Titanium alloy ti55531 bar and method of making the same
Patent Information
- Application Number
- CN202611298547.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-08-25
- Publication Date
- 2026-11-03
AI Technical Summary
While the strength of existing Ti55531 high-strength titanium alloys has been improved, their plasticity, toughness, and damage tolerance have decreased, making it difficult to achieve a balance between strength and toughness.
A multi-stage forging process and a specific heat treatment regime are adopted, including forging in the initial stage, forging in the single-phase region, forging in the two-phase region, forging before drawing, and heat treatment. By controlling the deformation temperature and method, the microstructure is optimized to achieve synergistic regulation of strength and toughness.
While maintaining a tensile strength of over 1350 MPa, the impact energy KU2 reaches over 30 J and the fracture toughness reaches over 70 MPa·m1/2, significantly improving the strength-toughness match of the material.
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Figure CN123024830A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of titanium alloy technology, specifically relating to a Ti55531 titanium alloy bar and its preparation method. Background Technology
[0002] Titanium alloys, as a lightweight metal material, possess excellent comprehensive properties such as high specific strength, corrosion resistance, non-magnetic properties, and weldability, making them a key structural component material in the current aerospace field. High-strength titanium alloys generally refer to titanium alloys with a tensile strength of over 1000 MPa, and are widely used in critical components such as aircraft main landing gear struts, engine plugs, nozzles, and fuselage load-bearing frames. Although significant progress has been made in the research and application of high-strength titanium alloys both domestically and internationally, while strength has been continuously improved, the plasticity, toughness, and damage tolerance of titanium alloys have decreased to varying degrees. Achieving a better balance between strength and toughness is key to promoting the further application of high-strength titanium alloys in aircraft.
[0003] Ti55531 is a typical β-type high-strength titanium alloy with great application potential in aerospace load-bearing components. In existing technologies, Ti55531 titanium alloy is often prepared into ingots through multiple VAR (vacuum arc remelting) processes, followed by multi-stage upsetting and drawing forging in the β single-phase and two-phase regions, combined with solution treatment. Aging or beta annealing heat treatments aim to achieve a balance between strength and toughness in the alloy. However, existing processes have significant technical limitations: as the tensile strength of the alloy increases, its plasticity, impact toughness, fracture toughness, and damage tolerance tend to decrease significantly.
[0004] Therefore, developing a Ti55531 titanium alloy preparation process that simultaneously improves strength and toughness is of great value for the engineering application of key load-bearing components in aircraft. Summary of the Invention
[0005] The purpose of this invention is to overcome the shortcomings of existing Ti55531 high-strength titanium alloys, which are difficult to balance between strength improvement and toughness reduction, and to provide a method for synergistic control of strength and toughness of Ti55531 high-strength titanium alloys.
[0006] To achieve the above objectives, the present invention adopts the following technical solution: According to a first aspect of the present invention, a method for preparing Ti55531 titanium alloy rods is provided, comprising the following steps: S1. Forging: The Ti55531 titanium alloy ingot is upset and drawn at 1100~1150℃. The upsetting pressure is 35~40%. The drawing is done by octagonal drawing. After drawing, the height-to-diameter ratio is controlled at 1.9~2.1 to obtain the first-grade forging billet. S2. Single-phase forging: The first-stage forging billet is upset forged at 30~200℃ above the β phase transformation point. The upset pressure is 35~40%, and the drawing is done by octagonal drawing. After drawing, the height-to-diameter ratio is controlled at 1.9~2.1 to obtain the second-stage forging billet. S3. Two-phase region forging: The secondary forging billet is upset forged at 40~60℃ below the β phase transformation point. The upset pressure is 30~33%, and the drawing is diagonal. After drawing, the height-to-diameter ratio is controlled at 1.9~2.1 to obtain the tertiary forging billet. S4. Forging before drawing: The three-stage forging billet is upset forged at 10~20℃ below the β phase transformation point, with an upsetting deformation of 50~60%. After upsetting, it is drawn radially to obtain a square billet with a height-to-diameter ratio of 4.0~4.5. S5. Drawing and forging: The billet is drawn and forged at 10~20℃ below the β phase transformation point, with a single drawing reduction of ≤30mm, to obtain a bar of the target size. S6. Heat treatment: The bar is heated to 20-40°C above the β phase transformation point and held for a first time. Then it is cooled to 10-20°C below the β phase transformation point at a rate of 1-3°C / min and held for a second time. After the holding time is completed, it is air-cooled and then held at 650-700°C for a third time. After that, it is air-cooled to obtain the finished Ti55531 titanium alloy bar.
[0007] As a further implementation scheme, in step S1, the Ti55531 titanium alloy ingot is subjected to a single-fire upsetting and drawing forging process, which involves two axial upsetting and drawing operations.
[0008] As a further implementation scheme, in step S2, the first-level forging billet is subjected to upsetting and drawing forging at decreasing temperatures for 4 to 6 times, with each upsetting and drawing forging consisting of two upsettings and two drawings.
[0009] As a further implementation plan, when the forging temperature of the first upsetting and drawing is higher than 100°C but not higher than 200°C, the two upsetting and two drawing are completed continuously without needing to be reheated in between; when the forging temperature of the first upsetting and drawing is not lower than 30°C but not higher than 100°C, after completing one upsetting and one drawing, the furnace is air-cooled for 20-30 minutes, and then reheated for 1-2 hours at a temperature 20-30°C lower than the β phase transformation point, and then the furnace is removed to complete the remaining one upsetting and one drawing.
[0010] As a further implementation scheme, in step S3, the secondary forging billet is subjected to four-fire upsetting and drawing forging, with each fire involving three upsetting and three drawing operations. After completing one upsetting and one drawing operation, the forging billet is kept in the furnace at the original forging temperature for 1-2 hours before being taken out of the furnace for the next one upsetting and one drawing operation.
[0011] As a further implementation scheme, in step S4, the three-stage forging billet is subjected to one-fire upsetting and drawing forging.
[0012] As a further implementation scheme, in step S4, the three-stage forging billet is brushed with heat-insulating coating and wrapped with heat-insulating cotton before being heated in the furnace, and then axially upsetting is performed at a speed of 1~3mm / s after exiting the furnace.
[0013] As a further implementation scheme, in step S5, the billet is subjected to a single-fire drawing and forging process. During the drawing and forging process, if the temperature is below 700°C, it is returned to the furnace for heat preservation for 1 to 1.5 hours.
[0014] As a further implementation scheme, in step S6, the first time is determined based on the diameter of the bar, the second time is 2~3 hours, and the third time is 6~10 hours.
[0015] According to a second aspect of the present invention, a Ti55531 titanium alloy rod is provided, which is prepared by the above method.
[0016] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art: This invention achieves synergistic optimization of strength and toughness in Ti55531 titanium alloy through the synergistic control of multi-stage forging process and specific heat treatment regime. While maintaining tensile strength above 1350 MPa, the impact energy (KU2) reaches over 30 J, and the fracture toughness reaches 70 MPa·m. 1 / 2 above. Attached Figure Description
[0017] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description of the present invention will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other embodiments can be obtained based on these drawings without creative effort.
[0018] Figure 1 A flowchart illustrating the preparation method of Ti55531 titanium alloy rods provided by this invention. Detailed Implementation
[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.
[0020] Specific embodiments of the invention are disclosed herein as needed; however, it should be understood that the embodiments disclosed herein are merely examples of the invention that may be implemented in various alternative forms. In the following description, various operating parameters and components are described in several contemplated embodiments. These specific parameters and components are provided as examples only and are not intended to be limiting.
[0021] The endpoints and any values of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of the various ranges, the endpoint values of the various ranges and individual point values, and individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.
[0022] The first aspect of this invention provides a method for preparing Ti55531 titanium alloy rods. Figure 1 A flowchart illustrating the preparation method of the Ti55531 titanium alloy rod provided by this invention. Figure 1 As shown, the method includes the following steps: S1. Forging: The Ti55531 titanium alloy ingot is upset and drawn at 1100~1150℃. The upsetting pressure is 35~40%. The drawing is done by octagonal drawing. After drawing, the height-to-diameter ratio is controlled at 1.9~2.1 to obtain the first-grade forging billet. S2. Single-phase forging: The first-stage forging billet is upset forged at 30~200℃ above the β phase transformation point. The upset pressure is 35~40%. The drawing is done by octagonal drawing. After drawing, the height-to-diameter ratio is controlled at 1.9~2.1 to obtain the second-stage forging billet. S3. Two-phase region forging: The secondary forging billet is upset forged at 40~60℃ below the β phase transformation point. The upset pressure is 30~33%. The drawing is diagonal. After drawing, the height-to-diameter ratio is controlled at 1.9~2.1 to obtain the tertiary forging billet. S4. Forging before drawing: The third-grade forging billet is upset and drawn at 10~20℃ below the β phase transformation point. The upsetting deformation is 50~60%. After upsetting, it is drawn radially to obtain a square billet with a height-to-diameter ratio of 4.0~4.5. S5. Drawing and forging: The billet is drawn and forged at 10~20℃ below the β phase transformation point, with a single drawing reduction of ≤30mm, to obtain a bar of the target size. S6. Heat treatment: Heat the bar to 20~40℃ above the β phase transformation point and hold for the first time. Then cool it to 10~20℃ below the β phase transformation point at a rate of 1~3℃ / min and hold for the second time. After the holding time is completed, air cool it and then hold it at 650~700℃ for the third time. After that, air cool it to obtain the finished Ti55531 titanium alloy bar.
[0023] The method of this invention achieves synergistic optimization of strength and toughness in Ti55531 titanium alloy through the synergistic control of multi-stage forging process and specific heat treatment regime. While maintaining tensile strength above 1350 MPa, the impact energy KU2 reaches above 30 J, and the fracture toughness reaches 70 MPa·m. 1 / 2 above.
[0024] Specifically, step S1, the billet forging process, is carried out in the β single-phase high-temperature region of 1100–1150°C. A large upsetting pressure of 35–40% is used for upsetting deformation to fully break up the coarse as-cast structure inside the ingot, reducing and eliminating compositional segregation, and providing a β matrix structure with relatively uniform composition and grain size for all subsequent processes. Step S2, the single-phase forging process, is carried out 30–200°C above the β phase transformation point. In this temperature range, the alloy is completely in the β single-phase state. Large deformation upsetting forging promotes the dynamic transformation of the β grains. Recrystallization and reconstruction yield fine and uniform equiaxed β grains, constructing an isotropic β grain framework that lays an ideal foundation for the subsequent uniform precipitation of the α phase. Step S3, the two-phase forging process, is carried out in the α+β two-phase region at 40–60°C below the β phase transformation point. The upsetting pressure is precisely controlled at 30%–33%, and a diagonal elongation deformation method is used to drive the uniform dispersion and precipitation of fine equiaxed primary α phases at the β grain boundaries and within the grains. The content, size, and spatial distribution of the primary α phase directly determine the final strength of the material. The toughness matching level; Step S4, the forging process before drawing is set at 10-20℃ below the β phase transformation point. A large upsetting deformation of 50-60% is used to introduce high plastic strain, further breaking down the remaining coarse structure. Axial upsetting and radial drawing are carried out successively. By switching the deformation direction, the structure is preferentially oriented, and the texture effect is weakened, providing an intermediate billet with suitable size and uniform structure for subsequent drawing and forming; Step S5, the drawing and forging process is also completed in the range of 10-20℃ below the β phase transformation point. The main goal is to form the component, while protecting the excellent pre-formed structure obtained by the forging process. By limiting the single reduction of drawing to ≤30mm, the strain input of single deformation is controlled to avoid local deformation overload and the generation of adiabatic shear bands and internal microcracks, ensuring the surface quality and internal structure integrity of the bar; Step S6, the heat treatment process, precisely controls the morphology, size and spatial distribution of the secondary α phase, and finally achieves the synergy of high strength and high toughness of the material. Specifically, the transformation from α to β phase is achieved by solution cooling the bar material to 20-40°C above the β phase transformation point and holding it at this temperature. Then, it is slowly furnace-cooled at a rate of 1-3°C / min to 10-20°C below the β phase transformation point and held at this temperature. This controlled slow furnace cooling allows the α phase to nucleate uniformly and grow slowly within the β matrix. Furthermore, holding the material near the β phase transformation point controls the size and aspect ratio of the α phase, resulting in uniformly sized α phase lamellars with a certain thickness and length, thus avoiding the significant reduction in impact and fracture toughness caused by long, needle-like α phases. After holding, the material is air-cooled to "freeze" the microstructure, preserving the α / β microstructure formed within this temperature range. (650) The 700℃ heat treatment aims to perform high-temperature aging. Higher aging temperatures can further release residual internal stress in the forged bar and precipitate secondary α phase, achieving further strengthening of the material. Combined with the relatively coarse α phase lamellar layers constructed in the second heat treatment step, an excellent balance of strength and toughness is achieved. Each step in this invention is interconnected, mutually coupled, and indispensable. Relying on the synergistic effect of the entire process, tensile strength ≥1350MPa, impact energy KU2 ≥30J, and fracture toughness ≥70MPa are achieved. m¹ ² High-level strength and toughness matching.
[0025] Furthermore, the method of the present invention effectively eliminates the deformation inhomogeneity during the forging process by combining a specific forging method with precise control of the aspect ratio at each stage and the distribution of upsetting deformation during high and low temperature forging, and significantly improves the microstructure uniformity of Ti55531 titanium alloy bars.
[0026] The present invention uses a VAR-melted Ti55531 titanium alloy ingot as the billet, and the ingot body is peeled. In some embodiments, a Ti55531 titanium alloy ingot with a single weight of 3t (ingot size Φ(700~750)mm*L) and three VAR-melted is used.
[0027] In step S1, the initial forging temperature can typically, but not limited to, be set to 1100℃, 1110℃, 1120℃, 1130℃, 1140℃, or 1150℃; the upsetting pressure during initial forging can typically, but not limited to, be set to 35%, 36%, 37%, 38%, 39%, or 40%; and the height-to-diameter ratio after elongation during initial forging can typically, but not limited to, be set to 1.9, 2.0, or 2.1. The "octagonal elongation" described in this invention refers to the process where the forging billet rotates 45° around its own axis each time during elongation, sequentially forging the eight corners of the billet, gradually shaping the billet cross-section into an octagon, while simultaneously achieving axial elongation of the billet. This method improves the uniformity of the cross-sectional structure of the forging billet and weakens the texture through multi-directional deformation.
[0028] In step S2, the forging temperature in the single-phase region can typically, but not limited to, be set to 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, or 200°C above the β-phase transformation point; the upsetting pressure during single-phase region forging can typically, but not limited to, be set to 35%, 36%, 37%, 38%, 39%, or 40%; and the height-to-diameter ratio after drawing during single-phase region forging can typically, but not limited to, be set to 1.9, 2.0, or 2.1.
[0029] In step S3, the forging temperature in the two-phase region can typically, but not limited to, be set to 40°C, 50°C, or 60°C below the β-phase transformation point; the upsetting pressure during forging in the two-phase region can typically, but not limited to, be set to 30%, 31%, 32%, or 33%; and the height-to-diameter ratio after drawing during forging in the two-phase region can typically, but not limited to, be set to 1.9, 2.0, or 2.1. The "diagonal drawing" described in this invention refers to the forging billet rotating 90° around its own axis each time during drawing, forging the diagonal position of the square billet, and maintaining a square cross-section after drawing. This method aims to increase core penetration and ensure the uniformity of the cross-sectional structure.
[0030] In step S4, the forging temperature before drawing can typically, but not limited to, be set to 10°C, 15°C, or 20°C below the β phase transformation point; the upsetting deformation during forging before drawing can typically, but not limited to, be set to 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, or 60%; and the height-to-diameter ratio of the square billet obtained by forging before drawing can typically, but not limited to, be set to 4.0, 4.1, 4.2, 4.3, 4.4, or 4.5.
[0031] In step S5, the drawing forging temperature can typically, but not limited to, be set to 10°C, 15°C, or 20°C below the β phase transformation point; the single reduction during drawing forging can typically, but not limited to, be set to 30%, 25%, 20%, 15%, or 10%.
[0032] In step S6, the heat treatment is carried out in three stages: the first stage is solution treatment in the β phase region, the second stage is holding near the phase transformation point, and the third stage is high-temperature aging. The solution treatment temperature in the β phase region is typically, but not limited to, 20°C, 30°C, or 40°C above the β phase transformation point; the cooling rate is typically, but not limited to, 1°C / min, 2°C / min, or 3°C / min; the holding temperature near the phase transformation point is typically, but not limited to, 10°C, 15°C, or 20°C below the β phase transformation point; and the high-temperature aging temperature is typically, but not limited to, 650°C, 660°C, 670°C, 680°C, 690°C, or 700°C.
[0033] Preferably, in some embodiments, in step S1, the Ti55531 titanium alloy ingot is subjected to a single-fire upsetting and drawing forging, and the single-fire upsetting and drawing forging involves two axial upsetting and drawing operations. The "axial upsetting and drawing" described in this invention refers to the forging operation of upsetting and drawing along the axial direction of the forging blank, the purpose of which is to fully break down the coarse as-cast structure of the ingot and improve the uniformity of the structure.
[0034] Preferably, in some embodiments, in step S2, the primary forging billet undergoes 4 to 6 heats of decreasing temperature upsetting and drawing forging, with each heat consisting of two upsetting and two drawing operations. The "temperature decreasing upsetting and drawing forging" described in this invention refers to forging with gradually decreasing temperature from away from the phase transformation point to closer to the β phase transformation point.
[0035] Preferably, in some embodiments, when the forging temperature of the first upsetting and drawing is higher than the β phase transformation point +100°C but not higher than the β phase transformation point +200°C, two upsetting and two drawing processes are completed continuously without reheating in between; when the forging temperature of the first upsetting and drawing is not lower than the β phase transformation point +30°C but not higher than the β phase transformation point +100°C, after completing one upsetting and one drawing process, the process is air-cooled for 20-30 minutes, then reheated in the furnace at a temperature 20-30°C lower than the β phase transformation point for 1-2 hours, and then removed from the furnace to complete the remaining one upsetting and one drawing process. This invention sets differentiated deformation regimes for different superheat levels: the high-temperature section continuously completes the upsetting and drawing cycle, fully realizing β grain refinement and storing deformation energy; near the β phase transformation point, a "one-round upsetting and drawing" process is adopted. air cooling Reheating The intermittent deformation mode of "another round of upsetting and drawing" can avoid excessive temperature rise in the core and adiabatic shear, and also suppress the precipitation of continuous network α phase film at the β grain boundary, thus avoiding damage to the material's toughness by the network α.
[0036] Preferably, in some embodiments, in step S3, the secondary forging billet undergoes four-stage upsetting and drawing forging, with each stage involving three upsettings and three drawings. After each upsetting and drawing, the billet is held in the furnace at the original forging temperature for 1-2 hours before being removed from the furnace for the next upsetting and drawing. Holding the billet in the furnace at the forging temperature after each round of upsetting and drawing avoids uneven deformation and forging cracks caused by excessive temperature drop during continued forging. Combined with diagonal drawing, this increases the uniformity of the cross-sectional microstructure, resulting in a superior pre-structure with spheroidized and refined primary α-phase + β matrix, laying the microstructural foundation for subsequent heat treatment to achieve a balance between strength and toughness.
[0037] Preferably, in some embodiments, in step S4, the tertiary forging billet is subjected to a single upsetting and drawing forging.
[0038] Preferably, in some embodiments, in step S4, the third-stage forging billet is coated with heat-insulating paint and wrapped with heat-insulating cotton before being heated in the furnace, and then axially upsetting is performed at a speed of 1~3 mm / s after exiting the furnace. The purpose of applying heat-insulating paint and wrapping the forging billet with heat-insulating cotton is to suppress the rapid temperature drop of the billet surface after exiting the furnace and reduce the temperature difference between the billet core and surface.
[0039] Preferably, in some embodiments, in step S5, the billet is subjected to a single-pass drawing forging. During the drawing forging process, if the temperature is below 700°C, it is reheated in the furnace for 1 to 1.5 hours. Setting a 700°C reheating threshold prevents the accumulation of work hardening during the drawing process, avoids microcracks introduced by low-temperature deformation, and ensures the uniformity of the overall microstructure and properties of the finished bar.
[0040] Preferably, in some embodiments, in step S6, the initial determination is based on the diameter of the bar. For example, initially, it is determined according to d×(0.8). 1.0) min calculation, where d is the diameter of the rod in mm. The holding time is calculated with respect to the diameter d of the rod to ensure a uniform temperature field from the core to the surface of the rod, sufficient solid solution, and to prevent excessive holding time from causing β-grain growth.
[0041] Preferably, in some embodiments, the second time in step S6 is 2 to 3 hours. The second time can typically, but not limitedly, be set to 2 hours, 2.5 hours, or 3 hours.
[0042] Preferably, in some embodiments, the third time in step S6 is 6 to 10 hours. The third time can typically, but not limitedly, be set to 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours.
[0043] The second aspect of the present invention provides a Ti55531 titanium alloy rod, which is prepared by the above method.
[0044] The present invention will be further described below with reference to the embodiments.
[0045] Example 1 3t Ti55531 titanium alloy ingot, phase transformation point 845℃.
[0046] Step 1: The ingot is heated using an electric furnace. It is loaded into the furnace at 850℃ and held for 1.5~2.5 hours, then heated to 1150℃ at a rate of 80℃ / hour and held for 7 hours. After being taken out of the furnace, it undergoes two upsetting and drawing operations. The upsetting pressure is 40%, and the drawing is done in an octagonal shape. After drawing, the height-to-diameter ratio is controlled at 2.0.
[0047] Step Two: The forged billet obtained in Step One is heated in an electric furnace. It is loaded into the furnace at 850℃ and held for 1.5~2.5h, then heated to 1030℃ at a rate of 60℃ / h and held for 7h. After being taken out of the furnace, it is subjected to two upsetting and drawing operations. The upsetting pressure is 40%, and the drawing is performed in an octagonal shape. After drawing, the height-to-diameter ratio is controlled at 2.0.
[0048] Step 3: The forged billet obtained in Step 2 is heated in an electric heating furnace. It is loaded into the furnace at 850℃ and held for 1.5~2.5h, then heated to 990℃ at a rate of 60℃ / h and held for 7h. After being taken out of the furnace, it is subjected to two upsetting and drawing operations. The upsetting pressure is 40%, and the drawing is performed in an octagonal shape. After drawing, the height-to-diameter ratio is controlled at 2.0.
[0049] Step 4: The forged billet obtained in Step 3 is heated in an electric furnace at 800℃ for 1.5~2.5 hours, then heated to 940℃ at a rate of 60℃ / hour and held for 7 hours. After exiting the furnace, it undergoes two upsetting and drawing operations. The upsetting pressure is 40%, and the drawing is performed in an octagonal shape, with the height-to-diameter ratio controlled at 2.0 after drawing. After one upsetting and one drawing, it is air-cooled for 25 minutes, and then returned to the furnace at 820℃ for 2 hours.
[0050] Step 5: The forged billet obtained in Step 4 is heated in an electric furnace at 800℃ for 1.5~2.5 hours, then heated to 890℃ at a rate of 50℃ / hour and held for 7 hours. After exiting the furnace, it undergoes two upsetting and drawing operations. The upsetting pressure is 40%, and the drawing is performed in an octagonal shape, with the height-to-diameter ratio controlled at 2.0 after drawing. After one upsetting and one drawing, it is air-cooled for 25 minutes, and then returned to the furnace at 820℃ for 2 hours.
[0051] Step Six: The forged billet obtained in Step Five is heated in an electric furnace. It is loaded into the furnace at a temperature below 700℃, then heated to 800℃ at a rate of 80℃ / h and held for 8 hours. After exiting the furnace, it undergoes three upsetting and drawing operations. The upsetting pressure is 32%, and the drawing is performed diagonally, maintaining a height-to-diameter ratio of 2.0 after drawing. After each upsetting and drawing operation, the billet is returned to the furnace at the original temperature for 2 hours.
[0052] Step Seven: The forged billet obtained in Step Six is heated in an electric furnace. It is loaded into the furnace at a temperature below 700℃, then heated to 800℃ at a rate of 80℃ / h and held for 8 hours. After exiting the furnace, it undergoes three upsetting and drawing operations. The upsetting pressure is 32%, and the drawing is performed diagonally, maintaining a height-to-diameter ratio of 2.0 after drawing. After each upsetting and drawing operation, the billet is returned to the furnace at the original temperature for 2 hours.
[0053] Step 8: The forged billet obtained in Step 7 is heated in an electric furnace. It is loaded into the furnace at a temperature below 700℃, then heated to 800℃ at a rate of 80℃ / h and held for 8 hours. After exiting the furnace, it undergoes three upsetting and drawing operations. The upsetting pressure is 32%, and the drawing is done diagonally, maintaining a height-to-diameter ratio of 2.0 after drawing. After each upsetting and drawing operation, the billet is returned to the furnace at the original temperature and held for 2 hours.
[0054] Step Nine: The forged billet obtained in Step Eight is heated in an electric furnace. It is loaded into the furnace at a temperature below 700℃, then heated to 800℃ at a rate of 80℃ / h and held for 8 hours. After exiting the furnace, it undergoes three upsetting and drawing operations. The upsetting pressure is 32%, and the drawing is done diagonally, maintaining a height-to-diameter ratio of 2.0. After each upsetting and drawing operation, the billet is returned to the furnace at the original temperature for 2 hours.
[0055] Step 10: The forged billet obtained in Step 9 is coated with heat-insulating paint and wrapped with heat-insulating cotton. It is then heated in an electric furnace, loaded into the furnace at a temperature below 700℃, and then heated to 830℃ at a rate of 80℃ / h, and held at that temperature for 8 hours. After being taken out of the furnace, it is axially upset at a rate of 2mm / s, with an upsetting deformation of 55%. After upsetting, it is radially elongated to 400mm×400mm×1600mm.
[0056] Step 11: The forged billet obtained in Step 10 is heated in an electric furnace. It is loaded into the furnace at a temperature below 700℃, then heated to 830℃ at a rate of 80℃ / h and held for 6 hours. It is then drawn out of the furnace to a bar length of Ф310mm×L. The single drawing reduction is ≤30mm. The surface temperature of the billet is monitored in real time. If the temperature is below 700℃, it is returned to the furnace for holding for 1~1.5 hours.
[0057] Step 12: Heat treatment of the bar stock: load the furnace at 800℃ → heat to 870℃ and hold for 280 min → cool to 830℃ at 2℃ / min and hold for 2 h → air cool → heat to 680℃ and load the furnace, hold for 8 h → air cool.
[0058] The tensile strength, yield strength, elongation, impact energy (KU2) of the bar were obtained as follows: 1366 / 1378 MPa, 1210 / 1233 MPa, 12.3% / 12.4%, 33 / 32 / 37 J, and 75 / 73 / 77 MPa•m. 1 / 2 .
[0059] Example 2 3t Ti55531 titanium alloy ingot, phase transformation point 843℃.
[0060] Steps one through nine and step eleven are the same as in Example 1.
[0061] Step 10: The forged billet obtained in Step 9 is coated with heat-insulating paint and wrapped with heat-insulating cotton. Then, it is heated in an electric furnace, loaded into the furnace at a temperature below 700℃, and then heated to 825℃ at a rate of 80℃ / h, and held at that temperature for 8 hours. After being taken out of the furnace, it is axially upset at a rate of 1mm / s, with an upsetting deformation of 50%. After upsetting, it is radially elongated to 400mm×400mm×1600mm.
[0062] Step 12: Heat treatment of the bar stock: load the furnace at 800℃ → heat to 870℃ and hold for 280 min → cool to 830℃ at 3℃ / min and hold for 2 h → air cool → heat to 650℃ and load the furnace, hold for 8 h → air cool.
[0063] The tensile strength of the bar was obtained as 1389 / 1400 MPa, yield strength as 1244 / 1276 MPa, elongation as 11.7% / 10.4%, impact energy KU2 as 30 / 31 / 31 J, and fracture toughness as 72 / 70 / 74 MPa•m. 1 / 2 .
[0064] Comparative Example 1 Steps one through nine are the same as in Example 1.
[0065] Step 10 uses the traditional upsetting and drawing method: the forged billet obtained in step 9 is loaded into the furnace at a temperature below 700°C, and then heated to 800°C at a rate of 80°C / h, and held at that temperature for 8 hours. After exiting the furnace, it is subjected to one axial upsetting and drawing, with an upsetting pressure of 40%, and the length is drawn into an octagonal shape to a length of 400*L.
[0066] Step eleven employs the traditional drawing method: the forged billet obtained in step ten is heated in an electric furnace, loaded into the furnace at a temperature below 700°C, and then heated to 800°C at a rate of 80°C / h, and held at that temperature for 6 hours. It is then drawn out of the furnace to a bar with a diameter of Ф310mm×L.
[0067] Step 12: Using conventional heat treatment methods: heat treatment of the bar stock, furnace loading when the furnace temperature reaches 870℃, holding for 3 hours → furnace cooling to 630℃ at a rate of 2℃ / min, holding for 8 hours → air cooling.
[0068] The tensile strength, yield strength, elongation, impact energy (KU2) of the bar were obtained as follows: 1205 / 1230 MPa, 1099 / 1076 MPa, 13.7% / 13.4%, 25 / 24 / 20 J, and fracture toughness as follows: 55 / 62 / 63 MPa•m. 1 / 2 .
[0069] As can be seen from the above examples and comparative examples, compared with traditional processes, the tensile strength of the material obtained by traditional forging and conventional heat treatment is only 1205. 1230MPa, impact energy KU2 is only 20 25J, fracture toughness 55 63MPa m 1 / 2 The tensile strength of this invention can reach 1366 Nm. 1400MPa, impact energy KU2≥30J, fracture toughness≥70MPa m 1 / 2 The strength and toughness matching has been significantly improved.
[0070] Finally, it should be noted that the embodiments described above are only some, not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.
Claims
1. A method for preparing Ti55531 titanium alloy rods, characterized in that, Includes the following steps: S1. Forging: The Ti55531 titanium alloy ingot is upset and drawn at 1100~1150℃. The upsetting pressure is 35~40%. The drawing is done by octagonal drawing. After drawing, the height-to-diameter ratio is controlled at 1.9~2.1 to obtain the first-grade forging billet. S2. Single-phase forging: The first-stage forging billet is upset forged at 30~200℃ above the β phase transformation point. The upset pressure is 35~40%, and the drawing is done by octagonal drawing. After drawing, the height-to-diameter ratio is controlled at 1.9~2.1 to obtain the second-stage forging billet. S3. Two-phase region forging: The secondary forging billet is upset forged at 40~60℃ below the β phase transformation point. The upset pressure is 30~33%, and the drawing is diagonal. After drawing, the height-to-diameter ratio is controlled at 1.9~2.1 to obtain the tertiary forging billet. S4. Forging before drawing: The three-stage forging billet is upset and drawn at 10~20℃ below the β phase transformation point, with an upsetting deformation of 50~60%. After upsetting, it is drawn radially to obtain a square billet with a height-to-diameter ratio of 4.0~4.
5. S5. Drawing and forging: The billet is drawn and forged at 10~20℃ below the β phase transformation point, with a single drawing reduction of ≤30mm, to obtain a bar of the target size. S6. Heat treatment: The bar is heated to 20-40°C above the β phase transformation point and held for a first time. Then it is cooled to 10-20°C below the β phase transformation point at a rate of 1-3°C / min and held for a second time. After the holding time is completed, it is air-cooled and then held at 650-700°C for a third time. After that, it is air-cooled to obtain the finished Ti55531 titanium alloy bar.
2. The method for preparing Ti55531 titanium alloy rods according to claim 1, characterized in that, In step S1, the Ti55531 titanium alloy ingot is subjected to a single-fire upsetting and drawing forging process, which involves two axial upsetting and drawing operations.
3. The method for preparing Ti55531 titanium alloy rods according to claim 1, characterized in that, In step S2, the first-stage forging billet is subjected to upsetting and drawing forging at decreasing temperatures for 4 to 6 cycles, with each cycle consisting of two upsetting and two drawing operations.
4. The method for preparing Ti55531 titanium alloy rods according to claim 3, characterized in that, When the forging temperature of the first upsetting and drawing is higher than 100℃ but not higher than 200℃, the two upsetting and two drawing are completed continuously without needing to be reheated in between. When the forging temperature of the first upsetting and drawing is not lower than 30℃ but not higher than 100℃, after completing one upsetting and one drawing, air cool for 20~30 minutes, then reheat and hold at a temperature 20~30℃ lower than the β phase transformation point for 1~2 hours, and then remove from the furnace to complete the remaining one upsetting and one drawing.
5. The method for preparing Ti55531 titanium alloy rods according to claim 1, characterized in that, In step S3, the secondary forging billet is subjected to four-fire upsetting and drawing forging. Each upsetting and drawing forging involves three upsettings and three drawings. After one upsetting and one drawing is completed, the forging billet is kept in the furnace at the original forging temperature for 1 to 2 hours before being taken out of the furnace for the next one upsetting and one drawing.
6. The method for preparing Ti55531 titanium alloy rods according to claim 1, characterized in that, In step S4, the three-stage forging billet is subjected to a single-fire upsetting and drawing forging process.
7. The method for preparing Ti55531 titanium alloy rods according to claim 6, characterized in that, In step S4, the three-stage forging billet is brushed with heat-insulating coating and wrapped with heat-insulating cotton before being heated in the furnace. After exiting the furnace, it is axially upsetting at a speed of 1~3mm / s.
8. The method for preparing Ti55531 titanium alloy rods according to claim 1, characterized in that, In step S5, the billet is subjected to a single-fire drawing and forging process. During the drawing and forging process, if the temperature is below 700℃, it is returned to the furnace for heat preservation for 1 to 1.5 hours.
9. The method for preparing Ti55531 titanium alloy rods according to claim 1, characterized in that, In step S6, the first time is determined based on the diameter of the bar, the second time is 2-3 hours, and the third time is 6-10 hours.
10. A Ti55531 titanium alloy bar, characterized in that, It is prepared by any one of claims 1-9.