Bridge steel vertical position welding method

Abstract

The invention provides a vertical position welding method for bridge steel. The vertical position welding method comprises the steps that 1, a groove is manufactured, specifically, the X-shaped groove without a truncated edge is manufactured in a vertical position mode through a flame cutting technology; and the groove is polished and derusted according to requirements. 2, preheating, wherein the bridge steel is preheated to 75 DEG C in an electric heating mode; and 3, welding, wherein solid welding wire argon-rich mixed gas shielded welding is adopted for vertical position welding. And 4, post-weld heat treatment is conducted, specifically, after welding is completed, post-heat treatment is conducted at 200-250 DEG C through a crawler-type heater, and slow cooling is conducted to the room temperature after heat preservation is conducted for 3 hours. By researching and developing a welding material and a welding process matched with the Q890qE high-strength bridge steel, the technical problem of quality of a Q890qE vertical position butt welding seam is solved. Welding forming is stable, efficiency is high, deformation is small, the appearance is good, strength and weather resistance are balanced, the service life is long, and economical efficiency and environment friendliness are both considered; the method is especially suitable for engineering scenes with strict requirements on strength, toughness and durability such as long-span bridges and alpine region bridges, and has remarkable economic advantages and social value.

Description

Technical Field

[0001] This invention belongs to the field of welding technology, specifically relating to a method for welding steel beams in a bridge. Background Technology

[0002] In my country, the main structural steel grades used for bridges are Q500q, Q420q, Q370q, and Q345q, with limited engineering applications of higher strength steel grades. There is currently no comparable experience to refer to regarding the butt welding method for 890MPa grade bridge steel. Therefore, the following improved technical solution is proposed. Summary of the Invention

[0003] The technical problem solved by this invention is to provide a method for vertical welding of bridge steel, which solves the technical problem of the quality of vertical butt welds of Q890qE by developing welding materials and welding processes that match Q890qE high-strength bridge steel.

[0004] The technical solution adopted in this invention is: a method for vertical welding of bridge steel, wherein the welding method for bridge steel includes the following steps: Step 1, Beveling: Use flame cutting technology to vertically create an X-shaped bevel without blunt edges; grind and remove rust from the bevel of the steel plate joint as required.

[0005] Step 2, Preheating: Preheat the bridge steel to 75°C using electric heating.

[0006] Step 3, Welding: Vertical welding is performed using solid welding wire GMAW-Ar (argon-rich mixed gas shielded welding).

[0007] Step 4, Post-weld heat treatment: After welding, use a tracked heater for post-weld heat treatment. The post-heat temperature is 200-250℃. After holding at this temperature for 3 hours, turn off the power and slowly cool to room temperature.

[0008] In the above technical solution, the bridge steel is 40mm thick bridge steel of grade 890MPa; the mechanical properties of the cladding metal of the bridge steel are yield strength of 988MPa, tensile strength of 1103MPa, and elongation of 14.5%; the yield strength of the bridge steel is 924MPa, tensile strength of 1120MPa, and elongation of 15.0%.

[0009] In the above technical solution, the composition of the bridge steel is as follows: C: 0.063%, Si: 0.19%, Mn: 1.44%, P: 0.0093%, S: 0.0037%, Cr: 0.52%, Ni: 1.53%, Cu: 0.76%, Nb: 0.045%, V: 0.001%, Ti: 0.009%, Mo: 0.19%, Al: 0.021%; CEV=0.60%, Pcm=0.24%.

[0010] In the above technical solution, the chemical composition of the solid welding wire is: C: 0.53%, Si: 0.69%, Mn: 1.63%, P: 0.0067%, S: 0.0013%, Cu: 0.094%, Cr: 0.35%, Ni: 2.1%, Ti: 0.038%, Mo: 0.5%.

[0011] In the above technical solution, the X-shaped bevel is an X-shaped bevel with a 6mm gap; the bevel depth is H2=δ / 2, and the bevel angle is 40°.

[0012] In the above technical solution, the diameter of the solid welding wire in step 3 is Φ1.2mm; the interpass temperature during the vertical welding in step 3 is 160℃~175℃; and the argon-rich mixed gas for the argon-rich mixed gas shielded welding in step 3 is 80%Ar+20%CO2.

[0013] In the above technical solution, the welding process in step 3 is a combination of multi-layer, multi-pass continuous welding process and double-sided alternating welding process with a round rod ceramic backing attached to the back.

[0014] In the above technical solution, step 3 includes the following steps: Step 301: Attach a round rod ceramic pad to the back of the bevel.

[0015] Step 302: Use solid welding wire and argon-rich mixed gas shielded welding to weld the front weld bead, and fill the weld with H2=δ / 2.

[0016] Step 303: Remove the ceramic backing.

[0017] Step 304: Use solid welding wire and argon-rich mixed gas shielded welding to weld the back weld until it is filled, and then continue welding the remaining weld on the front bevel.

[0018] The above technical solution includes three steps: root pass, fill pass, and cover pass; root pass current is 180±20A, voltage is 18±2V, welding speed is 190±20mm / min, gas flow rate is 15~20L / min, and extension length is 15±3mm; fill pass and cover pass current is 200±20A, voltage is 20±2V, welding speed is 190±20mm / min, gas flow rate is 15~20L / min, and extension length is 15±3mm.

[0019] Advantages of this invention compared to existing technologies: 1. This invention is designed for the vertical butt joint of Q890qE ultra-high strength steel for bridge applications. It adopts solid welding wire and argon-rich mixed gas protection welding, which results in stable welding formation. There is no need to clean the weld bead coating during the welding process, and the weld deposition efficiency is high, effectively improving the welding efficiency.

[0020] 2. The X-shaped bevel of this invention, with a 6mm gap in the joint design, eliminates the need for carbon arc gouging before reverse welding when using a double-sided alternating welding process with ceramic backing. This avoids the adverse effects of cementite generated during carbon arc gouging on the chemical composition and mechanical properties of the weld, reduces the heat input of the weld, improves the welding efficiency of vertical butt welds, better controls welding deformation, and greatly reduces manufacturing costs.

[0021] 3. The solid welding wire of this invention has a high degree of chemical composition matching with Q890qE ultra-high strength bridge steel, and its mechanical properties are comparable to those of the steel. It adopts a multi-layer, multi-pass continuous welding process, and the mechanical properties of the weld fully meet the design requirements. After welding, the weld is subjected to post-heat treatment and heat preservation and slow cooling, which improves the micro-grain structure of the weld and effectively prevents the occurrence of welding cracks.

[0022] 4. This invention uses solid welding wire and argon-rich mixed gas (80%Ar+20%CO2) for welding protection, resulting in a weld microstructure of acicular ferrite. The welded joint has a low-temperature toughness (KV2) greater than 50J at -40℃ and an impact toughness of 166J in the heat-affected zone. This welded joint has excellent crack resistance and impact toughness reserves, making it suitable for steel bridge engineering applications in harsh environments with low temperatures.

[0023] 5. The present invention has simple beveling, easy welding process, good welding processability, good weld fusion during welding, and is not prone to welding defects such as cracks, porosity, inclusions, and slag inclusions after welding, and the weld appearance is good.

[0024] 6. This invention optimizes the chemical composition of bridge steel to achieve a balance between high strength and weather resistance.

[0025] 7. This invention focuses on a vertical welding method for 40mm thick bridge steel of 890MPa grade. Its technical solution, through systematic and coordinated design of chemical composition, groove preparation, preheating control, welding process optimization, and post-weld heat treatment, achieves efficient and low-defect welding of high-strength, weather-resistant bridge steel plates, particularly suitable for the long-life requirements of unpainted bridge structures. Its technical advantages lie in crack control, weather resistance assurance, improved production efficiency, and optimized overall cost, providing a reliable solution for large-scale steel structure projects.

[0026] 8. The chemical composition design of the solid welding wire of this invention achieves a perfect match with the 90MPa grade bridge steel base material through high Ni+Mo for enhanced toughness, low P / S for crack control, and Mn / Si / Ti for optimized processability. The weld metal exhibits lower-temperature toughness and crack resistance than the base material; its adaptability to vertical welding and low spatter characteristics make the welding process highly efficient and stable; it balances economy and environmental protection, with low cost and minimal pollution. This welding wire formulation provides key material support for high-quality welding of thick plate bridge steel, and is particularly suitable for the manufacture of paint-free, high-weather-resistant, and long-life bridge structures.

[0027] 9. The X-type bevel design of this invention achieves high efficiency and high reliability in welding 890MPa grade bridge steel through the coordinated optimization of gap, depth and angle. It is especially suitable for engineering scenarios with stringent requirements for strength, toughness and durability, such as long-span bridges and bridges in cold regions, and has significant technical and economic advantages.

[0028] 10. The welding process of this invention achieves high efficiency and high reliability in welding 890MPa grade bridge steel through the synergistic optimization of welding wire specifications, gas protection, temperature control, backing design and double-sided alternating welding. It is especially suitable for engineering scenarios with stringent requirements for strength, toughness and durability, such as long-span bridges and bridges in cold regions, and has significant technical and economic advantages.

[0029] 11. The layered welding parameter design of this invention achieves high efficiency and high reliability in welding 890MPa high-strength steel by ensuring quality with low heat input in the bottom layer, improving efficiency with high heat input in the filler layer, and precisely matching gas flow rate and weld extension length. Its technical advantages are particularly suitable for engineering scenarios with stringent requirements for weld strength, toughness, and durability, such as long-span bridges and bridges in cold regions, demonstrating significant economic benefits and social value. Attached Figure Description

[0030] Figure 1 This is the bevel form of the upright butt joint of the present invention; Figure 2 The bevel form of the butt joint of this invention is 40mm thick; Figure 3 This invention relates to the arrangement of weld beads in the upright butt joint. Figure 4 This is a macroscopic metallographic photograph of the upright butt joint of the present invention after welding; Figure 5 This is a flowchart of the welding method of the present invention; Detailed Implementation

[0031] The following will refer to the appendices in the embodiments of the present invention. Figure 1-4 The technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] A method for vertical welding of bridge steel is disclosed in this invention. The bridge steel used in this invention is 40mm thick bridge steel of 890MPa grade. The composition of the bridge steel is as follows: C: 0.063%, Si: 0.19%, Mn: 1.44%, P: 0.0093%, S: 0.0037%, Cr: 0.52%, Ni: 1.53%, Cu: 0.76%, Nb: 0.045%, V: 0.001%, Ti: 0.009%, Mo: 0.19%, Al: 0.021%; CEV = 0.60%, Pcm = 0.24%.

[0033] It should be noted that this invention optimizes the chemical composition to achieve a balance between high strength and weather resistance. A detailed analysis follows: Synergistic effect of alloying elements: Cr (0.52%) + Ni (1.53%) + Cu (0.76%): Forms a dense oxide film, improving atmospheric corrosion resistance and meeting the requirements for paint-free bridge steel.

[0034] Nb (0.045%) + Ti (0.009%): Microalloying refines the grains, improves strength and toughness, and suppresses coarse grain embrittlement in the weld heat-affected zone (HAZ).

[0035] Mo (0.19%): Enhances high-temperature strength and improves resistance to hydrogen-induced cracking.

[0036] Low CEV (0.60%) and Pcm (0.24%): The carbon equivalent (CEV) and cold crack sensitivity coefficient (Pcm) are at a low level, which significantly reduces the risk of welding cracks, especially suitable for welding thick plates (40mm).

[0037] The welding method for the bridge steel includes the following steps: Step 1, Beveling: Use flame cutting technology to vertically create an X-shaped bevel without blunt edges; grind and remove rust from the bevel of the steel plate joint as required.

[0038] It should be noted that the bevel preparation of this invention adopts flame cutting in a vertical position, which reduces the cost by 30% compared with mechanical processing, and improves welding efficiency and quality. Specifically, the X-shaped bevel without blunt edges, prepared by flame cutting in a vertical position, reduces machining allowance and lowers manufacturing costs. The symmetry of the X-shaped bevel optimizes arc penetration, ensuring double-sided fusion and reducing incomplete penetration defects. Bevel grinding and rust removal eliminate the cutting oxide layer and impurities, reducing hydrogen-induced crack sources and improving the purity of the weld metal.

[0039] Step 2, Preheating: Preheat the bridge steel to 75°C using electric heating.

[0040] It should be noted that the preheating operation of this invention reduces cracking tendency and residual stress. Electric heating is more uniform than flame preheating, and it allows for precise temperature control with a temperature difference ≤10℃. Electric preheating to 75℃, for 40mm thick plates, effectively slows down the post-weld cooling rate, preventing the formation of hardened structures (such as martensite) in the HAZ (hardened area zone), thus reducing the risk of cold cracking. Uniform preheating reduces welding stress concentration, making it particularly suitable for high-restraint bridge structures.

[0041] Step 3, Welding: Vertical welding is performed using solid welding wire GMAW-Ar (argon-rich mixed gas shielded welding).

[0042] It should be noted that the welding method of this invention achieves a balance between high efficiency and high quality. GMAW-Ar (argon-rich mixed gas shielded welding) improves welding efficiency by 2 times compared to manual arc welding. Specifically, the solid wire GMAW-Ar process, with its argon-rich mixed gas (Ar+CO2), enhances arc stability, refines molten droplets, reduces spatter, and improves weld formation.

[0043] Step 4, Post-weld heat treatment: After welding, use a tracked heater for post-weld heat treatment. The post-heat temperature is 200-250℃. After holding at this temperature for 3 hours, turn off the power and slowly cool to room temperature.

[0044] It should be noted that the post-weld heat treatment uses a tracked heater to remove hydrogen, relax stress, effectively reduce the crack rate, and optimize performance. Specifically, the post-weld heat treatment with the tracked heater (200-250℃, holding for 3 hours) accelerates the escape of hydrogen from the weld, preventing delayed cracking (such as hydrogen-induced cooling cracking). Stress relaxation refers to reducing residual welding stress, minimizing deformation, and improving the fatigue life of the structure. Microstructural stability refers to improving HAZ grain size, avoiding coarse-grain embrittlement, and ensuring the mechanical properties of the weld match those of the base metal.

[0045] The combined advantages of the above-mentioned process are: It meets the stringent requirements of bridge steel. Specifically, it ensures the reliability of thick plate welding: through bevel design, preheating, and coordinated heat treatment control, it solves problems such as lamellar tearing and HAZ embrittlement that are prone to occur when welding 40mm thick plates. It achieves a balance between weather resistance and mechanical properties: the chemical composition is matched with the welding process to ensure that the weld metal's corrosion resistance (I≥6.2) and low-temperature toughness (impact energy ≥41J at -40℃) meet the requirements of paint-free bridges. It is economical and environmentally friendly: argon-rich GMAW-Ar reduces welding material consumption and rework rate; post-heat treatment replaces traditional high-temperature tempering, reducing energy consumption and costs.

[0046] The mechanical properties of the cladding metal of the bridge steel described in this invention are: yield strength of 988 MPa, tensile strength of 1103 MPa, and elongation of 14.5%; the yield strength of the bridge steel is 924 MPa, tensile strength of 1120 MPa, and elongation of 15.0%.

[0047] As can be seen, this invention focuses on a vertical welding method for 40mm thick bridge steel of 890MPa grade. Its technical solution, through systematic and coordinated design of chemical composition, bevel preparation, preheating control, welding process optimization, and post-weld heat treatment, achieves efficient and low-defect welding of high-strength, weather-resistant bridge steel plates, particularly suitable for the long-life requirements of unpainted bridge structures. Its technical advantages lie in crack control, weather resistance assurance, improved production efficiency, and optimized overall cost, providing a reliable solution for large-scale steel structure projects.

[0048] In the above embodiments, the chemical composition of the solid welding wire is: C: 0.53%, Si: 0.69%, Mn: 1.63%, P: 0.0067%, S: 0.0013%, Cu: 0.094%, Cr: 0.35%, Ni: 2.1%, Ti: 0.038%, Mo: 0.5%.

[0049] It should be noted that the main technical advantages of the chemical composition design of the solid welding wire in the above embodiments lie in its compatibility with the 40mm thick bridge steel base material, its adaptability to welding processes, and the optimization of weld metal properties. Specific technical advantages are as follows: Synergistic compatibility between chemical composition and base material: Strength and Toughness Balance: Ni (2.1%) + Cr (0.35%) + Mo (0.5%): High Ni content significantly improves the low-temperature toughness of the weld metal (impact energy at -40℃), making it particularly suitable for the low-temperature resistance requirements of bridges in cold northern regions. The combined addition of Cr and Mo forms solid solution strengthening, while inhibiting grain coarsening in the weld heat-affected zone (HAZ), ensuring strength matching between the weld and the base metal (tensile strength ≥90MPa). Mn (1.63%) + Si (0.69%): Mn, as a deoxidizer and solid solution strengthening element, synergistically improves the yield strength of the weld metal with Si, while reducing oxygen content and porosity defects. The Si content is moderate (0.69%), avoiding excessive Si content that could lead to weld metal embrittlement.

[0050] Weather resistance optimization: Cu (0.094%) + Cr (0.35%): Although the Cu content is lower than that of the base metal (0.76%), it combines with Cr to form a dense oxide film, creating a protective layer on the weld metal surface and improving overall atmospheric corrosion resistance. The weather resistance of the weld metal is slightly lower than that of the base metal, but the difference in Cu content can be compensated for by reducing oxide inclusions through argon-rich gas shielded welding.

[0051] Low impurity control: Phosphorus (P) is readily soluble in ferrite, reducing plasticity and toughness, especially causing "cold brittleness" at low temperatures; sulfur (S) forms a network of iron sulfides, leading to "hot brittleness" and increasing the tendency for welding cracks. P and S contents are far below conventional standards (e.g., P≤0.03%, S≤0.03%), and combined with post-treatment heat treatment (200–250℃), residual stress can be eliminated, avoiding delayed cracking.

[0052] Adaptability optimization of welding processes: The compatibility of argon-rich mixed gas shielded welding (GMAW-Ar): Ti (0.038%): Ti, as a deoxidizer and grain refiner, works synergistically with argon-rich gas (Ar+CO2) to reduce welding spatter and improve weld formation. A moderate Ti content avoids excessive amounts that could decrease weld metal toughness. C (0.53%): The carbon content is higher than the base metal (0.063%), but through argon-rich gas protection and post-heat treatment (200–250℃), the hardening tendency of the weld metal can be effectively controlled, preventing cold cracking. Carbon, as a strengthening element, improves the hardness and wear resistance of the weld metal, making it suitable for the long-term service requirements of bridge steel.

[0053] Stability of vertical welding: Mn (1.63%) + Si (0.69%): High Mn and Si content improves the fluidity of the molten pool, reduces droplet fall during vertical welding, and ensures the quality of single-sided welding with double-sided forming. Low P and S content: Reduces weld porosity and inclusions, improves the fusion quality of vertical welding, and reduces the rework rate.

[0054] Improvement of weld metal properties: Ensuring low-temperature toughness: Ni (2.1%) + Mo (0.5%): The Ni content is significantly higher than that of the base metal (1.53%). Through solid solution strengthening and grain refinement, the impact energy of the weld metal at -40℃ reaches the standard of the base metal (≥41J), meeting the requirements of bridges in high-altitude and cold regions. Ti (0.038%): Refines the weld metal grains, improves low-temperature toughness, and avoids brittle fracture of the HAZ during thick plate welding.

[0055] Hydrogen-induced cracking resistance: Mo (0.5%) + low P, S: Mo improves the weld metal's resistance to hydrogen permeation, and combined with extremely low P and S content, it significantly reduces the risk of hydrogen-induced cold cracking, especially suitable for process conditions with low preheating temperatures (75℃). Synergistic effect of post-heat treatment: Holding at 200–250℃ for 3 hours after welding promotes hydrogen escape, further eliminating the potential for hydrogen-induced cracking in the weld metal.

[0056] In terms of economic and environmental benefits: Cost Optimization: Reduced Cu Content (0.094%): Compared to the base material (0.76%), the Cu content in the welding wire is significantly reduced, decreasing the use of precious metals and lowering material costs. Improved Argon-Rich Shielded Welding Efficiency: Continuous wire feeding and automatic shielding gas supply reduce downtime, increase welding speed, and lower overall costs by 15%–20%. Enhanced Environmental Friendliness: Low Spatter Design: The synergistic effect of Ti and Si reduces welding spatter, lowers post-weld cleaning costs, and reduces welding fume emissions, meeting green manufacturing requirements.

[0057] It is evident that the chemical composition design of this solid welding wire, through high Ni+Mo to enhance toughness, low P / S to control cracking, and Mn / Si / Ti to optimize processability, achieves a perfect match with the 90MPa grade bridge steel base material. The weld metal exhibits lower-temperature toughness and crack resistance than the base material; its adaptability to vertical welding and low spatter characteristics ensure efficient and stable welding processes; it balances economic efficiency and environmental friendliness, with low cost and minimal pollution. This welding wire formulation provides crucial material support for high-quality welding of thick-plate bridge steel, and is particularly suitable for the manufacture of paint-free, high-weather-resistant, and long-life bridge structures.

[0058] In the above embodiment, the X-shaped bevel is an X-shaped bevel with a 6mm gap; the bevel depth is H2=δ / 2, and the bevel angle is 40°.

[0059] It should be noted that in the welding of 40mm thick bridge steel of 890MPa grade, an X-groove design with a 6mm gap, H2=δ / 2 (20mm) depth, and a 40° angle was adopted. By optimizing the molten pool flow, heat input control, and stress distribution, the quality and process efficiency of the welded joint were significantly improved. Its technical advantages can be analyzed from five dimensions: penetration, heat control, stress management, process adaptability, and economy. Optimized penetration: Ensures uniform fusion across the entire thickness. The 6mm gap provides ample space for the molten pool, allowing the GMAW-Ar arc to penetrate fully, forming a uniform molten pool and preventing incomplete fusion due to an insufficient gap or collapse due to an excessively large gap. Back-side penetration guarantee: In vertical welding, the 6mm gap, combined with the droplet transfer characteristics of solid welding wire, ensures a back-side penetration rate ≥90%, reducing the need for back-side cleaning and lowering operational difficulty. Layered control at a depth of H2=δ / 2 (20mm). Symmetrical heat input: The bevel depth is half the plate thickness (20mm), ensuring even heat input distribution across the upper and lower layers, preventing deformation or burn-through caused by excessive heat input on one side. Multi-layer, multi-pass welding adaptability: The 20mm depth allows for 2-3 layers of welding, with each layer controlled at 8-12mm thickness, facilitating interpass temperature control (≤150℃) and reducing the width of the HAZ coarse grain zone.

[0060] Heat input control: Reduces the risk of HAZ embrittlement. Advantages of a 6mm gap for molten pool filling and enhanced molten pool fluidity: The 6mm gap provides ample space for the molten pool, allowing the argon-rich gas shielded welding (GMAW-Ar) arc to fully penetrate the gap, forming a uniform molten pool and avoiding incomplete fusion due to an excessively small gap or collapse caused by an excessively large gap. Guaranteed back penetration: In vertical welding, the 6mm gap, combined with the droplet transfer characteristics of solid welding wire, ensures a back penetration rate of ≥90%, reducing the need for back root cleaning and lowering operational difficulty. Layered control with a depth of H2=δ / 2 (20mm) for symmetrical heat input: The bevel depth is half the plate thickness (20mm), ensuring a uniform distribution of welding heat input between the upper and lower layers, avoiding deformation or burn-through caused by excessive heat input on one side.

[0061] Optimized heat diffusion at a 40° bevel angle: Balancing heat concentration and dispersion: The 40° angle concentrates the arc heat source at the root of the bevel (ensuring penetration) while diffusing it to the base material on both sides (reducing local overheating), avoiding heat concentration caused by an angle that is too small (e.g., 30°) or heat loss caused by an angle that is too large (e.g., 50°). HAZ grain refinement: By controlling the heat input (linear energy ≤25kJ / cm) and combining the heat dissipation characteristics of the 40° angle, the grain size in the HAZ region can be controlled to above ASTM 10, avoiding coarse grain embrittlement. Thermal convection compensation in vertical welding: In vertical welding, the molten pool is prone to sinking due to gravity. The 40° bevel angle promotes upward convection of the molten pool, compensating for the effect of gravity, ensuring uniform fusion between upper and lower layers, and reducing defects such as porosity and slag inclusions. X-shaped bevels are symmetrical, and the shrinkage stress between the upper and lower layers cancels each other out during welding, reducing residual stress by 30% to 40% compared to U-shaped bevels, significantly reducing welding deformation. The 6mm gap combined with a symmetrical structure avoids stress concentration caused by excessively deep bevels on one side, reducing the risk of cold cracking. The bevel design, combined with post-heat treatment at 200–250℃, further eliminates residual stress, especially by tempering the martensitic structure in the HAZ region, improving toughness and preventing delayed cracking.

[0062] In terms of process adaptability: Improved operational efficiency and quality. A 6mm gap, 40° bevel can be formed in one step via flame cutting, eliminating the need for additional machining and reducing process costs. The bevel surface roughness meets welding requirements, requiring minimal grinding and shortening preparation time. Argon-rich gas shielded welding combined with a 6mm gap provides high arc stability, with a spray-type droplet transfer, resulting in minimal spatter (spatter rate ≤3%) and aesthetically pleasing weld formation, making it particularly suitable for complex vertical operations. The welding wire composition (e.g., Ni 2.1%, Mo 0.5%) matches the bevel design, ensuring a balance between weld metal strength (≥890MPa) and toughness.

[0063] In terms of economics: Optimized life-cycle costs. A 6mm gap reduces welding wire consumption (saving approximately 15% compared to an 8mm gap), and 20mm deep layered welding reduces single-layer thickness, decreasing rework rates (defect rate ≤1%). The symmetrical bevel structure reduces straightening procedures, lowering overall labor costs by 25%–30%. Excellent joint performance extends bridge service life, and combined with improved corrosion resistance (Cr 0.35%, Ni 2.1%), life-cycle maintenance costs are reduced by 15%–20% compared to traditional methods.

[0064] It is evident that this X-shaped bevel design achieves high efficiency and high reliability in welding 890MPa grade bridge steel through the coordinated optimization of gap, depth, and angle. It is particularly suitable for engineering scenarios with stringent requirements for strength, toughness, and durability, such as long-span bridges and bridges in cold regions, and has significant technical and economic advantages.

[0065] In the above embodiments, the diameter of the solid welding wire in step 3 is Φ1.2mm; the interpass temperature during the vertical welding in step 3 is 160℃~175℃; and the argon-rich mixed gas used in the argon-rich mixed gas shielded welding in step 3 is 80%Ar+20%CO2.

[0066] It should be noted that: the welding wire diameter is Φ1.2mm: balancing deposition efficiency and operational precision. The interpass temperature is 160℃~175℃ to precisely control the HAZ microstructure and properties. Maintaining the interpass temperature at 160℃~175℃ avoids residual heat from the previous weld causing grain coarsening in the HAZ region of the subsequent weld (e.g., grain size ≥ ASTM 10), reducing the tendency for coarse-grain embrittlement. Experimental data shows that within this temperature range, the HAZ impact toughness (AKV) is improved by 20%~30% compared to uncontrolled temperature processes, meeting the requirements for low-temperature service at -20℃. The upper limit of the interpass temperature at 175℃ prevents stress concentration caused by localized overheating, while the lower limit of 160℃ ensures sufficient interpass temperature, avoiding the risk of cold cracking (especially in hydrogen-induced cracking sensitive areas of high-strength steel). An argon-rich gas mixture of 80%Ar + 20%CO2 optimizes arc characteristics and weld quality. Comparative experiments show that under 80% Ar + 20% CO2 gas, the weld porosity is ≤0.5%, which is significantly lower than that under pure CO2 gas (porosity ≥3%). The inertness of Ar can reduce the oxidation loss of alloying elements such as Ni, Cr, and Mo, ensuring that the chemical composition of the weld metal is consistent with the design value and guaranteeing performance stability.

[0067] In the above embodiments, the welding process in step 3 is a combination of a multi-layer, multi-pass continuous welding process and a double-sided alternating welding process with a round rod ceramic backing attached to the back. This improves penetration and balances profitability.

[0068] In the above embodiments, step 3 further includes the following steps: Step 301: Attach a round rod ceramic pad to the back of the bevel.

[0069] It should be noted that a round ceramic liner is attached to the back of the bevel. This liner can withstand high temperatures (≥1500℃) and prevent the molten pool from sagging, ensuring a back-side penetration rate of ≥90% and reducing the need for back-side cleaning. The liner's advantages include: the round bar design (diameter and gap matching) provides uniform support to the molten pool, avoiding localized incomplete fusion caused by traditional flat liner liner.

[0070] Step 302: Use solid welding wire and argon-rich mixed gas shielded welding to weld the front weld bead, and fill the weld with H2=δ / 2.

[0071] Step 303: Remove the ceramic backing.

[0072] Step 304: Use solid welding wire and argon-rich mixed gas shielded welding to weld the back weld until it is filled, and then continue welding the remaining weld on the front bevel.

[0073] It should be noted that alternating front-to-back welding disperses stress. First, weld the front weld bead to H2=δ / 2, using the heat input from the front to preheat the back weld, reducing the temperature gradient during back weld. After removing the backing, weld the back weld until it is filled, then weld the remaining bevel on the front. This alternating shrinkage on both sides cancels out the stress, reducing residual stress by 50%–60% compared to single-sided welding. Multi-layer, multi-pass continuous welding with interlayer fusion, each layer thickness controlled at 8–12 mm, combined with interpass temperature control, ensures good interlayer fusion and avoids incomplete fusion defects. The weld metal density is ≥7.85 g / cm³. 3 The tensile strength standard deviation is ≤15MPa, and the performance uniformity is significantly better than single-pass thick-film welding. Double-sided alternating welding reduces the rework rate (defect rate ≤0.8%), and the overall labor cost is reduced by 20% to 25%.

[0074] It is evident that this welding process, through the synergistic optimization of welding wire specifications, gas protection, temperature control, backing design, and double-sided alternating welding, achieves high efficiency and high reliability in welding 890MPa grade bridge steel. It is particularly suitable for engineering scenarios with stringent requirements for strength, toughness, and durability, such as long-span bridges and bridges in cold regions, and has significant technical and economic advantages.

[0075] The above embodiments include three steps: root pass, fill pass, and cover pass; root pass current is 180±20A, voltage is 18±2V, welding speed is 190±20mm / min, gas flow rate is 15~20L / min, and overpass length is 15±3mm; fill pass and cover pass current is 200±20A, voltage is 20±2V, welding speed is 190±20mm / min, gas flow rate is 15~20L / min, and overpass length is 15±3mm.

[0076] It should be noted that the above embodiments significantly improve the quality stability, efficiency, and economy of 890MPa grade high-strength steel welded joints through precise layered control of welding parameters (root pass, fill pass, and cover pass), combined with the synergistic optimization of current, voltage, welding speed, gas flow rate, and weld extension length.

[0077] Layered welding parameters are designed to precisely match the requirements of each stage. Low current and low voltage control during the root pass stage can reduce overheating of the molten pool, prevent the root pass from burning through or sticking to the ceramic backing, and ensure that the penetration depth meets the full thickness requirement.

[0078] Low voltage (16-20V) combined with a short arc (arc length ≈ dry extension length 15mm) enhances arc concentration, improves root fusion quality, and reduces incomplete fusion defects. Welding speed of 190±20mm / min balances deposition efficiency and heat input, avoiding excessively fast welding speed leading to rapid solidification of the weld pool (causing cold cracks) or excessively slow welding speed causing heat accumulation (grain coarsening).

[0079] The gas flow rate is 15-20 L / min. A moderate flow rate can form a stable air curtain to prevent oxidation of the bottom layer (especially at the root of the bevel where air is easily drawn in), while avoiding excessive flow rate that could lead to turbulence (entrapment of the pores).

[0080] During the fill and capping stages, the current is 200±20A and the voltage is 20±2V: High current increases the deposition rate, quickly fills the bevel, and reduces the number of weld passes. High voltage prolongs the arc, improves the fluidity of the molten pool, and ensures full fusion between the fill layer and the root pass, as well as between adjacent passes, reducing incomplete fusion between layers. The welding speed is 190±20mm / min, the same as for the root pass, simplifying parameter adjustments for operators and reducing the risk of misoperation; a gas flow rate of 15~20L / min provides continuous and stable protection, preventing oxidation of the capping layer (improving surface gloss).

[0081] Wire extension length control: Optimizing arc stability and wire melting. Experimental data: With a wire extension length of 15mm, the arc voltage fluctuation is ≤±1V, and the spatter rate is ≤2%, which is significantly lower than the spatter rate (≥5%) when the wire extension length is 20mm. At a wire extension length of 15mm, the wire is fully preheated, the melting rate is matched with the wire feed speed, reducing spheroidization at the wire end and ensuring uniform metal composition in each weld pass.

[0082] The process is simplified and costs are reduced due to its economic and applicability. The filler and cover layers use the same welding speed (190±20mm / min) and weld extension length (15±3mm) as the root pass, eliminating the need for frequent parameter adjustments and reducing human error. Wire consumption: Φ1.2mm wire with a medium current (180~220A) achieves a deposition efficiency of 10~12g / min, saving approximately 20% of material compared to Φ1.6mm wire. The cost of the 80%Ar+20%CO2 mixed gas is 30%~40% lower than pure Ar, and the gas consumption per meter of weld is ≤0.8L at a flow rate of 15~20L / min, resulting in a 15%~20% reduction in overall cost. Layer parameter control ensures a defect rate of ≤0.5% (compared to ≥1.5% in traditional processes), reducing rework time by 60%~70%.

[0083] It is evident that this layered welding parameter design achieves high efficiency and high reliability in welding 890MPa high-strength steel by ensuring quality with low heat input in the bottom layer, improving efficiency with high heat input in the filler layer, and precisely matching gas flow rate and weld extension length. Its technical advantages are particularly suitable for engineering scenarios with stringent requirements for weld strength, toughness, and durability, such as long-span bridges and bridges in cold regions, demonstrating significant economic benefits and social value.

[0084] Based on the experiment: see Table 1 Table 1: Test Results of Mechanical Properties of Q890qE High-Strength Bridge Steel Erecting Butt Joints

[0085] Welding procedure qualification was conducted according to Appendix C of Q / CR 9211-2015 "Specifications for Manufacturing Railway Steel Bridges". Test results showed that the weld strength was higher than the standard value of the base metal; the elongation of the weld metal was higher than the standard value of the base metal; and the bending test results were all good. The impact energy of the weld and heat-affected zone at -40℃ was not less than 54J, meeting the relevant specifications. The hardness of the base metal zone, weld zone, and heat-affected zone of the welded joint all met 380HV10, indicating a low hardening tendency. Macroscopic metallographic photographs of the welded joint showed good weld fusion, with no welding defects such as cracks, porosity, inclusions, or slag inclusions. The weld appearance was well-formed and the transition was smooth.

[0086] It should be understood that although this specification describes one embodiment, it does not mean that the embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in this embodiment can also be appropriately arranged and combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for vertical welding of bridge steel, characterized in that: The welding method for the bridge steel includes the following steps: Step 1, Beveling: Use flame cutting technology to vertically create an X-shaped bevel without blunt edges; grind and remove rust from the bevel of the steel plate joint as required; Step 2, Preheating: Preheat the bridge steel to 75℃ using electric heating; Step 3, Welding: Vertical welding using solid welding wire GMAW-Ar (argon-rich mixed gas shielded welding); Step 4, Post-weld heat treatment: After welding, use a tracked heater for post-weld heat treatment. The post-heat temperature is 200-250℃. After holding at this temperature for 3 hours, turn off the power and slowly cool to room temperature.

2. The bridge steel vertical welding method according to claim 1, characterized in that: The bridge steel is 40mm thick bridge steel of grade 890MPa; the mechanical properties of the cladding metal of the bridge steel are yield strength of 988MPa, tensile strength of 1103MPa, and elongation of 14.5%; the yield strength of the bridge steel is 924MPa, tensile strength of 1120MPa, and elongation of 15.0%.

3. The bridge steel vertical welding method according to claim 1, characterized in that: The bridge steel composition is as follows: C: 0.063%, Si: 0.19%, Mn: 1.44%, P: 0.0093%, S: 0.0037%, Cr: 0.52%, Ni: 1.53%, Cu: 0.76%, Nb: 0.045%, V: 0.001%, Ti: 0.009%, Mo: 0.19%, Al: 0.021; CEV=0.60%, Pcm=0.24%.

4. The bridge steel vertical welding method according to claim 1, characterized in that: The chemical composition of the solid welding wire is as follows: C: 0.53%, Si: 0.69%, Mn: 1.63%, P: 0.0067%, S: 0.0013%, Cu: 0.094%, Cr: 0.35%, Ni: 2.1%, Ti: 0.038%, Mo: 0.5%.

5. The bridge steel vertical welding method according to claim 1, characterized in that: The X-shaped bevel has a 6mm gap; the bevel depth is H2=δ / 2, and the bevel angle is 40°.

6. The bridge steel vertical welding method according to claim 1, characterized in that: The solid welding wire in step 3 has a diameter of Φ1.2mm; the interpass temperature during the vertical welding in step 3 is 160℃~175℃; the argon-rich mixed gas used in the argon-rich mixed gas shielded welding in step 3 is 80%Ar+20%CO2.

7. The bridge steel vertical welding method according to claim 1 or 6, characterized in that: The welding process in step 3 is a combination of multi-layer, multi-pass continuous welding process and double-sided alternating welding process with a round rod ceramic backing attached to the back.

8. The bridge steel vertical welding method according to claim 7, characterized in that: Step 3 includes the following steps: Step 301: Attach a round rod ceramic pad to the back of the bevel; Step 302: Weld the front weld bead using solid welding wire and argon-rich mixed gas shielded welding, with the weld filler being H2=δ / 2; Step 303: Remove the ceramic backing; Step 304: Use solid welding wire and argon-rich mixed gas shielded welding to weld the back weld until it is filled, and then continue welding the remaining weld on the front bevel.

9. The bridge steel vertical welding method according to claim 7, characterized in that: Step 3 welding includes three steps: root pass, fill pass, and cover pass; root pass current 180±20A, voltage 18±2V, welding speed 190±20mm / min, gas flow rate 15~20L / min, and overhang length 15±3mm; fill pass and cover pass current 200±20A, voltage 20±2V, welding speed 190±20mm / min, gas flow rate 15~20L / min, and overhang length 15±3mm.

Images