TC16 titanium alloy for cold heading fastener and preparation method of large-piece-weight disc round wire

Abstract

The invention belongs to the technical field of titanium alloy wire rolling, and particularly relates to a TC16 titanium alloy for a cold heading fastener and a preparation method of a large-piece-weight disc round wire, and the TC16 titanium alloy comprises the following components in percentage by mass: less than or equal to 0.008% of C, less than or equal to 0.005% of N, less than or equal to 0.005% of H, less than or equal to 0.06% of O, less than or equal to 0.03% of Si, 3.0%-3.75% of Al, 4.0%-4.8% of V, 5.0%-5.4% of Mo, less than or equal to 0.02% of Fe and the balance of Ti and inevitable impurities. According to the preparation method, the TC16 titanium alloy is selected, the large-piece-weight wire rod with the uniform and refined structure and high performance stability is obtained after preparation, and the large-piece-weight wire rod is not cracked after continuous large-deformation cold heading.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium alloy wire rolling, and in particular relates to a preparation method of TC16 titanium alloy and large single weight round wire for cold heading fasteners. Background Art

[0002] TC16 titanium alloy has a nominal composition of Ti-3Al-5Mo-4.5V and a β stability coefficient of 0.83. Compared with TC4 alloy (β stability coefficient 0.27), it has better hardenability and can be used to manufacture larger specifications of fasteners.

[0003] Traditional TC16 titanium alloy adds interstitial elements such as O, C, N and impurity Fe elements to improve strength. However, interstitial elements such as O, C, N will significantly reduce the plasticity and cold formability of TC16 titanium alloy, which is one of the main reasons for the cold heading deformation and cracking of TC16 rods and wires. In order to obtain TC16 titanium alloy rods and wires with stable microstructure and properties for cold heading fasteners, the present invention innovatively designs low-interstitial TC16 titanium alloy.

[0004] There is little systematic research on the chemical composition of TC16 titanium alloy for cold heading fasteners, the microstructure regulation and performance stability control of large unit weight wire, and the matching technology of cold heading performance of fasteners and rod and wire performance in my country. The main research directions include annealing system, solution aging, cold deformation strengthening of TC16 alloy, the influence of TC16 alloy microstructure and deformation behavior, the relationship between TC16 alloy microstructure and dynamic compression deformation behavior, and the preparation of small unit weight rod and wire for hot heading and cold heading fasteners.

[0005] The microstructure of TC16 titanium alloy rod and wire after annealing depends not only on the heat treatment system of the finished product, but also on the original microstructure after continuous rolling and drawing. In the early days, the construction of continuous rolling production lines suitable for rolling large single-weight billets of titanium alloys in China was insufficient, and high-speed wire mills in the steel industry were often used to continuously roll titanium alloy billets. The unreasonable deformation design of high-speed wire mills in the steel industry for rolling titanium alloys and the excessively fast exit speed of the final rolling stand led to the increase in the core temperature of the continuous rolling billet, the enlargement of the α phase size, and the dissolution problem. Through the subsequent drawing and heat treatment to control the microstructure, subject to the specifications of the TC16 finished rod and wire, the difference in the microstructure of the edge and the center cannot be completely eliminated, which leads to the problem of inconsistent deformation of the fasteners and poor roundness of the rivet head. Therefore, designing a continuous rolling production line suitable for titanium and titanium alloys and controlling the pass type, pass deformation amount, and deformation temperature of each stand of the continuous rolling mill are the key to obtaining large single-weight round wires with fine and uniform microstructure and stable performance. There are also methods for preparing TC16 titanium alloy large single weight round wire, but there are still problems such as difficulty in controlling ultrafine grain structure, difficulty in controlling the performance stability of large single weight wire, local cracking during the upsetting process of fasteners, and poor roundness of rivet heads.

[0006] In view of this, the present invention is proposed. Summary of the invention

[0007] The object of the present invention is to overcome the above-mentioned shortcomings of the prior art and to provide a method for preparing TC16 titanium alloy and large single weight round wire for cold heading fasteners.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions: On the one hand, the present invention provides a low-clearance TC16 titanium alloy for cold heading fasteners, which is composed of the following components in mass percentage: C ≤0.008%, N ≤0.005%, H ≤0.005%, O ≤0.06%, Si ≤0.03%, Al 3.0%~3.75%, V 4.0%~4.8%, Mo 5.0%~5.4%, Fe ≤0.02%, and the balance is Ti and unavoidable impurities.

[0009] Optionally, it is composed of the following components in mass percentage: C ≤0.006%, N ≤0.003%, H ≤0.005%, O≤0.06%, Si ≤0.03%, Al 3.1%~3.6%, V 4.3%~4.8%, Mo 5.0%~5.4%, Fe ≤0.02%, and the balance is Ti and unavoidable impurities.

[0010] Optionally, it is composed of the following components in mass percentage: C ≤0.005%, N ≤0.003%, H ≤0.003%, O≤0.05%, Si ≤0.03%, Al 3.2%~3.75%, V 4.3%~4.8%, Mo 5.0%~5.4%, Fe ≤0.02%, and the balance is Ti and unavoidable impurities.

[0011] Specifically, the above raw materials are processed into low-gap TC16 titanium alloy through an existing smelting process. The low-gap TC16 titanium alloy can be ingots, billets, bars, plates, etc.

[0012] On the other hand, the present invention provides a method for preparing a low-gap TC16 titanium alloy large single weight round wire for cold heading fasteners, based on the low-gap TC16 titanium alloy for cold heading fasteners as described above, comprising the following steps: Step 1, selecting low-gap TC16 titanium alloy bar billet as continuous rolling billet; Step 2, heating and keeping the continuous rolling billet in step 1 in a heating furnace, and then rolling and annealing the billet using a rod and wire continuous rolling mill to obtain a continuous rolling wire billet; Step 3, pre-treating the continuous rolled wire blank in step 2, and then performing eddy current flaw detection, and after removing surface defects, preparing finished wire by roller die cold drawing combined with intermediate annealing; Step 4, heat treating the finished wire prepared in step 3 to obtain an annealed large single weight round wire; Step 5: pretreat the large single weight round wire obtained in step 4, and then coat it with a lubricating coating to obtain the target large single weight round wire.

[0013] In step 1, the selected bar blank (low interstitial TC16 titanium alloy bar blank) has preferred main elements and ultra-low interstitial elements and impurity elements, and the bar blank has a uniform and fine two-phase equiaxial structure in the horizontal and vertical directions. The bar blank is an annealed bar blank of Φ85mm~Φ100mm.

[0014] Further, in step 2, the heating and heat preservation process is as follows: First, the continuous rolling billet is placed in a heating furnace at 800°C to 820°C for 1 hour for preheating, and then the continuous rolling billet is heated to 30°C to 110°C above the β-transformation temperature at a heating rate of 1 to 2°C / min, and then kept at this temperature for 30min to 40min to allow the continuous rolling billet to be completely heated through; The cumulative rolling deformation of the bar and wire continuous rolling mill group is 97.48%~98.56%.

[0015] Further, in step 2, the bar and wire continuous rolling mill group includes a roughing mill group and a finishing mill group; specifically, the bar and wire continuous rolling mill group is a bar and wire continuous rolling mill group with 20 or 22 stands arranged horizontally, of which the first 6 stands are roughing mill groups and the last 14 or 16 stands are finishing mill groups.

[0016] The rolling process is as follows: the heated and heat-insulated continuous rolling billet is rolled in the rough rolling mill, the initial rolling temperature is controlled to be ≥820°C, the final rolling temperature is controlled to be 750°C to 820°C, and the average elongation coefficient of the rough rolling mill is 1.20 to 1.25, that is, the average elongation coefficient of the first 6 rolling mills is 1.20 to 1.25; After the rough rolling mill is finished, the rolling mill enters the finishing mill for rolling. The average elongation coefficient of the finishing mill is 1.18-1.23, that is, the average elongation coefficient of the last 14 or 16 rolling mills is 1.18-1.23, and the final rolling temperature is 730°C-785°C; The annealing temperature is 750℃~820℃.

[0017] In step 2, the continuous rolled billet is first preheated at 800°C~820°C for 1h, and then gradually heated to 30°C~110°C above the β transformation temperature, which is beneficial to eliminate the residual stress of the continuous rolled billet and avoid premature recrystallization of β grains, ultimately making the β annealing recrystallization structure of the continuous rolled billet more uniform.

[0018] Furthermore, the rolling is near-β rolling or cross-phase rolling. Specifically, the initial temperature is set to ≥820°C so that an ultra-fine near-equiaxed structure of fine basket structure → elongated / crushed spheroidized α phase layers is formed successively between subsequent stands, which is beneficial to making the grains and initial α phase of the continuous rolled wire billet prepared in step 2 finer.

[0019] Furthermore, in step 2, the heating furnace is a walking-beam or box-type resistance heating furnace, which can continuously heat the continuously rolled billet and achieve the effect of rapid and uniform heating.

[0020] Furthermore, the rough rolling mill set is of flat ellipse-round hole type, and the finishing rolling mill set is of ellipse-round hole type.

[0021] It should be noted that the rough rolling mill adopts a flat elliptical-round hole type, which is more conducive to uniform deformation of larger-sized billets and greatly reduces the "deformation dead zone" compared with the flat-square hole type and the elliptical-round hole type. The finishing mill adopts an elliptical-round hole type, which has more advantages in controlling the surface quality and roundness of smaller-sized wire billets or continuous rolling billets than flat-square hole types and flat elliptical-round hole types; in addition, it has the characteristics of more uniform and sufficient deformation compared with the same-shaped hole type. The flat elliptical-round hole type is used for the first 6 rolling mills, combined with the elliptical-round hole type for the last 14 or 16 rolling mills, which can fully ensure the uniformity of deformation of the continuous rolling wire billet and make it have good surface quality.

[0022] Furthermore, in step 3, the pretreatment includes peeling and polishing the continuous rolled wire billet in sequence, and controlling the surface roughness of the continuous rolled wire billet to ≤1.6 μm; A horizontal-vertical two-joint roller die is used for cold drawing, and the roller die cold drawing process is divided into a first stage and a second stage; in the first stage, when the cumulative deformation of the pre-treated continuous rolled wire billet after cold drawing is 55.17%~68.05%, intermediate vacuum annealing is performed, and the second stage is entered after the annealing is completed; in the second stage, the roller die cold drawing is continued until the cumulative deformation is 34.33%~39.64%, and the finished wire is obtained.

[0023] Furthermore, in the first stage of roller die cold drawing, the deformation of the last drawing pass is set to 12.89%~17.36%, and the deformation of the remaining drawing passes is 23.05%~28.74%. The intermediate vacuum annealing includes keeping warm at 780℃~840℃ in a vacuum furnace for 60min~120min.

[0024] It should be noted that the innovative vacuum annealing in the middle of cold deformation can effectively utilize the recrystallization of the α phase to make the longitudinal structure equiaxial, while further refining and homogenizing the transverse and longitudinal lamellae and grains.

[0025] The last drawing pass has the function of rounding and shaping the continuous rolled wire billet. When the cold drawing deformation is large, it is easy to cause the surface roundness and flatness of the continuous rolled wire billet to decrease. Therefore, the deformation of this pass is set to be smaller than that of the other passes.

[0026] Furthermore, in step 4, the heat treatment includes controlling the annealing temperature to 740°C to 790°C, the holding time to 1.5h to 2.5h, furnace cooling to 600°C and then air cooling.

[0027] Furthermore, in step 5, the pretreatment includes sequentially performing peeling, sandblasting, cleaning and phosphating treatment on the large single weight round wire to obtain a large single weight round wire with a uniform phosphating film layer.

[0028] Specifically, the large single-weight round wire is peeled to remove the surface oxide scale, and then a 320-mesh brown corundum (Al 2 O 3 ) Sand blasting, and then washing with deionized water. After washing, the large single weight round wire is placed in a tank containing phosphating solution. The phosphating temperature is 30℃~40℃, and the phosphating time is 10min~30min to obtain a large single weight round wire with a uniform phosphating film layer. Finally, a wire coating machine is used to coat the large single weight round wire with a lubricating coating. After coating, it is cured at 120℃~150℃. After curing, the preparation is completed.

[0029] Specifically, the ratio of the phosphating solution is: sodium phosphate 55g / L, sodium fluoride 28g / L, oxalic acid 8.5g / L, 40% HF 6g / L, and deionized water 1L.

[0030] Specifically, the coating ratio is: WS 2 Powder 32g, sodium silicate 12g, silica sol 5g, deionized water 70g, surfactant 0.2g, defoamer 0.1g, antimony trioxide 0.3g.

[0031] The large single-weight round wire prepared by the present invention has a weight of 100kg to 180kg.

[0032] On the other hand, the present invention provides an application of a low-gap TC16 titanium alloy large single weight round wire. The large single weight round wire prepared by the preparation method as described above is applied to cold heading and hot heading fasteners.

[0033] Compared with the prior art, the present invention has the following beneficial effects: 1) The present invention provides a low-interstitial TC16 titanium alloy for cold heading fasteners. By designing low-interstitial ingredients and combining the existing high-purity smelting process, a TC16 titanium alloy with ultra-low interstitial impurity elements with uniform organizational composition is obtained. Specifically, low contents of interstitial elements such as O, C, and N are added, and the contents of Al, V, and Mo elements are adjusted at the same time to ensure that the strength of the alloy meets the design and standard requirements, and the room temperature cold heading plasticity and cold formability are good.

[0034] 2) The present invention provides a method for preparing a low-gap TC16 titanium alloy large single-weight round wire for cold heading fasteners, which adopts a proprietary titanium alloy continuous rolling production line, and then controls the structure, heating temperature, rough rolling unit outlet temperature, initial rolling temperature and other parameters of the continuous rolling billet through production line layout and hole design, and pass deformation, so as to obtain a continuous rolling wire billet with ultrafine grains and equiaxial structure in the transverse and longitudinal directions; in addition, the structure is further refined through roller die cold drawing, and the intermediate annealing is matched to make the longitudinal structure equiaxial. At the same time, through the cumulative deformation, the last annealing deformation, and the intermediate annealing temperature matching design, the wire structure after efficient cold drawing is uniformly refined and the performance stability is high, which solves the problem of high cracking tendency in the later continuous large deformation cold heading.

[0035] 3) The present invention provides a method for preparing a low-gap TC16 titanium alloy large single-weight round wire for cold heading fasteners, which increases the specific surface area of ​​polishing after peeling by sandblasting, adds a bridge phosphating film layer after phosphating, and uses WS 2 The coating has high temperature resistance and can be used for short-time hot upsetting. The coating and pretreatment solution solve the problem of easy coating shedding and die jamming during continuous cold upsetting of TC16 large single weight round wire. At the same time, it can also adapt to the future requirements for unified standards of raw materials for cold upsetting and hot upsetting. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings are incorporated in and constitute a part of this specification and, together with the description, serve to explain the principles of the present invention.

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0038] Figure 1 is a flow chart of the preparation method of the present invention; Figure 2 This is a 2000x SEM photograph of the continuous rolling billet at the transverse position R / 2 of the present invention; Figure 3 This is a 2000x SEM photograph of the continuous rolling billet at R / 2 in the longitudinal direction of the present invention; Figure 4 This is a 2000x SEM photograph of the continuous rolled wire billet at the transverse position R / 2 of the present invention; Figure 5 This is a 2000x SEM photograph of the longitudinal R / 2 position of the continuous rolled wire billet of the present invention; Figure 6 This is a transverse ×2000x SEM photograph of the annealed state of the TC16 finished wire prepared by the present invention; Figure 7 This is a longitudinal ×2000x SEM photograph of the annealed TC16 finished wire prepared by the present invention; Figure 8 This is a 2500× SEM photograph of the phosphate coating on the surface of the TC16 large single-weight round wire prepared by the present invention. DETAILED DESCRIPTION

[0039] Here, exemplary embodiments will be described in detail, and the embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Instead, they are only examples consistent with some aspects of the present invention described in detail in the appended claims.

[0040] On the one hand, the present invention provides a low-clearance TC16 titanium alloy for cold heading fasteners, which is composed of the following components in mass percentage: C ≤0.008%, N ≤0.005%, H ≤0.005%, O ≤0.06%, Si ≤0.03%, Al 3.0%~3.75%, V 4.0%~4.8%, Mo 5.0%~5.4%, Fe ≤0.02%, and the balance is Ti and unavoidable impurities.

[0041] On the other hand, Figure 1 As shown, the present invention provides a method for preparing a low-gap TC16 titanium alloy large single weight round wire for cold heading fasteners, comprising the following steps: Step 1: Continuous rolling billet: Select low-gap TC16 titanium alloy billet as the continuous rolling billet, specifically Φ85mm~Φ100mm annealed billet, the billet is transversely ( Figure 2 )、Vertical( Figure 3 ) is a uniform and fine equiaxed structure; the rod blank is a low-gap TC16 titanium alloy in this embodiment; Step 2, heating and continuous rolling, annealing: heating and keeping the continuous rolling billet in step 1 in a heating furnace, and then rolling and annealing with a rod and wire continuous rolling mill to obtain a continuous rolled wire billet; Specifically, the continuous rolling billet is placed in a walking beam or box-type resistance heating furnace at 800℃~820℃ for 1h for preheating, and then the billet is heated to 30℃~110℃ above the β transformation temperature at a heating rate of 1~2℃ / min, and then kept warm for 30min~40min; a 20-rack or 22-rack horizontal and vertical continuous rolling mill for bars and wires is used, of which the first 6 racks are rough rolling mills, and a flat elliptical-round hole type is selected, with an average elongation coefficient of 1.20~1.25, starting The rolling temperature is ≥820℃, the outlet temperature of the first 6 rolling mills (temperature after rough rolling) is 750℃~820℃, the last 14 or 16 rolling mills are finishing mills, and the elliptical-round hole type is selected, the average elongation coefficient is 1.18~1.23, the final rolling temperature is 730℃~785℃, the cumulative deformation is 97.48%~98.56%, and the continuous rolling wire billet is obtained; the continuous rolling wire billet is placed in an annealing furnace and annealed at 750℃~820℃ to obtain the annealed continuous rolling wire billet transverse ( Figure 4 )、Vertical( Figure 5 ) are all ultrafine-grained equiaxed structures; Step 3, roller die cold drawing combined with intermediate annealing: pre-treat the continuous rolled wire billet in step 2, then perform eddy current flaw detection, and after removing surface defects (cold drawing has high requirements on the surface structure of the continuous rolled wire billet, so surface defects must be removed for subsequent cold drawing operations), use roller die cold drawing combined with intermediate annealing to prepare finished wire; Specifically, the continuous rolled wire billet is stripped by a centerless lathe to remove 0.5 mm of skin, polished with a sanding belt to a surface roughness of ≤1.6 μm, and then cold-drawn by a flat-vertical two-pass roller die after eddy current flaw detection to remove surface defects. The deformation of the last drawing pass is 12.89%~17.36%, and the deformation of the remaining drawing passes is 23.05%~28.74%. The cumulative deformation of the wire in the first stage of cold drawing is 55.17%~68.05%, and then a vacuum furnace is used for intermediate annealing at 780℃~840℃ for 60min~120min; after annealing, the cumulative deformation of cold drawing by a flat-vertical two-pass roller die is 34.33%~39.64%; Step 4, heat treatment of finished product: heat treatment of the finished wire prepared in step 3 to obtain an annealed large single weight round wire; Specifically, the annealing temperature of the finished wire is 740°C~790°C, the holding time is 1.5h~2.5h, the furnace is cooled to 600°C and then air-cooled; Step 5, pretreatment of the surface of the large single weight round wire and coating of a lubricating coating: the large single weight round wire obtained in step 4 is pretreated, and then coated with a lubricating coating to obtain the target large single weight round wire.

[0042] The pretreatment includes sequentially peeling, sandblasting, cleaning and phosphating the large single weight round wire to obtain a large single weight round wire with a uniform phosphating film layer.

[0043] Specifically, the large single weight round wire is first peeled off by 0.05 mm to remove the surface oxide scale, and then sandblasted with 320 mesh brown corundum sand by a sandblasting machine. After sandblasting, it is washed with deionized water. After washing, the large single weight round wire is placed in a tank containing a phosphating solution. The phosphating temperature is 30°C~40°C, and the phosphating time is 10min~30min to obtain a large single weight round wire with a uniform phosphating film layer. Finally, a wire coating machine is used to coat the large single weight round wire with a lubricating coating. After coating, it is cured at 120°C~150°C. After curing, a large single weight round wire with a coating is obtained.

[0044] In this embodiment, the ratio of the phosphating solution is: 55 g / L sodium phosphate, 28 g / L sodium fluoride, 8.5 g / L oxalic acid, 6 g / L 40% HF, and 1 L of deionized water.

[0045] In this embodiment, the coating ratio is: WS 2 Powder 32g, sodium silicate 12g, silica sol 5g, deionized water 70g, surfactant 0.2g, defoamer 0.1g, antimony trioxide 0.3g.

[0046] Figure 6 This is a transverse ×2000 SEM photo of the annealed TC16 finished wire prepared by the present invention. Figure 7 This is a longitudinal ×2000 SEM photo of the annealed TC16 finished wire prepared by the present invention. Figure 6 , Figure 7 It can be seen that the TC16 large single weight round wire prepared by the present invention has a uniform and fine structure, and an equiaxial structure in both the transverse and longitudinal directions. Figure 8 This is a 2500x SEM photograph of the phosphate film of the TC16 large single-weight round wire prepared by the present invention, and it can be seen that the phosphate film is well crystallized.

[0047] On the other hand, the present invention provides an application of a low-gap TC16 titanium alloy large single weight round wire. The large single weight round wire prepared by the preparation method as described above is applied to cold heading and hot heading fasteners. Example 1

[0048] This embodiment provides a method for preparing a low-gap TC16 titanium alloy large single-weight round wire for cold heading fasteners, comprising the following steps: Step 1, continuous rolling billet: select low gap TC16 titanium alloy bar billet as continuous rolling billet, specifically Φ85mm annealed bar billet, the bar billet β transformation temperature is 850℃, the bar billet has uniform and fine equiaxed structure in the transverse and longitudinal directions; the bar billet is composed of the following components in mass percentage: C ≤0.008%, N ≤0.005%, H ≤0.005%, O ≤0.06%, Si ≤0.03%, Al3.0%~3.75%, V 4.0%~4.8%, Mo 5.0%~5.4%, Fe ≤0.02%, and the balance is Ti and unavoidable impurities; the weight percentage (average value) of the gap and impurity elements of the bar billet is: C 0.005 wt%, N<0.003 wt%, H 0.0008wt%, O 0.047 wt%, Si 0.025 wt%; Step 2, heating and continuous rolling, annealing: the continuous rolling billet of step 1 is placed in a walking beam heating furnace at 800°C for 1h for preheating, and then the continuous rolling billet is heated to 880°C at an average heating rate of 1°C / min, and then kept warm for 30min, and a 20-stand horizontal and vertical bar and wire continuous rolling mill is used, wherein the first 6 stands are rough rolling mills, and a flat elliptical-round hole type is selected, the average elongation coefficient is 1.25, and the initial rolling temperature is ≥820°C. The outlet temperature of the first 6 rolling mills (temperature after rough rolling) is 750°C~790°C, and the last 14 stands are finishing mills, and an elliptical-round hole type is selected, the average elongation coefficient is 1.18, the final rolling temperature is 730°C~765°C, and the cumulative deformation is 97.48%, and a hot-processed Φ13.5mm continuous rolling wire billet is obtained; the continuous rolling wire billet is placed in an annealing furnace, and annealed at 750°C / 120min to obtain an annealed continuous rolling wire billet; Step 3, roller die cold drawing combined with intermediate annealing: pre-treat the continuous rolled wire blank in step 2, and then perform eddy current flaw detection. After removing surface defects, roller die cold drawing combined with intermediate annealing is used to prepare the finished wire; Specifically, the continuous rolled wire billet is stripped by a centerless lathe to remove 0.5mm of skin, polished with a sanding belt to a surface roughness of ≤1.6μm, and after eddy current flaw detection to remove surface defects, it is cold-drawn with a flat-vertical two-joint roller die, and the diameter is reduced by drawing for 5 passes. The deformation of the first 4 passes is 23.05%~25.68%, and the deformation of the 5th pass is 12.89%. In the first stage, the wire is cold-drawn to Φ8.7mm, and the cumulative deformation is 55.21%. It is annealed in a vacuum furnace at 840℃ / 60min; after annealing, it is continued to be cold-drawn to Φ7.05mm with a flat-vertical two-joint roller die, and the cumulative deformation is 34.33%; Step 4, heat treatment of finished product: heat treatment of the finished wire prepared in step 3 to obtain an annealed large single weight round wire; Specifically, the annealing temperature is 790°C, the holding time is 1.5 h, the furnace is cooled to 600°C and then air-cooled; Step 5, surface pretreatment of large single-weight round wire and coating of lubricating coating: the large single-weight round wire obtained in step 4 is first peeled off by 0.05 mm to remove the surface oxide scale, and then sandblasted with 320-mesh brown corundum sand by a sandblasting machine. After sandblasting, it is washed with deionized water. After washing, the large single-weight round wire is placed in a tank containing phosphating solution. The phosphating temperature is 30°C and the phosphating time is 30 minutes to obtain a large single-weight round wire with a uniform phosphating film layer. Finally, a wire coating machine is used to coat the large single-weight round wire with a lubricating coating. After coating, it is cured at 120°C. After curing, the preparation is completed to obtain a Φ7.0 mm coated large single-weight round wire. Example 2

[0049] This embodiment provides a method for preparing a low-gap TC16 titanium alloy large single-weight round wire for cold heading fasteners, comprising the following steps: Step 1, continuous rolling billet: select low gap TC16 titanium alloy bar billet as continuous rolling billet, specifically Φ90mm annealed bar billet, the bar billet β transformation temperature is 860℃, the bar billet has uniform and fine equiaxed structure in transverse and longitudinal directions; the bar billet is composed of the following components in mass percentage: C ≤0.006%, N ≤0.003%, H ≤0.005%, O ≤0.06%, Si ≤0.03%, Al 3.1%~3.6%, V 4.3%~4.8%, Mo 5.0%~5.4%, Fe ≤0.02%, and the balance is Ti and unavoidable impurities; Step 2, heating and continuous rolling, annealing: the continuous rolling billet of step 1 is placed in a walking beam heating furnace at 810°C for 1h for preheating, and then the continuous rolling billet is heated to 930°C at an average heating rate of 1.5°C / min, and then kept warm for 35min; a 22-stand horizontal and vertical bar and wire continuous rolling mill is used, of which the first 6 stands are rough rolling mills, a flat elliptical-round hole type is selected, the average elongation coefficient is 1.20~1.23, and the starting rolling temperature is ≥84 0℃, the outlet temperature of the first 6 rolling mills (temperature after rough rolling) is 770℃~800℃, the last 16 rolling mills are finishing mills, an elliptical-round hole type is selected, the average elongation coefficient is 1.19~1.23, the final rolling temperature is 740℃~785℃, the cumulative deformation is 98.22%, and a hot-processed Φ12mm continuous rolling wire billet is obtained; the continuous rolling wire billet is placed in an annealing furnace and annealed at 780℃ / 100min to obtain an annealed continuous rolling wire billet; Step 3, roller die cold drawing combined with intermediate annealing: pre-treat the continuous rolled wire blank in step 2, and then perform eddy current flaw detection. After removing surface defects, roller die cold drawing combined with intermediate annealing is used to prepare the finished wire; Specifically, the continuous rolled wire billet is stripped by a centerless lathe to remove 0.5mm of skin, polished with a sanding belt to a surface roughness of ≤1.6μm, and inspected by eddy current flaw detection to remove surface defects. It is then cold-drawn with a flat-vertical two-pass roller die, and the diameter is reduced by drawing for 5 passes. The deformation of the first 4 passes is 23.44%~28.74%, and the deformation of the 5th pass is 14.79%. In the first stage, the wire is cold-drawn to Φ7.7mm, and the cumulative deformation is 55.17%. It is annealed in a vacuum furnace at 810℃ / 60min. After annealing, it is continuously cold-drawn with a flat-vertical two-pass roller die to Φ6.05mm, and the cumulative deformation is 38.27%. Step 4: Heat treatment of finished product: heat treatment of the finished wire prepared in step 3 to obtain annealed large single-weight round wire Specifically, the annealing temperature is 780°C, the holding time is 2h, the furnace is cooled to 600°C and then air-cooled; Step 5, surface pretreatment of large single-weight round wire and coating of lubricating coating: the large single-weight round wire obtained in step 4 is first peeled off by 0.05 mm to remove the surface oxide scale, and then sandblasted with 320-mesh brown corundum sand by a sandblasting machine. After sandblasting, it is washed with deionized water. After washing, the large single-weight round wire is placed in a tank containing phosphating solution. The phosphating temperature is 35°C and the phosphating time is 20 minutes to obtain a large single-weight round wire with a uniform phosphating film layer. Finally, the large single-weight round wire is coated with a lubricating coating by a wire coating machine. After coating, it is cured at 130°C. After curing, the preparation is completed to obtain a Φ6.0 mm coated large single-weight round wire. Example 3

[0050] This embodiment provides a method for preparing a low-gap TC16 titanium alloy large single-weight round wire for cold heading fasteners, comprising the following steps: Step 1, continuous rolling billet: select low gap TC16 titanium alloy bar billet as continuous rolling billet, specifically Φ100mm annealed bar billet, the bar billet β transformation temperature is 860℃, the bar billet has uniform and fine equiaxed structure in transverse and longitudinal directions; the bar billet is composed of the following components in mass percentage: C ≤0.005%, N ≤0.003%, H ≤0.003%, O ≤0.05%, Si ≤0.03%, Al 3.2%~3.75%, V 4.3%~4.8%, Mo 5.0%~5.4%, Fe ≤0.02%, and the balance is Ti and unavoidable impurities; Step 2, heating and continuous rolling, annealing: the continuous rolling billet of step 1 is placed in a walking beam heating furnace at 820°C for 1h for preheating, and then the continuous rolling billet is heated to 970°C at an average heating rate of 2°C / min, and then kept warm for 40min; a 22-stand horizontal and vertical bar and wire continuous rolling mill is used, of which the first 6 stands are rough rolling mills, a flat elliptical-round hole type is selected, the average elongation coefficient is 1.20~1.23, and the starting rolling temperature is ≥860 ℃, the outlet temperature of the first 6 rolling mills (temperature after rough rolling) is 790℃~820℃, the last 16 rolling mills are finishing mills, an elliptical-round hole type is selected, the average elongation coefficient is 1.19~1.23, the final rolling temperature is 740℃~785℃, the cumulative deformation is 98.56%, and a hot-processed Φ12mm continuous rolling wire billet is obtained; the continuous rolling wire billet is placed in an annealing furnace and annealed at 820℃ / 60min to obtain an annealed continuous rolling wire billet; Step 3, roller die cold drawing combined with intermediate annealing: pre-treat the continuous rolled wire blank in step 2, and then perform eddy current flaw detection. After removing surface defects, roller die cold drawing combined with intermediate annealing is used to prepare the finished wire; Specifically, the continuous rolled wire billet is stripped by a centerless lathe to remove 0.5mm of skin, polished with a sanding belt to a surface roughness of ≤1.6μm, and after eddy current flaw detection to remove surface defects, it is cold-drawn with a flat-vertical two-joint roller die, and the diameter reduction drawing is performed for 5 passes. The deformation of the first 4 passes is 23.44%~28.74%, and the deformation of the 5th pass is 17.36%. In the first stage, the wire is cold-drawn to Φ6.5mm, and the cumulative deformation is 68.05%. It is annealed in a vacuum furnace at 780℃ / 60min; after annealing, it is continuously cold-drawn to Φ5.05mm with a flat-vertical two-joint roller die, and the cumulative deformation is 39.64%. Step 4, heat treatment of finished product: heat treatment of the finished wire prepared in step 3 to obtain an annealed large single weight round wire; Specifically, the annealing temperature is 740°C, the holding time is 2.5 h, the furnace is cooled to 600°C and then air-cooled; Step 5, surface pretreatment of large single-weight round wire and coating of lubricating coating: the large single-weight round wire obtained in step 4 is first peeled off by 0.05 mm to remove the surface oxide scale, and then sandblasted with 320-mesh brown corundum sand by a sandblasting machine. After sandblasting, it is washed with deionized water. After washing, the large single-weight round wire is placed in a tank containing phosphating solution. The phosphating temperature is 40°C and the phosphating time is 10 minutes to obtain a large single-weight round wire with a uniform phosphating film layer. Finally, a wire coating machine is used to coat the large single-weight round wire with a lubricating coating. After coating, it is cured at 150°C. After curing, the preparation is completed to obtain a Φ5.0 mm coated large single-weight round wire.

[0051] In order to prove the efficacy of the present invention, the present invention has done the following tests: The room temperature tensile properties of the heads and tails of the annealed finished wires and solution-aged wire samples (solution: 800°C / 120min, water cooling; aging: 540°C / 600min, air cooling) prepared in Examples 1 to 3 were tested according to GB / T 228.1-2015, and the shear strength of the solution-aged wire samples was tested according to GJB 715.26A. The results are shown in Table 1.

[0052] Table 1 Test results of Example 1 to Example 3

[0053] Depend on Figure 6 , Figure 7 As can be seen from Table 1, the mechanical properties and organization of the TC16 heavy single-weight round wire prepared by the present invention meet the requirements of the corresponding standards, and no upsetting cracks are observed in the fasteners after continuous large deformation cold upsetting. Comparative Example 1

[0054] This comparative example and Example 1 use the same process route and parameters, except for the contents of interstitial elements and impurity elements in the selected rod blank in step 1. Specifically, the weight percentages (average values) of interstitial and impurity elements in the rod blank in this comparative example are: C 0.008 wt%, N 0.003 wt%, H 0.0013 wt%, O 0.090 wt%, and Si 0.052 wt%. Comparative Example 2

[0055] This comparative example and Example 1 use the same process route and parameters, except for the contents of interstitial elements and impurity elements in the selected rod blank in step 1. Specifically, the weight percentages (average values) of interstitial and impurity elements in the rod blank in this comparative example are: C 0.013 wt%, N 0.004 wt%, H 0.0026 wt%, O 0.066 wt%, and Si 0.047 wt%.

[0056] In order to verify the efficacy of the present invention, the present invention conducted cold forming tests on the large single weight round wire prepared in Example 1, Comparative Example 1 and Comparative Example 2. The test results are shown in Table 2.

[0057] Table 2 Cold forming test results of Example 1, Comparative Example 1 and Comparative Example 2

[0058] It can be seen from Table 2 that the low gap strategy of the present invention can avoid cold heading cracking.

[0059] Comparative Example 3 The difference between this comparative example and Example 1 is that the preparation method of this comparative example lacks intermediate annealing treatment in step 3.

[0060] In order to verify the efficacy of the present invention, the present invention conducted mechanical property and cold heading forming property tests on the large single weight round wire prepared in Example 1 and Comparative Example 3. The test results are shown in Table 3.

[0061] Table 3 Test results of mechanical properties and cold heading properties

[0062] It can be seen from Table 3 that the roller die cold drawing combined with intermediate annealing method of the present invention can further improve the cold deformation plasticity and avoid cold heading cracking without significantly reducing the strength of the wire.

[0063] The above description is only a specific embodiment of the present invention, so that those skilled in the art can understand or implement the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention.

[0064] It should be understood that the present invention is not limited to what has been described above and that various modifications and changes may be made without departing from its scope. The scope of the present invention is limited only by the appended claims.

Claims

1. A low clearance TC16 titanium alloy for cold heading fasteners, characterized in that: It is composed of the following components in mass percentage: C ≤0.008%, N ≤0.005%, H ≤0.005%, O ≤0.06%, Si ≤0.03%, Al 3.0%~3.75%, V 4.0%~4.8%, Mo 5.0%~5.4%, Fe ≤0.02%, and the balance is Ti and unavoidable impurities.

2. A method for preparing low-gap TC16 titanium alloy large single weight round wire for cold heading fasteners, characterized in that: The low-clearance TC16 titanium alloy for cold heading fasteners according to claim 1 comprises the following steps: Step 1, selecting low-gap TC16 titanium alloy bar billet as continuous rolling billet; Step 2, heating and keeping the continuous rolling billet in step 1 in a heating furnace, and then rolling and annealing the billet using a rod and wire continuous rolling mill to obtain a continuous rolling wire billet; Step 3, pre-treating the continuous rolled wire blank in step 2, and then performing eddy current flaw detection, and after removing surface defects, preparing finished wire by roller die cold drawing combined with intermediate annealing; Step 4, heat treating the finished wire prepared in step 3 to obtain an annealed large single weight round wire; Step 5: pretreat the large single weight round wire obtained in step 4, and then coat it with a lubricating coating to obtain the target large single weight round wire.

3. The method for preparing the low-gap TC16 titanium alloy large single-weight round wire for cold heading fasteners according to claim 2, characterized in that: In step 2, the heating and heat preservation process is as follows: First, the continuous rolling billet is placed in a heating furnace at 800°C to 820°C for 1 hour for preheating, and then the continuous rolling billet is heated to 30°C to 110°C above the β-transformation temperature at a heating rate of 1 to 2°C / min, and then kept warm for 30min to 40min; The cumulative rolling deformation of the bar and wire continuous rolling mill group is 97.48%~98.56%.

4. The method for preparing the low-gap TC16 titanium alloy large single-weight round wire for cold heading fasteners according to claim 2, characterized in that: In step 2, the bar and wire continuous rolling mill group includes a roughing mill group and a finishing mill group; The rolling process is as follows: the heated and heat-insulated continuous rolling billet is rolled in the rough rolling mill, the initial rolling temperature is controlled to be ≥820°C, the final rolling temperature is controlled to be 750°C to 820°C, and the average elongation coefficient of the rough rolling mill is controlled to be 1.20 to 1.25; After the rough rolling unit is finished, the product enters the finishing rolling unit for rolling, wherein the average elongation coefficient of the finishing rolling unit is 1.18-1.23, and the final rolling temperature is 730°C-785°C; The annealing temperature is 750℃~820℃.

5. The method for preparing the low-gap TC16 titanium alloy large single-weight round wire for cold heading fasteners according to claim 4, characterized in that: The rough rolling mill set is of flat ellipse-round hole type, and the finishing rolling mill set is of ellipse-round hole type.

6. The method for preparing the low-gap TC16 titanium alloy large single-weight round wire for cold heading fasteners according to claim 2, characterized in that: In step 3, the pretreatment includes sequentially peeling and polishing the continuous rolled wire blank; The roller die cold drawing process is divided into a first stage and a second stage; in the first stage, when the cumulative deformation of the pre-treated continuous rolled wire billet after cold drawing is 55.17%~68.05%, intermediate vacuum annealing is performed, and after the annealing is completed, the second stage is entered; in the second stage, the roller die cold drawing is continued until the cumulative deformation is 34.33%~39.64%, and the finished wire is obtained.

7. The method for preparing the low-gap TC16 titanium alloy large single-weight round wire for cold heading fasteners according to claim 6, characterized in that: In the first stage of roller die cold drawing, the deformation of the last drawing pass is set to 12.89%~17.36%, and the deformation of the remaining drawing passes is 23.05%~28.74%. The intermediate vacuum annealing includes keeping warm at 780℃~840℃ in a vacuum furnace for 60min~120min.

8. The method for preparing the low-gap TC16 titanium alloy large single-weight round wire for cold heading fasteners according to claim 2, characterized in that: In step 4, the heat treatment includes controlling the annealing temperature to 740° C. to 790° C., the holding time to 1.5 h to 2.5 h, furnace cooling to 600° C. and then air cooling.

9. The method for preparing the low-gap TC16 titanium alloy large single-weight round wire for cold heading fasteners according to claim 2, characterized in that: In step 5, the pretreatment includes sequentially performing peeling, sandblasting, cleaning and phosphating treatment on the large single weight round wire to obtain a large single weight round wire with a uniform phosphating film layer.

10. An application of a low-gap TC16 titanium alloy large single weight round wire, characterized in that: The large single weight round wire prepared by the preparation method according to any one of claims 2 to 9 is used in cold heading and hot heading fasteners.

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