Welding method of titanium-steel double-metal composite structure and application of welding method

Abstract

The invention discloses a welding method of a titanium-steel bimetal composite structure and application of the welding method, and relates to the technical field of welding. The titanium-steel bimetal composite structure comprises a steel layer and a titanium layer, according to the welding method, the stepped U-shaped groove is designed in the steel layer, the titanium layer at the bottom is completely exposed, and contact between titanium and steel is completely isolated while full fusion of a welding seam is achieved; and besides, the U-shaped groove of the to-be-welded part is welded in a butt joint mode, mutual fusion between layers is effectively prevented through the reasonable and feasible welding sequence and the optimized welding technology, and therefore formation of Fe-Ti compounds between brittle metal is restrained, and the strength of the titanium steel composite structure connector is improved. The titanium-steel double-metal composite structure manufactured through the welding method is expected to be popularized and applied in the fields of marine equipment and petroleum.

Description

Technical Field

[0001] The invention relates to the technical field of welding, and in particular to a welding method for a titanium-steel bimetallic composite structure and application thereof. Background Art

[0002] Titanium-steel composite structures (composite plates or composite pipes) are bimetallic composite materials with steel as the substrate and titanium as the cladding. They have the good corrosion resistance of titanium and can reduce the application cost at the same time. They are ideal materials widely used in marine equipment and petroleum fields. However, due to the large difference in the physical metallurgical properties of titanium and steel, and the fact that Fe and Ti elements easily react to form brittle intermetallic compounds, the welding difficulty of titanium-steel composite structures is large and the joint strength is low, which restricts their wide application.

[0003] In view of this, the present invention is proposed. Summary of the invention

[0004] The object of the present invention is to provide a welding method for a titanium-steel bimetallic composite structure and its application to solve the above technical problems.

[0005] The present invention is achieved in that:

[0006] In a first aspect, an embodiment of the present invention provides a method for welding a titanium-steel bimetallic composite structure, wherein the titanium-steel bimetallic composite structure includes a steel layer and a titanium layer;

[0007] The welding method comprises: processing a stepped U-shaped groove on a steel layer, and providing a stepped area connected to a titanium layer at the bottom of the U-shaped groove to obtain a workpiece to be welded; butt welding is performed at the U-shaped groove of the workpiece to be welded;

[0008] Among them, the sum of the slope height of the U-shaped groove and the height of the step area is equal to the thickness of the steel layer; the height of the step area is equal to the blunt edge of the U-shaped groove; and the titanium layer in the step area is in contact with the atmosphere.

[0009] In a second aspect, an embodiment of the present invention provides an application of a titanium-steel bimetallic composite structure prepared by the aforementioned welding method in the field of marine equipment and petroleum.

[0010] The present invention has the following beneficial effects:

[0011] The welding method of the titanium-steel bimetallic composite structure provided by the embodiment of the present invention designs a stepped U-shaped groove on the steel layer to completely expose the titanium layer at the bottom, which helps to completely isolate the contact between titanium and steel while achieving full fusion of the weld; in addition, a reasonable and feasible welding sequence and an optimized welding process effectively prevent mutual melting between the layers, thereby inhibiting the formation of brittle intermetallic Fe-Ti compounds and improving the strength of the titanium-steel composite structure joint. The titanium-steel bimetallic composite structure obtained by this welding method is expected to be promoted and applied in the fields of marine equipment and petroleum. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0013] Figure 1 It is a schematic diagram of the stepped U-shaped groove structure;

[0014] Figure 2 This is a schematic diagram of the butt welding sequence of the parts to be welded;

[0015] Figure 3 This is a scanning image of the welding cross section of the titanium-steel bimetallic composite structure prepared in Example 1;

[0016] Figure 4 This is a scanning image of the welding cross section of the titanium-steel bimetallic composite structure prepared in Comparative Example 1.

[0017] Explanation of main component symbols: 100-schematic diagram of stepped U-shaped groove structure; 101-steel layer; 102-titanium layer; 103-root radius; 104-blunt edge; 105-root gap; 106-groove width; 200-schematic diagram of butt welding sequence of welded parts; 203-first weld; 204-second weld; 205-first steel layer; 206-second steel layer; 207-third steel layer; 208-fourth steel layer; 209-covering layer. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0019] At present, there are two common welding methods for titanium-steel composite plates. The first is the contactless welding method, which uses layered welding to transform the bimetallic structure into the same material welding of titanium and steel. However, in order to avoid mutual melting between steel and titanium, there is always about 1mm of unpenetrated space at the interface between the titanium layer and the steel layer. This unwelded area makes it difficult for the overall strength of the joint to meet the application requirements. The second is to use a variety of filler materials for layer-by-layer welding, adding a transition layer between the welds to improve the joint performance, such as adding Nb and V that have good compatibility with Fe and Ti, adding Cu elements to preferentially generate Cu-Ti intermetallic compounds with good toughness, and adding high melting point materials such as Mo to isolate Fe from Ti. However, intermetallic compounds such as Fe-Ti, Cu-Ti, and Fe-Mo will still be generated at the interface of different filler materials and the interface between titanium and steel layers.

[0020] Chinese patent CN117206642A, the patent name is a method for butt-joining titanium-steel composite plates. In step S3, the titanium layer is welded while the remaining 1mm portion of the steel layer is welded through. This process causes direct contact between titanium and steel. When filling the CuSi10 wire in step S4, the steel layer, transition layer and titanium layer also have mutually melted areas. In other words, this technology does not completely isolate the titanium and steel layers, and there is a possibility of forming Fe-Ti intermetallic compounds. In addition, this technology uses manual argon arc welding for CuSi10 wire filling, which is inefficient.

[0021] In order to solve the above technical problems, the present invention provides the following specific implementation methods:

[0022] In a first aspect, an embodiment of the present invention provides a welding method for a titanium-steel bimetallic composite structure, wherein the titanium-steel bimetallic composite structure includes a steel layer 101 and a titanium layer 102;

[0023] The welding method comprises: processing a stepped U-shaped groove on the steel layer 101, and providing a stepped area connected to the titanium layer 102 at the bottom of the U-shaped groove to obtain a workpiece to be welded; butt welding is performed at the U-shaped groove of the workpiece to be welded;

[0024] The sum of the slope height of the U-shaped groove and the height of the step area is equal to the thickness of the steel layer 101; the height of the step area is equal to the blunt edge 104 of the U-shaped groove; and the titanium layer 102 in the step area is in contact with the atmosphere.

[0025] It should be noted that in the embodiment of the present invention, the groove design scheme is changed, the alloy barrier layer is welded between steel and titanium, and the overall welding sequence, process flow and process parameters are adjusted to minimize or completely eliminate the formation of the brittle intermetallic phase Fe-Ti, thereby improving the strength of the titanium-steel composite structure joint. No microcracks are found in the welded joint obtained by this method, and the tensile strength of the joint is not less than 85% of the parent material; while the tensile strength of the joint obtained by the conventional welding method is only 65% ​​of the parent material at most.

[0026] In an optional embodiment of the present invention, the blunt edge 104 of the U-shaped groove is 1.0 mm-2.5 mm, the root gap 105 is 5 mm-10 mm, the groove width 106 is 10 mm-20 mm, and the root radius 103 is 0.5 mm-1.5 mm.

[0027] It should be noted that when the blunt edge 104 in the U-shaped groove is less than 1mm, there is a risk that the shielding effect will not be effective during the barrier layer cladding process, and Fe-Ti intermetallic compounds and cracks are easily formed; when the blunt edge 104 in the U-shaped groove is greater than 2.5mm, gaps may appear between the titanium layer and the barrier layer, which will have an adverse effect on the mechanical properties of the joint.

[0028] When the root gap 105<5mm, the steel layer may melt at the same time when welding the titanium layer, forming brittle Fe-Ti intermetallic compounds and cracks; when the root gap 105>10mm, more passes are required to fill the U-shaped groove of the steel layer, which will have a negative impact on welding productivity.

[0029] The groove width 106 value is affected by the thickness of the steel layer. When the groove width 106 <10mm, it is impossible to perform fill welding (surfacing) on ​​the steel layer on the barrier layer, and the arc may start to jump from the bottom of the groove to the side wall, resulting in defects in the surfacing layer and unstable weld quality; when the groove width 106 >20mm, more passes are required to fill the U-shaped groove of the steel layer, which greatly reduces welding efficiency and increases costs.

[0030] The root of the weld is where stress concentrates during welding. Designing the root of the groove as a chamfer can reduce welding stress and the stress concentration intensity at the root of the weld, thereby avoiding the generation of weld cracks. The chamfer design makes it easier to guide the welding rod into the chamfer and avoid the inability to fuse the edges of the groove. In addition, it can also weaken the raised part of the welding point, making the welding rod and the base material more closely combined, which is beneficial to the circulation of metal at the welding point, avoiding the occurrence of porosity, cracking and other problems, thereby enhancing the quality of the weld.

[0031] In an optional embodiment of the present invention, the material of the titanium layer 102 is pure titanium or titanium alloy, and the thickness S1 is 1 mm-3 mm; the material of the steel layer 101 is stainless steel or carbon steel, and the thickness S2 is 10 mm-20 mm.

[0032] In an optional implementation manner of the present invention, the workpiece to be welded with the processed U-shaped groove is polished, cleaned and dried to remove impurities on the welding surface.

[0033] Specifically, the welded parts with U-shaped grooves are polished with sandpaper, cleaned with acetone, and dried to remove impurities such as grease and scale on the welding surface. In other optional embodiments of the present invention, the polishing method, cleaning agent, and drying method of the welded parts can be reasonably adjusted according to actual conditions.

[0034] In an optional embodiment of the present invention, the order of butt welding the dried parts to be welded includes: welding the titanium layer 102 using any one of pulse plasma welding technology, laser welding technology or electron beam welding technology to form a first weld 203; and single-pass butt welding without filler wire is used when welding the first weld 203.

[0035] It should be noted that the welding technology is directly related to the welding filler wire material. In the embodiment of the present invention, the optimal welding technology and welding process parameters are selected for welding according to different welding filler wires.

[0036] Among them, plasma welding forms high-temperature, high-energy, and high-speed plasma through gas ionization, thereby achieving rapid heating, melting, and welding of metals. This technology has fast welding speed, small heat-affected zone, and low evaporation loss, and is particularly suitable for welding thin metal workpieces. However, its equipment cost is high, welding stability is easily affected by the environment, and it requires high skills of operators.

[0037] Laser welding uses a laser beam with high light concentration and high power density to achieve rapid and accurate heating, melting and welding of metal materials. Its advantages are high-precision welding, high welding quality, small molten pool, beautiful joints, and guaranteed metal material quality. However, laser welding equipment is expensive and requires high special properties of metal materials and high operating skills.

[0038] Electron beam welding has an extremely high power density, which makes its heating concentrated, thermal efficiency high, and welding speed fast; it can penetrate thicker metal plates, and does not require beveling or adding welding wire when welding thick plates. It is dozens of times faster than conventional fusion welding methods and can significantly improve production efficiency. However, electron beam welding equipment is complex, the one-time investment is large, and the protection requirements for operators are high.

[0039] Single-pass butt welding refers to the situation where the weld can be completed with only one weld. The weld width is uniform, the surface is smooth, and there are no obvious defects such as protrusions, depressions or cracks. This welding method can ensure the uniformity of metal melting, cooling and crystallization during the welding process, thereby ensuring the strength and sealing of the welded joint. However, it is a great challenge to the technical level and professional ability of the welder.

[0040] By adopting the welding process without filler wire, the welding joint will hardly produce welding defects such as inclusions, thus ensuring the welding quality; in addition, the use of toxic and harmful chemicals can be avoided, reducing the pollution of smoke and odor.

[0041] In a preferred embodiment of the present invention, the welding technology is pulse plasma welding technology, wherein the outer surface shape of the plasma forming nozzle is a rectangle with an aspect ratio of 1.4-1.8, and the length direction of the rectangle is along the welding direction; the length of the nozzle is 8mm-19mm, the diameter of the plasma channel inside the nozzle is 1.2mm-3.2mm, and the fillet radius of the nozzle cut is 3mm±0.5mm; the maximum value of the pulse current is 110A-120A, and the minimum value is 60A-70A; the arc voltage is 20V-22V, the welding speed is 200mm / min-400mm / min, the plasma arc gas flow rate is 0.4L / min-0.8L / min, and the shielding gas flow rate is 45L / min-55L / min; argon gas is used to protect the weld during the welding process.

[0042] It should be noted that the nozzle length is related to the thickness of the steel layer 101, and the diameter of the plasma channel inside the nozzle is related to the thickness of the titanium layer 102, which can be reasonably adjusted according to the actual parameters of the welded parts.

[0043] In an optional embodiment of the present invention, the order of butt welding also includes: using soft arc plasma welding technology to deposit shielding material on the first weld 203 so that it completely covers the stepped area at the bottom of the U-shaped groove to form a second weld 204.

[0044] Among them, the line energy of soft arc plasma is 100J / mm-150J / mm, and the welding current is 80A-100A; argon gas is used to protect the weld during the welding process.

[0045] It should be noted that if the line energy exceeds 150 J / mm, it will affect the quality of the weld. Specifically, the shielding material and titanium are mixed to a certain extent, and after the steel is deposited on the shielding material layer, it leads to the formation of intermetallic compounds of the Fe-Ti system and the formation of cracks.

[0046] The second weld 204 is deposited by surfacing welding, and the number of weld passes is reasonably adjusted according to the parameters of the actual welded parts; if the number of weld passes is large, that is, multiple welding may cause overheating, deformation or cracks in the weld, and cracks may reduce the strength and reliability of the weld. If the number of weld passes is 1, during the surfacing process, it can be achieved by increasing the swing of the nozzle.

[0047] The titanium layer 102 in the step area is in contact with the atmosphere, that is, the titanium layer 102 in the step area is completely exposed to the air. Filling the shielding material here as a barrier layer for complete coverage can effectively isolate the contact between titanium and steel, effectively avoid the formation of brittle intermetallic Fe-Ti compounds, and is beneficial to enhancing the strength of the titanium-steel composite structure joint.

[0048] Furthermore, the shielding material is selected from any one of CuSi3Mn1 alloy, Nb and V.

[0049] It should be noted that the shielding material, as an alloy barrier layer, helps to achieve full fusion of the weld while completely isolating the contact between titanium and steel. Compared with the traditional steel barrier layer, the alloy barrier layer has higher strength, greater hardness, and better durability. It can withstand greater pressure and weight, is not easily deformed or damaged, and can be used in a variety of harsh environments. The alloy barrier layer is also corrosion-resistant and can be used for a long time in acidic, alkaline, and high-salinity environments.

[0050] In an optional embodiment of the present invention, the shielding material is a CuSi3Mn1 alloy; in terms of mass percentage, the elements in the CuSi3Mn1 alloy include Si 2.5%-5.5%, Mn 0.3%-2.0%, other inevitable impurities 0%-0.7%, and the balance Cu. In other embodiments of the present invention, the shielding material can be selected from Nb or V according to actual needs.

[0051] In an optional embodiment of the present invention, the sequence of butt welding further includes: surfacing the first steel layer 205 on the second weld 204 using pulsed arc gas metal shielded welding technology.

[0052] Among them, the diameter of the melting electrode used is 0.8mm-1.0mm, the ratio of pulse time to pause time is (1.5-2.5): 1, the pulse frequency is 3Hz-10 Hz, the wire energy is 150J / mm-200J / mm, the current is 30A-45A, the arc voltage is 15V-20V, the welding speed is 180mm / min-220mm / min, the wire feeding speed is 1.5m / min-2.0m / min, the shielding gas flow rate is 10L / min-15L / min, and the welding process is protected by a mixed gas of argon and carbon dioxide.

[0053] It should be noted that the operation of gas metal arc welding is relatively simple. It usually uses carbon dioxide or mixed gas as the shielding gas, which can effectively prevent the weld from being oxidized and contaminated during the welding process. Gas metal arc welding is suitable for workpieces of various materials, sizes and shapes; its welding speed is fast and can significantly improve production efficiency; in addition, the weld quality of gas metal arc welding is higher, the weld strength is higher, and the weld appearance is beautiful.

[0054] During the pulse arc generation process, the power supply provides high voltage pulses to ionize the gas molecules between the electrodes to form plasma. This plasma has high conductivity and can allow large currents to pass through, thereby generating strong arc discharge.

[0055] In an optional embodiment of the present invention, the sequence of butt welding further includes: using a metal arc welding method to continue surfacing the second steel layer 206 , the third steel layer 207 and the fourth steel layer 208 on the first steel layer 205 .

[0056] It should be noted that in the embodiment of the present invention, the metal active gas shielded arc welding method (ie, MAG welding) is specifically used to weld the second steel layer 206 to the fourth steel layer 208. In other embodiments of the present invention, the welding method can be adjusted according to actual needs.

[0057] Among them, the diameter of the melting electrode used is 1.0mm-1.2mm, the wire energy is 300J / mm-350J / mm, the welding current is 100A-120A, the arc voltage is 18V-22V, the welding speed is 280mm / min-320mm / min, the wire feeding speed is 2.8m / min-3.2m / min, and the shielding gas flow rate is 14L / min-18L / min; the welding process is protected by a mixed gas of argon and carbon dioxide.

[0058] In an optional embodiment of the present invention, when surfacing the second steel layer 206, the third steel layer 207 and the fourth steel layer 208, the height of the surfacing steel layer, the welding current and the arc voltage satisfy the relationship of formula (1): δ = 2n·e 1 / (I·U) (1).

[0059] In formula (1), δ is the height of the surfacing steel layer (mm); n is the deposition sequence number of the surfacing second steel layer 206, the third steel layer 207 and the fourth steel layer 208 (n=1, 2, 3); I is the welding current (A); and U is the arc voltage (V).

[0060] In an optional embodiment of the present invention, the sequence of butt welding further includes: surfacing a cap layer 209 on the fourth steel layer 208 by using a metal arc welding method.

[0061] It should be noted that the embodiment of the present invention specifically adopts the metal active gas shielded arc welding method (ie, MAG welding) to weld the capping layer 209. In other embodiments of the present invention, the welding method can be adjusted according to actual needs.

[0062] The surfacing layer 209 on the fourth steel layer 208 has the following features: (1) improving the appearance of the weld and making the weld surface smoother; (2) filling and leveling, making a smooth transition between the weld and the parent material surface and reducing undercut defects; (3) regulating the weld size to meet the design requirements, such as excess height, width, etc.

[0063] It should be noted that the thickness of the cap layer 209 is directly related to the thickness of the titanium layer 102 and is affected by the appearance design of the weld. It needs to be reasonably adjusted according to the actual working conditions. Taking 2 mm excess height as an example, the thickness of the cap layer 209 is calculated as follows:

[0064] If the thickness of the steel layer 101 is 10 mm, the thickness of the second steel layer 206 is 2 mm, the thickness of the third steel layer 207 is 4 mm, and the thickness of the fourth steel layer 208 is 6 mm, the steel layer 101 is just completely filled (leaving a 2 mm excess height), so there is no need to build up the cover layer 209; if the thickness of the steel layer 101 is 20 mm, it is necessary to repeatedly build up the fourth steel layer 208 on the fourth steel layer 208 with a thickness of 6 mm, that is, a total of 18 mm is filled, so the cover layer 209 can reach 4 mm (leaving a 2 mm excess height).

[0065] In an optional embodiment of the present invention, the diameter of the melting electrode used is 1.0mm-1.2mm, the line energy is 300J / mm-350J / mm, the welding current is 100A-120A, the arc voltage is 18V-22V, the welding speed is 100mm / min-150mm / min, the wire feeding speed is 2.8m / min-3.2m / min, and the shielding gas flow rate is 14L / min-18L / min; the welding process is protected by a mixed gas of argon and carbon dioxide.

[0066] It should be noted that the height of the cap layer 209 is directly related to the thickness of the titanium layer 102. If the thickness of the steel layer 101 is 10 mm, the cap layer 209 may not be welded. If the thickness of the steel layer 101 is 20 mm, the thickness of the cap layer 209 may reach 4 mm.

[0067] In an optional embodiment of the present invention, when the welding process parameters of the first weld 203 to the second weld 204, the first steel layer 205 to the fourth steel layer 208, and the cover layer 209 are within the set range, the performance of the welded joint is similar, and no holes or microcracks appear at the welded joint; if the welding process parameters exceed the set range, the welded joint will appear to be unfused or melted through; from a theoretical point of view or actual cost, data outside the welding process parameter range will not be set for welding.

[0068] In a second aspect, an embodiment of the present invention provides an application of a titanium-steel bimetallic composite structure prepared by the aforementioned welding method in the field of marine equipment and petroleum.

[0069] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0070] Example 1

[0071] This embodiment provides a welding method for a titanium-steel bimetallic composite structure, which includes the following implementation steps:

[0072] (1) Processing of parts to be welded:

[0073] Please refer to Figure 1 , a schematic diagram of a stepped U-shaped groove structure of a titanium-steel bimetallic composite structure 100. The titanium layer 102 is pure titanium, and its thickness S1 is 2 mm; the steel layer 101 is stainless steel, and its thickness S2 is 18 mm.

[0074] The design range of groove parameters is as follows: blunt edge 104 is 1.8 mm, root gap 105 is 8 mm, groove width 106 is 15 mm, and root radius 103 is 1.2 mm.

[0075] (2) Clean the parts to be welded:

[0076] The processed parts to be welded are sanded, cleaned with acetone, and dried to remove impurities such as grease and oxide scale on the welding surface.

[0077] (3) Butt welding of the parts to be welded:

[0078] Please refer to the schematic diagram 200 of the welding sequence of the butt welding parts to be welded Figure 2 .

[0079] (3.1) Welding of the first weld 203:

[0080] The titanium layer 102 is butt-jointed in a single pass by using pulse plasma welding technology without filler wire to form a first weld 203 .

[0081] The outer surface shape of the plasma forming nozzle used is a rectangle with an aspect ratio of 1.6, and the length direction is along the welding direction; the nozzle length is 15mm (depending on the thickness of the steel layer 101), the diameter of its internal plasma channel is 2mm (corresponding to the thickness of the titanium layer 102), and the fillet radius of the nozzle cut is 3mm. The maximum value of the pulse current is 120A, the minimum value is 65A, the arc voltage is 20V, the welding speed is 300mm / min, the plasma arc gas flow rate is 0.6L / min, and the shielding gas flow rate is 50L / min. Argon gas is used to protect the weld during the welding process.

[0082] (3.2) Welding of the second weld 204:

[0083] Soft arc plasma is used to deposit shielding material CuSi3Mn1 as an alloy barrier layer on the welded first weld 203 to form a second weld 204 so as to completely cover the step area at the bottom of the U-shaped groove.

[0084] The soft arc plasma line energy is 120J / mm, the welding current is 85A, the welding speed is 250mm / min, and the wire feeding speed is 1.2m / min. Argon gas is used for protection during the welding process.

[0085] In terms of mass percentage, the elements in the CuSi3Mn1 alloy include: Si 4.5%, Mn 1.2%, other impurities <0.3% and the balance Cu.

[0086] (3.3) Welding of the first steel layer 205:

[0087] A pulse arc gas metal shielded welding method is used to build up a 2 mm thick first steel layer 205 on the second weld 204 formed by CuSi3Mn1. The diameter of the metal electrode used is 0.8 mm. A trapezoidal welding current pulse shape with a pulse time to pause time ratio of 2:1 and a pulse frequency of 5 Hz is used. The line energy is 180 J / mm, the current is 35 A, the arc voltage is 17 V, the welding speed is 200 mm / min, the wire feeding speed is 1.8 m / min, and the shielding gas flow rate is 12 L / min. The welding process is protected by a mixed gas of argon and carbon dioxide.

[0088] (3.4) Welding of the second steel layer 206 to the fourth steel layer 208:

[0089] The second steel layer 206, the third steel layer 207 and the fourth steel layer 208 are continuously surfacing on the first steel layer 205 by using a consumable active gas shielded arc welding method (i.e., MAG welding); the consumable electrode diameter used is 1.0 mm, the line energy is 320 J / mm, the welding current is 110 A, the arc voltage is 20 V, the welding speed is 300 mm / min, the wire feeding speed is 3 m / min, the shielding gas flow rate is 16 L / min, and the welding process is protected by a mixed gas of argon and carbon dioxide. When surfacing the second steel layer 206, the third steel layer 207 and the fourth steel layer 208, their heights should meet the relationship of formula (1):

[0090] δ = 2n·e 1 / (I·U) (1).

[0091] In formula (1), δ is the height of the surfacing steel layer (mm); n is the deposition sequence number of the surfacing second steel layer 206, the third steel layer 207 and the fourth steel layer 208 (n=1, 2, 3); I is the welding current (A); and U is the arc voltage (V).

[0092] The thickness of the second steel layer 206 is 2 mm, the thickness of the third steel layer 207 is 4 mm, and the thickness of the fourth steel layer 208 is 6 mm.

[0093] (3.5) Welding of the cover layer 209:

[0094] A cap layer 209 is built up on the fourth steel layer 208 by using a metal active gas shielded arc welding method (ie, MAG welding).

[0095] The diameter of the melting electrode used is 1.0 mm, the line energy is 300 J / mm, the welding current is 100 A, the arc voltage is 18 V, the welding speed is 120 mm / min, the wire feeding speed is 3 m / min, and the shielding gas flow rate is 16 L / min. The thickness of the steel layer 101 is 15 mm, and the thickness of the cover layer 209 can reach 3.6 mm. The welding process is protected by a mixed gas of argon and carbon dioxide.

[0096] Example 2

[0097] This embodiment provides a welding method for a titanium-steel bimetallic composite structure, which differs from Embodiment 1 only in that:

[0098] (3.1) Welding of the first weld 203:

[0099] The titanium layer 102 is butt-jointed in a single pass by using pulse plasma welding technology without filler wire to form a first weld 203 .

[0100] The maximum value of pulse current is 110A, the minimum value is 60A, the arc voltage is 20V, the welding speed is 200mm / min, the plasma arc gas flow is 0.6L / min, and the shielding gas flow is 50L / min. Argon gas is used to protect the weld during the welding process.

[0101] Comparative Example 1

[0102] This comparative example provides a conventional welding method for a titanium-steel bimetallic composite structure, which includes the following implementation steps:

[0103] A conventional V-shaped groove design is adopted, with the titanium layer facing up and the steel layer facing down. The plate and welding wire are preheated for 30 minutes. First, TIG technology is used to start welding from the bottom of the steel layer. Two passes of welding are used at the root of the groove with a current of 120A. Multi-pass welding is used to fill the groove with a current of 140A until the steel layer is filled. Using TIG technology, Cu and V layers are sequentially built on the steel filling layer with a current of 100A. Finally, laser-arc hybrid welding technology is used for titanium layer welding, with a laser power of 1kW and a welding current of 100A.

[0104] Test Example 1

[0105] In this test example, the welded sections of the titanium-steel bimetallic composite structure prepared in Example 1 and Comparative Example 1 were scanned. The test instrument was an optical microscope, model Leica Neophot-32. Figure 3 (Example 1), Figure 4 (Comparative Example 1).

[0106] from Figure 3 As can be seen from the results, no microcracks were found in the welded joint obtained by the welding method of Example 1; Figure 4 In the joints obtained by comparative welding method, more holes and microcracks were found at the junction of steel and titanium.

[0107] Test Example 1

[0108] In this test example, the tensile strength of the titanium-steel bimetallic composite structure welded joint and the base material prepared in Example 1 and Comparative Example 1 was tested using a universal tensile testing machine CMT5105, in accordance with the standard GB / T2651-2008. The specific results are shown in Table 1.

[0109] Table 1 Tensile strength data

[0110] Base Material Example 1 Comparative Example 1 Tensile strength / MPa 430 395 280

[0111] From the data in Table 1, it can be concluded that the tensile strength of the welded joint in Example 1 is 91.9% of that of the parent material; while the tensile strength of the welded joint obtained by conventional welding method, i.e., Comparative Example 1, is only 65.1% of that of the parent material at most.

[0112] In summary, the welding method of the titanium-steel bimetallic composite structure provided by the embodiment of the present invention designs a stepped U-shaped groove on the steel layer 101 to completely expose the bottom titanium layer 102, which helps to completely isolate the contact between titanium and steel while achieving full fusion of the weld; in addition, a reasonable and feasible welding sequence and an optimized welding process effectively prevent mutual melting between the layers, thereby inhibiting the formation of brittle intermetallic Fe-Ti compounds and improving the strength of the titanium-steel composite structure joint. The titanium-steel bimetallic composite structure obtained by this welding method is expected to be promoted and applied in the fields of marine equipment and petroleum.

[0113] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A welding method for a titanium-steel bimetallic composite structure, characterized in that: The titanium-steel bimetallic composite structure comprises a steel layer and a titanium layer; The welding method comprises: processing a stepped U-shaped groove on a steel layer, and providing a stepped area connected to a titanium layer at the bottom of the U-shaped groove to obtain a workpiece to be welded; then, welding is performed at the U-shaped groove of the workpiece to be welded in a butt-jointed manner; The sum of the slope height of the U-shaped groove and the height of the step area is equal to the thickness of the steel layer; the height of the step area is equal to the blunt edge of the U-shaped groove; and the titanium layer in the step area is in contact with the atmosphere.

2. The welding method according to claim 1, characterized in that: The U-shaped groove has a blunt edge of 1.0mm-2.5mm, a root gap of 5mm-10mm, a groove width of 10mm-20mm, and a root radius of 0.5mm-1.5mm; Preferably, the material of the titanium layer is pure titanium or titanium alloy, and the thickness S1 is 1mm-3mm; the material of the steel layer is stainless steel or carbon steel, and the thickness S2 is 10mm-20mm; Preferably, the workpiece to be welded with the U-shaped groove processed is ground, cleaned and dried to remove impurities on the welding surface.

3. The welding method according to claim 1, characterized in that: The sequence of butt welding of the dried parts to be welded includes: The titanium layer is welded by using any one of pulse plasma welding technology, laser welding technology or electron beam welding technology to form a first weld; when welding the first weld, a single-pass butt joint is used without filler wire; Preferably, the welding technology is pulse plasma welding technology; wherein, the outer surface shape of the plasma forming nozzle is a rectangle with an aspect ratio of 1.4-1.8, and the length direction of the rectangle is along the welding direction; the length of the nozzle is 8mm-19mm, the diameter of the plasma channel inside the nozzle is 1.2mm-3.2mm, and the fillet radius of the nozzle cut is 3mm±0.5mm; the maximum value of the pulse current is 110A-120A, and the minimum value is 60A-70A; the arc voltage is 20V-22V, the welding speed is 200mm / min-400mm / min, the plasma arc gas flow rate is 0.4L / min-0.8L / min, and the shielding gas flow rate is 45L / min-55L / min; argon gas is used to protect the weld during the welding process.

4. The welding method according to claim 3, characterized in that: The butt welding sequence also includes: The shielding material is deposited on the first weld using soft arc plasma welding technology so that it completely covers the stepped area at the bottom of the U-shaped groove to form a second weld; The energy of the soft arc plasma is 100 J / mm-150 J / mm, and the welding current is 80 A-100 A. Argon gas is used to protect the weld during the welding process. Preferably, the shielding material is selected from any one of CuSi3Mn1 alloy, Nb and V.

5. The welding method according to claim 4, characterized in that: The shielding material is CuSi3Mn1 alloy; in terms of mass percentage, the elements in the CuSi3Mn1 alloy include: Si 2.5%-5.5%, Mn 0.3%-2.0%, inevitable impurities 0%-0.7%, and the balance Cu.

6. The welding method according to claim 4, characterized in that: The butt welding sequence also includes: The first steel layer is welded on the second weld using pulse arc gas metal shielded welding technology; Among them, the diameter of the melting electrode used is 0.8mm-1.0mm, the ratio of pulse time to pause time is (1.5-2.5): 1, the pulse frequency is 3Hz-10 Hz, the wire energy is 150J / mm-200J / mm, the current is 30A-45A, the arc voltage is 15V-20V, the welding speed is 180mm / min-220mm / min, the wire feeding speed is 1.5m / min-2.0m / min, the shielding gas flow rate is 10L / min-15L / min, and the welding process is protected by a mixed gas of argon and carbon dioxide.

7. The welding method according to claim 6, characterized in that: The butt welding sequence also includes: Using the metal arc gas shielded welding method, continue to build up the second steel layer, the third steel layer and the fourth steel layer on the first steel layer; Among them, the diameter of the melting electrode used is 1.0mm-1.2mm, the wire energy is 300J / mm-350J / mm, the welding current is 100A-120A, the arc voltage is 18V-22V, the welding speed is 280mm / min-320mm / min, the wire feeding speed is 2.8m / min-3.2m / min, and the shielding gas flow rate is 14L / min-18L / min; the welding process is protected by a mixed gas of argon and carbon dioxide.

8. The welding method according to claim 7, characterized in that: When surfacing the second steel layer, the third steel layer and the fourth steel layer, the surfacing steel layer height, welding current and arc voltage satisfy the relationship of formula (1): δ=2n·e 1 / (I·U) (1) In formula (1), δ is the height of the surfacing steel layer (mm); n is the deposition sequence number of the second, third and fourth surfacing steel layers (n=1, 2, 3); I is the welding current (A); and U is the arc voltage (V).

9. The welding method according to claim 7, characterized in that: The butt welding sequence also includes: Using the metal arc welding method, a capping layer is welded on the fourth steel layer; Among them, the diameter of the melting electrode used is 1.0mm-1.2mm, the wire energy is 300J / mm-350J / mm, the welding current is 100A-120A, the arc voltage is 18V-22V, the welding speed is 100mm / min-150mm / min, the wire feeding speed is 2.8m / min-3.2m / min, and the shielding gas flow rate is 14L / min-18L / min; the welding process is protected by a mixture of argon and carbon dioxide.

10. Application of a titanium-steel bimetallic composite structure prepared by the welding method according to any one of claims 1 to 9 in marine equipment and petroleum fields.

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