JPH0676613B2 - Dephosphorization method of high manganese molten iron - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention uses high-melting manganese iron having a manganese content [Mn] of 5% by weight or more by using an inexpensive dephosphorization agent and reducing the oxidation loss of [Mn]. The present invention relates to a method for efficiently removing phosphorus while suppressing the above.

(Prior Art) In recent years, as the fields of use of steel materials have diversified, many new steel types have been developed, but the manganese content is about 5%.
(Hereinafter, "%" means "% by weight" unless otherwise specified).

High-manganese steel as a non-magnetic steel is not only cheaper than austenitic stainless steel containing Ni, which is a competitive material, but also has the advantage of high strength and low magnetic permeability. Non-magnetic steel for magnetic levitation railway members, nuclear fusion device members, degaussing device members, electrical equipment members, etc.
Applications are expanding as structural steel and wear-resistant steel.

By the way, phosphorus in high-manganese steel is generally a harmful substance that adversely affects the hot workability and the weld crack resistance, so it is desirable to make it as low as possible. When inexpensive ferro-manganese is used as the Mn source in the melting of high manganese steel, the P contained in it moves to the molten iron and the P of molten iron
The content [P] becomes high. Therefore, it has always been the case that ferromanganese is added as the Mn source as long as the [P] standard allows, and the remaining Mn content is supplemented with metallic manganese so that [P] does not rise.

However, in this method, since expensive metal manganese is used in a large amount, the melting cost becomes high. Therefore, as a lower-cost melting technique, it is indispensable to establish a technique for producing low-phosphorus high-manganese molten iron from the obtained high-manganese molten iron having a high phosphorus content by mixing most of Mn with ferromanganese.

In response to such a request, some dephosphorization methods for high-manganese molten iron have been proposed so far, but they have not been put into practical use.

For example, even a reductive dephosphorization method using a relatively inexpensive CaC ₂ —CaF ₂ system flux is difficult to put to practical use for the following reasons.

In this reductive dephosphorization method, [Ca] is produced by the decomposition reaction as in formula (1), and this is combined with molten iron [P] as in formula (2) to dephosphorize.

(CaC ₂ ) → [Ca] +2 [C] ………… (1) 3 [Ca] +2 [P] → (Ca ₃ P ₂ ) ………… (2) Here, the decomposition shown in equation (1) In order to accelerate the reaction, the lower the [C] in the molten iron, the more advantageous it is. Therefore, decarburization treatment in advance is indispensable.

In order to prevent the air oxidation loss of [Ca], it is necessary to carry out the reductive dephosphorization in a non-oxidizing atmosphere, and the dephosphorizing efficiency is easily affected by the atmosphere.

After the dephosphorization treatment, the slag easily reacts with water in the atmosphere as shown by the formula ( ₃ ) to generate harmful phosphine (PH ₃ ).

(Ca ₃ P ₂ ) + 3H ₂ O → 3 (CaO) + 2PH ₃ (3) On the other hand, the oxidative dephosphorization method, which is the dephosphorization method for ordinary carbon steel and low alloy steel, that is, the converter Even if strong oxidation refining such as O ₂ blowing using CaO-based slag at the time of blowing is applied as a dephosphorization method for high-manganese molten iron, only [Mn] is preferentially oxidized, and molten iron [P ] Cannot be removed.

However, JP-A-61-272312 and JP-A-62-30
As disclosed in JP-A No. 810 and JP-A-62-227063, [P] in molten iron is oxidized as shown in formula (4) with a weak oxidizing power that does not excessively oxidize [Mn]. Then, as shown in the formula (5), the dephosphorization product acidic oxide P ₂ O ₅ is stabilized in the slag by BaO, which is a basic oxide significantly stronger than CaO in the converter slag. As a result, [P] in the molten iron can be removed.

2 [P] +5 [O] = (P ₂ O ₅ ) ………… (4) (P ₂ O ₅ ) +3 (BaO) = (3BaO · P ₂ O ₅ ) ………… (5) This BaO The dephosphorization method using a system slag is easy to process, and there is no problem of slag after the dephosphorization process, but BaO system slag is very expensive, and the cost of dephosphorization is high and it is difficult to adopt it for large-scale processing.

Furthermore, as an oxidative dephosphorization method for high-manganese molten iron, "Iron and Steel" 1974 (1988) No. 9 P.1778 describes Na ₄ SiO ₄ (sodium orthosilicate), Na ₄ SiO ₄ -NaF ₂ flux. Using N
The dephosphorization method using a ₂ O slag is introduced.

A very high dephosphorization rate can be obtained by the dephosphorization method using the Na ₂ O-based flux, but Na ₄ SiO ₄ is expensive.
White smoke is generated during the dephosphorization process. It is difficult to put this method into practical use because of a large amount of [Mn] oxidation loss in molten iron (0.9-1.6% [Mn] loss in 14% Mn-5% C hot metal).

In order to solve the problems of the conventional dephosphorization method of high-manganese molten iron as described above, the present applicant has decided to use Na ₂ CO ₃ that is inexpensive and easily available.
A method for dephosphorizing high-manganese molten iron by using a flux containing SiO ₂ as a main component was developed and filed as Japanese Patent Application No. 1-306136.

In the dephosphorization method of high manganese molten iron of the above-mentioned prior invention, Na ₂ C
A flux containing O ₃ and SiO ₂ as main components is used. Of the main component
Na ₂ CO ₃ decomposes at high temperature as shown in equation (6).

(Na ₂ CO ₃ ) → (Na ₂ O) + CO ₂ (6) The strongly basic oxide Na ₂ O produced is an acidic oxide P ₂ produced by oxidizing [P] in molten iron. O ₅ (reaction of the above formula (4)) is fixed in the slag as shown in the following formula (7), so that dephosphorization is achieved.

(P ₂ O ₅ ) + 3 (Na ₂ O) → (3Na ₂ O · P ₂ O ₅ ) …………
(7) A part of the CO ₂ generated at the same time can be used to generate MnO serving as an oxidizing agent of [P] by the reaction shown in the formula (8).

CO ₂ + [Mn] → CO + [MnO] (8) The other main component, SiO _2, is Na, which easily evaporates at high temperatures.
Appropriate amount is added to keep ₂ O in slag at high temperature. It is considered that Na ₂ O and SiO _{2 form} (Na ₂ O) _x · SiO ₂ (x ≧ 1), and a part of them is dissociated to participate in the dephosphorization reaction according to the formula (7).

As described above, according to the method for dephosphorizing molten iron with high manganese previously proposed by the present applicant, molten iron with low phosphorus and high manganese can be produced even if a large amount of inexpensive phosphorus-containing ferromanganese is added.

However, when [P] in high-manganese molten iron is oxidatively dephosphorized by the above reactions, [Mn] in molten iron is simultaneously oxidized according to the above formula (8). This lowers the Mn yield of molten iron, so it is necessary to take measures to prevent this. That is, if the oxidation loss of Mn can be suppressed when dephosphorization is carried out by the method of the invention of the prior application, it is possible to manufacture the high-melting manganese iron at a lower cost.

(Problems to be Solved by the Invention) An object of the present invention is a method for dephosphorizing high-manganese molten iron by using a flux containing Na ₂ CO ₃ and SiO ₂ as main components, which comprises oxidation of Mn in molten iron. It is to provide a dephosphorization method of high manganese molten iron with less loss.

(Means for Solving the Problem) The present inventor has conducted various studies on means for suppressing the oxidation loss of Mn in molten iron during the dephosphorization treatment of molten iron with high manganese by the Na ₂ CO ₃ —SiO ₂ system flux. As a result, Na ₂ CO ₃
When an appropriate amount of manganese oxide is added to the -SiO ₂ -based flux, the dephosphorization rate is slightly reduced, but it was found that the oxidation loss of Mn in molten iron can be significantly reduced, and this does not significantly impair the dephosphorization effect, and it It was confirmed to be an extremely practical method for reducing the manufacturing cost of manganese steel.

The present invention is a method for dephosphorizing molten iron of high manganese using a Na ₂ CO ₃ —SiO ₂ -based flux, which is the main compounding ingredient Na ₂ CO ₃
And a flux of a mixture of manganese oxide with SiO ₂ is brought into contact with molten iron having a manganese content of 5 wt% or more ”.

In this method, by mixing manganese oxide in the Na ₂ CO ₃ -SiO ₂ -based flux in advance, [Mn] in molten iron (hereinafter, the molten iron component is represented by the [] symbol, and the slag component is represented by () (Indicated by a symbol), but when the manganese oxide is MnO ₂ , the blending amount is Na ₂ O in Na ₂ CO ₃ blended in the flux and [Si] in the blending amount in the flux. It is desirable that the amount is 10 to 25 parts by weight with respect to the total 100 parts by weight of SiO ₂ including the amount of oxidization produced.

Manganese oxide to be blended is, MnO ₂ except for example MnO, Mn ₂
It may be O ₃ , Mn ₃ O ₄ or the like.

In addition, in this dephosphorization method, (Na ₂
O) _x · SiO ₂ (x ≧ 1) is mainly used for dephosphorization, but Na ₂ O in the slag is used.
The ratio of SiO _2, i.e. (Na ₂ O) / to use a flux such as (SiO ₂₎ is 1.25 to 1.5 is desirable. (Na
₂ O) / (SiO ₂ ) is N in Na ₂ CO ₃ compounded in the flux.
It is the ratio of the a ₂ O content to the sum of SiO ₂ compounded in the flux and SiO ₂ produced by the oxidation of [Si] in the molten iron.

The amount of SiO ₂ produced by the oxidation of [Si] in the molten iron is
Since it can be calculated assuming that [Si] is substantially all SiO ₂ , it can be easily calculated from the [Si] content of the molten iron to be treated.

(Operation) FIG. 1, FIG. 2 and FIG. 3 show the results of a basic test (crucible experiment) in developing the method of the present invention. The test was conducted under the following conditions.

(A) Treated molten iron: [Mn] ≈13%, [C] ≈4%, [P] ≈0.06% molten iron 2 kg, treatment temperature = 1300 ° C. (b) Flux used: Na ₂ CO ₃ —SiO ₂ -MnO ₂ flux. However, since molten iron does not substantially contain [Si], it is not necessary to consider SiO ₂ generated during the dephosphorization treatment here. Therefore, the flux should be (Na ₂ O) / (SiO ₂ ) about 1.25,
Molten iron per ton ratio of:: (45kg SiO _2), i.e., (Na ₂ CO ₃ 95kg) + _{a:: (45kg SiO 2) =} Na 2 CO 3 and SiO ₂ at a rate of 100kg (Na ₂ O 55kg) + In order to prevent Mn oxidation loss, 20 kg of MnO ₂ was added.

FIG. 1 shows [P] and [Mn] of molten iron and (MnO) and (Na ₂ O) / (Si in the slag with the lapse of treatment time.
This shows the change in O ₂ ). [P] is initially 0.060%
However, the dephosphorization rate reaches 70% after treatment for 30 minutes, down to 0.018%. The [Mn] in the molten iron lost about 0.5% during the treatment. The reason for this is that, as shown in the above formula (6), excess CO in the added Na ₂ CO _3
2 (8) that Mn is oxidized as shown in the expression and Na ₂ by oxidizing power of O itself, as shown in the following equation (9) [Mn] is estimated that in, is oxidized It

Na ₂ O + Mn → MnO + 2Na (9) Therefore, the concentration of slag (MnO) after dephosphorization is 20%.
Has risen to nearly 30%. Oxidation loss of [Mn] is (8)
In the case of proceeding by the reactions of the formulas and the formula (9), it is considered that the oxidation loss of [Mn] can be suppressed by previously mixing manganese oxides such as MnO and MnO _{2 in the} flux. In addition, since Na ₂ O evaporates during the treatment, (Na ₂ O) /
(SiO ₂ ) decreases from the pre-treatment flux of 1.25 over time.

Fig. 2 shows the dephosphorization rate, [Mn] oxidation loss, and (MnO) concentration after treatment by changing the amount of MnO ₂ added (other conditions are the same as in Fig. 1, but the treatment time is 30 minutes). It shows the results of the examination.

As shown in FIG. _2, by mixing MnO ₂ in the flux, the oxidation loss of [Mn] is reduced. However
On the contrary, when the compounding amount of MnO ₂ exceeds 25 kg / T, the oxidation loss of [Mn] increases. It is considered that this is due to the fact that the oxidizing power of the slag becomes too large and the [Mn] is oxidized.

As for the dephosphorization rate, the content of MnO ₂ increases and (MnO) in slag
It gradually decreases as the concentration increases. This is because the (Na ₂ O) concentration in the slag decreases due to the dilution accompanying the incorporation of MnO ₂ , and since MnO is a weak basic oxide compared to Na ₂ O, the basicity of the entire slag becomes weak. It depends.

Therefore, it is possible to obtain the same dephosphorization rate (65-70% or more under the present experimental conditions) as when MnO ₂ is not added and [M
The oxidation amount of loss n], MnO ₂ with respect to 1.3% in the case of no addition, in order to suppress below _{0.5%, Na 2 CO 3 -SiO} 2 based flux _{{(Na 2 O) + (} SiO 2 )} It is desirable that the content of MnO _{2 be 10} to 25 kg / T with respect to 100 kg / T.

Fig. 3 shows the change in flux (Na ₂ O) / (SiO ₂ ) value (other conditions are the same as in Fig. 1, but the treatment time is 30 minutes), the dephosphorization rate, [Mn] The result of examining the oxidation loss is Mn
This is a comparison between the case where O ₂ is added and the case where O ₂ is not added.

As shown in the figure, when manganese oxide is added to the flux (solid curve in Fig. 3), the dephosphorization rate is slightly lower than when it is not added, but the oxidation loss amount of [Mn] is about 0.5 to It can be reduced by 1.5%. The dephosphorization reaction proceeds with (Na ₂ O) / (SiO ₂ ) ≧ 1.0 regardless of whether MnO ₂ is mixed, and the larger the value of (Na ₂ O) / (SiO ₂ ), the dephosphorization rate becomes logarithmic. It increases functionally, and the amount of [Mn] oxidation loss increases exponentially.

When (Na ₂ O) / (SiO ₂ ) <1.25, the oxidation loss amount of [Mn] is suppressed to a low level, but the dephosphorization rate is significantly reduced. (Na
₂ O) / (SiO ₂ ) in the range of 1.5 to 2.0, the dephosphorization rate slightly improves and reaches the upper limit value, whereas the oxidation loss amount of [Mn] increases rapidly, but MnO ₂ is added to the flux. By doing so, the amount of oxidation loss can be reduced by about 0.5 to 1.5%.
From the practical point of view of suppressing the amount of [Mn] oxidation loss to the lower limit without significantly inhibiting the dephosphorization rate, the flux satisfies the condition of 1.25 ≦ (Na ₂ O) / (SiO ₂ ) ≦ 1.5. Therefore, it is desirable that Na ₂ CO ₃ and SiO ₂ are blended. However, as described above, when the molten iron before treatment contains Si, (SiO ₂ ) is the total amount of the compounding amount in the flux and the SiO ₂ production amount due to the oxidation of [Si] in the molten iron.

Next, the conditions for the molten iron component will be described.

The higher the [C] in the molten iron, the more desirable it is for phosphorus removal. This is due to the following two reasons. One is that the higher the [C], the lower the melting point of the molten iron, and therefore the dephosphorization treatment can be performed at a low temperature. Generally, the oxidative dephosphorization reaction is an exothermic reaction,
The lower the temperature, the better for dephosphorization. Another reason is that the higher [C] is, the more thermodynamic concentration (activity) of P in molten iron increases due to the interaction of C—P, which is advantageous for dephosphorization.

However, there is an upper limit of [C] in actual operation in the sense that the decarburization step, which is a post-step of dephosphorization, is not burdened. Taking these points together, 2% ≦ [C] ≦ 4%
Can be said to be a desirable range.

[Si] in molten iron causes an increase in the amount of slag and a decrease in the basicity of slag in the case of oxidative dephosphorization with CaO-based and BaO-based basic slag, so the upper limit of [Si] should be restricted. Is common. However, in the method of the present invention, [S
There is no hard limit on the upper limit of [i]. This is also one of the major features of the method of the present invention. That is, since Na ₂ CO ₃ is used as a Na ₂ O source in the method of the present invention, [Si] is oxidized by CO ₂ generated during the treatment, and S is added to the slag layer.
It is removed as iO ₂ and becomes dephosphorized slag as (Na ₂ O) _x · SiO ₂ (x ≧ 1). Therefore, when the amount of [Si] in the molten iron is high, it can be dealt with by reducing the amount of SiO ₂ to be blended, and the usual pre-desiliconization treatment of molten iron is not essential. For example, (Na ₂
O) + (SiO ₂ ) flux is 100 kg per ton of molten iron
When used to produce a slag with (Na ₂ O) / (SiO ₂ ) = 1.5, [Si] is acceptable up to about 1.8%.

Fig. 4 shows the effect of [Mn] in molten iron on the dephosphorization rate and the amount of [Mn] oxidation loss when dephosphorization of high-manganese molten iron was performed using Na ₂ CO ₃ -SiO ₂ system flux. As shown in the figure, the achieved dephosphorization rate is about 5 to 30% compared to the case where the Mn concentration [Mn] _{ini in} molten iron before treatment is 18% compared to 13%.
Low. The amount of [Mn] oxidation loss was almost the same at this [Mn] _ini level.

According to the method of the present invention, the addition of manganese oxide in the flux makes it possible to further suppress [Mn] oxidation loss.
(Na ₂ O) / may be used flux Na ₂ CO ₃ -SiO ₂ system to 1.5 to 2.0 to the upper limit value of the dephosphorization rate the value of (SiO ₂₎ is obtained.

Next, the dephosphorization treatment temperature will be described.

The dephosphorization treatment temperature is, for the thermodynamic reason described above,
The lower temperature is better for the reason that evaporation of Na ₂ O is suppressed and melting loss of refractory material is reduced.

For example, it is preferably about 50 to 100 ° C. higher than the melting point of molten iron. In actual operation, it is desirable that the molten iron temperature before the dephosphorization treatment is 150 to 450 ° C. higher than the melting point, depending on the capacity of the furnace, considering the temperature drop due to the addition of flux.

Next, the amount of flux added will be described.

The required addition amount of flux depends on the initial [P] amount of molten iron to be treated and the target dephosphorization rate.
It is sufficient to select the required amount within the range of 20 kg to 120 kg per ton of molten iron.

The properties of the flux to be used are solid particles or powder, and the addition method may be either the top-up method or the injection method into molten iron, but the most effective method is the powder flux injection method. Dephosphorization progresses.

It is better to mix Na ₂ CO ₃ and SiO ₂ which compose the flux in advance before adding them. This is because Na ₂ O and SiO ₂ can be rapidly reacted to minimize evaporation of the Na ₂ O content. It is preferable to mix the manganese oxide with the powder in advance in the flux.

In addition, as an apparatus for carrying out the method of the present invention, AO
The D furnace is another furnace in which stirring gas can be introduced from the bottom. In addition, bubbling stirring with Ar gas etc. in a ladle,
It is also possible to perform treatment by impeller stirring.

(Example) Each of three types of high-manganese molten iron having the composition (before treatment) shown in Table 1 was melted in the atmosphere in a 10-ton electric furnace, and after pouring in an AOD furnace,
Similarly, the temperature was adjusted to the predetermined temperature shown in Table 1.

Then, the flux shown in Table 2 was added on the molten iron, and Ar was added.
Dephosphorization treatment was performed while stirring with gas for about 10 minutes. In the comparative example, the flux shown in Table ₂ and containing no MnO ₂ was used.

The chemical composition after the treatment is also shown in Table 1. The (Na ₂ O) / (SiO ₂ ) value in Table ₂ takes into consideration the amount of SiO ₂ produced by the oxidation of [Si] during the treatment.

As is clear from Table 1, in Example 1 and Comparative Example 1 in which [Mn] _ini was about 11%, the dephosphorization rate was 76%.
And 79%, the amount of [Mn] oxidation loss is 0.5% and
It was 1.2%.

In Example 2 and Comparative Example 2 in which [Mn] _ini was about 20%, the dephosphorization rate was 64% and 67%, and the [Mn] oxidation loss amount was 1.5% and 2.4%, respectively.

In Example 3 and Comparative Example 3 in which [Mn] _ini was about 24%, the dephosphorization rates were 60% and 65%, respectively, and the [Mn] oxidation loss amounts were 1.8% and 3.6%, respectively.

From the above results, by carrying out the method of the present invention,
Without significantly inhibiting the dephosphorization of high-manganese molten iron [M
n] It is clear that the amount of oxidation loss can be reduced.

(Effects of the Invention) According to the method of the present invention, by incorporating a manganese oxide in an inexpensive and easily available Na ₂ CO ₃ —SiO ₂ -based flux, the oxidation loss amount of Mn in molten iron is suppressed to a high level. Molten iron manganese can be efficiently dephosphorized. The method of the present invention is
It is extremely useful for manufacturing low-cost high-manganese steel whose production has been increasing in recent years.

[Brief description of drawings]

FIGS. 1, 2 and 3 show the results of dephosphorization experiments of high manganese molten iron with Na ₂ CO ₃ —SiO ₂ —MnO ₂ system flux. FIG. 1 shows [P] in molten iron. And [Mn], and (MnO) and (Na ₂ O) / (SiO ₂ ) in the slag, showing changes with time during dephosphorization treatment. FIG. 2 shows the amount of MnO ₂ added and the dephosphorization rate, [Mn ] shows the relationship between (MnO) of oxide loss amount and the slag, FIG. 3 shows the relationship between (Na ₂ O) / values and dephosphorization ratio and [Mn] oxidation loss of (SiO ₂₎ FIG. Figure 4 is shows the dephosphorization experiments of high manganese molten iron by Na ₂ CO ₃ -SiO ₂ based _{flux, (Na 2 O) / (} SiO
It is a figure which shows the relationship between the value of ₂ ), the dephosphorization rate, and the amount of [Mn] oxidation loss, comparing [Mn] _ini of 13% and 18%.

Claims (3)

[Claims] 1. A molten iron having a manganese content of 5% by weight or more,
A method for dephosphorizing high-manganese molten iron, which comprises contacting a flux containing Na ₂ CO ₃ , SiO ₂ and manganese oxide as main components. 2. The amount of Na ₂ O in Na ₂ CO ₃ compounded in the flux, and the total amount of SiO ₂ compounded in the flux and SiO ₂ produced by the oxidation of Si in the molten iron, 100 parts by weight, based on MnO.
_{2. The} method for dephosphorizing high-manganese molten iron according to claim 1, wherein a flux containing 10 to 25 parts by weight of ₂ is used. 3. The ratio of the Na ₂ O content in Na ₂ CO ₃ compounded in the flux to the total amount of SiO ₂ compounded in the flux and SiO ₂ produced by the oxidation of Si in the molten iron, that is, (Na ₂ O)
The compounding ratio of the flux is determined so that / (SiO ₂ ) is 1.25 to 1.5. (1) or (2)
The method for dephosphorizing high-manganese molten iron according to 1.