KR20140131790A - Gran-oriented electrical steel sheet and manufacturing method for the same - Google Patents
Gran-oriented electrical steel sheet and manufacturing method for the same Download PDFInfo
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- KR20140131790A KR20140131790A KR20130050841A KR20130050841A KR20140131790A KR 20140131790 A KR20140131790 A KR 20140131790A KR 20130050841 A KR20130050841 A KR 20130050841A KR 20130050841 A KR20130050841 A KR 20130050841A KR 20140131790 A KR20140131790 A KR 20140131790A
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
- C21D8/1244—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the heat treatment(s) being of interest
- C21D8/1255—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the heat treatment(s) being of interest with diffusion of elements, e.g. decarburising, nitriding
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/12—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials
- H01F1/14—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys
- H01F1/16—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys in the form of sheets
Abstract
Description
The present invention relates to a grain-oriented electrical steel sheet and a method of manufacturing the same, and more particularly, to a grain-oriented electrical steel sheet having improved magnetic properties by adding bismuth (Bi) will be.
Generally, a directional electrical steel sheet refers to a steel sheet having an aggregate structure in which the grain orientation containing 3.1% Si component is aligned in the {110} < 001 > direction and has extremely excellent magnetic properties in the rolling direction. Obtaining such a {110} < 001 > texture can be achieved by a combination of various manufacturing processes. Particularly, components, slab heating, hot rolling, annealing of hot-rolled sheet, primary recrystallization annealing, It is important.
Since the grain-oriented electrical steel sheet is intended to suppress the growth of the primary recrystallized grains and to exhibit excellent magnetic properties by the secondary recrystallized structure obtained by selectively growing crystal grains oriented in the {110} < 001 > The growth inhibitor of primary recrystallization is particularly important. It is the core of the directional electric steel sheet manufacturing technology to stably preferentially grow crystal grains having an aggregate structure of {110} < 001 > orientations among the crystal grains whose growth is suppressed in the final annealing process.
MnS, AlN, MnSe, and the like are currently used industrially widely as inhibitors satisfying the above-mentioned conditions. Of these, a typical known technique for manufacturing an electric steel sheet using only MnS as an inhibitor is disclosed in Japanese Patent Publication No. 30-3651. This manufacturing method is a method of producing a stable secondary recrystallized structure by cold rolling two times including intermediate annealing . However, a method using only MnS as an inhibitor can not obtain a high magnetic flux density and is manufactured by cold rolling two times, resulting in an increase in manufacturing cost. In addition, MnS or AlN contained in the slab of the grain-oriented electrical steel sheet must be reheated at a high temperature for a long time to be solidified to form a precipitate having an appropriate size and distribution during the cooling process after hot rolling. Therefore, .
In order to solve the above problems, a low-temperature heating method using a nitride inhibitor has been studied, which is disclosed in Japanese Patent Application Laid-Open Nos. 1-230721, 1-283324, 1997-48184, Patent Publication No. 97-28305. In these methods, ammonia gas is used to form a nitrogen atmosphere. The ammonia gas has a property of decomposing into hydrogen and nitrogen at a temperature of about 500 DEG C or more, and nitrogen is supplied using the above characteristics.
Recently, a method of adding a bismuth (Bi) element in order to maximize the magnetic property in a low-temperature heating method has been studied. Korean Patent Publication No. 1994-0012299, Korean Patent Publication No. 2000-0040613, Korean Patent Publication No. 2013-0041891, 2009-209428, Japanese Patent Application Laid-Open No. 1999-124627, Japanese Patent Application Laid-Open No. 2001-303131, etc.
The bismuth not only has the effect of increasing the fraction of crystal grains having a {110} < 001 > orientation in the primary recrystallized texture, but also has the effect of uniformly precipitating sulfides. Further, since bismuth can be precipitated in grain boundaries to suppress crystal grain growth, there is an advantage that the grain size of the secondary recrystallization can be reduced. Therefore, the effect of miniaturization due to miniaturization of the secondary recrystallized grain can also be obtained.
However, despite the excellent magnetic properties of the oriental electric steel sheet to which bismuth has been added, it has been difficult to industrially apply it to heat the surface quality. When the bismuth is added to the oriented electrical steel sheet, the oxidation behavior is changed, and the bismuth element segregates on the surface in a certain temperature range, causing the oxide layer peeling phenomenon. Therefore, the iron core material such as a transformer, an electric motor, a generator, Making it difficult.
Therefore, there is an urgent need to improve the surface quality in a method of producing a directional electrical steel sheet to which a bismuth element is added.
In addition, Fe 2 SiO 4 and SiO 2 formed in the decarburization annealing process react with MgO coated with an annealing separator to form a glass coating (Mg 2 SiO 4 ) in a high-temperature annealing process to impart electrical insulation and adhesion, In the product, unnecessary components are removed from the material, and secondary recrystallization is completed to impart magnetic properties to the product.
However, the bismuth element is segregated on the surface of the oxide layer in the decarburization annealing process, which complicates the formation of Fe 2 SiO 4 and SiO 2 and induces serious film peeling, which is difficult to apply industrially. Further, the oxide abnormally generated in the decarburization annealing step is a situation which forms a poor Paul Stephen light (Mg 2 SiO 4) adhesion to suppress the reaction of MgO in the high-temperature annealing step, and this problem becomes the magnetic properties disadvantage is pointed out .
In order to solve the above problems, the present invention provides a directional electrical steel sheet having improved magnetic properties by adding a bismuth element and improving the surface quality of a glass coating film, and a method of manufacturing the same.
The present invention also provides a directional electrical steel sheet having excellent adhesion and magnetic properties by controlling atmospheric gas and annealing temperature in a decarburization annealing process, and a method for producing the same.
In addition, it is intended to provide a method for imparting insulation properties to a film formed in a high-temperature annealing process by mixing colloidal silica with an annealing separator.
In one or more embodiments of the present invention, there is provided a method of manufacturing a grain-oriented electrical steel sheet comprising heating a steel slab, followed by hot rolling, cold rolling, decarburization annealing, an annealing separator applying step and a final annealing step, 0.01 to 0.03% by weight of Si, 0.01 to 0.03% by weight of Sb, 0.01 to 0.020% by weight of Mn, 0.020 to 0.040% by weight of Al, , N: 10 to 50 ppm, and S: 0.001 to 0.005% by weight, the balance being Fe and other unavoidable impurities, and the decarburization annealing step is carried out in such a manner that the oxygen content of the decarburized and annealed sheet is controlled to 450 to 750 ppm A manufacturing method can be provided.
The decarburization annealing step is characterized in that iron oxide is controlled to 0.01 to 0.07 g / m 2 and silicon dioxide (SiO 2 ) is controlled to 0.50 to 1.20 g / m 2 in the oxide layer of the decarburized and annealed sheet.
The decarburization annealing process is characterized in that the oxidizing ability is controlled in the range of (P H2O / P H2 ) 0.002 to 1.008.
In the decarburization annealing step, the dew point is controlled in the range of 40 to 70 ° C, and the decarburization annealing temperature is controlled in the range of 650 to 980 ° C.
The annealing separator applying step is a step of applying a mixture of 100 parts by weight of MgO and 2 to 30 parts by weight of colloidal silica to a coil.
In one or more embodiments of the present invention, it is preferable that the content of Si is from 2.5 to 3.7% by weight, the content of Bi is from 0.01 to 0.04% by weight, the content of Sb is from 0.01 to 0.03% by weight, the content of Al is from 0.020 to 0.040% , The balance being Fe and other unavoidable impurities, in an amount of 0.20 to 0.20% by weight, C: 0.04 to 0.07% by weight, N: 10 to 50 ppm and S: 0.001 to 0.005% by weight.
According to the embodiment of the present invention, it is possible to provide a grain-oriented electrical steel sheet having excellent adhesion and magnetic properties by controlling the amounts of iron oxide and silicon dioxide in the decarburization annealing process.
Further, by mixing the annealing separator with the colloidal silica, it is possible to control the ceramic coating film formed in the high-temperature annealing process, thereby forming a glass coating film having uniform and excellent insulating performance over the entire surface of the coil.
Advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described in detail below. However, it is to be understood that the present invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. It is intended that the disclosure of the present invention be limited only by the terms of the appended claims.
According to an embodiment of the present invention, there is provided a method for improving the adhesion of a glass film and surface quality of a grain-oriented electrical steel sheet improved in magnetic properties by adding a bismuth element.
First, the grain-oriented electrical steel sheet according to an embodiment of the present invention comprises 2.5 to 3.7% by weight of Si, 0.01 to 0.04% by weight of Bi, 0.01 to 0.03% by weight of Sb, 0.020 to 0.040% By weight of Cr, 0.04 to 0.07% by weight of C, 10 to 50 ppm of N and 0.001 to 0.005% by weight of S, and the hot rolling, preliminary annealing, cold rolling, decarburization annealing, final annealing, (Fe 2 SiO 4 , FeSiO 3 , FeO) is controlled to be in the range of 0.01 to 0.07 g / cm 3 in the decarburization annealed sheet oxidation layer, and the amount of iron oxide m 2 , and the silicon dioxide (SiO 2 ) is controlled to 0.50 to 1.20 g / m 2 .
The reasons for limiting the above components will be described below.
Si: 2.5 to 3.7 wt%
When the content of Si is less than 2.5% by weight, the specific resistance of the steel becomes small and the iron loss characteristic deteriorates. When the annealing is performed at high temperature, the second phase is unstable , And when it exceeds 3.7% by weight, the brittleness is increased and cold rolling becomes difficult. Therefore, in the embodiment of the present invention, the content of Si is limited to 2.5 to 3.7% by weight.
Bi: 0.01 to 0.04 wt%
Since Bi is an element which interferes with the movement of grain boundaries as a grain boundary segregation element, generation of goss grain in {110} < 001 > orientation is promoted as a grain growth inhibitor and secondary recrystallization is well developed, . If the content of Bi is less than 0.01% by weight, the effect is deteriorated. If the Bi content is more than 0.04% by weight, crystal grain boundary segregation occurs severely and the brittleness of the steel sheet becomes large. Therefore, the content of Bi in the embodiment of the present invention is limited to 0.01 to 0.04% by weight.
Sb: 0.01 to 0.03 wt%
Sb is an element promoting the generation of a goss grain in a {110} < 001 > orientation. When the content is less than 0.01% by weight, sufficient effect as a goss grain growth promoter can not be expected. So that formation of an oxide layer is suppressed and surface defects occur. Therefore, the Sb content in the embodiment of the present invention is limited to 0.01 to 0.03% by weight.
Acid soluble Al: 0.020 to 0.040 wt%
Al is ultimately made of nitride of AlN, (Al, Si) N, (Al, Si, Mn) N type and acts as an inhibitor. When the content is not more than 0.02%, sufficient effect as an inhibitor can not be expected. If it is too high, the nitride of the Al system precipitates and grows too much, and the effect as an inhibitor becomes insufficient. Therefore, the content of Al is limited to 0.020 to 0.040% by weight in the embodiment of the present invention.
Mn: 0.01 to 0.20 wt%
Mn has the effect of increasing the resistivity and decreasing the iron loss by the same way as Si and reacting with the nitrogen introduced by the nitriding treatment together with Si to form precipitates of N (Al, Si, Mn), whereby the growth of the primary recrystallized grains And it is an important element for causing secondary recrystallization. However, addition of more than 0.20% by weight accelerates the austenite phase transformation during hot rolling, thereby reducing the size of the primary recrystallized grains and making secondary recrystallization unstable. Therefore, Mn should be 0.20 wt% or less. In addition, Mn is an austenite forming element, which increases the austenite fraction during hot rolling reheating to increase the amount of precipitates to be large, thereby reducing the excess of primary recrystallization through MnS formation, . Therefore, in the embodiment of the present invention, Mn is limited to 0.01 to 0.2 wt%.
C: 0.04 to 0.07 wt%
C is a component which does not greatly contribute to the improvement of the magnetic properties of the grain-oriented electrical steel sheet in the embodiment of the present invention, and is preferably removed as much as possible. However, when the steel has a certain level or more in the rolling process, it promotes the austenite transformation of the steel to thereby miniaturize the hot rolled steel during hot rolling, thereby helping to form a uniform microstructure. . However, when the content is excessive, coarse carbides are produced and it is difficult to remove the carbonaceous material during decarburization. Therefore, the content is limited to 0.07 wt% or less.
N: 10 to 50 ppm
N is an element that reacts with Al or the like to refine the crystal grains. When these elements are appropriately distributed, as described above, after the cold rolling, the structure may be appropriately finely fine to assure proper primary recrystallization grain size. If the content is excessive, however, the primary recrystallization is excessively refined and the result The driving force that causes crystal grain growth during the secondary recrystallization increases due to the fine crystal grain, and the crystal grain of the undesired orientation can be grown. Also, if the N content is excessive, it takes a long time to remove it in the final annealing process, which is not preferable. Therefore, the upper limit of the nitrogen content is 50 ppm, and the content of nitrogen dissolved in the slab reheating should be 10 ppm or more, so the lower limit of the nitrogen content is limited to 10 ppm.
S: 0.001 to 0.005 wt%
When S is contained in an amount of 0.005% or more, it is reused in heating the hot-rolled slab and finely precipitates. Therefore, the size of the primary recrystallized grains is decreased to lower the secondary recrystallization starting temperature and deteriorate the magnetic properties. In addition, since it takes a long time to remove S in the solid state in the secondary crack region of the final annealing process, the productivity of the oriented electrical steel sheet is lowered. On the other hand, when the S content is as low as 0.005% or less, since the initial grain size before cold rolling is effective, the number of grains having {110} < 001 > orientation nucleated in the strain band in the first recrystallization process is increased. Therefore, the size of the secondary recrystallization is reduced to improve the magnetic properties of the final product, so S is set to 0.005% or less. In addition, S forms MnS and affects the primary recrystallized grain size to some extent, and therefore, it is preferable that S contains 0.001 wt% or more. Therefore, in the embodiment of the present invention, S is limited to 0.001 to 0.005% by weight.
In the decarburization annealing step, the oxidizing power (P H2O / P H2 ) is controlled in the range of 0.002 to 1.008, the dew point is controlled in the range of 40 to 70 ° C, the annealing temperature is controlled in the range of 650 to 980 ° C do.
According to an embodiment of the present invention, after the decarburization annealing, an annealing separator in a slurry state containing MgO as a main component and 2 to 30 parts by weight of colloidal silica are added to 100 parts by weight of the annealing separator.
The MgO has a specific surface area (BET) value of 1 to 110, a volume specific gravity of 0.20 to 1.20, and a particle size of 10 to 110 탆. The MgO has a loss on ignition (LOI) Use 1.0 ~ 2.5% under agitation conditions. The colloidal silica having a particle size in the range of 5 to 50 nm may be used. When the MgO and the colloidal silica are applied to a steel sheet in the form of a slurry, the rotating speed in the mixing tank is stirred at 1100 to 3000 rpm for 5 to 30 minutes in the slurry adjusting step.
Hereinafter, the present invention will be described in more detail.
The process related to the grain-oriented electrical steel sheet according to the embodiment of the present invention is a decarburization annealing process in which cold-rolling oil and contaminants are removed by burn-off or cleaning treatment, P H2O / P H2 ), and the main components of Fe 2 SiO 4 and SiO 2 , which play an important role in forming a glass coating film, form an oxide film to improve the final surface quality.
The directional electric steel sheet is basically a steel sheet containing about 3% Si component, but the oxidation behavior is greatly influenced by the presence of the additive element. Particularly, when the Bi element is added to the grain-oriented electrical steel sheet, the internal oxidation rate is irregular, and the SiO 2 particle dispersion becomes rough. Also, the growth rate and composition of the external oxide film are affected, and an excessive amount of Fe 2 SiO 4 oxide may be formed.
Therefore, when the dispersion of the SiO 2 particles generated in the decarburization annealing process is irregular, a coarse SiO 2 layer is formed on the substrate and the oxide layer interface, and stress is generated due to the difference in thermal expansion coefficient between the substrate and the substrate during cooling after annealing, as well as be generated, generating an excess to the oxide layer a surface layer of iron oxides (Fe 2 SiO 4, FeSiO 3 , FeO) is to suppress the reaction between MgO and SiO 2 at a high temperature annealing step poor surface morphology Paul Stephen light (Mg 2 SiO 4 ) are formed and the magnetic properties are disadvantageously generated.
In addition, after the decarburization annealing, the annealing separator containing MgO as a main component is applied to the steel sheet, and the glass coating film formed in the high temperature annealing process can not be thin and dense, resulting in a problem of opening the insulating property.
Therefore, in the embodiment of the present invention, the following technique is proposed to solve the problem of insulation characteristic dislocation and film peeling that occurs when Bi element is added in a directional electric steel sheet process.
(Fe 2 SiO 4 , FeSiO 3 , FeO) produced in the decarburization annealing process when the Bi element was added had an oxygen content of 450 to 700 ppm and an oxidizing ability (P H2O / P H2 ) of the decarburized and annealed sheet, 0.002 to 1.008, and the dew point was controlled at 40 to 70 캜. Through the above-described method, it was possible to form a pole stellite (Mg 2 SiO 4 ) film having a good surface shape in a high temperature annealing step and to manufacture a directional electric steel sheet excellent in magnetic properties.
Second, the problems of film peeling and poor adhesion caused by irregular dispersion of SiO 2 particles in the decarburization annealing process were solved by controlling the annealing temperature in the range of 650 to 980 ° C. By controlling the annealing temperature in the above range, the dispersion rate of SiO 2 is suppressed to form dense SiO 2 , and the adhesion of the interface between the substrate iron and the oxide layer is improved.
Third, after decarburization annealing, 2 to 30 parts by weight of colloidal silica is added to 100 parts by weight of MgO, thereby forming a glass coating film having uniform and excellent insulating properties over the whole coil.
Hereinafter, embodiments according to the present invention will be described in more detail.
In the decarburization annealing process, the Bi element is precipitated in grain boundaries to inhibit grain growth and increase the fraction of crystal grains having a {110} < 001 > orientation in the primary recrystallization texture. However, the directional electrical steel sheet to which the Bi element is added has a strong oxidizing property, thereby promoting external oxidation in the atmospheric condition of the decarburization annealing process, thereby increasing the production of ferrous oxide (FeO). Ferrous oxide (FeO) produced in an excessive amount reacts with SiO 2 , which is an internal oxide layer, to promote the formation of FeSiO 3 and Fe 2 SiO 4, thereby forming a polestate (Mg 2 SiO 4 ) having a poor surface shape in a high temperature annealing process Thereby causing a problem that the magnetic characteristics are inferior.
In the embodiment according to the present invention, the above problem is solved by controlling the oxygen amount of the decarburized and annealed sheet in the range of 450 to 700 ppm in the decarburization annealing process. If the oxygen amount exceeds 700 ppm, the inner and outer oxidation rates are further promoted, The surface properties are deteriorated by forming iron oxide. In addition, when the oxygen amount is less than 450 ppm, a thin polestick (Mg 2 SiO 4 ) layer may be formed in the high temperature annealing step, resulting in tissue exposure defects.
In addition, in the decarburization annealing process, the surface properties were improved by controlling the oxidizing ability (P H2O / P H2 ) in the range of 0.002 to 1.008 to form the optimum iron oxide (Fe 2 SiO 4 , FeSiO 3 , FeO) If it is more than 1.008, the diffusion rate of oxygen increases to form a thick inner oxide layer, and a film peeling defect occurs. If the oxidation ability is less than 0.002, the inner oxide layer may be formed thin and the insulating characteristic may be dulled. The oxidizing ability is limited to the above range.
In the embodiment of the present invention, the dew point of the decarburization annealing process is controlled to be in the range of 40 to 70 ° C to improve the surface properties by forming good iron oxide (Fe 2 SiO 4 , FeSiO 3 , FeO) .
When the electric steel sheet is heat treated in a gas atmosphere containing hydrogen, it is necessary to control the dew point temperature in order to control the partial pressure of oxygen. That is, when heat treatment is performed in a gas atmosphere containing hydrogen, if water is present in the gas, equilibrium is established between the water and hydrogen, and oxygen is present on the surface of the metal. At this time, if the dew point is high, the amount of moisture increases in the atmosphere gas, and the partial pressure of oxygen in the atmosphere gas increases.
In the embodiment according to the present invention, when the dew point temperature is 70 ° C or higher, an external oxide film, which is mainly composed of FeSiO 3 and Fe 2 SiO 4, is formed excessively and peeling off defect occurs. When the dew point temperature is 40 ° C or lower, And a small amount of SiO 2 is formed and the film tension can be weakened. Therefore, the dew point temperature in the decarburization annealing process of one embodiment of the present invention is limited to the above range.
The problems of film peeling and adhesion degradation caused by irregular dispersion of SiO 2 grains in the decarburization annealing step were solved by controlling the decarburization annealing temperature in the range of 650 to 980 ° C. If the annealing temperature is controlled in the above range, the dispersion rate of SiO 2 is suppressed to form dense SiO 2 , which contributes to the improvement of the adhesion of the interface between the base steel and the oxide layer. At this time, if the annealing temperature exceeds 980 ° C, a coarse SiO 2 layer is formed at the interface between the base steel and the oxide layer, and if the annealing temperature is less than 650 ° C, the internal oxidation rate is lowered, Of SiO 2 is formed and a tissue exposure defect occurs in the high temperature annealing process.
According to the embodiment of the present invention, if the cold-rolled sheet to which the Bi element is added is subjected to decarburization annealing by the above-described method, the iron oxide (Fe 2 SiO 4 , FeSiO 3 , FeO) g / m 2 , and silicon dioxide (SiO 2 ) was controlled to be 0.50 to 1.20 g / m 2 . At this time, if it exceeds the amount of the iron oxide to 0.07 g / m 2, Fe 3 O, and the fourth forming reactions can be faster the Fe 3 O 4 readily formed, 0.03 g / m by controlling the two less than the base coat (base coating ) Is slowed and the oxide layer is formed later to form an unreactive porous base coating to deteriorate the adhesiveness, so that the amount of iron oxide in the decarburization annealing sheet oxidation layer of the present invention is controlled within the above range.
When the amount of the silicon dioxide exceeds 1.20 g / m 2 , a thick SiO 2 layer is formed in the decarburization annealing step, and the decarburization reaction is delayed to cause carbon in the steel to remain, resulting in poor magnetic properties If it is less than 0.50 g / m 2 , the base coating may be formed to be thin to cause surface defects. Therefore, silicon dioxide in the oxide layer of the decarburized annealed sheet is controlled in the above range in one embodiment of the present invention.
After the decarburization annealing, the annealing separator containing MgO as a main component is stirred into water to form a slurry. The slurry is coated on a steel sheet using a roll or the like and dried, and then wound with a coil. Coating, annealing and heat flattening to produce the final product.
The reaction of forming the glass coating in the high temperature annealing process of the directional electric steel sheet forms a polestate (Mg 2 SiO 4 ) film by the reaction between MgO which is the main component of the annealing separator and SiO 2 which is the main component of the oxide film formed in the decarburization annealing process .
The film formation reaction is carried out by the following reaction formula.
2MgO + SiO 2 → Mg 2 SiO 4
However, the cold-rolled sheet to which the Bi element is added undergoes a decarburization annealing process, and the Bi element segregates on the surface of the oxide layer, and the glass-film forming reaction is inhibited. Further, there is a problem that the thickness of the glass coating formed in the high-temperature annealing process is thin and porous and the insulating characteristic is opened.
The above problem is solved by the colloidal silica which is added in an amount of 2 to 30 parts by weight based on 100 parts by weight of MgO after decarburization annealing. When the content of the colloidal silica is less than 2%, the insulating property is poor. When the content of the colloidal silica is more than 30%, a color deviation defect occurs on the surface of the glass coating film.
Hereinafter, embodiments of the present invention will be described in detail.
[Example 1]
2.5 to 3.7% by weight of Si and 0.01 to 0.04% by weight of Bi was heated at a temperature of 1150 占 폚 for 210 minutes and hot-rolled to prepare a hot-rolled steel sheet having a thickness of 2.3 mm. The hot rolled sheet was heated to 1120 占 폚, held at 920 占 폚 for 90 seconds, quenched in water, pickled, and then cold-rolled to a thickness of 0.30 mm. The cold rolled steel sheet was subjected to simultaneous decarburization and primary recrystallization annealing in a mixed atmosphere of hydrogen, nitrogen, and ammonia by controlling dew point temperature and oxidation ability in a furnace maintained at 860 ° C. Table 1 shows the characteristics of oxygen, iron oxide, adhesion, and surface appearance measured for each condition. Table 1 below shows that when the dew point temperature and the oxidation ability are lowered than the conventional example, the adhesion is excellent and the surface is beautiful.
Particularly, in Examples 2 and 3, the surface appearance is the most excellent.
Good: Excellent, Good: Good, Fair: Fair, Poor: ▽, Bad: X
[Example 2]
2.5 to 3.7% by weight of Si and 0.01 to 0.04% by weight of Bi was heated at a temperature of 1150 占 폚 for 210 minutes and hot-rolled to prepare a hot-rolled steel sheet having a thickness of 2.3 mm. The hot rolled sheet was heated to 1120 占 폚, held at 920 占 폚 for 90 seconds, quenched in water, pickled, and then cold-rolled to a thickness of 0.30 mm. Thereafter, concurrent decarburization steep annealing was performed in a continuous annealing line at a dew point (55 DEG C) and a mixed gas atmosphere (hydrogen, nitrogen, ammonia) at 830 DEG C for 150 seconds. The oxygen amount of the steel sheet at this time was 610 ppm.
Thereafter, colloidal silica was mixed with the annealing separator containing MgO as a main component to prepare a slurry, and the resultant was applied to a steel sheet using a roll or the like, and then finally annealed. During the final annealing, the primary cracking temperature was 700 ° C, the secondary cracking temperature was 1200 ° C, and the temperature was 15 ° C / hr in the temperature rising period. The atmosphere at the final annealing was a mixed atmosphere of 25% nitrogen + 75% hydrogen until 1200 ° C, and after reaching 1200 ° C, it was kept in a hydrogen atmosphere of 100% for 15 hours and then cooled. Followed by application of a normal tension coating and planarization treatment. Table 2 shows the magnetic properties and surface characteristics measured for each condition. It can be seen that when colloidal silica is added as compared with the conventional example, the insulating property is excellent.
Silica
Good: Excellent, Good: Good, Fair: Fair, Poor: ▽, Bad: X
While the present invention has been described in connection with certain exemplary embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims.
It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be interpreted as being included in the scope of the present invention .
Claims (8)
Wherein the steel slab comprises: 2.5 to 3.7 wt% of Si; 0.01 to 0.04 wt% of Bi; 0.01 to 0.03 wt% of Sb; 0.020 to 0.040 wt% of an acid soluble Al; 0.01 to 0.20 wt% 0.07% by weight, N: 10 to 50 ppm, S: 0.001 to 0.005% by weight, the balance being Fe and other unavoidable impurities,
Wherein the decarburization annealing step is controlled so that the oxygen amount of the decarburized annealed sheet is controlled to 450 to 750 ppm.
Wherein the decarburization annealing step is carried out by controlling the amount of iron oxide within the oxide layer of the decarburized annealed sheet to 0.01 to 0.07 g / m < 2 >.
Wherein the decarburization annealing step comprises controlling the silicon dioxide (SiO 2 ) to 0.50 to 1.20 g / m 2 inside the oxide layer of the decarburized annealed sheet.
Wherein the decarburization annealing step controls the oxidizing power to be in the range of 0.002 to 1.008 (P H2O / P H2 ).
Wherein the decarburization annealing process is controlled at a dew point in a range of 40 to 70 占 폚.
Wherein the decarburization annealing step is controlled so that the decarburization annealing temperature is in the range of 650 to 980 占 폚.
Wherein the annealing separator applying step is a step of applying a mixture obtained by mixing 2 to 30 parts by weight of colloidal silica to 100 parts by weight of MgO to a coil.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR101632871B1 (en) * | 2014-12-23 | 2016-06-23 | 주식회사 포스코 | Method of manufacturing oriented electrical steels |
| WO2017111507A1 (en) * | 2015-12-22 | 2017-06-29 | 주식회사 포스코 | Insulation film composition for grain-oriented electrical steel sheet, method for forming insulation film for grain-oriented electrical steel sheet using same, and grain-oriented electrical steel sheet |
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2013
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Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR101632871B1 (en) * | 2014-12-23 | 2016-06-23 | 주식회사 포스코 | Method of manufacturing oriented electrical steels |
| WO2017111507A1 (en) * | 2015-12-22 | 2017-06-29 | 주식회사 포스코 | Insulation film composition for grain-oriented electrical steel sheet, method for forming insulation film for grain-oriented electrical steel sheet using same, and grain-oriented electrical steel sheet |
| CN108475553A (en) * | 2015-12-22 | 2018-08-31 | Posco公司 | Oriented electrical steel insulating coating composition, using the insulating coating composition oriented electrical steel insulating coating forming method and oriented electrical steel |
| CN110634592A (en) * | 2015-12-22 | 2019-12-31 | Posco公司 | Insulating film composition for oriented electrical steel sheet, method for forming insulating film on oriented electrical steel sheet, and oriented electrical steel sheet |
| CN108475553B (en) * | 2015-12-22 | 2021-09-10 | Posco公司 | Insulating film composition for oriented electrical steel sheet, method for forming insulating film on oriented electrical steel sheet, and oriented electrical steel sheet |
| CN110634592B (en) * | 2015-12-22 | 2021-11-12 | Posco公司 | Insulating film composition for oriented electrical steel sheet, method for forming insulating film on oriented electrical steel sheet, and oriented electrical steel sheet |
| US11335475B2 (en) | 2015-12-22 | 2022-05-17 | Posco | Insulation film composition for grain-oriented electrical steel sheet, method for forming insulation film for grain-oriented electrical steel sheet using same, and grain-oriented electrical steel sheet |
| US11848122B2 (en) | 2015-12-22 | 2023-12-19 | Posco Co., Ltd | Insulation film composition for grain-oriented electrical steel sheet, method for forming insulation film for grain-oriented electrical steel sheet using same, and grain-oriented electrical steel sheet |
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