Preparation method of TC4 titanium alloy supercritical specification bar with equiaxed structure uniformity for aero-engine

Abstract

The invention discloses a preparation method of a TC4 titanium alloy supercritical specification bar for an aero-engine with equiaxed structure uniformity, which is characterized in that a TC4 titanium alloy ingot is used, the bar is fully deformed through multi-dimensional upsetting and drawing in radial and transverse extension directions in a forging mode of two upsetting and two drawing in each heating number, the deformation amount in each heating number is 80-95%, and the deformation amount in each heating number is 80-95%; the upsetting and drawing temperature is carried out in a beta-phase region or a two-phase region, and finally the supercritical equiaxed structure bar with the diameter phi of 600-900 mm is obtained. According to the method, the composite forging technology of single-heating-number two-upsetting and two-drawing and multi-dimensional reversing upsetting and drawing is adopted, the material deformation amount is increased, the core structure is more fully broken, the structure uniformity of the TC4 titanium alloy large-specification bar is improved, structure equiaxing is achieved, the forged bar with the performance meeting the technical requirements of an aero-engine is obtained, industrial production is achieved, and the method is suitable for industrial production. And the processing and application potential of the titanium alloy is widened.

Description

Technical Field

[0001] The invention belongs to the field of metallurgy and relates to a titanium alloy hot processing technology, in particular to a method for preparing a TC4 titanium alloy supercritical specification bar with equiaxed structural uniformity for an aero-engine. Background Art

[0002] As aircraft engines develop towards high thrust-to-weight ratio and long life, in order to meet the trend of large-scale and integrated structural design, the size of forgings for aircraft engines continues to break through traditional specifications and form supercritical specification bars. The diameter of such bars usually exceeds the critical size (above Φ500mm) that can be stably prepared by conventional forging processes, and the control of its internal organizational uniformity becomes a key problem that restricts material performance. As one of the most commonly used titanium alloys in the aviation field, TC4 titanium alloy has the advantages of light weight, high specific strength, and good machinability. Its application performance is closely related to the material organizational morphology.

[0003] In order to ensure the reliability and long life of key components, the organizational uniformity of TC4 titanium alloy for aviation must be strictly controlled to ensure the stability of titanium alloy under different temperatures and environments. During the forging process, the refinement and organizational homogenization of titanium alloy grains can be achieved by controlling the temperature and deformation degree. The uniformity of grain size and distribution can improve the plasticity and toughness of the material and reduce anisotropy, thereby ensuring the performance stability of aircraft engine components under complex loads. The present invention adopts a composite forging process of single-fire two-upsetting and two-drawing and multi-dimensional reversing, and the operation replaces the original unidirectional upsetting and drawing, increases the degree of material deformation, and contributes to the crushing of grains and the transformation of organizational morphology. The core organization can be more fully crushed, equiaxed, and the organizational uniformity of large-size bars of TC4 alloy can be improved. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a TC4 titanium alloy supercritical specification bar for aircraft engines with equiaxed uniformity. The method for preparing the TC4 titanium alloy supercritical specification bar for aircraft engines with equiaxed uniformity is to solve the technical problems in the prior art that the TC4 titanium alloy bars are small in size, have elongated α structure in the longitudinal direction, and have insufficient equiaxility.

[0005] The present invention provides a method for preparing a TC4 titanium alloy supercritical specification bar for an aero-engine with equiaxed structural uniformity, comprising the following steps: S1, a step of preparing a TC4 titanium alloy ingot, wherein the diameter of the TC4 titanium alloy ingot is Φ860-1000 mm; S2, a step of preparing a forging blank, Determine the original radial height direction Z, transverse width direction X and thickness direction Y of the TC4 titanium alloy ingot; S21, adding the TC4 titanium alloy ingot when the furnace temperature is 800-900°C, and keeping the temperature for 8-12h after the temperature reaches 1100-1200°C, firstly performing upsetting deformation on the TC4 titanium alloy ingot along the radial height Z direction, then flipping 90° with the thickness Y direction as the axis, and then stretching along the Z direction, flipping 90° once on the transverse extension surface perpendicular to the Z direction, obtaining an intermediate square billet, and then chamfering the small edges, and then flipping 90° with the thickness Y direction as the axis, and then continuing to perform upsetting deformation along the Z direction, and then stretching along the original transverse width X direction, and flipping 45° once on the YZ extension surface perpendicular to the X direction, to obtain a first octagonal billet of Φ680-980mm; S22, the first octagonal billet of Φ680-980 mm obtained in step S21 is put into a furnace at a furnace temperature of 700-850°C, and is kept warm for 2-6 hours after the temperature reaches 1010-1070°C, and the billet is first subjected to upsetting deformation along the width X direction, and then turned 90° with the thickness Y direction as the axis, and then stretched along the X direction, and turned 90° once on the YZ extension surface, to obtain an intermediate square billet, and then the small edges are chamfered, and then the billet is turned 90° with the thickness Y direction as the axis, and then the upsetting deformation is continued along the X direction, and then stretched along the radial height Z direction, and turned 45° once on the transverse extension surface, to obtain a second octagonal billet of Φ680-980 mm; The upsetting deformation in any of the above steps is controlled to be 80~95%; S3, a step of forging bars, The second octagonal billet is forged through 4 to 8 fires to obtain an octagonal billet of Φ680-980 mm, the deformation amount of each fire is 80-95%, the forging upsetting process includes a reversing operation of drawing length, the billet is heated and kept warm in the β phase region or the two-phase region before each upsetting, the temperature of the β phase region is 1010-1070°C, and the temperature of the two-phase region is 930-980°C, and finally a TC4 titanium alloy supercritical specification bar for aero-engines with equiaxed microstructure uniformity of Φ600-900 mm is obtained; During the upsetting process, the upsetting operation is first performed in the Z direction, and then in the X direction, and the upsetting operations are performed alternately in sequence; When operating in the Z direction, heat preservation is performed in the β phase region for 2 to 6 hours or in the two-phase region for 4 to 8 hours, and the xth octagonal billet is upset and stretched along the radial height Z direction. During the stretching process, the horizontal extension surface is turned over 90° once, and x is an integer, 2≤x≤7. After obtaining the intermediate square billet, the small edges are chamfered, and the billet is turned over 90° with the thickness Y direction as the axis, and then upset and deformed along the Z direction and stretched along the X direction. The billet is turned over 45° once on the YZ extension surface to obtain the (x+1)th octagonal billet of Φ680~980mm; When operating in the X direction, keep warm in the β phase region for 2~6h or in the two-phase region for 4~8h, upset and stretch along the X direction, turn over 90° on the YZ extension surface during the stretching process, obtain the intermediate square billet and then chamfer the small edges, turn over 90° with the thickness Y direction as the axis, do upsetting deformation along the X direction and then stretch along the Z direction, turn over 45° on the transverse extension surface, and obtain the (x+2) octagonal billet of Φ680~980mm; then air cool for 4~8h.

[0006] Preferably, in the step of preparing the TC4 titanium alloy ingot in step S1, the titanium alloy ingot is obtained by at least three vacuum consumable smelting processes.

[0007] Preferably, a step of preparing the blank in step S2 is: Step S3 includes at least one heating and heat preservation process in the β phase region and at least one heating and heat preservation process in the two-phase region.

[0008] Preferably, in step S3, the step of obtaining a rod with a diameter of Φ600-900 mm by upsetting the second octagonal blank six times is as follows: S31, adding the second octagonal billet when the furnace temperature is 600-700°C, and keeping the temperature for 4-8h after the temperature reaches 930-980°C, upsetting and stretching the second octagonal billet along the radial height Z direction, turning 90° on the transverse extension surface during the stretching process, obtaining an intermediate square billet, and then chamfering the small edges, turning 90° with the thickness Y direction as the axis, upsetting and deforming in the Z direction, and then stretching in the X direction, turning 45° on the YZ extension surface, to obtain a third octagonal billet of Φ680-980mm; S32, adding the third octagonal billet when the furnace temperature is 600-700°C, keeping the temperature at 930-980°C for 4-8h, upsetting and stretching along the X direction, turning 90° on the YZ extension surface during the stretching process, obtaining the intermediate square billet, chamfering the small edges, turning 90° along the Y direction of the thickness as the axis, upsetting and deforming along the X direction, and then stretching along the Z direction, turning 45° on the transverse extension surface, to obtain the fourth octagonal billet of Φ680-980mm; and then air cooling for 4-8h; S33, adding the fourth octagonal billet when the furnace temperature is 700-850°C, and keeping the temperature for 2-6h after the temperature reaches 1010-1070°C, upsetting and stretching the billet along the radial height Z direction, turning 90° on the transverse extension surface during the stretching process, obtaining an intermediate square billet, and then chamfering the small edges, turning 90° with the thickness Y direction as the axis, upsetting and deforming in the Z direction, and then stretching in the X direction, turning 45° on the YZ extension surface, to obtain a fifth octagonal billet of Φ680-980mm; S34, adding the fifth octagonal billet when the furnace temperature is 600-700°C, keeping the temperature at 930-980°C for 4-8h, upsetting and stretching along the X direction, turning 90° on the YZ extension surface during the stretching process, obtaining an intermediate square billet, chamfering the small edges, turning 90° with the thickness Y direction as the axis, upsetting and deforming along the X direction, and then stretching along the Z direction, turning 45° on the transverse extension surface, to obtain a sixth octagonal billet of Φ680-980mm; S35, adding the sixth octagonal billet when the furnace temperature is 700-850°C, and keeping the temperature for 2-6h after the temperature reaches 1010-1070°C, upsetting and stretching the billet along the radial height Z direction, turning 90° on the transverse extension surface during the stretching process, obtaining an intermediate square billet, and then chamfering the small edges, turning 90° with the thickness Y direction as the axis, upsetting and deforming in the Z direction, and then stretching in the X direction, turning 45° on the YZ extension surface, to obtain a seventh octagonal billet of Φ680-980mm; S36, add the 7th octagonal billet when the furnace temperature is 600-700℃, keep the temperature at 930-980℃ for 4-8h, upset and stretch the billet along the X direction, turn the YZ extension surface 90° once during the stretching process, obtain the intermediate square billet, chamfer the small edges, turn the thickness Y direction 90° along the X direction, do upsetting deformation, and then stretch it along the Z direction, finally return to the radial height Z direction, radial forge to obtain Φ600-900mm large-size bars, then air cool for 4-8h, and finally obtain TC4 bars with a diameter of Φ600-900mm.

[0009] The present invention also provides a TC4 titanium alloy supercritical specification bar for aircraft engines with equiaxed structural uniformity prepared by the above method, wherein the weight percentages of the components in the TC4 titanium alloy supercritical specification bar are: Al: 6.5~6.8%, V: 4.1~4.5%, Fe≤0.2%, C≤0.05%, N≤0.05%, H≤0.0125%, O≤0.20%, the balance is Ti, a single impurity is ≤0.1%, and the total amount of impurities is ≤0.2%.

[0010] Furthermore, the grain size of the TC4 titanium alloy supercritical specification rod is ≤23 μm, the grain size is 11-13 grades according to GB / T 6394-2017 standard, and the primary α phase content is 70-90%.

[0011] Furthermore, the tensile strength of the TC4 titanium alloy supercritical specification bar is ≥960MPa, the yield strength is ≥920MPa, the elongation is ≥12.5%, and the cross-sectional shrinkage is ≥36%; the tensile strength at 400°C is ≥630MPa, the elongation is ≥16%, and the cross-sectional shrinkage is ≥48%. The endurance test at 570MPa and 400°C meets the requirement of 101h without breaking, and the diameter of the flat-bottom hole in the ultrasonic flaw detection is less than or equal to 3.2mm.

[0012] In the manufacturing method of the present invention: The present invention uses TC4 titanium alloy ingots with a diameter of Φ860~1000mm, which are obtained through at least three vacuum self-consumptions, and large ingots are selected to meet the forging of large-sized bars. However, the cross-sectional dimensions of large ingots are relatively large. During the forging process, due to the forgeability of TC4 titanium alloy, it is more difficult to control the uniformity of heat transfer and metal deformation. In order to obtain equiaxed structure in large ingots after forging, higher requirements are required for the forging process. In contrast, due to their smaller size, small-sized ingots are easier to be uniform in heat transfer and deformation under the same forging process conditions, and it is easier to obtain equiaxed structure. Therefore, the use of large ingots for upsetting to obtain equiaxed structure significantly increases the difficulty of forging.

[0013] The invention controls the deformation of the single fire in the β phase region and the α+β region to 80-95%. The large deformation in the β phase region can break the original coarse cast structure of the ingot, achieve grain refinement, and provide an easily broken structure for subsequent upsetting; the large deformation in the α+β region can transform the α phase from a coarse sheet to a fine equiaxed shape, and the equiaxed α phase structure has better isotropy, while enhancing the α / β phase interface bonding force, refining the β phase grains, improving the material strength, and maintaining the material's good plasticity and toughness, thereby obtaining a TC4 titanium alloy forged rod with good comprehensive mechanical properties.

[0014] The present invention adopts a gradient temperature field design and a segmented heating strategy. Preferably, in the heating process of the upsetting and drawing blank, the bar is first preheated at a low temperature to slowly increase the overall temperature of the bar, reduce the temperature difference between the inside and outside, and prevent the blank from cracking; then the temperature is gradually increased to a suitable forging temperature. By heat preservation, the temperature inside and outside of the material is consistent, reducing the risk of cracking. This operation effectively ensures that the temperature of each part of the bar is uniform, avoiding uneven deformation during forging due to local overheating or overcooling, which affects the quality of the forged bar.

[0015] The present invention adopts high-temperature pre-forging in the β phase region and forging in the α+β two-phase region to form a gradient deformation field during the forging process of the β phase region. During the forging process of the β phase region, the broken β grains are recrystallized to form new and fine grains, which is helpful to break the original cast structure, refine the β grains, and construct the basic structure morphology. During the forging in the α+β two-phase region, the temperature is reduced to below the β transformation temperature, the β phase is transformed into the α phase through the nucleation and growth mechanism, and the α phase nucleus is preferentially formed inside the β grains and at the grain boundaries. This process is helpful to finely control the structure and optimize the final performance.

[0016] The forging process of the present invention adopts an air cooling method. Compared with water cooling, it can effectively avoid excessive thermal stress inside the TC4 large-size bar due to excessive cooling speed, thereby reducing the risk of defects such as deformation and cracking of the bar; compared with air cooling, the cooling rate of air cooling is conducive to the improvement of the nucleation rate, inhibiting the growth of grains, and preventing further coarsening of the core structure during the cooling process. Therefore, air cooling helps to obtain fine grain structure in the TC4 large-size bar, which can not only improve the strength and hardness of the material, but also improve its plasticity and toughness, reduce anisotropy, and make the performance of the bar in different directions more uniform and stable, meeting the strict requirements of engineering applications on material properties; and air cooling can shorten the cooling time, which can significantly improve the production efficiency for large-scale production, reduce the production cycle, and facilitate the next step of the process in time.

[0017] In the present invention, during the upsetting operation in the Z direction or the X direction, the cross-section of the intermediate square billet after the small edges are chamfered is octagonal, and the billets after single-fire forging all present an octagonal cross-section: compared with the square cross-section, the metal flow is better guided, ensuring that the metal flow is relatively uniform in the next upsetting operation, reducing the stress concentration phenomenon at the corners and edges, and helping to reduce cracks and folding.

[0018] The multi-dimensional reversing upsetting in the forging process of the present invention can fully deform the TC4 titanium alloy billet in multiple directions, thereby improving the uniformity of the structure and reducing the horizontal and vertical directional differences of the structure. Reversing upsetting can refine the grains, eliminate internal defects, improve material properties, reduce crack generation, and increase the bar forging yield.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1) The present invention adopts a forging process of reversing upsetting and drawing, and the operation replaces the original upsetting and drawing, which increases the degree of material deformation, can more fully break the core structure, and realize equiaxed. In addition, the temperature of the forging billet is gradually reduced during the subsequent operation, which is conducive to the crushing of grains and the transformation of organizational morphology, and improves the organizational uniformity of large-size TC4 alloy bars.

[0020] 2) The large-size TC4 titanium alloy rods prepared by this method have broken through the bottleneck of controlling the uniformity of the supercritical specification rods. The microstructure of the TC4 titanium alloy rods is a uniformly distributed equiaxed structure with a grain size of ≤23μm, an isotropic degree KD≤1.5, and a primary α phase content of 70~90%. The TC4 rods with this uniform structure can be used in many titanium alloy fields and have great application value.

[0021] 3) By reversing the drawing length, the forging permeability is improved, the production cost and material loss are reduced, the uniformity of the structure of large-size bars is improved, and the TC4 titanium alloy bars with equiaxed structure are obtained.

[0022] 4) The supercritical rods prepared by this method have a transverse room temperature tensile strength of ≥950MPa and an elongation of ≥12%, which meet the performance requirements of large-size titanium alloy forgings for aviation engines. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of forging an octagonal billet of the present invention; Figure 2 This is a low-magnification microstructure photograph of a Φ600 mm TC4 titanium alloy bar obtained in Example 1 of the present invention; Figure 3 This is a high-magnification microstructure photograph of a Φ600 mm TC4 titanium alloy bar obtained in Example 1 of the present invention; Figure 4 This is a low-magnification microstructure image of the Φ800 mm TC4 titanium alloy bar obtained in Example 2 of the present invention; Figure 5 This is a high-magnification microstructure image of the Φ800mm TC4 titanium alloy bar obtained in Example 2 of the present invention; Figure 6 This is a low-magnification microstructure image of the Φ900 mm TC4 titanium alloy bar obtained in Example 3 of the present invention; Figure 7 This is a high-magnification microstructure image of the Φ900 mm TC4 titanium alloy bar obtained in Example 3 of the present invention; Figure 8 This is a low-magnification microstructure image of the TC4 titanium alloy bar obtained in the comparative example; Fig. 9 This is a high-magnification microstructure image of the TC4 titanium alloy rod obtained in the comparative example. DETAILED DESCRIPTION

[0024] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] Example 1 A method for preparing a TC4 titanium alloy supercritical rod with a diameter of Φ600 mm and uniform equiaxed structure for use in aircraft engines, the chemical composition ratio of which is shown in Table 1, and the preparation method comprises the following steps: S1. Preparation of TC4 titanium alloy ingot Prepare TC4 titanium alloy ingot with a diameter of Φ860mm; S2. Preparation of forging blank S21, put the TC4 titanium alloy ingot into the furnace at a furnace temperature of 800°C, keep the temperature at 1100°C for 8 hours, and upset the TC4 titanium alloy ingot along the radial height Z direction ( Figure 1 Middle a), pull long ( Figure 1 b), during the drawing process, the horizontal extension surface is turned 90° once to obtain the intermediate billet, and then the small edges are turned down. The billet is turned 90° along the thickness Y direction and upsetting deformation is performed along the Z direction ( Figure 1 c) and then stretch along the X direction ( Figure 1 Middle (d) A single flip of 45° on the YZ extension plane was performed to obtain the first octagonal billet of Φ680 mm; S22, put the first octagonal billet into the furnace at a temperature of 700℃, keep it at 1010℃ for 2h, and upset it along the X direction ( Figure 1 Middle e), pull long ( Figure 1 In the middle f), the YZ extension surface is flipped 90° during the drawing process to obtain the intermediate billet, and then the small edges are chamfered. The billet is flipped 90° along the thickness Y direction and upsetting is performed along the X direction ( Figure 1 g) and then stretch along the Z direction ( Figure 1 h), a single flip of 45° on the transverse extension surface to obtain the second octagonal blank of Φ680mm; S3, Forged bars S31, put the second octagonal billet into the furnace at a temperature of 600°C, keep the temperature at 930°C for 4 hours, and upset the second octagonal billet along the radial height Z direction ( Figure 1 Middle a), pull long ( Figure 1 b), during the drawing process, the horizontal extension surface is turned 90° once, and the intermediate billet is obtained and then the small edges are chamfered. The billet is turned 90° along the thickness Y direction and upsetting is performed along the Z direction ( Figure 1 c) After deformation, it is stretched along the X direction ( Figure 1 Middle (d) A single flip of 45° on the YZ extension plane yields the third octagonal billet of Φ680 mm; S32, put the third octagonal billet into the furnace at a temperature of 600°C, keep it at 930°C for 4 hours, and upset it along the X direction ( Figure 1 Middle e), pull long ( Figure 1 In the middle f), the billet is turned 90° on the YZ extension surface during the drawing process, and the intermediate billet is obtained and then the small edges are chamfered. The billet is turned 90° along the thickness Y direction and upsetting is performed along the X direction ( Figure 1 g) After deformation, it is stretched along the Z direction ( Figure 1 h), a single flip of 45° on the transverse extension surface was performed to obtain the fourth octagonal billet of Φ680mm; and then air-cooled for 4h; S33, put the fourth octagonal billet into the furnace at a temperature of 700°C, keep it at that temperature for 2 hours after the temperature reaches 1010°C, and upset the billet along the radial height Z direction ( Figure 1 Middle a), pull long ( Figure 1 b), during the drawing process, the horizontal extension surface is turned 90° once to obtain the intermediate billet, and then the small edges are turned down. The billet is turned 90° along the thickness Y direction and upsetting deformation is performed along the Z direction ( Figure 1 c) and then stretch along the X direction ( Figure 1 Middle (d) A single flip of 45° on the YZ extension plane yields the fifth octagonal blank with a diameter of 680 mm; S34, put the 5th octagonal billet into the furnace at a temperature of 600℃, keep it at 930℃ for 4h, and upset it along the X direction ( Figure 1 Middle e), pull long ( Figure 1 In the middle f), the YZ extension surface is flipped 90° during the drawing process to obtain the intermediate billet, and then the small edges are chamfered. The billet is flipped 90° along the thickness Y direction and upsetting is performed along the X direction ( Figure 1 g) and then stretch along the Z direction ( Figure 1 h), a single flip of 45° on the transverse extension surface to obtain the 6th octagonal blank with a diameter of 680 mm; S35, put the sixth octagonal billet into the furnace at a temperature of 700°C, keep it at that temperature for 2 hours after the temperature reaches 1010°C, and upset the billet along the radial height Z direction ( Figure 1 Middle a), pull long ( Figure 1 b), during the drawing process, the horizontal extension surface is turned 90° once to obtain the intermediate billet, and then the small edges are turned down. The billet is turned 90° along the thickness Y direction and upsetting deformation is performed along the Z direction ( Figure 1 c) and then stretch along the X direction ( Figure 1 Middle (d) A single flip of 45° on the YZ extension plane yields the seventh octagonal blank with a diameter of 680 mm; S36, put the 7th octagonal billet into the furnace at a temperature of 600°C, keep it warm for 4 hours after the temperature reaches 930°C, and upset the billet along the X direction ( Figure 1 Middle e), pull long ( Figure 1 In the middle f), the YZ extension surface is flipped 90° during the drawing process to obtain the intermediate billet, and then the small edges are chamfered. The billet is flipped 90° along the thickness Y direction and upsetting is performed along the X direction ( Figure 1 g) and then stretch along the Z direction ( Figure 1 The rod is cut into small pieces (1x4, 2x5, 4x6, 5x8, 7x9, 8x10, 1x2, 1x2, 1x3, 1x4, 1x5, 7x8, 8x9, 9x10 ...

[0026] The obtained rods were tested for microstructure and mechanical properties, and the properties are shown in Table 2; Figure 2 The following is a low-magnification microstructure photograph of a Φ600mm TC4 titanium alloy rod. It can be seen from the picture that there are no visible cracks, shrinkage holes, pores, folds, inclusions, segregation or other defects that affect use in the microstructure. The low-magnification microstructure has no obvious, visually visible clear grains.

[0027] Figure 3 These are the microstructure photos of the Φ600mm TC4 titanium alloy rod obtained under high magnification. It can be seen from the pictures that the microstructure is equiaxed, the content of primary α phase in the microstructure is more than 80%, and the equiaxed primary α phase is distributed on the matrix of the β transformation microstructure. All the original β grain boundaries are fully broken, and there is no continuous network of α phase on the original β grain boundaries.

[0028] Example 2 A method for preparing a TC4 titanium alloy supercritical rod with a diameter of Φ800 mm and uniform equiaxed structure for use in aircraft engines, the chemical composition ratio of which is shown in Table 1, and the preparation method comprises the following steps: S1. Preparation of TC4 titanium alloy ingot Preparing a TC4 titanium alloy ingot with a diameter of Φ960 mm; S2. Preparation of forging blank S21, placing the TC4 titanium alloy ingot into a furnace at a furnace temperature of 850°C, and keeping the temperature for 10 hours after the temperature reaches 1150°C, upsetting and stretching the billet in the radial height Z direction, and turning the billet 90° at a time on the transverse extension surface during the stretching process to obtain an intermediate square billet, and then chamfering the small edges, turning the billet 90° with the thickness Y direction as the axis, upsetting and deforming the billet in the Z direction, and then stretching the billet in the X direction, and turning the billet 45° at a time on the YZ extension surface to obtain a first octagonal billet of Φ880 mm; S22, putting the first octagonal billet into the furnace at a furnace temperature of 800°C, keeping the temperature for 4 hours after the temperature reaches 1050°C, upsetting and stretching along the X direction, turning 90° on the YZ extension surface during the stretching process, obtaining an intermediate square billet, chamfering the small edges, turning 90° with the thickness Y direction as the axis, upsetting and deforming along the X direction, and then stretching along the Z direction, turning 45° on the transverse extension surface, and obtaining a second octagonal billet of Φ880 mm; S3, Forged bars S31, putting the second octagonal billet into the furnace at a furnace temperature of 650°C, and keeping the temperature for 6 hours after the temperature reaches 960°C, upsetting and stretching the billet in the radial height Z direction, turning 90° on the transverse extension surface during the stretching process, obtaining an intermediate square billet, and then chamfering the small edges, turning 90° with the thickness Y direction as the axis, upsetting and deforming in the Z direction, and then stretching in the X direction, turning 45° on the YZ extension surface, and obtaining a third octagonal billet of Φ880 mm; S32, the third octagonal billet is put into the furnace at a furnace temperature of 650°C, and after the temperature reaches 960°C, it is kept warm for 6 hours, and is upset and stretched along the X direction. During the stretching process, it is turned 90° on the YZ extension surface once to obtain an intermediate square billet, and then the small edges are chamfered. The billet is turned 90° along the Y direction of the thickness as the axis, and is upset and deformed along the X direction, and then stretched along the Z direction. The billet is turned 45° on the transverse extension surface once to obtain a fourth octagonal billet of Φ880 mm; and then air-cooled for 6 hours; S33, putting the fourth octagonal billet into the furnace at a furnace temperature of 800°C, and keeping the temperature for 4 hours after the temperature reaches 1050°C, upsetting and stretching the billet in the radial height Z direction, turning 90° on the transverse extension surface during the stretching process, obtaining an intermediate square billet, and then chamfering the small edges, turning 90° with the thickness Y direction as the axis, upsetting and deforming in the Z direction, and then stretching in the X direction, turning 45° on the YZ extension surface, to obtain a fifth octagonal billet of Φ880 mm; S34, the fifth octagonal billet is put into the furnace at a furnace temperature of 650°C, and after the temperature reaches 960°C, it is kept warm for 6 hours, and is upset and stretched along the X direction. During the stretching process, it is turned 90° on the YZ extension surface once to obtain an intermediate square billet, and then the small edges are chamfered. The billet is turned 90° with the thickness Y direction as the axis, and is upset and deformed along the X direction, and then stretched along the Z direction. The billet is turned 45° on the transverse extension surface once to obtain a sixth octagonal billet of Φ880 mm; S35, putting the sixth octagonal billet into the furnace at a furnace temperature of 800°C, and keeping the temperature for 6 hours after the temperature reaches 1050°C, upsetting and stretching the billet in the radial height Z direction, turning 90° on the transverse extension surface during the stretching process, obtaining an intermediate square billet, and then chamfering the small edges, turning 90° with the thickness Y direction as the axis, upsetting and deforming in the Z direction, and then stretching in the X direction, turning 45° on the YZ extension surface, and obtaining a seventh octagonal billet of Φ880 mm; S36. The 7th octagonal billet is put into the furnace at a furnace temperature of 650°C. After the temperature reaches 960°C, it is kept warm for 6 hours. The billet is upset and stretched along the X direction. During the stretching process, it is turned 90° on the YZ extension surface once to obtain the intermediate square billet, and then the small edges are inverted. It is turned 90° along the thickness Y direction as the axis, upset and deformed along the X direction, and then stretched to Φ800mm along the Z direction. Finally, it is changed back to the radial height Z direction, and then air-cooled for 6 hours to finally obtain a large-sized bar with a diameter of Φ800mm.

[0029] The obtained rods were tested for microstructure and mechanical properties, and the properties are shown in Table 2; Figure 4 The following is a low-magnification microstructure photograph of a Φ800mm TC4 titanium alloy rod. It can be seen from the picture that there are no visible cracks, shrinkage holes, pores, folds, inclusions, segregation or other defects that affect use in the microstructure. The low-magnification microstructure has no obvious, visually visible clear grains.

[0030] Figure 5 These are the microstructure photos of the Φ800mm TC4 titanium alloy rod obtained under high magnification. It can be seen from the pictures that the microstructure is equiaxed, the content of primary α phase in the microstructure is more than 80%, and the equiaxed primary α phase is distributed on the matrix of the β transformation microstructure. All the original β grain boundaries are fully broken, and there is no continuous network of α phase on the original β grain boundaries.

[0031] Example 3 A method for preparing a TC4 titanium alloy supercritical rod with a diameter of Φ900 mm and uniform equiaxed structure for use in aircraft engines, the chemical composition ratio of which is shown in Table 1, and the preparation method comprises the following steps: S1. Preparation of TC4 titanium alloy ingot Prepare TC4 titanium alloy ingot with a diameter of Φ1000mm; S2. Preparation of forging blank S21, placing the TC4 titanium alloy ingot into a furnace at a furnace temperature of 900°C, and keeping the temperature for 12 hours after the temperature reaches 1200°C, upsetting and stretching the billet in the radial height Z direction, and turning the billet 90° at a time on the transverse extension surface during the stretching process to obtain an intermediate square billet, and then chamfering the small edges, turning the billet 90° with the thickness Y direction as the axis, upsetting and deforming the billet in the Z direction, and then stretching the billet in the X direction, and turning the billet 45° at a time on the YZ extension surface to obtain a first octagonal billet of Φ980 mm; S22, putting the first octagonal billet into the furnace at a furnace temperature of 850°C, keeping the temperature for 6 hours after the temperature reaches 1070°C, upsetting and stretching along the X direction, turning 90° on the YZ extension surface during the stretching process, obtaining an intermediate square billet, chamfering the small edges, turning 90° with the thickness Y direction as the axis, upsetting and deforming along the X direction, and then stretching along the Z direction, turning 45° on the transverse extension surface, and obtaining a second octagonal billet of Φ980 mm; S3, Forged bars S31, putting the second octagonal billet into the furnace at a furnace temperature of 700°C, and keeping the temperature for 8 hours after the temperature reaches 980°C, upsetting and stretching the billet in the radial height Z direction, turning 90° on the transverse extension surface during the stretching process, obtaining an intermediate square billet, and then chamfering the small edges, turning 90° with the thickness Y direction as the axis, upsetting and deforming in the Z direction, and then stretching in the X direction, turning 45° on the YZ extension surface, to obtain a third octagonal billet of Φ980 mm; S32, the third octagonal billet is put into the furnace at a furnace temperature of 700°C, and after the temperature reaches 980°C, it is kept warm for 8h, and is upset and stretched along the X direction. During the stretching process, it is turned 90° on the YZ extension surface once to obtain an intermediate square billet, and then the small edges are chamfered. The billet is turned 90° along the Y direction of the thickness as the axis, and is upset and deformed along the X direction, and then stretched along the Z direction. The billet is turned 45° on the transverse extension surface once to obtain a fourth octagonal billet of Φ980mm; and then air-cooled for 8h; S33, putting the fourth octagonal billet into the furnace at a furnace temperature of 850°C, and keeping the temperature for 6 hours after the temperature reaches 1070°C, upsetting and stretching the billet in the radial height Z direction, turning 90° on the transverse extension surface during the stretching process, obtaining an intermediate square billet, and then chamfering the small edges, turning 90° with the thickness Y direction as the axis, upsetting and deforming in the Z direction, and then stretching in the X direction, turning 45° on the YZ extension surface, and obtaining a fifth octagonal billet of Φ980 mm; S34, putting the fifth octagonal billet into the furnace at a furnace temperature of 700°C, keeping the temperature for 8 hours after the temperature reaches 980°C, upsetting and stretching in the X direction, turning 90° on the YZ extension surface during the stretching process, obtaining an intermediate square billet, chamfering the small edges, turning 90° with the thickness Y direction as the axis, upsetting and deforming in the X direction, and then stretching in the Z direction, turning 45° on the transverse extension surface, and obtaining a sixth octagonal billet of Φ980 mm; S35, putting the sixth octagonal billet into the furnace at a furnace temperature of 850°C, and keeping the temperature for 8 hours after the temperature reaches 1070°C, upsetting and stretching the billet in the radial height Z direction, turning 90° on the transverse extension surface during the stretching process, obtaining an intermediate square billet, and then chamfering the small edges, turning 90° with the thickness Y direction as the axis, upsetting and deforming in the Z direction, and then stretching in the X direction, turning 45° on the YZ extension surface, and obtaining a seventh octagonal billet of Φ980 mm; S36, putting the 7th octagonal billet into the furnace at a furnace temperature of 700°C, keeping the temperature for 8h after the temperature reaches 980°C, upsetting and stretching along the X direction, turning 90° on the YZ extension surface during the stretching process, obtaining the intermediate square billet, chamfering the small edges, turning 90° with the thickness Y direction as the axis, upsetting and deforming along the X direction, and then stretching along the Z direction, turning 45° on the transverse extension surface, to obtain the 8th octagonal billet of Φ980mm; and then air cooling for 8h; S37, putting the 8th octagonal billet into the furnace at a furnace temperature of 850°C, and keeping the temperature for 6 hours after the temperature reaches 1070°C, upsetting and stretching the billet in the radial height Z direction, turning 90° on the transverse extension surface during the stretching process, obtaining an intermediate square billet, and then chamfering the small edges, turning 90° with the thickness Y direction as the axis, upsetting and deforming in the Z direction, and then stretching in the X direction, turning 45° on the YZ extension surface, to obtain a 9th octagonal billet of Φ980 mm; S38. The 9th octagonal billet is put into the furnace at a furnace temperature of 700°C. After the temperature reaches 980°C, it is kept warm for 8 hours. The billet is upset and stretched along the X direction. During the stretching process, it is turned 90° on the YZ extension surface once to obtain the intermediate square billet, and then the small edges are chamfered. The billet is turned 90° with the thickness Y direction as the axis, upset and deformed along the X direction, and then stretched to Φ900mm along the Z direction. Finally, it is changed back to the radial height Z direction, and then air-cooled for 8 hours to finally obtain a large-sized bar with a diameter of Φ900mm.

[0032] The obtained rods were tested for microstructure and mechanical properties, and the properties are shown in Table 2; Figure 6 The following is a low-magnification microstructure photograph of a Φ900mm TC4 titanium alloy rod. It can be seen from the picture that there are no visible cracks, shrinkage holes, pores, folds, inclusions, segregation or other defects that affect use in the microstructure. The low-magnification microstructure has no obvious, visually visible clear grains.

[0033] Figure 7 These are the microstructure photos of the Φ900mm TC4 titanium alloy rods obtained under high magnification. It can be seen from the pictures that the microstructure is equiaxed, the content of primary α phase in the microstructure reaches more than 85%, and the primary α phase grain size rating reaches level 13 in the GB / T6394-2017 metal average grain size determination method. Equiaxed primary α phase is distributed on the matrix of the β transformation microstructure, all original β grain boundaries are fully broken, and there is no continuous network of α phase on the original β grain boundaries.

[0034] Comparative Example A method for preparing a TC4 titanium alloy rod with a diameter of Φ800mm, the chemical composition ratio is shown in Table 1. Table 1 Chemical composition of Φ600~900mm TC4 titanium alloy bars Unit: mass percentage

[0035] The preparation method thereof comprises the following steps: S1. Preparation of TC4 titanium alloy ingot Preparing a TC4 titanium alloy ingot with a diameter of Φ960 mm; S2. Preparation of forging blank S21, placing the TC4 titanium alloy ingot into a furnace at a furnace temperature of 850° C., and keeping the temperature at 1150° C. for 10 hours, subjecting the billet to upsetting and drawing deformation to obtain a first billet of 880 mm; S22, putting the blank into the furnace at a furnace temperature of 800°C, and keeping the temperature for 4 hours after the temperature reaches 1050°C, and deforming the blank by upsetting and drawing to obtain a second blank of Φ880 mm; S3, Forged bars S31, putting the second blank into the furnace at a furnace temperature of 650°C, keeping the temperature at 960°C for 6 hours, and deforming the blank by upsetting and drawing to obtain a third blank of Φ880 mm; S32, the third blank is put into the furnace at a furnace temperature of 650°C, and after the temperature reaches 960°C, it is kept warm for 6 hours, and the blank is deformed by upsetting and drawing to obtain the fourth blank of Φ880mm; and then air-cooled.

[0036] S33, putting the fourth blank into the furnace at a furnace temperature of 800° C., and keeping the temperature at 1050° C. for 4 hours, deforming the blank by upsetting and drawing, and obtaining a fifth blank of Φ880 mm; S34, putting the fifth blank into the furnace at a furnace temperature of 650° C., and keeping the temperature for 6 hours after the temperature reaches 960° C., and performing upsetting and drawing deformation on the blank to obtain a sixth blank of Φ880 mm; S35, putting the sixth blank into the furnace at a furnace temperature of 800° C., and keeping the temperature at 1050° C. for 4 hours, deforming the blank by upsetting and drawing, and obtaining a seventh blank of Φ880 mm; S36. The seventh billet is put into the furnace at a furnace temperature of 650°C. After the temperature reaches 960°C, it is kept warm for 6 hours. The billet is deformed by upsetting and drawing, and then air-cooled to finally obtain a large-sized bar with a diameter of Φ800mm.

[0037] The obtained rods were tested for microstructure and mechanical properties, and the properties are shown in Table 2; Table 2 Tensile properties of Φ600~900mm TC4 titanium alloy bars

[0038] It can be seen from Table 2 that the diameter of the rods prepared in Examples 1 to 3 of the present invention can reach Φ600 to 900 mm, the tensile strength of the rods is ≥960 MPa, the yield strength is ≥920 MPa, the elongation is ≥12.5%, and the cross-sectional shrinkage is ≥36%. The tensile strength of the TC4 titanium alloy rod at a high temperature of 400°C is ≥630 MPa, the elongation is ≥16%, and the cross-sectional shrinkage is ≥48%, indicating that the TC4 titanium alloy rod prepared by the method of the present invention has high strength and high plasticity in the case of larger specifications, and can meet the requirements of large-size rods for aircraft engines.

[0039] In the preparation process of the blank in the comparative example, only a single upsetting and drawing was performed, the upsetting and drawing direction was unidirectional (along the Z direction), and the cooling method was air cooling. The cooling rate was low, resulting in coarse core structure. The yield strength of the obtained rod was 921MPa, and the high temperature tensile strength was 819MPa, which were lower than the mechanical properties of the rod obtained by upsetting and drawing in the X direction.

[0040] Figure 8 The microstructure photograph of the Φ800mm TC4 titanium alloy rod obtained for the comparative example at low magnification is shown. It can be seen from the picture that the low-magnification microstructure is uneven and does not meet the requirements for rods in GJB1538.

[0041] Fig. 9 This is a high-magnification microstructure photograph of a Φ800mm TC4 titanium alloy rod obtained for comparison. It can be seen from the picture that the content of primary α phase in the microstructure is about 60%, there is little primary equiaxed α phase, long strips of α phase are distributed on the matrix of the β transformation microstructure, the original β grain boundaries are not fully broken, and the microstructure uniformity is poor.

[0042] The embodiments described above are only descriptions of the preferred implementation modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing TC4 titanium alloy supercritical specification bars for aircraft engines with equiaxed structural uniformity, characterized in that The steps include: S1, a step of preparing a TC4 titanium alloy ingot, wherein the diameter of the TC4 titanium alloy ingot is Φ860-1000 mm; S2, a step of preparing a forging blank, Determine the original radial height direction Z, transverse width direction X and thickness direction Y of the TC4 titanium alloy ingot; S21, adding the TC4 titanium alloy ingot when the furnace temperature is 800-900°C, and keeping the temperature for 8-12h after the temperature reaches 1100-1200°C, firstly performing upsetting deformation on the TC4 titanium alloy ingot along the radial height Z direction, then flipping 90° with the thickness Y direction as the axis, and then stretching along the Z direction, flipping 90° once on the transverse extension surface perpendicular to the Z direction, obtaining an intermediate square billet, and then chamfering the small edges, and then flipping 90° with the thickness Y direction as the axis, and then continuing to perform upsetting deformation along the Z direction, and then stretching along the original transverse width X direction, and flipping 45° once on the YZ extension surface perpendicular to the X direction, to obtain a first octagonal billet of Φ680-980mm; S22, the first octagonal billet of Φ680-980 mm obtained in step S21 is put into a furnace at a furnace temperature of 700-850°C, and is kept warm for 2-6 hours after the temperature reaches 1010-1070°C, the first octagonal billet is first subjected to upsetting deformation along the width X direction, and then flipped 90° with the thickness Y direction as the axis and stretched along the X direction, and flipped 90° on the YZ extension surface once to obtain an intermediate square billet, and then the small edges are chamfered, and then the thickness Y direction is flipped 90° and the upsetting deformation is continued along the X direction, and then stretched along the radial height Z direction, and flipped 45° on the transverse extension surface once to obtain a second octagonal billet of Φ680-980 mm; The upsetting deformation in any of the above steps is controlled to be 80~95%; S3, a step of forging bars, The second octagonal billet is forged for 4 to 8 times to obtain an octagonal billet of Φ680-980 mm, the deformation amount of each fire is 80-95%, the forging upsetting process includes a reversing operation of drawing length, and the billet is heated and kept in the β phase region or the two-phase region before each upsetting, the temperature of the β phase region is 1010-1070°C, and the temperature of the two-phase region is 930-980°C, and finally a TC4 titanium alloy supercritical specification bar for aero-engines with equiaxed microstructure uniformity of Φ600-900 mm is obtained; During the upsetting process, the upsetting operation is first performed in the Z direction, and then in the X direction, and the upsetting operations are performed alternately in sequence; When operating in the Z direction, keep warm in the β phase region for 2 to 6 hours or in the two-phase region for 4 to 8 hours. x The octagonal billet is upset and stretched along the radial height Z direction. During the stretching process, the horizontal extension surface is turned over 90° once. x is an integer, 2≤x≤7. After obtaining the intermediate square billet, the small edge is chamfered. After turning over 90° with the thickness Y direction as the axis, it is upset along the Z direction and then stretched along the X direction. It is turned over 45° once on the YZ extension surface to obtain the first (Φ680~980mm) x +1) Octagonal billet; When operating in the X direction, keep warm in the β phase region for 2 to 6 hours or in the two-phase region for 4 to 8 hours. x +1) The octagonal billet is upset and stretched along the X direction. During the stretching process, it is turned 90° on the YZ extension surface to obtain the intermediate square billet, and then the small edges are chamfered. After turning 90° with the thickness Y direction as the axis, it is upset along the X direction and then stretched along the Z direction. It is turned 45° on the transverse extension surface to obtain the first (Φ680~980mm) x +2) Octagonal blank; then air-cool for 4~8h.

2. The method for preparing a TC4 titanium alloy supercritical specification bar for an aero-engine with equiaxed structural uniformity according to claim 1, characterized in that: In the step of preparing the TC4 titanium alloy ingot in step S1, at least three vacuum consumable smeltings are performed to obtain the TC4 titanium alloy ingot of Φ860-1000 mm.

3. The method for preparing a TC4 titanium alloy supercritical specification bar for aircraft engines with equiaxed structural uniformity according to claim 1, characterized in that: In one step of preparing the rod in step S3, at least one heating and heat preservation process is included in the β phase region, and at least one heating and heat preservation process is included in the two-phase region.

4. The method for preparing a TC4 titanium alloy supercritical specification bar for aircraft engines with equiaxed structural uniformity according to claim 1, characterized in that: In step S3, the steps of forging the second octagonal billet six times to obtain a bar with a diameter of Φ600-900 mm are as follows: S31, adding the second octagonal billet when the furnace temperature is 600-700°C, and keeping the temperature for 4-8h after the temperature reaches 930-980°C, upsetting and stretching the second octagonal billet along the radial height Z direction, turning 90° on the XY extension surface during the stretching process, and then chamfering the small edges after obtaining the intermediate square billet, turning 90° along the Z direction with the thickness Y direction as the axis, and then stretching along the X direction, and turning 45° on the YZ extension surface to obtain the third octagonal billet of Φ680-980mm; S32, adding the third octagonal billet when the furnace temperature is 600-700°C, keeping the temperature after reaching 930-980°C for 4-8h, upsetting and stretching along the X direction, turning 90° once on the YZ extension surface during the stretching process, obtaining the intermediate square billet, chamfering the small edges, turning 90° along the Y direction of the thickness as the axis, upsetting and deforming along the X direction, and then stretching along the Z direction, turning 45° once on the XY extension surface, to obtain the fourth octagonal billet of Φ680-980mm; and then air cooling for 4-8h; S33, adding the fourth octagonal billet when the furnace temperature is 700-850°C, keeping the temperature for 2-6h after the temperature reaches 1010-1070°C, upsetting and stretching along the radial height Z direction, turning 90° on the transverse extension surface during the stretching process, obtaining an intermediate square billet, chamfering the small edges, turning 90° with the thickness Y direction as the axis, upsetting and deforming along the Z direction, and then stretching along the X direction, turning 45° on the YZ extension surface, to obtain a fifth octagonal billet of Φ680-980mm; S34, adding the fifth octagonal billet when the furnace temperature is 600-700°C, keeping the temperature after the temperature reaches 930-980°C for 4-8h, upsetting and stretching along the X direction, turning 90° on the YZ extension surface during the stretching process, obtaining the intermediate square billet, chamfering the small edges, turning 90° along the Y direction of the thickness as the axis, upsetting and deforming along the X direction, and then stretching along the Z direction, turning 45° on the transverse extension surface, to obtain the sixth octagonal billet of Φ680-980mm; and then air cooling for 4-8h; S35, adding the sixth octagonal billet when the furnace temperature is 700-850°C, and keeping the temperature for 2-6h after the temperature reaches 1010-1070°C, upsetting and stretching the billet along the radial height Z direction, and turning 90° on the transverse extension surface during the stretching process, and after obtaining the intermediate square billet, the small edge is turned 90° with the thickness Y direction as the axis, and then upsetting and deforming in the Z direction, and then stretching in the X direction, and turning 45° on the YZ extension surface, to obtain the seventh octagonal billet of Φ680-980mm; S36, add the 7th octagonal billet when the furnace temperature is 600-700℃, keep the temperature at 930-980℃ for 4-8h, upset and stretch the billet along the X direction, turn the billet 90° once on the YZ extension surface during the stretching process, obtain the intermediate square billet, chamfer the small edges, turn the billet 90° with the thickness Y direction as the axis, upset and deform along the X direction, and then stretch it along the Z direction, finally return to the original radial height Z direction, radial forge to obtain large-size bars of Φ600-900mm, then air cool for 4-8h, and finally obtain TC4 bars with a diameter of Φ600-900mm.

5. A TC4 titanium alloy supercritical bar for aircraft engines with equiaxed structural uniformity prepared by the method according to any one of claims 1 to 4, characterized in that: The weight percentages of the components in the TC4 titanium alloy supercritical specification rod are: Al: 6.5~6.8%, V: 4.1~4.5%, Fe≤0.2%, C≤0.05%, N≤0.05%, H≤0.0125%, O≤0.20%, the balance is Ti, a single impurity ≤0.1%, and a total impurity amount ≤0.2%.

6. The TC4 titanium alloy supercritical bar material for aircraft engines with equiaxed structural uniformity as claimed in claim 5, characterized in that: The grain size of the TC4 titanium alloy supercritical specification bar is ≤23 μm, the grain size is 11-13 grades according to GB / T 6394-2017 standard, and the primary α phase content is 70-90%.

7. The TC4 titanium alloy supercritical bar material for aircraft engines with equiaxed structural uniformity as claimed in claim 5, characterized in that: The tensile strength of the TC4 titanium alloy supercritical specification bar is ≥960MPa, the yield strength is ≥920MPa, the elongation is ≥12.5%, and the cross-sectional shrinkage is ≥36%; the tensile strength at 400°C is ≥630MPa, the elongation is ≥16%, and the cross-sectional shrinkage is ≥48%. The endurance test at 570MPa and 400°C meets the requirement of 101h without breaking, and the diameter of the flat-bottom hole in the ultrasonic flaw detection is less than or equal to 3.2mm.

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