A vacuum furnace bright annealing method for large-scale nuclear-grade zirconium alloy coils and its application

Abstract

The present invention discloses a vacuum furnace bright annealing method and application for large-scale nuclear-grade zirconium alloy coils. The method utilizes different annealing temperatures for different zirconium alloy coils to meet the microstructural requirements for finished zirconium alloy rolling. By inserting workpiece pair thermometers during furnace loading, a matching relationship between the number of workpiece pairs and the different coil sizes is established, precisely controlling the temperature consistency of the entire coil and achieving precise control of vacuum annealing for large-scale nuclear-grade zirconium alloy coils. Different coil sizes utilize different holding times during different heating stages to reliably and precisely control the internal structure of the entire coil, ensuring uniform and consistent microstructure and properties at different locations in the finished strip.

Description

Technical Field

[0001] The present invention relates to the technical field of material preparation, and in particular to a vacuum furnace bright annealing method for a large-scale nuclear-grade zirconium alloy strip coil and its application. Background Art

[0002] Zirconium has excellent nuclear properties and is widely used as the cladding material and core structure material for water-cooled power reactors, making it an important application material for nuclear power plants. Nuclear-grade zirconium alloy strip is a key material for the nuclear fuel positioning grid of pressurized water reactors, and its performance directly affects the safety, reliability, and economy of nuclear power plants. The preparation of nuclear-grade zirconium alloy strip from coil to finished strip requires multiple cold working processes. Due to the close-packed hexagonal crystal structure of zirconium alloy at room temperature, few slip systems, and significant work hardening, the plasticity of the strip after cold rolling is poor, which in turn affects the subsequent processing performance of the zirconium alloy coil and even its final physical and chemical properties. Zirconium alloy strip also has strict control requirements for gas elements. Therefore, vacuum furnace bright annealing must be used after cold rolling to control the mechanical properties and microstructure of the material.

[0003] The mechanical properties and microstructure of zirconium alloy strip are directly related to vacuum annealing. The slow efficiency of radiation heat transfer under vacuum conditions leads to differences between the inside and outside of large-sized strips. Zirconium alloy is sensitive to annealing temperature and has a narrow controllable temperature range. Traditional processes rely on experience-based control and cannot accurately control the temperature consistency of the entire roll. After annealing, there are large differences in the mechanical properties and microstructure of the entire roll, making it impossible to achieve bright annealing of large-sized strips (strip wall thickness exceeds 30mm) in a vacuum furnace. Summary of the Invention

[0004] The present invention aims to solve one of the technical problems in the related art at least to a certain extent.

[0005] To this end, embodiments of the present invention provide a vacuum furnace bright annealing method and application for large-scale nuclear-grade zirconium alloy coils.

[0006] In a first aspect, the present invention provides a vacuum furnace bright annealing method for a large-scale nuclear-grade zirconium alloy coil, comprising the following steps:

[0007] (1) Select different annealing temperatures according to different types of zirconium alloy coils;

[0008] (2) arranging workpiece pairs on the zirconium alloy coil, and determining the number of the workpiece pairs to be arranged according to the coil wall thickness of the zirconium alloy coil;

[0009] (3) The zirconium alloy coil is heated to the annealing temperature by a multi-stage heating method and kept warm to complete the annealing.

[0010] Furthermore, the zirconium alloy coil includes one of a Zr-Sn series zirconium alloy, a Zr-Nb series zirconium alloy, and a Zr-Sn-Nb series zirconium alloy.

[0011] Furthermore, the annealing temperature of the Zr-Sn series zirconium alloy is 620-680°C, and the annealing temperature of the Zr-Nb series zirconium alloy or the Zr-Sn-Nb series zirconium alloy is 560-610°C.

[0012] Furthermore, the zirconium alloy coil is obtained by hot continuous rolling of large slabs or welding of plates into coils.

[0013] Furthermore, when the wall thickness of the zirconium alloy coil is not greater than 30 mm, no workpiece pair is set; when the wall thickness of the zirconium alloy coil is 30~60 mm, a workpiece pair is inserted in the center of the zirconium alloy coil; when the wall thickness of the zirconium alloy coil is greater than 60 mm, workpiece pairs are respectively set at the top, bottom and center of the zirconium alloy coil.

[0014] Furthermore, the step (3) includes:

[0015] Place the zirconium alloy coil in a vacuum furnace and preheat it to 200°C at a heating rate not exceeding 8°C / min, and fill it with protective gas until the pressure in the vacuum furnace reaches 30~50KPa;

[0016] Continue heating to 350°C at a heating rate not exceeding 5°C / min and perform the first holding;

[0017] Continue heating to 450°C at a heating rate not exceeding 3°C / min and perform a second holding period;

[0018] Continue heating at a heating rate of no more than 3°C / min to 20°C below the annealing temperature, and perform a third heat preservation, while extracting the protective gas in the vacuum furnace until the vacuum degree of the vacuum furnace is less than 0.1Pa;

[0019] Continue to raise the temperature to the annealing temperature and perform the fourth insulation.

[0020] Furthermore, the step (3) further includes refilling the protective gas to a pressure of 30-50 kPa in the vacuum furnace after the fourth heat preservation, and naturally cooling the furnace to a temperature below 100° C. before taking the furnace out of the furnace.

[0021] Furthermore, when the wall thickness of the zirconium alloy coil does not exceed 30 mm, the minimum insulation time for the first insulation, second insulation, third insulation, and fourth insulation are 60 min, 30 min, 30 min, and 120 min, respectively; when the wall thickness of the zirconium alloy coil is 30-60 mm, the minimum insulation time for the first insulation, second insulation, third insulation, and fourth insulation are 90 min, 45 min, 45 min, and 150 min, respectively.

[0022] Furthermore, when the wall thickness of the zirconium alloy coil is 60~100mm, the minimum insulation time for the first insulation, second insulation, third insulation, and fourth insulation are 120min, 60min, 60min, and 180min, respectively; when the wall thickness of the zirconium alloy coil is 100~180mm, the minimum insulation time for the first insulation, second insulation, third insulation, and fourth insulation are 150min, 75min, 75min, and 210min, respectively; when the wall thickness of the zirconium alloy coil is 180~260mm, the minimum insulation time for the first insulation, second insulation, third insulation, and fourth insulation are 180min, 90min, 90min, and 240min, respectively.

[0023] In a second aspect, the present invention proposes the application of the method proposed in the first aspect in vacuum furnace bright annealing of large-scale nuclear-grade zirconium alloy coils.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention adopts different annealing temperatures according to different zirconium alloy coils to meet the microstructure requirements required for rolling zirconium alloy finished products.

[0026] The present invention adopts the method of inserting a workpiece pair insulation gauge when loading the furnace to establish a matching relationship between coils of different specifications and the number of workpiece pairs, accurately control the temperature consistency of the entire coil, and realize precise control of vacuum annealing of large-size nuclear-grade zirconium alloy coils.

[0027] The coils of different specifications of the present invention adopt different holding times in different heating stages to reliably and accurately control the internal structure of the entire coil of material, ensuring that the structural properties of different positions of the finished strip are uniform and consistent.

[0028] The present invention has good mechanical properties and microstructure consistency of the entire coil after annealing, and can realize vacuum furnace bright annealing of large-size coils (coil wall thickness exceeds 30 mm). BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0030] Figure 1 This is a flow chart of the vacuum furnace bright annealing method for large-scale nuclear-grade zirconium alloy coils of the present invention;

[0031] Figure 2 A schematic diagram of a workpiece pair is provided for the present invention;

[0032] Figure 3 A schematic diagram of setting three workpiece pairs for the present invention;

[0033] Figure 4Schematic diagram of the annealing process of the present invention. DETAILED DESCRIPTION

[0034] The following describes embodiments of the present invention in detail, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and are not to be construed as limiting the present invention.

[0035] like Figure 1 As shown, the vacuum furnace bright annealing method of a large-scale nuclear-grade zirconium alloy coil of the present invention comprises the following steps:

[0036] (1) Select different annealing temperatures according to different types of zirconium alloy coils;

[0037] (2) Setting workpiece pairs on the zirconium alloy coil, and determining the number of workpiece pairs to be set according to the coil wall thickness of the zirconium alloy coil;

[0038] (3) The zirconium alloy coil is heated to the annealing temperature by a multi-stage heating method and kept warm to complete the annealing.

[0039] In step (1), the zirconium alloy coil is obtained by hot continuous rolling of large slabs or welding of plates into coils. The surface of the coil is free of oxide scale, clean, and free of oil contamination. The zirconium alloy coil includes one of a Zr-Sn series zirconium alloy, a Zr-Nb series zirconium alloy, and a Zr-Sn-Nb series zirconium alloy.

[0040] The annealing temperature of the Zr—Sn series zirconium alloy is 620-680°C. In some embodiments, the annealing temperature of the Zr—Sn series zirconium alloy is 620°C, 630°C, 640°C, 650°C, 660°C, 670°C, 680°C, or a value within a range consisting of any two values.

[0041] The annealing temperature of the Zr-Nb zirconium alloy or the Zr-Sn-Nb zirconium alloy is 560-610°C. In some embodiments, the annealing temperature of the Zr-Nb zirconium alloy or the Zr-Sn-Nb zirconium alloy is 560°C, 570°C, 580°C, 590°C, 600°C, 610°C, or a value within a range consisting of any two values.

[0042] The eutectic point temperature of Nb element in Zr-Nb zirconium alloy and Zr-Sn-Nb zirconium alloy is 610℃. In order to meet the recrystallization requirements while suppressing the precipitation of Nb element in the brittle phase and optimizing the second phase distribution, the same annealing temperature can be used.

[0043] Zr-Sn zirconium alloys are different from Zr-Nb zirconium alloys or Zr-Sn-Nb zirconium alloys in composition, microstructure control and performance requirements, and therefore, different annealing temperatures are used.

[0044] The purpose of annealing zirconium alloy coils is to eliminate work hardening and restore plasticity. After annealing, the grain size of the zirconium alloy coils shall not be less than grade 9.0.

[0045] In step (2), in order to accurately control the temperature consistency of the entire zirconium alloy coil and achieve precise control of vacuum annealing of large-sized nuclear-grade zirconium alloy coils, workpiece pairs are set on the zirconium alloy coil, and the number of workpiece pairs is determined according to the coil wall thickness of the zirconium alloy coil.

[0046] In some embodiments, when the wall thickness of the zirconium alloy coil is not greater than 30 mm, no workpiece pair is provided, and during the annealing process, it is only necessary to control the furnace temperature to reach a preset temperature.

[0047] In some embodiments, when the wall thickness of the zirconium alloy coil is 30-60 mm, a workpiece pair is inserted in the center of the zirconium alloy coil, that is, Figure 2 As shown, a workpiece pair is set in the hollow position at the center of the zirconium alloy coil. During the annealing process, when the test data of the workpiece pair reaches the preset temperature, it is considered that the temperature of the entire coil reaches the preset temperature.

[0048] In some embodiments, when the wall thickness of the zirconium alloy coil is greater than 60 mm, workpiece pairs are respectively set at the top, bottom and center of the zirconium alloy coil, such as Figure 3 As shown, a workpiece couple is set at the center position, the middle of the upper section, and the middle of the lower section of the zirconium alloy coil respectively. The temperature consistency of the entire coil is controlled according to the temperature data of the three workpiece couples. Since the workpiece couple at the center position reaches the preset temperature last, when the workpiece couple at the center position reaches the preset temperature, it is considered that the entire coil has reached the preset temperature, so that the temperature of the entire coil is consistent.

[0049] Step (3) is the annealing process, which uses a multi-stage heating method to allow coils of different specifications to use different holding times in different heating stages, thereby reliably and accurately controlling the internal structure of the entire coil material and ensuring that the structural properties of different positions of the finished strip are uniform and consistent.

[0050] Annealing process Figure 4 As shown, a five-stage heating method is adopted, including the following processes:

[0051] (a) Place the zirconium alloy coil in a vacuum furnace and preheat it to 200°C at a heating rate not exceeding 8°C / min, and fill it with protective gas until the pressure in the vacuum furnace reaches 30~50KPa;

[0052] (b) continuing heating to 350°C at a heating rate not exceeding 5°C / min and performing a first holding temperature;

[0053] (c) continuing heating to 450°C at a heating rate not exceeding 3°C / min and performing a second holding period;

[0054] (d) Continue heating at a heating rate of no more than 3°C / min to 20°C below the annealing temperature, and perform a third heat preservation, while removing the protective gas in the vacuum furnace until the vacuum degree of the vacuum furnace is less than 0.1 Pa;

[0055] (e) Continue to heat up to the annealing temperature and carry out the fourth heat preservation. After the fourth heat preservation, fill the protective gas again to the pressure in the vacuum furnace to 30~50KPa, cool naturally to the furnace temperature below 100℃ and take it out of the furnace.

[0056] Step (a) is a preheating process, and the protective gas is argon or helium with a concentration of 99.995% or higher. In step (d), if a workpiece pair is provided in the zirconium alloy coil, a third soaking step is performed when the workpiece pair at the center reaches a temperature 20°C below the annealing temperature. If no workpiece pair is provided, a third soaking step is performed when the furnace temperature reaches a temperature 20°C below the annealing temperature. Figure 4 In the figure, t1 is the first holding time, t2 is the second holding time, t3 is the third holding time, t4 is the fourth holding time, and T is the annealing temperature.

[0057] In some embodiments, when the wall thickness of the zirconium alloy coil does not exceed 30 mm, the minimum insulation time for the first insulation, the second insulation, the third insulation, and the fourth insulation are 60 minutes, 30 minutes, 30 minutes, and 120 minutes, respectively.

[0058] In some embodiments, when the wall thickness of the zirconium alloy coil is 30-60 mm, the minimum insulation time for the first insulation, the second insulation, the third insulation, and the fourth insulation are 90 min, 45 min, 45 min, and 150 min, respectively.

[0059] In some embodiments, when the wall thickness of the zirconium alloy coil is 60-100 mm, the minimum insulation time for the first insulation, the second insulation, the third insulation, and the fourth insulation are 120 min, 60 min, 60 min, and 180 min, respectively.

[0060] In some embodiments, when the wall thickness of the zirconium alloy coil is 100-180 mm, the minimum insulation time for the first insulation, the second insulation, the third insulation, and the fourth insulation are 150 min, 75 min, 75 min, and 210 min, respectively.

[0061] In some embodiments, when the wall thickness of the zirconium alloy coil is 180-260 mm, the minimum insulation time for the first insulation, the second insulation, the third insulation, and the fourth insulation are 180 min, 90 min, 90 min, and 240 min, respectively.

[0062] The present invention is described in detail below with reference to the embodiments.

[0063] Example 1

[0064] Zirconium alloy coils are produced by hot continuous rolling of large slabs or by tailor-welding sheets into coils. The coils are scale-free, clean, and free of oil and contamination. 2mm zirconium alloy coils are made from a Zr-Sn alloy with a wall thickness of 25mm. For coils with a wall thickness of 30mm or less, no workpiece pair is required; the annealing process only requires controlling the furnace temperature to a preset temperature.

[0065] The multi-stage heating method allows coils of different specifications to use different holding times in different heating stages, thereby reliably and accurately controlling the internal structure of the entire coil of material and ensuring uniform and consistent structural properties at different positions of the finished strip.

[0066] Annealing process Figure 4 As shown, a five-stage heating method is adopted, including the following processes:

[0067] (a) The zirconium alloy coil was placed in a vacuum furnace and preheated to 200°C at a heating rate of 8°C / min. The furnace was filled with argon gas (>99.995%) and the pressure in the vacuum furnace was 45 kPa.

[0068] (b) Continue heating to 350°C at a heating rate of 5°C / min and perform the first holding time for 75 min;

[0069] (c) heating to 450°C at a rate of 3°C / min and holding for a second time for 45 min;

[0070] (d) Heating was continued at a heating rate of 3°C / min to 630°C, and the third holding temperature was performed for 45 min. The protective gas in the vacuum furnace was evacuated until the vacuum degree of the vacuum furnace was less than 0.1 Pa;

[0071] (e) Continue to heat up to the annealing temperature and carry out the fourth heat preservation, the heat preservation time is 150 minutes, after the fourth heat preservation, fill the protective gas again to the pressure of 45KPa in the vacuum furnace, cool naturally to the furnace temperature of 60℃ and take out of the furnace.

[0072] The annealing temperature of the Zr-Sn series zirconium alloy is 650°C. After annealing, the grain sizes of the head, middle and tail of the zirconium alloy coil are all 9.5.

[0073] Example 2

[0074] Zirconium alloy coils are made by hot rolling large slabs or welding plates into coils. The coil surface is free of scale, clean, and oily contamination. The 2mm zirconium alloy coil is a Zr-Sn zirconium alloy with a coil wall thickness of 50mm. A workpiece pair is inserted in the center of the zirconium alloy coil, i.e. Figure 2 As shown, a workpiece pair is set in the hollow position at the center of the zirconium alloy coil. During the annealing process, when the test data of the workpiece pair reaches the preset temperature, it is considered that the temperature of the entire coil reaches the preset temperature.

[0075] The multi-stage heating method allows coils of different specifications to use different holding times in different heating stages, thereby reliably and accurately controlling the internal structure of the entire coil of material and ensuring uniform and consistent structural properties at different positions of the finished strip.

[0076] Annealing process Figure 4 As shown, a five-stage heating method is adopted, including the following processes:

[0077] (a) The zirconium alloy coil was placed in a vacuum furnace and preheated to 200°C at a heating rate of 7°C / min. The furnace was filled with argon gas (>99.995%) and the pressure in the vacuum furnace was 45 kPa.

[0078] (b) Continue heating to 350°C at a heating rate of 4°C / min and perform the first holding time for 90 min;

[0079] (c) heating to 450°C at a heating rate of 3°C / min and holding for a second time for 60 min;

[0080] (d) Continue heating at a heating rate of 3°C / min until the workpiece at the center reaches 610°C, then perform a third heat preservation process for 60 min. The protective gas in the vacuum furnace is evacuated until the vacuum degree of the vacuum furnace is less than 0.1 Pa.

[0081] (e) Continue to heat up to the annealing temperature and carry out the fourth heat preservation, the heat preservation time is 150 minutes, after the fourth heat preservation, fill the protective gas again to the pressure of 45KPa in the vacuum furnace, cool naturally to the furnace temperature of 60℃ and take out of the furnace.

[0082] The annealing temperature of the Zr-Sn series zirconium alloy is 630°C. After annealing, the grain sizes of the head, middle and tail of the zirconium alloy coil are all 10.0.

[0083] Example 3

[0084] Zirconium alloy coils are produced by hot rolling large slabs or welding plates into coils. The coil surface is free of scale, clean, and oily contamination. The 1.5mm zirconium alloy coil is a Zr-Sn-Nb zirconium alloy with a coil wall thickness of 90mm. Workpiece pairs are placed on the top, bottom, and center of the zirconium alloy coil, such as Figure 3 As shown, a workpiece couple is set at the center position, the middle of the upper section, and the middle of the lower section of the zirconium alloy coil respectively. The temperature consistency of the entire coil is controlled according to the temperature data of the three workpiece couples. Since the workpiece couple at the center position reaches the preset temperature last, when the workpiece couple at the center position reaches the preset temperature, it is considered that the entire coil has reached the preset temperature, so that the temperature of the entire coil is consistent.

[0085] The multi-stage heating method allows coils of different specifications to use different holding times in different heating stages, thereby reliably and accurately controlling the internal structure of the entire coil of material and ensuring uniform and consistent structural properties at different positions of the finished strip.

[0086] Annealing process Figure 4 As shown, a five-stage heating method is adopted, including the following processes:

[0087] (a) The zirconium alloy coil was placed in a vacuum furnace and preheated to 200°C at a heating rate of 6°C / min. The furnace was filled with argon gas (>99.995%) and the pressure in the vacuum furnace was 45 kPa.

[0088] (b) Continue heating to 350°C at a heating rate of 3°C / min and perform the first holding time for 120 min;

[0089] (c) heating to 450°C at a heating rate of 3°C / min and holding for a second time for 60 min;

[0090] (d) Continue heating at a heating rate of 3°C / min until the workpiece at the center reaches 580°C, then perform a third heat preservation process for 60 min. Then, evacuate the protective gas in the vacuum furnace until the vacuum degree of the vacuum furnace is less than 0.1 Pa.

[0091] (e) Continue to heat up to the annealing temperature and carry out the fourth heat preservation, the heat preservation time is 180 minutes, after the fourth heat preservation, fill the protective gas again to the pressure of 45KPa in the vacuum furnace, cool naturally to the furnace temperature of 50℃ and take out of the furnace.

[0092] The annealing temperature of the Zr-Sn-Nb series zirconium alloy is 600°C. After annealing, the grain sizes of the head, middle and tail of the zirconium alloy coil are all 10.0.

[0093] Example 4

[0094] Zirconium alloy coils are produced by hot rolling large slabs or welding plates into coils. The coil surface is free of scale, clean, and oily contamination. The 1.2mm zirconium alloy coil is a Zr-Sn-Nb zirconium alloy with a coil wall thickness of 160mm. Workpiece pairs are placed on the top, bottom, and center of the zirconium alloy coil, such as Figure 3 As shown, a workpiece couple is set at the center position, the middle of the upper section, and the middle of the lower section of the zirconium alloy coil respectively. The temperature consistency of the entire coil is controlled according to the temperature data of the three workpiece couples. Since the workpiece couple at the center position reaches the preset temperature last, when the workpiece couple at the center position reaches the preset temperature, it is considered that the entire coil has reached the preset temperature, so that the temperature of the entire coil is consistent.

[0095] The multi-stage heating method allows coils of different specifications to use different holding times in different heating stages, thereby reliably and accurately controlling the internal structure of the entire coil of material and ensuring uniform and consistent structural properties at different positions of the finished strip.

[0096] Annealing process Figure 4 As shown, a five-stage heating method is adopted, including the following processes:

[0097] (a) The zirconium alloy coil was placed in a vacuum furnace and preheated to 200°C at a heating rate of 5°C / min. The furnace was filled with argon gas (>99.995%) and the pressure in the vacuum furnace was 45 kPa.

[0098] (b) Continue heating to 350°C at a heating rate of 3°C / min and perform the first holding time for 150 min;

[0099] (c) heating to 450°C at a heating rate of 2°C / min and holding for a second time for 90 min;

[0100] (d) Continue heating at a heating rate of 2°C / min until the workpiece at the center reaches 560°C, then perform a third heat preservation process for 90 min. Then, evacuate the protective gas in the vacuum furnace until the vacuum degree of the vacuum furnace is less than 0.1 Pa.

[0101] (e) Continue to heat up to the annealing temperature and carry out the fourth heat preservation, the heat preservation time is 210 minutes, after the fourth heat preservation, fill the protective gas again to the pressure in the vacuum furnace of 45KPa, cool naturally to the furnace temperature of 50℃ and take out of the furnace.

[0102] The annealing temperature of the Zr-Sn-Nb zirconium alloy is 580°C. After annealing, the grain sizes of the head, middle and tail of the zirconium alloy coil are all 10.5.

[0103] Example 5

[0104] Zirconium alloy coils are produced by hot rolling large slabs or welding plates into coils. The coil surface is free of scale, clean, and oily contamination. The 0.8mm zirconium alloy coil is a Zr-Nb zirconium alloy with a coil wall thickness of 240mm. Workpiece pairs are placed on the top, bottom, and center of the zirconium alloy coil, such as Figure 3 As shown, a workpiece couple is set at the center position, the middle of the upper section, and the middle of the lower section of the zirconium alloy coil respectively. The temperature consistency of the entire coil is controlled according to the temperature data of the three workpiece couples. Since the workpiece couple at the center position reaches the preset temperature last, when the workpiece couple at the center position reaches the preset temperature, it is considered that the entire coil has reached the preset temperature, so that the temperature of the entire coil is consistent.

[0105] The multi-stage heating method allows coils of different specifications to use different holding times in different heating stages, thereby reliably and accurately controlling the internal structure of the entire coil of material and ensuring uniform and consistent structural properties at different positions of the finished strip.

[0106] Annealing process Figure 4 As shown, a five-stage heating method is adopted, including the following processes:

[0107] (a) The zirconium alloy coil was placed in a vacuum furnace and preheated to 200°C at a heating rate of 4°C / min. The furnace was filled with argon gas (>99.995%) and the pressure in the vacuum furnace was 45 kPa.

[0108] (b) Continue heating to 350°C at a heating rate of 2°C / min and perform the first holding time for 180 min;

[0109] (c) heating to 450°C at a heating rate of 2°C / min and holding for a second time for 90 min;

[0110] (d) Continue heating at a heating rate of 2°C / min until the workpiece at the center reaches 560°C, then perform a third heat preservation process for 90 min. Then, evacuate the protective gas in the vacuum furnace until the vacuum degree of the vacuum furnace is less than 0.1 Pa.

[0111] (e) Continue to heat up to the annealing temperature and carry out the fourth heat preservation, the heat preservation time is 240 minutes, after the fourth heat preservation, fill the vacuum furnace with protective gas again to the pressure of 45KPa, cool naturally to the furnace temperature of 50℃ and take out of the furnace.

[0112] The annealing temperature of the Zr-Nb series zirconium alloy is 580°C. After annealing, the grain sizes of the head, middle and tail of the zirconium alloy coil are all 11.0.

[0113] Comparative Example 1

[0114] Zirconium alloy coils are produced by hot-rolling large slabs or welding them together. The coils are surface-scaling, clean, and free of oil and contamination. The 1.5mm zirconium alloy coils are made from a Zr-Sn-Nb alloy with a wall thickness of 120mm.

[0115] The annealing process is as follows:

[0116] (a) The zirconium alloy coil was placed in a vacuum furnace and preheated to 200°C at a heating rate of 8°C / min. The furnace was filled with argon gas (>99.995%) and the pressure in the vacuum furnace was 45 kPa.

[0117] (b) Continue heating to 350°C at a heating rate of 5°C / min and perform the first holding time for 150 min;

[0118] (c) Continue heating to 450°C at a heating rate of 3°C / min and perform a second holding time of 75 min;

[0119] (d) Heating was continued at a heating rate of 3°C / min to 580°C, and the third holding time was 75 min. The protective gas in the vacuum furnace was evacuated until the vacuum degree of the vacuum furnace was less than 0.1 Pa;

[0120] (e) Continue to heat up to the annealing temperature and carry out the fourth heat preservation, the heat preservation time is 210 minutes, after the fourth heat preservation, fill the protective gas again to the pressure of 45KPa in the vacuum furnace, cool naturally to the furnace temperature of 50℃ and take out of the furnace.

[0121] The annealing temperature of the Zr-Sn-Nb zirconium alloy is 600°C. After annealing, the grain size of the head and tail of the zirconium alloy coil is both 9.0, and the middle structure is not completely recrystallized, which does not meet the rating requirements.

[0122] Comparative Example 2

[0123] Zirconium alloy coils are produced by hot-rolling large slabs or welding them together. The coils are surface-scaling, clean, and free of oil and contamination. The 2mm zirconium alloy coils are made from a Zr-Sn-Nb alloy with a wall thickness of 120mm.

[0124] The annealing process is as follows:

[0125] (a) The zirconium alloy coil was preheated to 300°C in a vacuum furnace at a heating rate of 8°C / min.

[0126] (b) Continue heating to 600°C at a heating rate of 5°C / min and keep at this temperature for 120 min;

[0127] (c) After the insulation is completed, the protective gas is filled again to the pressure of 45KPa in the vacuum furnace, and the furnace is naturally cooled to 50℃ and then taken out of the furnace.

[0128] The annealing temperature of the Zr-Sn-Nb zirconium alloy is 600°C. After annealing, the grain size of the head and tail of the zirconium alloy coil is both 8.5, and the middle structure is not completely recrystallized, which does not meet the rating requirements.

[0129] Test example

[0130] The coils prepared in Examples 1 to 5 and Comparative Examples 1 and 2 were subjected to grain size testing, corrosion performance testing, room temperature transverse tensile testing, and room temperature longitudinal tensile testing. The test results are shown in Table 1 below.

[0131] Corrosion performance: According to ASTM G2 / G2M standards, a corrosion test is conducted in high-temperature steam at 400±3℃ and 10.3±0.7MPa for 72~80 hours. After the test, the surface of the sample is a continuous, black, shiny oxide film without white, brown or any other abnormal corrosion products, and the corrosion weight gain should not exceed 22.0mg / dm 2 .

[0132] Table 1:

[0133]

[0134] According to Table 1, the grain size of the zirconium alloy strips prepared in Examples 1 to 5 meets the rating requirements, the corrosion performance meets the requirements, and the room temperature transverse tensile performance and room temperature longitudinal tensile performance are consistent.

[0135] The middle portion of the coils prepared in Comparative Examples 1 and 2 did not meet the rating requirements, and compared with Examples 1 to 5, the corrosion performance was relatively poor, and the consistency of the room temperature transverse tensile properties and room temperature longitudinal tensile properties at different positions was poor.

[0136] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms may be directed to different embodiments or examples. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are mutually inconsistent.

[0137] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0138] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to the embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the claims and their equivalents.

Claims

1. A vacuum furnace bright annealing method for large-scale nuclear-grade zirconium alloy coils, characterized in that: The following steps are involved: (1) Select different annealing temperatures according to different types of zirconium alloy coils; (2) arranging workpiece pairs on the zirconium alloy coil, and determining the number of the workpiece pairs to be arranged according to the coil wall thickness of the zirconium alloy coil; (3) Using a multi-stage heating method to heat the zirconium alloy coil to the annealing temperature and keep it warm to complete the annealing. When the wall thickness of the zirconium alloy coil is not greater than 30 mm, no workpiece pair is provided; when the wall thickness of the zirconium alloy coil is 30-60 mm, a workpiece pair is inserted in the center of the zirconium alloy coil; when the wall thickness of the zirconium alloy coil is greater than 60 mm, workpiece pairs are provided at the top, bottom and center of the zirconium alloy coil respectively. The step (3) includes: Place the zirconium alloy coil in a vacuum furnace and preheat it to 200°C at a heating rate not exceeding 8°C / min, and fill it with protective gas until the pressure in the vacuum furnace reaches 30~50KPa; Continue heating to 350°C at a heating rate not exceeding 5°C / min and perform the first holding; Continue heating to 450°C at a heating rate not exceeding 3°C / min and perform a second holding period; Continue heating at a heating rate of no more than 3°C / min to 20°C below the annealing temperature, and perform a third heat preservation, while extracting the protective gas in the vacuum furnace until the vacuum degree of the vacuum furnace is less than 0.1Pa; Continue to raise the temperature to the annealing temperature and perform the fourth insulation.

2. The method according to claim 1, wherein The zirconium alloy coil comprises one of a Zr-Sn series zirconium alloy, a Zr-Nb series zirconium alloy, and a Zr-Sn-Nb series zirconium alloy.

3. The method according to claim 2, wherein The annealing temperature of the Zr-Sn series zirconium alloy is 620-680°C, and the annealing temperature of the Zr-Nb series zirconium alloy or the Zr-Sn-Nb series zirconium alloy is 560-610°C.

4. The method according to claim 1, wherein The zirconium alloy coil is obtained by hot continuous rolling of large slabs or welding of plates into coils.

5. The method according to claim 1, wherein The step (3) further includes refilling the vacuum furnace with protective gas to a pressure of 30-50 kPa after the fourth heat preservation, and naturally cooling the furnace to a temperature below 100° C. before taking the furnace out of the furnace.

6. The method according to claim 1, wherein When the wall thickness of the zirconium alloy coil does not exceed 30 mm, the minimum insulation time for the first insulation, second insulation, third insulation, and fourth insulation is 60 min, 30 min, 30 min, and 120 min, respectively; when the wall thickness of the zirconium alloy coil is 30-60 mm, the minimum insulation time for the first insulation, second insulation, third insulation, and fourth insulation is 90 min, 45 min, 45 min, and 150 min, respectively.

7. The method according to claim 1, wherein When the wall thickness of the zirconium alloy coil is 60-100 mm, the minimum insulation time for the first insulation, second insulation, third insulation, and fourth insulation are 120 min, 60 min, 60 min, and 180 min, respectively; when the wall thickness of the zirconium alloy coil is 100-180 mm, the minimum insulation time for the first insulation, second insulation, third insulation, and fourth insulation are 150 min, 75 min, 75 min, and 210 min, respectively; when the wall thickness of the zirconium alloy coil is 180-260 mm, the minimum insulation time for the first insulation, second insulation, third insulation, and fourth insulation are 180 min, 90 min, 90 min, and 240 min, respectively.

8. Use of the method according to any one of claims 1 to 7 in vacuum furnace bright annealing of large-sized nuclear-grade zirconium alloy coils.

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