Wire rod for tire cord steel and preparation method of wire rod

Abstract

The invention relates to a wire rod for tire cord steel and a preparation method of the wire rod, and belongs to the technical field of steelmaking. The production process flow of molten iron pre-desulfurization, electric furnace smelting, LF refining, continuous casting, rolling and temperature control cooling is adopted, and the abnormal structure of the wire rod grain boundary network cementite is relieved through the whole flow of continuous casting, steel rolling and temperature control cooling. According to the steel grade C content, the pulling speed of a continuous casting machine, the crystallizer and secondary cooling water amount, electromagnetic stirring and other technological parameters are set, the stirring effect of an electromagnetic stirrer at the tail end is fully played, the center density of a continuous casting billet is improved, center shrinkage cavities are eliminated, center looseness and segregation are relieved in combination with large withdrawal and straightening machine pressing force, and the continuous casting billet is obtained by controlling rolling and temperature control cooling technological parameters. The grade of tire cord steel wire rod net carbon cementite is effectively reduced, the structure uniformity of the wire rod is improved, center segregation, looseness and shrinkage of a 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 mainly used to make skeleton materials such as automobile tire meridians. In recent years, with the rise of new energy vehicles and the requirements for low carbon emissions, high reinforcement is the main development direction of steel cord. Improving strength can not only reduce the use of steel cord, but also reduce the use of rubber materials. For the high reinforcement of steel cord, it is usually achieved by increasing the carbon content and adding micro-alloying elements. With the increase of carbon content, it is more difficult to control the performance of wire rod structure, especially the control of network cementite. Therefore, it is necessary to consider the whole process from continuous casting to rolling to reduce the influence of network cementite.

[0003] At present, the main methods for controlling the network cementite of wire rod are: 1. Control of continuous casting process parameters, such as light pressure, reducing the segregation index of continuous casting billet, and then using the two-fire material forming process to control the network cementite of wire rod; 2. Optimization of 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 network cementite caused by segregation, that is, re-austenitizing the wire rod, using 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] The patent application with publication number CN115055654A discloses a high carbon steel wire rod and its production method, which mainly controls the center segregation of the continuous casting billet by light pressing treatment on the continuous casting billet, and then adopts the "two-fire material forming" process to obtain the wire rod. Although the segregation and looseness problems in the center area of ​​the continuous casting billet are significantly improved from the source, its production efficiency is reduced and the production cost is greatly increased.

[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 subjected to a salt bath 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] The patent application with publication number CN112375975A introduces a production method for controlling network cementite for wire rods of ultra-high-strength steel wire. By controlling the continuous casting superheat, crystallizer and end electromagnetic stirring, and light pressure reduction technology, the central carbon segregation coefficient is controlled within 1.08. At the same time, the rolling temperature and cooling control system are designed to control the segregation level within 1.0 and the network cementite is controlled within 2.0 on average. However, this method does not specifically quantify the crystallizer and end electromagnetic stirring and light pressure reduction technology, and the network cementite is controlled within a range of 2.0, which is too wide to meet the use requirements of fine steel cords.

[0007] The patent application with publication number CN111850400A introduces a method for controlling network cementite in ultra-high carbon cold-drawn steel wire rods. The method mainly achieves stable control of network cementite in ultra-high carbon cold-drawn steel wire rods 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 also belongs to 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 scheme thereof is as follows: A method for preparing a 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: Step 1: Pre-desulfurization of molten iron. Before desulfurization, the temperature of molten iron is ≥1400℃, the sulfur content in molten iron is ≤0.03%, and desulfurizer is added to the molten iron for pre-desulfurization. The consumption of desulfurizer is 4-6kg per ton of iron. After desulfurization, the temperature of molten iron is ≥1300℃, the sulfur content is ≤0.010%, and the slag removal rate is ≥98%; 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 mass content of C in tapped steel is ≥0.30%, the temperature of molten steel is ≥1630℃, the bottom blowing Ar control valve of the ladle 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 circle of the molten steel surface to be 1 / 120-1 / 100 of the diameter of the ladle, 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 circle of the molten steel surface to be 1 / 170-1 / 150 of the diameter of the ladle, 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 powder 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 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, when the mass content of steel grade C is 0.70%≤C<0.80%, the pulling speed is 2.95-3.05m / min, the water volume of the crystallizer is 2000-2050L / min, the specific 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 terminal 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 pulling 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; Continuously casting to obtain a continuous casting billet; 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; heating section, the furnace temperature is 900-960℃, the time is 24-30min; soaking section, the furnace temperature is 1000-1060℃, the time is 40-50min; Step 6: Cooling under controlled temperature.

[0010] Furthermore, in the step 1, the mass ratio of CaO to CaF in the desulfurizer is 9:1.

[0011] Furthermore, the continuous casting adopts an 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.

[0012] 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.

[0013] Furthermore, the electromagnetic stirrer at the end of continuous casting is 1.0 m long and is installed at 9 m from the lower mouth of the crystallizer. The straightening machine is installed at 13 m from the lower mouth of the crystallizer, and the frequency is 12 Hz.

[0014] 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 level, and a central shrinkage cavity of 0 level.

[0015] Furthermore, in the rolling process, the starting rolling temperature is 940-1000°C, and the spinning temperature is 800-860°C.

[0016] Furthermore, step 6 adopts the Stelmor controlled cooling process, and 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, and is numbered 1#-20# from the entrance section to the exit section, wherein 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, 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.

[0017] A wire rod for cord steel is prepared by the above-mentioned preparation method of the wire rod for cord steel. The diameter of the wire rod for cord steel is 5.0-6.0 mm, and the rating of the network cementite in the wire rod is less than or equal to level 1.

[0018] 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.

[0019] The principle of the present invention is as follows: In order to solve the problem of cementite network at grain boundaries of cord steel wire rod, the whole process of continuous casting, steel rolling and temperature controlled cooling is considered to reduce the abnormal structure of cementite network at grain boundaries of wire rod.

[0020] In the continuous casting process, first, the molten steel in the tundish is poured at a low superheat, which is conducive to the formation of equiaxed crystals inside the continuous casting billet and reduces the center segregation; secondly, according to the C content of the steel grade, the process parameters such as the continuous casting machine pulling speed, the crystallizer and the amount of secondary cooling water are adjusted, and the proportion of the liquid core of the continuous casting billet at the end electromagnetic stirrer position is controlled to be 30% to 40%, and the crystallizer and the end electromagnetic stirring parameter values ​​are adjusted to give full play to the stirring effect of the end electromagnetic stirrer, promote the flow of molten steel, and reduce the center segregation; finally, the continuous casting billet enters the straightening area, and a larger straightening machine is used to press down to increase the density of the center of the continuous casting billet, which plays a role in eliminating the center shrinkage cavity, looseness and reducing the center segregation. In summary, the center looseness of the continuous casting billet is 0-0.5, the center shrinkage cavity is 0, and the C segregation value at the center position is 0.95-1.05.

[0021] 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 starting rolling temperature and the wire drawing temperature is helpful to reduce the size of austenite, reduce the grain boundary enrichment concentration of C, further improve the quality of the wire rod, and ensure better uniformity of the wire rod.

[0022] The temperature-controlled cooling process adopts the Stelmor controlled cooling process, that is, the post-rolling cooling of the wire rod is realized on the Stelmor line, which is convenient for effectively controlling the cooling rate. Among them, the Stelmor cooling line is located between the laying head and the coiler and has a roller table for conveying the wire rod. The cooling speed of the wire rod is controlled by adjusting the roller table speed and the air volume of the fan, and the network cementite level in the wire rod is controlled to be less than or equal to level 1.

[0023] The beneficial effects of the present invention are: The present invention adjusts the process parameters such as the casting speed of the continuous casting machine, the amount of water in the crystallizer and the secondary cooling water, and the electromagnetic stirring parameters according to the C content of the steel grade, gives full play to the stirring effect of the terminal electromagnetic stirrer, and combines with the relatively large pressing force of the drawing and straightening machine to improve the central density of the continuous casting billet, eliminate the central shrinkage cavity, and reduce the central looseness and segregation; by controlling the rolling and temperature-controlled cooling process parameters, it is ensured that the grade of the grain boundary network cementite in the wire rod is less than or equal to level 1. DETAILED DESCRIPTION

[0024] 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 used to limit the scope of the present invention. Example 1

[0025] The following production process is adopted: hot metal pre-desulfurization → electric furnace smelting → LF refining → continuous casting → rolling and temperature-controlled cooling to produce LX72A wire rod, which specifically includes the following steps: Hot metal pre-desulfurization process: The molten iron is mechanically stirred, and lime powder and fluorite are sprayed in for desulfurization. Before desulfurization, the molten iron temperature is 1410℃, the S content is 0.025%, the mass ratio of CaO and CaF in the desulfurizer used is 9:1, the desulfurizer consumption per ton of iron is 6kg, and after desulfurization, the molten iron temperature is 1340℃, the S content is ≤0.010%, and the slag removal rate is ≥98%.

[0026] Electric furnace smelting process: The molten iron obtained by desulfurization is poured into the converter, and oxygen is blown to heat the molten iron, decarbonize and dephosphorize to obtain molten steel. The scrap steel loading is 60t, the molten iron loading is 60t, the total smelting time is 40min, the power-on time is 20min, the oxygen supply time is 15min, the submerged arc slag is used when the power is turned on, and the Ar gas supply intensity of the electric furnace bottom blowing is 0.03m 3 / (min·t), C content in tapped steel is 0.30%, molten steel temperature is 1630℃, the Ar control valve for bottom blowing of the ladle is opened before tapping, and the Ar control valve for bottom blowing 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 diameter of the ladle. 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, and the diameter of the bright circle on the molten steel surface is 1 / 150 of the diameter of the ladle. During the hoisting of the ladle to the refining process, argon must be blown throughout the bottom blowing process.

[0027] LF refining process: The molten steel is hoisted to the refining process for degassing, alloying, and temperature control to obtain molten steel with temperature and composition that meet the requirements. After the ladle is in place, the bottom blowing argon is connected and turned on, and the bottom blowing Ar control valve is adjusted according to each operation. When adding alloys to fine-tune the composition, the bottom blowing Ar control valve is adjusted, and the diameter of the bright circle on the molten steel surface is 1 / 120 of the ladle diameter; when adding lime and fluorite to make slag, 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; when adding SiC and SiFe powders to deoxidize the molten steel, the bottom blowing Ar control valve is adjusted, and the diameter of the bright circle on the molten steel surface is 1 / 180 of the ladle diameter; when the power is turned on to increase the temperature, the bottom blowing Ar control valve is adjusted, and the diameter of the bright circle on the molten steel surface is 1 / 210 of the ladle diameter; when there is no above operation and the molten steel in the ladle is softly stirred, the bottom blowing Ar control valve is adjusted, and the diameter of the bright circle on the molten steel surface is 1 / 250 of the ladle diameter.

[0028] Continuous casting process: The molten steel with the required temperature and composition is hoisted to the continuous casting platform for protective pouring to obtain the continuous casting billet. The cross-sectional size of 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, its upper edge 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, the end electromagnetic stirrer is 1.0m long and is installed at a position 9m away from the lower mouth of the crystallizer, and the tension straightening machine is installed at a position 13m away from the lower mouth of the crystallizer.

[0029] The molten steel forms a shell of a certain thickness in the crystallizer. The continuous casting billet is pulled by the straightening machine and enters the secondary cooling zone for water spray cooling. The continuous casting machine pulling speed is 3.00m / min, the superheat of the molten steel in the tundish is 15℃, the water volume of the crystallizer is 2020L / min, the specific water volume of the secondary cooling zone is 1.52L / kg, the current of the crystallizer electromagnetic stirrer is 630A and the frequency is 4Hz, the current of the terminal electromagnetic stirrer is 330A and the frequency is 12Hz, and the pressure value of the straightening machine is 23bar.

[0030] Take a low-magnification sample of the continuous casting billet, do a cross-section pickling, observe its central shrinkage cavity and central porosity, and analyze the C segregation at the central position. The central porosity of the continuous casting billet is level 0, the central shrinkage cavity is level 0, and the C segregation value at the central position is 0.98-1.02.

[0031] Rolling process and temperature control cooling process: The continuous casting billet is transported to the heating furnace for heating, and the wire rod is obtained through rough rolling, finishing rolling, water cooling, wire drawing, and Stelmor wire cooling. The continuous casting billet is heated in the heating furnace, which is divided into three sections: the preheating section has a furnace temperature of 800°C and a time of 16 minutes; the heating section has a furnace temperature of 900°C and a time of 24 minutes; the soaking section has a furnace temperature of 1000°C and a time of 40 minutes. The rolling start 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# on the air cooling line is 100%, the air volume of fans 7# and 8# is 80%, and the other fans are turned off.

[0032] The finished wire rod has a specification of 6mm and is corroded using a 4% nitric acid alcohol solution. A metallographic microscope is used to observe that the grade of the grain boundary network cementite structure at its center is level 0. Example 2

[0033] The following production process is adopted: hot metal pre-desulfurization → electric furnace smelting → LF refining → continuous casting → rolling and temperature-controlled cooling to produce LX87A wire rod, which specifically includes the following steps: Hot metal pre-desulfurization process: The molten iron is mechanically stirred, and lime powder and fluorite are sprayed in for desulfurization. Before desulfurization, the molten iron temperature is 1430℃, the S content is 0.023%, the mass ratio of CaO and CaF in the desulfurizer is 9:1, the desulfurizer consumption per ton of iron is 5kg, and after desulfurization, the molten iron temperature is 1360℃, the S content is ≤0.009%, and the slag removal rate is ≥98%.

[0034] Electric furnace smelting process: The molten iron obtained by desulfurization is poured into the converter, and oxygen is blown to heat the molten iron, decarbonize and dephosphorize to obtain molten steel. The scrap steel loading is 55t, the molten iron loading is 65t, the total smelting time is 38min, the power-on time is 18min, the oxygen supply time is 17min, the submerged arc slag is used when the power is turned on, 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 bottom blowing Ar control valve of the ladle is opened before tapping, and the bottom blowing Ar control valve is adjusted when about 30t of steel is tapped, 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 turn, and the bottom blowing Ar control valve is adjusted after 110t of steel is tapped, the diameter of the bright circle on the molten steel surface is 1 / 160 of the ladle diameter, and argon is blown throughout the bottom blowing process when the ladle is hoisted to the refining process.

[0035] LF refining process: The molten steel is hoisted to the refining process for degassing, alloying, and temperature control to obtain molten steel with temperature and composition that meet the requirements. After the ladle is in place, the bottom blowing argon is connected and turned on, and the bottom blowing Ar control valve is adjusted according to each operation. When adding alloys to fine-tune the composition, the bottom blowing Ar control valve is adjusted, and the diameter of the bright circle on the molten steel surface is 1 / 130 of the ladle diameter; when adding lime and fluorite to make slag, 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; when adding SiC and SiFe powders to deoxidize the molten steel, the bottom blowing Ar control valve is adjusted, and the diameter of the bright circle on the molten steel surface is 1 / 190 of the ladle diameter; when the power is turned on to increase the temperature, the bottom blowing Ar control valve is adjusted, and the diameter of the bright circle on the molten steel surface is 1 / 220 of the ladle diameter; when there is no above operation and the molten steel in the ladle is softly stirred, the bottom blowing Ar control valve is adjusted, and the diameter of the bright circle on the molten steel surface is 1 / 260 of the ladle diameter.

[0036] Continuous casting process: The molten steel with the required temperature and composition is hoisted to the continuous casting platform for protective pouring to obtain the continuous casting billet. The cross-sectional size of 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, its upper edge 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, the end electromagnetic stirrer is 1.0m long and is installed at a position 9m away from the lower mouth of the crystallizer, and the tension straightening machine is installed at a position 13m away from the lower mouth of the crystallizer.

[0037] The molten steel forms a shell of a certain thickness in the crystallizer. The continuous casting billet is pulled by the straightening machine and enters the secondary cooling zone for water spray cooling. The continuous casting machine pulling speed is 2.85m / min, the superheat of the molten steel in the tundish is 14℃, the water volume of the crystallizer is 1920L / min, the specific water volume of the secondary cooling zone is 1.42L / kg, the current of the crystallizer electromagnetic stirrer is 530A and the frequency is 4Hz, the current of the terminal electromagnetic stirrer is 430A and the frequency is 12Hz, and the pressure value of the straightening machine is 33bar.

[0038] Take a low-magnification sample of the continuous casting billet, do a cross-section pickling, observe its central shrinkage cavity and central porosity, and analyze the C segregation at the central position. The central porosity of the continuous casting billet is level 0, the central shrinkage cavity is level 0, and the C segregation value at the central position is 0.96-1.04.

[0039] Rolling process and temperature control cooling process: The continuous casting billet is transported to the heating furnace for heating, and the wire rod is obtained through rough rolling, finishing rolling, water cooling, wire drawing, and Stelmor wire cooling. The continuous casting billet is heated in the heating furnace, which is divided into three sections: the preheating section has a furnace temperature of 830°C and a time of 18 minutes; the heating section has a furnace temperature of 930°C and a time of 27 minutes; the soaking section has a furnace temperature of 1030°C and a time of 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# on the air cooling line is 100%, the air volume of fans 7# and 8# is 80%, and the other fans are turned off.

[0040] The finished wire rod has a specification of 5.5mm and is corroded using a 4% nitric acid alcohol solution. A metallographic microscope is used to observe that the grade of the grain boundary network cementite structure at its center is level 0. Example 3

[0041] The following production process is adopted: hot metal pre-desulfurization → electric furnace smelting → LF refining → continuous casting → rolling and temperature-controlled cooling to produce LX96A wire rod, which specifically includes the following steps: Hot metal pre-desulfurization process: The molten iron is mechanically stirred, and lime powder and fluorite are sprayed in for desulfurization. Before desulfurization, the molten iron temperature is 1450℃, the S content is 0.020%, the mass ratio of CaO and CaF in the desulfurizer is 9:1, the desulfurizer consumption per ton of iron is 4kg, and after desulfurization, the molten iron temperature is 1380℃, the S content is ≤0.008%, and the slag removal rate is ≥98%.

[0042] Electric furnace smelting process: The molten iron obtained by desulfurization is poured into the converter, and oxygen is blown to heat the molten iron, decarbonize and dephosphorize to obtain molten steel. The scrap steel loading is 50 tons, the molten iron loading is 70 tons, the total smelting time is 36 minutes, the power-on time is 16 minutes, the oxygen supply time is 19 minutes, and the submerged arc slag is used when the power is turned on. 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 bottom blowing Ar control valve of the ladle is opened before tapping, and the bottom blowing Ar control valve is adjusted when about 30t of steel is tapped, 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 turn, and the bottom blowing Ar control valve is adjusted after 110t of steel is tapped, the diameter of the bright circle on the molten steel surface is 1 / 170 of the ladle diameter, and argon is blown throughout the bottom blowing process when the ladle is hoisted to the refining process.

[0043] LF refining process: The molten steel is hoisted to the refining process for degassing, alloying, and temperature control to obtain molten steel with temperature and composition that meet the requirements. After the ladle is in place, the bottom blowing argon is connected and turned on, and the bottom blowing Ar control valve is adjusted according to each operation. When adding alloys to fine-tune the composition, the bottom blowing Ar control valve is adjusted, and the diameter of the bright circle of the molten steel surface is 1 / 140 of the diameter of the ladle; when adding lime and fluorite to make slag, the bottom blowing Ar control valve is adjusted, and the diameter of the bright circle of the molten steel surface is 1 / 170 of the diameter of the ladle; when adding SiC and SiFe powders to deoxidize the molten steel, the bottom blowing Ar control valve is adjusted, and the diameter of the bright circle of the molten steel surface is 1 / 200 of the diameter of the ladle; when the power is turned on to increase the temperature, the bottom blowing Ar control valve is adjusted, and the diameter of the bright circle of the molten steel surface is 1 / 230 of the diameter of the ladle; when there is no above operation and the molten steel in the ladle is softly stirred, the bottom blowing Ar control valve is adjusted, and the diameter of the bright circle of the molten steel surface is 1 / 270 of the diameter of the ladle.

[0044] Continuous casting process: The molten steel with the required temperature and composition is hoisted to the continuous casting platform for protective pouring to obtain the continuous casting billet. The cross-sectional size of 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, its upper edge 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, the end electromagnetic stirrer is 1.0m long and is installed at a position 9m away from the lower mouth of the crystallizer, and the tension straightening machine is installed at a position 13m away from the lower mouth of the crystallizer.

[0045] The molten steel forms a shell of a certain thickness in the crystallizer. The continuous casting billet is pulled by the straightening machine and enters the secondary cooling zone for water spray cooling. The continuous casting machine pulling speed is 2.70m / min, the superheat of the molten steel in the tundish is 13℃, the crystallizer water volume is 1820L / min, the specific water volume in the secondary cooling zone is 1.32L / kg, the crystallizer electromagnetic stirrer current is 430A, the frequency is 4Hz, the terminal electromagnetic stirrer current is 530A, the frequency is 12Hz, and the straightening machine pressure value is 43bar.

[0046] Take a low-magnification sample of the continuous casting billet, do a cross-section pickling, observe its central shrinkage cavity and central porosity, and analyze the C segregation at the central position. The central porosity of the continuous casting billet is 0.5 level, the central shrinkage cavity is 0 level, and the C segregation value at the central position is 0.95-1.05.

[0047] Rolling process and temperature control cooling process: The continuous casting billet is transported to the heating furnace for heating, and the wire rod is obtained through rough rolling, finishing rolling, water cooling, wire drawing, and Stelmor wire cooling. The continuous casting billet is heated in the heating furnace, which is divided into three sections: the preheating section has a furnace temperature of 860°C and a time of 20 minutes; the heating section has a furnace temperature of 960°C and a time of 30 minutes; the soaking section has a furnace temperature of 1060°C and a time of 50 minutes. The rolling start 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# on the air cooling line is 100%, the air volume of fans 7# and 8# is 80%, and the other fans are turned off.

[0048] The finished wire rod has a specification of 5mm and is corroded using a 4% nitric acid alcohol solution. A metallographic microscope is used to observe that the grade of the grain boundary network cementite structure at its center is level 1.

[0049] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope 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 hot metal pre-desulfurization → electric furnace smelting → LF refining → continuous casting → rolling → temperature controlled cooling, specifically: Step 1: Pre-desulfurization of molten iron. Before desulfurization, the temperature of molten iron is ≥1400℃, the sulfur content in molten iron is ≤0.03%, and desulfurizer is added to the molten iron for pre-desulfurization. The consumption of desulfurizer is 4-6kg per ton of iron. After desulfurization, the temperature of molten iron is ≥1300℃, the sulfur content is ≤0.010%, and the slag removal rate is ≥98%; 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 mass content of C in tapped steel is ≥0.30%, the temperature of molten steel is ≥1630℃, the bottom blowing Ar control valve of the ladle 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 circle of the molten steel surface to be 1 / 120-1 / 100 of the diameter of the ladle, 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 circle of the molten steel surface to be 1 / 170-1 / 150 of the diameter of the ladle, 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 powder 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 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, when the mass content of steel grade C is 0.70%≤C<0.80%, the pulling speed is 2.95-3.05m / min, the water volume of the crystallizer is 2000-2050L / min, the specific 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 terminal 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 pulling 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; Continuously casting to obtain a continuous casting billet; Step 5: rolling, the continuous casting billet is put into a 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; Step 6: Cooling under controlled temperature.

2. The method for preparing a wire rod for cord steel according to claim 1, characterized in that: In the step 1, the mass ratio of CaO to CaF in the desulfurizer is 9:

1.

3. The method for preparing a wire rod for cord steel according to claim 1, characterized in that: 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 degree of molten steel is 13-15℃.

4. The method for preparing a wire rod for cord steel according to claim 1, characterized in that: 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.

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

6. The method for preparing a wire rod for cord steel according to claim 1, characterized in that: 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.

7. The method for preparing a wire rod for cord steel according to claim 1, characterized in that: In the rolling process, the starting rolling temperature is 940-1000°C and the spinning temperature is 800-860°C.

8. The method for preparing a wire rod for cord steel according to claim 1, characterized in that: 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 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, 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.

9. A wire rod for cord steel, characterized in that: The wire rod for cord steel is prepared by the preparation method of the wire rod for cord steel according to any one of claims 1 to 6, wherein the diameter of the wire rod for cord steel is 5.0-6.0 mm, and the rating of the network cementite in the wire rod is less than or equal to grade 1.

10. The wire rod for cord steel according to claim 7, characterized in that: 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.