A method for producing a super austenitic seamless steel pipe by cross piercing

Abstract

The application discloses a kind of S31254 super austenitic seamless steel tube's piercer production method, including blank outer surface treatment, sawing, centering and blank piercer pre-processing treatment;Heating: according to the heating temperature and heating time of the preheating section, heating section and soaking section of the inclined bottom furnace are set according to the material properties, to achieve ideal high temperature tissue performance;Piercer: the key parameters set in the production process of the piercer are defined in the piercer process, cooling treatment: the highest temperature of cooling mode and cooling termination is determined. Roll design: including the degrees of entry rolling angle and exit rolling angle of roll and the diameter size of working strip roll and other contents. Through the above series of steps and tool design, the material is successfully produced on the piercer The quality of steel pipe reaches the standard requirements.

Description

Technical Field

[0001] This invention relates to the field of seamless steel pipe manufacturing technology, and more particularly to a method for producing super austenitic seamless steel pipes by skew rolling and piercing. Background Technology

[0002] S31254 is a super austenitic stainless steel. Due to its high Mo content, it has better resistance to acid corrosion, pitting corrosion, crevice corrosion, stress corrosion and general corrosion than conventional austenitic stainless steel. It is widely used in industries such as seawater desalination and paper bleaching.

[0003] Due to its relatively high content of Ni, Cr, Mo, N, etc., its yield strength and tensile strength are higher than those of conventional austenitic stainless steel. It has a large resistance to high-temperature deformation and a narrow hot working temperature range. Currently, it is mainly produced by extrusion. However, the characteristics of extrusion production are that the metal loss from extrusion billet machining, expansion, and pressing is large. Therefore, the yield of extrusion production is relatively low, and the energy and auxiliary material consumption of extrusion production are also large.

[0004] To address some or all of the technical problems existing in the prior art, this invention provides a method for producing S31254 super austenitic seamless steel pipe by skew rolling and piercing, which effectively reduces the amount of machining required for the billet, achieves virtually no metal loss during the hot working process, and significantly improves the material yield. Summary of the Invention

[0005] The purpose of this invention is to address the above-mentioned problems by providing a method for producing super austenitic seamless steel pipes by skew rolling and piercing.

[0006] The objective of this invention is achieved as follows: A method for producing super austenitic seamless steel pipes by skew rolling and piercing, comprising the following steps: Step 1: Billet outer surface treatment: Peeling is performed on the incoming round steel. After peeling, the outer diameter deviation of the entire billet does not exceed 1.5mm, and the outer surface of the round steel is free of cracks and black scale, ensuring the smoothness of the peeled surface; Step 2: Billet sawing: The billet sawing length is set as needed, with both ends flush. The outer diameter must be measured before marking, and sawing is performed according to the standards of the process card. After sawing, the material information is clearly marked on the billet; Step 3: Centering: Before centering, the incoming material condition is checked, and whether the end face cutting angle is within the process requirements range is checked. Secondly, the centering clamping device is checked for eccentricity; Step 4: Heating: Heating is divided into three sections according to the different temperature ranges of the furnace: preheating section, heating section, and soaking section; Step 5: Mandrel design: The mandrel design includes the maximum diameter of the mandrel working section, the total diameter of the mandrel, etc. Step 6: Guide Plate Design: The guide plate design includes the angle between the guide plate's hypotenuse and the bottom plane, the inlet cone angle, the inlet section arc, the top arc, the outlet cone angle, the outlet arc, the bottom cone angle, the length from the bottom cone of the guide plate to the working surface, the inlet section width, the outlet section width, the total length of the guide plate, the bite section length, and the ejection section length; Step 7: Roll Design: The roll design includes the selection of tapered rolls, the roll inlet cone angle, the outlet cone angle, the roll surface length, the inlet working surface length, and the working rolling center roll diameter; Step 8: Setting Parameters for Skew Rolling Piercing Deformation Process: This includes the selection of the mill unit, the determination of the piercing specifications, the selection of the mandrel specifications, and the setting of the roll distance, guide plate distance, and mandrel forward extension; Step 9: Cooling Treatment: After hot rolling, the rolls are cooled in water.

[0007] In step one, the outer diameter tolerance of the blank after peeling is ±0.5mm, and the depth of the cutting tool marks after peeling is <0.5mm.

[0008] In step two, the blank is cut to a length of 2700mm-2750mm, with both ends flush, and a sawing tolerance of ±1mm; the sawing bevel is <2mm.

[0009] In step three, the inner diameter of the centering hole is 49.5mm-50.5mm, the inner depth tolerance is 29mm-31mm, and the eccentricity of the centering hole is ≤1mm.

[0010] In step four, the preheating temperature is 650-700℃ and the furnace dwell time is 3-4 hours; the steel temperature in the heating section is controlled at 1120-1130℃ and the furnace dwell time is 2.5-3 hours; the steel temperature in the soaking section is controlled at 1140-1150℃ and the furnace dwell time is controlled between 1.5-2 hours.

[0011] In step five, the maximum diameter of the mandrel working section is φ109mm-φ111mm, the total length of the mandrel is 204mm-206mm, the reverse taper radius is R9mm-R11mm, the reverse taper length is 8-10mm, the straight section length is 9.5-10.5mm, the rolling angle is designed to be 2.7°-3.3°, the rolling section length is 64mm-69mm, the nose arc radius is R5mm-R7mm, the deformation section arc radius is R198mm-R203mm, the connection thread method is left-handed, and the connection thread size is M64*4-M65*5.

[0012] In step six, the angle between the inclined side of the guide plate and the bottom plane is 56°-63°, the inlet cone angle is 5.3°-5.6°, the inlet section arc is R107mm-R112mm, the top arc is R106mm-R111mm, the outlet cone angle is 2.3°-2.7°, the outlet arc is R215mm-R211mm, the bottom cone angle is 130°-133°, the length from the bottom cone of the guide plate to the working surface is 80mm-85mm, the inlet section width is 125mm-127mm, the outlet section width is 167mm-172mm, the total length of the guide plate is 558mm-663mm, the bite section length is 207mm-212mm, and the ejection section length is 348mm-353mm.

[0013] In step seven, the rolls are designed as tapered rolls with an inlet cone angle of 2.6°-2.9°, an outlet cone angle of 2.9°-3.2°, a roll surface length of 745mm-751mm, an inlet working surface length of 306mm-308mm, and a working rolling center roll diameter of 992mm-1013mm.

[0014] In step eight, the roll gap is 131.4mm-132.2mm, the guide plate gap is 147.5mm-149mm, and the mandrel extension is 64mm-66mm.

[0015] In step nine, the circulating water temperature should not exceed 50℃.

[0016] The beneficial effects of this invention are: 1) This invention achieves the production of seamless S31254 super austenitic steel pipes through skew rolling piercing, rather than by extrusion. The skew rolling piercing production method achieves the goal of high yield for this material.

[0017] 2) This invention achieves the heating of the material by controlling the heating method of the inclined bottom furnace.

[0018] 3) This invention achieves the deformation of S31254 steel by designing relevant molds and dies, including the design of the mandrel, guide plate and roll deformation mold.

[0019] 4) This invention sets various deformation parameters for the skew rolling piercing mill, creating favorable deformation conditions for the material.

[0020] S31254 material is currently produced entirely through extrusion. Its characteristics include losses during billet preparation due to the rounding, flaring, and deep-hole processes, as well as metal losses during hot expansion and hot extrusion. The yield of seamless square tubes obtained through extrusion is approximately 85%. In contrast, production via skew rolling and piercing eliminates metal loss during billet preparation, and the losses during piercing are negligible, resulting in a final yield of over 96%. Attached Figure Description

[0021] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and constitute a part of this invention, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings: Figure 1 This is a schematic diagram of the mandrel design for a production method of S31254 super austenitic seamless steel pipe according to the present invention.

[0022] Figure 2 This is a schematic diagram of the guide plate design in the production method of S312554 super austenitic seamless steel pipe of the present invention.

[0023] Figure 3 This is a schematic diagram of the design of the rolling mill in the production method of S31254 super austenitic seamless steel pipe of the present invention. Detailed Implementation

[0024] Because S31254 super austenitic seamless steel pipe has a high Mo content of 6% and contains N, it exhibits very high resistance to high-temperature deformation. However, its melting point is relatively low, resulting in a very narrow heating range. Extrusion production is carried out under triaxial compressive stress, which greatly reduces the tendency for the billet to crack during production. Furthermore, the 6000-ton extrusion pressure provides sufficient thrust to overcome deformation resistance, even at lower billet extrusion temperatures. At higher temperatures, the triaxial compressive stress further reduces the likelihood of crack formation. Therefore, when produced by extrusion, this material has a very wide hot working range, potentially reaching 70℃-100℃.

[0025] However, the biggest drawback of extrusion production is its low yield. Metal loss includes three aspects: cold working loss, heating loss, and hot working waste loss generated by the process design. Cold working loss includes: rounding loss of the billet end face, deep hole loss of the billet, and flaring loss of the billet end face. Waste loss during extrusion includes: expansion waste and pressing waste. The total loss reaches between 13% and 15%.

[0026] The deformation characteristics of skew rolling piercing are biaxial compressive stress and uniaxial tensile stress. The production process utilizes the principle of creating a cavity through the transition from an ellipse to a circle. When producing steel pipes using this method, internal cracks are very likely to occur. To avoid these defects, cooling measures are typically used during production. However, for steel grades with high resistance to high-temperature deformation, lower temperatures will cause the deformation resistance to exceed the frictional force provided to the billet by the rolls, resulting in the billet becoming stuck.

[0027] However, the advantages of skew rolling piercing are also obvious, namely, the yield of the billet is very high, the loss of the billet during processing is only between 1% and 3%, the burning loss is no more than 1%, and the total yield can reach more than 96%, which can improve the yield by 10% compared with extrusion production.

[0028] For S31254, a super austenitic stainless steel, its deformation resistance is high and its hot working temperature range is narrow. If stable production can be achieved through piercing, it will be groundbreaking and of great significance.

[0029] Therefore, we ensured good surface conditions and stress preparation for billet production by setting technical requirements for billet processing. Secondly, based on the material characteristics, we set accurate heating temperatures and times to ensure relatively low high-temperature deformation resistance of the billet without causing rapid grain growth. Finally, through the design of the die, which has better streamlines, is more suitable for the deformation angle, and is matched with the rolling mill parameters, the deformation process of the billet is smoother, deformation resistance is dispersed, and the tendency for internal cracks to form is reduced, enabling the successful implementation of skew rolling piercing for the production of seamless steel pipes of this material.

[0030] This invention provides a method for skew rolling piercing of S31254 seamless steel pipe. The technical solution is as follows: 1. Surface treatment of the billet: The incoming round steel is peeled. After peeling, the outer diameter of the billet is ±0.5mm. The setting of the peeled outer diameter tolerance affects the bite-in of the pierced billet and the rolling stress process when setting the piercing parameters. The depth of the cutting tool marks after peeling is <0.5mm to ensure that there are no cracks, unevenness, or other defects on the outer surface after rolling. The outer surface is free of obvious cracks and black scale, and the smoothness of the peeled surface is guaranteed. The outer diameter deviation of the entire billet after peeling shall not exceed 1.5mm. This tolerance ensures more uniform stress during the transformation of the billet from round steel to pipe.

[0031] 2. Billet sawing: The billet sawing length is set according to the pipe requirements, with both ends flush. The outer diameter must be measured before marking. Sawing is performed according to the standards on the process card. After sawing, the material information is clearly marked on the billet. The billet sawing length is 2750mm, with both ends flush. The sawing tolerance is ±1mm. If the tolerance is too large, the set steel pipe length will not meet the final length requirement. The sawing bevel is <2mm. The sawing bevel tolerance setting ensures centering accuracy during the centering process.

[0032] 3. Before centering, the incoming material must be checked to ensure that the end face bevel is within the process requirements. Secondly, the centering clamping device must be checked for eccentricity. The centering hole size is D50mm*30mm, the inner diameter tolerance is ±0.5mm, the inner depth tolerance is ±1mm, and the centering hole eccentricity is ≤1mm. The centering hole must be smooth and burr-free. The accuracy deviation of the centering hole directly affects the wall deviation at the head of the rolled steel pipe.

[0033] 4. Heating is divided into three sections according to different temperature ranges in the furnace: preheating section, heating section, and soaking section. The heating temperature and time for each section are set separately based on the material properties, billet outer diameter, and the specifications of the rough tube to be produced. The preheating section temperature is 650-700℃, and the furnace dwell time is 3-4 hours; the heating section steel temperature is controlled at 1120-1130℃, and the furnace dwell time for this section is 2.5-3 hours; the soaking section steel temperature is controlled at 1140-1150℃, and the furnace dwell time is controlled between 1.5-2 hours. Due to the very high Cr and Ni content in the material, and the Mo content exceeding 3% of ordinary duplex steel, reaching 6%, this alloy characteristic results in a very narrow hot working temperature range and very high deformation resistance. Therefore, selecting the optimal heating temperature and heating time is crucial.

[0034] 5. The mandrel design includes the maximum diameter of the working section, the total length of the mandrel, the inverted cone curvature, the inverted cone length, the straight section length, the rolling angle, the rolling section length, the nose radius, the deformation section radius, the connecting thread type, and the connecting thread size. The maximum diameter of the working section of the mandrel is determined based on the gap between it and the inner diameter of the rough tube during the rolling process. The length of the mandrel directly determines the number of rolling passes during the rolling process. The maximum diameter of the working section of the mandrel is φ110mm, the total length of the mandrel is 205mm, the inverted cone curvature is R10mm, and the inverted cone length is 9mm. This curvature and length ensure that the inner hole of the rough tube is not scratched when it leaves the mandrel. The straight section length is 10mm. Although the straight length of the mandrel does not participate in the deformation process of the rough tube, it is crucial in the rounding process of the rough tube. The rolling angle is designed to be 3°, and the rolling section length is 65mm to ensure smooth expansion of the inner hole. The nose section has a radius of curvature of R5mm. This radius is designed to match the porosity formed in the middle during the elliptical deformation of the rough tube. The deformed section has a radius of curvature of R200mm. This curvature is designed as the gradual curve from the billet to the tube, and its size needs to be determined based on the specifications of the rough tube. The connection thread is left-handed, with a thread size of M64*4, ensuring a reliable transition connection between the mandrel and the mandrel without affecting the strength of the mandrel end.

[0035] 6. The guide plate design includes the angle between the guide plate's hypotenuse and the bottom plane, the inlet cone angle, the inlet section curvature, the top curvature, the outlet cone angle, the outlet curvature, the bottom cone angle, the length from the bottom cone of the guide plate to the working surface, the inlet section width, the outlet section width, the total length of the guide plate, the bite section length, and the ejection section length. The angle between the guide plate's hypotenuse and the bottom plane is 60°. This angle design must match the angle of the guide plate frame, and its degree design must ensure the stability of the guide plate frame in fixing the guide plate. The inlet cone angle is 5.4°. This angle design, while meeting the piercing rolling parameters, ensures smooth one-time bite of the billet and rolls. The inlet section curvature is R109mm, and the top curvature is R109mm. The design of these two curvatures is closely related to the billet diameter and ellipticity design. The outlet cone angle is 2.5°, and the outlet curvature is R218mm. This cone angle design ensures the roundness of the rough tube during the forming process. The bottom cone angle is 130°, ensuring a tight fit between the guide plate and the guide plate frame. The length from the bottom cone of the guide plate to the working surface is 80mm. This thickness is designed to meet both the strength requirements of the guide plate itself and the travel requirements of the guide plate distance. The inlet section width is 126±1mm, the outlet section width is 170mm, and the total length of the guide plate is 560mm. These three parameters are designed to ensure that the guide plate fits snugly according to the angle of the rolls, ensuring that the guide plate will not wear the rolls during the deformation process, nor will it cause chain-like issues during the forming process. The bite section length is 210mm, and the ejection section length is 350mm. These two lengths are designed to address the force distribution on the guide plate during the deformation process of the raw tube.

[0036] 7. The roll design includes the selection of tapered rolls, roll inlet cone angle, roll outlet cone angle, roll surface length, inlet working surface length, and working rolling center roll diameter. The rolls are tapered with an inlet cone angle of 2.7° and an outlet cone angle of 3°. These angles largely determine the billet diameter and the expansion amount of the rough tube after piercing. The roll surface length is 750mm, and the inlet working surface length is 307mm. These dimensions ensure the deformation stroke span from the billet to the rough tube, resulting in complete deformation of the rough tube. The working rolling center roll diameter is 1000mm. The large roll diameter design of the 160 unit ensures a wide contact area between the rolls and the billet, resulting in uniform stress distribution during billet deformation.

[0037] 8. Parameter settings for the skew rolling piercing deformation process: This includes the selection of the mill unit, the determination of the piercing specifications, the selection of the mandrel specifications, and the setting of the roll gap, guide plate distance, and mandrel extension. A larger 160mm piercing mill unit is used, which has a larger roll body and greater width, resulting in better surface quality of the pierced billet. The selection of the piercing specifications and mandrel must ensure the clearance between the billet and the mandrel, making the piercing deformation smoother and effectively preventing excessive tearing of the billet core. A reasonable roll gap setting provides sufficient longitudinal pressure for the smooth passage of the billet, ensuring the frictional force for the billet's spiral forward movement. The guide plate distance and the billet size are set according to the billet's outer diameter and the roll gap. A reasonable mandrel extension setting ensures smooth initial piercing bite while preventing excessive tearing of the billet center before the second bite. Specifically: roll gap 132mm, guide plate distance 148mm, mandrel extension 65mm.

[0038] 9. Cooling treatment: After hot rolling, the billet is subjected to water cooling treatment. The circulation and cooling of the water in the cooling pool should be controlled, and the circulating water temperature should not exceed 50℃, so that the water temperature is low enough to meet the cooling rate after the billet is rolled, so as to ensure that the steel pipe forms a good solution treatment effect.

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0040] The technical solutions provided by the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0041] Example 1

[0042] (1) Surface treatment of billet: The incoming round steel is peeled. After peeling, the outer diameter of the billet is φ148±0.5mm. The depth of the cutting tool marks after peeling is <0.5mm. There are no obvious cracks or black skin on the outer surface. The deviation of the outer diameter of the whole piece after peeling shall not exceed 1.5mm.

[0043] (2) Sawing: The blank is sawn to a length of 2750mm, with both ends flush. The outer diameter must be measured before marking. Sawing is carried out according to the standard of the process card. After sawing, the material information is clearly marked on the blank. The sawing tolerance is ±1mm; the sawing slope is <2mm.

[0044] (3) Centering: Before centering, the incoming material condition must be checked and whether the end face cutting angle is within the process requirements. Secondly, it is necessary to check whether the centering clamping device is eccentric. The centering hole size is D50mm*30mm, the inner hole diameter tolerance is ±0.5mm, the inner hole depth tolerance is ±1mm, the centering hole eccentricity is ≤1mm, and the centering hole is required to be smooth and burr-free.

[0045] (4) Heating: Heating is divided into three sections according to the different temperature ranges of the furnace: preheating section, heating section and soaking section. The heating temperature and heating time of each section are shown in the table below.

[0046]

[0047] (5) Design and selection of skew rolling piercing die: 5.1 Mandrel design: The maximum diameter of the mandrel working section is φ110mm, the total length of the mandrel is 205mm, the reverse cone arc is R10mm, the reverse cone length is 9mm, the straight section length is 10mm, the rolling angle is designed to be 3°, the rolling section length is 65mm, the nose arc radius is R5mm, the deformation section arc radius is R200mm, the connecting thread method is left-handed, and the connecting thread is M64*4.

[0048] 5.2 Guide plate design: The angle between the inclined side of the guide plate and the bottom plane is 60°, the inlet cone angle is 5.4°, the inlet section arc is R109mm, the top arc is R109mm, the outlet cone angle is 2.5°, the outlet arc is R218mm, the bottom cone angle is 130°, the length from the bottom cone of the guide plate to the working surface is 80mm, the inlet section width is 126±1mm, the outlet section width is 170mm, the total length of the guide plate is 560mm, the bite section length is 210mm, and the ejection section length is 350mm.

[0049] 5.3 Roll Design: The rolls are designed as tapered rolls with an inlet cone angle of 2.7°, an outlet cone angle of 3°, a roll surface length of 750mm, an inlet working surface length of 307mm, and a working rolling center roll diameter of 1000mm.

[0050] (6) The piercing rolling parameters are set as shown in the table below.

[0051]

[0052] (7) Cooling treatment: After hot rolling, the water should be put into the cooling pool immediately. The water in the cooling pool should be circulated and the temperature of the circulating water should not exceed 50°C.

[0053] The above steps successfully produced 155*20 rough steel pipes. The produced steel pipes had no cracks on the inner and outer walls, meeting the quality requirements of skew-rolled perforated steel pipes.

[0054] The losses during this production process include peeling, sawing, centering, burning, and piercing and rolling wear. Compared with the weight of the rough steel pipe and the billet, the yield rate is as high as 97.59%. Example 2

[0055] This case is a scheme to produce 155*20 steel pipes of the same specification by extrusion: (1) Sawing: the billet is sawed to a length of 790mm, with both ends flush, and is cut using a 7650 saw.

[0056] (2) Deep hole: The deep hole of the billet must penetrate the entire billet. The size of the deep hole is selected as 60mm, and the eccentricity of the deep hole is ≤1.5mm.

[0057] (3) Round arc: One end of the blank needs to be rounded, with an arc radius of R30mm.

[0058] (4) Flared mouth: The flared mouth is machined on the same side of the arc end of the blank, and the maximum diameter of the flared mouth cone is 135mm.

[0059] (5) Hole enlargement: The enlargement cone is 130mm, and the enlargement produces an enlargement allowance of 200mm.

[0060] (6) Extrusion: The extrusion needle is 117.5mm, the extrusion die is 159mm, the extrusion produces a residual diameter of 290mm and a length of 230mm.

[0061] The 155*20 extruded steel pipe produced through the above steps involves material loss processes including: sawing, deep hole drilling, arc forming, ring furnace burn-off, induction furnace burn-off, expansion loss, and pressing loss. Comparing the weight of the 155*20 extruded rough pipe with a 790mm billet, the yield rate is 86.82%.

[0062] The above description is only a specific embodiment of the present invention, but the structural features protected by the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.

Claims

1. A method for producing super austenitic seamless steel pipe by skew rolling and piercing, characterized in that: Includes the following steps: Step 1: Surface treatment of billet: Peel the incoming round steel. After peeling, the outer diameter deviation of the whole piece should not exceed 1.5mm. After peeling, there should be no cracks or black skin on the outer surface of the round steel, ensuring the smoothness of the peeled surface. Step 2: Blank sawing: The sawing length of the blank is set as needed, with both ends flush. The outer diameter must be measured before marking. The blank is sawed according to the standard of the process card. After sawing, the material information is clearly marked on the blank. Step 3: Centering: Before centering, check the incoming material and whether the end face bevel is within the process requirements. Secondly, check whether the centering clamping device is eccentric. Step 4: Heating: Heating is divided into three sections according to the different temperature ranges of the furnace: preheating section, heating section, and soaking section; Step 5: Mandrel Design: The mandrel design includes the maximum diameter of the working section of the mandrel, the total length of the mandrel, the inverted taper radius, the inverted taper length, the straight section length, the rolling angle, the rolling section length, the radius of the nose arc, the radius of the deformed section arc, the connection thread method, and the connection thread size; Step Six: Guide Plate Design: The guide plate design includes the angle between the guide plate's hypotenuse and the bottom plane, the inlet cone angle, the inlet section curvature, the top curvature, the outlet cone angle, the outlet curvature, the bottom cone angle, the length from the bottom cone of the guide plate to the working surface, the inlet section width, the outlet section width, the total length of the guide plate, the bite section length, and the ejection section length. Step 7: Roll Design: The roll design includes the selection of tapered rolls, roll inlet cone angle, roll outlet cone angle, roll surface length, inlet working surface length, and working rolling center roll diameter; Step 8: Setting parameters for the skew rolling piercing deformation process: including the selection of the mill, the determination of the piercing specifications, the selection of the mandrel specifications, and the setting of the roll gap, guide plate gap, and mandrel forward extension. Step 9: Cooling treatment: After hot rolling, the product is placed in water for cooling. In step five, the maximum diameter of the mandrel working section is φ109mm-φ111mm, the total length of the mandrel is 204mm-206mm, the reverse taper radius is R9mm-R11mm, the reverse taper length is 8-10mm, the straight section length is 9.5-10.5mm, the rolling angle is designed to be 2.7°-3.3°, the rolling section length is 64mm-69mm, the nose arc radius is R5mm-R7mm, the deformation section arc radius is R198mm-R203mm, the connection thread method is left-hand thread, and the connection thread size is M64*4-M65*5. In step six, the angle between the inclined side of the guide plate and the bottom plane is 56°-63°, the inlet cone angle is 5.3°-5.6°, the inlet section arc is R107mm-R112mm, the top arc is R106mm-R111mm, the outlet cone angle is 2.3°-2.7°, the outlet arc is R215mm-R211mm, the bottom cone angle is 130°-133°, the length from the bottom cone of the guide plate to the working surface is 80mm-85mm, the inlet section width is 125mm-127mm, the outlet section width is 167mm-172mm, the total length of the guide plate is 558mm-663mm, the bite section length is 207mm-212mm, and the ejection section length is 348mm-353mm. In step seven, the rolls are designed as tapered rolls with an inlet cone angle of 2.6°-2.9°, an outlet cone angle of 2.9°-3.2°, a roll surface length of 745mm-751mm, an inlet working surface length of 306mm-308mm, and a working rolling center roll diameter of 992mm-1013mm. In step eight, the roll gap is 131.4mm-132.2mm, the guide plate gap is 147.5mm-149mm, and the mandrel extension is 64mm-66mm.

2. The method for producing super austenitic seamless steel pipe by skew rolling and piercing according to claim 1, characterized in that: In step one, the outer diameter tolerance of the blank after peeling is ±0.5mm, and the depth of the cutting tool marks after peeling is <0.5mm.

3. The method for producing super austenitic seamless steel pipe by skew rolling and piercing according to claim 1, characterized in that: In step two, the blank is cut to a length of 2700mm-2750mm, with both ends flush, and a sawing tolerance of ±1mm; the sawing bevel is <2mm.

4. The method for producing super austenitic seamless steel pipe by skew rolling and piercing according to claim 1, characterized in that: In step three, the inner diameter of the centering hole is 49.5mm-50.5mm, the inner depth tolerance is 29mm-31mm, and the eccentricity of the centering hole is ≤1mm.

5. The method for producing super austenitic seamless steel pipe by skew rolling and piercing according to claim 1, characterized in that: In step four, the preheating temperature is 650-700℃ and the furnace dwell time is 3-4 hours; the steel temperature in the heating section is controlled at 1120-1130℃ and the furnace dwell time is 2.5-3 hours; the steel temperature in the soaking section is controlled at 1140-1150℃ and the furnace dwell time is controlled between 1.5-2 hours.

6. The method for producing super austenitic seamless steel pipe by skew rolling and piercing according to claim 1, characterized in that: In step nine, the circulating water temperature should not exceed 50℃.

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