JP2897640B2 - Dephosphorization method of high chromium high manganese molten alloy iron - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for effectively removing phosphorus (P) as an impurity from a high Cr high Mn molten alloy iron.

[0002]

2. Description of the Related Art High-Mn steel has the advantages of low cost, high strength, and low magnetic permeability compared with Ni-containing austenitic stainless steel. In recent years, magnetic levitation railways, nuclear fusion devices, Its use is expanding as non-magnetic steel, structural steel, and wear-resistant steel used for members such as degaussing equipment and electric equipment.

In recent years, in order to improve the corrosion resistance of the high Mn steel, a high Mn steel containing 2% by weight or more of Cr has been studied. For example, a high Cr high Mn steel such as an 18% Cr 15% Mn steel has been studied. Demand is increasing.

[0004] In general, P in a high Cr high Mn steel is a harmful component that adversely affects hot workability and melt cracking. High Cr
In the production of high Mn steel, ferrochrome and ferromanganese containing a large amount of P are used as the Cr source and the Mn source [P]
By adding as much as the specifications allow (or in some cases, as long as the [C] specifications allow), the remaining Cr and Mn are supplemented with metallic Cr and metallic Mn to form [P] It always satisfies the standard.

[0005] However, in this method, expensive metal Cr and metal Mn are used in large amounts, so that the melting cost is increased.
In order to inexpensively produce high Cr high Mn steel, most of the Cr
And ferrous manganese are supplied by inexpensive ferrochrome and ferromanganese, and high-Cr, high-Mn molten alloy iron (hereinafter, molten iron is referred to as molten iron) can be dephosphorized (hereinafter, referred to as P). Establishment is essential.

[0006] Regarding the removal of molten iron containing Cr or Mn,
The following technique is disclosed in which a slag having a P removal ability is formed by adding an additive for removing P to the surface of molten iron to remove P by mechanical stirring or gas bubbling.

[0007] The molten iron containing Cr is disclosed in Japanese Patent Application Laid-Open No. 58-3101.
No. 1 discloses a BaO-BaCl ₂ -Cr oxide-based de-P method using an additive for removing P, and JP-A-59-47349 discloses BaCO ₃ -BaCl ₂
A method for removing P with an additive for system removal of P is shown.

[0008] The molten iron containing Mn is disclosed in JP-A-62-3081.
0, JP-A-61-272312, JP-A-62-227063 or JP-A-2-267211 include BaO, BaCO ₃ , and BaCl _{3 on the} same principle as in the method of JP-A-59-47349. ₂ , Ba (OH)
It is shown that de-P by ₂ or the like is possible.

[0009] That is, the de-P
The principle is that, as shown in the following equation (1), P in the molten iron is oxidized with a weak oxidizing power (oxygen or oxygen gas from solid oxide) that does not oxidize Cr or Mn, and then the following (2) as shown in equation, the BaO is significantly stronger basic oxide than CaO in converter slag, acidic oxide P ₂ is a de-P product
The O ₅ by stabilizing in the slag, is that the removal of P in the molten iron.

2 [P] +5 [O] → (P ₂ O ₅ ) ・ ・ ・ ・ ・ ・ (1) (P ₂ O ₅ ) +3 (BaO) → (3BaO · P ₂ O ₅ ) ・ ・ ・ ( 2) BaCO ₃ , BaCl ₂ , Ba (OH) _2, etc. are slags containing BaO after the reaction, and these are collectively referred to as BaO-based flux and slag as BaO-based slag.

[0011]

The above-mentioned prior art includes the following problems in the case of molten iron containing both high concentrations of Cr and Mn.
No method has been disclosed for effectively removing P without losing Mn or Mn, and development of an optimal dephosphorization method is desired.

It is an object of the present invention to provide a suitable P removal method for high Cr high Mn molten alloy iron.

[0013]

The gist of the present invention is as follows.
In the way.

In a molten iron containing 2% or more of Cr and 2% or more of Mn in weight%, at least one of BaO, BaCO ₃ , Ba (OH) ₂ and BaSO ₄ contains 20 to 90% in terms of BaO, BaCl ₂ and mixtures of one or more BaF ₂ consists of 20-80%, further Cr oxide with respect to the 100 parts by weight, Mn oxide, 10 to 30 parts by weight of one or more of Fe oxide and the oxidizing gas A method for removing high Cr and high Mn molten alloy iron, comprising adding a mixed additive for removing P.

[0015] The additive for removing P is one or more of BaO-based flux, one or more of BaCl ₂ and BaF ₂ as a solvent, and Mn, Cr or Fe as an oxidizing agent to suppress the oxidation of Mn and Cr. One or more oxides or oxidizing gases are used in combination.

[0016]

The molten iron targeted for de-P in the method of the present invention is [C
r] and [Mn] are both high Cr and high Mn molten iron of 2% or more,
For example, Mn: High manganese steel of 2 to 30%. In addition to Mn, Cr:
This is molten iron for producing steel containing 2% or more and other alloying elements. This is melted by an ordinary method using an inexpensive ferromanganese or ferrochrome as an Mn source or a Cr source by an electric furnace, a converter, or the like.

Such molten iron is housed in a vessel such as a furnace or a ladle into which a stirring gas can be introduced from the bottom of the furnace, and an additive for removing P is added by an injection method or an overhead method to remove P. Allow the reaction to take place. In addition, as a container, a refining furnace such as a ladle or an AOD furnace equipped with a gas injection lance or an impeller stirring device can be used.

The additive for removing P used in the method of the present invention is Ba
It consists of three types of components: O-based flux, medium solvent and oxidizing agent. That is, BaO which is a strongly basic oxide and has a de-P ability or a compound which produces BaO 2 at a high temperature
Based on a mixture of at least one BaO-based flux of CO ₃ , Ba (OH) ₂ and BaSO ₄ and at least one medium solvent of BaCl ₂ and BaF ₂ (hereinafter referred to as BaO-based flux and medium solvent) (Hereinafter referred to as a base mixture), and an oxidizing gas typified by Mn oxide, Cr oxide, Fe oxide, oxygen and the like as an oxidizing agent for oxidizing P according to the above formula (1). A mixture of more than one species.

The reason why the composition of the additive for removing P used in the method of the present invention is determined as described above will be described. % Means% by weight.

(1) BaO in base mixture: FIG.
Shows an example of the relationship between the (BaO) concentration in the slag and the de-P ratio when the molten iron of [C] = 3%, [Cr] = 18%, and [Mn] = 15% is de-P-treated. FIG. The de-P ratio (%) is defined by the following equation.

[0021] In the de-P treatment, 2 kg of the high Cr high Mn molten iron was melted in the air in a high frequency furnace and maintained at 1400 ° C., and further a Mn oxide and a Cr oxide were added to a base mixture containing BaO and BaCl _2. Demixing
An additive for P was added from above the molten iron, and the reaction was performed for 30 minutes while publishing with Ar gas.

[P] in the molten iron is expressed by the equation (1) described above.
Reaction into slag by reacting according to equation (2), approximately
It decreased from the initial value of 0.060 to 0.100% to about 0.020 to 0.050%.

As shown, (BaO) up to 60% (BaO)
As O) increases, the de-P ratio increases. This is (Ba
This is because the higher the O), the higher the basicity of the slag, and the more stable the acidic oxide P ₂ O ₅ is in the slag. However, when (BaO) exceeds 60%, the P removal ratio tends to decrease. This is presumably because the higher the (BaO) 2, the higher the viscosity of the slag, and the more difficult it is to physically remove P.

From the above results, it is clear that (BaO) should be in the range of 20 to 90%, more preferably 40 to 80%, so that the range of BaO in the base mixture is 20 to 90%.
%.

The components of the BaO-based flux include, in addition to BaO, BaCO ₃ , Ba (OH) ₂ , and BaSO ₄ which form BaO after the reaction.
Can be used. When using BaCO ₃ , Ba (OH) ₂ , or BaSO ₄ instead of BaO or together with BaO,
The amount may be adjusted so that the value converted into BaO or the sum thereof is in the above range.

(2) BaCl ₂ and BaF ₂ in the base mixture: Both BaCl ₂ and BaF ₂ remain in the slag, lower the melting point of the slag, promote slagging, and promptly remove P. It is a component that acts as a medium solvent for the progress, and it is necessary to select one or both of them and blend them in the range of 20 to 80%.

The upper limit of the blending amount of 80% is a value necessary to secure at least 20% or more of the above-mentioned (BaO) having the P-removing ability in the slag. If the ratio of the solvent exceeds 80%, the (BaO) concentration will be too low, and the P removal ratio will be low. On the other hand, the lower limit of 20% is a value necessary for giving sufficient fluidity to the slag in the de-P treatment and promoting de-P. That is, the ratio of the solvent is less than 20% or 80%
Is exceeded, the de-P efficiency decreases.

(3) Regarding the oxidizing agent in the additive for removing P: The additive for removing P used in the method of the present invention by adding an oxidizing agent for oxidizing P to the base mixture having the above composition. And

The oxidizing agent is a valuable metal in the molten iron.
It has weaker oxidizing power than oxygen gas so as not to oxidize Cr and Mn, and can maintain (MnO) and (Cr ₂ O ₃ ) in BaO-based slag at a high level from the beginning of the de-P treatment. It is desirable to use one or two of Mn oxide and Cr oxide.

However, in the case where the loss of Mn or Cr is slightly tolerated, an inexpensive general Fe or Cr oxide is added to either the Mn oxide or the Cr oxide.
Oxidizing gas typified by oxide or oxygen There is no problem to mix oxidizing gas typified by Fe oxide or oxygen with both Mn oxide and Cr oxide.

The proper mixing ratio of the oxidizing agent to the base mixture is 10 to 30 parts by weight based on 100 parts by weight of the base mixture. Here, 100 parts by weight of the base mixture means Ba
Consists of one or more of O, BaCO ₃ , Ba (OH) ₂ and BaSO ₄
The sum of BaO-converted weight and BaC
the sum of the sum of the weight of the medium solvent consisting of one or more of l ₂ and BaF ₂ is obtained as 100.

The reason why the appropriate mixing ratio of the oxidizing agent is limited to the above range will be described with reference to FIGS.

FIG. 2 shows Mn in the oxidizing agent when the composition of the base mixture of the additive for removing P and the mixing ratio of the oxidizing agent are fixed.
It is a figure which shows an example of the relationship between the compounding ratio of oxide and Cr oxide, and the change of [Mn] and [Cr] in molten iron before and after P removal processing.
The components and temperature conditions of the molten iron are the same as those in FIG.

As shown in the figure, it can be seen that the loss of Mn and Cr can be suppressed by setting the mixing ratio of Mn oxide in the oxidizing agent to 20 to 80%.

FIG. 3 is a graph showing an example of the relationship between the mixing ratio of the oxidizing agent and the P removal ratio when the composition of the base mixture of the P removal additive is constant. The components and temperature conditions of the molten iron are the same as those in FIG.

As shown in the figure, on average, the P
It can be seen that the total mixing ratio of the oxidizing agent needs to be 10 to 30 parts by weight to obtain the ratio. Here, the lower limit is a value that obtains the minimum oxidizing power required for de-P, and the upper limit is a value that ensures the fluidity of the additive for de-P and physically promotes de-P.

The amount of the base mixture consisting of the BaO-based flux and the solvent is determined by the P content of the molten iron to be treated,
Determined from the target P content after dephosphorization and other conditions, it is about 20-120 kg per ton of molten iron, usually 50-10
A range of 0kg is acceptable.

As a method for adding the dephosphorizing additive to the molten iron, a method in which granules or aggregates are placed on the bath surface may be used, but a powdery dephosphorizing additive is added to the molten iron by a suitable gas. According to the injection method, a good phosphorus removal effect can be obtained. In this case, the particle size of the powder is desirably in the range of 50 to 200 μm. The upper and lower limits of the particle size are the minimum and maximum particle sizes at which the powder can be smoothly transported by the carrier gas. When an oxidizing gas is used as the oxidizing agent, a mixed gas of the oxidizing gas and the inert gas is preferably used as a carrier gas for injection.

The temperature for removing P is desirably as low as possible in order to reduce the erosion of the refractory because the reaction of the formula (1) is an exothermic reaction.

[0040]

EXAMPLES High Cr and high Mn having the components shown in Tables 1 and 2
The molten iron was melted in the air in a 50-ton electric furnace and poured into a molten iron at about 1600 ° C into a 50-ton AOD furnace.
An additive for use (particle size: 10 to 50 mm) was added by an overhead method, and the mixture was stirred by bubbling treatment in which Ar gas was blown in through a horizontal bottom tuyere for 10 minutes. Tables 1 and 2 show the change in components and the P removal ratio before and after the P removal treatment.

[0041]

[Table 1]

[0042]

[Table 2]

In the de-P treatment according to the method of the present invention, [P] after the treatment was low in each case, and the de-P ratio was attained about 40 to 70%. As shown in Comparative Examples 1 and 2, when the (BaO) conversion value in the base mixture is out of the range of 20 to 90% by weight, and as shown in Comparative Examples 3 and 4, the mixing ratio of the oxidizing agent is In the case where the amount is out of the range of 10 to 30 parts by weight with respect to 100 parts by weight of the base mixture, both reached (P),
Both the P removal rates were poor.

[0044]

According to the method of the present invention, it is possible to effectively remove the impurity P from the high Cr high Mn molten iron, and it is possible to remove the P by about 40 to 70%.
Is achieved.

[Brief description of the drawings]

FIG. 1 (BaO) in slag when molten iron with [C] = 3%, [Cr] = 18%, and [Mn] = 15% is de-P-treated by the method of the present invention (overlaying method). It is a figure showing an example of the relation between concentration and the removal of P ratio.

FIG. 2 is a graph showing an example of the relationship between the mixing ratio of Mn oxide and Cr oxide in an oxidizing agent and changes in [Mn] and [Cr] in molten iron before and after P removal treatment.

FIG. 3 is a graph showing an example of the relationship between the mixing ratio of the oxidizing agent and the P removal ratio.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C21C 1/02 110 C21C 7/00 C21C 7/04 C21C 7/064

Claims (1)

(57) [Claims] 1. A molten ferroalloy containing 2% or more of Cr and 2% or more of Mn in terms of% by weight includes BaO, BaCO ₃ , Ba (OH) ₂ and BaS
At least one of O ₄ is 20-90% in terms of BaO, BaCl ₂ and BaF
_A mixture comprising at least one of ₂ to 20% to 80%,
[0086] High Cr high Mn characterized by adding an additive for dephosphorization obtained by mixing 10 to 30 parts by weight of at least one of Cr oxide, Mn oxide, Fe oxide and oxidizing gas with respect to parts by weight. Dephosphorization method of molten alloy iron.