GRAIN-ORIENTED ELECTRICAL STEEL SHEET AND IRON CORE USING SAME

Abstract

Provided are a grain-oriented electrical steel sheet having excellent iron loss property without using magnetic domain refining treatment and an iron core produced using the same. The steel sheet comprises: a predetermined chemical composition; and a steel microstructure in which: crystal grains are made up of coarse secondary recrystallized grains of 5.0 mm or more, fine grains of more than 2.0 mm and less than 5.0 mm contained at a frequency of 0.2 to 5 grains per cm.sup.2, and very fine grains of 2.0 mm or less; for each coarse secondary recrystallized grain extending through the sheet in a thickness direction, an area ratio of a region in which projected surfaces of exposed areas of the coarse secondary recrystallized grain on a front side and a back side of the sheet coincide with each other to each of the exposed areas is 95% or more.

Claims

1. A grain-oriented electrical steel sheet comprising: a chemical composition containing, in mass %, Si: 1.5% to 8.0%, Mn: 0.02% to 1.0%, and at least one selected from Sn: 0.010% to 0.400%, Sb: 0.010% to 0.400%, Mo: 0.010% to 0.200%, and P: 0.010% to 0.200%, with a balance being Fe and inevitable impurities; and a microstructure in which: crystal grains are made up of coarse secondary recrystallized grains of 5.0 mm or more in grain size, fine grains of more than 2.0 mm and less than 5.0 mm in grain size, and very fine grains of 2.0 mm or less in grain size; for each coarse secondary recrystallized grain extending through the steel sheet in a thickness direction among the coarse secondary recrystallized grains, an area ratio of a region in which projected surfaces of exposed areas of the coarse secondary recrystallized grain on a front side and a back side of the steel sheet coincide with each other to each of the exposed areas is 95% or more; and the fine grains of more than 2.0 mm and less than 5.0 mm in grain size are contained at a frequency of 0.2 grains to 5 grains per cm.sup.2, wherein the steel sheet is not magnetic domain refining treated.

2. The grain-oriented electrical steel sheet according to claim 1, wherein an average of misorientation angles between crystal orientations of the fine grains of more than 2.0 mm and less than 5.0 mm in grain size and Goss orientation is 15° or more.

3. The grain-oriented electrical steel sheet according to claim 1, wherein the chemical composition further contains, in mass %, one or more selected from Cr: 0.01% to 0.50%, Cu: 0.01% to 0.50%, Ni: 0.01% to 0.50%, Bi: 0.005% to 0.50%, and Nb: 0.001% to 0.01%.

4. A coil iron core produced using the grain-oriented electrical steel sheet according to claim 1.

5. The grain-oriented electrical steel sheet according to claim 2, wherein the chemical composition further contains, in mass %, one or more selected from Cr: 0.01% to 0.50%, Cu: 0.01% to 0.50%, Ni: 0.01% to 0.50%, Bi: 0.005% to 0.50%, and Nb: 0.001% to 0.01%.

6. A coil iron core produced using the grain-oriented electrical steel sheet according to claim 2.

7. A coil iron core produced using the grain-oriented electrical steel sheet according to claim 3.

8. A coil iron core produced using the grain-oriented electrical steel sheet according to claim 5.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0063] In the accompanying drawings:

[0064] FIG. 1 is a diagram illustrating the relationship between the number of fine grains in each product steel sheet and the iron loss of the product steel sheet;

[0065] FIG. 2 is a diagram explaining the area ratio of the region in which the projected surfaces coincide with each other; and

[0066] FIG. 3 is a diagram illustrating the relationship between the area ratio of the region in which the projected surfaces coincide with each other and the iron loss of the product steel sheet.

DETAILED DESCRIPTION

[0067] The presently disclosed technique will be described in detail below. The reasons for limiting the chemical composition to the foregoing range in the present disclosure will be described first. Hereafter, “%” and “ppm” with regard to the composition denote “mass %” and “mass ppm”, respectively. Si: 1.5% to 8.0%

[0068] Si is a necessary element to enhance the specific resistance of the steel and improve the iron loss. If the Si content is less than 1.5%, the effect of adding Si is insufficient. If the Si content is more than 8.0%, the workability of the steel degrades, which hinders rolling. The Si content is therefore limited to 1.5% to 8.0%. The Si content is preferably 2.5% to 4.5%.

[0069] Mn: 0.02% to 1.0%

[0070] Mn is a necessary element to improve the hot workability. If the Mn content is less than 0.02%, the effect is insufficient. If the Mn content is more than 1.0%, the magnetic flux density of the product steel sheet decreases. The Mn content is therefore limited to 0.02% to 1.0%. The Mn content is preferably 0.04% to 0.20%.

[0071] To cause fine grains for suppressing grain boundary migration to be present in a certain proportion in the steel sheet as mentioned above, at least one selected from Sn: 0.010% to 0.400%, Sb: 0.010% to 0.400%, Mo: 0.010% to 0.200%, and P: 0.010% to 0.200% as segregation elements needs to be contained. For each element, if the content is less than the lower limit, the frequency of the fine grains decreases, and the iron loss reduction effect cannot be achieved. If the content is more than the upper limit, the steel embrittles, and the risk of impairing the productivity, such as occurrence of a fracture during production, increases. Preferable ranges are Sn: 0.020% to 0.100%, Sb: 0.020% to 0.100%, Mo: 0.020% to 0.070%, and P: 0.012% to 0.100%.

[0072] While the basic components according to the present disclosure have been described above, the chemical composition according to the present disclosure may optionally further contain the following elements.

[0073] One or more selected from Cr: 0.01% to 0.50%, Cu: 0.01% to 0.50%, Ni: 0.01% to 0.50%, Bi: 0.005% to 0.50%, and Nb: 0.001% to 0.01% may be added in order to improve the magnetic properties. For each element, if the content is less than the lower limit, the magnetic property improving effect cannot be achieved. If the content is more than the upper limit, the development of secondary recrystallized grains is inhibited and the magnetic properties degrade.

[0074] The balance other than the elements described above consists of Fe and inevitable impurities. Examples of the inevitable impurities include C, Al, N, S, and Se which are considerably reduced as a result of purification or decarburization. Their inevitable impurity levels are not limited, but preferably C is less than 30 ppm, N is less than 20 ppm, and Al, S, and Se are each less than 10 ppm.

[0075] For the reasons stated above, it is essential that: the crystal grains in the product steel sheet are made up of coarse secondary recrystallized grains of 5.0 mm or more in grain size, fine grains of more than 2.0 mm and less than 5.0 mm in grain size, and very fine grains of 2.0 mm or less in grain size; for each coarse secondary recrystallized grain extending through the steel sheet in the thickness direction from among the coarse secondary recrystallized grains, the area ratio of the region in which the projected surfaces of the respective areas of the coarse secondary recrystallized grain exposed on the front and back sides of the steel sheet coincide with each other to each of the areas of the coarse secondary recrystallized grain exposed is 95% or more; and the fine grains of more than 2.0 mm and less than 5.0 mm in grain size are contained at a frequency of 0.2 grains to 5 grains per cm.sup.2. In the calculation of the grain size of each crystal grain, the grain boundary is extracted through image analysis and elliptically approximated by an elliptical approximation method, and the average of the major axis length and the minor axis length is taken to be the grain size of the crystal grain.

[0076] A method of producing the grain-oriented electrical steel sheet according to the present disclosure will be described below.

[0077] As the method of producing the grain-oriented electrical steel sheet according to the present disclosure, a typical electrical steel sheet production method may be used. In detail, a molten steel adjusted to a predetermined composition may be subjected to typical ingot casting or continuous casting to produce a slab, or subjected to direct casting to produce a thin slab or thinner cast steel of 100 mm or less in thickness. The foregoing preferred components (Si, Mn, segregation elements, optional component elements) are preferably added in the molten steel stage as it is difficult to add them in an intermediate step. The contents of Si, Mn, segregation elements, and optional component elements in the slab produced in this way are maintained in the chemical composition of the product steel sheet.

[0078] The contents of the inevitable impurities such as C, Al, N, S, and Se in the slab are not limited. To achieve the foregoing inevitable impurity levels in the product steel sheet, for example, the contents of the inevitable impurities are preferably C: 0.10% or less, Al: 500 ppm or less, N: 100 ppm or less, and each of S and Se: 200 ppm or less.

[0079] Before hot rolling, the slab is heated by a usual method. For a slab having a chemical composition with low content of an inhibitor component, high-temperature annealing for dissolving the inhibitor is unnecessary. Accordingly, the slab heating temperature is preferably a low temperature of less than 1300° C. from the viewpoint of cost reduction. The slab heating temperature is more preferably 1250° C. or less. For a slab having a chemical composition with high content of an inhibitor component, the slab heating temperature is preferably 1300° C. or more in order to dissolve the inhibitor.

[0080] The steel slab heated to the slab heating temperature is then hot rolled to obtain a hot-rolled steel sheet. The hot rolling conditions are not limited, and may be any conditions.

[0081] The hot-rolled steel sheet is then optionally subjected to hot-rolled sheet annealing. The hot-rolled sheet annealing temperature is preferably about 950° C. to 1150° C. It the hot-rolled sheet annealing temperature is lower than this range, non-recrystallized parts remain. It the hot-rolled sheet annealing temperature is higher than this range, the grain size after the annealing is excessively coarse, causing the subsequent primary recrystallized microstructure to be inappropriate. The hot-rolled sheet annealing temperature is preferably 1000° C. or more. The hot-rolled sheet annealing temperature is preferably 1100° C. or less.

[0082] The steel sheet after the hot rolling or the hot-rolled sheet annealing is subjected to cold rolling once or subjected to cold rolling twice or more with intermediate annealing therebetween, to obtain a cold-rolled sheet with a final thickness. The annealing temperature in the intermediate annealing is preferably in a range of 900° C. to 1200° C. If the annealing temperature is less than 900° C., the recrystallized grains after the intermediate annealing become fine, and also the Goss-oriented nuclei in the primary recrystallized microstructure decrease and the magnetic properties of the product steel sheet decrease. If the annealing temperature is more than 1200° C., the crystal grains coarsen excessively as in the hot-rolled sheet annealing, making it difficult to obtain primary recrystallized microstructure of uniformly-sized grains.

[0083] The cold-rolled sheet with the final thickness is then subjected to decarburization annealing and primary recrystallization annealing. In the case where the primary recrystallization annealing also serves as the decarburization annealing, the annealing temperature is preferably in a range of 800° C. to 900° C. and the annealing atmosphere is preferably a wet atmosphere, from the viewpoint of facilitating decarburization reaction. The primary recrystallization annealing and the decarburization annealing may be performed separately.

[0084] In Experiments 1 and 2 described above, the foregoing product steel sheet is obtained by a method whereby the steel sheet is heated to 700° C. at a high heating rate and then, without soaking, immediately rapid-cooled after cold rolling and before decarburization annealing, and subsequently reheated and subjected to decarburization annealing. In the present disclosure, such a step of heating to 700° C. at a high heating rate and immediately cooling to around room temperature at a high cooling rate without soaking is preferably performed before the decarburization annealing. This is intended to form at least a certain number of fine grains of more than 2.0 mm and less than 5.0 mm in grain size and thus effectively reduce the iron loss of the product steel sheet. From the viewpoint of ensuring the formation of the fine grains, the heating rate in the step is preferably in a range of 100° C./s to 3000° C./s, and the cooling rate in the step is preferably in a range of 5° C./s to 200° C./s.

[0085] After applying an annealing separator mainly composed of MgO to the steel sheet that has undergone the decarburization annealing and the primary recrystallization annealing, the steel sheet is subjected to secondary recrystallization annealing also serving as purification annealing. This enables secondary recrystallized microstructure to develop and a forsterite film to form. To develop secondary recrystallization, the secondary recrystallization annealing is preferably performed at 800° C. or more. Moreover, in the present disclosure, the retention temperature is preferably 1250° C. or more, to make the grain boundary of each coarse secondary recrystallized grain perpendicular to the sheet surface and, for each coarse secondary recrystallized grain extending through the steel sheet in the thickness direction, set the area ratio of the region in which the projected surfaces of the exposed areas of the coarse secondary recrystallized grain on the front and back sides of the steel sheet coincide with each other to each of the exposed areas to a high area ratio of 95% or more. The retention temperature is more preferably 1260° C. or more. In the present disclosure, the production method is not limited, but it is preferable to perform secondary recrystallization annealing also serving as purification annealing at a higher retention temperature than usual.

[0086] It is effective to perform, after the purification annealing, water washing, brushing, pickling, or the like to remove the unreacted annealing separator adhering to the front and back sides of the steel sheet. By subsequently performing flattening annealing for shape adjustment, the iron loss can be reduced effectively.

[0087] In the case of using the steel sheet in a stacked state, it is effective to form an insulation coating on the front and back sides of the steel sheet before or after the flattening annealing, in order to improve the iron loss. A coating capable of imparting tension to the steel sheet is preferable for iron loss reduction. A coating method of applying a tension coating through a binder or a coating method of depositing an inorganic substance onto the steel sheet surface layer by physical vapor deposition or chemical vapor deposition is preferably used as it provides excellent coating adhesion and has a considerable iron loss reduction effect.

[0088] The grain-oriented electrical steel sheet according to the present disclosure can be suitably obtained by the above-described production method. The production method for the grain-oriented electrical steel sheet is, however, not limited to such, as long as the grain-oriented electrical steel sheet has the features defined in the present disclosure.

[0089] The grain-oriented electrical steel sheet according to the present disclosure is not magnetic domain refining treated. Herein, “the steel sheet is not magnetic domain refining treated” means that the steel sheet is produced without treatment of introducing non-uniformity (stress) to the steel sheet surface by a physical method and refining the magnetic domain width. Non-limiting examples of such treatment include heat resistant stress introduction such as linear or spot groove formation and non-heat resistant stress introduction by irradiation with a laser beam, an electron beam, a plasma flame, ultraviolet light, or the like.

[0090] Since the grain-oriented electrical steel sheet according to the present disclosure is not magnetic domain refining treated, removal of non-heat resistant stress by stress relief annealing in coil iron core production and a decrease in magnetic flux density caused by heat resistant magnetic domain refining can be prevented. Such a grain-oriented electrical steel sheet is useful as a material of a coil iron core produced through stress relief annealing.

EXAMPLES

[0091] In Examples 1 and 2, grain-oriented electrical steel sheets according to examples and comparative examples were produced and their property values were studied by the following measurement methods.

[0092] The measurement methods will be described in detail below.

[0093] [Area Ratio of Region in which Projected Surfaces Coincide with Each Other]

[0094] A sample of 336 cm.sup.2 in total area (equivalent to four Epstein samples) cut out of a product steel sheet was immersed in a 10% hydrochloric acid aqueous solution of 80° C. for 180 sec, and the films on the front and back sides were removed to expose secondary recrystallized grains.

[0095] An image of the sample with the exposed secondary recrystallized grains was captured by a scanner with image quality of 300 dpi, the grain boundaries were detected using image analysis software (Photoshop CS6 produced by Adobe Inc.), and an image of only the grain boundaries was generated. This imaging was performed on both the front and back sides of the sample. The image of the front side and the image of the back side were made distinguishable using different colors (e.g. red color on the front side and blue color on the back side), and the two images were superimposed after the image of the back side was mirror-reversed horizontally or vertically. Thus, an orthogonal projection of the grain boundaries on the front side and an orthogonal projection of the grain boundaries on the back side were mapped on one plane parallel to the sheet surface (rolling surface). For every secondary recrystallized grain of 5.0 mm or more in grain size contained in the sample, the region in which the part enclosed by the grain boundary on the front side and the part enclosed by the grain boundary on the back side overlap (coincide) on the same plane as illustrated in FIG. 2 was identified as a “region in which the projected surfaces coincide with each other”, and its area (cm.sup.2) was calculated. The calculated area was divided by the average value of the area of the part enclosed by the grain boundary on the front side and the area of the part enclosed by the grain boundary on the back side, to calculate the area ratio (%) of the region in which the projected surfaces coincide with each other.

[0096] [Grain Size Distribution and Fine Grain Precipitation Frequency]

[0097] Based on the image of only the grain boundaries acquired using image analysis software as described above, the area of each grain was calculated, and, the grain size was calculated as an equivalent circle diameter. Thus, the proportions of coarse secondary recrystallized grains of 5.0 mm or more in grain size, fine grains of more than 2.0 mm and less than 5.0 mm in grain size, and very fine grains of 2.0 mm or less in grain size were calculated.

[0098] Based on the grain sizes calculated by the foregoing method, the number of fine grains of more than 2.0 mm and less than 5.0 mm in grain size per cm.sup.2 was counted.

[0099] [Measurement of Misorientation Angle Between Fine Grain Orientation and Goss Orientation]

[0100] The sample with the exposed secondary recrystallized grains was sheared to 20 mm square, and the crystal orientation of every fine grain of more than 2.0 mm and less than 5.0 mm in grain size in the obtained 20 mm square sample piece was measured. Here, the crystal orientation was measured from an electron backscatter diffraction image using an electron back-scattering pattern (EBSP) device accompanying a SEM. The average of the misorientation angles between the measured crystal orientations and the Goss orientation was then calculated.

Example 1

[0101] Each steel slab containing C: 0.015%, Si: 3.72%, Mn: 0.05%, Al: 0.020%, N: 0.0070%, and Sn: 0.15% with the balance being Fe and inevitable impurities was produced by continuous casting, subjected to slab heating of soaking at 1300° C. for 45 min, and then hot rolled to a thickness of 2.6 mm. The resultant hot-rolled steel sheet was subjected to hot-rolled sheet annealing at 950° C. for 60 sec in a dry nitrogen atmosphere, and then cold rolled to a thickness of 0.23 mm. The resultant cold-rolled steel sheet was heated to 700° C. at the heating rate listed in Table 1 in a dry nitrogen atmosphere, and immediately cooled to room temperature at a cooling rate of 80° C./s on average without soaking. Following this, the steel sheet was subjected to primary recrystallization annealing also serving as decarburization annealing at 850° C. for 90 sec in a wet atmosphere of 60% H.sub.2-40% N.sub.2 and a dew point of 60° C. Further, an annealing separator mainly composed of MgO was applied to the steel sheet, and the steel sheet was subjected to secondary recrystallization annealing also serving as purification annealing of retaining at the temperature listed in Table 1 for 10 hr in a hydrogen atmosphere.

[0102] The iron loss W.sub.17/50 (iron loss when excited to 1.7 T at 50 Hz) of a sample cut out of each resultant product steel sheet was measured by the method described in HS C 2550-1: 2011. Moreover, the obtained sample was immersed in a 10% hydrochloric acid aqueous solution of 80° C. for 180 sec, and the films on the front and back sides were removed so that secondary recrystallized grains would be recognizable. The grain size distribution of the secondary recrystallized grains was then determined by image analysis. Furthermore, for each coarse secondary recrystallized grain extending through the steel sheet in the thickness direction from among the coarse secondary recrystallized grains of 5 mm or more in grain size, the area ratio of the region in which the projected surfaces of the respective areas of the coarse secondary recrystallized grain exposed on the front and back sides of the steel sheet coincide with each other to each of the areas of the coarse secondary recrystallized grain exposed was calculated for each condition. The area of the sample studied to determine the grain size distribution and the area ratio was 336 cm.sup.2 (equivalent to four Epstein samples). The steel substrate composition of the product steel sheet studied using the sample from which the films on the front and back sides had been removed contained, in mass ratio, Si: 3.73%, Mn: 0.05%, and Sn: 0.15%, with the balance being Fe. That is, in the product steel sheet, while C, Al, N, S, and Se were reduced to inevitable impurity levels as a result of decarburization and purification, the contents of the other components were approximately the same as those in the slab.

[0103] The results are listed in Table 1. In Table 1, the underlines indicate outside the range according to the present disclosure.

[0104] The average misorientation angle between the crystal orientations of the fine grains of more than 2.0 mm and less than 5.0 mm in grain size and the Goss orientation measured for the product steel sheet according to each example was 33.5°.

[0105] As is clear from Table 1, favorable iron loss property was achieved with the conditions within the range according to the present disclosure.

TABLE-US-00001 TABLE 1 Heating rate Area ratio of of heating Retention coincidence before temperature on decarburization in purification Number of front and Iron loss annealing annealing fine grains back sides W.sub.17/50 ID (° C./s) (° C.) (/cm.sup.2) (%) (W/kg) Remarks 1 50 1200 0.08 94.1 0.876 Comparative Example 2 50 1275 0.06 99.4 0.871 Comparative Example 3 150 1200 0.25 93.8 0.843 Comparative Example 4 150 1275 0.24 99.3 0.817 Example 5 400 1200 1.35 93.5 0.835 Comparative Example 6 400 1275 1.25 99.0 0.812 Example 7 700 1200 3.61 92.2 0.830 Comparative Example 8 700 1275 3.53 98.4 0.805 Example 9 1000 1200 4.23 89.9 0.826 Comparative Example 10 1000 1275 4.17 95.4 0.797 Example 11 2000 1200 7.97 87.5 0.911 Comparative Example 12 2000 1275 7.10 94.2 0.899 Comparative Example

Example 2

[0106] Each steel slab containing the components listed in Table 2 with the balance being Fe and inevitable impurities was produced by continuous casting, subjected to slab heating of soaking at 1320° C. for 50 min in the case of containing sol. Al: 150 ppm or more and subjected to slab heating of soaking at 1230° C. for 50 min in the case of containing sol. Al: less than 150 ppm, and then hot rolled to a thickness of 2.0 mm. The resultant hot-rolled steel sheet was subjected to hot-rolled sheet annealing at 1125° C. for 20 sec in a dry nitrogen atmosphere, and then cold rolled to a thickness of 0.20 mm. The resultant cold-rolled steel sheet was heated to 720° C. at a heating rate of 700° C./s in a dry nitrogen atmosphere, and immediately cooled to room temperature at a cooling rate of 120° C./s on average without soaking. Following this, the steel sheet was subjected to decarburization annealing at 830° C. for 140 sec in a wet atmosphere of 45% H.sub.2-55% N.sub.2 and a dew point of 48° C. Further, an annealing separator mainly composed of MgO was applied to the steel sheet, and the steel sheet was subjected to secondary recrystallization annealing also serving as purification annealing of retaining at 1275° C. for 10 hr in a hydrogen atmosphere. The heating rate in the secondary recrystallization annealing was 20° C./h.

[0107] In Table 2, the underlines indicate outside the range according to the present disclosure.

[0108] The iron loss W.sub.17/50 (iron loss when excited to 1.7 T at 50 Hz) and the magnetic flux density B.sub.8 (magnetic flux density when excited with a magnetizing force of 800 A/m) of a sample cut out of each resultant product steel sheet were measured by the method described in HS C 2550-1: 2011. Moreover, the obtained sample was immersed in a 10% hydrochloric acid aqueous solution of 80° C. for 180 sec, and the films on the front and back sides were removed so that secondary recrystallized grains would be recognizable. The grain size distribution of the secondary recrystallized grains was then determined by image analysis. Furthermore, for each coarse secondary recrystallized grain extending through the steel sheet in the thickness direction from among the coarse secondary recrystallized grains of 5 mm or more in grain size, the area ratio of the region in which the projected surfaces of the respective areas of the coarse secondary recrystallized grain exposed on the front and back sides of the steel sheet coincide with each other to each of the areas of the coarse secondary recrystallized grain exposed was calculated for each condition. The results are listed in Table 3. The area of the sample studied to determine the grain size distribution and the area ratio was 336 cm.sup.2 (equivalent to four Epstein samples).

[0109] The steel substrate composition of the product steel sheet studied using the sample from which the films on the front and back sides had been removed is also listed in Table 3. In Table 3, the underlines indicate outside the range according to the present disclosure.

[0110] The average misorientation angle between the crystal orientations of the fine grains of more than 2.0 mm and less than 5.0 mm in grain size and the Goss orientation measured for the product steel sheet according to each example was 26.9°.

TABLE-US-00002 TABLE 2 Slab chemical composition (mass % or mass ppm) C Si Mn N sol•Al S Se Sn Sb Mo P Others ID (%) (%) (%) (ppm) (ppm) (ppm) (ppm) (%) (%) (%) (%) (%, ppm) A 0.012 2.99 0.15 55 270 6 80 0.07 0.11 0.04 0.07 — B 0.013 3.02 0.14 47 280 7 70  0.015 — — — — C 0.015 3.01 0.15 58 270 7 70 —  0.018 — — — D 0.009 3.05 0.15 51 290 8 70 — —  0.018 — — E 0.016 3.02 0.16 53 270 6 80 — — —  0.011 — F 0.025 1.33 0.17 55 250 8 60 0.11 — — — — G 0.028 8.72 0.15 50 270 10 60 0.13 — — — — H 0.022 3.07 0.01 49 260 9 50 0.18 — — — — I 0.024 3.11 1.11 55 270 8 50 0.08 — — — — J 0.026 2.98 0.11 55 280 7 70 0.52 — — — — K 0.024 3.07 0.19 56 280 7 70 — 0.48 — — — L 0.025 3.05 0.18 48 260 6 80 — — 0.25 — — M 0.018 3.04 0.11 50 270 7 70 — — — 0.32 — N 0.081 3.45 0.04 78 420 33 — —  0.035 0.02 — Cr: 0.06%, Cu: 0.12% O 0.055 2.68 0.55 24 70 — 190  0.11 — — 0.03 Cr: 0.02%, Cu: 0.03%, Ni: 0.47%, Nb: 18 ppm P 0.061 3.36 0.28 11 30 61 — 0.23 0.07 — 0.18 Ni: 0.03%, Bi: 0.40%, Nb: 97 ppm Q 0.037 3.07 0.15 65 150 17 110  — 0.07 0.06 — Cr: 0.44%, Cu: 0.48%, Bi: 0.012%

TABLE-US-00003 TABLE 3 Area ratio of coincidence Magnetic Number on front flux Steel substrate composition of product sheet (mass % or mass ppm) of fine and back Iron loss density Si Mn Sn Sb Mo P Others grains sides W.sub.17/50 B.sub.8 ID (%) (%) (%) (%) (%) (%) (%, ppm) (/cm.sup.2) (%) (W/kg) (T) Remarks A 2.99 0.15 0.07 0.11 0.04 0.07 — 3.12 98.8 0.781 1.932 Example B 3.02 0.14  0.015 — — — — 3.25 99.0 0.782 1.937 Example C 3.01 0.15 —  0.018 — — — 3.84 99.7 0.779 1.934 Example D 3.05 0.15 — —  0.018 — — 3.45 96.4 0.786 1.932 Example E 3.02 0.16 — — —  0.011 — 3.40 98.1 0.780 1.936 Example F 1.33 0.17 0.11 — — — — 2.35 98.4 1.223 1.866 Comparative Example G 8.72 0.15 0.13 — — — — Not secondary 1.541 Comparative recrystallized Example H 3.07 0.01 0.18 — — — — Not secondary 1.562 Comparative recrystallized Example I 3.11 1.11 0.08 — — — — Not secondary 1.555 Comparative recrystallized Example J 2.98 0.11 0.52 — — — — 3.32 96.2 0.955 1.884 Comparative Example K 3.07 0.19 — 0.48 — — — 3.98 97.7 0.987 1.895 Comparative Example L 3.05 0.18 — — 0.25 — — 4.02 97.5 1.135 1.870 Comparative Example M 3.04 0.11 — — — 0.32 — Not secondary 1.558 Comparative recrystallized Example N 3.45 0.04 —  0.035 0.02 — Cr: 0.06%, Cu: 0.12% 3.55 98.3 0.759 1.940 Example O 2.68 0.55 0.11 — — 0.03 Cr: 0.02%, Cu: 0.03%, 3.69 98.1 0.764 1.942 Example Ni: 0.47%, Nb: 18 ppm P 3.36 0.28 0.23 0.07 — 0.18 Ni: 0.03%, Bi: 0.40%, 3.11 97.2 0.767 1.944 Example Nb: 97 ppm Q 3.07 0.15 — 0.07 0.06 — Cr: 0.44%, Cu: 0.48%, 3.48 99.1 0.774 1.944 Example Bi: 0.012%

[0111] As is clear from Table 3, favorable iron loss property was achieved with each chemical composition and steel microstructure within the range according to the present disclosure. In particular, the magnetic flux density of each steel sheet according to the present disclosure was 1.90 T or more.