550mpa grade multi-wire submerged arc welding wire rod and welding wire with 50~125kj / cm heat input

Abstract

This invention discloses a 550MPa grade multi-wire submerged arc welding wire rod capable of welding with a heat input of 50~125kJ / cm, belonging to the field of welding materials technology. The invention is characterized by the following chemical composition by mass percentage: C 0.03~0.12, Si≤0.09, Mn 1.70~1.95, P≤0.012, S≤0.005, Ni 0.05~0.5, Mo 0.20~0.38, Ti 0.13~0.24, Mg≤0.005, Ca≤0.0015, Al≤0.05, N≤0.0065, B 0.0005~0.002, La≤0.015, with the balance being Fe and unavoidable impurities. This invention also discloses a welding wire based on the above-mentioned wire rod. The welding wire of this invention has a simple chemical composition, high deposition efficiency, excellent low-temperature impact toughness, and strong adaptability to the welding heat input range. It is suitable for the efficient welding and manufacturing of large steel structures in fields such as bridges and ships.

Description

Technical Field

[0001] This invention belongs to the field of welding materials technology, specifically relating to a 550MPa grade multi-wire submerged arc welding wire and its wire rod that can be welded with a heat input of 50~125kJ / cm. It is suitable for high heat input multi-wire submerged arc welding, and the deposition efficiency is 2-4 times higher than that of conventional single-wire submerged arc welding. Background Technology

[0002] In recent years, with the rapid development of my country's transportation industry, bridge construction has been accelerating, moving towards larger scale, higher span, and higher performance. Currently, bridge steel plate welding uses conventional low heat input (20~40kJ / cm) welding, which is extremely inefficient for thicker bridge components. Using high heat input welding (≥50kJ / cm) with a higher deposition rate per unit time can effectively reduce the number of welding passes, saving production time and costs. However, when using high heat input welding with ordinary bridge steel welding materials, there is a problem of a sharp decrease in the toughness of the deposited metal, making it difficult to ensure a balance between the impact toughness of the deposited metal and high welding efficiency. This is because as the welding heat input increases, the cooling rate of the deposited metal decreases, resulting in severe microstructure coarsening, and the size of the hardened second phase increases significantly. At present, most of the high heat input welding wires used in my country are imported from abroad, which are expensive and rarely used in the field of steel structure bridge manufacturing. Therefore, in order to promote the development of the bridge manufacturing industry towards efficient and intelligent manufacturing, it has become increasingly important and necessary to develop high-efficiency submerged arc welding wire that can withstand high heat input to improve the efficiency of horizontal and vertical welding of large-span, thick-gauge bridge structural components, while shortening the manufacturing cycle and reducing costs.

[0003] Chinese invention patent application CN201410728048.4 discloses a high heat input submerged arc welding wire suitable for heat inputs of 60~160 kJ / cm. It uses 0.01~0.05% Ti to form TiN, which pins austenite grain boundaries and hinders austenite grain growth. On the other hand, it uses alloying elements such as Si, Mn, Ti, Al, Ce, and Mg to generate high-melting-point composite oxide inclusions of Si, Mn, Ti, Al, Ce, and Mg, thereby promoting acicular ferrite nucleation. However, during high heat input welding, Ti burn-off is severe, and the 0.01~0.05% titanium element, under high heat input, transitions to negligible amounts in the deposited metal, making it difficult to play an effective role. Therefore, in the embodiment, the low-temperature impact toughness at -40℃ in the weld center is low.

[0004] Chinese invention patent application CN201410666124.3 discloses a submerged arc welding wire with excellent low-temperature toughness for offshore platform construction. Its chemical composition, by weight (%), contains C 0.01~0.15%; Si 0.1~0.9%; Mn 0.5~2.0%; Ni 0.1~1.5%; Mo 0.1~0.6%; Ti 0.01~0.25%; Al ≤0.01%, and CE ≤0.4%. However, the upper limit of Si content in this invention is relatively high; excessively high or low Si content is detrimental to the impact toughness of the deposited metal. Furthermore, the invention lacks the addition of boron (B), which is not conducive to suppressing the formation of proeutectoid ferrite and side-plate ferrite structures that reduce impact toughness.

[0005] Chinese invention patent application CN200910046732.3 discloses a "high-toughness submerged arc welding wire" with moderate strength, high impact toughness, and high heat input resistance. This is achieved by optimizing carbon content, controlling the upper limit of silicon content, and combining it with a Mn-Ni system to effectively improve low-temperature toughness and resistance to high heat input environments. However, during high heat input welding, grain growth is significant, and simply adding Ni to refine ferrite grains and improve toughness is far from sufficient. Furthermore, adding too much Ni will increase the cost of welding wire smelting.

[0006] Chinese invention patent application CN01135349.X discloses a complete set of technologies for "high heat input submerged arc welding joint, its manufacturing method, and the welding wire and flux used". Its characteristics include a chemical composition by weight (%) of C: 0.03~0.10%, N: ≤0.0035%, Si: ≤0.4%, Mn: 1.0~2.5%, and Ti above 0.03% with a Ti / N ratio of 15~50. The welding wire also contains one or more elements selected from Mo, Nb, B, and Ni, and the composition of the welded joint's deposited metal must satisfy 0.6≤B / N≤1.2, and the area ratio of grain boundary ferrite in the deposited metal must be controlled below 10.0%. This invention patent technology is complex, has high requirements, and is difficult to implement. Meanwhile, although the submerged arc welding wire of this invention can be used for welding under a high heat input of 150 kJ / cm, the examples only provide the impact toughness at 0℃ and -20℃, but fail to provide the low-temperature impact toughness value at -40℃, thus lacking data on low-temperature impact toughness.

[0007] Therefore, under the condition of meeting the requirements of relevant standards and specifications for the mechanical properties of welded joints, in order to improve the welding manufacturing efficiency of large steel structures such as bridges, it is an important way to further improve the welding efficiency of steel structure manufacturing enterprises in my country, reduce production costs, and replace imported products, while meeting the requirements of relevant standards and specifications for the mechanical properties of welded joints. Summary of the Invention

[0008] The problem this invention aims to solve is to provide a 550MPa grade multi-wire submerged arc welding wire and its coil that can weld with a heat input of 50~125kJ / cm. It is compatible with Fe powder-MgO-SiO2-CaF2-Al2O3 alkaline sintered flux. During welding, the weld bead is smooth, the weld formation is aesthetically pleasing, the yield strength Rp0.2 of the deposited metal is not less than 420MPa, the tensile strength is not less than 550MPa, and the impact absorption energy at -40℃ is not less than 85J. This submerged arc welding wire has a simple chemical composition, high deposition efficiency, excellent low-temperature impact toughness, and strong adaptability to the welding heat input range, making it suitable for the efficient welding and manufacturing of large steel structures in fields such as bridges and ships.

[0009] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a 550MPa grade multi-wire submerged arc welding wire rod that can be welded with a heat input of 50~125kJ / cm, wherein the chemical composition of the wire rod by mass percentage includes: C 0.03~0.12, Si≤0.09, Mn 1.70~1.95, P≤0.012, S≤0.005, Ni 0.05~0.5, Mo: 0.20~0.38, Ti 0.13~0.24, Mg≤0.005, Ca≤0.0015, Al≤0.05, N≤0.0065, B 0.0005~0.002, La≤0.015, with the balance being Fe and unavoidable impurities.

[0010] Furthermore, the content of the five harmful elements Pb+Sn+As+Sb+Bi in the wire rod is ≤0.008.

[0011] Furthermore, the content of Si, Mn, Ni, Mo, Ti, B, and La elements in the wire rod satisfies 0.41≤φ≤0.85, where φ=(Ni+6Ti+4B+3Mo) / (8Si+2Mn+La).

[0012] Furthermore, the C, Mn, Ni, Mo, and Ti content in the wire rod satisfies 560≤θ≤650, where θ=10.8×(36.69+173.15C+5.22Mn+2.35Ni+6.37Mo+1.15Ti).

[0013] Furthermore, the wire rod contains three or more of the following: Mo, Mg, Ti, B, Ca, and La.

[0014] The present invention also provides a 550MPa grade multi-wire submerged arc welding wire that can be welded with a heat input of 50~125kJ / cm, which is drawn from the above-mentioned wire rod.

[0015] Furthermore, a copper plating layer is provided on the surface of the welding wire, and the thickness of the copper plating layer is 0.18 to 0.20 micrometers.

[0016] Furthermore, the welding wire uses an alkaline sintered flux, and the inclusion size of the deposited metal is more than 80% concentrated in the range of 0.3~1.2μm under a heat input of 50~125kJ / cm, and the proportion of acicular ferrite structure is not less than 72%.

[0017] Furthermore, when the welding wire is used with a sintered flux with a basicity BⅡW higher than 1.8, and when using double-wire or triple-wire submerged arc welding with a heat input of 50~125kJ / cm, the deposited metal has a KV2 ≥ 85J at -40℃, a yield strength of not less than 420MPa, a tensile strength Rm greater than 550MPa, and an elongation A ≥ 21%.

[0018] The beneficial effects of the present invention are: (1) The welding wire of the present invention, through reasonable design of chemical composition, has small inclusion size and dispersed distribution in the weld metal, which refines the microstructure of the weld metal, so that the content of acicular ferrite in the weld metal is still not less than 72% under high heat input welding. This ensures that the weld metal obtained under heat input of 50~125kJ / cm has excellent comprehensive performance, with high tensile strength and low temperature impact toughness. The weld metal of the welding wire of the present invention has the following mechanical properties: yield strength Rp0.2≥420MPa, tensile strength Rm≥550MPa, elongation A≥21%, and impact absorption energy at -40℃≥85J.

[0019] (2) The welding wire of the present invention is applicable to high heat input welding operations such as submerged arc welding and flux copper backing welding, and has a wide range of welding parameter adjustment. Under the heat input of 50~125kJ / cm, the welding process performance is stable, the molten pool has good fluidity, the deposited metal is beautifully formed, and the crack resistance is excellent.

[0020] (3) The welding wire alloy system of the present invention is reasonably controlled, and its wire rod smelting, rolling and welding wire drawing processes are easy to implement, with stable quality, and are suitable for large-scale promotion and application.

[0021] The present invention will now be described in detail with reference to the accompanying drawings. Attached Figure Description

[0022] Figure 1This is a distribution diagram of the deposited metal inclusions in Example 5;

[0023] Figure 2 This is a distribution diagram of the deposited metal inclusions in Example 7;

[0024] Figure 3 This is a diagram showing the distribution of inclusions in the weld metal in Comparative Example 6;

[0025] Figure 4 This is a diagram showing the distribution of inclusions in the weld metal in Comparative Example 7;

[0026] Figure 5 Metallographic image of the deposited metal in Example 5;

[0027] Figure 6 Metallographic image of the weld metal in Example 7;

[0028] Figure 7 The metallographic image of the weld metal in Comparative Example 6 is shown.

[0029] Figure 8 The metallographic image of the weld metal in Comparative Example 7 is shown.

[0030] Figure 9 This is a diagram showing the distribution of martensite / austenite (M / A) components in the weld metal of Example 5;

[0031] Figure 10 This is a distribution diagram of M / A components in the weld metal of Example 7;

[0032] Figure 11 The distribution diagram of M / A components in the weld metal of Comparative Example 6 is shown.

[0033] Figure 12 The distribution diagram of M / A components in the weld metal of Comparative Example 7 is shown. Detailed Implementation

[0034] This invention provides a 550MPa grade multi-wire submerged arc welding wire rod suitable for welding with a heat input of 50~125kJ / cm. The chemical composition of the wire rod, by mass percentage, includes: C 0.03~0.12, Si≤0.09, Mn 1.70~1.95, P≤0.012, S≤0.005, Ni 0.05~0.5, Mo 0.20~0.38, Ti 0.13~0.24, Mg≤0.005, Ca≤0.0015, Al≤0.05, N≤0.0065, B 0.0005~0.002, La≤0.015, with the balance being Fe and unavoidable impurities.

[0035] The chemical composition of wire rod contains five harmful elements: Pb+Sn+As+Sb+Bi≤0.008.

[0036] The chemical composition of wire rod contains C, Si, Mn, Ni, Mo, Ti, B, and La elements with contents satisfying 0.41 ≤ φ ≤ 0.85 and 560 ≤ θ ≤ 650.

[0037] φ=(Ni+6Ti+4B+3Mo) / (8Si+2Mn+La),

[0038] θ=10.8×(36.69+173.15C+5.22Mn+2.35Ni+6.37Mo+1.15Ti).

[0039] The wire rod contains three or more of the following elements: Mo, Mg, Ti, B, Ca, and La.

[0040] The functions and mechanisms of the various chemical components in wire rod are as follows.

[0041] C: Carbon can significantly improve the strength of the weld metal, but it also reduces its crack resistance. To improve toughness and crack resistance, the carbon content should be as low as possible. However, during submerged arc welding, a large heat input leads to significant carbon loss due to heat. Considering the above factors, the carbon content is limited to 0.03~0.12%, preferably 0.04~0.10%, and more preferably 0.05~0.07%.

[0042] Silicon (Si) is one of the effective deoxidizing elements in welding, often used in combination with manganese (Mn) for deoxidation. When the silicon content in the weld metal is less than 0.1%, the deoxidation effect is poor, and porosity is easily formed in the weld metal. Simultaneously, the number of inclusions in the deoxidation products decreases, and the nucleation rate of acicular ferrite is reduced. When the silicon content in the weld metal is greater than 0.6%, the inclusions in the weld metal become significantly coarser, reducing the toughness of the weld metal. For submerged arc welding, silicon is mainly transferred from the base metal and flux; therefore, the silicon content in the welding wire is limited to ≤0.09%, preferably 0.04~0.07%.

[0043] Mn: Manganese is an important element for deoxidation and desulfurization. Simultaneously, manganese plays a role in solid solution strengthening of the weld metal. Adding an appropriate amount of manganese to the weld metal can increase the AF content and improve impact toughness while ensuring the strength of the weld metal. However, when the manganese content is too high, segregation bands are easily formed in the weld metal, causing uneven microstructure and hardness, thus reducing toughness. Therefore, considering the significant manganese loss during high heat input submerged arc welding, the Mn content is controlled at 1.7~1.95%, preferably 1.72~1.90%, and more preferably 1.75~1.83%.

[0044] Mo: During high-heat input welding, molybdenum exhibits a relatively stable transition and minimal burn-off. Adding an appropriate amount of Mo to submerged arc welding wire can improve the strength of the deposited metal. Simultaneously, the addition of Mo lowers the austenite-to-ferrite transformation temperature (Ar3), refines the microstructure, and can improve the low-temperature impact toughness of the deposited metal. However, the Mo content should be controlled to avoid an increase in Ceq (cet strength) and hardness. Therefore, the Mo content in the welding wire composition is limited to 0.2~0.38%, preferably 0.2~0.34%, and more preferably 0.25~0.28%.

[0045] Ni: The addition of Ni can significantly improve the low-temperature toughness of the weld metal. The mechanism by which Ni improves low-temperature toughness is by toughening the ferrite matrix and lowering its brittle transition temperature. In high heat input welding, Ni will be lost to some extent by burning. Therefore, the Ni content in the welding wire composition should be limited to 0.05~0.5%, preferably 0.08~0.35%, and more preferably 0.08~0.26%.

[0046] The addition of Ti can form dispersed oxides and nitrides, effectively preventing the growth of austenite grains during welding thermal cycling. Simultaneously, increasing its volume content within an appropriate range can significantly promote the formation of acicular ferrite in the weld metal. Furthermore, the composite oxide inclusions formed by Ti with Si, Mn, Al, and Mg are beneficial for the nucleation of acicular ferrite, increasing its proportion and improving the low-temperature toughness of the weld metal under high heat input. However, in high heat input welding, Ti burn-off is severe, so the amount of Ti added should be increased. Therefore, the Ti content in the welding wire composition should be controlled at 0.13~0.24%, preferably 0.15~0.23%, and more preferably 0.16~0.22%.

[0047] Al (Al₂O₃) is a ferrite-forming element with a strong affinity for oxygen. When the weld metal contains a small amount of Al₂O₃, the resulting composite inclusions can act as nucleation sites for ferrite (AF), effectively refining the microstructure. However, Al has a stronger affinity for oxygen than Ti (Ti), so excessive Al content can affect the formation and distribution of Ti oxides. Excessive Al can also excessively shrink the austenite region, delaying or even hindering phase transformation, promoting the formation of large amounts of blocky ferrite, and thus reducing the impact toughness of the weld metal. Therefore, the Al content in the welding wire should be ≤0.05%, preferably 0.02~0.04%.

[0048] Mg: Mg is a strong deoxidizer, reducing the oxygen content of the weld through deoxidation reactions and improving the impact toughness of the deposited metal. The Mg-containing composite inclusion Ti-Mg-O has a significant effect on inhibiting austenite grain growth and promoting austenite arcing (AF). Furthermore, Al and Mg have low boiling points, which can easily cause process problems such as arc instability and spatter. Therefore, the Mg content in the welding wire should be ≤0.005%, preferably 0.001~0.005%.

[0049] Ca: Adding an appropriate amount of Ca can spheroidize the original strip-shaped MnS-based inclusions, promoting the nucleation and growth of AF (alloy fusion). Simultaneously, the Ca-formed CaS or CaO combines with other inclusions to induce AF formation, thereby improving the toughness of the weld metal. However, the Ca content should not exceed 0.0015%, otherwise coarse inclusions will form, reducing the toughness of the weld metal. Therefore, the Ca content in this welding wire is controlled at ≤0.0015%, preferably 0.001~0.0013%, and more preferably 0.0005~0.0009%.

[0050] Sulfur (S) and phosphorus (P): These elements negatively impact the toughness of the weld metal. Excessive S content can easily lead to cracking. Therefore, their content should be minimized, especially phosphorus (P). This is because the use of flux during submerged arc welding increases the P content in the weld metal. The recommended S content is no more than 0.005%, and the P content is no more than 0.012%.

[0051] N: The combination of N and B to form BN can promote ferrite nucleation, but an increase in N content leads to an increase in the aging sensitivity index, resulting in a significant decrease in the aging impact energy of the deposited metal. This invention controls the N content to N≤0.0065%.

[0052] Boron (B): Boron is a surface-active element with a very small atomic radius, requiring the protection of titanium (Ti) to exist freely. At high temperatures, B readily diffuses to and segregates at austenite grain boundaries, reducing austenite grain boundary energy, increasing austenite stability, inhibiting the formation of proeutectoid ferrite, and improving toughness. Considering that B will experience some burn-off during high-heat welding, the B content in this welding wire is controlled at 0.0005% ≤ B ≤ 0.002%.

[0053] La: Adding trace amounts of the rare earth element La to welding wire can effectively improve the composition, morphology, distribution, and properties of inclusions. Simultaneously, La can also improve the fluidity of the weld pool and enhance its metallurgical quality. In this invention, the La content is controlled at La ≤ 0.015%.

[0054] Mn, Si, Ni, and Mo often enhance the strength of the weld metal through solid solution strengthening. Trace elements such as Ti and B tend to form carbides or nitrides in the weld metal; these second phases often pin dislocations, resulting in precipitation strengthening. Simultaneously, Ni, Ti, and B also have a significant effect on refining ferrite grains, thus producing grain refinement strengthening. Furthermore, due to the significant burn-off of alloying elements during the high-heat-input welding process, their content in the weld metal varies considerably. According to welding metallurgical theory, at 1600℃, the order of oxygen affinity from lowest to highest is: Cu, Ni, Co, Fe, W, Mo, Cr, Mn, V, Si, Ti, Zr, Al. Since Fe has the highest concentration in the welding zone, some Fe will inevitably be oxidized; Ni, being the element to the left of Fe, has a lower affinity for oxygen, thus its oxidation loss is minimal. Although Mo is located to the right of Fe, its affinity for oxygen is close to that of Fe, and its concentration in the molten droplet and molten pool is relatively low, resulting in less oxidation loss and a larger transition coefficient. While the concentrations of Mn, Si, and Ti are not high, their strong affinity for oxygen leads to more severe oxidation loss. Furthermore, Ti, being highly reactive, will react with nitrogen in the arc atmosphere to form TiN, further reducing its alloy transition coefficient. Therefore, it is necessary to consider the element loss caused by high heat input welding in welding. By combining the transition allowance of each alloying element after high heat input welding with the strength increase caused by chemical composition, the contribution of alloying elements to strength when alloying ferrite can be expressed by the following formula: In the formula, K i C is the strengthening coefficient of element i (MPa / wt%). i Let be the weight percentage concentration of element i dissolved in ferrite. Assuming the additive effect of alloying elements is linear, the following formula can be used to calculate the strength value caused by chemical composition:

[0055] θ = 10.8 × (36.69 + 173.15C + 5.22Mn + 2.35Ni + 6.37Mo + 1.15Ti). The toughening factor θ satisfies 560 ≤ θ ≤ 650 to ensure the deposited metal has sufficient strength without generating excessive hardened structures such as martensite / austenite.

[0056] With increased heat input, the high-temperature residence time of the weld metal is prolonged, allowing for more complete diffusion of carbon atoms at high temperatures. This increases the size of the hardened MA phase in the weld metal, reducing the energy required for crack initiation. Simultaneously, with increased heat input, the austenite-to-ferrite transformation point Ar3 rises, the acicular ferrite content decreases, the microstructure coarsens, and the proportion of high-angle grain boundaries decreases, further reducing the energy required for crack propagation.

[0057] To ensure the toughness of the weld metal, the welding wire of this invention, when used in conjunction with a matching Fe powder-MgO-SiO2-CaF2-Al2O3 alkaline sintering flux, can be used for efficient welding of Q370~Q420qE grade steel plates under a welding heat input of 50~125kJ / cm. This invention employs a Mn-Mo-Ti-Ni system, with appropriate amounts of Ca and Mg added, and strictly controlled S and P contents. This refines the austenite grains and ferrite structure, promotes the formation of small-sized inclusions, and increases the number of acicular ferrite, effectively ensuring the strength and toughness of the weld metal. The main function of C, Mn, and Mo is to improve the strength of the weld metal through solid solution strengthening. Simultaneously, adding an appropriate amount of Mn to the weld metal can appropriately increase the proportion of acicular ferrite, and Mo can also refine the ferrite structure. The addition of Mg and Ti primarily forms fine, dispersed Ti-Mg-O inclusions, which significantly inhibit austenite grain growth and promote acicular ferrite nucleation. When combined with a matching Fe powder-MgO-SiO2-CaF2-Al2O3 alkaline sintering flux, an appropriate amount of Si reduces the viscosity of the molten pool, increases its fluidity, and ensures the removal of larger inclusions. Simultaneously, a suitable amount of Ni is used to toughen the ferrite matrix, improve the low-temperature toughness of the weld metal, and lower the brittle transition temperature. However, Ni is a precious metal, and its addition should be controlled to reduce costs. Furthermore, the appropriate addition of Ca achieves sulfide modification. The composition of each element is adjusted so that its composition ratio satisfies 0.41≤φ≤0.85, where φ=(Ni+6Ti+4B+3Mo) / (8Si+2Mn+La), to ensure that the molten pool has sufficient fluidity, reduce large-sized inclusions, and make the deposited metal structure sufficiently refined.

[0058] The present invention also provides a welding wire based on the above-mentioned wire rod, which is produced by drawing the wire rod into welding wire of the corresponding size and then plating and polishing it with copper. Specifically, the alloy composition of the welding wire of the present invention is smelted and cast into steel ingots, then forged, rolled into wire rods, drawn into welding wire of the corresponding size, and then plated and polished with copper, wherein the thickness of the copper plating layer is 0.18~0.20um, and finally packaged into finished products in coils.

[0059] The technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0060] Examples of chemical composition ratios for Examples 1-10 and Comparative Examples 1-10 are shown in Tables 1, 3 and 5. Based on the precisely calculated composition ratio of the welding wire, raw materials with low contents of P, S, gas and inclusions are selected, the amount of alloy added is calculated, and the steel for welding wire is smelted in a 75kg vacuum induction furnace. After charging, melting and refining, the steel is cast into steel ingots after the composition is qualified.

[0061] After the steel ingot is forged into a square billet, it is rolled into an 8.5mm wire rod. The wire rod is then drawn into a solid submerged arc welding wire with a diameter of 5.0mm through one coarse drawing and two fine drawing processes. The welding wire has stable quality. Further, the surface of the welding wire is coated with copper using a chemical copper plating method, and the copper plating thickness is controlled at 0.18~0.20um.

[0062] Table 1 Chemical composition ratios (mass percentage) of submerged arc welding wires in Examples 1-3 and Comparative Examples 1-3 (balance: Fe and unavoidable impurities)

[0063] .

[0064] Examples 1-3 and Comparative Examples 1-3 were tested with double-wire welding according to the bevel form and welding process parameters as shown in Table 2. The welding heat input was 50 kJ / cm, and the Fe powder-MgO-SiO2-CaF2-Al2O3 alkaline sintering flux was selected. The layer temperature was controlled to be no more than 160℃.

[0065] Table 2 Submerged Arc Welding Process Parameters

[0066] .

[0067] Table 3 Chemical composition ratios (mass percentage) of submerged arc welding wires in Examples 4-6 and Comparative Examples 4-6 (balance: Fe)

[0068] .

[0069] Examples 4-6 and Comparative Examples 4-6 were tested with double-wire welding according to the bevel form and welding process parameters shown in Table 4. The welding heat input was 100 kJ / cm, and the matching Fe powder-MgO-SiO2-CaF2-Al2O3 alkaline sintering flux was selected. The layer temperature was controlled to be no more than 160℃.

[0070] Table 4 Submerged Arc Welding Process Parameters

[0071] .

[0072] Table 5 Chemical composition ratios (mass percentage) of submerged arc welding wires in Examples 7-10 and Comparative Examples 7-10 of the present invention (balance: Fe)

[0073] .

[0074] Examples 7-10 and Comparative Examples 7-10 were tested with double-wire welding according to the bevel form and welding process parameters shown in Table 6. The welding heat input was 125 kJ / cm, and the matching Fe powder-MgO-SiO2-CaF2-Al2O3 alkaline sintering flux was selected. The layer temperature was controlled to be no more than 160℃.

[0075] Table 6 Submerged Arc Welding Process Parameters

[0076] .

[0077] Tensile test specimens were taken from the welded fusion metal, ensuring that the entire parallel length consisted of the fusion metal. The specimen dimensions and test methods were performed according to GB / T 228. Impact test specimens were taken from the center of the fusion metal, with the longitudinal axis of the impact specimen perpendicular to the length of the fusion metal, the notch face perpendicular to the surface of the fusion metal, and the notch axis located at the center of the fusion metal. The specimen dimensions were 10×10×55mm, and the impact test method was performed according to GB / T 229. The results of the tensile and impact tests on the welded metal are shown in Table 7, with the values ​​in parentheses representing average values.

[0078] Table 7 Mechanical properties of weld metal from the examples and comparative welding wires

[0079] .

[0080] Examples 1-10 have chemical compositions that meet the invention requirements. When θ satisfies 560≤θ≤650, the tensile strength of the weld metal is between 585-620 MPa, which meets the invention's strength requirements. When φ satisfies 0.41≤φ≤0.85, the impact absorption energy of the weld metal at -40℃ is not less than 104.8 J. However, the chemical compositions of Comparative Examples 1-10 do not meet the invention requirements, the strength of the weld metal does not meet the standard, and the impact toughness of the weld metal cannot be guaranteed.

[0081] Metallographic samples were taken from the impact specimens of the weld metal. It was found that the inclusions in Examples 1-10 were diffusely distributed, with fewer large inclusions. Over 80% of the inclusions were concentrated in the 0.3~1.2μm range. This ensured that the weld metal did not experience excessive stress concentration due to too many large inclusions, while simultaneously promoting the nucleation of acicular ferrite. Figure 1 and 2 In Examples 5 and 7, the inclusions in the weld metal are small and dispersed. In contrast, the weld metals in Comparative Examples 1-10 contain more large inclusions, leading to higher stress concentration and reduced impact toughness. Figure 3 and 4 In Comparative Examples 6 and 7 shown, the inclusions in the weld metal deposited by the welding wire are relatively large, which can easily cause stress concentration.

[0082] Meanwhile, the number of fine inclusions in Comparative Examples 1-10 was less than in the Examples, resulting in a weaker overall promoting effect on acicular ferrite nucleation. In Examples 1-10, the deposited metal microstructure was mainly composed of acicular ferrite, with a small amount of smaller grain boundary ferrite and granular bainite also present. Figure 5 and 6The weld metal microstructure shown in Examples 5 and 7 primarily consists of fine acicular ferrite, containing small amounts of M / A components and bulk ferrite. Therefore, the weld metal of this invention exhibits excellent low-temperature toughness. Statistical analysis of the acicular ferrite content in the weld metal of Examples 1-10 revealed that its content was not less than 72%. In contrast, the weld metal microstructure of Comparative Examples 1-10 showed very coarse grain boundary ferrite, along with a large amount of large-sized bulk ferrite, and a lower acicular ferrite content. Figure 7 and 8 In Comparative Examples 6 and 7, the weld metal microstructure shows coarse and predominantly large proeutectoid and massive ferrite, resulting in lower low-temperature toughness. The fine-sized acicular ferrite forms high-angle grain boundaries, effectively hindering crack propagation and thus improving impact toughness. After re-etching the metallographic samples, the M / A components in the weld metal were observed. In Examples 1-10, the M / A components were small, with an average size less than 1 μm. Figure 9 and 10 In Examples 5 and 7, the weld metal M / A components are small and dispersed, promoting acicular ferrite nucleation without causing high stress concentration. However, in Comparative Examples 1-10, the M / A components are generally larger, with an average size of approximately 2 μm. Figure 11 and 12 In Comparative Examples 6 and 7, the weld metal contains coarse M / A components with significantly increased content, which easily leads to higher stress concentration. The coarse M / A components and inclusions cause stress concentration, making crack initiation easier, while the reduction of high-angle grain boundaries makes crack propagation easier. The combined effect of these two factors results in the weld metal in Comparative Examples 1-10 having lower impact toughness than that in Examples 1-10.

[0083] The test results of the above embodiments show that the submerged arc welding solid wire of the present invention meets various specification requirements for the mechanical properties of the deposited metal within a heat input range of 50~125kJ / cm, achieving good strength and plasticity while also possessing excellent low-temperature impact toughness. The impact absorption energy of the deposited metal at -40℃ is 104.8~146.2J. Therefore, the submerged arc welding solid wire of the present invention can be applied to the production of large welded structural components and the efficient high-heat-input welding manufacturing in industries such as bridges, ships, and buildings.

[0084] 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 preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A wire rod for 550MPa grade multi-wire submerged arc welding wire capable of welding at a heat input of 50~125kJ / cm, characterized in that, The chemical composition of the wire rod, by mass percentage, includes: C 0.03~0.12, Si≤0.09, Mn 1.70~1.95, P≤0.012, S≤0.005, Ni 0.05~0.5, Mo 0.20~0.38, Ti 0.13~0.24, Mg 0.001~0.005, Ca≤0.0015, Al≤0.05, N≤0.0065, B 0.0005~0.002, La≤0.015, with the balance being Fe and unavoidable impurities; The content of Si, Mn, Ni, Mo, Ti, B, and La elements in the wire rod satisfies 0.41 ≤ φ ≤ 0.

85. φ=(Ni+6Ti+4B+3Mo) / (8Si+2Mn+La); The C, Mn, Ni, Mo, and Ti content in the wire rod satisfies 560 ≤ θ ≤ 650. θ=10.8×(36.69+173.15W) C +5.22W Mn +2.35W Ni +6.37W Mo +1.15W Ti ) Among them, W C The content of C in wire rod, W Mn W represents the Mn content in the wire rod. Ni W represents the Ni content in the wire rod. Mo W represents the Mo content in wire rod. Ti This represents the Ti content in the wire rod.

2. The wire rod for 550MPa grade multi-wire submerged arc welding wire, capable of welding at a heat input of 50~125kJ / cm, as described in claim 1, is characterized in that... The five harmful elements in the wire rod are Pb+Sn+As+Sb+Bi≤0.

008.

3. The wire rod for 550MPa grade multi-wire submerged arc welding wire, capable of welding at a heat input of 50~125kJ / cm, as described in claim 1, is characterized in that... The wire rod contains three or more of the following elements: Mo, Mg, Ti, B, Ca, and La.

4. A 550MPa grade multi-wire submerged arc welding wire capable of welding at a heat input of 50~125kJ / cm, characterized in that, It is drawn from wire rod as described in any one of claims 1-3.

5. The 550MPa grade multi-wire submerged arc welding wire capable of welding at a heat input of 50~125kJ / cm as described in claim 4, characterized in that, A copper plating layer is provided on the surface of the welding wire, and the thickness of the copper plating layer is 0.18 to 0.20 micrometers.

6. The 550MPa grade multi-wire submerged arc welding wire capable of welding at a heat input of 50~125kJ / cm as described in claim 4, characterized in that, The welding wire uses a sintered flux with a basicity BⅡW higher than 1.

8. Under a heat input of 50~125kJ / cm, the inclusion size of the deposited metal is more than 80% concentrated in the range of 0.3~1.2μm, and the proportion of acicular ferrite structure is not less than 72%.

7. The 550MPa grade multi-wire submerged arc welding wire capable of welding at a heat input of 50~125kJ / cm as described in claim 4, characterized in that, When the welding wire is used with a sintered flux with a basicity BⅡW higher than 1.8 and is used for double-wire or triple-wire submerged arc welding with a heat input of 50~125kJ / cm, the deposited metal has a KV2 ≥ 85J at -40℃, a yield strength of not less than 420MPa, a tensile strength Rm greater than 550MPa, and an elongation A ≥ 21%.

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