Processing method for high-precision thin-wall zirconium alloy tubes with low flaring wall thickness reduction rate and tube end flaring method

Abstract

The present invention discloses a processing method for high-precision thin-walled zirconium alloy tubes with a low flaring wall thickness reduction rate and a tube end flaring method. The processing method for the zirconium alloy tubes includes: cutting a zirconium alloy tube blank of a certain length; cold rolling the tube blank to obtain an intermediate tube; degreasing, pickling, vacuum annealing, straightening, and surface treatment of the obtained intermediate tube; cold rolling the intermediate tube, and after degreasing, pickling, vacuum annealing, straightening, and polishing treatment of the cold-rolled tube, a high-precision zirconium alloy tube is obtained. By designing the Q value and the deformation amount of multiple passes of rolling in the present invention, the radial texture factor Fr of the tube is greater than or equal to 0.55, realizing a low flaring wall thickness reduction rate of the tube. The obtained zirconium alloy tube is clamped by a pair of upper and lower female dies, and a variable taper mandrel is used to extend into the inner hole of the tube for end flaring. The present invention solves the important technical problems that are difficult to control, such as excessive wall thickness reduction at the flaring area and cracks on the inner surface of the flare when connecting the end of the zirconium alloy tube by flaring.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal pipes, and particularly relates to a processing method for high-precision thin-walled zirconium alloy pipes with a low wall thickness reduction rate during flaring and a pipe end flaring method. Background Art

[0002] Due to their excellent physical and chemical properties, zirconium alloy pipes are used as key structural materials for fuel assemblies in nuclear power plants and are widely used in nuclear power plants as structural components, cladding materials, guiding materials, etc. Structural components made of zirconium alloy pipes usually need to be processed by end flaring to connect with other components.

[0003] During the pipe flaring process, defects such as excessive wall thickness reduction, cracks, splits, and wrinkles are likely to occur in the flared and deformed parts of the pipe, resulting in unqualified products and unable to meet the usage requirements of nuclear power structural components. For thick-walled zirconium alloy pipes or zirconium alloy pipes that do not require flared connection, they can be prepared by traditional pipe rolling processes. However, when processing thin-walled zirconium alloy pipes by flaring, the wall thickness is prone to excessive reduction. Therefore, how to prepare zirconium alloy thin-walled pipes with resistance to wall thickness reduction during flaring and how to flare thin-walled zirconium alloy pipes to avoid defects such as flaring cracks, splits, and wrinkles are important issues that need to be faced and solved during the processing of thin-walled zirconium alloy pipes. Summary of the Invention

[0004] The main purpose of the present invention is to solve the problems of excessive wall thickness reduction, cracks, splits, and wrinkles easily appearing on the surface of the deformed area during flaring of thin-walled zirconium alloy pipes for current nuclear power plants, thereby providing a processing method for high-precision thin-walled zirconium alloy pipes with a low wall thickness reduction rate during flaring and a pipe end flaring method.

[0005] Specifically, the first aspect of the present invention provides a processing method for high-precision thin-walled zirconium alloy pipes with a low wall thickness reduction rate during flaring, including the following steps:

[0006] Step 1: Cut a zirconium alloy pipe blank of a certain length;

[0007] Step 2: Perform two passes of cold rolling on the zirconium alloy pipe blank in Step 1 to obtain an intermediate pipe;

[0008] Step 3: Subject the intermediate pipe obtained in Step 2 to degreasing, pickling, vacuum annealing, straightening, and polishing treatments;

[0009] Step 4: Perform two passes of cold rolling on the intermediate pipe obtained in Step 3. After the cold-rolled pipe undergoes degreasing, pickling, vacuum annealing, straightening, and polishing treatments, a high-precision thin-walled zirconium alloy pipe with a low wall thickness reduction rate during flaring is obtained.

[0010] As a further illustration of the present invention, the wall thickness of the zirconium alloy tube blank is 10 - 12 mm, and the outer diameter is 55 - 65 mm; the inner surface of the tube blank is processed by honing or broaching, the outer surface is polished, and the defects on the inner and outer surfaces of the tube blank are removed completely.

[0011] As a further illustration of the present invention, the wall thickness of the high-precision thin-walled zirconium alloy tube with a low flare wall thickness reduction rate obtained in step 4 is 0.3 - 0.6 mm, the nominal outer diameter is 15 - 20 mm, and the radial texture factor Fr is greater than or equal to 0.55, enabling the low flare wall thickness reduction rate of the tube.

[0012] As a further illustration of the present invention, the two-pass cold rolling in step 2 is carried out using a long-stroke high-speed ring-roll tube mill. The deformation amount of the two-pass cold rolling is 50% - 80%, and the rolling Q value (the ratio of the rolling wall thickness deformation amount to the outer diameter deformation amount) is greater than 1.0; the rolling speed is 80 - 120 times / min, and the feed amount is 1.0 - 2.5 mm / time; the wall thickness of the intermediate tube obtained after rolling is 5.0 - 3.5 mm, and the outer diameter is 32 - 22 mm.

[0013] As a further illustration of the present invention, the degreasing of the tube in step 3 and step 4 is ultrasonic degreasing. The degreasing agent used for degreasing is a strong alkaline degreasing agent. During degreasing, it is first cleaned in an ultrasonic degreasing tank at 50 - 80 °C, and the degreasing time is not less than 60 min. Then it is cleaned in a hot water tank at 60 - 70 °C for 2 - 10 minutes, and finally it is cleaned in a rinsing tank at room temperature for 2 - 10 minutes; the acid solution used for pickling the tube in step 3 and step 4 is a mixed acid solution prepared from hydrofluoric acid with a concentration of 2 - 3 wt%, nitric acid with a concentration of 20 - 30 wt% and water; the temperature of the pickling is 15 °C - 40 °C, and the time is 5 min - 10 min.

[0014] As a further illustration of the present invention, the vacuum annealing of the intermediate tube in step 3 is carried out in a vacuum annealing furnace. The annealing after the two-pass cold rolling is recrystallization annealing, the annealing temperature is 620 - 700 °C, and the annealing holding time is 2.5 - 3 h.

[0015] As a further illustration of the present invention, the two-pass cold rolling in step 4 is carried out using a high-precision multi-roll tube mill. The deformation amount of the two-pass cold rolling is 45% - 65%, and the rolling Q value is 2.9 - 5.7; the rolling speed is 50 - 100 times / min, and the feed amount is 0.5 - 1.2 mm / time; the wall thickness of the tube obtained after rolling is 0.3 - 0.6 mm (±0.01 mm), and the outer diameter is 15 - 20 mm (±0.01 mm).

[0016] As a further illustration of the present invention, the tube vacuum annealing in step 4 is carried out in a vacuum annealing furnace. The annealing after the two-pass cold rolling is recrystallization annealing, the annealing temperature is 620-650°C, and the annealing holding time is 2.5-3h.

[0017] As a further illustration of the present invention, in steps 3 and 4, the straightening of the tube is carried out by a pair of opposed roll straightening machines, and the straightness of the straightened tube is better than 0.2mm / 1000mm.

[0018] As a further illustration of the present invention, in steps 3 and 4, the polishing of the tube is carried out using a belt polishing machine, and the surface roughness Ra of the polished tube is better than 0.8μm.

[0019] The second aspect of the present invention provides a tube end flaring method for a high-precision thin-walled zirconium alloy tube with a low flaring wall thickness reduction rate, including:

[0020] Clamping the high-precision thin-walled zirconium alloy tube with a low flaring wall thickness reduction rate obtained by the tube processing method described in any one of the above through a pair of upper and lower female dies, and using a variable taper mandrel to extend into the inner hole of the thin-walled zirconium alloy tube for end flaring.

[0021] As a further illustration of the present invention, the diameter of the variable taper mandrel is represented by the following formula (1), the mandrel coefficient E is 2.0, and the flaring force and wall thickness reduction rate are the lowest;

[0022]

[0023] where D F is the inner diameter of the tube after flaring, D 0 is the inner diameter of the tube before flaring, L k is the length of the flaring transition zone, and E is the mandrel coefficient.

[0024] As a further illustration of the present invention, the flaring of the thin-walled zirconium alloy tube uses a special metal drawing oil for lubricating the flaring part to avoid defects on the inner surface of the flaring.

[0025] The wall thickness range of the finished tube prepared by the present invention is 0.3-0.6mm, the nominal outer diameter is 15-20mm, the allowable deviation of the wall thickness and outer diameter is ±0.01mm, the radial texture factor Fr is greater than or equal to 0.55, the outer diameter expansion rate is greater than 45%, the wall thickness reduction rate is lower than 5.5%, and there will be no cracks, splits and wrinkling defects in the flared part, and it can pass liquid penetration inspection to meet the use requirements of nuclear reactors.

[0026] Compared with the prior art, the present invention has the following beneficial technical effects:

[0027] The present invention uses a combination of two-roll cold rolling and multi-roll cold rolling to prepare thin-walled zirconium alloy tubes. Two-roll cold rolling has the characteristic of large deformation. By using two-roll cold rolling for blooming rolling, the uneven structure of the tube blank can be fully broken, and intermediate tubes with fine and uniform grain structure can be obtained. At the same time, the processing efficiency of the tubes is improved, making the tubes prepared by the present invention more economical.

[0028] After the zirconium alloy tube blank is subjected to two-roll large-deformation blooming rolling, the structure of the tube has been fully deformed and broken. On this basis, large-Q value deformation is realized on a multi-roll mill. After rolling, the grains have a preferred orientation, forming more significant anisotropy, ensuring that the radial texture factor Fr of the obtained finished zirconium alloy tube is greater than or equal to 0.55, thereby ensuring that the obtained high-precision thin-walled zirconium alloy tube has a low wall thickness reduction rate during flaring and can avoid excessive wall thickness reduction during flaring.

[0029] For the thin-walled tube with a low wall thickness reduction rate during flaring obtained by the present invention, a variable taper plug is used for flaring. The variable taper plug has the advantages of small flaring force, small wall thickness reduction of the tube after flaring, and not easy to generate defects. The tube is fixed by the upper and lower concave dies that can be opened and closed. The plug can be pushed into the tube between the upper and lower concave dies manually or by a hydraulic device. The operation is simple, and there are no defects on the surface of the tube after flaring. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 and Figure 2 is a schematic diagram of the tube end flaring device for the high-precision thin-walled zirconium alloy tube with a low wall thickness reduction rate during flaring provided by the present invention.

[0031] In the figure: 1. Deformation taper plug, 2. Upper concave die, 3. Lower concave die, 4. Three-jaw chuck of the lathe, 5. Tube. DETAILED DESCRIPTION OF THE INVENTION

[0032] In order to more clearly understand the above objects, features and advantages of the present invention, the present invention will be described in detail below with reference to the drawings and specific embodiments. It should be noted that, without conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0034] A processing method for a high-precision thin-walled zirconium alloy tube with a low wall thickness reduction rate during flaring and tube end flaring includes the following steps:

[0035] (1) Cut a zirconium alloy tube blank with a length of 1500 - 3000 mm; the wall thickness of the tube blank is 10 - 12 mm, and the outer diameter is 55 - 65 mm; the inner surface of the tube blank is processed by honing or broaching, and the outer surface is polished. The surface roughness Ra of the tube blank is better than 1.6 μm to ensure that the defects on the inner and outer surfaces of the tube blank are removed cleanly.

[0036] (2) Use a long - stroke high - speed ring - hole type two - roll cold - rolling tube mill to perform 2 passes of blooming rolling on the zirconium alloy tube blank obtained in step (1). The pass deformation amount is 50% - 80%, and the rolling Q value (the ratio of the wall - thickness deformation amount to the outer - diameter deformation amount) is greater than 1.0; the rolling speed is controlled in the range of 80 - 120 times / min, and the feed amount is controlled in the range of 1.0 - 2.5 mm; the wall thickness of the intermediate tube after rolling is controlled at 5.0 - 3.5 mm, and the outer diameter is 32 - 22 mm.

[0037] (3) Degrease, pickling, vacuum annealing, straightening and surface treatment are carried out on the intermediate tube obtained in step (2). Degreasing is ultrasonic degreasing. The degreasing agent used for degreasing is a strong - alkaline degreasing agent. First, clean it in an ultrasonic degreasing tank at a degreasing temperature of 50 - 80 °C for no less than 60 min, then clean it in a hot - water tank at 60 - 70 °C for 2 - 10 minutes, and finally clean it in a rinsing tank at room temperature for 2 - 10 minutes. The acid solution used for pickling the intermediate tube is a mixed acid solution prepared from hydrofluoric acid with a concentration of 2 - 3 wt%, nitric acid with a concentration of 20 - 30 wt% and water. The temperature of the pickling is 15 °C - 40 °C, and the time is 5 min - 10 min; the intermediate tube is vacuum - annealed in a vacuum annealing furnace. The annealing after the two - pass rolling is recrystallization annealing, and the annealing temperature is 620 - 700 °C, and the annealing holding time is 2.5 - 3 h; the intermediate tube is straightened by a pair - roll straightening machine, and the straightness of the straightened tube is better than 0.2 mm / 1000 mm; the surface treatment of the intermediate tube is polished by a sand - belt polishing machine, and the surface roughness Ra of the polished tube is better than 0.8 μm.

[0038] (4) Use a high - precision multi - roll cold - rolling tube mill to perform 2 passes of rolling on the surface - treated intermediate tube obtained in step (3). The deformation amount of rolling is controlled in the range of 45% - 65%, the rolling Q value is controlled in the range of 2.9 - 5.7, the rolling speed is controlled in the range of 50 - 100 times / min, the feed amount is controlled in the range of 0.5 - 1.2 mm / time, the wall thickness of the tube after rolling is controlled in the range of 0.3 - 0.6 (±0.01 mm), and the outer diameter of the tube after rolling is controlled in the range of 15 - 20 mm (±0.01 mm); the degreasing, pickling, straightening and polishing of the tube after cold rolling are the same as those in step (3); the tube after cold rolling is recrystallization - annealed in a vacuum annealing furnace. The annealing after the two - pass rolling is recrystallization annealing, and the annealing temperature is 620 - 650 °C, and the annealing holding time is 2.5 - 3 h.

[0039] (5) The zirconium alloy thin-walled tubes with a low flare wall thickness reduction rate obtained in step (4) are subjected to end flaring. The plug used for flaring is a variable taper plug. The diameter of the plug is represented by the following formula (1), and the plug coefficient E is 2.0. Special metal drawing oil is used for lubricating the flaring part of the tubes to avoid defects on the inner surface of the flare.

[0040]

[0041] In the formula, D F is the inner diameter of the tube after flaring, D 0 is the inner diameter of the tube before flaring, L k is the length of the flaring transition zone, and E is the plug coefficient.

[0042] To make the objectives, technical solutions and advantages of the present invention clearer, the preparation method of the present invention will be described in detail below by taking Zr-4 alloy tube preparation and expanding the outer diameter of the tube to a maximum of 26 mm as an example. The schematic implementation manners and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0043] Example 1

[0044] (1) A Zr-4 alloy tube blank with a specification of Φ63.5×11 mm and a length of 1500 - 2000 mm is intercepted. The surface roughness of the inner and outer surfaces of the tube is detected using a roughness meter. The surface roughness Ra of both the inner and outer surfaces of the tube blank is less than 0.8 μm. The tube blank is subjected to ultrasonic flaw detection in accordance with the provisions of GB / T34485 "Ultrasonic Testing Method for Zirconium and Zirconium Alloy Processed Products", and there are no defects on the inner and outer surfaces of the tube.

[0045] (2) The Zr-4 alloy tube blank obtained in step (1) is subjected to 2 passes of blanking rolling using a KPW50 long-stroke high-speed ring-rolling two-high cold rolling mill. The pass deformation amount is 50% - 80%, and the rolling Q value (the ratio of the rolling wall thickness deformation amount to the outer diameter deformation amount) is greater than 1.0. The rolling deformation process for each pass is shown in Table 1.

[0046] Table 1 Blanking rolling deformation process

[0047] Rolling pass Specification before rolling (mm) Specification after rolling (mm) Deformation amount (%) Q value P1 Φ63.5×11 Φ32×5.0 76.6％ 1.1 P2 Φ32×5.0 Φ23×3.0 55.6％ 1.4

[0048] The rolling speed for the P1 pass and the P2 pass is controlled within the range of 80 - 120 times / min, and the feed amount is controlled within the range of 1.0 - 2.5 mm. The average wall thickness control tolerance of the intermediate tube after rolling is ±0.15 mm, and the outer diameter control tolerance is ±0.05 mm.

[0049] (3) The intermediate tube obtained in step (2) is subjected to degreasing, pickling, vacuum annealing, straightening and surface treatment.

[0050] Degreasing of the intermediate pipe: The degreasing is ultrasonic degreasing, and the degreasing agent used for degreasing is a strongly alkaline degreasing agent. The degreased pipe is first cleaned in an ultrasonic degreasing tank at a degreasing temperature of 50 - 80°C for no less than 60 minutes, then cleaned in a hot water tank at 60 - 70°C for 2 - 10 minutes, and finally cleaned in a rinsing tank at room temperature for 2 - 10 minutes.

[0051] Pickling of the intermediate pipe: The pickling solution is a mixed acid solution prepared from hydrofluoric acid with a concentration of 2 wt%, nitric acid with a concentration of 30 wt% and water. The temperature of the pickling is 15°C - 40°C, the time is 5 min - 10 min, and the wall thickness removal amount of the pipe during pickling is 0.04 - 0.10 mm.

[0052] Vacuum annealing: The vacuum annealing of the intermediate pipe is carried out in a vacuum annealing furnace. The annealing after 2 passes of rolling is recrystallization annealing, the annealing temperature is 620 - 700°C, the annealing holding time is 2.5 - 3 h, and the heat treatment process parameters are shown in Table 2.

[0053] Table 2 Heat treatment process parameters of the intermediate pipe

[0054] Rolling pass Annealing temperature Insulation time Cooling method P1 650-700℃ 2.5-3h Quick cooling with argon filling P2 620-650℃ 2.5-3h Quick cooling with argon filling

[0055] Straightening: The intermediate pipe is straightened by a pair of roll straightening machines. Before straightening, the outer diameter tolerance of the incoming pipe is measured, the straightening center line is adjusted, and the inclination angle and reduction of the straightening rolls are adjusted to fit the pipe surface completely, and the contact length is greater than two-thirds of the roll body length. After straightening, the change in the outer diameter of the pipe is less than 8 μm, there are no pressure marks and straightening marks caused by straightening on the pipe surface, and the straightness of the straightened pipe is better than 0.2 mm / 1000 mm;

[0056] Surface treatment: The surface treatment of the intermediate pipe is carried out by overall polishing using a sand belt polishing machine. The polishing is achieved by the contact of the high-speed rotating sand belt with the pipe. The grit sizes of the sand belts used for polishing are 800 mesh respectively, the outer diameter removal amount for polishing is 0.02 - 0.06 mm, and the surface roughness Ra of the polished pipe is better than 0.8 μm.

[0057] (4) The surface-treated intermediate pipe obtained in step (3) is rolled in a high-precision multi-roll cold rolling mill for 2 passes, and the rolling deformation amount is controlled in the range of 45% - 65%, and the rolling Q value is controlled in the range of 2.9 - 5.7; The rolling deformation distribution for each pass is shown in Table 3.

[0058] Table 3 Intermediate and finished product rolling processes

[0059] Rolling pass Specification before rolling (mm) Specification after rolling (mm) Deformation amount (%) Q value P3 Φ23×3 Φ19×1.5 56.3％ 2.9 Finished product Φ19×1.5 Φ17×0.6 62.5％ 5.7

[0060] The rolling speed of the P3 pass and the finishing pass is controlled in the range of 50 - 100 times / min, the feed amount is controlled in the range of 0.5 - 1.2 mm / time, the wall thickness of the rolled tube is controlled in the range of 0.3 - 0.6 mm (±0.01 mm), and the outer diameter of the rolled tube is controlled in the range of 15 - 20 mm (±0.01 mm).

[0061] The Q value of the finishing rolling in this embodiment is the optimal value for this specification. For comparison, tubes of this specification with other Q values were produced and a comparative test was conducted. The radial texture factor Fr of the tubes is shown in Table 4.

[0062] Table 4 Results of the comparative test

[0063]

[0064]

[0065] The degreasing, pickling, straightening and polishing of the cold-rolled tube are the same as in step (3); the cold-rolled tube is subjected to recrystallization annealing in a vacuum annealing furnace. The annealing of the tube after the middle two passes of rolling is recrystallization annealing, the annealing temperature is 620 - 650 °C, and the annealing holding time is 2.5 - 3 h. The heat treatment process parameters are shown in Table 5.

[0066] Table 5 Heat treatment process parameters of the middle and finishing tubes

[0067] Rolling pass Annealing temperature Insulation time Cooling method P3 650℃ 2.5-3h Quick cooling with argon filling Finished product 620℃ 2.5-3h Quick cooling with argon filling

[0068] (5) The low-flare wall thickness reduction rate zirconium alloy thin-walled tube obtained in step (4) is subjected to end flaring, and the outer diameter expansion rate of the tube is 50%, as Figure 1 and 2 shown. The tube 5 is clamped by the upper die 2 and the lower die 3 with groove dimensions consistent with the flared tube on an ordinary lathe through the three-jaw chuck 4 of the lathe. The plug used for flaring is a variable taper plug 1, and the diameter of the plug is represented by the following formula (1), and the plug coefficient E is 2.0.

[0069]

[0070] where D F is the inner diameter of the flared tube, D 0 is the inner diameter of the tube before flaring, L k is the length of the flaring transition zone, and E is the plug coefficient.

[0071] The plug coefficient E of this embodiment is equal to 2.0, which is the optimal value. For comparison, plugs with different coefficients were made and a flaring comparative test was conducted. The wall thickness reduction rate of the maximum flaring force of the tubes is shown in Table 5.

[0072] Table 5 Results of the flaring comparative test with different plugs

[0073] Serial number Top core coefficient Maximum flaring force (KN) Wall thickness reduction rate (%) 1 E＝0 7.5 5.2 2 E＝1.5 8.0 5.5 3 E＝2.0 8.2 4.5 4 E＝2.5 8.7 6.0 5 E＝3.0 9.2 6.1

[0074] The top core 1 is manually pushed into the inner hole of the pipe along the central axis of the pipe. Before flaring the pipe, a special metal drawing oil is used to lubricate the flaring part to avoid defects on the inner surface of the flare. After the pipe is flared, the top core is withdrawn, the upper and lower female dies are opened, and the pipe is taken out.

[0075] The flared pipe is inspected in accordance with the standard GB / T 15147 "Penetrant Inspection Method for Components of Nuclear Fuel Assemblies". There are no cracks, fissures, and wrinkling defects caused by flaring on the inner and outer surfaces of the pipe. The outer diameter and wall thickness of the pipe are measured using a micrometer, meeting the usage requirements of nuclear power plants.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A processing method for high-precision thin-walled zirconium alloy tubes with a low flare wall thickness reduction rate, characterized in that, it includes the following steps: Step 1: Cut a zirconium alloy tube blank of a certain length; Step 2: Perform two passes of cold rolling on the zirconium alloy tube blank in Step 1 to obtain intermediate tubes; wherein, the two passes of cold rolling are carried out using a long-stroke high-speed ring-roll cold rolling mill, the deformation amount of the two passes of cold rolling is 50%-80%, and the rolling Q value is greater than 1.0; the rolling speed is 80-120 times / min, and the feed amount is 1.0-2.5 mm / time; the wall thickness of the intermediate tubes obtained after rolling is 5.0-3.5 mm, and the outer diameter is 32-22 mm; Step 3: Perform degreasing, pickling, vacuum annealing, straightening and polishing on the intermediate tubes obtained in Step 2; Step 4: Perform two passes of cold rolling on the intermediate tubes obtained in Step 3, wherein, the two passes of cold rolling are carried out using a high-precision multi-roll cold rolling mill, the deformation amount of the two passes of cold rolling is 45%-65%, and the rolling Q value is 2.9-5.7; the rolling speed is 50-100 times / min, and the feed amount is 0.5-1.2 mm / time; the wall thickness of the tubes obtained after rolling is 0.3-0.6 mm, and the outer diameter is 15-20 mm; the tubes after cold rolling are subjected to degreasing, pickling, vacuum annealing, straightening and polishing to obtain high-precision thin-walled zirconium alloy tubes with a low flare wall thickness reduction rate.

2. The processing method for high-precision thin-walled zirconium alloy tubes with a low flare wall thickness reduction rate according to claim 1, characterized in that, the wall thickness of the zirconium alloy tube blank is 10-12 mm, and the outer diameter is 55-65 mm; the inner surface of the tube blank is subjected to honing or broaching treatment, and the outer surface is subjected to polishing treatment, and the defects on the inner and outer surfaces of the tube blank are removed completely.

3. The processing method for high-precision thin-walled zirconium alloy tubes with a low flare wall thickness reduction rate according to claim 1, characterized in that, the wall thickness of the high-precision thin-walled zirconium alloy tubes with a low flare wall thickness reduction rate obtained in Step 4 is 0.3-0.6 mm, the nominal outer diameter is 15-20 mm, and the radial texture factor Fr is greater than or equal to 0.

55.

4. The processing method for high-precision thin-walled zirconium alloy tubes with a low flare wall thickness reduction rate according to claim 1, characterized in that, the degreasing of the tubes in Step 3 and Step 4 is ultrasonic degreasing, the degreasing agent used for degreasing is a strongly alkaline degreasing agent, during degreasing, first clean in an ultrasonic degreasing tank at 50-80 °C, and the degreasing time is not less than 60 min, then clean in a hot water tank at 60-70 °C for 2-10 minutes, and finally clean in a rinsing tank at room temperature for 2-10 minutes; the acid solution used for pickling the tubes in Step 3 and Step 4 is a mixed acid solution prepared from hydrofluoric acid with a concentration of 2-3 wt%, nitric acid with a concentration of 20-30 wt% and water; the temperature of the pickling is 15 °C-40 °C, and the time is 5 min-10 min.

5. The processing method for high-precision thin-walled zirconium alloy tubes with a low flare wall thickness reduction rate according to claim 1, characterized in that, The intermediate pipe vacuum annealing described in Step 3 is carried out in a vacuum annealing furnace. The annealing after the two-pass cold rolling is recrystallization annealing, and the annealing temperature is 620 - 700 °C, and the annealing holding time is 2.5 - 3 h.

6. The processing method of high-precision thin-walled zirconium alloy pipes with a low flaring wall thickness reduction rate according to claim 1, characterized in that, The pipe vacuum annealing described in Step 4 is carried out in a vacuum annealing furnace. The annealing after the two-pass cold rolling is recrystallization annealing, and the annealing temperature is 620 - 650 °C, and the annealing holding time is 2.5 - 3 h.

7. A pipe end flaring method for high-precision thin-walled zirconium alloy pipes with a low flaring wall thickness reduction rate, characterized in that, comprising: Clamping the high-precision thin-walled zirconium alloy pipe with a low flaring wall thickness reduction rate obtained by the pipe processing method described in any one of claims 1 - 6 by a pair of upper and lower female dies, and using a variable taper mandrel to extend into the inner hole of the thin-walled zirconium alloy pipe for end flaring.

8. The pipe end flaring method for high-precision thin-walled zirconium alloy pipes with a low flaring wall thickness reduction rate according to claim 7, characterized in that, The diameter of the variable taper mandrel is represented by the following formula (1), and the mandrel coefficient E is 2.0, and the flaring force and the wall thickness reduction rate are the lowest; (1) Where D F is the inner diameter of the pipe after flaring, D 0 is the inner diameter of the pipe before flaring, L k is the length of the flaring transition zone, and E is the mandrel coefficient.

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