A smelting method for filter steel and filter

Abstract

The present invention belongs to the technical field of metal material manufacturing, and specifically relates to a smelting method for filter steel and a filter. The smelting method includes: molten iron desulfurization treatment, converter smelting, refining, and continuous casting. The converter smelting includes: a converter tapping temperature of 1590°C to 1610°C. After tapping, a first top slag modifier is added to the molten steel to reduce the oxidizing property of the top slag; refining includes LF refining and RH refining. The LF refining includes: adding a second top slag modifier to the molten steel to increase the binary basicity of the top slag, increase the Al2O3 content in the top slag, and reduce the oxidizing property of the top slag, while simultaneously increasing the molten steel temperature. This can significantly increase the converter furnace life and reduce Al2O3 inclusions in the steel.

Description

Technical Field

[0001] The present invention relates to the technical field of metal material manufacturing, and in particular to a smelting method for filter steel and a filter. Background Art

[0002] The filter is an essential and important component in the automobile engine. It filters the air, oil and fuel entering the engine, thereby protecting the engine and improving the engine's operating efficiency.

[0003] The current steelmaking production process for filter steel is: molten iron desulfurization → converter → RH → continuous casting, which has the following defects: decarburization and adjustment of top slag composition are carried out in the RH process. In order to ensure the smooth progress of decarburization and top slag composition adjustment, it is necessary to maintain a high tapping temperature during converter tapping, usually around 1680°C, which has a great impact on the converter lining and reduces the service life of the converter; decarburization and adjustment of top slag composition will produce a large temperature drop. In order to ensure the pouring temperature, aluminum is usually added to increase the temperature, resulting in a large amount of Al2O3 inclusions in the steel. Filter housings are basically made using deep drawing technology. When hard inclusions exist in the steel, defects such as cracking and sand holes are prone to occur during the processing process. The working conditions of filters are complex and they must have good pressure resistance, vibration resistance, durability, low temperature resistance (-40°C), high temperature resistance (+140°C) and no oil leakage. Industry standards clearly require that filters must undergo hydraulic pulse fatigue tests and static pressure rupture tests. The filter shell materials currently prepared are difficult to meet the requirements.

[0004] It should be noted that this part of the present invention only provides background technology related to the present invention and does not necessarily constitute prior art or public known technology. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the prior art in that the converter for preparing filter steel has a low service life and the prepared steel contains a large number of Al2O3 inclusions, and to provide a smelting method for filter steel and a filter, which can significantly increase the converter service life and reduce the Al2O3 inclusions in the steel.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a smelting method for filter steel, the method comprising: molten iron desulfurization, converter smelting, refining, and continuous casting, wherein the converter smelting comprises: a converter tapping temperature of 1590°C to 1610°C, and after tapping, adding a first top slag modifier to the molten steel to reduce the oxidizing property of the top slag;

[0007] The refining includes LF refining and RH refining in sequence;

[0008] The LF refining sequentially comprises: adding a second top slag modifier into the molten steel to increase the binary basicity of the top slag and reduce the oxidizability of the top slag, and increasing the temperature of the molten steel.

[0009] In some preferred embodiments, the chemical composition of the first top slag modifier includes, by weight percentage: Al: 30.00% to 40.00%, CaO: 30.00% to 35.00%, SiO2: 3.50% to 5.50%, FeO: 0.80% to 1.00%, Al2O3: 20.5% to 25.00%, P≤0.03%, S≤0.03%, C≤1%, and the rest are unavoidable impurities.

[0010] Preferably, the particle size of the first top slag modifier is 1mm to 50mm, wherein the weight proportion of particles with a particle size of 10mm to 40mm is not less than 90%, and the sum of the weight proportions of particles with a particle size less than 10mm and particles with a particle size greater than 40mm is not higher than 10%.

[0011] Preferably, when the oxygen content in the molten steel obtained by tapping is 400ppm~500ppm, the amount of the first top slag modifier added is 2.55~3.0kg / ton of steel. When the oxygen content exceeds 500ppm, the amount of the first top slag modifier added increases by 0.25~0.35kg / ton of steel for every 50ppm increase in the oxygen content.

[0012] In some preferred embodiments, after the second top slag modifier is added to the molten steel, the ratio of CaO content to SiO2 content in the top slag is ≥10, the Al2O3 content is 28% to 33%, and the FeO content + MnO content is ≤0.8% in weight percentage;

[0013] Preferably, the ratio of CaO content to SiO2 content is 12-15.

[0014] In some preferred embodiments, the chemical composition of the second top slag modifier includes, by weight percentage: Al: 35% to 45%, CaO: 20% to 25%, SiO2≤5%, FeO≤0.90%, Al2O3: 18% to 20%, P≤0.03%, S≤0.03%, MgO≤4.00%, C≤1%, and the rest are unavoidable impurities.

[0015] Preferably, the particle size of the second top slag modifier is 5mm-30mm, wherein the weight proportion of particles with a particle size of 10mm-20mm is not less than 95%, and the sum of the weight proportions of particles with a particle size less than 10mm and particles with a particle size greater than 20mm is not higher than 5%.

[0016] In some preferred embodiments, the RH refining sequentially comprises: oxygen blowing decarburization treatment, adding aluminum to the molten steel at one time for deoxidation and alloying treatment, adding alloys other than aluminum to the molten steel for alloying treatment, soft blowing treatment, and calming treatment;

[0017] Preferably, the soft blowing treatment lasts for no less than 12 minutes, and the sedation treatment lasts for no less than 15 minutes.

[0018] Preferably, the final temperature of the increased molten steel temperature is the liquidus temperature of the steel grade + 30°C ± 5°C + ΔT, wherein ΔT is the value obtained by subtracting ΔT3 from the sum of ΔT1 and ΔT2, wherein ΔT1 is the difference between the outlet temperature of the LF refining and the outlet temperature of the RH refining, ΔT2 is the temperature drop of the molten steel caused by the addition of alloy in the RH refining, and ΔT3 is the temperature rise of the molten steel caused by deoxidation in the RH refining.

[0019] In a second aspect, the present invention provides a filter comprising a housing, wherein the housing is prepared by deep drawing a steel plate rolled from a casting obtained by the smelting method as described in the first aspect.

[0020] The smelting method of filter steel of the present invention includes molten iron desulfurization treatment, converter smelting, refining and continuous casting processes, and the refining process includes LF refining and RH refining. The converter smelting process includes adding a first top slag modifier to the molten steel after tapping to reduce the oxidizing property of the top slag. The LF refining process includes adding a second top slag modifier to the molten steel to increase the binary basicity of the top slag, increase the Al2O3 content in the top slag, reduce the oxidizing property of the top slag, and enhance the top slag's adsorption capacity for Al2O3 in the molten steel. The top slag composition is adjusted through LF refining, and the top slag composition is no longer adjusted during the RH refining process, which can reduce the temperature drop during the RH refining process. By increasing the molten steel temperature during LF refining, the temperature drop caused by decarburization, alloying, soft blowing, calming and other operations during the RH refining process can be compensated. The RH refining process does not require the addition of aluminum to increase the temperature, which can significantly reduce Al2O3 inclusions in the steel. The top slag composition is not adjusted during the RH refining process, which can reduce the converter tapping temperature to 1590℃~1610℃, which can significantly reduce the converter tapping temperature, reduce the impact on the converter lining, increase the service life of the converter lining, and increase the service life of the converter. DETAILED DESCRIPTION

[0021] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0022] The inventors of the present invention have found that the service life of the converter used to prepare filter steel in the prior art is short, and the prepared steel contains a large amount of Al2O3 inclusions, which leads to defects such as cracking and sand holes during the processing of the filter housing.

[0023] In this regard, in a first aspect, the present invention provides a smelting method for filter steel, the method comprising: molten iron desulfurization, converter smelting, refining and continuous casting, wherein the converter smelting comprises: a converter tapping temperature of 1590°C to 1610°C, and after tapping, adding a first top slag modifier to the molten steel to reduce the oxidizing property of the top slag;

[0024] The refining includes LF refining and RH refining in sequence;

[0025] The LF refining sequentially comprises: adding a second top slag modifier into the molten steel to increase the binary basicity of the top slag and reduce the oxidizability of the top slag, and increasing the temperature of the molten steel.

[0026] The smelting method of filter steel of the present invention includes molten iron desulfurization treatment, converter smelting, refining and continuous casting processes. After the converter smelts and taps the steel, a first top slag modifier is added to the molten steel to reduce the oxidizability of the top slag, and heat preservation reduces the temperature loss of the molten steel to avoid uneven composition caused by adding too much top slag modifier at one time. Refining includes LF refining and RH refining. The LF refining process includes adding a second top slag modifier to the molten steel to increase the binary basicity of the top slag, increase the Al2O3 content in the top slag and reduce the oxidizability of the top slag, thereby improving the adsorption capacity of the top slag on Al2O3 in the molten steel. The oxidizability of the top slag is adjusted in the converter smelting process and the LF refining process respectively, avoiding adjusting the top slag in the RH refining process. The oxidizing property of the present invention can, on the one hand, reduce the temperature drop in the RH refining process and improve the adsorption capacity of the top slag on Al2O3 in the molten steel; on the other hand, it can significantly reduce the converter tapping temperature, which can be reduced to 1590℃~1610℃. By reducing the converter tapping temperature, the influence of high temperature on the converter lining can be reduced, the service life of the converter lining can be improved, and the service life of the converter can be increased. The present invention can also compensate for the temperature drop caused by decarburization, alloying, soft blowing, calming and other working operations in the RH refining process by increasing the molten steel temperature during LF refining. There is no need to add aluminum to increase the temperature during the RH refining process, which can significantly reduce Al2O3 inclusions in the steel and avoid defects such as cracking and sand holes in the filter housing during processing.

[0027] Binary alkalinity refers to the ratio of the weight content of CaO to the weight content of SiO2.

[0028] The present invention does not limit the type of the first top slag modifier, as long as it can reduce the oxidizability of the top slag. In some preferred embodiments, the chemical composition of the first top slag modifier includes, by weight percentage, the following: Al: 30.00% to 40.00%, CaO: 30.00% to 35.00%, SiO2: 3.50% to 5.50%, FeO: 0.80% to 1.00%, Al2O3: 20.5% to 25.00%, P ≤ 0.03%, S ≤ 0.03%, C ≤ 1%, and the remainder are unavoidable impurities. The Al content refers to the content of Al element. Under this preferred scheme, the amount of Al added is 30.00% to 40.00%, and the amount of Al2O3 added is 20.5% to 25.00%. In view of the high oxygenity (FeO+MnO≥10%), high SiO2 content (SiO2≥13%), and low Al2O3 content (Al2O3≤2%) of the top slag after steel is tapped from the converter, the first top slag modifier is used to preliminarily adjust the top slag composition to reduce the oxidizability of the top slag and increase the Al2O3 content in the top slag. The Al in the modifier can be more dispersed to fully reduce the oxygen content of the top slag and increase the Al2O3 content in the top slag. According to the principle of like charges attract like substances, the high and dispersed Al2O3 content in the top slag is conducive to improving the top slag's ability to adsorb Al2O3 inclusions, and preliminarily reducing the endogenous alumina and existing alumina content in the steel.

[0029] In the first top slag modifier of the present invention, the Al content can be specifically, for example, 32wt%, 34wt%, 36wt% and 38wt%, the CaO content can be specifically, for example, 31wt%, 32wt%, 33wt% and 34wt%, the SiO2 content can be specifically, for example, 3.8wt%, 4wt%, 4.2wt%, 4.5wt%, 4.8wt%, 5wt% and 5.2wt%, the FeO content can be specifically, for example, 0.85wt%, 0.9wt% and 0.95wt%, and the Al2O3 content can be specifically, for example, 21wt%, 22wt%, 23wt% and 24wt%.

[0030] The present invention does not limit the particle size of the first top slag modifier. Preferably, the particle size of the first top slag modifier is 1mm to 50mm, wherein the weight proportion of particles with a particle size of 10mm to 40mm is not less than 90%, and the sum of the weight proportions of particles with a particle size less than 10mm and particles with a particle size greater than 40mm is not more than 10%. Under this preferred embodiment, the weight proportion of particles with a particle size of 10mm to 40mm is not less than 90%, which is more conducive to the rapid melting of the modifier into the existing top slag after addition, exerting the effect of the top slag modifier and increasing the slag formation speed.

[0031] Preferably, when the oxygen content in the molten steel obtained by tapping is 400ppm-500ppm, the amount of the first top slag modifier added is 2.55-3.0kg / ton of steel. When the oxygen content exceeds 500ppm, the amount of the first top slag modifier added is increased by 0.25-0.35kg / ton of steel for every 50ppm increase in the oxygen content. Under this preferred embodiment, when the oxygen content in the molten steel obtained by tapping is 400ppm-500ppm, the amount added is 2.55-3.0kg / ton of steel. When the oxygen content exceeds 500ppm, the amount added is increased by 0.25-0.35kg / ton of steel for every 50ppm increase in the oxygen content. Adding a large proportion of the first top slag modifier is more conducive to rapid top slag pre-deoxidation on the one hand. On the other hand, by gradually modifying the slag, it is avoided that too much top slag modifier is added at one time in the subsequent process, which is more conducive to avoiding poor slag formation and improving the ability of the top slag to adsorb inclusions such as Al2O3.

[0032] The inner wall temperature of the ladle for converter tapping of the present invention is preferably not lower than 950°C, the carbon content of the molten steel from the converter tapping is preferably 0.030wt%≤C≤0.070wt%, and oxygen determination is preferably performed after tapping is completed. During the oxygen determination operation, the depth of the oxygen determination gun inserted into the molten steel is preferably 400mm~500mm, and the time for the oxygen determination control head to be immersed in the molten steel is preferably 5s~7s. Preferably, after the first top slag modifier is added, a slag sample is taken for component analysis.

[0033] In some preferred embodiments, after adding the second top slag modifier to the molten steel, the ratio of the CaO content to the SiO2 content in the top slag is ≥10, the Al2O3 content is 28% to 33%, and the FeO content + MnO content is ≤0.8% by weight; preferably, the ratio of the CaO content to the SiO2 content is 12 to 15. Under this preferred embodiment, after adding the second top slag modifier, the ratio of the CaO content to the SiO2 content in the top slag is ≥10, the Al2O3 content in the slag is 28% to 33%, and the FeO content + MnO content is ≤0.8%, which is more conducive to improving the adsorption capacity of the top slag for Al2O3 in steel and reducing Al2O3 inclusions in the steel. The ratio of the CaO content to the SiO2 content is 12 to 15, which is more conducive to improving the adsorption capacity for Al2O3 in steel.

[0034] In some preferred embodiments, the chemical composition of the second top slag modifier includes, by weight percentage: Al: 35% to 45%, CaO: 20% to 25%, SiO2≤5%, FeO≤0.90%, Al2O3: 18% to 20%, P≤0.03%, S≤0.03%, MgO≤4.00%, C≤1%, and the rest are unavoidable impurities. Under this preferred embodiment, the Al content of the second top slag modifier is 35% to 45%, and the Al2O3 content is 18% to 20%. The Al2O3 content is lower than the Al2O3 content of the first top slag modifier. On the one hand, it can further reduce the oxidizability of the top slag, and is more conducive to enhancing the top slag's ability to adsorb Al2O3 inclusions, reducing the content of deoxidized alumina and existing alumina in the molten steel. Using a relatively low Al2O3 content is also more conducive to improving the top slag fluidity, avoiding the problem that the top slag adsorption capacity is reduced instead of increased due to excessive Al2O3 content in the top slag.

[0035] In the second top slag modifier of the present invention, the Al content can be, for example, 35wt%, 37wt%, 39wt%, 41wt%, 43wt% and 45wt%, the CaO content can be, for example, 20wt%, 21wt%, 22wt%, 23wt%, 24wt% and 25wt%, the SiO2 content can be, for example, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, the FeO content can be, for example, 0.1wt%, 0.3wt%, 0.5wt%, 0.7wt%, 0.9wt%, the Al2O3 content can be, for example, 18wt%, 18.5wt%, 19wt%, 19.5wt%, 20wt%, and the MgO content can be, for example, 1wt%, 2wt%, 3wt%, 4wt%.

[0036] The present invention does not limit the particle size of the second top slag modifier. Preferably, the particle size of the second top slag modifier is 5mm to 30mm, of which the weight proportion of particles with a particle size of 10mm to 20mm is not less than 95%, and the sum of the weight proportions of particles with a particle size greater than 20mm and particles with a particle size less than 10mm is not more than 5%. Under this preferred embodiment, a second top slag modifier with a smaller particle size than the first top slag modifier is used. Specifically, the weight proportion of particles with a particle size of 10mm to 20mm is not less than 95%, which is more conducive to rapid slag formation and uniformity of top slag composition in the LF refining process, thereby improving top slag performance.

[0037] The addition amount of the second top slag modifier of the present invention is preferably 1.0 to 2.5 kg per ton of steel.

[0038] In the LF refining process of the present invention, when the temperature of the molten steel is increased, the heating rate is preferably 6° C. to 8° C. / min.

[0039] In some preferred embodiments, the RH refining includes, in sequence: oxygen blowing decarburization treatment, adding aluminum to the molten steel at one time for deoxidation alloying treatment, adding alloys other than aluminum to the molten steel for alloying treatment, soft blowing treatment, and calming treatment; preferably, the time of the soft blowing treatment is not less than 12 minutes, and the time of the calming treatment is not less than 15 minutes. Among them, the deoxidation alloying treatment includes removing oxygen from the molten steel according to the target oxygen content of the steel for the filter. After decarburization, the molten steel contains a large amount of free oxygen. Under this preferred embodiment, adding aluminum to the molten steel at one time for deoxidation alloying treatment can produce a large amount of Al2O3 inclusions densely, which is beneficial to the collision growth and removal of the inclusions, and is more conducive to improving the purity of the molten steel and reducing the Al2O3 inclusions in the steel. Adding alloys other than aluminum to the molten steel for alloying treatment, soft blowing treatment, and calming treatment is more conducive to the full floating of inclusions such as Al2O3 in the molten steel and the reduction of Al2O3 inclusions in the steel. The soft blowing time is not less than 12 minutes, and the calming treatment time is not less than 15 minutes, which is more conducive to the full floating of inclusions such as Al2O3.

[0040] The amount of aluminum added in the deoxidation alloying treatment of the present invention is preferably calculated according to the following formula: Al = (1.125% [O] + △% [Al])·W / R·η, wherein: △% [Al] is the difference between the actual concentration of aluminum and the target concentration, W is the weight of the molten steel (kg), R is the efficiency of aluminum, η is the purity of aluminum, and % [O] is the free oxygen content in the molten steel.

[0041] The amount of alloy added in the alloying treatment is preferably calculated according to the following formula: the amount of ferroalloy added of a certain element = [(target value of the element - content of the element before alloying) × amount of molten steel treated] / yield of the alloying element × content of the element in the ferroalloy.

[0042] The circulating gas flow rate in the oxygen blowing decarburization process of the present invention is preferably 100m 3 / h~125m 3 / h, preferably a lower flow rate is used in the early stage to prevent splashing caused by oxygen decarburization, and a higher flow rate is used in the later stage to facilitate the rapid decarburization reaction. Preferably, when the C content of molten steel leaving the LF refining station is ≥0.07%, the oxygen lance position is adjusted to 12m~14m, and the oxygen blowing intensity is not higher than 1800m 3 / h. Preferably, after the deoxidation alloying treatment of aluminum is added, the circulating gas flow rate of RH refining is controlled at 250m 3 / h~320m 3 / h. After adding aluminum and circulating for 2-3 minutes, alloys other than aluminum are added to the molten steel for alloying. Preferably, the alloys are added in the order of FeMn → FeTi, with FeTi added after pure degassing to ensure the yield of Ti. After adding FeTi, soft blowing is performed, followed by a sedation treatment. The pure degassing time is preferably controlled according to the amount of aluminum added. When the amount of aluminum added is less than 350kg / furnace, the pure degassing time is greater than 8 minutes. When the amount of aluminum added is 350kg-500kg / furnace, the pure degassing time is ≥10 minutes.

[0043] Preferably, the final temperature of the elevated molten steel temperature is the liquidus temperature of the steel grade + 30°C ± 5°C + ΔT, where ΔT is the sum of ΔT1 and ΔT2 minus ΔT3. ΔT1 is the difference between the exit temperature of the LF refining and the exit temperature of the RH refining, ΔT2 is the temperature drop of the molten steel caused by the addition of the alloy during the RH refining, and ΔT3 is the temperature rise of the molten steel caused by deoxidation during the RH refining. This preferred embodiment is more conducive to avoiding the addition of aluminum to increase the temperature during the RH refining stage and reducing Al2O3 inclusions in the steel. The temperature drop of the molten steel caused by the addition of the alloy includes the temperature drop caused by the addition of room-temperature metallic manganese, ferrotitanium, and aluminum, and the temperature rise caused by deoxidation is the temperature rise caused by the oxidation reaction.

[0044] The steel composition of the filter steel prepared by the present invention is preferably C: 0.0010-0.0018%, Mn: 0.40-0.60%, S≤0.005%, P≤0.015%, Si≤0.015%, Ti: 0.04-0.055%, Als: 0.055-0.070%, and the balance is iron and inevitable impurities.

[0045] The sulfur content [S] in the steel after the molten iron desulfurization treatment of the present invention is preferably not more than 0.0025%, the exposed metal bright surface of the molten iron after desulfurization is preferably not less than 95%, and the outlet temperature of the molten iron after desulfurization is preferably not more than 1440°C, which provides convenience for converter dephosphorization.

[0046] The continuous casting of the present invention preferably includes protective pouring, long water nozzle, argon pressure of 0.40~1.0MPa, flow rate of 20~50L / min, argon plug rod, argon pressure of 0.40~1.0MPa, flow rate of 2~3.5L / min, inter-plate and upper water nozzle, argon pressure of 0.40~1.0MPa, flow rate of 5~8L / min, crystallizer liquid level fluctuation ≤±2.5mm, wherein constant pulling speed operation is adopted, and the pulling speed is 1.3m / min~1.4m / min.

[0047] In a second aspect, the present invention provides a filter, wherein the housing is prepared by deep drawing a steel plate rolled from a casting obtained by the smelting method described in the first aspect.

[0048] The filter of the present invention has no defects such as sand holes on the filter housing, and the filter has better pressure resistance, vibration resistance, durability, low temperature resistance and high temperature resistance.

[0049] The present invention is further described in detail below with reference to specific embodiments.

[0050] Example 1

[0051] The steel composition is C: 0.0010wt%~0.0018wt%, Mn: 0.40wt%~0.60wt%, S≤0.005wt%, P≤0.015wt%, Si≤0.015wt%, Ti: 0.04wt%~0.055wt%, Als: 0.055wt%~0.070%, and the balance is iron and inevitable impurities.

[0052] A smelting method for filter steel, comprising:

[0053] Step 1: Desulfurization of molten iron. After desulfurization, the sulfur content of the molten iron is 0.0015%. After desulfurization, the exposed metal surface of the molten iron is greater than 95%. The outlet temperature of the molten iron after desulfurization is 1400℃.

[0054] Step 2: Converter smelting, the ladle used for converter tapping is a Class A ladle, the inner wall temperature of the ladle is 1000°C, the converter tapping temperature is 1600°C, the carbon content of the molten steel from the converter tapping is 0.06wt%, after tapping is completed, oxygen treatment is performed, the depth of the oxygen gun inserted into the molten steel is 450mm, the oxygen control head is immersed in the molten steel for 6 seconds, and the first top slag modifier is added after oxygen determination, and the composition of the first top slag modifier is Al: 32.42wt%, CaO: 34.16wt%, SiO2: 4.35wt% , FeO: 0.95wt%, Al2O3: 24.73wt%, P: 0.015wt%, S: 0.02wt%, C: 0.15wt%, the balance being unavoidable impurities. The first top slag modifier is spherical in shape and has a particle size of 1mm to 50mm. The weight proportion of particles with a particle size of 10mm to 40mm is 95.7%, and the weight proportion of particles with a particle size greater than 40mm and particles with a particle size less than 10mm is 4.3%. The melting point of the first top slag modifier is 1360°C. The oxygen content in the molten steel is 460ppm. The addition rate of the first top slag modifier is 2.8kg / ton of steel. 5 minutes after the addition of the first top slag modifier, a top slag sample is taken for composition analysis.

[0055] Step 3: LF refining, after entering the LF refining furnace, temperature is measured, and a second top slag modifier is added to the molten steel. The composition of the second top slag modifier is Al: 43.91wt%, CaO: 24.32wt%, SiO2: 4.62wt%, FeO: 0.75wt%, Al2O3: 19.69wt%, P: 0.02wt%, S: 0.01wt%, MgO: 3.51wt%, C: 0.15wt%, and the remainder is unavoidable impurities. The shape of the second top slag modifier is spherical, with a particle size of 5mm to 30mm, and the weight proportion of particles with a particle size of 10mm to 20mm is 96.6%. The sum of the weight proportions of particles with a particle size of less than 10mm and particles with a particle size greater than 20mm is 3.4%. The addition amount of the second top slag modifier is 1.5kg / ton of steel. After the second top slag modifier is added to the molten steel, the weight percentage is 2.5%. According to the ratio, the ratio of CaO content to SiO2 content in the top slag is 13.5, the content of Al2O3 is 30.22%, and the content of FeO + MnO is 0.63%. Then the molten steel temperature is increased at a heating rate of 7°C / min. The target temperature is the liquidus temperature of the steel grade + 30°C + △T1 + △T2 - △T3, △T1 is the difference between the outlet temperature of LF refining and the outlet temperature of RH refining, wherein the ladle is a grade A ladle, the cooling rate is 1.5°C / min, △T2 is the temperature drop of the molten steel caused by the addition of alloys in RH refining, wherein the temperature drop of metallic manganese is 0.0076°C / kg, the temperature drop of ferrotitanium is 0.0058°C / kg, and the temperature drop of aluminum particles is 0.0033°C / kg, △T3 is the temperature rise of the molten steel caused by deoxidation in RH refining, and the temperature rises by 3.5°C for every 100 ppm of oxygen removed. Before LF refining leaves the station, a molten steel sample is taken for composition analysis;

[0056] Step 4: RH refining, oxygen blowing decarburization treatment, the circulating gas flow rate during the oxygen blowing decarburization treatment is 100m 3 / h~125m 3 / h, the circulation gas flow rate in the first stage is 100m 3 / h, the circulation gas flow rate of the second stage is 125m 3 / h, the carbon content of molten steel leaving the LF refining station is 0.09%, the oxygen lance position is 13m, and the oxygen blowing intensity is 1600m 3 / h, after decarburization to the required composition range of the steel grade, deoxidation and alloying treatment is carried out, and aluminum particles are added to the molten steel at one time according to the oxygen content. The amount of aluminum particles added is calculated according to the following formula: Al = (1.125% [O] + △% [Al])·W / R·η, where: △% [Al] is the difference between the actual concentration of aluminum and the target concentration, W is the weight of the molten steel (kg), R is the efficiency of aluminum, η is the purity of aluminum, % [O] is the free oxygen content in the molten steel, and after the aluminum particles are added, the RH circulating gas flow rate is adjusted to 300m 3 / h, after adding aluminum and circulating for 3 minutes, alloys other than aluminum are added to the molten steel for alloying treatment. The alloying treatment process is the addition of FeMn, pure degassing, and the addition of FeTi. The amount of alloy added is calculated according to the following formula: the amount of ferroalloy added of a certain element = [(target value of the element - content of the element before adding alloy) × amount of molten steel treated] / yield of the alloying element × content of the element in the ferroalloy. The pure degassing time is 10 minutes, followed by soft blowing treatment and calming treatment. The soft blowing time is 20 minutes, and the calming time is 30 minutes, so that inclusions in the molten steel can fully float up.

[0057] Step 5: Continuous casting, protective pouring, long water nozzle, argon pressure of 0.8MPa, flow rate of 30L / min, argon plug rod, argon pressure of 0.6MPa, flow rate of 3L / min, inter-plate and upper water nozzle, argon pressure of 0.6MPa, flow rate of 7.5L / min, crystallizer liquid level fluctuation ≤±2.5mm, constant pulling speed operation is adopted, and the pulling speed is 1.4m / min.

[0058] Example 2

[0059] The smelting method is carried out with reference to Example 1, except that in step 2, the amount of the first top slag modifier added is 1.9 kg / ton of steel, and in step 3, the amount of the second top slag modifier added is 2.3 kg / ton of steel. After adding the second top slag modifier to the molten steel, the ratio of the CaO content to the SiO2 content in the top slag is 12.6, the Al2O3 content in the top slag is 29.09%, and the FeO content + MnO content is 0.98% by weight.

[0060] Example 3

[0061] The smelting method is carried out with reference to Example 1, except that in step 2, the composition of the first top slag modifier is different, Al: 43.62wt%, CaO: 30.08wt%, SiO2: 3.65wt%, FeO: 0.92wt%, Al2O3: 20.52wt%, P: 0.01wt%, S: 0.02wt%, C: 0.15wt%, and the remainder is unavoidable impurities.

[0062] Example 4

[0063] The smelting method is carried out with reference to Example 1, except that in step 2, the composition of the first top slag modifier is different, Al: 37.62wt%, CaO: 34.16wt%, SiO2: 5.18wt%, FeO: 0.95wt%, Al2O3: 18.52wt%, P: 0.015wt%, S: 0.02wt%, C: 0.15wt%, and the remainder is unavoidable impurities.

[0064] Example 5

[0065] The smelting method was carried out with reference to Example 1, except that the amount of the second top slag modifier added was 2.1 kg / ton of steel. After the second top slag modifier was added to the molten steel, the ratio of the CaO content to the SiO2 content in the top slag was 9.8, the Al2O3 content in the top slag was 29.72%, and the FeO content + MnO content was 0.92%, calculated in weight percentage.

[0066] Example 6

[0067] The smelting method is carried out with reference to Example 1, except that the composition of the second top slag modifier is different, Al: 38.65wt%, CaO: 24.86wt%, SiO2: 3.58wt%, FeO: 0.83wt%, Al2O3: 22.69wt%, P: 0.02wt%, S: 0.01wt%, MgO: 2.85wt%, C: 0.23wt%, and the remainder is inevitable impurities. After adding the second top slag modifier to the molten steel, the ratio of CaO content to SiO2 content in the top slag is 11.23, the Al2O3 content in the top slag is 33.12%, and the FeO content + MnO content is 0.87%.

[0068] Comparative Example 1

[0069] The smelting method was similar to that of Example 1, except that the LF refining process was omitted, and the first and second top slag modifiers were not added. During the RH refining process, the top slag composition was adjusted by adding the top slag modifier after the RH process. The converter tapping temperature was adjusted to 1680°C, and aluminum was added during the RH refining process to ensure the pouring temperature.

[0070] The filter steel samples provided in Examples 1 to 6 and Comparative Example 1 were tested for Al2O3 inclusion control, and the test results are shown in Table 1. Microscopic inclusions were graded using GB / T 10561-2023, with requirements of A coarse (AH) ≤ 1.0, A fine (AT) ≤ 1.0; B coarse (BH) ≤ 0.5, B fine (BT) ≤ 1.0; C coarse (CH) ≤ 0.5, C fine (CT) ≤ 0.5; D coarse (DH) ≤ 0.5, D fine (DT) ≤ 1.0; and DS ≤ 0.5.

[0071] Table 1

[0072] Serial number <![CDATA[Al2O3 Microscopic Inclusion Detection Results (Grade)]]> Example 1 AT0,AH0,BT0,BH0,CT0,CH0,DT0,DH0,DS0 Example 2 AT0,AH0,BT0.5,BH0,CT0,CH0,DT0,DH0,DS0 Example 3 AT0,AH0,BT0.5,BH0,CT0,CH0,DT0,DH0,DS0 Example 4 AT0,AH0,BT0.5,BH0,CT0,CH0,DT0.5,DH0,DS0 Example 5 AT0,AH0,BT0,BH0,CT0,CH0,DT0.5,DH0,DS0 Example 6 AT0,AH0,BT0.5,BH0,CT0,CH0,DT0.5,DH0,DS0 Comparative Example 1 AT0,AH0,BT1.0,BH0,CT0,CH0,DT0,DH0.5,DS0.5

[0073] By comparing the embodiments and comparative examples, the method of the present invention is used to add a first top slag modifier to the molten steel after steel is tapped from the converter, and to add a second top slag modifier to the molten steel during LF refining, which can reduce the size and quantity of Al2O3 inclusions in the steel and improve the quality of steel for filters.

[0074] Comparing Example 1 and Example 2, it can be seen that when the oxygen content in the molten steel obtained by the steelmaking process of the present invention is 400ppm~500ppm, the addition amount of the first top slag modifier is 2.55~3.0kg / ton of steel, which is more conducive to improving the ability of the top slag to adsorb inclusions such as Al2O3, reducing the size and number of Al2O3 inclusions in the steel, and improving the quality of the steel for the filter; Comparing Examples 1, 3 and 4, the Al content of the first top slag modifier is 30.00wt%~40.00wt%, and the Al2O3 content is 20.5%~25.00%, which is more conducive to improving the ability of the top slag to adsorb inclusions such as Al2O3, reducing the size and number of Al2O3 inclusions in the steel, and improving the quality of the steel for the filter. l2O3 inclusions, thereby improving the quality of steel for filters; comparing Example 1 and Example 5, after adding the second top slag modifier to the molten steel, the ratio of CaO content to SiO2 content in the top slag is made ≥10, which is more conducive to improving the adsorption capacity of the top slag on Al2O3 in steel, reducing the size and quantity of Al2O3 inclusions in steel, and improving the quality of steel for filters; comparing Example 1 and Example 6, the Al2O3 content of the second top slag modifier is 18% to 20%, which is more conducive to improving the adsorption capacity of the top slag on Al2O3 in steel, reducing the size and quantity of Al2O3 inclusions in steel, and improving the quality of steel for filters.

Claims

1. A method for smelting filter steel, the method comprising: Hot metal desulfurization treatment, converter smelting, refining and continuous casting, characterized in that the converter smelting includes: the converter tapping temperature is 1590℃~1610℃, and after tapping, a first top slag modifier is added to the molten steel to reduce the oxidizing property of the top slag; The refining includes LF refining and RH refining in sequence; The LF refining sequentially comprises: adding a second top slag modifier to the molten steel to increase the binary basicity of the top slag and reduce the oxidizability of the top slag, and increasing the temperature of the molten steel; The chemical composition of the first top slag modifier includes, by weight percentage, Al: 30.00% to 40.00%, CaO: 30.00% to 35.00%, SiO2: 3.50% to 5.50%, FeO: 0.80% to 1.00%, Al2O3: 20.5% to 25.00%, P≤0.03%, S≤0.03%, C≤1%, and the rest are unavoidable impurities; The chemical composition of the second top slag modifier includes, by weight percentage, Al: 35% to 45%, CaO: 20% to 25%, SiO2≤5%, FeO≤0.90%, Al2O3: 18% to 20%, P≤0.03%, S≤0.03%, MgO≤4.00%, C≤1%, and the rest are unavoidable impurities.

2. The smelting method according to claim 1, characterized in that: The particle size of the first top slag modifier is 1mm to 50mm, wherein the weight proportion of particles with a particle size of 10mm to 40mm is not less than 90%, and the sum of the weight proportions of particles with a particle size less than 10mm and particles with a particle size greater than 40mm is not higher than 10%.

3. The smelting method according to claim 1, characterized in that: When the oxygen content in the molten steel obtained by tapping is 400ppm~500ppm, the addition amount of the first top slag modifier is 2.55~3.0kg / ton of steel. When the oxygen content exceeds 500ppm, the addition amount of the first top slag modifier increases by 0.25~0.35kg / ton of steel for every 50ppm increase in the oxygen content.

4. The smelting method according to claim 1, characterized in that: After the second top slag modifier is added to the molten steel, the ratio of CaO content to SiO2 content in the top slag is ≥10, the Al2O3 content is 28% to 33%, and the FeO content + MnO content is ≤0.8%, calculated by weight percentage.

5. The smelting method according to claim 4, characterized in that: After the second top slag modifier is added to the molten steel, the ratio of CaO content to SiO2 content in the top slag is 12 to 15 in weight percentage.

6. The smelting method according to claim 1, characterized in that: The particle size of the second top slag modifier is 5mm-30mm, wherein the weight proportion of particles with a particle size of 10mm-20mm is not less than 95%, and the sum of the weight proportions of particles with a particle size less than 10mm and particles with a particle size greater than 20mm is not more than 5%.

7. The smelting method according to claim 1, characterized in that: The RH refining includes: oxygen blowing decarburization treatment, adding aluminum into the molten steel at one time for deoxidation and alloying treatment, adding alloys other than aluminum into the molten steel for alloying treatment, soft blowing treatment, and calming treatment.

8. The smelting method according to claim 7, characterized in that: The time of the soft blowing treatment is not less than 12 minutes, and the time of the sedation treatment is not less than 15 minutes.

9. The smelting method according to claim 7, characterized in that: The final temperature of the increased molten steel temperature is the liquidus temperature of the steel grade + 30°C ± 5°C + ΔT, where ΔT is the value obtained by subtracting ΔT3 from the sum of ΔT1 and ΔT2, ΔT1 is the difference between the outlet temperature of the LF refining and the outlet temperature of the RH refining, ΔT2 is the temperature drop of the molten steel caused by the addition of alloy in the RH refining, and ΔT3 is the temperature rise of the molten steel caused by deoxidation in the RH refining.

10. A filter comprising a housing, characterized in that: The shell is prepared by deep drawing a steel plate rolled from a cast billet smelted by the smelting method according to any one of claims 1 to 9.