A Ferrochromium-Aluminum Alloy, Its Preparation Method and Application

Abstract

This invention belongs to the field of iron and steel smelting technology, specifically relating to an iron-chromium-aluminum alloy and its preparation method and application. The preparation method of the iron-chromium-aluminum alloy provided by this invention includes: (1) batching recycled chromium steel, high-carbon ferrochrome, carbon scrap steel and / or recycled scrap steel of the same steel grade, and melting it in a medium-frequency furnace; (2) adding the molten steel into an AOD furnace, and sequentially performing decarburization, reduction, denitrification, aluminum alloying, and titanium alloying; wherein, chromium steel is added to increase the steel strength during the decarburization process; (3) before tapping the steel from the AOD furnace, the ladle is vented with argon gas, and argon wind protection is formed at the furnace mouth by blowing argon with a side lance during the tapping process; (4) transferring the molten steel into an LF furnace for sequential temperature adjustment, calcium treatment, and argon blowing and stirring; (5) continuous casting. This invention improves the production efficiency of iron-chromium-aluminum alloy, reduces costs, and improves product quality, reducing [O] in the steel to below 10ppm, [N] to below 50ppm, and [C] to below 150ppm.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel smelting technology, specifically relating to an iron-chromium-aluminum alloy, its preparation method, and its application. Background Technology

[0002] Iron-chromium-aluminum alloys are important electrothermal alloys. Due to the high content of chromium and aluminum in their composition, a dense oxide film forms on the alloy surface at high temperatures, extending the service life of the alloy material. The high aluminum content increases resistivity, which effectively converts electrical energy into heat energy, saving on heating materials. Furthermore, iron-chromium-aluminum alloys are approximately 30% cheaper than nickel-based and stainless steel-based electrothermal alloys. Therefore, the excellent high-temperature oxidation resistance (up to 1400℃), high resistivity (up to 1.6), and low price of iron-chromium-aluminum alloys provide the conditions for their widespread use.

[0003] For a long time, these alloys could only be produced in small batches using specialized smelting equipment, resulting in low efficiency, high cost, and unstable quality, which severely restricted their large-scale application. Some companies have also attempted large-scale continuous casting production, but due to the low carbon and nitrogen content and high chromium-aluminum alloy content of the iron-chromium-aluminum materials, alloying is difficult during the smelting process due to their low melting point, low density, and susceptibility to oxidation. Aluminum alloying in the ladle is prone to melting at high temperatures, floating on top of the molten steel, and burning directly. If the amount added is too large, it cannot be alloyed in time, which can easily lead to localized gasification reactions and explosions. In addition, aluminum and titanium in the molten steel are prone to secondary oxidation, and the continuous casting process is prone to nodule formation and slag agglomeration, resulting in a low overall casting success rate and high smelting costs.

[0004] Therefore, it is essential to develop a low-cost, high-efficiency, large-scale production process for iron-chromium-aluminum alloy continuous casting billets to comprehensively improve the competitiveness of quality and cost and meet the needs of large-scale market applications. Summary of the Invention

[0005] To address the problems of small batch size, low efficiency, high smelting cost, and unstable quality in traditional production processes, as well as new problems such as difficulty in composition control, nodule formation, and steel leakage in conventional continuous casting processes, this invention provides an iron-chromium-aluminum alloy, its preparation method, and its applications.

[0006] Specifically, the method for preparing the iron-chromium-aluminum alloy provided by this invention includes:

[0007] (1) Returned chromium steel, high carbon ferrochrome, carbon scrap steel and / or scrap steel of this steel grade are batched and melted in a medium frequency furnace;

[0008] (2) The molten steel is poured into the AOD furnace and decarburized, reduced, denitrified, aluminum alloyed, and titanium alloyed in sequence; among them, chromium steel is added to increase the steel strength during the decarburization process;

[0009] (3) Before tapping steel from the AOD furnace, the ladle is vented with argon gas. At the same time, during the tapping process, argon is blown from the side lance to form argon wind protection at the furnace mouth.

[0010] (4) The molten steel is transferred to the LF furnace for temperature adjustment, calcium treatment and argon blowing and stirring in sequence;

[0011] (5) Continuous casting.

[0012] The above-mentioned method for preparing iron-chromium-aluminum alloys involves a tapping temperature of 1600℃-1650℃ in an intermediate frequency furnace, a tapping volume of 35-40 tons, a C content of 2.5-3.5wt%, a Cr content of 25-27wt%, and a Ni content of 0-0.15wt%.

[0013] In the above-mentioned method for preparing iron-chromium-aluminum alloy, in step (2), when the carbon content in the molten steel is ≤0.01wt%, reduction is started, the amount of aluminum shot added is 0.1-0.15% of the weight of the molten steel, the amount of slag removed after reduction is ≥90%, and at the same time, reduction slag material is added for secondary slag adjustment.

[0014] In the above-mentioned method for preparing iron-chromium-aluminum alloy, during the secondary slag conditioning process, 500-800 kg of lime and 300-500 kg of fluorite are used to ensure that the ternary basicity R (CaO / (SiO2+Al2O3)) of the steel slag sample is 2.5-3.0 and the content of (MnO+Cr2O3+FeO) in the slag is ≤0.3wt%.

[0015] In the above-mentioned method for preparing iron-chromium-aluminum alloy, in step (2), titanium alloying is carried out after aluminum alloying for 3-5 minutes, and the tapping temperature of the AOD furnace is 1680-1730℃.

[0016] In the above-mentioned method for preparing iron-chromium-aluminum alloy, in step (4), after adjusting the temperature of molten steel in the LF furnace to 1670-1680℃, 5-6 meters / ton of calcium wire is fed in, followed by hard blowing for 10-15 minutes and soft blowing for 5-15 minutes. The tapping temperature of the LF furnace is 1610-1630℃.

[0017] In the above-mentioned method for preparing iron-chromium-aluminum alloy, during continuous casting, the time from the tundish shut-off to the ladle opening is ≤10 minutes. After the ladle opens, no flow control is performed. When the tundish weight is 5-8 tons, the pouring begins, the emergence time is 15-20 seconds, and the superheat of the molten steel in the tundish is controlled at 55-65℃.

[0018] In the above-mentioned method for preparing iron-chromium-aluminum alloy, during continuous casting, electromagnetic stirring is used in the crystallizer and the end, the primary cooling water flow rate is 2000L / min, the secondary cooling water ratio is set at 0.25-0.30L / kg, and after cutting, the microstructure is sent to the heating furnace at a temperature greater than 300℃.

[0019] On the other hand, the present invention provides an iron-chromium-aluminum alloy, which is obtained by the above-described preparation method.

[0020] In another aspect, the present invention also provides the application of the iron-chromium-aluminum alloy obtained by the above preparation method or the above iron-chromium-aluminum alloy in the production of heating wire steel.

[0021] The technical solution of the present invention has the following beneficial effects:

[0022] (1) This invention solves the problems of high raw material cost, difficulty in controlling composition during smelting process, frequent accidents in continuous casting production, and unstable quality in smelting electric heating wire steel.

[0023] (2) This invention enables continuous casting of more than two furnaces, increases metal yield by more than 20%, achieves a casting success rate of 100%, and produces high-quality wire drawing.

[0024] (3) This invention enables the production of iron-chromium-aluminum alloys to be transformed from small-batch to large-scale production, thereby increasing output while ensuring quality.

[0025] (4) This invention improves the titanium yield, reduces secondary pollution, and achieves the goal of low nitrogen control;

[0026] (5) This invention improves production efficiency, reduces costs, and improves product quality. The [O] in steel is reduced to below 10 ppm, [N] to below 50 ppm, and [C] to below 150 ppm. Detailed Implementation

[0027] To fully understand the purpose, features, and effects of this invention, the following detailed embodiments are provided. Except as described below, the process methods of this invention employ conventional methods or apparatus in the art. Unless otherwise specified, the terms and expressions used below have the meanings commonly understood by those skilled in the art.

[0028] When a numerical range is disclosed in this invention, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Further, when the range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Moreover, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed in this invention should be understood to include any and all subranges to which they are incorporated.

[0029] The technical concept of this invention is as follows: A medium-frequency furnace melts low-cost raw materials (chromium steel, some high-carbon ferrochrome, carbon scrap steel, and recycled scrap steel of the same steel grade), increasing alloy yield; the excellent kinetic conditions of an AOD furnace are used for decarburization, deoxidation, and denitrification, as well as aluminum and titanium alloying; slag removal effectively removes inclusions such as alumina generated during the smelting process; the addition of some chromium steel to the AOD furnace increases the steel output and reduces smelting costs; the composition added to the AOD furnace is optimized to increase the carbon content of the medium-frequency furnace melt, providing favorable conditions for denitrification during AOD smelting; LF is used for temperature adjustment, argon blowing and stirring, and calcium treatment to further improve the quality of the molten steel; continuous casting is performed with protective casting, optimizing the time from stop-fire to start-up casting, reducing the temperature drop in the tundish, and optimizing the emergence time.

[0030] Specifically, the method for preparing the iron-chromium-aluminum alloy provided by this invention includes:

[0031] (1) Returned chromium steel, high carbon ferrochrome, carbon scrap steel and / or scrap steel of this steel grade are batched and melted in a medium frequency furnace;

[0032] (2) The molten steel is poured into the AOD furnace and decarburized, reduced, denitrified, aluminum alloyed, and titanium alloyed in sequence; among them, chromium steel is added to increase the steel strength during the decarburization process;

[0033] (3) Before tapping steel from the AOD furnace, the ladle is vented with argon gas. At the same time, during the tapping process, argon is blown from the side lance to form argon wind protection at the furnace mouth.

[0034] (4) The molten steel is transferred to the LF furnace for temperature adjustment, calcium treatment and argon blowing and stirring in sequence;

[0035] (5) Continuous casting.

[0036] The iron-chromium-aluminum alloy preparation method provided by this invention solves the problems of high raw material cost, difficulty in controlling the composition during the smelting process, frequent accidents in continuous casting production, and unstable quality. It achieves continuous casting of more than two heats, increases metal yield by more than 30%, achieves a casting success rate of 100%, and produces good wire drawing quality.

[0037] In some preferred embodiments, the method for preparing the iron-chromium-aluminum alloy provided by the present invention includes:

[0038] Medium frequency furnace smelting

[0039] Medium frequency furnaces can heat metal materials efficiently and stably in a short time, thereby achieving melting and heat treatment.

[0040] Preferably, the present invention uses chromium steel, high-carbon ferrochrome, carbon scrap steel, and recycled scrap steel of this steel grade as raw materials, which can effectively improve the alloy yield.

[0041] During the batching process, the amount of chromium added to AOD chromium steel is precisely calculated and chromium is added in a high-carbon ratio. As a result, the metal yield of medium-frequency furnace smelting can reach more than 99%.

[0042] Preferably, the tapping temperature of the medium-frequency furnace is 1600℃-1650℃, the C content of the tapped steel is 2.5-3.5wt%, the Cr content is 25-27wt%, and the Ni content is 0-0.15wt%. This invention provides favorable conditions for denitrification during AOD smelting by increasing the carbon content of the medium-frequency furnace melt.

[0043] AOD furnace smelting

[0044] AOD furnace smelting is an external refining technology that uses argon-oxygen gas to be blown into the molten steel pool to dilute the partial pressure of carbon monoxide, thereby achieving decarburization and chromium retention.

[0045] In this invention, the medium-frequency furnace is equipped with high carbon content, and the excellent kinetic conditions of the AOD furnace are used for decarburization, deoxidation, and denitrification, as well as aluminum and titanium alloying. The inclusions such as alumina generated during the smelting process are effectively removed by slag skimming. At the same time, some chromium steel is added to the AOD furnace to increase the steel output and reduce smelting costs.

[0046] Preferably, AOD is added to the molten steel in the medium-frequency furnace for oxygen blowing decarburization and heating. During the process, 3-5 tons of chromium steel are added to increase the steel content. When the carbon content in the molten steel is ≤0.01wt%, reduction begins. The amount of aluminum shot added is 0.1-0.15% of the weight of the molten steel. After reduction, the amount of slag removed is ≥90%, and at the same time, reduction slag is added for secondary slag adjustment.

[0047] Preferably, during the secondary slag conditioning process, lime and fluorite are added to ensure that the ternary basicity R (CaO / (SiO2+Al2O3)) of the steel slag sample is 2.5-3.0 and the content of (MnO+Cr2O3+FeO) in the slag is ≤0.3wt%, thereby reducing the oxygen content of the steel.

[0048] In one embodiment, the steel output of the intermediate frequency furnace is 35-40 tons, and during the secondary slag adjustment in the AOD furnace smelting, the amount of lime added is 500-800 kg, and the amount of fluorite added is 300-500 kg.

[0049] Preferably, after slag adjustment, aluminum is alloyed according to the reduction composition, with Al content of 5.50-6.50%. After aluminum alloying for 3-5 minutes, 40-60 kg of low-nitrogen titanium alloy recycled material is added, which improves the titanium yield, reduces secondary pollution, and achieves the goal of low nitrogen control.

[0050] Among them, aluminum shot is produced by adding aluminum shot to a high-level silo.

[0051] Preferably, the tapping temperature of the AOD furnace is 1680-1730℃.

[0052] In a further optimized manner, before tapping steel from the AOD furnace, the ladle is purged with argon for 3-5 minutes. At the same time, during the tapping process, a small flow of argon is blown through the side gun to form an argon wind protection at the furnace mouth, preventing secondary oxidation and nitrogen accumulation during tapping.

[0053] LF Smelting

[0054] LF furnace, or ladle refining furnace, is the main ladle refining equipment in steel production. It can be used for desulfurization, temperature regulation, precise composition fine-tuning, improving the purity of molten steel, and slag formation.

[0055] Preferably, after the molten steel enters the LF furnace, the temperature is adjusted to 1670-1680℃ to begin calcium treatment. 5-6 meters of calcium wire are fed in per ton of steel. After feeding the wire, hard blowing treatment is performed, with the hard blowing time controlled at 10-15 minutes and the total flow rate at 180 NL / min. The soft blowing time is controlled at 5-15 minutes and the total flow rate at 80 NL / min. During soft blowing, the slag surface shows obvious creep, the molten steel is not exposed, and inclusions are fully floated to the surface.

[0056] Preferably, the LF tapping temperature is controlled at 1610-1630℃.

[0057] This invention further improves the quality of molten steel by using LF for temperature adjustment, argon blowing and stirring, and calcium treatment.

[0058] Continuous casting

[0059] Continuous casting, short for continuous steel casting, is an advanced technology that directly pours molten steel into shape. Compared with traditional methods, continuous casting technology has significant advantages such as greatly improving metal yield and billet quality, and saving energy.

[0060] This invention ensures proper sealing of the tundish during continuous casting, purging the tundish with argon for 2-3 minutes before pouring, and timely replenishment of covering agent during continuous casting. It strictly prohibits the exposure of molten steel to prevent secondary oxidation and nitrogen accumulation.

[0061] Preferably, the time from the tundish shutdown to the ladle start pouring is ≤10 minutes. After the ladle starts pouring, no flow control is performed. Pouring begins when the tundish weight is 5-8 tons, with the emergence time set at 15-20 seconds. The superheat of the molten steel in the tundish is controlled at 55-65℃ to ensure good slag formation and protective slag effects during pouring, smooth pouring in the crystallizer, and to prevent cold steel, nodules, and other issues that could affect the performance of the protective slag and billet lubrication, thus increasing the risk of poor pouring.

[0062] To prevent porosity and shrinkage cavities in the cast billet, electromagnetic stirring is used in the crystallizer and the end. The primary cooling water flow rate is 2000 L / min, and the secondary cooling uses weak cooling. The specific water volume is set at 0.25-0.30 L / kg. After cutting, the billet is sent to the heating furnace at a temperature greater than 300℃.

[0063] This invention utilizes a process method for large-scale production of iron-chromium-aluminum alloys using a medium-frequency furnace-AOD-LF-square billet continuous casting machine. This method enables the transformation of iron-chromium-aluminum alloy production from small-batch to large-scale organization, increasing output while ensuring quality and solving problems such as high raw material costs, difficulty in controlling the composition during smelting, frequent accidents in continuous casting production, and unstable quality.

[0064] On the other hand, the present invention also provides an iron-chromium-aluminum alloy, which is obtained by the above-described preparation method.

[0065] Preferably, the chemical composition of the iron-chromium-aluminum alloy of the present invention, by weight percentage, is: C≤0.06%; Si≤0.6%; Mn≤0.5%; P≤0.025%; S≤0.02%; Ni≤0.20%; Cr 24.00~26.00%; Al 5.00~6.50%; Ti 0.08-0.2%; N≤0.02%; with the balance being iron and unavoidable impurities.

[0066] In another aspect, the present invention also provides the application of the above-mentioned iron-chromium-aluminum alloy in the production of heating wire steel.

[0067] The iron-chromium-aluminum alloy of the present invention has an [O] content of less than 10ppm, a [N] content of less than 50ppm, and a [C] content of less than 150ppm. It is free from porosity and shrinkage defects, and its overall competitiveness in terms of quality and cost is improved, meeting the requirements for heating wire steel.

[0068] Example

[0069] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments, unless otherwise specified, are performed according to conventional methods and conditions.

[0070] Chromium steel, high-carbon ferrochrome, carbon scrap steel, and recycled scrap steel of this steel grade are melted in an intermediate frequency furnace. The tapping temperature of the intermediate frequency furnace is 1645℃, the tapping amount is 38 tons, the tapping C is 3.0%, the tapping Cr is 26.5%, and the tapping Ni is 0.1%.

[0071] AOD is added to the molten steel in the medium-frequency furnace for oxygen blowing decarburization and heating. During the process, 5 tons of chromium steel are added to increase the steel content. When the carbon content reaches 0.01%, reduction is carried out. During reduction, aluminum shot is added using a high-level silo. The aluminum added during reduction is calculated at 0.13%. After reduction, 93% of the slag is removed. At the same time, secondary slag adjustment is carried out by adding reduction slag material, about 600 kg of low-carbon lime, and 350 kg of low-silicon low-carbon fluorite. The ternary basicity of the slag sample is 2.6, and the content of (MnO+Cr2O3+FeO) in the slag is 0.28%. After slag adjustment, aluminum alloying is carried out according to the reduction composition, and the Al content is 6.10%. After 4 minutes of aluminum alloying, 50 kg of low-nitrogen titanium alloy recycled material is added. The tapping temperature is controlled at 1710℃.

[0072] Before tapping steel at AOD, the ladle is purged with argon for 5 minutes. At the same time, during the tapping process, argon is blown at a low flow rate (300L / min) using a side lance to form an argon wind protection at the furnace mouth, preventing secondary oxidation and nitrogen accumulation during tapping.

[0073] After the molten steel enters the LF furnace, the temperature is adjusted. Calcium treatment begins at 1680℃, with 5 meters / ton of calcium wire fed in. After feeding the wire, hard blowing treatment is performed, with the hard blowing time controlled at 12 minutes and the soft blowing time controlled at 8 minutes. The LF tapping temperature is controlled at 1620℃.

[0074] For continuous casting, ensure the tundish is properly sealed. Purge the tundish with argon for 3 minutes before starting pouring. Add covering agent promptly during continuous casting, and strictly prohibit exposed molten steel to prevent secondary oxidation and nitrogen accumulation. Allow 9 minutes between tundish shutdown and ladle pouring. Do not control the flow after ladle pouring. Start pouring when the tundish weight reaches 7 tons, with a emergence time of 18 seconds. Maintain the tundish steel superheat at 60℃. Ensure good slag formation during pouring and the protective slag have good slag-forming effects. Pour into the crystallizer smoothly without cold steel or nodules.

[0075] The crystallizer and end are equipped with electromagnetic stirring. The primary cooling water flow rate is 2000L / min, the secondary cooling is weak cooling, and the specific water volume is set at 0.28L / kg. After cutting, the tissue is sent to the heating furnace at a temperature greater than 360℃.

[0076] The steel produced in this example has [O] content of 8 ppm, [N] content of 46 ppm, and [C] content of 100 ppm. No nodules or fish-like formations were observed during the continuous casting process, and the cast billet showed no porosity or shrinkage cavities, resulting in excellent wire drawing quality. This comprehensively improves both quality and cost competitiveness, meeting the requirements for hot-wire steel.

[0077] The present invention has been disclosed above with reference to preferred embodiments. However, those skilled in the art should understand that these embodiments are merely illustrative of the invention and should not be construed as limiting its scope. It should be noted that any variations and substitutions equivalent to these embodiments should be considered to be covered within the scope of the claims. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for preparing an iron-chromium-aluminum alloy, characterized in that, include: (1) Returned chromium steel, high-carbon ferrochrome, carbon scrap steel and / or scrap steel of this steel grade are batched and melted in a medium frequency furnace; (2) The molten steel is poured into the AOD furnace and decarburized, reduced, denitrified, aluminum alloyed, and titanium alloyed in sequence; among them, chromium steel is added to increase the steel strength during the decarburization process; When the carbon content in the molten steel is ≤0.01wt%, reduction begins. The amount of aluminum shot added is 0.1-0.15% of the weight of the molten steel. After reduction, the slag removal rate is ≥90%, and reducing slag is added for secondary slag conditioning. During the secondary slag conditioning process, 500-800 kg of lime and 300-500 kg of fluorite are added to ensure that the ternary basicity R(CaO / (SiO2+Al2O3)) of the slag sample is 2.5-3.0, and the content of (MnO+Cr2O3+FeO) in the slag is ≤0.3wt%. Among them, titanium alloying is carried out 3-5 minutes after aluminum alloying, and the tapping temperature of AOD furnace is 1680-1730℃. (3) Before tapping steel from the AOD furnace, the ladle is vented with argon gas, and argon gas is blown into the furnace mouth by the side lance during the tapping process to form argon wind protection. (4) The molten steel is transferred to the LF furnace for temperature adjustment, calcium treatment and argon blowing and stirring in sequence; (5) Continuous casting; During continuous casting, the time from tundish shutdown to ladle start-up is ≤10 minutes. After ladle start-up, no flow control is performed. When the tundish weight is 5-8 tons, the pouring begins, and the emergence time is 15-20 seconds. The superheat of the molten steel in the tundish is controlled at 55-65℃. During continuous casting, electromagnetic stirring is used in the crystallizer and the end stage. The primary cooling water flow rate is 2000L / min, and the secondary cooling water ratio is set at 0.25-0.30L / kg. After cutting, the steel is sent to the heating furnace at a temperature greater than 300℃. The iron-chromium-aluminum alloy, by weight percentage, has the following chemical composition: C≤0.06%; Si≤0.6%; Mn≤0.5%; P≤0.025%; S≤0.02%; Ni≤0.20%; Cr 24.00~26.00%; Al 5.00~6.50%; Ti 0.08-0.2%; N≤0.02%; with the balance being iron and unavoidable impurities.

2. The method for preparing the iron-chromium-aluminum alloy according to claim 1, characterized in that, The tapping temperature of the medium-frequency furnace is 1600℃-1650℃, the tapping amount is 35-40 tons, the C content is 2.5-3.5wt%, the Cr content is 25-27wt%, and the Ni content is 0-0.15wt%.

3. The method for preparing the iron-chromium-aluminum alloy according to claim 1, characterized in that, In step (4), after adjusting the temperature of the molten steel in the LF furnace to 1670-1680℃, 5-6 meters of calcium wire per ton of steel are fed in. After feeding the wire, hard blowing is performed for 10-15 minutes, soft blowing for 5-15 minutes, and the tapping temperature of the LF furnace is 1610-1630℃.

4. A ferrochromium-aluminum alloy, characterized in that, It is obtained by the preparation method described in any one of claims 1-3.

5. The application of the iron-chromium-aluminum alloy obtained by the preparation method according to any one of claims 1-3 or the iron-chromium-aluminum alloy according to claim 4 in the production of heating wire steel.