A cord steel, its preparation method and application

Abstract

The present invention belongs to the technical field of pure steel preparation, and specifically relates to a cord steel, its preparation method, and application. The preparation method of the cord steel provided by the present invention comprises subjecting the cord steel raw material to EAF electric furnace smelting, CAS refining, and continuous casting treatment in sequence; the CAS refining comprises setting 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 ladle is insulated using a carbonized rice husk covering agent. The specific preparation method of the present invention effectively reduces CaSi inclusions in steel and stably produces cord steel with high cleanliness.

Description

Technical Field

[0001] The present 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] Currently, the market has increasingly stringent requirements for inclusions in cord steel. In addition to strictly controlling Al2O3-type brittle inclusions, the size of silicate inclusions is also receiving increasing attention.

[0003] For cord steel deoxidized with silicon and manganese, four main types of inclusions are present: MnS, Al-rich inclusions, MnSi, and CaSi. MnS inclusions have a strong deformation capacity and deform at the same rate as the steel matrix during rolling, making them harmless to cord steel. As for Al-rich inclusions, steel companies have implemented strict procurement controls on the Al content of alloys, refractory materials, and auxiliary materials, and have avoided Al deoxidation, largely avoiding these large inclusions. MnSi inclusions (MnO-SiO2-Al2O3 system) are deoxidized inclusions generated by the deoxidation of ferrosilicon and ferromanganese in cord steel. CaSi inclusions (CaO-SiO2-Al2O3 system) result from the slag-metal reaction between molten steel and Ca-containing substances in the slag. Analysis of wire rod inclusions revealed that CaSi predominates among large inclusions (≥15μm), accounting for over 95%. With product upgrades, quality requirements are becoming increasingly higher. High-strength cord steel is drawn thinner and thinner in subsequent drawing, and large-sized CaSi inclusions need to be strictly controlled.

[0004] Traditional electric furnace steelmaking utilizes EAF (electric furnace electric agitation) followed by LF refining, vacuum VD / RH (vacuum smelting) and continuous CCM casting to produce cord steel. The main process routes are: 1) EAF + LF refining + vacuum VD / RH (vacuum smelting) + continuous CCM casting; 2) EAF + LF refining + continuous CCM casting. Cord steel produced by both processes is treated with LF.

[0005] LF is an off-furnace refining method utilizing electric arc heating, also known as a ladle heating furnace. This treatment method can perform functions such as electric arc heating, composite slag refining, argon blowing and stirring, and alloy adjustment. Large-sized inclusions are primarily CaSi-based, and while these inclusions are rare before LF treatment, they gradually increase during the LF process. This is primarily due to the increased Ca content as the contact time between the molten steel and the slag increases, the incorporation of refining slag, and the decrease in the oxygen potential of the molten steel. This results in a high number of CaSi-based inclusions, exceeding the specified standard. These inclusions are formed when CaO-containing substances in the slag enter the molten steel from top to bottom. Furthermore, the molten steel absorbs significant nitrogen during the LF refining process, necessitating the addition of a vacuum treatment step to reduce nitrogen. This increases the number of production steps and results in higher 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 its preparation method and application.

[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;

[0008] 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;

[0009] The continuous casting tundish is insulated using a carbonized rice husk covering agent.

[0010] Preferably, the preparation method of the cord steel specifically comprises the following steps:

[0011] 1) Mix desulfurized molten iron and raw steel for EAF smelting;

[0012] 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 recarburizer is added, and then the cord steel is added to synthesize the slag for reaction;

[0013] 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 inserted above the ladle to perform top-blowing of argon. When the exposed surface of the molten steel is larger than the diameter of the lower opening 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 of argon is stopped, and the first stirring is performed to obtain CAS refined steel liquid. The CAS refined steel liquid is then subjected to a soft stirring treatment;

[0014] 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 nozzle. The tundish is insulated with a carbonized rice husk covering agent, and then casting into continuous casting billets is started to obtain the cord steel.

[0015] The raw steel of the present invention may be scrap steel or raw steel obtained through preparation.

[0016] The top-blowing argon gun of the present invention is arranged in the isolation cover and 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.

[0017] 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.

[0018] The soft stirring described in the present invention refers to a method of stirring by introducing argon gas.

[0019] Optionally, the air hole below the ladle is a bottom blowing argon port.

[0020] Preferably, the top-blowing argon gun in step 3) includes 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°; the argon gas is discharged through the branch pipe away from the end of the main body to achieve a slag blowing effect.

[0021] 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 diameter of the lower mouth of the isolation cover.

[0022] 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;

[0023] And / or, the diameter of the isolation cover is 2 / 5-3 / 5 of the diameter of the upper opening of the ladle.

[0024] Preferably, the diameter of the isolation cover is 1 / 2 of the diameter of the upper opening of the ladle.

[0025] Preferably, the S content in the desulfurized molten iron in step 1) is ≤0.0025wt%, and the N content is ≤30ppm;

[0026] 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;

[0027] 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;

[0028] Preferably, b accounts for 45-85% of a;

[0029] and / or, placing the raw steel in an EAF furnace first, and then adding the desulfurized molten iron into the EAF furnace at a rate of 9-12 t / min;

[0030] And / or, the EAF smelting time is 35-45 minutes;

[0031] And / or, the EAF electric furnace smelting end temperature is not less than 1660°C;

[0032] And / or, after the EAF smelting in step 2) is completed, the O content in the tapped molten 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%.

[0033] 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;

[0034] And / or, the chemical composition of the ferrosilicon, calculated by 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;

[0035] And / or, the ferromanganese, in terms of mass percentage, has the following chemical composition: C≤0.6%, Si≤2%, Mn≥80%, P≤0.10%, S≤0.02%, with the balance being iron;

[0036] and / or, the amount of the synthetic slag for cord steel is 7-11 kg / ton of steel;

[0037] And / or, the composition of the synthetic slag for cord steel is, by mass percentage: SiO2 content 45-50%, CaO content 40-45%, Al2O3 content 4-7%, MgO ≤ 5%, and other unavoidable components;

[0038] And / or, the amount of the recarburizer added is 3.0-4.8 kg / ton of steel;

[0039] and / or, the ladle bottom blowing argon flow rate is 500-750 NL / min when adding the recarburizer, and the bottom blowing flow rate is 10-200 NL / min after the addition of the recarburizer is completed;

[0040] And / or, the recarburizer, in terms of mass percentage, has the following chemical compositions: fixed carbon ≥ 97%, H2O ≤ 0.5%, ash ≤ 2%, S ≤ 0.4%, N ≤ 0.03%, with the remainder being unavoidable impurities;

[0041] And / or, the reaction time of adding the cord steel synthetic slag is 3-10 minutes.

[0042] 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 50-90 ppm;

[0043] and / or, the argon flow rate of the bottom blowing argon gas through the air holes below the ladle is 200-500 NL / min;

[0044] Optionally, the air hole below the ladle is a bottom blowing argon port.

[0045] And / or, the first stirring time is 3-40 min;

[0046] and / or, when obtaining the CAS refined steel liquid, the temperature of the CAS refined steel liquid in the ladle is 1540-1543° C.;

[0047] And / or, during the soft stirring process in step 3), the bottom blowing argon flow rate is 50-80 NL / min, and the soft stirring is maintained for 15-20 minutes;

[0048] and / or, the slag composition after CAS refining, in terms of mass percentage, comprises: Al2O3: 5-7wt%, MgO: 5-8wt%, [MnO+T.Fe]: 2-5wt%, the balance being SiO2 and CaO, wherein the basicity CaO / SiO2: 0.9-1.2;

[0049] 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.

[0050] 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 ≤0.05 / mm 2 .

[0051] Optionally, the size of CaSi inclusions in the molten steel after CAS refining is no more than 28 μm.

[0052] 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 increase the C, Si, and Mn contents to the required range of the finished product.

[0053] Optionally, in step 3), the air holes below the ladle are made of single-hole air bricks, and the location of the air bricks is at a radius of 0.3-0.36 from the center of the ladle bottom.

[0054] Optionally, the air brick is positioned at a point 1 / 3 of the radius from the center of the ladle bottom.

[0055] 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;

[0056] and / or, the temperature of the molten steel in the tundish in step 4) is 1493-1499° C.;

[0057] The solid sample of molten steel from the tundish in step 4) was scanned and counted using a Zeiss scanning electron microscope. The number of CaSi inclusions >5μm in the molten steel was ≤0.05 / mm. 2 , the number of CaSi inclusions >15μm ≤0.03 / mm 2 ;

[0058] Optionally, the size of CaSi inclusions in the molten steel in the tundish is no more than 23 μm.

[0059] 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 is ≤ 120 g / m 3 .

[0060] The present invention specifically includes the following steps:

[0061] 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.

[0062] 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 electrodes are heated and melted by conductive heating. The tapping temperature of the electric furnace is controlled to be ≥1660℃.

[0063] Electric Furnace Tapping: After EAF smelting, the molten steel is placed in a ladle. During tapping, argon is not blown from the ladle bottom to prevent the molten steel from churning and coming into contact with air. When the tapped volume reaches 1 / 3 to 1 / 2, alloying materials are added in the following order: low-titanium, low-aluminum ferrosilicon, low-carbon ferromanganese, and lime. After tapping is complete and the ladle is opened, bottom argon is turned on and recarburizer is used. After recarburization is complete, the bottom blowing rate is reduced, and cord steel synthetic slag is added. After stirring for 3-10 minutes, the bottom argon blowing is turned off.

[0064] During the CAS refining process, after a ladle filled with molten steel arrives at the CAS station, an argon gas line is connected. Argon is blown through the holes in the air bricks below the ladle, dispersing the slag above the ladle surface. This releases a cluster of argon bubbles, exposing the molten steel. When the exposed surface approaches the diameter of the lower opening of the isolation hood, a top-blowing argon gun is introduced, blowing argon at a constant rate to further expand the exposed surface. Once the exposed surface exceeds the diameter of the lower opening of the isolation hood, the isolation hood is lowered and immersed in the molten steel, enveloping any bubbles that rise from the bottom of the hood. (The isolation hood reduces reaction losses caused by contact between the molten steel and added alloys and the slag outside the hood. Furthermore, by removing slag from the hood, it reduces the risk of bubbles from the bottom of the hood being drawn into the slag, as well as the introduction of inclusions by added alloy components.) Simultaneously, top-blowing argon is stopped, the top-blowing argon gun is raised (to protect it from corrosion and extend its service life), and the first stirring step begins. Take samples to analyze the composition of the molten steel, and add low-titanium, low-aluminum ferrosilicon and low-carbon ferromanganese based on the results to adjust the elemental composition of the molten steel to the required range.

[0065] 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.

[0066] During the continuous casting process, protective casting is ensured, including removing the isolation cover and top-blowing argon gun, transporting the ladle to the continuous casting process, and allowing the CAS refined steel in the ladle to enter the tundish through the nozzle. The nozzle of the tundish is sealed with argon to protect casting. The protective argon blowing pipe is inspected for leaks after each heat, and the nozzle seal of the tundish is replaced promptly. Ca-based tundish covering agents are not used, and carbonized rice hulls are used for insulation. Before pouring (before molten steel is injected into the tundish), the air in the tundish is purged with argon, and the molten steel is then cast into continuous casting billets.

[0067] Preferably, in the molten iron pretreatment, the KR method is adopted for molten iron pretreatment desulfurization, and a desulfurizer (a mixture of 90% lime and 10% fluorite) of 6-10 kg / t iron is added to the molten iron. Under the action of the vortex field formed by the rotating stirring head, the desulfurizer and the sulfur in the molten iron are fully reacted to form desulfurization slag, and then the desulfurization slag is removed by a slag scraper, thereby reducing the sulfur content in the molten iron to ≤0.0025wt%.

[0068] CAS refining is a refining method that involves blowing argon into the ladle and adjusting the composition. It uses argon to spray into the ladle to even out the composition and temperature of the molten steel. It can also adjust the composition, increase the alloy yield, eliminate large inclusions in the molten steel, and purify the molten steel.

[0069] The present invention provides a cord steel prepared by the above-mentioned cord steel preparation method.

[0070] 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.

[0071] The present invention also provides a use of the above-mentioned cord steel in preparing steel cord.

[0072] The technical solution of the present invention has the following advantages:

[0073] 1. The present invention provides a method for preparing cord steel, comprising sequentially subjecting the cord steel raw material to EAF (Electric Acid Furnace) smelting, CAS (Chemical Assay) refining, and continuous casting. The CAS refining includes installing a top-blowing argon gun above the ladle to perform CAS top-blowing argon deslagging, thereby ensuring that no slag remains within the isolation hood during the CAS refining process. The continuous casting tundish is insulated using a carbonized rice hull covering agent. The present invention employs the CAS method for refining, with top-blowing argon. This method prevents the generation of CaSi inclusions from the molten steel due to the slag-metal reaction from the top down caused by LF electrode heating. Furthermore, this method minimizes the generation of CaSi inclusions by creating a small slag-metal contact interface. The designed CAS top-blown argon gun ensures that the exposed surface within the isolation hood is free of slag before alloy addition to control the finished product composition, resulting in a high alloy yield and minimizing slag entrapment in the molten steel. Because the alloy melts and dissolves in contact with the molten steel within the isolation hood, reaction losses with the slag outside the hood are reduced. By eliminating the LF treatment, the ingress of large amounts of CaSi inclusions caused by LF heating is avoided, weakening the slag-metal reaction between the molten steel and slag, and preventing the generation of large amounts of CaSi inclusions (CaO-Al2O3-SiO2) during the refining process. This allows the production of high-purity cord steel using an electric furnace process. Furthermore, the process provided by this invention does not require VD or RH vacuum treatment, improving steel inclusion cleanliness while ensuring that gas content meets standards. Carbonized rice husks are used during continuous casting to protect the treated molten steel from secondary contamination and prevent nitrogen and oxygen absorption from air contact. The absence of CaO-containing tundish covering agents prevents the formation of CaSi inclusions during casting. This specific preparation method effectively reduces CaSi inclusions in steel, resulting in the stable production of highly clean cord steel.

[0074] 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, tapping is performed 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 hole below the ladle, and the slag on the liquid surface of the ladle is blown away to expose the molten steel. When the molten steel is exposed, After the surface is formed, a top-blowing argon gun is placed above the ladle to perform top-blowing of argon. When the exposed surface of the molten steel is larger than the diameter of the lower opening 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 of argon is stopped to perform the first stirring to obtain CAS refined steel liquid. The CAS refined steel liquid is then subjected to a soft stirring treatment. 4) After the CAS refined steel liquid in step 3 has undergone soft stirring, the isolation cover and 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 nozzle, where it is insulated with a carbonized rice husk covering agent. Casting into continuous casting billets is then started to obtain the cord steel. The specific preparation method of the present invention effectively reduces CaSi inclusions in the steel and stably produces cord steel with high cleanliness.

[0075] 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 the electric furnace tapping can be met; the main raw material uses molten iron that has been pre-desulfurized. One reason is that the cord steel refining uses an acidic slag system, which does not have desulfurization ability, so the S content of the electric furnace tapping meets the standard; the second reason is that during the desulfurization process, the molten iron comes into contact with air, and the N content brought out by the carbon-oxygen reaction and the temperature drop causes N precipitation, which will reduce the N content of the molten iron, avoiding the need to increase the vacuum treatment for denitrification. Smelting with a molten iron ratio of 45% or higher aims to increase the carbon content of the main raw materials and reduce the heating time by replacing some of the heating by electrical heating with a carbon-oxygen chemical reaction. Furthermore, decarburization in the furnace generates CO, which removes some nitrogen. The highly oxidizing atmosphere within the furnace and the foamy slag covering the molten steel reduce nitrogen absorption from the air, keeping the nitrogen content in the furnace within a low range.

[0076] 4. In the cord steel production method provided herein, the EAF electric furnace smelting temperature is no less than 1660°C, ensuring a sufficiently high temperature for the molten steel during the CAS refining process to avoid underheating. Ferrosilicon and ferromanganese are used for deoxidation during the EAF tapping process, and synthetic cord steel slag is added before refining to reduce slag-metal contact time.

[0077] 5. In the method for preparing cord steel provided by the present invention, the top-blowing argon gun in step 3) comprises a main pipe at the top and four branches at the bottom, each branch forming an angle of 15-25° with the horizontal direction; the top-blowing argon gun has an argon flow rate of 20-200 NL / min and a rotation speed of 20-50 rpm; and the isolation cover has a diameter of 1 / 2 the diameter of the ladle top. By specifically limiting the structure of the top-blowing argon gun, as well as the argon flow rate and rotation speed of the top-blowing argon, the present invention further prevents the top-down generation of CaSi inclusions into the molten steel, further ensures the effective reduction of CaSi inclusions in the steel, and further stably produces cord steel with high cleanliness.

[0078] 6. The method for preparing cord steel provided by the present invention comprises obtaining CAS refined steel liquid and subjecting the CAS refined steel liquid to a soft stirring process. The soft stirring process causes small slag inclusions and oxides in the CAS refined steel liquid to aggregate and float, further reducing CaSi inclusions in the steel and producing highly clean cord steel.

[0079] 7. The cord steel provided by the present invention produces high-cleanliness cord steel wire rods, with the number of large-sized CaSi inclusions (≥15μm) ≤0.02 / mm 2 . BRIEF DESCRIPTION OF THE DRAWINGS

[0080] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0081] Figure 1 Schematic diagram of a CAS refining device used to prepare cord steel according to an embodiment of the present invention;

[0082] Figure 2 A top view of a CAS top-blown argon gun used in preparing cord steel according to an embodiment of the present invention;

[0083] Figure numerals: 1- ladle, 2- isolation cover, 3- ejector argon gun, 4- alloy chute, 5- exhaust hole, 6- slag, 7- water nozzle, 8- bottom blowing argon port, 9- molten steel. DETAILED DESCRIPTION

[0084] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0085] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0086] 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, calculated by mass percentage, is as follows: 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.

[0087] Example 1

[0088] This embodiment provides a method for preparing cord steel, comprising the following steps:

[0089] 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, calculated 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 to the EAF electric furnace through the rear chute at a rate of 10t / min. The oxygen lance on the furnace wall starts blowing oxygen, and the power is turned on to start EAF electric furnace smelting. After smelting for 40 minutes, the EAF electric furnace smelting temperature is 1665℃, the electric furnace tapping rate is 90%, and the S content in 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%.

[0090] 2) Place the molten steel in a ladle. When the tapping volume reaches 40 tons, add 250kg of low-titanium, low-aluminum ferrosilicon (calculated by mass percentage, the low-titanium, low-aluminum ferrosilicon 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 (calculated by mass percentage, the low-carbon ferromanganese alloy 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. Then add 150kg of lime and the tapping volume is 40 tons. After the bundle is bundled, bottom blowing of argon is started at a bottom blowing flow rate of 600NL / min, and 450kg of recarburizer is added (the recarburizer is calculated by mass percentage and includes: fixed carbon: 98%, H2O: 0.2%, ash: 1%, S: 0.2%, N: 0.013%, and the balance is unavoidable impurities), then the bottom blowing flow rate is changed to 150NL / min, and 1000kg of cord steel synthetic slag is added (the cord steel synthetic slag is calculated by mass percentage and includes: SiO2 content 48%, CaO content 43%, Al2O3 content 5.5%, MgO: 3%, and the balance is unavoidable impurities) and stirred for reaction for 5 minutes;

[0091] 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 unit is as follows Figure 1 As shown, the inlet temperature is 1600℃, 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 injected above the ladle 1 (the top view of the top blowing argon gun is shown in FIG. Figure 2As shown, the top-blowing argon gun 3 includes a main body and four 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 pipes 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 rotates at 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 lowered, 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. The temperature of the molten steel in the ladle 1 is 1540°C. According to the sampling analysis of the spectrometer According to the analysis results, low-carbon ferromanganese, low-titanium and low-aluminum ferrosilicon, and recarburizers were used to increase the C, Si, and Mn contents to meet the composition requirements of the finished 72-grade cord steel product. The Al2O3 content in the refined slag was 5.8wt%, the MgO content was 7.7wt%, and the [MnO+T.Fe] content was 3.5wt%, with the remainder being SiO2 and CaO, with a compositional basicity (CaO / SiO2) of 1.02. The CAS refined steel liquid was then subjected to soft stirring treatment with a bottom blowing argon flow rate of 60NL / min and a soft stirring holding time of 18min. The bottom blowing argon port in the CAS refining ladle used a single-hole air brick, and the air brick was located at a radius of 1 / 3 from the center of the ladle bottom.

[0092] 4) After the soft stirring treatment of the CAS refined steel liquid is completed in step 3, 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 molten steel 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 comprises, by mass percentage, SiO2: 80%, C: 19%, and moisture: 1%. The natural bulk density of the carbonized rice husk is 110g / m 3 , and then began casting into a continuous casting billet to obtain the cord steel. The specific composition of the cord steel, in percentage by mass, is: 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 remainder is Fe and other unavoidable impurities.

[0093] Example 2

[0094] This embodiment provides a method for preparing cord steel, comprising the following steps:

[0095] 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, calculated 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 balance is Fe), and then 55 tons of desulfurized molten iron is added to the EAF electric furnace through the rear chute at a rate of 12t / min. The oxygen lance on the furnace wall starts blowing oxygen, and the power is turned on to start EAF electric furnace smelting. After smelting for 45 minutes, the EAF electric furnace smelting temperature ends at 1668℃, the electric furnace tapping rate is 89%, and the S content in 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%.

[0096] 2) Place the molten steel in a ladle. When the tapping volume reaches 40 tons, add 250kg of low-titanium, low-aluminum ferrosilicon (calculated by mass percentage, the low-titanium, low-aluminum ferrosilicon 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 (calculated by mass percentage, the low-carbon ferromanganese alloy 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. Then add 150kg of lime and the tapping volume is 40 tons. After the bundle is bundled, bottom blowing of argon is started at a bottom blowing flow rate of 750NL / min, and 400kg of recarburizer is added (the recarburizer, calculated by mass percentage, includes fixed carbon: 98%, H2O: 0.2%, ash: 1%, S: 0.2%, N: 0.013%, and the balance is unavoidable impurities). Then the bottom blowing flow rate is changed to 120NL / min, and 1000kg of cord steel synthetic slag is added (the cord steel synthetic slag, calculated by mass percentage, includes: SiO2 content 48%, CaO content 43%, Al2O3 content 5.5%, MgO: 3%, and the balance is unavoidable impurities) and stirred for reaction for 6 minutes;

[0097] 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 unit is as follows Figure 1 As shown, the inlet temperature is 1608℃, 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 injected above the ladle 1 (the top view of the top blowing argon gun is shown in FIG. Figure 2As shown, the top-blowing argon gun 3 includes a main body and four branch pipes arranged at one end of the main body. The branch pipes are connected to the main body, and the branch pipes discharge argon at a distance from the main body. The angle between the branch pipes and the horizontal direction is 25°) for top-blowing argon. The top-blowing argon flow rate is 200NL / min, and the rotation speed of the top-blowing argon gun 3 is 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 lowered. 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. At the same time, the top-blowing argon gun 3 is raised and the top-blowing argon is stopped. After stirring for 10 minutes, CAS refined steel liquid is obtained. The temperature of the molten steel in the ladle 1 is 1541°C. According to the sampling of the spectrometer Analysis results showed that low-carbon ferromanganese, low-titanium, low-aluminum ferrosilicon, and recarburizers were used to increase the C, Si, and Mn contents to meet the composition requirements of the finished 72-grade cord steel product. Testing of the refined slag revealed 5.6wt% Al2O3, 8.1wt% MgO, 3.4wt% [MnO+T.Fe], and the remainder SiO2 and CaO, with a basicity (CaO / SiO2) of 1.00. The CAS refined steel liquid was then subjected to soft stirring treatment with a bottom-blown argon flow rate of 80NL / min and a soft stirring holding time of 15min. The bottom-blown argon port in the CAS refining ladle used a single-hole permeable brick, located at a radius of 1 / 3 from the center of the ladle bottom.

[0098] 4) After the soft stirring treatment of the CAS refined steel liquid is completed in step 3), 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 molten steel 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 comprises, by mass percentage, 78% SiO2, 22% C, and 1% moisture. The natural bulk density of the carbonized rice husk is 80g / m3. 3 , and then begins casting into a continuous casting billet to obtain the cord steel. The specific composition of the cord steel, in percentage by mass, is: 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 remainder is Fe and other unavoidable impurities.

[0099] Example 3

[0100] This embodiment provides a method for preparing cord steel, comprising the following steps:

[0101] 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, calculated 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 balance is Fe), and then 55 tons of desulfurized molten iron is added to the EAF electric furnace through the rear chute at a rate of 9t / min. The oxygen lance on the furnace wall starts blowing oxygen, and the power is turned on to start EAF electric furnace smelting. After smelting for 35 minutes, the EAF electric furnace smelting temperature is 1663℃, the electric furnace tapping rate is 91%, and the S content in 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%.

[0102] 2) Place the molten steel in a ladle. When the tapping volume reaches 40 tons, add 250kg of low-titanium, low-aluminum ferrosilicon (calculated by mass percentage, the low-titanium, low-aluminum ferrosilicon 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 (calculated by mass percentage, the low-carbon ferromanganese alloy 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. Then add 150kg of lime and tap the steel. After completion, bottom blowing of argon was started at a flow rate of 500 NL / min, and 430 kg of recarburizer was added (the recarburizer, calculated by mass percentage, includes: fixed carbon: 98%, H2O: 0.2%, ash: 1%, S: 0.2%, N: 0.013%, and the balance is unavoidable impurities). Then, the bottom blowing flow rate was changed to 200 NL / min, and 1000 kg of cord steel synthetic slag was added (the cord steel synthetic slag, calculated by mass percentage, includes: SiO2 content 48%, CaO content 43%, Al2O3 content 5.5%, MgO: 3%, and the balance is unavoidable impurities). The mixture was stirred and reacted for 5 minutes.

[0103] 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 unit is as follows Figure 1 As shown, the inlet temperature is 1580℃, 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 injected above the ladle 1 (the top view of the top blowing argon gun is shown in FIG. Figure 2As shown, the top-blowing argon gun 3 includes a main body and four branch pipes arranged at one end of the main body. The branch pipes are connected to the main body, and the branch pipes discharge argon at a distance from the main body. The angle between the branch pipes and the horizontal direction is 17°) for top-blowing argon. The top-blowing argon flow rate is 40NL / min, and the rotation speed of the top-blowing argon gun 3 is 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 lowered. 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. At the same time, the top-blowing argon gun 3 is raised and the top-blowing argon is stopped. After stirring for 12 minutes, CAS refined steel liquid is obtained. The temperature of the molten steel in the ladle 1 is 1540°C. According to the sampling of the spectrometer Analysis results showed that low-carbon ferromanganese, low-titanium, low-aluminum ferrosilicon, and recarburizers were used to increase the C, Si, and Mn contents to meet the composition requirements of the finished 72-grade cord steel product. Testing of the refined slag revealed 5.8wt% Al2O3, 7.7wt% MgO, 3.5wt% [MnO+T.Fe], and the remainder SiO2 and CaO, with a basicity (CaO / SiO2) of 1.02. The CAS refined steel liquid was then subjected to soft stirring treatment with a bottom-blown argon flow rate of 70NL / min and a soft stirring holding time of 20min. The bottom-blown argon port in the CAS refining ladle used a single-hole permeable brick, located at a radius of 1 / 3 from the center of the ladle bottom.

[0104] 4) After the soft stirring treatment of the CAS refined steel liquid in step 3 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 1529°C. The refined molten steel 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 comprises, by mass percentage, SiO2: 80%, C: 19%, and moisture: 1%. The natural bulk density of the carbonized rice husk is 110g / m 3 , and then begins casting into a continuous casting billet to obtain the cord steel. The specific composition of the cord steel, in percentage by mass, is: 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 remainder is Fe and other unavoidable impurities.

[0105] Comparative Example 1

[0106] This comparative example provides a method for preparing cord steel, which adopts LF refining and includes the following steps:

[0107] 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, calculated 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 balance The 55 tons of desulfurized molten iron was then added to the EAF furnace through the rear chute at a rate of 10 t / min. The oxygen lance on the furnace wall began to blow oxygen, and the power was turned on for EAF smelting. After smelting for 40 minutes, the EAF smelting temperature was completed at 1665°C, the tapping rate was 90%, and the S content in the tapped steel was 0.008wt%, 0.008wt% P, 0.0028wt%, 0.25wt% C, and 0.046wt% oxygen.

[0108] 2) Place the molten steel in a ladle. When the tapping volume reaches 40 tons, add 250kg of low-titanium, low-aluminum ferrosilicon (calculated by mass percentage, the low-titanium, low-aluminum ferrosilicon 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 (calculated by mass percentage, the low-carbon ferromanganese alloy 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. Then add 150kg of lime and the tapping volume is 40 tons. After the bundle is bundled, bottom blowing of argon is started at a bottom blowing flow rate of 600NL / min, and 450kg of recarburizer is added (the recarburizer is calculated by mass percentage and includes: fixed carbon: 98%, H2O: 0.2%, ash: 1%, S: 0.2%, N: 0.013%, and the balance is unavoidable impurities), then the bottom blowing flow rate is changed to 150NL / min, and 1000kg of cord steel synthetic slag is added (the cord steel synthetic slag is calculated by mass percentage and includes: SiO2 content 48%, CaO content 43%, Al2O3 content 5.5%, MgO: 3%, and the balance is unavoidable impurities) and stirred for reaction for 5 minutes;

[0109] 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, and argon is blown through the air holes below the ladle at a flow rate of 300NL / min. After 35 minutes, LF refined steel liquid is obtained. The temperature of the steel liquid in the ladle is 1540℃. According to the sampling 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 various components of the finished product of grade 72 cord steel. After testing the A in the refined slag, The content of l2O3 is 5.8wt%, the content of MgO is 7.7wt%, the content of [MnO+T.Fe] is 3.5wt%, and the balance is SiO2 and CaO, with a compositional basicity (CaO / SiO2) of 1.02. The CAS refined steel liquid is then subjected to soft stirring treatment, with a bottom blowing argon flow rate of 60NL / min and a soft stirring holding time of 18 minutes. The bottom blowing argon port in the CAS refined ladle uses a single-hole air-permeable brick, and the air-permeable brick is located at 1 / 3 of the radius from the center of the ladle bottom.

[0110] 4) After the soft stirring treatment of the CAS refined steel liquid is completed in step 3), 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 molten steel enters the tundish through the nozzle. The temperature of the molten steel in the tundish is 1496°C. A carbonized rice husk covering agent is used in the tundish for heat preservation. The carbonized rice husk comprises, by mass percentage, 80% SiO2, 19% C, and 1% moisture. The natural bulk density of the carbonized rice husk is 110 g / m3. 3 , and then began casting into a continuous casting billet to obtain the cord steel. The specific composition of the cord steel, in percentage by mass, is: 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 remainder is Fe and other unavoidable impurities.

[0111] Comparative Example 2

[0112] This comparative example provides a method for preparing cord steel. This comparative example does not perform top blowing of argon gas and includes the following steps:

[0113] 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, calculated 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 balance The 55 tons of desulfurized molten iron was then added to the EAF furnace through the rear chute at a rate of 10 t / min. The oxygen lance on the furnace wall began to blow oxygen, and the power was turned on for EAF smelting. After smelting for 40 minutes, the EAF smelting temperature was completed at 1665°C, the tapping rate was 90%, and the S content in the tapped steel was 0.008wt%, 0.008wt% P, 0.0028wt%, 0.25wt% C, and 0.046wt% oxygen.

[0114] 2) Place the molten steel in a ladle. When the tapping volume reaches 40 tons, add 250kg of low-titanium, low-aluminum ferrosilicon (calculated by mass percentage, the low-titanium, low-aluminum ferrosilicon 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 (calculated by mass percentage, the low-carbon ferromanganese alloy 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. Then add 150kg of lime and the tapping volume is 40 tons. After the bundle is bundled, bottom blowing of argon is started at a bottom blowing flow rate of 600NL / min, and 450kg of recarburizer is added (the recarburizer is calculated by mass percentage and includes: fixed carbon: 98%, H2O: 0.2%, ash: 1%, S: 0.2%, N: 0.013%, and the balance is unavoidable impurities), then the bottom blowing flow rate is changed to 150NL / min, and 1000kg of cord steel synthetic slag is added (the cord steel synthetic slag is calculated by mass percentage and includes: SiO2 content 48%, CaO content 43%, Al2O3 content 5.5%, MgO: 3%, and the balance is unavoidable impurities) and stirred for reaction for 5 minutes;

[0115] 3) After the reaction in step 2) is completed, the ladle is transported to the CAS refining station. The inlet temperature is 1600°C and the inlet oxygen value is 70ppm. Argon is blown through the bottom blowing port below the ladle at a flow rate of 300NL / min to blow away the slag on the ladle surface to expose the molten steel. When the exposed surface of the molten steel is larger than the diameter of the lower opening of the isolation cover, the isolation cover is lowered. The diameter of the lower opening of the isolation cover is 1 / 2 of the diameter of the upper opening of the ladle. The lower end of the isolation cover is immersed in the molten steel and stirred for 9 minutes to obtain CAS refined steel liquid. The temperature of the molten steel in the ladle is 1540°C. According to the sampling analysis results of the spectrometer, low carbon ferromanganese, low titanium and low aluminum ferrosilicon, and recarburizer are taken to reduce the carbon content. , Si, and Mn contents were added to meet the requirements of the various components of the finished product of grade 72 cord steel. After testing, the Al2O3 content in the refined slag was 5.8wt%, the MgO content was 7.7wt%, [MnO+T.Fe] was 3.5wt%, and the balance was SiO2 and CaO, of which the basicity (CaO / SiO2) was 1.02; the CAS refined steel liquid was then subjected to soft stirring treatment, with the bottom blowing argon flow rate of soft stirring being 60NL / min and the soft stirring holding time being 18min; the bottom blowing argon port in the CAS refining ladle adopts a single-hole air-permeable brick, and the location of the air-permeable brick is at 1 / 3 of the radius from the center of the ladle bottom;

[0116] 4) After the soft stirring treatment of the CAS refined steel liquid is completed in step 3), 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 molten steel enters the tundish through the nozzle. The temperature of the molten steel in the tundish is 1496°C. A carbonized rice husk covering agent is used in the tundish for heat preservation. The carbonized rice husk comprises, by mass percentage, 80% SiO2, 19% C, and 1% moisture. The natural bulk density of the carbonized rice husk is 110 g / m3. 3 , and then began casting into a continuous casting billet to obtain the cord steel. The specific composition of the cord steel, in percentage by mass, is: 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 remainder is Fe and other unavoidable impurities.

[0117] Comparative Example 3

[0118] This embodiment provides a method for preparing cord steel. In this comparative example, a CaO covering agent is used in a tundish for heat preservation, comprising the following steps:

[0119] 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, calculated 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 balance The 55 tons of desulfurized molten iron was then added to the EAF furnace through the rear chute at a rate of 10 t / min. The oxygen lance on the furnace wall began to blow oxygen, and the power was turned on for EAF smelting. After smelting for 40 minutes, the EAF smelting temperature was completed at 1665°C, the tapping rate was 90%, and the S content in the tapped steel was 0.008wt%, 0.008wt% P, 0.0028wt%, 0.25wt% C, and 0.046wt% oxygen.

[0120] 2) Place the molten steel in a ladle. When the tapping volume reaches 40 tons, add 250kg of low-titanium, low-aluminum ferrosilicon (calculated by mass percentage, the low-titanium, low-aluminum ferrosilicon 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 (calculated by mass percentage, the low-carbon ferromanganese alloy 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. Then add 150kg of lime and the tapping volume is 40 tons. After the bundle is bundled, bottom blowing of argon is started at a bottom blowing flow rate of 600NL / min, and 450kg of recarburizer is added (the recarburizer is calculated by mass percentage and includes: fixed carbon: 98%, H2O: 0.2%, ash: 1%, S: 0.2%, N: 0.013%, and the balance is unavoidable impurities), then the bottom blowing flow rate is changed to 150NL / min, and 1000kg of cord steel synthetic slag is added (the cord steel synthetic slag is calculated by mass percentage and includes: SiO2 content 48%, CaO content 43%, Al2O3 content 5.5%, MgO: 3%, and the balance is unavoidable impurities) and stirred for reaction for 5 minutes;

[0121] 3) After the reaction in step 2) is completed, the ladle is transported to the CAS refining station with an inlet temperature of 1600°C and an inlet oxygen value of 70ppm. 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 ladle liquid surface to expose the molten steel. When the exposed surface of the molten steel appears, a top blowing argon gun is put above the ladle (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 interconnected, the branch pipes are away from the main body to discharge argon, and the angle between the branch pipes and the horizontal direction is 20°) to perform top blowing of argon. The top blowing argon flow rate is 40NL / min, and the top blowing argon gun speed is 40 rpm. When the exposed surface of the molten steel is larger than the diameter of the lower opening of the isolation cover, the isolation cover is lowered. The diameter of the lower opening of the isolation cover is 1 / 2 of the diameter of the upper opening of the ladle. The lower end of the isolation cover is immersed in the molten steel, and the top blowing argon gun is raised at the same time. The top argon blowing was started and stopped, and after stirring for 9 minutes, CAS refined steel liquid was obtained. The temperature of the steel liquid in the ladle was 1540℃. According to the sampling analysis results of the spectrometer, low-carbon ferromanganese, low-titanium and low-aluminum ferrosilicon, and a recarburizer were used to add C, Si, and Mn to meet the requirements of the various components of the 72-grade cord steel finished product. The Al2O3 content, MgO content, [MnO+T.Fe] content, and the balance of SiO2 and CaO in the refined slag were tested. The basicity (CaO / SiO2) was 1.02. The CAS refined steel liquid was then subjected to soft stirring treatment. The bottom blowing argon flow rate of the soft stirring was 60NL / min, and the soft stirring was maintained for 18 minutes. The bottom blowing argon port in the CAS refined ladle used a single-hole air brick, and the location of the air brick was 1 / 3 of the radius from the center of the ladle bottom.

[0122] 4) After the soft stirring treatment of the CAS refined steel in step 3 is completed, the isolation cover and top-blowing argon gun are removed, and the ladle is transported to the continuous casting process. The molten steel in the ladle is at a temperature of 1530°C. The refined steel enters the tundish through the nozzle, and the molten steel in the tundish reaches a temperature of 1496°C. A CaO covering agent is used in the tundish to maintain the temperature. The continuous casting process then begins, producing the cord steel. The specific composition of the cord steel, by mass percentage, is as follows: 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%, with the remainder being Fe and other unavoidable impurities.

[0123] Test Case

[0124] The cord steels obtained in Examples 1-3 of the present invention and Comparative Examples 1-3 were subjected to soaking, rolling, and Stelmor controlled cooling processes using the same process to obtain wire rods of the same specifications.

[0125] The CAS refined steel liquid 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 CAS refined steel, continuous casting tundish steel, and corresponding prepared wire rods. The cross-sections of the CAS refined steel obtained in Examples 1-3 and Comparative Examples 1-3, the cross-sections of the steel in the continuous casting tundish, and the corresponding 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.

[0126] Table 1 Statistics of the number and size of CaSi inclusions

[0127]

[0128] Note: "pieces / mm" in the table 2 ” indicates the number of inclusions per square millimeter of cross section.

[0129] As shown in Table 1, the use of the specific CAS refining method of Example 1 significantly reduced the number of large-sized (>15μm) CaSi inclusions and the maximum size of the inclusions compared to Comparative Example 1, which used LF refining, and Comparative Example 2, which did not use top argon blowing. 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 ≤0.05 / mm 2 The size of CaSi inclusions in the molten steel after CAS refining is not greater than 28μm. The number of CaSi inclusions > 5μm in the molten steel in the tundish is ≤ 0.05 / mm 2 , the number of CaSi inclusions >15μm ≤0.03 / mm 2 ; The size of CaSi inclusions in the molten steel in the tundish is not greater than 23μm.

[0130] The present invention takes the 72-grade 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 cord steel produced by a converter process route, and can solve the problem of excessive large-sized CaSi inclusions in all cord steels.

[0131] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing cord steel, characterized in that: The process includes subjecting the cord steel raw materials to EAF electric furnace smelting, CAS refining and continuous casting in sequence; The CAS refining comprises blowing argon gas from the bottom of 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 set above the ladle to perform CAS top-blowing argon slag removal, so that there is no slag in the isolation cover during the CAS treatment. The top-blown argon gun includes a main body and at least one branch pipe provided 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 degrees; rotating the top-blowing argon gun during the top-blowing of argon; The continuous casting tundish is insulated using a carbonized rice husk covering agent.

2. The method for preparing the 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 recarburizer 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 inserted above the ladle to perform top-blowing of argon. When the exposed surface of the molten steel is larger than the diameter of the lower opening 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 of argon is stopped, and the first stirring is performed to obtain CAS refined steel liquid. The CAS refined steel liquid is then subjected to a 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 nozzle. The tundish is insulated with a carbonized rice husk covering agent, and then casting into continuous casting billets is started to obtain the cord steel.

3. The method for preparing the cord steel according to claim 1 or 2, characterized in that: During the top-blowing of argon, the top-blowing argon gun is rotated at a rotation speed of 20-50 rpm; 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 the cord steel according to claim 2, characterized in that: The S content in the desulfurized molten iron 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, placing the raw steel in an EAF furnace first, and then adding the desulfurized molten iron into the EAF furnace at a rate of 9-12 t / min; And / or, the EAF smelting time is 35-45 minutes; And / or, the EAF electric furnace smelting end temperature is not less than 1660°C; And / or, after the EAF smelting in step 2) is completed, the O content in the tapped molten 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 the 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, calculated by mass percentage, includes: C≤0.02%, Si≥74%, P≤0.015%, Al≤0.15%, Ti≤0.05%, Ti≤0.02%, and the balance is iron; And / or, the ferromanganese, in terms of mass percentage, has the following chemical composition: C≤0.6%, Si≤2%, Mn≥80%, P≤0.10%, S≤0.02%, with the balance being iron; and / or, the amount of the synthetic slag for cord steel is 7-11 kg / ton of steel; And / or, the composition of the synthetic slag for cord steel, calculated by mass percentage, is as follows: 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 recarburizer added is 3.0-4.8 kg / ton of steel; and / or, the ladle bottom blowing argon flow rate is 500-750 NL / min when adding the recarburizer, and the bottom blowing flow rate is 10-200 NL / min after the addition of the recarburizer is completed; And / or, the recarburizer, in terms of mass percentage, has the following chemical compositions: fixed carbon ≥ 97%, H2O ≤ 0.5%, ash ≤ 2%, S ≤ 0.4%, N ≤ 0.03%, with the remainder being unavoidable impurities; And / or, the reaction time of adding the cord steel synthetic slag is 3-10 minutes.

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

2.

7. The method for preparing the cord steel according to claim 2 or 4, characterized in that: After removing the isolation cover and top-blowing argon gun in step 4), the ladle is transported to the continuous casting process. During the continuous casting process, the temperature of the molten steel in the ladle is 1529-1535°C. 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 is ≤ 120 g / m 3 .

8. A cord steel, characterized in that: The cord steel is prepared by the preparation method of 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 produced by the method for producing cord steel according to any one of claims 1 to 7 or the cord steel according to claim 8 or 9 in producing steel cord.

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