JPH03180419A - Refining method by blowing in converter - Google Patents

Abstract

PURPOSE:To enhance the yields of Mn and Fe and to inhibit the erosion of refractories by adding an MgO source to steel making slag in the last stage of refining by blowing so as to lower the potential of oxygen in the slag and to reduce the ability of the slag to capture MnO and FeO. CONSTITUTION:Molten pig iron is pretreated to remove Si, P and S. When this treated molten pig iron is refined by blowing in a converter, the concn. of MgO in slag can be increased by adding an MgO source to the slag in the early stage of refining but the m.p. of the slag is increased by the increased concn. Of MgO and it becomes difficult to allow slagging to proceed. As a result, the erosion of refractories and defective dephosphorization are caused. In order to prevent the erosion and defective dephosphorization, the MgO source is added to the slag in the last stage of refining.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention reduces the accuracy of blowstop C and increases the S content when pretreated hot metal is subjected to converter blowing with a minimum slag. This invention relates to a method that can increase the Mn yield without causing such problems.

[Prior art] When hot metal that has been pretreated (de-St, de-P, de-S) on a hot metal gutter, in a ladle, or in a hot metal pre-treatment furnace is blown into a converter, de-P and de-S are carried out in the converter. Since there is no need to perform S, etc., the amount of slag-forming agent added is kept to the minimum amount necessary to protect the converter firewall, reducing the slag-forming agent consumption rate and reducing Mn.
Efforts are being made to reduce the amount of Mn@ added by improving yield.

In this case, in order to further reduce the amount of Mn trapped in the slag and increase the Mn yield, and to reduce the amount of T-Fe in the slag, a C source (coke, graphite, etc.) is added to the slag at the final stage of blowing. A method has also been proposed in which Mn oxides and Fe oxides in slag are reduced to yield molten steel.

[Problem to be solved by the invention] However, when a C source is added to the slag at the final stage of blowing, the C
Not only does a part of the carbon source dissolve into the molten steel, reducing the accuracy of blow-stop C, but also the impurities contained in the carbon source are incorporated into the molten steel, increasing the S concentration. will arise.

The present invention has been made in view of these problems, and its purpose is to reduce the accuracy of blowstop C accuracy and to reduce the accuracy of blow stop C when blowing hot metal that has undergone preliminary treatment in a converter furnace with minimum slag. without causing problems such as an increase in Sili
The aim is to establish a blowing method that can reduce the amount of Mn and T-Fe in slag and increase their yield.

[Means for Solving the Problems] The configuration of the converter blowing method according to the present invention that can solve the above problems is that Si is removed by preliminary treatment.

The gist of this method is to add an MgO source to the slag at the final stage of blowing when hot metal that has been subjected to P and S removal treatment is subjected to converter blowing.

[Operations] When blowing hot metal that has been buried in a converter to remove Si, P, and SIA through preliminary treatment, it is only necessary to form enough slag to suppress melting damage of the converter refractory wall as described above. Therefore, as mentioned above, the minimum amount of slag-forming agent (CaO, light calcined dolomite, etc.) is required.
In addition, slag minimum operation is carried out. Therefore, compared to normal blowing operations, the amount of Mn and Fe lost as oxides in the slag can be suppressed to a low level, but a considerable amount of Mn oxides and Fe oxides are still trapped in the slag. In particular, Mn is easily oxidized and is easily captured by lithium slag, which is an oxide. Therefore, Mn ore, Mn-based ferroalloy, etc. are added as a Mn source before the start of blowing or at an appropriate time during blowing operation. However, some of the Mn is taken into the slag and becomes a loss. From this point, the Mn@ compound in the slag is reduced to produce Mn.
In order to increase the yield of Mn into molten steel, a method has been proposed in which the Mn oxides in the slag are reduced by adding a C source at the end of the blowing process, as described above, but this method causes the problems mentioned above. It's coming.

Therefore, the Mn
As a result of conducting various studies in an attempt to develop a method that could increase the yield, it was found that adding an MgO source at the final stage of blowing lowers the oxygen potential of the slag and causes Mn trapped in the slag to migrate into the molten steel. It has been found that the amount of T-Fe in the slag is reduced and the yield of Mn and Fe can be effectively increased, and the problems pointed out in the prior art do not occur at all.

The reason why such an effect can be obtained is considered as follows. That is, when an MgO source is added to the slag to increase the MgO concentration, the oxygen potential in the slag decreases, the amount of T-Fe decreases, and the Mn trapping ability also decreases. For example, Figure 1 shows the isoactivity diagram of FeO in steelmaking slag, and as is clear from this diagram, as the amount of MgO in the slag increases, the oxygen potential of the slag decreases. . Moreover, FIG. 2 shows S i O, -C
This shows a saturation curve diagram of each component in the aO-MgO-Fern system, and from this diagram, the white arrows [A]
As shown in , when the amount of MgO in the slag is increased, Fern
It can be confirmed that the saturation amount of slag decreases and the oxygen potential of the slag decreases.

Thus, steelmaking slag at the final stage of blowing! : By adding the MgO source, the oxygen potential of the slag is reduced, and the MnO and FeO trapping ability of the slag is reduced. As a result, excess Fe and Mn are transferred to molten steel, and the yield of Mn and Fe is improved. Therefore, the amount of Mn source added for adjusting the amount of Mn can be reduced compared to the conventional example. Moreover, since MgO has a high melting point (approximately 2800°C), adding an MgO source to steelmaking slag makes the slag have a high melting point and increases viscosity, suppressing slag foaming and causing melting of the converter firewall. The suppressive effect is also enhanced. In addition to MgO, light calcined dolomite (CaO/Mg0) is an MgO source.
, raw dolomite (Ca COs ・M g COs )
, metallic Mg, etc. are used, but since these do not contain C, there is no risk of adversely affecting the accuracy of the blow-stop C, and they also contain almost no harmful components such as S. , there is no problem of increasing the S concentration of molten steel.

By the way, as for the timing of adding the MgO source, it is possible to increase the MgO concentration in the slag from the beginning by adding it at the beginning of blowing, but in this case, the melting point of the slag will rise due to the increase in the MgO concentration. However, it becomes difficult for the slag to become slag. As a result, problems such as melting of the refractory and poor dephosphorization reaction due to unslag formation tend to occur, so it is preferable to add it at the final stage of blowing (for example, about 1 to 2 minutes before the end of blowing). is good, and taking economic efficiency into consideration, the preferable addition amount is M
In terms of gO, it is about 0.1 to 5 kg per ton of hot metal.

[Example] Under the following conditions, a converter blowing experiment of 30 charges was conducted for each of Groups (1) and (2), and the Mn yield and blow-off C amount of the obtained molten steel were compared.

Group ■ (comparative example): 2.5 liters of coke 1 minute before blow-off
Added 2.5 kg/kg/kg (30 charges) Group ■ (Example): Added 2.5 kg/lightly calcined dolomite 1 minute before blow-off (30 charges) (Experimental conditions) Nigelup [Co., Ltd.], ■ Common Disaster Ridan ...
95 tons of hot metal + 5 tons of scrap 4 companies 1-C: 4
．． 00-4.1G, Si: tr.

Mn: 0.50-0.60. P:
0.010 to 0.013. S: 0.014~
0.017, Temperature = 1300-1320°C Kensou 1...CaO: 7.3kg/)n, light calcined dolomite: 5.2kg/)n, and Sin
2:t, OKG/)) is pre-charged immediately after the start of blowing. All gaseous oxygen is supplied from the top blowing oxygen lance at a constant oxygen supply rate (2.8 ONm'/min/ton). The supply and lance height was set at 2000m+* from the hot water level.

i Back end...Blow end C: 0.25%, Blow end temperature: 1
The temperature was controlled to be 60°C.

The results are shown in Table 1 as average values.

As is clear from Table 1, the conventional method (group ■)
In contrast, in the present invention (Group ■), no increase in blow-off C was observed, and the standard deviation was also large and the Mn yield was relatively low. The deviation is also small, and the Mn yield is improved by about 2%. In the above-mentioned blowing experiment, when we visually observed the state of slag coating on the refractory surface after blowing, we found that Group ■ (method of the present invention) had better coating due to the improvement in viscosity caused by the rise in the melting point of the slag. It was confirmed that they were demonstrating their sexuality.

[Effects of the Invention] The present invention is configured as described above, and has a high level of blowout C.
M while maintaining accuracy and without increasing S concentration.
n Yield can be improved, and T-F in slag can be improved.
Fe loss can also be reduced by reducing e. Moreover, it is possible to obtain practical effects such as the ability to suppress melting loss of converter refractories by improving the viscosity of the slag.

[Brief explanation of drawings]

Figure 1 is the isoactivity diagram of FeO in steelmaking slag, Figure 2
The figure shows S 10 x -Ca O-M g O-FeOn
This figure shows a saturation curve diagram of each component in the system slag.

Claims (1)

[Claims] A converter blowing method characterized by adding an MgO source to slag at the final stage of blowing when hot metal that has been subjected to preliminary treatment to remove Si, P, and S is subjected to converter blowing.