A method for improving heat treatment effect of duplex titanium alloy plate

Abstract

This invention provides a method for improving the heat treatment effect of duplex titanium alloy sheets, comprising the following steps: Step S1. A titanium alloy slab is hot-rolled in multiple passes, with the reduction in each pass controlled to be 10-20 mm, to obtain sheet one; Step S2. Sheet one after hot rolling in Step S1 is annealed once; Step S3. Sheet one after high-temperature annealing in Step S2 is warm-rolled, then straightened using a hot straightening process, and then cooled to obtain sheet two; Step S4. Sheet two after Step S3 is annealed a second time, and the finished product is obtained through finishing treatment. This method for improving the heat treatment effect of duplex titanium alloy sheets utilizes the 15%-20% thickness allowance during hot rolling and the annealing temperature to deform the microstructure, introducing dislocation defects into the microstructure, and precipitating fine grains in the non-precipitate region, thereby improving the strength of the sheet.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy rolling technology, specifically a method for improving the heat treatment effect of duplex titanium alloy sheets. Background Technology

[0002] Titanium alloys, due to their high specific strength and corrosion resistance, have been widely used in modern development. In particular, titanium alloy plates are used as key components in aerospace, aviation, and marine industries. Titanium alloys are generally classified into α, α+β, and β titanium alloys, among which α+β titanium alloys are the most widely used. α+β titanium alloys, also known as duplex titanium alloys, possess excellent comprehensive performance and are widely used in aerospace, marine engineering, and chemical engineering. Duplex titanium alloys exhibit diverse microstructures. By employing different heat treatment processes, various microstructures can be obtained, including Widmanstätten structure, basketweave structure, biphase, and equiaxed structure. Due to the temperature sensitivity of titanium alloys, heat treatment typically requires a significant amount of time to complete the microstructure transformation, and the heating temperature, heating time, and cooling time are all crucial factors. A series of factors, including the production process, affect the microstructure and properties of titanium alloy sheets, resulting in long production cycles and high costs. The microstructure of the sheet material has a significant impact on the alloy's properties, including the size, distribution, and morphology of the grains. Duplex titanium alloy sheets can have their microstructure altered through a double annealing heat treatment process after hot working. However, the double annealing process has already pushed the strength performance of titanium alloy sheets to its limit, and further improvements may not be possible to achieve the optimal strength-ductility balance of duplex titanium alloys. This invention further enhances the strength performance of the sheet material by introducing small-deformation warm rolling on top of the double annealing heat treatment process. Summary of the Invention

[0003] The purpose of this invention is to overcome and supplement the shortcomings of existing technologies, and to provide a method for improving the heat treatment effect of duplex titanium alloy plates, thereby improving the strength properties of duplex titanium alloy plates and reducing the heat treatment time. Based on the traditional double annealing process, this invention uniquely proposes a method to improve the microstructure strength through small-deformation warm rolling. In actual production, the residual temperature of high-temperature annealing can be used for warm rolling, causing deformation of the microstructure and introducing a large number of dislocation defects. Then, through annealing, secondary α-dislocations are formed at the defect locations. s The increased interphase size enhances the alloy's strength. Furthermore, warm rolling deformation can accelerate microstructural transformation and reduce the heat treatment time of titanium alloy sheets.

[0004] The technical solution adopted in this invention is:

[0005] A method for improving the heat treatment effect of duplex titanium alloy sheets, comprising the following steps:

[0006] Step S1. Perform multiple hot rolling passes on a titanium alloy slab, controlling the reduction in each hot rolling pass to be 10-20mm, to obtain plate 1;

[0007] Step S2. Anneal the sheet material after hot rolling in step S1;

[0008] Step S3. The high-temperature annealed sheet material from step S2 is subjected to warm rolling, and then the sheet material is straightened using a hot straightening process, followed by cooling to obtain sheet material two.

[0009] Step S4. The second sheet material from step S3 is subjected to secondary annealing, and then finished through finishing treatment to obtain the finished product.

[0010] Preferably, in the method for improving the heat treatment effect of duplex titanium alloy sheet, the first annealing in step S2 specifically involves: feeding the hot-rolled sheet into a roller hearth furnace, controlling the temperature in the roller hearth furnace to rise to a first temperature at a rate of 8-15℃ / min, holding it at that temperature for 30 minutes, and then cooling the roller hearth furnace to a second temperature and holding it at that temperature for 1-2 hours.

[0011] Preferably, in the method for improving the heat treatment effect of duplex titanium alloy sheet, the first temperature is 80-100℃ lower than the β-phase transformation point temperature of the titanium alloy sheet, and the second temperature is 150-200℃ lower than the β-phase transformation point temperature of the titanium alloy sheet.

[0012] Preferably, in the method for improving the heat treatment effect of duplex titanium alloy sheet, the temperature during warm rolling in step S3 is 20-50°C lower than the second temperature.

[0013] Preferably, in the method for improving the heat treatment effect of duplex titanium alloy sheet, the temperature during straightening in step S3 is 50-100℃ lower than the second temperature, and the straightening speed is 0.5-1m / s.

[0014] Preferably, in the method for improving the heat treatment effect of duplex titanium alloy sheet, the rolling reduction in step S3 is 15%-20% of the finished thickness; and the grinding amount in step S4 is 0.2-0.5 mm.

[0015] Preferably, in the method for improving the heat treatment effect of duplex titanium alloy sheet, the temperature of the secondary annealing in step S4 is 500℃-700℃, and the annealing time is 1-3h.

[0016] Advantages of this invention:

[0017] (1) The method of the present invention for improving the heat treatment effect of duplex titanium alloy plates utilizes the pre-reserved 15%-20% finished thickness during hot rolling and the temperature during annealing to deform the microstructure. By introducing dislocation defects into the microstructure, fine secondary α particles can be precipitated in the β matrix through subsequent annealing.s This strengthens the structure and improves the strength of the board.

[0018] (2) The method of improving the heat treatment effect of duplex titanium alloy sheet of the present invention introduces small deformation warm rolling during double annealing. It can directly perform warm rolling at the temperature of high temperature annealing treatment, and only one rolling pass is needed. After hot straightening, the sheet shape can be maintained. This method can provide driving force for the microstructure through deformation, induce the microstructure to transform faster, and reduce the annealing time. Attached Figure Description

[0019] Figure 1 This diagram illustrates the double annealing process and the introduction of a small deformation warm rolling process of the present invention. Wherein a represents the process without warm rolling; b represents the process with warm rolling.

[0020] Figure 2 The images show the microstructure of the plates prepared in Example 1 and Comparative Example 1. Detailed Implementation

[0021] The present invention will be further described below with reference to specific embodiments.

[0022] Example 1

[0023] A method for improving the heat treatment effect of duplex titanium alloy sheets, comprising the following steps:

[0024] Step S1, Hot Rolling Thickness Reserve: Based on the dimensions of the finished sheet, a TC4 slab with a thickness of 250mm is hot rolled. This process is a conventional multi-pass rolling. In this embodiment, the final finished sheet thickness is 30mm, and the reduction per pass is 15mm. To ensure that a 5mm thickness reserve can be made in the subsequent small deformation warm rolling step S3, the reduction per pass needs to be reduced during the hot rolling process. In addition, a 0.3mm grinding allowance also needs to be reserved. Therefore, the final thickness of the hot-rolled sheet should be 30mm (finished thickness) + 5mm (reserved thickness) + 0.3mm (grinding allowance), which is 35.3mm.

[0025] Step S2, High-temperature annealing: The sheet material after hot rolling in step S1 is sent into a roller hearth furnace for primary annealing. According to the phase transformation point of TC4, which is 980℃, the primary annealing temperature is 880℃, and it is held for 0.5h. Then, it is cooled down to 800℃ and held for 1h.

[0026] Step S3, small deformation warm rolling: After the high temperature annealing and heat preservation is completed, the plate from step S2 is taken out directly and fed into the rolling mill through the transport rollers for warm rolling. The reduction is 5mm, the rolling speed is 2m / s, the rolling temperature is controlled above 750℃, the temperature of hot straightening is not lower than 700℃, and after rolling is completed, it is air cooled to room temperature on the cooling bed.

[0027] Step S4, Annealing: The sheet material rolled in step S3 is subjected to a second annealing at a temperature of 580℃ for 2 hours, followed by air cooling to room temperature. After heat treatment, the sheet material is subjected to finishing processes such as grinding to remove the surface oxide layer, micro-cracks, and oil stains, ultimately yielding a 30mm thick finished sheet material.

[0028] Example 2

[0029] A method for improving the heat treatment effect of duplex titanium alloy sheets, comprising the following steps:

[0030] Step S1, Hot Rolling Thickness Reserve: Based on the dimensions of the finished sheet, a 100mm thick TC11 slab is hot rolled. This process is a conventional multi-pass rolling. In this embodiment, the final finished sheet thickness is 18mm, and the reduction per pass can be 12mm. To ensure a 2.5mm thickness reserve is available in the subsequent small deformation warm rolling step 3, the reduction per pass needs to be reduced during hot rolling. Additionally, a 0.2mm grinding allowance needs to be reserved. Therefore, the final thickness of the hot-rolled sheet should be 18mm (finished thickness) + 2.5mm (reserved thickness) + 0.2mm (grinding allowance), which is 20.7mm.

[0031] Step S2, High-temperature annealing: The hot-rolled sheet from step 1 is sent into a roller hearth furnace for heating and annealing. Based on the phase transformation point of TC11 being 995℃, the annealing temperature can be set to 950℃, held for 0.5 hours, and then cooled to 850℃ and held for 1 hour.

[0032] Step S3, small deformation warm rolling: After the high temperature annealing and heat preservation is completed, the plate from step S2 is directly taken out and fed into the rolling mill through the transport rollers for warm rolling. The reduction is 2.5mm, the rolling speed is 2m / s, the rolling temperature is controlled above 800℃, the temperature of hot straightening is not lower than 750℃, and after rolling is completed, it is air cooled to room temperature on the cooling bed.

[0033] Step S4, Annealing: The sheet material rolled in step S3 is subjected to a second annealing at a temperature of 650℃ for 2 hours, followed by air cooling to room temperature. After heat treatment, the sheet material is polished and other finishing processes to remove the surface oxide layer, micro-cracks and oil stains, finally obtaining an 18mm thick finished sheet material.

[0034] Example 3

[0035] A method for improving the heat treatment effect of duplex titanium alloy sheets, comprising the following steps:

[0036] Step S1, Hot Rolling Reserve: Hot Rolling Thickness Reserve: According to the size of the finished plate, a TC21 slab with a thickness of 150mm is hot rolled. This process is a conventional multi-pass rolling process with a grinding amount of 0.2mm. In this embodiment, the final finished plate thickness is 18mm, and the reduction per pass is 18mm. To ensure that a thickness of 2.5mm can be reserved in the small deformation warm rolling in the subsequent step S3, the reduction per pass needs to be reduced during the hot rolling process. In addition, a grinding amount of 0.2mm needs to be reserved according to the finished plate. Therefore, the final thickness of the hot-rolled plate should be 18mm finished thickness + 2.5mm reserved thickness + 0.2mm grinding amount, which is 20.7mm.

[0037] Step S2, High-temperature annealing: The sheet material after hot rolling in step S1 is sent into a roller hearth furnace for heating and annealing. According to the phase transformation point of TC21, which is 950℃, the annealing temperature can be set to 850℃, held for 0.5h, and then cooled to 800℃ and held for 1h.

[0038] Step S3, small deformation warm rolling: After the high temperature annealing and heat preservation is completed, the plate from step S2 is directly taken out and fed into the rolling mill through the transport rollers for warm rolling. The reduction is 2.5mm, the rolling speed is 2m / s, the rolling temperature is controlled above 750℃, the temperature of hot straightening is not lower than 700℃, and after rolling is completed, it is air cooled to room temperature on the cooling bed.

[0039] Step S4, Annealing: The sheet material rolled in step S3 is subjected to a second annealing at a temperature of 550℃ for 2 hours, followed by air cooling to room temperature. After heat treatment, the sheet material is polished and other finishing processes to remove the surface oxide layer, micro-cracks and oil stains, finally obtaining an 18mm thick finished sheet material.

[0040] Comparative Example 1

[0041] A method for improving the heat treatment effect of duplex titanium alloy sheets, comprising the following steps:

[0042] A TC4 sheet of the same specifications as in Example 1, with a thickness of 250 mm, was hot-rolled to a thickness of 30.3 mm. After rolling, a high-temperature annealing temperature of 880°C was set and held for 0.5 hours, followed by cooling to 800°C and holding for 1 hour. After air cooling to room temperature, a second annealing treatment was performed, heating to 590°C in a resistance furnace and holding for 4 hours. After holding, the sheet was removed and air-cooled to room temperature. Finishing processes, including grinding, were then performed to remove surface oxide layers, micro-cracks, and oil stains, ultimately yielding a 30 mm thick finished sheet.

[0043] Comparative Example 2

[0044] A method for improving the heat treatment effect of duplex titanium alloy sheets, comprising the following steps:

[0045] A 100mm thick TC11 sheet of the same specifications is hot-rolled to a thickness of 18.2mm. After rolling, the first annealing temperature is set to 950℃ and held for 0.5 hours, then cooled to 850℃ and held for 1 hour. After air cooling to room temperature, a second annealing treatment is performed by heating to 650℃ in a resistance furnace and holding for 4 hours. After holding, it is removed and air-cooled to room temperature. Then, it undergoes finishing treatments such as grinding to remove the surface oxide layer, micro-cracks, and oil stains, finally obtaining an 18mm thick finished sheet.

[0046] Comparative Example 3

[0047] A method for improving the heat treatment effect of duplex titanium alloy sheets, comprising the following steps:

[0048] A 150mm thick TC21 sheet of the same specification is hot-rolled to a thickness of 18.2mm. After rolling, the first annealing temperature is set to 950℃ and held for 0.5 hours, then cooled to 850℃ and held for 1 hour. After air cooling to room temperature, a second annealing treatment is performed by heating to 550℃ in a resistance furnace and holding for 4 hours. After holding, it is removed and air-cooled to room temperature. Then, it undergoes finishing treatments such as grinding to remove the surface oxide layer, micro-cracks, and oil stains, finally obtaining an 18mm thick finished sheet.

[0049] Samples were taken from the plates of Comparative Example 1 (untreated) and Example 1 (treated). The untreated sample was labeled 'a', and the treated sample was labeled 'b'. The marked samples were sanded and polished. The etching solution used was HF + HNO3 + H2O (volume ratio 1:2:7). The microstructure of the alloy was observed using a field emission scanning electron microscope. Figure 2 As shown in the figure, label 1 represents the secondary α phase, label 2 represents the β phase matrix, and label 3 represents the secondary α phase. s Phase, it is very obvious that extremely fine secondary α phases exist in the microstructure of the warm-rolled sample. s The phase is densely distributed on the β matrix, and these fine grains play a role in grain refinement and strengthening of the microstructure. In addition, the grain size of sample a after annealing for 4 hours is almost the same as that of sample b after annealing for 2 hours. This proves that the introduction of warm rolling accelerates the transformation process of the microstructure, thereby reducing the heat treatment time to a certain extent.

[0050] Standard tensile specimens with dimensions of Φ8mm×100mm and a middle gauge length of Φ5mm×25mm were prepared from the plates of Examples 1-3 and Comparative Examples 1-3 along the rolling direction of the plate. Three specimens were subjected to tensile testing for each treatment method, and the average value was taken as the result. The test results are shown in Table 1.

[0051] Table 1

[0052] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 tensile strength 1039MPa 1206MPa 1246MPa 958MPa 1130MPa 1157MPa Yield strength 938MPa 1110MPa 1134MPa 873MPa 1049MPa 1071MPa elongation 14.5％ 8.2％ 12.7％ 15.7％ 9.3％ 14.3％

[0053] As shown in Table 1, compared with Comparative Example 1, the tensile strength of the warm-rolled sheet of Example 1 increased by approximately 81 MPa and the yield strength increased by 65 MPa. Overall, the introduction of small deformation warm rolling significantly improved the strength of the sheet. Compared with Comparative Example 2, the tensile strength of the warm-rolled sheet of Example 2 increased by approximately 76 MPa and the yield strength increased by 61 MPa. Compared with Comparative Example 3, the tensile strength of the warm-rolled sheet of Example 3 increased by approximately 89 MPa and the yield strength increased by 63 MPa.

[0054] The method for improving the heat treatment effect of titanium alloy plates according to the present invention has the advantage that, compared with the ordinary double annealing heat treatment process, only one additional warm rolling pass is needed to improve the room temperature tensile strength and reduce the subsequent annealing time; in addition, the warm rolling process used in the present invention can utilize the residual heat after annealing for rolling, reducing the time required for cooling and reheating.

[0055] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for improving the heat treatment effect of duplex titanium alloy plates, characterized in that: Includes the following steps: Step S1. A titanium alloy slab is hot rolled in multiple passes, with the reduction in each pass controlled to be 10-20 mm, to obtain plate 1. Step S2. Anneal the sheet material obtained in step S1 once; Step S3. The high-temperature annealed sheet material from step S2 is subjected to warm rolling. The rolling reduction is 15%-20% of the finished thickness. The sheet material is then straightened using a hot straightening process and cooled to obtain sheet material two. Step S4. The second sheet material from step S3 is subjected to a second annealing, followed by finishing to obtain the finished product; The first annealing in step S2 is as follows: the hot-rolled plate is fed into a roller hearth furnace, and the temperature in the roller hearth furnace is raised to the first temperature at a rate of 8-15℃ / min, held for 30min, and then the roller hearth furnace is cooled to the second temperature and held for 1-2h. The first temperature is 80-100℃ lower than the β phase transformation point temperature of the titanium alloy slab, and the second temperature is 150-200℃ lower than the β phase transformation point temperature of the titanium alloy slab. The temperature during warm rolling in step S3 is 20-50℃ lower than the second temperature.

2. The method for improving the heat treatment effect of duplex titanium alloy plates as described in claim 1, characterized in that: In step S3, the temperature during straightening is 50-100℃ lower than the second temperature, and the straightening speed is 0.5-1m / s.

3. The method for improving the heat treatment effect of duplex titanium alloy plates as described in claim 1, characterized in that: The grinding amount in step S4 is 0.2-0.5mm.

4. The method for improving the heat treatment effect of duplex titanium alloy plates as described in claim 1, characterized in that: In step S4, the temperature for the second annealing is 500℃-700℃, and the annealing time is 1-3 hours.

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