characteristics of a grain-oriented electrical steel sheet used for power conversion as a core material of a transformer are high magnetic flux density and low core loss characteristics. The high magnetic flux density can not only improve power conversion efficiency but also improve design magnetic flux density, and thus has an advantage that the size of the transformer can be reduced using less core materials. In addition, when core loss, which is a loss spontaneously generated in the grain-oriented electrical steel sheet during power conversion, is generated, there is an advantage in that no-load loss of the transformer can be reduced.
Research and technical development of oriented electrical steel sheets have been conducted so far mostly in order to reduce iron loss. The iron Loss of the grain-oriented electrical steel sheet is classified into several major components, i.e., Hysteresis Loss (hysteris Loss), conventional Eddy Current Loss (classic Eddy Current Loss), and abnormal Eddy Current Loss (abnormal Eddy Current Loss), as follows.
The hysteresis loss is a loss of the electrical steel sheet itself caused by the degree of magnetization of the oriented electrical steel sheet, and is small when there is no impurity or defect in the oriented electrical steel sheet and the concentration of the gaussian orientation is high.
The conventional eddy current loss is a loss caused by an eddy current generated from the steel sheet itself during magnetization of the oriented electrical steel sheet, and it has been attempted to reduce the loss by maximizing the eddy current of the steel sheet by increasing the Si content and reducing the thickness of the steel sheet. Another abnormal eddy current loss is a loss associated with movement and rotation of magnetic domains (magnetic domains) of an oriented electrical steel sheet under an alternating current of a transformer operation, which has a characteristic that the loss is reduced as the magnetic domain size (2L) is smaller. The research for improving the abnormal eddy current loss is a research recently performed with respect to the aforementioned research for improving the hysteresis loss and the conventional eddy current loss, and techniques developed are: a method of irradiating a laser beam on the surface of a steel sheet to apply a local stress to the surface of the steel sheet to thereby cause temporary magnetic domain miniaturization; and a method of imparting a predetermined pattern of curvature to the surface of the steel sheet to cause a change in the structural magnetic domain, thereby causing the permanent magnetic domain to be miniaturized. Another method developed as a method for miniaturizing magnetic domains is to apply coating substances having different expansion coefficients to the surface of a steel sheet to impart tension to the surface of the steel sheet due to the difference in expansion coefficients, thereby miniaturizing the magnetic domains.
The present inventors have repeatedly conducted studies for reducing abnormal eddy current loss of a grain-oriented electrical steel sheet, and found that the magnetic domain size can be reduced when the grain size of the grain-oriented electrical steel sheet is reduced, and along with this, the overall iron loss of the grain-oriented electrical steel sheet can be greatly reduced.
In general, the domain size and the grain size have the following relationship (1).
That is, the smaller the crystal grain size, the smaller the magnetic domain size, and the smaller the abnormal eddy current loss.
It is reported that the abnormal eddy current loss has a relationship with the conventional eddy current loss as in the following formula (2).
Wea＝[1.63×(2L/d)–1]×Wec (2)
In equation (2), Wea represents the abnormal eddy current loss, Wec represents the conventional eddy current loss, 2L represents the magnetic domain size, and d represents the steel sheet thickness.
As shown in equation (2), if the magnetic domain size is reduced when the steel sheet thickness is constant, the abnormal eddy current loss is also reduced.
If the grain size of the gaussian orientation is reduced, the magnetic domain size can be greatly reduced according to the correlation formula (1) between the grain size and the magnetic domain size, and accordingly, the iron loss of the oriented electrical steel sheet can be greatly reduced.
In summary, in order to reduce the core loss of the oriented electrical steel sheet, it is necessary to reduce the hysteresis loss by obtaining excellent magnetization characteristics by forming the gaussian-oriented recrystallized grains, and to reduce the conventional eddy current loss by increasing the Si content and reducing the thickness of the steel sheet, and finally to reduce the abnormal eddy current loss by miniaturizing the size of the gaussian-oriented grains and the size of the magnetic domain. In order to reduce the overall loss of the oriented electrical steel sheet, it is preferable to reduce all of the hysteresis loss, the conventional eddy current loss and the abnormal eddy current loss, but according to circumstances, even if there is no great improvement in the hysteresis loss or the conventional eddy current loss, only the abnormal eddy current loss is greatly improved by minimizing the gaussian-oriented grain size, and the oriented electrical steel sheet which is easy to produce and excellent in magnetic characteristics can be manufactured.
The method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention includes: providing a slab comprising in weight%: si: more than 0% and 4.0% by weight or less, C: 0.001 to 0.4 wt%, and Mn: 0.001 to 2.0 wt%, the balance consisting of Fe and other impurities that are inevitably mixed in; reheating the slab; hot rolling the slab to manufacture a hot-rolled steel sheet; carrying out hot-rolled plate annealing on the hot-rolled steel plate; performing primary cold rolling on the hot rolled steel plate subjected to the hot rolled plate annealing; performing decarburization annealing on the cold-rolled steel sheet; performing secondary cold rolling on the steel plate subjected to decarburization annealing; and performing final annealing on the cold-rolled steel plate. In addition to this, the method for manufacturing the oriented electrical steel sheet may further include other steps as needed.
Next, the steps are explained in detail.
First providing a slab comprising in weight%: si: more than 0% and 4.0% by weight or less, C: 0.001 to 0.4 wt% and Mn: 0.001 to 2.0 wt%, the balance consisting of Fe and other impurities that are inevitably mixed in.
The reason for limiting the composition is as follows.
Silicon (Si) can reduce magnetic anisotropy of the oriented electrical steel sheet and increase specific resistance to improve iron loss. An embodiment of the present invention is characterized in that the abnormal eddy current loss is greatly reduced by reducing the grain size of the final product, but the iron loss is improved as Si is increased, and therefore, it is preferable to add Si in a predetermined amount or more. Therefore, Si may be added in a content range in which cold rolling can be performed, i.e., 4 wt%. When the Si content is too large, brittleness is increased at the time of cold rolling, and there is a problem that cold rolling cannot be performed. More specifically, the Si content may be 1 wt% or less (except for 0 wt%).
Carbon (C) is an element that promotes austenite transformation, and is an important element for producing a grain-oriented electrical steel sheet having excellent magnetic properties by homogenizing the hot-rolled structure of the grain-oriented electrical steel sheet and promoting the formation of gaussian-oriented grains during cold rolling. However, when C is included in the final product, a magnetic aging phenomenon is caused to degrade magnetic characteristics, and thus C should be present in the finally manufactured electrical steel sheet at 0.003 wt% or less. In order to promote transformation and recrystallization of the gaussian-oriented grains by adding C, it is effective when C is added to the slab at 0.001 wt% or more, and secondary recrystallization is unstably formed due to uneven hot-rolled structure at a content of less than 0.001 wt%. However, when the content of C added to the slab is more than 0.4 wt%, austenite phase is generated during hot rollingA fine hot rolled structure is formed, primary recrystallized grains are fine, coarse carbides are likely to be formed in a coiling process after completion of hot rolling or a cooling process after annealing of a hot rolled sheet, and Fe is formed at normal temperature 3 C (cementite), which tends to cause uneven texture. Further, in the decarburization step and the final annealing step, there is a problem that the annealing time is increased in the process of decarburization until the C content becomes 0.003 wt% or less. Therefore, the C content in the slab may be limited to 0.001 wt% to 0.4 wt%.
Manganese (Mn) has an effect of increasing specific resistance to reduce iron loss similarly to Si, and is an important element for promoting austenite transformation and reducing grain size in hot rolling and annealing processes similarly to C. When the amount of Mn added is less than 0.001 wt%, sufficient phase transformation cannot be generated, the slab and hot rolled structure become coarse, the grain size of the final product is not sufficiently fine, and the effect of improving the iron loss due to the increase in specific resistance is also weak, as in the case of the effect of C. When the amount of Mn added is greater than 2.0 wt%, Fe is formed on the surface of the steel sheet 2 SiO 4 In addition, manganese Oxide (Mn Oxide) is formed, and decarburization does not proceed smoothly in the final annealing step. Therefore, the preferable addition amount of Mn is 0.001 to 2.0 wt%. More specifically, the amount of Mn added is 0.01 to 1.0% by weight.
In one embodiment of the present invention, aluminum (Al) is regarded as an inevitable impurity. That is, the Al content can be minimized in the slab and the steel sheet. Specifically, when Al is further contained, the range thereof may be limited to 0.01 wt% or less.
The above components are the basic composition of the present invention, and the effect of improving the iron loss by the miniaturization of the gaussian-oriented grains, which is a feature of the present invention, cannot be weakened even if other alloy elements which are unavoidable or other alloy elements capable of improving the magnetic properties are added.
The method for manufacturing a slab from the molten steel having the above composition may be a block method, a continuous casting method, a thin slab casting or a strip casting.
Next, the slab may be reheated. The slab reheating temperature may be 1050 to 1350 ℃. When reheating a slab, if the temperature is low, the rolling load increases; if the temperature is high, the following problems may occur: that is, low-melting point and high-temperature oxides are formed, so that a slab washing (washing) phenomenon occurs, the yield is reduced, and the hot rolled structure is coarsened, which adversely affects the magnetic properties.
Next, the slab after reheating is hot-rolled to manufacture a hot-rolled steel sheet. In the hot rolling, the hot rolling may be performed in a temperature range in which an austenite phase exists, thereby manufacturing a hot-rolled steel sheet. At a low temperature where no austenite phase is present, not only is the rolling load increased, but also the effect of grain miniaturization by transformation cannot be obtained.
Next, the hot rolled steel sheet is subjected to hot rolled sheet annealing. The hot-rolled sheet may be subjected to hot-rolled sheet annealing at a temperature above a temperature capable of causing recrystallization and transformation. Specifically, in order to prevent the generation of a low melting point oxide layer due to high temperature heating, hot-rolled sheet annealing may be performed at a temperature of 850 ℃ to 1150 ℃. The atmosphere in annealing the hot-rolled sheet may be an atmosphere containing hydrogen and having a dew point temperature of 0 ℃ or higher, which causes a decarburization reaction of the hot-rolled sheet.
Next, the hot rolled steel sheet subjected to the hot rolled sheet annealing is subjected to primary cold rolling. After the hot-rolled sheet annealing is performed, the steel sheet may be pickled and cold-rolled. The reduction ratio at the time of cold rolling may be 50% to 70%.
Next, the cold-rolled steel sheet is decarburization annealed. The cold-rolled steel sheet is annealed for recrystallization at a temperature of 800 ℃ to 1150 ℃ in an atmosphere containing hydrogen and at a dew point temperature of 0 ℃ or higher so as to cause decarburization reaction. If the temperature is too low, decarburization is difficult to be carried out; if the temperature is too high, a thick oxide layer is formed, which may adversely inhibit the decarburization reaction. If the dew point temperature is too low, the decarburization reaction may be inhibited. More specifically, the dew point temperature may be 10 ℃ to 70 ℃.
Next, the decarburized and annealed steel sheet is subjected to secondary cold rolling. The reduction ratio at the time of cold rolling may be 50% to 70%. The step of decarburization annealing the cold-rolled steel sheet and the step of secondary cold rolling the steel sheet after completion of the decarburization annealing may be repeated two or more times. As an example, when the annealing is repeated twice, the primary cold rolling step, the decarburization annealing step, the secondary cold rolling step, the decarburization annealing step, the tertiary cold rolling step, and the final annealing step may be performed in this order. In this case, the final cold rolling step is performed until the final product thickness is reached, and annealing is performed at a temperature of 800 ℃ to 1150 ℃ in an atmosphere containing hydrogen gas at a dew point temperature of 0 ℃ or higher so that decarburization reaction can be caused in each decarburization step.
Next, the finish annealing is performed on the steel sheet that has been cold rolled.
In the method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention, the final annealing may be continuously performed after the secondary cold rolling, unlike the conventional batch (batch) method.
The final annealing step may include a first step performed at a temperature of 850 to 1150 ℃ in an atmosphere having a dew point temperature of 10 to 70 ℃, and a second step performed at a temperature of 900 to 1200 ℃ in an atmosphere of a mixed gas including hydrogen and nitrogen having a dew point temperature of 10 ℃ or less. The first step may be performed for 300 seconds or less, and the second step may be performed for 60 seconds to 300 seconds.
The cold-rolled sheet before the final annealing is in a state where at least 40 to 60% by weight of the carbon content of the silicon steel remains in the slab due to the decarburization annealing. Therefore, in the first step at the time of the final annealing, the crystal grains formed in the surface layer portion diffuse inward as the carbon is desorbed. In the first step, decarburization may be performed so that the amount of carbon in the steel sheet is 0.01 wt% or less.
Thereafter in a second step, the texture with gaussian orientation diffused in the first step is grown. Unlike the conventional case where the grain growth is caused by abnormal grain growth, the grain size in the gaussian texture in the method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention may be within 1 mm. Therefore, the oriented electrical steel sheet according to an embodiment of the present invention may have a microstructure composed of gaussian oriented grains having a very small grain size, as compared to conventional oriented electrical steel sheets.
The amount of carbon in the electrical steel sheet subjected to the final annealing may be 0.003 wt% or less.
The oriented electrical steel sheet after the final annealing may be dried after being coated with the insulating coating liquid as required.
In addition, in the conventional Batch (Batch) type final annealing, the MgO coating layer may exist due to the application of the annealing separator containing MgO as a main component, but the grain-oriented electrical steel sheet according to an embodiment of the present invention may not have the MgO coating layer because the final annealing may be performed in a continuous manner rather than a Batch manner.
The gaussian orientation (orientation within 15 degrees from the {110} <001> orientation) crystal grains generated by one embodiment of the present invention tend to increase in crystal grains as the cold rolling and decarburization annealing are repeated, and the volume fraction of the crystal grains having the gaussian orientation in the steel sheet increases by at least 50% or more after the cold rolling and decarburization annealing are performed at least twice.
The grain diameter of the crystal grain generated by the embodiment of the invention is less than 5mm, and the volume fraction of the crystal grain from 20 mu m to 1000 mu m is more than 50%. As a result, the size of the magnetic domain existing within the grains is very small. The magnetic domain size seen in the conventional grain-oriented electrical steel sheet is larger than the conventional steel sheet thickness, but the magnetic domain size 2L existing in the grains of the steel sheet manufactured according to an embodiment of the present invention is smaller than the steel sheet thickness D.
The oriented electrical steel sheet according to an embodiment of the present invention includes, in wt%: si: more than 0% and 4.0% by weight or less, C: more than 0 wt% and 0.003 wt% or less, and Mn: 0.001 to 2.0 wt%, the balance being Fe and other impurities which are inevitably mixed in, and the size 2L of the magnetic domain existing in the grains being smaller than the thickness D of the steel plate.
The composition of the oriented electrical steel sheet is the same as that of the slab, and the composition range does not substantially vary during the production of the oriented electrical steel sheet, so that repeated descriptions thereof will be omitted. However, as described above, since decarburization is performed in the decarburization annealing and the finish annealing, the carbon content is 0.003 wt% or less.
The oriented electrical steel sheet according to an embodiment of the present invention has excellent iron loss and magnetic flux density because the volume fraction of the grains having a gaussian orientation in the steel sheet is increased by at least 50%. In addition, in the grain-oriented electrical steel sheet, 50% or more of the grains having a grain size of 20 to 1000um are present, and the maximum value of the grain size does not exceed 5mm, and at this time, the size of the magnetic domain present in the grains is smaller than the thickness of the steel sheet. Due to such a fine magnetic domain structure, the abnormal eddy current loss of the steel sheet manufactured by the present invention is greatly reduced as compared with the abnormal eddy current loss of the oriented electrical steel sheet manufactured by the conventional method, and the overall iron loss is greatly improved.
More specifically, the size 2L of the magnetic domain existing within the grains may be 10 μm to 500 μm.
The present invention will be described in further detail below with reference to examples. However, this embodiment is merely to illustrate the present invention, and the present invention is not limited thereto.
Example 1
Heating at a temperature of 1100 ℃ a mixture comprising, in weight%: 2.0 wt%, C: 0.15% and Mn: 0.05% and the balance Fe and inevitable impurities, hot rolled to a thickness of 3mm, then annealed at an annealing temperature of 1000 ℃, cooled, then pickled, and then cold rolled to a final thickness of 0.27 mm. In the cold rolling to the final gauge, a method of directly cold rolling to the final gauge without including the decarburization annealing between the cold rolling and the cold rolling, and a method of performing the decarburization annealing more than once and performing the multi-step cold rolling between the cold rolling and the cold rolling are performed. The decarburization annealing was performed at a temperature of 1000 ℃ in a wet mixed gas atmosphere of hydrogen and nitrogen (dew point temperature of 60 ℃).
When the final annealing is performed thereafter, annealing is performed at a temperature of 1000 ℃ for two minutes in a wet mixed gas atmosphere of hydrogen and nitrogen (dew point temperature 60 ℃), and then annealing is performed at 1100 ℃ for three minutes in a mixed gas atmosphere of hydrogen and nitrogen in a dry state (dew point temperature 0 ℃).
In the steel sheets having completed the final annealing treatment, the relationship between the fraction of the gaussian-oriented grains and the magnetic characteristics was compared and shown in table 1.
In this method, for the evaluation of the fraction of the gaussian-oriented crystal grains, the volume fraction of the crystal grains having an orientation within an error of 15 degrees from the ideal {110} <001> orientation was measured by a conventional crystal orientation measurement method.
Then, the magnetic domains were observed in a demagnetized state of the electrical steel sheet using a kerr microscope to measure the average size of the magnetic domains.
[ Table 1]
As shown in table 1, when the hot-rolled sheet annealing is performed and then the intermediate annealing in which decarburization occurs at least once is included in the process of cold rolling to the final thickness, the fraction of the gaussian-oriented grains in the final product can be ensured to be at least 50% or more, and a minute magnetic domain size can be obtained. By such a high gaussian orientation fraction and a small magnetic domain size, excellent magnetic flux density and low core loss characteristics can be obtained in the final product.
Example 2
Slabs were manufactured with varying Si content in the slabs as shown in table 2 below, which contained C in wt%: 0.2% and Mn: 0.05%, and the balance of Fe and inevitable impurities. The hot rolled plate blank was hot rolled to a thickness of 3mm at a temperature of 1150 c, then hot rolled plate annealing was performed at an annealing temperature of 950 c and cooling was performed, and then acid pickling was performed, and cold rolled at a reduction of 60%. Then, recrystallization and decarburization annealing were performed on the cold-rolled sheet in a mixed gas atmosphere of hydrogen and nitrogen at a temperature of 900 ℃ and a dew point temperature of 60 ℃. Thereafter, the same cold rolling and decarburization annealing were further repeated twice. Finally, after cold rolling to a thickness of 0.23mm, decarburization annealing is performed for 180 seconds in a mixed gas atmosphere of hydrogen and nitrogen at a temperature of 950 ℃ and a dew point temperature of 60 ℃ (first step), and then heat treatment is performed for 100 seconds in a hydrogen atmosphere at a temperature of 1000 ℃ and dry (dew point 0 ℃) (second step). The magnetic properties of the final annealed steel sheets with varying Si content are shown in table 2.
[ Table 2]
As shown in table 2, when the Si content is 4 wt% or less, the final grain size of the microstructure is ensured to be 1000 μm or less by the multiple cold rolling and decarburization annealing, and in this case, the magnetic domain size is ensured to be smaller than the thickness of the steel sheet, and as a result, excellent iron loss can be ensured. In the case where the Si content is more than 4 wt%, brittleness increases, a sheet is broken when cold rolling is performed, cold rolling to a final thickness is difficult, and decarburization is not achieved during decarburization annealing, exhibiting a small grain size and poor magnetic characteristics.
Example 3
Heating at a temperature of 1200 ℃ a mixture comprising in weight%: 3.0 wt%, C: 0.25% and Mn: 0.5% and the balance of Fe and inevitable impurities, hot-rolled into a thickness of 2.5mm, then hot-rolled in a mixed gas atmosphere of hydrogen and nitrogen at an annealing temperature of 1100 ℃ and a dew point temperature of 40 ℃, cooled, and then pickled, and then cold-rolled once at a reduction of 65%. Next, decarburization annealing is performed on the cold-rolled sheet in a wet mixed gas atmosphere of hydrogen and nitrogen at a temperature of 1050 ℃ and a dew point temperature of 60 ℃. Thereafter, the primary decarburized annealed sheet was subjected to secondary cold rolling to a final thickness of 0.30mm, and then to final annealing. In the finish annealing, when the annealing temperature was changed as shown in table 3 below, decarburization annealing was performed in a wet mixed gas atmosphere of hydrogen and nitrogen at a dew point temperature of 65 ℃ (first step) so that the carbon content could be 0.003 wt% or less. Finally, immediately after the decarburization annealing, the temperature is further raised, and final heat treatment is performed in a dry hydrogen atmosphere at 1150 ℃ and a dew point of 0 ℃ (second part). The grain size of the steel sheet finished with the final annealing was measured, and the magnetic domain size was measured using a kerr microscope and compared with the magnetic characteristics as shown in table 3 below.
[ Table 3]
As shown in table 3, in the case where the final annealing temperature (first step) was 850 to 1150 ℃, the ratio of crystal grains having a grain size of 20 to 1000 μm in the final product was 50% or more, and along with this, the magnetic domain size was also smaller than the thickness of the steel sheet, and excellent iron loss characteristics were exhibited. When the decarburization annealing temperature is less than 850 ℃, the size of the expressed magnetic domain is very small, but the reason why the overall magnetic properties are poor is considered to be that the gaussian orientation fraction in the crystal grains is 50% or less. On the contrary, in the case where the decarburization annealing temperature is higher than 1150 ℃, the grain size is large, and accordingly the magnetic domain size is larger than the thickness of the steel sheet, and the iron loss is not improved.
The present invention is not limited to the above-described embodiments, and can be manufactured in various forms. It will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. It should therefore be understood that the above-described embodiments are illustrative in all respects, rather than restrictive.
Claims (13)
1. A method for manufacturing a grain-oriented electrical steel sheet, comprising the steps of:
providing a slab comprising in weight percent: si: more than 0% and 4.0% by weight or less, C: 0.001 to 0.4 wt%, and Mn: 0.001 to 2.0 wt%, the balance consisting of Fe and other impurities that are inevitably mixed in;
reheating the slab;
hot rolling the slab to manufacture a hot-rolled steel sheet;
carrying out hot-rolled plate annealing on the hot-rolled steel plate;
performing primary cold rolling on the hot rolled steel plate subjected to annealing;
performing decarburization annealing on the cold-rolled steel sheet;
performing secondary cold rolling on the steel plate subjected to decarburization annealing; and
the steel sheet having been cold rolled is subjected to final annealing,
wherein the final annealing step includes a first step performed at a temperature of 850 ℃ to 1150 ℃ in an atmosphere having a dew point temperature of 10 ℃ to 70 ℃, and a second step performed at a temperature of 900 ℃ to 1200 ℃ in a mixed gas atmosphere containing hydrogen and nitrogen having a dew point temperature of 10 ℃ or less,
wherein the first step is performed for 300 seconds or less, the second step is performed for 60 seconds to 300 seconds,
wherein the size of the magnetic domain 2L existing in the grains of the steel sheet after the final annealing is smaller than the thickness D of the steel sheet,
wherein the volume fraction of crystal grains having an orientation within 15 degrees from a {110} <001> orientation in the steel sheet after the finish annealing is 50% or more.
2. The method for manufacturing a grain-oriented electrical steel sheet according to claim 1,
the slab comprises more than 0 wt% and 1 wt% or less of Si.
3. The method for manufacturing a grain-oriented electrical steel sheet according to claim 1,
the slab further comprises greater than 0 wt% and 0.01 wt% or less Al.
4. The method for manufacturing a grain-oriented electrical steel sheet according to claim 1,
the slab is reheated at a temperature of 1050 ℃ to 1350 ℃.
5. The method for manufacturing a grain-oriented electrical steel sheet according to claim 1,
the reduction ratios in the step of the primary cold rolling and the step of the secondary cold rolling are 50% to 70%, respectively.
6. The method for manufacturing a grain-oriented electrical steel sheet according to claim 1,
the step of decarburization annealing the cold-rolled steel sheet and the step of secondary cold rolling the steel sheet having been subjected to the decarburization annealing are repeated two or more times.
7. The method of manufacturing a grain-oriented electrical steel sheet as set forth in claim 1,
the decarburization annealing step is performed at a temperature of 800 ℃ to 1150 ℃ in an atmosphere containing hydrogen at a dew point temperature of 0 ℃ or higher.
8. The method for manufacturing a grain-oriented electrical steel sheet according to claim 1,
the step of final annealing is continuously performed after the step of cold rolling.
9. The method for manufacturing a grain-oriented electrical steel sheet according to claim 1,
the amount of carbon in the electrical steel sheet after the step of final annealing is greater than 0 wt% and 0.003 wt% or less.
10. The method for manufacturing a grain-oriented electrical steel sheet according to claim 1,
the volume fraction of crystal grains having a grain diameter of 20 to 1000 [ mu ] m in the steel sheet subjected to the finish annealing is 50% or more.
11. A kind of oriented electrical steel plate is provided,
comprising in weight%: si: greater than 0 wt% and 4.0 wt% or less, C: greater than 0 wt% and 0.003 wt% or less and Mn: 0.001 to 2.0 wt%, the balance consisting of Fe and other impurities which are inevitably mixed in,
the size 2L of the magnetic domains present in the grains is smaller than the thickness D of the steel plate,
wherein the volume fraction of crystal grains having a particle diameter of 20 to 1000 μm is 50% or more,
wherein the volume fraction of crystal grains having an orientation within 15 degrees from the {110} <001> orientation is 50% or more,
wherein the domain size 2L existing in the crystal grain is 10 μm to 500. mu.m.
12. The oriented electrical steel sheet as claimed in claim 11,
contains more than 0 wt% and 1.0 wt% or less of Si.
13. The oriented electrical steel sheet as claimed in claim 11,
further contains more than 0 wt% and 0.01 wt% or less of Al.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| KR1020150182839A KR101675318B1 (en) | 2015-12-21 | 2015-12-21 | Oriented electrical steel sheet and method for manufacturing the same |
| KR10-2015-0182839 | 2015-12-21 | ||
| PCT/KR2016/014945 WO2017111432A1 (en) | 2015-12-21 | 2016-12-20 | Oriented electrical steel sheet and manufacturing method therefor |
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| CN108431244A CN108431244A (en) | 2018-08-21 |
| CN108431244B true CN108431244B (en) | 2022-09-27 |
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| US (2) | US20180371571A1 (en) |
| EP (1) | EP3395959B1 (en) |
| JP (1) | JP6622919B2 (en) |
| KR (1) | KR101675318B1 (en) |
| CN (1) | CN108431244B (en) |
| PL (1) | PL3395959T3 (en) |
| WO (1) | WO2017111432A1 (en) |
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| KR101642281B1 (en) * | 2014-11-27 | 2016-07-25 | 주식회사 포스코 | Oriented electrical steel sheet and method for manufacturing the same |
| EP3715479A1 (en) * | 2019-03-26 | 2020-09-30 | Thyssenkrupp Electrical Steel Gmbh | Lean method for secondary recrystallization of grain oriented electrical steel in a continuous processing line |
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Also Published As
| Publication number | Publication date |
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| US20220106657A1 (en) | 2022-04-07 |
| EP3395959A1 (en) | 2018-10-31 |
| KR101675318B1 (en) | 2016-11-11 |
| PL3395959T3 (en) | 2020-09-21 |
| EP3395959B1 (en) | 2020-04-22 |
| US20180371571A1 (en) | 2018-12-27 |
| JP6622919B2 (en) | 2019-12-18 |
| CN108431244A (en) | 2018-08-21 |
| EP3395959A4 (en) | 2019-01-02 |
| JP2019505671A (en) | 2019-02-28 |
| WO2017111432A1 (en) | 2017-06-29 |
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