A method for improving transverse temperature uniformity and suppressing residual stress in hot-rolled strip steel

Abstract

This invention relates to a method for improving transverse temperature uniformity and suppressing residual stress in hot-rolled strip steel, belonging to the field of hot-rolled strip shape control technology in the metallurgical industry. The technical solution is as follows: During the post-rolling cooling stage of hot-rolled strip steel, the cooling in the strip width direction is divided into three zones: the middle of the strip steel is the normal cooling zone, the edge of the strip steel is the zone sensitive to strip temperature and residual stress, and the outer side of the strip steel is the unsprayed zone. The ultra-fast cooling manifold cooling nozzles in the normal cooling zone in the middle of the strip steel and the outer side of the strip steel are perpendicular to the strip surface. The ultra-fast cooling manifold cooling nozzles in the edge zone sensitive to strip temperature and residual stress are deflected towards the center of the strip steel at a certain angle α. The formula for calculating the number of nozzles is: [Formula omitted]. The beneficial effects of this invention are: it improves the transverse temperature uniformity of the strip steel, which is lower at the edges and higher in the middle, reduces the timing difference in the strip entering the phase transformation process, enhances the uniformity of the microstructure, and thus reduces the residual stress in the hot-rolled strip steel.

Description

Technical Field

[0001] This invention relates to a method for improving transverse temperature uniformity and suppressing residual stress in hot-rolled strip steel, belonging to the field of hot-rolled strip shape control technology in the metallurgical industry. Background Technology

[0002] During the post-rolling cooling process of hot-rolled strip steel, uneven transverse temperature distribution can lead to different cooling rates in different areas, resulting in residual stress. The presence of residual stress not only affects the strip's shape quality, causing flatness defects and other problems, but may also trigger a series of performance instabilities during subsequent processing and use.

[0003] See attached document Figure 1 , 2 The cooling nozzles in the ultra-fast cooling manifold are all non-adjustable nozzles, evenly arranged along the width of the strip, and the spray direction is perpendicular to the strip. During the cooling stage, the strip inherently exhibits the phenomenon of "overcooling at the edges and overheating in the middle," the root cause of which is:

[0004] (1) Two-dimensional heat dissipation (thickness + width direction) at the edge of the strip, the cooling rate is about 1.3-1.5 times that of the middle part;

[0005] (2) After the jet impacts the middle of the strip, the cooling water flows laterally along the width direction, further enhancing the heat exchange at the edge.

[0006] (3) The difference in latent heat of phase transformation leads to different timing of microstructure transformation, resulting in macroscopic residual stress between tensile and compressive phases.

[0007] The above-mentioned coupling effect has strong nonlinear and transient characteristics, and it changes dynamically with multiple variables such as steel grade, width, thickness, final rolling temperature, and water pressure.

[0008] To address the aforementioned phenomenon of "overcooling at the edges and overheating in the middle" in strip steel, the following three methods are typically employed: First, a "flow reduction at the edges" scheme using fixed nozzles and segmented water flow is employed. However, this cannot solve the problem of lateral water flow migration, with actual field measurements showing that the edge temperature drop is only reduced by 3–5℃, and the residual stress is only improved by ≤10MPa. Second, baffles are inserted between the ultra-fast cooling manifolds to change the cooling water flow and direction. This mechanical structure is complex and prone to jamming steel, resulting in high maintenance costs. Third, edge shielding is used. This method is only suitable for laminar flow cooling equipment, and its application in ultra-fast cooling equipment is limited. Furthermore, relying solely on edge shielding to improve edge temperature drop is insufficient. Summary of the Invention

[0009] The purpose of this invention is to provide a method for improving the transverse temperature uniformity of hot-rolled strip steel and suppressing residual stress, thereby improving the transverse temperature non-uniformity of the strip steel with lower edge temperature and higher center temperature, reducing the timing difference of the strip entering the phase transformation process, enhancing the uniformity of the microstructure, and thus reducing the residual stress of hot-rolled strip steel, solving the problems existing in the background art.

[0010] The technical solution of this invention is:

[0011] A method for improving transverse temperature uniformity and suppressing residual stress in hot-rolled strip steel involves dividing the cooling process in the strip width direction into three zones during the post-rolling cooling stage: the middle section of the strip is the normal cooling zone, the edge section is the zone sensitive to temperature and residual stress, and the outer section is the unsprayed zone. The ultra-fast cooling manifold nozzles in the middle section and the outer section are perpendicular to the strip surface, while the ultra-fast cooling manifold nozzles in the edge section are deflected towards the center of the strip at a certain angle α.

[0012] The formula for calculating the number of cooling nozzles in the ultrafast cooling manifold assembly in the strip edge temperature and residual stress sensitive influence zone is as follows:

[0013]

[0014] In the formula, m is the number of nozzles on one side of the strip, rounded up;

[0015] n represents the number of cooling nozzles in the ultra-fast cooling manifold assembly along the width of the strip.

[0016] L t The length of the strip's temperature and residual stress-sensitive region is in mm.

[0017] L b The length of the outer side of the strip that was not sprayed, in mm;

[0018] L n The length of the normal cooling zone in the middle of the strip, in mm;

[0019] The length of the strip temperature and residual stress sensitive influence zone was obtained through simulation experiments.

[0020] The strip steel W=L n +L t ·2 mm; Ultra-fast cooling manifold width L all =(L b +L t )·2+L n , mm.

[0021] The ultra-fast cooling manifold cooling nozzles in the strip edge temperature and residual stress sensitive influence zone are deflected towards the strip center at an angle α of 5°–20°.

[0022] The water flow rate of the cooling nozzles in the ultra-fast cooling manifold is determined based on the thickness of the strip steel.

[0023] The beneficial effects of this invention are as follows: By changing the angle of the water jet from the edge nozzles, the water jet is directed towards the edge, reducing the amount of water sprayed at the edge of the strip. At the same time, it weakens the phenomenon that the water jet from the middle to the edge flows after hitting the upper surface of the strip, which would otherwise enhance the cooling of the strip edge. This makes the water jet stagnate more strongly in the middle of the strip, ultimately weakening the cooling effect at the edge of the strip while enhancing the cooling effect in the middle. This improves the uneven transverse temperature of the strip, which is lower at the edge and higher in the middle, reduces the timing difference in the phase transformation process of the strip, further enhances the uniformity of the microstructure, and thus reduces the residual stress of the hot-rolled strip and improves the shape of the hot-rolled strip. Attached Figure Description

[0024] Figure 1 Three-view diagram of the ultrafast cooling nozzle for background technology;

[0025] Figure 2 This is a schematic diagram of the ultrafast cooling nozzle arrangement in the background technology.

[0026] Figure 3 These are three views of the ultrafast cooling nozzle of the present invention;

[0027] Figure 4 This is a schematic diagram of the ultrafast cooling nozzle arrangement of the present invention;

[0028] Figure 5 This is a diagram of the low-temperature region during the strip cooling process after rolling in this invention.

[0029] Figure 6 This is a diagram showing the residual stress influence area during the strip cooling process after rolling in this invention.

[0030] Figure 7 This is a schematic diagram illustrating the calculation method for the change in the number of edge nozzles in this invention;

[0031] Figure 8 This is a geometric schematic diagram of the nozzle angle scheme of the present invention;

[0032] Figure 9 The simulation results for different nozzle angle schemes of the present invention are shown in the figure. Detailed Implementation

[0033] The invention will be further described below with reference to the accompanying drawings and examples.

[0034] See attached document Figure 1-9A method for improving transverse temperature uniformity and suppressing residual stress in hot-rolled strip steel is proposed. During the post-rolling cooling stage, the cooling of the strip steel in the width direction is divided into three zones: the middle of the strip steel is the normal cooling zone, the edge of the strip steel is the zone sensitive to temperature and residual stress, and the outer side of the strip steel is the unsprayed zone. The ultra-fast cooling manifold cooling nozzles in the normal cooling zone in the middle of the strip steel and the outer side of the strip steel are perpendicular to the strip steel surface, while the ultra-fast cooling manifold cooling nozzles in the edge of the strip steel, which is sensitive to temperature and residual stress, are deflected towards the center of the strip steel by a certain angle α.

[0035] The formula for calculating the number of cooling nozzles in the ultrafast cooling manifold assembly in the strip edge temperature and residual stress sensitive influence zone is as follows:

[0036]

[0037] In the formula, m is the number of nozzles on one side of the strip, rounded up;

[0038] n represents the number of cooling nozzles in the ultra-fast cooling manifold assembly along the width of the strip.

[0039] L t The length of the strip's temperature and residual stress-sensitive region is in mm.

[0040] L b The length of the outer side of the strip that was not sprayed, in mm;

[0041] L n The length of the normal cooling zone in the middle of the strip, in mm;

[0042] The length of the strip temperature and residual stress sensitive influence zone was obtained through simulation experiments.

[0043] The strip steel W=L n +L t ·2 mm; Ultra-fast cooling manifold width L all =(L b +L t )·2+L n , mm.

[0044] The ultra-fast cooling manifold cooling nozzles in the strip edge temperature and residual stress sensitive influence zone are deflected towards the strip center at an angle α of 5°–20°.

[0045] The water flow rate of the cooling nozzles in the ultra-fast cooling manifold is determined based on the thickness of the strip steel.

[0046] Example 1:

[0047] The purpose of this embodiment is to illustrate the specific application of the present invention in 1540*4.65 specification strip steel, and to verify the effectiveness of the present invention in increasing the edge temperature of the strip steel, improving temperature uniformity, and reducing residual stress during the post-rolling cooling process. The specific steps include:

[0048] 1. The nozzles of the ultra-fast cooling equipment have been changed from nozzles with non-adjustable spray angles to nozzles with adjustable spray angles;

[0049] 2. Adjust the side nozzles from their original angle perpendicular to the horizontal direction to be angled towards the center of the nozzle group that performs the cooling function, thereby changing the angle of the water jet, as shown in the attached diagram. Figure 4 As shown;

[0050] 3. By combining simulation, experimentation, or other methods with the parameters of the ultra-fast cooling equipment and the strip specifications, determine the appropriate nozzle spray angle and even the number of edge nozzles involved, thereby improving the transverse temperature uniformity and residual stress of the hot-rolled strip. Specific details are as follows:

[0051] 1) A coupled model of the temperature field, phase transformation field, and stress field during the post-rolling cooling process of hot-rolled strip was established using simulation. The low-temperature region and residual stress influence region during the post-rolling cooling process were calculated. Simulation results showed that for a 1540×4.65mm strip, the low-temperature region... Figure 5 As shown, the area occupying approximately 100mm of the edge has a higher residual stress, as shown in the figure. Figure 6 As shown, the edge area occupies 150mm. Here, 150mm is taken as the basis for subsequent judgment on the number of edge nozzles involved, that is, the strip temperature and residual stress sensitive influence area L. t =150mm;

[0052] 2) Based on the parameters of the ultra-fast cooling equipment and the specifications of the strip steel, determine the number of edge nozzles involved. The calculation formula is as follows, and the corresponding schematic diagram is shown below. Figure 7 As shown.

[0053]

[0054] In the formula, m is the number of nozzles on one side, rounded up; n is the number of cooling nozzles in the ultra-fast cooling manifold assembly at the same width; L t This refers to the area sensitive to temperature and residual stress in the strip, measured in mm and L. b The area on the outer side of the strip that was not sprayed, mm; L n This is the normal cooling area, in mm;

[0055] Where W = L n +L t ·2, W is the strip width, mm; L all =(L b +Lt )·2+L n L all The width of the ultra-fast cooling manifold is in mm.

[0056] In this embodiment, W = 1540 mm, L all =2050mm, n=50, then L n =1240mm, L b =255mm, m=4, the final number of edge nozzles involving one side was determined to be 4, and the nozzles involved were located at Figure 7 The area shown is sensitive to temperature and residual stress in the strip.

[0057] 3) Determine the water pressure based on the strip thickness specifications. When the thickness is greater than or equal to 2mm and less than 5mm, the water pressure is 0.85MPa; when the thickness is greater than 5mm, the water pressure is 1.05MPa. Therefore, the water pressure is set at 0.85MPa.

[0058] 4) Design different nozzle angles. In this embodiment, the nozzle angle schemes include 0°, 5°, 10°, 15°, and 20°, such as... Figure 8 As shown, a suitable scheme is then selected based on the simulation results, as shown in the simulation results. Figure 9 As shown, a comparative analysis can be conducted from two perspectives: the temperature of the strip edge during coiling and the residual stress at room temperature.

[0059] Among the five options above, it can be found that 15° has the best effect on increasing the temperature of the strip edge, improving temperature uniformity and reducing residual stress. Therefore, the appropriate nozzle (jet water flow) angle under this working condition is determined to be 15°.

[0060] The application effect of the present invention has been verified. Compared with the application of the present invention, the temperature of the strip edge during winding is increased by about 51°C, the temperature uniformity is improved by about 46%, and the residual stress at room temperature is reduced by about 91 MPa, a percentage reduction of 36.2%.

[0061] Example 2:

[0062] The purpose of this embodiment is to illustrate the specific application of the present invention in 1000*3.0 specification strip steel.

[0063] Simulation results revealed that the temperature and residual stress sensitive influence area L of the 1000×3.0mm strip was... t =120mm;

[0064] In this embodiment, W = 1000 mm, L all =2050mm, n=50, then L n =760mm, L b=525mm, m=3, and the final number of edge nozzles involving one side was determined to be 3;

[0065] The water pressure is determined based on the thickness of the strip steel. When the thickness is greater than or equal to 2 mm and less than 5 mm, the water pressure is 0.85 MPa. When the thickness is greater than 5 mm, the water pressure is 1.05 MPa. Therefore, the water pressure is determined to be 0.85 MPa.

[0066] Different nozzle angle schemes were designed, and a suitable scheme was selected based on the simulation results. Finally, the nozzle angle scheme was determined to be 5°.

[0067] The rest is the same as in Example 1.

[0068] Example 3:

[0069] The purpose of this embodiment is to illustrate the specific application of the present invention in 1000*5.0 specification strip steel.

[0070] Simulation results revealed that the temperature and residual stress sensitive influence area L of the 1000×5.0mm strip was... t =120mm;

[0071] In this embodiment, W = 1000 mm, L all =2050mm, n=50, then L n =760mm, L b =525mm, m=3, the final determination of the number of edge nozzles involving one side is 3, and the nozzles involved are located at Figure 8 The area shown is sensitive to temperature and residual stress in the strip.

[0072] The water pressure is determined based on the thickness of the strip steel. When the thickness is greater than or equal to 2 mm and less than 5 mm, the water pressure is 0.85 MPa. When the thickness is greater than 5 mm, the water pressure is 1.05 MPa. Therefore, the water pressure is set at 1.05 MPa.

[0073] Different nozzle angle schemes were designed, and a suitable scheme was selected based on the simulation results. Finally, the nozzle angle scheme was determined to be 5°.

[0074] The rest is the same as in Example 1.

[0075] Example 4:

[0076] The purpose of this embodiment is to illustrate the specific application of the present invention in 1200*3.0 specification strip steel.

[0077] Simulation results revealed that the temperature and residual stress sensitive influence area L of the 1200×3.0mm strip was... t =130mm;

[0078] In this embodiment, W = 1200 mm, L all=2050mm, n=50, then L n =940mm, L b =425mm, m=4, and the final number of edge nozzles involving one side was determined to be 4;

[0079] The water pressure is determined based on the thickness of the strip steel. When the thickness is greater than or equal to 2 mm and less than 5 mm, the water pressure is 0.85 MPa. When the thickness is greater than 5 mm, the water pressure is 1.05 MPa. Therefore, the water pressure is determined to be 0.85 MPa.

[0080] Different nozzle angle schemes were designed, and a suitable scheme was selected based on the simulation results. The four nozzles on one side were numbered 1, 2, 3, and 4 from the furthest point to the horizontal center. The other side was treated symmetrically. The most suitable scheme was determined to be 5° for nozzle 1, 10° for nozzles 2 and 3, and 15° for nozzles 4 and 5.

[0081] The rest is the same as in Example 1.

[0082] Example 5:

[0083] The purpose of this embodiment is to illustrate the specific application of the present invention in 1200*5.0 specification strip steel.

[0084] Simulation results revealed that the temperature and residual stress sensitive influence area L of the 1200×5.0mm strip was... t =130mm;

[0085] In this embodiment, W = 1200 mm, L all =2050mm, n=50, then L n =940mm, L b =425mm, m=4, and the final number of edge nozzles involving one side was determined to be 4.

[0086] The water pressure is determined based on the thickness of the strip steel. When the thickness is greater than or equal to 2 mm and less than 5 mm, the water pressure is 0.85 MPa. When the thickness is greater than 5 mm, the water pressure is 1.05 MPa. Therefore, the water pressure is set at 1.05 MPa.

[0087] Different nozzle angle schemes were designed, and a suitable scheme was selected based on the simulation results. The four nozzles on one side were numbered 1, 2, 3, and 4 from the furthest point to the horizontal center. The other side was treated symmetrically. The most suitable scheme was determined to be 5° for nozzle 1, 10° for nozzles 2 and 3, and 15° for nozzles 4 and 5.

[0088] Example 6:

[0089] The purpose of this embodiment is to illustrate the specific application of the present invention in 1400*3.0 specification strip steel.

[0090] Simulation results revealed that the temperature and residual stress sensitive influence area L of the 1400×3.0mm strip was... t =140mm;

[0091] In this embodiment, W = 1400 mm, L all =2050mm, n=50, then L n =1120mm, L b =325mm, m=4, and the final number of edge nozzles involving one side was determined to be 4.

[0092] The water pressure is determined based on the thickness of the strip steel. When the thickness is greater than or equal to 2 mm and less than 5 mm, the water pressure is 0.85 MPa. When the thickness is greater than 5 mm, the water pressure is 1.05 MPa. Therefore, the water pressure is determined to be 0.85 MPa.

[0093] Different nozzle angle schemes were designed, and a suitable scheme was selected based on the simulation results. The four nozzles on one side were numbered 1, 2, 3, and 4 from the furthest point to the horizontal center. The other side was treated symmetrically. The scheme was determined to be 10° for nozzle 1 and 15° for nozzles 2, 3, 4, and 5.

[0094] The rest is the same as in Example 1.

[0095] Example 7:

[0096] The purpose of this embodiment is to illustrate the specific application of the present invention in 1400*5.0 specification strip steel.

[0097] Simulation results revealed that the temperature and residual stress sensitive influence area L of the 1400×5.0mm strip was... t =140mm;

[0098] In this embodiment, W = 1400 mm, L all =2050mm, n=50, then L n =1120mm, L b =325mm, m=4, the final number of edge nozzles involving one side was determined to be 4, and the nozzles involved were located at Figure 8 The area shown is sensitive to temperature and residual stress in the strip.

[0099] The water pressure is determined based on the thickness of the strip steel. When the thickness is greater than or equal to 2 mm and less than 5 mm, the water pressure is 0.85 MPa. When the thickness is greater than 5 mm, the water pressure is 1.05 MPa. Therefore, the water pressure is set at 1.05 MPa.

[0100] Different nozzle angle schemes were designed, and a suitable scheme was selected based on the simulation results. The four nozzles on one side were numbered 1, 2, 3, and 4 from the furthest point to the horizontal center. The other side was treated symmetrically. The scheme was determined to be 10° for nozzle 1 and 15° for nozzles 2, 3, 4, and 5.

[0101] The rest is the same as in Example 1.

[0102] Example 8:

[0103] The purpose of this embodiment is to illustrate the specific application of the present invention in 1600*3.0 specification strip steel.

[0104] Simulation results revealed that the temperature and residual stress sensitive influence area L of the 1600×3.0mm strip was... t =180mm;

[0105] In this embodiment, W = 1600 mm, L all =2050mm, n=50, then L n =1240mm, L b =225mm, m=5, the final number of edge nozzles involving one side was determined to be 5, and the nozzles involved were located at Figure 8 The area shown is sensitive to temperature and residual stress in the strip.

[0106] The water pressure is determined based on the thickness of the strip steel. When the thickness is greater than or equal to 2 mm and less than 5 mm, the water pressure is 0.85 MPa. When the thickness is greater than 5 mm, the water pressure is 1.05 MPa. Therefore, the water pressure is determined to be 0.85 MPa.

[0107] Different nozzle angle schemes were designed, and a suitable scheme was selected based on the simulation results. The five nozzles on one side were numbered 1, 2, 3, 4 and 5 from the farthest to the horizontal center. The other side was treated symmetrically. The scheme was determined to be that nozzles 1, 2, 3 and 4 were 15° and nozzle 5 was 20°.

[0108] The rest is the same as in Example 1.

[0109] Example 9:

[0110] The purpose of this embodiment is to illustrate the specific application of the present invention in 1600*5.0 specification strip steel.

[0111] Simulation results revealed that the temperature and residual stress sensitive influence area L of the 1600×5.0mm strip was... t =200mm;

[0112] In this embodiment, W = 1600 mm, L all =2050mm, n=50, then L n=1240mm, L b =225mm, m=5, the final number of edge nozzles involving one side was determined to be 5, and the nozzles involved were located at Figure 8 The area shown is sensitive to temperature and residual stress in the strip.

[0113] The water pressure is determined based on the thickness of the strip steel. When the thickness is greater than or equal to 2 mm and less than 5 mm, the water pressure is 0.85 MPa. When the thickness is greater than 5 mm, the water pressure is 1.05 MPa. Therefore, the water pressure is set at 1.05 MPa.

[0114] Different nozzle angle schemes were designed, and a suitable scheme was selected based on the simulation results. The five nozzles on one side were numbered 1, 2, 3, 4, and 5 from the furthest point to the horizontal center. The other side was treated symmetrically. The scheme determined to be 15° for nozzles 1 and 2 and 20° for nozzles 3, 4, and 5.

[0115] The rest is the same as in Example 1.

Claims

1. A method for improving transverse temperature uniformity and suppressing residual stress in hot-rolled strip steel, characterized in that: During the post-rolling cooling stage of hot-rolled strip steel, the cooling in the width direction of the strip steel is divided into three zones: the middle of the strip steel is the normal cooling zone, the edge of the strip steel is the zone sensitive to strip steel temperature and residual stress, and the outer side of the strip steel is the unsprayed zone. The ultra-fast cooling manifold cooling nozzles in the normal cooling zone in the middle of the strip steel and the outer side of the strip steel are perpendicular to the strip steel surface, while the ultra-fast cooling manifold cooling nozzles in the edge of the strip steel, which is sensitive to strip steel temperature and residual stress, are deflected towards the center of the strip steel at a certain angle α.

2. The method for improving transverse temperature uniformity and suppressing residual stress in hot-rolled strip steel according to claim 1, characterized in that: The formula for calculating the number of cooling nozzles in the ultrafast cooling manifold assembly in the strip edge temperature and residual stress sensitive influence zone is as follows: In the formula, This represents the number of nozzles on one side of the strip, rounded up. This refers to the number of cooling nozzles in the ultra-fast cooling manifold assembly along the width of the strip. The length of the strip's temperature and residual stress-sensitive region is in mm. The length of the outer side of the strip that was not sprayed, in mm; The length of the normal cooling zone in the middle of the strip, in mm.

3. The method for improving transverse temperature uniformity and suppressing residual stress in hot-rolled strip steel according to claim 2, characterized in that: The length of the strip temperature and residual stress sensitive influence zone was obtained through simulation experiments.

4. The method for improving transverse temperature uniformity and suppressing residual stress in hot-rolled strip steel according to claim 2, characterized in that: The strip steel mm; Width of ultra-fast cooling manifold , mm.

5. The method for improving transverse temperature uniformity and suppressing residual stress in hot-rolled strip steel according to claim 1, characterized in that: The ultra-fast cooling manifold cooling nozzles in the strip edge temperature and residual stress sensitive influence zone are deflected towards the center of the strip by an angle α of 5°–20°.

6. The method for improving transverse temperature uniformity and suppressing residual stress in hot-rolled strip steel according to claim 1, characterized in that: The water flow rate of the cooling nozzles in the ultra-fast cooling manifold is determined based on the thickness of the strip steel.

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