JP3239691B2 - Arc furnace melting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an arc furnace melting method, and more particularly to a secondary combustion technique in an arc furnace for efficiently melting an iron raw material such as iron scrap.

[0002]

2. Description of the Related Art In an arc furnace melting method for manufacturing molten steel by melting iron raw materials such as iron scrap, pig iron, and DRI, it is a major problem to improve the production efficiency by shortening the melting time. In order to solve the above-mentioned problems, there are UHP operation in which the amount of input electric power per unit time is increased, use of an auxiliary burner, and oxygen-enrichment operation.

[0003] The oxygen enrichment operation is an operation in which oxygen gas is blown onto the molten metal surface in the furnace during the melting period and at the end of the melting period. At the same time, the carbonaceous raw material added and the carbon contained in the molten metal burn according to the following formula (3) (this is called primary combustion), and generate heat.

C + 1 / 2O ₂ → CO (3) Simultaneously, components in the molten metal, such as Fe, Si, and Mn, are also oxidized by oxygen gas, and the heat of the reaction is also added to promote the dissolution of scrap, thereby increasing production efficiency. Can be improved.

Further, as a technique for pursuing the dissolution of scrap, a technique has been proposed in which CO gas generated by the oxygen enrichment operation or the like is actively secondary burned in a furnace.

In the techniques described in JP-A-63-93815 and JP-A-5-98364, the gas is generated by supplying oxygen gas into a space inside an arc furnace and blowing a carbonaceous material into a molten metal. A method has been proposed in which CO gas to be subjected to secondary combustion is converted into CO ₂ by the following equation (4) (this is referred to as secondary combustion). CO + 1 / 2O ₂ → CO ₂ (4)

In the technique described in Japanese Patent Application Laid-Open No. 59-104419, oxygen gas is blown into a molten metal during a melting period and / or an oxidizing period to decarbonize the molten metal, and the carbon content is reduced to 0.1.
20% or less of the molten metal is obtained, and subsequently, the carbonaceous material is blown into the molten metal and / or into the slag bath together with the carrier gas to generate CO gas, and into the furnace space and / or the slag bath. In this method, a part of the amount of generated CO gas is secondarily burned into CO ₂ by blowing in oxygen gas for the next combustion.

[0008]

However, Japanese Patent Application Laid-Open No.
In the technology disclosed in Japanese Patent No. 93815 and Japanese Patent Laid-Open No. 5-98364, since the secondary combustion place is the space inside the furnace, the combustion heat generated by the reaction of the above formula (4) is sufficiently transmitted to the molten metal and the slag bath. It is not heated (this is called heating).
In these methods, heat is transferred to the water-cooled part of the furnace lid or the furnace wall, or is lost as sensible heat in the exhaust gas,
The combustion heat from the secondary combustion is not effectively used.

In addition, the secondary combustion oxygen gas introduced into the furnace space directly reacts with the graphite electrode, causing a problem that the electrode is oxidized and consumed.

In view of the high heat transfer efficiency to the molten metal by the heat of secondary combustion, a method of performing secondary combustion in a slag bath is preferable.
This technique is disclosed in Japanese Patent Application Laid-Open No. 59-104419, and numerous disclosures are also made in the smelting reduction process of iron. (For example, development of secondary combustion technology in a pressure converter type smelting reduction furnace; iron and steel 76 (1990), p. 1887) However, compared with the converter method which can easily secure a slag bath of 3 m or more. In addition, in the electric furnace method, the depth of the slag bath can be at most only about 50 to 100 cm from the furnace body structure, so that it is difficult to efficiently perform secondary combustion in the slag bath.

On the other hand, in the above prior art, a secondary combustion technique is applied in a scrap batch charging method. In this case, the amount of scrap dissolved in one heat is charged in two to four times. Therefore, the charging amount per operation is as large as several tens tons (usually 10 to 70 tons), and the conditions for secondary combustion in the slag bath, in other words, a smooth molten metal surface and a molten metal temperature capable of forming are obtained. It takes a long time to complete the process, during which time the secondary combustion technology cannot be applied. As a result,
The secondary combustion application time is short, and the expected effect of dissolving scrap is not obtained.

The present invention has been proposed in order to solve the above problems, and an arc which cannot secure a sufficient slag bath thickness when secondary iron is melted by secondary combustion in an arc furnace. It is an object of the present invention to provide a technique for efficiently performing secondary combustion in a furnace to promote a scrap melting rate.
Further, the present invention provides a technique capable of increasing the application time of the secondary combustion during one heat melting to substantially achieve the scrap melting acceleration effect.

[0013]

According to the present invention, a carbonaceous material and an oxygen gas for the primary combustion are blown into a molten metal to generate a CO gas to form a slag bath, while the oxygen gas for the secondary combustion is formed in the slag bath. In the arc furnace melting method in which CO gas is blown into the secondary combustion, the thickness of the slag bath is 5
The secondary combustion oxygen gas flow rate Q (Nm ³ / min) blown from each hole while maintaining the position of the discharge hole of the lance having at least one discharge hole at least 400 mm from the molten metal surface. And discharge angle θ (degree)
Is controlled so as to satisfy the following formulas (1) and (2), and the discharge port is immersed in the slag bath or placed above the slag bath, and oxygen gas for secondary combustion is supplied in the slag bath. Is an arc furnace melting method.

Q ≧ 7.5 (1) 10 ≦ θ ≦ 56−1.55 × Q (2) However, the discharge angle θ is The angle between the direction in which the secondary combustion oxygen gas is discharged and the surface of the molten metal is defined.

An arc furnace melting method in which an iron raw material is continuously charged into the furnace at this time and arc melting is performed.

[0016]

According to the present invention, a carbonaceous material (usually blown using a lance together with an inert gas such as Ar gas as a carrier gas; hereinafter referred to as a carbon material) and an oxygen gas for the primary combustion are blown. By immersing the lance in the molten metal or by disposing the lance on the molten metal surface and spraying the lance toward the molten metal surface, the carbon material and the oxygen gas for the primary combustion are blown into the molten metal.

At this time, the carbon contained in the carbon material and the molten metal and the oxygen gas for the primary combustion cause an exothermic reaction by the primary combustion according to the equation (3) in the molten metal to generate a CO gas. . This CO gas forms bubbles in the process of floating in the slag bath, stirs the slag bath, heats the slag bath, makes the slag bath temperature uniform, and promotes slagging, and forms the slag bath. .

At this time, by appropriately selecting the composition of the auxiliary raw materials, the amount of the auxiliary raw materials, the flow rate of the oxygen gas for the primary combustion, and the like, the slag bath thickness of 500 mm or more is secured in the present invention, and the oxygen for the secondary combustion is secured. In order to secure the position of the discharge hole of the lance at least 400 mm from the surface of the molten metal, a sufficient floating time of the CO gas floating in the slag bath is ensured.

In the present invention, the secondary combustion oxygen gas is immersed in the slag bath separately from the primary combustion oxygen gas while controlling the slag bath thickness and the discharge hole position within the aforementioned ranges. The secondary combustion oxygen gas is diffused over a wide area in the slag bath and blown up in the slag bath because the gas is blown or placed above the slag bath and blown into the slag bath to blow into the slag bath. Upon contact, a secondary combustion reaction occurs according to equation (4).

At this time, the air is blown in from each discharge hole.
Secondary combustion oxygen gas flow rate Q (Nm ^Three/ Min) and
The discharge angle θ (degree) is defined by the shaded area shown in FIG.
And control within a range satisfying the expressions (1) and (2).
Thereby, the secondary combustion efficiency is increased. The following describes this effect.
I will tell.

When the range regulated by the equation (1), that is, the oxygen gas flow rate Q is maintained at 7.5 Nm ³ / min or more, the kinetic energy of the discharged oxygen gas is large, and the kinetic energy of the discharged oxygen gas is wide in the slag bath. Diffuses and floats in the slag bath C
Secondary combustion occurs in contact with O gas. This combustion is an exothermic reaction, and as described above, a sufficient reaction time is secured in the slag bath, and the calorific value is directly transmitted to the molten metal via the slag bath, so that the dissolution of the scrap is promoted, Secondary combustion efficiency increases.

At less than 7.5 Nm ³ / min, the above-mentioned kinetic energy is insufficient, and the oxygen gas decelerates immediately and floats up and escapes from the slag bath surface into the furnace space. For this reason, it cannot come into contact with the CO gas in the slag bath over a wide range, and the secondary combustion efficiency is not improved.

The range restricted by the left side of equation (2), that is,
When the discharge angle θ is secured to 10 degrees or more, oxygen gas penetrates deeply into the slag bath, and C
Since it can come into contact with O gas, the secondary combustion efficiency increases.

However, if the discharge angle θ is less than 10 degrees, the penetration depth of the oxygen gas is shallow, and the oxygen gas immediately floats and escapes from the slag bath, so that the secondary combustion time is not secured and the secondary combustion efficiency is not improved. .

The range restricted by the right side of equation (2), that is,
In the range where the ejection angle θ is 56-1.55 × Q or less,
As the oxygen gas flow rate Q for the secondary combustion increases, the discharge angle θ
Decreases linearly. In other words, the kinetic energy increases with an increase in the oxygen gas flow rate Q, but the penetration depth becomes shallower with this, so that the oxygen gas does not pass through the slag bath and reach the molten metal. CO inside
Since the gas can be contacted over a wide range, the secondary combustion efficiency is increased.

However, if the discharge angle θ does not satisfy this range, oxygen gas penetrates the slag bath and reaches the molten metal, and directly reacts with the molten metal. As a result, the oxygen gas acts to oxidize carbon, Si, and Mn in the molten metal, and the secondary combustion efficiency is not improved.

When the thickness of the slag bath is 500 mm or less and the position of the discharge hole is 400 mm or less from the surface of the molten metal, the discharge angle and the oxygen gas flow rate for the secondary combustion are controlled within the range of equations (1) and (2). Even so, oxygen gas penetrates into the molten metal, and also in this case, carbon, Si,
It acts to oxidize with Mn and does not contribute to an increase in secondary combustion efficiency.

Furthermore, in the present invention, arc melting is performed while the iron raw material is continuously supplied into the furnace, so that the secondary combustion application time is increased.

Here, the meaning of the continuous charging means that the iron raw material is charged continuously at a constant supply rate without interruption, or when the interval between interruptions is short, for example, when a pusher is used. This includes the case of intermittent charging.

The supply rate of the iron raw material is represented by the sum of the arc power energy supplied per unit time and the heat energy given to the iron raw material by the secondary combustion.
The speed should be equal to or higher than the melting energy of the continuously supplied iron raw material.

For this reason, even if the iron raw material is supplied during the one-heat smelting, the molten metal temperature is constant and does not fluctuate, or at least does not decrease. And the forming thickness according to the present invention can be secured.

Further, since a large amount of unmelted scrap does not exist or accumulate in the furnace, the secondary combustion lance does not come into contact with them, and the discharge port height according to the present invention can be secured from the initial stage of melting. .

In particular, by leaving several tens of tons of molten metal in the furnace at the time of heat tapping, which is referred to as seed water, the secondary combustion conditions according to the present invention can be maintained over almost the entire melting period from the start of melting to tapping. , The application time for secondary combustion during one heat melting can be greatly increased, and the scrap melting speed can be further increased.

[0034]

【Example】

Confirmation test (1): Investigation of the effects of the discharge angle θ and the height of the secondary combustion lance FIG. 1 shows a secondary combustion test using a 120 ton capacity DC arc electric furnace to confirm the effect of the present invention. Shows the situation where

Here, 1 is an arc furnace body, 2 is a side wall, 3
Is a furnace lid, 4 is a graphite electrode, 5 is a furnace bottom electrode, 6 is a primary combustion oxygen lance, 7 is a carbon material injection lance, 8 is a secondary combustion oxygen lance, 9 is a furnace space, and 11 is molten metal. , 12 are slag baths.

Table 1 shows the results of the examination of the secondary combustion test conditions and the scrap dissolution rate in this test.

In this test, desulfurization scouring and component adjustment were not performed in the arc furnace, and after melting the scrap, the temperature of the molten metal was 155.
When the temperature reached 0 ° C., the melting was judged to be completed, and the steel was removed. Therefore, the time required from the start of melting to tapping to melt 120 tons of scrap charged in one heat (however,
The value obtained by dividing by the scrap dissolution rate (t)
on / min).

[0038]

[Table 1]

In this test, iron scrap 7 was used as the main raw material.
0 tons and 3 tons of auxiliary material mainly composed of limestone were initially charged, and melting was started at an arc voltage of 550 V and an arc current of 120 KA. Thereafter, 50 tons of iron scrap were additionally charged during melting.

As shown in FIG. 1, the side wall 2 of the arc furnace furnace body 1 extends from the start of melting to immediately before tapping for the entire melting period.
A lance 7 for injecting carbonaceous material and an oxygen lance 6 for primary combustion are inserted into the furnace from the working port provided in the furnace to the molten metal 11, and the carbonaceous material is injected with the carrier gas through the lance 7 for injecting carbonaceous material at 50 kg / min. Oxygen gas was blown from the next combustion oxygen lance 6 toward the molten metal 11 at a supply speed of 60 Nm ³ / min.

After the slag bath is formed due to the progress of slagging of the auxiliary raw material with the dissolution of the scrap, the carbon material blown from the lance 7 and the oxygen gas for the primary combustion blown from the lance 6 are: The slag bath was burned in the molten metal, and the slag bath was expanded and formed by the CO gas generated by the burning.

In about 40 minutes from the start of melting, a smooth molten metal 11
After the slag bath 12 is formed, two oxygen lances 8 for secondary combustion are introduced from the working port into the slag bath 12 (FIG. 1).
In this case, only one is shown), and the supply rate of oxygen gas is 30 Nm ³ / min (15 Nm ³ / mi per one)
In step n), the mixture was blown for about 15 minutes.

The thickness of the slag bath 12 during the injection of the oxygen gas for secondary combustion is maintained at about 800 mm, and the position of the discharge hole of the oxygen lance 8 is maintained at 600 mm from the surface of the molten metal.
The control was performed within a range of 30 mm.

The oxygen lance 8 is a single tube, and has one discharge hole with a diameter of 20 mm at the tip of the lance. Therefore, the flow rate of oxygen gas discharged from this discharge hole is calculated to be 796
m / sec (approximately twice the speed of sound), and the oxygen gas for secondary combustion is in a jetting state (this is called an oxygen gas jet, in which state it is difficult to decelerate), and extends over a wide range in the slag bath. Diffused and contacted with slag bath.

Example 1 is a case where the discharge angle θ of the oxygen gas for secondary combustion is set to 25 degrees in the downward direction with respect to the molten metal surface. Dissolution rate is 2.38 ton / m
High values of in were obtained.

On the other hand, in Comparative Examples 1 and 2, the discharge angle θ was 45 ° and 7 ° (set outside the range of the present invention), and the scrap dissolution rate was 2.09 and 2.08 ton / min, and a lower value than that of Example 1 was obtained. The reason is that in Comparative Example 1, the discharge angle θ is large, so that the oxygen gas jet penetrates deeply into the molten metal 11 and some oxygen gas is used for the secondary combustion shown in the equation (4). This is because a part of the oxygen gas was consumed to burn carbon, Fe, Si, Mn, etc. contained in the molten metal 11 and was not used for the secondary combustion, and did not work to promote the dissolution of scrap.

On the other hand, in Comparative Example 2, since the discharge angle θ was small, the depth of penetration was shallow, and most of the oxygen gas levitated without reacting and jumped out into the furnace space. This is because they did not burn and did not work to promote the dissolution of scrap.

In Comparative Example 3, the discharge angle θ was the same as in Example 1.
Is 25 degrees, but the secondary combustion is performed by controlling the position of the discharge hole of the lance 8 within a range of 250 ± 30 mm from the surface of the molten metal, and the scrap melting rate is 2.09 ton / min.
Low values were obtained. The reason is that the oxygen gas penetrates deeply into the molten metal 11 because the lance height from the molten metal surface is low, and most of the oxygen gas is consumed for secondary combustion as in the case of Comparative Example 1. And did not work to promote the dissolution of scrap.

In the conventional example to which the secondary combustion technique is not applied, the result is still lower than those of the comparative examples.
min.

Confirmation test (2): Investigation of the influence of the flow rate Q of oxygen gas for secondary combustion per hole FIG. 3 shows the results obtained by using a porous lance having two or three discharge holes per lance. This shows the situation where the next combustion test is being performed.

The discharge hole diameter of the lance 8 used in this test was:
The holes were all 20 mm, and were drilled on the same circumference every 180 degrees with a two-hole lance and every 120 degrees with a three-hole lance. Also,
When the lance 8 was arranged in a direction perpendicular to the surface of the molten metal, the discharge holes were drilled so that the discharge angle θ was 25 degrees in the downward direction.

Then, a through hole is provided in the furnace lid 3 and the lance 8
Was immersed into the slag bath 12 from above the furnace lid 3 through this through hole. Other test conditions are the same as in the confirmation test (1), and are shown in Table 1.

In the second embodiment, the secondary combustion oxygen gas flow rate 30
Nm ³ / min is blown in using one two-hole lance,
The oxygen gas flow rate per hole was 15 Nm ³ /
min, and a scrap dissolution rate of 2.37 ton / min equivalent to that of Example 1 was obtained.

As a result, it was confirmed that if the discharge angle θ and the oxygen gas flow rate per hole were the same, the same secondary combustion efficiency could be obtained regardless of the structure and shape of the discharge hole of the lance 8. .

In Example 3, two two-hole lances were used, and
The oxygen gas flow rate per hole is 7.5 Nm ^Three/ Min (Example
2, but the oxygen gas flow rate is 398 m / sec.
Exceeds the speed of sound). As a result,
Secondary combustion efficiency equivalent to 2 is obtained, and scrap dissolution rate
Obtained 2.36 ton / min.

In Comparative Example 4, two three-hole lances were used.
The oxygen gas flow rate Q for secondary combustion per hole is 5.0 Nm ³ / m
In (in the case of 1/3 of the second embodiment, the oxygen gas flow rate is 265 m / sec, which is lower than the sound velocity).
As a result, the scrap dissolution rate was 2.10 ton / mi.
Low values were obtained with n. The reason is 5.0 Nm ³ / min.
In this case, since the velocity is lower than the sound speed, an oxygen gas jet is not formed, and the oxygen gas jet does not diffuse over a wide range, so that sufficient secondary combustion efficiency cannot be secured.

Confirmation test (3): Investigation of the influence of the forming slag thickness In this test, the forming slag thickness was changed to the secondary combustion efficiency,
In other words, the effect on the scrap dissolution rate was investigated.

In Example 4, as shown in Table 1, the forming slag bath thickness was 800 mm, and the oxygen lance 8 for the secondary combustion was used.
The discharge port position is 550 mm from the surface of the molten metal, using two single tube lances, the discharge angle θ is 20 degrees, and the oxygen gas flow rate is 40 N.
m ³ / min, the flow rate of oxygen gas per hole is 20 Nm ³ / min.
min (oxygen gas flow rate is 1061 m / sec, about three times the speed of sound). As a result, a scrap dissolution rate equivalent to that of Examples 1 to 3 was 2.41 ton / mi.
n was obtained.

In Comparative Example 5, the thickness of the slag bath was adjusted to 300 mm by adjusting the amount of the auxiliary material charged, and the other test conditions were the same as in Example 4. As a result, the scrap dissolution rate was a low value of 2.10 ton / min. The reason for this is
This is because the secondary combustion time in the slag bath was not secured because the slag bath thickness was as thin as 300 mm, and the secondary combustion efficiency was reduced.

Confirmation test (4): Effect of combination with continuous scrap supply method In this test, the continuous scrap supply method was adopted instead of the batch charging method from confirmation test (1) to confirmation test (3).
By combining this with the secondary combustion technique according to the present invention, the effect on the dissolution accelerating effect of scrap was investigated.

FIG. 4 shows a continuous scrap supplying facility 13 penetrating the side wall 2 of the 120 ton DC arc electric furnace.
A situation in which the scrap conveyor 15 is continuously charged into the arc furnace main body 1 by driving the transport conveyor 14 to melt the arc, and secondary burning in the furnace to promote the melting of the scrap is shown.

The scrap melting rate in the continuous scrap supply method is determined by measuring the temperature of the molten metal during the supply of the scrap when the arc power (in this test, the arc voltage is 550 V and the arc current is 120 KA) and the secondary combustion is performed. Does not decrease, and the scrap supply speed does not cause residual melting,
In other words, the scrap supply speed is defined as a balance between the power supply amount and the total amount of heat energy provided by the secondary combustion.

In the fifth embodiment, at the time of tapping of the pre-charge, 30 tons of molten steel is left in the furnace, and the scrap of the next charge is supplied from the start of melting to tapping at a constant supply rate of 2.9 tons per minute. A total of 90 tons was fed for 31 minutes.

Simultaneously with the start of the supply of the scrap, 3 tons of auxiliary material mainly composed of limestone was charged by driving the conveyor 14 and melting was started under the above-mentioned arc melting conditions. The secondary combustion was performed under the same conditions as in Example 3 over the entire melting period from the start of melting to tapping.

As a result, the scrap dissolution rate was 2.90.
A high value of ton / min was obtained. This value is about 23% higher than that of Example 3 in which the batch charging method and the secondary combustion technique are combined, and is a dissolution promoting effect due to an increase in the secondary combustion application time ratio.

Comparative Example 6 was a case where only the scrap continuous supply method was employed and the secondary combustion technique was not applied, and the scrap dissolution rate was 2.31 ton / min.

In the present invention, when the secondary combustion oxygen gas flow rate Q is large, the use of a porous lance having two or more holes allows a large flow rate to be supplied with a small number of lances, so that the lance operation can be simplified.

According to the present invention, since the secondary combustion efficiency is increased, the amount of oxygen gas for secondary combustion discharged into the furnace space is also reduced, so that the amount of electrode oxidation can be reduced.

[0069]

According to the present invention, by controlling the thickness of the slag bath, the discharge position of the oxygen gas for secondary combustion, the flow rate of oxygen gas per hole and the discharge angle thereof within an appropriate range, the inside of the slag bath is controlled. Secondary combustion can be performed efficiently,
The scrap melting speed in the arc furnace can be greatly increased. Furthermore, by combining the secondary combustion technology according to the present invention with the continuous scrap supply method, the secondary combustion application time ratio can be greatly increased, and the scrap dissolution rate can be promoted.

[Brief description of the drawings]

FIG. 1 is a diagram showing an implementation state of a secondary combustion test in a confirmation test (1).

FIG. 2 is a diagram showing a range of the present invention in which a secondary combustion oxygen gas flow rate Q and a discharge angle θ satisfy Expressions (1) and (2).

FIG. 3 is a diagram showing an implementation state of a secondary combustion test in a confirmation test (2).

FIG. 4 is a diagram showing an implementation state of a secondary combustion test in a confirmation test (4).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Arc furnace furnace body 2 Side wall 3 Furnace lid 4 Graphite electrode 6 Primary combustion oxygen lance 7 Carbon material injection lance 8 Secondary combustion oxygen lance 9 Furnace space 11 Melt 12 Slag bath

Continuation of the front page (72) Inventor Shunichi Sugiyama 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Hiroshi Kubo 1-1-2, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Takahiro Hosokawa 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Michio Nakayama 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (58) Field surveyed (Int. Cl. ⁷ , DB name) C21C 5/52 F27D 3/16 F27D 3/18

Claims (2)

(57) [Claims] 1. A secondary combustion oxygen gas is blown into a slag bath while a carbonaceous material and a primary combustion oxygen gas are blown into a molten metal to generate a CO gas and form a slag bath. In the arc furnace melting method for the next combustion, the thickness of the slag bath is 500 mm or more,
While maintaining the position of the discharge hole of the lance having at least one discharge hole at 400 mm or more from the molten metal surface, the secondary combustion oxygen gas flow rate Q (Nm ³
/ Min) and the discharge angle θ (degree) are controlled so as to satisfy the following expressions (1) and (2), and the discharge holes are immersed in the slag bath or arranged above the slag bath, An arc furnace melting method comprising supplying oxygen gas for secondary combustion into a slag bath. Q ≧ 7.5 (1) 10 ≦ θ ≦ 56−1.55 × Q (2) However, the discharge angle θ is secondary combustion. The angle between the direction in which the service oxygen gas is discharged and the surface of the molten metal. 2. The arc furnace melting method according to claim 1, wherein the arc melting is performed while continuously charging the iron raw material into the furnace.