A method for preparing fine-grained Ti-5Al-5V-5Mo-3Cr titanium alloy wire for fasteners

Abstract

A method for preparing fine-grained Ti‑5Al‑5V‑5Mo‑3Cr titanium alloy wire for fasteners, using a heat working method below the phase transition point of free forging in a temperature zone below the phase transition + radial forging in a temperature zone below the phase transition + hot rolling in a temperature zone below the phase transition, in the process of processing the Ti‑5553 titanium alloy ingot into a rod, inducing dynamic recrystallization of most Beta grains in the Ti‑5553 titanium alloy, and preliminarily refining the Beta grains in the alloy rod. After hot working below the phase transition, the Beta grains reach 5μm to 100μm. The Beta grains in the wire are completely refined by using a method of large plastic deformation cold rolling + two-phase zone solution treatment. During the cold rolling process, high-density dislocations are formed inside the coarse Beta grains; during the solution treatment process, the dislocations are transformed into new grain boundaries. After cold rolling-solution treatment, the Beta grains in the wire are 5μm to 15μm. The present invention can achieve excellent matching of strength and plasticity. The average tensile strength of the aged wire material can reach 1482MPa, the average yield strength can reach 1393MPa, the average elongation after break can reach 10.3%, and the average cross-sectional shrinkage can reach 37%.

Description

Technical Field

[0001] The invention relates to the technical field of titanium alloy processing, in particular to an engineering preparation method for Ti-5Al-5V-5Mo-3Cr titanium alloy wire material for fine-grained fasteners with a Beta grain size ranging from 5μm to 15μm. Technical Background

[0002] Ti-5Al-5V-5Mo-3Cr (Ti-5553) titanium alloy is a new type of high-strength titanium alloy for aviation. When the Beta grain of Ti-5553 titanium alloy is refined to less than 20μm, the tensile strength of the alloy after aging heat treatment can reach 1525MPa and the elongation after fracture can reach 9.5%, which has excellent strength and plasticity matching. At present, the 1500MPa-grade aviation fasteners in service in my country are all made of iron-based / nickel-based alloys such as PH13-8Mo iron-based alloy and GH4169 nickel-based alloy. The tensile strength of the above iron-based / nickel-based alloys is in the range of 1515MPa to 1650MPa, and the density is 7.9×10 3 kg / m 3 ~8.2×10 3 kg / m 3 Although the tensile strength of fine-grained high-strength Ti-5553 titanium alloy is lower than the upper limit of the tensile strength of the above-mentioned iron-based / nickel-based alloys, the density of Ti-5553 titanium alloy is only 4.6×10 3 kg / m 3 , the specific strength of the alloy is 65% higher than that of iron-based / nickel-based alloys. Therefore, Ti-5553 titanium alloy is an ideal material for manufacturing 1500MPa-grade lightweight fasteners for aviation. Given that refined Beta grains are a prerequisite for ensuring the strength-plasticity matching of 1500MPa-grade Ti-5553 titanium alloy, establishing an engineering preparation method for fine-grained Ti-5553 titanium alloy wire plays an important supporting role in manufacturing 1500MPa-grade Ti-5553 titanium alloy fasteners.

[0003] A hot working method for improving the microstructure and properties of Ti-5553 titanium alloy is disclosed in the invention with publication number CN 102517530. The method is aimed at optimizing the microstructure and properties of Ti-5553 titanium alloy forging parts, but is not suitable for preparing fine-grained Ti-5553 titanium alloy wire.

[0004] In the invention with application number 201810431403.X, a method for preparing high-strength titanium alloy wire is disclosed. The method adopts a technical route of alternating temperatures above and below the phase transition point during ingot casting and hot rolling to break the Beta grains of the alloy. Since the Beta grains of Ti-5553 titanium alloy are prone to rapid growth in the temperature zone above the phase transition point, the hot working method that alternately uses temperatures above and below the phase transition point cannot refine the Beta grains in the Ti-5553 titanium alloy wire to less than 20μm. Therefore, this method is not suitable for preparing fine-grained Ti-5553 titanium alloy wire.

[0005] The invention with the publication number of CN 108580577 A discloses a method for preparing high-strength Beta titanium alloy wire for springs. The method adopts the technical route of hot drawing in the temperature range of 650℃ to 750℃ to break the Beta grains in the alloy. However, the deformation resistance of Ti-5553 titanium alloy in this temperature range is too large, and the alloy is prone to fracture during the hot drawing process, and the wire cannot be formed.

[0006] The invention with the publication number CN 101343706A discloses a method for preparing Beta titanium alloy for fasteners, which uses hot rolling in the temperature range of 900°C to 1000°C to crush the Beta grains of the alloy. However, this temperature range is above the phase transition point of the Ti-5553 titanium alloy, and the Beta grains cannot be crushed to less than 100 μm.

[0007] In the invention with the publication number CN 122251639 A, a high-strength titanium alloy rod, wire and preparation method thereof are proposed. In the method, it is proposed that the method of "forging + hot rolling + hot drawing" can realize the nano-sizing of Alpha grains in Ti-(5.5-6.5)Al-(3.5-4.5)V-(4-6)Cu (mass fraction, the same below) martensitic titanium alloy, wherein the forging temperature zone is a temperature zone above 1000°C, the hot rolling temperature zone is (750°C-850°C), and the hot drawing temperature zone is (600°C-700°C). First, the temperature zone above 1000°C is more than 155°C higher than the phase transition point (845°C) of Ti-5553 titanium alloy. After forging in this temperature zone, the size of Beta grains in the alloy will be greater than 200μm, and subsequent hot rolling and hot drawing are not easy to fully refine the Beta grains in the alloy. Secondly, the purpose of hot rolling in the (750℃~850℃) temperature zone is to break the martensitic laths in the Ti-(5.5~6.5)Al-(3.5~4.5)V-(4~6)Cu alloy, while there are no martensitic laths in the Ti-5553 titanium alloy; in addition, the upper limit temperature of this temperature zone, 850℃, is higher than the phase transition point of the Ti-5553 titanium alloy. At this temperature, hot rolling cannot effectively break the Beta grains of the Ti-5553 titanium alloy to less than 100μm. Thirdly, the deformation resistance of the Ti-5553 titanium alloy in the (600℃~700℃) temperature zone is too large, and the alloy is prone to breakage during the hot drawing process, which is not conducive to the continuous industrial production of wire. Therefore, this method is not suitable for the preparation of fine-grained Ti-5553 titanium alloy wire.

[0008] In the invention with the publication number CN 112981174 A, a method for preparing high-strength and plastic titanium alloy wire is proposed. In this method, a method of "forging + hot rolling in a temperature zone above the phase transformation point + hot drawing" is proposed to prepare high-strength and plastic Ti-(3.5-5.0)Al-(2.5-4.0)V-(4.0-6.0)Mo-(4.5-6.0)Cr-(0.6-1.5)Fe alloy wire is proposed, wherein the forging temperature zone is (950℃~1150℃), the hot rolling temperature zone is a temperature zone above the alloy phase transformation point (80℃~150℃), and the hot drawing temperature zone is (760℃~820℃). In this method, the forging temperature zone and the hot rolling temperature zone are both in the single-phase zone. If the method is used to prepare Ti-5553 titanium alloy wire, the Beta grains of the wire will be abnormally coarse after hot rolling. Due to the strain inhomogeneity of Ti-5553 titanium alloy during deformation in the temperature zone below the phase transformation point, hot drawing processing in the temperature zone (760℃~820℃) alone cannot fully refine the Beta grains in Ti-5553 titanium alloy wire.

[0009] In summary, although the processing and preparation methods of titanium alloy wire for fasteners have been reported in the prior art, the processing technologies and hot processing parameters involved in these methods are not completely suitable for the engineering preparation of fine-grained Ti-5553 titanium alloy wire for fasteners. The main problems are: 1. The forging temperature is too high, and the Beta grains in the wire are not refined by forging in the temperature zone below the phase transformation point; 2. The hot rolling temperature is too high, and the Beta grains in the wire are not refined by hot rolling in the temperature zone below the phase transformation point; 3. The cold processing technology of the wire has not been developed, and the effect of cold processing on the refinement of the Beta grains of the refined wire is ignored. Summary of the invention

[0010] In order to fill the blank in the processing method of fine-grained Ti-5553 titanium alloy wire, the present invention provides a preparation method of fine-grained Ti-5Al-5V-5Mo-3Cr titanium alloy wire for fasteners.

[0011] The specific process of the present invention is:

[0012] Step 1, preparing finished ingot:

[0013] A tertiary ingot with a composition of Ti-5.07Al-5.11V-5.17Mo-2.97Cr-0.0094O is obtained through three smeltings; the tertiary ingot is processed to obtain a finished ingot.

[0014] The process of preparing the finished ingot is:

[0015] The raw material of Ti-5553 titanium alloy ingot is pressed into a plurality of electrode blocks; the plurality of electrode blocks are welded into three consumable electrode rods; the three consumable electrode rods are melted into ingots respectively; and three primary ingots are obtained.

[0016] The three primary ingots are welded into a consumable electrode rod. The consumable electrode rod is subjected to secondary smelting to obtain a secondary ingot.

[0017] The obtained secondary ingot is used as a consumable electrode rod. The consumable electrode rod after the secondary smelting is smelted for the third time to obtain a tertiary ingot.

[0018] Step 2, free forging:

[0019] The obtained finished ingot is heated, and a multi-forging process of 9 to 12 forging times is carried out with the phase transformation point of the finished ingot as the boundary. Among them: the forging times above the phase transformation point of the ingot are 5 to 7 times, the forging temperature is 850±10℃~1200±10℃; the roughening deformation is 60%, and the number of roughening-stretching times is 3 times. The forging times below the phase transformation point of the ingot are 4 or 5 times, the forging temperature is 750±10℃~840±10℃; the roughening deformation is 50%, and the number of roughening-stretching times is 2 times.

[0020] After free forging, a forging billet with a specification of 160mm×160mm×L is obtained.

[0021] When forging for multiple times above the phase transformation point of the ingot, heat the box-type resistance furnace to the set forging temperature of 850±10℃~1200±10℃, load the Ti-5553 titanium alloy forging billet, and keep it warm for 2h. Forge the Ti-5553 titanium alloy forging billet. Roughing-stretching is performed 3 times during each forging process, and the roughing deformation amount is 60% each time. Water cooling after forging.

[0022] After each forging, a Ti-5553 titanium alloy forging blank forged by the forging is obtained, and micro cracks on the surface of the Ti-5553 titanium alloy forging blank forged by the forging are ground, until the multi-forging above the phase transformation point of the ingot is completed.

[0023] When the ingot is forged for multiple times below the phase transformation point, the box-type resistance furnace is heated to the set forging temperature of 750±10℃~840±10℃, and then the Ti-5553 titanium alloy forging billet forged above the phase transformation point is loaded and kept warm for 2h.

[0024] The Ti-5553 titanium alloy forging blank forged above the phase transformation point is forged, and two upsetting and stretching operations are performed during each forging process, with each upsetting deformation amount being 50%, and water cooling is performed after forging.

[0025] After each forging, a Ti-5553 titanium alloy forging blank forged by the forging is obtained, and micro cracks on the surface of the Ti-5553 titanium alloy forging blank forged by the forging are ground, until the multi-forging below the phase transformation point of the ingot is completed.

[0026] Step 3, drawing and forging:

[0027] The obtained forging billet is subjected to 2 to 4 rounds of drawing forging in a temperature zone below the phase transformation point by using a fast forging machine, and the 160mm×160mm×L forging billet is drawn and forged into a Φ80mm×L forging billet.

[0028] During each forging process, the forging blank is heated to the required temperature of 750±10℃~840±10℃ and kept at this temperature for 2h. After each forging process, it is water-cooled. A forging blank of Φ80mm is obtained after forging process.

[0029] Step 4, radial forging:

[0030] Heat the box-type resistance furnace to the temperature of 750±10℃~840±10℃ required for radial forging; load the forging billet after drawing and forging, keep the temperature for 1h, and perform radial forging. Air cooling is performed to obtain radial forging billet.

[0031] The obtained radial forged bars are sawn into sections.

[0032] Step 5, hot rolling:

[0033] The obtained forged bar billet is placed in a box-type resistance furnace at a temperature of 720±10℃~835±10℃ for 1 hour; it is hot-rolled in a rolling mill for one heat and multiple passes to obtain hot-rolled bars. Cooling is performed. The obtained hot-rolled bars are sawn into sections as required.

[0034] The hot rolling speed is 1m / -3m / s, and the deformation amount of each pass is less than 50%.

[0035] Step 6, preparing cold-rolled wire billet:

[0036] Ⅰ Thermal Straightening

[0037] The hot-rolled bars cut into segments are placed in a box-type resistance furnace at 820°C ± 10°C for 1 hour. The hot-rolled bars are straightened by a straightening machine and air-cooled.

[0038] ⅡRemove the oxide scale of heat-straightened bars.

[0039] The oxide scale of the bar is removed using a centerless lathe.

[0040] Ⅲ Use a centerless grinder to grind the outer surface of the rod so that the roughness of the outer surface of the rod is Ra<1.6, and a Φ15mm×2500mm cold-rolled wire billet is obtained.

[0041] Step 7, cold rolling:

[0042] The obtained cold-rolled wire billet is continuously and multi-pass cold-rolled into wire material by a tandem rolling mill.

[0043] The cold rolling speed is less than 1m / s, and the deformation per pass is less than 30%.

[0044] The obtained Ti-5553 titanium alloy wire is in the cold-rolled state of Φ5.5mm to Φ8.5mm.

[0045] The cold-rolled Ti-5553 titanium alloy wire is sawn to obtain a semi-finished wire product.

[0046] When cold rolling the wire, the wire blank is sequentially put into the holes of each roller in the longitudinal rolling mill for multiple continuous cold rolling to obtain cold-rolled Ti-5553 titanium alloy wire. The holes of each roller have different apertures.

[0047] Step 8, solution treatment and heat straightening:

[0048] The temperature of the box-type resistance furnace is heated to the target solution treatment temperature; the semi-finished titanium alloy wire is loaded into the box-type resistance furnace for solution treatment. The titanium alloy wire after solution treatment is taken out from the resistance furnace and heat straightened. Air cooling is performed to obtain titanium alloy wire with a diameter of Φ5.5 mm to Φ8.5 mm.

[0049] The solution treatment temperature is 820℃±10℃. The solution treatment time is 30min

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] 1. The "hot working + cold working in the temperature zone below the phase transition point" technical route proposed in the present invention can be used to engineer fine-grained Ti-5553 titanium alloy wire, and the size of the Beta grains in the wire is within the range of 5μm to 15μm. First, the present invention uses the hot working method below the phase transition point of "free forging in the temperature zone below the phase transition point + radial forging in the temperature zone below the phase transition point + hot rolling in the temperature zone below the phase transition point", which not only processes the Ti-5553 titanium alloy ingot into a rod and realizes the preliminary forming of the wire, but also can induce dynamic recrystallization of most Beta grains in the Ti-5553 titanium alloy, and preliminarily refines the Beta grains in the alloy rod. After hot working below the phase transition point, the size of the Beta grains in the rod is within the range of 5μm to 100μm. Secondly, the present invention uses the method of "large plastic deformation cold rolling + two-phase zone solid solution treatment" to eliminate the residual coarse Beta grains in the rod, and realizes the complete refinement of the Beta grains in the wire. During the cold rolling process, high-density dislocations are formed inside the coarse Beta grains; during the solution treatment, high-density dislocations are transformed into new grain boundaries. After cold rolling-solution treatment, the size of the Beta grains in the wire is within the range of 5μm to 15μm.

[0052] 2. The fine-grained Ti-5553 titanium alloy wire prepared by the present invention can obtain excellent strength and plasticity matching after aging heat treatment. In order to verify the effect of the present invention, Xi'an Han Tang Analysis and Testing Co., Ltd. was commissioned to measure the mechanical properties of Φ8mm wire after aging treatment according to the detection method specified in GB / T228.1-2021. The results are shown in Table 1. The average tensile strength of the aged Φ8mm wire can reach 1482MPa, the average yield strength can reach 1393MPa, the average elongation after break can reach 10.3%, and the average cross-sectional shrinkage can reach 37%.

[0053] Table 1 Room temperature tensile test results of aged fine-grained Ti-5553 titanium alloy straight wire

[0054]

[0055] BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 This is an optical microscope photograph of Φ2.0mm solid solution Ti-5553 titanium alloy wire.

[0057] Figure 2 This is an optical microscope photograph of Φ5.5mm solid solution Ti-5553 titanium alloy wire.

[0058] Figure 3 This is an optical microscope photograph of Φ8.5mm solid solution Ti-5553 titanium alloy wire.

[0059] Figure 4 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0060] The present invention is a method for preparing Φ8.5mm fine-grained Ti-5553 titanium alloy wire, and its technical scheme will be described in detail through four embodiments.

[0061] The specific process of the present invention is:

[0062] Step 1, smelting Ti-5553 titanium alloy ingot:

[0063] The raw materials for smelting Ti-5553 titanium alloy ingots include grade 0 titanium sponge, Al 40 Mo 60 Master alloy, Al 15 V 85 Master alloy, Al beans with a purity of 99.99% and Cr particles with a purity of 99.99%.

[0064] The Al 40 Mo 60 In the master alloy, the mass percentage of Mo is 60%, and the mass percentage of Al is 40%; 15 V 85 The mass percentage of V in the master alloy is 85%, and the mass percentage of Al is 15%.

[0065] During smelting, a 2000-ton hydraulic press is used to press the raw materials into electrode blocks; the size of the electrode blocks is Φ50mm×300mm, and the number is 21 pieces.

[0066] Use a vacuum plasma welding box to weld every 7 electrode blocks in sequence along the length direction to form a consumable electrode rod, and weld three consumable electrode rods in total.

[0067] The three consumable electrode rods are melted into ingots using a vacuum consumable arc furnace to obtain three primary ingots with a diameter of 90 mm. The vacuum degree of vacuum melting is ≤5×10 -1 Pa.

[0068] The three primary ingots obtained are welded into a consumable electrode rod. The consumable electrode rod is subjected to secondary smelting in a vacuum consumable arc furnace to obtain a secondary ingot with a diameter of 120 mm; the vacuum degree of the secondary smelting is ≤5×10 -2 Pa.

[0069] The obtained secondary ingot is used as a consumable electrode rod. The consumable electrode rod after the secondary smelting is smelted for a third time using a vacuum consumable arc furnace to obtain a tertiary ingot with a diameter of 160 mm. The smelting vacuum degree is ≤5×10 -2 Pa.

[0070] The composition of the obtained tertiary ingot is Ti-5.07Al-5.11V-5.17Mo-2.97Cr-0.0094O. The ingot is subjected to skinning, riser cutting and ingot bottom cutting to obtain a finished ingot.

[0071] The size of the finished ingot is Φ158mm×380mm.

[0072] Step 2, free forging:

[0073] The ingot was heated in a Nabertherm LH 216 / 14 box-type resistance furnace and subjected to multi-fire forging of 9 to 12 forging fires with the phase transformation point of the ingot as the boundary.

[0074] The forging times above the phase transformation point of the ingot is 5 to 7 times, the forging temperature is 850±10℃~1200±10℃; the roughening deformation amount is 60%, and the roughening-drawing times are 3 times.

[0075] The forging times below the phase transformation point of the ingot is 4 or 5 times, the forging temperature is 750±10℃~840±10℃; the roughening deformation is 50%, and the roughening-stretching times is 2 times.

[0076] When the ingot is forged for multiple times above the phase transformation point, the box-type resistance furnace is heated to a set forging temperature of 850°C±10°C to 1200°C±10, and then the Ti-5553 titanium alloy forging billet is loaded and kept warm for 2 hours. Before forging, the time for transferring the Ti-5553 titanium alloy forging billet from the box-type resistance furnace to the fast forging machine is less than 1 minute.

[0077] The Ti-5553 titanium alloy forging blank was forged by a 2000-ton fast forging machine. During each forging process, three upsetting and stretching operations were performed according to the conventional method, and the upsetting deformation amount was 60% each time. After forging, the blank was water-cooled.

[0078] After each forging, a Ti-5553 titanium alloy forging blank forged by the fire is obtained, and microcracks on the surface of the Ti-5553 titanium alloy forging blank forged by the fire are ground, until multiple forgings above the ingot phase transformation point are completed to obtain a forging blank with a specification of 160mm×160mm×L.

[0079] Table 1 Forging parameters of free forging above the phase transformation point of Ti-5553 titanium alloy

[0080]

[0081]

[0082] When the ingot is forged for multiple times below the phase transformation point, the box-type resistance furnace is heated to a set forging temperature of 750±10°C to 840±10°C, and the Ti-5553 titanium alloy forging billet forged above the phase transformation point is loaded and kept warm for 2 hours. Before forging, the time for transferring the Ti-5553 titanium alloy forging billet from the box-type resistance furnace to the fast forging machine is less than 1 minute.

[0083] The Ti-5553 titanium alloy forging blank is forged by a 2000-ton fast forging machine. During each forging process, two upsetting and stretching operations are performed according to conventional methods, and the upsetting deformation amount is 50% each time. Water cooling is performed after forging.

[0084] After each forging, a Ti-5553 titanium alloy forging blank forged by the fire is obtained, and micro cracks on the surface of the Ti-5553 titanium alloy forging blank forged by the fire are ground, until multiple forgings below the ingot phase transformation point are completed to obtain a forging blank with a specification of 160mm×160mm×L.

[0085] Table 2 Forging parameters of free forging below the phase transformation point of Ti-5553 titanium alloy

[0086]

[0087]

[0088] Step 3, drawing and forging:

[0089] A 2000-ton fast forging machine is used to carry out 2 to 4 rounds of drawing forging in the temperature zone below the phase transformation point, and the 160mm×160mm×L forging billet is drawn and forged into a Φ80mm×L round rod forging billet.

[0090] The temperature of the drawing forging is 750℃±10℃~840℃±10℃. It is heated to the drawing forging temperature by a box-type resistance furnace; the holding time for each fire is 2h. After each fire forging, the forging blank is cooled by water. A Φ80mm forging blank is obtained after drawing forging.

[0091] Before drawing forging, the time for transferring the forging billet from the box-type resistance furnace to the radial forging machine is less than 1 minute.

[0092] Table 3 Process parameters of the embodiment in step 3

[0093]

[0094]

[0095] Step 4, radial forging:

[0096] The temperature range of the radial forging is 750±10℃~840±10℃. When the temperature of the box-type resistance furnace reaches the radial forging temperature, the forging blank after the drawing and forging is loaded, and the temperature is kept for 1h, and radial forging is performed. The radial forging bar is obtained. The forging blank is forged into a Φ50mm bar by a radial forging machine. Air cooling.

[0097] Before radial forging, the time for transferring the forging billet from the box-type resistance furnace to the radial forging machine is less than 1 minute.

[0098] Table 4 Temperature parameters of radial forging

[0099]

[0100] The obtained radial forged bars are sawn into hot-rolled billets of Φ50mm×800mm.

[0101] Step 5, hot rolling:

[0102] The hot-rolled bar billet is hot-rolled into bars through one heat and multiple passes by a tandem rolling mill. The hot rolling temperature range is 720±10℃~835±10℃. After the temperature of the box-type resistance furnace is heated to the set hot rolling temperature, the Φ50mm×800mm hot-rolled bar billet is loaded and kept warm for 1h. After the insulation is completed, the heated hot-rolled bar billet is loaded from the box-type resistance furnace into the rolling mill. Start the hot rolling mill and perform multiple passes of hot rolling on the hot-rolled bar billet. The hot rolling speed range is 1m / ~3m / s, and the deformation amount of each pass is less than 50%. Cooling. A hot-rolled bar with a diameter that meets the requirements is obtained.

[0103] The obtained hot rolled bars are sawn into sections as required.

[0104] Table 5. Technical parameters of hot rolling

[0105]

[0106]

[0107] Step 6, preparing cold-rolled wire billet:

[0108] Ⅰ Thermal Straightening

[0109] The hot straightening temperature is 820℃±10℃. When the temperature of the box-type resistance furnace reaches the target hot straightening temperature, the hot-rolled bars of Φ15.5mm×2500mm are loaded and kept at temperature for 1h. The hot-rolled bars are hot straightened by a straightening machine. After the hot straightening is completed, the bars are air-cooled to obtain the bars for cold rolling.

[0110] ⅡRemove the oxide scale of heat-straightened bars.

[0111] The bar is descaled in the conventional manner using a centerless lathe.

[0112] Ⅲ Use a centerless grinder to grind the outer surface of the bar to ensure that the roughness of the outer surface of the bar Ra is less than 1.6, and obtain a Φ15mm×2500mm cold-rolled wire billet.

[0113] Step 6, cold rolling:

[0114] The obtained cold-rolled wire billet is subjected to multiple continuous cold rolling processes to obtain a wire material.

[0115] The conventional method is adopted during continuous cold rolling, and the obtained wire blank is continuously and multi-pass hot rolled into wire material using a longitudinal rolling mill.

[0116] During the cold rolling process, the cold rolled wire billet is sequentially placed in the holes of the rollers in the longitudinal rolling mill for multiple continuous cold rolling to obtain a cold rolled Ti-5553 titanium alloy wire. After the cold rolling is completed, the cold rolled Ti-5553 titanium alloy wire is sawn to the required length to obtain a semi-finished wire product.

[0117] The holes of the rollers have different hole diameters.

[0118] The cold rolling speed is less than 1m / s, and the deformation per pass is less than 30%.

[0119] The obtained cold-rolled Ti-5553 titanium alloy wire has no microcracks on its surface.

[0120] Table 6 Technical parameters of step 6 of each embodiment

[0121]

[0122] Step 7: Solution treatment and heat straightening

[0123] The solution treatment temperature is 820°C ± 10°C. When the temperature of the box-type resistance furnace reaches the target solution treatment temperature, the semi-finished titanium alloy wire is loaded and solution treated according to the conventional method for 30 minutes.

[0124] After the solution treatment, the titanium alloy wire that has undergone the solution treatment is taken out from the resistance furnace, and is heat straightened by a straightening machine, and air-cooled to obtain Ti-5553 titanium alloy wire.

Claims

1. A method for preparing fine-grained Ti-5Al-5V-5Mo-3Cr titanium alloy wire for fasteners, characterized in that: The specific process is: Step 1, preparing finished ingot: A tertiary ingot with a composition of Ti-5.07Al-5.11V-5.17Mo-2.97Cr-0.0094O is obtained by tertiary smelting; the tertiary ingot is processed to obtain a finished ingot; Step 2, free forging: The obtained finished ingot is heated, and multi-forging of 9 to 12 forging times is performed with the phase transformation point of the finished ingot as the boundary; wherein: the forging times above the phase transformation point of the ingot are 5 to 7, the forging temperature is 850±10°C to 1200±10°C, the roughening deformation is 60%, and the number of roughening-stretching times is 3 times; the forging times below the phase transformation point of the ingot are 4 or 5, the forging temperature is 750±10°C to 840±10°C, the roughening deformation is 50%, and the number of roughening-stretching times is 2 times; After free forging, a forging blank is obtained; Step 3, drawing and forging: The obtained forging blank is subjected to 2 to 4 heats of drawing forging in a temperature zone below the phase transformation point by using a fast forging machine; Step 4, radial forging: Heat the box-type resistance furnace to the temperature of 750±10℃~840±10℃ required for radial forging; load the forging billet after drawing and forging, and keep it at temperature for 1h; air cool to obtain radial forging billet; Saw the obtained radial forged bars into segments; Step 5, hot rolling: The obtained radial forged bar is placed in a box-type resistance furnace at a temperature of 720±10℃~835±10℃ for 1 hour; hot-rolled in a rolling mill for one fire and multiple passes; hot-rolled bar is obtained; cooled; and the obtained hot-rolled bar is sawn into sections as required; The hot rolling speed is 1m / s to 3m / s, and the deformation of each pass is less than 50%; Step 6, preparing cold-rolled wire billet: Ⅰ Thermal Straightening The hot-rolled bars cut into segments are placed in a box-type resistance furnace at 820°C±10°C for 1 hour; the hot-rolled bars are straightened by a straightening machine; and air-cooled; Ⅱ Removal of oxide scale from heat-straightened bars; Use a centerless lathe to remove the oxide scale from the bar; Ⅲ. Grinding the outer surface of the bar with a centerless grinder to make the roughness of the outer surface of the bar Ra < 1.6 to obtain a cold-rolled wire blank; Step 7, cold rolling: The obtained cold-rolled wire billet is continuously and multi-pass cold-rolled into wire material by a tandem rolling mill; Cold rolling speed <1m / s, deformation per pass <30%; The obtained cold-rolled Ti-5553 titanium alloy wire material with a diameter of Φ5.5 mm to Φ8.5 mm; The cold-rolled Ti-5553 titanium alloy wire is sawn to obtain a semi-finished wire product; Step 8, solution treatment and heat straightening: The temperature of the box-type resistance furnace is heated to the target solution treatment temperature; the semi-finished titanium alloy wire is loaded into the box-type resistance furnace for solution treatment; the titanium alloy wire after the solution treatment is taken out from the resistance furnace and heat straightened; air cooling is performed; and titanium alloy wire with a diameter of Φ5.5 mm to Φ8.5 mm is obtained; After cold rolling-solution treatment, the size of Beta grains in the wire is 5μm to 15μm.

2. The method for preparing fine-grained Ti-5Al-5V-5Mo-3Cr titanium alloy wire for fasteners according to claim 1, characterized in that: The process of preparing the finished ingot is: The raw material of Ti-5553 titanium alloy ingot is pressed into a plurality of electrode blocks; the plurality of electrode blocks are welded into three consumable electrode rods; the three consumable electrode rods are smelted into ingots respectively; three primary ingots are obtained; the three primary ingots are welded into a consumable electrode rod; the consumable electrode rod is subjected to secondary smelting to obtain a secondary ingot; The obtained secondary ingot is used as a consumable electrode rod; the consumable electrode rod that has undergone secondary smelting is smelted for a third time to obtain a tertiary ingot.

3. The method for preparing fine-grained Ti-5Al-5V-5Mo-3Cr titanium alloy wire for fasteners according to claim 1, characterized in that: In step 2, when the ingot is forged for multiple times above the phase transformation point, the box-type resistance furnace is heated to a set forging temperature of 850±10°C to 1200±10°C, and the Ti-5553 titanium alloy forging blank is loaded and kept warm for 2 hours; the Ti-5553 titanium alloy forging blank is forged; three times of roughening and stretching are performed during each forging process, and the roughening deformation amount is 60% each time; and water cooling is performed after forging; After each forging, a Ti-5553 titanium alloy forging blank forged by the forging is obtained, and micro cracks on the surface of the Ti-5553 titanium alloy forging blank forged by the forging are ground; until multiple forgings above the phase transformation point of the ingot are completed.

4. The method for preparing fine-grained Ti-5Al-5V-5Mo-3Cr titanium alloy wire for fasteners according to claim 1, characterized in that: In step 2, when the ingot is forged for multiple times below the phase transformation point, the box-type resistance furnace is heated to a set forging temperature of 750±10°C to 840±10°C, and the Ti-5553 titanium alloy forging billet forged above the phase transformation point is loaded and kept warm for 2 hours; Forging the Ti-5553 titanium alloy forging blank that has been forged above the phase transformation point; performing two upsetting-drawing processes in each forging process, with each upsetting deformation amount being 50%; and water cooling after forging; After each forging, a Ti-5553 titanium alloy forging blank forged by the forging is obtained, and micro cracks on the surface of the Ti-5553 titanium alloy forging blank forged by the forging are ground; until multiple forgings below the phase transformation point of the ingot are completed.

5. The method for preparing fine-grained Ti-5Al-5V-5Mo-3Cr titanium alloy wire for fasteners according to claim 1, characterized in that: In step 3, during each stretch forging, the obtained forging blank is heated to the required temperature of 750±10°C to 840±10°C and kept warm for 2 hours; after each forging, it is water-cooled; and a Φ80mm forging blank after stretch forging is obtained.

6. The method for preparing fine-grained Ti-5Al-5V-5Mo-3Cr titanium alloy wire for fasteners according to claim 1, characterized in that: In step 4, the radial forging temperature zone is 750±10°C to 840±10°C.

7. The method for preparing fine-grained Ti-5Al-5V-5Mo-3Cr titanium alloy wire for fasteners according to claim 1, characterized in that: In step 5, the hot rolling temperature range is 720±10°C to 835±10°C.

8. The method for preparing fine-grained Ti-5Al-5V-5Mo-3Cr titanium alloy wire for fasteners according to claim 1, characterized in that: When the wire is cold rolled in step 6, the wire blank is sequentially placed in the holes of each roller in the longitudinal rolling mill for multiple continuous cold rolling to obtain a cold-rolled Ti-5553 titanium alloy wire; the holes of each roller have different apertures.

9. The method for preparing fine-grained Ti-5Al-5V-5Mo-3Cr titanium alloy wire for fasteners according to claim 1, characterized in that: The solution treatment temperature is 820℃±10℃; the solution treatment time is 30min.

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