Production method of 9Cr thick-walled stainless steel seamless steel pipe with yield strength of 110 steel grade

Abstract

The present invention relates to a production method of a 9Cr thick-walled seamless stainless steel pipe with a yield strength of 110 steel grade, comprising the steps of: (1) blank preparation, (2) blank annealing, (3) blank processing, (4) extrusion molding, (5) annealing treatment, (6) double-liquid quenching treatment and (7) stress relief treatment. The blank preparation includes: (1) molten iron pretreatment, (2) arc furnace smelting, (3) refining outside the furnace, (4) vacuum degassing, and (5) continuous casting or rolling or die casting to produce a round blank. Extrusion molding includes a hole expansion process, an extrusion process and a cooling process. The present invention improves the mechanical properties of the 9Cr seamless steel pipe, overcomes the problems of water quenching cracks, oil quenching ignition and smoking, low yield rate and poor performance in the prior art process, is conducive to improving the yield rate and product quality of the 9Cr thick-walled seamless stainless steel pipe with a yield strength of 110 steel grade, and reduces the production cost.

Description

Technical Field

[0001] The invention belongs to the technical field of industrial equipment production, and relates to a production method of a 9Cr thick-walled stainless steel seamless pipe with a yield strength of 110 steel grade. Background Art

[0002] As the resources of easily exploitable oil and gas fields decrease, people begin to turn to the exploitation of oil and gas fields under harsh conditions of high temperature, high pressure, high mineralization, high corrosion, etc. Ordinary carbon steel pipes can no longer meet the use requirements. There are many oil and gas well shutdown and scrapping accidents caused by corrosion, which has caused great economic losses. High alloys such as duplex steel and nickel-based alloys have excellent performance, but are expensive. After heat treatment, 9Cr has excellent mechanical properties and corrosion resistance, and is economical. It is widely used in the production of petroleum machinery and equipment and pipes, and has a good development prospect. 9Cr steel has good CO2 corrosion resistance and excellent toughness. It is very suitable for use in corrosive environments with high temperature, high CO2 partial pressure and trace H2S content. Its comprehensive performance is better than that of ordinary L80-13Cr. It has become the main material for steel used in oil and gas field exploitation environments. At present, the mature production process of L80-9Cr steel pipe is: ingot casting-forging billet-bill processing-hot piercing rolling forming-quenching and tempering treatment. The steel pipe is prone to defects such as rolling and cracking, and the yield rate is low.

[0003] As working conditions become more complex, ordinary low-grade L80-9Cr steel is difficult to withstand complex high stresses, and the material needs to have higher strength performance and good impact toughness. Under the condition that the material composition remains unchanged, L80-9Cr can be tempered to 110 steel grade by lowering the tempering temperature. However, at this time, the plasticity and toughness are greatly reduced, the brittleness is extremely large, it is very easy to crack, and it cannot be used. It is necessary to fundamentally optimize the composition, combine the factors that affect strength, impact toughness and corrosion resistance, study the chemical composition and production process of higher-strength 110 steel grade, achieve high impact energy under high-strength conditions, and improve the quality of steel pipes. It is of great significance to overcome this technology. Summary of the invention

[0004] The purpose of the present invention is to provide a production method of 9Cr thick-walled stainless steel seamless pipe with a yield strength of 110 steel grade, so as to improve the strength and toughness of the steel used for the stainless steel seamless pipe and to be used for the manufacture of equipment for exploiting oil and gas fields containing carbon dioxide.

[0005] The technical solution of the present invention is: a production method of a 9Cr thick-walled stainless steel seamless pipe with a yield strength of 110 steel grade, comprising the following steps:

[0006] ⑴ Billet preparation: using molten iron as raw material, smelting molten steel through electric arc furnace + refining outside the furnace + vacuum degassing process, producing 9Cr initial raw materials through continuous casting, rolling or die casting, and forging round billets;

[0007] ⑵ Anneal the blank. Heat the round blank in a chamber furnace to 800°C - 860°C for annealing to homogenize the structure and reduce the hardness.

[0008] ⑶ Process the blank. Cut the annealed round blank; then machine 5 mm - 10 mm off the outer diameter unilaterally and machine a through-hole with a diameter of 30 mm - 90 mm in the center, removing the oxide scale on the outer surface and the central porosity and cracks inside.

[0009] ⑷ Extrusion forming, including an expanding hole process, an extrusion process, and a cooling process. Extrude the steel pipe using a 6300T horizontal extrusion unit to obtain the finished steel pipe.

[0010] ⑸ Annealing treatment. Heat the steel pipe to 840°C - 870°C, hold for a certain time, then cool in the furnace to below 500°C and then air-cool to room temperature.

[0011] ⑹ Double-fluid quenching treatment. Heat the steel pipe to 950°C - 980°C, hold for 90 min - 150 min, immerse it in water for rapid cooling, and when the temperature of the steel pipe reaches 200°C - 400°C, quickly transfer it to oil and cool to below 80°C and then air-cool to room temperature.

[0012] ⑺ Tempering treatment. Heat the steel pipe to 560°C - 600°C, hold for 200 min - 300 min, and then water-cool to room temperature.

[0013] ⑻ Straightening treatment. Straighten it using a pressure straightening method.

[0014] ⑼ Stress relief treatment. Heat the steel pipe to 500°C - 550°C, hold for 120 min - 180 min, and then air-cool to room temperature to obtain the production method of a 9Cr thick-walled stainless steel seamless pipe with a yield strength of 110 steel grade.

[0015] The chemical composition of the steel used for the seamless steel pipe by mass percentage is: C: 0.10 - 0.16, Si: 0.40 - 1.20, Mn: 0.40 - 0.90, P: ≤0.020, S: ≤0.006, Cr: 8.5 - 10.5, Ni: 0.20 - 0.50, Mo: 0.92 - 1.15, Nb: 0.02 - 0.06, V: 0.05 - 0.10, Al: 0.01 - 0.05, Ca: 0.0003 - 0.02, Cu: ≤0.25, N: ≤0.050, O: ≤0.0040, H: ≤0.0004, and the rest is Fe and unavoidable impurities.

[0016] The process of blank preparation is as follows: ① Molten iron pretreatment, where the molten iron is heated to 1250°C - 1300°C, and in the molten iron, P ≤ 0.08 and S ≤ 0.10 (mass percentage). ② Electric arc furnace smelting, with the temperature of the electric arc furnace at 1650°C and the tapping temperature ≥ 1635°C, controlling C ≥ 0.06 and P ≤ 0.008 (mass percentage). ③ Refining furnace refining, during ladle refining, 250 kg / t - 300 kg / ladle of quicklime is used, and the quantity is fine-tuned according to the slag condition. In the early stage of refining, deoxidation and desulfurization are strengthened. According to the slag condition, the consumption of fluorite is adjusted to ≤ 1.5 kg / t, the white slag time is 20 min - 60 min. When tapping, aluminum wire is fed, and the Alt component is controlled according to the mass percentage of 0.010 - 0.045%, and the tapping temperature ≥ 1600°C. ④ Vacuum degassing, with the vacuum degree ≤ 67 Pa, maintained for 20 min - 35 min. During the pressure holding process, it is strictly prohibited to close the argon gas. After breaking the vacuum, stir for 1 min - 2 min and then take samples for analysis. Add calcium silicate wire, and control the Ca / Al mass ratio: 0.12 - 0.25. Pour the molten steel when the temperature is between 1500°C and 1570°C. ⑤ Prepare round blanks by continuous casting or rolling or die casting to produce 9Cr initial raw materials. Among them, continuous casting or rolling directly produces round blanks, and die-cast raw materials are forged into round blanks.

[0017] The compression ratio of the rolled round blank is 3.0 - 10.0. Die casting requires a forging process to produce round blanks. The initial forging temperature is 1050°C - 1100°C, the final forging temperature is not lower than 900°C - 920°C, the trimming temperature is 800°C - 880°C, the reduction per pass is 15 mm - 80 mm, the feed rate is 50 mm - 150 mm, and the deformation amount in the last heat treatment is greater than 15%.

[0018] In the hole expanding process, the cold blank is heated 4 times in an induction furnace. The heating power in the first pass is 350 KW, and the surface temperature of the blank reaches 800°C - 900°C. The heating power in the second pass is 500 KW, and the surface temperature reaches 1000°C - 1050°C. The heating power in the third and fourth passes is 600 KW - 900 KW, and the surface temperature of the blank reaches 1140°C - 1200°C to complete the heating. Then, high-pressure water descaling, uniformly apply glass powder lubricant on the inner and outer surfaces, put the blank into the hole expanding barrel, and place lubricating glass pellets at the bell mouth of the blank. Use a 2500T vertical hole expanding machine for hole expanding. The outer diameter of the blank is 5 mm - 10 mm smaller than the inner diameter of the hole expanding barrel. The hole expanding barrel is preheated to a temperature of 100°C - 200°C, the hole expanding speed is 150 - 250 mm / s, and the hole expanding ratio is 1.01 - 1.36.

[0019] In the extrusion process, the billet after hole expansion is heated twice by a secondary electromagnetic induction furnace. The heating power for the first time is 500KW, and the billet temperature reaches 1050°C to 1100°C. The heating power for the second time is 800KW, and the billet temperature reaches 1140°C to 1200°C. High-pressure water descaling at 18MPa to 23MPa is carried out, and the inner and outer surfaces are evenly coated with glass powder lubricant. A lubricating glass pad is placed at the front end of the extrusion die, and the inner cavity of the glass pad is 20mm to 40mm larger than the inner cavity of the extrusion die; it is extruded with a 6300T horizontal extrusion machine. The diameter of the expanded billet is 4mm to 10mm smaller than the inner diameter of the extrusion barrel. The extrusion barrel is preheated to a temperature of 260°C to 450°C, the extrusion speed is 200mm to 350mm / s, and the extrusion ratio is 5 to 15.

[0020] The process of double-fluid quenching treatment is as follows: ① Send the steel pipe into the quenching furnace and heat it to 950°C to 980°C, hold for min, and immediately take it out of the furnace after completion of holding. ② Quickly transfer the steel pipe to the rotating supporting wheels in the water tank filled with circulating water. The rotating speed of the supporting wheels is 30rpm to 40rpm, the distance between each pair of supporting wheels is 0.8m to 1.6m, the steel pipe rotates driven by the supporting wheels, and the inner nozzle arranged at one end of the steel pipe is opened. The inner diameter of the inner nozzle is 25mm to 50mm smaller than the inner diameter of the steel pipe, and the inner sprayed water is sprayed axially into the inner hole of the steel pipe. ③ After the inner sprayed water cools for 5s to 10s, the whole rotating supporting wheel device sinks, so that the steel pipe is immersed below the water surface by 200mm in the diameter direction, and the steel pipe continues to cool under the simultaneous action of inner spraying and immersion. ④ When the temperature of the steel pipe cools to 200°C to 400°C, the whole rotating supporting wheel device rises to make the steel pipe leave the water surface. ⑤ Quickly transfer the water-quenched steel pipe to the fixed support in the cooling oil tank, use quenching oil as the cooling medium to reduce the quenching stress and avoid cracks. ⑥ The steel pipe is cooled to below 80°C to end the quenching.

[0021] In the processing of the billet, an external fillet with a radius of R35mm is machined at the head, the inner and outer circles are machined, ground and polished, the surface roughness Ra ≤ 3.2μm, the diameter deviation is ±1.0mm, the length deviation is ±10mm, the two ends are flat end faces of 90°, and the head flare angle is 41° to 46°.

[0022] The properties of the seamless steel pipe are as follows: tensile strength ≥ 880MPa, Rp0.2 yield strength 758 - 950MPa, elongation ≥ 15%, reduction of area ≥ 40%, hardness 275 - 320HBW, transverse Charpy V-notch full-size impact energy at -10°C ≥ 25J.

[0023] The P110 steel grade standard requirements: tensile ≥ 862Mpa, yield strength: 758 - 965Mpa, elongation > 15%. The matrix is tempered sorbite obtained by quenching + high-temperature tempering method.

[0024] The present invention produces a 9Cr thick-walled seamless stainless steel pipe with a yield strength of 110 steel grade by combining a method of optimizing the composition of the billet + electric arc furnace smelting + continuous casting billet or rolling billet or ingot casting + hot extrusion process forming + water and oil double liquid quenching heat treatment, thereby improving the mechanical properties of the 9Cr seamless steel pipe, overcoming the problems of water quenching cracks, serious oil quenching smog, low yield rate and poor performance in the prior art, and being conducive to improving the yield rate and product quality of the 9Cr thick-walled seamless stainless steel pipe with a yield strength of 110 steel grade, and reducing production costs. The seamless steel pipe produced by the present invention has good surface quality, high mechanical properties after water + oil double liquid quenching heat treatment, and has high strength and good toughness. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the process of the production device of 9Cr thick-walled stainless steel seamless steel pipe with a yield strength of 110 steel grade;

[0026] Figure 2 This is a schematic diagram of the process flow of 9Cr thick-walled stainless steel seamless pipe with a yield strength of 110 steel grade;

[0027] Figure 3 It is a schematic diagram of the structure of a circular blank;

[0028] Figure 4 It is a structural schematic diagram of the hole expanding machine;

[0029] Figure 5 It is a structural schematic diagram of an extruder;

[0030] Figure 6 It is a schematic diagram of the quenching cooling water tank structure;

[0031] Figure 7 This is a schematic diagram of the quenching cooling oil tank structure.

[0032] Among them: 1-arc furnace, 2-refining furnace, 3-vacuum degassing furnace, 4-forging mill, 5-blanket annealing furnace, 6-blanket processing equipment, 7-primary electromagnetic induction heating furnace, 8-hole reamer, 9-secondary electromagnetic induction heating furnace, 10-extruder, 11-steel pipe annealing furnace, 12-quenching furnace, 13-cooling water tank, 14-cooling oil tank, 15-tempering furnace, 16-straightening machine, 17-ejection mechanism, 18-hole reamer base, 19-shear ring support, 20-shear Ring, 21 - reaming barrel, 22 - reaming rod, 23 - reaming head, 24 - die base, 25 - extrusion die, 26 - die support, 27 - extrusion barrel lining, 28 - extrusion barrel middle layer, 29 - extrusion barrel jacket, 30 - core rod, 31 - extrusion pad, 32 - extrusion rod, 33 - inner nozzle, 34 - rotating support wheel, 35 - circulating water, 36 - water tank, 37 - fixed bracket, 38 - quenching oil, 39 - stirring device, 40 - oil tank, 41 - billet, 42 - steel pipe. DETAILED DESCRIPTION

[0033] The present invention will be described in detail below with reference to embodiments and the accompanying drawings. The protection scope of the present invention is not limited to the embodiments, and any modifications made by those skilled in the art within the scope defined by the claims also fall within the protection scope of the present invention.

[0034] The production device of 9Cr thick-walled stainless steel seamless steel pipe of 110 steel grade is as Figure 1 shown, including an electric arc furnace 1, a refining furnace 2, a vacuum degassing furnace 3, a forging and rolling mill 4, a billet annealing furnace 5, a billet processing equipment 6, a primary electromagnetic induction heating furnace 7, a hole expanding machine 8, a secondary electromagnetic induction heating furnace 9, an extrusion machine 10, a steel pipe annealing furnace 11, a quenching furnace 12, a cooling water tank 13, a cooling oil tank 14, a tempering furnace 15, and a straightening machine 16. The electric arc furnace, the refining furnace, the vacuum degassing furnace, the forging and rolling mill, the billet annealing furnace, the billet processing equipment, the primary electromagnetic induction heating furnace, the hole expanding machine, the secondary electromagnetic induction heating furnace, the extrusion machine, the steel pipe annealing furnace, the quenching furnace, the cooling water tank, the cooling oil tank, the tempering furnace, and the straightening machine are arranged in sequence.

[0035] As Figure 4 shown, the hole expanding machine is a 2500T vertical hole expanding machine, provided with an ejection mechanism 17, a hole expanding barrel base 18, a shear ring support 19, a shear ring 20, a hole expanding barrel 21, a hole expanding rod 22, and a hole expanding head 23. The diameter of the hole expanding rod is 5 mm to 10 mm smaller than the diameter of the hole expanding head, the inner diameter of the shear ring is 1 mm to 2 mm larger than the hole expanding head, and the diameter of the billet is 5 mm to 10 mm smaller than the inner diameter of the hole expanding barrel.

[0036] As Figure 5 shown, the extrusion machine is a 6300T horizontal extrusion machine, provided with a die holder 24, an extrusion die 25, a die support 26, an extrusion barrel inner lining 27, an extrusion barrel intermediate layer 28, an extrusion barrel outer sleeve 29, a mandrel 30, an extrusion pad 31, and an extrusion rod 32. The material of the steel pipe forming die is H13, the die hardness is HRC48 - 51, and the cavity of the die support is 20 mm to 40 mm larger than the cavity of the extrusion die.

[0037] As Figure 6 shown, the cooling water tank 36 is provided with an inner nozzle 33 and a rotating supporting wheel 34. The rotating supporting wheel 34 is used to horizontally place the seamless steel pipe during cooling, and the inner nozzle 33 is used to spray circulating water into the inner hole of the seamless steel pipe along the axial direction. The cooling water tank 36 is filled with circulating water, and the cooling water tank 36 is provided with a water outlet, and the water outlet is connected to the inner nozzle 33 through a water pump.

[0038] As Figure 7 shown, the cooling oil tank 40 is provided with a fixed support 37 and a stirring device 39; the fixed support 37 is used to horizontally place the seamless steel pipe during oil cooling, and the stirring device 39 is used to stir the quenching oil to promote the flow of the quenching oil in the cooling oil tank.

[0039] Embodiment 1

[0040] 9Cr thick-walled stainless steel seamless steel pipe with a yield strength of 110 steel grade, the production specification is outer diameter φ180mm × wall thickness 45mm, and the chemical composition is shown in Table 1.1:

[0041] Table 1.1 Chemical composition of φ180mm × 45mm seamless steel pipe / (mass percentage %)

[0042]

[0043] Remarks: The rest are Fe and inevitable impurities.

[0044] The method for producing 9Cr thick-walled stainless steel seamless steel pipe with a yield strength of 110 steel grade according to the present invention, the production process is as Figure 2 shown, and includes the following steps:

[0045] ⑴ Blank preparation, preparing a round continuous casting blank through an electric arc furnace + secondary refining + vacuum degassing + continuous casting. ① Molten iron pretreatment, heating the molten iron at a temperature greater than 1250 °C, and the component mass percentage is P ≤ 0.08, S ≤ 0.10. ② Electric arc furnace smelting, controlling the steel component mass percentage during electric arc furnace smelting as C ≥ 0.06, P ≤ 0.008, and the tapping temperature ≥ 1635 °C. ③ Refining furnace refining, the temperature ≥ 1535 °C. During secondary refining, add 250 kg / t - 300 kg / furnace of quicklime, and fine-tune the quantity according to the slag condition. Strengthen deoxidation and desulfurization in the early stage of refining, adjust the dosage of fluorite ≤ 1.5 kg / t according to the slag condition, the white slag time is 20 min - 60 min, feed aluminum wire when tapping slag, and control according to the Alt component mass percentage of 0.010% - 0.045%, and the tapping temperature ≥ 1600 °C. ④ Vacuum degassing, the vacuum degree ≤ 67 Pa, keep it for 20 min - 35 min, it is strictly prohibited to close the argon gas during the pressure holding process. After breaking the vacuum, stir for 1 min - 2 min and take samples for analysis, and add calcium silicate wire, controlling the Ca / Al mass ratio: 0.12 - 0.25. ⑤ Continuous casting blank, pouring the molten steel at a temperature of 1500 °C - 1570 °C, and producing a round continuous casting blank 41 with a 9Cr diameter of φ375mm through the continuous casting process.

[0046] ⑵ Blank annealing, heating the round blank to 800 °C - 860 °C for annealing in a chamber furnace, keeping it warm for 5 h - 10 h, cooling at a rate of 20 °C - 50 °C / h to 350 °C - 500 °C, and taking it out of the furnace and air-cooling to room temperature.

[0047] ⑶ Blanking processing: Cut the annealed round blank according to the length of the finished steel pipe to process a blank with an outer diameter of φ358mm / inner diameter of φ65mm × length of 900mm. Machine an outer fillet with a radius of R35mm at the head, machine, grind, and polish the inner and outer circles, with a surface roughness Ra ≤ 3.2μm, a diameter deviation of ±1.0mm, a length deviation of ±10mm, flat end faces of 90° at both ends, and a head flare angle of 46°.

[0048] ⑷ Steel pipe extrusion forming, including a hole expanding process, an extrusion process, and a cooling process.

[0049] ① Hole expanding process: Heat the cold blank 4 times in a primary electromagnetic induction furnace. The heating power for the first time is 350KW, and the surface temperature of the blank reaches 800℃ - 900℃; the heating power for the second time is 500KW, and the surface temperature reaches 1000℃ - 1050℃; the heating power for the third and fourth times is 600KW - 900KW, and the surface temperature of the blank reaches 1140℃ - 1200℃ to complete the heating. Then, perform high-pressure water descaling in sequence, evenly apply glass powder lubricant on the inner and outer surfaces, put the blank into the hole expanding barrel, and place lubricating glass pellets at the flare of the blank. Use a 2500T vertical hole expanding machine for hole expanding. The inner diameter of the hole expanding barrel is φ369mm, the hole expanding barrel is preheated to a temperature of 100℃ - 200℃, the hole expanding speed is 150 - 250mm / s, and the diameter of the hole expanding head is φ102mm.

[0050] ② Extrusion process: Heat the hole-expanded blank twice in a secondary electromagnetic induction furnace. The heating power for the first time is 500KW, and the temperature of the blank reaches 1050℃ - 1100℃. The heating power for the second time is 800KW, and the temperature of the blank reaches 1140℃ - 1200℃. Perform high-pressure water descaling at 18MPa - 23MPa, evenly apply glass powder lubricant on the inner and outer surfaces, place a lubricating glass pad at the front end of the extrusion die, and the inner cavity of the glass pad is 20mm - 40mm larger than the inner cavity of the extrusion die. Use a 6300T horizontal extrusion machine for extrusion. The inner diameter of the extrusion barrel is φ375mm. The extrusion barrel is preheated to a temperature of 260℃ - 450℃, the extrusion speed is 200mm - 350mm / s, the diameter of the mandrel is φ91mm, the inner diameter of the extrusion die is φ183.5mm, and extrude a steel pipe with φ180mm × 45mm.

[0051] ③ Cooling process: After extrusion, air-cool the steel pipe to obtain a steel pipe with the finished product size.

[0052] ⑸ Annealing treatment: Heat the steel pipe to 840℃ - 870℃, after holding for a certain time, cool it in the furnace to below 500℃, and then air-cool it to room temperature.

[0053] ⑹ Double-fluid quenching treatment, including water quenching and oil quenching. The process of double-fluid quenching treatment is as follows: ① Feed the steel pipe into the quenching furnace and heat it to 950°C - 980°C. Immediately take it out of the furnace after completion of heat preservation. ② Quickly transfer the steel pipe to the rotating supporting wheels on the water tank filled with circulating water. The rotating speed of the supporting wheels is 30 rpm - 40 rpm, and the distance between each pair of supporting wheels is 0.8 m - 1.6 m. The steel pipe rotates driven by the supporting wheels. Open the inner nozzle arranged at one end of the steel pipe. The inner diameter of the inner nozzle is 25 mm - 50 mm smaller than the inner diameter of the steel pipe. The inner sprayed water is sprayed axially into the inner hole of the steel pipe. ③ After the inner sprayed water cools for 5 s - 10 s, the whole rotating supporting wheel device sinks, making the steel pipe immersed below the water surface by 200 mm in the diameter direction. The steel pipe continues to cool under the combined action of inner spraying and immersion. ④ When the temperature of the steel pipe cools to 200°C - 400°C, the whole rotating supporting wheel device rises to make the steel pipe leave the water surface. ⑤ Quickly transfer the water-quenched steel pipe to the fixed support in the cooling oil tank, and use quenching oil as the cooling medium to reduce the quenching stress and avoid cracks. ⑥ When the steel pipe cools to below 80°C, the quenching ends.

[0054] ⑺ Tempering treatment: Heat the steel pipe to 560°C - 600°C, keep it warm for 200 min - 300 min, and then cool it to room temperature with water.

[0055] ⑻ Straightening treatment: Straighten the steel pipe by using the pressure straightening method.

[0056] ⑼ Stress relief treatment: Heat the steel pipe to 500°C - 550°C, keep it warm for 120 min - 180 min, and then air-cool it to room temperature to obtain a 9Cr thick-walled stainless steel seamless steel pipe with a yield strength of steel grade 110. Conduct performance inspection on the produced 9Cr thick-walled stainless steel seamless steel pipe with a yield strength of steel grade 110. The inspection data is shown in Table 1.2.

[0057] Table 1.2. Performance of 9Cr thick-walled stainless steel seamless steel pipe with a yield strength of steel grade 110 and φ180mm×45mm

[0058]

[0059] Example 2

[0060] The 9Cr thick-walled stainless steel seamless steel pipe with a yield strength of steel grade 110 has a production specification of outer diameter φ219mm×wall thickness 35mm, and the chemical composition is shown in Table 2.1:

[0061] Table 2.1 Chemical composition of φ219mm×35mm seamless steel pipe / (mass percentage %)

[0062]

[0063] Remarks: The rest are Fe and inevitable impurities.

[0064] The production process of 9Cr thick-walled stainless steel seamless steel pipes with a yield strength of 110 steel grade includes the following steps:

[0065] ⑴ Blank preparation: Prepare round continuous casting billets through an electric arc furnace + secondary refining + vacuum degassing + rolling. ① Molten iron pretreatment: Heat the molten iron to a temperature above 1250°C, with the component mass percentages being P≤0.08 and S≤0.10. ② Electric arc furnace smelting: During smelting, control the steel component mass percentages to C≥0.06 and P≤0.008, and the tapping temperature≥1635°C. ③ Refining furnace refining: The temperature≥1535°C. During secondary refining, use 250 kg / t - 300 kg / furnace of quicklime, and fine-tune the quantity according to the slag condition. Strengthen deoxidation and desulfurization in the early stage of refining, adjust the consumption of fluorite≤1.5 kg / t according to the slag condition, with the white slag time being 20 min - 60 min. Feed aluminum wire when discharging from the station, and control the Alt component mass percentage to be 0.010% - 0.045%, and the tapping temperature≥1600°C. ④ Vacuum degassing: The vacuum degree≤67 Pa, and maintain for 20 min - 35 min. During the pressure-holding process, it is strictly prohibited to close the argon gas. After breaking the vacuum, stir for 1 min - 2 min and then take samples for analysis. Add calcium silicate wire and control the Ca / Al mass ratio to be 0.12 - 0.25. Pour the molten steel when the temperature is between 1500°C and 1570°C. ⑤ Roll the billet: Produce 9Cr round billets with a diameter of φ430 mm through rolling.

[0066] ⑵ Billet annealing: Heat the round billet in a chamber furnace to 820°C - 850°C for annealing, keep it warm for 5 h - 10 h, cool it at a rate of 20°C - 50°C / h to 350°C - 500°C, and then take it out of the furnace and air-cool it to room temperature.

[0067] ⑶ Billet processing: Cut the round billet according to the length of the finished steel pipe to process billets with an outer diameter of φ415 mm / inner diameter of φ60 mm×length of 950 mm. Process an outer fillet with a radius of R35 mm at the head. Machine, grind, and polish the inner and outer circles, with the surface roughness Ra≤3.2 μm, the diameter deviation being ±1.0 mm, the length deviation being ±10 mm, the two ends being flat end faces at 90°, and the head bell mouth angle being 45°.

[0068] ⑷ Steel pipe extrusion forming, including an expanding hole process, an extrusion process, and a cooling process.

[0069] ① Reaming process: The cold billet is heated 4 times in a primary electromagnetic induction furnace. The heating power for the first time is 350KW, and the surface temperature of the billet reaches 800℃ - 900℃. The heating power for the second time is 500KW, and the surface temperature reaches 1000℃ - 1050℃. The heating power for the third and fourth times is 600KW - 900KW, and the surface temperature of the billet reaches 1140℃ - 1200℃, completing the heating. Then, high-pressure water descaling is carried out in sequence, the inner and outer surfaces are evenly coated with glass powder lubricant, the billet is put into the reaming barrel, and lubricating glass pellets are placed at the bell mouth of the billet. Reaming is carried out with a 2500T vertical reaming machine. The inner diameter of the reaming barrel is φ425mm, the reaming barrel is preheated to a temperature of 100℃ - 200℃, the reaming speed is 150 - 250mm / s, and the diameter of the reaming head is φ162mm.

[0070] ② Extrusion process: The reamed billet is heated twice in a secondary electromagnetic induction furnace. The heating power for the first time is 500KW, and the billet temperature reaches 1050℃ - 1100℃. The heating power for the second time is 800KW, and the billet temperature reaches 1140℃ - 1200℃. High-pressure water descaling at 18MPa - 23MPa is carried out, the inner and outer surfaces are evenly coated with glass powder lubricant, a lubricating glass pad is placed at the front end of the extrusion die, and the inner cavity of the glass pad is 20mm - 40mm larger than the inner cavity of the extrusion die; extrusion is carried out with a 6300T horizontal extrusion machine. The inner diameter of the extrusion barrel is φ435mm. The extrusion barrel is preheated to a temperature of 260℃ - 450℃, the extrusion speed is 200mm - 350mm / s, the diameter of the mandrel is φ151mm, the inner diameter of the extrusion die is φ223mm, and a φ219mm×35mm steel pipe is extruded.

[0071] ③ Cooling process: The extruded steel pipe is air-cooled to obtain a steel pipe with the finished size.

[0072] ⑸ Annealing treatment: The steel pipe is heated to 840℃ - 870℃, cooled in the furnace to below 500℃ after holding, and then air-cooled to room temperature.

[0073] ⑹ Double-fluid quenching treatment, including water quenching and oil quenching. The process of double-fluid quenching treatment is as follows: The process of double-fluid quenching treatment is as follows: ① Feed the steel pipe into the quenching furnace and heat it to 950°C - 980°C. Immediately take it out of the furnace after completion of heat preservation. ② Quickly transfer the steel pipe to the rotating supporting wheels on the water tank filled with circulating water. The rotating speed of the supporting wheels is 30 rpm - 40 rpm, and the distance between each pair of supporting wheels is 0.8 m - 1.6 m. The steel pipe rotates driven by the supporting wheels. Open the inner nozzle arranged at one end of the steel pipe. The inner diameter of the inner nozzle is 25 mm - 50 mm smaller than the inner diameter of the steel pipe. The inner water spray is sprayed axially into the inner hole of the steel pipe. ③ After the inner water spray cools for 5 s - 10 s, the whole rotating supporting wheel device sinks, so that the steel pipe is immersed below the water surface by 200 mm in the diameter direction. The steel pipe continues to cool under the simultaneous action of inner spraying and immersion. ④ When the temperature of the steel pipe cools to 200°C - 400°C, the whole rotating supporting wheel device rises to make the steel pipe leave the water surface; ⑤ Quickly transfer the water-quenched steel pipe to the fixed support in the cooling oil tank, and use quenching oil as the cooling medium to reduce the quenching stress and avoid cracks; ⑥ When the steel pipe cools to below 80°C, the quenching ends.

[0074] ⑺ Tempering treatment: Heat the steel pipe to 560°C - 600°C, keep it warm for 200 min - 300 min, and then cool it to room temperature with water

[0075] ⑻ Straightening treatment: Straighten it by means of pressure straightening.

[0076] ⑼ Stress relief treatment: Heat the steel pipe to 500°C - 550°C, keep it warm for 120 min - 180 min, and then air-cool it to room temperature to obtain a 9Cr thick-walled stainless steel seamless steel pipe with a yield strength of steel grade 110.

[0077] Conduct performance inspection on the produced 9Cr thick-walled stainless steel seamless steel pipe with a yield strength of steel grade 110. The inspection data are shown in Table 2.2.

[0078] Table 2.2. Performance of 9Cr thick-walled stainless steel seamless steel pipe with φ219mm×35mm and a yield strength of steel grade 110

[0079]

[0080]

Claims

1. A production method of 9Cr thick-walled stainless steel seamless steel pipe with a yield strength of 110 steel grade, the outer diameter of the seamless steel pipe is φ120 - φ500mm, and the wall thickness is 25mm - 70mm; characterized in that: The properties of the seamless steel pipe are as follows: tensile strength ≥ 880 MPa, Rp0.2 yield strength 758 - 950 MPa, elongation ≥ 15%, reduction of area ≥ 40%, hardness 275 - 320 HBW, transverse Charpy V-notch full-size impact energy at -10 °C ≥ 25 J; the production method includes the following steps: ⑴ Blank preparation: Using molten iron as raw material, steel water is smelted through the process of electric arc furnace + secondary refining + vacuum degassing, and 9Cr initial raw materials are produced by continuous casting or rolling or die casting, and circular blanks are forged. ⑵ Blank annealing: The circular blanks are heated to 800 °C - 860 °C in a chamber furnace for annealing. ⑶ Blank processing: The annealed circular blanks are cut, and the outer surface scale and internal central porosity and cracks are removed. ⑷ Extrusion forming: It includes an expanding hole process, an extrusion process and a cooling process. The steel pipe is extruded with a 6300T horizontal extrusion unit to obtain the finished steel pipe. ⑸ Annealing treatment: The steel pipe is heated to 840 °C - 870 °C, cooled in the furnace to below 500 °C after holding, and then air-cooled to room temperature. ⑹ Double-fluid quenching treatment: The steel pipe is heated to 950 °C - 980 °C, held for 90 min - 150 min, quickly cooled in water, and when the temperature of the steel pipe reaches 200 °C - 400 °C, it is quickly transferred to oil and cooled to below 80 °C and then air-cooled to room temperature. ⑺ Tempering treatment: The steel pipe is heated to 560 °C - 600 °C, held for 200 min - 300 min, and water-cooled to room temperature. ⑻ Straightening treatment: Straightening is carried out by means of pressure straightening. ⑼ Stress relief treatment: The steel pipe is heated to 500 °C - 550 °C, held for 120 min - 180 min, and air-cooled to room temperature to obtain a 9Cr thick-walled stainless steel seamless steel pipe of yield strength grade 110. The chemical composition of the steel used for the seamless steel pipe by mass percentage is: C: 0.10 - 0.16, Si: 0.40 - 1.20, Mn: 0.40 - 0.90, P: ≤ 0.020, S: ≤ 0.006, Cr: 8.5 - 10.5, Ni: 0.20 - 0.50, Mo: 0.92 - 1.15, Nb: 0.02 - 0.06, V: 0.05 - 0.10, Al: 0.01 - 0.05, Ca: 0.0003 - 0.02, Cu: ≤ 0.25, N: ≤ 0.050, O: ≤ 0.0040, H: ≤ 0.0004, and the rest is Fe and unavoidable impurities.

2. The production method of the 9Cr thick-walled stainless steel seamless steel pipe with a yield strength of 110 steel grade according to claim 1, characterized in that: The process of blank preparation is as follows: ① Molten iron pretreatment, heating the molten iron to 1250°C - 1300°C, with P ≤ 0.08 and S ≤ 0.10 in the molten iron; ② Electric arc furnace smelting, the temperature of the electric arc furnace is 1650°C, the tapping temperature ≥ 1635°C, controlling C ≥ 0.06 and P ≤ 0.008 (mass percentage); ③ Refining furnace refining, during secondary refining, 250 kg / t - 300 kg / furnace of quicklime, fine-tuning the quantity according to the slag condition, strengthening deoxidation and desulfurization in the early stage of refining, adjusting the consumption of fluorite ≤ 1.5 kg / t according to the slag condition, the white slag time is 20 min - 60 min, feeding aluminum wire when tapping, controlling according to the Alt component mass percentage of 0.010 - 0.045%, and the tapping temperature ≥ 1600°C; ④ Vacuum degassing, the vacuum degree ≤ 67 Pa, maintaining for 20 min - 35 min, strictly prohibiting closing the argon gas during the pressure holding process, after breaking the vacuum, stirring for 1 min - 2 min for sampling analysis, adding calcium silicate wire, controlling the Ca / Al mass ratio: 0.12 - 0.25, and pouring the molten steel when the temperature is 1500°C - 1570°C; ⑤ Preparing round blanks, producing 9Cr initial raw materials through continuous casting or rolling or die casting, among which continuous casting or rolling directly produces round blanks, and die-casting raw materials are forged into round blanks.

3. The production method of the 9Cr thick-walled stainless steel seamless steel pipe with a yield strength of 110 steel grade according to claim 2, characterized in that: The reduction ratio of the rolled round blank is 3.0 - 10.0; the die-casting raw materials need to go through the forging process to produce round blanks, the initial forging temperature is not lower than 1050°C, the final forging temperature is not lower than 900°C, the trimming temperature is 800°C - 880°C, the reduction per pass is 15 mm - 80 mm, the feed rate is 50 mm - 150 mm, and the deformation amount in the last heat treatment is greater than 15%.

4. The production method of the 9Cr thick-walled stainless steel seamless steel pipe with a yield strength of 110 steel grade according to claim 1, characterized in that: In the hole expanding process, the cold blank is heated 4 times in a primary electromagnetic induction furnace; the heating power in the first pass is 350 KW, and the surface temperature of the blank reaches 800°C - 900°C; the heating power in the second pass is 500 KW, and the surface temperature reaches 1000°C - 1050°C; the heating power in the third and fourth passes is 600 KW - 900 KW, and the surface temperature of the blank reaches 1140°C - 1200°C to complete the heating; successively perform high-pressure water descaling, evenly apply glass powder lubricant on the inner and outer surfaces, put the blank into the hole expanding barrel, and place lubricating glass pellets at the bell mouth of the blank; use a 2500T vertical hole expanding machine for hole expanding, the outer diameter of the blank is 5 mm - 10 mm smaller than the inner diameter of the hole expanding barrel, the hole expanding barrel is preheated to a temperature of 100°C - 200°C, the hole expanding speed is 150 - 250 mm / s, and the hole expanding ratio is 1.01 - 1.

36.

5. The production method of the 9Cr thick-walled stainless steel seamless steel pipe with a yield strength of 110 steel grade according to claim 1, characterized in that: For the extrusion process, the billet after hole expansion is heated twice in a secondary electromagnetic induction furnace. The heating power for the first time is 500KW, and the billet temperature reaches 1050°C - 1100°C. The heating power for the second time is 800KW, and the billet temperature reaches 1140°C - 1200°C. High-pressure water descaling at 18MPa - 23MPa is carried out, and glass powder lubricant is evenly applied to the inner and outer surfaces. A lubricating glass pad is placed at the front end of the extrusion die, and the inner cavity of the glass pad is 20mm - 40mm larger than the inner cavity of the extrusion die. It is extruded with a 6300T horizontal extrusion machine. The diameter of the billet after expansion is 4mm - 10mm smaller than the inner diameter of the extrusion barrel. The extrusion barrel is preheated to a temperature of 260°C - 450°C, the extrusion speed is 200mm - 350mm / s, and the extrusion ratio is 5 - 15.

6. The production method of the 9Cr thick-walled stainless steel seamless steel pipe with a yield strength of 110 steel grade according to claim 1, characterized in that: The process of the double-fluid quenching treatment is as follows: ① Send the steel pipe into the quenching furnace and heat it to 950°C - 980°C. Immediately take it out of the furnace after completion of heat preservation. ② Quickly transfer the steel pipe to the rotating supporting wheels on the water tank filled with circulating water. The rotating speed of the supporting wheels is 30rpm - 40rpm, the distance between each pair of supporting wheels is 0.8m - 1.6m, the steel pipe rotates driven by the supporting wheels, and open the inner nozzle arranged at one end of the steel pipe. The inner diameter of the inner nozzle is 25mm - 50mm smaller than the inner diameter of the steel pipe, and the inner water spray is sprayed axially into the inner hole of the steel pipe. ③ After the inner water spray cools for 5s - 10s, the whole rotating supporting wheel device sinks, so that the steel pipe is immersed below the water surface by 200mm in the diameter direction, and the steel pipe continues to cool under the simultaneous action of the inner spray and immersion. ④ When the temperature of the steel pipe cools to 200°C - 400°C, the whole rotating supporting wheel device rises to make the steel pipe leave the water surface. ⑤ Quickly transfer the water-quenched steel pipe to the fixed support in the cooling oil tank. ⑥ The steel pipe cools to below 80°C, and the quenching ends.

7. The production method of the 9Cr thick-walled stainless steel seamless steel pipe with a yield strength of 110 steel grade according to claim 1, characterized in that: For the processing of the billet, an outer fillet with a radius of R35mm is machined at the head. The inner and outer circles are machined, ground, and polished. The surface roughness Ra ≤ 3.2μm, the diameter deviation is ±1.0mm, the length deviation is ±10mm, the flat end faces at both ends are 90°, and the head flare angle is 41° - 46°.

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