Free forging method for preparing AAA nondestructive inspection grade large-specification TC4 alloy bar

Abstract

The invention relates to a free forging method for preparing an AAA nondestructive inspection grade large-specification TC4 alloy bar, and belongs to the technical field of titanium alloy hot working. According to the method, as-cast grains are fully crushed and refined through high-temperature and large-deformation forging in the cogging stage; high-low-high heating forging at the lower phase transformation point and the upper phase transformation point is used for promoting the high-temperature dynamic recrystallization process so as to homogenize crystal grains; the corner deformation dead zone is fully reduced through multi-heating-number diagonal drawing-out forging, and a U-shaped anvil is adopted in the forming stage to reduce metal flowing in all directions in the rolling stage. According to the free forging method for the large-specification TC4 alloy bar, the structure uniformity of the TC4 alloy bar can be improved, and the AAA-level nondestructive testing requirement is met.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium alloy hot processing, and in particular relates to a free forging method for preparing AAA non-destructive testing grade large-size TC4 alloy bars. Background Art

[0002] TC4 alloy is a medium-strength α+β two-phase titanium alloy successfully developed by the Watertown Arsenal in the United States in 1954. It contains 6% α-stabilizing element Al and 4% β-stabilizing element V. The alloy has excellent comprehensive properties and good process performance, and its long-term working temperature can reach 400°C. In the aviation industry, it is mainly used to manufacture engine fans and compressor disks and blades, as well as important load-bearing components such as beams, joints and bulkheads in aircraft structures.

[0003] Due to the poor thermal conductivity, high deformation resistance and sensitive organization to temperature and deformation process parameters of titanium alloy, the uniformity of deformation of titanium alloy decreases during forging, and defects such as overheating, local coarse grains and bright bands are easily generated in the organization, which will seriously affect its microstructure uniformity and mechanical properties. In addition, in order to ensure the reliability of TC4 titanium alloy parts during use, ultrasonic flaw detection must be carried out for bars, forgings, free forgings and die forgings used to manufacture compressor disks, blades and aircraft structural parts. Existing research shows that the reasons affecting the ultrasonic flaw detection results of metal materials and the generation of clutter are mainly concentrated in the microstructure, but the existing Φ160~Φ260mm large-size TC4 bars generally have large grain size, low α-phase spheroidization and uneven microstructure, which will increase clutter reflection in ultrasonic testing, seriously affecting the ultrasonic flaw detection level of large-size TC4 bars, and it is impossible to ensure that it meets the specified index requirements. Summary of the invention

[0004] Based on the current industry forging technology, the present invention provides a free forging method for preparing AAA non-destructive testing grade large-size TC4 alloy bars, which is used to solve the technical problem that Φ160-Φ260mm TC4 alloy bars cannot meet AAA grade ultrasonic testing. The Φ160-Φ260mm TC4 bars prepared by the present invention meet AAA grade ultrasonic testing, have uniform microstructure, and can obtain excellent mechanical properties after heat treatment, meeting the use requirements of existing TC4 bars.

[0005] In order to achieve the above object, the present invention provides the following technical solutions.

[0006] On the one hand, the present invention provides a free forging method for preparing AAA non-destructive testing grade large-size TC4 alloy bars, comprising:

[0007] Step 1: Forging the TC4 alloy ingot:

[0008] The TC4 alloy ingot is forged by reversing heating across the fires at the phase transition point, the remelting temperature is reduced by each fire, and the square billet ingot is forged by a combination of upsetting and reversing elongation. The ingot is cooled after forging to fully break up the as-cast coarse structure and fully recrystallize the forged billet at the high temperature stage to refine the grains.

[0009] Step 2: The billet ingot obtained in step 1 is subjected to forging below the phase transition point and cross-fire forging above the phase transition point:

[0010] The square billet ingot obtained in step 1 is heated and forged at the phase transition point, and the deformation process is upsetting and diagonal stretching; then it is returned to the furnace and heated to the phase transition point, and is deformed into an intermediate square billet by upsetting and diagonal stretching, and cooled after forging;

[0011] Step 3: Perform two-phase multi-fire forging on the intermediate billet obtained in step 2:

[0012] The intermediate square billet obtained in step 2 is subjected to multiple upsetting and diagonal stretching to obtain a square billet blank, which is then cooled after forging;

[0013] Step 4: U-shaped anvil rounding and forging:

[0014] The square billet obtained in step 3 is subjected to bar forming by U-shaped anvil rounding and precision forging, so that the edges and surfaces of the square billet are deformed into circular surfaces.

[0015] Furthermore, the step 1 is two-fire forging, and the specific process is as follows:

[0016] First fire: heating temperature 1100 ~ 1200 ℃, heating insulation coefficient 0.6 ~ 0.8, TC4 alloy ingot cylinder diagonal vertical to the ground placed on the hammer anvil for upsetting, upsetting after drawing length into square billet; re-melting insulation temperature 1050 ~ 1100 ℃, heating insulation coefficient 0.1 ~ 0.3, deformation 60% ~ 80%;

[0017] Second firing: heating temperature 1000-1100°C, heating insulation coefficient 0.6-0.8; returning to the furnace and holding temperature 1000-1050°C, heating insulation coefficient 0.1-0.3, deformation 70%-80%, upsetting and reversing drawing forging.

[0018] Furthermore, in step 2, the heating temperature for forging at the phase transformation point is 15-40°C below the phase transformation point, and the heating insulation coefficient is 0.6-0.8; the heating temperature for cross-fire forging at the phase transformation point is 30-50°C above the phase transformation point, and the insulation coefficient is 0.3-0.4. A total of two upsetting and two drawing forging deformations are performed, and the deformation amount is 70%-80%.

[0019] Furthermore, in step 2, chamfering is performed after drawing to prevent cracking and folding during subsequent forging deformation.

[0020] Further, in step three, the billet height-to-diameter ratio after upsetting is 0.9-1.0, and the billet height-to-diameter ratio after diagonal elongation is 1.9-2.0, with a total of four fires, and the specific process is: the heating temperature of each fire is 15-40° C. below the phase change point, the heating insulation coefficient is 0.6-0.8; the reheating insulation coefficient is 0.1-0.3, and the deformation amount is 70%-80%;

[0021] Further, in step 4, the square billet is stretched and squared and then rolled into a round shape. The specific process is as follows:

[0022] Lengthening and octagonal forging: Forging is carried out using upper and lower flat anvils, with a heating temperature of 15-40°C below the phase change point, a heating insulation coefficient of 0.6-0.8, a deformation of 30%-40%, and the cross section is forged into an octagon, and then returned to the furnace for rounding;

[0023] Rounding: U-shaped anvil forging is adopted, the heating temperature is 15-40℃ below the phase change point, the heating insulation coefficient is 0.1-0.3, the deformation amount of the fire is 30%-40%, and then fine forging is carried out.

[0024] Furthermore, in step 4, the precision forging process sets the forging times according to the finished product size, with a deformation amount of 20% to 30% in each time, and the steel is drawn at a uniform speed during the precision forging process, and air-cooled to room temperature after forging.

[0025] Furthermore, in step 1 and step 4, the cooling method is air cooling, and in step 2 and step 3, the cooling method is water cooling. The specific process is:

[0026] In step 1 and step 4, after forging, the forging is air-cooled to room temperature and surface defects such as cracks are polished;

[0027] In step 2 and step 3, after forging, the forging is placed in a water cooling zone for 15 to 60 minutes.

[0028] On the other hand, the present invention also provides a AAA non-destructive testing grade large-size TC4 alloy bar, which is prepared by the above-mentioned free forging method for preparing AAA non-destructive testing grade large-size TC4 alloy bar.

[0029] Furthermore, the size of the prepared AAA non-destructive testing grade large-size TC4 alloy rod is Φ160~Φ260mm.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] High temperature heating and long-term heat preservation heating are used in the blanking stage. The forging blank is fully recrystallized in the high temperature stage to refine the structure, and the cast grains are fully broken in the forging with large deformation and reversing drawing. After blanking, heating forging is adopted at and above the phase transformation point. The heating forging at the phase transformation point can reserve sufficient distortion energy for the secondary high temperature forging, so that the secondary high temperature heating and forging process can fully recrystallize and refine the structure. The diagonal drawing process is adopted in the two-phase zone forging. The edges and faces are deformed alternately during the drawing process, which improves the phenomenon of angular deformation dead zone caused by single surface deformation during the drawing process. The cooling method of water cooling after forging is adopted. The high temperature structure is retained in the low temperature environment through rapid cooling, which can provide sufficient crystal defects for the dynamic recrystallization process of subsequent forging. U-shaped anvil rolling forging is adopted in the forming stage to limit the axial metal flow and improve the overall structure uniformity of the bar.

[0032] The Φ160~Φ260mmTC4 alloy bars obtained by this method have a typical equiaxed structure, in which the primary α phase accounts for more than 40%, and the ultrasonic flaw detection reaches the AAA level in AMS STD-2154E. After heat treatment, the tensile strength of bars of different specifications is close, the range of the average tensile strength is less than 10MPa, and all mechanical performance indicators meet the requirements of existing aircraft engines and other demand products. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a low-magnification corrosion picture of a TC4 alloy rod with a specification of Φ180 mm prepared in Example 1 of the present invention;

[0034] Figure 2 This is a 100-fold transverse corrosion picture of a TC4 alloy bar with a specification of Φ180 mm prepared in Example 1 of the present invention;

[0035] Figure 3 This is a longitudinal 100-fold corrosion picture of a TC4 alloy bar with a specification of Φ180 mm prepared in Example 1 of the present invention;

[0036] Figure 4 This is a low-magnification corrosion picture of a TC4 alloy rod with a specification of Φ230 mm prepared in Example 2 of the present invention;

[0037] Figure 5 This is a 100-fold transverse corrosion picture of a TC4 alloy bar with a specification of Φ230 mm prepared in Example 2 of the present invention;

[0038] Figure 6 This is a longitudinal 100-fold corrosion picture of a TC4 alloy bar with a specification of Φ230 mm prepared in Example 2 of the present invention;

[0039] Figure 7 This is a low-magnification corrosion picture of a TC4 alloy rod with a specification of Φ250 mm prepared in Example 3 of the present invention;

[0040] Figure 8 This is a 100-fold transverse corrosion picture of a TC4 alloy bar with a specification of Φ250 mm prepared in Example 3 of the present invention;

[0041] Fig. 9 This is a longitudinal 100-fold corrosion picture of the TC4 alloy rod with a specification of Φ250 mm prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used in the specification of the present invention are only used for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0043] In the present invention, when it comes to numerical intervals (i.e., numerical ranges), unless otherwise specified, the optional numerical distribution is considered continuous within the above numerical interval, and includes the two numerical endpoints (i.e., the minimum and maximum values) of the numerical range, and each numerical value between the two numerical endpoints. Unless otherwise specified, when the numerical interval only refers to the integers within the numerical interval, it includes the two endpoint integers of the numerical range, and each integer between the two endpoints. In this article, it is equivalent to directly listing each integer, such as t is an integer selected from 1-10, indicating that t is any integer selected from the integer group consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10. In addition, when multiple ranges are provided to describe features or characteristics, these ranges can be combined. In other words, unless otherwise specified, the ranges disclosed herein should be understood to include any and all sub-ranges included therein.

[0044] The temperature parameters in the present invention, if not specifically limited, are allowed to be either constant temperature treatment or to vary within a certain temperature range. It should be understood that the constant temperature treatment allows the temperature to fluctuate within the precision range controlled by the instrument. Fluctuations within the range of ±5°C, ±4°C, ±3°C, ±2°C, and ±1°C are allowed.

[0045] The present invention provides a free forging method for preparing AAA non-destructive testing grade large-size TC4 alloy bars, comprising:

[0046] Step 1: Forging the TC4 alloy ingot:

[0047] The TC4 alloy ingot is forged by reversing heating across the fires at the phase transition point, the remelting temperature is reduced by each fire, and the square billet ingot is forged by a combination of upsetting and reversing elongation. The ingot is cooled after forging to fully break up the as-cast coarse structure and fully recrystallize the forged billet at the high temperature stage to refine the grains.

[0048] Step 2: The billet ingot obtained in step 1 is subjected to forging below the phase transition point and cross-fire forging above the phase transition point:

[0049] The square billet ingot obtained in step 1 is heated and forged at the phase transition point, and the deformation process is upsetting and diagonal stretching; then it is returned to the furnace and heated to the phase transition point, and is deformed into an intermediate square billet by upsetting and diagonal stretching, and cooled after forging;

[0050] Step 3: Perform two-phase multi-fire forging on the intermediate billet obtained in step 2:

[0051] The intermediate square billet obtained in step 2 is subjected to multiple upsetting and diagonal stretching to obtain a square billet blank, which is then cooled after forging;

[0052] Step 4: U-shaped anvil rounding and forging:

[0053] The square billet obtained in step 3 is subjected to bar forming by U-shaped anvil rounding and precision forging, so that the edges and surfaces of the square billet are deformed into circular surfaces.

[0054] In some embodiments, the present invention provides a free forging method for preparing AAA non-destructive testing grade large-size TC4 alloy bars, comprising:

[0055] Step 1: Forging the TC4 alloy ingot: The forging stage is to forge the TC4 alloy ingot with reversing heating across the phase transition point, and the remelting temperature is reduced with each refire. The square billet ingot is forged by a combination of flat hammer upsetting and reversing drawing. After forging, it is cooled to fully break the coarse structure of the cast state, and the forging billet is fully recrystallized at the high temperature stage to refine the grains. The specific process is as follows: first firing: heating temperature 1100-1200°C, heating insulation coefficient 0.6-0.8, placing the TC4 alloy ingot cylinder diagonally perpendicular to the ground on a hammer anvil for upsetting, and then drawing and squareing it into a square billet with a deformation of 60%-80%; returning to the furnace for insulation temperature 1050-1100°C, heating insulation coefficient 0.1-0.3, air cooling and grinding after forging; second firing: heating temperature 1000-1100°C, heating insulation coefficient 0.6-0.8, upsetting and reversing drawing forging, the reversing drawing is forcing the square billet along the radial direction of the original square billet after upsetting; returning to the furnace for insulation temperature 1000-1050°C, heating insulation coefficient 0.1-0.3, deformation 70%-80%, air cooling and grinding after forging.

[0056] Step 2: The square billet ingot obtained in step 1 is forged at the phase change point and forged across the phase change point: the square billet ingot obtained in step 1 is heated and forged at the phase change point, and the deformation process is upsetting and diagonal drawing; then it is returned to the furnace and heated to the phase change point, and deformed into an intermediate square billet by upsetting and diagonal drawing, and cooled after forging. Specific process: The heating temperature of the forging at the phase change point is 15-40°C below the phase change point, and the heating insulation coefficient is 0.6-0.8; the heating temperature of the cross-fire forging at the phase change point is 30-50°C above the phase change point, and the insulation coefficient is 0.3-0.4. A total of two upsetting and two drawing forging deformations are performed, the deformation amount is 70%-80%, and water cooling is performed after forging, and the water cooling time is 15-60 minutes. Preferably, chamfering is performed after drawing to prevent adverse effects such as cracking and folding in subsequent forging deformation.

[0057] Step 3: Perform multi-fire forging in two-phase region on the intermediate billet obtained in step 2, i.e., perform multi-fire upsetting and diagonal stretching to obtain billet blank, and cool after forging. The specific process is: the heating temperature for each fire is 15-40°C below the phase change point, the heating insulation coefficient is 0.6-0.8, upsetting and diagonal stretching forging are performed, the deformation amount is 70%-80%, the billet height-to-diameter ratio after upsetting is 0.9-1.0, and the billet height-to-diameter ratio after diagonal stretching is 1.9-2.0; the remelting insulation coefficient is 0.1-0.3, and water cooling is performed after forging, and the water cooling time is 15-60 minutes. After multi-fire diagonal stretching, the billet is fully deformed to improve the degree of organizational homogeneity.

[0058] Step 4: U-shaped anvil rolling and forging, the square billet obtained in step 3 is formed into a bar by U-shaped anvil rolling and fine forging, so that the edges and faces of the square billet are deformed into circular surfaces: first, the upper and lower flat anvils are used for stretching and inverted octagonal deformation, the cross section is forged to an octagon, and the forging is returned to the furnace; after being taken out of the furnace, U-shaped anvil rolling and forging are used, and finally fine forging is performed. Specific process: Lengthening and inverted octagon: upper and lower flat anvils are used for forging, the heating temperature is 15-40°C below the phase change point, the heating insulation coefficient is 0.6-0.8, the deformation amount is 30%-40%, the cross section is forged to an octagon, and the heat preservation is returned to the furnace for rounding, and the insulation coefficient is 0.1-0.3; rounding: U-shaped anvil is used for forging, the heating temperature is 15-40°C below the phase change point, the heating insulation coefficient is 0.1-0.3, the deformation amount is 30%-40%, and then fine forging is performed. The precision forging process sets the forging times according to the finished product size, the heating temperature of each time is 15-40°C below the phase change point, the heating insulation coefficient is 0.7-0.8, the deformation amount is 20%-30%, and the precision forging process is uniformly stretched. After forging, the formed rod is obtained and air-cooled to room temperature.

[0059] To clarify the purpose, technical solutions and advantages of the present invention, the present invention will be described in detail below in conjunction with specific embodiments and drawings. The specific embodiments described herein are only used to explain the present invention, and the present invention is not limited thereto.

[0060] Example 1 Preparation of Φ180mm TC4 alloy rod

[0061] Step 1: Forging the TC4 alloy ingot: The forging stage is to forge the TC4 alloy ingot with reversing heating across the phase transition point, and the remelting temperature is reduced by each refire. The square billet is forged by a combination of flat hammer riveting upsetting and reversing drawing, and then cooled after forging. This stage can fully break the as-cast coarse structure and make the forging billet fully recrystallize at the high temperature stage to refine the grains. The specific process is as follows: first firing: heating temperature 1150°C, heating insulation coefficient 0.6, placing the TC4 alloy ingot cylinder diagonally perpendicular to the ground on a hammer anvil for upsetting, and then drawing and squareing it into a square billet; returning to the furnace for insulation temperature 1100°C, heating insulation coefficient 0.2, deformation 65%, air cooling and grinding after forging; second firing: heating temperature 1080°C, heating insulation coefficient 0.7, upsetting and reversing drawing forging, deformation 70%; returning to the furnace for insulation temperature 1050°C, heating insulation coefficient 0.2, air cooling and grinding after forging.

[0062] Step 2, the square billet ingot obtained in step 1 is forged below the phase transformation point and forged above the phase transformation point: Specific process: the square billet ingot obtained in step 1 is heated at 960°C, and the heating insulation coefficient is 0.7; the heating temperature for the cross-fire forging above the phase transformation point is 1020°C, and the insulation coefficient is 0.4. A total of two upsetting and two drawing forging deformations are performed, with a deformation amount of 70%, and water cooling is performed after forging, and the water cooling time is 30 minutes.

[0063] Step 3, the intermediate square billet obtained in step 2 is subjected to two-phase zone multi-fire forging: specific process: the heating temperature of each fire is 960°C, the heating insulation coefficient is 0.7, upsetting and reversing drawing forging are performed, the billet height-to-diameter ratio after upsetting is 1.0, the billet height-to-diameter ratio after diagonal drawing is 2.0, and the deformation is 70%; the remelting insulation coefficient is 0.2, and the forging is water-cooled for 30 minutes.

[0064] Step 4, U-shaped anvil rolling and forming forging: Specific process: pulling and inverting into octagon: using upper and lower flat anvils for forging, heating temperature 960℃, heating and insulation coefficient 0.7, deformation 40%, forging the cross section into an octagon, returning to the furnace for insulation and then rolling, insulation coefficient 0.2; rolling: using U-shaped anvil for forging, heating temperature 960℃, heating and insulation coefficient 0.2, deformation 30%. The finishing forging is one fire, heating temperature 960℃, heating and insulation coefficient 0.7, deformation 20%, uniform pulling during the finishing forging process, and the formed bars are obtained after forging, and air-cooled to room temperature. Figure 1 to Figure 3As shown, the Φ180mm rod prepared in this embodiment has uniform high and low magnification structures, high degree of spheroidization, and the high magnification structure of the rod is a processed structure in the α+β two-phase region, without a complete original β grain boundary, and no obvious difference in the horizontal and vertical high magnification structures. The primary α phase content is greater than 50%, and the average grain size is only 21.9μm. The mechanical properties of the TC4 alloy rod prepared in this embodiment (heat treatment system: 780℃ / 170min, air cooling) are shown in Table 1. In Table 1, L represents the gauge length of the tensile specimen, and D represents the specimen diameter.

[0065] Table 1 Mechanical properties of Φ180mm TC4 alloy bars

[0066]

[0067] From the test results in Table 1, it can be seen that the mechanical properties of the head and tail of the rod are similar, with average tensile strength and elongation at break of 956 MPa and 19.1% respectively. The prepared rod has excellent strength-plasticity matching and meets the AAA standard in AMSSTD-2154E in ultrasonic flaw detection.

[0068] Example 2 Preparation of Φ230mm TC4 alloy rod

[0069] Step 1, the TC4 alloy ingot is forged: the first fire: heating temperature 1150 ° C, heating and insulation coefficient 0.6, the TC4 alloy ingot cylinder is placed on the hammer anvil with the diagonal perpendicular to the ground for upsetting, and then drawn and squared into a square billet; the return furnace insulation temperature is 1100 ° C, the heating and insulation coefficient is 0.2, the deformation is 70%, and the air cooling and grinding are performed after forging; the second fire: heating temperature 1100 ° C, heating and insulation coefficient 0.6, upsetting and reversing drawing forging are performed, and the deformation is 70%; the return furnace insulation temperature is 1050 ° C, the heating and insulation coefficient is 0.2, and the air cooling and grinding are performed after forging.

[0070] Step 2, the square billet ingot obtained in step 1 is forged below the phase transformation point and forged above the phase transformation point: Specific process: the square billet ingot obtained in step 1 is heated at 960°C, and the heating insulation coefficient is 0.7; the heating temperature for the cross-fire forging above the phase transformation point is 1020°C, and the insulation coefficient is 0.4. A total of two upsetting and two drawing forging deformations are performed, with a deformation amount of 75%, and water cooling after forging, and the water cooling time is 30 minutes.

[0071] Step 3, the intermediate square billet obtained in step 2 is subjected to two-phase zone multi-fire forging: specific process: the heating temperature of each fire is 960°C, the heating insulation coefficient is 0.7, upsetting and reversing drawing forging are performed, the billet height-to-diameter ratio after upsetting is 1.0, the billet height-to-diameter ratio after diagonal drawing is 2.0, and the deformation is 75%; the remelting insulation coefficient is 0.2, and the forging is water-cooled for 30 minutes.

[0072] Step 4, U-shaped anvil rolling and forming forging: pulling and inverting into octagon: using upper and lower flat anvils for forging, heating temperature 960℃, heating and insulation coefficient 0.7, deformation 40%, forging the cross section into an octagon, returning to the furnace for insulation and then rolling, insulation coefficient 0.2; rolling: using U-shaped anvil for forging, heating temperature 960℃, heating and insulation coefficient 0.2, deformation 30%. The finishing forging is one fire, heating temperature 960℃, heating and insulation coefficient 0.7, deformation 20%, uniform pulling during the finishing forging process, and the formed bars are obtained after forging, and air-cooled to room temperature. Figures 4 to 6 As shown, the Φ230mm rod prepared in this embodiment has uniform high and low magnification structures, the high magnification structure of the rod is a processed structure in the α+β two-phase region, there is no complete original β grain boundary, there is no obvious difference in the horizontal and vertical high magnification structures, the primary α phase content is greater than 40%, and the average grain size is 26.1μm. The mechanical properties of the rod in this embodiment are shown in Table 2 (heat treatment system: 780℃ / 240min, air cooling).

[0073] Table 2 Mechanical properties of Φ230mm TC4 alloy bars

[0074]

[0075] In the sample specifications in Table 2, L represents the gauge length of the tensile sample, and D represents the sample diameter. From the test results in Table 2, it can be seen that the mechanical properties of the head and tail of the rod are similar, and the average tensile strength and elongation after fracture are 949MPa and 18.5% respectively. The prepared rod has excellent strength and plasticity matching, and meets the AAA standard in AMS STD-2154E in ultrasonic flaw detection.

[0076] Example 3 Preparation of Φ250mm TC4 alloy rod

[0077] Step 1, the TC4 alloy ingot is forged: the first fire: heating temperature 1150 ° C, heating and insulation coefficient 0.6, the TC4 alloy ingot cylinder is placed on the hammer anvil with the diagonal perpendicular to the ground for upsetting, and then drawn and squared into a square billet; the return furnace insulation temperature is 1100 ° C, the heating and insulation coefficient is 0.2, the deformation is 70%, and the air cooling and grinding are performed after forging; the second fire: heating temperature 1100 ° C, heating and insulation coefficient 0.6, upsetting and reversing drawing forging are performed, and the deformation is 70%; the return furnace insulation temperature is 1050 ° C, the heating and insulation coefficient is 0.2, and the air cooling and grinding are performed after forging.

[0078] Step 2, the square billet ingot obtained in step 1 is forged below the phase transformation point and forged above the phase transformation point: Specific process: the square billet ingot obtained in step 1 is heated at 960°C, and the heating insulation coefficient is 0.7; the heating temperature for the cross-fire forging above the phase transformation point is 1020°C, and the insulation coefficient is 0.4. A total of two upsetting and two drawing forging deformations are performed, with a deformation amount of 75%, and water cooling after forging, and the water cooling time is 30 minutes.

[0079] Step 3, the intermediate square billet obtained in step 2 is subjected to two-phase zone multi-fire forging: specific process: the heating temperature of each fire is 960°C, the heating insulation coefficient is 0.7, upsetting and reversing drawing forging are performed, the billet height-to-diameter ratio after upsetting is 1.0, the billet height-to-diameter ratio after diagonal drawing is 2.0, and the deformation is 75%; the remelting insulation coefficient is 0.2, and the forging is water-cooled for 30 minutes.

[0080] Step 4, U-shaped anvil rolling and forming forging: pulling and inverting into octagon: using upper and lower flat anvils for forging, heating temperature 960℃, heating and insulation coefficient 0.7, deformation 40%, forging the cross section into an octagon, returning to the furnace for insulation and then rolling, insulation coefficient 0.2; rolling: using U-shaped anvil for forging, heating temperature 960℃, heating and insulation coefficient 0.2, deformation 30%. The finishing forging is one fire, heating temperature 960℃, heating and insulation coefficient 0.7, deformation 20%, uniform pulling during the finishing forging process, and the formed bars are obtained after forging, and air-cooled to room temperature. Figure 7 to Figure 9 As shown, the high and low magnification structures of the Φ250mm rod prepared in this embodiment are uniform, the high magnification structure of the rod is a processed structure in the α+β two-phase region, there is no complete original β grain boundary, there is no obvious difference in the horizontal and vertical high magnification structures, the primary α phase content is greater than 40%, and the average grain size is 26.2μm. The mechanical properties of the rod in this embodiment 3 are shown in Table 3 (heat treatment system: 780℃ / 260min, air cooling).

[0081] Table 3 Mechanical properties of Φ250mm TC4 alloy bars

[0082]

[0083] In the sample specifications in Table 3, L represents the gauge length of the tensile sample, and D represents the sample diameter. From the test results in Table 3, it can be seen that the mechanical properties of the head and tail of the rod are similar, the average tensile strength and elongation after fracture are 937MPa and 18.0% respectively, and the prepared rod has excellent strength and plasticity matching, and meets the AAA standard in AMS STD-2154E in ultrasonic flaw detection.

[0084] The three specifications of TC4 rods prepared in Examples 1 to 3 have uniform microstructures, an average grain size of 21.9 μm to 26.2 μm, and test results of tensile mechanical properties have a certain margin compared with industry standards. Ultrasonic flaw detection has reached the AAA standard in AMSSTD-2154E.

[0085] It should be noted that the above-described embodiments are only preferred embodiments of the present invention. For those skilled in the art, without departing from the principles of the present invention, the present invention may be modified, improved and replaced with equivalents, and these modifications, improvements and equivalent replacements are also considered to fall within the scope of protection of the claims of the present invention.

Claims

1. A free forging method for preparing AAA non-destructive testing grade large-size TC4 alloy bars, characterized in that: include: Step 1: Forging the TC4 alloy ingot: The TC4 alloy ingot is forged by reversing heating across the fires at the phase transition point, the remelting temperature is reduced by each fire, and the square billet ingot is forged by a combination of upsetting and reversing elongation. The ingot is cooled after forging to fully break up the as-cast coarse structure and fully recrystallize the forged billet at the high temperature stage to refine the grains. Step 2: The billet ingot obtained in step 1 is subjected to forging below the phase transition point and cross-fire forging above the phase transition point: The square billet ingot obtained in step 1 is heated and forged at the phase transition point, and the deformation process is upsetting and diagonal stretching; then it is returned to the furnace and heated to the phase transition point, and is deformed into an intermediate square billet by upsetting and diagonal stretching, and cooled after forging; Step 3: Perform two-phase multi-fire forging on the intermediate billet obtained in step 2: The intermediate square billet obtained in step 2 is subjected to multiple upsetting and diagonal stretching to obtain a square billet blank, which is then cooled after forging; Step 4: U-shaped anvil rounding and forging: The square billet obtained in step 3 is subjected to bar forming by U-shaped anvil rounding and precision forging, so that the edges and surfaces of the square billet are deformed into circular surfaces.

2. The free forging method for preparing AAA non-destructive testing grade large-size TC4 alloy bars according to claim 1, characterized in that: The step 1 is two-fire forging, and the specific process is as follows: First fire: heating temperature 1100-1200°C, heating insulation coefficient 0.6-0.8, placing the TC4 alloy ingot cylinder on a hammer anvil with its diagonal perpendicular to the ground for upsetting, and then drawing and squared into a square billet after upsetting; re-melting insulation temperature 1050-1100°C, heating insulation coefficient 0.1-0.3, deformation 60%-80%; Second firing: heating temperature 1000-1100°C, heating insulation coefficient 0.6-0.8; returning to the furnace and holding temperature 1000-1050°C, heating insulation coefficient 0.1-0.3, deformation 70%-80%, upsetting and reversing drawing forging.

3. The free forging method for preparing AAA non-destructive testing grade large-size TC4 alloy bars according to claim 1, characterized in that: In the step 2, the heating temperature of the forging at the phase transformation point is 15-40°C below the phase transformation point, and the heating insulation coefficient is 0.6-0.8; the heating temperature of the cross-fire forging at the phase transformation point is 30-50°C above the phase transformation point, and the insulation coefficient is 0.3-0.

4. A total of two upsetting and two drawing forging deformations are performed, and the deformation amount is 70%-80%.

4. The free forging method for preparing AAA non-destructive testing grade large-size TC4 alloy bars according to claim 1, characterized in that: In step 2, chamfering is performed after the drawing to prevent cracking and folding during subsequent forging deformation.

5. The free forging method for preparing AAA non-destructive testing grade large-size TC4 alloy bars according to claim 1, characterized in that: In the step three, the billet height-to-diameter ratio after upsetting is 0.9-1.0, and the billet height-to-diameter ratio after diagonal stretching is 1.9-2.0, with a total of four fires. The specific process is: the heating temperature of each fire is 15-40°C below the phase change point, the heating insulation coefficient is 0.6-0.8; the re-melting insulation coefficient is 0.1-0.3, and the deformation amount is 70%-80%.

6. The free forging method for preparing AAA non-destructive testing grade large-size TC4 alloy bars according to claim 1, characterized in that: In the step 4, the square billet is stretched and then rounded, and the specific process is as follows: Lengthening and octagonal forging: Forging is carried out using upper and lower flat anvils, with a heating temperature of 15-40°C below the phase change point, a heating insulation coefficient of 0.6-0.8, a deformation of 30%-40%, and the cross section is forged into an octagon, and then returned to the furnace for rounding; Rounding: U-shaped anvil forging is adopted, the heating temperature is 15-40℃ below the phase change point, the heating insulation coefficient is 0.1-0.3, the deformation amount of the fire is 30%-40%, and then fine forging is carried out.

7. The free forging method for preparing AAA non-destructive testing grade large-size TC4 alloy bars according to claim 6, characterized in that: In the step 4, the precision forging process sets the forging times according to the finished product size, with a deformation of 20% to 30% in each time. The product is drawn at a uniform speed during the precision forging process, and air-cooled to room temperature after forging.

8. The free forging method for preparing AAA non-destructive testing grade large-size TC4 alloy bars according to claim 1, characterized in that: In step 1 and step 4, the cooling method is air cooling, and in step 2 and step 3, the cooling method is water cooling. The specific process is: In the steps 1 and 4, after forging, the forging is air-cooled to room temperature, and surface defects such as cracks are polished; In the step 2 and step 3, after forging, the forging is placed in a water cooling zone for 15 to 60 minutes.

9. A AAA non-destructive testing grade large-size TC4 alloy bar, characterized in that: The invention is prepared by the free forging method for preparing AAA non-destructive testing grade large-size TC4 alloy bars according to any one of claims 1 to 8.

10. The AAA non-destructive testing grade large-size TC4 alloy bar according to claim 9, characterized in that: The size of the AAA non-destructive testing grade large-size TC4 alloy bar is Φ160-Φ260 mm.

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