A method for producing a medium wall 85ksi-13cr seamless steel pipe

Abstract

The present application relates to a kind of production methods of medium thick wall 85KSI-13Cr seamless steel pipe, production steps include: (1) blank preparation, (2) forging bar, (3) forging bar annealing, (4) forging bar processing, (5) extrusion forming, (6) normalizing treatment, (7) quenching treatment, (8) first tempering treatment, (9) second tempering treatment and (10) performance detection.The outside diameter of the seamless steel pipe is φ90-φ325mm, and the wall thickness is 25mm-45mm.The present application overcomes the problems of long process flow, serious water quenching crack, oil quenching fire and smoke, oil aging, low yield and poor performance in the prior art, improves the yield and product quality, and reduces the production cost.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of industrial equipment production, and particularly relates to a production method of a medium-thick-wall 85KSI-13Cr seamless steel pipe. BACKGROUND

[0002] In recent years, the difficulty of oil and gas resource development gradually increases, and the development conditions of high temperature, high pressure, high salinity and containing CO2 are more and more, and the corrosion problem of downhole oil well pipe brings great difficulty to safe and economic material selection. For the acid oil and gas field with low H2S content, the use of nickel-based alloy will cause product quality surplus, and the ordinary steel material still has the risk of corrosion cracking.

[0003] The Cr-based martensitic stainless steel with an alloy content of 13% has excellent mechanical properties and corrosion resistance after proper quenching and tempering treatment, and is good in economy, and becomes the first choice for oil and gas field development, and has good development prospect. The production process of L80-13Cr in the traditional API5CT standard is: ingot casting-forging-forging blank outer skin stripping and polishing-extrusion blank inner hole machining-hot piercing or hot extrusion forming-oil quenching and tempering treatment.

[0004] The disadvantages of the traditional L80-13Cr production process and method are low yield, long production process, easy cracking of separate water quenching, easy fire of separate oil quenching and tempering treatment, serious smoking, serious aging of quenching oil, poor safety of on-site operation, low impact energy of product, great brittleness and easy cracking, and no high strength and high toughness. It is necessary to fundamentally optimize the chemical composition design, design a new production process, combine the factors affecting the strength, impact toughness and corrosion resistance, research the chemical composition and production process of 85KSi-13Cr with higher strength and toughness, realize the higher impact energy under the condition of high strength, and have CO2 corrosion resistance, and it is of great significance to overcome this technology. SUMMARY

[0005] The purpose of the present application is to provide a production method of a medium-thick-wall 85KSI-13Cr seamless steel pipe, to optimize the production process of the medium-thick-wall seamless steel pipe, to simplify the process, to improve the quality of the seamless steel pipe, and to improve the strength and impact toughness of the steel pipe.

[0006] The technical scheme of the present application is a production method of a medium-thick-wall 85KSI-13Cr seamless steel pipe, comprising the following steps:

[0007] 1) Billet preparation, taking scrap steel as raw material, smelting by electric arc furnace and feeding into LF furnace for refining, and feeding Al block; when the temperature of the molten steel is 1570-1650℃, VD furnace vacuum treatment is carried out, the vacuum degree is 20-50Pa, Si-Ca wire is added before vacuum, and the vacuum holding time is 15-30min; when the temperature of the molten steel is 1450-1550℃, ingot casting or continuous casting is carried out;

[0008] 2) Forging and pressing, the ingot or continuous casting billet is heated and forged into a forging rod, the compression ratio is 1.01-6.0, the initial forging temperature is 1180-1200℃, the final forging temperature is 900-950℃, the reduction per pass is 10-50mm, and the feed amount is 50-120mm;

[0009] 3) Annealing of the forging rod, the forging rod obtained in step 2) is annealed in a chamber furnace to reduce hardness;

[0010] 4) Machining of the forging rod, the outer circle of the forging rod obtained in step 3) is machined by 3-8mm on one side, the center hole is machined to a diameter of 30-85mm, and the outer surface oxide skin and the center loose part are removed;

[0011] 5) Extrusion forming, the forging rod is heated to 1190-1260℃ by electromagnetic induction furnace, then high-pressure water descaling is carried out at 18-23MPa, then glass powder lubrication is carried out, and the 63MN horizontal extrusion machine group is used for extruding a medium-thick wall steel pipe;

[0012] 6) Normalizing treatment, the steel pipe is heated to 900-959℃ in a trolley furnace, and is kept for 30-60min, and is air cooled to room temperature;

[0013] 7) Quenching treatment, the steel pipe is heated to 920-980℃ in a trolley furnace, and is kept for 60-80min, and is immersed in water for fast cooling, and when the temperature of the steel pipe reaches 300-600℃, it is quickly transferred to quenching oil for cooling to 20-80℃, and then air cooling and cleaning of residual oil are carried out;

[0014] 8) First tempering treatment, the steel pipe is heated to 660-700℃, kept for 200-240min, air cooled to room temperature, and then pressure straightening is carried out;

[0015] 9) Second tempering treatment, the steel pipe is heated to 500-600℃, kept for 120-180min, air cooled to room temperature, and a medium-thick wall 85KSI-13Cr seamless steel pipe is obtained;

[0016] 10) Performance detection, the detection items include tensile strength, Rt0.5 yield strength, elongation, hardness and impact energy.

[0017] In step 2, the ingot or continuous casting billet is heated to a furnace temperature of 500-550°C, and held for 2.0 hours; then heated to 880-920°C at a rate of 45-65°C / hour, and held for 1.5-2.0 hours; and then heated to 1220-1230°C at a rate of 70-80°C / hour, and held for 3-5 hours. In step 3, the forged bar is annealed at a temperature of 700-760°C, and held for 6-12 hours, and then furnace cooled to 300-350°C, and air cooled to room temperature.

[0018] In step 8, the extrusion forming process includes: 1. hole expansion by a hole expander at a speed of 100-250 mm / s and an expansion ratio of 1.01-1.35; and 2. extrusion by an extruder at a speed of 50-250 mm / s and an extrusion ratio of 3-10. During the extrusion forming stage, the cold billet is heated in an electromagnetic induction furnace for 4 times; the first time at a power of 350 KW, the outer surface of the billet reaching a temperature of 800-850°C; the second time at a power of 400 KW, the outer surface reaching a temperature of 1000-1050°C; the third time at a power of 500 KW, the outer surface reaching a temperature of 1150-1180°C; and the fourth time at a power of 800 KW, the outer surface reaching a temperature of 1190-1260°C, and the heating is completed.

[0019] In step 9, the quenching process includes: 1. the steel pipe is sent into a quenching furnace and heated to 920-980°C, and immediately taken out after the holding is completed; 2. the steel pipe is quickly transferred to a rotating support wheel in a water tank filled with circulating water, the rotating speed of the support wheel is 30-40 rpm, the distance between each pair of support wheels is 0.5-1.2 m, the steel pipe is rotated by the rotating support wheel, an inner nozzle arranged at one end of the steel pipe is opened, the inner diameter of the inner nozzle is 30-40 mm smaller than the inner diameter of the steel pipe, and the inner nozzle sprays water into the inner hole of the steel pipe along the axial direction; 3. after the inner nozzle sprays water for 5-10 seconds, the rotating support wheel device is lowered as a whole, so that the steel pipe is immersed in water by 1 / 2 of the diameter, and the steel pipe continues to cool under the combined action of the inner nozzle and the immersion; 4. when the temperature of the steel pipe cools to 300-600°C, the rotating support wheel device is raised as a whole, so that the steel pipe is separated from the water surface; 5. the quenched steel pipe is quickly transferred to a fixed support in a cooling oil tank, and quenched oil is used as a cooling medium to reduce the quenching stress and avoid cracks; and 6. the steel pipe is cooled to 20-80°C, and the quenching is completed.

[0020] The components of the steel for seamless steel pipe are as follows in percentage by mass: C: 0.10-0.19, Si: 0.15-0.55, Mn: 0.50-0.85, Cr: 12.2-13.2, Ni: 0.40-0.50, Mo: 0.10-0.45, Ti: 0.01-0.04, Nb: 0.005-0.03, V: 0.05-0.10, Al: 0.01-0.03, Ca: 0.0005-0.008, N: 0.005-0.030, Nb+V+Ti+Al: ≤0.15, Cu: ≤0.25, O: ≤0.0030, H: ≤0.0003, P: ≤0.015, S: ≤0.004, and the rest is Fe and inevitable impurities.

[0021] The properties of the seamless steel pipe are as follows: tensile strength ≥670 MPa, Rt0.5 yield strength 587-670 MPa, elongation ≥20%, hardness ≤23.5 HRC. The average value of the transverse Charpy V-notch full-size impact energy of the seamless steel pipe at -10 ℃ is ≥30 J, and the average value of the longitudinal Charpy V-notch full-size impact energy at -10 ℃ is ≥41 J. The outside diameter of the seamless steel pipe is φ90-φ325 mm, and the wall thickness is 25-45 mm.

[0022] The present application adopts the process method of ingot casting or continuous casting billet + small compression ratio forging + hot extrusion molding + water and oil double liquid quenching heat treatment to produce the medium-thick-wall 85KSI-13Cr seamless steel pipe, which overcomes the problems of long process flow, serious water quenching crack, oil quenching fire and smoke, oil aging, low yield and poor performance in the prior art, is beneficial to improve the yield and quality of the medium-thick-wall 85KSI-13Cr seamless steel pipe and reduce the production cost. The seamless steel pipe produced by the present application has good surface quality, high mechanical properties after water + oil double liquid quenching heat treatment, high strength and good toughness, and is widely used in the oil field exploitation process containing CO2. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 It is the production process flow chart of the medium-thick-wall 85KSI-13Cr seamless steel pipe in the present application;

[0024] Figure 2 It is the flowchart of the medium-thick-wall 85KSI-13Cr martensitic stainless steel seamless steel pipe production device;

[0025] Figure 3 It is the structural schematic diagram of the annealing furnace;

[0026] Figure 4 It is the structural schematic diagram of the extruder

[0027] Figure 5 It is the structural schematic diagram of the cooling water tank;

[0028] Figure 6 A schematic diagram of a cooling oil tank structure is shown.

[0029] Wherein: 1 - electric arc furnace, 2 - refining furnace, 3 - ingot heating furnace, 4 - forging machine, 5 - annealing furnace, 6 - blank processing equipment, 7 - electromagnetic induction heating furnace, 8 - hole expanding machine, 9 - extrusion machine, 10 - quenching furnace, 11 - cooling water tank, 12 - cooling oil tank, 13 - tempering furnace, 14 - cooling bed, 15 - straightening machine, 16 - refractory material, 17 - heat insulation material, 18 - furnace body steel frame, 19 - burner, 20 - thermocouple, 21 - smoke outlet, 22 - heat exchanger, 23 - lifting device, 24 - furnace door, 25 - furnace body support, 26 - die tail seat, 27 - die middle seat, 28 - die seat, 29 - die support, 30 - extrusion die, 31 - extrusion cylinder intermediate layer, 32 - extrusion cylinder inner lining, 33 - extrusion cylinder outer layer, 34 - core rod, 35 - extrusion pad, 36 - extrusion rod, 37 - inner nozzle, 38 - rotating support wheel, 39 - seamless steel pipe, 40 - circulating water, 41 - fixed support, 42 - quenching oil, 43 - stirring device. DETAILED DESCRIPTION

[0030] The present application will be described in detail below with reference to the embodiments and the accompanying drawings. The scope of protection of the present application is not limited to the embodiments, and any modification made by those skilled in the art within the scope defined by the claims is also within the scope of protection of the present application.

[0031] The thick-walled 85KSI-13Cr martensitic stainless steel seamless pipe production device in the present application is shown in FIG. 1, which includes an electric arc furnace 1, a refining furnace 2, an ingot heating furnace 3, a forging machine 4, an annealing furnace 5, a blank processing equipment 6, an electromagnetic induction heating furnace 7, a hole expanding machine 8, an extrusion machine 9, a quenching furnace 10, a cooling water tank 11, a cooling oil tank 12, a tempering furnace 13, a cooling bed 14, and a straightening machine 15. The electric arc furnace, the refining furnace, the ingot heating furnace, the forging machine, the annealing furnace, the blank processing equipment, the electromagnetic induction heating furnace, the hole expanding machine, the extrusion machine, the quenching furnace, the cooling water tank, the cooling oil tank, the tempering furnace, the cooling bed, and the straightening machine are arranged in sequence. Figure 2 As shown in FIG. 2, the annealing furnace is a chamber type gas furnace, which is provided with a refractory material 16, a heat insulation material 17, a furnace body steel frame 18, a burner 19, a thermocouple 20, a smoke outlet 21, a heat exchanger 22, a lifting device 23, a furnace door 24, and a furnace body support 25.

[0032] Figure 3 As shown in FIG. 3, the extrusion machine is a 63MN horizontal extrusion machine, which includes a die tail seat 26, a die middle seat 27, a die seat 28, a die support 29, an extrusion die 30, an extrusion cylinder intermediate layer 31, an extrusion cylinder inner lining 32, an extrusion cylinder outer layer 33, a core rod 34, an extrusion pad 35, and an extrusion rod 36.

[0033] As shown in FIG. 4, the extrusion die is provided with an inner nozzle 37 and a rotating support wheel 38. Figure 4

[0034] As shown in FIG. 5, the extrusion cylinder is provided with a seamless steel pipe 39, circulating water 40, a fixed support 41, quenching oil 42, and a stirring device 43.​​Figure 5 As shown in the figure, the cooling water tank 11 is provided with an inner nozzle 37 and a rotating support wheel 38. The rotating support wheel 38 is used to horizontally place the seamless steel pipe 39 during cooling, and the inner nozzle 37 is used to spray circulating water 40 into the inner hole of the seamless steel pipe in the axial direction. The cooling water tank 11 is filled with circulating water, and the cooling water tank 11 is provided with a water outlet connected to the inner nozzle 37 through a water pump.

[0035] As shown in the figure, the cooling oil tank 12 is provided with a fixed support 41 and a stirring device 43. The fixed support 41 is used to horizontally place the seamless steel pipe 39 during oil cooling, and the stirring device 43 is used to stir the quenching oil 42 to promote the flow of the quenching oil in the cooling oil tank. Figure 6

[0036] Example 1

[0037] The medium-thick-wall 85KSI-13Cr seamless steel pipe has a production specification of an outer diameter of φ146mm x a wall thickness of 28mm, and the chemical composition is shown in Table 1:

[0038] Table 1. Component analysis data of the 85KSI-13Cr seamless steel pipe of φ146mm x 28mm (mass percentage %)

[0039]

[0040] Note: The rest is Fe and unavoidable impurities.

[0041] The production process of the medium-thick-wall 85KSI-13Cr seamless steel pipe in the present application includes the following steps:

[0042] 1. Billet preparation: The 85KSI-13Cr continuous casting billet is cast by arc furnace + refining furnace smelting, and the smelting steps are as follows: scrap steel as raw material, smelting by arc furnace and feeding into LF furnace for refining, and feeding Al block. When the molten steel temperature is 1600℃-1630℃, VD furnace vacuum treatment is performed, the vacuum degree is 3.50Pa-4.00Pa, Si-Ca wire is added before vacuum, and the vacuum holding time is 25min-30min. When the molten steel temperature is 1500℃-1520℃, a φ380mm continuous casting billet is cast.

[0043] 2. Forging and pressing the forging rod: The heating process of the continuous casting billet is as follows: when the furnace temperature is 520℃, the temperature is kept for 2.0h, the temperature is raised to 900℃ at a speed of 55℃ / h, the temperature is kept for 2.0h, and the temperature is raised to 1220℃-1230℃ at a speed of 75℃ / h, and the temperature is kept for 4h. After the φ380mm continuous casting billet is heated, a φ368mm forging rod is forged, the initial forging temperature is 1190℃, and the final forging temperature is 920℃.

[0044] ​⑶ forging rod annealing, annealing the forging rod obtained in step ⑵ in a chamber furnace, the temperature of the forging rod annealing is 750℃, the holding time is 8h, the furnace is cooled to 300℃-325℃, then the furnace is discharged and air-cooled, and the hardness is reduced.

[0045] ⑷ forging rod processing, the forging rod obtained in step ⑶ is processed with 5mm single-side outer circle, the center hole is processed with 45mm diameter, the outer surface oxide and the center loose are removed, and a short forging rod with outer diameter φ357mm / inner diameter φ45mm×length 920mm is processed.

[0046] ⑸ extrusion forming, the cold billet is heated for 4 times in an electromagnetic induction furnace. The first heating power is 350KW, the outer surface temperature of the billet reaches 830℃-850℃; the second heating power is 400KW, the outer surface temperature reaches 1020℃-1040℃; the third heating power is 500KW, the outer surface temperature of the billet reaches 1150℃-1180℃; the fourth heating power is 800KW, the outer surface temperature of the billet reaches 1190℃-1210℃, and the heating is completed. Then the billet is descaled by 20MPa high-pressure water, and then lubricated by glass powder, the inner lubrication is by medium alkali powder, the outer lubrication is by 844-7, and the glass pad powder is by medium alkali powder. The steel pipe is extruded by a 63MN horizontal extruder, including ① hole expanding machine process, the hole expanding speed is 200mm-230mm / s, and ② extruder process, the extruding speed is 200mm-220mm / s.

[0047] ⑹ normalizing treatment, the steel pipe is heated to 940℃-950℃ in a trolley furnace, the holding time is 50min, and the steel pipe is air-cooled to room temperature.

[0048] ⑺ quenching treatment, the steel pipe is heated to 960℃-980℃ in a trolley furnace, the holding time is 80min, the steel pipe is quickly cooled by immersion in water, and then quickly transferred to oil when the temperature of the steel pipe reaches 550℃-580℃, and then cooled to 60℃, and then air-cooled and cleaned of residual oil.

[0049] ⑻ first tempering treatment, the steel pipe is heated to 690℃-700℃, the holding time is 200min, the steel pipe is quickly cooled by air blowing to room temperature, and then pressure straightened.

[0050] ⑼ second tempering treatment, the steel pipe is heated to 580℃-600℃, the holding time is 120min, the steel pipe is quickly cooled by air blowing to room temperature, and a medium-thick-wall 85KSI-13Cr seamless steel pipe is obtained.

[0051] ⑽ performance detection, the performance of the produced 85KSI-13Cr seamless steel pipe is detected, and the detection data is shown in Table 2.

[0052] Table 2. Performance detection results of the 85KSI-13Cr seamless steel pipe with φ146mm×28mm

[0053]

[0054] Example 2

[0055] Another embodiment of the present application is to produce a medium wall 85KSI-13Cr seamless steel pipe with a size of φ132mm x 36mm, and the chemical composition is shown in Table 3:

[0056] Table 3. Component analysis data of 85KSI-13Cr seamless steel pipe of φ132mm x 36mm (mass percentage %)

[0057]

[0058] Note: The rest is Fe and inevitable impurities.

[0059] The production process of the medium wall 85KSI-13Cr seamless steel pipe includes the following steps:

[0060] 1. Billet preparation, 85KSI-13Cr ingot is cast by arc furnace + refining furnace smelting, the smelting steps are as follows: scrap steel as raw material, smelted by arc furnace and sent to LF furnace for refining, and Al block is fed, when the temperature of the molten steel is 1600℃-1630℃, VD furnace vacuum treatment is carried out, the vacuum degree is 3.50Pa, Si-Ca wire is added before vacuum, the vacuum holding time is 25min, when the temperature of the molten steel is 1520℃-1550℃, 3.25T ingot is cast.

[0061] 2. Forging and pressing the forged rod, the heating process of the ingot is as follows: when the furnace temperature is 520℃-540℃, the temperature is kept for 2.0h, the temperature is raised to 900℃ at a speed of 60℃ / h, the temperature is kept for 2.0h, the temperature is raised to 1220℃-1230℃ at a speed of 70℃-80℃ / h, the temperature is kept for 3.5h. After heating, a φ370mm forged rod is forged, the initial forging temperature is 1190℃, the final forging temperature is 1220℃, and the feed amount is 100mm.

[0062] 3. Annealing of the forged rod, the forged rod obtained in step 2 is annealed in a chamber furnace, the annealing temperature of the forged rod is 750℃-760℃, the temperature is kept for 10h, the furnace is cooled to 320℃-340℃, then the furnace is taken out and air cooled to reduce the hardness.

[0063] 4. Machining of the forged rod, the outer circle of the forged rod obtained in step 3 is machined by 6mm on one side, the center hole is machined to a diameter of 45mm, the outer surface scale and the center porosity are removed, and a short forged rod with an outer diameter of φ358mm / inner diameter of φ45mm x length of 900mm is machined.

[0064] ⑸Extrusion forming, cold billet is heated in electromagnetic induction furnace for 4 times. The first heating power is 350KW, the billet outer surface temperature reaches 830-850℃; the second heating power is 400KW, the outer surface temperature reaches 1020-1040℃; the third heating power is 500KW, the billet outer surface temperature reaches 1160-1180℃; the fourth heating power is 800KW, the billet outer surface temperature reaches 1220-1240℃, and the heating is completed. Then the billet is descaled by 22MPa high pressure water, and then lubricated by glass powder, and the inner lubrication is by medium alkali powder, the outer lubrication is by 844-7, and the glass pad powder is by medium alkali powder. The steel pipe is extruded by 63MN horizontal extruder, including ① hole expanding machine process, hole expanding speed is 180mm / s, ② extruder process, extrusion speed is 220mm / s.

[0065] ⑹Normalizing treatment, the steel pipe is heated to 950-959℃ in a trolley furnace, and is kept for 50-60min, and is air cooled to room temperature.

[0066] ⑺Quenching treatment, the steel pipe is heated to 950-970℃ in a trolley furnace, and is kept for 80min, and is quickly cooled by immersing in water, and is quickly transferred to oil when the steel pipe temperature reaches 400℃, and is cooled to 50℃, and then is air cooled, and is cleaned of residual oil.

[0067] ⑻First tempering treatment, the steel pipe is heated to 660-680℃, and is kept for 240min, and is quickly cooled by air blowing to room temperature, and then is press straightened.

[0068] ⑼Second tempering treatment, the steel pipe is heated to 580-600℃, and is kept for 80min, and is quickly cooled by air blowing to room temperature, and a medium-thick wall 85KSI-13Cr seamless steel pipe is obtained.

[0069] ⑽Performance detection, the performance of the produced 85KSI-13Cr seamless steel pipe is detected, and the detection data is shown in Table 4.

[0070] Table 4. Performance detection results of φ132mm x 36mm 85KSI-13Cr seamless steel pipe

[0071]

Claims

1. A method of producing a medium heavy wall 85 KSI - 13 Cr seamless steel pipe characterized by: The method comprises the following steps: 1) blank preparation, taking scrap steel as raw material, smelting in an electric arc furnace, feeding into an LF furnace for refining, feeding Al block, when the temperature of the molten steel is 1570-1650℃, carrying out vacuum treatment in a VD furnace, vacuum degree 20-50Pa, adding Si-Ca wire before vacuum, vacuum holding time 15-30min; when the temperature of the molten steel is 1450-1550℃, pouring into a mold ingot or continuous casting blank; 2) forging and pressing the ingot or blank after heating to forge into a forged rod, compression ratio 1.01-6.0, initial forging temperature 1180-1200℃, final forging temperature 900-950℃, each pass reduction 10-50mm, feed amount 50-120mm; 3) annealing the forged rod obtained in step 2) in a chamber furnace to reduce hardness; 4) processing the forged rod obtained in step 3), processing the outer circle of the forged rod by 3-8mm, processing the center hole to a diameter of 30-85mm, removing the outer surface oxide skin and the center loose portion; 5) extruding, heating the forged rod to 1190-1260℃ in an electromagnetic induction furnace, then removing the scale under high pressure water of 18-23MPa, then lubricating with glass powder, and extruding the thick-walled steel pipe by a 63MN horizontal extruder; 6) normalizing, heating the steel pipe to 900-959℃ in a trolley furnace, holding for 30-60min, and air cooling to room temperature; 7) quenching, heating the steel pipe to 920-980℃ in a trolley furnace, holding for 60-80min, immersing in water for fast cooling, and then quickly transferring to quenching oil when the temperature of the steel pipe reaches 300-600℃, cooling to 20-80℃, and then air cooling and cleaning residual oil; 8) first tempering, heating the steel pipe to 660-700℃, holding for 200-240min, air cooling to room temperature, and then pressure straightening; 9) second tempering, heating the steel pipe to 500-600℃, holding for 120-180min, air cooling to room temperature, to obtain the thick-walled 85KSI-13Cr seamless steel pipe; 10) performance detection, the detection items include tensile strength, Rt0.5 yield strength, elongation, hardness and impact energy.

2. The method of producing a medium heavy wall 85 KSI - 13 Cr seamless steel pipe according to claim 1, characterized by: In step 2), the mold ingot or continuous casting blank is heated to a furnace temperature of 500-550℃, holding for 2.0h; then heated to 880-920℃ at a temperature rising speed of 45-65℃ / h, holding for 1.5-2.0h; and then heated to 1220-1230℃ at a temperature rising speed of 70-80℃ / h, holding for 3-5h.

3. The method of producing a medium heavy wall 85 KSI - 13 Cr seamless steel pipe as claimed in claim 1, wherein: In step 3), the temperature for annealing the forged rod is 700-760℃, holding for 6-12h, and then furnace cooling to 300-350℃ to be discharged and air cooled to room temperature.

4. The method of producing a medium heavy wall 85 KSI - 13 Cr seamless steel pipe as claimed in claim 1, wherein: In the extrusion forming stage of step 8, the cold blank is heated for 4 times in the electromagnetic induction furnace; the first heating power is 350KW, the outer surface temperature of the blank reaches 800-850℃; the second heating power is 400KW, the outer surface temperature reaches 1000-1050℃; the third heating power is 500KW, the outer surface temperature of the blank reaches 1150-1180℃; the fourth heating power is 800KW, the outer surface temperature of the blank reaches 1190-1260℃, and the heating is completed.

5. The method of producing a medium heavy wall 85 KSI - 13 Cr seamless steel pipe as claimed in claim 1, wherein: In the quenching treatment stage of step 10, 1) the steel pipe is sent into the quenching furnace and heated to 920-980℃, and then taken out immediately after the heat preservation is completed; 2) the steel pipe is quickly transferred to the rotating support wheel in the water tank filled with circulating water, the rotating speed of the support wheel is 30-40rpm, the distance between each pair of support wheels is 0.5-1.2m, the steel pipe rotates under the driving of the support wheel, the inner nozzle arranged at one end of the steel pipe is opened, the inner diameter of the inner nozzle is 30-40mm smaller than the inner diameter of the steel pipe, and the inner nozzle sprays water into the inner hole of the steel pipe along the axial direction; 3) after the inner nozzle sprays water for 5-10s, the rotating support wheel device sinks as a whole, and the steel pipe is immersed into the water surface by 1 / 2 of the diameter, and the steel pipe continues to cool under the action of the inner nozzle and the immersion; 4) when the temperature of the steel pipe cools to 300-600℃, the rotating support wheel device rises as a whole to make the steel pipe leave the water surface; 5) the quenched steel pipe is quickly transferred to the fixed support in the cooling oil tank, and the quenching stress is reduced by using the quenching oil as the cooling medium to avoid cracks; 6) the steel pipe is cooled to 20-80℃, and the quenching is completed.

6. The method of producing thick wall 85 KSI-13Cr seamless steel pipe as claimed in claim 1, wherein: The extrusion forming process comprises 1) hole expansion by the hole expander at an expansion speed of 100-250mm / s and an expansion ratio of 1.01-1.35; and 2) extrusion by the extruder at an extrusion speed of 50-250mm / s and an extrusion ratio of 3-10.

7. The method of producing a medium heavy wall 85 KSI - 13 Cr seamless steel pipe as claimed in claim 1, wherein: The composition of the steel for the seamless steel pipe comprises, by mass percent, C: 0.10-0.19, Si: 0.15-0.55, Mn: 0.50-0.85, Cr: 12.2-13.2, Ni: 0.40-0.50, Mo: 0.10-0.45, Ti: 0.01-0.04, Nb: 0.005-0.03, V: 0.05-0.10, Al: 0.01-0.03, Ca: 0.0005-0.008, N: 0.005-0.030, Nb+V+Ti+Al: ≤0.15, Cu: ≤0.25, O: ≤0.0030, H: ≤0.0003, P: ≤0.015, S: ≤0.004, and the balance of Fe and inevitable impurities.

8. The method of producing a medium heavy wall 85 KSI - 13 Cr seamless steel pipe as claimed in claim 1, wherein: The seamless steel pipe has the properties of tensile strength ≥670MPa, Rt0.5 yield strength 587-670MPa, elongation ≥20%, and hardness ≤23.5HRC; the average value of the full-size impact energy of the seamless steel pipe at -10℃ in the transverse Charpy V-notch is ≥30J, and the average value of the full-size impact energy of the seamless steel pipe at -10℃ in the longitudinal Charpy V-notch is ≥41J.

9. The method of producing a medium heavy wall 85 KSI - 13 Cr seamless steel pipe as claimed in claim 1, wherein: The seamless steel pipe has an outer diameter of φ90-φ325mm and a wall thickness of 25-45mm.

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