JP6347199B2 - Hot metal refining method - Google Patents

Description

  The present invention relates to a hot metal refining method for performing hot metal preliminary dephosphorization treatment and hot metal decarburization treatment of the hot metal subjected to the preliminary dephosphorization treatment using the same top-bottom blowing converter type refining vessel.

  In recent years, with the increase in iron ore price, it is required to use cheaper iron ore in the steel manufacturing process by the blast furnace method. Inexpensive iron ore often has a high phosphorus concentration, and hot metal produced using such iron ore in a blast furnace has a high phosphorus concentration. Therefore, a more efficient dephosphorization method has been developed in the steelmaking process. Is required. In recent years, dephosphorization of hot metal is clearly separated from decarburization, dephosphorization is performed prior to decarburization, and at least part of the slag after the dephosphorization is eliminated, and then the dephosphorization is performed. A combination of a hot metal preliminary dephosphorization process and a decarburization process of the hot metal, which decarburizes the hot metal afterwards, has become common.

  Since the present invention assumes such a combination, the preliminary dephosphorization treatment described above is simply referred to as hot metal dephosphorization treatment, and the dephosphorization treatment described above is simply described as decarburization treatment. It shall refer to the subsequent decarburization process.

  For hot metal dephosphorization, a process using various equipment such as a torpedo car, a hot metal ladle, or a converter is employed. Among them, the converter has a large freeboard, can blow a large amount of oxygen gas, and can be processed in a short time with high heat tolerance, which is advantageous in terms of high productivity. .

  The converter is often installed mainly for hot metal decarburization, but for the above reasons, it is sometimes used for hot metal dephosphorization. In some converters, hot metal dephosphorization and decarburization may be mixed. In some cases, after hot metal dephosphorization, the hot water from the converter is poured into the hot metal ladle and poured again into the converter for decarburization. However, to reduce heat loss as much as possible, hot metal dephosphorization is performed. In some cases, the furnace is tilted to discharge a part of the dephosphorization slag from the furnace port, and the dephosphorization hot metal in the furnace is subsequently decarburized.

  Against this background, the converter is not only used as a dedicated furnace for hot metal dephosphorization or only for decarburization, but both hot metal dephosphorization and decarburization are performed in a single converter. It may be required to be ready. In the converter, oxygen gas is blown from the top blowing lance to the hot metal to perform hot metal dephosphorization and decarburization, but the hot metal dephosphorization process increases (% T. Fe) in the slag to increase the dephosphorization rate. In soft blow and decarburization treatment, hard blow is intended to reduce iron content loss by reducing (% T.Fe) in the slag.

  When both hot metal dephosphorization treatment and decarburization treatment are performed in a single converter, the top blow lance is used for soft blow lance and decarburization treatment for hot metal dephosphorization treatment. It is necessary to provide two types of lances of hard blow lance.

  For example, as a hot metal dephosphorization lance, as disclosed in Patent Document 1, there is a method of designing a soft blow so that the top blown oxygen is blocked by slag and oxygen does not contact the hot metal directly. Moreover, in order to reduce (% T.Fe) in the slag as a top blow lance for decarburization treatment, not only a lance having a nozzle having a small hole diameter is used for hard blow, but also disclosed in Patent Document 2. As is done, there is also a method of suppressing the oxidation of iron by moving the fire point by rotating the lance.

JP 2005-139529 A Sho 62-130111 JP 2000-001714 A

  However, until now, it has been difficult to achieve soft blow conditions suitable for hot metal dephosphorization treatment and hard blow conditions suitable for decarburization treatment with one type of lance. In order to obtain a soft blow suitable for hot metal dephosphorization or a hard blow suitable for decarburization with one type of lance, it is often difficult to adjust the lance height alone. It is necessary to adjust. In the case of a lance suitable for decarburization hard blow, it was necessary to raise the lance height and lower the oxygen flow rate in hot metal dephosphorization.

  In a recent general converter facility, a lance cart having two lances is installed for one converter. The reason for providing two lances is to prepare a lance so that a healthy lance can be used immediately when the lance in use needs to be replaced due to a leakage of water. Therefore, although it is possible to provide two lances even now, it is often difficult to provide two types of lances.

  Therefore, an object of the present invention is to provide a molten steel refining method capable of realizing high-efficiency dephosphorization and high-efficiency decarburization with one lance even when the hot metal dephosphorization process and the decarburization process are performed in the same furnace.

  The present inventors examined various effects when rotating the porous lance twisted in the direction of the nozzle described in Patent Document 3 from the viewpoint of realizing high-efficiency hot metal dephosphorization and high-efficiency decarburization. Decided to do.

  Here, the porous lance in which the direction of the nozzle is twisted is a type of lance having a plurality of Laval nozzles (hereinafter referred to as “nozzles”) having the same shape at the tip of the lance. FIG. 1 is a schematic view showing the tip portion of the lance 10, but for convenience of explanation, one is arbitrarily extracted from the plurality of nozzles 11 and illustrated. The xyz coordinate system shown in FIG. 1 is such that the central axis 12 of the upper blowing lance (hereinafter referred to as “lance”) 10 for the converter blowing is the z axis, and the positive direction of the z axis is the outlet of the nozzle 11. The right-handed xyz determined so that the center of the outlet 13 of the nozzle 11 from which one is extracted is positioned on the positive side on the y-axis. Cartesian coordinate system.

  Here, the xyz coordinate system of the right hand system is a coordinate system in which the thumb, index finger, and middle finger of the hand are orthogonal to each other, the thumb is the x axis, the index finger is the y axis, and the middle finger is the z axis.

  Then, in the nozzle 11, the angle formed by the projection of the central axis 14 (hereinafter referred to as “nozzle axis”) 14 on the xy plane with the y-axis passes through the center of the outlet 13 of the nozzle 11, and the twist angle α. When the angle formed between the straight line 15 parallel to the z-axis and the nozzle axis 14 is an inclination angle β, the twist angle α and the inclination angle β of the nozzle 11 are the same in a plurality of nozzles having the same shape.

The following examination was performed using such a lance.
The numerical analysis method is used for the examination, and the lance 10 in which the direction of the nozzle 11 is twisted is rotated in the direction in which the nozzle 11 is twisted and in the direction opposite to the direction in which the nozzle 11 is twisted. The behavior was investigated. Here, the direction in which the direction of the nozzle 11 is twisted means that the lance axis (z axis) 12 is a rotation axis and the projection of the nozzle axis 14 onto the xy plane includes its extension line on the positive side on the x axis. When intersecting the axis, it is the direction to rotate counterclockwise when viewed from the upstream side of the upper blown oxygen, and the projection of the nozzle axis 14 includes the extension line and intersects the x axis on the negative side on the x axis. In this case, the rotation direction is clockwise when viewed from the upstream side of the upper blown oxygen.

  The analysis is a steady analysis, and the rotation of the lance 10 is considered by rotating the coordinates around the lance shaft 12 as a rotation axis, and only the gas phase is taken into consideration without considering the molten iron, and the jet flow when the lance 10 is rotated. Was analyzed.

  As a result, it was found that when the lance 10 twisted in the direction of the nozzle 11 is rotated, the behavior of the jet varies depending on the rotation direction. The difference in the rotational direction is the dynamic pressure of the jet. Even if the rotational speed is the same, when the nozzle 11 is rotated in the direction twisted, the dynamic pressure of the jet is greater than when rotating in the opposite direction. I found it smaller. This is because when the lance 10 is rotated in the direction in which the direction of the nozzle 11 is twisted, as the rotational speed is increased, the jet flutters in the opposite direction to the rotational direction. This is thought to be due to the fact that the jet is getting closer to the stationary state where there is no flow of the jet, and the jet attenuation is increased. Further, when the lance 10 is rotated in the direction opposite to the direction in which the direction of the nozzle 11 is twisted, even if the rotational speed is increased, the jet does not fly as compared with the case where the lance is rotated in the twisted direction. This is considered to be because the space of this is difficult to approach a stationary state and the attenuation of the jet is small. Thus, when the lance 10 with the nozzle 11 twisted is rotated in the direction in which the nozzle 11 is twisted, soft blow is likely to occur, and when the nozzle 11 is rotated in the opposite direction to the direction in which the nozzle 11 is twisted, soft blow is unlikely to occur. Became clear.

  From the above results, when performing the hot metal dephosphorization process using the lance 10 in which the direction of the nozzle 11 is twisted, the lance 10 is rotated in the direction in which the nozzle 11 is twisted, and the soft blow effect (% T. Fe) ) To improve the dephosphorization efficiency, and when performing the decarburization process, the lance 10 is rotated in the direction opposite to the direction in which the nozzle 11 is twisted to prevent soft blow, and decarburization is especially achieved by moving the fire point. We obtained the knowledge that high-efficiency decarburization with good iron content yield was achieved by suppressing the iron oxidation at the end stage and reducing (% T.Fe) in the slag. As a result, the gist of the present invention can be summarized as follows.

(1) Using the same top-bottom blowing converter-type smelting vessel, oxygen was blown up from one top blowing lance for converter blowing, and the hot metal was preliminarily dephosphorized and preliminarily dephosphorized. In the hot metal refining method for decarburizing hot metal,
The top blowing lance for converter smelting has a plurality of Laval nozzles having the same shape in which outlets of the nozzles are arranged at equal intervals on the same circumference of the tip surface of the lance, and
The center axis of the upper blowing lance for converter smelting is defined as the upstream side of the upper blowing oxygen ejected from the outlet of the nozzle with the central axis as the z axis, and any one of the plurality of Laval nozzles In the right-handed xyz Cartesian coordinate system in which the center of the exit surface is positioned on the positive side on the y-axis,
An angle formed by projection of the central axis of the arbitrary nozzle on the xy plane with respect to the y axis is a twist angle α, a straight line passing through the center of the outlet surface of the nozzle and parallel to the z axis, and the central axis of the nozzle Is the same as the inclination angle β, the twist angle α and the inclination angle β of each of the plurality of nozzles are the same, and the twist angle α (°) is the equation (1) and the inclination angle β (° ) Satisfies the formula (2), and
When the intersection of the central axis projection of the arbitrary one nozzle on the xy plane and the x axis is located on the positive side on the x axis, the preliminary dephosphorization treatment of the hot metal is performed for the converter blowing With the central axis of the top blowing lance as the rotation axis, the top blowing lance is rotated counterclockwise as viewed from the upstream side of oxygen. On the other hand, in the decarburization treatment of the hot metal subjected to the preliminary dephosphorization treatment, Rotating the lance in the reverse direction,
and,
When the intersection of the projection of the center axis of the arbitrary one nozzle on the xy plane and the x axis is located on the negative side on the x axis, the preliminary dephosphorization treatment of the hot metal is performed for the converter blowing The upper blow lance is rotated clockwise with the central axis of the upper blow lance as viewed from the upstream side of the oxygen. On the other hand, in the decarburization treatment of the hot metal that has been subjected to the preliminary dephosphorization treatment, A method for refining hot metal, which comprises rotating a lance in the reverse direction.

10 ° <α <100 ° (1)
10 ° <β <30 ° (2)

  According to the present invention, even when hot metal dephosphorization treatment and decarburization treatment are performed in the same furnace, high efficiency dephosphorization and high efficiency decarburization can be realized with one lance.

1 is a schematic view of the tip portion of the lance, FIG. 1 (a) is a cross-sectional view of the lance as viewed from the upstream side of oxygen, and FIG. 1 (b) is aa ′ in FIG. 1 (a). FIG. 1C is a cross-sectional view taken along the line bb ′ of FIG. 1A, and FIG. 1D is a cross-sectional view taken along the line cc ′ of FIG. FIG. 2 is a graph showing the relationship between the lance rotation speed and the dephosphorization rate when the lance is rotated in the direction in which the nozzle is twisted. FIG. 3 is a diagram showing the relationship between the lance rotation speed and the dephosphorization rate when the lance is rotated in the direction opposite to the direction in which the nozzle is twisted. FIG. 4 shows the lance rotation speed and T.V. when the lance is rotated in the direction in which the nozzle is twisted. It is a figure which shows the relationship with Fe density | concentration. FIG. 4 shows the lance rotation speed and T.V. when the lance is rotated in the direction opposite to the direction in which the nozzle is twisted. It is a figure which shows the relationship with Fe density | concentration.

A mode for carrying out the present invention will be described with reference to the drawings.
1. Top blowing lance for converter blowing (1) Relationship between lance and xyz coordinate system In the present invention, it is necessary to clarify the relationship between the lance and the xyz coordinate system in order to define the rotation direction of the lance. As shown in FIG. 1, the xyz coordinate system defined in the present invention is such that the central axis 12 of the lance 10 is the z-axis, and the positive direction of the z-axis is the upward blown oxygen jetting from the outlet 13 of the nozzle 11. This is a right-handed xyz orthogonal coordinate system determined so as to face the upstream side and the center of the outlet 13 of the nozzle 11 is positioned on the positive side on the y-axis. Although only one nozzle is shown in FIG. 1 for convenience of explanation, the lance used in the present invention is a porous lance, all nozzles have the same shape, and the outlets of the nozzles are on the same circumference of the lance tip surface. It is arranged at equal intervals.

  When such an xyz coordinate system is used, the center of the outlet 13 of any one nozzle 11 of the lance 10 used in the present invention is located on the positive side on the y axis, and the nozzle axis 14 of the nozzle axis 14 to the xy plane is located. The projection has an intersection on the positive side of the x-axis or the negative side of the x-axis, including the extension line.

(2) Nozzle angle In the nozzle 11 of the present invention, the angle formed by the projection of the nozzle axis 14 on the xy plane and the y axis is a twist angle α, a straight line 15 passing through the center of the outlet 13 of the nozzle 11 and parallel to the z axis. When the angle between the nozzle axis 14 and the nozzle shaft 14 is the inclination angle β, the twist angle α and the inclination angle β of each nozzle 11 are the same. This is because high dephosphorization efficiency and high decarburization efficiency can be exhibited by changing the rotation direction of the lance between dephosphorization and decarburization.

  In the nozzle 11, the twist angle α (deg) satisfies the expression (1) and the inclination angle β (deg) satisfies the expression (2).

10 ° <α <100 ° (1)
10 ° <β <30 ° (2)
When the twist angle α of the lance with the nozzle orientation twisted is 10 ° or less, the effect of the present invention is small, and when it is 100 ° or more, the interference between the jets becomes large. When the nozzle inclination angle β is 10 ° or less, the interference between jets becomes large, and when the nozzle inclination angle is 30 ° or more, the distance between the fire point and the refractory becomes small and the refractory is melted. ) Must be in the range of the formula.

(3) Nozzle shape The nozzle 11 is preferably a Laval nozzle as shown in FIG. 1 in order to increase the jet speed. The nozzle 11 has a throat straight pipe portion 18 extending in communication with the upper blowing oxygen flow path 17 and a divergent portion 19 extending in communication with the throat straight pipe portion 18. The throat straight pipe portion 18 has a cylindrical shape, for example. The throat straight pipe portion 18 and the divergent portion 19 share a boundary surface 20. The divergent portion 19 has a substantially truncated elliptical cone shape in which the cross-sectional area increases from the boundary surface 20 toward the outlet 13 of the nozzle 11. The boundary surface 20 is a virtual surface surrounded by a boundary portion between the throat straight pipe portion 18 and the divergent portion 19. For example, the boundary surface 20 may be orthogonal to the nozzle shaft 14 as shown in FIG. There may be.

(4) Number of nozzles Three to six nozzles are suitable. If the number of nozzles is less than 3, the number of nozzles is very small and hard blow is likely to occur, and it is necessary to make the nozzle throat diameter very large or make the lance height very high. However, since the throat diameter becomes too large, it becomes difficult to manufacture the lance in consideration of securing a cooling water channel or the like. In addition, when the lance height is very high, the spread of the jet becomes large, so that it is difficult to prevent both jets from interfering with each other and the jet is close to the refractory. If the number of nozzles is 7 or more, the interference coalescence of the jet becomes significant, which is inappropriate.

(5) Shape of Lance Tip A tip surface 21 of the lance 10 is a conical surface having a half apex angle γ (°) about the lance center axis 12 as shown in FIG. 1, for example. The outlet 13 of the nozzle 11 is located on the same circumference. As for γ, it is preferable to make the angle formed by the nozzle shaft 14 and the tip surface 14 as close to orthogonal as possible, specifically, 60 ° to 80 °.

2. Hot metal refining method according to the present invention (1) Verification experiment In the converter experiment, the effect of the present invention and the conditions for producing the effect were examined.

  In a 2.5t top-bottom blow converter, install a rotary joint on the top of the lance so that the motor, gear, oxygen gas pipe and cooling water pipe can be rotated. The blowing lance can be rotated. Then, the tip of a porous lance with the nozzle orientation twisted or the tip of a normal lance without twisting the nozzle orientation was attached to the tip of the rotating lance, and hot metal dephosphorization experiment and decarburization experiment were conducted. .

  In the hot metal dephosphorization experiment, 2.0 t of hot metal was charged, 30.0 kg of lump lime with a maximum particle size of 15 mm was added, oxygen was blown from the top blowing lance to the hot metal, and dephosphorization was performed. An experiment was conducted to investigate the dephosphorization rate. In addition, the CaO density | concentration in lump lime is 92%.

  The temperature of the hot metal was 1300 ° C., [% C] = 4.2 mass%, [% Si] = 0.4 mass%, [% Mn] = 0.3 mass%, [% P] = 0.1 mass%. , [% S] = 0.001 mass% was charged into a 2.5 t converter. The bath depth was 385 mm.

  The top blowing lance is a 5-hole lance in which Laval nozzles with a throat diameter of 5.8 mm and a nozzle inclination angle of 20 ° are arranged at equal intervals on the same circumference, and the lance with the nozzle orientation twisted has a twist angle α. The lances were given 15 ° and 30 °. The lance that does not twist the nozzle has a twist angle α of 0 °, and the other specifications are the same as those of the lance that twists the nozzle.

The top blowing oxygen flow rate was constant at 8.0 Nm ³ / min, and the blowing time was 4.0 min. An experiment was conducted in which the height of the lance was fixed to 500 mm, and when rotating the lance, the rotation speed was constant during blowing, and the rotation speed and rotation direction were changed. Stirring with the bottom blowing gas was also performed to stir the hot metal, and the bottom blowing was performed with four tuyere, and Ar gas was allowed to flow at 0.2 Nm ³ / min from each bottom blowing tuyere during dephosphorization blowing.

  In the decarburization experiment, 2.0 t of dephosphorized hot metal was charged, 35.0 kg of lump lime with a maximum particle size of 15 mm and 10 kg of lump meteorite with a maximum particle size of 15 mm were added, and then oxygen was introduced into the hot metal from the top blowing lance. An experiment was conducted to investigate the dephosphorization rate after treatment by spraying and dephosphorizing. The dephosphorized iron has a temperature of 1350 ° C., [% C] = 3.5 mass%, [% Si] = 0.0 mass%, [% Mn] = 0.05 mass%, [% P] = 0.015. The 2.5 t converter was charged under the conditions of mass% and [% S] = 0.001 mass%. The bath depth was 385 mm.

The top blowing lance is a five-hole lance in which nozzles having a diameter of 5.8 mm and a nozzle inclination angle of 20 ° are arranged at equal intervals on the same circumference, similar to the lance used in the hot metal dephosphorization experiment described above, The lance in which the direction of the nozzle was twisted was a lance having a twist angle α of 15 ° and 30 °. A lance that does not twist the direction of the nozzle has a twist angle α of 0 °, and the other specifications are the same as those of the lance that twists the direction of the nozzle. The upper blowing oxygen flow rate was constant at 8.0 Nm ³ / min, the blowing time was about 9.0 min, and the [% C] in the molten steel after blowing was 0.05 to 0.06 mass%. . An experiment was conducted in which the height of the lance was fixed at 400 mm, and when the lance was rotated, the rotation speed was constant during blowing, and the rotation speed and rotation direction were changed. In order to stir the hot metal, the bottom blowing gas is also stirred, and the bottom blowing is set to four tuyere, and Ar gas is supplied from each bottom blowing tuyere at 0.2 Nm ³ / min during the blowing as with hot metal dephosphorization blowing. Washed away.

The results obtained in the hot metal dephosphorization experiment are shown in FIG. 2 and FIG.
2 and 3 show the relationship between the rotation speed of the lance and the dephosphorization rate after the experiment. Under any condition, the dephosphorization rate is improved by rotating the lance. The dephosphorization rate increased in all cases up to 10 rpm. In particular, if a lance with a twisted nozzle is used and the lance is rotated in the direction in which the nozzle is twisted, it will be more dephosphorized than if it is rotated in the opposite direction or if a normal lance is used. The rate was greatly improved up to 30 rpm. This is presumably because the lance with the nozzle twisted is rotated in the twisted direction, the jet attenuation is promoted, and (% T.Fe) in the slag is increased to increase the dephosphorization rate. When the lance was rotated in the direction in which the nozzle was twisted, the dephosphorization rate gradually increased to 100 rpm, but no change was observed with the normal lance.

  Therefore, in the case of hot metal dephosphorization, using a lance twisted in the direction of the nozzle at a rotation speed of 10 rpm or more in the direction twisted in the nozzle increases the dephosphorization rate compared to the method of rotating the normal lance. I knew I could do it. In particular, it is preferable to increase the rotational speed to 30 rpm, since the effect of improving the dephosphorization rate appears remarkably, and it can be said that this effect has been confirmed to increase gradually up to 100 rpm as the rotational speed increases.

The results obtained in the decarburization experiment are shown in FIG. 4 and FIG.
4 and 5 show the relationship between the rotational speed of the lance and the slag obtained after the experiment (% T. Fe). Under any condition, (T.Fe) decreased by rotating the lance. This is because, at the end of decarburization where the movement of C in the molten steel is rate-determining, the hot spot moves on the bath surface by rotating the lance, thereby increasing the reaction interfacial area and promoting the decarburization reaction. it is conceivable that. (% T. Fe) decreased in all cases up to 10 rpm, and there was almost no influence due to the difference in the type of lance and the rotation direction.

  However, when a lance with a twisted nozzle is used and the lance is rotated in the direction opposite to the direction in which the nozzle is twisted, the rotation speed is set to 10 rpm or more (% T. Fe). It became clear that there was an effect of lowering, and the effect increased to 30 rpm. This is because the rotation of the lance twisted in the direction of the nozzle is rotated in the direction opposite to the twisted direction, the jet attenuation is suppressed, and the reduction effect (% T. Fe) due to the movement of the fire point by the lance rotation can be enjoyed efficiently. It is thought that it was because of. When the lance with the nozzle direction twisted was rotated in the opposite direction to the twisted direction, (% T. Fe) gradually decreased to 100 rpm, but no change was observed with the normal lance.

  From the above, it has been found that when the lance with the nozzle direction twisted is rotated, the behavior of the jet is significantly different between when the nozzle is rotated in the twisted direction and when rotated in the opposite direction. In dephosphorization blowing, a high dephosphorization rate due to an increase in (% T. Fe) was obtained by rotating a lance with the nozzle direction twisted in the direction twisted so that the jet tends to be soft blow. Also, in decarburization blowing, T. by the movement of the fire point by rotating the lance that twists the direction of the nozzle in the direction opposite to the direction twisted so as not to be soft blow. It was found that the Fe reduction effect can be enjoyed.

  As described above, when a twist lance having predetermined requirements is used, suitable conditions for the dephosphorization treatment and the decarburization treatment of the hot metal can be changed only by changing the rotation direction while using the same top blowing lance. Therefore, the refining method used by rotating the lance according to the present invention is considered to be particularly suitable for the hot metal dephosphorization treatment and the method for decarburizing the hot metal using the same converter.

  The effect of the present invention was confirmed using an upper bottom blowing converter with a heat size of 300 t / Ch. First, refining treatment conditions common to the examples and the comparative examples will be described.

  In the hot metal dephosphorization treatment, 270 t of hot metal and 30 t of scrap were charged, and 4.0 t of massive lime having a maximum particle size of 30 mm was added, and then dephosphorization was performed by blowing oxygen to the hot metal from an upper blowing lance.

  The hot metal has a temperature of 1300 to 1340 ° C., [% C] = 4.5 to 4.7 mass%, [% Si] = 0.4 to 0.5 mass%, [% Mn] = 0.3 to 0.00. The converter was charged under the conditions of 4% by mass, [% P] = 0.10 to 0.11% by mass, and [% S] = 0.003 to 0.006% by mass.

The top blowing oxygen flow rate was constant 1200 Nm ³ / min, and the blowing time was 4.0 min.

  Thereafter, a sample was taken from the hot metal after the dephosphorization treatment, and 70 to 80% of the slag after the treatment was eliminated, and then the hot metal after the dephosphorization treatment was decarburized using the same converter. .

  In the decarburization treatment, after adding 3.0 tons of massive lime with a maximum particle size of 30 mm, 0.8 tons of massive limestone with a maximum particle size of 30 mm and 0.2 tons of MgO brick scrap, oxygen is melted from the top blowing lance. Decarburized and blown.

The hot metal has a temperature of 1330 to 1360 ° C., [% C] = 3.5 to 3.9% by mass, [% Si] = 0.02% by mass, [% Mn] = 0.15% by mass, [% P] = 0.018-0.035 mass% and [% S] = 0.003-0.006 mass%. In this hot metal, the upper blowing oxygen flow rate was kept constant at 1200 Nm ³ / min, and the blowing time was adjusted so that the [% C] after the treatment was 0.04 mass%.

  Then, the dephosphorization rate during hot metal dephosphorization treatment and the iron yield during decarburization treatment were evaluated under the following conditions.

(Comparative Example 1)
First, in the dephosphorization treatment, a six-hole normal lance in which nozzles having a throat diameter of 68 mm and a nozzle inclination angle of 20 ° are arranged at equal intervals on the same circumference was used as the upper blowing lance. The height of the lance was kept constant at 3000 mm from the hot water surface of the hot metal, and the lance was not rotated. As a result, the phosphorus removal rate after the treatment was 68%.

  In the decarburization treatment, the same top blowing lance as that in the dephosphorization treatment was used, and the height of the lance was kept constant at 3000 mm from the hot water surface of the hot metal, and the lance was not rotated. Under this condition, the average iron yield of 10 Ch was 98.2%.

(Comparative Example 2)
First, in the hot metal treatment, the normal lance used in Comparative Example 1 was used as the top blowing lance, the height of the lance was also kept constant at 3000 mm from the hot water surface of the hot metal, and the lance was rotated at a constant 50 rpm during the treatment. As a result, the phosphorus removal rate after the treatment was 70%.

  In the decarburization treatment, the same top blowing lance as that in the dephosphorization treatment was used, and the height of the lance was kept constant at 3000 mm from the hot water surface of the hot metal, and the lance was rotated at a constant 50 rpm during the treatment. Under this condition, the average iron yield of 10 Ch was 98.3%.

Example 1
First, in the hot metal treatment, a twist lance in which six nozzles having a throat diameter of 68 mm, a nozzle inclination angle of 20 °, and a twist angle α of 30 ° were arranged at equal intervals on the same circumference was used as the upper blowing lance. The height of the lance was constant at 3000 mm from the surface of the still water of the bowl, and the lance was rotated in the direction in which the nozzle was twisted, and the rotation speed was constant at 50 rpm during processing. As a result, the phosphorus removal rate after the treatment was 82%.

  In the decarburization treatment, the same top blowing lance as in the dephosphorization treatment is used, and the height of the lance is kept constant at 3000 mm from the hot water surface of the hot metal, and the lance is rotated at a constant 50 rpm in the direction opposite to the direction of twisting the nozzle during the treatment. I let you. Under this condition, the average iron yield of 10 Ch was 98.5%.

Claims (1)

Using the same top-bottom blown-type refining vessel, oxygen was blown up from one top-blowing lance for converter blowing, so that the hot metal was preliminarily dephosphorized and the preliminary dephosphorized hot metal was desorbed In the hot metal refining method for charcoal processing,
The top blowing lance for converter smelting has a plurality of Laval nozzles having the same shape in which outlets of the nozzles are arranged at equal intervals on the same circumference of the tip surface of the lance, and
The center axis of the upper blowing lance for converter smelting is defined as the upstream side of the upper blowing oxygen ejected from the outlet of the nozzle with the central axis as the z axis, and any one of the plurality of Laval nozzles In the right-handed xyz Cartesian coordinate system in which the center of the exit surface is positioned on the positive side on the y-axis,
An angle formed by projection of the central axis of the arbitrary nozzle on the xy plane with respect to the y axis is a twist angle α, a straight line passing through the center of the outlet surface of the nozzle and parallel to the z axis, and the central axis of the nozzle Is the same as the inclination angle β, the twist angle α and the inclination angle β of each of the plurality of nozzles are the same, and the twist angle α (°) is the equation (1) and the inclination angle β (° ) Satisfies the formula (2), and
When the intersection of the central axis projection of the arbitrary one nozzle on the xy plane and the x axis is located on the positive side on the x axis, the preliminary dephosphorization treatment of the hot metal is performed for the converter blowing With the central axis of the top blowing lance as the rotation axis, the top blowing lance is rotated counterclockwise as viewed from the upstream side of oxygen. On the other hand, in the decarburization treatment of the hot metal subjected to the preliminary dephosphorization treatment, Rotating the lance in the reverse direction, and
When the intersection of the projection of the center axis of the arbitrary one nozzle on the xy plane and the x axis is located on the negative side on the x axis, the preliminary dephosphorization treatment of the hot metal is performed for the converter blowing The upper blow lance is rotated clockwise with the central axis of the upper blow lance as viewed from the upstream side of the oxygen. On the other hand, in the decarburization treatment of the hot metal that has been subjected to the preliminary dephosphorization treatment, A method for refining hot metal, which comprises rotating a lance in the reverse direction.
10 ° <α <100 ° (1)
10 ° <β <30 ° (2)

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