Wire rod for low-carbon Si-Mn series gas shielded welding wire and production method

Abstract

The invention relates to a wire rod for a low-carbon Si-Mn series gas shielded welding wire and a production method. The wire rod comprises the following chemical components: 0.06%-0.10% of C, 0.70%-0.90% of Si, 1.80%-2.00% of Mn, less than or equal to 0.020% of P, less than or equal to 0.013% of S, less than or equal to 0.20% of Ni, less than or equal to 0.20% of Cr, less than or equal to 0.20% of Cu, less than or equal to 0.10% of Mo, less than or equal to 0.020% of V, less than or equal to 0.010% of Al, less than or equal to 0.0015% of Ca, less than or equal to 0.0020% of O, less than or equal to 0.0040% of N and the balance of Fe and impurities. By optimizing the technological parameters of the whole process of converter-LF refining-continuous casting-controlled rolling and controlled cooling, key technical links such as component design, rolling temperature, gradient cooling and surface quality control are emphatically broken through, the comprehensive goals of low surface defect, fine and uniform structure and low harm of inclusions of the wire rod are achieved, and the drawing performance of the welding wire and the welding metallurgy quality are improved.

Description

Technical Field

[0001] This invention relates to the field of wire rod production technology, and in particular to a low-carbon Si-Mn series gas shielded welding wire wire rod and its production method. Background Technology

[0002] As a core material in the modern welding industry, the quality of gas-shielded welding wire directly determines the final welding wire's process performance, mechanical properties, and the reliability of the welded joint. Low-carbon Si-Mn alloy systems have become the preferred material in the welding of carbon steel and low-alloy steels due to their excellent strength-toughness ratio, good deoxidation effect, and cost controllability. However, with the development of industries such as shipbuilding, bridge engineering, and pressure vessels, and the continuous improvement in requirements for welding efficiency, green manufacturing, and weld quality, the production of traditional Si-Mn welding wire rods faces a series of severe challenges.

[0003] First, surface quality defects in wire rod are a key factor restricting the yield of welding wire. Wire rod produced using conventional high-speed continuous casting processes (such as ER70S-6 type wire rod) is prone to surface microcracks and peeling defects during hot rolling due to iron oxide scale indentation, scratches, or residual vibration marks. These defects further expand during subsequent drawing and diameter reduction (usually requiring multiple drawing processes to ø0.8~ø1.2mm), leading to increased wire breakage rate, decreased copper plating adhesion, and ultimately affecting arc stability and wire feeding smoothness during welding. Studies have shown that surface defects in welding wire can increase the spatter rate of CO2 gas shielded welding by more than 15% and significantly reduce the impact toughness of the weld metal.

[0004] Secondly, the uniformity of the microstructure and the level of inclusion control of the wire rod directly determine its welding metallurgical performance. Si-Mn welding wire requires the combined deoxidation of Si and Mn elements to form silicate inclusions, but the Al2O3 clusters remaining from traditional aluminum deoxidation processes can easily lead to problems such as arc drift and uneven penetration. In addition, if the wire rod rolling and cooling process is improper, proeutectoid ferrite will precipitate along the austenite grain boundaries, which will lead to deterioration of pull-out plasticity; while banded structures may cause weld composition segregation and reduce low-temperature impact toughness. Although the current national standard GB / T3429-2015 "Steel Wire Rods for Welding" specifies the chemical composition, tensile strength, and non-metallic inclusion grades of wire rods for welding wire, it has not yet put forward quantitative requirements for microstructure refinement and banded structure levels.

[0005] Furthermore, the low-carbon and environmentally friendly production process for low-carbon welding wire rod has not yet been systematized. In the traditional production process, the energy-intensive billet reheating process (heating temperature exceeding 1150℃) not only causes significant carbon emissions but also leads to grain coarsening, requiring subsequent controlled rolling and cooling to compensate, increasing the difficulty of process control. In recent years, scholars have attempted to reduce energy consumption using technologies such as direct rolling and low-temperature rolling, but a mature solution is still lacking in how to balance deformation resistance and final microstructure refinement during low-temperature rolling. Meanwhile, to reduce pickling pollution, acid-free peeling technology has begun to be applied to wire rod pretreatment, but its adaptability to surface oxide scale structures is extremely high.

[0006] Currently, advanced enterprises have adopted the integrated technology of ultra-high speed continuous casting and headless rolling to produce welding wire rods. Their products have advantages in terms of purity and dimensional accuracy. However, the investment in core technology equipment is huge, and the dedicated process database for low-carbon Si-Mn series wire rods is not yet complete.

[0007] Therefore, there is an urgent need to develop a production process for Si-Mn series gas-shielded welding wire rods that integrates low carbon emissions, zero surface defects, uniform microstructure, and precise control of inclusions, in order to break through the current technical bottlenecks and meet the urgent need for the localization of high-end welding materials. Summary of the Invention

[0008] This invention provides a low-carbon Si-Mn gas-shielded welding wire rod and its production method, overcoming the problems of high surface defect rate, poor microstructure uniformity, high energy consumption, and heavy pollution in the existing production of Si-Mn gas-shielded welding wire rod. By optimizing the process parameters of the entire process from converter to LF refining to continuous casting to controlled rolling and cooling, and by making key breakthroughs in key technical aspects such as composition design, rolling temperature, gradient cooling, and surface quality control, the invention achieves the comprehensive goal of low surface defects, fine and uniform microstructure, and low harm of inclusions in the wire rod, thereby improving the drawing performance of the welding wire and promoting the upgrading of welding material manufacturing towards green, efficient, and high-stability directions.

[0009] To achieve the above objectives, the present invention employs the following technical solution: A low-carbon Si-Mn gas-shielded welding wire rod has the following chemical composition by mass percentage: C: 0.06%–0.10%, Si: 0.70%–0.90%, Mn: 1.80%–2.00%, P≤0.020%, S≤0.013%, Ni≤0.20%, Cr≤0.20%, Cu≤0.20%, Mo≤0.10%, V≤0.020%, Al≤0.010%, Ca≤0.0015%, O≤0.0020%, N≤0.0040%, with the remainder being Fe and unavoidable impurity elements, and the total amount of impurity elements ≤0.50%.

[0010] The metallographic structure of the wire rod consists of pearlite and ferrite, with pearlite accounting for 7% to 9% and ferrite accounting for 91% to 93% by volume percentage; the grain size is ≥8.5.

[0011] The wire rod has a tensile strength ≤530MPa, an elongation after fracture ≥27%, and a reduction of area ≥75%.

[0012] Non-metallic inclusions in wire rod: Class A + Class C ≤ 2.0; Class B + Class D ≤ 1.0.

[0013] Non-metallic inclusions are classified as follows: Class A ≤ 1.0, Class B ≤ 0.5, Class C ≤ 1.0, Class D ≤ 0.5, and Class DS ≤ 0.5.

[0014] A method for producing low-carbon Si-Mn based gas-shielded welding wire rod includes the following steps: 1) Hot metal pretreatment: Desulfurizing agent is injected into the hot metal ladle to ensure that the sulfur content in the hot metal is ≤0.030% by mass; 2) Converter smelting: A top-and-bottom blowing converter is used for smelting. The purity of the top-blown oxygen is >99.5%, and the oxygen pressure is 1.0~1.35MPa. Argon is supplied for the bottom blowing, and the argon pressure is 1.0~1.35MPa. The tapping temperature is 1605~1645℃. Slag is strictly prohibited during tapping, and spot blowing should be avoided. 3) Steel ladle alloying: Alloying treatment is carried out during the tapping process, with the addition of auxiliary materials such as active lime and dolomite, and silicon-manganese alloy; argon blowing time ≥5min, and the temperature of molten steel after treatment is 1510~1550℃; 4) LF furnace refining: The overall smelting cycle is ≤60min, the energizing time is ≤30min, the furnace is kept under a slight positive pressure of 45~65kPa, and the arc light is kept invisible during submerged arc heating; white slag refining is used, with 6.3~7.8kg / t steel of active lime and 1.5~2.0kg / t steel of fluorite added; during alloy adjustment, 1.3~1.5kg / t steel of manganese silicon and 1.35~1.92kg / t steel of ferrosilicon are added; the soft blowing time is ≥12.5min; the LF furnace temperature at the station is 1570~1600℃. 5) Continuous casting: Protective casting is adopted in the continuous casting process, and electromagnetic stirring is used. The electromagnetic stirring current at the crystallizer is 240-260A and the frequency is 4-6Hz. The electromagnetic stirring current at the end of solidification is 300-360A and the frequency is 7-10Hz. Low-carbon or carbon-free covering agent is used in the tundish, and calcium wire is prohibited. Low-carbon protective slag for billets is used in the crystallizer. The platform ladle temperature is 1565-1575℃, the tundish temperature is 1530℃-1550℃, the superheat is ≤35℃, and the constant casting speed is 2.1-2.5m / min. After the billet leaves the line, it is placed in the heat preservation pit for slow cooling for more than 50 hours. 6) Heating: A walking beam furnace is used for heating. The preheating section temperature is 830-930℃, the heating section temperature is 1070-1130℃, the soaking section temperature is 1100-1140℃, and the heating time is 1.5-3 hours. 7) Rolling: Roughing temperature 980~1040℃; Finishing inlet temperature 850~910℃; Wire drawing temperature 880~920℃; Air-cooled roller conveyor head speed 0.09~0.12m / s; Roller speed increase 0~5%, all insulation covers closed; 8) Insulation: After rolling, the material is placed in a closed insulation channel for insulation treatment, and the temperature inside the insulation channel is ≥60℃.

[0015] In step 1), the desulfurizing agent consists of 85% to 95% lime powder and 5% to 15% fluorite powder by mass percentage.

[0016] In step 2), the scrap steel accounts for 10% to 15% of the weight in the converter smelting, with the remainder being molten iron; the amount of slag steel in the scrap steel is ≤4.5 tons, and the use of desulfurized slag steel and nickel-copper-containing scrap steel is prohibited.

[0017] In step 3), low-aluminum ferrosilicon and low-carbon ferromanganese are used for alloying; the amount of active lime added in the auxiliary materials is 27.5-28 kg / t steel, the amount of dolomite added is 10.5-11 kg / t steel, and the amount of silicon-manganese alloy added is 26.2-26.6 kg / t steel.

[0018] In step 5), the tundish is purged with argon gas before casting for ≥3 min; the central porosity of the billet is ≤0.5 grade; the central segregation is ≤1.0 grade; the shrinkage cavity is ≤1.0 grade; the corner crack is ≤1.0 grade; the subcutaneous crack is ≤1.0 grade; the intermediate crack is ≤0.5 grade; the central crack is ≤0.5 grade; and the subcutaneous bubble is ≤1.0 grade.

[0019] Compared with the prior art, the beneficial effects of the present invention are: 1. The synergistic design of low carbon and high manganese achieves the best balance between strength, toughness and processability, which is also the key to achieving the matching of strength and toughness of welding wire.

[0020] Low carbon content (C: 0.06%~0.10%) is adopted; the extremely low carbon content fundamentally ensures the excellent welding processability of the welding wire; it can significantly reduce welding spatter, avoid porosity and cracks in the weld, and at the same time provide excellent low-temperature impact toughness for the weld metal. A high-manganese alloy (Mn: 1.80%–2.00%) is used as the core alloying element. The high manganese content combined with low carbon effectively compensates for the strength loss caused by carbon reduction through solid solution strengthening. At the same time, manganese and silicon work together to deoxidize and desulfurize, fixing the sulfur in the weld to MnS, thereby refining the sulfide morphology and significantly improving the weld's resistance to hot cracking.

[0021] 2. By precisely controlling the silicon element, both deoxidation and metallurgical stability are taken into account.

[0022] Precise control of the silicon content (Si: 0.70%–0.90%) is crucial. Silicon is a strong deoxidizer, and this composition range ensures sufficient deoxidation of the molten steel, inhibiting the formation of CO porosity during welding. Simultaneously, silicon, as an important alloying element, can dissolve in ferrite, providing stable strengthening to the weld metal without excessively compromising toughness. This invention precisely controls the Si content within the optimal window, avoiding the decrease in weld metal ductility and toughness and the increase in silicate inclusions caused by excessive silicon content.

[0023] 3. By synergistically controlling extreme purification and harmful elements, metallurgical quality and service safety are ensured.

[0024] The use of low sulfur and phosphorus levels and control of impurity elements (P≤0.020%, S≤0.013%, total impurity elements≤0.50%) is a core measure to improve the purity of weld metal and prevent crystallization cracks and low-temperature embrittlement.

[0025] Extreme control is exercised over residual and gaseous elements. Upper limits are set for the content of residual elements such as Ni, Cr, Cu, and Mo to prevent the uncontrolled accumulation of residual elements from negatively impacting welding performance. In particular, the Al content (≤0.010%) is strictly controlled to avoid the formation of high-melting-point Al₂O₃ inclusions, which can degrade arc stability, clog welding nozzles, and become crack initiation sites in the weld. Simultaneously, an extremely low Ca content (≤0.0015%) is used to prevent the formation of hard calcium aluminate inclusions, thereby ensuring smooth wire feeding and improving weld fatigue performance.

[0026] 4. Optimize ingredients for specific application scenarios.

[0027] The composition design of the wire rod described in this invention is particularly suitable for gas shielded welding scenarios with high requirements for toughness and crack resistance (such as welding of marine steel and high-strength steel structures). It does not rely on expensive microalloying elements (such as V and Nb), but achieves a perfect balance between performance and cost through an economical and efficient alloying path of "low carbon-high manganese-high silicon" combined with the metallurgical concept of extreme purity. This ensures that the welding wire can still obtain high-quality welds with beautiful shape, internal purity, uniform mechanical properties and reliability under harsh welding conditions. Attached Figure Description

[0028] Figure 1 This is a typical metallographic photograph of the low-carbon Si-Mn gas shielded welding wire rod described in this invention (microscope scale bar is 100μm, and the microscope scale bar of the magnified part is 20μm). Detailed Implementation

[0029] The present invention discloses a low-carbon Si-Mn gas-shielded welding wire rod. The chemical composition of the wire rod, by mass percentage, is as follows: C: 0.06%–0.10%, Si: 0.70%–0.90%, Mn: 1.80%–2.00%, P≤0.020%, S≤0.013%, Ni≤0.20%, Cr≤0.20%, Cu≤0.20%, Mo≤0.10%, V≤0.020%, Al≤0.010%, Ca≤0.0015%, O≤0.0020%, N≤0.0040%, with the remainder being Fe and unavoidable impurity elements, and the total amount of impurity elements ≤0.50%.

[0030] The rationale and technical advantages of the composition design of the low-carbon Si-Mn gas-shielded welding wire rod described in this invention are mainly reflected in the following aspects: 1. Synergistic Innovative Design of Low Carbon and High Manganese: This invention strictly controls the carbon content within an extremely low range of 0.06% to 0.10%, while simultaneously setting the manganese content at a high level of 1.80% to 2.00%. This unique "low carbon, high manganese" matching effectively overcomes the technical challenges of large spatter, porosity, and high crack sensitivity caused by high carbon content, ensuring excellent welding process stability and superior low-temperature toughness. At the same time, the solid solution strengthening effect of high manganese precisely compensates for the strength loss caused by carbon reduction, achieving the optimal balance between high strength and high toughness in the weld metal.

[0031] 2. Precise deoxidation and alloying design of silicon element: The present invention precisely limits the silicon content to the range of 0.70% to 0.90%. This composition range can ensure that the molten steel is fully deoxidized and effectively inhibit the formation of CO porosity in welding. It can also be used as an alloying element to achieve stable solid solution strengthening of weld metal. At the same time, it avoids the problems of plasticity and toughness deterioration and the increase of harmful silicate inclusions caused by excessive silicon content.

[0032] 3. Synergistic Control of Extreme Purity and Key Impurity Elements: This invention implements extremely strict control over harmful and impurity elements, particularly limiting the content of aluminum (Al≤0.010%) and calcium (Ca≤0.0015%). The innovation of this design lies in the fact that ultra-low aluminum control fundamentally avoids the formation of high-melting-point Al2O3 inclusions, thereby significantly improving arc stability, effectively preventing nozzle clogging, and eliminating weld crack initiation points. Ultra-low calcium control effectively avoids the formation of hard calcium aluminate inclusions, ensuring extremely smooth wire feeding and improving weld fatigue performance. Combined with strict control over sulfur, phosphorus, and other residual elements, this invention significantly improves the metallurgical purity of the welding wire, providing a fundamental guarantee for the stable and reliable overall performance of the weld.

[0033] In summary, this invention, through the composition design concept of combining "low carbon and high manganese synergistic strengthening" with "extreme purification", has successfully developed a high-performance gas-shielded welding wire rod with excellent weld processability, outstanding weld strength and toughness matching, and excellent crack resistance without relying on expensive microalloying elements.

[0034] The present invention discloses a method for producing low-carbon Si-Mn gas-shielded welding wire rod, comprising the following steps: 1) Hot metal pretreatment: The main purpose is to remove sulfur from the hot metal; specifically, desulfurizing agent is sprayed into the hot metal ladle to carry out desulfurization treatment to ensure that the mass content of S in the hot metal is ≤0.030%; preferably, the desulfurizing agent is composed of 85% to 95% lime powder and 5% to 15% fluorite powder by mass percentage.

[0035] 2) Converter smelting: In converter smelting, scrap steel accounts for 10%–15% of the weight, with the remainder being molten iron; the amount of slag steel in the scrap steel is ≤4.5 tons, and the use of desulfurized slag steel and nickel-copper-containing scrap steel is prohibited. A top-and-bottom blowing converter is used for smelting, with top-blown oxygen purity >99.5% and oxygen pressure 1.0–1.35 MPa. Argon gas is supplied for the secondary blowing, with an argon gas pressure of 1.0–1.35 MPa. The tapping temperature is 1605–1645℃. Slag addition is strictly prohibited during tapping, and spot blowing should be avoided to ensure that the final carbon content and temperature are achieved on the first attempt. If secondary spot blowing occurs, the hood must be lowered first.

[0036] 3) Steel ladle alloying: During the tapping process (preferably 2.5 min after tapping), low-aluminum ferrosilicon and low-carbon ferromanganese are used for alloying; active lime and dolomite are added as auxiliary materials, along with silicon-manganese alloy; preferably, the amount of active lime added is 27.5–28 kg / t steel, the amount of dolomite added is 10.5–11 kg / t steel, and the amount of silicon-manganese alloy added is 26.2–26.6 kg / t steel. To ensure the alloy is fully dissolved and homogenized, the argon blowing time is ≥5 min (preferably medium blowing for 3 min first, followed by weak blowing), and the temperature of the molten steel after treatment is 1510–1550℃.

[0037] 4) LF furnace refining: The overall smelting cycle is ≤60min, the energizing time is ≤30min, the furnace is kept under a slight positive pressure of 45~65kPa, and the arc light is kept invisible during the submerged arc heating process; white slag refining is used, and 6.3~7.8kg / t steel of active lime and 1.5~2.0kg / t steel of fluorite are added; when adjusting the alloy, 1.3~1.5kg / t steel of manganese silicon and 1.35~1.92kg / t steel of ferrosilicon are added; the soft blowing time is ≥12.5min; the LF furnace temperature is 1570~1600℃.

[0038] 5) Continuous Casting: Protective casting is used in the continuous casting process. To ensure an oxygen-free atmosphere in the tundish, the tundish is purged with argon gas before casting for ≥3 minutes. Electromagnetic stirring is used during continuous casting. The electromagnetic stirring current at the crystallizer is 240-260A, frequency 4-6Hz, and the electromagnetic stirring current at the end of solidification is 300-360A, frequency 7-10Hz. Low-carbon or carbon-free covering agent is used in the tundish, and calcium wire is prohibited. Low-carbon protective slag from billets is used in the crystallizer. The ladle temperature is 1565-1575℃, the tundish temperature is 1530℃-1550℃, the superheat is ≤35℃, and the constant casting speed is 2.1-2.5m / min (the casting speed is kept constant after selection to reduce liquid level fluctuations). After the billet leaves the casting line, it is placed in a heat preservation pit for slow cooling for more than 50 hours. The central porosity of the billet is ≤0.5 grade; central segregation is ≤1.0 grade; shrinkage cavity is ≤1.0 grade; corner crack is ≤1.0 grade; subcutaneous crack is ≤1.0 grade; intermediate crack is ≤0.5 grade; central crack is ≤0.5 grade; subcutaneous bubble is ≤1.0 grade.

[0039] To address potential issues such as carbon center segregation, central porosity, or shrinkage cavities in cast billets, this invention fundamentally ensures the internal quality of the cast billet by comprehensively utilizing a combination of key technologies, including molten steel superheat control, billet pulling speed adjustment, and full-process electromagnetic stirring (both in the crystallizer and at the end).

[0040] 6) Heating: A walking beam furnace is used for heating. The preheating section temperature is 830-930℃, the heating section temperature is 1070-1130℃, and the soaking section temperature is 1100-1140℃. The heating time is 1.5-3 hours. In case of maintenance or sudden accidents (such as steel piling, gas compression, etc.), the rolling stop time should be confirmed, and cooling measures should be taken to control the furnace temperature in accordance with the relevant waiting process system of the steel rolling mill.

[0041] 7) Rolling: Roughing temperature 980~1040℃; Finishing inlet temperature 850~910℃; Wire drawing temperature 880~920℃; Head roller speed of air-cooled roller conveyor 0.09~0.12m / s; Roller speed increase 0~5% (adjustable within this range); Close all insulation covers. 8) Thermal Insulation: After rolling, the coils are placed in a sealed thermal insulation channel for insulation treatment. The temperature inside the thermal insulation channel must be ≥60℃, and there must be no less than 15 coils inside the thermal insulation channel. In northern regions, the doors and windows of the thermal insulation channel should be closed from November to March.

[0042] The wire rods obtained using the above chemical composition and process have the following characteristics and properties: Typical metallographic images of the low-carbon Si-Mn gas-shielded welding wire rods described in this invention are shown below. Figure 1 As shown, the metallographic structure of the wire rod consists of pearlite and ferrite, with pearlite accounting for 7% to 9% and ferrite accounting for 91% to 93% by volume percentage; the grain size is ≥8.5.

[0043] The wire rod has a tensile strength ≤530MPa, an elongation after fracture ≥27%, and a reduction of area ≥75%.

[0044] Non-metallic inclusions in wire rod: Class A + Class C ≤ 2.0; Class B + Class D ≤ 1.0.

[0045] Non-metallic inclusions are classified as follows: Class A ≤ 1.0, Class B ≤ 0.5, Class C ≤ 1.0, Class D ≤ 0.5, and Class DS ≤ 0.5.

[0046] To more intuitively illustrate the present invention, the embodiments of the present invention will be further described in conjunction with the examples. The following examples are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any technical solutions that can be obviously obtained by those skilled in the art within the scope of the technology disclosed in the present invention, including simple variations or equivalent substitutions, are all within the scope of protection of the present invention.

[0047]

Example

[0048] Table 1 Chemical composition of wire rod Table 2. Results of low-magnification microstructure analysis of wire rod. Table 3. Test results of mechanical properties of wire rod Table 4. Inspection Results of Non-metallic Inclusions in Wire Rod Table 5. Microstructure and Grain Size of Wire Rod 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 equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A low-carbon Si-Mn gas-shielded welding wire rod, characterized in that, The chemical composition of the wire rod, by mass percentage, is as follows: C: 0.06%–0.10%, Si: 0.70%–0.90%, Mn: 1.80%–2.00%, P≤0.020%, S≤0.013%, Ni≤0.20%, Cr≤0.20%, Cu≤0.20%, Mo≤0.10%, V≤0.020%, Al≤0.010%, Ca≤0.0015%, O≤0.0020%, N≤0.0040%, with the remainder being Fe and unavoidable impurity elements, and the total amount of impurity elements ≤0.50%.

2. The low-carbon Si-Mn gas-shielded welding wire rod according to claim 1, characterized in that, The metallographic structure of the wire rod consists of pearlite and ferrite, with pearlite accounting for 7% to 9% and ferrite accounting for 91% to 93% by volume percentage; the grain size is ≥8.

5.

3. The low-carbon Si-Mn gas-shielded welding wire rod according to claim 1, characterized in that, The wire rod has a tensile strength ≤530MPa, an elongation after fracture ≥27%, and a reduction of area ≥75%.

4. The low-carbon Si-Mn gas-shielded welding wire rod according to claim 1, characterized in that, Non-metallic inclusions in wire rod: Class A + Class C ≤ 2.0; Class B + Class D ≤ 1.

0.

5. The low-carbon Si-Mn gas-shielded welding wire rod according to claim 4, characterized in that, Non-metallic inclusions are classified as follows: Class A ≤ 1.0, Class B ≤ 0.5, Class C ≤ 1.0, Class D ≤ 0.5, and Class DS ≤ 0.

5.

6. A method for producing low-carbon Si-Mn gas-shielded welding wire rod as described in any one of claims 1 to 5, characterized in that, Includes the following steps: 1) Hot metal pretreatment: Desulfurizing agent is injected into the hot metal ladle to ensure that the sulfur content in the hot metal is ≤0.030% by mass; 2) Converter smelting: A top-and-bottom blowing converter is used for smelting. The purity of the top-blown oxygen is >99.5%, and the oxygen pressure is 1.0~1.35MPa. Argon is supplied for the bottom blowing, and the argon pressure is 1.0~1.35MPa. The tapping temperature is 1605~1645℃. Slag is strictly prohibited during tapping, and spot blowing should be avoided. 3) Steel ladle alloying: Alloying treatment is carried out during the tapping process, with the addition of auxiliary materials such as active lime and dolomite, and silicon-manganese alloy; argon blowing time ≥5min, and the temperature of molten steel after treatment is 1510~1550℃; 4) LF furnace refining: The overall smelting cycle is ≤60min, the energizing time is ≤30min, the furnace is kept under a slight positive pressure of 45~65kPa, and the arc light is kept invisible during submerged arc heating; white slag refining is used, with 6.3~7.8kg / t steel of active lime and 1.5~2.0kg / t steel of fluorite added; during alloy adjustment, 1.3~1.5kg / t steel of manganese silicon and 1.35~1.92kg / t steel of ferrosilicon are added; the soft blowing time is ≥12.5min; the LF furnace temperature at the station is 1570~1600℃. 5) Continuous casting: Protective casting is adopted in the continuous casting process, and electromagnetic stirring is used. The electromagnetic stirring current at the crystallizer is 240-260A and the frequency is 4-6Hz. The electromagnetic stirring current at the end of solidification is 300-360A and the frequency is 7-10Hz. Low-carbon or carbon-free covering agent is used in the tundish, and calcium wire is prohibited. Low-carbon protective slag for billets is used in the crystallizer. The platform ladle temperature is 1565-1575℃, the tundish temperature is 1530℃-1550℃, the superheat is ≤35℃, and the constant casting speed is 2.1-2.5m / min. After the billet leaves the line, it is placed in the heat preservation pit for slow cooling for more than 50 hours. 6) Heating: A walking beam furnace is used for heating. The preheating section temperature is 830-930℃, the heating section temperature is 1070-1130℃, the soaking section temperature is 1100-1140℃, and the heating time is 1.5-3 hours. 7) Rolling: Roughing temperature 980~1040℃; Finishing inlet temperature 850~910℃; Wire drawing temperature 880~920℃; Air-cooled roller conveyor head speed 0.09~0.12m / s; Roller speed increase 0~5%, all insulation covers closed; 8) Insulation: After rolling, the material is placed in a closed insulation channel for insulation treatment, and the temperature inside the insulation channel is ≥60℃.

7. The method for producing low-carbon Si-Mn gas-shielded welding wire rod according to claim 6, characterized in that, In step 1), the desulfurizing agent consists of 85% to 95% lime powder and 5% to 15% fluorite powder by mass percentage.

8. The method for producing low-carbon Si-Mn gas-shielded welding wire rod according to claim 6, characterized in that, In step 2), the scrap steel accounts for 10% to 15% of the weight in the converter smelting, with the remainder being molten iron; the amount of slag steel in the scrap steel is ≤4.5 tons, and the use of desulfurized slag steel and nickel-copper-containing scrap steel is prohibited.

9. The method for producing low-carbon Si-Mn gas-shielded welding wire rod according to claim 6, characterized in that, In step 3), low-aluminum ferrosilicon and low-carbon ferromanganese are used for alloying; the amount of active lime added in the auxiliary materials is 27.5-28 kg / t steel, the amount of dolomite added is 10.5-11 kg / t steel, and the amount of silicon-manganese alloy added is 26.2-26.6 kg / t steel.

10. The method for producing low-carbon Si-Mn gas-shielded welding wire rod according to claim 6, characterized in that, In step 5), the tundish is purged with argon gas before casting for ≥3 min; the central porosity of the billet is ≤0.5 grade; the central segregation is ≤1.0 grade; the shrinkage cavity is ≤1.0 grade; the corner crack is ≤1.0 grade; the subcutaneous crack is ≤1.0 grade; the intermediate crack is ≤0.5 grade; the central crack is ≤0.5 grade; and the subcutaneous bubble is ≤1.0 grade.

Images