JP2023004698A - Electric furnace and electric furnace steel making method - Google Patents

Abstract

To provide an electric furnace and an electric furnace steel making method capable of improving a carburization speed while using an inexpensive carbonaceous material and realizing carburization to molten iron without elongating a cycle time.SOLUTION: An electric furnace 1 has a graphite electrode 2 and a carbonaceous material addition device 3. Regarding an intersection point (electrode center point 22) between a vertical line passing through a figure center of gravity of an electrode lower end viewed from below in a vertical direction and a molten iron stationary face, and an arrival position (carbonaceous material arrival point 23) from the carbonaceous material addition device 3 to the molten iron stationary face of a carbonaceous material, a position and an angle of the carbonaceous material addition device are set so that a distance between the carbonaceous material arrival point 23 and the electrode center point 22 falls within a range within an electrode radius r, and further, even when the electric furnace has an oxygen lance 8 feeding oxygen into the furnace, an oxygen arrival point 24 of the oxygen lance 8 is not positioned at a position within the double of the electrode radius r from the electrode center position 22.SELECTED DRAWING: Figure 1

Description

The present invention relates to an electric furnace and an electric furnace steelmaking method.

In the electric furnace steelmaking method using an electric furnace, it is necessary to melt the raw material, and to supply a carbon source to the molten iron for degassing and reduction treatment. In particular, when producing low-nitrogen high-grade steel, it is necessary to maintain a high carbon concentration in the molten iron during electric furnace tapping by carburizing in order to promote denitrification by decarburization in the post-process.

As a carbon source for carburizing molten iron, carbon materials such as coke and graphite as in Patent Document 1, high carbon alloys such as ferrochromium, ferromanganese, and pig iron as in Patent Document 2, and further as in Patent Document 3 It is known that recarburizers containing these are used. Patent Document 1 discloses a method of ejecting powdered coke that has been pressure-fed together with oxygen and compressed air from a nozzle at the tip of a stabilizing burner, and using unburned powdered coke as a recarburizing agent for molten steel and a reducing agent for oxides. is described. Patent Document 2 describes a molten steel smelting method in which a carbon-containing substance is added to the molten steel to adjust the carbon concentration of the molten steel within the composition range after reducing the carbon concentration in the molten steel with a vacuum degassing facility. It is Patent Document 3 describes an electric furnace refining method in which a recarburizing material having an apparent density higher than the calculated density of slag in electric furnace refining is added to molten iron.

In the present invention, the rate of increase of the carbon concentration in the molten iron after the carbonaceous material is added to the molten iron during electric furnace refining is called "carburization rate".

When a normal carbonaceous material such as coke is used as a carbon source, which is a carbonaceous material added to molten iron, the carburization rate is low, which leads to an extension of cycle time and a decrease in productivity. Also, the high carbon alloy is expensive, which leads to an increase in cost.

Conventionally, as a method of supplying a carbon material for recarburizing by charging the carbon material onto the surface of the molten material of an electric furnace, for example, a charging chute or a carbon material using a lance as described in Patent Document 4 has been used. is known. In Patent Document 4, the direction of addition of the carbonaceous material is the direction away from the arc heating region.

JP-A-60-174813 Japanese Patent Application Laid-Open No. 2003-27128 JP 2017-186607 A JP 2020-94247 A

Since the carburizing rate is determined by the type of carbonaceous material and the temperature of the molten steel in any of the above conventional charging methods, in order to improve the carburizing rate and shorten the cycle time when inexpensive carbonaceous materials are used, The current situation is that this has not yet been achieved.

An object of the present invention is to provide an electric furnace and an electric furnace steelmaking method that can improve the rate of carburization while using inexpensive carbonaceous materials and realize carburization of molten iron without extending the cycle time. aim.

That is, the gist of the present invention is as follows.
[1] In an electric furnace using a graphite electrode, the intersection of a vertical line passing through the center of gravity of the lower end of the graphite electrode viewed vertically from below and the stationary surface of the molten iron is called an "electrode center point". An addition device is provided, and the position at which the carbon material from the carbon material addition device reaches the molten iron stationary surface is called a "carbon material arrival point", and the distance between the carbon material arrival point and the electrode center point is within the electrode radius. The position and angle of the carbon material addition device are set so that the range of The electric furnace characterized in that the axial center of the oxygen lance is not directed to a position within the range.
[2] The electric furnace according to [1], wherein the carbon material addition device is a blowing lance or an injection chute.
[3] The electric furnace according to [1] or [2], wherein the carbon material addition device is capable of changing the addition direction of the carbon material.
[4] The graphite electrode is a hollow electrode, and the carbonaceous material is added through the hollow portion of the hollow electrode instead of or together with the carbonaceous material addition device [ 1] The electric furnace according to any one of [3].
[5] The oxygen lance is provided to supply oxygen into the furnace, and the oxygen lance is installed at a position at least twice the electrode radius away from the center point of the electrode, with the axial center of the oxygen lance facing. The electric furnace according to any one of [1] to [4].

[6] An electric furnace steelmaking method in which molten iron is carburized in an electric furnace using a graphite electrode, wherein the intersection of a vertical line passing through the center of gravity of the lower end of the graphite electrode viewed from vertically below and the stationary surface of the molten iron is defined as "electrode The electric furnace has a carbon material addition device, and the carbon material addition device supplies the carbon material to a range within the same radius as the electrode radius from the electrode center point, and further oxygen is introduced into the furnace. An electric furnace steelmaking method, wherein oxygen is not supplied to a position within twice the electrode radius from the center point of the electrode when an oxygen lance for supplying oxygen is provided.
[7] The electric furnace steelmaking method according to [6], wherein the carbon material addition device is a blowing lance or an injection chute.
[8] The electric furnace steelmaking method according to [6] or [7], wherein the carbon material addition device is capable of changing the addition direction of the carbon material.
[9] The graphite electrode is a hollow electrode, and the carbonaceous material is added through the hollow portion of the hollow electrode instead of or together with the carbonaceous material addition device [ 6] The electric furnace steelmaking method according to any one of [8].
[10] Oxygen is supplied into the furnace using the oxygen lance along with the addition of the carbonaceous material, and is supplied to a position at least twice the electrode radius from the electrode center point [6]-[ 9], the electric furnace steelmaking method according to any one of the above.

By utilizing the high temperature field of the arc spot, we have improved the carburization speed while using inexpensive carbon material, and realized carburization of molten iron without extending the cycle time.

It is a figure which shows an example of the electric furnace of this invention. FIG. 4 is a schematic diagram showing the relationship between the arrangement of a carbon material blowing lance and an oxygen lance, and the carbon material reaching point and oxygen reaching point.

In order to realize high-speed carburization of molten iron using an inexpensive carbonaceous material, the inventor of the present invention came up with the idea of utilizing the high-temperature field of the arc spot in an electric furnace.

ここでｔ：時間、Ａ：反応界面積、Ｖ：溶鉄体積、ｋ_ｔ：総括反応速度定数、[Ｃ]_ｓ：飽和炭素濃度、[Ｃ]_ｂ：溶鉄の炭素濃度である。 It has been reported that the dissolution of the carbonaceous material added to the molten iron into the molten iron is represented by Equation (1) as a first-order reaction equation of the carbon concentration.

Here, _t : time, A: reaction interfacial area, V: molten iron volume, kt: overall reaction rate constant, [C] _s : saturated carbon concentration, [C] _b : carbon concentration of molten iron.

The overall reaction rate constant kt is expressed by Equation (2) using the dissolution reaction rate constant _kr at the interface between the carbonaceous material and the molten iron and the mass transfer coefficient _km of carbon atoms in the _molten iron. It has been reported that carbonaceous dissolution is controlled by a mixture of dissolution and mass transfer at the interface.

ここでＡ：原子の衝突頻度に関する係数である。式（３）より温度Ｔを高くすることでｋ_ｒが増大する。また、ｋ_ｍも高温ほど大きくなることが知られているため、温度Ｔを高くすることによりｋ_ｔを増大せしめる。 Therefore, if one or both of _kr and _km can be increased, the overall reaction rate constant _kt will also increase, and it is possible to increase the reaction rate of equation (1). Of these, the dissolution reaction rate constant _kr is expressed by the equation (3) using the reaction activation energy _Ea and the temperature T.

Here, A is a coefficient relating to the collision frequency of atoms. According to equation (3), increasing the temperature T increases _kr . Also, since it is known that _km increases as the temperature increases, increasing the temperature _T increases kt.

Based on the above, the present inventor conceived of utilizing the arc spot generated directly under the electrode of the electric furnace as a means for raising the temperature of the molten iron at the position where the carbonaceous material is melted. Normally, the temperature of molten iron in an electric furnace is about 1700°C at most, but the internal temperature of the arc generated from the electrode to the molten iron surface directly below the electrode is 5000°C or higher, and the arc spot on the molten iron surface is also about 2000°C. Therefore, if the carbonaceous material is supplied to the arc spot during carburization, it is possible to melt the carbonaceous material at a higher temperature than when the carbonaceous material is supplied to molten iron other than the arc spot. At this time, for example, in coke with an activation energy _Ea of about 300 to 480 kJ/mol, when the molten iron temperature is 2000 ° C. compared to 1700 ° C., the dissolution reaction rate constant k _r increases by 11 to 47 times, resulting in an increase. Greatly increases charcoal velocity.

The present invention will be described below with reference to FIGS. 1 and 2. FIG.
As a method of supplying the carbon material to the molten iron 20 in the electric furnace 1, the carbon material addition device 3 can be used. As the carbon material adding device 3, a method of blowing the carbon material together with the blowing gas using the blowing lance 4 is conceivable. Also, other supply methods such as addition by the injection chute 7 can be used. The addition direction of the carbon material in the carbon material addition device 3 can be fixed or movable (changeable). When the graphite electrode is a hollow electrode, it can be added through the hollow portion of the hollow electrode instead of the carbon material addition device or together with the carbon material addition device. In any supply method, a high-temperature arc spot can be utilized by designing the supply position of the carbonaceous material to be the arc spot under the electrode. In this embodiment, the electric furnace has one electrode, but even in an electric furnace with a plurality of electrodes, the hot arc spot is utilized by supplying the carbon material to the arc spot directly below one of the electrodes. It is possible to

Hereinafter, in an electric furnace using a graphite electrode, the intersection of a vertical line passing through the figure center of gravity of the lower end of the electrode and the molten iron stationary surface 21 is referred to as an "electrode center point 22" (see FIG. 2(A)). . Further, the position at which the carbon material from the carbon material adding device 3 reaches the molten iron stationary surface 21 is called a "carbon material arrival point 23". The position of the carbon material arrival point 23 can be determined by adding the carbon material in advance using the carbon material adding device 3 . Alternatively, the arrival position of the carbon material on the molten iron stationary surface 21 can be determined based on the trajectory 25 of the carbon material calculated from the speed of the carbon material at the discharge part of the carbon material addition device 3 (see FIG. 2A). ). In order to supply the carbon material to the arc spot directly under the electrode, the position and angle of the carbon material addition device 3 are set so that the distance between the carbon material arrival point 23 and the electrode center point 22 is within the range of the electrode radius r. It is good if it is.

In an electric furnace, an oxygen lance 8 may be used to supply oxygen gas toward molten iron 20 in the furnace for the purpose of oxidative refining such as desiliconization and dephosphorization. If the supplied oxygen gas reacts with the undissolved carbonaceous material, it hinders carburization. Therefore, it is necessary to supply the carbonaceous material for the purpose of carburization and the oxygen gas to separate positions. In the present invention, if the electric furnace has an oxygen lance 8 that supplies oxygen into the furnace, in other words, even if the electric furnace has an oxygen lance 8 that supplies oxygen into the furnace, the electrode center point It is characterized in that the axial center 26 of the oxygen lance 8 is not directed to a position within twice the electrode radius r from 22 (see FIG. 2(B)). When the furnace has an oxygen lance 8 for supplying oxygen into the furnace, the axial center 26 of the oxygen lance 8 faces a position away from the electrode center point 22 by two times the electrode radius r or more. As a result, the carbonaceous material to be carburized and the oxygen gas can be supplied to separate positions. Hereinafter, the direction in which the axial center 26 of the oxygen lance 8 is directed on the molten iron stationary surface 21 is also referred to as the "oxygen reaching point 24".

The following table shows an example in which the present invention is carried out in an electric furnace 1 having a furnace shell with an inner diameter of 6.5 m, a steel output of 105 tons, and leaving 15 tons of seed metal in the furnace at the time of tapping, together with comparative examples. The molten steel bath depth in the electric furnace 1 is 1250 mm when the amount of molten steel in the furnace is 120 tons, and 400 mm when the amount of molten steel in the furnace is 15 tons. As the graphite electrode 2, one graphite electrode having a diameter of 24 inches, that is, 609.6 mm (radius r is 304.8 mm) is provided.

The electric furnace 1 has, as a carbon material adding device 3, a charging chute 7 for charging only the carbon material, and three blowing lances 4 (fixed lances 5) fixed to the wall capable of supplying the carbon material into the furnace (fixed lance A (5A), fixed lance B (5B), fixed lance C (5C)), and a manipulator 11 having a movable blowing lance 4 (movable lance 6). All of the blowing lances 4 use argon gas as a carrier gas when supplying the carbonaceous material. Of these, the three blowing lances 4 (fixed lances 5) fixed to the wall are structured such that their positions and angles cannot be changed.

The blowing lance 4 (fixed lance 5) fixed to the wall has a nozzle for supplying carbon material and a nozzle for supplying oxygen. A nozzle portion for supplying carbon material functions as three blowing lances 4 (fixed lances 5) fixed to the wall (fixed lance A, fixed lance B, and fixed lance C). Further, the nozzle portion for supplying oxygen functions as three oxygen lances 8 (fixed oxygen lances 9) (fixed oxygen lance A, fixed oxygen lance B, fixed oxygen lance C) for supplying oxygen into the furnace.

The manipulator 11 has an oxygen lance 8 (movable oxygen lance 10) together with the movable blowing lance 4 (movable lance 6 for supplying carbon material). The movable lance 6 and the movable oxygen lance 10 can independently supply carbon material and oxygen into the furnace.

The throwing chute 7 can change the throwing direction, and the distance between the carbon material arrival point 23 of the carbon material thrown from the throwing chute 7 and the electrode center point 22 can be changed. The manipulator 11 can also change the directions of the movable lance 6 (carbon material spraying) and the movable oxygen lance 10 .

One of the fixed blowing lances 4 (fixed lance A (5A)) is positioned at the electrode center point 22 (the figure center of gravity of the lower end of the electrode as seen from the vertically downward direction) on the molten iron stationary surface 21 when the bath depth of the molten iron is 1250 mm. 100 mm in the horizontal direction from the intersection of the vertical line passing through and the molten iron stationary surface 21) is the carbon material arrival point 23 (the arrival position of the carbon material from the carbon material addition device 3 to the molten iron stationary surface 21). In addition, the other two (fixed lance B (5B) and fixed lance C (5C)) are positioned and angled so that the carbon material reaching point 23 is 635 mm away from the center point 22 of the electrode. is installed in In addition, the fixed lance 5 (for carbon material spraying) and the fixed oxygen lance 9 are installed with their axial centers separated by 51 mm as described above, and the direction in which the axial center 26 of the fixed oxygen lance 9 is directed (oxygen The arrival point 24) is on the molten iron stationary surface 21, the fixed oxygen lance A (9A) is 250 mm from the electrode center point 22, the fixed oxygen lance B (9B) and the fixed oxygen lance C (9C) are 785 mm from the electrode center point 22. is the position of Therefore, when carbon material and oxygen are simultaneously blown from the fixed lance 5 and the fixed oxygen lance 9 at the same position, the carbon material reaching point 23 and the oxygen reaching point 24 (oxygen supply position) are separated by 150 mm.

In both the present invention examples and the comparative examples, scrap was used as a raw material, and anthracite coal was used as the carbonaceous material. Also, in any case where the blowing lance 4 (fixed lance 5, movable lance 6) was used to supply the carbon material, the average initial velocity of the carbon material at the nozzle exit was 70 m/s. Further, the linear flow velocity of the oxygen jet when supplying oxygen from the oxygen lance 8 was set to 500 m/s.

In the test, the scrap was first melted by energization, and then the carbon material was added from the blowing lance 4 at a total rate of 40 kg/min for 15 minutes while the energization was continued, or the carbon material was added from the charging chute 7, and the carbon material was added. We evaluated the carbon concentration of the metal samples collected before and after . Sampling for analyzing the [C] concentration in the molten steel before and after the addition of the carbon material was performed 1 minute before the start of the addition of the carbon material and 1 minute after the end of the addition of the carbon material. In addition, in all the examples shown in Table 1, the supply of the carbonaceous material was started when the molten iron bath depth reached 1100 mm. Therefore, the molten metal surface rose by 150 mm during the supply of the carbonaceous material, and the distance from the center point of the electrode to the carbonaceous material arrival point also changed when the supply position of the carbonaceous material was not changed. Molten steel was tapped from the electric furnace 5 minutes after the end of the carbon material addition. Assuming that all the carbonaceous material supplied here is carbon content, a total of 600 kg of carbon content is supplied to the molten iron. In this test, if 50% by mass or more of the carbon content supplied was carburized into the molten iron, that is, if the [C] concentration in the molten iron increased by 0.25% by mass or more before and after the carbon material was supplied, the molten iron was good. It was evaluated that it was carburized to.

Electric furnace steelmaking was performed using the carbon material supply conditions and oxygen blowing conditions shown in Table 1. The distance between the electrode center point 22 and the carbon material arrival point 23 is described in the "carbon material-electrode distance", and the distance between the electrode center point 22 and the oxygen arrival point 24 is described in the "oxygen-electrode distance". described. The descriptions are for bath depths of 1100 mm and 1250 mm, respectively. Table 1 shows the results. When the carbon material reaching point 23 and the blowing lance 4, and the oxygen reaching point 24 and the oxygen lance 8 are positioned on different sides from the electrode center point 22, "*" is attached to the right end of the numerical values in Table 1. ing. In Table 1, numerical values outside the scope of the present invention are underlined.

Inventive Examples 1 to 7 in Table 1 are inventive examples.
In Examples 1 to 4 of the present invention, oxygen was not blown, and the distance between the carbon material and the electrode was within the radius r (304.8 mm) of the graphite electrode. In Invention Examples 3 and 4, the manipulator 11 is used to add the carbonaceous material. Among them, in Inventive Example 3, the supply position is fixed, and in Inventive Example 4, the molten iron bath depth is changed according to the rise of the molten iron surface during operation. The movable lance 6 of the manipulator 11 was operated so as to supply the carbonaceous material to the electrode center point 22 (*2 in Table 1).
Inventive Examples 5 to 8 are cases with oxygen blowing, the carbon material-electrode distance is within the graphite electrode radius r (304.8 mm), and the oxygen-electrode distance is twice the graphite electrode radius r ( 609.6 mm), satisfying the conditions of the present invention, and the state of carburization was good.

Comparative Examples 1 to 7 in Table 1 are comparative examples.
In Comparative Examples 1 to 3, no oxygen was blown, and the distance between the carbon material and the electrode exceeded the graphite electrode radius r (304.8 mm), which did not satisfy the conditions of the present invention, and the carburization conditions were unsatisfactory.
Comparative Examples 4 to 7 are cases with oxygen blowing, and in Comparative Examples 4 to 6, the carbon material-electrode distance was within the graphite electrode radius r (304.8 mm), but the oxygen-electrode distance was It was within twice the graphite electrode radius r (609.6 mm), did not satisfy the conditions of the present invention, and was unsatisfactory in the state of carburization. In Comparative Example 7, neither the carbon material-electrode distance nor the oxygen-electrode distance satisfied the conditions of the present invention, and the state of carburization was unsatisfactory.

1 Electric Furnace 2 Graphite Electrode 3 Carbon Material Addition Device 4 Blowing Lance 5 Fixed Lance 5A Fixed Lance A
5B Fixed lance B
5C Fixed lance C
6 movable lance 7 injection chute 8 oxygen lance 9 fixed oxygen lance 9A fixed oxygen lance A
9B Fixed oxygen lance B
9C fixed oxygen lance C
10 Movable oxygen lance 11 Manipulator 20 Molten iron 21 Molten iron stationary surface 22 Electrode center point 23 Carbon material arrival point 24 Oxygen arrival point 25 Carbon material trajectory 26 Axis center r Electrode radius

Claims (10)

In an electric furnace using a graphite electrode, the intersection of a vertical line passing through the center of gravity of the lower end of the graphite electrode viewed vertically from below and the stationary surface of the molten iron is called an "electrode center point", and the electric furnace includes a carbon material addition device. The position at which the carbon material from the carbon material addition device reaches the stationary surface of the molten iron is called a "carbon material arrival point", and the distance between the carbon material arrival point and the electrode center point is within the radius of the electrode. The position and angle of the carbon material addition device are set so that The electric furnace characterized in that the axial center of the oxygen lance is not directed toward. 2. The electric furnace according to claim 1, wherein said carbon material adding device is a blowing lance or an injection chute. 3. The electric furnace according to claim 1, wherein said carbon material addition device is capable of changing the addition direction of the carbon material. The graphite electrode is a hollow electrode, and the carbonaceous material is added through the hollow portion of the hollow electrode instead of or together with the carbonaceous material addition device. The electric furnace according to claim 3. 2. A furnace according to claim 1, wherein said oxygen lance is provided for supplying oxygen into the furnace, and the axial center of said oxygen lance faces a position at least twice the electrode radius from said electrode center point. The electric furnace according to any one of claims 4 to 4. An electric furnace steelmaking method for recarburizing molten iron in an electric furnace using graphite electrodes, wherein the intersection of a vertical line passing through the center of the figure of the lower end of the graphite electrode viewed from the vertical downward direction and the stationary surface of the molten iron is the "electrode center point" The electric furnace has a carbonaceous material addition device, the carbonaceous material is supplied from the center point of the electrode to a range within the same radius as the electrode radius by the carbonaceous material addition device, and further oxygen is supplied into the furnace. An electric furnace steelmaking method characterized in that, when a lance is provided, oxygen is not supplied to a position within twice the electrode radius from the center point of the electrode. 7. The electric furnace steelmaking method according to claim 6, wherein said carbon material adding device is a blowing lance or an injection chute. 8. The electric furnace steelmaking method according to claim 6, wherein said carbon material adding device is capable of changing the adding direction of the carbon material. The graphite electrode is a hollow electrode, and the carbonaceous material is added through the hollow portion of the hollow electrode instead of or together with the carbonaceous material addition device. The electric furnace steelmaking method according to claim 8 . Oxygen is supplied into the furnace using the oxygen lance along with the addition of the carbonaceous material, and the oxygen is supplied to a position at least twice the electrode radius from the center point of the electrode. The electric furnace steelmaking method according to any one of claims 1 to 3.

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