A forging method for improving the mechanical property uniformity of titanium alloy bar ends

Abstract

The application discloses a kind of to improve the forging method of the mechanical property uniformity of titanium alloy bar end, adopt continuous round section forging of blooming→cross fire change direction heating forging→elongation when rib surface alternate forging→U type anvil forming forging process;It utilizes high temperature continuous forging of blooming fire to speed up as-cast structure dynamic recrystallization, and control blank to be round section, improve the uniformity of circumferential deformation;Recrystallization fire is below phase transition point, above phase transition point cross fire change direction forging, inhibit the influence of end dead zone on structure uniformity;Enter two-phase region by the forging mode of rib surface alternation, finally in combination forming fire U type anvil forging, improve end metal flow uniformity.The forging method of the application effectively improves the end effect problem that large specification titanium alloy bar is caused because of the limitation of free forging method, end forging dead zone is big, metal flow is not uniform, while reducing the cutting amount of end, greatly improves the yield of titanium alloy bar.

Description

Technical Field

[0001] This invention belongs to the field of non-ferrous metal processing technology, specifically relating to a forging method for improving the uniformity of mechanical properties at the ends of titanium alloy bars, mainly used for preparing finished TC4 titanium alloy bars with specifications of Φ200mm~Φ300mm. Background Technology

[0002] As is well known, titanium and titanium alloys are widely used in the aerospace field due to their excellent comprehensive properties, such as low density, high specific strength, low coefficient of thermal expansion, good corrosion resistance, high compatibility, and easy welding. They are used to manufacture aircraft structural components, engine parts, propellers, missiles, and satellites.

[0003] Among these applications, the uniformity of the mechanical properties of titanium alloys is even more stringent when used in the manufacture of aero-engine components. Currently, most titanium alloys used in aero-engine components are formed by die forging. The billets used in die forging are produced by free forging, typically by sawing a single long cylindrical bar according to the part's dimensions. During free forging, the metal flow is less constrained by the die, but the flow is restricted in the area in contact with the hammer and anvil due to friction, creating a deformation dead zone. This characteristic naturally results in differences between the dead zone and the streamlined zone in free-forged products, especially at the end area in contact with the hammer and anvil during upsetting. The combined effect of the deformation dead zone and the rapid temperature drop at the free end leads to insufficient deformation at the end, leaving uneven microstructure. This results in poor uniformity of mechanical properties at different locations in the billet, often referred to as the end effect of free-forged bars. For ordinary structures, this difference is acceptable, but for aero-engine structures, this difference should be minimized or even eliminated. Taking TC4 titanium alloy free-forged bars with a common specification of Ф200mm~Ф300mm for aero-engine parts as an example, their length-to-diameter ratio is often above 8, while the original billet for forging a bar has a maximum length-to-diameter ratio (or height-to-diameter ratio) of 2. Furthermore, titanium alloys are difficult to deform, often requiring repeated upsetting and drawing processes. This results in a significant inhomogeneity in the microstructure and properties of the final forged bar ends compared to the center. According to bar inspection specifications, test specimens are sawn from the ends of the bars. After heat treatment, a set of tensile specimens is taken circumferentially from the D / 4 position of the specimens for testing. The difference between the maximum and minimum room temperature tensile strength Rm can reach 30MPa, and the difference between the maximum and minimum elongation after fracture A can reach 15%, making them unusable directly. The conventional solution to this problem is to improve the overall uniformity of the core and edges of the bar while increasing the amount of material removed from the ends. However, this has failed to develop an effective method for improving the performance uniformity of the bar end region, resulting in a very low yield.

[0004] In view of this, this invention is hereby proposed. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a forging method to improve the uniformity of mechanical properties at the ends of titanium alloy bars. This method is mainly used to solve the problem that the end effect of titanium alloy bars after free forging leads to poor uniformity of microstructure and properties at the ends of the forged bars.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A forging method for improving the uniformity of mechanical properties at the ends of titanium alloy bars includes the following steps:

[0008] Step 1: Forging of continuous circular cross-section billet

[0009] In the billet opening stage, upsetting with a flat anvil and transverse elongation are used, followed by continuous furnace reheating for forging. This fully utilizes the dynamic recrystallization at high temperature to refine the as-cast structure and maintains a round cross-section after forging, resulting in relatively uniform circumferential deformation of the billet.

[0010] Step 2, Cross-fire reversal forging

[0011] The recrystallization process begins by heating the billet below the phase transformation point. After exiting the furnace, the billet is axially uplifted to the radial direction of the original ingot. At this point, the metal from the original end is distributed on the circumferential surface of the billet. The billet is then returned to the furnace for another heat and heated above the phase transformation point. The circumferential surface (original end face) with stored strain energy undergoes further static recrystallization and refinement in the furnace. After exiting the furnace, the billet is axially uplifted to the axial direction of the original ingot, thus achieving end reversion. This completes one round of cross-heat reversal forging. During this process, the billet has a square cross section.

[0012] Step 3: Alternate forging of the facets during drawing.

[0013] When the billet enters the two-phase region elongation forging stage, the forging method of alternately pressing down the edges and faces of the cross section is used to change the phenomenon of large differences in end metal flow resistance caused by the different contact areas between the edges and faces of the billet end and the hammer and anvil during the elongation process, thereby improving the uniformity of end deformation.

[0014] Step 4: U-shaped anvil forming and forging

[0015] The forming process employs U-shaped anvil forging, which increases the constraint on the circumferential surface of the billet during the forging process and further reduces the difference in the direction of metal flow in the billet.

[0016] Furthermore, the continuous circular cross-section forging in step 1 is a two-stage continuous forging process, specifically as follows:

[0017] The first heating temperature is 1100℃~1200℃, the heating and heat preservation coefficient is 0.65~0.85, and the total deformation of upsetting and transverse elongation is 50%~65%.

[0018] The second heating temperature is 1030℃~1100℃, and the holding time is 60min~210min; the total deformation of upsetting and transverse elongation is 45%~55%.

[0019] Furthermore, in step 1, the continuous circular cross-section forging process of the billet is carried out using upper and lower flat anvils. Each forging involves two upsetting and two drawing operations. The axial direction of the billet is always along the original axial direction of the ingot. After each drawing operation, the billet is square in cross-section. The billet is then placed horizontally on the flat anvil and rolled forged into a circular cross-section. After forging, it is air-cooled.

[0020] Furthermore, the specific process of cross-fire reversal forging in step 2 is divided into the following two stages:

[0021] First stage: Heat to 30℃~50℃ below the phase transformation point, with a heat preservation coefficient of 0.65~0.75. Use upper and lower flat anvils for forging, upsetting once and then radial drawing. The cross section after forging is square. The total forging ratio is controlled between 1.7 and 2.5, so that the original end of the billet is moved to the circumference of the billet. After forging, return to the furnace.

[0022] Second stage: The temperature is raised to 30℃~50℃ above the phase transformation point, with a heat preservation coefficient of 0.4~0.5. After exiting the furnace, the upper and lower flat anvils are used for upsetting once and then axial drawing. The cross section after forging is octagonal, and the forging ratio is between 1.4 and 1.8. The axial direction of the billet returns to the original axial direction, and the billet is water-cooled after forging.

[0023] Furthermore, the specific process of alternating forging of the facets during the elongation process in step 3 is as follows:

[0024] The billet is heated to 30℃~50℃ below the phase transformation point, with a heat retention coefficient of 0.65~0.75. It is forged using an anvil with both upper and lower flat anvils. The length-to-diameter ratio of the billet before drawing is controlled at 0.8~1.2, and the cross-section is square. The billet is pressed down and drawn along the edges of the square cross-section. The rotation angle of the billet between each pass is controlled at 45°. The edges and faces are forged separately in adjacent passes. The edge deformation is small in the first pass, and the amount of pressing down is marked as ①. Then, the billet is rotated 45° for the second pass, and the large face is deformed. The amount of pressing down is marked as ②. Then, the billet is rotated 45° for the third pass, and the edge deformation is small. The amount of pressing down is marked as ③. Where ①+③=②. Then, the billet is shaped by conventional flat anvil with a single pressing down amount less than or equal to ③ until the cross-section is nearly circular.

[0025] Furthermore, in step 3, during the alternating forging of the elongated facets, the pressing rate for each step is 30mm / s to 60mm / s, and the feed rate is 100mm to 200mm.

[0026] Furthermore, in step 4, during the U-shaped anvil forming forging, the sizing zone length of the U-shaped anvil is 400mm to 550mm, the deformation per forging is ≤15%, the forging is carried out at a uniform speed, and the finished product is air-cooled.

[0027] Furthermore, the forging method is mainly used to prepare finished TC4 titanium alloy bars with a specification of Φ200mm~Φ300mm, in order to improve the uniformity of the mechanical properties at the ends of the finished TC4 titanium alloy bars. Of course, it can also be used to prepare other grades of titanium alloys, such as TA15 and TC17 titanium alloy bars for aero-engines, which will not be described in detail here.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The forging method provided by this invention,

[0030] By controlling the circular cross-section forging during the initial forging process, the direction of forging across and above the phase transformation point, and the alternating forging of the faceted surfaces, and finally using a U-shaped anvil to constrain the free widening of the ends, the deformation differences in various directions during the free forging process of the bar are effectively reduced. This results in a significant improvement in the mechanical properties of the bar ends and a substantial increase in yield. Furthermore, practical verification has shown that using this method to prepare finished TC4 titanium alloy bars with specifications ranging from Φ200mm to Φ300mm, the room temperature tensile test results meet the standard requirements, with a tensile strength range within 10MPa and an elongation at fracture range within 3%, fully meeting the high standard requirements for uniform mechanical properties of titanium alloy materials in aero-engines. This forging method is also applicable to the preparation of TA15 and TC17 titanium alloy bars for aero-engines. Attached Figure Description

[0031] The accompanying drawings are incorporated in and form part of this specification, and together with the description serve to explain the principles of the invention.

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a flowchart of a forging method for improving the uniformity of mechanical properties at the ends of titanium alloy bars according to the present invention;

[0034] Figure 2 This is a low-magnification corrosion microstructure of the end of a TC4 titanium alloy bar with a diameter of Φ300mm prepared in Example 1 of this invention;

[0035] Figure 3 This is a 200x magnified corrosion microstructure image of the end of a TC4 titanium alloy bar with a diameter of Φ300mm prepared in Example 1 of this invention;

[0036] Figure 4This is a 500x magnified corrosion microstructure image of the end of a TC4 titanium alloy bar with a diameter of Φ300mm prepared in Example 1 of this invention;

[0037] Figure 5 This is a low-magnification corrosion microstructure image of the end of a TC4 titanium alloy bar with a diameter of Φ220mm prepared in Example 2 of this invention;

[0038] Figure 6 This is a 200x magnified corrosion microstructure image of the end of a TC4 titanium alloy bar with a diameter of Φ220mm prepared in Example 2 of this invention;

[0039] Figure 7 This is a 500x magnification image of the corrosion structure at the end of a TC4 titanium alloy bar with a diameter of Φ220mm prepared in Example 2 of this invention. Detailed Implementation

[0040] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatuses consistent with some aspects of the invention as detailed in the appended claims.

[0041] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0042] Please see Figure 1 As shown, the present invention provides a forging method for improving the uniformity of mechanical properties at the ends of titanium alloy bars, specifically including the following steps:

[0043] Step 1: Forging of continuous circular cross-section billet

[0044] In the billet opening stage, a flat anvil is used for upsetting and transverse elongation, followed by continuous furnace reheating forging. This fully utilizes the dynamic recrystallization at high temperatures to refine the as-cast structure and maintains a circular cross-section after forging, resulting in relatively uniform circumferential deformation of the billet.

[0045] Specifically, the continuous circular cross-section forging of the billet is a two-stage continuous forging process, the specific process of which is as follows:

[0046] The first heating temperature is 1100℃~1200℃, the heating and heat preservation coefficient is 0.65~0.85, the total deformation of the upsetting and transverse drawing is 50%~65%, after upsetting and drawing to a square cross section, it is rolled and forged into a circle with a transverse anvil, with a total of 2 upsetting and 2 drawing. The axial direction of the billet is always along the original axial direction of the ingot, and it is returned to the furnace for the second heating.

[0047] The second heating temperature is 1030℃~1100℃, and the holding time is 60min~210min; the total deformation of the upsetting and transverse drawing is 45%~55%, with a total of 2 upsetting and 2 drawing. After upsetting and drawing to a square cross section, it is rolled and forged into a circle with a transverse anvil. The axial direction of the billet is always along the original axial direction of the ingot, and it is air-cooled to room temperature.

[0048] Step 2, Cross-fire reversal forging

[0049] The recrystallization furnace first heats the billet below the phase transformation point. After exiting the furnace, the billet is axially uplifted to the radial direction of the original ingot. At this time, the metal at the original end is distributed on the circumferential surface of the billet. Then, it is returned to the furnace for another furnace and heated to above the phase transformation point for holding. The circumferential surface with stored strain energy is further statically recrystallized and refined in the furnace. After exiting the furnace, the billet is axially uplifted to the axial direction of the original ingot, realizing the end return. This completes one round of cross-fire reversal forging. During this process, the billet has a square cross section.

[0050] Specifically, the process of cross-fire reversal forging is divided into the following two stages:

[0051] First stage: Heat to 30℃~50℃ below the phase transformation point, with a heat preservation coefficient of 0.65~0.75. Use upper and lower flat anvils for forging, upsetting once and then radial drawing. The cross section after forging is square. The total forging ratio is controlled between 1.7 and 2.5, so that the original end of the billet is moved to the circumference of the billet. After forging, return to the furnace.

[0052] Second stage: The temperature is raised to 30℃~50℃ above the phase transformation point, with a heat preservation coefficient of 0.4~0.5. After exiting the furnace, the upper and lower flat anvils are used for upsetting once and then axial drawing. The cross section after forging is octagonal, and the forging ratio is between 1.4 and 1.8. The axial direction of the billet returns to the original axial direction, and the billet is water-cooled after forging.

[0053] Step 3: Alternate forging of the facets during drawing.

[0054] When the billet enters the two-phase elongation forging stage, the forging method of alternating pressing down the edges and faces of the cross section changes the phenomenon of large differences in end metal flow resistance caused by the different contact areas between the edges and faces of the billet and the hammer and anvil during the elongation process, thereby improving the uniformity of end deformation.

[0055] Specifically, the process of alternating forging of edges and faces during elongation is as follows: The billet is heated to 30℃~50℃ below the phase transformation point, with a heat preservation coefficient of 0.65~0.75. Flat anvils are used for forging. The length-to-diameter ratio of the billet before elongation is controlled at 0.8~1.2, and the cross-section is square. The billet is pressed down and elongated along the edges of the square cross-section. The rotation angle of the billet between each pass is controlled at 45°. The edges and faces are forged separately in adjacent passes. The first pass has a small deformation of the edges, and the amount of pressing down is marked as ①. Then, the billet is rotated 45° for the second pass, and a large deformation is made on the large face, and the amount of pressing down is marked as ②. Then, the billet is rotated 45° for the third pass, and a small deformation is made on the original edges, and the amount of pressing down is marked as ③. Where ①+③=②, and then the standard flat anvil shaping is performed with a single pressing down amount less than or equal to ③ until the cross-section is nearly circular. If the forging temperature is lower than the set temperature during the process, it needs to be returned to the furnace for reheating. At the same time, the pressing rate is required to be 30mm / s to 60mm / s each time, and the feed rate is required to be 100mm to 200mm.

[0056] Step 4: U-shaped anvil forming and forging

[0057] The forming process employs U-shaped anvil forging, which increases the constraint on the circumferential surface of the billet during the forging process and further reduces the difference in the direction of metal flow in the billet.

[0058] Specifically, during U-shaped anvil forming forging, the sizing zone length of the U-shaped anvil is 400mm to 550mm, the deformation per single forging is ≤15%, the forging is carried out at a uniform speed, and the finished product is air-cooled.

[0059] To further verify the effectiveness of the forging method of the present invention, the inventors conducted the following specific embodiments:

[0060] Example 1 (Preparation of TC4 titanium alloy rods with a diameter of 300 mm)

[0061] 1) Continuous forging after billet preparation

[0062] TC4 titanium alloy ingots with a diameter of Ф720mm and a phase transformation point of 990℃ were used. The first heating temperature was 1150℃, and the holding coefficient was 0.75. Using a flat anvil, the ingots were forged into square billets by two upsetting and two transverse elongation forgings with a total deformation of 55%, and then the cross-section was shaped into a circle. After forging, the billets were returned to the furnace for a second heating at 1050℃ and held for 120 minutes. After the second heating, the billets were forged again by two upsetting and two transverse elongation forgings with a total deformation of 50%, and then the cross-section was shaped into a circle. Finally, the billets were air-cooled.

[0063] 2) Cross-fire reversing forging

[0064] After the billet is loaded into the furnace, it is heated to 950℃ with a holding coefficient of 0.70. It is then forged using upper and lower flat anvils. The billet is upsetting and radially elongated once with a total forging ratio of 2.0. The cross-section after forging is square. After forging, it is returned to the original heating furnace. It is then heated to 1020℃ and held for 200 minutes. After being taken out of the furnace, it is upsetting and axially elongated once with upper and lower flat anvils with a total forging ratio of 1.7. The cross-section after forging is regular octagonal. After forging, it is water-cooled for 3 hours.

[0065] 3) Alternating forging of facets during drawing

[0066] After the billet is loaded into the furnace, it is heated to 940℃ with a holding coefficient of 0.75. Forging is carried out using upper and lower flat anvils with a pressing rate of 40mm / s. After loading, the billet is rotated 45° to start pressing and drawing from the edge, with a pressing amount of 80mm. After rotating 45°, the second drawing is started with a pressing amount of 140mm. After rotating 45° again, the third drawing is started with a pressing amount of 60mm. At this time, the billet produces new edges. The pressing rate is set to 40mm / s and the pressing amount is 60mm. Shaping begins. After completing 4 passes, the billet is returned to the furnace for reheating. After holding at the temperature for 60 minutes, the billet is removed from the furnace and shaped until the cross-section of the billet is nearly circular. At this time, the nominal diameter of the billet is 330mm. The billet is then air-cooled after forging.

[0067] 4) U-shaped anvil finished product forging

[0068] The billet was heated to 940℃ and held for 210 minutes before being taken out of the furnace. The drawing rate was set to 30 mm / s and the feed rate to 100 mm. A U-shaped anvil with a sizing zone length of 450 mm was used for drawing the finished product. The target diameter of the finished product reached 310 mm. After forging, the product was air-cooled and finally machined to produce TC4 titanium alloy finished bars with a specification of Φ300 mm.

[0069] A low-magnification sample was cut from the end of a 300mm TC4 titanium alloy finished bar prepared in this embodiment. The microstructure after corrosion is shown in the image below. Figure 2 As shown, a metallographic sample is taken from a low-power section and observed under a microscope at high power to examine the microstructure. Figure 3 , 4 As shown, the uniformity of the microstructure at the end of the bar is evaluated. After standard heat treatment, tangential tensile specimens are taken at six positions along the D / 4 mark of the specimen to test the mechanical properties. The results are shown in Table 1.

[0070] Table 1. Room temperature tensile properties of the bar ends in Example 1 (Heat treatment regime: 790℃ / 120min, air cooling)

[0071]

[0072] from Figures 2-4It can be seen that the Φ300mm typical specification bar prepared by the embodiment of the present invention has uniform low and high magnification at the ends. At the same time, the test data in Table 1 shows that the bar prepared by this forging method meets the standard requirements in the room temperature tensile test, and its maximum tensile strength difference is only 10MPa, and the maximum elongation after fracture is only 3%. The TC4 titanium alloy Φ300mm bar with good end performance uniformity was obtained, which fully meets the high standard requirements of aero-engine for the uniformity of mechanical properties of titanium alloy materials.

[0073] Example 2 (Preparation of TC4 titanium alloy rods with a diameter of Φ220mm)

[0074] 1) Continuous forging after billet preparation

[0075] TC4 titanium alloy ingots with a diameter of Ф820mm and a phase transformation point of 995℃ were used. The first heating temperature was 1160℃, and the holding coefficient was 0.75. Using a flat anvil, the ingots were forged into square billets by two upsetting and two transverse elongation forgings with a total deformation of 60%. The cross-section was then shaped into a circle. After forging, the billets were returned to the furnace for a second heating at 1080℃ and held for 150 minutes. After the second heating, the billets were forged again by two upsetting and two transverse elongation forgings with a total deformation of 52%. The cross-section was then shaped into a circle, and the billets were air-cooled.

[0076] 2) Cross-fire reversing forging

[0077] After the billet is loaded into the furnace, it is heated to 945℃ with a holding coefficient of 0.75. It is then forged using upper and lower flat anvils. The billet is upsetting and radially elongated once with a total forging ratio of 2.2. The cross-section after forging is square. After forging, it is returned to the original heating furnace. It is then heated to 1025℃ and held for 240 minutes. After being taken out of the furnace, it is upsetting and axially elongated once with upper and lower flat anvils with a total forging ratio of 1.8. The cross-section after forging is regular octagonal. It is then water-cooled for 3 hours.

[0078] 3) Alternating forging of facets during drawing

[0079] After the billet is loaded into the furnace, it is heated to 955℃ with a holding coefficient of 0.75. Forging is carried out using upper and lower flat anvils, and the pressing rate is set to 45mm / s. After loading, the billet is rotated 45° to start pressing and drawing from the edge, with a pressing amount of 100mm. After rotating 45°, the second drawing begins, with a pressing amount of 150mm. After rotating 45° again, the third drawing begins, with a pressing amount of 50mm. At this time, the billet produces new edges, and the pressing rate is set to 50mm / s, with a pressing amount of 60mm. Shaping begins. After completing 4 passes, the billet is returned to the furnace for reheating. After holding at the temperature for 30 minutes, the billet is removed from the furnace and shaped until the cross-section of the billet is nearly circular. At this time, the nominal diameter of the billet is 250mm. The billet is then air-cooled after forging.

[0080] 4) U-shaped anvil finished product forging

[0081] The billet was heated to 950℃ and held for 150 minutes before being taken out of the furnace. The drawing rate was set to 30 mm / s and the feed rate to 100 mm. A U-shaped anvil with a sizing zone length of 450 mm was used for drawing the finished product. The target diameter of the finished product reached 230 mm. After forging, the product was air-cooled and finally machined to produce TC4 titanium alloy finished bars with a specification of Φ220 mm.

[0082] A low-magnification sample was cut from the end of a 220mm TC4 titanium alloy finished bar prepared in this embodiment. The microstructure after corrosion is shown in the image below. Figure 5 As shown, a metallographic sample is taken from a low-power section and observed under a microscope at high power to examine the microstructure. Figure 6 , 7 As shown, the uniformity of the microstructure at the end of the bar is evaluated. After standard heat treatment, tangential tensile specimens are taken at four positions along the D / 4 mark of the specimen to test the mechanical properties. The results are shown in Table 2.

[0083] Table 1. Room temperature tensile properties of the bar ends in Example 2 (heat treatment regime: 790℃ / 120min, air cooling)

[0084]

[0085] from Figures 5-7 It can be seen that the Φ220mm typical specification bar prepared by the embodiment of the present invention has uniform low and high magnification at the ends. At the same time, the test data in Table 2 shows that the bar prepared by this forging method meets the standard requirements in the room temperature tensile test, and its maximum tensile strength range is only 7MPa, and the elongation after fracture range is only 2%. The TC4 titanium alloy Φ220mm bar with good end performance uniformity was obtained, which fully meets the high standard requirements of aero-engine for the uniformity of mechanical properties of titanium alloy materials.

[0086] In summary, the forging method of the present invention for improving the uniformity of mechanical properties at the ends of titanium alloy bars produces bars with uniform microstructure at both high and low magnification, resulting in more uniform mechanical properties. This effectively improves the end effect problem caused by large dead zones and uneven metal flow at the ends of large-size titanium alloy bars due to the limitations of free forging methods. At the same time, it reduces the amount of material removed from the ends and significantly improves the yield of titanium alloy bars.

[0087] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention.

[0088] It should be understood that the present invention is not limited to the content already described above, and various modifications and changes can be made without departing from its scope. The scope of the present invention is limited only by the appended claims.

Claims

1. A forging method for improving the uniformity of mechanical properties at the ends of titanium alloy bars, characterized in that, Includes the following steps: Step 1: Forging of continuous circular cross-section billet In the billet opening stage, upsetting with a flat anvil and transverse elongation are used, followed by continuous furnace reheating for forging. This fully utilizes the dynamic recrystallization at high temperature to refine the as-cast structure and maintains a round cross-section after forging, resulting in relatively uniform circumferential deformation of the billet. Step 2, Cross-fire reversal forging The recrystallization process begins by heating the billet below the phase transformation point. After exiting the furnace, the billet is axially uplifted to the radial direction of the original ingot. At this point, the metal from the original end is distributed on the circumferential surface of the billet. The billet is then returned to the furnace for another heat and heated above the phase transformation point. The circumferential surface, which stores strain energy, undergoes further static recrystallization and refinement in the furnace. After exiting the furnace, the billet is axially uplifted again to the axial direction of the original ingot, thus achieving end reversion. This completes one round of cross-heat reversal forging. During this process, the billet has a square cross section. Step 3: Alternate forging of the facets during drawing. When the billet enters the two-phase region elongation forging stage, the forging method of alternately pressing down the edges and faces of the cross section is used to change the phenomenon of large differences in end metal flow resistance caused by the different contact areas between the edges and faces of the billet end and the hammer and anvil during the elongation process, thereby improving the uniformity of end deformation. Step 4: U-shaped anvil forming and forging The forming process employs U-shaped anvil forging, which increases the constraint on the circumferential surface of the billet during the forging process and further reduces the difference in the direction of metal flow in the billet.

2. The forging method for improving the uniformity of mechanical properties at the ends of titanium alloy bars according to claim 1, characterized in that, The continuous circular cross-section forging in step 1 is a two-stage continuous forging process, specifically as follows: The first heating temperature is 1100℃~1200℃, the heating and heat preservation coefficient is 0.65~0.85, and the total deformation of upsetting and transverse elongation is 50%~65%. The second heating temperature is 1030℃~1100℃, and the holding time is 60min~210min; the total deformation of upsetting and transverse elongation is 45%~55%.

3. The forging method for improving the uniformity of mechanical properties at the ends of titanium alloy bars according to claim 2, characterized in that, In step 1, the continuous circular cross-section forging process of the billet is carried out using upper and lower flat anvils. Each forging involves two upsetting and two drawing operations. The axial direction of the billet is always along the original axial direction of the ingot. After each drawing operation, the billet is square in cross-section. The billet is then placed horizontally on the flat anvil and rolled forging into a circular cross-section. After forging, it is air-cooled.

4. The forging method for improving the uniformity of mechanical properties at the ends of titanium alloy bars according to claim 1, characterized in that, The specific process of cross-fire reversal forging in step 2 is divided into the following two stages: First stage: Heat to 30℃~50℃ below the phase transformation point, with a heat preservation coefficient of 0.65~0.

75. Use upper and lower flat anvils for forging, upsetting once and then radial drawing. The cross section after forging is square. The total forging ratio is controlled between 1.7 and 2.5, so that the original end of the billet is moved to the circumference of the billet. After forging, return to the furnace. Second stage: The temperature is raised to 30℃~50℃ above the phase transformation point, with a heat preservation coefficient of 0.4~0.

5. After exiting the furnace, the upper and lower flat anvils are used for upsetting once and then axial drawing. The cross section after forging is octagonal, and the forging ratio is between 1.4 and 1.

8. The axial direction of the billet returns to the original axial direction, and the billet is water-cooled after forging.

5. The forging method for improving the uniformity of mechanical properties at the ends of titanium alloy bars according to claim 1, characterized in that, The specific process of alternating forging of the facets during the elongation process in step 3 is as follows: The billet is heated to 30℃~50℃ below the phase transformation point, with a heat retention coefficient of 0.65~0.

75. It is forged using an anvil with both upper and lower flat anvils. The length-to-diameter ratio of the billet before drawing is controlled at 0.8~1.2, and the cross-section is square. The billet is pressed down and drawn along the edges of the square cross-section. The rotation angle of the billet between each pass is controlled at 45°. The edges and faces are forged separately in adjacent passes. The edge deformation is small in the first pass, and the amount of pressing down is marked as ①. Then, the billet is rotated 45° for the second pass, and the large face is deformed. The amount of pressing down is marked as ②. Then, the billet is rotated 45° for the third pass, and the edge deformation is small. The amount of pressing down is marked as ③. Where ①+③=②. Then, the billet is shaped by conventional flat anvil with a single pressing down amount less than or equal to ③ until the cross-section is nearly circular.

6. The forging method for improving the uniformity of mechanical properties at the ends of titanium alloy bars according to claim 5, characterized in that, In step 3, during the alternating forging of the elongated facets, the pressing rate is 30mm / s to 60mm / s each time, and the feed rate is 100mm to 200mm.

7. The forging method for improving the uniformity of mechanical properties at the ends of titanium alloy bars according to claim 1, characterized in that, In step 4, during the U-shaped anvil forming forging, the sizing zone length of the U-shaped anvil is 400mm to 550mm, the deformation per forging is ≤15%, the forging is carried out at a uniform speed, and the finished product is air-cooled.

8. The forging method for improving the uniformity of mechanical properties at the ends of titanium alloy bars according to any one of claims 1 to 7, characterized in that, The forging method is mainly used to prepare finished TC4 titanium alloy bars with specifications of Φ200mm~Φ300mm, in order to improve the uniformity of the mechanical properties at the ends of the finished TC4 titanium alloy bars.

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