Method for producing electrothermal alloy iron-chromium-aluminum

Abstract

The iron-chromium-aluminum electrothermal alloy is a high-temperature functional material which contains 10-30% of Cr and is added with 1.0-6.0% of Al, rare earth and other elements, has the advantages of high use temperature, low price, long service life and the like, and is widely used in the fields of electric heating, heat-resistant industrial furnaces, food machinery, household appliances, environmental protection facilities and other electric heating and carriers. The traditional process is low in production efficiency, low in Al yield and poor in raw material adaptability, the RH is innovatively introduced to produce the iron-chromium-aluminum electrothermal alloy, under the condition that oxygen blowing decarburization is not carried out on the RH, the adaptability of the raw materials is widened, the Al alloying efficiency and yield are improved, original waste steel is recycled to the maximum extent, and the production cost of iron-chromium-aluminum is effectively reduced.

Description

Technical Field

[0001] The invention relates to the field of electrothermal alloy production and manufacturing, and in particular to a method for producing electrothermal alloy iron-chromium-aluminum. Background Art

[0002] Iron-chromium-aluminum electric heating alloy is a high-temperature functional material with a Cr content of 10-30% and 1.0-6.0% of Al, rare earth and other elements added. It has the advantages of high operating temperature, low price and long life. It is widely used in electric heating, heat-resistant industrial furnaces, food machinery, household appliances, environmental protection facilities and other electric heating and carrier fields.

[0003] Due to the difficulty in Al alloying in the production process of Fe-Cr-Aluminum electrothermal alloy and the high crack sensitivity of the material, it is difficult to achieve large-scale mass production. At present, the domestic generally adopts small-scale production of induction furnace + ingot casting + electroslag remelting. This process has the disadvantages of small production batch, poor component control stability and high production cost. In addition, the converter (AOD) + VOD + continuous casting process developed by a domestic factory is subject to weak ladle stirring, easy occurrence of molten steel splashing and explosion when Al is added in large batches, and poor raw material adaptability. At the same time, there is a low Al recovery rate due to slag reaction in the smelting process, resulting in low production efficiency, difficulty in multi-furnace continuous casting and high production cost.

[0004] Therefore, in order to produce Fe-Cr-Al electric heating alloy efficiently, stably and at low cost, solving the problems of low Al yield, low production efficiency and high cost has become a problem restricting the large-scale production of Fe-Cr-Al.

[0005] The purpose of the present invention is to develop a method for producing electric heating alloy iron-chromium-aluminum by RH+LF, so as to create conditions for improving the production efficiency of iron-chromium-aluminum, reducing production costs, expanding the adaptability of raw materials, and realizing low-cost large-scale production of electric heating alloys. Summary of the invention

[0006] The purpose of the present invention is to provide a method for producing an electric heating alloy Fe-Cr-Al in view of the above problems.

[0007] The object of the present invention is achieved as follows: 1. A method for producing an electric heating alloy iron-chromium-aluminum, comprising the following steps: Step 1: AOD is loaded with dephosphorized molten iron, oxygen blowing and decarburization are first performed, and when the temperature is greater than 1500°C, high carbon ferrochrome is added in 3-5 batches according to the Cr content control target of different varieties, and the Cr recovery rate is calculated according to 90-95%; Step 2: After adding high carbon ferrochrome, the decarburization operation is continued according to the operation mode of AOD, and when the C in the molten steel is less than 0.02%, the reduction operation is started or the steel is directly tapped without reduction; Step 3: The ladle is hoisted into the slag removal station for slag removal operation, and after the slag is removed cleanly, a 50-100 mm thick ferrochrome is added to the ladle. Refining slag, the amount of refining slag added is 5-10kg / t; Step 4: lift the molten steel after slagging to the RH, and then lift the ladle to the height where the RH can be vacuumed, that is, the RH immersion tube is inserted 300-500mm below the molten steel surface, and the molten steel with qualified C and Cr is subjected to Al alloying operation in the RH. During the operation, the vacuum degree in the RH vacuum tank is controlled at 100-200mbar, and aluminum is added in batches, and each batch of aluminum is controlled at 300-1000kg; Step 5: After the Al alloying is completed, continue to circulate in the RH for 5-15min, then break the vacuum and end the RH operation; Step 6: After the LF furnace refining is completed, continuous casting or mold casting is carried out.

[0008] The refined slag in step 2 is 25-50% Al2O3, 50-60% CaO refined slag.

[0009] The beneficial effects of the present invention are: 1) the present invention expands the production method of iron-chromium-aluminum electrothermal alloy and improves production efficiency through the innovation of process route.

[0010] 2) The present invention expands the adaptability of raw materials and can use long process, short process and original variety return materials for production. At the same time, the front process can be AOD, GOR, KOBM-S, induction furnace, etc.

[0011] 3) Compared with the traditional process, the present invention has high production efficiency, especially high aluminum alloying efficiency, high Al yield rate and wide raw material range.

[0012] The implementation of the present invention expands the production process route of the iron-chromium-aluminum electrothermal alloy, improves the efficiency of aluminum alloying and the aluminum yield, and reduces the production cost. DETAILED DESCRIPTION

[0013] The present invention develops a method for producing electric heating alloy iron-chromium-aluminum by RH+LF, which creates conditions for improving the production efficiency of iron-chromium-aluminum, reducing production costs, expanding the adaptability of raw materials, and realizing low-cost large-scale production of electric heating alloys. The process is characterized by strong adaptability of raw materials, and can use blast furnace molten iron to be dephosphorized after being pretreated in a converter or molten iron, and then added to an AOD furnace for refining, and can also use recycled stainless steel scrap, recycled carbon scrap, iron-chromium-aluminum recycled waste, etc., which are melted in an electric furnace or an induction alloy melting furnace and then added to AOD for smelting, and deep decarburization and Cr alloying are achieved in the AOD refining process. According to different varieties, Cr and C are adjusted to a suitable range in the AOD refining process, and then they are not reduced or not completely reduced (the target of the end point Si is less than 0.05%), and then the molten steel is poured into a ladle, and the ladle is hoisted to the slag removal place to remove all the slag on the top, and then refined slag containing 25-50% Al2O3 and 50-60% CaO is added to ensure that the thickness of the slag layer on the top of the ladle is 50mm.

[0014] In addition, the return material of the electrothermal alloy can be melted in the induction furnace and then directly fine-tuned in the RH, eliminating the process of oxygen blowing and decarburization, effectively utilizing the Al in the return waste of iron, chromium, and aluminum, reducing the waste of Al and the pollution of molten steel caused by the use of other varieties.

[0015] Before the molten steel is hoisted into place, RH puts enough metallic aluminum into the vacuum aluminum hopper in advance. After the molten steel is hoisted to RH, the ladle is lifted and vacuum is started when the dipping tube is inserted into the molten steel. This process does not carry out oxygen blowing and decarburization in RH. After RH circulates for 5 minutes at the ultimate vacuum degree and controls the vacuum degree at 100-200mbar, aluminum is added in batches from the aluminum vacuum hopper of RH. After the aluminum is added to the target, temperature measurement and sampling are carried out, and during this period, circulation under vacuum continues for 5-15 minutes.

[0016] The key control parameters for the implementation of this solution include the following: 1. Ar or CO2 must be used for the side-blowing gas in the AOD process. All alloys are completed in the first three stages of AOD decarburization. From the fourth stage of decarburization, Ar (CO2) / O2 is used for deep decarburization. When the C content in the steel is less than 0.015% and the molten steel temperature is greater than 1700°C, no reduction operation is performed and the molten steel is poured into the ladle; AOD controls C and Cr to the appropriate range without reduction or incomplete reduction to ensure that the Si content in the solution is less than 0.05%, and then pours the molten liquid into the ladle or the induction furnace melts the return material of the original variety and pours it into the ladle.

[0017] 2. In order to control the extremely low Si content in the melt, AOD controls C and Cr to the appropriate range without reducing or reducing them completely, ensuring that the Si content in the solution is less than 0.05%, and then pours the melt into the ladle; or the induction furnace melts the return material of the original variety and pours it into the ladle.

[0018] 3. The slag in the molten steel ladle must be completely removed (the molten steel is basically completely exposed), and then 50-100mm thick refined slag containing 25-50% Al2O3 and 50-60% CaO is added to the ladle.

[0019] 4. The qualified melt of C and Cr is subjected to Al alloying operation in RH. During the operation, the vacuum degree in the RH vacuum tank should be controlled at 100-200mbar, which can effectively prevent splashing during the alloying process.

[0020] 5. After Al alloying is completed, continue to circulate in RH for 5-15 minutes to control the Al vapor in the system to prevent the risk of explosion from air entering the vacuum system.

[0021] 6. If rare earth alloying or temperature rhythm adjustment is required, the RH treated melt can continue to be refined in the LF furnace. When the LF furnace needs to be powered on to heat up, the bottom blowing flow rate is controlled at 100-200Nl / min. After the LF is heated up, the bottom blowing flow rate is stirred at 400-600Nl / min to achieve uniform temperature. The weak stirring time before the end of the LF furnace refining is controlled at 10-20min, and the weak stirring flow rate is controlled at 60-100Nl / min. When rare earth alloying is required, rare earth blocks are added to the ladle through a silo or by hand at the beginning of LF weak stirring. The rare earth content is controlled to 0.05-0.10%, and the rare earth recovery rate is calculated at 30-50%.

[0022] 7. After LF furnace refining is completed, continuous casting or mold casting can be carried out.

[0023] 8. The composition requirements of Fe-Cr-Al electric heating alloy are shown in Table 1.

[0024] 9. The gas ratio of AOD process is shown in Table 2.

[0025] Embodiment 1 (AOD+RH+LF)

[0026] 1. AOD is loaded with dephosphorized molten iron, and oxygen blowing decarburization is first performed. When the temperature is greater than 1500℃, high carbon ferrochrome is added in 3-5 batches according to the Cr content required by the variety (Cr recovery rate is calculated as 93%). All alloys are completed before DEC3. From DEC4-DEC8, deep decarburization operation is started by adjusting the Ar (CO2) / O2 ratio of the side-blowing gas (the specific gas ratio mode is controlled according to Table 2). When the C in the steel reaches <0.015%, and the molten steel temperature is greater than 1700℃, the molten steel is not reduced or not completely reduced (the Si in the molten steel is controlled to be less than 0.05%), and the molten steel is poured into the ladle.

[0027] 2. Lift the ladle into the slag removal station for slag removal operation. The slag removal standard is that the molten steel is completely exposed, and then add refined slag at a rate of 5-10kg / t to ensure that the slag thickness is 50-100mm.

[0028] 3. Lift the molten steel after slagging to the RH, then lift the ladle to the height where the RH can be vacuumed, and then fine-tune the height of the ladle appropriately according to the control of the vacuum degree to ensure that the RH immersion tube is inserted 300-500mm below the molten steel surface.

[0029] 4. Then the vacuum degree of RH is pumped to the limit, and then maintained at the limit vacuum degree for 5-10 minutes to further decarburize, deoxidize, degasify and other operations on the molten steel.

[0030] 5. After the previous step is completed, adjust the vacuum degree of RH to 100-200mbar to prepare for Al alloying operation. During the Al alloying process, aluminum can be added continuously. If there is splashing during the process, aluminum addition can be suspended and aluminum addition can be started again after the molten steel level stabilizes. This operation can be repeated.

[0031] 6. After the Al alloying operation is completed, continue to evacuate the air at a vacuum degree of 100-200 mbar for more than 5 minutes, then break the vacuum and end the RH operation.

[0032] 7. If the production rhythm or temperature is not suitable and rare earth alloying operation is required, the ladle will be lifted to the LF furnace for refining.

[0033] 8. When the LF furnace needs to be powered up to heat up, the bottom blowing flow rate is controlled at 100-200Nl / min.

[0034] 9. After LF is heated up, the uniform temperature bottom blowing flow rate is 400-600Nl / min for stirring.

[0035] 10. Before the end of LF furnace refining, the weak stirring time is controlled at 10-20min, and the weak stirring flow rate is controlled at 60-100Nl / min.

[0036] 11. When rare earth alloying is required, rare earth blocks are added into the ladle through the silo or hand throwing at the beginning of LF weak stirring. The rare earth content is controlled to 0.05-0.10%, and the rare earth recovery rate is calculated at 30-50%.

[0037] 12. After LF furnace refining is completed, continuous casting or mold casting can be carried out. Embodiment 2 (induction furnace + RH + LF)

[0038] 1. The alloy melting furnace mixes the recycled waste materials of iron, chromium and aluminum, the scraps inside the steel plant and the cutting waste, and then loads them into the furnace and melts them with electricity.

[0039] 2. The melting process can be loaded in batches according to the material type and melting speed.

[0040] 3. The melted iron, chromium and aluminum return charges are poured into the ladle. Part of the prepared refined slag can be added to the ladle in advance, and the remaining refined slag can be added after the induction furnace is finished tapping.

[0041] 4. Lift the ladle to the RH, then lift the ladle to the height where the RH can be vacuumed, and then fine-tune the ladle height appropriately according to the control of the vacuum degree to ensure the safety of the vacuum process.

[0042] 5.RH does not need to draw the vacuum degree to the limit. After the vacuum degree is controlled at 100-200mbar, the composition is fine-tuned according to the composition of the melt after melting in the induction furnace. After the composition is adjusted appropriately, continue to evacuate at a vacuum degree of 100-200mbar for more than 5 minutes, then break the vacuum and end the RH operation.

[0043] 6. If the production rhythm or temperature is not suitable and rare earth alloying operation is required, the ladle will be lifted to the LF furnace for refining.

[0044] 7. When the LF furnace needs to be powered up to heat up, the bottom blowing flow rate is controlled at 100-200Nl / min.

[0045] 8. After LF is heated up, the uniform temperature bottom blowing flow rate is 400-600Nl / min for stirring.

[0046] 9. Before the end of LF furnace refining, the weak stirring time is controlled at 10-20min, and the weak stirring flow rate is controlled at 60-100Nl / min.

[0047] 10. When rare earth alloying is required, rare earth blocks are added into the ladle through the silo or hand throwing at the beginning of LF weak stirring. The rare earth content is controlled to 0.05-0.10%, and the rare earth recovery rate is calculated at 30-50%.

[0048] 11. After LF furnace refining is completed, continuous casting or mold casting can be carried out.

[0049] The above description is only a specific embodiment of the present invention, but the structural features of the protection scope of the present invention are not limited thereto. Any changes or modifications made by any technician in the field of the present invention are all covered by the patent scope of the present invention.

Claims

1. A method for producing an electric heating alloy iron-chromium-aluminum, characterized in that: The following steps are involved: Step 1: AOD is loaded with dephosphorized molten iron, and oxygen decarburization is first performed. When the temperature is greater than 1500°C, high carbon ferrochrome is added in 3-5 batches according to the Cr content control target of different varieties, and the Cr recovery rate is calculated at 90-95%; Step 2: After adding high carbon ferrochrome, continue to perform decarburization operation according to the AOD operation mode, and when the C in the molten steel is less than 0.02%, start reduction operation or directly tap steel without reduction; Step 3: Lift the ladle into the slag removal station for slag removal. After the slag is removed, add 50-100mm thick refined slag into the ladle. The amount of refined slag added is 5-10kg / t. Step 4: transport the molten steel after slagging to the RH, and then lift the ladle to the height where the RH can be vacuumed, that is, the RH immersion tube is inserted 300-500mm below the molten steel surface, and the molten steel with qualified C and Cr is subjected to Al alloying operation in the RH. During the operation, the vacuum degree in the RH vacuum tank is controlled at 100-200mbar, and aluminum is added in batches, and each batch of aluminum is controlled at 300-1000kg; Step 5: After Al alloying is completed, continue to circulate in RH for 5-15 minutes, then break the vacuum and end the RH operation; Step 6: After LF furnace refining is completed, continuous casting or mold casting is carried out.

2. The method for producing an electric heating alloy Fe-Cr-Al according to claim 1, characterized in that: The refined slag in step 2 is 25-50% Al2O3, 50-60% CaO refined slag.

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