A strengthening and toughening control method for high-strength titanium alloy welded joints

Abstract

The present invention provides a strengthening and toughening control method for a high-strength titanium alloy welded joint, which relates to the technical field of metal material welding and comprises the following steps: S1: during welding, multi-layer and multi-pass gradient heat input is adopted, the heat input of the front welding is Q1, the heat input of the rear welding is Q2, and Q1>Q2; S2: after welding, the welding area is cooled in stages, inert gas forced convection cooling is adopted in the initial cooling stage, water mist pulse cooling is adopted when the temperature is cooled to the medium temperature stage, and natural air cooling is adopted when the temperature is cooled to the low temperature stage; through the synergistic effect of multi-layer and multi-pass gradient heat input and staged cooling, the microstructure and properties of the high-strength titanium alloy welded joint can be effectively regulated, the microstructure gradient of the titanium alloy welded joint can be regulated, the tensile strength, elongation, fracture toughness and creep performance of the welded joint can be improved, and at the same time, the process can be simplified and deformation can be reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of metal material welding, and in particular to a method for controlling the strengthening and toughening of a high-strength titanium alloy welded joint. Background Art

[0002] With the rapid development of high-strength titanium alloy equipment, the demand for high-quality and efficient welding of thick titanium alloy plates has become increasingly urgent. However, while existing arc welding methods for thick titanium alloy plates can meet the penetration requirements of engineering applications through multi-layer, multi-pass welding with filler wire, significant increases in equipment size and weld thickness (≥40 mm) lead to significant welding distortion and inefficiency. This also increases the difficulty of controlling defects such as porosity, lack of fusion, and cracks during the arc welding process. Vacuum electron beam welding, on the other hand, allows for deep penetration welding of thick titanium alloy plates in a single pass, offering high efficiency and minimal distortion. This significantly improves the structural development process in engineering practice. Conventional electron beam welding, however, requires no filler wire, and the deep penetration welding process cannot control the composition of the weld zone. This results in poor composition and strength-toughness matching between the joint and base metal zones. The weld pool experiences significant molten pool disturbance during welding, and the heat input experiences an energy gradient attenuation along the penetration direction. This leads to significant microstructure and performance heterogeneity along the penetration direction of the joint, compromising the performance evaluation of electron beam welded thick titanium alloy plates.

[0003] In the existing technology, the welding of high-strength titanium alloys has the following problems: 1. Coarse columnar β grains are formed in the weld area of ​​the weld joint due to rapid solidification, and the strengthening elements cannot be effectively precipitated, resulting in solid solution strengthening, which leads to a decrease in plasticity and toughness; 2. The heat-affected zone of the weld joint undergoes phase transformation during the welding heating process, resulting in coarsening of the β phase and uneven precipitation of the α phase and the strengthening phase, which causes stress concentration, and easily generates cracks that affect the performance of the joint; 3. It is difficult to take into account both creep resistance and welding efficiency at the same time.

[0004] In the existing technology, many patents use a single heat input welding method, which leads to insufficient uniformity of the weld joint structure and makes it difficult to achieve simultaneous improvement of strength and plasticity.

[0005] Patent CN115846867A proposes a laser wire-filling welding method based on Ti-6Al-4V titanium alloy. Although the joint strength is improved through flux-cored wire filling and heat treatment process, the plastic toughness is still poor.

[0006] Patent CN119282393A uses a vacuum laser welding method, which suppresses oxidation and porosity defects but does not involve microstructure gradient control, leaving room for improvement in the overall performance of the joint. Preheat welding improves the performance of welded joints to a certain extent, but still suffers from insufficient microstructure control.

[0007] Patent CN119282492A achieves uniform preheating of the welding area by designing an advanced preheating structure combined with a lifting mechanism and a cantilever, effectively reducing the occurrence of thermal cracks, but the problem of uneven joint structure is not effectively solved.

[0008] Patent CN119282321A proposes a welding method for titanium alloy heat exchange tubes and tube sheets, which improves the uniformity and density of the weld through argon protection, but does not involve the design of gradient structure, resulting in insufficient matching of joint strength and plasticity.

[0009] Patent CN222429708U designs a titanium alloy butt welding protection device, which optimizes the sealing of the welding environment but does not solve the technical problem of tissue gradient regulation.

[0010] The common problem of the above-mentioned patented technologies is that they fail to achieve gradient control of the weld joint organization, resulting in insufficient overall performance of the joint. Specifically, there is a mismatch between strength and plasticity. A single heat input or preheating welding method is difficult to simultaneously improve the strength and plasticity of the joint, resulting in the joint being prone to fracture or deformation in actual applications. Insufficient tissue uniformity. The existing technology fails to effectively control the microstructure of the weld joint, resulting in poor tissue uniformity, affecting the mechanical properties and durability of the joint. The process is highly complex. Although some patented technologies have proposed complex welding processes, they have failed to fundamentally solve the problem of tissue gradient control, increasing production costs and technical difficulties. By comparing and analyzing existing patented technologies, it can be seen that a single heat input or preheating welding method has obvious deficiencies in the control of the tissue gradient of titanium alloy welded joints, and cannot achieve tissue gradient control, resulting in insufficient overall performance of the joint. Summary of the Invention

[0011] In view of this, the present invention aims to propose a strengthening and toughening control method for high-strength titanium alloy welded joints to solve the problem in the prior art that titanium alloy welded joints cannot achieve tissue gradient regulation, resulting in insufficient comprehensive performance of the joints.

[0012] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0013] A method for controlling the toughening of a high-strength titanium alloy welded joint comprises the following steps:

[0014] S1: When welding, multi-layer and multi-pass gradient heat input is adopted. The heat input of the front welding is Q1, and the heat input of the back welding is Q2, then Q1>Q2;

[0015] S2: After welding, the welding area is cooled in stages. In the initial cooling stage, forced convection cooling with inert gas is used. When the temperature drops to the medium temperature stage, water mist pulse cooling is used. When the temperature drops to the low temperature stage, natural air cooling is used.

[0016] High heat input during the front-pass welding can fully melt the welding molten pool, and β-stabilizing elements (such as Mo and V) are uniformly dissolved in the β-phase matrix to form a supersaturated solid solution, providing a uniform matrix for subsequent precipitation strengthening. At the same time, high heat input can also promote the flow of the molten pool and reduce defects such as porosity and lack of fusion. Low heat input during the subsequent welding can reduce the molten pool temperature and slow down the cooling rate, prompting the strengthening elements (such as Si and Mo) in the supersaturated solid solution to precipitate in the form of fine particles (such as Ti5Si3 phase), achieving precipitation strengthening. At the same time, low heat input can also inhibit the secondary growth of β grains. Combined with staged cooling control, it can achieve a gradient refinement of β grain size from the center to the edge of the weld (40→10μm).

[0017] Rapid cooling in the high-temperature zone can inhibit the excessive growth of β grains, while fixing the alloying elements in the supersaturated solid solution, and preventing the strengthening elements from precipitating prematurely at high temperatures to form coarse particles; the medium-temperature zone is the key temperature range for β→α phase transformation and precipitation phase formation. The slower cooling rate allows the α phase to precipitate uniformly in lamellar form (aspect ratio 3-5:1), improving toughness, and the strengthening elements (such as Si and Mo) diffuse and aggregate to form fine and dispersed precipitates (such as Ti5Si3), achieving precipitation strengthening. At the same time, intermittent cooling by water mist pulse cooling can promote the periodic release of stress in the molten pool and reduce welding cracks caused by uneven thermal expansion and contraction; when cooling to the low-temperature stage, the phase transformation of the titanium alloy is basically completed, and natural air cooling allows the residual stress to be slowly released, which is used to suppress the microcracks caused by the martensitic phase transformation, prolong the low-temperature residence time, and promote the further growth of the secondary α phase and trace precipitates, forming a stable structure of "β matrix + lamellar α + fine precipitates", thereby improving room temperature plasticity and fracture toughness.

[0018] This setting can effectively regulate the microstructure and properties of high-strength titanium alloy welded joints through the synergistic effect of multi-layer and multi-channel gradient heat input and staged cooling, realize the structural gradient regulation of titanium alloy welded joints, improve the tensile strength, elongation, fracture toughness and creep properties of the welded joints, and at the same time simplify the process and reduce deformation.

[0019] Furthermore, in step S1, Q1=1.8-2.0 kJ / mm, Q2=0.8-1.2 kJ / mm.

[0020] The high heat input in the front pass makes the welding pool temperature high enough to ensure that β-stabilizing elements (such as Mo, V, and Cr) are fully dissolved in the β-phase matrix to form a uniform supersaturated solid solution. This process avoids component segregation due to undissolved elements and lays the foundation for subsequent precipitation strengthening. The low heat input in the back pass makes the weld pool temperature lower and the cooling rate faster, which inhibits the secondary growth of β grains. At the same time, the "low-temperature aging" effect promotes the precipitation of strengthening elements (such as Si and Mo) in the supersaturated solid solution in the form of fine particles (such as Ti5Si3 phase, size <1μm). The front pass solid solution strengthening + the back pass precipitation strengthening + the fine grain strengthening make the room temperature tensile strength of the joint ≥950MPa.

[0021] This setting accurately matches the phase change requirements of "dissolution-precipitation-refinement" in high-strength titanium alloy welding through the timing control of "front-stage solid solution foundation and back-stage aging strengthening". It not only solves the problems of penetration depth and defects in thick plate welding, but also achieves the simultaneous improvement of strength, toughness and creep resistance through tissue gradient regulation.

[0022] Furthermore, in step S1, the gradient reduction rate of the heat input is controlled at 15-20% / pass.

[0023] If the decline rate exceeds 20%, the energy of the subsequent weld may not be sufficient to effectively heat the surface of the previous weld, resulting in insufficient interlayer fusion and defects such as cold shut and lack of fusion. A gradient decline rate of 15-20% can ensure a smooth transition of heat input between adjacent welds, ensuring that the subsequent weld pool can penetrate the top 1-2mm of the previous weld and form a good metallurgical bond.

[0024] On the other hand, if the decline rate is lower than 15%, the heat input in the subsequent process is still high, which may cause the strengthening phase precipitated in the previous process to dissolve again and fail to achieve effective strengthening. When the decline rate exceeds 20%, the cooling rate is too fast, which will cause the precipitate phase size to be too small (<0.5μm). The gradient of 15-20% can make the cooling rate moderate, which can not only avoid the strengthening elements (such as Si and Y) from precipitating prematurely to form coarse particles at high temperature, but also provide sufficient time for the full precipitation of fine precipitates (such as Ti5Si3) in the medium temperature stage, so that the precipitate phase size is stabilized at 1-2μm, achieving the best strengthening effect.

[0025] Furthermore, in step S2, the temperature range of the initial cooling stage is 1200-600°C, the temperature range of the medium temperature stage is 600-400°C, and the temperature range of the low temperature stage is less than 400°C.

[0026] The initial cooling stage can achieve rapid cooling of the joint, so that the β-stabilizing elements (such as Mo and V) are fully retained in the β-phase solid solution, avoiding premature decomposition of the β-phase due to slow cooling (such as precipitation of coarse α-phase or intermetallic compounds), laying the foundation for precipitation strengthening in the subsequent medium-temperature stage; the lower cooling rate in the medium-temperature stage allows the α-phase to precipitate uniformly in lamellar form, thereby improving toughness; the low-temperature stage allows the remaining supersaturated solid solution to slowly precipitate secondary α-phase and trace precipitates at low temperatures, forming a stable structure of "β-matrix + lamellar α + fine secondary α-phase", further improving room-temperature plasticity.

[0027] Furthermore, in step S2, when forced convection cooling by inert gas is used, the cooling efficiency is 50-80°C / s, and when water mist pulse cooling is used, the cooling efficiency is 20-30°C / s.

[0028] The use of forced convection of inert gas can not only accelerate cooling through heat conduction, but also form an air curtain in the welding area, isolating impurities such as O, N, and H in the air, and improving the purity of the weld; 600-400℃ is the main range of β→α phase transformation, and the cooling rate of 20-30℃ / s just matches the optimal thermodynamic window for the precipitation of lamellar α phase. The slower cooling rate allows the α phase to form a regular lamellar structure through the "nucleation-growth" mechanism. The lamellar α phase can increase the fracture toughness by 20-30%. In addition, water mist pulse cooling can release welding stress periodically through intermittent cooling, reducing microcracks caused by phase transformation volume shrinkage.

[0029] Furthermore, 0.5-1.2 wt% of Mo element and 0.05-0.1 wt% of Y element are added to the welding wire.

[0030] Adding 0.5-1.2wt% Mo element can reduce the β phase transformation temperature of titanium alloy, so that the β phase is retained to a lower temperature during the cooling process of the welding pool, providing more supersaturated solid solution for subsequent precipitation strengthening;

[0031] Y has a strong affinity for O, N, and C. Adding 0.05-0.1wt% Y element can form high-melting-point compounds (such as Y2O3, YN), fixing harmful impurities (O, N) in the weld as dispersed particles, preventing them from segregating at the grain boundary to form brittle phases (such as Ti4C2O, TiN), and improving grain boundary strength;

[0032] This setting solves the core problems of "strength-toughness mismatch", "grain boundary embrittlement" and "insufficient high-temperature performance" in high-strength titanium alloy welding.

[0033] Furthermore, 0.5-1.2 wt% of Mo element and 0.05-0.1 wt% of Si element are added to the welding wire.

[0034] As a β-stabilizing element, Mo can not only expand the β phase region and improve the strength through solid solution strengthening, but also combine with Ti and Si to form a high-temperature stable composite strengthening phase (such as Ti-Mo-Si phase), inhibiting high-temperature dislocation slip and making the creep life of the joint at 500℃ and 100MPa ≥500h; Si, as a precipitation phase strengthening element, can generate fine and dispersed Ti5Si3 phase with Ti in situ, further improving the strength through precipitation strengthening, while refining the β grains. Combined with the grain inhibition effect of Mo, a synergistic improvement of the room temperature tensile strength of the joint is achieved, ≥950MPa, and the elongation is ≥10%. The synergistic effect of the two can also improve the fluidity of the molten pool and reduce welding defects, forming a composite strengthening system of "solid solution strengthening + precipitation strengthening + fine grain strengthening", which solves the problems of strength-toughness mismatch and insufficient creep resistance in traditional processes.

[0035] Furthermore, 0.5-1.2 wt% of Mo element, 0.05-0.1 wt% of Y element, and 0.05-0.1 wt% of Si element are added to the welding wire.

[0036] Mo, as a β-stabilizing element, improves the matrix strength through solid solution strengthening and synergizes with Si to form a Ti-Mo-Si composite strengthening phase and fine Ti5Si3 phase, achieving precipitation strengthening and improving creep resistance, making the creep life of the joint ≥500h at 500℃ and 100MPa. Y, as a rare earth element, purifies the grain boundaries and captures impurities such as O and N to form high-melting-point compounds (such as Y2O3 and YN), reducing the risk of grain boundary embrittlement and promoting β grain refinement. Combined with the grain growth inhibition effect of Mo, it significantly improves toughness, making the elongation of the joint ≥10% and the fracture toughness ≥60MPa・m 1 / 2 The addition of Si further strengthens the precipitation phase system, and together with Y regulates the grain boundary precipitation behavior, so that the lamellar α phase is evenly distributed; the synergistic construction of the multiple mechanisms of "solid solution strengthening + precipitation strengthening + grain boundary purification + fine grain toughening" solves the problems of uneven organization, strength-toughness mismatch and insufficient high-temperature performance in traditional processes, and achieves a room temperature tensile strength of the joint ≥950MPa, as well as a comprehensive improvement in plasticity and creep resistance.

[0037] Compared with the prior art, the strengthening and toughening control method of the high-strength titanium alloy welded joint described in the present invention has the following advantages:

[0038] Through the synergistic effect of multi-layer and multi-channel gradient heat input and staged cooling, the microstructure and properties of high-strength titanium alloy welded joints can be effectively controlled, the organizational gradient control of titanium alloy welded joints can be achieved, the tensile strength, elongation, fracture toughness and creep properties of the welded joints can be improved, and at the same time, the process can be simplified and deformation can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a structural diagram of a welded joint;

[0040] Figure 2 3 are microstructure metallurgical comparison diagrams of welded joints, A is welded using the traditional process, and B is welded using this embodiment.

[0041] Description of reference numerals:

[0042] 1. The front road; 2. The back road. DETAILED DESCRIPTION

[0043] To make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention. It should be noted that, unless there is a conflict, the features in the embodiments and embodiments of the present invention may be combined with each other.

[0044] Example 1

[0045] like Figure 1 As shown, a high-strength titanium alloy Ti5321 alloy is welded using a high-strength titanium alloy weld joint strengthening and toughening control method of the present invention, and the specific process steps are as follows:

[0046] 1. Multi-layer and multi-channel gradient heat input

[0047] Aiming at the high-strength titanium alloy Ti5321 with high β-stabilizing elements, its chemical composition (w / %) is: AI5.02, Mo3.03, V2.99, Cr2.06, Nb1.37, Zr2.01, Fe0.99, O0.064, H0.0011, N0.0004, and the balance is Ti. By setting multi-layer and multi-pass gradient heat input, while reducing the heat input of the second pass welding, the heat input of the second pass welding is controlled to achieve effective refinement of the weld of the first pass and effective precipitation of strengthening elements, thereby achieving precipitation strengthening, which has a great impact on the strength and toughness of the welded joint. The properties can be effectively regulated, and the precipitated strengthening phase is also beneficial to improving the creep resistance of the material. For high-strength titanium alloy, the front 1 welding high heat input is adopted, and the heat input is Q1=1.8-2.0kJ / mm, for coarse grain control, and solid solution is achieved through rapid cooling. The back 2 welding low heat input, the heat input is Q2=0.8-1.2kJ / mm, for fine grain strengthening, and partial strengthening phase is precipitated through low temperature aging. At the same time, the gradient decrease rate of heat input is controlled at 15-20% / pass, which is used to achieve a gradient refinement of β grain size from the center to the edge of the weld from 40→10μm.

[0048] To explain here, multi-layer and multi-pass gradient heat input means that during the welding process, the thick plate welding is decomposed into multiple layers (such as 5-10 layers), each layer contains multiple welds (such as 3-5 welds per layer), and the welding is completed by stacking layer by layer. The heat input of adjacent welds or weld layers decreases according to a certain rule (such as 15-20% / pass), forming a gradient distribution of "high heat input in the front pass 1 → low heat input in the back pass 2". The superposition effect of the welding heat cycle can be utilized to achieve solid solution strengthening through the high heat input of the front pass 1 weld, and precipitation strengthening and grain refinement through the low heat input of the back pass 2 welds. Finally, a gradient structure of "coarse grain → fine grain → ultrafine grain" is formed in the cross section of the weld to match the mechanical requirements of different regions (such as center load bearing and edge crack resistance).

[0049] 2. Cooling in stages

[0050] In order to further control the joint structure during the welding cooling process, thereby achieving the regulation of joint strength and toughness, in the initial cooling stage of 1000-600℃ after welding, inert gas forced convection cooling is adopted, and the cooling rate is controlled at 50-80℃ / s; when the temperature drops to the medium temperature stage of 600-400℃, water mist pulse cooling is adopted, and the cooling rate is controlled at 20-30℃ / s; when the temperature drops to the low temperature stage below 400℃, natural air cooling is adopted to increase the growth time of the secondary phase, inhibit the generation of martensitic phase transformation stress, and improve the toughness of the joint.

[0051] Preferably, the inert gas is argon.

[0052] Preferably, water mist pulse cooling is to spray fine water mist onto the welding area through a nozzle, and circulate according to a preset cycle (such as cooling for 5-10 seconds and pausing for 3-5 seconds) to form intermittent cooling. The core of this method is to adjust the average cooling rate in the medium temperature stage (600-400℃) by controlling parameters such as cooling time, pause time, and water mist pressure.

[0053] Example 2

[0054] This embodiment improves the welding wire based on embodiment 1 by adding 0.5wt% Mo (β-stabilizing element) + 0.05wt% Si into the welding wire. After welding, fine Ti5Si3 strengthening phase is generated in situ in the weld, which is beneficial to improving creep resistance.

[0055] As a β-stabilizing element, Mo can not only expand the β phase region and improve the strength through solid solution strengthening, but also combine with Ti and Si to form a high-temperature stable composite strengthening phase (such as Ti-Mo-Si phase), inhibiting high-temperature dislocation slip and making the creep life of the joint at 500℃ and 100MPa ≥500h; Si, as a precipitation phase strengthening element, can generate fine and dispersed Ti5Si3 phase with Ti in situ, further improving the strength through precipitation strengthening, while refining the β grains. Combined with the grain inhibition effect of Mo, a synergistic improvement of the room temperature tensile strength of the joint is achieved, ≥950MPa, and the elongation is ≥10%. The synergistic effect of the two can also improve the fluidity of the molten pool and reduce welding defects, forming a composite strengthening system of "solid solution strengthening + precipitation strengthening + fine grain strengthening", which solves the problems of strength-toughness mismatch and insufficient creep resistance in traditional processes.

[0056] Preferably, 0.75wt% Mo (β-stabilizing element) and 0.075wt% Si are added to the welding wire. This configuration provides a more balanced strengthening effect, with Mo solid solution strengthening and Si precipitation strengthening acting synergistically, further refining the β grains and promoting a uniform distribution of the lamellar α phase. This significantly improves fracture toughness while maintaining strength, further optimizes weld pool fluidity, and reduces welding defects.

[0057] Preferably, 1.2wt% Mo (a β-stabilizing element) and 0.1wt% Si are added to the welding wire. This configuration maximizes the Mo solid solution strengthening effect, expands the β phase region to its peak value, increases the content of high-temperature stable composite strengthening phases, and significantly improves creep resistance. Si precipitation strengthening is enhanced, the Ti5Si3 phase density increases, and the fine grain strengthening effect is most significant. The room temperature tensile strength and elongation of the joint reach the upper limit of the range, making it suitable for applications with extremely high requirements for high-temperature performance and toughness.

[0058] Example 3

[0059] This embodiment improves the welding wire based on the embodiment 1 by adding 0.5 wt % of Mo element and 0.05 wt % of Y element into the welding wire.

[0060] Adding 0.5-1.2wt% Mo element can reduce the β phase transformation temperature of titanium alloy, so that the β phase is retained to a lower temperature during the cooling process of the welding pool, providing more supersaturated solid solution for subsequent precipitation strengthening;

[0061] Y has a strong affinity for O, N, and C. Adding 0.05-0.1wt% Y element can form high-melting-point compounds (such as Y2O3, YN), fixing harmful impurities (O, N) in the weld as dispersed particles, preventing them from segregating at the grain boundary to form brittle phases (such as Ti4C2O, TiN), and improving grain boundary strength;

[0062] This setting solves the core problems of "strength-toughness mismatch", "grain boundary embrittlement" and "insufficient high-temperature performance" in high-strength titanium alloy welding.

[0063] Preferably, 0.75wt% Mo and 0.075wt% Y are added to the welding wire. This configuration balances the solid solution strengthening effect of Mo with the grain boundary purification effect of Y. Mo inhibits the growth of β grains, while Y promotes β grain refinement. The two work together to achieve grain refinement and toughening, improve fracture toughness, and enable more complete impurity purification, significantly increasing grain boundary strength and further optimizing joint elongation and creep resistance.

[0064] Preferably, 1.2wt% Mo and 0.1wt% Y are added to the welding wire. This configuration maximizes Mo solid solution strengthening, maximizes β-phase supersaturation, reaches the upper limit of matrix strength, maximizes Y's ability to capture impurities, almost completely suppresses grain boundary brittle phases, and maximizes grain boundary strength. This configuration is suitable for applications requiring extremely high-temperature performance and toughness, achieving optimal joint fracture toughness and creep life.

[0065] Example 4

[0066] This embodiment improves the welding wire based on the embodiment 1 by adding 0.5 wt % of Mo element, 0.05 wt % of Y element, and 0.05 wt % of Si element into the welding wire.

[0067] Mo, as a β-stabilizing element, improves the matrix strength through solid solution strengthening and synergizes with Si to form a Ti-Mo-Si composite strengthening phase and fine Ti5Si3 phase, achieving precipitation strengthening and improving creep resistance, making the creep life of the joint ≥500h at 500℃ and 100MPa. Y, as a rare earth element, purifies the grain boundaries and captures impurities such as O and N to form high-melting-point compounds (such as Y2O3 and YN), reducing the risk of grain boundary embrittlement and promoting β grain refinement. Combined with the grain growth inhibition effect of Mo, it significantly improves toughness, making the elongation of the joint ≥10% and the fracture toughness ≥60MPa・m 1 / 2 The addition of Si further strengthens the precipitation phase system, and together with Y regulates the grain boundary precipitation behavior, so that the lamellar α phase is evenly distributed; the synergistic construction of the multiple mechanisms of "solid solution strengthening + precipitation strengthening + grain boundary purification + fine grain toughening" solves the problems of uneven organization, strength-toughness mismatch and insufficient high-temperature performance in traditional processes, and achieves a room temperature tensile strength of the joint ≥950MPa, as well as a comprehensive improvement in plasticity and creep resistance.

[0068] Preferably, 0.75wt% Mo, 0.075wt% Y, and 0.075wt% Si are added to the welding wire. This configuration enhances synergy, achieving a more balanced Mo solid solution strengthening and Si precipitation strengthening, refining β grains and promoting a uniform distribution of lamellar α phases. Y also provides a more effective grain boundary cleansing effect, reducing stress concentration, improving joint performance uniformity, and achieving optimal overall strength and toughness.

[0069] Preferably, 1.2wt% Mo, 0.1wt% Y, and 0.1wt% Si are added to the welding wire. This configuration maximizes Mo solid solution strengthening, increases β-phase supersaturation, and reaches the upper limit of matrix strength. The density of Si precipitates increases, leading to significant grain refinement and room-temperature tensile strength reaching the range peak, maximizing grain boundary strength. Combined with slow, low-temperature air cooling, martensite microcracks are suppressed, achieving optimal fracture toughness and creep life, making the wire suitable for extreme operating conditions.

[0070] It should be noted here that the welding wire in this application is a conventional welding wire in the prior art, and after being improved according to the above-mentioned embodiments 2-4, the corresponding technical effects can be achieved.

[0071] The present invention provides a method for controlling the strengthening and toughening of high-strength titanium alloy welded joints. After welding, the non-destructive testing of the welded joint meets the NB / T47013 Level I qualification, the joint strength reaches more than 95% of the parent material, the performance difference at different positions of the joint is less than 10%, and the fracture toughness reaches more than 60% of the parent material, effectively improving the strength-toughness matching and performance uniformity of the welded joint and the parent material, thereby improving the quality of the high-strength titanium alloy welded joints.

[0072] like Figure 2 As shown, A is a metallographic microstructure diagram of the welded joint after welding using the traditional process, and B is a metallographic microstructure diagram of the welded joint after welding using this embodiment.

[0073] Compared with the prior art, the method for controlling the toughening of high-strength titanium alloy welded joints described in the present invention has the following advantages:

[0074] 1) It can quickly and reliably achieve welding of high-strength titanium alloys with simple operation; 2) Through gradient heat input and staged cooling, the microstructure of the weld and heat-affected zone is controlled, thereby achieving the control of the strength and toughness of the joint. The weld zone obtains a lamellar α phase (aspect ratio of 3-5:1), and the HAZ forms a β grain gradient transition zone (size gradient change rate ≤5% / 100μm); 3) Through staged cooling and welding wire design, fine grain strengthening and precipitation phase strengthening are achieved, ensuring strength while improving toughness. When welding high-strength titanium alloys using the present invention, the room temperature tensile strength of the joint is ≥950MPa, the elongation is ≥10%, and the fracture toughness is not less than 60MPa*m 1 / 2, the creep life of the joint at 500℃ and 100MPa is ≥500h.

[0075] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined by the claims.

Claims

1. A method for controlling the toughening of high-strength titanium alloy welded joints, characterized in that: The steps include: S1: When welding, multi-layer and multi-pass gradient heat input is used. The heat input of the front pass (1) is Q1, and the heat input of the back pass (2) is Q2. Then Q1>Q2; S2: After welding, the welding area is cooled in stages. In the initial cooling stage, forced convection cooling with inert gas is adopted. When the temperature drops to the medium temperature stage, water mist pulse cooling is adopted. When the temperature drops to the low temperature stage, natural air cooling is adopted. In step S1, Q1 = 1.8-2.0 kJ / mm, Q2 = 0.8-1.2 kJ / mm, and the gradient decrease rate of heat input is controlled at 15-20% / pass. In step S2, the temperature range of the initial cooling stage is 1200-600°C, the temperature range of the medium temperature stage is 600-400°C, and the temperature range of the low temperature stage is less than 400°C. When forced convection cooling with inert gas is adopted, the cooling efficiency is 50-80°C / s, and when water mist pulse cooling is adopted, the cooling efficiency is 20-30°C / s.

2. The method for controlling the strengthening and toughening of a high-strength titanium alloy welded joint according to claim 1, characterized in that: 0.5-1.2wt% Mo element and 0.05-0.1wt% Y element are added to the welding wire.

3. The method for controlling the strengthening and toughening of a high-strength titanium alloy welded joint according to claim 1, characterized in that: 0.5-1.2wt% Mo element and 0.05-0.1wt% Si element are added to the welding wire.

4. The method for controlling the strengthening and toughening of a high-strength titanium alloy welded joint according to claim 1, wherein: 0.5-1.2 wt% of Mo element, 0.05-0.1 wt% of Y element, and 0.05-0.1 wt% of Si element are added to the welding wire.

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