A method for preparing TC18 titanium alloy forging plate with large width-to-thickness ratio

Abstract

The invention relates to the technical field of titanium alloy forging preparation, and discloses a method for preparing a TC18 titanium alloy forging plate with a large width-to-thickness ratio, wherein the blank is subjected to upsetting forging before the flattening square forging in the blank forming stage, and a reversing flattening square forging method is used for forging in the second flattening square forging in the first fire forging. The patent of the present invention changes the existing forging process, upsetting the blank before the flattening square forging, and adopting the reversing flattening square forging method to prepare the TC18 titanium alloy forging plate with a large width-to-thickness ratio in the forging forming stage, thereby solving the problem of uneven structure when preparing the TC18 titanium alloy forging plate with a large width-to-thickness ratio in the prior art.

Description

Technical Field

[0001] The invention relates to the technical field of titanium alloy forging preparation, and in particular to a method for preparing a TC18 titanium alloy forging plate with a large width-to-thickness ratio. Background Art

[0002] The nominal composition of TC18 titanium alloy is Ti-5Al-5Mo-5V-1Cr-1Fe. It is a near-β-type titanium alloy with the advantages of high strength, high toughness, high hardenability and weldability, and is widely used in aircraft manufacturing. The conventional TC18 titanium alloy free forging process mainly includes the billet reforging stage and the billet forming stage. The billet reforging stage adopts the traditional "high-low-high-low" forging process to obtain a relatively uniform low-magnification structure. In the billet forming stage, the existing technology mainly adopts the flattening square forging process to flatten the reforged billet into a square shape, and finally obtains a TC18 titanium alloy forging plate of a predetermined shape and size. In the existing TC18 titanium alloy forging plate preparation process, for conventional free forgings with a small width-to-thickness ratio, the anisotropy of the structure during the forging process is controllable and small, but when the width-to-thickness ratio of the TC18 titanium alloy free forging is large, it is easy to have a large anisotropy of the structure, the finished product structure is uneven, and the mechanical properties of the forged plate in the width direction and height direction have obvious differences. Summary of the invention

[0003] The present invention is intended to provide a method for preparing a TC18 titanium alloy forging plate with a large width-to-thickness ratio, so as to solve the problem of uneven structure that is easily occurred when preparing the TC18 titanium alloy forging plate with a large width-to-thickness ratio in the prior art.

[0004] To solve the above problems, the present invention adopts the following technical solution: a method for preparing a TC18 titanium alloy forging plate with a large width-to-thickness ratio, in which the blank is subjected to upsetting forging before or during flattening forging in the blank forming stage.

[0005] The inventors found that in the prior art, a relatively uniform low-magnification microstructure billet can be obtained after the billet reforging stage, while in the billet forming stage, when the width-to-thickness ratio of the TC18 titanium alloy forging plate is relatively large (for example, the width-to-thickness ratio is greater than 5), in order to avoid the problem of uneven microstructure in the finished product during forging in the billet forming stage, the solution is generally to minimize the accumulation of microstructure unevenness during the forging process. Therefore, the conventional means is to increase the single reduction amount in a single fire to speed up the forming speed so as to minimize the accumulation of microstructure unevenness during the forming process. However, increasing the single reduction amount will cause the temperature in the core of the billet to rise sharply and overheat, resulting in excessive temperature difference between the inside and outside of the material, which in turn increases the microstructure unevenness.

[0006] At the same time, the inventors also found that in the billet forming stage, the current forging process mainly adopts flattening square forging, that is, continuous flattening in a single direction. During the flattening process, the cross-sectional area of ​​the billet gradually decreases and the length of the billet gradually increases. In this forming process, the billet is compressed and deformed along a single direction, and the billet is more likely to produce anisotropy when it is always compressed and deformed in a single direction, which ultimately leads to an increase in the degree of structural unevenness. In response to this problem, the inventors have tried technical improvements, such as changing the forming direction during the forging process, so as to offset or even eliminate the anisotropy caused by the compression deformation in a single direction, so as to obtain a forged plate with uniform structure. However, through actual operation, the improvement effect on the uniformity of the structure is still not particularly obvious.

[0007] The principle and beneficial effects of this scheme are as follows: in this application, the conventional forging process is broken, and the billet is subjected to upsetting forging before the flattening square forging in the billet forming stage to increase the cross-sectional area of ​​the billet, and then the upsetting billet is forged into a preset forging plate size. Since a relatively uniform low-magnification structure has been obtained in the billet forging stage, when the billet with a low-magnification structure is upset before the flattening square forging in the billet forming stage, the billet can be shortened and deformed along the length direction, while the flattening square forging process deforms along the thickness direction of the billet. The deformation direction of upsetting and the deformation direction of flattening square forging are perpendicular to each other. Compared with only using the flattening square forging process, the original deformation compression direction of the billet can be changed, so that in the preparation process of TC18 titanium alloy forging plates with a large width-to-thickness ratio, the anisotropy caused by the original unidirectional compression deformation is weakened or even offset by the change of direction, thereby achieving the excellent effect of ultimately reducing the anisotropy of the forging plate.

[0008] In addition, by adopting the technical scheme in the present application, for forging plates with the same final length, width and thickness, compared with the blanks prepared by directly adopting the flattened square forging method, the blanks in the present application are in a state with a smaller cross-sectional area in the initial state, and compared with the blanks with a larger cross-sectional size adopted by directly adopting the flattened square forging method in the prior art, when the thickness of the final forged plate is equal, the thickness deformation of the blank when it is processed from the initial state thickness to the final product is smaller than the deformation of the processing method in the prior art, that is, when the size of the final product is the same, the deformation of the blank in the thickness direction is smaller, and the uneven structure of the forging plate during the forging process mainly occurs in the forging process in the thickness direction. Therefore, a smaller deformation in thickness can reduce the anisotropy in the forging process, effectively improve the preparation quality of the forging plate, especially for TC18 titanium alloy forging plates with a large width-to-thickness ratio, and obtain better quality products.

[0009] Preferably, as an improvement, the deformation amount of the billet during upsetting forging is 20-50%.

[0010] In this scheme, the deformation amount of the billet during upsetting forging is controlled between 20% and 50%, so that the amount of upsetting of the billet is appropriate, so that the deformation amount during the upsetting process and the anisotropy generated during the subsequent flattening square forging process can be better offset, thereby preparing a forging with uniform structure.

[0011] Preferably, as an improvement, the flattened square forging includes at least a first fire forging, wherein the first fire forging includes a first flattened square forging and a second flattened square forging, during the second flattened square forging process, a reversing flattened square forging method is adopted for forging, and water cooling is performed after the second flattened square forging.

[0012] In the conventional forging process, the flattened square forging is processed and deformed along the thickness direction of the billet. In this scheme, the reversing flattened square forging process is adopted in the second flattened square forging process, that is, the reversing operation is assisted in the forging process. On the one hand, since the billet is upset forged before the flattened square forging in this scheme, in order to enable the billet to be finally forged into a forged plate with a large width-to-thickness ratio, the reversing flattened square forging method is adopted in the second flattened square forging process of the first fire forging in this scheme, so that the cross section of the billet can be accurately forged into a forging with a large width-to-thickness ratio; on the other hand, compared with the method of flattening square forging in one direction in the prior art, the reversing flattening square forging method in this scheme is conducive to the forward flow of metal during the forging process, and combined with the previous upsetting operation, the forged structure of the billet is more uniform.

[0013] Preferably, as an improvement, the empty furnace is heated to 820-850°C before the first flattening forging and then transferred to the warm charging furnace for a holding time equal to the billet diameter or maximum thickness × (0.6-0.8) min.

[0014] In this scheme, the billet holding time is determined according to the diameter or maximum thickness of the billet after upsetting, so as to better perform the first flattening square forging later. It should be noted here that due to the possibility of forging errors in the billet during the actual forging process, there may be small differences in the thickness of the billet at different positions, and the actual holding time needs to be determined based on the actual maximum thickness of the billet. Therefore, the "maximum thickness" is used for limitation in this scheme.

[0015] Preferably, as an improvement, before the second flattening square forging, the hot material of the billet from the first flattening square forging is returned to the furnace for insulation at a temperature of 820-850°C for a time equal to the billet diameter or maximum thickness × (0.3-0.4) min.

[0016] In this scheme, when the billet is kept warm after the first flattening square forging, the insulation temperature range is still determined by the billet diameter or maximum thickness value. Since the billet has completed the first flattening square forging at this time, it is easier to complete the heating and insulation process during the insulation process. Therefore, the insulation time is reduced compared to before the first flattening square forging.

[0017] Preferably, as an improvement, the single pressing amount of the first flattened square forging and the second flattened square forging is ≤60mm, the final forging temperature of the first flattened square forging and the second flattened square forging is ≥720°C, and the transfer time from the billet being taken out of the furnace to the forging machine is ≤60 seconds.

[0018] In this scheme, the single reduction amount of the first flattened square forging and the second flattened square forging is ≤60mm, so as to avoid excessive single reduction which may cause the core temperature to be too high and increase the uneven structure; at the same time, the final forging temperature of the first flattened square forging and the second flattened square forging is ≥720℃, and the transfer time from the billet to the forging machine is controlled to be ≤60 seconds, so as to avoid the heat dissipation and cooling of the billet during the forging process which may cause the temperature to be too low and fail to obtain the corresponding structure.

[0019] Preferably, as an improvement, second and third fire forging are performed after the first fire forging.

[0020] In this solution, after the first fire forging, the second or third fire forging is performed until the blank is accurately forged into a forged plate with a predetermined width-to-thickness ratio.

[0021] Preferably, as an improvement, the second fire forging includes second fire heating and quasi-β forging, the second fire heating process is to heat the empty furnace to 840-860°C, and after the warm furnace is charged, the holding time is equal to the billet diameter or maximum thickness × (0.5-0.6) min, and then the furnace is heated to Tβ+ (10-30)°C, and the holding time is equal to the billet diameter or maximum thickness × (0.2-0.4) min, the single reduction amount of the quasi-β forging is ≤20mm, and the final forging temperature is greater than or equal to 750°C, and the quasi-β forging is air-cooled.

[0022] In this scheme, Tβ is the phase transition temperature of the material, and the temperature of the second firing is slightly higher than that of the first firing, so as to quickly heat the billet to the single-phase region for quasi-β forging.

[0023] Preferably, as an improvement, the third forging includes third heating and shaping. The third heating process is to heat the empty furnace to 820-850°C, and after the warm furnace is charged, the insulation time is equal to the billet diameter or maximum thickness × (0.5-0.6) min, and air cooling is performed after shaping.

[0024] In this scheme, a forged plate of precise size is obtained after shaping, and a product with uniform structure can be obtained by air cooling.

[0025] Preferably, as an improvement, the blank is ground between the first fire forging and the second fire forging, and between the second fire forging and the third fire forging, to remove surface defects of the blank.

[0026] In this solution, the blank is polished between the first forging and the second forging, and between the second forging and the third forging, so as to effectively control the surface quality of the blank during the forging process, so as to obtain a forged plate with good quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a microstructure diagram of the forged plate in Example 1 of the present invention.

[0028] Figure 2 This is the microstructure diagram of this comparative example. DETAILED DESCRIPTION

[0029] The following is further described in detail through specific implementation methods:

[0030] Example 1

[0031] A method for preparing a TC18 titanium alloy forging plate with a large width-to-thickness ratio, wherein the blank that has completed the blank reforming stage in the prior art is subjected to blank forming forging. For ease of description, the blank referred to below refers to the blank that has undergone the reforming stage before special explanation. The blank forming forging mainly includes the first fire forging, the second fire forging and the third fire forging, and the three fire forgings are all forged by flattening the square, wherein multiple flattening square forgings are performed in the blank forming forging. In this embodiment, the blank is subjected to upsetting forging before all the flattening square forgings. For example, in this embodiment, the first fire forging includes the first flattening square forging and the second flattening square forging, and the blank is subjected to upsetting forging before the first flattening square forging, and the deformation amount of the blank upsetting forging is 20-50%, and the deformation amount in this embodiment is preferably 25%.

[0032] During the first fire forging, the first flattened square forging is performed by conventional flattened square forging method. First, the furnace temperature is heated to 820-850°C, and the furnace is charged with temperature. The holding time is equal to the billet diameter or maximum thickness × (0.6-0.8) min. Then, the hot material is returned to the furnace after the billet is flattened and forged. The furnace temperature is controlled to be maintained between 820-850°C, and the holding time is equal to the billet diameter or maximum thickness × (0.3-0.4) min. Then, the second flattened square forging is performed. During the second flattened square forging, the billet is flattened by reversing the direction of the billet by reversing the direction of the flattened square forging. After the second flattened square forging is completed, water cooling is performed. In this embodiment, the furnace temperature before the first flattening square forging and the second flattening square forging is set to 835°C. Taking the billet diameter of 560mm before the first flattening square forging and the maximum billet thickness of 420mm before the second flattening square forging as an example, the billet is kept warm in the furnace for 6h before the first flattening square forging, and the billet is kept warm in the furnace for 150min before the second flattening square forging.

[0033] At the same time, the single pressing amount of the first flattening square forging and the second flattening square forging is ≤60mm, the final forging temperature of the first flattening square forging and the second flattening square forging is ≥720℃, and the transfer time from the billet to the forging machine is ≤60 seconds. In this embodiment, the first flattening square forging and the second flattening square forging have a single pressing amount of 20mm, the final forging temperature is 720℃, the transfer time from the billet to the forging machine is 30 seconds, and in order to obtain a better forging effect, the anvil, hammer head and clamp need to be preheated before forging, and the preheating temperature is 150-250℃, preferably 220℃.

[0034] After the first fire forging is completed, the second fire forging is carried out. First, the furnace temperature is raised to 840-860°C, preferably 845°C. After the furnace is charged to the temperature, the holding time is equal to the billet diameter or maximum thickness × (0.5-0.6) min. Taking the maximum thickness of the billet after the second flattening square forging as 360 mm as an example, it is preferably 200 min. Then the temperature is raised to Tβ+(10-30)°C, preferably 895°C, and the holding time is equal to the billet diameter or maximum thickness × (0.2-0.4) min, and the holding time is preferably 100 min. Then, quasi-β forging is carried out. The quasi-β forging adopts the conventional flattening square forging method. The single reduction is ≤20 mm, preferably 15 mm, and the final forging temperature is ≥750°C, and the actual value is 780°C. After forging, air cooling is performed.

[0035] After the second fire forging is completed, the third fire forging is carried out. The third fire forging includes third fire heating and shaping. During the third fire heating, the furnace temperature is raised to 820-850°C in an empty furnace, preferably 835°C. After the furnace is charged to the temperature, the holding time is equal to the billet diameter or maximum thickness × (0.5-0.6) min. Calculated based on the maximum billet thickness of 265 mm during quasi-β forging, the holding time is preferably 150 min. Then the billet is shaped to obtain a forged plate with a precise width-to-thickness ratio. The final forging temperature is ≥720°C, and the actual value is 735°C. After shaping, it can be air-cooled.

[0036] In this embodiment, the blank is subjected to upsetting forging before the first flattening forging in the first fire forging, so that the blank is compressed and deformed in the length direction, and then the first fire forging, the second fire forging and the third fire forging are performed, and finally a TC18 titanium alloy forging plate with a large width-to-thickness ratio is prepared by forging. Compared with the prior art in which a blank with a larger cross-section is directly formed into a forging plate by flattening, this embodiment breaks the conventional thinking, uses a blank with a smaller cross-section, and then performs upsetting forging before flattening to increase the cross-sectional area of ​​the blank, and then prepares the forging plate by flattening. On the one hand, the blank is first compressed and deformed in the length direction by upsetting forging, and the subsequent flattening is performed. As the width-to-thickness ratio and length of the billet continue to change, the billet becomes thinner along the thickness direction and its length continues to increase. Therefore, the anisotropy of the billet generated in the upsetting forging and the anisotropy generated in the subsequent flattening forging process can offset or even eliminate each other, thereby obtaining a forged plate with a more uniform structure. On the other hand, in this embodiment, a reversing flattening forging process is adopted in the second flattening forging process, which changes the forging process of unidirectionally flattening the billet into a forged plate in the prior art. This not only enables the billet to be effectively and accurately forged into a forged plate with a large width-to-thickness ratio, but also changes the original deformation and compression direction of the billet by reversing the flattening forging process, so that the structure of the billet during the forging process is more uniform.

[0037] The forging method in this embodiment is compared with the forging method in the prior art:

[0038] The forging method of this embodiment is shown in Table 1:

[0039]

[0040] Table 1: Forging process parameters of forging plate in this embodiment

[0041] The forging method of the comparative example in the prior art is shown in Table 2:

[0042]

[0043] Table 2: Comparative Example A forging plate forging preparation process parameters

[0044] The difference between the preparation method in the present embodiment corresponding to Table 1 and the preparation method in the comparative example in Table 2 is that, although the size of the forged plates finally obtained is the same, the initial size of the billet used in the preparation method in the present embodiment is □500×L0, while the initial size of the billet in the comparative example is □620×L0, and the initial cross-sectional area of ​​the billet in the present embodiment is smaller; in addition, in the preparation process, compared with the comparative example, the present embodiment performs upsetting forging before the first flattening forging in the first fire forging and reversing forging during the second flattening, and the subsequent second and third fire forging processes are basically the same. Figure 1 The microstructure of the forged plate prepared in Table 1 is shown in Table 1. Figure 2 The microstructure of the forged plate prepared in Table 2 is compared Figure 1 and Figure 2 It can be seen that the structure of the forged plate prepared according to the preparation method in this embodiment is obviously more uniform.

[0045] Table 3 shows the mechanical properties of the forged plates obtained in this embodiment and the comparative example:

[0046]

[0047] According to Table 3, by comparing the mechanical properties of the forged plates obtained in this embodiment and the comparative example, it can be seen that the TC18 titanium alloy forged plate obtained by the preparation method in this embodiment can achieve a significant improvement in the impact toughness of the forged plate compared to the preparation process of the prior art, while the tensile strength, elongation and elongation after fracture are all improved. Therefore, the preparation method of this embodiment can obtain a forged plate with better performance.

[0048] Example 2

[0049] The difference between Example 2 and Example 1 is that the difference between this example and Example 1 is that the blank is polished between the first fire forging and the second fire forging, and between the second fire forging and the third fire forging, and the surface defects of the blank are checked and polished to obtain a forged plate with better quality.

[0050] The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions and / or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing a TC18 titanium alloy forging plate with a large width-to-thickness ratio, characterized in that: Before the flattening forging in the billet forming stage, the billet is subjected to upsetting forging to increase the cross-sectional area of ​​the billet, and the billet is shortened and deformed along the length direction, the deformation direction of the upsetting is perpendicular to the deformation direction of the flattening forging, and the deformation amount of the billet in the upsetting forging is 20-50%; The flattened square forging includes at least a first fire forging, and after the first fire forging, a second fire forging and a third fire forging are performed; The first fire forging includes the first flattening square forging and the second flattening square forging; before the first flattening square forging, the empty furnace is heated to 820-850℃, and then the temperature is charged to the warm furnace. The holding time is equal to the billet diameter or maximum thickness × (0.6-0.8) min. Before the second flattening square forging, the hot material of the billet forged in the first flattening square is returned to the furnace for holding. The holding temperature is 820-850℃, and the holding time is equal to the billet diameter or maximum thickness × (0.3-0.4) min. During the second flattening square forging process, the forging is carried out by the reversing flattening square forging method, and the second flattening square forging is water-cooled; the single pressing amount of the first flattening square forging and the second flattening square forging is ≤60mm, the final forging temperature of the first flattening square forging and the second flattening square forging is ≥720℃, and the transfer time from the billet out of the furnace to the forging machine is ≤60 seconds; The second forging includes second heating and quasi-β forging. The second heating process is to heat the empty furnace to 840-860°C, and then heat the furnace for a holding time equal to the billet diameter or maximum thickness × (0.5-0.6) min, and then heat the furnace to T β + (10 ~ 30) ℃, holding time is equal to the billet diameter or maximum thickness × (0.2 ~ 0.4) min, the single reduction of quasi-β forging is ≤ 20mm, and the final forging temperature is greater than or equal to 750℃, and air cooling is performed after quasi-β forging; The third forging includes third heating and shaping. The third heating process is to heat the empty furnace to 820-850°C. After the temperature is reached, the holding time is equal to the billet diameter or maximum thickness × (0.5-0.6) min, and air cooling is performed after shaping.

2. The method for preparing a TC18 titanium alloy forging plate with a large width-to-thickness ratio according to claim 1, characterized in that: The blank is ground between the first and second fire forgings, and between the second and third fire forgings, to remove surface defects of the blank.

Images