Large-size titanium alloy bar-shaped special cross-section forging streamline control method

Abstract

The application is a large-size titanium alloy bar-shaped special-shaped cross-section forging streamline control method, which is mainly used for solving the problems of low matching degree of the streamline of the large-size special-shaped cross-section forging and the performance requirement of the forging and poor uniformity of the organization and performance, and further increasing the service life of the part. The streamline control method is based on the titanium alloy bar, and by controlling the parameters such as the bar blank preparation, the blank forming, the deformation amount, the deformation speed and the deformation temperature in the die forging process, the best matching of the streamline of the forging and the performance of the forging is realized, and the service life of the part is improved.

Description

Technical Field

[0001] This invention relates to a method for controlling the streamlines of large-size titanium alloy rod-shaped forgings with irregular cross-sections, belonging to the field of metal plastic forming. Background Technology

[0002] With the rapid development of aerospace technology, the manufacturing requirements for aircraft components are constantly increasing. Some critical components not only need to achieve weight reduction but also exhibit excellent mechanical properties and structural stability, placing high demands on manufacturing processes. Titanium alloys, with their high specific strength and good heat resistance, are widely used in the aerospace field to reduce component weight. Currently, manufacturing methods for aerospace components include forging, casting, and powder metallurgy. Among these, titanium alloy parts manufactured by forging exhibit good overall performance and are the primary processing method for key components.

[0003] Streamlines are a microstructure that is regularly distributed along the flow direction during metal forging deformation, and can improve the strength and fatigue performance of forgings. Titanium alloys have poor thermal conductivity and their rheological stress is sensitive to temperature changes. Currently, the processing technology for small-diameter titanium alloy bars and forgings is relatively mature, and the control of microstructure and property uniformity can fully meet product requirements. However, for large-diameter titanium alloy bars and forgings, due to the influence of equipment, environment, process, and personnel, the control of microstructure and properties is more difficult, and the product qualification rate is not high. Existing processing parameters for small-diameter titanium alloy bars and forgings cannot be fully applied to large-diameter titanium alloy bars and forgings. During the production process, the deformation rate, deformation temperature, and deformation amount have a significant impact on large-size forgings, which can easily lead to problems such as incomplete forging, excessively fast deformation rate, and surface undercooling, resulting in microstructure defects such as overheated microstructure, wheel-like microstructure, coarse grains, through-flow, and turbulent flow, affecting the final mechanical properties of the forgings. Therefore, the design of the processing technology and parameters for large-size titanium alloy bars and forgings is the most important part of the forging production process, determining the quality of the microstructure and properties of the forgings. Summary of the Invention

[0004] Based on the existing technology, this invention proposes a method for controlling the streamline of large-size titanium alloy rod-shaped cross-section forgings (hereinafter referred to as forgings). The forgings have a single piece weight of not less than 600 kg and a length of 800 mm to 1200 mm. The purpose is to control the consistency between the streamline and the outline of the forging during the die forging process by pre-treating the billet and controlling the deformation amount and deformation area during billet preparation, so as to improve the mechanical properties of the forgings and the service life of the parts.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] The streamline control method for large-size titanium alloy bar-shaped forgings with irregular cross-sections described in this invention is for large-size titanium alloy bar-shaped forgings with irregular cross-sections, weighing no less than 600 kg and with a length of 800 mm to 1200 mm. The steps of this method are as follows:

[0007] Step 1: Determine the specifications and weight of the titanium alloy raw material bars to be used.

[0008] The maximum cross-sectional area A of the forging along its length is calculated using 3D digital modeling software. The diameter of the titanium alloy raw material bar used for the forging is calculated as 1.5A to 2.0A, and the weight of the titanium alloy raw material bar is calculated as 1.2 to 1.4 times the weight of the forging. Then, the material is cut according to the above specifications and weight.

[0009] Specifications and cutting weight

[0010] The maximum cross-sectional area A of the forging along its length is calculated using 3D digital modeling software. The diameter of the titanium alloy raw material bar used for the forging is calculated as 1.5A to 2.0A, and the weight of the titanium alloy raw material bar is calculated as 1.2 to 1.4 times the weight of the forging. Then, the material is cut according to the above specifications and weight.

[0011] Step 2: Pretreatment of titanium alloy raw material bars

[0012] For large-sized titanium alloy forgings, the titanium alloy bars selected for billet preparation generally have a diameter of not less than Φ500mm, which falls under the category of large-sized titanium alloy bars. With the increased diameter of the titanium alloy bar, the microstructure consistency between its core and outer edge is not high; typically, the core microstructure is coarser and the edge microstructure is finer. Using existing forging processing methods, the forgings produced have poor microstructure and property uniformity, resulting in a low yield rate. Compared to smaller-sized titanium alloy bars, the streamline distribution in large-sized titanium alloy bars also shows significant differences, with local streamline orientations deviating significantly from the bar's axial direction. Therefore, this invention employs the following method to treat the microstructure and properties of large-sized titanium alloy bar billets for consistency:

[0013] First, the titanium alloy raw material bar is placed in a heating furnace and heated evenly. Then, it is upsetting and drawing deformation is completed on a forging machine. The upsetting deformation is 40% to 50%, and the pressing speed is controlled at 3 mm / s to 6 mm / s. The drawing adopts an alternating method of squaring and faceting, and the single pressing amount is controlled within 100 mm. Finally, the cross-sectional area of ​​the drawn billet is consistent with the cross-sectional area of ​​the titanium alloy raw material bar.

[0014] The above upsetting and drawing deformation processes involve five heating cycles, with the heating temperature and holding time for each cycle as follows:

[0015] First and second firings: The heating temperature T0 for the first and second firings is according to T β- (20℃~80℃) calculation, the holding time t0 for the first and second firing cycles is calculated according to calculate;

[0016] Third heating cycle: The heating temperature T1 for the third heating cycle is according to T β Calculated using (10℃~30℃), the holding time for the third firing is t0;

[0017] The fourth and fifth heating cycles: The heating temperature for the fourth and fifth heating cycles is T0, and the holding time for the fourth and fifth heating cycles is t0.

[0018] The first, second, fourth, and fifth firings are used to improve the uniformity of the billet's microstructure and properties; the third firing is mainly used to refine the microstructure and improve the uniformity of the billet's grain size.

[0019] The above T β The phase transformation temperature of the titanium alloy used in the forging;

[0020] Step 3: Billet Preparation and Streamline Control

[0021] The pretreatment in step two significantly improves the uniformity of the microstructure and the consistency of the streamlines in the titanium alloy raw material billet. The streamlines are essentially aligned with the axis of the forging. Further squarening of the billet enhances the consistency of the streamlines and facilitates subsequent billet forming and forging streamline control. The specific squarening method is as follows: First, the billet obtained after the pretreatment in step two is placed in a heating furnace and heated uniformly at a temperature of T0 for a holding time of t0. Then, it is squared on a forging machine, with a square billet cross-sectional area A. p According to calculations from 1.1A to 1.2A, the square cutting process starts from one end of the billet and gradually transitions to the other end, with an axial feed rate of 50mm to 120mm during the transition.

[0022] After the square billet is squared, a local area of ​​the billet is forged and shaped. The forging is carried out in the order of the cross-sectional area from large to small and from the middle to the two ends, so that the metal mainly flows longitudinally when the billet is deformed, and the flow line direction is consistent with the outline of the billet, thus obtaining the billet.

[0023] For large-size titanium alloy forgings, in order to further improve the consistency of streamline distribution and the uniformity of microstructure, and to minimize the deformation in the final die forging, the projected profile of the billet in the forging direction of the final die forging should be approximately the same as that of the forging. The similarity θ between the projection of the billet and the forging in the forging direction of the final die forging should be 75% to 90%. In addition, the billet should retain 20% to 40% of the deformation for the final die forging of the forging.

[0024] Step 4: Correcting the billet

[0025] In order to reduce the flow and turbulence of local metal during forging and to make the surface streamlines consistent with the forging contour, the billet is ground or rough machined to remove sharp edges and forging defects from the billet surface.

[0026] Step 5: Forge the billet into shape.

[0027] Compared to hot forging, isothermal forging is more conducive to the uniform flow of the billet in the mold, and the streamline of the forging matches the outline of the forging better. Therefore, this invention uses isothermal forging to finally forge the billet. The process includes uniformly heating the billet in a heating furnace at a heating temperature of T0, holding time t2 calculated at 0.8 mm / min × maximum width of the billet, placing the billet in the middle of the mold, forging speed of 0.2 mm / s to 1 mm / s, and removing the forging after the billet fills the mold cavity.

[0028] Step Six: Heat Treatment of Forgings

[0029] According to the mechanical property requirements of the forgings, the forgings are heat-treated by annealing, solution treatment and aging.

[0030] In practice, the similarity θ between the projected shape of the billet and the forging in the forging direction of the final die forging of the forging, as described in step three, is equal to the ratio of the perimeter area of ​​the forging, C. 锻 / The ratio of the perimeter to the area of ​​the billet C 坯 .

[0031] During implementation, before forging a local area of ​​the billet as described in step three, the heating temperature of the billet is T0, and the holding time t1 is calculated as 0.4 mm / min × billet width.

[0032] During implementation, when forging a local area of ​​the billet as described in step three, the billet is flipped along its longitudinal direction to ensure uniform distribution of streamlines.

[0033] In implementation, in step four, edges with included angles less than 120° on the blank are rounded, with the rounded radius R controlled within the range of 10mm to 20mm. Further, in step four, the rounded radius R = 15mm.

[0034] During implementation, before die forging as described in step five, a lubricant is sprayed onto the surface of the billet to improve the flowability of the billet in the die and make the streamline more in line with the forging contour.

[0035] In practice, the heating temperature of the heat treatment described in step six is ​​lower than T. β -20℃. Attached Figure Description

[0036] Figure 1 Schematic diagram of the rod-shaped irregular cross-section forging in the embodiment of the technical solution of the present invention

[0037] Figure 2 for Figure 1 Schematic diagram of the cross-section of the forging along its length.

[0038] Figure 3 for Figure 1 Schematic diagram of the blank forging in the middle Detailed Implementation

[0039] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments:

[0040] The technical solution of the present invention is not limited to the specific embodiments of titanium alloy forgings listed below.

[0041] See appendix Figure 1 , 2 As shown, this embodiment is a TB6 titanium alloy forging for a certain aircraft. The forging has a roughly square bar shape, with irregularly shaped bosses at both ends and in the middle. The steps for controlling the streamline during the forging process using the technical solution of this invention are as follows:

[0042] Step 1: Determine the specifications and weight of the titanium alloy raw material bars to be used.

[0043] The maximum cross-sectional area A of the forging along its length was calculated to be 230900 mm² using 3D digital modeling software. 2 The diameter of the titanium alloy raw material bar used for forging is calculated according to 1.5A, resulting in a diameter of Φ665mm. The weight of the titanium alloy raw material bar is calculated as 1.23 times the weight of the forging, resulting in a weight of 882kg. The material is then cut according to the above specifications and weight, and the length of the titanium alloy raw material bar is 827mm.

[0044] Step 2: Pretreatment of titanium alloy raw material bars

[0045] First, the titanium alloy raw material bar is placed in a heating furnace and heated evenly. Then, it is upsetting and drawing deformation is completed on a forging machine. The upsetting deformation is 40% to 50%, and the pressing speed is controlled at 3 mm / s to 6 mm / s. The drawing adopts an alternating method of squaring and faceting, and the single pressing amount is controlled within 100 mm. Finally, the cross-sectional area of ​​the drawn billet is consistent with the cross-sectional area of ​​the titanium alloy raw material bar.

[0046] The above upsetting and drawing deformation processes involve five heating cycles, with the heating temperature and holding time for each cycle as follows:

[0047] First and second firings: The heating temperature T0 for the first and second firings is according to T β Calculated at -40℃, the holding time t0 for the first and second firing cycles is based on... Calculation, ≈532 minutes;

[0048] Third heating cycle: The heating temperature T1 for the third heating cycle is according to T β Calculated at +10℃, the holding time for the third firing is t0;

[0049] The fourth and fifth heating cycles: The heating temperature for the fourth and fifth heating cycles is T0, and the holding time for the fourth and fifth heating cycles is t0.

[0050] The above T β The phase transformation temperature of the titanium alloy used in the forging;

[0051] Step 3: Billet Preparation and Streamline Control

[0052] First, the billet obtained after the pretreatment in step two is placed in a heating furnace and heated uniformly at a temperature of T0 for a holding time of t0. Then, it is squared on a forging machine, with a square billet cross-sectional area A. p According to calculation 1.1A, the square billet is formed starting from one end of the billet and gradually transitioning to the other end, with an axial feed of 50mm to 120mm during the transition; the final billet dimensions are 460mm (width) × 600mm (height) × 693mm (length).

[0053] After the square billet is squared, a local area of ​​the billet is forged and shaped. The process is as follows: the billet is put back into the heating furnace and heated to a temperature of T0. The holding time is t1 = 0.4 mm / min × billet width = 184 min. After exiting the furnace, the billet is first drawn from one end. The cross-sectional dimensions after drawing are 270 mm × 600 mm and the length is 563 mm. Then, the second drawing begins at a position 305 mm from the larger end. The cross-sectional dimensions after drawing are 210 mm × 600 mm and the length is 490 mm. During the drawing process, the billet is flipped multiple times along the longitudinal axis to make the billet deform evenly. The transition between adjacent cross-sections of different sizes is achieved by a slope. The angle between the slope and the longitudinal direction of the billet is between 30° and 60°.

[0054] The forging process follows a sequence from largest to smallest cross-sectional area, starting with the middle and then moving to both ends. This ensures that the metal flows primarily longitudinally during billet deformation, maintaining consistency between the flow lines and the billet's outline, resulting in a billet material, such as... Figure 3 As shown;

[0055] The projected profile of the billet in the forging direction of the final die forging of the finished forging should be approximately the same as that of the forging. The similarity θ between the projected profile of the billet and the forging in the forging direction of the final die forging should be 75% to 90%. In addition, the billet should retain 20% to 40% of the deformation for the final die forging of the finished forging.

[0056] Step 4: Correct forging defects on the surface of the billet.

[0057] Forging defects on the surface of the billet are removed by grinding or rough machining. The width-to-depth ratio of the pits after defect removal is not less than 10:1. Edges with included angles less than 120° are rounded with a radius R of not less than 10mm.

[0058] Step 5: On a forging press, the billet is forged into shape using a die.

[0059] Isothermal forging is used to finally forge the billet. The process includes uniformly heating the billet in a heating furnace at a temperature of T0±10℃, holding it for t2 at a rate of 0.8mm / min × maximum width of the billet = 368min, transferring the heated billet to the die cavity, spraying forging lubricant on the surface of the die cavity, forging speed of 0.5mm / s~1mm / s, and removing the forging after the billet has filled the die cavity.

[0060] Step Six: Heat Treatment of Forgings

[0061] The forging is rough-machined to reduce its thickness. It is then subjected to solution heat treatment at a heating temperature T. β Heat the forging at -40℃±10℃ for 220 minutes, then water-cool it to room temperature. Next, perform an aging heat treatment at 515±10℃ for 610 minutes.

Claims

1. A method for controlling the streamlines of large-size titanium alloy bar-shaped forgings with irregular cross-sections, wherein the weight of a single large-size titanium alloy bar-shaped forging is not less than 600 kg and the length is 800 mm to 1200 mm, characterized in that: The steps of this method are as follows: Step 1: Determine the specifications and weight of the titanium alloy raw material bars to be used. The maximum cross-sectional area A of the forging along its length is calculated using 3D digital modeling software. The diameter of the titanium alloy raw material bar used for the forging is calculated as 1.5A to 2.0A, and the weight of the titanium alloy raw material bar is calculated as 1.2 to 1.4 times the weight of the forging. Then, the material is cut according to the above specifications and weight. Step 2: Pretreatment of titanium alloy raw material bars First, the titanium alloy raw material bar is placed in a heating furnace and heated evenly. Then, it is upsetting and drawing deformation is completed on a forging machine. The upsetting deformation is 40% to 50%, and the pressing speed is controlled at 3 mm / s to 6 mm / s. The drawing adopts an alternating method of squaring and faceting, and the single pressing amount is controlled within 100 mm. Finally, the cross-sectional area of ​​the drawn billet is consistent with the cross-sectional area of ​​the titanium alloy raw material bar. The above upsetting and drawing deformation processes involve five heating cycles, with the heating temperature and holding time for each cycle as follows: First and second firings: The heating temperature T0 for the first and second firings is according to T β - (20℃~80℃) Calculation, the holding time t0 for the first and second firing cycles is 0.85min / mm× ~1.28min / mm× calculate; Third heating cycle: The heating temperature T1 for the third heating cycle is according to T β Calculated using (10℃~30℃), the holding time for the third firing is t0; The fourth and fifth heating cycles: The heating temperature for the fourth and fifth heating cycles is T0, and the holding time for the fourth and fifth heating cycles is t0. The above T β The phase transformation temperature of the titanium alloy used in the forging; Step 3: Billet Preparation and Streamline Control First, the billet obtained after the pretreatment in step two is placed in a heating furnace and heated uniformly at a temperature of T0 for a holding time of t0. Then, it is squared on a forging machine, with a square billet cross-sectional area A. p According to calculations from 1.1A to 1.2A, the square cutting process starts from one end of the billet and gradually transitions to the other end, with an axial feed rate of 50mm to 120mm during the transition. After the square billet is squared, a local area of ​​the billet is forged and shaped. The forging is carried out in the order of the cross-sectional area from large to small and from the middle to the two ends, so that the metal mainly flows longitudinally when the billet is deformed, and the flow line direction is consistent with the outline of the billet, thus obtaining the billet. The projected profile of the billet in the forging direction of the final die forging of the finished forging should be approximately the same as that of the forging. The similarity θ between the projection of the billet and the forging in the forging direction of the final die forging should be 75% to 90%. In addition, the billet should retain 20% to 40% of the deformation for the final die forging of the finished forging. The similarity θ between the projected shape of the billet and the forging in the forging direction of the final die forging of the forging, as described in step three, is equal to the ratio of the perimeter area of ​​the forging, C. 锻 / The ratio of the perimeter to the area of ​​the billet C 坯 ; Step 4: Correcting the billet Grinding or rough machining of the billet removes sharp edges and forging defects from the billet surface; Step 5: Forge the billet into shape. Isothermal forging is used to forge the billet into its final shape. The process includes uniformly heating the billet in a heating furnace at a temperature of T0, holding time t2 calculated as 0.8 min / mm × maximum width of the billet, forging speed of 0.2 mm / s to 1 mm / s, and removing the forging after the billet fills the mold cavity. Step Six: Heat Treatment of Forgings The forgings are heat-treated by annealing, solution treatment and aging.

2. The method for controlling the streamlines of large-size titanium alloy rod-shaped forgings with irregular cross-sections according to claim 1, characterized in that: Before forging a local area of ​​the billet as described in step three, the heating temperature of the billet is T0, and the holding time t1 is calculated as 0.4 min / mm × billet width.

3. The method for controlling the streamlines of large-size titanium alloy rod-shaped irregular cross-section forgings according to claim 1, characterized in that: In step three, when forging a local area of ​​the billet, the billet is flipped along its longitudinal direction to ensure a uniform distribution of streamlines.

4. The method for controlling the streamlines of large-size titanium alloy rod-shaped irregular cross-section forgings according to claim 1, characterized in that: In step four, the edges of the blank with an included angle of less than 120° are rounded, and the radius of the rounded corner R is controlled within the range of 10mm to 20mm.

5. The method for controlling the streamlines of large-size titanium alloy rod-shaped irregular cross-section forgings according to claim 4, characterized in that: In step four, the fillet radius R = 15mm.

6. The method for controlling the streamlines of large-size titanium alloy rod-shaped irregular cross-section forgings according to claim 1, characterized in that: Before die forging as described in step five, a lubricant is sprayed onto the surface of the billet to improve the flowability of the billet in the die and make the streamline more in line with the forging contour.

7. The method for controlling the streamlines of large-size titanium alloy rod-shaped irregular cross-section forgings according to claim 1, characterized in that: The heating temperature for the heat treatment in step six is ​​lower than T. β -20℃.

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