Wire rod for cord steel and preparation method thereof

Abstract

The present invention relates to a wire rod for cord steel and a preparation method thereof, and belongs to the technical field of steelmaking. The production process of "molten iron pre-desulfurization → electric furnace smelting → LF refining → continuous casting → rolling → temperature-controlled cooling" is adopted to reduce the abnormal network cementite structure of the wire rod grain boundary from the entire process of continuous casting, steel rolling and temperature-controlled cooling. According to the C content of the steel grade, the process parameters such as the continuous casting machine casting speed, the crystallizer and the secondary cooling water volume, and the electromagnetic stirring are set to give full play to the stirring effect of the terminal electromagnetic stirrer. Combined with the large pressing force of the straightening machine, the density of the center of the continuous casting billet is improved, the center shrinkage cavity is eliminated, and the center looseness and segregation are reduced. By controlling the rolling and temperature-controlled cooling process parameters, the carbon cementite level of the cord steel wire rod network is effectively reduced, the organizational uniformity of the wire rod is improved, the center segregation, looseness and shrinkage cavity of the continuous casting billet are effectively improved, and the quality of the wire rod is improved.

Description

Technical Field

[0001] The invention relates to a wire rod for cord steel and a preparation method thereof, belonging to the technical field of steelmaking. Background Art

[0002] Cord steel is primarily used to make radials and other structural materials for automotive tires. In recent years, with the rise of new energy vehicles and the demand for low carbon emissions, high strength has become a major development trend in steel cord. Improving strength not only reduces the use of steel cord but also reduces the use of rubber. High strength in steel cord is typically achieved by increasing carbon content and adding microalloying elements. However, increasing carbon content increases the difficulty in controlling the microstructure and properties of the wire rod, particularly the cementite network. Therefore, mitigating the impact of cementite network requires comprehensive consideration throughout the entire process, from continuous casting to rolling.

[0003] At present, the main methods for controlling the network cementite in wire rods are: 1. Control of the continuous casting process parameters, such as light reduction, to reduce the segregation index of the continuous casting billet, and then use the two-fire material forming process to control the network cementite in the wire rod; 2. Optimization of the rolling process, increasing the billet heating temperature or extending the heating time, promoting the diffusion of segregation, and increasing the cooling rate; 3. Elimination of the network cementite caused by segregation, that is, re-austenitizing the wire rod, using a salt bath or water bath treatment, so that the wire rod structure is transformed into a uniform sorbitized structure. The above methods will reduce production efficiency and increase production costs. Therefore, for those skilled in the art, how to use small square billets to produce cord steel wire rods that meet quality requirements has become a technical problem that needs to be solved urgently.

[0004] Patent application CN115055654A discloses a high-carbon steel wire rod and its production method. This method primarily involves subjecting continuous casting slabs to a light reduction treatment to control central segregation, followed by a "two-fired" process to produce the wire rod. While this significantly addresses the segregation and porosity issues in the central region of the slab, it also reduces production efficiency and significantly increases costs.

[0005] The patent application with publication number CN113512630A mainly introduces a method for eliminating network cementite in hypereutectoid steel wire rod. The hypereutectoid steel wire rod with network cementite is uncoiled and then introduced into a heating furnace and kept in the uniform temperature section of the heating furnace for 4-10 minutes. The wire rod is then transferred from the heating furnace to a salt bath tank and salt bathed for 30-120 seconds. However, this method is an after-the-fact solution, that is, a solution after network carbon appears, and cannot control wire rod segregation and network carbon formation from the source.

[0006] Patent application CN112375975A describes a method for producing ultra-high-strength steel wire rod with controlled cementite network. By controlling the continuous casting superheat, electromagnetic stirring at the mold and end, and soft reduction techniques, the central carbon segregation coefficient is controlled within 1.08. Furthermore, through designing the rolling temperature and controlled cooling system, the segregation level is controlled within 1.0, and the average cementite network is controlled within 2.0. However, this method does not specifically quantify the mold, end electromagnetic stirring, and soft reduction techniques, and the range of controlled cementite network at 2.0 is too wide to meet the requirements for fine steel cord.

[0007] Patent application with publication number CN111850400A introduces a method for controlling network cementite in ultra-high carbon cold-drawn steel wire rod. The method mainly achieves stable control of network cementite in ultra-high carbon cold-drawn steel wire rod through measures such as high-temperature diffusion, reducing rolling speed, increasing rolling temperature and spinning temperature, increasing recovery section length, and increasing cooling speed. This method is also a way of solving the problem after the fact and does not improve the segregation of continuous casting billets.

[0008] In order to solve the above problems, the present invention provides a wire rod for cord steel and a preparation method thereof. Summary of the Invention

[0009] In order to solve the above problems, the present invention discloses a wire rod for cord steel and a preparation method thereof, and the specific technical solution is as follows:

[0010] A method for preparing wire rod for cord steel includes a process flow of molten iron pre-desulfurization → electric furnace smelting → LF refining → continuous casting → rolling → temperature-controlled cooling, specifically:

[0011] Step 1: Pre-desulfurization of molten iron. Before desulfurization, the molten iron temperature is ≥1400℃, the sulfur content in the molten iron is ≤0.03%, and a desulfurizer is added to the molten iron for pre-desulfurization. The desulfurizer consumption is 4-6kg per ton of iron. After desulfurization, the molten iron temperature is ≥1300℃, the sulfur content is ≤0.010%, and the slag skimming rate is ≥98%;

[0012] Step 2: Electric furnace smelting, scrap steel loading is 50-60t, molten iron loading is 60-70t, total smelting time is 36-40min, power-on time is ≤20min, oxygen supply time is ≥15min, submerged arc slag is used when power is on, and the Ar gas supply intensity of the electric furnace bottom blowing is 0.03-0.05m 3 / (min·t), the C mass content of the tapped steel is ≥0.30%, the molten steel temperature is ≥1630℃, the ladle bottom blowing Ar control valve is opened before tapping, and the bottom blowing Ar control valve is adjusted when 30t of steel is tapped to control the diameter of the bright ring on the molten steel surface to be 1 / 120-1 / 100 of the ladle diameter, silicon-manganese alloy, ferrosilicon alloy, carbon powder, and lime are added to the ladle in sequence, and the bottom blowing Ar control valve is adjusted after 110t of steel is tapped to control the diameter of the bright ring on the molten steel surface to be 1 / 170-1 / 150 of the ladle diameter, and argon is blown throughout the bottom blowing process when the ladle is hoisted to the LF refining process;

[0013] Step 3: LF refining, adjust the bottom blowing Ar control valve to control the diameter of the bright circle on the molten steel surface to 1 / 140-1 / 120 of the ladle diameter;

[0014] When adding lime and fluorite to make slag, adjust the bottom blowing Ar control valve to control the diameter of the bright circle on the molten steel surface to 1 / 170-1 / 150 of the ladle diameter;

[0015] When adding SiC and SiFe powders to deoxidize the molten steel, adjust the bottom blowing Ar control valve to control the diameter of the bright circle on the molten steel surface to 1 / 200-1 / 180 of the ladle diameter;

[0016] When the power is turned on and the temperature is raised, adjust the bottom blowing Ar control valve to control the diameter of the bright circle on the molten steel surface to be 1 / 230-1 / 210 of the ladle diameter;

[0017] When the molten steel in the ladle is softly stirred, adjust the bottom blowing Ar control valve to control the diameter of the bright circle on the molten steel surface to be 1 / 270-1 / 250 of the ladle diameter;

[0018] Step 4: Continuous casting, when the mass content of steel grade C is 0.70%≤C<0.80%, the casting speed is 2.95-3.05m / min, the water volume of the crystallizer is 2000-2050L / min, the water volume of the secondary cooling zone is 1.50-1.55L / kg, the current of the crystallizer electromagnetic stirrer is 600-650A, the current of the end electromagnetic stirrer is 300-350A, and the pressure value of the straightening machine is 20-25bar;

[0019] When the steel grade C mass content is 0.80%≤C<0.90%, the pulling speed is 2.80-2.90m / min, the water volume of the crystallizer is 1900-1950L / min, the water volume of the secondary cooling zone is 1.40-1.45L / kg, the current of the crystallizer electromagnetic stirrer is 500-550A, the current of the end electromagnetic stirrer is 400-450A, and the pressure value of the straightening machine is 30-35bar;

[0020] When the steel grade C mass content is 0.90%≤C≤1.00%, the drawing speed is 2.65-2.75m / min, the water volume of the crystallizer is 1800-1850L / min, the water volume of the secondary cooling zone is 1.30-1.35L / kg, the current of the crystallizer electromagnetic stirrer is 400-450A, the current of the end electromagnetic stirrer is 500-550A, and the pressure value of the straightening machine is 40-45bar;

[0021] Continuous casting to obtain continuous casting billets;

[0022] Step 5: Rolling, the continuous casting billet is put into the heating furnace for heating, including: preheating section, furnace temperature is 800-860℃, time is 16-20min; heating section, furnace temperature is 900-960℃, time is 24-30min; soaking section, furnace temperature is 1000-1060℃, time is 40-50min;

[0023] Step 6: Cooling under controlled temperature.

[0024] Furthermore, in the step 1, the mass ratio of CaO to CaF in the desulfurizer is 9:1.

[0025] Furthermore, the continuous casting adopts induction heating tundish, the current value of the induction heating tundish is 0-1600A, the frequency is 500Hz, and the superheat of the molten steel is 13-15°C.

[0026] Furthermore, the cross-sectional size of the continuous casting billet produced by the continuous casting is 140mm×140mm, the length of the crystallizer is 1.0m, the height of the crystallizer electromagnetic stirrer is 0.5m, the upper edge of the crystallizer electromagnetic stirrer is 0.05m away from the upper mouth of the crystallizer, the meniscus of the molten steel is 0.13m away from the upper mouth of the crystallizer, and the frequency is 4Hz.

[0027] Furthermore, the electromagnetic stirrer at the end of continuous casting is 1.0m long and is installed at a position 9m away from the lower mouth of the crystallizer. The straightening machine is installed at a position 13m away from the lower mouth of the crystallizer, with a frequency of 12Hz.

[0028] Furthermore, the continuous casting billet obtained in the continuous casting process has a central C segregation index of 0.95-1.05, a central porosity of 0, and a central shrinkage cavity of 0.

[0029] Furthermore, in the rolling process, the starting rolling temperature is 940-1000°C, and the spinning temperature is 800-860°C.

[0030] Furthermore, step 6 adopts the Stelmor controlled cooling process. The Stelmor cooling line includes an inlet section, sections 1-10 and an outlet section. Each section is provided with two fans along the length direction of the roller. The sections are numbered 1#-20# from the inlet section to the outlet section, wherein the roller speed of the inlet section is 0.8m / s, the roller speed of the 1st section is 1.1m / s, the roller speed of the 2nd section is 1.3m / s, the roller speed of the 3rd section is 1.5m / s, the roller speed of sections 4-7 is 1.5m / s, the roller speed of sections 8-10 is 1.35m / s, the roller speed of the outlet section is 1.2m / s, the air volume of fans 1 to 6 is 100%, the air volume of fans 7# and 8# is 80%, and the remaining fans are turned off.

[0031] A wire rod for cord steel is produced by the above-mentioned method for producing the wire rod for cord steel. The wire rod for cord steel has a diameter of 5.0-6.0 mm and a network cementite rating of less than or equal to level 1 in the wire rod.

[0032] Furthermore, the chemical composition and mass content of the wire rod for cord steel are: 0.70%≤C≤1.00%, 0.30%≤Si≤0.50%, 0.30%≤Mn≤0.50%, 0.20%≤Cr≤0.40%, P≤0.015%, S≤0.01%, Al≤0.0006%, Ti≤0.0010%, N≤0.0030%, O≤0.0025%, and the balance is Fe and other inevitable impurities.

[0033] The principles of the present invention are as follows:

[0034] Aiming at the problem of network cementite at the grain boundaries of cord steel wire rod, the author considers how to reduce the abnormal organization of network cementite at the grain boundaries of wire rod from the whole process of continuous casting, rolling and temperature controlled cooling.

[0035] During the continuous casting process, molten steel from the tundish is poured at a low superheat, which promotes the formation of equiaxed grains within the continuous casting billet and reduces center segregation. Secondly, process parameters such as the casting speed, mold, and secondary cooling water volume are adjusted based on the carbon content of the steel grade. The liquid core of the continuous casting billet at the end electromagnetic stirrer is controlled to account for 30% to 40% of the billet. The mold and end electromagnetic stirring parameters are adjusted to maximize the stirring effect of the end electromagnetic stirrer, promote molten steel flow, and reduce center segregation. Finally, the continuous casting billet enters the straightening zone, where a higher pressure is applied to the straightening machine to increase the density of the continuous casting billet at the center, eliminating center shrinkage and porosity, and reducing center segregation. In summary, the continuous casting billet has a center porosity of 0-0.5, a center shrinkage of 0, and a center carbon segregation of 0.95-1.05.

[0036] In the rolling process, the temperature and time of the continuous casting billet in the preheating section, heating section and soaking section in the heating furnace are controlled to ensure that the billet temperature rises steadily. High temperature is conducive to the diffusion of C content inside the continuous casting billet, further reducing the local C segregation in the center. Controlling the rolling start temperature and the wire drawing temperature helps to reduce the austenite size and reduce the grain boundary enrichment concentration of C, further improving the wire rod quality and ensuring better wire rod uniformity.

[0037] The temperature-controlled cooling process utilizes the Stelmor controlled cooling process, meaning that post-rolling cooling of the wire rod is achieved on a Stelmor cooling line, which facilitates effective control of the cooling rate. The Stelmor cooling line, located between the laying head and the coiler, features a roller conveyor for conveying the wire rod. Adjusting the roller speed and fan volume controls the wire rod cooling rate, maintaining the network cementite level within the wire rod at or below level 1.

[0038] The beneficial effects of the present invention are:

[0039] The present invention adjusts process parameters such as the continuous casting machine drawing speed, the crystallizer and secondary cooling water volume, and the electromagnetic stirring parameters according to the C content of the steel grade, fully utilizes the stirring effect of the terminal electromagnetic stirrer, and combines with the large drawing and leveling machine pressing force to improve the center density of the continuous casting billet, eliminate the center shrinkage cavity, and reduce the center looseness and segregation; by controlling the rolling and temperature-controlled cooling process parameters, it is ensured that the grain boundary network cementite level in the wire rod is less than or equal to level 1. DETAILED DESCRIPTION

[0040] The present invention will be further described below in conjunction with specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. Example 1

[0041] The following production process is used to produce LX72A wire rod: hot metal pre-desulfurization → electric furnace smelting → LF refining → continuous casting → rolling and temperature-controlled cooling, which specifically includes the following steps:

[0042] Hot metal pre-desulfurization process:

[0043] The molten iron was mechanically stirred and desulfurized with lime powder and fluorite sprayed in. Before desulfurization, the molten iron temperature was 1410°C, the sulfur content was 0.025%, and the desulfurizer used had a CaO to CaF mass ratio of 9:1. The desulfurizer consumption was 6 kg per ton of iron. After desulfurization, the molten iron temperature was 1340°C, the sulfur content was ≤0.010%, and the slag removal rate was ≥98%.

[0044] Electric furnace smelting process:

[0045] The molten iron obtained by desulfurization is poured into the converter, and oxygen is blown into the molten iron to increase the temperature, decarburize and dephosphorize to obtain molten steel. The scrap steel loading amount is 60t, the molten iron loading amount is 60t, the total smelting time is 40min, the power-on time is 20min, and the oxygen supply time is 15min. When the power is on, submerged arc slag is used, and the Ar gas supply intensity of the electric furnace bottom blowing is 0.03m 3 / (min·t), the C content of the tapped steel is 0.30%, the molten steel temperature is 1630℃, the ladle bottom blowing Ar control valve is opened before tapping, and the bottom blowing Ar control valve is adjusted when about 30t of steel is tapped, and the diameter of the bright circle on the molten steel surface is 1 / 100 of the ladle diameter. Silicon manganese alloy, ferrosilicon alloy, carbon powder and lime are added to the ladle in sequence. After 110t of steel is tapped, the bottom blowing Ar control valve is adjusted, and the diameter of the bright circle on the molten steel surface is 1 / 150 of the ladle diameter. During the transportation of the ladle to the refining process, argon is blown at the bottom throughout the process.

[0046] LF refining process:

[0047] The molten steel is hoisted to the refining process for degassing, alloying, and temperature control to achieve molten steel with the required temperature and composition. Once the ladle is in place, bottom argon blowing is connected and started. The bottom argon control valve is adjusted according to the various operations. When adding alloys to fine-tune the composition, the bottom argon control valve is adjusted to a diameter of 1 / 120 of the ladle diameter. When adding lime or fluorite to form slag, the bottom argon control valve is adjusted to a diameter of 1 / 150 of the ladle diameter. When adding SiC or SiFe powders to deoxidize the steel, the bottom argon control valve is adjusted to a diameter of 1 / 180 of the ladle diameter. When power is turned on to increase the temperature, the bottom argon control valve is adjusted to a diameter of 1 / 210 of the ladle diameter. When not performing the above operations or when the molten steel in the ladle is softly stirred, the bottom argon control valve is adjusted to a diameter of 1 / 250 of the ladle diameter.

[0048] Continuous casting process:

[0049] Molten steel that meets the required temperature and composition is hoisted onto the continuous casting platform for protected pouring to produce continuous casting billets. The continuous casting machine has a cross-sectional dimension of 140mm x 140mm, a mold length of 1.0m, and an electromagnetic stirrer at a height of 0.5m, with its upper edge 0.05m from the mold top. The meniscus of the molten steel is 0.13m from the mold top. The end electromagnetic stirrer is 1.0m long and is installed 9m from the mold bottom. The tension leveler is installed 13m from the mold bottom.

[0050] The molten steel forms a shell of a certain thickness in the mold. The continuous cast slab is then pulled by the straightening machine and then cooled by water spray in the secondary cooling zone. The casting speed of the continuous casting machine is 3.00m / min, the superheat of the molten steel in the tundish is 15°C, the water flow in the mold is 2020L / min, the specific water flow in the secondary cooling zone is 1.52L / kg, the current of the electromagnetic stirrer in the mold is 630A and the frequency is 4Hz, the current of the electromagnetic stirrer at the end is 330A and the frequency is 12Hz, and the pressure in the straightening machine is 23bar.

[0051] A low-magnification sample was taken from the continuous casting billet, and the cross section was pickled to observe its central shrinkage and central porosity, and analyze the C segregation at the central position. The central porosity of the continuous casting billet was level 0, the central shrinkage was level 0, and the C segregation value at the central position was 0.98-1.02.

[0052] Rolling process and temperature control cooling process:

[0053] The continuous casting billet is transported to a heating furnace for heating. After rough rolling, finishing rolling, water cooling, wire drawing, and Stelmor cooling, the wire rod is produced. The continuous casting billet enters the heating furnace for heating. The heating furnace is divided into three sections: a preheating section at 800°C for 16 minutes; a heating section at 900°C for 24 minutes; and a soaking section at 1000°C for 40 minutes. The starting rolling temperature is 940°C, and the wire drawing temperature is 800°C. The roller speed of the entrance section is 0.8m / s, the roller speed of the first section is 1.1m / s, the roller speed of the second section is 1.3m / s, the roller speed of the third section is 1.5m / s, the roller speed of sections 4-7 is 1.5m / s, the roller speed of sections 8-10 is 1.35m / s, and the roller speed of the exit section is 1.2m / s. The air volume of fans 1# to 6# in the air cooling line is 100%, the air volume of fans 7# and 8# is 80%, and the other fans are turned off.

[0054] The finished wire rod has a specification of 6mm and is corroded with 4% nitric acid alcohol solution. The metallographic microscope is used to observe that the grain boundary network cementite structure at the center is grade 0. Example 2

[0055] The following production process is used to produce LX87A wire rod: hot metal pre-desulfurization → electric furnace smelting → LF refining → continuous casting → rolling and temperature-controlled cooling, which specifically includes the following steps:

[0056] Hot metal pre-desulfurization process:

[0057] The molten iron was mechanically stirred and desulfurized with lime powder and fluorite sprayed in. Before desulfurization, the molten iron temperature was 1430°C, the sulfur content was 0.023%, and the desulfurizer used had a CaO to CaF mass ratio of 9:1. The desulfurizer consumption was 5 kg per ton of iron. After desulfurization, the molten iron temperature was 1360°C, the sulfur content was ≤0.009%, and the slag removal rate was ≥98%.

[0058] Electric furnace smelting process:

[0059] The molten iron obtained by desulfurization is poured into the converter, and oxygen is blown into the molten iron to increase the temperature, decarburize and dephosphorize to obtain molten steel. The scrap steel loading amount is 55t, the molten iron loading amount is 65t, the total smelting time is 38min, the power-on time is 18min, and the oxygen supply time is 17min. When the power is turned on, submerged arc slag is used, and the Ar gas supply intensity of the electric furnace bottom blowing is 0.05m 3 / (min·t), the C content of the tapped steel is 0.35%, the molten steel temperature is 1640℃, the ladle bottom blowing Ar control valve is opened before tapping, and the bottom blowing Ar control valve is adjusted when about 30t of steel is tapped, and the diameter of the bright circle on the molten steel surface is 1 / 110 of the ladle diameter. Silicon manganese alloy, ferrosilicon alloy, carbon powder and lime are added to the ladle in sequence. After 110t of steel is tapped, the bottom blowing Ar control valve is adjusted, and the diameter of the bright circle on the molten steel surface is 1 / 160 of the ladle diameter. During the transportation of the ladle to the refining process, argon is required to be blown at the bottom throughout the process.

[0060] LF refining process:

[0061] The molten steel is hoisted to the refining process for degassing, alloying, and temperature control to achieve molten steel with the required temperature and composition. Once the ladle is in place, bottom argon blowing is connected and started. The bottom argon control valve is adjusted according to the various operations. When adding alloys to fine-tune the composition, the bottom argon control valve is adjusted to a diameter of 1 / 130 of the ladle diameter. When adding lime or fluorite to form slag, the bottom argon control valve is adjusted to a diameter of 1 / 160 of the ladle diameter. When adding SiC or SiFe powders to deoxidize the steel, the bottom argon control valve is adjusted to a diameter of 1 / 190 of the ladle diameter. When power is turned on to increase the temperature, the bottom argon control valve is adjusted to a diameter of 1 / 220 of the ladle diameter. When not performing the above operations or when the molten steel in the ladle is softly stirred, the bottom argon control valve is adjusted to a diameter of 1 / 260 of the ladle diameter.

[0062] Continuous casting process:

[0063] Molten steel that meets the required temperature and composition is hoisted onto the continuous casting platform for protected pouring to produce continuous casting billets. The continuous casting machine has a cross-sectional dimension of 140mm x 140mm, a mold length of 1.0m, and an electromagnetic stirrer at a height of 0.5m, with its upper edge 0.05m from the mold top. The meniscus of the molten steel is 0.13m from the mold top. The end electromagnetic stirrer is 1.0m long and is installed 9m from the mold bottom. The tension leveler is installed 13m from the mold bottom.

[0064] The molten steel forms a shell of a certain thickness in the mold. The continuous cast slab is then pulled by the straightening machine and then cooled by water spray in the secondary cooling zone. The casting speed of the continuous casting machine is 2.85m / min, the superheat of the molten steel in the tundish is 14°C, the water flow rate in the mold is 1920L / min, the specific water flow rate in the secondary cooling zone is 1.42L / kg, the current of the electromagnetic stirrer in the mold is 530A and the frequency is 4Hz, the current of the electromagnetic stirrer at the end is 430A and the frequency is 12Hz, and the pressure in the straightening machine is 33bar.

[0065] A low-magnification sample was taken from the continuous casting billet, and the cross section was pickled to observe its central shrinkage and central porosity, and analyze the C segregation at the central position. The central porosity of the continuous casting billet was level 0, the central shrinkage was level 0, and the C segregation value at the central position was 0.96-1.04.

[0066] Rolling process and temperature control cooling process:

[0067] The continuous casting billet is transported to a heating furnace for heating. It undergoes rough rolling, finishing rolling, water cooling, wire drawing, and Stelmor cooling to produce wire rod. The continuous casting billet enters the heating furnace for heating. The heating furnace is divided into three sections: a preheating section at 830°C for 18 minutes; a heating section at 930°C for 27 minutes; and a soaking section at 1030°C for 45 minutes. The starting rolling temperature is 970°C, and the wire drawing temperature is 830°C. The roller speed of the entrance section is 0.8m / s, the roller speed of the first section is 1.1m / s, the roller speed of the second section is 1.3m / s, the roller speed of the third section is 1.5m / s, the roller speed of sections 4-7 is 1.5m / s, the roller speed of sections 8-10 is 1.35m / s, and the roller speed of the exit section is 1.2m / s. The air volume of fans 1# to 6# in the air cooling line is 100%, the air volume of fans 7# and 8# is 80%, and the other fans are turned off.

[0068] The finished wire rod has a specification of 5.5mm and is corroded with 4% nitric acid alcohol solution. The metallographic microscope is used to observe that the grain boundary network cementite structure at the center is grade 0. Example 3

[0069] The following production process is used to produce LX96A wire rod: hot metal pre-desulfurization → electric furnace smelting → LF refining → continuous casting → rolling and temperature-controlled cooling, which specifically includes the following steps:

[0070] Hot metal pre-desulfurization process:

[0071] The molten iron was mechanically stirred and desulfurized with lime powder and fluorite sprayed in. Before desulfurization, the molten iron temperature was 1450°C, the sulfur content was 0.020%, and the desulfurizer used had a CaO to CaF mass ratio of 9:1. The desulfurizer consumption was 4 kg per ton of iron. After desulfurization, the molten iron temperature was 1380°C, the sulfur content was ≤0.008%, and the slag removal rate was ≥98%.

[0072] Electric furnace smelting process:

[0073] The molten iron obtained by desulfurization is poured into the converter, and oxygen is blown into the molten iron to increase the temperature, decarburize and dephosphorize to obtain molten steel. The scrap steel loading amount is 50t, the molten iron loading amount is 70t, the total smelting time is 36min, the power-on time is 16min, and the oxygen supply time is 19min. When the power is turned on, submerged arc slag is used, and the Ar gas supply intensity of the electric furnace bottom blowing is 0.05m 3 / (min·t), the C content of the tapped steel is 0.40%, the molten steel temperature is 1650℃, the ladle bottom blowing Ar control valve is opened before tapping, and the bottom blowing Ar control valve is adjusted when about 30t of steel is tapped, and the diameter of the bright circle on the molten steel surface is 1 / 120 of the ladle diameter. Silicon manganese alloy, ferrosilicon alloy, carbon powder and lime are added to the ladle in sequence. After 110t of steel is tapped, the bottom blowing Ar control valve is adjusted, and the diameter of the bright circle on the molten steel surface is 1 / 170 of the ladle diameter. During the transportation of the ladle to the refining process, argon is blown at the bottom throughout the process.

[0074] LF refining process:

[0075] The molten steel is hoisted to the refining process for degassing, alloying, and temperature control to achieve molten steel with the required temperature and composition. Once the ladle is in place, bottom argon blowing is connected and started. The bottom argon control valve is adjusted according to the various operations. When adding alloys to fine-tune the composition, the bottom argon control valve is adjusted to keep the diameter of the molten steel surface bright ring at 1 / 140 of the ladle diameter. When adding lime or fluorite to form slag, the bottom argon control valve is adjusted to keep the diameter of the molten steel surface bright ring at 1 / 170 of the ladle diameter. When adding SiC and SiFe powders to deoxidize the molten steel, the bottom argon control valve is adjusted to keep the diameter of the molten steel surface bright ring at 1 / 200 of the ladle diameter. When power is turned on to increase the temperature, the bottom argon control valve is adjusted to keep the diameter of the molten steel surface bright ring at 1 / 230 of the ladle diameter. When not performing the above operations or when the molten steel in the ladle is softly stirred, the bottom argon control valve is adjusted to keep the diameter of the molten steel surface bright ring at 1 / 270 of the ladle diameter.

[0076] Continuous casting process:

[0077] Molten steel that meets the required temperature and composition is hoisted onto the continuous casting platform for protected pouring to produce continuous casting billets. The continuous casting machine has a cross-sectional dimension of 140mm x 140mm, a mold length of 1.0m, and an electromagnetic stirrer at a height of 0.5m, with its upper edge 0.05m from the mold top. The meniscus of the molten steel is 0.13m from the mold top. The end electromagnetic stirrer is 1.0m long and is installed 9m from the mold bottom. The tension leveler is installed 13m from the mold bottom.

[0078] The molten steel forms a shell of a certain thickness in the mold. The continuous cast slab is then pulled by the straightening machine and then cooled by water spray in the secondary cooling zone. The casting speed of the continuous casting machine is 2.70m / min, the superheat of the molten steel in the tundish is 13°C, the water flow rate in the mold is 1820L / min, the specific water flow rate in the secondary cooling zone is 1.32L / kg, the current of the electromagnetic stirrer in the mold is 430A and the frequency is 4Hz, the current of the electromagnetic stirrer at the end is 530A and the frequency is 12Hz, and the pressure in the straightening machine is 43bar.

[0079] Take a low-magnification sample of the continuous casting billet, perform pickling on the cross section, observe its central shrinkage and central porosity, and analyze the C segregation at the central position. The central porosity of the continuous casting billet is 0.5, the central shrinkage is 0, and the C segregation value at the central position is 0.95-1.05.

[0080] Rolling process and temperature control cooling process:

[0081] The continuous casting billet is transported to a heating furnace for heating. After rough rolling, finishing rolling, water cooling, wire drawing, and Stelmor cooling, the wire rod is produced. The continuous casting billet enters the heating furnace for heating. The heating furnace is divided into three sections: a preheating section at 860°C for 20 minutes; a heating section at 960°C for 30 minutes; and a soaking section at 1060°C for 50 minutes. The starting rolling temperature is 1000°C, and the wire drawing temperature is 860°C. The roller speed of the entrance section is 0.8m / s, the roller speed of the first section is 1.1m / s, the roller speed of the second section is 1.3m / s, the roller speed of the third section is 1.5m / s, the roller speed of sections 4-7 is 1.5m / s, the roller speed of sections 8-10 is 1.35m / s, and the roller speed of the exit section is 1.2m / s. The air volume of fans 1# to 6# in the air cooling line is 100%, the air volume of fans 7# and 8# is 80%, and the other fans are turned off.

[0082] The finished wire rod has a specification of 5mm and is corroded with 4% nitric acid alcohol solution. The metallographic microscope is used to observe that the grain boundary network cementite structure at the center is grade 1.

[0083] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A method for preparing a wire rod for cord steel, characterized in that: The process includes molten iron pre-desulfurization → electric furnace smelting → LF refining → continuous casting → rolling → temperature controlled cooling, specifically: Step 1: Pre-desulfurization of molten iron. Before desulfurization, the molten iron temperature is ≥1400℃, the sulfur content in the molten iron is ≤0.03%, and a desulfurizer is added to the molten iron for pre-desulfurization. The desulfurizer consumption is 4-6kg per ton of iron. After desulfurization, the molten iron temperature is ≥1300℃, the sulfur content is ≤0.010%, and the slag removal rate is ≥98%. The mass ratio of CaO to CaF in the desulfurizer is 9:

1. Step 2: Electric furnace smelting, scrap steel loading is 50-60t, molten iron loading is 60-70t, total smelting time is 36-40min, power-on time is ≤20min, oxygen supply time is ≥15min, submerged arc slag is used when power is on, and the Ar gas supply intensity of the electric furnace bottom blowing is 0.03-0.05m 3 / (min·t), the C mass content of the tapped steel is ≥0.30%, the molten steel temperature is ≥1630℃, the ladle bottom blowing Ar control valve is opened before tapping, and the bottom blowing Ar control valve is adjusted when 30t of steel is tapped to control the diameter of the bright ring on the molten steel surface to be 1 / 120-1 / 100 of the ladle diameter, silicon-manganese alloy, ferrosilicon alloy, carbon powder, and lime are added to the ladle in sequence, and the bottom blowing Ar control valve is adjusted after 110t of steel is tapped to control the diameter of the bright ring on the molten steel surface to be 1 / 170-1 / 150 of the ladle diameter, and argon is blown throughout the bottom blowing process when the ladle is hoisted to the LF refining process; Step 3: LF refining, adjust the bottom blowing Ar control valve to control the diameter of the bright circle on the molten steel surface to 1 / 140-1 / 120 of the ladle diameter; When adding lime and fluorite to make slag, adjust the bottom blowing Ar control valve to control the diameter of the bright circle on the molten steel surface to 1 / 170-1 / 150 of the ladle diameter; When adding SiC and SiFe powders to deoxidize the molten steel, adjust the bottom blowing Ar control valve to control the diameter of the bright circle on the molten steel surface to 1 / 200-1 / 180 of the ladle diameter; When the power is turned on and the temperature is raised, adjust the bottom blowing Ar control valve to control the diameter of the bright circle on the molten steel surface to be 1 / 230-1 / 210 of the ladle diameter; When the molten steel in the ladle is softly stirred, adjust the bottom blowing Ar control valve to control the diameter of the bright circle on the molten steel surface to be 1 / 270-1 / 250 of the ladle diameter; Step 4: Continuous casting. The continuous casting machine uses an induction heating tundish. When the mass content of steel C is 0.70%≤C<0.80%, the casting speed is 2.95-3.05m / min, the water volume of the crystallizer is 2000-2050L / min, the water volume of the secondary cooling zone is 1.50-1.55L / kg, the current of the crystallizer electromagnetic stirrer is 600-650A, the current of the end electromagnetic stirrer is 300-350A, and the pressure value of the straightening machine is 20-25bar. When the steel grade C mass content is 0.80%≤C<0.90%, the pulling speed is 2.80-2.90m / min, the water volume of the crystallizer is 1900-1950L / min, the water volume of the secondary cooling zone is 1.40-1.45L / kg, the current of the crystallizer electromagnetic stirrer is 500-550A, the current of the end electromagnetic stirrer is 400-450A, and the pressure value of the straightening machine is 30-35bar; When the steel grade C mass content is 0.90%≤C≤1.00%, the drawing speed is 2.65-2.75m / min, the water volume of the crystallizer is 1800-1850L / min, the water volume of the secondary cooling zone is 1.30-1.35L / kg, the current of the crystallizer electromagnetic stirrer is 400-450A, the current of the end electromagnetic stirrer is 500-550A, and the pressure value of the straightening machine is 40-45bar; Continuous casting to obtain continuous casting billets; Step 5: rolling, the continuous casting billet is put into the heating furnace for heating, including: preheating section, the furnace temperature is 800-860℃, the time is 16-20min; In the heating section, the furnace temperature is 900-960℃ and the time is 24-30min; in the soaking section, the furnace temperature is 1000-1060℃ and the time is 40-50min; the spinning temperature is 800-860℃; Step 6: Cooling under controlled temperature.

2. The method for preparing a wire rod for cord steel according to claim 1, wherein: The current value of the induction heating tundish is 0-1600A, the frequency is 500Hz, and the superheat of the molten steel is 13-15°C.

3. The method for preparing a wire rod for cord steel according to claim 1, wherein: The cross-sectional size of the continuous casting billet produced by the continuous casting machine is 140mm×140mm, the length of the crystallizer is 1.0m, the height of the crystallizer electromagnetic stirrer is 0.5m, the upper edge of the crystallizer electromagnetic stirrer is 0.05m away from the upper mouth of the crystallizer, the meniscus of the molten steel is 0.13m away from the upper mouth of the crystallizer, and the frequency is 4Hz.

4. The method for preparing a wire rod for cord steel according to claim 1, wherein: The electromagnetic stirrer at the end of the continuous casting machine is 1.0m long and is installed at a position 9m away from the lower mouth of the crystallizer. The straightening machine is installed at a position 13m away from the lower mouth of the crystallizer, with a frequency of 12Hz.

5. The method for preparing a wire rod for cord steel according to claim 1, wherein: The continuous casting billet obtained in the continuous casting process has a center C segregation index of 0.95-1.05, a center porosity of 0, and a center shrinkage cavity of 0.

6. The method for preparing a wire rod for cord steel according to claim 1, wherein: In the rolling process, the starting rolling temperature is 940-1000°C.

7. The method for preparing a wire rod for cord steel according to claim 1, wherein: The step 6 adopts the Stelmor controlled cooling process. The Stelmor cooling line includes an entrance section, sections 1-10 and an exit section. Each section is provided with two fans along the length direction of the roller. The sections are numbered 1#-20# from the entrance section to the exit section. The roller speed of the entrance section is 0.8m / s, the roller speed of the 1st section is 1.1m / s, the roller speed of the 2nd section is 1.3m / s, the roller speed of the 3rd section is 1.5m / s, the roller speed of sections 4-7 is 1.5m / s, the roller speed of sections 8-10 is 1.35m / s, the roller speed of the exit section is 1.2m / s, the air volume of fans 1 to 6 is 100%, the air volume of fans 7# and 8# is 80%, and the remaining fans are turned off.

8. A wire rod for cord steel, characterized in that: The wire rod for cord steel is produced by the method for producing the wire rod for cord steel according to any one of claims 1 to 7, wherein the wire rod for cord steel has a diameter of 5.0-6.0 mm and a network cementite rating of less than or equal to grade 1 in the wire rod; The chemical composition and mass content of the wire rod for cord steel are: 0.70%≤C≤1.00%, 0.30%≤Si≤0.50%, 0.30%≤Mn≤0.50%, 0.20%≤Cr≤0.40%, P≤0.015%, S≤0.01%, Al≤0.0006%, Ti≤0.0010%, N≤0.0030%, O≤0.0025%, and the balance is Fe and other inevitable impurities.