A method for manufacturing a large-diameter seamless steel pipe

Abstract

The present application relates to the technical field of seamless steel pipe production, and discloses a preparation method of large-diameter seamless steel pipe, which comprises the following steps: step 1, heating a steel ingot under first preset conditions; step 2, forging the steel ingot according to a preset forging ratio to form a pipe blank, wherein the temperature at the time of stopping forging is greater than or equal to 850 DEG C; step 3, heat treating the pipe blank; step 4, heating the pipe blank under second preset conditions; step 5, processing the pipe blank to form a hollow pipe; step 6, heat treating the hollow pipe; step 7, heat expanding the hollow pipe to form a steel pipe product; and step 8, heat treating the steel pipe product. The preparation method can manufacture large-diameter seamless steel pipes with long single-piece length at low cost and is suitable for batch production through the forging of large-size pipe blanks, the hot rolling and heat expansion forming of large-size seamless steel pipes, and the heat treatment of large-size seamless steel pipes.

Description

Technical Field

[0001] This invention relates to the field of seamless steel pipe production technology, and in particular to a method for preparing large-diameter seamless steel pipes. Background Technology

[0002] Currently, hot-rolled seamless steel pipes can be manufactured in specifications ranging from 51mm to 534mm in outer diameter and 5mm to 120mm in wall thickness. Seamless steel pipes are widely used in weaponry and aerospace fields. The technology is mature, has passed evaluation, and is in the stage of industrialized mass production.

[0003] However, some new models and products now require larger diameter steel pipes. During the research and development phase, due to the small demand and numerous specifications, manufacturers typically use hot-rolled rings for supply. Hot-rolled rings have a short production cycle but high cost. In special cases (such as when a single piece exceeds 1 meter in length), ring rolling is difficult to achieve, necessitating the welding of 2-3 rings, which is unsuitable for mass production. Therefore, there is an urgent need to research a method for manufacturing seamless steel pipes with larger diameters suitable for mass production. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing large-diameter seamless steel pipes. This method manufactures large-diameter seamless steel pipes by forging large-size tube blanks, hot rolling and hot expansion forming of large-size seamless steel pipes, and heat treatment of large-size seamless steel pipes. It can produce large-diameter seamless steel pipes with relatively long single pieces, and the cost is low, making it suitable for mass production.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for manufacturing a large-diameter seamless steel pipe, comprising:

[0007] Step 1: Heating the steel ingot under the first preset conditions;

[0008] Step 2: Forge the steel ingot according to the preset forging ratio to form a tube blank, wherein the temperature at which forging stops is greater than or equal to 850°C;

[0009] Step 3: Heat treat the tube blank;

[0010] Step 4: Heating the tube blank under the second preset conditions;

[0011] Step 5: Process the tube blank to form a hollow tube;

[0012] Step 6: Perform heat treatment on the hollow tube;

[0013] Step 7: Perform heat expansion treatment on the hollow tube to form a finished steel pipe;

[0014] Step 8: Perform heat treatment on the finished steel pipe.

[0015] In the above-mentioned process route for preparing large-diameter seamless steel pipes, large-diameter seamless steel pipes are manufactured by forging large-size tube blanks, hot rolling and hot expansion forming of large-size seamless steel pipes, and heat treatment of large-size seamless steel pipes. This method can produce large-diameter seamless steel pipes with relatively long single pieces, and the cost is low, making it suitable for mass production.

[0016] Optionally, the first preset condition in step 1 includes: the heating temperature is greater than or equal to 1180℃ and less than or equal to 1240℃, and the heat preservation time is greater than or equal to 5h and less than or equal to 8h;

[0017] The second preset condition in step 4 includes: a heating temperature greater than or equal to 1180℃ and less than or equal to 1250℃, and a heat preservation time greater than or equal to 5h and less than or equal to 8h.

[0018] Optionally, the heat treatment in step 3 includes annealing, with an annealing heating temperature greater than or equal to 660°C and less than or equal to 720°C, and a holding time greater than or equal to 20h and less than or equal to 30h.

[0019] Optionally, step 5 specifically includes:

[0020] The tube blank is subjected to a piercing process, a rolling process, and a sizing process in sequence to form the hollow tube.

[0021] Optionally, the heat treatment in step 6 includes annealing, with an annealing heating temperature greater than or equal to 660°C and less than or equal to 720°C, and a holding time greater than or equal to 4 hours and less than or equal to 6 hours.

[0022] Optionally, the method for preparing the large-diameter seamless steel pipe further includes: after step 3 and before step 4, straightening the pipe blank, peeling off the surface, and performing flaw detection on the pipe blank.

[0023] Optionally, the method for preparing the large-diameter seamless steel pipe further includes: step 9, inspecting, grinding, and testing the finished steel pipe.

[0024] Optionally, the heat treatment in step 8 includes:

[0025] First, normalizing is performed, followed by annealing. The normalizing temperature is greater than or equal to 890℃ and less than or equal to 930℃, and the holding time is greater than or equal to 1 hour and less than or equal to 3 hours, followed by air cooling. The annealing temperature is greater than or equal to 700℃ and less than or equal to 760℃, and the holding time is greater than or equal to 3 hours and less than or equal to 6 hours, followed by furnace cooling.

[0026] Optionally, the heat treatment in step 8 includes:

[0027] First, normalizing is performed, followed by tempering. The normalizing temperature is greater than or equal to 890℃ and less than or equal to 930℃, and the holding time is greater than or equal to 1 hour and less than or equal to 3 hours, followed by cooling in air. The tempering temperature is greater than or equal to 700℃ and less than or equal to 760℃, and the holding time is greater than or equal to 6 hours and less than or equal to 10 hours, followed by cooling in air.

[0028] Optionally, the outer diameter of the finished steel pipe is greater than or equal to 51 mm and less than or equal to 1200 mm, and the wall thickness of the finished steel pipe is greater than or equal to 5 mm and less than or equal to 120 mm. Attached Figure Description

[0029] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein:

[0030] Figure 1 This is a schematic flowchart illustrating a method for preparing a large-diameter seamless steel pipe as provided in this embodiment. Detailed Implementation

[0031] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. Various examples are provided by way of explanation and not by way of limitation. Indeed, those skilled in the art will recognize that modifications and variations can be made to the invention without departing from its scope or spirit. For example, a feature shown or described as part of one embodiment may be used in another embodiment to produce yet another embodiment. Therefore, it is desirable that the invention encompass such modifications and variations falling within the scope of the appended claims and their equivalents.

[0032] In the description of this invention, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," and "bottom," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and do not require the invention to be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on the invention. The terms "connected," "linked," and "set up" used in this invention should be interpreted broadly. For example, they can refer to a fixed connection or a detachable connection; they can refer to a direct connection or an indirect connection through intermediate components. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0033] refer to Figure 1As shown, this invention provides a method for preparing large-diameter seamless steel pipes, the method specifically including:

[0034] Step S1: Heating the steel ingot under the first preset conditions; specifically, the first preset conditions include: heating temperature of 1180℃~1250℃ and holding time of 5h~8h.

[0035] Step S2: Forging the steel ingot according to a preset forging ratio to form a tube blank. The temperature at the stop of forging is ≥850℃. The temperature of the steel ingot must be above 850℃ at the end of the entire forging process, and this temperature must be maintained above 850℃ throughout the forging process. If the temperature drops during a necessary pause in the forging process, the steel ingot needs to be reheated to raise its temperature and maintain it above 850℃. Preferably, when forging the steel ingot, the forging method can be selected according to the requirements for the size and microstructure of the tube blank. For example, one-upsetting and one-drawing forging, two-upsetting and two-drawing forging, three-upsetting and three-drawing forging, or other forging methods can be selected.

[0036] Step S3 involves heat treating the tube blank to remove internal stress, reduce hardness, and improve plasticity.

[0037] Step S4: Heating the tube blank under the second preset conditions; specifically, the second preset conditions include: heating temperature of 1180℃~1250℃ and heat preservation time of 5h~8h.

[0038] Step S5: Process the tube blank to form a hollow tube; specifically, a large-diameter seamless steel pipe skew rolling mill can be used to perform piercing, rolling and sizing processes on the tube blank in sequence, so that the tube blank forms a hollow tube.

[0039] Step S6 involves heat-treating the hollow tube to remove internal stress, reduce hardness, and improve plasticity.

[0040] Step S7 involves heat-expanding the hollow tube to form a finished steel pipe. Specifically, the hollow tube undergoes heat expansion to form a steel pipe that meets the required dimensions. Furthermore, the dimensional tolerances for the finished steel pipe are set as follows: the outer diameter D of the finished steel pipe has a tolerance of -1%D to +1.5%D; the wall thickness δ of the finished steel pipe has a tolerance of -10%δ to +12.5%δ.

[0041] Step S8 involves heat treating the finished steel pipe to address internal stress and microstructure requirements. Specifically, the finished steel pipe can be first normalized and then annealed. The normalizing temperature is 890℃~930℃, held for 1h~3h, and then cooled in air; the annealing temperature is 700℃~760℃, held for 3h~6h, and then cooled in a furnace. Alternatively, the finished steel pipe can be first normalized and then tempered. The normalizing temperature is 890℃~930℃, held for 1h~3h, and then cooled in air; the tempering temperature is 700℃~760℃, held for 6h~10h, and then cooled in air. Different heat treatments are applied to the finished steel pipe to meet different mechanical properties and microstructure requirements.

[0042] In the above-mentioned process route for preparing large-diameter seamless steel pipes, large-diameter seamless steel pipes are manufactured by forging large-size tube blanks, hot rolling and hot expansion forming of large-size seamless steel pipes, and heat treatment of large-size seamless steel pipes. This method can produce large-diameter seamless steel pipes with relatively long single pieces, and the cost is low, making it suitable for mass production.

[0043] In one possible implementation, the heat treatment in step S3 of the above-mentioned method for preparing large-diameter seamless steel pipes specifically includes annealing, with an annealing heating temperature of 660℃~720℃ and a holding time of 20h~30h.

[0044] Specifically, in the above-mentioned method for preparing large-diameter seamless steel pipes, the heat treatment in step S6 includes annealing, with an annealing heating temperature greater than or equal to 660°C and less than or equal to 720°C, and a holding time greater than or equal to 4 hours and less than or equal to 6 hours.

[0045] Specifically, the above-mentioned method for preparing large-diameter seamless steel pipes further includes: after step S3 and before step S4, straightening the billet, peeling its surface, and performing flaw detection on the billet to ensure its quality, which is beneficial to subsequent steel pipe preparation and ensures the quality of the steel pipe. Preferably, peeling the surface of the billet includes grinding and peeling the surface of the billet with a grinding wheel. Flaw detection of the billet is performed using a φ3.2mm flat-bottomed ultrasonic flaw detection method.

[0046] Specifically, the above-mentioned method for preparing large-diameter seamless steel pipes also includes: step S9, inspecting, surface grinding, and flaw detection of the finished steel pipe. The mechanical properties and composition of the finished steel pipe are inspected, and the surface of the finished steel pipe is ground using a grinding wheel. An automated ultrasonic flaw detection device is used to perform flaw detection on the finished steel pipe to ensure its quality.

[0047] Preferably, the above-described method for preparing large-diameter seamless steel pipes can produce steel pipes with an outer diameter of 51mm to 1200mm and a wall thickness of 5mm to 120mm. The length of a single steel pipe prepared is greater than 1m. Specifically, the length of a single steel pipe prepared can be 4m to 12m, and preferably 7m to 12m. For example, the steel pipe prepared by the above method can have an outer diameter of 500mm to 1200mm, a wall thickness of 5mm to 120mm, and a length of 8m to 11m.

[0048] Specifically, the manufacturing of large-diameter steel pipes in two different sizes will be used as an example:

[0049] Example 1:

[0050] Step S1a: Heating of 12t vacuum consumable steel ingots at 1180℃ for 6 hours.

[0051] Step S2a involves three upsetting and three drawing operations on the steel ingot, with a forging ratio of 8.5 and a stopping temperature of 890℃, resulting in a tube blank with a diameter of 600mm and an actual tolerance of [-2mm, +6mm].

[0052] Step S3a: Anneal the tube blank at a heating temperature of 700℃ and a holding time of 22h.

[0053] After the tube blank is straightened and the surface is peeled off with a grinding wheel, it passes ultrasonic testing using a Φ3.2mm flat-bottom hole.

[0054] Step S4a: The billet is heated to 1220℃ and held for 6 hours.

[0055] In step S5a, the tube blank is subjected to piercing, rolling and sizing processes to form a hollow tube with an outer diameter of 797.94 mm to 818.09 mm and a wall thickness of 37.35 mm to 46.69 mm.

[0056] Step S6a: Anneal the hollow tube at a heating temperature of 700℃ for 5 hours.

[0057] Step S7a: Hollow tube is hot expanded and formed to form a finished steel pipe with an outer diameter of 806mm, a wall thickness of 41.5mm, and a length of 7m.

[0058] Step S8a, heat treatment of finished steel pipe: normalizing heating at 920℃, holding for 1 hour, and air cooling; tempering at 740℃, holding for 6 hours, and air cooling.

[0059] Step 9a: After inspecting and grinding the finished steel pipe, the finished pipe is tested for defects using an automated ultrasonic testing device.

[0060] Example 2:

[0061] Step S1b: Heating 10t electroslag steel ingots at a heating temperature of 1220℃ and a holding time of 5.5h.

[0062] Step S2b, tube blank forging, the steel ingot is upset and drawn in one go, the forging ratio is 2.5, forming a tube blank with a diameter of 800mm, the forging stop temperature is 890℃, and the actual tolerance of the tube blank diameter is [-10mm, +10mm].

[0063] Step S3b: Anneal the tube blank at a heating temperature of 700℃ and a holding time of 22h.

[0064] After the tube blank is straightened and the surface is peeled off with a grinding wheel, it passes ultrasonic testing using a Φ3.2mm flat-bottom hole.

[0065] Step S4b: The billet is heated to 1260℃ and held for 6 hours.

[0066] In step S5b, the tube blank undergoes piercing, rolling, and sizing processes to form a hollow tube. The finished outer diameter of the hollow tube meets the requirements, with an outer diameter of 789.30 mm to 800.58 mm and a wall thickness of 44.60 mm to 49.70 mm.

[0067] Step S6b: Anneal the hollow tube at a heating temperature of 700℃ for 5 hours.

[0068] Step S7b: Hollow tube is hot expanded to form a finished steel pipe with an outer diameter of 800mm, a wall thickness of 42mm, and a length of 7.5m.

[0069] Step S8b, heat treatment of finished steel pipe: normalizing at 900℃, holding for 2 hours, and air cooling; annealing at 720℃, holding for 3 hours, furnace cooling to 500℃, and then air cooling.

[0070] Step 9b: After inspecting and grinding the finished steel pipe, it is tested for defects using an automated ultrasonic testing device.

[0071] The above are merely preferred embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a large-diameter seamless steel pipe, characterized in that, include: Step 1: Heating the steel ingot under the first preset conditions, the first preset conditions include: heating temperature greater than or equal to 1180℃ and less than or equal to 1240℃, and holding time greater than or equal to 5h and less than or equal to 8h. Step 2: Forge the steel ingot according to the preset forging ratio to form a tube blank. During the forging process, the temperature of the steel ingot is maintained above 850°C, and the temperature at the time of stopping forging is greater than or equal to 850°C. Step 3: Heat treat the tube blank; The heat treatment in step 3 includes annealing, with an annealing heating temperature greater than or equal to 660℃ and less than or equal to 720℃, and a holding time greater than or equal to 20h and less than or equal to 30h. Step 4: Heating the tube blank under the second preset conditions; The second preset condition in step 4 includes: heating temperature greater than or equal to 1180℃ and less than or equal to 1250℃, and heat preservation time greater than or equal to 5h and less than or equal to 8h; Step 5: Process the tube blank to form a hollow tube; Step 6, heat treatment is performed on the hollow tube, and the heat treatment in step 6 includes annealing, the annealing heating temperature is greater than or equal to 660℃ and less than or equal to 720℃, and the holding time is greater than or equal to 4h and less than or equal to 6h. Step 7: Perform heat expansion treatment on the hollow tube to form a finished steel pipe; Step 8: Perform heat treatment on the finished steel pipe; The heat treatment in step 8 includes: First, normalizing is performed, followed by annealing. The normalizing temperature is greater than or equal to 890℃ and less than or equal to 930℃, and the holding time is greater than or equal to 1 hour and less than or equal to 3 hours, followed by air cooling. The annealing temperature is greater than or equal to 700℃ and less than or equal to 760℃, and the holding time is greater than or equal to 3 hours and less than or equal to 6 hours, followed by furnace cooling. Alternatively: the heat treatment in step 8 includes: First, normalizing is performed, followed by tempering. The normalizing temperature is greater than or equal to 890℃ and less than or equal to 930℃, and the holding time is greater than or equal to 1 hour and less than or equal to 3 hours, followed by air cooling. The tempering temperature is greater than or equal to 700℃ and less than or equal to 760℃, and the holding time is greater than or equal to 6 hours and less than or equal to 10 hours, followed by air cooling. The outer diameter of the finished steel pipe is greater than or equal to 51 mm and less than or equal to 1200 mm, and the wall thickness of the finished steel pipe is greater than or equal to 5 mm and less than or equal to 120 mm.

2. The method for preparing large-diameter seamless steel pipes according to claim 1, characterized in that, Step 5 specifically includes: The tube blank is subjected to a piercing process, a rolling process, and a sizing process in sequence to form the hollow tube.

3. The method for preparing large-diameter seamless steel pipes according to claim 1, characterized in that, Also includes: After step 3 and before step 4, the tube blank is straightened, its surface is peeled off, and it is inspected for defects.

4. The method for preparing large-diameter seamless steel pipes according to claim 1, characterized in that, Also includes: Step 9: Inspect the finished steel pipe, perform surface grinding, and conduct flaw detection.

Images