Welding method for achieving 830 MPa weld joint strength of low-alloy high-strength steel with yield strength of 800 MPa

Abstract

The invention belongs to the field of welding, and relates to a welding method for achieving 830 MPa weld joint strength of low-alloy high-strength steel with the yield strength of 800 MPa. The welding method comprises the following steps that S1, base metal and welding wires are provided; and S2, preheating treatment is conducted on the groove area of the base metal. And S3, a gas metal arc welding process is adopted, and the base metal is welded along the butt-joint grooves in a multi-layer and multi-pass welding mode. Wherein the welding heat input of the backing weld bead is lower than the welding heat input of the filling weld bead and the cosmetic weld bead, and the interlayer temperature of the weld joint is 100-250 DEG C. And S4, post-treatment is conducted on the weld joint area after welding, and a welded joint with the weld joint tensile strength larger than or equal to 830 MPa is obtained. On the premise of ensuring excellent low-temperature toughness and low-crack sensitivity of the welding seam, the target that the tensile strength of the welding seam reaches 830 MPa or above is stably achieved, and the technical problems that in the prior art, the strength, the toughness and the crack resistance are difficult to consider at the same time, and the process stability is poor are effectively solved.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and specifically to a welding method for achieving a weld strength of 830MPa with low-alloy high-strength steel with a yield strength of 800MPa. Background Technology

[0002] In the manufacturing of heavy machinery such as hydraulic supports for coal mines, low-alloy high-strength steel with a yield strength of 800MPa is widely used in key load-bearing structural components due to its excellent strength-to-weight ratio. The welding quality of this type of steel directly affects the safety and lifespan of the equipment; therefore, the reliability of the welding process has become one of the core technologies in the manufacturing process.

[0003] For welding low-alloy high-strength steel with a yield strength of 800MPa, the industry generally follows the principle of equal strength matching or even super-strength matching. For example, solid welding wire with a strength grade of 900MPa is selected, and gas metal arc welding is used for construction. The conventional process parameters have a wide range, and the heat input value is usually controlled between 0.9 and 1.4 kJ / mm. It also has high requirements for ambient temperature and humidity.

[0004] However, while the aforementioned traditional welding methods can meet basic strength requirements, they have inherent drawbacks when pursuing a stable weld strength of over 830 MPa while simultaneously considering high reliability and mass production needs. On one hand, when using 900 MPa-grade high-strength welding materials, the weld metal strength often falls within the 900-1100 MPa range, resulting in significant overstrength issues. Because these high-strength welding materials contain high levels of alloys and carbon to meet their strength requirements, the low-temperature toughness of the weld metal decreases substantially, and the susceptibility to hydrogen-induced cold cracking increases significantly. This not only increases on-site construction risks but also makes it difficult to guarantee product qualification rates. On the other hand, existing welding process parameters have a wide range, and the control over key processes such as welding heat input, interpass temperature, and post-heat regime is relatively crude. This leads to large fluctuations in weld strength and toughness, poor performance repeatability, and difficulty in meeting the stability requirements of high-end equipment for welding quality.

[0005] Therefore, there is a need for a welding method that can stably achieve a tensile strength of over 830 MPa while ensuring that the weld has excellent low-temperature toughness and low crack sensitivity. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] To address the problems in existing technologies, such as insufficient low-temperature toughness of weld metal and high sensitivity to cold cracking when using high-strength welding materials, as well as large fluctuations and poor repeatability of joint performance due to poor welding processes, this invention provides a welding method for achieving a weld strength of 830MPa with low-alloy high-strength steel of yield strength of 800MPa.

[0008] (II) Technical Solution

[0009] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0010] A welding method for achieving a weld strength of 830 MPa with low-alloy high-strength steel of yield strength of 800 MPa includes the following steps:

[0011] S1: Provides base metal and welding wire; the base metal is low-alloy high-strength steel with a yield strength of 800MPa; the welding wire has a yield strength ≥700MPa, and the chemical composition of the welding wire by mass percentage includes: C: ≤0.10%, Si: 0.40-0.80%, Mn: 1.50-1.90%, S: ≤0.015%, P: ≤0.015%, Ni: 0.70-1.75%, Mo: 0.15-0.50%, Cr: ≤0.5%, Cu: ≤0.20%, Ti: 0.02-0.10%, V: ≤0.03%, B: ≤0.006%, with the remainder being Fe and unavoidable impurity elements;

[0012] S2: Preheat the bevel area of ​​the base material;

[0013] S3: The gas metal arc welding process is adopted, and the base material is welded along the butt joint bevel in a multi-layer, multi-pass welding manner. During the welding process, the welding is carried out in the order of root pass, fill pass, and cover pass. The welding heat input of the root pass is lower than that of the fill pass and cover pass, and the interpass temperature of the weld is controlled at 100-250℃ to obtain the weld intermediate.

[0014] S4: Post-weld treatment is performed on the weld area to obtain a welded joint with a tensile strength ≥830MPa.

[0015] In the welding method described above, preferably, in step S1, the chemical composition of the base material, by mass percentage, includes: 0.07%≤C≤0.12%, 0.35%≤Si≤0.5%, 1.5%≤Mn≤2%, P≤0.015%, S≤0.01%, Al≤0.06%, Cr≤1%, Ni≤1%, Cu≤0.8%, V≤0.2%, Nb≤0.2%, Ti≤0.2%, B≤0.003%, Mo≤0.3%, with the remainder being Fe and unavoidable impurity elements.

[0016] In the welding method described above, preferably, in step S1, the welding wire has a tensile strength of 830-980 MPa, an elongation of ≥17%, an impact energy of ≥68 J at -20℃, and a hardness of 200-260 HB.

[0017] In the welding method described above, preferably, the preheating temperature in step S2 is 80-150°C.

[0018] In the welding method described above, preferably, in step S3, a mixture of Ar and CO2 is used as the shielding gas in the gas metal arc welding process, the flow rate of the shielding gas is 18-22 L / min, and welding is performed using a DC reverse polarity.

[0019] In the welding method described above, preferably, in step S3, the welding heat input during the root pass welding process is 0.6-0.7 kJ / mm, the welding current is 150-180 A, the welding voltage is 16-18 V, and the welding speed is 3.0-5.0 mm / s; the welding heat input during the fill pass and cap pass welding processes is 0.8-1.2 kJ / mm, the welding current is 280-330 A, the welding voltage is 26-32 V, and the welding speed is 6.0-10.0 mm / s.

[0020] In the welding method described above, preferably, in step S4, the weld area is wrapped with heat-insulating material to make the cooling rate ≤10℃ / min, and then the welding intermediate is subjected to heat aging treatment to obtain the welded joint.

[0021] The welding method described above, preferably, includes the following steps: heating the welding intermediate at a temperature of <300°C, heating it to 500-520°C at a rate of ≤220°C / h and holding it at that temperature for at least 3 hours, then cooling it at a rate of ≤275°C / h, and finally air cooling it after the temperature drops below 300°C to obtain the welded joint.

[0022] In the welding method described above, preferably, the welded joint obtained in step S4 has an impact energy ≥47J at -40℃, and the hardness HV10 of the base material, heat-affected zone and weld in the welded joint is less than 450, and the tensile strength of the weld is ≥830MPa.

[0023] (III) Beneficial Effects

[0024] This invention selects low-strength matching welding wire with a yield strength ≥700MPa. Its specific micro-alloying composition design significantly reduces the alloy and carbon content of the weld metal while ensuring weld strength. This effectively avoids the problems of decreased low-temperature toughness and increased sensitivity to hydrogen-induced cold cracking caused by excessive strength in traditional 900MPa grade welding materials. As a result, the weld can maintain excellent low-temperature toughness and crack resistance while achieving a tensile strength of ≥830MPa, thereby greatly reducing on-site construction risks and ensuring the product qualification rate.

[0025] Meanwhile, this invention also implements segmented heat input control during the welding process, ensuring that the heat input for the root pass is lower than that for the fill and cover passes, and strictly controlling the interpass temperature within the range of 100-250℃. This refined process control overcomes the performance fluctuation problems caused by the broad process parameters and rough control of traditional methods, significantly improving the consistency of weld strength and toughness, ensuring good performance repeatability, and meeting the stability requirements of high-end equipment for welding quality.

[0026] Furthermore, the welding method of this invention has a clear process window, relatively reduces the requirements for welder operation, and is conducive to large-scale mass production, resulting in significant economic and social benefits. Therefore, while ensuring that the weld has excellent low-temperature toughness and low crack sensitivity, this invention stably achieves the goal of weld tensile strength of over 830 MPa, effectively solving the technical problems of difficulty in simultaneously achieving strength, toughness, and crack resistance, as well as poor process stability in the prior art. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the beveling process of the base material in this invention;

[0028] Figure 2 This is a schematic diagram of the bevel form of the welded joint in the test plate of the present invention;

[0029] Figure 3 This is a schematic diagram of the welding sequence and layer number distribution of multi-layer, multi-pass welding in this invention;

[0030] Figure 4 This is a schematic diagram showing the location of the test points in the hardness test of this invention. Detailed Implementation

[0031] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] This invention provides a welding method for achieving a weld strength of 830MPa with low-alloy high-strength steel of yield strength of 800MPa, characterized by comprising the following steps:

[0033] S1: Provides base metal and welding wire. The base metal is low-alloy high-strength steel with a yield strength of 800 MPa; the welding wire has a yield strength ≥700 MPa, and its chemical composition by mass percentage includes: C: ≤0.10%, Si: 0.40-0.80%, Mn: 1.50-1.90%, S: ≤0.015%, P: ≤0.015%, Ni: 0.70-1.75%, Mo: 0.15-0.50%, Cr: ≤0.5%, Cu: ≤0.20%, Ti: 0.02-0.10%, V: ≤0.03%, B: ≤0.006%, with the remainder being Fe and unavoidable impurity elements.

[0034] S2: Preheat the bevel area of ​​the base material.

[0035] S3: Gas metal arc welding (GMAW) is used to weld adjacent base materials along the butt joint bevel in a multi-layer, multi-pass welding manner. During the welding process, the welding is performed in the order of root pass, fill pass, and cover pass. The welding heat input of the root pass is lower than that of the fill pass and cover pass, and the interpass temperature of the weld is controlled at 100-250℃ to obtain the weld intermediate.

[0036] S4: Post-weld treatment is performed on the weld area to obtain a welded joint with a tensile strength ≥830MPa.

[0037] This invention addresses the welding of low-alloy high-strength steel with a yield strength of 800 MPa, providing a welding method that stably achieves a weld tensile strength of over 830 MPa while maintaining excellent low-temperature toughness and low crack sensitivity. The advantages of this invention are: First, it employs a low-strength matched metal-core welding wire with a yield strength ≥700 MPa. Through micro-alloying design, it reduces alloy and carbon content while ensuring weld strength, fundamentally solving the problems of decreased toughness and increased cold crack sensitivity caused by traditional high-strength welding materials. Second, it implements segmented heat input control during welding, ensuring that the heat input of the root pass is lower than that of the fill and cap passes, and strictly controls the interpass temperature within the range of 100-250℃. This refined process control overcomes the performance fluctuations caused by the broad process parameters and rough control of traditional methods, achieving a stable match between weld strength and toughness.

[0038] Preferably, in step S1 above, the composition of the weld metal of the base material, by mass percentage, includes: 0.07%≤C≤0.12%, 0.35%≤Si≤0.5%, 1.5%≤Mn≤2%, P≤0.015%, S≤0.01%, Al≤0.06%, Cr≤1%, Ni≤1%, Cu≤0.8%, V≤0.2%, Nb≤0.2%, Ti≤0.2%, B≤0.003%, Mo≤0.3%, with the remainder being Fe and unavoidable impurity elements. A further preferred composition includes: C: 0.089%, Si: 0.456%, Mn: 1.94%, P: 0.01%, S: 0.0006%, Al: 0.024%, Cr: 0.028%, Ni: 0.053%, Cu: 0.013%, V: 0.0063%, Nb: 0.0545%, Ti: 0.0151%, B: 0.00122%, Mo: 0.0028%, with the remainder being Fe and unavoidable impurity elements. It should be noted that the range of base material chemical composition given in step S1 is intended to achieve a yield strength of 800 MPa or higher. That is, the 800 MPa yield strength grade low-alloy high-strength steel described in this invention actually covers steel grades with a yield strength ≥ 800 MPa. Through the adjustment of this composition system, the base material ensures high strength while also taking into account good toughness and weldability, providing reliable base conditions for the subsequent welding process.

[0039] In step S1, the base material, through the combined effect of the aforementioned elements and the production process of controlled rolling and cooling + high-temperature tempering, can achieve excellent high strength and high weldability. Its strengthening mechanism mainly includes solid solution strengthening and slight precipitation strengthening: elements such as C, Mn, and Si improve the matrix strength through solid solution strengthening; microalloying elements such as Nb, V, and Ti precipitate fine carbonitrides during controlled rolling and cooling, producing a precipitation strengthening effect and refining the grains; elements such as Ni and Mo improve hardenability and enhance microstructure uniformity; the trace addition of B further optimizes hardenability; elements such as Cr and Cu assist in strengthening; and strict control of the content of impurity elements such as P and S ensures the low-temperature toughness and crack resistance of the base material.

[0040] Through the synergistic effect of the above-mentioned component design and process control, the base material of this invention achieves excellent comprehensive mechanical properties, namely: yield strength ≥ 800 MPa, tensile strength 880-1000 MPa, elongation ≥ 14%, and impact energy at -20℃ ≥ 47 J. This base material exhibits a good balance between strength and toughness, providing a solid foundation for obtaining high-quality welded joints in subsequent welding processes.

[0041] In the specific implementation of this invention, the sample preparation material can be made of low-alloy high-strength steel with a yield strength of 800MPa. It can be cut to the required specifications such as 500mm×200mm×30mm and beveled at 30°. Figure 1 As shown in the figure, value B represents the rolling direction of the steel plate.

[0042] Preferably, in step S1, the welding wire is an 80-grade copper-free welding wire, with specifications such as Φ1.2mm. The welding wire has a tensile strength of 830-980MPa, an elongation of ≥17%, an impact energy of ≥68J at -20℃, and a hardness of 200-260HB. This mechanical property design achieves a low-strength match: the welding wire yield strength is ≥700MPa, lower than the base material's 800MPa, but through reasonable welding process control, the final weld tensile strength can reach 830MPa or higher, achieving the technical effect of low-strength welding material and high-strength weld. Compared with traditional 900MPa-grade high-strength welding materials, the welding wire of this invention has a lower alloy content, especially with effective control over carbon content and total alloy element content. Therefore, the deposited metal has good plasticity and toughness reserves and a moderate hardness level, which lays a material foundation for reducing the cold cracking sensitivity of the welded joint and ensuring low-temperature toughness.

[0043] Preferably, in step S2 above, the preheating temperature is 80-150℃. This temperature effectively slows down the cooling rate of the near-weld zone during welding, reduces welding restraint stress, decreases the risk of hydrogen-induced cracking, and improves the solidification structure and plasticity of the weld metal. This preheating temperature range is moderate, meeting the crack resistance requirements of 800MPa grade low-alloy high-strength steel without causing grain coarsening or joint strength reduction due to excessively high preheating temperatures. It ensures the reliability of the welded joint while providing good on-site operability, which is beneficial for stable batch production. Simultaneously, the ambient temperature during welding should not be lower than 5℃, and the relative humidity should be lower than 70%. Preheating can be performed uniformly on the bevel area using an electric heating furnace or flame heating method, and the temperature should be measured at 50mm from the edge of the bevel using instruments such as a temperature gun to confirm that the required temperature has been achieved.

[0044] Preferably, in step S3 above, the gas metal arc welding process uses a mixture of Ar and CO2 as the shielding gas, with a flow rate of 18-22 L / min, and employs a direct current reverse polarity (DC reverse polarity) for welding. Specifically, the shielding gas is an argon-rich mixture of 80% Ar and 20% CO2. In subsequent embodiments, the ratio of the two gases is a volume ratio. This volume ratio provides good arc stability and droplet transfer characteristics: Ar gas ensures stable arc combustion and good weld formation, while the addition of CO2 enhances arc stiffness and penetration, and its oxidizing properties help clean the weld metal. Controlling the gas flow rate within the range of 18-22 L / min ensures effective protection, preventing air intrusion and weld oxidation, while avoiding excessive flow causing airflow turbulence and reduced protection. The DC reverse polarity facilitates cathode breakage, improves droplet transfer stability, reduces spatter, and achieves good weld formation and quality.

[0045] Preferably, in step S3 above, the welding heat input during the root pass welding process is 0.6-0.7 kJ / mm, the welding current is 150-180 A, the welding voltage is 16-18 V, and the welding speed is 3.0-5.0 mm / s. The welding heat input during the fill pass and cap pass welding processes is 0.8-1.2 kJ / mm, the welding current is 280-330 A, the welding voltage is 26-32 V, and the welding speed is 6.0-10.0 mm / s.

[0046] In this invention, a smaller heat input is used for the root pass, primarily considering the following factors: First, the root pass needs to ensure root penetration and back-side formation; a smaller heat input helps control the molten pool morphology, avoiding burn-through and weld beads. Second, the root pass is in direct contact with the base metal, resulting in rapid cooling; a smaller heat input reduces the width of the heat-affected zone and the degree of grain coarsening. Third, a smaller heat input helps control the fusion ratio, ensuring the stability of the weld metal's chemical composition and properties. By precisely controlling the heat input of the root pass within a narrow window of 0.6-0.7 kJ / mm, combined with appropriate current, voltage, and speed matching, this invention can obtain a root pass with good root penetration and aesthetically pleasing back-side formation.

[0047] In this invention, a larger heat input is used for both the filler and capping welds, primarily considering the following factors: First, a larger heat input improves deposition efficiency, shortens welding time, and meets the needs of mass production. Second, a larger heat input promotes full fusion and homogenization of the weld metal, fostering the formation of ideal microstructures such as fine-grained bainite, achieving the optimal balance between strength and toughness. Third, a larger heat input facilitates control over weld bead formation, resulting in a smooth and even weld surface. By precisely controlling the heat input of the filler and capping welds within a narrow window of 0.8-1.2 kJ / mm, combined with interpass temperature control, this invention ensures the stability and consistency of the weld metal's performance.

[0048] In the detailed welding process of this invention, the form of the test plate welding joint is as follows: Figure 2 As shown. The welding sequence and number of layers are as follows. Figure 3 As shown, 1 is the first root pass weld, 2-16 are the second to seventh filler passes, and 17-21 are the eighth cover pass weld.

[0049] The multi-layer, multi-pass welding of this invention employs a specific welding sequence and number of passes. The specific welding sequence is as follows: first, the first root pass is welded; then, the second to seventh filler passes are welded in sequence; and finally, the eighth cover pass is welded. Each pass uses gas metal arc welding (MAG) process, the welding material specification is Φ1.2mm, the welding current type and polarity are both DC reverse polarity, and the process parameters of each pass strictly follow the preset range.

[0050] In step S3, the interpass temperature during welding is strictly controlled within the range of 100-250℃. This ensures good fusion quality between adjacent weld passes, preventing welding defects such as incomplete fusion and slag inclusions caused by excessively low interpass temperatures. It also prevents excessively coarse grains in the weld and heat-affected zone due to excessively high interpass temperatures. Furthermore, a reasonable interpass temperature range effectively controls the peak value and cooling rate of the welding thermal cycle, reducing residual welding stress and cold cracking sensitivity. This significantly reduces fluctuations in the strength and toughness of the weld joint, resulting in higher repeatability of mechanical properties. This provides a crucial guarantee for achieving a stable weld strength of 830MPa while maintaining excellent low-temperature toughness. During multi-layer, multi-pass welding, the interpass temperature must be monitored in real-time using a thermometer. If the temperature falls below the lower limit of 100℃, reheating to the specified range is required. If the temperature exceeds the upper limit of 250℃, welding must be suspended until it cools to the specified range.

[0051] If the interpass temperature is below 100℃, the previous weld pass cools too quickly, leading to insufficient fusion between subsequent weld passes and the previous pass. This can easily result in defects such as incomplete fusion and slag inclusions. Simultaneously, low temperatures exacerbate welding stress concentration, increasing the risk of cold cracking and causing weld embrittlement, thus reducing joint toughness. If the interpass temperature is above 250℃, excessive accumulated welding heat input can cause rapid grain growth in the weld and heat-affected zone, destroying the fine-grained structure and resulting in decreased weld strength and significantly reduced low-temperature toughness. Furthermore, excessively high temperatures can increase welding deformation, affecting joint dimensional accuracy and even exacerbating hydrogen diffusion, further increasing susceptibility to cold cracking.

[0052] Preferably, in step S4, the weld area can be wrapped with insulation material, such as insulation blanket or insulation cotton, to make the cooling rate ≤10℃ / min, and then the welding intermediate is subjected to heat aging treatment to obtain the welded joint.

[0053] After welding, the weld and heat-affected zone are at high temperatures. If the natural cooling rate is too rapid, the weld metal will form a hardened structure, exacerbating stress concentration and significantly increasing the susceptibility to cold cracking. This also leads to increased performance differences between the weld and the base metal and heat-affected zone, affecting the overall stability of the joint. Completely encasing the weld area with insulation material can effectively slow down the cooling rate, strictly controlling it to ≤10℃ / min, preventing the formation of hardened structures, promoting hydrogen diffusion and escape from the weld, reducing hydrogen-induced cold cracking, and effectively reducing residual welding stress, laying a good foundation for subsequent heat aging treatment.

[0054] Preferably, the heat aging treatment specifically includes: starting the welding intermediate at a temperature of <300°C, heating it to 500-520°C at a rate of ≤220°C / h and holding it at that temperature for at least 3 hours, then cooling it at a rate of ≤275°C / h, and air cooling it after the temperature drops below 300°C to obtain the welded joint.

[0055] Heat aging treatment, as a core post-weld treatment step, can further eliminate residual welding stress, stabilize the microstructure, optimize the strength-toughness ratio, and compensate for microstructural defects that may occur during welding. Specifically, starting the heating of the welding intermediate at a temperature below 300℃ effectively avoids secondary stress caused by excessive initial temperature differences, preventing joint deformation or cracking. This is especially important for 800MPa grade low-alloy high-strength steel, which has high strength and toughness requirements; avoiding secondary stress effectively ensures joint dimensional accuracy and performance stability. Slow heating at a rate ≤220℃ / h ensures uniform temperature rise across all parts of the welding intermediate, avoiding problems such as uneven microstructure and coarse grains caused by excessively high local temperatures or rapid heating, while also facilitating the gradual release of residual stress. Heating to 500-520℃ and holding for at least 3 hours falls within the tempering temperature range of the base metal and weld metal. This temperature range effectively eliminates residual stress generated during welding without significantly reducing joint strength. It also promotes homogenization of the weld and heat-affected zone microstructure, stabilizes precipitates, further refines grains, and improves joint toughness. Furthermore, it effectively eliminates residual hydrogen in the weld, fundamentally reducing cold cracking susceptibility. After holding at this temperature, slow cooling at a rate of ≤275℃ / h prevents the generation of new residual stress and hardened microstructure during cooling, further stabilizing the joint microstructure and properties. Air cooling is then performed after the temperature drops below 300℃, ensuring uniform cooling of the joint, improving production efficiency, and avoiding performance fluctuations caused by over-cooling.

[0056] The welded joint obtained by this invention has an impact energy of ≥47J at -40℃. The hardness HV10 of the base material, heat-affected zone and weld is less than 450. The tensile strength of the weld is ≥830MPa.

[0057] The aforementioned performance directly reflects the synergistic effect of the entire welding process of this invention. Specifically, the weld tensile strength ≥830MPa achieves the core objective of this invention. Through the synergistic effect of micro-alloying design of the welding wire, segmented heat input control, precise interpass temperature control, and post-weld heat treatment, the weld strength is stable and reliable, achieving good strength matching with the 800MPa base material and ensuring the overall load-bearing capacity of the joint. The welded joint exhibits an impact energy ≥47J at -40℃, indicating excellent low-temperature impact resistance, meeting the requirements of low-temperature, heavy-load, and impact conditions in coal mines and other similar environments. This effect is mainly attributed to the low-strength matching welding wire reducing the alloy and carbon content of the weld metal. Combined with interpass temperature control, post-weld slow cooling, and heat aging treatment, this effectively avoids weld embrittlement and significantly improves the low-temperature toughness of the joint. The hardness HV10 of the base metal, heat-affected zone, and weld is less than 450, indicating that the microstructure of each area of ​​the joint is uniform and there is no tendency to harden. This avoids the risk of increased brittleness and cold cracking caused by excessive hardness, while ensuring the plasticity and toughness of the joint, so that the welded joint has good crack resistance and service reliability.

[0058] To further clarify the present invention and its technological advancements, the following description is provided in conjunction with specific embodiments and technical effects.

[0059] Example 1:

[0060] This embodiment provides a welding method for achieving a weld strength of 830MPa with low-alloy high-strength steel of yield strength of 800MPa, including the following steps:

[0061] S1: Provide base metal and welding wire: The base metal is selected from low-alloy high-strength steel with a yield strength of 800MPa. Its chemical composition, by mass percentage, includes: C: 0.089%, Si: 0.456%, Mn: 1.94%, P: 0.01%, S: 0.0006%, Al: 0.024%, Cr: 0.028%, Ni: 0.053%, Cu: 0.013%, V: 0.0063%, Nb: 0.0545%, Ti: 0.0151%, B: 0.00122%, Mo: 0.0028%, with the remainder being Fe and unavoidable impurities. The base metal is cut to a size of 500mm × 200mm × 30mm and machined with a 30° bevel.

[0062] The welding wire is grade 80 copper-free metal-core welding wire with a specification of Φ1.2mm. The chemical composition of the welding wire, by mass percentage, is: C: 0.08%, Si: 0.6%, Mn: 1.7%, S: 0.012%, P: 0.012%, Ni: 1.25%, Mo: 0.3%, Cr: 0.4%, Cu: 0.18%, Ti: 0.07%, V: 0.02%, B: 0.005%, with the remainder being Fe and unavoidable impurities. The mechanical properties of the welding wire are: tensile strength of 907MPa, elongation of 19.4%, impact energy at -20℃ of 76J, hardness of 245HB, and yield strength of 737MPa.

[0063] S2: Preheating treatment: The welding environment temperature is 10℃ and the relative humidity is 69%. An electric heating furnace is used to uniformly preheat the bevel area of ​​the base material to a preheating temperature of 90℃. After preheating, a temperature measuring gun is used to measure and confirm the temperature at a distance of 50mm from the edge of the bevel.

[0064] S3: Multi-layer, multi-pass welding: Gas metal arc welding (GMAW) is used to weld adjacent base materials along the butt joint bevel in a multi-layer, multi-pass manner. The shielding gas is a mixture of 80% Ar and 20% CO2, with a gas flow rate of 20 L / min, and welding is performed using DC reverse polarity.

[0065] The welding sequence is as follows: first, weld the first layer of root pass weld, i.e., weld 1; then weld the second to seventh layers of filler passes, i.e., weld 2-16; and finally weld the eighth layer of cover pass weld, i.e., weld 17-21.

[0066] The process parameters for each weld bead are as follows:

[0067] Root pass: Welding current 151A, arc voltage 17.5V, welding speed 3.6mm / s, heat input 0.62kJ / mm, interpass temperature 100℃.

[0068] Filler welds: Welding currents were 286A, 297A, 305A, 305A, 310A, 315A, 310A, 308A, 309A, 325A, 316A, 318A, 319A, 315A, and 325A respectively, and arc voltages were 27.5V, 29.7V, 29.9V, 30.1V, 30.5V, 30.6V, and 30V respectively. The welding speeds were 8.3 mm / s, 9.1 mm / s, 8.6 mm / s, 7.6 mm / s, 8.1 mm / s, 7.7 mm / s, 8.1 mm / s, 7.1 mm / s, 7.4 mm / s, 7.1 mm / s, 8.1 mm / s, 6.9 mm / s, 7.9 mm / s, 6.8 mm / s, and 7.6 mm / s, respectively, at 0V, 30V, 30.1V, 30V, 30.1V, 30V, 30.1V, 30V, 30.1V, 30V, 30.1V, 30V, 30.1V, 30.1V, 30.1V, 30.1V, 30.1V, 30.1V, 30.1V, 30.1V, 30.1V, 7.7 mm / s, 8.1 mm / s, 7.1 mm / s, 7.4 mm / s, 7.1 mm / s, 8.1 mm / s, 6.9 mm / s, 7.9 mm / s, 6.8 mm / s, and 7.6 mm / s, respectively. The heat inputs were 0.80 kJ / mm, 0.82 kJ / mm, 0.90 kJ / mm, 1.03 kJ / mm, 1.00 kJ / mm, 1.07 kJ / mm, and 1.16 kJ, respectively. / mm, 1.00kJ / mm, 1.17kJ / mm, 1.03kJ / mm, 1.19kJ / mm, 1.10kJ / mm, with interlayer temperatures of 102℃, 131℃, 152℃, 179℃, 188℃, 206℃, 176℃, 206℃, 234℃, 162℃, 181℃, 206℃, 218℃, 242℃, and 156℃, respectively.

[0069] Cover pass: Welding currents were 323A, 295A, 306A, 322A, and 308A; arc voltages were 30.7V, 30.1V, 29.9V, 30.1V, and 30V; welding speeds were 7.7mm / s, 8.1mm / s, 9.6mm / s, 6.8mm / s, and 7.1mm / s; heat inputs were 1.10kJ / mm, 0.94kJ / mm, 0.81kJ / mm, 1.20kJ / mm, and 1.10kJ / mm; and interpass temperatures were 179℃, 208℃, 221℃, 192℃, and 226℃.

[0070] S4: Post-weld treatment: Immediately after welding, wrap the weld area with an insulation blanket to achieve a weld cooling rate of 8℃ / min. Then, place the wrapped weld intermediate into an aging furnace for heat aging treatment: the furnace temperature is 259℃, heated to 510℃ at a rate of 200℃ / h, held for 3.5h, and then cooled at a rate of 250℃ / h. After the furnace temperature drops below 300℃, remove the welded part from the furnace and air cool to obtain the final welded joint.

[0071] Example 2:

[0072] This embodiment provides a welding method for achieving a weld strength of 830MPa with low-alloy high-strength steel of yield strength of 800MPa, including the following steps:

[0073] S1: Provide base metal and welding wire: The base metal is selected from low-alloy high-strength steel with a yield strength of 800MPa. Its chemical composition, by mass percentage, includes: C: 0.07%, Si: 0.35%, Mn: 1.5%, P: 0.015%, S: 0.01%, Al: 0.06%, Cr: 1%, Ni: 1%, Cu: 0.8%, V: 0.2%, Nb: 0.2%, Ti: 0.2%, B: 0.003%, Mo: 0.3%, with the remainder being Fe and unavoidable impurities. The base metal is cut to a size of 500mm × 200mm × 30mm and machined with a 30° bevel.

[0074] The welding wire is grade 80 copper-free metal-core welding wire with a specification of Φ1.2mm. The chemical composition of the welding wire, by mass percentage, is: C: 0.10%, Si: 0.40%, Mn: 1.50%, S: 0.015%, P: 0.015%, Ni: 0.70%, Mo: 0.15%, Cr: 0.5%, Cu: 0.20%, Ti: 0.02%, V: 0.03%, B: 0.006%, with the remainder being Fe and unavoidable impurities. The mechanical properties of the welding wire are: tensile strength of 830MPa, elongation of 17%, impact energy at -20℃ of 68J, hardness of 200HB, and yield strength of 700MPa.

[0075] S2: Preheating treatment: The welding environment temperature is 5℃ and the relative humidity is 65%. Flame heating is used to uniformly preheat the bevel area of ​​the base material to 80℃. After preheating, the temperature is confirmed by measuring with a temperature gun at a distance of 50mm from the edge of the bevel.

[0076] S3: Multi-layer, multi-pass welding: Gas metal arc welding (GMAW) is used to weld adjacent base materials along the butt joint bevel in a multi-layer, multi-pass manner. The shielding gas is a mixture of 80% Ar and 20% CO2, with a gas flow rate of 18 L / min, and welding is performed using DC reverse polarity.

[0077] The welding sequence is as follows: first, weld the first layer of root pass weld, i.e., weld 1; then weld the second to seventh layers of filler passes, i.e., weld 2-16; and finally weld the eighth layer of cover pass weld, i.e., weld 17-21.

[0078] The process parameters for each weld bead are as follows:

[0079] Root pass: Welding current 155A, arc voltage 17.2V, welding speed 3.2mm / s, heat input 0.65kJ / mm, interpass temperature 105℃.

[0080] Filler welds: Welding currents were 288A, 299A, 302A, 307A, 312A, 313A, 309A, 306A, 311A, 322A, 314A, 317A, 320A, 316A, and 323A, respectively, with arc voltages of 27.8V, 29.5V, 30.0V, 30.2V, 30.3V, 30.4V, and 29.8V, respectively. The voltage levels were 9.9V, 29.7V, 30.2V, 29.9V, 30.0V, 30.2V, 30.0V, and 30.2V, with welding speeds of 8.1mm / s, 8.9mm / s, 8.4mm / s, 7.8mm / s, 7.9mm / s, 7.5mm / s, 8.2mm / s, 7.3mm / s, 7.2mm / s, 7.3mm / s, 8.0mm / s, 7.0mm / s, 7.8mm / s, 6.9mm / s, and 7.4mm / s, respectively. The heat inputs were 0.82kJ / mm, 0.83kJ / mm, 0.92kJ / mm, 1.01kJ / mm, 1.02kJ / mm, 1.05kJ / mm, 0.97kJ / mm, 1.08kJ / mm, 1.09kJ / mm, and 1.14kJ / mm, respectively. The values ​​are 1.01 kJ / mm, 1.15 kJ / mm, 1.05 kJ / mm, 1.17 kJ / mm, and 1.12 kJ / mm, with interlayer temperatures of 105℃, 133℃, 150℃, 177℃, 186℃, 204℃, 178℃, 204℃, 232℃, 164℃, 183℃, 204℃, 216℃, 240℃, and 158℃, respectively.

[0081] Cover pass weld: Welding currents were 321A, 297A, 304A, 320A, and 306A; arc voltages were 30.5V, 30.2V, 29.8V, 30.2V, and 29.9V; welding speeds were 7.5mm / s, 8.0mm / s, 9.4mm / s, 6.9mm / s, and 7.2mm / s; heat inputs were 1.12kJ / mm, 0.96kJ / mm, 0.83kJ / mm, 1.18kJ / mm, and 1.12kJ / mm; and interpass temperatures were 177℃, 206℃, 219℃, 194℃, and 224℃.

[0082] S4: Post-weld treatment: Immediately after welding, wrap the weld area with insulating cotton to achieve a weld cooling rate of 10℃ / min. Place the wrapped weld intermediate into an aging furnace for heat aging treatment: the furnace temperature is 280℃, heated to 500℃ at a rate of 220℃ / h, held for 3 hours, and then cooled at a rate of 275℃ / h. After the furnace temperature drops below 300℃, remove the welded part from the furnace and air cool to obtain the final welded joint.

[0083] Example 3:

[0084] This embodiment provides a welding method for achieving a weld strength of 830MPa with low-alloy high-strength steel of yield strength of 800MPa, including the following steps:

[0085] S1: Provide base metal and welding wire: The base metal is selected from low-alloy high-strength steel with a yield strength of 800MPa. Its chemical composition, by mass percentage, includes: C: 0.12%, Si: 0.5%, Mn: 2%, P: 0.015%, S: 0.0007%, Al: 0.04%, Cr: 0.1%, Ni: 0.1%, Cu: 0.02%, V: 0.1%, Nb: 0.1%, Ti: 0.08%, B: 0.002%, Mo: 0.009%, with the remainder being Fe and unavoidable impurities. The base metal is cut to a size of 500mm × 200mm × 30mm and machined with a 30° bevel.

[0086] The welding wire is grade 80 copper-free metal-core welding wire with a specification of Φ1.2mm. The chemical composition of the welding wire, by mass percentage, is: C: 0.09%, Si: 0.80%, Mn: 1.90%, S: 0.013%, P: 0.014%, Ni: 1.75%, Mo: 0.50%, Cr: 0.35%, Cu: 0.15%, Ti: 0.10%, V: 0.03%, B: 0.004%, with the remainder being Fe and unavoidable impurities. The mechanical properties of the welding wire are: tensile strength of 980MPa, elongation of 19.9%, impact energy at -20℃ of 80J, hardness of 260HB, and yield strength of 780MPa.

[0087] S2: Preheating treatment: The welding environment temperature is 5℃ and the relative humidity is 63%. An electric heating furnace is used to uniformly preheat the bevel area of ​​the base material to a preheating temperature of 150℃. After preheating, a temperature measuring gun is used to measure and confirm the temperature at a distance of 50mm from the edge of the bevel.

[0088] S3: Multi-layer, multi-pass welding: Gas metal arc welding (GMAW) is used to weld adjacent base materials along the butt joint bevel in a multi-layer, multi-pass manner. The shielding gas is a mixture of 80% Ar and 20% CO2, with a gas flow rate of 18-22 L / min, and welding is performed using DC reverse polarity.

[0089] The welding sequence is as follows: first, weld the first layer of root pass weld, i.e., weld 1; then weld the second to seventh layers of filler passes, i.e., weld 2-16; and finally weld the eighth layer of cover pass weld, i.e., weld 17-21.

[0090] The process parameters for each weld bead are as follows:

[0091] Root pass: Welding current 158A, arc voltage 17.8V, welding speed 3.8mm / s, heat input 0.61kJ / mm, interpass temperature 108℃.

[0092] Filler welds: Welding currents were 285A, 295A, 304A, 306A, 308A, 316A, 311A, 307A, 310A, 324A, 315A, 319A, 318A, 314A, and 324A, respectively, with arc voltages of 27.6V, 29.6V, 29.8V, 30.3V, 30.4V, 30.5V, and 29.9V, respectively. The voltage levels were 0.1V, 29.8V, 30.3V, 30.1V, 30.2V, 30.3V, 30.2V, and 30.3V, with welding speeds of 8.2mm / s, 9.0mm / s, 8.5mm / s, 7.7mm / s, 8.0mm / s, 7.6mm / s, 8.0mm / s, 7.2mm / s, 7.3mm / s, 7.2mm / s, 8.2mm / s, 6.8mm / s, 7.7mm / s, 7.0mm / s, and 7.5mm / s, respectively, and heat inputs of 0.81kJ / mm, 0.81kJ / mm, 0.89kJ / mm, 1.04kJ / mm, 1.01kJ / mm, 1.08kJ / mm, 0.99kJ / mm, 1.09kJ / mm, 1.08kJ / mm, and 1.15kJ / mm, respectively. The values ​​are 0.99 kJ / mm, 1.16 kJ / mm, 1.04 kJ / mm, 1.18 kJ / mm, and 1.11 kJ / mm, with interlayer temperatures of 100℃, 130℃, 154℃, 178℃, 189℃, 205℃, 175℃, 205℃, 233℃, 160℃, 180℃, 205℃, 217℃, 241℃, and 155℃, respectively.

[0093] Cover pass weld: Welding currents were 322A, 296A, 305A, 321A, and 307A; arc voltages were 30.6V, 30.0V, 29.7V, 30.0V, and 30.1V; welding speeds were 7.6mm / s, 8.2mm / s, 9.5mm / s, 7.0mm / s, and 7.0mm / s; heat inputs were 1.11kJ / mm, 0.95kJ / mm, 0.82kJ / mm, 1.19kJ / mm, and 1.11kJ / mm; and interpass temperatures were 178℃, 207℃, 220℃, 193℃, and 225℃.

[0094] S4: Post-weld treatment: Immediately after welding, wrap the weld area with an insulation blanket to achieve a weld cooling rate of 8℃ / min. Then, place the wrapped weld intermediate into an aging furnace for heat aging treatment: the furnace loading temperature is 293℃, heated to 520℃ at a rate of 200℃ / h, held for 3 hours, and then cooled at a rate of 270℃ / h. After the furnace temperature drops below 300℃, remove the welded intermediate and air-cool it to obtain the final welded joint.

[0095] Example 4:

[0096] This embodiment provides a welding method for achieving a weld strength of 830MPa with low-alloy high-strength steel of yield strength of 800MPa, including the following steps:

[0097] S1: Provide base metal and welding wire: The base metal is selected from low-alloy high-strength steel with a yield strength of 800MPa. Its chemical composition, by mass percentage, includes: C: 0.09%, Si: 0.4%, Mn: 1.6%, P: 0.012%, S: 0.0006%, Al: 0.03%, Cr: 0.04%, Ni: 0.05%, Cu: 0.03%, V: 0.02%, Nb: 0.09%, Ti: 0.05%, B: 0.001%, Mo: 0.05%, with the remainder being Fe and unavoidable impurities. The base metal is cut to a size of 500mm × 200mm × 30mm and machined with a 30° bevel.

[0098] The welding wire is grade 80 copper-free metal-core welding wire with a specification of Φ1.2mm. The chemical composition of the welding wire, by mass percentage, is: C: 0.10%, Si: 0.45%, Mn: 1.7%, S: 0.011%, P: 0.012%, Ni: 1.32%, Mo: 0.33%, Cr: 0.37%, Cu: 0.20%, Ti: 0.06%, V: 0.03%, B: 0.005%, with the remainder being Fe and unavoidable impurities. The mechanical properties of the welding wire are: tensile strength of 884MPa, elongation of 17.8%, impact energy at -20℃ of 71J, hardness of 253HB, and yield strength of 736MPa.

[0099] S2: Preheating treatment: The welding environment temperature is 5℃ and the relative humidity is 68%. An electric heating furnace is used to uniformly preheat the bevel area of ​​the base material to a preheating temperature of 131℃. After preheating, a temperature measuring gun is used to measure and confirm the temperature at a distance of 50mm from the edge of the bevel.

[0100] S3: Multi-layer, multi-pass welding: Gas metal arc welding (GMAW) is used to weld adjacent base materials along the butt joint bevel in a multi-layer, multi-pass manner. The shielding gas is a mixture of 80% Ar and 20% CO2, with a gas flow rate of 21 L / min, and welding is performed using direct current reverse polarity.

[0101] The welding sequence is as follows: first, weld the first layer of root pass weld, i.e., weld 1; then weld the second to seventh layers of filler passes, i.e., weld 2-16; and finally weld the eighth layer of cover pass weld, i.e., weld 17-21.

[0102] The process parameters for each weld bead are as follows:

[0103] Root pass: Welding current 153A, arc voltage 17.6V, welding speed 3.4mm / s, heat input 0.63kJ / mm, interpass temperature 122℃.

[0104] Filler welds: Welding currents were 287A, 298A, 303A, 308A, 311A, 314A, 308A, 309A, 312A, 323A, 317A, 316A, 321A, 317A, and 322A, respectively, with arc voltages of 27.7V, 29.8V, 29.7V, 30.0V, 30.2V, 30.3V, and 29.7V, respectively. The voltage levels were 9.8V, 30.0V, 30.1V, 29.8V, 30.1V, 30.0V, 30.3V, and 30.1V, with welding speeds of 8.0mm / s, 8.8mm / s, 8.3mm / s, 7.9mm / s, 8.2mm / s, 7.4mm / s, 8.3mm / s, 7.4mm / s, 7.1mm / s, 7.4mm / s, 7.9mm / s, 7.1mm / s, 7.6mm / s, 6.7mm / s, and 7.7mm / s, respectively. The heat inputs were 0.83kJ / mm, 0.84kJ / mm, 0.91kJ / mm, 1.02kJ / mm, 0.99kJ / mm, 1.06kJ / mm, 0.96kJ / mm, 1.11kJ / mm, 1.06kJ / mm, and 1.13kJ / mm, respectively. The values ​​are 1.02 kJ / mm, 1.14 kJ / mm, 1.06 kJ / mm, 1.20 kJ / mm, and 1.09 kJ / mm, with interlayer temperatures of 103℃, 132℃, 151℃, 176℃, 187℃, 203℃, 177℃, 203℃, 231℃, 163℃, 182℃, 203℃, 215℃, 239℃, and 157℃, respectively.

[0105] Cover pass weld: Welding currents were 320A, 298A, 307A, 319A, and 309A; arc voltages were 30.4V, 30.3V, 29.6V, 30.3V, and 29.8V; welding speeds were 7.8mm / s, 7.9mm / s, 9.7mm / s, 6.7mm / s, and 7.3mm / s; heat inputs were 1.09kJ / mm, 0.93kJ / mm, 0.80kJ / mm, 1.21kJ / mm, and 1.09kJ / mm; and interpass temperatures were 180℃, 209℃, 222℃, 191℃, and 223℃.

[0106] S4: Post-weld treatment: Immediately after welding, wrap the weld area with insulating cotton to achieve a weld cooling rate of 10℃ / min. Place the wrapped weld intermediate into an aging furnace for heat aging treatment: the furnace loading temperature is 284℃, heated to 506℃ at a rate of 220℃ / h, held for 3.3h, and then cooled at a rate of 275℃ / h. After the furnace temperature drops below 300℃, remove from the furnace and air cool to obtain the final welded joint.

[0107] Comparative Example 1:

[0108] This comparative example provides a welding method for low-alloy high-strength steel with a yield strength of 800MPa. The difference from Example 1 is that it uses traditional 900MPa-grade high-strength welding materials, while the remaining steps are the same as in Example 1.

[0109] Comparative Example 2:

[0110] This comparative example provides a welding method for low-alloy high-strength steel with a yield strength of 800MPa. Steps S1, S2, and S4 are exactly the same as in Example 1. The difference from Example 1 is that in step S3, the root pass / fill pass / cover pass is not distinguished during welding, and the heat input is uniformly 1.1kJ / mm. All other steps are the same as in Example 1.

[0111] Comparative Example 3

[0112] This comparative example provides a welding method for low-alloy high-strength steel with a yield strength of 800 MPa. Steps S1, S2, and S4 are exactly the same as in Example 1. In step S3, the process parameters such as welding current, arc voltage, welding speed, and heat input for each weld pass are exactly the same as in Example 1. The difference from Example 1 is that no interpass temperature is measured, recorded, or adjusted during the entire welding process. Welding is performed continuously in each pass, and the interpass temperature rises naturally with the accumulation of welding heat input without intervention.

[0113] Mechanical property tests and cold crack sensitivity tests were conducted on the welded joints prepared in Examples 1-4 and Comparative Examples 1-3. Specifically, these tests included tensile tests, bending tests, impact tests, hardness tests, and weld crack tests on oblique Y-groove joints. The test points for the hardness tests were located as follows: Figure 4 .

[0114] The mechanical properties of the welded joints prepared in Example 1 were tested according to the above testing method. A total of 3 samples were tested, and the results are as follows:

[0115] Table 1. Statistical table of tensile properties of welded joints obtained in Example 1

[0116]

[0117] Table 2. Statistical table of bending properties of welded joints obtained in Example 1

[0118]

[0119] Table 3. Statistical table of impact resistance of welded joints obtained in Example 1

[0120]

[0121] Table 4. Statistical results of welded joints with oblique Y-groove weld cracks (small iron stencil) obtained in Example 1.

[0122]

[0123] The hardness test results show that the hardness HV10 of the base material, heat-affected zone, and weld areas of the weld joint in Example 1 is less than 450, which meets the requirements and is qualified.

[0124] Examples 2-4 were tested using the same test method as Example 1, and the results are as follows:

[0125] The welded joints obtained in Examples 2-4 all met the requirement of tensile strength ≥830MPa. Specifically, the tensile strength of multiple samples from Example 2 was 830-838MPa, that of multiple samples from Example 3 was 845-850MPa, and that of multiple samples from Example 4 was 836-842MPa. All examples passed the 180° bending test without cracking. In the impact test, the average impact energy at the weld center was above 110J at -20℃ and ≥47J at -40℃. Hardness tests showed that the hardness HV10 of the base metal, heat-affected zone, and weld was less than 450. The surface crack rate and cross-sectional crack rate in the Y-groove weld crack test were both 0.

[0126] Comparative Examples 1-3 were tested using the same test method as Example 1, and the results are as follows:

[0127] The welded joints prepared in Comparative Example 1 showed tensile strengths of 905-1020 MPa in multiple samples, significantly exceeding the target range. The impact energy at -40℃ was only 18-25 J, far below the required 47 J. The hardness (HV10) ranged from 420-510, with some areas exceeding 450. The surface crack rate in the Y-groove weld crack test was 15-30%, and the cross-sectional crack rate was 20-40%. Localized microcracks appeared in the bending test, with a pass rate of approximately 60%.

[0128] The welded joints prepared in Comparative Example 2 showed significant fluctuations in tensile strength across multiple specimens, ranging from 780 to 860 MPa, with some specimens below 830 MPa. The impact energy at -40℃ ranged from 32 to 45 J, with some specimens below 47 J. The hardness (HV10) fluctuated between 380 and 470, with some areas exceeding the limit. The surface crack rate and cross-sectional crack rate of the oblique Y-groove weld crack test were 5-10%. The back of the root pass weld showed poor formation and incomplete penetration defects.

[0129] The welded joints prepared in Comparative Example 3 showed significant fluctuations in tensile strength, ranging from 805 to 855 MPa across multiple samples. The impact energy at -40℃ ranged from 28 to 46 J, a marked decrease and falling below requirements in some areas. The hardness (HV10) fluctuated between 360 and 480, exceeding the standard in some regions. The surface crack rate in the Y-groove weld crack test was 8-15%, and the cross-sectional crack rate was 10-20%. Furthermore, the excessively low interpass temperature in the early weld bead and the excessively high interpass temperature in the later weld bead resulted in uneven microstructure and coarse grains.

[0130] Comparing the test results of Examples 1-4 with Comparative Example 1, it can be seen that the choice of welding material has a decisive influence on the low-temperature toughness and crack resistance of the welded joint. Examples 1-4 used low-strength matching welding wire with a yield strength ≥700MPa. Its alloy content was low, and the deposited metal had good plasticity and toughness reserves. The impact energy at -40℃ consistently reached over 47J, and the crack rate in the oblique Y-groove crack test was 0. In contrast, Comparative Example 1 used traditional 900MPa-grade high-strength welding material. To meet its strength grade, a higher alloy and carbon content was added, resulting in a significant decrease in the low-temperature toughness of the weld metal. Specifically, the impact energy at -40℃ was only 18-25J, and the sensitivity to hydrogen-induced cooling cracking was significantly increased, specifically reflected in a crack rate of 15-40%. This indicates that selecting low-strength matching welding wire is crucial to ensuring the low-temperature toughness and crack resistance of the weld metal.

[0131] Comparing the test results of Examples 1-4 with Comparative Example 2, it can be seen that segmented heat input control plays a crucial role in weld formation quality and performance stability. Examples 1-4 employ a segmented control strategy with low heat input for the root pass and higher heat input for the fill and cap passes. This results in good root penetration in the root pass, aesthetically pleasing back pass formation, sufficient fusion between each pass, uniform weld microstructure, and stable tensile strength above 830 MPa with minimal fluctuation. In contrast, Comparative Example 2 uses a single heat input. The excessive heat input in the root pass leads to root burn-through and poor back pass formation. The heat input in the fill pass is relatively insufficient, resulting in low deposition efficiency. The weld microstructure is uneven, with alternating coarse and fine grain regions, leading to large fluctuations in tensile strength, with some areas exhibiting strength below 830 MPa, and a decrease in impact energy at -40℃. This demonstrates that the segmented heat input control employed in this invention is key to achieving stable weld strength and uniform performance.

[0132] Comparing the test results of Examples 1-4 with Comparative Example 3, it can be seen that interpass temperature control plays a crucial role in the uniformity of weld microstructure and crack resistance. Examples 1-4 strictly controlled the interpass temperature within the range of 100-250℃, ensuring similar thermal conditions for each weld pass, guaranteeing uniform microstructure and grain size in each weld pass and the heat-affected zone, stable achievement of the -40℃ impact energy standard, and a crack rate of 0%. In contrast, Comparative Example 3 did not implement interpass temperature control. The interpass temperature in the early weld passes was too low, leading to insufficient fusion between weld passes and a tendency to form incomplete fusion defects. In the later weld passes, the interpass temperature became too high due to heat accumulation, causing rapid grain growth in the weld and heat-affected zone, destroying the fine-grained microstructure. The -40℃ impact energy dropped to 28-46 J, and the crack rate increased to 8-20%. This demonstrates that strictly controlling the interpass temperature within the range of 100-250℃ is key to ensuring the uniformity of weld microstructure and crack resistance.

[0133] In summary, this invention, through the synergistic effect of microalloying design of low-alloy high-strength steel with a yield strength of 800MPa and low-strength matching welding wire with a tensile strength of 700MPa, segmented heat input control, precise interpass temperature control, and post-weld heat aging treatment, successfully solves the technical problems of excessive strength, insufficient low-temperature toughness, high sensitivity to cold cracking, and large performance fluctuations caused by rough process control in the prior art. It achieves a stable tensile strength of over 830MPa for the weld, while also possessing excellent low-temperature toughness and low crack sensitivity.

[0134] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A welding method for achieving a weld strength of 830 MPa with low-alloy high-strength steel of yield strength of 800 MPa, characterized in that, Includes the following steps: S1: Provides base metal and welding wire; the base metal is low-alloy high-strength steel with a yield strength of 800MPa; the welding wire has a yield strength ≥700MPa, and the chemical composition of the welding wire by mass percentage includes: C: ≤0.10%, Si: 0.40-0.80%, Mn: 1.50-1.90%, S: ≤0.015%, P: ≤0.015%, Ni: 0.70-1.75%, Mo: 0.15-0.50%, Cr: ≤0.5%, Cu: ≤0.20%, Ti: 0.02-0.10%, V: ≤0.03%, B: ≤0.006%, with the remainder being Fe and unavoidable impurity elements; S2: Preheat the bevel area of ​​the base material; S3: The gas metal arc welding process is adopted, and the base material is welded along the butt joint bevel in a multi-layer, multi-pass welding manner. During the welding process, the welding is carried out in the order of root pass, fill pass, and cover pass. The welding heat input of the root pass is lower than that of the fill pass and cover pass, and the interpass temperature of the weld is controlled at 100-250℃ to obtain the weld intermediate. S4: Post-weld treatment is performed on the weld area to obtain a welded joint with a tensile strength ≥830MPa.

2. The welding method according to claim 1, characterized in that, In step S1, the chemical composition of the base material, by mass percentage, includes: 0.07%≤C≤0.12%, 0.35%≤Si≤0.5%, 1.5%≤Mn≤2%, P≤0.015%, S≤0.01%, Al≤0.06%, Cr≤1%, Ni≤1%, Cu≤0.8%, V≤0.2%, Nb≤0.2%, Ti≤0.2%, B≤0.003%, Mo≤0.3%, with the remainder being Fe and unavoidable impurity elements.

3. The welding method according to claim 1, characterized in that, In step S1, the welding wire has a tensile strength of 830-980MPa, an elongation of ≥17%, an impact energy of ≥68J at -20℃, and a hardness of 200-260HB.

4. The welding method according to claim 1, characterized in that, In step S2, the preheating temperature is 80-150℃.

5. The welding method according to claim 1, characterized in that, In step S3, the gas metal arc welding process uses a mixture of Ar and CO2 as the shielding gas, with a flow rate of 18-22 L / min, and welding is performed using a DC reverse polarity method.

6. The welding method according to claim 1, characterized in that, In step S3, the welding heat input during the root pass welding process is 0.6-0.7 kJ / mm, the welding current is 150-180 A, the welding voltage is 16-18 V, and the welding speed is 3.0-5.0 mm / s; the welding heat input during the fill pass and cap pass welding processes is 0.8-1.2 kJ / mm, the welding current is 280-330 A, the welding voltage is 26-32 V, and the welding speed is 6.0-10.0 mm / s.

7. The welding method according to claim 1, characterized in that, In step S4, the weld area is wrapped with insulation material to make the cooling rate ≤10℃ / min, and then the welding intermediate is subjected to heat aging treatment to obtain the welded joint.

8. The welding method according to claim 7, characterized in that, The heat aging treatment includes: starting the welding intermediate at a temperature of <300℃, heating it to 500-520℃ at a rate of ≤220℃ / h and holding it at that temperature for no less than 3h, then cooling it at a rate of ≤275℃ / h, and finally air cooling it after the temperature drops below 300℃ to obtain the welded joint.

9. The welding method according to claim 1, characterized in that, The welded joint obtained in step S4 has an impact energy of ≥47J at -40℃. The hardness HV10 of the base material, heat-affected zone and weld is less than 450. The tensile strength of the weld is ≥830MPa.

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