Classifications

• • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/12—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
• • 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
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
• • 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
• • 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
  • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur

Definitions

• the present invention relates to grain-oriented electrical steel sheets and methods for manufacturing them.
• Grain-oriented electrical steel sheet is a soft magnetic material that is primarily used as the iron core material for transformers. For this reason, grain-oriented electrical steel sheet is required to have magnetic properties, including high magnetization and low iron loss. Iron loss is the power loss consumed as thermal energy when an iron core is excited by an AC magnetic field, and from the perspective of energy conservation, iron loss should be as low as possible.
• iron loss characteristics are magnetic flux density (for example, B8: magnetic flux density in a magnetic field of 800 A/m), and higher magnetic flux density values tend to result in lower iron loss.
• B8 magnetic flux density in a magnetic field of 800 A/m
• higher magnetic flux density values tend to result in lower iron loss.
• the crystal orientation is generally concentrated in the Goss orientation, which is favorable for magnetic properties, during the manufacturing process (increasing the degree of orientation concentration).
• Low iron loss is achieved by refining the magnetic domain structure of grain-oriented electrical steel sheets, which have a high magnetic flux density.
• Patent Documents 1 to 4 disclose that grooves are formed in the steel sheet to divide the crystal grains and shorten the length of the secondary recrystallized grains in the rolling direction. Furthermore, Patent Documents 5 and 6 disclose that heat treatment using laser beam irradiation is performed either before or after the decarburization annealing process to divide the crystal grains in the product.
• JP 2011-208196 A Japanese Patent Application Laid-Open No. 2002-294416 International Publication No. 2012/033197 Japanese Patent Application Publication No. 7-268474 International Publication No. 2012/014290 Japanese Patent Application Publication No. 2-258928
• Patent Documents 1 to 4 do indeed enable control of the crystal grain size, the productivity of groove formation is low. Furthermore, the presence of grooves poses the issue of a reduced space factor when formed into a transformer. Furthermore, the conventional techniques for dividing crystal grains by irradiating them with a laser beam, as described in Patent Documents 5 and 6, do not always achieve low iron loss, leaving room for improvement.
• This disclosure relates to the following grain-oriented electrical steel sheet and its manufacturing method.
• the thickness of the base steel plate is 0.30 mm or less.
• the average heating rate from 450°C to 750°C is set to 400 to 2000°C/sec.
• P 0 to 0.05%
• P phosphorus
• the P content is preferably 0.05% or less, more preferably 0.04% or less, and even more preferably 0.03% or less.
• the lower limit of the P content is not limited and may include 0%, but P is also an element that has the effect of improving texture and magnetic properties. To achieve this effect, the P content may be more than 0%, may be 0.005% or more, or may be 0.01% or more.
• Mo 0-0.05% Mo (molybdenum) is an element that has the effect of improving magnetic properties. Therefore, Mo may be contained as necessary. However, if its content is excessive, cold rolling properties may be reduced, leading to fracture. Therefore, the Mo content is preferably 0.05% or less, more preferably 0.04% or less, and even more preferably 0.03% or less. There is no need to set a lower limit for the Mo content; it may be 0% or more than 0%. To ensure the above effects, the Mo content is preferably 0.005% or more, more preferably 0.01% or more, and even more preferably 0.02% or more.
• Ta 0-0.05%
• Ta is an element that has the effect of stabilizing secondary recrystallization. Therefore, Ta may be contained as necessary. However, if its content is excessive, secondary recrystallization may become unstable. Therefore, the Ta content is preferably 0.05% or less, more preferably 0.04% or less, and even more preferably 0.03% or less. There is no need to set a lower limit for the Ta content, and it may be 0%. To reliably obtain the above effect, the Ta content is preferably more than 0%, more preferably 0.0005% or more, and even more preferably 0.001% or more.
• V 0 to 0.50%
• V vanadium
• the V content is preferably 0.50% or less, more preferably 0.40% or less, and even more preferably 0.30% or less. There is no need to set a lower limit for the V content; it may be 0% or more than 0%. To ensure the above effects, the V content is preferably 0.01% or more, more preferably 0.02% or more, and even more preferably 0.03% or more.
• Te 0 ⁇ 0.0150% Te (tellurium) is an element that has the effect of stabilizing secondary recrystallization. Therefore, Te may be contained as necessary. However, if its content is excessive, hot rolling property and cold rolling property may be deteriorated, which may lead to fracture. Therefore, the Te content is preferably 0.0150% or less, more preferably 0.0100% or less, and even more preferably 0.0050% or less. There is no need to set a lower limit for the Te content, and it may be 0%. To reliably obtain the above effect, the Te content is preferably more than 0%, more preferably 0.0005% or more, and even more preferably 0.0010% or more.
• Bi 0 ⁇ 0.0150%
• Bi bismuth
• the Bi content is preferably 0.0150% or less, more preferably 0.0100% or less, and even more preferably 0.0050% or less.
• the Bi content is preferably 0.0005% or more, more preferably 0.0010% or more, and even more preferably 0.0020% or more.
• Impurities include, for example, one or more selected from the group consisting of Ca: 0-0.001%, Mg: 0-0.002%, O: 0-0.01%, As: 0-0.10%, Co: 0-0.10%, Zr: 0-0.003%, W: 0-0.10%, Hf: 0-0.02%, Sr: 0-0.02%, Zn: 0-0.02%, Pb: 0-0.10%, REM: 0-0.02%, Ba: 0-0.02%, Cd: 0-0.02%, Pt: 0-0.02%, Au: 0-0.02%, Ga: 0-0.02%, and Ge: 0-0.02%.
• REM refers to a total of 17 elements consisting of Sc, Y, and lanthanides
• the REM content refers to the total content of these elements. If multiple impurity elements are contained, the total content of these elements is preferably 0 to 0.05%.
• the manufacturing method of the grain-oriented electrical steel sheet according to this embodiment includes the following steps.
• (A) Hot Rolling Process a slab having the chemical composition described below is heated to 1280°C or higher, and the heated slab is hot-rolled to produce a hot-rolled steel sheet. If the heating temperature is lower than 1280°C, inclusions formed in the slab cannot be dissolved, and inhibitors are not sufficiently formed in the hot rolling process or the hot-rolled sheet annealing process. Therefore, the slab heating temperature is set to 1280°C or higher. There is no upper limit for the slab heating temperature, but if the slab is heated to a temperature higher than 1450°C, the slab will melt, making hot rolling difficult. Therefore, the slab heating temperature is preferably 1450°C or lower.
• Hot rolling conditions are not particularly limited and may be set appropriately based on the desired properties.
• the thickness of the hot-rolled steel sheet obtained by hot rolling is preferably within the range of 1.0 mm to 4.0 mm, for example.
• Si 3.00-3.70%
• Silicon (Si) is an extremely effective element for increasing the electrical resistance (resistivity) of steel and reducing eddy current loss, which constitutes part of iron loss.
• the Si content of the slab is preferably 3.00% or more, more preferably 3.10% or more, and even more preferably 3.20% or more.
• Mn 0.01-0.30%
• Mn manganese
• the Mn content of the slab is preferably 0.01% or more, more preferably 0.03% or more, and even more preferably 0.06% or more.
• the Mn content of the slab is preferably 0.30% or less, more preferably 0.28% or less, and even more preferably 0.26% or less.
• Ni 0-0.50%
• Ni nickel
• Ni is an element effective in increasing electrical resistance and reducing iron loss.
• Ni is also an element effective in controlling the metal structure of a hot-rolled steel sheet and improving its magnetic properties. Therefore, Ni may be contained as needed.
• the Ni content is preferably 0.50% or less, more preferably 0.40% or less, and even more preferably 0.30% or less. There is no need to set a lower limit for the Ni content; it may be 0% or more.
• the Ni content is preferably 0.01% or more, more preferably 0.02% or more, and even more preferably 0.03% or more.
• Cu 0-0.50%
• Cu (copper) is an element that contributes to increasing the Goss orientation occupancy rate in the secondary recrystallization structure and also contributes to improving the adhesion of the glass coating. Therefore, Cu may be contained as necessary. However, if its content is excessive, the steel sheet may become embrittled during hot rolling. Therefore, the Cu content is preferably 0.50% or less, more preferably 0.30% or less, and even more preferably 0.10% or less. There is no need to set a lower limit for the Cu content; it may be 0% or more. To reliably obtain the above effects, the Cu content is preferably 0.01% or more, more preferably 0.02% or more, and even more preferably 0.03% or more.
• Sb 0-0.30%
• Sb antimony
• the Sb content is preferably 0.30% or less, more preferably 0.20% or less, and even more preferably 0.10% or less. There is no need to set a lower limit for the Sb content; it may be 0% or more than 0%. To ensure the above effects, the Sb content is preferably 0.01% or more, more preferably 0.02% or more, and even more preferably 0.03% or more.
• Sn 0-0.30%
• Sn (tin) is an element that has the effect of improving magnetic properties. Therefore, Sb may be contained as necessary. However, if the Sn content is excessive, the glass coating may deteriorate and sufficient tension for magnetic domain refinement may not be obtained, which may result in a decrease in core loss characteristics. Therefore, the Sn content is preferably 0.30% or less, more preferably 0.20% or less, and even more preferably 0.10% or less. There is no need to set a lower limit for the Sn content; it may be 0% or more. To ensure the above effects, the Sn content is preferably 0.01% or more, more preferably 0.02% or more, and even more preferably 0.03% or more.
• Cr 0-0.50% Cr (chromium) is an element that contributes to increasing the Goss orientation occupancy rate in the secondary recrystallization structure and also contributes to improving the adhesion of the glass coating. Therefore, Cr may be contained as necessary. However, if the Cr content is excessive, Cr oxides may be formed, which may degrade the magnetic properties. Therefore, the Cr content is preferably 0.50% or less, more preferably 0.30% or less, and even more preferably 0.10% or less. There is no need to set a lower limit for the Cr content; it may be 0% or more. To ensure the above effects, the Cr content is preferably 0.01% or more, more preferably 0.02% or more, and even more preferably 0.03% or more.
• P 0 to 0.05%
• P phosphorus
• the P content is preferably 0.05% or less, more preferably 0.04% or less, and even more preferably 0.03% or less.
• the lower limit of the P content is not limited and may include 0%, but P is also an element that has the effect of improving texture and magnetic properties. To achieve this effect, the P content may be more than 0%, may be 0.005% or more, or may be 0.01% or more.
• Ta 0-0.05%
• Ta is an element that has the effect of stabilizing secondary recrystallization. Therefore, Ta may be contained as necessary. However, if its content is excessive, secondary recrystallization may become unstable. Therefore, the Ta content is preferably 0.05% or less, more preferably 0.04% or less, and even more preferably 0.03% or less. There is no need to set a lower limit for the Ta content, and it may be 0%. To reliably obtain the above effect, the Ta content is preferably more than 0%, more preferably 0.0005% or more, and even more preferably 0.001% or more.
• Nb 0-0.010%
• Nb niobium
• the Nb content is preferably 0.010% or less, more preferably 0.0050% or less, and even more preferably 0.0030% or less. There is no need to set a lower limit for the Nb content, and it may be 0%. To reliably obtain the above effect, the Nb content is preferably more than 0%, more preferably 0.0005% or more, and even more preferably 0.0010% or more.
• B 0-0.010%
• B boron
• the B content is preferably 0.010% or less, more preferably 0.0050% or less, and even more preferably 0.0030% or less. There is no need to set a lower limit for the B content, and it may be 0%. To reliably obtain the above effect, the B content is preferably more than 0%, more preferably 0.0005% or more, and even more preferably 0.0010% or more.
• Te 0 ⁇ 0.0200% Te (tellurium) is an element that has the effect of stabilizing secondary recrystallization. Therefore, Te may be contained as necessary. However, if its content is excessive, hot rolling property and cold rolling property may be deteriorated, which may lead to fracture. Therefore, the Te content is preferably 0.0200% or less, more preferably 0.0150% or less, and even more preferably 0.0100% or less. There is no need to set a lower limit for the Te content, and it may be 0%. To reliably obtain the above effect, the Te content is preferably more than 0%, more preferably 0.0005% or more, and even more preferably 0.0010% or more.
• Bi 0 ⁇ 0.0200%
• Bi bismuth
• the Bi content is preferably 0.0200% or less, more preferably 0.0150% or less, and even more preferably 0.0100% or less.
• the Bi content is preferably 0.0005% or more, more preferably 0.0010% or more, and even more preferably 0.0020% or more.
• Impurities include, for example, one or more selected from the group consisting of Ca: 0-0.001%, Mg: 0-0.002%, O: 0-0.01%, As: 0-0.10%, Co: 0-0.10%, Zr: 0-0.003%, W: 0-0.10%, Hf: 0-0.02%, Sr: 0-0.02%, Zn: 0-0.02%, Pb: 0-0.10%, REM: 0-0.02%, Ba: 0-0.02%, Cd: 0-0.02%, Pt: 0-0.02%, Au: 0-0.02%, Ga: 0-0.02%, and Ge: 0-0.02%.
• REM refers to a total of 17 elements consisting of Sc, Y, and lanthanides
• the REM content refers to the total content of these elements. If multiple impurity elements are contained, the total content of these elements is preferably 0 to 0.05%.
• the hot-rolled sheet annealing process is a process of annealing a hot-rolled steel sheet manufactured through a hot-rolling process. By performing such an annealing treatment, recrystallization occurs in the steel sheet structure, making it possible to achieve good magnetic properties.
• the hot-rolled steel sheet manufactured through the hot-rolling process may be annealed according to a known method.
• the means for heating the hot-rolled steel sheet during annealing is not particularly limited, and known heating methods can be adopted.
• the annealing conditions are not particularly limited, but for example, the hot-rolled steel sheet can be annealed in a temperature range of 900 to 1200°C for 10 seconds to 5 minutes.
• (C) Cold Rolling Step the hot-rolled steel sheet after the hot-rolled sheet annealing step is subjected to cold rolling including multiple passes to obtain a cold-rolled steel sheet.
• the cold rolling may be a single cold rolling, or multiple cold rolling passes may be performed, with the cold rolling interrupted before the final pass of the cold rolling step and at least one or two intermediate annealings performed between the cold rolling passes.
• intermediate annealing it is preferable to hold the steel at a temperature of 1000 to 1200°C for 5 to 180 seconds.
• the annealing atmosphere is not particularly limited. Considering production costs, the number of intermediate annealings is preferably three or less.
• the surface of the hot-rolled steel sheet may be pickled under known conditions.
• (D) Decarburization Annealing Step the cold-rolled steel sheet is subjected to decarburization annealing to produce a decarburization annealed steel sheet.
• the decarburization annealing step the cold-rolled steel sheet is subjected to primary recrystallization, and C, which adversely affects magnetic properties, is removed from the steel sheet.
• the decarburization annealing step includes a temperature-raising step and a soaking step.
• local heat treatment is performed using a laser beam after the temperature-raising step and before the soaking step.
• the cold-rolled steel sheet is heated in a non-oxidizing atmosphere from a temperature range of 450°C or below to the decarburization annealing temperature range of 750-950°C.
• This heating promotes the nucleation of Goss-oriented grains.
• the average heating rate between 450°C and 750°C is set to 40°C/sec or higher.
• the average heating rate is preferably set to 400°C/sec or higher to achieve a low-angle grain boundary ratio of 50% or higher.
• the average heating rate is set to 2000°C/sec or lower.
• the non-oxidizing atmosphere is a nitrogen atmosphere or a nitrogen/hydrogen mixed atmosphere, and is an atmosphere with a dew point of ⁇ 50°C or higher and 0°C or lower.
• the dew point is preferably ⁇ 5°C or lower, more preferably ⁇ 10°C or lower.
• the dew point may be ⁇ 40°C or higher.
• both the front and back surfaces of the cold-rolled steel sheet are irradiated with a laser beam in a direction intersecting with the rolling direction under conditions that satisfy the following formulas (i) and (ii) so that the laser beams overlap when viewed from a direction perpendicular to the surfaces.
• Up is the instantaneous input energy (J/mm 2 ) expressed as 4/ ⁇ P/(Dl ⁇ Vc) where P (W) is the average intensity of the laser beam, Dl (mm) is the average focused diameter of the focused spot in the rolling direction, and Vc (mm/ sec ) is the average scanning speed of the laser beam, and d in the above formula (ii) is the irradiation interval (mm) of the laser beam.
• the temperature of the cold-rolled steel sheet during laser beam irradiation is below 650°C, it becomes difficult to reduce the diameter of secondary recrystallized grains, making it difficult to achieve a Dr of 20.0 mm or less and a Dt/Dr of 1.20 or more.
• the temperature of the cold-rolled steel sheet during laser beam irradiation exceeds 850°C, it becomes impossible to increase Dt, making it difficult to achieve a Dt/Dr of 1.20 or more.
• Up is less than 0.2 J/ mm2 , the crystal grains are divided and grain boundaries of secondary recrystallized grains cannot be formed, making it difficult to achieve a Dr of 20.0 mm or less and a Dt/Dr of 1.20 or more.
• Up exceeds 22.3 J/ mm2 , it is not possible to increase Dt, making it difficult to achieve a Dt/Dr of 1.20 or more.
• Up is preferably 11.9 J/ mm2 or less.
• the irradiation interval will be too wide, making it difficult to achieve Dr of 20.0 mm or less and Dt/Dr of 1.20 or more.
• Dt cannot be increased, making it difficult to achieve Dt/Dr of 1.20 or more.
• the direction in which the laser beam is irradiated may be any direction intersecting the rolling direction, but it is preferable for it to be a direction that forms an angle of 30 to 150° with respect to the rolling direction. If the laser beam is irradiated in multiple rows, the irradiation intervals for all of them must satisfy formula (ii) above.
• the oxygen potential (PH 2 O/PH 2 ) in the heat treatment atmosphere be 0.20 or less.
• a soaking process is performed.
• the oxygen potential (PH 2 O/PH 2 ) in the annealing atmosphere may be set to 0.15 to 1.0, and the temperature may be held in the range of 750 to 950°C for 10 to 600 seconds.
• finish annealing step a predetermined annealing separator is applied to one or both sides of the decarburization-annealed steel sheet obtained in the decarburization-annealing step, and then the steel sheet is subjected to finish annealing to obtain a finish annealed sheet.
• Finish annealing is generally performed for a long period of time while the steel sheet is wound into a coil. Therefore, prior to the finish annealing, an annealing separator is applied to the decarburization-annealed steel sheet and dried in order to prevent seizure between the inside and outside of the coil winding.
• the annealing separator to be applied is an annealing separator containing MgO as the main component (e.g., containing 80% or more by weight).
• MgO a glass coating
• a primary coating glass coating
• the primary coating is an Mg2SiO4 or MgAl2O4 compound, and if MgO is not the main component, there will be a shortage of Mg, which is necessary for the formation reaction.
• Finish annealing can be performed, for example, by raising the temperature to 1150-1250°C in an atmospheric gas containing hydrogen and nitrogen, and annealing at that temperature for 10-60 hours.
• (F) Insulating Coating Forming Step In the insulating coating forming step, excess annealing separator is removed from the surface of the finish-annealed sheet obtained in the finish-annealing step by water washing, pickling, or the like, and then a secondary coating, which is an insulating coating, is formed.
• This insulating coating applies tension to the grain-oriented electrical steel sheet, reducing the iron loss of each individual steel sheet, and when grain-oriented electrical steel sheets are stacked together, it ensures electrical insulation between the steel sheets, thereby reducing the iron loss of the iron core.
• the insulating coating is formed by applying a coating solution primarily composed of aluminum phosphate and colloidal silica to the surface of the finish-annealed sheet, baking it at a temperature of, for example, 350 to 600°C, and then heat treating it at a temperature of 800 to 1000°C.
• the grain-oriented electrical steel sheet obtained by the above steps may be further subjected to a magnetic domain refinement treatment.
• the magnetic domain refinement treatment may be performed using a known method, such as forming grooves on the steel sheet surface by a mechanical method or irradiating the steel sheet surface with a laser beam or electron beam to introduce local strain. Note that the magnetic domain refinement treatment does not change the size of the crystal grains.
• the above-mentioned Dt and Dr are the same before and after the magnetic domain refinement treatment.
• a slab having the chemical composition shown in Table 1 was heated to 1340°C in a heating furnace.
• the heated slab was subjected to a hot rolling process to produce a hot-rolled steel sheet with a thickness of 2.3 mm.
• the hot-rolled steel sheet was then heated to a temperature of 1100°C to recrystallize, and then annealed at 900°C for 30 seconds to produce a hot-rolled annealed steel sheet.
• a cold rolling process was carried out to produce a cold-rolled steel sheet with the thickness shown in Table 2.
• a decarburization annealing step was carried out.
• the temperature-raising step of the decarburization annealing step the temperature was raised to 880°C at the temperature-raising rate shown in Table 2.
• the steel sheet was cooled to the temperature shown in Table 2, and then irradiated with a laser beam under the conditions shown in Table 2. Thereafter, the steel sheet was decarburized by soaking at 850°C for 150 seconds with the oxygen potential (PH 2 O/PH 2 ) in the annealing atmosphere set to 0.50, to obtain a decarburization annealed steel sheet.
• the oxygen potential PH 2 O/PH 2
• An annealing separator (water slurry) primarily composed of MgO was applied to the surface of the decarburized annealed steel sheet.
• the decarburized annealed steel sheet coated with the annealing separator was then wound into a coil.
• the coil was then subjected to finish annealing to produce the finish annealed steel sheet.
• the finish annealing temperature was 1150°C, and the holding time at the finish annealing temperature was 30 hours.
• the annealing separator was removed from the steel sheets, and then the secondary coating process (insulating coating process) was carried out. Specifically, a secondary coating agent (insulating coating agent) primarily composed of colloidal silica and phosphate was applied to the surface (on the glass coating) of each final annealed steel sheet, and the final annealed steel sheet to which the secondary coating agent had been applied was then baked to form a secondary coating, which is a tension insulating coating, on top of the primary coating. Grain-oriented electrical steel sheets with each test number were manufactured using the above manufacturing process.
• the chemical composition of the base steel sheet was measured by the following method.
• the primary coating and secondary coating were removed from the base steel sheet by the following method. Specifically, the grain-oriented electrical steel sheet on which the secondary coating was formed was immersed in a sodium hydroxide aqueous solution of 30 mass % NaOH + 70 mass % H 2 O at 80°C for 5 minutes, and after immersion, it was washed with water and dried. By this process, the secondary coating was removed from the grain-oriented electrical steel sheet.
• the grain-oriented electrical steel sheet from which the secondary coating had been removed and from which the primary coating remained was immersed in high-temperature hydrochloric acid to remove the coating. Specifically, the grain-oriented electrical steel sheet from which the primary coating remained was immersed in 30% by mass hydrochloric acid at 80°C for 1 minute, and then rinsed with water and dried. Through these steps, a base steel sheet from which the secondary coating and primary coating had been removed was obtained.
• the chemical composition of the resulting steel plate was measured using a method in accordance with JIS G 0321:2017. Specifically, chips were first collected from the resulting base steel plate, and the collected chips were dissolved in acid to obtain a solution. The solution was then subjected to ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry) for elemental analysis of the chemical composition. The carbon and sulfur contents were determined using the well-known high-frequency combustion method (combustion-infrared absorption method). The nitrogen content was determined using the well-known inert gas fusion-thermal conductivity method. Specifically, measurements were performed using a Shimadzu component analyzer (product name: ICPS-8000).
• test pieces for measuring magnetic properties were taken from the grain-oriented electrical steel sheets with the respective test numbers.
• the test pieces were taken from the inner peripheral side of the coil in the final annealing process.
• the magnetic flux density B8 of the taken test pieces for measuring magnetic properties was measured using the method described above.
• a test piece with a magnetic flux density B8 of 1.930 T or higher was evaluated as having excellent magnetic properties and passing the test.
• the test pieces for measuring magnetic properties were then subjected to a magnetic domain refining treatment using laser beam irradiation. Specifically, the irradiation pitch was set to 4 mm, and the energy density Ua was set to 1.25 mJ/ mm2 .
• the iron loss W17 /50 of the test pieces for measuring magnetic properties after the magnetic domain refining treatment was measured using the method described above. In this example, if the iron loss W17 /50 after the magnetic domain refining treatment was 0.711 W/kg or less, it was determined that low iron loss was obtained.
• test pieces for grain measurement were taken from the grain-oriented electrical steel sheets with each of the above test numbers.
• the test pieces were taken from the inner peripheral side of the coil during the finish annealing process.
• Dr, Dt, and the low-angle grain boundary ratio were determined using the methods described above. Note that if the measured value of the magnetic flux density B8 described above was less than 1.700 T, it was determined to be secondary recrystallization failure, and crystal orientation measurement was not performed.
• Test No. 13 had a small Up value. As a result, Dr was not adequately controlled and was excessive. As a result, the magnetic flux density B8 was less than 1.930 T due to the coil setting, and iron loss was also poor.
• Test No. 14 had an excessively long irradiation interval. As a result, Dr increased, the magnetic flux density B8 was less than 1.930 T due to the coil setting, and iron loss was also poor.
• Test No. 16 was irradiated on one side. As a result, Dr was large, and the magnetic flux density B8 was less than 1.930 T due to the coil setting, resulting in poor magnetic properties and poor iron loss.
• Test No. 17 had a high temperature during irradiation.
• the temperature during irradiation is high, excessive heat input causes magnetically inferior grains to form in the area irradiated by the laser beam, and although Dr is controlled, Dt decreases, with Dt/Dr being less than 1.20.
• the low-angle grain boundary ratio was also less than 50%.
• the magnetic flux density B8 was less than 1.930 T and the iron loss was also significantly inferior.
• Test No. 18 was irradiated at a low temperature.
• Dr increased.
• the low-angle grain boundary ratio was 50% or more.
• the magnetic flux density B8 was less than 1.930 T and the iron loss was also poor.
• test number 37 the laser beam was irradiated before the temperature was raised, so the effect of increasing the low-angle grain boundary ratio due to rapid heating was not fully realized, and the low-angle grain boundary ratio was less than 50%.
• Dt/Dr was 1.20 or more and magnetic flux density B8 was 1.930 T or more, iron loss was inferior.

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