Non-oriented silicon steel without normalizing and manufacturing method thereof

Abstract

This invention discloses a non-oriented silicon steel of a certain grade that is exempt from normalizing and its manufacturing method. The chemical composition of the silicon steel is: C≤0.003%, S≤0.0010%, N≤0.0010%, Si: 1.40~2.0%, Al: 0.2~0.5%, Mn: 0.5~1.0%, Sn: 0.01~0.05%, P≤0.02%, Nb+V+Ti≤50ppm. The manufacturing method includes smelting, continuous casting, hot rolling, cold rolling, and recrystallization annealing. The continuous casting speed is ≤0.8m / min, the hot rolling finishing temperature is 920±15℃, the coiling temperature is 750±20℃, the annealing temperature is 950~1050℃, and the annealing time is 3~8min. The iron loss P of the non-oriented silicon steel of this invention is... 1.5 / 50 ≤2.9W / kg, magnetic induction B 5000 With a capacity of 1.68~1.70T, it meets the demand of high-efficiency industrial motors and compressors for high-performance, low-cost silicon steel materials.

Description

Technical Field

[0001] This invention belongs to the field of non-oriented silicon steel technology, specifically relating to a non-normalizing medium-grade non-oriented silicon steel and its manufacturing method, and more particularly to a non-normalizing medium-grade non-oriented silicon steel and its manufacturing method for use in electric bicycles, home appliances and other fields. Background Technology

[0002] Non-oriented silicon steel is a key soft magnetic material for manufacturing motor cores, and its performance directly affects the motor's efficiency, energy consumption, and temperature rise. With the increasing global energy efficiency standards, the performance requirements for silicon steel sheets in fields such as electric bicycles, high-efficiency home appliances, and compressors are becoming increasingly stringent. Newly promulgated technical standards (such as the new national standard for electric bicycles and the new energy efficiency standard for home appliances) generally require motors to have higher efficiency and power density, which directly translates into a demand for lower iron losses and higher magnetic induction in silicon steel materials.

[0003] Medium-grade non-oriented silicon steel refers to a type of material in the non-oriented silicon steel product system with medium magnetic properties, generally referring to the iron loss value P. 1.5 / 50 Cold-rolled non-oriented silicon steel with an iron loss (P) between 4 and 6 W / kg. Currently, mainstream medium-grade non-oriented silicon steels such as 35W550 are widely used in the home appliance and electric bicycle markets. However, with the upgrading of end products, existing users have clearly stated their need to upgrade the material grade to a higher performance level while maintaining current procurement costs. Currently, medium-grade non-oriented silicon steel requires a higher iron loss (P). 1.5 / 50 Significantly reducing while maintaining high magnetic permeability means that materials need to achieve a better balance between low loss and high permeability.

[0004] In existing technologies, producing higher-grade non-oriented silicon steel typically relies on stricter chemical composition control, higher silicon and aluminum content, cleaner molten steel, and more complex rolling and heat treatment processes, including a normalizing annealing process. Normalizing annealing, an intermediate annealing process performed after hot-rolled sheet coiling and before cold rolling, effectively improves the uniformity of the hot-rolled sheet's microstructure, eliminates internal stress, and coarsens unfavorable {100} texture components, laying the foundation for obtaining favorable textures and properties in subsequent processes. However, this process is energy-intensive, has a long production cycle, and significantly increases costs, which sharply contradicts the user's requirement of "low cost."

[0005] Therefore, the industry urgently needs to develop an innovative manufacturing technology for medium-grade non-oriented silicon steel that eliminates the normalizing and annealing process. This technology, by completely omitting the normalizing and annealing steps, must overcome the challenges of microstructure inheritance and texture control caused by the lack of normalizing through systematic composition design, hot rolling process optimization, and annealing process control. Ultimately, it should stably achieve higher performance indicators, with overall production costs no higher than those of medium-grade non-oriented silicon steel products such as 35W550. This is not only a significant challenge to existing production processes but also crucial for seizing the high-end market, meeting user upgrade needs, and enhancing the core competitiveness of enterprises.

[0006] Chinese patent application CN202311105861.1, entitled "A Medium-Grade Non-Oriented Silicon Steel Without Normalizing and its Manufacturing Method," describes a method that increases the Mn content to control the grain morphology and size of hot-rolled steel, allowing the cold-rolled steel to achieve sufficient deformation storage. The steel is then fully recrystallized during annealing without normalizing to obtain 50W470 non-oriented silicon steel with excellent magnetic properties. However, the product obtained by this method generally exhibits lower iron loss and magnetic properties compared to steel produced through normalizing.

[0007] Chinese patent application CN202510831707.5, entitled "A Method for Producing Non-Oriented Electrical Steel Without Normalization," describes a method that uses a low Si (0.1%~1.0%) composition and adds Sn+Sb, elements that improve texture, to achieve a higher P-value in 0.50mm silicon steel. 1.5 / 50 Controlled below 5W / kg, magnetic induction B 5000 ≥1.69T. This method is mainly for the production of low-grade non-oriented silicon steel without normalization, and it involves the addition of too many precious metals Sn and Sb, resulting in high costs and making it uncompetitive in the market.

[0008] Chinese patent application CN202510994176.1, entitled "Method for Producing High-Grade Non-Oriented Electrical Steel Without Normalizing," describes a method that adjusts the hot-rolling reduction rate, adds a heat-insulating pit, and increases the hot-rolling coiling temperature. It replaces the traditional normalizing step with self-annealing using residual heat from hot rolling, and employs a two-stage cold rolling process to obtain high-efficiency non-oriented electrical steel with excellent dimensions and properties. While this technology primarily targets high-grade non-oriented silicon steel, it does not shorten the production process; the process is lengthy and its economic efficiency remains low. Summary of the Invention

[0009] To address the aforementioned technical problems in the prior art, this invention provides a normalization-free non-oriented silicon steel and its manufacturing method.

[0010] The method for manufacturing non-oriented silicon steel without normalizing provided by this invention adopts a process route of smelting → continuous casting → hot rolling → cold rolling → recrystallization annealing, omitting the normalizing annealing process, and specifically includes the following steps: (1) Composition design and smelting: Clean molten steel is obtained by converter smelting and RH vacuum treatment. The chemical composition of the molten steel is controlled by mass percentage as follows: C≤0.003wt%, S≤0.0010wt%, N≤0.0010wt%, Si:1.40~2.0wt%, Al:0.2~0.5wt%, Mn:0.5~1.0wt%, Sn:0.01~0.05wt%, P≤0.02wt%, and (Nb+V+Ti)≤50ppm, with the remainder being Fe and unavoidable impurities; (2) Continuous casting: The molten steel obtained in step (1) is continuously cast into a billet. The casting speed is controlled to be ≤0.8m / min. Electromagnetic stirring is added during the continuous casting process. (3) Hot rolling: The billet obtained in step (2) is heated, rolled and coiled to obtain a hot rolled coil of the target thickness specification. The heating temperature is controlled at 1100℃~1150℃, the holding time is controlled at ≥80min, the final rolling temperature is controlled at 920±15℃, and the coiling temperature is controlled at 750±20℃. (4) Cold rolling: The hot-rolled coil obtained in step (3) is pickled and then cold-rolled to the target thickness specification in one step; (5) Recrystallization annealing: The cold-rolled coil obtained in step (4) is subjected to recrystallization annealing. The recrystallization annealing atmosphere is a strong reducing atmosphere. The recrystallization annealing temperature is controlled at 950℃~1050℃ and the recrystallization annealing time is controlled at 3min~8min. Then, a coating is applied and the coil is rolled up to obtain non-oriented silicon steel.

[0011] Furthermore, in the above-mentioned method for manufacturing non-oriented silicon steel of the grade without normalization, in step (2), the equiaxed crystal ratio of the billet is controlled to ≥85% by electromagnetic stirring.

[0012] Furthermore, in the above-mentioned method for manufacturing non-oriented silicon steel of grade A without normalization, in step (3), phosphorus is not removed during the finishing rolling stage of hot rolling, and the hot-rolled coil is quickly fed into the heat preservation cover for heat preservation.

[0013] Furthermore, in the above-mentioned method for manufacturing non-oriented silicon steel of the grade without normalization, in step (3), the thickness of the hot-rolled coil is controlled to be 1.5mm~2.0mm.

[0014] Furthermore, in the above-mentioned method for manufacturing non-oriented silicon steel of the grade without normalization, in step (3), the billet heating time is controlled to be ≥200 min.

[0015] Furthermore, in the above-mentioned method for manufacturing non-oriented silicon steel of grade A without normalization, in step (4), the pickling solution used for pickling the hot-rolled coil is a hydrochloric acid solution with a concentration of 15% to 30%, and the temperature of the pickling solution is controlled at 60°C to 90°C.

[0016] Furthermore, in the above-mentioned method for manufacturing non-oriented silicon steel of the grade without normalization, in step (4), the thickness specification of the cold-rolled coil is 0.35mm.

[0017] Furthermore, in the above-mentioned method for manufacturing non-oriented silicon steel of grade A without normalization, in step (5), the recrystallization annealing atmosphere is a mixture of H2 and N2, wherein the volume ratio of H2 to N2 is H2:N2 > 1:1.

[0018] The non-normalized medium-grade non-oriented silicon steel provided by this invention is produced by the above-described method for manufacturing non-normalized medium-grade non-oriented silicon steel. The chemical composition of the non-normalized medium-grade non-oriented silicon steel by mass percentage is as follows: C≤0.003wt%, S≤0.0010wt%, N≤0.0010wt%, Si: 1.40~2.0wt%, Al: 0.2~0.5wt%, Mn: 0.5~1.0wt%, Sn: 0.01~0.05wt%, P≤0.02wt%, and (Nb+V+Ti)≤50ppm, with the remainder being Fe and unavoidable impurities.

[0019] Furthermore, the iron loss P of the aforementioned non-oriented silicon steel grades exempt from normalization... 1.5 / 50 ≤2.9W / kg, magnetic induction B 5000 The value is 1.68~1.70T.

[0020] The present invention provides non-normalized non-oriented silicon steel of various grades and its manufacturing method, which have the following advantages and beneficial effects: This invention synergistically optimizes the composition and process, successfully achieving excellent magnetic performance indicators by completely omitting the traditional normalizing heat treatment step. Specifically, it achieves a low iron loss P0.05 for medium-grade non-oriented silicon steel. 1.5 / 50 ≤2.9W / kg, magnetic induction B 5000 With a capacity of 1.68~1.70T, a simple and efficient process, significantly reduced energy consumption, and stable product performance, the medium-grade non-oriented silicon steel of this invention, which combines low iron loss and high magnetic induction, can effectively improve the energy efficiency of motors and meet the demand for high-performance, low-cost silicon steel materials in fields such as high-efficiency industrial motors and high-efficiency compressors, and has good prospects for industrial application.

[0021] This invention employs a synergistic technical approach of "ultra-pure steel and microalloying + low-speed continuous casting + thin-gauge hot rolling in the full austenitic region." This involves extremely low C, S, and N content, the addition of trace amounts of Sn, strict limitations on Nb, V, and Ti content, and increased Mn content. This is combined with a low casting speed (≤0.8 m / min), thin-gauge hot rolling (1.5~2.0 mm), high-temperature hot rolling at a final rolling temperature of 920±15℃ and a coiling temperature of 750±20℃, and a high-temperature rolling process at 950℃~1050℃ for 3~8 minutes under a strongly reducing atmosphere. High-temperature short-time annealing and other process controls comprehensively optimize the microstructure of the billet from the source, the hot-rolled phase transformation and texture evolution, and the final recrystallization microstructure. Under the premise of completely eliminating the traditional normalizing heat treatment, medium-grade non-oriented silicon steel with low iron loss and high magnetic induction is obtained. This represents a technological advancement in the production of high-performance non-oriented silicon steel and solves the technical problems of long production process, high energy consumption, and reliance on normalizing heat treatment to improve magnetic properties in existing non-oriented silicon steel production technologies. It has significant advantages in terms of technological advancement and economic feasibility. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. 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.

[0023] In order to accurately respond to users' urgent need to upgrade products without increasing costs, and to seize the market opportunities brought about by the implementation of new standards in fields such as electric bicycles and home appliances, this invention has developed a normalization-free medium-grade non-oriented silicon steel and its manufacturing method.

[0024] The chemical composition of the non-oriented silicon steel of the non-normalizing grade provided by this invention is designed by mass percentage as follows: C≤0.003wt%, S≤0.0010wt%, N≤0.0010wt%, Si:1.40~2.0wt%, Al:0.2~0.5wt%, Mn:0.5~1.0wt%, Sn:0.01~0.05wt%, P≤0.02wt%, and (Nb+V+Ti)≤50ppm, with the remainder being Fe and unavoidable impurities.

[0025] The method for manufacturing non-oriented silicon steel without normalizing provided by this invention adopts a process route of smelting → continuous casting → hot rolling → cold rolling → recrystallization annealing, omitting the normalizing annealing process, and specifically includes the following steps: (1) Composition design and smelting: Clean molten steel is obtained by converter smelting and RH vacuum treatment. The chemical composition of the molten steel is controlled by mass percentage as follows: C≤0.003wt%, S≤0.0010wt%, N≤0.0010wt%, Si:1.40~2.0wt%, Al:0.2~0.5wt%, Mn:0.5~1.0wt%, Sn:0.01~0.05wt%, P≤0.02wt%, and (Nb+V+Ti)≤50ppm, with the remainder being Fe and unavoidable impurities; (2) Continuous casting: The molten steel obtained in step (1) is continuously cast into a 230mm thick billet. The continuous casting speed is controlled to be ≤0.8m / min. Electromagnetic stirring is added during the continuous casting process. The equiaxed crystal ratio of the billet is controlled to be ≥85%. (3) Hot rolling: The billet obtained in step (2) is heated, rolled and coiled to obtain a hot rolled coil of the target thickness specification. The heating temperature is controlled at 1100℃~1150℃, the heating time is controlled at ≥200min, the holding time is controlled at ≥80min, the finishing rolling stage of hot rolling is not dephosphorized, the final rolling temperature is controlled at 920±15℃, the coiling temperature is controlled at 750±20℃, the thickness specification of the hot rolled coil is 1.5mm~2.0mm, and the hot rolled coil is quickly sent into the heat preservation cover for heat preservation. (4) Cold rolling: The hot-rolled coil obtained in step (3) is pickled and then cold-rolled to the target thickness specification in one step. The thickness specification of the cold-rolled coil is 0.35 mm. The pickling solution is a hydrochloric acid solution with a concentration of 15%~30%, and the temperature of the pickling solution is controlled at 60℃~90℃. (5) Recrystallization annealing: The cold-rolled coil obtained in step (4) is subjected to recrystallization annealing. The recrystallization annealing atmosphere is a strong reducing atmosphere. Preferably, the recrystallization annealing atmosphere is a mixture of H2 and N2, wherein the volume ratio of H2 to N2 is H2:N2>1:1. The recrystallization annealing temperature is controlled at 950℃~1050℃ and the recrystallization annealing time is controlled at 3min~8min. Then, a coating is applied and the coil is rolled up to obtain non-oriented silicon steel.

[0026] The main technological innovations and related principles of the present invention regarding the non-normalizing, non-oriented silicon steel and its manufacturing method include: 1. Composition Design and Smelting: Converter smelting is adopted, followed by RH vacuum circulation degassing and refining to obtain steel with the target composition. The core lies in extreme purity control and specific microalloying, controlling interstitial atoms (C, N) and impurity elements (S) at extremely low levels to minimize magnetic domain pinning and magnetic aging tendency, laying a pure matrix foundation for high magnetic properties; adding 0.01~0.05wt% trace amounts of Sn, utilizing its surface segregation effect to suppress the growth of unfavorable texture components during annealing; strictly limiting strong carbonitride forming elements, requiring (Nb+V+Ti)≤50ppm, to prevent the formation of fine precipitates that hinder grain boundary movement and magnetic domain wall displacement; increasing the Mn content to 0.5~1.0wt% to expand and stabilize the austenite phase region, ensuring that subsequent hot rolling is carried out entirely within the single-phase austenite region at high temperatures, avoiding mixed crystals and texture deterioration caused by two-phase rolling.

[0027] 2. Continuous casting and electromagnetic stirring: The key technical step in the continuous casting of refined molten steel is to use a low casting speed of ≤0.8m / min in conjunction with electromagnetic stirring. The low casting speed helps to slow down the growth rate of columnar crystal regions, providing more time for equiaxed crystal nucleation and growth. The electromagnetic force generated by electromagnetic stirring can break dendrites, increase melt flow, and promote crystal nucleus proliferation and uniform distribution. The synergistic effect of low casting speed and electromagnetic stirring aims to obtain a thick billet with a high proportion of equiaxed crystals. A high proportion of equiaxed crystals means a uniform as-cast microstructure and small compositional segregation, providing a uniform initial microstructure for subsequent hot rolling and optimizing the heritability of the microstructure from the source.

[0028] 3. Hot rolling process: The billet is heated to 1100℃~1150℃ and held at that temperature for thorough homogenization, allowing the alloying elements to fully dissolve and the original as-cast microstructure to become homogenized. The core innovation of the hot rolling process lies in "austenitic zone rolling + thin-gauge control + prefabrication of normalization-free texture," specifically: 3.1 Finishing rolling without dephosphorization: The retained iron oxide scale may play a certain role in lubrication and heat insulation during subsequent rolling, which helps to maintain temperature uniformity.

[0029] 3.2 Rolling in the entire austenitic region: Based on the high Mn composition design, it is ensured that rolling is completed within the single-phase austenitic region at the final rolling temperature. Rolling in this region allows for sufficient dynamic and static recrystallization, making it easy to obtain fine, equiaxed recrystallized austenite grains. This microstructure effectively avoids corrugated defects caused by deformation bands or the inheritance of unrecrystallized austenite after cold rolling and annealing.

[0030] 3.3 High-Temperature Coiling and Thin-Gauge Hot Rolling: Utilizing a higher coiling temperature allows for sufficient recovery and moderate grain growth during the slow cooling process of the hot-rolled sheet. This facilitates stress release and optimizes texture. Combined with hot rolling to 1.5~2.0mm thin gauges, it reduces subsequent cold rolling reduction. The optimized hot-rolled microstructure and texture (stronger {100} and {Goss} texture components) can be more effectively inherited to the final annealed state, partially replacing the function of normalizing annealing in optimizing texture, thereby directly improving the magnetic induction intensity of the final product. Furthermore, rapid feeding into a heat-insulating hood after rolling aims to slow the cooling rate and further promote the stability of the favorable microstructure.

[0031] 4. Cold rolling and recrystallization annealing: After pickling, the hot-rolled plate is directly cold-rolled to the target thickness in one step. The subsequent recrystallization annealing is carried out in a strongly reducing atmosphere (H2:N2 > 1:1) at 950℃~1050℃ for 3~8 minutes. This high-temperature, short-time annealing process aims to: 4.1 Achieve complete recrystallization of the cold-rolled deformed structure to form coarse and uniform ferrite grains, thereby reducing hysteresis loss.

[0032] 4.2 The surface of the steel strip is further purified by using high temperature and reducing atmosphere to promote grain growth.

[0033] 4.3 Precisely matching the high-quality hot-rolled microstructure and texture pre-fabricated by the aforementioned process promotes the preferential development and growth of the {100}<0vw> and {Goss} textures, which are beneficial to magnetic induction, during recrystallization, while inhibiting {111} <uvw>Unfavorable textures, etc., thereby synergistically enhancing magnetic properties.

[0034] Therefore, the medium-grade non-oriented silicon steel and its manufacturing method provided by this invention utilize a three-pronged synergistic approach: "extremely pure steel quality and microalloying design, hot-rolled thin specifications and full austenitic rolling, and coordinated control of texture throughout the continuous casting-hot rolling-annealing process." This approach completely eliminates the traditional normalizing heat treatment step, comprehensively optimizing the initial billet microstructure, hot-rolling phase transformation and texture evolution, and the final recrystallization microstructure. Ultimately, this achieves a comprehensive improvement in the overall magnetic properties of medium-grade non-oriented silicon steel, resulting in low iron loss and high magnetic induction. By eliminating the normalizing step, the iron loss P of the medium-grade non-oriented silicon steel of this invention is significantly reduced. 1.5 / 50 ≤2.9W / kg, magnetic induction B 5000 With a capacity of 1.68~1.70T, a simple and efficient process, significantly reduced energy consumption, and stable product performance, this invention's medium-grade non-oriented silicon steel product, which combines low iron loss and high magnetic induction, can effectively improve motor energy efficiency and meet the demand for high-performance, low-cost silicon steel materials in fields such as high-efficiency industrial motors and high-efficiency compressors, and has good prospects for industrial application.

[0035] The following detailed embodiments and comparative examples further illustrate the non-normalizing grade non-oriented silicon steel and its manufacturing method of the present invention.

[0036] Example 1 The chemical composition of the non-oriented silicon steel of the non-normalizing grade in Example 1 was designed by mass percentage as follows: C: 0.0025wt%, S: 0.0008wt%, N: 0.0009wt%, Si: 1.65wt%, Al: 0.35wt%, Mn: 0.80wt%, Sn: 0.03wt%, P: 0.015wt%, and (Nb+V+Ti)=40ppm, with the remainder being Fe and unavoidable impurities.

[0037] The specific implementation process of the method for manufacturing non-oriented silicon steel of intermediate grades without normalization in Example 1 is as follows: (1) Composition design and smelting: Clean molten steel is obtained by converter smelting and RH vacuum circulation degassing. The chemical composition of the molten steel is controlled by mass percentage as follows: C: 0.0025wt%, S: 0.0008wt%, N: 0.0009wt%, Si: 1.65wt%, Al: 0.35wt%, Mn: 0.80wt%, Sn: 0.03wt%, P: 0.015wt%, and (Nb+V+Ti)=40ppm, with the remainder being Fe and unavoidable impurities; (2) Continuous casting: The molten steel is continuously cast into a 230mm thick billet. The casting speed is controlled at 0.75m / min. Electromagnetic stirring is used in the continuous casting process. The equiaxed crystal ratio of the billet is controlled at about 90%. (3) Hot rolling: The billet is heated, rolled and coiled to obtain a hot rolled coil with a thickness of 1.8 mm. The heating temperature is controlled at 1120℃ and the holding time is controlled at 90 min. After rough rolling, fine rolling is carried out. The phosphorus is not removed during fine rolling. The final rolling temperature is controlled at 915℃ and the coiling temperature is controlled at 755℃. The hot rolled coil is quickly sent into the heat preservation cover for heat preservation. (4) Cold rolling: After pickling, hot-rolled coils are cold-rolled to a thickness of 0.35 mm in one pass; (5) Recrystallization annealing: The cold-rolled coil is subjected to recrystallization annealing. The recrystallization annealing atmosphere is a mixture of H2 and N2, wherein the volume ratio of H2 to N2 is H2:N2=2:1. The recrystallization annealing temperature is controlled at 1000℃ and the recrystallization annealing time is controlled at 5min. After annealing, a coating is applied and the coil is rolled up to obtain non-oriented silicon steel.

[0038] Actual testing revealed the following properties of the non-oriented silicon steel product from Example 1: iron loss P 1.5 / 50 =2.82W / kg, magnetic induction B 5000 =1.685T, with excellent magnetic properties.

[0039] Example 2 The chemical composition of the non-oriented silicon steel of the non-normalizing grade in Example 2 was designed by mass percentage as follows: C: 0.0025wt%, S: 0.0008wt%, N: 0.0009wt%, Si: 1.65wt%, Al: 0.35wt%, Mn: 0.80wt%, Sn: 0.03wt%, P: 0.015wt%, and (Nb+V+Ti)=40ppm, with the remainder being Fe and unavoidable impurities.

[0040] The specific implementation process of the method for manufacturing non-oriented silicon steel of intermediate grades without normalization in Example 2 is as follows: (1) Composition design and smelting: Clean molten steel is obtained by converter smelting and RH vacuum circulation degassing. The chemical composition of the molten steel is controlled by mass percentage as follows: C: 0.0025wt%, S: 0.0008wt%, N: 0.0009wt%, Si: 1.65wt%, Al: 0.35wt%, Mn: 0.80wt%, Sn: 0.03wt%, P: 0.015wt%, and (Nb+V+Ti)=40ppm, with the remainder being Fe and unavoidable impurities; (2) Continuous casting: The molten steel is continuously cast into a 230mm thick billet. The casting speed is controlled at 0.75m / min. Electromagnetic stirring is used in the continuous casting process. The equiaxed crystal ratio of the billet is controlled at about 90%. (3) Hot rolling: The billet is heated, rolled and coiled to obtain a hot rolled coil with a thickness of 1.8 mm. The heating temperature is controlled at 1120℃ and the holding time is controlled at 90 min. After rough rolling, fine rolling is carried out. The phosphorus is not removed during fine rolling. The final rolling temperature is controlled at 935℃ and the coiling temperature is controlled at 775℃. The hot rolled coil is quickly sent into the heat preservation cover for heat preservation. (4) Cold rolling: After pickling, hot-rolled coils are cold-rolled to a thickness of 0.35 mm in one pass; (5) Recrystallization annealing: The cold-rolled coil is subjected to recrystallization annealing. The recrystallization annealing atmosphere is a mixture of H2 and N2, wherein the volume ratio of H2 to N2 is H2:N2=2:1. The recrystallization annealing temperature is controlled at 1000℃ and the recrystallization annealing time is controlled at 5min. After annealing, a coating is applied and the coil is rolled up to obtain non-oriented silicon steel.

[0041] Actual testing revealed the following properties of the non-oriented silicon steel product from Example 2: iron loss P 1.5 / 50 =2.85W / kg, magnetic induction B 5000 =1.701T, with excellent magnetic properties.

[0042] Compared with Example 1, Example 2, by moderately increasing the hot rolling final rolling temperature and coiling temperature, is conducive to further improving the magnetic induction while maintaining good iron loss performance.

[0043] Example 3 The chemical composition of the non-oriented silicon steel of the non-normalizing grade in Example 3 was designed by mass percentage as follows: C: 0.0025wt%, S: 0.0008wt%, N: 0.0009wt%, Si: 1.65wt%, Al: 0.35wt%, Mn: 0.80wt%, Sn: 0.03wt%, P: 0.015wt%, and (Nb+V+Ti)=40ppm, with the remainder being Fe and unavoidable impurities.

[0044] The specific implementation process of the method for manufacturing non-oriented silicon steel of intermediate grades without normalization in Example 3 is as follows: (1) Composition design and smelting: Clean molten steel is obtained by converter smelting and RH vacuum circulation degassing. The chemical composition of the molten steel is controlled by mass percentage as follows: C: 0.0025wt%, S: 0.0008wt%, N: 0.0009wt%, Si: 1.65wt%, Al: 0.35wt%, Mn: 0.80wt%, Sn: 0.03wt%, P: 0.015wt%, and (Nb+V+Ti)=40ppm, with the remainder being Fe and unavoidable impurities; (2) Continuous casting: The molten steel is continuously cast into a 230mm thick billet. The casting speed is controlled at 0.75m / min. Electromagnetic stirring is used in the continuous casting process. The equiaxed crystal ratio of the billet is controlled at about 90%. (3) Hot rolling: The billet is heated, rolled and coiled to obtain a hot rolled coil with a thickness of 1.5 mm. The heating temperature is controlled at 1120℃ and the holding time is controlled at 90 min. After rough rolling, fine rolling is carried out. The phosphorus is not removed during fine rolling. The final rolling temperature is controlled at 915℃ and the coiling temperature is controlled at 755℃. The hot rolled coil is quickly sent into the heat preservation cover for heat preservation. (4) Cold rolling: After pickling, hot-rolled coils are cold-rolled to a thickness of 0.35 mm in one pass; (5) Recrystallization annealing: The cold-rolled coil is subjected to recrystallization annealing. The recrystallization annealing atmosphere is a mixture of H2 and N2, wherein the volume ratio of H2 to N2 is H2:N2=2:1. The recrystallization annealing temperature is controlled at 1000℃ and the recrystallization annealing time is controlled at 5min. After annealing, a coating is applied and the coil is rolled up to obtain non-oriented silicon steel.

[0045] Actual testing revealed the following properties of the non-oriented silicon steel product from Example 3: iron loss P 1.5 / 50 =2.88W / kg, magnetic induction B 5000 =1.695T, with excellent magnetic properties.

[0046] Compared with Example 1, Example 3 further reduces the thickness of the hot-rolled plate, which is beneficial to further improve the magnetic induction while maintaining good iron loss performance.

[0047] Comparative Example 1 Comparative Example 1 is used to illustrate the effect of excessively low Mn content on the magnetic properties of non-oriented silicon steel by comparing it with the Example.

[0048] (1) Composition design: In order to compare the effect of Mn, the mass percentage content of Mn in Comparative Example 1 was significantly reduced to 0.25wt%, and the other components were basically the same as those in Example 1.

[0049] (2) Process parameters: The manufacturing process and parameters are strictly implemented in accordance with Example 1.

[0050] (3) Results and problems: After subsequent annealing, the finished steel plate of Comparative Example 1 showed obvious "corrugated" defects and uneven microstructure; the performance test results were: iron loss P 1.5 / 50 =3.65W / kg, magnetic induction B 5000 =1.655T, iron loss increases significantly, magnetic induction decreases significantly, and overall magnetic properties deteriorate significantly. This comparison proves that the Mn content (0.5~1.0wt%) in this invention is crucial for expanding the austenite region, ensuring rolling in the entire austenite region, preventing corrugated defects, and obtaining a superior final microstructure.

[0051] Comparative Example 2 Comparative Example 2 is used to illustrate the effect of excessively low hot rolling temperature on the magnetic properties of non-oriented silicon steel by comparing it with the Example.

[0052] (1) Ingredient design: The ingredients are the same as in Example 2.

[0053] (2) Hot rolling temperature adjustment: In Comparative Example 2, the final rolling temperature was reduced to 880°C and the coiling temperature was reduced to 700°C. Other process flow and parameters remained the same as in Example 2.

[0054] (3) Results and problems: Due to the low final rolling temperature, some rolling may occur in the two-phase region, resulting in mixed crystals and unfavorable texture in the microstructure of the hot-rolled plate. The final product performance is: P 1.5 / 50 =3.25W / kg, magnetic induction B 5000 =1.665T, iron loss increases significantly, magnetic induction decreases significantly, and overall magnetic properties deteriorate significantly. This comparison proves that the "high temperature" process of controlling the final rolling temperature at 920±15℃ and the coiling temperature at 750±20℃ in this invention is the key to ensuring high magnetic induction under normalization-free conditions.

[0055] Comparative Example 3 Comparative Example 3 is used to illustrate the effect of excessive hot-rolled sheet thickness on the magnetic properties of non-oriented silicon steel by comparing it with the Example.

[0056] (1) Ingredient design: The ingredients are the same as in Example 3.

[0057] (2) Adjustment of hot-rolled plate specifications: Comparative Example 3 does not use the thin-gauge hot rolling of the present invention, but increases the thickness of the hot-rolled plate to 2.6 mm. As a result, in order to ensure the final product thickness of 0.35 mm, the subsequent cold rolling reduction is significantly increased. Other process flows and parameters remain consistent with Example 3.

[0058] (3) Results and problems: Due to the thickness of the hot-rolled plate, the favorable {100} and {Goss} texture inheritance effects are weakened, while the large cold rolling reduction strengthens the unfavorable texture. The final product performance is: iron loss P 1.5 / 50 =3.10W / kg, magnetic induction B 5000 =1.672T, the magnetic properties are lower than those of Example 3 which uses a 1.5mm thin hot-rolled plate. This comparison proves that controlling the thickness of the hot-rolled plate to 1.5~2.0mm is a necessary process step to achieve "replacing part of the normalized function with hot rolling", optimize texture inheritance, and thus obtain high magnetic induction.

[0059] In summary, the present invention provides a method for manufacturing medium-grade non-oriented silicon steel without normalizing processes, through synergistic optimization of composition and process. By completely omitting the traditional normalizing heat treatment step, it successfully achieves excellent magnetic properties, particularly the iron loss P of the medium-grade non-oriented silicon steel. 1.5 / 50 ≤2.9W / kg, magnetic induction B 5000 Reaching a strength of 1.68~1.70T, this performance combination has reached the advanced level in the industry, effectively improving motor energy efficiency and meeting the demand for high-performance, low-cost silicon steel materials in fields such as high-efficiency industrial motors and high-efficiency compressors, demonstrating promising prospects for industrial application. Compared with existing technologies, the normalization-free non-oriented silicon steel and its manufacturing method of this invention have the following advantages and beneficial effects: This invention employs a synergistic technical approach of "ultra-pure steel and microalloying + low-speed continuous casting + thin-gauge hot rolling in the full austenitic region." This involves extremely low C, S, and N content, the addition of trace amounts of Sn, strict limitations on Nb, V, and Ti content, and increased Mn content. This is combined with a low casting speed (≤0.8 m / min), thin-gauge hot rolling (1.5~2.0 mm), high-temperature hot rolling at a final rolling temperature of 920±15℃ and a coiling temperature of 750±20℃, and a high-temperature rolling process at 950℃~1050℃ for 3~8 minutes under a strongly reducing atmosphere. High-temperature short-time annealing and other process controls comprehensively optimize the microstructure of the billet from the source, the hot-rolled phase transformation and texture evolution, and the final recrystallization microstructure. Under the premise of completely eliminating the traditional normalizing heat treatment, medium-grade non-oriented silicon steel with low iron loss and high magnetic induction is obtained. This represents a technological advancement in the production of high-performance non-oriented silicon steel and solves the technical problems of long production process, high energy consumption, and reliance on normalizing heat treatment to improve magnetic properties in existing non-oriented silicon steel production technologies. It has significant advantages in terms of technological advancement and economic feasibility.

[0060] In the description of this specification, the reference to the terms "embodiment," "example," etc., means that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, those skilled in the art can combine or combine the different embodiments or examples described in this specification and the features therein without causing contradiction.

[0061] It should be noted that, unless otherwise specified, the terms used herein have the meanings commonly understood by those skilled in the art. Furthermore, when a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum. Further, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Moreover, when multiple ranges are provided to describe features, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0062] It should also be noted that, in this document, the term "comprising" or any other variation thereof is intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the present invention.< / uvw>

Claims

1. A method for manufacturing non-oriented silicon steel of a certain grade without normalization, characterized in that, The process route adopts smelting → continuous casting → hot rolling → cold rolling → recrystallization annealing, omitting the normalizing annealing process, and specifically includes the following steps: (1) Composition design and smelting: Clean molten steel is obtained by converter smelting and RH vacuum treatment. The chemical composition of the molten steel is controlled by mass percentage as follows: C≤0.003wt%, S≤0.0010wt%, N≤0.0010wt%, Si:1.40~2.0wt%, Al:0.2~0.5wt%, Mn:0.5~1.0wt%, Sn:0.01~0.05wt%, P≤0.02wt%, and (Nb+V+Ti)≤50ppm, with the remainder being Fe and unavoidable impurities; (2) Continuous casting: The molten steel obtained in step (1) is continuously cast into a billet. The casting speed is controlled to be ≤0.8m / min. Electromagnetic stirring is added during the continuous casting process. (3) Hot rolling: The billet obtained in step (2) is heated, rolled and coiled to obtain a hot rolled coil of the target thickness specification. The heating temperature is controlled at 1100℃~1150℃, the holding time is controlled at ≥80min, the final rolling temperature is controlled at 920±15℃, and the coiling temperature is controlled at 750±20℃. (4) Cold rolling: The hot-rolled coil obtained in step (3) is pickled and then cold-rolled to the target thickness specification in one step; (5) Recrystallization annealing: The cold-rolled coil obtained in step (4) is subjected to recrystallization annealing. The recrystallization annealing atmosphere is a strong reducing atmosphere. The recrystallization annealing temperature is controlled at 950℃~1050℃ and the recrystallization annealing time is controlled at 3min~8min. Then, a coating is applied and the coil is rolled up to obtain non-oriented silicon steel.

2. The method for manufacturing non-oriented silicon steel without normalization as described in claim 1, characterized in that, In step (2), the equiaxed crystal ratio of the billet is controlled to be ≥85% by electromagnetic stirring.

3. The method for manufacturing non-oriented silicon steel without normalization as described in claim 1, characterized in that, In step (3), phosphorus is not removed during the finishing stage of hot rolling, and the hot-rolled coil is quickly fed into the heat preservation cover for heat preservation.

4. The method for manufacturing non-oriented silicon steel without normalization as described in claim 1, characterized in that, In step (3), the thickness of the hot-rolled coil is controlled to be 1.5mm~2.0mm.

5. The method for manufacturing non-oriented silicon steel without normalization as described in claim 1, characterized in that, In step (3), the heating time of the billet is controlled to be ≥200 min.

6. The method for manufacturing non-oriented silicon steel without normalization as described in claim 1, characterized in that, In step (4), the pickling solution used for hot-rolled coil pickling is a hydrochloric acid solution with a concentration of 15% to 30%, and the temperature of the pickling solution is controlled at 60℃ to 90℃.

7. The method for manufacturing non-oriented silicon steel without normalization as described in claim 1, characterized in that, In step (4), the thickness specification of the cold-rolled coil is 0.35 mm.

8. The method for manufacturing non-oriented silicon steel without normalization as described in claim 1, characterized in that, In step (5), the recrystallization annealing atmosphere is a mixture of H2 and N2, wherein the volume ratio of H2 to N2 is H2:N2 > 1:

1.

9. A non-normalizing, medium-grade non-oriented silicon steel, produced by the non-normalizing, medium-grade non-oriented silicon steel manufacturing method as described in any one of claims 1 to 8, characterized in that, The chemical composition of the non-oriented silicon steel of the aforementioned non-normalizing grade is as follows by mass percentage: C≤0.003wt%, S≤0.0010wt%, N≤0.0010wt%, Si: 1.40~2.0wt%, Al: 0.2~0.5wt%, Mn: 0.5~1.0wt%, Sn: 0.01~0.05wt%, P≤0.02wt%, and (Nb+V+Ti)≤50ppm, with the remainder being Fe and unavoidable impurities.

10. The non-normalizing, non-oriented silicon steel as described in claim 9, characterized in that, The iron loss P of the non-oriented silicon steel of the aforementioned non-normalization grade 1.5 / 50 ≤2.9W / kg, magnetic induction B 5000 The value is 1.68~1.70T.