A preheating-free 690mpa grade high-strength and high-toughness submerged-arc welding wire, a preparation method thereof and a submerged-arc welding process

Abstract

The application relates to a preheating-free 690MPa-grade high-strength and high-toughness submerged-arc welding wire and a preparation method and a submerged-arc welding process thereof, and belongs to the technical field of welding materials. The chemical components of the welding wire include C: 0.07-0.10% (mass percent), Si: 0.25-0.50%, Mn: 1.20-1.50%, Cr: 0.20-0.50%, Ni: 2.10-3.30%, Mo: 0.45-0.65%, Ti: 0.03-0.05%, S: less than or equal to 0.005%, P: less than or equal to 0.005%, and the balance is Fe. By optimizing the C content, the Ni ratio and introducing the Ti micro-alloying method, combining with the low-S, P control and the hydrogen control process, the preheating-free welding of the 690MPa-grade low-temperature high-strength steel under normal temperature or low-temperature conditions is realized, the traditional preheating operation is avoided, the energy consumption is saved, and the process is simplified.

Description

Technical Field

[0001] This invention relates to the field of welding materials technology, and in particular to a preheat-free 690MPa grade high-strength and high-toughness submerged arc welding wire, its preparation method, and submerged arc welding process. Background Technology

[0002] With the rapid advancement of polar oil and gas resource development, marine engineering equipment manufacturing, and cryogenic storage and transportation technologies, 690MPa-grade low-temperature high-strength steel is increasingly widely used in structures operating in extreme environments, such as liquefied natural gas (LNG) storage tanks, polar drilling platforms, and critical components of cold-weather vessels. These service scenarios often involve harsh conditions such as low temperatures, high humidity, complex loads, and alternating stresses, placing more stringent demands on the comprehensive performance of welded joints. Especially in low-temperature environments, welded joints must not only ensure sufficient strength to meet load-bearing requirements but also possess excellent low-temperature impact toughness to resist low-temperature brittle fracture failure. Simultaneously, to meet the demands of rapid deployment and efficient manufacturing under complex conditions, the welding process should possess good adaptability and simplicity, enabling preheating-free welding at room temperature to improve welding efficiency, reduce construction energy consumption, and meet the urgent needs of modern engineering for intelligent and automated welding technologies.

[0003] Although some existing welding wire products have made positive progress in improving the low-temperature toughness of welded joints or enhancing their adaptability to high heat input, the following technical limitations still exist: First, the applicable strength grades are relatively low. They are mainly designed for 500-600MPa grade structural steel, and the matched alloy systems and welding properties are insufficient to meet the dual requirements of strength and toughness for 690MPa grade high-strength steel under extreme environments. Second, low-temperature performance is not adequately guaranteed. While some welding materials possess good toughness indicators at room temperature or -20 to -40℃, their reliability in ultra-low temperature service environments at -50℃ and below lacks verification. Third, they rely heavily on preheating or heat treatment, resulting in poor process adaptability. They are difficult to eliminate their dependence on preheating or complex welding parameters, which hinders the realization of intelligent and automated welding. Summary of the Invention

[0004] Based on the above analysis, the present invention aims to provide a preheat-free 690MPa grade high-strength and high-toughness submerged arc welding wire, its preparation method and submerged arc welding process, which does not require preheating treatment during the welding process and can improve welding strength and low-temperature toughness at -50℃.

[0005] On the one hand, the present invention provides a preheat-free 690MPa grade high-strength and high-toughness submerged arc welding wire. The chemical composition of the welding wire, by mass percentage, includes C: 0.07% to 0.10%; Si: 0.25% to 0.50%; Mn: 1.20% to 1.50%; Cr: 0.20% to 0.50%; Ni: 2.10% to 3.30%; Mo: 0.45% to 0.65%; Ti: 0.03% to 0.05%; S≤0.005%; P≤0.005%; with the balance being Fe and unavoidable impurities.

[0006] Furthermore, the chemical composition of the welding wire, by mass percentage, includes: C: 0.075%–0.082%; Si: 0.34%–0.42%; Mn: 1.25%–1.44%; Cr: 0.25%–0.44%; Ni: 2.50%–3.14%; Mo: 0.54%–0.65%; Ti: 0.032%–0.046%; S≤0.005%; P≤0.005%; with the balance being Fe and unavoidable impurities.

[0007] Furthermore, the welding wire is used to prepare the deposited metal, wherein the yield strength of the deposited metal is above 700 MPa, the tensile strength is above 750 MPa, and the elongation is above 24%.

[0008] Furthermore, the welding wire is used to prepare the deposited metal, and the impact absorption energy of the deposited metal at -50°C is above 91J.

[0009] Furthermore, a weld metal is prepared from the welding wire, the microstructure of which consists of acicular ferrite, lath ferrite and lath bainite.

[0010] On the other hand, the present invention provides a method for preparing a 690MPa grade high-strength and high-toughness submerged arc welding wire without preheating, which obtains the welding wire through vacuum smelting, forging, rolling, pickling and annealing, bright drawing and surface layer winding steps.

[0011] Furthermore, the average diffusible hydrogen content of the welding wire is below 3.28 ml / 100g.

[0012] This invention provides a submerged arc welding process, which uses the welding wire described in this invention or the welding wire obtained by the preparation method described in this invention, and is combined with JF690 flux.

[0013] Furthermore, the flux should be baked at 300℃~350℃ for more than 2 hours before use.

[0014] Furthermore, during the welding process, the welding current is 525–575A, the welding voltage is 28–30V, the welding speed is 39–41cm / min, and the average heat input is 20–26kJ / cm.

[0015] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0016] 1. By optimizing the C content and Ni ratio, and introducing Ti microalloying, the sensitivity of welds to cold cracking is effectively reduced. Combined with low S and P control and hydrogen control processes, preheating-free welding of 690MPa grade low-temperature high-strength steel is achieved under normal or low-temperature conditions, avoiding traditional preheating operations, saving energy and simplifying the process; the yield strength of the deposited metal is above 700MPa, the tensile strength is above 750MPa, the elongation is above 24%, and the impact absorption energy at -50℃ is above 91J.

[0017] 2. With a Ni content of only 2.20% to 2.60%, high impact toughness of 91J at -50℃ is achieved through the synergistic strengthening of multiple elements such as Cr, Mo, Mn and Ti. This performance is superior to that of traditional high Ni welding wire, while reducing material costs by about 30%.

[0018] 3. The present invention is designed for submerged arc welding processes with high heat input of 20-26 kJ / cm. Even under conditions of no preheating and multi-layer and multi-pass welding, it can still obtain uniform acicular ferrite + lath ferrite, without obvious coarse grains or embrittlement zones, thus ensuring stable joint performance.

[0019] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0020] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0021] Figure 1 The macroscopic morphology of the weld metal cross section in Example 1;

[0022] Figure 2 The microstructure of the deposited metal in Example 1 is shown.

[0023] Figure 3 The microstructure of the weld metal in Comparative Example 1 is shown. Detailed Implementation

[0024] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0025] In low-temperature environments, welded joints must not only ensure sufficient strength to meet load-bearing requirements, but also possess excellent low-temperature impact toughness to resist low-temperature brittle fracture failure. Simultaneously, to meet the demands for rapid deployment and efficient manufacturing under complex working conditions, the welding process should possess good adaptability and simplicity, enabling preheating-free welding at room temperature to improve welding efficiency, reduce construction energy consumption, and meet the urgent needs of modern engineering for intelligent and automated welding technologies.

[0026] Although some existing welding wire products have made positive progress in improving the low-temperature toughness of welded joints or enhancing their adaptability to high heat input, the following technical limitations still exist: First, the applicable strength grades are relatively low. They are mainly designed for 500-600MPa grade structural steel, and the matched alloy systems and welding properties are insufficient to meet the dual requirements of strength and toughness for 690MPa grade high-strength steel under extreme environments. Second, low-temperature performance is not adequately guaranteed. While some welding materials possess good toughness indicators at room temperature or -20 to -40℃, their reliability in ultra-low temperature service environments at -50℃ and below lacks verification. Third, they rely heavily on preheating or heat treatment, resulting in poor process adaptability. They are difficult to eliminate their dependence on preheating or complex welding parameters, which hinders the realization of intelligent and automated welding.

[0027] Therefore, the present invention provides a preheat-free 690MPa grade high-strength and high-toughness submerged arc welding wire. The chemical composition of the welding wire, by mass percentage, includes: C: 0.07%–0.10%; Si: 0.25%–0.50%; Mn: 1.20%–1.50%; Cr: 0.20%–0.50%; Ni: 2.10%–3.30%; Mo: 0.45%–0.65%; Ti: 0.03%–0.05%; S≤0.005%; P≤0.005%; with the balance being Fe and unavoidable impurities.

[0028] Compared with existing technologies, the welding wire provided by this invention effectively reduces the sensitivity of weld seams to cold cracking by optimizing C content, Ni ratio, and introducing Ti microalloying. Combined with low S and P control and hydrogen control processes, it enables preheating-free welding of 690MPa grade low-temperature high-strength steel under normal or low-temperature conditions, avoiding traditional preheating operations, saving energy and simplifying the process. The yield strength of the deposited metal is above 700MPa, the tensile strength is above 750MPa, the elongation is above 24%, and the impact absorption energy at -50℃ is above 91J.

[0029] With a Ni content of only 2.20% to 2.60%, a high impact toughness of 91J at -50℃ is achieved through the synergistic strengthening of multiple elements such as Cr, Mo, Mn, and Ti. This performance is superior to that of traditional high-Ni welding wire, while reducing material costs by about 30%.

[0030] The role of each element:

[0031] C (0.07%–0.10%): This invention controls the C content to 0.07–0.10% to compensate for insufficient hardening under high heat input in submerged arc welding, ensuring that the deposited metal and heat-affected zone still achieve sufficient strength under slow cooling rates. Furthermore, to avoid increased susceptibility to cold cracking due to excessively high C content, this invention strictly controls the S and P content, utilizes Ti to capture N, and adjusts the Mn / Mo content to control the overall hardening tendency, thereby balancing strength and cold crack resistance requirements.

[0032] Si (0.25%–0.50%): Si is mainly used for deoxidation and improving the fluidity of the molten pool, while also helping to promote the formation of acicular / lamellar ferrite and fine bainite. It ensures effective deoxidation while minimizing negative impacts on impact toughness. Good deoxidation reduces the source of hydrogen content, and combined with low S and P content, it helps reduce diffusible hydrogen and mitigate the risk of cold cracking.

[0033] Mn (1.20%–1.50%): Provides necessary deoxidation, desulfurization, and solid solution strengthening, while avoiding excessive Mn content that could increase the overall hardening tendency. Mn helps suppress the formation of brittle martensite under slow cooling conditions in submerged arc welding, thus supporting preheating-free processes.

[0034] Cr (0.20%–0.50%): Cr can improve the matrix strength and high-temperature softening resistance, and also promote the stability of bainitic / tempered structures. It ensures strength while avoiding excessive amounts that could lead to loss of plasticity and toughness. Synergistic effect with Mo: Cr and Mo work together to promote high-strength and tough bainitic / tempered structures, suitable for the thermal cycles of submerged arc welding.

[0035] Ni (2.10%–3.30%): Ni is an important element for lowering the embrittlement transition temperature (DBTT) and improving low-temperature impact toughness. This invention enhances low-temperature toughness redundancy while ensuring cost control.

[0036] Mo (0.45%–0.65%): In this invention, Mo is beneficial for improving the strength after quenching and tempering, and for improving the stability of high-temperature tempering, while having a limited effect on toughness within a controlled range. Furthermore, Mo and Cr together promote the formation of fine bainite or fine-grained tempered structures, enhance the strength retention capacity under high heat input, and synergistically reduce DBTT with Ni.

[0037] Ti (0.03%–0.05%): The amount of Ti is precisely controlled, preferentially combining with N to form stable TiN particles. These particles act as fine non-metallic inclusions, promoting the formation of acicular ferrite or dispersed crystal nuclei, thereby refining the weld metal microstructure. Stable TiN can reduce harmful MnS-type inclusions with low melting points and a tendency to form bands, reducing the formation of localized weak zones and improving the cold crack resistance of preheat-free welding.

[0038] S, P (≤0.005%): In this invention, S and P are strictly controlled to significantly reduce the impact of segregation and inclusions on brittleness and susceptibility to hot cracking. The strict reduction of S and P directly reduces the binding sites of crack initiation sites and diffusible hydrogen, supporting the reliability of the preheating-free process from a metallurgical perspective.

[0039] Submerged arc welding is a welding method characterized by high heat input and slow cooling. While the slower cooling rate reduces the tendency for martensite formation, it can also lead to coarsening of the microstructure and decreased strength. To achieve mechanical properties of 690 MPa without preheating, this invention compensates for the strength loss caused by heat input by moderately increasing carbon (C) and combining it with medium-to-high molybdenum (Mo) content and an appropriate amount of Cr. Simultaneously, by reducing manganese (Mn), strictly controlling sulfur (S) and phosphorus (P), and adding titanium (Ti) to capture inclusions / nitrogen, it suppresses the networking of diffusible hydrogen and harmful sulfides, thereby controlling cold cracking sensitivity and achieving a safe window for preheating-free operation.

[0040] Inert particles such as TiN, in combination with Si and Mn, promote the nucleation of fine acicular ferrite or dispersed bainite, inhibiting the formation of coarse lath / network structures. This results in a microstructure dominated by fine acicular ferrite and fine-grained bainite (or a refined tempered microstructure after tempering). This type of microstructure exhibits good energy absorption capacity at low temperatures. The addition of Ni further lowers the ductile-brittle transition temperature of the material, and its combination with Mo and Cr can improve strength without sacrificing plasticity.

[0041] Lower S, P, and Ti levels can capture N, and combined with high-cleanliness smelting during production (such as vacuum degassing and secondary refining) and control of the moisture content / hygroscopicity of the welding wire coating, the content of diffusible hydrogen can be reduced to a low level, significantly reducing the risk of cold cracking, thus providing the necessary metallurgical protection for the preheat-free process.

[0042] The high heat input of submerged arc welding will prolong the cooling time. This invention chooses to make a trade-off between three aspects: strength compensation, toughness protection and low hydrogen sensitivity. Slightly higher C and Mo / Cr ensure strength, Ni and microstructure refinement measures ensure toughness, and low S, P and Ti capture ensure low hydrogen / low crack sensitivity, thus achieving the feasibility of no preheating required.

[0043] Preferably, the chemical composition of the welding wire, by mass percentage, includes: C: 0.075%–0.082%; Si: 0.34%–0.42%; Mn: 1.25%–1.44%; Cr: 0.25%–0.44%; Ni: 2.50%–3.14%; Mo: 0.54%–0.65%; Ti: 0.032%–0.046%; S ≤ 0.005%; P ≤ 0.005%; with the balance being Fe and unavoidable impurities.

[0044] Specifically, the weld metal is prepared from welding wire, and the weld metal has a yield strength of 700 MPa or higher, a tensile strength of 750 MPa or higher, an elongation of 24% or higher, and an impact absorption energy of -50℃ of 91 J or higher.

[0045] Specifically, the weld metal is prepared from welding wire, and the microstructure of the weld metal consists of acicular ferrite, lath ferrite and lath bainite.

[0046] It should be noted that acicular ferrite is a typical high-toughness microstructure in low-carbon, low-alloy high-strength steel. Its rapid growth rate, fine grains, and complex grain boundaries effectively increase fracture resistance and significantly enhance low-temperature impact toughness. Lath ferrite maintains its refined morphology even after multiple layers and multiple thermal cycles, helping to maintain the synergy between strength and plasticity of the deposited metal. The appropriate amount of lath bainite further improves tensile strength and hardenability, while not forming a continuous hard and brittle microstructure network, thus not affecting the overall toughness. The microstructure is uniformly distributed, with no obvious coarse grains, segregation, or brittle microstructure regions observed.

[0047] This invention achieves a stable and refined multiphase microstructure even under conditions of no preheating, low ambient temperature, and high heat input through precise control of alloy composition and reasonable controlled cooling and heating strategies. This results in the deposited metal exhibiting excellent impact toughness even at temperatures below -50°C, significantly superior to traditional high-strength welding wires of the same grade, thus meeting the service requirements for structural welding in extremely cold regions.

[0048] This invention provides a method for preparing a 690MPa grade high-strength and high-toughness submerged arc welding wire without preheating. The welding wire is obtained through vacuum smelting, forging, rolling, pickling and annealing, bright drawing and surface layer winding.

[0049] Specifically, the method for preparing the welding wire includes the following steps:

[0050] S1: Smelting is carried out using a vacuum induction furnace or electric arc furnace + refining process to ensure that S and P ≤ 0.005%. During the smelting process, the composition of the molten steel is controlled to be uniform, the hydrogen content is < 2 ppm, and the casting temperature is 1550~1580℃ to obtain steel ingots with uniform composition and low inclusions.

[0051] S2: Forging, the ingot is heated and held at 1150-1180℃ and then forged. The final forging temperature is controlled at 850-900℃ to break up the as-cast structure and refine the grains to obtain a uniform and dense forging billet.

[0052] S3: Rolling, the forging billet is heated and then hot rolled in multiple passes at a rolling temperature of 1050~1100℃, with the final rolling temperature controlled above 850℃, to obtain wire rod with a diameter of Φ6.5mm, ensuring a fine structure and good surface quality.

[0053] S4: Pickling and annealing. The hot-rolled wire rod is pickled to remove the oxide scale, and then annealed at 650-700℃ to restore the structure and improve plasticity, which facilitates subsequent cold working.

[0054] S5: Bright drawing. After annealing, the wire rod is cold-drawn in multiple passes under clean and lubricated conditions, with the compression rate per pass controlled to ≤15%, and then drawn into Φ4.0mm welding wire. During the drawing process, surface defects must be strictly controlled to maintain the uniform diameter of the welding wire and the surface roughness ≤Ra0.8.

[0055] S6: Surface layer winding. A copper plating layer or other anti-oxidation layer is uniformly applied to the surface of the welding wire. The copper plating thickness is controlled between 0.20 and 0.35 μm to ensure the corrosion resistance and arc stability of the welding wire during storage and welding. The final product is a welding wire with a diameter of Φ4.0 mm.

[0056] It should be noted that during the entire welding wire preparation process, strict control of the chemical composition and purity of smelting, the temperature range and deformation of forging and rolling, the temperature and atmosphere of annealing, and the compression ratio and lubrication conditions of drawing passes are all key to ensuring that the welding wire has stable composition, excellent strength and toughness, and good welding process performance.

[0057] Specifically, the average diffusible hydrogen content of the welding wire is below 3.28 ml / 100g.

[0058] It should be noted that excessively high hydrogen content can lead to the accumulation of hydrogen atoms at grain boundaries, dislocations, and inclusions, inducing hydrogen-induced cold cracking and brittle fracture. This weakens the load-bearing capacity of the weld and significantly reduces its low-temperature impact absorption energy, increasing the risk of cold cracking, especially in high-strength steels. Once cold cracks occur, the effective load-bearing area of ​​the weld decreases, resulting in unstable strength performance or even premature failure. Therefore, this invention controls the hydrogen content to a low level below 3.28 ml / 100g, effectively ensuring the strength stability and excellent low-temperature impact performance of the weld metal.

[0059] This invention provides a submerged arc welding process, which uses the welding wire provided by this invention and is used in conjunction with JF690 flux.

[0060] This invention provides a submerged arc welding process, which uses the preheat-free 690MPa grade high-strength and high-toughness submerged arc welding wire provided by this invention, and is used in conjunction with JF690 flux.

[0061] It should be noted that the JF690 flux is an alkaline sintering type fusion flux. Its chemical composition and performance optimization design are intended to match high-strength and high-toughness welding wire, ensuring that the weld metal obtains excellent deoxidation and purification effects and stable mechanical properties.

[0062] The main chemical composition of the flux is:

[0063] CaO+MgO: 30.2~33.2%;

[0064] Al2O3+MnO2: 22.3~25.3%;

[0065] SiO2+TiO2: 13.3~19.3%;

[0066] CaF2: 20.4–26.4%;

[0067] The sulfur (S) content is less than 0.01%, the phosphorus (P) content is less than 0.02%, the water content is less than 0.01%, and the alkalinity is controlled between 1.5 and 3.5.

[0068] This flux exhibits excellent slag-forming and deoxidizing properties, effectively adsorbing inclusions and harmful elements in the weld metal, improving its purity, and reducing cold cracking susceptibility. Simultaneously, the CaF2 to Al2O3 ratio in the flux contributes to the formation of a moderately alkaline slag system, enhancing the impact toughness and crack resistance of the weld metal. During welding, JF690 flux demonstrates good arc stability and forming properties, resulting in a dense and aesthetically pleasing weld metal microstructure.

[0069] When used in conjunction with the welding wire described in this invention, stable submerged arc welding of 690MPa high-strength steel can be achieved without preheating. The weld metal exhibits excellent comprehensive properties and significantly improved low-temperature impact toughness, meeting the stringent requirements of high-strength steel structures for the performance of welded joints.

[0070] Specifically, a submerged arc welding process includes the following steps:

[0071] Step 1: Flux preheating treatment. The flux needs to be baked before use.

[0072] Step 2: Welding material preparation. According to the welding process requirements, fill the automatic submerged arc welding equipment with welding wire and baked flux, and adjust the flux layer thickness to ensure stable arc combustion.

[0073] Step 3: Welding parameter setting;

[0074] Step 4: Welding process control. During the welding process, the interpass temperature should be strictly controlled between 105 and 120°C.

[0075] Step 5: Weld formation and inspection.

[0076] Preferably, the flux is baked at 300℃~350℃ for more than 2 hours before use, the welding current is 525~575A, the welding voltage is 28~30V, the welding speed is 39~41cm / min, and the average heat input is 20~26kJ / cm.

[0077] It should be noted that the flux needs to be baked before use to remove moisture and prevent cold cracking caused by increased hydrogen content during welding. Baking the flux at 300℃~350℃ for 2 hours, then removing it and storing it in an insulated container, is recommended for immediate use.

[0078] The welding current is set between 525 and 575 A, the welding voltage is controlled between 28 and 30 V, and the welding speed is controlled between 39 and 41 cm / min. When these parameters are used in combination, the average heat input of the weld is 24 kJ / cm, which ensures that the deposited metal obtains a refined acicular ferrite and bainite structure, achieving excellent strength and low-temperature toughness.

[0079] During welding, the interpass temperature should be strictly controlled between 105 and 120°C to avoid excessively high temperatures leading to coarsening of the microstructure or excessively low temperatures causing cold cracking. After welding, check whether the weld surface is smooth and free from defects such as porosity, lack of fusion, and slag inclusions.

[0080] To more clearly describe the present invention, the following embodiments and comparative examples are provided for further illustration.

[0081] Example 1

[0082] Preparation of welding wire:

[0083] S1: Smelting is carried out using a vacuum induction furnace or electric arc furnace + refining process to ensure that S and P ≤ 0.005%. During the smelting process, the composition of the molten steel is controlled to be uniform, the hydrogen content is < 2 ppm, and the casting temperature is 1550~1580℃ to obtain steel ingots with uniform composition and low inclusions.

[0084] S2: Forging, the ingot is heated and held at 1150-1180℃ and then forged. The final forging temperature is controlled at 850-900℃ to break up the as-cast structure and refine the grains to obtain a uniform and dense forging billet.

[0085] S3: Rolling, the forging billet is heated and then hot rolled in multiple passes at a rolling temperature of 1050~1100℃, with the final rolling temperature controlled above 850℃, to obtain wire rod with a diameter of Φ6.5mm, ensuring a fine structure and good surface quality.

[0086] S4: Pickling and annealing. The hot-rolled wire rod is pickled to remove the oxide scale, and then annealed at 650-700℃ to restore the structure and improve plasticity, which facilitates subsequent cold working.

[0087] S5: Bright drawing. After annealing, the wire rod is cold-drawn in multiple passes under clean and lubricated conditions, with the compression rate per pass controlled to ≤15%, and then drawn into Φ4.0mm welding wire. During the drawing process, surface defects must be strictly controlled to maintain the uniform diameter of the welding wire and the surface roughness ≤Ra0.8.

[0088] S6: Surface layer winding. A copper plating layer or other anti-oxidation layer is uniformly applied to the surface of the welding wire to ensure corrosion resistance and arc stability during storage and welding. The final product is a welding wire with a diameter of Φ4.0mm.

[0089] Welding wires with different compositions were prepared using the above method. The composition of the welding wires is shown in Table 1 (the proportion of alloy raw materials can be adjusted during the smelting stage to obtain welding wires with different compositions).

[0090] Table 1. Components (mass fraction, %) of the embodiments and comparative examples of the present invention.

[0091] Group C Si Mn S P Cr Ni Mo Ti Example 1 0.075 0.34 1.36 0.004 0.005 0.25 2.49 0.56 0.032 Example 2 0.082 0.42 1.44 0.004 0.005 0.37 2.63 0.54 0.041 Example 3 0.097 0.37 1.25 0.004 0.005 0.44 3.14 0.55 0.046 Comparative Example 1 0.087 0.52 1.45 0.005 0.009 0.62 4.75 0.82 0.003 Comparative Example 2 0.115 0.65 1.76 0.008 0.013 1.43 3.97 0.65 0.005 Comparative Example 3 0.127 0.57 1.34 0.005 0.005 1.59 4.69 0.73 0.004

[0092] Welding process:

[0093] The submerged arc welding wire of this invention has a diameter of φ4.0mm. Welding is performed using this wire on a 20mm thick S690 high-strength steel test plate. Straight weld beads are used, and JF690 flux is employed. The process includes the following steps:

[0094] Step 1: Flux preheating treatment, baking at 300℃~350℃ for 2 hours;

[0095] The main chemical composition of the flux is:

[0096] CaO+MgO: 32.2%; Al2O2+MnO2: 23.3%; SiO2+TiO2: 19.3%; CaF2: 25.2.%;

[0097] The sulfur (S) content is less than 0.01%, the phosphorus (P) content is less than 0.02%, the water content is less than 0.01%, and the alkalinity is controlled between 1.5 and 3.5.

[0098] Step 2: Welding material preparation. According to the welding process requirements, fill the automatic submerged arc welding equipment with welding wire and baked flux, and adjust the flux layer thickness to ensure stable arc combustion.

[0099] Step 3: Welding parameter settings; Welding current is 540A, welding voltage is 29V, welding speed is 40cm / min, average heat input is 24kJ / cm, ambient temperature is 3℃, and relative humidity is 48%.

[0100] Step 4: Welding process control. During the welding process, the interpass temperature should be strictly controlled between 105 and 120°C.

[0101] Step 5: Weld formation and inspection.

[0102] The mechanical properties of the weld metal are shown in Table 2, the diffusible hydrogen content of the weld metal is shown in Table 3, and the results of the rigid butt weld crack test are shown in Table 4.

[0103] Table 2 Mechanical properties of the weld metal in the embodiments and comparative examples of the present invention

[0104]

[0105] Table 3. Determination of diffusible hydrogen content in welded metal of embodiments and comparative examples of the present invention.

[0106]

[0107] The rigid butt weld crack test was conducted in an environment with an ambient temperature of 18–20℃ and a relative humidity of 23–25%. The test results are shown in Table 4.

[0108] Table 4. Test results of rigid butt weld cracks in the embodiments and comparative examples of the present invention.

[0109]

[0110] A comparison of the data from the embodiments and comparative examples in Tables 1 and 2 shows that the welding wire of the present invention, even in a low-Ni design system with a Ni content of only 2.10%–3.30% and a Cr content controlled at 0.20%–0.50%, still exhibits excellent mechanical properties and low-temperature toughness, fully verifying the feasibility of the design concept of a 690MPa-grade low-temperature high-strength steel high-toughness submerged arc welding wire that requires no preheating. The yield strength of the deposited metal in Examples 1–3 is 701–723MPa, the tensile strength is 759–774MPa, the impact energy at -50℃ reaches 94J, 97J, and 91J respectively, and the elongation is maintained above 24%, with comprehensive performance significantly better than that of the comparative welding wire.

[0111] In contrast, the Ni content in the comparative samples was generally between 3.9% and 4.75%. Although the strength was slightly improved, the low-temperature impact energy was significantly reduced, with the lowest being only 48J. The elongation also dropped to 19.0% to 20.5%, showing obvious toughness deterioration and making it difficult to meet the safety requirements under extreme service conditions.

[0112] Regarding the control of diffusible hydrogen, as shown in Table 3, the diffusible hydrogen content of the welding wire of the present invention, tested under standard collection conditions (45℃×72h), is only 2.35~3.28ml / 100g, significantly lower than the 6.04~7.36ml / 100g of the comparative welding wire. The average diffusible hydrogen content of the examples remains below 3.28ml / 100g, demonstrating the significant advantages of the clean metallurgy and hydrogen and impurity control process adopted by the welding wire of the present invention in reducing the diffusible hydrogen level and reducing the risk of hydrogen-induced cooling cracks.

[0113] Further analysis of the rigid butt welding crack test results in Table 4 shows that, under conditions of normal temperature, relative humidity of 23–25%, and high welding heat input, the weld metals of Examples 1–3 exhibited 0% surface crack rate, sectional crack rate, and root crack rate, with no cold cracks observed. In contrast, the comparative samples generally showed crack defects, with a root crack rate as high as 10%, verifying that the welding wire of the present invention possesses excellent crack resistance and can adapt to harsh conditions such as low-temperature, preheating-free, multi-layer, and multi-pass welding.

[0114] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A preheat-free 690MPa grade high-strength, high-toughness submerged arc welding wire, characterized in that, The chemical composition of the welding wire, by mass percentage, includes: C: 0.07%–0.10%; Si: 0.25%–0.42%; Mn: 1.20%–1.50%; Cr: 0.20%–0.50%; Ni: 2.10%–3.30%; Mo: 0.45%–0.65%; Ti: 0.03%–0.05%; S≤0.005%; P≤0.005%; with the balance being Fe and unavoidable impurities; the average diffusible hydrogen content of the welding wire is below 3.28 ml / 100g. The weld metal is prepared from welding wire, and the microstructure of the weld metal consists of acicular ferrite, lath ferrite and lath bainite.

2. The preheat-free 690MPa grade high-strength and high-toughness submerged arc welding wire according to claim 1, characterized in that, The chemical composition of the welding wire, by mass percentage, includes: C: 0.075%–0.082%; Si: 0.34%–0.42%; Mn: 1.25%–1.44%; Cr: 0.25%–0.44%; Ni: 2.50%–3.14%; Mo: 0.54%–0.65%; Ti: 0.032%–0.046%; S≤0.005%; P≤0.005%; with the balance being Fe and unavoidable impurities.

3. The preheat-free 690MPa grade high-strength and high-toughness submerged arc welding wire according to claim 1 or 2, characterized in that, The weld metal is prepared from welding wire, wherein the yield strength of the weld metal is above 700 MPa, the tensile strength is above 750 MPa, and the elongation is above 24%.

4. The preheat-free 690MPa grade high-strength and high-toughness submerged arc welding wire according to claim 1 or 2, characterized in that, The weld metal is prepared from welding wire, and the impact absorption energy of the weld metal at -50°C is above 91J.

5. A method for preparing a preheat-free 690MPa grade high-strength and high-toughness submerged arc welding wire as described in any one of claims 1-4, characterized in that, Welding wire is obtained through vacuum smelting, forging, rolling, pickling and annealing, bright drawing and surface layer winding.

6. The method for preparing a preheat-free 690MPa grade high-strength and high-toughness submerged arc welding wire according to claim 5, characterized in that, The average diffusible hydrogen content of the welding wire is below 3.28 ml / 100g.

7. A submerged arc welding process, characterized in that, The welding wire described in any one of claims 1-4 or the welding wire obtained by the preparation method described in claim 5 or 6 is used in conjunction with JF690 flux.

8. The submerged arc welding process according to claim 7, characterized in that, The flux should be baked at 300℃~350℃ for more than 2 hours before use.

9. The submerged arc welding process according to claim 7, characterized in that, During the welding process, the welding current is 525-575A, the welding voltage is 28-30V, the welding speed is 39-41cm / min, and the average heat input is 20-26kJ / cm.

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