Grain-oriented silicon steel with low core loss and manufacturing method therefore

Abstract

A grain-oriented silicon steel with low iron loss, wherein the silicon steel is provided with a plurality of grooves on its surface, each of the grooves is 10-60 μm in width and 5-40 μm in depth, and the spacing between adjacent grooves is 1-10 mm. The manufacturing method therefor comprises: scoring the surface of the grain-oriented silicon steel with low iron loss by using a laser in order to form the grooves. The grain-oriented silicon steel with low iron loss can maintain the magnetic domain refining effect in a stress-relief annealing process, and avoid the introduction of more residual stress.

Claims

1. A grain-oriented silicon steel with low iron loss, wherein the grain-oriented silicon steel comprises a plurality of grooves on a surface of said grain-oriented silicon steel, and each groove is 10-60 μm in width and 5-40 μm in depth, and the spacing between adjacent grooves is 1-10 mm; and wherein the grain-oriented silicon steel has ΔP.sub.17/50%, a relative change rate of iron loss before and after stress-relief annealing, of 5% or less, and wherein $\Delta P_{17/50}\%=\frac{P_{17/50}\left(\mathrm{after}\mathrm{annealing}\right)-P_{17/50}\left(\mathrm{before}\mathrm{annealing}\right)}{P_{17/50}\left(\mathrm{after}\mathrm{annealing}\right)},$ P.sub.17/50 is an iron loss of a grain-oriented silicon steel sheet, in unit of W/kg, and wherein the P.sub.17/50 after annealing >P.sub.17/50 before annealing.

2. The grain-oriented silicon steel with low iron loss of claim 1, wherein an angle formed between the groove and the width direction of a steel sheet is not more than 30°.

3. The grain-oriented silicon steel with low iron loss of claim 1, wherein the grooves are formed by laser scoring.

4. The grain-oriented silicon steel with low iron loss of claim 1, wherein one or both the surfaces of the grain-oriented silicon steel have the grooves.

5. A method for producing a grain-oriented silicon steel with low iron loss, comprising the steps of scoring a surface of the grain-oriented silicon steel with a laser to form grooves, and each groove is 10-60 μm in width and 5-40 μm in depth, and the spacing between adjacent grooves is 1-10 mm; wherein an average single-pulse energy flux density J.sub.F and the pulse width t.sub.p of the laser satisfy the following relationship:
0.005≤t.sub.p√{square root over (J.sub.F)}≤1,and wherein the unit of the pulse width t.sub.p is ns; and the unit of J.sub.F is J/mm.sup.2, and wherein the average single pulse energy flux density J.sup.F is expressed as: $J_F=\frac{P}{f_{r}S},$ wherein P is the output power of the laser in W; f.sub.r is the repetition frequency of laser in Hz; S is the spot area in mm.sup.2.

6. The method for producing a grain-oriented silicon steel with low iron loss of claim 5, wherein an angle formed between the groove and the width direction of a steel sheet is not more than 30°.

7. The method for producing a grain-oriented silicon steel with low iron loss of claim 5, wherein the laser is one or more selected from a CO.sub.2 laser, a solid laser, and a fiber optic laser.

8. The method for producing a grain-oriented silicon steel with low iron loss of claim 5, wherein the laser has an average single-pulse instantaneous peak power density of 2.0×10.sup.6 W/mm.sup.2 or more.

9. The method for producing a grain-oriented silicon steel with low iron loss of claim 5, wherein the laser has a wavelength of 1066 nm or less.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the local stress field produced by the mechanical scoring of the prior art.

(2) FIG. 2 shows the stress distribution in the groove of the grain-oriented silicon steel with low iron loss according to the present invention.

(3) FIG. 3 shows the improvement of the magnetic induction and iron loss of the grain-oriented silicon steel with low iron loss according to the present invention at different relative change rates of iron loss ΔP.sub.17/50%.

(4) FIG. 4 shows the relative change rate ΔP.sub.17/50% and improvement rate of iron loss before and after annealing of the oriented silicon steel with low iron loss of the present invention at different average single-pulse peak power densities p.sub.0.

(5) FIG. 5 shows the relative change rate ΔP.sub.17/50% and improvement rate of iron loss before and after stress-relief annealing of the grain-oriented silicon steel with low iron loss of the present invention at different t.sub.p√{square root over (J.sub.F)}.

DETAILED DESCRIPTION

(6) The grain-oriented silicon steel with low iron loss and manufacturing method therefor of the present invention will be further explained and illustrated below with reference to the accompanying drawings and specific Examples. However, the explanations and illustrations do not unduly limit the technical solutions of the present invention.

EXAMPLES A1-A19 AND COMPARATIVE EXAMPLES B1-B13

(7) The grain-oriented silicon steel with low iron loss of Examples A1-A19 and the conventional grain-oriented silicon steel of Comparative Examples B1-B13 were obtained by the following steps:

(8) (1) The raw material was subjected to iron making, steel making, continuous casting, and hot rolling process. Next, single cold rolling was performed to roll the steel to a thickness of 0.23-0.27 mm. The thicknesses of Examples A1 to A15 and Comparative Examples B1 to B10 were 0.23 mm, and the thicknesses of Examples A16 to A19 and Comparative Examples B11 to B13 were 0.27 mm. After the decarburization annealing at 850° C., the surface oxide layer was formed. Then, the steel was coated with MgO separator on the surface, and subjected to high-temperature annealing at 1200° C. for 20 hours after winding into a coil. Then, an insulating coating was applied to the surface of the steel, and final annealing was performed to obtain a finished silicon steel sheet.

(9) (2) The surface of the silicon steel sheet of each of the Examples and the Comparative Examples was scored with a laser to form grooves. The specific process parameters are shown in Table 1.

(10) Table 1 lists the specific process parameters in the step (2) of the grain-oriented steel with low iron loss in each Example.

(11) TABLE-US-00001 TABLE 1 Angle Average Spacing between single-pulse Average between groove instantaneous single pulse Groove Groove adjacent and width peak power Pulse energy flux Laser width depth grooves direction of density p.sub.0 width density J.sub.F wavelength Number (μm) (μm) (mm) steel sheet Laser source (W/mm.sup.2) t.sub.p (ns) (J/cm.sup.2) t.sub.P√{square root over (J.sub.F)} (nm) Example A1 20 20 5 10° CO.sub.2 laser 1.3 × 10.sup.7 0.2 6.63 0.515 533 A2 20 20 5 10° Solid laser 1.3 × 10.sup.7 0.2 6.63 0.515 267 A3 20 20 5 10° Fiber-optic 1.3 × 10.sup.7 0.2 6.63 0.515 267 laser A4 20 15 4 12° CO.sub.2 laser + 1.3 × 10.sup.7 0.9 1.22 0.996 533 Solid laser A5 20 15 4 12° CO.sub.2 laser + 1.1 × 10.sup.7 0.03 0.03 0.005 267 Fiber-optic laser A6 20 15 4 12° Fiber-optic 2.1 × 10.sup.6 0.6 0.13 0.214 533 laser + Solid laser A7 43 20   4.5  8° CO.sub.2 laser + 4.0 × 10.sup.6 0.2 1.99 0.282 267 Solid laser + Fiber-optic laser A8 15 20 5 20° CO.sub.2 laser 1.3 × 10.sup.7 0.2 6.63 0.515 533 A9 10 18   4.5  8° Solid laser 1.1 × 10.sup.7 0.2 5.31 0.461 267 A10 60 20   4.5  8° Fiber-optic 4.0 × 10.sup.7 0.2 1.99 0.282 267 laser A11 15 40   4.5  8° CO.sub.2 laser + 1.3 × 10.sup.7 0.2 6.63 0.515 267 Solid laser A12 15  5   4.5  8° CO.sub.2 laser + 2.7 × 10.sup.6 0.2 1.32 0.23  533 Fiber-optic laser A13 15 20 1  8° Fiber-optic 1.3 × 10.sup.7 0.2 6.63 0.515 267 laser + Solid laser A14 15 20 10   8° CO.sub.2 laser + 1.3 × 10.sup.7 0.2 6.63 0.515 533 Solid laser + Fiber-optic laser A15 15 20 5 30° CO.sub.2 laser 1.3 × 10.sup.7 0.2 6.63 0.515 267 A16 60   10.8 5  6° Solid laser 2.9 × 10.sup.6 0.2 1.45 0.241 267 A17 50   12.6 5  6° Fiber-optic 3.5 × 10.sup.6 0.2 1.77 0.266 267 laser A18 40   13.9 5  6° CO.sub.2 laser + 4.4 × 10.sup.6 0.2 2.21 0.297 533 Solid laser A19 20   16.8 5  6° CO.sub.2 laser + 8.8 × 10.sup.6 0.2 4.43 0.421 267 Fiber-optic laser Comparative B1 8 20 5 10° Fiber-optic 1.3 × 10.sup.7 0.2 6.63 0.515 533 Example laser + Solid laser B2 20 20 11  10° CO.sub.2 laser + 1.3 × 10.sup.7 0.2 6.63 0.515 267 Solid laser + Fiber-optic laser B3 20  4 4 12° CO.sub.2 laser 1.9 × 10.sup.6 0.2 0.04 0.039 267 B4 20 15 13  12° Solid laser 3.4 × 10.sup.7 0.7 2.39 1.082 267 B5 15 42 5 31° Fiber-optic 1.3 × 10.sup.7 0.2 6.63 0.515 533 laser B6 9 20 5 12° CO.sub.2 laser + 2.0 × 10.sup.7 0.2 9.95 0.631 267 Solid laser B7 15 20   0.9 12° CO.sub.2 laser + 1.3 × 10.sup.7 0.2 6.63 0.515 267 Fiber laser B8 15 20  10.5 12° Fiber-optic 1.3 × 10.sup.7 0.2 6.63 0.515 533 laser + Solid laser B9 15 41 5 12° CO.sub.2 laser + 5.3 × 10.sup.6 0.2 2.66 0.326 533 Solid laser + Fiber-optic laser B10 15   4.5 5 12° CO2 laser 2.2 × 10.sup.6 0.2 1.10 0.21  267 B11 61   10.5 5  6° Solid laser 2.8 × 10.sup.6 0.2 1.42 0.238 533 B12 63   10.1 5  6° Fiber-optic 2.7 × 10.sup.6 0.2 1.35 0.232 267 laser B13 70   15.5 5  6° CO.sub.2 laser + 2.5 × 10.sup.6 0.2 1.24 0.223 533 Solid laser

(12) The grain-oriented silicon steel with low iron loss of Examples A1-A3 and the conventional silicon steel of Comparative Example B1-B2 were made into primary energy efficient wound core distribution transformers having a capacity of 315 kVA. The design weight of the core was 430 kg, and the no-load loss and load loss were measured. The results are shown in Table 2.

(13) TABLE-US-00002 TABLE 2 Before laser After laser scoring Improvement scoring P.sub.17/50 (W/kg) rate of iron P.sub.17/50 Before After ΔP.sub.17/50% loss of No-load Load Number (W/kg) annealing annealing (%) scoring(%) loss (W) loss (W) Example A1 0.908 0.802 0.803 0.1 11.6 330.2 3045 A2 0.903 0.793 0.811 2.3 10.2 328.5 3038 A3 0.906 0.801 0.840 4.6 7.3 339.8 3065 Comparative B1 0.901 0.805 0.848 5.1 5.9 342.8 3068 Example B2 0.905 0.801 0.862 7.1 4.8 348.3 3075

(14) $\mathrm{Improvement}\mathrm{rate}\mathrm{of}\mathrm{iron}\mathrm{loss}\mathrm{of}\mathrm{scoring}=\frac{P_{17/50}\left(\mathrm{before}\mathrm{scoring}\right)-P_{17/50}\left(\mathrm{after}\mathrm{scoring}-\mathrm{after}\mathrm{annealing}\right)}{P_{17/50}\left(\mathrm{before}\mathrm{scoring}\right)}$

(15) It can be seen from Table 2 that in the Examples A1-A3, ΔP.sub.17/50% is 5% or less, the improvement rate of iron loss of scoring is more than 6%, the no-load loss of the manufactured distribution transformer is less than 340 W, and the load loss is 3065 W or less. On the other hand, in the Comparative Example B1-B2, ΔP.sub.17/50% is greater than 5%, the improvement rate of iron loss of scoring is less than 6%, and both the no-load loss and load loss of distribution transformer were higher than those of Examples A1-A3.

(16) Table 3 lists the laser parameters used in the grain-oriented silicon steel with low iron loss of Examples A4-A6 and the conventional silicon steel of Comparative Example B3-B4, and the test results of the iron loss P.sub.17/50 measured by the 500 mm×500 mm method.

(17) TABLE-US-00003 TABLE 3 Average Width of single-pulse Laser beam in the Transverse instantaneous After laser scoring output Repetition Pulse rolling width of Laser peak power P.sub.17/50 (W/kg) power frequency width direction a beam b scan density p.sub.0 Before After ΔP.sub.17/50% No. P (W) fr (kHz) t.sub.p (ns) (mm) (mm) times (W/mm.sup.2) t.sub.P√{square root over (J.sub.F)} annealing annealing (%) Example A4 20 800 0.9 0.02 0.13 1 1.3 × 10.sup.7 0.996 0.767 0.806 4.8 A5 1.5 600 0.03 0.1 0.1 20 1.1 × 10.sup.7 0.005 0.801 0.805 0.5 A6 8 400 0.6 0.1 0.2 5 2.1 × 10.sup.6 0.214 0.762 0.801 4.9 Comparative B3 10 400 0.2 0.1 0.82 2 1.9 × 10.sup.6 0.039 0.791 0.842 6.1 Example B4 15 200 0.7 0.02 0.2 2 3.4 × 10.sup.7 1.082 0.788 0.832 5.3

(18) As can be seen from Table 3, in Comparative Examples B3 and B4, the average single-pulse energy flux density J.sub.F and pulse width t.sub.p of the laser did not satisfy the relationship: 0.005≤t.sub.p√{square root over (J.sub.F)}≤1 and the ΔP.sub.17/50% was greater than 5%. In Examples A4-A6, the relationship of 0.005≤t.sub.p√{square root over (J.sub.F)}≤1 is satisfied, and the ΔP.sub.17/50% is less than 5%.

(19) Table 4 lists the laser parameters used in the grain-oriented silicon steel with low iron loss of Examples A7-A15 and the conventional silicon steel of Comparative Example B5-B10, and the test results of the iron loss P.sub.17/50 measured by the 500 mm×500 mm method.

(20) TABLE-US-00004 TABLE 4 Average Length of single-pulse spot in the Transverse instantaneous Before P.sub.17/50 rolling length of peak power Laser annealing (W/kg) direction spot density p.sub.0 scan B8 Before After ΔP.sub.17/50% No. (mm) (mm) (W/mm.sup.2) t.sub.P√{square root over (J.sub.F)} times (T) annealing annealing (%) Example A7 0.04 0.2 4.0 × 10.sup.6 0.282 1 1.902 0.803 0.808 0.6 A8 0.012 0.2 1.3 × 10.sup.7 0.515 1 1.908 0.801 0.803 0.2 A9 0.01 0.3 1.1 × 10.sup.7 0.461 1 1.912 0.812 0.813 0.1 A10 0.04 0.2 4.0 × 10.sup.7 0.282 2 1.901 0.797 0.802 0.6 A11 0.012 0.2 1.3 × 10.sup.7 0.515 3 1.901 0.791 0.799 1.0 A12 0.012 1.0 2.7 × 10.sup.6 0.230 1 1.915 0.821 0.821 0.0 A13 0.012 0.2 1.3 × 10.sup.7 0.515 1 1.9 0.788 0.796 1.0 A14 0.012 0.2 1.3 × 10.sup.7 0.515 1 1.913 0.823 0.825 0.2 A15 0.012 0.2 1.3 × 10.sup.7 0.515 1 1.911 0.822 0.823 0.1 Comparative B5 0.012 0.2 1.3 × 10.sup.7 0.515 1 1.911 0.831 0.842 1.3 Example B6 0.008 0.2 2.0 × 10.sup.7 0.631 1 1.917 0.838 0.845 0.8 B7 0.012 0.2 1.3 × 10.sup.7 0.515 2 1.897 0.782 0.793 1.4 B8 0.012 0.2 1.3 × 10.sup.7 0.515 2 1.918 0.837 0.841 0.5 B9 0.012 0.5 5.3 × 10.sup.6 0.326 4 1.898 0.783 0.798 1.9 B10 0.012 1.2 2.2 × 10.sup.6 0.210 1 1.919 0.839 0.841 0.2

(21) As can be seen from Table 4, the parameters in the laser process and the surface scoring process of the grain-oriented silicon steel with low iron loss of Examples A7-A15 are within the scope defined by the present invention. That is to say, in the grain-oriented silicon steel with low iron loss of Examples A7-A15, the groove has a width of 10 to 60 μm and a depth of 5 to 40 μm, the spacing between adjacent grooves is 1 to 10 mm, an angle formed between the groove and the width direction of the steel sheet is not more than 30°, the average single-pulse instantaneous peak power density of the laser is not less than 2.0×10.sup.6 W/mm.sup.2, and the average single-pulse energy flux density J.sub.F and the pulse width t.sub.p of the laser satisfy the following relationship: 0.005≤t.sub.p√{square root over (J.sub.F)}≤1. Therefore, the grain-oriented silicon steel with low iron loss of each Example has good performance, a magnetic induction B8 of 1.90 T or more, and iron losses P.sub.17/50 before and after annealing of 0.825 W/kg or less. On the other hand, the conventional silicon steel of Comparative Example B5-B9 is inferior in performance to Examples A7-A15 of the present invention.

(22) The grain-oriented silicon steel with low iron loss of Examples A16-A19 and the conventional silicon steel of Comparative Examples B11-B13 were tested for iron loss P.sub.17/50 by the 500 mm×500 mm method, and subjected to a continuous salt spray test for 7 hr according to the IEC68-2-11 standard. The corrosion resistance characteristics of the surface of the silicon steel sheets were evaluated. The test results obtained are shown in Table 5.

(23) TABLE-US-00005 TABLE 5 Average Length of single-pulse spot in the Transverse instantaneous Before P.sub.17/50 rolling length of peak power Laser annealing (W/kg) Rust direction spot density p.sub.0 scan B8 Before After ΔP.sub.17/50% area No. (mm) (mm) (W/mm.sup.2) t.sub.P√{square root over (J.sub.F)} times (T) annealing annealing (%) (%) Example A16 0.055 0.2 2.9 × 10.sup.6 0.241 1 1.905 0.885 0.901 1.8 2 A17 0.045 0.2 3.5 × 10.sup.6 0.266 1 1.911 0.891 0.905 1.5 1 A18 0.036 0.2 4.4 × 10.sup.6 0.297 1 1.912 0.879 0.890 1.2 0 A19 0.018 0.2 8.8 × 10.sup.6 0.421 1 1.915 0.868 0.873 0.6 0 Comparative B11 0.056 0.2 2.8 × 10.sup.6 0.238 1 1.903 0.873 0.882 1.0 5 Example B12 0.059 0.2 2.7 × 10.sup.6 0.232 1 1.901 0.877 0.890 1.5 6 B13 0.064 0.2 2.5 × 10.sup.6 0.223 2 1.900 0.866 0.879 1.5 10

(24) From Table 5, and if necessary, in conjunction with Table 1, it can be seen that since the groove width of Examples A16-A19 of the present invention is 60 μm or less, the rust area of the silicon steel sheet in the salt spray test is 2% or less, indicating that the grain-oriented silicon steel with low iron loss of each Example of the present invention is excellent in corrosion resistance. On the other hand, since the groove width of Comparative Examples B11-B13 is more than 60 μm, the corrosion resistance of the silicon steel sheet is greatly attenuated.

(25) FIG. 1 shows the local stress field produced by the mechanical scoring of the prior art. As can be seen from FIG. 1, since it is necessary to apply a mechanical stress greater than the tensile strength on the silicon steel sheet substrate to form a groove on the surface, the pressure value required generally exceeds 200 MPa, and the distribution of the stress field throughout the entire thickness direction of the silicon steel sheet in the rolling direction of the steel sheet greatly exceeds the deformation region of the score. A large number of sub-magnetic domains are generated in the residual stress region after processing, which increases the hysteresis loss and reduces the magnetic induction characteristics of a silicon steel sheet. Therefore, the silicon steel in prior art cannot be directly applied to the manufacture of a laminated core transformer.

(26) FIG. 2 shows the stress distribution in the groove of the grain-oriented silicon steel with low iron loss according to the present invention. As can be seen from FIG. 2, since the present invention uses a high-energy pulsed laser to perform a heat-resistant scoring, the distribution of stress in the vicinity of the groove is very limited and the area affected by the stress is greatly reduced. Therefore, the iron loss of the silicon steel sheet after stress-relief annealing is not significantly increased. Therefore, the grain-oriented silicon steel with low iron loss according to the present invention can be applied to the manufacture of a wound core and a laminated core transformer.

(27) FIG. 3 shows the improvement of the magnetic induction and iron loss of the grain-oriented silicon steel with low iron loss according to the present invention at different relative change rates of iron loss ΔP.sub.17/50%. As can be seen from FIG. 3, the grain-oriented silicon steel with low iron loss of the present invention in the range of I has a good improvement rate of magnetic induction B8 and an obvious improvement rate of iron loss P.sub.17/50 (an improvement rate of more than 6%). Therefore, the grain-oriented silicon steel with low iron loss according to the present invention can be used for the manufacture of a wound core transformer, and also can be directly used for the manufacture of a laminated core transformer without stress-relief annealing. In the figure, I indicates that ΔP.sub.17/50% is in the range of 5% or less, II represents a curve of the improvement rate of the magnetic induction of the grain-oriented silicon steel, and III represents a curve of the improvement rate of the iron loss P.sub.17/50 of the grain-oriented silicon steel.

(28) FIG. 4 shows the relative change rate ΔP.sub.17/50% and improvement rate of iron loss before and after annealing stress-relief of the grain-oriented silicon steel with low iron loss of the present invention at different average single-pulse peak power densities p.sub.0. It can be seen from FIG. 4 that, when it is in the IV range, the grain-oriented silicon steel with low iron loss according to the present invention has a relative change rate of iron loss ΔP.sub.17/50% before and after the stress-relief annealing of 5% or less, and the improvement rate of iron loss is high. In the figure, IV indicates that the average single-pulse peak power density p.sub.0 is 2.0×10.sup.6 W/mm.sup.2 or more, V represents the improvement rate of iron loss of the grain-oriented silicon steel, and VI represents the relative change rate of iron loss ΔP.sub.17/50% before and after the stress relief annealing.

(29) FIG. 5 shows the relative change rate ΔP.sub.17/50% and improvement rate of iron loss before and after stress-relief annealing of the grain-oriented silicon steel with low iron loss of the present invention at different t.sub.p√{square root over (J.sub.F)}. It can be seen from FIG. 5 that, when it is in the VII range, the grain-oriented silicon steel with low iron loss according to the present invention has a relative change rate of iron loss ΔP.sub.17/50% before and after the stress-relief annealing of 5% or less, and the improvement rate of iron loss is high. In the figure, VII indicates that the average single-pulse energy flux density J.sub.F and the pulse width t.sub.p of the laser satisfy the relationship of 0.005≤t.sub.p√{square root over (J.sub.F)}≤1, VIII represents the improvement rate of iron loss of the grain-oriented silicon steel, IX represents the relative change rate of iron loss ΔP.sub.17/50% before and after the stress relief annealing, and X represents the laser processing area.

(30) It should be noted that the above are only specific examples of the present invention. It will be apparent that the invention is not limited to the above examples but has many similar variations. All modifications derived or conceived by those skilled in the art from the disclosure of the present invention should fall within the scope of the present invention.