Method for smelting stainless steel through AOD furnace double-slag method

Abstract

The invention provides a method for smelting stainless steel by an AOD (Argon Oxygen Decarburization) furnace double-slag process, which relates to the technical field of stainless steel smelting, and comprises the following steps: S1, adding molten iron into a first AOD furnace, adding lime into the molten iron for the first time, then blowing oxygen to decarburize and desiliconize, adding high-carbon ferrochrome according to the chromium content of the produced steel grade after the temperature of the molten iron rises, blowing until the high-carbon ferrochrome is completely melted down, and pouring slag; then supplementing lime into the furnace again, and tapping after blowing is finished; s2, the tapping molten steel of the first AOD furnace is transferred into a second AOD furnace, lime is added into the second AOD furnace for blowing for the first time, a cold material is added, and when the temperature of the molten steel reaches 1630-1700 DEG C, lime is added again for blowing for molten steel decarburization; s3, a reducing agent and fluorite balls are added into the decarburized molten steel, deslagging is conducted after reaction, and tapping is conducted after components are finely adjusted; according to the method, through step-by-step type double AOD furnace collaborative smelting, deslagging control and slag system blending are optimized, fluorite consumption is remarkably reduced, and the smelting efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of stainless steel smelting, and in particular to a method for smelting stainless steel by the double slag method in an AOD furnace. Background Art

[0002] The double slag method for an AOD furnace of stainless steel refers to an operation method in which during the blowing process, part of the slag is poured out midway, and then new slag materials are added to make slag again. Its characteristic lies in that a relatively small amount of slag is always maintained in the furnace, which can avoid splashing caused by a large amount of slag, and the small amount of slag is easy to melt, and a high phosphorus removal and sulfur removal efficiency can be obtained; the double slag method is suitable for the situation where the silicon, phosphorus, and sulfur contents in the hot metal are relatively high, and is especially suitable for producing high-carbon steel and low-phosphorus steel grades.

[0003] The traditional process for smelting stainless steel by the double slag method in an AOD furnace is completed in a single AOD furnace, and slag making is carried out twice in the same AOD furnace. For the first time, the oxidized slag is poured out, that is, the slag in the steel melting stage, and then auxiliary materials are added for the second slag making, and the slag is poured out to complete the smelting. The traditional double slag method for an AOD furnace has the following problems:

[0004] 1. Poor slag pouring effect: Single furnace operation results in a large amount of residual slag in the furnace (residual slag > 30%), affecting the subsequent decarburization and dephosphorization efficiency;

[0005] 2. High consumption of fluorite: To adjust the fluidity of the slag system, the single consumption of fluorite balls needs to be ≥ 24 kg / t, and the cost is high;

[0006] 3. Complex process control: The amount of residual slag in a single furnace is unstable, affecting the temperature and slag-steel reaction, with high energy consumption and poor operation stability.

[0007] Therefore, there is an urgent need for a new AOD furnace smelting process that can efficiently control the amount of slag and reduce the consumption of auxiliary materials.

[0008] In view of this, the present invention is specifically proposed. Summary of the Invention

[0009] The purpose of the present invention is to provide a method for smelting stainless steel by the double slag method in an AOD furnace, which significantly reduces the consumption of fluorite and improves the smelting efficiency by the coordinated smelting of step-by-step double AOD furnaces and optimizing the slag pouring control and slag system preparation.

[0010] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0011] The present invention provides a method for smelting stainless steel by the double slag method in an AOD furnace, including the following steps:

[0012] S1. Pour molten iron into the first AOD furnace, add lime to the molten iron for the first time, then blow oxygen to decarbonize and desiliconize. After the temperature of the molten iron rises above 1580 °C, add high-carbon ferrochrome according to the chromium content of the steel grade to be produced and blow it until it is completely melted and refined, and then perform the first slag tapping; then add lime to the furnace again, and through blowing, make the remaining slag adsorb onto the lime. After the blowing is completed, tap the steel.

[0013] S2. Transfer the molten steel tapped from the first AOD furnace to the second AOD furnace, first add lime to the second AOD furnace for blowing and add cold materials. When the temperature of the molten steel reaches 1630 - 1700 °C, add lime again for blowing to decarbonize the molten steel.

[0014] S3. Add a reducing agent and fluorite balls to the decarbonized molten steel, tap the slag after the reaction, and tap the steel after fine-tuning the composition.

[0015] The lime and the remaining slag of the molten steel remaining in the first AOD furnace after tapping in step S1 are used for the next batch of AOD furnace smelting.

[0016] Further, in step S1, for the first addition of lime, the addition amount of lime is calculated according to the total silicon content of the molten iron and high-carbon ferrochrome, and the binary basicity is controlled to be 1.20 - 1.50.

[0017] Further, in step S1, the addition amount of the high-carbon ferrochrome is 160 - 400 kg / t of molten iron;

[0018] And / or, the temperature at which the high-carbon ferrochrome is completely melted and refined is 1480 - 1560 °C.

[0019] Further, in step S1, the slag tapping amount of the first slag tapping is ≥70%, and the remaining slag amount is ≤30%.

[0020] Further, in step S1, the amount of lime added for supplementation is 40 - 60 kg of lime per ton of molten iron;

[0021] And / or, the carbon content in the molten steel during tapping is 2.50 - 4.0 wt%, and the silicon content is <0.20 wt%.

[0022] Further, in step S2, the addition amounts of lime for the two times are 20 - 30 kg of lime per ton of molten iron respectively.

[0023] Further, in step S2, the cold materials are one or more of high-carbon ferromanganese, slag steel, scrap iron, and return materials;

[0024] And / or, the addition amount of the cold materials is 0 - 120 kg per ton of molten iron.

[0025] Further, in the step S2, the carbon content of the hot metal after decarburization is determined according to the target value of the steel grade to be produced.

[0026] Further, in the step S2, the oxygen-nitrogen ratio required in the decarburization process of the molten steel is adjusted in real time according to the molten steel temperature and the molten steel carbon content, and the molten steel temperature is controlled within the range of 1630-1700 °C by adjusting the oxygen-nitrogen ratio.

[0027] Further, in the step S3, the reducing agent is one or more of ferrosilicon and silicomanganese alloy;

[0028] And / or, the addition amount of the reducing agent is calculated according to the amount of metal oxides in the steel slag, and the silicon in the added reducing agent reacts with the metal oxides to reduce the metal oxides;

[0029] And / or, the addition amount of the fluorite is ≤15 kg per ton of molten steel;

[0030] And / or, the reaction time is 6-8 minutes;

[0031] And / or, the reaction temperature is 1550-1650 °C.

[0032] A method for smelting stainless steel by the double-slag method in an AOD furnace provided by the present invention has the beneficial effects that:

[0033] (1) Double-furnace collaborative step-by-step treatment realizes precise control of the slag amount. The first slag pouring rate is ≥70%, and then by adding lime, the remaining silicon slag is bound by the adsorption of lime. Thus, the remaining slag stays in the first AOD furnace after the first tapping, which can ensure that the slag amount of the molten steel is less than 10% at the start of the secondary smelting in the second AOD furnace, reducing the interference of the remaining slag on the subsequent smelting;

[0034] (2) Retain lime to participate in the second batch of smelting after the first slag pouring, reducing the total lime consumption;

[0035] (3) Combine the temperature and carbon content to adjust the blowing oxygen-nitrogen parameters in real time, improving the decarburization efficiency;

[0036] (4) By optimizing the fluidity of the slag system, the single consumption of fluorite balls is reduced to 10-15 kg per ton of molten steel, with a reduction rate of ≥40%, and the smelting efficiency is increased by more than 3%. Detailed implementation mode

[0037] To make the objectives, technical solutions and advantages of the present invention clearer, the following will describe the technical solutions in the embodiments of the present invention clearly and completely in conjunction with the embodiments of the present invention. Those skilled in the art should understand that the described embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. The process parameters without specific conditions noted in the following embodiments are usually in accordance with conventional conditions.

[0038] In the ranges disclosed in the present invention, the endpoints and any values of the ranges are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in the present invention.

[0039] A method for smelting stainless steel by the double slag method in an AOD furnace provided by the present invention includes the following steps:

[0040] S1. Pour molten iron into the first AOD furnace, add lime to the molten iron for the first time, and then blow oxygen to decarbonize and desiliconize. After the temperature of the molten iron rises above 1580 °C, add high-carbon ferrochrome according to the chromium content of the steel type to be produced and blow until it is completely melted and cleared, and then perform the first slag tapping; then add lime to the furnace again, and after blowing, make the remaining slag adsorb onto the lime. After the blowing is completed, tap the steel.

[0041] S2. Transfer the molten steel tapped from the first AOD furnace to the second AOD furnace, add lime to the second AOD furnace for the first time and blow, and add cold materials. When the temperature of the molten steel reaches 1630 - 1700 °C (such as 1640 °C, 1650 °C, 1660 °C, 1670 °C, 1680 °C, 1690 °C), add lime again and blow to decarbonize the molten steel.

[0042] S3. Add a reducing agent and fluorite balls to the decarbonized molten steel, tap the slag after the reaction, and tap the steel after fine-tuning the composition.

[0043] After tapping the steel in step S1, the lime and the remaining slag of the molten steel remaining in the first AOD furnace are used for the next batch of AOD smelting.

[0044] The method for smelting stainless steel by the new double slag method in an AOD furnace provided by the present invention is applicable to all stainless steels smelted by the double slag method (such as austenitic stainless steel and ferritic stainless steel). The hot metal is smelted twice in two AOD furnaces. Lime is added and oxygen is blown in the first AOD furnace for desiliconization and decarburization. The temperature in the furnace is increased by burning silicon and carbon. When tapping, the carbon content has not been reduced to the target value, and the carbon content is generally between 2.5% and 4.0 wt%. When tapping, the lime remains in the first AOD furnace. After tapping is completed, hot metal is added to the first AOD furnace again for the second batch of smelting. At this time, when calculating the amount of lime added to the first AOD furnace during the second batch of smelting, the remaining amount of lime added again after the first slag tapping is completed should be taken into account. The remaining lime can be used continuously, which plays a role in reducing the total lime consumption. The second AOD furnace is used to continue decarburizing, heating up, and alloying the molten steel poured out from the first AOD furnace (easily oxidized alloy materials are added in the second AOD furnace) to achieve the composition and temperature required for the steel grade and complete the steelmaking in the AOD furnace.

[0045] The optimization of slag system formulation in the present invention is carried out in the following way: By the first slag tapping, more than half of the silicon slag in the hot metal is removed, and preferably the slag tapping amount is more than 70% of the total slag mass. For the remaining small amount of silicon slag, by adding an appropriate amount of lime into the furnace continuously, this part of the silicon slag can be agglomerated through the adsorption of lime. At this time, the hot metal is poured out into the second AOD furnace for smelting. In this way, the remaining amount of silicon slag in step S2 can be controlled to be less than 10% (it is very difficult to remove 80% of the silicon slag by the traditional double slag method). The method of the present invention significantly reduces the slag amount in S2 and S3, and realizes a substantial decrease in the consumption of lime and fluorite balls.

[0046] In step S1 of the present invention, the supplementary addition of lime is to make the remaining slag after the first slag tapping stay in the first AOD furnace during tapping. Specifically, after the supplementary addition of lime and blowing for at least 2 minutes, for example, the furnace slag will be adsorbed on the lime. At this time, a large amount of the remaining slag can be left in the first AOD furnace during tapping, realizing the slag retention operation. According to production needs, nickel iron can also be added in the present invention to balance the heat, which is beneficial to the control of the temperature during slag removal, or to make up for the shortage of the amount of hot metal. If the amount of hot metal is sufficient or there is no surplus heat, nickel iron is not added.

[0047] The hot metal added in step S1 of the present invention can be selected as blast furnace hot metal. The chemical composition of the blast furnace hot metal is by mass percentage: C: 4% - 6%, Cr: 3% - 5%, Mn: 0.5% - 2.0%, Cu: 0.03% - 0.04%, Ni: 1.3% - 1.8%, P < 0.05%, S < 0.2%, and the balance is Fe and unavoidable impurities;

[0048] The classical composition of high-carbon ferrochrome by mass percentage is: C: 6% - 8%, Cr: 48% - 55%, Si: 3.0% - 6.0%, P < 0.03%, S < 0.03%, and the rest are Fe and inevitable impurities; high-carbon ferrochrome is added when the temperature of the molten iron rises above 1580°C.

[0049] The classical composition of low-nickel iron chunks by mass percentage is: C: 4% - 5%, Cr: 3% - 4%, Si: 0.5% - 3.0%, P < 0.06%, S < 0.05%, and the rest are Fe and inevitable impurities.

[0050] In step S2 of the present invention, adding lime for decarburization again when the molten bath temperature reaches 1630 - 1700°C takes into account the three-phase equilibrium relationship of carbon-chromium-temperature in the later stage of decarburization. As the carbon content decreases, a certain high temperature must be ensured to ensure that carbon is oxidized prior to chromium, thereby reducing the oxidation loss of chromium.

[0051] The shortening of the smelting time in the present invention is mainly reflected in step S2. When there is less silicon slag in step S2, adding lime to form slag again has a fast effect, a thin slag layer, and good gas permeability, which can improve the oxygen utilization rate, thereby improving the decarburization efficiency and further enhancing the smelting efficiency.

[0052] The cold materials added to the second AOD furnace can be high-carbon ferromanganese, slag steel, scrap iron, return materials of the same type of steel grade, etc. The purpose of adding cold materials is to reduce iron consumption and further alloying. Cold materials with compositions similar to the steel grade to be produced can be added, and there is no requirement for the addition amount, which can be added or not. The maximum addition amount of cold materials does not exceed 120 kg / t of molten steel; after the first addition of lime in the second AOD furnace, the molten bath temperature is high enough, and cold materials can be added at any time, but generally, they should be added before the carbon content of the molten steel drops to 0.8 wt%.

[0053] Reducing agents and fluorite balls are added to the molten iron after decarburization. The addition of reducing agents is to reduce the chromium, manganese, and iron oxides that are oxidized into the slag during the decarburization process of the molten steel back from the slag, thereby increasing the metal yield; adding fluorite balls is to lower the melting point of the slag, making the slag change from a solid state to a liquid slag with good fluidity during the reduction period, so as to fully contact and react with the reducing agent, improve the reaction efficiency, and fully recover the metals in the slag.

[0054] As an alternative embodiment of the present invention, in step S1, for the first addition of lime, the addition amount of lime is calculated according to the total silicon content of the molten iron and high-carbon ferrochrome, and the binary basicity is controlled to be 1.20 - 1.50 (such as 1.30, 1.40).

[0055] In the calculation of the above lime addition amount, if ferronickel is added during the process, the silicon content contained in the ferronickel should also be calculated in the total silicon content.

[0056] As an alternative embodiment of the present invention, in step S1, the addition amount of high-carbon ferrochrome is 160 - 400 kg / t hot metal (such as 180 kg / t hot metal, 200 kg / t hot metal, 220 kg / t hot metal, 240 kg / t hot metal, 260 kg / t hot metal, 280 kg / t hot metal, 300 kg / t hot metal, 320 kg / t hot metal, 340 kg / t hot metal, 360 kg / t hot metal, 380 kg / t hot metal);

[0057] and / or, the temperature at which the high-carbon ferrochrome is completely melted is 1480 - 1560 °C (such as 1490 °C, 1500 °C, 1510 °C, 1520 °C, 1530 °C, 1540 °C, 1550 °C).

[0058] The present invention comprehensively determines the addition amount of high-carbon ferrochrome according to the chromium content and other components in the steel grade composition produced at the end. For example, for a certain 200-series stainless steel with a chromium content of 14%, the addition amount of high-carbon ferrochrome is 200 - 240 kg / t hot metal; for a certain 300-series stainless steel with a chromium content of 18%, the addition amount of high-carbon ferrochrome is 300 - 340 kg / t hot metal. The specific addition amount can be determined as long as there is the steel grade composition and the material formula.

[0059] As an alternative embodiment of the present invention, in step S1, the slag tapping amount of the first slag tapping ≥ 70% (such as 70%, 72%, 74%, 76%, 80%, 85%, 90%, 95%, 100%), and the remaining slag amount ≤ 30% (such as 30%, 25%, 20%, 15%, 10%, 5%, 0%).

[0060] As an alternative embodiment of the present invention, in step S1,

[0061] the amount of lime added is 40 - 60 kg (such as 45 kg, 50 kg, 55 kg) of lime per ton of hot metal;

[0062] and / or, the carbon content of the molten steel during tapping is 2.50 - 4.0 wt% (such as 3.0 wt%, 3.5 wt%), and the silicon content < 0.20 wt% (such as 0.19 wt%, 0.18 wt%, 0.17 wt%, 0.16 wt%).

[0063] As an alternative embodiment of the present invention, in step S2, the addition amounts of lime for the two times are 20 - 30 kg (such as 22 kg, 24 kg, 26 kg, 28 kg) of lime per ton of hot metal respectively.

[0064] In step S2 of the present invention, adding lime twice both has the effect of decarburization.

[0065] As an alternative embodiment of the present invention, in step S2, the cold charge is one or several of ferromanganese, slag steel, scrap iron, and return material;

[0066] The addition amount of the cold charge is 0 - 120 kg per ton of hot metal (such as 10 kg, 20 kg, 30 kg, 40 kg, 50 kg, 60 kg, 70 kg, 80 kg, 90 kg, 100 kg, 110 kg).

[0067] The addition amount of the cold charge is determined according to the heat balance of smelting and is affected by the on-site cold charge inventory. If there is no cold charge inventory, it can be not added.

[0068] When the cold charge of the present invention is ferromanganese, its addition amount is not higher than 80 kg per ton of hot metal. If smelting 300 series stainless steel, ferromanganese is not used. If smelting 200 series stainless steel, 30 - 80 kg of ferromanganese is added; when the cold charge is slag steel, its addition amount is not higher than 120 kg per ton of hot metal; when the cold charge is scrap iron, its addition amount is not higher than 80 kg per ton of hot metal; when the cold charge is return material, its addition amount is not higher than 120 kg per ton of hot metal.

[0069] The component of the cold charge material of the present invention is respectively: cold charge 1, ferromanganese. The chemical composition of the ferromanganese is by mass percentage: C: 6% - 8%, Mn: 65% - 80%, Si: 1% - 3%, P < 0.25%, S ≤ 0.03%, and the rest is Fe and inevitable impurities;

[0070] Cold charge 2, slag steel. The chemical composition of the slag steel is by mass percentage: C: 2% - 4%, Cr: 12% - 18%, Mn: 0.5% - 10%, Si: 0% - 0.7%, P < 0.05%, S ≤ 0.03%, and the rest is Fe and inevitable impurities;

[0071] Cold charge 3, scrap iron, 99% iron, and the rest are inevitable impurities;

[0072] Cold charge 4: return material, which is a finished product material with a composition similar to the steel grade being smelted.

[0073] As an alternative embodiment of the present invention, in step S2, the carbon content of the hot metal after decarburization is determined according to the target value of the steel grade.

[0074] As an alternative embodiment of the present invention, in step S2, the oxygen-nitrogen ratio required during the decarburization of the molten steel is adjusted in real time according to the molten steel temperature and the molten steel carbon content, and the molten steel temperature is controlled within the range of 1630 - 1700 °C by adjusting the oxygen-nitrogen ratio.

[0075] Adjusting the oxygen-nitrogen ratio according to the molten steel temperature and carbon content is carried out by adjusting the oxygen flow rate and nitrogen flow rate of the main lance. In stainless steel smelting, when the carbon content of the molten steel is reduced to a certain extent, there is a three-phase equilibrium relationship among carbon, chromium, and temperature. If the carbon content is to be further reduced, the temperature needs to be increased or the chromium content needs to be reduced (oxidizing part of the chromium). In the later stage of decarburization, the increase in the molten bath temperature mainly depends on metal oxidation. In order to reduce metal oxidation, the temperature cannot keep rising in the later stage of steelmaking. In order to achieve the purpose of decarburizing and protecting chromium, reducing chromium oxidation, and increasing the chromium recovery rate, it is necessary to adjust the oxygen-nitrogen ratio according to the carbon content and molten steel temperature, reduce the CO partial pressure, promote carbon oxidation, and at the same time reduce metal oxidation, and control the molten steel temperature within the range of 1630 - 1700 °C through the oxygen-nitrogen ratio.

[0076] For the smelting of steel grades with particularly low N content requirements in steel, the nitrogen in the oxygen and nitrogen used in the decarburization process in step S2 can be replaced by argon, especially switching nitrogen to argon in the later stage of the decarburization process to ensure that the nitrogen content of the steel grade meets the requirements of the steel grade. For example, for 300 series steel grades, the nitrogen content requirement is within 0.05 wt%, and attention should be paid to switching nitrogen to argon in the later stage of the decarburization process. For 200 series steel grades, the nitrogen content requirement is 0.1 - 0.2 wt%, and oxygen and nitrogen can be used during decarburization without replacing nitrogen with argon. The role of blowing argon is to reduce the nitrogen content in the molten steel to the target value.

[0077] As an optional implementation manner of the present invention, in step S3, the reducing agent is one or more of ferrosilicon and silicomanganese alloy;

[0078] And / or, the addition amount of the reducing agent is calculated according to the amount of metal oxides in the steel slag, and the silicon in the added reducing agent reacts with the metal oxides to reduce the metal oxides; for example, when it is ferrosilicon, its addition amount is 10 - 30 kg per ton of molten steel (such as 15 kg, 20 kg, 25 kg); when the reducing agent is silicomanganese alloy, its addition amount is calculated according to the equivalent silicon content in the ferrosilicon amount consumed per ton of molten steel;

[0079] And / or, the addition amount of the fluorite is ≤15 kg per ton of molten steel (such as 15 kg, 14 kg, 13 kg, 12 kg, 8 kg, 6 kg, 4 kg, 2 kg, 0 kg);

[0080] And / or, the reaction time is 6 - 8 minutes (such as 7 minutes);

[0081] And / or, the reaction temperature is 1550 - 1650 °C (such as 1560 °C, 1570 °C, 1580 °C, 1590 °C, 1600 °C, 1610 °C, 1620 °C, 1630 °C, 1640 °C).

[0082] If ferrosilicon is used as the reducing agent in the present invention, the addition amount of ferrosilicon per ton of molten steel is 10 - 30 kg; if silicomanganese alloy is used, the amount of silicomanganese alloy shall be converted according to the equivalent silicon content in the consumed ferrosilicon amount. For example, if 20 kg of ferrosilicon is used, the silicon content of ferrosilicon is 75%, and the silicon content of silicomanganese alloy is 21%, then the equivalent silicon conversion is 20 * 0.75 / 0.21 = 71.43 kg. Since there are various silicon contents in silicomanganese alloy, such as 0.17% - 0.28%, it shall be converted according to the actual use.

[0083] Ferrosilicon is used as a reducing agent, and its function is to reduce metal oxides in steelmaking slag, including metal oxides such as chromium, manganese, and iron. The content of components such as chromium, manganese, and iron in the molten steel at the end of oxidation can be analyzed by taking a steel water sample, so as to accurately calculate the mass of the oxidized metal oxides. Then, according to the reduction reaction equation of metal oxides and silicon, the required amount of ferrosilicon can be calculated.

[0084] In step S3, after adding the reducing agent, the temperature is raised by burning silicon. After sufficient reduction, the slag is poured out, and the molten steel is tapped after fine-tuning the components.

[0085] The present invention will be further described in detail below with specific examples and comparative examples.

[0086] The compositions of the raw material hot metal in Example 1 and Comparative Example 1 are as follows:

[0087] By mass percentage, C: 2.8%, Cr: 3.0%, Mn: 0.5%, Cu: 0.03%, Ni: 10.6%, Si: 0.5%, P: 0.041%, S: 0.075%, and the balance is Fe and unavoidable impurities;

[0088] The compositions of the raw material hot metal in Example 2 and Comparative Example 2 are as follows:

[0089] By mass percentage, C: 5.0%, Cr: 4.5%, Mn: 1.0%, Cu: 0.03%, Ni: 1.46%, Si: 0.75%, P: 0.041%, S: 0.075%, and the balance is Fe and unavoidable impurities;

[0090] Example 1

[0091] S1. Charge 60 tons of hot metal with a silicon content of 0.5% into the first AOD furnace. Add 59 kg of lime per ton of hot metal and control the binary basicity at 1.30. After blowing oxygen until the hot metal temperature reaches 1580°C, add 24 tons of high-carbon ferrochrome (chromium content 52%, with a total silicon mass of 1140 kg). Blow until it is completely melted, and the melting temperature at this time is 1500°C. Then perform the first slag pouring, and the slag pouring amount is 75%. Add lime to the furnace again, with the added amount being 40 kg of lime per ton of hot metal. After blowing for 2 minutes, tap the steel. At this time, the C content in the molten steel is 2.23% and the Si content is 0.12%. This step takes 40 minutes.

[0092] S2. Transfer the molten steel tapped from the first AOD furnace to the second AOD furnace. Add 25 kg of lime per ton of hot metal for blowing and add 5 tons of cold charge. The cold charge is 304 cuttings. When the molten pool temperature reaches 1650°C, add lime for blowing again, with the added amount being 25 kg of lime per ton of hot metal. According to the carbon content detected by sampling the molten steel, dynamically adjust the oxygen-nitrogen volume ratio to 3:1, 2:1, 1:1, 1:2, 1:3. When the detected carbon content is 0.4 - 0.5%, dynamically adjust the oxygen-nitrogen ratio to 3:1; when the detected carbon content is 0.3 - 0.4%, switch nitrogen to argon and dynamically adjust the oxygen-argon ratio to 2:1; when the detected carbon content is 0.2 - 0.3%, dynamically adjust the oxygen-argon ratio to 1:1; when the detected carbon content is 0.1 - 0.2%, dynamically adjust the oxygen-argon ratio to 1:2; when the detected carbon content is less than 0.1%, dynamically adjust the oxygen-argon ratio to 1:3 until the carbon content drops below 0.05 wt%. This step takes 45 minutes.

[0093] S3. Reduction and refining: Add ferrosilicon and fluorspar balls to the decarburized hot metal in the second AOD furnace. The addition amount of ferrosilicon is 20 kg per ton of molten steel, and the addition amount of fluorspar balls is 12 kg per ton of molten steel. After blowing argon for reduction for 7 minutes, pour the slag, finely adjust the composition and temperature, and tap the steel at 1600°C. The obtained molten steel composition by mass percentage is C: 0.03%, Ni: 8.03%, Cr: 18.05%, Mn: 0.85%, Si: 0.43%, P: 0.031%, S: 0.004%, N 0.037%. This step takes 20 minutes.

[0094] Example 2

[0095] S1. Charge 57 tons of hot metal with a silicon content of 0.75% into the first AOD furnace. Add 52 kg of lime per ton of hot metal and control the binary basicity at 1.30. After blowing oxygen until the hot metal temperature reaches 1580°C, add 14.5 tons of high-carbon ferrochrome (chromium content 52%, total silicon mass 507 kg). Blow and refine until it is completely melted and cleared. At this time, the melting and clearing temperature is 1516°C, and then perform the first slag tapping with a slag tapping amount of 70%. Add lime to the furnace again, with an additional amount of 45 kg of lime per ton of hot metal. After blowing for 2 minutes, tap the steel. At this time, the C content in the molten steel is 3.0% and the Si content is 0.08%. This step takes 35 minutes.

[0096] S2. Transfer the molten steel tapped from the first AOD furnace to the second AOD furnace. Add 23 kg of lime per ton of hot metal for blowing and add 8 tons of cold materials. The cold materials are 5 tons of 201 slag steel, 1 ton of scrap iron, and 2 tons of high-carbon ferromanganese. When the molten pool temperature reaches 1650°C, add lime for blowing again, with an additional amount of 25 kg of lime per ton of hot metal. Dynamically adjust the oxygen-nitrogen ratio to 3:1, 2:1, 1:1, 1:2, 1:3 according to the carbon content. When the detected carbon content is 0.4 - 0.5%, dynamically adjust the oxygen-nitrogen ratio to 3:1; when the detected carbon content is 0.3 - 0.4%, dynamically adjust the oxygen-nitrogen ratio to 2:1; when the detected carbon content is 0.2 - 0.3%, dynamically adjust the oxygen-nitrogen ratio to 1:1; when visually observing the carbon content is 0.1 - 0.2%, dynamically adjust the oxygen-nitrogen ratio to 1:2; when the detected carbon content is less than 0.1%, dynamically adjust the oxygen-nitrogen ratio to 1:3 until the carbon content drops below 0.07 wt%. This step takes 40 minutes.

[0097] S3. Reduction and refining: Add high-silicon silicomanganese, low-carbon ferromanganese, and fluorite balls to the decarburized hot metal in the second AOD furnace. The addition amount of high-silicon silicomanganese is 64 kg per ton of molten steel, the addition amount of low-carbon ferromanganese is 42 kg per ton of molten steel, and the addition amount of fluorite balls is 15 kg per ton of molten steel. After blowing nitrogen for reduction for 7 minutes, tap the slag, finely adjust the composition and temperature, and tap the steel at 1570°C to obtain molten steel with the following chemical composition by mass percentage: C: 0.10%, Ni: 1.08%, Cr: 13.65%, Mn: 9.85%, Si: 0.40%, P: 0.042%, S: 0.004%, N 0.15%. This step takes 25 minutes.

[0098] Comparative Example 1

[0099] This example is a traditional AOD furnace double-slag process.

[0100] S1. Charge 59 tons of hot metal with a silicon content of 0.5% into the AOD furnace. Add 58 kg of lime per ton of hot metal and control the binary basicity at 1.30. After blowing oxygen until the hot metal temperature reaches 1580°C, add 23.6 tons of high-carbon ferrochrome and blow until it is completely melted. At this time, the melting temperature is 1500°C, and then perform the first slag tapping with a slag tapping amount of 75%. This step takes 38 minutes.

[0101] S2. Add lime to the AOD furnace. The addition amount of lime is 40 kg per ton of hot metal. Blow and add 4.5 tons of cold charge. The cold charge is 304 waste cutting head material. When the molten pool temperature reaches 1650°C, add lime again for blowing. The supplementary addition amount is 30 kg of lime per ton of hot metal. Dynamically adjust the oxygen-nitrogen ratio to 3:1, 2:1, 1:1, 1:2, 1:3. Detect that the carbon content is 0.4 - 0.5%, and dynamically adjust the oxygen-nitrogen ratio to 3:1. Detect that the carbon content is 0.3 - 0.4%, switch nitrogen to argon, and dynamically adjust the oxygen-argon ratio to 2:1. Detect that the carbon content is 0.2 - 0.3%, and dynamically adjust the oxygen-argon ratio to 1:1. Detect that the carbon content is 0.1 - 0.2%, and dynamically adjust the oxygen-argon ratio to 1:2. Detect that the carbon content is less than 0.1%, and dynamically adjust the oxygen-argon ratio to 1:3 until the carbon content drops below 0.05 wt%. This step takes 50 minutes.

[0102] S3. Add ferrosilicon and fluorspar balls to the molten steel after decarburization in the AOD furnace. The addition amount of ferrosilicon is 28 kg per ton of hot metal, and the addition amount of fluorspar balls is 30 kg per ton of molten steel. After reacting for 7 minutes, tap the slag and tap the steel at 1600°C. The obtained molten steel composition is by mass percentage: C: 0.03%, Ni: 8.04%, Cr: 18.09%, Mn: 0.91%, Si: 0.38%, P: 0.033%, S: 0.005%, N 0.039%. This step takes 21 minutes.

[0103] Comparative Example 2

[0104] This example is the traditional AOD furnace double-slag process.

[0105] S1. Charge 58 tons of hot metal with a silicon content of 0.8% into the AOD furnace. Add 58 kg of lime per ton of hot metal and control the binary basicity at 1.30. After blowing oxygen until the hot metal temperature reaches 1585°C, add 14.8 tons of high-carbon ferrochrome and blow until it is completely melted. At this time, the melting temperature is 1516°C, and then perform the first slag tapping with a slag tapping amount of 70%. This step takes 33 minutes.

[0106] S2. Add lime to the AOD furnace. The addition amount of lime is 40 kg per ton of hot metal. Blow and add 6.5 tons of cold charge. The cold charge consists of 4.5 tons of 201 scrap cuttings and 2 tons of high-carbon ferromanganese. When the molten pool temperature reaches 1650 °C, add lime again for blowing. The supplementary addition amount is 30 kg of lime per ton of hot metal. Dynamically adjust the oxygen-nitrogen ratio to 3:1, 2:1, 1:1, 1:2, 1:3. When the detected carbon content is 0.4 - 0.5%, dynamically adjust the oxygen-nitrogen ratio to 3:1; when the detected carbon content is 0.3 - 0.4%, dynamically adjust the oxygen-nitrogen ratio to 2:1; when the detected carbon content is 0.2 - 0.3%, dynamically adjust the oxygen-nitrogen ratio to 1:1; when the detected carbon content is 0.1 - 0.2%, dynamically adjust the oxygen-nitrogen ratio to 1:2; when the detected carbon content is less than 0.1%, dynamically adjust the oxygen-nitrogen ratio to 1:3 until the carbon content drops below 0.05 wt%. This step takes 46 minutes.

[0107] S3. Add high-silicon silicomanganese, low-carbon ferromanganese, and fluorspar balls to the hot metal after decarburization in the second AOD furnace. The addition amount of high-silicon silicomanganese is 67 kg per ton of molten steel, the addition amount of low-carbon ferromanganese is 40 kg per ton of molten steel, and the addition amount of fluorspar balls is 28 kg per ton of molten steel. After blowing nitrogen for reduction for 7 minutes, pour the slag. Fine-tune the composition and temperature, and tap the steel at 1570 °C. The obtained molten steel composition by mass percentage is: C: 0.11%, Ni: 1.10%, Cr: 13.62%, Mn: 9.80%, Si: 0.41%, P: 0.045%, S: 0.005%, N 0.14%. This step takes 25 minutes.

[0108] Effect description

[0109] In Example 1 and Comparative Example 1, the quality of the subsequent steel billets is normal, and the quality of the hot-rolled and cold-rolled coils is normal.

[0110] In Example 1, the single consumption of fluorspar balls is 12 kg / t of hot metal, and in Comparative Example 1, i.e., the traditional process, the single consumption of fluorspar balls is 30 kg / t of hot metal.

[0111] In Example 2 and Comparative Example 2, the quality of the subsequent steel billets is normal, and the quality of the hot-rolled and cold-rolled coils is normal.

[0112] In Example 2, the single consumption of fluorspar balls is 15 kg / t of hot metal, and in Comparative Example 2, i.e., the traditional process, the single consumption of fluorspar balls is 28 kg / t of hot metal.

[0113] For the comparison of the process time of Example 1 - 2 and Comparative Example 1 - 2, see Table 1 below. It can be seen from Table 1 that the total smelting time of Example 1 is about 3.8% shorter than that of the traditional process in Comparative Example 1. The total smelting time of Example 2 is 4% shorter than that of the traditional process in Comparative Example 2.

[0114] Table 1: Time consumption of each step in Examples and Comparative Examples

[0115] Example 1 Example 2 Comparative Example 1 Comparative Example 2 Time consumed by S1 / min 40 35 38 33 Time consumed by S2 / min 45 40 50 46 Time consumed by S3 / min 20 25 21 25 Total time consumed / min 105 100 109 104

[0116] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for smelting stainless steel by the double slag method in an AOD furnace, characterized in that, It includes the following steps: S1. Pour molten iron into the first AOD furnace, add lime to the molten iron for the first time, then blow oxygen to decarburize and desiliconize. After the temperature of the molten iron rises above 1580 °C, add high-carbon ferrochrome according to the chromium content of the steel grade to be produced and blow it until it is completely melted and refined, and then carry out the first slag tapping; then add lime to the furnace again, and through blowing, make the remaining slag adsorb onto the lime. After the blowing is completed, tap the steel; S2. Transfer the molten steel tapped from the first AOD furnace into the second AOD furnace, add lime to the second AOD furnace for the first time for blowing and add cold materials. When the temperature of the molten steel reaches 1630 - 1700 °C, add lime again for blowing to decarburize the molten steel; S3. Add a reducing agent and fluorspar balls to the decarburized molten steel, tap the slag after the reaction, and tap the steel after fine-tuning the composition; The lime and the remaining slag of the molten steel retained in the first AOD furnace after tapping in step S1 are used for the next batch of AOD furnace smelting.

2. The method for smelting stainless steel by the double slag method in an AOD furnace according to claim 1, characterized in that, In step S1, for the first addition of lime, the addition amount of lime is calculated according to the total silicon content of the molten iron and high-carbon ferrochrome, and the binary basicity is controlled to be 1.20 - 1.

50.

3. The method for smelting stainless steel by the double slag method in an AOD furnace according to claim 1, characterized in that, In step S1, the addition amount of the high-carbon ferrochrome is 160 - 400 kg / t of molten iron; And / or, the temperature at which the high-carbon ferrochrome is completely melted and refined is 1480 - 1560 °C.

4. The method for smelting stainless steel by the double slag method in an AOD furnace according to claim 1, characterized in that In step S1, the slag tapping amount of the first slag tapping is ≥70%, and the remaining slag amount is ≤30%.

5. The method for smelting stainless steel by the double slag method in an AOD furnace according to claim 1, characterized in that, In step S1, the amount of lime added for supplementary addition is 40 - 60 kg of lime per ton of molten iron; And / or, the carbon content in the molten steel during tapping is 2.50 - 4.0 wt%, and the silicon content is <0.20 wt%.

6. The method for smelting stainless steel by the double slag method in an AOD furnace according to claim 1, wherein, In step S2, the addition amounts of lime for the two times are 20 - 30 kg of lime per ton of molten iron respectively.

7. The method for smelting stainless steel by the double slag method in an AOD furnace according to claim 1, wherein, In step S2, the cold materials are one or several of high-carbon ferromanganese, slag steel, scrap iron, and return materials; And / or, the addition amount of the cold materials is 0 - 120 kg per ton of molten iron.

8. The method for smelting stainless steel by the double slag method in an AOD furnace according to claim 1, characterized in that, In step S2, the carbon content of the decarburized molten iron is determined according to the target value of the steel grade to be produced.

9. The method for smelting stainless steel by the double slag method in an AOD furnace according to claim 1, characterized in that, In step S2, the oxygen-nitrogen ratio required during the decarburization of the molten steel is adjusted in real time according to the temperature and carbon content of the molten steel, and the temperature of the molten steel is controlled within the range of 1630 - 1700 °C by adjusting the oxygen-nitrogen ratio.

10. The method for smelting stainless steel by the double slag method in an AOD furnace according to claim 1, characterized in that, In step S3, the reducing agent is one or more of ferrosilicon and silicomanganese alloy; And / or, the addition amount of the reducing agent is calculated according to the amount of metal oxides in the steel slag, and the silicon in the added reducing agent reacts with the metal oxides to reduce the metal oxides; And / or, the addition amount of the fluorspar is ≤15 kg per ton of molten steel; And / or, the reaction time is 6 - 8 minutes; And / or, the reaction temperature is 1550 - 1650 °C.