Method for reducing internal residual stress and cutting distortion amount of L-shaped steel for ship

Abstract

The application discloses a method for reducing internal residual stress and cutting distortion deformation of ship L-shaped steel, and belongs to the field of ship structure steel manufacturing. The L-shaped steel is subjected to rough rolling and finish rolling, and then is rapidly cooled in an ultra-fast cooling device to reduce the temperature difference between the face plate and the web plate of the L-shaped steel. Subsequently, the L-shaped steel is air-cooled to room temperature on a cooling bed, and then is straightened to obtain low-stress ship L-shaped steel. The ship L-shaped steel produced by the method has significantly reduced internal residual stress. The residual stress magnetic field intensity trend of the L-shaped steel is relatively gentle, the change amplitude of the stress magnetic field intensity in the x direction is less than 150 A / m, the change amplitude of the stress magnetic field intensity in the y direction is less than 250 A / m, and the distortion deformation caused by the residual stress after cutting is less than 2 mm.

Description

Technical Field

[0001] This invention belongs to the field of marine structural steel manufacturing, and specifically relates to a method for reducing the internal residual stress of marine L-shaped steel. Background Technology

[0002] L-shaped steel is mainly used in shipbuilding and offshore engineering platforms, playing a vital role in the shipbuilding and offshore engineering industries, with demand increasing year by year. Also known as unequal-sided and unequal-thickness angle steel, L-shaped steel has different lengths and thicknesses in its face and web plates, resulting in significant cross-sectional asymmetry. Due to its structural characteristics, L-shaped steel is prone to uneven cooling during production, leading to residual stress. The presence of internal residual stress affects the subsequent performance of L-shaped steel, mainly in terms of dimensional stability, stiffness, stable load-bearing capacity, fatigue, and fracture performance. As users demand higher standards for residual stress in L-shaped steel, manufacturers face a series of challenges.

[0003] The primary cooling method for producing L-shaped steel is direct air cooling on a cooling bed. Air cooling makes it difficult to ensure uniform cooling of the L-shaped steel, resulting in uneven shrinkage and significant internal stress. If this internal stress cannot be eliminated after production, it forms residual stress. Controlling residual stress in L-shaped steel is of great significance to both manufacturers and downstream users. Residual stress testing methods are categorized into destructive testing and non-destructive testing, depending on whether they damage the component. Metal magnetic memory testing technology is a non-destructive testing method that utilizes the magnetic memory effect of metals to rapidly detect stress in components. This method represents the stress distribution as a magnetic field distribution, and the magnetic field distribution shows the same trend as the stress distribution. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for reducing internal residual stress in marine L-shaped steel. The marine L-shaped steel, after rough rolling and finish rolling, undergoes ultra-rapid cooling. After final cooling, the L-shaped steel reheats and is then conveyed via roller conveyor to a cooling bed for air cooling to room temperature. Finally, it enters a straightening machine for straightening to obtain the finished marine L-shaped steel. This method effectively reduces the residual stress level of the L-shaped steel and the amount of stress-induced deformation after cutting. The specific technical solution is as follows: A method for reducing internal residual stress in marine L-beams includes the following steps: Step 1: The marine L-shaped steel after rough rolling and finish rolling enters the cooling equipment for ultra-rapid cooling. The overall cooling rate of the L-shaped steel is 40~170℃ / s, the cooling time is 3~7s, and the final cooling temperature is 500~740℃. Among them, the cooling rate on both sides of the face plate is 50~170℃ / s, and the cooling rate on both sides of the web plate is 40~140℃ / s. At the same time, the flow rate of a single nozzle on the inner side of the face plate is greater than that on the outer side of the face plate, which is greater than that on the inner side of the web plate, which is greater than that on the outer side of the web plate. The cooling rate of the face plate is greater than that of the web plate, thus obtaining the final cooled marine L-shaped steel.

[0005] Step 2: After final cooling, the marine L-shaped steel undergoes a reheating process at a temperature of 550~800℃. The temperature difference between the cross sections after reheating is controlled to be no more than 10℃ to reduce the generation of internal stress. Subsequently, the L-shaped steel is conveyed to the cooling bed via roller conveyor for air cooling and cooling to room temperature. Finally, it enters the straightening machine for straightening to obtain the finished marine L-shaped steel.

[0006] The composition requirements for the aforementioned marine L-beams are as follows: the chemical composition and the mass percentage of each chemical composition are as follows: C: 0.12-0.175%, Si: 0.26-0.52%, Mn: 0.4-1.6%, P: ≤0.04%, S: ≤0.029%, Cu: ≤0.36%, Cr: ≤0.27%, Ni: 0.21-0.41%, Nd: ≤0.045%, V: ≤0.08%, Ti: ≤0.023%, Mo: ≤0.07%, with the balance being Fe and unavoidable impurities.

[0007] The marine L-beams refer to both general strength and high strength steels, and are available in various sizes and specifications.

[0008] The cooling device has four cooling nozzles on the outer side of the panel, 5cm from the cooling surface; two cooling nozzles on the inner side of the panel, 20cm from the cooling surface; eight cooling nozzles on the outer side of the belly plate, 5cm from the cooling surface; and six cooling nozzles on the inner side of the belly plate, 15cm from the cooling surface. The nozzles are fan-shaped, with the water jet angle between them being 20-30°. The angle between the nozzles on the outer side of the panel and the outer side of the belly plate is 20°, and the angle between the nozzles on the inner side of the panel and the inner side of the belly plate is 30°. The water jets from the nozzles are perpendicular to the cooling surface.

[0009] The maximum reduction in the straightening process shall not exceed 12 mm.

[0010] The roughing rolling temperature of the marine L-shaped steel is 1100~1180℃, the finishing rolling temperature is 1000~1100℃, and the temperature of the final rolled marine L-shaped steel is 860~1000℃.

[0011] The length of the L-shaped steel used in the ship is 10 to 30 meters.

[0012] The water pressure of the cooling equipment is 0.8~1.5MPa.

[0013] The internal residual stress of the marine L-shaped steel is significantly reduced, the residual stress magnetic field intensity trend of the L-shaped steel bar is relatively gentle, the stress magnetic field intensity change range in the x-direction is less than 150 A / m, the stress magnetic field intensity change range in the y-direction is less than 250 A / m, and the torsional deformation caused by residual stress after cutting is less than 2 mm.

[0014] The present invention provides a method for reducing internal residual stress in marine L-beams, which, compared with the prior art, has the following advantages: I. This invention reduces the residual stress level inside L-shaped steel, thereby reducing the amount of deformation caused by stress during L-shaped steel cutting. After using the method described in this invention, the residual stress magnetic field intensity trend of the L-shaped steel bar is relatively gentle, with the stress magnetic field intensity change range in the x-direction being less than 150 A / m and the stress magnetic field intensity change range in the y-direction being less than 250 A / m. The torsional deformation caused by residual stress after cutting is less than 2 mm.

[0015] Second, the method described in this invention has good feasibility. Attached Figure Description

[0016] Figure 1 The internal residual stress magnetic field distribution of the marine L-shaped steel in Example 1 was measured along its length.

[0017] Figure 2 The internal residual stress magnetic field distribution of the marine L-shaped steel in Example 2 was measured along its length.

[0018] Figure 3 The distribution of internal residual stress magnetic field along the length direction of the marine L-shaped steel in Comparative Example 1 is shown.

[0019] Figure 4 The distribution of internal residual stress magnetic field along the length direction of the marine L-shaped steel in Comparative Example 2 is shown. Detailed Implementation

[0020] The following are specific implementation cases and appendices. Figure 1-4 The present invention will be further described, but the present invention is not limited to these embodiments.

[0021] Example 1 A method for reducing internal residual stress in marine L-beams includes the following steps: Step 1: The marine L-shaped steel after rough rolling and finish rolling enters the cooling equipment for ultra-fast cooling. The overall cooling rate of the L-shaped steel is 97℃ / s, the cooling time is 4s, and the final cooling temperature is 594℃. The cooling rate on both sides of the face plate is 95~105℃ / s, and the cooling rate on both sides of the web plate is 82~98℃ / s. At the same time, the flow rate of a single nozzle on the inner side of the face plate is greater than that on the outer side of the face plate, which is greater than that on the inner side of the web plate, which is greater than that on the outer side of the web plate. The cooling rate of the face plate is greater than that of the web plate, thus obtaining the final cooled marine L-shaped steel.

[0022] Step 2: After final cooling, the marine L-shaped steel undergoes a reheating process at a temperature of 682~690℃. After reheating, the temperature difference between the face plate and the web plate is 8℃. Subsequently, the L-shaped steel is conveyed to the cooling bed via roller conveyor for air cooling and cooling to room temperature. Then, it enters the straightening machine for straightening to obtain the finished marine L-shaped steel.

[0023] The composition requirements for the aforementioned marine L-beams are as follows: the chemical composition and the mass percentage of each chemical composition are: C: 0.152%, Si: 0.46%, Mn: 1.1%, P: 0.036%, S: 0.027%, Cu: 0.22%, Cr: 0.27%, Ni: 0.3%, with the balance being Fe and unavoidable impurities.

[0024] The marine L-shaped steel has a strength grade of A and a specification of L250×90×10×15.

[0025] The cooling device has four cooling nozzles on the outer side of the panel, 5cm from the cooling surface; two cooling nozzles on the inner side of the panel, 20cm from the cooling surface; eight cooling nozzles on the outer side of the belly plate, 5cm from the cooling surface; and six cooling nozzles on the inner side of the belly plate, 15cm from the cooling surface. The nozzles are fan-shaped, with the water jet angle between them being 20-30°. The angle between the nozzles on the outer side of the panel and the outer side of the belly plate is 20°, and the angle between the nozzles on the inner side of the panel and the inner side of the belly plate is 30°. The water jets from the nozzles are perpendicular to the cooling surface.

[0026] The maximum reduction in the straightening process is 8mm.

[0027] The roughing rolling temperature of the marine L-shaped steel is 1152℃, the finishing rolling temperature is 1064℃, and the final rolling temperature of the marine L-shaped steel is 982℃.

[0028] The length of the L-shaped steel used in the ship is 17.7m.

[0029] The cooling equipment has a water pressure of 1.1 MPa.

[0030] The residual stress magnetic field strength of the marine L-shaped steel bar is relatively gentle (see...). Figure 1 The stress magnetic field strength variation range in the x-direction is 127 A / m, and the stress magnetic field strength variation range in the y-direction is 188 A / m. The torsional deformation caused by residual stress after cutting is 0.5 mm.

[0031] Example 2 A method for reducing internal residual stress in marine L-beams includes the following steps: Step 1: The marine L-shaped steel after rough rolling and finish rolling enters the cooling equipment for ultra-fast cooling. The overall cooling rate of the L-shaped steel is 130℃ / s, the cooling time is 3s, and the final cooling temperature is 580℃. The cooling rate on both sides of the face plate is 126~138℃ / s, and the cooling rate on both sides of the web plate is 124~132℃ / s. At the same time, the flow rate of a single nozzle on the inner side of the face plate is greater than that on the outer side of the face plate, which is greater than that on the inner side of the web plate. The cooling rate of the face plate is greater than that of the web plate. The final cooled marine L-shaped steel is obtained.

[0032] Step 2: After final cooling, the marine L-shaped steel undergoes a reheating process at a temperature of 667~677℃. After reheating, the temperature difference between the face plate and the web plate is 10℃. Subsequently, the L-shaped steel is conveyed to the cooling bed via roller conveyor for air cooling and cooling to room temperature. Then, it enters the straightening machine for straightening to obtain the finished marine L-shaped steel.

[0033] The composition requirements for the aforementioned marine L-beams are as follows: the chemical composition and the mass percentage of each chemical composition are: C: 0.16%, Si: 0.36%, Mn: 1.5%, P: 0.025%, S: 0.028%, Cu: 0.3%, Cr: 0.19%, Ni: 0.3%, Nd: 0.03%, V: 0.06%, Ti: 0.019%, Mo: 0.05%, with the balance being Fe and unavoidable impurities.

[0034] The marine L-shaped steel has a strength grade of AH36 and a specification of L200×90×9×14.

[0035] The cooling device has four cooling nozzles on the outer side of the panel, 5cm from the cooling surface; two cooling nozzles on the inner side of the panel, 20cm from the cooling surface; eight cooling nozzles on the outer side of the belly plate, 5cm from the cooling surface; and six cooling nozzles on the inner side of the belly plate, 15cm from the cooling surface. The nozzles are fan-shaped, with the water jet angle between them being 20-30°. The angle between the nozzles on the outer side of the panel and the outer side of the belly plate is 20°, and the angle between the nozzles on the inner side of the panel and the inner side of the belly plate is 30°. The water jets from the nozzles are perpendicular to the cooling surface.

[0036] The maximum reduction in the straightening process is 9 mm.

[0037] The roughing rolling temperature of the marine L-shaped steel is 1137℃, the finishing rolling temperature is 1044℃, and the final rolling temperature of the marine L-shaped steel is 970℃.

[0038] The length of the marine L-shaped steel is 19.2m.

[0039] The cooling equipment has a water pressure of 1.5 MPa.

[0040] The residual stress magnetic field strength of the marine L-shaped steel bar is relatively gentle (see...). Figure 2 The stress magnetic field strength variation range in the x-direction is 50 A / m, and the stress magnetic field strength variation range in the y-direction is 227 A / m. The torsional deformation caused by residual stress after cutting is 1.5 mm.

[0041] Example 3 A method for reducing internal residual stress in marine L-beams includes the following steps: Step 1: The marine L-shaped steel after rough rolling and finish rolling enters the cooling equipment for ultra-fast cooling. The overall cooling rate of the L-shaped steel is 112℃ / s, the cooling time is 4s, and the final cooling temperature is 535℃. The cooling rate on both sides of the face plate is 108~115℃ / s, and the cooling rate on both sides of the web plate is 105~112℃ / s. At the same time, the flow rate of a single nozzle on the inner side of the face plate is greater than that on the outer side of the face plate, which is greater than that on the inner side of the web plate, which is greater than that on the outer side of the web plate. The cooling rate of the face plate is greater than that of the web plate, thus obtaining the final cooled marine L-shaped steel.

[0042] Step 2: After final cooling, the marine L-shaped steel undergoes a reheating process at a temperature of 610~616℃. After reheating, the temperature difference between the face plate and the web plate is 6℃. Subsequently, the L-shaped steel is conveyed to the cooling bed via roller conveyor for air cooling and cooling to room temperature. Then, it enters the straightening machine for straightening to obtain the finished marine L-shaped steel.

[0043] The composition requirements for the aforementioned marine L-beams are as follows: the chemical composition and the mass percentage of each chemical composition are: C: 0.142%, Si: 0.39%, Mn: 1.2%, P: 0.022%, S: 0.02%, Cu: 0.35%, Cr: 0.13%, Ni: 0.29%, Nd: 0.04%, V: 0.066%, Ti: 0.013%, Mo: 0.02%, with the balance being Fe and unavoidable impurities.

[0044] The marine L-beam has a strength grade of DH40 and a specification of L300×90×11×16.

[0045] The cooling device has four cooling nozzles on the outer side of the panel, 5cm from the cooling surface; two cooling nozzles on the inner side of the panel, 20cm from the cooling surface; eight cooling nozzles on the outer side of the belly plate, 5cm from the cooling surface; and six cooling nozzles on the inner side of the belly plate, 15cm from the cooling surface. The nozzles are fan-shaped, with the water jet angle between them being 20-30°. The angle between the nozzles on the outer side of the panel and the outer side of the belly plate is 20°, and the angle between the nozzles on the inner side of the panel and the inner side of the belly plate is 30°. The water jets from the nozzles are perpendicular to the cooling surface.

[0046] The maximum reduction in the straightening process is 7mm.

[0047] The roughing rolling temperature of the marine L-shaped steel is 1155℃, the finishing rolling temperature is 1050℃, and the final rolling temperature of the marine L-shaped steel is 983℃.

[0048] The length of the marine L-shaped steel is 22.5m.

[0049] The cooling equipment has a water pressure of 1.3 MPa.

[0050] The residual stress magnetic field strength of the marine L-shaped steel bar is relatively gentle, with a stress magnetic field strength variation range of 89 A / m in the x-direction and 198 A / m in the y-direction. The torsional deformation caused by residual stress after cutting is 1 mm.

[0051] Example 4 A method for reducing internal residual stress in marine L-beams includes the following steps: Step 1: The marine L-shaped steel after rough rolling and finish rolling enters the cooling equipment for ultra-fast cooling. The overall cooling rate of the L-shaped steel is 93℃ / s, the cooling time is 5s, and the final cooling temperature is 523℃. The cooling rate on both sides of the face plate is 89~98℃ / s, and the cooling rate on both sides of the web plate is 83~94℃ / s. At the same time, the flow rate of a single nozzle on the inner side of the face plate is greater than that on the outer side of the face plate, which is greater than that on the inner side of the web plate, which is greater than that on the outer side of the web plate. The cooling rate of the face plate is greater than that of the web plate. The marine L-shaped steel after final cooling is obtained.

[0052] Step 2: After final cooling, the marine L-shaped steel undergoes a reheating process at a temperature of 601~610℃. After reheating, the temperature difference between the face plate and the web plate is 9℃. Subsequently, the L-shaped steel is conveyed to the cooling bed via roller conveyor for air cooling and cooling to room temperature. Then, it enters the straightening machine for straightening to obtain the finished marine L-shaped steel.

[0053] The composition requirements for the aforementioned marine L-beams are as follows: the chemical composition and the mass percentage of each chemical composition are: C: 0.17%, Si: 0.44%, Mn: 1%, P: 0.02%, S: 0.018%, Cu: 0.28%, Cr: 0.18%, Ni: 0.38%, Nd: 0.035%, V: 0.067%, Ti: 0.014%, Mo: 0.055%, with the balance being Fe and unavoidable impurities.

[0054] The marine L-beam has a strength grade of EH36 and a specification of L350×100×12×17.

[0055] The cooling device has four cooling nozzles on the outer side of the panel, 5cm from the cooling surface; two cooling nozzles on the inner side of the panel, 20cm from the cooling surface; eight cooling nozzles on the outer side of the belly plate, 5cm from the cooling surface; and six cooling nozzles on the inner side of the belly plate, 15cm from the cooling surface. The nozzles are fan-shaped, with the water jet angle between them being 20-30°. The angle between the nozzles on the outer side of the panel and the outer side of the belly plate is 20°, and the angle between the nozzles on the inner side of the panel and the inner side of the belly plate is 30°. The water jets from the nozzles are perpendicular to the cooling surface.

[0056] The maximum reduction in the straightening process is 8mm.

[0057] The roughing rolling temperature of the marine L-shaped steel is 1116℃, the finishing rolling temperature is 1060℃, and the final rolling temperature of the marine L-shaped steel is 988℃.

[0058] The length of the marine L-shaped steel is 22.5m.

[0059] The cooling equipment has a water pressure of 1 MPa.

[0060] The residual stress magnetic field intensity of the marine L-shaped steel bar is relatively gentle, with a stress magnetic field intensity variation range of 114 A / m in the x-direction and 209 A / m in the y-direction. The torsional deformation caused by residual stress after cutting is 1.3 mm.

[0061] Comparative Example 1 A method for producing marine L-shaped steel, which differs from Example 1 mainly in the cooling method, includes the following steps: Step 1: The marine L-shaped steel after rough rolling and fine rolling is directly air-cooled.

[0062] Step 2: The L-shaped steel is then conveyed to the cooling bed via roller conveyor for further air cooling and cooling to room temperature. Finally, it enters the straightening machine for straightening to obtain the finished marine L-shaped steel.

[0063] The composition requirements for the aforementioned marine L-beams are as follows: the chemical composition and the mass percentage of each chemical composition are: C: 0.152%, Si: 0.46%, Mn: 1.1%, P: 0.036%, S: 0.027%, Cu: 0.22%, Cr: 0.27%, Ni: 0.3%, with the balance being Fe and unavoidable impurities.

[0064] The marine L-shaped steel has a strength grade of A and a specification of L250×90×10×15.

[0065] The maximum reduction in the straightening process is 8mm.

[0066] The roughing rolling temperature of the marine L-shaped steel is 1133℃, the finishing rolling temperature is 1040℃, and the final rolling temperature of the marine L-shaped steel is 967℃.

[0067] The length of the marine L-shaped steel is 12.3m.

[0068] The residual stress magnetic field strength of the marine L-shaped steel bar fluctuates significantly (see...). Figure 3 The stress magnetic field strength variation range in the x-direction is 197.5 A / m, and the stress magnetic field strength variation range in the y-direction is 1412 A / m. The torsional deformation caused by residual stress after cutting is 10 mm.

[0069] Comparative Example 2 A method for producing marine L-shaped steel, which differs from Example 1 mainly in the uniformity of cooling, includes the following steps: Step 1: After rough rolling and finish rolling, the marine L-shaped steel enters the cooling equipment for ultra-fast cooling. The overall cooling rate of the L-shaped steel is 97℃ / s, and the cooling time is 4s. The cooling rate of the face plate and the web plate is 97℃ / s. Step 2: After final cooling, the marine L-shaped steel undergoes a reheating process at a temperature of 675~750℃. After reheating, the temperature difference between the face plate and the web plate is 75℃. Subsequently, the L-shaped steel is conveyed to the cooling bed via roller conveyor for air cooling and cooling to room temperature. Then, it enters the straightening machine for straightening to obtain the finished marine L-shaped steel.

[0070] The composition requirements for the aforementioned marine L-beams are as follows: the chemical composition and the mass percentage of each chemical composition are: C: 0.152%, Si: 0.46%, Mn: 1.1%, P: 0.036%, S: 0.027%, Cu: 0.22%, Cr: 0.27%, Ni: 0.3%, with the balance being Fe and unavoidable impurities.

[0071] The marine L-shaped steel has a strength grade of A and a specification of L250×90×10×15.

[0072] The cooling device has four cooling nozzles on the outer side of the panel, 5cm from the cooling surface; two cooling nozzles on the inner side of the panel, 20cm from the cooling surface; eight cooling nozzles on the outer side of the belly plate, 5cm from the cooling surface; and six cooling nozzles on the inner side of the belly plate, 15cm from the cooling surface. The nozzles are fan-shaped, with the water jet angle between them being 20-30°. The angle between the nozzles on the outer side of the panel and the outer side of the belly plate is 20°, and the angle between the nozzles on the inner side of the panel and the inner side of the belly plate is 30°. The water jets from the nozzles are perpendicular to the cooling surface.

[0073] The maximum reduction in the straightening process is 8mm.

[0074] The roughing rolling temperature of the marine L-shaped steel is 1155℃, the finishing rolling temperature is 1061℃, and the final rolling temperature of the marine L-shaped steel is 986℃.

[0075] The length of the marine L-shaped steel is 12.3m.

[0076] The cooling equipment has a water pressure of 1.1 MPa.

[0077] The residual stress magnetic field strength of the marine L-shaped steel bar fluctuates significantly (see...). Figure 4 The stress magnetic field strength variation range in the x-direction is 207 A / m, and the stress magnetic field strength variation range in the y-direction is 1392 A / m. The torsional deformation caused by residual stress after cutting is 8 mm.

[0078] Comparative Example 3 A method for producing marine L-shaped steel, which differs from Example 2 mainly in the cooling method, includes the following steps: Step 1: The marine L-shaped steel after rough rolling and fine rolling is directly air-cooled.

[0079] Step 2: The L-shaped steel is then conveyed to the cooling bed via roller conveyor for air cooling and cooling to room temperature. It then enters the straightening machine for straightening to obtain the finished marine L-shaped steel.

[0080] The composition requirements for the aforementioned marine L-beams are as follows: the chemical composition and the mass percentage of each chemical composition are: C: 0.16%, Si: 0.36%, Mn: 1.5%, P: 0.025%, S: 0.028%, Cu: 0.3%, Cr: 0.19%, Ni: 0.3%, Nd: 0.03%, V: 0.06%, Ti: 0.019%, Mo: 0.05%, with the balance being Fe and unavoidable impurities.

[0081] The marine L-shaped steel has a strength grade of AH36 and a specification of L200×90×9×14.

[0082] The maximum reduction in the straightening process is 9 mm.

[0083] The roughing rolling temperature of the marine L-shaped steel is 1140℃, the finishing rolling temperature is 1051℃, and the final rolling temperature of the marine L-shaped steel is 973℃.

[0084] The length of the marine L-shaped steel is 19.2m.

[0085] The residual stress magnetic field strength of the marine L-shaped steel bar fluctuates greatly, with a variation range of 210 A / m in the x-direction and 1321 A / m in the y-direction. The torsional deformation caused by residual stress after cutting is 6 mm.

[0086] Comparative Example 4 A method for producing marine L-beams, which differs from Example 2 mainly in the uniformity of cooling, includes the following steps: Step 1: After rough rolling and finish rolling, the marine L-shaped steel enters the cooling equipment for ultra-fast cooling. The overall cooling rate of the L-shaped steel is 130℃ / s, and the cooling time is 3s. The cooling rate of the face plate and the web plate is 130℃ / s. Step 2: After final cooling, the marine L-shaped steel undergoes a reheating process at a temperature of 654~740℃. After reheating, the temperature difference between the face plate and the web plate is 86℃. Subsequently, the L-shaped steel is conveyed to the cooling bed via roller conveyor for air cooling and cooling to room temperature. Then, it enters the straightening machine for straightening to obtain the finished marine L-shaped steel.

[0087] The composition requirements for the aforementioned marine L-beams are as follows: the chemical composition and the mass percentage of each chemical composition are: C: 0.16%, Si: 0.36%, Mn: 1.5%, P: 0.025%, S: 0.028%, Cu: 0.3%, Cr: 0.19%, Ni: 0.3%, Nd: 0.03%, V: 0.06%, Ti: 0.019%, Mo: 0.05%, with the balance being Fe and unavoidable impurities.

[0088] The marine L-shaped steel has a strength grade of AH36 and a specification of L200×90×9×14.

[0089] The cooling device has four cooling nozzles on the outer side of the panel, 5cm from the cooling surface; two cooling nozzles on the inner side of the panel, 20cm from the cooling surface; eight cooling nozzles on the outer side of the belly plate, 5cm from the cooling surface; and six cooling nozzles on the inner side of the belly plate, 15cm from the cooling surface. The nozzles are fan-shaped, with the water jet angle between them being 20-30°. The angle between the nozzles on the outer side of the panel and the outer side of the belly plate is 20°, and the angle between the nozzles on the inner side of the panel and the inner side of the belly plate is 30°. The water jets from the nozzles are perpendicular to the cooling surface.

[0090] The maximum reduction in the straightening process is 9 mm.

[0091] The roughing rolling temperature of the marine L-shaped steel is 1131℃, the finishing rolling temperature is 1038℃, and the final rolling temperature of the marine L-shaped steel is 977℃.

[0092] The length of the marine L-shaped steel is 19.2m.

[0093] The cooling equipment has a water pressure of 1.5 MPa.

[0094] The residual stress magnetic field strength of the marine L-shaped steel bar fluctuates greatly, with a variation range of 183 A / m in the x-direction and 1278 A / m in the y-direction. The torsional deformation caused by residual stress after cutting is 5 mm.

[0095] Comparative Example 5 A method for producing marine L-beams, which differs from Example 3 mainly in the maximum straightening reduction, includes the following steps: Step 1: The marine L-shaped steel after rough rolling and finish rolling enters the cooling equipment for ultra-fast cooling. The overall cooling rate of the L-shaped steel is 112℃ / s, the cooling time is 4s, and the final cooling temperature is 527℃. The cooling rate on both sides of the face plate is 108~115℃ / s, and the cooling rate on both sides of the web plate is 105~112℃ / s. At the same time, the flow rate of a single nozzle on the inner side of the face plate is greater than that on the outer side of the face plate, which is greater than that on the inner side of the web plate. The cooling rate of the face plate is greater than that of the web plate. The final cooled marine L-shaped steel is obtained.

[0096] Step 2: After final cooling, the marine L-shaped steel undergoes a reheating process at a temperature of 601~609℃. After reheating, the temperature difference between the face plate and the web plate is 8℃. Subsequently, the L-shaped steel is conveyed to the cooling bed via roller conveyor for air cooling and cooling to room temperature. Then, it enters the straightening machine for straightening to obtain the finished marine L-shaped steel.

[0097] The composition requirements for the aforementioned marine L-beams are as follows: the chemical composition and the mass percentage of each chemical composition are: C: 0.142%, Si: 0.39%, Mn: 1.2%, P: 0.022%, S: 0.02%, Cu: 0.35%, Cr: 0.13%, Ni: 0.29%, Nd: 0.04%, V: 0.066%, Ti: 0.013%, Mo: 0.02%, with the balance being Fe and unavoidable impurities.

[0098] The marine L-beam has a strength grade of DH40 and a specification of L300×90×11×16.

[0099] The cooling device has four cooling nozzles on the outer side of the panel, 5cm from the cooling surface; two cooling nozzles on the inner side of the panel, 20cm from the cooling surface; eight cooling nozzles on the outer side of the belly plate, 5cm from the cooling surface; and six cooling nozzles on the inner side of the belly plate, 15cm from the cooling surface. The nozzles are fan-shaped, with the water jet angle between them being 20-30°. The angle between the nozzles on the outer side of the panel and the outer side of the belly plate is 20°, and the angle between the nozzles on the inner side of the panel and the inner side of the belly plate is 30°. The water jets from the nozzles are perpendicular to the cooling surface.

[0100] The maximum reduction in the straightening process is 18mm.

[0101] The roughing rolling temperature of the marine L-shaped steel is 1152℃, the finishing rolling temperature is 1045℃, and the final rolling temperature of the marine L-shaped steel is 975℃.

[0102] The length of the marine L-shaped steel is 22.5m.

[0103] The cooling equipment has a water pressure of 1.3 MPa.

[0104] The residual stress magnetic field intensity of the marine L-shaped steel bar is relatively gentle, with a stress magnetic field intensity variation range of 173 A / m in the x-direction and 845 A / m in the y-direction. The torsional deformation caused by residual stress after cutting is 3.5 mm.

Claims

1. A method for reducing internal residual stress and cutting torsional deformation of marine L-beams, characterized in that, It includes the following steps: Step 1: After rough rolling and finish rolling, the marine L-shaped steel enters the cooling equipment for ultra-rapid cooling. The overall cooling rate of the L-shaped steel is 40~170℃ / s, the cooling time is 3~7s, and the final cooling temperature is 500~740℃. The cooling rate on both sides of the panel is 50~170℃ / s, and the cooling rate on both sides of the web is 40~140℃ / s, resulting in the final cooled marine L-shaped steel. The length of the marine L-shaped steel is 10~30m. The cooling equipment has 4 cooling nozzles on the outer side of the L-shaped steel panel, 5cm away from the cooling surface. There are two cooling nozzles on the inner side of the panel, 20cm from the cooling surface; eight cooling nozzles on the outer side of the belly plate, 5cm from the cooling surface; and six cooling nozzles on the inner side of the belly plate, 15cm from the cooling surface. The angle of the water jet from the nozzles is 20~30°. At any given time, the flow rate of a single nozzle on the inner side of the panel is greater than that of a single nozzle on the outer side of the panel, which is greater than that of a single nozzle on the inner side of the belly plate. The cooling rate of the panel is greater than that of the belly plate. The water pressure of the cooling equipment is 0.8~1.5MPa. Step 2: After final cooling, the marine L-shaped steel undergoes a reheating process at a temperature of 550~800℃. The temperature difference between the face plate and the web plate is controlled to be no more than 10℃. Subsequently, the L-shaped steel is conveyed to the cooling bed via roller conveyor for air cooling and cooling to room temperature. Finally, it enters the straightening machine for straightening to obtain the finished marine L-shaped steel. The maximum reduction in the straightening process does not exceed 12mm.

2. The method for reducing internal residual stress and cutting torsion deformation of marine L-beams according to claim 1, characterized in that, The chemical composition of the marine L-beam steel, by mass percentage, is: C: 0.12–0.175%, Si: 0.26–0.52%, Mn: 0.4–1.6%, P: ≤0.04%, S: ≤0.029%, Cu: ≤0.36%, Cr: ≤0.27%, Ni: 0.21–0.41%, Nd: ≤0.045%, V: ≤0.08%, Ti: ≤0.023%, Mo: ≤0.07%, with the balance being Fe and unavoidable impurities.

3. The method for reducing internal residual stress and cutting torsion deformation of marine L-beams according to claim 1, characterized in that, The nozzles are fan-shaped nozzles, wherein the water flow angle between the nozzles on the outer side of the panel and the outer side of the belly plate is 20°, and the water flow angle between the nozzles on the inner side of the panel and the inner side of the belly plate is 30°, and the water flow from the nozzles is perpendicular to the cooling surface.

4. The method for reducing internal residual stress and cutting torsion deformation of marine L-beams according to claim 1, characterized in that, The internal residual stress of marine L-shaped steel is significantly reduced. The residual stress magnetic field intensity of L-shaped steel bars shows a gradual trend. The variation range of the stress magnetic field intensity in the x-direction is less than 150 A / m, and the variation range of the stress magnetic field intensity in the y-direction is less than 250 A / m. The torsional deformation caused by residual stress after cutting is less than 2 mm.

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