JPH052723B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial field of application] In converters, blowing is often performed on hot metal that has been treated in a pretreatment furnace, etc. However, there are cases where preliminary treatment is not possible due to furnace repairs or troubles, etc. In this case, non-pretreated hot metal will be introduced directly into the converter. The present invention relates to a converter blowing method that is applied when refining non-pretreated hot metal in a converter, and particularly in a top/bottom blowing converter or a bottom blowing converter from non-pretreated hot metal to medium/ The present invention relates to a converter blowing method that exhibits excellent dephosphorous performance in producing high carbon steel and makes it possible to produce medium to high carbon steel. [Conventional technology] Converter blowing methods include top blowing method, bottom blowing method, top blowing method, and top blowing method.
There are bottom blowing methods, among which the bottom blowing method and top blowing method.
The bottom blowing method is considered to be a blowing method with excellent refining performance because it can utilize the stirring power generated by bubbling the bottom blowing gas. However, for the dephosphorization reaction, which is said to proceed mainly at the slag-metal interface, the stirring force of bottom blowing is not necessarily effective, and it is difficult to obtain a satisfactory dephosphorization effect in the production of low carbon steel. However, the dephosphorization performance of the bottom blowing method and the top/bottom blowing method in the production of medium and high carbon steel cannot be said to be very high, as will be described later. In other words, the reason why the dephosphorization ability decreases in the production of medium- to high-carbon steel is that the C-
This is because it is necessary to lower the oxygen potential in the steel due to O equilibrium, and it is also necessary to keep the total iron (FeO, Fe ₂ O _3, etc.) in the slag, which indicates oxidizing ability, to a low value. In other words, the dephosphorization reaction is said to depend on the total iron oxidation ability and CaO _activity shown by _the reaction formula below. As the oxygen potential decreases, the P oxidation ability of the slag decreases, and furthermore, the slag formation of lump quicklime (CaO source), which influences CaO activity, deteriorates, resulting in a decrease in P removal performance. In the end, although bottom-blown converters and top/bottom-blown converters are effective for refining reactions such as decarburization, they are not suitable for directly producing medium- to high-carbon steel from non-pretreated hot metal with a high P concentration. Therefore, the implementation of hot metal pretreatment is considered essential. Therefore, in steel plants that must produce both low carbon steel and medium/high carbon steel in top/bottom blowing converters, when producing medium/high carbon steel, the bottom blowing gas flow rate is reduced to a level that does not clog the nozzle. In ironworks that essentially carry out top-blowing refining and produce only medium- and high-carbon steel, bottom-blowing converters and top/bottom-blowing converters are rarely used, and the effects of bottom-blowing are not enjoyed. I don't have it. [Problems to be Solved by the Invention] The present invention has been made in view of these circumstances, and the present invention has been made by focusing on the above-mentioned circumstances. The purpose of this invention is to provide a converter blowing method that can be carried out when using a furnace or a top/bottom blowing converter. As mentioned above, the bottleneck in producing medium- to high-carbon steel from non-pretreated hot metal is the dephosphorization process.
This is a decrease in performance, and several proposals have been made regarding means for improving P removal performance. In other words, the idea of improving P removal performance is to
As can be understood from the reaction equation, the two methods are to increase the total iron in the slag or to promote the formation of lump quicklime into slag, and for the former method, adding FeO to the slag layer has also been proposed. However, since it also oxidizes the carbon in the steel and lowers the carbon concentration, it cannot be said to be a preferable means for producing medium- to high-carbon steel. On the other hand, the mechanism of turning lump quicklime into slag is thought to be as follows. Generation of low basicity slag by oxidation of Si Generation of 2CaO/SiO ₂ on the surface of lump quicklime Dissolution of _two layers of 2CaO/SiO into slag (liquid) (rate-limiting step) Dissolution of CaO at high basicity and the above One of these steps is the rate-determining step of slag formation, and in order to increase the sludge formation rate, it is effective to increase the dissolution rate. From this perspective
It has also been proposed to add CaF ₂ to improve the fluidity of slag. The present invention was developed as a result of research aimed at promoting the slag formation of lumpy quicklime under such circumstances, and as a result, it was discovered that the addition of Mn oxide was effective, and as a result of further research, it was completed. be. [Means for solving the problems] However, the method of the present invention performs bottom blowing of 0.03 Nm ³ /t・min or more on non-pretreated hot metal,
When performing converter blowing so that the blow-off carbon is 0.13% or more and the total iron in the blow-off slag is ₁₅ % or less, Mn is By charging oxide, the MnO in the blowing slag is
The key point is to control the amount to 8%. [Function] When Mn oxide is added to the slag, the melting point of the lump quicklime is lowered, and the lowering of the melting point promotes slag formation of the lump quicklime, increasing the dephosphorization reaction rate. The reaction progresses throughout the blowing period, but since it is assumed that the lump quicklime turns into slag, Mn oxide must be added during the entire blowing period before 60% of the total amount of O ₂ is blown. It may be added not only after the start of refining but also before the start of blowing. Regarding the amount of Mn oxide added,
It can be determined based on the amount of MnO in the blow-off slag, and it is necessary to add Mn oxide so that the MnO content in the blow-off slag is 4 to 8%. If the amount of MnO is less than 4%, the addition of Mn oxide is insufficient and the dephosphorization ability cannot be sufficiently increased;
If the amount exceeds 8%, MnO in the slag becomes too high, resulting in a decrease in CaO concentration and a decrease in P removal ability. In addition, added in the present invention
Examples of Mn oxide include Mn ore and iron-Mn ore. The constituent elements of the present invention are as described above, but as stated earlier, the method of the present invention is effective in producing medium- and mineral-carbon steel by blowing non-pretreated hot metal. Yes, the assumption is that the blow-off carbon is 0.13
% or more, and the total iron in the blowstop slag is
It is necessary to carry out blowing so that it is less than 15%. In addition, it is necessary to adopt a blowing method that performs at least bottom blowing, and the bottom blowing method or top/bottom blowing method is applied, and the amount of bottom blowing gas needs to be 0.03 Nm ³ /t・min or more. . Furthermore, the amount of bottom-blown gas is 0.03m ³ /
When the time is less than t.minutes, the problem arises that slopping becomes severe and iron loss increases. [Examples] The present invention will be further described below based on Examples. Using a converter reaction simulation system based on computer analysis, we determined the conditions for inputting auxiliary materials when producing medium- to high-carbon steel with a blowout carbon of 0.13% or more from non-pretreated hot metal with different amounts of Si. The results shown in Table 1 were obtained. Furthermore, the blowing temperature is 1675℃
The conditions were determined by setting the basicity to 3.0 to 4.4 and the amount of MnO in the blow-off slag to 5% (however, the amount of MnO contained in the non-pretreated hot metal was 2%).

[Table] Experiment 1 The slag making conditions were determined based on the auxiliary material input conditions in Table 1, and the hot metal (85 tons) shown in Table 2 was subjected to converter blowing, and the results shown in Table 2 were obtained. It was done. On the other hand, hot metal having the same composition was subjected to converter blowing under conventional slag-making conditions, and the results were compared with those of the above examples.

【table】

[Table] As shown in Table 2, by adopting the slag-forming conditions according to the present invention, the Mn yield was improved even though the slag-forming agent cost could not be reduced much, and the following effects were obtained. That is, in the present invention, the Mn ore added to promote the dephosphorization reaction increases the amount of Mn in the steel,
There is no need to add Fe-Mn again after converter blowing, and the reduction in Fe-Mn cost and the arc power cost required to melt Fe-Mn in an arc furnace have great economic effects. This is a contributing factor to the increase. Experiment 2 Non-pretreated hot metal was blown under the following slag making conditions, and the results of S removal and P removal using the method of the present invention were investigated, and the results shown in FIGS. 1 and 2 were obtained. As a comparative example, the results obtained when the same hot metal was blown under conventional slag forming conditions are also shown. The blow-off temperature is below 1675℃, and the blow-off carbon is
It was set at 0.15-0.40%. In addition, after blowing, the furnace was oscillated twice in opposite directions to calm down the slag, thereby preventing slag from flowing out from the furnace mouth when tapping started. As shown in FIG. 1, in terms of S removal, the Examples were slightly superior to the Comparative Examples, with almost no difference. On the other hand, regarding P removal, the Example lowered the blowout P concentration, confirming that the method of the present invention has an excellent P removal effect. [Effect of the invention] The present invention is configured as described above, and conventionally
We succeeded in achieving a sufficient dephosphorization effect in bottom-blowing or top- and bottom-blowing converter blowing of medium- and high-carbon steels, which had problems in terms of performance, and have successfully removed medium- and high-carbon steel from non-pretreated hot metal in converters. It became possible to produce steel.

[Brief explanation of drawings]

Figure 1 is a graph showing the S removal results of the example method and the conventional method, and Figure 2 is a graph showing the P removal results of the example method and the conventional method.
It is a graph showing the results.

Claims (1)

[Claims] 1. 0.03Nm ³ /t・ for non-pretreated hot metal
When converter blowing is performed by bottom blowing for more than 10 minutes, and the blow-off carbon is 0.13% or more and the total iron in the blow-off slag is 15% or less, 60% of the total O ₂ is emitted before the start of blowing. Before blowing, Mn oxide is charged to remove MnO in the blowing slag.
A converter blowing method characterized by controlling the temperature to ~8%.