Tire cord steel as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of pure steel preparation, and particularly relates to tire cord steel and a preparation method and application thereof. The preparation method of the tire cord steel comprises the steps that tire cord steel raw materials are sequentially subjected to EAF electric furnace smelting, CAS refining and continuous casting treatment; the CAS refining comprises the steps that a top-blowing argon gun is arranged above a steel ladle, and CAS top-blowing argon deslagging is carried out, so that no slag exists in an isolation hood during CAS treatment; and the continuous casting tundish is subjected to heat preservation by using a carbonized rice husk covering agent. According to the specific preparation method, CaSi type inclusions in the steel are effectively reduced, and the tire cord steel with high cleanliness is stably produced.

Description

Technical Field

[0001] The invention belongs to the technical field of pure steel preparation, and in particular relates to a cord steel and a preparation method and application thereof. Background Art

[0002] At present, the market has increasingly strict requirements on cord steel inclusions. In addition to strictly controlling Al 2 O 3 In addition to brittle inclusions, the size of silicate inclusions is also receiving increasing attention.

[0003] For silicon-manganese deoxidized cord steel, there are four main types of inclusions in the steel, namely MnS, Al-rich inclusions, MnSi, and CaSi. Among them, MnS inclusions have strong deformation ability and deform in the same way as the steel matrix during rolling. Such inclusions are considered harmless to cord steel; for Al-rich inclusions, various steel companies have strengthened the purchase and control of the Al content of alloys, refractory materials, and auxiliary materials, and have not adopted Al deoxidation, which has basically avoided such large particle inclusions; MnSi (MnO-SiO 2 -Al 2 O 3 The inclusions are deoxidized inclusions generated by deoxidation of ferrosilicon and ferromanganese in cord steel; CaSi type (CaO-SiO 2 -Al 2 O 3 The inclusions are produced by the reaction between molten steel and Ca-based substances in the slag. Analysis of wire rod inclusions found that large-sized (≥15μm) inclusions are mainly CaSi-based, accounting for more than 95%. With product upgrades, quality requirements are getting higher and higher. The subsequent drawing of high-strength cord steel is getting thinner and thinner, and large-sized CaSi-based inclusions need to be strictly controlled.

[0004] The traditional electric furnace steelmaking process uses the process of electric furnace EAF, refined LF, vacuum VD / RH, and continuous casting CCM to produce cord steel. The main process routes are: 1) electric furnace EAF + refined LF + vacuum VD, RH + continuous casting CCM; 2) electric furnace EAF + refined LF + continuous casting CCM. The cord steel produced by these two processes is processed with LF.

[0005] LF is an off-furnace refining method that uses electric arc heating, also known as a ladle heating furnace. This treatment method can achieve functions such as electric arc heating, composite slag refining, argon blowing stirring and alloy adjustment. Large-sized inclusions are mainly CaSi, and the number of such inclusions is very small before LF treatment, and gradually increases during the LF treatment process. The main reason is that as the contact time between molten steel and slag increases, the Ca content increases after the refining slag is involved and the oxygen potential of the molten steel decreases, and the number of CaSi inclusions produced is large, and there is a problem of exceeding the standard. This type of inclusion is formed when CaO-containing substances in the slag enter the molten steel from top to bottom. In addition, the molten steel absorbs nitrogen seriously during the LF refining process, so a vacuum treatment process is added to reduce nitrogen, which increases the production process and increases costs. Summary of the invention

[0006] Therefore, the technical problem to be solved by the present invention is to overcome the defect of the existing cord steel having many large-sized CaSi inclusions, thereby providing a cord steel and a preparation method and application thereof.

[0007] The present invention provides a method for preparing cord steel, comprising sequentially subjecting the cord steel raw material to EAF electric furnace smelting, CAS refining, and continuous casting treatment; The CAS refining includes arranging a top-blowing argon gun above the ladle to perform CAS top-blowing argon slag removal, so that there is no slag in the isolation cover during CAS treatment; The continuous casting tundish is insulated with a carbonized rice husk covering agent.

[0008] Preferably, the preparation method of the cord steel specifically comprises the following steps: 1) Mix desulfurized molten iron and raw steel for EAF smelting; 2) After the EAF smelting in step 1) is completed, the tapping process is performed so that the tapped molten steel is placed in a ladle. When the tapping amount reaches 1 / 3-1 / 2, ferrosilicon, ferromanganese and lime are added to the ladle. After the tapping is completed, a carburizer is added, and then the cord steel is added to synthesize the slag for reaction; 3) After the reaction in step 2) is completed, the ladle is transported to the CAS station, and argon is blown through the air holes below the ladle to blow away the slag on the ladle surface to expose the molten steel. When the exposed surface of the molten steel appears, a top-blowing argon gun is placed above the ladle to blow argon. When the exposed surface of the molten steel is larger than the lower diameter of the isolation cover, the isolation cover is lowered, and the lower end of the isolation cover is immersed in the molten steel. At the same time, the top-blowing argon gun is raised and the top-blowing argon is stopped, and the first stirring is performed to obtain CAS refined molten steel, and the CAS refined molten steel is subjected to soft stirring treatment; 4) After the soft stirring treatment is completed, the isolation cover and the top-blowing argon gun are removed, and the ladle is transported to the continuous casting process. The CAS refined steel liquid in the ladle enters the tundish through the water inlet, and the tundish is insulated with a carbonized rice husk covering agent, and then casting into a continuous casting billet is started to obtain the cord steel.

[0009] The raw steel of the present invention may be scrap steel or raw steel obtained through preparation.

[0010] The top-blowing argon gun of the present invention is arranged in the isolation cover, and the top-blowing argon gun can slide up and down in the isolation cover to achieve the effect of the top-blowing argon gun approaching or moving away from the CAS refined steel liquid.

[0011] It can be understood that when the exposed surface of the molten steel is larger than the diameter of the lower opening of the isolation cover, the present invention can also lower the isolation cover, immerse the lower end of the isolation cover in the molten steel, lift the top blowing argon gun and stop the top blowing of argon; in the process of lowering the isolation cover, the top blowing argon gun is above the exposed surface of the molten steel and is not immersed in the molten steel.

[0012] The soft stirring described in the present invention refers to a method of stirring by introducing argon gas.

[0013] Optionally, the air hole below the ladle is a bottom blowing argon port.

[0014] Preferably, the top-blowing argon gun in step 3) comprises a main body and at least one branch pipe arranged at one end of the main body, the branch pipe and the main body are interconnected, and the angle between the branch pipe and the horizontal direction is 15-25°; argon is discharged through the branch pipe away from one end of the main body to achieve a slag blowing effect.

[0015] The top-blowing argon gun described in the present invention includes a main body and at least one branch pipe arranged at one end of the main body. It can be understood that the number of branch pipes arranged at one end of the main body of the present invention can be set according to actual conditions. For example, the number of branch pipes arranged at one end of the main body can be 1, 2, 3, 4, 5 or 6; optionally, the top-blowing argon gun described in the present invention includes a main body and 4 branch pipes arranged at one end of the main body, which can further achieve the slag blowing effect, expand the exposed surface of the molten steel, and further ensure that the exposed surface of the molten steel is larger than the lower opening diameter of the isolation cover.

[0016] and / or, rotating the top-blowing argon gun during the top-blowing of argon, wherein the rotation speed is 20-50 rpm; and the argon flow rate of the top-blowing argon is 20-200 NL / min; And / or, the diameter of the isolation cover is 2 / 5-3 / 5 of the diameter of the upper opening of the ladle.

[0017] Preferably, the diameter of the isolation cover is 1 / 2 of the upper diameter of the ladle.

[0018] Preferably, the S content in the desulfurized iron water in step 1) is ≤0.0025wt%, and the N content is ≤30ppm; And / or, in the raw steel, N≤40ppm, Cr≤0.06wt%, Ni≤0.06wt%, Cu≤0.06wt%, Mo≤0.010wt%, Sn≤0.007wt%, S≤0.008wt%, and the balance is Fe; And / or, the total mass of the raw steel and the desulfurized molten iron is recorded as a, the mass of the desulfurized molten iron is recorded as b, and b accounts for more than 45% of a; Preferably, b accounts for 45-85% of a; And / or, the raw steel is first placed in an EAF electric furnace, and then the desulfurized molten iron is added into the EAF electric furnace, and the adding speed of the desulfurized molten iron is 9-12 t / min; And / or, the EAF smelting time is 35-45min; And / or, the EAF electric furnace smelting end temperature is not less than 1660°C; And / or, after the EAF electric furnace smelting in step 2) is completed, the O content in the tapped steel is ≤0.050wt%, the C content is ≥0.20wt%, the P content is ≤0.010wt%, the S content is ≤0.010wt%, and the N content is ≤0.0040wt%.

[0019] Preferably, in step 2), the amount of ferrosilicon added is 2.3-2.7 kg / ton of steel, the amount of ferromanganese added is 4.0-5.2 kg / ton of steel, and the amount of lime added is 1.3-1.7 kg / ton of steel; And / or, the chemical composition of the ferrosilicon, in terms of mass percentage, includes: C≤0.02%, Si≥74%, P≤0.015%, Al≤0.15%, Ti≤0.05%, S≤0.02%, and the balance is iron; And / or, the chemical composition of the ferromanganese, calculated by mass percentage, includes: C≤0.6%, Si≤2%, Mn≥80%, P≤0.10%, S≤0.02%, and the balance is iron; and / or, the amount of the synthetic slag for the cord steel is 7-11 kg / ton of steel; And / or, the composition of the synthetic slag of the cord steel is, by mass percentage: SiO 2 Content 45-50%, CaO content 40-45%, Al 2 O 3 Content 4-7%, MgO ≤ 5%, and other unavoidable components; And / or, the amount of the carburizer added is 3.0-4.8 kg / ton of steel; and / or, when adding the carburizer, the argon gas flow rate of the ladle bottom blowing is 500-750NL / min, and after the carburizer is added, the bottom blowing flow rate is 10-200NL / min; And / or, the recarburizer, by mass percentage, has chemical compositions including: fixed carbon ≥ 97%, H 2 O≤0.5%, ash≤2%, S≤0.4%, N≤0.03%, the remainder is unavoidable impurities; And / or, the reaction time of adding the synthetic slag of the cord steel is 3-10 minutes.

[0020] Preferably, the ladle in step 3) is transported to the CAS station at an inlet temperature of 1580-1620°C, and the inlet oxygen value is 50-90ppm; and / or, the argon flow rate of the bottom blowing argon gas through the air hole below the ladle is 200-500NL / min; Optionally, the air hole below the ladle is a bottom blowing argon gas port.

[0021] And / or, the first stirring time is 3-40 min; and / or, when obtaining CAS refined steel liquid, the temperature of CAS refined steel liquid in the ladle is 1540-1543° C.; And / or, in step 3), during the soft stirring process, the bottom blowing argon flow rate is 50-80 NL / min, and the soft stirring is maintained for 15-20 min; and / or, the composition of the slag after CAS refining, in percentage by mass, includes: Al 2 O 3 :5-7wt%,MgO:5-8wt%,[MnO+T.Fe]:2-5wt%,the balance is SiO 2 and CaO, where the basicity is CaO / SiO 2 : 0.9-1.2; In the present invention, T.Fe represents total iron, and [MnO+T.Fe] in the slag composition after CAS refining represents the sum of the mass percentage of MnO in the slag composition and the mass percentage of total iron in the slag composition.

[0022] The solid sample of molten steel after CAS refining in step 3) was scanned and counted using a Zeiss scanning electron microscope. The number of CaSi inclusions > 5 μm in the molten steel after CAS refining was ≤ 0.08 / mm 2 , the number of CaSi inclusions >15μm is ≤0.05 / mm 2 .

[0023] Optionally, the size of CaSi inclusions in the molten steel after CAS refining is no more than 28 μm.

[0024] Optionally, after sampling and testing of CAS refined steel liquid, if the C, Si and Mn contents do not meet the requirements of the finished product, low-carbon ferromanganese, low-titanium and low-aluminum ferrosilicon and low-nitrogen recarburizers can be used to add the C, Si and Mn contents to the required range of the finished product.

[0025] Optionally, in step 3), the air holes below the ladle are made of single-hole air-permeable bricks, and the location of the air-permeable bricks is at a radius of 0.3-0.36 from the center of the bottom of the ladle.

[0026] Optionally, the air brick is positioned at a point 1 / 3 of the radius from the center of the bottom of the ladle.

[0027] Preferably, after the isolation cover and the top-blowing argon gun are removed in step 4), the ladle is transported to the continuous casting process, and the temperature of the molten steel in the ladle during the continuous casting process is 1529-1535°C; And / or, the temperature of the molten steel in the tundish in step 4) is 1493-1499°C; The solid sample of molten steel in the tundish in step 4) was scanned and counted using a Zeiss scanning electron microscope. The number of CaSi inclusions > 5 μm in the molten steel was ≤ 0.05 / mm. 2 , the number of CaSi inclusions >15μm is ≤0.03 / mm 2 ; Optionally, the size of CaSi inclusions in the molten steel in the tundish is no more than 23 μm.

[0028] And / or, the carbonized rice husk in step 4) comprises, by mass percentage: SiO 2 : 70-90%, C: 10-30%, moisture ≤ 3%, natural bulk density of carbonized rice husk ≤ 120g / m 3 .

[0029] The present invention specifically comprises the following steps: Hot metal KR treatment: KR desulfurization is performed on blast furnace hot metal to reduce the sulfur content in the hot metal and obtain desulfurized hot metal.

[0030] EAF process: Desulfurized molten iron and high-quality clean scrap steel are used as the main raw materials in the electric furnace. The furnace door oxygen lance, furnace wall oxygen lance and carbon lance are used for fluxing and the electrode conduction heating is used for melting. The steel-out temperature of the electric furnace is controlled to be ≥1660℃.

[0031] Electric furnace tapping: After the EAF electric furnace smelting is completed, the tapping process is carried out so that the tapped molten steel is placed in the ladle. When the electric furnace is tapping, the ladle is not opened for argon blowing to avoid the molten steel in the ladle from churning and contacting with the air. When the tapping volume reaches 1 / 3 to 1 / 2, alloy auxiliary materials are added in the order of addition: low-titanium and low-aluminum ferrosilicon, low-carbon ferromanganese, and lime. After the tapping is completed and the ladle is opened, the bottom argon is opened and the low-nitrogen carburizer is used for carburization. After the carburization is completed, the bottom blowing flow rate is reduced, and the cord steel synthetic slag is added. After stirring for 3-10 minutes, the bottom argon is turned off.

[0032] CAS refining process: After the ladle filled with molten steel is transported to the CAS station, the argon pipeline is connected, and argon is blown from the bottom through the air-permeable brick holes below the ladle to blow away the slag on the ladle surface. The bottom-blown argon bubble group exposes the molten steel. When the exposed surface is close to the size of the lower opening of the isolation cover, a top-blowing argon gun is put in to blow argon at a certain speed to further expand the exposed surface of the molten steel. When the exposed surface is larger than the diameter of the lower opening of the isolation cover, the isolation cover is lowered, and the isolation cover body is immersed in the molten steel. After immersion, it covers the bubbles that are blown up from the bottom in the molten steel (on the one hand, the isolation cover can reduce the reaction loss caused by the contact between the molten steel and the additional alloy and the slag outside the cover. On the other hand, after the slag is removed from the isolation cover, it can reduce the bubbles that are blown up from the bottom in the cover and the situation where the alloy supplement components are drawn into the slag, thereby introducing inclusions). At the same time, the top-blowing argon is stopped, and the top-blowing argon gun is lifted up (to protect the top-blowing argon gun from corrosion and extend its service life), and the first stirring is carried out. Take samples to analyze the composition of the molten steel, and based on the results, add low-titanium, low-aluminum ferrosilicon and low-carbon ferromanganese to adjust the elemental composition of the molten steel to the required range.

[0033] Soft stirring process: After the molten steel has been refined by CAS, the bottom blowing of argon is reduced to keep the slag surface slightly fluctuating, and soft stirring treatment is started and maintained for a period of time before continuous casting.

[0034] Continuous casting process: do a good job of protective casting, including: remove the isolation cover and top blowing argon gun, transport the ladle to the continuous casting process, the CAS refined steel liquid in the ladle enters the tundish through the water nozzle, the water nozzle of the tundish is protected by argon sealing for casting, the protective argon blowing pipe is checked for air leakage in each furnace, and the water nozzle sealing ring of the tundish is replaced in time. Do not use Ca-based tundish covering agent, use carbonized rice husk for heat preservation, use argon to purge the air in the tundish before pouring (before the molten steel is injected into the tundish), and then cast the molten steel into continuous casting billets.

[0035] Preferably, in the molten iron pretreatment, the KR method is adopted for molten iron pretreatment desulfurization, and 6-10kg / t iron of a desulfurizer (a mixture of 90% lime and 10% fluorite) is added to the molten iron. Under the action of the vortex field formed by the rotating stirring of the stirring head, the desulfurizer and the sulfur in the molten iron are fully reacted to form desulfurization slag, and the desulfurization slag is then removed by a slag scraper, thereby reducing the sulfur content in the molten iron to ≤0.0025wt%.

[0036] CAS refining is a refining method that involves blowing argon into the ladle and adjusting the composition. It involves blowing argon into the ladle to even out the temperature of the molten steel composition. It can also adjust the composition, increase the alloy yield, eliminate large inclusions in the molten steel, and purify the molten steel.

[0037] The present invention provides a cord steel, which is prepared by the cord steel preparation method described above.

[0038] Preferably, the chemical composition of the cord steel includes, by mass percentage: C: 0.70-0.95%, Si: 0.15-0.45%, Mn: 0.25-0.80%, P≤0.015%, S≤0.012%, Alt≤0.0020%, N≤0.0060%, and the rest is Fe and other inevitable impurities.

[0039] The present invention also provides a use of the above-mentioned cord steel in preparing steel cords.

[0040] The technical solution of the present invention has the following advantages: 1. The preparation method of the cord steel provided by the present invention comprises sequentially subjecting the cord steel raw material to EAF electric furnace smelting, CAS refining, and continuous casting treatment; the CAS refining comprises arranging a top-blowing argon gun above the ladle to perform CAS top-blowing argon slag removal, so that there is no slag in the isolation cover during CAS treatment; the continuous casting tundish is insulated with a carbonized rice husk covering agent. The refining of the present invention adopts the CAS method and performs top blowing of argon. On the one hand, the slag-metal reaction caused by LF electrode heating is avoided to generate CaSi inclusions from top to bottom into the molten steel. On the other hand, the slag-metal contact interface of this method is small, thereby minimizing the generation of CaSi inclusions. The designed CAS top-blown argon gun can ensure that there is no slag on the exposed surface in the isolation cover before the alloy is added, and the alloy recovery rate is high, so as to minimize the slag from being involved in the molten steel. Because the alloy is melted and dissolved in contact with the molten steel in the isolation cover, the reaction loss in contact with the slag outside the cover can be reduced. By canceling the LF treatment, a large amount of CaSi inclusions caused by LF heating can be avoided, the slag-metal reaction between the molten steel and the slag is weakened, and the CaSi inclusions (CaO-Al 2 O 3 -SiO 2) is generated in large quantities, and the electric furnace process route can be used to produce high-cleanliness cord steel. The process provided by the present invention does not require VD or RH vacuum treatment, which can improve the cleanliness of inclusions in the steel while ensuring that the gas content meets the standard. Carbonized rice husks are used for continuous casting protection during continuous casting to prevent the treated molten steel from being contaminated by secondary pollution and to avoid nitrogen and oxygen absorption from contact with the air; CaO-containing ladle covering agents are not used to avoid the generation of CaSi inclusions during casting. The specific preparation method of the present invention effectively reduces CaSi inclusions in steel and stably produces cord steel with high cleanliness.

[0041] 2. The preparation method of the cord steel provided by the present invention specifically comprises the following steps: 1) mixing desulfurized molten iron and raw steel for EAF electric furnace smelting; 2) after the EAF electric furnace smelting described in step 1) is completed, the steel is tapped so that the molten steel is placed in a ladle, and when the tapping amount reaches 1 / 3-1 / 2, ferrosilicon, ferromanganese and lime are added to the ladle, and a carburizer is added after the tapping is completed, and then the cord steel synthetic slag is added for reaction; 3) after the reaction in step 2) is completed, the ladle is transported to a CAS station, argon is blown through the bottom of the air holes below the ladle, the slag on the liquid surface of the ladle is blown away to expose the molten steel, and when the molten steel is exposed After the surface is formed, a top-blowing argon gun is placed above the ladle for top-blowing argon. When the exposed surface of the molten steel is larger than the lower diameter of the isolation cover, the isolation cover is lowered, and the lower end of the isolation cover is immersed in the molten steel. At the same time, the top-blowing argon gun is raised and the top-blowing argon is stopped. The first stirring is performed to obtain CAS refined steel liquid, and the CAS refined steel liquid is subjected to soft stirring treatment; 4) After the CAS refined steel liquid in step 3 is subjected to soft stirring treatment, the isolation cover and the top-blowing argon gun are removed, and the ladle is transported to the continuous casting process. The refined steel liquid enters the tundish through the water inlet, and the carbonized rice husk covering agent is used in the tundish for heat preservation, and then it is cast into a continuous casting billet to obtain the cord steel. The specific preparation method of the present invention effectively reduces CaSi inclusions in steel and stably produces cord steel with high cleanliness.

[0042] 3. The preparation method of the cord steel provided by the present invention, in step 1), the S content in the desulfurized molten iron is ≤0.0025wt%, and the N content is ≤30ppm; in the raw steel, N≤40ppm, Cr≤0.06wt%, Ni≤0.06wt%, Cu≤0.06wt%, Mo≤0.010wt%, Sn≤0.007wt%, S≤0.008wt%, and the balance is Fe; the desulfurized molten iron accounts for more than 45% of the total mass of the raw steel and the desulfurized molten iron; by selecting specific raw materials, the temperature, composition and other requirements of electric furnace steelmaking can be met; the main raw material uses molten iron that has been pre-treated by desulfurization. One of the reasons is that the cord steel refining uses an acidic slag system, which does not have desulfurization ability, so the S content of electric furnace steelmaking meets the standard; the second reason is that during the desulfurization process, the molten iron contacts with the air, the N content brought out by the carbon-oxygen reaction and the temperature drop cause N precipitation, and the N content of the molten iron will be reduced, avoiding the increase of vacuum treatment for N removal. The purpose of using a 45% or more hot metal ratio for smelting is to increase the carbon content in the main raw material and replace part of the heating by power-on through carbon-oxygen chemical reaction to reduce the power-on time. At the same time, the decarburization of the electric furnace to generate CO can remove part of the N element. The strong oxidizing atmosphere in the furnace and the foamy slag covering the molten steel can reduce the absorption of N from the air, and control the N content of the electric furnace within a low range.

[0043] 4. In the preparation method of cord steel provided by the present invention, the EAF electric furnace smelting end temperature is not less than 1660°C, which can ensure that the temperature of the molten steel is high enough during the refining CAS treatment to avoid insufficient temperature. The EAF electric furnace steelmaking process adopts ferrosilicon and ferromanganese deoxidation, and cord steel synthetic slag is added before the refining treatment to reduce the slag-metal contact time.

[0044] 5. In the preparation method of the cord steel provided by the present invention, the top-blown argon gun in step 3) has a main pipe on the top and four branches on the bottom, and the angle between the branches and the horizontal direction is 15-25°; the argon flow rate of the top-blown argon gun is 20-200NL / min, and the rotation speed of the top-blown argon gun is 20-50 rpm; the diameter of the isolation cover is 1 / 2 of the upper diameter of the ladle. The present invention further avoids the generation of CaSi inclusions from top to bottom into the molten steel by specifically limiting the structure of the top-blown argon gun, as well as the argon flow rate and rotation speed of the top-blown argon, further ensures the effective reduction of CaSi inclusions in the steel, and further stably produces cord steel with high cleanliness.

[0045] 6. The method for preparing cord steel provided by the present invention obtains CAS refined steel liquid, and the CAS refined steel liquid is subjected to soft stirring treatment. After the soft stirring treatment, small-sized slag inclusions and oxides in the CAS refined steel liquid are aggregated and floated, further reducing CaSi inclusions in the steel, and producing cord steel with high cleanliness.

[0046] 7. The cord steel provided by the present invention produces high-cleanliness cord steel wire rods, and the number of large-size CaSi inclusions (≥15μm) is ≤0.02 pieces / mm 2 . BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0048] Figure 1 A schematic diagram of a CAS refining device used for preparing cord steel according to an embodiment of the present invention; Figure 2 A top view of a CAS refining top-blowing argon gun used in preparing cord steel according to an embodiment of the present invention; Figure numerals: 1- ladle, 2- isolation cover, 3- ejector argon gun, 4- alloy chute, 5- exhaust hole, 6- slag, 7- water inlet, 8- bottom blowing argon inlet, 9- molten steel. DETAILED DESCRIPTION

[0049] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0050] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0051] The embodiments of the present invention and the comparative examples take the preparation of grade 72 cord steel as an example, and the chemical composition of the obtained cord steel is as follows, by mass percentage: C is 0.70-0.75%, Mn is 0.45-0.55%, Si is 0.16-0.28%, P≤0.015%, S≤0.0012%, N≤0.0060%, Alt≤0.0020%, Ti≤0.0008%, Ni≤0.08%, Cu≤0.08%, Mo≤0.010%, Sn≤0.010% and As≤0.010%, and the rest is Fe and other unavoidable impurities.

[0052] Example 1 This embodiment provides a method for preparing cord steel, comprising the following steps: 1) The blast furnace hot metal with a S content of 0.026wt% and a N content of 37ppm was pre-treated and desulfurized by the KR method to obtain a desulfurized hot metal with a S content of 0.0022wt% and a N content of 24ppm; then 60 tons of raw scrap steel (the raw scrap steel, by mass percentage, includes N: 35ppm, Cr: 0.02wt%, Ni: 0.01wt%, Cu: 0.02wt%, Mo: 0.003wt%, Sn: 0.002wt%, S: 0.003 wt%, the balance is Fe), and then 55 tons of desulfurized molten iron is added into the EAF electric furnace through the rear chute of the furnace, the adding speed is 10t / min, the oxygen lance of the furnace wall starts to blow oxygen, and the EAF electric furnace smelting is started. After smelting for 40 minutes, the EAF electric furnace smelting end temperature is 1665℃, the electric furnace tapping rate is 90%, and the S content of the tapped steel is: 0.008wt%, P content is 0.008wt%, N content is: 0.0028wt%, C content is 0.25wt%, and oxygen content is 0.046wt%; 2) Put the molten steel into the ladle. When the tapping amount reaches 40 tons, add 250kg of low-titanium and low-aluminum ferrosilicon (the low-titanium and low-aluminum ferrosilicon, calculated by mass percentage, includes C: 0.01%, Si: 76%, P: 0.01%, Al: 0.10%, Ti: 0.02%, S: 0.01%, and the balance is iron) and 500kg of low-carbon ferromanganese alloy (the low-carbon ferromanganese alloy, calculated by mass percentage, includes C: 0.3%, Si: 1.5%, Mn: 82%, P: 0.06%, S: 0.01%, and the balance is iron) into the ladle for deoxidation and alloying, and then add 150kg of lime. After the tapping is completed, start bottom blowing of argon with a bottom blowing flow rate of 600NL / min, and add 450kg of recarburizer (the recarburizer, calculated by mass percentage, includes: fixed carbon: 98%, H 2 O: 0.2%, ash: 1%, S: 0.2%, N: 0.013%, the remainder is unavoidable impurities), then the bottom blowing flow rate is changed to 150NL / min, and 1000kg of cord steel synthetic slag is added (cord steel synthetic slag is calculated by mass percentage, including: SiO 2 Content 48%, CaO content 43%, Al 2 O 3 Content 5.5%, MgO: 3%, the balance is inevitable impurities) stirred for 5 minutes; 3) After the reaction in step 2) is completed, the ladle is transported to the CAS refining station. The schematic diagram of the CAS refining device is as follows Figure 1As shown, the inlet temperature is 1600°C, the inlet oxygen value is 70ppm, and argon is blown through the bottom blowing argon port 8 below the ladle 1 at a flow rate of 300NL / min to blow away the slag 6 on the liquid surface of the ladle 1 to expose the molten steel 9. When the molten steel 9 is exposed, a top blowing argon gun 3 is introduced above the ladle 1 (the top view of the top blowing argon gun is as shown in FIG. Figure 2 As shown, the top-blowing argon gun 3 includes a main body and 4 branch pipes arranged at one end of the main body, the branch pipes and the main body are interconnected, the branch pipes discharge argon away from the main body, and the angle between the branch pipe and the horizontal direction is 20°) for top-blowing argon, the top-blowing argon flow rate is 40NL / min, the top-blowing argon gun 3 has a rotation speed of 40 rpm, when the exposed surface of the molten steel is larger than the lower diameter of the isolation cover 2, the isolation cover 2 is put down, the lower diameter of the isolation cover 2 is 1 / 2 of the upper diameter of the ladle, the lower end of the isolation cover 2 is immersed in the molten steel, and the top-blowing argon gun 3 is lifted and the top-blowing argon is stopped. After stirring for 9 minutes, CAS refined steel liquid is obtained, and the temperature of the steel liquid in the ladle 1 is 1540°C. According to the sampling and analysis results of the spectrometer, low-carbon ferromanganese, low-titanium and low-aluminum ferrosilicon, and a carburizer are used to add C, Si, and Mn contents to meet the requirements of the components of the 72-grade cord steel finished product; Al in the refined slag is detected 2 O 3 The content is 5.8wt%, the MgO content is 7.7wt%, [MnO+T.Fe] is 3.5wt%, and the balance is SiO 2 and CaO, where the basicity of the components (CaO / SiO 2 ) is 1.02; then the CAS refined steel liquid is subjected to soft stirring treatment, the bottom blowing argon flow rate of soft stirring is 60NL / min, and the soft stirring holding time is 18min; the bottom blowing argon port of the ladle for CAS refining treatment adopts a single-hole air-permeable brick, and the position of the air-permeable brick is 1 / 3 of the radius from the center of the bottom of the ladle; 4) Step 3) After the CAS refined steel liquid is softly stirred, the isolation cover and the top-blown argon gun are removed, and the ladle is transported to the continuous casting process. The temperature of the molten steel in the ladle is 1530°C. The refined steel liquid enters the tundish through the nozzle 7. The temperature of the molten steel in the tundish is 1496°C. Carbonized rice husk covering agent is used in the tundish for heat preservation. The carbonized rice husk, by mass percentage, includes: SiO 2 : 80%, C: 19%, moisture 1%, natural bulk density of carbonized rice husk 110g / m 3, and then began to cast into a continuous casting billet to obtain the cord steel. The specific composition of the cord steel is, by mass percentage: C: 0.718%, Mn: 0.51%, Si: 0.19%, P: 0.007%, S: 0.006%, N: 0.0035%, Alt: 0.0013%, Ti: 0.0004%, Ni: 0.006%, Cu: 0.02%, Mo: 0.003%, Sn: 0.003%, As: 0.002%, and the rest is Fe and other inevitable impurities.

[0053] Example 2 This embodiment provides a method for preparing cord steel, comprising the following steps: 1) The blast furnace hot metal with a S content of 0.026wt% and a N content of 37ppm was pre-treated and desulfurized by the KR method to obtain a desulfurized hot metal with a S content of 0.0021wt% and a N content of 22ppm; then 60 tons of raw scrap steel (the raw scrap steel, by mass percentage, includes: N: 35ppm, Cr: 0.02wt%, Ni: 0.01wt%, Cu: 0.02wt%, Mo: 0.003wt%, Sn: 0.002wt%, S: 0.00 3wt%, the remainder is Fe), and then 55 tons of desulfurized molten iron is added into the EAF electric furnace through the rear chute of the furnace, the adding speed is 12t / min, the oxygen lance of the furnace wall starts to blow oxygen, and the EAF electric furnace smelting is started. After smelting for 45 minutes, the EAF electric furnace smelting end temperature is 1668℃, the electric furnace tapping rate is 89%, and the S content of the tapped steel is: 0.005wt%, P content is 0.007wt%, N content is: 0.003wt%, C content is 0.30wt%, and oxygen content is 0.047wt%; 2) Put the molten steel into the ladle. When the tapping amount reaches 40 tons, add 250kg of low-titanium and low-aluminum ferrosilicon (the low-titanium and low-aluminum ferrosilicon, calculated by mass percentage, includes C: 0.01%, Si: 76%, P: 0.01%, Al: 0.10%, Ti: 0.02%, S: 0.01%, and the balance is iron) and 500kg of low-carbon ferromanganese alloy (the low-carbon ferromanganese alloy, calculated by mass percentage, includes C: 0.3%, Si: 1.5%, Mn: 82%, P: 0.06%, S: 0.01%, and the balance is iron) into the ladle for deoxidation and alloying, and then add 150kg of lime. After the tapping is completed, start bottom blowing of argon with a bottom blowing flow rate of 750NL / min, and add 400kg of recarburizer (the recarburizer, calculated by mass percentage, includes fixed carbon: 98%, H 2 O: 0.2%, ash: 1%, S: 0.2%, N: 0.013%, the remainder is unavoidable impurities), then the bottom blowing flow rate is changed to 120NL / min, and 1000kg of cord steel synthetic slag is added (cord steel synthetic slag is calculated by mass percentage, including: SiO2 Content 48%, CaO content 43%, Al 2 O 3 Content 5.5%, MgO: 3%, the balance is inevitable impurities) stirred for 6 minutes; 3) After the reaction in step 2) is completed, the ladle is transported to the CAS refining station. The schematic diagram of the CAS refining device is as follows Figure 1 As shown, the inlet temperature is 1608°C, the inlet oxygen value is 90ppm, and argon is blown through the bottom blowing argon port 8 below the ladle 1 at a flow rate of 500NL / min to blow away the slag 6 on the liquid surface of the ladle 1 to expose the molten steel 9. When the molten steel 9 is exposed, a top blowing argon gun 3 is put above the ladle 1 (the top view of the top blowing argon gun is as shown in the figure). Figure 2 As shown, the top-blowing argon gun 3 includes a main body and 4 branch pipes arranged at one end of the main body, the branch pipe and the main body are interconnected, the branch pipe discharges argon away from the main body, and the angle between the branch pipe and the horizontal direction is 25°) for top-blowing argon, the top-blowing argon flow rate is 200NL / min, the top-blowing argon gun 3 has a rotation speed of 20 rpm, when the exposed surface of the molten steel is larger than the lower diameter of the isolation cover 2, the isolation cover 2 is put down, the lower diameter of the isolation cover 2 is 1 / 2 of the upper diameter of the ladle, the lower end of the isolation cover 2 is immersed in the molten steel, and the top-blowing argon gun 3 is lifted and the top-blowing argon is stopped. After stirring for 10 minutes, CAS refined steel liquid is obtained, and the temperature of the steel liquid in the ladle 1 is 1541°C. According to the sampling and analysis results of the spectrometer, low-carbon ferromanganese, low-titanium and low-aluminum ferrosilicon, and a carburizer are used to add C, Si, and Mn contents to meet the requirements of the components of the 72-grade cord steel finished product; Al in the refined slag is detected 2 O 3 The content is 5.6wt%, the MgO content is 8.1wt%, [MnO+T.Fe] is 3.4wt%, and the balance is SiO 2 and CaO, where the basicity of the components (CaO / SiO 2 ) is 1.00; then the CAS refined steel liquid is subjected to soft stirring treatment, the bottom blowing argon flow rate of soft stirring is 80NL / min, and the soft stirring holding time is 15min; the bottom blowing argon port of the ladle for CAS refining treatment adopts a single-hole air-permeable brick, and the position of the air-permeable brick is 1 / 3 of the radius from the center of the bottom of the ladle; 4) Step 3) After the soft stirring treatment of the CAS refined steel liquid is completed, the isolation cover and the top blowing argon gun are removed, and the ladle is transported to the continuous casting process. The temperature of the molten steel in the ladle is 1535°C. The refined steel liquid enters the tundish through the nozzle 7. The temperature of the molten steel in the tundish is 1499°C. Carbonized rice husk covering agent is used in the tundish for heat preservation. The carbonized rice husk, by mass percentage, includes: SiO 2 : 78%, C: 22%, moisture 1%, natural bulk density of carbonized rice husk 80g / m 3, and then began to cast into a continuous casting billet to obtain the cord steel. The specific composition of the cord steel is, by mass percentage: C: 0.725%, Mn: 0.52%, Si: 0.19%, P: 0.008%, S: 0.007%, N: 0.0039%, Alt: 0.0015%, Ti: 0.0004%, Ni: 0.007%, Cu: 0.01%, Mo: 0.002%, Sn: 0.002%, As: 0.003%, and the rest is Fe and other inevitable impurities.

[0054] Example 3 This embodiment provides a method for preparing cord steel, comprising the following steps: 1) The blast furnace hot metal with a S content of 0.026wt% and a N content of 37ppm was pre-treated and desulfurized by the KR method to obtain a desulfurized hot metal with a S content of 0.0023wt% and a N content of 23ppm; then 60 tons of raw scrap steel (the raw scrap steel, by mass percentage, includes N: 35ppm, Cr: 0.02wt%, Ni: 0.01wt%, Cu: 0.02wt%, Mo: 0.003wt%, Sn: 0.002wt%, S: 0.00 3wt%, the remainder is Fe), and then 55 tons of desulfurized molten iron is added into the EAF electric furnace through the rear chute of the furnace, the adding speed is 9t / min, the oxygen lance of the furnace wall starts to blow oxygen, and the EAF electric furnace smelting is started. After smelting for 35 minutes, the EAF electric furnace smelting end temperature is 1663℃, the electric furnace tapping rate is 91%, and the S content of the tapped steel is: 0.006wt%, P content is 0.008wt%, N content is: 0.005wt%, C content is 0.28wt%, and oxygen content is 0.050wt%; 2) Put the molten steel into the ladle. When the tapping amount reaches 40 tons, add 250kg of low-titanium and low-aluminum ferrosilicon (the low-titanium and low-aluminum ferrosilicon is calculated by mass percentage, including: C: 0.01%, Si: 76%, P: 0.01%, Al: 0.10%, Ti: 0.02%, S: 0.01%, and the balance is iron) and 500kg of low-carbon ferromanganese alloy (the low-carbon ferromanganese alloy is calculated by mass percentage, including: C: 0.3%, Si: 1.5%, Mn: 82%, P: 0.06%, S: 0.01%, and the balance is iron) into the ladle for deoxidation and alloying, and then add 150kg of lime. After the tapping is completed, start bottom blowing of argon with a bottom blowing flow rate of 500NL / min, and add 430kg of recarburizer (the recarburizer is calculated by mass percentage, including: fixed carbon: 98%, H 2 O: 0.2%, ash: 1%, S: 0.2%, N: 0.013%, the remainder is unavoidable impurities), then the bottom blowing flow rate is changed to 200NL / min, and 1000kg of cord steel synthetic slag is added (cord steel synthetic slag is calculated by mass percentage, including: SiO2 Content 48%, CaO content 43%, Al 2 O 3 Content 5.5%, MgO: 3%, the balance is inevitable impurities) stirred for 5 minutes; 3) After the reaction in step 2) is completed, the ladle is transported to the CAS refining station. The schematic diagram of the CAS refining device is as follows Figure 1 As shown, the inlet temperature is 1580°C, the inlet oxygen value is 50ppm, and argon is blown through the bottom blowing argon port 8 below the ladle 1 at a flow rate of 300NL / min to blow away the slag on the liquid surface of the ladle 1 to expose the molten steel 9. When the molten steel 9 is exposed, a top blowing argon gun 3 is put above the ladle 1 (the top view of the top blowing argon gun is as shown in the figure below). Figure 2 As shown, the top-blowing argon gun 3 includes a main body and 4 branch pipes arranged at one end of the main body, the branch pipe and the main body are interconnected, the branch pipe discharges argon away from the main body, and the angle between the branch pipe and the horizontal direction is 17°) for top-blowing argon, the top-blowing argon flow rate is 40NL / min, the top-blowing argon gun 3 has a rotation speed of 30 rpm, when the exposed surface of the molten steel is larger than the lower diameter of the isolation cover 2, the isolation cover 2 is put down, the lower diameter of the isolation cover 2 is 1 / 2 of the upper diameter of the ladle, the lower end of the isolation cover 2 is immersed in the molten steel, and the top-blowing argon gun 3 is lifted and the top-blowing argon is stopped. After stirring for 12 minutes, CAS refined steel liquid is obtained, and the temperature of the steel liquid in the ladle 1 is 1540°C. According to the sampling and analysis results of the spectrometer, low-carbon ferromanganese, low-titanium and low-aluminum ferrosilicon, and carburizer are used to add C, Si, and Mn contents to meet the requirements of each component of the 72-grade cord steel finished product; Al in the refined slag is detected 2 O 3 The content is 5.8wt%, the MgO content is 7.7wt%, [MnO+T.Fe] is 3.5wt%, and the balance is SiO 2 and CaO, where the basicity of the components (CaO / SiO 2 ) is 1.02; then the CAS refined steel liquid is subjected to soft stirring treatment, the bottom blowing argon flow rate of soft stirring is 70NL / min, and the soft stirring holding time is 20min; the bottom blowing argon port of the CAS refining ladle adopts a single-hole air-permeable brick, and the position of the air-permeable brick is 1 / 3 of the radius from the center of the bottom of the ladle; 4) Step 3) After the CAS refined steel liquid is softly stirred, the isolation cover and the top-blown argon gun are removed, and the ladle is transported to the continuous casting process. The temperature of the molten steel in the ladle is 1529°C. The refined steel liquid enters the tundish through the nozzle 7. The temperature of the molten steel in the tundish is 1493°C. Carbonized rice husk covering agent is used in the tundish for heat preservation. The carbonized rice husk, by mass percentage, includes: SiO 2 : 80%, C: 19%, moisture 1%, natural bulk density of carbonized rice husk 110g / m 3, and then began to cast into a continuous casting billet to obtain the cord steel. The specific composition of the cord steel is, by mass percentage: C: 0.732%, Mn: 0.53%, Si: 0.19%, P: 0.006%, S: 0.005%, N: 0.0040%, Alt: 0.0014%, Ti: 0.0003%, Ni: 0.007%, Cu: 0.01%, Mo: 0.003%, Sn: 0.002%, As: 0.003%, and the rest is Fe and other inevitable impurities.

[0055] Comparative Example 1 This comparative example provides a method for preparing cord steel, which adopts LF refining and comprises the following steps: 1) The blast furnace hot metal with a S content of 0.026wt% and a N content of 37ppm was pre-treated and desulfurized by the KR method to obtain a desulfurized hot metal with a S content of 0.0022wt% and a N content of 24ppm; then 60 tons of raw scrap steel (the raw scrap steel, by mass percentage, includes N: 35ppm, Cr: 0.02%, Ni: 0.01%, Cu: 0.02%, Mo: 0.003%, Sn: 0.002%, S: 0.003%, and the remainder Fe), and then 55 tons of desulfurized molten iron is added into the EAF electric furnace through the rear chute of the furnace, the adding speed is 10t / min, the oxygen lance of the furnace wall starts to blow oxygen, and the EAF electric furnace smelting is started. After smelting for 40 minutes, the EAF electric furnace smelting end temperature is 1665℃, the electric furnace tapping rate is 90%, and the S content of the tapped steel is: 0.008wt%, P content is 0.008wt%, N content is: 0.0028wt%, C content is 0.25wt%, and oxygen content is 0.046wt%; 2) Put the molten steel into the ladle. When the tapping amount reaches 40 tons, add 250kg of low-titanium and low-aluminum ferrosilicon (the low-titanium and low-aluminum ferrosilicon, calculated by mass percentage, includes C: 0.01%, Si: 76%, P: 0.01%, Al: 0.10%, Ti: 0.02%, S: 0.01%, and the balance is iron) and 500kg of low-carbon ferromanganese alloy (the low-carbon ferromanganese alloy, calculated by mass percentage, includes C: 0.3%, Si: 1.5%, Mn: 82%, P: 0.06%, S: 0.01%, and the balance is iron) into the ladle for deoxidation and alloying, and then add 150kg of lime. After the tapping is completed, start bottom blowing of argon with a bottom blowing flow rate of 600NL / min, and add 450kg of recarburizer (the recarburizer, calculated by mass percentage, includes: fixed carbon: 98%, H 2 O: 0.2%, ash: 1%, S: 0.2%, N: 0.013%, the remainder is unavoidable impurities), then the bottom blowing flow rate is changed to 150NL / min, and 1000kg of cord steel synthetic slag is added (cord steel synthetic slag is calculated by mass percentage, including: SiO2 Content 48%, CaO content 43%, Al 2 O 3 Content 5.5%, MgO: 3%, the balance is inevitable impurities) stirred for 5 minutes; 3) After the reaction in step 2) is completed, the ladle is transported to the LF refining station, the station temperature is 1600℃, the station oxygen value is 70ppm, argon is blown through the air holes below the ladle, the flow rate is 300NL / min, and LF refined steel liquid is obtained after 35 minutes. The temperature of the steel liquid in the ladle is 1540℃. According to the sampling and analysis results of the spectrometer, low-carbon ferromanganese, low-titanium and low-aluminum ferrosilicon, and recarburizer are used to add C, Si, and Mn to meet the requirements of the components of the finished product of grade 72 cord steel. The Al in the refined slag is detected. 2 O 3 The content is 5.8wt%, the MgO content is 7.7wt%, [MnO+T.Fe] is 3.5wt%, and the balance is SiO 2 and CaO, where the basicity of the components (CaO / SiO 2 ) is 1.02; then the CAS refined steel liquid is subjected to soft stirring treatment, the bottom blowing argon flow rate of soft stirring is 60NL / min, and the soft stirring holding time is 18min; the bottom blowing argon port of the ladle for CAS refining treatment adopts a single-hole air-permeable brick, and the position of the air-permeable brick is 1 / 3 of the radius from the center of the bottom of the ladle; 4) Step 3) After the soft stirring treatment of CAS refined steel liquid is completed, the isolation cover and the top blowing argon gun are removed, and the ladle is transported to the continuous casting process. The temperature of the molten steel in the ladle is 1530°C. The refined steel liquid enters the tundish through the nozzle. The temperature of the molten steel in the tundish is 1496°C. Carbonized rice husk covering agent is used in the tundish for heat preservation. The carbonized rice husk, by mass percentage, includes: SiO 2 : 80%, C: 19%, moisture 1%, natural bulk density of carbonized rice husk 110g / m 3 , and then began to cast into a continuous casting billet to obtain the cord steel. The specific composition of the cord steel is, by mass percentage: C: 0.718%, Mn: 0.51%, Si: 0.19%, P: 0.007%, S: 0.006%, N: 0.0035%, Alt: 0.0013%, Ti: 0.0004%, Ni: 0.006%, Cu: 0.02%, Mo: 0.003%, Sn: 0.003%, As: 0.002%, and the rest is Fe and other inevitable impurities.

[0056] Comparative Example 2 This comparative example provides a method for preparing cord steel, and this comparative example does not perform top blowing of argon gas, and comprises the following steps: 1) The blast furnace hot metal with a S content of 0.026wt% and a N content of 37ppm was pre-treated and desulfurized by the KR method to obtain a desulfurized hot metal with a S content of 0.0022wt% and a N content of 24ppm; then 60 tons of raw scrap steel (the raw scrap steel, by mass percentage, includes N: 35ppm, Cr: 0.02%, Ni: 0.01%, Cu: 0.02%, Mo: 0.003%, Sn: 0.002%, S: 0.003%, and the remainder Fe), and then 55 tons of desulfurized molten iron is added into the EAF electric furnace through the rear chute of the furnace, the adding speed is 10t / min, the oxygen lance of the furnace wall starts to blow oxygen, and the EAF electric furnace smelting is started. After smelting for 40 minutes, the EAF electric furnace smelting end temperature is 1665℃, the electric furnace tapping rate is 90%, and the S content of the tapped steel is: 0.008wt%, P content is 0.008wt%, N content is: 0.0028wt%, C content is 0.25wt%, and oxygen content is 0.046wt%; 2) Put the molten steel into the ladle. When the tapping amount reaches 40 tons, add 250kg of low-titanium and low-aluminum ferrosilicon (the low-titanium and low-aluminum ferrosilicon, calculated by mass percentage, includes C: 0.01%, Si: 76%, P: 0.01%, Al: 0.10%, Ti: 0.02%, S: 0.01%, and the balance is iron) and 500kg of low-carbon ferromanganese alloy (the low-carbon ferromanganese alloy, calculated by mass percentage, includes C: 0.3%, Si: 1.5%, Mn: 82%, P: 0.06%, S: 0.01%, and the balance is iron) into the ladle for deoxidation and alloying, and then add 150kg of lime. After the tapping is completed, start bottom blowing of argon with a bottom blowing flow rate of 600NL / min, and add 450kg of recarburizer (the recarburizer, calculated by mass percentage, includes: fixed carbon: 98%, H 2 O: 0.2%, ash: 1%, S: 0.2%, N: 0.013%, the remainder is unavoidable impurities), then the bottom blowing flow rate is changed to 150NL / min, and 1000kg of cord steel synthetic slag is added (cord steel synthetic slag is calculated by mass percentage, including: SiO 2 Content 48%, CaO content 43%, Al 2 O 3 Content 5.5%, MgO: 3%, the balance is inevitable impurities) stirred for 5 minutes; 3) After the reaction in step 2) is completed, the ladle is transported to the CAS refining station, the station temperature is 1600℃, the station oxygen value is 70ppm, argon is blown through the bottom blowing port below the ladle, the flow rate is 300NL / min, the slag on the ladle surface is blown open to expose the molten steel, when the exposed surface of the molten steel is larger than the lower diameter of the isolation cover, the isolation cover is lowered, the lower diameter of the isolation cover is 1 / 2 of the upper diameter of the ladle, the lower end of the isolation cover is immersed in the molten steel, and after stirring for 9 minutes, CAS refined steel liquid is obtained, the temperature of the molten steel in the ladle is 1540℃, according to the sampling and analysis results of the spectrometer, low carbon ferromanganese, low titanium and low aluminum ferrosilicon, and recarburizer are used to add C, Si, and Mn to meet the requirements of the components of the 72 grade cord steel finished product. The Al in the refined slag is detected 2 O 3 The content is 5.8wt%, the MgO content is 7.7wt%, [MnO+T.Fe] is 3.5wt%, and the balance is SiO 2 and CaO, where the basicity of the components (CaO / SiO 2 ) is 1.02; then the CAS refined steel liquid is subjected to soft stirring treatment, the bottom blowing argon flow rate of soft stirring is 60NL / min, and the soft stirring holding time is 18min; the bottom blowing argon port of the ladle for CAS refining treatment adopts a single-hole air-permeable brick, and the position of the air-permeable brick is 1 / 3 of the radius from the center of the bottom of the ladle; 4) Step 3) After the soft stirring treatment of CAS refined steel liquid is completed, the isolation cover and the top blowing argon gun are removed, and the ladle is transported to the continuous casting process. The temperature of the molten steel in the ladle is 1530°C. The refined steel liquid enters the tundish through the nozzle. The temperature of the molten steel in the tundish is 1496°C. Carbonized rice husk covering agent is used in the tundish for heat preservation. The carbonized rice husk, by mass percentage, includes: SiO 2 : 80%, C: 19%, moisture 1%, natural bulk density of carbonized rice husk 110g / m 3 , and then began to cast into a continuous casting billet to obtain the cord steel. The specific composition of the cord steel is, by mass percentage: C: 0.718%, Mn: 0.51%, Si: 0.19%, P: 0.007%, S: 0.006%, N: 0.0035%, Alt: 0.0013%, Ti: 0.0004%, Ni: 0.006%, Cu: 0.02%, Mo: 0.003%, Sn: 0.003%, As: 0.002%, and the rest is Fe and other inevitable impurities.

[0057] Comparative Example 3 This embodiment provides a method for preparing cord steel. In this comparative example, a CaO covering agent is used in the tundish for heat preservation, comprising the following steps: 1) The blast furnace hot metal with a S content of 0.026wt% and a N content of 37ppm was pre-treated and desulfurized by the KR method to obtain a desulfurized hot metal with a S content of 0.0022wt% and a N content of 24ppm; then 60 tons of raw scrap steel (the raw scrap steel, by mass percentage, includes N: 35ppm, Cr: 0.02%, Ni: 0.01%, Cu: 0.02%, Mo: 0.003%, Sn: 0.002%, S: 0.003%, and the remainder Fe), and then 55 tons of desulfurized molten iron is added into the EAF electric furnace through the rear chute of the furnace, the adding speed is 10t / min, the oxygen lance of the furnace wall starts to blow oxygen, and the EAF electric furnace smelting is started. After smelting for 40 minutes, the EAF electric furnace smelting end temperature is 1665℃, the electric furnace tapping rate is 90%, and the S content of the tapped steel is: 0.008wt%, P content is 0.008wt%, N content is: 0.0028wt%, C content is 0.25wt%, and oxygen content is 0.046wt%; 2) Put the molten steel into the ladle. When the tapping amount reaches 40 tons, add 250kg of low-titanium and low-aluminum ferrosilicon (the low-titanium and low-aluminum ferrosilicon, calculated by mass percentage, includes C: 0.01%, Si: 76%, P: 0.01%, Al: 0.10%, Ti: 0.02%, S: 0.01%, and the balance is iron) and 500kg of low-carbon ferromanganese alloy (the low-carbon ferromanganese alloy, calculated by mass percentage, includes C: 0.3%, Si: 1.5%, Mn: 82%, P: 0.06%, S: 0.01%, and the balance is iron) into the ladle for deoxidation and alloying, and then add 150kg of lime. After the tapping is completed, start bottom blowing of argon with a bottom blowing flow rate of 600NL / min, and add 450kg of recarburizer (the recarburizer, calculated by mass percentage, includes: fixed carbon: 98%, H 2 O: 0.2%, ash: 1%, S: 0.2%, N: 0.013%, the remainder is unavoidable impurities), then the bottom blowing flow rate is changed to 150NL / min, and 1000kg of cord steel synthetic slag is added (cord steel synthetic slag is calculated by mass percentage, including: SiO 2 Content 48%, CaO content 43%, Al 2 O 3 Content 5.5%, MgO: 3%, the balance is inevitable impurities) stirred for 5 minutes; 3) After the reaction in step 2) is completed, the ladle is transported to the CAS refining station, the inlet temperature is 1600°C, the inlet oxygen value is 70ppm, and argon is blown through the bottom blowing argon port below the ladle at a flow rate of 300NL / min to blow away the slag on the liquid surface of the ladle to expose the molten steel. When the molten steel appears exposed, a top blowing argon gun (the top blowing argon gun includes a main body and 4 branch pipes arranged at one end of the main body, the branch pipes and the main body are connected to each other, the branch pipes are away from the main body to discharge argon, and the angle between the branch pipe and the horizontal direction is 20°) is put above the ladle for top blowing of argon, and the top blowing argon flow rate is 4 0NL / min, the top blowing argon gun speed is 40 rpm, when the exposed surface of the molten steel is larger than the lower diameter of the isolation cover, put down the isolation cover, the lower diameter of the isolation cover is 1 / 2 of the upper diameter of the ladle, the lower end of the isolation cover is immersed in the molten steel, and the top blowing argon gun is raised and the top blowing argon is stopped. After stirring for 9 minutes, CAS refined steel liquid is obtained, and the temperature of the steel liquid in the ladle is 1540℃. According to the sampling and analysis results of the spectrometer, low carbon ferromanganese, low titanium and low aluminum ferrosilicon and recarburizer are used to add C, Si and Mn contents to meet the requirements of each component of the finished product of grade 72 cord steel. The Al in the refined slag is detected. 2 O 3 The content is 5.8wt%, the MgO content is 7.7wt%, [MnO+T.Fe] is 3.5wt%, and the balance is SiO 2 and CaO, where the basicity of the components (CaO / SiO 2 ) is 1.02; then the CAS refined steel liquid is subjected to soft stirring treatment, the bottom blowing argon flow rate of soft stirring is 60NL / min, and the soft stirring holding time is 18min; the bottom blowing argon port of the ladle for CAS refining treatment adopts a single-hole air-permeable brick, and the position of the air-permeable brick is 1 / 3 of the radius from the center of the bottom of the ladle; 4) Step 3) After the soft stirring treatment of CAS refined steel liquid is completed, the isolation cover and the top blowing argon gun are removed, and the ladle is transported to the continuous casting process. The temperature of the molten steel in the ladle is 1530°C, and the refined steel liquid enters the tundish through the nozzle. The temperature of the molten steel in the tundish is 1496°C. CaO covering agent is used in the tundish for heat preservation, and then casting into continuous casting billets is started to obtain the cord steel. The specific composition of the cord steel is calculated by mass percentage: C: 0.718%, Mn: 0.51%, Si: 0.19%, P: 0.007%, S: 0.006%, N: 0.0035%, Alt: 0.0013%, Ti: 0.0004%, Ni: 0.006%, Cu: 0.02%, Mo: 0.003%, Sn: 0.003%, As: 0.002%, and the rest is Fe and other unavoidable impurities.

[0058] Test Case The cord steels obtained in Examples 1-3 of the present invention and Comparative Examples 1-3 are subjected to the same process of homogenization, rolling, and Stelmor controlled cooling to obtain wire rods of the same specification.

[0059] The CAS refined molten steel after CAS refining and the molten steel in the continuous casting tundish in Examples 1-3 of the present invention and Comparative Examples 1-3 were sampled and cooled to a solid state using a Zeiss scanning electron microscope to obtain steel after CAS refining, steel in the continuous casting tundish, and correspondingly prepared wire rods. The cross-sections of the steel after CAS refining obtained in Examples 1-3 and Comparative Examples 1-3, the cross-sections of the steel in the continuous casting tundish, and the correspondingly prepared wire rods were scanned using a Zeiss scanning electron microscope, and the number and size of CaSi inclusions were counted. The statistical results are shown in Table 1.

[0060] Table 1 Statistical results of the number and size of CaSi inclusions

[0061] Note: "pcs / mm" in the table 2 ” indicates the number of inclusions per square millimeter of cross section.

[0062] As can be seen from Table 1, in Example 1, the specific CAS refining of the present invention was used, and compared with Comparative Example 1 using LF refining and Comparative Example 2 without top blowing of argon, the number of large-sized (>15μm) CaSi inclusions and the maximum size of the inclusions were significantly reduced. In the embodiment of the present invention, the number of CaSi inclusions >5μm in the molten steel after CAS refining was ≤0.08 / mm 2 , the number of CaSi inclusions >15μm is ≤0.05 / mm 2 The size of CaSi inclusions in molten steel after CAS refining is no more than 28μm. The number of CaSi inclusions > 5μm in molten steel in the tundish is ≤ 0.05 / mm 2 , the number of CaSi inclusions >15μm is ≤0.03 / mm 2 ; The size of CaSi inclusions in the molten steel in the tundish is not greater than 23μm.

[0063] The present invention takes the grade 72 cord steel produced by an electric furnace as an example, but is not limited to the production method using an electric furnace. In fact, the present invention is also applicable to the cord steel produced by the converter process route, and can solve the problem of excessive CaSi large-sized inclusions in all cord steels.

[0064] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A method for preparing cord steel, characterized in that: The process includes sequentially subjecting the cord steel raw materials to EAF electric furnace smelting, CAS refining and continuous casting; The CAS refining includes arranging a top-blowing argon gun above the ladle to perform CAS top-blowing argon slag removal, so that there is no slag in the isolation cover during CAS treatment; The continuous casting tundish is insulated with a carbonized rice husk covering agent.

2. The method for preparing cord steel according to claim 1, characterized in that: The following steps are involved: 1) Mix desulfurized molten iron and raw steel for EAF smelting; 2) After the EAF smelting in step 1) is completed, the tapping process is performed so that the tapped molten steel is placed in a ladle. When the tapping amount reaches 1 / 3-1 / 2, ferrosilicon, ferromanganese and lime are added to the ladle. After the tapping is completed, a carburizer is added, and then the cord steel is added to synthesize the slag for reaction; 3) After the reaction in step 2) is completed, the ladle is transported to the CAS station, and argon is blown through the air holes below the ladle to blow away the slag on the ladle surface to expose the molten steel. When the exposed surface of the molten steel appears, a top-blowing argon gun is placed above the ladle to blow argon. When the exposed surface of the molten steel is larger than the lower diameter of the isolation cover, the isolation cover is lowered, and the lower end of the isolation cover is immersed in the molten steel. At the same time, the top-blowing argon gun is raised and the top-blowing argon is stopped, and the first stirring is performed to obtain CAS refined molten steel, and the CAS refined molten steel is subjected to soft stirring treatment; 4) After the soft stirring treatment is completed, the isolation cover and the top-blowing argon gun are removed, and the ladle is transported to the continuous casting process. The CAS refined steel liquid in the ladle enters the tundish through the water inlet, and the tundish is insulated with a carbonized rice husk covering agent, and then casting into a continuous casting billet is started to obtain the cord steel.

3. The method for preparing cord steel according to claim 1 or 2, characterized in that: The top-blowing argon gun in step 3) comprises a main body and at least one branch pipe arranged at one end of the main body, the branch pipe and the main body are connected to each other, and the angle between the branch pipe and the horizontal direction is 15-25°; and / or, rotating the top-blowing argon gun during the top-blowing of argon, wherein the rotation speed is 20-50 rpm; and the argon flow rate of the top-blowing argon is 20-200 NL / min; And / or, the diameter of the lower opening of the isolation cover is 2 / 5-3 / 5 of the diameter of the upper opening of the ladle.

4. The method for preparing cord steel according to claim 2, characterized in that: The S content in the desulfurized iron water in step 1) is ≤0.0025wt%, and the N content is ≤30ppm; And / or, in the raw steel, N≤40ppm, Cr≤0.06wt%, Ni≤0.06wt%, Cu≤0.06wt%, Mo≤0.010wt%, Sn≤0.007wt%, S≤0.008wt%, and the balance is Fe; And / or, the total mass of the raw steel and the desulfurized molten iron is recorded as a, the mass of the desulfurized molten iron is recorded as b, and b accounts for more than 45% of a; And / or, the raw steel is first placed in an EAF electric furnace, and then the desulfurized molten iron is added into the EAF electric furnace, and the adding speed of the desulfurized molten iron is 9-12 t / min; And / or, the EAF smelting time is 35-45min; And / or, the EAF electric furnace smelting end temperature is not less than 1660°C; And / or, after the EAF electric furnace smelting in step 2) is completed, the O content in the tapped steel is ≤0.050wt%, the C content is ≥0.20wt%, the P content is ≤0.010wt%, the S content is ≤0.010wt%, and the N content is ≤0.0040wt%.

5. The method for preparing cord steel according to claim 2 or 4, characterized in that: In step 2), the amount of ferrosilicon added is 2.3-2.7 kg / ton of steel, the amount of ferromanganese added is 4.0-5.2 kg / ton of steel, and the amount of lime added is 1.3-1.7 kg / ton of steel; And / or, the chemical composition of the ferrosilicon, in terms of mass percentage, includes: C≤0.02%, Si≥74%, P≤0.015%, Al≤0.15%, Ti≤0.05%, ≤0.02%, and the balance is iron; And / or, the chemical composition of the ferromanganese, calculated by mass percentage, includes: C≤0.6%, Si≤2%, Mn≥80%, P≤0.10%, S≤0.02%, and the balance is iron; and / or, the amount of the synthetic slag for the cord steel is 7-11 kg / ton of steel; And / or, the composition of the synthetic slag of the cord steel, by mass percentage: SiO2 content 45-50%, CaO content 40-45%, Al2O3 content 4-7%, MgO ≤ 5%, and the balance is unavoidable impurities; And / or, the amount of the carburizer added is 3.0-4.8 kg / ton of steel; and / or, when adding the carburizer, the argon gas flow rate of the ladle bottom blowing is 500-750NL / min, and after the carburizer is added, the bottom blowing flow rate is 10-200NL / min; And / or, the recarburizer, in terms of mass percentage, has chemical compositions including: fixed carbon ≥ 97%, H2O ≤ 0.5%, ash ≤ 2%, S ≤ 0.4%, N ≤ 0.03%, and the remainder being unavoidable impurities; And / or, the reaction time of adding the synthetic slag of the cord steel is 3-10 minutes.

6. The method for preparing cord steel according to claim 2 or 4, characterized in that: Step 3) The inlet temperature of the ladle transported to the CAS station is 1580-1620℃, and the inlet oxygen value is 50-90ppm; and / or, the argon flow rate of the bottom blowing argon gas through the air hole below the ladle is 200-500NL / min; And / or, the first stirring time is 3-40 min; and / or, when obtaining CAS refined molten steel, the temperature of the CAS refined molten steel in the ladle is 1540-1543° C.; And / or, in step 3), during the soft stirring process, the bottom blowing argon flow rate is 50-80NL / min, and the soft stirring is maintained for 15-20min; And / or, the composition of the slag after CAS refining, by mass percentage, includes: Al2O3: 5-7%, MgO: 5-8%, [MnO+T.Fe]: 2-5%, and the balance is SiO2 and CaO, wherein the basicity CaO / SiO2: 0.9-1.

2.

7. The method for preparing cord steel according to claim 2 or 4, characterized in that: After the isolation cover and top-blowing argon gun are removed in step 4), the ladle is transported to the continuous casting process, and the temperature of the molten steel in the ladle is 1529-1535°C during the continuous casting process; And / or, the temperature of the molten steel in the tundish in step 4) is 1493-1499°C; And / or, the carbonized rice husk in step 4) comprises, by mass percentage, SiO2: 70-90%, C: 10-30%, moisture ≤ 3%, and the natural bulk density of the carbonized rice husk ≤ 120 g / m 3 .

8. A cord steel, characterized in that: The cord steel is prepared by the preparation method of the cord steel according to any one of claims 1 to 7.

9. The cord steel according to claim 8, characterized in that: The chemical composition of the cord steel includes, by mass percentage, C: 0.70-0.95%, Si: 0.15-0.45%, Mn: 0.25-0.80%, P≤0.015%, S≤0.012%, Alt≤0.0020%, N≤0.0060%, and the rest is Fe and other inevitable impurities.

10. Use of the cord steel prepared by the method for preparing the cord steel according to any one of claims 1 to 7 or the cord steel according to claim 8 or 9 in preparing steel cord.

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