JPS6233740A - Method for dephosphorizing mn alloy - Google Patents

Abstract

PURPOSE:To remove P from a powdery or granular Mn alloy efficiently by heat treating the Mn alloy together with a specified flux for dephosphorization at a temp. between the m.p. of the flux and a temp. below the m.p. of the Mn alloy. CONSTITUTION:A flux for dephosphorization contg. an inorg. salt which generates an oxidizing gas by heat treatment as the principal component is added to a powdery or granular Mn alloy. The flux has a lower m.p. than the Mn alloy and may contain the carbonate of an alkali or alkaline earth metal such as Na2CO3, K2CO3 or Li2CO3 as the principal component. The Mn alloy is heat treated together with the flux at a temp. between the m.p. of the flux and a temp. below the m.p. of the Mn alloy.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to Mn alloys (ferromanganese, silicomanganese, etc.) used as a Mn source when manufacturing high Mn steel, etc.
The present invention relates to a technology that can efficiently remove phosphorus contained in the water with a relatively simple operation.

[Conventional technology]

Among Mn alloys, ferromanganese and ferrosilicon are particularly important Mn sources when producing Mn-containing steel, and even in ordinary steel, about 0.5% Mn is usually added to improve mechanical properties. In high-grade steels used in areas with severe usage conditions, 1 to 2% or more may be added.

Recently, there has also been an increase in demand for high Mn steel containing 514 to 25% Mn as a nonmagnetic steel to replace austenitic stainless steel.

On the other hand, reducing P content is extremely important in improving the properties of steel materials, and in particular, in order to improve weldability, stress corrosion cracking resistance, etc., the P content in steel must be reduced as much as possible.

However, ordinary ferromanganese and silicomanganese contain about 0.15 to 0.2% of P, for example, 2%
If we try to use ferromanganese as the Mn source when manufacturing Mn steel, the P content in the steel will be 0.003 to 0.
．． 0O increases by about 5%, and P becomes low (usually P≦o, oot%
) will not be able to respond to requests. Therefore, as a Mn source used in the production of Mn-containing ultra-low P steel, very expensive Mn, etc., must be used, and an increase in production costs has become a serious problem.

Under these circumstances, various studies have been conducted with the aim of reducing the P content of ferromanganese, such as (a) a method of treating molten ferromanganese with a CaC2-CaF2 flux, and (b) a method of treating molten ferromanganese with a CaC2-CaF2 system flux; Several dephosphorization methods have been proposed, such as a method in which metallic Mg is used in combination with CaCl2 or MgC12, and solid state ferromanganese is added to a molten flux. However, all of these methods are reductive deP methods in which P is removed by converting it into Ca3P2 or Mg3P2, and have the advantage of no loss of Mn, but the deP atmosphere must be strictly controlled. Moreover, since highly active Ca and Mg are used, the treatment container is severely damaged, and furthermore, when the slag after the P treatment comes into contact with water, highly toxic PH3 is generated, making post-treatment difficult. There is. In particular, when solid ferromanganese is treated with molten flux, water must be used to separate the ferromanganese, which imposes a large burden of danger on the workers.

In addition, metal Ca, which is the most common Ca source used in the above-mentioned reductive dephosphorization method, is expensive and unsuitable for large-scale treatment.Moreover, when applied to ferromanganese, which has a large carbon content, Ca Since CaC2 is produced by reacting with the ferromanganese, it can only be applied to low carbon ferromanganese.

In addition, as an oxidative dephosphorization method for ferromanganese, it has been reported that a molten ferromanganese was treated with a 2Co, -KF-based dephosphorization flux to obtain a dephosphorization rate of about 60%. Dephosphorization is impractical because the oxidative consumption of Mn is significant.

[Problems to be Solved by the Invention] The present invention has been made focusing on the above-mentioned circumstances, and its purpose is to efficiently remove P contained in a Mn alloy by a simple method. The purpose of this project is to establish a technology for eliminating P.

[Means for Solving the Problems] The structure of the method of the present invention that has achieved the above-mentioned purpose is based on a desulfurization method mainly composed of an inorganic salt that has a lower melting point than Mn alloy and generates oxidizing gas by heat treatment. The gist is that the flux for P is heat-treated together with the granular Mn alloy at a temperature higher than the melting point of the flux and lower than the melting point of the Mn alloy.

[Function] In the present invention, the Mn alloy powder to be dephosphorized is
The dephosphorization reaction is promoted by heat treatment with a dephosphorization flux whose main component is an inorganic salt that has a lower melting point than the n-alloy and releases oxidizing gas upon heat treatment.
As an example of the basic deP mechanism during this period, alkali gold Ji
! Examples of cases where carbonate is used are as follows.

x2 co3 = x2 o+co2 co2 = co+.

2F+50=P205 nX20+P205= nX20 ・P205 (however, X
In the present invention, the deP reaction is carried out at a temperature higher than the melting point of the deP flux and lower than the melting point of the Mn alloy. The reason for setting the treatment temperature in this way is as follows. That's right. That is, the basic Pfi removal structure in the present invention is one that succumbs to oxidative dephosphorization as described above, and since the dephosphorization product is acidic, in order for the dephosphorization reaction to proceed efficiently, dephosphorization is necessary.
It is necessary to increase the basicity of the flux [concentration of basic oxides/concentration of S-type oxides (particularly 5iO2)], and in this sense, the amount of 5i02 produced should be suppressed as much as possible. However, since Si in the system has the function of increasing the activity of P and promoting the deP reaction, it is desirable that the Si concentration be as high as possible as long as Si oxidation (increase in Si02i) can be suppressed. When considering deP of Mn alloys, for example, if silicomanganese is subjected to deP treatment in a molten state, the deP flux and St react preferentially to form 5i02, and the basicity of the deP flux decreases. Not only does this decrease and the deP reaction is inhibited,
A large amount of Mn is oxidized and the Mn yield decreases. However, when Mn alloy powder is processed in an unmolten solid state, Si
The oxidation of Mn and Mn is suppressed to a low level, and the dephosphorization reaction can proceed efficiently. However, regarding the flux for removing P,
In order to increase the contact efficiency with the Mn alloy powder and efficiently proceed with the dephosphorization reaction, it is necessary to contact the Mn alloy powder in a molten state. In addition, dephosphorization is performed at a temperature below the melting point of the Mn alloy.
The dephosphorization flux used in the present invention, which is to be subjected to the reaction, is mainly composed of an inorganic salt that has a lower melting point than the M n alloy and generates oxidizing gas by heat treatment, as described above. Specific examples include alkali metal carbonates such as Na2CO3, 2COa, and Li2Cog, alkaline earth metal carbonates, and halides of alkali metals and alkaline earth metals. can be used in combination of two or more.

It should be noted that oxidative dephosphorization progresses more easily at lower temperatures when viewed from the reaction equilibrium, and for this purpose it is effective to lower the melting point of the flux.

AlCl3. It is also effective to mix an appropriate amount of a melting point depressant such as fluorite (fluorite, etc.) to lower the melting point of the flags for dephosphorization, thereby lowering the dephosphorization treatment temperature. Further, the treatment atmosphere is preferably an oxidizing atmosphere in order to efficiently promote oxidative dephosphorization, and the treatment is usually carried out in an air atmosphere. After the deP treatment, the Mn alloy can be recovered by dissolving and removing the deP flux by washing with water after the temperature is lowered.The basic structure of the present invention is as described above, and the specific deP effect will be described later. As will be made clear in the examples, as the P removal progresses, the S removal reaction and the St removal reaction also progress, and the effect of lowering the concentration of harmful impurities as a Mn source can also be enjoyed. On the other hand, a considerable amount of Mn is oxidized and consumed in the oxidative dephosphorization process;
Even when taking into account the reduction in yield, the cost as a Mn source can be significantly reduced compared to electrolytic Mn or the like.

[Example] Example 1 Mn-Fe alloy 7 ground to 145 mesh or less
．． 58 and Na2C0315g were mixed and put into a Ni crucible, held at 900°C for 1 hour to perform deP treatment, and then cooled down and washed with water to dissolve and remove the deP flux.
A Mn-Fe alloy was recovered. The chemical composition of the Mn-Fe alloy before and after the P removal treatment is as shown in Table 1, and the P content can be reduced to about 1/7, and the S content can also be reduced to about 1720. There is.

Table 1 (% by weight) Example 2 M n -F e -C ground to 145 mesh or less
Alloy 7.58 was mixed with 15 g of Na2CO3, put into a Ni crucible, and held at 900° C. for 30 minutes to remove P. After the treatment, the temperature was lowered, and the Mn-Fe-C alloy was recovered by washing with water and dissolving and separating the dephosphorous flux. The chemical composition of the M n -F e -C alloy before and after the P removal treatment is as shown in Table 2, and the P content can be reduced to 115 or less, and the S content can also be reduced to 1/10 or less. has been done.

Table 2 (% by weight) Example 3 7.5 g of silicomanganese ground into 16-32 meshes
and 15g of Na2CO3 were mixed and put into a Ni crucible.
Dephosphorization was performed by holding at 900"C for 2 hours. After treatment, the temperature was lowered and water was washed to dissolve and separate the dephosphorized flags to recover silicon manganese. The chemical components of silicomanganese before and after dephosphorization treatment were As shown in Table 3, in addition to being able to reduce the P content to below A, the S content was also reduced to below A.

Table 3 (% by weight) Example 4 Fe-Mn-C ground into 16-32 meshes
Alloy 7.58 and 2CO3 were mixed and put into a Ni crucible, and held at 1000°C for 1 hour to remove P.

After treatment, the temperature is lowered and washed with water to dissolve and remove the dephosphorized flux.
The e-Mn-C alloy was recovered. The chemical composition of the Fe-Mn-C alloy before and after the deP treatment is as shown in Table 4, and an excellent deP◆desulfurization effect is obtained.

Table 4 (!if1%) Example 5 Fe-Mn-C ground into 16-32 meshes
Alloy 7.58 with 15g of Na2COq and NaClBg
The mixture was combined with IR and put into a Ni crucible, and held at 800°C for 1 hour to remove P. After the treatment, the temperature was lowered and the product was washed with water to dissolve and remove the dephosphorous flux, thereby recovering the Fe--Mn--C alloy. The chemical composition of the Fe-Mn-C alloy before and after the deP treatment is as shown in Table ff15, and good deP and deS effects are obtained despite the low treatment temperature.

Table 5 (wt%) [Effects of the invention] The present invention is constructed as follows, but in short, it uses a dephosphorizing flux containing a specific inorganic salt as a main component, and is heated at temperatures above the melting point of the flux. In addition, by processing at a temperature below the melting point of the Mn alloy, P and S in the Mn alloy can be efficiently removed, and low PII and low S Mn alloys (ferromanganese, ferrosilicon, etc.) can be manufactured at low cost. I ended up getting it. As a result, it has become possible to obtain a Mn-containing steel with a low P content and excellent weldability and stress corrosion cracking resistance using an inexpensive Mn source such as ferromanganese or ferrosilicon.

Claims (1)

[Claims] A dephosphorization flux mainly composed of an inorganic salt that has a melting point lower than that of the Mn alloy and generates oxidizing gas by heat treatment is used together with a granular Mn alloy at a temperature above the melting point of the flux and below the melting point of the Mn alloy. A method for dephosphorizing a Mn alloy, the method comprising heat treatment.