A method for manufacturing high-strength cold-rolled tube

Abstract

The present invention relates to a method for manufacturing a high-strength cold-rolled tube. The high-strength cold-rolled tube is obtained by curling and forming three layers of different steel materials, i.e., inner, middle and outer layers, and then cold-rolling. Compared with the material using only low-carbon cold-rolled steel tubes, the axial compressive resistance is improved by more than 20%, and the radial compressive resistance is improved by more than 15%. When stacking the materials, the medium-carbon steel is stacked in a multi-row arrangement, so that the low-carbon steel is not prone to axial fracture defects when cold-rolling. At the same time, since two cold rolling and weld inspection are used during cold rolling, it is ensured that no cracks will appear in the weld during cold rolling. The inner and outer surfaces are polished by using corundum, which has better polishing effect and lower cost. During annealing, an annealing process specially suitable for multi-layer materials is designed to ensure the improvement of the compressive resistance of the steel tube after annealing.

Description

Technical Field

[0001] The invention relates to a cold-rolled tube manufacturing process, in particular to a high-strength cold-rolled tube manufacturing method. Background Art

[0002] Cold rolling is a common process for forming seamless pipes, and the equipment used is a cold rolling mill. The cold rolling mill includes a roll assembly, a roll cage, a head, a main drive mechanism and a main transmission mechanism. The main transmission mechanism transmits the power of the main drive mechanism to the head and the roll cage to drive the head and the roll cage to reciprocate axially. The roll assembly is installed on the roll cage, so that it reciprocates axially with the roll cage to achieve rolling of the tube blank.

[0003] Application No. CN202010354420.5 discloses a seamless pipe and its production process. The cold rolling pipe machine does not have the problem of difficulty in balancing the first-order and second-order inertial forces, so it can be used to roll large-diameter seamless pipes. When rolling large-diameter seamless pipes, no vibration, abnormal noise, and poor product flatness will occur, and the surface smoothness of the product can be guaranteed without sacrificing the amount of reduction and elongation.

[0004] However, in the prior art, the cold-rolled tube has not yet involved the cold-rolled tube manufacturing process of the composite multi-layer material, and the strength of the general cold-rolled tube is generally difficult to further improve due to the single material. Summary of the invention

[0005] In view of the above content, in order to solve the above problems, a method for producing a high-strength cold-rolled tube is provided, including layered smelting of substrate, production of straight seam steel tubes, welding, weld treatment, primary cold rolling, primary weld detection, secondary cold rolling, secondary weld detection and polishing steps.

[0006] The substrate in the substrate layered smelting step is divided into three layers, wherein the outer layer and the inner layer are low carbon alloy steel with a carbon content of less than 0.25%, and the middle layer is medium carbon steel with a carbon content of 0.25% to 0.35%; the inner, middle and outer three layers of the substrate are melted into plates respectively, and after melting, they are obliquely cut and stacked to obtain a substrate with low carbon alloy steel on both sides and medium carbon steel in the middle; wherein the thickness of the outer layer and the inner layer are 0.5-1mm respectively, and the thickness of the middle layer is 0.5-1mm.

[0007] The straight seam steel pipe is produced by stamping. The strip steel plate cut from the substrate is stamped and curled to directly obtain an unwelded straight seam steel pipe; the outer diameter of the steel pipe is 30-50cm;

[0008] The welding steps include pre-welding, internal welding, sand filling and external welding. Pre-welding is to make a joint of the pipe and then pre-weld it to obtain a steel pipe; internal welding is to use an internal welding machine to perform internal welding inside the steel pipe, and the welding depth only involves the inner layer of low-carbon alloy steel; after internal welding, sand is filled inside the pipe, and high-speed rotating internal grinding and polishing are performed after sand filling, and the inner wall of the pipe is polished by sand filling; then the steel pipe is externally welded, and the depth of external welding only involves the outer layer of low-carbon alloy steel;

[0009] The weld processing step is to pickle the external weld and then grind and polish it to make the surface of the weld smooth;

[0010] The first cold rolling step is to cold roll the steel pipe for the first time, and the outer diameter of the steel pipe after cold rolling is reduced by 5-10 cm compared with that before the first cold rolling;

[0011] The primary weld inspection is to use ultrasonic testing to inspect the weld after the primary cold rolling to confirm that there are no internal cracks in the weld;

[0012] The secondary cold rolling step is to perform the first cold rolling on the steel pipe, and the outer diameter of the steel pipe after cold rolling is reduced by 5-10 cm compared with that before the secondary cold rolling;

[0013] Secondary weld inspection is to use ultrasonic testing to inspect the welds after secondary cold rolling to confirm that there are no internal cracks in the welds;

[0014] After the secondary weld inspection, qualified steel pipes are polished on the outer wall and then annealed to obtain high-strength cold-rolled pipes.

[0015] In the step of layered smelting of the substrate, the composition of the low carbon alloy steel is: 0.1% manganese, 0.01% cobalt, 0.05% aluminum, 0.04% silicon, 0.02% vanadium, 0.05% niobium, 0.03% titanium, 0.12% carbon, and the rest is iron;

[0016] The composition of medium carbon steel is: 0.01% manganese, 0.01% nickel, 0.01% cobalt, 0.05% niobium, 0.03% titanium, 0.28% carbon, and the rest is iron;

[0017] The cutting width of the outer and inner layers is 1-1.5m, and the length is 10-20m; the cutting width of the middle layer is 20-30cm, and the length is 10-20m. The bevel cutting angle during cutting is 45°, that is, the angle between the cut section and the surface of the steel plate is 45°;

[0018] When stacking, a layer of low-carbon alloy steel is laid on the bottom layer, and then adhesive is applied on it. Then, a middle layer of medium carbon steel with a width of 20-30cm is bonded side by side on the low-carbon alloy steel, and a spacing of 3-5mm is retained between adjacent medium carbon steels; then adhesive is applied on it, and finally a layer of low-carbon alloy steel is bonded on the medium carbon steel.

[0019] During the stamping process of the straight seam steel pipe production, the inner wall will be deformed due to the stamping, which will cause the inner layer to curl more seriously than the middle and outer layers, and the inner and middle layers will be separated. At this time, the inner layer curling shall prevail. When the inner layer curling reaches a cutting section spacing of less than 5cm, the stamping is stopped;

[0020] The welding step is to place the unwelded steel pipe under the action of two external semicircular extrusion heads so that the end faces of the steel pipe weld are in contact with each other, and then pre-weld the outer layer. The welding depth is less than half of the thickness of the outer layer. Since the end face contact is formed under external extrusion, the delamination and separation of the inner and outer layers are eliminated at this time, and the inner, middle and outer layers are in close contact.

[0021] Then use an internal welding machine to reach into the steel pipe to perform internal welding. The welding depth is guaranteed to be greater than 90% of the thickness of the inner layer of low-carbon alloy steel. After the internal welding is completed, silicon carbide corundum is added into the steel pipe, and the steel pipe is controlled to rotate rapidly under external drive, with a speed of 500-800r / min; the rotation time is 20-30min; after the completion, the corundum is removed and external welding is performed. The depth of external welding is guaranteed to be greater than 90% of the thickness of the outer layer of low-carbon alloy steel.

[0022] The weld treatment steps are to use sulfuric acid to pickle the outer weld. The sulfuric acid concentration is 10%, and it is sprayed onto the weld area. After the sulfuric acid is in contact for 5 minutes, it is rinsed with clean water, and then 300, 800, and 1000 mesh emery cloths are used for grinding and polishing.

[0023] The first cold rolling step is to cold roll the steel pipe for the first time, using a three-roll cold rolling tube cold rolling mill for cold rolling; during the cold rolling process, the spacing between the medium carbon steels in the middle layer is eliminated due to the cold rolling effect, and the medium carbon steels in the middle layer are in close contact;

[0024] After one cold rolling, a weld inspection is performed. Ultrasonic weld inspection is performed using a contact hot shoe. The hot shoe is placed at the outer weld. Ultrasonic waves are transmitted from the hot shoe to the outer wall weld of the cold-rolled steel pipe, and reflected back to the hot shoe at the interface between the outer layer and the middle layer. The outer weld is inspected for cracks based on the echo. The hot shoe is then placed at the inner weld. Ultrasonic waves are transmitted from the hot shoe to the inner wall weld of the cold-rolled steel pipe, and reflected back to the hot shoe at the interface between the inner layer and the middle layer. The inner weld is inspected for cracks based on the echo.

[0025] If there are no cracks, a secondary cold rolling is performed;

[0026] The secondary cold rolling step is to cold roll the steel pipe for the second time, using a three-roll cold rolling tube cold rolling mill for cold rolling; during the cold rolling process, the contact between the middle carbon steel layers is closer;

[0027] After the secondary cold rolling, the secondary weld inspection is carried out, and the contact hot shoe is used for ultrasonic weld inspection. The hot shoe is placed at the outer weld, and the ultrasound is transmitted from the hot shoe to the outer wall weld of the cold-rolled steel pipe, and is reflected back to the hot shoe at the interface between the outer layer and the middle layer; the outer weld is detected based on the echo to see if there is a crack; then the hot shoe is placed at the inner weld, and the ultrasound is transmitted from the hot shoe to the inner wall weld of the cold-rolled steel pipe, and is reflected back to the hot shoe at the interface between the inner layer and the middle layer; the inner weld is detected based on the echo to see if there is a crack;

[0028] If there are no cracks, polishing annealing is performed.

[0029] The polishing step is to bury the entire steel pipe in corundum and then oscillate it at a frequency of 50-200Hz. The corundum and the steel pipe rub against each other under the action of the oscillation to achieve surface polishing. The particle size of the corundum is 100-500μm.

[0030] The polished steel pipe is annealed, and the specific parameters of annealing are:

[0031] In a hydrogen atmosphere, the temperature is kept at 720°C for 2 hours, and then the hydrogen is removed; the hydrogen atmosphere requires that the concentration of hydrogen is greater than 95%, and the remaining gas is a rare gas, and does not contain oxygen and nitrogen;

[0032] In a helium atmosphere, the temperature is 685°C, and the temperature is maintained for 3-4 hours, and then the helium is removed; wherein the helium atmosphere requires the concentration of helium to be greater than 98%, and the remaining gas is nitrogen, and does not contain oxygen;

[0033] In a nitrogen atmosphere, the temperature is 670°C and kept warm for more than 5 hours; the nitrogen concentration is greater than 98% and does not contain oxygen.

[0034] The present invention has the following beneficial effects:

[0035] The present invention uses the method of curling and forming three layers of different steel materials, namely, inner, middle and outer layers, and then cold rolling to obtain a high-strength cold-rolled tube. Compared with the material using only low-carbon cold-rolled steel tubes, the axial compressive resistance is improved by more than 20%, and the radial compressive resistance is improved by more than 15%; when stacking the materials, the medium-carbon steel is stacked in a multi-row arrangement, so that the low-carbon steel is not prone to axial fracture defects when cold-rolling; at the same time, since two cold rolling and weld inspection are used during cold rolling, it is ensured that the weld will not crack during cold rolling; the inner and outer surfaces are polished by diamond sand, which has better polishing effect and lower cost; during annealing, an annealing process specially suitable for multi-layer materials is designed to ensure the improvement of the compressive resistance of the steel tube after annealing. Generally, the cold rolling method is applied to small-diameter steel tubes. The scheme of the present invention is suitable for steel tubes with larger diameters and a wider range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a process flow chart of the present invention;

[0037] Figure 2 is a structural diagram of a substrate of the present invention;

[0038] Figure 3 It is a schematic diagram of the ultrasonic detection principle of the present invention. DETAILED DESCRIPTION

[0039] The advantages, features and methods of achieving the above objects of the present invention will become clear from the accompanying drawings and the following detailed description.

[0040] Embodiment 1:

[0041] A method for manufacturing a high-strength cold-rolled tube comprises the steps of layered smelting of a substrate, manufacturing of a straight seam steel tube, welding, weld treatment, primary cold rolling, primary weld detection, secondary cold rolling, secondary weld detection and polishing.

[0042] The substrate in the substrate layered smelting step is divided into three layers, wherein the outer layer 1 and the inner layer 2 are low carbon alloy steel with a carbon content of less than 0.25%, and the middle layer 3 is medium carbon steel with a carbon content of 0.25% to 0.35%; the inner, middle and outer three layers of the substrate are melted into plates respectively, and after melting, they are obliquely cut and superimposed to obtain a substrate with low carbon alloy steel on both sides and medium carbon steel in the middle; wherein the thickness of the outer layer 1 and the inner layer 2 are 0.5-1mm respectively, and the thickness of the middle layer 3 is 0.5-1mm.

[0043] The straight seam steel pipe production process adopts a stamping method, and the strip steel plate obtained by cutting the substrate is stamped and curled to directly obtain an unwelded straight seam steel pipe; the outer diameter of the steel pipe is 30cm;

[0044] The welding steps include pre-welding, internal welding, sand filling and external welding steps. Pre-welding is to make a joint of the pipe and then pre-weld it to obtain a steel pipe; internal welding is to use an internal welding machine to perform internal welding inside the steel pipe, and the welding depth only involves the inner layer 2 low-carbon alloy steel; after internal welding, sand is filled inside the pipe, and high-speed rotating internal grinding and polishing are performed after sand filling, and the inner wall of the pipe is polished by sand filling; then the steel pipe is externally welded, and the depth of external welding only involves the outer layer 1 low-carbon alloy steel;

[0045] The weld processing step is to pickle the external weld and then grind and polish it to make the surface of the weld smooth;

[0046] The first cold rolling step is to cold roll the steel pipe for the first time, and the outer diameter of the steel pipe after cold rolling is reduced by 5 cm compared with that before the first cold rolling;

[0047] The primary weld inspection is to use ultrasonic testing to inspect the weld after the primary cold rolling to confirm that there are no internal cracks in the weld;

[0048] The secondary cold rolling step is to perform the first cold rolling on the steel pipe, and the outer diameter of the steel pipe after cold rolling is reduced by 5 cm compared with that before the secondary cold rolling;

[0049] Secondary weld inspection is to use ultrasonic testing to inspect the welds after secondary cold rolling to confirm that there are no internal cracks in the welds;

[0050] After the secondary weld inspection, qualified steel pipes are polished on the outer wall and then annealed to obtain high-strength cold-rolled pipes.

[0051] In the step of layered smelting of the substrate, the composition of the low carbon alloy steel is: 0.1% manganese, 0.01% cobalt, 0.05% aluminum, 0.04% silicon, 0.02% vanadium, 0.05% niobium, 0.03% titanium, 0.12% carbon, and the rest is iron;

[0052] The composition of medium carbon steel is: 0.01% manganese, 0.01% nickel, 0.01% cobalt, 0.05% niobium, 0.03% titanium, 0.28% carbon, and the rest is iron;

[0053] The outer layer 1 and the inner layer 2 are cut to a width of 1m and a length of 10-20m; the middle layer 3 is cut to a width of 20-30cm and a length of 10-20m, and the bevel angle during cutting is 45°, that is, the angle between the cut section and the surface of the steel plate is 45°;

[0054] When stacking, a layer of low-carbon alloy steel is laid on the bottom layer, and then adhesive is applied on it. Then, a middle layer of 3 medium carbon steels with a width of 20-30cm is bonded side by side on the low-carbon alloy steel, and a spacing of 3-5mm is retained between adjacent medium carbon steels; then adhesive is applied on it, and finally a layer of low-carbon alloy steel is bonded on the medium carbon steel.

[0055] During the punching process of the straight seam steel pipe manufacturing process, the inner wall will be deformed due to the punching, which will cause the curling of the inner layer 2 to be more serious than that of the middle layer 3 and the outer layer 1, and the inner layer 2 and the middle layer 3 will be separated. At this time, the curling of the inner layer 2 shall prevail. When the curling of the inner layer 2 reaches a cross-sectional spacing of less than 5 cm, the punching is stopped;

[0056] The welding step is to place the unwelded steel pipe under the action of two external semicircular extrusion heads so that the end faces of the steel pipe at the weld are in contact with each other, and then pre-weld the outer layer 1. The welding depth is less than half the thickness of the outer layer 1. Since the end face contact is formed under external extrusion, the delamination phenomenon of the inner and outer layers 1 is eliminated at this time, and the inner layer 2, the middle layer 3, and the outer layer 1 are in close contact.

[0057] Then use an internal welding machine to reach into the interior of the steel pipe to perform internal welding, and the welding depth is guaranteed to be greater than 90% of the thickness of the inner layer 2 low-carbon alloy steel; after the internal welding is completed, silicon carbide corundum is added into the steel pipe, and the steel pipe is controlled to rotate rapidly under external drive, with a speed of 500r / min; the rotation time is 20-30min; after the completion, the corundum is removed and external welding is performed, and the depth of the external welding is guaranteed to be greater than 90% of the thickness of the outer layer 1 low-carbon alloy steel.

[0058] The weld treatment steps are to use sulfuric acid to pickle the outer weld. The sulfuric acid concentration is 10%, and it is sprayed onto the weld area. After the sulfuric acid is in contact for 5 minutes, it is rinsed with clean water, and then 300, 800, and 1000 mesh emery cloths are used for grinding and polishing.

[0059] The first cold rolling step is to cold roll the steel pipe for the first time, using a three-roll cold rolling tube cold rolling mill for cold rolling; during the cold rolling process, the spacing between the medium carbon steels of the middle layer 3 is eliminated due to the cold rolling effect, and the medium carbon steels of the middle layer 3 are in close contact;

[0060] After one cold rolling, a weld inspection is performed. An ultrasonic weld inspection is performed using a contact hot shoe 4. The hot shoe 4 is placed at the weld of the outer layer 1. Ultrasonic waves are transmitted from the hot shoe 4 to the weld of the outer wall of the cold-rolled steel pipe, and reflected back to the hot shoe 4 at the interface between the outer layer 1 and the middle layer 3. The outer weld is inspected for cracks based on the echo. The hot shoe 4 is then placed at the weld of the inner layer 2. Ultrasonic waves are transmitted from the hot shoe 4 to the weld of the inner wall of the cold-rolled steel pipe, and reflected back to the hot shoe 4 at the interface between the inner layer 2 and the middle layer 3. The inner weld is inspected for cracks based on the echo.

[0061] If there are no cracks, a secondary cold rolling is performed;

[0062] The secondary cold rolling step is to cold roll the steel pipe for the second time, using a three-roll cold rolling tube cold rolling mill for cold rolling; during the cold rolling process, the medium carbon steel in the middle layer 3 is in closer contact with each other;

[0063] After the secondary cold rolling, the secondary weld inspection is carried out, and the contact hot shoe 4 is used for ultrasonic weld inspection. The hot shoe 4 is placed at the weld of the outer layer 1, and the ultrasound is transmitted from the hot shoe 4 to the weld of the outer wall of the cold-rolled steel pipe, and is reflected back to the hot shoe 4 at the interface between the outer layer 1 and the middle layer 3; the outer weld is detected based on the echo to see if there is a crack; then the hot shoe 4 is placed at the weld of the inner layer 2, and the ultrasound is transmitted from the hot shoe 4 to the weld of the inner wall of the cold-rolled steel pipe, and is reflected back to the hot shoe 4 at the interface between the inner layer 2 and the middle layer 3; the inner weld is detected based on the echo to see if there is a crack;

[0064] If there are no cracks, polishing annealing is performed.

[0065] The polishing step is to bury the entire steel pipe in corundum and then oscillate it at a frequency of 50-200Hz. The corundum and the steel pipe rub against each other under the action of the oscillation to achieve surface polishing. The particle size of the corundum is 100-500μm.

[0066] The polished steel pipe is annealed, and the specific parameters of annealing are:

[0067] In a hydrogen atmosphere, the temperature is kept at 720°C for 2 hours, and then the hydrogen is removed; the hydrogen atmosphere requires that the concentration of hydrogen is greater than 95%, and the remaining gas is a rare gas, and does not contain oxygen and nitrogen;

[0068] In a helium atmosphere, the temperature is 685°C, and the temperature is maintained for 3-4 hours, and then the helium is removed; wherein the helium atmosphere requires the concentration of helium to be greater than 98%, and the remaining gas is nitrogen, and does not contain oxygen;

[0069] In a nitrogen atmosphere, the temperature is 670°C and kept warm for more than 5 hours; the nitrogen concentration is greater than 98% and does not contain oxygen.

[0070] Embodiment 2:

[0071] A method for manufacturing a high-strength cold-rolled tube comprises the steps of layered smelting of a substrate, manufacturing of a straight seam steel tube, welding, weld treatment, primary cold rolling, primary weld detection, secondary cold rolling, secondary weld detection and polishing.

[0072] The substrate in the substrate layered smelting step is divided into three layers, wherein the outer layer 1 and the inner layer 2 are low carbon alloy steel with a carbon content of less than 0.25%, and the middle layer 3 is medium carbon steel with a carbon content of 0.25% to 0.35%; the inner, middle and outer three layers of the substrate are melted into plates respectively, and after melting, they are obliquely cut and superimposed to obtain a substrate with low carbon alloy steel on both sides and medium carbon steel in the middle; wherein the thickness of the outer layer 1 and the inner layer 2 are 0.5-1mm respectively, and the thickness of the middle layer 3 is 0.5-1mm.

[0073] The straight seam steel pipe production process adopts a stamping method, and the strip steel plate obtained by cutting the substrate is stamped and curled to directly obtain an unwelded straight seam steel pipe; the outer diameter of the steel pipe is 50cm;

[0074] The welding steps include pre-welding, internal welding, sand filling and external welding steps. Pre-welding is to make a joint of the pipe and then pre-weld it to obtain a steel pipe; internal welding is to use an internal welding machine to perform internal welding inside the steel pipe, and the welding depth only involves the inner layer 2 low-carbon alloy steel; after internal welding, sand is filled inside the pipe, and high-speed rotating internal grinding and polishing are performed after sand filling, and the inner wall of the pipe is polished by sand filling; then the steel pipe is externally welded, and the depth of external welding only involves the outer layer 1 low-carbon alloy steel;

[0075] The weld processing step is to pickle the external weld and then grind and polish it to make the surface of the weld smooth;

[0076] The first cold rolling step is to cold roll the steel pipe for the first time, and the outer diameter of the steel pipe after cold rolling is reduced by 10 cm compared with that before the first cold rolling;

[0077] The primary weld inspection is to use ultrasonic testing to inspect the weld after the primary cold rolling to confirm that there are no internal cracks in the weld;

[0078] The secondary cold rolling step is to perform the first cold rolling on the steel pipe, and the outer diameter of the steel pipe after cold rolling is reduced by 10 cm compared with that before the secondary cold rolling;

[0079] Secondary weld inspection is to use ultrasonic testing to inspect the welds after secondary cold rolling to confirm that there are no internal cracks in the welds;

[0080] After the secondary weld inspection, qualified steel pipes are polished on the outer wall and then annealed to obtain high-strength cold-rolled pipes.

[0081] In the step of layered smelting of the substrate, the composition of the low carbon alloy steel is: 0.1% manganese, 0.01% cobalt, 0.05% aluminum, 0.04% silicon, 0.02% vanadium, 0.05% niobium, 0.03% titanium, 0.12% carbon, and the rest is iron;

[0082] The composition of medium carbon steel is: 0.01% manganese, 0.01% nickel, 0.01% cobalt, 0.05% niobium, 0.03% titanium, 0.28% carbon, and the rest is iron;

[0083] The outer layer 1 and the inner layer 2 are cut to a width of 1.5m and a length of 10-20m; the middle layer 3 is cut to a width of 20-30cm and a length of 10-20m, and the bevel angle during cutting is 45°, that is, the angle between the cut section and the surface of the steel plate is 45°;

[0084] When stacking, a layer of low-carbon alloy steel is laid on the bottom layer, and then adhesive is applied on it. Then, a middle layer of 3 medium carbon steels with a width of 20-30cm is bonded side by side on the low-carbon alloy steel, and a spacing of 3-5mm is retained between adjacent medium carbon steels; then adhesive is applied on it, and finally a layer of low-carbon alloy steel is bonded on the medium carbon steel.

[0085] During the punching process of the straight seam steel pipe manufacturing process, the inner wall will be deformed due to the punching, which will cause the curling of the inner layer 2 to be more serious than that of the middle layer 3 and the outer layer 1, and the inner layer 2 and the middle layer 3 will be separated. At this time, the curling of the inner layer 2 shall prevail. When the curling of the inner layer 2 reaches a cross-sectional spacing of less than 5 cm, the punching is stopped;

[0086] The welding step is to place the unwelded steel pipe under the action of two external semicircular extrusion heads so that the end faces of the steel pipe at the weld are in contact with each other, and then pre-weld the outer layer 1. The welding depth is less than half the thickness of the outer layer 1. Since the end face contact is formed under external extrusion, the delamination phenomenon of the inner and outer layers 1 is eliminated at this time, and the inner layer 2, the middle layer 3, and the outer layer 1 are in close contact.

[0087] Then use an internal welding machine to reach into the interior of the steel pipe to perform internal welding, and the welding depth is guaranteed to be greater than 90% of the thickness of the inner layer 2 low-carbon alloy steel; after the internal welding is completed, silicon carbide corundum is added into the steel pipe, and the steel pipe is controlled to rotate rapidly under external drive, with a speed of 800r / min; the rotation time is 20-30min; after the completion, the corundum is removed and external welding is performed, and the depth of the external welding is guaranteed to be greater than 90% of the thickness of the outer layer 1 low-carbon alloy steel.

[0088] The weld treatment steps are to use sulfuric acid to pickle the outer weld. The sulfuric acid concentration is 10%, and it is sprayed onto the weld area. After the sulfuric acid is in contact for 5 minutes, it is rinsed with clean water, and then 300, 800, and 1000 mesh emery cloths are used for grinding and polishing.

[0089] The first cold rolling step is to cold roll the steel pipe for the first time, using a three-roll cold rolling tube cold rolling mill for cold rolling; during the cold rolling process, the spacing between the medium carbon steels of the middle layer 3 is eliminated due to the cold rolling effect, and the medium carbon steels of the middle layer 3 are in close contact;

[0090] After one cold rolling, a weld inspection is performed. An ultrasonic weld inspection is performed using a contact hot shoe 4. The hot shoe 4 is placed at the weld of the outer layer 1. Ultrasonic waves are transmitted from the hot shoe 4 to the weld of the outer wall of the cold-rolled steel pipe, and reflected back to the hot shoe 4 at the interface between the outer layer 1 and the middle layer 3. The outer weld is inspected for cracks based on the echo. The hot shoe 4 is then placed at the weld of the inner layer 2. Ultrasonic waves are transmitted from the hot shoe 4 to the weld of the inner wall of the cold-rolled steel pipe, and reflected back to the hot shoe 4 at the interface between the inner layer 2 and the middle layer 3. The inner weld is inspected for cracks based on the echo.

[0091] If there are no cracks, a secondary cold rolling is performed;

[0092] The secondary cold rolling step is to cold roll the steel pipe for the second time, using a three-roll cold rolling tube cold rolling mill for cold rolling; during the cold rolling process, the medium carbon steel in the middle layer 3 is in closer contact with each other;

[0093] After the secondary cold rolling, the secondary weld inspection is carried out, and the contact hot shoe 4 is used for ultrasonic weld inspection. The hot shoe 4 is placed at the weld of the outer layer 1, and the ultrasound is transmitted from the hot shoe 4 to the weld of the outer wall of the cold-rolled steel pipe, and is reflected back to the hot shoe 4 at the interface between the outer layer 1 and the middle layer 3; the outer weld is detected based on the echo to see if there is a crack; then the hot shoe 4 is placed at the weld of the inner layer 2, and the ultrasound is transmitted from the hot shoe 4 to the weld of the inner wall of the cold-rolled steel pipe, and is reflected back to the hot shoe 4 at the interface between the inner layer 2 and the middle layer 3; the inner weld is detected based on the echo to see if there is a crack;

[0094] If there are no cracks, polishing annealing is performed.

[0095] The polishing step is to bury the entire steel pipe in corundum and then oscillate it at a frequency of 50-200Hz. The corundum and the steel pipe rub against each other under the action of the oscillation to achieve surface polishing. The particle size of the corundum is 100-500μm.

[0096] The polished steel pipe is annealed, and the specific parameters of annealing are:

[0097] In a hydrogen atmosphere, the temperature is kept at 720°C for 2 hours, and then the hydrogen is removed; the hydrogen atmosphere requires that the concentration of hydrogen is greater than 95%, and the remaining gas is a rare gas, and does not contain oxygen and nitrogen;

[0098] In a helium atmosphere, the temperature is 685°C, and the temperature is maintained for 3-4 hours, and then the helium is removed; wherein the helium atmosphere requires the concentration of helium to be greater than 98%, and the remaining gas is nitrogen, and does not contain oxygen;

[0099] In a nitrogen atmosphere, the temperature is 670°C and kept warm for more than 5 hours; the nitrogen concentration is greater than 98% and does not contain oxygen.

[0100] The above is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for producing a high-strength cold-rolled tube, comprising the steps of layered smelting of a substrate, production of a straight seam steel tube, welding, weld treatment, primary cold rolling, primary weld inspection, secondary cold rolling, secondary weld inspection and polishing, characterized in that: In the step of layered smelting of the substrate, the substrate is divided into three layers, wherein the outer layer (1) and the inner layer (2) are low carbon alloy steel with a carbon content of less than 0.25%, and the middle layer (3) is medium carbon steel with a carbon content of 0.25% to 0.35%. The inner, middle and outer three layers of the substrate are smelted into plates respectively, and after smelting, the plates are cut obliquely and stacked to obtain a substrate with low carbon alloy steel on both sides and medium carbon steel in the middle. The thickness of the outer layer (1) and the inner layer (2) are 0.5-1 mm respectively, and the thickness of the middle layer (3) is 0.5-1 mm. The straight seam steel pipe is produced by stamping. The strip steel plate cut from the substrate is stamped and curled to directly obtain an unwelded straight seam steel pipe; the outer diameter of the steel pipe is 30-50cm; The welding steps include pre-welding, internal welding, sand filling and external welding steps. Pre-welding is to make a joint of the pipe and then pre-weld it to obtain a steel pipe. Internal welding is to use an internal welding machine to perform internal welding inside the steel pipe, and the welding depth only involves the inner layer (2) of low-carbon alloy steel. After internal welding, sand is filled inside the pipe, and after sand filling, high-speed rotating internal grinding and polishing are performed to polish the inner wall of the pipe by sand filling. After that, the steel pipe is externally welded, and the depth of external welding only involves the outer layer (1) of low-carbon alloy steel. The weld processing step is to pickle the external weld and then grind and polish it to make the surface of the weld smooth; The first cold rolling step is to cold roll the steel pipe for the first time, and the outer diameter of the steel pipe after cold rolling is reduced by 5-10 cm compared with that before the first cold rolling; The primary weld inspection is to use ultrasonic testing to inspect the weld after the primary cold rolling to confirm that there are no internal cracks in the weld; The secondary cold rolling step is to perform the first cold rolling on the steel pipe, and the outer diameter of the steel pipe after cold rolling is reduced by 5-10 cm compared with that before the secondary cold rolling; Secondary weld inspection is to use ultrasonic testing to inspect the welds after secondary cold rolling to confirm that there are no internal cracks in the welds; After the secondary weld inspection, qualified steel pipes are polished on the outer wall and then annealed to obtain high-strength cold-rolled pipes; In the step of layered smelting of the substrate, the composition of the low carbon alloy steel is: 0.1% manganese, 0.01% cobalt, 0.05% aluminum, 0.04% silicon, 0.02% vanadium, 0.05% niobium, 0.03% titanium, 0.12% carbon, and the rest is iron; The composition of medium carbon steel is: 0.01% manganese, 0.01% nickel, 0.01% cobalt, 0.05% niobium, 0.03% titanium, 0.28% carbon, and the rest is iron; The outer layer (1) and the inner layer (2) have a cutting width of 1-1.5 m and a length of 10-20 m; the middle layer (3) has a cutting width of 20-30 cm and a length of 10-20 m, wherein the bevel cutting angle during cutting is 45°, that is, the angle between the cut section and the surface of the steel plate is 45°; When stacking, a layer of low-carbon alloy steel is laid on the bottom layer, and then an adhesive is applied thereon, and then a middle layer (3) of medium carbon steel with a width of 20-30 cm is bonded side by side on the low-carbon alloy steel, with a spacing of 3-5 mm between adjacent medium carbon steels; then an adhesive is applied thereon, and finally a layer of low-carbon alloy steel is bonded on the medium carbon steel; During the punching process of the straight seam steel pipe manufacturing step, the inner wall is deformed by punching, which causes the inner layer (2) to curl more severely than the middle layer (3) and the outer layer (1), and the inner layer (2) and the middle layer (3) to separate from each other. At this time, the curling of the inner layer (2) is taken as the standard. When the curling of the inner layer (2) reaches a cross-sectional spacing of less than 5 cm for cutting, the punching is stopped. The welding step is to place the unwelded steel pipe under the action of two external semicircular extrusion heads so that the end faces of the steel pipe at the weld are in contact with each other, and then pre-weld the outer layer (1). The welding depth is less than half the thickness of the outer layer (1). Since the end face contact is formed under external extrusion, the delamination and separation of the inner and outer layers (1) are eliminated, and the inner layer (2), the middle layer (3), and the outer layer (1) are in close contact. Then, an internal welding machine is used to extend into the interior of the steel pipe to perform internal welding, and the welding depth is guaranteed to be greater than 90% of the thickness of the inner layer (2) of low-carbon alloy steel. After the internal welding is completed, silicon carbide corundum is added into the steel pipe, and the steel pipe is controlled to rotate rapidly under external drive, with a speed of 500-800r / min; the rotation time is 20-30min; after completion, the corundum is removed and external welding is performed, and the depth of the external welding is guaranteed to be greater than 90% of the thickness of the outer layer (1) of low-carbon alloy steel.

2. The method for producing a high-strength cold-rolled tube according to claim 1, characterized in that: The weld treatment steps are to use sulfuric acid to pickle the external weld. The sulfuric acid concentration is 10%, and it is sprayed onto the weld area. After the sulfuric acid is in contact for 5 minutes, it is rinsed with clean water, and then 300, 800, and 1000 mesh emery cloths are used for grinding and polishing.

3. The method for producing a high-strength cold-rolled tube according to claim 1, characterized in that: The first cold rolling step is to cold roll the steel pipe for the first time, using a three-roll cold rolling tube cold rolling mill for cold rolling; during the cold rolling process, the spacing between the medium carbon steels in the middle layer (3) is eliminated due to the cold rolling effect, and the medium carbon steels in the middle layer (3) are in close contact; After a cold rolling operation, a weld inspection is performed. An ultrasonic weld inspection is performed using a contact hot shoe (4). The hot shoe (4) is placed at the weld of the outer layer (1). Ultrasonic waves are transmitted from the hot shoe (4) to the weld of the outer wall of the cold-rolled steel pipe, and reflected back to the hot shoe (4) at the interface between the outer layer (1) and the middle layer (3). The outer weld is inspected for cracks based on the echo. The hot shoe (4) is then placed at the weld of the inner layer (2). Ultrasonic waves are transmitted from the hot shoe (4) to the weld of the inner wall of the cold-rolled steel pipe, and reflected back to the hot shoe (4) at the interface between the inner layer (2) and the middle layer (3). The inner weld is inspected for cracks based on the echo. If there are no cracks, a secondary cold rolling is performed; The secondary cold rolling step is to cold roll the steel pipe for the second time, using a three-roll cold rolling mill for cold rolling; during the cold rolling process, the medium carbon steel in the middle layer (3) is in closer contact with each other; After the secondary cold rolling, secondary weld inspection is performed, and ultrasonic weld inspection is performed using a contact hot shoe (4). The hot shoe (4) is placed at the weld of the outer layer (1), and ultrasound is transmitted from the hot shoe (4) to the weld of the outer wall of the cold-rolled steel pipe, and is reflected back to the hot shoe (4) at the interface between the outer layer (1) and the middle layer (3); the outer weld is inspected for cracks based on the echo; then the hot shoe (4) is placed at the weld of the inner layer (2), and ultrasound is transmitted from the hot shoe (4) to the weld of the inner wall of the cold-rolled steel pipe, and is reflected back to the hot shoe (4) at the interface between the inner layer (2) and the middle layer (3); the inner weld is inspected for cracks based on the echo; If there are no cracks, polishing annealing is performed.

4. The method for producing a high-strength cold-rolled tube according to claim 3, characterized in that: The polishing step is to bury the entire steel pipe in corundum and then oscillate it at a frequency of 50-200Hz. The corundum and the steel pipe rub against each other under the action of the oscillation to achieve surface polishing. The particle size of the corundum is 100-500μm. The polished steel pipe is annealed, and the specific parameters of annealing are: In a hydrogen atmosphere, keep the temperature at 720°C for 2 hours, and then remove the hydrogen; the hydrogen atmosphere requires that the concentration of hydrogen is greater than 95%, and the remaining gas is a rare gas, without oxygen and nitrogen; In a helium atmosphere, the temperature is 685°C, kept warm for 3-4 hours, and then the helium is removed; the helium atmosphere requires the helium concentration to be greater than 98%, and the remaining gas is nitrogen, without oxygen; In a nitrogen atmosphere, the temperature is 670°C and kept warm for more than 5 hours; the nitrogen concentration is greater than 98% and does not contain oxygen.

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