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
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
• • 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
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
• • 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
  • H01F1/18—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 with insulating coating

Definitions

• the present invention relates to a grain-oriented electrical steel sheet and a method for manufacturing the same.
• Grain-oriented electrical steel sheets are primarily used in transformers. Transformers are continuously excited over long periods of time, from installation to disposal, resulting in continuous energy loss. Therefore, the energy loss when magnetized by alternating current, i.e., iron loss, is a key indicator that determines the performance of a transformer.
• tension to steel sheet is effective in reducing iron loss.
• Forming a coating made of a material with a smaller thermal expansion coefficient than steel sheet at high temperatures on the steel sheet surface is an effective way to reduce iron loss.
• Forsterite-based coatings (inorganic coatings) with excellent coating adhesion are produced during the finish annealing process of electrical steel sheet when oxides on the steel sheet surface react with annealing separators, and are a coating that can apply tension to steel sheet.
• Patent Document 1 the method disclosed in Patent Document 1, in which a coating liquid primarily composed of colloidal silica and phosphate is baked onto the surface of a steel sheet to form an insulating coating, is an effective method for reducing iron loss because it effectively applies tension to the steel sheet. Therefore, the typical method for manufacturing grain-oriented electrical steel sheets is to leave the forsterite-based coating formed in the final annealing process and then apply an insulating coating primarily composed of phosphate on top of it.
• grain-oriented electrical steel sheets are required to have excellent high-field iron loss characteristics, i.e., good iron loss even at high magnetic flux densities.
• forsterite-based coatings hinder domain wall movement, adversely affecting iron loss.
• magnetic domains change due to domain wall movement under an AC magnetic field. Smooth and rapid domain wall movement is effective in reducing iron loss.
• forsterite-based coatings also called glass coatings or primary coatings
• Patent Document 2 discloses a technique in which, after normal finish annealing, the steel sheet is pickled to remove surface deposits, and then chemically or electrolytically polished to a mirror finish. It has been found that even better iron loss improvement effects can be achieved by forming a tensioned insulating coating on the surface of grain-oriented electrical steel sheet that does not have a forsterite-based coating, which has been obtained using such a known method. Furthermore, in addition to improving iron loss, tensioned insulating coatings can also impart various other properties, such as corrosion resistance, heat resistance, and slip resistance.
• forsterite-based coatings also function as intermediate layers that ensure adhesion when forming tension coatings (tension-applying insulating coatings). That is, because forsterite-based coatings are formed in a state where they penetrate deeply into the steel sheet, they have excellent adhesion to the metal steel sheet. Therefore, when a tension-applying coating (tension coating) containing colloidal silica, phosphate, or the like as a main component is formed on the surface of a forsterite-based coating, the coating has excellent adhesion.
• tension coating tension coating
• bonding between metals and oxides is generally difficult, it has been difficult to ensure sufficient adhesion between a tension coating and the steel sheet surface in the absence of a forsterite-based coating. Therefore, when forming a tension coating on a grain-oriented electrical steel sheet that does not have a forsterite-based coating, it is being considered to provide a layer that takes the role of the intermediate layer of the forsterite-based coating.
• Patent Document 3 discloses a technique for ensuring the adhesion of a tension-applying insulating coating by applying a coating to serve as an intermediate layer beforehand when forming the tension-applying coating.
• the technique disclosed in Patent Document 3 has a problem in that it is not possible to maintain a tensioned insulating coating having a large tension with good adhesion.
• Patent Document 4 discloses a grain-oriented electrical steel sheet having a base steel sheet and an insulating coating formed on the surface of the base steel sheet, the insulating coating being formed on the side of the base steel sheet, an intermediate layer containing a crystalline metal phosphate, and a tensile coating layer formed on the surface side of the insulating coating.
• Patent Document 4 discloses that the grain-oriented electrical steel sheet does not have a forsterite-based coating, and has excellent coating adhesion, excellent coating tension, and excellent magnetic properties.
• grain-oriented electrical steel sheets may be subjected to stress relief annealing after being processed into a specified shape.
• stress relief annealing may result in a decrease in the adhesion of the coating.
• Patent Documents 1 to 4 do not disclose grain-oriented electrical steel sheets that do not have a forsterite-based coating and that exhibit excellent coating adhesion even when stress relief annealing is performed (after stress relief annealing). Therefore, an object of the present invention is to provide a grain-oriented electrical steel sheet that does not have a forsterite-based coating, and that can ensure coating tension, corrosion resistance, resistance to phosphorus elution from the coating, and space factor and core loss when used as a core that are equal to or better than conventional ones, while also providing excellent coating adhesion even after stress relief annealing, and a method for manufacturing the same.
• the present inventors have investigated the effect of stress relief annealing on the adhesion of an insulating coating. As a result, they discovered that by forming a phosphate coating that serves as an intermediate layer and an insulating coating by chemical conversion treatment on the surface of grain-oriented electrical steel sheet that does not have a forsterite-based coating, fusing the intermediate layer and the insulating coating during stress relief annealing, and forming a layer containing Si oxide (oxide layer) directly below the insulating coating obtained by the fusion, it is possible to suppress a decrease in the adhesion of the insulating coating without deteriorating the magnetic properties or other coating properties.
• the ratio of the length of the interface between the oxide layer and the insulating coating to the length of the interface between the base steel sheet and the insulating coating may be 30% or more.
• the insulating coating may have a void area ratio of 30% or less.
• a method for producing a grain-oriented electrical steel sheet includes a finish annealing step of applying an annealing separator containing 10 to 100% by mass of Al 2 O 3 to a steel sheet, drying the steel sheet, and then finish annealing the steel sheet; an annealing separator removing step of removing excess annealing separator from the steel sheet after the finish annealing step; a light pickling step of pickling the steel sheet after the annealing separator removing step with 0.1 to 5.0% by mass of inorganic acid for 10 to 60 seconds; a water rinsing step of rinsing the steel sheet after the light pickling step with water and drying it; and a first insulating coating forming step of immersing the steel sheet after the water rinsing step in a treatment solution having a liquid temperature of 30 to 85°C and a metal phosphate concentration of 1.0 to 10.0% by mass for 5 to 150 seconds, removing the treatment solution with water, and then
• the annealing separator may further contain one or both of MgO: 5 to 90 mass % and
• the above-described aspects of the present invention provide a grain-oriented electrical steel sheet that exhibits excellent coating adhesion even after stress relief annealing, as well as a method for manufacturing the same.
• FIG. 1 is an example of a photograph of a cross section of a grain-oriented electrical steel sheet according to an embodiment of the present invention, including an insulating coating and a base steel sheet.
• This section describes a grain-oriented electrical steel sheet according to one embodiment of the present invention (grain-oriented electrical steel sheet according to this embodiment) and its manufacturing method.
• the grain-oriented electrical steel sheet according to this embodiment has a base steel sheet 11 and an insulating coating 21 containing a metal phosphate formed on the surface of the base steel sheet 11 .
• a base steel sheet 11 has a base steel sheet 11 and an insulating coating 21 containing a metal phosphate formed on the surface of the base steel sheet 11 .
• the base steel sheet 11 has an oxide layer 12 containing an oxide of Si in a region in contact with an interface IF between the base steel sheet 11 and an insulating coating 21.
• the portion other than the oxide layer 12 is made of steel sheet.
• an oxide layer containing oxides of Si is formed in the region of the base steel sheet that contacts the interface between the base steel sheet and the insulating coating.
• This oxide layer contributes to improving the adhesion between the base steel sheet and the insulating coating. Without the oxide layer, sufficient adhesion cannot be ensured.
• the average thickness of the oxide layer from the interface between the base steel sheet and the insulating coating is 0.5 to 2.5 ⁇ m. If the average thickness is less than 0.5 ⁇ m, the effect of improving adhesion is small. On the other hand, if the average thickness exceeds 2.5 ⁇ m, the magnetic properties will be inferior.
• the oxide layer is present in the region that contacts the interface between the base steel sheet and the insulating coating, i.e., it constitutes the interface with the insulating coating, thereby improving adhesion (adhesion of the coating).
• adhesion of the coating it is preferable that the ratio of the length of the interface between the oxide layer and the insulating coating to the length of the interface between the base steel sheet and the insulating coating (coverage rate) be 30% or more. The length ratio may also be 100%.
• the oxide layer mainly contains an oxide of Si, and the Si content in the Si oxide layer is preferably 60 to 70 mass %.
• the Si oxide includes composite oxides containing Si, such as SiO2 and FeSiO4 .
• the oxide layer may also contain iron oxide, aluminum oxide, chromium oxide, etc.
• the P content in the oxide layer is 1.0 mass % or less, making it clearly distinguishable from an insulating coating.
• the oxide layer of the grain-oriented electrical steel sheet according to this embodiment is formed as part of the base steel sheet, and therefore has extremely high adhesion to the base steel sheet.
• Whether an oxide layer is formed, the average thickness of the oxide layer, and the proportion of the oxide layer in the interface (coverage) can be determined by the following methods.
• a cross section of the steel sheet including the vicinity of the surface layer is photographed at a magnification of 30,000 times using a transmission electron microscope (TEM) along the interface with a length of 10 ⁇ m or more.
• TEM transmission electron microscope
• the captured image makes it possible to distinguish between the base steel sheet and the insulating coating. This is because the base steel is composed almost entirely of iron atoms, while the insulating coating contains phosphate, aggregated colloidal silica, and voids.
• the base steel sheet has an oxide layer as an internal oxidation layer, but since it is composed almost entirely of silica, has a low P content, and is present inside the base material, its difference from an insulating coating mainly composed of phosphate can be confirmed by elemental analysis. If the image resolution is low and a clear image cannot be obtained, it can be clarified using an image processing device such as Luzex.
• the interface between the insulating coating and the base metal may be determined as the point where the distribution of P element rapidly decreases from the insulating coating side, because P element exists in the form of phosphoric acid or phosphorus oxide in the insulating coating and hardly diffuses into the steel.
• the interface between the insulating coating and the base material may be determined as a location where the amount of Al, Mg, Mn, Zn, Ca, Cu, Co, and Li, which are presumed to be present as cations in the insulating coating, decreases sharply.
• the thicknesses of the oxide layer measured at three locations in each image i.e., a total of nine or more locations are averaged to obtain the average thickness of the oxide layer.
• the Si content of the oxide layer is determined by performing elemental analysis of three or more locations in each of three fields of view using an energy dispersive X-ray analyzer attached to a transmission electron microscope, and averaging the measurement results.
• the chemical composition of the portion (steel plate portion) other than the oxide layer of the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment may be within a range known for grain-oriented electrical steel sheets in order to obtain the properties generally required of grain-oriented electrical steel sheets.
• the chemical components constituting the chemical composition preferably include the following: In this embodiment, % relating to chemical components is mass % unless otherwise specified.
• C 0.010% or less
• C (carbon) is an element effective for controlling the structure of the steel sheet in the manufacturing process up to the completion of the decarburization annealing process.
• the C content is preferably 0.010% or less.
• the C content is more preferably 0.005% or less.
• Si 2.50-4.00%
• Silicon (Si) is an element that increases the electrical resistance of grain-oriented electrical steel sheets and improves their iron loss characteristics. If the Si content is less than 2.50%, a sufficient eddy current loss reduction effect cannot be obtained. Therefore, the Si content is preferably 2.50% or more. The Si content is more preferably 2.70% or more, and even more preferably 3.00% or more. On the other hand, if the Si content exceeds 4.00%, the grain-oriented electrical steel sheet becomes embrittled and the threading property deteriorates significantly. Furthermore, the workability of the grain-oriented electrical steel sheet deteriorates, and the steel sheet may break during rolling. Therefore, the Si content is preferably 4.00% or less. The Si content is more preferably 3.80% or less, and even more preferably 3.70% or less.
• N 0.010% or less
• N nitrogen
• the N content is preferably 0.010% or less.
• the N content is more preferably 0.008% or less.
• the lower limit of the N content is not particularly specified, but reducing it to less than 0.001% would only increase the manufacturing cost, so the N content may be 0.001% or more.
• the chemical composition of the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment may contain the above-mentioned elements, with the balance being Fe and impurities.
• Sn, Cu, Se, and Sb may also be contained in the ranges shown below.
• other elements than these such as one or more of W, Nb, Ti, Ni, Co, V, Cr, and Mo, are contained in a total amount of 1.0% or less, this does not impair the effects of the grain-oriented electrical steel sheet according to this embodiment.
• impurities refer to elements that are mixed in from raw materials such as ore or scrap, or the manufacturing environment, when the base steel sheet is industrially manufactured, and are permissible to be contained in amounts that do not adversely affect the function of the grain-oriented electrical steel sheet according to this embodiment.
• Sn 0-0.50% Sn (tin) is an element that contributes to improving magnetic properties through controlling the primary recrystallization structure.
• the Sn content is preferably 0.01% or more.
• the Sn content is more preferably 0.02% or more, and even more preferably 0.03% or more.
• the Sn content is preferably 0.50% or less.
• the Sn content is more preferably 0.30% or less, and even more preferably 0.10% or less.
• Cu is an element that contributes to increasing the Goss orientation occupancy rate in the secondary recrystallized structure.
• the Cu content is preferably 0.01% or more.
• the Cu content is more preferably 0.02% or more, and even more preferably 0.03% or more.
• the Cu content is preferably 0.50% or less.
• the Cu content is more preferably 0.30% or less, and even more preferably 0.10% or less.
• Se is an element that has a magnetic property improving effect.
• the Se content is preferably 0.001% or more in order to effectively exhibit the magnetic property improving effect.
• the Se content is more preferably 0.003% or more, and even more preferably 0.006% or more.
• the Se content is preferably 0.020% or less, more preferably 0.015% or less, and even more preferably 0.010% or less.
• Sb 0-0.50% Sb (antimony) is an element that has a magnetic property improving effect.
• the Sb content is preferably 0.005% or more in order to effectively exhibit the magnetic property improving effect.
• the Sb content is more preferably 0.01% or more, and even more preferably 0.02% or more.
• the Sb content is preferably 0.50% or less, more preferably 0.30% or less, and even more preferably 0.10% or less.
• the chemical composition of the base steel sheet of the grain-oriented electrical steel sheet is, for example, one that contains the elements described above, with the remainder consisting of Fe and impurities.
• the chemical composition of the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment can be measured using the known ICP atomic emission spectroscopy method. However, if an insulating coating is formed on the surface, it must be removed before measurement.
• the removal method involves immersing the sheet in a highly concentrated alkaline solution (for example, a 30% sodium hydroxide solution heated to 85°C) for 20 minutes or more. Peeling can be determined visually. For small samples, removal can also be achieved by surface grinding.
• the thickness of the base steel plate is not limited, but is preferably 0.15 to 0.35 mm in terms of iron loss.
• the proportions of metal phosphate and Si content in the insulating coating can be measured using SEM-EDS, as described below.
• the area ratio of voids in the insulating coating is preferably 30% or less. By reducing the area ratio of voids, the effect of further improving the coating tension can be obtained.
• the void area ratio of the insulating coating is determined by the following method. Based on an image of a steel sheet cross section, including the vicinity of the surface, taken with a transmission electron microscope (TEM) at 30,000 times magnification and measuring 10 ⁇ m or more in length, the phosphate-based insulating coating and voids are confirmed by elemental analysis, and the void area is determined. The percentage of the void area in the total area of the observation field is taken as the void area ratio (%). If the image resolution is low and a clear image cannot be obtained, it can be clarified using an image processing device such as Luzex.
• TEM transmission electron microscope
• the thickness of the insulating coating 21 is preferably 1.0 to 10.0 ⁇ m in terms of space factor.
• the thickness of the insulating coating is determined by the following method. For the flat portion, a sample having a size of 10 mm square (10 mm in the rolling direction and 10 mm in the direction perpendicular to the rolling direction) was taken, and the cross section of the sample in the thickness direction perpendicular to the rolling direction was observed with a scanning electron microscope. The thickness was measured at five or more points, and the average of the measurements was taken as the thickness of the insulating coating.
• the P content is measured using an energy dispersive elemental analyzer, and the position where the distribution of P element rapidly decreases from the insulating coating side (surface side) is defined as the interface between the insulating coating and the base steel sheet.
• the position where Al, Mg, Mn, Zn, Ca, Cu, Co, and Li, which are presumed to be present as cations in the insulating coating, rapidly decrease may be defined as the interface between the insulating coating and the base steel sheet.
• the mass percentage of metal phosphate and the type of metal phosphate are determined using a scanning electron microscope and an energy dispersive elemental analyzer.
• the Si content can also be measured using a scanning electron microscope and an energy dispersive elemental analyzer.
• the mass percentage of metal phosphate and the Si content are measured at three locations and the average values are used.
• the grain-oriented electrical steel sheet according to this embodiment can achieve the above-described effects regardless of the manufacturing method, but can be preferably manufactured by a manufacturing method including the following steps, for example.
• a hot rolling step of heating the slab and hot rolling the slab into a hot-rolled sheet (ii) a hot-rolled sheet annealing step of annealing the hot-rolled sheet; (iii) a pickling step of pickling the hot-rolled sheet after the hot-rolled sheet annealing step; (iv) a cold rolling step in which the hot-rolled sheet after the pickling step is cold-rolled to obtain a steel sheet (cold-rolled sheet);
• a decarburization annealing step of subjecting the steel sheet to decarburization annealing (vi) a finish annealing step of applying an annealing separator containing 10 to 100 mass% of Al 2 O 3 to the steel sheet after the decarburization annealing, drying the steel sheet, and then
• the method for producing a grain-oriented electrical steel sheet according to this embodiment is characterized by the (vi) finish annealing step to the (xii) heat treatment step, and the (i) hot rolling step to the (v) decarburization annealing step are not particularly limited, and known conditions can be applied.
• a steel billet such as a slab having a predetermined chemical composition is heated and then hot rolled to obtain a hot-rolled sheet.
• the heating temperature of the steel billet is preferably within the range of 1100 to 1450°C, and more preferably 1300 to 1400°C.
• the chemical composition of the slab may be changed depending on the chemical composition of the base steel sheet of the grain-oriented electrical steel sheet that is ultimately to be obtained, but an example of such a chemical composition may include, in mass %, C: 0.01 to 0.20%, Si: 2.50 to 4.00%, sol.
• the hot rolling conditions are not particularly limited and may be appropriately set based on the desired properties.
• the thickness of the hot rolled sheet is preferably within a range of 2.0 mm to 3.0 mm, for example.
• the hot-rolled sheet annealing process In the hot-rolled sheet annealing process, the steel sheet (hot-rolled sheet) after the hot rolling process is annealed. By performing such annealing treatment, recrystallization occurs in the steel sheet structure, making it possible to achieve good magnetic properties.
• the hot-rolled sheet annealing process of this embodiment the hot-rolled sheet manufactured through the hot rolling process may be annealed according to a known method.
• the means for heating the hot-rolled sheet during annealing is not particularly limited, and known heating methods can be adopted. For example, so-called continuous annealing may be used, or the hot-rolled sheet may be coiled and subjected to batch annealing.
• the annealing conditions are also not particularly limited, but for example, the hot-rolled sheet may be annealed in a temperature range of 900 to 1200°C for 10 seconds to 5 minutes.
• the atmosphere is not particularly limited, but it is preferable to suppress oxidation of the steel sheet, and it is preferable to perform the annealing in a non-oxidizing atmosphere such as nitrogen, argon, or hydrogen.
• Cold rolling process In the cold rolling process, the steel sheet after the pickling process is cold rolled to form a cold-rolled sheet (a steel sheet having the same sheet thickness as the base steel sheet of the grain-oriented electrical steel sheet).
• the cold rolling may be a single cold rolling (a series of cold rolling without intermediate annealing) or may be multiple cold rolling passes with intermediate annealing between them, with the cold rolling being interrupted and at least one or two or more intermediate annealing passes being performed before the final pass of the cold rolling process.
• the cold rolling conditions may be in accordance with known methods.
• the cold rolling reduction of grain-oriented electrical steel sheet has a significant effect on its magnetic properties.
• the final reduction has a particularly large effect, and the final reduction can be set to 80 to 95%.
• decarburization annealing process In the decarburization annealing step, the cold-rolled steel sheet after the grinding step is subjected to decarburization annealing, which removes (decarburizes) carbon from the steel sheet, which adversely affects magnetic properties, and also causes primary recrystallization of the cold-rolled steel sheet.
• the decarburization annealing conditions are not limited, but the annealing is performed in a nitrogen-hydrogen mixed atmosphere for decarburization, with the oxygen potential increased by humidification.
• the humidification temperature (dew point) is determined from the viewpoint of the annealing temperature required for recrystallization and the oxygen potential that allows decarburization at the annealing temperature.
• the annealing temperature is, for example, about 700 to 900° C., and since annealing is generally performed in a continuous annealing process, soaking is performed for 30 to 90 seconds.
• Nitriding treatment may be carried out between the decarburization annealing step and the finish annealing step described below.
• the decarburization-annealed steel sheet is subjected to nitriding treatment by maintaining the steel sheet in a nitriding atmosphere (an atmosphere containing hydrogen, nitrogen, and ammonia or other nitriding gases) at approximately 700 to 850°C.
• a nitriding atmosphere an atmosphere containing hydrogen, nitrogen, and ammonia or other nitriding gases
• the nitrogen concentration of the steel sheet is preferably 40 ppm (0.0040 mass%) or more by the nitriding process.
• the nitrogen concentration of the steel sheet after the nitriding process is preferably 1000 ppm or less.
• an annealing separator containing 10 to 100 mass % of Al 2 O 3 is applied to the steel sheet after the decarburization annealing step (or the nitriding treatment step), dried, and then final annealing is performed.
• an annealing separator mainly composed of MgO is applied and then finish annealing is performed to form a forsterite-based coating on the surface of the steel sheet (cold-rolled sheet).
• an annealing separator containing 10% by mass or more of Al2O3 is used so as not to form a forsterite-based coating.
• the Al2O3 content is preferably 40% by mass or more.
• the proportion of Al2O3 may be 100% by mass, but from the viewpoint of preventing Al2O3 from seizing onto the steel sheet surface, in the method for producing a grain-oriented electrical steel sheet according to this embodiment, it is preferable that the annealing separator contains MgO. While the MgO content may be 0%, to obtain the above effect, the proportion of MgO is preferably 5% by mass or more.
• the proportion of MgO is 90% by mass or less to ensure 10% by mass or more of Al2O3 .
• the proportion of MgO is preferably 50% by mass or less. It is sufficient that the total of Al2O3 and MgO exceeds 50% by mass in terms of solid content relative to the annealing separator.
• the annealing separator may further contain chloride. The inclusion of chloride in the annealing separator provides the effect of making it more difficult for a forsterite-based coating to form.
• the chloride content is not particularly limited and may be 0%, but to obtain the above effect, a content of 0.5 to 10.0 mass% is preferred.
• Examples of effective chlorides include bismuth chloride, calcium chloride, cobalt chloride, iron chloride, and nickel chloride.
• the conditions for the finish annealing are not limited, but for example, conditions in which the steel is held at a temperature of 1150 to 1250° C. for 10 to 60 hours can be adopted.
• annealing separator removal process In the annealing separator removal step, excess annealing separator is removed from the steel sheet after the finish annealing step. For example, excess annealing separator can be removed by washing with water.
• the steel sheet after the annealing separator removal step is pickled with 0.1 to 5.0 mass % of an inorganic acid for 10 to 60 seconds. If the conditions for light pickling are not favorable, excess annealing separator will remain on the surface of the steel sheet, increasing the surface roughness and reducing the space factor. If the acid is too strong, the surface of the steel sheet will be etched, resulting in reduced magnetic properties.
• First insulation film forming step In the first insulating coating formation process, the steel sheet after the water-rinsing process is immersed for 5 to 150 seconds in a treatment solution having a liquid temperature of 30 to 85°C and a metal phosphate concentration of 1.0 to 10.0 mass %, and after the treatment solution is washed away with water, the steel sheet is dried, thereby forming a first insulating coating on the surface of the steel sheet.
• the temperature of the treatment solution is less than 30°C, the amount of the first insulating coating formed will be too small, resulting in localized poor adhesion of the insulating coating, whereas if the temperature is above 85°C, the first insulating coating will become too thick in some areas, ultimately resulting in increased surface roughness and a reduced space factor. Furthermore, if the metal phosphate concentration is less than 1.0 mass %, the formation of the first insulating coating takes too long, which is disadvantageous in terms of cost, whereas if the metal phosphate concentration is more than 10.0 mass %, the first insulating coating will be thick in some places, ultimately resulting in an uneven insulating coating.
• the treatment time is less than 5 seconds, the amount of the first insulating coating formed will be too small, resulting in partial deterioration of the adhesiveness of the insulating coating, whereas if the treatment time is more than 150 seconds, the time will be too long and will be disadvantageous in terms of cost.
• the coating liquid contains a metal phosphate and colloidal silica in an amount of 30 to 150 parts by mass of colloidal silica per 100 parts by mass of the metal phosphate.
• the solids concentration of the coating liquid is 10 to 40% by mass, and the total of the metal phosphate and colloidal silica, calculated as solids, is preferably more than 50% by mass of the coating liquid.
• the metal phosphate may be, for example, one or a mixture of two or more selected from aluminum phosphate, zinc phosphate, magnesium phosphate, nickel phosphate, copper phosphate, lithium phosphate, cobalt phosphate, etc.
• the coating solution may contain additional elements such as vanadium, tungsten, molybdenum, and zirconium.
• Colloidal silica can be of type S or type C.
• Type S colloidal silica refers to colloidal silica in which the silica solution is alkaline
• type C colloidal silica refers to silica in which the surface of the silica particles is aluminum-treated and the silica solution is alkaline to neutral.
• Type S colloidal silica is widely used and relatively inexpensive, but care must be taken as there is a risk of aggregation and precipitation when mixed with an acidic metal phosphate solution.
• Type C colloidal silica is stable even when mixed with a metal phosphate solution and there is no risk of precipitation, but it is relatively expensive due to the large number of processing steps required. It is preferable to use the appropriate type depending on the stability of the coating liquid to be prepared.
• the surface of the insulating coating (the surface of the insulating coating of a grain-oriented electrical steel sheet comprising a base steel sheet and an insulating coating) may be irradiated with energy rays to perform 180° magnetic domain refinement.
• the magnetic domain subdivision process may be carried out by any known method, such as forming linear or dot-like grooves extending in a direction intersecting the rolling direction at predetermined intervals along the rolling direction to narrow the width of the 180° magnetic domains (subdividing the 180° magnetic domains).
• a mechanical groove forming method using gears or the like, a chemical groove forming method using electrolytic etching, a thermal groove forming method using laser irradiation, or the like can be applied. If the insulating coating is damaged by the formation of stress-strained portions or grooves, and the insulating properties and other characteristics are deteriorated, the insulating coating may be formed again to repair the damage.
• the steel sheet after the second insulating coating formation step is heated to a temperature range of 700 to 900°C in an atmosphere having a dew point of 0 to 30°C, a nitrogen content of 50 to 100% by volume, and a hydrogen content of 0 to 50% by volume, and is held at this temperature range for 10 to 180 minutes, thereby fusing the first insulating coating and the second insulating coating to form an insulating coating and forming an oxide layer in the steel sheet.
• This heat treatment step can also serve as stress relief annealing.
• the steel sheet may be processed to change its shape into a predetermined shape (for example, into an iron core shape) before the heat treatment step.
• the dew point is lower than 0° C., the oxide layer is not sufficiently formed, whereas if the dew point is higher than 30° C., the average thickness of the oxide layer becomes excessive. If the hydrogen content in the atmosphere exceeds 50% by volume, there is a risk that the oxide layer will not be formed sufficiently. If the heat treatment temperature is less than 700°C, the rate of oxide layer formation is slow and the oxide is not sufficiently formed. On the other hand, if the heat treatment temperature is more than 900°C, the rate of oxide formation becomes too fast and varies greatly, resulting in an excessively thick oxide layer.
• additional annealing may be performed in conjunction with the formation of the oxide layer, for example, by heating for 10 minutes in an atmosphere with a dew point of 20°C, followed by annealing for 120 minutes in an atmosphere of 100% nitrogen with a dew point of -20°C.
• an annealing separator containing 48 mass % of MgO, 48 mass % of Al 2 O 3 , and 4 mass % of BiCl 3 was applied, dried, and then heated to 1200° C. and held for 20 hours for finish annealing. After the finish annealing, the steel sheet was washed with water to remove excess annealing separator, and it was found that no forsterite-based coating was formed on the surface of the steel sheet. This steel sheet was subjected to light pickling under the conditions shown in Table 1. Thereafter, the steel plate was washed with water and dried.
• This steel sheet was immersed in a treatment solution containing a mixture of metal phosphate salts shown in Table 1 and additives such as preservatives and viscosity adjusters. After the treatment solution was removed by rinsing with water, the steel sheet was dried to form a first insulating coating. Thereafter, a coating liquid containing a metal phosphate and colloidal silica in the ratio shown in Table 2 was applied and dried to form a second insulating coating. Thereafter, grooves 20 ⁇ m deep and 50 ⁇ m wide were formed on the surface of the steel sheet at intervals of 6 mm in a direction tilted by 80° from the rolling direction using a tooth profile. Thereafter, heat treatment was carried out under the conditions shown in Table 3 to obtain grain-oriented electrical steel sheets.
• the chemical composition of the base steel plate (excluding the oxide layer) was Si: 3.30 mass%, C: 0.0018 mass%, Mn: 0.06 mass%, sol. Al: 0.002 mass%, with the remainder being Fe and impurities.
• the resulting grain-oriented electrical steel sheets were also measured for coating adhesion, coating tension, corrosion resistance, elution resistance, space factor, and iron loss using the following procedures. The results are shown in Table 5.
• the coating tension was calculated by back-calculating from the state of curvature when one side of the insulating coating was peeled off. If the obtained coating tension was 4.0 MPa or more, it was determined that the coating had sufficient tension.
• Corrosion resistance was evaluated by subjecting the sample to a 5% NaCl aqueous solution that was allowed to fall naturally onto the sample for 7 hours in a 35°C atmosphere in accordance with the JIS salt spray test (JIS Z2371:2015). Thereafter, the rusted area was evaluated on a scale of 1 to 10. The evaluation criteria were as follows: A score of 5 or more was considered to be excellent in corrosion resistance.
• the resistance to elution was evaluated based on whether or not the elution of phosphoric acid from the sample could be inhibited.
• the amount of elution was measured by boiling the sample in boiling pure water for 10 minutes, measuring the amount of phosphoric acid eluted in the pure water, and dividing the amount of phosphoric acid by the area of the insulating coating of the boiled grain-oriented electrical steel sheet.
• the amount of phosphoric acid eluted in the pure water was calculated by cooling the pure water (solution) into which the phosphoric acid had eluted, diluting the cooled solution with pure water, and measuring the phosphoric acid concentration of the sample using ICP-AES. If the amount of elution was less than 40 mg/ m2 , the elution resistance was deemed to be excellent.
• the space factor was measured according to JIS C 2550-5 (2020). Thirty test pieces, each 30 mm wide and 320 mm long, were used. After measuring the total mass of the sample, the space factor was calculated by measuring the distance between the upper and lower backing plates sandwiching the laminate under a pressure of 1 MPa. If the space factor was 96.0% or more, it was determined that a high space factor was ensured.
• the obtained steel sheets were measured for B8 (magnetic flux density at a magnetizing force of 800 A/m) and W17/50 (iron loss per mass at a magnetic flux density amplitude of 1.7 T and 50 Hz). These characteristic values were measured by a single sheet magnetic property measurement method (Single Sheet Tester: SST) in accordance with JIS C2556 (2015). If the iron loss was 0.74 W/kg or less, it was determined that the magnetic properties were excellent.
• the grain-oriented electrical steel sheets corresponding to the examples of the invention obtained by the preferred manufacturing methods had a base steel sheet and an insulating coating containing a metal phosphate formed on the surface of the base steel sheet, and the base steel sheet had an oxide layer containing an oxide of Si in the region in contact with the interface between the base steel sheet and the insulating coating, and the average thickness of the oxide layer from the interface was 0.5 to 2.5 ⁇ m, and as a result, the coating adhesion, coating tension, corrosion resistance, elution resistance, space factor, and iron loss were all excellent.
• one or more of the conditions in the first coating formation process, the second coating formation process, and the heat treatment process were outside the ranges of the present invention, so the specified oxide layer was not formed and one or more of the coating adhesion, coating tension, corrosion resistance, elution resistance, space factor, and iron loss fell below the targets.

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