JPS6014813B2 - Method for smelting molten steel using sodium fluoride flux - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a new molten steel that rapidly dephosphorizes, desulfurizes, and deoxidizes high-alloy molten steel (hereinafter referred to as molten steel) similar to ordinary molten steel and high-nickel molten steel. This relates to a smelting method.

Flux or slag components conventionally known as dephosphorization and desulfurization agents for molten steel include Ca○, CaCQ, CaC12, and CaS.
04, CaF2 containing metal Ca, Na20
, ZNa2C03, Na2S04, Na2&07, K2
0, &03, FeC12, MnC12, CrC13, F
There are eF3, MnF2, CrF3, etc., and these are smelted in a container lined with magnesia-based, dolomite-based, alumina-based, or graphite refractories, either alone or by adding two or more of these at the same time. In some cases, oxygen gas, iron oxide, manganese oxide, etc. are added as oxidizing agents to improve the dephosphorization rate. Among these additives, CaF2 is added for the purpose of lowering the melting temperature of flux or slag and improving fluidity, and although it has the effect of increasing the dephosphorization and desulfurization rate, it does not directly affect the dephosphorization and desulfurization reaction. It is not involved. The present invention is completely different from the above-mentioned known smelting method that uses a simultaneous dephosphorization and desulfurization agent. A rapid and effective simultaneous dephosphorization and desulfurization reaction is caused by contacting molten iron with sodium fluoride alone or a sodium fluoride flux prepared by adding quicklime in an amount of not more than 2% by weight at the same time using a strained container. This is a novel smelting method characterized by allowing deoxidation to proceed to a considerable extent.

The quicklime-based crucible or container lined with quicklime-based refractories used in the present invention refers to quicklime containing at least 95% by weight of Ca09 or more, or a small amount of calcium chloride and/or titanium oxide. It is a refining vessel lined with a lime-based crucible and refractories of the same quality, at least in the part that comes into contact with molten steel.

The findings obtained through experiments conducted by the present inventor using the above-mentioned container will be summarized below along with specific methods.

Put 300 kg of pure iron in a Ca○ crucible, evacuate the atmosphere, introduce argon, heat by high frequency induction in an atmosphere of 1 atm of argon, maintain at about 1550 ml, and add appropriate amounts of fluorophosphol and iron sulfide. After adjusting the P and S contents in the molten steel to approximately 0.1%, immediately add sodium fluoride alone or a mixture of sodium fluoride and quicklime in a weight ratio of 9:1 for 30 minutes each. Add the flux in 3 times or 10 minutes each, and hold for 30 to 40 minutes with the time when the added flux melts as the smelting start time.During this period, sample the molten steel with a quartz tube at 10 minute intervals. Collect by suction.

The temperature of the molten steel was measured by a platinum-platinum rhodium thermocouple inserted into the magnesia protection tube, and the high frequency input was adjusted to
The temperature was maintained at a temperature range of 30 mm to 160 mm. After holding for a predetermined time, heating was stopped and the molten sickle was solidified. Analytical samples were prepared from suction samples and solidified steel ingots taken at appropriate times during this period, and P, S, and O were analyzed. For comparison, a flux treatment similar to that described above was performed using a magnesia crucible. Experimental results of these examples of the present invention and comparative examples using a magnesia crucible will be explained in detail with reference to the drawings. Figure 1 shows the P, S, 0 content, dephosphorization rate, desulfurization rate, and deoxidation rate in molten steel when 30% NaF is added at once using a Ca○ crucible (hereinafter abbreviated as A crucible). The solid line in the figure shows the relationship between the P, S, and 0 contents and the elapsed time, and the broken line shows the corresponding relationship between the dephosphorization rate, desulfurization rate, deoxidation rate and time. shows the relationship curve.

In the figure, white circles and black circles indicate repeated experimental examples, and white squares and black squares indicate the P, S, and 0 contents in the final solidified steel ingot obtained in each experimental example. It corresponds to dephosphorization rate, desulfurization rate, and deoxidation rate. As seen in this example, when NaF is added, rapid dephosphorization, desulfurization, and deoxidation occur immediately, and rephosphorization and resulfurization do not occur. is increasing. 3. FIG. 2 shows an example in which an experiment similar to that in FIG. 1 was conducted using a Ca○ crucible (hereinafter abbreviated as B crucible) containing about 4% CaC12. The curves and symbols in the figure are the same as in FIG. In this example as well, a rapid dephosphorization and desulfurization tendency 3 is observed as in the case of FIG. Figure 3 uses crucible A (white circle) and B crucible (black circle).
One example each was shown in which F30 was added in three divided doses of 10 times each.

In the same figure, the point at which the arrow is attached at the top indicates that NaF was added. As seen in the figure, dephosphorization and desulfurization occurred each time NaF was added, and a dephosphorization rate of about 95% and a maximum desulfurization rate of 73% were obtained. Although not significant, there is also a tendency for deoxidation. Figure 4 uses an Mg0 crucible, and the first and second
A comparative experimental example is shown in which a test exactly similar to that shown in the figure was conducted.

The two examples are shown with white circles and black circles, but in the dissolution experiment example marked with white circles, some of the initially added NaF fell outside the crucible, so about 20 minutes of NaF was added at the time of the arrow after 8 minutes. and added.

As can be seen from this figure, dephosphorization, desulfurization, and deoxidation are also observed in the Mg0 crucible, and the tendency is exactly the same as in the examples of A and B crucibles, but the dephosphorization rate is at most 50%, and the desulfurization rate is at most 1.
9%, and the deoxidation rate was a maximum of 41%, and it is clear that the use of crucible A and crucible B is superior in dephosphorization rate, desulfurization rate, and deoxidation rate. In Figure 5, crucible A (white circle) and B crucible (black circle) are used, and the above-mentioned 9:1 mixture of NaF and Ca0 is used as the flux for 30 minutes.
One example each is shown in which the additives were added in the same manner as in the example shown in FIG.

In this example as well, dephosphorization and desulfurization and desulfurization occurred immediately after addition of flux, and a maximum dephosphorization rate of 94%, a maximum desulfurization rate of 73%, and a maximum deoxidation rate of 66% were obtained. Almost no rephosphorization is observed. FIG. 6 is a comparative example in which a 9:1 mixture of NaF and Cao was added in the same manner as in FIG. 5 using an M carp crucible. In this case, dephosphorization, desulfurization, and deoxidation also occur, but the degree of deoxidation is almost the same as in the example using crucibles A and B (Fig. 5), but both the dephosphorization rate and the desulfurization rate are I know it's inferior. Next, in order to confirm whether NaF actually acts effectively on dephosphorization, desulfurization, and deoxidation, pure iron was melted using an A crucible, a B crucible, and an MgO crucible. After adding appropriate amounts of ferrophosphor and FeS with a target of 0.1%, the melted state was maintained in an argon atmosphere for about 30 minutes in the same manner as shown in Figures 1 to 6 without adding flux, and the crucible was heated. A blank experiment was conducted to understand the influence of materials.

The results are shown as comparative examples in FIG. 7 for crucible A, FIG. 8 for crucible B, and FIG. 9 for crucible M. In the case of A crucible and B crucible, dephosphorization occurs gradually even without adding flux, but the dephosphorization rate is significantly lower in both cases than in the case of adding flux, and no desulfurization is observed, and 0 means gradual increase. However, no decrease was observed.
The increase in 0 is due to the oxidation of the molten steel by oxygen gas contained as an impurity in the argon.

In addition, in the case of M Yaratsuba, no dephosphorization and desulfurization was observed, and 0
One case showed a gradual increase and one case showed almost no change. The latter is the case when the partial pressure of oxygen in argon is particularly low.
Comparing the above No. 1 and Fig. 6 with Figs. 7 to 9, it is clear that the addition of NaF alone or a 9:1 mixture flux of NaF and Ca○ is rapid and effective for dephosphorization, desulfurization, and deoxidation. It is clear that it has an effect. The flux in which the amount of Ca○ to NaF was increased to 8:2 by weight showed a semi-molten state even near the steel-making temperature.

This suggests that the solubility limit of Ca○ in molten NaF is 2% by weight or less, in other words, Ca
This shows that even if NaF flux is added to molten steel using a container lined with ○, the Ca0 of the lining will dissolve only 20% or less of the added amount of flux at the steelmaking temperature. In addition, if NaF is added to molten steel that has been dissolved in a Mg○-based or dolomite-based container, the effect of Ca0, that is, its activity, will be lower than in a Ca○-based or Ca○-based container, so the dephosphorization rate and desulfurization rate will increase. It can be seen from the above-mentioned Examples and Comparative Examples that the deoxidation rate is inferior. All of the above experiments were carried out by P and S.
The test results are for a pure steel system containing no coexisting elements other than C, Si, Mn,
Five elements, Cr and Ni, are individually added to molten steel at varying concentrations, and after adjusting the composition so that P and S are both approximately 0.1%, NaF is added to the molten steel at a concentration of 5% to 7% (minimum 4.1%, maximum 10%) was added, and the influence of these elements was investigated using a B crucible at steelmaking temperature.

Holding time is 10 to 20 minutes (minimum 6 minutes, maximum 40 minutes)
During this period, molten iron samples were collected and analyzed.
Experiments were conducted at four levels of C: 0.1, 0.2, 0.3 and 4.2%.

C.O. At 1%, the dephosphorization rate was 84%, CO. At 2%, the dephosphorization rate is 6.
2%, desulfurization rate 74%, CO. In the case of 3%, the dephosphorization rate is 41
%, and at C4.2%, the dephosphorization rate further decreases to lo
%, but the desulfurization rate was over 90%. These results are because as the C content in the molten steel increases, the dephosphorization conditions worsen, but the desulfurization conditions improve. Si is 0
．． Experiments were conducted at four levels: 0.3%, 0.57%, and 0.61%. If Si is 0.3% or more, no 0.1 in 10 minutes,
However, 0.2% of dephosphorization was observed, and the dephosphorization rate was 15% or less or no dephosphorization occurred. When Si was 0.05%, it was removed and dephosphorized at the same time, and the dephosphorization rate was 73%. Therefore, while keeping the Si content as low as possible, NaF
The amount of addition must be increased. Regarding desulfurization, S
io. 05%, 78%, Sio. 84 for 3% or more
None, 96%. Regarding deoxidation, see Sio.
In the case of 05%, the deoxidation rate is 38%, and as the Si content increases, the deoxidation rate improves as a matter of course. At 3%, it was 79%. Mn is 0.2, 0. Fu 0.01.3
Experiments were conducted at 5 levels of 10.8% and 10.8%.

If the Mm content is 1.3% or less, the dephosphorization rate is 70L.
The desulfurization rate was 47% and 81%, but M
When n was 10.8%, almost no dephosphorization was observed, while the desulfurization rate was 56% to 70%. Deoxidation rate is up to 1
8 and 61% were obtained, but the amount of oxygen showed a tendency to gradually increase again as the holding time progressed. Ni is 1, 4
Experiments were conducted at three levels: and 8%.

When Ni is included in the molten steel, dephosphorization is promoted, and dephosphorization rates of 94 and 97% were obtained in both cases. Desulfurization rate is Ni
66% for l%, 72 to 7 for Ni4 and 8%
It showed a desulfurization rate of 3%. Therefore, NaF is particularly effective for dephosphorization and desulfurization of alloy steel with a large Ni content. Cr
Experiments were conducted at four levels: 0.04, 10 and 18%.

Cro. At 6% Cr, the dephosphorization rate was 72%, but as the Cr content increased, the dephosphorization rate decreased, and at 4 to 10% Cr, the dephosphorization rate was 22 to 33%, and at 18% Cr, the dephosphorization rate was 6%.
%. Therefore, in order to perform effective dephosphorization, it is necessary to keep the Cr content as low as possible and increase the amount of flux added. Regarding desulfurization, the desulfurization rate is 40% at 4% Cr, 75% at Crlo%, and 84% at 18% Cr, and Cr improves the desulfurization rate. Regarding deoxidation, refer to Cro. Deoxidation rate is 9% at 6% and 28% at 4% Cr.
When the Cr content was 10% or more, a deoxidation rate of about 90% was obtained. Combining the above experimental results, in order to effectively dephosphorize molten steel by adding NaF at steel-making temperature in a quicklime-based refractory container, and simultaneously desulfurize and deoxidize,
The maximum permissible content of coexisting elements is CO. 2% or less, Sio.
05% or less, Mhl. 3% or less and Crl% or less, and Ni promotes dephosphorization at least up to about 8%.

When C, Si, Mn, and Cr coexist in amounts greater than the above-mentioned contents, the desulfurization rate and deoxidation rate improve, but the dephosphorization rate decreases.
Therefore, the maximum permissible content of the above-mentioned coexisting elements will depend on whether emphasis is placed on dephosphorization or desulfurization. The NaF-based flux used in the present invention has an extremely high vapor pressure, so when added within the molten steel temperature range, almost the entire amount vaporizes within 5 minutes and no flux remains on the molten steel surface. It is desirable to use an appropriate method such as dipping or gas blowing to make contact with the flux as good as possible. Furthermore, it has the characteristic that the flux can be recovered by installing an exhaust gas dust collection device in the container.

[Brief explanation of the drawing]

Figure 1 shows the P and S in molten steel when a Ca○ crucible (A crucible) is used and a single NaF flux is added at once.
, 0 content and the relationship between dephosphorization rate, desulfurization rate, deoxidation rate and elapsed time. Figure 3 is a diagram showing the experimental results of a dissolution test similar to the above, Figure 3 is a diagram showing the experimental results when NaF was added in three parts using A or B crucible, and Figure 4 is a diagram showing the experimental results when NaF was added in three parts. Figure 5 shows the results of a comparative experiment when the same dissolution test as in Figure 1 was conducted using crucible A or B, and NaF and Ca
Shows the relationship between the content of P, S, and 0 in molten steel and the dephosphorization rate, desulfurization rate, deoxidation rate, elapsed time, and 0 when a flux mixed with ○ at a weight ratio of 9:1 is added at once. Figure 6 is a diagram showing the results of a comparative experiment when a melting test similar to that in Figure 5 was conducted using a Mg○ crucible, and Figure 7 is a diagram showing the results of a comparative experiment when pure iron was melted using an A crucible and P Figure 8 shows the results of a blank experiment in which three powders were held in an argon atmosphere tank without adding flux after adjusting the and S content to a constant value. FIG. 9 is a diagram showing the results of an empty experiment similar to that shown in FIG. 7 using an Mg0 crucible. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9

Claims (1)

[Claims] 1 Using a quicklime-based crucible or a container lined with a quicklime-based refractory, phosphorus, sulfur, and oxygen in molten steel are removed using sodium fluoride or a sodium fluoride-based flux containing up to 20% by weight of quicklime. A method for smelting molten steel using a sodium fluoride flux, which is characterized by simultaneously removing .