An ultrathin oriented silicon steel strip and a method for manufacturing the same

Abstract

The application discloses an ultrathin oriented silicon steel strip and a preparation method thereof, and belongs to the technical field of ultrathin oriented silicon steel, and overcomes the defects of long preparation process and complex process of the ultrathin oriented silicon steel strip with low loss. The preparation method of the ultrathin oriented silicon steel strip comprises the following steps: step 1, selecting an oriented silicon steel strip with a grain size of 1.0-2.0 cm and an isometricity of 0.8-1.2 as a raw material; step 2, performing two-pass rolling on the raw material to obtain a cold-rolled ultrathin strip; the total reduction of the two-pass rolling is 70%-85%, and the reduction ratio of the first-pass rolling to the second-pass rolling is 7.5:2.5-9.0:1.0; and step 3, annealing the cold-rolled ultrathin strip; the annealing temperature is 800-880 DEG C, the annealing time is 5-20 min, the annealing atmosphere is high-purity hydrogen, the unit cross-sectional area front tension is 0.15-0.5 kg / mm 2 , and the unit cross-sectional area back tension is 0.15-0.3 kg / mm 2 . The preparation method has a simple process flow, and the prepared ultrathin oriented silicon steel strip has low medium-frequency loss, high magnetic induction and low magnetostriction noise.

Description

Technical Field

[0001] This invention belongs to the field of ultra-thin oriented silicon steel technology, specifically relating to an ultra-thin oriented silicon steel strip and its preparation method. Background Technology

[0002] Ultra-thin grain-oriented silicon steel refers to iron-silicon alloy strips with a thickness of ≤0.1mm. It exhibits excellent magnetic properties along the rolling direction and is primarily used in the manufacture of cores for electrical equipment such as anode saturated reactors and intermediate frequency transformers at intermediate frequencies of ≥400Hz. High-end electrical equipment such as anode saturated reactors and intermediate frequency transformers require low losses, small size, light weight, and high adaptability to service environments. Therefore, ultra-thin grain-oriented silicon steel, as the core material, needs to possess characteristics such as low intermediate frequency losses, high magnetic flux density, and low magnetostrictive noise.

[0003] Chinese patent CN104438325A discloses a method for preparing ultra-thin silicon steel sheets, which involves rolling strips with a width of 130-160 mm in four passes. This method involves many rolling passes, and the rolling process is complex, lengthy, and inefficient.

[0004] Chinese patent CN104726669A discloses a method for preparing ultra-thin grained silicon steel strip for low-iron-loss medium-frequency applications, including pickling to remove the bottom layer, cold rolling, coating with a release agent, bell-type furnace annealing, stretching and leveling annealing, and coating with an insulating film. This method has a long process flow. Pickling to remove the bottom layer is required before rolling, and a release agent needs to be coated before annealing. The bell-type furnace annealing process has a long annealing time and complex control of annealing process parameters.

[0005] Chinese patent CN104831038B discloses a manufacturing process for ultra-thin oriented silicon steel strip. This method adopts a technical route of two-stage cold rolling + intermediate annealing. The process is also long, and the coordination requirements between the first and second cold rolling processes are high.

[0006] Chinese patent CN111485089A discloses a method for preparing ultrathin oriented silicon steel. The ultrathin oriented silicon steel prepared by this method has poor magnetic properties, with the lowest intermediate frequency loss being 12.1W / kg and the magnetic induction B800 being only 1.75T, making it unsuitable for use in the field of high-end electrical equipment.

[0007] Chinese patent CN116240348A discloses a method and product for producing ultra-thin high-magnetic-induction oriented silicon steel through secondary rolling. This method uses conventional oriented silicon steel preparation technology with a thickness of 0.18mm-0.35mm, requires design from the initial composition, and uses technologies such as secondary rolling and laser marking. The process is complex and the process flow is long. The magnetic properties of the product are more for the power frequency of 50Hz, while the magnetic properties under the medium frequency condition of ≥400Hz are unknown.

[0008] Chinese patent CN115896596A discloses an ultra-thin grain-oriented silicon steel and its preparation method. This method also employs conventional grain-oriented silicon steel preparation technology, including processes such as smelting, hot rolling, normalizing, cold rolling, and high-temperature annealing, which are lengthy. Furthermore, this method adds rare earth elements during the smelting process, significantly increasing costs and making it unsuitable for the industrial production of ultra-thin grain-oriented silicon steel.

[0009] Chinese patent CN115747445A discloses an ultra-thin cold-rolled grain-oriented silicon steel and its preparation method, proposing a grid stress scoring technique. Scoring techniques are usually used for conventional thickness grain-oriented silicon steel because its coarse grain structure leads to high hysteresis loss. After scoring treatment, the loss can be significantly reduced. However, ultra-thin grain-oriented silicon steel is thin (≤0.1mm), and the control requirements for scoring techniques are very high. It is difficult to control the scoring depth, and it is difficult to guarantee the smoothness, flatness, stacking coefficient, and surface quality of the strip after scoring.

[0010] The paper "Effects of pre-annealing and rolling condition on magnetic property of thin-gauged 3% Si-Fe sheet" describes a method for preparing 0.1 mm thick ultrathin oriented silicon steel. This method involves preheating a 2.5 mm thick hot-rolled sheet before cold rolling it three times. Preheating is difficult to control in actual production, and it is impossible to preheat the hot-rolled strip coil during the rolling process. This method can only be used for laboratory research.

[0011] European Patent EP 0374948A2 discloses an ultra-thin electrical steel strip with low loss and high magnetic flux density and its production method. The method adopts a preparation technology similar to that of conventional oriented silicon steel, which requires smelting, hot rolling, cold rolling, decarburization annealing, coating with release agent, high temperature annealing and other processes. The preparation process is long and complex. Summary of the Invention

[0012] Therefore, the present invention provides an ultrathin oriented silicon steel strip and its preparation method. The preparation method of the ultrathin oriented silicon steel strip of the present invention is simple to operate, has a short process flow, and high production efficiency; the obtained ultrathin oriented silicon steel strip has low medium frequency loss, high magnetic induction, and low magnetostriction noise.

[0013] To this end, the present invention provides the following technical solution.

[0014] In a first aspect, the present invention provides a method for preparing ultrathin oriented silicon steel strip, comprising the following steps:

[0015] Step 1: Select grain-oriented silicon steel strip with a grain size of 1.0 to 2.0 cm and an equiaxation of 0.8 to 1.2 as raw material;

[0016] Step 2: The raw material is rolled in two passes to obtain a cold-rolled ultrathin strip.

[0017] The total reduction rate of the two-pass rolling is 70% to 85%, and the ratio of the reduction rate of the first pass rolling to the second pass rolling is 7.5:2.5 to 9.0:1.0.

[0018] Step 3: Anneal the cold-rolled ultrathin strip;

[0019] Annealing temperature: 800–880℃; annealing time: 5–20 min; annealing atmosphere: high-purity hydrogen; pre-tension per unit cross-sectional area: 0.15–0.5 kg / mm. 2 The tensile strength per unit cross-sectional area is 0.15–0.3 kg / mm². 2 High-purity hydrogen refers to hydrogen gas with a purity of 99.999%.

[0020] Furthermore, the total rolling force for the first rolling pass is 50-100T, the initial tension is 35-55kN, and the subsequent tension is 25-35kN.

[0021] Furthermore, the total rolling force for the second rolling pass is 15–45T, the front tension is 20–40KN, and the back tension is 20–30KN.

[0022] Furthermore, the raw material is oriented silicon steel strip without a magnesium silicate underlayer.

[0023] Furthermore, the width of the raw material is 350–550 mm.

[0024] Furthermore, it also includes step 4, applying an insulating coating.

[0025] Furthermore, the insulating coating is composed of a coating that can withstand high temperatures above 750°C.

[0026] Furthermore, the thickness of the insulating coating is 0.8-1.5μm.

[0027] Secondly, the present invention also discloses an ultrathin oriented silicon steel strip prepared according to the above method.

[0028] The technical solution of this invention has the following advantages:

[0029] 1. The preparation method of ultra-thin oriented silicon steel strip provided by the present invention includes the following steps: Step 1, selecting oriented silicon steel strip with a grain size of 1.0-2.0 cm and an equiaxation of 0.8-1.2 as raw material; Step 2, subjecting the raw material to two-pass rolling to obtain cold-rolled ultra-thin strip; the total reduction rate of the two-pass rolling is 70%-85%, and the reduction rate ratio of the first pass rolling to the second pass rolling is 7.5:2.5-9.0:1.0; Step 3, annealing the cold-rolled ultra-thin strip; the annealing temperature is 800-880℃, the annealing time is 5-20 min, the annealing atmosphere is high-purity hydrogen, and the pre-tension per unit cross-sectional area is 0.15-0.5 kg / mm. 2 The tensile strength per unit cross-sectional area is 0.15–0.3 kg / mm². 2 .

[0030] Conventional grain-oriented silicon steel has a coarse microstructure with grain sizes ranging from 3 to 10 cm. The strip is brittle and hard, making two-pass rolling impossible with coarse and uneven grains. Uneven deformation during rolling and the high reduction rate in the first pass can lead to strip breakage, hindering continuous production. This invention uses grain-oriented silicon steel strip with a grain size of 1.0–2.0 cm and an equiaxation of 0.8–1.2 as raw material. The small grain size, low equiaxation, and uniform microstructure of the raw material result in a fine and uniform microstructure in the final ultra-thin grain-oriented silicon steel, leading to low mid-frequency magnetic performance loss. Furthermore, the small and uniform grain size of the raw material improves its processing performance, preventing edge cracks and strip breakage caused by a high reduction rate in the first pass.

[0031] This invention employs a two-pass rolling process, with a high reduction ratio between the first and second passes. Compared to three- or four-pass rolling, this process is shorter and easier to control. The high reduction ratio between the first and second passes ensures sufficient shear band formation, promoting the nucleation of easily magnetized oriented grains at the shear band during annealing, thus improving the magnetic properties of the product, resulting in high magnetic flux density and low mid-frequency loss. When the reduction ratio between the first and second passes is less than 7.5:2.5, the resulting ultrathin oriented silicon steel exhibits poor magnetic properties and low mid-frequency loss P. 1.5T / 400HzThe reduction ratio should be above 13.0 W / kg. A high reduction ratio in the first rolling pass results in a more uniform shear band, higher density, and a more uniform annealed microstructure. However, if the reduction ratio exceeds 9.0:1.0, it will also affect the magnetic properties of the product. An excessively high ratio leads to an excessively high shear band density, significantly increasing the nucleation rate of easily magnetized Goss-oriented grains per unit area. Under rapid annealing conditions, the grain size becomes too small (i.e., the proportion of grain boundaries increases, and grain boundaries are not conducive to magnetization), thus increasing the magnetostrictive loss of the strip and the overall iron loss. At the same time, an excessively high reduction ratio will lead to poor magnetic properties of the strip and obvious edge cracks, or even strip breakage. Therefore, the reduction ratio should be controlled between 7.5:2.5 and 9.0:1.0.

[0032] This invention employs a micro-tension rapid annealing method, which significantly shortens the annealing time and improves production efficiency compared to bell-type furnace annealing. The micro-tension annealing technology ensures the strip is flat and wrinkle-free, improving strip quality. Furthermore, it eliminates the need for a release agent coating process.

[0033] The micro-tension rapid continuous annealing method of this invention is an adjustment based on the previous two-pass rolling technology. The two-pass rolling with high pressure ratio can improve the rolling storage energy and adjust the density and distribution characteristics of the shear band. In the subsequent rapid annealing process, rapid recrystallization can be achieved, improving the uniformity of the grain structure and thus reducing losses.

[0034] High tension can affect the microstructure and lead to increased losses. In addition, high tension can cause changes in the strip shape (waves appearing from the edge to the middle of the strip). Strip shape problems can affect the processing of cores for transformers, reactors, etc. in subsequent applications. Therefore, this invention adopts a low-tension method to ensure the strip shape while minimizing the impact of tension on the strip during annealing.

[0035] This invention employs a combination of uniformly structured raw materials, high-pressure two-pass rolling, and micro-tension rapid annealing, significantly shortening the preparation time and improving efficiency. It can be used to prepare wide-width, high-performance, ultra-thin oriented silicon steel, exhibiting excellent mid-frequency magnetic properties to meet the requirements of mid-frequency electrical equipment, and is simple to operate. The resulting ultra-thin oriented silicon steel strip has low mid-frequency loss, high magnetic induction, and low magnetostrictive noise, and the process flow is simple.

[0036] In this invention, each process, such as the selection of raw materials, two-pass rolling, and micro-tension rapid continuous annealing, is based on the previous process. The process parameters are coordinated to achieve the preparation of high-performance ultra-thin oriented silicon steel and reduce losses.

[0037] 2. In the method for preparing ultra-thin oriented silicon steel strip provided by this invention, the total rolling force of the first rolling pass is 50-100T, the front tension is 35-55kN, and the back tension is 25-35kN; the total rolling force of the second rolling pass is 15-45T, the front tension is 20-40kN, and the back tension is 20-30kN. The reduction rate, front and back tensions, and total rolling force are coordinated to ensure the strip shape and to ensure that the ultra-thin oriented silicon steel strip is flat and free of edge cracks.

[0038] 3. In the preparation method of ultrathin oriented silicon steel strip provided by the present invention, the raw material is oriented silicon steel strip without magnesium silicate underlayer. This eliminates the need for pickling and further shortens the process flow. Detailed Implementation

[0039] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0040] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0041] Example 1

[0042] This embodiment provides a method for preparing ultrathin oriented silicon steel strip, the steps of which are as follows:

[0043] 1) Select a non-grain-oriented silicon steel strip with a width of 350mm, a thickness of 0.3mm, a grain size of 2.0cm, and an equiaxation of 1.2;

[0044] 2) The raw material is rolled in two passes, with a total reduction of 85% for the two passes. The ratio of the reduction of the first pass to the second pass is 7.5:2.5.

[0045] The total rolling force for the first rolling pass is 50T, with a front tension of 35kN and a rear tension of 25kN.

[0046] The total rolling force for the second rolling pass is 15T, with a front tension of 20kN and a rear tension of 20kN.

[0047] 3) Low-tension rapid annealing process: annealing temperature 880℃, annealing time 5min, annealing atmosphere is high-purity hydrogen, and the pre-tension per unit cross-sectional area is 0.15kg / mm. 2 Tensile strength per unit cross-sectional area is 0.15 kg / mm² 2 .

[0048] 4) Applying an insulating coating: According to Example 3 of Patent CN 110229549 A, an insulating coating with a thickness of 1 μm is applied to the surface of the product after annealing in step 3) to obtain an ultra-thin oriented silicon steel strip finished product.

[0049] Example 2

[0050] This embodiment provides a method for preparing ultrathin oriented silicon steel strip, the steps of which are as follows:

[0051] 1) Select a non-grained silicon steel strip with a width of 550mm, a thickness of 0.3mm, a grain size of 1.0cm, and an equiaxation of 0.8;

[0052] 2) The raw material is subjected to two passes of rolling, with a total reduction of 70% for the two passes. The ratio of the reduction of the first pass to the second pass is 9.0:1.0.

[0053] The total rolling force of the first rolling pass is 100T, the front tension is 55kN, and the rear tension is 35kN.

[0054] The total rolling force for the second rolling pass is 45T, the front tension is 40KN, and the rear tension is 30kN.

[0055] 3) Low-tension rapid annealing process: annealing temperature 800℃, annealing time 20min, annealing atmosphere is high-purity hydrogen, and the pre-tension per unit cross-sectional area is 0.5kg / mm. 2 Tensile strength per unit cross-sectional area is 0.3 kg / mm² 2 .

[0056] 4) Applying an insulating coating: According to Example 3 of Patent CN 110229549 A, an insulating coating with a thickness of 1 μm is applied to the surface of the product after annealing in step 3) to obtain an ultra-thin oriented silicon steel strip finished product.

[0057] Example 3

[0058] This embodiment provides a method for preparing ultrathin oriented silicon steel strip, the steps of which are as follows:

[0059] 1) Select a non-grained silicon steel strip with a width of 450mm, a thickness of 0.3mm, a grain size of 1.0cm, and an equiaxation of 0.8;

[0060] 2) The raw material is subjected to two-pass rolling with a total reduction of 75% and a reduction ratio of 8.0:2.0 between the first and second passes.

[0061] The total rolling force of the first rolling pass is 80T, the front tension is 48kN, and the rear tension is 34kN.

[0062] The total rolling force for the second rolling pass is 35T, the front tension is 35kN, and the rear tension is 20kN.

[0063] 3) Low-tension rapid annealing process: annealing temperature 850℃, annealing time 13min, annealing atmosphere is high-purity hydrogen, and the pre-tension per unit cross-sectional area is 0.23kg / mm. 2 Tensile strength per unit cross-sectional area is 0.18 kg / mm² 2 .

[0064] 4) Applying an insulating coating: According to Example 3 of Patent CN 110229549 A, an insulating coating with a thickness of 1 μm is applied to the surface of the product after annealing in step 3) to obtain an ultra-thin oriented silicon steel strip finished product.

[0065] Example 4

[0066] This embodiment provides a method for preparing ultrathin oriented silicon steel strip, the steps of which are as follows:

[0067] 1) Select a non-grained silicon steel strip with a width of 500mm, a thickness of 0.3mm, a grain size of 1.2cm, and an equiaxation of 0.9;

[0068] 2) The raw material is subjected to two-pass rolling, with a total reduction rate of 78% for the two passes. The ratio of the reduction rates of the first and second passes is 7.8:2.2.

[0069] The total rolling force for the first rolling pass is 75T, the front tension is 45kN, and the back tension is 35kN.

[0070] The total rolling force for the second rolling pass is 37T, the front tension is 39KN, and the rear tension is 22kN.

[0071] 3) Low-tension rapid annealing process: annealing temperature 830℃, annealing time 18min, annealing atmosphere is high-purity hydrogen, and the pre-tension per unit cross-sectional area is 0.25kg / mm. 2 Tensile strength per unit cross-sectional area is 0.19 kg / mm² 2 .

[0072] 4) Applying an insulating coating: According to Example 3 of Patent CN 110229549 A, an insulating coating with a thickness of 1 μm is applied to the surface of the product after annealing in step 3) to obtain an ultra-thin oriented silicon steel strip finished product.

[0073] Comparative Example 1

[0074] A method for preparing ultrathin silicon steel strip, the preparation method is the same as in Example 4, except that in the ultrathin rolling step, the ratio of the reduction rate of the first pass to the second pass is 6.5:3.5.

[0075] Comparative Example 2

[0076] A method for preparing ultrathin silicon steel strip, the preparation method is the same as in Example 4, except that in the ultrathin rolling step, the ratio of the reduction rate of the first pass to the second pass is 9.3:0.7.

[0077] Comparative Example 3

[0078] A method for preparing ultrathin silicon steel strip, the preparation method is the same as in Example 4, except that in the micro-tension rapid annealing step, the annealing temperature is 900℃, the time is 25min, and the pre-tension per unit cross-sectional area is 0.8kg / mm. 2 Tensile strength per unit cross-sectional area: 0.7 kg / mm 2 .

[0079] Comparative Example 4

[0080] A method for preparing an ultrathin silicon steel strip, the preparation method is the same as in Example 4, except that a non-oriented silicon steel strip with a width of 350 mm, a grain size of 3.0 cm, and an equiaxation of 2.1 is selected.

[0081] Experimental Example

[0082] The mid-frequency loss P of the ultrathin silicon steel strips prepared in Examples 1-4 and Comparative Examples 1-3 were tested respectively. 1.5T / 400Hz Magnetic induction B 800 Magnetostrictive noise LvA 1.5 / 400. The test results are shown in Table 1:

[0083] Table 1 Test Results of Ultra-thin Silicon Steel Strip

[0084]

[0085]

[0086] As shown in Table 1, the ultra-thin silicon steel strip prepared by the method of this invention has the advantages of low mid-frequency loss, high magnetic induction, and low magnetostrictive noise. In particular, the test results from the examples and comparative examples show that by employing the ultra-thin rolling and micro-tension rapid annealing steps provided by this invention, the specific range of total reduction rate, high-ratio two-pass reduction rate, total rolling force, and front and rear tensions, along with the specific annealing temperature, annealing rate, and annealing tension, can improve the magnetic properties of the finished ultra-thin oriented silicon steel.

[0087] This method is simple to operate, highly efficient, and meets the needs of enterprises for high-efficiency production.

[0088] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing ultrathin oriented silicon steel strip, characterized in that, Includes the following steps: Step 1: Select grain-oriented silicon steel strip with a grain size of 1.0~2.0cm and an equiaxation of 0.8~1.2 as raw material; Step 2: The raw material is rolled in two passes to obtain a cold-rolled ultrathin strip. The total reduction rate of the two-pass rolling is 70%~85%, and the reduction rate ratio of the first pass rolling to the second pass rolling is 7.5:2.5~9.0:1.0; The total rolling force of the first rolling pass is 50~100T, the front tension is 35~55kN, and the back tension is 25~35kN; The total rolling force of the second rolling pass is 15~45T, the front tension is 20~40KN, and the back tension is 20~30KN; Step 3: Anneal the cold-rolled ultrathin strip; Annealing temperature: 800~880℃; annealing time: 5~20min; annealing atmosphere: high-purity hydrogen; pre-tension per unit cross-sectional area: 0.15~0.5kg / mm. 2 The tensile strength per unit cross-sectional area is 0.15~0.3 kg / mm. 2 .

2. The method for preparing ultrathin oriented silicon steel strip according to claim 1, characterized in that, The raw material is oriented silicon steel strip without magnesium silicate underlayer.

3. The method for preparing ultrathin oriented silicon steel strip according to claim 1, characterized in that, The width of the raw material is 350~550mm.

4. The method for preparing ultrathin oriented silicon steel strip according to claim 1, characterized in that, It also includes step 4, applying an insulating coating.

5. The method for preparing ultrathin oriented silicon steel strip according to claim 4, characterized in that, The insulating coating is resistant to temperatures above 750°C.

6. The method for preparing ultrathin oriented silicon steel strip according to claim 4, characterized in that, The thickness of the insulating coating is 0.8-1.5μm.

7. The ultrathin oriented silicon steel strip obtained by the method according to any one of claims 1-6.

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