Steel for handheld heating electric appliance motor and production method thereof

Abstract

The invention belongs to the technical field of steel production, and particularly relates to steel for a handheld heating electric appliance motor, which comprises the following chemical components in percentage by mass: less than or equal to 0.003% of C, 0.50-1.50% of Si, 0.1-0.5% of Mn, 0.01-0.05% of Zr, 0.01-0.05% of Y, 0.005-0.02% of B, 0.05-0.2% of Ni, less than or equal to 0.001% of S, less than or equal to 0.002% of N, 0.10-0.30% of Als and the balance of Fe and inevitable residual elements. The ultra-thin specification strip steel produced by the method disclosed by the invention has the advantages of low iron loss, high strength, low thermal expansion, high oxidation resistance and dimensional stability. And the comprehensive requirements of low noise, high energy efficiency, light weight and long service life of the handheld heating electric appliance motor are comprehensively met.

Description

Technical Field

[0001] This invention belongs to the field of steel production technology, and specifically relates to a method for producing steel for a handheld heating appliance motor. Background Technology

[0002] Handheld heating appliances, such as hair dryers and handheld garment steamers, are widely used in daily life due to their convenience and efficiency. As consumer demands become increasingly diverse, the performance requirements for handheld heating appliances are also constantly rising. Users not only expect the devices to provide a quiet operating environment and reduce the impact of noise on the user experience, but also desire motors with higher energy efficiency ratios. At the same time, since these appliances generate heat during use, safety has become a key concern for users. The motor materials need to possess good thermal stability and mechanical strength to ensure the safe operation of the device under high temperature and high load conditions.

[0003] Currently, most handheld heating appliances use ordinary silicon steel sheets for their motors, with thicknesses typically ranging from 0.35mm to 0.5mm. However, with the increasing complexity and diversification of applications for handheld heating appliances, especially for high-end products requiring lightweight and high-efficiency motors, existing materials are no longer sufficient to meet performance requirements. Ordinary non-oriented silicon steel has insufficient electromagnetic properties, leading to increased motor temperature rise; its insufficient oxidation resistance and thermal stability at high temperatures not only increase operating noise but also affect the motor's safety and reliability; furthermore, magnetic aging is a defect of ordinary silicon steel sheets, causing a gradual decline in magnetic properties during prolonged high-temperature operation. These shortcomings affect the overall performance and user experience of handheld heating appliances. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for producing steel for handheld heating appliance motors, which meets the operating requirements of handheld heating appliance motors under special working conditions and can also significantly improve the reliability of the motors.

[0005] To achieve the above objectives, the present invention employs the following technical solution: A type of steel for a handheld heating appliance motor has the following chemical composition by mass fraction: C ≤ 0.003%, Si: 0.50%–1.50%, Mn: 0.1%–0.5%, Zr: 0.01%–0.05%, Y: 0.01%–0.05%, B: 0.005%–0.02%, Ni: 0.05%–0.2%, S ≤ 0.001%, N ≤ 0.002%, Als: 0.10%–0.30%, with the remainder being Fe and unavoidable residual elements.

[0006] A type of steel for the motor of a handheld heating appliance, with a thickness of 0.15mm to 0.25mm.

[0007] A type of steel for handheld heating appliance motors, with the following mechanical properties: yield strength Rp0.2 ranging from 320MPa to 350MPa, and coefficient of thermal expansion α ≤ 11.0 × 10⁻⁶. -6 / ℃.

[0008] The functions of chemical elements are as follows: Silicon (Si) can significantly increase the resistivity of silicon steel and reduce iron loss, thereby improving the efficiency of motors. In this invention, the silicon content is controlled at 0.50% to 1.50%, which can effectively reduce iron loss while ensuring that the material has good processing performance.

[0009] Manganese (Mn) primarily functions as a deoxidizer and sulfur fixative in silicon steel. Appropriate amounts of manganese can combine with sulfur to form manganese sulfide, thereby reducing the harmful effects of sulfur on material properties. Simultaneously, manganese can also improve the strength and toughness of the material to some extent. In this invention, the manganese content is controlled at 0.1%–0.5%, which satisfies the requirements for deoxidation and sulfur fixation without negatively impacting the electromagnetic properties of the material. Excessive manganese content will increase the magnetic aging of the material and reduce its electromagnetic properties.

[0010] Aluminum (Al) can increase the resistivity of materials to a certain extent, which helps to reduce iron loss. In this invention, the aluminum content is controlled at 0.10% to 0.30%, which has a positive impact on electromagnetic properties.

[0011] Zirconium (Zr) is a strong carbide-forming element that can combine with carbon in steel to form stable zirconium carbide, thereby reducing the free carbon content in the material and mitigating magnetic aging. Simultaneously, zirconium can refine the grain size, improving the material's strength and toughness. In this invention, the zirconium content is controlled at 0.01%–0.05%, which effectively reduces magnetic aging and improves the material's mechanical properties by refining the grain size.

[0012] Yttrium (Y) is a rare earth element with good thermal stability and oxidation resistance. Adding yttrium to silicon steel can improve the material's oxidation resistance and thermal stability, thereby enhancing its performance under high-temperature conditions. Furthermore, yttrium can form stable compounds with impurities such as sulfur and oxygen in the steel, further improving the material's purity. In this invention, the yttrium content is controlled at 0.01% to 0.05%.

[0013] Boron (B) primarily functions to refine grain size and increase the strength of silicon steel. Simultaneously, boron can also improve the electromagnetic properties of the material to some extent. In this invention, the boron content is controlled between 0.005% and 0.02%.

[0014] Nickel (Ni) can improve the strength and toughness of materials. Adding nickel to silicon steel can improve the mechanical properties of the material, and also has a positive effect on its electromagnetic properties. In this invention, the nickel content is controlled at 0.05% to 0.2%.

[0015] Carbon (C), sulfur (S), and nitrogen (N) are harmful elements in steel, as they reduce the material's electromagnetic and mechanical properties. In this invention, their content is strictly controlled to ensure the material possesses good electromagnetic and mechanical properties. By controlling the content of these harmful elements, magnetic aging can be reduced, improving the material's purity and processing performance.

[0016] A method for producing steel for a handheld heating appliance motor, comprising the following steps: steelmaking, continuous casting, hot rolling, pickling, normalizing, cold rolling, and finished product annealing, specifically including: 1) Hot rolling: The heating furnace soaking temperature is controlled at 1180℃~1280℃, the heating time is set at 180min~240min, the temperature gradient in the heating furnace is controlled at ≤10℃ / m, the reduction rate per pass of rough rolling is controlled at 10%~25%, the rolling speed is controlled at 2.2m / s~2.8m / s, the rolling temperature range is 1120℃~1180℃, and the final rolling temperature is set at 850℃~920℃. The final rolled thickness is 2.2mm~2.6mm; 2) Pickling: The pickling temperature is controlled at 65℃~75℃, and multi-stage countercurrent water washing is adopted; 3) Normalizing: The heating rate of the normalizing furnace is controlled at 200℃ / min~240℃ / min, the normalizing homogenization temperature is 860℃~920℃, the homogenization time is set within the range of 4min~6min, and the atmosphere inside the furnace is pure nitrogen atmosphere; 4) After normalization, perform a second hydrochloric acid pickling with a hydrochloric acid mass fraction of 15% to 18%, a temperature range of 55 to 65°C, and a pickling time of 8 to 12 seconds to peel off the Fe3O4-Fe2O3 composite oxide film and near-surface silicon-poor layer generated during normalization. 5) Cold rolling: The pickled coils are fed into a cold rolling mill for cold rolling. Cold rolling adopts multi-pass rolling. Except for the finishing pass, the work rolls are rough rolls: the Ra value of the rough rolls is in the range of 1μm to 3μm. The finishing pass uses smooth rolls, and the Ra value of the smooth rolls is recommended to be in the range of 0.1μm to 0.2μm. From the first pass to the last pass, the tensile stress of the strip is set to gradually increase. 6) Finished product annealing: Before entering the continuous annealing furnace, the cold-rolled sheet is leveled with an elongation of 0.2% to 0.6% using a pre-furnace tension roller. During the leveling process, the tension of the tension roller should be controlled between 5kN and 10kN. The annealing homogenization temperature is controlled between 880℃ and 960℃, and the homogenization time is set between 2min and 4min. During the annealing process, a mixture of hydrogen and nitrogen is used as the protective atmosphere. The average grain size of the final product is required to be between 80μm and 120μm.

[0017] The steelmaking process is as follows: the converter smelting temperature is controlled within the range of 1520℃ to 1580℃. During smelting, ferrosilicon and ferromanganese are added first, stirred evenly, and held at this temperature for 5 to 10 minutes. Then, ferrizircon and ferronickel are added, stirred evenly, and held at this temperature for 3 to 5 minutes. Finally, ferroaluminum is added, stirred evenly, and held at this temperature for 2 to 3 minutes. Refining employs vacuum degassing technology to control the sulfur content in the molten steel to ≤10ppm and the nitrogen content to ≤20ppm. The refining temperature is controlled within the range of 1560℃ to 1620℃, and the refining time is no less than 35 minutes. During the refining process, argon blowing is used for stirring to ensure that inclusions in the molten steel float to the surface.

[0018] The continuous casting process is as follows: casting speed 4.0~5.5m / min, tundish superheat 15~25℃; crystallizer electromagnetic stirring current 300~350A, frequency 12Hz, to ensure central equiaxed crystal ratio ≥55%; secondary cooling adopts gas-mist two-phase dynamic water distribution model, specific water volume 0.8~1.1L / kg, billet surface temperature gradient ≤8℃ / cm, billet 160mm.

[0019] In step 6), the volume fraction of hydrogen is controlled at 6% to 12%, and the volume fraction of nitrogen is controlled at 88% to 94%.

[0020] Compared with existing technologies, the beneficial effects of this invention are: 1) In terms of composition design, this invention is based on ultra-low C, extremely low S and N nitrogen, and incorporates Si and Al to increase resistivity ρ and reduce eddy current loss at 400Hz; Zr can fix free carbon, suppress magnetic aging and refine grains, and at the same time increase yield strength by 30-40MPa; Y generates two-phase particles to pin grain boundaries, which increases the oxidation resistance temperature of strip steel and extends thermal fatigue life; B works synergistically with Ni to strengthen grain boundaries, and finally obtains strip steel products that meet the requirements of use.

[0021] 2) In terms of process flow, the two pickling processes before and after normalization remove Fe3O4-Fe2O3 and the Si-poor layer, further optimizing the final product plate shape and surface quality.

[0022] From the first pass to the last pass, the cold rolling tensile stress increases progressively. The continuous longitudinal micro-tension increases the flatness of the sheet shape and offsets the increase in rolling force caused by hardening with the tension increment, suppressing edge crack defects in ultra-thin products, improving the thickness difference between the sheet and the product to ≤1.5%, and ensuring good sheet shape.

[0023] The finished product is smoothed by a small extension before the annealing furnace. The annealing process is precisely controlled, and after final annealing, an equiaxed ferrite matrix with complete recrystallization and a grain size of 80-120μm (ASTM 4-5 grade) is obtained; the {111}∥ND and γ-fiber texture strength are <2.5, and there is no banded segregation.

[0024] 3) The ultra-thin strip steel produced by this invention achieves low iron loss, high strength, low thermal expansion, high oxidation resistance, and dimensional stability. The lamination factor of the handheld heating appliance motor is increased by more than 2%, the dimensional change is ≤1.1μm at a temperature rise of 100℃, the air gap fluctuation is <2%, and the noise is reduced by 3-5dB. It fully meets the comprehensive requirements of low noise, high energy efficiency, lightweight, and long lifespan for handheld heating appliance motors. Detailed Implementation

[0025] It should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein in the specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The reference to "embodiment" herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0026] A type of steel for a handheld heating appliance motor has the following chemical composition by mass fraction: C ≤ 0.003%, Si: 0.50%–1.50%, Mn: 0.1%–0.5%, Zr: 0.01%–0.05%, Y: 0.01%–0.05%, B: 0.005%–0.02%, Ni: 0.05%–0.2%, S ≤ 0.001%, N ≤ 0.002%, Als: 0.10%–0.30%, with the remainder being Fe and unavoidable residual elements.

[0027] A type of steel for the motor of a handheld heating appliance, with a thickness of 0.15mm to 0.25mm.

[0028] A type of steel for handheld heating appliance motors, with the following mechanical properties: yield strength Rp0.2 ranging from 320MPa to 350MPa, and coefficient of thermal expansion α ≤ 11.0 × 10⁻⁶. -6 / ℃.

[0029] A method for producing steel for a handheld heating appliance motor includes: (1) Steelmaking: The converter smelting temperature is controlled within the range of 1520℃~1580℃. During smelting, the main alloying elements such as ferrosilicon and ferromanganese are added first, stirred evenly and kept at the temperature for 5min~10min, then ferrizircon and ferronickel are added, stirred evenly and kept at the temperature for 3min~5min, and finally ferroaluminum is added, stirred evenly and kept at the temperature for 2min~3min. Vacuum degassing technology is used for refining to control the sulfur content in the molten steel to ≤10ppm and the nitrogen content to ≤20ppm. The refining temperature is controlled within the range of 1560℃~1620℃ and the refining time is not less than 35min. During the refining process, argon blowing and stirring are used to make the inclusions in the molten steel float to the surface and improve the purity of the molten steel.

[0030] (2) Continuous casting: A 160mm×(800–1300mm) thin slab continuous casting machine is used with a casting speed of 4.0–5.5m / min and a tundish superheat of 15–25℃. The electromagnetic stirring (EMS) current in the crystallizer is 300–350A and the frequency is 12Hz, so that the equiaxed crystal ratio in the center is ≥55%. The secondary cooling adopts a gas-mist two-phase dynamic water distribution model with a specific water volume of 0.8–1.1L / kg and a surface temperature gradient of ≤8℃ / cm. The casting adopts a 3–5mm end light pressure and full-process protective casting to provide billet guarantee for the subsequent ultra-low carbon, low inclusion, and high purity handheld heating appliance steel.

[0031] (3) Hot rolling: The heating furnace temperature is controlled at 1180℃~1280℃, and the heating time is set at 180min~240min. Overheating or underheating should be avoided during the heating process to ensure that the billet has good plasticity and toughness. To ensure heating uniformity, the temperature gradient in the heating furnace is controlled at ≤10℃ / m. The reduction rate of each pass in rough rolling is controlled at 10%~25%, the rolling speed is controlled at 2.2m / s~2.8m / s, and the rolling temperature range is 1120℃~1180℃. Reasonable control of the reduction rate and rolling speed in the rough rolling process can ensure that the billet has good deformation uniformity and structural stability during the rolling process, while avoiding rolling defects caused by excessive reduction rate or excessive rolling speed. The final rolling temperature is set at 850℃~920℃, and the final thickness is 2.2mm~2.6mm.

[0032] (4) Pickling: Hydrochloric acid pickling is used, and the pickling temperature is controlled at 65℃~75℃. Water washing adopts multi-stage countercurrent water washing. The purpose of pickling is to quickly remove oxide scale and silicon-depleted layer, restore uniform Si distribution, reduce iron loss, and provide a clean surface guarantee for the low noise and high energy efficiency of the finished motor steel.

[0033] (5) Normalizing: The heating rate of the coil after entering the normalizing furnace is controlled at 200℃ / min to 240℃ / min. A reasonable heating rate can ensure that the temperature of the coil rises uniformly during the heating process, avoiding thermal stress concentration caused by excessive heating, thereby reducing internal cracks and defects in the material. The normalizing temperature is 860℃ to 920℃, and the normalizing time is set within the range of 4min to 6min. The atmosphere inside the furnace is pure nitrogen to prevent oxidation of the coil surface. During the cooling process, the cooling rate is kept uniform to avoid local overcooling or overheating.

[0034] (6) After normalization, a second hydrochloric acid pickling is performed to remove the Fe3O4-Fe2O3 composite oxide film and near-surface silicon-poor layer generated during normalization, ensuring stable bite of the cold rolling rough roll, thereby further optimizing the final product plate shape and surface quality, directly reducing the noise of the handheld heating appliance motor by 1-3dB and extending the high-temperature operating life of the motor.

[0035] (7) Cold rolling: The pickled coils are fed into a cold rolling mill for cold rolling. Cold rolling is performed in multiple passes. Except for the finishing pass, rough-surfaced rolls are used on the work rolls: the Ra value of the rough-surfaced rolls is in the range of 1μm to 3μm. This is to ensure that the material has good bite-in properties during the rolling process, and at the same time reduce surface scratches caused by excessive surface roughness. Smooth-surfaced rolls are used on the finishing pass. The Ra value of the smooth-surfaced rolls is recommended to be in the range of 0.1μm to 0.2μm to ensure the surface quality of the final product. From the first pass to the last pass, the strip tension is gradually increased; the tension in the first pass is 120–140 MPa, and then gradually increases in each subsequent pass until the tension in the last pass is 210–250 MPa. The purpose of this gradual increase in tension is to continuously improve the flatness of the strip through sustained longitudinal micro-tension, and to offset the increase in rolling force caused by hardening with the increase in tension, suppressing edge cracking defects commonly seen in the rolling of ultra-thin products (0.15–0.25 mm), improving the thickness difference between the strip and the plate, and laying the foundation for deformation energy storage for the homogenization of the strip's microstructure after annealing. This tension adjustment strategy effectively improves the dimensional accuracy and surface quality of the material, ensuring that the thickness difference between the strip and the plate required for the finished steel product for handheld heating appliances is ≤1.5%.

[0036] (8) Finished product annealing: Before entering the continuous annealing furnace, the cold-rolled sheet is leveled with a small elongation using a pre-furnace tension roller to further improve the strip shape. The leveling elongation is controlled at 0.2% to 0.6%. During the leveling process, the tension of the tension roller used for leveling should be controlled at 5kN to 10kN. The annealing homogenization temperature is controlled at 880℃ to 960℃, and the homogenization time is set within the range of 2min to 4min. During the annealing process, a mixture of hydrogen and nitrogen is used as the protective atmosphere, with the volume fraction of hydrogen controlled at 6% to 12% and the volume fraction of nitrogen controlled at 88% to 94%. The final finished product grain size is required to be in the range of 80 to 120μm. This grain size range improves corrosion resistance and optimizes electromagnetic properties, providing a comprehensive performance balance for high-performance thin-gauge non-oriented silicon steel for handheld heating appliance motors.

[0037] To make the objectives, technical solutions, and technical effects of this invention clearer, the technical solutions in the embodiments of this invention are now described clearly and completely. However, the embodiments described below are only some embodiments of this invention, not all embodiments. All other embodiments obtained by those skilled in the art in conjunction with the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0038] The chemical composition of the examples is shown in Table 1; Table 1: Chemical Composition (%) Example 1: Steel for the motor of a handheld heating appliance, the production method is as follows: a) Steelmaking The target temperature for converter melting is 1520℃. First, add the main alloying elements such as ferrosilicon and ferromanganese, stir until homogeneous, and hold at this temperature for 5 minutes. Then add ferrizircon and ferronickel, stir until homogeneous, and hold at this temperature for 5 minutes. Finally, add ferroaluminum, stir until homogeneous, and hold at this temperature for 2 minutes. Vacuum refining technology is used to achieve a sulfur (S) content of 0.0007% and a nitrogen (N) content of 0.0019%. The target refining temperature is 1570℃, and the total refining time is 42 minutes.

[0039] b) Hot-rolled The target range for slab homogenization temperature is 1200±20℃; the heating time is set to 180min; the reduction rates for the four passes in the roughing stage are 23%, 22%, 15%, and 10%, respectively; the rolling speed is controlled at 2.2m / s; the rolling temperature is set at 1140±20℃; the target range for the final rolling temperature is 870±20℃; and the final hot-rolled thickness is 2.2mm.

[0040] c) Pickling Hydrochloric acid pickling is used, and the pickling temperature is controlled at 68±3℃.

[0041] d) Normalization The heating rate of the coil after entering the normalizing furnace is controlled at 240℃ / min. The target normalizing temperature is 920℃, and the normalizing time is set within a range of 4 minutes. The furnace atmosphere is pure nitrogen.

[0042] e) Secondary pickling After normalization, a second hydrochloric acid pickling was performed at a hydrochloric acid mass fraction of 15%, a temperature of 55℃, and a pickling time of 12s.

[0043] f) Cold rolling The finished product thickness is 0.15 mm. Cold rolling is carried out in 6 passes. The work rolls for passes 1 to 5 are rough rolls with a Ra value of 1 μm. The 6th pass uses smooth rolls with a Ra value of 0.1 μm. From the first pass to the last pass, the strip pre-tension stress is set in the ranges of 140–150 MPa, 170–180 MPa, 180–190 MPa, 200–210 MPa, 210–220 MPa, and 240–250 MPa, respectively, to ensure the dimensional accuracy and surface quality of the strip during the rolling process.

[0044] g) Finished product annealing Before entering the continuous annealing furnace, the cold-rolled sheet is leveled with a small elongation using a furnace-front tension roller. The target elongation during leveling is 0.2 ± 0.1%. During leveling, the tension roller is set to 5 kN. The annealing homogenization temperature is controlled at 880℃, and the homogenization time is set to 4 minutes. The annealing protective atmosphere is a mixture of hydrogen and nitrogen, with a hydrogen volume fraction of 6% and a nitrogen volume fraction of 94%. The target thickness of the insulating coating is 1.5 μm. The average grain size of the final product is 85 μm.

[0045] The performance of the 0.15mm specification product is shown in Table 2; Table 2: Example 2: Steel for the motor of a handheld heating appliance, the production method is as follows: a) Steelmaking The target temperature for converter melting is 1550℃. First, add the main alloying elements such as ferrosilicon and ferromanganese, stir until homogeneous, and hold at this temperature for 7 minutes. Then add ferrizircon and ferronickel, stir until homogeneous, and hold at this temperature for 4 minutes. Finally, add ferroaluminum, stir until homogeneous, and hold at this temperature for 3 minutes. Vacuum refining technology is used to achieve a sulfur (S) content of 0.0009% and a nitrogen (N) content of 0.0016%. The target refining temperature is 1590℃, and the total refining time is 45 minutes.

[0046] b) Hot-rolled The target range for slab homogenization temperature is 1220±20℃; the heating time is set to 200min; the reduction rates for the four passes in the roughing stage are 25%, 22%, 13%, and 10%, respectively; the rolling speed is controlled at 2.6m / s; the rolling temperature is set at 1150±20℃; the target range for the final rolling temperature is 880±20℃; and the final hot-rolled thickness is 2.3mm.

[0047] c) Pickling Hydrochloric acid pickling is used, and the pickling temperature is controlled at 70±3℃.

[0048] d) Normalization The heating rate of the coiled steel sheet entering the normalizing furnace before normalizing is controlled at 220℃ / min. The target normalizing temperature is 890℃, and the normalizing time is set within a range of 5 minutes. The furnace atmosphere is pure nitrogen.

[0049] e) Secondary pickling After normalization, a second hydrochloric acid pickling was performed. The hydrochloric acid mass fraction was 17%, the temperature was 60℃, and the pickling time was 10s.

[0050] f) Cold rolling The finished product thickness is 0.20 mm. Cold rolling is carried out in 6 passes. The work rolls for passes 1 to 5 are rough rolls with a Ra value of 2 μm. The 6th pass uses smooth rolls with a Ra value of 0.15 μm. From the first pass to the last pass, the reference ranges for the strip pre-tension stress are set as follows: 140–150 MPa, 150–160 MPa, 170–180 MPa, 180–190 MPa, 210–220 MPa, and 220–230 MPa, respectively, to ensure the dimensional accuracy and surface quality of the strip during the rolling process.

[0051] g) Finished product annealing Before entering the continuous annealing furnace, the cold-rolled sheet is leveled with a small elongation using a furnace-front tension roller. The target elongation for leveling is 0.4 ± 0.1%. During leveling, the tension of the leveling tension roller is set to 8 kN. The annealing homogenization temperature is controlled at 930℃, and the homogenization time is set to 3 minutes. The annealing protective atmosphere is a mixture of hydrogen and nitrogen, with a hydrogen volume fraction of 10% and a nitrogen volume fraction of 90%. The target thickness of the insulating coating is 1.2 μm. The average grain size of the final product is 102 μm.

[0052] The performance of the 0.20mm specification product is shown in Table 3; Table 3: Example 3: Steel for the motor of a handheld heating appliance, the production method is as follows: a) Steelmaking The target temperature for converter melting is 1570℃. First, add the main alloying elements such as ferrosilicon and ferromanganese, stir until homogeneous, and hold at this temperature for 10 minutes. Then add ferrizircon and ferronickel, stir until homogeneous, and hold at this temperature for 3 minutes. Finally, add ferroaluminum, stir until homogeneous, and hold at this temperature for 3 minutes. Vacuum refining technology is used to achieve a sulfur (S) content of 0.0010% and a nitrogen (N) content of 0.0019%. The target refining temperature is 1620℃, and the total refining time is 40 minutes.

[0053] b) Hot-rolled The target range for slab homogenization temperature is 1260±20℃; the heating time is set to 240min; the reduction rates for the four passes in the roughing stage are 25%, 23%, 12%, and 10%, respectively; the rolling speed is controlled at 2.8m / s; the rolling temperature is set at 1160±20℃; the target range for the final rolling temperature is 900±20℃; and the final hot-rolled thickness is 2.6mm.

[0054] c) Pickling Hydrochloric acid pickling was used, with the pickling temperature controlled at 72±3℃. d) Normalization The heating rate of the coil after entering the normalizing furnace is controlled at 200℃ / min. The target normalizing temperature is 860℃, and the normalizing time is set within a range of 6 minutes. The furnace atmosphere is pure nitrogen.

[0055] e) Secondary pickling After normalization, a second hydrochloric acid pickling was performed. The hydrochloric acid mass fraction was 18%, the temperature range was 65℃, and the pickling time was 8 seconds.

[0056] f) Cold rolling The finished product thickness is 0.25 mm. Cold rolling is carried out in 6 passes. The work rolls for passes 1 to 5 are rough rolls with a Ra value of 3 μm. The 6th pass uses smooth rolls with a Ra value of 0.2 μm. From the first pass to the last pass, the reference ranges for the strip pre-tension stress are set as follows: 120–130 MPa, 130–140 MPa, 140–150 MPa, 170–180 MPa, 190–200 MPa, and 200–210 MPa, respectively, to ensure the dimensional accuracy and surface quality of the strip during the rolling process.

[0057] g) Finished product annealing Before entering the continuous annealing furnace, the cold-rolled sheet is leveled with a small elongation using a furnace-front tension roller. The target elongation for leveling is 0.5 ± 0.1%. During leveling, the tension of the leveling tension roller is set to 10 kN. The annealing homogenization temperature is controlled at 960℃, and the homogenization time is set to 2 minutes. The annealing protective atmosphere is a mixture of hydrogen and nitrogen, with a hydrogen volume fraction of 12% and a nitrogen volume fraction of 88%. The target thickness of the insulating coating is 1.0 μm. The average grain size of the final product is 115 μm.

[0058] The performance of the 0.25mm specification product is shown in Table 4; Table 4: Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A type of steel for a handheld heating appliance motor, characterized in that, Its chemical composition by mass fraction is as follows: C ≤ 0.003%, Si: 0.50%~1.50%, Mn: 0.1%~0.5%, Zr: 0.01%~0.05%, Y: 0.01%~0.05%, B: 0.005%~0.02%, Ni: 0.05%~0.2%, S ≤ 0.001%, N ≤ 0.002%, Als: 0.10%~0.30%, with the remainder being Fe and unavoidable residual elements.

2. The steel for a handheld heating appliance motor according to claim 1, characterized in that, The steel plate thickness is 0.15mm to 0.25mm.

3. The steel for a handheld heating appliance motor according to claim 1, characterized in that, Mechanical properties: Yield strength Rp0.2 ranges from 320MPa to 350MPa; coefficient of thermal expansion α ≤ 11.0 × 10⁻⁶. -6 / ℃.

4. A method for producing steel for a handheld heating appliance motor, characterized in that, Process steps: steelmaking, continuous casting, hot rolling, pickling, normalizing, cold rolling, and finished product annealing, specifically including: 1) Hot rolling: The heating furnace soaking temperature is controlled at 1180℃~1280℃, the heating time is set at 180min~240min, the temperature gradient in the heating furnace is controlled at ≤10℃ / m, the reduction rate of each pass of rough rolling is controlled at 10%~25%, the rolling speed is controlled at 2.2m / s~2.8m / s, the rolling temperature range is 1120℃~1180℃, the final rolling temperature is set at 850℃~920℃, and the thickness of the hot rolled plate is 2.2mm~2.6mm; 2) Pickling: The pickling temperature is controlled at 65℃~75℃, and multi-stage countercurrent water washing is adopted; 3) Normalizing: The heating rate of the normalizing furnace is controlled at 200℃ / min~240℃ / min, the normalizing homogenization temperature is 860℃~920℃, the homogenization time is set within the range of 4min~6min, and the atmosphere inside the furnace is pure nitrogen atmosphere; 4) After normalization, perform a second hydrochloric acid pickling with a hydrochloric acid mass fraction of 15% to 18%, a temperature range of 55 to 65°C, and a pickling time of 8 to 12 seconds to peel off the Fe3O4-Fe2O3 composite oxide film and near-surface silicon-poor layer generated during normalization. 5) Cold rolling: The pickled coils are fed into a cold rolling mill for cold rolling. Cold rolling adopts multi-pass rolling. Except for the finishing pass, the work rolls are rough rolls: the Ra value of the rough rolls is in the range of 1μm to 3μm. The finishing pass uses smooth rolls, and the Ra value of the smooth rolls is recommended to be in the range of 0.1μm to 0.2μm. From the first pass to the last pass, the tensile stress of the strip is set to gradually increase. 6) Finished product annealing: Before entering the continuous annealing furnace, the cold-rolled sheet is leveled with an elongation of 0.2% to 0.6% using a tension roller in front of the furnace. During the leveling process, the tension of the tension roller used for leveling should be controlled at 5kN to 10kN. The annealing homogenization temperature is controlled at 880℃ to 960℃, and the homogenization time is set within the range of 2min to 4min. During the annealing process, a mixture of hydrogen and nitrogen is used as the protective atmosphere. The average grain size of the final product is required to be in the range of 80 to 120μm.

5. A method for producing steel for a handheld heating appliance motor according to claim 4, characterized in that, The steelmaking process is as follows: the converter smelting temperature is controlled within the range of 1520℃ to 1580℃. During smelting, ferrosilicon and ferromanganese are added first, stirred evenly and kept at the temperature for 5 to 10 minutes. Then, ferrizircon and ferronickel are added, stirred evenly and kept at the temperature for 3 to 5 minutes. Finally, ferroaluminum is added, stirred evenly and kept at the temperature for 2 to 3 minutes. The refining process uses vacuum degassing technology to control the sulfur content in the molten steel to ≤10ppm and the nitrogen content to ≤20ppm. The refining temperature is controlled within the range of 1560℃ to 1620℃, and the refining time is not less than 35 minutes. During the refining process, argon blowing is used for stirring to ensure that the inclusions in the molten steel float to the surface.

6. A method for producing steel for a handheld heating appliance motor according to claim 4, characterized in that, The continuous casting process is as follows: casting speed 4.0~5.5m / min, tundish superheat 15~25℃; crystallizer electromagnetic stirring current 300~350A, frequency 12Hz, to ensure central equiaxed crystal ratio ≥55%; secondary cooling adopts gas-mist two-phase dynamic water distribution model, specific water volume 0.8~1.1L / kg, billet surface temperature gradient ≤8℃ / cm, billet 160mm.

7. A method for producing steel for a handheld heating appliance motor according to claim 4, characterized in that, In step 6), the volume fraction of hydrogen is controlled at 6% to 12%, and the volume fraction of nitrogen is controlled at 88% to 94%.

Images