TKY joint high-strength high-toughness corrosion-esistant welding method for deep water jacket

Abstract

To provide a TKY joint high-strength high-toughness corrosion-resistant welding method for a deep water jacket.SOLUTION: A TKY joint high-strength high-toughness corrosion-resistant welding method for a deep water jacket includes preheating a T / K / Y joint at a predetermined temperature according to wall thickness of a base material, setting different welding parameters to different welding processes, performing rooting weld on the T / K / Y joint preheated by a coated arc welding process, then performing filling weld by a gas shield metal arc welding process, and finally performing capping weld by a gas shield metal arc welding process, wherein in the rooting weld, a corresponding welding rod is used, the performing capping weld selects a welding wire according to a low-strength principle, the filling weld selects a welding wire according to an equal-strength principle, and diffusible hydrogen contents of both an arbitrary welding rod and an arbitrary welding wire are equal to or less than a predetermined diffusible hydrogen content.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention belongs to the technical field of welding, and more specifically, relates to a high-strength and high-toughness corrosion-resistant welding method for TKY joints for deep-water jackets.

Background Art

[0002] Fixed jacket platforms for offshore oil engineering are the most commonly used structural forms in the exploitation of oil and gas resources in deep-water areas. The intersection joints (TKY joints) of large pipes are the most important welded structures. As the main load-bearing structure in ocean engineering, due to the self-weight of structures and equipment, etc., and extreme loads such as waves and storms, high stress concentration occurs at the connection between the main pipe and the branch pipe of the TKY joint. Due to the interaction of alternating loads and seawater corrosion, corrosion, fatigue, and fracture damage are likely to occur easily at the welded part. Therefore, in order to meet the long-term use of offshore platforms, it is required that TKY joints have excellent low-temperature toughness, weather corrosion resistance, and seawater corrosion resistance. The welding quality of high-strength steel directly affects the performance of TKY joints. If unreasonable welding is carried out, cold cracking may occur or the toughness may decrease. Due to the action of the welding thermal cycle, the structure and properties of the base metal on both sides of the welded part change greatly, the heat-affected zone of the welding softens or embrittles, and the performance of the TKY welded joint decreases. Current research on commonly used welding methods mainly focuses on the control of the heat input during welding and the optimization of the welding thermal cycle in order to reduce the adverse effects on the heat-affected zone of the welding. Furthermore, due to the composition of the filler metal and the action of the welding thermal cycle, the weld metal is usually the weak area of the joint. Especially at the position of the welding root, its composition changes greatly due to the dilution of the base metal, which may easily cause local embrittlement of the weld metal.

[0003] In the field of ocean engineering, gas shielded welding and submerged arc welding are the most widely used welding methods. For example, Chinese Patent CN108453340B discloses a welding method for steel structure TKY joints, and its focus is on the formation of welding and the solution of defects. CN112935601A discloses a multi-layer multi-pass welding method for thick plates of low alloy high strength steel, which solves the problem of insufficient strength of the welded part by combining gas shielded welding and submerged arc welding. CN109128550B discloses a gas shielded welding process for high tensile strength bridge steel, which combines two different welding wires and CO 2 The gas shielded welding process ensures that the entire welded joint has high plastic toughness. CN116765665A discloses a welding process for 500MPa weathering steel, and by combining flux-cored wire and cold metal transfer welding process, the low temperature impact performance of the welded joint is improved. The above prior arts have optimized the welding process of high strength steel according to various purposes and improved the performance of the welded part to a certain extent. However, it is difficult to optimize the welding process of steel for offshore platform structures using the above methods. The damage of the welded joint of high strength steel caused by inappropriate welding processes or substandard welded part performance has a significant impact on the safety of deep-water platforms.

[0004] Therefore, for a complex marine environment, it is necessary to have a welding process that ensures that the tensile strength of the entire welded part meets the standard, the root and cap of the welded part have high toughness and high corrosion resistance, and the thick-walled welded structure of the TKY joint has comprehensive performance of unstable fracture resistance and high corrosion resistance.

Summary of the Invention

[0005] Aiming at the defects of the prior art, the object of the present invention is to provide a high-strength, high-toughness and corrosion-resistant welding method for TKY joints for deep-water jackets, so as to solve the problems that the toughness of the welded joint is low, the corrosion resistance is poor, and cold cracking is likely to occur in the welding process of the conventional TKY joints for deep-water platform jackets.

[0006] To achieve the above object, the present invention provides a high-strength and high-toughness anti-corrosion welding method for TKY joints of deep-water jackets, which includes the following steps. S1: Preheat the T / K / Y joint at a predetermined temperature according to the wall thickness of the base material. S2: Set different welding parameters for different welding processes. S3: Perform root welding on the preheated T / K / Y joint by the covered arc welding process and welding rod, then perform build-up welding by the gas shielded metal arc welding process and welding wire, and finally perform finish welding by the gas shielded metal arc welding process. Here, for root welding, select the welding rod according to the under-match principle, for finish welding, select the first welding wire according to the under-match principle, for build-up welding, select the second welding wire according to the even-match principle, and the diffusible hydrogen content of the welding rod, the first welding wire and the second welding wire is all below a predetermined diffusible hydrogen content.

[0007] Furthermore, when the wall thickness W of the base material satisfies 38mm < W ≤ 50mm, the preheating temperature is in the range of 65°C to 150°C.

[0008] Furthermore, when the wall thickness W of the base material satisfies 50mm < W ≤ 80mm, the preheating temperature is in the range of 110°C to 150°C.

[0009] Furthermore, the predetermined diffusible hydrogen content is 5.0 ml / 100g. Preferably, the diffusible hydrogen content of the welding rod, the first welding wire and / or the second welding wire may be the same or different.

[0010] Furthermore, the diameter of the first welding wire and / or the second welding wire is 1mm or 1.2mm.

[0011] Furthermore, the dry extension of the first welding wire and / or the second welding wire is 10 to 12 times their respective diameters.

[0012] Furthermore, the first welding wire and the second welding wire may have the same or different yield strengths, tensile strengths, and / or impact toughnesses.

[0013] Furthermore, in step S3, when performing buildup welding and / or finish welding, the shielding gas used is 82% Ar and 18% CO 2 and preferably, the flow rate of the shielding gas during welding is from 20 L / min to 25 L / min.

[0014] Furthermore, the welding parameters corresponding to different welding processes are set such that the interlayer distance between adjacent welding layers is from 3 mm to 5 mm and the interlayer temperature between adjacent welding layers is less than 250°C.

[0015] Furthermore, when performing root welding by the covered arc welding process, the corresponding welding parameters are: welding current: from 90 A to 120 A, arc voltage: from 20 V to 23 V, welding speed: from 65 mm / min to 90 mm / min.

[0016] Furthermore, when performing buildup welding and finish welding by the gas shielded metal arc welding process, for the buildup welding, the welding voltage is from 18 V to 24 V, the welding current is from 160 A to 190 A, the welding speed is from 300 mm / min to 500 mm / min, and the wire feeding speed is from 6 m / min to 9 m / min.

[0017] Furthermore, when performing finish welding by the gas shielded metal arc welding process, the corresponding welding parameters are: welding voltage: from 22 V to 24 V, welding current: from 175 A to 190 A, welding speed: from 300 mm / min to 500 mm / min, wire feeding speed: from 8 m / min to 9 m / min.

[0018] Furthermore, when performing buildup welding and / or finish welding, the welding equipment oscillates at an oscillation frequency of 2.5 Hz - 4 Hz and an oscillation amplitude of 1 mm - 2 mm.

[0019] The technical means of the present invention have the following advantages compared with the prior art. In the present invention, the KTY joint to be welded is preheated at a high temperature, root welding is performed by SMAW (shielded metal arc welding), build-up welding and finish welding are performed by GMAW (gas shielded metal arc welding). In root welding, a welding rod is selected according to the under-match principle, in finish welding, a corresponding first welding wire is used according to the under-match principle, in build-up welding, a second welding wire is used according to the even-match principle, and the diffusible hydrogen content of the corresponding welding wire and welding rod used in the welding of each pass is all below a predetermined diffusible hydrogen content. Thereby, the toughness of the whole welded part is improved by different alloying strategies, and the occurrence of cold cracking is prevented.

[0020] In the present invention, by combining low heat input parameters corresponding to different welding processes for welding, the width of the heat affected zone in the welded part is further reduced, which is beneficial to reducing the dilution of the base metal to the welded part, avoiding the generation of brittle phases in the welded part metal due to the action of the heat cycle, and reducing the occurrence of local embrittlement.

[0021] Based on the combination of high preheating and low heat input, in the root / capping pass and filling pass, welding rods or welding wires with low hydrogen, high toughness and high corrosion resistance with different performances such as yield strength, tensile strength and impact toughness are used, that is, high-performance welding of joints for deep-water TKY jackets is completed by different alloying strategies. Thereby, the occurrence of cold cracking is prevented and reduced, the toughness of the whole welded part is improved, the strength of the whole welded part meets the standard, and the root and cap parts of the welded part have high strength, high toughness and high corrosion resistance. By combining the two methods, the thick-walled structure of high-strength steel for deep-water platforms has high comprehensive performance of unstable fracture resistance and corrosion resistance.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

[0023] Explanation of symbols 1 - Root welding, 2 - Build - up welding of the first pass, 3 - Build - up welding of the second pass, 4 - Build - up welding of the third pass, 5 - Build - up welding of the fourth pass, 6 - Build - up welding of the fifth pass, 7 - Finish welding of the first pass, 8 - Finish welding of the second pass.

Embodiment for carrying out the invention

[0024] To make the object, technical means and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. The specific embodiments described in this specification are only for explaining the present invention and do not limit the present invention.

[0025] The present invention provides a high - strength and high - toughness corrosion - resistant welding method for a TKY joint of a deep - water jacket. This method includes the following steps. S1: According to the wall thickness of the base material, pre - heat the T / K / Y joint at a specific temperature at a predetermined temperature. S2: Set different welding parameters for different welding processes. S3: Root - weld the pre - heated T / K / Y joint by the shielded metal arc welding process and welding rod, then perform build - up welding by the gas - shielded metal arc welding process and welding wire, and finally perform finish welding by the gas - shielded metal arc welding process, using different alloyed welding wires. Here, in root welding, use a high - toughness and high - corrosion - resistant welding rod according to the "undermatched principle", in finish welding, use a high - toughness and high - corrosion - resistant first welding wire according to the "undermatched principle", and in build - up welding, use a second welding wire close to the strength of the base material according to the "even - matched principle", so as to ensure that the strength of the entire welded part meets the standard, and the diffusible hydrogen content of the welding rod, the first welding wire and the second welding wire is guaranteed to be below a predetermined diffusible hydrogen content.

[0026] In this embodiment, the wall thickness of a general medium-thickness base material is 38 mm - 80 mm. When the wall thickness W of the base material satisfies 38 mm < W ≤ 50 mm, the preheating temperature is in the range of 65°C to 150°C. For example, when W is 45 mm, the preheating temperature is 80°C or higher, and when W is 50 mm, the minimum preheating temperature is 100°C.

[0027] In this embodiment, when the wall thickness W of the base material satisfies 50 mm < W ≤ 80 mm, the preheating temperature is in the range of 110°C to 150°C. When W is 65 mm, the preheating temperature is 115°C or higher, and when W is 80 mm, the minimum preheating temperature is 140°C.

[0028] In this embodiment, the diffusible hydrogen content of the welding rod, the first welding wire, and the second welding wire is all 5.0 ml / 100 g or less. For example, it is 5.0 ml / 100 g, 4.0 ml / 100 g, 3.0 ml / 100 g, 2.0 ml / 100 g, etc. Specifically, the diffusible hydrogen content of the welding rod, the first welding wire, and / or the second welding wire may be the same or different.

[0029] In this embodiment, the diameter of the first welding wire and / or the second welding wire is 1 mm or 1.2 mm. For example, for the first welding wire, the diameter of the first welding wire is 1.2 mm, and the diameter of the second welding wire is 1 mm.

[0030] In this embodiment, the dry extension of the first welding wire and / or the second welding wire is 10 to 12 times the diameter of each welding wire. For example, when the diameter of the corresponding welding wire is 1 mm, its dry extension is 11 mm or 12 mm, and when the diameter of the corresponding welding wire is 1.2 mm, its dry extension is 12 mm or 14.4 mm. If it is too long, the arc voltage will decrease, there will be too much weld metal, the formation of the welded joint will be poor, the penetration depth will be small, the arc will be unstable, and the spatter will be large. If it is too short, the contact tip will be burned by the arc, and the nozzle will be easily clogged by metal spatter.

[0031] In this embodiment, the yield strength, tensile strength, and / or impact toughness of the first welding wire and the second welding wire may be the same or different. For example, the yield strength, tensile strength, and impact toughness of the first welding wire and the second welding wire are all different. Also, for example, the yield strength, tensile strength, and impact toughness of the first welding wire and the second welding wire are all the same. Further, for example, the yield strength and tensile strength of the first welding wire and the second welding wire are different, but the impact toughness is the same.

[0032] In this embodiment, the yield strength, tensile strength, and impact toughness of any one of the above welding rods are different from the yield strength, tensile strength, and impact toughness of any one of the welding wires (the first welding wire and the second welding wire), respectively.

[0033] In this embodiment, in step S3, the shielding gas used when performing buildup welding and / or finish welding consists of 82% Ar and 18% CO 2 Specifically, the flow rate of the shielding gas during welding is from 20 L / min to 25 L / min. For example, the gas flow rate may be 20 L / min, 21 L / min, 22 L / min, 23 L / min, 24 L / min, or 25 L / min. In this case, a stable welding environment and relatively high welding quality can be ensured.

[0034] In this embodiment, due to the welding parameters corresponding to different welding processes, the interlayer distance is from 3 mm to 5 mm, and the interlayer temperature (i.e., the interpass temperature) is 250°C or lower, whereby it is guaranteed that the welding quality of each pass is qualified.

[0035] In this embodiment, when performing root welding by the coated arc welding process, the corresponding welding parameters are set as follows. That is, the welding current is from 90 A to 120 A, for example, 90 A, 100 A, 110 A, 120 A, etc., the arc voltage is from 20 V to 23 V, for example, 20 V, 21 V, 22 V, 23 V, etc., and the welding speed is from 65 mm / min to 90 mm / min, for example, 65 mm / min, 70 mm / min, 75 mm / min, 80 mm / min, 85 mm / min, 90 mm / min, etc.

[0036] In this embodiment, when performing buildup welding and finish welding by the gas shielded metal arc welding process, the welding voltage for buildup welding is from 18 V to 24 V, for example, 18 V, 20 V, 22 V, 23 V, 24 V, etc., the welding current is from 160 A to 190 A, for example, 160 A, 170 A, 180 A, 190 A, etc., the welding speed is from 300 mm / min to 500 mm / min, for example, 300 mm / min, 350 mm / min, 400 mm / min, 450 mm / min, 500 mm / min, etc., and the wire feeding speed is from 6 m / min to 9 m / min, for example, 6 m / min, 7 m / min, 8 m / min, 9 m / min, etc.

[0037] In this embodiment, when performing finish welding by the gas shielded metal arc welding process, the corresponding welding parameters are as follows. That is, the welding voltage is from 22 V to 24 V, for example, 22 V, 23 V, 24 V, etc., the welding current is from 175 A to 190 A, for example, 175 A, 180 A, 185 A, 190 A, etc., the welding speed is from 300 mm / min to 500 mm / min, for example, 300 mm / min, 350 mm / min, 400 mm / min, 450 mm / min, 500 mm / min, etc., and the wire feeding speed is from 8 m / min to 9 m / min, for example, 8 m / min, 8.5 m / min, 9 m / min, etc.

[0038] By welding with a combination of low heat input parameters corresponding to the different welding processes, the width of the heat affected zone of the welded joint is reduced, which is advantageous for reducing the dilution of the base material with respect to the welded joint, and a decrease in welding strength is avoided.

[0039] In this embodiment, when performing buildup welding and / or finishing welding, the welding equipment oscillates at an oscillation frequency of 2.5 Hz - 4 Hz and an oscillation amplitude of 1 mm - 2 mm. For example, the oscillation frequency may be 2.5 Hz, 3 Hz, 3.5 Hz, 4 Hz, etc., and the oscillation amplitude may be 1 mm, 1.5 mm, 2 mm, etc.

[0040] To better explain the implementation details of the present invention, the present invention will be described below by way of examples. The following examples are only the optimal embodiments and do not limit the protection scope of the present invention.

[0041] Example 1 Taking steel D36 for TKY joints where pipe members intersect as an example, this material has a yield strength of 355 MPa and a tensile strength of 490 - 630 MPa. The specific welding steps include the following. Step 1: According to the wall thickness and diameter of the D36 base material, perform beveling and assembly strictly in accordance with parameters such as the bevel form, root face, and welding gap of the joint specified in the American Welding Society standard AWS D1.1, and plan the welding path with the bevel and welding pass shown in Figure 2.

[0042] Step 2: Arrange welding equipment such as a welding torch, welding power source, cooling water tank, and gas cylinder.

[0043] Step 3: Preheat the TKY joint structure. When the wall thickness is 38 mm < W ≤ 50 mm, the preheat temperature is 65 °C or higher; when the wall thickness is 50 mm < W ≤ 80 mm, the preheat temperature is 110 °C or higher.

[0044] Step 4: Set different welding parameters according to the specific bevel size, match the welding wire, and perform welding. When performing root welding on welding pass 1 (root pass) by SMAW, the welding parameters are set as follows. That is, the welding current is set to 90A - 120A, the arc voltage is set to 20V - 23V, the welding speed is set to 65mm / min - 90mm / min, and the matching welding rod has a yield strength of 390MPa, a tensile strength of 470MPa, and an impact toughness of 100J (-50°C). When welding welding passes 2 to 6 by GMAW to form the first to fifth filling passes, the welding parameters are set as follows. That is, when welding filling passes 2 - 4, the welding voltage is set to 18V - 20V, the welding current is set to 160A - 170A, the wire feeding speed range is 6m / min - 7m / min, and the welding speed is set to 300mm / min - 500mm / min. When welding filling passes 5 - 6, the welding voltage is set to 20 - 24V, the welding current is set to 170 - 180A, the wire feeding speed is 7 - 9m / min, and the welding speed is set to 300 - 500mm / min. When welding the filling passes 2 - 6, the oscillation frequency of the welding torch is set to 2.5HZ - 4HZ, the oscillation amplitude is set to 1mm, and the matching second welding wire has a yield strength of 495MPa, a tensile strength of 575MPa, and an impact toughness of 105J (-20°C).

[0045] When performing finish welding on welding passes (capping passes) 7 - 8 by GMAW, the welding voltage is set to 22V - 24V, the welding current is set to 175A - 190A, the wire feeding speed range is 8m / min - 9m / min, the welding speed is set to 300mm / min - 500mm / min, the oscillation frequency is set to 2.5HZ - 4HZ, and the oscillation amplitude is set to 2mm. The yield strength of the matching first welding wire is 390MPa, the tensile strength is 470MPa, and the impact toughness is 100J (-50°C).

[0046] In the said step 4, the diffusible hydrogen content of the weld metal of the welding rod, the first welding wire and the second welding wire used for welding each pass is all 5.0 ml / 100 g or less. The first welding wire and the second welding wire are different in yield strength, tensile strength and impact toughness, and the diameters of the first welding wire and the second welding wire are both 1.0 mm or 1.2 mm. The dry extension is 10 to 12 times the diameter of each of the first welding wire and the second welding wire. The shielding gas is 82% Ar and 18% CO 2 and the gas flow rate is 20 L / min - 25 L / min.

[0047] The specific welding parameters of the welded part of each pass must be selected so that the interlayer distance is 3 mm - 5 mm and the interlayer temperature is 250°C or less. After the welding of each layer is completed, it is necessary to perform slag removal treatment in a timely manner.

[0048] Example 2 In this example, the base material is the same as that in Example 1. The yield strength of the material is 355 MPa, and the tensile strength is 490 - 630 MPa. The welding steps and the corresponding welding parameters are basically the same, but the welding wires used are different. When welding the root pass 1 by SMAW, the matched welding rod has a yield strength of 390 MPa, a tensile strength of 470 MPa, an impact toughness of 100 J (-50°C), a diameter of 1.0 mm, a dry extension of 11 mm, and the diffusible hydrogen content of the weld metal of the welding rod is 4.0 ml / 100 g. When welding the first filling pass 2 to the sixth filling pass 6 by GMAW, the matched second welding wire according to the even match principle has a yield strength of 495 MPa, a tensile strength of 575 MPa, an impact toughness of 105 J (-20°C), a diameter of 1.2 mm, a dry extension of 12 mm, and the diffusible hydrogen content of the weld metal of the second welding wire is 5.0 ml / 100 g. When welding the capping pass 7-8 by GMAW, the first welding wire used in accordance with the under-match principle has a yield strength of 390 MPa, a tensile strength of 470 MPa, an impact toughness of 100 J (-50 °C), a diameter of 1 mm, a dry extension of 11 mm, and the diffusible hydrogen content of the weld metal of the welding wire is 4.0 ml / 100 g.

[0049] In any one of the above embodiments, based on the combination of low-hydrogen welding wire, high preheating, and low heat input during welding, different alloying strategies for the root / capping pass and the filling pass are used to complete the high-performance welding of the joints for deep-water TKY jackets. By this means, the occurrence of cold cracking is prevented and reduced, and the toughness of the entire welded part is improved. Due to the different alloying strategies for the root / capping pass and the filling pass, the strength of the entire welded part meets the standard, and the root and cap (weld surface) parts have high strength, high toughness, and high corrosion resistance. By combining the two methods, the thick-walled structure of high-strength steel for deep-water platforms has high comprehensive performance of resistance to unstable fracture and corrosion resistance.

[0050] In the present invention, the terms "first" and "second" are used only for the purpose of description and should not be understood as indicating relative importance, implying, or implicitly indicating the number of the indicated technical features. Therefore, the features limited by "first" and "second" may include one or more of these features explicitly or implicitly. In this specification, "a plurality" means two or more unless otherwise explicitly limited.

[0051] The above description is only a preferred embodiment of the present invention and does not limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should all be included within the protection scope of the present invention.

Claims

1. A high-strength, high-toughness, corrosion-resistant welding method for a deep-water jacket TKY joint, comprising the following steps S1 to S3: S1: Preheat the T / K / Y joint at a predetermined temperature according to the wall thickness of the base material, where the wall thickness of the base material is greater than 38 mm; S2: Set different welding parameters for different welding processes, where when the wall thickness W of the base metal satisfies 38 mm < W ≦ 50 mm, the preheating temperature is 65 ° C to 150 ° C, and when the wall thickness W of the base metal satisfies 50 mm < W ≦ 80 mm, the preheating temperature is 110 ° C to 150 ° C; S3: Root welding is performed on the preheated T / K / Y joints by a shielded metal arc welding process, then filling welding is performed by a gas shielded metal arc welding process, and finally capping welding is performed by a gas shielded metal arc welding process. wherein for root welding, a welding rod is selected according to the undermatch principle, the welding current is 90A to 120A, the arc voltage is 20V to 23V, and the welding speed is 65mm / min to 90mm / min; for finish welding, a first welding wire is selected according to the undermatch principle, the welding current is 175A to 190A, the welding voltage is 22V to 24V, the welding speed is 300mm / min to 500mm / min, and the wire feed speed is 8m / min to 9m / min; for build-up welding, a second welding wire is selected according to the even-match principle, the welding current is 160A to 190A, the welding voltage is 18V to 24V, the welding speed is 300mm / min to 500mm / min, and the wire feed speed is 6m / min to 9m / min; In step S3, the diffusible hydrogen amounts of the welding rod, the first welding wire, and the second welding wire are all equal to or less than a predetermined diffusible hydrogen amount, and the shielding gas used when performing build-up welding and / or finish welding is 82% Ar and 18% CO. ２ and preferably, the flow rate of the shielding gas during welding is 20 L / min to 25 L / min.

2. 2. The welding method according to claim 1, wherein the predetermined amount of diffusible hydrogen is 5.0 ml / 100 g.

3. The welding method according to claim 2 , wherein the diffusible hydrogen amounts of the welding rod, the first welding wire and / or the second welding wire may be the same or different.

4. The welding method according to claim 1 , wherein the first welding wire and / or the second welding wire has a diameter of 1 mm or 1.2 mm.

5. 5. The method of claim 4, wherein the dry extension of the first welding wire and / or the second welding wire is 10 to 12 times the diameter of each of the first and second welding wires.

6. The welding method according to claim 1 , wherein the first welding wire and the second welding wire may have the same or different yield strength, tensile strength and / or impact toughness.

7. 2. The welding method according to claim 1, wherein the welding parameters corresponding to different welding processes are set such that the interlayer distance of adjacent welding layers is 3mm to 5mm, and the interlayer temperature of adjacent welding layers is less than 250°C.

Images