A method for preventing hot-rolled strip steel from flat banding

Abstract

The application discloses a method for preventing hot-rolled strip steel flat coil, and belongs to the technical field of hot-rolled strip steel production. The method comprises the following steps: hot rolling, laminar flow cooling, coiling and flattening. When the strip steel is discharged from the outlet of a finishing mill, the crown is less than or equal to 45 microns, the wedge shape is controlled to be between -10 microns and +10 microns, the wedge shape curve is a sinusoidal curve, and the center symmetry line is a wedge shape equal to 0. The cooling mode and the coiling parameters are set according to the specifications of the strip steel in the laminar flow cooling step and the coiling step. The crown and the wedge shape of the strip steel are effectively controlled, and the appropriate cooling mode and the coiling parameters are matched, so that the problem of the 500-600 MPa grade hot-rolled strip steel flat coil is effectively solved, the product performance meets the requirements, the flattening efficiency of the next step is increased by 8%-13%, and the strip steel yield is increased by 5%-10%.

Description

Technical Field

[0001] This invention belongs to the field of hot-rolled strip steel production technology, and specifically relates to a method for preventing hot-rolled strip steel from flattening. Background Technology

[0002] In the hot rolling process of 500-600MPa grade hot-rolled strip steel, for thicknesses of 1.8-3.5mm and widths of 1000-2000mm, the core is initially round after hot rolling with the support of the coiling rollers. However, after uncoiling, the roundness of the core gradually becomes elliptical, also known as flattening. Elliptical coiling of hot-rolled strip steel not only makes leveling and coiling difficult in the next process but also reduces leveling efficiency by 8-13%. In severe cases, it may even prevent leveling and coiling altogether, resulting in scrapped steel and a loss of approximately 1100-1300 yuan per ton of steel.

[0003] Chinese patent CN107812789B discloses a method for preventing hot-rolled strip from flattening, employing a coiling temperature of 650–700℃ or 500–550℃, and holding the coil on the coiler for 5–20 seconds after coiling, thereby improving the problem of flattening and collapse after hot-rolled strip coiling. Chinese patent CN102335681B discloses a coiling method for preventing hot-rolled strip from flattening, employing a coiling temperature of 500–600℃, and holding the coil on the coiler drum for 20–60 seconds after coiling, effectively improving the problem of flattening after hot-rolled strip coiling. While both of these disclosed technologies can effectively improve the problem of elliptical coils, they affect production rhythm and daily production output.

[0004] Chinese patent CN113458152B discloses a method for controlling flat coils in hot-rolled high-strength strip steel. This method involves controlling the target coiling temperature to 20-70°C above the bainitic transformation point, shaping the coiling temperature curve into an asymmetrical "U-shape," with the temperature at the beginning and end being 20-40°C higher than the middle section, increasing the coiling tension to 1.3-1.6 times, and rotating the coil 90° clockwise before unwinding. This method aims to eliminate flat coil defects. However, the asymmetrical "U-shape" coiling temperature curve proposed in this patent requires strict cooling control, making it difficult to achieve in actual production. Furthermore, it does not consider the impact of crown and wedge shape on uneven friction between strip layers, which can lead to flat coils. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preventing hot-rolled strip steel from flattening. This method involves strictly controlling the convexity and wedge shape of the steel strip during the hot-rolling process, and rationally coordinating cooling methods, coiling temperatures, and coiling torques according to different thicknesses and widths. This improves the problem of elliptical coils in hot-rolled strip steel, increases the leveling efficiency of the next process, and accelerates the production pace.

[0006] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0007] A method for preventing hot-rolled strip steel from flattening includes hot rolling, laminar flow cooling, coiling, and leveling processes;

[0008] Hot rolling process: When the strip exits the finishing mill, the crown is ≤45μm, the wedge shape is controlled between -10μm and +10μm, and the wedge curve is a sine curve with the central symmetry line being equal to 0.

[0009] Laminar flow cooling process and coiling process: The cooling method and coiling parameters are set according to the specifications of the strip steel as follows:

[0010] (1) For strip steel with a thickness of 1.8mm ≤ 2.0mm and a width of 1000mm ≤ 1500mm, the cooling method is front-end 1 / 2 cooling, the cooling rate is 23~25℃ / s, and the coiler torque is controlled at 60KN·m~65KN·m;

[0011] (2) For strip steel with a thickness of 2.0mm and a width of 1000mm and a thickness of 1700mm, the cooling method is front-section 3 / 4 cooling, the cooling rate is 26~28℃ / s, and the coiler torque is controlled at 60KN·m~65KN·m;

[0012] (3) For strip steel with a thickness of 2.5mm and a width of 1000mm and a thickness of 3.0mm, the cooling method is front-end centralized cooling with a cooling rate of 28 to 33℃ / s and the coiler torque is controlled at 65KN·m to 70KN·m.

[0013] (4) For strip steel with a thickness of 3.0mm and a width of 1000mm and a thickness of 3.5mm, the cooling method is front-end centralized cooling with a cooling rate of 28 to 33℃ / s and the coiler torque is controlled at 70KN·m to 75KN·m.

[0014] Furthermore, in the hot rolling process, the strip steel is rolled using a "2+7" rolling method, where 2 stands are for roughing mills and 7 stands are for finishing mills. After roughing, the thickness of the intermediate slab is guaranteed to be 35-45mm. Before finishing, the centering accuracy of the mill inlet side guide is guaranteed to be ±3mm and the centering accuracy of the vertical roller is guaranteed to be ±2mm.

[0015] Furthermore, the winding temperature in the winding process is controlled at 550–580°C.

[0016] The above method is applicable to hot-rolled strip steel with a tensile strength of 500-600 MPa.

[0017] This invention controls the crown of hot-rolled strip steel to ≤45μm, mainly to increase the friction between strip steel layers during the coiling process and prevent loose coiling. The wedge shape is controlled between -10μm and +10μm, and the wedge curve is a sine curve. The central symmetry line is when the wedge shape equals 0. This is mainly to ensure the stability of the circumferential friction of the entire coil during the coiling process, to prevent the wedge shape from being too large, and to prevent the coil from collapsing to one side or the roundness of the two sides of the core of the coil from being inconsistent due to asymmetrical wedge shape.

[0018] The reason why this invention distinguishes between different thicknesses and widths and matches appropriate cooling methods, winding temperatures, and winding machine torques is that different specifications of steel strips have different stiffness and air cooling rates. Thin-gauge, narrow-section steel strips have faster cooling rates, lower stiffness, and are more difficult to control in terms of shape. Therefore, a lower cooling rate is used to avoid bainitic phase transformation, which would affect performance, and a lower winding tension is used to avoid narrowing of the width. On the other hand, for thick-gauge, wide-section steel strips, the cooling rate is relatively slower, the stiffness is relatively higher, and the shape is relatively easier to control. Therefore, a higher cooling rate is used, and a larger winding tension is appropriately matched to increase the friction between the steel strip layers and ensure the roundness of the steel coil core.

[0019] The beneficial effects of adopting the above technical solution are as follows: By effectively controlling the convexity and wedge shape of the strip steel, and matching it with appropriate cooling methods, coiling temperature and coiling machine torque, the present invention effectively solves the problem of flat coils of 500MPa to 600MPa grade hot-rolled strip steel, increases the leveling efficiency of the next process by 8% to 13%, increases the strip steel yield by 5% to 10%, and increases the profit per ton of steel by RMB 1,100 to RMB 1,300. Attached Figure Description

[0020] Figure 1 This is a diagram showing the coil state of the hot-rolled strip steel produced by this invention. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to the embodiments.

[0022] Example 1

[0023] The chemical composition of the 500-600MPa grade hot-rolled strip steel in this embodiment is as follows (mass percentage): C: 0.15%, Si: 0.25%, Mn: 1.25%, P: 0.015%, S: 0.008%, Nb: 0.008%, Als: 0.030%, with the remainder being Fe and unavoidable trace impurities.

[0024] The production process of the above-mentioned hot-rolled strip steel includes: molten iron pretreatment - converter smelting - LF refining - continuous casting - 2250mm unit hot continuous rolling - laminar flow cooling - coiling - leveling - inspection - packaging and delivery.

[0025] The hot continuous rolling process parameters for the 2250mm unit in the above process are shown in Table 1 below, the specific control parameters for the laminar flow cooling-coiling process are shown in Table 2 below, and the test results for each performance are shown in Table 3.

[0026] Table 1. Process parameters for 2250mm hot rolling in Example 1

[0027]

[0028] Table 2 Control parameters for laminar flow cooling-winding process in Example 1

[0029]

[0030] Table 3. Test results of various properties of hot-rolled strip steel in Example 1.

[0031]

[0032] Example 2

[0033] The chemical composition of the 500-600MPa grade hot-rolled strip steel in this embodiment is as follows (mass percentage): C: 0.16%, Si: 0.28%, Mn: 1.28%, P: 0.014%, S: 0.003%, Nb: 0.010%, Als: 0.033%, with the remainder being Fe and unavoidable trace impurities.

[0034] The production process of the above-mentioned hot-rolled strip steel includes: molten iron pretreatment - converter smelting - LF refining - continuous casting - 2250mm unit hot continuous rolling - laminar flow cooling - coiling - leveling - inspection - packaging and delivery.

[0035] The hot continuous rolling process parameters for the 2250mm unit in the above process are shown in Table 1 below, the specific control parameters for the laminar flow cooling-coiling process are shown in Table 2 below, and the test results for each performance are shown in Table 3.

[0036] Table 4. Process parameters for 2250mm hot rolling in Example 2.

[0037]

[0038] Table 5. Control parameters for laminar flow cooling-winding process in Example 2

[0039]

[0040] Table 6. Test results of various properties of hot-rolled strip steel in Example 2.

[0041]

[0042] Example 3

[0043] In this embodiment, the chemical composition of the 500-600MPa grade hot-rolled strip steel has the following mass percentages: C: 0.17%, Si: 0.30%, Mn: 1.30%, P: 0.018%, S: 0.003%, Nb: 0.010%, Als: 0.031%, with the remainder being Fe and unavoidable trace impurities.

[0044] The production process of the above-mentioned hot-rolled strip steel includes: molten iron pretreatment - converter smelting - LF refining - continuous casting - 2250mm unit hot continuous rolling - laminar flow cooling - coiling - leveling - inspection - packaging and delivery.

[0045] The hot continuous rolling process parameters for the 2250mm unit in the above process are shown in Table 1 below, the specific control parameters for the laminar flow cooling-coiling process are shown in Table 2 below, and the test results for each performance are shown in Table 3.

[0046] Table 7. Process parameters for 2250mm hot rolling in Example 3.

[0047]

[0048]

[0049] Table 8. Control parameters for laminar flow cooling-winding process in Example 3.

[0050]

[0051] Table 9. Test results of various properties of hot-rolled strip steel in Example 3.

[0052]

[0053] Example 4

[0054] The chemical composition of the 500-600MPa grade hot-rolled strip steel in this embodiment is as follows (mass percentage): C: 0.17%, Si: 0.29%, Mn: 1.35%, P: 0.016%, S: 0.007%, Nb: 0.012%, Als: 0.035%, with the remainder being Fe and unavoidable trace impurities.

[0055] The production process of the above-mentioned hot-rolled strip steel includes: molten iron pretreatment - converter smelting - LF refining - continuous casting - 2250mm unit hot continuous rolling - laminar flow cooling - coiling - leveling - inspection - packaging and delivery.

[0056] The hot continuous rolling process parameters for the 2250mm unit in the above process are shown in Table 1 below, the specific control parameters for the laminar flow cooling-coiling process are shown in Table 2 below, and the test results for each performance are shown in Table 3.

[0057] Table 10. Process parameters for 2250mm hot rolling in Example 4

[0058]

[0059]

[0060] Table 11 Control parameters for laminar flow cooling-winding process in Example 4

[0061]

[0062] Table 12 Results of various performance tests for hot-rolled strip steel in Example 4

[0063]

[0064] Note: In each embodiment, the ellipse roll amount = the longest axis of the roll core - the shortest axis of the roll core, and the measuring ruler passes through the center of the roll core.

Claims

1. A method for preventing hot-rolled strip steel from flattening, characterized in that, This includes hot rolling, laminar flow cooling, coiling, and leveling processes; Hot rolling process: When the strip exits the finishing mill, the crown is ≤45μm, the wedge shape is controlled between -10μm and +10μm, and the wedge curve is a sine curve with the central symmetry line being equal to 0. Laminar flow cooling process and coiling process: The cooling method and coiling parameters are set according to the specifications of the strip steel as follows: (1) For strip steel with a thickness of 1.8mm ≤ thickness ≤ 2.0mm and a width of 1000mm ≤ width ≤ 1500mm, the cooling method is front-end 1 / 2 cooling, and the coiler torque is controlled at 60KN·m~65KN·m; (2) For strip steel with a thickness of 2.0mm and a width of 1000mm and a thickness of 1700mm, the cooling method is front-end 3 / 4 cooling, and the coiler torque is controlled at 60KN·m~65KN·m; (3) For strip steel with a thickness of 2.5mm and a width of 1000mm and a thickness of 3.0mm, the cooling method is front-end centralized cooling, and the coiler torque is controlled at 65KN·m to 70KN·m; (4) For strip steel with a thickness of 3.0mm and a width of 1000mm and a thickness of 3.5mm, the cooling method is front-end centralized cooling, and the coiler torque is controlled at 70KN·m~75KN·m.

2. The method for preventing hot-rolled strip steel from flattening according to claim 1, characterized in that: In the hot rolling process, the strip steel is rolled using a "2+7" rolling method, where 2 stands are two roughing mills and 7 stands are seven finishing mills. After roughing is completed, the thickness of the intermediate slab is guaranteed to be 35-45 mm.

3. The method for preventing hot-rolled strip steel from flattening according to claim 2, characterized in that: In the hot rolling process, before finishing rolling, the centering accuracy of the mill inlet side guide is guaranteed to be ±3mm, and the centering accuracy of the vertical roll is ±2mm.

4. The method for preventing hot-rolled strip steel from flattening according to claim 3, characterized in that: The cooling rate of the front half cooling section is 23-25℃ / s.

5. The method for preventing hot-rolled strip steel from flattening according to claim 3, characterized in that: The cooling rate of the front 3 / 4 cooling section is 26-28°C / s.

6. The method for preventing hot-rolled strip steel from flattening according to claim 3, characterized in that: The cooling rate of the front-end centralized cooling is 28–33 °C / s.

7. The method for preventing hot-rolled strip steel from flattening according to any one of claims 1-6, characterized in that: The winding temperature in the winding process is controlled at 550–580°C.

8. The method for preventing hot-rolled strip steel from flattening according to claim 7, characterized in that: The tensile strength grade of hot-rolled strip steel is 500-600 MPa.

Images