Fine-grained pure titanium plate and method for producing the same

Abstract

The application discloses a fine-grained pure titanium plate and a preparation method thereof. The preparation method comprises the following steps: performing alternative phase change rolling on the plate: rolling the plate in a high-temperature beta phase zone and a low-temperature alpha phase zone for multiple cycles, and returning the plate to 880+ / -5 DEG C after each cycle; changing the rolling path of the plate for multi-directional rolling in multiple cycles in the alternative phase change rolling, and synchronously applying pulse current auxiliary treatment; and slowly cooling the plate after the alternative phase change rolling is completed. Through the synergistic process of the alternative phase change rolling, the multi-directional rolling, the pulse current auxiliary treatment and the slow cooling, three-dimensional uniform refinement of the grain size is realized, the complex process flow of the traditional fine-grained preparation is simplified, energy consumption and equipment cost are reduced, and an industrialized solution is provided for high-end titanium material application in the fields of aerospace, biological medicine and the like.

Description

Technical Field

[0001] This invention relates to the field of metal material processing technology, specifically to a fine-grained pure titanium plate and its preparation method. Background Technology

[0002] Pure titanium and its alloys are widely used in aerospace, medical implants, and chemical equipment due to their excellent specific strength, corrosion resistance, and biocompatibility. However, industrial pure titanium (such as TA1) has low room temperature strength. Currently, the industrial production of pure titanium plates mainly includes two methods: EB furnace and VAR furnace. Although the strength can be improved by grain refinement, there are still bottlenecks in terms of grain size and performance of pure titanium billets after processing.

[0003] Regarding grain size: EB furnace-melted pure titanium billets naturally contain coarse, centimeter-sized primary grains (size > 10 mm), which are difficult to refine using traditional rolling. Although VAR furnace-melted pure titanium billets avoid centimeter-sized coarse grains through forging, subsequent traditional rolling and annealing still result in relatively large grain sizes (only grade 4-6) and significant anisotropy in mechanical properties (ΔRp0.2 ≥ 100 MPa). The temperature window for the billet near the α / β phase transformation point is narrow. Rolling in the high-temperature β phase region (> 882.5℃) easily induces abnormal grain growth, while rolling in the low-temperature α phase region (< 800℃) induces microcracks due to a sudden increase in deformation resistance, and the grain size can only be maintained at grade 4-6.

[0004] In terms of performance: the traditional unidirectional rolling path leads to significant anisotropy of the plate, with a yield strength difference ΔRp0.2≥100MPa, and the lamellar α phase is unevenly distributed, affecting the consistency of mechanical properties.

[0005] To address the aforementioned bottlenecks, there are some directions for improvement in existing technologies. For example, although the intense plastic deformation technology (equal channel angle extrusion, cumulative rolling) can achieve nanocrystals (<200nm), the process is complex, costly, and difficult to scale up. Conventional cladding rolling or heat treatment can easily cause ω-phase brittleness or insufficient martensitic phase transformation, resulting in plasticity loss and performance fluctuations.

[0006] In summary, existing technologies have not yet broken through the technical barrier of synergistic improvement of the strength and uniformity of pure titanium, and there is a lack of efficient and industrially feasible methods for preparing fine-grained pure titanium. Summary of the Invention

[0007] To overcome the technical problems of grain size and performance bottlenecks in the preparation of existing pure titanium billets, this invention provides a fine-grained pure titanium plate and its preparation method, which can be used for the industrial production of pure titanium plates in existing EB furnaces and VAR furnaces, and simultaneously improves the strength and performance uniformity of pure titanium.

[0008] The method for preparing fine-grained pure titanium plates involves alternating phase transformation rolling of the plates: rolling the plates multiple times in the high-temperature β-phase region and the low-temperature α-phase region, and after each cycle, the plates are cooled to 880±5℃; during the multiple cycles of alternating phase transformation rolling, the rolling path of the plates is changed to perform multi-directional rolling, and pulsed current is applied simultaneously for auxiliary treatment; after the alternating phase transformation rolling is completed, the plates are slowly cooled.

[0009] This invention achieves three-dimensional uniform grain refinement and microstructure stability control through a synergistic process combining alternating phase transformation rolling, multi-directional rolling, pulsed current assistance, and slow cooling. This provides an industrial solution for high-end titanium applications in aerospace, biomedicine, and other fields. Alternating phase transformation rolling utilizes the reversible volume shrinkage effect (approximately 7%) associated with α / β phase transformation to repeatedly break down the original coarse grains. Pulsed current-induced electron wind and Joule heating promote dislocation movement and dynamic recrystallization, while the synergistic multi-directional rolling deformation path suppresses structural anisotropy. The multi-field coupling technology of alternating phase transformation rolling, multi-directional rolling, and pulsed current assistance achieves three-dimensional uniform grain refinement, simplifying the complex process of traditional fine grain preparation and reducing energy consumption and equipment costs. Simultaneously, slow cooling controls the fine grain structure, reducing product anisotropy and unevenness, significantly improving the strength-toughness matching and industrial application reliability of pure titanium plates.

[0010] In some embodiments, the process of alternating phase transformation rolling of the sheet metal includes:

[0011] High-temperature β-phase region rolling: temperature 900-910℃, single-pass deformation 30%-40%;

[0012] Low-temperature α-phase region rolling: temperature 780-800℃, single-pass deformation 20%-40%;

[0013] After completing a single cycle of rolling in multiple cycles, the plate is cooled to 880±5℃, and the rolling process is repeated at least 3 times to control the final cumulative deformation to 85%-97%.

[0014] In some embodiments, in multiple cycles of alternating phase transformation rolling, the high-temperature β-phase region rolling and the low-temperature α-phase region rolling in each cycle are respectively performed by longitudinal rolling and transverse rolling.

[0015] In some embodiments, the applied pulse current parameters are: frequency 250-500Hz, current intensity 200-400A.

[0016] In some embodiments, the applied pulse current parameters are: frequency 300-400Hz, current intensity 250-350A, and the pulse current application direction is at a 45° angle to the rolling direction.

[0017] In some embodiments, the final rolling in alternating phase transformation rolling is performed on the sheet metal, and the final rolling temperature is controlled to be 650-720°C.

[0018] In some embodiments, the process of slow cooling of the sheet after alternating phase transformation rolling includes controlling the cooling rate of the sheet within the range of 15-30°C / min after final rolling.

[0019] In some embodiments, after alternating phase transformation rolling, the process of slow cooling the sheet includes: after final rolling, the sheet is transferred to a preheated slow cooling furnace, the cooling rate of the sheet is controlled within the range of 15-30°C / min, and after slow cooling to below 200°C, it is taken out of the furnace and air-cooled to room temperature.

[0020] The present invention also provides a fine-grained pure titanium plate, which is made by the fine-grained pure titanium plate preparation method described in any of the above embodiments.

[0021] Furthermore, the fine-grained pure titanium plate has a grain size ≤22.5μm, a hardness of HRB 75-80, an unevenness ≤8mm / m, and a difference in yield strength between the transverse and longitudinal directions ΔRp0.2<50MPa.

[0022] The beneficial effects of this invention are:

[0023] By employing a synergistic process combining alternating phase transformation rolling, multi-directional rolling, pulsed current assistance, and slow cooling, three-dimensional uniform grain refinement and microstructure stability control are achieved, providing an industrial solution for high-end titanium applications in aerospace, biomedicine, and other fields. Alternating phase transformation rolling utilizes the reversible volume shrinkage effect (approximately 7%) associated with α / β phase transformation to repeatedly break down the original coarse grains. Pulsed current-induced electron wind and Joule heating promote dislocation movement and dynamic recrystallization, while the synergistic multi-directional rolling deformation path suppresses structural anisotropy. The multi-field coupling technology of alternating phase transformation rolling, multi-directional rolling, and pulsed current assistance achieves three-dimensional uniform grain refinement, simplifying the complex process of traditional fine-grain preparation and reducing energy consumption and equipment costs. Simultaneously, slow cooling controls the fine-grain microstructure, reducing product anisotropy and unevenness, significantly improving the strength-toughness matching and industrial application reliability of pure titanium plates. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0025] This invention provides a fine-grained pure titanium plate and its preparation method.

[0026] The method for preparing fine-grained pure titanium plates involves alternating phase transformation rolling of the plates: rolling the plates multiple times in the high-temperature β-phase region and the low-temperature α-phase region, and after each cycle, the plates are cooled to 880±5℃; during the multiple cycles of alternating phase transformation rolling, the rolling path of the plates is changed to perform multi-directional rolling, and pulsed current is applied simultaneously for auxiliary treatment; after the alternating phase transformation rolling is completed, the plates are slowly cooled.

[0027] This invention achieves three-dimensional uniform grain refinement and microstructure stability control through a synergistic process combining alternating phase transformation rolling, multi-directional rolling, pulsed current assistance, and slow cooling. This provides an industrial solution for high-end titanium applications in aerospace, biomedicine, and other fields. Alternating phase transformation rolling utilizes the reversible volume shrinkage effect (approximately 7%) associated with α / β phase transformation to repeatedly break down the original coarse grains. Pulsed current-induced electron wind and Joule heating promote dislocation movement and dynamic recrystallization, while the synergistic multi-directional rolling deformation path suppresses structural anisotropy. The multi-field coupling technology of alternating phase transformation rolling, multi-directional rolling, and pulsed current assistance achieves three-dimensional uniform grain refinement, simplifying the complex process of traditional fine grain preparation and reducing energy consumption and equipment costs. Simultaneously, slow cooling controls the fine grain structure, reducing product anisotropy and unevenness, significantly improving the strength-toughness matching and industrial application reliability of pure titanium plates.

[0028] Preferably, the process of alternating phase transformation rolling of the sheet metal includes:

[0029] High-temperature β-phase region rolling: temperature 900-910℃, single-pass deformation 30%-40%;

[0030] Low-temperature α-phase region rolling: temperature 780-800℃, single-pass deformation 20%-40%;

[0031] After completing a single cycle of rolling in multiple cycles, the plate is cooled to 880±5℃, and the rolling process is repeated at least 3 times to control the final cumulative deformation to 85%-97%.

[0032] As described above, near the α / β phase transformation point of pure titanium (880±20℃), alternating high-temperature β-phase region rolling (900-910℃, 30%-40% deformation per pass) and low-temperature α-phase region rolling (780-800℃, 20%-40% deformation per pass) are performed. After each high-low temperature rolling cycle, the temperature is relaxed to 880±5℃ and held for a period of time. The reversible volume shrinkage effect (approximately 7%) accompanying the α / β phase transformation is used to repeatedly break down the original coarse grains. The number of cycles is at least 3.

[0033] The single-pass deformation amount here refers to the thickness reduction rate after a single-pass rolling, and the formula is: Single-pass deformation amount = (thickness before rolling - thickness after rolling) / thickness before rolling × 100%. The cumulative deformation amount here refers to the total thickness reduction rate from the initial billet to the final rolled product, which can be derived from the single-pass deformation amount of multiple passes.

[0034] Preferably, in multiple cycles of alternating phase transformation rolling, the high-temperature β-phase region rolling and the low-temperature α-phase region rolling in each cycle are respectively performed by longitudinal rolling and transverse rolling.

[0035] In multiple cycles of alternating phase transformation rolling, multidirectional rolling is achieved through longitudinal and transverse rolling during the multiple rolling processes. Preferably, within one cycle, the high-temperature β-phase region rolling and the low-temperature α-phase region rolling adopt longitudinal rolling and transverse rolling, respectively. For example, in each cycle, the high-temperature β-phase region rolling adopts a longitudinal rolling path, and the low-temperature α-phase region adopts a transverse rolling path.

[0036] Preferably, the applied pulsed current parameters are: frequency 250-500Hz, current intensity 200-400A. The pulsed current-induced electron wind and Joule heating effect promote dislocation movement and dynamic recrystallization, while the synergistic multi-directional deformation path suppresses texture anisotropy.

[0037] Furthermore, the applied pulse current parameters are: frequency 300-400Hz, current intensity 250-350A, and the pulse current application direction is at a 45° angle to the rolling direction.

[0038] Preferably, the final rolling in the alternating phase transformation rolling process is performed on the sheet metal, and the final rolling temperature is controlled at 650-720℃.

[0039] The final rolling temperature here refers to the temperature at which the final rolling process is completed.

[0040] Regarding microstructure control: When the final rolling temperature is higher than the β phase transformation point (approximately 885℃), it leads to drastic growth of β grains, forming large microstructures after cooling and deteriorating mechanical properties. Below 650℃, titanium is in a cold-worked state, making it difficult to undergo sufficient recrystallization, which results in work hardening and residual stress.

[0041] Regarding deformation resistance control: the final rolling temperature is controlled at 650-720℃, which can significantly reduce rolling load and energy consumption, while ensuring good plastic deformation capacity and avoiding edge cracks and surface cracks.

[0042] Regarding surface quality and oxidation control: Titanium is chemically reactive and readily reacts with elements such as oxygen and nitrogen at high temperatures to form a brittle surface layer. The oxidation rate accelerates significantly above 720°C, while controllable oxidation can be achieved in the 650-720°C range, reducing oxide scale thickness, improving surface quality, and minimizing material loss. This is particularly important for products requiring subsequent pickling, as it can reduce processing costs and improve surface quality.

[0043] In summary, controlling the final rolling temperature at 650-720℃ ensures the optimal combination of high strength and high ductility.

[0044] In this embodiment, the process of slow cooling of the plate after alternating phase transformation rolling includes controlling the cooling rate of the plate within the range of 15-30℃ / min after final rolling.

[0045] Furthermore, after alternating phase transformation rolling, the process of slow cooling the plate includes: after final rolling, the plate is transferred to a preheated slow cooling furnace, the cooling rate of the plate is controlled within the range of 15-30℃ / min, and after slow cooling to below 200℃, it is taken out of the furnace and air-cooled to room temperature.

[0046] Here, slow cooling is used to control the microstructure and stress. After final rolling, the high-temperature plate is quickly transferred to a preheating and slow cooling furnace. In practice, it can be placed in within 10 seconds. Through a programmed temperature control system, the plate is slowly cooled from the final rolling temperature at a rate of 15-30℃ / min. After being slowly cooled to below 200℃, it is taken out of the furnace and air-cooled to room temperature, which promotes sufficient recovery and recrystallization inside the plate.

[0047] Through the above process, the total cumulative deformation during rolling reaches 85-97%, and the final rolling temperature is strictly controlled within the α-phase region (650-720℃), ensuring no instability induced by phase transformation during grain refinement. The resulting fine-grained pure titanium plate has the following characteristics: grain size ≤22.5μm (level 8), significantly refined to the submicron scale; excellent uniformity of mechanical properties: hardness HRB 75-80, unevenness ≤8mm / m, and the difference in yield strength between longitudinal and transverse directions ΔRp0.2<50MPa, significantly improving the contradiction between the coarse-grained structure and strong anisotropy of traditional pure titanium plates. Through a multi-field coupling mechanism of phase transformation-deformation-electric pulse-slow cooling, the synergistic improvement of pure titanium grain refinement, high uniformity, and precise plate shape control is achieved, providing an industrial solution for high-end titanium material applications in aerospace, biomedicine, and other fields.

[0048] Example 1

[0049] This embodiment uses TA1 pure titanium ingots (original grain size 12mm, thickness 50mm) smelted in an EB furnace as raw material.

[0050] After being heated to 880℃ and held for a period of time, alternating phase transformation rolling is performed: high-temperature β phase region rolling (905℃, 40% deformation per pass) and low-temperature α phase region rolling (790℃, 35% deformation per pass) constitute a single cycle.

[0051] Multi-directional rolling path and pulsed current assistance are introduced in the rolling cycle: first, rolling is carried out longitudinally, and then rolling is carried out transversely, while pulsed current assistance (frequency 350Hz, current intensity 300A, current direction is at a 45° angle with the rolling direction) is applied simultaneously. The pulsed current induces dislocation slip to promote dynamic recrystallization and optimize texture uniformity.

[0052] After each cycle in multiple cycles, the temperature was relaxed and warmed to 880℃ for 30 seconds, and this process was repeated 3 times. The total cumulative deformation reached 94%, and the final rolling temperature was controlled in the α phase region (700℃).

[0053] After final rolling, the sheet is quickly transferred to a slow-cooling furnace preheated to 500°C for slow cooling. The cooling rate is controlled at 20°C / min. After slow cooling to 200°C, the sheet is removed from the furnace and air-cooled to room temperature to promote sufficient recovery and recrystallization inside the sheet.

[0054] The resulting pure titanium plate has a grain size refined to 20μm, a hardness of HRB 78, a flatness of 3.5mm / m, and a longitudinal and transverse yield strength difference ΔRp0.2=25MPa.

[0055] Example 2

[0056] This embodiment uses TA2 pure titanium ingots (original grain size 15mm, thickness 60mm) smelted in an EB furnace as raw material.

[0057] After being heated to 880℃ and held for a period of time, alternating phase transformation rolling is performed: high-temperature β phase region rolling (910℃, 40% deformation per pass) and low-temperature α phase region rolling (785℃, 20% deformation per pass) constitute a single cycle.

[0058] Multi-directional rolling path and pulsed current assistance are introduced into the rolling cycle: first, rolling is carried out longitudinally, and then rolling is carried out transversely, while pulsed current assistance (frequency 400Hz, current intensity 350A, current direction is at a 45° angle with the rolling direction) is applied simultaneously. High-energy pulsed current activates dislocation movement and accelerates grain boundary migration.

[0059] After each cycle in multiple cycles, the temperature was relaxed and warmed to 880℃ for 30 seconds, and this process was repeated 4 times, resulting in a total cumulative deformation of 95%. The final rolling temperature was controlled in the α phase region (720℃).

[0060] After final rolling, the sheet is quickly transferred to a slow-cooling furnace preheated to 500°C for slow cooling. The cooling rate is controlled at 20°C / min. After slow cooling to 200°C, the sheet is removed from the furnace and air-cooled to room temperature to promote sufficient recovery and recrystallization inside the sheet.

[0061] The resulting pure titanium plate has a grain size of 22μm, a hardness of HRB 80, a flatness of 3mm / m, and a yield strength difference of ΔRp0.2 between the longitudinal and transverse directions of 30MPa.

[0062] Example 3

[0063] This embodiment uses TA1 pure titanium billet (forged billet grain size > 40um, thickness 40mm) smelted in a VAR furnace as raw material.

[0064] After being heated to 880℃ and held for a period of time, alternating phase transformation rolling is performed: high-temperature β phase region rolling (902℃, single-pass deformation amount 30%) and low-temperature α phase region rolling (792℃, single-pass deformation amount 25%) constitute a single cycle.

[0065] Multi-directional rolling path and pulsed current assistance are introduced in the rolling cycle: first, rolling is carried out longitudinally, and then the direction is reversed to be rolled transversely, while pulsed current assistance (frequency 250Hz, current intensity 220A, current direction is at a 45° angle with the rolling direction) is applied simultaneously to reduce energy consumption and maintain dislocation activity through low-frequency pulsed current.

[0066] After each cycle in multiple cycles, the temperature was relaxed and warmed to 880℃ for 30 seconds, and this process was repeated 3 times, resulting in a total cumulative deformation of 86%. The final rolling temperature was controlled in the α phase region (700℃).

[0067] After final rolling, the sheet is quickly transferred to a slow-cooling furnace preheated to 500°C for slow cooling. The cooling rate is controlled at 20°C / min. After slow cooling to 200°C, the sheet is removed from the furnace and air-cooled to room temperature to promote sufficient recovery and recrystallization inside the sheet.

[0068] The resulting pure titanium plate has a grain size of 19μm, a hardness of HRB 75, a flatness of 5mm / m, and a difference in yield strength between the longitudinal and transverse directions of ΔRp0.2=20MPa.

[0069] Example 4

[0070] This embodiment uses TA2 pure titanium billets (forged billet grain size > 50um, thickness 45mm) smelted in a VAR furnace as raw material to meet the needs of thin plate production.

[0071] After being heated to 880℃ and held for a period of time, alternating phase transformation rolling is performed: high-temperature β phase region rolling (900℃, single-pass deformation 35%) and low-temperature α phase region rolling (795℃, single-pass deformation 25%) constitute a single cycle.

[0072] Multi-directional rolling path and pulsed current assistance are introduced in the rolling cycle: first, rolling is carried out longitudinally, and then rolling is carried out transversely, while pulsed current assistance (frequency 280Hz, current intensity 250A) is applied simultaneously to reduce the deformation resistance of the thin plate by using low-energy pulsed current assistance.

[0073] After each cycle in multiple cycles, the temperature was relaxed and warmed to 880℃ for 30 seconds, and this process was repeated 4 times, resulting in a total cumulative deformation of 94%. The final rolling temperature was controlled in the α-phase region (710℃).

[0074] After final rolling, the sheet is quickly transferred to a slow-cooling furnace preheated to 500°C for slow cooling. The cooling rate is controlled at 18°C / min. After slow cooling to 200°C, the sheet is removed from the furnace and air-cooled to room temperature to promote sufficient recovery and recrystallization inside the sheet.

[0075] The resulting pure titanium plate has a grain size of 16μm, a hardness of HRB 76, a flatness of 5mm / m, and a difference in yield strength between the longitudinal and transverse directions of ΔRp0.2=20MPa.

[0076] In summary, this invention achieves a synergistic improvement in the fine grain size, high uniformity, and precise shape control of pure titanium through a multi-field coupling mechanism of alternating phase transformation rolling, multi-directional rolling, pulsed current assistance, and slow cooling. This meets the needs of high-end medical implants (such as bone screws and joint shells) and aerospace structural components. The applicant compares the new technology in this application with traditional processes, noting that it offers a premium of 80,000-100,000 RMB / ton over traditional coarse-grained pure titanium, increases the yield to 94%, and increases annual effective output by 70 tons. Pulsed current assistance reduces deformation resistance by 30% and rolling energy consumption by 15%, with estimated annual economic benefits reaching millions to tens of millions of RMB, significantly improving enterprise profitability and promoting industrial upgrading and the establishment of market competitive advantages.

[0077] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing fine-grained pure titanium plates, characterized in that, Alternating phase transformation rolling is performed on the sheet metal: the sheet metal is rolled multiple times in the high-temperature β phase region and the low-temperature α phase region. The high-temperature β phase region rolling temperature is 900-910℃, and the single-pass deformation is 30%-40%. The low-temperature α phase region rolling temperature is 780-800℃, and the single-pass deformation is 20%-40%. In the multiple cycles, after each cycle, the sheet metal is cooled to 880±5℃ and held at that temperature. The rolling process is repeated at least 3 times to control the final cumulative deformation to be 85%-97%. In multiple cycles of alternating phase transformation rolling, the rolling path of the plate is changed to perform multi-directional rolling, and pulsed current is applied simultaneously for auxiliary treatment. The applied pulsed current parameters are: frequency 250-500Hz, current intensity 200-400A. In each cycle, the high-temperature β phase region rolling and the low-temperature α phase region rolling are respectively carried out by longitudinal rolling and transverse rolling. The final rolling in alternating phase transformation rolling is performed on the plate, and the final rolling temperature is controlled at 650-720℃. After alternating phase transformation rolling, the plate is slowly cooled, and the cooling rate of the plate is controlled within the range of 15-30℃ / min after final rolling.

2. The method for preparing fine-grained pure titanium plate as described in claim 1, characterized in that, The applied pulse current parameters are: frequency 300-400Hz, current intensity 250-350A, and the pulse current application direction is at a 45° angle to the rolling direction.

3. The method for preparing fine-grained pure titanium plate as described in claim 1, characterized in that, After alternating phase transformation rolling, the process of slow cooling the plate includes: after final rolling, the plate is transferred to a preheated slow cooling furnace, the cooling rate of the plate is controlled within the range of 15-30℃ / min, and after slow cooling to below 200℃, it is taken out of the furnace and air-cooled to room temperature.

4. Fine-grained pure titanium plate, characterized by: It is made by the method for preparing fine-grained pure titanium plate according to any one of claims 1-3.

5. The fine-grained pure titanium plate as described in claim 4, characterized in that the grain size... The dimensions are ≤22.5μm, the hardness is HRB 75-80, the unevenness is ≤8mm / m, and the difference between transverse and longitudinal yield strength ΔRp0.2<50Mpa.