A high-magnetic-induction low-iron-loss gradient high-silicon steel thin strip and a preparation method thereof

Abstract

This invention provides a high-magnetic-induction, low-iron-loss gradient high-silicon steel strip and its preparation method, belonging to the field of materials preparation technology. The invention involves cold rolling a hot-rolled low-silicon steel sheet to obtain a cold-rolled sheet; the cold-rolled sheet is then subjected to alkali washing, decarburization annealing, siliconizing, and diffusion annealing treatments sequentially to obtain the high-magnetic-induction, low-iron-loss gradient high-silicon steel strip. During the siliconizing treatment, the crystal structure is austenitic. This invention, through optimized composition design and synergistic control of cold rolling, decarburization annealing, siliconizing, and diffusion annealing, obtains a high-silicon steel strip that simultaneously possesses high magnetic induction, low iron loss, and good machinability. By controlling Mn and Si, the crystal structure of the base strip is maintained as austenitic during siliconizing, allowing silicon to be better enriched on the surface, increasing the silicon concentration gradient, reducing iron loss, and improving saturation magnetic induction.

Description

Technical Field

[0001] This invention relates to the field of materials preparation technology, and in particular to a high magnetic induction, low iron loss gradient high silicon steel strip and its preparation method. Background Technology

[0002] Silicon steel, an indispensable soft magnetic material in power, electronics, and other electromagnetic equipment, is primarily used as a core component in electromagnetic devices such as transformers and motors. Its magnetic properties have a decisive impact on the operating efficiency and energy loss of these devices. Increasing the silicon content can significantly reduce iron loss and enhance the material's magnetic flux density. However, increasing the silicon content leads to a decrease in the material's plasticity and toughness, thus affecting its processing performance. Therefore, maintaining good processability while producing high-silicon-content silicon steel has become a critical issue that urgently needs to be addressed in the field of silicon steel manufacturing technology.

[0003] Currently, the columnar crystal structure and its crystal orientation (e.g., the {100} and {110} crystal planes) of silicon steel have a significant impact on its magnetic properties. Current technology has not yet been able to effectively control the proportion and orientation of the columnar crystal structure. For example, related technologies disclose the use of low-carbon, low-silicon steel strips as raw materials, employing a decarburization heat treatment process to obtain a single-phase ferrite columnar crystal structure with a {100} orientation texture. This grain orientation texture is retained during subsequent silicon infiltration, resulting in enhanced {100} and {110} texture components and weakened {111} texture components, which are beneficial for improving the magnetic properties of high-silicon steel. However, problems such as low magnetic induction and high iron loss still exist. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a high-silicon steel strip with a high magnetic induction and low iron loss gradient, and a method for preparing the same. The high-silicon steel strip prepared by this invention has a silicon content that gradually increases from the core to the surface, exhibiting a large silicon content concentration gradient and excellent properties of high magnetic induction and low iron loss.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing high-magnetic-induction, low-iron-loss, high-silicon steel thin strips, comprising the following steps: Low-silicon steel hot-rolled sheet is cold-rolled to obtain cold-rolled sheet, wherein the low-silicon steel hot-rolled sheet comprises the following elements by mass percentage: Si: 0.5%~2.0%, C: 0.01%~0.1%, Al: 0.01~0.5%, Mn: 0.1~0.8%, with the balance being Fe and unavoidable impurities; The cold-rolled sheet is subjected to alkali washing, decarburization annealing, silicon diffusion treatment and diffusion annealing in sequence to obtain the high magnetic induction, low iron loss gradient high silicon steel strip. The crystal structure during the silicon diffusion treatment is austenitic phase.

[0006] Preferably, the silicon infiltration treatment is performed at a temperature of 1050~1200℃ for 1~10 minutes.

[0007] Preferably, the silicon infiltration process is performed using chemical vapor deposition.

[0008] Preferably, the decarburization annealing treatment is carried out under the protection of a mixed gas, which includes H2, N2 and water vapor (H2O(g)), wherein the volume ratio of H2 to N2 in the mixed gas is 1:1, and the dew point of the water vapor is 20~50℃.

[0009] Preferably, the decarburization annealing treatment is performed at a temperature of 700~1000℃ for a time of 4~20 minutes.

[0010] Preferably, the carbon content in the strip steel obtained after the decarburization annealing treatment is ≤0.005wt%.

[0011] Preferably, the strip has a columnar structure, wherein the proportion of columnar crystals in the columnar structure is 50% to 100%, and based on the area, the proportion of {100} and {110} oriented columnar crystals is 20% to 50% of the columnar crystals.

[0012] Preferably, the diffusion annealing treatment is performed at a temperature of 1150~1220℃ for 5~20 minutes.

[0013] The present invention also provides a high magnetic induction, low iron loss, gradient high silicon steel strip prepared by the preparation method described in the above technical solution.

[0014] Preferably, the silicon content of the high magnetic induction, low iron loss gradient high silicon steel strip increases gradually from the core to the surface, with the silicon content near the surface of the cross-section being 4.5~8.5wt% and the silicon content in the core of the cross-section being 0.5~2.0wt%, and the range of the gradually increasing silicon content being 4~8wt%.

[0015] This invention provides a method for preparing a high-magnetic-induction, low-iron-loss gradient high-silicon steel strip, comprising the following steps: cold rolling a low-silicon steel hot-rolled plate to obtain a cold-rolled sheet, wherein the low-silicon steel hot-rolled plate comprises the following elements by mass percentage: Si: 0.5%~2.0%, C: 0.01%~0.1%, Al: 0.01~0.5%, Mn: 0.1~0.8%, with the balance being Fe and unavoidable impurities; the cold-rolled sheet is sequentially subjected to alkaline washing, decarburization annealing, siliconizing treatment, and diffusion annealing treatment to obtain the high-magnetic-induction, low-iron-loss gradient high-silicon steel strip, wherein the crystal structure during siliconizing treatment is austenitic phase.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention solves the problems of uneven silicon content control and poor crystal orientation in the prior art by synergistic control of composition optimization design, cold rolling, decarburization annealing, silicon infiltration and diffusion annealing, thereby obtaining a high-silicon steel strip with high magnetic induction, low iron loss and good processability. In this invention, aluminum and silicon play similar roles, increasing resistivity and promoting the shrinkage of the austenite region. This is more conducive to the formation of columnar ferrite crystals during decarburization annealing and also promotes grain growth, reducing iron loss. Manganese expands the austenite layer. By controlling Mn and Si, the crystal structure of the substrate is ensured to be austenitic (face-centered cubic, FCC) during silicon infiltration. The density of the FCC structure is higher than that of the body-centered cubic structure, resulting in lower silicon infiltration efficiency during silicon infiltration. This allows for better enrichment of silicon on the surface, increasing the silicon concentration gradient and improving the balance between the surface magnetic properties and core mechanical properties of the thin strip. The Si localization material manufactured using the austenitic region silicon infiltration method exhibits a larger Si concentration gradient compared to traditional Si concentration gradient magnetic materials, reducing iron loss and increasing saturation magnetic induction. Furthermore, manganese reacts with sulfur, an unavoidable impurity, to form MnS, preventing hot embrittlement caused by the formation of low-melting-point FeS along grain boundaries and improving hot rolling plasticity.

[0017] Furthermore, the silicon infiltration process described in this invention has significantly reduced the time required, has strong process applicability, and is suitable for large-scale industrial production.

[0018] Furthermore, the decarburization annealing temperature of the present invention is 700~1000℃, and the decarburization annealing is a two-phase decarburization, which can form a columnar crystal structure. The C element content in the strip steel obtained by decarburization annealing is ≤0.005wt%. C is a harmful element in silicon steel. The reduction of C content reduces the inner oxide layer and inner nitride layer, further reducing iron loss. On the other hand, before siliconizing treatment, the strip steel forms columnar crystal structures of {100} and {110}, which form a texture that is beneficial to magnetic properties.

[0019] The present invention also provides a method for preparing high magnetic induction, low iron loss gradient, high silicon steel strip as described in the above technical solution. The preparation method of the present invention is simple to operate and suitable for industrial application. Attached Figure Description

[0020] Figure 1 The phase diagram of the strip steel before decarburization annealing treatment in Example 1; Figure 2 The phase diagram is shown for the strip steel after decarburization annealing treatment in Example 1. Figure 3 This is an electron probe microanalysis image of the strip after silicon infiltration treatment in Example 1; Figure 4 This is an electron probe line scan of the strip steel after silicon infiltration treatment in Example 1; Figure 5 This is an electron probe line scan of the strip after diffusion annealing in Example 1; Figure 6 The phase diagram of the strip steel before decarburization annealing treatment in Example 2; Figure 7 The phase diagram is shown for the strip steel after decarburization annealing treatment in Example 2. Figure 8 This is an electron probe line scan of the strip steel after silicon infiltration treatment in Example 2; Figure 9 This is an electron probe line scan of the strip after diffusion annealing in Example 2; Figure 10 The image shows the EBSD pattern of the strip after diffusion annealing in Example 2. Figure 11 The phase diagram of the strip steel before siliconizing treatment in Comparative Example 1 is shown. Figure 12 The electron probe line scan image is shown for the silicon-diffused strip of Comparative Example 1. Figure 13 This is an electron probe line scan of Comparative Example 1 after diffusion annealing. Figure 14 This is a schematic diagram of the near-surface and core structure of a high-silicon steel strip with high magnetic induction, low iron loss gradient. Detailed Implementation

[0021] This invention provides a method for preparing high-magnetic-induction, low-iron-loss, high-silicon steel thin strips, comprising the following steps: Low-silicon steel hot-rolled sheet is cold-rolled to obtain cold-rolled sheet, wherein the low-silicon steel hot-rolled sheet comprises the following elements by mass percentage: Si: 0.5%~2.0%, C: 0.01%~0.1%, Al: 0.01~0.5%, Mn: 0.1~0.8%, with the balance being Fe and unavoidable impurities; The cold-rolled sheet is subjected to alkali washing, decarburization annealing, silicon diffusion treatment and diffusion annealing in sequence to obtain the high magnetic induction, low iron loss gradient high silicon steel strip. The crystal structure during the silicon diffusion treatment is austenitic phase.

[0022] Unless otherwise specified, all raw materials used in this invention are commercially available products in the field.

[0023] This invention involves cold rolling a low-silicon steel hot-rolled sheet to obtain a cold-rolled thin sheet. The low-silicon steel hot-rolled sheet comprises the following elements by mass percentage: Si: 0.5%~2.0%, C: 0.01%~0.1%, Al: 0.01~0.5%, Mn: 0.1~0.8%, with the balance being Fe and unavoidable impurities.

[0024] In this invention, the mass percentage of Si is preferably 0.5%, 1.0%, 1.8%, or 2.0%. In silicon steel, as the silicon content increases, the resistivity increases and the iron loss decreases. In this invention, the mass percentage of silicon is not higher than 2.0%. This is primarily to ensure the preparation of the base strip steel, as the preparation of low-silicon steel is relatively simple and the surface quality of cold-rolled products is better. Additionally, it is to ensure that the crystal state of the steel strip is controlled in the austenitic phase at the silicon diffusion treatment temperature.

[0025] In this invention, the mass percentage of C is preferably 0.02%, 0.05%, or 0.1%. In non-oriented silicon steel, the iron loss increases abnormally with the increase of carbon content. The addition of carbon in this invention is to prepare a ferrite columnar crystal structure with strong {100} and {110} texture through two-phase decarburization in the subsequent decarburization process, thereby enabling higher magnetic properties to be obtained after silicon diffusion treatment.

[0026] In this invention, the mass percentage of Al is preferably 0.02%, 0.05%, 0.1% or 0.3%. Aluminum and silicon have similar functions: increasing resistivity, promoting the shrinkage of the austenite region, and being more conducive to the formation of columnar ferrite crystals during decarburization, which can increase grain size and reduce iron loss.

[0027] In this invention, the mass percentage of Mn is preferably 0.1%, 0.3%, or 0.65%. In silicon steel, manganese reacts with sulfur to form MnS, which can prevent hot brittleness caused by the formation of low-melting-point FeS along grain boundaries. Therefore, a certain amount of manganese is required to improve hot rolling plasticity. In this invention, since manganese is an austenitic element, it can be controlled by adjusting Mn and Si to ensure that the crystal structure of the baseband is austenitic at the silicon diffusion treatment temperature.

[0028] In this invention, the unavoidable impurities preferably include: phosphorus (P) ≤ 0.02%, sulfur (S) ≤ 0.003%, nitrogen (N) ≤ 0.002%, and titanium (Ti) ≤ 0.008%.

[0029] The present invention preferably involves vacuum smelting and casting the base strip into an ingot, followed by hot rolling, and then cold rolling with a smooth and clean low-silicon steel hot-rolled plate as the base material to obtain the cold-rolled sheet.

[0030] In this invention, the cold rolling is preferably multi-pass cold rolling. This invention does not have any special limitations on the specific parameters of the multi-pass cold rolling, and any method known to those skilled in the art can be used.

[0031] In this invention, the thickness of the cold-rolled sheet is preferably 0.1~0.5mm, specifically 0.1, 0.2, 0.3, 0.4 or 0.5mm.

[0032] After obtaining the cold-rolled sheet, the present invention sequentially performs alkaline washing, decarburization annealing, silicon diffusion treatment and diffusion annealing on the cold-rolled sheet to obtain the high magnetic induction, low iron loss gradient high silicon steel strip, wherein the crystal structure during the silicon diffusion treatment is austenitic phase.

[0033] In this invention, the alkaline washing preferably uses NaOH alkaline washing solution, the concentration of the NaOH alkaline washing solution is preferably 2~5wt%, and the temperature of the alkaline washing is preferably 75℃, to remove surface rolling oil and surface oxides and keep the surface clean.

[0034] In this invention, the decarburization annealing treatment is preferably carried out under the protection of a mixed gas, which preferably includes H2, N2 and water vapor (H2O(g)). The volume ratio of H2 to N2 in the mixed gas is preferably 1:1, and the dew point of the water vapor is preferably 20~50℃, specifically 20, 25, 30, 35, 40, 45 or 50℃.

[0035] In this invention, the preferred temperature for the decarburization annealing treatment is 700~1000℃, specifically 700, 750, 800, 850, 930, 950 or 1000℃, and the preferred time is 4~20min, specifically 4, 5, 10, 15 or 20min. The temperature of the decarburization annealing treatment is within the two-phase region temperature. In this invention, the phase region of the strip at different temperatures is calculated using Thermo-cale software based on the strip composition, and the two-phase region temperature is obtained from the phase diagram to determine the temperature of the decarburization annealing treatment.

[0036] In this invention, the C content in the strip steel obtained after the decarburization annealing treatment is preferably ≤0.005wt%, specifically 0.004wt% or 0.002wt%. C is a harmful element in silicon steel. Reducing the C content reduces the inner oxide layer and inner nitride layer, thereby reducing iron loss. On the other hand, the decarburization annealing treatment before siliconizing treatment forms columnar crystal structures of {100} and {110}, which creates a texture that is beneficial to magnetic properties.

[0037] In this invention, the strip steel preferably has a columnar structure, and the proportion of columnar crystals in the columnar structure is preferably 50% to 100%, specifically 50%, 60%, 70%, 80%, 90% or 100%. Based on the area, the proportion of {100} and {110} oriented columnar crystals to columnar crystals is preferably 20% to 50%, specifically 20%, 30%, 40% or 50%.

[0038] This invention utilizes compositional design to decarburize carbon-containing silicon steel in a two-phase region under a mixed gas atmosphere of H2+N2+H2O(g). The decarburized strip exhibits columnar crystal structure, forming a {100} and {110} texture comprising 20%–50% of the area. This texture set provides excellent magnetic properties, facilitating the inheritance of the favorable texture during subsequent siliconizing and decarburizing annealing processes. This reduces iron loss in the final product, maintaining excellent magnetic properties. Furthermore, the columnar crystal structure significantly enhances the magnetic induction of the silicon steel, resulting in a final product with good magnetic properties. The decarburizing annealing process optimizes the columnar crystal structure and crystal orientation distribution, further improving the material's high magnetic induction and low iron loss performance. This contributes to achieving low iron loss and high magnetic induction, making the preparation of high-magnetic-induction, low-iron-loss, high-silicon steel possible.

[0039] In this invention, the silicon infiltration temperature is preferably 1050~1200℃, specifically 1050, 1150, or 1200℃. Since FeCl2, a product generated during CVD vapor deposition of high-silicon steel, easily adsorbs onto the surface of the strip, it affects the silicon infiltration efficiency. The boiling point of FeCl2 is 1023℃, therefore the silicon infiltration temperature cannot be lower than 1023℃. As the Si content in the steel increases, the melting point of the steel gradually decreases. When the Si content reaches 14wt%, the melting point of Fe3Si drops below 1250℃. In other words... When the reaction temperature of CVD is above 1250℃, the FegSi layer generated by the reaction will melt. Therefore, the reaction temperature during CVD treatment should not exceed 1250℃. The silicon diffusion treatment temperature makes the crystal structure austenitic phase. In this invention, the phase region of the strip at different temperatures is calculated using Thermo-cale software based on the strip composition. The silicon diffusion treatment temperature is obtained from the phase diagram, and then the silicon diffusion treatment temperature is determined to make the crystal structure austenitic phase. The preferred time is 1~10 min, specifically 5 or 8 min. This invention controls the content of Mn and Si elements to maintain the austenitic phase crystal structure when heated to the silicon infiltration temperature. The face-centered cubic structure has a higher density than the body-centered cubic structure, and the silicon infiltration efficiency is lower in the face-centered cubic structure than in the body-centered cubic structure during the silicon infiltration stage. This allows for better enrichment of silicon on the surface, achieving a gradient distribution of silicon content. This improves the balance between the magnetic properties of the thin strip surface and the mechanical properties of the core. Compared with previous CVD silicon infiltration methods, the Si localization material manufactured using the austenitic region silicon infiltration method has a larger Si concentration gradient than traditional Si concentration gradient magnetic materials. Therefore, the core can be de-Si-rich, further reducing eddy current losses (iron losses) and increasing saturation magnetic induction. Simultaneously, this invention significantly reduces silicon infiltration time, has strong process applicability, and is suitable for large-scale industrial production.

[0040] In this invention, the silicon infiltration process is preferably performed using chemical vapor deposition (CVD).

[0041] In this invention, the temperature of the diffusion annealing treatment is preferably 1150~1220℃, specifically 1150, 1200 or 1220℃, and the time is preferably 5~20min, specifically 5, 10, 15 or 20min.

[0042] The present invention also provides a high magnetic induction, low iron loss, gradient high silicon steel strip prepared by the preparation method described in the above technical solution.

[0043] In this invention, the silicon content of the high magnetic induction, low iron loss gradient high silicon steel strip preferably increases gradually from the core to the surface. The silicon content near the surface of the cross-section is preferably 4.5 to 8.5 wt%, specifically 6.6 wt% or 7.5 wt%, and the silicon content in the core of the cross-section is preferably 0.5 to 2.0 wt%, specifically 1.8 wt% or 2 wt%. The range of the gradually increasing silicon content is preferably 4 to 8 wt%, specifically 4 wt%, 4.5 wt%, 4.8 wt%, 5.1 wt%, 5.5 wt%, or 6.0 wt%.

[0044] In this invention, the silicon content near the surface of the cross-section refers to the silicon content on the upper and lower surfaces along the thickness direction of the high-magnetic-induction, low-iron-loss gradient high-silicon steel strip, while the silicon content at the center of the cross-section refers to the silicon content at the center position along the thickness direction of the high-magnetic-induction, low-iron-loss gradient high-silicon steel strip. Specifically, as follows... Figure 14 As shown.

[0045] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0046] In the embodiments and comparative examples of this invention, according to GB / T 13789-2022, the magnetic properties were tested using a MATS-2010M magnetic tester. The magnetic induction B50 was measured under a magnetic field strength of 5000 A / m, and the iron loss P... 10 / 50 Measurements were taken at a magnetic flux density of 1.0 T and a frequency of 50 Hz.

[0047] In the embodiments and comparative examples of the present invention, the near-surface silicon content refers to the silicon content on the upper and lower surfaces in the thickness direction of the strip, and the core silicon content refers to the silicon content at the center position in the thickness direction of the strip.

[0048] Example 1 1. Raw material composition: The silicon steel composition is designed by mass percentage as follows: Si 2.0%, C 0.05%, Al 0.05%, Mn 0.65%, P≤0.02%, S≤0.003%, N≤0.002%, Ti≤0.008%, and the remainder is Fe.

[0049] 2. Cold rolling process: Low silicon steel hot-rolled plate is selected as the base material. Through multiple cold rolling passes, the thickness of the strip is controlled at 0.2mm and the reduction is 93%.

[0050] 3. Alkaline washing treatment: After cold rolling, the strip steel is placed in a 2% (w / w) NaOH alkaline washing solution for cleaning. The temperature of the alkaline washing solution is 75℃.

[0051] 4. Based on the strip steel composition, the phase region of the strip steel at different temperatures was calculated using Thermo-cale software. From the phase diagram ( Figure 1 It can be seen that the temperature of the two-phase region of the strip is 760~930℃. In order to accelerate the decarburization rate, decarburization annealing treatment at 920℃ is selected.

[0052] 5. Decarburization annealing treatment: The strip steel after alkali washing is placed in a wet hydrogen mixed gas atmosphere with a volume ratio of H2:N2 of 1:1 and a dew point of 45℃ for water vapor, and decarburized and annealed at 920℃ for 10 minutes. After decarburization annealing treatment, columnar crystal structure is formed, with columnar crystal accounting for 80% and {100} and {110} grains accounting for 40%. The carbon content of the strip steel is reduced to 0.004wt%.

[0053] 6. After the strip steel undergoes decarburization annealing, the phase region of the strip steel at different temperatures is calculated using Thermo-cale software. Figure 2 As can be seen from the phase diagram, when siliconizing at temperatures above 1100℃, the strip is in the austenitic phase region within the siliconizing temperature range. Therefore, 1150℃ is selected for siliconizing treatment.

[0054] 7. Silicon infiltration and diffusion annealing: The decarburized and annealed strip was placed in a CVD (chemical vapor deposition) system and siliconized at 1150℃ for 5 minutes, maintaining the austenitic phase crystal structure during the silicon infiltration process. Subsequently, diffusion annealing was performed at 1200℃ for 10 minutes to obtain a high-magnetic-induction, low-iron-loss gradient high-silicon steel strip. Field emission electron probe microanalysis was used to detect the silicon content in the near-surface and core of the strip. The silicon content was measured after cooling following silicon infiltration: near-surface silicon content 13.6 wt%, core silicon content 2.0 wt%. After diffusion annealing and cooling, the silicon content was measured: near-surface silicon content 7.5 wt%, core silicon content 2.0 wt%, with a gradient increase in silicon content of 5.5 wt%.

[0055] Magnetic flux density (B50) of high-silicon steel strip with high magnetic flux density and low iron loss: 1.67T, iron loss (P 10 / 50 ): 0.95W / kg.

[0056] The silicon content near the surface and in the core indicates that silicon forms a clear gradient distribution between the surface and core of the strip, resulting in a high-silicon steel strip with high magnetic induction and low iron loss, and a silicon gradient distribution between the surface and core.

[0057] Figure 3 The image shows an electron probe microanalysis of the strip after silicon diffusion treatment. It can be seen that the silicon concentration is high in the near-surface layer of the cross-section after silicon diffusion treatment, while the silicon concentration is low in the core. Figure 4 The image shows an electron probe line scan of the strip after silicon diffusion treatment. It can be seen that there is a clear concentration difference from the surface to the core after silicon diffusion treatment.

[0058] Figure 5 The electron probe line scan image after diffusion annealing shows that the silicon concentration in the surface layer gradually diffuses towards the center after diffusion annealing, and the near-surface silicon concentration in the cross-section decreases, but the trend of silicon concentration change gradually flattens out.

[0059] Example 2 1. Raw material composition: The silicon steel composition is designed by mass percentage as follows: Si 1.8%, C 0.02%, Al 0.02%, Mn 0.3%, P≤0.02%, S≤0.003%, N≤0.002%, Ti≤0.008%, and the remainder is Fe.

[0060] 2. Cold rolling process: Low silicon steel hot-rolled plate is selected as the base material. Through multiple cold rolling passes, the strip thickness is controlled at 0.5 mm and the reduction is 83%.

[0061] 3. Alkaline washing treatment: After cold rolling, the strip steel is placed in a 2% (w / w) NaOH alkaline washing solution for cleaning. The temperature of the alkaline washing solution is 75℃.

[0062] 4. Based on the strip steel composition, the phase region of the strip steel at different temperatures was calculated using Thermo-cale software. From the phase diagram ( Figure 6 It can be seen that the temperature of the two-phase region of the strip is 762~1063℃. In order to accelerate the decarburization rate, decarburization annealing treatment at 950℃ is selected.

[0063] 5. Decarburization annealing treatment: The strip steel after alkali washing is placed in a wet hydrogen mixed gas atmosphere with a volume ratio of H2:N2 of 1:1 and a dew point of 45℃ for water vapor, and decarburized and annealed at 950℃ for 15 minutes. After decarburization annealing treatment, columnar crystal structure is formed, with columnar crystals accounting for 60% and {100} and {110} grains accounting for 40%. The carbon content of the strip steel is reduced to 0.002wt%.

[0064] 6. After the strip steel undergoes decarburization annealing, the phase region of the strip steel at different temperatures is calculated using Thermo-cale software. Figure 7 As can be seen from the phase diagram, when siliconizing at temperatures above 1100℃, the strip is in the austenitic phase region within the siliconizing temperature range. Therefore, 1200℃ is selected for siliconizing treatment.

[0065] 7. Silicon infiltration and diffusion annealing: The decarburized and annealed strip was placed in a CVD (chemical vapor deposition) system and siliconized at 1200℃ for 8 minutes, maintaining the austenitic phase crystal structure during the silicon infiltration process. Subsequently, diffusion annealing was performed at 1200℃ for 10 minutes to obtain a high-magnetic-induction, low-iron-loss gradient high-silicon steel strip. Field emission electron probe microanalysis was used to detect the silicon content in the near-surface and core of the strip. The silicon content was measured after cooling following silicon infiltration: near-surface silicon content 13.5 wt%, core silicon content 1.8 wt%. After diffusion annealing and cooling, the silicon content was measured: near-surface silicon content 6.6 wt%, core silicon content 1.8 wt%, with a gradient increase in silicon content of 4.8 wt%.

[0066] Magnetic flux density (B50) of high-silicon steel strip with high magnetic flux density and low iron loss gradient: 1.69T, iron loss (P 10 / 50 ): 1.2W / kg.

[0067] The silicon content near the surface and in the core indicates that silicon forms a clear gradient distribution between the surface and core of the strip, resulting in a high-silicon steel strip with high magnetic induction and low iron loss, and a silicon gradient distribution between the surface and core.

[0068] Figure 8 The image shows an electron probe line scan of the strip after silicon diffusion treatment. It can be seen that there is a clear concentration difference from the surface to the core after silicon diffusion treatment.

[0069] Figure 9 The electron probe line scan of the strip after diffusion annealing shows that the silicon concentration in the surface layer gradually diffuses towards the center after diffusion annealing, and the silicon concentration in the near-surface layer of the cross section decreases, but the trend of silicon concentration change gradually flattens out.

[0070] Figure 10 The image shows the EBSD pattern of the strip after decarburization annealing. It can be seen that the strip formed grains with {100} and {110} orientations after decarburization annealing.

[0071] Comparative Example 1 1. Raw material composition: The silicon steel composition is designed by mass percentage as follows: Si 3.2%, C 0.003%, Al 0.67%, Mn 0.35%, P≤0.02%, S≤0.003%, N≤0.002%, Ti≤0.008%, and the remainder is Fe.

[0072] 2. Cold rolling process: Low silicon steel hot-rolled plate is selected as the base material. Through multiple cold rolling passes, the thickness of the strip is controlled at 0.2mm and the reduction is 93%.

[0073] 3. Alkaline washing treatment: After cold rolling, the strip steel is placed in a 2% (w / w) NaOH alkaline washing solution for cleaning. The temperature of the alkaline washing solution is 75℃.

[0074] 4. Based on the strip steel composition, the phase region of the strip steel at different temperatures was calculated using Thermo-cale software, and the phase diagram was obtained ( Figure 11 As can be seen from the data, the phase temperature of the strip steel is between 1050 and 1200℃, and it is entirely in the ferrite region (BCC). In order to accelerate the decarburization rate, silicon diffusion treatment is carried out at 1150℃.

[0075] 5. Silicon infiltration and diffusion annealing: The strip was placed in a CVD (Chemical Vapor Deposition) system and silicon infiltrated at 1150℃ for 5 minutes, maintaining the ferrite phase crystal structure during the silicon infiltration process. Subsequently, diffusion annealing was performed at 1200℃ for 10 minutes to obtain a high-silicon steel strip. Field emission electron probe microanalysis was used to detect the silicon content in the near-surface and core of the strip. After silicon infiltration, the strip was cooled and tested; the results were as follows: near-surface silicon content 13.9 wt%, core silicon content 4.2 wt%. After diffusion annealing, the strip was cooled and tested; the results were as follows: near-surface silicon content 7.0 wt%, core silicon content 5.3 wt%, with a gradient increase in silicon content of 1.7 wt%.

[0076] Magnetic flux density (B50) of high-silicon steel strip with high magnetic flux density and low iron loss gradient: 1.6T, iron loss (P 10 / 50 ): 1.1W / kg.

[0077] The silicon content in the near-surface and core layers indicates that silicon forms a clear gradient distribution between the surface and core of the strip.

[0078] Figure 12 The image shows an electron probe line scan of the strip after silicon diffusion treatment. It can be seen that there is a clear concentration difference from the surface to the core after silicon diffusion treatment.

[0079] Figure 13 The image shows an electron probe line scan after diffusion annealing. It can be seen that after diffusion annealing, silicon atoms gradually diffuse towards the center, and the near-surface silicon concentration in the cross-section decreases.

[0080] As can be seen from Comparative Example 1 and Example 1, when siliconizing under the same siliconizing conditions, the slope of the silicon concentration gradient from the surface to the core differs significantly. When the crystal structure is in the ferrite phase region during siliconizing, the siliconizing efficiency is higher than when the crystal structure is in the austenite phase region. This is because the density of a body-centered cubic lattice is lower than that of a face-centered cubic lattice, resulting in relatively slower element diffusion. Therefore, under the same siliconizing and diffusion annealing conditions, the silicon content in the core after siliconizing under a ferrite structure is higher than that of the original strip, while the silicon content in the core after siliconizing under an austenite structure remains the same as that of the original strip. This results in a large difference in silicon content between the surface and the core, achieving localization of silicon on the surface of the thin strip. Through comparison of magnetic properties, it was found that silicon diffusion treatment in the austenite phase region can improve magnetic induction and reduce iron loss. In addition, in Example 1, decarburization annealing was performed, which formed a large number of {100} and {110} oriented grains, thus resulting in better magnetic properties.

[0081] Example 3 Same as Example 1, except that the silicon infiltration temperature is 1200°C.

[0082] After the silicon-diffused strip was cooled, it was tested. The test results are as follows: the silicon content in the near-surface layer was 14.0 wt%, and the silicon content in the core was 2.0 wt%. After the diffusion annealing strip was cooled, it was tested. The test results are as follows: the silicon content in the near-surface layer was 8 wt%, the silicon content in the core was 2.0 wt%, and the silicon content in the gradient increased to 6.0 wt%.

[0083] Magnetic flux density (B50) of high-silicon steel strip: 1.65T, iron loss (P 10 / 50 ): 0.91W / kg.

[0084] Example 4 Same as Example 1, except that the mass percentage of Mn is 0.1%.

[0085] After the silicon-diffused strip was cooled, it was tested. The test results are as follows: the silicon content in the near-surface layer was 13.3 wt%, and the silicon content in the core was 2.0 wt%. After the diffusion annealing strip was cooled, it was tested. The test results are as follows: the silicon content in the near-surface layer was 7.1 wt%, the silicon content in the core was 2.0 wt%, and the silicon content in the gradient increased to 5.1 wt%.

[0086] Magnetic flux density (B50) of high-silicon steel strip: 1.69T, iron loss (P 10 / 50 ): 0.96W / kg.

[0087] Comparative Example 2 Same as Example 1, except that the mass percentage of Mn is 0.9%.

[0088] After the silicon-diffused strip was cooled, it was tested. The test results are as follows: the silicon content in the near-surface layer was 12.8 wt%, and the silicon content in the core was 2.0 wt%. After the diffusion annealing strip was cooled, it was tested. The test results are as follows: the silicon content in the near-surface layer was 5.8 wt%, the silicon content in the core was 2.0 wt%, and the silicon content in the gradient increased to 3.8 wt%.

[0089] Magnetic flux density (B50) of high-silicon steel strip: 1.64T, iron loss (P 10 / 50 ): 1.32W / kg.

[0090] Comparative Example 3 Same as Example 1, except that the mass percentage of Mn is 0.05%.

[0091] After the silicon-diffused strip was cooled, it was tested. The test results are as follows: the silicon content in the near-surface layer was 14.1 wt%, and the silicon content in the core was 3.8 wt%. After the diffusion annealing treatment, the strip was tested after cooling. The test results are as follows: the silicon content in the near-surface layer was 6.8 wt%, the silicon content in the core was 4.1 wt%, and the silicon content in the gradient increased to 2.7 wt%.

[0092] Magnetic flux density (B50) of high-silicon steel strip: 1.58T, iron loss (P 10 / 50 ): 0.98W / kg.

[0093] Comparative Example 4 Same as Example 1, except that the silicon infiltration temperature is 1030°C.

[0094] After the silicon-diffused strip was cooled, it was tested. The test results are as follows: the silicon content in the near-surface layer was 13.0 wt%, and the silicon content in the core was 2.0 wt%. After the diffusion annealing strip was cooled, it was tested. The test results are as follows: the silicon content in the near-surface layer was 4.6 wt%, the silicon content in the core was 2.0 wt%, and the silicon content in the gradient increased to 2.6 wt%.

[0095] Magnetic flux density (B50) of high-silicon steel strip: 1.52T, iron loss (P 10 / 50 ): 1.15W / kg.

[0096] Comparative Example 5 Same as Example 1, except that the silicon infiltration temperature is 1240°C.

[0097] After the silicon-diffused strip was cooled, it was tested. The test results are as follows: the silicon content in the near-surface layer was 13.2 wt%, and the silicon content in the core was 2.0 wt%. After the diffusion annealing treatment, the strip was tested after cooling. The test results are as follows: the silicon content in the near-surface layer was 4.8 wt%, the silicon content in the core was 2.0 wt%, and the silicon content in the gradient increased to 2.8 wt%.

[0098] Magnetic flux density (B50) of high-silicon steel strip: 1.55T, iron loss (P 10 / 50 ): 1.17W / kg.

[0099] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing high-magnetic-induction, low-iron-loss, high-silicon steel thin strips, characterized in that, Includes the following steps: Low-silicon steel hot-rolled sheet is cold-rolled to obtain cold-rolled sheet, wherein the low-silicon steel hot-rolled sheet comprises the following elements by mass percentage: Si: 0.5%~2.0%, C: 0.01%~0.1%, Al: 0.01~0.5%, Mn: 0.1~0.8%, with the balance being Fe and unavoidable impurities; The cold-rolled sheet is subjected to alkali washing, decarburization annealing, silicon diffusion treatment and diffusion annealing in sequence to obtain the high magnetic induction, low iron loss gradient high silicon steel strip. The crystal structure during the silicon diffusion treatment is austenitic phase.

2. The preparation method according to claim 1, characterized in that, The silicon infiltration treatment is performed at a temperature of 1050~1200℃ for 1~10 minutes.

3. The preparation method according to claim 1 or 2, characterized in that, The silicon infiltration process is performed using chemical vapor deposition.

4. The preparation method according to claim 1, characterized in that, The decarburization annealing treatment is carried out under the protection of a mixed gas, which includes H2, N2 and water vapor. The volume ratio of H2 to N2 in the mixed gas is 1:1, and the dew point of the water vapor is 20~50℃.

5. The preparation method according to claim 1 or 4, characterized in that, The decarburization annealing treatment is performed at a temperature of 700~1000℃ for a time of 4~20 minutes.

6. The preparation method according to claim 1 or 4, characterized in that, The carbon content in the strip obtained after the decarburization annealing treatment is ≤0.005wt%.

7. The preparation method according to claim 6, characterized in that, The strip has a columnar structure, in which columnar crystals account for 50% to 100% of the structure. Based on area, {100} and {110} oriented columnar crystals account for 20% to 50% of the columnar crystals.

8. The preparation method according to claim 1, characterized in that, The diffusion annealing treatment is performed at a temperature of 1150~1220℃ for 5~20 minutes.

9. A high-magnetic-induction, low-iron-loss, gradient high-silicon steel strip prepared by the preparation method according to any one of claims 1 to 8.

10. The high magnetic induction, low iron loss gradient high silicon steel strip according to claim 9, characterized in that, The silicon content of the high magnetic induction, low iron loss gradient high silicon steel strip increases gradually from the core to the surface. The silicon content near the surface of the cross section is 4.5~8.5wt%, and the silicon content in the core of the cross section is 0.5~2.0wt%. The range of the gradually increasing silicon content is 4~8wt%.

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