JPH055113A - Method for dephosphorizing molten high manganese iron - Google Patents

Abstract

PURPOSE:To dephosphorize molten high manganese iron while preventing erosion refractory by using Na2O base flux. CONSTITUTION:The flux mainly containing Na2CO3, SiO2 and MgO, is brought into contact with the molten iron having >=5wt.% Mg content. This MgO may be blended in the flux so as to become 5-20wt.parts to 100wt.parts the total of Na2O content in Na2CO3 blended in the flux, SiO2 content blended in the flux and SiO2 content produced with oxidation of Si in the molten iron and MgO content blended in the flux. Further, in order to reduce oxidizing loss of manganese at the time of dephosphorizing treatment, manganese oxide may be blended in the flux. In this case, blending ratio of the manganese oxide may become 10-25wt.parts to 100 parts the total of Na2O content in Na2CO3 blended in the flux, SiO2 content blended in the flux and SiO2 content produced with oxidation of Si in the molten iron and MgO content blended in the flux.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention efficiently dephosphorizes high-manganese molten iron having a manganese content [Mn] of 5% by weight or more by using a dephosphorizing agent which is inexpensive and suppresses the melting loss of refractory materials. On how to do.

[0002]

2. Description of the Related Art In recent years, as the fields of use of steel materials have diversified, many new steel types have been developed. However, the manganese content is about 5% (hereinafter, "%" means "% by weight" unless otherwise specified). The above means high manganese steel is one of them.

High-manganese steel as a non-magnetic steel has the advantages of not only being less expensive than austenitic stainless steel containing Ni, which is a competing material, but also having high strength and low magnetic permeability. In recent years, magnetic levitation railway members,
Applications are expanding as non-magnetic steels, structural steels, and wear-resistant steels for nuclear fusion device members, degaussing device members, electrical equipment members, and the like.

By the way, phosphorus in high-manganese steel is generally a harmful substance which adversely affects the hot workability and the resistance to weld cracking, so that 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, P contained in the manganese moves to the molten iron and the P content [P] of the molten iron increases. So Mn
It was customary to add ferromanganese as a source as far as the [P] standard allows, and supplement the remaining Mn content with metallic manganese so that [P] does not rise.

However, in this method, a large amount of expensive metallic manganese is used, so that 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 blending most of Mn with ferromanganese.

[0006] In response to such a demand, some methods of dephosphorizing molten iron of high manganese have been proposed so far, but they have not been put to practical use.

For example, even the 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 the formula (1), and this is converted into [P] in molten iron.
Dephosphorization is achieved by binding as in formula (2).

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

In order to prevent the air oxidation loss of [Ca], the reductive dephosphorization must be carried out in a non-oxidizing atmosphere. Therefore, the dephosphorization efficiency is easily affected by the atmosphere.

After the dephosphorization treatment, the slag easily reacts with moisture in the atmosphere as shown by the formula (3), and harmful phosphine (P
H ₃ ) is generated.

(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, Even when applying strong oxidation refining such as blowing oxygen with CaO-based slag during converter blowing as a dephosphorization method for high manganese molten iron, only [Mn] is preferentially oxidized and molten iron [P] cannot be removed. However, as proposed in JP-A-61-272312, JP-A-62-30810, and JP-A-62-227063, with a weak oxidizing power that does not excessively oxidize [Mn].
As shown in formula (4), [P] in molten iron is oxidized, and
As shown in the formula (5), the acid oxide P ₂ O ₅ which is a dephosphorization product
[P] in the molten iron can be removed by stabilizing Ba in the slag with BaO, which is a basic oxide that is significantly stronger than CaO in the converter slag.

2 [P] +5 [O] = (P ₂ O ₅ ) ... (4) (P ₂ O ₅ ) +3 (BaO) = (3BaO.P ₂ O ₅ ) ... (5) The dephosphorization method using BaO-based slag is easy to treat, and there is no problem of slag after dephosphorization treatment, but BaO-based slag is very expensive and the phosphorus removal cost is high, making it difficult to use for large-scale treatment. ..

As another method for oxidative dephosphorization of molten iron containing high manganese, “iron and steel” No. 74 (1988) No. 9 P. 1778, Na ₄
A dephosphorization method using Na ₂ O-based slag using SiO ₄ (sodium orthosilicate) and Na ₄ SiO ₄ —NaF ₂ flux has been introduced.

Although a very high dephosphorization rate can be obtained by the dephosphorization method using the Na ₂ O-based flux, Na ₄ SiO ₄ is expensive, white smoke is generated during the dephosphorization treatment, Mn] has a large amount of oxidation loss (0.9% for 14% Mn-5% C hot metal)
(There is ~ 1.6% [Mn] loss), and MgO refractories (e.g. magchrome and pure magnesia refractories) have large melting loss for Na ₂ O flux. This method is also difficult to put into practical use.

In order to solve the above-mentioned problems of the conventional dephosphorization method of high manganese molten iron, the present applicant has used an inexpensive and easily available flux containing Na ₂ CO ₃ and SiO ₂ as main components,
A method for dephosphorizing high manganese molten iron was developed, and Japanese Patent Application No. 1-
Filed as 306136.

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

(Na ₂ CO ₃ ) → (Na ₂ O) + CO ₂ (6) The strong basic oxide Na ₂ O produced is an acidic oxide produced by oxidizing [P] in molten iron. P ₂ O ₅ (reaction of the above formula (4))
Is fixed in the slag as shown in equation (7) below, 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 by the reaction shown in the formula (8) [ P] can be used to generate MnO 2 which acts as an oxidant.

CO ₂ + [Mn] → CO + (MnO) (8) The other main component, SiO _2, is Na, which easily evaporates at high temperatures.
_An appropriate amount is blended to keep ₂ O in the 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 equation (7).

As described above, according to the above method of dephosphorizing molten iron of high manganese proposed by the present applicant, it is possible to produce molten iron of low phosphorus and high manganese even if a large amount of ferro-manganese containing phosphorus is incorporated. You can In this dephosphorization treatment, in order to suppress the generation of white smoke during the treatment, the Na ₂ O content in Na ₂ CO ₃ mixed with the flux, the SiO ₂ content also mixed with the flux and the Si in the molten iron are oxidized. To generate Si
The ratio to the total of O ₂ minutes, that is, Na ₂ O / SiO ₂ may be set to 1.25 to 1.5.

When [P] in molten high-manganese 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 Mn oxidation loss can be suppressed when dephosphorization is performed by the method of the invention of the prior application, it is possible to manufacture high-melting iron manganese at a lower cost.

Therefore, the inventor of the present invention has proposed the above-mentioned Japanese Patent Application No. 1-3061.
The invention used in the invention of No. 36 further comprises a manganese oxide compounded with the flux.
Filed as No. 968. The manganese oxide, minutes Na ₂ O in Na ₂ CO ₃ were blended in flux, also a total of 100 weight of SiO ₂ minutes Si of SiO ₂ minutes and molten iron formulated in the flux generated by oxidation It is advisable to mix it in a proportion of 10 to 25 parts by weight with respect to parts.

As described above, the dephosphorization method of molten high-manganese iron developed by the present inventors has taken advantage of the use of Na ₂ O-based flux and solved most of its problems. Magnesia, pure magnesia, etc.
The prevention of melting damage of MgO-based refractories has not been solved.

[0025]

The object of the present invention is to provide Na ₂ C.
Using Na ₂ O-based flux containing O ₃ and SiO ₂ as main components, the method for dephosphorizing high-manganese molten iron is further improved,
It is an object of the present invention to provide a method for dephosphorizing high-manganese molten iron, which can prevent melting damage of refractory materials in a container for dephosphorization treatment.

[0026]

The present invention is characterized in that "a molten iron having a manganese content of 5% by weight or more is brought into contact with a flux containing Na ₂ CO ₃ , SiO ₂ and MgO as main components. Method of dephosphorization of molten iron manganese ”

The above MgO is Na ₂ C compounded in the flux.
O Na ₂ O content in the _3, SiO ₂ minutes to produce by oxidation of Si in SiO ₂ minutes and molten iron formulated in the flux, and 100 parts by weight of the total amount of MgO component formulated in the flux 5
It is advisable to mix it in the flux so that it becomes ~ 2O parts by weight.

Further, in order to reduce the oxidation loss of manganese during the dephosphorization treatment, MnO ₂ , MnO ₂ and Mn are contained in the flux.
₂ O _3, the Mn ₃ 0 ₄ oxide of manganese or the like may be blended. In that case, the amount of manganese oxide compounded was Na ₂ O in Na ₂ CO ₃ compounded in the flux, and compounded in the flux.
SiO ₂ minutes to produce by oxidation of the SiO ₂ minutes and the molten iron in Si,
In addition, it is preferable that the total amount of MgO contained in the flux is 100 to 25 parts by weight based on 100 parts by weight.

Furthermore, the ratio of the Na ₂ O content in Na ₂ CO ₃ blended in the flux to the total amount of SiO ₂ content blended in the flux and SiO ₂ fraction produced by the oxidation of Si in the molten iron, that is, , (Na ₂ O) / (SiO ₂ ) is preferably 1.25 to 1.5.

[Si] in molten iron is produced by oxidation.
The amount of SiO ₂ is [Si] is so may be calculated as being substantially all the SiO _2, can be easily obtained from the [Si] content of processed molten iron.

In the method of the present invention, MgO is preliminarily mixed in the Na ₂ CO ₃ --SiO ₂ type flux,
It prevents melting of refractory during dephosphorization. The operation will be described below. In the following description, molten iron components are indicated by [] symbols, and slag components are represented by ().
) Symbol.

[0032]

FIG. 1 shows the result of the crucible experiment which is the basis of the present invention. The test was conducted under the following conditions.

(A) Treated molten iron: [Mn] ≈18%, [C]
4kg, [P] ≒ 0.06% molten iron 2kg, treatment temperature: 1300 ° C (b) Flux used: Na ₂ CO ₃ -SiO ₂ -MnO ₂ -MgO 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 is (Na ₂ O) / (Si
O ₂ ) is about 1.5, and per ton of molten iron (Na ₂ O + Si
It was blended so that O ₂ ) = 100 kg. Furthermore, to prevent Mn oxidation loss, 20 kg of MnO 2 was added per ton of molten iron.

(C) Crucible used: MgO calcining crucible FIG. 1 shows the amount of MgO compounded in the flux (the weight when the total amount of Na ₂ CO ₃ , SiO ₂ and MgO compounded in the flux was 100 parts by weight). Part), the dephosphorization rate and (M
It is a figure which shows the relationship with the increase amount of gO). (Mg in the slag
The amount of O) increase is the amount of MgO eluted from the crucible.

From FIG. 1, it is clear that by premixing MgO in the flux, the elution of MgO from the crucible can be suppressed. The effect becomes clear from around 5 parts by weight of MgO, but it is desirable to add 10 parts by weight or more to almost completely suppress the elution of MgO from the crucible.

On the other hand, the dephosphorization rate does not substantially change up to about 20 parts by weight with the amount of MgO compounded, but if it exceeds that, it rapidly deteriorates. This is probably because the melting point of MgO is high and the fluidity of the slag decreases. Therefore, the MgO content in the flux should be limited to 20 parts by weight.

When the dephosphorization treatment is carried out using the Na ₂ O-based flux as described above, [Mn] in the molten iron is oxidized and transferred to the slag, resulting in a loss of [Mn]. .. This is because, as shown in Eq. (6) above, excess CO ₂ in the added Na ₂ CO ₃ oxidizes Mn as shown in Eq. (8), and the oxidation of Na ₂ O itself. It is presumed that [Mn] is oxidized by force as shown in the following equation (9).

Na ₂ O + Mn → MnO + 2Na (9) Such an oxidation loss of [Mn] can be suppressed by previously mixing manganese oxides such as MnO ₂ and MnO _{2 in the} flux. However, when the content of manganese oxide is excessive, 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. Further, the dephosphorization rate gradually decreases as the content of manganese oxide increases and the (MnO) concentration in the slag increases. This is the (Na
₂ O) concentration decreases due to dilution accompanying MnO ₂ formulation,
And MnO is a weaker basic oxide than Na ₂ O, which weakens the basicity of the entire slag.

Taking these points into consideration, when a manganese oxide is compounded in the flux, the amount of the Na ₂ CO ₃ --SiO ₂ based flux is {(Na ₂ O) + (SiO ₂ )} 100 kg / T. On the other hand, it is desirable that the compounding amount of manganese oxide be 10 to 25 kg / T.

Further, it is desirable to adjust the (Na ₂ O) / (SiO ₂ ) value of the flux. That is, as the value of (Na ₂ O) / (SiO ₂ ) increases, the dephosphorization rate increases, but the amount of [Mn] oxidation loss also increases. 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. In the range where (Na ₂ O) / (SiO ₂ ) exceeds 1.5, [Mn]
The amount of oxidative loss is rapidly increasing. Therefore, from the practical viewpoint of suppressing the oxidation loss amount of [Mn] to the lower limit value without significantly inhibiting the dephosphorization rate, the flux is 1.25 ≦ (Na ₂ O)
It is desirable that Na ₂ CO ₃ and SiO ₂ are blended so as to satisfy the condition of / (SiO ₂ ) ≦ 1.5. 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 produced by the oxidation of [Si] in the molten iron.

The required addition amount of the flux depends on the initial amount [P] of the molten iron to be treated and the target dephosphorization rate, but the required amount may be selected within the range of approximately 20 kg to 120 kg per ton of molten iron. ..

The flux used is in the form of solid particles or powder, and its addition method may be either the superposition method or the injection method into molten iron.
Dephosphorization proceeds most effectively in the case of the powdered flux injection method.

Na ₂ CO ₃ and SiO ₂ which compose the flux are preferably added after being mixed in advance. Then with Na ₂ O
This is because SiO ₂ can be reacted rapidly and evaporation of Na ₂ O content can be minimized. It is also advisable to mix the powder of MgO and manganese oxide in the flux in advance.

An apparatus for carrying out the method of the present invention is an AOD furnace or other furnace capable of introducing a stirring gas from the bottom of the furnace. It is also possible to perform bubbling stirring with Ar gas or the like and impeller stirring in a ladle. In any case, MgO is used as the refractory lining.
A system refractory is desirable. The reason is that zirconia-based and alumina-based refractories are inferior in corrosion resistance to basic slag containing a large amount of BaO and CaO. Even if a MgO 2 refractory is used, the method of the present invention can effectively prevent the melting of the refractory during the dephosphorization treatment.

[0045]

[Examples] Two types of high-manganese molten iron having the compositions shown in Table 1 before treatment were melted in the atmosphere in a 10-ton electric furnace, poured into an AOD furnace lined with magcro brick, and then adjusted to a temperature of 1550 ° C.

The flux shown in Table 1 was added to these molten irons, and dephosphorization treatment was performed while stirring with Ar gas for about 10 minutes. The flux used in the comparative example does not contain MgO.

The chemical composition of the molten iron after the treatment is also shown in Table 1. In addition, (MgO) in the flux in Table 1 is the weight% of MgO content with respect to the total amount of Na ₂ CO ₃ , SiO ₂ , MnO ₂ and MgO constituting the flux, and (Na ₂ O) /
The (SiO ₂ ) value is the SiO generated by the oxidation of [Si] during processing.
_{2 The} amount is taken into consideration.

As is clear from Table 1, in the examples in which MgO was previously mixed and the flux was used, Mg from the refractory was
Almost no elution of O 2 occurred. On the other hand, in the comparative example using the flux containing no MgO, the MgO was not found in the slag after the treatment even though the flux before treatment had no MgO.
Is also present at 10.6 parts by weight. This is Mg eluted from refractory
O.

There is no great difference in the dephosphorization rate between the examples and the comparative examples. In addition, since MnO ₂ is added to both fluxes, Mn loss is extremely small.

[0050]

[Table 1]

[0051]

According to the method of the present invention, it is inexpensive and easily available.
Using Na ₂ CO ₃ -SiO ₂ type flux, it is possible to efficiently remove phosphorus from high-manganese molten iron while suppressing melting loss of refractory materials. Further, if a manganese oxide is further added to the flux, the amount of [Mn] oxidation loss can be reduced to perform the treatment. INDUSTRIAL APPLICABILITY The method of the present invention is extremely useful for producing high manganese steel, which has been increasing in production in recent years, at low cost.

[Brief description of drawings]

[Fig. 1] Amount of MgO compounded in the flux (parts by weight when the total amount of Na ₂ CO ₃ , SiO ₂ and MgO compounded in the flux is 100 parts by weight), dephosphorization rate and (MgO in slag) )
It is a figure which shows the relationship with the increase amount of.

Claims (1)

Claims: 1. 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 MgO as main components. _2. The Na ₂ O content in Na ₂ CO ₃ mixed with the flux,
SiO ₂ minutes to produce by oxidation of Si in SiO ₂ minutes and molten iron formulated in the flux, and the 5~2O parts by weight per 100 parts by weight of the total amount of MgO component formulated in the flux
The method for dephosphorizing high manganese molten iron according to claim 1, wherein a flux containing MgO is used. _3. A Na ₂ O content in Na ₂ CO ₃ compounded in the flux,
Mg of 5~2O parts SiO ₂ minutes, and 100 parts by weight of the total amount of MgO component formulated in the flux that produced by the oxidation of the SiO ₂ minutes and the molten iron in Si formulated in the flux
2. The method for dephosphorizing high manganese molten iron according to claim 1, wherein a flux containing O and 10 to 25 parts by weight of manganese oxide is used. 4. A ratio of the Na ₂ O content in Na ₂ CO ₃ blended in the flux to the total amount of SiO ₂ content blended in the flux and SiO ₂ content produced by the oxidation of Si in the molten iron, that is, (Na ₂
The method for dephosphorizing high-manganese molten iron according to claim 1, 2 or 3, wherein the compounding ratio of the flux is determined such that O) / (SiO ₂ ) is 1.25 to 1.5.