Method for connecting titanium metal and steel with medium-high carbon content

Abstract

The invention discloses a method for connecting titanium metal and steel with medium and high carbon content, which is characterized in that a layer of vanadium (V) material, a layer of copper (Cu) material and a layer of nickel (Ni) material are sequentially inserted between the titanium metal and the steel with the medium and high carbon content as an intermediate layer, and then heating and pressurizing are performed to realize diffusion welding connection. The method is applied to diffusion welding connection between titanium and titanium alloy and steel with medium and high carbon content, the problems of harmful diffusion of C element in the steel, generation of interface brittle phase, interface deformation discordance and the like can be effectively solved, and the interface bonding quality and the joint mechanical property are improved.

Description

Technical Field

[0001] This invention relates to the field of dissimilar metal welding technology, and in particular to a joining technology between titanium and titanium alloys and medium- to high-carbon steel. Background Technology

[0002] Steel, due to its low cost and mature processing technology, is one of the most widely used metallic materials in engineering applications. It possesses excellent processability and weldability, and is widely used in pressure vessels, mechanical structures, building construction, and transportation equipment. However, due to its high density, using steel as the sole structural material would significantly increase the overall weight of components, making it difficult to meet lightweight design requirements. In contrast, titanium and titanium alloys offer advantages such as high specific strength and lower density, effectively complementing steel in performance. By constructing steel / titanium composite structures, the performance advantages of both materials can be utilized simultaneously. Therefore, a reliable connection between titanium and steel is a fundamental requirement for industrial applications. Vacuum diffusion welding is a precise solid-state bonding process that, under specific temperature, pressure, and holding time conditions, ensures full contact between the surfaces of the workpieces to be welded, achieving metallurgical bonding through the interdiffusion of interfacial atoms. This method is particularly suitable for joining complex internal structures or large-sized structural components and is a commonly used technique for fabricating steel / titanium composite structures.

[0003] However, due to significant differences in physical and chemical properties between steel and titanium, particularly the mismatch in their coefficients of thermal expansion and chemical affinity, hard and brittle compounds easily form at the interface during diffusion welding, leading to a significant decrease in the mechanical properties of the joint. This is especially true when the carbon content in the steel is high. In such cases, the interface is more likely to form a continuous carbide layer dominated by carbon, thereby further reducing the reliability of the joint connection.

[0004] In practical engineering applications, high-carbon steel is often combined with titanium. For example, Stanford Advanced Materials developed the CLD1442 titanium-clad carbon steel structure for oil and gas pipelines and aerospace components. The carbon content is approximately Low-alloy ultra-high strength steel for aircraft landing gear and solid-fuel rocket engine casings. Its carbon content is close to .

[0005] Patent CN201110123247 discloses a diffusion welding method for titanium alloys and stainless steel. This method involves pre-welding a block structure using plates of the same material as the workpieces. The block structure is then longitudinally sliced ​​into thin sheets to form an intermediate layer. This intermediate layer is then processed and vertically placed between the workpieces for diffusion welding. Because an intermediate layer of the same material as the workpieces is used, the joint's heterogeneous interface bonding is changed to a combination of half homogeneous workpieces and half heterogeneous workpieces, ultimately achieving a high-strength connection between titanium or titanium alloys and stainless steel workpieces. However, this welding method has a complex process flow and does not fundamentally solve the problems of interdiffusion of interfacial elements and the formation of brittle phases.

[0006] Direct diffusion welds between titanium and titanium alloys and medium-to-high carbon steel exhibit poor strength. This is due not only to the formation of brittle phases between the main elements (Ti and Fe), but also to the diffusion of carbon (C) towards the titanium side, negatively impacting the interfacial bonding quality. Therefore, achieving better bonding between titanium and titanium alloys and medium-to-high carbon steel while suppressing the harmful diffusion of carbon from the steel has become a core technical challenge in titanium / steel diffusion welding and a key bottleneck restricting the improvement of joint strength. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is: how to provide a method for connecting titanium metal and medium-to-high carbon content steel that can better suppress the diffusion of carbon elements, improve the metallurgical compatibility of the composite interface, and improve the connection strength.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0009] A method for joining titanium metal and medium-to-high carbon content steel is characterized by sequentially inserting a layer of vanadium (V), a layer of copper (Cu), and a layer of nickel (Ni) as an intermediate layer between the titanium metal and the medium-to-high carbon content steel, followed by heating and pressurizing to achieve diffusion welding. The titanium metal mentioned in this method refers to titanium or a titanium alloy.

[0010] The applicant's research revealed that diffusion welding of titanium and steel without an interlayer or with single / double interlayers struggles to achieve a high-quality bonding interface. This is attributed to the interdiffusion of Ti, Fe, and C elements, with C exhibiting particularly significant harmful diffusion. Therefore, to suppress harmful C diffusion and improve the metallurgical compatibility of the composite interface, the applicant developed the scheme described in this application. This scheme uses sequentially stacked vanadium (V), copper (Cu), and nickel (Ni) materials as interlayer materials. Vanadium (V) is chosen as the first interlayer, immediately adjacent to the titanium and titanium alloy substrate. At high temperatures, it forms a solid solution with the titanium substrate, enhancing the bonding strength. Furthermore, vanadium exhibits a certain degree of solid solubility with copper, effectively enabling their interconnection. The vanadium, acting as a barrier between the titanium and the other two layers, effectively prevents the formation of brittle intermetallic compounds through contact. The selected copper (Cu) and nickel (Ni) materials both possess excellent ductility and toughness, effectively accommodating joint deformation during the initial loading stage. Both materials effectively suppress carbon diffusion and carbide formation (Cu and Ni have extremely low solid solubility for C and do not readily form stable carbides, preventing the formation of continuous compound layers at the interface; simultaneously, the introduction of a Cu-Ni interlayer significantly extends the effective diffusion path of C towards the titanium side, thus acting as a diffusion barrier layer kinetically). Furthermore, they are infinitely miscible at high temperatures. Ni is also a common strengthening element in steel and exhibits excellent compatibility with steel, resulting in very high bonding strength when the two are bonded together. Among the three interlayer materials used, when V and Ni are in direct contact, they tend to form thermodynamically stable brittle phases over a wide compositional range. Therefore, copper was used to separate them, avoiding this defect and better achieving bonding with vanadium and nickel. Thus, the final V / Cu / Ni multi-interlayer structure exhibits extremely high bonding strength. This diffusion bonding method for titanium and titanium alloys with medium- to high-carbon steel effectively controls the harmful diffusion of carbon and inhibits the formation of brittle phases at the interface, greatly improving the tensile strength of the composite interface.

[0011] Furthermore, the vanadium material is in the form of pure metal foil or chemical plating, the copper material is in the form of pure metal foil or chemical plating, and the nickel material is in the form of pure metal foil or chemical plating. In specific implementation, the V, Cu, and Ni foils are first cleaned to remove oxidation, avoiding impurities and oxide films that hinder atomic diffusion and reduce joint performance. When using chemical plating, the intermediate layer material can be plated sequentially or separately onto the surface of titanium metal or medium-to-high carbon steel, and then heated and pressurized to achieve diffusion bonding. It should be ensured that the plated titanium or steel side surface is clean and free of oxidation, avoiding impurities and oxide films.

[0012] Furthermore, the thickness of the vanadium (V) material interlayer (V foil or V electroless plating) is controlled within 40–100 μm, the thickness of the copper (Cu) material interlayer (Cu foil or Cu electroless plating) is controlled within 10–40 μm, and the thickness of the nickel (Ni) material interlayer (Ni foil or Ni electroless plating) is controlled within 10–40 μm. This is because: when the thickness of the V foil or electroless V plating is less than 40 μm, V's barrier effect on Ti is insufficient, allowing Ti to easily penetrate the V interlayer and react with Cu, forming a brittle phase; when the V thickness is greater than 100 μm, an excessively thick V interlayer significantly increases the atomic diffusion distance, hindering sufficient interdiffusion of interfacial elements. Controlling the thickness of Cu and Ni within the range of 10–40 μm ensures effective suppression of carbon diffusion and improved interfacial compatibility, while avoiding reduced diffusion connection efficiency and decreased joint mechanical properties due to excessively thick interlayers.

[0013] Furthermore, before diffusion welding, the surfaces of titanium metal and medium-to-high carbon steel to be welded are ground with metallographic sandpaper (preferably 120~3000#) and then mechanically polished. These are then used as the base material for welding. The polished base material is then ultrasonically cleaned in acetone solution for 15 minutes, followed by ultrasonic cleaning in anhydrous ethanol solution for 15 minutes. This process ensures a cleaner surface and improves the weld strength.

[0014] Furthermore, before welding, the titanium and titanium alloy surfaces to be welded are placed face up, and V foil, Cu foil, and Ni foil are placed in sequence. Then, the medium-high carbon steel surface to be welded is brought into contact with the topmost Ni foil; or V is chemically plated on one side of the titanium and titanium alloy surface to be welded, and Ni and Cu are chemically plated in sequence on the other side of the medium-high carbon steel surface to be welded. Finally, after stacking, they are welded into a combination of titanium and titanium alloy - V / Cu / Ni - medium-high carbon steel.

[0015] Furthermore, during diffusion welding, the objects to be welded are located in a vacuum autoclave, and a pressure of 10~50 MPa is applied. When the vacuum level inside the autoclave reaches... Start heating at a certain time, heating from room temperature to 700 ℃ at a heating rate of 10~30 ℃ / min, then heating from 700 ℃ to 800 ℃~1000 ℃ at a heating rate of 5~15 ℃ / min, holding at this temperature for 20~80 min, depressurizing after holding, and cooling with the furnace to below 100 ℃ before taking it out.

[0016] In this way, the use of this welding process control can effectively avoid contamination of the base material and interface, and achieve precise control of welding parameters. The principle is that the vacuum environment significantly weakens the interference of active elements such as oxygen, nitrogen, and hydrogen on the interface reaction. At the same time, under the action of controlled high temperature and pressure, the material softens and undergoes micro-plastic deformation, thereby promoting the tight adhesion of the contact interface and forming a continuous and dense metallurgical bond.

[0017] Furthermore, the optimal range of applied pressure is 25~35 MPa.

[0018] Furthermore, the optimal range for vacuum degree inside the hot press furnace is: .

[0019] Furthermore, during diffusion welding, the optimal heating rate range for heating from room temperature to 700 ℃ is 15~25 ℃ / min, and the optimal heating rate range for heating from 700 ℃ to 800 ℃~1000 ℃ is 7~13 ℃ / min.

[0020] Furthermore, the optimal heating temperature range is 850~950 ℃.

[0021] Furthermore, the optimal heat preservation time ranges from 40 to 60 minutes.

[0022] The beneficial effects of this invention are:

[0023] (1) By introducing V / Cu / Ni multiple intermediate layers, the interdiffusion of harmful elements between titanium and titanium alloys and medium-high carbon steel can be suppressed, especially the diffusion of harmful elements such as C, and no brittle phase or carbide layer is formed at each interface.

[0024] (2) The V / Cu / Ni multi-intermediate layer has good compatibility with the base material, and the interface forms a continuous and dense solid solution region with sufficient atomic diffusion. The mechanical properties of the joint can exceed those of pure titanium base material.

[0025] (3) The V / Cu / Ni multi-intermediate layer has good plasticity and deformation capacity. During the loading process, it can effectively alleviate the stress concentration at the interface through coordinated deformation, thereby reducing the residual stress in the joint.

[0026] (4) It is suitable for diffusion bonding between titanium and titanium alloys and steels with different carbon contents, with a wide process window and high joint reliability.

[0027] In summary, this invention is applied to diffusion welding between titanium and titanium alloys and medium-to-high carbon steel, which can effectively solve problems such as harmful diffusion of C element in steel, formation of brittle phases at the interface, and incoordination of interface deformation, thereby improving the interface bonding quality and joint mechanical properties. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of each layer of material during welding using the method of the present invention.

[0029] Figure 2 This is a scanning electron microscope image of the diffusion welded head obtained in Experiment Example 1 of the present invention.

[0030] Figure 3 This is a scanning electron microscope image of the diffusion welded head obtained in Experiment Example 2 of the present invention.

[0031] Figure 4 This is a scanning electron microscope image of the diffusion welded head obtained in Experiment Example 3 of the present invention. Detailed Implementation

[0032] The present invention will now be described in further detail with reference to specific embodiments.

[0033] Implementation method: A method for connecting titanium metal and medium-to-high carbon content steel, characterized in that, see [link to implementation details]. Figure 1 A layer of vanadium (V) material 2, copper (Cu) material 3, and nickel (Ni) material 4 are sequentially inserted between titanium metal 1 and medium-high carbon steel 5 as an intermediate layer, and then diffusion welding is achieved by heating and pressurizing. In practice, the titanium metal refers to titanium or titanium alloy; in this embodiment, pure titanium base material is used.

[0034] In this embodiment, the vanadium, copper, and nickel materials are all obtained from pure metal foils. Other embodiments may also employ chemical plating. Specifically, the V, Cu, and Ni foils are first cleaned to ensure they are free of oxidation, preventing impurities and oxide films from hindering atomic diffusion and reducing joint performance. When using chemical plating, the intermediate layer material can be plated sequentially or separately onto the surface of titanium or medium-to-high carbon steel, followed by heating and pressurization to achieve diffusion bonding. It is essential to ensure that the plated titanium or steel surface is clean and free of oxidation, avoiding impurities and oxide films.

[0035] In practice, the thickness of the vanadium (V) material intermediate layer is controlled between 40 and 100 μm, specifically 50 μm in this embodiment; the thickness of the copper (Cu) material intermediate layer is controlled between 10 and 40 μm, specifically 20 μm in this embodiment; and the thickness of the nickel (Ni) material intermediate layer is controlled between 10 and 40 μm, specifically 10 μm in this embodiment.

[0036] During implementation, before diffusion welding, the surfaces of titanium metal and medium-to-high carbon steel to be welded are ground and mechanically polished using 120~3000# metallographic sandpaper. These polished base materials are then ultrasonically cleaned in acetone solution for 15 minutes, followed by ultrasonic cleaning in anhydrous ethanol solution for another 15 minutes. This process ensures a cleaner surface and improves the weld strength.

[0037] During implementation, before welding, the titanium and titanium alloy surfaces to be welded are placed with the V foil, Cu foil, and Ni foil placed in sequence. Then, the medium-to-high carbon steel surfaces to be welded are brought into contact with the topmost Ni foil. Alternatively, V foil can be chemically plated on one side of the titanium and titanium alloy surfaces to be welded, and Ni and Cu foil can be chemically plated in sequence on the other side of the medium-to-high carbon steel surfaces to be welded. Finally, after stacking, they are welded into a combination of titanium and titanium alloy - V / Cu / Ni - medium-to-high carbon steel.

[0038] During implementation, when performing diffusion welding, the objects to be welded are located in a vacuum autoclave, and a pressure of 10~50 MPa (preferably 25~35 MPa) is applied. When the vacuum level inside the autoclave reaches... (Preferred to be) Heating begins at 700°C, with a heating rate of 10-30°C / min (preferably 15-25°C / min) from room temperature to 700°C. Then, the temperature is increased from 700°C to 800°C-1000°C (preferably 850-950°C) at a heating rate of 5-15°C / min (preferably 7-13°C / min). The temperature is then held at this temperature for 20-80 min (preferably 40-60 min). After the holding period, the pressure is released, and the furnace is cooled to below 100°C before removal.

[0039] To better verify the effectiveness of the present invention, the applicant, based on the above-mentioned requirements of the embodiments, selected carbon steel with different carbon contents as the steel side base material for experiments to verify the inhibitory effect of V / Cu / Ni multi-intermediate layer combination on C element diffusion and the interfacial metallurgical compatibility, and carried out three sets of specific experimental examples.

[0040] Experimental Example 1

[0041] In this experimental example 1, the pure titanium base material is TA2, the carbon steel base material is 20# low carbon steel, and the diffusion welding temperature is 880 ℃.

[0042] First, TA2 and 20# carbon steel are processed into The cylindrical material to be welded was successively polished with metallographic sandpaper of 120#, 240#, 400#, 800#, 1000#, 1500#, 2000# and 3000#, and polished to a mirror finish on a polishing machine. Then the base material to be welded and the three pure metal foils were successively cleaned in acetone and anhydrous ethanol solutions for 15 minutes each.

[0043] Then, the assembled The assembly is placed in a vacuum autoclave and a pressure of 30 MPa is applied. When the vacuum level inside the autoclave reaches... Heating begins at a certain time, with a heating rate of 15 °C / min from room temperature to 700 °C, followed by a heating rate of 10 °C / min from 700 °C to 880 °C. The temperature is held at this level for 40 min. After the holding period, the pressure is released, and the sample is removed from the furnace and cooled to below 100 °C.

[0044] Experimental Example 2

[0045] The difference between Experiment 2 and Experiment 1 is that the carbon steel base material is 45# medium carbon steel, while the rest is the same as Experiment 1.

[0046] Experimental Example 3

[0047] The difference between Experiment 3 and Experiment 1 is that the carbon steel base material is 85# high carbon steel, while the rest is the same as Experiment 1.

[0048] The applicant conducted tensile strength tests on the welded joints obtained from the above three sets of experimental examples. The test results are shown in the table below, where the unit of tensile strength is MPa and the unit of joint connection efficiency is _____.

[0049]

[0050] See Figures 2-4 The welding interfaces of the three experimental examples were characterized by scanning electron microscopy. In Experiment 1, no defects such as voids or incomplete welding were found in the composite interface. The pure titanium / V interface showed good bonding, the V / Cu interface was relatively distinct, the Cu / Ni interface showed good fusion, and the Ni / 20# carbon steel interface showed uniform interdiffusion. In Experiment 2, the overall morphology of the composite interface was similar to that of Experiment 1, and no defects such as voids or incomplete welding were found. The interfaces showed good bonding. In Experiment 3, no defects such as voids or incomplete welding were found in the composite interface, and the interfaces showed good bonding.

[0051] By comparing three sets of experimental examples, the V / Cu / Ni multi-intermediate layer can effectively suppress the harmful diffusion of C element in steels with different carbon contents. No continuous carbides or brittle phases are formed at each interface, and high-quality metallurgical connection is formed at the interface. The joint connection efficiency reaches more than 90%, and the maximum tensile strength of the diffusion weld joint exceeds that of the TA2 pure titanium base material after welding, achieving a firm connection.

Claims

1. A method for connecting titanium metal and medium-to-high carbon content steel, characterized in that, A layer of vanadium, copper, and nickel is sequentially inserted between titanium metal and medium-to-high carbon steel as an intermediate layer, and then diffusion welding is achieved by heating and pressurizing.

2. The method for connecting titanium metal and medium-to-high carbon content steel as described in claim 1, characterized in that, The vanadium material is in the form of pure metal foil or chemical plating, the copper material is in the form of pure metal foil or chemical plating, and the nickel material is in the form of pure metal foil or chemical plating.

3. The method for connecting titanium metal and medium-to-high carbon content steel as described in claim 1, characterized in that, The thickness of the intermediate layer for vanadium is controlled at 40~100 μm, the thickness of the intermediate layer for copper is controlled at 10~40 μm, and the thickness of the intermediate layer for nickel is controlled at 10~40 μm.

4. The method for connecting titanium metal and medium-to-high carbon content steel as described in claim 1, characterized in that, Before diffusion welding, the surfaces of titanium metal and medium-to-high carbon steel to be welded are ground with metallographic sandpaper and then mechanically polished. These are used as the base materials for welding. The polished base materials are then ultrasonically cleaned in acetone solution for 15 minutes and then ultrasonically cleaned in anhydrous ethanol solution for 15 minutes.

5. The method for connecting titanium metal and medium-to-high carbon content steel as described in claim 1, characterized in that, Before diffusion welding, the titanium and titanium alloy surfaces to be welded are placed upwards, and V foil, Cu foil, and Ni foil are placed in sequence. Then, the medium-to-high carbon steel surface to be welded is brought into contact with the topmost Ni foil. Alternatively, V is chemically plated on one side of the titanium and titanium alloy surface to be welded, and Ni and Cu are chemically plated in sequence on the other side of the medium-to-high carbon steel surface to be welded. Finally, after lamination, the components are welded into a combination of titanium and titanium alloy - V / Cu / Ni - medium-to-high carbon steel.

6. The method for connecting titanium metal and medium-to-high carbon content steel as described in claim 1, characterized in that, During diffusion welding, the objects to be welded are placed in a vacuum autoclave, and a pressure of 10~50 MPa is applied. When the vacuum degree inside the autoclave reaches 5×10⁻⁶ MPa... -2 ~1×10 -3 Heating begins at Pa, with a heating rate of 10~30 ℃ / min from room temperature to 700 ℃, followed by a heating rate of 5~15 ℃ / min from 700 ℃ to 800 ℃~1000 ℃. The temperature is held at this level for 20~80 min. After holding, the pressure is released, and the furnace is cooled to below 100 ℃ before removal.

7. The method for connecting titanium metal and medium-to-high carbon content steel as described in claim 6, characterized in that, The applied pressure range is 25~35 MPa.

8. The method for connecting titanium metal and medium-to-high carbon steel as described in claim 6, characterized in that, The vacuum level inside the hot press furnace is 1×10 -2 ~5×10 -3 Pa.

9. The method for connecting titanium metal and medium-to-high carbon content steel as described in claim 6, characterized in that, During diffusion welding, the heating rate from room temperature to 700 ℃ is 15~25 ℃ / min, and the heating rate from 700 ℃ to 800 ℃~1000 ℃ is 7~13 ℃ / min.

10. The method for connecting titanium metal and medium-to-high carbon content steel as described in claim 6, characterized in that, The heating temperature range is 850~950 ℃; the holding time range is 40~60 min.

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