Non-coated non-oriented silicon steel and method for manufacturing the same

Abstract

The application provides a kind of non-coated non-oriented silicon steel and its manufacturing method, components: C≤0.0025%, Si 0.8%-1.2%, Als 0.2%-0.3%, Mn 0.15-0.3%, S≤0.005%, P≤0.04%, N≤0.0025%, the balance is Fe and inevitable impurities.In production and manufacture, control cold rolling reduction, improve surface roughness, shape after rolling is good, longitudinal thickness fluctuation ±3μm, transverse same plate difference ≤7μm, meet the requirements of frequency conversion compressor rotor.After pickling S5 and smoothing machine are used together, the roughness of finished plate can reach 1.6-1.9μm. Annealing uses vertical annealing furnace, improves annealing speed.The iron loss of non-coated non-oriented silicon steel produced by the application after secondary annealing is lower than that of the same grade non-oriented silicon steel with coating produced by traditional horizontal annealing furnace.

Description

Technical Field

[0001] This invention belongs to the field of non-oriented silicon steel manufacturing, specifically relating to an uncoated non-oriented silicon steel and its manufacturing method. Background Technology

[0002] Non-oriented silicon steel can be used to produce compressor motor cores. With the development of high-efficiency, energy-saving and green production in global manufacturing, as well as the development of the compressor field, high efficiency and energy saving have become a consensus in the compressor industry.

[0003] Traditional non-oriented silicon steel is produced using horizontal annealing furnaces, requiring a smooth coating before delivery. Users then stamp it into stators and rotors for secondary annealing, but this secondary annealing process results in a low rate of improvement in iron loss. Furthermore, the use of horizontal annealing furnaces leads to high annealing temperatures, slow production speeds, and surface coatings, resulting in high production costs.

[0004] Furthermore, in existing technologies, the elongation rate of tension leveling is relatively low, the work roll uses only one frame chamfering roll, resulting in poor plate thickness variation and a 10μm pass rate of only 80%. Moreover, the annealing is carried out in a horizontal furnace at a high temperature of 850℃, and the annealing speed is 150m / min, resulting in low production efficiency and increased costs due to surface coating.

[0005] A low-cost uncoated non-oriented silicon steel and its production method, disclosed on August 28, 2020, with publication number CN 111593262 A, has the following composition: C≤0.01%, 0.5%≤Si≤1.2%, 0.25%≤Mn≤0.35%, 0.050%≤P≤0.085%, S≤0.003%, 0.3%≤Als≤0.5%, Ti≤0.0025%, O≤0.0025%, N≤0.0035%, with the balance being Fe and unavoidable impurities. The production process is as follows: hot metal desulfurization—converter—RH refining—CSP continuous casting and rolling—pickling—cold rolling—baffle annealing—leveling. The leveling elongation rate used is between 0.6% and 0.8%, resulting in poor uniformity of the produced sheet. Summary of the Invention

[0006] The purpose of this invention is to provide an uncoated, non-oriented silicon steel and its manufacturing method. Through optimization of composition and production process, the steel is produced with low annealing temperature, fast annealing speed, and low production cost. The iron loss after secondary annealing is better than that of the same grade coated product produced by horizontal annealing furnace, and the difference between the same plate can reach less than 7μm, demonstrating excellent performance.

[0007] The specific technical solution of this invention is as follows:

[0008] An uncoated, non-oriented silicon steel comprises the following components by weight percentage:

[0009] C≤0.0025%, Si 0.8%-1.2%, Als 0.2%-0.3%, Mn 0.15-0.3%, S≤0.005%, P≤0.04%, N≤0.0025%, balance Fe and unavoidable impurities.

[0010] The microstructure of the uncoated, non-oriented silicon steel is ferrite and a small amount of cementite, with a grain size of 5.0-5.5.

[0011] The surface roughness of the uncoated, non-oriented silicon steel plate reaches 1.6-1.9μm, the iron loss after one annealing is 6.0-6.3W / kg, the magnetic induction is 1.72-1.73T, the yield strength is 280-300MPa, and the Vickers hardness is 120-130HV; the iron loss after two annealing is 3.4-3.7W / kg.

[0012] The present invention provides a method for manufacturing uncoated, non-oriented silicon steel, comprising the following processes:

[0013] Hot rolling, cold rolling, annealing and leveling;

[0014] The hot rolling process involves a heating temperature of 1110-1150℃, an RT2 exit temperature of 910-950℃, an FT7 temperature of 850-900℃, and a coiling temperature of 660-700℃. Coiling temperatures above 700℃ can lead to thick iron oxide scale, making pickling difficult. During cold rolling, slippage can cause significant thickness fluctuations.

[0015] For the hot rolling process, the thickness of the hot-rolled raw material is controlled at 2.55-2.75 mm, and the thickness of the cold-rolled finished product is 0.495-0.505 mm. To ensure consistent quality within the same sheet, the hot-rolled coil crown is required to be 15-35 μm, and the wedge shape is controlled within ±20 μm.

[0016] The cold rolling process employs pickling and continuous rolling, with a tension leveling elongation of 2.0-2.5%. The tension leveling over the weld seam is continuous, effectively breaking down the surface oxide scale and improving pickling quality and speed. To reduce transverse plate thickness differences, the pickling rolling process does not involve edge trimming, and the number of chamfering stands is increased. Chamfering rolls are used on the work rolls of the first and second stands of the continuous rolling mill. Since users of uncoated, non-oriented silicon steel will perform annealing and bluing treatments, high surface roughness is required to prevent sticking during stator and rotor annealing. To further improve surface roughness, the surface roughness of the work rolls on the fifth stand is 4.0-6.0 μm, the unit rolling force on the fifth stand is 6-7 MN / m, and the post-rolling surface roughness can reach 1.2-1.6 μm.

[0017] Furthermore, the reduction rate of each cold rolling stand and the tension between stands are as follows:

[0018] The reduction rates of the first, second, third, fourth, and fifth cold rolling mills are 38%-40%, 36%-39%, 28%-31%, 24%-27%, and 0.5%-1%, respectively. The main deformation is achieved by the first four stands, with the reduction rate decreasing sequentially due to work hardening. The fifth stand is used as a leveling mill, with a lower reduction rate to ensure good sheet shape. The unit tension between the first and second cold rolling mills is 120-130 N / mm. 2 The unit tension between the second and third cold rolling mills is 130-140 N / mm. 2 The unit tension between the third and fourth cold rolling mills is 150-170 N / mm. 2 The unit tension between the fourth and fifth cold rolling mills is 150-170 N / mm. 2 The unit tension at the outlet is 40-50 N / mm. 2 .

[0019] After cold rolling, the sheet has a good shape, with longitudinal thickness fluctuation of ±3μm and transverse thickness difference of ≤7μm, which meets the requirements of the stator and rotor of the variable frequency compressor.

[0020] The annealing process utilizes a vertical annealing furnace, divided into preheating, heating, soaking, slow cooling, rapid cooling, over-aging, and final cooling sections. The annealing temperatures for the uncoated, non-oriented silicon steel vertical annealing furnace are as follows: preheating section 140-150℃, heating and soaking sections 835-845℃, slow cooling section 645-655℃, rapid cooling section 495-505℃, over-aging section 400-470℃, and final cooling section 180-190℃. Increasing the temperatures of the heating and soaking sections promotes ferrite grain growth and reduces iron loss. Therefore, the temperatures of the heating and soaking sections are set at 835-845℃. The annealing speed is 200-250 m / min. Compared to a horizontal annealing furnace, the annealing time can be shortened due to the longer strip length within the furnace, thus improving production efficiency. Based on a speed of 200 m / min, if a coil of steel is 4800 meters long, the annealing time is 24 minutes, while the fastest time using a traditional horizontal annealing furnace is 30 minutes.

[0021] The leveling process, since the finished product surface is uncoated, requires a high surface roughness to prevent sticking during stator and rotor annealing. To achieve this high surface roughness, in addition to using high-roughness texturing rolls on the cold rolling S5 work rolls, high-roughness work rolls are used for leveling after annealing. The leveling work rolls have a roughness of 4.0-5.0 μm, a leveling elongation of 1.0-1.8%, a leveling rolling force of 2000-3000 KN, and a tension leveler elongation of 0.5%. The main function of tension leveling is to improve the sheet shape. By using texturing rolls in conjunction with the acid rolling S5 and leveling mill, the surface roughness of the finished product can reach 1.6-1.9 μm.

[0022] Furthermore, to prevent the board surface from rusting, an oil coating of 300 mg / m² is applied.2 .

[0023] Furthermore, a second annealing process is performed at a temperature of 750-780℃. After the second annealing, the iron loss can be reduced to 3.4-3.7 W / kg.

[0024] To achieve high surface roughness, the strip steel was leveled after annealing. This leveling process caused work hardening, grain elongation, and increased stress, leading to higher iron loss in the finished product, reaching 6.0-6.3 W / kg, and a magnetic induction of 1.72-1.73 T. To eliminate the stress generated during leveling, lamination, and stacking, and to promote grain recrystallization, the stacked stator and rotor underwent secondary annealing. The annealing temperature was 750-780℃. After secondary annealing, the iron loss was reduced to 3.4-3.7 W / kg, achieving an iron loss improvement rate of 40%-45%, meeting user requirements. In contrast, the same grade of coated non-oriented silicon steel produced in a traditional horizontal annealing furnace had an iron loss of 4.6-5.0 W / kg, and after secondary annealing, the iron loss was 4.0-4.2 W / kg, with a lower improvement rate of only about 10%. The iron loss of uncoated non-oriented silicon steel after secondary annealing is lower than that of coated non-oriented silicon steel of the same grade produced by a traditional horizontal annealing furnace.

[0025] The design concept of this invention is as follows:

[0026] C, S, and N are harmful elements in silicon steel, so their levels should be kept as low as possible. Si and Al play an important role in magnetism. As the content of Si and Al increases, resistivity increases and iron loss decreases, but magnetic induction also decreases. However, the effect of adding Al on the strength and hardness of steel is not as significant as that of Si. Adding Al causes less lattice distortion in iron than adding Si, with a smaller increase in brittleness and a smaller increase in hardness. Therefore, adding Al can reduce the strength of steel while maintaining magnetic properties, which is beneficial for production and post-processing. Mn partially forms MnS compounds with S. The solid solubility of MnS in the γ phase is lower than that in the α phase, which can promote MnS coarsening and is conducive to grain growth. Part of it can increase hardness in solid solution form. Mn can also improve stamping properties and machinability, and reduce adhesion during stamping. P increases resistivity and can reduce iron loss, but too much P content can lead to embrittlement. During manufacturing, controlling the cold rolling reduction rate improves surface roughness, resulting in a good sheet shape after rolling. Longitudinal thickness fluctuation is ±3μm, and transverse thickness difference is ≤7μm, meeting the requirements of variable frequency compressor stators and rotors. Using a pickling and rolling S5 mill and a smoothing mill with texturing rolls, the finished sheet surface roughness can reach 1.6μm-1.9μm. Annealing is performed in a vertical annealing furnace to increase the annealing rate. The iron loss of the uncoated, non-oriented silicon steel produced by this invention after secondary annealing is significantly lower than that of the same grade coated non-oriented silicon steel produced using a traditional horizontal annealing furnace.

[0027] Compared with the prior art, the present invention provides a high-roughness uncoated product. Through optimization of composition and production process, the production annealing temperature is low, the annealing speed is fast, and the production cost is low. The iron loss after secondary annealing is better than that of the same grade coated product produced by horizontal annealing furnace, and the difference between the same plate can reach less than 7μm, which is excellent performance. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1

[0030] An uncoated, non-oriented silicon steel comprises the following components by weight percentage as shown in Table 1, with the balance not shown in Table 1 being Fe and unavoidable impurities.

[0031] Table 1. Composition (%) of uncoated non-oriented silicon steel in each embodiment and comparative example

[0032] Example C Si Als Mn S P N Example 1 0.0020 0.968 0.2468 0.18 0.0028 0.022 0.0018 Example 2 0.0023 1.15 0.2037 0.156 0.0019 0.018 0.0005 Example 3 0.0015 0.883 0.2945 0.249 0.0048 0.038 0.0025 Comparative Example 1 0.0023 0.66 0.256 0.155 0.0030 0.028 0.0014 Comparative Example 2 0.0020 1.28 0.233 0.167 0.0025 0.030 0.0008 Comparative Example 3 0.0018 1.00 0.15 0.196 0.0023 0.020 0.0010

[0033] Example 1

[0034] The manufacturing method for uncoated, non-oriented silicon steel specifically includes the following processes:

[0035] Hot rolling, cold rolling, annealing and leveling;

[0036] The hot rolling process involves a heating temperature of 1110-1150℃, an RT2 exit temperature of 910-950℃, an FT7 temperature of 850-900℃, and a coiling temperature of 660-700℃.

[0037] For the hot rolling process, the thickness of the hot-rolled raw material is controlled at 2.55-2.75 mm, and the thickness of the cold-rolled finished product is 0.495-0.505 mm. To ensure consistent quality within the same sheet, the hot-rolled coil crown is required to be 15-35 μm, and the wedge shape is controlled within ±20 μm.

[0038] The cold rolling process employs pickling and continuous rolling, with a tension leveling elongation of 2.0-2.5%. The tension leveling over the weld seam is continuous. To reduce transverse plate thickness differences: the pickling rolling process does not trim the edges, and a second stand with chamfered rolls is added; that is, the work rolls of the first and second stands in the continuous rolling process use chamfered rolls. The surface roughness of the work rolls on the fifth stand is 4.0-6.0 μm, the unit rolling force on the fifth stand is 6-7 MN / m, and the surface roughness of the rolled plate can reach 1.2-1.6 μm. The reduction rate and inter-stand tension of each cold rolling stand are as follows:

[0039] The reduction rates of the first, second, third, fourth, and fifth cold rolling mills are 38%-40%, 36%-39%, 28%-31%, 24%-27%, and 0.5%-1%, respectively. The main deformation is achieved by the first four stands, with the reduction rate decreasing sequentially due to work hardening. The fifth stand is used as a leveling mill, with a lower reduction rate to ensure good sheet shape. The unit tension between the first and second cold rolling mills is 120-130 N / mm. 2 The unit tension between the second and third cold rolling mills is 130-140 N / mm. 2 The unit tension between the third and fourth cold rolling mills is 150-170 N / mm. 2 The unit tension between the fourth and fifth cold rolling mills is 150-170 N / mm. 2 The unit tension at the outlet is 40-50 N / mm. 2 .

[0040] After cold rolling, the sheet shape is good, the longitudinal thickness fluctuates by ±3μm, and the transverse thickness difference is ≤7μm.

[0041] The annealing process employs a vertical annealing furnace, which is divided into a preheating section, a heating section, a soaking section, a slow cooling section, a rapid cooling section, an over-aging section, and a final cooling section. The annealing temperatures for the vertical annealing furnace of uncoated, non-oriented silicon steel are as follows: preheating section 140-150℃, heating and soaking sections 835-845℃, slow cooling section 645-655℃, rapid cooling section 495-505℃, over-aging section 400-470℃, and final cooling section 180-190℃.

[0042] The leveling process involves a leveling work roll with a roughness of 4.0-5.0 μm, a leveling elongation of 1.0%-1.8%, a leveling rolling force of 2000-3000 KN, and a tension leveler elongation of 0.5%. The main function of tension leveling is to improve the shape of the plate.

[0043] Furthermore, to prevent the board surface from rusting, an oil coating of 300 mg / m² is applied. 2 .

[0044] Furthermore, after stamping, users will perform a second annealing at a temperature of 750-780℃. After the second annealing, the iron loss can be reduced to 3.4-3.7W / kg.

[0045] The process parameters for each embodiment and comparative example are shown in Tables 2, 3, 4 and 5.

[0046] Table 2 Hot rolling parameters for each embodiment and comparative example

[0047]

[0048] Table 3 Cold rolling parameters for each embodiment and comparative example

[0049]

[0050] Table 4 Annealing parameters for each embodiment and comparative example

[0051]

[0052]

[0053] Table 5. Leveling and straightening parameters for each embodiment and comparative example.

[0054]

[0055] For production processes and parameters not shown in Tables 1-5, the same control methods shall be used.

[0056] The non-oriented silicon steel produced in the above embodiments and comparative examples was tested, as shown in Table 6. Yield strength values ​​were tested according to GB / T 228.1-2021 standard, and Vickers hardness was tested according to GB / T 4340.1-2009 standard. Iron loss and magnetic induction were tested according to GB / T 3655-2022 standard, and surface roughness was measured according to GB / T2523-2022 standard. Longitudinal and transverse plate differences were obtained using an online thickness gauge and edge drop meter.

[0057] Table 6. Performance of Non-oriented Silicon Steel in Each Example and Comparative Example

[0058]

[0059]

[0060] The non-oriented silicon steels of each embodiment and comparative example were subjected to secondary annealing at an annealing temperature of 760°C. After annealing under the same conditions, their iron loss was tested, and the results are shown in Table 7.

[0061] Table 7 Iron loss after secondary annealing in each embodiment and comparative example.

[0062]

[0063] The data underlined above do not meet the requirements of this invention.

[0064] The above description of the embodiments is intended to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. An uncoated, non-oriented silicon steel, characterized in that, The uncoated, non-oriented silicon steel comprises the following components by weight percentage: C≤0.0025%, Si 0.8%-1.2%, Als 0.2%-0.3%, Mn 0.15-0.3%, S≤0.005%, P≤0.04%, N≤0.0025%, balance being Fe and unavoidable impurities; The manufacturing method of the uncoated non-oriented silicon steel includes: hot rolling, cold rolling, annealing and leveling; The cold rolling process involves a tension leveling elongation of 2.0-2.5%, with continuous tension leveling over the weld seam. The work rolls of the first and second stands in the continuous rolling mill are chamfered rolls. The surface roughness of the work rolls of the fifth stand is 4.0-6.0 μm, the unit rolling force of the fifth stand is 6-7 MN / m, and the surface roughness of the rolled plate is 1.2-1.6 μm. After cold rolling, the longitudinal thickness fluctuates by ±3μm, and the transverse thickness difference within the same plate is ≤7μm; The annealing process employs a vertical annealing furnace with the following temperatures: preheating section temperature 140-150℃, heating and soaking section temperature 835-845℃, slow cooling section temperature 645-655℃, rapid cooling section temperature 495-505℃, over-aging section temperature 400-470℃, final cooling section temperature 180-190℃, and annealing speed 200-250 m / min. The uncoated, non-oriented silicon steel has an iron loss of 6.0-6.3 W / kg, a magnetic induction of 1.72-1.73 T, a yield strength of 280-300 MPa, and a Vickers hardness of 120-130 after one annealing; and an iron loss of 3.4-3.7 W / kg after two annealings.

2. The uncoated, non-oriented silicon steel according to claim 1, characterized in that, The surface roughness of the uncoated, non-oriented silicon steel plate reaches 1.6-1.9 μm.

3. A method for manufacturing uncoated, non-oriented silicon steel as described in claim 1 or 2, characterized in that, The manufacturing method includes: hot rolling, cold rolling, annealing and leveling; The cold rolling process involves a tension leveling elongation of 2.0-2.5%, with continuous tension leveling over the weld seam. The work rolls of the first and second stands in the continuous rolling mill are chamfered rolls. The surface roughness of the work rolls of the fifth stand is 4.0-6.0 μm, the unit rolling force of the fifth stand is 6-7 MN / m, and the surface roughness of the rolled plate is 1.2-1.6 μm. After cold rolling, the longitudinal thickness fluctuates by ±3μm, and the transverse thickness difference within the same plate is ≤7μm; The annealing process employs a vertical annealing furnace with the following temperatures: preheating zone temperature 140-150℃, heating and soaking zone temperature 835-845℃, slow cooling zone temperature 645-655℃, rapid cooling zone temperature 495-505℃, over-aging zone temperature 400-470℃, final cooling zone temperature 180-190℃, and annealing speed 200-250 m / min.

4. The manufacturing method according to claim 3, characterized in that, The hot rolling process involves a heating temperature of 1110-1150℃, an RT2 exit temperature of 910-950℃, an FT7 temperature of 850-900℃, and a coiling temperature of 660-700℃.

5. The manufacturing method according to claim 3, characterized in that, The hot rolling process controls the thickness of the hot-rolled raw material to be 2.55-2.75 mm, the hot-roll crown to be 15-35 μm, and the wedge shape to be within ±20 μm.

6. The manufacturing method according to claim 3, characterized in that, The leveling process has the following characteristics: leveling work roll roughness 4.0-5.0μm, leveling elongation 1.0%-1.8%, leveling rolling force 2000-3000KN, and tension leveling machine elongation 0.5%.

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