Strengthening and toughening control method for high-strength titanium alloy welded joint

Abstract

The invention provides a strengthening and toughening control method for a high-strength titanium alloy welded joint, and relates to the technical field of metal material welding, the strengthening and toughening control method comprises the following steps: S1, during welding, multi-layer and multi-channel gradient heat input is adopted, the heat input quantity of front-channel welding is Q1, the heat input quantity of rear-channel welding is Q2, and Q1 is greater than Q2; s2, after welding, cooling a welding area by stages, adopting inert gas forced convection cooling in a primary cooling stage, adopting water mist pulse cooling when the welding area is cooled to a medium temperature stage, and adopting natural air cooling when the welding area is cooled to a low temperature stage; through the synergistic effect of multi-layer multi-channel gradient heat input and staged cooling, the microstructure and performance of the high-strength titanium alloy welded joint can be effectively regulated and controlled, the structure gradient regulation and control of the titanium alloy welded joint are achieved, the tensile strength, the ductility, the fracture toughness and the creep property of the welded joint are improved, meanwhile, the process can be simplified, and deformation is reduced.

Description

Technical Field

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

[0002] With the rapid development of high-strength titanium alloy equipment, the demand for high-quality and high-efficiency welding of thick-plate titanium alloys has become increasingly urgent. However, for the welding of thick-plate titanium alloys, although the existing arc welding methods can meet the welding penetration requirements of engineering applications through multi-layer and multi-pass wire filling welding, when the volume size of the equipment structure and the weld thickness (≥40 mm) increase significantly, the welding deformation is large and the efficiency is low. The control difficulty of defects such as pores, lack of fusion, and cracks increases during the arc welding process. The use of vacuum electron beam welding technology can achieve deep penetration welding of thick-plate titanium alloys at one time, with high welding efficiency and small welding deformation, which can greatly improve the progress of structure development in engineering practice. Conventional electron beam welding does not require wire filling, and the composition of the weld zone cannot be regulated during the deep penetration welding process, resulting in poor matching of the composition, strength, and toughness between the joint zone and the base metal zone. The molten pool is severely disturbed during the welding process, and there is an energy gradient attenuation of the heat input along the penetration direction, resulting in obvious non-uniformity of the microstructure and properties in the penetration direction of the joint, affecting the evaluation and assessment of the performance of thick-plate titanium alloy electron beam welded joints.

[0003] In the prior art, there are the following problems in the welding of high-strength titanium alloys: 1. Coarse columnar β grains are formed in the weld zone of the welded joint due to rapid solidification, and at the same time, strengthening elements cannot be effectively precipitated, resulting in solid solution strengthening, leading to a decrease in plasticity and toughness; 2. Phase transformation occurs in the heat-affected zone of the welded joint during the welding heating process, resulting in coarsening of the β phase and non-uniform precipitation of the α phase and strengthening phases, triggering stress concentration, and thus prone to crack formation, affecting the service performance of the joint; 3. It is difficult to simultaneously take into account the creep resistance and welding efficiency.

[0004] In the prior art, many patents adopt a single heat input welding method, resulting in insufficient uniformity of the welded joint microstructure and difficulty in simultaneously improving 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 processes, the plasticity and toughness are still poor.

[0006] Patent CN119282393A adopts a vacuum laser welding method. Although oxidation and pore defects are suppressed, it does not involve the regulation of the tissue gradient, and there is still room for improvement in the comprehensive performance of the joint. The preheating welding method improves the performance of the welded joint to a certain extent, but there are still problems with insufficient tissue regulation.

[0007] Patent CN119282492A achieved uniform preheating of the welding area by designing an advanced preheating structure, combined with a lifting mechanism and a cantilever, effectively reducing the generation of hot cracks. However, the problem of non-uniformity of the joint microstructure has not been effectively solved.

[0008] Patent CN119282321A proposed a welding method for titanium alloy heat exchange tubes and tube sheets. By using argon protection, the uniformity and density of the weld seam were improved, but the design of gradient microstructure was not involved, resulting in insufficient matching of joint strength and plasticity.

[0009] Patent CN222429708U designed a protection device for butt welding of titanium alloys. Although the sealing performance of the welding environment was optimized, the technical problem of microstructure gradient regulation was not solved.

[0010] The common problem of the above-mentioned patented technologies is the failure to achieve gradient regulation of the microstructure of the welded joint, resulting in insufficient comprehensive performance of the joint. The specific manifestations are as follows: The mismatch between strength and plasticity, it is difficult for a single heat input or preheating welding method to simultaneously improve the strength and plasticity of the joint, resulting in easy fracture or deformation of the joint in practical applications. Insufficient microstructure uniformity, the existing technologies have not effectively regulated the microstructure of the welded joint, resulting in poor microstructure uniformity, affecting the mechanical properties and durability of the joint. High process complexity, although some patented technologies have proposed complex welding processes, they have not fundamentally solved the problem of microstructure gradient regulation, increasing production costs and technical difficulties. Through comparative analysis of the existing patented technologies, it can be seen that there are obvious deficiencies in the gradient regulation of the microstructure of titanium alloy welded joints by a single heat input or preheating welding method, and the gradient regulation of the microstructure cannot be achieved, resulting in insufficient comprehensive 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 that the microstructure gradient regulation of titanium alloy welded joints cannot be achieved in the prior art, resulting in insufficient comprehensive performance of the joint.

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

[0013] A strengthening and toughening control method for high-strength titanium alloy welded joints, comprising the following steps:

[0014] S1: During welding, a multi-layer and multi-pass gradient heat input is adopted. The heat input of the previous pass of welding is Q1, and the heat input of the subsequent pass of 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 adopted. When cooling to the medium temperature stage, water mist pulse cooling is adopted. When cooling to the low temperature stage, natural air cooling is adopted.

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

[0017] Rapid cooling in the high-temperature zone can inhibit the excessive growth of β grains and fix the alloying elements in the supersaturated solid solution, preventing the premature precipitation of strengthening elements at high temperatures to form coarse particles. The medium-temperature zone is the critical temperature range for the β→α phase transformation and the formation of precipitation phases. A slower cooling rate allows the α phase to precipitate uniformly in a lamellar shape (aspect ratio 3-5:1), improving toughness. The strengthening elements (such as Si, Mo) diffuse and aggregate to form fine and dispersed precipitation phases (such as Ti5Si3), achieving precipitation strengthening. At the same time, the intermittent cooling of water mist pulse cooling can promote the periodic release of internal stress in the molten pool, reducing welding cracks caused by uneven thermal expansion and contraction. When the temperature drops 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 inhibit the microcracks generated by the martensitic transformation. Prolonging the low-temperature residence time can promote the further growth of the secondary α phase and trace precipitation phases, forming a stable structure of "β matrix + lamellar α + fine precipitation phases", improving the room-temperature plasticity and fracture toughness.

[0018] Through the synergistic effect of multi-layer and multi-pass gradient heat input and staged cooling, this setting can effectively regulate the microstructure and properties of the high-strength titanium alloy welded joint, achieve the gradient regulation of the microstructure of the titanium alloy welded joint, improve the tensile strength, elongation, fracture toughness and creep properties of the welded joint, and at the same time, it can also simplify the process and reduce deformation.

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

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

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

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

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

[0024] On the other hand, if the decreasing rate is lower than 15%, the heat input in the back pass is still relatively high, which may cause the strengthening phases that have precipitated in the front pass to redissolve, making effective strengthening impossible. When the decreasing rate exceeds 20%, the cooling rate is too fast, resulting in too small a size of the precipitated phase (< 0.5 μm). A gradient of 15 - 20% can make the cooling rate moderate, which can not only prevent strengthening elements (such as Si, Y) from precipitating prematurely at high temperatures to form coarse particles but also provide enough time for the full precipitation of fine precipitated phases (such as Ti5Si3) in the medium-temperature stage, making the size of the precipitated phase stable at 1 - 2 μm to achieve 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 precipitation phases 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 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.

[0028] The use of inert gas forced convection can not only accelerate cooling through heat conduction, but also form an air curtain in the welding area to isolate impurities such as O, N, H in the air and improve 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 by 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 change volume shrinkage.

[0029] Furthermore, 0.5-1.2wt% Mo element and 0.05-0.1wt% 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 molten 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), fix harmful impurities (O, N) in the weld as dispersed particles, avoid their segregation at the grain boundary to form brittle phases (such as Ti4C2O, TiN), and improve the 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, 0.5-1.2wt% Mo element and 0.05-0.1wt% Si element are added to the welding wire.

[0034] Mo, as a β-stabilizing element, can not only expand the β-phase region and enhance the strength through solid solution strengthening, but also combine with Ti and Si to form high-temperature stable composite strengthening phases (such as Ti-Mo-Si phase), inhibit high-temperature dislocation slip, and make the creep life of the joint ≥500 h at 500 °C and 100 MPa; Si, as a precipitation strengthening element, can in-situ generate fine and dispersed Ti5Si3 phase with Ti, further enhance the strength through precipitation strengthening, and at the same time refine the β grains. Cooperating with the grain inhibition effect of Mo, it realizes the synergistic improvement of the room-temperature tensile strength of the joint ≥950 MPa and the elongation ≥10%; the synergistic effect of the two can also improve the fluidity of the molten pool, reduce welding defects, and form a composite strengthening system of "solid solution strengthening + precipitation strengthening + fine grain strengthening", solving the problems of strength-ductility mismatch and insufficient creep resistance in traditional processes.

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

[0036] Mo, as a β-stabilizing element, enhances the matrix strength through solid solution strengthening. At the same time, it synergistically forms Ti-Mo-Si composite strengthening phase and fine Ti5Si3 phase with Si, realizing precipitation strengthening and improvement of creep resistance, and making the creep life of the joint ≥500 h at 500 °C and 100 MPa; 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, YN), reducing the risk of grain boundary embrittlement. At the same time, it promotes the refinement of β grains. Cooperating with the grain growth inhibition effect of Mo, it significantly improves the toughness, making the elongation of the joint ≥10% and the fracture toughness ≥60 MPa・m 1 / 2 ; The addition of Si further strengthens the precipitation phase system and jointly regulates the grain boundary precipitation behavior with Y, making the lamellar α phase evenly distributed; synergistically constructing multiple mechanisms of "solid solution strengthening + precipitation strengthening + grain boundary purification + fine grain toughening", solving the problems of uneven microstructure, strength-ductility mismatch and insufficient high-temperature performance in traditional processes, and realizing the room-temperature tensile strength of the joint ≥950 MPa and the comprehensive improvement of plasticity and creep resistance.

[0037] Compared with the prior art, the method for controlling the strength and toughness 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 multi-pass gradient heat input and staged cooling, the microstructure and properties of the high-strength titanium alloy welded joint can be effectively regulated, realizing the tissue gradient regulation of the titanium alloy welded joint, improving the tensile strength, elongation, fracture toughness and creep resistance of the welded joint. At the same time, it can also simplify the process and reduce deformation. Brief Description of the Drawings

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

[0040] Figure 2 It is a metallographic comparison diagram of the microstructure of the welded joint. A is welded by the traditional process, and B is welded by the method of this embodiment.

[0041] Explanation of the reference numerals:

[0042] 1. Front pass; 2. Rear pass. Specific embodiments

[0043] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with 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 only used to explain the present invention and are not used to limit the present invention. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0044] Embodiment 1

[0045] As Figure 1 shown, for the high-strength titanium alloy Ti5321 alloy, a method for controlling the strength and toughness of a high-strength titanium alloy welded joint of the present invention is used for welding. The specific process steps are as follows:

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

[0047] For 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 rear pass 2, through the control of the heat input of the rear pass 2, the effective refinement of the weld of the front pass 1 and the effective precipitation of strengthening elements are realized, so as to achieve precipitation strengthening, effectively regulate the strength and toughness of the welded joint. At the same time, the precipitated strengthening phase is also beneficial to improving the creep resistance of the material. For the high-strength titanium alloy, a high heat input is used for the front pass 1 welding, and the heat input is Q1 = 1.8 - 2.0 kJ / mm for coarse grain control, and solid solution is achieved through rapid cooling. The rear pass 2 welding has a low heat input, and the heat input is Q2 = 0.8 - 1.2 kJ / mm for fine grain strengthening. Through low-temperature aging, some strengthening phases are precipitated. At the same time, the gradient reduction rate of the heat input is controlled at 15 - 20% / pass to achieve gradient refinement of the β grain size from the weld center to the edge of 40 → 10 μm.

[0048] Here it should be noted that multi-layer and multi-pass gradient heat input means that during the welding process, the welding of thick plates is disassembled into multiple layers (such as 5 - 10 layers), each layer contains multiple weld beads (such as 3 - 5 weld beads per layer), and the welding is completed by stacking layer by layer. The heat input of adjacent weld beads or weld layers decreases according to a certain rule (such as 15 - 20% / pass), forming a gradient distribution of "high heat input in the previous pass 1 → low heat input in the subsequent pass 2". The superposition effect of the welding thermal cycle can be utilized. The high heat input of the previous pass 1 weld bead realizes solution strengthening, and the low heat input of the subsequent pass 2 weld bead realizes precipitation strengthening and grain refinement. Finally, a gradient structure of "coarse grains → fine grains → ultrafine grains" is formed in the weld cross-section to match the mechanical requirements of different regions (such as central load-bearing and edge crack resistance).

[0049] 2. Stepwise cooling

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

[0051] Preferably, the inert gas is argon.

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

[0053] Example 2

[0054] In this example, the welding wire was improved on the basis of Example 1 by adding 0.5 wt% Mo (β-stabilizing element) + 0.05 wt% Si to the welding wire. After welding, fine Ti5Si3 strengthening phases were in-situ formed in the weld, which is beneficial to improving the creep resistance.

[0055] Mo, as a β-stabilizing element, can not only expand the β-phase region and enhance the strength through solid solution strengthening, but also combine with Ti and Si to form high-temperature stable composite strengthening phases (such as Ti-Mo-Si phase), inhibit high-temperature dislocation slip, and make the creep life of the joint ≥500 h at 500 °C and 100 MPa; Si, as a precipitation strengthening element, can in-situ generate fine and dispersed Ti5Si3 phase with Ti, further enhance the strength through precipitation strengthening, refine the β grains at the same time, cooperate with the grain inhibition effect of Mo, and achieve the synergistic improvement of the room-temperature tensile strength of the joint ≥950 MPa and the elongation ≥10%; The synergistic effect of the two can also improve the fluidity of the molten pool, reduce welding defects, and form a composite strengthening system of "solid solution strengthening + precipitation strengthening + fine grain strengthening", solving the problems of strength-ductility mismatch and insufficient creep resistance in traditional processes.

[0056] Preferably, 0.75 wt% Mo (β-stabilizing element) + 0.075 wt% Si is added to the welding wire. The strengthening effect of this setting is more balanced, the synergistic effect of Mo solid solution strengthening and Si precipitation strengthening is enhanced, the β grains are further refined and the lamellar α phase is promoted to be evenly distributed, significantly improving the fracture toughness while ensuring the strength, and the optimization effect of the molten pool fluidity is more significant and there are fewer welding defects.

[0057] Preferably, 1.2 wt% Mo (β-stabilizing element) + 0.1 wt% Si is added to the welding wire. The Mo solid solution strengthening effect of this setting is maximized, the β-phase region expands to the peak, the content of high-temperature stable composite strengthening phases is higher, and the creep resistance is significantly improved; the Si precipitation strengthening effect is enhanced, the density of Ti5Si3 phase increases, and the fine grain strengthening effect is the most significant. The room-temperature tensile strength and elongation of the joint reach the upper limit of the range, which is suitable for scenarios with extremely high requirements for high-temperature performance and strength-ductility.

[0058] Example 3

[0059] In this example, the welding wire was improved on the basis of Example 1, and 0.5 wt% Mo element and 0.05 wt% Y element were added to the welding wire.

[0060] Adding 0.5 - 1.2 wt% Mo element can reduce the β transformation temperature of the titanium alloy, making the β phase remain at a lower temperature during the cooling process of the welding molten pool, providing more supersaturated solid solutions for subsequent precipitation strengthening;

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

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

[0063] Preferably, 0.75 wt% Mo element and 0.075 wt% Y element are added to the welding wire. This setting makes the solid solution strengthening effect of Mo and the grain boundary purification effect of Y more balanced. Mo inhibits the growth of β grains, and Y promotes the refinement of β grains. The two work together to achieve fine-grain toughening, improve the fracture toughness, make the impurity purification more thorough, significantly improve the grain boundary strength, and further optimize the joint elongation and creep resistance.

[0064] Preferably, 1.2 wt% Mo element and 0.1 wt% Y element are added to the welding wire. This setting maximizes the solid solution strengthening of Mo, the supersaturation degree of the β phase is the highest, the matrix strength reaches the upper limit of the range, the ability of Y to capture impurities is the strongest, the brittle phases at the grain boundaries are almost completely inhibited, and the grain boundary strength is maximized. It is suitable for scenarios with extremely high requirements for high-temperature performance and strength-toughness. The joint fracture toughness and creep resistance life reach the optimal level.

[0065] Example 4

[0066] In this example, the welding wire was improved on the basis of Example 1. 0.5 wt% Mo element, 0.05 wt% Y element, and 0.05 wt% Si element were added to the welding wire.

[0067] As a β-stabilizing element, Mo improves the matrix strength through solid solution strengthening. At the same time, it cooperates with Si to form Ti-Mo-Si composite strengthening phases and fine Ti5Si3 phases, realizing precipitation strengthening and improvement of creep resistance. The creep life of the joint at 500 °C and 100 MPa ≥ 500 h; As a rare earth element, Y purifies the grain boundaries and captures impurities such as O and N to form high-melting-point compounds (such as Y2O3, YN), reducing the risk of grain boundary embrittlement. At the same time, it promotes the refinement of β grains and, combined with the grain growth inhibition effect of Mo, significantly improves the toughness, making the elongation of the joint ≥ 10% and the fracture toughness ≥ 60 MPa・m 1 / 2 ; The addition of Si further strengthens the precipitation phase system, jointly regulates the precipitation behavior at the grain boundaries with Y, and makes the lamellar α phase evenly distributed; Cooperatively constructs a multiple mechanism of "solid solution strengthening + precipitation strengthening + grain boundary purification + fine-grain toughening", solving the problems of uneven organization, strength-toughness mismatch, and insufficient high-temperature performance in traditional processes, and achieving a room-temperature tensile strength of the joint ≥ 950 MPa and a comprehensive improvement in plasticity and creep resistance.

[0068] Preferably, 0.75 wt% Mo element, 0.075 wt% Y element, and 0.075 wt% Si element are added into the welding wire. This setting enhances the synergistic effect, making the solid solution strengthening of Mo and the precipitation strengthening of Si more balanced, refining the β grains and promoting the uniform distribution of the lamellar α phase. The effect of Y in purifying the grain boundaries is more sufficient, the stress concentration is reduced, the uniformity of the joint performance is improved, and the comprehensive strength and toughness are optimal.

[0069] Preferably, 1.2 wt% Mo element, 0.1 wt% Y element, and 0.1 wt% Si element are added into the welding wire. This setting maximizes the solid solution strengthening of Mo, increases the supersaturation degree of the β phase, and the matrix strength reaches the upper limit. The density of the Si precipitation phase increases, and the fine grain strengthening is significant. The room temperature tensile strength reaches the peak value in the range. The grain boundary strength is maximized. Combined with slow low-temperature air cooling, the martensite microcracks are inhibited, and the fracture toughness and creep resistance life reach the optimal level, which is applicable to extreme working conditions.

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

[0071] A method for controlling the strength and toughness of a high-strength titanium alloy welded joint provided by the present invention. After welding, the non-destructive testing of the welded joint meets the requirements of Grade I in NB / T47013. The joint strength reaches more than 95% of the base metal, the performance difference at different positions of the joint is less than 10%, and the fracture toughness reaches more than 60% of the base metal, effectively improving the strength and toughness matching and performance uniformity between the welded joint and the base metal, and improving the quality of the high-strength titanium alloy welded joint.

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

[0073] Compared with the prior art, the method for controlling the strength and toughness of a high-strength titanium alloy welded joint provided by the present invention has the following advantages:

[0074] 1) It can quickly and reliably realize the welding of high-strength titanium alloy, and the operation is simple; 2) Through gradient heat input and staged cooling, the microstructure control of the weld and the heat affected zone is realized, and then the control of the strength and toughness of the joint is realized. The weld zone obtains the lamellar α phase (aspect ratio 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 realized, and the toughness is improved while ensuring the strength. When using the present invention to weld high-strength titanium alloy, the room temperature tensile strength of the joint is ≥ 950 MPa, the elongation is ≥ 10%, and the fracture toughness is not less than 60 MPa*m 1 / 2, the creep life of the joint at 500°C and 100 MPa ≥ 500 h.

[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 protection scope of the present invention should be subject to the scope defined by the claims.

Claims

1. A method for controlling the strengthening and toughening of a high-strength titanium alloy welded joint, characterized in that, It includes the following steps: S1: During welding, multi-layer and multi-pass gradient heat input is adopted. When welding the previous pass (1), the heat input is Q1, and when welding the subsequent pass (2), the heat input is Q2, then Q1 > Q2; S2: After welding, the welded area is cooled in stages. During the initial cooling stage, forced convection cooling with inert gas is adopted. When cooling to the medium temperature stage, water mist pulse cooling is adopted. When cooling to the low temperature stage, natural air cooling is adopted.

2. The toughening control method for the high-strength titanium alloy welded joint according to claim 1, wherein, In step S1, Q1 = 1.8 - 2.0 kJ / mm, Q2 = 0.8 - 1.2 kJ / mm.

3. The toughening control method of the high-strength titanium alloy welded joint according to claim 1, wherein In step S1, the gradient decreasing rate of the heat input is controlled at 15 - 20% / pass.

4. The toughening control method for the high-strength titanium alloy welded joint according to claim 1, characterized in that 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.

5. The toughening control method for the high-strength titanium alloy welded joint according to claim 1, characterized in that, In step S2, 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.

6. The toughening control method for the high-strength titanium alloy welded joint according to claim 1, characterized in that, Add 0.5 - 1.2 wt% Mo element and 0.05 - 0.1 wt% Y element to the welding wire.

7. The toughening control method of the high-strength titanium alloy welded joint according to claim 1, wherein Add 0.5 - 1.2 wt% Mo element and 0.05 - 0.1 wt% Si element to the welding wire.

8. The toughening control method of the high-strength titanium alloy welded joint according to claim 1, characterized in that, Add 0.5 - 1.2 wt% Mo element, 0.05 - 0.1 wt% Y element, and 0.05 - 0.1 wt% Si element to the welding wire.

Images