Preparation method of TC4 titanium alloy rod for fastener

Abstract

The application discloses a preparation method of a TC4 titanium alloy rod for fasteners, and comprises the following steps: firstly, TC4 titanium alloy ingots are obtained by welding and smelting after pressing electrodes on raw materials; secondly, precision forging rod blanks are obtained by forging after heating and heat preservation of the TC4 titanium alloy ingots; thirdly, precision forging rods are obtained by precision forging after heating and heat preservation of the precision forging rod blanks; fourthly, the precision forging rods are debarked, ground and cut to obtain rolling rod blanks; fifthly, the rolling rod blanks are water quenched after beta heat treatment; sixthly, rolling rods are obtained by rolling after heating and heat preservation; and seventhly, the rolling rods are solid solution and aging heat treated to obtain the TC4 titanium alloy rod for fasteners. By controlling the design value of the chemical composition of the TC4 titanium alloy ingots, combining the premixing of titanium sponge and titanium dioxide, and controlling the forging, precision forging and rolling processes and the beta heat treatment and solid solution and aging, the strength performance of the TC4 titanium alloy rod reaches the maximum and the most stable state, and is suitable for fasteners.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy material processing technology, specifically relating to a method for preparing TC4 titanium alloy bars for fasteners. Background Technology

[0002] Fasteners, as essential general-purpose components, play a crucial role in industry and are often referred to as the "rice of industry." In the aerospace field, aircraft connections are still primarily mechanical, relying heavily on various fasteners for assembly and connection. Similarly, in the space industry, connections between aircraft components also depend on fasteners. With the development of lightweight equipment, titanium alloys, due to their advantages such as low density, high specific strength, high melting point, low coefficient of thermal expansion, and low modulus of elasticity, are increasingly widely used in aerospace fasteners. The history of titanium alloy fastener applications abroad can be traced back to the 1950s when the United States pioneered the use of TC4 titanium alloy bolts in the B-52 bomber, achieving significant weight reduction. This marked the beginning of titanium alloy fastener applications in the aerospace field. Currently, in developed countries such as the United States and France, over 95% of titanium alloy fasteners are manufactured using the internationally recognized TC4 titanium alloy material. In some advanced aircraft models, titanium alloy fasteners have completely replaced 30CrMnSiA steel, significantly reducing aircraft weight.

[0003] TC4 titanium alloy is a medium-strength two-phase titanium alloy and is the most researched and applied titanium alloy material. Most titanium alloy materials used in fasteners are TC4 titanium alloy. However, when manufacturing fasteners with TC4 titanium alloy, the strength still cannot meet or cannot stably and uniformly meet the requirements of the GJB2219A-2015 standard "Specification for Titanium and Titanium Alloy Rods and Wires for Fasteners", especially when the specification is ≥19mm, traditional processes are difficult to meet the standard requirements. Specific mechanical property requirements are shown in Table 1.

[0004] Table 1 shows the mechanical property requirements for TC4 in GJB2219A-2015.

[0005]

[0006] Summary of the Invention

[0007] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a method for preparing TC4 titanium alloy bars for fasteners. This method, through controlling the designed chemical composition of the TC4 titanium alloy ingot, combining the premixing of sponge titanium and titanium dioxide, and controlling the forging, precision forging, and rolling processes, as well as the β-heat treatment and solution aging heat treatment, enables the TC4 titanium alloy bars to achieve maximum and most stable strength properties, making them suitable for fasteners.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing TC4 titanium alloy rods for fasteners, characterized in that the method includes the following steps:

[0009] Step 1: Press the sponge titanium, aluminum vanadium, aluminum briquettes, titanium dioxide, and ferrotitanium raw materials into electrodes, then weld them and perform three smelting processes. After peeling, cutting the risers and the bottom of the ingot, a TC4 titanium alloy ingot with a diameter of 620mm or 690mm is prepared.

[0010] Step 2: Place the TC4 titanium alloy ingot obtained in Step 1 in a box-type resistance heating furnace and heat it to 1150℃~1170℃ and hold it there. Then, use a 2500-ton high-speed forging machine for forging. The forging process is as follows: square to □400mm → multiple drawing and chamfering to □250mm → grinding the surface oxide scale and cracks → blanking. Then, place the blanked □250mm billet in a box-type resistance heating furnace and heat it to 950℃~960℃ and hold it there. Continue to perform the following processes: □250mm → drawing and chamfering to ○250mm → drawing with a V-shaped anvil to ○140mm~○150mm → grinding the surface oxide scale and cracks → blanking to obtain a precision forged bar billet.

[0011] Step 3: Place the precision forged billet obtained in Step 2 into a box furnace and heat it to 930℃~950℃ and hold it at that temperature. Then, use an SX-16 precision forging machine to perform 1~2 forging cycles. Finally, straighten it with residual heat to obtain a precision forged bar with a diameter of φ50mm±1mm~φ65mm±1mm.

[0012] Step 4: Peel off the surface of the precision forged bar obtained in Step 3 by at least 0.5 mm on one side, then grind and cut the bar to obtain the rolled bar billet.

[0013] Step 5: Perform β heat treatment on the rolled bar billet obtained in Step 4. The specific process is as follows: place the rolled bar billet in a box furnace and heat it to 1020℃ and hold it for 50min to 70min, followed by water quenching.

[0014] Step 6: Place the rolled bar billet after β heat treatment in Step 5 into a box furnace and heat it to 900℃~920℃ and hold it for 60min~80min. Then, use a 250 tandem rolling mill to roll it 6~10 times, and control the linear speed at 1.4m / s~1.8m / s during the rolling process to obtain rolled bars with a diameter of φ14mm~φ28mm.

[0015] Step 7: The rolled bar obtained in Step 6 is subjected to solution aging heat treatment. The solution aging heat treatment process is as follows: first, hold at 950℃~960℃ for 60min~100min, water cool, then hold at 530℃ for 360min, air cool, and after surface machining and polishing, TC4 titanium alloy bar for fasteners is obtained.

[0016] This invention employs a series of processes including pressing electrode block melting, hot forging, hot precision forging, β heat treatment, multi-pass hot rolling, and solution aging heat treatment to prepare TC4 titanium alloy bars for fasteners. By controlling the design values ​​of the chemical composition of the TC4 titanium alloy ingot, a foundation is laid for the product to meet standard requirements. The premixing of sponge titanium and titanium dioxide ensures uniform melting of oxygen. The control of the forging, precision forging, and rolling processes ensures uniform deformation of the material. The control of β heat treatment and solution aging heat treatment ensures that the bar undergoes optimized heat treatment, resulting in the TC4 titanium alloy bar achieving maximum and most stable strength performance.

[0017] The above-mentioned method for preparing TC4 titanium alloy rods for fasteners is characterized in that the titanium dioxide described in step one is dried at 120°C for 120 min to 180 min, and then mixed with sponge titanium at a mass ratio of 1:20 in a V-type mixer. The mass of the mixed raw material added to each electrode is calculated according to the oxygen content requirements designed in the TC4 titanium alloy ingot.

[0018] The above-mentioned method for preparing TC4 titanium alloy rods for fasteners is characterized in that the chemical composition design value of the TC4 titanium alloy ingot in step one is Ti-6.65~6.75Al-4.35~4.5V-0.24~0.26Fe-0.17~0.20O.

[0019] The method for preparing TC4 titanium alloy bars for fasteners described above is characterized in that the process of drawing and chamfering from □250mm to ○250mm in step two should be repeated with the "face to edge, edge to face" operation until the desired size is achieved. This forging process alters the deformation zone and the easily deformable zone, contributing to the uniformity of deformation in all parts of the billet. It avoids the large differences in microstructure caused by the unchanged easily deformable and difficult-to-deformable zones and inconsistent deformation degrees in different areas when using traditional square billet direct drawing.

[0020] The above-mentioned method for preparing TC4 titanium alloy bars for fasteners is characterized in that the precision forging process in step three is carried out using a pull-forging method. The precision forging machine has two chucks, each clamping one end of the bar. There are two forging methods: push-forging and pull-forging. Push-forging involves one chuck pushing forward while the other chuck follows; pull-forging involves one chuck pulling backward while the other chuck follows. This invention, by employing a pull-forging method for precision forging, helps to achieve uniform flow lines in the forged bar's microstructure and is also beneficial for controlling the bar's dimensions and straightness.

[0021] The above-mentioned method for preparing TC4 titanium alloy bars for fasteners is characterized in that the transfer time of the billet after water quenching in step five does not exceed 20 seconds.

[0022] The above-mentioned method for preparing TC4 titanium alloy rods for fasteners is characterized in that the water-cooled billet transfer time in step seven does not exceed 15 seconds.

[0023] The above-mentioned method for preparing TC4 titanium alloy bars for fasteners is characterized in that the box-type resistance furnaces in steps two and three and the box-type heating furnaces in steps five and six meet the Class III furnace requirements in HB5425 "Method for Determining the Effective Heating Zone of Heat Treatment Furnaces for Aerospace Components", and the box-type resistance furnace used for the solution aging heat treatment in step seven meets the Class 2 furnace requirements in AMS2750E "High Temperature Determination Method".

[0024] In this invention, “□” represents the side length of the square cross-section of the object being processed, and “○” represents the diameter of the circular cross-section of the object being processed.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] 1. This invention adjusts the chemical composition of TC4 titanium alloy ingots and controls the forging, rolling, and heat treatment processes of the bars to maximize and stabilize the strength of TC4 titanium alloy bars, making them suitable for fasteners.

[0027] 2. In this invention, the dried titanium dioxide and sponge titanium are premixed before being added to the electrode block. This effectively avoids the risks of uneven distribution of titanium dioxide and enrichment in some areas due to the agglomeration of titanium dioxide caused by moisture and the direct addition of titanium dioxide to the electrode block. This avoids the problems of uneven distribution of oxygen in the TC4 titanium alloy ingot or the formation of hard oxides due to the enrichment of titanium dioxide and its high melting point during the subsequent melting process, which would affect the uniformity of the microstructure and mechanical properties of the finished bar. This improves the strength and strength uniformity of the TC4 titanium alloy bar for fasteners.

[0028] 3. The present invention adopts a method of controlling the rolling speed, which effectively avoids the temperature rise of the rolled bar during the rolling process, ensuring that the TC4 titanium alloy bar for fasteners has no overheated structure, and further ensuring its structural uniformity.

[0029] 4. The present invention designs the composition of TC4 titanium alloy ingots so that Al, V, Fe and O are controlled at the upper limit of the standard, so as to meet the standard strength requirements of TC4 titanium alloy bars for fasteners to the greatest extent.

[0030] 5. This invention limits the types of heating furnaces used in the production process to ensure the uniformity of heating in each stage of heat treatment, and specifies the transfer time of the heat-treated billet, i.e., the water immersion time, to ensure the effect of heat treatment.

[0031] 6. The TC4 titanium alloy rods for fasteners prepared by this invention have a diameter of 10mm to 28mm, uniform strength, meet standard requirements, and have a margin of more than 5%.

[0032] The technical solution of the present invention will be further described in detail below through embodiments. Detailed Implementation

[0033] Example 1

[0034] This embodiment includes the following steps:

[0035] Step 1: Dry titanium dioxide at 120℃ for 120 minutes, then mix it with sponge titanium at a mass ratio of 1:20 in a V-type mixer. Calculate the mass of the mixed raw materials to be added to each electrode according to the oxygen content requirements designed for the TC4 titanium alloy ingot. Press the electrodes with sponge titanium, aluminum vanadium, aluminum briquettes, and ferrotitanium raw materials, then weld and perform three melting processes. After peeling, cutting the riser and ingot bottom, a TC4 titanium alloy ingot with a diameter of 620 mm is prepared. Its chemical composition is shown in Table 2 below.

[0036] Table 2 Chemical composition of TC4 titanium alloy ingots prepared in Example 1

[0037]

[0038] Step 2: Place the TC4 titanium alloy ingot obtained in Step 1 in a box-type resistance heating furnace and heat it to 1150℃. Then, use a 2500-ton high-speed forging machine for forging. The forging process is as follows: square to □400mm → multiple drawing and chamfering to □250mm → grinding the surface oxide scale and cracks → blanking. Then, place the blanked □250mm billet in a box-type resistance heating furnace and heat it to 950℃. Continue to perform the following processes: □250mm → drawing and chamfering, repeating the "face to edge, edge to face" operation until it is forged to ○250mm → drawing to ○150mm with a V-shaped anvil → grinding the surface oxide scale and cracks → blanking to obtain a precision forged bar billet.

[0039] Step 3: Place the precision forging billet obtained in Step 2 into a box furnace and heat it to 930℃ and hold it there. Then, use an SX-16 precision forging machine to perform two forging cycles. The entire precision forging process is carried out by pulling and striking. Then, straighten it with residual heat to obtain a precision forging billet with a diameter of φ50mm±1mm.

[0040] Step 4: Peel off the surface of the precision forged bar obtained in Step 3 by at least 0.5 mm on one side, then grind and cut the bar to obtain the rolled bar billet.

[0041] Step 5: Perform β heat treatment on the rolled billet obtained in Step 4. The specific process is as follows: place the rolled billet in a box furnace and heat it to 1020℃ and hold it for 50 minutes. Then perform water quenching treatment. The transfer time of the billet after water quenching is 20 seconds, based on the time when the last billet enters the furnace.

[0042] Step 6: Place the rolled bar billet after β heat treatment in Step 5 into a box furnace and heat it to 900℃ and hold it for 60 minutes. Then, use a 250 tandem rolling mill to roll it in 10 passes, and control the linear speed at 1.4 m / s during the rolling process to obtain a rolled bar with a diameter of φ14 mm.

[0043] Step 7: The rolled bar obtained in Step 6 is subjected to solution aging heat treatment. The solution aging heat treatment process is as follows: first, it is held at 950℃ for 60 minutes, then water-cooled, and the transfer time of the water-cooled billet is 15 seconds. Then, it is held at 530℃ for 360 minutes, air-cooled, and after surface machining and polishing, a TC4 titanium alloy bar for fasteners with a diameter of φ12mm is obtained.

[0044] In this embodiment, the box-type resistance furnaces in steps two and three, and the box-type heating furnaces in steps five and six, meet the Class III furnace requirements in HB5425 "Method for Determining the Effective Heating Zone of Heat Treatment Furnaces for Aerospace Parts". The box-type resistance furnace used for the solution aging heat treatment in step seven meets the Class 2 furnace requirements in AMS2750E "High Temperature Determination".

[0045] The performance of the TC4 titanium alloy rod for fasteners prepared in this embodiment was tested and is shown in Table 3 below.

[0046] Table 3. Performance of TC4 titanium alloy rods for fasteners prepared in Example 1

[0047] project Rm / MPa Rp0.2 / MPa A / ％ Z / ％ Standard requirements ≥1140 ≥1070 ≥10 ≥20 bar head 1273 1157 14.5 51 bar tail 1258 1142 14.0 52

[0048] Example 2

[0049] This embodiment includes the following steps:

[0050] Step 1: Dry titanium dioxide at 120℃ for 180 min, then mix it with sponge titanium at a mass ratio of 1:20 in a V-type mixer. Calculate the mass of the mixed raw materials to be added to each electrode according to the oxygen content requirements designed for the TC4 titanium alloy ingot. Press the electrodes with sponge titanium, aluminum vanadium, aluminum briquettes, and ferrotitanium raw materials, then weld and perform three melting processes. After peeling, cutting the risers and ingot bottom, a TC4 titanium alloy ingot with a diameter of 690 mm is prepared. Its chemical composition is shown in Table 4 below.

[0051] Table 4 Chemical composition of TC4 titanium alloy ingots prepared in Example 2

[0052]

[0053] Step 2: Place the TC4 titanium alloy ingot obtained in Step 1 in a box-type resistance heating furnace and heat it to 1150℃. Then, use a 2500-ton high-speed forging machine for forging. The forging process is as follows: square to □400mm → multiple drawing and chamfering to □250mm → grinding the surface oxide scale and cracks → blanking. Then, place the blanked □250mm billet in a box-type resistance heating furnace and heat it to 960℃. Continue to perform the following processes: □250mm → drawing and chamfering, repeating the "face to edge, edge to face" operation until it is forged to ○250mm → drawing to ○140mm with a V-shaped anvil → grinding the surface oxide scale and cracks → blanking to obtain a precision forged bar billet.

[0054] Step 3: Place the precision forging billet obtained in Step 2 into a box furnace and heat it to 950℃ and hold it there. Then, use an SX-16 precision forging machine to perform one pass of precision forging. The entire precision forging process is carried out by pulling and striking. Then, straighten it with residual heat to obtain a precision forging bar with a diameter of φ65mm±1mm.

[0055] Step 4: Peel off the surface of the precision forged bar obtained in Step 3 by at least 0.5 mm on one side, then grind and cut the bar to obtain the rolled bar billet.

[0056] Step 5: Perform β heat treatment on the rolled billet obtained in Step 4. The specific process is as follows: place the rolled billet in a box furnace and heat it to 1020℃ and hold it for 70 minutes. Then perform water quenching treatment. The transfer time of the billet after water quenching is 18 seconds, based on the time when the last billet enters the furnace.

[0057] Step 6: Place the rolled bar billet after β heat treatment in Step 5 into a box furnace and heat it to 920℃ and hold it for 80 minutes. Then, use a 250 tandem rolling mill to perform 8 passes of rolling, and control the linear speed at 1.8 m / s during the rolling process to obtain a rolled bar with a diameter of φ28 mm.

[0058] Step 7: The rolled bar obtained in Step 6 is subjected to solution aging heat treatment. The solution aging heat treatment process is as follows: first, it is held at 960℃ for 100 min, then water-cooled, and the transfer time of the water-cooled billet is 14 s. Then, it is held at 530℃ for 360 min, air-cooled, and after surface machining and polishing, a TC4 titanium alloy bar for fasteners with a diameter of φ26mm is obtained.

[0059] In this embodiment, the box-type resistance furnaces in steps two and three, and the box-type heating furnaces in steps five and six, meet the Class III furnace requirements in HB5425 "Method for Determining the Effective Heating Zone of Heat Treatment Furnaces for Aerospace Parts". The box-type resistance furnace used for the solution aging heat treatment in step seven meets the Class 2 furnace requirements in AMS2750E "High Temperature Determination".

[0060] The performance of the TC4 titanium alloy rod for fasteners prepared in this embodiment, as shown in Table 5 below, was tested.

[0061] Table 5. Performance of TC4 titanium alloy rods for fasteners prepared in Example 2.

[0062] project Rm / MPa Rp0.2 / MPa A / ％ Z / ％ Standard requirements ≥1069 ≥1000 ≥10 ≥20 bar head 1157 1072 16.5 47 bar tail 1158 1076 16.0 50

[0063] As shown in Table 5, the performance of the TC4 titanium alloy rod for fasteners prepared in this embodiment meets the standard requirements.

[0064] Example 3

[0065] This embodiment includes the following steps:

[0066] Step 1: Dry titanium dioxide at 120℃ for 150 min, then mix it with sponge titanium at a mass ratio of 1:20 in a V-type mixer. Calculate the mass of the mixed raw materials to be added to each electrode according to the oxygen content requirements designed for the TC4 titanium alloy ingot. Press the electrodes with sponge titanium, aluminum vanadium, aluminum briquettes, and ferrotitanium raw materials, then weld and perform three smelting processes. After peeling, cutting the risers and ingot bottom, a TC4 titanium alloy ingot with a diameter of 690 mm is prepared. Its chemical composition is shown in Table 6 below.

[0067] Table 6 Chemical composition of TC4 titanium alloy ingots prepared in Example 3

[0068]

[0069]

[0070] Step 2: Place the TC4 titanium alloy ingot obtained in Step 1 in a box-type resistance heating furnace and heat it to 1170℃. Then, use a 2500-ton high-speed forging machine for forging. The forging process is as follows: square to □400mm → multiple drawing and chamfering to □250mm → grinding the surface oxide scale and cracks → blanking. Then, place the blanked □250mm billet in a box-type resistance heating furnace and heat it to 960℃. Continue to perform the following processes: □250mm → drawing and chamfering, repeating the "face to edge, edge to face" operation until it is forged to ○250mm → drawing to ○150mm with a V-shaped anvil → grinding the surface oxide scale and cracks → blanking to obtain a precision forged bar billet.

[0071] Step 3: Place the precision forging billet obtained in Step 2 into a box furnace and heat it to 950℃ and hold it there. Then, use an SX-16 precision forging machine to perform two forging cycles. The entire precision forging process is carried out by pulling and striking. Then, straighten it with residual heat to obtain a precision forging billet with a diameter of φ50mm±1mm.

[0072] Step 4: Peel off the surface of the precision forged bar obtained in Step 3 by at least 0.5 mm on one side, then grind and cut the bar to obtain the rolled bar billet.

[0073] Step 5: Perform β heat treatment on the rolled billet obtained in Step 4. The specific process is as follows: place the rolled billet in a box furnace and heat it to 1020℃ and hold it for 60 minutes. Then perform water quenching treatment. The transfer time of the billet after water quenching is 19 seconds, based on the water entry time of the last billet in the furnace.

[0074] Step 6: Place the rolled bar billet after β heat treatment in Step 5 into a box furnace and heat it to 910℃ and hold it for 70 minutes. Then, use a 250 tandem rolling mill to perform 6 passes of rolling, and control the linear speed at 1.4 m / s during the rolling process to obtain a rolled bar with a diameter of φ20 mm.

[0075] Step 7: The rolled bar obtained in Step 6 is subjected to solution aging heat treatment. The solution aging heat treatment process is as follows: first, it is held at 954℃ for 80 minutes, then water-cooled, and the transfer time of the water-cooled billet is 15 seconds. Then, it is held at 530℃ for 360 minutes, air-cooled, and after surface machining and polishing, a TC4 titanium alloy bar for fasteners with a diameter of φ18mm is obtained.

[0076] In this embodiment, the box-type resistance furnaces in steps two and three, and the box-type heating furnaces in steps five and six, meet the Class III furnace requirements in HB5425 "Method for Determining the Effective Heating Zone of Heat Treatment Furnaces for Aerospace Parts". The box-type resistance furnace used for the solution aging heat treatment in step seven meets the Class 2 furnace requirements in AMS2750E "High Temperature Determination".

[0077] The performance of the TC4 titanium alloy rod for fasteners prepared in this embodiment, as shown in Table 7 below, was tested.

[0078] Table 7. Performance of TC4 titanium alloy rods for fasteners prepared in Example 3.

[0079] project Rm / MPa Rp0.2 / MPa A / ％ Z / ％ Standard requirements ≥1103 ≥1034 ≥10 ≥20 bar head 1212 1103 16.0 52 bar tail 1193 1079 18.5 56

[0080] As shown in Table 7, the performance of the TC4 titanium alloy rod for fasteners prepared in this embodiment meets the standard requirements.

[0081] Comparative Example 1

[0082] This embodiment includes the following steps:

[0083] Step 1: Press titanium dioxide with sponge titanium, aluminum vanadium, aluminum briquettes and ferrotitanium raw materials to form electrodes, then weld and melt three times, and then peel off the skin, cut the riser and the bottom of the ingot to prepare a TC4 titanium alloy ingot with a diameter of 620mm. Its chemical composition is shown in Table 8 below.

[0084] Table 8 Chemical composition of TC4 titanium alloy ingots prepared in Comparative Example 1

[0085] Sampling location Al V Fe C N H O superior 6.21 4.05 0.139 0.010 0.004 0.0006 0.16 middle 6.29 4.10 0.138 0.014 0.003 0.0006 0.15 Down 6.21 4.07 0.144 0.015 0.006 0.0006 0.17

[0086] Step 2: Place the TC4 titanium alloy ingot obtained in Step 1 in a box-type resistance heating furnace and heat it to 1150℃ and hold it there. Then, use a 2500-ton fast forging machine to forge it. The forging process is as follows: square to □400mm → multiple drawing and chamfering to □250mm → grinding the surface oxide scale and cracks → blanking. Then, place the blanked □250mm billet in a box-type resistance heating furnace and heat it to 960℃ and hold it there. Continue to perform the following process: □250mm → V-shaped anvil drawing to ○150mm → grinding the surface oxide scale and cracks → blanking to obtain a precision forged bar billet.

[0087] Step 3: Place the precision forging billet obtained in Step 2 into a box furnace and heat it to 930℃ and hold it there. Then, use an SX-16 precision forging machine to perform two forging cycles. Finally, straighten it with residual heat to obtain a precision forging bar with a diameter of φ50mm±1mm.

[0088] Step 4: Peel off the surface of the precision forged bar obtained in Step 3 by at least 0.5 mm on one side, then grind and cut the bar to obtain the rolled bar billet.

[0089] Step 5: Place the rolled bar obtained in Step 4 into a box furnace and heat it to 1020℃ and hold it for 50 minutes. Then, use a 250 tandem rolling mill to roll it in 10 passes, and control the linear speed at 1.4 m / s during the rolling process to obtain a rolled bar with a diameter of φ14 mm.

[0090] Step 6: The rolled bar obtained in Step 5 is subjected to solution aging heat treatment. The solution aging heat treatment process is as follows: first, hold at 950℃ for 60 minutes, then water cool, then hold at 530℃ for 360 minutes, then air cool. After surface machining and polishing, a TC4 titanium alloy bar for fasteners with a diameter of φ12mm is obtained.

[0091] The performance of the TC4 titanium alloy rods for fasteners prepared in this comparative example was tested and is shown in Table 9 below.

[0092] Table 9. Properties of TC4 titanium alloy bars for fasteners prepared in Comparative Example 1.

[0093] project Rm / MPa Rp0.2 / MPa A / ％ Z / ％ Standard requirements ≥1103 ≥1034 ≥10 ≥20 bar head 1137 1015 18 55 bar tail 1056 933 18.5 47

[0094] As shown in Table 9, the performance of the TC4 titanium alloy rod for fasteners prepared in this comparative example does not meet the standard requirements, i.e., the performance is unqualified.

[0095] Comparing Example 1 with Comparative Example 1, it can be seen that by controlling the design value of the chemical composition of TC4 titanium alloy ingots, combining the premixing of sponge titanium and titanium dioxide, and controlling the forging, precision forging and rolling processes, as well as the control of β heat treatment and solution aging heat treatment, the present invention enables the strength performance of TC4 titanium alloy bars to reach the maximum and most stable state, thus meeting the requirements for fastener use.

[0096] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for producing a TC4 titanium alloy bar for fasteners, characterized in that, The method includes the following steps: Step 1: Press the sponge titanium, aluminum vanadium, aluminum briquettes, titanium dioxide, and ferrotitanium raw materials into electrodes, then weld them and perform three smelting processes. After peeling, cutting the risers and the bottom of the ingot, a TC4 titanium alloy ingot with a diameter of 620mm or 690mm is prepared. Step 2: Place the TC4 titanium alloy ingot obtained in Step 1 in a box-type resistance heating furnace and heat it to 1150℃~1170℃ and hold it there. Then, use a 2500-ton high-speed forging machine for forging. The forging process is as follows: square to □400mm → multiple drawing and chamfering to □250mm → grinding the surface oxide scale and cracks → blanking. Then, place the blanked □250mm billet in a box-type resistance heating furnace and heat it to 950℃~960℃ and hold it there. Continue to perform the following processes: □250mm → drawing and chamfering to ○250mm → drawing with a V-shaped anvil to ○140mm~○150mm → grinding the surface oxide scale and cracks → blanking to obtain a precision forged bar billet. Step 3: Place the precision forged billet obtained in Step 2 into a box furnace and heat it to 930℃~950℃ and hold it at that temperature. Then, use an SX-16 precision forging machine to perform 1~2 forging cycles. Finally, straighten it with residual heat to obtain a precision forged bar with a diameter of φ50mm±1mm~φ65mm±1mm. Step 4: Peel off the surface of the precision forged bar obtained in Step 3 by at least 0.5 mm on one side, then grind and cut the bar to obtain the rolled bar billet. Step 5: Perform β heat treatment on the rolled bar billet obtained in Step 4. The specific process is as follows: place the rolled bar billet in a box furnace and heat it to 1020℃ and hold it for 50min to 70min, followed by water quenching. Step 6: Place the rolled bar billet after β heat treatment in Step 5 into a box furnace and heat it to 900℃~920℃ and hold it for 60min~80min. Then, use a 250 tandem rolling mill to roll it 6~10 times, and control the linear speed at 1.4m / s~1.8m / s during the rolling process to obtain rolled bars with a diameter of φ14mm~φ28mm. Step 7: The rolled bar obtained in Step 6 is subjected to solution aging heat treatment. The solution aging heat treatment process is as follows: first, hold at 950℃~960℃ for 60min~100min, water cool, then hold at 530℃ for 360min, air cool, and after surface machining and polishing, TC4 titanium alloy bar for fasteners is obtained.

2. The method of producing a TC4 titanium alloy bar for fasteners according to claim 1, characterized in that, The titanium dioxide described in step one is dried at 120℃ for 120 min to 180 min, and then mixed with sponge titanium at a mass ratio of 1:20 in a V-type mixer. Based on the oxygen content requirements designed in the TC4 titanium alloy ingot, the mass of the mixed raw material added to each electrode is calculated.

3. The method for preparing TC4 titanium alloy rods for fasteners according to claim 1, characterized in that, The chemical composition design value of the TC4 titanium alloy ingot mentioned in step one is Ti-6.65~6.75Al-4.35~4.5V-0.24~0.26Fe-0.17~0.20O.

4. The method for preparing TC4 titanium alloy rods for fasteners according to claim 1, characterized in that, The process described in step two, from □250mm to ○250mm, involving drawing and chamfering, should be repeated with the "face to edge, edge to face" operation until the desired size is achieved.

5. The method for preparing TC4 titanium alloy rods for fasteners according to claim 1, characterized in that, The precision forging process described in step three is all carried out using a pulling and striking method.

6. The method for preparing TC4 titanium alloy rods for fasteners according to claim 1, characterized in that, The transfer time of the billet after water quenching in step five shall not exceed 20 seconds.

7. The method for preparing TC4 titanium alloy rods for fasteners according to claim 1, characterized in that, The water-cooled billet transfer time described in step seven shall not exceed 15 seconds.

8. The method for preparing TC4 titanium alloy rods for fasteners according to claim 1, characterized in that, The box-type resistance furnaces in steps two and three, and the box-type heating furnaces in steps five and six, meet the Class III furnace requirements in HB5425 "Method for Determining the Effective Heating Zone of Heat Treatment Furnaces for Aerospace Parts". The box-type resistance furnace used for the solution aging heat treatment in step seven meets the Class 2 furnace requirements in AMS2750E "High Temperature Determination".

Images