A heat treatment method for TC4 titanium alloy wire for medical use

Abstract

The present invention relates to the technical field of heat treatment of metal materials, and in particular to a heat treatment method for TC4 titanium alloy wire for medical use. A heat treatment method for TC4 titanium alloy wire for medical use includes S100, solution treatment, solution annealing, annealing temperature of 700-780°C, holding time of 2-3 hours, and air cooling after being taken out of the furnace; S200, sinusoidal straightening: TC4 titanium alloy coils are opened for sinusoidal straightening, and then cut into straight wires after straightening; S300, aging treatment: the straight titanium wires are arranged and pressed by a pressing plate, and then annealed, annealing temperature range of 500-540°C, after holding for a preset time, air cooling, and staged cooling; S400, fine grinding treatment: fine grinding to the finished product dimensional tolerance, sampling, flattening, and packaging. A heat treatment method for TC4 titanium alloy wire for medical use has the advantages of greatly reducing residual stress, meeting the requirements of relevant standards, improving production efficiency and yield rate, and maintaining stable microstructure, performance, and quality of the finished product.

Description

Technical Field

[0001] The present invention relates to the technical field of heat treatment of metal materials, and in particular to a heat treatment method of a TC4 titanium alloy wire for medical use. Background Art

[0002] Ti-6A1-4V (ELI) titanium alloy, with its lightweight, high specific strength, excellent biocompatibility, and corrosion resistance, is widely used in high-strength surgical implants. After years of development and clinical validation, it has gained widespread recognition within the medical device industry. Titanium alloy rods and wires, as important processing materials, are primarily used to manufacture functional structural materials for human implants, such as long-tail pedicle screws, directional pedicle screws, retrograde femoral intramedullary nails, and connector rods. The unique service environment dictates that raw material rods and wires must not only exhibit excellent microstructure properties but also possess excellent processing properties, such as straightness and dimensional tolerances. Wires with diameters under φ7mm are commonly used in surgical implants. Compared to rods φ8mm and above, wire production processes are more complex and require significantly more stable quality control. This is particularly true after secondary hot rolling, requiring multiple drawing passes in coiled form, which greatly complicates final straightening and performance control. Hot straightening with inclined rollers is the primary straightening method for rods φ8mm and above, resulting in minimal performance changes before and after straightening. The production process for straight wires under 7mm (φ) typically involves coiling and heat treatment, followed by sinusoidal cold straightening and cutting into straight wire. However, straightening leaves significant residual stress, and during tensile testing, the yield strength drops significantly by 10-15% due to the Bauschinger effect, thus failing to meet standard requirements.

[0003] Patent 201921989243.7 invented a method to remove the influence of residual stress on yield strength by adding induction heating before sinusoidal straightening. However, the straightening process is located after the heat treatment, and some residual stress will inevitably remain after the straightening, affecting the strong plasticity and performance stability. In order to ensure the microstructure performance, the annealing temperature is high, and the filaments are prone to form temperature stress after straightening and cooling, causing secondary deformation and bending. In addition, the production efficiency is low, and the output per hour is only 3 to 8 kg.

[0004] Patent 202220482201.X improves the surface quality of wire by reducing friction between the straightening die and the wire in a sinusoidal straightening device. Patent 200910254558.1 invents a vertical electrothermal tension straightener capable of straightening rods and wires with sizes ranging from 5 to 13 mm. However, it can only perform tension straightening on a single wire at a time, resulting in low efficiency. Each wire requires a margin at the clamping end, resulting in a low yield rate. Furthermore, due to the high-power, short-term heating, overheating is very likely to occur, affecting the structural properties and quality stability. Therefore, based on the shortcomings of existing straightening methods and the heat treatment characteristics of titanium alloys, a new method has been proposed. Summary of the Invention

[0005] In view of this, the present invention aims to provide a heat treatment method for TC4 titanium alloy wire for medical use. The method employs S100 solution treatment: After drawing, the coil undergoes solution annealing in a vacuum or atmospheric annealing furnace at a temperature of 700-780°C for 2-3 hours, followed by air cooling after removal from the furnace. A second, sinusoidal straightening step: The TC4 titanium alloy coil undergoes open-coil sinusoidal straightening and is then cut into straight wires. A third, aging treatment step: I25b steel, made of Q235, with cross-sectional dimensions of 250×118×10mm, meeting the GB / T 706-2016 "Hot-rolled Steel Sections" standard, and a length of 3500mm is used. Before the titanium wire is laid, the inner surface of the channel steel is cleaned and a ceramic anti-oxidation coating is applied to the inner wall. The titanium wire is placed at a height of ≤40mm, followed by a flexible liner with a thickness of 0.5-2mm. Finally, a steel plate pressure plate is placed, with a thickness of 20-50mm and an unevenness of ≤3mm / m. The titanium wire is laid out from bottom to top, following the principle of thicker materials first, thinner materials second, and longer materials second, shorter materials third. After the laying of the wires is completed, the temperature is raised to the predetermined annealing temperature, which ranges from 500-540°C. The holding time is calculated as t = (total height of the titanium wire × K + 30-60) min, where K is the insulation efficiency coefficient, which is 1.8-2.0 min / mm. After the holding time, the furnace door is opened 20-50mm to cool to 350-400°C, then opened 80-150mm to cool to 100-200°C, and then removed from the furnace and air-cooled to room temperature. The fourth step is fine grinding: fine grinding to the finished product's dimensional tolerance, sampling, flattening, and packaging. It solves the problems of leaving more residual stress after straightening, which does not meet the standard requirements; the filaments are prone to form temperature stress after straightening and cooling, causing secondary deformation and bending, low production efficiency, and the need to reserve a margin at the clamping end of both rods and wires, resulting in a low yield rate. At the same time, due to high-power short-term heating, overburning is very likely to occur, affecting the organizational performance and quality stability.

[0006] To solve the above problems, the present invention provides a heat treatment method for medical TC4 titanium alloy wire, comprising:

[0007] S100, solution treatment, after drawing, the coil is solution annealed in a vacuum annealing furnace or an atmospheric annealing furnace, the annealing temperature is 700-780℃, the holding time is 2-3h, and it is air-cooled after being taken out of the furnace;

[0008] S200, Sine straightening: TC4 titanium alloy coil is subjected to open sine straightening and then cut into straight wires;

[0009] S300, aging treatment, after the straight titanium wire is placed, it is pressed by a pressing plate on the top, and then annealed. The annealing temperature range is 500-540℃. After annealing, it is kept warm for a preset time and then air-cooled. The air cooling adopts a staged cooling method.

[0010] S400, fine grinding: fine grinding to the finished product size tolerance, sampling, flattening, and packaging.

[0011] Furthermore, in step S300, the method of placing the titanium wire includes:

[0012] Place the titanium wire into the slotted space and press it tightly with a pressing plate.

[0013] Furthermore, the trough-shaped space is made of section steel, and the section steel is made of Q235;

[0014] The height of the titanium wire placed in the channel steel is ≤40mm.

[0015] Furthermore, the steel section is I25b steel section, and according to the GB / T 706-2016 "Hot-rolled steel section" standard, the cross-sectional dimensions adopted are 250×118×10 mm and the length is 3500 mm.

[0016] Furthermore, the inner wall of the steel section is coated with a ceramic anti-oxidation coating.

[0017] Furthermore, the pressing plate is a steel plate with a thickness of 20 to 50 mm, and the unevenness of the steel plate is ≤ 3 mm / m;

[0018] A lining plate is arranged between the steel plate and the titanium wire, and the lining plate is a titanium plate with a thickness of 0.5 to 2 mm.

[0019] Furthermore, the titanium wire is placed according to the principle of thick first and thin later, long first and short later from bottom to top.

[0020] Furthermore, the preset annealing time is tmin, which is calculated by formula (1);

[0021] t=(H×K+30~60)min………………(1)

[0022] Among them, H is the height of the titanium wire;

[0023] K-thermal insulation effectiveness coefficient, take 1.8~2.0min / mm;

[0024] Furthermore, in step S300, the staged air cooling method includes:

[0025] The furnace door is opened to a first preset opening, the temperature is cooled to the first preset temperature range, the furnace door is opened to a second preset opening, the temperature is cooled to the second preset temperature range, and finally the furnace is taken out of the furnace and cooled to room temperature.

[0026] Furthermore, the first preset opening is 20-50 mm, and the first preset temperature range is 350-400° C.;

[0027] The second preset opening is 80-150 mm, and the first preset temperature range is 100-200°C.

[0028] Compared with the prior art, the heat treatment method of medical TC4 titanium alloy wire described in the present invention has the following advantages:

[0029] The advantages of this technical solution are that it greatly reduces residual stress, meets the requirements of relevant standards, improves production efficiency and yield rate, and ensures stable microstructure, performance and quality of finished products. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the swinging structure of the titanium alloy wire according to an embodiment of the present invention.

[0031] Description of reference numerals:

[0032] 1-Titanium wire, 2-Steel, 3-Liner, 4-Pressing plate, 5-Paint. DETAILED DESCRIPTION

[0033] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0034] In the present invention, the descriptions involving "first," "second," "upper," and "lower," etc. are for descriptive purposes only and should not be understood as indicating or implying their relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined as "first," "second," "upper," and "lower" may explicitly or implicitly include at least one of such features. In addition, the technical solutions between the various embodiments may be combined with each other, but this must be based on the fact that they can be implemented by a person of ordinary skill in the art. When the technical solutions between the embodiments can be combined, they are all within the scope of protection claimed by the present invention.

[0035] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0036] like Figure 1 As shown, a heat treatment method for TC4 titanium alloy wire for medical use comprises:

[0037] S100, solution treatment, after drawing, the coil is solution annealed in a vacuum annealing furnace or an atmospheric annealing furnace, the annealing temperature is 700-780℃, the holding time is 2-3h, and it is air-cooled after being taken out of the furnace;

[0038] S200, Sine straightening: TC4 titanium alloy coil is subjected to open sine straightening and then cut into straight wires;

[0039] S300, aging treatment, such as Figure 1As shown, I25b steel 2 is made of Q235 steel with cross-sectional dimensions of 250*118*10mm, meeting the GB / T 706-2016 "Hot-rolled Steel" standard, and a length of 3500mm. Before placing the titanium wire, clean the inner surface of the channel steel. To prevent adhesion between the steel and titanium plates, oxidation of the steel plates, and the intrusion of foreign matter into the titanium plates, direct contact between the titanium wire 1 and the steel is avoided. A ceramic anti-oxidation coating 5 is applied to the inner surface. After the coating 5 has fully dried, the titanium wire 1 is pressed and laid out, with a height of ≤40mm. A liner 3 made of titanium plate with a thickness of 0.5-2mm and a certain degree of flexibility is then placed on top. Finally, a steel plate pressure plate 4 is placed, with a thickness of 20-50mm and the same length as the steel 2. The unevenness of the steel plate 4 should be ≤3mm / m. The titanium wire 1 is laid out from bottom to top, following the principle of thicker material first, thinner material later, and longer material later, shorter material later.

[0040] After the swinging is completed, the temperature is raised to the predetermined annealing temperature, which is in the range of 500-550°C. To ensure that the titanium wire is fully heated through, it is air-cooled after a preset time of heat preservation after annealing. The preset annealing time is tmin, which is calculated by formula (1);

[0041] t=(H×K+30~60)min………………(1)

[0042] Among them, H is the height of the titanium wire;

[0043] K-thermal insulation effectiveness coefficient, take 1.8~2.0min / mm.

[0044] During air cooling, the temperature is lowered in stages, i.e., the furnace door is opened to a first preset opening, the temperature is cooled to the first preset temperature range, then the furnace door is opened to a second preset opening, the temperature is cooled to the second preset temperature range, and finally the furnace is removed from the furnace and cooled to room temperature. Preferably, the first preset opening is 20-50mm, and the first preset temperature range is 350-400°C; the second preset opening is 80-150mm, and the first preset temperature range is 100-200°C.

[0045] S400, fine grinding: fine grinding to the finished product size tolerance, sampling, flattening, and packaging.

[0046] Example 1

[0047] S100, solution treatment: the φ2.7mm round coil after drawing is solution annealed in a vacuum annealing furnace or an atmospheric annealing furnace, the annealing temperature is 750℃, the holding time is 2h, and it is air-cooled after being taken out of the furnace.

[0048] S200, Sine straightening: The TC4 titanium alloy coil is opened for sinusoidal straightening and then cut into straight wires.

[0049] S300, Aging Treatment: Use I25b steel, made of Q235, with cross-sectional dimensions of 250*118*10mm, meeting the GB / T 706-2016 "Hot-rolled Steel" standard, and a length of 3500mm. Before placing the titanium wire, clean the inner surface of the channel steel. To prevent adhesion between the steel and titanium plates, oxidation of the steel plates, and the intrusion of foreign matter into the titanium plates, direct contact between the titanium wire and the steel should be avoided. Apply a ceramic anti-oxidation coating to the inner surface. After the coating has fully dried, pressurize the titanium wires and lay them at a height of 37.8mm. A flexible titanium liner, 0.5mm thick, is then placed on top. Finally, a 20mm thick steel plate, the same length as the section steel, is placed, with an unevenness of ≤3mm / m.

[0050] After the material is placed, the temperature is raised to the predetermined annealing temperature, which is within the range of 500°C. To ensure that the titanium wire is fully heated through, the holding time is set to t = 120 minutes. To avoid bending defects caused by sudden cooling, after the holding time, the furnace door is opened 20mm to cool to 350°C, then opened 80mm to cool to 100°C, and then taken out of the furnace and air-cooled to room temperature.

[0051] S400, fine grinding: fine grinding to the finished product size tolerance, sampling, flattening, and packaging.

[0052] The mechanical properties and straightness of the finished φ2.5mm TC4 wire are shown in Table 1.

[0053] Example 2

[0054] S100, solution treatment: the φ4.3mm round coil after drawing is solution annealed in a vacuum annealing furnace or an atmospheric annealing furnace, the annealing temperature is 700℃, the holding time is 2.5h, and it is air-cooled after being taken out of the furnace.

[0055] S200, Sine straightening: The TC4 titanium alloy coil is opened for sinusoidal straightening and then cut into straight wires.

[0056] S300, Aging Treatment: Use I25b steel, made of Q235, with cross-sectional dimensions of 250*118*10mm, meeting the GB / T 706-2016 "Hot-rolled Steel" standard, and a length of 3500mm. Before placing the titanium wire, clean the inner surface of the channel steel. To prevent adhesion between the steel and titanium plates, oxidation of the steel plates, and the intrusion of foreign matter into the titanium plates, direct contact between the titanium wire and the steel should be avoided. Apply a ceramic anti-oxidation coating to the inner surface. After the coating has fully dried, pressurize the titanium wires and lay them at a height of 38.7mm. A flexible titanium liner, 0.5mm thick, is then placed on top. Finally, a steel plate pressure plate is placed. The plate should be 40mm thick and the same length as the section steel, with an unevenness of ≤3mm / m.

[0057] After the material is placed, the temperature is raised to the predetermined annealing temperature, which is within the range of 530°C. To ensure that the titanium wire is fully heated through, the holding time is set to t = 130 minutes when the temperature reaches the temperature. To avoid bending defects caused by sudden cooling, after the holding time, the furnace door is opened 20mm to cool to 350°C, then opened 80mm to cool to 100°C, and then taken out of the furnace and air-cooled to room temperature.

[0058] S400, fine grinding: fine grinding to the finished product size tolerance, sampling, flattening, and packaging.

[0059] The mechanical properties and straightness of the finished φ4.0mm TC4 wire are shown in Table 1.

[0060] Example 3:

[0061] S100, solution treatment: the φ6.3mm round coil after drawing is solution annealed in a vacuum annealing furnace or an atmospheric annealing furnace, the annealing temperature is 750℃, the holding time is 2.5h, and it is air-cooled after being taken out of the furnace.

[0062] S200, Sine straightening: The TC4 titanium alloy coil is opened for sinusoidal straightening and then cut into straight wires.

[0063] S300, Aging Treatment: Use I25b steel, made of Q235, with cross-sectional dimensions of 250*118*10mm, meeting the GB / T 706-2016 "Hot-rolled Steel" standard, and a length of 3500mm. Before placing the titanium wire, clean the inner surface of the channel steel. To prevent adhesion between the steel and titanium plates, oxidation of the steel plates, and the intrusion of foreign matter into the titanium plates, direct contact between the titanium wire and the steel should be avoided. Apply a ceramic anti-oxidation coating to the inner surface. After the coating has fully dried, pressurize the titanium wires and lay them at a height of 37.8mm. A flexible titanium liner, 0.5mm thick, is then placed on top. Finally, a 50mm thick steel plate, the same length as the section steel, is placed, with an unevenness of ≤3mm / m.

[0064] After the material is placed, the temperature is raised to the predetermined annealing temperature, which is within the range of 540°C. To ensure that the titanium wire is fully heated through, the holding time is set to t = 135 minutes. To avoid bending defects caused by sudden cooling, after the holding time, the furnace door is opened 50mm to cool to 350°C, then opened 100mm to cool to 200°C, and then taken out of the furnace and air-cooled to room temperature.

[0065] S400, fine grinding: fine grinding to the finished product size tolerance, sampling, flattening, and packaging.

[0066] The mechanical properties and straightness of the finished φ6.0mm TC4 wire are shown in Table 1.

[0067] Table 1

[0068]

[0069] As can be seen from Table 1, the TC4 titanium alloy wire with a diameter of less than φ7 mm prepared by the heat treatment method of the present invention fully meets the requirements of the GB / T 13810-2017 standard, and has a tensile strength Rm ≥ 1030 MPa, a straightness ≤ 0.3 mm / m, and a straightness ≤ 0.5 mm / piece.

[0070] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined by the claims.

Claims

1. A heat treatment method for TC4 titanium alloy wire for medical use, characterized in that: include: S100, solution treatment, after drawing, the coil is solution annealed in a vacuum annealing furnace or an atmospheric annealing furnace, the annealing temperature is 700-780℃, the holding time is 2-3h, and it is air-cooled after being taken out of the furnace; S200, Sine straightening: TC4 titanium alloy coil is subjected to open sine straightening and then cut into straight wires; S300, aging treatment, after the straight titanium wire is placed, it is pressed by a pressing plate on the top, and then annealed. The annealing temperature range is 500~540℃. After annealing, it is kept warm for a preset time and then air-cooled. The air cooling adopts a staged cooling method. The preset annealing time is tmin, which is calculated by formula (1); t=(H×K+30~60)min………………(1) Among them, H is the height of the titanium wire; K-thermal insulation effectiveness coefficient, take 1.8~2.0min / mm; Staged air cooling methods include: Open the furnace door to a first preset opening, cool the temperature to a first preset temperature range, then open the furnace door to a second preset opening, cool the temperature to a second preset temperature range, and finally take the furnace out of the furnace and cool to room temperature; The first preset opening is 20-50 mm, and the first preset temperature range is 350-400° C. The second preset opening is 80-150 mm, and the first preset temperature range is 100-200°C; S400, fine grinding: fine grinding to the finished product size tolerance, sampling, flattening, and packaging.

2. The heat treatment method of medical TC4 titanium alloy wire according to claim 1, characterized in that: In step S300, the method for placing the titanium wire includes: Place the titanium wire into the slotted space and press it tightly with a pressing plate.

3. The heat treatment method of medical TC4 titanium alloy wire according to claim 2, characterized in that: The trough space is made of Q235 steel. The height of the titanium wire placed in the channel steel is ≤40mm.

4. The heat treatment method of medical TC4 titanium alloy wire according to claim 3, characterized in that: The steel section is I25b steel section. According to the GB / T 706-2016 "Hot-rolled Steel Section" standard, the cross-sectional dimensions adopted are 250×118×10mm and the length is 3500mm.

5. The heat treatment method of medical TC4 titanium alloy wire according to claim 4, characterized in that: The inner wall of the steel section is coated with a ceramic anti-oxidation coating.

6. The heat treatment method of medical TC4 titanium alloy wire according to claim 2, characterized in that: The pressing plate is a steel plate with a thickness of 20 to 50 mm, and the unevenness of the steel plate is ≤ 3 mm / m; A lining plate is arranged between the steel plate and the titanium wire, and the lining plate is a titanium plate with a thickness of 0.5-2 mm.

7. The heat treatment method of medical TC4 titanium alloy wire according to claim 2, characterized in that: The titanium wire is placed from bottom to top in the principle of thick first and thin later, long first and short later.

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