Manufacturing method of ultra-large seamless steel tube with diameter of 2000mm

Abstract

The invention discloses a manufacturing method of an ultra-large seamless steel pipe with the diameter of 2000 mm, and belongs to the technical field of seamless steel pipe manufacturing in the metallurgical industry. The method comprises the following steps: heating a solid round tube blank, carrying out skew rolling by adopting a micro-expanding process to obtain a pierced billet, manufacturing the pierced billet into a hollow billet with an expanded diameter by utilizing a skew rolling expanding process, further expanding the diameter by using a flattening skew rolling process and simultaneously improving the dimensional precision and the surface quality of the hollow billet, and obtaining a semi-finished steel tube with the diameter of 2000mm by adopting a controlled rolling sizing process. And the semi-finished steel pipe is subjected to heat treatment, flaw detection and finishing procedures to directly obtain the ultra-large seamless steel pipe finished product of 2000 mm According to the method, materials are formed through one-time heating, only pipe blank heating is needed, heat treatment and reheating are not needed, energy is saved, and performance is improved; the on-line structure regulation and control method taking controlled cooling as the core thoroughly turns the passive situation that seamless steel pipes excessively depend on alloying and off-line heat treatment in the past, breaks through the bottleneck of the traditional process, and develops a new process and a new method for high-quality and high-efficiency manufacturing of the steel pipes.

Description

Technical Field

[0001] The invention relates to the technical field of seamless steel pipe manufacturing in the metallurgical industry, and in particular to a method for manufacturing an ultra-large seamless steel pipe with a diameter of 2000 mm and a wall thickness of 230 mm. Background Art

[0002] In the prior art, the existing processes for producing large diameter seamless steel pipes include extrusion and forging.

[0003] Among them, the process of the extrusion method is: after the die-cast steel ingot is cleaned and heated, a hole is first punched in the center of the steel ingot using a push rod and a die, and then a mandrel is inserted in the middle to perform extrusion deformation on the die of the extruder, and the blind end is cut off after the deformation is completed. Its characteristics are that the push rod is slender and easy to be eccentric during punching, resulting in serious uneven wall thickness; the metal slides on the surface of the die, the lubrication condition is poor, the surface of the steel pipe is easily scratched, the surface quality is poor, the degree of automation is low, the yield rate is low, the production efficiency is low, the cost is very high, and it is not conducive to large-scale efficient production. In addition, this method can only produce medium-thick wall seamless steel pipes.

[0004] The process of forging is: after cleaning and heating the die-cast steel ingot, use the ejector and die to punch a hole in the center of the steel ingot, cut off the blind end at the lower end, insert the mandrel in the middle and perform gradual hole expansion forging on the forging machine, and form the rough pipe after forging by mechanical processing methods such as inner boring and outer picking. This method takes a long time to forge, and needs to be repeatedly heated and forged. The size accuracy of the rough pipe after forging is poor and cannot meet the requirements of the finished steel pipe. The inner and outer surfaces must be processed by mechanical processing to meet the requirements of the finished steel pipe. Its defects also include low degree of automation, extremely low yield rate, extremely low production efficiency, and extremely high cost, which is not conducive to large-scale and efficient production. In addition, this method can only produce medium and thick wall seamless steel pipes, and the maximum length cannot exceed 5000mm.

[0005] In summary, the existing processes for producing large-diameter seamless steel pipes all have their own defects. Generally speaking, none of them can meet the urgent requirements of high-efficiency, low-consumption and high-quality production. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for producing an ultra-large diameter seamless steel pipe with a diameter of 2000 mm to meet the market demand for high temperature, high pressure and high safety.

[0007] The present invention is achieved through the following technical solutions: A method for manufacturing an ultra-large seamless steel pipe with a diameter of 2000 mm, wherein a solid round tube blank is heated, and then a micro-expansion process is used to perform oblique rolling to obtain a rough tube, and the rough tube is made into a rough tube with an enlarged diameter by using the oblique rolling diameter expansion process, and then a leveling oblique rolling process is used to further expand the diameter and improve the dimensional accuracy and surface quality of the rough tube, and a controlled rolling and sizing process is used to obtain a semi-finished steel pipe with a diameter of 2000 mm, and the semi-finished steel pipe is directly obtained through heat treatment, flaw detection, and finishing processes to obtain a finished 2000 mm ultra-large seamless steel pipe: The maximum diameter of the solid round tube is 1300 mm; The solid round tube blank is processed with a center positioning hole before heating; The outer diameter of the rough pipe obtained by the micro-expansion process is 1550mm and the wall thickness is 300mm; The outer diameter of the rough tube obtained after the oblique rolling and expansion is 1650mm and the wall thickness is 250mm; The outer diameter of the steel pipe obtained after the leveling and oblique rolling process is 1750 mm and the wall thickness is 230 mm; The leveling oblique rolling process is to roll the rough tube through a conical oblique rolling roller at an oblique rolling diameter expansion rate not exceeding 6.2%; The leveling oblique rolling process is to roll the rough pipe through a hot two-roller oblique rolling mill between the oblique rolling expansion and the sizing to level the rough pipe. The leveling oblique rolling mill equipment includes a front feeding device, a two-roller oblique rolling main machine, and a back-end discharging device. The diameter of the leveling plug of the leveling cross-rolling is 1000-1400 mm, and the temperature of the workpiece of the leveling cross-rolling is 1120-1200° C. After the rough tube is controlled and sizing, the maximum outer diameter of the steel pipe is 2000mm and the wall thickness is 230mm.

[0008] The controlled rolling and sizing process is as follows: the rough pipe after leveling and oblique rolling is heated online by 200°C, the pipe body temperature is 1050°C, the head-to-tail temperature difference is ±15°C, the radial-circumferential temperature difference is ±5°C, and temperature-controlled cooling is performed after sizing.

[0009] The solid round tube billet is heated at a heating rate of 150-200°C / h until the temperature of the solid round tube billet reaches 1250°C and then kept warm for 460-500 min.

[0010] The online organizational control method with controlled cooling of seamless steel pipe as the core, during online controlled cooling, when the residual heat of continuous rolling sizing is ≥800℃, the temperature of the sizing steel pipe is cooled to below 200℃ within 1 minute through high-pressure water spraying equipment, the cooling rate of the inner and outer surfaces of the steel pipe is 50~150℃ / S, and the temperature difference of the entire length of the steel pipe is ≤30℃.

[0011] Compared with the prior art, the present invention has the following beneficial effects: 1. The rolling in the present invention is a large-diameter rolling process combining oblique rolling and leveling oblique rolling. The oblique rolling can be used for oblique diameter expansion rolling. The tube blank metal is deformed in both the longitudinal and transverse directions, which is beneficial to maintaining uniform organizational properties of the steel tube.

[0012] 2. The present invention adopts a leveling process for thin-walled tubes with a diameter-to-wall ratio greater than 30. Ordinary oblique rolling is prone to produce spiral tracks, which affects dimensional accuracy. Subsequent processes must undergo a finishing grinding process and heating annealing to eliminate the spiral tracks, which seriously affects production efficiency and increases costs. The small deformation leveling plug continuous rolling process greatly improves production efficiency, reduces production costs, and improves longitudinal dimensions and performance quality; it is beneficial to eliminate oblique rolling threads, even longitudinal deformation, improve dimensional accuracy, and reduce subsequent finishing grinding processes.

[0013] 3. The present invention heats the solid round tube billet to increase the temperature of the tube billet to facilitate subsequent processing, and then perforates the billet to form a rough tube, and then performs oblique rolling and diameter expansion rolling on the rough tube to form a rough tube; the rough tube is subjected to oblique rolling and strengthening rolling to improve the dimensional accuracy and surface quality of the steel tube and refine the grains at the same time, thereby improving the mechanical strength of the steel tube; the steel tube is subjected to controlled cooling treatment to improve the comprehensive mechanical properties of the steel tube.

[0014] 4. The present invention manufactures a seamless steel pipe with a diameter of 2000 mm through the above process steps. The product has good quality, few processes, relatively low production cost and large production capacity. It can meet the characteristics of high quality requirements, cost sensitivity and high output requirements for power steam pipeline construction. The production organization is flexible, the production efficiency is high, and large-scale automated production can be achieved, which is particularly suitable for the construction needs of large-scale natural gas pipeline networks.

[0015] 5. The present invention can produce the product in one fire. Heating only requires heating of the tube blank, and no heat treatment and reheating are required, which saves energy and improves performance. The online organization control method with controlled cooling as the core has completely reversed the passive situation of seamless steel pipes that were overly dependent on alloying and offline heat treatment in the past, breaking through the bottleneck of traditional technology and opening up new technology and methods for high-quality and efficient manufacturing of steel pipes. DETAILED DESCRIPTION

[0016] The present invention is further described below in conjunction with embodiments: Example

[0017] 1. P92 Steel Composition The composition of the refined molten steel was analyzed and the content of each element is shown below.

[0018] C: 0.07~0.13%, Si: ≤0.50%, Mn: 0.30~0.60%, P: ≤0.015%, S: ≤0.005%, Cr: 8.50~9.50%, Ni: ≤0.40%, Mo: 0.30~0.60%, Cu: ≤0.50b%, Nb: ≤0.04~0.09%, V: 0.15~0.25%, Ti: ≤0.01%, W: 1.5-2%, N:: 0.03-0.07%, O: ≤30ppm%, H: ≤2ppm%, the remainder is Fe and unavoidable impurities.

[0019] 2. Production process of continuous casting round tube with outer diameter of 1300mm: The refined molten steel is continuously cast into a solid continuous casting round tube billet with an outer diameter of 1300 mm.

[0020] The continuous casting process sequentially undergoes tundish electromagnetic stirring, secondary electromagnetic stirring and terminal electromagnetic stirring.

[0021] The pulling speed is 0.10 m / min.

[0022] The length of the central crack is ≤120mm.

[0023] The depth of surface cracks, pits and flat areas is ≤20mm.

[0024] The curvature of the tube billet is ≤10mm per meter, and the total curvature is not more than 0.6% of the total length.

[0025] 3. 2000mm seamless pipe production process: 1. Cut the continuous casting round tube billet to obtain a solid round tube billet with an outer diameter of 1300mm and a single length of 2400~4000mm.

[0026] 2. Place the round tube in a chamber furnace or a trolley heating furnace for heating. The heating rate is controlled at 150°C / h. The maximum temperature of the tube is 1250°C and the holding time is 480 min.

[0027] 3. Use a tapered roller perforator to perforate and obtain a rough tube with an outer diameter of 1550mm and a wall thickness of 300mm. The use of tapered rollers for perforation is convenient for eliminating defects such as central looseness and cracks in large-diameter continuous casting round billets, which is conducive to the circumferential flow and deformation of metals and is more suitable for producing large-diameter seamless steel pipes with billets with a relatively small diameter relative to the finished product.

[0028] During the perforation process, for extra-large diameter thick-walled perforations, the perforation is circumferential expansion perforation, and the elongation of the perforation is about 2.5~3. In this way, the wall thickness of the punched rough tube is the most uniform, which prepares for the subsequent tube rolling.

[0029] 5. Use a two-roller oblique rolling mill to diagonally roll and expand the rough pipe to obtain a rough pipe with an outer diameter of 1650 mm and a wall thickness of 250 mm. Selecting a tapered roller for rolling facilitates the deformation and expansion of the rough pipe, which is suitable for subsequent pipe rolling. In the process of pipe rolling and expansion, the oblique rolling mill considers the purpose and rolling capacity of subsequent ultra-large diameter continuous rolling, and the designed oblique rolling and expansion hole parameters are: the deformation not only meets the size requirements of the rolling feed, but also takes into account the influence of the rolling deformation ratio on the surface quality of the longitudinal rolling extension, so that the rough pipe rolled out has the best quality.

[0030] 6. The rough pipe after oblique rolling is subjected to leveling oblique rolling by an oblique rolling mill. The temperature of the steel pipe during leveling oblique rolling is 1120℃~1200℃. The rolling temperature of this process comes entirely from the residual heat of the oblique rolling expansion in the previous process. A closed deformation space is formed by the built-in leveling plug die and two external active rollers, which generates huge shear force and rolling force, and realizes the unique internal extrusion and external pressure double-sided rolling. The contact area is large and the deformation is uniform. The inner and outer surface spiral tracks caused by oblique rolling expansion, as well as ultra-large diameter casting defects such as chemical composition segregation are eliminated to the greatest extent, the grain nucleation rate is increased, the grains are refined, and precipitation strengthening and dislocation strengthening of the oblique rolling process are realized. The steel pipe with excellent size and performance is obtained, with a diameter of 1750mm and a wall thickness of 230mm. There is no visible spiral track on the surface, and the spiral track height is ≤0.1mm.

[0031] 7. Use 1800 reciprocating sizing machine for sizing. After hot sizing, the outer diameter of the steel pipe is 1650mm and the wall thickness is 230mm.

[0032] Sizing characteristics: The reciprocating sizing machine has a large diameter reduction, a set of sizing hole types can produce a large size group of sizing finished products, the reciprocating sizing machine has a low investment cost, and a set of hole types can produce a variety of finished product specifications; Disadvantages: The reciprocating sizing machine is hot processing, there is burning, the accuracy is not too high, and the general tolerance range is large. The finished product can be directly produced (subsequent shot blasting treatment), and internal and external grinding will be increased for higher precision.

[0033] 8. After hot rolling and sizing of carbon steel and alloy steel, the steel pipe is subjected to online controlled cooling, the starting temperature of controlled cooling is ≥860°C, and the cooling rate is greater than 600°C / min. The waste heat of online controlled cold rolling effectively utilizes energy and improves the efficiency of heat treatment. At the same time, the precipitation strengthening structure after uniform oblique rolling and sizing is completely and effectively preserved. The strengthening of the low alloy steel of the present invention mainly relies on the dislocation strengthening of rolling deformation strengthening and the precipitation strengthening of carbides. Therefore, dislocation strengthening is the basis, and in the subsequent online controlled cold cooling phase transformation process, fine acicular ferrite or multi-directional bainite structure with large-angle grain orientation is induced to significantly improve the strength of the steel.

[0034] 9. After the steel pipe is cooled online, the hot outer diameter shrinks from 1660mm to 1650mm in the cold state. The wall thickness becomes 230mm after internal and external sandblasting and removal of oxide scale.

[0035] 10. Use 2500 medium frequency pipe expansion and sizing machine, the sizing size is 2000mm and the wall thickness is 200mm.

[0036] Sizing characteristics: The inner diameter dimensional accuracy of the steel pipe sizing by medium frequency is relatively high, the cost is low, and the yield rate is high; it is suitable for the production of thick-walled seamless steel pipes with particularly large outer diameters and high inner diameter requirements.

[0037] 11. Carry out online flaw detection on steel pipes, take samples to test the quality of steel pipes, saw blind areas, and cut to size.

[0038] 12. Product labeling and storage.

[0039] 4. Application: The seamless steel pipes obtained were tested in high temperature environments or extremely cold environments and high-pressure pipelines. The results showed that they can meet the safety requirements of high temperature, extreme cold and high pressure, and can significantly reduce construction costs.

[0040] V. Summary: The present invention utilizes a solid round tube blank with a diameter of 1300 mm to produce a seamless steel tube with a diameter of 2000 mm and a wall thickness of 230 mm. This method not only produces products with high dimensional accuracy and excellent organizational performance, but also has simple procedures, moderate equipment investment, compact production, a yield rate of 91%, and a single production line production capacity of 600,000 tons / year.

[0041] The maximum diameter of the solid round tube blank of the present invention is 1300mm. If the diameter of the tube blank is too small, the outer diameter of the rough tube produced will be too small. To meet the requirement of 2000mm outer diameter of the finished steel pipe, on the one hand, the number of processes will increase, the equipment investment will be too large, the process time will be long, and the production efficiency will be low; on the other hand, the process time is long, the steel pipe cools down quickly, and the subsequent expansion and sizing temperature drops too quickly, requiring reheating, and the one-fire material process is difficult to achieve. Therefore, the present invention preferably uses a tube blank with a diameter of 1300mm as the raw material.

[0042] The heating rate of the present invention is 150-200°C / h during heating, until the temperature of the solid round tube reaches 1250°C and then kept warm for 480 minutes. If the heating rate is too fast, due to the influence of heat transfer efficiency, large temperature stress will be formed on the inner and outer surfaces of the tube, thereby causing cracking during the heating process of the tube, affecting the quality of the product, so the heating rate is designed to be 150°C / h.

[0043] If the temperature of the tube billet is higher than 1280℃, it is easy to cause overburning of the tube billet and cause intergranular decarburization. If it is too low, it will reduce the high-temperature rolling plasticity of the tube billet, greatly increase the rolling force, and cause equipment damage. If the holding time is too low, it will cause uneven temperatures on the inner and outer surfaces of the tube billet, inconsistent plasticity during piercing and rolling, and uneven deformation of the wall thickness of the steel pipe. Therefore, the design holding time is 480 minutes.

[0044] The diameter of the leveling plug of the leveling cross rolling of the present invention is 1000-1400 mm, and the temperature of the workpiece of the leveling cross rolling is 1120-1200° C. The leveling cross rolling deformation is a small deformation leveling plug rolling.

[0045] The present invention is an online organization control method with controlled cooling of seamless steel pipe as the core. For ordinary low alloy steel materials to produce steel pipes, when online controlled cooling is used, the temperature of the sizing steel pipe is cooled to below 200°C within 1 minute by high-pressure water spraying equipment when the residual heat of continuous rolling sizing is ≥800°C, the cooling rate of the inner and outer surfaces of the steel pipe is 50~150°C / S, and the temperature difference of the steel pipe is ≤30°C. That is, the precipitation strengthening phase structure of the material under the rolling state is ensured to be completely retained by making the cooling rate of the steel pipe greater than 600°C / min through the controlled cooling process before the cooling phase change occurs. If the rolling outlet temperature is too low during controlled cooling, the cooling phase change has occurred and the desired organization cannot be obtained; if the temperature is too high, the deformation strengthening and precipitation strengthening effects of hot rolling will be eliminated, resulting in the performance not meeting the requirements, so it is designed to be 800~960°C.

[0046] In addition, the present invention can also adopt other sizing methods at different process stages: A 4500-ton cold-drawn sizing machine is used, with a sizing size of 1500mm and a wall thickness of 150mm; Features: Cold drawing is done with inner and outer dies, with high dimensional accuracy, high production efficiency and low production cost. It can be used for finished products with high production precision.

[0047] Adopt 1500 cold rolling sizing mill, sizing size 1016mm, wall thickness 70mm; Features: The dimensional accuracy of 1500 cold-rolled sizing steel pipe is close to or exceeds that of machined products, and the yield rate is much higher than that of machined products. For products with particularly high dimensional accuracy, cold-rolled sizing machines can be used to produce finished products; In summary, the above are only preferred embodiments of the present invention and are not intended to limit the scope of implementation of the present invention. All equivalent changes and modifications to the shapes, structures, features and spirits described in the claims of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for manufacturing an ultra-large seamless steel pipe with a diameter of 2000 mm, characterized in that: After the solid round tube billet is heated, it is obliquely rolled by a micro-expansion process to obtain a rough tube. The rough tube is made into a rough tube with an enlarged diameter by the oblique rolling and expansion process. The diameter is further enlarged by the leveling oblique rolling process, and the dimensional accuracy and surface quality of the rough tube are improved. The semi-finished steel tube with a diameter of 2000mm is obtained by the controlled rolling and sizing process. The semi-finished steel tube is directly obtained by heat treatment, flaw detection and finishing processes to obtain a 2000mm ultra-large seamless steel tube finished product: The maximum diameter of the solid round tube is 1300 mm; The solid round tube blank is processed with a center positioning hole before heating; The outer diameter of the rough pipe obtained by the micro-expansion process is 1550mm and the wall thickness is 300mm; The outer diameter of the rough tube obtained after the oblique rolling and expansion is 1650mm and the wall thickness is 250mm; The outer diameter of the steel pipe obtained after the leveling and oblique rolling process is 1750 mm and the wall thickness is 230 mm; The leveling oblique rolling process is to roll the rough tube through a conical oblique rolling roller at an oblique rolling diameter expansion rate not exceeding 6.2%; After the rough tube is sized by controlled rolling, the maximum outer diameter of the steel tube is 2000 mm and the wall thickness is 230 mm.

2. The method for manufacturing a 2000mm diameter super-large seamless steel pipe according to claim 1, characterized in that: The controlled rolling and sizing process is as follows: the rough pipe after leveling and oblique rolling is heated online by 200°C, the pipe body temperature is 1050°C, the head-to-tail temperature difference is ±15°C, the radial-circumferential temperature difference is ±5°C, and temperature-controlled cooling is performed after sizing.

3. The method for manufacturing a 2000mm diameter super-large seamless steel pipe according to claim 1, characterized in that: The solid round tube billet is heated at a heating rate of 150-200°C / h until the temperature of the solid round tube billet reaches 1250°C and then kept warm for 460-500 min.

4. The method for manufacturing a super-large seamless steel pipe with a diameter of 2000 mm according to claim 1, characterized in that: The online organizational control method with controlled cooling of seamless steel pipe as the core, during online controlled cooling, when the residual heat of continuous rolling sizing is ≥800℃, the temperature of the sizing steel pipe is cooled to below 200℃ within 1 minute through high-pressure water spraying equipment, the cooling rate of the inner and outer surfaces of the steel pipe is 50~150℃ / S, and the temperature difference of the entire length of the steel pipe is ≤30℃.