JPS6356286B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for dephosphorizing hot metal, and in particular, in a refining process to obtain molten steel from hot metal as a raw material, as a preliminary step in steelmaking, a bottom blowing converter, a top and bottom blowing combined converter, or a top and bottom blowing converter are used. We are proposing improvements in the process of adding molten iron to molten iron in a blowing vessel that has similar functions to these, and this preliminary step is a continuation of this process. An additional process that precedes blowing in a normal steelmaking furnace such as a bottom-blowing converter, a top-bottom-blowing converter, or a top-blowing converter, which almost exclusively performs decarburization.
In other words, it belongs to the category of pretreatment methods for hot metal for steel making. (Prior art) Usually C/4.5, Si/0.20, Mn/0.40, P/0.140,
Hot metal containing S/0.020 (all of the above have a fat content of % by weight, and the same applies in the following descriptions) is injected with oxygen in the range of 8 to 18 Nm ³ per ton of hot metal through the furnace bottom tuyere. 30% each of finely powdered quicklime and fluorite per ton of hot metal in an oxygen stream
Add C/
3.7, Si<0.01, Mn/0.3, P/0.010, S/0.010
In the conventional hot metal pretreatment method, which can be summarized as obtaining low phosphorus, low sulfur hot metal that has been pretreated to a degree of Since it is added to the molten steel, the fine powder refining agent can be easily and properly blown into the molten steel.
In a short period of about 4 minutes, more than 90% dephosphorization can be achieved. The purpose of blending fluorite into the fine powder refining agent and adding it to the hot metal bath is to lower the viscosity of the slag during treatment and increase the reaction interface area with the hot metal, thereby increasing the dephosphorization effect. Located in
In particular, blowing powdered fluorite through the hearth tuyere is believed to be effective in reducing the viscosity of slag by increasing the chances of contact with powdered quicklime, and has traditionally been used. It has been implemented. However, in general, fluorite, which is obtained as a raw material, is turned into a fine powder, which requires large crushing equipment, electricity, and fuel. There were many problems in that it required facilities such as tanks for gas storage and extraction, and the maintenance costs for these facilities increased. (Problems to be Solved by the Invention) In order to solve the above-mentioned problems when using finely powdered fluorite, the present invention has developed a method in which fluorite is made finely powdered and blown from the bottom tuyeres of the hearth, unlike the conventional method. By injecting the fluorite into the blowing vessel from the top opening in the form of a lump without pulverizing it, the effect is not only the same as that of the conventional method of crushing the fluorite, but is even better than expected. This is a method for dephosphorizing hot metal that was invented based on the results of experiments. (Means for solving the problem) Hot metal is received in a blowing vessel that has a bottom blowing function for refining gas and can also add top blowing of the refining gas if necessary, and the bottom blowing refining gas is used in combination with the carrier gas. In the preliminary blowing treatment of hot metal, in which a powdered refining agent is injected into the hot metal, during which desilting and subsequent dephosphorization treatment are performed together with additional desulfurization treatment. The temperature rise of hot metal due to heat generation is suppressed by charging a coolant consisting of at least one of ore, mill scale, and scrap, and the temperature of hot metal during blowing is maintained in the range of 1250 to 1450 ° C. At the same time, the powdered refining agent is used to increase the slag basicity CaO/SiO ₂ after hot metal treatment with calcium oxide, its main component.
is blown into the hot metal under the condition that the value of In the case of bottom-blown refining gas, which is in the form of a lump and is charged from the top opening of the blowing vessel, the amount of oxygen is excluded, but the amount of oxygen based on the charging of the coolant consumed in the desiliconization reaction is included in the ton of hot metal. 8~15Nm per ³
per minute per ton of hot metal at the amount of oxygen determined within the range of
This is a hot metal dephosphorization treatment method characterized by blowing at a feed rate of 0.5Nm3 or ^higher . Many facilities such as the above-mentioned crushing equipment are no longer necessary according to this invention, and the auxiliary material inputting shooter, which is always installed in a general steel factory, can be used to input fluorite. ,
Since bulk fluorite can be charged and a higher dephosphorization rate can be obtained than in conventional methods, it also leads to a significant cost reduction in hot metal processing. (Function) In order to elucidate the dephosphorization mechanism when a bottom-blowing converter is used not specifically as a steelmaking furnace, but for hot metal pretreatment in the pre-steelmaking stage, we conducted various experiments to clarify the effects of fireflies on dephosphorization. Since it was unclear whether the significant effect of stone addition was due to its contribution to the lime grains sucked in from the bottom tuyeres or the effect on the slag on the hot metal, the inventors added fluorite in the furnace. It was discovered that when other operational factors are not changed, much higher dephosphorization results can be obtained than by injecting fine powdered fluorite, and the amount of fluorite used can be reduced compared to conventional methods. . Now, using a bottom-blowing converter for hot metal pretreatment to remove desulfurization in a short time, to proceed with dephosphorization, and to perform concomitant desulfurization, for example, Tetsu-to-Hagane 1980 No. 11 S730 ~733 reported. When carrying out the hot metal pretreatment method as described above, this invention first requires that the temperature of the hot metal during blowing be maintained at 1250 to 1450°C, and that calcium oxide, which is the main component of the powdered refining agent, be added to the furnace bottom tuyere. CaO/ after injection and treatment
The SiO ₂ should be 3 or more, and the blowing oxygen amount (gas oxygen supply amount + oxygen amount derived from the coolant - oxygen amount consumed for desiliconization) should be 8 to 15 Nm ³ per ton of hot metal. The grounds for limiting such conditions are shown in Figures 1, 2, and 3, respectively. The lower limit of the range limit is the minimum temperature at which the molten metal will not solidify even if the temperature drops during the next process, and the upper limit is the dephosphorization rate of at least 85% to eliminate the need for dephosphorization treatment in the next process. Therefore, it is limited based on the results shown in Figure 1. The lower limit of CaO/SiO ₂ is shown in Figure 2.
When SiO ₂ is 3 or more, it has a remarkable effect on improving the dephosphorization rate and reducing the demanganization rate, whereas when it is less than 3, there is no significant improvement in the dephosphorization rate, but the reduction in the demanganization rate is insufficient. By being. The lower limit of the amount of blowing oxygen is shown in Figure 3, and as with the upper limit of temperature, the upper limit is set to ensure a dephosphorization rate of 85%, and the upper limit is set at 3.0 C concentration, which does not require carburization to raise the temperature in the next process. %, the maximum amount to avoid decarburization exceeding this amount is 15 Nm ³ /t. The most important condition of this invention is that the fluorite to be charged as a solvent is charged from the top opening of the blowing vessel in the form of a lump, instead of being crushed or blown from the bottom tuyere as in the conventional method. That's true. Figure 4a shows the improvement in the dephosphorization rate and the decrease in the demanganization rate when powdered fluorite is used in combination with quicklime as a refining agent using the conventional method. In contrast, Fig. 4b shows an experiment in which quicklime powder was blown through the bottom tuyere, while fluorite was charged in the form of a lump from the top opening of the blowing vessel. . As is clear from comparing the two figures, even when bulk fluorite is used, the tendency for the dephosphorization rate to improve and the demanganization rate to decrease is the same as in Figure a. What is particularly noteworthy is that the minimum amount of fluorite required to obtain the lower limit of 85% dephosphorization rate mentioned above is 5% by weight of quicklime when simultaneously injecting powdered fluorite, whereas in this case when bulk fluorite is introduced. In the invention, about 2% by weight is sufficient. In order to further clarify this, only the dephosphorization rate is compared and shown in FIG. In other words, it is better to use powdered fluorite in the past.
It has been thought that it is highly effective in dephosphorizing by accelerating the decrease in the viscosity of the slag, but in fact, the opposite results were produced as shown in Figure 4 a and b. The reason for this is not yet clear, but the inventors found that when powdered fluorite is injected, some of the injected fluorite is incorporated into oxygen bubbles, which prevents it from coming into contact with quicklime and causes it to float to the surface. It was speculated that fluorite escapes from the furnace together with the generated gas without forming slag, and its effect on reducing the viscosity of slag is inferior to that of adding bulk fluorite. Above, we have explained the case where fluorite is used alone as a solvent, but in addition, cryolite, colemanite, and red mud can be used alone or in combination with fluorite.
When we conducted an experiment using more than one species in the same way, we found that
Even at the same blending ratio as shown in FIG. 5, charging the bulk powder above the furnace was more effective in improving the dephosphorization rate than fine powder injection. Table 1 shows the data of the embodiment according to the present invention in comparison with the conventional method.

【table】

[Table] The only operating condition that differs from the conventional method in this invention is that the fluorite is added in the form of a lump over the furnace, but the same processed hot metal can be obtained with a smaller amount of fluorite. There is. (Effect of the invention) By implementing this invention, the cost of crushing fluorite (electricity and heating cost for removing moisture) will be completely eliminated.
In addition, maintenance costs for equipment for crushing fluorite and transportation piping become unnecessary. In addition, when constructing a new facility for hot metal pretreatment using a bottom-blown blowing vessel,
Conventionally, crushing equipment was required not only for crushing quicklime but also for crushing fluorite, but in the future, equipment for fluorite will no longer be necessary, and equipment costs can be expected to be reduced. As described above, according to the present invention, the amount of the solvent used to promote the effective dephosphorization effect of the hot metal pretreatment in which the powdered refining agent is blown into the hot metal bath together with the bottom blowing gas is increased. It becomes possible to reduce the contribution rate to below, especially by omitting the crushing process. In addition, although the example shows the case where a bottom blowing converter is used as the blowing vessel, the key point of the method of this invention is to charge the solvent such as fluorite from above the furnace in the form of lumps. Needless to say, it can be applied in exactly the same way to a top-bottom blowing converter.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the hot metal temperature during blowing and the dephosphorization rate, and Figure 2 is the basicity of the slag after treatment.
Figure 3 shows the relationship between CaO/SiO ₂ , dephosphorization rate, and demanganization rate. Relationship graph, Figure 4a is a graph of the relationship between the fluorite blending ratio, dephosphorization rate, and demanganization rate when powdered fluorite is injected from the bottom tuyere, Figure 4b
Figure 5 is a graph showing a similar relationship when fluorite is charged in the form of a lump from above the furnace, and Figure 5 is a graph comparing the dephosphorization rate between fluorite injection and furnace charging.

Claims (1)

[Claims] 1. Hot metal is received in a blowing vessel which has a bottom blowing function for refining gas and can also add top blowing of the refining gas if necessary, and the bottom blowing refining gas is used together with the carrier gas to form powder. In the preliminary blowing process of hot metal, in which a refining agent is injected into the hot metal, and during this process desilicification and subsequent dephosphorization treatment are performed together with additional desulfurization treatment. The temperature rise of the hot metal produced is suppressed by charging a coolant consisting of at least one of ore, mill scale, and scrap, and the temperature of the hot metal during blowing is maintained in the range of 1250 to 1450 ° C. , The slag basicity CaO/SiO ₂ after hot metal treatment using the above powdered refining agent with its main component calcium oxide
is blown into the hot metal under the condition that the value of In the case of bottom-blown refining gas, which is in the form of a lump and is charged from the top opening of the blowing vessel, the amount of oxygen is excluded, but the amount of oxygen based on the charging of the coolant consumed in the desiliconization reaction is included in the ton of hot metal. 8~15Nm per ³
per minute per ton of hot metal at the amount of oxygen determined within the range of
A hot metal dephosphorization treatment method characterized by blowing at a feed rate of 0.5Nm3 ^or higher. 2. The method according to claim 1, wherein the blowing vessel is a bottom blowing converter. 3. The method according to claim 1, wherein the blowing vessel is a top-bottom blowing converter.