A method for producing seamless steel pipes by three consecutive drawing

Abstract

The present application provides a method for producing seamless steel pipe by three times drawing, which comprises the following steps in sequence: preparing material, chemical treatment, first cold drawing, lubrication, second cold drawing, head cutting, pickling and phosphating, head treatment, lubrication, third cold drawing, heat treatment and straightening to obtain the seamless steel pipe. The present application solves the problem that the pipe needs to be heat treated after each cold drawing in the traditional method for producing seamless steel pipe, and in the process of producing seamless steel pipe with outer diameter of 18-20 mm and wall thickness of 1.9-2.1 mm, the method of multiple heat treatment is not needed, and only heat treatment after the last cold drawing is needed, so that the mechanical properties and the cycle time can be reduced, and energy can be saved.

Description

Technical Field

[0001] This invention relates to the field of seamless steel pipe production technology, and more specifically to a method for producing seamless steel pipes using a three-stage continuous drawing process. Background Technology

[0002] With social development and the advancement of science and technology, the application of cold-drawn precision seamless steel pipes is becoming increasingly widespread. These seamless steel pipes not only lack oxide layers on both the inner and outer walls, preventing leakage under high pressure and cracking during flaring and flattening, but also boast relatively high precision and smoothness, with rust-proofing treatment already applied to the surface. These advantages have led to their widespread use in mechanical structures, hydraulic equipment, and many other fields.

[0003] Typically, the main raw material for cold-drawn precision seamless steel pipe production is ordinary cold-drawn steel pipe. To ensure the quality of the precision steel pipe, the raw material needs to undergo a precision drawing process, and the production process needs to be adjusted appropriately according to the actual production conditions. The specific cold drawing process is as follows: First, the blank tube is pickled, phosphated, and lubricated, and then precision cold drawing is performed. Precision cold drawing usually involves multiple passes, with the deformation gradually decreasing in each pass, ultimately yielding the pre-produced product. After each pass, the pipe needs to undergo heat treatment. For example, for 19×2 products, the original process design requires 2-3 heat treatments, which greatly increases the production cycle and cost of the steel pipe. In addition to wasting energy, multiple heat treatments can also lead to decarburization of the seamless steel pipe, and may also result in burn-damaged surfaces, severe oxide scale, and poor cooling effect, which can also lead to Widmanstätten structure. Summary of the Invention

[0004] To address the aforementioned technical problems, a method for producing seamless steel pipes using a three-stage continuous drawing process is provided. This method proposes a cold drawing process with only one heat treatment, tailored to the diameter and wall thickness of the pre-produced seamless steel pipe, ensuring that the resulting seamless steel pipe fully meets the requirements.

[0005] The technical means employed in this invention are as follows:

[0006] A method for producing seamless steel pipes using a three-stage continuous drawing process includes:

[0007] S1. Material preparation: Select pipes for production. The outer diameter of the pipes is 46-48mm, and the wall thickness is 2.8-2.9mm. The pipes come with a rolling head with an outer diameter of 24-26mm and a length of 160-180mm.

[0008] S2. Chemical treatment of the pipes:

[0009] After surface pretreatment, the pipe surface is then subjected to pickling, phosphating, and lubrication in sequence.

[0010] S3. Perform the first cold drawing on the pipe, with an outer diameter of 34-36 mm and a wall thickness of 2.6-2.8 mm.

[0011] S4. Lubricate the pipes;

[0012] S5. Perform a second cold drawing on the pipe, resulting in a pipe with an outer diameter of 27-29 mm and a wall thickness of 2.3-2.5 mm.

[0013] S6. Cut off the rolled head portion that comes with the pipe;

[0014] S7. Pickling and phosphating of the pipes;

[0015] S8. Roll the end of the pipe that did not originally have a rolling head. The outer diameter of the rolling head is 17-19mm and the length of the rolling head is 170-190mm, which facilitates the third cold drawing.

[0016] S9. Lubricate the pipes;

[0017] S10. Perform a third cold drawing on the pipe, with an outer diameter of 18-20 mm and a wall thickness of 1.9-2.1 mm, to complete the three-stage drawing of the pipe.

[0018] S11. After heat treatment, the pipe is straightened to obtain a seamless steel pipe.

[0019] Preferably, in the pickling process of step S2, the pickling solution is sulfuric acid with a concentration of 5-10%, the pickling time is 35-45 min, and the pickling solution temperature is 50-60℃.

[0020] Preferably, in the pickling process of step S7, the pickling solution, solution concentration, and pickling temperature are the same as in step S2, and the pickling time is 15-20 minutes.

[0021] Preferably, the phosphating process in steps S2 and S7 is the same, namely: the pipe directly enters the phosphating process after the pickling process, the phosphating solution uses the forming agent PB-181XM and the accelerator AC-131, the ratio of the forming agent to the accelerator to water is 35:1:1400, the total acidity of the phosphating solution is 25-30g / L, the temperature is 70-80℃, and the phosphating time is 7-15min, so that the inner and outer surfaces of the pipe are evenly covered with bluish-gray crystals with glitter and a dense phosphate film, which makes the pipe adhere to the lubricant and play a role in rust prevention.

[0022] Preferably, the lubrication process in steps S2 and S9 is as follows: the lubricating solution is LUB-235, the ratio of lubricating solution to water is 1:40, the concentration of lubricating solution is 1.5-2.5 pt, the total acidity is less than 1 pt, the lubrication temperature is 70-90℃, and the lubrication time is 20-25 min.

[0023] Preferably, the lubricating solution, ratio, concentration, total acidity, and lubrication temperature in step S4 are the same as in step S2, and the lubrication time is 1 to 2 minutes.

[0024] Preferably, in step S11, the heat treatment process includes normalizing and recrystallization annealing. The normalizing process temperature is 880-920°C and the heating time is 3-4 min. The recrystallization annealing process temperature is 660-700°C and the heating time is 3-4 min.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] In traditional seamless steel pipe production methods, the pipe needs to undergo heat treatment after each cold drawing. However, research has shown that in the production of seamless steel pipes with an outer diameter of 18–20 mm and a wall thickness of 1.9–2.1 mm, multiple heat treatments are unnecessary. Heat treatment is only required after the final cold drawing. This method can ensure the mechanical properties of the product while reducing the number of heat treatments, greatly shortening the product delivery cycle, saving energy, and increasing sales profits.

[0027] Based on the above reasons, this invention can be widely promoted in fields such as seamless steel pipes. Detailed Implementation

[0028] It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of this invention can be combined with each other. The invention will now be described in detail with reference to the embodiments. The described embodiments are merely some embodiments of the invention, not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0029] A method for producing seamless steel pipes using a three-stage continuous drawing process includes:

[0030] S1. Material preparation: Select pipes for production. The outer diameter of the pipes is 46-48mm, and the wall thickness is 2.8-2.9mm. The pipes come with a rolling head with an outer diameter of 24-26mm and a length of 160-180mm.

[0031] S2. Chemical treatment of the pipes:

[0032] After surface pretreatment, the pipe surface is then subjected to pickling, phosphating, and lubrication in sequence.

[0033] The pickling process is as follows: the pickling solution uses sulfuric acid with a concentration of 5-10%, the pickling time is 35-45 minutes, and the temperature of the pickling solution is 50-60℃.

[0034] The phosphating process is as follows: After pickling, the pipes are directly subjected to phosphating. The phosphating solution uses PB-181XM forming agent and AC-131 accelerator. The ratio of forming agent to accelerator to water is 35:1:1400. The total acidity of the phosphating solution is 25-30 g / L, the temperature is 70-80℃, and the phosphating time is 7-15 min. This process results in the pipes being uniformly covered with bluish-gray crystals with a shimmering appearance and a dense phosphate film on both the inner and outer surfaces. This process allows the pipes to adhere to the lubricant while also providing rust prevention.

[0035] The lubrication process is as follows: the lubricating solution used is LUB-235, the ratio of lubricating solution to water is 1:40, the concentration of the lubricating solution is 1.5-2.5 pt, the total acidity is less than 1 pt, the lubrication temperature is 70-90℃, and the lubrication time is 20-25 min.

[0036] S3. Perform the first cold drawing on the pipe. The cold drawing is for pipes with an outer diameter of 34-36mm and a wall thickness of 2.6-2.8mm. The cold drawing uses internal and external molds, namely floating external mold and floating internal mold.

[0037] S4. Lubricate the pipe. The lubrication process is the same as in step S2, except that the time is 1 to 2 minutes.

[0038] S5. Perform a second cold drawing on the pipe. The cold drawing is for pipes with an outer diameter of 27-29 mm and a wall thickness of 2.3-2.5 mm. The cold drawing uses internal and external molds, namely floating external mold and floating internal mold.

[0039] S6. Cut off the rolled head portion that comes with the pipe;

[0040] S7. Pickle and phosphate the pipes. The pickling process is the same as step S2, but the pickling time is 15-20 minutes. The phosphate process is the same as step S2.

[0041] S8. Roll the end of the pipe that did not originally have a rolling head. The outer diameter of the rolling head is 17-19mm and the length of the rolling head is 170-190mm, which facilitates the third cold drawing.

[0042] S9. Lubricate the pipes. The lubrication process is the same as in step S2.

[0043] S10. Perform a third cold drawing on the pipe. The pipe has an outer diameter of 18-20 mm and a wall thickness of 1.9-2.1 mm. This completes the three-stage drawing of the pipe. The cold drawing uses internal and external molds, namely a floating external mold and a floating internal mold.

[0044] S11. After heat treatment, the pipe is straightened to obtain a seamless steel pipe.

[0045] The heat treatment process includes normalizing and recrystallization annealing. The normalizing process temperature is 880-920℃ and the heating time is 3-4 minutes. The recrystallization annealing process temperature is 660-700℃ and the heating time is 3-4 minutes.

[0046] The present invention will be described in detail with reference to Example 1:

[0047] Example 1

[0048] A method for producing 19×2 seamless steel pipes using three consecutive drawing processes includes:

[0049] S1. Material preparation: Select the pipes to be used in production. The dimensions of the pipes are 47mm (outer diameter) × 2.85mm (wall thickness) × 3600mm (length).

[0050] S2. Chemical treatment of the pipes:

[0051] After surface pretreatment, the pipe surface is then subjected to pickling, phosphating, and lubrication in sequence.

[0052] The pickling solution used is sulfuric acid.

[0053] The phosphating solution uses the forming agent PB-181XM and the accelerator AC-131, with a ratio of forming agent to accelerator to water of 35:1:1400.

[0054] The lubricating solution used is LUB-235, mixed with water at a ratio of 1:40.

[0055] The specific process is shown in the table below:

[0056] temperature 60℃ 75℃ 70℃ concentration 9％ 28g / l 2.5pt time 45min 15min 25min

[0057] S3. Perform the first cold drawing on the pipe to produce a pipe with an outer diameter of 35.05 mm and a wall thickness of 2.775 mm. The cold drawing uses inner and outer molds, with the outer mold having an actual size of 35.05 mm and the inner mold having an actual size of 29.5 mm.

[0058] S4. Lubricate the pipe. The lubrication process is the same as in step S2, except that the time is 2 minutes.

[0059] S5. Perform a second cold drawing on the pipe to obtain a pipe diameter of 28.13mm × 2.39mm. The cold drawing uses internal and external molds, with the external mold having an actual size of 28.13mm and the internal mold having an actual size of 23.35mm.

[0060] S6. Cut off the rolled head portion that comes with the pipe;

[0061] S7: Pickling and phosphating the pipe; the pickling process is the same as that in step S2, except that the pickling time is 15 min, and the phosphating process is the same as that in step S2.

[0062] S8: Performing point rolling on the end of the pipe that originally has no rolled head, wherein the outer diameter of the rolled head is 18.5 mm and the length of the rolled head is 170 mm, so as to facilitate the third cold drawing;

[0063] S9: Lubricating the pipe, wherein the lubrication process is the same as that in step S2;

[0064] S10: Performing third cold drawing on the pipe to obtain a pipe of 19.05 mm×1.975 mm, wherein inner and outer molds are adopted for cold drawing, a floating outer mold with an actual size of 19.05 mm and a floating inner mold with an actual size of 15.1 mm are used. So far, the three-time continuous drawing of the pipe is finished, and the total elongation coefficient reaches 3.8. The specification of 19.05 mm×1.975 mm is within the allowable error range of the pipe.

[0065] S11: Subjecting the pipe to heat treatment and then straightening to obtain the seamless steel pipe.

[0066] The heat treatment process comprises normalizing and recrystallization annealing, wherein the normalizing process has a temperature of 900°C and a heating time of 3 min, and the recrystallization annealing process has a temperature of 700°C and a heating time of 3 min.

[0067] Taking steel grade 10# as an example, mechanical property tests (tension, flattening, flaring, hardness) are carried out on the seamless steel pipe: the tensile strength is between 330-490 MPa, the yield strength needs to be greater than or equal to 205 MPa, and the elongation is more than 24%, which fully complies with the standard. Non-destructive testing is carried out on the seamless steel pipe, the testing method is eddy current testing or ultrasonic testing, the testing is carried out according to the GB / T7735-2016 standard, the notch standard is E3H. After the sample tube alarms, the flaw detector is increased by 2-6 dB. If the flaw detector alarms, the tube is considered unqualified, otherwise it is qualified. The detection shows that the seamless steel pipe meets the standard.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: it is still possible to modify the technical solutions described in the foregoing embodiments, or equivalently replace some or all of the technical features; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for producing seamless steel pipes using a three-stage continuous drawing process, characterized in that, include: S1. Material preparation: Select pipes for production. The outer diameter of the pipes is 46-48mm, and the wall thickness is 2.8-2.9mm. The pipes come with a rolling head with an outer diameter of 24-26mm and a length of 160-180mm. S2. Chemical treatment of the pipes: After surface pretreatment, the pipe surface is then subjected to pickling, phosphating, and lubrication in sequence. S3. Perform the first cold drawing on the pipe. The cold drawing is for pipes with an outer diameter of 34~36mm and a wall thickness of 2.6~2.8mm. The cold drawing uses internal and external molds, namely floating external mold and floating internal mold. S4. Lubricate the pipes; S5. Perform a second cold drawing on the pipe, with an outer diameter of 27~29mm and a wall thickness of 2.3~2.5mm; the cold drawing uses internal and external molds, namely floating external mold and floating internal mold; S6. Cut off the rolled head portion that comes with the pipe; S7. Pickling and phosphating of the pipes; S8. Roll the end of the pipe that did not originally have a rolling head. The outer diameter of the rolling head is 17~19mm and the length of the rolling head is 170~190mm, which facilitates the third cold drawing. S9. Lubricate the pipes; S10. Perform a third cold drawing on the pipe. The pipe has an outer diameter of 18~20mm and a wall thickness of 1.9~2.1mm. This completes the three-stage drawing of the pipe. The cold drawing uses internal and external molds, namely a floating external mold and a floating internal mold. S11. After heat treatment, the pipe is straightened to obtain a seamless steel pipe.

2. The method for producing seamless steel pipes using three consecutive drawing operations according to claim 1, characterized in that, In the pickling process of step S2, the pickling solution is sulfuric acid with a concentration of 5-10%, the pickling time is 35-45 minutes, and the temperature of the pickling solution is 50-60℃.

3. A method for producing seamless steel pipes using three consecutive drawing operations according to claim 1 or 2, characterized in that, In the pickling process of step S7, the pickling solution, solution concentration, and pickling temperature are the same as in step S2, and the pickling time is 15-20 minutes.

4. The method for producing seamless steel pipes using three consecutive drawing operations according to claim 1, characterized in that, The phosphating process in steps S2 and S7 is the same: the pipe directly enters the phosphating process after the pickling process. The phosphating solution uses the forming agent PB-181XM and the accelerator AC-131. The ratio of the forming agent to the accelerator to water is 35:1:1400. The total acidity of the phosphating solution is 25-30 g / L, the temperature is 70-80℃, and the phosphating time is 7-15 min. This makes the inner and outer surfaces of the pipe uniformly covered with bluish-gray crystals with a glittering appearance and a dense phosphate film, which makes the pipe adhere to the lubricant and also plays a role in rust prevention.

5. The method for producing seamless steel pipes using three consecutive drawing operations according to claim 1, characterized in that, The lubrication process in steps S2 and S9 is as follows: the lubricating solution is LUB-235, the ratio of lubricating solution to water is 1:40, the concentration of lubricating solution is 1.5-2.5 pt, the total acidity is less than 1 pt, the lubrication temperature is 70-90℃, and the lubrication time is 20-25 min.

6. The method for producing seamless steel pipes using three consecutive drawing operations according to claim 5, characterized in that, The lubricating solution, ratio, concentration, total acidity, and lubrication temperature in step S4 are the same as in step S2, and the lubrication time is 1~2 minutes.

7. The method for producing seamless steel pipes using three consecutive drawing operations according to claim 1, characterized in that, In step S11, the heat treatment process includes normalizing and recrystallization annealing. The normalizing process temperature is 880~920℃ and the heating time is 3~4min. The recrystallization annealing process temperature is 660~700℃ and the heating time is 3~4min.