Preparation method of high-strength and tough TC21 titanium alloy sheet

Abstract

The present invention discloses a preparation method for a high-strength and high-toughness TC21 titanium alloy sheet, comprising: forging a TC21 ingot; performing adaptive rolling on the slab obtained after forging after heat preservation at 40-50 °C above the β-transformation temperature of the TC21 titanium alloy; performing heat treatment on the slab obtained after adaptive rolling to obtain a high-strength and high-toughness TC21 titanium alloy sheet; wherein, during the adaptive rolling process, the slab is not reheated in the furnace, and the following operations are performed according to the real-time temperature of the slab: when the slab temperature > β-transformation temperature, controlling the pass reduction to be 20-30%; when β-transformation temperature > slab temperature > 20 °C below the β-transformation temperature, controlling the pass reduction to be 15-25%; when the slab temperature < 20 °C below the β-transformation temperature, controlling the pass reduction to be 5-10%. By adopting the adaptive rolling method and reasonably distributing the pass reduction, the present invention can obtain a high-strength and high-toughness TC21 titanium alloy sheet.

Description

Technical Field

[0001] The present invention relates to the technical field of titanium alloy preparation, and particularly relates to a method for preparing a high-strength and high-toughness TC21 titanium alloy sheet. Background Art

[0002] The damage tolerance design criterion is an important criterion that modern aircraft need to abide by to achieve low-cost and long-life safe flight. With the increasing requirements for aircraft safety and economy, the requirements for the damage tolerance performance of materials are also getting higher and higher. For this reason, units such as Beijing Institute of Aeronautical Materials, Northwest Institute for Nonferrous Metal Research, Northwestern Polytechnical University, and Hongyuan Aeronautical Forging and Casting Industry Company established a joint research group and successfully developed a new type of high-strength, high-toughness, damage-tolerant weldable (α + β) two-phase titanium alloy, named TC21 alloy.

[0003] TC21 titanium alloy is a two-phase alloy. To obtain better damage tolerance performance, hot deformation is often carried out in the β phase region or the upper part of the two-phase region to construct a basket weave structure. However, due to the complexity of the deformation process and the sensitivity to external deformation conditions, the internal structure change of the alloy is easily affected by deformation conditions such as temperature and strain rate, resulting in a large range of changes in the microstructure morphology of TC21 titanium alloy.

[0004] Open die forging is the main method for producing TC21 titanium alloy, but it is difficult to control the temperature during the open die forging process, resulting in low quality of the formed large-sized forgings of TC21 titanium alloy at present, and the qualified rate does not meet the requirements. Summary of the Invention

[0005] The main purpose of the present invention is to provide a method for preparing a high-strength and high-toughness TC21 titanium alloy sheet to solve the problem that it is difficult to achieve the desired structure and performance by the existing TC21 titanium alloy preparation methods.

[0006] According to one aspect of the present invention, a method for preparing a high-strength and high-toughness TC21 titanium alloy sheet is provided, including:

[0007] Forging a TC21 ingot;

[0008] After the slab obtained by forging is heat-insulated at 40 - 50 °C above the β transformation temperature of the TC21 titanium alloy, perform adaptive rolling;

[0009] Perform heat treatment on the slab obtained by adaptive rolling to obtain the high-strength and high-toughness TC21 titanium alloy sheet;

[0010] Wherein, during the adaptive rolling process, the slab is not reheated, and the following operations are performed according to the real-time temperature of the slab:

[0011] When the slab temperature > the β transformation temperature, control the pass reduction to be 20 - 30%;

[0012] When the β transformation temperature > slab temperature > 20°C below the β transformation temperature, control the reduction per pass to be 15 - 25%;

[0013] When the slab temperature < 20°C below the β transformation temperature, control the reduction per pass to be 5 - 10%.

[0014] According to an embodiment of the present invention, during the adaptive rolling process, 90% of the total rolling deformation is completed at a temperature above 20°C below the β transformation temperature.

[0015] According to an embodiment of the present invention, forging the TC21 ingot includes:

[0016] Keep the TC21 ingot at a temperature of 150 - 200°C above the β transformation temperature for 6 hours, and then perform two upsetting and two drawing operations. The upsetting reduction is 70%, and the drawing length-diameter ratio is 1.9 - 2.0;

[0017] Return the billet after two upsetting and two drawing operations to the furnace, keep it at a temperature of 40 - 80°C above the β transformation temperature for 4 hours, then perform upsetting with a reduction of 50%, and draw it into a square billet with a length-diameter ratio of 1.9 - 2.0; then perform upsetting with a reduction of 30% again, and draw it into a slab with a predetermined thickness.

[0018] According to an embodiment of the present invention, performing the heat treatment includes:

[0019] Perform the first annealing on the slab after adaptive rolling at a temperature of 70 - 80°C below the β transformation temperature;

[0020] Perform the second annealing on the slab after the first annealing at a temperature of 590 - 600°C.

[0021] According to an embodiment of the present invention, the high-strength and tough TC21 titanium alloy sheet has a basket-weave structure, and its tensile strength is 1120 - 1145 MPa, yield strength is 1052 - 1061 MPa, elongation after fracture is 15.0 - 16.5%, reduction of area is 36 - 38%, and fracture toughness is greater than 75 MPa·m 1 / 2 .

[0022] In the preparation method of the high-strength and tough TC21 titanium alloy sheet according to the embodiment of the present invention, by adopting the adaptive rolling method and reasonably distributing the reduction per pass, a high-strength and tough TC21 titanium alloy sheet can be obtained. Detailed implementation manners

[0023] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the following further elaborates on the embodiments of the present invention in combination with specific embodiments.

[0024] It should be noted that all the expressions using "first" and "second" in the embodiments of the present invention are for distinguishing two entities or parameters with the same name but different identities. It can be seen that "first" and "second" are only for the convenience of expression and should not be construed as a limitation on the embodiments of the present invention. This will not be elaborated one by one in the subsequent embodiments.

[0025] The present invention provides a method for preparing a high-strength and tough TC21 titanium alloy sheet, comprising:

[0026] Forging a TC21 ingot;

[0027] After the slab obtained by forging is held at a temperature 40 - 50 °C above the β-transus temperature of the TC21 titanium alloy (for example, held for at least 3 h), adaptive rolling is carried out; wherein, the β-transus temperature of the TC21 titanium alloy is generally 955 ± 10 °C;

[0028] Heat-treating the slab obtained by adaptive rolling to obtain the high-strength and tough TC21 titanium alloy sheet;

[0029] Wherein, during the adaptive rolling process, the slab is not reheated in the furnace, and the adaptive rolling includes: according to the following control method, controlling the reduction per pass according to the real-time temperature of the slab (for example, the temperature of the slab can be monitored in real time using a hand-held temperature measuring instrument):

[0030] When the slab temperature > the β-transus temperature, controlling the reduction per pass to be 20 - 30%;

[0031] When the β-transus temperature > the slab temperature > 20 °C below the β-transus temperature, controlling the reduction per pass to be 15 - 25%;

[0032] When the slab temperature < 20 °C below the β-transus temperature, controlling the reduction per pass to be 5 - 10% (at this time, only small deformation sizing is carried out to the specified size).

[0033] As mentioned in the above background art, the inventors of the present application recognize that the temperature control in the open-die forging process is difficult, resulting in low quality of the currently formed TC21 titanium alloy forgings and the qualification rate not meeting the requirements. The inventors further recognize that compared with forging, the deformation speed in the rolling process is fast and the temperature control is more convenient. Therefore, the present invention adopts a rolling-forging substitution method to produce TC21 titanium alloy sheets and uses an adaptive rolling method to reasonably distribute the reduction per pass, thereby obtaining high-strength and tough TC21 titanium alloy sheets.

[0034] Through the above control method, it can be realized that during the adaptive rolling process, 90% of the total rolling deformation is completed at a temperature above 20 °C below the β-transus temperature. This can reduce the low-temperature rolling deformation amount, avoid the occurrence of the spheroidization process, ensure that the structure of the obtained product is a basket-weave structure, and the basket-weave structure lamellae are fine.

[0035] In some embodiments, forging the TC21 ingot includes: holding the TC21 ingot at a temperature 150 - 200°C above the β-transformation temperature for 6 h and then performing two upsetting and two drawing operations, where the upsetting reduction is 70%, and the aspect ratio of the drawn billet is 1.9 - 2.0; returning the billet after two upsetting and two drawing operations to the furnace, holding it at a temperature 40 - 80°C above the β-transformation temperature for 4 h, then performing upsetting with a reduction of 50% and drawing it into a square billet with an aspect ratio of 1.9 - 2.0; and then performing upsetting with a reduction of 30% again and drawing it into a slab with a predetermined thickness (e.g., 100 mm thick).

[0036] In some embodiments, the forging process is four upsetting and four drawing operations. First, use an electric heating furnace to heat the TC21 ingot to a temperature 200°C above the β-transformation temperature, hold it for 6 h. After taking it out of the furnace, cool the heating furnace to a temperature 40°C above the β-transformation temperature, and perform upsetting and drawing forging on the ingot using a hydraulic press. The first upsetting reduction is 70%, then turn it over and draw it into a square billet with an aspect ratio of 1.9 - 2.0. After that, perform upsetting with a reduction of 70% again and turn it over and draw it into a square billet with an aspect ratio of 1.9 - 2.0. After two upsetting and two drawing operations, return the billet to the furnace and hold it at a temperature 40°C above the β-transformation temperature for 4 h. After taking it out of the furnace, perform upsetting with a reduction of 50% on the billet on the press and draw it into a square billet with an aspect ratio of 1.9 - 2.0; then perform upsetting with a reduction of 30% again and draw it into a slab with a thickness of 100 mm thick.

[0037] In other embodiments, other forging processes can also be adopted, and the number of upsetting and drawing operations, holding temperature, holding time, upsetting reduction, and aspect ratio of the drawn billet, etc. can be adjusted according to the actual situation.

[0038] In some embodiments, the heat treatment includes: holding the slab after adaptive rolling at a temperature 70 - 80°C below the β-transformation temperature for, for example, 1 h for the first annealing, and then taking it out of the furnace and air-cooling; holding the slab after the first annealing at 590 - 600°C for, for example, 1 h for the second annealing, and then taking it out of the furnace and air-cooling. The performance is further improved and the structure is adjusted through double annealing.

[0039] In some embodiments, the high-strength and tough TC21 titanium alloy sheet prepared by the above method has a basketweave structure with fine and uniform lamellae, and the tensile strength of the sheet is 1120 - 1145 MPa, the yield strength is 1052 - 1061 MPa, the elongation after fracture is 15.0 - 16.5%, the reduction of area is 36 - 38%, and the fracture toughness is greater than 75 MPa·m 1 / 2 。

[0040] In summary, the present invention provides a method for preparing high-strength and tough TC21 titanium alloy sheets by combining forging and hot rolling processes. Its advantage lies in that compared with free forging with difficult temperature control, the temperature control during the rolling process is more precise. Moreover, the present invention adopts an adaptive rolling process, adjusts the reduction per pass during the rolling process according to the actual temperature of the billet, and controls that 90% of the total rolling deformation is completed at a temperature 20°C or more below the β-transus temperature, reducing the low-temperature rolling deformation and avoiding the occurrence of the spheroidization process, ensuring that the structure of the obtained product is a basket weave structure, and the lamellae of the basket weave structure are fine.

[0041] The following is an illustration based on specific examples and comparative examples.

[0042] Example 1

[0043] Prepare TC21 titanium alloy sheets according to the following method:

[0044] Step 1: First, use an electric heating furnace to heat the TC21 ingot to (β-transus temperature + 200°C), hold for 6 h. After taking it out of the furnace, cool the heating furnace to (β-transus temperature + 40°C), and perform upsetting and drawing forging on the ingot using a hydraulic press. The first upsetting reduction is 70%, then reverse draw to a square billet with a height-to-diameter ratio of 1.9 - 2.0, and then perform upsetting again with a reduction of 70% and reverse draw to a square billet with a height-to-diameter ratio of 1.9 - 2.0; after two upsetting and two drawing operations, put the billet back into the furnace and hold for 4 h at β-transus temperature + 40°C. After taking it out of the furnace, perform upsetting with a reduction of 50% on the billet on the press and draw it to a square billet with a height-to-diameter ratio of 1.9 - 2.0; then perform upsetting again with a reduction of 30% and draw it to a slab with a thickness of 100 mm.

[0045] Step 2: Heat the slab in an electric heating furnace to (β-transus temperature + 40 - 50°C), hold for 3 h. After taking it out of the furnace, adopt an adaptive rolling process, that is, use a hand-held temperature measuring instrument to monitor the temperature of the slab and adjust the reduction per pass without reheating in the middle. The control method is as follows: when the slab temperature is above the β-transus temperature, the reduction per pass is controlled at 30%; when β-transus temperature > slab temperature > (β-transus temperature - 20°C), the reduction per pass is controlled at 20%; when the slab temperature < (β-transus temperature - 20°C), the reduction per pass is controlled at 5%, and at this time, only perform small deformation shaping to the specified size.

[0046] Step 3: Adopt double annealing treatment. The first annealing is carried out at 70 - 80°C below the β-transus temperature for 1 h, take it out of the furnace and air cool, and the second annealing is carried out at 590 - 600°C for 1 h, take it out of the furnace and air cool.

[0047] Comparative Example 1

[0048] The difference between Comparative Example 1 and Example 1 is that during rolling, the reduction per pass is controlled at 20%, and the others are the same as in Example 1.

[0049] Comparative Example 2

[0050] Prepare TC21 titanium alloy sheets according to the following method:

[0051] Step 1:

[0052] ① First, use an electric heating furnace to heat the TC21 ingot to (β transformation temperature + 200 °C), hold for 6 h. After taking it out of the furnace, cool the heating furnace to (β transformation temperature + 100 °C), and use a hydraulic press to perform upsetting and drawing forging on the ingot. The first upsetting reduction is 70%, then reverse draw to a square billet with a height-to-diameter ratio of 1.9 - 2.0, then perform upsetting again with a reduction of 70% and reverse draw to a square billet with a height-to-diameter ratio of 1.9 - 2.0; after two upsetting and two drawing operations, return the billet to the furnace and hold at (β transformation temperature + 100 °C) for 4 h. After taking it out of the furnace, perform upsetting with a reduction of 50% on the billet on the press and draw to a square billet with a height-to-diameter ratio of 1.9 - 2.0; then perform upsetting with a reduction of 50% again and draw to a square billet with a height-to-diameter ratio of 1.9 - 2.0, throw it out for air cooling, and grind the entire surface;

[0053] ② After grinding, heat to (β transformation temperature + 50 °C) and hold for 4 h, perform two upsetting and two drawing operations. The first upsetting reduction is 40%, then reverse draw to a square billet with a height-to-diameter ratio of 1.9 - 2.0, then perform upsetting again with a reduction of 40% and reverse draw to a square billet with a height-to-diameter ratio of 1.9 - 2.0, throw it out for air cooling, and grind the entire surface;

[0054] ③ After grinding, heat to (β transformation temperature - 20 °C) and hold for 4 h, perform two upsetting and two drawing operations. The first upsetting reduction is 40%, then reverse draw to a square billet with a height-to-diameter ratio of 1.9 - 2.0, then perform upsetting again with a reduction of 40% and reverse draw to a square billet with a height-to-diameter ratio of 1.9 - 2.0, throw it out for air cooling, and grind the entire surface;

[0055] ④ After grinding, heat to (β transformation temperature - 20 °C) and hold for 4 h, perform two upsetting and two drawing operations. The first upsetting reduction is 40%, then reverse draw to a square billet with a height-to-diameter ratio of 1.9 - 2.0, then perform upsetting again with a reduction of 40% and reverse draw to a square billet with a height-to-diameter ratio of 1.9 - 2.0, throw it out for air cooling, and grind the entire surface;

[0056] ⑤ After grinding is completed, heat to (β transformation temperature - 20 °C) and hold for 4 h, then perform two upsetting and two drawing operations. The reduction ratio of the first upsetting is 40%, then reverse the direction and draw to a square billet with a height-to-diameter ratio of 1.9 - 2.0. After that, perform upsetting again with a reduction ratio of 40%, reverse the direction and draw to a square billet with a height-to-diameter ratio of 1.9 - 2.0, throw out and air-cool, and grind the entire surface;

[0057] ⑥ After grinding is completed, heat to (β transformation temperature - 20 °C) and hold for 4 h, then perform two upsetting and two drawing operations. The reduction ratio of the first upsetting is 40%, then reverse the direction and draw to a square billet with a height-to-diameter ratio of 1.9 - 2.0. After that, perform upsetting again with a reduction ratio of 20%, and draw to the specified size, throw out and air-cool;

[0058] Step 2: Adopt double annealing treatment. For the first annealing, hold at 70 - 80 °C below the β transformation temperature for 1 h, take out of the furnace and air-cool. For the second annealing, hold at 590 - 600 °C for 1 h, take out of the furnace and air-cool.

[0059] Test the room temperature mechanical properties of the TC21 plates obtained in Example 1, Comparative Example 1, and Comparative Example 2. The data are shown in Table 1.

[0060] Table 1 Room temperature mechanical properties of TC21 plates

[0061]

[0062] It can be seen from the room temperature mechanical properties shown in Table 1 that the TC21 plate prepared in Example 1 has better strength and toughness matching. The structure of the obtained plate is a basketweave structure with fine and uniform lamellae. The tensile strength σ b of the plate is 1120 MPa, the yield strength σ 0.2 is 1050 MPa, the elongation after fracture A is 15%, the reduction of area Z is 36%, and the fracture toughness KIC can reach about 80 MPa·m 1 / 2 . In Comparative Example 1, the adaptive rolling method was not adopted, and in Comparative Example 2, the hot rolling process was not adopted. The elongation after fracture A, reduction of area Z, and fracture toughness KIC of both are lower than those in Example 1, and their strength and toughness are inferior to those in Example 1.

[0063] Those of ordinary skill in the art should understand that: The discussion of any above embodiment is only exemplary, and is not intended to imply that the scope (including the claims) disclosed in the embodiments of the present invention is limited to these examples; Under the idea of the embodiments of the present invention, the technical features in the above embodiments or different embodiments can also be combined, and there are many other variations in different aspects of the embodiments of the present invention as described above, which are not provided in detail for the sake of brevity. Therefore, any omission, modification, equivalent replacement, improvement, etc. made within the spirit and principle of the embodiments of the present invention shall be included within the protection scope of the embodiments of the present invention.

Claims

1. A preparation method of a high-strength and high-toughness TC21 titanium alloy sheet, characterized in that, Including: Forging the TC21 ingot; After forging, the obtained slab is held at a temperature 40 - 50 °C above the β-transformation temperature of the TC21 titanium alloy and then subjected to adaptive rolling; The slab obtained after adaptive rolling is heat-treated to obtain the high-strength and high-toughness TC21 titanium alloy sheet; Wherein, during the adaptive rolling process, the slab is not reheated in the furnace, and the following operations are performed according to the real-time temperature of the slab: When the slab temperature > the β-transformation temperature, controlling the pass reduction to be 20 - 30%; When the β-transformation temperature > the slab temperature > 20 °C below the β-transformation temperature, controlling the pass reduction to be 15 - 25%; When the slab temperature < 20 °C below the β-transformation temperature, controlling the pass reduction to be 5 - 10%; During the adaptive rolling process, 90% of the total rolling deformation is completed at a temperature above 20 °C below the β-transformation temperature.

2. The method according to claim 1, wherein The slab obtained after forging is held at a temperature 40 - 50 °C above the β-transformation temperature of the TC21 titanium alloy for 3 h.

3. The method according to claim 1, wherein The forging of the TC21 ingot includes: The TC21 ingot is held at a temperature 150 - 200 °C above the β-transformation temperature for 6 h and then subjected to two upsetting and two drawing operations, where the upsetting reduction is 70%, and the drawing length-diameter ratio is 1.9 - 2.

0.

4. The method according to claim 3, wherein The forging of the TC21 ingot further includes: The billet after two upsetting and two drawing operations is returned to the furnace, held at a temperature 40 - 80 °C above the β-transformation temperature for 4 h, then upset with a reduction of 50% and drawn into a square billet with a length-diameter ratio of 1.9 - 2.0; then upset again with a reduction of 30% and drawn into a slab with a predetermined thickness.

5. The method according to claim 1, characterized in that The heat treatment includes: The slab after adaptive rolling is subjected to the first annealing at a temperature 70 - 80 °C below the β-transformation temperature; The slab after the first annealing is subjected to the second annealing at 590 - 600 °C.

6. The method according to claim 5, wherein The holding time of the first annealing is 1 h.

7. The method according to claim 5, characterized in that The holding time of the second annealing is 1 h.

8. The method according to claim 1, characterized in that The high-strength and high-toughness TC21 titanium alloy sheet has a basket-weave structure.

9. The method according to claim 1, wherein The tensile strength of the high-strength and high-toughness TC21 titanium alloy sheet is 1120 - 1145 MPa, the yield strength is 1052 - 1061 MPa, the elongation after fracture is 15.0 - 16.5%, the reduction of area is 36 - 38%, and the fracture toughness is greater than 75 MPa·m 1 / 2 .

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