JP3134789B2 - Demanganese method for high chromium molten iron alloy - 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 producing stainless steel having low manganese at a low cost, which relates to a method for removing manganese in refining stainless steel, particularly a stainless steel containing 5% by weight or more of chromium.

[0002]

2. Description of the Related Art Generally, stainless steel is used in an electric furnace, AOD.
When manufacturing by a process using a furnace, VOD furnace or VIM furnace, iron scrap and Fe-Cr are used as raw materials.
When alloys are used, but low-grade raw materials are used, manganese contained in those raw materials
Manganese level in stainless steel increases.

[0003] The standard value of the manganese content of stainless steel products is variously determined depending on the product characteristics such as weldability, but when the manganese content in the molten iron alloy becomes higher than the manganese standard value of the product. In manganese, manganese becomes an impurity.

Therefore, conventionally, raw materials are selected according to the manganese standard value of each stainless steel. For this reason, when the manganese standard value of the product is, for example, 0.5 to 0.1% by weight or less, the use of high-quality and high-quality raw materials is inevitable, resulting in high costs.

[0005] On the other hand, there is no disclosure of a method of effectively oxidizing and removing manganese which is an impurity while suppressing oxidation of chromium in a melting stage of an iron alloy containing chromium which is an easily oxidizable element. .

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a low-manganese stainless steel at low cost in a stainless steel, particularly a stainless steel containing 5% by weight or more of chromium. An object of the present invention is to provide a demanganese method capable of easily achieving a demanganese ratio of 70% or more.

[0007]

The gist of the present invention resides in the following method for removing manganese.

A method for removing manganese from a high chromium molten iron alloy containing 5% by weight or more of chromium, comprising a flux containing CaO as a main component and one or both of iron oxide and chromium oxide. The slag formed on the molten iron alloy has a basicity of 1.5
Hereinafter, the content of Al ₂ O ₃ in the slag is 10 to 30% by weight.
A method for removing manganese from a high chromium molten iron alloy, wherein the method comprises removing manganese.

Basicity = (% CaO) / (% SiO ₂ +% Al ₂ O ₃ ) In the above-described demanganese method of the present invention, the basicity of the slag formed on the molten iron alloy is determined in the flux and the flux. SiO ₂ and Al ₂ O ₃ in the slag existing on the molten iron alloy before addition of Si and Si in the molten iron alloy
Determine the SiO ₂ and Al ₂ O ₃ to produce a by oxidation of Al is preferable.

The flux used is CaO
And iron oxide or / and chromium oxide as an oxidizing agent, as well as SiO ₂ for adjusting the basicity, melting point and fluidity of slag formed on the molten iron alloy,
It is desirable to use one or more of Al ₂ O ₃ and CaF ₂ .

Furthermore, the lower limit of the desirable slag basicity is about 0.3, the desirable upper limit of the chromium content in the molten iron alloy is about 40% by weight, and the temperature of the molten iron alloy is 160
The temperature is desirably 0 ° C. or lower. Further, the lower limit of the temperature of the molten iron alloy is desirably set to a temperature that is about 50 ° C. higher than the melting point of the molten iron alloy from the viewpoint that the fluidity of the molten iron alloy can be secured.

In the present invention, as a method of inexpensively producing stainless steel, particularly low-manganese stainless steel containing chromium of 5% by weight or more, an inexpensive raw material is used regardless of the manganese standard value of the product, and the melting of the iron alloy is performed. Attention was paid to a method of effectively oxidizing and removing only manganese which is an impurity without oxidizing loss of chromium at the stage.

Specifically, in the molten iron alloy stage containing chromium, an oxidizing flux containing CaO and one or both of iron oxide and / or chromium oxide as an oxidizing agent is used, and molten iron is used. The manganese in the molten iron alloy is oxidized and removed by appropriately adjusting the basicity of the slag formed on the alloy and the Al ₂ O ₃ content in the slag.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION When smelting stainless steel from an inexpensive raw material, manganese mixed from the raw material causes
The manganese content in the molten iron alloy may rise above the specification upper limit of the product.

First, the reason why the subject of the method of the present invention is "a molten iron alloy containing 5% by weight or more of chromium" will be described.

In order to remove Mn in the molten iron alloy,
It is necessary to oxidize Mn to MnO by oxidative refining to make MnO a stable compound that is not easily reduced in slag. However, when the molten iron alloy containing chromium is oxidized and refined by an AOD furnace or a VOD furnace, the Cr in the molten iron alloy is oxidized simultaneously with Mn, and the Cr in the molten iron alloy is oxidized.
Also decreases. In particular, when the chromium content is 5% by weight or more, C
The oxidation of r is significant. This Cr loss causes an increase in manufacturing cost and must be avoided.

Therefore, in the method of the present invention, the object of the molten iron alloy is defined as "containing 5% by weight or more of chromium" which is required to reduce manganese. Although the upper limit of the chromium content is not limited, the method of the present invention can be applied to, for example, general stainless steel having a relatively high chromium content of about 30 to 40% by weight.

An important feature of the method of the present invention is that it contains CaO as a main component, contains one or both of iron oxide and chromium oxide as an oxidizing agent, has a relatively low basicity, and has a low basicity. With a flux that has a strong oxidizing power,
It is to remove manganese by oxidation without causing oxidation of chromium. That is, manganese ([Mn]) in the molten iron alloy is oxidized by oxygen ((O)) in the slag according to the following formula (A).

[Mn] + (O) → (MnO) (A) Next, the generated manganese oxide is stably retained in the slag by the acidic slag having a relatively low basicity, and the slag is used as a system. Remove outside.

More specifically, a flux containing CaO and one or both of iron oxide and chromium oxide as an oxidizing agent is brought into contact with the molten iron alloy containing chromium.

At this time, it is effective to mix one or more of SiO ₂ , Al ₂ O ₃ and CaF ₂ in order to adjust the basicity, melting point and fluidity of the slag. In particular, Al ₂ O ₃ has a lower acidity than SiO ₂ , but is itself an acidic oxide, can reduce the basicity of the slag, improve the fluidity of the slag, and It is effective in lowering the melting point of the slag to physically accelerate the reaction. Therefore, it is preferable to mix an appropriate amount of Al ₂ O ₃ .

In order to further improve the fluidity of the slag, it is effective to mix CaF _2.
When F ₂ is blended, the refractory is easily melted.
It is preferable to use Al ₂ O ₃ as much as possible.

Here, the slag subjected to demanganese is mainly a flux for demanganese addition and a slag brought in from a previous step before the flux is added to the molten iron alloy (hereinafter, referred to as a preslag). , And oxides such as silicon, aluminum, manganese, and chromium in the molten iron alloy oxidized during the demanganese treatment.

By the way, when a molten iron alloy containing chromium is brought into contact with a flux containing CaO as a main component and one or both of iron oxide and chromium oxide as an oxidizing agent, only manganese is obtained. Is oxidized and chromium is hardly oxidized for the following reason. That is, when the basicity of the slag is low (a state close to acidic), the manganese oxide is more stable in the slag than the chromium oxide.

[0025] In the method of the present invention, SiO ₂ in the flux to be added and Al ₂ O _3, and SiO ₂ before the slag and Al ₂ O _3, and SiO ₂ by oxidation of the fusion KimuTetsu in Si and Al and Al ₂ O ₃ into consideration, the basicity obtained by the following formula slag produced from these SiO ₂ and Al ₂ O ₃ with the flux in CaO is brought into contact with the molten iron alloy 1.5 or less, Al ₂ in the slag O ₃ content of 10-3
It must be 0% by weight.

Basicity = (% CaO) / (% SiO ₂ +% Al ₂ O ₃ ) Next, the results of a basic experiment that led to the above findings will be described.

18% by weight of chromium in a Tamman furnace
After melting 2 kg of the contained molten iron alloy into the atmosphere with a dense crucible made of MgO and adjusting the temperature to 1500 ° C., the CaO—Si
O ₂ -Al ₂ O ₃ 0.2k a -Fe ₂ O ₃ based flux
g was added, bubbling stirring was performed with Ar gas, and a demanganese treatment was performed. Note that Fe ₂ O ₃ in the flux
The amount was 0.02 kg. The initial components of manganese, carbon, and silicon in the molten iron alloy were 0.2%, 1.0%, and trace (tr.), Respectively, by weight. This experimental result will be described with reference to FIG.

FIG. 1 is a diagram showing the effect of slag basicity on the demanganese removal rate. As shown, the demanganese rate increases as the slag basicity decreases. From this result, it was found that the condition of the slag basicity for the demanganese ratio to be 70% or more was in the following range.

(% CaO) / (% SiO ₂ +% Al ₂ O ₃ ) ≦ 1.5 The lower limit of the slag basicity is not particularly limited. This is not preferred because the properties are significantly reduced. Further, when the slag basicity is 1.0 or less, the chromium oxidation loss of the molten iron alloy tends to be slightly large.

Next, a similar experiment was carried out with the slag basicity set to 1.5 and the temperature of the molten iron alloy kept constant at 1500 ° C., and the Al ₂ O ₃ content in the formed slag varied. This result will be described with reference to FIG.

FIG. 2 is a graph showing the effect of the Al ₂ O ₃ content in the slag on the demanganese removal rate. As shown in FIG. 2, the content of Al ₂ O ₃ in the produced slag is 10 to 10.
It can be seen that when the content is 30% by weight, the demanganese removal rate becomes 70% or more. This is because by adding an appropriate amount of Al ₂ O ₃ , the slag can be made less basic, the fluidity of the slag can be improved, and the melting point of the slag can be lowered to promote the reaction. From this result, the demanganese rate was 70%.
The Al ₂ O ₃ content in the slag for achieving the above is 10 to 10.
It turned out to be 30% by weight.

Further, it is desirable to control the temperature of the molten iron alloy to 1600 ° C. or less. In addition, the lower limit of the molten iron alloy temperature is necessary to ensure sufficient fluidity of the molten iron alloy,
Desirably, the temperature is about 50 ° C. higher than the melting point of the molten iron alloy.

Next, other desirable refining conditions for demanganese will be described.

The range of the total amount of the oxidizing agent (iron oxide, chromium oxide) in the flux is 3 to 3 times the total amount of the slag formed.
It is desirable to mix so as to be 40% by weight. That is, when the oxidizing agent in the total amount of slag is less than 3% by weight, demanganese does not progress due to insufficient oxidizing power of the slag. On the other hand, if it exceeds 40% by weight, the oxidation of chromium in the molten iron alloy is promoted and the amount of Cr ₂ O _{3 in} the slag increases, so that the melting point of the slag increases and the fluidity of the slag deteriorates.

It should be noted that within the above range, the mixing ratio when both iron oxide and chromium oxide are mixed is not limited.

The iron oxide used as the oxidizing agent in the flux includes, for example, Fe ₂ O ₃ , Fe ₃ O ₄ , FeO and compounds and mixtures thereof, and the chromium oxide includes, for example, Cr ₂ O ₃ And compounds and mixtures containing the same. Among them, chromium oxide is particularly effective because it has a function of preventing chromium in the molten iron alloy from being oxidized when the flux is added.

Further, a method of oxidizing iron and chromium in the molten iron alloy by blowing or blowing an oxidizing gas (eg, oxygen gas) to the molten iron alloy to easily adjust the composition of the slag oxidizing agent is easily considered. Can be However, in this case, it must be considered that the temperature of the molten iron alloy rises and that iron and chromium are oxidized and lost.

When SiO ₂ , Al ₂ O ₃ or CaF ₂ is used, the composition is as follows.

The desirable amount of CaF _{2 in} the flux is not more than 20% by weight of the total amount of slag formed. 2
If it exceeds 0% by weight, the refractory will be severely melted, making it difficult to use a flux.

The preferred amount of Al ₂ O ₃ in the flux, before the Al ₂ O ₃ by oxidation of the Al ₂ O ₃ and fusion KimuTetsu in Al in the slag in view, the slag basicity to be formed “(% CaO) / (% SiO ₂ +% Al ₂ O
₃ )) should be 0.3 or more and 1.5 or less. However, the amount of addition must be 10 to 30% by weight of the total amount of slag formed as described above.
This is because the Al ₂ O ₃ content in the slag is 1% of the total slag.
If the amount is less than 0% by weight or more than 30% by weight, the fluidity of the slag deteriorates, and the reaction is not accelerated.

The desired amount of SiO _{2 in} the flux is determined by the amount of SiO ₂ in the pre-slag and the amount of S _{2 in the} molten iron alloy.
The basicity of the slag “(% CaO) / (% SiO ₂ +% Al ₂ O ₃ )” may be set to 0.3 or more and 1.5 or less in consideration of SiO ₂ due to oxidation of i. .

The desirable range of the flux addition varies depending on the manganese content in the molten iron alloy, the target product manganese standard value, the silicon content in the molten iron alloy before treatment, and the like. 150kg / alloy-t
It is about.

C (carbon) in the molten iron alloy does not directly affect the demanganese behavior directly, but the higher the C, the lower the melting point of the molten iron alloy. It is.

The method for adding the flux is not particularly limited as long as the flux can be brought into contact with the molten iron alloy. For example, the method of injection from the top of the molten iron alloy is sufficient, but injection into the molten iron alloy is more effective.

In the method of the present invention, stirring of the molten iron alloy and the slag is important. That is, as a stirring method, bubbling stirring by Ar gas is generally used, but mechanical stirring by an impeller, and further, a stirring effect by natural fall such as addition of a flux when a molten iron alloy before processing is received in a processing vessel. The use of is also conceivable.

Accordingly, the container and the timing of the treatment for removing manganese are carried out in the electric furnace after melting down in the electric furnace, or when receiving from the furnace to the ladle, and further in the ladle, the AOD furnace and the VOD furnace. And the like.

It is desirable that the slag after demanganese removal be removed from the molten iron alloy in order to prevent manganese from being deoxidized in the next step of deoxidation. However, slag chill (solidification of slag) is performed by adding massive CaO or the like. ).

[0048]

【Example】

(Example of the present invention) In melting various stainless steels,
Using a 40 ton AOD furnace, the A content for 1 wt% C content
1, Si, Mn and Cr have the contents shown in Table 1,
A flux having a composition shown in Table 1 was added to a molten iron alloy having a temperature of 1500 ° C. Ar gas amount of bottom blowing stirring is 2
0 Nm ³ / min and the processing time were 10 min. Table 1 also shows the Mn and the demanganese ratio in the molten alloy before and after the treatment.

[0049]

[Table 1]

As shown in Table 1, the present invention examples (Nos. 1 to 6)
In each case, the demanganese ratio was as good as 70% or more.

On the other hand, the comparative example (No. 7) having a slag basicity of 1.6 and the No. 8 and 9 containing Al ₂ O ₃ in the slag as large as 9% by weight and 33% by weight, respectively. Also, the demanganese rate was unsatisfactory at 55% or less.

[0052]

According to the method for removing manganese of the present invention, stainless steel, in particular, low manganese stainless steel containing 5% by weight or more of chromium can be produced at low cost.

[Brief description of the drawings]

FIG. 1 is a diagram showing the effect of slag basicity on the demanganese rate.

FIG. 2 shows the effect of Al ₂ O _{3 in} slag on the rate of demanganese removal
FIG. 4 is a diagram showing the influence of the amount.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-9-104913 (JP, A) JP-A-47-33810 (JP, A) JP-A-3-158410 (JP, A) JP-A 52-104 133015 (JP, A) "Materials and processes" vol. 9, No. 4 (1996) The Iron and Steel Institute of Japan p. 869 (58) Field surveyed (Int. Cl. ⁷ , DB name) C21C 7/00, 7/04, 7/076

Claims (3)

(57) [Claims] 1. A method for removing manganese from a high chromium molten iron alloy containing 5% by weight or more of chromium, comprising CaO as a main component and one or both of iron oxide and chromium oxide. Using the flux, the basicity determined by the following equation of the slag formed on the molten iron alloy is 1.5
Hereinafter, the content of Al ₂ O ₃ in the slag is 10 to 30% by weight.
A method for removing manganese from a high chromium molten iron alloy, wherein the method comprises removing manganese. Basicity = (% CaO) / (% SiO ₂ +% Al ₂ O ₃ ) 2. The basicity is determined by oxidizing SiO ₂ and Al ₂ O ₃ in slag present in the flux and on the molten iron alloy before adding the flux, and by oxidizing Si and Al in the molten iron alloy. de manganese method of high chromium molten iron alloy according to claim 1, wherein the determination by the SiO ₂ and Al ₂ O ₃ to be generated. 3. The flux according to claim 1, wherein the flux is SiO ₂ , Al ₂ O.
_{3. The} method for removing manganese from a high chromium molten iron alloy according to claim 1, comprising one or more of CaF ₂ and CaF _{2. 4} .