JPS6112818A - Dephosphorizing agent for molten iron containing chromium - Google Patents

Abstract

PURPOSE:To prevent the hardening of slag and to facilitate the removal of slag by incorporating a specified amount of carbon into BaCO3 in a BaCO3-base flux. CONSTITUTION:A BaCO3-base flux used as a dephosphorizing agent for molten iron contg. Cr is composed of 30-50wt% (expressed in terms of BaO) BaCO3 and the balance BaCl2 with inevitable impurities, and carbon is incorporated into the BaCO3 by >=2wt% of the amount of the BaCO<3>. When the amount of carbon exceeds 10wt%, the effect is not further enhanced, so the amount of carbon is regulated to 2-10wt%.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a dephosphorizing treatment agent for chromium (cr)-containing molten iron that has excellent dephosphorization (CP) properties.

<Prior art> In general, P in high Cr steel or nutless steel is a harmful impurity that does not adversely affect mechanical properties or stress corrosion cracking resistance. Strict regulations are being put in place for P.

However, the dephosphorization method for molten iron alloys containing Or, that is, the dephosphorization method using Ca0-FeO system or quicklime, etc.
In the method of adding a treatment agent as a flux and performing oxygen blowing, Cr is preferentially oxidized in large quantities, the nlug hardens, and oxidation of P is prevented, making it almost impossible to remove P. Therefore, in the production of low-P nutless steel, etc., expensive low-P
There was a problem in that it was necessary to deal with the use of ferroalloy, which inevitably led to high costs. Therefore,
In order to overcome the above problems, a few new blanks that perform so-called reductive dephosphorization using Ca have been proposed, but all of them can be said to be insufficient in that they involve the generation of harmful gases. It wasn't.

Against this background, the applicant previously filed a patent application filed in 1983.
As No. 38549, ``Dephosphorization (and removal S) was proposed. In this method, P in molten iron is reduced to P, 20 by an oxidizing agent.
This is an oxidative dephosphorization method in which the oxide of Z is stabilized with an oxide of an alkaline earth metal.This method achieves effective dephosphorization of molten iron containing Or, and also eliminates the generation of harmful gas. It is excellent and does not involve.

By the way, in the above-mentioned flux, a carbonate of the alkaline earth metal can be used instead of the oxide of the alkaline earth metal, and in this case, the C0.2 produced by the decomposition of the carbonate acts as an oxidizing agent. Therefore, it is reasonable that there is no need to separately add an oxidizing agent. Among these carbonates, EaCOJ is the most promising in terms of both effectiveness and price. However, with this flux using BaCO3, in the treatment of Or-containing pig iron, the nulag hardens and is difficult to remove, and as a result, the phenomenon of so-called re-P in the molten iron becomes noticeable.
In the end, sufficient P removal effect may not be obtained.

<Object of the invention> The present invention completely improves the above BaCO3-based flux, and
The purpose of the present invention is to provide a dephosphorous treatment agent that prevents the hardening of nulag in the treatment of pig iron and facilitates slag removal. , found the following facts. That is, dephosphorization of Or-containing pig iron using BaCO3-alkaline earth metal halide system Fufutsuknu
In, BaC0JO pyrolysis in flux: B
The C0.2 generated by aCO3-+Ba○+C0,2 is mixed with the metal Or in the molten iron, B COa + rcr)
→The reaction of Crλ03+3CO occurs to generate Cr, 203, which is dissolved in the slag. This Cr
The solubility of 2O3 is, for example, BaC0,, r 40Wf;
X ('BaO equivalent) - It is about 6% for BaCAs-based wax (melting point: about 1200°C), but in such cases, the properties of the Nurag vary greatly depending on the Crλ03 content. That is, the amount of Crλ03 in the Nurag As the amount of Cr-03 increases, the fluidity gradually decreases, and if the amount of Cr-03 exceeds 5%, it becomes difficult to remove the sludge due to hardening of the Cr-03. As shown in Figure 1, as the amount of Cr5O3 in pufferfish increases, the C
When the amount of raCD is 5% or more (region of arrow A), it suddenly becomes noticeable.

This generation of Crs○3, that is, C0 of metal Cr in molten iron.
As a countermeasure to suppress the oxidation caused by BaCO
3 contains a required amount of carbon (C) in advance, and Ba
00.00 between the C and COJ in the thermal decomposition of CO3.
An effective method is to cause the reaction 2+0→2CO to convert CO2 into CO. This method effectively reduces the amount of Cr2O3 produced in the slag, ensures the fluidity of the slag, and facilitates slag removal. This makes it possible to easily and effectively suppress back-up.

The present invention was made based on the above findings, and
Contains a o ~50 wt% in terms of iBa○, the remainder is B
This is a complete summary of a Cr-containing deP treatment agent characterized in that aC1-2 and impurity-like flux are baked and the Ba CO, y contains 2% or more of carbon.

Next, salting out of each component in the dephosphorization treatment agent of the present invention will be explained.

In the present invention, the amount of carbon contained in BaCO3 is limited to 2 or more because if it is less than 2%, the above formula CO-+C→
The reaction with 2CO is not sufficiently carried out and the CO of C0,2
This is because the conversion will be insufficient. Note that this amount of carbon is 1
If it exceeds 0%, the effect will be saturated, so it is desirable to set it to 2 to 10%.

Figure 2 shows BaC03 (BaO equivalent 40V9t%) -
The amount of carbon in the flux in the dephosphorization treatment of Or-containing pig iron using (4-containing BaC (b-BaCLλ-C) flux in BaCO3 of BaCt-based flux and varying the amount of carbon. (BaC0JJl
FIG. 2 is a diagram showing the relationship between the ratio of Cr (the same applies hereinafter) and the amount of Cr-03 produced in the slag. As is clear from the figure,
As the amount of carbon in the flux increases, the amount of Cr2O3 generated in the slag gradually decreases, and when the amount of carbon is 2% or more, a sulfur gas of less than 0r-035%, which has no problem in removing slag, can be obtained, and therefore the recycled Pg is also low. can be suppressed to Also, the amount of carbon 2
Between 10% and 10%, the effect of reducing the amount of CI" and 203 produced gradually improves, and the amount of Cr and 03 produced tends to gradually decrease, but when the amount of carbon exceeds 10%, the effect becomes saturated and levels off. .

In addition, EaCCb (D content is 30-5 in terms of BaO)
The reason why it is limited to 0 wt% is that if it is less than 30 wt%, the stabilizing effect of PJO,t produced by oxidation of P will be insufficient, and if it exceeds 50 wt%, flacne will not become a slag.

In addition, as a bathing agent for Flaknu, especially BaCt, 2
Among the alkaline earth metal halides, BaCCIJ was used because it is the most advantageous in the sense that it can effectively contribute to the reaction and fully demonstrate its functions. is.

<Effect of the invention> The present invention will be explained in detail by way of examples.

Example 1 Figure 3 shows the BaCO3-BaCt2-C system 7-
7'/All deP treatment of Cr-containing molten iron by Kunu f? :
, is a diagram showing the electric color-AOD furnace process. That is, first, Cr-containing bath pig iron adjusted to a required composition is melted in a melting step (1) in Denshiki, and then tapped in a tapping step (2) and charged into an AOD furnace. In the AOD furnace, after temperature elevation de-S1 in the de-S1 step (3), slag is removed in the slag removal step (4) to obtain bath iron having the composition shown in Table 1. 5), BaO4Q wt%-B
BaC0r Ba corresponding to ac, z60wt% composition
BaCO3-BaC-C based dephosphorizing agent 110 #/T of the present invention containing 6% C in BaC0J of Cta based 7"i'7 box was added, and A was heated at a temperature of 1500℃.
The molten iron is stirred for 8 minutes using an R-Ganu to remove phosphorus, and then the slag is removed in the slag removal step (6), and then the product is obtained in the normal refining step (7).The molten iron is treated according to these steps. Table 1 also shows the molten iron components at the time when the P removal process (5) is completed (before slag removal), and the diagram in Figure 4 shows the molten iron components before deP treatment, after deP treatment, and after normal smelting. The P content is shown.

In the above test, as shown in Table 1, the removal of P, furthermore, the removal of S and It was stopped very slightly at .002%.

Example 2 BaC○J (4 g wt% in terms of BaO) -Ba
Molten iron was treated under exactly the same conditions as in Example 1 except for using a dephosphorization treatment agent containing 1% carbon in Ct-based 7-7 Tsuknu BaC (b). Later P
The behavior of P, such as content and amount of returned P, was investigated.

Table 2 shows the results of the investigation in comparison with the results of Example 1 (example of the present invention).

Table 2 In the above test, in the example of the present invention, the slag was easily removed after adding the dephosphorizing treatment agent, whereas in the comparative example, the amount of carbon was too small, so the slag hardened and it was difficult to remove the slag. there were. As a result, as shown in Table 2, there was a large difference in the amount of regenerated P, and in the comparative example, the amount of regenerated P was 0.006%, and the P content after normal refining was 0.
．． 015%, whereas in the example of the present invention, the amount of returned P was 0.
．． The P content after normal refining was only 0.010%, achieving a sufficiently low P content.

As is clear from the above explanation, the theory P treatment agent of the present invention is
This is a high-quality, high-Cr steel that prevents a decrease in the fluidity of slag in the deP treatment of molten iron containing Or, facilitates slag removal, and minimizes return PM to reduce P. This greatly contributes to the production of steel and Nutenrenu steel.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between Cr in slag, the amount of 203 produced and Pi, and Figure 2 is a diagram showing the relationship between the amount of carbon contained in the dephosphorization treatment agent and the amount of Cr and 03 produced in slag. Figure 3 shows the BaCO3-EaCta-C flacunol 0r.
(Process diagram showing an example of the process of deP treatment of molten iron containing il-,
Figure 4 shows the process before and after the P removal treatment in the process of Figure 3.
It is a diagram showing the transition of P content after normal refining. 1: Melting process, 2: Steel tapping process, 3: Si removal process, 4.6
: Slag removal process, 5: P removal treatment process, 7: Normal smelting process

Claims (1)

[Claims] (1) Dephosphorization treatment of chromium-containing molten iron, characterized in that BaCO_3 contains 2% or more of carbon in a flux containing 30 to 50 wt% of BaCO_3 in terms of BaO, the balance being BaCl_2 and impurities. agent.