JPH02163311A - Method for removing cr in molten iron - Google Patents

Abstract

PURPOSE:To reduce Cr content in molten steel without eroding lining refractory in a vessel for molten steel of a ladle, etc., by bringing molten slag containing oxide of Fe, MgO and ZrO2 into contact with the molten steel having much Cr content. CONSTITUTION:The molten steel having much Cr content refined with the converter, etc., is charged into the ladle and after removing the molten slag, without any deoxidizing treatment, the flux of composition containing of >=20wt.% Fe oxide of FeO, Fe2O3, Fe3O4, etc., >=10wt.% the total of MgO and ZrO2, or further containing >=20wt.% MnO and the balance of 50-60wt.% the total of one or more kinds among CaO, SiO2, Al2O3 and CaF2, is added. The molten slag having strong oxidation is generated, and Cr in the molten steel is oxidized into Cr2O3 and made to the slag and removed to stably produce the low Cr-containing steel. In this case, as the MgO and ZrO2 is contained in the molten slag being the same kinds of components as the lining refractory in the ladle, the lining refractory in the ladle is not eroded.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for removing Cr from molten iron, particularly a method for removing Cr from molten iron in a ladle.
Regarding the method.

(Prior art) When repairing molten metal that falls outside of the Cr standard after blowing in a converter or electric furnace, or for low-C steel such as cold-rolled steel sheets for automobiles, etc.
When melting r1jl, if the Cr content exceeds the target value, it is necessary to perform a Cr removal process.

In other words, if carbon steel has a high Cr content, its cold workability and deep drawability will deteriorate. -, that is, [Cr] is 0.03~0.05%
It is necessary to reduce it to below.

Now, when carbon steel is melted, a sudden increase in Cr occurs, for example, due to the addition of scrap to hot metal in a converter. This is because stainless steel chips and the like may be mixed into the scrap. Although scrap management methods are currently being strengthened, the occurrence of non-standard Cr after converter blowing is still a problem.

If such a Cr deviation occurs, the (C
) is sometimes used to remove Cr, but there is a limit to reducing Cr by such a method, and such a method also causes severe erosion of the converter refractories.
Currently, it is necessary to change the steel type for molten steel that is significantly out of specification.

On the other hand, the amount of scrap tends to increase more and more. Therefore, in the future, if scrap becomes available in large quantities and at low cost when producing carbon steel, it is expected that the molten metal ratio in the converter will be lowered and the scrap ratio will be increased. In such a case, the probability of deviating from the Cr standard due to the contamination of stainless steel scraps as mentioned above will be high, and the range of deviation from the Cr standard will also become large, and it is clear that changing the steel type alone will not be enough to deal with the problem. .

In this way, when producing carbon steel (8), in a converter? 8
If the pig iron rate is lowered and the scrap ratio is increased, Cr in i8N
suddenly increases, increasing the possibility that the Cr standard will be exceeded. However, in such cases, there has been no method to easily remove Cr from molten steel.

(Problems to be Solved by the Invention) Therefore, it is necessary to consider oxidation removal of Cr in molten steel.

As already mentioned, in order to remove Cr from molten steel after converter blowing, the first idea is to blow down (Cl) in the converter and accelerate the oxidation of (Cr). Since some of the Cr contained in the
) by blowing down the slag T, Pes clogging (T, F
e1l increases, melting tl of the converter refractory becomes intense, and this method is economically disadvantageous.

In addition, in this case, as the decarbonization progresses, the oxidation of Mn also proceeds at the same time, so depending on the type of steel, it is necessary to add additional Mn after the treatment is completed, making the operation rather expensive.

An object of the present invention is to provide an economical and effective method for removing Cr from molten iron.

In addition, a specific object of the present invention is to economically and effectively remove Cr in the converter or in the ladle after blowing in the converter under conditions that suppress melting loss of refractories during carbon steel melting. An object of the present invention is to provide a method for oxidizing and removing.

(Means for Solving the Problems) The present inventors have conducted various studies to achieve the above-mentioned objectives, and have obtained the following knowledge.

First, as described in Japanese Patent Application No. 63-52099, T8 steel and slag are brought into contact with each other in a ladle or the like. In order to oxidize and remove Cr in No. 8 steel, the slag needs to have strong oxidizing power.

Additionally, depending on the type of steel, as mentioned in Japanese Patent Application No. 1983-83598, slag, which has strong oxidizing power, may contain sufficient Mn oxides so that it does not oxidize Mn, which is a beneficial component in molten steel. is necessary.

Subsequent research revealed that it is preferable to increase (T, Fe) in slag in order to improve the Cr removal rate; however, when (T, Fe) increases in slag, Refractory? 8h4 becomes significant and becomes economically disadvantageous. Therefore, after considering these points, we found that since refractories are partially composed of materials containing MgO, ZnO2, etc., we added MgO and ZrO□ to the slag for removing Cr in order to prevent them from melting. When one or more of these were blended, not only was it possible to prevent the melting of refractories, but the Cr removal rate was also significantly improved, and ff1
The inventors discovered that the problems of the prior art described in No. 7 can be effectively solved, leading to the present invention.

Here, the gist of the present invention is that Fe
A mixture containing 20% or more of oxides, MgO and/or 2'0□ 1O% or more in total, and further containing 60% or less in total of one or more of CaO, 5jO2, AQzO+ and CaFz mainly as melting point depressants. Alternatively, it is a method for removing Cr from molten iron, which is characterized by adding synthetic flux to molten iron.

Furthermore, according to a preferred embodiment of the present invention, the flux may contain 20% or more of Mn oxide. In that case, C
One or more of aO, 5iO1, AQzo*, and CaF are blended in a total amount of 50% or less. This is because, depending on the type of steel, it is necessary to avoid oxidation consumption of Mn into the slag.

As described above, according to the present invention, when 1-go or ZrO□ is one of the main components of the refractory, it is possible to suppress the melting of the refractory by the slag for removing Cr.

(2) Since hgo selectively forms a compound with Cr oxide, it is effective in promoting Cr removal.

■Zr (h is an acidic oxide, so basic C
Effective for stabilizing r-oxides in slag.

(Function) Next, details of each processing operation of the Cr removal method of the present invention will be explained.

First, according to the present invention, after the converter blowing, the above-mentioned mixed flux or synthetic flux is added for the purpose of removing Cr, but it is only necessary to add the above-mentioned mixed flux or synthetic flux after the converter blowing II and before deoxidation. . Preferably, it is added as soon as possible after the converter slag is removed after the converter blowing is completed. Therefore, the treatment is generally carried out in the ladle after being discharged, but if necessary, the Cr removal treatment according to the present invention may be carried out after removing the converter slag in the converter.

The reason why it is preferable to perform the Cr removal treatment on the deoxidized surface is that oxygen needs to exist not only in the slag but also in the molten steel in order to oxidize and remove Cr.

Note that the converter blowing itself prior to the Cr removal treatment is not limited in any way in the present invention, and a normal one is sufficient. The treatment according to the present invention only needs to be applied when the Cr content finally exceeds the target value.

Next, in the Cr removal treatment according to the present invention, it is sufficient to add flux from the upper part of the molten steel, but injection into the molten steel is more effective.

In addition, the amount of flux added should be determined to achieve the desired Cr1i removal (
(usually about 0.05-0.1%) and simultaneous de-c
It is determined by l, etc., but usually 10-50kg/↑・
Molten steel is sufficient.

Flux may also be used in the form of a mixed flux made from a mixture of various compounds, or in the form of a synthetic flux obtained by melting these mixtures, cooling them, and pulverizing them before adding them to molten steel. From the viewpoint of stability of flux properties, the latter synthetic 7-laffus is preferred.

The amount of flux added and the mix of these components v1 will vary depending on the molten steel composition, especially the Cr content, but as a general example: Flux amount: 10 to 50 kg/T Molten steel flux components (Fe oxide) ≧20% (MgO and/or Z
r0t)≧10% Depending on the steel type, (Mnn oxide ≧20%), and other flux components include CaO1S
One or more of 10□, CaFz, and 8QzOs may be added in a total amount of 60% or less for the purpose of lowering the melting point of the flux. 50% when adding 10 oxides
The following shall apply.

By adding such a melting point depressant, the melting point of the flux changes depending on the formulation, 91°C, and the Cr removal treatment temperature (17°C).
00°C to 1550°C).

In addition, the more desirable flux blending ratio is (Fe oxide) 230% 50% ≧ (MgO and/or Zr0z) ≧IO
Depending on the type of steel, it may be further (Mn oxide) 230%.

When performing the Cr removal process using this ladle, it is desirable to remove the converter slag that inevitably enters the ladle, but if repurposing is not a problem, leave a small amount of converter slag. The composition of the added flux may be controlled so that the slag component has the above properties.

Furthermore, in the method according to the present invention, stirring of molten steel and slag is important from a practical standpoint.

That is, as a stirring method, Huffling stirring using argon is generally used, but it is also possible to use the stirring effect of natural falling of molten steel to which flux is added during tapping. This is because, in the case of the present invention, if the oxidizing power is sufficient, the reaction proceeds quickly.

The slag after removing Cr is subjected to the next step of deoxidation, R11 treatment, etc.
Although it is desirable to remove Cr in order to prevent re-creation in the i11 gas step, a method of slag chilling (hardening the slag) with lumpy quicklime or the like may also be used.

It goes without saying that the method according to the present invention can also be applied to the production of carbon steel using scrap as the main raw material using an electric furnace.

Next, the composition of the slag will be described in more detail.

First, the slag for removing Cr used in the present invention has strong oxidizing power because the purpose is to remove [Cr] into the slag as Cr oxide by the oxidation reaction shown in the following formula (11). It is necessary.

(Cr) +x(Fed) =(Cry,) +X (
F(+) (1) Therefore, the slag for removing Cr needs to contain a large amount of Fe oxide.

As shown in FIG. 1, consider the relationship between (T, Fe) and the Cr removal rate. At this time, the 18fi4 initial 'M composition was C#0.0
5%, 5i=Lr,,Mn! -io, 15%, P=0.
015%, 81.01%, Cr'-0.10%, and the molten steel temperature was 1600°C.

Flufx with different levels of Fe oxide was added to this, the amount of (T, Fe) in the slag was changed, and the Cr removal rate at that time was determined. The results are shown graphically in FIG.

In FIG. 1, the upper curve shows the basicity of the slag (in the case of 3), and the lower curve shows the basicity of the slag (in the case of 3).

This is because the Cr oxide produced after the Cr removal treatment is slightly basic, so the more acidic the slag is, the more easily the Cr oxide is stabilized in the slag, and therefore the Cr removal tends to progress. Note that the flux amount was 50 kg/T.

As is clear from the results shown in Figure 1, (
The higher the T, Fe), the higher the Cr removal rate.

For example, when a Cr removal rate of 40% or more is required, (T, Fe) in the slag needs to be about 15% or more, and S in Fe oxide needs to be about 20% or more.

Further, when a Cr removal rate of 50% or more is required, the (T, Fe) content of the slag must be about 20% or more, or about 30% or more in terms of Fe11 compound.

Here, Fe oxides include FeO, Fezes, Fe5
Refers to 0< etc.

However, the Cr-removal slag having such a high (T, Fe) content has a particularly strong corrosive force against the refractories of a converter or a ladle. Therefore, in a preferred embodiment of the present invention, removing Cr
In order to prevent the refractory/81 members caused by the refractory slag, the Cr-removal slag contains one or more compounds that are the main components of the refractory.

For example, when the refractory is an MgO-based refractory (mag carbon brick, spinel brick, etc.), the compound that is the main component of the refractory is M[0 or MgO-containing compound, such as 1'' It is preferable to add.

For example, when the refractory is a zircon brick, it is preferable to add a zirconia-containing compound, such as zircon, as a "compound that is one component of the refractory."

Here, in the case of slag for removing Cr containing 11go, the slag properties were measured using an X-ray microanalyzer with 1Xt! As a result of i'E, there is a tendency for MgO and Cr oxide to selectively form a compound. Therefore, MgO is a very effective additive not only for preventing melting of refractories (but also for improving the Cr removal rate).

In addition, in the case of slag for removing Cr containing ZrO2, ZrO2
Since ZrO□ is an acidic oxide, ZrO□ can stabilize Crv, which is a basic oxide, in the slag. Therefore, it is not enough to prevent the melting of refractories, and to remove Cr.
For this reason, ZrO□ is a very effective additive; the total amount of MgO and/or ZrO□ is 10% or more. It is preferably 10% or more and 50% or less. That is, 50%≧(hO and/or Zr0
z) 410%. This lower limit is the minimum value at which the effect begins to appear, and the lower limit is a value taking into consideration the fluidity of the slag, but it varies depending on the blending of other compounds.

In the present invention, the slag for removing Cr used has strong oxidizing power, so it can be used at the same time as [Cr]. g (Mn), a beneficial component in IJ, is also removed by oxidation. Depending on the type of steel, it is necessary to contain a large amount of (MnQ) in order to prevent this.

Figure 2 shows (MnO) in slag and [Mn] in molten steel.
The relationship between yields is shown in a graph. In the figure, the upper curve is (S1
0□)+(8LOs)(Si(h)+(AQzO+) Here, the Mn yield is defined as follows.

The results shown in Figure 2 were obtained in the same manner as in Figure 1, and from this result, it is clear that a large amount of (MnO) is required to prevent the oxidation loss of (Mnl). it is obvious.

For example, in order to make the yield of molten steel exceed 50%, the (MnO) content in the slag needs to be 15% or more, or about 20% or more in terms of Mn oxide. In addition, in order to make the Mn yield of molten steel exceed 70%, it is necessary to
) is required to be 25% or more, approximately 30% or more for Mn oxide.

Here, the Mnfi compound is mainly MnO□ (some of it is Mn0
).

In addition, the FeflJ compound mentioned below is blended with hgo and/or ZrO□, and depending on the steel type, Mn oxide is further blended, and in other raw materials, CaO is added for the purpose of promoting slag formation.
A Cr-free flank is prepared using a melting point depressant such as 1Si(h, A+220., Care, etc.), and it has already been mentioned that they are added as a mixed flux or a synthetic flux.

Next, the Cr removal treatment according to the present invention will be explained in more detail with reference to Examples.

Example 1 2 kg of carbon steel was melted in the atmosphere in a MgO crucible using a Tammann furnace and held at 1600°C. 100 g of flux shown in test numbers 1 to 26 in Table 1 was added, and the melt was melted with argon gas. , Bubbling stirring was performed for 20 minutes to remove Cr. The results are summarized in the same table.

In this way, Cr removal progresses satisfactorily even though it is accompanied by C removal. In addition, in test numbers 1 to 24, the amount of increase in hgO in the slag was small, so SgO/8t from the MgO crucible
It is thought that M could be made smaller. Also, test number 1-1
8 and 26, Mn is added to the flux in advance.
By incorporating a fi compound in advance, it was possible to suppress deportation.

However, as shown in Test No. 27 in the same table, when the (T, Fe) of the slag was small, Cr removal did not progress much. In addition, as shown in test number 28 in the same table, if ZrO□ or MgO is not added to the Cr-removed flux in advance, the increase in MgO in the slag is large, and this is thought to be due to melting from the MgO crucible. Also, the Cr removal rate is relatively not very good.

Example 2 Charcoal, W @ 2 kg, was melted in the atmosphere in a MgO crucible using a Tammann furnace, and held at 1600°C. After that, 100 g of flux shown in test numbers 29 to 40 in Table 2 was added, and argon gas was added. Bubbling agitation was performed for 20 minutes to remove Cr. The results are summarized in the same table.

In this way, yllCr progresses well. In addition, regarding test numbers 29 to 37, since the amount of increase in Zr0z in the i-ma slag was small, zroziSt from the Zr0z crucible
It is thought that the number of staff members could be reduced.

However, as shown in test number 41 in the same table,
If Zr01 or MgO is not added to the r flux in advance, the amount of ZrO2 in the slag will increase significantly, and this is thought to be due to the Zr(h) melting away from the crucible, and the Cr removal rate is also relatively poor. .

Example 3 A 250-ton converter was used to produce zircon bricks (250°C) (1680°C) after the completion of normal converter blowing.
60% Zr0z, 34% Sing) Place the pasting in a ladle,
10) The fluxes shown in Table 3 were packaged in bags in a steel tap, added in portions, and stirred with argon gas to remove Cr. The results are summarized in Table 3.

In this way, good Cr removal progressed. In addition, since there is not much ZrO□ in the slag before and after treatment, the refractory is /8
It is thought that the number of members is small. After the Cr-removal treatment, the Cr-removal slag was removed, AQ was added at RH, and the heat was raised using the oxidation reaction heat of AQ to perform degassing.

In addition, the flux used was a mixture of oxide scale for FezOzitl+, Mnt and stone for MnOzfi, quicklime for CaO, and zircon brick for ZrO□-3iO□, all of which had a particle size of 5-fat or less. .

(Effects of the Invention) As described in detail above, by adopting the present invention, it is possible to prevent melting of refractories while redressing the failure of molten iron to exceed the Cr standard. The significance is great.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between (T, Fe) in slag and Cr removal rate; and Figure 2 is a graph showing the relationship between (MnO) in slag and [Mn!] in molten steel. It is a graph showing the relationship between yields.

Claims (2)

[Claims] (1) Molten iron is mainly composed of 20% or more of Fe oxide, a total of 10% or more of MgO and/or ZrO_2, and further contains CaO, SiO_2, Al_2O_3, and CaF_
Decarbonization of molten iron characterized by adding a mixed or synthetic flux containing 60% or less of one or more of 2.
r method. (2) Further, 20% or more of Mn oxide is added to the flux, and CaO, SiO_2, Al_2O_
The method for removing Cr from molten iron according to claim 1, characterized in that the total amount of one or more of 3 and CaF_2 is 50% or less.