A method for smelting and casting low-carbon, low-silicon aluminum-killed steel by single-casting

Abstract

The present invention discloses a method for smelting and casting low-carbon, low-silicon, aluminum-killed steel in a single cast furnace, belonging to the technical field of steel production. The method comprises converter smelting, LF furnace refining, and continuous casting machine protection casting. The low-carbon, low-silicon, aluminum-killed steel contains 0.035% to 0.045% C, 0.035% to 0.055% Si, and 0.02% to 0.05% Al in molten steel. In the LF furnace refining, the following steps are performed: (1) slag modification; (2) deoxidation control; (3) slag formation control; (4) two-stage soft blowing time control; and (5) calcium treatment control. Compared with the prior art, the method can effectively reduce precipitates at the tundish nozzle.

Description

Technical Field

[0001] The present invention is a divisional application of the invention patent "A method for reducing the precipitates from the tundish nozzle in the first pouring furnace of a thin slab continuous casting production line" (2022104559480), which relates to a steel production technology, in particular, a method for smelting and casting low-carbon, low-silicon, aluminum-killed steel in the first pouring furnace based on a thin slab continuous casting production line. Background Art

[0002] The tundish nozzle of the thin slab continuous casting production line adopts an integrated design. The nozzle is flat and duck-billed to ensure the high steel throughput required for rolling. Therefore, the nozzle cannot be replaced online during the casting process. However, due to the preheating and baking of the tundish refractory, the oxidizing properties are strong, and the molten steel suffers from severe secondary oxidation during the first casting. This leads to precipitates and severe nodules in the nozzle. Combined with the analysis of the precipitate composition, the precipitates in the nozzle are mainly oxidized inclusions, the main component of which is aluminum oxide. Excessive precipitates lead to nozzle blockage, reduced steel throughput, and precipitates easily fall off and enter the crystallizer. In severe cases, this can lead to accidents such as steel leakage and unplanned downtime, and defects such as warping in the finished product.

[0003] Therefore, the applicant disclosed control methods for reducing inclusions in "A Method for Controlling Inclusions in Pipeline Steel" (Authorization Announcement No. CN112779458B) and "A Method for Controlling Inclusions in Rolled Steel and Rolled Steel" (Publication No. CN113604723A). However, the above methods are targeted at continuous casting furnaces, while the conditions for open casting furnaces are more complex. Control according to conventional continuous casting furnaces cannot meet production conditions. Summary of the Invention

[0004] The technical task of the present invention is to address the shortcomings of the above-mentioned existing technologies and provide a method for smelting and casting low-carbon, low-silicon, aluminum-killed steel in a single pour. By optimizing the smelting process, controlling the formation of non-metallic inclusions, and improving the removal and modification of inclusions, especially alumina inclusions, the method can control the precipitates at the tundish nozzle in the first pour of the thin slab low-carbon, low-silicon, aluminum-killed steel, thereby performing the smelting and casting of the low-carbon, low-silicon, aluminum-killed steel in a single pour.

[0005] The technical solution to the technical problem is: a method for smelting and casting low-carbon, low-silicon, aluminum-killed steel in a single cast cycle, including converter smelting, LF furnace refining, and continuous casting machine protection casting, characterized in that: the low-carbon, low-silicon, aluminum-killed steel molten steel contains 0.035% to 0.045% C, 0.035% to 0.055% Si, and 0.02% to 0.05% Al; the amount of aluminum ingot added during the converter discharge process is 1.2-1.5 kg / t; and the LF furnace refining is performed as follows:

[0006] (1) Steel slag modification: Add about 1.5-3 kg / t of low-carbon and low-silicon steel casting slag;

[0007] (2) Deoxidation control: Aluminum wire should be added ≤ 4 times during the refining process; the last addition of aluminum particles or aluminum wire should be greater than 12 minutes after calcium treatment;

[0008] (3) Slag control: the first batch of lime ≥ 6kg / t, if the headroom allows, the lime dosage ≥ 8kg / t, the last lime addition (S ≤ 0.005%) ≤ 1kg / t; after the first large-scale desulfurization, the number of lime additions ≤ 1 time; the number of lime additions during the whole process ≤ 4 times;

[0009] (4) Two-stage soft blowing time control: the first soft blowing time is 8-12 minutes, and the second soft blowing time is 8-15 minutes;

[0010] (5) Calcium treatment control: After the first soft blowing, calcium wire is fed in, and the amount of calcium wire is controlled at 1.8-2m / t.

[0011] Furthermore, in the above-mentioned LF furnace refining, the amount of aluminum added is 15-25 kg / time.

[0012] Furthermore, in the above-mentioned calcium treatment control, the Ca content in the molten steel is controlled to be ≥ 0.0026%.

[0013] Furthermore, in the above-mentioned continuous casting machine protection casting, the tundish baking temperature is ≥1300°C; the tundish pouring start temperature is controlled at: 1558~1568°C.

[0014] Compared with the prior art, the present invention has the following outstanding beneficial effects:

[0015] 1. Reduce the precipitation of the tundish nozzle during the pouring of low-carbon, low-silicon, aluminum-killed steel for thin slabs, ensure smooth pouring, and reduce the accidents of stopper flow and steel leakage;

[0016] 2. Reduce rolling defects caused by precipitation of non-metallic inclusions, such as warping;

[0017] 3. Reduce the negative impact of excessive alumina inclusions on the yield strength and tensile strength of finished steel coils. DETAILED DESCRIPTION

[0018] The present invention will be further described below with reference to specific embodiments.

[0019] For purposes of the following detailed description, it should be understood that the present invention may assume various alternative variations and step sequences, unless expressly indicated to the contrary. Furthermore, except in any operating examples or where otherwise indicated, all numbers expressing, for example, the amounts of ingredients used in the specification and claims should be understood as being modified by the term "about" in all cases. At the very least, and without attempting to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be interpreted in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0020] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values ​​set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

[0021] It should also be understood that any numerical range recited herein is intended to include all subranges subsumed therein. For example, a range of "1 to 10" is intended to include all subranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value equal to or less than 10.

[0022] In this application, unless otherwise specifically stated, the use of the singular includes the plural and the plural encompasses the singular. In addition, in this application, unless otherwise specifically stated, the use of "or" means "and / or," even though "and / or" may be explicitly used in certain circumstances. Further, in this application, unless otherwise specifically stated, the use of "a" or "an" means "at least one." For example, "a" first material, "a" coating composition, etc., refers to one or more of any of these items.

[0023] The invention comprises the following steps in sequence: converter smelting, LF furnace refining and continuous casting machine protective casting.

[0024] S1. Converter smelting:

[0025] The tapping temperature is 1620-1640°C, T[O] is 450-750 ppm, and in the optimized solution, it is 550-600 ppm. Point blowing is prohibited at the endpoint, the tapping port is in good condition, the tapping time is ≥4 minutes, and the steel flow does not disperse. Slag is blocked by a slide plate, and 2.6-3 kg / t of top slag lime is added for slag washing during the tapping process. 1.2-1.5 kg / t of aluminum ingots are added during the tapping process. The selection of a ladle requires normal double-vent argon gas flow, with bypass argon gas blowing a steel flower with a diameter of ≥500 mm to ensure sufficient mixing of the slag and effective adsorption of inclusions. Existing technologies do not control the permeability of the ladle, resulting in insufficient adsorption of inclusions due to poor argon gas flow.

[0026] S2, LF furnace refining:

[0027] During the first pouring, the tundish baking time is long, the oxygen content is high, and the molten steel is in an unstable state. This makes it more likely for the molten steel to be oxidized again, resulting in excessive inclusions. Therefore, in the LF furnace refining process of the present invention, the following control is performed on the basis of the existing technology:

[0028] (1) Slag modification: Adding about 1.5-3 kg / t of low-carbon, low-silicon steel casting slag facilitates rapid slag formation and arc submersion during LF furnace smelting, reduces oxygen absorption by the molten steel surface, and thus reduces alumina inclusions caused by deoxidizers for aluminum products. Existing technology uses lime and fluorite for slag formation, which is slow and takes a long time to slag.

[0029] (2) Deoxidation control: During the converter steel discharge process, the amount of aluminum ingots added should be 1.2-1.5 kg / t to increase the amount of precipitated deoxidation products, facilitating adsorption and removal. Control the number of aluminum wire additions to the refining furnace: ≤ 4 times during the refining process. During the slag adjustment process, the amount of aluminum pellets added should be 15-25 kg / time. The last addition of aluminum pellets or aluminum wire should be >12 minutes after the calcium treatment to ensure sufficient floating of large alumina inclusions. Existing technology requires that aluminum addition is prohibited within 8 minutes before the calcium treatment.

[0030] (3) Slag control: The first batch of lime should be ≥6kg / t. If clearance is allowed, the lime dosage should be ≥8kg / t. The final lime addition amount (S≤0.005%) should be ≤1kg / t. After the first large-scale desulfurization, the number of lime additions should be ≤1; the number of lime additions during the entire process should be ≤4. The final slag should be white or off-white, with FeO+MnO≤1.0%. After cooling, the surface should be loose and porous. Existing technologies do not require a specific time for lime addition, and the steel slag absorbs oxygen repeatedly during the process, resulting in an increase in inclusion formation.

[0031] (4) Two-stage soft blowing time control: the first soft blowing time is 8-12 minutes, and the second soft blowing time is 8-15 minutes, so as to ensure that the inclusions are fully floated. The existing technology has a short front blowing time (3-5 minutes), which results in the inclusions not being able to fully float, and a long back blowing time (>12 minutes), which causes the back blowing molten steel to absorb oxygen and increase the formation of inclusions.

[0032] (5) Calcium treatment control: Calcium wire is fed after the first soft blowing. Considering the high oxidizability of the tundish due to baking, the amount of calcium wire is controlled at 1.8-2 m / t, equivalent to 540-610 m / furnace, effectively controlling the Ca content of the molten steel to ≥ 0.0026%, and transforming the alumina inclusions that have not been desorbed from the steel grade into 7Al2O3·12CaO inclusions with a lower melting point, so as to achieve good molten steel purity. The existing technology feeds a wire at a rate of 196 m / furnace, which results in insufficient transformation of the inclusions.

[0033] S3, continuous casting machine protection casting

[0034] Before pouring begins, use a large amount of argon to displace the gas in the tundish. The argon flow rate should be ≥1500 L / min, and the argon seal flow rate at the long shroud should be ≥120 L / min. Pipeline damage and leakage are strictly prohibited. The tundish baking temperature should be ≥1300°C; the tundish pouring temperature should be controlled between 1558°C and 1568°C. Existing tundish baking temperatures of ≥1200°C result in low molten steel temperatures during the pouring phase, causing low-temperature flocculants.

[0035] In order to better compare the formulation of the present application with the prior art, a comparative test was conducted.

[0036] The molten steel chemistry was defined as low-carbon, low-silicon, aluminum-killed steel. To achieve a consistent baseline, the chemical composition and weight percentages of the molten steel used in each group were as follows: C: 0.035%-0.045%, Si: 0.035%-0.055%, Mn: 0.08%-0.20%, P: 0-0.018%, S: 0-0.003%, Al: 0.02%-0.05%, Ca: 0.0015%-0.0035%, N: 0-0.0050%, with the remainder being Fe and unavoidable impurities.

[0037] Groups 1 to 4 of Examples were controlled using the technical solution of this application.

[0038] The control group adopted the solution of the technology submitted by the applicant, "A method for controlling inclusions in rolled steel and rolled steel" (publication number CN113604723A).

[0039] All embodiments and control group schemes are used for the first pouring of thin slab low-carbon, low-silicon aluminum killed steel.

[0040] S1. Converter smelting:

[0041] Examples 1-4: The tapping temperature was 1630-1640°C, the T[O] was 550-600 ppm, there was no spot blowing, the tapping time was ≥4.5 min, the slag was blocked by a slide plate, and there was no slag dispersion. During the tapping process, 800 kg of top slag lime was added per furnace for slag washing, and 400 kg of aluminum ingots were added during the tapping process. The double-vent argon gas flow was normal, and the bypass argon gas flowed the steel flower with a diameter of ≥500 mm.

[0042] The control group had a tapping temperature of 1640°C, T[O] of 600 ppm, no spot blowing, a tapping time of ≥3.5 min, a slide plate to block slag, and no slag dispersion. During the tapping process, 300 kg of top-slag lime and 100 kg of modifier were added for slag washing. The dual-vent argon gas flow was normal on one side, but weak on the other.

[0043] S2, LF furnace refining:

[0044] (1) Slag making parameters are as follows: lime is added once after the first large-scale desulfurization in each group, lime is added 3-4 times in the whole process of the embodiment, and 5 times in the control.

[0045]

[0046]

[0047] (2) Some parameters of deoxidation, two-stage soft blowing and calcium treatment are controlled as follows:

[0048]

[0049] S3, continuous casting machine protection casting

[0050] Before pouring, use large amounts of argon to replace the gas in the tundish. The argon flow rate, the argon seal flow rate at the long water nozzle, and the tundish baking temperature are shown in the table below.

[0051]

[0052]

[0053] The comparison results of each group are shown in the table below:

[0054] result Highest rod position (mm) Whether to punch the rod Example 1 19.5 no Example 2 18.9 no Example 3 20.1 no Example 4 18.5 no Control Example 25.6 yes

[0055] The above results show that using the embodiments of the present invention for the first pour of low-carbon, low-silicon, aluminum-killed thin slab steel significantly reduced deposits at the tundish nozzle, effectively reducing stopper flow. The highest stopper height did not exceed 20.1 mm, and no stopper flow occurred during the first pour, thus avoiding steel breakout accidents. In contrast, the control example showed significant deposits at the tundish nozzle, with the highest stopper height reaching 25.61 mm, and stopper flow occurred during the first pour.

[0056] It should be noted that the specific embodiments of the present invention have been described in detail. For those skilled in the art, various obvious changes to it without departing from the spirit and scope of the present invention are within the scope of protection of the present invention.

Claims

1. A method for smelting and casting low-carbon, low-silicon aluminum-killed steel in a single cast cycle, comprising converter smelting, LF furnace refining, and continuous casting machine protective casting, characterized in that: The low-carbon, low-silicon aluminum-killed steel contains 0.035% to 0.045% C, 0.035% to 0.055% Si, and 0.02% to 0.05% Al in the molten steel. During the steel discharge process in the converter, the amount of aluminum ingot added is 1.2-1.5 kg / t. In the LF furnace refining, the following steps are performed: (1) Steel slag modification: Add 1.5-3 kg / t of low-carbon and low-silicon steel casting slag; (2) Deoxidation control: Aluminum wire is added ≤ 4 times during the refining process; the last addition of aluminum particles or aluminum wire is greater than 12 minutes after calcium treatment; (3) Slag control: the first batch of lime ≥ 6kg / t, if the headroom allows, the lime dosage ≥ 8kg / t, when S ≤ 0.005%, the last lime addition amount ≤ 1kg / t; after the first large-scale desulfurization, the number of lime additions ≤ 1 time; the number of lime additions during the whole process ≤ 4 times; (4) Two-stage soft blowing time control: the first soft blowing time is 8-12 minutes, and the second soft blowing time is 8-15 minutes; (5) Calcium treatment control: After the first soft blowing, calcium wire is fed in, and the amount of calcium wire is controlled at 1.8-2m / t.

2. The method for smelting and casting low-carbon, low-silicon aluminum-killed steel by single-casting according to claim 1, characterized in that: In the LF furnace refining, the amount of aluminum added is 15-25 kg / time.

3. The method for smelting and casting low-carbon, low-silicon aluminum-killed steel by single-casting according to claim 1, characterized in that: In the calcium treatment control, the Ca content in the molten steel is controlled to be ≥ 0.0026%.

4. The method for smelting and casting low-carbon, low-silicon aluminum-killed steel by single-casting according to claim 1, characterized in that: In the continuous casting machine protection casting, the tundish baking temperature is ≥1300°C; the tundish pouring start temperature is controlled at: 1558~1568°C.

Images