Method for manufacturing static wind tunnel large-diameter high-precision pipe body through low-carbon austenitic stainless steel

Abstract

The invention relates to a method for manufacturing a static wind tunnel large-diameter high-precision pipe body through low-carbon austenitic stainless steel. The production process of the method comprises the steps of argon oxygen refining, ladle refining, continuous casting, electroslag remelting, 7000-ton fast forging hydraulic machine forging forming, annealing after forging, rough machining, heat treatment solid solution aging, multiple times of semi-finish machining destressing tempering, finish machining to the product size, honing to the inner hole precision and roughness and inspection. By means of the method, the large-diameter hollow pipe body with the high machining precision on the inner surface of the S30458 pipe body material can be machined, and the problems that the performance is not matched with the uniformity of the surface of the pipe body, machining deformation occurs, and machining is difficult can be effectively solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of steel material product manufacturing process, and specifically relates to a method for manufacturing a large-diameter, high-precision pipe body for a static wind tunnel from low-carbon austenitic stainless steel, that is, a method for processing a large-diameter hollow pipe body with a high processing precision on the inner surface of an S30458 pipe body material, which can effectively solve the problems of performance not meeting the uniformity of the pipe body surface, processing deformation and processing difficulties. Background Art

[0002] my country is now vigorously developing the aerospace industry, and the foundation of development is to build various types of wind tunnel test equipment. Each set of equipment is expensive and has a good prospect. The static wind tunnel is equivalent to the scale of the wind tunnel. It is built to study the most difficult problems in the scientific community (transition problems), and higher requirements are put forward for the dimensional accuracy and geometric tolerance of the wind tunnel. The calculation and estimation of transition problems are the key prerequisites for designing aircraft. The construction of static wind tunnels is in a leading position in the industry.

[0003] The characteristics of the ultra-large high-precision tube body of the static wind tunnel are as follows: it contains high-temperature and high-pressure air, passes through multiple sections of the tube body and is released from the end of the tube body to form a high-speed airflow. It is made of low-carbon austenitic stainless steel, with a single-section inner diameter ≥800mm±0.05 and a single-section length of more than 6 meters. The required overall length is tens of meters, and the coaxiality requirement is Φ0.1mm, the inner hole roundness is Φ0.05mm, and the step difference between the two sections of the tube body is required to be 0.05mm in the direction of the airflow. The coaxiality, inner hole roundness and airflow step of large-diameter stainless steel are not easy to meet; the large tube body is required to have a thin wall of 40mm, and the product should not be stressed or deformed after processing, which is not easy to meet; the flange of the large-diameter stainless steel tube body is prone to cracking due to integral forging, which is not easy to meet; the installation surface is required to be wear-resistant and non-adhesive during loading and unloading, which is not easy to meet. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and to provide a method for manufacturing large-diameter, high-precision pipe bodies for static wind tunnels using carbon austenitic stainless steel, which solves the problem of cracking during forging that affects subsequent processing when using pressure-bearing austenitic stainless steel S30458 to produce pipe bodies; solves the problem that pipe bodies require high straightness and roundness and are difficult to meet processing dimensions; solves the problem that stainless steel thin-walled pipe bodies are prone to stress deformation during processing; and solves the problem that it is difficult to ensure the reverse airflow step on the connection surface.

[0005] The object of the present invention is achieved in that: A method for making a large-diameter, high-precision pipe body for a static wind tunnel from low-carbon austenitic stainless steel, wherein the production process of the method is: argon oxygen refining + ladle refining + continuous casting → electroslag remelting → forging with a 7,000-ton fast forging hydraulic press → annealing after forging → rough machining → heat treatment and solid solution aging → multiple semi-finishing stress relief tempering → finishing to product size → honing to inner hole accuracy and roughness → inspection, and the specific steps are as follows: Step 1), forging, roughing and semi-finishing size allowance control: semi-finishing is divided into two times, and the outer circle and inner hole are required to be relative to the product size. The first semi-finishing diameter is required to leave a 20mm allowance, and the second semi-finishing is required to leave a 10mm allowance, and a 20mm allowance in the length direction; the roughing size requires the outer circle and inner hole to be relative to the product size, with a 40mm allowance in the diameter and a 30mm allowance in the length direction; the forging size requires the outer circle and inner hole to be relative to the roughing size, with a 60mm allowance in the diameter and a 50mm allowance in the length direction; Step 2), smelting: This type of steel is low-carbon austenitic stainless steel, and has strict requirements on high and low magnification, ultrasonic flaw detection and performance. Powdered lime shall not be used, and the chemical composition shall be adjusted according to the internal control composition. The charge includes scrap steel or steel scraps and pig iron above level 2. Miscellaneous scrap steel is not allowed to be added. The carbon content is ≥1.00%, the temperature is ≥1550℃, and the sampling and analysis control composition is carried out. The tapping temperature is ≥1660℃. After the composition is appropriate, the induction furnace is used for tapping. This steel process is rigorous in slag removal; the electrode head, residual steel and slag of the refining furnace should be cleaned in advance to avoid carbon increase; this type of steel contains Cr and Ni alloys, and the soup channel, middle injection pipe and residual scrap steel after smelting should be cleaned to prevent scrap steel pollution; the number of electric furnace bodies is ≥2 times, and the number of ladles is ≥2 times; the induction furnace equipment and lining meet the smelting requirements, and the electroslag ingot is subjected to ultra-detection after cooling to check that there are no cracks inside to ensure that high-purity and dense ingots are obtained, laying the foundation for subsequent production; Step 3), forging: The stainless steel forging billet with an inner hole of Φ800mm of the pipe body product is hollow forged: heating in a heating furnace, controlling the furnace temperature at 1250-1350℃, taking it out, using a 7000-ton fast forging hydraulic press for upsetting, the initial forging temperature is above 1230℃, drawing it to Φ1300mm on the upsetting plate, upsetting it slowly, drawing it twice on the upsetting plate and the lower platform, and drawing it to Φ1280mm by flattening, with a reduction of not less than 25%, and paying attention to the inverted eight sides. , rolling; upsetting again to a height of H1500mm, flattening the end face, punching Φ650mm, expanding the hole to Φ780mm, stretching and pressing the step forming, and repair forging to the size required by the forging drawing. During this period, the final forging temperature is controlled to be not less than 850℃, and the repair forging temperature is not less than 830℃. Pay attention to temperature control and multi-fire forging; ensure the required forging ratio, ensure the uniformity of the hardness of the forging, obtain finer grains and uniform forging blanks, and at the same time provide guarantees for the rough processing quality and heat treatment performance; Step 4), rough machining: Use a 10-meter heavy-duty lathe to rough the outer circle, and use a 10-meter deep hole boring machine to bore the inner hole. The rough machining size requires that the outer circle and inner hole are relative to the product size, leaving a 40mm margin on the diameter and a 30mm margin in the length direction; strictly control the overall straightness ≤1, strictly control the machining wall thickness difference within 1mm, reduce bending during heat treatment, and ensure the quality of heat treatment and subsequent finishing; Step 5), heat treatment: the workpiece charging temperature is less than 200℃, the workpiece is heated to 550-650℃ for preheating, the heating rate is controlled to ≤70℃ per hour, and the workpiece is kept warm for two hours. The heating rate is ≤80℃ per hour and the temperature is raised to 900℃ for 2.5 hours, and the temperature is raised to 1090℃ for two hours, and the temperature is kept warm for two hours. After slow cooling, air cooling, and then water cooling for 15-20 minutes, the grain structure of the parts is optimized and the mechanical properties required by the product are obtained; Step 6), two semi-finishing: use a 10-meter CNC finishing lathe to turn the outer circle of the workpiece, and use a 10-meter deep hole drilling and boring machine to bore the inner hole. Semi-finishing is divided into two times. The outer circle and inner hole are required to be relative to the product size. The first semi-finishing diameter is left with a 20mm margin, the second semi-finishing is left with a 10mm margin, and a 20mm margin in the length direction; Step 7), two stress relief tempering: After each semi-finishing, the workpiece is heated to 300-400℃ in a heating furnace and then slowly cooled for stress relief heat treatment after being kept at this temperature for not less than 2 hours. The purpose of this process is to gradually release the internal processing stress of the workpiece, ensure the uniformity of the finishing, and avoid deformation caused by processing; Step 8), finishing: use a 10-meter CNC finishing lathe to turn the outer circle of the workpiece, use a 10-meter deep hole drilling and boring machine to bore the inner hole, and finish the workpiece into the drawing size according to the drawing. After the finishing boring is completed, ensure that the honing and polishing allowance is 0.25-0.35; Step 9), honing to inner hole accuracy and roughness: after finishing the workpiece according to the drawing, ensure the honing polishing allowance of 0.25-0.35, and the honing size to Ø800. The left end air flow inlet is 500mm long to ensure the honing size of Ø800 (0, +0.05), and the right end outlet is 500mm long to ensure the honing size of Ø800 (0, -0.05); the surface roughness meets the design requirements to ensure that there is no reverse airflow step after subsequent installation and connection.

[0006] The invention has the following beneficial effects: according to the invention, a large-diameter high-precision pipe body for a static wind tunnel made of low-carbon austenitic stainless steel that meets the design requirements can be produced, which solves the problem that the pressure-bearing austenitic stainless steel S30458 is used to produce the pipe body, and the forging is prone to cracking, which affects the subsequent processing; solves the problem that the pipe body requires high straightness and roundness, and the processing size is difficult to meet; solves the problem that the stainless steel thin-walled pipe body product is prone to stress deformation during processing; solves the problem that the reverse airflow step of the connection surface is difficult to ensure. Processing by this method not only ensures product quality, but also has high production efficiency, and economical and scientific production process. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1This is a typical representative product diagram of the low-carbon austenitic stainless steel static wind tunnel large-diameter high-precision tube body of the present invention, with a single-section inner diameter of 800mm±0.05, a coaxiality requirement of Φ0.1mm, an inner hole roundness of Φ0.05mm, and a single tube length of 6170mm.

[0008] Figure 2 This is a forging dimension diagram of a typical representative product of the present invention.

[0009] Figure 3 This is a rough-sized diagram of a typical representative product of the present invention.

[0010] Figure 4 This is a semi-precision dimension drawing of a typical representative product of the present invention. DETAILED DESCRIPTION

[0011] A method for making a large-diameter, high-precision pipe body for a static wind tunnel from low-carbon austenitic stainless steel, the specific production process is: argon oxygen refining + ladle refining + continuous casting → electroslag remelting → forging with a 7,000-ton fast forging hydraulic press → annealing after forging → surface inspection, cutting, physical and chemical testing (low magnification, ultrasonic flaw detection) → rough machining → physical and chemical testing (ultrasonic flaw detection, color flaw detection) → heat treatment solution aging → physical and chemical testing (mechanical properties, ultrasonic flaw detection) → multiple semi-finishing stress relief tempering → finishing to product size → honing to inner hole accuracy and roughness → coloring inspection, size inspection. The specific steps are as follows: Step 1), forging, roughing and semi-finishing size allowance control: semi-finishing is divided into two times, the first semi-finishing allows a 20mm allowance on the diameter, the second semi-finishing allows a 10mm allowance, and a 20mm allowance on the length direction; the roughing size requires that the outer circle and inner hole are relative to the product size, with a 40mm allowance on the diameter and a 30mm allowance on the length direction; the forging size requires that the outer circle and inner hole are relative to the roughing size, with a 60mm allowance on the diameter and a 50mm allowance on the length direction; Step 2), smelting: This steel is a low-carbon austenitic stainless steel, which has strict requirements on high and low magnification, ultrasonic flaw detection and performance. The smelting operation of each stage should be strengthened, powdered lime shall not be used, and the chemical composition shall be adjusted according to the internal control composition. The charge includes scrap steel or steel scraps and pig iron above level 2. Miscellaneous scrap steel is not allowed to be added. The carbon content is ≥1.00%, the temperature is ≥1550℃, and the sampling and analysis control composition is carried out. The tapping temperature is ≥1660℃. After the composition is appropriate, the induction furnace is used for tapping. The steel process is rigorous in slag removal; the electrode head, residual steel and slag of the refining furnace should be cleaned in advance to avoid carbon increase; this steel contains Cr and Ni alloys, and the soup channel, middle injection pipe and residual scrap steel after smelting should be cleaned to prevent scrap steel pollution; the number of electric furnace bodies is ≥2 times, and the number of ladles is ≥2 times; the induction furnace equipment and lining meet the smelting requirements, and the electroslag ingot is subjected to ultra-detection after cooling to check whether there are cracks inside to ensure that high-purity and dense ingots are obtained, laying the foundation for subsequent production; Step 3), forging: The stainless steel forging billet with an inner hole of Φ800mm of the pipe body product is hollow forged: heating in a heating furnace, controlling the furnace temperature at 1250-1350℃, taking it out, using a 7000-ton fast forging hydraulic press for upsetting, the initial forging temperature is above 1230℃, drawing it to Φ1300mm on the upsetting plate, upsetting it slowly, drawing it twice on the upsetting plate and the lower platform, and drawing it to Φ1280mm by flattening, with a reduction of not less than 25%, and paying attention to the inverted eight sides. , rolling; upsetting again to a height of H1500mm, flattening the end face, punching Φ650mm, expanding the hole to Φ780mm, stretching and pressing the step forming, and repair forging to the size required by the forging drawing. During this period, the final forging temperature is controlled to be not less than 850℃, and the repair forging temperature is not less than 830℃. Pay attention to temperature control and multi-fire forging; ensure the required forging ratio, ensure the uniformity of the hardness of the forging, obtain finer grains and uniform forging blanks, and at the same time provide guarantees for the rough processing quality and heat treatment performance; Step 4), rough machining: Use a 10-meter heavy-duty lathe to rough the outer circle, and use a 10-meter deep hole boring machine to bore the inner hole. The rough machining size requires that the outer circle and inner hole are relative to the product size, leaving a 40mm margin on the diameter and a 30mm margin in the length direction; strictly control the overall straightness ≤1, strictly control the machining wall thickness difference within 1mm, reduce bending during heat treatment, and ensure the quality of heat treatment and subsequent finishing; Step 5), heat treatment: the workpiece charging temperature is less than 200℃, the workpiece is heated to 550-650℃ for preheating, the heating rate is controlled to ≤70℃ per hour, and the workpiece is kept warm for two hours. The heating rate is ≤80℃ per hour and the temperature is raised to 900℃ for 2.5 hours, and the temperature is raised to 1090℃ for two hours, and the temperature is kept warm for two hours. After slow cooling, air cooling, and then water cooling for 15-20 minutes, the grain structure of the parts is optimized and the mechanical properties required by the product are obtained; Step 6), two semi-finishing: use a 10-meter CNC finishing lathe to turn the outer circle of the workpiece, and use a 10-meter deep hole drilling and boring machine to bore the inner hole. Semi-finishing is divided into two times. The outer circle and inner hole are required to be relative to the product size. The first semi-finishing diameter is left with a 20mm margin, the second semi-finishing is left with a 10mm margin, and a 20mm margin in the length direction; Step 7), two stress relief tempering: After each semi-finishing, the workpiece is heated to 300-400℃ in a heating furnace and then slowly cooled for stress relief heat treatment after being kept at this temperature for not less than 2 hours. The purpose of this process is to gradually release the internal processing stress of the workpiece, ensure the uniformity of the finishing, and avoid deformation caused by processing; Step 8), finishing: use a 10-meter CNC finishing lathe to turn the outer circle of the workpiece, use a 10-meter deep hole drilling and boring machine to bore the inner hole, and finish the workpiece into the drawing size according to the drawing. After the finishing boring is completed, ensure that the honing and polishing allowance is 0.25-0.35; Step 9), honing to inner hole accuracy and roughness: after finishing the workpiece according to the drawing, ensure the honing polishing allowance of 0.25-0.35, and the honing size to Ø800. The left end air flow inlet is 500mm long to ensure the honing size of Ø800 (0, +0.05), and the right end outlet is 500mm long to ensure the honing size of Ø800 (0, -0.05); the surface roughness meets the design requirements to ensure that there is no reverse airflow step after subsequent installation and connection.

[0012] Example: Produce a batch of low-carbon austenitic stainless steel to make large-diameter high-precision pipes for static wind tunnels: Take the manufacture of pipes with an inner diameter of φ800mm as an example. Figure 1 As shown, the inner diameter of a single section is 800mm±0.05, the coaxiality requirement is Φ0.1mm, the inner hole roundness is Φ0.05mm, the length of a single tube is 6170mm, the wall thickness is 40mm, the tube body is Ø800, the inner hole step along the airflow is <0.05mm, the temperature resistance is 600K, and the material used is S30458.

[0013] After comprehensive consideration, the actual production and manufacturing process of the pipe body is: argon oxygen refining + ladle refining + continuous casting → electroslag remelting → forging with a 7,000-ton fast forging hydraulic press → annealing after forging → surface inspection, cutting, physical and chemical testing (low magnification, ultrasonic flaw detection) → rough machining → physical and chemical testing (ultrasonic flaw detection, color flaw detection) → heat treatment solution aging → physical and chemical testing (mechanical properties, ultrasonic flaw detection) → multiple semi-finishing stress relief tempering → finishing to product size → honing to inner hole accuracy and roughness → color detection, size inspection. The actual implementation of the main processes in its production: Step 1), smelting: This steel is a low-carbon austenitic stainless steel, which has strict requirements on high and low magnification, ultrasonic flaw detection and performance. The smelting operation of each stage should be strengthened, powdered lime shall not be used, and the chemical composition shall be adjusted as much as possible according to the internal control composition. The charge shall be scrap steel or steel scraps and pig iron of level 2 or above, and random scrap steel shall not be allowed to be added. The carbon content shall be ≥1.00%, the temperature shall be ≥1550℃ for sampling and analysis to control the composition, and the tapping temperature shall be ≥1660℃. After the composition is appropriate, the induction furnace shall be used for tapping. The steel process is rigorous in slag removal. The electrode head, residual steel and slag of the furnace cover of the refining furnace shall be cleaned in advance to avoid carbon increase. This steel contains Cr and Ni alloys, and the management of scrap steel such as the soup channel, the middle injection pipe and the injection residue after smelting shall be done well to prevent scrap steel pollution. The number of electric furnace bodies shall be ≥2 times, and the number of ladle shall be ≥2 times. The induction furnace equipment and lining meet the smelting requirements. After the electroslag ingot is cooled, the ultra-detection test shall be carried out to check whether there are serious defects such as cracks inside. This ensures that high-purity, dense steel ingots are obtained, laying the foundation for subsequent production.

[0014] Step 2), forging: The stainless steel forging billet with an inner hole of Φ800mm for the pipe body product is hollow forged. Heat in a heating furnace and control the furnace temperature at 1250-1350℃. Take it out and use a 7000-ton fast forging hydraulic press for upsetting. The initial forging temperature is above 1230℃. Draw it to Φ1300mm on the upsetting plate, upset slowly, and draw it twice on the upsetting plate and the lower platform. Draw it to Φ1280mm by flattening. The reduction should not be less than 25%. Pay attention to inverting and rounding. Upset again to a high of H1500mm, flatten the end face, punch a hole of Φ650mm, expand the hole to Φ780mm, draw and press the step to form, and forge it to the size required by the forging drawing. During this period, control the final forging temperature to be not less than 850℃, and the forging temperature to be not less than 830℃. Pay attention to temperature control, forge it 10 times, and press it. Figure 2 Control the size.

[0015] Step 3), roughing: use a 10-meter heavy lathe to rough the outer circle, and use a 10-meter deep hole boring machine to bore the inner hole. Figure 3 Control the size, control the straightness of the entire length ≤1, and control the processing wall thickness difference within 1mm.

[0016] Step 4), heat treatment: the workpiece charging temperature is less than 200℃, the workpiece is heated to 550-650℃ for preheating, the heating rate is controlled to ≤70℃ per hour, and the workpiece is kept warm for two hours. The heating rate is ≤80℃ per hour and the temperature is raised to 900℃ for 2.5 hours, and the temperature is raised to 1090℃ for two hours, and the temperature is kept warm for two hours. After slow cooling, air cooling, and then water cooling for 15-20 minutes. Cut the test piece for testing, the yield is 310MPa, the tensile strength is 600MPa, the elongation after forging is 60%, and the mechanical properties are good.

[0017] Step 5), semi-finishing: use a 10-meter CNC lathe to turn the outer circle of the workpiece, use a 10-meter deep hole boring inner hole, press Figure 4 Control the size and perform two semi-finishing additions.

[0018] Step 6) Stress relief tempering: After each semi-finishing, the workpiece is heated to 350±10℃ in a heating furnace and kept warm for 2.5 hours before slowly cooling in air to release the internal processing stress of the workpiece.

[0019] Step 7) Finishing: Use a 10-meter CNC lathe to turn the outer circle of the workpiece, use a 10-meter deep hole boring machine to bore the inner hole, and press the workpiece Figure 1 Finishing is completed and there is no deformation after finishing.

[0020] Step 8) Honing to inner hole accuracy and roughness: press Figure 1 The honing size is up to Ø800, the left air flow inlet is 500mm long to ensure the honing size of Ø800 (+0.01, +0.05), and the right outlet is 500mm long to ensure the honing size of Ø800 (0, -0.05); the surface roughness meets the design requirements to ensure that there is no reverse air flow step after subsequent installation and connection.

Claims

1. A method for manufacturing a large-diameter, high-precision tube body for a static wind tunnel using low-carbon austenitic stainless steel, characterized in that: The production process of the method is: argon oxygen refining + ladle refining + continuous casting → electroslag remelting → forging with a 7000-ton fast forging hydraulic press → annealing after forging → rough machining → heat treatment solid solution aging → multiple semi-finishing stress relief tempering → finishing to product size → honing to inner hole accuracy and roughness → inspection. The specific steps are as follows: Step 1), forging, roughing and semi-finishing size allowance control: semi-finishing is divided into two times, the first semi-finishing allows a 20mm allowance on the diameter, the second semi-finishing allows a 10mm allowance, and a 20mm allowance on the length direction; the roughing size requires that the outer circle and inner hole are relative to the product size, with a 40mm allowance on the diameter and a 30mm allowance on the length direction; the forging size requires that the outer circle and inner hole are relative to the roughing size, with a 60mm allowance on the diameter and a 50mm allowance on the length direction; Step 2), smelting: This type of steel is low-carbon austenitic stainless steel, and has strict requirements on high and low magnification, ultrasonic flaw detection and performance. Powdered lime shall not be used, and the chemical composition shall be adjusted according to the internal control composition. The charge includes scrap steel or steel scraps and pig iron above level 2. Miscellaneous scrap steel is not allowed to be added. The carbon content is ≥1.00%, the temperature is ≥1550℃, and the sampling and analysis control composition is carried out. The tapping temperature is ≥1660℃. After the composition is appropriate, the induction furnace is used for tapping. This steel process is rigorous in slag removal; the electrode head, residual steel and slag of the refining furnace should be cleaned in advance to avoid carbon increase; this type of steel contains Cr and Ni alloys, and the soup channel, middle injection pipe and residual scrap steel after smelting should be cleaned to prevent scrap steel pollution; the number of electric furnace bodies is ≥2 times, and the number of ladles is ≥2 times; the induction furnace equipment and lining meet the smelting requirements, and the electroslag ingot is subjected to ultra-detection after cooling to check that there are no cracks inside to ensure that high-purity and dense ingots are obtained, laying the foundation for subsequent production; Step 3), forging: The stainless steel forging billet with an inner hole of Φ800mm of the pipe body product is hollow forged: heating in a heating furnace, controlling the furnace temperature at 1250-1350℃, taking it out, using a 7000-ton fast forging hydraulic press for upsetting, the initial forging temperature is above 1230℃, drawing it to Φ1300mm on the upsetting plate, upsetting it slowly, drawing it twice on the upsetting plate and the lower platform, and drawing it to Φ1280mm by flattening, with a reduction of not less than 25%, and paying attention to the inverted eight sides. , rolling; upsetting again to a height of H1500mm, flattening the end face, punching Φ650mm, expanding the hole to Φ780mm, stretching and pressing the step forming, and repair forging to the size required by the forging drawing. During this period, the final forging temperature is controlled to be not less than 850℃, and the repair forging temperature is not less than 830℃. Pay attention to temperature control and multi-fire forging; ensure the required forging ratio, ensure the uniformity of the hardness of the forging, obtain finer grains and uniform forging blanks, and at the same time provide guarantees for the rough processing quality and heat treatment performance; Step 4), rough machining: Use a 10-meter heavy-duty lathe to rough the outer circle, and use a 10-meter deep hole boring machine to bore the inner hole. The rough machining size requires that the outer circle and inner hole are relative to the product size, leaving a 40mm margin on the diameter and a 30mm margin in the length direction; strictly control the overall straightness ≤1, strictly control the machining wall thickness difference within 1mm, reduce bending during heat treatment, and ensure the quality of heat treatment and subsequent finishing; Step 5), heat treatment: the workpiece charging temperature is less than 200℃, the workpiece is heated to 550-650℃ for preheating, the heating rate is controlled to ≤70℃ per hour, and the workpiece is kept warm for two hours. The heating rate is ≤80℃ per hour and the temperature is raised to 900℃ for 2.5 hours, and the temperature is raised to 1090℃ for two hours, and the temperature is kept warm for two hours. After slow cooling, air cooling, and then water cooling for 15-20 minutes, the grain structure of the parts is optimized and the mechanical properties required by the product are obtained; Step 6), two semi-finishing: use a 10-meter CNC finishing lathe to turn the outer circle of the workpiece, and use a 10-meter deep hole drilling and boring machine to bore the inner hole. Semi-finishing is divided into two times. The outer circle and inner hole are required to be relative to the product size. The first semi-finishing diameter is left with a 20mm margin, the second semi-finishing is left with a 10mm margin, and a 20mm margin in the length direction; Step 7), two stress relief tempering: After each semi-finishing, the workpiece is heated to 300-400℃ in a heating furnace and then slowly cooled for stress relief heat treatment after being kept at this temperature for not less than 2 hours. The purpose of this process is to gradually release the internal processing stress of the workpiece, ensure the uniformity of the finishing, and avoid deformation caused by processing; Step 8), finishing: use a 10-meter CNC finishing lathe to turn the outer circle of the workpiece, use a 10-meter deep hole drilling and boring machine to bore the inner hole, and finish the workpiece into the drawing size according to the drawing. After the finishing boring is completed, ensure that the honing and polishing allowance is 0.25-0.35; Step 9), honing to inner hole accuracy and roughness: after finishing the workpiece according to the drawing, ensure the honing polishing allowance of 0.25-0.35, and the honing size to Ø800. The left end air flow inlet is 500mm long to ensure the honing size of Ø800 (0, +0.05), and the right end outlet is 500mm long to ensure the honing size of Ø800 (0, -0.05); the surface roughness meets the design requirements to ensure that there is no reverse airflow step after subsequent installation and connection.

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