Method for eliminating Q235B transverse crease defect

Abstract

The invention provides a method for eliminating Q235B transverse crease defects. The method comprises the following steps: (1) controlling chemical components; (2) plate shape control is conducted, specifically, the straightness long-term coefficient is controlled to be-10 IU to-40 IU, and the roll bending force of a finish rolling equipment rack is increased to 20-40 tons; (3) adjusting the upper and lower water spraying proportions of laminar cooling: determining the water spraying mode and the upper and lower water spraying proportions of laminar cooling according to carbon structural steel Q235B of different specifications, and controlling the side spraying pressure of a curling area to be 11-13MPa when no steel exists; (4) adjusting process temperature control on line; (5) coiling temperature control adopts two temperature systems of winter and summer; and (6) judging whether the steel plate possibly generates a transverse crease defect or not through a transverse crease pre-alarm system, and if the transverse crease defect is possibly generated, enabling the steel plate to enter a flattening processing stage. According to the technical scheme, the product quality of the hot-rolled common carbon structural steel can be improved, and the quality objection caused by transverse crease defects after the hot-rolled commercial coil is uncoiled is eliminated.

Description

Technical Field

[0001] The invention relates to the technical field of hot-rolled coil production, and in particular to a method for eliminating transverse fold defects of Q235B. Background Art

[0002] Q235B transverse crease refers to the strip crease perpendicular to the rolling direction that appears at a certain part of the coil during the uncoiling process of hot-rolled and cold-rolled coils. In severe cases, it runs through the entire width of the plate and feels concave and convex when touched by hand. The spacing between the creases is not fixed. After straightening, the creases become dense, which seriously affects the use of the steel plate.

[0003] The hot rolling mill has a very large production capacity for carbon structural steel Q235B, accounting for more than 31%. The main quality defects of this type of steel are through-coiling or local transverse crease defects, which cannot be found during the production process and are visually obvious after the user unrolls the coil. For processed structural parts with strict surface requirements, they cannot meet the use requirements. This defect is also the main source of quality objections in the hot rolling mill. The specifications are mainly concentrated in 2.75-4.75mm. Summary of the invention

[0004] In order to eliminate the transverse fold defect of Q235B, the present invention provides a method for eliminating the transverse fold defect of Q235B, which can improve the product quality of hot-rolled ordinary carbon structural steel and eliminate the quality objection caused by the transverse fold defect found after the hot-rolled commercial coil is unrolled.

[0005] The technical means adopted by the present invention are as follows:

[0006] A method for eliminating Q235B transverse crease defects. The production process of carbon structural steel Q235B includes: molten iron pretreatment → converter smelting → refining outside the furnace → continuous casting → heating → hot rolling → laminar cooling → curling → sampling → inspection → packaging and delivery. The method for eliminating Q235B transverse crease defects specifically includes the following contents:

[0007] (1) Chemical composition control during the production of carbon structural steel Q235B

[0008] (2) Plate shape control

[0009] In the finishing stage of the hot rolling step, the long-term coefficient of flatness is controlled to -10 to -40 IU by the plate shape control system, and the bending roll force of the finishing rolling equipment frame is increased to 20 to 40 tons;

[0010] (3) Adjust the upper and lower water spray ratio of laminar cooling

[0011] For different specifications of carbon structural steel Q235B, the water spraying method and the upper and lower water spraying ratio of laminar cooling are determined according to the following table:

[0012]

[0013] And control the side spray pressure in the curling area to 11-13MPa when there is no steel;

[0014] (4) Online adjustment of process temperature control

[0015] In the hot rolling step, the process temperature control system is adjusted online to adjust the final rolling temperature and coiling temperature online according to the chemical composition content of the slab;

[0016] (5) The coiling temperature control of Q235B steel with specifications of 3.5 mm and below adopts two temperature systems: winter and summer;

[0017] (6) Through the transverse crease early warning system, it is determined whether the steel plate is likely to have a transverse crease defect based on the usage unit, thickness specification, composition and actual convexity of the produced steel plate, as well as the finishing rolling exit speed and cooling rate during the production process. If a transverse crease defect is likely to occur, the steel plate will enter the flattening processing stage.

[0018] Furthermore, (1) chemical composition control includes:

[0019] In terms of mass percentage, the standard composition range is: C≤0.20, Si≤0.35, Mn≤1.40, P≤0.045, S≤0.045;

[0020] In terms of mass percentage, the internal control composition range is: C: 0.15-0.17, Si: 0.12-0.18, Mn: 0.20-0.40, P≤0.025, S≤0.015;

[0021] Furthermore, in terms of mass percentage, the target component contents are: C: 0.16, Si: 0.15, Mn: 0.25, P≤0.020, S≤0.010.

[0022] Furthermore, the laminar cooling step is provided with 2-7 groups of pre-spraying water nozzles, thereby shortening the cooling section and improving the cooling efficiency.

[0023] Furthermore, the coiling temperature is controlled at 630°C in winter and 600°C in summer.

[0024] Furthermore, the specific process of the transverse crease early warning system determining whether the steel plate may have a transverse crease defect includes:

[0025] (1) According to the preset assignment standard, the use unit, thickness specification, composition, actual crown, finishing exit speed and cooling rate data of the steel plate are assigned values ​​respectively, and the assignment results are a1, a2, a3, a4, a5, and a6;

[0026] (2) According to the preset score proportions b1, b2, b3, b4, b5, b6 corresponding to the usage unit, thickness specification, composition, actual crown, finishing exit speed and cooling rate, the scores A1, A2, A3, A4, A5, A6 corresponding to the usage unit, thickness specification, composition, actual crown, finishing exit speed and cooling rate are calculated respectively;

[0027] (3) Calculate the sum A of A1, A2, A3, A4, A5, and A6. Assume that the full score is B. The judgment results are shown in the following table:

[0028]

[0029] When the transverse crease pre-alarm system determines the result as an alarm, it means that the steel plate may have a transverse crease defect, and the steel plate needs to enter the flattening processing stage before leaving the factory.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] The method for eliminating the transverse fold defect of Q235B provided by the present invention can improve the product quality of hot-rolled ordinary carbon structural steel, eliminate the quality objection caused by the transverse fold defect found after the hot-rolled commercial coil is unrolled, and reduce economic losses. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0033] Figure 1 This is the hot rolling production process flow chart.

[0034] Figure 2 It is the actual curve of bending roll force adjustment during plate shape control. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] The present invention provides a method for eliminating the transverse fold defect of Q235B. The production process of carbon structural steel Q235B includes: molten iron pretreatment (DS) → converter smelting (LD) → refining outside the furnace (LF) → continuous casting (CC) → heating → hot rolling → laminar cooling → curling → sampling → inspection → packaging and delivery. The hot rolling production process is as follows: Figure 1 As shown: HF1-HF3: three heating furnaces; HSB: dephosphorization for rough rolling; R1D: dephosphorization before R1; R2D: dephosphorization before R2; E1, E2: vertical rollers before rough rolling; RT: pyrometer before rough rolling; R1, R2: two rolling mills for rough rolling; CB: hot coil box; CS: flying shear; FET: pyrometer at the entrance of finishing rolling; FSB: dephosphorization for finishing rolling; F1E: vertical rollers before finishing rolling; F1-F7: 7 rolling mills for finishing rolling; FDT: pyrometer at the exit of finishing rolling; LCS: laminar cooling mechanism; CT: pyrometer before coiling; DC1-DC3: three down coiling machines for taking out;

[0037] The method for eliminating the transverse crease defect of Q235B specifically includes the following contents:

[0038] (1) Chemical composition control during the production of carbon structural steel Q235B

[0039] (2) Plate shape control

[0040] In the finishing stage of the hot rolling step, the long-term coefficient of flatness is controlled by the plate shape control system to be -10 to -40 IU (preferably, the long-term coefficient of flatness is -30 IU), so as to ensure that the plate shape of the hot rolled plate out of the finishing rolling is in the middle wave trend, such as Figure 2 As shown, the bending roll force of the finishing rolling equipment frame is increased to 20-40 tons; the present invention can effectively reduce the transverse folding defect by controlling the plate shape in the finishing rolling stage;

[0041] (3) Adjust the upper and lower water spray ratio of laminar cooling

[0042] For different specifications of carbon structural steel Q235B, the water spraying method and the upper and lower water spraying ratio of laminar cooling are determined according to the following table:

[0043]

[0044] and controlling the side spray pressure of the curling area to be 11-13 MPa when there is no steel, preferably 12 MPa;

[0045] The present invention can reduce the yield strength difference between the upper and lower surfaces of the plate strip by optimizing the upper and lower water spraying ratios of laminar cooling, thereby improving the unwinding arch defect, and at the same time increasing the side spraying pressure, which can reduce the buckling phenomenon caused by water and the occurrence of transverse folding defects;

[0046] (4) Online adjustment of process temperature control

[0047] In the hot rolling step, the process temperature control system is adjusted online, and the final rolling temperature and coiling temperature are adjusted online according to the chemical composition content of the slab to avoid defects; low final rolling temperature control causes a low yield platform, which has a certain impact on the horizontal folding. Reasonable control of the furnace temperature, refusing to roll low-temperature steel, provides a guarantee for final rolling temperature control;

[0048] The online process temperature control system adopts the control method for online adjustment of the target temperature of hot-rolled strip provided by patent CN202310966630.3, which can obtain the corresponding mechanical property change range according to the chemical composition content of the slab through comprehensive simulation and measurement. For slabs in the unsatisfactory performance prediction range, the hot rolling unit takes corresponding final rolling temperature and coiling temperature setting compensation measures to achieve the ideal performance requirements, realizing full-automatic online automatic identification and temperature regulation without manual intervention setting and parameter control, avoiding the instability of mechanical properties of some slabs due to chemical composition fluctuations; the control method for online adjustment of the target temperature of hot-rolled strip is adopted, and the specific adjustment of the final rolling temperature and coiling temperature according to the component content of Q235B is shown in the following table:

[0049]

[0050]

[0051] The main chemical components adopted include: carbon, silicon, and manganese. According to the empirical values, the performance impact ratios are 55%, 20%, and 25% respectively. At the same time, each component is divided into four intervals, and the corresponding values ​​are 20, 40, 60, and 70 respectively, that is, the actual chemical composition falls into which interval to take the corresponding value; the sum of the impact ratio of each component * the corresponding value is used to obtain the specific impact value; six different data ranges are divided, corresponding to the final rolling and coiling temperature adjustment temperature values; in which interval the impact value falls, the corresponding temperature control value is increased or decreased based on the target value; for example:

[0052]

[0053] 0.55*40+0.2*60+0.25*40=44, in the fifth interval, the corresponding coiling temperature increases by 20°C and the final rolling temperature increases by 20°C;

[0054] (5) The coiling temperature control of Q235B steel with specifications of 3.5 mm and below adopts two temperature systems: winter and summer;

[0055] (6) Through the transverse crease early warning system, it is determined whether the steel plate is likely to have a transverse crease defect based on the unit of use, thickness specification, composition and actual convexity of the produced steel plate, as well as the finishing rolling exit speed and cooling rate during the production process. If a transverse crease defect is likely to occur, the steel plate is put into the flattening processing stage to prevent the occurrence of transverse crease defects and cause objections.

[0056] Furthermore, (1) chemical composition control includes:

[0057] In terms of mass percentage, the standard composition range is: C≤0.20, Si≤0.35, Mn≤1.40, P≤0.045, S≤0.045;

[0058] In terms of mass percentage, the internal control composition range is: C: 0.15-0.17, Si: 0.12-0.18, Mn: 0.20-0.40, P≤0.025, S≤0.015;

[0059] Preferably, in terms of mass percentage, the target component content, i.e., the optimal controlled ratio, is: C: 0.16, Si: 0.15, Mn: 0.25, P≤0.020, S≤0.010.

[0060] Furthermore, the laminar cooling step is provided with 2-7 groups of pre-spraying water nozzles, thereby shortening the cooling section and improving the cooling efficiency.

[0061] Furthermore, the coiling temperature is controlled at 630°C in winter and 600°C in summer.

[0062] Furthermore, the specific process of the transverse crease early warning system determining whether the steel plate may have a transverse crease defect includes:

[0063] (1) According to the preset assignment standard, the use unit, thickness specification, composition, actual crown, finishing exit speed and cooling rate data of the steel plate are assigned values ​​respectively, and the assignment results are a1, a2, a3, a4, a5, and a6;

[0064] (2) According to the preset score proportions b1, b2, b3, b4, b5, b6 corresponding to the usage unit, thickness specification, composition, actual crown, finishing exit speed and cooling rate, the scores A1, A2, A3, A4, A5, A6 corresponding to the usage unit, thickness specification, composition, actual crown, finishing exit speed and cooling rate are calculated respectively;

[0065] (3) Calculate the sum A of A1, A2, A3, A4, A5, and A6. Assume that the full score is B. The judgment results are shown in the following table:

[0066]

[0067] When the transverse crease pre-alarm system determines the result as an alarm, it means that the steel plate may have a transverse crease defect, and the steel plate needs to enter the flattening processing stage before leaving the factory.

[0068] Furthermore, in this embodiment, the value assignment standards of thickness specification, actual convexity, finishing rolling exit speed and cooling rate are respectively shown in the following table:

[0069] Thickness specification mm Assignment ＜3.0 20 5.1-7.0 20 4.1-5.0 40 3.0-4.0 60

[0070]

[0071]

[0072] Finishing rolling exit speed m / s Assignment ＞8.0 20 7.0-8.0 40 ＜7.0 60

[0073] Cooling rate℃ / s Assignment ＞60 10 50-60 20 41-50 40 30-40 60 ＜30 70

[0074] The value assigned to the component is the sum of the values ​​assigned to the three components of C, Si, and Mn. The value assignment standards for C, Si, and Mn are shown in the following table:

[0075]

[0076] When assigning values ​​to the units of use, higher values ​​are assigned to manufacturers that often raise objections. The following table gives examples of assigning values ​​to the units of use:

[0077] Use Unit Assignment SUMEC International Technology Trading Co., Ltd. 20 Shenyang Zhongbing Logistics Co., Ltd. (on behalf of Haoxing) 40 Liaoning Shengshuo Industrial Co., Ltd. 40 Benxi Heli 60 Tianjin Binhai Yiyou Trading Co., Ltd. 60 Xiamen JiJin Supply Chain Co., Ltd. 70

[0078] In this embodiment, the scoring proportions corresponding to the unit of use, thickness specification, composition, actual convexity, finishing exit speed and cooling rate are 25, 10, 25, 15, 10, and 15, respectively.

[0079] By adopting the method for eliminating the transverse crease defect of Q235B provided by the present invention, a series of measures are taken to control the chemical composition, plate shape, upper and lower water spray ratios of laminar cooling, process temperature, and coiling temperature, as well as to determine whether the steel plate needs to enter flattening processing through a transverse crease early warning system, so that the transverse crease defect on the plate surface after uncoiling is well improved.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for eliminating the transverse crease defect of Q235B. The production process of carbon structural steel Q235B includes: Hot metal pretreatment → converter smelting → refining outside the furnace → continuous casting → heating → hot rolling → laminar cooling → curling → sampling → inspection → packaging and shipment, characterized in that the method for eliminating the transverse crease defect of Q235B specifically includes the following contents: (1) Chemical composition control during the production of carbon structural steel Q235B (2) Plate shape control In the finishing stage of the hot rolling step, the long-term coefficient of flatness is controlled to -10 to -40 IU by the plate shape control system, and the bending roll force of the finishing rolling equipment frame is increased to 20 to 40 tons; (3) Adjust the upper and lower water spray ratio of laminar cooling For different specifications of carbon structural steel Q235B, the water spraying method and the upper and lower water spraying ratio of laminar cooling are determined according to the following table: And control the side spray pressure in the curling area to 11-13MPa when there is no steel; (4) Online adjustment of process temperature control In the hot rolling step, the process temperature control system is adjusted online to adjust the final rolling temperature and coiling temperature online according to the chemical composition content of the slab; (5) The coiling temperature control adopts two temperature systems: winter and summer; (6) Through the transverse crease early warning system, it is determined whether the steel plate is likely to have a transverse crease defect based on the usage unit, thickness specification, composition and actual convexity of the produced steel plate, as well as the finishing rolling exit speed and cooling rate during the production process. If a transverse crease defect is likely to occur, the steel plate will enter the flattening processing stage.

2. The method for eliminating the transverse crease defect of Q235B according to claim 1, characterized in that: (1) Chemical composition control includes: In terms of mass percentage, the standard composition range is: C≤0.20, Si≤0.35, Mn≤1.40, P≤0.045, S≤0.045; In terms of mass percentage, the internal controlled component range is: C: 0.15~0.17, Si: 0.12~0.18, Mn: 0.20~0.40, P≤0.025, S≤0.

015.

3. The method for eliminating the transverse crease defect of Q235B according to claim 2, characterized in that: In terms of mass percentage, the target component contents are: C: 0.16, Si: 0.15, Mn: 0.25, P≤0.020, S≤0.

010.

4. The method for eliminating the transverse crease defect of Q235B according to claim 1, characterized in that: The laminar cooling step is provided with 2-7 groups of pre-spraying water nozzles, thereby shortening the cooling section and improving the cooling efficiency.

5. The method for eliminating the transverse crease defect of Q235B according to claim 1, characterized in that: The coiling temperature is controlled at 630℃ in winter and 600℃ in summer.

6. The method for eliminating the transverse crease defect of Q235B according to claim 1, characterized in that: The specific process of the transverse crease early warning system to determine whether the steel plate may have transverse crease defects includes: (1) According to the preset assignment standard, the use unit, thickness specification, composition, actual crown, finishing exit speed and cooling rate data of the steel plate are assigned values ​​respectively, and the assignment results are a1, a2, a3, a4, a5, and a6; (2) According to the preset score proportions b1, b2, b3, b4, b5, b6 corresponding to the usage unit, thickness specification, composition, actual crown, finishing exit speed and cooling rate, the scores A1, A2, A3, A4, A5, A6 corresponding to the usage unit, thickness specification, composition, actual crown, finishing exit speed and cooling rate are calculated respectively; (3) Calculate the sum A of A1, A2, A3, A4, A5, and A6. Assume that the full score is B. The judgment results are shown in the following table: When the transverse crease pre-alarm system determines the result as an alarm, it means that the steel plate may have a transverse crease defect, and the steel plate needs to enter the flattening processing stage before leaving the factory.

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