JP2000256724A - Converter steelmaking method excellent in stability of operation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a converter steelmaking method, with which the stable operation having little adverse effect caused by spitting can be executed even in the case of blowing molten pre-treated iron having little slag quantity at high feeding speed of oxygen. SOLUTION: As a top-blown lance, two kinds of Laval nozzles having different inclining angles are alternately disposed in the circumferential direction of jetting surface of the lance and also, the lance, in which the ratio of the nozzle diameter having larger inclining angle to the nozzle diameter having smaller inclining angle is made to the range of >1.0 to 2.0, is used and the basicity of the slag is regulated to 2.8-3.8 to execute the blowing. In such a case, desirably, the oxygen feeding speed from the blown lance is controlled in the range of 2.6-2.9 Nm3/min.t at the initial stage of the blowing, and in the range of 3.0-3.4 Nm3/min.t from the middle stage to the end stage of the blowing to execute the blowing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a converter steelmaking method capable of suppressing the adverse effects of spitting and enabling a stable operation.

[0002] Regardless of the top-blowing converter or the top-bottom-blowing converter, in order to improve productivity and extend the life of refractories in a steelmaking process using a converter, the rate of acid supply from a lance is increased. It is essential to shorten the blowing time. However, if the acid supply rate is easily increased, slopping (a phenomenon in which the formed slag overflows from the furnace opening of the converter) and spitting (a phenomenon in which molten steel is scattered by an oxygen jet blown upward) occur. However, not only the steelmaking cost is deteriorated due to the decrease in the iron content yield, but also the operation is hindered due to the adhesion of the metal to the auxiliary equipment.

[0003] In recent years, however, since the pretreatment of molten iron has become extremely popular, the amount of slag produced in converter steelmaking has been reduced, and the danger of slopping has been significantly reduced. However, the problem of spitting during high-speed blowing still remains. Therefore, at present, there is a strong demand for a stable converter operation technique that does not cause spitting even when high-speed blowing is performed.

[0004]

2. Description of the Related Art Conventionally, in order to reduce the above-mentioned "spitting", it is effective to disperse the collision energy of an oxygen jet (oxygen jet) to a bath surface by making the upper blowing lance porous. It has been common practice to use a porous lance. This porous lance is obtained by disposing a plurality of nozzles (injection holes) having a constant inclination angle on the same circumference of the lance injection surface. The greater the number of holes, the greater the effect of dispersing the collision energy of the oxygen jet. It is common to use a four or six hole lance.

[0005] However, when such a porous lance is used, there is a problem of overlapping of cavities (bath surface depression due to collision of oxygen jet) generated on the molten metal bath surface corresponding to each nozzle, and the overlapping area ratio of the cavities is reduced. The phenomenon that the amount of spitting increased remarkably when it became large was seen.

In order to solve this problem, for example, Japanese Unexamined Patent Publication (Kokai) No. 6-57320 discloses an overlapping area ratio of cavities formed in a geometrically arranged state on a bath surface during converter blowing. Focusing on the phenomenon that the amount of spitting is remarkably reduced when the water content is suppressed to 30% or less, "in a porous lance, the inclination angles of adjacent nozzles are alternately changed, thereby forming a bath surface cavity. -A top blowing lance capable of suppressing the geometrical overlapping area ratio to 30% or less has been proposed.

[0007] However, according to the study of the present inventors,
It became clear that the above proposal had the following problems. That is, in the case of the converter operating conditions in which the amount of slag is relatively large and the acid feed rate is less than 3.0 Nm ³ / min · t under normal iron blowing, it is proposed in JP-A-6-57320. By using the porous lance, it was possible to suppress the amount of spitting and stable operation was possible,
Acid transfer rate under slag blowing using hot metal pre-treated iron
When the operation was performed at 3.0 Nm ³ / min · t or more, it was found that metal sticking to incidental facilities due to spitting became remarkable, and stable operation became difficult.

In view of the above, an object of the present invention is to provide a stable operation with less harmful effects due to spitting even when high-speed blowing of molten iron pretreated iron with a small amount of slag is performed at a high acid feed rate. The objective was to establish a converter steelmaking method that could be performed.

[0009]

The present inventors have conducted intensive studies to achieve the above object, and as a result, have obtained the following new findings. a) It is extremely difficult to completely prevent the occurrence of spitting in a converter operation with an increased acid feed rate. However, one of the most serious problems among spitting is the occurrence of ingot sticking to incidental equipment. "Spitting that scatters at an angle close to the vertical direction". If this can be suppressed, the stability of the converter operation will be significantly improved. B) And the upper blowing lance will be "alternately changing the inclination angle of adjacent nozzles By making the porous lance having two kinds of inclination angles, and making the diameter of the nozzle having the smaller inclination angle smaller than the diameter of the other nozzle, the angle close to the vertical direction can be obtained without adversely affecting the operation speed. C) In addition, in converter steelmaking, the above “top-blowing porous lance”
When slag is blown with the basicity of the slag kept at 3.8 or less, good fluidity of the slag is ensured and the molten metal bath surface is sufficiently covered, thereby reducing spitting. In addition, the effect of suppressing the spitting generated from scattering out of the system is enhanced, and the adverse effects of spitting are further reduced. D) If necessary, if the soft blowing is performed at the beginning of blowing, Since a slag having good fluidity is quickly formed at the initial stage of the blowing, the effect of preventing spitting outside the system throughout the entire process is further improved.

The present invention has been made based on the above findings and the like, and provides the following converter steelmaking method in which spitting is effectively suppressed. (1) As the upper blowing lance, two types of Laval nozzles having different inclination angles are alternately arranged in the circumferential direction of the lance ejection surface, and the ratio of the other nozzle diameter to the nozzle diameter of the smaller inclination angle is changed. A converter steelmaking method excellent in operation stability, characterized in that a blast furnace with a slag basicity of 2.8 to 3.8 is used and the blast furnace is blown with a slag basicity of 2.8 to 3.8. (2) Reduce the acid feed rate from the top blowing lance to 2.6 to
In the range of 2.9 Nm ³ / min · t, the acid feed rate from the top blowing lance in the middle stage to the end stage of blowing is 3.0 to 3.4.
Blowing is performed in the range of Nm ³ / min · t.
The converter steelmaking method according to the above (1).

[0011]

Hereinafter, the present invention will be described in detail together with its operation. First, a first feature of the present invention is that, as an upper blowing lance used in converter steelmaking, "two types of Laval nozzles having different inclination angles are alternately arranged in the circumferential direction of the lance injection surface, and The ratio of the other nozzle diameter to the smaller nozzle diameter is smaller than 1.0, and the ratio is less than 2.0.
The point is applied.

FIG. 1 and FIG. 2 are an explanatory view of a lower surface (ejection surface) and a longitudinal section (A-A section of FIG. 1) of an upper blowing lance used in the method of the present invention, respectively. The 1 and as can be seen from Figure 2, on the lance 1 for use in the present invention method, "the inclination angle (center axis lance angle between the central axis of the nozzle) is Ro in theta ₁ - DOO Nozzle 2- with diameter d _t1
Ro 1 "and" tilt angle _{θ 2 (θ 1 <θ 2} ) - alternately nozzle 2-2 "and is in the circumferential direction by the same number of bets diameter _{d t2 (d t1 <d t2} ), preferably Are alternately arranged at equal intervals, and the nozzle 3 arranged at the center is provided to prevent the adhesion of the metal to the center of the lance bottom surface.

[0013] When such a "porous lance in which two types of Laval nozzles having different inclination angles are alternately arranged in the circumferential direction of the lance injection surface" is used, "conversion furnace blowing", which has been conventionally confirmed, is used. In addition, the cavity formed in a geometric arrangement on the bath surface can reduce the spitting effect brought about by reducing the overlapping area ratio of each other. Is smaller than the other nozzle diameter, so that spitting is further reduced, and the amount of spitting scattered outside the system from the furnace port is significantly reduced. This mechanism will be described with reference to FIG.

FIG. 3 is an explanatory view showing a spitting generation mechanism in a use state of the upper blowing lance according to the present invention. As shown, the smaller the inclination angle (θ ₁ )
It is geometrically evident that the spitting generated by the nozzle of No. scatters in a direction close to the vertical, and the spitting generated by the nozzle with the larger inclination angle (θ ₂ ) scatters in a direction farther than the vertical, The former (the nozzle with the smaller inclination angle) has a smaller slot diameter than the latter (the nozzle with the larger inclination angle), so that the oxygen jet of the former is weaker than that of the latter, so that the amount of spitting by the former is reduced. However, the amount of spitting by the latter increases. That is, when the top-blowing lance according to the present invention is used, the amount of spitting scattered in a direction closer to the vertical decreases, and the amount of spitting scattered in a direction farther than the vertical increases.

Here, spitting that scatters in a direction close to the vertical is likely to jump out of the system from the furnace port, but spitting that scatters in a direction farther than the vertical collides with the furnace wall and returns to the molten metal again. From the above, by using the upper blowing lance according to the present invention in which the amount of spitting scattered in the direction close to the vertical is small, the amount of spitting scattered out of the furnace port from the furnace port can be reduced as a result.

Here, if the ratio of the diameter of the "nozzle having a large inclination angle (θ ₂ )" to the diameter of the "nozzle having a small inclination angle (θ ₁ )" is 1.0 or less, the above-mentioned out-of-system scattering is considered. Needless to say, the effect of reducing the amount of spitting cannot be obtained.However, when the ratio exceeds 2.0, the intensity of the oxygen jet ejected from the nozzle having the larger inclination angle becomes excessively large, thereby increasing spitting. Have done
The desired effect of reducing spitting cannot be obtained.
Accordingly, the ratio of the other nozzle diameter to the nozzle diameter having the smaller inclination angle is limited to “the range of more than 1.0 and less than or equal to 2.0”, but is more preferably set to 1.2 to 1.8.

A second aspect of the present invention, in addition to the use of specific on-blown porous lance described above, "the slag basicity {= (% CaO) / ( % SiO 2)} to 2.8 to 3.8 Set and blow. " In other words, spattering has a large effect on the spattering properties.If the surface of the molten metal in the converter is uniformly covered with slag and good fluidity, the spattering will be greatly reduced. The basicity has a great influence on the fluidity of the slag. In order to improve the fluidity of the slag slag to an extent effective for preventing spitting, it is important to maintain the slag basicity at 3.8 or less. However,
The lower the basicity, the lower the viscosity of the slag and the easier it is to cover the molten metal surface evenly.
In the range of less than 2.8, the viscosity of the slag extremely decreases, and particularly when the CO gas generation rate is high, such as in high-speed blowing, there is a high risk of causing abnormal slopping, which is not desirable. Therefore, in the present invention, "the basicity of slag is 2.8
Set to 3.8 and perform blowing. "

By the way, in order to further enhance the effect of suppressing spattering scattering by covering the molten metal surface with the slag slag, slagging of the added auxiliary material is completed at an early stage and the final slag flow is reduced. It is desirable that the surface of the molten metal be covered with a cover slag having good fluidity. Then, in order to complete the slag slagging early, it is effective to promote the lowering of the melting point of the slag by maintaining (FeO) in the slag at a high level. Means for maintaining the slag (FeO) at a high level include:
Soft blowing at the beginning of blowing is effective. Therefore, in the present invention, if necessary, the acid supply rate from the upper blowing lance in the initial stage of blowing is in the range of 2.6 to 2.9 Nm ³ / min · t, and the feeding from the upper blowing lance in the middle stage of blowing to the end of blowing is performed. Blowing is performed by controlling the acid speed in the range of 3.0 to 3.4 Nm ³ / min · t.

FIG. 4 is an acid sending rate pattern diagram according to an example of the method of the present invention in which soft blowing is performed at the beginning of blowing. As described above, by suppressing the acid supply rate in the early stage of blowing and soft-blowing, it is possible to stabilize (FeO) in the slag to a high level. Can be completed.

Here, the reason why the acid feed rate at the time of soft blowing at the initial stage of blowing is 2.6 to 2.9 Nm ³ / min · t is that the acid feed rate at this time is higher than 2.9 Nm ³ / min · t. In addition, it is not possible to stabilize (FeO) in the slag to a high level, so that the slag cannot be rapidly lowered in melting point, and the effect of suppressing spitting scattering at the initial stage of blowing is reduced. On the other hand, if the acid feed rate during soft blowing is lower than 2.6 Nm ³ / min · t, the blowing time is prolonged, which adversely affects productivity and the refractory life of the converter. In the present invention, the term "initial blowing" refers to a period from the start of blowing until about 20% of the total blowing time elapses, and at least this period is set as a soft blow to suppress scattering of spitting. The effect is further improved.

Further, the acid feeding rate in the middle stage of the blowing to the last stage of the blowing is controlled to 3.0 to 3.4 Nm ³ / min · t, and the acid feeding rate in this period is less than 3.0 Nm ³ / min · t. And the blowing time is prolonged, which is disadvantageous in terms of productivity and the life of the refractory of the converter. On the other hand, if the acid supply rate exceeds 3.4 Nm ³ / min · t, the spitting amount increases remarkably, which is preferable. Absent.

Next, the present invention will be described by way of examples in comparison with the conventional method.

Example A low-carbon steel was melted by decarburization blowing under the conditions shown in Table 1, using a top-bottom blow converter with a molten steel amount of about 260 t / ch. The generated amount and iron yield were investigated. In addition, all blowing is a slag blowing using dephosphorized hot metal, and CO ₂ 200 is used as bottom blowing gas.
It was kept constant at 0 Nm ³ / hr. Here, the 6-hole lances used in the conventional method and the present invention have different specifications of the hole diameter and the inclination angle, but have an average sectional area of 1.66 per nozzle.
× 10 ³ mm ^2, were substantially the same as the 1.67 × 10 ³ mm ^2.

[0023]

[Table 1]

The results of the above investigation are summarized. First, FIG. 5 shows the "relationship between the amount of spitting generated during blowing and the amount of slag".
showed that. From the results shown in FIG. 5, it can be seen that both the conventional method and the method of the present invention increase the effect of suppressing spitting which is scattered with an increase in the amount of slag. Show me,
It can be seen that the method of the present invention can reduce the amount of spitting to approximately half that of the conventional method.

FIG. 6 is a graph comparing the iron yield between the conventional method and the method of the present invention. From FIG. 6, it can be confirmed that in the method of the present invention, the iron content scattered outside the system is suppressed due to the reduction in spitting, so that the iron content yield is improved as compared with the conventional method.

[0026]

[Summary of Effects] As described above, according to the present invention, it is possible to significantly reduce spitting during blowing in converter steelmaking, thereby avoiding troubles caused by sticking of metal to auxiliary equipment. In addition, the stability of the converter operation is remarkably increased, and industrially useful effects such as an improvement in the yield of iron, a prolonged life of refractory by shortening the processing time, and an energy saving effect can be secured. .

[Brief description of the drawings]

FIG. 1 is an explanatory view of a lower surface (ejection surface) of an upper blowing lance used in the method of the present invention.

FIG. 2 is an explanatory view of a vertical section (section AA in FIG. 1) of an upper blowing lance used in the method of the present invention.

FIG. 3 is an explanatory view showing a spitting generation mechanism in a use state of the upper blowing lance according to the present invention.

FIG. 4 is an acid feed rate pattern diagram according to an example of the method of the present invention in which soft blowing is performed at the beginning of blowing.

FIG. 5 is a graph showing “the relationship between the amount of spitting generated during blowing and the amount of slag” obtained in the example.

FIG. 6 is a graph comparing the iron yield of the conventional method and the method of the present invention confirmed in the examples.

Claims (2)

[Claims] 1. As an upper blowing lance, two types of Laval nozzles having different inclination angles are alternately arranged in the circumferential direction of a lance ejection surface, and the other nozzle diameter is smaller than the nozzle diameter having a smaller inclination angle. Use a ratio of 1.0 to 2.0 or less, and set the slag basicity to 2.8 to
A converter steelmaking method with excellent operational stability, characterized by blowing at 3.8. 2. The acid supply rate from the upper blowing lance in the initial stage of blowing is in the range of 2.6 to 2.9 Nm ³ / min · t.
2. The converter steelmaking method according to claim 1, wherein the blowing is performed by controlling each of the flow rates in a range of 3.0 to 3.4 Nm ³ / min · t.