A method for preparing corrosion-resistant alloy structural steel and seamless steel pipe thereof

Abstract

The invention discloses a method for preparing a corrosion-resistant alloy structural steel and a seamless steel pipe thereof, which comprises, by weight percentage, 0.06% to 0.09% C, 0.21% to 0.31% Si, 0.37% to 0.43% Mn, 2.01% to 2.11% Cr, 0.008% to 0.011% P, 0.001% to 0.004% S, 0.51% to 0.58% Al, 0.03% to 0.06% Cu, 0.01% ~0.02% Ni, 0.31%~0.36% Mo, 0.0009%~0.0013% O, 0.0025%~0.0032% RE, 0.0057%~0.0071% N, and the balance is Fe. The present invention optimizes the composition, adds trace rare earth elements RE, and at the same time puts forward strict requirements on the control of residual harmful elements P and S, which lays a foundation for improving the mechanical properties such as strength, plasticity and toughness of the material and improving the corrosion resistance.

Description

Technical Field

[0001] The invention relates to the field of alloy structural steel, and in particular to a method for preparing corrosion-resistant alloy structural steel and a seamless steel pipe thereof. Background Art

[0002] Oil pipe is an important pipeline for the transportation of liquids such as oil and natural gas. The uses of oil pipe include liquid transportation: oil pipe is mainly used for long-distance transportation of liquids such as oil and natural gas. Through pumping and pressure systems, liquids such as oil and natural gas are transported from the mining site to storage facilities or transportation vehicles. Pipeline transportation: oil pipe can be used as part of the pipeline transportation system to transport liquids such as oil and natural gas from the mining site to processing plants, storage tank stations and users along the line. Oil and gas separation: oil pipe can also be used in the oil and gas separation process of oil and gas fields to separate oil and natural gas from underground and perform preliminary processing and separation. Downhole operations: In downhole operations, oil pipe is used to connect the wellhead and downhole equipment for drilling, well repair, logging and other operations. Chemical pipeline: oil pipe can be used as part of the chemical pipeline system to transport various chemical raw materials and products, such as acids, alkalis, solvents, etc.

[0003] According to the material, the oil pipe can be divided into carbon steel oil pipe, alloy steel oil pipe, stainless steel oil pipe, etc. Oil pipes of different materials have different corrosion resistance, strength and high temperature resistance.

[0004] Classification by processing method: Petroleum pipes can be divided into seamless steel pipes and welded steel pipes according to the processing method. Seamless steel pipes are made by seamless rolling or extrusion process, with high strength and corrosion resistance; welded steel pipes are made by welding process, with high flexibility and adaptability.

[0005] In short, oil pipes have many uses and categories. Choosing the right oil pipe according to different needs and occasions is the key to ensuring the safe and stable operation of the pipeline system. At the same time, due to the special properties and uses of oil pipes, the quality requirements for their manufacturing and use are also very strict.

[0006] Traditional alloy structural steel has poor corrosion resistance and short material service life. Therefore, how to improve the corrosion resistance of steel used for petroleum pipe billets has become a major difficulty in the industry. Summary of the invention

[0007] In view of the deficiencies of the prior art, the present invention solves the technical problems by adopting the following technical solution: The corrosion-resistant alloy structural steel described in the present invention comprises, by weight percentage:

[0008] 0.06%~0.1% C, 0.2%~0.5% Si, 0.3%~0.6% Mn, 2%~2.3% Cr, P≤0.015%, S≤0.008%, 0.3%~0.7% Al, Cu≤0.2%, Ni≤0.2%, 0.3%~0.5% Mo, O≤0.003%, 0.001%~0.0045% RE, N≤0.008%, and the balance is Fe.

[0009] A method for preparing corrosion-resistant alloy structural steel comprises the following steps:

[0010] S1: First, electric furnace smelting is carried out. In order to ensure the stability of steel output, the weight of steel materials entering each furnace is controlled: 90±1.0 tons of clean and dry scrap steel and 20±1.0 tons of pig iron. The steel discharge C at the end of the electric furnace is controlled to be 0.03%-0.05%, P≤0.008%. The steel is retained and slag is discharged. The steel is discharged from the eccentric bottom. The steel output is controlled to be 100±1.0 tons. Slag is prevented during the steel discharge process.

[0011] S2: Secondly, LF furnace refining is carried out. During the LF refining process, 100-300 kg of lime is added depending on the sulfur content to produce high-basicity slag, control the binary basicity of the LF furnace final slag, control the S of the molten steel at the end of LF refining to be ≤0.005%, feed aluminum wire before refining and tapping, and control the aluminum content of the LF to be 0.07%-0.1%;

[0012] S3: VD vacuum treatment is then performed, and the ultimate vacuum degree is maintained for 12 minutes. After the VD vacuum is broken, aluminum cake is added to the VD aluminum to increase aluminum, and the aluminum content is controlled to be 0.5%-0.65%. After the aluminum addition is completed, vacuum treatment is performed again, and the added Al is fully stirred. After the VD is completed, the molten steel is soft-blown for 25-50 minutes;

[0013] S4: Continuous casting is then performed, and rare earth elements are controlled by feeding rare earth cored wire into the continuous casting crystallizer;

[0014] S5: Finally, rolling is performed, and the ingot is heated and rolled to obtain round steel.

[0015] Preferably, during the S1 electric furnace smelting and steelmaking process, 2.0 kg / ton of aluminum cake and 150 kg / furnace of calcium carbide are added for early deoxidation of molten steel, 900 kg / furnace of lime and 300 kg / furnace of synthetic slag are added for slag making, and low-carbon ferrochrome, low-carbon ferromanganese and ferrosilicon are added for alloying.

[0016] Preferably, in S4, the number of continuous casting furnaces is controlled to be ≤9, and the superheat of molten steel is controlled, the open casting furnace is ≤35°C, and the continuous casting furnace is ≤25°C; slow drawing speed casting is adopted, and the drawing speed is controlled to be 0.70±0.02m / min, the La in the cored wire is 55%-70%, and the Ce is 30%-45%. In order to prevent large stirring in the crystallizer, the electromagnetic stirring of the crystallizer adopts weak stirring, and the intensity is controlled: current 180±3A, frequency 2±0.2Hz, and steel retention operation is performed, with a steel retention amount of 5±1 tons. The temperature of the ingot entering the slow cooling pit is ≥600°C, and the ingot is slowly cooled to a temperature below 100°C before exiting the pit, and the wire feeding speed is controlled to be 1-2m / min.

[0017] Preferably, in the LF furnace refining process in S2, 50-100 kg of calcium carbide and 100-150 kg of aluminum particles are used for diffusion deoxidation of molten steel to improve the desulfurization capacity of LF refining and control the binary basicity of the LF furnace final slag to 6.0-8.5. After the VD aluminum addition in S3 is completed, vacuum treatment is performed for 3-5 minutes.

[0018] A method for preparing a corrosion-resistant alloy structural steel seamless steel pipe comprises the following steps:

[0019] A1: After the round steel is cut by sawing, it is placed in a heating furnace for high-temperature heating. To ensure that the temperature of the inner and outer surfaces of the round steel is uniform during heating, the round steel must be continuously rolled in the furnace during heating, and then it is taken out of the furnace and sent to the punching machine for punching;

[0020] A2: After the round steel is bitten into the roller, during the repeated rolling process of the roller, a cavity is formed inside, and a qualified rough pipe is punched out under the action of the perforated roller, the upper and lower guide plates and the front head;

[0021] A3: Then the rough pipe is air-cooled to room temperature on a cold table and passed the process requirements test: there are no scratches, pits, depressions and other defects on the surface of the rough pipe that affect the subsequent cold processing. Because there is water cooling during the perforation process, the hardness of the rough pipe is very high and uneven, so it must be annealed, and then slowly cooled after heat preservation. After annealing, the rough pipe is pickled to remove the oxide scale on the inner and outer surfaces, and the surface is phosphated and saponified before cold drawing to the finished steel pipe;

[0022] A4: The finished steel pipe is obtained as seamless steel pipe after heat treatment.

[0023] Preferably, the A1 is heated to a medium-high temperature of 1280°C to 1320°C and kept in the high temperature zone for 10 minutes to 20 minutes. The punching plug adopts a molybdenum-based plug. Because the round steel contains Cr, Mo, Al, and RE alloy, the roller speed of the punching machine must be adjusted to be lower than that of 10# to 45# steel. The roller speed of the punching machine is 10% to 15% lower than that of 10# to 45# steel.

[0024] Preferably, the A3 is kept warm for 30-40 minutes, and the rough tube annealing temperature is controlled at 850°C to 880°C.

[0025] Preferably, the heat treatment process in A4 is: 900°C to 930°C normalizing + 700°C to 720°C tempering.

[0026] The beneficial effects of the present invention are as follows:

[0027] 1. The present invention optimizes the composition design, adds trace rare earth elements RE, and puts forward strict requirements on the control of residual harmful elements P and S, which lays a foundation for improving the mechanical properties such as strength, plasticity and toughness of the material and improving the corrosion resistance. The electric furnace strictly controls the P content of molten steel, strengthens the pre-deoxidation of molten steel, and LF refines high-basicity slag to improve the deoxidation and desulfurization capacity of molten steel. The VD process adjusts the Al element, adopts the method of vacuum first, then adding Al, and then vacuuming, which not only ensures the vacuum degassing and inclusion removal effect, but also improves the uniformity of the composition.

[0028] 2. Rare earth elements are adjusted by feeding rare earth into the continuous casting crystallizer, which not only improves the element recovery rate, but also prevents water plugging accidents caused by adding rare earth into the ladle or the intermediate ladle, and can effectively improve the recovery rate of rare earth elements. The hot working process of the tube billet adopts high-temperature heating, and molybdenum-based plugs are used instead of traditional material plugs, which improves the surface quality of the steel pipe, reduces the consumption of plugs and significantly improves the production efficiency.

[0029] 3. The rough pipe adopts a reasonable annealing temperature to improve the cold processing performance of the rough pipe and reduce mold loss. The finished pipe adopts a reasonable heat treatment temperature to improve the comprehensive mechanical properties of the finished pipe. Through the above collaborative efforts, not only the surface quality and production efficiency of the steel pipe are improved, but also the strong plasticity mechanical properties and corrosion resistance of the material are improved. When the steel pipe is used in the petroleum and petrochemical refining of high-sulfur crude oil, it reduces the corrosion of hydrogen sulfide to the material and the corrosion of H and Cl ions mixed in seawater during seabed oil mining. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a flow chart of the preparation method of the corrosion-resistant alloy structural steel of the present invention;

[0031] Figure 2 The present invention is a flow chart of the method for preparing the corrosion-resistant alloy structural steel seamless steel pipe. DETAILED DESCRIPTION

[0032] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The embodiments of the present invention are provided for the purpose of illustration and description, and are not intended to be exhaustive or to limit the present invention to the disclosed forms. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiments are selected and described in order to better illustrate the principles and practical applications of the present invention, and to enable those of ordinary skill in the art to understand the present invention and thereby design various embodiments with various modifications suitable for specific uses.

[0033] Example 1

[0034] A corrosion-resistant alloy structural steel comprises, by weight percentage, 0.08% C, 0.25% Si, 0.38% Mn, 2.05% Cr, 0.010% P, 0.003% S, 0.56% Al, 0.06% Cu, 0.01% Ni, 0.33% Mo, 0.0012% O, 0.0063% N, 0.0027% RE, and the balance is Fe.

[0035] The process is 100-ton electric furnace smelting - LF refining - VD vacuum treatment - continuous casting - rolling - tube blank hot processing - rough tube annealing - rough tube cold processing - finished steel tube heat treatment;

[0036] Electric furnace process:

[0037] Weight of steel materials entering the furnace: 90.5 tons of clean and dry scrap steel + 19.8 tons of pig iron. The final discharge of the electric furnace is C0.04%, P0.007%. The output of steel is 100.6 tons. During the steel tapping process, 2.0 kg of aluminum cake / ton and 150 kg of calcium carbide / furnace are added. Slag-making materials are added: 900 kg of lime / furnace and 300 kg of slag / furnace.

[0038] LF furnace refining process:

[0039] During the LF refining process, 80 kg of calcium carbide and 135 kg of aluminum particles are used for diffusion deoxidation of the molten steel slag surface. At the same time, 200 kg of lime is added during the LF refining process to control the binary basicity of the LF furnace final slag to 7.5. At the end of LF refining, the S content of the molten steel is 0.002%, and the aluminum content of the LF is 0.083%.

[0040] VD vacuum treatment process:

[0041] The ultimate vacuum degree is maintained for 12 minutes, and aluminum cakes are added to increase aluminum in VD to control the aluminum content to 0.63%. After the aluminum addition is completed, vacuum treatment is carried out for another 4 minutes. After the VD is completed, the molten steel is soft-blown for 36 minutes.

[0042] Continuous casting process:

[0043] The superheat of molten steel is 23℃; the pulling speed is 0.70±0.02m / min; the rare earth elements are controlled by feeding rare earth cored wire into the continuous casting crystallizer, the wire feeding speed is controlled at 1.5m / min, the crystallizer electromagnetic stirring control intensity: current 180±3A, frequency 2±0.2Hz, steel retention operation is carried out, the steel retention amount is 4.5 tons, the temperature of the ingot entering the slow cooling pit is 625℃, and the ingot temperature is slowly cooled to 85℃ before leaving the pit.

[0044] Rolling process:

[0045] The ingot is heated and rolled to obtain round steel.

[0046] Hot working process of tube blank:

[0047] After the round steel is cut, it is placed in a heating furnace and heated to 1290℃ and kept warm for 18 minutes. Then it is taken out of the furnace and sent to a piercing machine for perforation. The perforating head is made of molybdenum-based material to produce qualified rough pipes.

[0048] Annealing of rough pipe:

[0049] After the rough pipe with smooth inner and outer surfaces is tested and qualified, it is annealed at 865℃, kept warm for 32 minutes and slowly cooled, and the surface hardness is 168HB.

[0050] Cold processing of rough pipe:

[0051] After annealing, the rough pipe is pickled to remove the oxide scale on the inner and outer surfaces, and the surface is phosphated and saponified before cold drawing (cold rolling) and other processing techniques to produce the finished steel pipe.

[0052] Heat treatment of finished steel pipe:

[0053] The finished steel pipe undergoes 915℃ normalizing + 705℃ tempering heat treatment.

[0054] Example 2

[0055] A corrosion-resistant alloy structural steel comprises, by weight percentage, 0.07% C, 0.24% Si, 0.37% Mn, 2.07% Cr, 0.009% P, 0.002% S, 0.54% Al, 0.05% Cu, 0.01% Ni, 0.32% Mo, 0.0011% O, 0.0057% N, 0.0028% RE, and the balance is Fe.

[0056] The process is 100-ton electric furnace smelting - LF refining - VD vacuum treatment - continuous casting - rolling - tube blank hot processing - rough tube annealing - rough tube cold processing - finished steel tube heat treatment;

[0057] Electric furnace process:

[0058] Weight of steel materials entering the furnace: 90.7 tons of clean and dry scrap steel + 19.9 tons of pig iron. C0.05% and P0.007% of steel are discharged at the end of the electric furnace. The amount of steel discharged is 100.8 tons. During the steel discharge process, 2.0 kg of aluminum cakes / ton and 150 kg of calcium carbide / furnace are added. Slag-making materials are added: 900 kg of lime / furnace and 300 kg of slag / furnace.

[0059] LF furnace refining process:

[0060] During the LF refining process, 75 kg of calcium carbide and 140 kg of aluminum particles are used for diffusion deoxidation of the molten steel slag surface. At the same time, 180 kg of lime is added during the LF refining process to control the binary basicity of the LF furnace final slag to 6.9. At the end of LF refining, the S content of the molten steel is 0.002%, and the aluminum content of the LF is 0.078%.

[0061] VD vacuum treatment process:

[0062] The ultimate vacuum degree is maintained for 12 minutes, and aluminum cakes are added to increase aluminum in VD, and the aluminum content is controlled to be 0.60%. After the aluminum addition is completed, vacuum treatment is carried out for another 5 minutes. After the VD is completed, the molten steel is soft-blown for 35 minutes.

[0063] Continuous casting process:

[0064] The superheat of molten steel is 20℃; the pulling speed is 0.70±0.02m / min; the rare earth elements are controlled by feeding rare earth cored wire into the continuous casting crystallizer, the wire feeding speed is controlled at 1.7m / min, the crystallizer electromagnetic stirring control intensity: current 180±3A, frequency 2±0.2Hz, steel retention operation is carried out, the steel retention amount is 4.7 tons, the temperature of the ingot entering the slow cooling pit is 620℃, and the ingot temperature is slowly cooled to 90℃ before leaving the pit.

[0065] Rolling process:

[0066] The ingot is heated and rolled to obtain round steel.

[0067] Hot working process of tube blank:

[0068] After the round steel is cut, it is placed in a heating furnace and heated to 1295℃ and kept warm for 17 minutes. It is then taken out of the furnace and sent to a piercing machine for perforation. The perforating head is made of molybdenum-based material to produce qualified rough pipes.

[0069] Annealing of rough pipe:

[0070] After the rough pipe with smooth inner and outer surfaces is tested and qualified, it is annealed at 875℃, kept warm for 33 minutes and slowly cooled, and the surface hardness is 165HB.

[0071] Cold processing of rough pipe:

[0072] After annealing, the rough pipe is pickled to remove the oxide scale on the inner and outer surfaces, and the surface is phosphated and saponified before cold drawing (cold rolling) and other processing techniques to produce the finished steel pipe.

[0073] Heat treatment of finished steel pipe:

[0074] The finished steel pipe undergoes 918℃ normalizing + 707℃ tempering heat treatment.

[0075] Example 3

[0076] A corrosion-resistant alloy structural steel comprises, by weight percentage, 0.08% C, 0.27% Si, 0.42% Mn, 2.04% Cr, 0.008% P, 0.001% S, 0.58% Al, 0.04% Cu, 0.01% Ni, 0.35% Mo, 0.0013% O, 0.0061% N, 0.0025% RE, and the balance is Fe.

[0077] The process is 100-ton electric furnace smelting - LF refining - VD vacuum treatment - continuous casting - rolling - tube blank hot processing - rough tube annealing - rough tube cold processing - finished steel tube heat treatment;

[0078] Electric furnace process:

[0079] Weight of steel materials entering the furnace: 90.9 tons of clean and dry scrap steel + 19.1 tons of pig iron. The final discharge of the electric furnace is C0.04%, P0.006%. The output of steel is 100.4 tons. During the steel tapping process, 2.0 kg of aluminum cake / ton and 150 kg of calcium carbide / furnace are added. Slag-making materials are added: 900 kg of lime / furnace and 300 kg of slag / furnace.

[0080] LF furnace refining process:

[0081] During the LF refining process, 70 kg of calcium carbide and 145 kg of aluminum particles are used for diffusion deoxidation of the molten steel slag surface. At the same time, 230 kg of lime is added during the LF refining process to control the binary basicity of the LF furnace final slag to 7.4. At the end of LF refining, the S content of the molten steel is 0.003%, and the aluminum content of the LF is 0.088%.

[0082] VD vacuum treatment process:

[0083] The ultimate vacuum is maintained for 12 minutes, and aluminum cakes are added to increase aluminum in VD to control the aluminum content to 0.64%. After the aluminum addition is completed, vacuum treatment is carried out for another 5 minutes. After the VD is completed, the molten steel is soft-blown for 40 minutes.

[0084] Continuous casting process:

[0085] The superheat of molten steel is 22℃; the pulling speed is 0.70±0.02m / min; the rare earth elements are controlled by feeding rare earth cored wire into the continuous casting crystallizer, the wire feeding speed is controlled at 1.3m / min, the crystallizer electromagnetic stirring control intensity: current 180±3A, frequency 2±0.2Hz, steel retention operation is carried out, the steel retention amount is 4.7 tons, the temperature of the ingot entering the slow cooling pit is 630℃, and the ingot temperature is slowly cooled to 95℃ before leaving the pit.

[0086] Rolling process:

[0087] The ingot is heated and rolled to obtain round steel.

[0088] Hot working process of tube blank:

[0089] After the round steel is cut, it is placed in a heating furnace and heated to 1308℃ and kept warm for 16 minutes. Then it is taken out of the furnace and sent to a piercing machine for perforation. The perforating head is made of molybdenum-based material to produce qualified rough pipes.

[0090] Annealing of rough pipe:

[0091] After the rough pipe with smooth inner and outer surfaces is tested and qualified, it is annealed at 868℃, kept warm for 34 minutes and slowly cooled, and the surface hardness is 169HB.

[0092] Cold processing of rough pipe:

[0093] After annealing, the rough pipe is pickled to remove the oxide scale on the inner and outer surfaces, and the surface is phosphated and saponified before cold drawing (cold rolling) and other processing techniques to produce the finished steel pipe.

[0094] Heat treatment of finished steel pipe:

[0095] The finished steel pipe undergoes 919℃ normalizing + 713℃ tempering heat treatment.

[0096] Example 4

[0097] A corrosion-resistant alloy structural steel comprises, by weight percentage, 0.06% C, 0.31% Si, 0.39% Mn, 2.11% Cr, 0.011% P, 0.004% S, 0.51% Al, 0.03% Cu, 0.02% Ni, 0.31% Mo, 0.0009% O, 0.0071% N, 0.0032% RE, and the balance is Fe.

[0098] The process is 100-ton electric furnace smelting - LF refining - VD vacuum treatment - continuous casting - rolling - tube blank hot processing - rough tube annealing - rough tube cold processing - finished steel tube heat treatment;

[0099] Electric furnace process:

[0100] Weight of steel materials entering the furnace: 89.7 tons of clean and dry scrap steel + 20.6 tons of pig iron. The final discharge of the electric furnace is C0.05%, P0.008%. The output of steel is 100.2 tons. During the steel-making process, 2.0 kg of aluminum cakes / ton and 150 kg of calcium carbide / furnace are added. Slag-making materials are added: 900 kg of lime / furnace and 300 kg of slag / furnace.

[0101] LF furnace refining process:

[0102] During the LF refining process, 85 kg of calcium carbide and 120 kg of aluminum particles are used for diffusion deoxidation of the molten steel slag surface. At the same time, 210 kg of lime is added during the LF refining process to control the binary basicity of the LF furnace final slag to 8.0. At the end of LF refining, the S content of the molten steel is 0.004%, and the aluminum content of the LF is 0.095%.

[0103] VD vacuum treatment process:

[0104] The ultimate vacuum degree is maintained for 12 minutes, and aluminum cakes are added to increase aluminum in VD, and the aluminum content is controlled to be 0.59%. After the aluminum addition is completed, vacuum treatment is carried out for another 4 minutes. After the VD is completed, the molten steel is soft-blown for 37 minutes.

[0105] Continuous casting process:

[0106] The superheat of molten steel is 25℃; the pulling speed is 0.70±0.02m / min; the rare earth elements are controlled by feeding rare earth cored wire into the continuous casting crystallizer, the wire feeding speed is controlled at 1.3m / min, the crystallizer electromagnetic stirring control intensity: current 180±3A, frequency 2±0.2Hz, steel retention operation is carried out, the steel retention amount is 4.9 tons, the temperature of the ingot entering the slow cooling pit is 620℃, and the ingot temperature is slowly cooled to 75℃ before leaving the pit.

[0107] Rolling process:

[0108] The ingot is heated and rolled to obtain round steel.

[0109] Hot working process of tube blank:

[0110] After the round steel is cut, it is placed in a heating furnace and heated to 1315℃ and kept warm for 13 minutes. Then it is taken out of the furnace and sent to a piercing machine for perforation. The perforating head is made of molybdenum-based material to produce qualified rough pipes.

[0111] Annealing of rough pipe:

[0112] After the rough pipe with smooth inner and outer surfaces is tested and qualified, it is annealed at 852℃, kept warm for 38 minutes and slowly cooled, and the surface hardness is 166HB.

[0113] Cold processing of rough pipe:

[0114] After annealing, the rough pipe is pickled to remove the oxide scale on the inner and outer surfaces, and the surface is phosphated and saponified before cold drawing (cold rolling) and other processing techniques to produce the finished steel pipe.

[0115] Heat treatment of finished steel pipe:

[0116] The finished steel pipe undergoes 925℃ normalizing + 717℃ tempering heat treatment.

[0117] Example 5

[0118] A corrosion-resistant alloy structural steel comprises, by weight percentage, 0.09% C, 0.21% Si, 0.43% Mn, 2.01% Cr, 0.010% P, 0.002% S, 0.55% Al, 0.06% Cu, 0.02% Ni, 0.36% Mo, 0.0012% O, 0.0069% N, 0.0030% RE, and the balance is Fe.

[0119] The process is 100-ton electric furnace smelting - LF refining - VD vacuum treatment - continuous casting - rolling - tube blank hot processing - rough tube annealing - rough tube cold processing - finished steel tube heat treatment;

[0120] Electric furnace process:

[0121] Weight of steel materials entering the furnace: 90.1 tons of clean and dry scrap steel + 20.2 tons of pig iron. The final discharge of the electric furnace is C0.04%, P0.007%. The output of steel is 100.7 tons. During the steel tapping process, 2.0 kg of aluminum cake / ton and 150 kg of calcium carbide / furnace are added. Slag-making materials are added: 900 kg of lime / furnace and 300 kg of slag / furnace.

[0122] LF furnace refining process:

[0123] During the LF refining process, 90 kg of calcium carbide and 115 kg of aluminum particles are used for diffusion deoxidation of the molten steel slag surface. At the same time, 220 kg of lime is added during the LF refining process to control the binary basicity of the LF furnace final slag to 7.2. At the end of LF refining, the S content of the molten steel is 0.004%, and the aluminum content of the LF is 0.082%.

[0124] VD vacuum treatment process:

[0125] The ultimate vacuum degree is maintained for 12 minutes, and aluminum cakes are added to increase aluminum in VD, and the aluminum content is controlled to be 0.61%. After the aluminum addition is completed, vacuum treatment is carried out for another 3 minutes. After the VD is completed, the molten steel is soft-blown for 36 minutes.

[0126] Continuous casting process:

[0127] The superheat of molten steel is 20℃; the pulling speed is 0.70±0.02m / min; the rare earth elements are controlled by feeding rare earth cored wire into the continuous casting crystallizer, the wire feeding speed is controlled at 1.6m / min, the crystallizer electromagnetic stirring control intensity: current 180±3A, frequency 2±0.2Hz, steel retention operation is carried out, the steel retention amount is 4.9 tons, the temperature of the ingot entering the slow cooling pit is 622℃, and the ingot temperature is slowly cooled to 83℃ before leaving the pit.

[0128] Rolling process:

[0129] The ingot is heated and rolled to obtain round steel.

[0130] Hot working process of tube blank:

[0131] After the round steel is cut, it is placed in a heating furnace and heated to 1305℃ and kept warm for 14 minutes. Then it is taken out of the furnace and sent to a piercing machine for perforation. The perforating head is made of molybdenum-based material to produce qualified rough pipes.

[0132] Annealing of rough pipe:

[0133] After the rough pipe with smooth inner and outer surfaces is tested and qualified, it is annealed at 860℃, kept warm for 34 minutes and slowly cooled, and the surface hardness is 160HB.

[0134] Cold processing of rough pipe:

[0135] After annealing, the rough pipe is pickled to remove the oxide scale on the inner and outer surfaces, and the surface is phosphated and saponified before cold drawing (cold rolling) and other processing techniques to produce the finished steel pipe.

[0136] Heat treatment of finished steel pipe:

[0137] The finished steel pipe undergoes 911℃ normalizing + 709℃ tempering heat treatment.

[0138] Comparative Example 1

[0139] Compared with Example 1, in Comparative Example 1, no rare earth element was added during the composition design, and other operations were the same as those in Example 1.

[0140] Comparative Example 2

[0141] Compared with Example 1, Comparative Example 2 has the following main differences: the LF furnace does not use high-basicity slag, the slag basicity is controlled to be 4.0, and other operations are the same as those in Example 1.

[0142] Comparative Example 3

[0143] Compared with Example 1, Comparative Example 3 mainly differs in that the adjustment of rare earth elements is changed to feeding rare earth wire into the big bag after the VD vacuum is completed, and other operations are the same as those in Example.

[0144] Comparative Example 4

[0145] Compared with Example 1, Comparative Example 4 mainly differs in that the tube blank heating process is different, the heating temperature of the round steel is reduced to 1200° C., and other operations are the same as those in Example 1.

[0146] Comparative Example 5

[0147] Compared with Example 1, Comparative Example 5 mainly differs in that the normalizing temperature is lowered during heat treatment of the finished pipe: the finished steel pipe is subjected to 880°C normalizing + 705°C tempering heat treatment, and other operations are the same as those of the example.

[0148] The comprehensive properties of the seamless steel pipes made from Examples 1-5 and Comparative Examples 1-5 were tested, and the results of the comprehensive properties test are shown in the following table:

[0149]

[0150] Steel pipe corrosion rate determination standard: The corrosion rate of the material placed in an 80℃ HCl-H2O system for 24 hours, where the HCl concentration is 3%;

[0151] According to the data in the table, through the optimization and adjustment of the chemical composition, the strict control of the residual harmful elements P and S, especially the addition of rare earth elements, the foundation has been laid for the improvement of the mechanical properties and corrosion resistance of the material; in addition, through the optimization of electric furnace smelting, LF refining, VD vacuum treatment, continuous casting process and pipe threading process parameters, the purity, strength, elongation and other indicators of the material have been effectively improved, the surface quality of the seamless steel pipe has been improved, and the pipe threading efficiency has been improved, thereby stably improving the comprehensive performance of the material.

[0152] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field and related fields without creative work should fall within the scope of protection of the present invention. The structures, devices and operating methods not specifically described and explained in the present invention are implemented according to the conventional means in the field unless otherwise specified and limited.

Claims

1. A corrosion-resistant alloy structural steel, characterized in that: Included by weight percentage: 0.06% to 0.09% C, 0.21% to 0.31% Si, 0.37% to 0.43% Mn, 2.01% to 2.11% Cr, 0.008% to 0.011% P, 0.001% to 0.004% S, 0.51% to 0.58% Al, 0.03% to 0.06% Cu, 0.01% to 0.02% Ni, 0.31% to 0.36% Mo, 0.0009% to 0.0013% O, 0.0025% to 0.0032% RE, 0.0057% to 0.0071% N, the balance is Fe; The preparation method of the corrosion-resistant alloy structural steel comprises the following steps: S1: First, electric furnace smelting is carried out, and the end point of the electric furnace is controlled to release steel C: 0.03%-0.05%, P≤0.008%; S2: LF furnace refining is then carried out. During the LF refining process, 100-300 kg of lime is added to control the S of the molten steel at the end of LF refining to be ≤0.005%. Aluminum wire is fed before refining and the aluminum content of the LF is controlled to be 0.07% to 0.1%; S3: VD vacuum treatment is then performed. After the VD vacuum is broken, aluminum cake is added to the VD aluminum to control the aluminum content to 0.5%-0.65%. After the aluminum addition is completed, vacuum treatment is performed again. After the VD is completed, the molten steel is soft-blown for 25-50 minutes; S4: Continuous casting is then performed, and rare earth elements are controlled by feeding rare earth cored wire into the continuous casting crystallizer; S5: Finally, rolling is performed, and the ingot is heated and rolled to obtain round steel; In the LF furnace refining process in S2, 50-100 kg of calcium carbide and 100-150 kg of aluminum particles are used to diffuse deoxidize the molten steel, and the binary basicity of the LF furnace final slag is controlled to be 6.0-8.

5. After the VD aluminum is added in S3, vacuum treatment is performed for 3-5 minutes.

2. The method for preparing the corrosion-resistant alloy structural steel according to claim 1, characterized in that: During the S1 electric furnace smelting and steelmaking process, 2.0 kg / ton of aluminum cake and 150 kg / furnace of calcium carbide are added for early deoxidation of molten steel, 900 kg / furnace of lime and 300 kg / furnace of synthetic slag are added for slag making, and low-carbon ferrochrome, low-carbon ferromanganese and ferrosilicon are added for alloying.

3. The method for preparing the corrosion-resistant alloy structural steel according to claim 1, characterized in that: In the S4, the number of continuous casting furnaces is controlled to be ≤9, the superheat of molten steel is controlled to be ≤35°C for the open casting furnace and ≤25°C for the continuous casting furnace; slow drawing speed casting is adopted, the drawing speed is controlled to be 0.70±0.02m / min, La: 55%-70%, Ce: 30%-45% in the cored wire, the temperature of the ingot entering the slow cooling pit is ≥600°C, and the ingot is slowly cooled to a temperature below 100°C before exiting the pit, and the wire feeding speed is 1-2m / min.

4. A method for preparing a corrosion-resistant alloy structural steel seamless steel pipe, characterized in that: The following steps are involved: A1: After the circular steel saw described in any one of claims 1 to 3 is cut into pieces, the pieces are placed in a heating furnace for high-temperature heating, and then taken out of the furnace and sent to a punching machine for punching; A2: After the round steel is bitten into the roller, during the repeated rolling process of the roller, a cavity is formed inside, and a qualified rough pipe is punched out under the action of the perforated roller, the upper and lower guide plates and the front head; A3: Then the rough pipe is cooled to room temperature, kept warm and slowly cooled. After annealing, the rough pipe is pickled to remove the oxide scale on the inner and outer surfaces, phosphated and saponified, and then cold drawn to the finished steel pipe; A4: The finished steel pipe is obtained by heat treatment to obtain a seamless steel pipe; The heat treatment process in A4 is: 900℃~930℃ normalizing + 700℃~720℃ tempering; The A3 is kept warm for 30-40 minutes, and the rough tube annealing temperature is controlled at 850°C to 880°C.

5. The method for preparing a corrosion-resistant alloy structural steel seamless pipe according to claim 4, characterized in that: The A1 is heated to 1280°C to 1320°C at a medium-high temperature, and kept in the high-temperature zone for 10 to 20 minutes. The punching head adopts a molybdenum-based plug, and the roll speed of the punching machine is 10% to 15% lower than that of 10# to 45# steel.

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