Preparation method of titanium alloy bar for aerospace fastener

Abstract

The invention belongs to the technical field of titanium alloy processing, and discloses a preparation method of a TC4 titanium alloy bar for an aerospace fastener. According to the preparation method, on the basis of smelting of an electron beam cold bed furnace and a vacuum consumable electric arc furnace, a full-process temperature control and rolling control production line such as cast ingot smelting, forging, polishing, primary rolling, centreless turning peeling, acid pickling and polishing and secondary rolling is adopted to roll large-piece-weight hot rolled coils with uniform structures and consistent performance; and a finished bar with the diameter phi of 6-21 mm is prepared through machining processes such as drawing, peeling, saw cutting and heat treatment. Compared with a finished product bar prepared by rolling a hot-rolled bar through a transverse rolling mill, the TC4 titanium alloy bar for the fastener prepared through the method is more uniform in structure performance and higher in microscopic structure grade, and better meets the heading requirements of a fastener factory and the service requirements of the finished product fastener.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium alloy processing, and in particular relates to a method for preparing a titanium alloy bar for aerospace fasteners. Background Art

[0002] Titanium alloys have the advantages of high specific strength, good corrosion resistance and non-magnetic properties. The extensive use of titanium structural parts on aircraft can achieve significant weight reduction and improve aircraft maneuverability and combat effectiveness. In addition to larger structural parts, there are tens of thousands of fasteners used in aircraft. With the increasing demand for composite materials and titanium alloys in future advanced aircraft, the use of titanium alloy fasteners will also increase year by year. In view of the large-scale use and complex working conditions in aerospace, titanium alloy fasteners must have high consistency and reliability to ensure that no failure occurs during use. This puts higher requirements on the purity, performance consistency and microstructure grade of titanium alloy fastener bars.

[0003] At present, domestic TC4 titanium alloy bars are mostly melted into ingots by three times of vacuum arc remelting (VAR). Due to the low melting temperature of this technology, high melting point, high and low density inclusions are not easy to remove, and there is a risk of poor purity of the ingot, which has a great impact on the subsequent fastener processing and work. At the same time, most domestic manufacturers use small forging billets for straight bars, and use multi-frame horizontal rolling mills for rolling. The main models are 430, 350, 280, 250, etc. There are many uncontrollable factors in the production process. There is a risk of performance differences in the same batch of billets, and due to the limitations of tooling, personnel operation, and billet temperature drop, billets need to be continuously sawed and polished when they are transferred. The closer to the finished product specifications, the smaller the unit weight of the billet, which ultimately leads to the risk of differences in organization and performance between batches. As the specifications of the finished bar structure increase, the microstructure becomes coarser and the microstructure grade becomes lower and lower. After being upset into bolts / nuts and subjected to heat treatment, the needle-like α structure increases, which seriously affects the service life of the tooling. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a method for preparing titanium alloy bars for aerospace fasteners. Based on the smelting in an electron beam cold hearth furnace (EB) plus a vacuum consumable arc furnace, the method adopts a full-process temperature-controlled rolling production line to roll a large single weight (200kg) hot-rolled coil with uniform structure and consistent performance, and prepares the finished bar (Φ6-21mm) through machining processes such as drawing, peeling, sawing, and heat treatment. Compared with the preparation of finished bars by rolling hot-rolled bars in a horizontal rolling mill, the processing cost and loss are reduced, and the performance and organizational consistency of the bars are improved.

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

[0006] In one aspect, the present invention provides a method for preparing a TC4 titanium alloy bar for aerospace fasteners, the preparation method comprising the following steps:

[0007] S1 Ingot Melting:

[0008] Ingot electrode alloy ingredients are prepared according to a predetermined ratio, wherein the ingot electrode alloy ingredients include sponge titanium, aluminum vanadium, aluminum particles, iron particles, TiO2, and titanium carbide; the ingot electrode alloy ingredients are subjected to electron beam cooling furnace melting and vacuum consumable arc furnace melting to obtain TC4 titanium alloy ingot blanks, and the TC4 titanium alloy ingot blanks are peeled and the risers and ingot bottoms are cut off to prepare TC4 titanium alloy ingots of Φ720-820 mm;

[0009] S2 Ingot Forging:

[0010] The TC4 titanium alloy ingot obtained in step S1 is heated to 1100°C-1170°C for heat preservation, blanked to □490-520×L, polished and sawed, and then the forging blank is heated to 920°C-980°C for heat preservation, and double-fire forged to □210-240×L, and the final forging temperature is ≥800°C;

[0011] S3 forging grinding:

[0012] Grinding the surface oxide scale and cracks of the forging blank obtained in step S2 to obtain a ground □210-240×L forging blank;

[0013] S4 first rolling:

[0014] The □210-240×L forging billet obtained in step S3 is heated to 40-100°C above the phase transformation point, and kept warm, and rolled by a two-roller reversible rolling mill for multiple passes to obtain □140×170×L-□160×190×L rolled square billets; the rolled square billets are heated to 40-100°C below the phase transformation point, and kept warm, and rolled by a two-roller reversible rolling mill for multiple passes to obtain Φ99-102×L rolled bars;

[0015] S5 centerless turning, peeling, pickling and grinding:

[0016] The rolled bar obtained in step S4 is peeled by a centerless lathe with a thickness of not less than 0.5 mm on one side, and then pickled and polished until there are no cracks on the surface;

[0017] S6 second rolling:

[0018] The rolled bar obtained in step S5 is heated to 40-100° C. below the phase transition point, and kept warm, and subjected to one-fire low-temperature rolling using a BD600 two-roll reversible rolling mill, an intermediate rolling mill, and a finishing rolling / kocks tandem rolling mill to obtain a hot-rolled coil with a diameter of ≤22 mm;

[0019] S7 machine plus:

[0020] The hot rolled coil obtained in step S6 is machined by hot drawing, peeling, straightening, grinding, and flattening and chamfering to obtain TC4 titanium alloy bars for aerospace fasteners.

[0021] Furthermore, the step S7 specifically includes the following steps:

[0022] S7.1 The hot rolled coil obtained in step S6 is hot drawn at 720-760° C. using a hot drawing machine, so that the peeling and grinding amount is 70-80 wires;

[0023] S7.2 Use a centerless peeling machine to peel the drawn material at least 0.3 mm, until there is no black skin or cracks on the surface, and cut it to a fixed length of 2.5 to 3 m;

[0024] S7.3 Place the sawn billet in a box-type annealing furnace for heat treatment at 740-800°C and keep it warm for 60-120 minutes, and use a straightening machine to straighten the billet to a straightness of ≤0.5mm / m;

[0025] S7.4 uses a centerless grinder to perform rough and fine grinding on the annealed and straightened bar blanks, and performs multiple grinding passes according to different specifications;

[0026] S7.5 flat head chamfering to remove end burrs and chamfer 2×C1mm;

[0027] S7.6 uses a polishing machine to remove the small amount of scratches and pulls on the surface of the bar that have not been ground off, and ensures that the size of the finished bar is within the tolerance range to obtain the finished TC4 titanium alloy bar.

[0028] Furthermore, in step S1, the weight percentages of the components in the ingot electrode alloy ingredients include: Al content of 6.1-6.5%, V content of 3.9-4.3%; Fe content of 0.10-0.25%; C content of 0.01-0.03%; N content of 0.001-0.010%; O content of 0.10-0.18%; and the balance is Ti.

[0029] Furthermore, in step S2, the deformation amount from blanking to □490~520×L is 47~53%; the deformation amount from second-fire forging to □210~240×L is 77~84%.

[0030] Further, in step S4, the □210~240×L forging billet obtained in step S3 is heated and kept warm for 160~200min, and is rolled by a two-roll reversible rolling mill for multiple passes with a deformation of 32~58% to obtain □140×170×L~□160×190×L rolled square billets; the rolled square billets are heated and kept warm for 120~150min, and are rolled by a two-roll reversible rolling mill for multiple passes with a deformation of 66~75% to obtain Φ99~102×L rolled bars.

[0031] Furthermore, in step S6, the heat preservation time is 60 to 90 minutes.

[0032] Furthermore, in step S6, the deformation amount of the first-fire low-temperature rolling is 95-99%.

[0033] Furthermore, in step S7.1, the pulling speed is 1 to 1.2 m / min.

[0034] On the other hand, the present invention also provides a TC4 titanium alloy bar for aerospace fasteners, which is prepared according to the above preparation method.

[0035] Furthermore, the diameter of the TC4 titanium alloy rod is 6 mm to 21 mm.

[0036] In the present invention, □ represents the side length of the cross-sectional square of the processed object, and L represents the length of the processed object.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. The present invention adjusts the chemical composition and smelting method of TC4 titanium alloy ingots and controls the forging, rolling, machining and heat treatment processes of the bars, so that the organizational properties of the TC4 titanium alloy bars reach the best and most stable state, making them suitable for fasteners.

[0039] 2. The present invention changes the TC4 ingot smelting method 3×VAR to the EB+VAR smelting method. In line with the first-class foreign technology, the EB furnace can remove high and low density inclusions in the ingot during the smelting process, and the chemical composition of the ingot can be more uniform after VAR smelting.

[0040] 3. The present invention adopts a 100MN fast forging machine to fully break the cast structure, providing a powerful environment for subsequent low-temperature forging and rolling; the whole process temperature-controlled and rolling production line is adopted to roll the bars / hot-rolled coils, which reduces the temperature rise in the process, improves the consistency of the material, further ensures the uniformity of the structure, and meets the standard requirements of titanium alloy bars for aerospace fasteners to the maximum extent.

[0041] 4. The present invention regulates the structure of billets of different specifications by adjusting the rolling temperature and the number of firings, and adopts a full-process temperature-controlled and rolling production line to produce large unit weight (200kg) Φ8-22mm hot-rolled coils with good consistency in rolling structure and performance.

[0042] 5. Compared with the finished bars made by rolling hot-rolled bars in a horizontal rolling mill, the finished bars with a specification of Φ6-21mm are made by large single weight (200kg) hot-rolled coils through drawing, peeling, sawing, heat treatment and other machining processes. The microstructure grade is higher and the organizational properties are more uniform, which is more in line with the requirements of upsetting in fastener factories and the service requirements of finished fasteners.

[0043] 6. The present invention limits various types of heating furnaces used in the production process to ensure the heating uniformity during the thermal processing at each stage, and stipulates the transfer time of the blank after heat treatment to ensure the effect of heat treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 (a)-(b) are transverse and longitudinal microstructure photographs of the Φ8.7 mm TC4 titanium alloy rod prepared in Example 1 of the present invention, respectively.

[0045] Figure 2 (a)-(b) are transverse and longitudinal microstructure photographs of the Φ14.5 mm TC4 titanium alloy rod prepared in Example 2 of the present invention, respectively.

[0046] Figure 3 (a)-(b) are transverse and longitudinal microstructure photographs of the Φ16.5 mm TC4 titanium alloy rod prepared in Example 3 of the present invention, respectively. DETAILED DESCRIPTION

[0047] 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.

[0048] 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.

[0049] 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.

[0050] The present invention provides a method for preparing a TC4 titanium alloy bar for aerospace fasteners, which is characterized by comprising the following steps:

[0051] A method for preparing TC4 titanium alloy bars for aerospace fasteners, characterized in that it comprises the following steps:

[0052] S1 Ingot Melting:

[0053] Ingot electrode alloy ingredients are prepared according to a predetermined ratio, wherein the ingot electrode alloy ingredients include sponge titanium, aluminum vanadium, aluminum particles, iron particles, TiO2, and titanium carbide; the ingot electrode alloy ingredients are subjected to electron beam cooling furnace melting and vacuum consumable arc furnace melting to obtain TC4 titanium alloy ingot blanks, and the TC4 titanium alloy ingot blanks are peeled and the risers and ingot bottoms are cut off to prepare TC4 titanium alloy ingots of Φ720-820 mm;

[0054] S2 Ingot Forging:

[0055] The TC4 titanium alloy ingot obtained in step S1 is heated to 1100°C-1170°C for heat preservation, blanked to □490-520×L, polished and sawed, and then the forging blank is heated to 920°C-980°C for heat preservation, and double-fire forged to □210-240×L, and the final forging temperature is ≥800°C;

[0056] S3 forging grinding:

[0057] Grinding the surface oxide scale and cracks of the forging blank obtained in step S2 to obtain a ground □210-240×L forging blank;

[0058] S4 first rolling:

[0059] The □210-240×L forging billet obtained in step S3 is heated to 40-100°C above the phase transformation point, and kept warm, and rolled by a two-roller reversible rolling mill for multiple passes to obtain □140×170×L-□160×190×L rolled square billets; the rolled square billets are heated to 40-100°C below the phase transformation point, and kept warm, and rolled by a two-roller reversible rolling mill for multiple passes to obtain Φ99-102×L rolled bars;

[0060] S5 centerless turning, peeling, pickling and grinding:

[0061] The rolled bar obtained in step S4 is peeled by a centerless lathe with a thickness of not less than 0.5 mm on one side, and then pickled and polished until there are no cracks on the surface;

[0062] S6 second rolling:

[0063] The rolled bar obtained in step S5 is heated to 40-100° C. below the phase transition point, and kept warm, and subjected to one-fire low-temperature rolling using a BD600 two-roll reversible rolling mill, an intermediate rolling mill, and a finishing rolling / kocks tandem rolling mill to obtain a hot-rolled coil with a diameter of ≤22 mm;

[0064] S7 machine plus:

[0065] The hot rolled coil obtained in step S6 is machined by hot drawing, peeling, straightening, grinding, and flattening and chamfering to obtain TC4 titanium alloy bars for aerospace fasteners.

[0066] In some embodiments, the present invention provides a method for preparing a titanium alloy bar for aerospace fasteners, comprising the following steps:

[0067] S1 Ingot Melting:

[0068] An ingot electrode alloy ingredient is prepared according to a predetermined proportion, wherein the ingot electrode alloy ingredient includes sponge titanium, aluminum vanadium, aluminum particles, iron particles, TiO2, and titanium carbide; the ingot electrode alloy ingredient is subjected to electron beam cooling hearth furnace melting and vacuum consumable arc furnace melting to obtain a TC4 titanium alloy ingot blank, the TC4 titanium alloy ingot blank is peeled and the riser and ingot bottom are cut off to prepare a TC4 titanium alloy ingot with a diameter of 720 to 820 mm; preferably, the ingot electrode alloy ingredient is subjected to one electron beam cooling hearth furnace melting and one vacuum consumable arc furnace melting. The weight percentages of the components in the ingot electrode alloy ingredients include: Al content of 6.1-6.5%, V content of 3.9-4.3%, Fe content of 0.10-0.25%, C content of 0.01-0.03%, N content of 0.001-0.010%, O content of 0.10-0.18% and the balance of Ti.

[0069] S2 Ingot Forging:

[0070] The TC4 titanium alloy ingot obtained in step S1 is placed in a box-type resistance heating furnace and heated to 1100°C-1170°C for insulation. A 100MN fast forging machine is used to forge the blank to □490-520×L, with a deformation of 47-53%, and the blank is polished until there is no crack on the surface and sawed off. The forging blank is then placed in a box-type resistance heating furnace and heated to 920°C-980°C for insulation. A 2500T fast forging machine is used for double-fire forging to □210-240×L, with a deformation of 77-84%, and the final forging temperature is ≥800°C;

[0071] S3 forging grinding:

[0072] Grinding the surface oxide scale and cracks of the forging blank obtained in step S2 to obtain a ground □210-240×L forging blank;

[0073] S4 first rolling:

[0074] The □210-240×L forging billet obtained in step S3 is placed in a box-type resistance heating furnace and heated to 40-100°C above the phase change point, and kept warm for 160-200 minutes, and rolled by a two-roller reversible rolling mill for multiple passes, with a deformation amount of 32-58%, to obtain □140×170×L-□160×190×L rolled square billets; the □150×180×L square billet is placed in a box-type resistance heating furnace and heated to 40-100°C below the phase change point, and kept warm for 120-150 minutes, and rolled by a two-roller reversible rolling mill for multiple passes, with a deformation amount of 66-75%, to obtain Φ99-102×L rolled bars;

[0075] S5 centerless turning, peeling, pickling and grinding:

[0076] The rolled bar obtained in step S4 is peeled by a centerless lathe with a thickness of not less than 0.5 mm on one side, and then pickled and polished until there are no cracks on the surface;

[0077] S6 second rolling:

[0078] The rolled bar obtained in step S5 is placed in a box-type resistance heating furnace and heated to 40-100° C. below the phase change point, and kept warm for 60-90 minutes, and then the bar is subjected to one-fire low-temperature rolling in sequence using a BD600 two-roll reversible rolling mill, an intermediate rolling mill, and a finishing rolling / kocks tandem rolling mill, with a cumulative deformation of 95-99%, to obtain a hot-rolled coil with a diameter of ≤22 mm;

[0079] S7 machine plus:

[0080] The hot rolled coil obtained in step S6 is machined by hot drawing, peeling, straightening, grinding, and flattening and chamfering to obtain a TC titanium alloy finished bar.

[0081] Preferably, step S7 specifically includes the following steps:

[0082] S7.1 The hot rolled coil obtained in step S6 is hot drawn at 720-760° C. using a hot drawing machine, ensuring that the subsequent peeling and grinding amount is 70-80 wires, preferably, the drawing speed is 1-1.2 m / min;

[0083] S7.2 Use a centerless lathe to peel the drawn material to at least 0.3 mm, until there is no black skin or cracks on the surface, and then cut to size;

[0084] S7.3 Place the sawn billet in a box-type annealing furnace for heat treatment at 740-800°C and keep the temperature for 60-120 minutes, and use a straightening machine to straighten the billet to make the straightness ≤0.5mm / m. Preferably, the time interval between straightening the first bar and the last bar is no more than 45 minutes;

[0085] S7.4 uses a centerless grinder to perform rough and fine grinding on the annealed and straightened bar blanks, and performs multiple grinding passes according to different specifications;

[0086] S7.5 flat head chamfering to remove end face burrs and chamfer 2×C1mm.

[0087] S7.6 Use a polishing machine to remove a small amount of scratches and pulls on the surface of the bar that have not been ground off, to ensure that the size of the finished bar is within the tolerance range, and obtain the finished TC titanium alloy bar. The specific machining process flow in this step is: the finished machined bar process is: bar blank → hot drawing → centerless turning peeling → sawing → annealing and straightening → centerless grinding → flat head, chamfering → polishing → ultrasonic flaw detection 100% → quality inspection (Φ6mm~21mm).

[0088] 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.

[0089] Example 1

[0090] This embodiment provides a method for preparing a titanium alloy bar for aerospace fasteners, comprising the following steps:

[0091] S1 Ingot Melting:

[0092] An ingot electrode alloy ingredient is prepared according to a predetermined ratio, wherein the ingot electrode alloy ingredient includes sponge titanium, aluminum vanadium, aluminum particles, iron particles, TiO2, and titanium carbide; the ingot electrode alloy ingredient is subjected to one electron beam cooling hearth furnace smelting and one vacuum consumable arc furnace smelting to obtain a TC4 titanium alloy ingot blank, and the TC4 titanium alloy ingot blank is peeled and the riser and the ingot bottom are cut off to prepare a TC4 titanium alloy ingot with a diameter of 800 mm; the percentage of the content of each component of the TC4 titanium alloy ingot blank in this embodiment is shown in Table 1 below.

[0093] S2 Ingot Forging:

[0094] The TC4 titanium alloy ingot obtained in step S1 is placed in a box-type resistance heating furnace and heated to 1100°C for insulation. A 100MN fast forging machine is used to forge the blank to □500×L with a deformation of 50.2%. The blank is polished until there are no cracks on the surface and sawed. The forging blank is then placed in a box-type resistance heating furnace and heated to 950°C for insulation. A 2500T fast forging machine is used for secondary forging to □220×L with a deformation of 80.6%. The final forging temperature is ≥800°C.

[0095] S3 forging grinding:

[0096] Grinding the surface oxide scale and cracks of the forging blank obtained in step S2 to obtain a polished □220×L forging blank;

[0097] S4 first rolling:

[0098] The □220×L forging billet obtained in step S3 is placed in a box-type heating resistance furnace and heated to 1040°C, and kept warm for 180 minutes, and rolled by a two-roller reversible rolling mill for multiple passes, with a deformation amount of 55.8%, to obtain a □150×180×L rolled square billet; the □150×180×L square billet is placed in a box-type heating resistance furnace and heated to 940°C, and kept warm for 120 minutes, and rolled by a two-roller reversible rolling mill for multiple passes, with a deformation amount of 69.7%, to obtain a Φ102×L rolled bar;

[0099] S5 centerless turning, peeling, pickling and grinding:

[0100] The rolled bar obtained in step S4 is peeled by a centerless lathe with a thickness of not less than 0.5 mm on one side, and then pickled and polished until there are no cracks on the surface;

[0101] S6 second rolling:

[0102] The Φ100×L rolled bar obtained in step S5 is placed in a box-type resistance heating furnace and heated to 920° C., and kept warm for 60 minutes, and then subjected to one-fire low-temperature rolling using a BD600 two-roll reversible rolling mill, an intermediate rolling mill, and a finishing rolling / kocks tandem rolling mill in sequence, with a cumulative deformation of 98.7%, to obtain a hot-rolled coil with a diameter of 11.2 mm;

[0103] S7 machine plus:

[0104] S7.1 The hot rolled coil obtained in step S6 is hot drawn at 740° C. using a hot drawing machine at a drawing speed of 1 to 1.2 m / min until the coil is drawn to Φ9.4 mm;

[0105] S7.2 Use a centerless peeling machine to peel the drawn material to 9.1mm, with no black skin or cracks on the surface, and saw it at intervals of 3000mm;

[0106] S7.3 Place the sawn blank in a box-type annealing furnace for heat treatment at 750°C and keep the temperature for 60 minutes, and use a straightening machine to straighten the bar blank so that the straightness is ≤0.5mm / m. Preferably, the time interval between straightening the first bar and the last bar is no more than 45 minutes;

[0107] S7.4 uses a centerless grinder to rough and fine grind the annealed and straightened bar blanks, and performs multiple passes of grinding to Φ8.7mm according to different specifications;

[0108] S7.5 flat head chamfering to remove end burrs and chamfer 2×C1mm;

[0109] S7.6 uses a polishing machine to remove the small amount of scratches and traces on the surface of the bar that have not been ground off, to ensure the dimensional tolerance of the finished bar, and obtain a Φ8.7mm TC4 titanium alloy finished bar.

[0110] The box-type resistance heating furnace in steps S2, S4 and S6 of this embodiment meets the requirements of Class III furnace in HB5425 "Method for Determining the Effective Heating Zone of Heat Treatment Furnaces for Aviation Parts", and the box-type annealing furnace used in the heat treatment in step S7 meets the requirements of Class 2 furnace in AMS2750E "High Temperature Determination Method".

[0111] Example 2

[0112] This embodiment provides a method for preparing a titanium alloy bar for aerospace fasteners, comprising the following steps:

[0113] S1 Ingot Melting:

[0114] The ingot electrode alloy ingredients are prepared according to a predetermined ratio, and the ingot electrode alloy ingredients include sponge titanium, aluminum vanadium, aluminum particles, iron particles, TiO2, and titanium carbide; the ingot electrode alloy ingredients are subjected to one electron beam cold hearth furnace smelting and one vacuum consumable arc furnace smelting to obtain a TC4 titanium alloy ingot blank, and the TC4 titanium alloy ingot blank is peeled and the riser and ingot bottom are cut off to prepare a TC4 titanium alloy ingot with a diameter of 800 mm. The percentages of the components of the TC4 titanium alloy ingot blank in this embodiment are shown in Table 1 below.

[0115] S2 Ingot Forging:

[0116] The TC4 titanium alloy ingot obtained in step S1 is placed in a box-type resistance heating furnace and heated to 1100°C for insulation. A 100MN fast forging machine is used to forge the blank to □500×L with a deformation of 50.2%. The blank is polished until there are no cracks on the surface and sawed. The forging blank is then placed in a box-type resistance heating furnace and heated to 950°C for insulation. A 2500T fast forging machine is used for secondary forging to □220×L with a deformation of 80.6%. The final forging temperature is ≥800°C.

[0117] S3 forging grinding:

[0118] Grinding the surface oxide scale and cracks of the forging blank obtained in step S2 to obtain a polished □220×L forging blank;

[0119] S4 first rolling:

[0120] The □220×L forging billet obtained in step S3 is placed in a box-type heating resistance furnace and heated to 1040°C, and kept warm for 180 minutes, and rolled by a two-roller reversible rolling mill for multiple passes, with a deformation amount of 55.8%, to obtain a □150×180×L rolled square billet; the □150×180×L square billet is placed in a box-type heating resistance furnace and heated to 940°C, and kept warm for 120 minutes, and rolled by a two-roller reversible rolling mill for multiple passes, with a deformation amount of 69.7%, to obtain a Φ102×L rolled bar;

[0121] S5 centerless turning, peeling, pickling and grinding:

[0122] The rolled bar obtained in step S4 is peeled by a centerless lathe with a thickness of not less than 0.5 mm on one side, and then pickled and polished until there are no cracks on the surface;

[0123] S6 second rolling:

[0124] The Φ100×L rolled bar obtained in step S5 is placed in a box-type resistance heating furnace and heated to 920° C., and kept warm for 60 minutes, and then subjected to one-fire low-temperature rolling using a BD600 two-roll reversible rolling mill, an intermediate rolling mill, and a finishing rolling / kocks tandem rolling mill in sequence, with a cumulative deformation of 97.7%, to obtain a hot-rolled coil with a diameter of 15.2 mm;

[0125] S7 machine plus:

[0126] S7.1 Use a centerless peeling machine to peel the drawn material to 14.9mm, with no black skin or cracks on the surface, and saw it at intervals of 3000mm;

[0127] S7.2 Place the sawn billet in a box-type annealing furnace for heat treatment at 750°C and keep the temperature for 60 minutes, and use a straightening machine to straighten the billet to make the straightness ≤ 0.5 mm / m. Preferably, the time interval between straightening the first bar and the last bar is no more than 45 minutes;

[0128] S7.3 The annealed and straightened bar blanks are rough ground and fine ground using a centerless grinder, and multiple passes are performed to Φ14.5mm according to different specifications;

[0129] S7.4 flat head chamfering to remove end burrs and chamfer 2×C1mm;

[0130] S7.5 uses a polishing machine to remove the small amount of scratches and traces on the surface of the bar that have not been ground off, to ensure the dimensional tolerance of the finished bar, and obtain a TC4 titanium alloy finished bar of Φ14.5mm.

[0131] The box-type resistance heating furnace in steps S2, S4 and S6 of this embodiment meets the requirements of Class III furnace in HB5425 "Method for Determining the Effective Heating Zone of Heat Treatment Furnaces for Aviation Parts", and the box-type annealing furnace used in the heat treatment in step S7 meets the requirements of Class 2 furnace in AMS2750E "High Temperature Determination Method".

[0132] Example 3

[0133] This embodiment provides a method for preparing a titanium alloy bar for aerospace fasteners, comprising the following steps:

[0134] S1 Ingot Melting:

[0135] The ingot electrode alloy ingredients are prepared according to a predetermined ratio, and the ingot electrode alloy ingredients include sponge titanium, aluminum vanadium, aluminum particles, iron particles, TiO2, and titanium carbide; the ingot electrode alloy ingredients are subjected to one electron beam cold hearth furnace smelting and one vacuum consumable arc furnace smelting to obtain a TC4 titanium alloy ingot blank, and the TC4 titanium alloy ingot blank is peeled and the riser and ingot bottom are cut off to prepare a TC4 titanium alloy ingot with a diameter of 800 mm. The percentage of each component content in this embodiment is shown in Table 1 below.

[0136] S2 Ingot Forging:

[0137] The TC4 titanium alloy ingot obtained in step S1 is placed in a box-type resistance heating furnace and heated to 1100°C for insulation. A 100MN fast forging machine is used to forge the blank to □500×L with a deformation of 50.2%. The blank is polished until there are no cracks on the surface and sawed. The forging blank is then placed in a box-type resistance heating furnace and heated to 950°C for insulation. A 2500T fast forging machine is used for secondary forging to □220×L with a deformation of 80.6%. The final forging temperature is ≥800°C.

[0138] S3 forging grinding:

[0139] Grinding the surface oxide scale and cracks of the forging blank obtained in step S2 to obtain a polished □220×L forging blank;

[0140] S4 first rolling:

[0141] The □220×L forging billet obtained in step S3 is placed in a box-type heating resistance furnace and heated to 1040°C, and kept warm for 180 minutes, and rolled by a two-roller reversible rolling mill for multiple passes to obtain a □150×180×L rolled square billet with a deformation of 55.8%; the □150×180×L square billet is placed in a box-type heating resistance furnace and heated to 940°C, and kept warm for 120 minutes, and rolled by a two-roller reversible rolling mill for multiple passes to obtain a Φ102×L rolled bar with a deformation of 69.7%;

[0142] S5 centerless turning, peeling, pickling and grinding:

[0143] The rolled bar obtained in step S4 is peeled by a centerless lathe with a thickness of not less than 0.5 mm on one side, and then pickled and polished until there are no cracks on the surface;

[0144] S6 second rolling:

[0145] The Φ100×L rolled bar obtained in step S5 is placed in a box-type resistance heating furnace and heated to 920° C., and kept warm for 60 minutes, and then subjected to one-fire low-temperature rolling in sequence using a BD600 two-roll reversible rolling mill, an intermediate rolling mill, and a finishing rolling / kocks tandem rolling mill, with a cumulative deformation of 97.0%, to obtain a hot-rolled coil with a diameter of 17.2 mm;

[0146] S7 machine plus:

[0147] S7.1 Use a centerless peeling machine to peel the drawn material to 16.9mm, with no black skin or cracks on the surface, and saw it at intervals of 3000mm;

[0148] S7.2 Place the sawn billet in a box-type annealing furnace for heat treatment at 750°C and keep the temperature for 60 minutes, and use a straightening machine to straighten the billet to make the straightness ≤ 0.5 mm / m. Preferably, the time interval between straightening the first bar and the last bar is no more than 45 minutes;

[0149] S7.3 Use a centerless grinder to rough and fine grind the annealed and straightened bar blanks, and grind them to Φ16.5mm in multiple passes according to different specifications;

[0150] S7.4 flat head chamfering to remove end burrs and chamfer 2×C1mm;

[0151] S7.5 uses a polishing machine to remove the small amount of scratches and traces on the surface of the bar that have not been ground off, to ensure the dimensional tolerance of the finished bar, and obtain a TC4 titanium alloy finished bar of Φ16.5mm.

[0152] The box-type resistance heating furnace in steps S2, S4 and S6 of this embodiment meets the requirements of Class III furnace in HB5425 "Method for Determining the Effective Heating Zone of Heat Treatment Furnaces for Aviation Parts", and the box-type annealing furnace used in the heat treatment in step S7 meets the requirements of Class 2 furnace in AMS2750E "High Temperature Determination Method".

[0153] Table 1 shows the component contents of the TC4 titanium alloy ingots in Examples 1 to 3.

[0154] Table 1 Ingot component content (wt%)

[0155] Location Al V Fe C N O superior 6.17 4.08 0.10 0.019 0.004 0.144 middle 6.16 4.09 0.13 0.02 0.004 0.145 Down 6.15 4.01 0.12 0.02 0.004 0.141

[0156] Figures 1 to 3 The transverse and longitudinal microstructure schematic diagrams of Φ8.7mm, Φ14.5mm and Φ16.5mm TC4 titanium alloy bars prepared in Examples 1 to 3 of the present invention are shown respectively. As can be seen from the figure, the microstructure of the finished TC4 titanium alloy bar is composed of equiaxed α+intergranular β. Compared with other straight bar preparation processes, the microstructure of the present invention has smaller grains, which is more in line with the requirements of A1~A3 and AA1~AA3 in the ETTC2 standard for TC4 titanium alloy bars for aerospace fasteners, and has a higher microstructure grade. After being upset into bolts / nuts and subjected to heat treatment, it is beneficial to improve the service life of the tooling.

[0157] Table 2 below shows the properties of the TC4 titanium alloy bars prepared in Examples 1 to 3 of the present invention.

[0158]

[0159] In Table 2, M represents the annealed state. As can be seen from Table 1, the mechanical properties of the TC4 titanium alloy bars prepared in Examples 1 to 3 of the present invention can meet customer requirements, and the preparation of straight bars from coiled wire has better performance stability consistency between batches, which is conducive to the upsetting of TC4 titanium alloy bars.

[0160] 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 method for preparing TC4 titanium alloy bars for aerospace fasteners, characterized in that: The steps include: S1 Ingot Melting: Ingot electrode alloy ingredients are prepared according to a predetermined ratio, wherein the ingot electrode alloy ingredients include sponge titanium, aluminum vanadium, aluminum particles, iron particles, TiO2, and titanium carbide; the ingot electrode alloy ingredients are subjected to electron beam cooling furnace melting and vacuum consumable arc furnace melting to obtain TC4 titanium alloy ingot blanks, and the TC4 titanium alloy ingot blanks are peeled and the risers and ingot bottoms are cut off to prepare TC4 titanium alloy ingots of Φ720-820 mm; S2 Ingot Forging: The TC4 titanium alloy ingot obtained in step S1 is heated to 1100°C-1170°C for heat preservation, blanked to □490-520×L, polished and sawed, and then the forging blank is heated to 920°C-980°C for heat preservation, and double-fire forged to □210-240×L, and the final forging temperature is ≥800°C; S3 forging blank grinding: Grinding the surface oxide scale and cracks of the forging blank obtained in step S2 to obtain a ground □210-240×L forging blank; S4 first rolling: The □210-240×L forging billet obtained in step S3 is heated to 40-100°C above the phase transformation point, and kept warm, and rolled by a two-roller reversible rolling mill for multiple passes to obtain □140×170×L-□160×190×L rolled square billets; the rolled square billets are heated to 40-100°C below the phase transformation point, and kept warm, and rolled by a two-roller reversible rolling mill for multiple passes to obtain Φ99-102×L rolled bars; S5 centerless turning, peeling, pickling and grinding: The rolled bar obtained in step S4 is peeled by a centerless lathe with a thickness of not less than 0.5 mm on one side, and then pickled and polished until there are no cracks on the surface; S6 second rolling: The rolled bar obtained in step S5 is heated to 40-100° C. below the phase transition point, and kept warm, and subjected to one-fire low-temperature rolling using a BD600 two-roll reversible rolling mill, an intermediate rolling mill, and a finishing rolling / kocks tandem rolling mill to obtain a hot-rolled coil with a diameter of ≤22 mm; S7 machine plus: The hot rolled coil obtained in step S6 is machined by hot drawing, peeling, straightening, grinding, and flattening and chamfering to obtain TC4 titanium alloy bars for aerospace fasteners.

2. The method for preparing TC4 titanium alloy bars for aerospace fasteners according to claim 1, characterized in that: The step S7 specifically includes the following steps: S7.1 The hot rolled coil obtained in step S6 is hot drawn at 720-760° C. using a hot drawing machine, so that the peeling and grinding amount is 70-80 wires; S7.2 Use a centerless peeling machine to peel the drawn material at least 0.3 mm, until there is no black skin or cracks on the surface, and cut it to a fixed length of 2.5 to 3 m; S7.3 Place the sawn billet in a box-type annealing furnace for heat treatment at 740-800°C and keep it warm for 60-120 minutes, and use a straightening machine to straighten the billet to a straightness of ≤0.5mm / m; S7.4 uses a centerless grinder to perform rough and fine grinding on the annealed and straightened bar blanks, and performs multiple grinding passes according to different specifications; S7.5 flat head chamfering to remove end burrs and chamfer 2×C1mm; S7.6 uses a polishing machine to remove the small amount of scratches and pulls on the surface of the bar that have not been ground off, and ensures that the size of the finished bar is within the tolerance range to obtain the finished TC4 titanium alloy bar.

3. The method for preparing TC4 titanium alloy bars for aerospace fasteners according to claim 1, characterized in that: In step S1, the weight percentages of the components in the ingot electrode alloy ingredients include: Al content of 6.1-6.5%, V content of 3.9-4.3%; Fe content of 0.10-0.25%; C content of 0.01-0.03%; N content of 0.001-0.010%; O content of 0.10-0.18%; and the balance is Ti.

4. The method for preparing TC4 titanium alloy bars for aerospace fasteners according to claim 1, characterized in that: In step S2, the deformation amount of blanking to □490~520×L is 47~53%; the deformation amount of second-fire forging to □210~240×L is 77~84%.

5. The method for preparing TC4 titanium alloy bars for aerospace fasteners according to claim 1, characterized in that: In step S4, the □210~240×L forging billet obtained in step S3 is heated and kept warm for 160~200min, and is rolled by a two-roll reversible rolling mill for multiple passes with a deformation of 32~58%, thereby obtaining □140×170×L~□160×190×L rolled square billets; the rolled square billets are heated and kept warm for 120~150min, and are rolled by a two-roll reversible rolling mill for multiple passes with a deformation of 66~75%, thereby obtaining Φ99~102×L rolled bars.

6. The method for preparing TC4 titanium alloy rod for aerospace fasteners according to claim 1, characterized in that: In step S6, the heat preservation time is 60 to 90 minutes.

7. The method for preparing TC4 titanium alloy rods for aerospace fasteners according to claim 1, characterized in that: In step S6, the deformation amount of the first heat low temperature rolling is 95-99%.

8. The method for preparing TC4 titanium alloy rods for aerospace fasteners according to claim 2, characterized in that: In step S7.1, the pulling speed is 1 to 1.2 m / min.

9. A TC4 titanium alloy bar for aerospace fasteners, characterized in that: The method is prepared according to any one of claims 1 to 8.

10. The TC4 titanium alloy bar according to claim 9, characterized in that: The diameter of the TC4 titanium alloy rod is 6 mm to 21 mm.

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