A method for preparing high shear strength Nb55Ti wire

Abstract

This invention proposes a method for preparing high-shear-strength Nb55Ti wire, including ingot preparation, intermediate billet forging, machining, rolling, round drawing, peeling and inspection, vacuum annealing, finished product roll drawing, finished product polishing, inspection and rewinding, making the finished product into rivets, shearing and stamping, and annealing at 800-900℃. This invention prepares ingots through vacuum consumable melting, then prepares intermediate billets with fine and uniform microstructure through six-stage drawing, and then prepares small-gauge wires through one-stage rolling, cold drawing and two-stage vacuum annealing of the ingots. The final Nb55Ti wire has high precision, uniform microstructure and consistent mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy preparation technology, and in particular to a method for preparing high shear strength Nb55Ti wire. Background Technology

[0002] There is a large domestic market demand for niobium-titanium wire for aerospace fasteners, but the following problems exist in the preparation of niobium-titanium alloy wire: (1) Partial component segregation occurs during melting. Since niobium has a high melting point, solving the problem of niobium non-fusible block becomes a difficult point in the preparation of niobium-titanium ingot blanks; (2) During hot / cold deformation, niobium-titanium alloy will undergo an extreme large deformation across scales, making it difficult to ensure the uniformity of the structure and the consistency of the mechanical properties of the whole roll of wire; (3) The existing niobium-titanium wire preparation technology has low shear strength, and it is urgent to break through the existing shear strength and ensure the matching of wire strength and toughness.

[0003] Chinese patent CN117483473A discloses a processing method for Ti45Nb titanium alloy straight wire. The method involves forging a Ti45Nb titanium alloy ingot that has passed composition inspection; repeatedly upsetting and drawing the forged billet; hot rolling the billet; cold drawing using a roll die; intermediate annealing; cold drawing again using a roll die; argon-filled online continuous annealing; and vertical electrical straightening. The Ti45Nb titanium alloy straight wire prepared using this method is simple to operate, with a stable and controllable process. It exhibits straightness ≤2.0mm / m, ellipticity ≤0.02mm, surface roughness Ra≤1.0μm, uniform and fine microstructure, passes eddy current testing, and demonstrates consistent and stable room-temperature mechanical properties in the annealed state, meeting relevant standard requirements. However, the wire prepared by this patent has a room-temperature tensile strength of 552MPa, a yield strength of 515MPa, an elongation of 22.8%, a reduction of area of ​​77.4%, and a shear strength of 378MPa. These properties are relatively low and cannot meet the increasingly stringent strength requirements.

[0004] Chinese patent CN107282688B discloses a method for preparing Ti45Nb alloy coiled wire. The method comprises: 1. Cold rolling of the rod: Selecting a uniformly composed, longitudinally and transversely uniformly structured annealed Ti45Nb rod, and using a two-roll reversible cold rolling mill with square-hole type rolls to cold roll it into a square rod blank; 2. Die drawing: Using a wire drawing machine, drawing the rod into a round blank using a two-stage square-to-round-hole type die, and then drawing the round blank with the die to obtain a certain specification and dimensional tolerance. The process involves five steps: 1. **Circular Wire Rods:** 2. **Intermediate Specification Vacuum Annealing:** The circular wire rods are annealed in a vacuum furnace to obtain annealed circular wire rods with a bright surface. 3. **Cold Continuous Rolling:** The bright circular wire rods are cold-rolled using alternating horizontal and vertical rolls on a cold continuous rolling mill. The rolls employ a twelve-square-hole design to roll the wire rods from larger to smaller specifications. The final two stands of the cold continuous rolling mill are equipped with alternating horizontal and vertical rounding-hole rolls to obtain round wire with a certain dimensional accuracy. 4. **Rounding:** The round wire is degreased and then rounded. This patent uses a continuous rolling method to round the intermediate billet, which incurs extremely high production costs, making small-batch production difficult. Furthermore, the shear strength of the wire rods prepared by this patent is only 350-400 MPa, which cannot meet the increasingly higher strength requirements.

[0005] Chinese patent CN111705279A discloses a heat treatment method for Ti45Nb titanium alloy wire. The method involves placing Ti45Nb wire prepared by rotary forging in a muffle furnace, preheating it to 750-860℃, holding it at that temperature for 0.5-1.6 hours, and then cooling it to room temperature. This method, by controlling the preheating temperature, holding time, and cooling method, ensures a uniform microstructure of the heat-treated Ti45Nb titanium alloy wire. It also improves the tensile strength to 595 MPa, yield strength to 545 MPa, shear strength to 368 MPa, and elongation to 13.6%, comprehensively enhancing the mechanical properties of the wire and providing technical support for the application of Ti45Nb titanium alloy wire in the production of aerospace fasteners. However, because titanium alloys are easily burned during muffle furnace annealing, this heat treatment preparation scheme is difficult to implement in industrial production. Furthermore, the wire prepared by this patent has a low elongation and poor strength-plasticity ratio.

[0006] Ma Fanjiao et al. published a paper on the recrystallization behavior of Ti45Nb titanium alloy. This paper systematically studied the effects of different heat treatment temperatures and hot working deformation parameters on the recrystallization behavior of Ti45Nb titanium alloy for new fasteners. The results showed that the degree of recrystallization gradually increased with increasing heat treatment temperature; the complete recrystallization temperature gradually decreased with increasing deformation. For forged samples, a recrystallization temperature of 850℃ was selected; for hot-rolled samples, 800℃ was selected. This paper provides guidance for the production of Ti45Nb wire. Controlling the heat treatment temperature and deformation amount significantly affects the wire's performance; therefore, developing a suitable heat treatment regime is of great significance for the mass production of niobium-titanium wire. However, this paper did not describe the actual industrial application.

[0007] Fan Kailun et al. published a paper on the effect of annealing cooling regime on the shear strength of Ti45Nb alloy rivets. This paper studied the influence of different annealing regimes on the shear strength of Ti45Nb rivets. The results showed that the shear strength of Ti45Nb rivets increased with decreasing annealing cooling rate, reaching 380 MPa under air cooling. This paper also demonstrated the extremely high sensitivity of heat treatment regimes to wire properties, highlighting the importance of developing a reasonable wire annealing regime. However, this paper did not discuss practical industrial applications. Summary of the Invention

[0008] In view of the above defects, this invention proposes a method for preparing high shear strength Nb55Ti wire, comprising the following steps:

[0009] S1 Ingot Preparation: Mix Nb: 40-48% by mass; Fe: ≤0.03; O≤0.18; N≤0.03; C≤0.04; H≤0.001, with the balance being Ti, to form φ500-600mm Nb55Ti ingots;

[0010] S2 intermediate billet forging: Six-stage intermediate billet upsetting and drawing forging to obtain φ82~92×Lmm, air cooling;

[0011] S3 machining: Machining to 80-90×L mm;

[0012] S4 rolling: Heat to 650-700℃, hold for 80-90 minutes; roll in multiple passes to φ9.5-10mm, air cool, and test H content;

[0013] S5 gauge round drawing: φ9.5~10mm rolled billet; φ9.0~9.2mm;

[0014] S6 peeling and repair: peeling down to φ8.5~8.7mm;

[0015] S7 Vacuum Annealing: Heat to 650-700℃, hold for 60-80 minutes, then furnace cool;

[0016] S8 Finished Product Roller Drawing: Obtain the finished product;

[0017] S9 finished product polishing: dimensional tolerance controlled between -0.01 and -0.02;

[0018] S10 detection and rewinding;

[0019] S11 processes the finished product into rivets, which are then sheared, stamped, and annealed at 800-900℃.

[0020] Preferably, the six-stage intermediate billet upsetting and forging in S2 includes the following steps:

[0021] First heat: Preheat to 820-850℃, hold for 100-120 minutes, raise to 1130-1160℃, hold for 150-200 minutes; upsetting and drawing twice, then diagonally drawing and chamfering to 400-410×Lmm; return to furnace at 980-1040℃; upsetting and drawing once, then diagonally drawing and chamfering to 400-410×Lmm; round the chamfered edges to φ430-440×Lmm, water cooling; after forging, completely grind, pickle, and re-inspect.

[0022] Second heat treatment: Ensure the material surface is clean, homogenize the heat treatment at 1200-1280℃, and hold for 10-15 hours;

[0023] Third heat: Preheat to 820-850℃, hold in the furnace for 60-80 minutes, then raise the temperature to 900-950℃ and hold for 120-150 minutes; two upsettings and three drawings to 450-480×Lmm, one of which is a transverse drawing; after chamfering the large edges, return to the furnace at 920-950℃; two upsettings and three drawings to 400-410×Lmm, one of which is a transverse drawing and the other is a diagonal drawing; chamfer and roll to φ430-440×Lmm, water cooling; spot grinding after forging;

[0024] Fourth heat: Preheat to 820-850℃, hold in the furnace for 60-80 minutes, then raise the temperature to 900-950℃ and hold for 120-150 minutes; two upsettings and three drawings to 400-410×Lmm, one of which is a transverse drawing; after chamfering the large edges, return to the furnace at 900-920℃; one upsetting and three drawings to 250-280×Lmm, one of which is a transverse drawing; eight-sided drawing and rounding to φ220-240×Lmm, air cooling; spot grinding after forging;

[0025] Fifth firing: Heat the empty furnace to 880-910℃, load the furnace and hold for 120-150 minutes; draw to 120×L; round the V-shaped anvil to φ110-120×Lmm; after forging, grind and pickle completely and then re-inspect.

[0026] Sixth firing: Heat the empty furnace to 800-820℃, load the furnace and hold for 90-140 minutes; precision forge to φ82-92×Lmm, air cool, and straighten after forging.

[0027] This invention prepares ingots through vacuum consumable melting, then prepares intermediate billets with fine and uniform microstructure through six-stage drawing, and then prepares small-gauge wires through one-stage rolling, cold drawing and two-stage vacuum annealing of the ingots. The final Nb55Ti wire has high precision, uniform microstructure and consistent mechanical properties. Attached Figure Description

[0028] Figure 1 X-ray test results of the head and tail of the φ240mm intermediate billet: (a) head, (b) tail.

[0029] Figure 2 The diagram shows the metallographic structure of samples taken from the head, middle, and tail of the first billet after six firings. (a) Nb55Ti - head, (b) Nb55Ti - middle, (c) Nb55Ti - tail.

[0030] Figure 3 , 4 The image shows the 100X crystal phase diagrams of Ti45Nb238111 with a diameter of 7.5mm in both the transverse and longitudinal directions.

[0031] Figure 5 , 6 The image shows the 100X crystal phase diagrams of Ti45Nb238111 with a diameter of 6.48 mm in both the transverse and longitudinal directions.

[0032] Figure 7 , 8 The image shows the 100X crystal phase diagrams of Ti45Nb238111 with a diameter of 5.6 mm in both the transverse and longitudinal directions.

[0033] Figure 9 , 10 The image shows the 100X crystal phase diagrams of Ti45Nb238111 with a diameter of 4.9 mm in both the transverse and longitudinal directions.

[0034] Figure 11 , 12 The image shows the 100X crystal phase diagrams of Ti45Nb238111 with a diameter of 4.5mm in both the transverse and longitudinal directions. Detailed Implementation

[0035] Example 1

[0036] Stability testing of high shear strength Nb55Ti wires with diameters of 7.5mm, 6.48mm, 5.6mm, 4.9mm, and 4.5mm (batch number Ti45Nb238111):

[0037] S1 Ingot Preparation: Mix Nb: 40-48% by mass; Fe: ≤0.03; O≤0.18; N≤0.03; C≤0.04; H≤0.001, with the balance being Ti, to form φ500-600mm Nb55Ti ingots;

[0038] S2 intermediate billet forging: Six-stage intermediate billet upsetting and drawing forging to obtain φ82~92×Lmm, air cooling;

[0039] First heat: Preheat to 850℃, hold for 100 minutes, raise to 1130℃, hold for 150 minutes; upsetting and drawing twice, then diagonally drawing and chamfering to 400-410×Lmm; return to furnace at 980℃; upsetting and drawing once, then diagonally drawing and chamfering to 410×Lmm; round the chamfer to φ430×Lmm, water cooling; after forging, completely grind, pickle, and re-inspect;

[0040] Second heat treatment: Ensure the material surface is clean, perform homogenization heat treatment at 1280℃, and hold for 10 hours;

[0041] Third heat: Preheat to 850℃, hold in the furnace for 80 minutes, then raise the temperature to 950℃ and hold for 150 minutes; two upsettings and three drawings to 480×Lmm, one of which is a transverse drawing; after chamfering the large edges, return to the furnace at 950℃; two upsettings and three drawings to 400×Lmm, one of which is a transverse drawing and the other is a diagonal drawing; chamfer and roll to φ430×Lmm, water cooling; spot grinding after forging;

[0042] Fourth heat: Preheat to 850℃, hold in the furnace for 60 minutes, then raise the temperature to 900℃ and hold for 120 minutes; two upsettings and three drawings to 400×Lmm, one of which is a transverse drawing; after chamfering the large edges, return to the furnace at 920℃; one upsetting and three drawings to 250×Lmm, one of which is a transverse drawing; eight-sided drawing and rounding to φ240×Lmm, air cooling; spot grinding after forging;

[0043] After the fourth firing, X-ray samples were taken from both ends of the intermediate φ240mm bar billet for testing. The results are shown below. Figure 1 The X-ray images show a relatively uniform distribution of Ti and Nb across the entire cross-sectional field of view, with no obvious titanium-rich, niobium-rich, or niobium-insoluble blocks, indicating stable process control during ingot smelting and forging.

[0044] Fifth firing: Heat the empty furnace to 880℃, load the furnace and hold for 120 minutes; draw to 120×L; round the V-shaped anvil to φ120×Lmm; after forging, completely grind and pickle, then re-inspect.

[0045] Sixth firing: Heat the empty furnace to 800℃, load the furnace and hold for 140 minutes; precision forge to φ82×Lmm, air cool, and straighten after forging.

[0046] S3 machining: Machining to 90×L mm;

[0047] S4 rolling: Heat to 650℃, hold for 80 minutes, then roll in multiple passes to φ10mm, air cool, and test H content;

[0048] S5 gauge round drawing: φ9.5mm rolled billet; up to φ9.0mm;

[0049] S6 peeling and repair: peeling down to φ8.5mm;

[0050] S7 Vacuum Annealing: Heat to 700℃, hold for 60 minutes, then furnace cool;

[0051] S8 Finished Product Roller Drawing: Obtain the finished product;

[0052] S9 finished product polishing: dimensional tolerance controlled within -0.01;

[0053] S10 detection and rewinding;

[0054] S11 processes the finished product into rivets, which are then sheared, stamped, and annealed at 900℃.

[0055] Samples were taken from the head, middle, and tail sections of the billet after six firing cycles for metallographic and hardness analysis. The microstructure analysis results are shown below. Figure 2 The hardness test results of the forged (R) billets are shown in Table 1. The hardness test results of the billets show that the hardness deviation between the head, middle and tail is small, and the performance consistency of the forged billets is good. The grain size of the head, middle and tail of the billets is uniform, and the forging process has greatly improved the uniformity of the ingot structure, refined the grains, and made the billet structure more consistent, laying a good microstructure foundation for subsequent wire processing.

[0056] Table 1. Hardness test results of bars

[0057]

[0058] Example 2

[0059] Stability testing of high shear strength Nb55Ti wires with diameters of 7.5mm, 6.48mm, 5.6mm, 4.9mm, and 4.5mm (batch number Ti45Nb238110):

[0060] The steps are the same as in Example 1, with adaptive adjustments to the process parameters.

[0061] Example 3

[0062] Stability testing of high shear strength Nb55Ti wires with diameters of 7.5mm, 6.48mm, 5.6mm, 4.9mm, and 4.5mm (batch number Ti45Nb238104):

[0063] The steps are the same as in Example 1, with adaptive adjustments to the process parameters.

[0064] Metallographic images of three batches of products tested, such as... Figure 3-12 The mechanical properties were tested and are shown in Table 2. The figure shows that the different specifications of the products exhibit uniform microstructure in both the transverse (cross-sectional direction) and longitudinal (length direction) directions. Both the transverse and longitudinal grains are fine, exhibiting an equiaxed microstructure. Due to cold drawing, the longitudinal direction also shows a banded structure. These two structures together determine the excellent shear strength level. The data in the table show that all specifications of the wire maintain a shear strength of 430-465 MPa and high toughness, achieving a good balance between strength and toughness.

[0065]

[0066]

[0067] The embodiments of this solution have been described in detail above with reference to the accompanying drawings. However, this solution is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of this patent.

Claims

1. A method of producing a high shear strength Nb55Ti wire, characterized by Includes the following steps: S1 ingot preparation: Mix Nb according to mass fraction: 40-48%; Fe: ≤0.03; O≤0.18; N≤0.03; C≤0.04; H≤0.001, with the balance being Ti in φ500~600mm Nb55Ti ingots; S2 intermediate billet forging: Six-stage intermediate billet upsetting and drawing forging to obtain φ82~92×Lmm, air cooling; S3 machining: Machining to 80-90×Lmm; S4 rolling: Heat to 650-700℃, hold for 80-90 minutes, then roll in multiple passes to φ9.5-10mm, air cool, and test H content; S5 gauge round drawing: φ9.5~10mm rolled billet; φ9.0~9.2mm; S6 peeling and repair: peeling down to φ8.5~8.7mm; S7 vacuum annealing: Heat to 650-700℃, hold for 60-80 minutes, then furnace cool; S8 Finished Product Roller Drawing: Obtain the finished product; S9 finished product polishing: dimensional tolerance controlled between -0.01 and -0.02; S10 detection and rewinding; S11 involves shaping the finished product into rivets, shearing and stamping, and annealing at 800-900℃; The six-stage intermediate billet upsetting and forging process in S2 includes the following steps: First heat: Preheat to 820-850℃, hold for 100-120 minutes, raise to 1130-1160℃, hold for 150-200 minutes; upsetting and drawing twice, then diagonally drawing and chamfering to 400-410×Lmm; return to furnace at 980-1040℃; upsetting and drawing once, then diagonally drawing and chamfering to 400-410×Lmm; round the chamfered edges to φ430-440×Lmm, water cooling; after forging, completely grind, pickle, and re-inspect. Second heat treatment: Ensure the material surface is clean, homogenize the heat treatment at 1200-1280℃, and hold for 10-15 hours; Third heat: Preheat to 820-850℃, hold in the furnace for 60-80 minutes, then raise the temperature to 900-950℃ and hold for 120-150 minutes; two upsettings and three drawings to 450-480×Lmm, one of which is a transverse drawing; after chamfering the large edges, return to the furnace at 920-950℃; two upsettings and three drawings to 400-410×Lmm, one of which is a transverse drawing and the other is a diagonal drawing; chamfer and roll to φ430-440×Lmm, water cooling; spot grinding after forging; Fourth heat: Preheat to 820-850℃, hold in the furnace for 60-80 minutes, then raise the temperature to 900-950℃ and hold for 120-150 minutes; two upsettings and three drawing processes to 400-410×Lmm, one of which is a transverse drawing; after chamfering the large edges, return to the furnace at 900-920℃; one upsetting and three drawing processes to 250-280×Lmm, one of which is a transverse drawing; eight-sided drawing and rounding to φ220-240×Lmm, then air cool; Post-forging spot grinding; Fifth firing: Heat the empty furnace to 880-910℃, load the furnace and hold for 120-150 minutes; draw to 120×L; round the V-shaped anvil to φ110-120×Lmm; after forging, grind and pickle completely and then re-inspect. Sixth fire: empty furnace temperature to 800~820 ℃, loading furnace for 90~140 minutes; precision forging to φ82~92 × L mm, air cooling, straightening after forging.

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