JPS5852539B2 - Manufacturing method of low link chromium alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for inexpensively producing a low phosphorus chromium alloy, which is an alloying agent for producing high chromium steel with a limited phosphorus content.

Usually, high carbon 7-erochromium is used as the main chromium source for producing high chromium steels such as stainless steel.

High-carbon quechrome is produced by melting and reducing chromite ore or its solid phase pre-reduced product in the presence of an excess of carbon agent such as coke.

In this process, nearly 90% of the phosphorus introduced as impurities in raw materials, such as chromium ore and coke, is transferred to the high carbon ferrochrome product.

Therefore, the phosphorus content of high carbon ferrochrome is almost uniquely determined by the phosphorus content of the various raw materials;
In recent years, the phosphorus content of chromite ore and coke has been increasing due to changes in the resource situation, and reflecting this, the phosphorus content of high carbon ferrochrome has also increased.

On the other hand, in the steelmaking stage, once the chromium content of the molten steel reaches 4 or higher, it is impossible to dephosphorize it using the oxidation refining method under basic slag. The phosphorus content of high chromium steel produced by melting also increases directly.

Therefore, it is becoming difficult to satisfy the phosphorus content standards for stainless steel.

On the other hand, as the negative effects of phosphorus on the quality of stainless steel become clearer, the number of steel types that require lower phosphorus content than before is increasing.

In response to this situation, there is an increasing demand for chromium sources with low phosphorus content.

Metallic chromium is commercially available as a chromium source with low phosphorus content, but it is very expensive, and if it is used even as a part of the chromium source, the cost of molten steel will increase significantly.

It is known that silicochrome, which is an intermediate product in the production of low carbon ferrochrome, can be dephosphorized by using a suitable slag (Japanese Patent Publication No. 36-3661).

That is, the molten metal with Si>47 (C<0.2) is mixed with basic slag (CaO・MgO−8iO2・
This is a method of processing with Al2O3 system).

Regarding the mechanism by which dephosphorization is carried out, see Japanese Patent Publication No. 36-3661.
Although it is not stated in detail, according to the research of the present inventors, 2(CaO) + [Si) → 2(Ca) + C3i02 2)
.

・・・・・・ As shown in (1), CaO is reduced by Si in the molten metal to generate free metal Ca, and 3(Ca)+2(P)→(CaaP2) ”” (
Through the reaction 2), it combines with phosphorus in the molten metal to produce calcium phosphide.

Note that () indicates the components in the slag, and [] indicates the components in the molten metal.

This method targets low carbon silicochrome, and this low carbon content is an essential condition for achieving dephosphorization in the above-mentioned slag.

That is, if the Si content in silicon chromium is less than 30%, the carbon content will be about 1% or more, but in this case, dephosphorization will hardly occur even if the flux is used.

This is because once the metal Ca is generated, it combines with carbon rather than phosphorus in the molten metal and is consumed as (Ca)+2C-+(CaC2) (3).

In the manufacturing process of low carbon ferrochrome, low carbon ferrochrome obtained by dephosphorizing with silicochrome and then desiliconization has the following drawbacks as a low phosphorous chromium source required for steelmaking. There is.

(1) Phosphorus content is not low enough.

Silicochrome 4 obtained by the above method is reacted with a mixture of chromium ore and quicklime to remove silica and reduce chromium,
It is made into low carbon ferrochrome, but at this time, almost all the phosphorus brought in from the chromium ore and lime enters the low carbon ferrochrome molten metal.

Therefore, even if the phosphorus is reduced at the silicochrome stage.

Phosphorus pickup occurs in proportion to the amount required for desilication.

Therefore, in order to finally obtain a chromium source with low phosphorus, it is desirable to lower the silicon ratio (higher chromium ratio) as much as possible at the stage of dephosphorization, but if the silicon ratio is less than 30, then For these reasons, efficient dephosphorization cannot be performed using known methods.

(2) Decarburization is not as difficult as the current advances in steelmaking technology, which is expensive.

Therefore, as a low-phosphorous chromium source, it is not necessary to simultaneously be low-carbon, but the low-phosphorous ferrochrome produced by the method of patent application No. 36-3661 is necessarily low-carbon for the reasons mentioned above, and has a low-linkage content. As a ROM source, the cost is relatively high.

These drawbacks should be solved by finding a method for efficiently dephosphorizing molten chromium alloys with low Si% (and therefore not low c%).

The present invention was obtained through various studies from this point of view, and includes adding calcium oxide of 30 to 75 weight percent, calcium fluoride of 10 to 50 weight percent, and calcium carbide to a molten chromium alloy containing Si of 8 to 30 percent. 943-50
This is a method for producing a low phosphorous chromium alloy, which is characterized by adding a flux containing a weight fraction as a main component and causing a reaction.

Hereinafter, a detailed explanation will be given based on examples.

First, a molten chromium alloy containing 8% or less of Si is prepared.

It is desirable that the Cr4 content in this molten metal be as high as possible and obtained at low cost, and the following method is used.

(1) Chromite ore, silica stone, and reducing please are blended and melted and reduced in an electric furnace.

(2) High carbon ferrochrome (usually Si content is 7% or less) is subjected to an operation to increase its Si content.

(a) Adding ferrosilicon or metal Si to high carbon ferrochrome molten metal.

(b) Mix high carbon ferrochrome molten metal and silicochrome molten metal.

(C) High carbon ferrochrome metal is melted and reduced by adding prescribed silica stone and reducing glass.

All chromium alloys obtained by such methods contain carbon close to the saturation value of their components, and also contain Cr.
The ratio of Cr/Fe depends on the grade of the chromite ore used as a raw material, but is approximately 1.5 to 2.5.

The reason for containing 8 to 30q6 Si is not to reduce carbonization of the molten metal as in the low-carbon ferrochrome manufacturing process, but to reduce calcium silicate to generate metal Ca according to formula (1).

When the Si content is 8% or less, the reducing power of the molten metal is weak, and the metal Ca required for dephosphorization cannot be generated in the slag.

On the other hand, if 5i is 30% or more, as mentioned above, the phosphorus pickup during desilization of the molten metal after dephosphorization becomes too large, which is not preferable.

From the viewpoint of reducing power and suppression of phosphorus pickup during desiliconization, it is necessary to set the Si content to 8 to 30, but practically it is 5i.
Optimally 1O~24%.

This molten metal is transferred to a container for dephosphorization treatment.

The reaction vessel may be a ladle-shaped vessel lined with a refractory material such as magnesia, and for reasons described later, it is desirable to be able to prevent atmospheric air from entering the vessel by covering it with a lid or the like.

A flux containing as main components 30 to 75 parts by weight of calcium oxide, 10 to 50 parts by weight of calcium fluoride, and 3 to 50 parts by weight of calcium carbide is added to the molten metal in the reaction vessel to cause a reaction.

Calcium oxide is used to generate metallic Ca necessary for dephosphorization, and because it is generated as a result of equation (1), dissolves SiO2 and reduces its activity, and causes the reaction of equation (1) to proceed to the right. is necessary.

Metallic Ca necessary for dephosphorization must be present in the slag in an amount of 0.s% or more, and for this purpose, the CaO content in the flux must be 30% or more.

On the other hand, if Ca0% is too high, the melting point will rise by 7 lacs, and the temperature of the molten metal that can be carried out in a normal ladle (1300 to 160
(0°C), molten slag cannot be obtained and the reaction cannot proceed efficiently.

Therefore, from the point of view of melting point adjustment, CaO must be less than 70%.

On the other hand, calcium fluoride lowers the melting point of flux, creating a slag with good fluidity, and the metal C produced.
In order to increase the dephosphorization efficiency, Ha Although it is indispensable, it is necessary to contain 10 parts or more in the flux for such a function to take place.

On the other hand, if the ratio is too high, it may increase the corrosion of the lining refractory or lower the Ca0% (it must be less than 50%).

Addition of calcium carbide is one of the points of the present invention.

This makes it possible to efficiently dephosphorize a high chromium molten metal with a CO content of 2% or more, which is impossible with known methods.

That is, a certain amount of Ca C in the flux in advance
By allowing 2 to exist, the reaction proceeds to the right side according to equation (3), and the generated metal Ca can be efficiently used.
This can be linked to dephosphorization according to formula (2).

The required minimum CaC2% depends on the c% of the molten metal to be treated, but the C% is approximately determined by Si4 (S i 8%
C%z for 60%, C% for 5i30% and 10%).

Required CaC for the aforementioned limit value of Si4: 8.30%
The 2' ratios are 2o and 3%, respectively.

If CaC2% is too low, the amount of metallic Ca to be deactivated increases according to equation (3), so in order to obtain a certain metallic Ca concentration, the amount of Si02 generated according to equation (1) increases, and This causes a vicious cycle in which the amount of metallic Ca further decreases, making it impossible to carry out efficient dephosphorization.

On the other hand, if CaC2 exceeds 50 weight, (CaC2)+2[Si]→(Ca)+2(SiC)・
... (4) The SiC generated in step 3 inhibits the fluidity of the slag, so that the reaction progresses poorly.

The most preferred range of ingredients is 40 to 60% calcium oxide, 20 to 3o% calcium fluoride, and 20 to 40qb calcium carbide when treating a molten metal with Si of 15%.

The above three components are necessary for dephosphorization, but other Fe
O, MnO, 5i02. It is desirable that the content of Al2O3, MgO, etc. is low, and the total amount that can be tolerated as impurities is 30 parts or less.

None of these impurities have a positive effect on the progress of dephosphorization in the present invention, but they have an adverse effect of lowering the (Ca) concentration due to dilution or oxidizing (Ca).

As such a flux, a combination of quicklime, fluorite) and calcium carbide is practically used.

After adding the flux, the molten metal and the flux are stirred by appropriate means to promote slag formation and dephosphorization reaction.

As a means for this, non-oxidizing gas may be blown through a porous plug attached to the bottom of the reaction vessel, or mechanical stirring may be performed using a stirrer.

In addition, in order to increase the dephosphorization efficiency, the metal Ca generated by equation (1) reacts with oxygen and nitrogen in the atmosphere to form 2(Ca)+02−+2(CaO) ”” (5)
In order to suppress consumption as 2(Ca)+N2→(Ca s N2), it is desirable to lower the oxygen partial pressure and nitrogen partial pressure in the atmosphere inside the reaction vessel.

For this purpose, it is sufficient to cover the reaction vessels and blow argon, hydrocarbon, etc. into each reaction vessel.

The molten metal subjected to the dephosphorization treatment as described above is subjected to a slag separation Lm, if necessary, and then subjected to a desilization treatment, and then cast.

For the desiliconization treatment, it is preferable to react with a molten mixture of chromium ore and lime in the same manner as in the production of ordinary low-carbon ferrochrome.

However, it is easier to work if 1-3% of Si remains in the molten metal, since the latent flow can be maintained well.

EXAMPLE The following five types of chromium alloys containing Si4 were prepared by mixing a high carbon ferrochrome melt and a silicochrome melt.

An auxiliary material consisting of a mixture of quicklime, fluorite, and calcium carbide in various proportions was added to this, and the mixture was stirred for 5 minutes using an impeller.

Ar gas was blown into the atmosphere to make it non-oxidizing.

After the dephosphorization treatment, a sample was taken and the molten metal was then desilicated using a molten mixture of chromite ore and quicklime.

The test conditions and analysis results are as follows.

As described above, the low phosphorus chromium alloy obtained by the present invention is a medium to high carbon Cr-Fe-Si alloy.

Alternatively, it is a Cr-Fe alloy, which has a higher Cr(1)C% than the low-phosphorus, low-carbon ferrochrome obtained by conventional methods, but has the characteristics of a high -ratio (2) low cost, and is suitable for steel making. As a low phosphorus chromium source for quality,
This is preferable from both cost standpoints.

The key points for producing such a low phosphorous chromium source are (1) adjusting the Si% in the molten metal before treatment to between 8 and 30; and (2) efficiently using 7 lux of CaO-CaF2 CaC2 system. This method is different from known methods in that it allows for dephosphorization (addition of 3 to 50% calcium carbide and restricts components that adversely affect dephosphorization).

The chromium source with a low impurity content obtained by this process is suitable as a raw material for smelting high-grade stainless steel whose impurity content is strictly regulated.

Claims (1)

[Claims] ISi: Calcium oxide 30-75% by weight, calcium fluoride 10-5% in chromium alloy melt containing 8-3o%
1. A method for producing a low phosphorous chromium alloy, characterized in that a reaction is carried out by adding a flux containing 0% by weight and 3 to 50% by weight of calcium carbide.