Chemical formula of high-performance niobium-titanium pipe and research on preparation process of high-performance niobium-titanium pipe

Abstract

The invention discloses a high-performance niobium-titanium pipe chemical formula and preparation process research thereof. The high-performance niobium-titanium pipe chemical formula comprises the following chemical components in percentage by mass: 0.25-0.45% of Zr, 0.015-0.025% of O, less than or equal to 0.010% of N, less than or equal to 0.002% of H, less than or equal to 0.010% of C, less than or equal to 0.050% of Fe and Ni, 45.0-48.0% of Nb, the balance of Ti, the sum of Nb and Ti being 99.475-99.688%, and the balance of other unavoidable impurities. The niobium-titanium alloy pipe with high strength, high toughness, high yield and excellent corrosion resistance is prepared through the steps of vacuum induction melting, double vacuum arc remelting, hot forging, nano BN / MoS coating core rod extrusion punching, multi-pass cold drawing, intermediate vacuum annealing, solid solution-aging composite heat treatment, precise pickling passivation and the like. The process is suitable for the fields of aerospace, ocean engineering and nuclear industry.

Description

Technical Field

[0001] This invention relates to the field of metal material preparation and chemical formulation, specifically to a chemical formulation and process for manufacturing high-performance niobium-titanium alloy tubing, which is particularly suitable for the preparation of seamless niobium-titanium (Nb-Ti) alloy tubing with high strength, low coefficient of thermal expansion, and high corrosion resistance in aerospace, deep-sea equipment, and superconducting magnets. Background Technology

[0002] Niobium-titanium alloy (Nb-Ti), as a typical superconducting and corrosion-resistant structural material, is widely used in high-magnetic-field superconductors, marine engineering, and the nuclear industry. However, the fabrication technology of seamless niobium-titanium alloy tubes mainly suffers from the following problems:

[0003] 1. Insufficient control of trace elements: The control of interstitial elements such as oxygen, nitrogen, and hydrogen is not precise enough (it is difficult to achieve within ±0.005%), which leads to a decrease in material toughness and a decrease in superconducting performance.

[0004] 2. Poor uniformity of structure: The ingot structure has severe segregation, which easily leads to defects such as central cracks and peeling during subsequent pipe processing.

[0005] 3. Poor adaptability to forming and processing: Although some formulations have high tensile strength, they are prone to brittle cracking during cold processing into thin-walled tubes, resulting in a yield rate of less than 75%.

[0006] Taking its adaptability to forming and processing as the research object, the search revealed that although existing patents proposed optimized elements for Nb-Ti alloys, they did not combine the method of fine chemical composition control with two-stage vacuum cleaning heat treatment, resulting in insufficient strength of the seamless tubes prepared by the alloy, and cracks were still easily generated during the cold working process.

[0007] Therefore, there is an urgent need for a new chemical formula and manufacturing process to solve the above problems. Summary of the Invention

[0008] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0009] In view of the problems existing in the current niobium-titanium alloy seamless tube manufacturing process, the present invention is proposed.

[0010] Therefore, the technical problem solved by this invention is: the existing niobium-titanium alloy seamless tube manufacturing process does not combine precise chemical composition control with a two-stage vacuum cleaning heat treatment method, resulting in insufficient strength of the alloy-made seamless tube and easy cracking during cold working.

[0011] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a high-performance niobium-titanium pipe chemical formula, the chemical composition of which, by mass percentage, is: Zr 0.25–0.45%, O 0.015–0.025%, N≤0.010%, H≤0.002%, C≤0.010%, Fe+Ni≤0.050%, Nb 45.0–48.0%, with Ti as the balance, and the sum of Nb and Ti is 99.475–99.688%, with the balance being other unavoidable impurities.

[0012] To solve the above-mentioned technical problems, the present invention also provides the following technical solution: a study on the preparation process of a chemical formula for high-performance niobium-titanium pipes, wherein the high-performance niobium-titanium pipes are prepared by the above-mentioned chemical formula, specifically including the following processes:

[0013] S1: Vacuum Induction Melting (VIM) Temperature Controlled Feeding

[0014] Under vacuum conditions ≤2×10⁻³Pa, high-purity Nb (purity ≥99.95%) is first added and heated to 1870±10℃;

[0015] Add high-purity Ti (purity ≥ 99.98%) and Zr in proportion;

[0016] Control the stirring frequency to 8–12 Hz to ensure that the homogenization time of the melt composition is ≥18 min;

[0017] S2: Vacuum Arc Remelting (VAR) Refining

[0018] The intermediate obtained in step S1 was remelted twice, with the arc current set to 6.5–7.0 kA;

[0019] One step involves performing spectral analysis after remelting to ensure that the O / N / H ratio meets the target.

[0020] S3: Hot forging fragmentation structure

[0021] At 1100–1150℃, the remelted steel ingot is subjected to triaxial hot forging (reduction ratio ≥3) to break up the original as-cast structure;

[0022] S4: Extrusion and mandrel perforation tube making

[0023] The extrusion temperature is 850–900℃, and the extrusion pressure is 380–420 MPa.

[0024] The mandrel surface is coated with a nano MoS2 / BN hybrid lubricating layer (BN particle size <200nm).

[0025] S5: Multi-pass cold drawing and intermediate heat treatment

[0026] Among them, the deformation amount of each cold drawing is ≤15%, and the cumulative deformation rate is ≥60%;

[0027] During the intermediate heat treatment, the vacuum annealing temperature is 780±5℃, the holding time is 1.5h, and the vacuum degree is ≤5×10⁻³Pa.

[0028] S6: Solution-Aging Composite Heat Treatment

[0029] Solution treatment: 880±5℃, 2 h → water cooling;

[0030] Aging: 480±3℃, heat preservation for 10h → air cooling, precipitation of metastable strengthening phase Nb2Ti or α″ phase;

[0031] S7: Final pickling and surface passivation

[0032] The pickling solution was prepared with the following ratio: HF (40 wt%) : HNO3 (68 wt%) = 1:7 (volume ratio), diluted with deionized water to an acidity of approximately 12%.

[0033] The pickling time is ≤120 s, followed by passivation with 0.5 M HNO3 for 15 min to form a continuous passivation film, thereby completely preparing high-performance niobium-titanium tubing.

[0034] As a preferred embodiment of the chemical formulation preparation process for high-performance niobium-titanium tubing described in this invention, the S1 vacuum induction melting (VIM) temperature-controlled feeding step, after stirring and homogenization, further includes: using three-stage degassing (1870℃→1650℃→1500℃) to reduce interstitial elements.

[0035] As a preferred embodiment of the chemical formulation preparation process for high-performance niobium-titanium tubing described in this invention, in the S3 hot forging and crushing step, the cooling rate is set to 10–15℃ / s to prevent coarse grains.

[0036] As a preferred embodiment of the chemical formulation preparation process for high-performance niobium-titanium tubing described in this invention, in the S4 extrusion and mandrel piercing tubing steps, the piercing speed is ≤20 mm / s to avoid surface cracks.

[0037] As a preferred embodiment of the chemical formulation preparation process for high-performance niobium-titanium tubing described in this invention, the lubricating layer is composed of 60–70 wt% hexagonal boron nitride (particle size ≤ 200 nm) and 30–40 wt% molybdenum disulfide, with a coating thickness of 5–8 μm.

[0038] This invention provides a chemical formula and preparation process for high-performance niobium-titanium tubing, which has the following beneficial effects:

[0039] 1. The precise addition of trace amounts of Zr, combined with dual-stage vacuum purification, controls the optimal range of interstitial elements, thereby improving overall performance;

[0040] 2. The mandrel piercing technology using a nano-BN / MoS2 lubricating coating reduces the risk of surface cracks during the extrusion process;

[0041] 3. Solution-aging composite heat treatment combined with chemical composition optimization achieves a balance between ultra-high strength and excellent low-temperature toughness;

[0042] 4. The purity of raw materials, O / N / H content and microstructure are fully controlled, and the pipe yield is as high as 92% or more. Attached Figure Description

[0043] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0044] Figure 1 This is a flowchart of the high-performance niobium-titanium tube preparation method involved in this invention. Detailed Implementation

[0045] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0046] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0047] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0048] Taking the adaptability of niobium-titanium alloy seamless tubes as the research object, it was found that although existing patents have proposed optimized elements for Nb-Ti alloys, they have not combined the method of fine chemical composition control with two-stage vacuum cleaning heat treatment, resulting in insufficient strength of the seamless tubes prepared by the alloy and easy cracking during cold working.

[0049] Therefore, the purpose of this invention is to provide a chemical formula and process for high-performance niobium-titanium pipes, which achieves high strength (tensile strength ≥850 MPa), high and low temperature toughness (impact energy ≥40 J / cm² at –253℃), uniform structure and excellent resistance to hydrogen embrittlement, while having a yield of ≥90%.

[0050] Specifically, this invention provides a chemical formula for high-performance niobium-titanium tubing, the chemical composition of which, by mass percentage, is: Zr 0.25–0.45%, O 0.015–0.025%, N ≤0.010%, H ≤0.002%, C ≤0.010%, Fe+Ni ≤0.050%, Nb 45.0–48.0%, with Ti as the balance, and the sum of Nb and Ti is 99.475–99.688%, with the balance being other unavoidable impurities.

[0051] It should be noted that, from the perspective of the general mechanism of action, the Nb used in this invention is a matrix element, which enhances the superconducting critical magnetic field and corrosion resistance; Ti is a matrix element, which improves toughness and processing performance; Zr is used to refine grains, suppress hydrogen embrittlement, and improve high-temperature strength; O is used for solid solution strengthening, but excessive amounts can easily cause embrittlement, and it is an impurity / interstitial element, originating from the oxide film on the surface of the raw material and the atmosphere during smelting; N is used to control low-temperature toughness, and it is an impurity / interstitial element, originating from the smelting atmosphere and the penetration of protective gas; H is used to avoid hydrogen embrittlement, and it is an impurity / interstitial element, originating from pickling and adsorption in humid environments; C is used to control inclusion phases and increase hardness, and it is an impurity / interstitial element, originating from wear of raw materials or furnace lining during smelting; Fe+Ni is used to avoid a decrease in magnetic properties, and it is an impurity / interstitial element, originating from contamination of raw materials and stainless steel tools.

[0052] The aforementioned trace impurities are strictly controlled in the formulation of this invention to ensure the high performance of the final product.

[0053] Furthermore, this invention provides a study on the preparation process of a chemical formula for high-performance niobium-titanium tubing. The preparation process using the aforementioned chemical formula for high-performance niobium-titanium tubing specifically includes the following steps:

[0054] S1: Vacuum Induction Melting (VIM) Temperature Controlled Feeding

[0055] Under vacuum conditions ≤2×10⁻³Pa, high-purity Nb (purity ≥99.95%) is first added and heated to 1870±10℃;

[0056] Add high-purity Ti (purity ≥ 99.98%) and Zr in proportion;

[0057] Control the stirring frequency to 8–12 Hz to ensure that the homogenization time of the melt composition is ≥18 min;

[0058] Three-stage degassing (1870℃→1650℃→1500℃) is used to reduce interstitial elements;

[0059] It should be noted that during the specific temperature-controlled feeding process of vacuum induction melting (VIM):

[0060] Objective: To achieve complete and uniform melting of Nb, Ti, and Zr; to remove interstitial impurities such as oxygen, nitrogen, and hydrogen to the maximum extent; and to prevent element oxidation and volatilization.

[0061] Step-by-step instructions:

[0062] ① Vacuum control

[0063] Initial vacuum degree ≤2×10⁻³ Pa (mechanical pump + molecular pump combination can be used);

[0064] If the vacuum is too low, nitrogen and oxygen from the residual gas will escape into the melt and introduce impurities.

[0065] ② Heating control

[0066] The electromagnetic induction coil frequency is 5–8 kHz;

[0067] The melting temperature is precisely controlled at 1870±10℃ (close to the boiling point of Ti, but able to melt Nb sufficiently and quickly).

[0068] ③ Feeding sequence

[0069] First add Nb (melting point 2468℃), and after it partially melts, add Ti (melting point 1668℃) and Zr (melting point 1855℃).

[0070] Control the rate at which Ti is added to reduce evaporation losses.

[0071] ④ Melt pool stirring

[0072] High-frequency electromagnetic stirring at 8–12 Hz, homogenization time ≥18 min, ensures uniform composition.

[0073] ⑤ Three-stage degassing

[0074] Hot → Cold → Hot cycle (1870℃ → 1650℃ → 1500℃);

[0075] By utilizing changes in solubility, gases are allowed to escape from the melt, reducing the content of O, N, and H.

[0076] The experimental results of step S1 are compared as shown in the table below (Table 1: Influence of VIM vacuum on interstitial elements): Vacuum degree / Pa O / % N / % H / % 5×10⁻³ 0.032 0.012 0.0028 3×10⁻³ 0.026 0.009 0.0021 2×10⁻³ (This invention) 0.020 0.007 0.0015

[0077] The lower the vacuum level, the more significant the O / N / H ratio decreases.

[0078] S2: Vacuum Arc Remelting (VAR) Refining

[0079] The intermediate obtained in step S1 was remelted twice, with the arc current set to 6.5–7.0 kA;

[0080] One step involves performing spectral analysis after remelting to ensure that the O / N / H ratio meets the target.

[0081] Secondary remelting is used to reduce segregation;

[0082] It should be noted that in the specific vacuum arc remelting (VAR) refining process:

[0083] Objective: To further reduce inclusions and impurities; to eliminate component segregation and shrinkage cavities.

[0084] Step-by-step instructions:

[0085] ① Electrical parameters

[0086] Arc current 6.5–7.0 kA, voltage 20–30 V;

[0087] Avoid excessive current to prevent the evaporation and loss of alloying elements.

[0088] ② Number of remelting times

[0089] Two VARs:

[0090] First, eliminate macroscopic shrinkage cavities and homogenize the ingot material;

[0091] The second refining process removes impurities and improves the coagulation structure.

[0092] ③ Testing process

[0093] Chemical composition was analyzed by spectroscopic analysis after the first VAR.

[0094] If O / N / H exceeds the limit, adjust the vacuum level and cooling rate for the next VAR process.

[0095] ④ Cooling control

[0096] Water jacket cooling stabilizes the solidification rate and prevents coarse grains and component stratification.

[0097] The experimental results of step S2 are compared in the following table (Table 2: Effect of remelting times on microstructure): Number of remelting times First-order segregation index PI* Average grain size / μm 1 0.28 65 2 (This invention) 0.06 38

[0098] Segregation index PI: The difference between the maximum and minimum values ​​of chemical components.

[0099] The second VAR reduced the segregation index by 78% and refined the grain size by 42%.

[0100] S3: Hot forging fragmentation structure

[0101] At 1100–1150℃, the remelted steel ingot is subjected to triaxial hot forging (reduction ratio ≥3) to break up the original as-cast structure;

[0102] The cooling rate is set to 10–15℃ / s to prevent coarse grains.

[0103] It should be noted that in the specific hot forging and fragmentation process:

[0104] Objective: To break up coarse columnar crystals and dendrites in the as-cast state; to improve subsequent plastic workability.

[0105] Step-by-step instructions:

[0106] ①Temperature range

[0107] 1100–1150℃ (approximately 200℃ above the recrystallization temperature to prevent cold cracking);

[0108] ②Reduction ratio

[0109] The total compression ratio is ≥3 (ratio of initial to final cross-sectional area), which is sufficient to break up the primary tissue.

[0110] ③ Triaxial forging

[0111] Change the forging direction each time to prevent the fiber structure from becoming too directional.

[0112] ④ Cooling method

[0113] After hot forging, air cool at medium speed (10–15℃ / s) to avoid abnormal grain growth or excessive phase precipitation.

[0114] The experimental results of step S3 are compared as shown in the table below (Table 3: Effect of compression ratio on the elongation of the finished product): compression ratio Average elongation / % 2.0 19 2.5 21 3.0 (This invention) 23

[0115] When the reduction ratio is ≥3, the deformation uniformity and plasticity are optimal.

[0116] S4: Extrusion and mandrel perforation tube making

[0117] The extrusion temperature is 850–900℃, and the extrusion pressure is 380–420 MPa.

[0118] The mandrel surface is coated with a nano MoS2 / BN hybrid lubricating layer (BN particle size <200nm).

[0119] Among them, the perforation speed is ≤20 mm / s to avoid surface cracks;

[0120] It should be noted that in the specific extrusion and mandrel piercing tube manufacturing process:

[0121] Objective: To process ingots into tube blanks and ensure the quality of the inner and outer walls.

[0122] Step-by-step instructions:

[0123] ①Extrusion temperature

[0124] 850–900℃ (balancing plasticity and inhibiting Zr compound coarsening);

[0125] ② Extrusion pressure

[0126] 380–420 MPa. Too low a pressure can easily lead to uneven wall thickness in the tube blank, while too high a pressure can easily cause cracks.

[0127] ③ Mandrel Coating

[0128] Nano-sized BN (particle size ≤200nm): High temperature resistance, low friction;

[0129] MoS2: Provides stable lubrication in low-oxygen environments;

[0130] The coating thickness is 5–8 μm to prevent adhesion between the metal and the mandrel.

[0131] ④ Drilling speed

[0132] ≤20 mm / s to reduce the risk of internal surface tearing.

[0133] The experimental results of step S4 are compared as shown in the table below (Table 4: Influence of coating on extruded surface quality): Coating type Surface crack rate / % Uncoated 4.8 <![CDATA[Micron BN / MoS2]]> 2.3 <![CDATA[Nano BN / MoS2 (This invention)]]> 0.4

[0134] The nano-coating reduces the crack rate to 0.4%, significantly improving surface quality.

[0135] S5: Multi-pass cold drawing and intermediate heat treatment

[0136] Among them, the deformation amount of each cold drawing is ≤15%, and the cumulative deformation rate is ≥60%;

[0137] During the intermediate heat treatment, the vacuum annealing temperature is 780±5℃, the holding time is 1.5h, and the vacuum degree is ≤5×10⁻³Pa.

[0138] It should be noted that in the specific multi-pass cold drawing and intermediate heat treatment process:

[0139] Objective: To control the amount of deformation and obtain the target dimensions; to eliminate work hardening and maintain machinability.

[0140] Step-by-step instructions:

[0141] ①Deformation rate per pass

[0142] ≤15%, to prevent excessive work hardening that could lead to brittleness.

[0143] ② Cumulative deformation rate

[0144] ≥60%, refines grain size, and improves strength.

[0145] ③ Intermediate heat treatment

[0146] Vacuum annealing temperature: 780±5℃;

[0147] Insulate for 1.5 h, vacuum degree ≤5×10⁻³ Pa;

[0148] Objective: To eliminate internal stress, restore plasticity, and prevent oxidation.

[0149] The experimental results of step S5 are compared as shown in the table below (Table 5: Influence of intermediate annealing on machining cracks): Annealing Finished product appearance crack rate / % Average hardness HV No annealing 3.2 285 Annealing (this invention) 0.5 240

[0150] Intermediate annealing significantly eliminates work hardening and greatly reduces the crack rate.

[0151] S6: Solution-Aging Composite Heat Treatment

[0152] Solution treatment: 880±5℃, 2 h → water cooling;

[0153] Aging: 480±3℃, heat preservation for 10h → air cooling, precipitation of metastable strengthening phase Nb2Ti or α″ phase, significantly improving strength and toughness;

[0154] It should be noted that in the specific solution-aging composite heat treatment process:

[0155] Purpose:

[0156] Solid solution: dissolves secondary phases, improving plasticity and compositional uniformity;

[0157] Aging: Fine reinforcing phases precipitate, improving strength and toughness.

[0158] Step-by-step instructions:

[0159] ①Solution treatment

[0160] 880±5℃, hold for 2 h (too short a time will not allow for complete solidification, too long a time will result in grain growth).

[0161] Rapid water cooling prevents the precipitation of harmful phases.

[0162] ② Time-sensitive processing

[0163] 480±3℃, keep warm for 10 hours;

[0164] The precipitation of metastable strengthening phases Nb2Ti or fine α″ phases provides precipitation strengthening.

[0165] ③ Cooling

[0166] After aging, air cool to avoid thermal stress cracking.

[0167] The experimental results of step S6 are compared as shown in the table below (Table 6: Influence of composite heat treatment on mechanical properties): state Tensile strength / MPa Impact energy –253℃ / J·cm⁻² After solution 805 39 Solution treatment + aging (this invention) 862 42

[0168] Aging can increase strength by approximately 7% while maintaining toughness.

[0169] S7: Final pickling and surface passivation

[0170] The pickling solution was prepared with the following ratio: HF (40 wt%) : HNO3 (68 wt%) = 1:7 (volume ratio), diluted with deionized water to an acidity of approximately 12%.

[0171] The pickling time is ≤120 s, followed by passivation with 0.5 M HNO3 for 15 min to form a continuous passivation film, thereby completely preparing high-performance niobium-titanium tubing.

[0172] It should be noted that during the specific pickling and surface passivation process:

[0173] Objective: To remove oxide scale and surface contaminants; to form a stable protective passivation film.

[0174] Step-by-step instructions:

[0175] ① Pickling solution ratio

[0176] HF (40 wt%): HNO3 (68 wt%) = 1:7 (V / V);

[0177] Dilute to approximately 12% acidity to prevent over-corrosion.

[0178] ② Pickling time

[0179] ≤120 s, to prevent excessive surface dissolution that could lead to dimensional deviations.

[0180] ③ Passivation solution

[0181] 0.5 M HNO3, 15 min;

[0182] Objective: To generate a stable Nb / Ti oxide film and improve corrosion resistance.

[0183] The experimental results of step S7 are compared as shown in the table below (Table 7: Comparison of corrosion rates before and after passivation). state Corrosion rate / mm·a Unpassivated 0.021 Passivation (in this invention) 0.009

[0184] Passivation reduces the corrosion rate by 57%.

[0185] Furthermore, the lubricating layer consists of 60–70 wt% hexagonal boron nitride (particle size ≤200 nm) and 30–40 wt% molybdenum disulfide, with a coating thickness of 5–8 μm.

[0186] This invention provides a chemical formula and preparation process for high-performance niobium-titanium tubing, which has the following beneficial effects:

[0187] 1. The precise addition of trace amounts of Zr, combined with dual-stage vacuum purification, controls the optimal range of interstitial elements, thereby improving overall performance;

[0188] 2. The mandrel piercing technology using a nano-BN / MoS2 lubricating coating reduces the risk of surface cracks during the extrusion process;

[0189] 3. Solution-aging composite heat treatment combined with chemical composition optimization achieves a balance between ultra-high strength and excellent low-temperature toughness;

[0190] 4. The purity of raw materials, O / N / H content and microstructure are fully controlled, and the pipe yield is as high as 92% or more.

[0191] To verify the beneficial effects of the formulation of this invention, the following experimental verification process was conducted:

[0192] I. Experimental Objective

[0193] Verification shows that the Nb-Ti-Zr alloy seamless tubes prepared according to the formula and process of this invention are superior to existing technologies in terms of mechanical properties, low-temperature toughness, corrosion resistance, and yield.

[0194] II. Test Materials

[0195] raw material:

[0196] High-purity Nb (purity ≥ 99.95%), high-purity Ti (purity ≥ 99.98%), high-purity Zr (purity ≥ 99.95%)

[0197] Formula (wt%):

[0198] Nb: 46.5;

[0199] Ti: 52.9 (balance);

[0200] Zr: 0.35;

[0201] O: 0.020;

[0202] N: 0.007;

[0203] H: 0.0015;

[0204] C: 0.006;

[0205] Fe+Ni: 0.030;

[0206] Comparison objects:

[0207] Alloy tubing A prepared from other existing patented formulations;

[0208] Commercial Nb-Ti alloy tubing B;

[0209] III. Preparation Process

[0210] Melting: Vacuum Induction Melting (VIM) + Double Vacuum Arc Remelting (VAR);

[0211] Hot working: 1100–1150℃ triaxial forging, reduction ratio ≥3;

[0212] Tube manufacturing: Mandrel extrusion and perforation at 850–900℃, with nano-BN / MoS2 coating on the mandrel surface;

[0213] Cold working: multi-pass cold drawing (single-pass deformation rate ≤15%), cumulative deformation ≥60%, intermediate vacuum annealing at 780℃×1.5 h;

[0214] Heat treatment: solution treatment at 880℃ for 2 hours → water cooling, aging at 480℃ for 10 hours → air cooling;

[0215] Surface treatment: HF-HNO3 pickling ≤120 s, 0.5 M HNO3 passivation 15 min;

[0216] Using the above process steps, a seamless pipe with a length of 2 m, an outer diameter of 25 mm, and a wall thickness of 2 mm is prepared.

[0217] IV. Test Methods

[0218] 1. Mechanical property testing

[0219] Tensile strength (Rm), yield strength (Rp0.2), elongation (E1%);

[0220] According to GB / T 228.1–2010 Standard for Tensile Testing at Room Temperature;

[0221] 2. Low-temperature impact toughness test

[0222] Temperature: –253℃ (liquid helium environment);

[0223] According to GB / T 229–2020 Charpy impact test standard;

[0224] 3. Microstructural analysis

[0225] Optical microscope (OM), scanning electron microscope (SEM);

[0226] 4. Corrosion resistance test

[0227] Medium: 3.5% NaCl solution;

[0228] Mass loss method after soaking for 48 hours;

[0229] 5. Calculation of yield rate

[0230] Finished pipe length / Total original billet length × 100%;

[0231] V. Experimental Data and Results

[0232] Table 8 Comparison of Mechanical Properties (Room Temperature) Sample number Tensile strength Rm / MPa Yield strength Rp0.2 / MPa Elongation El / % This invention 862 780 23 A is currently available. 785 710 17 Existing B 792 720 18

[0233] Table 9 Low-temperature impact toughness (–253℃) Sample number Impact energy / J·cm⁻² This invention 42 A is currently available. 30 Existing B 28

[0234] Table 10 Corrosion resistance (3.5% NaCl solution, 48 h weight loss method) Sample number Mass loss / mg·cm⁻² Corrosion rate / mm·a This invention 0.15 0.009 A is currently available. 0.28 0.017 Existing B 0.32 0.019

[0235] Table 11. Statistics on yield rate Sample number Yield / % This invention 92.3 A is currently available. 75.1 Existing B 80.4

[0236] VI. Results Analysis

[0237] Mechanical properties: The material of this invention has an average tensile strength advantage of about 9.3%–9.7% and an elongation improvement of about 27%–35% compared with existing A and B materials, indicating that it maintains good plasticity on the basis of high strength.

[0238] Low-temperature toughness: The impact energy at -253℃ is increased by about 40%–50%, indicating that the Zr micro-optimization and composite heat treatment effectively suppress embrittlement.

[0239] Corrosion resistance: Mass loss is reduced by approximately 46%–53%, which is closely related to the formation of a stable passivation film.

[0240] Yield: Increased by approximately 12%–17%, directly enhancing the economics of industrial applications.

[0241] It is important to note that the constructions and arrangements of this application shown in several different exemplary embodiments are merely illustrative. Although only a few embodiments are described in detail in this disclosure, those who consult this disclosure will readily understand that many modifications are possible (e.g., changes in the size, dimensions, structure, shape, and proportions of various elements, as well as parameter values ​​(e.g., temperature, pressure, etc.), mounting arrangements, use of materials, color, orientation, etc.) without substantially departing from the novel teachings and advantages of the subject matter described in this application). For example, an element shown as integrally formed may be composed of multiple parts or elements, the position of elements may be inverted or otherwise altered, and the nature or number or position of discrete elements may be changed or altered. Therefore, all such modifications are intended to be included within the scope of the invention. The order or sequence of any process or method steps may be changed or rearranged according to alternative embodiments. In the claims, any "device plus function" clause is intended to cover the structure described herein that performs the function, and not only structurally equivalent but also equivalent in structure. Other substitutions, modifications, alterations, and omissions may be made in the design, operation, and arrangement of the exemplary embodiments without departing from the scope of the invention. Therefore, the present invention is not limited to the specific embodiments, but extends to various modifications that still fall within the scope of the appended claims.

[0242] Furthermore, in order to provide a concise description of exemplary embodiments, not all features of actual embodiments (i.e., those features that are not relevant to the currently considered best mode for carrying out the invention, or those features that are not relevant to implementing the invention) may be omitted.

[0243] It should be understood that numerous specific implementation decisions can be made during the development of any practical implementation, such as in any engineering or design project. Such development efforts may be complex and time-consuming, but for those skilled in the art who benefit from this disclosure, the development effort will be a routine work of design, manufacturing, and production without requiring much experimentation.

[0244] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the invention.

Claims

1. A chemical formula for high-performance niobium-titanium tubing, characterized in that, Its chemical composition by mass percentage is as follows: Zr 0.25–0.45%, O 0.015–0.025%, N ≤0.010%, H ≤0.002%, C ≤0.010%, Fe+Ni ≤0.050%, Nb 45.0–48.0%, with Ti as the balance, and the sum of Nb and Ti is 99.475–99.688%, with the balance being other unavoidable impurities.

2. A study on a chemical formulation preparation process for high-performance niobium-titanium tubing, comprising the following processes: The high-performance niobium-titanium tubing is prepared using the chemical formulation described in claim 1. S1: Vacuum Induction Melting (VIM) Temperature Controlled Feeding Under vacuum conditions ≤2×10⁻³Pa, high-purity Nb (purity ≥99.95%) is first added and heated to 1870±10℃; Add high-purity Ti (purity ≥ 99.98%) and Zr in proportion; Control the stirring frequency to 8–12 Hz to ensure that the homogenization time of the melt composition is ≥18 min; S2: Vacuum Arc Remelting (VAR) Refining The intermediate obtained in step S1 was remelted twice, with the arc current set to 6.5–7.0 kA; in, Spectroscopic analysis was performed after the first remelting to ensure that the O / N / H ratio met the target. S3: Hot forging fragmentation structure At 1100–1150℃, the remelted steel ingot is subjected to triaxial hot forging (reduction ratio ≥3) to break up the original as-cast structure; S4: Extrusion and mandrel perforation tube making The extrusion temperature is 850–900℃, and the extrusion pressure is 380–420 MPa. The mandrel surface is coated with a nano MoS2 / BN hybrid lubricating layer (BN particle size <200nm). S5: Multi-pass cold drawing and intermediate heat treatment Among them, the deformation amount of each cold drawing is ≤15%, and the cumulative deformation rate is ≥60%; During the intermediate heat treatment, the vacuum annealing temperature is 780±5℃, the holding time is 1.5h, and the vacuum degree is ≤5×10⁻³Pa. S6: Solution-Aging Combined Heat Treatment Solution treatment: 880±5℃, 2 h → water cooling; Aging: 480±3℃, heat preservation for 10h → air cooling, precipitation of metastable strengthening phase Nb2Ti or α″ phase; S7: Final pickling and surface passivation The pickling solution was prepared with the following ratio: HF (40 wt%) : HNO3 (68 wt%) = 1:7 (volume ratio), diluted with deionized water to an acidity of approximately 12%. The pickling time is ≤120 s, followed by passivation with 0.5 M HNO3 for 15 min to form a continuous passivation film, thereby completely preparing high-performance niobium-titanium tubing.

3. The research on the preparation process of high-performance niobium-titanium tubing chemical formulation according to claim 2, characterized in that, In the temperature-controlled feeding step of S1 vacuum induction melting (VIM), after stirring and homogenization, the process also includes: using three-stage degassing (1870℃→1650℃→1500℃) to reduce interstitial elements.

4. The research on the preparation process of high-performance niobium-titanium tubing chemical formulation according to claim 3, characterized in that: In the S3 hot forging and crushing process, the cooling rate is set to 10–15℃ / s to prevent coarse grains.

5. The research on the preparation process of high-performance niobium-titanium tubing chemical formulation according to claim 4, characterized in that: In the S4 extrusion and mandrel piercing tube making process, the piercing speed should be ≤20 mm / s to avoid surface cracks.

6. The research on the preparation process of high-performance niobium-titanium tubing chemical formulation according to claim 5, characterized in that: The lubricating layer consists of 60–70 wt% hexagonal boron nitride (particle size ≤200 nm) and 30–40 wt% molybdenum disulfide, with a coating thickness of 5–8 μm.

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