Uncoated zirconium alloy corrosion resistant pipe and method of making same using low temperature vacuum pressing

Abstract

The application discloses a kind of low-temperature vacuum pressing preparation no-coating zirconium alloy anticorrosion pipe fittings and method thereof, belong to material surface treatment technical field, the method is in the vacuum softening annealing process of no-coating industrial grade zirconium alloy seamless pipe fittings Synchronous implementation ironing pressure, specifically at 400~550 under vacuum softening annealing 2h, ironing pressure processing is carried out simultaneously, ironing pressure vibration amplitude 15~25, feed 750~850, ironing pressure cutter head temperature is 400~550, workpiece rotating speed 100~800.The method is in the vacuum softening annealing process by ironing pressure optimization no-coating industrial grade zirconium alloy seamless pipe fittings surface structure and introduce residual compressive stress, significantly improve its surface density and oxidation resistance, so that no-coating industrial grade zirconium alloy seamless pipe fittings in chemical corrosion environment greatly enhance the service life and safety.

Description

Technical Field

[0001] This invention belongs to the field of material surface treatment technology, and more specifically, it refers to a composite treatment process that combines annealing and pressing to improve the corrosion resistance of uncoated zirconium alloy anti-corrosion pipe fittings.

[0002] Low-temperature vacuum ironing refers to ironing at 400°C. ~550 Low temperature environment, vacuum degree to The vibration amplitude is 15 ~25 The ironing process performed below. Background Technology

[0003] Zirconium and zirconium alloys possess excellent corrosion resistance, high strength, high melting point, and low coefficient of thermal expansion, making them widely used in medicine, chemicals, nuclear energy, aerospace, and aviation. Currently, equipment and components manufactured from zirconium and zirconium alloys are widely used in corrosive and other harsh environments.

[0004] Material corrosion is the phenomenon of damage, deterioration, or deterioration of materials and their properties under the chemical, electrochemical, and physical effects of the surrounding environment. Material corrosion is inseparable from the surrounding environment; they constitute a corrosion system. Therefore, preventing material corrosion requires consideration of both material and environmental factors. The methods and means adopted to achieve the purpose of material corrosion protection are called material corrosion protection technologies. All protection technologies can be approached from two aspects: (1) changing the material composition, surface treatment process, and engineering structure design; (2) changing the environment, including media treatment (drying, degassing, desalination, etc.), using corrosion inhibitors, and coatings that can isolate the environment. See Modern Material Corrosion and Protection, Huang Yongchang et al., Shanghai Jiaotong University Press, September 2012, 1st edition, pp. 3, 344.

[0005] Annealing is a heat treatment process in which the workpiece is heated to a suitable temperature, held for a certain time, and then slowly cooled. See "Annealing Process of TiZrNbTa High-Entropy Alloy," Zhao Mian, Harbin Institute of Technology, CNKI, 2025, No. 07, which discloses "Microstructure and Mechanical Properties of TiZrNbTa High-Entropy Alloy in As-cast and Annealed States, Finding that the Yield Strength of TiZrNbTa High-Entropy Alloy Strongly Depends on Annealing Temperature and Annealing Time." See also "The Effects of Annealing and Annealing Pressure on..." "The Impact of Rejuvenation on Metallic Glass," Li Jingyan, China University of Mining and Technology, CNKI, 2022, No. 03, published "Achieving Rejuvenation in Both Energy States and Mechanical Properties through Molecular Dynamics Simulations." This study investigates the effects of annealing temperature, annealing rate, and annealing pressure on the microstructure of metallic glasses during annealing and annealing pressurization, and explores the impact of changes in microstructure on... The impact of aging on metallic glass.

[0006] Ironing is a chip-free machining method that uses a hard indenter to apply force, causing continuous plastic deformation on the metal surface and smoothing out the unevenness of the sample surface. See "Ironing Pressure Using PCD Tools," Luo Hongyun et al., Journal of Changchun University of Technology, Vol. 23, Supplement, August 2002, which discloses a study on the mechanical properties of ironing using cylindrical PCD tools. See "Study on Ironing Strengthening of Aluminum Alloy Surface," Zhao Tianshu and Luo Hongyun, Metal Heat Treatment, Vol. 44, Supplement, September 2019, which discloses that "ironing is performed using artificial polycrystalline diamond (PCD) elastic tools. The PCD tools are (semi-)circular with a radius of 1 mm or 1.5 mm." See CN116200787A, which discloses a method for achieving corrosion resistance treatment of titanium alloy surfaces through stacked ironing and electrodeposition, which is a pretreatment process added before electrochemical deposition to improve the corrosivity of the electrochemically deposited coating.

[0007] Zirconium alloy seamless tubes, due to their excellent corrosion resistance, low thermal neutron absorption cross-section, and good mechanical properties, are widely used in key structural components of chemical equipment, such as reactors, heat exchangers, pumps, valves, and pipelines that come into contact with highly corrosive media. They represent high-end corrosion-resistant structural materials for chemical equipment. (See *Practical Handbook of Metallic Materials*, 2nd edition, Liu Shengxin et al., Machinery Industry Press, January 2017, pp. 1402-1410. This book discloses the room-temperature mechanical properties of industrial-grade zirconium alloys with different compositions and seamless tubes of different grades.) However, zirconium alloy seamless tubes still face severe corrosion challenges when serving in harsh environments with long-term high temperature, high pressure, and highly corrosive media. Once corrosion failure occurs, it will lead to serious consequences. Summary of the Invention

[0008] To improve the corrosion resistance and mechanical properties of uncoated industrial-grade zirconium alloy seamless tubes, this invention employs hot pressing during the annealing process of preparing uncoated industrial-grade zirconium alloy seamless tubes. This low-temperature vacuum hot pressing process, combined with annealing, enhances the corrosion resistance and mechanical properties of the uncoated industrial-grade zirconium alloy seamless tubes. The composite process of annealing and hot pressing is based on a complementary mechanism of microstructure regulation acting on the volume scale and hot pressing acting on the surface scale.

[0009] The low-temperature vacuum pressing method of this invention aims to solve the following defects in the existing manufacturing and processing technology of uncoated industrial-grade zirconium alloy seamless tubes:

[0010] (1) Insufficient surface properties: Traditional annealing processes only focus on the recovery and recrystallization of the overall material structure, and do not actively optimize the surface microstructure. As a result, the corrosion resistance of the material surface has not been fundamentally improved, making it a weak link in the component in a corrosive environment. In addition, existing technologies often consider microstructure optimization or surface smoothing in isolation, which limits the improvement of corrosion resistance of industrial-grade zirconium alloys.

[0011] (2) Lengthy process chain and high cost: To improve surface performance, it is usually necessary to add independent surface treatment processes after conventional processing, such as spraying, plating, ion implantation, etc. This not only prolongs the production cycle and increases energy and material consumption, but may also introduce new problems such as poor adhesion between the coating and the substrate and easy peeling of the coating, thus increasing processing costs and quality risks.

[0012] (3) Lack of integrated modification methods: Existing technologies lack a composite processing method that can be deeply integrated with the inherent hot working process of uncoated industrial-grade zirconium alloy seamless pipe fittings, and simultaneously achieve surface refinement, densification and performance improvement without significantly increasing the number of processes and costs.

[0013] (4) Surface roughness is a sensitive factor in corrosion. Defects such as grooves and micro-pits on rough surfaces can become the starting point for the preferential adsorption and erosion of corrosive media. However, most existing technologies ignore the decisive influence of "surface roughness" as a key initial variable on the corrosion initiation point, which limits the improvement of the corrosion resistance of industrial-grade zirconium alloys.

[0014] Compared with existing technologies, the composite processing method of low-temperature vacuum softening annealing and ironing proposed in this invention has the following significant advantages:

[0015] (1) Tissue optimization effect based on thermo-mechanical synergistic enhancement

[0016] The thermally activated environment provided by vacuum softening annealing promotes the reorganization and annihilation of dislocations introduced by pressing, making it easier to form a stable and uniform fine-grained layer on the surface. This facilitates the formation of a continuous, dense, and strongly adherent protective oxide film on uncoated industrial-grade zirconium alloy seamless pipe fittings in the early stages of corrosion. Simultaneously, the vacuum pressing process introduces a beneficial residual compressive stress layer on the zirconium alloy surface, effectively offsetting or delaying the tensile stress required for corrosive media intrusion and corrosion crack propagation, thus mechanically improving the stress corrosion cracking threshold of the zirconium alloy.

[0017] (2) The process is simple and the cost-effectiveness is outstanding.

[0018] The low-temperature vacuum softening annealing-ironing composite processing method of this invention achieves simultaneous completion of "annealing" and "surface strengthening" without interrupting the traditional rolling-annealing production process or adding a separate surface treatment workshop and process. Compared with the subsequent process of adding a protective coating, the method of this invention directly improves the corrosion resistance of the zirconium alloy substrate itself, avoiding the cost of coating materials, additional energy consumption, and coating failure risk. It has the outstanding advantages of simple process, short production cycle, and low overall cost.

[0019] (3) Excellent surface roughness improvement and finishing effect

[0020] Vacuum ironing, as a chip-free finishing technique, effectively smooths out microscopic peaks and valleys on the material surface while simultaneously strengthening the surface through fine grains, significantly reducing surface roughness. After treatment with this invention, the surface roughness value of uncoated industrial-grade zirconium alloy seamless tubing can be stably controlled at 0.8. The following is a summary of the benefits of a smooth surface. A smooth surface not only reduces the specific surface area for the adhesion and accumulation of corrosive media, directly slowing down the uniform corrosion rate, but more importantly, it greatly eliminates stress concentration points and corrosion initiation points caused by original machining marks, microcracks, etc., fundamentally inhibiting the origin of localized corrosion such as pitting and crevice corrosion. This is an independent and crucial effect that is difficult to achieve with a single heat treatment or a single pressing process.

[0021] This invention discloses a method for preparing uncoated zirconium alloy corrosion-resistant pipe fittings using low-temperature vacuum ironing. The method involves simultaneously ironing and annealing to complete the surface processing of the seamless uncoated zirconium alloy pipe fittings. Specifically, the seamless uncoated zirconium alloy pipe fitting is placed in an ironing chamber; under vacuum, both the ironing chamber and the ironing cutter are heated; then, the vibration amplitude and feed rate of the ironing cutter are controlled, and the workpiece rotation speed is adjusted to perform low-temperature vacuum softening annealing ironing processing. Specifically:

[0022] Evacuate to achieve a vacuum level of [missing information]. ;

[0023] Heating the ironing chamber to 400 ~550 ;

[0024] Heat the ironing blade to 400 degrees Celsius. ~550 ;

[0025] Adjust the processing position of the ironing head and the workpiece;

[0026] Adjust the vibration amplitude of the ironing head to 15. ~25 Feed rate 750-850 ;

[0027] Adjust the workpiece speed from 100 to 800 rpm. ;

[0028] Set up a combined processing mode of low-temperature vacuum softening annealing and ironing. After processing, remove the workpiece. Attached Figure Description

[0029] Figure 1 This is a simplified diagram of the system structure of the present invention for achieving a composite processing of low-temperature vacuum softening annealing and ironing.

[0030] Figure 2 This is a cross-sectional structural diagram of the low-temperature vacuum ironing chamber in this invention.

[0031] Figure 3 This is a structural diagram of the ironing blade and clamp in the present invention patent application.

[0032] Figure 4 This is a processing trajectory diagram of the low-temperature vacuum softening annealing and ironing of the present invention.

[0033] Figure 5 It is the result of the electrochemical polarization curve (PDP).

[0034] Figure 6 It is a corrosion current density and self-corrosion potential diagram calculated from electrochemical polarization curves (PDP).

[0035] Figure 7 These are photographs of the corrosion morphology of a composite process involving traditional annealing, low-temperature vacuum softening annealing, and ironing.

[0036] Figure 8 The results are the hardness test results of traditional annealing and low-temperature vacuum softening annealing combined with ironing. Detailed Implementation

[0037] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. The examples of the parameters listed are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

[0038] See Figure 1 , Figure 2 , Figure 3 As shown, a low-temperature vacuum pressing chamber is added to a traditional CNC machining center, where uncoated industrial-grade zirconium alloy seamless tubes undergo a composite process of low-temperature vacuum softening annealing and pressing.

[0039] (1) Connection between the vacuum system and the low-temperature vacuum ironing chamber: An opening is made in the wall of the low-temperature vacuum ironing chamber and a first flexible hose is connected thereto. The other end of the first flexible hose is connected to the vacuum system. The vacuum system provides power to the low-temperature vacuum ironing chamber. The degree of vacuum.

[0040] (2) Connection between the feed system and the low-temperature vacuum ironing chamber: The connector at the output end of the feed system is connected to the tool holder of the low-temperature vacuum ironing chamber. The feed system provides the ironing head with a vibration amplitude of 15. ~25 Feed rate 750-850 It is applied to the surface of an uncoated industrial-grade zirconium alloy seamless tube.

[0041] (3) Connection between the heating system and the low-temperature vacuum ironing chamber: Heating systems are distributed around the inner wall of the low-temperature vacuum ironing chamber to raise the indoor temperature to 400°C. ~550 A heater, such as a resistance wire, is used. The inner walls of the ironing tool's blade holder are wrapped with heat-generating elements to raise the blade temperature to 400°C. ~550 The heater, such as a resistance wire, is used. The heating system provides 400°C heating to the interior of the low-temperature vacuum ironing chamber. ~550 The low-temperature processing environment, on the other hand, keeps the cutting head at 400°C. ~550 .

[0042] (4) Connection between the cooling system and the low-temperature vacuum pressing chamber: A hole is made in the wall of the low-temperature vacuum pressing chamber and a second flexible hose is connected thereto. The other end of the second flexible hose is connected to the cooling system. The cooling system provides an inert gas (such as argon) to the low-temperature vacuum pressing chamber to achieve rapid cooling.

[0043] Furthermore, the heating system, cooling system, and temperature sensor installed on the low-temperature vacuum ironing chamber are connected.

[0044] (I) Design of Low-Temperature Vacuum Ironing Chamber

[0045] See Figure 1 , Figure 2 As shown, the low-temperature vacuum ironing chamber includes an ironing chamber, a left support, a right support, an ironing cutter, a vacuum system providing a vacuum environment, a feed system providing the cutter head to move along the workpiece axial direction, and a 400° feed rate. ~550 The heating system provides the working environment, and the cooling system provides the cooling environment. The left support and the right support have the same structure. The end of the left support is the left chuck. The left support is mounted on the left bearing, which is fixed to the left chamber wall. The spindle mechanism of the CNC machining center drives the left and right support to rotate simultaneously, so that the workpiece rotates.

[0046] The low-temperature vacuum ironing chamber designed in this invention is installed on the left and right columns of a CNC machining center. A left support member is installed on the left column, and a left chuck at the end of the left support member is used to clamp one end of the workpiece. A right support member is installed on the right column, and a right chuck at the end of the right support member is used to clamp the other end of the workpiece. The workpiece refers to an uncoated industrial-grade seamless zirconium alloy tube.

[0047] The inner walls of the low-temperature vacuum ironing chamber are equipped with features to raise the indoor temperature to 400°C. ~550 Heaters, such as resistance wires.

[0048] An ironing tool is installed inside the low-temperature vacuum ironing chamber. The tool holder is fixed to the chamber wall, and the connector at the output end of the feed system is connected to the tool holder of the low-temperature vacuum ironing chamber. The tool connecting rod is connected to the tool holder, and the tool head is installed at the end of the tool holder.

[0049] The vacuum environment required for a low-temperature vacuum ironing chamber is provided by a vacuum system, namely... The degree of vacuum.

[0050] The low-temperature working environment required for a low-temperature vacuum ironing chamber is 400°C. ~550 It is supplied by a heater, which is controlled by a heating system.

[0051] A cooling system for the air-cooled working environment required for a low-temperature vacuum ironing chamber is provided.

[0052] The cutting head in the ironing tool requires a low-temperature operating environment of 400°C. ~550 It is supplied by a heater, which is controlled by a heating system.

[0053] The low-temperature vacuum ironing chamber is made of carbon steel, with a middle layer of heat-insulating material such as refractory fiber, and the inner wall material is refractory brick.

[0054] In this invention, the spindle mechanism of a CNC machining center drives the left and right support members to rotate coaxially, and the spindle mechanism provides the workpiece with a rotational speed of 100-800 rpm. (a) In the combined processing of low-temperature vacuum softening annealing and pressing, the cutting head is controlled by the feed system (vibration amplitude 15). ~25 Feed rate 750-850 The lower edge works in the axial direction, while the workpiece is driven by the spindle mechanism (speed is 100-800). (ii) In the combined processing of low-temperature vacuum softening annealing and ironing, axial ironing is achieved by rotating the workpiece from its starting position to the next processing position. Figure 4 As shown. The workpiece is driven by the spindle mechanism (speed 100-800 rpm). After turning over one machining surface, the cutter head stops and remains stationary, with the feed system controlling the vibration amplitude (15). ~25 Feed rate 750-850 The ironing is performed along the axial direction of the lower edge, thus achieving axial ironing of the workpiece.

[0055] (II) Design of ironing blades

[0056] In this invention, the structure of the ironing blade is as follows: Figure 2 , Figure 3 As shown, it includes an ironing head, a head clamp, and a tool holder. The head clamp is connected to the connecting rod of the tool holder. A heater (such as a resistance wire) is installed inside the head clamp. The ironing head is installed at the lower end of the head clamp. The ironing head is made of polycrystalline diamond (PCD).

[0057] The ironing blade is spherical or ellipsoidal with a radius of curvature of 5–10 mm. The straight-line distance h from the center point D of the blade's arc to the outline is 5 mm, and the straight-line distance d from the end point H of the blade's arc to the center point D of the blade's arc is 8 mm.

[0058] The tool holder is made of a high-strength heat-resistant alloy (such as Inconel 718).

[0059] The tool holder has an embedded heating and insulation layer inside. The heating wire (or resistance wire) is used to preheat the pressing tool before processing to reduce thermal shock to the preheated workpiece. The ceramic insulation layer is used to block the heat from the workpiece from being conducted to the rear of the pressing tool, protecting the fixture, connecting rod and sensor.

[0060] (III) Process route design for preparing uncoated industrial-grade zirconium alloy corrosion-resistant pipe fittings by low-temperature vacuum pressing

[0061] In this invention, surface processing of uncoated zirconium alloy seamless tubes is completed by simultaneously annealing and pressing. Specifically, the uncoated zirconium alloy seamless tube is placed in a pressing chamber; under vacuum, both the pressing chamber and the pressing head are heated; then, the vibration amplitude and feed rate of the pressing head are controlled, and the workpiece rotation speed is adjusted to perform low-temperature vacuum softening annealing pressing. The low-temperature vacuum pressing of uncoated industrial-grade zirconium alloy seamless tubes involves the following steps:

[0062] First, evacuate the room to achieve a vacuum level of [missing information]. ;

[0063] Second, heat the ironing chamber to 400 degrees Celsius. ~550 ;

[0064] Third, heat the ironing blade to 400 degrees Celsius. ~550 ;

[0065] Fourth, adjust the processing position of the ironing head and the workpiece;

[0066] Fifth, adjust the vibration amplitude of the ironing blade to 15. ~25 Feed rate 750-850 ;

[0067] Sixth, adjust the workpiece speed to 100-800 rpm. ;

[0068] Seventh, set up a combined processing mode of low-temperature vacuum softening annealing and ironing. After processing, remove the workpiece.

[0069] In the workpiece clamping of the present invention, the door on the ironing chamber is opened, one end of the workpiece is fixed on the left clamp, and the other end of the workpiece is fixed on the right clamp.

[0070] Referring to industrial-grade zirconium alloy grades, HZr-2 uncoated industrial-grade zirconium alloy seamless pipe fittings were selected as the workpieces to be processed.

[0071] The VMC500 CNC machining center was selected for composite machining of low-temperature vacuum softening annealing and pressing.

[0072] Comparative Example 1

[0073] Mount the workpiece onto the left and right chucks, and set... Vacuum degree, annealing temperature 500 After annealing for 2 hours, argon gas is introduced to lower the temperature of the pressing chamber to 50°C. Workpiece A is obtained. The charge transfer resistance of workpiece A is... .

[0074] Comparative Example 2

[0075] Mount the workpiece onto the left and right chucks, and set... Vacuum degree, annealing temperature 550 After annealing for 2 hours, argon gas is introduced to lower the temperature of the pressing chamber to 50°C. Workpiece B is obtained. The charge transfer resistance of workpiece B is... .

[0076] Comparative Example 3

[0077] Mount the workpiece onto the left and right chucks, and set... Vacuum degree, annealing temperature 400 After annealing for 2 hours, argon gas is introduced to lower the temperature of the pressing chamber to 50°C. Workpiece C is obtained. The charge transfer resistance of workpiece C is... .

[0078] Example 1

[0079] The steps of low-temperature vacuum softening annealing and ironing according to this invention application are as follows:

[0080] First, evacuate the room to achieve a vacuum level of [missing information]. ;

[0081] Second, heat the ironing chamber to 500. ;

[0082] Third, heat the ironing blade to 500. ;

[0083] Fourth, adjust the processing position of the ironing head and the workpiece;

[0084] Fifth, adjust the vibration amplitude of the ironing blade to 20. Feed rate 800 ;

[0085] Sixth, adjust the workpiece rotation speed to 300. The workpiece's starting position is moved to the next workpiece processing position by rotating the workpiece's rotation speed.

[0086] Seventh, the combined processing mode of low-temperature vacuum softening annealing and ironing is set as axial ironing, such as... Figure 4 As shown, after annealing and ironing for 2 hours, argon gas was introduced to lower the temperature of the ironing chamber to 50°C. The workpiece is removed, resulting in workpiece 1. The charge transfer resistance of workpiece 1 is... .

[0087] Example 2

[0088] The steps of low-temperature vacuum softening annealing and ironing according to this invention application are as follows:

[0089] First, evacuate the room to achieve a vacuum level of [missing information]. ;

[0090] Second, heat the ironing chamber to 550 degrees Celsius. ;

[0091] Third, heat the ironing blade to 550 degrees Celsius. ;

[0092] Fourth, adjust the processing position of the ironing head and the workpiece;

[0093] Fifth, adjust the vibration amplitude of the ironing blade to 15. Feed rate 750 ;

[0094] Sixth, adjust the workpiece rotation speed to 300. ;

[0095] Seventh, the combined processing mode of low-temperature vacuum softening annealing and ironing is set as spiral ironing. After 2 hours of combined annealing and ironing, argon gas is introduced to lower the temperature of the ironing chamber to 50°C. Remove the workpiece to obtain workpiece 2. The charge transfer resistance of workpiece 2 is... .

[0096] Example 3

[0097] The steps of low-temperature vacuum softening annealing and ironing according to this invention application are as follows:

[0098] First, evacuate the room to achieve a vacuum level of [missing information]. ;

[0099] Second, heat the ironing chamber to 400 degrees Celsius. ;

[0100] Third, heat the ironing blade to 400 degrees Celsius. ;

[0101] Fourth, adjust the processing position of the ironing head and the workpiece;

[0102] Fifth, adjust the vibration amplitude of the ironing blade to 25. Feed rate 850 ;

[0103] Sixth, adjust the workpiece rotation speed to 800. The workpiece's starting position is moved to the next workpiece processing position by rotating the workpiece's rotation speed.

[0104] Seventh, the combined processing mode of low-temperature vacuum softening annealing and ironing is set as axial ironing. After 2 hours of combined annealing and ironing, argon gas is introduced to lower the temperature of the ironing chamber to 50°C. The workpiece is removed, resulting in workpiece 3. The charge transfer resistance of workpiece 3 is... .

[0105] Electrochemical impedance spectroscopy (EIS) and polarization plotting (PDP) were performed using a CHI660E electrochemical workstation based on a three-electrode system in an aqueous environment containing 1000 ppm boron and 3.5 ppm lithium. Workpieces (workpieces A, B, C and workpieces 1, 2, 3) served as the working electrodes, a platinum electrode as the auxiliary electrode, and a 217-type saturated calomel electrode (SCE) as the reference electrode.

[0106] Electrochemical impedance spectroscopy (EIS)

[0107] Electrochemical impedance spectroscopy (EIS) tests were performed on different workpieces. The results showed that the charge transfer resistance of the annealing process was [value missing]. The charge transfer resistance of the composite process of this invention is This indicates that the corrosion resistance of uncoated industrial-grade zirconium alloy seamless tubes prepared by the composite process is significantly stronger than that of uncoated industrial-grade zirconium alloy seamless tubes prepared by the traditional annealing process.

[0108] Electrochemical polarization curve (PDP)

[0109] Electrochemical polarization curve (PDP) tests were performed on uncoated industrial-grade zirconium alloy seamless tubes. The test results are as follows: Figure 5 As shown, the horizontal axis The vertical axis represents the logarithm of the current density per unit area (base 10). The electrode potential is given. The corrosion current density was calculated using the Tafel extrapolation method. ) and self-corrosion potential ( )like Figure 6 As shown. Uncoated industrial-grade seamless zirconium alloy tubes prepared using traditional annealing processes. yes , yes Uncoated industrial-grade seamless zirconium alloy tubes prepared using composite processes yes , yes Therefore, compared with the traditional annealing process, the passivation film formed by the composite process has better integrity and adhesion, reduces pitting corrosion sensitivity, and thus improves the corrosion resistance of the uncoated industrial-grade zirconium alloy seamless tubes prepared by the composite process.

[0110] Corrosion morphology observation

[0111] Corrosion morphology images of uncoated industrial-grade zirconium alloy seamless tubes after electrochemical polarization curve testing were observed using a scanning electron microscope (JSM-6010). Figure 7 (a) A photograph of the corrosion morphology of an uncoated industrial-grade zirconium alloy seamless tube prepared by conventional annealing process. The pitting pits have clear outlines and are mostly circular or nearly elliptical, with an average diameter of approximately [missing information]. . Figure 7 (b) A photograph of the corrosion morphology of an uncoated industrial-grade zirconium alloy seamless tube prepared by a composite process. The pitting pits are irregularly distributed, and the average diameter of the pits is only about [missing information]. Compared with traditional processes, the corrosion resistance is reduced by nearly 1.7 times, which further confirms that the uncoated industrial-grade zirconium alloy seamless tubes prepared by composite processing technology have better corrosion resistance.

[0112] Hardness test

[0113] Hardness tests were performed on workpieces A and 1 using a hardness tester (FM-800). Figure 8As shown. To eliminate measurement errors and ensure data reliability, 10 different locations were randomly selected on different workpieces for testing, with a test load of [value missing]. The pressure holding time is After removing the maximum and minimum values ​​from the 10 sets of data, the average value of the remaining 8 sets of valid data was taken as the hardness of the sample. The results show that compared with the traditional annealing process, the hardness of the uncoated industrial-grade zirconium alloy seamless tube prepared by the composite processing technology of this invention is significantly improved by about 1.2 times.

[0114] This invention introduces a composite processing technique of vacuum softening annealing and hot pressing into the traditional annealing process for preparing uncoated industrial-grade zirconium alloy seamless tubes. This results in an approximately 20-fold improvement in electrochemical impedance spectroscopy, a 0.25V positive shift in the electrochemical polarization curve, an approximately 1.7-fold reduction in pitting diameter, and an approximately 1.2-fold increase in hardness. The prepared uncoated industrial-grade zirconium alloy seamless tubes effectively resist the penetration of corrosive media, significantly improving the corrosion resistance of industrial-grade zirconium alloy seamless tubes and also effectively enhancing their mechanical properties.

Claims

1. A method for producing a non-coated zirconium alloy corrosion resistant pipe and fitting by low temperature vacuum pressing, characterized in that The process includes the following steps: Surface processing of uncoated zirconium alloy seamless tubes is completed by annealing and pressing simultaneously. Specifically, the uncoated zirconium alloy seamless tubes are placed in a pressing chamber; the pressing chamber and pressing head are heated in a vacuum environment, and then the vibration amplitude and feed rate of the pressing head are controlled, the workpiece speed is adjusted, and low-temperature vacuum softening annealing pressing is performed.

2. The method of claim 1, wherein the method of manufacturing a non-coated zirconium alloy corrosion resistant pipe fitting by low temperature vacuum pressing is characterized in that The steps are as follows: The vacuum is drawn to a vacuum level of ; Heat the press chamber to 400 ~ 550 ; Heat the ironing blade to 400 degrees Celsius. ~550 ; Adjust the processing position of the ironing head and the workpiece; Adjust the vibration amplitude of the ironing head to 15. ~25 Feed rate 750-850 ; Adjusting workpiece rotation speed 100-800 ; Set up a combined processing mode of low-temperature vacuum softening annealing and ironing. After processing, remove the workpiece.

3. The method of claim 1, wherein the method of manufacturing a non-coated zirconium alloy corrosion resistant pipe and fitting by low temperature vacuum pressing is characterized by: The combined processing mode of low-temperature vacuum softening annealing and ironing is spiral ironing or axial ironing.

4. The method for preparing uncoated zirconium alloy corrosion-resistant pipe fittings by low-temperature vacuum pressing according to claim 1, characterized in that: The combined processing of low-temperature vacuum softening annealing and ironing is used to improve the surface corrosion resistance of uncoated industrial-grade zirconium alloy seamless tubes.

5. A low temperature vacuum sintering chamber for producing uncoated zirconium alloy corrosion resistant pipe fittings by low temperature vacuum sintering, characterized by: The low-temperature vacuum ironing chamber includes an ironing chamber, a left support, a right support, an ironing cutter, a vacuum system providing a vacuum environment, a feed system providing axial movement of the cutter head along the workpiece, and a 400° feed rate. ~550 The heating system provides the working environment, and the cooling system provides the cooling environment. The left support and the right support have the same structure. The end of the left support is the left chuck. The left support is mounted on the left bearing, which is fixed to the left chamber wall. The spindle mechanism of the CNC machining center drives the left and right support to rotate simultaneously to achieve workpiece rotation.

6. The low temperature vacuum press chamber for manufacturing the uncoated zirconium alloy corrosion resistant pipe fitting by low temperature vacuum press according to claim 5, characterized in that: The low-temperature vacuum ironing chamber enables a combined processing operation of low-temperature vacuum softening annealing and ironing.

7. The low temperature vacuum press chamber for manufacturing the uncoated zirconium alloy corrosion resistant pipe fitting by low temperature vacuum press according to claim 5, characterized in that: When the combined processing mode of low-temperature vacuum softening annealing and ironing is spiral ironing, the vibration amplitude of the ironing head is 15. ~25 Feed rate 750-850 Workpiece rotation speed 100-800 .

8. The low temperature vacuum press chamber for manufacturing the uncoated zirconium alloy corrosion resistant pipe fitting by low temperature vacuum press according to claim 5, characterized in that: When the combined processing mode of low-temperature vacuum softening annealing and ironing is axial ironing, the vibration amplitude of the ironing head is 15. ~25 Feed rate 750-850 After completing one axial ironing press, rotate the workpiece to the next ironing position.

9. The low temperature vacuum press chamber for manufacturing the uncoated zirconium alloy corrosion resistant pipe fitting by low temperature vacuum press according to claim 5, characterized in that: The ironing tool includes an ironing head, a head clamp, and a tool holder. The ironing head is made of synthetic polycrystalline diamond and is spherical or ellipsoidal in shape with a radius of curvature of 5mm to 10mm. The head clamp is equipped with a heater and a heat insulation layer inside.

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