A method for preparing large-size pure titanium fine-grain rod

Abstract

The present application relates to a kind of preparation methods of large-scale pure titanium fine-grained bar, comprising the following steps: S1, single-phase zone forging: the blank is forged above phase transition point temperature, and the original cast structure of blank is fully broken by increasing deformation amount;S2, two-phase zone forging: the blank is forged below phase transition point temperature, and blank structure is further refined and homogenized;S3, low-temperature forming forging: the blank is forged below phase transition point temperature;S4, recrystallization annealing: the blank is recrystallized annealing below phase transition point temperature to obtain bar blank, and finished bar material is obtained after machining. The method uses free forging forming, the deformation amount of single-phase zone and the deformation amount of two-phase zone are optimized by optimizing heating and holding temperature, the number of traditional processes is greatly reduced, and the organization of bar material is controlled by matching recrystallization annealing temperature, and finally large-scale pure titanium fine-grained bar is prepared.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy processing technology and relates to a method for preparing large-size pure titanium fine-grained rods. Background Technology

[0002] Pure titanium is lightweight, corrosion-resistant, and possesses excellent biocompatibility, making it an ideal material for medical implants. Pure titanium exhibits high corrosion resistance in most media, particularly neutral, oxidizing, and seawater media, and its excellent weldability also leads to its widespread application in chemical equipment, ship hull parts, and seawater desalination plants. Currently, traditional forging methods for producing fine-grained pure titanium mainly involve increasing the deformation in both single-phase and two-phase regions. However, these methods have drawbacks such as requiring multiple forging passes, long processing cycles, high costs, low yield, and resulting in a coarse and uneven microstructure. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and propose a method for preparing large-size pure titanium fine-grained rods. The method adopts free forging and by optimizing the heating and holding temperature, the deformation amount in the single-phase region and the deformation amount in the two-phase region, the number of heating steps in the traditional process is greatly reduced. The microstructure of the rod is controlled by matching the recrystallization annealing temperature. The large-size pure titanium fine-grained rods finally prepared can achieve a grain size of grade 7 or above in the ASTM E112-13 standard.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A method for preparing large-size pure titanium fine-grained rods includes the following steps:

[0006] S1. Single-phase forging: Forging the billet above the phase transformation point temperature, thereby increasing the deformation amount so that the original as-cast structure of the billet can be fully broken.

[0007] S2, Two-phase region forging: Forging the billet below the phase transformation point temperature to further refine and homogenize the billet structure;

[0008] S3, Low-temperature forming forging: Forging the billet below the phase transformation point temperature;

[0009] S4. Recrystallization annealing: The billet is recrystallized and annealed below the phase transformation point temperature to obtain a billet, which is then machined to obtain the finished bar.

[0010] Furthermore, in step S1, the billet is forged in two passes above the phase transformation point temperature. The specific steps are as follows:

[0011] First heating: The heating temperature is 1040℃~1170℃, and the heating coefficient is 0.45min / mm~0.65min / mm. First, the four corners of the billet are upset at a rate of 50~90mm / s. Then, the forging process is adopted, and the upset-drawing ratio is controlled at 1.6~2.0. The upsetting is done by slow hammer upsetting at a rate of 5~25mm / s. The lengthening is done by cross anvil drawing at a rate of 50~90mm / s. After forging, the billet is air-cooled.

[0012] The second forging process involves heating at 940℃~1020℃ with a heating coefficient of 0.45min / mm~0.65min / mm. It employs an upsetting and drawing process with an octagonal forging ratio controlled at 1.6~2.0. Slow-speed hammer upsetting is used with a rate of 5~25mm / s. The drawing method is axial drawing with a rate of 50~90mm / s. The first drawing is unidirectional, and the second is a reciprocating drawing. The feed rate during axial drawing is 100~300mm. Post-forging cooling is air cooling.

[0013] The cumulative deformation of the single-phase forging is controlled to be greater than 30. At the beginning of the first forging, the surface temperature drop of the material is ≤150℃, and at the end of the first forging, the surface temperature drop of the material is ≤250℃. At the beginning of the second forging, the surface temperature drop of the material is ≤150℃, and at the end of the second forging, the surface temperature drop of the material is ≤250℃.

[0014] Furthermore, in S1, the upper anvil of the single-phase forging die uses a flat anvil with an anvil width of 500-700mm, and the lower anvil uses a flat anvil with an anvil width of 800-1000mm.

[0015] Furthermore, in step S2, the billet is forged in two passes at a temperature 80°C to 150°C below the phase transformation temperature, with a heating coefficient of 0.60 min / mm to 0.80 min / mm. The specific steps are as follows:

[0016] First forging: The billet is forged using upsetting, drawing, upsetting, and drawing processes. After the first forging is completed, the hot material is returned to the furnace and the holding time in the furnace is 60 min to 120 min.

[0017] The second forging process involves drawing and octagonalizing the billet, followed by air cooling after forging.

[0018] The drawing in the first and second heats is axial reciprocating drawing, with a drawing rate of 50-90 mm / s. During the axial drawing process, the first hammer feed is 300-350 mm, and the remaining feeds are 200 mm. The upsetting-drawing-forging ratio in the first and second heats is 1.5-1.8.

[0019] To control the cumulative deformation of the two-phase forging to be greater than 8, the material surface temperature drop should be ≤150℃ at the beginning of the first forging and ≤250℃ at the end of the first forging; the material surface temperature drop should be ≤150℃ at the beginning of the second forging and ≤250℃ at the end of the second forging.

[0020] Furthermore, in S2, the upper anvil of the two-phase forging die uses a flat anvil with an anvil width of 500-700mm, and the lower anvil uses a flat anvil with an anvil width of 500-700mm.

[0021] Furthermore, in step S3, the billet is forged in two passes below the phase transformation point temperature. The specific steps are as follows:

[0022] First heat treatment: The billet is held at 600℃~750℃ and drawn out, with a heating coefficient of 0.60min / mm~0.80min / mm and a drawing rate of 50~90mm / s. The feed amount during the first hammer drawing process is 200mm~250mm, and the feed amount during the remaining drawing processes is 200mm. After the first heat treatment is completed, the hot material is returned to the furnace.

[0023] The second heat treatment: the holding time in the furnace is 60 min to 120 min, the holding temperature is 600℃ to 750℃, the drawing and rounding process is adopted, and the forging cooling method is followed by air cooling;

[0024] To control the cumulative deformation of low-temperature forming forging to be greater than 4.5, the material surface temperature drop should be ≤150℃ at the beginning of the first forging and ≤250℃ at the end of the first forging; the material surface temperature drop should be ≤150℃ at the beginning of the second forging and ≤250℃ at the end of the second forging.

[0025] Furthermore, in S3, the upper anvil used during the stretching process is a flat anvil with a width of 300-500mm, and the lower anvil used is a flat anvil with a width of 300-500mm. During the rounding process, the upper anvil used is a flat anvil with a width of 300-500mm, and the lower anvil used is a V-shaped anvil.

[0026] Furthermore, the recrystallization annealing environment in S4 is atmospheric, the annealing temperature is 600℃~750℃, the holding time is 120min~360min, and the cooling method is air cooling.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] A method for preparing large-size pure titanium fine-grained rods is disclosed. This method controls the heating temperature, initial forging temperature, final forging temperature, deformation per forging pass, number of forging passes, and cumulative deformation per forging pass during single-phase forging, two-phase forging, and low-temperature forming forging. It also controls the recrystallization annealing temperature and cooling method to ultimately control the microstructure and properties of the pure titanium rods. The large-size pure titanium fine-grained rods prepared using this invention have a uniform microstructure, with a grain size reaching grade 7 or higher in the ASTM E112-13 standard. Flaw detection and room temperature tensile properties meet the technical agreement requirements.

[0029] Other features and advantages of the present invention will become clear from the following detailed description of exemplary embodiments of the invention with reference to the accompanying drawings. Attached Figure Description

[0030] 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.

[0031] 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.

[0032] Figure 1(a) shows the transverse high magnification microstructure of the large-size pure titanium fine-grained rod prepared in Example 1 after annealing;

[0033] Figure 1(b) shows the longitudinal high-magnification microstructure of the large-size pure titanium fine-grained rod prepared in Example 1 after annealing;

[0034] Figure 2(a) shows the transverse high magnification microstructure of the large-size pure titanium fine-grained rod prepared in Example 2 after annealing;

[0035] Figure 2(b) shows the longitudinal high-magnification microstructure of the large-size pure titanium fine-grained rod prepared in Example 2 after annealing;

[0036] Figure 3(a) shows the transverse high magnification microstructure of the large-size pure titanium fine-grained rod prepared in Example 3 after annealing;

[0037] Figure 3(b) shows the longitudinal high-magnification microstructure of the large-size pure titanium fine-grained rod prepared in Example 3 after annealing. Detailed Implementation

[0038] 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.

[0039] 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.

[0040] A method for preparing large-size pure titanium fine-grained rods specifically includes the following steps:

[0041] Step 1: Single-phase forging:

[0042] The first heating temperature is 1040℃~1170℃, and the heating coefficient is 0.45min / mm~0.65min / mm. The incoming material is first upset at the four corners with an upsetting speed of 50~90mm / s. The first heating adopts the upsetting and drawing process, with slow hammer upsetting at a speed of 5~25mm / s. The drawing is done with a cross anvil, and the cooling method after forging is air cooling.

[0043] The second heating temperature is 940℃~1020℃, with a heating coefficient of 0.45min / mm~0.65min / mm. An upsetting and drawing process with an octagonal forging is employed, using slow, multi-hammer upsetting at a rate of 15mm / s. The drawing is axial, with the first drawing being unidirectional and the second a reciprocating process at a rate of 50~90mm / s. The feed amount during axial drawing is 100~300mm. After final drawing, an octagonal treatment is performed. Forging cooling is achieved through air cooling. The single-phase zone upsetting-drawing ratio is controlled between 1.6 and 2.0, ensuring the cumulative deformation in the single-phase zone forging exceeds 30%. The upper anvil of the single-phase zone forging die uses a flat anvil with a width of 500~700mm, and the lower anvil uses a flat anvil with a width of 800~1000mm. At the start of the first forging, the surface temperature drop of the material is ≤150℃, and at the end of the first forging, the surface temperature drop of the material is ≤250℃; at the start of the second forging, the surface temperature drop of the material is ≤150℃, and at the end of the second forging, the surface temperature drop of the material is ≤250℃.

[0044] Step 2, Two-phase region forging:

[0045] The billet obtained in step one is forged in the two-phase region. At least two heat treatments are performed within a temperature range of 80℃ to 150℃ below the phase transformation point, with a heating coefficient of 0.60 min / mm to 0.80 min / mm. The first heat treatment uses an upsetting + drawing + upsetting + drawing process; the second heat treatment uses a drawing + octagonal forging process. Slow upsetting is performed at a rate of 5-25 mm / s; the two-phase region drawing is axial drawing, a reciprocating drawing process, with a drawing rate of 50-90 mm / s; during the axial drawing process, the first hammer feed is 300 mm to 350 mm, and the remaining feeds are 200 mm; the upsetting-drawing-forging ratio is 1.5 to 1.8. After the final drawing, an octagonal treatment is performed to control the cumulative deformation of the two-phase region forging to be greater than 8. After the first heat treatment, the hot material is returned to the furnace, and the furnace holding time is 60 min to 120 min. For two-phase forging dies, both the upper and lower anvils use flat anvils with a width of 500–700 mm. At the start of the first forging pass, the material surface temperature drop is ≤150℃, and at the start of the first forging pass, it is ≤250℃. At the start of the second forging pass, the material surface temperature drop is ≤150℃, and at the end of the second forging pass, it is ≤250℃. Air cooling is used after forging.

[0046] Step 3: Low-temperature forming and forging:

[0047] The billet obtained in step 2 is held at 600℃~750℃ and drawn, with a heating coefficient of 0.60min / mm~0.80min / mm. A drawing + rounding process is used, with a drawing rate of 50~90mm / s. The feed amount during the first drawing is 200mm~250mm, and the subsequent feed amounts are 200mm. The cumulative deformation of the low-temperature forming forging is controlled to be greater than 4.5. During drawing, a flat anvil with a width of 300~500mm is used for both the upper and lower anvils. During rounding, a flat anvil with a width of 300~500mm is used for both the upper and lower anvils.

[0048] After the first forging, the hot material is returned to the furnace, and the holding time is 60-120 minutes. At the start of the first forging, the surface temperature drop of the material is ≤150℃, and at the end of the first forging, the surface temperature drop is ≤250℃. At the start of the second forging, the surface temperature drop of the material is ≤150℃, and at the end of the second forging, the surface temperature drop is ≤250℃. Air cooling is used after forging.

[0049] Step 4: Recrystallization Annealing

[0050] The hot-worked bars obtained in step 3 were subjected to atmospheric recrystallization annealing in a recrystallization annealing furnace. The recrystallization annealing temperature was 610℃~680℃, the holding time was 120min~280min, and the cooling method was air cooling to control the microstructure of the annealed bars. The residual heat from the recrystallization annealing was used to straighten the bars and control their curvature. After machining, large-size fine-grained pure titanium bars were finally obtained.

[0051] The following explanation details the specific processing steps:

[0052] Example 1

[0053] Step 1: Single-phase forging:

[0054] Grade TA2, ingot size Ф620mm, phase transformation point 910℃, first-flush heating temperature 1040℃, heating coefficient 0.45min / mm, incoming material is first upset at four corners at an upsetting rate of 50mm / s, the first flush uses an upsetting and drawing process, slow hammer upsetting at an upsetting rate of 5mm / s; drawing is done with a horizontal anvil, upsetting-drawing-forging ratio 1.6~1.8, the first flush uses a 500mm flat anvil for the upper part and an 800mm flat anvil for the lower part. At the start of the first flush, the surface temperature of the material drops by 150℃, and at the end of the first flush, the surface temperature drops by 120℃. Post-forging cooling is air cooling.

[0055] The second forging process involves heating to 940℃ with a heating coefficient of 0.45 min / mm. The forging is performed using a reverse octagonal upsetting process with slow, multi-hammer upsetting at a rate of 5 mm / s. The drawing is axial, with the first drawing being unidirectional and the second a reciprocating process at a rate of 50 mm / s. The feed rate during axial drawing is 100-300 mm. After final drawing, the material undergoes a reverse octagonal treatment, with an upsetting-drawing-forging ratio of 1.6–1.8. At the start of the second forging process, the material surface temperature drops to 250℃, and at the end, it drops to 220℃. Post-forging cooling is achieved through air cooling.

[0056] Step 2, Medium-temperature forging:

[0057] The billet obtained in step 1 is forged in the two-phase region, with two heating cycles at a temperature 80°C below the phase transformation point (i.e., 830°C), and a heating coefficient of 0.60 min / mm.

[0058] The first forging process employs an upsetting + drawing + upsetting + drawing process; the second forging process employs a drawing + octagonal forging process. All drawing is axial, reciprocating, at a rate of 50 mm / s. During axial drawing, the first hammer feed is 300-350 mm, and subsequent feeds are 200 mm. The upsetting-drawing ratio is 1.5-1.8. After final drawing, an octagonal treatment is performed. The cumulative deformation in the two-phase zone forging is 8.6. After the first forging, the hot material is returned to the furnace for a 60-minute holding time. For the two-phase zone forging, both the upper and lower anvils are 500 mm flat. At the start of the first forging, the material surface temperature drops to 130°C, and at the end of the first forging, the material surface temperature drops to 110°C. At the start of the second forging, the surface temperature of the material dropped to 240°C, and at the end of the second forging, the surface temperature dropped to 210°C. The cooling method after forging was air cooling.

[0059] Step 3: Low-temperature forming and forging:

[0060] The billet obtained in step 2 is held at 600℃ and drawn, with a heating coefficient of 0.60 min / mm. The first forging cycle uses a drawing process, and the second forging cycle uses a drawing + rounding process. The drawing rate is 50 mm / s. The feed amount during the first hammer drawing process is 200 mm to 250 mm, and the feed amount for the remaining cycles is 200 mm. The cumulative deformation of the low-temperature forming forging is 4.9. After the first forging cycle, the hot material is returned to the furnace, and the holding time is 60 min. For the low-temperature forming forging drawing, a 300 mm flat anvil is used for both the upper and lower anvils. For the rounding process, a 300 mm flat anvil is used for the upper anvil, and a V-shaped anvil is used for the lower anvil. At the beginning of the first forging cycle, the surface temperature drop of the material is 130℃, and at the end of the first forging cycle, the surface temperature drop of the material is 110℃. At the beginning of the second forging cycle, the surface temperature drop of the material is 240℃, and at the end of the second forging cycle, the surface temperature drop of the material is 210℃. Forging cooling method followed by air cooling.

[0061] Step 4: Atmospheric recrystallization annealing:

[0062] The hot-worked bar obtained in step 3 was subjected to atmospheric recrystallization annealing in a recrystallization annealing furnace. The recrystallization annealing holding temperature was 610℃, the holding time was 120 min, and the cooling method was air cooling to control the microstructure of the annealed bar. The residual heat from the recrystallization annealing was used to straighten the bar and control its curvature. After machining, a Φ160mm pure titanium fine-grained bar was finally obtained.

[0063] Table 1 shows the room temperature mechanical properties of TA2 product after recrystallization annealing in Example 1. The results meet the requirements and have a certain margin. Figure 1(a) and Figure 1(b) show the transverse high magnification microstructure and longitudinal high magnification microstructure of Φ160mm pure titanium fine-grained rod after annealing, respectively. It can be seen that its transverse and longitudinal microstructures are uniform and fine, and the grain size can reach level 7 or above in the ASTM E112-13 standard.

[0064] Table 1.

[0065]

[0066]

[0067] Example 2

[0068] Step 1: Single-phase forging:

[0069] Grade TA2, ingot size Ф690mm, phase transformation point 920℃, first-flush heating temperature 1100℃, heating coefficient 0.55min / mm, incoming material is first upset at four corners at an upsetting rate of 90mm / s, the first flush uses an upsetting and drawing process, slow hammer upsetting at an upsetting rate of 15mm / s; drawing is done with a horizontal anvil, upsetting-drawing-forging ratio of 1.7~1.9, the first flush uses a 600mm upper flat anvil and an 800mm lower flat anvil. At the start of the first flush, the material surface temperature drops by 150℃, and at the end of the first flush, the material surface temperature drops by 120℃, and the post-forging cooling method is air cooling.

[0070] The second forging process involves heating to 1000℃ with a heating coefficient of 0.55 min / mm. The forging is performed using a reverse octagonal upsetting process with slow, multi-hammer upsetting at a rate of 15 mm / s. The drawing is axial; the first drawing is unidirectional, while the second is a reciprocating process at a rate of 90 mm / s. The feed rate during axial drawing is 100-300 mm. After final drawing, the material undergoes a reverse octagonal treatment, with an upsetting-drawing-forging ratio of 1.7–1.9. At the start of the second forging process, the material surface temperature drops to 250℃, and at the end, it drops to 220℃. Post-forging cooling is achieved through air cooling.

[0071] Step 2, Medium-temperature forging:

[0072] The billet obtained in step 1 is forged in the two-phase region. The forging process involves two heat treatments at 830℃ (90℃ below the phase transformation point), with a heating coefficient of 0.70 min / mm. The first heat treatment uses an upsetting + drawing + upsetting + drawing process. The second heat treatment uses a drawing + octagonal forging process. All drawing is axial, reciprocating, at a rate of 90 mm / s. During axial drawing, the first hammer feed is 300 mm–350 mm, and the subsequent feeds are 200 mm. The upsetting-drawing ratio is 1.6–1.8. After the final drawing, an octagonal treatment is performed. The cumulative deformation in the two-phase region forging is 9. After the first heat treatment, the hot material is returned to the furnace for a holding time of 60 min. For the two-phase region forging, both the upper and lower anvils are 600 mm flat anvils. At the start of the first forging, the surface temperature of the material drops by 130°C, and at the end of the first forging, the surface temperature drops by 110°C. At the start of the second forging, the surface temperature of the material drops by 240°C, and at the end of the second forging, the surface temperature drops by 210°C. The cooling method after forging is air cooling.

[0073] Step 3: Low-temperature forming and forging:

[0074] The billet obtained in step 2 is held at 700℃ and drawn, with a heating coefficient of 0.70 min / mm. The first forging uses a drawing process, and the second forging uses a drawing + rounding process. The drawing rate is 90 mm / s. The feed amount during the first hammer drawing process is 200 mm to 250 mm, and the feed amount for the remaining processes is 200 mm. The cumulative deformation of the low-temperature forming forging is 5.2. After the first forging, the hot material is returned to the furnace, and the holding time is 90 min. For the low-temperature forming forging drawing, a 400 mm flat anvil is used for both the upper and lower anvils. For the rounding process, a 400 mm flat anvil is used for the upper anvil, and a V-shaped anvil is used for the lower anvil. At the beginning of the first forging, the surface temperature drop of the material is 130℃, and at the end of the first forging, the surface temperature drop is 110℃. At the beginning of the second forging, the surface temperature drop of the material is 240℃, and at the end of the second forging, the surface temperature drop is 200℃. Forging cooling method followed by air cooling.

[0075] Step 4: Atmospheric recrystallization annealing:

[0076] The hot-worked bar obtained in step 3 was subjected to atmospheric recrystallization annealing in a recrystallization annealing furnace. The recrystallization annealing holding temperature was 650℃, the holding time was 150 min, and the cooling method was air cooling to control the microstructure of the annealed bar. The residual heat from the recrystallization annealing was used to straighten the bar and control its curvature. After machining, a Φ210mm pure titanium fine-grained bar was finally obtained.

[0077] Table 2 shows the room temperature mechanical properties of the TA2 product after recrystallization annealing in Example 2. The results meet the requirements and have a certain margin. Figure 2(a) and Figure 2(b) show the transverse high magnification microstructure and longitudinal high magnification microstructure of the Φ210mm pure titanium fine-grained rod after annealing, respectively. It can be seen that its transverse and longitudinal microstructures are uniform and fine, and the grain size can reach level 7 or above in the ASTM E112-13 standard.

[0078] Table 2.

[0079]

[0080] Example 3

[0081] Step 1: Single-phase forging:

[0082] Grade TA4, ingot size Ф690mm, phase transformation point 955℃, first-flush heating temperature 1170℃, heating coefficient 0.65min / mm, incoming material is first upset at four corners at an upsetting rate of 90mm / s, the first flush uses an upsetting and drawing process, slow hammer upsetting at an upsetting rate of 25mm / s; drawing is done with a horizontal anvil, upsetting-drawing-forging ratio of 1.8~2.0, the first flush uses a 700mm upper anvil and a 10000mm lower anvil. At the start of the first flush, the material surface temperature drops by 130℃, and at the end of the first flush, the material surface temperature drops by 100℃, and the post-forging cooling method is air cooling.

[0083] The second forging process involves heating at 1020℃ with a heating coefficient of 0.65 min / mm. The forging is performed using a reverse octagonal upsetting process with slow, multi-hammer upsetting at a rate of 15 mm / s. The drawing is axial, with the first drawing being unidirectional and the second a reciprocating process at a rate of 90 mm / s. The feed rate during axial drawing is 100-300 mm. After final drawing, the material undergoes a reverse octagonal treatment, with an upsetting-drawing-forging ratio of 1.8–2.0. At the start of the second forging process, the material surface temperature drops to 250℃, and at the end, it drops to 220℃. Post-forging cooling is achieved through air cooling.

[0084] Step 2, Medium-temperature forging:

[0085] The billet obtained in step 1 is forged in the two-phase region. The forging process involves two heat treatments at 805℃ (150℃ below the phase transformation point), with a heating coefficient of 0.80 min / mm. The first heat treatment uses an upsetting + drawing + upsetting + drawing process. The second heat treatment uses a drawing + octagonal forging process. All drawing is axial, reciprocating, at a rate of 90 mm / s. During axial drawing, the first hammer feed is 300 mm–350 mm, and the subsequent feeds are 200 mm. The upsetting-drawing ratio is 1.6–1.8. After the final drawing, an octagonal treatment is performed. The cumulative deformation of the two-phase region forging is 9.3. After the first heat treatment, the hot material is returned to the furnace for a holding time of 120 min. For the two-phase region forging, both the upper and lower anvils are 700 mm flat anvils. At the start of the first forging, the surface temperature of the material drops by 130°C, and at the end of the first forging, the surface temperature drops by 110°C. At the start of the second forging, the surface temperature of the material drops by 240°C, and at the end of the second forging, the surface temperature drops by 210°C. The cooling method after forging is air cooling.

[0086] Step 3: Low-temperature forming and forging:

[0087] The billet obtained in step 2 is held at 750℃ and drawn, with a heating coefficient of 0.80 min / mm. The first forging process uses a drawing process, and the second forging process uses a drawing + rounding process. The drawing rate is 90 mm / s. The feed amount during the first hammer drawing process is 200 mm to 250 mm, and the feed amount for the remaining processes is 200 mm. The cumulative deformation of the low-temperature forming forging is 4.1. After the first forging, the hot material is returned to the furnace, and the holding time is 120 min. For the low-temperature forming forging drawing, a 500 mm flat anvil is used for both the upper and lower anvils. For the rounding process, a 500 mm flat anvil is used for the upper anvil, and a V-shaped anvil is used for the lower anvil. At the beginning of the first forging, the surface temperature drop of the material is 130℃, and at the end of the first forging, the surface temperature drop is 110℃. At the beginning of the second forging, the surface temperature drop of the material is 240℃, and at the end of the second forging, the surface temperature drop is 210℃. Forging cooling method followed by air cooling.

[0088] Step 4: Atmospheric recrystallization annealing:

[0089] The hot-worked bar obtained in step 3 was subjected to atmospheric recrystallization annealing in a recrystallization annealing furnace. The recrystallization annealing holding temperature was 700℃, the holding time was 280 min, and the cooling method was air cooling to control the microstructure of the annealed bar. The residual heat from the recrystallization annealing was used to straighten the bar and control its curvature. After machining, a Φ400mm pure titanium fine-grained bar was finally obtained.

[0090] Table 3 shows the room temperature mechanical properties of TA4 product after recrystallization annealing in Example 3. The results meet the requirements and have a certain margin. Figure 3(a) and Figure 3(b) show the transverse high magnification microstructure and longitudinal high magnification microstructure of Φ400mm pure titanium fine-grained rod after annealing, respectively. It can be seen that its transverse and longitudinal microstructures are uniform and fine, and the grain size can reach level 7 or above in the ASTM E112-13 standard.

[0091] Table 3.

[0092]

[0093]

[0094] The large-size pure titanium fine-grained rods prepared using this invention have a uniform microstructure and a grain size that can reach level 7 or above in the ASTM E112-13 standard. The flaw detection and room temperature tensile properties meet the technical agreement requirements.

[0095] 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.

[0096] 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 method for preparing large-size pure titanium fine-grained rods, characterized in that, Includes the following steps: S1. Single-phase forging: The billet is forged in two stages above the phase transformation point temperature. First stage: The heating temperature is 1040℃~1170℃, and the heating coefficient is 0.45min / mm~0.65min / mm. The four corners of the billet are first upset at a rate of 50~90mm / s. Upsetting and drawing processes are used for forging, and the upsetting-drawing ratio is controlled at 1.6~2.

0. Slow-speed hammer upsetting is used at a rate of 5~25mm / s. Lengthening is done using a transverse anvil at a rate of 50~90mm / s. After forging, the billet is air-cooled. The second forging process involves heating at 940℃~1020℃ with a heating coefficient of 0.45 min / mm~0.65 min / mm. An octagonal upsetting and drawing process is employed, with an upsetting-drawing ratio controlled at 1.6~2.

0. Slow-speed hammer upsetting is used at a rate of 5~25 mm / s. The drawing process is axial, with a rate of 50~90 mm / s. The first drawing is unidirectional, while the second is a reciprocating process. The feed rate during axial drawing is 100~300 mm. Post-forging cooling is air cooling. Increasing the deformation amount allows for thorough fragmentation of the original as-cast structure of the billet. S2. Two-phase forging: Forging the billet below the phase transformation temperature further refines and homogenizes the billet microstructure; the billet undergoes two-stage forging at 80℃~150℃ below the phase transformation temperature, with a heating coefficient of 0.60min / mm~0.80min / mm. The specific steps are as follows: First forging: The billet is forged using upsetting, drawing, upsetting, and drawing processes. After the first forging is completed, the hot material is returned to the furnace and the holding time in the furnace is 60-120 minutes. The second forging process involves drawing and octagonalizing the billet, followed by air cooling after forging. The first and second firings are both axial reciprocating drawing, with a drawing rate of 50~90mm / s. During the axial drawing process, the first hammer feed is 300mm~350mm, and the remaining feeds are 200mm. At the start of the first forging, the surface temperature drop of the material is ≤150℃, and at the end of the first forging, the surface temperature drop of the material is ≤250℃; at the start of the second forging, the surface temperature drop of the material is ≤150℃, and at the end of the second forging, the surface temperature drop of the material is ≤250℃. S3. Low-temperature forming forging: The billet is forged in two passes below the phase transformation temperature. The specific steps are as follows: First heat treatment: The billet is held at 600℃~750℃ and drawn out, with a heating coefficient of 0.60min / mm~0.80min / mm and a drawing rate of 50~90mm / s. The feed amount during the first hammer drawing process is 200mm~250mm, and the feed amount during the remaining drawing processes is 200mm. After the first heat treatment is completed, the hot material is returned to the furnace. The second forging process involves holding the material in the furnace for 60 to 120 minutes at a temperature of 600°C to 750°C, using a drawing and rounding process, and air cooling after forging. At the start of the first forging, the surface temperature drop of the material is ≤150℃, and at the end of the first forging, the surface temperature drop of the material is ≤250℃; at the start of the second forging, the surface temperature drop of the material is ≤150℃, and at the end of the second forging, the surface temperature drop of the material is ≤250℃. S4. Recrystallization annealing: The billet is recrystallized and annealed below the phase transformation point temperature to obtain a billet, which is then machined to obtain the finished bar.

2. The method for preparing large-size pure titanium fine-grained rods according to claim 1, characterized in that, In S1, at the start of the first forging, the surface temperature drop of the material is ≤150℃, and at the end of the first forging, the surface temperature drop of the material is ≤250℃; at the start of the second forging, the surface temperature drop of the material is ≤150℃, and at the end of the second forging, the surface temperature drop of the material is ≤250℃.

3. The method for preparing large-size pure titanium fine-grained rods according to claim 2, characterized in that, In S1, the upper anvil of the single-phase forging die uses a flat anvil with an anvil width of 500-700mm, and the lower anvil uses a flat anvil with an anvil width of 800-1000mm.

4. The method for preparing large-size pure titanium fine-grained rods according to claim 1, characterized in that, In S2, the upper anvil of the two-phase forging die uses a flat anvil with an anvil width of 500-700mm, and the lower anvil uses a flat anvil with an anvil width of 500-700mm.

5. The method for preparing a large-size pure titanium fine-grained rod according to claim 1, characterized in that, In the S3 process, the upper anvil used during the stretching process is a flat anvil with a width of 300-500mm, and the lower anvil used is a flat anvil with a width of 300-500mm. During the rounding process, the upper anvil used is a flat anvil with a width of 300-500mm, and the lower anvil used is a V-shaped anvil.

6. The method for preparing a large-size pure titanium fine-grained rod according to claim 1, characterized in that, The recrystallization annealing environment in S4 is atmospheric, the annealing temperature is 600℃~750℃, the holding time is 120min~360min, and the cooling method is air cooling.

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