Control method for improving shape of cold-rolled high-strength steel plate

Abstract

The invention discloses a control method for improving the shape of a cold-rolled high-strength steel plate. The control method comprises the following steps that a high-strength steel casting blank is taken to be subjected to rough rolling, finish rolling, laminar cooling, coiling, acid rolling and continuous annealing. The high-strength steel obtained through the control method comprises the following components in percentage by mass: 0.05%-0.20% of C, 1.30%-3.0% of Mn, 0.20%-1.30% of Si, 0.010%-0.030% of Als, less than or equal to 0.016% of P, less than or equal to 0.0025% of S, less than or equal to 0.004% of N, 0.010%-0.80% of Cr, 0.003%-0.060% of Nb, 0.003%-0.080% of Ti, 0.002%-0.50% of Mo and the balance of Fe and inevitable impurities. According to the control method for improving the shape of the cold-rolled high-strength steel plate, by comprehensively controlling hot rolling, acid rolling and subsequent continuous annealing processes, the product has a good plate shape, quality defects in production are reduced, and the plate shape before use by a user is guaranteed. The control method is simple and easy to implement, extra thickening and equipment increasing are not needed, and the method can be implemented on an existing conventional production line.

Description

Technical Field

[0001] The invention relates to the technical field of cold-rolled high-strength steel manufacturing, and in particular to a control method for improving the plate shape of cold-rolled high-strength steel. Background Art

[0002] In the production of cold-rolled high-strength steel, as the thickness of the strip becomes thinner and the strength increases, it becomes increasingly difficult to control the shape of the product. Common shape defects include edge waves, middle waves, rib waves, compound waves, etc. These shape defects are difficult to eliminate in the subsequent production process, which directly affects the quality of the strip and the normal use of customers.

[0003] Most of the existing cold-rolled high-strength steel plate shape control methods use the post-tension control method of the pickling mill. For example, Chinese invention patent application number CN201710757095.5 discloses a cold-rolled thin strip steel plate shape control method, which adjusts the strip post-tension distribution in real time to eliminate the uneven plastic extension strain difference generated along the width direction of the strip, thereby improving the plate shape defects. For example, the Chinese invention patent application number CN200910046535.1 discloses a rolling control method for high-strength cold-rolled strip steel, and provides a rolling process for high-strength cold-rolled strip steel with the goal of optimizing the plate shape. In the cold rolling stage, the plate shape of the cold-rolled sheet is controlled by the following five methods: (1) the proportional convexity of the incoming material is controlled to be less than 0.05, and the ratio of the wedge shape to the plate thickness is less than 0.04; (2) a support roll shape technology with a special roll shape is adopted; (3) the working rolls of the five cold rolling stands are set to have variable convexity; (4) the fifth stand adopts a constant rolling force mode; (5) the plate shape target curve is set to a micro-medium wave mode, and the elongation difference is 10±2IU. The plate shape of the cold-rolled high-strength steel is controlled by the following methods, and a good control effect is achieved. A Chinese patent application numbered CN201811233342.2 discloses a method for controlling the double-side wave and middle-side wave shape of a five-stand cold-rolled high-strength steel strip. The method presets a shape control target in the pickling mill and timely adjusts the bending roll force according to the difference between the actual shape and the preset target, thereby achieving the purpose of controlling the shape.

[0004] The main methods adopted in the above existing technologies are concentrated in the pickling stage, and the strip shape is controlled by means of pickling tension, bending roll force and roll cooling to obtain good results. These methods are universal, but in the production of certain special steel grades, such as steel with a high Si content, the plate shape is greatly affected by the organizational changes of each process, and only using the above methods cannot obtain good results.

[0005] Therefore, the applicant considered controlling the plate shape by comprehensively controlling the entire process of hot rolling, pickling and annealing. Summary of the invention

[0006] In order to overcome the shortcomings of the above-mentioned technology, the purpose of the present invention is to provide a control method for improving the shape of cold-rolled high-strength steel plates, and to obtain a good plate shape through comprehensive control of hot-rolled incoming materials, acid rolling process and subsequent annealing process.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] A control method for improving the shape of cold-rolled high-strength steel plates comprises the following steps: taking high-strength steel ingots for heating, rough rolling, finish rolling, laminar cooling, coiling, pickling and continuous annealing.

[0009] Preferably, the control method for improving the shape of cold-rolled high-strength steel plate comprises the following steps: steelmaking and continuous casting to obtain high-strength steel ingots, followed by heating, rough rolling, finish rolling, laminar cooling, coiling, pickling and continuous annealing.

[0010] Preferably, the finishing step adopts F1-F7 finishing mills; wherein, the finishing rolling F7 rolling reduction rate is 3-15%, and the finishing rolling temperature is 900-960°C. If the finishing temperature is too low, the hot rolling deformation resistance increases, which is easy to cause uneven deformation in the length and width directions, resulting in poor plate shape. If the finishing temperature is too high, it is easy to cause uneven oxidation of the plate surface, affecting the cooling uniformity in the width and length directions of the plate during the subsequent cooling process, and it is easy to produce uneven organization and cause poor plate shape.

[0011] Preferably, the laminar cooling step adopts three-stage cooling. The three-stage cooling can accurately control the hot rolling structure transformation, improve the structure control accuracy, thereby improving the structure uniformity of the strip in the full length and full width direction, which is conducive to achieving uniform deformation of the strip in the full length and full width direction.

[0012] Preferably, in the three-stage cooling process, the cooling rate of the first stage is 60-200°C / s, the cooling time is 0.5-5s, the cooling rate of the second stage is 2-20°C / s, the cooling time is 3-15s, and the cooling rate of the third stage is 10-60°C / s, and the cooling time is 3-20s. Too low or too high cooling rate in the first stage, too long or too short cooling time are likely to lead to uneven organization, resulting in uneven plate shape; accurate control of the cooling rate and time in the second stage is conducive to improving the uniformity of the organization, and producing a certain soft phase organization, creating conditions for the uniform deformation of the subsequent strip. Too high or too low cooling rate is likely to lead to uneven organization, too much or too little soft phase organization, resulting in uneven deformation and poor plate shape. Too high or too long cooling rate in the third stage will produce too much hard phase organization, which is not conducive to uniform deformation. Too low cooling rate in the third stage and too short time will easily lead to uneven organization in the width and length directions, resulting in uneven deformation and poor plate shape.

[0013] Preferably, in the coiling step, the coiling temperature is 460-600° C. Too low or too high a coiling temperature can easily lead to uneven organization of the strip head, middle and tail and in the width direction, thereby causing uneven cold rolling deformation and poor plate shape.

[0014] Preferably, in the pickling step, the pickling rolling speed is 200-600 m / min, the pickling rolling reduction rate is 45-70%, the total reduction rate of the first and second pickling stands is 35-60%, and the reduction rate of the last stand is 3-10%. Too low a pickling rolling speed affects production efficiency, and too high a pickling rolling speed easily leads to too high a deformation speed, uneven hardness in the full length and full width of the strip, and uneven deformation, resulting in poor plate shape. Too low a pickling rolling reduction rate cannot effectively eliminate the poor plate shape caused by hot rolling, and too high a pickling rolling reduction rate easily aggravates the uneven deformation in the length and width of the strip, resulting in poor plate shape. Too low a total reduction rate of the pickling 1-2 stands leads to an increase in the deformation amount of the subsequent process, an increase in the hardness of the plate shape, and uneven deformation of the full length and width of the plate, resulting in poor plate shape. Too high a deformation rate leads to excessive work hardening, and the steel strip is not easy to deform, resulting in poor plate shape. If the reduction rate of the last stand is too low, the plastic deformation of the strip in the full length and width directions is insufficient, resulting in poor plate shape. If the reduction rate is too high, the plate and strip will suffer from severe work hardening, which will also lead to poor plate shape.

[0015] Preferably, in the continuous annealing step, the continuous annealing temperature is 820-880° C. If the continuous annealing temperature is too low or too high, it is easy to cause the strip structure to be uneven in length and width, resulting in poor plate shape.

[0016] Preferably, the control method further comprises performing skinning or flattening after the continuous annealing step to obtain a high-strength steel strip; during the skinning or flattening process, the reduction rate is 0.2% to 1.0%. If the reduction rate is too low, plastic deformation cannot be ensured in the full length and full width directions, which is not conducive to correcting poor plate shape. If the reduction rate is too high, the work hardening is too great, which is also not conducive to plate shape control.

[0017] Preferably, the strip steel has a thickness of 0.7-2.5 mm, a width of 900-1800 mm, and a width-to-thickness ratio of 500-2000.

[0018] The high-strength steel prepared by the above control method includes the following components, calculated by mass fraction: C 0.05%-0.20%, Mn 1.30%-3.0%, Si 0.20%-1.30%, Als 0.010%-0.030%, P≤0.016%, S≤0.0025%, N≤0.004%, Cr 0.010%-0.80%, Nb 0.003%-0.060%, Ti0.003%-0.080%, Mo 0.002%-0.50%, and the rest is Fe and unavoidable impurities.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention provides a control method for improving the shape of cold-rolled high-strength steel plates. By comprehensively controlling hot rolling, acid rolling and subsequent continuous annealing processes, the product has a good plate shape, reduces quality defects in production, and ensures the plate shape before users use it. The control method of this method is simple and easy to implement, does not require additional thickening and equipment, and can be implemented on existing conventional production lines. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a straightness curve diagram after acid rolling in Example 1 of the present invention, in which the ordinate represents the straightness in μm and the abscissa represents the strip length in m;

[0022] Figure 2 This is a plate shape diagram after continuous retreat in Example 1 of the present invention;

[0023] Figure 3 This is the straightness curve after acid rolling in Comparative Example 1 of the present invention. In the figure, the ordinate represents the straightness in μm, and the abscissa represents the strip length in m. DETAILED DESCRIPTION

[0024] In order to better explain the present invention, the main contents of the present invention are further explained below in conjunction with the accompanying drawings, Examples 1 to 5 and Comparative Examples 1 to 6, but the contents of the present invention are not limited to the following examples.

[0025] The main components of the high-strength steel of Examples 1 to 5 and Comparative Examples 1 to 6 are shown in Table 1, wherein the main components of the high-strength steel of Examples 1 to 3 and Comparative Examples 1 to 4 are shown in Component 1 in Table 1, and the main components of Examples 4 to 5 and Comparative Examples 5 to 6 are shown in Component 2 in Table 1.

[0026] Table 1: Main components of high-strength steel of Examples 1 to 5 and Comparative Examples 1 to 6

[0027] Components C Si Mn Als Nb Ti N P S Cr Mo 1 0.09 0.45 2.1 0.020 0.005 0.010 0.0015 0.016 0.0020 0.015 0.03 2 0.13 0.72 1.70 0.015 0.012 0.012 0.0035 0.012 0.002 0.20 0.10

[0028] Table 2: Some process parameters of high-strength steel of Examples 1 to 5 and Comparative Examples 1 to 6

[0029]

[0030] Examples 1 to 5 and Comparative Examples 1 to 6 are all produced by the following steps, the difference between which is the different process parameters of the relevant steps, wherein the process parameters are shown in Tables 2 and 3. The production steps include: steelmaking, continuous casting, heating, rough rolling, finishing rolling, laminar cooling, coiling, pickling, continuous annealing, and leveling to obtain high-strength steel strip. Among them, the finishing rolling step uses F1-F7 finishing mills.

[0031] Table 3: Some process parameters of high-strength steel of Examples 1 to 5 and Comparative Examples 1 to 6

[0032]

[0033] Depend on Figures 1-2 From the straightness curve after acid rolling and the plate shape diagram after continuous retreat in Example 1 shown, it can be seen that within the full length of 2000m, the straightness of the strip steel after acid rolling in Example 1 is less than 5μm, and its plate shape is well controlled.

[0034] The process parameter control and organization of Examples 1 to 5 are all within the scope of the present invention, so the plate shape is well controlled.

[0035] like Figure 3 As shown, within the full length of 1750m, the straightness of the strip in Example 1 after pickling is greater than 5μm, especially at the tail of the strip, the straightness reaches 20μm. Its final rolling temperature is low, and the laminar cooling adopts one-stage cooling, which leads to poor plate shape of the hot-rolled coil, and ultimately leads to poor plate shape after pickling and continuous annealing. In Comparative Example 2, its laminar cooling adopts one-stage cooling, and the coiling temperature is low, which leads to poor plate shape of the hot-rolled coil, and ultimately leads to poor plate shape after pickling and continuous annealing. In Comparative Example 3, its laminar cooling adopts one-stage cooling, and the reduction rate of the last stand of pickling is high, which leads to poor plate shape after pickling, and ultimately leads to poor plate shape after continuous annealing. In Comparative Example 4, its pickling reduction rate is too high, the rolling speed is too high, and the continuous annealing temperature is low, which leads to poor plate shape after pickling and continuous annealing. In Comparative Example 5, the plate shape is poor due to the low reduction rate of the first and second passes of pickling, the high reduction rate of the final stand, the high annealing temperature, and the low flatness rate. In Comparative Example 6, the plate shape is poor due to the high hot rolling temperature, the high reduction rate of the final stand of pickling, and the high annealing temperature.

[0036] In summary, the present invention provides a control method for improving the shape of cold-rolled high-strength steel plates. By comprehensively controlling hot rolling, acid rolling and subsequent continuous annealing processes, the product has a good plate shape, reduces quality defects in production, and ensures the plate shape before use by users. The control method of this method is simple and easy to implement, does not require additional thickening and equipment, and can be implemented on existing conventional production lines.

Claims

1. A control method for improving the shape of cold-rolled high-strength steel plate, characterized in that: The following steps are involved: The high-strength steel ingot is heated, rough rolled, finish rolled, laminar cooled, coiled, pickled and annealed.

2. The control method according to claim 1, characterized in that: The finishing rolling step adopts F1-F7 finishing rolling mills; wherein, the finishing rolling F7 rolling reduction rate is 3-15%, and the finishing rolling final rolling temperature is 900-960°C.

3. The control method according to claim 1, characterized in that: The laminar cooling step adopts three-stage cooling.

4. The control method according to claim 3, characterized in that: In the three-stage cooling process, the cooling rate of the first stage is 60-200°C / s, the cooling time is 0.5-5s, the cooling rate of the second stage is 2-20°C / s, the cooling time is 3-15s, and the cooling rate of the third stage is 10-60°C / s, and the cooling time is 3-20s.

5. The control method according to claim 1, characterized in that: In the coiling step, the coiling temperature is 460 to 600°C.

6. The control method according to claim 1, characterized in that: In the acid rolling step, the acid rolling rolling speed is 200-600 m / min, the acid rolling reduction rate is 45-70%, the total reduction rate of the first and second acid rolling stands is 35-60%, and the reduction rate of the last stand is 3-10%.

7. The control method according to claim 1, characterized in that: In the continuous annealing step, the annealing temperature is 820-880°C.

8. The control method according to any one of claims 1 to 7, characterized in that: The method also includes performing skinning or flattening after the continuous annealing step to obtain a high-strength steel strip; during the skinning or flattening process, the reduction rate is 0.2% to 1.0%.

9. The control method according to claim 8, characterized in that: The strip steel has a thickness of 0.7 to 2.5 mm, a width of 900 to 1800 mm, and a width-to-thickness ratio of 500 to 2000.

10. The high-strength steel prepared by the control method according to any one of claims 1 to 9, characterized in that: Calculated by mass fraction, it includes the following components: C 0.05%-0.20%, Mn 1.30%-3.0%, Si0.20%-1.30%, Als0.010%-0.030%, P≤0.016%, S≤0.0025%, N≤0.004%, Cr0.010%-0.80%, Nb0.003%-0.060%, Ti 0.003%-0.080%, Mo 0.002%-0.50%, and the rest are Fe and unavoidable impurities.

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