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

Abstract

This invention relates to a method for manufacturing large-diameter, high-precision tubes for static wind tunnels using low-carbon austenitic stainless steel. The production process is as follows: argon-oxygen refining + ladle refining + continuous casting → electroslag remelting → forging with a 7000-ton high-speed hydraulic press → post-forging annealing → rough machining → heat treatment solution aging → multiple semi-finishing stress-relieving tempering → finishing to product dimensions → honing to inner hole accuracy and roughness → inspection. This method effectively solves the problems of inconsistent performance, uniform surface of the tube, processing deformation, and processing difficulties.

Description

Technical Field

[0001] This invention belongs to the field of steel material product manufacturing technology, specifically involving a method for manufacturing large-diameter, high-precision tubes for static wind tunnels using low-carbon austenitic stainless steel. Specifically, it involves processing large-diameter hollow tubes with high machining precision on the inner surface of S30458 tube material, which can effectively solve the problems of inconsistent performance, tube surface uniformity, processing deformation, and processing difficulties. Background Technology

[0002] my country is currently vigorously developing its aerospace industry, and the foundation for this development is the construction of various types of wind tunnel testing facilities. Each set of equipment is expensive, but the prospects are promising. The still wind tunnel is essentially the benchmark for wind tunnels. Built to study the most challenging problems in science, it places higher demands on the dimensional accuracy and geometric tolerances of the wind tunnel. Calculation and prediction are crucial prerequisites for aircraft design, and China is a leader in the construction of still wind tunnels.

[0003] The characteristics of the ultra-large, high-precision tube body of the static wind tunnel are as follows: it contains high-temperature, high-pressure air, which flows through multiple tube sections and is released from the end of the tube to form a high-speed airflow. It is made of low-carbon austenitic stainless steel, with a single section inner diameter ≥800mm±0.05mm and a single section length of more than 6 meters. The total required length is tens of meters. The coaxiality requirement is Φ0.1mm, the inner hole roundness is Φ0.05mm, and the step difference between two tube sections is required to be 0.05mm in the direction of airflow. It is not easy to meet the requirements of coaxiality, inner hole roundness, and airflow step difference for large-diameter stainless steel. It is required that the large tube body with a thin wall of 40mm is free from stress deformation after processing. It is also required that the flange of the large-diameter stainless steel tube body be integrally forged to prevent cracking. It is also required that the installation surface is wear-resistant and does not stick during loading and unloading. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a method for manufacturing large-diameter, high-precision tubes for static wind tunnels using carbon austenitic stainless steel. This method solves the problems of easy cracking during forging and subsequent processing when using pressure-bearing austenitic stainless steel S30458 to produce tubes; it also solves the problem of difficulty in meeting the high straightness and roundness requirements of the tubes during processing; it addresses the problem of stress deformation during the processing of thin-walled stainless steel tubes; and it solves the problem of difficulty in ensuring the backflow steps at the connection surface.

[0005] The objective of this invention is achieved as follows: a method for manufacturing large-diameter, high-precision tubes for static wind tunnels using low-carbon austenitic stainless steel. The production process is as follows: argon-oxygen refining + ladle refining + continuous casting → electroslag remelting → forging using a 7000-ton high-speed hydraulic press → post-forging annealing → rough machining → heat treatment with solution aging → multiple semi-finishing and stress-relieving tempering → finishing to product dimensions → honing to achieve the required inner hole accuracy and surface roughness → inspection. The specific steps are as follows: Step 1) Forging, roughing, and semi-finishing dimensional allowance control: Semi-finishing is done in two stages. For the first semi-finishing, leave a 20mm allowance in diameter and a 10mm allowance in length relative to the product dimensions for the outer diameter and inner hole, respectively. For roughing, leave a 40mm allowance in diameter and a 30mm allowance in length relative to the product dimensions for the outer diameter and inner hole. For forging, leave a 60mm allowance in diameter and a 50mm allowance in length relative to the roughing dimensions for the outer diameter and inner hole. Step 2) Smelting: This steel grade is low-carbon austenitic stainless steel, with strict requirements for high and low magnification, ultrasonic flaw detection, and performance. Powdered lime is not allowed. The chemical composition is adjusted according to the internal control composition. The furnace charge includes grade II or higher scrap steel or steel chips and pig iron. Mixed scrap steel is not allowed. The carbon content is ≥1.00%. Sampling and analysis are conducted at a temperature ≥1550℃ to control the composition. The tapping temperature is ≥1660℃. After the composition is suitable, the steel is tapped in an induction furnace. Slag addition is strictly prohibited during this steelmaking process. The electrode head, furnace cover residual steel, and slag of the refining furnace should be cleaned in advance to avoid carbon increase. This steel grade contains Cr and Ni alloys. The smelting runner, intermediate pouring pipe, and residual scrap steel should be cleaned after smelting to prevent scrap steel contamination. The electric furnace body is ≥2 times, and the ladle is ≥2 times. The induction furnace equipment and furnace lining meet the smelting requirements. After the electroslag ingot cools, ultrasonic testing is performed to check for internal cracks, ensuring that high-purity and dense steel ingots are obtained, laying the foundation for subsequent production. Step 3) Forging: The stainless steel forging billet with an inner diameter of Φ800mm for the tube product is hollow forged: Heating in a heating furnace, controlling the furnace temperature at 1250~1350℃, removing it, and upsetting it using a 7000-ton fast forging hydraulic press. The initial forging temperature is above 1230℃. It is drawn to Φ1300mm on the upsetting plate, slowly upsetting, and drawn twice on the upsetting plate and the lower platform, then drawn to Φ1280mm in a flattened shape, with a reduction of not less than 25%. Note the octagonal shape. 1. Round the blank; 2. Upset again to a height of H1500mm, flatten the end face, punch a Φ650mm hole, expand the hole to Φ780mm, draw and press into steps to form the blank, and forge to the dimensions required by the forging drawing. During this process, control the final forging temperature to be no less than 850℃ and the finishing forging temperature to be no less than 830℃. Pay attention to temperature control and perform multiple forgings. Ensure the required forging ratio, guarantee the uniformity of hardness of the forging, obtain finer grains and uniform forging blanks, and at the same time provide a guarantee for the quality of rough machining and heat treatment performance. Step 4) Rough machining: Use a 10-meter heavy-duty lathe to rough machine the outer diameter and a 10-meter deep hole boring machine to bore the inner diameter. The rough machining dimensions require that the outer diameter and inner diameter be relative to the product dimensions, leaving a 40mm allowance in the diameter and a 30mm allowance in the length direction. Strictly control the straightness of the entire process to ≤1 and the wall thickness difference to be within 1mm to reduce bending during heat treatment and ensure the quality of heat treatment and subsequent precision machining. Step 5) Heat treatment: The workpiece is loaded into the furnace at a temperature of less than 200℃. The workpiece is preheated to 550-650℃, with the heating rate controlled at ≤70℃ per hour. It is then held at this temperature for two hours. The heating rate is then increased to ≤80℃ per hour, and the temperature is raised to 900℃. The temperature is then held at this temperature for 2.5 hours. The temperature is then raised to 1090℃, and the temperature is held at this temperature for two hours. After slow cooling, the workpiece is air-cooled and then water-cooled for 15-20 minutes to optimize the grain structure of the parts and obtain the mechanical properties required by the product. Step 6) Two semi-finishing operations: Use a 10-meter CNC precision lathe to turn the outer diameter of the workpiece and use a 10-meter deep hole drilling and boring machine to bore the inner diameter. The semi-finishing is done in two stages. The outer diameter and inner diameter should be relative to the product dimensions. Leave a 20mm allowance in diameter for the first semi-finishing operation and a 10mm allowance for the second semi-finishing operation. Leave a 20mm allowance in the length direction. Step 7) Two stress-relief tempering processes: After each semi-finishing process, the workpiece is heated to 300-400℃ in a heating furnace and held at that temperature for at least 2 hours before being slowly cooled to relieve stress. The purpose of this process is to gradually release the internal machining stress of the workpiece, ensure the uniformity of the finishing process, and avoid deformation caused by the machining process. Step 8) Finishing: Use a 10-meter CNC precision lathe to turn the outer diameter of the workpiece and use a 10-meter deep hole drilling and boring machine to bore the inner diameter, and finish the workpiece to the dimensions shown in the drawing. Step 9) Honing to achieve the required inner hole accuracy and roughness: After the workpiece is precision-machined and bored according to the drawing, ensure that the honing and polishing allowance is 0.25~0.35, and the honing dimension is Ø800. Ensure that the honing dimension of the left end airflow inlet (500mm long) is Ø800 (0, +0.05), and the honing dimension of the right end outlet (500mm long) is 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] This invention offers the following advantages: It enables the production of large-diameter, high-precision tubes for static wind tunnels using low-carbon austenitic stainless steel that meets design requirements. This solves the problem of easy cracking during forging when using pressure-bearing austenitic stainless steel S30458, which affects subsequent processing. It also addresses the difficulty in meeting the high straightness and roundness requirements of the tubes during processing; the problem of stress deformation during the processing of thin-walled stainless steel tubes; and the difficulty in ensuring proper protection of the backflow steps at the connection surfaces. Processing using this method not only guarantees product quality but also results in high production efficiency and an economical and scientific production process. Attached Figure Description

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

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

[0009] Figure 3 This is a rough dimension drawing of a typical representative product of the present invention.

[0010] Figure 4 This is a semi-finished dimension drawing of a typical representative product of the present invention. Detailed Implementation

[0011] A method for manufacturing large-diameter, high-precision tubes for static wind tunnels using low-carbon austenitic stainless steel, the specific production process is as follows: argon-oxygen refining + ladle refining + continuous casting → electroslag remelting → forging on a 7000-ton high-speed hydraulic press → post-forging annealing → surface inspection, blanking, and physical and chemical testing (low magnification, ultrasonic testing) → rough machining → physical and chemical testing (ultrasonic testing, dye penetrant testing) → heat treatment solution aging → physical and chemical testing (mechanical properties, ultrasonic testing) → multiple semi-finishing and stress-relief tempering → finishing to product dimensions → honing to achieve internal hole accuracy and roughness → dye penetrant testing and dimensional inspection. The specific steps are as follows: Step 1) Dimensional allowance control for forging, roughing, and semi-finishing: Semi-finishing is done in two stages. The first semi-finishing leaves a 20mm allowance in diameter, and the second semi-finishing leaves a 10mm allowance, with a 20mm allowance in length. For roughing, the outer diameter and inner hole should be relative to the product dimensions, with a 40mm allowance in diameter and a 30mm allowance in length. For forging, the outer diameter and inner hole should be relative to the roughing dimensions, with a 60mm allowance in diameter and a 50mm allowance in length. Step 2) Smelting: This steel grade is low-carbon austenitic stainless steel, with strict requirements for high and low magnification, ultrasonic flaw detection, and performance. Smelting operations at each stage should be strengthened. Powdered lime must not be used. Chemical composition should be adjusted according to internal control. The furnace charge includes grade II or higher scrap steel or steel chips and pig iron. Mixed scrap steel is not allowed. Carbon content should be ≥1.00%. Sampling and analysis should be conducted at a temperature ≥1550℃ to control composition. Tapping temperature should be ≥1660℃. After the composition is suitable, the steel should be tapped in an induction furnace. Slag addition is strictly prohibited during this process. The electrode head, furnace cover, residual steel, and slag of the refining furnace should be cleaned in advance to avoid carbon increase. This steel grade contains Cr and Ni alloys. The smelting runner, intermediate sluice pipe, and residual scrap steel should be cleaned after smelting to prevent scrap steel contamination. The electric furnace body should be smelted ≥2 times, and the ladle ≥2 times. The induction furnace equipment and lining must meet smelting requirements. After the electroslag ingot cools, ultrasonic testing should be performed to check for internal cracks, ensuring high-purity, dense steel ingots are obtained, laying the foundation for subsequent production. Step 3), Forging: Inner hole Φ of the tube product The 800mm stainless steel forging billet is hollow forged: Heating in a furnace, controlling the furnace temperature at 1250-1350℃, removing it, and upsetting it using a 7000-ton high-speed hydraulic forging press. The initial forging temperature is above 1230℃. It is then drawn to Φ1300mm on the upsetting plate, slowly upsetting again, with two passes on the upsetting plate and lower platform, drawing it flat to Φ1280mm, with a reduction of not less than 25%, paying attention to the octagonal shape and rounding. It is then upset again to a height of H1500mm, with a flattened end face, punching a Φ650mm hole, expanding it to Φ780mm, drawing and pressing into steps, and finishing forging to the dimensions required by the forging drawings. During this process, the final forging temperature is controlled to be not less than 850℃, and the finishing forging temperature not less than 830℃. Multiple forging passes are used to ensure the required forging ratio, guarantee the uniformity of the forging hardness, obtain finer grains and a uniform forging billet, and simultaneously ensure the quality of rough machining and heat treatment performance. Step 4) Rough machining: Use a 10-meter heavy-duty lathe to rough machine the outer diameter and a 10-meter deep hole boring machine to bore the inner diameter. The rough machining dimensions require that the outer diameter and inner diameter be relative to the product dimensions, leaving a 40mm allowance in the diameter and a 30mm allowance in the length direction. Strictly control the straightness of the entire process to ≤1 and the wall thickness difference to be within 1mm to reduce bending during heat treatment and ensure the quality of heat treatment and subsequent precision machining. Step 5) Heat treatment: The workpiece is loaded into the furnace at a temperature of less than 200℃. The workpiece is preheated to 550-650℃, with the heating rate controlled at ≤70℃ per hour. It is then held at this temperature for two hours. The heating rate is then increased to ≤80℃ per hour, and the temperature is raised to 900℃. The temperature is then held at this temperature for 2.5 hours. The temperature is then raised to 1090℃, and the temperature is held at this temperature for two hours. After slow cooling, the workpiece is air-cooled and then water-cooled for 15-20 minutes to optimize the grain structure of the parts and obtain the mechanical properties required by the product. Step 6) Two semi-finishing operations: Use a 10-meter CNC precision lathe to turn the outer diameter of the workpiece and use a 10-meter deep hole drilling and boring machine to bore the inner diameter. The semi-finishing is done in two stages. The outer diameter and inner diameter should be relative to the product dimensions. Leave a 20mm allowance in diameter for the first semi-finishing operation and a 10mm allowance for the second semi-finishing operation. Leave a 20mm allowance in the length direction. Step 7) Two stress-relief tempering processes: After each semi-finishing process, the workpiece is heated to 300-400℃ in a heating furnace and held at that temperature for at least 2 hours before being slowly cooled to relieve stress. The purpose of this process is to gradually release the internal machining stress of the workpiece, ensure the uniformity of the finishing process, and avoid deformation caused by the machining process. Step 8) Finishing: Use a 10-meter CNC precision lathe to turn the outer diameter of the workpiece and use a 10-meter deep hole drilling and boring machine to bore the inner diameter, and finish the workpiece to the dimensions shown in the drawing. Step 9) Honing to achieve the required inner hole accuracy and roughness: After the workpiece is precision-machined and bored according to the drawing, ensure that the honing and polishing allowance is 0.25~0.35mm, and the honing size is Ø800mm. Ensure that the honing size is Ø800(0,+0.05)mm for the 500mm length of the airflow inlet at the left end, and Ø800(0,-0.05)mm for the 500mm length of the outlet at the right end. The surface roughness meets the design requirements to ensure that there are no reverse airflow steps after subsequent installation and connection.

[0012] Example: Manufacturing a batch of low-carbon austenitic stainless steel to produce large-diameter, high-precision tubes for static wind tunnels: Taking the manufacture of tubes with an inner diameter of φ800mm as an example, such as... Figure 1 As shown, the single-section inner diameter is 800mm ± 0.05mm, the coaxiality requirement is Φ 0.1mm, the inner hole roundness is Φ 0.05mm, the single pipe length is 6170mm, the wall thickness is 40mm, the pipe body Ø800 inner hole has a flow-oriented step of <0.05mm, the temperature resistance is 600K, and the material used is S30458.

[0013] After comprehensive consideration, the actual manufacturing process of this pipe body is as follows: argon-oxygen refining + ladle refining + continuous casting → electroslag remelting → forging on a 7000-ton high-speed hydraulic press → post-forging annealing → surface inspection, blanking, and physical and chemical testing (low magnification, ultrasonic testing) → rough machining → physical and chemical testing (ultrasonic testing, dye penetrant testing) → heat treatment solution aging → physical and chemical testing (mechanical properties, ultrasonic testing) → multiple semi-finishing and stress-relieving tempering → finishing to product dimensions → honing to achieve internal hole accuracy and roughness → dye penetrant testing and dimensional inspection. The actual implementation of the main processes in production is as follows: Step 1) Smelting: This steel grade is a low-carbon austenitic stainless steel, with strict requirements for high and low magnification, ultrasonic flaw detection, and performance. Smelting operations at each stage should be strengthened. Powdered lime must not be used. The chemical composition should be adjusted according to internal control as much as possible. The furnace charge should consist of grade II or higher scrap steel, steel chips, and pig iron; mixed scrap steel is not allowed. The carbon content should be ≥1.00%. Sampling and analysis should be conducted at a temperature ≥1550℃ to control the composition. The tapping temperature should be ≥1660℃. After the composition is suitable, the steel should be tapped in an induction furnace. Slag removal is strictly controlled during this steelmaking process. The electrode head, furnace cover, residual steel, and slag of the refining furnace should be cleaned in advance to avoid carbon increase. This steel grade contains Cr and Ni alloys; proper management of scrap steel from the smelting runner, intermediate pouring pipe, and pouring residue should be ensured to prevent contamination. The electric furnace body should be smelted ≥2 times, and the ladle ≥2 times. The induction furnace equipment and lining must meet smelting requirements. After cooling, the electroslag ingot should be subjected to ultrasonic testing to check for internal cracks and other serious defects. This ensures the production of high-purity, dense steel ingots, laying the foundation for subsequent production.

[0014] Step 2) Forging: The Φ800mm stainless steel forging billet for the tube body is hollow forged. Heating in a furnace, controlling the furnace temperature at 1250-1350℃, remove and upset using a 7000-ton high-speed hydraulic forging press. Initial forging temperature above 1230℃. Lengthen to Φ1300mm on the upsetting plate, slowly upsetting, lengthening twice on the upsetting plate and lower platform, flattening to Φ1280mm, with a reduction of not less than 25%, paying attention to the octagonal shape and rounding. Upset again to a height of H1500mm, flatten the end face, punch a Φ650mm hole, expand to Φ780mm, lengthen and press into steps to form the shape, and finish forging to the dimensions required by the forging drawings. During this process, control the final forging temperature to not less than 850℃ and the finish forging temperature to not less than 830℃. Pay attention to temperature control, forging in 10 passes, according to… Figure 2 Controlling dimensions; Step 3) Roughing: Roughly shape the outer diameter using a 10-meter heavy-duty lathe, and bore the inner diameter using a 10-meter deep-hole boring machine. Figure 3 Control the dimensions, ensure the overall straightness is ≤1, and control the processing wall thickness difference to within 1mm.

[0015] Step 4) Heat treatment: The workpiece is loaded into the furnace at a temperature of less than 200℃. The workpiece is preheated to 550-650℃, with a heating rate of ≤70℃ per hour. It is then held at this temperature for two hours. The heating rate is then increased to ≤80℃ per hour, and the temperature is raised to 900℃. It is then held at this temperature for 2.5 hours. The temperature is then raised to 1090℃, and the temperature is held at this temperature for two hours. After slow cooling, it is air-cooled and then water-cooled for 15-20 minutes. Test pieces are cut and tested. The yield strength is 310MPa, the tensile strength is 600MPa, and the elongation after forging is 60%, indicating good mechanical properties. Step 5) Semi-finishing: Use a 10-meter CNC lathe to turn the outer diameter of the workpiece and use a 10-meter deep hole boring machine to bore the inner diameter, according to... Figure 4 Control the dimensions by performing two semi-finishing processes; Step 6) Stress-relief tempering: After each semi-finishing process, the workpiece is heated to 350±10℃ in a furnace, held at that temperature for 2.5 hours, and then slowly cooled by air cooling to relieve stress. This releases the internal machining stress of the workpiece.

[0016] Step 7) Finishing: Use a 10-meter CNC lathe to turn the outer diameter of the workpiece and use a 10-meter deep hole boring machine to bore the inner diameter of the workpiece. Figure 1 The finishing process is complete, and there is no deformation after finishing. Step 8) Honing to achieve the required inner hole accuracy and surface roughness: according to... Figure 1 The honing size is Ø800. The left end airflow inlet is 500mm long to ensure the honing size is Ø800 (+0.01, +0.05)mm, and the right end outlet is 500mm long to ensure the honing size is Ø800 (0, -0.05)mm. The surface roughness meets the design requirements to ensure that there are no reverse airflow steps after subsequent installation and connection.

Claims

1. A method for manufacturing a large-diameter high-precision pipe body of a low-carbon austenitic stainless steel for a static wind tunnel, characterized by: The production process is as follows: argon-oxygen refining + ladle refining + continuous casting → electroslag remelting → forging with a 7000-ton high-speed hydraulic press → post-forging annealing → rough machining → heat treatment solution aging → multiple semi-finishing stress-relieving tempering → finishing to product dimensions → honing to achieve internal hole accuracy and roughness → inspection. The specific steps are as follows: Step 1) Dimensional allowance control for forging, roughing, and semi-finishing: Semi-finishing is done in two stages. The first semi-finishing leaves a 20mm allowance in diameter, and the second semi-finishing leaves a 10mm allowance, with a 20mm allowance in length. For roughing, the outer diameter and inner hole should be relative to the product dimensions, with a 40mm allowance in diameter and a 30mm allowance in length. For forging, the outer diameter and inner hole should be relative to the roughing dimensions, with a 60mm allowance in diameter and a 50mm allowance in length. Step 2) Smelting: This steel grade is low-carbon austenitic stainless steel, with strict requirements for high and low magnification, ultrasonic flaw detection, and performance. Powdered lime is not allowed. The chemical composition is adjusted according to the internal control composition. The furnace charge includes grade II or higher scrap steel or steel chips and pig iron. Mixed scrap steel is not allowed. The carbon content is ≥1.00%. Sampling and analysis are conducted at a temperature ≥1550℃ to control the composition. The tapping temperature is ≥1660℃. After the composition is suitable, the steel is tapped in an induction furnace. Slag addition is strictly prohibited during this steelmaking process. The electrode head, furnace cover residual steel, and slag of the refining furnace should be cleaned in advance to avoid carbon increase. This steel grade contains Cr and Ni alloys. The smelting runner, intermediate pouring pipe, and residual scrap steel should be cleaned after smelting to prevent scrap steel contamination. The electric furnace body is ≥2 times, and the ladle is ≥2 times. The induction furnace equipment and furnace lining meet the smelting requirements. After the electroslag ingot cools, ultrasonic testing is performed to check for internal cracks, ensuring that high-purity and dense steel ingots are obtained, laying the foundation for subsequent production. Step 3), Forging: Inner hole Φ of the tube product The 800mm stainless steel forging billet is hollow forged: Heating in a furnace, controlling the furnace temperature at 1250-1350℃, removing it, and upsetting it using a 7000-ton high-speed hydraulic forging press. The initial forging temperature is above 1230℃. It is then drawn to Φ1300mm on the upsetting plate, slowly upsetting again, with two passes on the upsetting plate and lower platform, drawing it flat to Φ1280mm, with a reduction of not less than 25%, paying attention to the octagonal shape and rounding. It is then upset again to a height of H1500mm, with a flattened end face, punching a Φ650mm hole, expanding it to Φ780mm, drawing and pressing into steps, and finishing forging to the dimensions required by the forging drawings. During this process, the final forging temperature is controlled to be not less than 850℃, and the finishing forging temperature not less than 830℃. Multiple forging passes are used to ensure the required forging ratio, guarantee the uniformity of the forging hardness, obtain finer grains and a uniform forging billet, and simultaneously ensure the quality of rough machining and heat treatment performance. Step 4) Rough machining: Use a 10-meter heavy-duty lathe to rough machine the outer diameter and a 10-meter deep hole boring machine to bore the inner diameter. The rough machining dimensions require that the outer diameter and inner diameter be relative to the product dimensions, leaving a 40mm allowance in the diameter and a 30mm allowance in the length direction. Strictly control the straightness of the entire process to ≤1 and the wall thickness difference to be within 1mm to reduce bending during heat treatment and ensure the quality of heat treatment and subsequent precision machining. Step 5) Heat treatment: The workpiece is loaded into the furnace at a temperature of less than 200℃. The workpiece is preheated to 550-650℃, with the heating rate controlled at ≤70℃ per hour. It is then held at this temperature for two hours. The heating rate is then increased to ≤80℃ per hour, and the temperature is raised to 900℃. The temperature is then held at this temperature for 2.5 hours. The temperature is then raised to 1090℃, and the temperature is held at this temperature for two hours. After slow cooling, the workpiece is air-cooled and then water-cooled for 15-20 minutes to optimize the grain structure of the parts and obtain the mechanical properties required by the product. Step 6) Two semi-finishing operations: Use a 10-meter CNC precision lathe to turn the outer diameter of the workpiece and use a 10-meter deep hole drilling and boring machine to bore the inner diameter. The semi-finishing is done in two stages. The outer diameter and inner diameter should be relative to the product dimensions. Leave a 20mm allowance in diameter for the first semi-finishing operation and a 10mm allowance for the second semi-finishing operation. Leave a 20mm allowance in the length direction. Step 7) Two stress-relief tempering processes: After each semi-finishing process, the workpiece is heated to 300-400℃ in a heating furnace and held at that temperature for at least 2 hours before being slowly cooled to relieve stress. The purpose of this process is to gradually release the internal machining stress of the workpiece, ensure the uniformity of the finishing process, and avoid deformation caused by the machining process. Step 8) Finishing: Use a 10-meter CNC precision lathe to turn the outer diameter of the workpiece and use a 10-meter deep hole drilling and boring machine to bore the inner diameter, and finish the workpiece to the dimensions shown in the drawing. Step 9) Honing to achieve the required inner hole accuracy and roughness: After the workpiece is precision-machined and bored according to the drawing, ensure that the honing and polishing allowance is 0.25~0.35mm, and the honing size is Ø800mm. The left end airflow inlet is 500mm long, ensuring the honing size is Ø800(0,+0.05)mm, and the right end outlet is 500mm long, ensuring the honing size is Ø800(0,-0.05)mm. The surface roughness meets the design requirements to ensure that there are no reverse airflow steps after subsequent installation and connection.

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