JPS5949281B2 - Stabilization treatment method for halide dephosphorization flux of calcium carbide and alkaline earth metals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides molten metals that are difficult to dephosphorize by ordinary oxidation refining methods.
For example, calcium carbide and alkaline earth metal halides such as CaC2 used to dephosphorize high chromium molten metal.
- A method for stabilizing CaF2-based flux.

Hot metal and molten steel of normal composition can be easily dephosphorized by oxidative refining in the presence of basic slag.

However, in molten metal containing large amounts of easily oxidized elements such as chromium and silicon, when oxidation refining is performed for dephosphorization, a large amount of these valuable elements will be oxidized, and they will enter the slag and cause physical and chemical damage. Until now, no effective dephosphorization method has been found because it weakens the dephosphorization ability.

However, in recent years, the quality of raw materials for ferrochrome production, such as coke and chromium ore, has been deteriorating, and in particular, the phosphorus content has been on the rise.As a result, the phosphorus content of raw materials for stainless steel melting, such as ferrochrome and stainless steel scrap, is increasing.

On the other hand, the phosphorus content of stainless steel, which is a final product, is increasingly being regulated due to material considerations.

Therefore, there is a strong demand for dephosphorization treatment of high chromium molten metal.

As a method to enable dephosphorization of high-chromium molten metal, the present inventors first developed a method for dephosphorizing high-chromium molten metal.
He invented a method for reacting a flux containing 2 as the main component under conditions where the atmosphere is sealed from the atmosphere and the supply of oxygen from the slag is suppressed. 5O-99143).

In this method, by selecting various conditions such as the carbon content of the molten metal, the flux component and the amount used, it is possible to perform arbitrary dephosphorization even on high-chromium molten metal.

This method is completely different in principle from conventional dephosphorization by oxidative refining, and can be called "reductive dephosphorization."

That is, when carbon-unsaturated molten metal and fluff whose main components are calcium carbide and calcium oxide are reacted in a non-oxidizing atmosphere, (CaC2) → (Ca) +2 [Ca ・ ・ ・
・ ・ Fist (1) produces free metallic calcium, 3 (Ca) + 2 (P) - + (Ca3P2) * - * (2
) dephosphorization occurs.

In implementing this, the important techniques are to prevent phosphorus from returning to the molten metal after dephosphorization treatment and to stabilize the separated flux.

In other words, if the atmosphere becomes oxidizing after dephosphorization, the metallic calcium in the flux will be oxidized and consumed (
2) The reverse reaction of the formula proceeds and rephosphorus occurs.

In order to avoid this, it is necessary to separate the molten metal and stainless steel as completely as possible after the dephosphorization reaction is completed.

When this separated flux is cooled in the atmosphere, phosphorus compounds in the flux react with water vapor to generate phosphine (PH3).

(ca3p2) +3H20-3(Cab) +2PH
3↑ (3) Since phonosphine is a toxic and odorous gas, it is necessary to stabilize 7 lux to prevent the reaction of formula (3) from proceeding.

One way to do this is to oxidize the flux.

That is, (Ca=sP2)+40z→3 (Cab)
By converting phosphorus in France into an oxide form through the reaction of +P2O5 (4), it is possible to prevent the generation of phosphine through reaction with water vapor.

However, in actual processes, it is not easy to completely stabilize the phosphorus in 7 lux.

This is because if, for example, an oxidizing gas is sprayed onto the flux while it is in a molten state, phosphorus can be almost completely oxidized in a relatively short period of time.

However, when dephosphorized stainless steel is separated from the molten metal, it is inevitable that a portion of the stainless steel will solidify due to heat dissipation.

. If heating is performed to maintain the molten state, the reaction between the molten stainless steel and the refractory, especially the flux, may easily seep into the refractory, in which case the refractory may generate or become a source of phosphine. .

Therefore, at least a portion of the flux is in a solidified state at the time of oxidation, but when oxidizing gas is sprayed, the oxidation reaction proceeds from the surface and forms grains, resulting in a phenomenon in which the subsequent oxidation reaction rate decreases. It becomes extremely difficult to completely stabilize stainless steel.

Flux that has only the surface layer of the free surface oxidized is almost stable against water vapor in the atmosphere, but if it is left in a place exposed to rain, it will react with water and generate phosphine, causing problems. becomes.

The present invention was obtained as a result of various studies in view of the above circumstances, and the present invention is based on the method of refining molten metal containing stainless steel whose main components are calcium carbide and alkaline earth metal halides, for example, mainly containing Ca C2 and Ca F2. The flux (CaC2CaF2 type flux) contained as a component will be explained below.

), and after separating the molten metal and the flux, the method for stabilizing CaC2CaF2 dephosphorization flux is characterized in that the flux is reacted with another molten metal in an oxidizing atmosphere. This will be explained in detail based on 1) a typical example.

The molten metal to be dephosphorized is a molten metal that is difficult to dephosphorize by normal oxidation refining, such as ferrochrome or stainless steel with a high chromium content.

The flux used for dephosphorization is Ca C2 / Ca F 2
It contains two components as main components, for example, a mixture of calcium carbide and goldstone.

According to the formula (1), Ca C2 in the flux is essential for reacting with the carbon-unsaturated molten metal to produce metallic calcium necessary for the dephosphorization reaction (when the molten metal has a low degree of carbon unsaturation) When a part of Ca C2 is replaced with metallic calcium or its alloy, the concentration of metallic calcium in stainless steel is increased, which is advantageous for dephosphorization.

) CaF2 is necessary to adjust the melting point of the flux and to make metallic calcium stably exist in the slag.

The blending ratio of Ca C2 and Ca F 2 is Ca C2/C
The optimum range is aF2=0.5 to 5.

The remaining component is C a O+ 8 mixed as an impurity.
102, etc., but it is desirable that the amount of oxides that are easily reduced is as small as possible.

This flux and the above-mentioned molten metal are used under conditions in which oxidative consumption of metallic calcium is unlikely to occur (specifically, the atmosphere is sealed from the atmosphere and the supply of oxygen from mixed slag and molten metal is suppressed). A contact reaction is carried out.

Various forms of contact between the molten metal and the flux are possible, as in the case of normal slag refining methods, but since the flux of the present invention has a high content of CaF2 and easily interacts with water-resistant substances, it is possible to minimize the reaction rate. Efforts must be made to shorten the time required.

For this purpose, it is effective to use, for example, the agitation effect when transferring the molten metal, or to perform stirring by blowing gas into the molten metal.

After dephosphorization is performed by promoting the contact reaction between the molten metal and flux under controlled atmosphere, the stainless steel and molten metal are separated.

At the end of the dephosphorization reaction, phosphorus mainly exists in the flux as a compound with Ca (Ca 3 P 2).

The total phosphorus content in the flux varies depending on the molten metal and flux conditions, but is approximately 0.2 to 3%.

If the flux after dephosphorization is mixed with the molten metal in an oxidizing atmosphere such as the air, rephosphorization is likely to occur, and if the flux is not sufficiently separated, rephosphorization will also occur when the molten metal is decarburized in the next process. , separation of flux and molten metal requires some ingenuity.

For example, a nozzle is attached to the bottom of the reaction vessel used for dephosphorization, and after the dephosphorization reaction is completed, the nozzle is opened and the molten metal flows out into another vessel, leaving the flux in the reaction vessel.
Alternatively, an effective method is to weaken the reactivity of the flux by adding a chilling material such as quicklime or brick shavings to the dephosphorized flux, then tilt the reaction vessel and discharge the flux.

The phosphorus-containing flux thus separated from the molten metal is exposed to an oxidizing atmosphere to oxidize the free surface.

In this process, a grain is formed on the free surface of the flux in such a way that the generation of phosphine is within acceptable limits even when it reacts with atmospheric water vapor.

Next, the flux whose surface layer portion has been stabilized in this manner is reacted with another molten metal in an oxidizing atmosphere.

The purpose of this step is to rephosphorus the phosphorus present in the dephosphorization flux as a compound unstable to water vapor into another molten metal, or to make it stably exist as phosphorus oxide in the oxidizing slag. .

Therefore, unlike in the dephosphorization process, the atmosphere must be oxidizing.

To achieve this, either the oxygen partial pressure in the atmosphere is high or iron oxide or the like is added to the slag.

It is necessary to use a molten metal used in this step that does not cause any problem even if rephosphorization occurs, or has a composition that allows easy dephosphorization by oxidative refining in a subsequent step even if rephosphorization occurs.

An example of the former is when using a high-chromium molten metal such as stainless steel, the phosphorus removed from the molten metal to be refined is transferred to another molten metal, which may have a higher than normal phosphorus content. Practical only when combined.

Examples of the latter include molten metals with a Cr content of 4 or less, such as hot metal or carbon steel.

If the Cr content is 4% or less, even if post-phosphorization is performed, dephosphorization can be performed while suppressing the adverse effects associated with chromium oxidation by selecting an appropriate slag composition and oxygen supply method in the next step.

Therefore, in this case, the molten metal, which is difficult to dephosphorize through normal oxidation refining, will be dephosphorized using CaC2CaF2-based flux, and the phosphorus will eventually be transferred to the oxidizing slag. All three problems can be solved: dephosphorizing the molten metal, making the removed phosphorus stably exist in the slag, and removing contamination from the molten metal used to stabilize the flux.

There are two specific embodiments of this step:

(1) Leaving slag in the reaction vessel used for dephosphorization,
Inject molten metal into this.

In this case, silica, iron oxide, etc. may be added to lower the melting point of the dephosphorizing flux and to sufficiently oxidize it.

When the Cr content of the molten metal is low, if oxidation refining using blowing acid or the like is continued, the phosphorus that has returned to the molten metal can be dephosphorized again by the oxidizing slag.

The slag thus obtained is as stable against moisture as ordinary converter slag, and can be disposed of in the same manner as converter slag.

(2) The dephosphorization flux is charged as part of an auxiliary material into a converter or an electric furnace, and the slag is melted and oxidized in an oxidizing atmosphere.

In the case of a converter, U = CaC2, Ca5P2-Ca, etc.
Liebe becomes CaO, phosphorus is converted to P2O, and is captured in the oxidizing slag, so that the purpose can be achieved without being particularly different from the usual blowing method.

In the case of an electric furnace, it may be charged as part of the auxiliary material during the melting or oxidation stage.

Oxidation of flux also occurs during the reduction period, resulting in Ca C2
If the concentration of Ca decreases, the atmosphere in the furnace is included in the oxidizing atmosphere referred to in the present invention, but if the concentration of CaC2 in the reduction slag is too high, some of the phosphorus becomes C which is unstable to moisture.
There is a possibility that it may remain as a3P2.

Moreover, if it is added to the reduction period, there is a problem that dephosphorization after rephosphorization cannot be performed regardless of the molten steel composition.

Therefore, it is practical to charge before the oxidation period.

By the method described above, it is possible to stabilize the flux used to dephosphorize a molten metal that is difficult to dephosphorize by ordinary oxidation refining.

We have mainly talked about Ca 3 P 2 and phosphine, which may be generated when it reacts with water vapor.
By this method, it is possible to stably release acetylene gas, H2S, etc. that may be generated from the flux without harming the working environment.

As a method for stabilizing CaC2-CaF2-based dephosphorization flux, compared to the method of oxidizing only the flux after dephosphorization, the method of oxidizing in the presence of another molten metal as in the present invention has the following characteristics. It is as follows.

(a) In order to sufficiently oxidize the flux, it is necessary to maintain the temperature at a high temperature for a sufficiently long time, but this condition is easily satisfied in the presence of molten metal.

(b) In order to completely stabilize the flux, the degree of oxidation,
It is desirable to significantly change basicity, etc.

It is quite difficult to achieve such a drastic change in composition using only stainless steel in terms of equipment (heating) and cost.

On the other hand, if this stainless steel is regarded as a part of the auxiliary material as Cab@, the composition can be easily and effectively changed, which is reasonable.

Example 1 Crude molten stainless steel (C2 0.61%) in an electric furnace.

Cr: 18.0%, Ni near, 9%, P:
0.028'%.

S: 0.019%) was melted and poured into a reaction vessel in which the atmosphere was kept non-oxidizing through a pony ladle.
, CaO: 12%) is added at 5 ky/ to perform dephosphorization (molten metal component after dephosphorization: C: 0.69%, C
r: 18.0%, Ni: 8.0%, P: 0
．． 013%, S: 0.007).

After tapping, the sliding nozzle provided at the bottom of the reaction vessel is opened to allow the molten metal to flow out into another ladle, and before the flux flows out, the sliding nozzle is closed to allow the stainless steel to remain in the reaction vessel.

This reaction vessel receives molten steel with a slag temperature north of 400°C, and at this time iron oxide (5 kf/l), crushed sand (3
4/l).

The compositions of the molten metal and slag before and after this treatment are as follows.

Example 2 The procedure was the same as in Example 1 until the high chromium molten metal and flux were separated after the dephosphorization reaction was completed.

Next, the hot metal is received in a reaction vessel with residual flux, charged into a converter, and subjected to normal blowing.

Examples of molten metal and slag compositions before and after this treatment are as follows.

Claims (1)

[Claims] 1 The molten metal to be refined is subjected to a dephosphorization reaction using stainless steel containing calcium carbide and alkaline earth metal halides as main components, and then the molten metal and 7 lux are separated, and the flux is mixed with another molten metal in an acidic atmosphere. A method for stabilizing a halide dephosphorization slack of calcium carbide and an alkaline earth metal, which is characterized by causing a reaction between calcium carbide and an alkaline earth metal.