Directional silicon steel and method for producing the same

Abstract

The present invention provides a grain-oriented silicon steel including a silicon steel substrate and an insulating coating formed on the surface of the silicon steel substrate. The insulating coating does not contain magnesium silicate and / or oxides of magnesium and aluminum. The grain-oriented silicon steel has low iron loss, low magnetic strain, high stacking factor, and high surface coating adhesiveness. The present invention further provides a method for manufacturing the grain-oriented silicon steel. Compared with the prior art, in this method, laser treatment is performed on the silicon steel substrate according to appropriate parameters, the embedded layer and the continuous layer in the silicon steel substrate are removed, and the surface roughness of the silicon steel substrate is adjusted, as a result, a grain-oriented silicon steel having excellent comprehensive properties is obtained. The removal process in this method is precise, controllable, less contaminated, can be automated, and is easy to operate.

Description

Technical Field

[0001] Technical Field The present invention relates to steel and a method for manufacturing the same, and more particularly, to a grain-oriented silicon steel having low loss and low magnetostriction and a method for manufacturing the same.

Background Art

[0002] Background Existing transformer cores are generally made of grain-oriented silicon steel by lamination or coil winding. In the process of manufacturing and applying transformers, the main indicators of concern are two characteristics: no-load loss characteristics and no-load exciting current, which correspond to the loss and magnetizing force of grain-oriented silicon steel, respectively. In recent years, as social demands for environmental noise increase, the noise of transformers also mainly originates from the magnetostriction of grain-oriented silicon steel and has become an important indicator for evaluating the performance of transformers. The main cause of magnetostriction is the change in the number and rotation of 90° magnetic domains perpendicular to the easy magnetization direction parallel to the rolling direction during the magnetization of grain-oriented silicon steel.

[0003] In an ideal state, the finished grain-oriented silicon steel should have only 180° magnetic domains. However, due to defects such as deviation in orientation degree, inclusions, and grain boundaries, in the actual finished grain-oriented silicon steel, in order to reduce its overall magnetostatic energy, small additional magnetic domains - lanceolate domains of 90° magnetic domains naturally appear between the 180° magnetic domains, which leads to the improvement of the magnetostriction of the finished grain-oriented silicon steel. Therefore, by reducing the 90° magnetic domains, the magnetostriction can be effectively reduced.

[0004] Currently, grain-oriented silicon steel is generally prepared by a method including the following steps: a) smelting and casting; b) heating; c) annealing; d) cold rolling; e) decarburization annealing; f) finish annealing; g) hot stretch annealing.

[0005] In the decarburization annealing step e), it is usually necessary to coat the surface of the steel sheet annealed with an annealing separating agent mainly composed of magnesium oxide; in the finish annealing step f), MgO acting as an annealing separating agent reacts with SiO2 formed on the surface of the steel sheet during the decarburization annealing process, and then a bottom layer (also referred to as "primary coating") mainly composed of magnesium silicate (Mg2SiO4) is formed on the surface of the silicon steel substrate. In the hot rolling and annealing step g), after forming the magnesium silicate layer, an insulating coating liquid mainly composed of colloidal silica and phosphate is coated on the surface of the steel sheet and then sintered to form a tension insulation coating (also referred to as "secondary coating").

[0006] The base structure of the grain-oriented silicon steel is shown in FIG. 1, where the magnesium silicate layer formed on the surface of the silicon steel substrate is divided into two parts: a continuous layer 3 formed by the diffusion and concentration of SiO2 on the surface of the silicon steel substrate, and an embedded layer 2 formed by the embedding of oxide particles such as SiO2 and Al2O3 (the precipitates in the silicon steel substrate prevent diffusion to the surface) into the core of the substrate. The main component of the continuous layer 3 is magnesium silicate, and the main components of the embedded layer 2 are magnesium silicate (Mg2SiO4) and a small amount of oxides of magnesium and aluminum (MgAl2O4). The embedded layer 2 is generated during the high-temperature annealing process and has a thermal expansion coefficient smaller than that of the steel. Therefore, a local stress field is generated around the oxide particles in the embedded layer, and as a result, 90° surface closure domains are formed in the silicon steel substrate, which affects the magnetostrictive performance of the resulting finished grain-oriented silicon steel. Furthermore, these oxide particles also have a fixing effect on the movement of 180° magnetic walls in the silicon steel substrate and prevent the magnetic domain rotation of the silicon steel substrate in a changing magnetic field, resulting in an increase in the loss of the finished grain-oriented silicon steel.

[0007] The methods used in the prior art to reduce the losses of grain-oriented silicon steel mainly include the following methods: (1) increasing the degree of orientation of the (110)

[0001] orientation of the finished product to increase the magnetic flux density and thus reduce the hysteresis loss; (2) increasing the Si content in the silicon steel substrate to increase the resistivity or reducing the thickness of the steel sheet to thus reduce the classical eddy current loss; (3) performing laser etching on the grain-oriented silicon steel to reduce the width of the magnetic domain and thus reduce the abnormal eddy current loss.

[0008] The methods used in the prior art to reduce the magnetostriction of grain-oriented silicon steel mainly include the following methods: (1) a method of improving the crystal orientation degree of the finished product; (2) a method of reducing the thickness of the finished product; (3) a method of increasing the tension of the coating. By the above three methods, the magnetostriction of the grain-oriented silicon steel finished product can be reduced, thereby reducing the noise level of the transformer.

[0009] In the prior art, there are already some technical solutions to reduce the influence of the embedded layer on the magnetostriction performance and iron loss performance of the grain-oriented silicon steel finished product by removing the embedded layer.

[0010] For example, Chinese Patent Application CN113272456A (published on August 17, 2021) discloses a method for manufacturing a grain-oriented electromagnetic steel sheet in which the atmosphere in the decarburization annealing process is set to an oxidation degree at which iron-based oxides are not generated, and then the silicon steel substrate is coated with an annealing separating agent containing alumina as the main component in the subsequent process. In this technical solution, by strictly controlling the decarburization dew point, iron-based oxides (such as Fe2SiO4, FeO, etc.) are not formed during the decarburization annealing process, so the purpose of effectively removing the oxide-based inclusions on the surface can be achieved. However, in this method, since aluminum oxide does not react with silica and does not form the bottom layer on the substrate surface, the inhibitor is unstable and easily decomposed during the high-temperature annealing process, the secondary recrystallization is unstable, and the coating characteristics and stability of the obtained grain-oriented silicon steel are poor.

[0011] Chinese Patent Application CN113272454A (published on August 17, 2021) discloses a method for manufacturing a grain-oriented electromagnetic steel sheet. In this method, the residual annealing release agent on the surface of the silicon steel substrate is removed by chemical polishing. As a result, the annealed plate surface has a roughness Ra of 0.1 μm or less, and finally, a grain-oriented silicon steel without a magnesium silicate coating is obtained. However, in this technical solution, due to the use of chemical polishing, it is necessary to solve problems such as equipment settings for controlling the concentration and temperature of the chemical solution. Therefore, from the production perspective, the practicality of this technical solution is low. It is difficult to keep the concentration and temperature of the chemical solution constant during the production of long threads.

[0012] Chinese Patent Application CN113286905A (published on August 20, 2021) discloses a method for manufacturing a grain-oriented electromagnetic steel sheet. In this patent document, as the annealing release agent, at least one of chlorides containing an alkali metal, an alkaline earth metal, or Bi, that is, MCl, is used. By using an annealing release agent containing MCl, a steel sheet on which a magnesium silicate coating is not formed due to the corrosion of MCl in the annealing release agent during the final annealing process can be obtained. However, in this technical solution, since the requirement for atmosphere control in the annealing process of the finished product is high, it is easy to cause the decomposition of inhibitors such as AlN and (Al,Si)N, and secondary recrystallization is unstable. Therefore, it cannot be said to be an ideal manufacturing method.

Summary of the Invention

Means for Solving the Problems

[0013] Summary In order to solve the above technical problems existing in the prior art, on the one hand, the present invention provides a grain-oriented silicon steel, which includes a silicon steel substrate and an insulating coating formed on the surface of the silicon steel substrate. The grain-oriented silicon steel does not contain magnesium silicate (Mg2SiO4) and / or magnesium and aluminum oxides (MgAl2O4). The grain-oriented silicon steel of the present invention has the advantages of low iron loss, low magnetostriction, high stacking factor, and high adhesion of the insulating coating on the surface.

[0014] The "magnesium and aluminum oxides" in the grain-oriented silicon steel of the present invention refers to magnesium aluminum oxide (MgAl2O4) unless otherwise specified.

[0015] Preferably, the silicon steel substrate contains the following chemical elements by mass percentage: C: 0.057~0.062%, Si: 3.12~3.25%, Mn: 0.011~0.020%, acid-soluble Al: 0.026~0.029%, N: 0.008~0.009%, and the balance is Fe and inevitable impurities.

[0016] Preferably, the insulating coating is formed by an insulating coating liquid, and the insulating coating liquid is an aqueous solution containing anhydrous chromic acid, colloidal SiO2, and phosphates of Mg and Al; more preferably, the insulating coating liquid contains the following chemical components by mass percentage: aluminum dihydrogen phosphate and / or magnesium dihydrogen phosphate: 2%~25%, colloidal silica: 4%~16%, anhydrous chromic acid 0.15%~4.50%, and the balance is water and inevitable impurities.

[0017] Preferably, the coating amount of the insulating coating on the silicon steel substrate is 4.0 g / m 2 ~4.5 g / m 2 is.

[0018] Preferably, the grain-oriented silicon steel has a magnetostriction speed-sound pressure level LvA of ≦50 db(A).

[0019] Preferably, the grain-oriented silicon steel has an iron loss P17 / 50 of 0.90 W / Kg or less, preferably 0.80 W / Kg or less.

[0020] Preferably, the grain-oriented silicon steel has an occupancy ratio of ≧97%.

[0021] On the other hand, the present invention also provides a method for manufacturing the above-described grain-oriented silicon steel, which sequentially includes the following steps: 1) A step of smelting and casting molten steel to produce a slab; 2) A step of heating the slab; 3) A step of normalizing; 4) A step of cold rolling to produce a cold-rolled sheet; 5) A step of decarburizing annealing; 6) A step of high-temperature annealing to produce a silicon steel substrate, where the silicon steel substrate has a core, a continuous layer, and an embedded layer between the core and the continuous layer, the embedded layer contains magnesium silicate and / or an oxide of magnesium and aluminum, and the continuous layer contains magnesium silicate; 7) A step of laser processing: Under nitrogen protection, subject the silicon steel substrate to double-sided laser processing to remove the embedded layer and the continuous layer from the silicon steel substrate; and 8) A step of coating with an insulating coating and performing hot stretching annealing to produce a grain-oriented silicon steel.

[0022] Preferably, the total thickness H of the silicon steel substrate after laser processing f satisfies the following: H0 - 2h1 - 2h2 - 2 μm ≦ H f ≦ H0 - 2h1 - 2h2, where H0 represents the initial total thickness of the silicon steel substrate, h1 represents the thickness of the continuous layer, and h2 represents the thickness of the embedded layer; more preferably, H0: 0.19 to 0.29 mm, h1 ≦ 4 μm, h2 ≦ 4 μm.

[0023] Preferably, in step 7): In the laser processing, the energy density I of the laser is 300 to 600 mJ / mm 2and here, the energy density I of the laser is calculated using the following formula:

[0024] [Number]

[0025] where P is the laser output in watts; f is the pulse repetition frequency in kilohertz; and d is the spot diameter in micrometers.

[0026] Preferably, in step 7): in the laser processing, the laser light source uses an infrared laser light source.

[0027] Preferably, in step 7): in the laser processing, the laser uses a nanosecond pulsed laser.

[0028] Preferably, in step 7): in the laser processing, the scanning speed of the laser is 5 to 6 m / s, preferably 5.5 m / s; the laser output P of the laser is 50 to 100 W, preferably 50 to 80 W; the pulse repetition frequency f of the laser is 65 to 90 kHz; and the spot diameter of the laser is 40 to 60 μm.

[0029] Preferably, in step 7): in the laser processing, the double-sided laser processing is performed in two steps, where in the first step, the continuous layer is removed, and the energy density of the laser used in the first step is I1 or more, where

[0030] [Number]

[0031] where h1 represents the thickness of the continuous layer in micrometers; and in the second step, the embedded layer is removed, and the energy density of the laser used in the second step is I2 or more, where

[0032] [Number]

[0033] Here, h2 represents the thickness of the embedded layer in μm; the units of I1 and I2 are mJ / mm 2 is.

[0034] Preferably, in step 7): in laser processing, the energy density of the laser is I2 or more, where

[0035]

Number

[0036] Here, h2 represents the thickness of the embedded layer.

[0037] Preferably, the silicon steel substrate after laser processing has a surface roughness Sa of 6 - 8 μm.

[0038] Preferably, the method for manufacturing the above - mentioned oriented silicon steel satisfies one or more of the following conditions:

[0039] Step 3): In annealing, a two - stage annealing process is adopted: First, the slab is heated to 1100 - 1200 °C, then cooled to 900 - 1000 °C at a cooling rate of 1 °C / second - 10 °C / second, and then further cooled to room temperature at a cooling rate of 10 °C / second - 70 °C / second;

[0040] Step 4): In cold rolling, either one - pass cold rolling or two - pass cold rolling including an intermediate annealing step is adopted;

[0041] Step 5): In decarburization annealing, primary recrystallization annealing is performed at a temperature of 800 - 900 °C, and then an annealing separating agent is coated on the surface of the cold - rolled sheet, where the annealing separating agent is magnesium oxide;

[0042] Step 6): In high - temperature annealing, the annealing temperature is 1100 - 1200 °C, and the holding time is 20 - 30 hours; and

[0043] Step 8): In hot stretch annealing, heat the silicon steel substrate coated with an insulating coating to 800 - 900 °C, hold at that temperature for 10 - 30 seconds, and then cool to room temperature at a cooling rate of 5 °C / s - 50 °C / s to obtain oriented silicon steel.

[0044] Also, in the coating of the insulating coating in Step 8) of the present invention, the insulating coating can be coated on the silicon steel substrate in a manner commonly used in the art, for example, by spraying an insulating coating liquid onto the surface of the silicon steel substrate using a spray method, and then baking and sintering to form an insulating coating on the surface of the silicon steel substrate. Preferably, the insulating coating liquid contains the following chemical components by mass percentage: aluminum dihydrogen phosphate and / or magnesium dihydrogen phosphate: 2% - 25%, colloidal silica: 4% - 16%, anhydrous chromic acid 0.15% - 4.50%, and the balance is water and unavoidable impurities.

[0045] In conclusion, the oriented silicon steel of the present invention does not contain magnesium silicate and / or oxides of magnesium and aluminum, and has good insulating coating adhesion, high stacking factor, low iron loss, and low magnetostriction. Therefore, a transformer core with reduced noise can be fabricated using the above - mentioned oriented silicon steel.

[0046] In the method of the present invention, by performing appropriate laser processing on the silicon steel substrate under nitrogen protection, the embedded layer and continuous layer in the silicon steel substrate are removed, and the surface roughness of the silicon steel substrate is adjusted. As a result, an oriented silicon steel having low iron loss, low magnetostriction, high stacking factor, and excellent adhesion of the surface insulating coating is obtained. In this method, the removal process is precise, controllable, less contaminated, can be automated, and the operation is simple.

Brief Description of the Drawings

[0047]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0048] Detailed Description Definition Surface roughness Sa: It refers to the arithmetic mean height of the surface, which refers to the arithmetic mean or geometric mean of the distance between points within the contour surface and the central plane, and is used to characterize the roughness of the two-dimensional form of the object surface.

[0049] Iron loss P17 / 50: It indicates the iron loss per unit kg of the sample when the magnetic induction intensity is 1.7 T and the frequency is 50 Hz. The iron loss of the grain-oriented silicon steel sample is measured according to the national standard GBT 3655-2008 "Method for Measuring Magnetic Properties of Electrical Steel Sheets and Strips by Epstein Frame".

[0050] Magnetostriction test: According to the IEC technical report IEC / TP 62581, the magnetostriction vibration velocity - sound pressure level of the grain-oriented silicon steel sample is measured at B = 1.7 T using a non-contact laser Doppler vibrometer.

[0051] Occupancy ratio test: The occupancy ratio of the grain-oriented silicon steel sample is measured according to the national standard GBT 19289-2003 "Method for Measuring Density, Resistivity and Occupancy Ratio of Electrical Steel Sheets and Strips".

[0052] In the method of the present invention, by performing appropriate laser processing on the silicon steel substrate under nitrogen protection, the embedded layer and the continuous layer in the silicon steel substrate are removed, and the surface roughness of the silicon steel substrate is adjusted. As a result, a grain-oriented silicon steel with low iron loss, low magnetostriction, high occupancy ratio and excellent adhesiveness of the surface insulation coating is obtained.

[0053] In the manufacturing process of grain-oriented silicon steel in the prior art, it is necessary to coat an annealing release agent such as magnesium oxide on the surface of the silicon steel substrate before high-temperature annealing to prevent the bonding of steel sheets at high temperatures. Therefore, an embedded layer and a continuous layer are formed on the surface of the silicon steel substrate after annealing at high temperature. The occluded oxide particles mainly composed of magnesium silicate (Mg2SiO4) and oxides of magnesium and aluminum (MgAl2O4) in the embedded layer are the main factors affecting the magnetostriction and iron loss of grain-oriented silicon steel.

[0054] As shown in FIG. 1, the embedded layer 2 is disposed between the core 1 of the silicon steel substrate and the continuous layer 3. Therefore, when the embedded layer 2 is removed, the continuous layer 3 also needs to be removed. Compared with the removal methods based on pickling or mechanical methods in the prior art, the laser is very stable, easy to adjust, can be automatically processed, has a simple operation, and its removal process is accurate and controllable, with less pollution and a good removal effect. By removing the embedded layer 2, the fixation of 90° surface closure domains and 180° magnetic wall movement caused by the oxide particles in the embedded layer 2 can be removed.

[0055] In addition, the process of removing the embedded layer in the present invention needs to be carried out in a nitrogen atmosphere, thereby avoiding the formation of an oxide coating on the surface of the silicon steel substrate, and avoiding the influence on the adhesion of the subsequent insulating coating on the surface of the silicon steel substrate. At the same time, the inhibitor (such as AlN) in the high-temperature annealing process can be prevented from being affected by the atmosphere, and as a result, incomplete secondary recrystallization can be avoided. Specifically, fine AIN and other precipitates act as inhibitors, which inhibit the grain boundary migration of primary recrystallized grains in the decarburization annealing process by fixation or segregation, and the primary particles in the (110)

[0001] orientation promote the abnormal growth of secondary recrystallization by engulfing the surrounding particles in other orientations during the high-temperature annealing process. Therefore, the finished product of the oriented silicon steel has a stable and uniform (110)

[0001] structure and good magnetic properties.

[0056] In the technical solution of the present invention, magnetic domain refinement is not carried out. This is because there is no insulating coating on the surface of the silicon steel substrate during laser processing in the present invention, and the laser acts directly on the silicon steel substrate. In this case, the absorption rate of the laser is low, and there is a limit to the improvement of the magnetic properties of the silicon steel. Therefore, the purpose of reducing iron loss by general magnetic domain refinement cannot be achieved.

[0057] The total thickness H of the laser-treated silicon steel sheet substrate of the present invention f satisfies the following: H0 - 2h1 - 2h2 - 2μm ≤ H f ≤ H0 - 2h1 - 2h2. In the present invention, H0 is the thickness of the silicon steel substrate after high-temperature annealing, which is measured by a micrometer; h1 and h2 are measured from the metallographic photograph of the cross-section along the thickness direction of the silicon steel substrate using an optical microscope. h1 is the average thickness of the continuous layer, which is the average value of the thicknesses of the continuous layers in 10 different fields of view. h2 is the average thickness of the embedded layer, which is the average value of the thicknesses of the embedded layers in 10 different fields of view.

[0058] In the present invention, it is necessary to finely control the degree of laser etching on the surface of the silicon steel substrate after high-temperature annealing. It is not only necessary to completely remove the embedded layer 2 and the continuous layer 3, but also to avoid excessive defects in the core structure. Specifically, in the present invention, while ensuring that the etching depth of the core 1 is within 2 μm, it is desirable to completely remove the embedded layer.

[0059] Generally, the thickness H0 of the silicon steel substrate after high-temperature annealing is 0.19 - 0.29 mm, the thickness h1 of the continuous layer is ≤ 4 μm, and the thickness h2 of the embedded layer is ≤ 4 μm.

[0060] In the laser processing step of the present invention, the energy density I of the laser is 300 - 600 mJ / mm 2 and the energy density I of the laser is calculated by the following formula:

[0061]

Equation

[0062] Here, P is the laser output in units of W; f is the pulse repetition frequency in units of kHz; and d is the spot diameter in units of μm.

[0063] Specifically, in the process of performing laser etching on the silicon steel substrate after high-temperature annealing by using a double-sided laser, first, in the first region of the silicon steel substrate, the laser energy density I is adjusted. In this process, the laser output P, the pulse repetition frequency f, and the spot diameter d can be continuously changed, and multiple laser etching operations are performed until the laser energy density I is determined, where the embedded layer can be completely removed and the etching depth of the core of the silicon steel substrate is within 2 μm. Next, the second region of the silicon steel substrate is etched with the determined energy density I, where the second region is the region other than the first region in the silicon steel substrate.

[0064] As shown in Fig. 2, when the energy density of the laser is in the range of 300 to 600 mJ / mm 2 , the embedded layer and the continuous layer on the surface of the silicon steel substrate can be effectively removed without excessive loss of the core structure of the substrate. Since the thickness of the embedded layer is usually 4 μm or less, the energy density of the laser is usually 600 mJ / mm 2 or less. When the energy density of the laser exceeds 600 mJ / mm 2 , not only energy saving is not achieved, but also the substrate is excessively removed; on the other hand, even if the thickness of the embedded layer is very thin, in order to ensure that the embedded layer is completely removed, the energy density of the laser needs to be selected to be 300 mJ / mm 2 or more.

[0065] Since the main components of the embedded layer and the continuous layer are both magnesium silicate, in the laser processing of the present invention, the laser light source is preferably an infrared laser light source with a high absorption rate and a low reflectance for magnesium silicate, for example, an infrared laser light source with a wavelength of 1064 nm.

[0066] Preferably, a nanosecond pulsed laser is used to remove the embedded layer and the continuous layer in order to achieve a high single-pulse instantaneous peak output density.

[0067] As a result of repeated experiments and analyses, the inventor has found that the laser energy density required to remove the continuous layer and the embedded layer can be determined by the thickness h1 of the continuous layer and the thickness h2 of the embedded layer.

[0068] Specifically, Fig. 2 shows the relationship between the thicknesses of the continuous layer and the embedded layer and the required energy density of the pulsed laser when laser processing is performed in two steps under nitrogen protection. When the continuous layer is removed in the first step, the energy density of the laser is I1 or more, where

[0069]

Equation

[0070] Here, h1 represents the thickness of the continuous layer; when the embedded layer is removed in the second stage, the energy density of the laser is I2 or more, where

[0071]

Number

[0072] Here, h2 represents the thickness of the embedded layer.

[0073] In the first stage of removing the continuous layer, since the continuous layer (magnesium silicate layer) is an opaque oxide layer, the removal mechanism is an ablation removal mechanism: continuously irradiating pulses on the silicon steel substrate using a laser with an energy density of I1, and increasing the surface temperature of the continuous layer due to the heat accumulation of the pulses, thereby changing the form and properties of the continuous layer, and separating the continuous layer from the silicon steel substrate.

[0074] In the second stage of removing the embedded layer, when the laser energy density exceeds the complete removal threshold of the continuous layer, the pulsed laser irradiates the embedded layer, and the temperature of the oxide particles in the embedded layer rises rapidly after absorbing the laser energy, resulting in a series of physical effects such as bulk, gasification, thermal shock, thermal vibration, and fragmentation of acoustic shock. Finally, the embedded layer (mainly the oxide particles in the embedded layer) is separated from the core, thereby achieving the removal of the embedded layer.

[0075] Since the laser energy density required for removing the embedded layer is higher than the laser energy density required for removing the continuous layer, it is not necessary to remove the continuous layer and the embedded layer in two steps respectively. In practice, the value of I2 can be calculated according to the thickness of the embedded layer, and then a laser energy density with a value of I2 or more can be selected to remove the continuous layer and the embedded layer together.

[0076] To achieve complete removal of the embedded layer, it should be noted that I2 also needs to be in the range of 300 - 600 mJ / mm 2 Preferably, I2 is set to a value that can achieve the purpose of low noise when the transformer core made of grain-oriented silicon steel operates.

[0077] The surface roughness Sa of the silicon steel substrate determines the adhesion of the insulating coating on the silicon steel substrate and the stacking factor of the grain-oriented silicon steel finished product. The smaller the surface roughness, the worse the adhesion of the insulating coating; the larger the surface roughness, the better the adhesion of the insulating coating, but the thickness of the insulating coating also increases, and as a result, the stacking factor of the grain-oriented silicon steel finished product decreases. Therefore, it is necessary to control the surface roughness of the silicon steel substrate within an appropriate range. In the present invention, the surface roughness Sa of the silicon steel substrate is preferably in the range of 6 - 8 μm. Under the condition of this surface roughness, the insulating coating can be firmly attached to the surface of the silicon steel substrate, and the stacking factor of the grain-oriented silicon steel can be 97% or more.

[0078] The surface roughness Sa of the silicon steel substrate is mainly affected by the laser output, scanning speed, and repetition frequency.

[0079] After laser processing, a grooved "wavy" morphology remains on the substrate surface at equal intervals. The "valleys" of the waves in the laser-treated surface micro-region are determined by the width and depth of the grooves, and the "peaks" of the waves in the surface micro-region are determined by the molten dendrite structure at the spot overlap part. The unevenness between the "valleys" and "peaks" of the waves directly affects the value of the surface roughness Sa in the micro-region.

[0080] The laser output P has the most significant influence on the surface roughness. When the laser output increases, the width and depth of the grooves increase, and the value of the surface roughness Sa increases. In the present invention, the laser output P is preferably in the range of 50 - 100 W, and more preferably in the range of 50 - 80 W.

[0081] The surface roughness Sa of the silicon steel substrate is also affected by the scanning speed of the laser. In the present invention, the scanning speed of the laser is preferably in the range of 5 to 6 m / s, and more preferably 5.5 m / s. When the scanning speed of the laser is higher than 6 m / s, the value of the "wave crest" at the spot overlapping part becomes high, and as a result, the surface roughness Sa becomes too high. When the scanning speed of the laser is less than 5 m / s, the thermal influence caused by the overlapping of the spots increases, and the groove depth further increases, that is, the value of the "wave trough" becomes deep, and as a result, the surface roughness Sa becomes too high.

[0082] Furthermore, the repetition frequency f of the laser also affects the surface roughness Sa of the silicon steel substrate. In the present invention, the repetition frequency f of the laser is preferably 65 to 90 kHz. When the laser output is constant and the repetition frequency f is less than 65 kHz, the energy density of a single pulse increases, and the width and depth of the groove further increase, and as a result, the value of the surface roughness Sa becomes too high. When the repetition frequency f is greater than 90 kHz, the energy density of a single pulse decreases, it is necessary to reduce the scanning speed, the thermal influence caused by the overlapping of the spots increases, and the depth of the groove increases, that is, the value of the "wave trough" becomes deep, and as a result, the value of the surface roughness Sa becomes too high.

[0083] The insulating coating is used to improve the insulating properties of the surface of the silicon steel substrate. The insulating coating liquid widely used in the prior art is mainly an aqueous solution containing anhydrous chromic acid, colloidal SiO2, and phosphates of Mg and Al. After the insulating coating liquid is sintered, a transparent insulating coating is formed on the surface of the silicon steel substrate.

[0084] If the thickness of the insulating coating is too thin, the tension applied to the substrate by the insulating coating becomes small, and magnetic optimization becomes insufficient. If the thickness of the insulating coating is too thick, the occupation ratio of the finished product is affected, and defects such as powder falling and white edges in the shearing process are likely to occur. In the present invention, the coating amount of the insulating coating on the silicon steel substrate is preferably 4.0 to 4.5 g / m 2 is preferred.

[0085] In the description of an embodiment of the present application, terms such as "first" and "second" are used only for distinguishing the description and are not to be understood as indicating or implying relative importance.

[0086] Also, unless explicitly specified and limited, the terms "arrange", "connected", and "connect" should be understood in a broad sense. For example, it can be understood as a direct connection, or an indirect connection implemented through an intermediary, or internal communication between two components. It should be noted that those skilled in the art can understand the specific meaning of the above terms in an embodiment of the present application according to specific situations.

[0087] To make the objectives, technical solutions, and advantages of the present invention clearer, an embodiment of the present invention will be described in more detail below with reference to the accompanying drawings.

[0088] Examples 1 to 6 and Comparative Examples 1 to 15 The oriented silicon steel of Examples 1 to 6 was produced by sequentially performing the following steps: 1) Melting and casting step: According to the formulation shown in Table 1, molten steel was melted and cast to produce a slab; 2) Slab heating step: The slab was heated to 1200 to 1280 °C and held at that temperature for 1 to 4 hours, and then hot-rolled; 3) Annealing process: A two-stage annealing treatment was used. First, the slab was heated to 1100 - 1200 °C, then cooled to 900 - 1000 °C at a cooling rate of 1 °C / s - 10 °C / s, and then cooled to room temperature at a cooling rate of 10 °C / s - 70 °C / s; 4) Cold rolling process: Cold rolled sheets were manufactured using one cold rolling or two cold rollings including an intermediate annealing process; 5) Decarburization annealing process: Primary recrystallization annealing was performed at a temperature of 800 - 900 °C, and then an annealing release agent was coated on the surface of the cold rolled sheet; 6) High-temperature annealing process: The annealing temperature was 1100 - 1200 °C, and the holding time was 20 - 30 hours; 7) Laser processing process: The silicon steel substrate was subjected to double-sided laser processing using a nanosecond pulsed laser under nitrogen protection to remove the embedded layer and the continuous layer from the silicon steel substrate, and the laser processing conditions are shown in Table 4; 8) Coating with an insulating coating and then hot stretching annealing process: An insulating coating liquid was coated on the surface of the silicon steel substrate, baked, and sintered to form an insulating coating on the surface of the silicon steel substrate; then the silicon steel substrate coated with the insulating coating was heated to 800 - 900 °C, held at that temperature for 10 - 30 seconds, and then cooled to room temperature at a cooling rate of 5 °C / s - 50 °C / s to obtain a grain-oriented silicon steel.

[0089] The grain-oriented silicon steels in Comparative Examples 1 - 15 were prepared basically in the same manner as above, except that in Comparative Examples 1, 6, and 11, the laser processing of the present invention was not used, and in other comparative examples, the energy density of the laser processing was not adjusted according to the thickness of the continuous layer and the embedded layer, and / or the surface roughness Sa of the laser-treated silicon steel substrate was not controlled.

[0090] Table 1 shows the chemical compositions other than Fe and inevitable impurities of the silicon steel substrate and the thickness H (including the total thickness of the silicon steel substrate and the insulating coating on its surface) of the finished grain-oriented silicon steels in Examples 1 - 6 and Comparative Examples 1 - 15 of the present invention.

[0091]

Table 1

[0092] In Examples 1 to 6 and Comparative Examples 1 to 15 of the present invention, the insulating coating liquid coated on the surface of the silicon steel substrate contains the following chemical components by mass percentage: aluminum dihydrogen phosphate and / or magnesium dihydrogen phosphate: 2% to 25%, colloidal silica: 4% to 16%, chromic anhydride 0.15% to 4.50%, and the balance is water and inevitable impurities.

[0093] Table 2 shows the chemical composition of the insulating coating liquid coated on the surface of the silicon steel substrate in Examples 1 to 6 and Comparative Examples 1 to 15 of the present invention.

[0094]

Table 2

[0095] Table 3 shows the specific parameters of the manufacturing process of the oriented silicon steel in Examples 1 to 6 and Comparative Examples 1 to 15 of the present invention.

[0096]

Table 3

[0097] In Examples 1 to 6 and Comparative Examples 1 to 15 of the present invention, the thicknesses of the continuous layer and the embedded layer in the silicon steel substrate after high-temperature annealing, the laser output, the repetition frequency, the scanning speed, and the spot diameter used in the laser processing process, the theoretical required laser energy density I2 and the actually used laser energy density I for removing the embedded layer, and the surface roughness Sa after laser processing are shown in Table 4.

[0098]

Table 4

[0099] The grain-oriented silicon steels prepared in Examples 1 to 6 and Comparative Examples 1 to 15 were each sampled, and the magnetostrictive performance (magnetostriction velocity - sound pressure level LvA) of the grain-oriented silicon steel samples in the examples and comparative examples was measured at B = 1.7 T and f = -2 MPa (in the actual use conditions of the transformer, the grain-oriented silicon steel is subjected to a compressive stress of 2 to 3 MPa) using a non-contact laser Doppler vibrometer (TD9600). Specific measurement methods can be found in the technical report of the International Electrotechnical Commission (IEC) - IEC / TP 62581.

[0100] Test sheets of 300 mm × 30 mm were cut out from the grain-oriented silicon steel samples on which an insulating coating was formed in Examples 1 to 6 and Comparative Examples 1 to 15. This sample was tightly wound around a brass cylinder with a diameter of 20 mm, gradually bent 180°, and then flattened. Subsequently, the peeled area of the coating on the inner surface of the sample without cracks was measured, and the residual area ratio (%) of the insulating coating was calculated.

[0101] The adhesion of the insulating coating was evaluated in three grades: "◎" means that the residual area ratio of the insulating coating was 100%. "〇" means that the residual area ratio of the insulating coating was 90% or more. "×" means that the residual area ratio of the insulating coating was less than 90%.

[0102] Iron loss P17 / 50 (representing the iron loss per kilogram of the sample when the magnetic induction intensity is 1.7 T and the frequency is 50 Hz): The iron losses of the grain-oriented silicon steels in Examples 1 to 6 and Comparative Examples 1 to 15 were determined using the national standard GBT 3655-2008 "Method for Measuring Magnetic Properties of Electromagnetic Steel Sheets and Strip by Epstein Frame".

[0103] Occupancy ratio: The occupancy ratio was measured using the national standard GBT 19289-2003 "Method for Measuring Density, Resistivity and Occupancy Ratio of Electromagnetic Steel Sheets and Strip".

[0104] Table 5 shows the performance test results of the grain-oriented silicon steel in Examples 1 to 6 and Comparative Examples 1 to 15.

[0105]

Table 5

[0106] As shown in Table 5, compared with Comparative Examples 1 to 15, the comprehensive performance including iron loss, magnetostriction, occupancy ratio, and adhesiveness of each example of the present invention is superior to the comprehensive performance of Comparative Examples 1 to 15.

[0107] As shown in Table 5, in Comparative Examples 1, 6, and 11 where the grain-oriented silicon steel was not subjected to laser treatment, the adhesiveness was good, but the occupancy ratio was less than 97%, and both the iron loss and magnetostriction were poor.

[0108] In Comparative Examples 2, 7, and 12, the grain-oriented silicon steel was treated with a laser, but the energy density of the laser used was low. Therefore, only the continuous layer was removed, and the embedded layer was not removed. As a result, the above problems caused by the presence of the embedded layer in the grain-oriented silicon steel cannot be solved. The obtained grain-oriented silicon steel is inferior in iron loss, magnetostriction, and adhesiveness of the insulating coating.

[0109] In Comparative Examples 3, 8, and 13, the grain-oriented silicon steel was treated with a laser, but the output and energy density of the laser processing were too high. Therefore, not only the embedded layer was removed, but also the core of the substrate was largely removed. Therefore, in the obtained grain-oriented silicon steel, the iron loss and magnetostriction are relatively low, but the occupancy ratio and coating adhesiveness are relatively poor.

[0110] In Comparative Examples 4, 9, and 14, the grain-oriented silicon steel was treated with a laser, and the energy density of the laser used was appropriate, but the output of the laser used was too low. Therefore, although the embedded layer was completely removed, the surface roughness Sa of the substrate was too low, which caused the adhesiveness of the insulating coating to deteriorate significantly.

[0111] In Comparative Examples 5, 10, and 15, the oriented silicon steel was laser-treated, and the energy density of the laser used was appropriate, but the output of the laser used was too high. Therefore, although the embedded layer was completely removed, the surface roughness Sa of the substrate was too high, which caused a significant decrease in the occupancy rate.

[0112] In summary, in the present invention, by controlling the parameters of laser processing, the continuous layer and the embedded layer in the silicon steel substrate are removed, and by detecting the surface roughness of the silicon steel substrate after laser processing, the adhesiveness and occupancy rate of the insulating coating are improved, and thus an oriented silicon steel having low loss, low magnetostriction, high occupancy rate, and high adhesiveness of the insulating coating can be obtained.

[0113] It should be noted that all the technical features described in this application can be freely combined or joined in any way as long as they do not conflict with each other. It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the scope of the present invention. For example, the features described or illustrated as part of one embodiment can be used in combination with another embodiment to obtain still another embodiment. Therefore, the present invention is intended to cover such modifications and variations that fall within the scope of the appended claims and their equivalents.

Claims

1. A grain-oriented silicon steel, comprising: a silicon steel substrate, and an insulating coating formed on the surface of the silicon steel substrate, wherein the grain-oriented silicon steel does not contain magnesium silicate and / or oxides of magnesium and aluminum.

2. The grain-oriented silicon steel according to Claim 1, wherein the silicon steel substrate contains the following chemical elements in mass percentage: C: 0.057 to 0.062%, Si: 3.12 to 3.25%, Mn: 0.011 to 0.020%, acid-soluble Al: 0.026 to 0.029%, N: 0.008 to 0.009%, and the balance is Fe and inevitable impurities.

3. The insulating coating is formed by an insulating coating solution, and the insulating coating solution is an aqueous solution containing chromic anhydride, colloidal silica SiO 2 , and phosphates of Mg and Al; preferably, the insulating coating solution contains the following chemical components by mass percentage: aluminum dihydrogen phosphate and / or magnesium dihydrogen phosphate: 2% to 25%, colloidal silica: 4% to 16%, chromic anhydride 0.15% to 4.50%, and the balance is water and unavoidable impurities; preferably, the coating amount of the insulating coating on the silicon steel substrate is 4.0 g / m 2 to 4.5 g / m 2 , The grain-oriented silicon steel according to claim 1.

4. The grain-oriented silicon steel according to any one of Claims 1 to 3, wherein the grain-oriented silicon steel has a magnetostriction velocity - sound pressure level LvA of ≤ 50 dB(A).

5. The grain-oriented silicon steel according to any one of Claims 1 to 3, wherein the grain-oriented silicon steel has an iron loss P17 / 50 of 0.90 W / Kg or less, preferably 0.80 W / Kg or less.

6. The grain-oriented silicon steel according to any one of Claims 1 to 3, wherein the grain-oriented silicon steel has an occupancy rate of ≥ 97%.

7. A method for manufacturing the grain-oriented silicon steel according to any one of Claims 1 to 6, comprising the following steps in sequence: 1) A step of smelting and casting molten steel to produce a slab; 2) A step of heating the slab; 3) A step of normalizing; 4) A step of cold rolling to produce a cold-rolled sheet; 5) A step of decarburizing annealing; 6) A step of high-temperature annealing to produce a silicon steel substrate, wherein the silicon steel substrate has a core, a continuous layer, and an embedded layer between the core and the continuous layer, and wherein the embedded layer contains magnesium silicate and / or oxides of magnesium and aluminum, and the continuous layer contains magnesium silicate; 7) A step of laser processing: subjecting the silicon steel substrate to double-sided laser processing under nitrogen protection to remove the embedded layer and the continuous layer from the silicon steel substrate; and 8) A step of coating with an insulating coating and performing hot tensile annealing to obtain a grain-oriented silicon steel.

8. Total thickness H of the silicon steel substrate after laser processing f The method according to claim 7, wherein H 0 -2h 1 -2h 2 -2 μm ≤ H f ≤ H 0 -2h 1 -2h 2 wherein H 0 represents the initial total thickness of the silicon steel substrate, h 1 represents the thickness of the continuous layer, and h 2 represents the thickness of the embedded layer.

9. H 0 : 0.19 to 0.29 mm, h 1 ≤ 4 μm, h 2 ≤ 4 μm, the method according to claim 8

10. Step 7): In laser processing, the energy density I of the laser is 300 to 600 mJ / mm 2 wherein the energy density I of the laser is calculated using the following formula, the method according to claim 8: 【Number 1】 Here, P is the laser output in unit W; f is the pulse repetition frequency in unit kHz; d is the spot diameter in unit μm.

11. Step 7): In laser processing, the laser scanning speed is 5 to 6 m / s, preferably 5.5 m / s; the laser output P is 50 to 100 W, preferably 50 to 80 W; the pulse repetition frequency f is 65 to 90 kHz; and the spot diameter is 40 to 60 μm, the method according to claim 10.

12. Step 7): In laser processing, double-sided laser processing is performed in two steps, where in the first step, a continuous layer is removed and the energy density of the laser used in the first step is I 1 or higher, where 【Number 2】 Here, h 1 represents the thickness of the continuous layer; and in the second stage, the embedded layer is removed, and the energy density of the laser used in the second stage is I 2 or more, where [Number 3] Here, h 2 is the method according to claim 10, representing the thickness of the embedding layer.

13. Step 7): In laser processing, the energy density I of the laser is I 2 or higher, where 【Number 4】 Here, h 2 is the method according to claim 10, representing the thickness of the embedding layer.

14. The method according to any one of claims 7 to 13, wherein the silicon steel substrate after laser processing has a surface roughness Sa of 6 to 8 μm.

15. The method according to any one of claims 7 to 13, satisfying one or more of the following conditions: Step 3): In normalizing, a two-stage normalizing process is employed: First, the slab is heated to 1100 to 1200 °C, then cooled to 900 to 1000 °C at a cooling rate of 1 °C / second to 10 °C / second, and then further cooled to room temperature at a cooling rate of 10 °C / second to 70 °C / second; Step 4): In cold rolling, either single cold rolling or double cold rolling including an intermediate annealing process is employed; Step 5): In decarburization annealing, primary recrystallization annealing is performed at a temperature of 800 to 900 °C, and then an annealing separator is coated on the surface of the cold-rolled sheet, where the annealing separator is magnesium oxide; Step 6): In high-temperature annealing, the annealing temperature is 1100 to 1200 °C, and the holding time is 20 to 30 hours; and Step 8): In hot stretch annealing, the silicon steel substrate coated with an insulating coating is heated to a temperature of 800 to 900 °C, held at that temperature for 10 to 30 seconds, and then cooled to room temperature at a cooling rate of 5 °C / s to 50 °C / s to obtain a grain-oriented silicon steel.

16. The method according to any one of claims 7 to 13, wherein the insulating coating is formed by an insulating coating liquid, and the insulating coating liquid contains the following chemical components by mass percentage: aluminum dihydrogen phosphate and / or magnesium dihydrogen phosphate: 2% to 25%, colloidal silica: 4% to 16%, anhydrous chromic acid: 0.15% to 4.50%, and the balance is water and unavoidable impurities.

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