JPS621445B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing steel using an oxygen top-blown steelmaking method. When adding a slag-forming agent to molten iron (molten pig iron or molten steel) in the oxygen top-blown steelmaking process, simply adding the auxiliary raw materials such as quicklime, limestone, fluorite, and dolomite in powder form will cause the slag to be generated by reactions in the furnace. Since it scatters due to the pressure of carbon oxide gas, etc., to prevent this, it is usually added in the form of a lump. In such steel manufacturing methods, sloping usually tends to occur before and after the desiliconization stage. This trend is
This is particularly noticeable in high-speed blowing, which is performed to improve productivity. The reason for this is that the main component of quicklime and limestone is calcium oxide (CaO), which has a high melting point (2570°C), so it is difficult to completely dissolve them during the desiliconization stage and promote slag formation. Moreover, even if a large amount of these is added, a highly foamable slag with a slag basicity of about 1.5 to 1.6 at the end of the desiliconization period is produced. Furthermore, after the desiliconization is completed, the amount of gas generated rapidly increases due to the decarburization reaction, which also promotes the occurrence of slopping. To deal with this, a stirring gas such as inert gas, oxygen gas, carbon dioxide gas, nitrogen gas, propane gas, etc. is blown below the bath surface to allow the slag metal reaction to proceed uniformly and prevent rapid gas generation. However, it is difficult to sufficiently suppress the occurrence of slopping caused by high-speed blowing. Furthermore, if the slag-forming agent is added in the form of lumps, the slag formation at the end of blowing will become unstable, and the phosphorus concentration [P] in the molten steel at the end of blowing will not be constant. Problems such as a decrease in productivity and an increase in consumption of ferroalloy and solvent arise due to the implementation of blowing. On the other hand, for example, the applicant of the present application
As proposed in No. 9311, a powder of one type of slag-forming agent or a powder of a mixture of two or more types of slag-forming agents is mixed into a top-blown oxygen stream and added to molten iron, and the blowing is performed by top-blowing with oxygen. During the period of operation or until the subsequent discharge period after completion of blowing, inert gas, nitrogen gas,
There is a refining method in which a stirring gas such as oxygen gas is blown below the bath surface, and this method has excellent refining properties. However, with this method, depending on the addition rate of powder such as quicklime, the slag basicity may change before or after the end of the desiliconization period.
1.5 to 1.6 and slopping occurs, or if the addition of powder is completed in the middle of blowing, as the steel bath temperature rises in the later stages of blowing, rephosphorization from the slag to the steel bath will occur, causing the end point of blowing to occur. Problems arise such as the phosphorus concentration [P] in the molten steel being inconsistent. Furthermore, if the entire amount of the slag forming agent is added as a powder, there is also the problem that the cost of pulverizing the slag forming agent into powder is high. The present invention was made to solve these problems, and it prevents the occurrence of sloping before and after the end of the desiliconization period, prevents rephosphorization due to the rise in steel bath temperature in the late blowing period, and By stabilizing slag formation at the final stage of blowing, the aim is to stabilize blowing, improve the quality of finished steel, and improve raw material yield.
Furthermore, it is an object of the present invention to reduce the cost of crushing a slag-forming agent to obtain a powdered slag-forming agent necessary for top-blowing the powder of the slag-forming agent. The steel manufacturing method according to the present invention is an oxygen top-blown steel manufacturing method that involves blowing stirring gas below the bath surface, and a slag-forming agent containing one or more of quicklime, limestone, dolomite, etc. and, if necessary, manganese. Less than 70% of the total addition amount of ore and/or iron oxide is added to the molten iron in the form of lumps, and the rest is mixed into the top-blown oxygen stream in the form of powder and added to the molten iron, and the desiliconization period is completed. By this time, the basicity of the slag is set to 2 or more by adding a slag-forming agent in powder form, and the slag-forming agent is added in powder form at least 2 minutes before the end of blowing until the end of blowing. It is characterized by DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail based on the drawings. FIG. 1 is a schematic vertical cross-sectional view showing the implementation state of the present invention, FIG. 2 is a vertical cross-sectional view showing the configuration of the nozzle head of a top-blowing oxygen lance used in the implementation of the present invention, and FIG. 3 is a bottom view of the same. It is. CV is a converter, and hot metal tapped from the blast furnace is charged into the converter CV after being subjected to _hot metal preliminary treatment. Oxygen gas for blowing is blown by the blowing oxygen lance L, and converter blowing is performed. Further, the top-blowing oxygen lance L is also used to blow a powder slag forming agent together with the blowing oxygen gas, as will be described in detail later. Above the converter CV, there is an exhaust gas recovery hood H that collects exhaust gas generated in the furnace during blowing and guides it to exhaust gas treatment equipment (not shown). It is placed above ₁ . An auxiliary raw material inputting chute S is provided at an appropriate position of this exhaust gas recovery hood H, and the slag-forming agent is fed into the converter furnace in the form of lumps from the chute S.
Added to CV. The top-blown oxygen lance L is located at the nozzle head portion A.
The interior of the nozzle head part A includes a powder supply passage 11, an oxygen supply passage 12, and a cooling water supply passage through cylindrical walls 1, 2, 3, and 4 arranged concentrically. A supply passage 13 and a cooling water drainage passage 14 are formed concentrically in this order from the center side to the outer circumferential side of the nozzle head portion. The lower surface of the nozzle head part A has a central nozzle 1 that opens at its center.
5 and three peripheral nozzles 16 that are opened on a concentric circle of the central nozzle 15 and spaced apart from each other at equal angles.
The lower end of the powder supply path 11 is connected to the central nozzle 15, and the oxygen supply path 12 is closed.
The lower ends of the cooling water supply passage 13 and the cooling water discharge passage 14 are connected to each other by a communication passage 17 below the cylindrical wall 3 formed in the nozzle head portion A. It is communicated. The upper end of each of the cylindrical walls 1 to 4 of the nozzle head part A has the same diameter as each of the cylindrical walls 1 to 4 constituting the lance body B, and an inner tube 5 disposed concentrically;
It is connected to the lower ends of the inner tube 6, the partition tube 7, and the outer tube 8. Although not shown in the drawing, the upper end of the inner tube 5 is made of powder of one type of sludge-forming agent such as quicklime, limestone, fluorite, and dolomite, or a powder of a mixture of two or more of them (hereinafter simply referred to as powder). ), and if necessary, connected to a tank for storing one or more types of manganese ore and iron oxide, and a tank for carrier gas such as oxygen gas, inert gas (argon gas, etc.), nitrogen gas, water vapor, etc. The powder is guided to the central nozzle 15 through the inner tube 5 and the powder supply passage 11 formed in the cylindrical wall 1, accompanied by a carrier gas such as oxygen gas or inert gas. The upper end of the middle pipe 6 is connected to an oxygen tank (not shown), and each Peripheral nozzle 16
guided by. The upper end of the partition pipe 7 is connected to a water supply tank (not shown), and the upper end of the outer pipe 8 is connected to a drainage basin (not shown). The cooling water supply path 13 formed between the cooling water supply path 13 and 3 reaches a communication path 17 at the lower end of the cooling water supply path 13, and through this communication path 17, water flows between the cylindrical walls 3 and 4 and between the outer tube 8 and the partition tube 7. The water is drained through the formed cooling water discharge passage 14 to cool the nozzle head A and the lance body B. The central nozzle 15 is constructed by forming an introduction part 15a connected to the lower end of the powder supply passage 11 and a cylindrical part 15b serving as a throat part connected to the lower end of the introduction part 15a, concentrically with the axis of the powder supply passage 11. There is. The introduction part 15a is formed so that its diameter gradually decreases as it goes downward from the lower end of the powder supply path 11, that is, toward the injection port, so that the inner circumferential wall forms an inverted truncated cone shape, and the cylindrical part 1
5b has the same diameter as the lower end of the introduction part 15a, and its lower end is opened at the lower bottom surface of the nozzle head part A as an injection port, and the powder is fed through the powder supply path 11 with the carrier gas. The body is introduction part 15
a, it is pressurized through the cylindrical portion 15b, and is injected straight onto the extension of the cylindrical portion 15b. Introductory part 15 to the axis of the powder supply path 11
a, the inclination angle α of the peripheral wall, the length l ₁ in the axial direction of the introduction part 15a, the diameter d of the cylindrical part 15b, and the cylindrical part 1
There is no particular limitation on the axial length _l2 of 5b, but if the inclination angle α of the peripheral wall of introduction part 5a is too large, the resistance to the powder, in other words, the influence of the grinding action from the powder. Since this increases, it is desirable to make it as small as possible within the range that allows the necessary powder velocity to be obtained. Further, the peripheral nozzle 16 is constituted by a cylindrical portion 16a that is a throat portion continuous to the lower end of the oxygen supply path 12, and a diverging portion 16b continuous to the cylindrical portion 16a. The cylindrical portion 16a is formed obliquely downward at an angle θ from the inner bottom of the U-shaped blocking wall at the lower end of the oxygen supply path 12 so that the lower end approaches or moves away from the axis of the central nozzle 15. Further, the divergent part 16b is formed with a diameter gradually increasing from the upper end side to the lower end side, and its axial center line is on the same straight line as the axial center line of the cylindrical part 16a, and the lower end side is the central part. It is formed to be inclined at an angle θ toward or away from the axis of the nozzle 15, and the peripheral wall of the diverging portion 16b on the powder supply path 11 side is inclined with respect to the axis of the central nozzle 15. The peripheral wall on the opposite side is inclined at an angle θ ₂ in a direction away from the axis of the central nozzle ₁₅ , so that the oxygen supplied in the oxygen supply path 12 is The oxygen gas is pressurized through the cylindrical portion 16a and the diverging portion 16b, is accelerated, and is injected onto an extension line of the diverging portion 16b. The top-blown oxygen lance L configured in this way is
As shown in Figure 1, the tip position is at the required height relative to the molten iron level in the converter CV (hot metal charged into the converter CV after preliminary treatment or molten steel being refined). It is inserted like this. The powder that is injected from the central nozzle 15 of the lance L together with the carrier gas and the oxygen gas that is injected from the peripheral nozzle 16 have a mutual flux at the surface or the fire point of the molten iron. The jets are cross-injected, so that the powder is guided into the bath without being scattered. The reason why the powder is mixed into the top-blown oxygen stream and added to the molten iron is that the powder, which becomes turbid in the top-blown oxygen stream, is directly supplied to the ignition point, rapidly turned into slag, and can be added to the molten iron at any time. The basicity of the slag can be controlled, and after the powder rushes into the molten iron with oxygen, dephosphorization proceeds directly during the floating process, and together with rapid slag formation after floating, dephosphorization and desulfurization occur. This is because it is carried out smoothly. Note that it is also possible to mix the powder into the blowing oxygen stream using a normal lance as a top-blowing oxygen lance, but according to this method, the powder is supplied into the high-pressure oxygen gas pipe. This method requires a device, which is undesirable because it increases equipment costs, and it also has the disadvantage that the Laval nozzle is subject to severe wear and tear due to powder, resulting in a short lance life. The converter CV is provided with one or more (in FIG. 1, two at the bottom) tuyere N on the bottom or side wall of the converter. gas, etc.), nitrogen gas, oxygen gas, carbon monoxide gas, carbon dioxide gas, etc.
The seeds or more are blown in at a blowing rate of 0 to 0.5 Nm ³ /min·T. This blowing amount is 0 to 0.5Nm ³ /min.
The reason for this is that when it exceeds 0.5Nm ³ /min・T, the concentration of iron oxide (FeO) in the slag in the medium and high coal region decreases rapidly, and the powder (for example, powdered lime) is exposed to top-blown oxygen. This is because even if it is mixed and added to the air stream, the dephosphorization of medium and high carbon steel will not be achieved sufficiently. Now, when performing converter blowing as described above, the conditions for adding a slag forming agent to molten iron are such that the slag basicity is 2 or more from the start of blowing to the end of desiliconization, and The slag forming agent in powder form shall be added from at least 2 minutes before the end of blowing until the end of blowing. The reason why the slag basicity should be 2 or more by the end of the desiliconization period is to prevent sloping that occurs before and after the desiliconization period, to prevent loss of iron, etc., and to improve operational efficiency. This is to stabilize the situation. That is, gas generation due to the decarburization reaction becomes significant around the end of the desiliconization period, but if the slag basicity is 2 or more by that point, the foaming property of the slag will be small and the expansion of the slag due to gas will be suppressed. This is because the occurrence of sloping is prevented. In addition, in the present invention, since the powder is mixed into the top-blown oxygen stream and supplied directly to the ignition point, the slag conversion rate at the time of supply is approximately 100%, and the slag is easily removed. The basicity can be controlled, and the slag basicity can be effectively made 2 or more by the end of the desiliconization period. By the way,
FIG. 4 is a graph showing the comparison results of the slag formation rate when the method of adding the slag forming agent is changed, with the horizontal axis representing the carbon concentration [C] in molten steel and the vertical axis representing the slag formation rate. .
In the figure, A indicates the injection of stirring gas below the bath surface (bottom blowing gas: argon gas, injection amount: 0.1Nm ³ /min.
A method of top-blowing slag-forming agent powder while carrying out T);
B is a method in which the slag-forming agent is added in chunks while blowing stirring gas under the bath surface, and c is a method in which the slag-forming agent is added in chunks without blowing stirring gas under the bath surface. The method of adding as is is shown below, and it can be seen that the slag formation rate in case A according to the present invention is approximately 100% as described above, which is extremely excellent. In addition, the condition of adding the powder by mixing it into the top-blowing oxygen stream at least 2 minutes before the end of blowing is to stabilize the slag formation at the end of blowing, and to add the powder to the top blowing oxygen stream at least 2 minutes before the end of blowing. In addition to stabilizing the phosphorus concentration [P], it also prevents phosphorus from returning to the steel bath from slag, which occurs as the bath temperature rises at the end of blowing during the melting of medium-high carbon steel. This is to stabilize the That is, if the addition of the powder is stopped more than 2 minutes before the end of blowing, a rephosphorization phenomenon will occur from the slag to the steel bath as the steel bath temperature rises, and the re-injection of powder will be inhibited. Since a sufficient dephosphorization effect cannot be obtained by adding the slag-forming agent even if the process starts 2 minutes before the end of blowing, the powder is mixed into the top-blown oxygen stream again at least 2 minutes before the end of blowing. Therefore, we decided to add it. By performing the blowing process as described above, it is possible to prevent the occurrence of slopping before and after the end of the desiliconization period, to prevent post-phosphorus formation due to the rise in steel bath temperature in the late blowing period, and to stabilize slag formation at the end of the blowing period. be able to. Further, as long as the powder can be added so as to satisfy the above-mentioned conditions, a part of the slag-forming agent may be added in the form of a lump. The amount that can be added in lump form depends on the target phosphorus concentration in molten steel [P]
Although it varies depending on the level of slag forming agent, according to numerous experiments by the present inventors, for steel types with a normal end point [P] level ([P] 0.020%), 70% of the total amount of slag-forming agent added It is possible to add it in the form of lumps up to By adding a considerable amount of the slag-forming agent in the form of a lump in this way, it is possible to reduce the grinding cost for turning the slag-forming agent into powder. Next, examples of the method of the present invention will be described. In a 15-ton pure oxygen top-blown converter equipped with two tuyeres each having a bottom-blowing nozzle with an inner diameter of 12.7 mmφ, a top-blowing oxygen lance (peripheral nozzle) similar to that explained in Figs. 2 and 3 was used. The inner diameter of the throat is 14
Converter blowing was performed using a diameter of 16 mmφ and the inner diameter of the central nozzle was 16 mmφ. Table 1 shows the slag-forming agent addition conditions, and Table 2 shows the hot metal conditions. The conditions are those according to the present invention, the conditions are that the timing of addition of the powder slag forming agent at the end of the blowing stage is shifted, and the conditions are that 70% or more of the slag forming agent is added in the form of lumps (therefore, the desiliconization period has ended). (It is not possible to ensure the slag basicity to 2 or more and to control dephosphorization at the end of blowing), and the conditions are that the entire blowing period cannot be controlled without considering the cost of the slag-forming agent, especially its crushing cost. (Until the end of the desiliconization period, the powder was blown so that the basicity of the slag was 2 or more.)
In both cases, the top blowing oxygen flow rate is 2200N.
m ³ /hour, powder carrier gas flow rate is 200Nm ³ /
At this time, the flow rate of bottom blowing gas (argon gas) is 200N.
m ³ /hour, and the distance between the lance surfaces was 1000 mm. Furthermore, the main raw materials in each case are hot metal: 15T and scrap: 3T. The blowing results are shown in Table 3. From this table, it can be seen that in the case of the present invention, the occurrence of sloping and the phosphorus concentration [P] in the molten steel at the end point were lower than in the case of other conditions except for the following conditions. It can be seen that the results are also excellent. In addition, the case according to the present invention shows comparable results even when compared with the case under these conditions, and it can be said that the case according to the present invention is superior when considering the crushing cost of the slag forming agent, etc. As detailed above, in the present invention, in the method of melting steel using the oxygen top-blown steelmaking method,
Powdered slag-forming agent is mixed into the top-blown oxygen stream under specified conditions and added to hot metal, and the total amount of slag-forming agent added is
Since 70% or less is added as a lump, it prevents slopping before and after the completion of desiliconization, prevents rephosphorization due to rise in steel bath temperature in the late stage of blowing, and prevents slag formation in the final stage of blowing. It is possible to stabilize the blowing process, improve the quality of finished steel, and improve the raw material yield, as well as reduce the cost of crushing the slag forming agent required to obtain the powder slag forming agent. The present invention has excellent advantages in melting steel.

【table】

【table】

【table】 be effective.

[Brief explanation of the drawing]

FIG. 1 is a schematic vertical cross-sectional view showing the implementation state of the present invention, FIG. FIG. 4 is a graph showing changes in the sludge forming rate due to differences in the method of adding the sludge forming agent. CV...Converter, L...Top-blowing oxygen lance, A...Nozzle head, B...Lance body, 15...Central nozzle, 16...Peripheral nozzle, S...Sub-material input chute, N...Tuyere.

Claims (1)

[Scope of Claims] 1. In an oxygen top-blown steelmaking process involving the injection of stirring gas below the bath surface, a slag-forming agent containing one or more of quicklime, limestone, fluorite, dolomite, etc.; One or more types of manganese ore and iron oxide are added to the molten iron in the form of lumps, up to 70% of the total addition amount, and the rest is mixed into the top-blown oxygen stream in the form of powder and added to the molten iron. The slag basicity is set to 2 or more by the end of the desiliconization period, and the slag forming agent is added in powder form from at least 2 minutes before the end of the blowing to the end of the blowing. Steel manufacturing method.