Method for complex deoxidation of aluminum killed steel and control of steel cleanliness

Abstract

The invention provides a method for composite deoxidation of aluminum killed steel and control of steel cleanliness, which comprises a converter process and a continuous casting process, when 1 / 10-1 / 9 of converter tapping is carried out, a deoxidation composite alloy, an aluminum-iron alloy, a silicon-iron alloy and a silicon-manganese alloy are added into a steel ladle to carry out deoxidation alloying, and argon is blown from the bottom of the steel ladle to forcibly stir in the tapping process; in the continuous casting process, argon is blown to the bottom of molten steel in a steel ladle in the first middle stage of steel ladle pouring; the deoxidized composite alloy is spherical, the inner core is calcium-magnesium-iron alloy, the middle layer is aluminum-silicon-iron alloy, and the outer layer is steel ladle slag modifier. According to the invention, the inclusion in the steel is modified by active metals such as magnesium and calcium in the deep part of the steel ladle, and the problems of low alloy yield and large environmental smoke caused by the reaction on the surface of the molten steel by directly adding iron alloys such as magnesium and calcium are avoided. After the method is applied, the number of Al2O3 inclusions larger than or equal to 3 microns in a casting blank is reduced by 50% or above, and the number of non-metal oxide inclusions is reduced by 48% or above.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting, and in particular relates to a method for composite deoxidation of aluminum-killed steel and controlling steel cleanliness. Background Art

[0002] As my country's energy conservation and emission reduction work continues to deepen, more and more steelmaking companies are exploring the elimination of the LF process to achieve economical and efficient production of steel grades. For non-special purpose steels such as low-carbon aluminum killed steel and ordinary carbon steel, more and more manufacturers are adopting the short process of "converter-continuous casting" to produce them.

[0003] However, for low-carbon aluminum series steel, due to the low control of carbon content of converter steel, high oxygen activity in steel and high oxidation of converter final slag, the amount of deoxidation alloy added is large, resulting in more non-metallic oxide inclusions generated by deoxidation. It is difficult to achieve full and effective floating of inclusions under the short process; in addition, due to the lack of strong stirring through LF, the steel-slag reaction is not sufficient, and the Al2O3 inclusions in the steel have not been effectively modified and still exist in large quantities in the molten steel; due to the large surface tension of Al2O3 inclusions, they are very easy to aggregate during continuous casting, causing nodules and even interruption of casting; and the clustered Al2O3 inclusions remaining in the steel are very easy to form product surface defects during cold rolling.

[0004] Therefore, in order to solve the above problems when using the "converter-continuous casting" short process to produce low-carbon aluminum series steel, steelmaking companies often use the process of adding lime and other modifiers during the converter steel-making process to modify the inclusions in the steel, and at the end of steel-making, argon is blown from the bottom of the ladle to promote the floating of inclusions. However, since the melting point of lime is as high as 2572℃ and its density is much lower than that of molten steel, a large amount of unmelted lime still floats on the ladle surface at the end of steel-making, and the inclusions in the steel are not effectively modified. Summary of the invention

[0005] The purpose of the present invention is to provide a method for composite deoxidation of aluminum killed steel and control of steel cleanliness. The method of the present invention can efficiently deoxidize and effectively improve the steel cleanliness of aluminum killed steel.

[0006] The present invention provides a method for composite deoxidation of aluminum-killed steel and control of steel cleanliness, comprising a converter process and a continuous casting process, characterized in that in the converter process: when the converter taps to 1 / 10 to 1 / 9 of the molten steel volume, a deoxidation composite alloy, an aluminum-iron alloy, a silicon-iron alloy and a silicon-manganese alloy are added into a ladle for deoxidation and alloying, and argon gas is blown at the bottom of the ladle for strong stirring during the tapping process;

[0007] In the continuous casting process: argon is blown into the bottom of the molten steel in the ladle during the early and middle stages of ladle pouring;

[0008] The deoxidized composite alloy is spherical, with a core of calcium-magnesium-iron alloy, a middle layer of aluminum-silicon-iron alloy, and an outer layer of ladle slag modifier;

[0009] The calcium-magnesium-iron alloy of the inner core includes the following components by mass fraction: Ca: 1.1%~1.9%, Mg: 2.1%~2.9%, Re: 0.2%~0.9%, and the rest is Fe and unavoidable impurities;

[0010] The aluminum-silicon-iron alloy of the middle layer includes the following components by mass fraction: Al: 49%~60%, Si: 15.1%~23.9%, and the rest is Fe and inevitable impurities;

[0011] The outer layer of ladle slag modifier includes the following components in mass fraction: CaO: 15%~29%, Al2O3: 7%~15%, C: 31%~56%, Na2CO3: 3%~6%, among which CaO / Al2O3 is 1.9~2.6, and the rest are unavoidable impurities.

[0012] Preferably, the mass ratio of the inner core, the middle layer and the outer layer is 1:(1.9-4.6):(2.0-4.8).

[0013] Preferably, the particle size of the calcium-magnesium-iron alloy of the inner core is 1-5 mm, the particle size of the aluminum-silicon-iron alloy of the middle layer is 0.1-2 mm, and the particle size of the ladle slag modifier of the outer layer is 280-700 nm.

[0014] Preferably, the particle size of the deoxidized composite alloy is 10-40 mm.

[0015] Preferably, the addition amount of the deoxidizing composite alloy is 0.95-3.5 kg / (t steel).

[0016] Preferably, argon gas is blown into the ladle for 1 to 2 minutes before tapping the converter.

[0017] Preferably, in the converter process, a deoxidized composite alloy is added into the ladle with bottom-blown argon and strong stirring, and 31 to 45 seconds after the deoxidized composite alloy is added, ferrosilicon alloy and ferromanganese alloy are added.

[0018] Preferably, in the converter process, the argon flow rate of the bottom blowing argon for strong stirring of the ladle during the steel tapping process is 300-500NL / min, and the time of the bottom blowing argon for strong stirring is 1.0-2.4min.

[0019] Preferably, in the continuous casting process, when the pouring platform on the ladle is waiting for pouring to start, the argon flow rate of the bottom blowing argon is 100~120 NL / min, after the ladle starts pouring until the ladle pours 1 / 4~1 / 3 of the molten steel, the argon flow rate of the bottom blowing argon of the ladle is 70~100 NL / min, and when the ladle pours 2 / 3-3 / 4 of the molten steel, the bottom blowing argon is stopped.

[0020] The invention provides a method for composite deoxidation of aluminum-killed steel and control of steel cleanliness, comprising a converter process and a continuous casting process, characterized in that in the converter process: when 1 / 10 to 1 / 9 of the converter is tapped, a deoxidation composite alloy, an aluminum-iron alloy, a silicon-iron alloy and a silicon-manganese alloy are added into a ladle for deoxidation and alloying, and argon is blown at the bottom of the ladle for strong stirring during the tapping process; in the continuous casting process: argon is blown at the bottom of the molten steel in the ladle in the early and middle stages of ladle pouring; the deoxidation composite alloy is spherical, the inner core is a calcium-magnesium-iron alloy, the middle layer is an aluminum-silicon-iron alloy, and the outer layer is a ladle slag modifier; the internal calcium-magnesium-iron alloy comprises the following components by mass fraction: Ca: 1.1 %~1.9%, Mg: 2.1%~2.9%, Re: 0.2%~0.9%, and the rest are Fe and inevitable impurities; the aluminum-silicon-iron alloy of the middle layer includes the following components in mass fraction: Al: 49%~60%, Si: 15.1%~23.9%, and the rest are Fe and inevitable impurities; the ladle slag modifier of the outer layer includes the following components in mass fraction: CaO: 15%~29%, Al2O3: 7%~15%, C: 31%~56%, Na2CO3: 3%~6%, among which CaO / Al2O3 is 1.9~2.6, and the rest are inevitable impurities.

[0021] The deoxidized composite alloy ball of the present invention is added into the steel and mixed with the molten steel at the beginning of steel tapping, the ultrafine slag adjusting agent of the outermost layer of the alloy ball is quickly melted in the molten steel, the carbon powder in the slag adjusting agent performs primary deoxidation on the molten steel to remove the free oxygen in the steel to 80-150ppm, the generated CO2 further intensifies the steel slag reaction and drives the slag adjusting agent to float to the surface of the ladle, the molten steel is kept warm and secondary oxidation is prevented, and the problem of poor steel cleanliness due to the existing short-process technology that relies solely on metal deoxidation is avoided; since the middle layer and the inner core of the deoxidized alloy ball contain a large amount of ferroalloy, the density is relatively large, the deoxidized alloy is flushed into the bottom of the ladle with the molten steel, and the aluminum-silicon-iron alloy of the second layer is melted in the process of slowly floating and the residual free oxygen in the steel is removed to 5-15×10 -6, generating Al2O3 deoxidation products, as the alloy ball further melts, the calcium-magnesium-iron alloy in the center layer further removes the residual oxygen in the steel, and modifies the Al2O3 inclusions in the steel, generating dispersed small-sized magnesium-aluminum spinel, calcium-aluminate or rare earth oxide inclusions, preventing the nozzle from being blocked during the continuous casting process. The present invention realizes the modification of inclusions in the steel by active metals such as magnesium and calcium in the depth of the ladle, avoiding the existing magnesium and calcium wire feeding and direct addition of magnesium, calcium and other iron alloy processes that start to react on the surface of the molten steel, resulting in low alloy yield and large environmental dust. After the method of the present invention is applied, the number of Al2O3 inclusions ≥3μm in the ingot is reduced by more than 50%, and the number of non-metallic oxide inclusions is reduced by more than 48%. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0023] Figure 1 It is a schematic diagram of the structure of the deoxidized composite alloy in the present invention;

[0024] Figure 1 Among them, ① is calcium-magnesium-iron alloy, ② is aluminum-iron alloy, and ③ is ladle slag modifier;

[0025] Figure 2 This is a morphology diagram of inclusions in the cast steel in Example 1 of the present invention;

[0026] Figure 3 This is a morphology diagram of inclusions in the cast steel in Example 2 of the present invention;

[0027] Figure 4 This is a morphology diagram of inclusions in the cast steel in Comparative Example 1 of the present invention;

[0028] Figure 5 This is a morphology diagram of inclusions in the cast steel in Comparative Example 2 of the present invention;

[0029] Figure 6 This is a morphology diagram of inclusions in the cast steel in Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0030] The present invention provides a method for composite deoxidation of aluminum-killed steel and control of steel cleanliness, including a converter process and a continuous casting process. In the converter process: when the converter taps steel to 1 / 10 to 1 / 9 of the molten steel volume, a deoxidation composite alloy, an aluminum-iron alloy, a silicon-iron alloy and a silicon-manganese alloy are added into a ladle for deoxidation and alloying, and argon gas is blown at the bottom of the ladle for strong stirring during the tapping process;

[0031] In the continuous casting process: argon is blown into the bottom of the molten steel in the ladle during the early and middle stages of ladle pouring;

[0032] The deoxidized composite alloy is spherical, with a core of calcium-magnesium-iron alloy, a middle layer of aluminum-silicon-iron alloy, and an outer layer of ladle slag modifier;

[0033] The internal calcium-magnesium-iron alloy includes the following components by mass fraction: Ca: 1.1%~1.9%, Mg: 2.1%~2.9%, Re: 0.2%~0.9%, and the rest is Fe and unavoidable impurities;

[0034] The aluminum-silicon-iron alloy of the middle layer includes the following components by mass fraction: Al: 49%~60%, Si: 15.1%~23.9%, and the rest is Fe and inevitable impurities;

[0035] The outer layer of ladle slag modifier includes the following components in mass fraction: CaO: 15%~29%, Al2O3: 7%~15%, C: 31%~56%, Na2CO3: 3%~6%, among which CaO / Al2O3 is 1.9~2.6, and the rest are unavoidable impurities.

[0036] The present invention designs a deoxidation composite alloy and steel cleanliness control process according to the element deoxidation capacity, avoiding the problem of poor steel cleanliness in the existing short-process process that relies solely on metal deoxidation; it realizes the modification of steel inclusions by active metals such as magnesium and calcium in the depth of the ladle, avoiding the problem that the molten steel starts to react on the surface of the molten steel in the existing magnesium and calcium wire feeding and direct addition of magnesium, calcium and other ferroalloy processes, resulting in low alloy yield and large environmental dust. This technology is suitable for the efficient and rapid modification of aluminum-killed steel short-process ladle slag and steel inclusions, and is of great significance for improving the cleanliness of aluminum-killed steel.

[0037] The method of the present invention is mainly aimed at improving the converter process and the continuous casting process, and specifically comprises the following steps:

[0038] In the converter process: before steel is tapped from the converter, argon is blown into the ladle for 1 to 2 minutes to exhaust the air in the ladle; when 1 / 10 to 1 / 9 of the steel is tapped, a deoxidizing composite alloy is added and a large amount of argon is blown from the bottom of the ladle for stirring, and then aluminum iron, ferrosilicon, ferromanganese and other alloys are added in sequence to adjust the alloy composition of the molten steel, control the carbon, silicon and manganese elements in the steel within the range of the finished product, and at the same time modify the inclusions in the steel, and after alloying, control the composition of the steel within the range of the finished product.

[0039] In the present invention, the deoxidized composite alloy is spherical and has a three-layer alloy layer structure, the inner core is a calcium-magnesium-iron alloy, the middle layer is an aluminum-silicon-iron alloy, and the outer layer is a ladle slag modifier. More preferably, the deoxidized composite alloy has a six-layer structure, and there is a thin iron sheet layer for wrapping between the inner core and the middle layer, between the middle layer and the outer layer, and on the outer surface of the outer layer. The thin iron sheet can increase the weight of the middle layer and the inner core, and can make the remaining middle layer and the inner core part sink to the bottom quickly after the initial outer layer is dissolved, and play a buffering role in the dissolution of the wrapped alloy material.

[0040] In the present invention, the deoxidized composite alloy is preferably prepared according to the following steps:

[0041] The calcium-magnesium-iron alloy of the inner core and the aluminum-silicon-iron alloy of the middle layer can be prepared according to the existing alloy process, such as crushing and grinding the raw materials weighed according to the alloy stoichiometric ratio and then screening.

[0042] The outer layer of the ladle slag modifier is preferably prepared according to the following steps:

[0043] The calcium oxide source, aluminum oxide source and sodium carbonate source are added into an induction furnace in accordance with the required proportions to melt and prepare pre-melted slag. After water cooling and drying, the crushed pre-melted slag is ground together with carbon powder into a powder of 280-700 nm and mixed evenly.

[0044] The CaO source is selected from at least one of CaO or industrial calcium carbonate; the Al2O3 source is selected from at least one of Al2O3, corundum slag, bauxite or other industrial raw materials or ores containing Al2O3; the Na2CO3 source raw material is selected from at least one of industrial raw materials such as industrial Na2CO3 or albite; the carbon powder is a carbonaceous material containing C>85%, such as at least one of petroleum coke, graphite, and anthracite.

[0045] The alloy powders of each layer of the present invention are wrapped layer by layer with thin iron sheets to form a spherical deoxidized composite alloy, and the thickness of the thin iron sheets is preferably 0.2-1.0 mm.

[0046] The calcium-magnesium-iron alloy of the inner core includes the following components by mass fraction: Ca: 1.1% to 1.9%, preferably 1.2% to 1.8%, such as 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, preferably a range value with any of the above values ​​as the upper or lower limit; Mg: 2.1% to 2.9%, preferably 2.2% to 2.8%, such as 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, preferably a range value with any of the above values ​​as the upper or lower limit; Re: 0.2%~0.9%, preferably 0.3~0.8%, such as 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, preferably a range value with any of the above values ​​as the upper or lower limit; the rest is Fe and unavoidable impurities; the particle size of the calcium-magnesium-iron alloy of the inner core is preferably 1~5mm, more preferably 2~4mm;

[0047] The aluminum-silicon-iron alloy of the middle layer includes the following components in mass fraction: Al: 49% to 60%, preferably 50 to 58%, such as 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, preferably a range value with any of the above values ​​as the upper or lower limit; Si: 15.1% to 23.9%, preferably 18 to 20%, such as 15.1%, 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 18.5%, 19%, 20%, 20.5%, 21%, 21.5%, 22%, 22.5%, 23%, 23.9%, preferably a range value with any of the above values ​​as the upper or lower limit; the rest is Fe and unavoidable impurity components; the particle size of the aluminum-silicon-iron alloy of the middle layer is preferably 0.1 to 2 mm, more preferably 0.5 to 1.5 mm;

[0048] The ladle slag modifier of the outer layer includes the following components by mass fraction: CaO: 15%~29%, preferably 20~25%, such as 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, preferably a range value with the above arbitrary values ​​as the upper or lower limit; Al2O3: 7%~15%, preferably 8~12%, such as 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, preferably a range value with the above arbitrary values ​​as the upper or lower limit; C: 31%~56%, preferably 35~50%, such as 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, preferably a range value with the above arbitrary numerical value as the upper or lower limit; Na2CO3: 3%~6%, preferably 4%~5%, wherein CaO / Al2O3 is 1.9~2.6, preferably 2.0~2.3, and the rest are inevitable impurities; The particle size of the outer layer of the ladle slag modifier is preferably 280~700nm, more preferably 300~600nm.

[0049] In the present invention, the alloy particle size in the three layers from the inner to the outer of the spherical deoxidized composite alloy decreases in sequence. This arrangement enables the modifier in the outer layer that first contacts the molten steel and has the smallest density to be quickly dissolved in the steel in a shorter time. The middle layer is a deoxidized alloy layer, and the inner core is an inclusion-modified alloy. The alloy particle size of the middle layer is smaller than that of the inner layer, which can ensure that the inclusions are modified after deoxidation is completed and deoxidized non-metallic inclusions are generated. Therefore, the present invention achieves the purpose of controlling the melting order of the alloy and controlling it to play a corresponding role at different times by controlling the distribution of different types of alloys in the deoxidized composite alloy in the three-layer alloy layer structure in the sphere, as well as the type and particle size of the alloy in each layer structure.

[0050] In the present invention, the mass ratio of the core, the middle layer and the outer layer in the deoxidized composite alloy is preferably 1: (1.9-4.6): (4.8-2.0), more preferably 1: (2.0-4.0): (4.5-2.5), wherein the mass ratio of the core and the middle layer in the deoxidized composite alloy is preferably 1: (1.9-4.6), more preferably 1: (2.0-4.0), such as 1: 1.9, 1: 2.0, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, 1:2.6, 1:2.7, 1:2.8, 1:2.9, 1:3.0, 1:3.1, 1:3.2, 1:3.3, 1:3.4, 1:3.5, 1:3.6, 1:3.7, 1:3.8, 1:3.9, 1:4.0, 1:4.1, 1:4.2, 1:4.3, 1:4.4, 1:4.5, 1:4.6, preferably a range value with any of the above values ​​as the upper or lower limit; the mass ratio of the core and the outer layer in the deoxidized composite alloy is preferably 1: (4.8-2.0), preferably 1: (4.5-2.5), such as 1:4.8, 1:4.7, 1:4.6, 1:4.5, 1:4.4, 1:4.3, 1:4.2, 1:4.1, 1:4.0 , 1:3.9, 1:3.8, 1:3.7, 1:3.6, 1:3.5, 1:3.4, 1:3.3, 1:3.2, 1:3.1, 1:3.0, 1:2.9, 1:2.8, 1:2.7, 1:2.6, 1:2.5, 1:2.4, 1:2.3, 1:2.2, 1:2.1, 1:2.0, preferably a range value with any of the above values ​​as the upper or lower limit.

[0051] In the present invention, the particle size of the deoxidized composite alloy is preferably 20-40 mm; the addition amount of the deoxidized composite alloy is preferably 1.5-2.5.

[0052] The present invention preferably adds ferrosilicon alloy and ferromanganese alloy 31 to 45 seconds after the addition of the deoxidized composite alloy is completed, preferably 35 to 42 seconds, such as 31 s, 32 s, 33 s, 34 s, 35 s, 36 s, 37 s, 38 s, 39 s, 40 s, 41 s, 42 s, 43s, 44 s, 45 s, preferably a range value with the above any numerical value as the upper or lower limit.

[0053] In the present invention, there is no special restriction on the composition ratio and dosage of the aluminum-iron alloy, silicon-iron alloy and silicon-manganese alloy, as long as the carbon, silicon, manganese and aluminum elements in the steel can be controlled within the range of the finished product.

[0054] In the converter process of the present invention, large argon is blown from the bottom of the ladle for strong stirring during the steel tapping process. In the present invention, the "large argon blowing from the bottom" means that the flow rate of the bottom blowing argon is larger, which can achieve strong stirring of the molten steel and the slag, thereby achieving sufficient slag-metal reaction. Preferably, the flow rate of argon is preferably 300~500 NL / min, more preferably 350~450NL / min, such as 300 NL / min, 350NL / min, 400 NL / min, 450 NL / min, 500 NL / min, preferably a range value with any of the above values ​​as the upper or lower limit, and the time for strong stirring of bottom blowing argon is 1.0~2.4min, more preferably 1.5~2.0min.

[0055] In the continuous casting process, a small amount of argon is blown into the bottom of the molten steel in the ladle before and during the middle stage of ladle pouring to promote the floating and removal of inclusions in the steel, thereby obtaining molten steel with higher cleanliness. Specifically, the following steps are included:

[0056] When the ladle is on the pouring platform waiting for pouring to start, the ladle is covered and soft argon blowing is started at the bottom of the ladle to promote the floating of inclusions in the steel. The argon blowing flow rate is 100-120 NL / min. After the ladle starts pouring until the ladle is poured to 1 / 4-1 / 3 of the molten steel volume, the bottom blowing flow rate of the ladle is 70-100 NL / min. When the ladle is poured to 2 / 3-3 / 4 of the molten steel volume, the bottom argon blowing is turned off.

[0057] In the present invention, the "bottom blowing small argon" refers to a smaller flow rate of bottom blowing argon. When waiting for pouring, the argon blowing flow rate is preferably 100~120 NL / min, more preferably 105~115 NL / min, such as 100 NL / min, 105 NL / min, 110 NL / min, 115 NL / min, 120 NL / min, and preferably a range value with any of the above values ​​as the upper or lower limit; after the ladle starts pouring until the ladle is poured 1 / 4-1 / 3, the bottom blowing argon flow rate is preferably 70~100 NL / min, more preferably 80~90 NL / min, such as 70 NL / min, 75 NL / min, 80 NL / min, 85 NL / min, 90 NL / min, 95 NL / min, 100NL / min, and preferably a range value with any of the above values ​​as the upper or lower limit.

[0058] The method of the present invention can be widely applied to high-quality steels such as pipeline steel, SPHC, STB series, etc. The method of the present invention is also suitable for inclusion modification of long-process steel grades, which is of great significance for the stable control of inclusions in steel and the low-cost cleanliness production of steel grades, and has significant economic and social benefits.

[0059] In order to further illustrate the present invention, a method for composite deoxidation of aluminum-killed steel and controlling steel cleanliness provided by the present invention is described in detail below in conjunction with embodiments, but it should not be construed as limiting the scope of protection of the present invention.

[0060] Example 1

[0061] The molten steel smelting adopts the process of "converter process-slab continuous casting process". The product composition is shown in Table 1:

[0062] Table 1 Steel grade composition requirements / wt%

[0063]

[0064] When the converter tapping volume reaches 1 / 10 of the molten steel, a deoxidizing composite alloy is added to the ladle. 31 seconds after the alloy is added, aluminum-iron alloy, silicon-iron alloy, silicon-manganese alloy, etc. are added to deoxidize and alloy the molten steel, control the carbon, silicon and manganese elements in the steel within the range of the finished product, and modify the inclusions in the steel at the same time. During the tapping process, argon is blown at the bottom of the ladle at 350 NL / min for 1 minute of strong stirring.

[0065] When the ladle is on the pouring platform waiting for pouring to start, the ladle is covered and soft argon blowing is started at the bottom of the ladle to promote the floating of inclusions in the steel. The argon blowing flow rate is 100 NL / min. After the ladle starts pouring until the ladle is poured to 1 / 4 of the molten steel, the bottom blowing flow rate is 70NL / min. When the ladle is poured to 3 / 4 of the molten steel, the bottom argon blowing is turned off.

[0066] Deoxidized composite alloy: the internal alloy particle size is 1~5mm, the middle layer particle size is 0.1~2mm, and the outer layer particle size is 280nm~700nm; the inner layer deoxidized alloy composition is Ca: 1.1%, Mg: 2.9%, Re: 0.9%, and the rest is Fe and inevitable impurities; the middle layer includes Al: 49%, Si: 23.9%, and the rest is iron and inevitable impurities; the outer composition is: CaO: 15%, Al2O3: 7%, C: 56%, Na2CO36%, and the rest is inevitable impurities. The mass ratio of the inner layer: middle layer: outer layer of the deoxidized composite alloy ball is 1:2.4:3.2.

[0067] The inclusion morphology of the obtained ingot steel was detected using OXFORD electron microscope and ASPEX inclusion analysis instrument. The results are as follows: Figure 2 shown.

[0068] Example 2

[0069] The molten steel smelting adopts the process of "converter process-slab continuous casting process". The product composition is shown in Table 2:

[0070] Table 2 Steel grade composition requirements / wt%

[0071]

[0072] When the converter tapping volume reaches 1 / 9 of the molten steel, a deoxidizing composite alloy is added to the ladle. 42 seconds after the alloy is added, aluminum-iron alloy, silicon-iron alloy, silicon-manganese alloy, etc. are added to deoxidize and alloy the molten steel, control the carbon, silicon and manganese elements in the steel within the range of the finished product, and at the same time modify the inclusions in the steel. During the tapping process, 300 NL / min of argon is blown from the bottom of the ladle for strong stirring for 2 minutes.

[0073] When the ladle is on the pouring platform waiting for pouring to start, the ladle is covered and soft argon blowing is started at the bottom of the ladle to promote the floating of inclusions in the steel. The argon blowing flow rate is 120 NL / min. After the ladle starts pouring until the ladle is poured to 1 / 3 of the molten steel, the bottom blowing flow rate is 100NL / min. When the ladle is poured to 2 / 3 of the molten steel, the bottom argon blowing is turned off.

[0074] Deoxidized composite alloy: the internal alloy particle size is 1~5mm, the middle layer particle size is 0.1~2mm, and the outer layer particle size is 280nm~700nm; the inner layer deoxidized alloy composition is Ca: 1.9%, Mg: 2.1%, Re: 0.2%, and the rest is Fe and inevitable impurities; the middle layer includes Al: 60%, Si: 15.1%, and the rest is iron and inevitable impurities; the outer composition is: CaO: 29%, Al2O3: 15%, C: 31%, Na2CO310%, and the rest is inevitable impurities. The mass ratio of the inner layer: middle layer: outer layer of the deoxidized composite alloy ball is 1:3.5:4.2.

[0075] The inclusion morphology of the obtained ingot steel was detected using OXFORD electron microscope and ASPEX inclusion analysis instrument. The results are as follows: Figure 3 shown.

[0076] Comparative Example 1

[0077] The molten steel smelting adopts the process of "converter process - argon blowing after the furnace - continuous casting process". The product composition is shown in Table 3:

[0078] Table 3 Main component requirements of steel grades / wt%

[0079]

[0080] Converter process: When the converter tapping is 1 / 10 of the molten steel, add the ladle slag modifier with the same composition as in Example 1; when the converter tapping is 1 / 2 of the molten steel, add a carburizer to the ladle, wait for 20 seconds of circulation, and then add aluminum iron, silicon iron, manganese iron, etc. to alloy the molten steel. After tapping, the molten steel is stirred with weak argon blowing, the argon blowing flow rate is 80NL / min, and the argon blowing time is 6min. After the argon blowing, the steel contains: a[O] 35×10 -4wt%, [C] 0.55wt%, [Si] 0.41wt%, [Mn] 0.50wt%, [P] 0.017wt%, [S] 0.010wt%, [Al] 0.05wt%.

[0081] RH process: The gas flow rate during the vacuum treatment is increased to 1400 NL / min, and the cycle lasts for 10 minutes before the vacuum is completed.

[0082] The inclusion morphology of the ingot steel obtained at the end of RH production of this heat was detected using an OXFORD electron microscope and an ASPEX inclusion analysis instrument. Figure 4 shown.

[0083] Comparative Example 2

[0084] The molten steel smelting adopts the process of "converter process-slab continuous casting process". The product composition is shown in Table 4:

[0085] Table 4 Steel grade composition requirements / wt%

[0086]

[0087] When the converter taps to 1 / 2 of the molten steel, a deoxidizing composite alloy (the same deoxidizing composite alloy as in Example 1) is added into the ladle, and ferrosilicon alloy, silicon-manganese alloy, etc. are added at the same time to deoxidize and alloy the molten steel, control the carbon, silicon and manganese elements in the steel within the range of the finished product, and modify the inclusions in the steel at the same time; during the tapping process, the ladle is bottom blown with 480NL / min of large argon and stirred for 1 minute.

[0088] When the ladle is on the pouring platform waiting for pouring to start, the ladle is covered and soft argon blowing is started at the bottom of the ladle to promote the floating of inclusions in the steel. The argon blowing flow rate is 100 NL / min. After the ladle starts pouring until the ladle is poured to 1 / 4 of the molten steel, the bottom blowing flow rate is 70NL / min. When the ladle is poured to 3 / 4 of the molten steel, the bottom argon blowing is turned off.

[0089] The inclusion morphology of the obtained ingot steel was detected using OXFORD electron microscope and ASPEX inclusion analysis instrument. The results are as follows: Figure 5 shown.

[0090] Comparative Example 3

[0091] The molten steel smelting adopts the process of "converter process-slab continuous casting process". The product composition is shown in Table 5:

[0092] Table 5 Steel grade composition requirements / wt%

[0093]

[0094] When the converter tapped 1 / 9 of the molten steel, a deoxidizing composite alloy (the same deoxidizing composite alloy as in Example 2) was added to the ladle. After 35 seconds of the alloy addition, ferrosilicon alloy, silicon-manganese alloy, etc. were added to deoxidize and alloy the molten steel, control the carbon, silicon and manganese elements in the steel within the range of the finished product, and at the same time, modify the inclusions in the steel. During the tapping process, the ladle was bottom blown with 400 NL / min of large argon and stirred for 2 minutes.

[0095] The pouring platform on the ladle is cast according to conventional technology, and there is no argon blowing at the bottom of the ladle.

[0096] The inclusion morphology of the obtained ingot steel was detected using OXFORD electron microscope and ASPEX inclusion analysis instrument. The results are as follows: Figure 6 shown.

[0097] The total number of inclusions larger than 3 μm in the ingots obtained in the above-mentioned embodiments and comparative examples was detected, and the results are shown in Table 6.

[0098] Table 6 Total number of inclusions larger than 3μm in the ingot before and after implementation, pieces / mm 2

[0099]

[0100] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for composite deoxidation of aluminum killed steel and control of steel cleanliness, comprising a converter process and a continuous casting process, characterized in that: In the converter process: when the converter tapping volume reaches 1 / 10~1 / 9 of the molten steel, add deoxidation composite alloy, aluminum-iron alloy, silicon-iron alloy and silicon-manganese alloy into the ladle for deoxidation and alloying. During the tapping process, argon gas is blown from the bottom of the ladle for strong stirring. In the continuous casting process: argon is blown into the bottom of the molten steel in the ladle during the early and middle stages of ladle pouring; The deoxidized composite alloy is spherical, with a core of calcium-magnesium-iron alloy, a middle layer of aluminum-silicon-iron alloy, and an outer layer of ladle slag modifier; The calcium-magnesium-iron alloy of the inner core includes the following components by mass fraction: Ca: 1.1%~1.9%, Mg: 2.1%~2.9%, Re: 0.2%~0.9%, and the rest is Fe and unavoidable impurities; The aluminum-silicon-iron alloy of the middle layer includes the following components by mass fraction: Al: 49%~60%, Si: 15.1%~23.9%, and the rest is Fe and inevitable impurities; The outer layer of ladle slag modifier includes the following components in mass fraction: CaO: 15%~29%, Al2O3: 7%~15%, C: 31%~56%, Na2CO3: 3%~6%, among which CaO / Al2O3 is 1.9~2.6, and the rest are unavoidable impurities.

2. The method according to claim 1, characterized in that The mass ratio of the inner core, the middle layer and the outer layer is 1:(1.9-4.6):(2.0-4.8).

3. The method according to claim 1, characterized in that The particle size of the calcium-magnesium-iron alloy of the inner core is 1-5 mm, the particle size of the aluminum-silicon-iron alloy of the middle layer is 0.1-2 mm, and the particle size of the ladle slag modifier of the outer layer is 280-700 nm.

4. The method according to claim 1, characterized in that: The particle size of the deoxidized composite alloy is 10-40 mm.

5. The method according to claim 1, characterized in that The addition amount of the deoxidizing composite alloy is 0.95-3.5 kg / (t steel).

6. The method according to claim 1, characterized in that Before tapping the converter, argon gas is blown into the ladle for 1 to 2 minutes.

7. The method according to claim 1, characterized in that In the converter process, a deoxidized composite alloy is added into the ladle with bottom blowing of argon gas for strong stirring. After 31 to 45 seconds of the deoxidized composite alloy being added, ferrosilicon alloy and ferromanganese alloy are added.

8. The method according to claim 1, characterized in that In the converter process, the argon flow rate of the ladle bottom blowing argon strong stirring during the steel tapping process is 300-500NL / min, and the bottom blowing argon strong stirring time is 1.0-2.4min.

9. The method according to claim 1, characterized in that: In the continuous casting process, when the ladle is on the pouring platform waiting for pouring to start, the argon flow rate of the bottom blowing argon is 100-120 NL / min. After the ladle starts pouring until the ladle pours 1 / 4-1 / 3 of the molten steel, the argon flow rate of the bottom blowing argon is 70-100 NL / min. When the ladle pours 2 / 3-3 / 4 of the molten steel, the bottom blowing argon is stopped.

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