Resistance arc synergic heating hot wire submerged arc welding method for offshore engineering steel pipe

Abstract

This application discloses a hot-wire submerged arc welding method for marine engineering steel pipes using resistance arc co-heating, relating to the field of welding technology. The method includes the following steps: forming a bevel on the steel pipe; controlling the extension of the submerged arc welding wire to 80 mm~100 mm, and performing zone welding starting from the bevel of the steel pipe, wherein the zone welding process sequentially includes root pass welding, fill pass welding, and cap pass welding; after welding, performing post-weld heat treatment on the steel pipe. This application simultaneously solves the technical problems of difficulty in simultaneously achieving low heat input and high welding efficiency in existing marine engineering steel pipe welding processes, as well as the significant attenuation of low-temperature fracture toughness after post-weld heat treatment.

Description

Technical Field

[0001] This application relates to the field of welding technology, and in particular to a hot wire submerged arc welding method for marine engineering steel pipes using resistance arc combined heating. Background Technology

[0002] Marine engineering structures are ultra-large welded steel structures, generally employing high-strength, thick-walled, and low-temperature toughness materials. As engineering construction requirements continue to increase, the efficient welding and fabrication of marine engineering pipelines meeting complex requirements has become crucial.

[0003] However, conventional submerged arc welding processes typically employ high current and high speed welding parameters to improve welding efficiency, resulting in high heat input, coarsening of the weld and heat-affected zone grains, and a significant decrease in low-temperature toughness. Conversely, to control heat input and ensure toughness, welding current and speed must be reduced, leading to slow wire melting speed, more welding passes, and longer pipe manufacturing cycles. In existing welding processes, it is difficult to achieve both low heat input and high welding efficiency simultaneously. Summary of the Invention

[0004] The main objective of this application is to provide a hot-wire submerged arc welding method for marine engineering steel pipes using resistance arc co-heating, aiming to solve the technical problem that it is difficult to achieve both low heat input and high welding efficiency in existing processes, thus affecting the toughness of marine engineering steel pipes after submerged arc welding.

[0005] To achieve the above objectives, this application provides a hot-wire submerged arc welding method for marine engineering steel pipes using resistance arc combined heating, comprising the following steps: Form a bevel on the steel pipe; The dry extension of the submerged arc welding wire is controlled to be 80 mm to 100 mm. Welding is carried out in sections starting from the bevel of the steel pipe. The section welding process includes root welding, fill welding and cover welding in sequence. After welding, the steel pipe is subjected to post-weld heat treatment.

[0006] In one feasible embodiment, the process parameters for the root weld include: The welding current is 400 A~450 A, the welding voltage is 34 V~36 V, the welding speed is 500 mm / min~600 mm / min, and the heat input is 1.85 kJ / mm~2.05 kJ / mm.

[0007] In one feasible embodiment, the process parameters for the filler soldering include: The welding current is 550 A~600 A, the welding voltage is 34 V~36 V, the wire feed speed is 220 cm / min~240 cm / min, the welding speed is 500 mm / min~600 mm / min, and the heat input is 2.10 kJ / mm~2.60 kJ / mm.

[0008] In one feasible embodiment, the process parameters for the capping weld include: The welding current is 400 A~450 A, the welding voltage is 36 V~38 V, the welding speed is 400 mm / min~500 mm / min, and the heat input is 2.40 kJ / mm~2.70 kJ / mm.

[0009] In one feasible embodiment, the bevel shape includes a double-sided X-shape or a double-sided K-shape.

[0010] In one feasible embodiment, the thickness of the steel pipe is 50 mm to 120 mm, and the pipe diameter is ≥ 600 mm; And / or, the material of the steel pipe includes one of DH36, API 2W Gr.50 and S355; And / or, the diameter of the submerged arc welding wire is 4.0 mm.

[0011] In one feasible embodiment, the step of performing post-weld heat treatment on the steel pipe includes: The holding temperature during the heat treatment process is controlled at 580 ℃±15 ℃, and the heating and / or cooling rate during the heat treatment process is ≤55 ℃ / h; When the thickness of the steel pipe is less than or equal to 76.2 mm, the heat preservation time is 2.5 h; When the thickness of the steel pipe is greater than 76.2 mm, the heat preservation time is determined based on the thickness of the steel pipe being greater than 76.2 mm.

[0012] In one feasible embodiment, when the thickness of the steel pipe is greater than 76.2 mm, the heat preservation time is increased by 1 min for every 1 mm increase in the thickness of the steel pipe.

[0013] In one feasible embodiment, the submerged arc welding wire is preheated to 500°C to 900°C before entering the molten pool.

[0014] In one feasible embodiment, the heat-treated steel pipe has a CTOD of ≥1.0 mm at -10℃ at both the weld center and the fusion line position.

[0015] This application provides a geometric basis for high cladding efficiency welding by forming a bevel on the steel pipe. The extension of the submerged arc welding wire is controlled to be 80 mm to 100 mm, and sectional welding begins from the bevel of the steel pipe. The sectional welding process includes root pass welding, fill pass welding, and cap pass welding. Using submerged arc welding wire and controlling the extension to 80 mm to 100 mm, significant resistance heat is generated when the welding current passes through this long extension section according to Joule's law. This ensures that the submerged arc welding wire is in a softened state close to melting when it reaches the arc zone, thus forming a synergistic heating and melting mechanism of resistance heat and arc heat. On the one hand, this increases the melting speed of the submerged arc welding wire compared to conventional cold welding wire, achieving high welding efficiency. On the other hand, since part of the energy for melting the submerged arc welding wire comes from resistance heat rather than arc heat, the heat input from the arc to the steel pipe is correspondingly reduced, resulting in a lower overall welding heat input. This breaks the traditional technical contradiction that "high efficiency inevitably comes with high heat input." Based on this, the zoned welding strategy of root welding, filler welding, and capping welding, combined with the aforementioned synergistic heating mechanism, forms a complete process match. The low heat input shortens the high-temperature residence time and reduces the peak temperature in the heat-affected zone, laying the foundation for maintaining a refined microstructure during subsequent post-weld heat treatment. After welding, the steel pipe undergoes post-weld heat treatment; this treatment eliminates residual stress without damaging the fine-grained state, ultimately resulting in good performance of the welded joint of the marine engineering steel pipe in a -10℃ CTOD test. Therefore, the embodiments of this application simultaneously solve the technical problems of the difficulty in achieving both low heat input and high welding efficiency in existing marine engineering steel pipe welding processes, as well as the significant attenuation of low-temperature fracture toughness after post-weld heat treatment. Attached Figure Description

[0016] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A schematic flowchart of a hot-wire submerged arc welding method for marine engineering steel pipes with resistance arc co-heating provided in this application embodiment; Figure 2 A schematic diagram of the hot-wire submerged arc welding method for marine engineering steel pipes with resistance arc combined heating provided in the embodiments of this application; Figure 3 A comparison diagram showing the differences in welding parameters between the hot-wire submerged arc welding method with resistance arc co-heating for marine engineering steel pipes and the conventional welding process is provided for the embodiments of this application. Figure 4 A schematic diagram of the heat treatment curve of the marine engineering steel pipe provided in the embodiments of this application; Figure 5 A schematic diagram of a sample showing the macroscopic morphology of an X-shaped bevel fracture surface of a marine engineering steel pipe provided in an embodiment of this application. Figure 6 Hardness dot diagram of submerged arc welding of marine engineering steel pipes provided in the embodiments of this application; Figure 7 A schematic diagram of the CTOD test curves of the weld center and heat-affected zone of the marine engineering steel pipe provided in the embodiments of this application.

[0019] The purpose, features, and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0021] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the hot-wire submerged arc welding method for marine engineering steel pipes according to this application. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for those skilled in the art to fully understand this application.

[0022] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is also expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0023] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0024] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0025] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0026] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0027] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0028] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the technical solution of this application is further described below in conjunction with the accompanying drawings and embodiments. However, this application is not limited to the listed embodiments, but should also include any other well-known modifications within the scope of the claims made in this application.

[0029] The term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of this application. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0030] To improve welding efficiency, conventional submerged arc welding processes typically employ high current and high speed welding parameters, resulting in high heat input, coarsening of the weld and heat-affected zone grains, and a significant decrease in low-temperature toughness. Conversely, to control heat input and ensure toughness, welding current and speed must be reduced, leading to slower wire melting speed, more welding passes, and longer pipe manufacturing cycles. In existing welding processes, low heat input and high welding efficiency are inversely related, and it is difficult to achieve both simultaneously.

[0031] Even more challenging is that, despite some efficient welding processes improving deposition efficiency through additional devices or increased heat input, thick-walled high-strength steel welded joints in marine engineering still face the problem of a sharp decline in low-temperature fracture toughness after PWHT (Post Weld Heat Treatment). While conventional submerged arc welded joints can achieve a CTOD of over 1.0 mm at -10℃ in the as-welded state, after 580℃ PWHT, due to coarsening of the weld and heat-affected zone microstructure and carbide precipitation along grain boundaries, the CTOD at -10℃ often drops sharply to around 0.1 mm, failing to meet the stringent service requirements for brittle fracture resistance in marine engineering structures.

[0032] This application provides a geometric basis for high cladding efficiency welding by forming a bevel on the steel pipe. The submerged arc welding wire extension is controlled to be 80 mm to 100 mm, and sectional welding begins from the bevel of the steel pipe. The sectional welding process includes root pass welding, fill pass welding, and cap pass welding. Using submerged arc welding wire and controlling the extension to 80 mm to 100 mm, significant resistance heat is generated when the welding current passes through this long extension section according to Joule's law. This ensures that the submerged arc welding wire is already in a red-hot softened state of 500℃ to 900℃ when it reaches the arc zone. This forms a synergistic heating and melting mechanism of resistance heat and arc heat. On the one hand, this increases the melting speed of the submerged arc welding wire compared to conventional cold welding wire, achieving high welding efficiency. On the other hand, since part of the energy for melting the submerged arc welding wire comes from resistance heat rather than arc heat, the heat input to the steel pipe from the arc is correspondingly reduced, resulting in a lower overall welding heat input. This breaks the traditional technical contradiction that "high efficiency inevitably comes with high heat input." Based on this, the zoned welding strategy of root welding, filler welding, and capping welding, combined with the aforementioned synergistic heating mechanism, forms a complete process match. The low heat input shortens the high-temperature residence time and reduces the peak temperature in the heat-affected zone, laying the foundation for maintaining a refined microstructure during subsequent post-weld heat treatment. After welding, the steel pipe undergoes post-weld heat treatment; this treatment eliminates residual stress without damaging the fine-grained state, ultimately resulting in good performance of the welded joint of the marine engineering steel pipe in a -10℃ CTOD test. Therefore, the embodiments of this application simultaneously solve the technical problems of the difficulty in achieving both low heat input and high welding efficiency in existing marine engineering steel pipe welding processes, as well as the significant attenuation of low-temperature fracture toughness after post-weld heat treatment.

[0033] The first aspect of this application provides a hot-wire submerged arc welding method for marine engineering steel pipes using resistance arc combined heating, referring to... Figure 1 This includes the following steps: Step S10: Form a bevel on the steel pipe; In one feasible embodiment, the bevel can be formed in various ways. For example, it can be achieved by machining methods such as milling or planing to obtain precise bevel dimensions and surface quality; or by thermal cutting methods such as oxy-acetylene flame cutting or plasma cutting to achieve faster bevel processing speeds. The design and processing quality of the bevel directly affect the penetration depth and weld formation of subsequent welding.

[0034] In one feasible implementation, the bevel shape includes a double-sided X-shape or a double-sided K-shape.

[0035] Optionally, a double-sided X-shaped bevel refers to processing bevels on both the front and back surfaces of the steel pipe, with the two bevels symmetrically distributed and the cross-sectional shape being "X".

[0036] Optionally, a double-sided K-type bevel refers to processing bevels on both the front and back surfaces of the steel pipe, with the two bevels symmetrically distributed and the cross-sectional shape resembling a "K".

[0037] Step S20: Control the dry extension of the submerged arc welding wire to 80 mm~100 mm, and start the sectional welding from the bevel of the steel pipe. The sectional welding process includes root welding, fill welding and cover welding in sequence. In one feasible embodiment, the submerged arc welding wire extension is controlled to be 80 mm to 100 mm. The wire is preheated to 500°C to 900°C using the resistance heat generated by the welding current passing through this extension before entering the molten pool, forming a synergistic heating and melting mechanism of resistance heat and arc heat. Then, zonal welding begins from the bevel of the steel pipe. Zonal welding refers to using different combinations of welding parameters for different layers of the weld (root weld, filler weld, and cap weld). For example, in the root weld stage, a relatively small current and voltage can be used to ensure good penetration and prevent burn-through; in the filler weld stage, the current and wire feed speed can be appropriately increased to improve deposition efficiency; and in the cap weld stage, fine-tuning of parameters may be necessary to obtain a smooth and aesthetically pleasing weld surface.

[0038] In one feasible implementation, the thickness of the steel pipe is 50 mm to 120 mm, and the pipe diameter is ≥ 600 mm; Optionally, the thickness of the steel pipe can be 50 mm, 60 mm, 70 mm, 80 mm, 90 mm, 100 mm, 110 mm, 120 mm, etc.

[0039] Optionally, if the thickness of the steel pipe is too small, it is easy to cause root burn-through and weld collapse; if the thickness of the steel pipe is too large, the maximum cladding capacity of the welding wire at a dry extension of 80 mm to 100 mm has an upper limit, which cannot further reduce the number of passes and weakens the efficiency advantage. In order to ensure root penetration, the heat input needs to be increased to 2.8 to 3.2 kJ / mm, which leads to the re-coarsening of grains in the heat-affected zone. After post-weld heat treatment, the CTOD value at -10℃ drops to below 1.0 mm.

[0040] In one feasible implementation, the steel pipe is made of one of the following materials: DH36, API 2W Gr.50, and S355.

[0041] In one feasible embodiment, the diameter of the submerged arc welding wire is 4.0 mm.

[0042] The diameter of the submerged arc welding wire is selected as 4.0 mm. This diameter of welding wire has good versatility in conventional submerged arc welding and can meet the welding needs of steel pipes of different thicknesses.

[0043] Optionally, the dry extension of the submerged arc welding wire can be 80 mm, 82 mm, 84 mm, 86 mm, 88 mm, 90 mm, 92 mm, 94 mm, 96 mm, 98 mm, 100 mm, etc.

[0044] Alternatively, when the wire extension is too small, according to Joule's law, due to the short current-carrying length of the welding wire resulting in a very low resistance value, even with a large current, the generated resistance heat is extremely limited. The tip of the welding wire can only be preheated to about 200℃~300℃, far from reaching the softened state close to the melting point. At this time, the melting of the welding wire almost entirely depends on the heat of the electric arc, and a synergistic heating mechanism cannot be formed. The melting speed of the welding wire can only be driven by the energy of the electric arc. At the same time, the electric arc needs to use a large amount of energy to melt the cold welding wire rather than to melt the base metal, resulting in a high heat input to the base metal, coarsening of the grains in the heat-affected zone, and a temperature drop of -10℃ after post-weld heat treatment. The CTOD value is reduced and cannot meet the stringent requirements of marine engineering. When the wire extension is too large, the excessive length of the welding wire leads to an excessively high resistance value. Under the same welding current, the resistance heat generated increases sharply, causing the end of the welding wire to be overheated to a temperature exceeding the softening temperature of the welding wire. Before entering the molten pool, the welding wire has already bent, shaken, or even melted prematurely due to its own weight or wire feeding force. This results in the welding wire not being able to accurately point to the root of the groove, the arc stability drops sharply, and problems such as frequent arc breaks, increased spatter, and deterioration of weld formation occur. At the same time, the overheated welding wire will bring in too much heat when entering the molten pool, which will cause the overall heat input to get out of control and aggravate the grain coarsening of the heat-affected zone.

[0045] In one feasible implementation, the process parameters for root welding include: The welding current is 400 A~450 A, the welding voltage is 34 V~36 V, the welding speed is 500 mm / min~600 mm / min, and the heat input is 1.85 kJ / mm~2.05 kJ / mm.

[0046] Optionally, the welding current for root welding can be 400 A, 410 A, 420 A, 430 A, 440 A, 450 A, etc. Insufficient welding current will result in insufficient arc penetration and inadequate root penetration, easily leading to incomplete penetration defects. Conversely, excessive welding current will cause excessive heat input to the root, which, when combined with gas shielded welding for sealing the root, can easily cause root burn-through or weld beads.

[0047] Optionally, the welding voltage for root welding can be 34 V, 35 V, 36 V, etc. If the welding voltage is too low, the arc will be too short, the molten pool will have poor fluidity, and the fusion on both sides of the root will be inadequate. If the welding voltage is too high, the arc will be too long, which will reduce the protective effect of the molten pool, increase spatter, and even produce porosity.

[0048] Optionally, the welding speed for root welding can be 500 mm / min, 520 mm / min, 540 mm / min, 560 mm / min, 580 mm / min, 600 mm / min, etc. Too low a welding speed will result in excessive heat input per unit length of weld, leading to overheating or even burn-through at the root. Too high a welding speed will cause the welding wire melting rate to lag behind the welding speed, resulting in insufficient root filling and the formation of depressions.

[0049] Optionally, the heat input for root welding can be 1.85 kJ / mm, 1.90 kJ / mm, 1.95 kJ / mm, 2.00 kJ / mm, 2.05 kJ / mm, etc. If the heat input for root welding is too low, insufficient fusion at the root can easily lead to incomplete fusion defects. If the heat input is too high, the risk of overheating and burn-through at the root increases sharply, and the back-side forming becomes uncontrolled.

[0050] In one feasible implementation, the process parameters for filler welding include: The welding current is 550 A~600 A, the welding voltage is 34 V~36 V, the wire feed speed is 220 cm / min~240 cm / min, the welding speed is 500 mm / min~600 mm / min, and the heat input is 2.10 kJ / mm~2.60 kJ / mm.

[0051] Optionally, the welding current for filler welding can be 550 A, 560 A, 570 A, 580 A, 590 A, 600 A, etc. If the welding current is too low, the advantages of resistance-arc synergistic heating brought by the Φ4.0mm welding wire and the 80~100mm wire extension cannot be fully utilized. The increase in wire melting speed is not significant, and the number of welding passes cannot be effectively reduced. If the welding current is too high, the resistance heat will be too strong, causing the welding wire to soften excessively and the wire feeding to become unstable. At the same time, the molten pool will be too large, and the grains in the heat-affected zone will coarsen again.

[0052] Optionally, the welding voltage for filler welding can be 34 V, 35 V, 36 V, etc. If the welding voltage is too low, the arc stiffness will be too large, which will easily lead to undercut. If the welding voltage is too high, the arc will diverge, resulting in excessive weld width and poor weld formation.

[0053] Optionally, the wire feed speed for filler welding can be 220 cm / min, 222 cm / min, 224 cm / min, 226 cm / min, 228 cm / min, 230 cm / min, 232 cm / min, 234 cm / min, 236 cm / min, 238 cm / min, 240 cm / min, etc. Too low a wire feed speed leads to insufficient deposition and reduced filling efficiency, while too high a wire feed speed causes the wire melting demand to exceed the supply capacity of the arc and resistance heat, resulting in wire breakage or arc interruption.

[0054] Optionally, the welding speed for filler welds can be 500 mm / min, 520 mm / min, 540 mm / min, 560 mm / min, 580 mm / min, 600 mm / min, etc. Too low a welding speed increases heat input and coarsens the grains, while too high a welding speed easily leads to insufficient filler and lack of fusion between passes.

[0055] Optionally, the heat input for filler welding can be 2.10 kJ / mm, 2.20 kJ / mm, 2.30 kJ / mm, 2.40 kJ / mm, 2.50 kJ / mm, 2.60 kJ / mm, etc. If the heat input is too low, the cladding efficiency of the filler welding decreases, requiring more passes; if the heat input is too high, the grains in the heat-affected zone coarsen, directly leading to a decrease in the -10℃ CTOD value after post-weld heat treatment.

[0056] In one feasible implementation, the process parameters for the cover weld include: The welding current is 400 A~450 A, the welding voltage is 36 V~38 V, the welding speed is 400 mm / min~500 mm / min, and the heat input is 2.40 kJ / mm~2.70 kJ / mm.

[0057] Optionally, the welding current for the cover weld can be 400 A, 410 A, 420 A, 430 A, 440 A, 450 A, etc. If the welding current is too low, the arc will not melt the base material sufficiently, and incomplete fusion may occur between the cover layer and the filler layer. If the welding current is too high, the cover layer reinforcement will be too low or even undercut may occur.

[0058] Optionally, the welding voltage for the cover weld can be 36 V, 37 V, 38 V, etc. If the welding voltage is too low, the cover layer will be too narrow and the base material on both sides will not be completely covered. If the welding voltage is too high, the cover layer will be too wide and the surface will be rough, resulting in an unsightly weld.

[0059] Optionally, the welding speed for the capping weld can be 400 mm / min, 420 mm / min, 440 mm / min, 460 mm / min, 480 mm / min, 500 mm / min, etc. Too low a welding speed results in excessive heat input to the capping layer, leading to overheating and oxide scale formation. Too high a welding speed results in insufficient filler material and insufficient reinforcement, failing to meet dimensional requirements. When the heat input is below 2.40 kJ / mm, the transition between the capping layer and the base material is not smooth, easily leading to stress concentration. When the heat input is above 2.70 kJ / mm, the capping layer grains coarsen and the surface is severely oxidized, affecting the weld appearance quality and fatigue resistance.

[0060] Optionally, the heat input for the cover weld can be 2.40 kJ / mm, 2.50 kJ / mm, 2.60 kJ / mm, 2.70 kJ / mm, etc. If the heat input is too low, the transition between the cover layer and the base material will not be smooth and stress concentration will easily occur. If the heat input is too high, the grains of the cover layer will coarsen and the surface will be severely oxidized, affecting the appearance quality and fatigue resistance of the weld.

[0061] Step S30: After welding is completed, the steel pipe undergoes post-weld heat treatment.

[0062] In one feasible embodiment, after welding is completed, the welded parts are subjected to a heat treatment process. The purpose of the heat treatment process is to eliminate residual stress generated by welding, improve the microstructure uniformity of the welded joint, and stabilize dimensional accuracy through a precisely controlled heating and cooling process.

[0063] In one feasible embodiment, the step of performing post-weld heat treatment on the steel pipe includes: The holding temperature during the heat treatment process is controlled at 580 ℃±15 ℃, and the heating and / or cooling rate during the heat treatment process is ≤55 ℃ / h; When the steel pipe thickness is less than or equal to 76.2 mm, the heat preservation time is 2.5 h; When the steel pipe thickness is greater than 76.2 mm, the insulation time is determined based on the thickness of the steel pipe.

[0064] In one feasible embodiment, by precisely controlling the holding temperature, heating and cooling rates, and holding time, the refined grain structure obtained by low heat input welding can be protected while eliminating residual welding stress.

[0065] Optionally, the insulation temperature can be 565 ℃, 570 ℃, 575 ℃, 580 ℃, 585 ℃, 590 ℃, 595 ℃, etc. Controlling the insulation temperature at 580 ℃ ± 15 ℃ can effectively eliminate residual welding stress without causing phase transformation or grain coarsening.

[0066] Optionally, the heating and cooling rates should not exceed 55℃ / h, in order to prevent additional thermal stress caused by excessively rapid temperature changes and avoid reheat cracking in thick plates.

[0067] 76.2 mm (3 inches) is a commonly used standard thickness in the field of marine engineering steel structures.

[0068] In one feasible implementation, when the steel pipe thickness is greater than 76.2 mm, the heat preservation time is increased by 1 min for every 1 mm increase in steel pipe thickness.

[0069] When performing post-weld heat treatment using the hot-wire submerged arc welding method with resistance arc co-heating for marine engineering steel pipes, if the steel pipe thickness is greater than 76.2 mm, setting the holding time solely based on the fixed thickness may result in insufficient heat treatment, thus failing to effectively eliminate internal residual stress and affecting the fatigue life and fracture toughness of the steel pipe.

[0070] As the thickness of the steel pipe increases, the time required for heat to conduct from the surface of the steel pipe to the center of the plate (i.e., the part furthest from the heat source) is correspondingly extended. If the heat preservation time is insufficient, the center of the plate cannot reach the set heat preservation temperature of 580℃, resulting in insufficient elimination of residual stress in the core, which in turn makes the welded joint susceptible to stress corrosion cracking during service. Conversely, if the heat preservation time is too long, it will not only reduce production efficiency and increase energy consumption, but may also cause over-aging of the weld and heat-affected zone or precipitation of carbides along grain boundaries, which will reduce the low-temperature fracture toughness.

[0071] In one feasible implementation, the submerged arc welding wire is preheated to 500~900°C before entering the molten pool.

[0072] Under the influence of welding current, the extended section of the welding wire generates significant resistance heat, raising its temperature to 500-900°C before reaching the arc zone. Although this does not reach the wire's melting point, it enters a distinct red-hot softening state, at which point the wire's yield strength decreases significantly while its plasticity increases substantially. The arc only needs to supplement the remaining heat to complete the droplet transfer, thus significantly increasing the melting rate compared to cold welding wire at room temperature. Secondly, because the welding wire is preheated to near-molten state, more of the arc's energy can be used to melt the base metal rather than heat the welding wire, directly resulting in a reduction in heat input to the base metal. The preheating temperature of 500-900°C is much higher than the room temperature or slight preheating of the welding wire in conventional submerged arc welding, achieving a synergistic heating process. This allows for both high efficiency and low heat input in the welding of marine engineering steel pipes.

[0073] In one feasible implementation, the heat-treated steel pipe has a CTOD of ≥1.0 mm at -10℃ at both the weld center and the fusion line.

[0074] In a feasible embodiment, CTOD (Crack Tip Opening Displacement) is used to evaluate the fracture toughness of the material, measured in mm. A higher CTOD value indicates a stronger resistance to crack propagation, i.e., better toughness. After complete processing, the fracture toughness of the resulting marine engineering steel pipe at -10℃ must reach or exceed 1.0 mm. When crack-like defects exist in the marine engineering steel pipe, the crack tip should be able to generate at least 1.0 mm of opening displacement without brittle fracture at -10℃, indicating that the marine engineering steel pipe possesses excellent resistance to brittle fracture.

[0075] For example, refer to Figure 2 , Figure 2 The left-middle figure illustrates the principle of preheated submerged arc welding. Preheated submerged arc welding increases the wire extension and utilizes the resistance heat generated by the welding current in the extended wire to preheat it to a higher temperature before feeding it into the arc zone. This increases the melting rate of the wire per unit current. Segment OA represents the complete process of heating and melting the wire for welding, with the wire extension being the length L of segment OA. x Section AB is the wire preheating stage, which uses the resistance heat generated by the welding current in the long-elongated welding wire to heat the welding wire to a higher temperature. Figure 2 The image on the right shows the actual welding process.

[0076] For example, refer to Figure 3 , Figure 3 Figures A and C show that the wire feed speed for a conventional process with a welding current of 600A is 81.5 ipm, while Figure 3 Figures B and D show that the preheating process increases the wire feed speed to 130.6 ipm, an increase of approximately 63%. This significant increase in wire feed speed means a substantial increase in the amount of metal delivered to the molten pool per unit time, effectively improving welding deposition efficiency and production speed. Preheating submerged arc welding utilizes the resistance heat generated by the current flowing through the welding wire to preheat it before it contacts the molten pool, ensuring it reaches a red-hot state. This not only eliminates the risk of overheating or incomplete fusion that might arise from increased wire feed speed but also ensures a stable arc and excellent weld formation even under high current and high wire feed speed conditions.

[0077] Example This invention provides a submerged arc welding process for thick-walled steel used in marine engineering, specifically applied to the welding and manufacturing of DH36 steel pipes with a thickness of 120 mm. A double-sided X-shaped bevel is machined on the steel, with a bevel angle of 60°, a blunt edge of 3 mm, an assembly gap of 2 mm, and an inner-outer depth ratio of 1:1 (approximately 60 mm depth on each side). A 4.0 mm diameter submerged arc welding wire is used, with the wire extension controlled at 100 mm, in conjunction with a dedicated submerged arc welding torch with an internal ceramic insulating conduit. The power supply uses DC reverse polarity. The process parameters for the sectional welding process include: Root welding: Welding current 420 A, welding voltage 35 V, welding speed 500 mm / min, heat input approximately 1.95 kJ / mm, the back side is sealed with gas shielded welding to prevent burn-through; Filler welding: welding current 550~600 A, welding voltage 34~36 V, wire feed speed 220~240 cm / min, welding speed 500~600 mm / min, heat input approximately 2.10~2.50 kJ / mm; Cover weld: Welding current 430 A, welding voltage 37 V, welding speed 420 mm / min, heat input approximately 2.55 kJ / mm; After welding, post-weld heat treatment is performed using electric heating bands, with the heat treatment curve referenced. Figure 4 The heating rate was controlled to not exceed 55 ℃ / h to reach 580 ℃, and held at that temperature for 195 min. The cooling rate was then controlled to not exceed 55 ℃ / h for further cooling. After cooling for 48 h post-weld, the sample passed 100% UT and RT non-destructive testing.

[0078] Then, mechanical property tests were conducted, and the test results are shown in Tables 1, 2, and 3.

[0079] Table 1 Transverse tensile test

[0080] Table 2 -50℃ Impact Test (Sample size: 10×10×55mm)

[0081] Figure 5 The image shown is a macroscopic image of the X-groove, which shows that the weld is free of defects such as slag inclusions, porosity, and cracks, indicating good weld quality.

[0082] Reference Figure 6 The hardness dot plot shown is used to test the hardness of the weld near the surface and root, and to test the performance of welds of different thicknesses. The Vickers hardness HV10 value is 160~240, the performance is stable, and the distribution is uniform without abnormalities.

[0083] Table 3 CTOD Experiment at -10℃

[0084] Reference Figure 7 The CTOD test curves of the weld center and heat-affected zone of the steel pipe are shown. The results show that after the curve reaches the peak load, the load remains at an extremely high level as the displacement increases, indicating that the steel pipe prepared in this embodiment has good low-temperature fracture toughness after post-weld heat treatment.

[0085] In this embodiment, by using a Φ4.0 mm welding wire and controlling the wire extension to 100 mm, significant resistance heat is generated when the welding current passes through this long extension section, preheating the welding wire to approximately 800℃~900℃, forming a synergistic heating and melting mechanism through the combined action of resistance heat and arc heat. Compared with conventional submerged arc welding, this embodiment has the following advantages: First, efficiency and performance are both improved: Under the same welding current conditions, due to the synergistic heating mechanism of resistance heating and arc heating, the wire melting speed is increased by 30% to 60%, the welding speed is increased by more than 30% simultaneously, the number of welding passes is reduced by 30% to 60%, and the construction cycle of thick plate pipe is shortened; at the same time, the overall welding heat input is reduced by 10% to 21%, the grains in the heat-affected zone are significantly refined, and the low-temperature toughness of the joint is improved, breaking the traditional technical contradiction that "high efficiency must be accompanied by high heat input".

[0086] Second, high CTOD retention after PWHT: After eliminating residual stress through a special post-weld heat treatment at 580℃, the CTOD value of the welded joint at -10℃ at the weld center and fusion line position is stably above 1.0 mm, solving the industry problem of "significant toughness reduction after PWHT" in thick-walled high-strength steel welding.

[0087] Third, low cost and material savings: No additional preheating power supply or complex equipment is required. It can be implemented by simply modifying the welding torch (using a built-in ceramic insulated conduit), and the modification cost is extremely low. At the same time, due to the reduction of welding passes by 30% to 60%, the consumption of electricity and flux is reduced by 10% to 21%, which makes the economic benefits in large-scale marine engineering pipe manufacturing projects extremely considerable.

[0088] Fourth, process reliability: the welding process is stable and the parameters are controllable, and the mechanical properties such as tensile strength, impact toughness, and hardness fully meet the performance requirements of marine engineering structures.

[0089] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A hot-wire submerged arc welding method for marine engineering steel pipes using resistance arc combined heating, characterized in that, Includes the following steps: Form a bevel on the steel pipe; The dry extension of the submerged arc welding wire is controlled to be 80 mm to 100 mm. Welding is carried out in sections starting from the bevel of the steel pipe. The section welding process includes root welding, fill welding and cover welding in sequence. After welding, the steel pipe is subjected to post-weld heat treatment.

2. The hot-wire submerged arc welding method for marine engineering steel pipes with resistance arc co-heating as described in claim 1, characterized in that, The process parameters for root welding include: The welding current is 400 A~450 A, the welding voltage is 34 V~36 V, the welding speed is 500 mm / min~600 mm / min, and the heat input is 1.85 kJ / mm~2.05 kJ / mm.

3. The hot-wire submerged arc welding method for marine engineering steel pipes with resistance arc co-heating as described in claim 1, characterized in that, The process parameters for the filler welding include: The welding current is 550 A~600 A, the welding voltage is 34 V~36 V, the wire feed speed is 220 cm / min~240 cm / min, the welding speed is 500 mm / min~600 mm / min, and the heat input is 2.10 kJ / mm~2.60 kJ / mm.

4. The hot-wire submerged arc welding method for marine engineering steel pipes with resistance arc co-heating as described in claim 1, characterized in that, The process parameters for the capping weld include: The welding current is 400 A~450 A, the welding voltage is 36 V~38 V, the welding speed is 400 mm / min~500 mm / min, and the heat input is 2.40 kJ / mm~2.70 kJ / mm.

5. The hot-wire submerged arc welding method for marine engineering steel pipes with resistance arc co-heating as described in claim 1, characterized in that, The bevel shape includes a double-sided X-shape or a double-sided K-shape.

6. The hot-wire submerged arc welding method for marine engineering steel pipes with resistance arc co-heating as described in claim 1, characterized in that, The thickness of the steel pipe is 50 mm to 120 mm, and the pipe diameter is ≥600 mm; And / or, the material of the steel pipe includes one of DH36, API 2W Gr.50 and S355; And / or, the diameter of the submerged arc welding wire is 4.0 mm.

7. The hot-wire submerged arc welding method for marine engineering steel pipes with resistance arc co-heating as described in claim 1, characterized in that, The step of performing post-weld heat treatment on the steel pipe includes: The holding temperature during the heat treatment process is controlled at 580 ℃±15 ℃, and the heating and / or cooling rate during the heat treatment process is ≤55 ℃ / h; When the thickness of the steel pipe is less than or equal to 76.2 mm, the heat preservation time is 2.5 h; When the thickness of the steel pipe is greater than 76.2 mm, the heat preservation time is determined based on the thickness of the steel pipe being greater than 76.2 mm.

8. The hot-wire submerged arc welding method for marine engineering steel pipes with resistance arc co-heating as described in claim 7, characterized in that, When the thickness of the steel pipe is greater than 76.2 mm, the heat preservation time increases by 1 min for every 1 mm increase in the thickness of the steel pipe.

9. The hot-wire submerged arc welding method for marine engineering steel pipes with resistance arc co-heating as described in claim 1, characterized in that, The submerged arc welding wire is preheated to 500℃~900℃ before entering the molten pool.

10. The hot-wire submerged arc welding method for marine engineering steel pipes with resistance arc co-heating as described in claim 1, characterized in that, After heat treatment, the CTOD of the steel pipe at -10℃ is ≥1.0 mm at both the weld center and the fusion line.

Images