Method for improving production efficiency of non-oriented silicon steel for automobile driving motor

Abstract

The invention relates to the technical field of non-oriented silicon steel for driving motors, in particular to a method for improving the production efficiency of non-oriented silicon steel for automobile driving motors, which adopts a high Si and Al component system with extremely low S content, low P content and addition of part of Sn element, and optimizes a primary annealing process after primary cold rolling. The surface oxidation degree of the steel plate after primary annealing is effectively reduced, the first-pass rolling force and the strip breaking frequency of the secondary cold rolling procedure are indirectly reduced, and the cold rolling yield is increased. The high-efficiency high-strength non-oriented silicon steel produced through the steps is bright in surface and high in magnetic induction, the rolling force of the first pass of second cold rolling is reduced by 40% or above, the cold rolling yield is increased by 2% or above, and the magnetic performance is more excellent than that of a traditional mark.

Description

Technical Field

[0001] The present invention relates to the technical field of non-oriented silicon steel for driving motors, and in particular to a method for improving the production efficiency of non-oriented silicon steel for automobile driving motors. Background Art

[0002] The automotive industry is one of the main areas of global greenhouse gas emissions. As my country's car ownership continues to increase, how to reduce carbon emissions in the automotive industry is a very important link. Reducing carbon emissions in the transportation sector mainly relies on the electrification of automobiles, and new energy vehicles will usher in a broad space for growth.

[0003] With the rapid development of economy and society, the performance requirements for new energy vehicles are getting higher and higher. The energy of automobile motors is mainly based on on-board batteries, which have limited energy storage, so the motors need to be as small, light and efficient as possible. Strong power is needed when starting a car, so the motor needs to provide strong torque. In order for a car to travel at high speed and save energy, the motor needs to have an extremely high speed to achieve it, so the motor should have a high comprehensive efficiency at high and low speeds. The high speed of automobile motors brings huge centrifugal force to the rotor, and the gap between the stator and the rotor needs to be closely matched. In summary, the silicon steel used for the motor is required to have high magnetic induction, low iron loss, high strength and other characteristics. In addition, in general, the stator of the drive motor is required to have good magnetic properties, and the rotor has high-strength mechanical properties. The production of the rotor alone requires precision machining, which will greatly increase the production cost of the core. From the perspective of reducing costs, it is more appropriate to use the same silicon steel sheet to stamp the stator and rotor cores, which requires the development of non-oriented silicon steel sheets that take both magnetic properties and mechanical properties into consideration.

[0004] At present, many steel manufacturing companies have developed thin-gauge, high-efficiency, high-strength non-oriented silicon steel products with excellent comprehensive performance, such as low medium-frequency iron loss, high magnetic induction, and strong mechanical properties through strenuous research and development. The research and development method of this type of product is mainly to increase the elements Si and Al that affect resistivity, improve mechanical properties while reducing hysteresis loss, and then use secondary cold rolling to increase the proportion of favorable textures such as cubic texture and Gaussian texture, and then improve the magnetic induction intensity, so as to achieve the goal of balancing iron loss, magnetic induction and mechanical properties.

[0005] High-efficiency and high-strength non-oriented silicon steel is a type of mass-produced product with the best comprehensive performance at present, but the production of such products often has many control points, a narrow process window, and great production difficulty. Taking the cold rolling process as an example, this type of product is rolled using the secondary method, and often requires an annealing and softening of the cold-rolled sheet after the first cold rolling. However, since the first annealing production does not apply a coating, the oxide layer and nitride layer produced by annealing oxidation increase the surface roughness of the steel sheet before the second cold rolling, making the rolling of such high-alloy products more difficult, and even more difficult during the second rolling, resulting in increased rolling pressure, frequent strip breaks, and a significant reduction in the cold rolling yield rate during the second cold rolling production.

[0006] Japanese patent publication number jp2011-241416a discloses a non-oriented electromagnetic steel sheet with excellent high-frequency iron loss and a method for manufacturing the same. The document proposes controlling the partial pressure ratio of water vapor and hydrogen according to P(H20) / P(H2)≤0.015×(Cr+Si+Al), and controlling the formation of the inner oxide layer by adjusting the partial pressure ratio according to the alloying elements. This method does not take into account the effect of the annealing process itself on the oxidizability, and in fact proves to be unfavorable for the control of the oxide layer.

[0007] The document with domestic patent number CN101812571A provides a method for preventing the inner oxide layer during normalization of hot-rolled strip of electrical steel. The patent controls the normalization process, i.e., direct fire heating is used in a non-oxidizing furnace, the air-fuel ratio, dew point and oxygen content in the furnace are controlled, and the furnace atmosphere is pure N2 to reduce and eliminate the inner oxide layer generated during normalization of the hot-rolled strip, thereby eliminating the nodules on the bottom rollers during the final annealing. This method only considers the normalization process, and the effect is not obvious for continuous annealing with faster speed and different processes.

[0008] The domestic patent number CN107245564A document discloses a method for controlling the inner oxide layer of non-oriented silicon steel. The patent controls the heating rate of the continuous furnace heating section, the partial pressure ratio of water vapor to hydrogen in the annealing heating section atmosphere P(H20) / P(H2), and the partial pressure ratio of water vapor to hydrogen in the annealing soaking section, so as to achieve the inner oxide layer thickness below 1μm and reduce its adverse effect on the magnetization process. At present, the carbon content of silicon steel smelting is extremely low, and the annealing furnace does not need to pass water vapor for decarburization. This method has no guiding significance for reducing the degree of surface oxidation in the current production of silicon steel products.

[0009] The present invention designs a method for improving the production efficiency of high-efficiency and high-strength non-oriented silicon steel for automobile drive motors. By adopting a method of specially designed components and processes, the surface oxidation degree and surface roughness of the steel plate during the first annealing production of thin-gauge high-efficiency and high-strength non-oriented silicon steel are effectively reduced, the first-pass rolling pressure and the frequency of strip breakage in the second cold rolling are significantly reduced, and the cold rolling yield rate is improved. Summary of the invention

[0010] The purpose of the present invention is to provide a method for improving the production efficiency of non-oriented silicon steel for automobile drive motors in view of the above problems.

[0011] The object of the present invention is achieved as follows: A method for improving the production efficiency of non-oriented silicon steel for automobile drive motors, comprising the following steps: Step 1: smelting and continuous casting: the components are as follows: C: 0.001~0.003wt%, Si: 3.3~3.7wt%, Al: 0.6~1.2wt%, Mn: 0.1~0.5wt%, Sn: 0.20~0.45wt%, S≤0.001wt%, P≤0.005wt%, and the rest are Fe and unavoidable impurities; Step 2: after smelting according to the components of step 1, the ingot is heated to 1000℃~1100℃, hot-rolled to a hot-rolled plate with a thickness of 1.0mm~2.0mm, and then normalized and cold-rolled for the first time to form a cold-rolled plate with a thickness of 0.30~0.80mm; Step 3: first annealing process: in H2+ Under N2 protective atmosphere, the first annealing is carried out at 980℃~1100℃, the annealing speed is 120m / min~150m / min, the H2 ratio is controlled at more than 55%, and the cooling rate of the steel plate in the cooling section is ≤20℃ / s; Step 4: Second cold rolling process: The annealed coil is cold rolled for the second time, the surface roughness of the steel plate before rolling Ra≤0.3μm, the first rolling force of the second cold rolling is ≤350t, and the rolling thickness is 0.15mm~0.30mm; Step 5: Second annealing process: The cold-rolled plate is recrystallized annealing, the annealing temperature is 1000℃~1100℃, and the coating obtains a non-oriented silicon steel thin strip with excellent performance of medium frequency iron loss P1.0 / 400 of 7~14W / kg, magnetic induction B5000 of 1.69~1.72T, and yield strength Rp0.2 of 440~520Mpa.

[0012] The temperature of the normalizing treatment in step 2 is 850-950°C and the time is 2-3 minutes.

[0013] The beneficial effects of the present invention are as follows: compared with the common high-efficiency and high-strength non-oriented silicon steel manufacturing process, the present invention adopts a component system with extremely low S content, low P content, high Si, Al and the addition of some Sn elements, and obtains a special organization of Sn elements segregated at the grain boundaries before the secondary cold rolling and a metal physical structure with thin oxide layer and nitride layer thickness by optimizing the primary annealing process after the first cold rolling. The steel plate organization based on this structure effectively reduces the first rolling force of the secondary cold rolling process after the first annealing, reduces the frequency of strip breaking, and improves the cold rolling yield. The high-efficiency and high-strength non-oriented silicon steel produced by this invention not only has smooth production and a high cold rolling yield, but also has better magnetic properties than traditional thin-gauge high-efficiency and high-strength non-oriented silicon steel products. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present invention will be further described below in conjunction with the accompanying drawings.

[0015] Figure 1 This is a graph of the orientation distribution function (φ2=45°, density levels 2, 4, 6, 8, 10) of the finished product of Comparative Example 2 of the present invention.

[0016] Figure 2 This is a graph of the orientation distribution function (φ2=45°, density levels 2, 4, 6, 8, 10) of the finished product of Example 2 of the present invention.

[0017] Figure 3 This is a graph of the orientation distribution function (φ2=45°, density levels 2, 4, 6, 8, 10) of the finished product of Example 1 of the present invention.

[0018] Figure 4 This is a graph of the orientation distribution function (φ2=45°, density levels 2, 4, 6, 8, 10) of the finished product of Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0019] The present invention designs a new high-efficiency and high-strength non-oriented silicon steel component system, and optimizes the annealing process after the first cold rolling based on this component system. It can significantly improve the rolling efficiency and cold rolling yield rate during the second cold rolling while obtaining better magnetic properties.

[0020] The present invention designs a component system with extremely low S content, low P content and added partial Sn element in the traditional high-efficiency and high-strength non-oriented silicon steel components, under the high Si and Al components that can be industrially produced.

[0021] Under the above-mentioned composition system, the annealing process after the first cold rolling adopts a high-temperature and high-speed method to make all Sn elements quickly dissolved, and then increase the H2 ratio during the first annealing, so that no obvious oxide layer and nitride layer are produced, that is, to avoid obvious oxidation on the surface of the steel plate. After that, the cooling section after the soaking section annealing requires slow cooling, so that the Sn element segregates and continuous segregated Sn components appear at the grain boundaries. Because extremely low S and low P control is achieved during smelting, the segregation of MnS and phosphide at the grain boundaries can be effectively avoided to hinder the grain boundary segregation of Sn.

[0022] The segregation of Sn element at the grain boundary effectively hinders the diffusion of oxygen and nitrogen components along the grain boundary, reduces the thickness of the inner oxide layer and nitride layer, significantly improves the surface color, and significantly reduces the roughness. During the secondary cold rolling, the first-pass rolling force caused by the oxide layer and nitride layer is significantly reduced, and the yield rate is improved.

[0023] Due to the segregation of Sn on the grain boundary, the thermal driving force for grain growth increases during annealing. During the second annealing, in order to make the grains grow to the optimal magnetic performance size, the second annealing temperature was adjusted. Since the addition of Sn can significantly increase the proportion of favorable textures for recrystallization annealing, such as {100} and {110}, the high-efficiency and high-strength non-oriented silicon steel produced by the new process not only improves the production efficiency of the second cold rolling, but also obtains better magnetic properties.

[0024] A method for improving the production efficiency of high-efficiency and high-strength non-oriented silicon steel for automobile drive motors, comprising the following steps: smelting, continuous casting, the composition is as follows: C 0.001~0.003wt%, Si 3.3~3.7wt%, Al 0.6~1.2wt%, Mn 0.1~0.5wt%, especially Sn 0.20~0.45wt%, S≤0.001wt%, P≤0.005wt%, the rest is Fe and inevitable impurities; (smelting according to the above composition, converter smelting temperature ≥1280℃, and then RH vacuum treatment and casting to form a billet.) (2) After smelting according to the above composition, the billet is heated to 1000℃~1100℃, hot rolled to a hot-rolled plate with a thickness of 1.0mm~2.0mm, and then normalized at a temperature of 900℃ for 3min and cold rolled for the first time to 0.30 ~0.80mm thick cold rolled plate; (3) in a H2+N2 protective atmosphere, the first annealing is carried out at 980℃~1100℃, the annealing speed is (120m / min~150m / min), the H2 ratio is ≥55%, and the cooling rate of the steel plate in the cooling section is ≤20℃ / s; (4) the annealed coil is subjected to a second cold rolling, the surface roughness of the steel plate before rolling Ra≤0.3μm, the first rolling force of the second cold rolling is ≤350t, and the rolling thickness is 0.15mm~0.30mm; (5) the cold rolled plate is subjected to high temperature recrystallization annealing, the annealing temperature is 1000℃~1100℃, and after coating, a non-oriented silicon steel thin strip with excellent performance is obtained, such as medium frequency iron loss P1.0 / 400 of 7~14W / kg, magnetic induction B5000 of 1.69~1.72T, and yield strength Rp0.2 of 440~520Mpa.

[0025] High-efficiency and high-strength silicon steel has the following composition: C 0.001~0.003wt%, Si 3.3~3.7wt%, Al 0.6~1.2wt%, Mn 0.1~0.5wt%, especially Sn 0.20~0.45wt%, S ≤ 0.001wt%, P ≤ 0.005wt%, and the rest are Fe and unavoidable impurities.

[0026] The first annealing process: in the H2+N2 protective atmosphere, the first annealing is carried out at 980℃~1100℃, the annealing speed is above 120m / min, the H2 ratio is controlled at above 55%, and the cooling rate of the steel plate in the cooling section is less than 20℃ / s.

[0027] Second cold rolling process: the surface roughness of the steel plate before cold rolling is Ra≤0.3μm, and the first rolling force of the second cold rolling is less than 350t; Second annealing process: high temperature recrystallization annealing is performed on the cold rolled plate, and the annealing temperature is above 1000℃. Example 1

[0028] The chemical composition of the ingot (in mass percentage) is: C0.0015wt%, Si3.6wt%, Al0.6wt%, Mn0.25wt%, especially Sn0.45wt%, S0.001wt%, P0.0035wt%, and the rest is Fe and inevitable impurities; after smelting according to the above composition, the ingot is heated to 1050℃, hot rolled to a 1.8mm thick hot rolled plate, and then normalized and cold rolled for the first time to a 0.70mm thick cold rolled plate; in H2+N 2. Under protective atmosphere, the first annealing is carried out at 1000℃, the annealing speed is 120m / min, the H2 ratio is controlled at 60%, and the cooling rate of the steel plate in the cooling section is 15℃ / s; the annealed coil is cold rolled for the second time, and the rolling is divided into two passes. The thickness of the second cold rolling is 0.30mm; the surface roughness of the steel plate before the second cold rolling is Ra0.25μm, and the rolling force of the first rolling is 300t and remains stable; the cold rolled plate is subjected to high temperature recrystallization annealing, the annealing temperature is 1050℃, and the coating is used to obtain the medium frequency iron loss P 1.0 / 400 13.2W / kg, magnetic induction B 5000 The non-oriented silicon steel strip with excellent performance is 1.72T and yield strength Rp0.2 is 480Mpa. The finished product texture strength is as follows Figure 3 , the surface of the thin strip is bright. Comparative Example 1

[0029] The chemical composition of the ingot (in mass percentage) is: C0.0015wt%, Si3.6wt%, Al0.6wt%, Mn0.25wt%, S0.003wt%, P0.02wt% and the rest is Fe and inevitable impurities; after smelting according to the above composition, the ingot is heated to 1050℃, hot rolled to a 1.8mm thick hot rolled plate, and then normalized and cold rolled for the first time to a 0.70mm thick cold rolled plate; in an H2+N2 protective atmosphere, 10 The first annealing was carried out at 00℃, the annealing speed was 120m / min, the H2 ratio was controlled at 60%, and the cooling rate of the steel plate in the cooling section was 15℃ / s; the annealed coil was cold rolled for the second time, the rolling was divided into two passes, and the thickness of the second cold rolling was 0.30mm; the surface roughness of the steel plate was detected before the second cold rolling, Ra0.65μm, and the rolling force of the first rolling was 650t and unstable; the cold rolled plate was subjected to high temperature recrystallization annealing, the annealing temperature was 1050℃, and the coating was obtained, that is, the medium frequency iron loss P 1.0 / 400 13.6W / kg, magnetic induction B 5000The non-oriented silicon steel strip has a temperature of 1.68T and a yield strength Rp0.2 of 480Mpa, and the surface of the strip is obviously oxidized and blackened.

[0030] Depend on Figure 3 , 4 By comparison, it can be seen that under the condition that the process of the subsequent steps is basically the same, the addition of Sn components and the control of the composition of elements such as S and P can achieve lower iron loss, better magnetic induction, and brighter surface state. The thickness of the oxide layer on the surface after one annealing is significantly lower, the roughness is lower, and the effect on the rolling force of the first pass of the second rolling is more obvious, which can effectively reduce the rolling force and the risk of strip breakage. Example 2

[0031] The chemical composition of the ingot (in mass percentage) is: C0.0020wt%, Si3.4wt%, Al0.8wt%, Mn0.45wt%, especially Sn0.25wt%, S0.001wt%, P0.0025wt%, and the rest is Fe and inevitable impurities; after smelting according to the above composition, the ingot is heated to 1100°C, hot-rolled to a hot-rolled plate with a thickness of 1.5mm, and then normalized and cold-rolled for the first time to be a cold-rolled plate with a thickness of 0.55mm; Under H2+N2 protective atmosphere, the first annealing was carried out at 1050℃, the annealing speed was 130m / min, the H2 ratio was controlled at 60%, and the cooling rate of the steel plate in the cooling section was 18℃ / s; the annealed coil was cold rolled for the second time, the rolling was divided into two passes, and the thickness of the second cold rolling was 0.20mm; the surface roughness before the second cold rolling was Ra0.3μm, and the rolling force of the first pass was 350t; the cold rolled plate was subjected to high temperature recrystallization annealing, the annealing temperature was 1100℃, and the coating was used to obtain the medium frequency iron loss P 1.0 / 400 The non-oriented silicon steel strip with excellent performance is 10.1W / kg, magnetic induction B5000 is 1.69T, and yield strength Rp0.2 is 455Mpa. The finished product texture strength is as follows Figure 2 , the surface of the thin strip is bright. Comparative Example 2

[0032] The chemical composition of the ingot (in mass percentage) is: C0.0020wt%, Si3.4wt%, Al0.8wt%, Mn0.45wt%, especially Sn0.25wt%, S0.001wt%, P0.0025wt%, and the rest is Fe and inevitable impurities; after smelting according to the above composition, the ingot is heated to 1100℃, hot rolled to a 1.5mm thick hot rolled plate, and then normalized and cold rolled for the first time to a 0.55mm thick cold rolled plate; 2+N2 protective atmosphere, the first annealing was carried out at 1050℃, the annealing speed was 130m / min, the H2 ratio was controlled at 20%, and the cooling rate of the steel plate in the cooling section was 60℃ / s; the annealed coil was cold rolled for the second time, the rolling was divided into two passes, and the thickness of the second cold rolling was 0.20mm; the surface roughness Ra0.4μm was detected before the second cold rolling, and the rolling force of the first rolling was 450t; the cold rolled plate was subjected to high temperature recrystallization annealing, the annealing temperature was 1100℃, and the coating was used to obtain the medium frequency iron loss P 1.0 / 400 The non-oriented silicon steel strip has a magnetic induction B5000 of 10.3W / kg, a magnetic induction B5000 of 1.67T, and a yield strength Rp0.2 of 455Mpa. The surface of the strip is obviously oxidized and blackened.

[0033] Depend on Figure 1 , 2 By comparison, it can be seen that when the composition and final annealing process are basically the same, the proportion of H2 in the primary annealing protective atmosphere is reduced, and after the cooling rate is fast, Sn does not have time to completely segregate, resulting in a certain degree of oxidation on the surface of the steel plate. When the final annealing temperature remains unchanged, the grains are easier to grow. The iron loss obtained is basically the same as that of Example 2, but the magnetic induction is general, the surface state is dark, there is a certain thickness of oxide layer on the surface after the primary annealing, the rolling force of the first rolling of the second rolling is high, and there is a certain risk of rolling breaking.

[0034] The above description is only a specific embodiment of the present invention, but the structural features of the protection scope of the present invention are not limited thereto. Any changes or modifications made by any technician in the field of the present invention are all covered by the patent scope of the present invention.

Claims

1. A method for improving the production efficiency of non-oriented silicon steel for automobile drive motors, characterized in that: The following steps are involved: Step 1: smelting and continuous casting: the composition is as follows: C: 0.001~0.003wt%, Si: 3.3~3.7wt%, Al: 0.6~1.2wt%, Mn: 0.1~0.5wt%, Sn: 0.20~0.45wt%, S≤0.001wt%, P≤0.005wt%, the rest is Fe and unavoidable impurities; Step 2: After smelting the composition in step 1, the ingot is heated to 1000°C~1100°C, hot-rolled to a hot-rolled plate with a thickness of 1.0mm~2.0mm, and then normalized and cold-rolled for the first time to form a cold-rolled plate with a thickness of 0.30~0.80mm; Step 3: First annealing process: In H2+N2 protective atmosphere, the first annealing is carried out at 980℃~1100℃, the annealing speed is 120m / min~150m / min, the H2 ratio is controlled at more than 55%, and the cooling rate of the steel plate in the cooling section is ≤20℃ / s; Step 4: Second cold rolling process: The annealed coil is subjected to a second cold rolling, the surface roughness of the steel plate before rolling is Ra≤0.3μm, the first rolling force of the second cold rolling is ≤350t, and the rolling thickness is 0.15mm~0.30mm; Step 5: Second annealing process: The cold-rolled sheet is subjected to recrystallization annealing at an annealing temperature of 1000°C~1100°C. The coating then obtains a non-oriented silicon steel strip with excellent performance, such as medium frequency iron loss P1.0 / 400 of 7~14W / kg, magnetic induction B5000 of 1.69~1.72T, and yield strength Rp0.2 of 440~520Mpa.

2. The method for improving the production efficiency of non-oriented silicon steel for automobile drive motors according to claim 1, characterized in that: The temperature of the normalizing treatment in step 2 is 850-950°C and the time is 2-3 minutes.

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