High-efficiency refining preparation method of high-aluminum steel and high-aluminum steel

Abstract

The present application discloses a method for efficiently refining and preparing high-aluminum steel and high-aluminum steel. The method includes subjecting the raw molten steel to LF refining under a reducing atmosphere throughout the process; LF refining includes adding hot refining slag of low-silicon steel to the raw molten steel, then adding aluminum to the raw molten steel and energizing to melt the aluminum, adding lime and low-silicon pre-melted refining slag during the process of energizing to melt the aluminum to obtain molten steel with deoxidation and alloying; subjecting the molten steel with deoxidation and alloying to RH refining to obtain high-aluminum steel molten steel after RH refining. According to the refining method of the present application, by adding lime for desulfurization and slag formation and adding hot refining slag of low-silicon steel in the deoxidation and alloying step, the slag system composition of the ladle slag is improved, which can not only reduce the secondary oxidation of aluminum during the treatment process, but also reduce the reaction between aluminum and SiO2 in the slag, reduce the ladle slag crusting, and solve the problem that aluminum in the molten steel of high-aluminum steel is prone to react with silicon dioxide in the ladle slag to form a ladle slag crust with high alkalinity and high melting point pointed out in the background art.

Description

Technical Field

[0001] This application belongs to the technical field of iron and steel metallurgy, and particularly relates to an efficient refining preparation method for high-aluminum steel and high-aluminum steel. Background Art

[0002] Due to its good corrosion resistance, low magnetic permeability, wear resistance, as well as high precision dimensions, high strength, light weight, and good ductility after treatment, high-aluminum steel is widely used in fields such as ships, military, aerospace, machinery manufacturing, automobiles, and chemicals.

[0003] However, during the smelting process of high-aluminum steel, aluminum in the molten steel easily reacts with silicon dioxide in the ladle slag to form a ladle slag crust with high alkalinity and high melting point, resulting in a reduction in the recovery rate of aluminum. Moreover, the reaction between aluminum in the molten steel and silicon dioxide and phosphorus pentoxide in the ladle slag leads to instability in the increase of silicon, phosphorus, and manganese in the molten steel, making it difficult to control the composition of the molten steel. Summary of the Invention

[0004] The embodiments of this application provide an efficient refining preparation method for high-aluminum steel, which can reduce the reaction between aluminum in the molten steel and silicon dioxide in the slag to form ladle slag and improve the recovery rate of aluminum.

[0005] In a first aspect, the embodiments of this application provide an efficient refining preparation method for high-aluminum steel, and the method includes:

[0006] LF refining of the raw molten steel is carried out throughout the process under a reducing atmosphere; wherein, LF refining includes:

[0007] Add low-silicon steel hot refining slag to the raw molten steel, then add aluminum to the molten steel and energize to melt the aluminum. During the process of melting the aluminum by energization, add lime and low-silicon pre-melted refining slag to the molten steel to obtain deoxidized and alloyed molten steel.

[0008] Carry out RH refining on the deoxidized and alloyed molten steel to obtain high-aluminum steel molten steel with an aluminum recovery rate ≥ 92wt% after RH refining.

[0009] In a second aspect, the embodiments of this application provide a high-aluminum steel, which is prepared according to the above-mentioned efficient refining preparation method for high-aluminum steel. By mass percentage, the components and contents of the high-aluminum steel are respectively:

[0010] C ≤ 0.06wt%, Si: 0.15wt% - 0.25wt%, Mn: 0.5wt% - 0.8wt%, Al: 3.5wt% - 5wt%, P ≤ 0.020wt%, S ≤ 0.006wt%, and the balance is iron and unavoidable impurities.

[0011] In one embodiment, the density of the above high-aluminum steel is 7.2g / mm 3 ~7.4g / mm3 。

[0012] The high-efficiency refining preparation method of high-aluminum steel according to the embodiments of the present application improves the slag system composition of the ladle slag by adding hot refining slag of low-silicon steel, adding lime for desulfurization and slag formation, and adding low-silicon pre-melted refining slag during the deoxidation alloying step. In this way, it can not only reduce the secondary oxidation of aluminum during the treatment process, but also reduce the reaction between aluminum and SiO2 in the slag, reduce the ladle slag crusting, and solve the problem that aluminum in the molten steel of high-aluminum steel in the background art is prone to react with silicon dioxide in the ladle slag to form a ladle slag crust with high alkalinity and high melting point. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required to be used in the embodiments of the present application will be briefly introduced below. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0014] Figure 1 It is a flow block diagram of the high-efficiency refining preparation method of high-aluminum steel provided by some embodiments of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0015] The features and exemplary embodiments of each aspect of the present application will be described in detail below. In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present application, rather than to limit the present application. For those skilled in the art, the present application can be implemented without some of these specific details. The following description of the embodiments is only intended to provide a better understanding of the present application by showing examples of the present application.

[0016] It should be noted that, in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without more limitations, the elements defined by the statement "including..." do not exclude the existence of additional identical elements in the process, method, article or device including the said elements.

[0017] To solve the problems of the existing technology, the embodiments of the present application provide an efficient refining preparation method for high-aluminum steel. First, the efficient refining preparation method for high-aluminum steel provided by the embodiments of the present application will be introduced below.

[0018] Figure 1 The flowchart of the efficient refining preparation method for high-aluminum steel provided by some embodiments of the present application is shown. As Figure 1 shown, the efficient refining preparation method for high-aluminum steel in the embodiments of the present application includes:

[0019] S4. LF refining of the raw molten steel is carried out throughout the process under a reducing atmosphere; wherein, the LF refining includes:

[0020] Adding hot low-silicon steel refining slag to the raw molten steel, then adding aluminum to the molten steel and energizing to melt the aluminum, and adding lime and low-silicon pre-melted refining slag during the process of energizing to melt the aluminum to obtain deoxidized and alloyed molten steel;

[0021] S5. RH refining of the deoxidized and alloyed molten steel is carried out to obtain high-aluminum steel molten steel with an aluminum recovery rate ≥ 92 wt% after RH refining.

[0022] In the efficient refining preparation method for high-aluminum steel in the embodiments of the present application, by adding hot low-silicon steel refining slag in the deoxidation and alloying step to improve the slag system composition of the ladle slag, and adding lime for desulfurization and slag formation, it can not only reduce the secondary oxidation of aluminum during the treatment process, but also reduce the reaction between aluminum and SiO2 in the slag, reduce the ladle slag crusting, and solve the problem that aluminum in the molten steel of high-aluminum steel is prone to react with silicon dioxide in the ladle slag to form a ladle slag crust with high alkalinity and high melting point pointed out in the background technology.

[0023] Different from the traditional process, in order to reduce the oxidation of aluminum and the problem of large fluctuations in the molten steel liquid level, in the efficient refining preparation method for high-aluminum steel in the embodiments of the present application, after adding aluminum blocks, instead of increasing the stirring by increasing the bottom blowing gas flow rate of the ladle to promote the melting of aluminum blocks, after adding aluminum, the aluminum is melted by power supply to accelerate the melting of aluminum, and combined with a reducing atmosphere to reduce the secondary oxidation of aluminum. At the same time, this also minimizes the steel slag reaction and stabilizes the components of the ladle slag.

[0024] As Figure 1 shown, in one embodiment, the efficient refining preparation method for high-aluminum steel in the embodiments of the present application further includes:

[0025] S1. The molten steel raw material is subjected to converter blowing to obtain raw molten steel with an oxygen content ≤ 0.07 wt%; wherein, the process parameters for converter blowing are: the height of the oxygen blowing lance from the molten steel liquid level in the early stage of converter blowing is 1.8 m to 2.0 m, the height of the oxygen blowing lance from the molten steel liquid level in the later stage of converter blowing is 1.4 - 1.8 m, and the bottom blowing flow rate is 0.06 M 3 / (t.min)~0.10M 3 / (t.min), and the end temperature is 1570°C to 1600°C. The C and P elements in the molten steel of the raw material are removed by converter blowing. The converter blowing time is 10 minutes to 14 minutes, preferably 12 minutes. The early stage of converter blowing refers to the first 9 minutes to 12 minutes of converter blowing. The bottom blowing gas is argon.

[0026] The molten slag is thin and vortex slag entrainment is likely to occur during tapping. P2O5 and SiO2 in the converter slag will react with the aluminum in the molten steel during LF treatment, resulting in an increase in silicon and phosphorus in the molten steel, and a decrease in the recovery rate of aluminum.

[0027] As Figure 1 shown, in one embodiment, the step of obtaining the molten steel of the raw material by subjecting the molten steel raw material to converter blowing, using an oxygen lance for converter blowing, further includes:

[0028] S2. After the oxygen lance stops blowing, before tapping the molten steel of the raw material, lime is added to the molten steel of the raw material to thicken the slag. The composition and content of the final converter slag obtained are: CaO: 52wt% - 58wt%, SiO2: 12wt% - 18wt%, MgO: 6wt% - 10wt%, FeO ≤ 18wt%, and the balance is impurities. Adding lime to the molten steel to thicken the slag reduces the sulfur content and oxygen content in the molten steel of the raw material. Adding lime to the molten steel of the raw material can increase the viscosity of the molten slag and make it thick, so that the molten slag is not easily carried by the molten steel to the next process, thereby reducing the slag content in the molten steel. Lime thickening slag is lime, in granular form, with a particle size less than or equal to 50 mm, so as to react with sulfur and oxygen elements in the molten steel.

[0029] In one embodiment, the composition of the final converter slag also needs to satisfy CaO / SiO2 ≥ 3 to improve the composition of the final converter slag and facilitate controlling the composition of the ladle slag system in LF furnace refining by subsequent operations of controlling converter slag tapping. The ratio of CaO and SiO2 is the basicity. The final converter slag with a basicity greater than 3 will thicken, reducing the slag entrainment phenomenon caused by vortex due to the too thin molten slag during tapping. As Figure 1 shown, in one embodiment, the step of obtaining the molten steel of the raw material by subjecting the molten steel raw material to converter blowing, further includes:

[0030] Transfer the molten steel of the raw material for tapping. During tapping, a slag blocking component is used to block the slag to weaken vortex slag entrainment. The slag blocking component is a slag stopper and / or a slide plate for slag blocking.

[0031] The high-efficiency refining preparation method of high-aluminum steel according to the embodiments of the present application uses a slag stopper and / or a slide plate to block the slag, so as to weaken the vortex slag entrainment caused by the thin molten slag during the tapping process, reduce the amount of slag flowing into the ladle during the tapping process, and make the amount of slag flowing into the ladle for each furnace of molten steel be 2.60 kg / ton to 3.80 kg / ton, or control the thickness of the slag flowing into the ladle ≤ 50 mm. By reducing the amount of slag flowing into the converter, the amount of slag in the LF refining step is reduced, thereby reducing the reaction between aluminum in the molten steel and SiO2 in the slag, controlling the composition of the ladle slag system, and reducing the secondary oxidation of aluminum in the molten steel and the formation of slag crust on the ladle during the treatment process.

[0032] Specifically, the control of the amount of slag flowing into the converter can be combined with a device for detecting the sensitivity of slag flow. The sensitivity of slag flow detection is set to the highest level, and an alarm is triggered when the amount of slag flowing into the converter final slag is greater than 10 wt%, and the continuous flow of the converter final slag is stopped.

[0033] As Figure 1 shown, in one embodiment, before the step of adding aluminum to the raw molten steel and energizing to melt the aluminum, it further includes:

[0034] S3. Add lime to the raw molten steel to remove the sulfur element in the raw molten steel, and obtain raw molten steel with sulfur ≤ 0.003 wt%.

[0035] Adjust the temperature of the raw molten steel with sulfur ≤ 0.003 wt% to ≤ 1580 °C, and add aluminum to the raw molten steel to reduce the oxidation of aluminum during the deoxidation alloying process.

[0036] Add low-silicon pre-melted refining slag to the raw molten steel to prepare for rapid slag formation in the refining furnace, which can improve the fluidity of the ladle slag, make the molten slag easy to foam, and facilitate LF submerged arc power transmission.

[0037] In one embodiment, the step S4 of adding low-silicon hot-state refining slag to the raw molten steel, then adding aluminum to the raw molten steel and energizing to melt the aluminum, and adding lime and low-silicon pre-melted refining slag during the process of energizing to melt the aluminum to obtain deoxidized alloyed molten steel includes:

[0038] S41. Add low-silicon hot-state refining slag to the raw molten steel. The composition and content of the low-silicon hot-state refining slag are: CaO: 52 wt% - 58 wt%, Al2O3: 26 wt% - 36 wt%, MgO: 5 wt% - 10 wt%, SiO2: ≤ 5 wt%, and the balance is inevitable impurities;

[0039] S42. Add aluminum to the raw molten steel to which the low-silicon hot-state refining slag has been added and energize to melt the aluminum, including:

[0040] Add aluminum to the raw molten steel in two batches, and apply electricity to melt the aluminum to obtain deoxidized and alloyed molten steel; during the process of melting aluminum by applying electricity, add lime to the molten steel to remove sulfur in the molten steel, so as to improve the fluidity of the ladle slag of high-aluminum steel, and obtain the refined slag system components and contents as follows: CaO: 50wt% - 55wt%, Al2O3: 45wt% - 50wt%, MgO: 5wt% - 10wt%, SiO2 ≤ 1wt%, FeO ≤ 0.5wt%, MnO ≤ 0.5wt%, and the balance is impurities; the mass ratio of calcium oxide to aluminum oxide in the refined slag system components also needs to satisfy: w(CaO) / w(Al2O3) = 0.8 - 1.2, so as to improve the fluidity of the ladle slag of high-aluminum steel and prevent the ladle slag from crusting;

[0041] S43. Add low-silicon pre-melted refining slag to the raw molten steel to achieve rapid slag formation in LF refining; among them, the components and contents of the low-silicon pre-melted refining slag are: CaO: 45wt% - 55wt%, Al2O3: 34wt% - 46wt%, MgO ≤ 6wt%, SiO2 ≤ 5wt%, Fe2O3 ≤ 1.5wt%, and the balance is inevitable impurities. The low-silicon pre-melted refining slag is the steel slag remaining in the ladle after the casting of low-silicon steel molten steel is completed.

[0042] In one embodiment, the step of adding aluminum to the raw molten steel in two batches includes:

[0043] Add aluminum to the raw molten steel for the first time to remove oxygen and sulfur elements in the raw molten steel, and obtain molten steel with an aluminum content of 0.05wt% - 0.10wt% and an Mn content of 0.8wt% - 0.9wt%;

[0044] Add aluminum to the molten steel from which oxygen and sulfur elements have been removed in batches for the second time to make the aluminum content in the molten steel meet the requirements of the steel grade. The aluminum content meeting the requirements of the steel grade means that the aluminum content in the molten steel reaches 3.5wt% - 5.0wt%.

[0045] In one embodiment, the process parameters for adding aluminum to the raw molten steel in batches are as follows: add aluminum in multiple times, with an interval of 1 minute to 3 minutes each time. Reduce the time interval for adding aluminum blocks several times to increase the aluminum content in a certain area of the molten steel, promote the precipitation rate of aluminum nitride, and reduce the adverse effects of the precipitation of aluminum nitride during casting on the mold powder. Avoid adding aluminum at high temperatures and increase the aluminum addition speed, which also helps to reduce the secondary oxidation of aluminum.

[0046] Specifically, add aluminum in 3 - 5 times, 2 tons each time, and the feeding time for each time is 20 seconds to 40 seconds, preferably 30 seconds.

[0047] In one embodiment, aluminum is added to the raw molten steel in the form of aluminum blocks, and the particle size of the aluminum blocks is 20 mm to 50 mm.

[0048] In one embodiment, in the step of electrically melting aluminum in the LF furnace refining, three-phase electricity is used for electrically melting aluminum. First, an arc is struck and power is supplied at a low current of 30,000 A to 34,000 A, and then it is gradually increased to 54,000 A to 55,000 A. Among them, when the difference between any two of the three-phase currents is less than 6,000 A, it is switched to 54,700 A to reduce the oxidation of aluminum during the LF process.

[0049] In one embodiment, in the step of electrically melting aluminum, a reducing atmosphere is used for the operation of electrically melting aluminum to reduce the secondary oxidation of aluminum.

[0050] In one embodiment, the LF furnace refining uses an argon reducing atmosphere for electrically melting aluminum. During the whole process of LF refining, the flow rate of bottom-blowing argon in the ladle is ≤800 NL / min, preferably 500 NL / min to 800 NL / min.

[0051] In one embodiment, for the molten steel in the LF refining process, the time of bottom-blowing argon after deoxidation and alloying of the molten steel is 8 minutes to 10 minutes; for the last batch of molten steel in the LF refining process, the time of bottom-blowing argon after deoxidation and alloying of the molten steel is ≥10 minutes to further remove alumina in the molten steel.

[0052] During the process of LF refining of the raw molten steel, there is less secondary oxidation and less alumina inclusions are generated. The calcium treatment process is cancelled to reduce costs. The calcium treatment process means that when many steel grades leave the LF furnace, calcium wire is added to the molten steel to modify the alumina inclusions in the molten steel so as to improve the castability of continuous casting.

[0053] As Figure 1 shown, in one embodiment, before the step of RH refining of the deoxidized and alloyed molten steel, it further includes:

[0054] Using the molten steel of a low-silicon steel grade to wash the RH vacuum tank to reduce the secondary oxidation of aluminum in the molten steel and the increase of titanium content. The oxygen in the RH vacuum tank is removed by washing the tank to reduce secondary oxidation.

[0055] In one embodiment, in the step of using the molten steel of a low-silicon steel grade to wash the RH vacuum tank, the low-silicon steel grade needs to meet: Si≤0.06 wt%, Ti≤0.01 wt%, and FeO+MnO≤1.0 wt% in the ladle slag of the low-silicon steel grade, that is, the sum of the contents of ferrous oxide and manganese oxide is less than or equal to 1.0 wt%. The low-silicon steel grade is an aluminum-killed steel.

[0056] In one embodiment, the time of using the low-silicon steel grade for washing the tank is ≥20 minutes.

[0057] As Figure 1 shown, in one embodiment, the step of RH refining of the deoxidized and alloyed molten steel further includes:

[0058] S6. After completing RH refining, a layer of mold powder is added to the molten steel surface around the immersion tube to reduce the slag crust on the ladle. The melting point of the mold powder is 1050°C to 1150°C, the viscosity is 0.10 to 0.15 Pa·s, and the alkalinity is 1.0 to 1.1.

[0059] In one embodiment, by mass percentage, the components and contents of the mold powder are: CaO 30wt% - 36wt%, SiO2 24wt% - 30wt%, A12O3 2wt% - 4wt%, F 8wt% - 10wt%, MgO ≤ 3wt%, Na2O: 11wt% - 14wt%, and the balance is inevitable impurities.

[0060] Then, the molten steel refined by RH is subjected to continuous casting, rolling, coiling, and cutting processes to obtain high-aluminum steel in the required form. The continuous casting, rolling, coiling, and cutting processes can be carried out using general process parameters in the technical field.

[0061] In a second aspect, an embodiment of the present application provides high-aluminum steel prepared by the above-mentioned efficient refining preparation method of high-aluminum steel. By mass percentage, the components and contents of the high-aluminum steel are as follows:

[0062] C ≤ 0.06wt%, Si: 0.15wt% - 0.25wt%, Mn: 0.5wt% - 0.8wt%, Al: 3.5wt% - 5.0wt%, P ≤ 0.020wt%, S ≤ 0.006wt%, and the balance is iron and inevitable impurities.

[0063] In one embodiment, the density of the above high-aluminum steel is 7.2g / mm 3 ~7.4g / mm 3 .

[0064] The technical solution of the present application will be described in detail below through specific examples.

[0065] Example 1: This example provides a high-aluminum steel. By mass percentage, the components and contents of the high-aluminum steel are: C ≤ 0.06wt%, Si: 0.15wt% - 0.25wt%, Mn: 0.5wt% - 0.8wt%, Al: 3.5wt% - 5wt%, P ≤ 0.020wt%, S ≤ 0.006wt%, and the balance is iron and inevitable impurities. Its density is 7.3g / mm 3 .

[0066] The efficient refining preparation method of the high-aluminum steel in this example is as follows, including:

[0067] Provide 210 tons of molten steel raw materials, and feed the molten steel raw materials into a top-bottom combined blown converter for blowing. The process parameters for the converter blowing of the molten steel raw materials are as follows: the converter blowing time is 12 minutes. In the early stage of converter blowing, that is, from the start of converter blowing to the 10th minute, the height of the oxygen lance from the molten steel surface is 1.8 meters; in the later stage of converter blowing, that is, in the last two minutes, the height of the oxygen lance from the molten steel surface is 1.5 m, and the flow rate of bottom-blown argon is 0.08 M 3 / (t.min), the end-point temperature is 1580°C to 1600°C. Control the end-point temperature and reduce the oxidability of the molten steel to make the oxygen content in the molten steel ≤ 0.07 wt% when tapping.

[0068] After the oxygen lance stops blowing, add 500 - 800 kg of lime thick slag with a particle size of 20 mm to 30 mm to the raw molten steel before tapping the raw molten steel. Control the composition of the converter final slag: CaO: 52 wt% - 58 wt%, SiO2: 12 wt% - 18 wt%, MgO: 6 wt% - 10 wt%, CaO / SiO2 ≥ 3, FeO ≤ 18 wt%, and the balance is impurities; to prevent vortex slag entrainment caused by thin molten slag during tapping, use a slag stopper + slide plate double slag blocking during tapping, and set the sensitivity of slag detection to the highest level (an alarm is triggered when the slag volume is greater than 10%), and control the thickness of the slag in the ladle to 50 mm.

[0069] After the molten steel raw materials complete converter blowing to obtain raw molten steel, conduct LF refining on the raw molten steel. This LF refining process includes deoxidation alloying and slag making. Slag making means adding low-silicon steel hot refining slag, lime, adding aluminum while power is on, and adding low-silicon pre-melted refining slag during the power-on process, and adding lime at the same time. Deoxidation alloying means adding lime and adding aluminum to adjust the aluminum content to meet the target requirements.

[0070] Specifically, move the ladle containing the molten steel after slag-blocking tapping to the LF refining furnace process, and add the low-silicon steel hot refining slag (silicon content ≤ 0.06 wt%) that has been poured in continuous casting at this moment into the raw molten steel in the ladle through the overhead crane to enable the molten steel to quickly form slag during LF refining; among them, the composition and content of the low-silicon steel hot refining slag are: CaO: 52 wt% - 58 wt%, Al2O3: 26 wt% - 36 wt%, MgO: 5 wt% - 10 wt%, SiO2: ≤ 5 wt%, and the balance is inevitable impurities. The low-silicon steel hot refining slag is the remaining molten steel and residue after LF refining of low-silicon steel.

[0071] Then add lime to the raw molten steel added with low-silicon steel hot refining slag to remove the sulfur element in the raw molten steel and obtain raw molten steel with sulfur ≤ 0.003 wt%; adjust the temperature of the raw molten steel with sulfur ≤ 0.003 wt% to ≤ 1570°C to reduce the oxidation of aluminum during deoxidation alloying.

[0072] Next, add aluminum blocks with a particle size of 20 mm to 50 mm to the molten raw steel with the temperature adjusted to ≤1570°C twice and energize to melt the aluminum to obtain deoxidized and alloyed molten steel; during the process of energizing to melt the aluminum, add lime to the molten steel to improve the fluidity of the ladle slag of high-aluminum steel, and obtain the refined slag system composition and content as follows: CaO: 50 wt% - 55 wt%, Al2O3: 45 wt% - 50 wt%, MgO: 5 wt% - 10 wt%, SiO2: ≤1 wt%, FeO ≤0.5 wt%, MnO ≤0.5 wt%, and the balance is impurities. The mass ratio of calcium oxide to aluminum oxide in the slag system composition of the refined slag is 1.0;

[0073] Add low-silicon pre-melted refining slag to the molten raw steel 2 minutes after adding aluminum to make the molten raw steel in the LF refining process form slag quickly; among them, the composition and content of the low-silicon pre-melted refining slag are: CaO: 45 wt% - 55 wt%, Al2O3: 34 wt% - 46 wt%, MgO ≤6 wt%, SiO2 ≤5 wt%, Fe2O3 ≤1.5 wt%, and the balance is inevitable impurities. The low-silicon pre-melted refining slag is the residue generated during the continuous casting of low-silicon steel.

[0074] Among them, the step of adding aluminum to the molten raw steel in two batches includes:

[0075] Add 400 kg to 600 kg of aluminum to the molten raw steel for the first time to remove oxygen and sulfur elements in the molten raw steel, and obtain molten steel with an aluminum content of 0.05 wt% - 0.10 wt% and an Mn content of 0.8 wt% - 0.9 wt%;

[0076] Add 9.6 tons to 9.4 tons of the remaining amount of aluminum in 10 tons of aluminum to the molten steel that has removed oxygen and sulfur elements in two batches, add it continuously in 4 times, 2 tons each time, and the interval between each addition is 3 minutes, so that the aluminum content in the molten steel reaches 3.5 wt% - 5 wt%. During the power supply process of energizing to melt the aluminum, add 800 kg - 1200 kg of lime to make slag, 200 kg each time. Reducing the number of times of adding aluminum blocks and increasing the addition amount per batch can increase the aluminum content in a certain area of the molten steel, promote the precipitation rate of aluminum nitride, and reduce the adverse effect of the precipitation of AlN during pouring on the mold powder. Avoid adding aluminum at high temperature and increasing the aluminum content in the molten steel also helps to reduce the secondary oxidation of aluminum.

[0077] To reduce the oxidation of aluminum, the molten steel level fluctuates greatly. Different from the traditional process, after adding aluminum blocks, instead of increasing the stirring by increasing the flow rate of bottom-blown argon in the ladle to promote the melting of aluminum blocks, the aluminum is melted by power supply after adding aluminum. The power supply process is a reducing atmosphere, which reduces the secondary oxidation of aluminum and the liquid level fluctuation during the bottom-blown gas process. The flow rate of bottom-blown argon in the ladle is ≤600 NL / min throughout the whole process of preparing high-aluminum steel. In this embodiment, the selected flow rate of bottom-blown argon is 500 NL / min to 800 NL / min. This is also to minimize the reaction between molten steel and slag and stabilize the components of the ladle slag.

[0078] In the step of melting aluminum by power supply, a reducing atmosphere is adopted and three-phase power supply is used to melt aluminum. During the LF refining process, each time power is supplied, the arc is first struck and the power is supplied at a low current of 32,800 A in gear 5, and then gradually increased to 54,000 A; among them, when the difference between any two of the three-phase currents is less than 5945 A, it is switched to 54,700 A to reduce the oxidation of aluminum during the LF refining process.

[0079] During the LF treatment process, the recovery rate of aluminum is ≥92%, the secondary oxidation is less, the generated alumina inclusions are less, the LF calcium treatment process is cancelled, and the soft blowing time of the molten steel after the last batch of alloying is ≥10 min.

[0080] After the raw molten steel is completed with LF refining, molten steel with an aluminum content meeting the requirements of 3.5 wt% to 5 wt% of the target steel grade is obtained, and this molten steel is sent to the RH refining furnace for RH refining.

[0081] RH refining: To reduce the secondary oxidation of aluminum in the molten steel and the increase of titanium in the molten steel, before smelting this steel grade in RH, the RH refining tank must be washed. The molten steel used for washing the tank is the molten steel of low-silicon steel grade (Si≤0.06 wt%, Ti≤0.01 wt%) aluminum-killed steel. The FeO+MnO in the ladle slag of this steel grade is ≤1.0 wt%, and the washing time of the tank is 25 min. Through the washing treatment, the oxygen in the RH refining equipment is reduced, and the oxidation of aluminum in the molten steel is reduced.

[0082] Normal RH treatment: After the RH treatment is completed, around the immersion tube, after the RH insertion tube is taken out, 100 kg of mold powder is added, which can reduce the caking of the ladle slag. Among them, the melting point of the mold powder is 1050℃ to 1150℃, the viscosity is 0.10 to 0.15 Pa·s, and the basicity is 1.0 to 1.1. The mold powder is prone to react with the molten steel and change during the casting process of high-aluminum steel molten steel. To protect the molten steel from changing, it is necessary to replace the mold powder that has been used for a long time with a new mold powder during the casting process of the molten steel.

[0083] Example 2: This example provides an efficient refining and preparation method for smelting 210 tons of high-aluminum steel. Other contents are the same as those in the above Example 1, and the differences include:

[0084] For the smelting of high-aluminum steel, the final converter slag has the following composition: CaO: 53.5 wt%, SiO2: 13.5 wt%, MgO: 7.8 wt%, Fe 16.0%, and 600 kg of lime thickening slag is added during tapping.

[0085] Before LF treatment, 500 kg of low-silicon hot refining slag and 500 kg of low-silicon pre-melted refining slag are added. The composition and content of the refining slag system obtained are: CaO: 54.5 wt%, Al2O3: 45.6 wt%, MgO: 6.2 wt%, SiO2: 0.5 wt%, FeO 0.38 wt%, MnO 0.30 wt%.

[0086] During the process of melting aluminum by electrifying in LF treatment, an arc is struck and power is supplied with a low current of 32000 A. After 40 seconds, when the difference between any two of the three-phase currents is less than 5940 A, the power is switched to 54700 A for heating up.

[0087] The RH vacuum tank is washed with molten steel of a low-silicon steel grade (silicon content 0.032%) for 21 minutes.

[0088] The total oxygen content in the molten steel of this high-aluminum steel detected is 0.0004 wt%; the nitrogen content is 0.0016 wt%; the aluminum content is 4.4 wt%, the aluminum recovery rate is 92.8%, the manganese recovery rate is 99.2%, the rephosphorization of the molten steel is 0.0005 wt%, and the silicon increase in the molten steel during LF treatment is 0.035 wt%. It can be seen from the detection results that the high-aluminum steel prepared by the preparation method of the embodiment of the present application has a low oxygen content, less aluminum in the molten steel is oxidized, the aluminum content reaches the standard of high-aluminum steel, and the recovery rate basically meets the requirements; the N content is small and it is not easy to increase nitrogen to form aluminum nitride; the increase in phosphorus and silicon content is small and both are within the requirements of the high-aluminum steel of the present application.

[0089] Example 3: This example provides an efficient refining preparation method for smelting 210 tons of high-aluminum steel. Other contents are the same as those in Example 1 above, and the differences include:

[0090] For the smelting of high-aluminum steel, the final converter slag has the following composition: CaO: 52.5 wt%, SiO2: 14.5 wt%, MgO: 7.9 wt%, Fe 17.0%, and 500 kg of lime thickening slag is added during tapping.

[0091] Before LF treatment, 600 kg of low-silicon hot refining slag and 600 kg of low-silicon pre-melted refining slag are added. The composition and content of the refining slag system obtained are: CaO: 53.5 wt%, Al2O3: 46.6 wt%, MgO: 6.5 wt%, SiO2: 0.4 wt%, FeO 0.34 wt%, MnO 0.25 wt%.

[0092] During the process of LF treatment for melting aluminum by power supply, an arc is struck and power is supplied with a low current of 32,000 A. After 30 seconds, when the difference between any two of the three-phase currents is less than 5,782 A, the power supply is switched to 54,700 A for heating up.

[0093] The RH vacuum tank is washed with molten steel of a low-silicon steel grade (silicon content 0.035%) for 21 minutes.

[0094] The total oxygen content in the molten steel of this high-aluminum steel is detected to be 0.0002 wt%; the nitrogen content is 0.0014 wt%; the aluminum content is 4.4 wt%. The aluminum recovery rate is 92.7%, the manganese recovery rate is 99.4%, the phosphorus return in the molten steel is 0.0006 wt%, and the silicon increase in the molten steel during LF treatment is 0.040 wt%. It can be seen from the detection results that for the high-aluminum steel prepared by the preparation method of the embodiment of the present application, the oxygen content is low, less aluminum in the molten steel is oxidized, the aluminum content reaches the standard of high-aluminum steel, and the recovery rate basically meets the requirements; the N content is small and it is not easy to increase nitrogen to form aluminum nitride; the phosphorus increase and silicon increase contents are small and are all within the requirements of the high-aluminum steel of the present application.

[0095] Example 4: This example provides an efficient refining preparation method for smelting 210 tons of high-aluminum steel. Other contents are the same as those of Example 1 above. The differences include:

[0096] For the smelting of high-aluminum steel, the final converter slag has CaO: 52.5 wt%, SiO2: 14.5 wt%, MgO: 7.8 wt%, Fe 16.5%, and 550 kg of lime is added during tapping to thicken the slag;

[0097] Before LF treatment, hot refined slag of low-silicon steel, 550 kg of low-silicon pre-melted refined slag, is added, and the composition and content of the refined slag system obtained are: CaO: 53.5 wt%, Al2O3: 46.6 wt%, MgO: 6.8 wt%, SiO2: 0.42 wt%, FeO 0.38 wt%, MnO 0.32 wt%;

[0098] During the process of LF treatment for melting aluminum by power supply, an arc is struck and power is supplied with a low current of 32,000 A. After 30 seconds, when the difference between the three-phase currents is less than 5,820 A, the power supply is switched to 54,700 A for heating up.

[0099] The RH vacuum tank is washed with molten steel of a low-silicon steel grade (silicon content 0.034%) for 21 minutes.

[0100] The total oxygen content in the molten high-aluminum steel was detected to be 0.0003 wt%; the nitrogen content was 0.0012 wt%; the aluminum content was 4.45 wt%, the aluminum yield was 92.9%, the manganese yield was 99.1%, the phosphorus reversion in the molten steel was 0.0004 wt%, and the silicon increase in the molten steel during the LF treatment was 0.041 wt%. It can be seen from the detection results that for the high-aluminum steel prepared by the preparation method of the embodiment of the present application, the oxygen content is low, less aluminum in the molten steel is oxidized, the aluminum content reaches the standard of high-aluminum steel, and the yield basically meets the requirements; the N content is low and it is not easy to increase nitrogen to form aluminum nitride; the phosphorus increase and silicon increase are small, both within the requirements of the high-aluminum steel of the present application.

[0101] Comparative example: This comparative example provides a preparation method for smelting 210 tons of high-aluminum steel. Other contents are the same as those of the above Embodiment 1, and the differences include:

[0102] For the high-aluminum steel smelting, the converter final slag had CaO: 52.2 wt%, SiO2: 19.5 wt%, MgO: 7.8 wt%, Fe: 21.5%, and no lime was added to thicken the slag during tapping;

[0103] Before the LF treatment, no hot refining slag for low-silicon steel and no pre-melted refining slag for low-silicon were added. The composition and content of the refined slag obtained were: CaO: 53.5 wt%, Al2O3: 46.6 wt%, MgO: 6.9 wt%, SiO2: 2.5 wt%, FeO 0.78 wt%, MnO 0.90 wt%;

[0104] During the process of electrically melting aluminum in the LF treatment, the temperature was directly raised by sending electricity with a current of 54700 A.

[0105] The RH vacuum chamber was not washed.

[0106] The total oxygen content in the molten high-aluminum steel was detected to be 0.0010%; the nitrogen content was 0.0024%; the aluminum content was 4.40%, the aluminum yield was 85.2%, the manganese yield was 96.1%, the phosphorus reversion in the molten steel was 0.0028%, and the silicon increase in the molten steel during the LF treatment was 0.085%. It can be seen from the detection results that for the high-aluminum steel prepared by the preparation method of this comparative example, without using lime to thicken the slag to change the ladle slag system in the converter smelting process, the oxygen content is one order of magnitude higher than that of the high-aluminum steel prepared by the preparation method of the present application, which may cause more aluminum in the molten steel to be oxidized; in the LF refining process, no hot refining slag for low-silicon steel and no pre-melted refining slag for low-silicon were added, and no variable three-phase current was used for aluminum melting treatment, nor was the washing treatment carried out. The aluminum content reached the standard of high-aluminum steel, and the yield basically met the requirements; however, the N content doubled, making it easy to increase nitrogen to form aluminum nitride; the phosphorus increase reached 5 to 6 times, and the silicon increase reached more than one time. The content of some components may exceed the requirements of the high-aluminum steel of the present application, making it easy to increase phosphorus, manganese, and silicon.

[0107] From the comparison results of the above Examples 2-4 and Comparative Examples, it can be seen that the efficient refining preparation method of the high-aluminum steel of the present application can obtain high-aluminum steel with an aluminum content of 3.5 wt% to 5.0 wt%, while reducing the oxidation amount of aluminum in the molten steel during smelting, increasing the recovery rate of aluminum, and reducing the effects of increasing phosphorus, manganese, and silicon.

[0108] The efficient refining preparation method of the high-aluminum steel in the embodiment of the present application controls the composition of the ladle slag system by adding lime thick slag in the converter blowing step and controlling the slag amount of the converter, as well as combining with slag making in the deoxidation alloying step, which can not only prevent the secondary oxidation of aluminum during the treatment process, but also reduce the ladle slag crusting. During the LF refining process of the raw molten steel, the molten steel can stably increase manganese and silicon, ensuring the precise control of the molten steel composition. Combining with the washing tank treatment before the RH refining step and using a low-alkalinity mold powder to protect the molten steel surface after the RH refining step, and adding the operation of timely replacing the mold powder, the aluminum content of this steel type is very high, ensuring that the recovery rate of aluminum ≥ 92%, and improving the phenomenon of ladle slag crusting of high-aluminum steel. Reduce the secondary oxidation of aluminum during the refining process and prevent the ladle slag crusting phenomenon during the later LF refining process.

[0109] As described above, the above is only the specific implementation manner of the present application. Those skilled in the art can clearly understand that for the convenience and simplicity of description, the specific working processes of the above-described systems, modules, and units can refer to the corresponding processes in the foregoing method embodiments, which will not be repeated here. It should be understood that the protection scope of the present application is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present application can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should be covered within the protection scope of the present application.

Claims

1. An efficient refining preparation method for high-aluminum steel, characterized in that, Including: Using an oxygen lance to blow-convert molten steel raw materials in a converter. And after the oxygen lance stops blowing, adding lime thick slag to the raw molten steel before tapping to obtain a converter final slag with the following composition and content: CaO: 52wt% - 58wt%, SiO2: 12wt% - 18wt%, MgO: 6wt% - 10wt%, FeO ≤ 18%, and the balance being impurities; among them, the composition of the converter final slag also needs to satisfy CaO / SiO2 ≥ 3; to obtain molten steel with an oxygen content ≤ 0.07wt%. The whole process uses a reducing atmosphere to conduct LF refining on the raw molten steel; among them, LF refining includes: adding lime to the raw molten steel to remove sulfur in the raw molten steel to obtain raw molten steel with sulfur ≤ 0.003wt%; adjusting the temperature of the raw molten steel with sulfur ≤ 0.003wt% to ≤ 1580°C to reduce the oxidation of aluminum during the deoxidation alloying process; adding a hot low-silicon steel refining slag to the raw molten steel, where the composition and content of the hot low-silicon steel refining slag are: CaO: 52wt% - 58wt%, Al2O3: 26wt% - 36wt%, MgO: 5wt% - 10wt%, SiO2: ≤ 5wt%, and the balance being inevitable impurities; and then adding aluminum to the raw molten steel and energizing to melt the aluminum, and adding lime and a low-silicon pre-melted refining slag during the process of energizing and melting the aluminum, where the composition and content of the low-silicon pre-melted refining slag are: CaO: 45wt% - 55wt%, Al2O3: 34wt% - 46wt%, MgO ≤ 6wt%, SiO2 ≤ 5wt%, Fe2O3 ≤ 1.5wt%, and the balance being inevitable impurities, to obtain deoxidized alloyed molten steel. Conducting RH refining on the deoxidized alloyed molten steel to obtain high-aluminum steel molten steel with an aluminum recovery rate ≥ 92wt% after RH refining.

2. The refining preparation method according to claim 1, characterized in that, The lime thick slag is granular with a particle size ≤ 50 mm.

3. The refining preparation method according to claim 1, characterized in that, The step of blowing-converting the molten steel raw materials to obtain raw molten steel further includes: Transferring and tapping the raw molten steel, and using a slag blocking component to block the slag during tapping to weaken vortex slag entrainment.

4. The refining preparation method according to claim 1, characterized in that, The step of adding aluminum to the raw molten steel and energizing to melt the aluminum, and adding lime and a low-silicon pre-melted refining slag during the process of energizing and melting the aluminum to obtain deoxidized alloyed molten steel includes: Adding aluminum to the raw molten steel with the hot low-silicon steel refining slag added in two portions and energizing to melt the aluminum to obtain deoxidized alloyed molten steel; adding lime to the molten steel during the process of energizing and melting the aluminum to improve the fluidity of the ladle slag of the high-aluminum steel to obtain a refining slag system with the following composition and content: CaO: 50wt% - 55wt%, Al2O3: 45wt% - 50wt%, MgO: 5wt% - 10wt%, SiO2: ≤ 1wt%, FeO ≤ 0.5wt%, MnO ≤ 0.5wt%, and the balance being impurities; the mass ratio of calcium oxide to aluminum oxide in the slag system of the refining slag also needs to satisfy: w(CaO) / w(Al2O3) = 0.8 - 1.

2. Add low-silicon pre-melted refining slag to the raw molten steel after adding aluminum, so that the raw molten steel in the LF refining process can form slag quickly.

5. The refining preparation method according to claim 4, characterized in that, The step of adding aluminum to the raw molten steel in two times includes: Add aluminum to the raw molten steel for the first time to remove oxygen and sulfur elements in the raw molten steel, and obtain molten steel with an aluminum content of 0.05wt% - 0.10wt% and a Mn content of 0.8wt% - 0.9wt%. Add the remaining amount of aluminum to the molten steel from which oxygen and sulfur elements have been removed in batches for the second time, so that the aluminum content in the molten steel meets the requirements of the steel grade.

6. The refining preparation method according to claim 1, characterized in that In the step of adding aluminum to the raw molten steel and energizing to melt the aluminum, three-phase electricity is used to energize and melt the aluminum. First, start the arc and send electricity with a low current of 30000A - 34000A, and then gradually increase to 54000A - 55000A; among them, when the difference between any two of the three-phase currents is less than 6000A, switch to 54700A to reduce the oxidation of aluminum in the LF process.

7. The refining preparation method according to claim 1, characterized in that, The step of energizing and melting the aluminum is carried out in an argon reducing atmosphere. During the whole process of LF refining, the flow rate of bottom-blowing argon in the ladle ≤ 800NL / min.

8. The refining preparation method according to claim 1, characterized in that, Before the step of carrying out RH refining on the deoxidized and alloyed molten steel, it also includes: Use the molten steel of a low-silicon steel grade to wash the RH vacuum tank to reduce the secondary oxidation of aluminum and the increase of titanium content in the molten steel; among them, the time for washing the tank with the molten steel of a low-silicon steel grade ≥ 20 minutes.

9. The refining preparation method according to claim 8, characterized in that, In the step of using the molten steel of a low-silicon steel grade to wash the RH vacuum tank, the low-silicon steel grade needs to meet: Si ≤ 0.06wt%, Ti ≤ 0.01wt%, and FeO + MnO ≤ 1.0wt% in the ladle slag of the low-silicon steel grade.

10. The refining preparation method according to claim 1, wherein The step of carrying out RH refining on the deoxidized and alloyed molten steel also includes: After completing RH refining, add a layer of mold powder to the molten steel liquid surface around the immersion tube to reduce the ladle slag crusting; among them, the melting point of the mold powder is 1050℃ - 1150℃, the viscosity is 0.10 - 0.15Pa﹒s, and the basicity is 1.0 - 1.

1.

11. A high-aluminum steel, characterized in that, Prepared by the high-efficiency refining preparation method of high-aluminum steel according to any one of claims 1 to 10.

12. The high-aluminum steel according to claim 11, wherein By mass percentage, the components and contents of the high-aluminum steel are as follows: C ≤ 0.06 wt%, Si: 0.15 wt% - 0.25 wt%, Mn: 0.5 wt% - 0.8 wt%, Al: 3.5 wt% - 5 wt%, P ≤ 0.020 wt%, S ≤ 0.006 wt%, and the balance is iron and unavoidable impurities; the density of the high-aluminum steel is 7.2 g / mm 3 ~7.4 g / mm 3 .

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