Method for deoxidizing molten steel, method for manufacturing steel material, and steel material

Abstract

The present invention provides a technique for improving the yield of Al with no increase in the cost of vacuum refining. In addition, a method for manufacturing steel with less variation in the amount of Al is provided. A method for deoxidizing and refining molten steel using a vacuum refining apparatus, in which an Al-containing substance is added to the molten steel in a vacuum tank, and the temperature change ΔT1 and ΔT2 of the molten steel in the Al deoxidation satisfy the following equation (1). The Al content of the Al-containing substance is preferably 30 to 80 mass%. The method for deoxidizing and refining molten steel described above as a deoxidation step enables the manufacture of steel in which the Al concentration in the steel after the deoxidation step is 0.02 mass% or less. ΔT1 + ΔT2 < 0 ··· (1) ΔT1 represents the temperature increase due to the heat of oxidation of Al, and ΔT2 represents the temperature decrease due to the sensible heat of the Al-containing substance.

Description

Technical Field

[0001] This invention relates to a deoxidation refining method for molten steel in which the yield of Al is improved by adding it during the deoxidation process of molten steel using a vacuum refining apparatus. Background Technology

[0002] In the steelmaking process of steelmaking, the following treatment is widely performed: decarburization blowing of molten iron in a converter (referred to as "primary refining"). Then, the molten steel is discharged into a ladle, and the molten steel in the ladle is circulated into the vacuum tank of a vacuum refining unit, such as an RH vacuum degassing unit, to refine the molten steel under reduced pressure ("secondary refining").

[0003] When vacuum refining equipment such as RH and DH is used in secondary refining to perform vacuum refining on undeoxidized or semi-deoxidized molten steel, deoxidation refining of the molten steel is usually carried out by adding metals such as Al to the molten steel in a vacuum tank with a vacuum atmosphere.

[0004] The vacuum refining unit is installed to cover the upper side of the ladle. The molten steel in the ladle rises into the vacuum tank of the vacuum refining unit for vacuum refining. A raw material inlet is provided on the upper side or top cover of the vacuum tank. Metallic Al, alloy Al, and other Al-containing substances are introduced into the vacuum tank through this inlet, and Al is used to deoxidize and refine the molten steel.

[0005] However, in the deoxidation refining of this molten steel, the yield of Al in the molten steel is poor for Al-containing substances added to the vacuum tank. Therefore, this becomes a major factor contributing to the increased cost of vacuum refining, including the increased amount of Al-containing substances added, longer processing time, and increased raw material costs. Furthermore, there are also issues such as unstable yields due to the reduced Al yield in the molten steel, leading to deviations in the Al content of the steel after the steelmaking process.

[0006] Therefore, in order to solve the above problems, a technique to improve the yield of added Al has been proposed.

[0007] For example, Patent Document 1 discloses a technique to suppress Al evaporation loss and improve yield by impregnating Al-containing substances into molten steel at a low vacuum of 40 Torr (5333 Pa) or higher until Al diffusion / alloying is performed. From the start of decompression until 12 minutes later, the vacuum is set to 40 Torr (5333 Pa) or higher to allow metallic Al to diffuse and alloy into the molten steel, thereby suppressing Al evaporation. This invention demonstrates a higher Al yield compared to the conventional method of immediately setting the vacuum to a high vacuum below 40 Torr (5333 Pa) after Al addition. The deoxidation treatment time is 15–20 minutes.

[0008] In addition, Non-Patent Document 1 proposes a technique that uses compressed gas to launch an Al projectile into molten steel, thereby increasing the Al yield by increasing the immersion depth of the Al projectile in the molten steel.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 3-211216

[0012] Non-patent literature

[0013] Non-patent literature 1: Sumitomo Metal Technical Report Vol. 25, p30 Summary of the Invention

[0014] The problem that the invention aims to solve

[0015] The aforementioned prior art has the following problems.

[0016] In the technology described in Patent Document 1, the vacuum level deteriorates compared to the past until deoxidation is completed (maintaining a vacuum level of 5333 Pa or higher for more than 12 minutes), thus lengthening the vacuum refining process. Furthermore, during Al addition in deoxidation, localized high-temperature zones are generated due to Al oxidation, resulting in Al vapor pressure exceeding atmospheric pressure even under low vacuum, leading to Al evaporation and insufficient reduction of Al evaporation losses.

[0017] Furthermore, the technology described in Non-Patent Document 1 has the problem of requiring the construction of a new gas bomb launching device, which increases equipment costs.

[0018] The present invention was made in view of the above circumstances, and its object is to provide a deoxidation refining method for molten steel with short processing time and increased Al addition yield during vacuum refining. Furthermore, its object is to provide a method for manufacturing steel with increased Al addition yield and smaller deviations in Al composition during vacuum refining.

[0019] Methods for solving problems

[0020] To address the aforementioned issues, the inventors of this application conducted in-depth experiments and research. The results showed that by adding Al-containing substances under conditions where the temperature decrease caused by the sensible heat of adding the Al-containing substance was greater than the temperature increase caused by the heat of oxidation of Al, the Al yield was improved.

[0021] Based on the above insights, the present invention is configured as follows.

[0022] [1] A deoxidation refining method for molten steel, which is a deoxidation refining method for molten steel using a vacuum refining device, wherein an Al-containing substance is added to the molten steel in a vacuum tank, and the temperature changes ΔT1 and ΔT2 of the molten steel in Al deoxidation satisfy equation (1).

[0023] ΔT1+ΔT2<0· · · (1)

[0024] Where ΔT1 and ΔT2 are respectively based on

[0025] ΔT1=(W Re_Al ×Q Al-O ) / (C steel ×W Re_STEEL (2)

[0026] ΔT2=-(V Al / 0.01X Al ×t1×Q Al_Alloy-C ) / (C steel ×W Re_STEEL )···(3)

[0027] Defined temperature change (°C),

[0028] t1 is the time (in seconds) from the start of the addition of the Al-containing substance to the point at which the molten steel in the vacuum tank at the start of the addition of the Al-containing substance begins to circulate and replace the molten steel.

[0029] W Re_Al Let be the mass (kg) of metallic Al used in the deoxidation reaction during time t1.

[0030] Q Al-O The heat of oxidation of Al (kJ / kg-Al)

[0031] C steel Specific heat of molten steel (kJ / kg / ℃)

[0032] W Re_STEEL The amount (kg) of molten steel used in the deoxidation reaction during time t1.

[0033] V Al The addition rate of metallic Al (kg / s) is given.

[0034] X Al The content of Al in Al-containing substances (mass%)

[0035] Q Al_Alloy-C The sensible heat and latent heat (kJ / kg) of Al-containing substances.

[0036] [2] Preferably, in the deoxidation refining method for molten steel described in [1] above, the Al content of the Al-containing substance is 30-80% by mass.

[0037] [3] A method for manufacturing steel, wherein the deoxidation and refining method of molten steel described in [1] or [2] above is used as a deoxidation process.

[0038] The Al concentration in the steel after this deoxidation process is below 0.02% by mass.

[0039] [4] Steel, which is produced by the deoxidation refining method of molten steel described in [1] or [2] above as a deoxidation process.

[0040] The Al concentration in the steel after this deoxidation process is below 0.02% by mass.

[0041] [5] Preferably, the Al concentration range of the steel described in [4] above is the standard range of Al composition.

[0042] Invention Effects

[0043] According to the present invention, in the vacuum refining process of steel manufacturing, the addition of Al results in a short deoxidation treatment time and an increased yield of Al, thereby achieving high productivity / low manufacturing cost, and can also provide products with very small deviations in the Al content of steel, resulting in significant industrial benefits and resource savings. Attached Figure Description

[0044] [ Figure 1 [This is a schematic longitudinal sectional view showing an example of an RH vacuum degassing device.]

[0045] [ Figure 2 [This is an enlarged cross-sectional view of the above-described RH vacuum degassing apparatus illustrating the concept of the present invention.]

[0046] [ Figure 3 [Figure 1] shows the effect of the change in heat of molten steel before and after Al addition on the Al evaporation rate.

[0047] [ Figure 4 [This is a graph showing the temperature behavior of molten steel during Al deoxidation caused by differences in Al addition conditions.] Detailed Implementation

[0048] In order to evaluate the Al evaporation loss during deoxidation, the inventors of this application conducted deoxidation tests on molten steel under various conditions using a small vacuum melting furnace. The results showed that, as... Figure 3As shown, the Al evaporation rate is related to the heat change of the molten steel before and after Al addition, especially in the region where the heat change becomes negative, the Al evaporation loss is significantly reduced. The heat change is the sum of (1) the heat of oxidation of Al during deoxidation and (2) the sensible heat of the Al-containing substance added per unit time. Furthermore, as... Figure 4 As shown, the evaporation temperature of Al in the RH vacuum degassing device was compared with the temperature shift of molten steel in the vacuum tank under various Al alloy addition conditions. The results showed that by increasing the addition rate of Al-containing substances and using FeAl as the Al-containing substance, the temperature drop caused by the sensible heat of the added substances increased, and the time for the temperature of the molten steel in the vacuum tank to exceed the Al evaporation temperature was shortened.

[0049] In this case, the inventors investigated the temperature changes caused by the sensible heat and oxidation heat of the added Al-containing substance and the yield of added Al in the deoxidation process of a vacuum refining apparatus. They studied in detail the effect of temperature changes at the reaction site based on the addition of the Al-containing substance on the yield of added Al. The results showed that the temperature of the reaction site caused by the sensible heat and oxidation heat of the added Al-containing substance affects the yield of added Al; by controlling the temperature of the reaction site, the Al yield can be increased.

[0050] In this invention, the temperature of the Al deoxidation reaction site is controlled such that the temperature decrease caused by the sensible heat of the Al-containing substance added to the molten steel is greater than the temperature increase caused by the heat of oxidation of the added Al. Furthermore, the technical concept of this invention is to significantly shorten the processing time and increase the yield of added Al compared to conventional deoxidation methods.

[0051] The following describes in detail the deoxidation and refining method for molten steel according to the present invention.

[0052] Vacuum refining apparatuses capable of performing the deoxidation refining method for molten steel according to the present invention include RH vacuum degassing apparatus, DH vacuum degassing apparatus, REDA vacuum degassing apparatus, etc., among which the RH vacuum degassing apparatus is the most representative.

[0053] Therefore, the vacuum refining method in the RH vacuum degassing unit will be explained first.

[0054] exist Figure 1 In the attached diagram, reference numerals 1 represent an RH-type vacuum degassing device, 2 a ladle, 3 molten steel, 4 slag, 5 a vacuum tank, 6 an upper tank, 7 a lower tank, 8 a rising-side immersion pipe (rising pipe), 9 a falling-side immersion pipe (falling pipe), 10 a circulating gas inlet pipe, 11 a pipeline, 12 a raw material inlet, and 13 a top-blowing nozzle. The vacuum tank 5 consists of an upper tank 6 and a lower tank 7. The top-blowing nozzle 13 is a device that blows oxygen and flux into the molten steel in the vacuum tank; it is located at the top of the vacuum tank 5 and can move up and down inside the vacuum tank 5.

[0055] In the RH-type vacuum degassing apparatus 1, a ladle 2 containing molten steel 3 is raised using a lifting device (not shown), immersing the rising-side immersion tube 8 and the descending-side immersion tube 9 in the molten steel 3 within the ladle 2. Meanwhile, an exhaust device (not shown) connected to pipe 11 is used to vent air from the inside of the vacuum tank 5, depressurizing the interior of the vacuum tank 5, and blowing circulating gas into the rising-side immersion tube 8 from the circulating gas inlet pipe 10. As the interior of the vacuum tank 5 is depressurized, the molten steel 3 in the ladle 2 rises proportionally to the pressure difference (vacuum degree) between atmospheric pressure and the vacuum tank 5, flowing into the vacuum tank 5. Simultaneously, due to the gas lifting effect of the circulating gas blown in from the circulating gas inlet pipe 10, the molten steel 3 and the circulating gas rise together in the rising-side immersion tube 8 and flow into the interior of the vacuum tank 5. Then, a flow returning to the ladle 2 via the descending-side immersion tube 9, known as circulation, is formed, thus performing RH-type vacuum refining. Molten steel 3 is exposed to a reduced-pressure atmosphere within a vacuum tank 5. The gaseous components in the molten steel 3 move into the atmosphere within the vacuum tank 5, undergoing a degassing reaction. In RH-type vacuum refining, when deoxidizing undeoxidized or semi-deoxidized molten steel, an alloy that reacts with oxygen to generate oxides is added as a deoxidizing agent to the molten steel 3 within the vacuum tank 5 through the raw material inlet 12. Depending on the strength of its deoxidizing ability, metallic Al or Al-containing alloys are typically used as the deoxidizing material.

[0056] In this invention, during the deoxidation of molten steel, in order to suppress the evaporation loss of Al, the temperature decrease caused by the sensible heat of the added Al-containing substance is greater than the temperature increase caused by the oxidation heat of the added Al. That is, the operating conditions are determined so that the sum of the former temperature change ΔT1 and the latter temperature change ΔT2, as shown in equation (1), becomes negative, and the deoxidation treatment is carried out.

[0057] ΔT1+ΔT2<0

[0058] The temperature change ΔT1 caused by the oxidation reaction heat of added Al and the temperature change ΔT2 caused by the sensible heat (including latent heat) of added Al-containing substances are defined as Equations (2) and (3), respectively. The temperature changes ΔT1 and ΔT2 are controlled by the energies of Equations (4) to (7) to satisfy Equation (1).

[0059] ΔT1+ΔT2<0···(1)

[0060] In equation (1), ΔT1 and ΔT2 are defined by equations (2) and (3).

[0061] ΔT1=(W Re_Al ×Q Al-O ) / (C steel ×W Re_STEEL (2)

[0062] ΔT2=-(V Al / 0.01X Al ×t1×Q Al_Alloy-C ) / (C steel ×W Re_STEEL )···(3)

[0063] W Re_Al =MIN[W Re_STEEL ×a0 / f0×1.0×10 -6 ×54 / 48, V Al ×t1]···(4)

[0064] MIN[A, B] refers to the smaller value between A and B.

[0065] W Re_STEEL =Q Cir ×t1···(5)

[0066] t1 = W V / Q Cir ···(6)

[0067] Q Cir =K×G 1 / 3 ×D 4 / 3 ×{ln(P0 / P1)} 1 / 3 ···(7)

[0068] t1 is the time (in seconds) from the start of the addition of the Al-containing substance to the point at which the molten steel in the vacuum tank at the start of the addition of the Al-containing substance begins to circulate and replace the molten steel.

[0069] W Re_Al Let be the mass (kg) of metallic Al used in the deoxidation reaction during time t1.

[0070] Q Al-O The heat of oxidation of Al (kJ / kg-Al)

[0071] C steel The specific heat of molten steel is 0.188 (kJ / kg / ℃).

[0072] W Re_STEEL The amount (kg) of molten steel used in the deoxidation reaction during time t1.

[0073] V Al The addition rate of metallic Al (kg / s) is given.

[0074] X Al The content of Al in Al-containing substances (mass%)

[0075] QAl_Alloy-C The sensible and latent heat of Al-containing substances (kJ / kg)

[0076] W V The volume of molten steel in the vacuum tank (kg)

[0077] Q Cir The circulation flow rate is (kg / s).

[0078] K is a constant (190),

[0079] G represents the circulating gas flow rate (Nl / min).

[0080] D is the inner diameter of the impregnation tube (m).

[0081] P0 is atmospheric pressure (101325 Pa).

[0082] P1 represents the vacuum level (Pa).

[0083] a0 represents the oxygen activity (ppm) of the molten steel.

[0084] f0 is the activity coefficient of oxygen in molten steel.

[0085] The oxygen activity of the molten steel was measured using an oxygen probe before deoxidation. The Al addition rate was calculated based on the time change of the alloy hopper weighing value during addition, or by using an in-tank monitoring camera to determine the timing of the start and end of addition, and then the total addition amount was divided by the addition time.

[0086] The volume of molten steel W in the vacuum tank V As shown in equations (8) and (9) below. Figure 2 The lengths are defined in the text.

[0087] W V =π / 4·D V 2 ×h V ×ρ L g···(8)

[0088] h V =(P0-P1) / (ρ L g)+lL···(9)

[0089] Among them, D V The inner diameter of the vacuum chamber (m)

[0090] h V The height of molten steel in the vacuum tank (m),

[0091] ρ L g is the density of molten steel (kg / m³) 3 ),

[0092] l represents the immersion depth (m) of the immersion tube into the molten steel.

[0093] L is the height (m) from the bottom of the impregnation tube to the vacuum tank pad.

[0094] The immersion depth l of the immersion tube into the molten steel is shown in the following formula (10).

[0095] l = l L -l FB -l LV · · · (10)

[0096] Among them, l L The distance (m) from the bottom of the ladle to the top of the ladle.

[0097] l FB The distance (m) from the top of the ladle to the surface of the molten steel in the ladle.

[0098] l LV The distance (m) from the bottom of the impregnation tube to the bottom of the ladle.

[0099] However, for l FB In this case, a molten steel level gauge is used to measure the height of the molten steel level, or a metal rod is immersed in the molten steel in the ladle to measure the length of the molten portion. The length is calculated based on the relative distance between the ladle and the vacuum tank obtained from the control system. LV .

[0100] The operating factors used to satisfy equation (1) are vacuum level, circulating gas flow rate, and Al addition rate. That is, the temperature changes ΔT1 and ΔT2 in the Al deoxidation reaction area are mainly controlled by vacuum level, circulating gas flow rate, and Al addition rate. Regarding vacuum level and circulating gas flow rate, in order to increase the absolute value of ΔT2, it is necessary to reduce vacuum level or reduce circulating gas flow rate. In addition, at this time, due to the deterioration of refining efficiency and the increase in processing time, it is desirable to adjust the Al addition rate. The Al addition rate is adjusted by increasing or decreasing the opening of the alloy hopper.

[0101] However, there is a limit to accelerating the Al addition rate by increasing the hopper opening. Therefore, efficiency can be further improved by using Al-containing materials with an Al content of less than 80% and increasing the sensible heat per unit of Al added.

[0102] Furthermore, this technology can be applied to vacuum refining apparatuses, such as DH vacuum degassing units and REDA vacuum degassing units, which circulate molten steel between a vacuum tank and a ladle. However, the circulation rate Q of the molten steel needs to be calculated. CirEquation (7) is a unique formula for the RH vacuum degassing device. Therefore, when this technology is applied in the DH vacuum degassing device or the REDA vacuum degassing device, it is necessary to pre-determine the uniform mixing time of Cu and other alloys and calculate the circulation flow rate of the molten steel under each operating condition.

[0103] Al content of added Al-containing substances: 30-80% by mass

[0104] One of the main reasons for Al loss during Al deoxidation of molten steel is the evaporation of Al in the locally heated molten steel due to the heat of the deoxidation reaction. By reducing the Al content of the added Al-containing substance and increasing the sensible heat per unit of added Al, the temperature drop ΔT2 caused by the sensible heat can be increased, thus more effectively suppressing Al evaporation. Therefore, it is preferable that the Al content of the added Al-containing substance is 80% by mass or less.

[0105] On the other hand, if the Al content of the added Al-containing substance is too low, in addition to the increase in the total amount of Al-containing substance added and the longer processing time, the temperature of the molten steel during processing may drop below the solidification temperature in the vacuum tank. Therefore, it is preferable that the Al content of the added Al-containing substance is 30% by mass or more.

[0106] When choosing the type of Al-containing material, it is preferable to use an aluminum-iron alloy (FeAl) in a manner that does not interfere with the adjustment of other steel composition. It should be noted that Al alloys containing components other than iron may also be used, depending on the target composition.

[0107] The Al concentration in the steel is below 0.02% by mass.

[0108] The deoxidation refining method of the present invention improves the Al yield and reduces the deviation in Al content of steel manufactured from steelmaking processes incorporating the present deoxidation refining method.

[0109] That is, the concentration of Al in the steel after the deoxidation process in the deoxidation refining method based on the present invention can be set to less than 0.02% by mass.

[0110] Specifically, regarding steel grades with the same target Al concentration range, the Al content (mass%) in the deoxidized and refined steel after each feed (one-time steel output) refers to the deviation range within a specific feed number (standard, characteristic, etc.). For example, the Al concentration range in the steel can also be set as the standard range of Al composition.

[0111] However, regarding the actual value of the Al content in the steel for the specific number of feeds mentioned above, the deviation range refers to 6 times its standard deviation.

[0112] If the concentration of Al in steel is below 0.02% by mass, then a narrow range of chemical composition values ​​in the product standard can be expected, preventing deviations from the target chemical composition values.

[0113] According to the deoxidation refining method of the present invention, if the Al yield becomes 85% or more, the Al concentration range in the steel can be set to 0.02% by mass or less. This is because the deviation in the Al concentration in the deoxidized steel mainly depends on the deviation in the Al yield; by making the Al yield close to 100%, the deviation in the Al yield is reduced. Furthermore, by increasing the Al yield, the necessary Al addition amount relative to the target Al concentration is reduced, which is also a reason for the reduction in the Al concentration deviation.

[0114] Example

[0115] The molten iron was decarburized and refined in a converter. 300 tons of molten steel were then discharged from the converter into a ladle, where it underwent vacuum refining using an RH vacuum device. The target steel grade was an ultra-low carbon steel with a [C] standard upper limit of 25 ppm. The chemical composition of the molten steel before vacuum refining was: C: 0.04–0.06 wt%, Si: 0.15–0.25 wt%, Mn: 0.1–0.5 wt%, P: less than 0.02 wt%, S: less than 0.003 wt%. The temperature of the molten steel before deoxidation was 1580–1630℃, and the oxygen activity a0 in the molten steel before deoxidation was 300–600 ppm. The vacuum degree was 267 Pa, and the circulating gas flow rate was 2500 Nl / min.

[0116] Al-containing materials use metallic Al containing 99% Al and FeAl alloys containing 20%, 40%, 70%, 80%, and 90% Al.

[0117] By primarily increasing the Al addition rate V Al The yield of Al varies within the range of 10–25 kg / s, and the yield is evaluated based on various values ​​of ΔT1 and ΔT2.

[0118] The experiment was carried out 30 times under each condition, and the Al yield and the addition time of Al-containing substances were evaluated using the average value of the 30 additions.

[0119] The range of Al concentration in steel is calculated based on the standard deviation of Al concentration in steel after deoxidation treatment under each condition (No. 1 to 10).

[0120] The values ​​of each of equations (2) to (10) are set to the following values.

[0121] t1: 4.2(s),

[0122] W Re_Al 4-7 (kg)

[0123] Q Al-O 27045 (kJ / kg-Al),

[0124] C STEEL Specific heat of molten steel: 0.188 (kJ / kg / ℃)

[0125] W Re_STEEL 11757 (kg)

[0126] V Al : 10~25 (kg / s)

[0127] X Al : 20-99 (%)

[0128] Q Al_Alloy-C : 1381~2163 (kJ / kg).

[0129] If the mass fraction and sensible heat of the added Al-containing substance containing component i (containing Al) are respectively set as X... i Q i_C (kJ / kg-i) is then

[0130] In the embodiment, Q is used. AlC =2163 (kJ / kg-Al), Q Fe_C =1186 (kJ / kg-Fe) for calculation.

[0131] W V 11760 (kg)

[0132] Q Cir 2903 (kg / s)

[0133] K = 190,

[0134] G: 2500 (Nl / min),

[0135] D: 0.7 (m)

[0136] P0: 1.01325x10 5 (Pa),

[0137] P1: 267 (Pa),

[0138] a0: 350~500 (ppm),

[0139] f0: 1,

[0140] l L 4.0 (m)

[0141] l FB1.2 (m)

[0142] l LV : 2.1(m).

[0143] Al yield is evaluated using equation (11). In equation (11), the numerator represents the sum of the mass of Al consumed during deoxidation and the mass of Al dissolved in the molten steel after deoxidation, and the denominator represents the total mass of the added Al components.

[0144] e Al ={(a0 / f0×1.0×10 -6 ×54 / 48+[%Al] / 100)×W}×100 / (W Al ×X Al / 100)···(11)

[0145] Among them, e Al Al yield (%)

[0146] [%Al] represents the Al concentration (mass%) in the deoxidized molten steel.

[0147] W is 300 tons (tons) in terms of the amount of molten steel it can handle.

[0148] W Al The amount of metallic Al or Al alloy added (kg)

[0149] X Al This refers to the Al content (mass%) in Al-containing substances.

[0150] [%Al] is determined by taking a metal sample after the RH-type vacuum refining process and calculating its analytical value.

[0151] The experimental results are shown in Table 1. Al yield refers to the percentage of the sum of the amount of Al consumed during deoxidation and the amount of Al corresponding to the increase in Al concentration in the steel, relative to the amount of Al in the added Al-containing material. In Invention Examples No. 1 to 8, under the condition that the absolute value of the temperature decrease ΔT2 due to Al addition exceeds the absolute value of the temperature increase ΔT1 due to the addition of Al, a good result of Al yield of 70% or more was obtained. Furthermore, at all levels, Al addition was carried out under a high vacuum of 267 Pa or less, without extending the processing time due to the lack of re-evacuation.

[0152] In Invention Examples No. 5 to 8, where the Al content of the added Al-containing substance was 80% by mass or less, the Al yield became 85% or more, resulting in further good results.

[0153] However, even though the Al content of Invention Example No. 5 was less than 30% by mass, a high Al yield was obtained. On the other hand, due to the increase in the necessary amount of Al added, the addition time was extended to more than 1 minute, and the vacuuming processing time was extended.

[0154] Therefore, the Al yield, which also takes into account the processing time, is divided into three stages as an evaluation, as shown in the rightmost column of Table 1.

[0155] ◎: Al yield is over 85%, and Al addition time is less than 1 minute.

[0156] ○: Al yield is 70% or higher but less than 85%, and Al addition time is less than 1 minute; or Al yield is 85% or higher, and Al addition time is more than 1 minute.

[0157] △: Al yield is less than 70%

[0158] In Invention Examples No. 5 to 8, where the Al yield is 85% or higher, the concentration deviation of the final Al component obtained by collecting and analyzing samples during the casting process is within the range of 0.02% by mass.

[0159] On the other hand, the concentration deviation of the final Al component in Comparative Examples No. 9-10, where the Al yield was less than 70%, was less than 0.035% by mass, which is a result of a greater concentration deviation than that in the Inventive Examples.

[0160] [Table 1]

[0161]

[0162] Industrial availability

[0163] The deoxidation refining method based on Al addition in the steelmaking process of the present invention can be applied to the manufacture of steels requiring low manufacturing costs and a narrow range of Al content.

[0164] Explanation of reference numerals in the attached figures

[0165] 1 RH vacuum degassing device

[0166] 2. Pouring ladle

[0167] 3. Molten Steel

[0168] 4. Slag

[0169] 5 Vacuum bath

[0170] 6. Upper groove

[0171] 7. Lower groove

[0172] 8. Rising side impregnation tube

[0173] 9. Descent-side impregnation tube

[0174] 10. Circulation gas inlet pipe

[0175] 11 Pipelines

[0176] 12 Raw material input port

[0177] 13 Top-blown spray gun

[0178] D V Vacuum tank inner diameter

[0179] D Inner diameter of the impregnation tube

[0180] L is the height from the bottom of the impregnation tube to the vacuum tank pad.

[0181] l Immersion depth of the immersion tube into the molten steel

[0182] l L Distance from the bottom to the top of the ladle

[0183] l LV Distance from the bottom of the impregnation tube to the bottom of the ladle

[0184] l FB Distance from the top of the ladle to the surface of the molten steel

[0185] h V The height of molten steel in the vacuum tank

[0186] h L Distance from the bottom of the ladle to the surface of the molten steel

Claims

1. A deoxidation refining method for molten steel, which is a deoxidation refining method for molten steel using a vacuum refining unit, wherein, When an Al-containing substance is added to molten steel in a vacuum tank, the temperature changes ΔT1 and ΔT2 of the molten steel during Al deoxidation satisfy equation (1). ΔT1+ΔT2<0···(1) Where ΔT1 and ΔT2 are respectively based on ΔT1=(W Re_Al ×Q Al-O ) / (C steel ×W Re_STEEL )···(2) ΔT2=-(V Al / (0.01×X Al )×t1×Q Al_Alloy-C ) / (C steel ×W Re_STEEL )···(3) Defined temperature change (°C). t1 is the time (in seconds) from the start of the addition of the Al-containing substance to the point at which the molten steel in the vacuum tank at the start of the addition of the Al-containing substance is circulated and replaced. W Re_Al The mass (kg) of metallic Al used in the deoxidation reaction during time t1. Q Al-O The heat of oxidation of Al (kJ / kg-Al) C steel Specific heat of molten steel (kJ / kg / ℃). W Re_STEEL The amount of molten steel (kg) used in the deoxidation reaction during time t1. V Al The addition rate of metallic Al is expressed as kg / s. X Al The content of Al in Al-containing substances (mass%). Q Al_Alloy-C The sensible heat and latent heat (kJ / kg) of Al-containing substances.

2. The deoxidation and refining method for molten steel according to claim 1, wherein, The Al content of the Al-containing substance is 30-80% by mass.

3. A method for manufacturing steel, comprising the deoxidation and refining method for molten steel as described in claim 1 or 2 as a deoxidation step. The Al concentration in the steel after this deoxidation process is below 0.02% by mass.

4. Steel, which is obtained by deoxidation refining of molten steel as described in claim 1 or 2 as a deoxidation process. The Al concentration in the steel after this deoxidation process is below 0.02% by mass.

5. The steel according to claim 4, wherein, The Al concentration range is the standard range for Al composition.

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