Non-oriented electrical steel sheet with high magnetic induction and low core loss and method for manufacturing the same

Abstract

The present invention provides a non-oriented electrical steel sheet having high magnetic induction and low iron loss, which contains the following components by mass percentage: 0 < C ≤ 0.0030%, Si: 1.20 - 2.40%, Mn: 0.10 - 0.40%, Al: 0.10 - 0.60%; the balance being Fe and unavoidable impurities, and Si + Al being 1.30 - 2.80%. Correspondingly, the present invention also provides a method for manufacturing a non-oriented electrical steel sheet having high magnetic induction and low iron loss, comprising the following steps: smelting and casting; heating; rough rolling, finish rolling, and coiling: wherein the number of passes in the rough rolling pass is controlled to be 2 - 4 times, and the reduction ratio in the final pass of rough rolling is 51% - 67%; during the cooling process after the coiling stage, the cooling rate is controlled to be 1.0 - 4.0 °C / min in the range of 400 - 650 °C; directly performing cold rolling after pickling without accompanied by box annealing; providing a method including continuous annealing and application of an insulating coating.

Description

[Technical Field]

[0001] The present invention relates to a steel sheet and a manufacturing method thereof, and more particularly to a non-oriented electrical steel sheet and a manufacturing method thereof. [Background technology]

[0002] As the requirements for energy saving, consumption reduction, and environmental protection become increasingly stringent, non-oriented electrical steel sheets as raw materials and auxiliary materials for various motors, compressors, EI cores, and drive motors need to exhibit higher magnetic induction and lower iron loss while maintaining relatively low production costs.

[0003] In the prior art, the common methods for optimizing electromagnetic performance mainly include:

[0004] In order to effectively reduce iron loss, increasing the content of Si and Al in steel is exemplified by the technical solution disclosed in JP-A-8-3699.

[0005] To enhance the magnetic induction of steel, thin slab continuous casting and rolling or thin strip continuous casting is carried out, as exemplified by the technical solution disclosed in Chinese Patent Application Publication No. 1948517A (Publication date: April 18, 2007; Title of invention: Method for producing cold-rolled electrical steel for compressors).

[0006] Adding elements Ca, Mg, RE, Sn, and Sb to steel to refine the quality of steel and improve its texture is exemplified by the technical solution disclosed in China Patent Publication No. 1078270A (Publication date: November 10, 1993; Title of invention: Non-oriented electrical steel sheet with excellent magnetic performance and its manufacturing method).

[0007] To optimize the good texture of steel, the implementation of normalizing annealing or intermediate annealing + secondary cold rolling is exemplified by the technical solution disclosed in the specification of Chinese Patent Application Publication No. 1370850A (Publication Date: September 25, 2002; Invention Title: High Magnetic Induction Non - Oriented Electrical Steel and Its Manufacturing Method).

[0008] The main problems of the above - mentioned method are that the manufacturing process is complex, the manufacturing cost is high, and it is necessary to further use continuous casting electromagnetic stirring, normalizing annealing, and other means to eliminate ridge defects.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

[0010] The object of the present invention is to provide a non - oriented electrical steel sheet that, by optimizing the chemical composition design and process design of steel, not only exhibits excellent electromagnetic properties but also achieves excellent surface quality without surface ridge defects.

[0011] To achieve the above object, the present invention provides a non - oriented electrical steel sheet containing the following components in mass percentage: 0 < C ≤ 0.0030%, Si: 1.20 - 2.40%, Mn: 0.10 - 0.40%, Al: 0.10 - 0.60%; the balance is Fe and unavoidable impurities, and the content of Si + Al in mass percentage is 1.30 - 2.80%.

[0012] Preferably, the inevitable impurities include S, N, O, and Ti, and the contents of S, N, O, and Ti satisfy at least one of S≤0.0020%, N≤0.0020%, O≤0.0020%, and Ti≤0.0010%.

[0013] The design concept of each element in the non-oriented electrical steel sheet of the present invention is as follows:

[0014] C: C easily combines with Nb, V, and Ti to form fine carbide inclusions, which deteriorate the electromagnetic performance of the finished steel sheet. Therefore, in the non-oriented electrical steel sheet of the present invention, the C content is controlled to be 0 < C ≤ 0.0030% in mass percentage, for example, 0.0008% ≤ C ≤ 0.0030%. As an example, the upper limit of the C content may alternatively be 0.0025% or the like.

[0015] Si: Si increases the electrical resistivity of the material, thereby improving the electromagnetic performance of the finished steel sheet. When the Si content is less than 1.20%, the iron loss cannot be sufficiently reduced, and when it exceeds 2.40%, the manufacturing cost increases significantly. Therefore, in the non-oriented electrical steel sheet of the present invention, the Si content is controlled to be 1.20 - 2.40% in mass percentage. As an example, the lower limit of the Si content may alternatively be 1.35%, 1.85%, etc., and the upper limit of the Si content may be 2.37%, among others.

[0016] Mn: Mn combines with S to form MnS inclusions, thereby inhibiting the harmful effects of S. When the Mn content is less than 0.10%, S cannot be properly fixed, and when it exceeds 0.40%, the manufacturing cost increases significantly. Therefore, in the non-oriented electrical steel sheet of the present invention, the Mn content is controlled to be 0.10 - 0.40% in mass percentage. As an example, the lower limit of the Mn content may alternatively be 0.12%, 0.18%, etc., and the upper limit of the Mn content may be 0.35%, among others.

[0017] Al: Al increases the electrical resistivity of the material, thereby improving the electromagnetic performance of the finished steel sheet. If the Al content is below 0.10%, iron loss cannot be sufficiently reduced, and if it exceeds 0.60%, manufacturing costs increase significantly. Therefore, in the non-oriented electrical steel sheet of the present invention, the Al content is controlled to 0.10 to 0.60% by mass percentage. For example, the lower limit of the Al content may alternatively be 0.18%, and the upper limit of the Al content may alternatively be 0.48%.

[0018] In the present invention, the combined content of Si and Al is limited to 1.30-2.80% for the following reasons: When the combined content of Si and Al is less than 1.30%, a γ→α phase transformation occurs during the hot rolling process, resulting in a fully recrystallized hot-rolled structure without ridge defects. When the combined content of Si and Al exceeds 2.80%, a normalizing annealing step must be added during the manufacturing process to improve magnetic induction and ensure a fully recrystallized hot-rolled structure without ridge defects. Therefore, the present invention specifically addresses the goal of achieving a non-oriented electrical steel sheet with excellent surface quality and no ridge defects without normalizing annealing when the combined content of Si and Al is within the range of 1.30-2.80%. As an example, the lower limit of the Si+Al content may alternatively be 1.83%, 2.28%, etc., and the upper limit of the Si+Al content may alternatively be 2.72%, 2.41%, etc.

[0019] Preferably, the microstructure of the non-oriented electrical steel sheet (i.e., the finished cold-rolled sheet) in the present invention is a ferrite equiaxed grain (fully recrystallized) with a regular morphology, coarse size (average grain size 10 to 30 μm larger than that of conventional products of the same grade), and uniform distribution. Preferably, the non-oriented electrical steel sheet has an average grain size of 60 to 140 μm as measured in accordance with GB T 6394-2017.

[0020] Preferably, the non-oriented electrical steel sheet of the present invention has a thickness of 0.35 to 0.65 mm.

[0021] Preferably, the non-oriented electrical steel sheet of the present invention has an iron loss P≦3.60 W / kg. 15 / 50 and magnetic induction B ≥ 1.730T 50 It has.

[0022] Another object of the present invention is to provide a method for producing non-oriented electrical steel sheet. By controlling the roughing passes and reduction rate during hot rolling, and the cooling rate after hot rolling and coiling, non-oriented electrical steel sheet with high magnetic induction and low core loss can be obtained. The steel sheet has excellent surface quality and is free of ridge defects (i.e., wavy defects characterized by uneven thickness, uneven roughness, and ridge-like patterns along the rolling direction of the finished steel sheet).

[0023] In order to achieve the above object, the present invention provides a method for producing a non-oriented electrical steel sheet, which includes the following steps: 1) Smelting and foundry; 2) heating; 3) Rough rolling, finish rolling, and coiling: the rough rolling passes are 2-4 times, and the reduction rate in the final pass of rough rolling is 51%-67%; during the cooling process after coiling, the cooling rate is controlled to be 1.0-4.0°C / min in the range of 400-650°C; 4) After pickling, direct cold rolling without normalizing annealing; 5) Continuous annealing and application of insulating coating.

[0024] In the manufacturing method of the present invention, controlling the number of rough rolling passes during hot rolling to two to four (e.g., three to four) and controlling the reduction rate of the final rough rolling pass to 51% to 67% ensures the complete destruction of residual secondary columnar crystals in the intermediate slab, thereby providing a base for the subsequent finish rolling to form fully recrystallized, regularly shaped equiaxed grains. A reduction rate of more than 67% in the final rough rolling pass results in excessive rolling loads, requiring higher equipment capacity. At the same time, the flatness of the hot-rolled sheet may be insufficient, increasing the risk of edge cracks. A reduction rate of less than 51% in the final rough rolling pass fails to completely destroy the residual secondary columnar crystals in the intermediate slab. The subsequent finish rolling still retains 5 to 20% of coarse columnar crystals or equiaxed grains with a minor-to-major axis ratio greater than 4, which reduces the electromagnetic performance of the finished steel sheet and causes ridge defects.

[0025] In the manufacturing method of the present invention, the cooling rate of the hot-rolled coil is controlled to 1.0-4.0°C / min in the temperature range of 400-650°C. This is because the residual heat of the coil after the sequential rough rolling, finish rolling, and coiling is utilized to promote the growth of the recrystallized microstructure and achieve a uniform equiaxed grain size in the steel. If the cooling rate is less than 1.0°C / min, excessive oxide and nitride layers are formed, which is detrimental to the electromagnetic performance of the finished steel sheet. If the cooling rate is greater than 4.0°C / min, insufficient growth of the recrystallized microstructure occurs, resulting in a high proportion of {111} textured grains with poor orientation, which are carried over to the cold-rolled and continuously annealed finished steel sheet and cause ridge defects.

[0026] Preferably, in step (1), molten steel from a blast furnace is sequentially subjected to molten steel pretreatment, converter smelting, RH smelting, and continuous casting to obtain a continuously cast slab (e.g., the continuously cast slab has a target nominal thickness of about 230 mm).

[0027] Preferably, in step (1), the molten steel is superheated at 15 to 45°C; and / or continuous casting is employed, and the resulting continuously cast slab has an equiaxed grain ratio (i.e., the percentage of equiaxed grains relative to all grains) of 18% to 64%, as measured in accordance with GB / T 226-2015 "Test Method for Macrostructure and Defects of Steel by Etching."

[0028] Preferably, in step (2), the furnace entry temperature is from room temperature to 850°C, and the furnace exit temperature is from 1050 to 1200°C.

[0029] Preferably, in step (3), the rough rolling is performed two to four times.

[0030] Preferably, in step (3), the finish rolling temperature is 700 to 950°C.

[0031] Preferably, in step (3), the microstructure of the obtained hot-rolled steel sheet is ferrite equiaxed grains with a recrystallization rate of 85 to 90%, which prevents the production of ridge defects without requiring a normalizing annealing step.

[0032] Preferably, in step (3), the coiling temperature is 550 to 780°C.

[0033] Preferably, in step (3), the thickness of the steel sheet obtained by coiling is 2.0 to 2.6 mm.

[0034] Preferably, in step (5), the continuous annealing temperature is 820 to 980°C.

[0035] The non-oriented electrical steel sheet and the manufacturing method thereof according to the present invention have the following advantages and beneficial effects.

[0036] By optimizing the chemical composition design of the steel while controlling the reduction rate during the rough rolling pass and hot rolling, as well as the cooling rate after hot rolling and coiling, the obtained non-oriented electrical steel sheet has an iron loss P of ≦3.60 W / kg. 15 / 50and magnetic induction B ≥ 1.730T 50 The steel plate has excellent surface quality without ridge defects and the production cost is low. [Brief explanation of the drawings]

[0037] [Figure 1] 1 shows the relationship between the cooling rate after coiling and magnetic induction B50 in the method for producing a non-oriented electrical steel sheet according to the present invention. [Figure 2] 3 shows the relationship between the reduction rate and the recrystallization rate in the final pass of rough rolling in the method for producing a non-oriented electrical steel sheet according to the present invention. [Figure 3] 1 shows the microstructure of the finished steel sheet of Example 1 of the non-oriented electrical steel sheet according to the present invention. [Figure 4] 1 shows the microstructure of the finished steel sheet of Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0038] The present inventors have found that the cooling rate after coiling of a non-oriented electrical steel sheet having a composition ratio specified in the present invention is sufficient to reduce the magnetic induction B 50 Figure 1 shows the relationship between the cooling rate after coiling and magnetic induction B in the manufacturing method of non-oriented electrical steel sheet according to the present invention, based on extensive experimental data. 50 This shows the relationship between

[0039] As shown in Figure 1, when the cooling rate after coiling exceeds 1°C / min, the magnetic induction B 50 On the other hand, the higher the cooling rate, the better. If the cooling rate exceeds 4°C / min, the magnetic induction B 50 is significantly reduced.

[0040] Furthermore, the inventors have discovered through research that for non-oriented electrical steel sheets having the composition ratios specified in the present invention, the reduction rate in the final pass of rough rolling is strongly correlated with the surface quality of the finished steel sheet. Figure 2 shows the relationship between the reduction rate in the final pass of rough rolling and the recrystallization rate in the manufacturing method of non-oriented electrical steel sheets according to the present invention, based on extensive experimental data.

[0041] As shown in Figure 2, when the reduction rate in the final pass of rough rolling is 51% to 67%, the recrystallization rate of the hot-rolled steel sheet can be controlled to 85% to 90%, which effectively prevents ridge defects on the finished steel sheet.

[0042] A more detailed description and illustration of the non-oriented electrical steel sheet and its manufacturing method according to the present invention will be provided below in conjunction with the specific examples and accompanying drawings of the specification, however, it should be noted that such description and illustration should not be construed as excessively limiting the technical solutions of the present invention.

[0043] Examples 1 to 6 and Comparative Examples 1 to 2 Table 1 lists the contents of chemical elements in the electrical steel sheets of Examples 1-6 and Comparative Examples 1-2. [Table 1]

[0044] All of the non-oriented electrical steel sheets of Examples 1 to 6 of the present invention were produced using the following process. (1) Molten steel from a blast furnace was sequentially subjected to molten steel pretreatment, converter smelting, RH smelting, and continuous casting to obtain a continuously cast slab with a target nominal thickness of 230 mm. (2) Heating: The furnace entry temperature was room temperature to 850°C, and the furnace exit temperature was 1050 to 1200°C. (3) Rough rolling, finish rolling, and coiling: The rough rolling passes were controlled to 2 to 4 passes, and the reduction rate of the final pass of rough rolling was 51% to 67%; the finish rolling temperature was 700 to 950°C; the coiling temperature was 550 to 780°C; in the cooling process after coiling, the cooling rate was 1.0 to 4.0°C / min in the range of 400 to 650°C, followed by natural cooling. (4) After pickling, direct cold rolling without normalizing annealing; (5) Continuous annealing and application of insulating coating under dry atmosphere conditions; the continuous annealing temperature was 820-980℃.

[0045] The manufacturing process of Comparative Example 1 was basically the same as that of the Examples of the present invention. However, Comparative Example 1 was not cooled after coiling but was naturally cooled, and the process parameters for rough rolling did not meet the requirements of the present invention. The manufacturing process of Comparative Example 2 was basically the same as that of the Examples of the present invention. However, the process parameters of Comparative Example 2 for cooling after coiling did not meet the requirements of the present invention.

[0046] Table 2 lists specific process parameters for the manufacturing methods of the electrical steel sheets of Examples 1 to 6 and Comparative Examples 1 and 2. [Table 2]

[0047] In order to analyze the non-oriented electrical steel sheet according to the present invention, the finished steel sheets of Example 1 and Comparative Example 1 were also sampled and their microstructures were analyzed. Figures 3 and 4 show the microstructures of the finished steel sheets of Example 1 and Comparative Example 1 of the present invention, respectively.

[0048] As shown in FIG. 3, the microstructure of the finished steel sheet of Example 1 is a fully recrystallized equiaxed ferrite grain characterized by regular morphology, coarse size and uniform distribution.

[0049] In contrast, as shown in Figure 4, the microstructure of the finished steel sheet of Comparative Example 1 also has fully recrystallized ferrite equiaxed grains, but the grain size distribution is non-uniform, with localized segregation and fine grains.

[0050] In addition, samples of the non-oriented electrical steel sheets of Examples 1 to 6 and the comparative steel sheets of Comparative Examples 1 and 2 were also collected, and the steel sheet samples of each of the Examples and Comparative Examples were observed. Various related performance properties were tested. The results obtained from the observations and related performance tests are listed in Table 3, and the specific test methods for the related performance properties are described below.

[0051] Iron loss test: Iron loss performance was evaluated using the Epstein frame method in accordance with the national standard GB / T 3658-1990. The test was carried out at a constant temperature of 20°C with a test piece size of 30mm x 300mm and a target mass of 0.5kg. The test parameters were P 15 / 50 is.

[0052] Magnetic induction test: In accordance with the national standard GB / T 3658-1990, the magnetic induction performance was evaluated using the Epstein frame method. The test was carried out at a constant temperature of 20°C with a test specimen size of 30mm x 300mm and a target mass of 0.5kg. The test parameters were B 50 is.

[0053] Table 3 lists the observation results and related performance test results for the non-oriented electrical steel sheets of Examples 1 to 6 and the comparative steel sheets of Comparative Examples 1 and 2. [Table 3]

[0054] In combination with Tables 1, 2 and 3, in Examples 1 to 6 that meet the design requirements of the present invention, due to the unique rough rolling process and controlled cooling process after coiling adopted in the present invention, even though normalizing annealing was not adopted, the final finished steel sheet had no ridge defects on the surface and an iron loss P of ≦3.6 W / kg. 15 / 50 and magnetic induction B ≥ 1.730T 50 It can be seen that the electromagnetic performance is excellent.

[0055] On the other hand, the rough rolling process of Comparative Example 1 does not meet the requirements of the present invention, and ridge defects appear on the surface.

[0056] The cooling rate after coiling in Comparative Example 2 was too high, resulting in a lower magnetic induction than in the examples of the present invention.

[0057] It should be noted that the combinations of technical features herein are not limited to those described in the claims or in the specific examples, and all technical features described in this specification can be freely combined in any way as long as they are not mutually contradictory.

[0058] It should also be noted that the above-listed embodiments are merely specific embodiments of the present invention. Obviously, the present invention should not be excessively limited to such specific embodiments. Similar changes or modifications that can be directly or easily derived from the present disclosure by those skilled in the art are intended to fall within the scope of protection of the present invention.

Claims

1. Consists of the following components in percentage by weight: A non-oriented electrical steel sheet comprising: 0<C≦0.0030%, Si: 1.20 to 2.40%, Mn: 0.10 to 0.40%, Al: 0.10 to 0.60%, and the balance being Fe and unavoidable impurities, with the content of Si+Al in mass percentage being 1.30 to 2.80%.

2. 2. The non-oriented electrical steel sheet according to claim 1, wherein the inevitable impurities include S, N, O, and Ti, and the contents of S, N, O, and Ti satisfy at least one of S≦0.0020%, N≦0.0020%, O≦0.0020%, and Ti≦0.0010%.

3. 2. The non-oriented electrical steel sheet according to claim 1, wherein the non-oriented electrical steel sheet has a ferritic equiaxed grain microstructure; preferably, the non-oriented electrical steel sheet has an average grain size of 60 to 140 μm, measured in accordance with GB T 6394-2017.

4. 2. The non-oriented electrical steel sheet according to claim 1, wherein the non-oriented electrical steel sheet has a thickness of 0.35 to 0.65 mm.

5. The non-oriented electrical steel sheet has an iron loss P of ≦3.60 W / kg. １５／５０ and magnetic induction B ≥ 1.730 T ５０ The non-oriented electrical steel sheet according to claim 1, having

6. The following steps: 1) Smelting and foundry; 2) Heating; 3) rough rolling, finish rolling, and coiling: wherein the rough rolling is performed in 2 to 4 passes, and the reduction rate in the final pass of the rough rolling is 51% to 67%; and during the cooling process after coiling, the cooling rate is controlled to be 1.0 to 4.0°C / min in the range of 400 to 650°C; 4) After pickling, direct cold rolling without normalizing annealing; 5) Application of continuous annealing and insulating coating The method for producing a non-oriented electrical steel sheet according to any one of claims 1 to 5, comprising:

7. 7. The method according to claim 6, wherein in step (1), the molten steel is superheated at 15 to 45°C; and / or continuous casting is employed for casting, and the obtained continuously cast slab has an equiaxed crystal ratio of 18% to 64%.

8. The method according to claim 6, wherein in step (2), the furnace entry temperature is room temperature to 850°C, and the furnace exit temperature is 1050 to 1200°C.

9. 7. The method according to claim 6, wherein in step (3), the thickness of the intermediate slab after rough rolling is 35 to 50 mm; and / or the finish rolling temperature is 700 to 950°C; and / or the microstructure of the obtained hot-rolled steel plate is ferrite equiaxed grains with a recrystallization rate of 85 to 90%.

10. The method according to claim 6, wherein in the step (3), the coiling temperature is 550 to 780°C; and / or the thickness of the steel sheet obtained by coiling is 2.0 to 2.6 mm.

11. The method according to claim 6, wherein in step (5), the continuous annealing temperature is 820 to 980°C.

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