A method for improving the edge quality of high-grade non-oriented silicon steel for new energy vehicle driving motor cold continuous rolling

Abstract

The application discloses a method for improving the edge quality of high-grade non-oriented silicon steel for new energy automobile driving motor in cold continuous rolling, which comprises the following steps: controlling the pickling time t of the hot-rolled raw material as T*Si% / 600<=t<=T*Si% / 300; setting the roll shifting amount of the intermediate roller in the continuous rolling machine as 30-80 mm; and controlling the ratio L / R of the length L of the working roller body of the continuous rolling machine to the surface curvature radius R of the working roller in the range of-0.25<=L / R<=-0.15. The application maximally weakens the generation of edge waves and improves the edge quality of the high-grade non-oriented silicon steel for new energy automobile driving motor in cold continuous rolling under the premise of inhibiting the edge cracks of the cold continuous rolling edge, realizes high-efficiency production, reduces the edge cutting loss after cold rolling, and improves the yield.

Description

Technical Field

[0001] This invention belongs to the field of application technology of non-oriented silicon steel, and specifically relates to a method for improving the edge quality of cold-rolled high-grade non-oriented silicon steel used in drive motors of new energy vehicles. Background Technology

[0002] Non-oriented silicon steel is a widely used soft magnetic material in the power and electronics industries. Especially in recent years, with the development of high-speed motors, such as those used in new energy vehicle drive motors, the demand for high-grade non-oriented silicon steel, particularly thin-gauge non-oriented silicon steel with a thickness of 0.30mm and below, has surged as a crucial material for reducing high-frequency iron losses in motors. Due to process limitations, high-grade non-oriented silicon steel for new energy vehicle drive motors is generally produced using single-stand rolling, resulting in low rolling efficiency. While existing 20-roll reversible single-stand rolling mills can produce high-grade non-oriented electrical steel for new energy vehicle drive motors, frequent roll changes and numerous sheet defects lead to low production efficiency and low yield. If a UCMW six-roll acid continuous rolling mill is used, the large diameter of the work rolls results in excessive rolling force, causing edge cracks and strip breakage.

[0003] To further improve the production capacity of high-grade non-oriented silicon steel for new energy vehicle drive motors, reduce production costs, and release the capacity of the 20-roll reversible mill, rolling high-grade non-oriented silicon steel for new energy vehicle drive motors on a continuous acid rolling mill, especially for steel with a thickness of 0.30mm and below, is becoming a future development trend. During the continuous rolling production of high-grade non-oriented silicon steel for new energy vehicle drive motors, the large diameter of the work rolls results in excessive rolling force. Simultaneously, due to its low elongation, micro-cracks easily initiate at the edges during cold rolling. These cracks continuously expand during rolling, causing the mill to slow down production and even leading to strip breakage, severely restricting the unit's output and rolling stability. During rolling, in addition to longitudinal flow, significant transverse flow occurs at the strip edge, further reducing the rolling pressure and roll flattening in the strip edge region. Under the same rolling force, the edges are more prone to thinning, resulting in edge drop. Controlling edge drop also leads to the generation of edge waves.

[0004] Currently, the most direct methods to suppress edge cracking in high-grade non-oriented silicon steel used in drive motors for new energy vehicles are preheating the steel coil to increase the initial rolling temperature or reducing the rolling speed during the rolling process. However, these methods all lead to increased production costs and reduced production efficiency. Another more complex method, which does not affect production efficiency or cost, is to control the deflection at both ends of the work rolls, i.e., bending the rolls. Roll deflection can be achieved by introducing artificial bending moments at both ends of the work rolls and / or by controlling the reduction rate per stand. However, this method largely depends on the experience of the cold rolling mill operators.

[0005] The following are relevant research results from both domestic and international sources regarding technologies for improving the edge quality of cold-rolled high-grade non-oriented silicon steel used in drive motors for new energy vehicles:

[0006] The patent "A Method for Controlling Edge Cracks in Cold Continuous Rolling of High-Grade Non-Oriented Silicon Steel" (application number: CN201510937541.1) aims to effectively reduce edge stress in strip steel and prevent edge cracking during cold continuous rolling of high-grade non-oriented silicon steel. It reduces the load distribution of the first stand from 33-36% under automatic system allocation to 25-30%; and sets the UCMW mill work roll shifting value to -40-20mm. While this patent improves the edge cracking problem of the exit strip by reducing the load distribution of the first stand, it inevitably increases the rolling load distribution of subsequent stands. Furthermore, with the increase in deformation resistance, the rolling load of subsequent stands will increase sharply, which is extremely detrimental to edge crack and strip shape control.

[0007] The patent "A Method for Producing 0.35mm Non-oriented Silicon Steel Using a Cold Continuous Rolling Mill" (application number: 202010420065.7) employs a single-pass rolling method to continuously cold roll the cold-rolled raw material coil in five stands. By controlling the reduction rate, rolling force, inter-stand tension, and inlet / outlet tension of each pass, and by using emulsion spraying for process lubrication and cooling, as well as by partitioning the work rolls for cooling, the thermal crown of the work rolls is controlled to adjust the strip shape, thereby obtaining an intermediate product of 0.35mm thick non-oriented silicon steel. Its main purpose is to obtain a 0.35mm product with good strip shape.

[0008] The paper "Research on High-Precision Section Control Technology of Silicon Steel in Wide-Specification Five-Stand Cold Rolling Mill" uses the five-stand mill of Lianyuan Steel as an example.

[0009] Taking the UCM cold continuous rolling mill as the research object, a two-dimensional variable thickness finite element model of the six-high mill roll system was established. An ECC work roll profile curve capable of high-precision cross-section control was developed, which can effectively control the edge drop of the product and improve the cross-sectional control accuracy of non-oriented silicon steel products.

[0010] The patent "A Technology for Preparing Non-Oriented High-Grade Stainless Steel" (application number: 200810229737.5) obtains full-length, edge-crack-free hot-rolled steel coils by controlling the steel's smelting composition and hot rolling process; increasing the cold-rolling uncoiling temperature to maintain the strip temperature above its brittle transition point; and employing a pickling-five-stand cold continuous rolling process, rationally allocating the reduction rate of each cold rolling pass, and utilizing the processing heat generated during strip rolling to achieve cold continuous rolling of non-oriented high-grade stainless steel. Its main focus is on steelmaking, where hot rolling improves raw material quality while utilizing deformation heat to mitigate the brittleness of cold rolling.

[0011] The above literature focuses on optimizing the edge quality of cold-rolled silicon steel, adjusting edge waviness and edge cracking through their respective methods. However, there is currently no perfect method to control edge waviness while effectively suppressing edge cracking, thereby obtaining good edge quality. Summary of the Invention

[0012] Existing methods for improving the edge quality of cold-rolled high-grade non-oriented silicon steel are relatively simple and difficult to simultaneously control edge waviness, edge flare, and edge cracking. The purpose of this invention is to provide a method for improving the edge quality of cold-rolled high-grade non-oriented silicon steel used in drive motors for new energy vehicles. By controlling the pickling time of the raw material, setting the position of the intermediate roll, and optimizing the bending force of the work roll, the method aims to reduce strip edge waviness and edge flare, thereby achieving optimal cold-rolled edge quality, improving production efficiency, and increasing product yield.

[0013] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0014] A method is provided to improve the edge quality of high-grade non-oriented silicon steel used in cold continuous rolling for drive motors of new energy vehicles, wherein the cold continuous rolling adopts a UCMW five-stand continuous rolling mill, and the method includes:

[0015] The pickling time t for hot-rolled raw materials is controlled as follows:

[0016] T×Si% / 600≤t≤T×Si% / 300

[0017] Where: T is the hot rolling coiling temperature, and Si% is the mass percentage of Si in high-grade non-oriented silicon steel;

[0018] Set the intermediate roll shifting amount of the continuous rolling mill to 30-80mm;

[0019] The control range for the ratio L / R of the work roll body length L to the work roll surface curvature radius R of a continuous rolling mill:

[0020] -0.25 ≤ L / R ≤ -0.15

[0021] Wherein: the working roll is a concave roll, corresponding to a negative bending roll, and R takes a negative value.

[0022] According to the above scheme, the Si% in non-oriented silicon steel is 2-4%.

[0023] According to the above scheme, the hot rolling coiling temperature is 550-750℃.

[0024] The method for improving the edge quality of cold-rolled high-grade non-oriented silicon steel used in drive motors of new energy vehicles, as described in this invention, has the following specific mechanism:

[0025] The impact of pickling time on edge cracks in high-grade silicon steel rolling mainly includes two aspects: (1) According to conventional pickling experience, if the pickling time is too long, the material is prone to over-pickling, which will affect the mechanical properties of the material and cause brittle fracture; (2) Pickling time will affect the morphology and roughness of the strip surface, which will lead to changes in the friction state between the strip and the roll, and increase the plastic damage at the edge; at the same time, a longer pickling time will also have an adverse effect on the quality of the strip edge, making the cracks at the strip edge more likely to expand under tensile stress and cause edge cracks.

[0026] Hot-rolled steel sheets with high silicon content are particularly prone to developing stubborn iron oxide scale. On the one hand, during the high-temperature heating process, Si and Fe easily form layered Fe2SiO4 (2FeO·SiO2) between the iron oxide scale and the steel substrate. Its solidification temperature is 1170℃. During hot rolling descaling, the interface temperature reduces Fe2SiO4 from the liquid phase to the solid phase. After forming a molten state, it penetrates into the iron oxide scale and the steel substrate in a wedge shape, resulting in poor peelability of the iron oxide scale.

[0027] As the coiling temperature decreases, the Fe2O3 content decreases, the oxide scale thickness gradually decreases, and the Si-rich layer between the oxide layer and the substrate also gradually thins. The surface morphology changes from island-like whisker distribution to clustered spiral columnar crystal structure, resulting in a loose and porous surface. Under internal stress, wrinkling, blistering, and even rupture and detachment occur, which is beneficial for pickling and descaling. The pickling time is closely related to the hot-rolled coiling temperature T and the silicon content. When t < T × Si% / 600, the iron oxide scale is difficult to remove completely, while when t > T × Si% / 300, over-pickling occurs, affecting the quality of the strip surface and edges. To achieve effective pickling, this invention controls the hot-rolled raw material pickling time t to be: T × Si% / 600 ≤ t ≤ T × Si% / 300, ensuring the quality of the strip surface and edges while completely removing the iron oxide scale.

[0028] In existing strip edge shape control technology for cold-rolled UCM mills, the first step is to subtract the target strip shape value from the measured strip edge shape meter channel at the last stand exit to obtain the edge shape deviation. Then, the strip edge shape state is determined based on the deviation: when the deviation exceeds a given upper limit, the strip edge is considered locally loose, corresponding to edge waviness; when the deviation is less than a given lower limit, the strip edge is considered locally tight, corresponding to edge cracking.

[0029] The intermediate roll alters the position of the CVC roll by switching the rolls, thereby changing the contact force distribution between the intermediate roll and the work roll. This further alters the deformation of the work roll, achieving control and adjustment of the strip shape. The roll gap crown adjustment range indirectly represents the mill's ability to control the strip shape. When the intermediate roll offset is less than 30mm, the strip edge becomes locally loose, which easily leads to edge waviness. When the intermediate roll offset is greater than 80mm, the strip edge becomes locally tight, which easily leads to edge cracking or even strip breakage.

[0030] If the rolling mill's bend roll shape is suitable, and the work rolls are set to appropriate convex or concave surfaces, edge cracking of the steel strip during cold rolling can be effectively suppressed. When using convex rolls (positive bend rolls), L / Rp > 0, resulting in a longer edge crack length. As Rp increases, L / Rp gradually decreases, and the edge crack length gradually diminishes. When L / Rp approaches 0, the convex roll becomes a flat roll. Edge cracking can also occur when using flat rolls because tensile stress exists in the rolling direction regardless of the work roll shape. When using concave rolls (negative bend rolls), L / R... N <0, the crack tip propagation rate will gradually slow down, L / R N When the value is less than -0.15, the crack tip closes and will not extend further. Even with larger reductions, the edge crack will not extend further and will close. When concave rolls are used, edge waviness is generated at the edges. The higher the material's ductility, the easier it is for the edges to extend during rolling. In this case, concave rolls increase the probability of large edge waviness during rolling. However, for high-grade non-oriented silicon steel, due to its higher alloy content and poorer ductility, the negative impact of concave rolls on edge waviness control is not significant. However, to improve the rolling yield and the same-plate difference level, a value of -0.25 ≤ L / R is selected. N <-0.15.

[0031] The beneficial effects of this invention are as follows:

[0032] This invention optimizes the pickling time of hot-rolled coils, adopts reasonable work roll profile dimensions, and adjusts the amount of intermediate roll shifting. Under the premise of suppressing edge cracking in cold continuous rolling, it maximizes the reduction of edge waviness. Under the condition that the hot-rolled raw material is not trimmed, it improves the edge quality of high-grade non-oriented silicon steel for drive motors of new energy vehicles in cold continuous rolling, realizes efficient production, reduces the amount of edge trimming after cold rolling, and improves the yield. Detailed Implementation

[0033] The technical solution of the present invention will be further explained and illustrated below through specific embodiments.

[0034] This invention provides a method for improving the edge quality of high-grade non-oriented silicon steel cold-rolled in continuous rolling mills, wherein the cold rolling process employs a UCMW five-stand continuous rolling mill, and the method includes:

[0035] 1) Control the pickling time t of hot-rolled raw materials as follows:

[0036] T×Si% / 600≤t≤T×Si% / 300

[0037] Where: T is the hot rolling temperature, and Si% is the mass percentage of Si in high-grade non-oriented silicon steel.

[0038] 2) Set the intermediate roll shifting amount of the continuous rolling mill to 30-80mm;

[0039] 3) The control range of the ratio L / R between the length L of the work roll body and the radius of curvature R of the work roll surface in a continuous rolling mill:

[0040] -0.25≤L / R≤-0.15

[0041] Wherein: the working roll is a concave roll, corresponding to a negative bending roll, and R takes a negative value.

[0042] The following is a specific example:

[0043] Example 1 and Comparative Example 1

[0044] The hot-rolled raw material has a silicon content of 3.30% and a thickness of 2.1 mm. The target product thickness is 0.30 mm. The hot-rolling coiling temperature, pickling time, intermediate roll and work roll parameters, and corresponding rolling conditions are shown in Table 1. In Table 1, Examples 1-1 to 1-5 are different groups of Example 1, and Comparative Examples 1-1 to 1-7 are different groups of Comparative Examples 1.

[0045] Table 1. Comparison of process and rolling conditions in Example 1 and Comparative Example 1

[0046]

[0047] Example 2 and Comparative Example 2

[0048] The hot-rolled raw material had a silicon content of 2.90% and a thickness of 2.2 mm. The target product thickness was 0.35 mm. The hot-rolling coiling temperature, pickling time, intermediate roll and work roll parameters, and corresponding rolling conditions are shown in Table 2. In Table 2, Examples 2-1 to 2-5 are different groups of Example 2, and Comparative Examples 2-1 to 2-7 are different groups of Comparative Examples 2.

[0049] Table 2. Process and rolling conditions of Example 2 and Comparative Example 2

[0050]

[0051] In Examples 1 and 2, the different components simultaneously met the requirements for pickling time, intermediate roll shifting amount, and L / R ratio, resulting in good surface quality of the steel sheets after cold continuous rolling, and good control of edge waviness and edge cracking. However, in Comparative Examples 1 and 2, some groups suffered from poor steel sheet surface quality due to inappropriate pickling time, some from poor edge waviness control due to inappropriate intermediate roll shifting amount, and some from severe edge cracking or even strip breakage due to improper L / R values.

[0052] Based on the examples and comparative cases, simultaneously meeting the requirements for appropriate pickling time, intermediate roll shifting amount, and L / R ratio can yield ideal edge quality for cold continuous rolling of high-grade non-oriented silicon steel for new energy vehicle drive motors.

Claims

1. A method for improving the edge quality of high-grade non-oriented silicon steel used in cold continuous rolling for drive motors of new energy vehicles, wherein the cold continuous rolling adopts a UCMW five-stand continuous rolling mill, characterized in that, The method includes: The pickling time t for hot-rolled raw materials is controlled as follows: T×Si% / 600≤t≤T×Si% / 300 Where: T is the hot rolling coiling temperature, and Si% is the mass percentage of Si in high-grade non-oriented silicon steel; Set the intermediate roll shifting amount of the continuous rolling mill to 30-80mm; The control range for the ratio L / R of the work roll body length L to the work roll surface curvature radius R of a continuous rolling mill: -0.25≤L / R≤-0.15 Wherein: the working roll is a concave roll, corresponding to a negative bending roll, and R takes a negative value.

2. The method according to claim 1, characterized in that, The Si content in high-grade non-oriented silicon steel is 2-4%.

3. The method according to claim 1, characterized in that, The hot rolling temperature is 550-750℃.

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