Ultrafine grain corrosion-resistant alloy capillary tube for aviation fire alarm detector and preparation process of ultrafine grain corrosion-resistant alloy capillary tube

Abstract

The invention relates to the field of manufacturing of corrosion-resistant alloy capillary tubes for aviation, in particular to an ultra-fine grain corrosion-resistant alloy capillary tube for an aviation fire alarm detector and a preparation process of the ultra-fine grain corrosion-resistant alloy capillary tube. The alloy comprises the following chemical components in percentage by mass: less than or equal to 0.15% of C; less than or equal to 0.50% of Si; mn < = 1.00%; p is less than or equal to 0.030%; less than or equal to 0.015% of S; 14 to 17 percent of Cr; ni > = 75%; 0.30% or less of Ti; 0.30% or less of Al; 0.50% or less of Cu; the content of Fe is 6.00 to 10.00 percent; 0.04% to 0.10% of Nb; 0.04 to 0.10 percent of V, and the balance of inevitable impurities; and the grain size of the microstructure is not lower than 10.0 grade. The preparation technology comprises the steps of raw material preparation, blank making and punching, inner wall coping, rough rolling, intermediate finish rolling and drawing alternate machining, finish rolling wall fixing, finished product finish drawing, dynamic heat treatment and inspection. Wherein intermediate heat treatment is carried out after each pass of cold machining of rough rolling, alternate machining and finish rolling wall fixing, and final solution treatment is carried out after all the cold machining is completed. According to the invention, the preparation of ultrafine grains of the material under the scale of millimeter outer diameter and micrometer wall thickness is realized, so that the capillary tube meets the use requirements of an aviation fire alarm detector.

Description

Technical Field

[0001] This invention relates to the field of manufacturing corrosion-resistant alloy capillary tubes for aviation applications, and in particular to an ultrafine-grained corrosion-resistant alloy capillary tube for aviation fire detectors and its preparation process. Background Technology

[0002] The harsh operating conditions in the aviation field are closely related to the performance requirements of detection components. Fire detectors are used in aircraft fire protection systems to detect fires and overheating in the engine compartment and issue fire alarm signals. The capillary tube, as the air inlet of the fire detector's diaphragm assembly, transmits gas pressure changes within the heat-sensitive component to the working chamber of the diaphragm assembly, thus providing an early warning function. This capillary tube is a core component of the fire protection system, with an outer diameter in the millimeter range and a wall thickness in the micrometer range. It possesses characteristics such as ultra-high pressure resistance, ultra-high heat resistance, ultra-high precision, ultra-lightweight design, extreme dimensions, and high reliability, making it crucial for improving fire detection sensitivity. Therefore, there is a significant market demand for it. The high-temperature and high-pressure operating conditions and usage requirements place extremely high demands on the cross-scale manufacturing technology of corrosion-resistant alloy capillary tubes.

[0003] Aero engines operate in extremely harsh environments, enduring high temperatures, pressures, and severe corrosion from exhaust gases. With the development of the aviation industry, corrosion-resistant alloys, due to their excellent corrosion resistance, high-temperature resistance, and oxidation resistance, play a crucial role in the aerospace field. Their application not only extends the service life of aircraft but also improves safety and reliability, thereby reducing total life-cycle costs.

[0004] However, there is very little publicly available information on the manufacturing process of corrosion-resistant alloy capillaries used in fire detectors for aero-engines, which is basically a technological gap and cannot meet the development needs of my country's aerospace industry. Therefore, it has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention To address the aforementioned technical problems in existing technologies, the present invention aims to provide an ultrafine-grained corrosion-resistant alloy capillary for aviation fire detectors and its manufacturing process. Through the coordinated control of raw material chemical composition, multi-stage deformation, and heat treatment parameters, ultrafine grains of the material are prepared at the millimeter outer diameter and micrometer wall thickness scale. This enables the capillary to simultaneously possess high strength and toughness, excellent dimensional accuracy and surface integrity, as well as reliable airtightness and pressure resistance. This fills the gap in related domestic technologies, breaks the predicament of relying on imports or being unable to mass-produce core components of high-end aviation fire protection systems, and meets market demand.

[0005] To achieve the above objectives, this invention discloses an ultrafine-grained corrosion-resistant alloy capillary for aviation fire detectors, the chemical composition of which, by mass percentage, is: C≤0.15%; Si≤0.50%; Mn≤1.00%; P≤0.030%; S≤0.015%; Cr: 14-17%; Ni≥75%; Ti≤0.30%; Al≤0.30%; Cu≤0.50%; Fe: 6.00~10.00%; Nb: 0.04-0.10%; V: 0.04-0.10%, with the balance being unavoidable impurities; its microstructure has a grain size of not less than 10.0 grade.

[0006] In this technical solution, the high-nickel and medium-chromium matrix design ensures the intrinsic stability of the material under the extreme environment of aero-engines. The nickel content, exceeding the 32% level of conventional 800 alloys, is key to resisting high-temperature carburization and chloride ion corrosion.

[0007] In addition, the precise addition of Nb and V elements serves two purposes: firstly, as grain boundary pinning points, it effectively inhibits grain coarsening; secondly, it controls recrystallization kinetics. Of particular note is that the Nb / C ratio is controlled within the ideal range to ensure the formation of fine NbC rather than coarse carbides, which is crucial for obtaining an ultrafine grain structure.

[0008] Furthermore, by controlling impurity elements such as S and P to extremely low levels, and limiting the content of Si and Mn, the brittleness of capillary manufacturing at micron-level wall thickness is directly addressed. The high purity ensures that the material can maintain its integrity even after undergoing dozens of severe deformations.

[0009] The fabrication process of the ultrafine-grained corrosion-resistant alloy capillary for aviation fire detectors of the present invention includes the following steps: S1. Raw material preparation: Select corrosion-resistant alloy billet; S2. Billet preparation and piercing: Cut the billet to length and perform deep hole machining to obtain a primary tube blank; S3. Grind the inner wall of the primary tube blank; S4. Rough rolling: Perform multiple cold rolling passes on the ground tube, with the deformation rate increasing with each pass; S5. Alternate intermediate finishing rolling and drawing: Perform multiple finishing rolling passes and multiple hollow drawing passes on the rough rolled tube in a preset sequence; S6. Finish rolling to fix the wall: Perform multiple rolling passes on the alternately finished tube, with the deformation rate increasing with each pass; S7. Finished product drawing: The pipe with the wall thickness precisely determined is subjected to multiple hollow drawing passes; S8. Dynamic heat treatment: After each cold working pass of S4, S5 and S6, the semi-finished product is subjected to intermediate heat treatment; and after all cold working is completed, the finished product is subjected to final solution treatment. S9. Finished Product Inspection: The final capillary tubes are inspected for performance and quality.

[0010] In this technical solution, the cold working path of rough rolling → alternating rolling and drawing → wall thickness determination → finish drawing is derived based on strain tensor analysis: In the rough rolling stage, a large deformation rate is used to rapidly accumulate dislocation density and establish a high-energy-storage deformable structure; in the alternating rolling and drawing stage, the stress state is redistributed through alternating compression and tension deformation modes, which not only prevents excessive texture development but also promotes uniform nucleation of subsequent recrystallization. The finish rolling and wall thickness determination is arranged after the alternating rolling and drawing stage because final wall thickness control is performed after the microstructure is relatively homogenized, avoiding wall thickness tolerance fluctuations caused by microstructure inhomogeneity; the precise gradient design of the deformation rate in the finish drawing stage is for final microstructure fine-tuning.

[0011] As a preferred technical solution, the S4 rough rolling deformation step includes 5 passes of cold rolling, with the elongation coefficient of each pass controlled at 1.3-2.2, the deformation rate at 24%-53%, the speed at 60-80 times / min, and the feed rate at 3-4mm.

[0012] As a preferred technical solution, in step S5, the alternation sequence of precision rolling and hollow drawing is fixed as follows: first intermediate drawing → first precision rolling → second precision rolling → third precision rolling → second intermediate drawing → third intermediate drawing → fourth precision rolling → fifth precision rolling → fourth intermediate drawing.

[0013] As a preferred technical solution, in step S5, the finishing rolling consists of 5 passes, with a single pass deformation of 16%-33%, a speed of 70-80 times / min, and a feed rate of 1.5-2mm; the intermediate drawing is a hollow drawing, consisting of 4 passes, with a single pass deformation rate of 12%-22%, and a drawing speed of 10-15m / min.

[0014] As a preferred technical solution, step S6 includes 4 rolling passes, with a single-pass deformation rate of 23%-30%, a machine speed of 50-60 times / min, and a feed rate of 0.5-1mm.

[0015] As a preferred technical solution, step S7 includes 5 hollow drawing passes, with a single-pass deformation rate of 15%-33% and a drawing speed of 5-10m / min.

[0016] As a preferred technical solution, in the S8 dynamic heat treatment step, the intermediate heat treatment temperature is 1010±10℃, and the conveyor belt speed is 0.4-0.7m / min.

[0017] In this technical solution, the intermediate treatment temperature of 1010℃ is higher than the complete recrystallization temperature of the alloy (about 950-980℃), but significantly lower than the rapid grain coarsening temperature (about 1050℃). The belt conveyor speed control of 0.4-0.7m / min is essentially to control the holding time within the range of 1-2 minutes, which precisely meets the minimum time required for complete recrystallization, while suppressing grain growth to the maximum extent. This high-temperature short-time process is the key to obtaining ultrafine grains.

[0018] As a preferred technical solution, the temperature of the final solution treatment is 980±10℃, and the conveyor belt speed is 0.8-1.2m / min.

[0019] The final solution treatment at 980℃, rather than at a higher temperature, is a design that breaks with technical bias. This is because after completing all cold working and intermediate heat treatment, the material has already obtained the target ultrafine grain structure. Traditional processes pursue high-temperature purification to unlock the structure, but this application operates in reverse, using the relatively low temperature of 980℃ to lock and fix the ultrafine grains. Although it cannot achieve the ultimate uniformity of the structure, it is sufficient to eliminate residual stress without causing significant grain growth and surface oxidation. This temperature window achieves the following technical effects: 1) inhibiting further grain growth and maintaining the already formed ultrafine structure; 2) facilitating the appropriate precipitation of Nb and V carbonitrides, enhancing grain boundary pinning, and building a protective barrier for grains to inhibit their growth; 3) while eliminating stress, directly controlling to the optimal combination of strength, toughness, and corrosion resistance.

[0020] As a preferred technical solution, the capillary tube prepared by the process from a 40mm rod blank has a hardness HV0.3≤200; an outer diameter of 1.0mm and a wall thickness of 0.35mm, and simultaneously meets the following requirements: tensile strength ≥552MPa, yield strength ≥241MPa, elongation after fracture A ≥30%, as well as preset requirements for air tightness and compressive strength.

[0021] In the process of reducing size by two orders of magnitude, from 40mm bars to 1mm×0.35mm capillaries, this invention achieves coordinated control of microstructure properties and dimensional accuracy.

[0022] Ultrafine grains of at least 10.0 provide a significant strength contribution through the Hall-Petch effect, while the increased proportion of large-angle grain boundaries in the ultrafine grain structure improves the toughness of the material. The dispersed distribution of Nb and V carbonitrides provides additional precipitation strengthening.

[0023] The uniform microstructure obtained by the alternating deformation process avoids localized weak points, which is the structural basis for ensuring no leakage under 10MPa water pressure. The extremely high surface finish (Ra≤0.8μm) not only reduces flow resistance, but more importantly, eliminates surface stress concentration points and improves fatigue and stress corrosion resistance.

[0024] The combination of a tensile strength of 552 MPa and an elongation of ≥30% is extremely rare in thin-walled capillary products, thanks to the unique high strength-high toughness synergistic effect of the ultrafine grain structure. Rigorous airtightness and pressure resistance tests validate the reliability and consistency of the entire process from materials to manufacturing.

[0025] The advantages and positive effects of this invention are: This invention achieves the preparation of materials with a grain size of ≥10.0 grade by synergistic control of raw material chemical composition, multi-stage deformation and heat treatment parameters, at the scale of millimeter outer diameter and micrometer wall thickness. This enables the capillary to simultaneously possess high strength and toughness, excellent dimensional accuracy and surface integrity, as well as reliable airtightness and pressure resistance, thereby meeting the high sensitivity and high reliability requirements of aviation fire detectors in high temperature, high pressure and corrosive environments.

[0026] This technology is not only applicable to capillary tubes in fire detectors, but its principles can also be widely applied to high-end fields such as fuel nozzles for aero-engines, microtubes for medical devices, and sensors for precision instruments, which has significant strategic importance and industrial radiation value. Detailed Implementation

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below; obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] This invention discloses an ultrafine-grained corrosion-resistant alloy capillary for aviation fire detectors. It is made of a corrosion-resistant alloy with a specific composition, the chemical composition by mass percentage of: C≤0.15%, Si≤0.50%, Mn≤1.00%, P≤0.030%, S≤0.015%, Cr: 14-17%, Ni≥75%, Ti≤0.30%, Al≤0.30%, Cu≤0.50%, Fe: 6.00~10.00%, Nb: 0.04-0.10%, V: 0.04-0.10%, with the balance being unavoidable impurities. This compositional system ensures excellent high-temperature oxidation and corrosion resistance, and provides a compositional basis for obtaining an ultrafine-grained structure through specific plastic processing and heat treatment.

[0029] The preparation process of the capillary includes the following steps: S1. Material selection: Select NS3102 corrosion-resistant alloy billet with a diameter of 40mm, a grain size of grade 7, and no defects such as shrinkage cavities, cracks, or inclusions on the surface as raw material. S2. Billet preparation and piercing: After the billet is cut to length, a piercing device with a molybdenum mandrel is used for deep hole drilling to obtain a primary tube billet. S3. Inner wall grinding: The inner wall of the pipe is machined and ground using a deep hole boring machine; S4. Rough rolling: The refurbished tube is cold rolled in 5 passes. The elongation coefficient of each pass is controlled at 1.3-2.2, and the deformation rate is controlled at 24%-53% and increases with each pass. The size of the rolls and mandrels are matched with the outer and inner diameters of the semi-finished products in each pass. The speed is 60-80 times / min and the feed rate is 3-4mm. The grains are initially refined through large deformation. S5. Alternating intermediate finishing rolling and drawing: The process is carried out in the following sequence: "first intermediate drawing → first finishing rolling → second finishing rolling → third finishing rolling → second intermediate drawing → third intermediate drawing → fourth finishing rolling → fifth finishing rolling → fourth intermediate drawing". The finishing rolling consists of 5 passes, with a single-pass deformation of 16%–33%, a speed of 70–80 times / min, and a feed rate of 1.5–2 mm. The intermediate drawing is a hollow drawing process, consisting of 4 passes, with a single-pass deformation rate of 12%–22%, and a drawing speed of 10–15 m / min. This alternating process effectively coordinates dimensional accuracy control and microstructure homogenization. S6. Finishing and wall-fixing: Four passes of rolling are performed, with a single-pass deformation rate of 23%-30%, a speed of 50-60 times / min, and a feed rate of 0.5-1mm. This process precisely controls the finished wall thickness and improves surface quality. S7. Finished product precision drawing: Perform 5 rounds of hollow drawing, with a single-pass deformation rate of 15%-33% and a drawing speed of 5-10m / min, to further calibrate the dimensions and optimize the surface condition. S8. Heat treatment: After each cold working of the semi-finished product, an intermediate heat treatment is performed at a temperature of 1010±10℃ and a conveyor speed of 0.4-0.7m / min; the finished product is finally subjected to solution treatment at a temperature of 980±10℃ and a conveyor speed of 0.8-1.2m / min, in order to eliminate processing stress, inhibit grain growth, and obtain a stable ultrafine grain structure. S9. Finished product inspection: The properties of the obtained capillary tubes shall meet the following requirements: Mechanical properties: tensile strength ≥ 552 MPa, yield strength ≥ 241 MPa, elongation after fracture A ≥ 30%; Microstructure: Grain size ≥ 10.0; Hardness HV0.3 ≤ 200; Dimensional tolerances: outer diameter 1.0mm, tolerance 0~+0.02mm; wall thickness 0.35mm, tolerance 0~-0.02mm; length 1000mm, length tolerance: ±10mm; Surface quality: External surface roughness ≤ 0.8 μm.

[0030] Internal quality: The alloy pipes are free from defects such as porosity, bubbles, holes, cracks, and delamination; Air tightness: Fill with clean helium gas at 0.5 MPa (gauge pressure), immerse the alloy tube in a water tank for 5 minutes, and check for any air leakage on the surface.

[0031] Inner wall water pressure resistance: The alloy pipe is kept under a pressure of 10MPa for 5 minutes, and no leakage or permanent deformation occurs at the joints or other parts of the alloy pipe.

[0032] The process of this invention involves multiple cycles of deformation, energy storage, and recrystallization, with each cycle refining and homogenizing the grains. A combination of nine intermediate heat treatments and one final solution treatment achieves a step-by-step evolution of the microstructure. Furthermore, the intermediate heat treatments not only address work hardening, eliminating high dislocation density, deformation bands, and elongated grains caused by cold working deformation, but more importantly, recrystallization allows for the spontaneous nucleation and growth of entirely new, equiaxed, stress-free fine grains within the material, completely replacing the old deformed microstructure. Ultimately, the original 7-level grains are progressively upgraded to ≥10.0-level ultrafine grains, enabling capillaries with millimeter outer diameters and micrometer wall thicknesses to simultaneously possess high strength and toughness matching, excellent dimensional accuracy and surface integrity, and reliable airtightness and pressure resistance. This meets the high sensitivity and high reliability requirements of aviation fire detectors operating in high-temperature, high-pressure, and corrosive environments.

[0033] The following describes in detail the preparation process of the capillary tube of the present invention through several embodiments: Example 1: (1) Material selection; Select a 40mm diameter corrosion-resistant alloy billet as the processing raw material. Its grain size should be grade 7, and the surface should be free of defects such as shrinkage cavities, shrinkage cavity marks, voids, cracks, inclusions, and pinholes. The primary carbide content (Class B) should be 2.0. The chemical composition of the NS3102 corrosion-resistant alloy should meet the requirements of the following table:

[0034] (2) Drilling; The specific steps of drilling include: cutting the bar blank from step 1 above into a fixed length of 220mm, and drilling a centering hole on one end face. The centering hole has a size of Φ8mm and a depth of 8mm. Drilling is performed using a deep hole drill with a diameter of 28mm to obtain a primary tube blank with a specification of φ40*6. (3) Grinding; The inner wall of the drilled pipe is machined twice using a deep hole boring machine to grind the pipe from φ40*6mm to φ40*5.5mm. The purpose is to ensure that the inner and outer surfaces of the pipe blank are smooth and free of defects that would affect subsequent processing, with a roughness Ra≤0.5μm.

[0035] (4) Rough rolling; This step involves using a rolling mill to roll the refurbished φ40*5.5 pipe through five passes to obtain a semi-finished product of φ16*1.5mm.

[0036]

[0037] (5) Intermediate finishing rolling and intermediate drawing are alternated; Intermediate finishing rolling and intermediate drawing are performed alternately, with the following steps: first intermediate drawing → first finishing rolling → second finishing rolling → third finishing rolling → second intermediate drawing → third intermediate drawing → fourth finishing rolling → fifth finishing rolling → fourth intermediate drawing.

[0038] The intermediate finishing rolling process consists of 5 passes, and the intermediate drawing process consists of 4 passes of hollow drawing. The outer diameter of the tube changes from φ16*1.5 to φ5*0.65mm.

[0039]

[0040] (6) Finish rolling of the wall: The rolling process involves four passes, resulting in a change in the tube's outer diameter from φ5*0.65mm to φ3*0.33mm. The final wall thickness is determined by controlling the wall thickness of the semi-finished product, while simultaneously reducing the machine speed and feed rate to ensure the surface quality of the rolled product. See the table below for details.

[0041] (7) Finished product is finely drawn After 5 passes of air drawing, the outer diameter of the pipe changes from φ3*0.33 to φ1*0.33 mm. This step controls the wall thickness and product surface quality by drawing with a small deformation rate, while also controlling dimensional tolerances; and by combining deformation amount with heat treatment, the final ultra-fine grain size is achieved.

[0042]

[0043] (8) Heat treatment process Each step of the semi-finished product cold processing requires heat treatment, with the intermediate treatment temperature being 1010±10℃ and the conveyor belt speed being 0.4-0.7m / min.

[0044] The solution treatment temperature for the finished product is selected as 980±10℃, and the conveyor belt speed is 0.8-1.2min.

[0045] (9) Finished product Mechanical properties: tensile strength 651 MPa, yield strength 399 MPa; Microstructure: Grain size 10.0 grade; HV0.3=190 Dimensional tolerances: Outer diameter 1.0mm, tolerance +0.02 / -0mm; Wall thickness 0.35mm, tolerance +0 / -0.02mm; Length 1000mm, length tolerance: ±5mm; Surface quality: External surface roughness 0.17μm Internal quality: The alloy pipes are free from defects such as porosity, bubbles, holes, cracks, and delamination; Air tightness: Fill with clean helium gas at 0.5 MPa (gauge pressure), immerse the alloy tube in a water tank for 5 minutes, and check for any air leakage on the surface.

[0046] Inner wall water pressure resistance: The alloy pipe is kept under a pressure of 10MPa for 5 minutes, and no leakage or permanent deformation occurs at the joints or other parts of the alloy pipe.

[0047] Example 2: (1) Material selection Select a 40mm diameter corrosion-resistant alloy billet as the processing raw material. Its grain size should be grade 7, and the surface should be free of defects such as shrinkage cavities, shrinkage cavity marks, voids, cracks, inclusions, and pinholes. The primary carbide content (Class B) should be 2.0. The chemical composition of the NS3102 corrosion-resistant alloy should meet the requirements of the following table:

[0048] (2) Drilling; The specific steps of drilling include: cutting the bar blank from step 1 above into a fixed length of 220mm, and drilling a centering hole on one end face. The centering hole has a size of Φ8mm and a depth of 8mm. Drilling is performed using a deep hole drill with a diameter of 28mm to obtain a primary tube blank with a specification of φ40*6. (3) Grinding; The inner wall of the drilled pipe is machined twice using a deep hole boring machine to grind the pipe from φ40*6mm to φ40*5.5mm. The purpose is to ensure that the inner and outer surfaces of the pipe blank are smooth and free of defects that would affect subsequent processing, with a roughness Ra≤0.5μm.

[0049] (4) Rough rolling; This step involves using a rolling mill to roll the ground φ40*5.5 pipe through five passes to obtain a semi-finished product of φ16*1.5mm. Through large deformation rate cold working, the grains are finely crushed, ensuring the uniformity of the product's microstructure.

[0050]

[0051] (5) Intermediate finishing rolling and intermediate drawing are alternated; Intermediate finishing rolling and intermediate drawing are performed alternately, with the following steps: first intermediate drawing → first finishing rolling → second finishing rolling → third finishing rolling → second intermediate drawing → third intermediate drawing → fourth finishing rolling → fifth finishing rolling → fourth intermediate drawing.

[0052] The intermediate finishing rolling process consists of 5 passes, the intermediate drawing process is hollow drawing, and the air drawing process consists of 4 passes. The outer diameter of the tube changes from φ16*1.5 to φ5*0.65mm.

[0053]

[0054] (6) Finish rolling of the wall The rolling process involves four passes, resulting in a change in the tube's outer diameter from φ5*0.65mm to φ3*0.33mm. The finished product wall thickness is determined by controlling the wall thickness of the semi-finished product, while simultaneously reducing the machine speed and feed rate to ensure the surface quality of the rolled product. See the table below for details.

[0055] (7) Finished product is finely drawn; After five passes of air drawing, the outer diameter of the tube changes from φ3*0.33 to φ1*0.33 mm. This step controls the wall thickness and surface quality of the product while controlling dimensional tolerances through small deformation rate drawing. The final ultra-fine grain size is achieved through the combined control of deformation amount and heat treatment.

[0056]

[0057] (8) Heat treatment process Each pass of the semi-finished product cold processing requires heat treatment. The intermediate treatment temperature is 1010±10℃, and the conveyor belt speed is 0.4-0.7m / min. The solution treatment temperature for the finished product pass is 980±10℃, and the conveyor belt speed is 0.8-1.2min.

[0058] (9) Finished product Mechanical properties: tensile strength 583 MPa, yield strength 367 MPa; Microstructure: Grain size 10.0 grade; HV0.3=185 Dimensional tolerances: Outer diameter 1.0mm, tolerance +0.01 / -0.01mm; Wall thickness 0.35mm, tolerance +0.01 / -0.02mm; Length 1000mm, length tolerance: ±7mm; Surface quality: External surface roughness 0.21μm Internal quality: The alloy pipes are free from defects such as porosity, bubbles, holes, cracks, and delamination; Air tightness: Fill with clean helium gas at 0.5 MPa (gauge pressure), immerse the alloy tube in a water tank for 5 minutes, and check for any air leakage on the surface.

[0059] Inner wall water pressure resistance: The alloy pipe is kept under a pressure of 10MPa for 5 minutes, and no leakage or permanent deformation occurs at the joints or other parts of the alloy pipe.

[0060] Example 3: (1) Material selection; Select a 40mm diameter corrosion-resistant alloy billet as the processing raw material. Its grain size should be grade 7, and the surface should be free of defects such as shrinkage cavities, shrinkage cavity marks, voids, cracks, inclusions, and pinholes. The primary carbide content (Class B) should be 2.0. The chemical composition of the NS3102 corrosion-resistant alloy should meet the requirements of the following table:

[0061] (2) Drilling; The specific steps of drilling include: cutting the bar blank from step 1 above into a fixed length of 220mm, and drilling a centering hole on one end face. The centering hole has a size of Φ8mm and a depth of 8mm. Drilling is performed using a deep hole drill with a diameter of 28mm to obtain a primary tube blank with a specification of φ40*6. (3) Grinding; The inner wall of the drilled pipe is machined twice using a deep hole boring machine to grind the pipe from φ40*6mm to φ40*5.5mm. The purpose is to ensure that the inner and outer surfaces of the pipe blank are smooth and free of defects that would affect subsequent processing, with a roughness Ra≤0.5μm.

[0062] (4) Rough rolling; This step involves using a rolling mill to roll the ground φ40*5.5 pipe through five passes to obtain a semi-finished product of φ16*1.5mm. Through large deformation rate cold working, the grains are finely crushed, ensuring the uniformity of the product's microstructure.

[0063]

[0064] (5) Intermediate finishing rolling and intermediate drawing are alternated; Intermediate finishing rolling and intermediate drawing are performed alternately, with the following steps: first intermediate drawing → first finishing rolling → second finishing rolling → third finishing rolling → second intermediate drawing → third intermediate drawing → fourth finishing rolling → fifth finishing rolling → fourth intermediate drawing.

[0065] The intermediate finishing rolling process consists of 5 passes, the intermediate hollow drawing process consists of 4 passes, and the diameter of the material is φ16*1.5→φ5*0.65mm.

[0066]

[0067] (6) Finish rolling of the wall The tube undergoes four rolling passes, resulting in a change in outer diameter from φ5*0.65 to φ3*0.33 mm. The final wall thickness is determined by controlling the wall thickness of the semi-finished product, while simultaneously reducing the machine speed and feed rate to ensure the surface quality of the rolled product.

[0068]

[0069] (7) Finished product is finely drawn; After five passes of air drawing, the outer diameter of the tube changes from φ3*0.33 to φ1*0.33 mm. This step controls the wall thickness and surface quality of the product while controlling dimensional tolerances through small deformation rate drawing. The final ultra-fine grain size is achieved through the combined control of deformation amount and heat treatment.

[0070]

[0071] (8) Heat treatment process; Each step of the semi-finished product cold processing requires heat treatment, with the intermediate treatment temperature being 1010±10℃ and the conveyor belt speed being 0.4-0.7m / min.

[0072] The solution treatment temperature for the finished product is selected as 980±10℃, and the conveyor belt speed is 0.8-1.2min.

[0073] (9) Finished product; Mechanical properties: tensile strength 631 MPa, yield strength 321 MPa; Microstructure: Grain size 10.0 grade; HV0.3=176 Dimensional tolerances: Outer diameter 1.0mm, tolerance +0.01 / -0.02mm; Wall thickness 0.35mm, tolerance +0.02 / -0.01mm; Length 1000mm, length tolerance: ±6mm; Surface quality: External surface roughness 0.56μm Internal quality: The alloy pipes are free from defects such as porosity, bubbles, holes, cracks, and delamination; Air tightness: Fill with clean helium gas at 0.5 MPa (gauge pressure), immerse the alloy tube in a water tank for 5 minutes, and check for any air leakage on the surface.

[0074] Inner wall water pressure resistance: The alloy pipe is kept under a pressure of 10MPa for 5 minutes, and no leakage or permanent deformation occurs at the joints or other parts of the alloy pipe.

[0075] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made in accordance with the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A fine-grained corrosion-resistant alloy capillary for an aviation fire detector, characterized in that: Its chemical composition, by mass percentage, is as follows: C≤0.15%; Si≤0.50%; Mn≤1.00%; P≤0.030%; S≤0.015%; Cr: 14-17%; Ni≥75%; Ti≤0.30%; Al≤0.30%; Cu≤0.50%; Fe: 6.00~10.00%; Nb: 0.04-0.10%; V: 0.04-0.10%, with the balance being unavoidable impurities; its microstructure grain size is not less than grade 10.

0.

2. The fabrication process of the ultrafine-grained corrosion-resistant alloy capillary for aviation fire detectors as described in claim 1, characterized in that, Includes the following steps: S1. Raw material preparation: Select corrosion-resistant alloy billet; S2. Billet preparation and piercing: Cut the billet to length and perform deep hole machining to obtain a primary tube blank; S3. Grind the inner wall of the primary tube blank; S4. Rough rolling: Perform multiple cold rolling passes on the ground tube, with a deformation rate of 24%-53% increasing with each pass; S5. Alternating intermediate finishing rolling and drawing: Perform multiple finishing rolling passes and multiple hollow drawing passes on the rough rolled tube in a preset sequence; S6. Finish rolling to fix the wall: Perform multiple rolling passes on the alternately finished tube, with the deformation rate increasing with each pass; S7. Finished product drawing: The pipe with the wall thickness precisely determined is subjected to multiple hollow drawing passes; S8. Dynamic heat treatment: After each cold working pass of S4, S5 and S6, the semi-finished product is subjected to intermediate heat treatment; and after all cold working is completed, the finished product is subjected to final solution treatment. S9. Finished Product Inspection: The final capillary tubes are inspected for performance and quality.

3. The fabrication process of the ultrafine-grained corrosion-resistant alloy capillary for aviation fire detectors as described in claim 2, characterized in that: The S4 rough rolling deformation step includes 5 passes of cold rolling, with the elongation coefficient of each pass controlled at 1.3-2.2, the speed at 60-80 times / min, and the feed rate at 3-4mm.

4. The fabrication process of the ultrafine-grained corrosion-resistant alloy capillary for aviation fire detectors as described in claim 2, characterized in that: In step S5, the alternation sequence of finishing rolling and hollow drawing is fixed as follows: first intermediate drawing → first finishing rolling → second finishing rolling → third finishing rolling → second intermediate drawing → third intermediate drawing → fourth finishing rolling → fifth finishing rolling → fourth intermediate drawing.

5. The fabrication process of the ultrafine-grained corrosion-resistant alloy capillary for aviation fire detectors as described in claim 4, characterized in that: In step S5, the finishing rolling consists of 5 passes, with a single pass deformation of 16%–33%, a speed of 70–80 passes / min, and a feed rate of 1.5–2 mm; the intermediate drawing is a hollow drawing, consisting of 4 passes, with a single pass deformation rate of 12%–22%, and a drawing speed of 10–15 m / min.

6. The fabrication process of the ultrafine-grained corrosion-resistant alloy capillary for aviation fire detectors as described in claim 2, characterized in that: The S6 step includes 4 rolling passes, with a single-pass deformation rate of 23%-30%, a machine speed of 50-60 times / min, and a feed rate of 0.5-1mm.

7. The fabrication process of the ultrafine-grained corrosion-resistant alloy capillary for aviation fire detectors as described in claim 2, characterized in that: The S7 step includes 5 hollow drawing passes, with a single-pass deformation rate of 15%-33% and a drawing speed of 5-10 m / min.

8. The fabrication process of the ultrafine-grained corrosion-resistant alloy capillary for aviation fire detectors as described in claim 2, characterized in that: In the S8 dynamic heat treatment step, the intermediate heat treatment temperature is 1010±10℃, and the conveyor belt speed is 0.4-0.7m / min.

9. The fabrication process of the ultrafine-grained corrosion-resistant alloy capillary for aviation fire detectors as described in claim 8, characterized in that: In the S8 dynamic heat treatment step, the final solution treatment temperature is 980±10℃, and the conveyor belt speed is 0.8-1.2m / min.

10. The fabrication process of the ultrafine-grained corrosion-resistant alloy capillary for aviation fire detectors as described in claim 2, characterized in that: The capillary tube prepared from a 40mm rod blank by the aforementioned process has a hardness HV0.3≤200; an outer diameter of 1.0mm and a wall thickness of 0.35mm, and simultaneously meets the following requirements: tensile strength ≥552MPa, yield strength ≥241MPa, elongation after fracture A ≥30%, as well as air tightness and compressive strength.

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