Silicon steel product with low iron loss for low-noise transformer, and manufacturing method thereof

Abstract

An oriented silicon steel product with a low iron loss for a low-noise transformer, and manufacturing method thereof are provided. The oriented silicon steel product comprises: a silicon steel substrate, a magnesium silicate bottom layer formed on a surface of the silicon steel substrate, and an insulation coating applied on the magnesium silicate bottom layer. The magnesium silicate bottom layer has a visible light normal reflectivity (R) of 40-60% for. By strictly controlling the visible light normal reflectivity of the magnesium silicate bottom layer of the silicon steel substrate and the evenness of the gloss of magnesium silicate bottom layer, lower iron loss, and reduced magnetostriction can be achieved, and thus a silicon steel product with low noise and particularly suitable for transformers can be obtained.

Claims

1. An oriented silicon steel product with low iron loss for a low-noise transformer, comprising a silicon steel substrate, a magnesium silicate bottom layer formed on a surface of the silicon steel substrate having a thickness of 0.5-3 μm, and an insulation coating applied on the magnesium silicate bottom layer, wherein the magnesium silicate bottom layer has a visible light normal reflectivity R of 40-60%; wherein R has a statistical distribution σ in 100 mm.sup.2 of the magnesium silicate bottom layer of 7.5 or less; and wherein the silicon steel substrate consists of the following chemical elements by mass percentages: C: 0.035-0.120%, Si: 2.5-4.5%, Mn: 0.05-0.20%, S: 0.005-0.012%, acid-soluble Al: 0.015-0.035%, N: 0.004-0.009%, Cu: 0.01-0.29%, Sn: 0.08-0.20%, Nb: 0.05-0.10%, the balance being Fe and other unavoidable impurities.

2. The oriented silicon steel product with low iron loss for a low-noise transformer according to claim 1, wherein the magnesium silicate bottom layer has a visible light normal reflectivity R of 45-55.3%.

3. The oriented silicon steel product with low iron loss for a low-noise transformer according to claim 1, wherein the statistical distribution σ of R in 100 mm.sup.2 of the magnesium silicate bottom layer is 4 or less.

4. The oriented silicon steel product with low iron loss for a low-noise transformer according to claim 1, wherein the magnesium silicate bottom layer has a surface roughness R.sub.a of 0.13-0.48 μm.

5. The oriented silicon steel product with low iron loss for a low-noise transformer according to claim 1, wherein the steel product has a thickness of 0.30 mm or less and an iron loss of 1.02 W/Kg or less.

6. A manufacturing method for the oriented silicon steel product with low iron loss for a low-noise transformer of claim 1, comprising the following steps in turn: (1) smelting and casting; (2) hot rolling; (3) normalizing; (4) cold rolling; (5) decarburization annealing to reduce the carbon content in the silicon steel substrate to 30 ppm or less and the oxygen content to 2.0 g/m.sup.2 or less; a nitriding treatment is performed before, after or simultaneously with the decarburization annealing to control the nitrogen content in the silicon steel substrate to 150-350 ppm; wherein in the heating stage, there is a rapid heating stage in which the initial temperature is 600° C. or less, the final temperature is 700° C. or more, and the heating rate is 80° C./s or more; in addition, the difference between oxidation potentials in the heating stage and oxidation potentials in the holding stage of decarburization annealing protective atmosphere satisfies the following formula: ${\left(\frac{P_{H_{2}O}}{P_{H_2}}\right)}_{\mathrm{Holding}}-{\left(\frac{P_{H_{2}O}}{P_{H_2}}\right)}_{\mathrm{Heating}}=A.Math.\frac{{\log }_{10}\left(V_h\right)}{100\times \left[\mathrm{Sn}\right]}$ in the formula, A is the technological coefficient of oxidation potential; P.sub.H.sub.2.sub.O and P.sub.H.sub.2 are partial pressures of H.sub.2O and H.sub.2 in decarburization annealing protective atmosphere, respectively, in units of Pa; V.sub.h is the heating rate of rapid heating stage, in units of ° C./s; [Sn] is the content of Sn in the substrate, in units of %; (6) high-temperature annealing: before the high-temperature annealing, the surface of the silicon steel substrate is coated with an annealing separator, wherein the annealing separator contains MgO; (7) applying an insulation coating; (8) laser scribing: scribing lines perpendicular to the rolling direction is formed on the surface of the product by laser scribing, wherein parameters of the laser scribing satisfy the following formula: $0.4\le \frac{p.Math.a.Math.\exp \left(-\frac{R}{{\lambda }_0}\right)}{d}\le 2$ in the formula, p is the energy density of the incident laser, in units of mJ/mm.sup.2; a is the length of the focused spot of laser in rolling direction, in units of mm; R is the visible light normal reflectivity of magnesium silicate bottom layer, in units of %; d is the spacing of scribing lines in rolling direction, in units of mm; λ.sub.0 is the wavelength of incident laser, in units of nm.

7. The manufacturing method according to claim 6, wherein the technological coefficient A of oxidation potential ranges from 0.08 to 1.6.

8. The manufacturing method according to claim 6, wherein the energy density p of the incident laser is 50-200 mJ/mm.sup.2.

9. The manufacturing method according to claim 6, wherein the length a of the focused spot of laser in rolling direction is 0.08 mm or less.

10. The manufacturing method according to claim 6, wherein in step (8), the residence time of laser on the surface of the product is no more than 0.005 ms.

11. The manufacturing method according to claim 6, wherein in step (6), the holding temperature of annealing is 1150-1250° C., and the holding time is 15 hr or more.

12. The manufacturing method according to claim 6, wherein in step (2), the slab is heated to 1090-1200° C. in a heating furnace, and then rolled.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a time-domain diagram of magnetic flux density and magnetostriction of a silicon steel sheet in the prior art.

(2) FIG. 2 is a schematic view showing curve distribution between the visible light normal reflectivity R and the iron loss/magnetic induction of the silicon steel product of the present invention.

(3) FIG. 3 is a schematic view showing curve distribution between the statistical distribution σ of visible light normal reflectivity R in 100 mm.sup.2 of the magnesium silicate bottom layer and the vibration noise of the silicon steel product of the present invention.

(4) FIG. 4 is a schematic view showing curve between the statistical distribution σ of different visible light normal reflectivity R and magnetostriction waveform/vibration noise of the silicon steel product of the present invention.

(5) FIG. 5 is a schematic view showing curve distribution between the technological coefficient A of oxidation potential and the visible light normal reflectivity R/statistical distribution σ of the silicon steel product of the present invention.

(6) FIG. 6 is a schematic view showing curve distribution between the parameters of laser scribing and the vibration noise of the silicon steel product of the present invention.

DETAILED DESCRIPTION

(7) The oriented silicon steel product with low iron loss for a low-noise transformer and manufacturing method thereof of the present invention will be further explained and illustrated below concerning the accompanying drawings and specific Examples. However, the explanations and illustrations do not unduly limit the technical solutions of the present invention.

(8) Examples A1-A9 and Comparative Examples B1-B8 were prepared by the following steps:

(9) (1) smelting and casting according to formula of chemical components listed in Table 1;

(10) (2) hot rolling: the slab was heated to 1090˜1200° C. in a heating furnace, and then rolled to a thickness of 2.3 mm;

(11) (3) normalizing: two-stage normalizing were used: in the first stage, the normalizing temperature was 1050˜1180° C., and the normalizing time was 1˜20 s; in the second stage, the normalizing temperature was 850˜950° C., and the normalizing time was 30˜200 s; then cooling was carried out at a cooling rate of 10˜60° C./s.

(12) (4) cold rolling: the steel sheet was rolled to a final thickness of 0.27 mm with a total cold rolling reduction ratio of 88.3% by a single cold reduction;

(13) (5) decarburization annealing was performed to reduce the carbon content in the silicon steel substrate to 30 ppm or less and the oxygen content to 2.0 g/m.sup.2 or less; a nitriding treatment was performed before, after or simultaneously with the decarburization annealing to control the nitrogen content in the silicon steel substrate to 150˜350 ppm; wherein, in the heating stage, there was a rapid heating stage in which the initial temperature was 600° C. or less, the final temperature was 700° C. or more, and the heating rate was 80° C./s or more; specific process parameters of the heating stage are shown in Table 2-2; in addition, the difference between oxidation potentials of decarburization annealing protective atmosphere in the heating section stage and oxidation potentials in the holding section stage of decarburization annealing protective atmosphere satisfies the following formula:

(14) ${\left(\frac{P_{H_{2}O}}{P_{H_2}}\right)}_{\mathrm{Holding}}-{\left(\frac{P_{H_{2}O}}{P_{H_2}}\right)}_{\mathrm{Heating}}=A.Math.\frac{{\log }_{10}\left(V_h\right)}{100\times \left[\mathrm{Sn}\right]}$

(15) in the formula, A is the technological coefficient of oxidation potential; P.sub.H.sub.2.sub.O and P.sub.H.sub.2 are partial pressures of H.sub.2O and H.sub.2 in decarburization annealing protective atmosphere, respectively, in units of Pa; V.sub.h is the heating rate of rapid heating stage, in units of ° C./s; [Sn] is the content of Sn in the substrate, in units of %;

(16) (6) high temperature annealing: the surface of the silicon steel substrate was coated with an annealing separator containing MgO; in the annealing, the holding temperature is 1150˜1250° C. and the holding time is 15 hr or more; further, a mixed gas containing H.sub.2 and N.sub.2 as main components was used as a protective gas, wherein the ratio of H.sub.2 is 25˜100%, and the atmospheric dew point (D.P.) of the was below 0° C.;

(17) (7) applying an insulation coating: after cleaning the residual magnesium oxide on the surface, an insulation coating was applied, and the silicon steel substrate was subjected to hot drawing-flattening annealing to obtain a preliminary silicon steel product;

(18) (8) laser scribing: laser scribing was used to form scribing lines perpendicular to the rolling direction on the surface of the product, wherein parameters of the laser scribing satisfy the following formula:

(19) $0.4\le \frac{p.Math.a.Math.\exp \left(-\frac{R}{{\lambda }_0}\right)}{d}\le 2.0$

(20) in the formula, p is the energy density of the incident laser, in units of mJ/mm.sup.2; a is the length of the focused spot of laser in rolling direction, in units of mm; R is the visible light normal reflectivity of magnesium silicate bottom layer, in units of %; d is the spacing of scribing lines in rolling direction, in units of mm; λ.sub.0 is the wavelength of incident laser, in units of nm.

(21) In addition, it should be noted that in step (8), the technological coefficient A of oxidation potential ranges from 0.08 to 1.6; the energy density p of the incident laser is 50˜200 mJ/mm.sup.2; the length a of the focused spot of laser in rolling direction is 0.08 mm or less; the residence time of laser on the surface of the product is no more than 0.005 ms; the incident laser has a wavelength of 1066 nm, a laser scanning speed of 200˜500 m/s, and a laser output power of 1000 W.

(22) Table 1 lists the mass percentage of chemical elements in Examples A1-A9 and Comparative Examples B1-B8.

(23) TABLE-US-00001 TABLE 1 (wt %, the balance is Fe and other inevitable impurity elements) Number C Si Mn S N Als Cu Sn Nb A1 0.054 3.26 0.12 0.009 0.006 0.028 0.12 0.12 0.05 A2 0.035 3.2 0.11 0.008 0.008 0.024 0.11 0.12 0.10 A3 0.12 3.35 0.1 0.007 0.009 0.019 0.11 0.12 0.08 A4 0.065 2.5 0.13 0.009 0.006 0.031 0.11 0.12 0.07 A5 0.062 4.5 0.15 0.01 0.007 0.034 0.11 0.12 0.06 A6 0.068 3.35 0.18 0.007 0.007 0.023 0.01 0.08 0.10 A7 0.071 3.15 0.14 0.009 0.008 0.018 0.29 0.08 0.09 A8 0.062 3.18 0.2 0.011 0.009 0.022 0.11 0.01 0.06 A9 0.065 3.21 0.12 0.009 0.008 0.03 0.11 0.2 0.06 B1 3.22 0.12 0.009 0.007 0.028 0.12 0.12 0.08 B2 3.08 0.11 0.009 0.006 0.029 0.14 0.11 0.07 B3 0.056 0.11 0.007 0.007 0.026 0.11 0.1 0.06 B4 0.048 0.11 0.009 0.006 0.025 0.15 0.12 0.09 B5 0.061 3.29 0.11 0.009 0.006 0.028 0.15 B6 0.069 3.31 0.11 0.009 0.007 0.025 0.15 B7 0.065 3.09 0.13 0.008 0.006 0.026 0.1 0.08 B8 0.069 3.12 0.12 0.009 0.006 0.031 0.1 0.06

(24) Tables 2-1 and 2-2 lists the specific process parameters in the manufacturing method of Examples A1-A9 and Comparative Examples B1-B8. Table 2-1 lists the specific process parameters in steps (2), (3), (4), (6) and (8), and Table 2-2 lists the specific process parameters in step (5).

(25) TABLE-US-00002 TABLE 2-1 Step (3) Normal- Normal- izing Normal- izing Normal- Step (6) Step (2) temper- izing temper- izing Holding Step (8) Heating ature time in ature time in temper- Volume Resi- temper- in first first in second second Cooling ature of Holding percent p dence ature stage stage stage stage rate anealing time of H.sub.2 D.P. R (mJ/ a time d V.sub.s No. (° C.) (° C.) (s) (° C.) (s) (° C./s) (° C.) (hr) (%) (° C.) (%) mm.sup.2) (mm) (ms) (mm) (m/s) A1 1090 1050 1 850 30 10 1150 15 25 −5 53 80 0.08 0.0025 5 200 A2 1200 1180 20 950 200 60 1250 15 50 −10 51 53 0.06 0.00125 4 400 A3 1095 1130 15 870 150 20 1200 15 75 −13.5 51 199 0.032 0.0025 6 200 A4 1200 1120 12 860 160 40 1150 18 100 −5 48 114 0.032 0.0014 8 350 A5 1090 1090 15 920 120 50 1180 18 15 −10 49 80 0.08 0.004 5 200 A6 1090 1080 10 900 140 30 1180 20 50 −13.5 54 53 0.06 0.002 4 400 A7 1200 1150 16 920 80 20 1180 20 75 −5 49 199 0.032 0.004 8 200 A8 1090 1050 16 910 100 15 1180 20 100 −10 58 80 0.032 0.0016 6 500 A9 1090 1130 15 900 150 20 1180 20 100 −13.5 43 80 0.08 0.005 5 200 B1 1090 1050 1 850 30 10 1150 15 25 −5 48 53 0.06 0.0025 4 400 B2 1200 1180 10 950 200 60 1250 15 50 −10 51 199 0.032 0.005 8 200 B3 1095 1130 15 870 150 20 1200 18 75 −13.5 45 80 0.032 0.002 6 500 B4 1200 1120 12 860 160 40 1150 18 100 −5 54 80 0.08 0.005 5 200 B5 1090 1090 15 920 120 50 1180 20 25 −10 46 53 0.06 0.0025 4 400 B6 1090 1080 10 900 140 30 1180 20 50 −13.5 51 199 0.032 0.005 8 200 B7 1200 1150 16 910 80 20 1180 20 75 −5 53 80 0.032 0.002 6 500 B8 1090 1050 16 900 100 15 1180 20 100 −10 45 80 0.08 0.005 5 200

(26) TABLE-US-00003 TABLE 2-2 Step(5) Initial Final Nitrogen temperature temperature content in rapid in rapid Rapid during Oxidation Oxidation heating heating heating Holding Holding Carbon Oxygen nitriding potential potential stage stage rate V.sub.h temperature time content content treatment in heating in holding No. (° C.) (° C.) (° C./s) (° C.) (s) (ppm) (g/m.sup.2) (ppm) stage stage A A1 600 730 95 832 132 8 1.03 173 0.35 0.46 0.67 A2 590 730 102 835 132 10 1.42 200 0.36 0.48 0.72 A3 580 730 110 840 132 11 1.13 223 0.37 0.50 0.76 A4 600 720 88 826 132 12 1.92 245 0.35 0.54 1.17 A5 600 710 80 845 132 14 0.86 347 0.35 0.52 1.07 A6 600 730 95 832 132 22 0.79 153 0.37 0.45 0.32 A7 590 730 102 835 132 13 1.83 212 0.29 0.56 1.07 A8 580 730 110 840 132 22 1.01 229 0.29 0.46 0.08 A9 600 720 88 826 132 17 0.78 298 0.41 0.56 1.54 B1 600 710 80 845 132 13 0.74 312 0.32 0.48 1.01 B2 600 730 95 832 132 9 1.02 330 0.35 0.44 0.50 B3 590 730 102 835 132 7 1.73 174 0.31 0.62 1.54 B4 580 730 110 840 132 8 0.91 198 0.41 0.46 0.29 B5 600 720 88 826 132 14 0.79 159 0.35 0.54 1.47 B6 600 710 80 845 132 16 1.02 189 0.39 0.46 0.55 B7 580 730 110 838 132 15 1.06 238 0.28 0.66 0.17 B8 600 730 95 838 132 13 0.77 286 0.35 0.48 1.38
Wherein, it should be noted that the oxidation potential in heating stage refers to

(27) ${\left(\frac{P_{H_{2}O}}{P_{H_2}}\right)}_{\mathrm{Heating}},$
and the oxidation potential in holding stage refers to

(28) ${\left(\frac{P_{H_{2}O}}{P_{H_2}}\right)}_{\mathrm{Holding}}.$

(29) The samples of oriented silicon steel products with low iron loss for a low-noise transformer of the above Examples A1-A9 and Comparative Examples B1-B8 were subjected to various tests: iron loss was measured using 500 mm*500 mm single sheet method; and AC magnetostrictive vibration noise was measured on a 100 mm*500 mm silicon steel sheet according to the method of IEC60076-10-1. The obtained performance parameters were listed in Table 3.

(30) Table 3 lists oriented silicon steel products with low iron loss for a low-noise transformer of Examples A1-A9 and Comparative Examples B1-B8.

(31) TABLE-US-00004 TABLE 3 P17/50 AWV1.7 Number (W/kg) (dBA) A1 0.823 56.5 A2 0.865 57.3 A3 0.873 57.8 A4 0.869 58.1 A5 0.885 56.9 A6 0.882 56.1 A7 0.873 58.1 A8 0.888 57.1 A9 0.871 57.9 B1 0.961 59.5 B2 1.006 60.1 B3 1.008 59.4 B4 0.972 61.4 B5 0.978 62.2 B6 0.979 60.3 B7 1.023 60.5 B8 1.001 61.1

(32) It can be seen from Table 3 that the iron loss of silicon steel products of Examples A1-A9 is 1.02 W/kg or less, and the AC magnetostrictive vibration noise is lower than 58.1 dBA. On the other hand, since the chemical component ratios of Comparative Examples B1-B8 are outside the scope defined by the present invention, the overall performance of the iron loss and the AC magnetostrictive vibration noise thereof are inferior to the Examples of the present invention.

(33) Further, in order to examine the influence of technological coefficient A of oxidation potential on magnetic properties, Examples A10-A14 and Comparative Examples B9-B11 were prepared by the following steps:

(34) (1) smelting and casting according to the following chemical composition: Si: 3.25%, C: 0.070%, Mn: 0.12%, S: 0.008%, N: 0.008%, Als: 0.023%, Cu: 0.11%, Sn: 0.09%, Nb: 0.08%, the balance being Fe and other inevitable impurity elements;

(35) (2) hot rolling: the slab was heated to 1150° C. in a heating furnace, and then rolled to a thickness of 2.3 mm;

(36) (3) normalizing: two-stage normalizing were used: in the first stage, the normalizing temperature was 1120° C., and the normalizing time was 15 s; in the second stage, the normalizing temperature was 870° C., and the normalizing time was 150 s; then cooling was carried out at a cooling rate of 20° C./s.

(37) (4) cold rolling: the steel sheet was rolled to a final thickness of 0.27 mm with a total cold rolling reduction ratio of 88.3% by single cold reduction;

(38) (5) decarburization annealing was performed to reduce the carbon content in the silicon steel substrate to 30 ppm and the oxygen content to 2.0 g/m.sup.2; a nitriding treatment was performed before, after or simultaneously with the decarburization annealing to control the nitrogen content in the silicon steel substrate to 200 ppm; wherein, in the heating stage, there was a rapid heating stage in which the initial temperature was 600° C. or less, the final temperature was 700° C. or more, and the heating rate was 80° C./s or more; temperature was heated to 845° C., then holding for 132s; in addition, the difference between oxidation potentials of decarburization annealing protective atmosphere in the heating section stage and oxidation potentials in the holding section stage of decarburization annealing protective atmosphere was controlled.

(39) (6) high temperature annealing: after cleaning the residual magnesium oxide on the surface, the surface of the silicon steel substrate was coated with an annealing separator containing MgO; wherein, the annealing temperature was 1200° C. and the holding time was 20 hr; further, the atmosphere was a nitrogen-hydrogen mixture with a volume percentage of H.sub.2 of 100% and an atmospheric dew point D.P. of −10° C.;

(40) (7) applying an insulation coating: after cleaning, an insulation coating was applied, and the silicon steel substrate was subjected to hot drawing-flattening annealing to obtain a preliminary silicon steel product;

(41) (8) laser scribing: after uncoiling, the steel sheet was cleaned, coated with an insulating coating, and annealed by hot-drawing-flattening; based on visible light normal reflectivity R and the statistical distribution σ thereof, scribing lines parallel to the rolling direction were formed on the surface by continuous laser scanning; wherein, parameters of the laser scribing are as follows: the energy density p of the incident laser is 141 mJ/mm.sup.2, the residence time is 0.005 ms, the length a of the focused spot of laser in rolling direction is 0.045 mm, the spacing d of the scribing lines in rolling direction is 5.0 mm, the incident laser has a wavelength of 1066 nm, a laser scanning speed of 200 m/s, and a laser output power of 1000 W.

(42) (9) sample testing: iron loss was measured using 500 mm*500 mm single sheet method; and AC magnetostrictive vibration noise was measured on a 100 mm*500 mm silicon steel sheet according to the method of IEC60076-10-1. The obtained performance parameters are listed in Table 4.

(43) TABLE-US-00005 TABLE 4 Rapid Oxidation Oxidation heating potential potential rate V.sub.h in heating in holding R P17/50 AWV1.7 Number (° C./s) stage stage A (%) σ (W/kg) (dBA) A10 80 0.271 0.61 1.6 43.2 6.8 0.885 58.9 A11 90 0.42 0.61 0.88 54.1 4.2 0.865 57.9 A12 100 0.51 0.61 0.45 52.2 3.6 0.851 57.5 A13 120 0.61 0.628 0.08 58.2 6.8 0.848 58.8 A14 150 0.56 0.61 0.21 56.7 5.5 0.846 58.5 B9 0.53 0.61 0.38 55.8 5 0.904 61.2 B10 100 0.32 0.68 40.1 0.928 60.1 B11 100 0.595 0.61 0.933 59.8
Wherein, it should be noted that the oxidation potential in heating stage refers to

(44) ${\left(\frac{P_{H_{2}O}}{P_{H_2}}\right)}_{\mathrm{Heating}},$
and the oxidation potential in holding stage refers to

(45) 0${\left(\frac{P_{H_{2}O}}{P_{H_2}}\right)}_{\mathrm{Holding}}.$

(46) It can be seen from Table 4 that the iron loss of silicon steel products of Examples A10-A14 is 1.02 W/kg or less, and the AC magnetostrictive vibration noise is 58.9 dBA or less. On the other hand, the heating rate of Comparative Example B9 is lower than the range defined by the present invention, so that the iron loss of Comparative Example B9 is large, and the AC magnetostrictive vibration noise value is high. Moreover, the process parameters of oxidation potential of Comparative Examples B10-B11 are outside the scope defined by the present invention. Therefore, the magnesium silicate bottom layer of Comparative Example B10-B11 has poor luster uniformity, a high σ value, and the iron loss and the AC magnetostrictive vibration noise thereof are not as good as those in the Examples.

(47) Further, in order to examine the influence of visible light normal reflectivity R and the statistical distribution σ thereof and laser scribing on magnetic properties, Examples A15-A20 and Comparative Examples B12-B19 were prepared by the following steps:

(48) (1) smelting and casting according to the following chemical composition: Si: 3.25%, C: 0.070%, Mn: 0.12%, S: 0.008%, N: 0.008%, Als: 0.023%, Cu: 0.11%, Sn: 0.09%, Nb: 0.10%, the balance being Fe and other inevitable impurity elements;

(49) (2) hot rolling: the slab was heated to 1150° C. in a heating furnace, and then rolled to a thickness of 2.6 mm;

(50) (3) normalizing: two-stage normalizing were used: in the first stage, the normalizing temperature was 1120° C., and the normalizing time was 15 s; in the second stage, the normalizing temperature was 870° C., and the normalizing time was 150s; then cooling was carried out at a cooling rate of 20° C./s.

(51) (4) cold rolling: the steel sheet was rolled to a final thickness of 0.27 mm with a total cold rolling reduction ratio of 89.6% by double cold reduction with intermediate annealing;

(52) (5) decarburization annealing were performed to reduce the carbon content in the silicon steel substrate to 30 ppm and the oxygen content to 2.0 g/m.sup.2; a nitriding treatment was performed before, after or simultaneously with the decarburization annealing to control the nitrogen content in the silicon steel substrate to 190 ppm; wherein, in the heating stage, there was a rapid heating stage in which the initial temperature was 600° C. or less, the final temperature was 700° C. or more, and the heating rate was 100° C./s; temperature was heated to 845° C., then holding for 132 s; and parameters in this step satisfies the following formula:

(53) ${\left(\frac{P_{H_{2}O}}{P_{H_2}}\right)}_{\mathrm{Holding}}-{\left(\frac{P_{H_{2}O}}{P_{H_2}}\right)}_{\mathrm{Heating}}=A.Math.\frac{{\log }_{10}\left(V_h\right)}{100\times \left[\mathrm{Sn}\right]}$

(54) wherein, A is 0.54,

(55) ${\left(\frac{P_{H_{2}O}}{P_{H_2}}\right)}_{\mathrm{Heating}}\mathrm{is}0.36,\mathrm{and}{\left(\frac{P_{H_{2}O}}{P_{H_2}}\right)}_{\mathrm{Holding}}$
is 0.48.

(56) (6) high temperature annealing: after cleaning the residual magnesium oxide on the surface, the surface of the silicon steel substrate was coated with an annealing separator containing MgO; wherein, the annealing temperature was 1200° C. and the holding time was 20 hr; further, the atmosphere was a nitrogen-hydrogen mixture with a volume percentage of H.sub.2 of 100% and an atmospheric dew point (D.P.) of −10° C.;

(57) (7) applying an insulation coating: after cleaning, an insulation coating was applied, and the silicon steel substrate was subjected to hot drawing-flattening annealing to obtain a preliminary silicon steel product;

(58) (8) laser scribing: after uncoiling, the steel sheet was cleaned, coated with an insulating coating, and annealed by hot drawing-flattening; based on visible light normal reflectivity R and the statistical distribution σ thereof, scribing lines parallel to the rolling direction were formed on the surface by continuous laser scanning; wherein, the incident laser has a wavelength of 533 nm, a laser scanning speed of 400 m/s, and a laser output power of 1300 W.

(59) (9) sample testing: iron loss was measured using 500 mm*500 mm single sheet method; and AC magnetostrictive vibration noise was measured on a 100 mm*500 mm silicon steel sheet according to the method of IEC60076-10-1. The obtained performance parameters are listed in Table 5.

(60) TABLE-US-00006 TABLE 5 R p t.sub.dwell a b d p*a*exp P17/50 AWV1.7T No. (%) σ (mJ/mm.sup.2) (ms) (mm) (mm) (mm) (−R/λ.sub.0)/d (W/kg) (dBA) A15 41 3.1 52 0.005 0.08 2 9.5 0.40 0.875 58.9 A16 48.3 3.8 103 0.0013 0.04 0.5 8 0.47 0.862 57.9 A17 59 3 166 0.0013 0.025 0.5 4 0.93 0.873 59.1 A18 59.7 3 197 0.005 0.021 2 2 1.85 0.856 57.4 A19 46.5 4 52 0.005 0.08 2 4.5 0.84 0.861 58.4 A20 52.1 7.4 197 0.0013 0.021 0.5 4.5 0.83 0.864 59.2 B12 2.7 69 0.0013 0.06 0.5 5 0.77 0.899 63.1 B13 3.2 138 0.005 0.03 2 4.5 0.82 0.912 62.6 B14 42.2 103 0.0025 0.04 1 8 0.48 0.873 63.8 B15 43.2 2.3 83 0.05 2.2 5 0.76 0.918 63.9 B16 48.2 2.3 0.0025 0.084 1 4 0.95 0.933 62.8 B17 48.2 2.3 0.0025 0.02 1 2 1.89 0.953 65.3 B18 42.3 2.3 69 0.0025 0.06 1 10 0.900 62.3 B19 40.5 3.1 197 0.0025 0.021 1 1.9 0.930 61

(61) As can be seen from Table 5, in Examples A15-A20, the visible light normal reflectivity R of the magnesium silicate bottom layer is 40˜60%, and the statistical distribution σ thereof is 7.5 or less, indicating that the luster of the magnesium silicate bottom layer is uniform. On the other hand, in Comparative Examples B12 and B13, the visible light normal reflectivity R of the magnesium silicate bottom layer is outside the scope defined by the present invention. Therefore, the iron loss and AC magnetostrictive vibration noise thereof are not as good as those in the Examples. In addition, the statistical distribution σ of Comparative Example B14 is greater than 7.5, indicating that the luster of the magnesium silicate bottom layer is not uniform, thus affecting the iron loss and the AC magnetostrictive vibration noise thereof. In addition, in Comparative Example B15-B19, the process parameters of laser scribing are outside the scope defined by the present invention. Specifically, the residence time of laser on the surface of the product in Comparative Example B15 is more than 0.005 ms; the energy density p of the incident laser of Comparative Example B16-B17 was outside the range defined by the present invention. Therefore, the iron loss and AC magnetostrictive vibration noise thereof are not as good as those in the Examples. In Comparative Example B18-B19, the magnesium silicate bottom layer and the laser scribing lines cannot precisely match, that is, the corresponding value of the formula defined by the present invention is outside the range of 0.4˜2.0. Therefore, the iron loss and AC magnetostrictive vibration noise thereof are not as good as those in the Examples.

(62) Further, in order to examine the influence of laser scribing process on magnetic properties, Examples A21-A26 and Comparative Examples B20-B27 were prepared by the following steps:

(63) (1) smelting and casting according to the following chemical composition: Si: 3.25%, C: 0.070%, Mn: 0.12%, S: 0.008%, N: 0.008%, Als: 0.023%, Cu: 0.11%, Sn: 0.09%, Nb: 0.07%, the balance being Fe and other inevitable impurity elements;

(64) (2) hot rolling: the slab was heated to 1150° C. in a heating furnace, and then rolled to a thickness of 2.3 mm;

(65) (3) normalizing: two-stage normalizing were used: in the first stage, the normalizing temperature was 1120° C., and the normalizing time was 15 s; in the second stage, the normalizing temperature was 870° C., and the normalizing time was 150 s; then cooling was carried out at a cooling rate of 20° C./s.

(66) (4) cold rolling: the steel sheet was rolled to a final thickness of 0.23 mm with a total cold rolling reduction ratio of 90% by a single cold reduction;

(67) (5) decarburization annealing was performed to reduce the carbon content in the silicon steel substrate to 30 ppm and the oxygen content to 2.0 g/m.sup.2; a nitriding treatment was performed before, after or simultaneously with the decarburization annealing to control the nitrogen content in the silicon steel substrate to 180 ppm; wherein, in the heating stage, there was a rapid heating stage in which the initial temperature was 580° C., the final temperature was 720° C., and the heating rate was 102° C./s; temperature was heated to 845° C., then holding for 132 s; and parameters in this step satisfies the following formula:

(68) ${\left(\frac{P_{H_{2}O}}{P_{H_2}}\right)}_{\mathrm{Holding}}-{\left(\frac{P_{H_{2}O}}{P_{H_2}}\right)}_{\mathrm{Heating}}=A.Math.\frac{{\log }_{10}\left(V_h\right)}{100\times \left[\mathrm{Sn}\right]},$
wherein, A is 0.54,

(69) ${\left(\frac{P_{H_{2}O}}{P_{H_2}}\right)}_{\mathrm{Heating}}\mathrm{is}0.36,\mathrm{and}{\left(\frac{P_{H_{2}O}}{P_{H_2}}\right)}_{\mathrm{Holding}}$
is 0.48.

(70) (6) high temperature annealing: after cleaning the residual magnesium oxide on the surface, the surface of the silicon steel substrate was coated with an annealing separator containing MgO; wherein, the annealing temperature was 1200° C. and the holding time was 22 hr; further, the atmosphere was a nitrogen-hydrogen mixture with a volume percentage of H.sub.2 of 100% and an atmospheric dew point D.P. of −10° C.;

(71) (7) applying an insulation coating: after cleaning, an insulation coating was applied, and the silicon steel substrate was subjected to hot drawing-flattening annealing to obtain a preliminary silicon steel product;

(72) (8) laser scribing: after uncoiling, the steel sheet was cleaned, applied with an insulating coating, and annealed by hot drawing-flattening; based on visible light normal reflectivity R and the statistical distribution σ thereof, scribing lines parallel to the rolling direction were formed on the surface by continuous laser scanning; wherein, the incident laser has a wavelength of 533 nm, a laser scanning speed of 350 m/s, and a laser output power of 1000 W.

(73) (9) sample testing: iron loss was measured using 500 mm*500 mm single sheet method; and AC magnetostrictive vibration noise was measured on a 100 mm*500 mm silicon steel sheet according to the method of IEC60076-10-1. The obtained performance parameters are listed in Table 6.

(74) TABLE-US-00007 TABLE 6 R p t.sub.dwell a b d p*a*exp P17/50 AWV1.7T No. (%) σ (mJ/mm.sup.2) (ms) (mm) (mm) (mm) (−R/λ.sub.0)/d (W/kg) (dBA) A21 40.5 3.1 52 0.0029 0.07 1.0 8.5 0.40 0.795 56.6 A22 46.2 2.5 91 0.0023 0.04 0.8 8 0.42 0.782 55.8 A23 58.7 2.6 146 0.0017 0.025 0.6 4 0.81 0.793 57.9 A24 59.5 2.8 173 0.0011 0.021 0.4 2 1.63 0.776 56.7 A25 43.2 3.9 52 0.0029 0.07 1.0 4.5 0.75 0.781 58.2 A26 55.2 7.4 173 0.0011 0.021 0.4 4.5 0.73 0.784 57.5 B20 3.5 61 0.0029 0.06 1.0 5 0.68 0.819 61.6 B21 3.2 121 0.0023 0.03 0.8 4.5 0.72 0.832 60.1 B22 51.2 7.7 91 0.0017 0.04 0.6 8 0.41 0.793 59.2 B23 45.3 2.5 73 0.05 2.0 5 0.67 0.838 60.3 B24 50.2 3.2 0.0029 0.075 1.0 4 0.83 0.853 61.2 B25 52.2 2.6 0.0017 0.018 0.6 2 1.65 0.873 63.5 B26 48.7 4.1 61 0.0013 0.06 0.45 10 0.82 60.6 B27 40.1 4.1 173 0.0009 0.021 0.3 1.6 0.84 61.2

(75) As can be seen from Table 6, in Examples A21-A26, the visible light normal reflectivity R of the magnesium silicate bottom layer is 40˜60%, and the statistical distribution σ is 7.5 or less, indicating that the luster of the magnesium silicate bottom layer is uniform. On the other hand, in Comparative Examples B20 and B21, the visible light normal reflectivity R of the magnesium silicate bottom layer is outside the scope defined by the present invention. Therefore, the iron loss and AC magnetostrictive vibration noise thereof are not as good as those in the Examples. In addition, the statistical distribution σ of Comparative Example B22 is greater than 7.5, indicating that the luster of the magnesium silicate bottom layer is not uniform, thus affecting the iron loss and the AC magnetostrictive vibration noise thereof. In addition, in Comparative Example B23-B27, the process parameters of laser scribing are outside the scope defined by the present invention. Specifically, the residence time of laser on the surface of the product in Comparative Example B23 is more than 0.005 ms; the energy density p of the incident laser of Comparative Example B24-B25 was outside the range defined by the present invention. Therefore, the iron loss and AC magnetostrictive vibration noise thereof are not as good as those in the Examples. In Comparative Example B26-B27, the magnesium silicate bottom layer and the laser scribing lines cannot precisely match, that is, the corresponding value of the formula defined by the present invention is outside the range of 0.4˜2.0. Therefore, the iron loss and AC magnetostrictive vibration noise thereof are not as good as those in the Examples.

(76) FIG. 1 is a time-domain diagram of magnetic flux density and magnetostriction of a silicon steel sheet in the prior art.

(77) As shown in FIG. 1, the solid line indicates the magnetic flux density, and the broken line indicates the magnetostriction. During the magnetization process, the silicon steel sheet vibrates at a frequency that is twice of the frequency of the applied alternating excitation field. Meanwhile, due to the hysteresis effect, the vibration has obvious harmonic characteristics, as shown by the fact that the magnetostriction of the silicon steel sheet has vibration spectrum which is an integral multiple of the fundamental frequency. The basic quantities characterizing the magnitude of magnetostriction are λ0-p and λp-p. λ0-p is the difference between the maximum magnetostriction at the specified external field strength and the magnetostriction in the absence of external field (the silicon steel sheet is in a free state). λp-p represents the difference between the maximum and minimum values of magnetostriction of the silicon steel sheet at the specified external field strength.

(78) The magnetostriction of silicon steel sheet defined by λ0-p and λp-p reflects the amplitude variation of the silicon steel sheet during AC magnetization process, but does not reflect information about the vibration frequency. The frequency of the vibration directly affects the magnitude of the noise. In order to comprehensively measure the vibration noise caused by the magnetostriction of silicon steel sheet, the AWV value at the specified magnetic field strength is used as an evaluation standard in IEC60076-10-1.

(79) $\begin{array}{cc}\mathrm{AWV}=20{\log }_{10}\frac{\rho c\sqrt{\underset{i}{.Math.}{\left[\left(2\pi f_i\right).Math.\left({\lambda }_i/\sqrt{2}\right).Math.{\alpha }_i\right]}^2}}{P_{e0}}& \left(1\right)\end{array}$

(80) wherein, AWV is the calculated value of vibration noise generated by magnetostriction of silicon steel sheet under A-weight; ρ is air density; c is the speed of sound in air; f.sub.i is the harmonic frequency of magnetostriction i times; λ.sub.i is the harmonic amplitude of magnetostriction i times; α.sub.i is the filtering weighting factor at frequency f.sub.i; P.sub.e0 is the reference minimum audible sound pressure, which is 2×10.sup.−5 Pa.

(81) AWV combines the amplitude and waveform of magnetostriction so as to more directly reflect the vibration and noise of silicon steel sheet. The magnetostriction waveform in FIG. 1 is converted into a frequency domain signal by Fourier transform, and the amplitude at each frequency is brought into the formula (1) to obtain the AWV value of the silicon steel sheet.

(82) FIG. 2 is a schematic view showing curve distribution between the visible light normal reflectivity R and the iron loss/magnetic induction of the silicon steel product of the present invention.

(83) As shown in FIG. 2, the magnetic permeability of a silicon steel product is shown as magnetic induction, which is generally represented by B8, that is, the magnetic flux density of the silicon steel product under the excitation magnetic field of 800 A/m, and the dimension of B8 is T. The iron loss of a silicon steel product is generally represented by P17/50, that is, the ineffective electric energy consumed by the magnetization of the silicon steel product when the magnetic flux density in the steel strip reaches 1.7T under an alternating excitation field of 50 Hz, and the dimension of P17/50 is W/kg. In FIG. 2, I represents a range of R of 40˜60% in the technical solutions of the present invention, and II represents a preferred range of R of 45˜55.3%.

(84) FIG. 3 is a schematic view showing curve distribution between the statistical distribution σ of visible light normal reflectivity R in 100 mm.sup.2 of the magnesium silicate bottom layer and the vibration noise of the silicon steel product of the present invention.

(85) As shown in FIG. 3, III shows the distribution of vibration noise when the statistical distribution σ is 7.5 or less (within the technical solutions of the present invention). IV shows the distribution of vibration noise when the statistical distribution σ is 4 or less (within the preferred technical solutions of the present invention).

(86) FIG. 4 is a schematic view showing curve between the statistical distribution σ of different visible light normal reflectivity R and magnetostriction waveform/vibration noise of the silicon steel product of the present invention.

(87) As shown in FIG. 4, the curve with a solid line indicates that the vibration noise is 58.94 dBA when σ is 7.9, and the curve with a broken line indicates that the vibration noise is 57.51 dBA when σ is 4.52.

(88) FIG. 5 is a schematic view showing curve distribution between the technological coefficient A of oxidation potential and the visible light normal reflectivity R/statistical distribution σ of the silicon steel product of the present invention.

(89) As shown in FIG. 5, V indicates that when the technological coefficient of oxidation potential is 0.08˜1.6, a silicon steel product having a visible light normal reflectivity R in the range of 40˜60% and a statistical distribution σ of 7.5 or less can be obtained, wherein, the straight line VI represents a visible light normal reflectivity R of 60%, and the straight line VII represents a statistical distribution σ of 7.5.

(90) FIG. 6 is a schematic view showing curve distribution between the parameters of laser scribing and the vibration noise of the silicon steel product of the present invention.

(91) As shown in FIG. 6, parameters of laser scribing satisfy the following formula:

(92) $0.4\le \frac{p.Math.a.Math.\exp \left(-\frac{R}{{\lambda }_0}\right)}{d}\le 2.0$

(93) in the formula, p is the energy density of the incident laser, in units of mJ/mm.sup.2; a is the length of the focused spot of laser in rolling direction, in units of mm; R is the visible light normal reflectivity of magnesium silicate bottom layer, in units of %; d is the spacing of scribing lines in rolling direction, in units of mm; λ.sub.0 is the wavelength of incident laser, in units of nm.

(94) As can be seen from FIG. 6, VIII indicates that when the laser scribing parameter is in the range of 0.4˜2, a silicon steel product having a vibration noise of less than 60 dBA can be obtained, wherein the straight line IX represents a vibration noise of 60 dBA.

(95) It should be noted that the above are merely illustrative of specific Examples of the invention. It is obvious that the present invention is not limited to the above Examples, but has many similar variations. All modifications that are directly derived or associated by those skilled in the art on the basis of the present application are intended to be within the scope of the present invention.