US20120131982A1 - Grain oriented electrical steel sheet - Google Patents

Grain oriented electrical steel sheet Download PDF

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US20120131982A1
US20120131982A1 US13/388,082 US201013388082A US2012131982A1 US 20120131982 A1 US20120131982 A1 US 20120131982A1 US 201013388082 A US201013388082 A US 201013388082A US 2012131982 A1 US2012131982 A1 US 2012131982A1
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sheets
steel sheet
precipitates
oriented electrical
ppm
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Takeshi Imamura
Yukihiro Shingaki
Mineo Muraki
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JFE Steel Corp
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JFE Steel Corp
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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
    • 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
    • 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
    • C21D8/1272—Final recrystallisation annealing
    • 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
    • C21D8/1277—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties involving a particular surface treatment
    • C21D8/1283—Application of a separating or insulating coating
    • 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
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • 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
    • 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
    • C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
    • 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
    • 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
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
    • 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
    • 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
    • C21D2201/00—Treatment for obtaining particular effects
    • C21D2201/05—Grain orientation

Definitions

  • This disclosure relates to a grain oriented electrical steel sheet suitably used as, for example, an iron-core material for transformers and, in particular, reduces degradation of magnetic characteristics in the case of the sheet being sheared.
  • Electrical steel sheets are a material widely used for iron cores of various transformers, motors, and the like.
  • electrical steel sheets that are referred to as grain oriented electrical steel sheets have crystal grains that are highly oriented in ⁇ 110 ⁇ 001>, which is referred to as the Goss orientation.
  • Japanese Examined Patent Application Publication No. 40-15644 discloses a method of making Al and S serving as inhibitor-forming elements be present in predetermined amounts, that is, a method of using AlN and MnS as inhibitors.
  • Japanese Examined Patent Application Publication No. 51-13469 discloses a method of making at least one of S and Se be present in a predetermined amount, that is, a method of using MnS or MnSe as an inhibitor. These methods are industrially used.
  • Japanese Unexamined Patent Application Publication No. 2000-129356 a technique of developing Goss oriented grains by the action of secondary recrystallization even in steel sheets having no inhibitor-forming elements has been recently presented.
  • this method does not require inhibitor-forming elements, the necessity of the step of purifying to remove inhibitor-forming elements is eliminated. In addition, it is not necessary to perform purification annealing at a high temperature and a step of finely dispersing inhibitor-forming elements in steel is no longer necessary. Hence, slab reheating at a high temperature that was indispensable for the fine dispersion is also no longer necessary. Thus, the method is highly advantageous in terms of steps, cost, and maintenance of equipment and the like.
  • an iron loss characteristic directly relates to energy loss of products and is considered to be the most important characteristic.
  • W 17/50 energy loss at an excitation magnetic flux density of 1.7 T and an excitation frequency of 50 Hz
  • the iron loss characteristic is also considered as an important characteristic. Even after transformers are produced, the transformers that are used need to be periodically measured in terms of iron loss characteristic for the purpose of controlling the iron loss characteristic.
  • electrical steel sheet products have the shape of a sheet and are cut to have a predetermined size in the production of transformers.
  • This cutting is generally performed by shearing (also referred to as slit processing) in which two blades vertically press against each other (the blades finally slide over each other) as in a pair of scissors.
  • the processed surfaces are formed by tearing due to a shearing force and a large amount of strain is introduced into the steel sheets. Accordingly, degradation of magnetic characteristics due to the introduced strain tends to occur in sheared electrical steel sheets, which is problematic.
  • stress relief annealing of annealing at 700° C. to 900° C. for several hours may be performed after shearing.
  • stress relief annealing is performed only for small transformers having a size (length) of 500 mm or less and it cannot be performed for, for example, iron cores of large transformers having a size of several meters.
  • Degradation of magnetic characteristics of grain oriented electrical steel sheets due to shearing can thus be effectively suppressed and iron cores having less energy loss can be produced for transformers.
  • FIG. 1 illustrates the relationship between Nb content in steel (abscissa axis: ppm) and the amount of degradation of iron loss due to shearing ( ⁇ W) (ordinate axis: W/kg).
  • FIG. 2 illustrates the relationship between the crystal grain size of secondary recrystallized grains (abscissa axis: mm) and the amount of degradation of iron loss due to shearing ( ⁇ W) (ordinate axis: W/kg).
  • C is an element that unavoidably enters steel. Since C causes degradation of magnetic characteristics by magnetic aging, the C content is desirably minimized. However, it is difficult to completely remove C and a C content of 0.005% or less is allowable in view of production cost, preferably 0.002% or less. There is no reason for particularly defining the lower limit of the C content.
  • the C content is industrially more than zero.
  • Si is an element necessary to increase the resistivity of steel and achieve improvement in terms of iron loss in final product sheets.
  • Si content is less than 1.0%, such an advantage is not sufficiently provided.
  • the Si content is more than 8.0%, the saturation flux density of a steel sheet considerably decreases. Accordingly, the Si content is limited to a range of 1.0% to 8.0%.
  • the lower limit of the Si content is preferably 3.0%.
  • the upper limit of the Si content is preferably 3.5%.
  • Mn is an element necessary to enhance formability in hot rolling.
  • the Mn content is less than 0.005%, the effect of enhancing workability is not sufficiently provided.
  • the Mn content is more than 1.0%, secondary recrystallization becomes unstable and magnetic characteristics are degraded. Accordingly, the Mn content is limited to a range of 0.005% to 1.0%.
  • the lower limit of the Mn content is preferably 0.02%.
  • the upper limit of the Mn content is preferably 0.20%.
  • Nb or the like it is necessary to make one or more selected from Nb, Ta, V, and Zr (hereafter, referred to as “Nb or the like”) be contained as precipitate-forming elements such that the total content thereof is 10 to 50 ppm. This is because, when the total content of Nb or the like is less than 10 ppm, precipitates that improve iron loss, which are a main feature, are not sufficiently generated. When the total content of Nb or the like is more than 50 ppm, the iron loss characteristic of a material itself is degraded as described above. Thus, the upper limit of the total content is defined as 50 ppm. The total content is preferably in the range of 10 to 30 ppm.
  • the precipitates of Nb or the like are present in a percentage of 10% or more and the precipitates have an average diameter (equivalent circle diameter) of 0.02 to 3 ⁇ m.
  • the average diameter is less than 0.02 ⁇ m, the precipitates are too small and stress is less likely to be concentrated.
  • the average diameter is more than 3 ⁇ m, the frequency of the presence (number) of the precipitates becomes small and the number of portions where stress is concentrated becomes small.
  • the precipitates preferably have an average diameter of 0.05 to 3 ⁇ m.
  • the lower limit is more preferably 0.12 ⁇ m, still more preferably 0.33 ⁇ m.
  • the upper limit is more preferably 1.2 ⁇ m, still more preferably 0.78 ⁇ m.
  • the precipitation percentage of the precipitates of Nb or the like is preferably 20% or more, more preferably 31% or more, still more preferably 48% or more. It is not necessary to define the upper limit and a precipitation percentage of 100% does not cause problems.
  • the average diameter of the precipitates of Nb or the like is preferably determined in the following manner: a section of an obtained sample is observed with a scanning electron microscope; micrographs of about 10 fields of view are taken at a magnification of about 10,000; the micrographs are subjected to image analysis and the average of equivalent circle diameters is determined.
  • the percentage of precipitates is preferably measured in accordance with the method described in Experiment 1 below. When a steel sheet contains two or more elements as Nb or the like, the total content (mass %) of Nb or the like in precipitates should be divided by the total content (mass %) of Nb or the like in the steel sheet.
  • Nb, V, and Zr are preferred because they are less likely to form defects in steel sheets during hot rolling.
  • Nb is preferred because defects during hot rolling can be reduced.
  • the essential range is also 10 to 50 ppm and the preferred range is also 10 to 30 ppm and a preferred diameter of precipitates and a preferred precipitation percentage are the same as those described above.
  • the average grain size of secondary recrystallized grains of a material is 5 mm or more.
  • a grain size is a general grain size in electrical steel sheets for large transformers having a size of several meters, regardless of such a sheet size, by controlling a temperature increase rate and an atmosphere in secondary recrystallization, the average grain size can be controlled to be 5 mm or more.
  • the average grain size of secondary recrystallized grains is preferably determined by the method described in Experiment 2 below.
  • Ni may be added.
  • the amount of Ni added is less than 0.010%, magnetic characteristics are not sufficiently enhanced.
  • the amount of Ni added is more than 1.50%, secondary recrystallization becomes unstable and magnetic characteristics may be degraded. Accordingly, the Ni content is preferably made in the range of 0.010% to 1.50%.
  • At least one of Cr, Cu, and P may be added.
  • the contents of the elements are preferably in the ranges described above, respectively.
  • At least one of Sn, Sb, Bi, and Mo may be added.
  • the contents of the elements are preferably in the ranges described above, respectively.
  • an electrical steel sheet may further contain at least one selected from 0.010% to 1.50% of Ni, 0.01% to 0.50% of Cr, 0.01% to 0.50% of Cu, 0.005% to 0.50% of P, 0.005% to 0.50% of Sn, 0.005% to 0.50% of Sb, 0.005% to 0.50% of Bi, and 0.005% to 0.100% of Mo. Further, as for a subset constituted by elements freely selected from the group of these elements, at least one selected from elements (group) constituting the subset may be made to be contained.
  • inhibitor-forming elements for example, AlN-forming elements: Al and N, MnS-forming elements: Mn and S, MnSe-forming elements: Mn and Se, and TiN-forming elements: Ti and N
  • a necessary amount publicly known
  • the balance is Fe and normal unavoidable impurities.
  • the unavoidable impurities include P, S, O, Al, N, Ti, Ca, and B (when Al and the like are not added as inhibitor-forming elements, they are impurities).
  • Grooves are preferably formed in a surface of a steel sheet, the grooves having the shape of a solid line or broken lines, a width of 50 to 1,000 ⁇ m, and a depth of 10 to 50 ⁇ m, and extending in a direction to intersect at an angle of 15° or less in a direction perpendicular to the rolling direction.
  • the formation of such grooves provides the magnetic domain refining effect, resulting in a further decrease in iron loss.
  • the space between the grooves (pitch) is preferably about 2 to 7 mm.
  • production steps for a standard grain oriented electrical steel sheet can be used. Specifically, a series of steps can be used in which slabs produced from a molten steel adjusted to have a predetermined component composition are hot-rolled; the resultant hot-rolled sheets are optionally subjected to hot-rolled sheet annealing and then subjected to a single cold-rolling step or two or more cold-rolling steps that include an intermediate annealing therebetween to have a final sheet thickness. The steel sheets are subsequently subjected to recrystallization annealing, then to purification annealing, and optionally to flattening annealing and the steel sheets are then coated.
  • the amount of C added in molten steel is preferably 0.10% or less.
  • the Si content may be adjusted to be 1.0% to 8.0%, which is the finally required content, in the adjustment of the component composition of molten steel.
  • the amount of Si added to molten steel may be less than the finally required content.
  • Nb, Ta, V, and Zr which are essential components, during steps after the molten steel state. Accordingly, it is most desirable that a required amount of such a component be added in the adjustment of the component composition of molten steel.
  • slabs may be produced by a standard ingot making process or a standard continuous casting process, or otherwise thin cast slabs having a thickness of 100 mm or less may be produced by direct casting process.
  • slabs are heated and hot-rolled in a standard manner, slabs after being cast may be instead directly hot-rolled without being heated. In the case of thin cast slabs, it may be hot-rolled or jump straight to next steps without being hot-rolled.
  • the heating temperature of slabs to be hot-rolled in a component system containing an inhibitor-forming element is normally a high temperature of about 1,400° C.
  • the heating temperature in a component system without inhibitor-forming elements is normally a low temperature of 1,250° C. or less, which is advantageous in terms of cost.
  • the temperature of the hot-rolled sheet annealing is preferably 800° C. or more and 1,150° C. or less. This is because, when the temperature of the hot-rolled sheet annealing is less than 800° C., a band texture due to hot rolling remains and it becomes difficult to achieve a primary recrystallization texture having uniformly-sized grains. Accordingly, the hot-rolled sheet annealing provides a relatively limited effect of promoting development of secondary recrystallized grains. When the temperature of the hot-rolled sheet annealing is more than 1,150° C., crystal grains after the hot-rolled sheet annealing become coarse. Accordingly, also in this case, it becomes difficult to achieve a primary recrystallization texture having uniformly-sized grains.
  • one or more cold-rolling steps optionally including a process an intermediate annealing therebetween are performed and recrystallization annealing is then performed.
  • it is effective to perform cold rolling in a temperature range of 100° C. to 300° C. and/or to perform one or more aging treatments in a range of 100° C. to 300° C. during the cold rolling process.
  • recrystallization annealing when decaburization is necessary, a wet atmosphere is employed in the recrystallization annealing. However, when decaburization is not necessary, the recrystallization annealing may be performed in a dry atmosphere. After the recrystallization annealing, a technique of increasing Si content by siliconization may be further employed.
  • the sheets are coated with an annealing separator mainly containing MgO and then subjected to final annealing (purification annealing) to develop a secondary recrystallization texture and to form a forsterite coating.
  • annealing separator mainly containing MgO
  • a heat-resistant inorganic material sheet (silica, alumina, or mica) may be used.
  • the final annealing is sufficiently performed at a temperature allowing for secondary recrystallization, and desirably at 800° C. or more.
  • An annealing condition under which secondary recrystallization is completed is desirable and it is generally desirable that the sheets be held at a temperature of 800° C. or more for 20 or more hours.
  • the holding temperature is desirably about 850° C. to 950° C. and the final annealing may be finished with this holding treatment.
  • the temperature is advantageously increased to about 1,200° C.
  • the cooling is desirably performed at a rate of 5° C./hr to 100° C./hr at least in a temperature range of 900° C. to 500° C.
  • the cooling is desirably performed at a rate of 5° C./hr to 100° C./hr in a temperature range of the holding temperature to 500° C. This is because, when the cooling rate is more than 100° C./hr in such a temperature range, there may be cases where precipitates become excessively fine or precipitation from a solid solution does not occur.
  • the lower limit of the cooling rate is more preferably 7.8° C./hr.
  • the upper limit of the cooling rate is more preferably 30° C./hr. In view of achieving results with stability, the upper limit of the cooling rate is still more preferably 14° C./hr.
  • the steel sheets When the steel sheets are laminated and used to achieve improvement in terms of iron loss, it is effective to form insulation coatings on the surfaces of the steel sheets before or after the flattening annealing. To decrease iron loss, coatings that can impart tension to steel sheets are desirable.
  • a method of coating the surfaces of a steel sheet with an inorganic substance by a tension coating application method with a binder, a physical vapor deposition method, a chemical vapor deposition method, or the like When a method of coating the surfaces of a steel sheet with an inorganic substance by a tension coating application method with a binder, a physical vapor deposition method, a chemical vapor deposition method, or the like is employed, the coating films exhibit high adhesion and iron loss is considerably decreased, which is particularly desirable.
  • a magnetic domain refining treatment is desirably performed.
  • An example of this treatment is, as generally performed, a method of forming grooves in final product sheets or linearly introducing thermal strain or impact strain with laser or plasma into final product sheets, or a method of forming grooves in intermediate products having a final sheet thickness such as cold-rolled sheets.
  • the method including shearing steel sheets and laminating the sheets without subjecting them to stress relief annealing. At this time, degradation of iron loss of the steel sheet due to the shearing can be suppressed to 0.1 W/kg or less (preferably, 0.041 W/kg or less).
  • the production method is particularly advantageous for producing large iron cores, for example, in the cases where a steel sheet is sheared into sheets having a longest side more than 500 mm.
  • Matters including the number of steel sheets stacked, the size and shape of steel sheets obtained by the shearing, the presence or absence of the grooves, the size of the grooves, the presence or absence of coating, and the type of coating may be appropriately determined on the basis of ordinary knowledge.
  • Grain oriented electrical steel sheets containing, by mass %, 3.30% to 3.34% of Si, 0.06% to 0.07% of Mn, 0.025% to 0.028% of Sb, and 0.03% to 0.04% of Cr; Nb added in various amounts of 4 ppm (on the level of unavoidable impurities), 22 ppm, 48 ppm, 65 ppm, 90 ppm, and 210 ppm; and the balance being Fe and unavoidable impurities were produced by a standard production method having recrystallization annealing (primary recrystallization annealing) and final annealing (purification annealing).
  • the steel sheets were heated at the maximum steel sheet temperature of 1,200° C. to dissolve the precipitate-forming element (Nb) therein and then cooled at an average cooling rate of 20° C./hr from 900° C. to 500° C. and cooled to room temperature.
  • FIG. 1 shows the results of a study about the relationship between ⁇ W (ordinate axis: W/kg) and Nb content in steel (abscissa axis: mass ppm), ⁇ W (hereafter, same definition) being determined by subtracting the iron loss value of a sample obtained by cutting with the wire cutter from the iron loss value of a sample obtained by cutting with the shearing machine.
  • ⁇ W in the figure substantially represents an iron loss amount equivalent to degradation due to remaining strain.
  • FIG. 1 thus shows that the presence of Nb results in reduction of degradation of the iron loss amount due to shearing.
  • Nb contained in a steel sheet is in two states of forming a solid solution and forming precipitates, as described above, it is probably important that Nb forms precipitates.
  • the sample containing 22 ppm of Nb was measured in terms of Nb precipitation percentage (percentage of Nb content in precipitates with respect to the total Nb content).
  • the total Nb content (content in a steel sheet: mass %) needs to be first determined.
  • the total Nb content can be determined by inductively-coupled plasma optical emission spectrometry (ICP optical emission spectrometry) described in JIS G 1237.
  • ICP optical emission spectrometry inductively-coupled plasma optical emission spectrometry
  • the contents of Ta, V and Zr can be respectively determined by methods described in JIS G 1236, JIS G 1221 and JIS G 1232.
  • the Nb content in precipitates (content in a steel sheet: mass %) can be determined by melting a steel sheet by electrolysis to capture precipitates only (by filtration), measuring the weight of Nb in the precipitates, and calculating from a decrease in the weight of the steel sheet due to electrolysis and the weight of Nb in the precipitates.
  • the quantitative value of Nb content in precipitates is determined in the following manner.
  • a product sheet is first cur to a size of 50 mm ⁇ 20 mm and immersed for 2 minutes in a 10% aqueous solution of HCl heated at 85° C. to remove the coating and film of the product. After that, the weight of the product sheet is measured.
  • the product sheet is electrolyzed with a commercially available electrolytic solution (10% AA solution: 10% acetylacetone-1% tetramethylammonium chloride-methanol) such that about 1 g of the product sheet is electrolyzed.
  • a commercially available electrolytic solution (10% AA solution: 10% acetylacetone-1% tetramethylammonium chloride-methanol) such that about 1 g of the product sheet is electrolyzed.
  • the product sheet is immersed in an ethanol solution and subjected to ultrasonic waves.
  • This ethanol solution and the electrolytic solution used in the electrolysis, which contain precipitates, are filtrated through a 0.1 ⁇ m-mesh filter paper (allowing capture of minimum precipitates having a size on the order of nanometers) to capture the precipitates.
  • the precipitates collected by the filtration are placed together with the filter paper in a platinum crucible, heated at 700° C. for an hour, mixed with Na 2 B 4 O 7 and NaCO 3 , and heated at 900° C. for 15 minutes. The resultant substance is cooled and then heated at 1,000° C. for 15 minutes.
  • the substance in the crucible coagulates.
  • the crucible containing the substance is placed into a 25% aqueous solution of HCl and the solution containing the crucible is heated at 90° C. for 30 minutes to melt the entirety of the substance.
  • the resultant solution is analyzed by ICP optical emission spectrometry described in JIS G 1237 to determine the weight of Nb in the precipitates.
  • the weight of Nb is divided by a decrease in the weight of the product sheet (steel sheet) due to electrolysis to determine the Nb content (mass %) in the precipitates.
  • the thus-determined Nb content (mass %) in the precipitates is divided by the total Nb content (mass %) to determine the Nb precipitation percentage.
  • the Nb precipitation percentage in the sample was 65%. We further performed studies and have found that precipitation of at least 10% of the total Nb content is necessary to provide desired advantages.
  • the amount of a precipitate-forming element such as Nb remaining in steel the better the ⁇ W characteristic seems to become.
  • precipitates also degrade the iron loss characteristic of a material itself to be processed. Accordingly, the amount of precipitates is preferably small within a range in which degradation of iron loss due to shearing is small.
  • the iron loss of the materials themselves degraded. Hence, the content needs to be suppressed to 50 ppm or less.
  • Steel slabs containing, by mass %, 0.035% of C, 3.31% of Si, 0.13% of Mn, 0.039% of Sb, 0.05% of Cr, and 0.012% of P; 42 ppm of N and 31 ppm of S; and the balance being Fe and unavoidable impurities were produced by continuous casting, subjected to slab reheating at 1,250° C., then hot-rolled to provide hot-rolled sheets having a thickness of 2.7 mm. The hot-rolled sheets were subsequently annealed at 1,000° C. for 15 seconds and then cold-rolled to provide sheets having a thickness of 0.30 mm.
  • the sheets were subjected to recrystallization annealing in a 50% N 2 -50% H 2 wet atmosphere (decarburization atmosphere) under soaking conditions in a temperature range of 800° C. to 880° C. for 60 seconds.
  • the sheets were then coated with an annealing separator mainly containing MgO and subsequently subjected to purification annealing by being retained in a temperature range of 1,050° C. to 1,230° C. for 10 hours.
  • the temperatures in the recrystallization annealing and the purification annealing were varied to vary crystal grain size provided by secondary recrystallization caused in the purification annealing.
  • the steel substrates were exposed by pickling and the crystal grain size of secondary recrystallized grains was measured.
  • the crystal grain size was determined by measuring the grain sizes of four Epstein specimens and averaging the measured grain sizes. Analysis of the components of the steel substrates revealed 0.0018% of C, 3.30% of Si, 0.13% of Mn, 0.039% of Sb, 0.05% of Cr, and 0.011% of P, and the contents of the other elements were less than the detection limits.
  • the relationship between ⁇ W (ordinate axis: W/kg) determined in the above-described manner and crystal grain size (abscissa axis: mm) is illustrated in FIG. 2 .
  • the steel slabs were subjected to slab reheating at 1,400° C. and then hot-rolled to sheets to a thickness of 2.4 mm.
  • the sheets were then subjected to hot-rolled sheet annealing at 1,000° C. for 40 seconds, subsequently to cold rolling so as to have a thickness of 1.6 mm, to intermediate annealing at 900° C., and then to cold rolling to sheets so as to have a thickness of 0.23 mm.
  • the resultant sheets were then subjected to recrystallization annealing in a 60% N 2 -40% H 2 wet atmosphere under soaking conditions at 850° C. for 90 seconds, subsequently coated with an annealing separator mainly containing MgO, and subjected to purification annealing at 1,220° C. for 6 hours.
  • the cooling rate for a range of 900° C. to 500° C. was controlled as described in Table 1 to thereby vary the diameter of Nb precipitates and Nb precipitation percentage.
  • the sheets were subjected to flattening annealing at 850° C. for 20 seconds.
  • the obtained samples were cut to a size of 30 mm ⁇ 280 mm. At this time, the cutting was performed under two conditions: cutting with a wire cutter and cutting with a shearing machine. Magnetic characteristics of obtained samples were measured by the method described in JIS C 2550 and the magnetic characteristics of the samples obtained by the cutting with the wire cutter are described in Table 1.
  • ⁇ W determined by subtracting the iron loss of a sample obtained by cutting with the wire cutter from the iron loss of a sample obtained by cutting with the shearing machine is also described in Table 1.
  • the samples having been subjected to the magnetic measurement were then subjected to pickling to remove coatings and the crystal grain size of secondary recrystallized grains was measured.
  • the results are also described in Table 1 together with the measurement results of the diameter and precipitation percentage of Nb precipitates.
  • the component composition of steel sheets of the coating-removed samples was measured. As a result, the component composition confirmed was 0.0016% of C, 3.24% of Si, 0.13% of Mn, and 18 ppm of Nb (for No. 7 steel only, 15 ppm of Nb), which satisfied our requirements.
  • Product sheets (sheet thickness: 0.23 mm) of grain oriented electrical steel sheets were provided that contained components described in Table 2 and that were produced by a standard production method in which recrystallization annealing was performed, followed by purification annealing at 1,150° C., and cooling at a cooling rate in the range of 900° C. to 500° C. of 25° C./hr.
  • the grain oriented electrical steel sheets were cut to a size of 30 mm ⁇ 280 mm. At this time, the cutting was performed under two conditions: cutting with a wire cutter and cutting with a shearing machine.
  • the magnetic characteristics of the obtained samples were measured by the method described in JIS C 2550 and the magnetic characteristics of the samples obtained by the cutting with the wire cutter are described in Table 2.
  • ⁇ W determined as in EXAMPLE 1 is also described in Table 2.
  • the samples having been subjected to the magnetic measurement were subjected to pickling to remove coatings and the crystal grain size of secondary recrystallized grains was measured.
  • the results are also described in Table 2 together with the measurement results of the diameter and precipitation percentage of precipitates of Nb or the like. Note that the component compositions of steel sheets in Table 2 are results obtained by measuring the component compositions of coating-removed samples after the pickling.
  • the precipitates were measured. As a result, the precipitates had an average diameter of 0.05 to 3.34 ⁇ m and a precipitation percentage of 0% to 79%.
  • Steel slabs containing 0.065% of C, 3.25% of Si, 0.13% of Mn, 0.05% of Cr, 240 ppm of Al, 70 ppm of N, 36 ppm of S, 0.013% of P, 0.075% of Sn, 0.036% of Sb, 0.011% of Mo, and 25 ppm of Nb, and the balance being Fe and unavoidable impurities, were produced by continuous casting.
  • the steel slabs were subjected to slab reheating at 1,400° C. and then hot-rolled to sheets to a thickness of 2.4 mm. The sheets were then subjected to hot-rolled sheet annealing at 1,000° C.
  • Linear grooves having a width of 100 ⁇ m and a depth of 25 ⁇ m were then formed by local electrolytic etching in the surfaces of the steel sheets to extend at an angle of 10° with respect to a direction perpendicular to the rolling direction at a pitch of 8 mm.
  • the sheets were then subjected to recrystallization annealing in a 60% N 2 -40% H 2 wet atmosphere under soaking conditions at 800° C. to 900° C. for 90 seconds.
  • the sheets were then coated with an annealing separator mainly containing MgO and subsequently subjected to purification annealing at 1,220° C. for 6 hours. After that, the sheets were cooled such that they were cooled from 900° C. to 500° C. at a cooling rate of 10° C./hr.
  • the sheets were then subjected to flattening annealing at 850° C. for 20 seconds.
  • the temperatures of the intermediate annealing and the temperatures of the recrystallization annealing were varied to vary the grain size after secondary recrystallization.
  • the obtained samples were cut into Epstein specimens having a size of 30 mm ⁇ 280 mm. At this time, the cutting was performed under two conditions: cutting with a wire cutter and cutting with a shearing machine.
  • the samples having been subjected to the magnetic measurement were subjected to pickling to remove coatings and the crystal grain size of secondary recrystallized grains was measured. The results are also described in Table 3 together with the measurement results of the diameter and precipitation percentage of Nb precipitates.
  • the component composition of steel sheets of the coating-removed samples was measured. As a result, the component composition confirmed was 0.0016% of C, 3.24% of Si, 0.13% of Mn, 0.05% of Cr, 0.011% of P, 0.074% of Sn, 0.036% of Sb, 0.011% of Mo, and 18 ppm of Nb, which satisfied our requirements.
  • EXAMPLES 1 to 3 show that grain oriented electrical steel sheets substantially having a ⁇ W of 0.1 W/kg or less and undergoing little degradation of magnetic characteristics due to shearing can be provided. Accordingly, production of a laminated iron core by shearing a steel sheet without performing stress relief annealing is effective for enhancing the magnetic characteristics of the iron core, in particular, for achieving improvement in terms of iron loss.
  • the diameter (average diameter) of the precipitates is 0.12 ⁇ m or more and 1.2 ⁇ m or less (preferably 0.78 ⁇ m or less; the precipitation percentage is preferably 48% or more) and ⁇ W is 0.038 W/kg or less.
  • the cooling rate after final annealing is preferably made 7.8° C./hr to 30° C./hr, more preferably 7.8° C./hr to 14° C./hr.

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US20160012949A1 (en) * 2013-02-28 2016-01-14 Jfe Steel Corporation Method for producing grain-oriented electrical steel sheet (as amended)
US20180171425A1 (en) * 2015-06-09 2018-06-21 Jfe Steel Corporation Grain-oriented electrical steel sheet and method for manufacturing the same
US10026534B2 (en) 2013-02-22 2018-07-17 Jfe Steel Corporation Hot-rolled steel sheet for producing non-oriented electrical steel sheet and method of producing same
US10988822B2 (en) 2015-02-13 2021-04-27 Jfe Steel Corporation Grain-oriented electrical steel sheet and method for manufacturing same
US11603572B2 (en) * 2018-09-27 2023-03-14 Posco Co., Ltd Grain-oriented electrical steel sheet and method for manufacturing same
US11651878B2 (en) 2018-01-31 2023-05-16 Nippon Steel Corporation Grain-oriented electrical steel sheet

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