Annealing process for ultra-thin oriented electrical steel roll iron core

Abstract

The invention discloses an annealing process for an ultra-thin oriented electrical steel roll iron core, and belongs to the technical field of ultra-thin oriented electrical steel. According to the method, aiming at the ultra-thin oriented electrical steel roll iron cores with different steel strip thicknesses, the destructive effect of stress on the texture and grain of the oriented electrical steel thin strip is eliminated by cooperatively regulating and controlling the heating speed, the annealing temperature, the annealing time and the cooling speed, so that the Goss texture and grain size of the oriented electrical steel thin strip are recovered, and the roll iron core with excellent magnetic performance is obtained; and the excellent magnetic performance of the oriented electrical steel ultra-thin strip roll iron core with different steel strip thicknesses can be realized.

Description

Technical Field

[0001] The invention belongs to the technical field of ultra-thin oriented electrical steel, and in particular relates to an annealing process for an ultra-thin oriented electrical steel coil core. Background Art

[0002] Ultra-thin oriented electrical steel with a thickness of 0.1mm or less is primarily used in the cores of medium- and high-frequency electrical appliances. Medium- and high-frequency magnetic components are key to achieving high capacity and compactness in high-power power electronic equipment. Therefore, using ultra-thin oriented electrical steel strip with a thickness of 0.1mm or less to manufacture rolled cores for use in medium- and high-frequency electrical appliance cores is an important development direction for cores.

[0003] During the manufacturing process of wound iron cores, stress will be generated in the transportation, shearing and winding of the electrical steel strip, and the loss will increase sharply. Therefore, after the iron core is wound, it is generally necessary to perform stress relief annealing treatment to restore the inherent electromagnetic properties of the electrical steel strip, so that there is no high magnetic resistance in any part of the magnetic circuit, thereby reducing no-load loss and excitation current.

[0004] Patent CN116042972A discloses a wound core annealing process that uses a vacuum horizontal annealing furnace for stress relief annealing. The vacuum is controlled at -0.1 to 0.5 MPa. The resistance strip is heated at a rate of 150 to 200°C / hour to 600°C and held for 30 to 60 minutes. The strip is then heated at a rate of 30 to 50°C / hour to 800°C and held for 60 to 90 minutes. The strip is then cooled from the 800°C furnace to 400°C before being removed from the furnace. This process is designed for wound cores of conventional thickness and is not suitable for cores thicker than 0.1 mm.

[0005] Patent CN101599358A discloses a method for processing silicon steel thin strip cores for high-frequency reactors for DC transmission and transformation. Silicon steel strips with a thickness of less than 0.08 mm are wound into cores, and then the primary cores are vacuum annealed at a vacuum degree of -2 MPa, a heating temperature of 820 ± 5 °C, a heating rate of 150 °C / h, and a constant temperature time of 5-8 hours. The cooling rate during annealing of the thin strip cores is controlled at 60 °C / h, and the cores are removed from the furnace when cooled to 300 °C.

[0006] However, since the thickness of ultra-thin oriented electrical steel is ≤0.1mm, the thinner the steel, the greater the stress effect on the texture and grain structure of the steel strip. As a result, the stress relief annealing process also has a greater impact on the microstructure and magnetic properties of the ultra-thin oriented electrical steel. Therefore, it is necessary to formulate different stress relief annealing process regulations for ultra-thin oriented electrical steel coil cores of different thicknesses to ensure the core's excellent magnetic properties. Summary of the Invention

[0007] The object of the present invention is to provide an annealing process for an ultra-thin oriented electrical steel coil core, so as to achieve excellent magnetic properties of oriented electrical steel coil cores with different steel strip thicknesses.

[0008] In order to solve the above technical problems, the present invention provides the following technical solutions: Provided is an annealing process for an ultra-thin oriented electrical steel coil core, comprising the following steps: The ultra-thin oriented electrical steel coil core with a thickness of x to be stress annealed is placed in an annealing furnace for stress relief annealing; the annealing is performed in a pure nitrogen atmosphere, and the temperature is raised with the furnace at a heating rate of V. 加 Heat to stress relief annealing temperature T, keep warm for t; finally cool at a cooling rate V 冷 Cool to 200-300℃ and take out of the furnace, then air cool to room temperature; Heating rate V 加 The relationship between the thickness of the steel strip and x is as follows: 100 / e 2x + 1.1 / x ≤ V 加 ≤ 100 / e x + 1.2 / x(1) The heating rate should not be too fast to ensure uniform heating of the inner and outer coils of the core. Thinner steel strips increase heating speed, improving efficiency; thicker steel strips slow heating, promoting uniform heating of the inner and outer coils. Thinner steel strips transfer heat faster and are more sensitive to heating rate, requiring higher precision in heating rate control.

[0009] The atmosphere is pure nitrogen. Annealing in nitrogen is beneficial to keep the temperature of the inner and outer coils of the coiled core consistent through the movement of the nitrogen atmosphere in the furnace, which is beneficial to improving the magnetic properties of the core.

[0010] The stress relief annealing temperature T, the steel strip thickness x, and the holding time t have the following relationship: 750 + 1 / x+10000 / t ≤ T ≤ 760 + 1.5 / x+10000 / t (2) Because thinner steel strips are more sensitive to the stresses of punching and shearing, and the resulting shifts in texture direction due to crystal slip, the stress relief annealing temperature should be increased to eliminate the effects of stress on grain size and microstructure. The thinner the steel strip, the shorter the holding time, and the higher the stress relief annealing temperature. However, the stress relief annealing temperature should not be too high, as this may cause non-Goss grain growth, reduce the proportion of Goss texture in ultra-thin grain-oriented electrical steel, and degrade the core's magnetic properties.

[0011] The holding time t and the steel strip thickness x have the following relationship: 120 + 2000 × x ≤ t ≤ 120 + 2200 × x (3) The thinner the steel strip, the shorter the holding time should be. The thinner the steel strip, the faster the heat transfer from the surface to the center of the wound core. Shortening the holding time helps improve production efficiency and reduce energy consumption. The holding time should not be too short. The thinner the steel strip, the more pronounced the grains affected by stress relief. The dislocations caused by crystal slip increase, leading to greater changes in texture direction. Sufficient time is required to promote grain recovery. The holding time should not be too long, as this will lead to excessively large non-Goss textured grains, affecting the proportion of Goss texture in the ultra-thin grain-oriented electrical steel and reducing the magnetic properties of the core.

[0012] After stress relief annealing, the core needs to be cooled before being taken out of the furnace. During the cooling process, the cooling rate of the rolled core needs to be controlled appropriately to avoid a large temperature difference between the inner and outer coils of the rolled core. While ensuring that the grains of the outer ring steel strip maintain the grain size during annealing, the inner ring will not continue to grow due to slow cooling, which will lead to a decrease in the magnetic properties of the core.

[0013] Core cooling rate V 冷 The relationship between the steel strip thickness x and the annealing temperature T is as follows: 200 / e x + 21 - 10 × lnT≤ V 冷 ≤ 235 / e x - 10 × lnT (4) The cooling rate of the core is related to the annealing temperature and the thickness of the steel strip. The higher the annealing temperature, the slower the cooling rate. This prevents the outer ring temperature from rapidly dropping while the inner ring temperature has insufficient time to cool, leading to a significant difference in grain size between the inner and outer coils and reduced magnetic properties. The thinner the steel strip, the faster the cooling rate. Because it conducts heat faster, the cooling rate can be appropriately increased to improve efficiency.

[0014] Ultra-thin oriented electrical steel strips of varying thicknesses are affected differently by shear forces. The thinner the strip, the greater the dislocations caused by the stress on the crystal slip, which in turn has a greater impact on the texture. Furthermore, the thinner the strip, the wider the range of stress at the shear edges, leading to a more pronounced performance degradation. During the stress relief annealing process for the coiled core, coordinated control of the heating rate, annealing temperature, annealing time, and cooling rate for ultra-thin oriented electrical steel coils of varying thicknesses helps restore the grain and texture of the strips to their pre-stress state, thereby restoring their magnetic properties. Furthermore, more precise control of the heating rate, annealing temperature, annealing time, and cooling rate helps restore the grain and texture at the shear edges of the strip, which are affected by stress.

[0015] In the above equations (1) to (4), V 加 , T, t, x, and V 冷 It is expressed as a unitless number, where x is expressed in mm, V 加 、V冷 The unit is ℃ / h, the unit of T is ℃, and the unit of t is min.

[0016] According to the above scheme, the thickness x of the steel strip is 0.03 - 0.1 mm.

[0017] According to the above scheme, the rolled iron core to be stress annealed is obtained by cutting ultra-thin oriented electrical steel into strips according to the core width requirements, and then winding the strips to make electrical steel wound iron cores; or directly purchasing finished rolled iron cores; or cutting and processing the finished rolled iron cores and then winding the iron cores.

[0018] According to the above scheme, before stress relief annealing, the magnetic induction B of the coiled core 800 1.60-1.57T; iron loss P 1.5 / 400 It is 16.3-18.5w / kg.

[0019] According to the above scheme, after stress relief annealing, the magnetic induction B of the iron core with different steel strip thickness is 800 The change range is 0.03T, and the iron loss P 1.5 / 400 The variation range is 0.8w / kg.

[0020] Preferably, after stress relief annealing, the magnetic induction B of the wound core is 800 1.85 - 1.87T; iron loss P 1.5 / 400 It is 9.5-10.3 w / kg.

[0021] The beneficial effects of the present invention are as follows: The present invention provides an annealing process for ultra-thin oriented electrical steel coil cores. For ultra-thin oriented electrical steel coil cores with different steel strip thicknesses, the process eliminates the destructive effect of stress on the texture and grains of the oriented electrical steel thin strip by coordinated regulation of the heating rate, annealing temperature, annealing time and cooling rate, thereby restoring the Goss texture and grain size of the oriented electrical steel thin strip, obtaining an electrical steel coil core with excellent magnetic properties, and facilitating the realization of excellent magnetic properties of the oriented electrical steel ultra-thin strip coil cores with different steel strip thicknesses. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0023] Examples 1-8 Provided is an annealing process for an ultra-thin oriented electrical steel coil core, comprising the following steps: The ultra-thin oriented electrical steel strip with a thickness of 0.03-0.10 mm is cut into strips according to the core width requirements, and then the strips are wound into electrical steel wound cores. The electrical steel wound cores are placed in an annealing furnace for stress relief annealing. The annealing is carried out in a pure nitrogen atmosphere. The temperature is raised with the furnace at a heating rate of V 加 Heat to stress relief annealing temperature T, keep warm for t; finally cool at a cooling rate V 冷 Cool to 200℃ and take out of the furnace, then air cool to room temperature. The specific process of stress relief annealing is shown in Table 1, where: Heating rate V 加 The relationship between the thickness of the steel strip and x is as follows: 100 / e 2x + 1.1 / x ≤ V 加 ≤ 100 / e x + 1.2 / x(1) The heating rate V in each embodiment 加 , see Table 1 for details.

[0024] The stress relief annealing temperature T, steel strip thickness x, and holding time t have the following relationship: 750 + 1 / x+10000 / t ≤ T ≤ 760 + 1.5 / x+10000 / t (2) The stress relief annealing temperature T in each embodiment is shown in Table 1.

[0025] The holding time t at stress relief annealing temperature and the thickness x of the steel strip have the following relationship: 120 + 2000 × x ≤ t ≤ 120 + 2200 × x (3) The holding time t in each embodiment is specifically shown in Table 1.

[0026] Winding core cooling speed V 冷 The relationship between the steel strip thickness x and the annealing temperature T is as follows: 200 / e x + 21 - 10×lnT≤ V 冷 ≤ 235 / e x - 10×lnT (4) The cooling rate V in each embodiment 冷 , see Table 1 for details.

[0027] Cool to 200℃, take out of the oven, and air cool to room temperature.

[0028] The magnetic properties of the electrical steel coil cores before and after stress relief annealing in each embodiment are shown in Table 2.

[0029] Comparative Example 1-2: The stress relief annealing ultra-thin oriented electrical steel coil core was prepared by referring to the specific steps of the embodiment, wherein the heating rate V under the stress relief annealing process is 加 , stress relief annealing temperature T, holding time at stress relief annealing temperature t, core cooling rate V 冷 See Table 1; the magnetic properties of the wound cores before and after stress relief annealing in each comparative example are shown in Table 2.

[0030] Table 1. Stress relief annealing process parameters in Examples and Comparative Examples

[0031] Table 2. Comparison of magnetic properties of the coiled iron cores of the embodiment and the comparative example before and after stress relief annealing

[0032] It can be seen from Table 2 that when the stress relief annealing process meets the technical solution of the present invention, the magnetic induction B 800 Higher, iron loss P at high frequency 1.5 / 400 Low, obtain the ultra-thin oriented electrical steel coil core with excellent magnetic properties, the magnetic properties are well restored. At the same time, the magnetic properties of the coil core with different steel strip thickness after annealing vary little, among which B 800 The change range is 0.03T, and the iron loss P 1.5 / 400 The variation range is 0.8w / kg, which realizes the stability of magnetic properties of coiled core after stress relief annealing under different steel strip thicknesses.

[0033] In Comparative Example 1, the heating rate does not satisfy the formula (1) proposed in the present invention, and the stress relief annealing temperature does not satisfy the formula (2) proposed in the present invention. The heating rate is too slow and the temperature is too low. The stress on the deflection displacement of the grains in the steel strip cannot be restored, which easily causes the grains of the non-Gaussian texture in the steel strip to be too large, and the orientation degree of the Gaussian texture in the steel strip is reduced, which ultimately results in a low magnetic induction of the core of the ultra-thin oriented electrical steel coil and a low iron loss P. 1.5 / 400 high.

[0034] In Comparative Example 2, the heating rate does not satisfy the formula (1) proposed by the present invention, the annealing holding time does not satisfy the formula (3) proposed by the present invention, and the cooling rate does not satisfy the formula (4) proposed by the present invention. The heating rate is too fast, the annealing time is too short, and the cooling rate is too fast, which easily causes a large temperature difference between the inner and outer coils of the coiled core. At the same time, the stress on the deflection displacement of the grains in the steel strip cannot be restored, which ultimately results in a low magnetic induction of the ultra-thin oriented electrical steel coil core and a low iron loss P. 1.5 / 400 high.

[0035] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all such improvements and changes should fall within the scope of protection of the appended claims of the present invention.

Claims

1. A process for annealing an ultra-thin oriented electrical steel coil core, characterized in that: The following steps are involved: The ultra-thin oriented electrical steel coil core with a thickness of x is placed in an annealing furnace for stress relief annealing. The annealing is carried out in a pure nitrogen atmosphere. The temperature is raised with the furnace at a heating rate of V. 加 Heat to stress relief annealing temperature T, keep warm for t; finally cool at a cooling rate V 冷 Cool to 200-300℃ and take out of the furnace, then air cool to room temperature; The heating rate V 加 The relationship between the thickness of the steel strip and x is as follows: 100 / e 2x + 1.1 / x ≤ V 加 ≤ 100 / e x + 1.2 / x(1) The stress relief annealing temperature T, the steel strip thickness x, and the holding time t have the following relationship: 750 + 1 / x+10000 / t ≤ T ≤ 760 + 1.5 / x+10000 / t (2) The holding time t and the steel strip thickness x have the following relationship: 120 + 2000 × x ≤ t ≤ 120 + 2200 × x (3) The cooling rate V 冷 The relationship between the steel strip thickness x and the annealing temperature T is as follows: 200 / e x + 21 - 10 × lnT≤ V 冷 ≤ 235 / e x - 10 × lnT(4) In the above equations (1) to (4), x, V 加 , T, t, and V 冷 It is expressed as a unitless number, where x is expressed in mm, V 加 、V 冷 The unit is ℃ / h, the unit of T is ℃, and the unit of t is min.

2. The annealing process according to claim 1, characterized in that The thickness x of the steel strip is 0.03 - 0.1 mm.

3. The annealing process according to claim 1, characterized in that The coiled iron core to be stress-relieved and annealed is obtained by cutting an extremely thin oriented electrical steel strip into strips according to the required core width, and then winding the strips into an electrical steel coiled iron core; or directly purchasing a finished coiled iron core; or cutting and processing the finished coiled iron core and then winding the iron core.

4. The annealing process according to claim 1, characterized in that Magnetic induction B of the coiled core before stress relief annealing 800 1.60-1.57T; iron loss P 1.5 / 400 It is 16.3-18.5w / kg.

5. The annealing process according to claim 1, characterized in that: After stress relief annealing, the magnetic induction B of the coiled core with different steel strip thickness 800 The change range is 0.03T, and the iron loss P 1.5 / 400 The variation range is 0.8w / kg.

6. The annealing process according to claim 5, characterized in that: After stress relief annealing, the magnetic induction B of the coiled core 800 1.85 - 1.87T; iron loss P 1.5 / 400 It is 9.5-10.3 w / kg.

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