Method for smelting ultralow-sulfur steel with low unit consumption of molten iron

Abstract

The invention provides a method for smelting ultralow-sulfur steel with low molten iron unit consumption, which comprises the following steps: converter smelting: molten iron and scrap steel are added into a converter for converter smelting to obtain molten steel and steel ladle top slag; converter tapping: transferring the molten steel and the steel ladle top slag out of the converter, and adding lime, an alloy, an aluminum block and a modifier into the transferred molten steel and steel ladle top slag to obtain pretreated molten steel and steel ladle top slag; ladle refining: transferring the pretreated molten steel and ladle top slag into a refining furnace, adding waste steel and recycled large ladle slag, and refining to obtain refined molten steel; rH vacuum treatment: carrying out vacuum treatment on the refined molten steel to obtain molten steel to be poured; and continuous casting forming is conducted, specifically, the to-be-poured molten steel is subjected to casting forming through a slab continuous casting machine, and the ultralow-sulfur steel is obtained. According to the method, the molten iron does not need to be pretreated, the ultralow-sulfur steel can be obtained under the condition that the unit consumption of the molten iron is 680-830 kg per ton of steel, the mass percentage content of sulfur is smaller than or equal to 0.0015%, the production efficiency and quality are improved, and the environmental protection benefits are improved.

Description

Technical Field

[0001] The present application belongs to the field of steel technology, and specifically relates to a method for smelting ultra-low sulfur steel with low molten iron consumption. Background Art

[0002] The unit consumption of molten iron is a key factor restricting steel production. Effectively reducing the unit consumption of molten iron can not only increase the output of steel billets and reduce the consumption of raw and auxiliary materials such as dolomite for steelmaking, but also reduce the emission of waste gas, waste water, waste slag, etc. Studies have shown that for every ton of scrap steel used to replace 1 ton of molten iron in the converter, at least 550 kg of standard coal can be saved. Therefore, reducing the unit consumption of molten iron has important environmental benefits.

[0003] Ultra-low sulfur steel refers to steel with a [S] content of ≤0.0015% in molten steel. High sulfur content in steel will have an adverse effect on the hot working properties of steel, that is, it will cause the steel to be "hot brittle". The production process of traditional ultra-low sulfur steel includes molten iron KR pretreatment, converter smelting, LF furnace refining, RH furnace vacuum treatment and continuous casting. This process has problems such as long route, high production cost, long smelting time, and furnace-machine mismatch. With the continuous development of iron and steel metallurgical technology, the requirements for S content in finished products are becoming more and more stringent, and ultra-low sulfur steel represented by sulfur-resistant pipeline steel has even higher requirements. Summary of the invention

[0004] The present application provides a method for smelting ultra-low sulfur steel with low molten iron consumption, which can obtain ultra-low sulfur steel under the condition of molten iron consumption of 680kg to 830kg per ton of steel, wherein the mass percentage of sulfur is ≤0.0015%, thereby improving production efficiency and quality and improving environmental benefits.

[0005] The present application provides a method for smelting ultra-low sulfur steel with low molten iron consumption, comprising:

[0006] Converter smelting: adding molten iron and scrap steel into the converter for converter smelting to obtain molten steel and ladle top slag;

[0007] Converter tapping: the molten steel and ladle top slag are tapped out from the converter, and lime, alloy, aluminum block and modifier are added to the tapped molten steel and ladle top slag to obtain pretreated molten steel and ladle top slag;

[0008] Ladle refining: The pre-treated molten steel and ladle top slag are transferred into the refining furnace, and scrap steel and recycled ladle slag are added for refining to obtain refined molten steel;

[0009] RH vacuum treatment: The refined molten steel is subjected to vacuum treatment to obtain molten steel to be poured;

[0010] Continuous casting: The molten steel to be poured is cast through slab continuous casting to obtain ultra-low sulfur steel; the mass percentage of sulfur in the ultra-low sulfur steel is ≤0.0015%.

[0011] In a feasible implementation manner of the present application, in the converter smelting step, the molten iron consumption of the ultra-low sulfur steel is 680kg to 830kg per ton of steel; and / or; the mass percentage of sulfur in the molten iron is 0.04% to 0.1%.

[0012] In a feasible implementation manner of the present application, in the converter smelting step: the amount of molten iron added is 150t / furnace to 170t / furnace; the amount of scrap steel added is 40t / furnace to 60t / furnace, the total amount added is 200t / furnace to 210t / furnace, and the initial amount of molten steel is 185t / furnace to 195t / furnace.

[0013] In a feasible implementation manner of the present application, in the step of tapping steel from the converter, the modifier includes the following composition in percentage by mass: Al: 35% to 50%, Al2O3: 12% to 25%, CaO: 18% to 28%, SiO2: 2.5% to 7.5%, MgO: 1.5% to 5.5%, and the rest are trace elements.

[0014] In a feasible implementation manner of the present application, in the step of tapping the converter, the binary basicity of the ladle top slag is 2-5.

[0015] In a feasible implementation manner of the present application, the steps of tapping steel from the converter include: adding 2kg / ton steel to 3.3kg / ton steel of lime for slag washing when the steel is tapped to 1 / 4 to 1 / 3; adding alloy and 1.6kg / ton steel to 2.2kg / ton steel of aluminum blocks for deoxidation and alloying when the steel is tapped to 1 / 2 to 4 / 5; and adding 0.95kg / ton steel to 1.7kg / ton steel of modifier to modify the ladle top slag after the steel is tapped.

[0016] In a feasible embodiment of the present application, during the step of tapping the converter, the flow rate of argon gas blown from the bottom of the ladle is controlled at 60 Nm 3 / h~120Nm 3 / h.

[0017] In a feasible implementation manner of the present application, in the step of tapping steel from the converter, a double-blocking operation of front and rear slag blocks is adopted during tapping, and the amount of slag is strictly controlled to prevent overoxidation of the top slag of the ladle.

[0018] In a feasible embodiment of the present application, in the step of ladle refining, the ladle slag includes the following mass percentage composition: CaO: 50% to 58%, SiO2: 5% to 12%, MgO: 4.8% to 6.5%, MnO: 0.05% to 0.16%, P2O5: 0.02% to 0.1%, TiO2: 0.2% to 0.8%, Fe t O t :0.2%~0.9%.

[0019] In a feasible implementation of the present application, the step of ladle refining includes: transferring the pre-treated molten steel and ladle top slag into a refining furnace, adding scrap steel and recycled ladle slag, adding lime and low-silicon refining pre-melted slag, and controlling the binary basicity of the final refined slag to be 6-8. The mass percentage of CaO in the final refined slag is 52%-58%, and the mass percentage of Fe t O t The mass percentage is 0.24% to 0.59%.

[0020] In a feasible implementation manner of the present application, the step of ladle refining includes: heating the pretreated molten steel to 1580℃~1620℃, adding 20t / furnace~35t / furnace of scrap steel, 205t / furnace~220t / furnace of molten steel and 2.9kg / ton steel~5.0kg / ton steel of ladle slag, controlling the argon flow rate to 980NL / min~220NL / min, adding 9kg / ton steel~12kg / ton steel of lime and 0.9kg / ton steel~1.9kg / ton steel of low silicon refining pre-melted slag for refining to obtain refined molten steel.

[0021] In a feasible embodiment of the present application, the RH vacuum treatment step includes: transferring the refined molten steel to the RH furnace, controlling the RH ultimate vacuum degree to ≤133Pa, and the circulating argon flow rate to 150Nm 3 / h~220Nm 3 / h, RH smelting time is 18min~25min; to obtain vacuum smelting molten steel.

[0022] In a feasible implementation manner of the present application, the continuous casting step includes: transferring the vacuum smelted molten steel to the continuous casting table for slab continuous casting, controlling the long water inlet sealing argon and the argon back pressure between the plates to be >0Mpa, and the superheat of the tundish to be 10℃~20℃. DETAILED DESCRIPTION

[0023] In order to make the invention purpose, technical scheme and beneficial technical effect of the present application clearer, the present application is further described in detail in conjunction with the embodiments below. It should be understood that the embodiments described in this specification are only for explaining the present application, not for limiting the present application.

[0024] For simplicity, only some numerical ranges are explicitly disclosed herein. However, any lower limit can be combined with any upper limit to form an unambiguous range; and any lower limit can be combined with other lower limits to form an unambiguous range, and any upper limit can be combined with any other upper limit to form an unambiguous range. In addition, although not explicitly stated, each point or single value between the range endpoints is included in the range. Thus, each point or single value can be combined with any other point or single value as its own lower limit or upper limit or with other lower limits or upper limits to form an unambiguous range.

[0025] In the description herein, when a composition is described as containing, comprising or including specific components, or when a process is described as containing, comprising or including specific process steps, it is expected that the composition of the present application also consists essentially of or consists of the components, and the process of the present application also consists essentially of or consists of the process steps.

[0026] The use of the terms "including," "comprising," "containing," and "having" should generally be interpreted as open ended and non-limiting unless expressly stated otherwise.

[0027] In the description of this article, it should be noted that, unless otherwise specified, “above” and “below” are inclusive of the number itself, and the “multiple” in “one or more” means more than two.

[0028] The above-mentioned summary of the invention of the present application is not intended to describe each disclosed embodiment or each implementation in the present application. The following description more specifically illustrates exemplary embodiments. In many places throughout the application, guidance is provided by a series of examples, which can be used in various combinations. In each example, enumeration is only used as a representative group and should not be interpreted as exhaustive.

[0029] Molten iron is the main heat source for converter smelting and is used to provide the energy required in the steel smelting process. When the unit consumption of molten iron decreases, it means that the amount of molten iron entering the converter is reduced, which will affect the energy supply in the smelting process. In addition, low unit consumption of molten iron may lead to reduced stability in the smelting process, increase the difficulty of the process, and increase the difficulty of obtaining steel with ultra-low sulfur content. In order to reduce the unit consumption of molten iron, it can be compensated by adding scrap steel, but the composition of scrap steel is complex and the sulfur content is high, so the preparation process needs to be further optimized.

[0030] In view of this, the inventors organically combined diffusion deoxidation and precipitation deoxidation in the smelting process based on theoretical calculation and analysis, gave full play to the thermodynamic and kinetic conditions of desulfurization, and after many on-site tests, developed a method for smelting ultra-low sulfur steel under low molten iron consumption conditions, without the need for molten iron pretreatment.

[0031] The present application provides a method for smelting ultra-low sulfur steel with low molten iron consumption, which can obtain ultra-low sulfur steel under the condition of molten iron consumption of 680kg to 830kg per ton of steel, wherein the mass percentage of sulfur is ≤0.0015%, thereby improving production efficiency and quality and improving environmental benefits.

[0032] The present application provides a method for smelting ultra-low sulfur steel with low molten iron consumption, comprising:

[0033] Converter smelting: adding molten iron and scrap steel into the converter for converter smelting to obtain molten steel and ladle top slag;

[0034] Converter tapping: the molten steel and ladle top slag are tapped out from the converter, and lime, alloy, aluminum block and modifier are added to the tapped molten steel and ladle top slag to obtain pretreated molten steel and ladle top slag;

[0035] Ladle refining: The pre-treated molten steel and ladle top slag are transferred into the refining furnace, and scrap steel and recycled ladle slag are added for refining to obtain refined molten steel;

[0036] RH vacuum treatment: The refined molten steel is subjected to vacuum treatment to obtain molten steel to be poured;

[0037] Continuous casting: The molten steel to be poured is cast through slab continuous casting to obtain ultra-low sulfur steel; the mass percentage of sulfur in the ultra-low sulfur steel is ≤0.0015%, and can be selected from 0.0008% to 0.0010%.

[0038] In the method of the present application, the molten iron does not need to be pretreated by KR. In the converter smelting process, lime, alloy, aluminum blocks and modifiers are added to the molten steel and ladle top slag produced by converter smelting, wherein the lime, alloy and aluminum blocks are used for deoxidation and alloying to reduce the oxygen content in the molten steel. The modifier is used to modify the ladle top slag to improve the quality and binary basicity of the ladle slag, improve the deoxidation efficiency, and reduce the oxygen content in the ladle. In the ladle refining process, the ladle slag remaining from continuous casting is recycled and reused as a slag-making material in the refining process. Substances such as calcium oxide and silicon dioxide in the ladle slag can reduce the refining time and accelerate the deoxidation efficiency in the refining process, thereby improving the desulfurization efficiency as a whole and reducing the sulfur content. Ultra-low sulfur steel with a sulfur mass percentage of 0.0008% to 0.0010% can be efficiently obtained.

[0039] In addition, the molten iron of the present application does not need to be pre-treated by KR, the process flow is short, and the production cost is reduced; under the requirement of low molten iron unit consumption of the converter, the problems of difficult desulfurization of ultra-low sulfur steel, long smelting time, difficult stable control of S content in steel, and mismatch between furnace and machine are solved. The production process route of the present application is short, the unit consumption of molten iron is low, the LF furnace does not need secondary slag making, the smelting rhythm is controlled, the desulfurization effect is stable, and the production cost is low, which greatly meets the requirements of mass production of ultra-low sulfur steel.

[0040] In some embodiments, the main equipment includes an iron ladle, a steel ladle, a crane, a converter, a LF refining furnace, a RH vacuum furnace, a slab continuous caster, etc.

[0041] In some embodiments, in the converter smelting step, the molten iron consumption of ultra-low sulfur steel is 680kg to 830kg / ton of steel, optionally 682kg to 743kg / ton of steel; and / or; the mass percentage of sulfur in the molten iron is 0.04% to 0.1%.

[0042] The sulfur content of the molten iron entering the furnace of the present application is relatively high because it has not been pretreated, which increases the difficulty of smelting ultra-low sulfur steel with low molten iron consumption.

[0043] In some embodiments, in the converter smelting step: the amount of molten iron added is 150t / furnace to 170t / furnace; the amount of scrap steel added is 40t / furnace to 60t / furnace, the total amount added is 200t / furnace to 210t / furnace, and the initial amount of molten steel is 185t / furnace to 195t / furnace.

[0044] In some embodiments, in the converter smelting step, the amount of scrap steel added is 28% to 40% of the molten iron.

[0045] In a feasible implementation manner of the present application, in the step of tapping steel from the converter, the modifier includes the following composition in percentage by mass: Al: 35% to 50%, Al2O3: 12% to 25%, CaO: 18% to 28%, SiO2: 2.5% to 7.5%, MgO: 1.5% to 5.5%, and the rest are trace elements.

[0046] Aluminum can react with iron oxide in steel slag to generate Al2O3 and iron, thereby reducing the oxygen content in steel. The above-mentioned mass percentage of aluminum can increase the Al2O3 content in the synthetic slag, and the added lime can increase the CaO content in the slag, thereby increasing the binary basicity of the slag and reducing the CaO / Al2O3 ratio in the slag. [S] in the molten steel reacts chemically with CaO to form calcium sulfide that is difficult to dissolve in the molten steel. Since the solubility of calcium sulfide in the molten steel is relatively low, it will precipitate in the form of solids and enter the slag with the help of argon blowing at the bottom of the ladle, ultimately achieving desulfurization. At the same time, aluminum can also combine with [S] in the molten steel to form a high-melting-point sulfide. This compound has a high stability in the molten steel, thereby accelerating the transfer of sulfur from the molten steel to the slag, further improving the desulfurization effect.

[0047] Alumina can reduce the viscosity of slag and promote desulfurization reaction, but too much alumina will inhibit the activity of CaO. The above-mentioned combination of alumina and aluminum in mass percentage can make the alumina in the ladle within a suitable range and achieve a good desulfurization effect.

[0048] CaO can increase the calcium oxide content in the slag, promote a lower oxygen potential at the interface between slag and molten steel, and drive the desulfurization reaction forward, thereby improving the desulfurization effect.

[0049] Silicon dioxide will also affect the basicity of the slag, but it will react with calcium oxide to reduce the desulfurization efficiency. Magnesium oxide can increase the fluidity of the slag, which is beneficial to the desulfurization reaction, but it is easy to deposit on the bottom of the furnace and reduce the desulfurization effect. The modifiers of silicon dioxide and magnesium oxide, aluminum, aluminum oxide and calcium oxide in the above range complement each other to increase the slag volume and basicity of the ladle and promote the desulfurization reaction.

[0050] In some embodiments, in the step of tapping steel from a converter, the binary basicity of the ladle top slag is 2 to 5, and can be optionally 2.7 to 3.2.

[0051] When the binary basicity of the ladle top slag of the present application is within the above range, it is beneficial to take into account the fluidity of the slag and the activity of the material, so that the steel slag has suitable kinetic conditions and reaction activity, thereby improving the desulfurization effect. When the basicity of the slag is further increased, the viscosity will decrease, the kinetic conditions of the reaction will deteriorate, and the desulfurization effect will be reduced.

[0052] In some embodiments, the step of tapping steel from a converter includes: adding 2kg / ton steel to 3.3kg / ton steel of lime for slag washing when the steel is tapped to 1 / 4 to 1 / 3; adding alloy and 1.6kg / ton steel to 2.2kg / ton steel of aluminum blocks for deoxidation and alloying when the steel is tapped to 1 / 2 to 4 / 5, calculating the amount of aluminum blocks added according to the final oxygen of the converter (600-950ppm), and pre-deoxidizing the molten steel according to 30kg of aluminum blocks with 100ppm deoxidation; after the steel is tapped, adding 0.95kg / ton steel to 1.7kg / ton steel modifier to modify the ladle top slag.

[0053] The inventors have found that the addition of lime, aluminum blocks and modifiers will also affect the effect of the reaction. The above materials in this application are combined with the above-mentioned addition timing, so that ultra-low sulfur steel can be prepared under low molten iron conditions.

[0054] In some embodiments, during the step of tapping the converter, the flow rate of argon gas at the bottom of the ladle is controlled at 60 Nm 3 / h~120Nm 3 / h.

[0055] In some embodiments, during the step of tapping steel from the converter, a double-blocking operation of front and rear slag blocks is adopted during tapping, and the amount of slag is strictly controlled to prevent overoxidation of the top slag of the ladle.

[0056] In some embodiments, in the step of ladle refining, the ladle slag comprises the following mass percentage composition: CaO: 50% to 58%, SiO2: 5% to 12%, MgO: 4.8% to 6.5%, MnO: 0.05% to 0.16%, P2O5: 0.02% to 0.1%, TiO2: 0.2% to 0.8%, Fe t O t :0.2%~0.9%.

[0057] In some embodiments, the step of ladle refining includes: transferring the pretreated molten steel and ladle top slag into a refining furnace, adding scrap steel and recycled ladle slag, adding lime and low-silicon refining pre-melted slag, and controlling the binary basicity of the final refined slag to be 6 to 8, and optionally 6.8 to 7.1. In some embodiments, the CaO mass percentage in the final refined slag is 52% to 58%, the SiO2 mass percentage is 6% to 9%, the Al2O3 mass percentage is 21% to 36%, and the Fe t O t The mass percentage is 0.24% to 0.59%.

[0058] The present application can achieve a better desulfurization effect and shorten the refining time when the basicity and composition of the refined slag are within the above-mentioned appropriate ranges, thereby achieving high production efficiency while improving production quality.

[0059] In some embodiments, in the ladle refining step, the refining time is 80 minutes to 110 minutes. The present application can obtain ultra-low sulfur steel S under the condition of low molten iron consumption through a shorter refining time.

[0060] In some embodiments, the ladle refining step includes: heating the pretreated molten steel to 1580°C ~ 1620°C, adding 20t / furnace ~ 35t / furnace of scrap steel, 205t / furnace ~ 220t / furnace of molten steel and 2.9kg / ton steel ~ 5.0kg / ton steel of ladle slag, controlling the argon flow rate to 980NL / min ~ 220NL / min, adding 9kg / ton steel ~ 12kg / ton steel of lime and 0.9kg / ton steel ~ 1.9kg / ton steel of low silicon refining pre-melted slag, and refining to obtain refined molten steel.

[0061] By recycling ladle slag, combining a reasonable power supply system for the LF furnace, a reasonable argon bottom blowing flow rate, and timely addition of lime to control the LF furnace refining slag system, the sulfur content in molten steel can be quickly removed to ≤0.0015%.

[0062] In some embodiments, the RH vacuum treatment step includes: transferring the refined molten steel to the RH furnace, controlling the RH ultimate vacuum degree to ≤ 133 Pa, and the circulating argon flow rate to 150 Nm 3 / h~220Nm 3 / h, RH smelting time is 18min~25min; to obtain vacuum smelting molten steel.

[0063] In some embodiments, the continuous casting step includes: transferring the vacuum smelted molten steel to the continuous casting table for slab continuous casting, controlling the long water inlet sealing argon gas and the argon gas back pressure between the plates to be greater than 0 MPa, and the superheat of the tundish to be 10°C to 20°C.

[0064] Example

[0065] The following examples more specifically describe the disclosure of the present application, which are intended for illustrative purposes only, as it will be apparent to those skilled in the art that various modifications and variations are possible within the scope of the disclosure of the present application. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0066] Example 1

[0067] Steel grade: GC9012A3

[0068] Composition: in mass percentage, C: 0.13-0.18%, Si: 0.2-0.4%, Mn: 1.3-1.5%, P≤0.02%, S≤0.0015%, Als: 0.02-0.06%, Cr: 0.2-0.5%, Mo: 0.3-0.6%, V: 0.02-0.045%, Nb: 0.02-0.04%, N≤0.006%, B: 0.001-0.003%, Ti: 0.01-0.03%, the balance is iron and other inevitable impurities.

[0069] The ladle capacity is 210t, and the smelting process is molten iron → converter smelting → LF refining → RH vacuum smelting → slab continuous casting. The smelting method of ultra-low sulfur steel without pretreatment process under the condition of low molten iron unit consumption is:

[0070] (1) In the converter process, the amount of molten iron added is 162 tons, the amount of scrap steel added is 47 tons, the total loading amount is 209 tons, the converter end oxygen is 743 ppm, the steel tapping temperature is 1605°C, and the amount of molten steel tapped is 190 tons.

[0071] (2) During the steel tapping process of the converter, the argon gas flow rate at the bottom of the ladle is controlled at 82Nm 3 / h, front and rear slag double-block operation is adopted during steel tapping, and the slag amount is strictly controlled to prevent overoxidation of the ladle top slag; when the steel is tapped to 1 / 3, 400kg (2.11kg / ton steel) of lime is added for slag washing; when the steel is tapped to 1 / 2, 591kg of metallic manganese, 896kg of high-carbon ferrochrome, 1300kg of ferromolybdenum, and 354kg of aluminum blocks (1.86kg / ton steel) are added for deoxidation and alloying; after the steel is tapped, 200kg (0.95kg / ton steel) of modifier is added to modify the ladle top slag.

[0072] (3) The molten steel obtained from the converter is transferred to the LF furnace. After the molten steel enters the station and is heated to 1608°C, 25 tons of scrap steel is added, and the molten steel volume is 218 tons. The unit consumption of molten iron is 743 kg / ton of steel. After the scrap steel is added, the ladle slag of the molten steel on the furnace is recycled, and the recycling volume is 650 kg (2.98 kg / ton of steel). Then the temperature of the molten steel is raised to 1625°C. In the early stage of power transmission, a low-speed current is used to start the arc. After the arc is started, a high-speed current is used to increase the temperature. During the power transmission process, lime and low-silicon refined pre-melted slag (whose chemical composition by mass percentage is Al2O3: 30%, CaO: 42%, SiO2: 3.2%) are added in batches. , MgO: 4.5%, the rest are trace elements), the bottom blowing argon flow rate during power transmission is 200NL / min, the molten steel temperature is reached and slag is quickly desulfurized, lime is added in time according to the slag thickness, the bottom blowing argon flow rate during desulfurization is 900NL / min, the total amount of lime added is 2452kg (11.24kg / ton steel), the amount of low silicon refined pre-melted slag added is 395kg (1.81kg / ton steel), the binary basicity of the refined final slag is 6.8, the CaO content in the slag is 58%, the mass percentage of SiO2 is 8.5%, the mass percentage of Al2O3 is 26.6%, and the Fe t O t The content is 0.43%, and the rest are trace elements. The above technical method can quickly reduce the sulfur content of molten steel to 0.0010%.

[0073] (4) The molten steel obtained from LF was transferred to the RH furnace. During the RH vacuum smelting process, the RH ultimate vacuum degree was 68Pa and the circulating argon gas flow rate was 175Nm 3 / h, RH smelting time is 20min.

[0074] (5) The molten steel obtained by RH is transferred to continuous casting, and the continuous casting is slab continuous casting. During the pouring process, protective pouring is performed to prevent secondary oxidation of the molten steel. The argon back pressure of the long water inlet seal is 0.48 Bar, the argon back pressure between the plates is 0.16 Bar, and the average superheat of the tundish is 18°C.

[0075] Embodiment 2:

[0076] Steel grade: GC9012A4

[0077] Composition: in mass percentage, C: 0.13-0.18%, Si: 0.2-0.4%, Mn: 1.3-1.5%, P≤0.02%, S≤0.0015%, Als: 0.02-0.06%, Cr: 0.3-0.6%, Mo: 0.4-0.7%, V: 0.02-0.045%, Nb: 0.02-0.04%, N≤0.006%, B: 0.001-0.003%, Ti: 0.01-0.03%, the balance is iron and other inevitable impurities.

[0078] The ladle capacity is 210t, and the smelting process is molten iron → converter smelting → LF refining → RH vacuum smelting → slab continuous casting. The smelting method of ultra-low sulfur steel without pretreatment process under the condition of low molten iron unit consumption is:

[0079] (1) In the converter process, the amount of molten iron added is 150 tons, the amount of scrap steel added is 55 tons, the total loading amount is 205 tons, the converter end oxygen is 896 ppm, the steel tapping temperature is 1602°C, and the amount of molten steel tapped is 185 tons.

[0080] (2) During the steel tapping process of the converter, the argon gas flow rate at the bottom of the ladle is controlled at 95 Nm 3 / h, front and rear slag blocking operation is adopted during steel tapping, and the slag amount is strictly controlled to prevent overoxidation of the ladle top slag; when the steel is tapped to 1 / 3, 604kg (3.2kg / ton steel) of lime is added for slag washing; when the steel is tapped to 1 / 2, 653kg of metallic manganese, 1320kg of high-carbon ferrochrome, 1580kg of ferromolybdenum, and 396kg of aluminum blocks (2.14kg / ton steel) are added for deoxidation and alloying; after the steel is tapped, 302kg (1.63kg / ton steel) of modifier is added to modify the ladle top slag.

[0081] (3) The molten steel obtained from the converter is transferred to the LF furnace. After the molten steel enters the station and is heated to 1615°C, 32 tons of scrap steel is added, the molten steel volume is 220 tons, and the molten iron consumption is 682 kg / ton steel. After adding the scrap steel, the ladle slag of the molten steel on the furnace is recycled, and the recycling volume is 720 kg (3.27 kg / ton steel). Then the temperature of the molten steel is raised to 1620°C. In the early stage of power transmission, low-speed current is used to start the arc, and high-speed current is used to increase the temperature after arc starting. Lime and low-silicon refined pre-melted slag are added in batches during the power transmission process. The bottom blowing argon flow rate during power transmission The flow rate of bottom blowing argon during desulfurization is 980NL / min, the total amount of lime added is 2236kg (10.16kg / ton steel), the amount of low silicon refined pre-melted slag added is 278kg (1.26kg / ton steel), the binary basicity of the refined final slag is 7.1, the CaO content in the slag is 52%, the mass percentage of SiO2 is 7.3%, the mass percentage of Al2O3 is 27.3%, and the Fe t O t The content is 0.24%, and the rest are trace elements. The above technical method can quickly reduce the sulfur content of molten steel to 0.0008%.

[0082] (4) The molten steel obtained from LF is transferred to the RH furnace. During the RH vacuum smelting process, the RH ultimate vacuum degree is 75Pa and the circulating argon flow rate is 190Nm 3 / h, RH smelting time is 18min.

[0083] (5) The molten steel obtained by RH is transferred to continuous casting, and the continuous casting is slab continuous casting. During the pouring process, protective pouring is performed to prevent secondary oxidation of the molten steel. The argon back pressure of the long water inlet seal is 0.43 Bar, the argon back pressure between the plates is 0.29 Bar, and the average superheat of the tundish is 15°C.

[0084] Embodiment 3:

[0085] Steel grade: GC9011A1

[0086] Composition: in mass percentage, C: 0.13-0.18%, Si: 0.1-0.3%, Mn: 1.3-1.5%, P≤0.02%, S≤0.0015%, Als: 0.02-0.06%, Cr: 0.2-0.5%, Mo: 0.3-0.6%, V: 0.02-0.045%, Nb: 0.02-0.04%, N≤0.006%, B: 0.001-0.003%, Ti: 0.01-0.03%, the balance is iron and other inevitable impurities.

[0087] The ladle capacity is 210t, and the smelting process is molten iron → converter smelting → LF refining → RH vacuum smelting → slab continuous casting. The smelting method of ultra-low sulfur steel without pretreatment process under the condition of low molten iron unit consumption is:

[0088] (1) In the converter process, the amount of molten iron added is 169 tons, the amount of scrap steel added is 40 tons, the total loading amount is 209 tons, the converter end oxygen is 883 ppm, the steel tapping temperature is 1597°C, and the amount of molten steel tapped is 185 tons.

[0089] (2) During the steel tapping process of the converter, the argon gas flow rate at the bottom of the ladle is controlled at 75 Nm 3 / h, front and rear slag double-block operation is adopted during steel tapping, and the slag amount is strictly controlled to prevent overoxidation of the ladle top slag; when the steel is tapped to 1 / 3, 592kg (3.2kg / ton steel) of lime is added for slag washing; when the steel is tapped to 1 / 2, 608kg of metallic manganese, 865kg of high-carbon ferrochrome, 1050kg of ferromolybdenum, and 296kg of aluminum blocks (1.6kg / ton steel) are added for deoxidation and alloying; after the steel is tapped, 289kg (1.56kg / ton steel) of modifier is added to modify the ladle top slag.

[0090] (3) The molten steel obtained from the converter is transferred to the LF furnace. After the molten steel enters the station and is heated to 1593°C, 20 tons of scrap steel is added, the molten steel volume is 205 tons, and the molten iron consumption is 824 kg / ton of steel. After the scrap steel is added, the ladle slag of the molten steel on the furnace is recycled, and the recycling volume is 610 kg (2.97 kg / ton of steel). Then the temperature of the molten steel is raised to 1618°C. In the early stage of power transmission, low-speed current is used to start the arc, and high-speed current is used to increase the temperature after arc starting. Lime and low-silicon refined pre-melted slag are added in batches during the power transmission process. Argon gas is blown from the bottom during power transmission. The amount is 200NL / min. After the molten steel temperature reaches the target, slag is made and desulfurized quickly. Lime is added in time according to the thickness of the slag. The bottom blowing argon flow rate during desulfurization is 999NL / min. The total amount of lime added is 2018kg (9.84kg / ton steel). The amount of low-silicon refined pre-melted slag added is 198kg (0.96kg / ton steel). The binary basicity of the refined final slag is 6.5, the CaO content in the slag is 54%, the SiO2 mass percentage is 8.3%, the Al2O3 mass percentage is 28.2%, and the Fe t O t The content is 0.59%, and the rest are trace elements. The above technical method can quickly reduce the sulfur content of molten steel to 0.0012%.

[0091] (4) The molten steel obtained from LF is transferred to the RH furnace. During the RH vacuum smelting process, the RH ultimate vacuum degree is 95Pa and the circulating argon flow rate is 180Nm 3 / h, RH smelting time is 22min.

[0092] (6) The molten steel obtained by RH is transferred to continuous casting, and the continuous casting is slab continuous casting. During the pouring process, protective pouring is performed to prevent secondary oxidation of the molten steel. The argon back pressure of the long water inlet seal is 0.45 Bar, the argon back pressure between the plates is 0.23 Bar, and the average superheat of the tundish is 13°C.

[0093] Example 4

[0094] Steel grade: GC9012A3

[0095] Composition: in mass percentage, C: 0.13-0.18%, Si: 0.2-0.4%, Mn: 1.3-1.5%, P≤0.02%, S≤0.0015%, Als: 0.02-0.06%, Cr: 0.2-0.5%, Mo: 0.3-0.6%, V: 0.02-0.045%, Nb: 0.02-0.04%, N≤0.006%, B: 0.001-0.003%, Ti: 0.01-0.03%, the balance is iron and other inevitable impurities.

[0096] The ladle capacity is 210t, and the smelting process is molten iron → converter smelting → LF refining → RH vacuum smelting → slab continuous casting. The smelting method of ultra-low sulfur steel without pretreatment process under the condition of low molten iron unit consumption is:

[0097] (6) In the converter process, the amount of molten iron added was 165 tons, the amount of scrap steel added was 48 tons, the total loading amount was 213 tons, the converter end oxygen was 785 ppm, the steel tapping temperature was 1609°C, and the amount of molten steel tapped was 193 tons.

[0098] (7) During the steel tapping process of the converter, the argon gas flow rate at the bottom of the ladle is controlled at 82Nm 3 / h, front and rear slag blocking operation is adopted during steel tapping, and the slag amount is strictly controlled to prevent overoxidation of the ladle top slag; when the steel tapping reaches 1 / 3, 400kg of lime is added for slag washing; when the steel tapping reaches 1 / 2, 595kg of metallic manganese, 887kg of high-carbon ferrochrome, 1310kg of ferromolybdenum and 354kg of aluminum blocks are added for deoxidation and alloying; after the steel is tapped, 200kg of modifier is added to modify the ladle top slag.

[0099] (8) The molten steel obtained from the converter is transferred to the LF furnace. After the molten steel enters the station and is heated to 1612°C, 25 tons of scrap steel is added, and the molten steel volume is 218 tons. The unit consumption of molten iron is 756 kg / ton of steel. After the scrap steel is added, the ladle slag of the molten steel on the furnace is recycled, and the recycling volume is 650 kg. Then the temperature of the molten steel is raised to 1622°C. In the early stage of power transmission, a low-speed current is used to start the arc. After the arc is started, a high-speed current is used to increase the temperature. During the power transmission process, lime and low-silicon refined pre-melted slag (whose chemical composition mass percentage is Al2O3: 30-45%, CaO: 40-55%) are added in batches. %, SiO2: 2-5%, MgO: 1.5-6.5%), the bottom blowing argon flow rate during power transmission is 200NL / min, the molten steel temperature is reached and slag is quickly desulfurized, lime is added in time according to the slag thickness, the bottom blowing argon flow rate during desulfurization is 900NL / min, the total amount of lime added is 2452kg, the amount of low silicon refined pre-melted slag added is 395kg, the binary basicity of the refined final slag is 7.2, the CaO content in the slag is 56%, the mass percentage of SiO2 is 7.8%, the mass percentage of Al2O3 is 32.6%, and the Fe t O t The content is 0.56%, and the rest are trace elements. The above technical method can quickly reduce the sulfur content of molten steel to 0.0011%.

[0100] (9) The molten steel obtained from LF was transferred to the RH furnace. During the RH vacuum smelting process, the RH ultimate vacuum was 72 Pa and the circulating argon flow rate was 178 Nm 3 / h, RH smelting time is 21min.

[0101] (10) The molten steel obtained by RH is transferred to continuous casting, and the continuous casting is slab continuous casting. During the pouring process, protective pouring is performed to prevent secondary oxidation of the molten steel. The argon back pressure of the long water inlet seal is 0.48 Bar, the argon back pressure between the plates is 0.16 Bar, and the average superheat of the tundish is 18°C.

[0102] Comparative Example 1

[0103] Steel grade: GC9012A3

[0104] Composition: in mass percentage, C: 0.13-0.18%, Si: 0.2-0.4%, Mn: 1.3-1.5%, P≤0.02%, S≤0.0015%, Als: 0.02-0.06%, Cr: 0.2-0.5%, Mo: 0.3-0.6%, V: 0.02-0.045%, Nb: 0.02-0.04%, N≤0.006%, B: 0.001-0.003%, Ti: 0.01-0.03%, the balance is iron and other inevitable impurities.

[0105] The ladle capacity is 210t, and the smelting process is molten iron → converter smelting → LF refining → RH vacuum smelting → slab continuous casting. The smelting method of ultra-low sulfur steel without pretreatment process under the condition of low molten iron unit consumption is:

[0106] (1) In the converter process, the amount of molten iron added was 165 tons, the amount of scrap steel added was 47 tons, the total loading amount was 212 tons, the converter end oxygen was 723 ppm, the steel tapping temperature was 1607°C, and the amount of molten steel tapped was 191 tons.

[0107] (2) During the steel tapping process of the converter, the argon gas flow rate at the bottom of the ladle is controlled at 85 Nm 3 / h, front and rear slag blocking operation is adopted during steel tapping, and the slag amount is strictly controlled to prevent overoxidation of the slag on the top of the ladle; when the steel is tapped to 1 / 3, 400kg (2.09kg / ton steel) of lime is added for slag washing; when the steel is tapped to 1 / 2, 591kg of metallic manganese, 896kg of high-carbon ferrochrome, 1300kg of ferromolybdenum and 354kg of aluminum blocks (1.85kg / ton steel) are added for deoxidation and alloying.

[0108] (3) The molten steel obtained from the converter is transferred to the LF furnace. After the molten steel enters the station and is heated to 1612°C, 27 tons of scrap steel is added, and the molten steel volume is 218 tons. The unit consumption of molten iron is 756 kg / ton of steel. After the scrap steel is added, the ladle slag of the molten steel on the furnace is recycled, and the recycling volume is 650 kg. Then the temperature of the molten steel is raised to 1625°C. In the early stage of power transmission, a low-speed current is used to start the arc, and a high-speed current is used to increase the temperature after the arc is started. During the power transmission process, lime and low-silicon refined pre-melted slag (whose chemical composition by mass percentage is Al2O3: 32%, CaO: 43.5%, SiO2: 3.1) are added in batches. %, MgO: 3.8%, the rest are trace elements), the bottom blowing argon flow rate during power transmission is 200NL / min, the molten steel temperature is reached and slag is quickly desulfurized, lime is added in time according to the slag thickness, the bottom blowing argon flow rate during desulfurization is 900NL / min, the total amount of lime added is 2452kg (11.24kg / ton steel), the amount of low silicon refined pre-melted slag added is 395kg, the binary basicity of the refined final slag is 6.9, the CaO content in the slag is 56%, the mass percentage of SiO2 is 8.1%, the mass percentage of Al2O3 is 25.3%, and the Fe t O t The content is 0.52%, and the rest are trace elements.

[0109] (4) The molten steel obtained from LF was transferred to the RH furnace. During the RH vacuum smelting process, the RH ultimate vacuum degree was 68Pa and the circulating argon gas flow rate was 175Nm 3 / h, RH smelting time is 20min.

[0110] (5) The molten steel obtained by RH is transferred to continuous casting, and the continuous casting is slab continuous casting. During the pouring process, protective pouring is performed to prevent secondary oxidation of the molten steel. The argon back pressure of the long water inlet seal is 0.48 Bar, the argon back pressure between the plates is 0.16 Bar, and the average superheat of the tundish is 18°C.

[0111] Comparative Example 2

[0112] Steel grade: GC9012A3

[0113] Composition: in mass percentage, C: 0.13-0.18%, Si: 0.2-0.4%, Mn: 1.3-1.5%, P≤0.02%, S≤0.0015%, Als: 0.02-0.06%, Cr: 0.2-0.5%, Mo: 0.3-0.6%, V: 0.02-0.045%, Nb: 0.02-0.04%, N≤0.006%, B: 0.001-0.003%, Ti: 0.01-0.03%, the balance is iron and other inevitable impurities.

[0114] The ladle capacity is 210t, and the smelting process is molten iron → converter smelting → LF refining → RH vacuum smelting → slab continuous casting. The smelting method of ultra-low sulfur steel without pretreatment process under the condition of low molten iron unit consumption is:

[0115] (1) In the converter process, the amount of molten iron added is 158 tons, the amount of scrap steel added is 51 tons, the total loading amount is 209 tons, the converter end oxygen is 823 ppm, the steel tapping temperature is 1601°C, and the amount of molten steel tapped is 190 tons.

[0116] (2) During the steel tapping process of the converter, the argon gas flow rate at the bottom of the ladle is controlled at 82Nm 3 / h, front and rear slag double-block operation is adopted during steel tapping, and the slag amount is strictly controlled to prevent overoxidation of the ladle top slag; when the steel tapping is 1 / 3, 400kg (2.11kg / ton steel) of lime is added for slag washing; when the steel tapping is 1 / 2, 591kg of metallic manganese, 896kg of high-carbon ferrochrome, 1300kg of ferromolybdenum, and 354kg of aluminum blocks (1.86kg / ton steel) are added for deoxidation and alloying; after the steel is tapped, 200kg (1.05kg / ton steel) of modifier is added to modify the ladle top slag.

[0117] (3) The molten steel obtained from the converter is transferred to the LF furnace. After the molten steel enters the station and is heated to 1617°C, 28 tons of scrap steel is added, and the molten steel volume is 218 tons. The molten iron consumption is 724 kg / ton of steel. After that, the temperature of the molten steel is raised to 1625°C. In the early stage of power transmission, a low-speed current is used to start the arc. After the arc is started, a high-speed current is used to increase the temperature. During the power transmission process, lime and low-silicon refined pre-melted slag (whose chemical composition by mass percentage is Al2O3: 32%, CaO: 43.5%, SiO2: 3.1%, MgO: 3.8) are added in batches. %, the rest are trace elements), the bottom blowing argon flow rate during power transmission is 200NL / min, the molten steel temperature is reached and slag is quickly desulfurized, lime is added in time according to the slag thickness, the bottom blowing argon flow rate during desulfurization is 900NL / min, the total amount of lime added is 2452kg, the amount of low silicon refining pre-melted slag added is 395kg, the binary basicity of the refined final slag is 6.5, the CaO content in the slag is 50%, the mass percentage of SiO2 is 7.7%, the mass percentage of Al2O3 is 26.3%, and the Fe t O t The content is 0.65%, and the rest are trace elements.

[0118] (4) The molten steel obtained from LF was transferred to the RH furnace. During the RH vacuum smelting process, the RH ultimate vacuum degree was 68Pa and the circulating argon gas flow rate was 175Nm 3 / h, RH smelting time is 20min.

[0119] (5) The molten steel obtained by RH is transferred to continuous casting, and the continuous casting is slab continuous casting. During the pouring process, protective pouring is done to prevent the secondary oxidation of the molten steel. The argon back pressure of the long water inlet seal is 0.48 Bar, the argon back pressure between the plates is 0.16 Bar, and the average superheat of the tundish is 18 °C.

[0120] The following Tables 1 and 2 summarize the relevant technical parameters in the preparation process. Table 2 lists the main components of the calcium agent, and the rest are trace elements.

[0121] Table 1 Related technical parameters of each embodiment and comparative example

[0122]

[0123] Table 2 Composition of modifier

[0124]

[0125] In summary, the method for smelting ultra-low sulfur steel without pretreatment process under the condition of low molten iron consumption provided by the present invention does not require KR pretreatment of molten iron, the process flow is short, the molten iron consumption is low, the LF furnace does not need secondary slag making, the smelting rhythm is controlled, the desulfurization effect is stable, and the production cost is low, which greatly meets the requirements of mass production of ultra-low sulfur steel. Under good process coordination conditions, when the molten iron consumption is lower than 700kg / ton of steel, the S mass content of the obtained ultra-low sulfur steel can be as low as 0.0008%.

[0126] The above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. 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 embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for smelting ultra-low sulfur steel with low molten iron consumption, characterized in that: include: Converter smelting: adding molten iron and scrap steel into the converter for converter smelting to obtain molten steel and ladle top slag; Converter tapping: the molten steel and ladle top slag are tapped out from the converter, and lime, alloy, aluminum block and modifier are added to the tapped molten steel and ladle top slag to obtain pretreated molten steel and ladle top slag; Ladle refining: The pre-treated molten steel and ladle top slag are transferred into the refining furnace, and scrap steel and recycled ladle slag are added for refining to obtain refined molten steel; RH vacuum treatment: The refined molten steel is subjected to vacuum treatment to obtain molten steel to be poured; Continuous casting: The molten steel to be poured is cast through slab continuous casting to obtain ultra-low sulfur steel; the mass percentage of sulfur in the ultra-low sulfur steel is ≤0.0015%.

2. The method for smelting ultra-low sulfur steel with low molten iron consumption according to claim 1, characterized in that: In the converter smelting step, the molten iron consumption of the ultra-low sulfur steel is 680kg to 830kg per ton of steel; and / or; the mass percentage of sulfur in the molten iron is 0.04% to 0.1%.

3. The method for smelting ultra-low sulfur steel with low molten iron consumption according to claim 1, characterized in that: In the converter smelting step: the amount of molten iron added is 150t / furnace to 170t / furnace; the amount of scrap steel added is 40t / furnace to 60t / furnace, the total amount added is 200t / furnace to 210t / furnace, and the initial amount of molten steel is 185t / furnace to 195t / furnace.

4. The method for smelting ultra-low sulfur steel with low molten iron consumption according to claim 1, characterized in that: In the step of tapping steel from the converter, the modifier comprises the following composition in percentage by mass: Al: 35% to 50%, Al2O3: 12% to 25%, CaO: 18% to 28%, SiO2: 2.5% to 7.5%, MgO: 1.5% to 5.5%, and the rest are trace elements.

5. The method for smelting ultra-low sulfur steel with low molten iron consumption according to claim 1, characterized in that: In the step of tapping steel from the converter, the binary basicity of the ladle top slag is 2-5.

6. The method for smelting ultra-low sulfur steel with low molten iron consumption according to claim 1, characterized in that: The steps of tapping steel from the converter include: adding 2kg / ton steel to 3.3kg / ton steel lime to perform slag washing when the steel is tapped to 1 / 4 to 1 / 3; adding alloy and 1.6kg / ton steel to 2.2kg / ton steel aluminum blocks to perform deoxidation and alloying when the steel is tapped to 1 / 2 to 4 / 5; and adding 0.95kg / ton steel to 1.7kg / ton steel modifier to modify the ladle top slag after the steel is tapped.

7. The method for smelting ultra-low sulfur steel with low molten iron consumption according to claim 1, characterized in that: In the step of ladle refining, the ladle slag comprises the following mass percentage composition: CaO: 50% to 58%, SiO2: 5% to 12%, MgO: 4.8% to 6.5%, MnO: 0.05% to 0.16%, P2O5: 0.02% to 0.1%, TiO2: 0.2% to 0.8%, Fe t O t :0.2%~0.9%.

8. The method for smelting ultra-low sulfur steel with low molten iron consumption according to claim 1, characterized in that: The ladle refining step comprises: transferring the pretreated molten steel and ladle top slag into a refining furnace, adding scrap steel and recycled ladle slag, adding lime and low-silicon refining pre-melted slag, and controlling the binary basicity of the refined final slag to be 6-8.

9. The method for smelting ultra-low sulfur steel with low molten iron consumption according to claim 1, characterized in that: The ladle refining step comprises: heating the pretreated molten steel to 1580°C to 1620°C, adding 20t / furnace to 35t / furnace of the scrap steel, 205t / furnace to 220t / furnace of the molten steel and 2.9kg / ton steel to 5.0kg / ton steel of the ladle slag, controlling the argon flow rate to 980NL / min to 220NL / min, adding 9kg / ton steel to 12kg / ton steel of lime and 0.9kg / ton steel to 1.9kg / ton steel of low silicon refining pre-melted slag for refining to obtain refined molten steel.

10. The method for smelting ultra-low sulfur steel with low molten iron consumption according to claim 1, characterized in that: The RH vacuum treatment step includes: transferring the refined molten steel to the RH furnace, controlling the RH limit vacuum degree to ≤133Pa, and the circulating argon flow rate to 150Nm 3 / h~220Nm 3 / h, RH smelting time is 18min~25min; to obtain vacuum smelting molten steel.

11. The method for smelting ultra-low sulfur steel with low molten iron consumption according to claim 1, characterized in that: The continuous casting step includes: transferring the vacuum smelting molten steel to a continuous casting table for slab continuous casting, controlling the argon gas sealing pressure of the long water inlet and the argon gas back pressure between the plates to be greater than 0 MPa, and the superheat degree of the tundish to be 10°C to 20°C.

Images