A 500 MPa multi-wire submerged arc welding wire rod and welding wire for welding with a high heat input of 100 - 200 kJ / cm

Abstract

The present invention discloses a 500 MPa multi - wire submerged arc welding wire rod capable of welding with a high heat input of 100 - 200 kJ / cm, comprising: C: 0.03 - 0.12, Si: ≤0.09, Mn: 2.30 - 2.55, P: ≤0.012, S: ≤0.005, Ni: 1.05 - 1.65, Mo: 0.20 - 0.38, Ti: 0.11 - 0.24, Mg: ≤0.005, Ce: ≤0.05, Cr: ≤0.05, Al: ≤0.05, N: ≤0.0065, and the balance being Fe and inevitable impurities. The present invention also provides a 500 MPa multi - wire submerged arc welding wire capable of welding with a high heat input of 100 - 200 kJ / cm. The welding wire of the present invention has simple chemical composition, high deposition efficiency, excellent low - temperature toughness, and strong adaptability to the welding heat input range.

Description

Technical Field

[0001] The present invention belongs to the field of special welding materials and is applicable to submerged arc automatic welding with large heat input and multi-wire common molten pool. The deposition efficiency is more than 2 to 5 times that of conventional single-wire submerged arc automatic welding. Specifically, it relates to a multi-wire submerged arc welding wire rod and an automatic welding wire that can be used for high-efficiency and easy-to-weld bridge steels Q345 to Q370qEHW with a large heat input of 100 to 200 kJ / cm. Background Art

[0002] In recent years, with the rapid development of manufacturing industries such as shipbuilding, offshore engineering, super high-rise buildings, bridges, pipelines, and pressure vessels, the production scale of welding of large and medium-thick plate components has expanded rapidly. For the conventional medium-thick plates produced in China at present, in order to ensure the strength and toughness of the welded area, only small heat input (≤50 kJ / cm) can be used for multi-layer and multi-pass welding, resulting in very low welding production efficiency and relatively high production costs, which can no longer meet the requirements of low-cost, high-efficiency, and reduction manufacturing demanded by modern economic development. Under this background, the manufacturing industries using medium-thick steel plates have gradually started to apply the more efficient submerged arc automatic welding method with large heat input for the purpose of improving construction efficiency and reducing costs. During large heat input welding, since the high-temperature residence time of the weld metal becomes longer, it is easy to cause significant coarsening of austenite grains, and it is also easy to form abnormal structures such as side-plate ferrite, Widmanstätten structure, and upper bainite. The number of M-A islands increases and becomes coarser, resulting in serious deterioration of the strength and toughness of the weld, and it is easy to generate defects such as cracks, leading to its inability to meet the service requirements and affecting the overall safe use of the component. Therefore, the research on the production process technology of medium-thick steel plates that can adapt to large heat input welding and the development of large heat input welding materials have attracted much attention.

[0003] At present, the submerged arc welding wires supporting Q345 to Q370qE bridge steels in the bridge field, such as H08MnE or H08Mn2E, are applicable to welding heat input not greater than 40 kJ / cm, and the -40°C low-temperature impact toughness of the deposited metal is usually about 60 to 120 J. At the present stage, if steel structure manufacturing enterprises use H08MnE or H08Mn2E for large heat input welding in order to improve production efficiency, there will be a sharp decline in the toughness of the metal in the weld zone, and it is difficult to ensure the matching problem between the mechanical properties of the metal in the weld zone and large heat input welding. The reason is that as the welding heat input increases, the cooling rate in the welding zone decreases, and the weld metal structure is prone to coarsening. At present, most of the welding materials for large heat input in domestic applications in fields such as pipelines, ships, and offshore engineering are imported from abroad, with high costs. Therefore, the development of high-efficiency and excellent-performance welding materials can have the advantages of high production efficiency, green energy conservation, beautiful forming, low pollution, and easy automation, and can promote the development of the bridge steel structure industry towards high-efficiency and intelligent manufacturing.

[0004] To solve the above problems, researchers engaged in the study of special welding materials have conducted some beneficial explorations in the area of submerged arc welding automatic wires resistant to high heat input.

[0005] Chinese Patent Application for Invention CN201410728048.4 discloses a "submerged arc welding wire for high heat input" applicable to a welding heat input of 60 - 160 kJ / cm. It adds 0.01 - 0.05% of Ti to form TiN to pin the austenite grain boundaries and prevent the growth of austenite grains. On the other hand, by adding alloying elements such as Si, Mn, Ti, Al, Ce, and Mg, it promotes the formation of complex oxide inclusions of high melting point elements such as Si, Mn, Ti, Al, Ce, and Mg, and promotes the generation of acicular ferrite. However, in the examples, a relatively low value appears in the -40°C low-temperature impact at the weld center. This may be because during the high heat input welding process (greater than 50 kJ / cm), the addition amount of 0.01 - 0.05% of Ti is relatively small. Due to its strong affinity with oxygen during welding, it is severely burned out, and the content of 0.01 - 0.05% of titanium element transferred to the deposited metal or weld metal is small, resulting in insufficient grain refinement.

[0006] Chinese Patent Application for Invention CN200910046732.3 discloses a "submerged arc welding wire with moderate strength, high impact toughness, and resistance to high heat input". This invention effectively improves the low-temperature toughness, high heat input resistance performance, and has appropriate yield strength and tensile strength by optimizing the carbon content, controlling the upper limit of the silicon content, and adopting the Mn-Ni system. Since the wire of this invention does not add elements Ti and Ce for refining the high heat input weld structure, during actual high heat input welding, the grain refinement is insufficient. And relying solely on adding Ni element to refine the grains of the ferrite phase to improve toughness will inevitably increase the cost of wire smelting.

[0007] Chinese Patent Application for Invention CN92105621.4 discloses a "low-carbon microalloyed submerged arc welding wire". It adds 1.2 - 1.6% of Mn and 0.2 - 0.4% of Mo to improve the strength of the weld through solid solution strengthening; adds 0.02 - 0.08% of Ti and 0.001 - 0.008% of B to improve the toughness of the weld through a combined effect, where Ti can also combine with free N. Although this invention adds elements Ti and B, the contents of Mn and Ni are relatively low. Even though it claims to be applicable to high heat input and high-speed welding, during actual high heat input welding, it is difficult to guarantee the mechanical properties of the weld, especially the low-temperature impact toughness of the joint.

[0008] Chinese Patent Application for Invention CN01135349.X discloses a complete set of technologies of "submerged arc welded joints with high heat input, manufacturing method of the joints, and welding wires and fluxes used". The welding wire for submerged arc welding with high heat input consists of C: 0.03 - 0.10%, N: ≤0.0035%, Si: ≤0.4%, Mn: 1.0 - 2.5%, and Ti above 0.03% and satisfying Ti / N: 15 - 50. The above wire composition also contains one or more selected from Mo, Nb, B, and Ni, and the weld metal composition of the welded joint also needs to satisfy 0.6 ≤ B / N ≤ 1.2, and control the amount of grain boundary ferrite formed in the weld metal to be below 10.0% in area. The invention patent technology is complex, with high requirements and great implementation difficulties. When the inventive welding wire is welded under the condition of a high heat input of 150 kJ / cm, only the low-temperature impact values at 0°C and -20°C at the weld center are given and the values are relatively low. It is speculated that the content of Ti element added to the inventive welding wire is small and the grain refinement is insufficient.

[0009] Chinese Patent Application for Invention CN200710139338.5 discloses an "X80 pipeline steel submerged arc welding wire", adopting the Mn-Mo-Ti-B system, adding 1.5 - 1.8% of Mn to obtain strength and toughness, 0.3 - 0.4% of Mo to ensure strength and promote ferrite formation, adding 0.1 - 0.2% of Ti to ensure high toughness of the weld metal, and adding 0.004 - 0.008% of B to ensure strength and promote the improvement of toughness by the acicular ferrite microstructure of the weld. The inventive welding wire is suitable for welding X80 pipeline steel, and the quality of its weld and heat affected zone can meet the requirements of relevant standards. If this welding wire is used in high heat input welding (greater than 50 kJ / cm), 0.25 - 0.35% of Si in the welding wire by mass, plus the Si element transferred from the base metal and submerged arc flux, is likely to cause a relatively high Si content in the weld metal, which will affect the low-temperature toughness of the weld metal. And there is no Ni element with a relatively stable transition coefficient in this welding wire. Under the condition of high heat input welding, it is very difficult to ensure the mechanical properties of the weld, especially the low-temperature impact toughness of the joint.

[0010] Therefore, to improve the welding manufacturing efficiency of large steel structures in steel structure manufacturing enterprises such as bridges while meeting the requirements for the mechanical properties of welded joints in relevant standards, specifications, etc., it is necessary to develop domestic automatic submerged arc welding wires suitable for a welding heat input of 100 - 200 kJ / cm for Q345 - Q370qE grades, which is an important way to further improve welding efficiency, reduce costs, improve the mechanical properties of welded joints, and replace imported products. Summary of the Invention

[0011] The problem to be solved by the present invention is to provide a 500 MPa multi-wire submerged arc welding wire rod and welding wire that can be welded with a large heat input of 100-200 kJ / cm. The applicable heat input range is 100-200 kJ / cm, which is matched with an Fe powder-containing basic sintered flux. The yield strength Rp0.2 / MPa of the deposited metal is 463-536 MPa, the tensile strength Rm / MPa is 561-619 MPa, the elongation A / % is 22-24%, the impact absorption work Akv-40℃ / J at -40℃ is 90.4-155 J, and the weld bead is neat and beautiful after welding. The chemical composition of the submerged arc welding wire is simple, with high deposition efficiency, excellent low-temperature toughness, strong adaptability to the welding heat input range, and is suitable for the high-efficiency intelligent welding manufacturing of large steel structures in fields such as bridges, ships, and buildings.

[0012] To solve the above technical problems, the technical solution adopted by the present invention is: a 500 MPa multi-wire submerged arc welding wire rod that can be welded with a large heat input of 100-200 kJ / cm. The chemical composition of the wire rod by mass percentage includes: C: 0.03-0.12, Si: ≤0.09, Mn: 2.30-2.55, P: ≤0.012, S: ≤0.005, Ni: 1.05-1.65, Mo: 0.20-0.38, Ti: 0.11-0.24, Mg: ≤0.005, Ce: ≤0.05, Cr: ≤0.05, Al: ≤0.05, N: ≤0.0065, and the balance is Fe and unavoidable impurities; the contents of C, Si, Mn, Cr, Ni, Mo, Ti, and Ce satisfy 0.51≤γ≤0.81, 561≤θ≤618, where γ=(10Ti + 60Ce) / (Si + 2Mn); θ = 9.8×(32 + 143C + 4.80Mn + 11.90Cr + 3.42Ni + 6.64Mo + 0.96Ti).

[0013] The present invention also provides a 500 MPa multi-wire submerged arc welding wire that can be welded with a large heat input of 100-200 kJ / cm, which is made by drawing the above-mentioned wire rod.

[0014] Furthermore, using a basic sintered flux and under the welding condition of a heat input of 100-200 kJ / cm, the proportion of inclusions with a size in the range of 0.6-1.8 μm in the deposited metal of the welding wire exceeds 80%, and the content of acicular ferrite in the structure is not less than 70%.

[0015] Furthermore, using a basic sintered flux and welding under a heat input of 100-200 kJ / cm, the KV2-type notch impact energy of the deposited metal of the welding wire at an ambient temperature of -40℃ ≥ 80 J.

[0016] Furthermore, by using alkaline sintered flux and welding at a heat input of 100-200 kJ / cm, the yield strength of the deposited metal of the welding wire is 463-536 MPa, the tensile strength is 561-619 MPa, and the elongation is 22-24%.

[0017] Furthermore, a copper plating layer is provided on the surface of the welding wire, and the thickness of the copper plating layer is 0.19-0.23 um.

[0018] In the above technical scheme, the functions and mechanisms of each component are as follows:

[0019] C: Carbon is the most important element to improve the strength of low alloy steel welds. Carbon can expand the austenite phase, improve hardenability, and improve weld metal strength and hardness, but it also reduces the plasticity and toughness of the weld. Carbon is burned out during submerged arc welding, so in order to ensure appropriate strength and minimize the impact of carbon on toughness and crack resistance, the carbon content is limited to 0.03~0.12%.

[0020] Si: Silicon is a ferrite-forming element. As the silicon content increases, the ferrite content increases accordingly. The main reason is that silicon, as an important element of deoxidizer, combines with oxygen to form inclusions in the weld and becomes the nucleation point of ferrite. However, the effect of silicon on ferrite is mainly affected by manganese. When the manganese element is low, the effect of silicon on the organizational transformation is greater. At the same time, studies have shown that the addition of silicon will also cause silicon to be enriched in inclusions, increase the size of inclusions, and reduce weld toughness. Since the flux and the base material contain a high amount of Si, the Si increase phenomenon is more serious during the welding process, so the Si content in the welding wire should be controlled. In this invention, the silicon content is limited to ≤0.09%.

[0021] Mn: Manganese is an important deoxidizing and desulfurizing element, which can not only improve the strength of weld metal but also reduce the tendency of welding hot cracks. At the same time, manganese is one of the few elements that can both improve weld strength and weld toughness. Mn mainly affects weld toughness by refining grains and affecting the size of concentrated inclusions in the weld. When the manganese content in the weld metal is too high, the toughness will decrease. Under 200kJ / cm heat input, manganese burns more seriously. Considering that manganese burns more during high-line energy submerged arc welding, the manganese content in the welding wire composition is limited to 2.30~2.55%.

[0022] Mo: In the process of high heat input welding, the transition coefficient of molybdenum is relatively high. Adding an appropriate amount of Mo element to the submerged arc welding wire can effectively reduce the transformation temperature of the austenite of the weld metal during the cooling process after welding, refine the weld metal structure, and improve the strength and toughness. However, the Mo content should be controlled to avoid the increase of strength and hardness. Therefore, the Mo content in the welding wire composition is limited to 0.20~0.38%.

[0023] Ni: In this invention, Ni element is added to the submerged arc welding wire. Its main function is to improve the low-temperature toughness of the weld metal. At the same time, it also utilizes its solution strengthening effect to increase the strength of the weld metal. The mechanism by which Ni improves low-temperature toughness is to toughen the ferrite matrix and lower its brittle transition temperature. At the same time, Ni and Mn are both austenite stabilizing elements, and both can reduce the austenite phase transformation temperature by appropriate addition. However, their effects on impact toughness are not exactly the same, so they can be added simultaneously. In welding with large heat input, the low-temperature toughness of the weld metal decreases significantly, and at the same time, Ni will also have a certain amount of burn-off. Therefore, the addition amount of Ni should be increased, and the Ni content in the wire composition is limited to 1.05 - 1.65%.

[0024] Ti: In this invention, Ti element is added to the submerged arc welding wire. Its main function is that the dispersed oxides and nitrides formed by it can effectively prevent the growth of austenite grains. And when its volume content increases within an appropriate range, it can significantly promote the formation of acicular ferrite in the weld metal. At the same time, the complex oxides inclusions of Ti with Si, Mn, Al, and Mg are beneficial to the nucleation and growth of acicular ferrite, and improve the low-temperature toughness of the weld metal under large heat input. In welding with large heat input, the burn-off of Ti is relatively serious, so the addition amount of Ti should be increased. Therefore, the Ti content in the wire composition is controlled at 0.11 - 0.24%.

[0025] Al: It has a strong affinity with oxygen. The complex inclusions formed when the weld contains a small amount of Al2O3 can be used as AF nucleation particles to effectively refine the weld structure. At the same time, the oxygen affinity of Al is greater than that of Ti. Therefore, when the Al content is too high, it will also affect the formation and distribution of Ti oxides, form large-sized Al2O3 in the weld, and reduce the impact toughness. Therefore, in terms of weld toughness, the Al content should be as low as possible. Therefore, the Al content in the wire composition is ≤0.05%.

[0026] Mg: It is a strong deoxidizer, which reduces the oxygen content in the weld through deoxidation reactions. The complex inclusion Ti-Mg-O containing Mg can pin the austenite grain boundaries, inhibit grain growth, refine grains, and improve toughness. In addition, the boiling points of Al and Mg are relatively low, which are likely to cause process problems such as unstable arc and spatter. Therefore, the Mg content in the wire composition is ≤0.005%.

[0027] Ce: Adding Ce to the welding wire mainly has three functions. First, it improves the composition of inclusions, forming inclusions rich in Ce, S, O, and Al elements with a low misfit with acicular ferrite, which become the nucleation sites of acicular ferrite, increasing the content of acicular ferrite. Second, it refines the size of inclusions. During the oxide metallurgy process in the molten pool reaction, the Ce-rich oxides combine with larger inclusions to form large inclusions, which float up and are discharged from the molten pool, thereby refining the inclusion size, reducing the possibility of larger-diameter inclusions becoming crack sources, and improving toughness. Another study shows that when the inclusion size in the weld metal is 0.6 - 1.8 μm, the probability of becoming the nucleation site of acicular ferrite can reach 80%, further refining the weld structure and improving toughness. In the present invention, the Ce content is controlled at Ce ≤ 0.05%.

[0028] S and P: They have a harmful effect on the toughness of the weld metal. Excessive content is likely to cause cracks in the weld, and their content should be reduced as much as possible, especially for the P element. Because during the submerged arc welding process, the use of the welding flux will increase the P element content in the weld metal. It is required that the content of the S element does not exceed 0.005% and the content of the P element does not exceed 0.012%.

[0029] In actual production, the strengthening of metal materials is often done by trying to prevent the movement of dislocations in defective metal crystals to improve strength. The specific strengthening and toughening methods include solid solution strengthening, dislocation strengthening, precipitation and dispersion strengthening, and grain boundary strengthening. In the weld metal, the content of Mn, Si, Ni and Mo that cause solid solution strengthening is relatively high, and the carbides or nitrides formed by trace elements such as Ti and B in the weld can also play a certain precipitation strengthening role in dislocation pinning. However, the increase in strength is particularly significant in solid solution strengthening and fine grain strengthening, which leads to body strengthening due to the atomic size effect, elastic modulus effect and solid solution ordering. At the same time, during the high heat input welding process, the content of each alloy element transitioning to the weld metal also changes greatly, which is related to the oxidation and burning of the alloy elements during the welding heat process. According to welding metallurgy theory, at 1600℃, the order of oxygen affinity of each element from small to large is: Cu, Ni, Co, Fe, W, Mo, Cr, Mn, V, Si, Ti, Zr, Al. Since the concentration of Fe is the highest in the welding zone, some Fe must be oxidized; Ni is an element located to the left of Fe and has a lower affinity with oxygen, so the oxidation loss is very small. Although Mo is located to the right of Fe, its affinity with oxygen is close to that of Fe, and its concentration in the molten droplet and the molten pool metal is lower, so the oxidation burnout is less and the transition coefficient is larger; although the concentrations of Mn, Si, and Ti are not high, their affinity with oxygen is very large, so the oxidation burnout is more serious. In addition, since Ti is very active, it will also react with nitrogen in the arc atmosphere to form TiN, etc., which will further reduce its alloy transition coefficient. Therefore, in high heat input welding, it is necessary to consider both the effect of alloy elements on the strengthening and toughening of weld metal and the element burnout caused by high heat input welding. Therefore, combining the transition margin of each alloy element after high heat input welding burnout with the strength increment caused by chemical composition, its contribution to the strength and toughness of weld metal can be expressed by the following formula θ:

[0030]

[0031] In the formula, K i is the product of the strengthening coefficient and transition coefficient of element i (MPa / wt%); C iis the weight percentage concentration of element i dissolved in ferrite. θ = 9.8×(32 + 143C + 4.80Mn + 11.90Cr + 3.42Ni + 6.64Mo + 0.96Ti), where the contents of C, Mn, Cr, Ni, Mo, and Ti must satisfy 563 ≤ θ ≤ 619. The research and development of the welding wire pays more attention to the problem of matching the strength and toughness of the welded test plate. Generally, a large amount of alloying elements or Si and Mn elements are added to the weld metal to improve the strength through solid solution strengthening, precipitation strengthening, grain refinement strengthening, precipitation strengthening, etc., but the toughness of the weld metal decreases to a certain extent, especially under the condition of high heat input, which is particularly prominent. The strength and toughness of the weld often show a negative correlation. Therefore, for steel plates with a tensile strength higher than 500 MPa grade, this welding wire puts forward strength range requirements for the deposited metal of the welding consumables. If it is lower than this range, the tensile strength of the welded joint cannot be guaranteed, and the crack resistance performance of the weld metal cannot be exerted; if it exceeds this range, it will form a super-strong match with the welded test plate, resulting in problems such as waste of alloying elements and damage to toughness to a certain extent.

[0032] It is generally believed that the mechanical properties of materials, whether strength or toughness, largely depend on the microstructure. Acicular ferrite in the low-alloy steel weld microstructure, as a kind of ferrite, is considered by many materials scholars to be a microstructure that can improve the low-temperature toughness of materials due to its characteristics of fine grains and large-angle grain boundaries. Under the condition of high heat input welding, the weld metal stays at high temperature for a long time, and it is easy to form coarse grain boundary ferrite and coarse blocky ferrite at the austenite grain boundaries, consuming the low-temperature toughness of the weld. To ensure the low-temperature toughness of the weld metal, the wire rod and welding wire of the present invention, when paired with the supporting Fe powder-MgO-SiO2-CaF2-Al2O3 series basic sintered flux, can be used for the high-efficiency welding of Q345~Q370qE grade steel plates under a welding heat input of 100~200 kJ / cm. Si, Mn, Ce, and Ti elements are added to the submerged arc welding wire to improve the welding metallurgical quality, obtaining fine complex inclusions rich in Si, Mn, Ce, Ti, and O elements. To increase the proportion of effective inclusions and thus increase the acicular ferrite content to ensure toughness, the Si, Mn, Ti, and Ce component ratios are adjusted so that their contents satisfy the relational expression 0.51 ≤ γ ≤ 0.81, where γ = (10Ti + 60Ce) / (Si + 2Mn). If it is lower than this range, the proportion and quantity of inclusions with a size between 0.6 μm and 1.8 μm both decrease, resulting in a significant decrease in the number of nucleation sites of acicular ferrite; if it exceeds this range, a large number of inclusions with a size above 1.8 μm will appear in the weld, increasing the crack sensitivity and reducing the crack initiation work.

[0033] The manufacturing technology of the welding wire of the present invention is the same as the prior art. The alloy components of the welding wire of the present invention are smelted to form an ingot, which is then forged, rolled into wire rods, drawn into welding wires of corresponding sizes, and then copper-plated and polished. The thickness of the copper-plated layer is 0.19 - 0.23 μm, and finally it is wound into rolls and packaged into finished products.

[0034] The beneficial effects of the present invention are as follows:

[0035] (1) For the weld metal obtained with the welding wire of the present invention under a heat input of 100 - 200 kJ / cm, the microstructure in the as-used state is a small amount of blocky ferrite at the austenite grain boundaries and fine acicular ferrite inside the grains. The matrix of the structure has dispersed sub-micron-sized composite oxide inclusions such as Si, Mn, Ti, and Ce, and more than 80% of them are in the size range of 0.6 - 1.8 μm. There are also manganese sulfide compounds. The probability of fine inclusions becoming the nucleation sites of acicular ferrite increases, so that the proportion of intragranular acicular ferrite under the condition of high heat input welding reaches more than 70% by area percentage. The acicular ferrite structure is very fine, and the ferrite laths grow radially, and the boundaries between the laths are large-angle grain boundaries, which has strong crack propagation resistance and can significantly improve the low-temperature toughness of the weld metal;

[0036] (2) The welding wire of the present invention is applicable to high heat input multi-wire common molten pool submerged arc automatic welding. The deposition efficiency is more than 2 - 5 times that of the conventional single-wire submerged arc automatic welding, and the range of welding parameter adjustment is wide. Under the heat input of 100 - 200 kJ / cm, the welding process performance is stable, the fluidity of the molten pool is good, the shape of the deposited metal is beautiful, and the crack resistance performance is excellent;

[0037] (3) The deposited metal of the welding wire of the present invention under the heat input of 100 - 200 kJ / cm has the following mechanical properties: yield strength Rp0.2 / MPa: 463 - 536 MPa, tensile strength Rm / MPa: 561 - 619 MPa, elongation A / %: 22 - 24%, impact absorption energy Akv-40°C / J at -40°C: 90.4 - 155 J;

[0038] (4) The alloy system of the welding wire of the present invention is reasonably regulated. The smelting, rolling of the wire rods and the drawing process of the welding wire are easy to implement, the quality is stable, and it is suitable for large-scale popularization and application.

[0039] The present invention will be described in detail below with reference to the accompanying drawings. Description of the Drawings

[0040] Figure 1a is the microscopic structure of the deposited metal in Example 1;

[0041] Figure 1b is the microscopic structure of the deposited metal in Example 7;

[0042] Figure 2a Microstructure of the deposited metal of Comparative Example 1;

[0043] Figure 2b Microstructure of the deposited metal of Comparative Example 7;

[0044] Figure 3 SEM electron microscope observation of inclusions in the deposited metal of Example 1;

[0045] Figure 4 EDS energy spectrum analysis diagram of inclusions in Example 1;

[0046] Figure 5a Metallographic diagram of inclusions in the deposited metal of Comparative Example 1;

[0047] Figure 5b Metallographic diagram of inclusions in the deposited metal of Example 1. Detailed implementation manners

[0048] The present invention provides a 500 MPa multi-wire submerged arc welding wire rod that can be welded with a high heat input of 100 - 200 kJ / cm. The chemical composition of the wire rod by mass percentage includes: C: 0.03 - 0.12, Si: ≤0.09, Mn: 2.30 - 2.55, P: ≤0.012, S: ≤0.005, Ni: 1.05 - 1.65, Mo: 0.20 - 0.38, Ti: 0.11 - 0.24, Mg: ≤0.005, Ce: ≤0.05, Cr: ≤0.05, Al: ≤0.05, N: ≤0.0065, and the balance is Fe and unavoidable impurities.

[0049] The contents of C, Si, Mn, Cr, Ni, Mo, Ti, Ce must meet 0.51 ≤ γ ≤ 0.81, 561 ≤ θ ≤ 618.

[0050] Wherein, γ = (10Ti + 60Ce) / (Si + 2Mn), θ = 9.8×(32 + 143C + 4.80Mn + 11.90Cr + 3.42Ni + 6.64Mo + 0.96Ti).

[0051] The present invention also provides a 500 MPa multi-wire submerged arc welding wire that can be welded with a high heat input of 100 - 200 kJ / cm, which is made by drawing the above-mentioned wire rod.

[0052] The present invention will be elaborated in detail below in combination with specific embodiments.

[0053] In the submerged arc welding solid wire of this embodiment, the chemical composition ratio examples are shown in Table 1, Table 3 and Table 5. According to the accurately calculated wire composition ratio, raw materials with low P, S, gas and inclusion contents are selected, and the addition amount of the alloy is calculated. Matching with alkaline (B ⅡWThe sintered flux (≥2.0) is suitable for multi-wire submerged arc welding. Among them, the welding heat input of 100 - 150 kJ / cm is suitable for double-wire and triple-wire automatic submerged arc welding, and the welding heat input of 150 - 200 kJ / cm is suitable for quadruple-wire automatic submerged arc welding.

[0054] The steel for the welding wire is smelted in a 75 kg vacuum induction furnace. After charging, melting, and refining, and with qualified composition, it is cast into an ingot. After the ingot is forged into a square billet, it is hot-rolled into a 6.5 mm wire rod. The wire rod is drawn through one rough drawing and two fine drawings to make a 5.0 mm solid submerged arc welding wire rod with a smooth and flat surface. Further, the surface of the welding wire is copper-plated by the method of electroless copper plating, and the copper plating thickness is controlled at 0.19 - 0.23 μm.

[0055] Table 1 Chemical composition ratios (mass percentages) of the submerged arc welding wires in Examples 1 - 3 and Comparative Examples 1 - 3 of the present invention (the balance is Fe)

[0056] 。

[0057] Using the above six welding wires (Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2, Comparative Example 3), a single-wire deposited metal test is carried out according to the welding process parameters in Table 2 below. The welding heat input is 100 kJ / cm, and a specially formulated basic sintered flux of the Fe powder - MgO - SiO2 - CaF2 - Al2O3 system is selected for welding, and the interpass temperature is controlled not to exceed 160°C.

[0058] Table 2 Groove form of the deposited metal test

[0059] 。

[0060] Table 3 Chemical composition ratios (mass percentages) of the submerged arc welding wires in Examples 4 - 6 and Comparative Examples 4 - 6 of the present invention (the balance is Fe)

[0061] 。

[0062] Using the above five welding wires (Example 4, Example 5, Example 6, Comparative Example 4, Comparative Example 5, Comparative Example 6), a triple-wire deposited metal test is carried out according to the groove form in Table 2 below. The welding heat input is 150 kJ / cm, and a specially formulated basic sintered flux of the Fe powder - MgO - SiO2 - CaF2 - Al2O3 system is selected for welding, and the interpass temperature is controlled not to exceed 160°C.

[0063] Table 4 Groove form of the deposited metal test

[0064] 。

[0065] Table 5 Chemical Composition Ratios (mass percentages) of Submerged Arc Welding Wires in Examples 7 - 9 and Comparative Examples 7 - 9 of the Present Invention (the balance is Fe)

[0066] 。

[0067] Using the above five kinds of welding wires (Example 7, Example 8, Example 9, Comparative Example 7, Comparative Example 8, Comparative Example 9), four - wire deposited metal tests were carried out according to the groove form in Table 6 below. The welding heat input was 200 kJ / cm, and a specially - prepared basic sintered flux of Fe powder - MgO - SiO2 - CaF2 - Al2O3 system was selected for welding. The interlayer temperature was controlled not to be greater than 160 °C.

[0068] Table 6 Groove Forms for Deposited Metal Tests

[0069] 。

[0070] After the specimens were welded, visual inspection was carried out. Non - destructive testing of the deposited metal was carried out using ultrasonic flaw detection technology. After passing the inspection, samples were taken from the welded deposited metal. The specimen size and test method were carried out in accordance with the provisions of GB / T 228. The impact specimens were intercepted from the center of the deposited metal. The longitudinal axis of the impact specimen was perpendicular to the length direction of the deposited metal, the notch surface was perpendicular to the surface of the deposited metal, and the notch axis was located at the center of the deposited metal. The specimen size was 10×10×55 mm, and the impact test method was carried out in accordance with the provisions of GB / T 229. The results of the tensile test and impact test of the deposited metal are shown in Table 7, and the values in brackets in the table are the averages.

[0071] Table 7 Mechanical Properties of Deposited Metals of Welding Wires in Examples and Comparative Examples

[0072] 。

[0073] The chemical compositions of Examples 1 - 10 meet the requirements of the invention. The specific chemical compositions are shown in Table 1, Table 3, and Table 5. When θ satisfies 561 ≤ θ ≤ 619, the tensile strength of the deposited metal is between 561 - 619 Mpa, meeting the strength requirements of the invention. When γ satisfies 0.51 ≤ γ ≤ 0.81, the impact absorption energy Akv of the deposited metal at - 40 °C is not less than 80 J. However, the chemical compositions of Comparative Examples 1 - 10 do not meet the requirements of the invention. The strength of the deposited metal is either too high or too low and does not meet the standard, nor can it guarantee the low - temperature impact toughness of the deposited metal.

[0074] Taking metallographic specimens from the impact specimens of the deposited metal, it was found that the deposited metal structures of Examples 1 - 10 were mainly composed of acicular ferrite, with a small amount of grain - boundary ferrite and granular bainite, such as Figure 1a 、 Figure 1b, and the content of acicular ferrite was counted as shown in Table 8, and the proportion of acicular ferrite was not less than 70%. The microstructure of the deposited metal in Comparative Examples 1-10 was mainly composed of massive ferrite, a small amount of acicular ferrite and granular bainite, such as Figure 2a , Figure 2b . Acicular ferrite has fine grains and large-angle grain boundaries, which can hinder the propagation of cracks and improve the impact toughness. EDSD observation was carried out on the weld metals of the examples and comparative examples, and the statistical results are as Figure 3 , and the proportion of large-angle grains in Example 1 and Example 7 increased significantly.

[0075] Table 8 Statistical results of the proportion of acicular ferrite in examples and comparative examples

[0076] .

[0077] To analyze the reason for the increase in the proportion of acicular ferrite, SEM electron microscopy observation and EDS testing were carried out on the metallographic specimens of Example 1, as Figure 3 , Figure 4 . It was found that the inclusions in the deposited metal of Example 1 were mainly complex inclusions enriched with Ce, Ti, Mn, and O elements, which became the nucleation sites of acicular ferrite. It was also found that the probability of inclusions with a size of 0.6-1.8 μm becoming nucleation sites increased. The sizes of inclusions in the examples and comparative examples were counted, as Figure 5a , Figure 5b , and the results are shown in Table 9.

[0078] Table 9 Statistical results of the proportion of effective inclusions in the deposited metal of examples and comparative examples

[0079] .

[0080] From the inspection results of the above examples, it can be seen that the submerged arc solid cored wire of the present invention has the mechanical properties of the deposited metal meeting the specification requirements within the range of heat input of 100-200 kJ / cm. That is, while obtaining good strength and plasticity, it also has excellent low-temperature impact toughness. The impact absorption work Akv of the weld metal at -40 °C is 90.4-155 J. It can be applied to the production and efficient welding manufacturing of large welded structural parts in industries such as bridges, ships and buildings.

[0081] Finally, it should be noted that the above examples 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 preferred examples, those of ordinary skill in the art should understand that: still can modify the specific implementation manners of the present invention or perform equivalent replacements for some technical features; without departing from the spirit of the technical solutions of the present invention, they should all be covered within the scope of the technical solutions claimed by the present invention.

Claims

1. A 500 MPa multi - wire submerged arc welding wire rod capable of welding with a high heat input of 100 - 200 kJ / cm, characterized in that, The chemical composition of the wire rod by mass percentage includes: C: 0.03 - 0.12, Si: ≤0.09, Mn: 2.30 - 2.55, P: ≤0.012, S: ≤0.005, Ni: 1.05 - 1.65, Mo: 0.20 - 0.38, Ti: 0.11 - 0.24, Mg: ≤0.005, Ce: ≤0.05, Cr: ≤0.05, Al: ≤0.05, N: ≤0.0065, and the balance is Fe and unavoidable impurities; The contents of C, Si, Mn, Cr, Ni, Mo, Ti, and Ce satisfy 0.51 ≤ γ ≤ 0.81, 561 ≤ θ ≤ 618, where, γ = (10Ti + 60Ce) / (Si + 2Mn); θ = 9.8×(32 + 143C + 4.80Mn + 11.90Cr + 3.42Ni + 6.64Mo + 0.96Ti).

2. A 500 MPa multi-wire submerged arc welding wire capable of welding with a high heat input of 100 - 200 kJ / cm, characterized in that, It is made by drawing the wire rod as described in claim 1.

3. The 500 MPa multi-wire submerged arc welding wire capable of welding with a high heat input of 100 - 200 kJ / cm, as claimed in claim 2, is characterized in that, Using basic sintered flux and under the welding condition of heat input of 100 - 200 kJ / cm, the proportion of inclusions with a size in the range of 0.6 - 1.8 μm in the deposited metal of the welding wire exceeds 80%, and the content of acicular ferrite in the microstructure is not less than 70%.

4. The 500 MPa multi - wire submerged arc welding wire capable of welding with a high heat input of 100 - 200 kJ / cm is characterized in that, Using basic sintered flux and welding under the heat input of 100 - 200 kJ / cm, the KV2 - type notch impact energy of the deposited metal of the welding wire at an ambient temperature of - 40°C ≥ 80 J.

5. The 500 MPa multi-wire submerged arc welding wire capable of welding with a high heat input of 100 - 200 kJ / cm, as claimed in claim 2, wherein Using basic sintered flux and welding under the heat input of 100 - 200 kJ / cm, the yield strength of the deposited metal of the welding wire is 463 - 536 MPa, the tensile strength is 561 - 619 MPa, and the elongation is 22 - 24%.

6. The 500 MPa multi-wire submerged arc welding wire capable of welding with a high heat input of 100 - 200 kJ / cm according to any one of claims 2 - 5, 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 0.19 - 0.23 μm.

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