A method of forging TC18 titanium alloy bar to reduce anisotropy

Abstract

The present application relates to the technical field of metal processing, and particularly relates to a forging method for reducing anisotropy of TC18 titanium alloy bar, which comprises the following steps: S1, heating a TC18 titanium alloy bar ingot, and upsetting and drawing forging to obtain a forged blank; S2, sequentially passing the forged blank through six times of upsetting and drawing forging to obtain a TC18 titanium alloy bar with low anisotropy; in S2, the upsetting amount in the first and second times of upsetting and drawing forging is 50-55%, the upsetting amount in the third, fourth, fifth and sixth times of upsetting and drawing forging is 20-25%, and the drawing amount in the sixth time of upsetting and drawing forging is greater than or equal to 200%.

Description

Technical Field

[0001] This invention relates to the field of metal processing technology, and in particular to a forging method for reducing the anisotropy of TC18 titanium alloy bars. Background Technology

[0002] TC18 titanium alloy is a highly alloyed, high-strength near-β-type titanium alloy with a nominal composition of Ti-5Al-5Mo-5V-1Cr-1Fe. In the annealed state, TC18 titanium alloy has a strength of up to 1080 MPa, which can be increased to 1300 MPa after strengthening heat treatment. Due to its high strength, high plasticity, and good hardenability, TC18 titanium alloy is widely used in the manufacture and processing of aerospace load-bearing structural components.

[0003] In TC18 titanium alloy, the body-centered cubic β phase accounts for approximately 50%, and its grain orientation significantly affects the alloy's macroscopic mechanical properties, such as strength, plasticity, and toughness. Generally speaking, the β phase... <111> It has the highest directional strength and toughness, but the lowest plasticity. <100> The β-phase exhibits the lowest strength and toughness, but the highest plasticity; the difference in room temperature tensile strength between the two directions is approximately 200 MPa. Therefore, it is necessary to minimize the β-phase texture during alloy preparation to reduce the anisotropy of the alloy, thereby improving the consistency and stability of the component's performance.

[0004] Chinese patent CN112139413A discloses a forging method to improve the uniformity of microstructure and texture of large-size TC18 titanium alloy bars. While ensuring the performance of large-size TC18 titanium alloy bars, it reduces the risk of strong β-phase texture appearing locally in the bars through a "high-low-high" and multi-heating, small-deformation upsetting and drawing forging process. This significantly improves the uniformity of the bar's microstructure, texture, and mechanical properties, ensuring the quality stability of the bars. This method mainly improves uniformity by reducing the upsetting amount during forging, thereby reducing the risk of β-phase {100} deformation texture. However, due to insufficient accumulation of deformation stored energy, the β-phase only recovers during heat treatment, still retaining the deformation texture. Therefore, it cannot fundamentally solve the anisotropy problem of TC18 titanium alloy bars. Summary of the Invention

[0005] To address the shortcomings of the aforementioned processes, this invention provides a forging method for reducing the anisotropy of TC18 titanium alloy bars. By reducing the size of the β phase and increasing the recrystallization ratio of the β phase, the anisotropy of the bars is reduced, thereby improving the performance consistency of the bars.

[0006] This invention provides a forging method for reducing the anisotropy of TC18 titanium alloy bars, the forging method comprising:

[0007] S1. Heat the TC18 titanium alloy bar ingot and then upsetting and forging it to obtain a forging billet;

[0008] S2. The forging billet is subjected to six upsetting and drawing processes in sequence to obtain TC18 titanium alloy bars with low anisotropy;

[0009] In S2, the upsetting amount in the first and second upsetting forging is 50-55%, the upsetting amount in the third, fourth and fifth upsetting forging is 20-25%, and the drawing amount in the sixth upsetting forging is greater than or equal to 200%.

[0010] In some embodiments, in step S1, the TC18 titanium alloy bar ingot is heated to 250-300°C above the phase transformation temperature, and the final forging temperature is not lower than 750°C.

[0011] This invention does not impose any special limitations on the heating equipment, which can be selected from commonly used types in the art, including but not limited to electric resistance furnaces.

[0012] In some embodiments, during the first upsetting forging in S2, the TC18 titanium alloy bar ingot is heated to 70-90°C below the phase transformation temperature.

[0013] In some embodiments, during the second upsetting forging in S2, the TC18 titanium alloy bar ingot is heated to 150-200°C above the phase transformation temperature.

[0014] In some embodiments, during the third upsetting forging in S2, the TC18 titanium alloy bar ingot is heated to 70-90°C below the phase transformation temperature.

[0015] In some embodiments, during the fourth upsetting forging in S2, the TC18 titanium alloy bar ingot is heated to 40-60°C above the phase transformation temperature.

[0016] In some embodiments, during the fifth upsetting forging in S2, the TC18 titanium alloy bar ingot is heated to 70-90°C below the phase transformation temperature.

[0017] In some embodiments, during the fifth upsetting forging in S2, the TC18 titanium alloy bar ingot is heated to 35-40°C below the phase transformation temperature.

[0018] In some embodiments, the six upsetting and drawing forging processes are all hexagonal forging processes.

[0019] In some embodiments, the TC18 titanium alloy bar with low anisotropy in S2 has an L-direction tensile strength of 1100-1200 MPa and an impact toughness of 45-50 J / cm in all directions. 2 The tensile strength in the C-direction is 1100-1200 MPa in all directions, and the impact toughness is 50-55 J / cm in all directions. 2 .

[0020] Furthermore, the forging method includes:

[0021] (1) Heat the TC18 titanium alloy bar ingot to 850℃ with a heat retention coefficient of 0.4-0.5, then heat it to 1150℃ with a heat retention coefficient of 0.4-0.5, and then upset and draw it to obtain a forging billet; the upsetting amount of the forging billet is 50-55%, and hexagonal forging is performed during the drawing process, with a drawing reduction of 80-120mm / time, and the final forging temperature is not lower than 750℃;

[0022] (2) First upsetting and drawing forging: The forging billet obtained in step (1) is heated to Tβ-80℃ with a heat retention coefficient of 0.8-1.0. It is then upsetting and drawing forging once using a high-speed forging machine to obtain forging billet one. The upsetting amount of forging billet one is 50-55%. During the drawing process, hexagonal forging is performed, and the drawing reduction is 80mm-120mm / time.

[0023] (3) Second upsetting and drawing forging: The forging billet obtained in step (2) is heated to 850℃ with a heat preservation coefficient of 0.4-0.5, and then heated to 1050℃ with a heat preservation coefficient of 0.4-0.5. The billet is then subjected to two upsetting and drawing forging processes using a high-speed forging machine to obtain the second forging billet. The upsetting amount of the second forging billet is 50-55%. During the drawing process, hexagonal forging is performed, and the drawing reduction is 80mm-120mm / time. The final forging temperature is not lower than 750℃.

[0024] (4) Third upsetting and drawing forging: The forging billet two obtained in step (3) is heated to Tβ-80℃ with a heat retention coefficient of 0.8-1.0. It is then upsetting and drawing forging once using a high-speed forging machine to obtain forging billet three. The upsetting amount of forging billet three is 20-25%. During the drawing process, hexagonal forging is performed, and the drawing reduction is 80mm-120mm / time.

[0025] (5) Fourth upsetting and drawing forging: The forging billet three obtained in step (4) is heated to 850℃ with a heat preservation coefficient of 0.4-0.5, and then heated to Tβ+50℃ with a heat preservation coefficient of 0.4-0.5. The forging billet four is obtained by two upsetting and drawing forgings using a fast forging machine. The upsetting amount of the forging billet four is 20-25%. During the drawing process, hexagonal forging is performed, and the drawing reduction is 80mm-120mm / time.

[0026] (6) Fifth upsetting and drawing forging: Heat the forging blank four obtained in step (5) to Tβ-80℃, with a heat retention coefficient of 0.8-1.0, and repeatedly forge it 3-5 times with a high-speed forging machine to obtain forging blank five. The single forging is a single upsetting and drawing forging, with an upsetting amount of 20-25%. During the drawing process, hexagonal forging is performed, with a drawing reduction of 80mm-120mm / time.

[0027] (7) Sixth upsetting and drawing forging: The forging billet obtained in step (6) is heated to Tβ-35℃-Tβ-40℃ with a holding coefficient of 0.8-1.0, and then drawn and forged to the required size using a high-speed forging machine. Specifications: TC18 titanium alloy bar.

[0028] Compared with the prior art, the present invention further reduces the forging heating temperature of the two-phase region before the final heat treatment, requiring the final heat treatment elongation to be greater than or equal to 200%. This allows sufficient deformation storage energy to be accumulated during forging, enabling the β phase to fully recrystallize during heat treatment without selective orientation. Therefore, the influence of deformation texture can be completely eliminated, thereby fundamentally solving the anisotropy problem of TC18 titanium alloy bars.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] This invention achieves thorough refinement of the β phase during TC18 titanium alloy forging, accumulating sufficient deformation storage energy to allow for complete recrystallization of the β phase during heat treatment. On one hand, recrystallization exhibits no preferred orientation, completely resolving the anisotropy problem of the bar stock; on the other hand, recrystallization further refines the β phase, improving the uniformity of the bar stock. Therefore, this invention can significantly improve the consistency and stability of the properties of TC18 titanium alloy bars. Attached Figure Description

[0031] Figure 1 This is a scanning electron microscope (SEM) image of the orientation characteristics of the β phase in Example 1.

[0032] Figure 2 This is a scanning electron microscope (SEM) image of the orientation characteristics of the β phase in Example 2.

[0033] Figure 3 This is a scanning electron microscope (SEM) image of the orientation characteristics of the β phase in Example 3.

[0034] Figure 4 This is a scanning electron microscope (SEM) image of the orientation characteristics of the β phase, as shown in Comparative Example 1.

[0035] Figure 5 This is a scanning electron microscope (SEM) image of the orientation characteristics of the β phase, as shown in Comparative Example 2.

[0036] Figure 6 This is a scanning electron microscope (SEM) image of the orientation characteristics of the β phase, shown in Comparative Example 3. Detailed Implementation

[0037] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Example 1

[0039] This embodiment provides a forging method for reducing the anisotropy of TC18 titanium alloy bars, the forging method comprising:

[0040] (1) Heat the TC18 titanium alloy bar ingot to 850℃ with a heat retention coefficient of 0.5, then heat it to 1150℃ with a heat retention coefficient of 0.5, and then upset and draw it to obtain a forging billet; the upsetting amount of the forging billet is 50%, and hexagonal forging is performed during the drawing process, with a drawing reduction of 120mm / time.

[0041] (2) First upsetting and drawing forging: The forging blank obtained in step (1) is heated to Tβ-80℃ with a heat preservation coefficient of 1.0. It is then upsetting and drawing forging once using a fast forging machine to obtain forging blank one. The upsetting amount of forging blank one is 55%. During the drawing process, hexagonal forging is performed, and the drawing reduction is 80mm / time.

[0042] (3) Second upsetting and drawing forging: The forging blank obtained in step (2) is heated to 850℃ with a heat preservation coefficient of 0.5, and then heated to 1050℃ with a heat preservation coefficient of 0.5. It is then subjected to two upsetting and drawing forgings using a high-speed forging machine to obtain the forging blank two. The upsetting amount of the forging blank two is 50%, and hexagonal forging is performed during the drawing process. The drawing reduction is 120mm / time.

[0043] (4) Third upsetting and drawing forging: The forging billet two obtained in step (3) is heated to Tβ-80℃ with a heat preservation coefficient of 0.8. It is then upsetting and drawing forging once using a fast forging machine to obtain forging billet three. The upsetting amount of forging billet three is 25%. During the drawing process, hexagonal forging is performed, and the drawing reduction is 80mm / time.

[0044] (5) Fourth upsetting and drawing forging: The forging billet three obtained in step (4) is heated to 850℃ with a heat preservation coefficient of 0.5, and then heated to Tβ+50℃ with a heat preservation coefficient of 0.5. The forging billet four is obtained by two upsetting and drawing forgings using a fast forging machine. The upsetting amount of the forging billet four is 25%, and hexagonal forging is performed during the drawing process. The drawing reduction is 120mm / time.

[0045] (6) Fifth upsetting and drawing forging: The forging blank four obtained in step (5) is heated to Tβ-80℃ with a heat retention coefficient of 0.8. It is forged repeatedly for 5 times using a high-speed forging machine to obtain forging blank five. The single forging is a single upsetting and drawing forging, with an upsetting amount of 25%. During the drawing process, hexagonal forging is performed, and the drawing reduction is 80mm / time.

[0046] (7) Sixth upsetting and drawing forging: The forging billet obtained in step (6) is heated to Tβ-35℃ with a holding coefficient of 1.0, and then drawn and forged to the required size using a high-speed forging machine. Specifications: TC18 titanium alloy bar.

[0047] Example 2

[0048] This embodiment provides a forging method for reducing the anisotropy of TC18 titanium alloy bars, the forging method comprising:

[0049] (1) Heat the TC18 titanium alloy bar ingot to 850℃ with a heat retention coefficient of 0.5, then heat it to 1150℃ with a heat retention coefficient of 0.5, and then upset and draw it to obtain a forging blank; the upsetting amount of the forging blank is 55%, and hexagonal forging is performed during the drawing process, with a drawing reduction of 120mm / time;

[0050] (2) First upsetting and drawing forging: The forging blank obtained in step (1) is heated to Tβ-80℃ with a heat preservation coefficient of 1.0. It is then upsetting and drawing forging once using a fast forging machine to obtain forging blank one. The upsetting amount of forging blank one is 55%. During the drawing process, hexagonal forging is performed, and the drawing reduction is 80mm / time.

[0051] (3) Second upsetting and drawing forging: The forging blank obtained in step (2) is heated to 850℃ with a heat preservation coefficient of 0.5, and then heated to 1050℃ with a heat preservation coefficient of 0.5. It is then subjected to two upsetting and drawing forgings using a high-speed forging machine to obtain the forging blank two. The upsetting amount of the forging blank two is 50%, and hexagonal forging is performed during the drawing process. The drawing reduction is 120mm / time.

[0052] (4) Third upsetting and drawing forging: The forging billet two obtained in step (3) is heated to Tβ-80℃ with a heat preservation coefficient of 0.8. It is then upsetting and drawing forging once using a fast forging machine to obtain forging billet three. The upsetting amount of forging billet three is 20%, and hexagonal forging is performed during the drawing process. The drawing reduction is 80mm / time.

[0053] (5) Fourth upsetting and drawing forging: The forging billet three obtained in step (4) is heated to 850℃ with a heat preservation coefficient of 0.5, and then heated to Tβ+50℃ with a heat preservation coefficient of 0.5. The forging billet four is obtained by two upsetting and drawing forgings using a fast forging machine. The upsetting amount of the forging billet four is 25%, and hexagonal forging is performed during the drawing process. The drawing reduction is 120mm / time.

[0054] (6) Fifth upsetting and drawing forging: The forging blank four obtained in step (5) is heated to Tβ-80℃ with a heat retention coefficient of 0.8. It is repeatedly forged three times with a high-speed forging machine to obtain forging blank five. The single forging is a one-time upsetting and drawing forging. The upsetting amount is 25%. During the drawing process, hexagonal forging is performed, and the drawing reduction is 80mm / time.

[0055] (7) Sixth upsetting and drawing forging: The forging billet obtained in step (6) is heated to Tβ-40℃ with a holding coefficient of 1.0, and then drawn and forged to the required size using a high-speed forging machine. Specifications: TC18 titanium alloy bar.

[0056] Example 3

[0057] This embodiment provides a forging method for reducing the anisotropy of TC18 titanium alloy bars, the forging method comprising:

[0058] (1) Heat the TC18 titanium alloy bar ingot to 850℃ with a heat retention coefficient of 0.5, then heat it to 1150℃ with a heat retention coefficient of 0.5, and then upset and draw it to obtain a forging blank; the upsetting amount of the forging blank is 55%, and hexagonal forging is performed during the drawing process, with a drawing reduction of 120mm / time;

[0059] (2) First upsetting and drawing forging: The forging billet obtained in step (1) is heated to Tβ-80℃ with a heat preservation coefficient of 1.0. It is then upsetting and drawing forging once using a fast forging machine to obtain forging billet one. The upsetting amount of forging billet one is 55%. During the drawing process, hexagonal forging is performed, and the drawing reduction is 120mm / time.

[0060] (3) Second upsetting and drawing forging: The forging blank obtained in step (2) is heated to 850℃ with a heat preservation coefficient of 0.5, and then heated to 1050℃ with a heat preservation coefficient of 0.5. It is then subjected to two upsetting and drawing forgings using a high-speed forging machine to obtain the forging blank two. The upsetting amount of the forging blank two is 50%, and hexagonal forging is performed during the drawing process. The drawing reduction is 120mm / time.

[0061] (4) Third upsetting and drawing forging: The forging billet two obtained in step (3) is heated to Tβ-80℃ with a heat preservation coefficient of 0.8. It is then upsetting and drawing forging once using a fast forging machine to obtain forging billet three. The upsetting amount of forging billet three is 20%, and hexagonal forging is performed during the drawing process. The drawing reduction is 120mm / time.

[0062] (5) Fourth upsetting and drawing forging: The forging billet three obtained in step (4) is heated to 850℃ with a heat retention coefficient of 0.4, and then heated to Tβ+50℃ with a heat retention coefficient of 0.4. The forging billet four is obtained by two upsetting and drawing forgings using a fast forging machine. The upsetting amount of the forging billet four is 25%, and hexagonal forging is performed during the drawing process. The drawing reduction is 120mm / time.

[0063] (6) Fifth upsetting and drawing forging: The forging blank four obtained in step (5) is heated to Tβ-80℃ with a heat retention coefficient of 0.8. It is forged repeatedly for 3 times using a high-speed forging machine to obtain forging blank five. The single forging is a single upsetting and drawing forging, with an upsetting amount of 25%. During the drawing process, hexagonal forging is performed, and the drawing reduction is 120mm / time.

[0064] (7) Sixth upsetting and drawing forging: The forging billet obtained in step (6) is heated to Tβ-35℃ with a holding coefficient of 1.0, and then drawn and forged to the required size using a high-speed forging machine. Specifications: TC18 titanium alloy bar.

[0065] Comparative Example 1

[0066] This comparative example provides a forging method for TC18 titanium alloy bars. The specific implementation method is the same as in Example 1, except that the forging heating temperature in steps (2), (4), and (6) is Tβ-30℃ and the upsetting amount is 20%. The forging method includes:

[0067] (1) Heat the TC18 titanium alloy bar ingot to 850℃ with a heat retention coefficient of 0.5, then heat it to 1150℃ with a heat retention coefficient of 0.5, and then upset and draw it to obtain a forging billet; the upsetting amount of the forging billet is 50%, and hexagonal forging is performed during the drawing process, with a drawing reduction of 120mm / time.

[0068] (2) First upsetting and drawing forging: The forging billet obtained in step (1) is heated to Tβ-30℃ with a heat preservation coefficient of 1.0. It is then upsetting and drawing forging once using a fast forging machine to obtain forging billet one. The upsetting amount of forging billet one is 20%. During the drawing process, hexagonal forging is performed, and the drawing reduction is 80mm / time.

[0069] (3) Second upsetting and drawing forging: The forging blank obtained in step (2) is heated to 850℃ with a heat preservation coefficient of 0.5, and then heated to 1050℃ with a heat preservation coefficient of 0.5. It is then subjected to two upsetting and drawing forgings using a high-speed forging machine to obtain the forging blank two. The upsetting amount of the forging blank two is 50%, and hexagonal forging is performed during the drawing process. The drawing reduction is 120mm / time.

[0070] (4) Third upsetting and drawing forging: The forging billet two obtained in step (3) is heated to Tβ-30℃ with a heat preservation coefficient of 0.8. It is then upsetting and drawing forging once using a fast forging machine to obtain forging billet three. The upsetting amount of forging billet three is 20%, and hexagonal forging is performed during the drawing process. The drawing reduction is 80mm / time.

[0071] (5) Fourth upsetting and drawing forging: The forging billet three obtained in step (4) is heated to 850℃ with a heat preservation coefficient of 0.5, and then heated to Tβ+50℃ with a heat preservation coefficient of 0.5. The forging billet four is obtained by two upsetting and drawing forgings using a fast forging machine. The upsetting amount of the forging billet four is 25%, and hexagonal forging is performed during the drawing process. The drawing reduction is 120mm / time.

[0072] (6) Fifth upsetting and drawing forging: The forging blank four obtained in step (5) is heated to Tβ-30℃ with a heat retention coefficient of 0.8. It is forged repeatedly for 5 times using a high-speed forging machine to obtain forging blank five. The single forging is a single upsetting and drawing forging. The upsetting amount is 20%. During the drawing process, hexagonal forging is performed, and the drawing reduction is 80mm / time.

[0073] (7) Sixth upsetting and drawing forging: The forging billet obtained in step (6) is heated to Tβ-35℃ with a holding coefficient of 1.0, and then drawn and forged to the required size using a high-speed forging machine. Specifications: TC18 titanium alloy bar.

[0074] Comparative Example 2

[0075] This comparative example provides a forging method for TC18 titanium alloy bars. The specific implementation method is the same as in Example 1, except that the forging heating temperature, upsetting amount, and forging sequence are different. The forging method includes:

[0076] (1) Heat the TC18 titanium alloy bar ingot to 850℃ with a heat retention coefficient of 0.5, and then heat it to 1150℃, 1050℃ and 950℃ respectively with a heat retention coefficient of 0.5. Repeatedly upsetting and drawing forging three times with a high-speed forging machine to obtain a forging billet; the upsetting amount of the forging billet is 50%, and hexagonal forging is performed during the drawing process, with a drawing reduction of 120mm / time;

[0077] (2) First upsetting and drawing forging: The forging billet obtained in step (1) is heated to Tβ-30℃ with a heat preservation coefficient of 1.0. It is then upsetting and drawing forging once using a fast forging machine to obtain forging billet one. The upsetting amount of forging billet one is 20%. During the drawing process, hexagonal forging is performed, and the drawing reduction is 120mm / time.

[0078] (3) Second upsetting and drawing forging: The forging blank obtained in step (2) is heated to 850℃ with a heat preservation coefficient of 0.5, and then heated to Tβ+50℃ with a heat preservation coefficient of 0.5. It is then subjected to two upsetting and drawing forgings using a high-speed forging machine to obtain the forging blank two. The upsetting amount of the forging blank two is 20%, and hexagonal forging is performed during the drawing process. The drawing reduction is 120mm / time.

[0079] (4) Third upsetting and drawing forging: The forging billet two obtained in step (3) is heated to Tβ-35℃ with a heat retention coefficient of 0.8. It is forged repeatedly for 4 times using a high-speed forging machine to obtain forging billet three. The single forging is a single upsetting and drawing forging. The upsetting amount is 20%. During the drawing process, hexagonal forging is performed, and the drawing reduction is 80mm / time.

[0080] (5) Fourth upsetting and drawing forging: The forging billet obtained in step (6) is heated to Tβ-40℃ with a holding coefficient of 1.0, and then drawn to the required size using a high-speed forging machine. Specifications: TC18 titanium alloy bar.

[0081] Comparative Example 3

[0082] This comparative example provides a forging method for TC18 titanium alloy bars. The specific implementation method is the same as in Example 1, except that the forging heating temperature, upsetting amount, and forging sequence are different. The forging method includes:

[0083] (1) Heat the TC18 titanium alloy bar ingot to 850℃ with a heat retention coefficient of 0.5, and then heat it to 1150℃, 1050℃ and 950℃ respectively with a heat retention coefficient of 0.5. Repeatedly upsetting and drawing forging three times with a high-speed forging machine to obtain a forging billet; the upsetting amount of the forging billet is 40%, and hexagonal forging is performed during the drawing process, with a drawing reduction of 120mm / time;

[0084] (2) First upsetting and drawing forging: The forging billet obtained in step (1) is heated to Tβ-30℃ with a heat retention coefficient of 1.0. It is then upsetting and drawing forging once using a fast forging machine to obtain forging billet one. The upsetting amount of forging billet one is 30%. During the drawing process, hexagonal forging is performed, and the drawing reduction is 120mm / time.

[0085] (3) Second upsetting and drawing forging: The forging blank obtained in step (2) is heated to 850℃ with a heat retention coefficient of 0.4, and then heated to Tβ+70℃ with a heat retention coefficient of 0.4. It is then subjected to two upsetting and drawing forging processes using a high-speed forging machine to obtain forging blank two. The upsetting amount of forging blank two is 30%, and hexagonal forging is performed during the drawing process. The drawing reduction is 120mm / time.

[0086] (4) Third upsetting and drawing forging: The forging billet two obtained in step (3) is heated to Tβ-30℃ with a heat retention coefficient of 0.8. It is forged repeatedly for 6 times using a high-speed forging machine to obtain forging billet three. The single forging is a single upsetting and drawing forging, with an upsetting amount of 30%. During the drawing process, hexagonal forging is performed, and the drawing reduction is 80mm / time.

[0087] (5) Fourth upsetting and drawing forging: The forging billet obtained in step (6) is heated to Tβ-45℃ with a holding coefficient of 0.8, and then drawn to the required size using a high-speed forging machine. Specifications: TC18 titanium alloy bar.

[0088] Performance testing

[0089] 100 mm thick physicochemical samples were cut from the TC18 titanium alloy bars prepared in Examples 1-3 and Comparative Examples 1-3 and subjected to heat treatment. The room temperature tensile properties and impact toughness of the L-axis and C-phase were tested, and the results are shown in Table 1. Metallographic samples of the cross-sections of Examples 1-3 and Comparative Examples 1-3 after heat treatment were cut, and after grinding and polishing, the orientation characteristics of the β-phase were tested using a scanning electron microscope with an EBSD probe. Different orientations resulted in different grain colors, and the results are shown in Table 1. Figures 1-3 , Figures 4-6 As shown, compared with Comparative Examples 1-3, the β-phase grains after heat treatment in Examples 1-3 underwent sufficient recrystallization, resulting in finer and more uniform grains without obvious selective orientation; the difference in room temperature tensile and impact toughness between the L and C directions was smaller, significantly reducing anisotropy.

[0090] Table 1

[0091]

[0092]

[0093] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method of reducing the anisotropy of TC18 titanium alloy bar stock by forging, characterized in that, The forging method comprises: S1. heating a TC18 titanium alloy bar ingot, upsetting and drawing to obtain a forged blank; S2. sequentially passing the forged blank through six times of upsetting and drawing to obtain a TC18 titanium alloy bar with low anisotropy; In S2, the upsetting amount in the first and second times of upsetting and drawing is 50-55%, the upsetting amount in the third, fourth, fifth and sixth times of upsetting and drawing is 20-25%, and the elongation in the sixth time of upsetting and drawing is greater than or equal to 200%; In S1, the TC18 titanium alloy bar ingot is heated to 250-300 DEG C above the phase transition temperature, and the final forging temperature is not lower than 750 DEG C; In the first time of upsetting and drawing in S2, the TC18 titanium alloy bar ingot is heated to 70-90 DEG C below the phase transition temperature; In the second time of upsetting and drawing in S2, the TC18 titanium alloy bar ingot is heated to 150-200 DEG C above the phase transition temperature; In the third time of upsetting and drawing in S2, the TC18 titanium alloy bar ingot is heated to 70-90 DEG C below the phase transition temperature; In the fourth time of upsetting and drawing in S2, the TC18 titanium alloy bar ingot is heated to 40-60 DEG C above the phase transition temperature; In the fifth time of upsetting and drawing in S2, the TC18 titanium alloy bar ingot is heated to 70-90 DEG C below the phase transition temperature; In the sixth time of upsetting and drawing in S2, the TC18 titanium alloy bar ingot is heated to 35-40 DEG C below the phase transition temperature; The six times of upsetting and drawing are all hexagonal forging. The L-direction tensile strength of the TC18 titanium alloy bar with low anisotropy in S2 is 1100-1200 MPa, and the impact toughness is 45-50 J / cm 2 ; the C-direction tensile strength is 1100-1200 MPa, and the impact toughness is 50-55 J / cm 2 .

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