A method for deoxidizing nickel-chromium-iron alloy steel smelted by electroslag furnace

Abstract

The application provides a deoxidation method for smelting nickel-chromium-iron alloy steel in an electric slag furnace, and belongs to the field of steel smelting. The method comprises the following steps: before smelting in the electric slag furnace, electrically conductive bottom material is added to the bottom of the electric slag furnace; slagging agent is added to the electric slag furnace, and electric arc starting is performed, followed by melting and smelting; during smelting in the electric slag furnace, when the charging amount in the electric slag furnace is 35% to 45% of the target charging amount, aluminum-containing scrap steel is added to the electric slag furnace, the added mass of the aluminum-containing scrap steel is less than or equal to 200 kg, the mass fraction of aluminum elements in the aluminum-containing scrap steel is 2% to 6%, and then silicon-calcium blocks and crystalline silicon are added to the electric slag furnace; at the end of smelting in the electric slag furnace, tapping and casting are performed. By using aluminum-containing scrap steel, silicon-calcium blocks and crystalline silicon for combined deoxidation, unstable oxides such as FeO and Cr2O3 in the molten slag are reduced to stable oxides such as Al2O3 and SiO2, so that the oxygen in the molten steel is reduced, and the kinetics condition of the metallurgical reaction is strengthened, so that the oxygen content in the steel is reduced to 20PPm.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel smelting, and particularly relates to a deoxidation method for smelting nickel-chromium-iron alloy steel in an electroslag furnace. BACKGROUND

[0002] Nickel-chromium-iron alloy steel has excellent high-temperature and room-temperature mechanical properties, a maximum use temperature of 1200 DEG C, stable electrical resistivity, and a long service life, and is therefore widely used in the fields of industrial furnaces, metallurgy, machinery, etc.

[0003] In order to ensure that the product has high purity and does not contain bubble defects, the oxygen content of molten steel needs to be as low as possible when nickel-chromium-iron alloy steel is smelted in an electroslag furnace. At present, crystalline silicon is often used as a deoxidizer to remove oxygen in molten steel. However, there is no more active element than silicon in the preparation material of nickel-chromium-iron alloy steel, and a low-melting-point deoxidation product cannot be formed to be contained in the slag, and the high-melting-point solid part remains in the molten steel. Therefore, the oxygen content in the steel cannot be reduced to the ideal range. Therefore, it is urgent to develop a method that can have a good deoxidation effect in the metallurgical process. SUMMARY

[0004] The present application provides a deoxidation method for smelting nickel-chromium-iron alloy steel in an electroslag furnace, which uses aluminum-containing scrap steel, silicon-calcium blocks and crystalline silicon for combined deoxidation to solve the problem of poor deoxidation effect in the prior art.

[0005] In a first aspect, the present application provides a deoxidation method for smelting nickel-chromium-iron alloy steel in an electroslag furnace, which comprises:

[0006] Before smelting in the electroslag furnace, conductive bottom material is added to the bottom of the electroslag furnace;

[0007] The slag-making agent is added to the electroslag furnace, and electric arc is started, and then melting and smelting are performed;

[0008] In the smelting in the electroslag furnace, when the charging amount in the electroslag furnace is 35% to 45% of the target charging amount, aluminum-containing scrap steel is added to the electroslag furnace, the added mass of the aluminum-containing scrap steel is less than or equal to 200 kg, the mass fraction of aluminum in the aluminum-containing scrap steel is 2% to 6%, and then silicon-calcium blocks and crystalline silicon are added to the electroslag furnace;

[0009] At the end of the smelting in the electroslag furnace, molten steel is tapped and cast.

[0010] Optionally, the added mass of the silicon-calcium block is 3 kg / t of molten steel to 5 kg / t of molten steel, and the added mass of the crystalline silicon is 7.5 kg / t of molten steel to 9 kg / t of molten steel.

[0011] Optionally, in the electroslag furnace smelting, calcium silicate powder is added to the electroslag furnace in batches. The mass of each batch of calcium silicate powder added is 0.8 kg to 1.2 kg, the interval between adjacent batches is 4 min to 6 min, and the total mass of calcium silicate powder added is 4.5 kg / t molten steel to 5.5 kg / t molten steel.

[0012] Optionally, the slag-forming agent includes quicklime, fluorite, and aluminum oxide.

[0013] Optionally, the mass ratio of the slag-forming agent satisfies: fluorite: quicklime: aluminum oxide = (3-5):(2-4):(2-4), and the mass of the slag-forming agent added is 50 kg / t·molten steel to 60 kg / t·molten steel.

[0014] Optionally, the conductive substrate includes at least one of micro-carbon ferrochrome and nickel plate, the added mass of the conductive substrate is 50kg to 80kg, and the thickness of the conductive substrate is 80mm to 100mm.

[0015] Optionally, when the aluminum-containing scrap steel, the silicon-calcium powder, the silicon-calcium blocks, and the crystalline silicon are added, the slag in the electroslag furnace is stirred for 10 to 20 seconds.

[0016] Optionally, the size of the silicon-calcium block and the crystalline silicon is 40mm to 60mm, wherein the size is the maximum distance between the two ends of the silicon-calcium block and the crystalline silicon.

[0017] Optionally, the tapping temperature is 1560℃~1600℃.

[0018] The technical solutions provided in this application have the following advantages compared with the prior art:

[0019] This application utilizes a combined deoxidation process involving aluminum-containing scrap steel, calcium silicate blocks, and crystalline silicon to reduce unstable oxides such as FeO and Cr2O3 in the slag into stable oxides such as Al2O3 and SiO2, thereby lowering the oxygen content in the molten steel. Furthermore, by enhancing the kinetics of the metallurgical reaction, the dissolved oxygen content in the steel can be controlled to decrease to 20 ppm. In addition, using aluminum-containing scrap steel can save significant amounts of natural resources and energy.

[0020] In particular, this deoxidation method can produce non-metallic inclusions with larger composite particles that are easy to float, while also changing the shape and properties of the non-metallic inclusions, which can be used to produce high-value-added nickel-chromium-iron alloy steel. Attached Figure Description

[0021] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0022] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic flowchart of a deoxidation method for smelting nickel-chromium-iron alloy steel in an electroslag furnace, provided as an embodiment of this application. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0025] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0026] Furthermore, in the description of this application, the terms "comprising," "including," etc., mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.

[0027] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0028] Firstly, this application provides a deoxidation method for smelting nickel-chromium-ferroalloy steel in an electroslag furnace. Please refer to [link to relevant documentation]. Figure 1 The method includes:

[0029] S1. Before smelting in the electroslag furnace, add conductive bottom material to the bottom of the electroslag furnace.

[0030] In some embodiments, the conductive substrate includes at least one of micro-carbon ferrochrome and nickel plate, the added mass of the conductive substrate is 50 kg to 80 kg, and the thickness of the conductive substrate is 80 mm to 100 mm. Because the steel grade smelted in this invention is nickel-chromium-ferrochrome alloy steel, the conductive material is selected from one or a mixture of two of micro-carbon ferrochrome and nickel plate, and its addition amount is based on the alloy composition requirements to ensure successful conduction and arc initiation.

[0031] The added mass of the conductive base material can be 50kg, 55kg, 60kg, 70kg, 75kg, 80kg, etc., and the thickness of the conductive base material can be 80mm, 85mm, 90mm, 95mm, 100mm, etc.

[0032] S2. Add the slag-forming agent to the electroslag furnace, apply electricity to ignite the arc, and then melt and smelt.

[0033] This application does not add an arc-initiating agent, but directly adds a slag-forming agent to initiate the arc, thus saving resources.

[0034] In some embodiments, the slagging agent includes quicklime, fluorite, and aluminum oxide.

[0035] Quicklime is used for slag formation to adsorb inclusions in molten steel and improve its cleanliness. Fluorite improves slag fluidity and enhances inclusion adsorption. Adding alumina increases slag resistivity, thereby increasing slag calorific value and accelerating alloy melting. Simultaneously, adding alumina does not reduce slag basicity and reduces chemical corrosion of the alkaline furnace lining. The slag-forming agent is added by pre-mixing quicklime, fluorite, and alumina before adding them to the electroslag furnace.

[0036] In some embodiments, the mass ratio of the slag-forming agent satisfies: fluorite: quicklime: aluminum oxide = (3-5):(2-4):(2-4), and the mass of the slag-forming agent added is 50 kg / t·molten steel to 60 kg / t·molten steel.

[0037] In the embodiments of this application, the positive effects of controlling the ratio of fluorite: quicklime: alumina = (3-5):(2-4):(2-4) are: ensuring stable resistivity of the smelting slag, good slag fluidity, and good adsorption capacity for inclusions. The mass ratio of fluorite, quicklime, and alumina can be 3:2:2, 4:2:2, 3.5:3:3.5, 4.5:3:2.5, 4:3:3, 5:3:4, 5:3:2, 4:3:4, 4:4:4, etc. The slag usage in this smelting process can be 50 kg / t molten steel, 52 kg / t molten steel, 54 kg / t molten steel, 56 kg / t molten steel, 58 kg / t molten steel, 60 kg / t molten steel, etc.

[0038] S3. In the electroslag furnace smelting, when the amount of material added in the electroslag furnace is 35% to 45% of the target amount of material added, aluminum-containing scrap steel is added to the electroslag furnace. The mass of the aluminum-containing scrap steel added is ≤200kg, and the mass fraction of aluminum element in the aluminum-containing scrap steel is 2% to 6%. Then, silicon-calcium blocks and crystalline silicon are added to the electroslag furnace.

[0039] This application utilizes a combined deoxidation process involving aluminum-containing scrap steel, calcium silicate blocks, and crystalline silicon to reduce unstable oxides such as FeO and Cr2O3 in the slag into stable oxides such as Al2O3 and SiO2, thereby lowering the oxygen content in the molten steel. The addition of aluminum for combined deoxidation removes oxygen introduced from the nickel-chromium-iron alloy raw materials and inhibits the transfer of airborne oxygen into the molten steel pool via FeO.

[0040] During the smelting process, when the measured slag temperature was 1700℃~1720℃ and the molten steel temperature was 1500℃~1520℃, silicon-calcium alloy and aluminum-containing scrap steel were added for precipitation deoxidation. By controlling the slag temperature and the time of adding silicon-calcium alloy and aluminum-containing scrap steel, the kinetic conditions of the metallurgical reaction can be enhanced, and the dissolved oxygen level in the steel can be better controlled.

[0041] In this invention, aluminum-containing scrap steel, calcium silicate blocks, and crystalline silicon are successively added to the furnace for melting along with ferrochrome. During the charging process, frequent small additions are required to avoid arcing. Close observation of the slag melting process within the furnace is essential during smelting; frequent tamping is necessary to accelerate melting, and concentrated charging should be avoided.

[0042] Controlling the added mass of aluminum-containing scrap steel to ≤200kg, with an aluminum content of 2%–6%, has the following positive effects: ensuring a balanced hot-cold ratio in the electroslag metallurgical process and meeting the alloy composition requirements. The added mass of aluminum-containing scrap steel can be 50kg, 70kg, 90kg, 110kg, 150kg, 170kg, 200kg, etc., with aluminum content of 2%, 3%, 4%, 5%, 6%, etc.

[0043] In the embodiments of this application, the mass of the added calcium silicon block is 3 kg / t·molten steel to 5 kg / t·molten steel, and the mass of the added crystalline silicon is 7.5 kg / t·molten steel to 9 kg / t·molten steel.

[0044] Using calcium silicate blocks and crystalline silicon to incorporate silicon into steel serves two purposes: firstly, it acts as a precipitating deoxidizer, and secondly, it increases the silicon content in the steel. Calcium silicate block deoxidation is a precipitation-based deoxidation method, characterized by its rapid deoxidation speed. The resulting deoxidation products quickly aggregate and float to the slag layer, achieving the purpose of deoxidizing the molten steel.

[0045] The addition mass of the calcium silicate block can be 3 kg / t·molten steel, 3.5 kg / t·molten steel, 4 kg / t·molten steel, 4.5 kg / t·molten steel, 5 kg / t·molten steel, etc., and the addition mass of the crystalline silicon can be 7.5 kg / t·molten steel, 7.5 kg / t·molten steel, 8 kg / t·molten steel, 8.5 kg / t·molten steel, 9 kg / t·molten steel, etc.

[0046] In the embodiments of this application, during the electroslag furnace smelting, silicon-calcium powder is added to the electroslag furnace in batches. The mass of each batch of silicon-calcium powder added is 0.8 kg to 1.2 kg, the interval between adjacent batches is 4 min to 6 min, and the total mass of silicon-calcium powder added is 4.5 kg / t·molten steel to 5.5 kg / t·molten steel.

[0047] During the electroslag furnace smelting process, the reaction in the molten steel is difficult to reach equilibrium in a short time. Therefore, calcium silicate powder is added to the molten steel in batches for deoxidation to further enhance the deoxidation effect of the calcium silicate powder and make the deoxidation reaction more thorough.

[0048] The added mass of the calcium silicate powder in each batch is 0.8 kg, 0.9 kg, 1.0 kg, 1.1 kg, 1.2 kg, etc., and the interval between adjacent batches is 4 min, 4.5 min, 5 min, 5.5 min, 6 min, etc., and the total added mass of the calcium silicate powder is 4.5 kg / t·molten steel, 5 kg / t·molten steel, 5.5 kg / t·molten steel, etc.

[0049] In this embodiment of the application, when the aluminum-containing scrap steel, the silicon-calcium powder, the silicon-calcium block and the crystalline silicon are added, the slag in the electroslag furnace is stirred for 10s to 20s.

[0050] Stirring can carry oxygen atoms and oxide inclusions into the slag through inert gas bubbles, thereby reducing the oxygen content in the molten steel. The stirring time can be 10s, 12s, 14s, 16s, 18s, 20s, etc.

[0051] In the embodiments of this application, the size of the silicon-calcium block and the crystalline silicon is 40mm to 60mm, wherein the size is the maximum distance between the two ends of the silicon-calcium block and the crystalline silicon.

[0052] The size of the silicon-calcium block and the crystalline silicon block can be 40mm, 45mm, 50mm, 55mm, 60mm, etc.

[0053] S4. At the end of the electroslag furnace smelting, the steel is tapped and cast.

[0054] In this embodiment of the application, the tapping temperature is 1560℃~1600℃.

[0055] The positive effects of controlling the tapping temperature in smelting to 1560℃~1600℃ include: ensuring smooth casting while reducing alloy loss due to oxidation. If the tapping temperature is too high, it will accelerate the oxidation and loss of alloying elements to some extent. If the tapping temperature is too low, it may cause the molten steel to solidify during casting, clogging the runner and affecting the quality of the steel bars. Suitable tapping temperatures include 1560℃, 1570℃, 1580℃, 1590℃, and 1600℃.

[0056] The present application is further illustrated below with reference to specific embodiments and comparative examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments, unless otherwise specified, are generally performed according to national standards. If no corresponding national standard exists, then common international standards, standard conditions, or conditions recommended by the manufacturer are followed.

[0057] Example 1

[0058] Before electroslag smelting, 58 kg of metallic chromium with a thickness of 90 mm is added to the bottom of the electroslag furnace. A mixture of 29 kg of quicklime, 38 kg of fluorite, and 30 kg of alumina is added to the electroslag furnace, and an electric arc is ignited before melting and smelting. Starting at approximately 800 kg (target feed amount is 2000 kg), stirring is performed continuously, and the melting status of the raw materials at the bottom of the furnace is checked with a steel rake. After temperature measurement, 200 kg of aluminum-containing scrap steel with an aluminum content of 5% is added to the molten pool, and process parameters are adjusted according to the slag temperature and melting status. Stirring should avoid causing magnesia to fall off. When 1000 kg has been smelted, SiCa powder is added to the electroslag furnace in batches of 1 kg each, with an interval of 5 minutes between adjacent batches, for a total addition of 5.0 kg / t of molten steel. Calcium silicate blocks (4 kg / t molten steel) and crystalline silicon (8.5 kg / t molten steel) are added to the furnace along with ferrochrome and melted. The slag quantity and fluidity are adjusted to prevent false slag temperatures. When 50 kg of slag remains before tapping, the bottom charge should be completely melted, and the slag should be cooled and observed to turn grayish-white. It should be thoroughly stirred with an iron spatula to ensure uniform composition and temperature. At the end of the electroslag furnace smelting process, the steel is tapped and cast at a temperature of 1592℃. The electroslag furnace has a volume of 2 tons.

[0059] Comparative Example 1

[0060] Before electroslag refining, 60 kg of metallic chromium with a thickness of 80 mm is added to the bottom of the electroslag furnace. A mixture of 30 kg of quicklime, 40 kg of fluorite, and 30 kg of alumina is added to the electroslag furnace, and an electric arc is ignited before melting and smelting. When 1000 kg of molten steel has been smelted (target charge is 2000 kg), SiCa powder is added to the electroslag furnace in batches of 0.9 kg, with a 5-minute interval between each batch. The total SiCa powder added is 5 kg / t of molten steel. Crystalline silicon, with a total mass of 15 kg / t of molten steel, is added to the furnace along with ferrochrome and melted. The slag volume and slag fluidity are adjusted to avoid false slag temperatures. When 50 kg of molten steel remains before tapping, the bottom charge should be completely melted, and the slag should be cooled and observed to turn grayish-white. The slag should be thoroughly stirred with an iron spatula to ensure uniform composition and temperature. At the end of the electroslag furnace smelting process, the steel is tapped and cast at a tapping temperature of 1580℃. The electroslag furnace has a volume of 2 tons.

[0061] Comparative Example 2

[0062] Before electroslag refining, 62 kg of metallic chromium with a thickness of 85 mm is added to the bottom of the electroslag furnace. A mixture of 33 kg of quicklime, 42 kg of fluorite, and 29 kg of alumina is added to the electroslag furnace, and an arc is ignited before melting and smelting. When smelting reaches 1000 kg (target charge is 2000 kg), SiCa powder is added to the electroslag furnace in batches of 1 kg, with a 5-minute interval between batches. The total SiCa powder added is 5 kg / t of molten steel. Calcium silicate blocks (4 kg / t of molten steel) and crystalline silicon (11 kg / t of molten steel) are added to the furnace along with ferrochrome and melted. The slag quantity and slag fluidity are adjusted to avoid false slag temperatures. When 50 kg of slag remains before tapping, the bottom charge should be completely melted, and the slag should be cooled and observed to turn grayish-white. The slag should be thoroughly stirred with an iron spatula to ensure uniform composition and temperature. At the end of the electroslag furnace smelting process, the steel is tapped and cast at a tapping temperature of 1590℃. The electroslag furnace has a volume of 2 tons.

[0063] In the 21 heats of nickel-chromium-iron alloy steel obtained from the examples and comparative examples, samples were taken for total oxygen testing, and the test results are shown in Table 1.

[0064] Table 1. Oxygen content in 21 heats of nickel-chromium-iron alloy steel obtained from the examples and comparative smelting.

[0065]

[0066] In Example 1, the average oxygen content in 21 heats of nickel-chromium-iron alloy was 23.4 ppm through combined deoxidation of crystalline silicon and silicon-calcium block aluminum alloy steel.

[0067] In Comparative Example 1, the average oxygen content in 21 heats of nickel-chromium-iron alloy was 80.5 ppm after deoxidation by crystalline silicon.

[0068] In Comparative Example 2, the average oxygen content in 21 heats of nickel-chromium-iron alloy was 43.9 ppm through combined deoxidation using crystalline silicon and calcium silicon blocks.

[0069] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method of deoxidizing a nickel-chromium-iron alloy steel smelted in an electroslag furnace, characterized in that, The method comprises: Before electroslag furnace smelting, an electrically conductive base material is added to the bottom of the electroslag furnace; A slagging agent is added to the electroslag furnace, and electric arc starting is performed, followed by melting and smelting; During electroslag furnace smelting, when the charge amount in the electroslag furnace is 35% to 45% of the target charge amount, aluminum-containing scrap steel is added to the electroslag furnace, the added mass of the aluminum-containing scrap steel is ≤200 kg, the mass fraction of aluminum in the aluminum-containing scrap steel is 2% to 6%, and then silicon-calcium blocks and crystalline silicon are added to the electroslag furnace; At the end of the electroslag furnace smelting, tapping and casting are performed.

2. The method of claim 1, wherein, The added mass of the silicon-calcium blocks is 3 kg / t of molten steel to 5 kg / t of molten steel, and the added mass of the crystalline silicon is 7.5 kg / t of molten steel to 9 kg / t of molten steel.

3. The method of claim 1, wherein, During the electroslag furnace smelting, silicon-calcium powder is added to the electroslag furnace in batches, the added mass of each batch of the silicon-calcium powder is 0.8 kg to 1.2 kg, the interval time between adjacent batches is 4 min to 6 min, and the total added mass of the silicon-calcium powder is 4.5 kg / t of molten steel to 5.5 kg / t of molten steel.

4. The method of claim 1, wherein, The slagging agent comprises lime, fluorite, and aluminum oxide.

5. The method according to claim 1 or 4, characterized in that, The mass ratio of the slagging agent satisfies: fluorite:lime:aluminum oxide=(3 to 5):(2 to 4):(2 to 4), and the added mass of the slagging agent is 50 kg / t of molten steel to 60 kg / t of molten steel.

6. The method of claim 1, wherein, The electrically conductive base material comprises at least one of micro-carbon chromium iron and a nickel plate, the added mass of the electrically conductive base material is 50 kg to 80 kg, and the thickness of the electrically conductive base material is 80 mm to 100 mm.

7. The method of claim 3, wherein, When the aluminum-containing scrap steel, the silicon-calcium powder, the silicon-calcium blocks, and the crystalline silicon are added, the slag in the electroslag furnace is stirred, and the stirring time is 10 s to 20 s.

8. The method of claim 1, wherein, The block size of the silicon-calcium blocks and the crystalline silicon is 40 mm to 60 mm, wherein the block size is the maximum distance between two ends of the silicon-calcium blocks and the crystalline silicon.

9. The method of claim 1, wherein, The tapping temperature is 1560°C to 1600°C.

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