Non-oriented silicon steel for motor iron core and preparation method of non-oriented silicon steel

Abstract

The invention relates to the technical field of non-oriented silicon steel production, and discloses non-oriented silicon steel for a motor iron core and a preparation method of the non-oriented silicon steel for the motor iron core, and the non-oriented silicon steel for the motor iron core comprises the following chemical components in percentage by weight: 3-3.4% of Si, less than or equal to 0.2% of Als, more than or equal to 0.1% of Mn (Si / Mn is more than or equal to 10), 5-5.8% of P / (Si + Als), less than or equal to 0.2% of N, less than or equal to 0.005% of C, less than or equal to 0.006% of C + Ti, less than or equal to 0.02% of S and the balance of Fe and inevitable impurities. According to the low-manufacturing-stress non-oriented silicon steel for the motor iron core, through component design and matching with processes such as continuous casting, heating, hot rolling, normalizing, cold rolling and continuous annealing, batch stable production of the low-manufacturing-stress non-oriented silicon steel for the motor iron core is achieved, and introduction of internal stress in the manufacturing and machining process is effectively reduced on the basis that good electromagnetic performance of a product is guaranteed.

Description

Technical Field

[0001] The invention relates to the technical field of non-oriented silicon steel production, and in particular to non-oriented silicon steel for motor core and a preparation method thereof. Background Art

[0002] As the core soft magnetic material for electromagnetic energy conversion, non-oriented silicon steel is an important material for manufacturing motor cores. Non-oriented silicon steel is generally formed into motor cores through processes such as punching and stacking, and the cores are further manufactured into motors through shaft installation, winding, and assembly. The changes in the shape and state of non-oriented silicon steel during the motor manufacturing process are bound to introduce manufacturing stress, among which the edge shearing stress caused by the punching process is the main source of manufacturing stress for the motor core. The existence of manufacturing stress causes the non-oriented silicon steel structure to change, and the resistance to movement of the magnetic domain wall and the coercive force increase during the magnetization process, resulting in increased iron loss and reduced magnetic induction intensity in the motor core, which in turn affects the overall efficiency, torque and other indicators of the motor.

[0003] During the punching process of non-oriented silicon steel, the steel plate undergoes elastic bending, elongation deformation, and crack propagation in the die edge area under the action of the upper and lower cutting forces, and four parts, namely, collapsed area, bright area, torn area, and burr area, are formed on the cross section of the steel plate. The bright area of ​​the cross section is generated when the steel plate undergoes plastic deformation, and the area of ​​the bright area of ​​the cross section reflects the degree of plastic deformation in the steel plate punching process, that is, the magnitude of the introduced manufacturing stress.

[0004] The document of Chinese patent CN107385178B discloses an improved annealing process for non-oriented cold-rolled silicon steel sheets. The invention places the silicon steel sheets after the first cold rolling into an annealing furnace, and the temperature in the furnace reaches 400-450°C, keeps the silicon steel sheets in a nitrogen atmosphere for 45-65 minutes, performs multiple heating and constant temperature maintenance, and then performs a second cold rolling on the silicon steel sheets that have been annealed for the first time. The cold-rolled silicon steel sheets need to be annealed for the second time to eliminate the internal stress in the silicon steel sheet processing process. The invention achieves the effect of eliminating stress by changing the annealing process in the silicon steel production process, which is of certain significance to the improvement of the internal stress brought about in the silicon steel sheet production process, but does not involve the improvement of the internal stress introduced in the subsequent processing of the steel sheet to manufacture the iron core.

[0005] The document of Chinese patent CN113897549B discloses a non-oriented silicon steel and its preparation method. The invention performs stress relief annealing on a silicon steel semi-finished product with a recrystallization rate of 70-90%, an average grain size of 10-15 μm, and a hardness HV of 140-170 at a temperature of T = (772-777) + 2900 × W (Si) to obtain a non-oriented silicon steel with an average grain size of more than 80 μm, which is not easily deformed during the stamping process. The invention improves the machinability by adjusting the mechanical properties of the silicon steel sheet, and also does not involve the improvement of the internal stress introduced during the processing and manufacturing of the iron core.

[0006] Patent application CN111235461A discloses a high-strength non-oriented electrical steel containing rare earth and high-carbon for new energy drive motors. This solution increases the carbon content in the composition and adds a certain degree of rare earth elements to obtain an electrical steel material with a tensile strength of more than 650MPa, a yield strength of more than 500MPa, an elongation of more than 16%, and a magnetic induction intensity B50 of up to 1.68T under 400Hz magnetic polarization conditions. This method provides a process solution for improving the strength of non-oriented silicon steel, but does not mention the loss in electromagnetic properties, and also does not involve the improvement of internal stress introduced during the processing and manufacturing of the iron core. Summary of the invention

[0007] The purpose of the present invention is to overcome the problem of deterioration of electromagnetic properties caused by manufacturing stress introduced during the processing of non-oriented silicon steel in the prior art, and to provide a non-oriented silicon steel for motor core and a preparation method thereof. The present invention mainly achieves stable batch production of low manufacturing stress non-oriented silicon steel for motor core through component design, matching of continuous casting, heating, hot rolling, normalizing, cold rolling and continuous annealing processes, and effectively reduces the introduction of internal stress during the manufacturing process while ensuring good electromagnetic properties of the product.

[0008] In order to achieve the above-mentioned object, the present invention provides a non-oriented silicon steel for motor core on one hand, wherein the non-oriented silicon steel for motor core comprises the following chemical components in weight percentage: Si: 3-3.4%, Als≤0.2%, Mn≥0.1% and Si / Mn≥10, P / (Si+Als): 5-5.8%, N≤0.2%, C≤0.005%, C+Ti≤0.006%, S≤0.02%, and the rest is Fe and unavoidable impurities.

[0009] In the present invention, the chemical components and content control reasons of the non-oriented silicon steel for the motor core are as follows:

[0010] Si: It is an alloying element in non-oriented silicon steel. As the Si content increases, the resistivity increases and the iron loss decreases. At the same time, as the Si content increases, the solid solution ratio in the steel plate increases, the strength increases, and the brittleness tendency increases; therefore, the present invention limits the Si content to the above range.

[0011] Als: Al is similar to Si. Adding Al to steel plates can improve the magnetic properties of silicon steel. However, the addition of Al has a significant effect on improving the deformation capacity of silicon steel, which increases the area of ​​plastic deformation of the steel plate during the subsequent punching process, which is not conducive to reducing processing stress. At the same time, higher aluminum elements can easily reduce titanium in the slag during the smelting process, which has a certain harm to the performance of silicon steel. Therefore, the content of Als should be properly controlled.

[0012] Mn: It is an alloying element of silicon steel. The addition of Mn can increase the proportion of favorable textures such as {100} and {110} in the matrix. At the same time, in order to prevent S and Fe from forming low-melting-point FeS and causing hot brittleness, some Mn needs to be added to the steel plate to form a solid solution with S, thereby improving the hot deformation ability. However, the addition of Mn can improve the cold deformation ability of silicon steel, so the Mn content should be controlled within a certain range.

[0013] P: P element can effectively increase silicon steel ρ and promote grain growth. At the same time, P has a larger atomic radius than Fe and Si. Therefore, P can improve the electromagnetic properties of silicon steel and improve the punching properties of silicon steel, and reduce the bright area of ​​the punching section. However, when the P element is too high, the embrittlement of the material is enhanced, which affects the cold rolling performance during the production process and reduces the number of bending times. Therefore, the P content should be controlled within the above range;

[0014] N, C, Ti and S: They are harmful elements in silicon steel. N is easy to form second phase inclusions such as AlN and TiN in silicon steel, which strongly hinders grain growth, increases the resistance to magnetic domain movement, and deteriorates the electromagnetic properties. Therefore, the N content should be controlled within 0.2%; when the C content exceeds 0.005%, the iron loss increases significantly and the magnetic aging is obvious; the Ti element has a particularly strong effect on the electromagnetic properties of non-oriented silicon steel. The precipitated TiC and TiN inclusions seriously hinder grain growth and greatly increase iron loss; S is an optimized element. In principle, the lower the N, C and Ti content, the better.

[0015] Further preferably, the iron loss P of the non-oriented silicon steel used for the motor core is 1.5 / 50 ≤2.20W / kg, magnetic induction B 50 ≥1.65W / kg, double-sided interlayer resistance is 200~600Ω·mm 2 .

[0016] Among them, the iron loss P 1.5 / 50 is the specific total loss measured at 1.5T with an alternating magnetic field frequency of 50Hz; magnetic induction B50 It is the magnetic polarization intensity measured under the condition of magnetic field strength of 5000A / m. The double-sided interlayer resistance is measured according to the method of GB / T2522-2017.

[0017] A second aspect of the present invention provides a method for preparing non-oriented silicon steel for a motor core, the method comprising the following steps:

[0018] (1) heating a slab and then hot rolling it to obtain a hot-rolled plate, normalizing, pickling and cold rolling the hot-rolled plate in sequence to obtain a steel coil, and continuously annealing the steel coil to obtain a continuously annealed steel coil;

[0019] (2) applying an insulating coating on the surface of the steel coil after continuous annealing, and then curing it to obtain non-oriented silicon steel for motor core.

[0020] In a preferred embodiment, in step (1), the slab preparation method comprises: blowing molten iron in a converter and then transferring it to RH for vacuum smelting and alloying treatment to obtain molten steel, and continuously casting the molten steel to obtain a slab with a thickness of 200 to 250 mm.

[0021] In the present invention, converter blowing and transfer to RH for vacuum smelting and alloying treatment are conventional operations in the art, wherein the alloying treatment mainly adds alloys of the required target components to ensure that molten steel with chemical composition meeting the requirements of the finished product is obtained.

[0022] In the present invention, the chemical composition of the slab is consistent with the chemical composition of the finished non-oriented silicon steel product for motor core.

[0023] Furthermore, during the continuous casting of molten steel, electromagnetic stirring is used throughout the crystallizer to break up the internal columnar structure and make it more uniform, thereby obtaining a higher proportion of equiaxed grains and improving the thermal deformation capacity of the material.

[0024] In step (1) of the present invention, after the slab is obtained, the slab is sent to a walking beam heating furnace for heating, and the heating conditions include: temperature of 1020-1120° C. and time ≤4h.

[0025] The present invention preferentially adopts low temperature heating in the heating operation before hot rolling to avoid solid solution of large-sized liquid inclusions in the steel billet. The solid-dissolved inclusions form precipitates during laminar cooling, which will hinder the growth of finished grains, affect the movement of magnetic domains, and deteriorate the electromagnetic properties of the product.

[0026] In the preferred case of step (1), the hot rolling conditions include: a final rolling temperature of 850-900°C and a coiling temperature of 580-680°C.

[0027] In the present invention, after the final rolling is completed, the steel sheet is water-cooled and air-cooled before being coiled.

[0028] The hot rolling used in the present invention is a conventional operation in the art, and the heated slab is hot-rolled into a hot-rolled plate with a thickness of 1.5 to 2 mm (preferably a thin target thickness). In a specific embodiment, the hot rolling adopts 5 rough rolling passes + 7 finish rolling passes.

[0029] In the present invention, the deformation process is placed in the hot rolling process, which can further reduce the deformation amount in the cold rolling process.

[0030] Furthermore, in step (1), the normalization conditions include: a temperature of 850 to 950° C. and a time of 2 to 5 min.

[0031] The normalizing process in the present invention preferably adopts a high temperature process. The increase in normalizing temperature can effectively improve the {100} and {110} favorable surface textures in the steel plate, reduce the {111} texture ratio, and effectively improve the electromagnetic properties of the finished product. At the same time, the increase in normalizing temperature increases the average grain size in the steel plate, and the structure can be inherited to the finished product process through cold rolling and annealing processes to increase the grain size of the finished product.

[0032] In a specific implementation of step (1), pickling is carried out in a turbulent acid tank, and cold rolling is carried out after pickling, wherein the cold rolling also adopts conventional operations in the field, and a single-stand reciprocating rolling mill is used to cold roll the steel strip to a target thickness of 0.35-0.5 mm in 6 passes to obtain a steel coil; wherein the compound rolling can increase the force direction of the strip rolling process, increase the selectivity of grain deformation and rotation direction, reduce the texture concentration, and reduce the performance difference of the finished steel plate in different directions.

[0033] Preferably, in step (1), the steel coil is continuously annealed under the protection of a mixed gas of H2 and N2, wherein the content of H2 in the mixed gas is 20 to 50 volume %; in a specific embodiment, the content of H2 in the mixed gas is 35 volume %, and the content of N2 in the mixed gas is 65 volume %.

[0034] In a preferred case, the conditions of the continuous annealing include: a temperature of 900-1000°C and a time of 90-150s; the present invention preferentially adopts a rapid heating combined with a high-temperature annealing process, and the grain size of the steel plate is fully grown after the annealing process, which effectively reduces the hysteresis loss while reducing the deformation capacity of the finished steel plate and reducing the introduction of manufacturing stress after punching.

[0035] Furthermore, in step (2) of the present invention, the curing conditions include: a temperature of 400 to 600°C, a time of 35 to 70 seconds, and the applied insulating coating is an insulating coating conventionally used in the art, and the applied insulating coating is required to ensure that the double-sided interlayer resistance of the finished steel plate is 200 to 600 Ω·mm2 , the thickness of the insulating coating is controlled at 0.3~1μm

[0036] The present invention mainly realizes the batch stable production of low manufacturing stress non-oriented silicon steel for motor core by component design, matching the process of continuous casting, heating, hot rolling, normalizing, cold rolling and continuous annealing, reduces the blanking stress introduced in the manufacturing process of motor core, effectively reduces the introduction of internal stress in the manufacturing process on the basis of ensuring good electromagnetic properties of the product, reduces the area where plastic deformation occurs in the steel plate blanking process, effectively reduces the manufacturing stress caused by plastic deformation, makes the core and the motor performance more excellent, and the iron loss P of the obtained non-oriented silicon steel for motor core is 1.5 / 50 ≤2.20W / kg, magnetic induction B 50 ≥1.65W / kg, the bright area of ​​the cross section after punching is ≤45%. The present invention changes the bright area of ​​the cross section during the steel plate punching process through the performance design of the non-oriented silicon steel product, thereby achieving the purpose of adjusting the manufacturing stress. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a scanning electron microscope image of the cross section of the non-oriented silicon steel for the motor core of Example 1 after punching. DETAILED DESCRIPTION

[0038] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings and examples. It should be understood that the specific implementation described herein is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0039] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0040] Example 1

[0041] (1) After being blown in a converter, molten iron is transferred to RH for vacuum smelting and alloying treatment to obtain molten steel, which is continuously cast into a slab with a thickness of 210 mm. During the continuous casting process, the crystallizer uses electromagnetic stirring throughout the process. The slab contains the following chemical compositions in weight percentage: Si: 3.25%; Als: 0.15%; Mn: 0.18%; P: 0.17%; N: 0.010%; C: 0.0025%; C+Ti: 0.0048%; S: 0.012%, and the rest is Fe and unavoidable impurities. The slab is sent to a walking beam heating furnace for heating. The heating conditions include: temperature of 1060°C, time of 230 min, and then hot rolled into a slab with a thickness of 1 .9mm hot-rolled plate, the hot rolling adopts 5 rough rolling + 7 finishing rolling, the final rolling temperature of hot rolling is 880℃, after water cooling and air cooling, it is coiled at a temperature of 620℃, the hot-rolled plate is normalized (normalization conditions include: temperature is 940℃, time is 180S), then pickled in a turbulent acid tank, and then a single-frame reciprocating rolling mill is used for 6 passes of cold rolling to a thickness of 0.35mm to obtain a steel coil, and then the steel coil is continuously annealed under the protection of a mixed gas of H2 and N2; the continuous annealing conditions include: temperature is 970℃, time is 130s, the H2 content in the mixed gas is 35% by volume, and the N2 content is 65% by volume, to obtain a steel coil after continuous annealing;

[0042] (2) applying an insulating coating to the surface of the continuously annealed steel coil obtained in step (1), and then curing the steel coil. The curing conditions include: a temperature of 540° C. and a time of 55 seconds to obtain non-oriented silicon steel for motor core.

[0043] The iron loss P of the non-oriented silicon steel used for the motor core obtained in this embodiment is 1.5 / 50 is 2.14W / kg, magnetic induction B 50 The double-sided interlayer resistance is 355Ω·mm. 2 (The double-sided interlayer resistance is measured according to the method of GB / T2522-2017), the thickness of the insulating coating is 0.5μm, and the steel plate is punched with 8% relative gap. The material section after punching is observed by scanning electron microscope, such as Figure 1 As shown in the figure, the bright area of ​​the material cross section after punching accounts for 43% of the total area. Stress relief annealing is adopted, and the process conditions are: temperature is 750℃, time is 2h, and pure nitrogen is used as the protective atmosphere. After testing, the iron loss improvement rate after stress relief annealing is 8%.

[0044] Example 2

[0045] The method of Example 1 is used, except that in step (1), the slab contains the following chemical components in weight percentage: Si: 3.32%; Als: 0.11%; Mn: 0.14%; P: 0.18%; N: 0.0010%; C: 0.0019%; C+Ti: 0.0046%; S: 0.010%, and the rest is Fe and unavoidable impurities; the thickness of the hot-rolled plate is 1.8 mm; the normalization time is 150 seconds;

[0046] The iron loss P of the non-oriented silicon steel used for the motor core obtained in this embodiment is 1.5 / 50 is 2.12W / kg, magnetic induction B 50 1.66W / kg, double-sided interlayer resistance 450Ω·mm 2 (The double-sided interlayer resistance is measured according to the method of GB / T2522-2017), the thickness of the insulating coating is 0.7μm, and the steel plate is punched with 8% relative gap. The cross section of the material after punching is observed with a scanning electron microscope. The bright area of ​​the cross section of the material after punching accounts for 42% of the total area. Stress relief annealing is adopted, and the process conditions are: temperature is 750℃, time is 2h, pure nitrogen is used as the protective atmosphere, and the iron loss improvement rate after stress relief annealing is tested to be 9%.

[0047] Example 3

[0048] The method of Example 1 is implemented, except that in step (1), the slab contains the following chemical components in weight percentage: Si: 3.19%; Als: 0.09%; Mn: 0.22%; P: 0.18%; N: 0.0011%; C: 0.0023%; C+Ti: 0.0050%; S: 0.007%, and the rest is Fe and unavoidable impurities; the thickness of the hot-rolled plate is 1.7 mm; the coiling temperature is 650° C.; the normalizing time is 150 seconds; the continuous annealing temperature is 960° C.;

[0049] The iron loss P of the non-oriented silicon steel used for the motor core obtained in this embodiment is 1.5 / 50 is 2.13W / kg, magnetic induction B 50 The double-sided interlayer resistance is 308Ω·mm. 2 (The double-sided interlayer resistance is measured according to the method of GB / T2522-2017), the thickness of the insulating coating is 0.4μm, and the steel plate is punched with 8% relative gap. The cross section of the material after punching is observed with a scanning electron microscope. The bright area of ​​the cross section of the material after punching accounts for 42% of the total area. Stress relief annealing is adopted, and the process conditions are: temperature is 750℃, time is 2h, pure nitrogen is used as the protective atmosphere, and the iron loss improvement rate after stress relief annealing is tested to be 9%.

[0050] Comparative Example 1

[0051] The method of Example 1 is implemented, except that in step (1), the slab contains the following chemical components in weight percentage: Si: 3.3%; Als: 0.55%; Mn: 0.20%; P: 0.01%; N: 0.0012%; C: 0.0020%; C+Ti: 0.0041%; S: 0.010%, and the rest is Fe and unavoidable impurities; the thickness of the hot rolled plate is 1.8 mm; the continuous annealing temperature is 960°C;

[0052] The iron loss P of the non-oriented silicon steel used for the motor core obtained in this embodiment is 1.5 / 50 is 2.11W / kg, magnetic induction B 50 1.66W / kg, double-sided interlayer resistance 500Ω·mm 2 (The double-sided interlayer resistance is measured according to the method of GB / T2522-2017), the thickness of the insulating coating is 0.7μm, and the steel plate is punched with 8% relative gap. The cross section of the material after punching is observed with a scanning electron microscope. The bright area of ​​the cross section of the material after punching accounts for 63% of the total area. Stress relief annealing is adopted, and the process conditions are: temperature is 750℃, time is 2h, pure nitrogen is used as the protective atmosphere, and the iron loss improvement rate after stress relief annealing is tested to be 16%.

[0053] It can be seen from the above results that the non-oriented silicon steel for motor core prepared by the present invention has a bright area of ​​the material cross-section that accounts for less than 45% of the total area after 8% relative gap punching, and the iron loss improvement rate after stress relief annealing is small. The present invention mainly reduces the introduction of internal stress in the manufacturing process while ensuring good electromagnetic properties of the prepared non-oriented silicon steel product for motor core through component design, matching of continuous casting, heating, hot rolling, normalizing, cold rolling and continuous annealing processes, so that the performance of the core and the motor is more excellent.

[0054] It should be understood that parts not elaborated in detail in this specification belong to the prior art.

[0055] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A non-oriented silicon steel for motor core, characterized in that: The non-oriented silicon steel for the motor core comprises the following chemical components in weight percentage: Si: 3-3.4%, Als≤0.2%, Mn≥0.1% and Si / Mn≥10, P / (Si+Als): 5-5.8%, N≤0.2%, C≤0.005%, C+Ti≤0.006%, S≤0.02%, and the rest is Fe and unavoidable impurities.

2. The non-oriented silicon steel for motor core according to claim 1, characterized in that: The iron loss P of the non-oriented silicon steel used in the motor core 1.5 / 50 ≤2.20W / kg, magnetic induction B 50 ≥1.65W / kg, double-sided interlayer resistance is 200~600Ω·mm 2 .

3. The method for preparing non-oriented silicon steel for motor core according to claim 1 or 2, characterized in that: The preparation method comprises the following steps: (1) heating a slab and then hot rolling it to obtain a hot-rolled plate, normalizing, pickling and cold rolling the hot-rolled plate in sequence to obtain a steel coil, and continuously annealing the steel coil to obtain a continuously annealed steel coil; (2) applying an insulating coating on the surface of the steel coil after continuous annealing, and then curing it to obtain non-oriented silicon steel for motor core.

4. The preparation method according to claim 3, characterized in that: In step (1), the slab preparation method comprises: blowing molten iron in a converter, performing vacuum smelting and alloying treatment to obtain molten steel, and continuously casting the molten steel to obtain a slab; The thickness of the slab is 200-250 mm.

5. The preparation method according to claim 3 or 4, characterized in that: In step (1), the heating conditions include: temperature of 1020-1120° C. and time of ≤4 h.

6. The preparation method according to claim 3, characterized in that: In step (1), the hot rolling conditions include: a final rolling temperature of 850 to 900°C and a coiling temperature of 580 to 680°C; The thickness of the hot-rolled plate is 1.5 to 2 mm.

7. The preparation method according to claim 3, characterized in that: In step (1), the normalization conditions include: temperature of 850-950° C. and time of 2-5 min.

8. The preparation method according to claim 3, characterized in that: In step (1), the thickness of the steel coil is 0.35-0.5 mm.

9. The preparation method according to claim 3, characterized in that: In step (1), the steel coil is continuously annealed under the protection of a mixed gas of H2 and N2; the content of H2 in the mixed gas is 20 to 50 volume %; The continuous annealing conditions include: a temperature of 900 to 1000° C. and a time of 90 to 150 seconds.

10. The preparation method according to claim 3, characterized in that: In step (2), the curing conditions include: a temperature of 400 to 600° C. and a time of 35 to 70 seconds.

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