A process method for improving forging of TC11 titanium alloy

Abstract

The application belongs to the technical field of titanium alloy forging modification forging, and particularly relates to a process method for TC11 titanium alloy modification forging. The process method comprises the following steps: in the first step, a square billet is prepared; in the second step, the square billet is subjected to grain refinement through 2 heating times; in the third step, the square billet after grain refinement is subjected to structure homogenization treatment through N heating times; and in the fourth step, the square billet after structure homogenization is subjected to pie forging for at least two heating times.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy forging modification and forging technology, specifically relating to a process method for forging modified TC11 titanium alloy. Background Technology

[0002] Titanium alloys are widely used in aerospace and shipbuilding due to their high specific strength, light weight, and high corrosion resistance. TC11 titanium alloy, as a type of two-phase titanium alloy, has high room temperature strength and excellent hot strength properties below 500℃, and is mainly used to manufacture parts such as compressor discs, blades, and drums for aero engines. As the performance requirements for forgings increase, the performance indicators of raw materials also need to be raised. Simply eliminating casting defects in titanium alloys through forging is no longer sufficient to meet production needs. Therefore, after the bars are produced, further hot working is required to improve the microstructure of the titanium alloy raw materials. The conventional method is to use a high-speed forging machine of appropriate tonnage (hammer and anvil speed 10mm / s-40mm / s) to forge and modify the bars, using flat anvil upsetting or shaped anvil upsetting. However, this method has low production efficiency and makes it difficult to control the processing parameters. Summary of the Invention

[0003] Purpose of the invention: To provide a process method for reforging TC11 titanium alloy.

[0004] Technical solution:

[0005] A process for forging TC11 titanium alloy, comprising:

[0006] The first step is to prepare a square billet;

[0007] The second step involves refining the grain size of the billet through two heating processes: The first heating process involves heating at 25℃±5℃ below the phase transformation point, with a heating coefficient calculated at 1.2min / mm-1.5min / mm, to perform upsetting and elongation deformation of the billet. The upsetting deformation is controlled at 35%–40%, followed by rapid circulating water cooling after forging. The second heating process involves heating at 30℃±3℃ below the phase transformation point, with a heating coefficient calculated at 1.2min / mm-1.5min / mm, to perform upsetting and elongation deformation of the billet. The upsetting deformation is controlled at 35%–40%, followed by rapid circulating water cooling after forging.

[0008] The third step is to homogenize the microstructure of the grain-refined billet by N heat treatments, where N is an even number: the heating temperature is 40℃±5℃ below the phase transformation point, and the heating coefficient is calculated as 0.8min / mm-1.0min / mm. The billet is deformed by upsetting, reversing quadrangular elongation, and chamfering elongation. The upsetting deformation is controlled at 30% to 35%. Through the same deformation process of N heat treatments, the cumulative distortion energy inside the billet reaches a certain level, which is greater than the critical deformation amount of TC11 but less than the grain coarsening deformation amount, resulting in a uniform and fine microstructure.

[0009] The fourth step involves forging the homogenized billet into a flat cake using at least two heat treatments: First heat: Using a high-speed forging mill, upsetting and rounding are performed, with upsetting deformation controlled at 40%–45%, followed by air cooling. Second heat: The heating temperature is 40℃±5℃ below the phase transformation point, with a heating coefficient calculated at 0.8 min / mm–1.0 min / mm. A screw press is used to upset the billet at a predetermined initial speed, with deformation controlled between 35% and 40%, followed by air cooling. Subsequent heat treatments: The heating temperature is 40℃±5℃ below the phase transformation point, with a heating coefficient calculated at 0.8 min / mm–1.0 min / mm. A screw press is used to upset the billet at a predetermined initial speed, with deformation determined based on the billet size, followed by air cooling.

[0010] Further, the first step, preparing the square billet, specifically includes:

[0011] The bar stock is heated to 40℃±5℃ below the phase transformation point, with a heating coefficient calculated as 0.8min / mm-1.0min / mm. Through upsetting and square drawing, the bar stock is forged into a square billet with a height-to-diameter ratio of 1.6-2.0. The upper and lower anvils are flat dies, and the initial pressing speed of the high-speed forging machine is controlled at 20-40mm / s. Air cooling is then performed.

[0012] Furthermore, in the second step, the first fire specifically includes:

[0013] Deformation is achieved through upsetting, reversing four-way elongation, and chamfering elongation, with the upsetting deformation controlled at 35% to 40%.

[0014] Furthermore, in the second step, the second fire specifically includes:

[0015] Deformation is achieved through upsetting, reversing four-way elongation, and chamfering elongation, with the upsetting deformation controlled at 35% to 40%.

[0016] Furthermore, in the third step, the grain-refined billet is subjected to a four-stage firing process to achieve uniform microstructure.

[0017] Furthermore, the first heating step in the fourth step specifically includes: The first heating step: the heating temperature is 40℃±5℃ below the phase transformation point, the heating coefficient is calculated as 0.8min / mm-1.0min / mm, a high-speed forging machine is used to perform upsetting and rounding, the upsetting deformation is controlled at 40%~45%, and air cooling is performed.

[0018] Furthermore, in the fourth step, the initial speed of the spiral press in the second fire is 200mm / s-400mm / s.

[0019] Furthermore, in the fourth step, the initial speed of the screw press in the third fire is 200mm / s-400mm / s.

[0020] Beneficial effects:

[0021] Using the modified forging method of this invention, TC11 bar stock is upset and drawn using a high-speed forging mill at an initial speed of 20mm / s-40mm / s on both upper and lower anvils. The bar stock is refined under different heating temperatures and cooling conditions by combining upset, square drawing, and chamfering drawing to obtain a finer initial microstructure. Finally, a screw press at a speed of 200mm / s-400mm / s is used for upset forging, resulting in a titanium alloy microstructure with uniform microstructure and good spheroidization of the primary α phase with fewer upsetting passes. Detailed Implementation

[0022] This invention focuses on a multi-stage forging process for TC11 bars. This method overturns the traditional method of using only a high-speed forging mill, effectively combining a high-speed forging mill with a high-speed screw press for forging large titanium alloy bars. The high-speed forging mill upsets and draws the bar into a square shape. After multiple stages of upsetting and drawing at different temperatures and cooling methods, a screw press is used for further upsetting. This improves the forgeability of the titanium alloy billet, allowing for full dynamic recrystallization of the α phase in the TC11 microstructure under high strain rate conditions. This improves the morphology of the primary α phase, refines the microstructure, and yields an equiaxed primary α microstructure with higher spheroidization.

[0023] The technical solution of the present invention will be further described in detail below.

[0024] The process method for forging TC11 titanium alloy of this invention mainly includes the following steps:

[0025] The first step is to prepare the billet (1 heat). The bar stock is heated to 40℃±5℃ below the phase transformation point. The heating coefficient is calculated as 0.8min / mm-1.0min / mm. Through upsetting and square drawing, the bar stock is forged into a square billet with a height-to-diameter ratio of 1.6-2.0. The upper and lower anvils are flat dies. The initial pressing speed of the high-speed forging machine is controlled at 20-40mm / s, and air cooling is performed.

[0026] Using this forging method, the bar stock is forged into a square billet with the required aspect ratio, which prepares billets of typical dimensions for subsequent reforging.

[0027] The second step is to refine the grains (two heating processes). The first heating process involves heating at 25℃±5℃ below the phase transformation point, with a heating coefficient calculated at 1.2min / mm-1.5min / mm. Deformation is achieved through upsetting, reversing quadrature elongation, and chamfering elongation. The upsetting deformation is controlled at 35% to 40%, followed by rapid circulating water cooling after forging. The second heating process involves heating at 30℃±3℃ below the phase transformation point, with a heating coefficient calculated at 1.2min / mm-1.5min / mm. Deformation is achieved through upsetting, reversing quadrature elongation, and chamfering elongation, with the upsetting deformation controlled at 35% to 40%. After forging, rapid circulating water cooling is performed. This step is to further refine the microstructure.

[0028] In this process, the first heating cycle uses a temperature of 25±5℃ below the phase transformation point, with a holding time and heating coefficient of 1.2min / mm-1.5min / mm, which is greater than the conventional heating coefficient. The high temperature and long heating time control the content of the primary α phase in the TC11 alloy to a relatively small level. The upsetting deformation is relatively large, ranging from 35% to 40%. Through upsetting and reversing elongation, sufficient distortion energy is accumulated inside the forging. After forging, the forging is rapidly cooled by circulating water, making the thin, elongated secondary α phase inside the microstructure finer, while retaining some fine recrystallized microstructure. The second heating cycle uses a temperature of 30±5℃ below the phase transformation point, with a heating coefficient of 1.2min / mm-1.5min / mm. Similar to the previous heating cycle, the large deformation further refines the microstructure. The even-numbered reversing elongation restores the axial and radial directions of the billet to be consistent with the bar stock. The third step involves homogenizing the microstructure of the grain-refined billet through N heating cycles, where N is an even number. The heating temperature is 40℃±5℃ below the phase transformation point, and the heating coefficient is calculated as 0.8min / mm-1.0min / mm. The billet is deformed through upsetting, reversing quadrangular elongation, and chamfering elongation. The upsetting deformation is controlled at 30% to 35%. Through the same deformation process of 4 heating cycles, the cumulative distortion energy inside the billet reaches a certain level, which is greater than the critical deformation amount of TC11 but less than the grain coarsening deformation amount, resulting in a uniform and fine microstructure.

[0029] The process employs N-stage upsetting, reversing four-way drawing, and chamfering drawing deformation to ensure that the structure of each part of the billet is deformed in a consistent manner, thereby improving the consistency of the internal structure of the billet. Furthermore, the billet accumulates deformation to induce more recrystallization and obtain a fine grain structure. The even-numbered reversing drawing avoids defects caused by anisotropy in the structure.

[0030] The fourth step involves forging the homogenized billet into a flat cake using at least two heating cycles: First heating cycle: Heating temperature is 40℃±5℃ below the phase transformation point, with a heating coefficient calculated at 0.8min / mm-1.0min / mm. A high-speed forging mill is used for upsetting and rounding, controlling the upsetting deformation at 40%-45%, followed by air cooling. Second heating cycle: Heating temperature is 40℃±5℃ below the phase transformation point, with a heating coefficient calculated at 0.8min / mm-1.0min / mm. A screw press is used, with an initial speed of 200mm / s-400mm / s for upsetting, controlling the deformation at 35%-40%, followed by air cooling. Subsequent heating cycles: Heating temperature is 40℃±5℃ below the phase transformation point, with a heating coefficient calculated at 0.8min / mm-1.0min / mm. A screw press is used, with an initial speed of 200mm / s-400mm / s for upsetting, the deformation determined based on the billet size, followed by air cooling.

[0031] This step first uses a high-speed forging machine to conventionally forge the billet, upsetting and rounding it to reduce its height and shape it. Then, a high initial speed screw press is used for upsetting. Considering that under higher strain rate conditions, the degree of recrystallization of the primary α phase can be improved, in order to achieve complete recrystallization, improve the morphology of the primary α phase, and obtain a primary α structure with a higher degree of spheroidization.

[0032] Example:

[0033] The TC11 bar stock has dimensions of Φ230×615mm, and the forging equipment includes a 16MN high-speed forging mill and a 365MN screw press. The raw material has a phase transformation point of 1013℃, and both the upper and lower anvils are flat dies. The initial pressing speed of the high-speed forging mill is controlled at 20-30mm / s.

[0034] The first step is to prepare the billet (1 heat). The bar stock is heated to 973℃, with a heating coefficient of 0.8 min / mm. The billet is prepared into a □250×410 billet by upsetting and square drawing, and then air-cooled.

[0035] The second step is to refine the grains (2 heats). After each heat, the grains are water-cooled using circulating water. First, the grains are heated to 988℃, with a heating coefficient calculated at 1.2 min / mm. Deformation is achieved through upsetting, reversing four-way elongation, and chamfering elongation. The upsetting deformation is controlled at 40%. After forging, the grains are rapidly water-cooled, and then heated to 983℃. The heating coefficient, deformation method, deformation amount, and cooling method are the same as the previous step. This step is to further refine the microstructure.

[0036] The third step is uniform (4 heats). The heating temperature is 973℃, and the heating coefficient is calculated as 0.8min / mm. The billet is deformed by upsetting, reversing four-way elongation, and chamfering elongation. Through the same deformation process of 4 heats, the cumulative distortion energy inside the billet reaches a certain level, which is greater than the critical deformation amount of TC11 but less than the grain coarsening deformation amount, resulting in a uniform and fine microstructure.

[0037] The fourth step is to form a cake (2 heats). The heating temperature is 973℃, and the heating coefficient is calculated as 0.8 min / mm. Using a high-speed forging machine, the Φ425×180mm is obtained by upsetting and rolling. It is then air-cooled and supported. The billet is then heated again at the same heating temperature and heating coefficient. Using a screw press, the cake is upset at an initial speed of 200mm / s-400mm / s, and the deformation is controlled between 35% and 40%, resulting in a Φ510×120mm. It is then air-cooled and supported.

[0038] The TC11 flaw detection standard HB5266 requires a noise level of -12dB for a Φ0.8mm flat-bottomed hole. Conventionally, using a high-speed forging mill for reforging, the noise level after one reforging is an average of -9dB, with some areas showing -4dB to -6dB, which does not meet the standard requirements and necessitates rework to achieve sufficient deformation to satisfy the standard. Using this forging method, after one reforging, the noise level is -12dB, with some isolated areas showing -9dB and -6dB, meeting the standard requirements.

Claims

1. A process for forging TC11 titanium alloy, characterized in that, include: The first step is to prepare a square billet; The second step involves refining the grain size of the billet through two heating processes: The first heating process involves heating at 25℃±5℃ below the phase transformation point, with a heating coefficient calculated at 1.2min / mm-1.5min / mm, to perform upsetting and elongation deformation of the billet. The upsetting deformation is controlled at 35%–40%, followed by rapid circulating water cooling after forging. The second heating process involves heating at 30℃±3℃ below the phase transformation point, with a heating coefficient calculated at 1.2min / mm-1.5min / mm, to perform upsetting and elongation deformation of the billet. The upsetting deformation is controlled at 35%–40%, followed by rapid circulating water cooling after forging. The third step is to homogenize the microstructure of the grain-refined billet by N heat treatments, where N is an even number: the heating temperature is 40℃±5℃ below the phase transformation point, and the heating coefficient is calculated as 0.8min / mm-1.0min / mm. The billet is deformed by upsetting, reversing quadrangular elongation, and chamfering elongation. The upsetting deformation is controlled at 30% to 35%. Through the same deformation process of N heat treatments, the cumulative distortion energy inside the billet reaches a certain level, which is greater than the critical deformation amount of TC11 but less than the grain coarsening deformation amount, resulting in a uniform and fine microstructure. The fourth step involves forging the homogenized billet into a flat cake using at least two heat treatments: First heat: Using a high-speed forging mill, upsetting and rounding are performed, with upsetting deformation controlled at 40%–45%, followed by air cooling. Second heat: The heating temperature is 40℃±5℃ below the phase transformation point, with a heating coefficient calculated at 0.8 min / mm–1.0 min / mm. A screw press is used to upset the billet at a predetermined initial speed, with deformation controlled between 35% and 40%, followed by air cooling. Subsequent heat treatments: The heating temperature is 40℃±5℃ below the phase transformation point, with a heating coefficient calculated at 0.8 min / mm–1.0 min / mm. A screw press is used to upset the billet at a predetermined initial speed, with deformation determined based on the billet size, followed by air cooling.

2. The process method for forging TC11 titanium alloy according to claim 1, characterized in that, The first step is to prepare the billet, which specifically includes: The bar stock is heated to 40℃±5℃ below the phase transformation point, with a heating coefficient calculated as 0.8min / mm-1.0min / mm. Through upsetting and square drawing, the bar stock is forged into a square billet with a height-to-diameter ratio of 1.6-2.

0. The upper and lower anvils are flat dies, and the initial pressing speed of the high-speed forging machine is controlled at 20-40mm / s. Air cooling is then performed.

3. The process method for forging TC11 titanium alloy according to claim 1, characterized in that, In the second step, the first fire specifically includes: Deformation is achieved through upsetting, reversing four-way elongation, and chamfering elongation, with the upsetting deformation controlled at 35% to 40%.

4. The process method for forging TC11 titanium alloy according to claim 1, characterized in that, In the second step, the second fire specifically includes: Deformation is achieved through upsetting, reversing four-way elongation, and chamfering elongation, with the upsetting deformation controlled at 35% to 40%.

5. The process method for forging TC11 titanium alloy according to claim 1, characterized in that, The third step is to perform a four-stage firing process to homogenize the microstructure of the refined square billet.

6. The process method for forging TC11 titanium alloy according to claim 1, characterized in that, The first heating step in the fourth step specifically includes: The heating temperature is 40℃±5℃ below the phase transformation point, and the heating coefficient is calculated as 0.8min / mm-1.0min / mm. A high-speed forging machine is used for upsetting and rounding. The upsetting deformation is controlled at 40% to 45%, and the machine is air-cooled.

7. The forging process of TC11 titanium alloy according to claim 1, characterized in that, In the fourth step, the initial speed of the spiral press in the second fire is 200mm / s-400mm / s.

8. The process method for forging TC11 titanium alloy according to claim 1, characterized in that, In the fourth step, the initial speed of the spiral press in the third fire is 200mm / s-400mm / s.