Low-hydrogen annealing method for titanium alloy plate

Abstract

The invention discloses a titanium alloy plate low-hydrogen annealing method in the technical field of titanium alloy plate heat treatment. The titanium alloy plate low-hydrogen annealing method comprises the following steps that an annealing box with a cover plate is manufactured; a titanium alloy plate to be annealed is stacked in the annealing box, and then the cover plate and the annealing box are sealed; the annealing box is put into an annealing furnace for annealing treatment; and after annealing, taking out the annealing box, air-cooling to room temperature, and then taking out the titanium alloy plate. According to the method, the titanium alloy plates are mainly stacked in the sealable annealing box to be annealed, so that vacuum annealing can be realized in a common annealing furnace, and compared with a mode of directly adopting a vacuum annealing furnace, the method has the advantages that the heating and cooling time in the annealing process can be shortened, and the energy consumption cost is greatly reduced. In addition, the annealing box can be further suitable for annealing treatment of titanium alloy sheets of different specifications in batches, single-batch multi-sheet continuous stacking annealing is achieved, the utilization rate of the annealing box can be increased, the raw material cost can be reduced, and the stability of the single-batch annealing quality is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of heat treatment of titanium alloy plates, in particular to a low-hydrogen annealing method for titanium alloy plates. Background Art

[0002] Titanium and titanium alloys are widely used in aerospace, medical, and other fields due to their high specific strength, fatigue resistance, high-temperature stability, and excellent biocompatibility. However, the overall performance of titanium alloys is significantly affected by impurity elements such as oxygen, nitrogen, and hydrogen, which exist as solid solutions or precipitated compounds, altering the alloy's mechanical properties, corrosion resistance, and processing characteristics. Among the many impurity elements in titanium alloys, hydrogen (H) has a particularly prominent impact. Because the solubility of H in β-Ti is much higher than that in α-Ti, and its solubility in α-Ti decreases sharply with decreasing temperature, brittle hydrides precipitate when the alloy cools to room temperature, causing hydrogen embrittlement and significantly reducing the material's toughness and fatigue properties. Therefore, in many applications, its allowable content is typically controlled to extremely low levels (≤150 ppm, and in the aviation and medical fields, even ≤50 ppm is required).

[0003] During the preparation process of titanium alloys, hydrogen absorption is very likely to occur, especially in the heat treatment (such as non-vacuum annealing) and surface treatment (such as hydrofluoric acid pickling). The main methods for reducing the hydrogen content of finished titanium alloys currently include vacuum annealing and conventional annealing combined with surface treatment, but these methods all have obvious defects. Although vacuum annealing can effectively reduce the hydrogen content, the annealing process has a long heating cycle, high energy consumption costs, and is prone to deformation of the workpiece; conventional annealing is carried out in a non-vacuum environment, which not only increases the risk of hydrogen absorption, but also introduces oxidation problems. The oxide layer needs to be removed by alkaline pickling subsequently, and the pickling process itself will bring new hydrogen contamination risks. In addition, although mechanical milling can directly remove the hydrogen absorption layer, it will cause more than 3% material loss, significantly increasing production costs.

[0004] Titanium alloy sheet, one of the most widely used material types, is typically categorized by thickness range into thin (0.5-4.75mm) and thick (greater than 4.75mm) sheets. These sheets offer excellent processing performance and functionality. However, compared to other material types, thin sheets have a greater surface area in contact with the environment during heat treatment. As thickness decreases and specific surface area increases, the risk of hydrogen absorption increases exponentially. This characteristic makes controlling hydrogen content during thin sheet processing even more critical. Developing precise, cost-effective, and efficient hydrogen control methods has become a key research area in titanium alloy sheet processing technology. Summary of the Invention

[0005] In order to overcome the shortcomings of high cost or high loss in the existing annealing process of finished titanium alloy thin plates, the present invention provides a low-hydrogen annealing method for titanium alloy plates that can significantly reduce energy consumption.

[0006] The technical solution adopted by the present invention to solve its technical problem is: A low-hydrogen annealing method for titanium alloy plates comprises the following steps: Step 1: Make an annealing box with a cover; Step 2: stack the titanium alloy plates to be annealed in the annealing box, and then seal the cover plate and the annealing box; Step 3: placing the annealing box containing the titanium alloy plate into the annealing furnace for annealing; Step 4: After annealing is completed, take out the annealing box and air-cool it to room temperature, then cut off the edges around the cover plate and take out the titanium alloy plate.

[0007] Furthermore, the depth of the annealing box does not exceed 35 mm.

[0008] Furthermore, the annealing box and the cover plate are both made of Q235 steel, and the wall thickness of the annealing box and the cover plate does not exceed 6 mm.

[0009] Furthermore, in step 2, the titanium alloy plate to be annealed is first immersed in an alkaline bath for degreasing, then rinsed and dried, and then placed in an annealing box.

[0010] Furthermore, in step 2, the stacking thickness of the titanium alloy plates does not exceed 80% of the depth of the annealing box.

[0011] Furthermore, in step 2, a vacuum electron beam welder is used to seal and weld the cover plate and the annealing box.

[0012] Furthermore, in step 3, the annealing temperature is +100~200℃, among which, is the annealing temperature, is the melting point temperature of the material.

[0013] Furthermore, in step 3, the temperature return control time is ,in, To control the temperature return time, is the thermal diffusivity (mm² / s), the typical value of titanium alloy is 2.5~3.5mm² / s, 、 、 They are the heating environment temperature (℃), the target temperature reached at the center point (℃), and the initial temperature of the material (℃). is the annealing box wall thickness, .

[0014] Furthermore, in step 3, the insulation control time is ,in, To keep warm control time, is the material coefficient of titanium alloy, ranging from 1.2 to 2.2. It is the thermal insulation index, ranging from 1.0 to 1.5.

[0015] The beneficial effects of the present invention are as follows: a vacuum annealing environment for titanium alloy thin plates is achieved by placing titanium alloy plates into a sealed annealing box, and an ordinary annealing furnace can be used for annealing. Compared with directly using a vacuum annealing furnace, the heating and cooling time of the annealing process can be shortened, and the energy consumption cost can be greatly reduced; at the same time, compared with conventional annealing methods, the risk of hydrogen absorption during thin plate annealing is avoided, and the annealing box can be suitable for batch annealing of titanium alloy thin plates of different specifications, realizing single-batch multi-piece continuous stacking annealing, which can improve the utilization rate of the annealing box, reduce raw material costs, and ensure the stability of the single-batch annealing quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a structural schematic diagram of the annealing box of the present invention; Figure 2 3 is a comparison chart of the hydrogen content before and after annealing of the embodiment of the present invention and the comparative example.

[0017] Marked in the figure, 1-cover plate, 2-titanium alloy plate, 3-annealing box. DETAILED DESCRIPTION

[0018] The present invention will be further described below with reference to the accompanying drawings.

[0019] The present invention provides a low-hydrogen annealing method for a titanium alloy plate, comprising the following steps: Step 1: Make an annealing box 3 with a cover plate 1; Step 2: stack the titanium alloy plate 2 to be annealed in the annealing box 3, and then seal the cover plate 1 and the annealing box 3; Step 3: placing the annealing box 3 containing the titanium alloy plate 2 into the annealing furnace for annealing; Step 4: After annealing is completed, take out the annealing box 3 and air-cool it to room temperature. Then, cut off the edges around the cover plate 1 and take out the titanium alloy plate 2.

[0020] The present invention primarily anneals titanium alloy sheets 2 by stacking them in a sealable annealing box 3. This allows for vacuum annealing in a conventional annealing furnace. Compared to directly using a vacuum annealing furnace, this shortens the heating and cooling times during the annealing process, significantly reducing energy costs. Furthermore, the annealing box 3 is also suitable for batch annealing of titanium alloy sheets of varying specifications, enabling continuous stacking of multiple sheets in a single batch. This improves the utilization rate of the annealing box 3, reduces raw material costs, and ensures the stability of the annealing quality of a single batch.

[0021] Wherein, the structure of annealing box 3 is as follows Figure 1As shown, the annealing box 3 and cover plate 1 can both be made of Q235 steel. Q235 steel has excellent mechanical properties and minimal deformation during annealing. Using it as a carrier for the titanium alloy sheet 2 can prevent deformation of the titanium alloy sheet 2 due to carrier deformation. Furthermore, to prevent the annealing box 3 from being too thick and affecting heat transfer, the wall thickness of the annealing box 3 and cover plate 1 is preferably no more than 6 mm. The size of the annealing box 3 can be designed based on the model of the annealing furnace or the size of the titanium alloy sheet 2, maximizing the number of titanium alloy sheets 2 that can be accommodated in a single annealing cycle.

[0022] At present, many titanium alloy plates 2 are annealed by single-piece annealing. Although the heat transfer is fast, the efficiency is low. Although stacked annealing can anneal multiple plates at a time, if the stack thickness is thick, it will also cause the plate in the middle to heat up slowly, which also affects the efficiency and quality of annealing. Therefore, based on continuous testing and optimization, it is obtained that the depth of the annealing box 3 is preferably not more than 35mm. On this basis, considering that the cover plate 1 itself has a certain thickness and needs to be overlap-welded with the periphery of the annealing box 3, the stacking thickness of the titanium alloy plate 2 is preferably not more than 80% of the depth of the annealing box 3, ensuring that the cover plate 1 does not contact the top titanium alloy plate 2, leaving a certain gap for the titanium alloy plate 2 to expand due to heat, so that the efficiency and quality of annealing can reach an optimal balance.

[0023] During annealing, the oil stains on the surface of the titanium alloy plate 2 may affect the heat transfer efficiency between the stacked plates. Therefore, in step 2, it is best to first immerse the titanium alloy plate 2 to be annealed in an alkaline bath for degreasing, then rinse and dry it, and then place it in the annealing box 3.

[0024] When sealing the cover plate 1 and the annealing box 3, considering that the annealing environment temperature is high, ordinary sealing materials cannot ensure the sealing effect at high temperatures. In addition, there is a certain amount of air in the annealing box 3 itself, and this part of air will also affect the annealing quality of the titanium alloy plate 2. Therefore, in step 2, it is best to use a vacuum electron beam welder to seal the cover plate 1 and the annealing box 3. The electron beam welding parameters can adopt an acceleration voltage of 60~150kV, a beam current of 10~50mA, and a welding speed of 0.5~2m / min. Because the vacuum electron beam welder itself is welded in a vacuum environment, it can ensure that there is a good vacuum state in the annealing box 3 after welding.

[0025] When annealing the titanium alloy plate 2, it is mainly necessary to control the annealing temperature and annealing time, which includes the return to temperature time and the holding time. Since this application adds an annealing box 3 and adopts a stacked annealing method, the annealing temperature and time are different from the conventional annealing method. After continuous comparison and optimization, the annealing process of this application is: the annealing temperature is: +100~200℃, among which, is the annealing temperature, is the melting point of the material. The temperature return control time is: ,in, To control the temperature return time, is the thermal diffusivity (mm² / s), the typical value of titanium alloy is 2.5~3.5mm² / s, 、 、 They are the heating environment temperature (℃), the target temperature reached at the center point (℃), and the initial temperature of the material (℃). is the annealing box wall thickness, The insulation control time is: ,in, To keep warm control time, is the material coefficient of titanium alloy, ranging from 1.2 to 2.2. It is the thermal insulation index, ranging from 1.0 to 1.5.

[0026] The present invention is further described below by way of examples and comparative examples.

[0027] Example 1

[0028] Taking TC4 with a thickness of 1.5×1000×Lmm as an example, annealing treatment is performed according to the annealing process provided by the present invention. The specific implementation method is as follows: Step 1: Immerse the TC4 titanium alloy sheet to be annealed in an alkaline bath for degreasing, followed by secondary rinsing and drying; Step 2: Use a vacuum cup lifter to neatly stack the TC4 sheets processed in step 1 layer by layer into the annealing box. The total stacking thickness is 27 mm. Add a cover plate on top of the stack, and keep the cover plate in close contact with the edge of the annealing box. Step 3: Use a vacuum electron beam welder to continuously seal the edges of the cover plate and the annealing box to form an annealing package with a sealed structure; Step 4: Place the annealing package in step 3 in a roller hearth continuous annealing furnace for annealing at 800°C, with a return temperature control time of 25 minutes and a holding time of 68 minutes; Step 5: After the insulation is completed, the annealing package is removed from the furnace and air-cooled to room temperature. Then the surrounding edges are cut off and the annealed sheet is taken out for surface whitening treatment.

[0029] After the whitening treatment, the TC4 titanium alloy sheet has no obvious color difference on the surface and the overall plate shape is flat. The hydrogen content of the sample taken at the same position before and after annealing increases by 0.0013%. The specific data are as follows: Figure 2 shown.

[0030] Example 2

[0031] Taking TA7ELI with a thickness of 1.0×1050×Lmm as an example, annealing treatment is performed according to the annealing process provided by the present invention. The specific implementation method is as follows: Step 1: Immerse the TA7ELI titanium alloy sheet to be annealed in an alkaline bath for degreasing, followed by secondary rinsing and drying; Step 2: Use a vacuum suction cup lifter to neatly stack the TA7ELI sheets processed in step 1 layer by layer into the annealing box. The total stacking thickness is 22 mm. Add a sealing cover plate on the top of the stack, and keep the cover plate tightly fitted with the edge of the annealing box. Step 3: Use a vacuum electron beam welder to continuously seal the edges of the cover plate and the annealing box to form an annealing package with a sealed structure; Step 4: Place the annealing package in step 3 in a roller hearth continuous annealing furnace for annealing at 750°C, with a return temperature control time of 21 minutes and a holding time of 57 minutes; Step 5: After the insulation is completed, the annealing package is removed from the furnace and air-cooled to room temperature. Then the surrounding edges are cut off and the annealed sheet is taken out for surface whitening treatment.

[0032] After whitening treatment, the TA7ELI titanium alloy sheet has no obvious color difference on the surface and the overall plate shape is good. The hydrogen content change of the sample taken at the same position before and after annealing is 0.0015%. The specific data are as follows: Figure 2 shown.

[0033] Example 3

[0034] Taking the TA15 finished product with a thickness of 2.5×1100×Lmm as an example, the annealing process provided by the present invention is performed, and the specific implementation method is as follows: Step 1: Immerse the TA15 titanium alloy sheet to be annealed in an alkaline bath for degreasing, followed by secondary rinsing and drying; Step 2: Use a vacuum suction cup lifter to neatly stack the TA7ELI sheets processed in step 1 layer by layer into the annealing box. The total stacking thickness is 25 mm. Add a sealing cover plate on the top of the stack, and keep the cover plate tightly fitted with the edge of the annealing box. Step 3: Use a vacuum electron beam welder to continuously seal the edges of the cover plate and the annealing box to form a sealed structure annealing package; Step 4: Place the annealing package in step 3 in a roller hearth continuous annealing furnace for annealing at 780°C, with a return temperature control time of 24 minutes and a holding time of 65 minutes; Step 5: After the insulation is completed, the annealing package is removed from the furnace and cooled to room temperature. Then the surrounding edges are cut off and the annealed sheet is taken out for surface whitening treatment.

[0035] After the whitening treatment, the surface of the TA15 titanium alloy sheet has no obvious color difference and the overall plate shape is flat. The hydrogen content of the sample taken at the same position before and after annealing increases by 0.0010%. The specific data are as follows: Figure 2 shown.

[0036] Comparative Example 1

[0037] This comparative example is TC4 with a thickness of 1.5×1000×Lmm, and is annealed in a conventional manner. The specific implementation method is as follows: Step 1: Immerse the TC4 titanium alloy sheet to be annealed in an alkaline bath for degreasing, followed by secondary rinsing and drying; Step 2: directly stack the TC4 titanium alloy plates in a roller hearth continuous annealing furnace for annealing treatment, with a total stacking thickness of 27 mm, an annealing temperature of 800°C, a temperature return control time of 25 minutes, and a holding time of 68 minutes; Step 3: After the insulation is completed, the furnace body is air-cooled to room temperature, and the annealed plate is taken out for alkaline pickling and surface whitening treatment.

[0038] After the whitening treatment, the TC4 titanium alloy sheet has a flat overall shape. The hydrogen content of the sample taken at the same position before and after annealing is increased by 0.0075%. The specific parameters are as follows: Figure 2 .

[0039] Comparative Example 2

[0040] This comparative example is a TC4 finished product with a thickness of 1.5×1000×Lmm, which is annealed in a vacuum annealing furnace. The specific implementation method is as follows: Step 1: Immerse the TC4 titanium alloy sheet to be annealed in an alkaline bath for degreasing, followed by secondary rinsing and drying; Step 2: directly stack the TC4 titanium alloy plates in a vacuum annealing furnace for annealing treatment, with a total stacking thickness of 27 mm, an annealing temperature of 800°C, heating to a temperature and holding time of 12 hours; Step 3: After the insulation is completed, the vacuum furnace is cooled to room temperature, and the annealed plate is taken out for surface whitening treatment.

[0041] After the whitening treatment, the TC4 titanium alloy sheet has a smooth overall shape. The hydrogen content of the sample taken at the same position before and after annealing is reduced by 0.001%. The specific parameters are as follows: Figure 2 .

[0042] By comparing the annealing time and test data of Example 1, Comparative Example 1, and Comparative Example 2, it can be found that in the annealing process of titanium alloy thin plates of the same grade, specification, and weight, the sample in Comparative Example 1 that did not adopt the technical solution of the present invention was directly exposed to the air environment, resulting in a significant increase in hydrogen content. At the same time, alkaline acid washing was required after surface oxidation, and ultimately failed to meet the high-standard hydrogen control requirements. Comparative Example 2, on the other hand, used a vacuum annealing furnace, and only after heating and holding for 12 hours did all the plate performance meet the standards, and the energy consumption cost was several times that of Example 1. Therefore, the thin-gauge titanium alloy finished product treated by the method of the present invention can not only effectively inhibit hydrogen absorption, but also significantly reduce the production cost of the heat treatment process, ensuring the stability and reliability of product performance.

Claims

1. A low hydrogen annealing method for titanium alloy sheets, characterized in that: The following steps are involved: Step 1: Make an annealing box (3) with a cover plate (1); Step 2: stacking the titanium alloy plates (2) to be annealed in the annealing box (3), and then sealing the cover plate (1) and the annealing box (3); Step 3: placing the annealing box (3) containing the titanium alloy plate (2) into an annealing furnace for annealing; Step 4: After annealing is completed, the annealing box (3) is taken out and air-cooled to room temperature, and then the edges of the cover plate (1) are cut off and the titanium alloy plate (2) is taken out.

2. The low-hydrogen annealing method for titanium alloy sheet according to claim 1, characterized in that: The depth of the annealing box (3) does not exceed 35 mm.

3. The low-hydrogen annealing method for titanium alloy sheet according to claim 2, characterized in that: The annealing box (3) and the cover plate (1) are both made of Q235 steel, and the wall thickness of the annealing box (3) and the cover plate (1) does not exceed 6 mm.

4. The low-hydrogen annealing method for titanium alloy sheet according to claim 1, characterized in that: In step 2, the titanium alloy plate (2) to be annealed is first immersed in an alkaline bath for degreasing, then rinsed and dried, and then placed in an annealing box (3).

5. The low-hydrogen annealing method for titanium alloy sheet according to claim 2, characterized in that: In step 2, the stacking thickness of the titanium alloy plates (2) does not exceed 80% of the depth of the annealing box (3).

6. The low-hydrogen annealing method for titanium alloy sheet according to claim 3, characterized in that: In step 2, a vacuum electron beam welder is used to seal and weld the cover plate (1) and the annealing box (3).

7. The low-hydrogen annealing method for a titanium alloy sheet according to any one of claims 1 to 6, wherein: In step 3, the annealing temperature is +100~200℃, among which, is the annealing temperature, is the melting point temperature of the material.

8. The low-hydrogen annealing method for titanium alloy sheet according to claim 7, characterized in that: In step 3, the temperature return control time is ,in, To control the temperature return time, is the thermal diffusivity (mm² / s), the typical value of titanium alloy is 2.5~3.5mm² / s, 、 、 They are the heating environment temperature (℃), the target temperature reached at the center point (℃), and the initial temperature of the material (℃). is the annealing box wall thickness, .

9. The low-hydrogen annealing method for titanium alloy sheet according to claim 8, characterized in that: In step 3, the insulation control time is ,in, To keep warm control time, is the material coefficient of titanium alloy, ranging from 1.2 to 2.

2. It is the thermal insulation index, ranging from 1.0 to 1.5.

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