JP7273306B2 - Melting method of high Al content steel - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for melting high Al content steel, and more particularly to a method for melting high Al content steel with a low nitrogen content in the steel.

With the improvement of steel quality, reduction of the nitrogen (N) concentration in steel is required.

When smelting steel in a refining furnace, the molten steel that has completed refining in the refining furnace is tapped from the refining furnace into a ladle. When the refining furnace is a converter, tap holes are arranged in the belly of the converter. Place in pot.

When the steel is tapped from the refining furnace to the ladle, the molten steel flow not only touches the atmosphere gas, but also hits the ladle wall and the surface of the molten steel inside the ladle. be done. As a result, the main component _N2 in the air comes into contact with the molten steel and tends to cause a nitrogen absorption reaction (so-called nitrogen pick-up) between the gas component and the molten steel.

In Patent Document 1, when molten steel refined in a converter is tapped, Si deoxidation is performed, and a CaO—SiO ₂ -based flux (CaO/SiO ₂ is limited to 0.7 to 1.1) is added. A method of receiving steel in a ladle and producing low Al steel is disclosed. By adding CaO—SiO ₂ based flux at the time of tapping, the added flux coats the molten steel surface during tapping in a molten state, thereby preventing absorption of nitrogen during tapping. CaO/SiO ₂ : It is said that the composition range of 0.7 to 1.1 has the lowest melting point and a good coating effect.

In Patent Document 2, as a method for melting high-carbon steel for ultra-fine wire rods, which is low-Al steel, when synthetic flux is added to steel discharged from a converter and flux treatment is performed by Ar stirring, Si deoxidation is excessive. To prevent this from progressing, a synthetic flux with an SiO ₂ activity of 0.4 or more is added to the ladle during tapping to suppress Al ₂ O ₃ contamination from the bricks. There is no disclosure of suppression of nitrogen absorption during tapping.

Patent Document 3 relates to a method for producing bearing steel, in which a CaO—SiO ₂ -based flux containing substantially no fluorine source is added to a ladle, and then deoxidized with Al in the atmosphere. The molten steel and the flux are stirred by blowing a stirring gas into the molten steel. Since Ca is added to forcibly change the composition of Al ₂ O ₃ inclusions in the molten steel to CaO—Al ₂ O ₃ inclusions, a CaO—SiO ₂ based flux that does not contain a fluorine source such as CaF ₂ is used. Even so, the absorption of CaO-- _{Al.sub.2 O.sub.3} inclusions in the steel bath by the flux is promoted, making it possible to manufacture bearing steel with high cleanliness and excellent rolling contact fatigue life characteristics. No mention is made of the composition of the CaO--SiO ₂ -based flux, and nothing is disclosed about the suppression of nitrogen absorption during tapping.

Non-Patent Documents 1 to 3 discuss the migration behavior of nitrogen between gas-slag-metal phases for efficient denitrification from molten steel. In order to achieve efficient denitrification, it is important to maintain a high oxygen partial pressure in the gas phase and a low oxygen potential at the slag-metal interface. It is considered effective to add an element capable of reducing nitrogen and transferring it to slag. Then, CaO-Al ₂ O ₃ system slag was formed on the molten steel surface, Al was added as a reducing agent, and the behavior of the nitrogen concentration in the molten steel after the lapse of the required time was investigated. As a result, a decrease in nitrogen concentration is observed.

In Non-Patent Document 4, regarding the nitrogen dissolution behavior of molten silicate slag (CaO--SiO ₂ , CaO--MgO--SiO ₂ , BaO--MgO--SiO ₂ systems), nitrogen partial pressure and oxygen partial pressure in the gas phase It is measured as a relationship between Then, when CaO-- _SiO.sub.2 -based slag is used, the higher the _SiO.sub.2 concentration or the higher the nitrogen partial pressure in the gas phase, the higher the % ^N.sub.3- in the slag. However, nothing is shown about the behavior of nitrogen between molten steel and slag.

JP-A-4-110413 JP-A-60-56011 JP 2010-196114 A

CAMP-ISIJ Vol.13(2000)-966 H.ONO-NAKAZATO et.al.ISIJ International, Vol.40(2000), Supplement, pp.S106-S109 H.ONO-NAKAZATO et al. ISIJ International, Vol.42(2002), No.1, pp.109-111 E. MARTINEZ et. al. Metallurgical Transactions B Vol.21B, February 1990 pp.97103

As described in Patent Document 1, a low-melting flux is added to coat the surface of molten steel during tapping in a molten state, thereby preventing absorption of nitrogen during tapping to some extent. Moreover, Patent Document 1 is intended for steels that undergo Si deoxidation, and is not intended for high-Al content steels having a high Al content. On the other hand, the present invention further enhances the effect of suppressing nitrogen absorption at the time of tapping when melting high Al content steel with a high Al content, and melts high Al content steel with a low nitrogen content in the steel. The purpose is to provide a method.

In the present invention, when tapping molten steel from a refining furnace to a ladle, a slag phase (CaO—SiO ₂ flux) with a high nitrogen absorption capacity is interposed between the high Al content molten steel and the gas phase (≒ atmosphere). , gas phase/slag phase interface≧slag phase>slag phase/molten steel interface as oxygen potential, nitrogen moves from molten steel to slag phase, and nitrogen absorption is suppressed in molten steel. At that time, the dissolved Al in the molten steel is oxidized and transferred to the slag as Al ₂ O ₃ , and the SiO ₂ in the slag phase is reduced and transferred to the molten steel as dissolved Si in the molten steel. decreases and the amount of Si increases. The amount of Si and the amount of Al are determined in consideration of the component change due to this oxidation-reduction.

That is, the gist of the present invention is as follows.
[1] A steel with a target composition containing 0.05% or more and 5% or less of Al and 0.1% or more and 7% or less of Si in mass% is smelted in a refining furnace so that the Si content is low relative to the target composition, Molten steel with a high Al content is melted ,
When tapping into the ladle, flux is added into the ladle. The timing of adding the flux in the ladle is before or during tapping.
20%≦CaO≦45%,
40%≦SiO ₂ ≦70%,
0≦Al ₂ O ₃ ≦20%,
0≦MgO≦20%,
total less than 10% of other oxide and fluoride components ;
The mass ratio of CaO/SiO ₂ in the added flux is
0.4≦CaO/SiO ₂ <0.7
A method for melting high Al content steel , characterized in that
[2] The smelting method for high Al content steel according to [1], characterized by predicting an increase in Si concentration and a decrease in Al concentration during tapping .
[3] The method for melting high Al content steel according to [1] or [2], wherein the total amount of added flux is 2 kg or more and 30 kg or less per 1 ton of molten steel.

The present invention relates to a method for smelting high-Al-containing steel in which the composition is aimed at containing 0.05% or more Al and 0.1% or more Si in terms of mass %. By adding a flux having a predetermined compounding composition to the ladle before or during tapping, the effect of preventing nitrogen absorption can be obtained. A method of melting containing steel can be provided.

Hereinafter, % indicates mass % and ppm indicates mass ppm.
As described above, according to Non-Patent Documents 1 to 3, when CaO—Al ₂ O ₃ system slag is formed on the surface of molten steel and Al is added as a reducing agent, nitrogen in the molten steel corresponding to the concentration of added Al is reduced. A decrease in concentration is seen. Therefore, when the molten steel melted in the high-frequency induction melting furnace is tapped into a ladle, CaO--Al ₂ O ₃ -based flux is put into the ladle to form slag on the surface of the molten steel in the ladle, and as a reducing agent When Al was added to the molten steel, it was not possible to obtain a sufficient suppressing effect on the nitrogen concentration increase in the molten steel during tapping.

On the other hand, according to Non-Patent Document 4, in the interaction between molten silicate slag and the nitrogen content in the gas phase, the higher the SiO ₂ concentration in the slag or the higher the nitrogen partial pressure in the gas phase, the more %N ^3- of . However, only the solubility of nitrogen in slag (nitride capacity) is evaluated, and the movement behavior of nitrogen from molten steel to the gas phase between gas-slag-metal phases is not evaluated. .

Therefore, in an atmospheric atmosphere, the slag formed on the surface of the molten steel in the ladle was changed from the CaO-Al ₂ O ₃ system of Non-Patent Documents 1 to 3 to a CaO-SiO ₂ system with a high oxygen potential, and the molten steel Al is contained at a high concentration in the molten steel to act as a reducing agent for nitrogen, and the oxygen potential on the molten steel side is lowered to create an oxygen potential difference at the interface of slag phase > slag phase/molten steel, thereby allowing molten steel to become slag. I came up with the idea that nitrogen could move more efficiently.

<<Behavior of concentration change of Al and Si in molten steel>>
Since the CaO—SiO ₂ -based flux has a high oxygen potential, the Al in the molten steel acts as a reducing agent, reducing the SiO ₂ in the flux and dissolving it into the molten steel as dissolved Si, while simultaneously oxidizing the dissolved Al in the molten steel. migrates as Al ₂ O ₃ into the molten flux. As a result, the Si concentration in molten steel increases and the Al concentration decreases.

Therefore, first, when tapping molten steel melted in a high-frequency induction melting furnace into a ladle, flux is put into the ladle to form molten slag on the surface of the molten steel in the ladle, and the slag formed on the surface of the molten steel is replaced by CaO. - SiO ₂ system, when molten steel is tapped after containing a high concentration of Al, at what rate does the reaction of oxidizing Al in the steel and reducing SiO ₂ in the slag proceed? In order to ascertain by experiment whether or not this is possible, it was decided to investigate changes in the concentration of Si and Al when CaO-- _SiO.sub.2 system flux coexists.

When tapping 1 ton of molten steel with an initial concentration of 0.01% C-3.0% Si-0.3% Mn-0.5% Al into a ladle, 15 kg of flux having the same composition as F7 shown in Table 2 below was put into the ladle in advance. Molten steel samples were taken in a high-frequency induction melting furnace before tapping and in a ladle after tapping, and analyzed for Si content and Al content.
Concentration changes are indicated by ΔSi and ΔAl (mass %).
ΔSi = (Si concentration after tapping) - (Si concentration before tapping) = +0.05%
ΔAl = (Al concentration after tapping) - (Al concentration before tapping) = -0.12%

Such changes in molten steel composition are due to oxidation-reduction reactions between molten steel, slag (molten flux), and the atmosphere, and are represented by the following chemical formula. [ ] means molten steel composition and ( ) means slag composition.
(SiO ₂ )=[Si]+2[O] (1)
₂ [Al]+3[O]=( _Al2O3 ) (2)
O ₂ (gas)=2[O] (3)
Equation (1) shows a reaction in which SiO ₂ in slag is reduced and Si in molten steel increases as dissolved Si. Equation (2) shows the reaction in which Al in molten steel is oxidized and absorbed into slag as Al ₂ O ₃ . In addition, equation (3) shows a reaction in which oxygen gas mixed from the atmosphere is absorbed by molten steel, and O on the right side of equation (3) is consumed as part of O on the left side of equation (2). From the balance of ΔSi and ΔAl measured above, it is confirmed that the reaction of formula (2) proceeds by the sum of the supply of [O] according to formula (1) and the supply of [O] according to formula (3). Recognize.

《Influence of flux composition》
Based on the above results, when tapping from the high-frequency induction melting furnace to the ladle, a CaO—SiO ₂ based flux was added to the ladle to make the molten steel contain Al at a high concentration before tapping. The behavior of the decrease in the Al concentration in the molten steel and the increase in the Si concentration was clarified. Next, an experiment was conducted to investigate the effect of flux on preventing nitrogen absorption in molten steel when the steel is tapped after adding flux to the ladle before tapping.

Using a high-frequency induction melting furnace, 1 ton of steel having the composition shown in Table 1 was melted. Electrolyzed iron with a nitrogen content of less than 10 ppm was used as an ultra-low nitrogen raw material for the experiment without depressurization means. In addition, in order to suppress nitrogen absorption from the molten steel surface during melting, Ar gas is flowed from above the furnace at a flow rate of 10 NL / min, and a small amount of cover slag 1 kg (composition is 50 mass % CaO, 50 mass % Al ₂ O ₃ ) was floated on the surface of the water. After adjusting the molten steel composition, the temperature was adjusted to 1650 ° C., a molten steel sample was taken from the furnace, 8 kg of the prescribed flux (Table 2) was added to the bottom of the ladle, and the furnace was tilted to discharge it into the ladle. steeled. At this time, the behavior of nitrogen in molten steel was evaluated. No flux was used for F14 in the table.

Molten steel samples were taken before and after tapping, and the nitrogen concentration and the Al and Si concentrations were investigated. Table 2 shows the nitrogen concentration before and after tapping and ΔN (ppm) in the following formula. The change in nitrogen concentration during tapping is 10 to 36 ppm, as indicated by ΔN (ppm) in Table 2.
△N = (nitrogen concentration after tapping) - (nitrogen concentration before tapping)
The Al content after tapping varied depending on the flux composition and was in the range of 0.35% to 0.47%. The Si content after tapping was also increased by about 0.05% compared to before tapping.

The nitrogen concentration change during tapping of F14 without using flux is +36 ppm.
In F1 to F10, the nitrogen concentration change ΔN during tapping was +10 to +18 ppm, and nitrogen pickup was further suppressed compared to F11 to F13. The difference between F1 to F10 and F11 to F13 was thought to be due to the difference in the inhibitory effect on nitrogen absorption depending on the flux composition. That is, F11 to F13 simply acted as cover slag to suppress the contact between the molten steel and the ambient gas, while F1 to F10 presumed that, in addition to the action of the cover slag, the action of suppressing nitrogen absorption worked.

As a result of the above experiments, when high Al steel is tapped from a refining furnace to a ladle, nitrogen absorption of molten steel is suppressed by forming slag with a predetermined slag composition in the ladle. It was found that the behavior of nitrogen absorption suppression was affected. It was also confirmed that the nitrogen content of molten steel can be effectively reduced by setting the flux composition to the following composition. Here, the flux means an additive mainly composed of an oxide containing a predetermined component, and the molten state of the flux added to the surface of the molten steel is called slag.
The composition of the ladle additive flux is 20% ≤ CaO ≤ 45% by mass%,
40%≦SiO ₂ ≦70%,
0≦Al ₂ O ₃ ≦20%
0≦MgO≦20%
Total less than 10% of other oxide or fluoride components. It may contain no other oxide or fluoride components. In Table 2, numerical values outside the flux composition range are underlined.

The main component of ladle additive flux is CaO--SiO ₂ system (CaO+SiO ₂ : 60-100%). With this flux composition, the equilibrium oxygen [%O] in the steel is about 40 to 110 ppm when equilibrated with the molten steel, and even if Al ₂ O ₃ is included at a maximum of 20%, the effect is small. Moreover, even if Al ₂ O ₃ or MgO alone is contained by a maximum of 20%, the melting point of the flux is 1500° C. or less, and there is no problem in the meltability on molten steel.

If CaO is less than 20%, the melting point becomes high and the sealing effect on the molten steel surface is impaired. If the CaO content exceeds 45%, the nitrogen absorption capacity decreases. Therefore, the content of CaO in the flux was set within the above range. A more preferable range for enhancing the nitrogen absorption suppressing action is 25%≦CaO≦40%.

If the SiO ₂ content is less than 40%, the nitrogen absorption capacity is lowered. If the SiO ₂ content exceeds 70%, the melting point becomes high and the sealing effect on the molten steel surface is impaired. Therefore, the SiO ₂ content of the flux was set within the above range. A more preferable range for enhancing the nitrogen absorption suppressing action is 45%≦SiO ₂ ≦65%.

If the Al ₂ O ₃ content exceeds 20%, the oxygen potential is lowered and the nitrogen absorption suppressing action is impaired. Therefore, the content of Al ₂ O ₃ in the flux was set within the above range. Although Al ₂ O ₃ may not be added as an initial flux component, part of the Al in the molten steel is oxidized during melting and is absorbed by the molten flux as Al ₂ O ₃ to inevitably increase.

MgO lowers the melting point of flux and enhances the sealing effect on the molten steel surface. When MgO exceeds 20%, the effect of lowering the melting point saturates and solid phase MgO is formed. MgO may not be contained. Therefore, the content of MgO in the flux is set within the above range.

Other oxide or fluoride components (BaO, _Na2O , CaF2 _, etc.) lower the melting point of the flux and enhance the sealing effect on the surface of the molten steel. If the total content of other components is 10% or more, the nitrogen absorption inhibitory action of the flux is reduced. Therefore, the blending of the other oxide or fluoride components of the flux is set within the above range. It should be noted that other oxide or fluoride components may not be contained.

From the results shown in Table 2, it was found that the following ranges are suitable for the compounding ratio CaO/SiO ₂ (mass ratio) of CaO and SiO ₂ , which is an index of the basicity of the flux.
0.4≦CaO/SiO ₂ <0.7
When CaO/SiO ₂ is less than 0.4 or greater than 0.7, the nitrogen absorption suppressing action tends to decrease.

《Influence of Molten Steel Components》
In the present invention, CaO—SiO ₂ -based slag is formed with molten steel with a high Al content, Al in the molten steel is oxidized and SiO ₂ in the slag is reduced, thereby reducing the nitrogen absorption of the molten steel at the time of tapping. do. A target composition is determined for the molten steel to be melted, and a target Al content is also determined for each product type. Here, an evaluation was made as to how the target Al content affects the nitrogen absorption reduction behavior of the present invention.

When smelting high Al content steel aiming at the composition shown in Table 3, 1 ton of steel was melted using a high-frequency induction melting furnace. Ar gas is flowed from above the furnace at a flow rate of 10 NL / min, and a small amount of 1 kg of cover slag (composition: 50% by mass CaO, 50% by mass Al ₂ O ₃ ) is placed on the surface of the melt so that the surface of the melt does not come into direct contact with the atmosphere gas. floated on After adjusting the components of the molten steel and adjusting the temperature to 1650° C., a molten steel sample was taken from the furnace. Regarding the components in the molten steel before tapping, the Al content was higher than the target composition in Table 3 by about 0.12%, and the Si content was lower than the target composition in Table 3 by about 0.05%. Regarding the addition of Al to the molten steel, S7 to S9 in Table 3 are all added to the molten steel in the refining furnace (high-frequency melting furnace), and for S1 to S6 and S10 to S12, Al is added to the ladle before tapping. Al was added to the molten steel in the ladle during tapping.
After adding 8 kg of flux having the composition of F7 in Table 2 to the bottom of the ladle, the furnace was tilted and tapped into the ladle.

As a result of analyzing the nitrogen concentration of molten steel samples before and after tapping, the change in nitrogen concentration during tapping is 11 to 23 ppm, as indicated by ΔN (ppm) in Table 3.

In S1 to S10, the nitrogen concentration change ΔN at the time of tapping was 16 ppm or less, and a remarkable nitrogen absorption suppression effect was confirmed. As for the contents of Si and Al in the molten steel, as shown in Table 3, "Components of molten steel in the ladle", melting with the target composition was achieved. The target Al content of S1 was 0.05%, which was relatively low, but the target Al content could be adjusted by adding in advance to the ladle the amount of Al corresponding to the decrease in the Al concentration at the time of tapping. .

For S11, the target Al content was as low as 0.03%, and the nitrogen concentration change during tapping reached 23 ppm even though the amount of Al corresponding to the decrease in Al concentration during tapping was added in advance to the ladle. It is presumed that the Al in the molten steel was consumed by the reaction with the oxygen gas mixed in from the atmosphere during tapping, and the tapped stream with a reduced Al concentration was exposed to the atmosphere gas, thereby impairing the nitrogen absorption suppressing action.
Although S12 was found to have an effect of suppressing nitrogen absorption during tapping, the Si content increased during tapping, so the actual Si content was 0.10%, which was excessive compared to the target Si content of 0.05%. rice field.

If the targeted Al content is less than 0.05%, the nitrogen absorption inhibitory action of the flux is significantly impaired. When Al is less than 0.05%, the oxygen potential in the molten steel rises, the oxygen potential difference at the molten flux (slag)/metal interface becomes small, and Al oxidation in the molten steel and _SiO2 reduction in the flux are sufficient. This is because nitrogen absorption by the flux does not proceed.
If the target Si content is less than 0.1%, there is a risk that the Si content in the molten steel will not increase due to the reaction between the flux and the molten steel, resulting in an out-of-composition (there is no particular upper limit).

Based on the above results, in the present invention, the target Al content of the molten steel to be produced is limited to 0.05% by mass or more and the Si content is limited to 0.1% by mass or more. Although there is no particular upper limit for the Al and Si contents, the present invention can be suitably used as long as the Al: 5% by mass and the Si: 7% by mass can be used to suppress nitrogen absorption during tapping. .

With respect to steel components other than Al and Si, the content of Mn and Cr is preferably low in order to increase the ability of molten steel to absorb nitrogen when added. If the Mn or Cr content exceeds 1.5%, the nitrogen absorption inhibitory action of the flux is significantly impaired. Mn and Cr do not have to be contained.

Therefore, the preferred chemical composition of the steel that is the object of the present invention is as follows.
Al≧0.05%
Si≧0.1%
More preferably Mn≤1.5%
Cr≦1.0%
In addition, low alloying level alloying elements may be used. In addition, other components are, for example, C: 0.001 to 1.0% (very low carbon to high carbon), P: 0.01 to 0.20%, S: 0.0005 to 0.01%. can be selected.

<<Molten steel components before treatment>>
As described above, when the flux having the composition of the present invention is added to the refining furnace to produce high Al content steel, the Al concentration in the molten steel decreases and the Si concentration increases. Therefore, depending on the refining furnace and ladle, capacity (steel amount), flux composition and amount added, etc., from the average value of the evaluation results of about 5 heats in advance, the amount of Al decrease and the amount of Si increase in the steel during processing is predicted, and it is preferable to melt using molten steel having initial components with a low Si content and a high Al content with respect to the target composition.
As for the timing of adding Al to the molten steel, Al may be added to the molten steel in the refining furnace before tapping, or part or all of the added amount of Al may be added to the molten steel after tapping. good. Regarding the addition of Al to the molten steel after tapping, it should be added at least until "1/10 of the time required for tapping" so that the Al content in the molten steel when it comes into contact with the flux is 0.05% or more. is preferable, and it is more preferable to put it in the ladle (before tapping).

《Addition of Flux》
As for the flux, it is desirable to use as an additive the flux raw material that has been mixed in advance at a predetermined compounding ratio, which is melted by heating at 1500° C., cooled and pulverized into powder or granules. Without performing such pre-melting, flux raw materials such as quicklime and silica sand are directly added to the ladle before tapping and/or the molten steel in the ladle during tapping (including the tapped stream). good too. This is because the radiant heat of the molten steel reacts the flux material to form molten flux.

By covering the molten steel surface, the flux has the effect of blocking the molten steel from the atmosphere gas, suppressing the absorption of oxygen and nitrogen from the atmosphere, and absorbing the nitrogen contained in the high Al content molten steel.

Flux is added to the ladle before tapping and/or the molten steel in the ladle during tapping (including the tapping stream). In particular, it is desirable to preliminarily add Ni to the ladle before tapping, when the molten steel and the air come into direct contact with each other. The reason why it is desirable to add it to the ladle in advance is that the molten steel and flux are strongly stirred from the initial stage when the tapped stream is poured into the ladle, and the nitrogen absorption effect of the flux is effective. It is for the sake of becoming.
When flux is added during tapping, it may be added all at once or intermittently/continuously. It is preferable that the time from the start of tapping to the end of flux addition be within 1/3 of the total tapping time from the start of tapping to the end of tapping. As a result, the nitrogen absorption suppressing action of the flux during tapping can be sufficiently exhibited.

If the refining furnace is an air melting furnace, in order to further suppress nitrogen absorption, flux is added to the molten steel in the refining furnace to form a slag layer on the surface of the molten steel in advance, and then remove it before tapping. Add some flux to the pot. Since the contact between the molten steel and the atmosphere gas can be continuously suppressed from the previous stage of tapping to the injection stage of the tapping stream, a remarkable nitrogen reduction effect can be obtained. In addition to adding flux into the refining furnace, adding flux directly to the injection stream during tapping provides a more effective suppression of nitrogen absorption.

The amount of flux to be added is preferably 2 kg or more and 30 kg or less per ton of molten steel. If it is less than 2 kg/ton, the effect of suppressing nitrogen absorption due to the contact of the molten flux with the molten steel flow at the time of tapping and the effect of covering the surface of the molten steel are reduced. Even if it exceeds 30 kg/ton, the effect of suppressing nitrogen absorption is saturated. Moreover, excessive addition tends to cause a temperature drop of molten steel due to heat transfer to the flux.

《Smelting Furnace》
As a refining furnace to which the high Al content steel smelting method of the present invention is applied, a converter and a high frequency induction melting furnace can be suitably used. When the refining furnace is a converter, it is possible to tap molten steel with a low nitrogen content. can get.

<<Example of the present invention>>
10 tons of raw material to be melted consisting of steel scrap and ferroalloy was charged into a high-frequency induction melting furnace, Ar gas was supplied to the furnace at a rate of 10 L/min, and the raw material was melted by induction heating. After melting, composition adjustment by alloy addition was performed by rapid analysis of molten steel. At that time, the target composition shown in Table 4 was adjusted to a lower Si content of 2.95% and a higher Al content of 0.45%, taking into account composition changes during tapping.

After adding 100 kg of flux consisting of CaO: 30%, SiO ₂ : 60%, Al ₂ O ₃ : 5%, and MgO: 5% in the ladle, the steel is tapped, the steel is received in the ladle, and the steel is placed in the ladle. Samples were taken from the molten steel and sampled for analysis. As a result, the nitrogen in the molten steel was 48 ppm, and compared with the nitrogen in the molten steel of 36 ppm before tapping, the nitrogen pick-up remained at 12 ppm, and the absorption of nitrogen by the flux was recognized. In addition, the target composition of Si in Table 4 within ±0.1% and the target composition of Al in Table 4 within ±0.05% were obtained, and the composition hit the target.

<<Comparative example>>
Under the same conditions as above, a flux consisting of CaO: 50%, SiO ₂ : 10%, Al ₂ O ₃ : 35%, and MgO: 5% is added into the ladle, then tapped and placed in the ladle. When steeled, nitrogen pick-up at tapping was greater than 21 ppm.

Under the same conditions as above, when no flux was used, the nitrogen pickup during tapping was 28 ppm or more.

Claims (3)

Steel with a target composition of 0.05% or more and 5% or less of Al and 0.1% or more and 7% or less of Si in terms of mass% is smelted in a refining furnace with a low Si content and a high Al content relative to the target composition. Molten steel with high composition ,
When tapping into the ladle, flux is added into the ladle. The timing of adding the flux in the ladle is before or during tapping.
20%≦CaO≦45%,
40%≦SiO ₂ ≦70%,
0≦Al ₂ O ₃ ≦20%,
0≦MgO≦20%,
total less than 10% of other oxide and fluoride components ;
The mass ratio of CaO/SiO ₂ in the added flux is
0.4≦CaO/SiO ₂ <0.7
A method for melting high Al content steel, characterized in that 2. The smelting method for high Al content steel according to claim 1, wherein an increase in Si concentration and a decrease in Al concentration during tapping are predicted. 3. The melting method of high Al content steel according to claim 1 or 2, wherein the total amount of added flux is 2 kg or more and 30 kg or less per 1 ton of molten steel.