Preparation method of TC16 titanium alloy and large single weight round wire for cold heading fasteners

Abstract

The invention belongs to the technical field of titanium alloy wire rolling, and particularly relates to a TC16 titanium alloy for cold heading fasteners and a preparation method of a large single-weight round wire. The TC16 titanium alloy is composed of the following components in percentage by mass: C ≤ 0.008%, N ≤ 0.005%, H ≤ 0.005%, O ≤ 0.06%, Si ≤ 0.03%, Al 3.0% to 3.75%, V 4.0% to 4.8%, Mo 5.0% to 5.4%, Fe ≤ 0.02%, and the balance being Ti and unavoidable impurities. The preparation method selects the TC16 titanium alloy of the invention, and after preparation, a large single-weight round wire with uniform and refined structure and high performance stability is obtained, and the large single-weight round wire will not crack when subjected to continuous large-deformation cold heading.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium alloy wire rolling, and particularly 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] Conventional TC16 titanium alloys contain interstitial elements such as O, C, and N, as well as impurity Fe, to enhance their strength. However, these interstitial elements significantly reduce the plasticity and cold formability of TC16 titanium alloys, contributing to the deformation and cracking of TC16 rods and wires during cold heading. To achieve TC16 titanium alloy rods and wires with stable microstructure and properties for cold-headed fasteners, the present invention innovatively designed a low-interstitial TC16 titanium alloy.

[0004] In my country, there is relatively little systematic research on the chemical composition of TC16 titanium alloy for cold heading fasteners, the microstructure and performance stability control of high-weight wire, and the matching technology between the cold heading properties of fasteners and those of rods and wires. Key research areas include annealing schedules, solution aging, and cold deformation strengthening for TC16 alloys; the effects of quenching temperature on the microstructure and deformation behavior of TC16 alloys; the relationship between the microstructure and dynamic compression deformation behavior of TC16 alloys; and the preparation of low-weight rods and wires for hot and cold heading fasteners.

[0005] The microstructure of TC16 titanium alloy rod and wire after annealing depends not only on the finished product heat treatment regime but also on the original microstructure after continuous rolling and drawing. Initially, domestic continuous rolling lines suitable for rolling large single-weight titanium alloy billets were insufficient, and high-speed wire mills used in the steel industry were often used for continuous rolling. Factors such as inappropriate deformation design and excessively fast exit speeds of the finishing mills during titanium alloy rolling in the steel industry lead to elevated temperatures in the core of the continuous-rolled billet, resulting in enlargement and dissolution of the α phase. Subsequent microstructure control through drawing and heat treatment, however, is limited by the specifications of the finished TC16 rod and wire. This difference in microstructure between the center and edge cannot be completely eliminated, leading to inconsistent deformation during fastener upsetting and poor roundness of rivet heads. Therefore, designing continuous rolling lines suitable for titanium and titanium alloys and controlling the pass profile, deformation per pass, and deformation temperature of each mill stand are key to achieving fine, uniform microstructure and stable performance in large, rounded coils. There are currently methods for preparing TC16 titanium alloy large-weight round wire, but there are still problems such as difficulty in controlling ultrafine-grained structure, difficulty in controlling the performance stability of large-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 purpose of the present invention is to overcome the 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:

[0009] On the one hand, the present invention provides a low-clearance TC16 titanium alloy for cold heading fasteners, 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% to 3.75%, V 4.0% to 4.8%, Mo 5.0% to 5.4%, Fe ≤ 0.02%, and the balance being Ti and unavoidable impurities.

[0010] 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.

[0011] 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.

[0012] Specifically, the 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.

[0013] 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:

[0014] Step 1: Select low-gap TC16 titanium alloy bar billet as continuous rolling billet;

[0015] Step 2: heating and keeping the continuous rolling billet in a heating furnace, and then rolling and annealing the billet using a bar and wire continuous rolling mill to obtain a continuous rolled wire billet;

[0016] Step 3: pre-treating the continuous rolled wire blanks in step 2, and then performing eddy current flaw detection. After removing surface defects, the finished wire is prepared by roller die cold drawing combined with intermediate annealing;

[0017] Step 4: heat-treating the finished wire prepared in step 3 to obtain an annealed large single-weight round wire;

[0018] Step 5: pre-treat the large single weight round wire obtained in step 4, and then apply a lubricating coating to obtain the target large single weight round wire.

[0019] In step 1, the selected billet (low-interstitial TC16 titanium alloy billet) has a preferred concentration of principal elements and ultra-low interstitial and impurity elements, and exhibits a uniform and fine two-phase equiaxed microstructure in both the transverse and longitudinal directions. The billet is an annealed billet measuring 85 mm to 100 mm in diameter.

[0020] Furthermore, in step 2, the heating and heat preservation process is as follows:

[0021] The continuous rolling billet is first placed in a heating furnace at 800°C to 820°C for 1 hour for preheating, and then heated to 30°C to 110°C above the β-transus temperature at a heating rate of 1 to 2°C / min, and then kept at this temperature for 30 to 40 minutes to allow the continuous rolling billet to be completely heated through;

[0022] The cumulative rolling deformation of the bar and wire continuous rolling mill group is 97.48%~98.56%.

[0023] Furthermore, 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.

[0024] The rolling process is as follows: the heated and heat-insulated continuous wire billet is rolled in the roughing mill, the starting rolling temperature is controlled to be ≥820°C, the finishing rolling temperature is controlled to be 750°C-820°C, and the average elongation coefficient of the roughing mill is 1.20-1.25, that is, the average elongation coefficient of the first six rolling mills is 1.20-1.25;

[0025] After rolling in the roughing mill, the steel 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.

[0026] The annealing temperature is 750℃~820℃.

[0027] In step 2, the continuous rolled billet is first preheated at 800°C~820°C for 1 hour, 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.

[0028] 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 in succession 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.

[0029] Furthermore, in step 2, the heating furnace is a walking-beam or box-type resistance heating furnace, which can continuously heat the continuous rolling billet and achieve the effect of rapid and uniform heating.

[0030] Furthermore, the roughing mill group is of flat ellipse-round hole type, and the finishing mill group is of ellipse-round hole type.

[0031] It should be noted that the roughing mill adopts a flat oval-round hole type, which is more conducive to uniform deformation of larger-sized billets and significantly reduces the "deformation dead zone" compared to the flat-square hole type and oval-round hole type.

[0032] The finishing mill utilizes an elliptical-round hole pattern, which offers superior surface quality and roundness control for smaller wire billets or continuous rolling stock compared to flat-square and flat elliptical-round hole patterns. Furthermore, compared to similar hole patterns, it offers more uniform and complete deformation. Using a flat elliptical-round hole pattern for the first six mill stands, combined with an elliptical-round hole pattern for the next 14 or 16 mill stands, this ensures uniform deformation and excellent surface quality for the continuous rolling billets.

[0033] Furthermore, in step 3, the pretreatment includes sequentially peeling and polishing the continuous rolled wire billet to control the surface roughness of the continuous rolled wire billet to ≤1.6 μm;

[0034] A horizontal-vertical two-piece 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 pretreated continuous rolled wire billet during cold drawing is 55.17% to 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% to 39.64%, thereby obtaining a finished wire.

[0035] Furthermore, during 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 set to 23.05%~28.74%. The intermediate vacuum annealing includes keeping the temperature at 780℃~840℃ in a vacuum furnace for 60min~120min.

[0036] 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 equiaxed, while further refining and homogenizing the transverse and longitudinal lamellae and grains.

[0037] 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 roundness and flatness of the surface 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.

[0038] Furthermore, in step 4, the heat treatment includes controlling the annealing temperature to be 740° C. to 790° C., holding time to be 1.5 h to 2.5 h, furnace cooling to 600° C. and then air cooling.

[0039] Furthermore, in step 5, the pretreatment includes sequentially performing peeling, sandblasting, cleaning and phosphating on the large single weight round wire to obtain a large single weight round wire with a uniform phosphating film layer.

[0040] Specifically, the large single-weight round wire is peeled to remove the surface oxide scale, and then sandblasted with 320-mesh brown corundum (Al2O3) sand using 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 to 40°C, and the phosphating time is 10min to 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 to 150°C. After curing, the preparation is completed.

[0041] 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.

[0042] Specifically, the coating ratio is: 32g WS2 powder, 12g sodium silicate, 5g silica sol, 70g deionized water, 0.2g surfactant, 0.1g defoaming agent, and 0.3g antimony trioxide.

[0043] The large single-weight round wire prepared by the present invention has a weight of 100kg to 180kg.

[0044] On the other hand, the present invention provides an application of a low-gap TC16 titanium alloy large unit weight round wire. The large unit weight round wire prepared by the preparation method described above is used in cold heading and hot heading fasteners.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] 1) The present invention provides a low-interstitial TC16 titanium alloy for cold heading fasteners. By designing low-interstitial ingredients and combining them with existing high-purity smelting processes, a TC16 titanium alloy with ultra-low interstitial impurity elements and uniform microstructure is obtained. Specifically, low levels of interstitial elements such as O, C, and N are added, and the contents of Al, V, and Mo are adjusted at the same time to ensure that the alloy strength meets the design and standard requirements, and that the room temperature cold heading plasticity and cold formability are good.

[0047] 2) The present invention provides a method for preparing low-gap TC16 titanium alloy large single-weight round wire for cold heading fasteners. The method adopts a proprietary titanium alloy continuous rolling production line, and then controls the microstructure, heating temperature, roughing mill 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 rolled wire billet with ultrafine grains and equiaxial microstructure in the transverse and longitudinal directions. In addition, the microstructure is further refined by roller die cold drawing, and intermediate annealing is matched to make the longitudinal microstructure equiaxial. At the same time, through the matching design of cumulative deformation, final annealing deformation, and intermediate annealing temperature, 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.

[0048] 3) The present invention provides a method for preparing low-clearance TC16 titanium alloy large single weight round wire for cold heading fasteners. The method increases the specific surface area of ​​the polished wire after stripping by sandblasting, adds a bridging phosphating film layer after phosphating, and adopts WS2 coating with high temperature resistance, which can be suitable for short-time hot heading. The coating and pretreatment scheme solve the problems of easy coating shedding and die jamming during the continuous cold heading of TC16 large single weight round wire, and can also adapt to the future requirements of unified standards for raw materials for cold heading and hot heading. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] 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 invention.

[0050] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0051] Figure 1is a flow chart of the preparation method of the present invention;

[0052] Figure 2 This is a 2000x SEM photograph of the continuous rolling billet at the transverse position R / 2 of the present invention;

[0053] Figure 3 This is a 2000x SEM photograph of the continuous rolling billet at R / 2 in the longitudinal direction of the present invention;

[0054] Figure 4 This is a 2000x SEM photograph of the horizontal position R / 2 of the continuous rolled wire billet of the present invention;

[0055] Figure 5 This is a 2000x SEM photograph of the longitudinal position R / 2 of the continuous rolled wire billet of the present invention;

[0056] Figure 6 This is a transverse ×2000x SEM photograph of the annealed TC16 finished wire prepared by the present invention;

[0057] Figure 7 This is a longitudinal ×2000x SEM photograph of the annealed TC16 finished wire prepared by the present invention;

[0058] Figure 8 This is a 2500x SEM photograph of the phosphate coating on the surface of the TC16 large single-weight round wire prepared by the present invention. DETAILED DESCRIPTION

[0059] 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.

[0060] On the one hand, the present invention provides a low-clearance TC16 titanium alloy for cold heading fasteners, 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% to 3.75%, V 4.0% to 4.8%, Mo 5.0% to 5.4%, Fe ≤ 0.02%, and the balance being Ti and unavoidable impurities.

[0061] On the other hand, Figure 1 As shown, the present invention provides a method for preparing a low-clearance TC16 titanium alloy large single weight round wire for cold heading fasteners, comprising the following steps:

[0062] Step 1, continuous rolling billet: select low gap TC16 titanium alloy billet as continuous rolling billet, specifically Φ85mm~Φ100mm annealed billet, the billet is horizontally ( Figure 2 ), vertical ( Figure 3 ) is a uniform and fine equiaxed structure; the rod blank is the low-gap TC16 titanium alloy in this embodiment;

[0063] Step 2, heating and continuous rolling, annealing: heating and keeping the continuous rolling billet in a heating furnace, and then rolling and annealing it using a bar and wire continuous rolling mill to obtain a continuous rolled wire billet;

[0064] 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-stand or 22-stand horizontal and vertical continuous rolling mill for bars and wires is used, of which the first 6 stands are roughing mills, and a flat elliptical-round hole type is selected with an average elongation coefficient of 1.20~1.25. 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 stands are finishing rolling 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 a continuous rolled wire billet is obtained; the continuous rolled wire billet is placed in an annealing furnace and annealed at 750℃~820℃ to obtain the annealed continuous rolled wire billet transverse ( Figure 4 ), vertical ( Figure 5 ) are all ultrafine-grained equiaxed structures;

[0065] Step 3, roller die cold drawing combined with intermediate annealing: The continuous rolled wire billet from step 2 is pre-treated and then inspected by eddy current testing. After surface defects are removed (cold drawing has high requirements on the surface structure of the continuous rolled wire billet, so surface defects must be removed to facilitate subsequent cold drawing operations), the finished wire is prepared by roller die cold drawing combined with intermediate annealing.

[0066] Specifically, the continuous rolled wire billet is stripped by a centerless lathe to remove 0.5 mm of skin, and polished with a sand belt to a surface roughness of ≤1.6 μm. After eddy current inspection to remove surface defects, it is cold-drawn using a flat-vertical two-pass roller die. 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%. Subsequently, a vacuum furnace is used for intermediate annealing at 780℃~840℃ for 60min~120min. After annealing, the cumulative deformation of cold drawing using a flat-vertical two-pass roller die is 34.33%~39.64%.

[0067] Step 4, heat treatment of finished product: heat treating the finished wire prepared in step 3 to obtain an annealed large single weight round wire;

[0068] Specifically, the annealing temperature of the finished wire is 740°C~790°C, the holding time is 1.5h~2.5h, and the furnace is cooled to 600°C and then air-cooled;

[0069] Step 5, pre-treating the surface of the large single weight round wire and applying a lubricating coating: pre-treating the large single weight round wire obtained in step 4, and then applying a lubricating coating to obtain the target large single weight round wire.

[0070] The pretreatment includes sequentially performing skinning, sandblasting, cleaning and phosphating on the heavy single weight round wire to obtain the heavy single weight round wire with a uniform phosphating film layer.

[0071] 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 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 coated large single weight round wire is obtained.

[0072] 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.

[0073] In this embodiment, the coating ratio is: 32g WS2 powder, 12g sodium silicate, 5g silica sol, 70g deionized water, 0.2g surfactant, 0.1g defoaming agent, and 0.3g antimony trioxide.

[0074] Figure 6 This is a transverse ×2000x SEM photograph of the annealed TC16 finished wire prepared by the present invention. Figure 7 This is a longitudinal ×2000x 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 coating of the TC16 large single-weight round wire prepared by the present invention, showing that the phosphate coating is well crystallized.

[0075] On the other hand, the present invention provides an application of a low-gap TC16 titanium alloy large unit weight round wire. The large unit weight round wire prepared by the preparation method described above is used in cold heading and hot heading fasteners. Example 1

[0076] This embodiment provides a method for preparing a low-clearance TC16 titanium alloy high-weight round wire for cold heading fasteners, comprising the following steps:

[0077] Step 1, continuous rolling billet: A low-interstitial TC16 titanium alloy bar billet is selected as the continuous rolling billet, specifically a Φ85 mm annealed bar billet with a β-transformation temperature of 850°C. The bar billet has a uniform and fine equiaxed structure in the transverse and longitudinal directions. The bar billet is composed of the following components by mass percentage: C ≤ 0.008%, N ≤ 0.005%, H ≤ 0.005%, O ≤ 0.06%, Si ≤ 0.03%, Al 3.0% to 3.75%, V 4.0% to 4.8%, Mo 5.0% to 5.4%, Fe ≤ 0.02%, and the balance is Ti and unavoidable impurities. The weight percentage (average value) of the interstitial and impurity elements of the bar billet is: C 0.005 wt%, N < 0.003 wt%, H 0.0008 wt%, O 0.047 wt%, and Si 0.025 wt%.

[0078] Step 2, heating and continuous rolling, annealing: placing the continuous rolling billet in step 1 in a walking beam heating furnace at 800°C for 1 hour for preheating, then heating the continuous rolling billet to 880°C at an average heating rate of 1°C / min, and then keeping it warm for 30 minutes, using a 20-stand horizontal and vertical bar and wire continuous rolling mill group, wherein the first 6 stands are roughing mills, using a flat oval-round hole type, an average elongation coefficient of 1.25, and a starting rolling temperature ≥820°C, the outlet temperature of the first 6 rolling mills (temperature after roughing rolling) is 750°C~790°C, and the last 14 stands are finishing mills, using an oval-round hole type, an average elongation coefficient of 1.18, a finishing rolling temperature of 730°C~765°C, and a cumulative deformation of 97.48%, to obtain a hot-worked Φ13.5 mm continuous rolled wire billet; placing the continuous rolled wire billet in an annealing furnace, annealing at 750°C / 120min, to obtain an annealed continuous rolled wire billet;

[0079] Step 3, roller die cold drawing combined with intermediate annealing: The continuous rolled wire billet of step 2 is pretreated, then subjected to eddy current flaw detection, and after surface defects are removed, the finished wire is prepared by roller die cold drawing combined with intermediate annealing;

[0080] Specifically, the continuous rolled wire billet was stripped by a centerless lathe to remove 0.5 mm of skin, and then polished with a sanding belt to a surface roughness of ≤1.6 μm. After eddy current inspection to remove surface defects, it was cold-drawn with a flat-vertical two-pass roller die, and the diameter reduction drawing was performed in 5 passes. The deformation of the first 4 passes was 23.05%~25.68%, and the deformation of the 5th pass was 12.89%. In the first stage, the wire was cold-drawn to Φ8.7 mm, with a cumulative deformation of 55.21%. It was then annealed in a vacuum furnace at 840°C / 60 min. After annealing, it was continued to be cold-drawn with a flat-vertical two-pass roller die to Φ7.05 mm, with a cumulative deformation of 34.33%.

[0081] Step 4, heat treatment of finished product: heat treating the finished wire prepared in step 3 to obtain an annealed large single weight round wire;

[0082] Specifically, the annealing temperature was 790°C, the holding time was 1.5 h, the furnace was cooled to 600°C and then air-cooled;

[0083] 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 0.05mm to remove the surface oxide scale, and then sandblasted with 320-mesh brown corundum sand using 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, the large single-weight round wire is coated with a lubricating coating using a wire coating machine. After coating, it is cured at 120°C. After curing, the preparation is completed to obtain a Φ7.0mm coated large single-weight round wire. Example 2

[0084] This embodiment provides a method for preparing a low-clearance TC16 titanium alloy high-weight round wire for cold heading fasteners, comprising the following steps:

[0085] Step 1, continuous rolling billet: low-gap TC16 titanium alloy bar billet is selected as the continuous rolling billet, specifically a Φ90 mm annealed bar billet, the bar billet β transformation temperature is 860°C, and the bar billet has a uniform and fine equiaxed structure in the transverse and longitudinal directions; the bar billet is composed of the following components by 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;

[0086] Step 2, heating and continuous rolling, annealing: the continuous rolling billet of step 1 is placed in a walking beam heating furnace at 810℃ for 1h for preheating, and then the continuous rolling billet is heated to 930℃ at an average heating rate of 1.5℃ / 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 roughing mills, and a flat elliptical-round hole type is selected, with an average elongation coefficient of 1.20~1.23, and a starting rolling temperature ≥84 0℃, the outlet temperature of the first 6 rolling mills (temperature after rough rolling) is 770℃~800℃, and the last 16 rolling mills are finishing mills. The elliptical-round hole type is selected, the average elongation coefficient is 1.19~1.23, the final rolling temperature is 740℃~785℃, and the cumulative deformation is 98.22%. A hot-processed Φ12mm continuous rolled wire billet is obtained; the continuous rolled wire billet is placed in an annealing furnace and annealed at 780℃ / 100min to obtain an annealed continuous rolled wire billet;

[0087] Step 3, roller die cold drawing combined with intermediate annealing: The continuous rolled wire billet of step 2 is pretreated, then subjected to eddy current flaw detection, and after surface defects are removed, the finished wire is prepared by roller die cold drawing combined with intermediate annealing;

[0088] Specifically, the continuous rolled wire billet was stripped by a centerless lathe to remove 0.5 mm of skin, and then polished with a sanding belt to a surface roughness of ≤1.6 μm. After eddy current inspection to remove surface defects, it was cold-drawn with a flat-vertical two-pass roller die, and the diameter reduction drawing was performed in 5 passes. The deformation of the first 4 passes was 23.44%~28.74%, and the deformation of the 5th pass was 14.79%. In the first stage, the wire was cold-drawn to Φ7.7 mm, with a cumulative deformation of 55.17%. It was then annealed in a vacuum furnace at 810°C / 60 min. After annealing, it was continued to be cold-drawn with a flat-vertical two-pass roller die to Φ6.05 mm, with a cumulative deformation of 38.27%.

[0089] 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

[0090] Specifically, the annealing temperature is 780°C, the holding time is 2 h, the furnace is cooled to 600°C and then air-cooled;

[0091] 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 0.05mm to remove the surface oxide scale, and then sandblasted with 320-mesh brown corundum sand using 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 using a wire coating machine. After coating, it is cured at 130°C. After curing, the preparation is completed to obtain a Φ6.0mm coated large single-weight round wire. Example 3

[0092] This embodiment provides a method for preparing a low-clearance TC16 titanium alloy high-weight round wire for cold heading fasteners, comprising the following steps:

[0093] Step 1, continuous rolling billet: A low-gap TC16 titanium alloy bar billet is selected as the continuous rolling billet, specifically a Φ100 mm annealed bar billet with a β-transformation temperature of 860°C. The bar billet has a uniform and fine equiaxed structure in the transverse and longitudinal directions; the bar billet is composed of the following components by mass percentage: C ≤ 0.005%, N ≤ 0.003%, H ≤ 0.003%, O ≤ 0.05%, Si ≤ 0.03%, Al 3.2% to 3.75%, V 4.3% to 4.8%, Mo 5.0% to 5.4%, Fe ≤ 0.02%, and the balance is Ti and unavoidable impurities;

[0094] Step 2, heating continuous rolling and annealing: the continuous rolling billet of step 1 is placed in a walking beam heating furnace at 820℃ for 1h for preheating, and then the continuous rolling billet is heated to 970℃ at an average heating rate of 2℃ / 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 roughing mills, and a flat elliptical-round hole type is selected, with an average elongation coefficient of 1.20~1.23, and a starting rolling temperature ≥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-worked Φ12mm continuous rolled wire billet is obtained; the continuous rolled wire billet is placed in an annealing furnace and annealed at 820℃ / 60min to obtain an annealed continuous rolled wire billet;

[0095] Step 3, roller die cold drawing combined with intermediate annealing: The continuous rolled wire billet of step 2 is pretreated, then subjected to eddy current flaw detection, and after surface defects are removed, the finished wire is prepared by roller die cold drawing combined with intermediate annealing;

[0096] Specifically, the continuous rolled wire billet is stripped by a centerless lathe to remove 0.5mm of skin, and polished with a sand belt to a surface roughness of ≤1.6μm. After eddy current inspection to remove surface defects, it is cold-drawn with a flat-vertical two-pass roller die, and the diameter reduction drawing is performed in 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, with a cumulative deformation of 68.05%. It is then annealed in a vacuum furnace at 780℃ / 60min. After annealing, it is continuously cold-drawn with a flat-vertical two-pass roller die to Φ5.05mm, with a cumulative deformation of 39.64%.

[0097] Step 4, heat treatment of finished product: heat treating the finished wire prepared in step 3 to obtain an annealed large single weight round wire;

[0098] Specifically, the annealing temperature was 740°C, the holding time was 2.5 h, the furnace was cooled to 600°C and then air-cooled;

[0099] 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 0.05mm to remove the surface oxide scale, and then sandblasted with 320-mesh brown corundum sand using 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, the large single-weight round wire is coated with a lubricating coating using a wire coating machine. After coating, it is cured at 150°C. After curing, the preparation is completed to obtain a Φ5.0mm coated large single-weight round wire.

[0100] In order to prove the efficacy of the present invention, the present invention has done the following tests:

[0101] The room temperature tensile properties of the heads and tails of the annealed finished wires and solution-aged wire samples (solution treatment: 800°C / 120 min, water cooling; aging: 540°C / 600 min, air cooling) prepared in Examples 1 to 3 were tested in accordance with GB / T 228.1-2015. The shear strength of the solution-aged wire samples was tested in accordance with GJB 715.26A. The results are shown in Table 1.

[0102] Table 1 Test results of Examples 1 to 3

[0103]

[0104] Depend on Figure 6 、 Figure 7 As shown in Table 1, the mechanical properties and microstructure 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

[0105] 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

[0106] 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%.

[0107] 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.

[0108] Table 2 Cold forming test results of Example 1, Comparative Example 1 and Comparative Example 2

[0109]

[0110] As can be seen from Table 2, the low-gap strategy of the present invention can avoid cold heading cracking.

[0111] Comparative Example 3

[0112] 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.

[0113] In order to verify the efficacy of the present invention, the present invention conducted mechanical property and cold heading forming performance tests on the large single weight round wire prepared in Example 1 and Comparative Example 3. The test results are shown in Table 3.

[0114] Table 3 Test results of mechanical properties and cold heading properties

[0115]

[0116] As shown in Table 3, the roller die cold drawing combined with intermediate annealing method of the present invention can further improve the cold deformation plasticity and avoid the cold heading cracking phenomenon without significantly reducing the strength of the wire.

[0117] The foregoing description is intended only to provide specific embodiments of the present invention, which will enable those skilled in the art to understand and implement the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention.

[0118] It should be understood that the present invention is not limited to the above description and that various modifications and changes may be made without departing from the scope thereof. 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: Select low-gap TC16 titanium alloy bar billet as continuous rolling billet; Step 2: heating and keeping the continuous rolling billet in a heating furnace, and then rolling and annealing the billet using a bar and wire continuous rolling mill to obtain a continuous rolled wire billet; Wherein, 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 wire billet is rolled in the roughing mill, wherein the average elongation coefficient of the roughing mill is 1.20-1.25; After the rough rolling mill is completed, the steel enters the finishing mill for rolling, and the average elongation coefficient of the finishing mill is 1.18-1.23; Step 3: pre-treating the continuous rolled wire blank in step 2, and then performing eddy current flaw detection. After removing surface defects, the finished wire is prepared 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: pre-treat the large single weight round wire obtained in step 4, and then apply 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 insulation process is as follows: The continuous rolling billet is first placed in a heating furnace at 800°C to 820°C for 1 hour for preheating, and then heated to 30°C to 110°C above the β-transus temperature at a heating rate of 1 to 2°C / min, and then kept at this temperature for 30 to 40 minutes; 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, in the roughing mill, the initial rolling temperature is controlled to be ≥820°C, and the final rolling temperature is 750°C~820°C; in the finishing mill, the final rolling temperature is 730°C~785°C; and the annealing temperature is 750°C~820°C.

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

6. The method for preparing 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 continuously 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%, thereby obtaining a finished wire material.

7. The method for preparing low-gap TC16 titanium alloy large single weight round wire for cold heading fasteners according to claim 6, characterized in that: During 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 set to 23.05%~28.74%. The intermediate vacuum annealing includes keeping the temperature at 780℃~840℃ in a vacuum furnace for 60min~120min.

8. The method for preparing 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., holding time to 1.5 h to 2.5 h, furnace cooling to 600° C. and then air cooling.

9. The method for preparing 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 on the heavy single weight round wire to obtain a heavy single weight round wire with a uniform phosphating film layer.

10. An application of 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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