Title of Invention: Grain-oriented electrical steel sheet and its manufacturing method
technical field
[One]
It relates to a grain-oriented electrical steel sheet and a method for manufacturing the same. More specifically, it relates to a grain-oriented electrical steel sheet that further improves magnetic flux density by controlling the composition of the steel sheet and simultaneously controlling the rolling conditions during hot rolling to form a crystal orientation with an excellent degree of integration, and a method for manufacturing the same.
background
[2]
Grain-oriented electrical steel sheet is used as an iron core material for electronic products such as large rotating machines such as transformers and generators. An extremely good electrical steel sheet is required.
[3]
Grain-oriented electrical steel sheet refers to a functional steel sheet having a texture (also called "Goss Texture") in which crystal grains secondary recrystallized through hot rolling, cold rolling and annealing processes are oriented in the {110}<001> direction in the rolling direction.
[4]
In this grain-oriented electrical steel sheet, the orientation of all grains on the steel sheet surface is the {110} plane, and the crystal orientation in the rolling direction forms a Goss texture parallel to the <001> axis, so the magnetic properties are very excellent in the rolling direction of the steel sheet. It is a magnetic material.
[5]
In general, the magnetic properties of an electrical steel sheet can be expressed in terms of magnetic flux density and iron loss, and high magnetic flux density can be obtained by accurately arranging grain orientations in {110}<001> orientations.
[6]
Electrical steel sheet with high magnetic flux density can reduce the size of the iron core material of electrical equipment, as well as reduce hysteresis loss, making it possible to miniaturize electrical equipment and increase efficiency at the same time. Iron loss is the power loss consumed as thermal energy when an arbitrary AC magnetic field is applied to the steel sheet, and it varies greatly depending on the magnetic flux density and thickness of the steel sheet, the amount of impurities in the steel sheet, specific resistance, and secondary recrystallization grain size. The higher the resistivity and the lower the plate thickness and the amount of impurities in the steel plate, the lower the iron loss and the efficiency of the electrical equipment increases.
[7]
In order to manufacture a grain-oriented electrical steel sheet with excellent magnetic properties, it must be strongly formed with a texture of {110}<001> orientation in the rolling direction of the steel sheet. It is important to very strictly control the entire manufacturing process such as rolling, hot-rolled sheet annealing, primary recrystallization annealing, and final annealing for secondary recrystallization for each process unit.
[8]
In order to manufacture a grain-oriented electrical steel sheet, it is necessary to form a growth inhibitor (hereinafter referred to as an 'inhibitor') in the tissue to suppress the growth of primary recrystallized grains, and it is stably maintained among the grains whose growth is suppressed in the final annealing process. It is necessary to control so that grains having a texture of {110}<001> orientation can preferentially grow (hereinafter, referred to as 'secondary recrystallization').
[9]
These inhibitors are fine precipitates or segregated elements and remain thermally stable up to a high temperature just before secondary recrystallization occurs, and then grow or decompose when the temperature is higher. .
[10]
Currently widely used inhibitors include MnS, AlN, and MnSe(Sb).
[11]
First, when MnS was used as a grain growth inhibitor and manufactured through two cold rolling and high temperature annealing, the magnetic flux density (magnetic flux density at B8, 800A/m) was 1.80 Tesla, and the iron loss was relatively high. And a method of manufacturing a grain-oriented electrical steel sheet that exhibits a magnetic flux density (B8) of 1.87 Tesla or more when manufactured by using AlN and MnS precipitates in combination as a grain growth inhibitor and cold rolling once at a cold rolling ratio of 80% or more This is known
[12]
However, this magnetic flux density level still needs improvement compared to the theoretical saturation magnetic flux density of 2.03 Tesla of grain-oriented electrical steel sheet containing 3% Si. do.
[13]
As a conventional magnetic flux density improvement technique, there is a technique that proposes a method for manufacturing a grain-oriented electrical steel sheet having a magnetic flux density (B8) of 1.95 Tesla or more by temperature gradient annealing during high temperature annealing. However, in view of the mass production process in which high-temperature annealing is performed in a coil state of 10 tons or more by weight, this method has high energy loss and is inefficient manufacturing method because it has to be heated from one side of the coil.
[14]
As another method of improving magnetic flux density, a manufacturing method of obtaining a product having a magnetic flux density (B8) of 1.95 Tesla or more is known by adding a Bi-containing material to the molten steel of a grain-oriented electrical steel sheet using AlN and MnS precipitates.
[15]
However, all of these techniques are component systems that use AlN and MnS precipitates in combination, and in order to use these precipitates efficiently, heat treatment was required to completely dissolve the precipitates by heating the slab containing the AlN and MnS precipitate forming elements to 1300°C or higher. .
[16]
This heat treatment can be seen as a high-cost, low-efficiency manufacturing method that increases the energy cost due to high-temperature heating of the slab, and causes edge cracks during slab washing and hot-rolling, in which the slab melts at high temperature, resulting in a low error rate.
[17]
In addition, although it is possible to secure high magnetic flux density characteristics through the addition of Bi, most of the previously proposed patents focus on the problem of surface and secondary recrystallization instability formation due to the main addition of Bi. To this end, various improvement ideas were proposed in the process after hot rolling, and it is difficult to produce stably in the actual manufacturing process and requires a lot of trial and error.
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[18]
A grain-oriented electrical steel sheet and a manufacturing method thereof are provided. Specifically, it aims to provide a grain-oriented electrical steel sheet and a method for manufacturing the same, in which the composition of the steel sheet is controlled and the rolling conditions during hot rolling and cold rolling are controlled at the same time to form a crystal orientation with an excellent degree of integration, thereby further improving magnetism.
means of solving the problem
[19]
Electrical steel sheet according to an embodiment of the present invention, by weight, C: 0.01% or less (excluding 0%), Si: 2.0% to 4.0%, Mn: 0.01% to 0.20%, acid soluble Al: 0.040% or less (excluding 0%), N: 0.008% (excluding 0%), S: 0.008% (excluding 0%), Se: 0.0001 to 0.008%, Cu: 0.002 to 0.1%, Ni: 0.005 Contains ~0.1%, Cr: 0.005~0.1%, P: 0.005%~0.1% and Sn: 0.005%~0.20%, Sb: 0.0005%~0.10%, Ge: 0.0005%~0.10%, As: 0.0005% ~0.10%, Pb: 0.0001%~0.10%, Bi: 0.0001%~0.10%, and Mo: 0.001~0.1% containing at least one kind, the remainder consisting of Fe and other unavoidable impurities, after the final secondary recrystallization Provided is a grain-oriented electrical steel sheet having a magnetic flux density (B8) of 1.92 Tesla or more.
[20]
In addition, it is preferable that the orientation difference with the accurate {110}<001> Goss orientation for the secondary recrystallized grains after the final secondary recrystallization of the grain-oriented electrical steel sheet according to an embodiment of the present invention is 4° or less.
[21]
The method of manufacturing an electrical steel sheet according to another embodiment of the present invention is, by weight, C: 0.01% to 0.1%, Si: 2.0% to 4.0%, Mn: 0.01% to 0.20%, acid soluble Al: 0.010% to 0.040%, N: 0.001% to 0.008%, S: 0.004% to 0.008%, Se: 0.0001 to 0.008%, Cu: 0.002 to 0.1%, Ni: 0.005 to 0.1%, Cr: 0.005 to 0.1%, P: 0.005 %~0.1% and Sn: 0.005%~0.20%, Sb: 0.0005%~0.10%, Ge: 0.0005%~0.10%, As: 0.0005%~0.10%, Pb: 0.0001%~0.10%, Bi: 0.0001% to 0.10% and Mo: containing at least one of 0.001 to 0.1%, preparing a slab consisting of the remainder Fe and other unavoidable impurities; heating the slab at 1280° C. or less; preparing a hot-rolled sheet by hot-rolling the heated slab and annealing the hot-rolled sheet; manufacturing a cold-rolled sheet by cold-rolling and intermediate annealing the hot-rolled sheet; first recrystallizing the cold-rolled sheet by heating the cold-rolled sheet to a temperature of 600° C. or more at a temperature increase rate of 20° C./sec or more, followed by decarburization annealing and nitriding; and final annealing the first recrystallized steel sheet by applying an annealing separator containing MgO as a main component to perform secondary recrystallization. To provide a method for manufacturing a grain-oriented electrical steel sheet in which hot rolling is performed after performing rough rolling with a rolling reduction of 20% or more at one time or more.
[22]
At this time, it is preferable that the total nitrogen content of the steel sheet is 0.01 to 0.05% by performing the decarburization annealing and nitriding treatment in the first recrystallization step.
[23]
In addition, it is more preferable to perform the rough rolling with a cumulative reduction ratio of 70% or more in the slab rough rolling step.
[24]
And it is preferable to cold-roll the rolling temperature in the temperature range of 150 ~ 300 ℃ during the cold rolling.
[25]
In addition, in the primary recrystallization annealing step, it is preferable to heat the cold-rolled sheet to a temperature of 600° C. or more at a temperature increase rate of 50° C./sec or more.
Effects of the Invention
[26]
According to one embodiment of the present invention, an excellent grain-oriented electrical steel sheet having a high magnetic flux density of 1.92 Tesla or more can be obtained by precisely controlling the composition of the electrical steel sheet and increasing the cumulative reduction ratio in the hot rolling step.
[27]
According to an embodiment of the present invention, after the final secondary recrystallization, the orientation of the secondary recrystallized grains is exact {110}<001> orientation difference (deviation angle, °) (α 2 + β 2 ) A grain-oriented electrical steel sheet with a high degree of Goss orientation integration can be obtained as 1/2 is 4° or less.
[28]
According to one embodiment of the present invention, a grain-oriented electrical steel sheet having high magnetic flux density and excellent magnetic properties can be manufactured, and an electronic device using the grain-oriented electrical steel sheet as an iron core material has excellent magnetic properties.
Modes for carrying out the invention
[29]
Terms such as first, second and third are used to describe, but are not limited to, various parts, components, regions, layers and/or sections. These terms are used only to distinguish one part, component, region, layer or section from another part, component, region, layer or section. Accordingly, a first part, component, region, layer or section described below may be referred to as a second part, component, region, layer or section without departing from the scope of the present invention.
[30]
The terminology used herein is for the purpose of referring to specific embodiments only, and is not intended to limit the present invention. As used herein, the singular forms also include the plural forms unless the phrases clearly indicate the opposite. As used herein, the meaning of “comprising” specifies a particular characteristic, region, integer, step, operation, element and/or component, and the presence or absence of another characteristic, region, integer, step, operation, element and/or component; It does not exclude additions.
[31]
When a part is referred to as being “on” or “on” another part, it may be directly on or on the other part, or the other part may be involved in between. In contrast, when a part refers to being “directly above” another part, the other part is not interposed therebetween.
[32]
Although not defined otherwise, all terms including technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs. Commonly used terms defined in the dictionary are additionally interpreted as having a meaning consistent with the related technical literature and the presently disclosed content, and unless defined, they are not interpreted in an ideal or very formal meaning.
[33]
Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention pertains can easily implement them. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.
[34]
In manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention, a manufacturing method for improving magnetic flux density characteristics is as follows.
[35]
First, in order to manufacture a grain-oriented electrical steel sheet having excellent magnetic flux density, it is necessary to form a large number of grains having an exact Goss texture, which is the nucleus of secondary recrystallization, in the steel sheet.
[36]
In order to make many grains of accurate Goss orientation, it is necessary to control the processing conditions in advance so that many grains of Goss orientation are generated from the initial deformation after slab manufacturing.
[37]
At this time, elements such as P, Sn, Sb, Ge, As, Pb, and Bi in the composition of the steel sheet segregate at grain boundaries to reduce deformation resistance of grains during rough rolling, thereby suppressing recrystallization in orientations other than Goss.
[38]
After all, during hot rolling, a lot of Goss-oriented crystal grains exist in the steel sheet after rough rolling and hot rolling, and when such steel sheet is annealed at high temperature after cold rolling, it becomes the basis for manufacturing a grain-oriented electrical steel sheet with excellent magnetic flux density.
[39]
In addition, in addition to the method of increasing the Goss orientation grains by adding a grain boundary segregation element, when rolling over a certain rolling reduction ratio during high temperature deformation such as rough rolling, shear deformation occurs. There are many in the steel plate.
[40]
When a steel sheet is deformed in a high temperature range of 1000°C or higher, dynamic recovery or dynamic recrystallization occurs. As the amount of deformation increases, the strain energy is concentrated at the grain boundary. When the temperature is sufficiently high, the phenomenon in which the strain energy concentrated at the grain boundary is naturally released is called dynamic recovery. This phenomenon is called dynamic recrystallization.
[41]
In one embodiment of the present invention, in the rough rolling step with the addition of the grain boundary segregation element, rough rolling with a rolling reduction of 20% or more is performed at least once, and when the cumulative reduction is 60% or more, the magnetic flux after the final high-temperature annealing Density becomes superior to 1.92 Tesla or more.
[42]
Regarding this, the inventors studied the correlation between the grain boundary segregation element and the rough rolling reduction. As a result, when the one-time rolling reduction is 20% or more, the crystal grains of the Goss orientation occur a lot due to high-temperature shear deformation, and the addition Many Goss-oriented grains existed in the steel sheet because the deformation resistance at the grain boundary was reduced by the intergranular segregation element and thus dynamic recovery was performed without dynamic recrystallization in other directions than Goss. Therefore, after the final high-temperature annealing, it was possible to secure high magnetic flux density characteristics of 1.92 Tesla or more.
[43]
On the other hand, such excellent high magnetic flux density characteristics are ultimately determined by how well the secondary recrystallized Goss-oriented grains are arranged in the most ideal {110}<001> orientation.
[44]
As a method for evaluating the orientation of these secondary recrystallized Goss grains, first, the orientation difference (°)α with respect to the normal direction (ND) to the rolling surface of the steel sheet, and the orientation difference with respect to the rolling right angle direction (TD). There is a method of evaluating the difference from the exact {110}<001> orientation by measuring the (deviation angle, °)β and the deviation angle (°)γ in the rolling direction (RD).
[45]
Among them, the deviation angle (°) that has the greatest effect on the magnetic flux density is α and β, and these orientation differences can be used to evaluate how far the <001> axis of the secondary recrystallized grains is deviating from the rolling direction. become the standard
[46]
In other words, a product with a high magnetic flux density of 1.92 Tesla or more means that the crystal orientation difference α and β with respect to the {110}<001> Goss orientation in which the crystal orientation of the secondary recrystallized grains is accurate is small. As a method for more quantitatively evaluating this, it can be expressed by the following formula.
[47]
[Equation 1]
[48]
Orientation difference for precise {110}<001> crystal orientation: (α 2 + β 2 ) 1/2
[49]
That is, the smaller the (α 2 + β 2 ) 1/2 value for the {110}<001> crystal orientation in which the orientation of the secondary recrystallized Goss grains is accurate, it means that the magnetic flux density is higher.
[50]
As a result of measuring the secondary recrystallization grain orientation of the grain-oriented electrical steel sheet prepared according to an embodiment of the present invention in order to secure high magnetic flux density characteristics of 1.92 Tesla or more, the precise {110} <001> crystal orientation was obtained. The azimuth difference was confirmed to be less than about 4°.
[51]
Hereinafter, the reason for limiting the components of the grain-oriented electrical steel sheet according to an embodiment of the present invention described above (% of the component elements in the present invention means all weight% unless otherwise specified) will be described in detail.
[52]
First, as an element that promotes austenite phase transformation, C is an important element for making the hot-rolled structure of the grain-oriented electrical steel sheet uniform and for promoting the formation of grains in the Goss direction during cold rolling to manufacture a grain-oriented electrical steel sheet with excellent magnetism. This effect can be seen only when 0.01% or more of C is added, and at a content less than that, secondary recrystallization is unstable due to the non-uniform hot-rolled structure. However, when 0.10% or more is added, the primary recrystallized grains become fine due to the formation of a fine hot-rolled structure due to the austenite phase transformation during hot rolling, and coarse carbide (carbide) is formed in the winding process after hot rolling or in the cooling process after hot-rolled sheet annealing. ) and forms cementite (Fe 3 C, Cementite) at room temperature, which is easy to cause non-uniformity in the tissue. Therefore, the content of C in the slab is preferably limited to 0.01 ~ 0.10%.
[53]
However, C is decarburized during the primary recrystallization process and its content is reduced. In addition, when a large amount of C remains in the final grain-oriented electrical steel sheet, it is an element that deteriorates magnetic properties by precipitating carbides formed due to the magnetic aging effect in the steel sheet. Therefore, it is preferable to include a C content of 0.01 wt% or less (excluding 0%) in the final manufactured grain-oriented electrical steel sheet. More specifically, C may be included in an amount of 0.005% by weight or less. More specifically, C may be included in an amount of 0.003 wt% or less.
[54]
Si is a basic composition of grain-oriented electrical steel sheet and serves to increase the specific resistance of the material, thereby lowering the core loss, that is, the iron loss. When the Si content is less than 2.0%, the specific resistance decreases and the iron loss characteristics deteriorate, and secondary recrystallization becomes unstable due to the presence of a phase transformation section during high temperature annealing. do. Therefore, Si is limited to 2.0-4.0%. Specifically, Si may be included in an amount of 3.0 to 4.0%.
[55]
Mn has the same effect as Si by increasing specific resistance to reduce iron loss, and is used as an inhibitor to inhibit the growth of primary recrystallized grains by reacting with S and Se to form Mn[S,Se] precipitates. In the present invention, when 0.200% or more is added, the Mn[S,Se] precipitates become coarse and the suppression power is lowered. Also, there is a problem that the slab must be heated to a high temperature in order to solutionize the Mn[S,Se] precipitates. Conversely, in order to control the content to 0.01% or less, the burden of refining increases in steelmaking, and the Mn[S,Se] precipitation is less formed to reduce the effect as an inhibitor, so the content of Mn is limited to 0.01~0.20%. Specifically, the content of Mn may be included in 0.05 to 0.15%.
[56]
S generally reacts with Mn to form MnS precipitates and acts as an inhibitor to inhibit the growth of primary recrystallized grains. In the present invention, since the MnS precipitate is used as a crystal growth inhibitor along with the AlN precipitate, a particularly large content is not added. When more than 0.008% of S is added, the MnS precipitate becomes coarse and the inhibitory power is weakened, and also there is a disadvantage that the precipitate is not completely dissolved during heating of the slab. Conversely, when added in an amount of 0.004% or less, the MnS precipitate is very small and the effect as an inhibitor is lowered, so the content of S in the slab in the present invention is limited to 0.004 to 0.008%.
[57]
However, since S has a process of forming or decomposing precipitates during the product manufacturing process, it is preferable that the content of S is 0.008 wt % or less (excluding 0 %) in the grain-oriented electrical steel sheet manufactured in the end.
[58]
Se generally reacts with Mn to form MnSe precipitates and acts as an inhibitor to inhibit the growth of primary recrystallized grains. In the present invention, since MnSe precipitates are used together with AlN and MnS as a crystal growth inhibitor, a particularly large content is not added. When 0.008% or more of Se is added, the MnSe precipitates become coarse and the suppression power is weakened, and also there is a disadvantage that the precipitates are not completely dissolved when the slab is heated. Conversely, when 0.0001% or less is added, MnSe precipitates are very small and the inhibitory effect is reduced, so the content of Se is limited to 0.0001 to 0.008% in the present invention. Specifically, the content of Se may be contained in a range of 0.001 to 0.008%. More specifically, the content of Se may be contained in the range of 0.005 to 0.008%.
[59]
Cu has an effect of suppressing the growth of crystal grains by forming Cu[S,Se] precipitates by bonding with S and Se in steel. The crystal growth inhibitory power is stronger because the Mn[S,Se] precipitate is finely precipitated faster than the Mn[S,Se] precipitate. To secure such crystal growth inhibitory power, the amount of Cu added is 0.002% or more. If the content is less than that, the formation of Cu[S,Se] precipitates is small, so it is difficult to secure the inhibitory power. Se] precipitates are increased, so the crystal growth inhibitory power is also decreased. Therefore, in the present invention, the content of Cu is preferably limited to 0.002 ~ 0.1%. Specifically, Cu may be included in an amount of 0.005 to 0.07%. More specifically, Cu may be included in an amount of 0.01 to 0.07%.
[60]
Al is a component of a typical grain growth inhibitor for forming secondary recrystallization of grain-oriented electrical steel sheets by combining with N in steel to form AlN. In the present invention, it is preferable to add 0.010 to 0.040% of Al in the steelmaking step because Al-based nitride is formed through nitriding in the primary recrystallization annealing process to secure the effect of inhibiting grain growth. If the Al content is less than 0.010%, the total amount of Al-based precipitates formed in the primary recrystallization and nitriding process is insignificant, so the primary recrystallization grain growth inhibitory power is insufficient. As it grows coarsely, the crystal grain growth suppression power is lowered, and magnetic properties of high magnetic flux density cannot be secured. Therefore, the content of Al in the slab is limited to 0.010 to 0.040%.
[61]
However, since Al has a process of forming or decomposing precipitates during the product manufacturing process, the content of Al in the final manufactured grain-oriented electrical steel sheet is preferably 0.040 wt% or less (excluding 0%).
[62]
N is an important element that reacts with Al to form AlN, which inhibits recrystallization grain growth. However, when the content of N is added to more than 0.008%, the formation of AlN precipitates increases in the slab manufacturing and hot-rolling steps, thereby preventing primary recrystallization and crystal growth. Interference makes the primary recrystallization microstructure non-uniform, making it difficult to secure high magnetic flux density characteristics. Conversely, addition of 0.001% or less increases the load of the refining process of steelmaking, and it is difficult to secure a uniform primary recrystallization microstructure because grain growth is promoted during primary recrystallization, so that high magnetic flux density characteristics cannot be secured. Therefore, the content of N in the steelmaking step is limited to 0.001 ~ 0.008%. Specifically, the content of N may be included in the range of 0.003 to 0.008%. More specifically, the content of N may be included in 0.005-0.008%. However, since N has a process of forming or decomposing precipitates during the product manufacturing process, the content of N in the final manufactured grain-oriented electrical steel sheet is preferably 0.008% by weight or less (excluding 0%).
[63]
Ni is an alloying element that promotes the formation of austenite, and it is important to promote a phase transformation together with C to create a uniform hot-rolled microstructure. And, in the hot rolling process, it promotes the formation of a texture in the {110}<001> orientation, which is an important shear strain texture for securing high magnetic flux density characteristics. Therefore, it is necessary to add 0.005% or more of Ni to promote the formation of {110}<001> texture. Conversely, if more than 0.1% is added, the formation of {110}<001> texture is good, but the formation of an oxide layer on the surface of the steel sheet is reduced. As a result, the surface quality of the final product is deteriorated. Therefore, in the present invention, it is preferable to limit the addition amount of Ni to 0.005 to 0.1%. Specifically, the content of Ni may be contained in the range of 0.005 to 0.08%. More specifically, the content of Ni may be contained in the range of 0.005 to 0.05%.
[64]
Mo promotes the formation of a texture in the {110}<001> orientation, which is an important shear strain texture for securing high magnetic flux density characteristics during hot rolling. In addition, there is an effect of suppressing grain boundary oxidation at a high temperature to suppress the occurrence of surface cracks in the hot rolling process. The addition of 0.001% or more of Mo can promote the formation of {110}<001> texture. Conversely, if more than 0.1% of Mo is added, the formation of {110}<001> texture is good, but since it is an expensive ferroalloy, the magnetic flux Compared to the increase in density, the effect of addition decreases. Therefore, in the present invention, it is preferable to limit the addition amount of Mo to 0.001 to 0.1%. Specifically, the content of Mo may be contained in the range of 0.003 to 0.07%.
[65]
Cr reacts the fastest with oxygen in the decarburization annealing process to form Cr 2 O 3 on the surface of the steel sheet . In general, since segregation elements show a tendency to segregate to the surface as well as grain boundaries, the decarburization reaction is smoothly performed by first forming Cr 2 O 3 in the surface layer before decarburization and surface oxidation layer formation by the segregation element are suppressed. . When the amount of Cr is added to 0.005% or less, there is no effect of addition, and when it is added to 0.1% or more, it does not significantly affect the formation of the surface oxide layer. Therefore, the preferred amount of Cr added is limited to 0.005 to 0.1%. Specifically, the content of Cr may be included in 0.01 to 0.08%.
[66]
P is a key grain boundary segregation element of the present invention, and it can play a role of inhibiting grain growth that hinders the movement of grain boundaries, and has the effect of improving the {110}<001> grain structure in terms of texture. If the content of P is less than 0.005%, there is no effect of addition, and if it is added more than 0.100%, brittleness increases and rollability is greatly deteriorated, so it is preferable to limit it to 0.005 to 0.100%. Specifically, the content of P may be included in the range of 0.005 to 0.07%.
[67]
Sn, as one of the important segregation elements of the present invention, acts as an auxiliary grain growth inhibitor with an excellent effect of interfering with grain boundary movement by segregating at grain boundaries. In addition, it is stably present at grain boundaries even at high temperatures and does not have a significant effect on decarburization and surface oxide layer formation. In addition, it promotes the generation of Goss-oriented grains during hot rolling, thereby helping to develop excellent magnetic secondary recrystallization. In the present invention, when Sn is less than 0.005%, the effect of addition is insignificant, and on the contrary, when more than 0.200% is added, grain boundaries and surface segregation occur severely, so that the load of the decarburization process gradually increases, and the possibility of plate breakage during cold rolling increases. Therefore, the Sn content is limited to 0.005 to 0.20%. Specifically, the content of Sn may be included in the range of 0.005 to 0.08%. More specifically, Sn may be included in an amount of 0.005 to 0.04%.
[68]
Sb, as one of the important segregation elements of the present invention, is an element having an excellent effect of interfering with the movement of the grain boundary by segregation at the grain boundary. In addition, by controlling the depth of the internal oxide layer formed in the decarburization process, magnetic domain movement is suppressed by the formation of the internal oxide layer, thereby minimizing the increase in iron loss. In the present invention, when the content of Sb is 0.0005% or less, the added amount is very small, so the effect of addition cannot be seen. In the steelmaking step, the Sb content is limited to 0.0005 to 0.10%. Specifically, Sb may be included in an amount of 0.001 to 0.05%.
[69]
Ge, as one of the important segregation elements of the present invention, acts as an auxiliary grain growth inhibitor with an excellent effect of interfering with the movement of grain boundaries by segregation at grain boundaries. In addition, it promotes the generation of Goss-oriented grains during hot rolling, helping to develop excellent magnetic secondary recrystallization. In the present invention, when Ge is less than 0.0005%, the effect of addition is insignificant, and on the contrary, when more than 0.10% is added, the decarburization load is increased and the magnetic flux density improvement characteristic is inferior compared to the addition effect. Therefore, the Ge content is limited to 0.0005 to 0.10%.
[70]
As is also one of the important segregation elements of the present invention along with Ge, and it is excellent in the effect of interfering with the movement of grain boundaries by segregation at the grain boundaries. help you do In the present invention, when the As content is less than 0.0005%, the effect of addition is insignificant, and when it is added more than 0.10%, the decarburization load is increased and the magnetic flux density improvement characteristic is inferior compared to the addition effect. Therefore, the As content is limited to 0.0005 to 0.10%.
[71]
Pb, along with Sn, Sb, As, and Ge, is one of the important segregation elements of the present invention. Secondary recrystallization helps to develop well. In the present invention, when the Pb content is less than 0.0001%, the effect of addition is insignificant, and when it is added more than 0.10%, the decarburization load is increased and the effect of improving the magnetic flux density is decreased. Therefore, the Pb content is limited to 0.0001 to 0.10%.
[72]
Bi, together with Pb, Sn, Sb, As, and Ge, is one of the important segregation elements of the present invention. It helps the magnetic secondary recrystallization to develop well. In the present invention, when the Bi content is less than 0.0001%, the effect of addition is insignificant, and on the contrary, when it is added more than 0.10%, the surface segregation increases to increase the decarburization load, and the formation of the oxide layer is unstable and surface defects increase. Therefore, the Bi content is limited to 0.0001 to 0.10%.
[73]
In the present invention, segregation elements such as P, Sn, Sb, As, Ge, Pb, and Bi increase the Goss orientation grains in the primary recrystallization, thereby improving the magnetic flux density and also having the effect of inhibiting the growth of the primary grains. For this reason, it is preferable to complexly add at least one kind of segregation element.
[74]
Hereinafter, a method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention will be described in detail.
[75]
First, prepare a slab having the composition described above. If the composition is adjusted within the range of components as described above, the crystal growth of primary recrystallized grains is suppressed by the formation of precipitates of AlN, Mn[S,Se] and Cu[S,Se] during the slab manufacturing and hot rolling process, and thus the Goss orientation It promotes secondary recrystallization of grains, relieves stress concentration at grain boundaries in the deformation process due to grain boundary segregation of P, Sn, Sb, As, Ge, Pb and Bi elements, and promotes Goss-oriented grain formation by shear deformation. The magnetic flux density can be improved by recrystallizing a lot of Goss-oriented grains in the vehicle recrystallization structure.
[76]
In addition, Ni and Mo promote the growth of Goss-oriented grains during hot rolling through solid solution strengthening, and it is possible to prevent the formation of an oxide layer from being unstable due to grain boundary segregation through the addition of Cr.
[77]
For the grain-oriented electrical steel sheet according to an embodiment of the present invention, as a method for manufacturing a hot-rolled sheet from steelmaking, a crushing method, a continuous casting method, and thin slab casting or strip casting are possible. Hereinafter, a method for manufacturing a hot-rolled sheet using a slab will be mainly described.
[78]
The slab having the above composition is charged into the heating furnace and then heated at 1,280°C or less. Specifically, the slab is heated at 1100 to 1280 °C. Hot rolling is performed using a heated slab.
[79]
In the hot rolling process, the heated slab is subjected to rough rolling and finish rolling at a high temperature of 900° C. or higher, and then rolled to a thickness of 1.0 to 3.5 mm, which is an appropriate thickness for cold rolling.
[80]
During the hot rolling process, structural shear deformation occurs due to the slab thickness and the rolling roll diameter, and accordingly, Goss-oriented grains are formed in the shear deformation structure. In addition to the fundamental shear deformation mechanism of the hot rolling process, the formation of Goss-oriented crystal grains is further promoted by the addition of the solid solution strengthening element and grain boundary segregation element described above.
[81]
In addition, the amount of deformation varies greatly depending on the rolling rate during rough rolling and hot rolling, which has a great influence on the formation of Goss-oriented grains. Moreover, if the rough rolling conditions are controlled so that the shear deformation is large during deformation of a material having a thick initial rolling thickness, such as rough rolling (that is, when a large rolling ratio is given), the formation of Goss-oriented grains is greatly promoted.
[82]
The rolling reduction during hot rolling will be described in more detail.
[83]
In order to hot-roll the heated slab to a thickness of 1.0 to 3.5 mm, it is rolled to a thickness suitable for hot rolling through several rounds of rough rolling. It is preferable to rough-roll a bar to a thickness of 30 mm or more from a thick slab in a heated state, and in this case, rough rolling produces a bar through at least one rolling. At this time, it was confirmed that when the rolling ratio was 20% or more at least once or more, the Goss texture was greatly developed due to shear deformation. Specifically, at least one rolling rate may be 20 to 40%.
[84]
In addition, when the cumulative rolling reduction from the slab to the bar thickness is at least 60% or more, when the rough rolling is performed, the Goss orientation grains increase in the final primary recrystallization microstructure, and the magnetic flux density characteristics when subjected to the subsequent high-temperature annealing process It was excellent at 1.92 Tesla or more. More preferably, the cumulative reduction ratio in the rough rolling step is 70% or more. Specifically, the cumulative reduction ratio in the rough rolling step may be 60 to 80%.
[85]
When the rolling ratio at one time was 20% or less during rough rolling in hot rolling, the amount of shear deformation was small, and thus, the formation of Goss-oriented grains was small. Conversely, the higher the rolling rate is, the greater the shear deformation and the formation of Goss orientation crystals are greatly helpful. It is preferable to manufacture a bar by performing rough rolling at least once, and then performing final hot rolling.
[86]
After manufacturing the bar by performing rough rolling in the same manner as above, hot rolling is performed to a thickness of 1.0 to 3.5 mm, but in general, taking into account the rolling load, the rolling is finished at a temperature of 850°C or higher and the temperature is 600°C or lower. It is preferable to wind up by cooling to temperature.
[87]
The hot-rolled steel sheet is then recrystallized in the hot-rolled deformed structure in the hot-rolled sheet annealing process to make rolling smooth to the final product thickness in the cold-rolling process, which is a subsequent process. The annealing temperature of the hot-rolled sheet is preferably heated to a temperature of 800° C. or higher for recrystallization and maintained for a certain period of time, and heated to a plurality of temperatures for the formation and size control of AlN, Mn[S,Se] and Cu[S,Se] precipitates. Annealing is also possible.
[88]
After the hot-rolled sheet annealing process, the hot-rolled sheet is pickled to remove the oxide layer on the surface of the steel sheet and then cold-rolled.
[89]
Cold rolling is a process of lowering the thickness of the steel sheet to the thickness of the final product, and in the present invention, cold rolling is performed once or more than once including intermediate annealing to roll to the thickness of the final product. At this time, since the cold rolling rate affects the improvement of magnetic flux density after the final secondary recrystallization annealing by strengthening the degree of integration of the Goss orientation, it is preferable to perform cold rolling at a rolling rate of at least 80% or more.
[90]
If the cold rolling ratio is less than 80%, the degree of integration of the Goth orientation is low, and the magnetic flux density of the final product is lowered. Therefore, the cold rolling rate should be at least 80% or more, and the maximum rolling rate may be rolled up to the maximum rolling possible range according to the rolling capacity of the rolling facility.
[91]
In addition, when the temperature of the cold-rolled steel sheet is raised to 150° C. or more during the cold rolling process, a lot of secondary recrystallization nuclei in the Goth orientation are generated due to work hardening by solid solution carbon, thereby improving the magnetic flux density of the final product. If the temperature of the cold-rolled steel sheet is less than 150 ℃, the secondary recrystallization nuclei in the Goth orientation are insignificant. Conversely, if it is 300℃ or more, the work hardening effect by solid solution carbon is weakened and the secondary recrystallization nuclei in the Goss orientation are weakened. Therefore, in the cold rolling process, it is preferable that the steel sheet is maintained in the region of the temperature of 150 ~ 300 ℃ at least once in the intermediate rolling step.
[92]
Next, after the cold-rolled steel sheet is subjected to a rolling oil removal process, it is subjected to primary recrystallization and decarburization and nitridation treatment processes to form an AlN precipitate having a uniform primary recrystallization microstructure of an appropriate grain size and strong crystal growth inhibition.
[93]
At this time, the cold-rolled steel sheet must be heated to a temperature of 600°C or higher at a temperature increase rate of 20°C/sec or higher to promote the primary recrystallization of Goss-oriented grains increased by addition of a segregation element in the previous process and rough rolling of 20% or more at a time. can be At this time, it is more preferable to heat the cold-rolled sheet to a temperature of 600° C. or more at a temperature increase rate of 50° C./sec or more. Specifically, the cold-rolled sheet may be heated to a temperature of 600 to 900°C at a temperature increase rate of 20 to 200°C/sec.
[94]
When the temperature increase rate is 20° C./sec or less, recrystallization of Goss-oriented grains is delayed due to the recovery phenomenon of tissues deformed by cold rolling, and the fraction of Goss-oriented grains decreases after primary recrystallization.
[95]
Therefore, in the case of primary recrystallization annealing of the cold-rolled sheet, it is preferable to increase the temperature at a temperature increase rate of 20° C./sec or more to the decarburization and recrystallization temperature range of 600° C. or more. In addition, it is necessary to suppress the crystal growth of primary recrystallized grains by forming AlN precipitates in the steel sheet through nitriding treatment using ammonia along with decarburization annealing.
[96]
At this time, it is preferable to limit the total nitrogen content in the nitriding steel sheet to 0.01 to 0.05%. If the total nitrogen content is less than 0.01%, the total amount of AlN precipitates formed through the nitriding treatment is too small, and it is difficult to secure the desired crystal growth inhibition power, so that secondary recrystallization is unstable and it is difficult to secure a magnetic flux density of 1.92 Tesla or more.
[97]
Conversely, when the total nitrogen content is increased to 0.05% or more, secondary recrystallization, which excessively increases crystal growth due to excessive AlN formation, is not easily formed. In addition, when excess nitrogen is decomposed from the steel sheet in a high temperature region of 1100° C. or higher, surface defects such as nitrogen outlets are caused on the surface of the steel sheet. Therefore, it is preferable to limit the total nitrogen content to 0.01 to 0.05% for nitriding treatment.
[98]
After the decarburization and nitriding treatment of the steel sheet, an annealing separator based on MgO is applied thereafter, and then the temperature is raised to 1000° C. or higher and crack annealed for a long time to cause secondary recrystallization, so that the {110} surface of the steel sheet is parallel to the rolling surface. and a grain-oriented electrical steel sheet having excellent magnetic properties is manufactured by forming a Goss-oriented texture in which the <001> direction is parallel to the rolling direction.
[99]
The grain-oriented electrical steel sheet manufactured under the conditions as described above uses AlN, Mn[S,Se] and Cu[S,Se] precipitates to secure strong crystal growth inhibition and at the same time P, Sn, Sb, As, Ge, The grain boundary segregation effect of Pb and Bi elements and the shear strain increase due to the addition of Ni and Mo promote the formation of Goss-oriented grains.
[100]
In addition, in the rough rolling process after heating the slab, rough rolling with a rolling ratio of 20% or more at one time is performed at least once, and rough rolling is performed so that the total cumulative reduction ratio is 60% or more. The bar is produced by accelerating the process, hot-rolled, cold-rolled to the thickness of the final product, and then heated to a temperature range of 600°C or higher at a temperature increase rate of 20°C/sec or higher for decarburization and primary recrystallization, followed by nitriding treatment. As a result, the total nitrogen content in the steel sheet was adjusted to 0.01~0.05%, and the crystal orientation of the secondary recrystallized Goss-oriented grains after the final high-temperature annealing was measured. 4° or less.
[101]
Therefore, the grain-oriented electrical steel sheet manufactured according to an embodiment of the present invention exhibited excellent magnetic properties with a magnetic flux density of 1.92 Tesla or more.
[102]
Hereinafter, the present invention will be described in more detail through examples. However, these examples are only for illustrating the present invention, and the present invention is not limited thereto.
[103]
Example 1
[104]
As shown in Table 1 below, C, Si, Mn, acid-soluble Al, N, S, Se, Cu, Ni, Cr and Mo are the basic compositions, and the P, Sn, Sb, Ge, As, Pb and Bi contents are changed. The steel component system was vacuum melted to make cast steel.
[105]
After heating the cast slab to a temperature of 1150° C., a bar of 40 mm was prepared through rough rolling 6 times, and then hot-rolled to a thickness of 2.3 mm, and then rapidly cooled to 600° C. and wound up.
[106]
At this time, 1, 2, and 3 rough rolling was performed at a rolling ratio of 20% or more, and rough rolling was performed with a total cumulative rolling reduction ratio of 60% or more.
[107]
These hot-rolled steel sheets were annealed at 1050° C. and then pickled, and then cold-rolled once to a thickness of 0.23 mm.
[108]
The cold-rolled steel sheet was heated to 850°C at a temperature increase rate of 50°C/sec, and then was maintained for 180 seconds in a humid gas atmosphere of hydrogen, nitrogen, and ammonia, followed by primary recrystallization annealing. As described above, the nitriding treatment was simultaneously performed so that the total nitrogen content of the steel sheet was 200 ppm during the primary recrystallization annealing.
[109]
Then, an annealing separator containing MgO as a main component was applied to the steel sheet, and secondary recrystallization high-temperature annealing was performed in a coil shape.
[110]
High-temperature annealing was carried out in a mixed gas atmosphere of 25% N 2 + 75% H 2 until 1200° C. , and after reaching 1200° C., it was maintained in a 100% H 2 gas atmosphere for 20 hours and then slowly cooled.
[111]
Table 1 shows the measurement results of magnetic flux density (B8) and iron loss characteristics (W17/50) after secondary recrystallization and high temperature annealing for each alloy component system. In addition, the orientation of the secondary recrystallized grains was measured by Laue diffraction measurement to measure the deviation angle (°) (α 2 + β 2 ) 1/2 from the correct {110}<001> orientation .
[112]
[Table 1]
[113]

[114]

[115]
As can be seen in Table 1 above, when the P, Sn, Sb, Ge, As, Pb and Bi contents were added, the orientations of the secondary recrystallized grains were exactly the orientation difference (deviation angle, °) from the {110}<001> orientation. ) (α 2 + β 2 ) 1/2 was less than 4.0°, and it can be seen that the magnetic flux density of 1.92 Tesla or more can be stably secured.
[116]
In addition, when one or more of these components were added to the grain-oriented electrical steel sheet, the magnetic flux density characteristics superior to 1.92 Tesla were secured.
[117]
Example 2
[118]
A slab prepared by vacuum dissolving having the composition of Inventive Material 12 evaluated in Example 1 was heated at 1200°C.
[119]
The heated slab was subjected to rough rolling by changing the number of rough rollings and reduction ratio, and then a hot-rolled sheet having a thickness of 2.6 mm was manufactured by hot rolling.
[120]
These hot-rolled steel sheets were annealed at 1080°C, pickled, and cold-rolled once to a thickness of 0.30 mm.
[121]
The cold-rolled steel sheet is heated to 860°C at a temperature increase rate of 30°C/sec, and then maintained for 150 seconds in a humid mixed gas atmosphere of hydrogen, nitrogen, and ammonia to form primary recrystallization and at the same time, the total nitrogen content of the steel sheet is 180ppm Nitriding treatment was performed simultaneously so that it might become this.
[122]
Then, an annealing separator containing MgO as a main component was applied to the steel sheet, and final high-temperature annealing was performed for secondary recrystallization in a coil shape.
[123]
High-temperature annealing was performed in a mixed gas atmosphere of 25% N 2 + 75% H 2 up to 1200° C., and after reaching 1200° C., it was maintained in a 100% H 2 gas atmosphere for 20 hours and then slowly cooled.
[124]
Table 2 shows the exact deviation angle (°) (α 2 + β 2 ) for the secondary recrystallization grains after high-temperature annealing for secondary recrystallization according to the number of rough rollings and one-time rolling rate. ) 1/2 and magnetic flux density (B8) and iron loss characteristics (W17/50) are measured.
[125]
[Table 2]
[126]

[127]

[128]
As shown in Table 2 above, when the one-time rough rolling reduction ratio is less than 20%, or when the cumulative reduction ratio is less than 60%, the orientation difference ( deviation angle, °) (α 2 + β 2 ) 1/2 was 4° or more, and it was difficult to secure excellent magnetic flux density of 1.92 Tesla or more.
[129]
Example 3
[130]
A slab prepared by vacuum dissolving having the composition of Inventive Material 8 evaluated in Example 1 was heated at 1130°C.
[131]
In performing rough rolling for a total of 6 times on the heated slab, at the time of rough rolling 3, 4, 5, and 6, a reduction ratio of 20% or more is applied and rough rolling is performed with a cumulative reduction ratio of 76.0% to manufacture a 60mm bar and then hot-rolled to a thickness of 2.3 mm.
[132]
These hot-rolled steel sheets were annealed at 1100° C. and pickled, and then cold-rolled once to a thickness of 0.23 mm.
[133]
During cold rolling, the rolling temperature is changed to 50~350℃ to roll to the thickness of the final product, and then the cold-rolled steel sheet is heated to 855℃ at a temperature increase rate of 70℃/sec, in a humid mixture of hydrogen, nitrogen, and ammonia gas atmosphere. The nitriding treatment was simultaneously performed so that the total nitrogen content of the steel sheet was 220 ppm while forming the primary recrystallization by maintaining it for 180 seconds.
[134]
Then, an annealing separator containing MgO as a main component was applied to the steel sheet, and secondary recrystallization high-temperature annealing was performed in a coil shape.
[135]
High-temperature annealing was performed in a mixed gas atmosphere of 50% N 2 + 50% H 2 up to 1200° C., and after reaching 1200° C., it was maintained in a 100% H 2 gas atmosphere for 20 hours and then slowly cooled.
[136]
Table 3 shows the exact orientation difference (deviation angle, °) for secondary recrystallized grains after final high-temperature annealing according to the rolling temperature during cold rolling (α 2 + β 2 ) 1/2 and Changes in magnetic flux density and iron loss are shown.
[137]
[Table 3]
[138]
As shown in Table 3 above, when the cold rolling temperature is less than 150 ° C, as opposed to 300 ° C or higher, the deviation angle (°) of the secondary recrystallized grain orientation from the correct {110} <001> orientation (α 2 + β 2 ) 1/2 was 4° or more, and it was difficult to secure a magnetic flux density of 1.92 Tesla or more.
[139]
Example 4
[140]
In carrying out decarburization and primary recrystallization annealing using the cold-rolled sheet of Inventive Material 2 (composition of Inventive Material 8 in Table 1) evaluated in Example 3 above, the temperature was increased by changing the temperature increase rate under the conditions shown in Table 4, and then added Decarburization and nitridation were carried out in the region of 850 ° C.
[141]
For the nitriding treatment, ammonia gas was used during decarburization annealing so that the total nitrogen content was 200 ppm.
[142]
Then, the nitrided steel sheet was subjected to secondary recrystallization high-temperature annealing in coil shape by applying an annealing separator containing MgO as a main component.
[143]
High-temperature annealing was performed in a mixed gas atmosphere of 75% N 2 + 25% H 2 until 1200° C. , and after reaching 1200° C., it was maintained in a 100% H 2 gas atmosphere for 20 hours and then slowly cooled.
[144]
Table 4 shows the exact {110}<001> orientation for secondary recrystallized grains after final high-temperature annealing according to the temperature increase rate during decarburization and primary recrystallization (deviation angle, °) (α 2 + β 2 ) 1 /2 and the change in magnetic flux density and iron loss.
[145]
[Table 4]
[146]
As shown in Table 4 above, when the temperature increase rate is increased to 20°C/sec or more to a temperature of 600°C or higher, the orientation difference (α 2 + β 2 ) 1/2 is 4° or less, and the magnetic flux density is 1.92 Tesla or more. can be found to be secured.
[147]
This is to connect the effects of adding grain boundary segregation elements such as P, Sn, Sb, Ge, As, Pb and Bi and performing rough rolling one or more times with a reduction ratio of 20% or more in the rough rolling step to the magnetic flux density of the final product. And it means that in the primary recrystallization annealing step, it is necessary to increase the temperature to a temperature range of 600 ° C. or higher to 20 ° C./sec or more.
[148]
The present invention is not limited to the embodiments, but can be manufactured in various different forms, and those of ordinary skill in the art to which the present invention pertains can use other specific forms without changing the technical spirit or essential features of the present invention. It will be appreciated that this may be practiced. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.
Claims
[Claim 1]
By weight%, C: 0.01% or less (excluding 0%), Si: 2.0% to 4.0%, Mn: 0.01% to 0.20%, acid solubility Al: 0.040% or less (excluding 0%), N: 0.008 % (excluding 0%), S: 0.008% (excluding 0%), Se: 0.0001 to 0.008%, Cu: 0.002 to 0.1%, Ni: 0.005 to 0.1%, Cr: 0.005 to 0.1%, P : 0.005% to 0.1% and Sn: 0.005% to 0.20%, Sb: 0.0005% to 0.10%, Ge: 0.0005% to 0.10%, As: 0.0005% to 0.10%, Pb: 0.0001% to 0.10%, Bi: 0.0001% to 0.10% and Mo: containing at least one of 0.001 to 0.1%, the remainder consisting of Fe and other unavoidable impurities, characterized in that the magnetic flux density (B8) after the final secondary recrystallization is 1.92 Tesla or more grain-oriented electrical steel sheet.
[Claim 2]
The orientation according to claim 1, wherein the orientation difference (α 2 + β 2 ) 1/2 with the accurate {110}<001> Goss orientation for the secondary recrystallized grains after the final secondary recrystallization is 4° or less. electric grater.
[Claim 3]
C: 0.01% to 0.1% by weight, Si: 2.0% to 4.0%, Mn: 0.01% to 0.20%, acid soluble Al: 0.010% to 0.040%, N: 0.001% to 0.008%, S: 0.004% to 0.008%, Se: 0.0001~0.008%, Cu: 0.002~0.1%, Ni: 0.005~0.1%, Cr: 0.005~0.1%, P: 0.005%~0.1% and Sn: 0.005%~0.20%, Sb: 0.0005% to 0.10%, Ge: 0.0005% to 0.10%, As: 0.0005% to 0.10%, Pb: 0.0001% to 0.10%, Bi: 0.0001% to 0.10%, and Mo: at least one of 0.001 to 0.1% containing, and preparing a slab consisting of the remainder Fe and other unavoidable impurities; heating the slab at 1280° C. or less; preparing a hot-rolled sheet by hot-rolling the heated slab and annealing the hot-rolled sheet; manufacturing a cold-rolled sheet by cold-rolling and intermediate annealing the hot-rolled sheet; first recrystallizing the cold-rolled sheet by heating the cold-rolled sheet to a temperature of 600° C. or more at a temperature increase rate of 20° C./sec or more, followed by decarburization annealing and nitriding; and final annealing the first recrystallized steel sheet by applying an annealing separator containing MgO as a main component to perform secondary recrystallization. A method of manufacturing a grain-oriented electrical steel sheet, characterized in that the hot rolling is performed after performing rough rolling with a reduction ratio of 20% or more at one time or more.
[Claim 4]
[4] The method of claim 3, wherein the total nitrogen content of the steel sheet is 0.01 to 0.05% by performing decarburization annealing and nitriding in the primary recrystallization step.
[Claim 5]
[Claim 5] The method for manufacturing grain-oriented electrical steel sheet according to claim 4, wherein the rough rolling is performed at a cumulative reduction ratio of 70% or more in the slab rough rolling step.
[Claim 6]
[Claim 6] The method of claim 5, wherein the cold rolling is performed at a rolling temperature of 150 to 300°C during the cold rolling.
[Claim 7]
The method of claim 6, wherein in the primary recrystallization annealing step, the cold-rolled sheet is heated at a temperature of 600°C or higher at a temperature increase rate of 50°C/sec or higher.
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