Method for controlling brittle inclusions in steel cord

Abstract

The present invention provides a method for controlling brittle inclusions in steel cord, in which an alloy is added in a primary smelting and tapping process in a furnace, silicon carbide and synthetic slag are added to the slag surface of the ladle after tapping is completed to produce slag, an alloy is added in a refining process, carbon wire is introduced, lime, silicon carbide and synthetic slag are added and the slag is melted by passing an electric current through it, and the slag components satisfy CaO / SiO2=0.9-1.2, Al2O3≦5%, MgO 4-8%, and [MnO+T.Fe] 2-5%.

Description

[Technical Field]

[0001] The present invention belongs to the technical field of steel smelting, and specifically relates to a method for controlling brittle inclusions in steel cord. [Background technology]

[0002] Currently, steel cord is primarily used in the industry for drawing into fine wire, typically drawn to a diameter of 0.12 to 0.35 mm; when used as saw wire, it must be drawn to a diameter of 0.12 mm or less. Saw wire, also known as cutting wire, cutting steel wire, or cutting wire, is a special wire material for dividing, and is widely used as a consumable material in the fields of energy, aviation, equipment, and public facilities, for example, for cutting and shaping solar cell silicon wafers, quartz materials, single-crystal silicon, and polycrystalline silicon. Furthermore, diamond particles can be embedded in saw wire to produce diamond saw wire, also known as diamond cutting wire, diamond cutting wire, or diamond wire.

[0003] In order to reduce losses during the cutting process of materials such as silicon, saw wire performance needs to be such that it has a smaller diameter, a longer length without breakage, and higher strength. However, the steel cords currently manufactured in the industry are affected by inclusions in the steel, and brittle inclusions such as Al2O3 and magnesia-alumina spinel (MgO·Al2O3) in particular are very likely to cause breakage problems during the manufacturing, processing, and use of steel cords. As a result, the performance of existing steel cords when used as saw wires does not meet market needs. As shown in Figures 1 to 4, Figure 1 shows the distribution of inclusions in a steel cord manufactured by a conventional manufacturing process in a SiO2-MnO-Al2O3 ternary phase diagram, Figure 2 shows the morphology of the fine wire fracture surface due to Al2O3 inclusions in the wire core portion of a steel cord manufactured by a conventional manufacturing process, Figure 3 shows the morphology of the fine wire fracture surface due to Al2O3 inclusions in the wire edge portion of a steel cord manufactured by a conventional manufacturing process, and Figure 4 shows the morphology of the fine wire fracture surface due to magnesia-alumina spinel (MgO·Al2O3) inclusions in the wire core portion of a steel cord manufactured by a conventional manufacturing process. Summary of the Invention

[0004] In order to solve at least one of the above technical problems, an object of the present invention is to provide a method for controlling brittle inclusions in steel cord.

[0005] In order to achieve one of the above objects, one embodiment of the present invention provides a method for controlling brittle inclusions in a steel cord having chemical compositions, in mass percent, of 0.70 to 0.95% C, 0.15 to 0.45% Si, 0.25 to 0.80% Mn, 0.10 to 0.45% Cr, P≦0.015%, S≦0.01%, Alt≦0.0008%, N≦0.003%, and O≦0.002%, with the balance being Fe and other unavoidable impurities, comprising: The primary smelting process in the furnace involves deoxidizing and alloying the molten steel, placing 0.5 to 1 kg / t of silicon carbide and 40 to 60% low-nitrogen carburizer at the bottom of the ladle that receives the molten steel before tapping, gradually adding the alloy during tapping, adding all of the alloy by the time the steel reaches 75%. When the steel reaches 80%, adding the remaining 40 to 60% of the low-nitrogen carburizer at a rate of 200 to 300 kg / min is started, and after the low-nitrogen carburizer has completely dissolved in the molten steel, tapping is completed and silicon carbide is added at 0.5 to 1 kg / t to the slag surface of the ladle and synthetic slag is added at 3 to 5 kg / t to create slag; The molten steel that has undergone primary smelting in the furnace is transferred to the LF furnace and refined to a mass percentage of C 0.70-0.95%, Si 0.15-0.45%, Mn 0.25-0.80%, Cr The temperature, chemical composition and contents of the molten steel are detected to adjust the chemical composition of the molten steel so that the content of the molten steel is 0.10-0.45%, P≦0.015%, S≦0.01%, Alt≦0.0008%, N≦0.003%, O≦0.002%, and the balance is Fe and other unavoidable impurities. The temperature, chemical composition and contents of the molten steel are then detected, and the alloy is added according to the detected chemical composition and contents of the molten steel. A carbon wire is then introduced, and lime, silicon carbide and synthetic slag are added and melted by applying an electric current. The temperature of the molten steel is adjusted to 1510-1535°C, and the slag composition is, in mass percent, CaO / SiO2=0.9-1.2, Al2O3≦5%, MgO 4-8%, [MnO+T.Fe] a refining process in which the content of molten steel is adjusted to 2-5%, with the remainder being other unavoidable impurities, and then the ladle bottom blowing is adjusted to a soft stirring mode, the soft stirring time is set to 20 min or more, and steel is tapped; a billet casting process in which the molten steel tapped in the refining process is transferred to a continuous casting platform and left to stand for 15 minutes or more, and when pouring into a large ladle, stopper sand is introduced into a slag receiver, and the molten steel is protectively poured into a tundish to form a continuously cast billet, in this order; The alloy contains ferrosilicon, metallic manganese, and ferrochromium, and the ferrosilicon contains Al≦0.035%, the metallic manganese contains Al≦0.015%, the ferrochromium contains Al≦0.020% and C≦0.15%, and the low-nitrogen carburizer contains N≦0.015%.

[0006] By controlling the chemical composition and mass percentage of the steel cord, and by pre-laying silicon carbide and low-nitrogen carburizer at the bottom of the ladle before tapping in the primary smelting process in the furnace, the boiling of molten steel is moderated by adding low-nitrogen carburizer at the bottom of the ladle at the beginning of tapping, and the amount of low-nitrogen carburizer added during the tapping process in the primary smelting process is significantly reduced, preventing a large amount of low-nitrogen carburizer from floating on the slag surface, causing a carbon-oxygen reaction on the slag surface to generate a large amount of gas and cause splashes, thereby reducing the bottom blowing flow rate of the ladle during tapping and This method not only reduces the time required for bottom-blown stirring, reduces refractory erosion and loss, and improves molten steel cleanliness, but also significantly reduces alloy deoxidation losses, reducing alloy costs. Using silicon carbide instead of calcium carbide allows for rapid deoxidation, allowing for a smaller volume of molten steel in the ladle at the beginning of tapping and a higher ladle clearance. This eliminates the risk of molten steel splashing due to deoxidation boiling, and the resulting SiO2 helps to lower the basicity of the slag in the ladle. Furthermore, adding carbon powder via carbon wire during the refining process and immediately adding the carbon powder to the molten steel avoids bottom-blown stirring, reduces refractory erosion, and reduces the formation of brittle inclusions such as Al2O3 and magnesia-alumina spinel (MgO·Al2O3). Adding lime or synthetic slag immediately after adjusting the chemical composition of the molten steel increases slag basicity and aids in the adsorption of Al2O3 and SiO2 inclusions. Furthermore, during the billet casting process, adding stopper sand to the slag receiver during pouring prevents the stopper sand from being mixed into the molten steel and increasing the amount of Al2O3 inclusions in the molten steel. Furthermore, controlling the Al content in the alloy reduces Al2O3 inclusions and SiO2-MnO-Al2O3 composite inclusions in the molten steel. This control method not only reduces refractory corrosion, but also reduces the acid-soluble aluminum (Als) in the molten steel and Al2O3 precipitation during the billet casting process. This effectively controls brittle inclusions such as Al2O3 and magnesia-alumina spinel (MgO·Al2O3) in steel cords, thereby reducing the breakage rate during manufacturing, processing, and use of steel cords.

[0007] In a further improvement of the embodiment of the present invention, the bottom bricks, molten pool bricks, and ladle mouth bricks of the ladle are all made of magnesia-carbon bricks, and the magnesia-carbon bricks contain Al2O3≦3%; the slag line bricks and breathable bricks of the ladle are made of magnesium-zirconium-carbon bricks, and the magnesium-zirconium-carbon bricks contain Al2O3≦3%; and the long nozzle of the ladle is made of corundum, and the inner wall of the long nozzle is coated with an SiO2 coating, and the thickness of the SiO2 coating is 3-8 mm. By limiting the types of refractory materials used for the ladle bottom bricks, molten pool bricks, ladle mouth bricks, slag line bricks, permeable bricks, and long nozzles, and controlling the Al2O3 content therein, and by applying an SiO2 coating to the inner wall of the long nozzle, the high-melting-point SiO2 coating can withstand molten steel at pouring temperatures of 1500-1520°C, reducing the risk of the Al2O3 contained in the long nozzle of a large ladle being mixed into the molten steel and forming Al2O3 inclusions. This reduces the erosion of the ladle refractory materials during steelmaking and reduces the amount of Al2O3 and MgO mixed into the molten steel. This significantly reduces the occurrence of brittle inclusions such as Al2O3 and magnesia-alumina spinel (MgO·Al2O3) in the final steel cord, further improving the stability of steel cord production quality.

[0008] In a further improvement of one embodiment of the present invention, the stopping sand is silicon-chromium stopping sand, in which Al2O3 is ≦5%, which can prevent the stopping sand from flowing into the tundish together with the molten steel during pouring, thereby reducing the amount of excess Al2O3 in the molten steel and reducing the occurrence of brittle inclusions such as Al2O3 and magnesia-alumina spinel (MgO·Al2O3) in the final steel cord.

[0009] In a further refinement of one embodiment of the present invention, the inner wall of the tundish is coated with a magnesium coating, the magnesium coating having an Al2O3 content of ≦2%, the tundish weir is a magnesium-zirconium-carbon weir, the magnesium-zirconium-carbon weir has an Al2O3 content of ≦5%, and the tundish top nozzle and submerged entry nozzle are both magnesia-carbon nozzles, the magnesia-carbon nozzle has an Al2O3 content of ≦5%. By specifying the tundish material and controlling its Al2O3 content, corrosion of the tundish refractory material during the steelmaking process can be reduced, and the amount of Al2O3 and MgO mixed into the molten steel can be reduced, thereby significantly reducing the occurrence of brittle inclusions such as Al2O3 and magnesia-alumina spinel (MgO·Al2O3) in the final steel cord.

[0010] In a further refinement of one embodiment of the present invention, the primary in-furnace smelting step is performed in a converter or electric furnace, and the molten steel temperature at the end of smelting is ≥ 1650°C, C ≥ 0.10%, and O ≤ 0.03%. By tapping the molten steel at a high carbon, low oxygen, and high temperature in the primary in-furnace smelting step, the strength of the reaction between the molten steel and the low-nitrogen carburizer pre-placed in the ladle can be reduced, and the molten steel can be quickly deoxidized by the silicon carbide pre-placed in the ladle, thereby reducing the degree of boiling of the molten steel and avoiding splashing of the molten steel.

[0011] As a further improvement of one embodiment of the present invention, in the in-furnace primary smelting step, the ladle bottom blowing flow rate is 100 to 200 NL / min during the initial tapping stage and during the alloying stage, the ladle bottom blowing flow rate is 600 to 800 NL / min when the remaining 40 to 60% of the low-nitrogen carburizer is started to be added after 80% of the steel has been tapped, and the ladle bottom blowing flow rate is 300 to 500 NL / min when silicon carbide and synthetic slag are added to the slag surface of the ladle to form slag after tapping is completed. By increasing the flow rate of the bottom blown ladle during the process of adding the remaining 40-60% of the low-nitrogen carburizer, the low-nitrogen carburizer is entrained in the molten steel. On the other hand, by using a medium to low flow rate of bottom blown at the beginning of tapping, during the alloying process, and during the slag production process, the stirring intensity of the molten steel is reduced, slag entrainment is avoided, erosion of the refractory material is reduced, loss of refractory material is reduced, the cleanliness of the molten steel is improved, and the formation of large amounts of brittle inclusions such as Al2O3 and magnesia-alumina spinel (MgO·Al2O3) in the molten steel is prevented.Furthermore, frequent breakage of wire during further processing due to their penetration into the wire rod during drawing is avoided.

[0012] In a further refinement of one embodiment of the present invention, the refining process includes a ladle bottom blowing rate of 100-150 nl / min during the step of detecting the molten steel temperature, chemical composition, and their contents, a ladle bottom blowing rate of 300-400 nl / min during the step of adding the alloy and introducing carbon wire, a ladle bottom blowing rate of 200-300 nl / min during the step of applying current to melt the slag, and a ladle bottom blowing rate of 30-80 nl / min during the soft stirring step. By using a medium-to-low bottom blowing rate throughout the entire refining process, the intensity of stirring the molten steel is reduced, slag entrainment is avoided, erosion of the refractory material is reduced, refractory material loss is reduced, the cleanliness of the molten steel is improved, and the formation of large amounts of brittle inclusions such as Al2O3 and magnesia-alumina spinel (MgO·Al2O3) in the molten steel is avoided, which in turn prevents frequent wire breakage due to their penetration into the wire during further processing.

[0013] In a further improvement of one embodiment of the present invention, from the end of tapping in the primary in-furnace smelting process until the completion of adjustment of the chemical composition of the molten steel in the refining process, the ladle slag basicity is maintained at 0.6 or less, and 1 to 2 kg / t of lime, 1 to 1.5 kg / t of silicon carbide, and 8 to 15 kg / t of synthetic slag are added in the refining process so that the ladle slag basicity is 0.9 to 1.2. By not adding lime during the tapping process in the primary in-furnace smelting process, and only adding a small amount of low-basicity synthetic slag, the low slag basicity in the ladle is guaranteed, and the oxidizing properties of the molten steel and slag are low, reducing the molten aluminum in the molten steel to an extremely low level, reducing the precipitation of Al2O3 inclusions during the continuous casting process, and allowing Al in the alloy to oxidize to Al2O3 and float on the slag to be separated from the molten steel. Furthermore, the small amount of slag, combined with the low ladle bottom blowing rate, significantly reduces erosion of the ladle refractory material. This weakens the slag and further reduces the formation of brittle inclusions such as Al2O3 and magnesia-alumina spinel (MgO·Al2O3). In the refining process, adding lime and synthetic slag immediately after accurately adjusting the molten steel composition to raise the slag basicity to 0.9-1.2 helps to adsorb Al2O3 inclusions and acidic SiO2 inclusions. Furthermore, with such low slag basicity in the refining process, the bottom blowing flow rate from the ladle can be reduced to less than 50% of the normal bottom blowing flow rate, significantly reducing the bottom blowing flow rate and further reducing the erosion of the ladle refractory material.

[0014] In a further refinement of one embodiment of the present invention, the chemical composition of the silicon carbide is, by weight, ≥99.3% SiC and other unavoidable impurities, and the chemical composition of the synthetic slag is, by weight, 35-45% CaO, 45-55% SiO2, 3-8% MgO, ≤2% Al2O3, and other unavoidable impurities. The high-purity silicon carbide not only enables rapid deoxidation, but also moderates the boiling of molten steel due to the low-nitrogen carburizer placed at the bottom of the ladle. The chemical composition and content of the synthetic slag are limited to ensure low basicity, thereby reducing the ladle bottom blowing rate and further reducing erosion of the ladle refractory material.

[0015] As a further improvement of one embodiment of the present invention, in the billet casting step, Als in the molten steel in the tundish is ≦0.0005%, the content of Al2O3 inclusions in the molten steel is ≦10%, the size of Al2O3 inclusions and magnesia-alumina spinel inclusions is <5 μm, and the density of Al2O3 inclusions and magnesia-alumina spinel inclusions with a size of 1 to 5 μm is ≦0.0005 pieces / mm 2 By controlling the content of acid-soluble aluminum Als in molten steel, it is possible to reduce the amount of Al2O3 precipitated during the continuous casting process, thereby reducing the content, size, and density of brittle inclusions such as Al2O3 inclusions and magnesia-alumina spinel inclusions in the final steel cord, thereby improving the cleanliness of the steel cord and reducing the wire breakage rate. [Brief explanation of the drawings]

[0016] [Figure 1] The distribution of inclusions in a steel cord manufactured by a conventional manufacturing process is shown in the SiO2-MnO-Al2O3 ternary phase diagram. [Figure 2] The figure shows the morphology of the fracture surface of a thin wire caused by Al2O3 inclusions in the core of the wire in a steel cord manufactured using a conventional manufacturing process. [Figure 3] The figure shows the morphology of the fracture surface of thin wires caused by Al2O3 inclusions at the wire edge in a steel cord manufactured using a conventional manufacturing process. [Figure 4] This shows the morphology of the fracture surface of thin wires caused by magnesia-alumina spinel (MgO·Al2O3) inclusions in the core of the wire in a steel cord manufactured using a conventional manufacturing process. [Figure 5] 1 shows the distribution of inclusions in a steel cord according to one embodiment of the present invention in a SiO2-MnO-Al2O3 ternary phase diagram. DETAILED DESCRIPTION OF THE INVENTION

[0017] One embodiment of the present invention provides a method for controlling brittle inclusions in a steel cord, wherein the chemical composition of the steel cord includes, in mass percent, 0.70-0.95% C, 0.15-0.45% Si, 0.25-0.80% Mn, 0.10-0.45% Cr, P≦0.015%, S≦0.01%, Alt≦0.0008%, N≦0.003%, O≦0.002%, and the balance being Fe and other unavoidable impurities.

[0018] The method for controlling brittle inclusions in a steel cord according to the present invention has been obtained based on many experiments and studies. The method for controlling brittle inclusions in a steel cord will be further described below with reference to specific examples.

[0019] The method for controlling brittle inclusions in a steel cord includes the following steps (1), (2), and (3) in this order.

[0020] (1) Primary smelting process in the furnace Smelting is carried out in a converter or electric furnace, and the molten steel is deoxidized. and Alloying A process of , molten steel temperature at the end of smelting ≧ 1650℃, C ≧ 0.10%, O ≦ 0.03% Let's say. At the end of smelting, the slag is stopped and the steel is tapped. Before tapping, 0.5 to 1 kg / t of silicon carbide and 40 to 60% low-nitrogen carburizer are placed at the bottom of the ladle receiving the molten steel. All alloys are added gradually during tapping to alloy the steel. All of the alloy is added by the time the steel reaches 75%. When the steel reaches 80%, the remaining 40 to 60% of the low-nitrogen carburizer is added at a rate of 200 to 300 kg / min. After the low-nitrogen carburizer has completely dissolved in the molten steel, tapping is stopped and 0.5 to 1 kg / t of silicon carbide is added to the slag surface of the ladle, and 3 to 5 kg / t of synthetic slag is added to make the slag.

[0021] Preferably, the alloy comprises ferrosilicon, metallic manganese and ferrochromium, wherein Al≦0.035% in the ferrosilicon, Al≦0.015% in the metallic manganese, Al≦0.020%, C≦0.15% in the ferrochromium, and N≦0.015% in the low-nitrogen carburizer.

[0022] Preferably, the bottom bricks, molten pool bricks, and ladle mouth bricks of the ladle are all made of magnesia-carbon bricks, and the magnesia-carbon bricks contain Al2O3≦3%; the slag line bricks and breathable bricks of the ladle are made of magnesium-zirconium-carbon bricks, and the magnesium-zirconium-carbon bricks contain Al2O3≦3%; and the long nozzle of the ladle is made of corundum, and the inner wall of the long nozzle is coated with an SiO2 coating, and the thickness of the SiO2 coating is 3 to 8 mm.

[0023] More preferably, the upper limit of the number of uses of the ladle bottom bricks, molten pool bricks, and ladle mouth bricks is set to 35 to 45, and the upper limit of the number of uses of the ladle slag line bricks and permeable bricks is set to 15 to 25. In this way, the quality stability of the refractory material of the ladle can be ensured, and it is possible to avoid a situation in which the erosion of the refractory material of the ladle becomes increasingly severe over time, causing a large amount of Al2O3 and MgO in the refractory material of the ladle to be mixed into molten steel, resulting in an excessive increase in brittle inclusions such as Al2O3 inclusions and magnesia-alumina spinel inclusions in the finally produced steel cord.

[0024] Preferably, the ladle bottom blowing flow rate is 100 to 200 NL / min in the initial stage of tapping and during the alloying process, 600 to 800 NL / min in the process of starting to add the remaining 40 to 60% of the low-nitrogen carburizer when 80% of the steel has been tapped, and 300 to 500 NL / min in the process of adding silicon carbide and synthetic slag to the slag surface of the ladle after tapping is completed to produce slag.

[0025] Preferably, the chemical composition of the silicon carbide includes, in mass percent, SiC≧99.3% and other unavoidable impurities, and the chemical composition of the synthetic slag includes, in mass percent, 35-45% CaO, 45-55% SiO2, 3-8% MgO, and ≦2% Al2O3, and other unavoidable impurities.

[0026] (2) Refining process The molten steel that has undergone primary smelting in the furnace is transferred to the LF furnace and refined to a mass percentage of C 0.70-0.95%, Si 0.15-0.45%, Mn 0.25-0.80%, Cr To adjust the chemical composition of molten steel to satisfy the following: CaO / SiO2 = 0.9-1.2, Al2O3 ≤ 5%, MgO 4-8%, [MnO + T.Fe] 2-5%, with the balance being Fe and other unavoidable impurities, the temperature, chemical composition, and contents of the molten steel are detected, and the alloy is added according to the detected chemical composition and contents of the molten steel. Carbon wire is then introduced, lime, silicon carbide, and synthetic slag are added, and an electric current is applied to melt the slag. The temperature of the molten steel is adjusted to 1510-1535°C, and the slag composition is adjusted to satisfy the following mass percents: CaO / SiO2 = 0.9-1.2, Al2O3 ≤ 5%, MgO 4-8%, [MnO + T.Fe] 2-5%, with the balance being other unavoidable impurities. Thereafter, the ladle bottom blowing is adjusted to soft stirring mode, the soft stirring time is set to > 20 minutes, and the steel is tapped.

[0027] Here, [MnO+T.Fe] represents the sum of the mass percentages of MnO and T.Fe.

[0028] Preferably, the ladle bottom blowing flow rate is 100 to 150 NL / min during the process of detecting the molten steel temperature, chemical components and their contents, 300 to 400 NL / min during the process of adding the alloy and introducing carbon wire, 200 to 300 NL / min during the process of applying current to melt the slag, and 30 to 80 NL / min during the soft stirring process.

[0029] Preferably, the slag basicity in the ladle is kept at 0.6 or less from the time when the tapping of steel is completed in the primary in-furnace smelting step until the adjustment of the chemical composition of the molten steel is completed in the refining step.

[0030] Preferably, in the refining step, 1 to 2 kg / t of lime, 1 to 1.5 kg / t of silicon carbide, and 8 to 15 kg / t of synthetic slag are added so that the slag basicity in the ladle is 0.9 to 1.2.

[0031] Preferably, the chemical composition of the silicon carbide includes, in mass percent, SiC≧99.3% and other unavoidable impurities, and the chemical composition of the synthetic slag includes, in mass percent, 35-45% CaO, 45-55% SiO2, 3-8% MgO, and ≦2% Al2O3, and other unavoidable impurities.

[0032] (3) Billet casting process The molten steel tapped in the refining process is transferred to the continuous casting platform and left to stand for 15 minutes or more. When pouring into the large ladle, stop sand is introduced into the slag receiver, and the molten steel is poured protectively into the tundish to form a continuously cast billet.

[0033] Preferably, the stopping sand is silicon chrome stopping sand, in which Al2O3 is ≦5%.

[0034] Preferably, a magnesium coating is applied to the inner wall of the tundish, and Al2O3 in the magnesium coating is ≦2%; a magnesium-zirconium-carbon weir is used for the tundish weir, and Al2O3 in the magnesium-zirconium-carbon weir is ≦5%; and a magnesia-carbon nozzle is used for both the top nozzle and the submerged nozzle of the tundish, and Al2O3 in the magnesia-carbon nozzle is ≦5%.

[0035] The results showed that the acid-soluble aluminum Als in the molten steel of the tundish was ≦0.0005%, the content of Al2O3 inclusions in the molten steel was ≦10%, the size of Al2O3 inclusions and magnesia-alumina spinel inclusions was <5 μm, and the density of Al2O3 inclusions and magnesia-alumina spinel inclusions with a size of 1-5 μm was ≦0.0005 pieces / mm 2 is.

[0036] To clarify the objectives, technical solutions, and advantages of one embodiment of the present invention, the method for controlling brittle inclusions in a steel cord according to this embodiment will be further described below with reference to Examples 1 and 2. Obviously, Examples 1 and 2 described are only a part of the examples of the present invention, but not all of the examples.

[0037] Example 1 (1) Primary smelting process in the furnace Smelting was carried out in a 135 t converter. Table 1 shows the molten steel temperature, C content, and O content at the end of smelting in converters (1) to (4). [Table 1]

[0038] At the end of the smelting process, slag addition was stopped and steel was tapped. Before tapping, silicon carbide and 40–60% low-nitrogen carburizer were placed in the bottom of the ladle receiving the molten steel. During tapping, alloys were added sequentially to form an alloy. All alloys were added by the time the steel reached 75%. When the steel reached 80%, the remaining 40–60% low-nitrogen carburizer was added at a rate of 200–300 kg / min. After the low-nitrogen carburizer was completely dissolved in the molten steel, tapping was stopped and silicon carbide was added to the slag surface of the ladle. Synthetic slag was added to form the slag, and the slag basicity of the ladle was ≤ 0.6. Table 2 shows the amounts of silicon carbide placed in the bottom of the ladle and the silicon carbide and synthetic slag added to the slag surface of the ladle after tapping for converters (1)–(4). [Table 2]

[0039] The bottom blowing of the ladle was carried out throughout the entire tapping process. Table 3 shows the flow rates of the bottom blowing of the ladle for converters (1) to (4) at the beginning of tapping, during the alloying process, when the remaining 40 to 60% of the low-nitrogen carburizer was added after 80% of the steel was tapped, and when silicon carbide and synthetic slag were added to the slag surface of the ladle after tapping was completed. [Table 3]

[0040] (2) Refining process The molten steel that has undergone primary smelting in the furnace is transferred to the LF furnace for refining, and the chemical composition of the molten steel is determined to be, in mass percent, C 0.70-0.95%, Si 0.15-0.45%, Mn 0.25-0.80%, Cr 0.10-0.45%, P 0.007-0.015%, S 0.006-0.01%, Alt 0.0005-0.0008%, N 0.0015-0.0030%, O To achieve a molten steel with a CaO / SiO2 ratio of 0.001-0.002%, with the balance consisting of Fe and other unavoidable impurities, the temperature, chemical composition, and content of the molten steel were measured. The alloy was then added according to the detected chemical composition and content. A carbon wire was then introduced, lime, silicon carbide, and synthetic slag were added, and the slag was melted by applying current. The temperature of the molten steel was adjusted to 1510-1535°C. The slag composition, by mass, was adjusted to CaO / SiO2 = 0.9-1.2, Al2O3 ≤ 5%, MgO 4-8%, [MnO + T.Fe] 2-5%, with the balance consisting of other unavoidable impurities. The ladle bottom blowing was then switched to soft stirring mode, with a soft stirring time of > 20 min, and the steel was then tapped. The amounts of lime, silicon carbide, and synthetic slag added to the LF furnaces (1)-(4) and the slag basicity of the slag in the ladle are shown in Table 4. [Table 4]

[0041] Table 5 shows the ladle bottom blowing flow rate and soft stirring time in the process of detecting the molten steel temperature, chemical composition and its content, the process of adding the alloy and adding carbon wire, the process of applying electricity to melt the slag, and the soft stirring process for the LF furnaces with furnace numbers (1) to (4). [Table 5]

[0042] Here, the alloy contains ferrosilicon, metallic manganese, and ferrochrome, and the Al contents in the ferrosilicon, metallic manganese, and ferrochrome are shown in Table 6. Also, the C content in the ferrochrome is ≦0.15%, and the N content in the low-nitrogen carburizer is ≦0.015%. [Table 6]

[0043] The chemical composition of the silicon carbide is SiC≧99.3% by mass, and contains other unavoidable impurities. The chemical composition and mass percentage of the synthetic slag are shown in Table 7. [Table 7]

[0044] (3) Billet casting process The molten steel tapped in the refining process was transferred to the continuous casting platform and left to stand for 15 minutes or more. When pouring the molten steel into the large ladle, stop sand was introduced into the slag receiver, and the molten steel was poured protectively into the tundish to form a continuously cast billet.

[0045] The ladle bottom bricks, molten pool bricks, and ladle mouth bricks were all magnesia-carbon bricks, and had been used no more than 35 to 45 times; the ladle slag line bricks and breathable bricks were magnesium-zirconium-carbon bricks, and had been used no more than 15 to 25 times; the ladle long nozzle was a corundum long nozzle, and the inner wall of the long nozzle was coated with an SiO2 coating, with a thickness of 3 to 8 mm; the stop sand was silicon-chromium stop sand, the inner wall of the tundish was coated with a magnesium coating; the tundish weir was a magnesium-zirconium-carbon weir; and the tundish top nozzle and submerged nozzle were both magnesia-carbon nozzles.

[0046] Table 8 shows the Al2O3 contents in the ladle bottom bricks, molten pool bricks, ladle mouth bricks, slag line bricks, permeable bricks, the stop sand, the magnesium coating of the tundish, the weir, the top nozzle, and the submerged nozzle. [Table 8]

[0047] The molten steel sample from the tundish was scanned with a Zeiss scanning electron microscope to count inclusions >1 μm in size. Scan area: 1000 mm 2 The Al2O3 content in the inclusions was measured to be ≦8.5%, no Al2O3, magnesia-alumina spinel inclusions larger than 5 μm were observed, and the density of Al2O3, magnesia-alumina spinel inclusions with a size of 1 to 5 μm was ≦0.0004 pieces / mm 2 It was.

[0048] Example 2 (1) Primary smelting process in the furnace Smelting was carried out in a 100 t electric furnace. Table 9 shows the molten steel temperature, C content, and O content at the end of smelting for the electric furnaces with furnace numbers (1) to (4). [Table 9]

[0049] At the end of the smelting process, slag addition was stopped and steel was tapped. Before tapping, silicon carbide and 40–60% low-nitrogen carburizer were placed in the bottom of the ladle receiving the molten steel. During tapping, alloys were added sequentially to form an alloy. All alloys were added by the time the steel reached 75%. When the steel reached 80%, the remaining 40–60% low-nitrogen carburizer was added at a rate of 200–300 kg / min. After the low-nitrogen carburizer was completely dissolved in the molten steel, tapping was stopped and silicon carbide was added to the slag surface of the ladle. Synthetic slag was added to form the slag, and the slag basicity of the ladle was ≤ 0.6. Table 10 shows the amounts of silicon carbide placed in the bottom of the ladle and the silicon carbide and synthetic slag added to the slag surface of the ladle after tapping for electric furnaces (1)–(4). [Table 10]

[0050] The bottom blowing of the ladle was carried out throughout the entire tapping process. Table 11 shows the flow rates of the bottom blowing of the ladle for the electric furnaces (1) to (4) at the beginning of tapping, during the alloying process, when the remaining 40 to 60% of the low-nitrogen carburizer was added after 80% of the steel was tapped, and when silicon carbide and synthetic slag were added to the slag surface of the ladle after tapping was completed. [Table 11]

[0051] (2) Refining process The molten steel that has undergone primary smelting in the furnace is transferred to the LF furnace for refining, and the chemical composition of the molten steel is determined to be, in mass percent, C 0.70-0.95%, Si 0.15-0.45%, Mn 0.25-0.80%, Cr 0.10-0.45%, P 0.01-0.015%, S 0.008-0.01%, Alt 0.0005-0.0008%, N 0.0019-0.0030%, O To satisfy the requirement that the composition of the molten steel be 0.0011-0.0020%, with the balance being Fe and other unavoidable impurities, the temperature, chemical composition, and their contents of the molten steel were detected, and the alloy was added according to the detected chemical composition and their contents. Carbon wire was then introduced, lime, silicon carbide, and synthetic slag were added, and electricity was passed through to melt the slag. The temperature of the molten steel was adjusted to 1510-1535°C, and the slag composition was adjusted to satisfy the requirements, in mass percent, of CaO / SiO2 = 0.9-1.2, Al2O3 ≦ 5%, MgO 4-8%, [MnO + T.Fe] 2-5%, with the balance being other unavoidable impurities. Thereafter, the ladle bottom blowing was adjusted to soft stirring mode, the soft stirring time was set to > 20 min, and the steel was tapped. Table 12 shows the amounts of lime, silicon carbide, and synthetic slag added to the LF furnaces with furnace numbers (1) to (4) and the slag basicity of the slag in the ladle. [Table 12]

[0052] Table 13 shows the ladle bottom blowing flow rate and soft stirring time for the LF furnaces (1) to (4) in the process of detecting the molten steel temperature, chemical composition and its content, the process of adding the alloy and adding carbon wire, the process of applying current to melt the slag, and the soft stirring process. [Table 13]

[0053] Here, the alloy contains ferrosilicon, metallic manganese, and ferrochrome, and the Al contents in the ferrosilicon, metallic manganese, and ferrochrome are shown in Table 14. Also, the C content in the ferrochrome is ≦0.15%, and the N content in the low-nitrogen carburizer is ≦0.015%. [Table 14]

[0054] The chemical composition of the silicon carbide is SiC≧99.3% by mass, and contains other unavoidable impurities. The chemical composition and mass percentage of the synthetic slag are shown in Table 15. [Table 15]

[0055] (3) Billet casting process The molten steel tapped in the refining process was transferred to the continuous casting platform and left to stand for 15 minutes or more. When pouring the molten steel into the large ladle, stop sand was introduced into the slag receiver, and the molten steel was poured protectively into the tundish to form a continuously cast billet.

[0056] The ladle bottom bricks, molten pool bricks, and ladle mouth bricks were all magnesia-carbon bricks, and had been used no more than 35 to 45 times; the ladle slag line bricks and breathable bricks were magnesium-zirconium-carbon bricks, and had been used no more than 15 to 25 times; the ladle long nozzle was a corundum long nozzle, and the inner wall of the long nozzle was coated with an SiO2 coating, with a thickness of 3 to 8 mm; the stop sand was silicon-chromium stop sand, the inner wall of the tundish was coated with a magnesium coating; the tundish weir was a magnesium-zirconium-carbon weir; and the tundish top nozzle and submerged nozzle were both magnesia-carbon nozzles.

[0057] The Al2O3 contents in the ladle bottom bricks, molten pool bricks, ladle mouth bricks, slag line bricks, permeable bricks, the stop sand, the magnesium coating of the tundish, the weir, the top nozzle, and the submerged nozzle are shown in Table 16. [Table 16]

[0058] The molten steel sample from the tundish was scanned with a Zeiss scanning electron microscope to count inclusions >1 μm in size. Scan area: 1000 mm 2 The Al2O3 content in the inclusions was measured to be ≦10%, no Al2O3, magnesia-alumina spinel inclusions larger than 5 μm were observed, and the density of Al2O3, magnesia-alumina spinel inclusions with a size of 1 to 5 μm was ≦0.0005 pieces / mm 2 It was.

[0059] Furthermore, Figure 5 shows the distribution of inclusions in a steel cord according to one embodiment of the present invention in a ternary phase diagram of the SiO2-MnO-Al2O3 system. Comparing Figure 5 with Figure 1, it is clear that the inclusions in the steel cord of the present invention are mainly SiO2-MnO inclusions, and that the amount of brittle inclusions such as Al2O3 and magnesia-alumina spinel (MgO·Al2O3) is significantly reduced compared to steel cords manufactured by conventional manufacturing processes, thereby significantly reducing the rate of wire breakage due to brittle inclusions during drawing.

Claims

1. 1. A method for controlling brittle inclusions in a steel cord having chemical compositions in mass percent of 0.70 to 0.95% C, 0.15 to 0.45% Si, 0.25 to 0.80% Mn, 0.10 to 0.45% Cr, P≦0.015%, S≦0.01%, Alt≦0.0008%, N≦0.003%, and O≦0.002%, with the balance being Fe and other unavoidable impurities, a primary smelting process in which 0.5-1 kg / t of silicon carbide and 40-60% of low-nitrogen carburizer are laid at the bottom of a ladle receiving the molten steel before tapping, and alloys are added successively during tapping to alloy the steel, and all of the alloy is added by the time the steel reaches 75% of the tapping volume; when the steel reaches 80%, the remaining 40-60% of the low-nitrogen carburizer is added at a rate of 200-300 kg / min; after the low-nitrogen carburizer is completely dissolved in the molten steel, tapping is completed, and 0.5-1 kg / t of silicon carbide is added to the slag surface of the ladle, and 3-5 kg / t of synthetic slag containing, by mass, 35-45% CaO, 45-55% SiO2, 3-8% MgO, ≦2% Al2O3, and other unavoidable impurities is added to produce slag; The molten steel that has undergone primary smelting in the furnace is transferred to an LF furnace for refining, and the temperature, chemical components, and contents of the molten steel are detected to adjust the chemical composition of the molten steel to satisfy, in mass percent, C 0.70-0.95%, Si 0.15-0.45%, Mn 0.25-0.80%, Cr 0.10-0.45%, P≦0.015%, S≦0.01%, Alt≦0.0008%, N≦0.003%, O≦0.002%, with the balance being Fe and other unavoidable impurities. The temperature, chemical components, and contents of the molten steel are detected, and the alloy is added according to the detected chemical components and contents of the molten steel, and carbon wire is introduced, and lime, silicon carbide, and synthetic slag are added and electric current is applied to melt the slag. The temperature of the molten steel is adjusted to 1510-1535°C, and the slag components are, in mass percent, CaO / SiO ２ =0.9~1.2, Al ２ O ３ a refining process in which the steel is tapped while satisfying the following conditions: [MnO + T.Fe] 4-8%, [MnO + T.Fe] 2-5%, and the balance being other unavoidable impurities, and then the ladle bottom blowing is adjusted to a soft stirring mode in which the ladle bottom blowing flow rate of the stirring gas is 30-80 NL / min, and the soft stirring time is more than 20 min; a billet casting step of transferring the molten steel tapped in the refining step to a continuous casting platform and leaving it to stand for 15 minutes or more, introducing stopper sand from the large ladle into a slag receiver when pouring the molten steel into the large ladle to prevent the stopper sand from being mixed into the molten steel, and pouring the molten steel into a tundish while protecting it from air to form a continuously cast billet, in this order; The stopper sand is silicon chrome stopper sand, and Al 2 O 3 therein is ≦5%; the alloy contains ferrosilicon, metallic manganese, and ferrochromium, the ferrosilicon having Al≦0.035%, the metallic manganese having Al≦0.015%, the ferrochromium having Al≦0.020% and C≦0.15%, and the low-nitrogen carburizer having N≦0.015%.

2. The bottom bricks of the ladle, the molten pool bricks, and the ladle mouth bricks are all made of magnesia carbon bricks. ２ O ３ ≦3%, and the slag line bricks and breathable bricks of the ladle are made of magnesium-zirconium-carbon bricks, and the Al content of the magnesium-zirconium-carbon bricks is ２ O ３ ≦3%, and the long nozzle of the ladle is a corundum long nozzle, and the inner wall of the long nozzle is coated with SiO ２ 2. The method for controlling brittle inclusions in steel cord according to claim 1, wherein a coating is applied.

3. A magnesium coating is applied to the inner wall of the tundish, and Al in the magnesium coating ２ O ３ ≦2%, and the tundish weir is a magnesium-zirconium-carbon weir, and the Al content in the magnesium-zirconium-carbon weir is ２ O ３ ≦5%, and the upper nozzle and the submerged nozzle of the tundish are both magnesia carbon nozzles, and the Al in the magnesia carbon nozzle ２ O ３ 2. The method for controlling brittle inclusions in a steel cord according to claim 1, wherein the content of brittle inclusions in a steel cord is ≦5%.

4. 2. The method for controlling brittle inclusions in steel cord according to claim 1, wherein the in-furnace primary smelting step is performed in a converter or an electric furnace, and the molten steel temperature at an end point of smelting is 1650°C or higher, C is 0.10%, and O is 0.03% or lower.

5. 2. The method for controlling brittle inclusions in a steel cord according to claim 1, wherein, in the in-furnace primary smelting step, the flow rate of the stirring gas blown from the bottom of the ladle is 100 to 200 NL / min during the initial stage of tapping and during the alloying step, the flow rate of the stirring gas blown from the bottom of the ladle is 600 to 800 NL / min during the step of starting to add the remaining 40 to 60% of the low-nitrogen carburizer when 80% of the steel has been tapped, and the flow rate of the stirring gas blown from the bottom of the ladle is 300 to 500 NL / min during the step of adding silicon carbide and synthetic slag to the slag surface of the ladle to form slag after tapping has been completed.

6. 2. The method for controlling brittle inclusions in a steel cord according to claim 1, wherein, in the refining step, the flow rate of the stirring gas blown from the bottom of the ladle is 100 to 150 NL / min in the step of detecting the molten steel temperature, chemical components and their contents, the flow rate of the stirring gas blown from the bottom of the ladle is 300 to 400 NL / min in the step of adding the alloy and introducing carbon wire, the flow rate of the stirring gas blown from the bottom of the ladle is 200 to 300 NL / min in the step of melting the slag by applying electricity, and the flow rate of the stirring gas blown from the bottom of the ladle is 30 to 80 NL / min in the soft stirring step.

7. 2. The method for controlling brittle inclusions in a steel cord according to claim 1, wherein a slag basicity in a ladle is set to 0.6 or less from the end of tapping in the in-furnace primary smelting step until adjustment of the chemical components of the molten steel is completed in the refining step, and 1 to 2 kg / t of lime, 1 to 1.5 kg / t of silicon carbide, and 8 to 15 kg / t of synthetic slag are added in the refining step so that the slag basicity in the ladle becomes 0.9 to 1.

2.

8. The chemical composition of the silicon carbide added in the refining process includes, in mass percent, SiC≧99.3% and other unavoidable impurities, and the chemical composition of the synthetic slag added in the refining process includes, in mass percent, 35-45% CaO, SiO ２ 45-55%, MgO 3-8%, Al ２ O ３ 2. The method for controlling brittle inclusions in steel cord according to claim 1, characterized in that the content of brittle inclusions in steel cord is ≦2%, and other unavoidable impurities are included.

9. In the billet casting process, Als in the molten steel in the tundish is ≦0.0005%, and Al in the inclusions in the molten steel is ２ O ３ The content of inclusions is ≦10%, and Al ２ O ３ Inclusions, magnesia-alumina spinel inclusions of size <5 μm, Al of size 1-5 μm ２ O ３ Density of inclusions and magnesia-alumina spinel inclusions ≦0.0005 pieces / mm ２ 2. The method for controlling brittle inclusions in a steel cord according to claim 1, wherein:

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