A hot-rolled round wire rod for high toughness gas shielded welding wire with a nominal diameter of 6.5 mm and a method for manufacturing the same

Abstract

The application discloses a hot-rolled round bar for high-toughness gas shield welding wire with a nominal diameter of 6.5 mm and a preparation method thereof. The application has the advantages of strong applicability and controllability, low cost, and the like. The ER70S-6 alloy welding wire steel hot-rolled round bar produced by the application is high in steel cleanliness, low in inclusions, low in gas content (O is less than or equal to 0.0020 wt%, and N is less than or equal to 0.0030 wt%), good in microstructure proportion (fine ferrite + a small amount of pearlite), and high in area reduction of fracture (greater than or equal to 83%), and has excellent plasticity, toughness and drawing deformation capacity. The round bar is not broken when being drawn into a welding wire with a diameter of 1.0 mm to 1.2 mm, and the breakage rate of the welding wire with a diameter of 0.8 mm is less than or equal to 0.04 times per ton, so that the breakage phenomenon in the drawing process is effectively avoided, and the market competitiveness of the product is significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel smelting technology, specifically relating to a hot-rolled round bar for high-toughness gas shielded welding wire with a nominal diameter of 6.5 mm and its preparation method. Background Technology

[0002] ER70S-6 hot-rolled alloy welding wire steel is used to manufacture gas-shielded welding wire. It uses CO2 or Ar as the shielding gas for welding, resulting in a stable arc, excellent weld performance, low energy consumption, and minimal welding spatter. It exhibits excellent welding performance and is widely used in welding applications such as automobiles, machinery, ships, and pressure vessels. Currently, ER70S-6 hot-rolled alloy welding wire steel is mainly used for drawing welding wires with diameters ranging from 0.8mm to 1.2mm. Due to the numerous drawing passes, fine drawing specifications, and large cold working deformation, the wire is required to have excellent drawing performance, good surface quality, minimal fluctuation in strength within the coil, and high purity of the molten steel.

[0003] Currently, ER70S-6 hot-rolled alloy welding wire steel bar is produced via a process route of hot metal pretreatment → converter smelting → LF furnace refining → (vacuum refining) → small billet full-process protective casting → high-speed wire rod controlled rolling and cooling. This process involves improving control measures and strengthening management throughout the entire steelmaking process, from raw materials and auxiliary materials to steelmaking and rolling equipment, process control technology, and production process management. The goal is to ensure that the wire rod surface is free of quality defects such as cracks, folds, scale, and burrs. However, the existing process produces ER70S-6 alloy welding wire steel hot-rolled round bars with a microstructure containing a small amount of granular bainite, and the reduction of area is mostly less than 80%. This results in partial wire breakage when drawing Φ1.0mm-Φ1.2mm welding wire, and easy breakage when drawing Φ0.8mm welding wire, hindering the improvement of wire rod drawing efficiency and product quality, and limiting the expansion of product applications. Summary of the Invention

[0004] To address the aforementioned problems, the purpose of this invention is to provide a hot-rolled disc bar for high-toughness gas-shielded welding wire with a nominal diameter of 6.5 mm and its preparation method, so as to improve the plasticity, toughness and draw deformation capacity of the existing hot-rolled disc bar ER70S-6 alloy welding wire steel.

[0005] The objective of this invention is achieved by a method for preparing a hot-rolled round bar for high-toughness gas-shielded welding wire with a nominal diameter of 6.5 mm, which is accomplished through the following steps:

[0006] A. Hot metal pretreatment and desulfurization: The blast furnace hot metal is transported to the KR process hot metal pretreatment unit for desulfurization treatment. The hot metal temperature is ≥1330℃, the insertion depth of the stirring head is controlled at 2400mm, and conventional CaO desulfurizing agent is added at a rate of 10.0~13.0kg / t of steel for desulfurization treatment. The stirring time is controlled at 6 minutes. After stirring, the slag is removed to ensure that the surface of the hot metal in the ladle is exposed at least 4 / 5, and the desulfurization slag is removed.

[0007] B. Steelmaking: The pretreated desulfurized molten iron from step A and high-quality scrap steel are added to the LD converter at a ratio of 860 kg / t steel and 200 kg / t steel, respectively, for conventional top and bottom combined blowing. The converter smelting adopts the double-slag method. In the early stage of smelting, the first batch of slag is mixed with lime and lightly calcined dolomite at a ratio of 12~17 kg / t steel and 8~12 kg / t steel, respectively, to form slag. After the first batch of slag is finished and the furnace is turned over, the second batch of slag is added. The second batch of slag is mixed with lime and lightly calcined dolomite at a ratio of 8~10 kg / t steel and 10 kg / t steel, respectively, to form slag again. The final steel carbon content is controlled at 0.035wt%-0.05wt%, and the tapping temperature is ≤1590℃. Before tapping, the following slag washing desulfurizing agent is added to the bottom of the ladle at a ratio of 1.0 kg / t steel for slag washing: CaF2 7.0wt%, SiO2 6.3wt%, CaO 59.5wt%, Na2O 6.7wt%, Al 2.0wt%, P 0.045wt%, S 0.040wt%, the remainder being unavoidable impurities. The tapping process adopts a bottom-blowing argon process throughout, with the argon flow rate controlled at 25~30NL / min.

[0008] C. Deoxidation and Alloying: After tapping the molten steel, when the amount of molten steel in the ladle is greater than 1 / 4, deoxidize and alloy in the following order: ferrosilicon → ferrosilicon-manganese alloy → low-carbon ferromanganese. Add the following substances to the ladle in sequence: Ferrosilicon 72.5wt%, Al 1.2wt%, P 0.045wt%, S 0.025wt%, with the remainder being Fe and unavoidable impurities, at a weight ratio of 10.3~11.4 kg / t of steel; ferrosilicon 17.5wt%, Al 1.2wt%, P 0.045wt%, S 0.025wt%, with the remainder being Fe and unavoidable impurities, at a weight ratio of 7.3~8.4 kg / t of steel; ferrosilicon 17.5wt%, Mn 65.8wt%, C 1.7wt%, P 0.085wt%, S 0.035wt%, with the remainder being Fe and unavoidable impurities, at a weight ratio of 10.1~11.2 kg / t of steel; low-carbon ferromanganese 84.2wt%, C 84.2wt%, P 84.2wt%, S ... 0.4wt%, P 0.053wt%, S 0.028wt%, the remainder being Fe and unavoidable impurities; the above alloys are added when the molten steel in the ladle reaches 4 / 5 of its volume;

[0009] D. Steel Refining in the LF Furnace: After tapping the steel in step C, hoist the molten steel to the LF furnace refining station and connect the argon gas line. Turn on the argon gas and purge with a small flow rate of 30-35 NL / min for 2 minutes. Then, lower the electrode and use setting 7-9 for slag formation. Add 0.4-0.6 kg / t steel of ferrosilicon powder to adjust the slag. After energizing for 8 minutes, raise the electrode to observe the slag formation in the furnace, then measure the temperature and take samples. If the slag is too thin, add 4.5-6.5 kg / t steel of lime, then add 0.7 kg / t steel of ferrosilicon powder and 0.6 kg / t steel of calcium carbide to adjust the slag. Conversely, add pre-melted lime. The refining slag is adjusted to control the slag basicity at 5.5~6.5; based on the steel sample analysis results, alloys are added to adjust the composition of the molten steel, ensuring that all chemical components are within the target range, and controlling the oxygen activity of the molten steel to ≤15ppm; the number of electrode passes during the refining process is controlled to ≤3; then the molten steel temperature is heated to 1610~1620℃, and a small argon flow rate of 20~25NL / min is used to soft-blow the molten steel for 20 minutes. Then, a steel covering agent is added, with the addition amount controlled at 1.0kg / t steel, and then the molten steel is hoisted to the casting station of the continuous casting platform.

[0010] E. Steel casting: Under the conditions of tundish temperature of 1530~1540℃, casting speed of 2.1~2.3m / min, secondary cooling water volume of 1.5~1.7L / kg, crystallizer electromagnetic stirring current intensity of 300A and operating frequency of 3.5Hz, molten steel is continuously cast into steel billets with a cross section of 165mm×165mm using a 7-strand small square billet casting machine with 7 R9m straight arc continuous straightening machine.

[0011] F. Steel billet heating: The steel billet from step E is sent into a heating furnace with a soaking temperature of 1090~1130℃. After heating for 50~60 minutes, the billet is tapped, descaled by high-pressure water, and pushed to a high-speed wire rod mill for rolling.

[0012] G. Controlled Rolling and Cooling: The billet from step F is fed into a 30-stand high-speed wire rod mill for rolling. Under rolling conditions of 0.32 m / s, it is roughed for 6 passes on the roughing mill; then, under rolling conditions of 12.0 m / s, it is intermediate rolled for 5 passes on the intermediate mill; then, under rolling conditions of 45.0 m / s, it is pre-finished for 5 passes on the finishing mill; then, under rolling conditions of 60 m / s, it is finished for 5 passes on the finishing mill; finally, under rolling conditions of 65 m / s... Under rolling conditions of / s, the wire rod is rolled in 3 passes on the reducing and sizing mill; then, it is spun into wire at a temperature of 860~890℃ and a speed of 65~85m / s; after spun wire, the wire rod enters the Steyrmo air-cooling line for atomized cooling and air-cooling control; all fans are turned off; the first two insulation covers are opened and the rest are closed; the roller speed is controlled at 0.30~0.45m / s; after the Steyrmo air-cooling is completed, the coil is naturally air-cooled to room temperature to obtain the target high-toughness gas-shielded welding wire hot-rolled round wire rod ER70S-6.

[0013] The hot-rolled round bar for high-toughness gas-shielded welding wire has the following chemical composition by weight percentage: C 0.05~0.07wt%, Si 0.82~0.87wt%, Mn 1.43~1.49wt%, S≤0.013wt%, P≤0.010wt%, N≤0.0030wt%, O≤0.0020wt%, with the remainder being Fe and unavoidable impurities.

[0014] This invention employs a top-and-bottom combined blowing argon blowing mode in converter smelting, controlling the final C content to 0.035wt%~0.05wt%. During tapping, a slag washing desulfurizing agent is used for full-process slag washing, reducing the [O], [N], and [S] content in the molten steel and improving its cleanliness. The converter smelting uses a dual-slag dephosphorization method with a dephosphorization rate >92%, significantly reducing the final P content in the molten steel and substantially decreasing the content of harmful elements. The LF furnace uses ferrosilicon powder for slag conditioning and deoxidation, avoiding the formation of brittle Al2O3 inclusions and improving drawing performance. The soft argon blowing time at the end of LF furnace refining is controlled at 20 minutes, promoting the full flotation and removal of inclusions in the molten steel, with non-metallic inclusions ≤1.0 grade, significantly improving the plasticity, toughness, and drawing performance of the wire rod. Controlling the initial rolling temperature, finishing rolling temperature, and wire drawing temperature in the steel rolling process promotes the refinement of austenite grains and accelerates the transformation rate of supercooled austenite during phase transformation, resulting in a fine blocky ferrite + pearlite microstructure that is easy to draw. After wire drawing, the wire rod is cooled using a delayed Stellmore cooling method at a low roller speed (0.30~0.45m / s) on the Stellmore roller conveyor, avoiding the formation of bainite and martensite "hard phase" structures and obtaining a fine-grained ferrite + pearlite microstructure. The ductility, toughness, and drawing deformation capacity of the steel are significantly improved, effectively avoiding wire breakage during the drawing of fine-gauge welding wire from the wire rod.

[0015] The beneficial effects of this invention are as follows: The process of this invention is highly applicable and controllable, with low cost. Through integrated innovation of multiple processes including chemical composition design, converter smelting, deoxidation and alloying, slag washing, LF furnace refining, continuous casting, rolling heating regime, controlled rolling, and Stellmore controlled cooling, the produced ER70S-6 alloy welding wire steel hot-rolled round bar has high steel cleanliness, few inclusions, low gas content (O≤0.0020wt%, N≤0.0030wt%), good microstructure ratio (fine-grained ferrite + a small amount of pearlite), and a reduction of area ≥83%. It possesses excellent plasticity, toughness, and drawing deformation capacity. When drawing Φ1.0mm-Φ1.2mm welding wire from the wire rod, there is no wire breakage; when drawing Φ0.8mm welding wire, the wire breakage rate is ≤0.04 times / ton, effectively avoiding wire breakage during the drawing process and significantly improving the product's market competitiveness. Detailed Implementation

[0016] The present invention will be further described below with reference to embodiments, but this is not intended to limit the present invention in any way. Any modifications or substitutions made based on the teachings of the present invention shall fall within the protection scope of the present invention.

[0017] This invention discloses a method for preparing a hot-rolled round bar of high-toughness gas-shielded welding wire with a nominal diameter of 6.5 mm, which is implemented according to the following steps:

[0018] A. Hot metal pretreatment and desulfurization: The blast furnace hot metal is transported to the KR process hot metal pretreatment unit for desulfurization treatment. The hot metal temperature is ≥1330℃, the insertion depth of the stirring head is controlled at 2400mm, and conventional CaO desulfurizing agent is added at a rate of 10.0~13.0kg / t of steel for desulfurization treatment. The stirring time is controlled at 6 minutes. After stirring, the slag is removed to ensure that the surface of the hot metal in the ladle is exposed at least 4 / 5, and the desulfurization slag is removed.

[0019] B. Steelmaking: The pretreated desulfurized molten iron from step A and high-quality scrap steel are added to the LD converter at a ratio of 860 kg / t steel and 200 kg / t steel, respectively, for conventional top and bottom combined blowing. The converter smelting adopts the double-slag method. In the early stage of smelting, the first batch of slag is mixed with lime and lightly calcined dolomite at a ratio of 12~17 kg / t steel and 8~12 kg / t steel, respectively, to form slag. After the first batch of slag is finished and the furnace is turned over, the second batch of slag is added. The second batch of slag is mixed with lime and lightly calcined dolomite at a ratio of 8~10 kg / t steel and 10 kg / t steel, respectively, to form slag again. The final steel carbon content is controlled at 0.035wt%-0.05wt%, and the tapping temperature is ≤1590℃. Before tapping, the following slag washing desulfurizing agent is added to the bottom of the ladle at a ratio of 1.0 kg / t steel for slag washing: CaF2 7.0wt%, SiO2 6.3wt%, CaO 59.5wt%, Na2O 6.7wt%, Al 2.0wt%, P 0.045wt%, S 0.040wt%, the remainder being unavoidable impurities. The tapping process adopts a bottom-blowing argon process throughout, with the argon flow rate controlled at 25~30NL / min.

[0020] C. Deoxidation and Alloying: After tapping the molten steel, when the amount of molten steel in the ladle is greater than 1 / 4, deoxidize and alloy in the following order: ferrosilicon → ferrosilicon-manganese alloy → low-carbon ferromanganese. Add the following substances to the ladle in sequence: Ferrosilicon 72.5wt%, Al 1.2wt%, P 0.045wt%, S 0.025wt%, with the remainder being Fe and unavoidable impurities, at a weight ratio of 10.3~11.4 kg / t of steel; ferrosilicon 17.5wt%, Al 1.2wt%, P 0.045wt%, S 0.025wt%, with the remainder being Fe and unavoidable impurities, at a weight ratio of 7.3~8.4 kg / t of steel; ferrosilicon 17.5wt%, Mn 65.8wt%, C 1.7wt%, P 0.085wt%, S 0.035wt%, with the remainder being Fe and unavoidable impurities, at a weight ratio of 10.1~11.2 kg / t of steel; low-carbon ferromanganese 84.2wt%, C 84.2wt%, P 84.2wt%, S ... 0.4wt%, P 0.053wt%, S 0.028wt%, the remainder being Fe and unavoidable impurities; the above alloys are added when the molten steel in the ladle reaches 4 / 5 of its volume;

[0021] D. Steel Refining in the LF Furnace: After tapping the steel in step C, hoist the molten steel to the LF furnace refining station and connect the argon gas line. Turn on the argon gas and purge with a small flow rate of 30-35 NL / min for 2 minutes. Then, lower the electrode and use setting 7-9 for slag formation. Add 0.4-0.6 kg / t steel of ferrosilicon powder to adjust the slag. After energizing for 8 minutes, raise the electrode to observe the slag formation in the furnace, then measure the temperature and take samples. If the slag is too thin, add 4.5-6.5 kg / t steel of lime, then add 0.7 kg / t steel of ferrosilicon powder and 0.6 kg / t steel of calcium carbide to adjust the slag. Conversely, add pre-melted lime. The refining slag is adjusted to control the slag basicity at 5.5~6.5; based on the steel sample analysis results, alloys are added to adjust the composition of the molten steel, ensuring that all chemical components are within the target range, and controlling the oxygen activity of the molten steel to ≤15ppm; the number of electrode passes during the refining process is controlled to ≤3; then the molten steel temperature is heated to 1610~1620℃, and a small argon flow rate of 20~25NL / min is used to soft-blow the molten steel for 20 minutes. Then, a steel covering agent is added, with the addition amount controlled at 1.0kg / t steel, and then the molten steel is hoisted to the casting station of the continuous casting platform.

[0022] E. Steel casting: Under the conditions of tundish temperature of 1530~1540℃, casting speed of 2.1~2.3m / min, secondary cooling water volume of 1.5~1.7L / kg, crystallizer electromagnetic stirring current intensity of 300A and operating frequency of 3.5Hz, molten steel is continuously cast into steel billets with a cross section of 165mm×165mm using a 7-strand small square billet casting machine with 7 R9m straight arc continuous straightening machine.

[0023] F. Steel billet heating: The steel billet from step E is sent into a heating furnace with a soaking temperature of 1090~1130℃. After heating for 50~60 minutes, the billet is tapped, descaled by high-pressure water, and pushed to a high-speed wire rod mill for rolling.

[0024] G. Controlled Rolling and Cooling: The billet from step F is fed into a 30-stand high-speed wire rod mill for rolling. Under rolling conditions of 0.32 m / s, it is roughed for 6 passes on the roughing mill; then, under rolling conditions of 12.0 m / s, it is intermediate rolled for 5 passes on the intermediate mill; then, under rolling conditions of 45.0 m / s, it is pre-finished for 5 passes on the finishing mill; then, under rolling conditions of 60 m / s, it is finished for 5 passes on the finishing mill; finally, under rolling conditions of 65 m / s... Under rolling conditions of / s, the wire rod is rolled in 3 passes on the reducing and sizing mill; then, it is spun into wire at a temperature of 860~890℃ and a speed of 65~85m / s; after spun wire, the wire rod enters the Steyrmo air-cooling line for atomized cooling and air-cooling control; all fans are turned off; the first two insulation covers are opened and the rest are closed; the roller speed is controlled at 0.30~0.45m / s; after the Steyrmo air-cooling is completed, the coil is naturally air-cooled to room temperature to obtain the target high-toughness gas-shielded welding wire hot-rolled round wire rod ER70S-6.

[0025] In step A, the chemical composition of the molten iron is: C 4.3-4.6wt%, Si 0.15-0.30wt%, Mn 0.15-0.25wt%, P 0.080-0.100wt%, S≤0.030wt%, with the remainder being Fe and unavoidable impurities.

[0026] In step B, the chemical composition of the pretreated deep desulfurized molten iron is: C 4.3-4.6wt%, Si 0.15-0.30wt%, Mn 0.15-0.25wt%, P 0.080-0.100wt%, S≤0.010wt%, with the remainder being Fe and unavoidable impurities;

[0027] The chemical composition of the high-quality scrap steel is as follows: C 0.21-0.25wt%, Si 0.35-0.50wt%, Mn 1.20-1.50wt%, P 0.020-0.035wt%, S 0.018-0.035wt%, with the remainder being Fe and unavoidable impurities.

[0028] In step F, the tapping temperature is 990~1020℃.

[0029] In step G, after the Stellmore air cooling is completed, the winding temperature is controlled at 560~580℃.

[0030] The present invention also provides a hot-rolled circular bar for high-toughness gas shielded welding wire with a nominal diameter of 6.5 mm obtained by the preparation method. The hot-rolled circular bar for high-toughness gas shielded welding wire has the following chemical composition by weight percentage: C 0.05~0.07wt%, Si 0.82~0.87wt%, Mn 1.43~1.49wt%, S≤0.013wt%, P≤0.010wt%, N≤0.0030wt%, O≤0.0020wt%, with the remainder being Fe and unavoidable impurities. Its process mechanical properties and microstructure are shown in Tables 1 and 2.

[0031] Table 1. Processing and mechanical properties of hot-rolled round bars for gas shielded welding wire with a nominal diameter of 6.5 mm produced by this invention.

[0032]

[0033] Table 2. Microstructure and inclusions of hot-rolled disc bars with a nominal diameter of 6.5 mm for gas shielded welding wire produced by this invention.

[0034]

[0035] Example 1

[0036] A. Hot metal pretreatment and desulfurization: Blast furnace hot metal (chemical composition: C 4.3wt%, Si 0.15wt%, Mn 0.15wt%, P 0.080wt%, S 0.018wt%, with the remainder being Fe and unavoidable impurities) is transported to the KR method hot metal pretreatment unit for desulfurization. The hot metal temperature is 1330℃, the stirring head insertion depth is controlled at 2400mm, and conventional CaO desulfurizing agent is added at a rate of 10.0kg / t steel for desulfurization. The stirring time is controlled at 6 minutes. After stirring, the slag is removed to ensure that the surface of the hot metal in the ladle is exposed at least 4 / 5, and the desulfurization slag is removed. The composition of the hot metal after pretreatment is controlled as follows: C 4.3wt%, Si 0.15wt%, Mn 0.15wt%, P 0.080wt%, S 0.005wt%, with the remainder being Fe and unavoidable impurities.

[0037] B. Steelmaking: The pretreated desulfurized molten iron from step A (C 4.3wt%, Si 0.15wt%, Mn 0.15wt%, P 0.080wt%, S 0.010wt%, the remainder being Fe and unavoidable impurities), and high-quality scrap steel (chemical composition C 0.21wt%, Si 0.35wt%, Mn 1.20wt%, P...) 0.020wt%, S0.018wt%, the remainder being Fe and unavoidable impurities) were added to the LD converter at proportions of 860kg / t steel and 200kg / t steel molten iron and scrap steel, respectively, for conventional top and bottom combined blowing. The converter smelting employed a double-slag method. In the early stages of smelting, the first batch of slag was mixed with lime and lightly calcined dolomite at proportions of 12kg / t steel and 8kg / t steel, respectively, to form slag. After the first batch of slag was slag-forming and the furnace was turned over, the second batch of slag was added. The second batch of slag was mixed with lime and lightly calcined dolomite at proportions of 8kg / t steel and 10kg / t steel, respectively, to form slag again. The final steel C content was controlled at 0.035wt%, and the tapping temperature was 1590℃. Before tapping, a slag washing desulfurizing agent with the following mass ratio was added to the bottom of the ladle at a rate of 1.0kg / t steel: CaF2 7.0wt%, SiO2 6.3wt%, CaO 59.5wt%, Na2O 6.7wt%, Al 2.0wt%, P 0.045wt%, S 0.040wt%, the remainder being unavoidable impurities. The tapping process employs a bottom-blowing argon process throughout, with the argon flow rate controlled at 25NL / min.

[0038] C. Deoxidation and Alloying: After tapping the molten steel from step B, when the ladle contains more than 1 / 4 of the steel, deoxidize and alloy it in the following order: ferrosilicon → ferrosilicon-manganese alloy → low-carbon ferromanganese. Add the following substances sequentially to the ladle: Ferrosilicon in the following mass ratio for 10.3 kg / t of steel: Si 72.5 wt%, Al 1.2 wt%, P 0.045 wt%, S 0.025 wt%, with the remainder being Fe and unavoidable impurities; ferrosilicon-manganese alloy in the following mass ratio for 7.3 kg / t of steel: Si 17.5 wt%, Mn 65.8 wt%, C 1.7 wt%, P 0.085 wt%, S 0.035 wt%, with the remainder being Fe and unavoidable impurities; low-carbon ferromanganese in the following mass ratio for 10.1 kg / t of steel: Mn 84.2 wt%, C 0.4 wt%, P 0.053 wt%, S 0.028 wt%, the remainder being Fe and unavoidable impurities; the above alloy is added when the molten steel in the ladle reaches 4 / 5 of its volume; after tapping, the molten steel is hoisted to the LF furnace for refining.

[0039] D. Steel Refining in the LF Furnace: After tapping the steel in step C, hoist the molten steel to the LF furnace refining station and connect the argon gas line. Turn on the argon gas and purge with a small argon flow rate (30 NL / min) for 2 minutes. Then, lower the electrode and use setting 7-9 for slag formation. Add 0.4 kg / t steel of ferrosilicon powder to adjust the slag. After energizing for 8 minutes, raise the electrode to observe the slag formation in the furnace, then measure the temperature and take samples. If the slag is too thin, add 4.5 kg / t steel of lime, then add 0.7 kg / t steel of ferrosilicon powder and 0.6 kg / t steel of calcium carbide to adjust the slag. Otherwise, add pre-melted lime. The refining slag was adjusted to control the slag basicity at 5.5. Based on the steel sample analysis results, alloys were added to adjust the composition of the molten steel, ensuring that all chemical components were within the target range and controlling the oxygen activity of the molten steel at 15 ppm. The number of electrode passes during the refining process was controlled to be 3. Then, the temperature of the molten steel was heated to 1610℃, and a small amount of argon gas with a flow rate of 20 NL / min was used to perform soft blowing of argon gas on the molten steel for 20 minutes. Then, a steel covering agent was added, with the amount added controlled at 1.0 kg / t of steel. Finally, the molten steel was hoisted to the casting station of the continuous casting platform.

[0040] E. Steel casting: Under the conditions of tundish temperature of 1530℃, casting speed of 2.3m / min, secondary cooling water volume of 1.7L / kg, crystallizer electromagnetic stirring current intensity of 300A and operating frequency of 3.5Hz, molten steel is continuously cast into billets with a cross section of 165mm×165mm using a 7-strand small square billet casting machine with R9m straight arc continuous straightening.

[0041] F. Steel billet heating: The steel billet from step E is sent into a heating furnace with a soaking temperature of 1090℃ and heated for 50 minutes. The steel billet exits at a temperature of 990℃. After descaling by high-pressure water, it is pushed to a high-speed wire rod mill for rolling.

[0042] G. Controlled Rolling and Cooling: The billet from step F is fed into a 30-stand high-speed wire rod mill for rolling. Under rolling conditions of 0.32 m / s, it is roughed for 6 passes on the roughing mill; then, under rolling conditions of 12.0 m / s, it is intermediate rolled for 5 passes on the intermediate mill; then, under rolling conditions of 45.0 m / s, it is pre-finished for 5 passes on the finishing mill; then, under rolling conditions of 60 m / s, it is finished for 5 passes on the sizing mill; finally, under rolling conditions of 65 m / s, it is sized and cooled on the reducing mill. Three passes were performed; then, the wire was spun at a temperature of 860℃ and a speed of 65m / s. After spun wire, the wire rod entered the Stellmore air-cooling line for atomized cooling and air-cooling control; all fans were turned off; the first two insulation covers were opened, and the rest were closed; the roller speed was controlled at 0.30~0.45m / s; after the Stellmore air-cooling was completed, the coil temperature was controlled at 560℃, and then the coil was naturally air-cooled to room temperature to obtain a hot-rolled round wire rod ER70S-6 with a nominal diameter of 6.5mm for high-toughness gas-shielded welding wire. Its chemical composition by weight percentage is as follows: C 0.05wt%, Si 0.82wt%, Mn 1.43wt%, S 0.007wt%, P 0.007wt%, N 0.0020wt%, O 0.0012wt%, with the remainder being Fe and unavoidable impurities. Its process mechanical properties and microstructure are shown in Tables 3 and 4, respectively.

[0043] Table 3. Process mechanical properties of hot-rolled round bars for gas shielded welding wire with a nominal diameter of 6.5 mm produced in Example 1.

[0044]

[0045] Table 4. Microstructure and inclusions of hot-rolled discs for gas shielded welding wire with a nominal diameter of 6.5 mm produced in Example 1.

[0046]

[0047] Example 2

[0048] A. Hot Metal Pretreatment and Desulfurization: Blast furnace hot metal (chemical composition: C 4.5wt%, Si 0.24wt%, Mn 0.20wt%, P 0.090wt%, S 0.025wt%, with the remainder being Fe and unavoidable impurities) is transported to the KR method hot metal pretreatment unit for desulfurization. The hot metal temperature is ≥1330℃, the stirring head insertion depth is controlled at 2400mm, and conventional CaO desulfurizing agent is added at a rate of 11.0kg / t steel for desulfurization treatment. The stirring time is controlled at 6 minutes. After stirring, the slag is removed to ensure that the surface of the hot metal in the ladle is exposed at least 4 / 5, and the desulfurization slag is removed. The composition of the hot metal after pretreatment is controlled as follows: C 4.5wt%, Si 0.24wt%, Mn 0.20wt%, P 0.090wt%, S 0.008wt%, with the remainder being Fe and unavoidable impurities.

[0049] B. Steelmaking: The pretreated desulfurized molten iron from step A (C 4.5wt%, Si 0.24wt%, Mn 0.20wt%, P 0.090wt%, S 0.008wt%, the remainder being Fe and unavoidable impurities), and high-quality scrap steel (chemical composition C 0.23wt%, Si 0.42wt%, Mn 1.35wt%, P 0.027wt%, S...) 0.026wt%, the remainder being Fe and unavoidable impurities) were added to the LD converter at proportions of molten iron and scrap steel at 860kg / t steel and 200kg / t steel, respectively, for conventional top and bottom combined blowing. The converter smelting employed a double-slag method. In the early stages of smelting, the first batch of slag was slag-forming with lime and lightly calcined dolomite at proportions of 15kg / t steel and 10kg / t steel, respectively. After the first batch of slag was slag-forming and the furnace was turned over, the second batch of slag was added. The second batch of slag was slag-forming again with lime and lightly calcined dolomite at proportions of 10kg / t steel and 10kg / t steel, respectively. The final steel C content was controlled at 0.04wt%, and the tapping temperature was 1585℃. Before tapping, a slag washing desulfurizing agent with the following mass ratio was added to the bottom of the ladle at a rate of 1.0kg / t steel: CaF 27.0wt%, SiO 26.3wt%, CaO 59.5wt%, Na 2O 6.7wt%, Al 2.0 wt%, P 0.045 wt%, S 0.040 wt%, the remainder being unavoidable impurities. The tapping process employs a bottom-blowing argon process throughout, with the argon flow rate controlled at 30 NL / min.

[0050] C. Deoxidation and Alloying: After tapping the molten steel from step B, when the ladle contains more than 1 / 4 tonnes of molten steel, deoxidize and alloy in the following order: ferrosilicon → ferrosilicon-manganese alloy → low-carbon ferromanganese. Add the following substances sequentially to the ladle: Ferrosilicon (based on 10.8 kg / t of steel): Si 72.5 wt%, Al 1.2 wt%, P 0.045 wt%, S 0.025 wt%, with the remainder being Fe and unavoidable impurities; Ferrosilicon-manganese alloy (based on 7.8 kg / t of steel): Si 17.5 wt%, Mn 65.8 wt%, C 1.7 wt%, P 0.085 wt%, S 0.035 wt%, with the remainder being Fe and unavoidable impurities; Low-carbon ferromanganese (based on 10.6 kg / t of steel): Mn 84.2 wt%, C 0.4 wt%, P 0.053 wt%, S 0.028 wt%, the remainder being Fe and unavoidable impurities; the above alloy is added when the molten steel in the ladle reaches 4 / 5 of its volume; after tapping, the molten steel is hoisted to the LF furnace for refining.

[0051] D. Steel Refining in the LF Furnace: After tapping the steel in step C, hoist the molten steel to the LF furnace refining station and connect the argon gas line. Turn on the argon gas and purge with a small argon flow rate (35 NL / min) for 2 minutes. Then, lower the electrode and use setting 7-9 for slag formation. Add 0.5 kg / t steel of ferrosilicon powder to adjust the slag. After energizing for 8 minutes, raise the electrode to observe the slag formation in the furnace, then measure the temperature and take samples. If the slag is too thin, add 5.5 kg / t steel of lime, then add 0.7 kg / t steel of ferrosilicon powder and 0.6 kg / t steel of calcium carbide to adjust the slag. Otherwise, add pre-melted lime. The refining slag was adjusted to control the slag basicity at 6.0. Based on the steel sample analysis results, alloys were added to adjust the composition of the molten steel, ensuring that all chemical components were within the target range and controlling the oxygen activity of the molten steel at 12 ppm. The number of electrode passes during the refining process was controlled to be 2. Then, the temperature of the molten steel was heated to 1615℃, and a small amount of argon gas with a flow rate of 25 NL / min was used to perform soft blowing of argon gas on the molten steel for 20 minutes. Then, a steel covering agent was added, with the amount added controlled at 1.0 kg / t steel. Finally, the molten steel was hoisted to the casting station of the continuous casting platform.

[0052] E. Steel casting: Under the conditions of tundish temperature of 1535℃, casting speed of 2.2m / min, secondary cooling water volume of 1.6L / kg, crystallizer electromagnetic stirring current intensity of 300A and operating frequency of 3.5Hz, molten steel is continuously cast into steel billets with a cross section of 165mm×165mm using a 7-strand small square billet casting machine with R9m straight arc continuous straightening.

[0053] F. Steel billet heating: The steel billet from step E is sent into a heating furnace with a soaking temperature of 1110℃ and heated for 60 minutes. The steel billet exits at a temperature of 1000℃. After descaling by high-pressure water, it is pushed to a high-speed wire rod mill for rolling.

[0054] G. Controlled Rolling and Cooling: The billet from step F is fed into a 30-stand high-speed wire rod mill for rolling. Under rolling conditions of 0.32 m / s, it is roughed for 6 passes on the roughing mill; then, under rolling conditions of 12.0 m / s, it is intermediate rolled for 5 passes on the intermediate mill; then, under rolling conditions of 45.0 m / s, it is pre-finished for 5 passes on the finishing mill; then, under rolling conditions of 60 m / s, it is finished for 5 passes on the sizing mill; finally, under rolling conditions of 65 m / s, it is sized and cooled on the reducing mill. Three passes were performed; then the wire was spun at a temperature of 875℃ and a speed of 75m / s; after spun wire, the wire rod entered the Stellmore air-cooling line for aerosol cooling and air-cooling control; all fans were turned off; the first two insulation covers were opened, and the rest were closed; the roller speed was controlled at 0.30~0.45m / s; after the Stellmore air-cooling was completed, the coil temperature was controlled at 570℃, and then the coil was naturally air-cooled to room temperature to obtain a hot-rolled round wire rod ER70S-6 with a nominal diameter of 6.5mm for high toughness gas shielded welding wire. It has the following chemical composition by weight percentage: C 0.06wt%, Si 0.85wt%, Mn 1.45wt%, S 0.010wt%, P 0.009wt%, N 0.0026wt%, O 0.0016wt%, with the remainder being Fe and unavoidable impurities. Its process mechanical properties and microstructure are shown in Tables 5 and 6, respectively.

[0055] Table 5. Process mechanical properties of hot-rolled round bars for gas shielded welding wire with a nominal diameter of 6.5 mm produced in Example 2.

[0056]

[0057] Table 6. Microstructure and inclusions of hot-rolled discs for 6.5mm nominal diameter gas shielded welding wire produced in Example 2.

[0058]

[0059] Example 3

[0060] A. Hot Metal Pretreatment and Desulfurization: Blast furnace hot metal (chemical composition: C 4.6wt%, Si 0.30wt%, Mn 0.25wt%, P 0.100wt%, S 0.030wt%, with the remainder being Fe and unavoidable impurities) is transported to the KR method hot metal pretreatment unit for desulfurization. The hot metal temperature is 1360℃, the stirring head insertion depth is controlled at 2400mm, and conventional CaO desulfurizing agent is added at a rate of 13.0kg / t steel for desulfurization. The stirring time is controlled at 6 minutes. After stirring, the slag is removed to ensure that the surface of the hot metal in the ladle is exposed at least 4 / 5, and the desulfurization slag is removed. The composition of the hot metal after pretreatment is controlled as follows: C 4.6wt%, Si 0.30wt%, Mn 0.25wt%, P 0.100wt%, S 0.010wt%, with the remainder being Fe and unavoidable impurities.

[0061] B. Steelmaking: The pretreated desulfurized molten iron from step A (C 4.6wt%, Si 0.30wt%, Mn 0.25wt%, P 0.100wt%, S 0.010wt%, the remainder being Fe and unavoidable impurities), and high-quality scrap steel (chemical composition C 0.25wt%, Si 0.50wt%, Mn 1.50wt%, P...) 0.035wt% S, 0.035wt% S, and the remainder being Fe and unavoidable impurities) were added to the LD converter at proportions of 860kg / t steel and 200kg / t steel, respectively, for conventional top and bottom combined blowing. The converter smelting employed a double-slag method. In the early stages of smelting, the first batch of slag was mixed with lime and lightly calcined dolomite at proportions of 17kg / t steel and 12kg / t steel, respectively, to form slag. After the first batch of slag was slag-forming and the furnace was turned over, the second batch of slag was added. The second batch of slag was mixed with lime and lightly calcined dolomite at proportions of 10kg / t steel and 10kg / t steel, respectively, to form slag again. The final steel C content was controlled at 0.05wt%, and the tapping temperature was 1582℃. Before tapping, a slag washing desulfurizing agent with the following mass ratio was added to the bottom of the ladle at a rate of 1.0kg / t steel: CaF 27.0wt%, SiO 26.3wt%, CaO 59.5wt%, Na 2O 6.7wt%, Al 2.0 wt%, P 0.045 wt%, S 0.040 wt%, the remainder being unavoidable impurities. The tapping process employs a bottom-blowing argon process throughout, with the argon flow rate controlled at 30 NL / min.

[0062] C. Deoxidation and Alloying: After tapping the molten steel from step B, when the ladle contains more than 1 / 4 tonnes of molten steel, deoxidize and alloy it in the following order: ferrosilicon → ferrosilicon-manganese alloy → low-carbon ferromanganese. Add the following substances sequentially to the ladle: Ferrosilicon in the following mass ratio for 11.4 kg / t of steel: Si 72.5 wt%, Al 1.2 wt%, P 0.045 wt%, S 0.025 wt%, with the remainder being Fe and unavoidable impurities; ferrosilicon-manganese alloy in the following mass ratio for 8.4 kg / t of steel: Si 17.5 wt%, Mn 65.8 wt%, C 1.7 wt%, P 0.085 wt%, S 0.035 wt%, with the remainder being Fe and unavoidable impurities; low-carbon ferromanganese in the following mass ratio for 11.2 kg / t of steel: Mn 84.2 wt%, C 0.4 wt%, P 0.053 wt%, S 0.028 wt%, the remainder being Fe and unavoidable impurities; the above alloy is added when the molten steel in the ladle reaches 4 / 5 of its volume; after tapping, the molten steel is hoisted to the LF furnace for refining.

[0063] D. Steel Refining in the LF Furnace: After tapping the steel in step C, hoist the molten steel to the LF furnace refining station and connect the argon gas line. Turn on the argon gas and purge with a small argon flow rate (35 NL / min) for 2 minutes. Then, lower the electrode and use setting 7-9 for slag formation. Add 0.6 kg / t steel of ferrosilicon powder to adjust the slag. After energizing for 8 minutes, raise the electrode to observe the slag formation in the furnace, then measure the temperature and take samples. If the slag is too thin, add 6.5 kg / t steel of lime, then add 0.7 kg / t steel of ferrosilicon powder and 0.6 kg / t steel of calcium carbide to adjust the slag. Otherwise, add pre-melted lime. The refining slag was adjusted to control the slag basicity at 6.5. Based on the steel sample analysis results, alloys were added to adjust the composition of the molten steel, ensuring that all chemical components were within the target range and controlling the oxygen activity of the molten steel at 10 ppm. The number of electrode passes during the refining process was controlled to be 2. Then, the molten steel temperature was heated to 1620℃, and a small argon flow rate of 25 NL / min was used to soft-blow the molten steel for 20 minutes. After that, a steel covering agent was added, with the addition amount controlled at 1.0 kg / t steel. Then, the molten steel was hoisted to the casting station of the continuous casting platform.

[0064] E. Steel casting: Under the conditions of tundish temperature of 1540℃, casting speed of 2.1m / min, secondary cooling water volume of 1.5L / kg, crystallizer electromagnetic stirring current intensity of 300A and operating frequency of 3.5Hz, molten steel is continuously cast into steel billets with cross section of 165mm×165mm using a 7-strand small square billet casting machine with R9m straight arc continuous straightening.

[0065] F. Steel billet heating: The steel billet from step E is sent into a heating furnace with a soaking section temperature of 1130℃ and heated for 60 minutes. The steel billet exits at a temperature of 1020℃. After descaling by high-pressure water, it is pushed to a high-speed wire rod mill for rolling.

[0066] G. Controlled Rolling and Cooling: The billet from step F is fed into a 30-stand high-speed wire rod mill for rolling. Under rolling conditions of 0.32 m / s, it is roughed for 6 passes on the roughing mill; then, under rolling conditions of 12.0 m / s, it is intermediate rolled for 5 passes on the intermediate mill; then, under rolling conditions of 45.0 m / s, it is pre-finished for 5 passes on the finishing mill; then, under rolling conditions of 60 m / s, it is finished for 5 passes on the sizing mill; finally, under rolling conditions of 65 m / s, it is sized and cooled on the reducing mill. Three passes were performed; then, the wire was spun at a temperature of 890℃ and a speed of 85m / s. After spun wire, the wire rod entered the Stellmore air-cooling line for aerosol cooling and air-cooling control; all fans were turned off; the first two insulation covers were opened, and the rest were closed; the roller speed was controlled at 0.30~0.45m / s; after the Stellmore air-cooling was completed, the coil temperature was controlled at 580℃, and then the coil was naturally air-cooled to room temperature to obtain a hot-rolled round wire rod ER70S-6 with a nominal diameter of 6.5mm for high-toughness gas-shielded welding wire. Its chemical composition by weight percentage is as follows: C 0.07wt%, Si 0.87wt%, Mn 1.49wt%, S 0.013wt%, P 0.010wt%, N 0.0030wt%, O 0.0020wt%, with the remainder being Fe and unavoidable impurities. Its process mechanical properties and microstructure are shown in Tables 7 and 8, respectively.

[0067] Table 7. Process mechanical properties of hot-rolled round bars for gas shielded welding wire with a nominal diameter of 6.5 mm produced in Example 3.

[0068]

[0069] Table 8. Microstructure and inclusions of hot-rolled discs for gas shielded welding wire with a nominal diameter of 6.5 mm produced in Example 3.

[0070]

Claims

1. A method for producing a hot-rolled coil for a high-toughness gas shielded welding wire having a nominal diameter of 6.5 mm, characterized in that, The hot-rolled wire rod has the following weight percentage chemical components: C 0.05~0.07wt%, Si 0.82~0.87wt%, Mn 1.43~1.49wt%, S≤0.013wt%, P≤0.010wt%, N≤0.0030wt%, O≤0.0020wt%, the rest being Fe and unavoidable impurities; the microstructure of the hot-rolled wire rod is fine blocky ferrite 91~92%+pearlite 8~9%, ferrite grain size 9.5~10.5 grade, tensile strength Rm 485~510MPa, reduction of area Z≥83.0, drawing Φ1.0mm-Φ1.2mm welding wire without breaking, drawing Φ0.8mm welding wire breaking rate≤0.04 times / ton; the preparation method is realized according to the following steps: A, hot metal pretreatment desulphurization: the hot metal from blast furnace is transported to KR hot metal pretreatment device for desulphurization treatment, the hot metal temperature is ≥1330℃, the insertion depth of stirring head is controlled to be 2400mm, the conventional CaO desulfurizer is added in an amount of 10.0~13.0kg / t 钢 , the stirring time is controlled to be 6 minutes; after stirring, the slag after scraping operation is performed, the hot metal surface in the ladle is ensured to be exposed ≥4 / 5, and the desulfurization slag is scraped clean; B, molten steel smelting: the pretreated desulfurization molten iron of step A, high-quality scrap steel are respectively loaded into LD converter according to 860kg / t 钢 , 200kg / t 钢 , and the conventional top and bottom combined blowing is carried out, double slag method is used in converter smelting, the first batch of slag material is added according to 12~17kg / t 钢 , 8~12kg / t 钢 before smelting, lime and light calcined dolomite are used for slagging, the second batch of slag material is added after the first batch of slag material is slagged and the converter is tapped, the second batch of slag material is added according to 8~10kg / t 钢 , 10kg / t 钢 , lime and light calcined dolomite are used for slagging again, the content of C in the molten steel at the end point is controlled to be 0.035wt%~0.05wt%, the tapping temperature is ≤1590℃; before tapping, the following slag washing desulfurizing agent with mass ratio is added to the bottom of the ladle according to 1.0kg / t 钢 : CaF27.0wt%, SiO26.3wt%, CaO 59.5wt%, Na2O 6.7wt%, Al 2.0wt%, P 0.045wt%, S 0.040wt%, the rest is unavoidable impurities, the whole process of bottom argon blowing process is used in the tapping process, the argon flow is controlled to be 25~30NL / min; C, deoxidation alloying: after the smelting of molten steel, when the amount of molten steel in the ladle is greater than 1 / 4, the following deoxidation alloying sequence is used: ferrosilicon→silicon manganese alloy→low carbon ferromanganese, the following substances are sequentially added to the ladle: ferrosilicon with the following mass ratio: Si 72.5wt%, Al 1.2wt%, P 0.045wt%, S 0.025wt%, and the rest is Fe and unavoidable impurities, in an amount of 10.3~11.4kg / t 钢 silicon manganese alloy with the following mass ratio: Si 17.5wt%, Mn 65.8wt%, C 1.7wt%, P 0.085wt%, S 0.035wt%, and the rest is Fe and unavoidable impurities, in an amount of 7.3~8.4kg / t 钢 low carbon ferromanganese with the following mass ratio: Mn 84.2wt%, C 0.4wt%, P 0.053wt%, S 0.028wt%, and the rest is Fe and unavoidable impurities, in an amount of 10.1~11.2kg / t 钢 the above alloys are added when the amount of molten steel in the ladle reaches 4 / 5. D, LF furnace refining of liquid steel: the C step of the steel is lifted to the LF furnace refining station with argon belt, open argon with small argon amount 30~35NL / min, then the electrode is used to adjust the slag with gear 7~9, and 0.4~0.6kg / t of ferrosilicon powder is added 钢 Slag adjustment; after 8 minutes of power on, the electrode is lifted to observe the slag condition in the furnace, then the temperature is measured and the sample is taken; if the slag condition is relatively thin, 4.5~6.5kg / t of lime is added 钢 Then 0.7kg / t of ferrosilicon powder is added 钢 , 0.6kg / t of calcium carbide is added 钢 Slag adjustment, otherwise, pre-melted refining slag is added for slag adjustment, and the slag basicity is controlled to be 5.5~6.5; according to the steel sample analysis result, alloy is added to adjust the composition of the molten steel, to ensure that each chemical composition is within the target range, and the oxygen activity of the molten steel is controlled to be ≤15ppm; the number of times of lowering the electrode during the refining process is controlled to be ≤3; then the temperature of the molten steel is heated to 1610~1620℃, and the molten steel is soft-blow argon with small argon amount of 20~25NL / min, the soft-blow argon time is 20 minutes, then the molten steel covering agent is added, and the addition amount is controlled to be 1.0kg / t 钢 Then the molten steel is lifted to the continuous casting platform casting station; E, molten steel casting: under the conditions of tundish temperature 1530~1540℃, drawing speed 2.1~2.3m / min, two cooling specific water consumption 1.5~1.7L / kg, crystallizer electromagnetic stirring current intensity 300A, and operation frequency 3.5Hz, the molten steel is fully protected continuous casting into a billet with a section of 165mm×165mm by using R9m straight arc continuous straightening 7-machine 7-stream small billet caster; F, billet heating: the billet of step E is sent into a heating furnace with a furnace temperature of 1090~1130℃ in the soaking section, and after heating for 50~60 minutes, the steel is discharged, high-pressure water descaling is performed, and the billet is pushed to a high-speed wire rod mill for rolling; G, controlled rolling and controlled cooling: the billet of step F is sent into a high-speed wire rod mill with 30 stands for rolling, under the rolling conditions of a speed of 0.32m / s, 6 passes of rough rolling in the rough rolling mill group; then under the rolling conditions of a speed of 12.0m / s, 5 passes of intermediate rolling in the intermediate rolling mill group; then under the rolling conditions of a speed of 45.0m / s, 5 passes of pre-precision rolling in the pre-precision rolling mill group; then under the rolling conditions of a speed of 60m / s, 5 passes of precision rolling in the precision rolling mill group; then under the rolling conditions of a speed of 65m / s, 3 passes of reducing and sizing in the reducing and sizing mill group; then under the conditions of a temperature of 860~890℃ and a speed of 65~85m / s, wire drawing; after wire drawing, the wire rod enters a Stelmor air cooling line for air mist cooling and air cooling control; the fan is fully closed; the heat preservation cover is opened for the first 2, and the rest is closed; The roller speed control is 0.30~0.45m / s; after Stelmor air cooling, the coil is naturally air cooled to room temperature to obtain the target high-toughness gas shielded welding wire hot-rolled wire rod.

2. The method of producing hot-rolled wire rod for high toughness gas shielded welding wire having a nominal diameter of 6.5 mm according to claim 1, characterized in that, In step A, the chemical components of the molten iron are: C 4.3-4.6wt%, Si 0.15-0.30wt%, Mn 0.15-0.25wt%, P 0.080-0.100wt%, S≤0.030wt%, the rest being Fe and unavoidable impurities.

3. The method of producing hot-rolled wire rod for high toughness gas shielded welding wire having a nominal diameter of 6.5 mm according to claim 1, characterized in that, In step B, the chemical composition of the pretreated desulfurized molten iron is: C 4.3-4.6wt%, Si 0.15-0.30wt%, Mn 0.15-0.25wt%, P 0.080-0.100wt%, S≤0.010wt%, and the rest is Fe and inevitable impurities; the chemical composition of the high-quality scrap steel is: C 0.21-0.25wt%, Si 0.35-0.50wt%, Mn 1.20-1.50wt%, P 0.020-0.035wt%, S 0.018-0.035wt%, and the rest is Fe and inevitable impurities.

4. The method of producing hot-rolled wire rod for high toughness gas shielded welding wire having a nominal diameter of 6.5 mm according to claim 1, characterized in that, In step F, the tapping temperature is 990-1020℃.

5. The method of producing hot-rolled wire rod for high toughness gas shielded welding wire having a nominal diameter of 6.5 mm according to claim 1, characterized in that, In step G, the coiling temperature after the Stelmor air cooling is controlled to be 560-580℃.

6. A hot-rolled round wire rod with a nominal diameter of 6.5mm for high-toughness gas shielded welding wire, obtained by the preparation method of any one of claims 1-5, wherein the microstructure of the hot-rolled round wire rod is 91-92% fine blocky ferrite + 8-9% pearlite, the ferrite grain size is 9.5-10.5 grade, the tensile strength Rm is 485-510MPa, the reduction of area Z is ≥83.0, and the wire breaking rate of drawing Φ1.0mm-Φ1.2mm welding wire is ≤0.04 times / ton, and the wire breaking rate of drawing Φ0.8mm welding wire is ≤0.04 times / ton.

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