CN115418429B - Method for smelting 200-series stainless steel by AOD furnace - Google Patents
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- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
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- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
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- C21C7/0685—Decarburising of stainless steel
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- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
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Abstract
The invention belongs to the field of steelmaking, and particularly relates to a method for smelting 200-series stainless steel by an AOD furnace, which sequentially comprises the following steps: (1) primary slag skimming: adding molten iron, a slag former and high-carbon ferrochrome into an AOD furnace, and then skimming slag; (2) adding high-carbon ferromanganese: adding a slag former after slag skimming, and adding high-carbon ferromanganese more than or equal to 40kg/t at 1600-1630 ℃; (3) decarburizing and manganese preserving: controlling the decarburization temperature to 1630-1685 ℃, reducing the proportion of oxygen in the decarburization gas along with the rise of the decarburization temperature, and ending decarburization when the content of C in the molten steel is lower than 0.1 wt%; (4) reduction: adding a reducing agent and a slag former, blowing, deslagging, detecting the temperature and components of molten steel, introducing argon, blowing, and tapping; the method improves the consumption of high-carbon ferromanganese to above 40kg/t, controls the smelting time to be less than or equal to 125min, meets the requirement of mass production, and simultaneously effectively reduces the unit consumption of electrolytic manganese.
Description
Technical Field
The invention belongs to the field of steelmaking, and particularly relates to a method for smelting 200-series stainless steel by an AOD furnace.
Background
Manganese is one of indispensable elements in steel production, manganese element is an important alloy element for steelmaking, and manganese element is in steel, so that the mechanical properties of the steel are mainly improved, and the strength, hardness, ductility, wear resistance and the like of the steel are improved. Manganese is used in a relatively large amount in a stainless steel grade of 200, because it occupies a relatively large amount.
The manganese alloy used for smelting 200 stainless steel in the AOD furnace comprises high-silicon manganese, common silicon manganese, high-carbon ferromanganese, low-carbon ferromanganese, electrolytic manganese and the like, wherein the unit consumption of the electrolytic manganese is between 30kg/t and 50kg/t according to different steel types.
The market situation of the raw materials is changed immediately in 2021, the price of the raw materials is increased continuously, and the production cost of the 200 series stainless steel is increased continuously. However, the price of electrolytic manganese increases seriously in the beginning of 2021, from 10000 yuan/ton to approximately 40000 yuan/ton, and the price becomes one of the most important factors affecting the cost in producing 200 series stainless steel.
The AOD smelting time of a steelworks is required to be matched with the continuous casting steel drawing speed, and the AOD smelting time is controlled to be generally not more than 125 minutes according to the production condition of stainless steel, or else, the AOD smelting time cannot be applied to mass production. At present, the process for increasing the consumption of high-carbon ferromanganese in the AOD smelting 200 system stainless steel does not have mature and stable technology, and when the smelting time is controlled within 125 minutes, the average unit consumption of the high-carbon ferromanganese is only about 13kg/t. If the consumption of high-carbon ferromanganese is increased, the manganese content in molten steel is greatly increased, the decarburization efficiency is reduced, the decarburization time is increased, the smelting period is obviously increased, and the method cannot be implemented in mass production.
Therefore, the consumption of high-carbon ferromanganese is increased while the smelting time is not increased, and the method has important significance for reducing the cost and improving the efficiency of the stainless steel of the current AOD smelting 200 system and completing the national 'energy consumption double control' target.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, and aims to provide a method for smelting 200-series stainless steel by an AOD furnace, which can improve the high-carbon ferromanganese consumption of 200-series stainless steel by the AOD furnace to more than 40kg/t, such as 40-70 kg/t, control the smelting time within 125 minutes, and effectively reduce the unit consumption of electrolytic manganese while meeting the requirement of mass production, thereby realizing cost reduction and efficiency enhancement.
A method for smelting 200 series stainless steel by an AOD furnace, which comprises the following steps in sequence:
(1) Primary slag skimming: adding molten iron and a slag former into an AOD furnace for converting, heating to 1580-1620 ℃ (e.g. 1590 ℃, 1600 ℃, 1610 ℃), adding high-carbon ferrochrome for further converting, and carrying out slag skimming when the temperature of molten steel reaches 1510-1580 ℃ (e.g. 1520 ℃, 1530 ℃, 1540 ℃, 1550 ℃, 1560 ℃ and 1570 ℃);
(2) Adding high-carbon ferromanganese: adding a slag former after slag skimming, heating to 1600-1630 ℃ (such as 1605 ℃, 1610 ℃, 1615 ℃, 1620 ℃ and 1625 ℃) and adding high-carbon ferromanganese into molten steel according to the amount of more than or equal to 40 kg/t;
(3) Decarburizing and preserving manganese: controlling the decarburization temperature to be 1630-1685 ℃ (for example 1640 ℃, 1650 ℃, 1660 ℃, 1670 ℃, 1680 ℃) and the decarburization gas to be oxygen and inert gas, reducing the oxygen content in the decarburization gas with the rise of the decarburization temperature, wherein the initial oxygen content in the decarburization gas is 60-100% (for example 65%, 70%, 75%, 80%, 85%, 90%, 95%) in volume percent, after the temperature reaches 1650 ℃, reducing the oxygen content in the decarburization gas, and ending decarburization when the C content in the molten steel is lower than 0.1 wt%;
(4) And (3) reduction: adding a reducing agent and a slag former, sequentially introducing oxygen and nitrogen for blowing, deslagging, detecting the temperature and components of molten steel, adjusting the components of the molten steel according to the requirements of the components of target steel types, introducing argon for blowing, and tapping; if the manganese content in the molten steel is lower than the component requirement of the target steel grade, the electrolytic manganese is supplemented to adjust the manganese content in the molten steel so as to enable the molten steel to meet the component requirement of the target steel grade;
the smelting time of the method for smelting 200-series stainless steel by the AOD furnace is less than or equal to 125 minutes.
The invention adopts the smelting process of the AOD furnace by a double slag method, and realizes more than 80 percent of one-pouring slag-removing quantity by controlling one-pouring slag-removing condition. The following three advantages are achieved by carrying out one slag skimming before adding high-carbon ferromanganese: firstly, the purpose of reducing phosphorus can be achieved, and conditions are created for the subsequent high-carbon ferromanganese to enter the furnace. The high-carbon ferromanganese and the silicon-manganese alloy both contain higher phosphorus content, and part of phosphorus in the molten iron is scraped through slag skimming operation so as to prevent the terminal component phosphorus from exceeding the standard; secondly, silicon in the blast furnace molten iron and the high-carbon ferrochrome is oxidized preferentially to enter slag in the early stage, and slag containing a large amount of silicon dioxide can be discharged out of the furnace by one-step slag skimming, so that the consumption of subsequent slag formers (lime and fluorite) is saved; thirdly, the addition of a follow-up slag former (mainly lime) is reduced after slag skimming, the slag layer is thinned, and the removal of CO gas generated in the furnace is facilitated, so that decarburization and manganese conservation are promoted.
In the above-mentioned method for smelting 200-series stainless steel in an AOD furnace, in the step (1), the molten iron is a blast furnace molten iron having a charging temperature of 1250 to 1350 ℃ (e.g., 1260 ℃, 1270 ℃, 1280 ℃, 1290 ℃, 1300 ℃, 1310 ℃, 1320 ℃, 1330 ℃, 1340 ℃); preferably, the blast furnace molten iron comprises the following components in percentage by weight: 4 to 6 percent of C, 0.5 to 1.5 percent of silicon, 3 to 5 percent of chromium, 0.5 to 2.0 percent of manganese, 0.03 to 0.04 percent of copper, 1.3 to 1.8 percent of nickel, 0.05 percent of phosphorus, 0.2 percent of sulfur and the balance of Fe and unavoidable impurities.
In the above method for smelting 200-series stainless steel in an AOD furnace, in the step (1), after adding high carbon ferrochrome, the components of the molten steel are adjusted in weight percentage: 2 to 4 percent of C, 0 to 0.2 percent of silicon, 13.5 to 15 percent of chromium, 0.2 to 1.5 percent of manganese, 0.03 to 0.04 percent of copper, 1.1 to 1.6 percent of nickel, 0.05 percent of phosphorus, 0.15 percent of sulfur and the balance of Fe and unavoidable impurities.
In the above method for smelting 200-series stainless steel in an AOD furnace, in the step (1), the gas used for blowing is a mixed gas of oxygen and nitrogen in a volume ratio of 6:1, wherein the oxygen pressure is 1.7-1.8 MPa.
In the above-mentioned method for smelting 200-series stainless steel in an AOD furnace, in the step (1), the temperature at the time of slag skimming is 1520 to 1580 ℃ (e.g., 1530 ℃, 1540 ℃, 1550 ℃, 1560 ℃, 1570 ℃); preferably, the slag fluidity at the time of slag skimming is 0.1 to 0.4 Pa.S (for example, 0.15 Pa.S, 0.2 Pa.S, 0.25 Pa.S, 0.3 Pa.S, 0.35 Pa.S), and the slag surface is free from agglomerate; preferably, the skimming amount reaches more than 80%; preferably, the thickness of the slag layer in the slag removing furnace is less than 30mm.
In the above-described method for smelting 200-series stainless steel in an AOD furnace, in the step (2), the temperature is raised by simultaneously feeding oxygen to an AOD furnace top gun and a side gun; preferably, the temperature is raised to 1600-1630 ℃ (for example 1605 ℃, 1610 ℃, 1615 ℃, 1620 ℃ and 1625 ℃) for 8min or less; preferably, the time for heating to 1600-1630 ℃ is 6-8 min (e.g. 6.5min, 7min, 7.5 min); preferably, the amount of high carbon ferromanganese added is 40 to 70kg/t (e.g., 45kg/t, 50kg/t, 55kg/t, 60kg/t, 65 kg/t).
In the invention, the top-bottom combined blowing is carried out by adopting the mode of simultaneously feeding oxygen to the AOD furnace top gun and the side gun so as to quickly raise the temperature. The temperature is rapidly increased to 1600-1630 ℃, the decarburization rate can be increased, the heat utilization rate is increased, conditions are created for adding high-carbon ferromanganese or other cold materials, and the smelting time is shortened.
The temperature of the added high-carbon ferromanganese is controlled to be 1600-1630 ℃, the manganese and the carbon can have the problem of selective oxidation at the steelmaking temperature, the temperature is controlled to be 1600-1630 ℃, and the carbon in the molten steel can be oxidized in preference to the manganese; when the temperature is lower than 1600 ℃, high-carbon ferromanganese is added, manganese is oxidized before carbon, the oxidation of carbon is restrained, the decarburization time is prolonged, the manganese is vaporized and evaporated due to the oxidation of manganese and long-time decarburization, and the yield of manganese is greatly reduced. The melting of high-carbon ferromanganese in the furnace is a gradual process, and a certain time is needed. When the addition temperature is higher than 1630 ℃, the decarburization speed of the molten pool is high, when the decarburization reaches the end, partial high-carbon ferromanganese possibly does not melt down to enter molten steel, and the decarburization is judged to be finished according to the carbon content of the molten steel at the moment and enters a reduction step, so that the carbon content of the end is out of standard, and the molten steel is scrapped.
In the above-described method for smelting 200-series stainless steel in an AOD furnace, in the step (3), the inert gas is nitrogen or argon, and more preferably, nitrogen for steelmaking.
In the above-described method for smelting 200-series stainless steel in an AOD furnace, in the step (3), oxygen and an inert gas are blown into the decarburization manganese-preserving step by using a side lance.
In the above-mentioned method for smelting 200-series stainless steel in an AOD furnace, in the step (3), after the decarburization temperature reaches 1650 to 1660 ℃ (e.g., 1651 ℃, 1652 ℃, 1653 ℃, 1654 ℃, 1655 ℃, 1656 ℃, 1657 ℃, 1658 ℃, 1659 ℃), the ratio of oxygen to inert gas volume is (0.8 to 1.2): 1 (e.g., 0.9:1, 1.0:1, 1.1:1); after the decarburization temperature reaches 1670 to 1675 ℃ (for example 1671 ℃, 1672 ℃, 1673 ℃ and 1674 ℃), the ratio of oxygen to inert gas volume is 1 (1.8 to 2.2) (for example 1:1.9, 1:2.0 and 1:2.1); after the decarburization temperature reaches 1680 to 1685 ℃, the ratio of oxygen to inert gas volume is 1 (3.8 to 4.2) (e.g., 1:3.9, 1:4.0, 1:4.1).
In the preferred embodiment of the invention, after the decarburization temperature reaches 1650 ℃, according to the three-phase balance relation of C-chromium-temperature, in order to ensure that decarburization is carried out smoothly, less oxidation of chromium is required, the temperature is fixed, the decarburization is required to preserve manganese, the partial pressure of CO is required to be reduced, and the partial pressure of CO is reduced by gradually increasing the nitrogen amount to accelerate the discharge of CO in molten steel. If the nitrogen ratio is not increased, the partial pressure of CO is large, and decarburization is suppressed.
At a temperature of 1650 ℃ or higher, the carbon content of the molten steel is low, and when pure oxygen is used for blowing, the proportion of oxygen for decarburization is relatively low, and most of oxygen oxidizes chromium, iron and the like in the molten steel, so that iron oxide in slag is increased, and manganese in the molten steel is further oxidized or burned. Therefore, when the temperature is higher than 1650 ℃, pure oxygen blowing can cause oxidation burning loss of metal, and the metal yield is reduced.
In the above method for smelting 200 series stainless steel in an AOD furnace, in the step (3), the decarburization temperature reaches 1630 ℃ and the ratio of oxygen to inert gas is 2:1 as a preferred embodiment; the decarburization temperature reaches 1650 ℃, and the ratio of oxygen to inert gas volume is 1:1; the decarburization temperature reaches 1670 ℃, and the ratio of oxygen to inert gas volume is 1:2; the decarburization temperature reaches 1680 ℃, and the ratio of oxygen to inert gas volume is 1:4; preferably, after decarburization, the temperature of the molten steel is 1650-1685 ℃ (for example 1655 ℃, 1660 ℃, 1665 ℃, 1670 ℃, 1675 ℃ and 1680 ℃), slag in the furnace is piled up, and a slag former is added to the molten steel when the piled slag does not meet the requirement; preferably, in step (3), the slag basicity, i.e. CaO/SiO in the slag 2 The mass fraction ratio is more than or equal to 3.5.
In the invention, after decarburization is finished, the terminal carbon content can be reduced to below 0.1wt% when the temperature of the molten steel is detected to be in the range of 1650-1685 ℃. The slag pile reaches the requirement, and the reaction decarburization is normal, and the metal oxide is less.
In the above method for smelting 200-series stainless steel in an AOD furnace, as a preferred embodiment, the slag former in step (1), step (2) and step (3) is lime; preferably, the amount of slag former used in step (1) is from 35 to 45kg/t (e.g. 37.5kg/t, 40kg/t, 42.5 kg/t); preferably, the amount of slag former used in step (2) is 30 to 40kg/t (e.g. 31kg/t, 32kg/t, 33kg/t, 34kg/t, 35kg/t, 36kg/t, 37kg/t, 38kg/t, 39 kg/t); preferably, the amount of slag former used in step 3 is 25 to 35kg/t (e.g., 26kg/t, 27kg/t, 28kg/t, 29kg/t, 30kg/t, 31kg/t, 32kg/t, 33kg/t, 34 kg/t).
In the invention, the problem of selective oxidation of manganese and carbon exists in the molten steel of an AOD furnace. In order to ensure that carbon is oxidized in preference to manganese and achieve the effect of decarbonizing and preserving manganese, the temperature of a molten pool after high-carbon ferromanganese is charged into a furnace is higher than the oxidation conversion temperature of carbon and manganese. In a preferred embodiment of the invention, the addition conditions of the high-carbon ferromanganese and the oxygen supply system are further combined: high-carbon ferromanganese is added when the temperature of the molten pool is increased to 1600-1630 ℃, the air supply proportion is adjusted, the oxidation and burning loss of terminal manganese are reduced, and the decarburization time is shortened.
In the above method for smelting 200-series stainless steel in an AOD furnace, in a preferred embodiment, in the step (4), the reducing agent is a silicomanganese alloy; preferably, the silicomanganese alloy is at least one of high silicomanganese, medium silicomanganese and common silicomanganese; preferably, the silicon-manganese alloy is used in an amount of 70 to 95kg/t (e.g., 75kg, 80kg, 85kg, 90 kg).
In the preferred embodiment of the invention, the dosage of the silicon-manganese alloy is 70-95 kg, and the silicon in the silicon-manganese alloy has three purposes, namely, the silicon-manganese alloy is mainly used for reducing oxides of chromium, manganese, iron and the like oxidized in the oxidation period, so that the metal yield is improved; secondly, according to the temperature control requirement, oxygen is sent to oxidize a part of silicon to increase the temperature of molten steel; thirdly, part of silicon in the silicon-manganese alloy is consumed by oxygen supply and temperature rise, part of the silicon is consumed by reduction oxide, and the rest of silicon is remained in molten steel for alloying. The silicon content in the 200 series stainless steel molten steel is required to be 0.3-0.7%, so that the silicon in the silicon-manganese alloy needs to be comprehensively considered to be alloyed by proper amount after being heated and reduced. When the amount of the added silicon-manganese alloy is small, the insufficient silicon possibly causes no reduction of oxides in the silicon-free slag due to no silicon, chromium and manganese oxides are wasted, the yield is low, the silicon content in molten steel is lower than 0.3%, and the components are unqualified; if the silicon content is excessive, and the silicon content in the molten steel exceeds 0.7%, so that the components are out of specification.
In the above method for smelting 200 series stainless steel in an AOD furnace, as a preferred embodiment, in the step (4), oxygen is introduced for blowing for 1 to 4 minutes; preferably, the nitrogen is introduced for blowing for 5-7 min; preferably, the time of blowing in argon is 2-4 min.
In the above-mentioned method for smelting 200-series stainless steel in an AOD furnace, as a preferred embodiment, in the step (4), the slag basicity, that is, caO/SiO in the slag 2 The mass fraction ratio is controlled to be 1.8-2.4 (for example, 1.9, 2.0, 2.1, 2.2 and 2.3); preferably, the slag former is at least one of fluorite balls, fluorite ores and ferrosilicon; preferably, the slag former is fluorite balls; preferably, the fluorite balls are used in an amount of 18 to 22kg/t (e.g., 19kg/t, 20kg/t, 21 kg/t); preferably, the temperature of the reducing agent after all of it is charged into the furnace is controlled to 1550-1600 ℃ (e.g. 1560 ℃, 1570 ℃, 1580 ℃, 1590 ℃); preferably, when the slag is discharged, the slag in the AOD furnace is completely liquefied and has fluidity, and the slag is taken out to be observed to be off-white or white; preferably, the tapping temperature is 1530 ℃ or higher.
In the preferred embodiment of the invention, the reduction stage promotes the reduction of manganese oxide through alkalinity control, temperature control and charging control, thereby improving the yield of manganese and realizing the purposes of improving the consumption of high-carbon ferromanganese by AOD and reducing the consumption of electrolytic manganese. Adopting silicon-manganese alloy as a reducing agent, reducing chromium, manganese and other oxides in a furnace by using silicon in the alloy, removing impurities, feeding oxygen, burning silicon, heating for 1-4 minutes, and controlling the temperature of a molten pool to be 1550-1600 ℃ after all the raw materials are fed into the furnace; stopping oxygen supply, switching nitrogen to reduce for 5-7 min, making the slag in the furnace be completely liquefied and have fluidity, taking slag to observe slag color ash or white slag, and discharging slag. Argon is reduced for 2-4 minutes, the temperature is controlled to be more than 1530 ℃, and tapping is carried out. The manganese yield reaches more than 93 percent.
The beneficial effects are that:
the method is suitable for smelting 200-series stainless steel in an AOD furnace, can improve the dosage of high-carbon ferromanganese to 40-70 kg/t, controls the smelting time to be less than or equal to 125min, and meets the requirement of the AOD furnace on large-scale production of 200-series stainless steel by using high-carbon ferromanganese.
The invention can increase the dosage of high-carbon ferromanganese, effectively realize the purposes of reducing the cost and improving the quality of smelting stainless steel, and has important significance for guiding the mass production of 200 series stainless steel.
Detailed Description
The invention is further described in connection with the following detailed description, which is not intended to limit the scope of the invention.
The main components of the silicon-manganese alloy used in the embodiment of the invention are as follows by weight percent:
high silicon manganese: 0.20% of C, 61% of Mn, 28% of Si, 0.10% of P, and the balance of iron and unavoidable impurities; medium silicon manganese: 0.90% of C, 65% of Mn, 20% of Si, 0.10% of P, and the balance of iron and unavoidable impurities. Silicon-manganese: 1.50% of C, 65% of Mn, 18% of Si, 0.18% of P, and the balance of iron and unavoidable impurities.
The high-carbon ferromanganese used in the embodiment of the invention comprises the following components in percentage by weight: c7%, manganese 71%, phosphorus 0.16%, sulfur 0.01%, silicon 0.35%, the balance being iron and unavoidable impurities.
The high-carbon ferrochrome used in the embodiment of the invention comprises the following components in percentage by weight: c7.4%, chromium 52%, silicon 3.5%, phosphorus 0.022%, sulfur 0.029%, the balance being iron and unavoidable impurities.
The% not specifically described in the following examples is mass%.
Example 1
The 200 series steel grade smelted in the embodiment has the following composition requirements: 0.11 to 0.16 percent of C, 0.3 to 0.7 percent of silicon, 13.0 to 13.4 percent of chromium, 9.70 to 10.5 percent of manganese, 1.0 to 1.8 percent of nickel, less than 0.05 percent of phosphorus and less than 0.005 percent of sulfur.
(1) The AOD furnace is added into blast furnace molten iron for 56 tons, and the molten iron comprises the following components: 4.5% of C, 0.85% of silicon, 4.32% of chromium, 1.23% of manganese, 1.46% of nickel, 0.04% of phosphorus, 0.13% of sulfur and 0.035% of copper, 40kg/t of lime is added to obtain the oxygen: nitrogen is 6:1 to the oxygen consumption of 1300m 3 When the temperature reaches 1603 ℃, adding 15 tons of high-carbon ferrochrome (52 wt% of chromium content) into the molten steel, and adjusting the components of the molten steel to be: 3.02% of C, 0.011% of silicon, 13.76% of chromium, 0.76% of manganese, 0.031% of copper, 1.23% of nickel, 0.039% of phosphorus and 0.076% of sulfur. The same gas proportion blowing is continued until the oxygen consumption is 2260m 3 (the temperature reaches 1511 ℃) and slag skimming operation is carried out, the fluidity of slag is 0.2 Pa.S when slag skimming is carried out, no agglomerate is formed on the surface of slag, and the thickness of a slag layer is detected to be about 25mm after slag skimming is finished.
(2) And (3) adding 40kg/t of lime after slag is removed, carrying out top-bottom combined blowing by adopting an AOD furnace top gun and a side gun to send oxygen at the same time, quickly heating to 1620 ℃, and adding 56kg/t of high-carbon ferromanganese.
(3) Continuously heating, wherein the decarburization temperature reaches 1641 ℃, and the ratio of oxygen to inert gas is 2:1; the decarburization temperature reaches 1655 ℃, the ratio of oxygen to inert gas is 1:1, and 27kg/t of lime is added; the decarburization temperature reaches 1671 ℃, and the ratio of oxygen to inert gas is 1:2; the decarburization temperature reached 1683℃and the ratio of oxygen to inert gas was 1:4. The carbon content of the molten steel was measured to be 0.08%, and the temperature of the molten steel was 1681 ℃.
(4) 60kg/t of high silicon manganese, 13kg/t of common silicon manganese, 22kg/t of fluorite balls, 2 minutes of oxygen, 7 minutes of nitrogen and slag discharge are added; the temperature of molten steel is measured at 1575 ℃, the components of the molten steel are detected, and after 4.12kg/t electrolytic manganese is added, the components of the molten steel are as follows: 0.11% of C, 0.46% of silicon, 13.23% of chromium, 9.75% of manganese, 1.10% of nickel, 0.046% of phosphorus and 0.002% of sulfur, tapping by feeding argon for 3 minutes, and finishing smelting in 116 minutes by the furnace.
The unit consumption of electrolytic manganese is reduced to 4.12kg/t, the manganese yield is 94.22%, and smelting is completed within 125 minutes, which indicates that the smelting of the furnace steel for improving the dosage of high-carbon ferromanganese is successful.
Example 2
The 200 series steel grade smelted in the embodiment has the following composition requirements: 0.10 to 0.13 percent of C, 0.3 to 0.7 percent of silicon, 13.5 to 14 percent of chromium, 9.50 to 10.2 percent of manganese, 1.0 to 1.8 percent of nickel, less than 0.05 percent of phosphorus and less than 0.005 percent of sulfur.
(1) The AOD furnace is added into blast furnace molten iron for 56 tons, and the molten iron comprises the following components: 4.7% of C, 0.96% of silicon, 4.01% of chromium, 1.03% of manganese, 1.43% of nickel, 0.040% of phosphorus, 0.13% of sulfur and 0.034% of copper, 40kg/t of lime is added to obtain the alloy with oxygen: nitrogen is 6:1 to oxygen consumption of 1210m 3 When the temperature reaches 1586 ℃, adding 15.3 tons of high-carbon ferrochrome (52%) and adjusting the components of molten steel to be: 2.78% of C, 0.08% of silicon, 13.95% of chromium, 0.69% of manganese, 0.032% of copper, 1.25% of nickel, 0.038% of phosphorus and 0.056% of sulfur. The same gas proportion blowing is continued until the oxygen consumption is 2360m 3 (the temperature reaches 1533 ℃) and slag skimming operation is carried out, the fluidity of slag is 0.3 Pa.S when skimming, no agglomerate is formed on the surface of slag, and the thickness of a slag layer is detected to be about 16mm after the slag skimming is finished.
(2) And (3) adding 40kg/t of lime after slag is removed, carrying out top-bottom combined blowing by adopting an AOD furnace top gun and a side gun to send oxygen at the same time, quickly heating to 1622 ℃, and adding 47kg/t of high-carbon ferromanganese.
(3) Continuously heating, wherein the decarburization temperature reaches 1635 ℃, and the ratio of oxygen to inert gas is 2:1; the decarburization temperature reaches 1656 ℃, the ratio of oxygen to inert gas is 1:1, and 26kg/t of lime is added; after the decarburization temperature reaches 1673 ℃, the ratio of oxygen to inert gas is 1:2; after the decarbonization temperature reached 1685 ℃, the ratio of oxygen to inert gas was 1:4. The carbon content of the molten steel is detected to be 0.07 percent, and the temperature of the molten steel is 1679 ℃.
(4) Adding 33kg/t of high silicon manganese, 60kg/t of common silicon manganese, 20kg/t of fluorite balls, feeding oxygen for 2 minutes, feeding nitrogen for 7 minutes, and discharging slag; the temperature of molten steel is measured at 1578 ℃, and the components of the detected molten steel are as follows: 0.12% of C, 0.52% of silicon, 13.64% of chromium, 9.85% of manganese, 1.08% of nickel, 0.048% of phosphorus and 0.002% of sulfur, and the furnace is used for finishing smelting in 112 minutes after feeding argon and stirring for 3 minutes without supplementing electrolytic manganese.
The unit consumption of electrolytic manganese is reduced to 0kg/t, the manganese yield is 94.01%, and smelting is completed within 125 minutes, which shows that the smelting of the furnace steel for improving the dosage of high-carbon ferromanganese is successful.
Example 3
The 200 series steel grade smelted in the embodiment has the following composition requirements: 0.11 to 0.16 percent of C, 0.3 to 0.7 percent of silicon, 13.0 to 13.4 percent of chromium, 9.70 to 10.5 percent of manganese, 1.0 to 1.8 percent of nickel, less than 0.05 percent of phosphorus and less than 0.005 percent of sulfur.
(1) The AOD furnace is added with 57 tons of blast furnace molten iron, and the molten iron comprises the following components: 5.1% of C, 0.79% of silicon, 3.96% of chromium, 1.24% of manganese, 1.45% of nickel, 0.038% of phosphorus, 0.09% of sulfur and 0.035% of copper, 43kg/t of lime is added to the mixture, and oxygen is used: nitrogen is 6:1 to the oxygen consumption 1169m 3 When the temperature reaches 1598 ℃, 16.1 tons of high-carbon ferrochrome (52%) is added, and the components of the molten steel are adjusted to be: 3.31 percent of C, 0.13 percent of silicon, 13.67 percent of chromium, 0.77 percent of manganese, 0.032 percent of copper, 1.26 percent of nickel, 0.037 percent of phosphorus and 0.046 percent of sulfur. The same gas proportion blowing is continued until the oxygen consumption is 2280m 3 (the temperature reaches 1523 ℃), slag skimming operation is carried out, the fluidity of slag is 0.2 Pa.S when skimming, no agglomerate is formed on the surface of slag, and the thickness of a slag layer is detected to be about 15mm after the completion of slag skimming.
(2) And (3) adding 40kg/t of lime after slag is removed, carrying out top-bottom combined blowing by adopting an AOD furnace top gun and a side gun to send oxygen at the same time, quickly heating to 1628 ℃, and adding 53kg/t of high-carbon ferromanganese.
(3) Continuously heating, wherein the decarburization temperature reaches 1639 ℃, and the ratio of oxygen to inert gas is 2:1; the decarburization temperature reaches 1652 ℃, the ratio of oxygen to inert gas is 1:1, and 26kg/t of lime is added; after the decarburization temperature reaches 1671 ℃, the ratio of oxygen to inert gas is 1:2; after the decarbonization temperature reached 1681 ℃, the ratio of oxygen to inert gas was 1:4. The carbon content of the molten steel is detected to be 0.08 percent, and the temperature of the molten steel is 1679 ℃.
(4) Adding 91kg/t of medium silicon-manganese, 21kg/t of fluorite balls, feeding oxygen for 2 minutes, feeding nitrogen for 7 minutes, and discharging slag; the temperature of molten steel is measured at 1578 ℃, and the components of the detected molten steel are as follows: 0.12% of C, 0.36% of silicon, 13.16% of chromium, 9.91% of manganese, 1.05% of nickel, 0.044% of phosphorus and 0.001% of sulfur, and the furnace is used for completing smelting in 117 minutes after feeding argon and stirring for 3 minutes without supplementing electrolytic manganese.
The unit consumption of electrolytic manganese is reduced to 0kg/t, the manganese yield is 93.11 percent, and smelting is completed within 125 minutes, which indicates that the smelting of the furnace steel for improving the dosage of high-carbon ferromanganese is successful.
Comparative example 1
The composition requirements of the 200 series steel grade smelted in the comparative example are as follows: 0.11 to 0.16 percent of C, 0.3 to 0.7 percent of silicon, 13.0 to 13.4 percent of chromium, 9.70 to 10.5 percent of manganese, 1.0 to 1.8 percent of nickel, less than 0.05 percent of phosphorus and less than 0.005 percent of sulfur.
(1) The AOD furnace is added with 57 tons of blast furnace molten iron, and the molten iron comprises the following components: c5%, silicon 0.92%, chromium 4.23%, manganese 1.08%, nickel 1.41%, phosphorus 0.042%, sulfur 0.16%, copper 0.036%, lime 40kg/t, oxygen: nitrogen is 6:1 to oxygen consumption of 1600m 3 When the temperature reaches 1615 ℃, 15.3 tons of high-carbon ferrochrome (52%) is added, and the components of the molten steel are adjusted to be: 2.35% of C, 0.16% of silicon, 13.66% of chromium, 0.65% of manganese, 0.031% of copper, 1.22% of nickel, 0.040% of phosphorus and 0.053% of sulfur, and the same gas proportion is continuously blown until the oxygen consumption reaches 2560m 3 And (the temperature reaches 1566 ℃) for slag skimming, wherein the fluidity of slag is 0.35 Pa.S when slag skimming, no agglomerate is formed on the surface of slag, and the thickness of a slag layer is detected to be about 50mm after slag skimming is finished.
(2) And (3) adding 40kg/t of lime after slag skimming, carrying out top-bottom combined blowing by adopting an AOD furnace top gun and a side gun to send oxygen at the same time, quickly heating to 1613 ℃, and adding 60kg/t of high-carbon ferromanganese.
(3) Continuously heating, and after the decarburization temperature reaches 1630 ℃, enabling the ratio of oxygen to inert gas to be 2:1; after the decarburization temperature reaches 1650 ℃, the ratio of oxygen to inert gas is 1:1, and 26.67kg/t of lime is added; after the decarburization temperature reaches 1670 ℃, the ratio of oxygen to inert gas is 1:2; after the decarburization temperature reached 1680 ℃, the ratio of oxygen to inert gas was 1:4. The carbon content of the molten steel is detected to be 0.10 percent, and the temperature of the molten steel is 1723 ℃.
(4) 66.67kg/t of high silicon manganese, 13.33kg/t of common silicon manganese, 20kg/t of fluorite ball, 1 minute of oxygen, 7 minutes of nitrogen and slag discharge are added; molten steel temperature measurement 1618 ℃, molten steel composition: 0.12% of C, 0.56% of silicon, 13.03% of chromium, 9.25% of manganese, 1.13% of nickel, 0.049% of phosphorus and 0.003% of sulfur, 400kg of electrolytic manganese is added, argon is fed, stirring is carried out for 3 minutes, and tapping is carried out, so that smelting is completed in 135 minutes.
Because the slag raking amount does not reach the standard, the decarburization efficiency is low, the heat release amount of the metal oxidation is high seriously, the molten steel temperature is too high after the decarburization is finished, the smelting time is over 125 minutes, and meanwhile, the manganese yield is 91.3%, which indicates that the smelting of the furnace steel for improving the high-carbon ferromanganese consumption is unsuccessful.
Comparative example 2
The composition requirements of the 200 series steel grade smelted in the comparative example are as follows: 0.11 to 0.16 percent of C, 0.3 to 0.7 percent of silicon, 13.0 to 13.4 percent of chromium, 9.70 to 10.5 percent of manganese, 1.0 to 1.8 percent of nickel, less than 0.05 percent of phosphorus and less than 0.005 percent of sulfur.
(1) Adding 58 tons of blast furnace molten iron into an AOD furnace, wherein the molten iron comprises the following components: c5.11%, si 0.66%, cr 3.85%, mn 0.96%, ni 1.41%, p 0.038%, s 0.15%, cu 0.034%, lime 40kg/t, oxygen: nitrogen is 6:1 to the oxygen consumption 1309m 3 When the temperature reaches 1589 ℃, 15.5 tons of high-carbon ferrochrome (52%) is added, and the components of the molten steel are adjusted to be: 3.35 percent of C, 0.09 percent of silicon, 13.75 percent of chromium, 0.72 percent of manganese, 0.032 percent of copper, 1.22 percent of nickel, 0.041 percent of phosphorus and 0.063 percent of sulfur, and the same gas proportion is continuously blown until the oxygen consumption is 2360m 3 And (the temperature reaches 1522 ℃) to carry out slag skimming operation, wherein the fluidity of slag is 0.25 Pa.S when slag skimming, no agglomerate is formed on the surface of slag, and the thickness of a slag layer is detected to be about 20mm after slag skimming is finished.
(2) And (3) adding 40kg/t of lime after slag skimming, carrying out top-bottom combined blowing by adopting an AOD furnace top gun and a side gun to send oxygen at the same time, quickly heating to 1613 ℃, and adding 53.33kg/t of high-carbon ferromanganese.
(3) Continuously heating, wherein the decarburization temperature reaches 1639 ℃, and the ratio of oxygen to inert gas is 2:1; after the decarburization temperature reaches 1650 ℃, the ratio of oxygen to inert gas is 1:1, and 26.67kg/t of lime is added; after the decarburization temperature reaches 1691 ℃, the ratio of oxygen to inert gas is 1:2; after the decarburization temperature reached 1708 ℃, the ratio of oxygen to inert gas was 1:4. The carbon content of the molten steel is detected to be 0.09%, and the temperature of the molten steel is 1709 ℃.
(4) 26.67kg/t of high silicon manganese, 66.67kg/t of common silicon manganese and 18.67kg/t of fluorite balls are added, oxygen is fed for 1 minute, nitrogen is fed for 7 minutes, and slag is discharged; molten steel temperature measurement 1623 ℃, molten steel composition: c0.14%, si 0.59%, cr 13.03%, mn 9.05%, ni 1.06%, P0.047% and S0.002%, 600kg of electrolytic Mn is added, argon is fed, stirring is carried out for 3 minutes, and tapping is carried out, and smelting is completed in 138 minutes.
Because the temperature of the molten pool at the later stage of decarburization reaches 1670 ℃, the oxygen supply proportion is adjusted to be larger, and excessive oxygen oxidizes metal in molten steel, so that the metal is seriously oxidized, the smelting time exceeds 125 minutes, and meanwhile, the manganese yield is 90.2%, which indicates that the smelting of the furnace steel for improving the consumption of high-carbon ferromanganese is unsuccessful.
Comparative example 3
The composition requirements of the 200 series steel grade smelted in the comparative example are as follows: 0.11 to 0.16 percent of C, 0.3 to 0.7 percent of silicon, 13.0 to 13.4 percent of chromium, 9.70 to 10.5 percent of manganese, 1.0 to 1.8 percent of nickel, less than 0.05 percent of phosphorus and less than 0.005 percent of sulfur.
(1) Substantially the same as in example 1, except that 56kg/t of high carbon ferromanganese in the step (2) was charged into the furnace together with 40kg/t of lime (at a bath temperature of 1511 ℃) after slag skimming.
(2) Continuously heating, wherein the decarburization temperature reaches 1641 ℃, and the ratio of oxygen to inert gas is 2:1; the decarburization temperature reaches 1655 ℃, the ratio of oxygen to inert gas is 1:1, and 27kg/t of lime is added; the decarburization temperature reaches 1671 ℃, and the ratio of oxygen to inert gas is 1:2; the decarburization temperature reached 1683℃and the ratio of oxygen to inert gas was 1:4. At this time, the carbon content of the molten steel was measured at 0.18% and the temperature of the molten steel at 1685 ℃. At this time, the slag pile in the furnace does not meet the requirement, the slag pile is flatly paved, lime 9kg/t is added, the ratio of oxygen to inert gas is 1:4, after blowing for 11 minutes, the carbon content of molten steel is detected to be 0.09%, and the temperature of molten steel is 1675 ℃.
(3) 60kg/t of high silicon manganese, 13kg/t of common silicon manganese, 22kg/t of fluorite balls, 2 minutes of oxygen, 7 minutes of nitrogen and slag discharge are added; the temperature of molten steel is measured at 1596 ℃, the components of the molten steel are detected, and after 7.30kg/t electrolytic manganese is added, the components of the molten steel are as follows: 0.13% of C, 0.42% of silicon, 13.12% of chromium, 9.79% of manganese, 1.09% of nickel, 0.048% of phosphorus and 0.002% of sulfur, and tapping after 3 minutes of argon feeding, the furnace finishes smelting in 133 minutes.
The unit consumption of electrolytic manganese is increased to 7.30kg/t, the manganese yield is 91.02 percent, and smelting is completed after 125 minutes, which indicates that the smelting of the furnace steel for improving the consumption of high-carbon ferromanganese is unsuccessful.
Comparative example 4
The composition requirements of the 200 series steel grade smelted in the comparative example are as follows: 0.11 to 0.16 percent of C, 0.3 to 0.7 percent of silicon, 13.0 to 13.4 percent of chromium, 9.70 to 10.5 percent of manganese, 1.0 to 1.8 percent of nickel, less than 0.05 percent of phosphorus and less than 0.005 percent of sulfur.
(1) substantially the same as in example 3 except that 53kg/t of high carbon ferromanganese in the step (2) was delayed until the decarburization temperature in the step (3) was reached to 1681℃and then added. According to the procedure of example 3, 53kg/t of high-carbon ferromanganese was added after the decarburization temperature had reached 1681℃and the ratio of oxygen to inert gas was 1:4. After 7 minutes of blowing, the carbon content of the molten steel is detected to be 0.07 percent, and the temperature of the molten steel is 1661 ℃.
(2) Adding 91kg/t of medium silicon-manganese, 21kg/t of fluorite balls, feeding oxygen for 2 minutes, feeding nitrogen for 7 minutes, and discharging slag; the temperature of molten steel is measured at 1548 ℃, and the components of the detected molten steel are as follows: 0.28% of C, 0.62% of silicon, 13.16% of chromium, 9.97% of manganese, 1.05% of nickel, 0.046% of phosphorus and 0.001% of sulfur.
The furnace steel high-carbon ferromanganese is added too late, the furnace steel high-carbon ferromanganese is not completely melted down, the carbon content is detected to be 0.07% in the step (3), when the reducing agent is added into the furnace, after the slag is melted, the high-carbon ferromanganese which is not melted down enters molten steel, the carbon brought by the high-carbon ferromanganese leads to the terminal carbon content exceeding 0.12%, the carbon component is unqualified, the molten steel is scrapped, and the furnace is returned for treatment. The furnace steel is proved to be unsuccessful in smelting by increasing the dosage of high-carbon ferromanganese.
Finally, it should be noted that the foregoing is merely a preferred embodiment of the present invention, and the present invention is not limited thereto, and although the present invention has been described in detail with reference to the embodiment, it will be apparent to those skilled in the art that modifications may be made to the technical solutions described in the foregoing embodiments, or equivalents may be substituted for some of the technical features thereof, but any modifications, equivalents, improvements or changes thereof may be made without departing from the spirit and principle of the present invention.
Claims (33)
1. A method for smelting 200 series stainless steel by an AOD furnace, which is characterized by comprising the following steps in sequence:
(1) Primary slag skimming: adding molten iron and a slag former into an AOD furnace for converting, heating to 1580-1620 ℃, adding high-carbon ferrochrome for continuous converting, and carrying out slag skimming when the temperature of molten steel is 1510-1580 ℃;
(2) Adding high-carbon ferromanganese: adding a slag former after slag skimming, heating to 1600-1630 ℃, and adding high-carbon ferromanganese into molten steel according to the amount of more than or equal to 40 kg/t;
(3) Decarburizing and preserving manganese: controlling the decarburization temperature to be 1630-1685 ℃, wherein the decarburization gas is oxygen and inert gas, reducing the oxygen content in the decarburization gas along with the increase of the decarburization temperature, wherein the initial oxygen content in the decarburization gas is 60-100% by volume percent, after the temperature reaches 1650 ℃, reducing the oxygen content in the decarburization gas, wherein the final oxygen content is 18-23%, and ending decarburization when the C content in the molten steel is lower than 0.1 wt%;
(4) And (3) reduction: adding a reducing agent and a slag former, sequentially introducing oxygen and nitrogen for blowing, deslagging, detecting the temperature and components of molten steel, adjusting the components of the molten steel according to the requirements of the components of target steel types, introducing argon for blowing, and tapping; if the manganese content in the molten steel is lower than the component requirement of the target steel grade, the electrolytic manganese is supplemented to adjust the manganese content in the molten steel so as to enable the molten steel to meet the component requirement of the target steel grade;
the smelting time of the method for smelting 200-series stainless steel by the AOD furnace is less than or equal to 125 minutes.
2. The method for producing 200-series stainless steel by AOD furnace according to claim 1, wherein in the step (1), the molten iron is blast furnace molten iron, and the charging temperature of the blast furnace molten iron is 1250 to 1350 ℃.
3. The method for AOD furnace smelting 200 series stainless steel according to claim 2, wherein the composition of the blast furnace molten iron is as follows in weight percent: 4% -6% of C, 0.5% -1.5% of silicon, 3% -5% of chromium, 0.5% -2.0% of manganese, 0.03% -0.04% of copper, 1.3% -1.8% of nickel, less than 0.05% of phosphorus, less than 0.2% of sulfur and the balance of Fe and unavoidable impurities.
4. The method for producing 200-series stainless steel by AOD furnace according to claim 1, wherein in the step (1), after adding high carbon ferrochrome, the composition of molten steel is adjusted in weight percent: 2% -4% of C, 0% -0.2% of silicon, 13.5% -15% of chromium, 0.2% -1.5% of manganese, 0.03% -0.04% of copper, 1.1% -1.6% of nickel, less than 0.05% of phosphorus, less than 0.15% of sulfur and the balance of Fe and unavoidable impurities.
5. The method for smelting 200-series stainless steel by an AOD furnace according to claim 1, wherein in the step (1), the gas used for blowing is a mixed gas of oxygen and nitrogen in a volume ratio of 6:1, and the oxygen pressure is 1.7-1.8 mpa.
6. The method for producing 200-series stainless steel by AOD furnace according to claim 1, wherein in the step (1), the temperature is 1520-1580 ℃.
7. The method for smelting 200-series stainless steel in an AOD furnace according to claim 1, wherein the slag fluidity during slag skimming is 0.1 to 0.4pa·s, and the slag surface is free from agglomerates.
8. The method for producing 200 series stainless steel by AOD furnace according to claim 1, wherein the amount of skimming is 80% or more.
9. The method for AOD furnace smelting 200 series stainless steel according to claim 1, wherein the thickness of the slag layer in the furnace after slag skimming is less than 30mm.
10. The method for producing a 200-series stainless steel by AOD furnace according to claim 1, wherein in the step (2), the temperature is raised by simultaneously feeding oxygen to the AOD furnace top lance and the side lance.
11. The method for producing 200-series stainless steel by AOD furnace according to claim 1, wherein in the step (2), the time for heating to 1600-1630 ℃ is 8min or less.
12. The method of claim 11, wherein in step (2), the time for heating to 1600 to 1630 ℃ is 6 to 8 minutes.
13. The method for smelting 200-series stainless steel by an AOD furnace according to claim 1, wherein the amount of high-carbon ferromanganese is 40-70 kg/t.
14. The method for producing a stainless steel 200 by AOD furnace according to claim 1, wherein in the step (3), the inert gas is nitrogen or argon.
15. The method of AOD furnace smelting 200 series stainless steel according to claim 14, wherein the nitrogen is steelmaking nitrogen.
16. The method for producing a stainless steel 200 by AOD furnace according to claim 1, wherein in the step (3), oxygen and inert gas are blown into the decarburization and manganese-keeping step by using a side lance.
17. The method for producing 200-series stainless steel by AOD furnace according to claim 1, wherein in the step (3), the ratio of oxygen to inert gas is (0.8-1.2) 1 after the decarburization temperature reaches 1650-1660 ℃; after the decarburization temperature reaches 1670-1675 ℃, the ratio of oxygen to inert gas volume is 1 (1.8-2.2); after the decarburization temperature reaches 1680-1685 ℃, the ratio of oxygen to inert gas volume is 1 (3.8-4.2).
18. The method for AOD furnace smelting 200 series stainless steel according to claim 1, wherein in the step (3), the decarburization temperature reaches 1630 ℃, and the ratio of oxygen to inert gas is 2:1; the decarburization temperature reaches 1650 ℃, and the ratio of oxygen to inert gas volume is 1:1; the decarburization temperature reaches 1670 ℃, and the ratio of oxygen to inert gas volume is 1:2; the decarburization temperature reached 1680℃and the ratio of oxygen to inert gas volume was 1:4.
19. The method for producing 200-series stainless steel by AOD furnace according to claim 1, wherein in the step (3), slag in the furnace is piled up at a temperature of 1650 ℃ to 1685 ℃ and a slag former is added to the molten steel when the piled slag does not meet the requirement.
20. The method for smelting 200-series stainless steel by an AOD furnace according to claim 19, wherein the slag former is lime in an amount of 25 to 35kg/t.
21. The method for producing 200-series stainless steel by AOD furnace according to claim 1, wherein in the step (3), the basicity of slag, that is, caO/SiO in slag 2 The mass fraction ratio is more than or equal to 3.5.
22. The method of AOD furnace smelting 200 series stainless steel according to claim 1, wherein the slag former in step (1) and step (2) is lime.
23. The method for smelting 200-series stainless steel by an AOD furnace according to claim 22, wherein the amount of the slag former used in the step (1) is 35 to 45kg/t; the consumption of the slag former in the step (2) is 30-40 kg/t.
24. The method of AOD furnace smelting 200 series stainless steel according to claim 1, wherein in step (4), the reducing agent is a silicomanganese alloy.
25. The method of AOD furnace smelting 200 series stainless steel according to claim 24, wherein the silicon-manganese alloy is at least one of high silicon-manganese, medium silicon-manganese and common silicon-manganese.
26. The method of claim 24, wherein the silicon-manganese alloy is used in an amount of 70-95 kg/t.
27. The method for smelting 200-series stainless steel by an AOD furnace according to claim 1, wherein in the step (4), oxygen is introduced for blowing for 1-4 min; blowing nitrogen for 5-7 min; and blowing argon for 2-4 min.
28. The method for producing 200-series stainless steel by AOD furnace according to claim 1, wherein in the step (4), the basicity of slag, that is, caO/SiO in slag 2 The mass fraction ratio is controlled to be 1.8-2.4.
29. The method for producing 200-series stainless steel according to claim 1, wherein in the step (4), the slag former is at least one of fluorite balls, fluorite ore, and ferrosilicon.
30. The method of AOD furnace smelting 200 series stainless steel according to claim 29, wherein the slag former is fluorite balls; the dosage of the fluorite balls is 18-22 kg/t.
31. The method for smelting 200-series stainless steel in an AOD furnace according to claim 1, wherein in the step (4), the temperature of the reducing agent after all the reducing agent is charged into the furnace is controlled to 1550-1600 ℃.
32. The method for producing 200-series stainless steel by AOD furnace according to claim 1, wherein in the step (4), the slag in the AOD furnace is completely liquefied and has fluidity when the slag is tapped, and the slag is taken out and observed to be off-white or white.
33. The method for producing a stainless steel of line 200 by AOD furnace according to claim 1, wherein in the step (4), the tapping temperature is 1530 ℃ or higher.
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