A titanium alloy thin-diameter thick-wall tube with a low yield ratio and its preparation method

Abstract

The present invention belongs to the technical field of titanium alloy tubes. The present invention provides a titanium alloy fine-diameter thick-wall tube with a low yield ratio and a preparation method thereof. An ultra-low impurity content titanium alloy ingot is successively subjected to blooming and forging, and the obtained titanium alloy round bar is subjected to multi-pass hot extrusion processing, sizing cutting and center hole drilling to obtain a titanium alloy drawing tube blank; the titanium alloy drawing tube blank is subjected to multi-pass composite drawing to obtain a drawn tube; the drawn tube is successively subjected to solution treatment, water quenching and aging treatment to obtain a rough tube; the rough tube is successively subjected to straightening, inner hole cleaning and outer surface centerless grinding and polishing to obtain a titanium alloy fine-diameter thick-wall tube with a low yield ratio. The preparation method of the present invention uses an ultra-low impurity content titanium alloy, so that the overall yield strength of the titanium alloy fine-diameter thick-wall tube is lower, the plasticity is better, and it is easier to carry out extrusion and drawing processing; multi-pass extrusion and drawing processing are carried out to retain the longitudinal processing streamline of the tube to the greatest extent and further reduce the yield ratio.

Description

Technical Field

[0001] The present invention relates to the technical field of titanium alloy pipes, and in particular to a low-yield-to-strength ratio titanium alloy thin-diameter thick-wall pipe and a preparation method thereof. Background Art

[0002] Titanium and titanium alloy materials are widely used in the fields of nuclear industry, chemical and petrochemical industry, aerospace, sporting goods, etc. At the same time, titanium alloy is non-toxic to the human body, lightweight, high in specific strength, and has excellent biocompatibility and corrosion resistance. It can be used as an implant material for implantation in the human body, etc., and is one of the ideal medical metal materials. Orthopedic medical devices are one of the important sub-industries of the medical device industry. From the perspective of the three sub-sectors of orthopedic implants, trauma products account for a large proportion, spinal and artificial joint products have a rapid growth rate, and intramedullary nails are typical orthopedic trauma products. Intramedullary nail fixation technology for fractures has been widely used in clinical practice, and closed interlocking intramedullary nail fixation has become the preferred method for treating femoral shaft and diaphyseal shaft fractures, especially for patients with multiple trauma.

[0003] The traditional processing technology of intramedullary nails has processing difficulties such as multiple angles, long spans, difficulty in bending, and slender inner holes, which will increase product errors due to multiple clamping. When drilling slender holes in intramedullary nails, due to the slender inner hole and poor thermal conductivity of titanium alloy, it is easy for the drilling to deviate from the center or the drill bit to break, resulting in a low processing yield. During the processing of intramedullary nails, a certain curvature needs to be bent to adapt to the physiological curvature of human bones. At present, intramedullary nails can be cold-bent, but stress concentration is likely to occur at the bend, and the bending effect and forming quality are relatively low; hot bending or hot molding can also be performed, but the need for secondary hot processing brings potential problems such as coarse microstructure and reduced mechanical properties to the titanium alloy material, and also increases the process steps and processing costs.

[0004] The yield strength ratio, or yield strength ratio, is a key indicator of metal materials. Compared to other metal materials, titanium alloys have a yield strength that is close to their tensile strength, meaning they have a higher yield strength ratio. Using thin-diameter, thick-walled titanium alloy tubing with a low yield strength ratio to process intramedullary nails can reduce or eliminate the need for center hole drilling. The curvature of the nail can be bent or molded at room temperature, avoiding potential problems such as coarsening of the microstructure and reduced mechanical properties that can occur with hot bending or hot molding. This reduces material consumption and improves processing efficiency and product performance.

[0005] Therefore, the research has yielded a titanium alloy thin-diameter thick-walled tube with a low yield-to-strength ratio, which is used for orthopedic hollow screws and intramedullary nails, which has important value and significance. Summary of the Invention

[0006] The object of the present invention is to provide a low-yield-to-tensile-ratio titanium alloy thin-diameter thick-walled tube and a preparation method thereof in order to overcome the deficiencies of the prior art.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides a method for preparing a low-yield ratio titanium alloy thin-diameter thick-walled tube, comprising the following steps:

[0009] 1) The ultra-low impurity content titanium alloy ingot is subjected to blanking and forging in sequence to obtain a titanium alloy round rod;

[0010] 2) subjecting the titanium alloy round rod to multiple hot extrusion processes to obtain an extruded rod, and the extruded rod is cut to length and drilled with a center hole to obtain a titanium alloy drawn tube blank;

[0011] 3) subjecting the titanium alloy drawn tube blank to a multi-pass composite drawing to obtain a drawn tube;

[0012] 4) subjecting the drawn tube to solution treatment, water quenching, and aging treatment in sequence to obtain a crude tube product;

[0013] 5) The crude pipe is straightened, the inner hole is cleaned, and the outer surface is centerlessly ground and polished in sequence to obtain a low-yield-to-strength ratio titanium alloy thin-diameter thick-walled pipe.

[0014] Preferably, in the ultra-low impurity content titanium alloy ingot in step 1), the mass percentages of impurity elements are as follows: C≤0.08%, N≤0.03%, H≤0.015%, O≤0.10%, Fe≤0.10%, and the mass percentages of other impurity elements are independently ≤0.10%;

[0015] Step 1) The diameter of the titanium alloy round rod is 40 to 60 mm.

[0016] Preferably, the multi-pass hot extrusion process in step 2) is 2 to 5 passes, the diameter of the extruded rod is 20 to 30 mm, the length of the cut-to-length rod is 400 to 600 mm, and the diameter of the center hole is 2 to 4 mm.

[0017] Preferably, the multi-pass composite drawing in step 3) is 3 to 6 passes, and the multi-pass composite drawing adopts composite drawing of a long core rod and a fixed core rod. In the multi-pass composite drawing, the diameter of the core rod is 0.8 to 4 mm, and the diameter of the core rod decreases as the number of passes increases.

[0018] Preferably, the titanium alloy drawn tube is preheated and then subjected to multi-pass composite drawing, the preheating temperature is 550-620° C., and the preheating time is 20-40 minutes.

[0019] Preferably, during each drawing process, the distance between the fixed end of the mandrel and the tube drawing die is 100 to 300 mm smaller than the length of the mandrel, the mandrel moves 50 to 150 mm with the tube, and then the mandrel is pulled out in the opposite direction of the drawing direction.

[0020] Preferably, the solution treatment in step 4) is carried out at a temperature of 850 - 920 °C for 20 - 40 min, and the aging treatment is carried out at a temperature of 450 - 500 °C for 50 - 90 min.

[0021] Preferably, the straightening in step 5) is multi-roll straightening. During the straightening process, the preheating temperature of the rough pipe is 700 - 750 °C, and the heat preservation time is 20 - 40 min.

[0022] The reagent for inner hole cleaning is a mixed aqueous solution of hydrofluoric acid and nitric acid. In the mixed aqueous solution, the mass fraction of hydrofluoric acid is 5 - 10%, and the mass fraction of nitric acid is 30 - 40%.

[0023] The present invention also provides a low yield ratio titanium alloy thin-diameter thick-wall tube prepared by the described preparation method. The outer diameter of the low yield ratio titanium alloy thin-diameter thick-wall tube is 7 - 15 mm, the inner diameter is 0.6 - 2.0 mm, the length is 1500 - 3000 mm, and the yield ratio is 0.7 - 0.9.

[0024] The present invention also provides an application of the described low yield ratio titanium alloy thin-diameter thick-wall tube as a medical implant material.

[0025] The beneficial effects of the present invention include the following points:

[0026] 1) The present invention uses a titanium alloy with ultra-low impurity content, making the overall yield strength of the titanium alloy thin-diameter thick-wall tube lower, with better plasticity and being more easily subjected to extrusion and drawing processes.

[0027] 2) The preparation method of the present invention performs multi-pass extrusion and drawing processes, retaining the longitudinal processing streamline of the pipe to the greatest extent and further reducing the yield ratio.

[0028] 3) Due to the lower overall yield strength and the retention of the processing streamline, the drawability of the pipe is better. A composite process combining a long mandrel and a fixed mandrel can be used to draw the titanium alloy pipe, eliminating the need for a core-pulling machine to extract the core and the need for a low-melting-point coating on the mandrel. The coating and the mandrel are removed along with the pipe during drawing, significantly improving the processing efficiency.

[0029] 4) The method of the present invention solves the problem that the yield ratio of thick-wall tubes prepared by traditional piercing rolling, drawing, or mechanical processing of the inner hole is too high, resulting in poor formability during subsequent room-temperature use. The thick-wall tubes obtained by the method of the present invention can be bent or formed by die at room temperature when used to make medical implant intramedullary nails and surgical tools, avoiding potential problems such as coarse microstructure and reduced mechanical properties caused by hot bending or hot die pressing of titanium alloy materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1Cross-sectional typical microstructure diagram of the low yield ratio titanium alloy thin-diameter thick-wall tube of Example 1;

[0031] Figure 2 Longitudinal-sectional typical processing streamline microstructure diagram of the low yield ratio titanium alloy thin-diameter thick-wall tube of Example 1. Specific implementation manners

[0032] The present invention provides a preparation method of a low yield ratio titanium alloy thin-diameter thick-wall tube, comprising the following steps:

[0033] 1) Subjecting a titanium alloy ingot with ultra-low impurity content to blooming and forging in sequence to obtain a titanium alloy round bar;

[0034] 2) Subjecting the titanium alloy round bar to multi-pass hot extrusion processing to obtain an extruded bar, and subjecting the extruded bar to fixed-length cutting and center hole drilling to obtain a titanium alloy drawing tube blank;

[0035] 3) Subjecting the titanium alloy drawing tube blank to multi-pass composite drawing to obtain a drawn tube;

[0036] 4) Subjecting the drawn tube to solution treatment, water quenching and aging treatment in sequence to obtain a rough tube;

[0037] 5) Subjecting the rough tube to straightening, inner hole cleaning and centerless grinding and polishing of the outer surface in sequence to obtain a low yield ratio titanium alloy thin-diameter thick-wall tube.

[0038] In the present invention, in the titanium alloy ingot with ultra-low impurity content in step 1), preferably, the mass percentages of impurity elements are as follows: C≤0.08%, N≤0.03%, H≤0.015%, O≤0.10%, Fe≤0.10%, and the mass percentages of other impurity elements are independently ≤0.10%; more preferably, the mass percentages of impurity elements are as follows: C≤0.04%, N≤0.02%, H≤0.009%, O≤0.08%, Fe≤0.08%, and the mass percentages of other impurity elements are independently ≤0.09%; the titanium alloy with ultra-low impurity content is preferably TC4 titanium alloy.

[0039] In the present invention, a titanium alloy ingot with ultra-low impurity content is prepared by vacuum consumable arc melting method. The number of times of vacuum consumable arc melting method is preferably 2 - 4 times, more preferably 3 times; the vacuum degree of the first vacuum consumable arc melting method is preferably 1 - 5 Pa, more preferably 2 - 4 Pa, still more preferably 3 Pa; the voltage of the first vacuum consumable arc melting method is preferably 25 - 35 V, more preferably 28 - 32 V, still more preferably 30 V; the current of the first vacuum consumable arc melting method is preferably 1900 - 2100 A, more preferably 1950 - 2050 A, still more preferably 2000 A; the air leakage rate of the first vacuum consumable arc melting method is preferably ≤0.5 Pa / min, more preferably ≤0.4 Pa / min; the vacuum degree of the 2nd - 4th vacuum consumable arc melting method is preferably 10 - 50 Pa, more preferably 15 - 45 Pa, still more preferably 20 - 40 Pa; the voltage of the 2nd - 4th vacuum consumable arc melting method is preferably 25 - 35 V, more preferably 28 - 32 V, still more preferably 30 V; the current of the 2nd - 4th vacuum consumable arc melting method is preferably 3900 - 4100 A, more preferably 3950 - 4050 A, still more preferably 4000 A; the air leakage rate of the 2nd - 4th vacuum consumable arc melting method is preferably ≤0.5 Pa / min, more preferably ≤0.4 Pa / min.

[0040] In the present invention, the temperature of the blanking in step 1) is preferably 950 - 980 °C, more preferably 960 - 970 °C; the temperature of forging is preferably 930 - 950 °C, more preferably 935 - 945 °C, still more preferably 940 °C.

[0041] In the present invention, the diameter of the titanium alloy round bar in step 1) is preferably 40 - 60 mm, more preferably 45 - 55 mm, still more preferably 50 mm.

[0042] In the present invention, the multi-pass hot extrusion processing in step 2) is preferably 2 - 5 passes, more preferably 3 - 4 passes; during the multi-pass hot extrusion processing, the extrusion temperature is independently preferably 910 - 930 °C, more preferably 915 - 925 °C, still more preferably 920 °C; the extrusion ratio is independently preferably 9 - 10, and the extrusion speed is independently preferably 100 - 120 mm / s, more preferably 105 - 115 mm / s, still more preferably 110 mm / s.

[0043] In the present invention, the diameter of the extruded rod in step 2) is preferably 20-30 mm, more preferably 22-28 mm, and more preferably 25-26 mm; the length of the cut-to-length is preferably 400-600 mm, more preferably 450-550 mm, and more preferably 500 mm; the diameter of the center hole is preferably 2-4 mm, more preferably 2.5-3.5 mm, and more preferably 3 mm; and the center hole is preferably drilled using a gun drill.

[0044] The titanium alloy drawn tube blank in step 2) of the present invention is an ultra-low gap titanium alloy drawn tube blank.

[0045] In the present invention, the multi-pass composite drawing in step 3) is preferably 3 to 6 passes, more preferably 4 to 5 passes; the multi-pass composite drawing preferably adopts composite drawing of a long core rod and a fixed core rod.

[0046] In the present invention, a mandrel is inserted before multi-pass composite drawing, and the diameter of the mandrel is preferably 0.8-4 mm. During the multi-pass composite drawing, the diameter of the mandrel decreases as the number of passes increases. The material of the mandrel is preferably 1RK91 stainless steel.

[0047] In the present invention, the titanium alloy drawn tube is preferably preheated before multi-pass composite drawing. The preheating temperature is preferably 550-620°C, more preferably 570-600°C, and more preferably 580-590°C; the preheating time is preferably 20-40 minutes, more preferably 25-35 minutes, and more preferably 30 minutes.

[0048] In the present invention, during each drawing process, one end of the mandrel is fixed and the other end passes through the tube. The distance between the fixed end of the mandrel and the tube drawing die is preferably 100-300 mm smaller than the length of the mandrel, and further preferably 150-250 mm smaller than the length of the mandrel; the moving speed of the mandrel is preferably 12-20 mm / s, further preferably 14-18 mm / s, and more preferably 16 mm / s; the distance that the mandrel moves with the tube blank is preferably 50-150 mm, further preferably 80-120 mm, and more preferably 90-110 mm. The drawing process within this distance is long core rod drawing. After the drawing is completed, the mandrel is pulled out in the opposite direction of the drawing direction, and then the next drawing and core pulling are carried out, and the drawing and core pulling are repeated; the core pulling speed is preferably 6-9 mm / s, and more preferably 7-8 mm / s.

[0049] In the present invention, the temperature of the solid solution in step 4) is preferably 850-920°C, more preferably 870-900°C, and more preferably 880-890°C; the solid solution time is preferably 20-40 min, more preferably 25-35 min, and more preferably 30 min; the aging treatment temperature is preferably 450-500°C, more preferably 460-490°C, and more preferably 470-480°C; the aging treatment time is preferably 50-90 min, more preferably 60-80 min, and more preferably 65-75 min.

[0050] In the present invention, the water quenching is preferably performed by placing the solutionized pipe into a water pool or flowing water. The water quenching is performed at room temperature to cool the solutionized pipe to room temperature. The water quenching time is preferably 3 to 8 minutes, more preferably 4 to 7 minutes, and more preferably 5 to 6 minutes.

[0051] In the present invention, the straightening in step 5) is preferably multi-roll straightening. During the straightening process, the preheating temperature of the crude pipe is preferably 700-750°C, more preferably 710-740°C, and more preferably 720-730°C; the holding time is preferably 20-40 min, more preferably 25-35 min, and more preferably 30 min.

[0052] In the present invention, the reagent for cleaning the inner hole is preferably a mixed aqueous solution of hydrofluoric acid and nitric acid, in which the mass fraction of hydrofluoric acid is preferably 5-10%, more preferably 6-9%, and more preferably 7-8%; the mass fraction of nitric acid is preferably 30-40%, more preferably 32-38%, and more preferably 34-36%; the time for cleaning the inner hole is preferably 3-5 minutes, and more preferably 4 minutes; the mixed aqueous solution of hydrofluoric acid and nitric acid removes the oxide layer and other impurities on the surface of the inner hole; after the inner hole cleaning is completed, it is preferably rinsed with high-pressure water 3-5 times and then dried with compressed air; the pressure of the high-pressure water is preferably 1-1.5 MPa, more preferably 1.1-1.4 MPa, and more preferably 1.2-1.3 MPa; the pressure of the compressed air is preferably 0.7-0.9 MPa, and more preferably 0.8 MPa; the exhaust volume of the compressed air is preferably 0.8-1m 3 / min, more preferably 0.9m 3 / min.

[0053] In the present invention, before the centerless grinding and polishing of the outer surface, two umbrella-shaped rubber plugs are preferably inserted into both ends of the pipe to prevent sand and grinding debris from entering the inner hole of the pipe during the grinding process. The umbrella-shaped rubber plugs are removed after the grinding is completed.

[0054] The present invention also provides a low yield ratio titanium alloy thin-diameter thick-wall tube prepared by the described preparation method. The outer diameter of the low yield ratio titanium alloy thin-diameter thick-wall tube is preferably 7 - 15 mm, more preferably 8 - 12 mm; the inner diameter is preferably 0.6 - 2.0 mm, more preferably 0.8 - 1.5 mm; the length is preferably 1500 - 3000 mm, more preferably 1700 - 2500 mm; the yield ratio is preferably 0.7 - 0.9, more preferably 0.75 - 0.85, and even more preferably 0.8.

[0055] The present invention also provides an application of the described low yield ratio titanium alloy thin-diameter thick-wall tube as a medical implant material; the medical implant material is preferably an orthopedic hollow screw or intramedullary nail.

[0056] The technical solutions provided by the present invention will be described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0057] Example 1

[0058] An ultra-low impurity content titanium alloy ingot was prepared by the triple vacuum consumable arc melting method. The vacuum degree of the first vacuum consumable arc melting method was 2 Pa, the voltage was 27 V, the current was 1950 A, and the air leakage rate was 0.48 Pa / min. The vacuum degrees of the second and third vacuum consumable arc melting methods were both 15 Pa, the voltages were both 27 V, the currents were both 3950 A, and the air leakage rates were both 0.48 Pa / min. The mass percentages of the impurity elements in the titanium alloy ingot were respectively: C ≤ 0.04%, N ≤ 0.02%, H ≤ 0.009%, O ≤ 0.08%, Fe ≤ 0.06%, and the mass percentages of each of the other impurity elements were ≤ 0.10%. The ultra-low impurity content titanium alloy ingot was bloomed at 955 °C and forged at 935 °C to obtain a titanium alloy round bar with a diameter of 55 mm. The titanium alloy round bar was subjected to 3 passes of hot extrusion processing. During each pass of hot extrusion processing, the extrusion temperature was 915 °C, the extrusion ratio was 9, and the extrusion speed was 105 mm / s to obtain a bar with a diameter of 25 mm, which was cut to a fixed length of 500 mm, and then a central hole with a diameter of 2.5 mm was drilled to obtain a titanium alloy drawing tube blank.

[0059] The titanium alloy drawn tube was subjected to a three-pass composite drawing process using a long mandrel and fixed mandrel composite hot drawing process. A 1RK91 stainless steel mandrel was inserted before drawing. The titanium alloy drawn tube was preheated at 600°C for 30 minutes before the three-pass composite drawing process. During the drawing process, one end of the mandrel was fixed while the other end passed through the tube. The distance between the fixed end of the mandrel and the tube drawing die was 100 mm less than the mandrel length. During the drawing process, the mandrel moved at a speed of 14 mm / s and moved 100 mm with the tube. During this distance, the drawing process was long mandrel drawing. The drawing process then stopped and the mandrel was withdrawn in the opposite direction of the drawing direction (the withdrawal distance of the mandrel was equal to the distance the mandrel moved with the tube) at a speed of 6.5 mm / s. The above drawing and core pulling process was repeated until the three-pass composite drawing process was completed to obtain the drawn tube. In the three-pass composite drawing, the outer diameters of the tubes are 25 mm, 18 mm, and 12 mm, respectively, and the diameters of the mandrels are 2.5 mm, 2.0 mm, and 1.5 mm, respectively.

[0060] The drawn tube was solutionized at 850°C for 25 minutes and then placed in a room temperature water pool for water quenching for 4 minutes. The tube was then aged at 450°C for 60 minutes to obtain a crude tube. The crude tube was straightened by multiple rollers. During the straightening process, the crude tube was preheated to 750°C for 20 minutes. The inner hole was then cleaned with a mixed aqueous solution containing hydrofluoric acid and nitric acid (the mass fraction of hydrofluoric acid in the mixed aqueous solution was 5% and the mass fraction of nitric acid was 30%) for 3.5 minutes. The tube was then rinsed with high-pressure water at a pressure of 1.2 MPa for 3 times and dried with compressed air at a pressure of 0.75 MPa. The exhaust volume of the compressed air was 0.85 m 3 / min, and finally two umbrella-shaped rubber plugs are inserted at both ends of the pipe, and the outer surface is subjected to centerless grinding and polishing to obtain a low-yield-to-strength ratio titanium alloy thin-diameter thick-walled pipe.

[0061] The low yield ratio titanium alloy thin-diameter thick-walled tube of Example 1 has an outer diameter of 12 mm, an inner diameter of 1.5 mm, a length of 2000-2500 mm, and a tube yield ratio of 0.86.

[0062] The typical cross-sectional microstructure of the low yield ratio titanium alloy thin diameter thick wall tube of Example 1 is shown in FIG. Figure 1 As shown; the longitudinal section of the typical processing streamline microstructure of the low yield ratio titanium alloy thin diameter thick wall tube of Example 1 is as shown Figure 2 As shown. Figure 1 It can be seen that the typical cross-sectional microstructure of the low yield ratio titanium alloy thin diameter thick wall tube is equiaxed structure. Figure 2 It can be seen that the longitudinal section of the low yield ratio titanium alloy thin diameter thick wall tube has obvious processing streamlines.

[0063] Example 2

[0064] Ultra-low impurity titanium alloy ingots were produced using a three-step vacuum consumable arc melting process. The first vacuum consumable arc melting process was conducted at a vacuum level of 5 Pa, a voltage of 33 V, a current of 2050 A, and a gas leakage rate of 0.45 Pa / min. The second and third vacuum consumable arc melting processes were conducted at a vacuum level of 45 Pa, a voltage of 33 V, a current of 4050 A, and a gas leakage rate of 0.45 Pa / min. The mass percentages of impurity elements in the titanium alloy ingots were: C ≤ 0.04%, N ≤ 0.02%, H ≤ 0.009%, O ≤ 0.05%, and Fe ≤ 0.08%. The mass percentages of all other impurity elements were ≤ 0.10%. The ultra-low impurity titanium alloy ingots were smelted at 975°C and forged at 945°C to produce titanium alloy round bars with a diameter of 60 mm. The titanium alloy round rod was subjected to four hot extrusion processes. During each hot extrusion process, the extrusion temperature was 925°C, the extrusion ratio was 10, and the extrusion speed was 115 mm / s to obtain a rod with a diameter of 30 mm. The rod was cut to a length of 450 mm, and then a center hole with a diameter of 3 mm was drilled to obtain a titanium alloy drawn tube blank.

[0065] The titanium alloy drawn tube was subjected to a four-pass composite drawing process using a long mandrel and fixed mandrel composite hot drawing process. A 1RK91 stainless steel mandrel was inserted before drawing. The titanium alloy drawn tube was preheated at 580°C for 25 minutes before the four-pass composite drawing process. During the drawing process, one end of the mandrel was fixed while the other end passed through the tube. The distance between the fixed end of the mandrel and the tube drawing die was 150 mm less than the mandrel length. During the drawing process, the mandrel moved at a speed of 18 mm / s and moved 80 mm with the tube. During this distance, the drawing process was long mandrel drawing. The drawing process then stopped and the mandrel was withdrawn in the opposite direction of the drawing direction (the withdrawal distance of the mandrel was equal to the distance the mandrel moved with the tube) at a speed of 8.5 mm / s. The above drawing and core pulling process was repeated until the four-pass composite drawing process was completed to obtain the drawn tube. In the four-pass composite drawing, the outer diameters of the tubes are 30 mm, 24 mm, 16 mm, and 10 mm, respectively, and the diameters of the mandrels are 2.5 mm, 2.0 mm, 1.5 mm, and 1.0 mm, respectively.

[0066] The drawn tube was solutionized at 870°C for 30 minutes and then placed in flowing room temperature water for water quenching for 8 minutes, and then aged at 470°C for 90 minutes to obtain a crude tube. The crude tube was straightened by multiple rollers. During the straightening process, the crude tube was preheated to 700°C and kept warm for 30 minutes. The inner hole was then cleaned with a mixed aqueous solution containing hydrofluoric acid and nitric acid (the mass fraction of hydrofluoric acid in the mixed aqueous solution was 10% and the mass fraction of nitric acid was 40%) for 5 minutes. The tube was then rinsed with high-pressure water at a pressure of 1.5 MPa for 4 times and dried with compressed air at a pressure of 0.85 MPa. The exhaust volume of the compressed air was 0.95 m 3 / min, and finally two umbrella-shaped rubber plugs are inserted at both ends of the pipe, and the outer surface is subjected to centerless grinding and polishing to obtain a low-yield-to-strength ratio titanium alloy thin-diameter thick-walled pipe.

[0067] The low yield ratio titanium alloy thin-diameter thick-walled tube of Example 2 has an outer diameter of 10 mm, an inner diameter of 1.0 mm, a length of 2500-2700 mm, and a tube yield ratio of 0.82.

[0068] Example 3

[0069] Ultra-low impurity titanium alloy ingots were produced using a three-step vacuum consumable arc melting process. The first vacuum consumable arc melting process was conducted at a vacuum level of 3 Pa, a voltage of 30 V, a current of 2000 A, and a gas leakage rate of 0.46 Pa / min. The second and third vacuum consumable arc melting processes were conducted at a vacuum level of 30 Pa, a voltage of 30 V, a current of 4000 A, and a gas leakage rate of 0.46 Pa / min. The mass percentages of impurity elements in the titanium alloy ingots were: C ≤ 0.04%, N ≤ 0.01%, H ≤ 0.006%, O ≤ 0.10%, and Fe ≤ 0.10%. The mass percentages of all other impurity elements were ≤ 0.10%. The ultra-low impurity titanium alloy ingots were smelted at 965°C and forged at 940°C to produce titanium alloy round bars with a diameter of 40 mm. The titanium alloy round rod was subjected to three hot extrusion processes. During each hot extrusion process, the extrusion temperature was 920℃, the extrusion ratio was 9.5, and the extrusion speed was 110mm / s to obtain a rod with a diameter of 20mm. The rod was cut to a length of 400mm, and then a center hole with a diameter of 2mm was drilled to obtain a titanium alloy drawn tube blank.

[0070] The titanium alloy drawn tube blank is subjected to 4 passes of composite drawing. The composite drawing adopts the composite hot drawing process of a long mandrel and a fixed mandrel. Before drawing, a 1RK91 stainless steel mandrel is inserted. The titanium alloy drawn tube blank is preheated at 550 °C for 20 min and then undergoes 4 passes of composite drawing. During the drawing process, one end of the mandrel is fixed and the other end passes through the tube. The distance between the fixed end of the mandrel and the tube drawing die is 100 mm less than the length of the mandrel. During the drawing process, the moving speed of the mandrel is 16 mm / s. The mandrel moves 50 mm along with the tube drawing. The drawing process within this distance is long mandrel drawing. Then the drawing action stops, and the mandrel is withdrawn in the direction opposite to the drawing direction (the withdrawal distance of the mandrel is equal to the moving distance of the mandrel along with the tube). The withdrawal speed of the mandrel is 7.5 mm / s. Then the above drawing and core rod withdrawal processes are repeated in sequence until 4 passes of composite drawing are completed to obtain the drawn tube. In the 4 passes of composite drawing, the outer diameters of the tube are 20 mm, 15 mm, 10 mm, and 8 mm in sequence, and the core rod diameters are 2.0 mm, 1.6 mm, 1.2 mm, and 0.8 mm in sequence.

[0071] The drawn tube is solution-treated at 850 °C for 20 min and then put into a room-temperature water pool for water quenching. The water quenching time is 6 min. Then it is aged at 450 °C for 50 min to obtain the rough tube. The rough tube is subjected to multi-roll straightening. During the straightening process, the rough tube is preheated to 700 °C and kept warm for 20 min. Then the inner hole is cleaned with a mixed aqueous solution containing hydrofluoric acid and nitric acid (in the mixed aqueous solution, the mass fraction of hydrofluoric acid is 10% and the mass fraction of nitric acid is 40%). The cleaning time of the inner hole is 4 min. Then it is rinsed 5 times with high-pressure water at a pressure of 1.3 MPa and dried with compressed air at a pressure of 0.8 MPa. The exhaust volume of the compressed air is 0.9 m 3 / min. Finally, two umbrella-shaped rubber plugging heads are inserted at both ends of the tube for centerless grinding and polishing of the outer surface to obtain the titanium alloy fine-diameter thick-wall tube with a low yield ratio.

[0072] The outer diameter of the titanium alloy fine-diameter thick-wall tube with a low yield ratio in Example 3 is 8 mm, the inner diameter is 0.8 mm, the length is 2400 - 2700 mm, and the yield ratio of the tube is 0.78.

[0073] Example 4

[0074] The ultra-low impurity content titanium alloy ingot is prepared by the triple vacuum consumable arc melting method. The vacuum degree of the first vacuum consumable arc melting method is 4 Pa, the voltage is 31 V, the current is 2020 A, and the air leakage rate is 0.4 Pa / min. The vacuum degrees of the second and third vacuum consumable arc melting methods are both 35 Pa, the voltages are both 31 V, the currents are both 4020 A, and the air leakage rates are both 0.4 Pa / min. The mass percentages of the impurity elements in the titanium alloy ingot are as follows: C≤0.04%, N≤0.02%, H≤0.009%, O≤0.04%, Fe≤0.04%, and the mass percentages of other impurity elements are all ≤0.10%. The ultra-low impurity content titanium alloy ingot is bloomed at 970 °C and forged at 942 °C to obtain a titanium alloy round bar with a diameter of 60 mm. The titanium alloy round bar is subjected to 3-pass hot extrusion processing. During each pass of the hot extrusion processing, the extrusion temperature is 922 °C, the extrusion ratio is 9.6, and the extrusion speed is 112 mm / s to obtain a bar with a diameter of 30 mm, which is cut to a fixed length of 600 mm, and then a central hole with a diameter of 4 mm is drilled to obtain a titanium alloy drawing tube blank.

[0075] The titanium alloy drawing tube blank is subjected to 4-pass composite drawing. The composite drawing adopts the composite hot drawing process of a long mandrel and a fixed mandrel. Before drawing, a 1RK91 stainless steel mandrel is inserted. After the titanium alloy drawing tube blank is preheated at 620 °C for 40 min, 4-pass composite drawing is carried out. During the drawing process, one end of the mandrel is fixed, and the other end passes through the tube. The distance between the fixed end of the mandrel and the drawing die of the tube is 300 mm smaller than the length of the mandrel. During the drawing process, the moving speed of the mandrel is 15 mm / s, and the mandrel moves 150 mm along with the drawing of the tube. The drawing process within this distance is long mandrel drawing. Then the drawing action stops, and the mandrel is withdrawn in the direction opposite to the drawing direction (the withdrawal distance of the mandrel is equal to the moving distance of the mandrel along with the tube). The withdrawal speed of the mandrel is 8 mm / s. Then the above drawing and core-pulling processes are repeated in sequence until 4-pass composite drawing is completed to obtain the drawn tube. During the 4-pass composite drawing, the outer diameters of the tube are 30 mm, 25 mm, 20 mm, and 14 mm in sequence, and the mandrel diameters are 4.0 mm, 3.2 mm, 2.5 mm, and 2.0 mm in sequence.

[0076] The drawn tube was solutionized at 920°C for 40 minutes and then placed in flowing room temperature water for water quenching for 5 minutes. The tube was then aged at 500°C for 90 minutes to obtain a crude tube. The crude tube was straightened by multiple rollers. During the straightening process, the crude tube was preheated to 750°C for 40 minutes. The inner hole was then cleaned with a mixed aqueous solution containing hydrofluoric acid and nitric acid (the mass fraction of hydrofluoric acid in the mixed aqueous solution was 5% and the mass fraction of nitric acid was 30%) for 4.5 minutes. The tube was then rinsed with high-pressure water at a pressure of 1.25 MPa for 3 times and dried with compressed air at a pressure of 0.85 MPa. The exhaust volume of the compressed air was 0.75 m 3 / min, and finally two umbrella-shaped rubber plugs are inserted at both ends of the pipe, and the outer surface is subjected to centerless grinding and polishing to obtain a low-yield-to-strength ratio titanium alloy thin-diameter thick-walled pipe.

[0077] The low yield ratio titanium alloy thin-diameter thick-walled tube of Example 4 has an outer diameter of 14 mm, an inner diameter of 2.0 mm, a length of 2700-2900 mm, and a tube yield ratio of 0.75.

[0078] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A preparation method of a titanium alloy thin-diameter thick-wall tube with a low yield ratio, characterized in that, It includes the following steps: 1) Subject the titanium alloy ingot with ultra-low impurity content to blooming and forging in sequence to obtain a titanium alloy round bar; 2) Subject the titanium alloy round bar to multi-pass hot extrusion processing to obtain an extruded bar. The extruded bar is subjected to sizing cutting and drilling of a center hole to obtain a titanium alloy drawing tube blank; 3) Subject the titanium alloy drawing tube blank to multi-pass composite drawing to obtain a drawn tube; 4) Subject the drawn tube to solution treatment, water quenching, and aging treatment in sequence to obtain a rough tube product; 5) Subject the rough tube product to straightening, inner hole cleaning, and centerless grinding and polishing of the outer surface to obtain a titanium alloy fine-diameter thick-wall tube with a low yield ratio; The multi-pass composite drawing adopts composite drawing with a long mandrel and a fixed mandrel; insert the mandrel before drawing. The titanium alloy drawing tube blank is subjected to multi-pass composite drawing. During the drawing process, one end of the mandrel is fixed, and the other end passes through the tube. The distance between the fixed end of the mandrel and the drawing die of the tube is 100 - 300 mm smaller than the length of the mandrel. The distance that the mandrel moves along with the tube is 50 - 150 mm. The drawing process within this distance is long mandrel drawing. Then the drawing action stops, and the mandrel is withdrawn in the direction opposite to the drawing direction. The withdrawal distance of the mandrel is equal to the moving distance of the mandrel along with the tube. Then repeat the above drawing and core withdrawal processes in sequence until the multi-pass composite drawing is completed; For the solution treatment in step 4), the temperature is 850 - 920 °C, and the time is 20 - 40 min. For the aging treatment, the temperature is 450 - 500 °C, and the time is 50 - 90 min.

2. The preparation method according to claim 1, characterized in that, In the titanium alloy ingot with ultra-low impurity content in step 1), the mass percentages of impurity elements are as follows: C ≤ 0.08%, N ≤ 0.03%, H ≤ 0.015%, O ≤ 0.10%, Fe ≤ 0.10%, and the mass percentages of other impurity elements are independently ≤ 0.10%; The diameter of the titanium alloy round bar in step 1) is 40 - 60 mm.

3. The preparation method according to claim 1 or 2, characterized in that, The multi-pass hot extrusion processing in step 2) is 2 - 5 passes. The diameter of the extruded bar is 20 - 30 mm. The length of the sizing cutting is 400 - 600 mm, and the diameter of the center hole is 2 - 4 mm.

4. The preparation method according to claim 3, characterized in that, The multi-pass composite drawing in step 3) is 3 - 6 passes. In the multi-pass composite drawing, the diameter of the mandrel is 0.8 - 4 mm, and the diameter of the mandrel decreases with the increase in the number of passes.

5. The preparation method according to claim 4, characterized in that, The titanium alloy drawing tube blank is preheated before multi-pass composite drawing. The preheating temperature is 550 - 620 °C, and the preheating time is 20 - 40 min.

6. The preparation method according to claim 4 or 5, characterized in that, During each pass of the drawing process, the distance between the fixed end of the mandrel and the drawing die of the tube blank is 100 - 300 mm smaller than the length of the mandrel. The distance that the mandrel moves along with the tube blank is 50 - 150 mm. Then the mandrel is withdrawn in the direction opposite to the drawing direction.

7. The preparation method according to claim 6, characterized in that, The straightening in step 5) is multi-roll straightening. During the straightening process, the preheating temperature of the rough tube product is 700 - 750 °C, and the holding time is 20 - 40 min; The reagent for inner hole cleaning is a mixed aqueous solution of hydrofluoric acid and nitric acid. In the mixed aqueous solution, the mass fraction of hydrofluoric acid is 5 - 10%, and the mass fraction of nitric acid is 30 - 40%.

8. The low yield ratio titanium alloy thin-diameter thick-wall tube prepared by the preparation method according to any one of claims 1 to 7, characterized in that, The outer diameter of the titanium alloy fine-diameter thick-wall tube with a low yield ratio is 7 to 15 mm, the inner diameter is 0.6 to 2.0 mm, the length is 1500 to 3000 mm, and the yield ratio is 0.7 to 0.

9.

9. Application of the titanium alloy fine-diameter thick-wall tube with a low yield ratio according to claim 8 as a medical implant material.

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