JPS6015683B2 - Method for dephosphorizing metals or alloys - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for refining (particularly dephosphorizing) a metal or an alloy (particularly a molten metal containing several percent or more of valuable elements that are more easily oxidized than iron).

In recent years, impurities, especially phosphorus content, in ores and carbonaceous reducing agents have increased due to the depletion of high-grade resources. For this reason, the phosphorus content in metals or alloys obtained by reducing ores is also on the rise. Oxidative refining is usually used to remove phosphorus.

This process oxidizes the molten metal in the presence of high basicity slag to convert phosphorus into P.
205, and is fixed as calcium phosphate in the slag. By this method, molten iron and molten steel with normal components can be relatively easily dephosphorized. However, Cr
When the above method is applied to a molten metal containing several percent or more of elements that are more easily oxidized than iron, such as , Si, Mn, Al, Mo, Zr, V, and Nb, the oxidation of these elements proceeds preferentially. , and the oxidation products migrate into the slag, significantly inhibiting the progress of dephosphorization from both physical (viscosity, etc.) and chemical (dephosphorization equilibrium) perspectives. Therefore, for example, stainless steel,
It was thought that dephosphorization was virtually impossible with high chromium molten metals such as ferrochrome. However, in recent years, various adverse effects of phosphorus as an impurity in metal materials have been revealed. For example, it has been confirmed that in high alloy steels such as stainless steel, it has an adverse effect on workability, corrosion resistance, weldability, etc.

Therefore, the phosphorus content of high-grade stainless steel materials used in particularly harsh environments is increasingly being regulated. In order to meet the demands for materials under the aforementioned resource situation, there is a strong demand for the development of a dephosphorization method for high chromium molten metal, which was thought to be impossible to dephosphorize using conventional methods. It has reached the point where

As a method to meet this demand, the present inventors have previously developed a method for using a molten metal or alloy whose carbon content is less than the saturated carbon concentration and a flux containing calcium carbide and calcium fluoride as main components in a non-oxidizing atmosphere. He invented a method of contacting the fish at the bottom (Tsubaki Kasho 50-2943 Tokubuta Sho 50-199143).

This method is (CaC2) this (Ca) 12 [C]...
......'11 Reaction produces free metallic calcium in slag, which is used for refining. For example, for phosphorus, 3 (Ca) 12 [P] → (C
Dephosphorization is performed by a3P2)...■.

Here, ( ) represents the component in the slag, and [ ] represents the component in the molten metal. Furthermore, flux refers to the refining agent before it is added to the molten metal, and slag refers to the substance generated by adding flux. In this method, metal calcium released from calcium carbide, which is extremely reactive, is used for refining, so the refining ability is strong, and in addition to lj, sulfur, nitrogen,
It is said that impurities such as oxygen and antimony can be removed at the same time, down to minute amounts. It has signs. However, on the other hand, the production and consumption of metallic calcium is easily affected by various conditions, and unless the refining conditions are strictly controlled, the refining effect tends to become unstable, especially with regard to dephosphorization. When carrying out this method on an industrial scale, it is most advantageous in terms of cost to use industrially produced calcium carbide as the calcium carbide source in the flux.

Calcium carbide is produced by charging quicklime and carbonaceous material such as coke into an electric furnace and heating it in an arc to obtain molten carbide.
It is manufactured by solidifying and cooling this outside the furnace and then crushing it to a suitable particle size. Therefore, the quality of the product, that is, the concentration of calcium carbide, depends on the quality of the raw materials, the blending ratio of carbonaceous materials, the operating conditions of the electric furnace, and the conditions of contact between the carbide and the atmosphere outside the electric furnace.
It is 5-85%. Ca○ accounts for most of the remainder. Ca0 has one origin: Ca○ in the raw material remains without reacting with the carbonaceous material, and calcium carbide once generated reacts with oxygen or water vapor in the atmosphere and is generated by oxidation. Other impurities include free carbon, sulfur, and phosphorus, and their amounts are much smaller than that of CaO. Among the flux components used for dephosphorization, calcium carbide is essential for producing metallic calcium according to the formula '1}.

In addition, alkaline metal halides, such as calcium fluoride, are metallic calcium produced by formula '1}, and
It allows Ca3P2 produced by the formula to stably exist in the slag, and also has the effect of adjusting the melting point and fluidity of the slag. Among the impurities contained in the flux, Si02
It goes without saying that it is desirable to have as few oxides as possible, such as , A2Q, which react with metallic calcium to oxidize and whose reduction product does not have a dephosphorizing effect.
Therefore, ordinary fluorite containing these oxides is not suitable for the purpose of the present invention, and it is desirable to use refined fluorite whose impurity content has been reduced by, for example, beneficiation techniques.
On the other hand, as for the calcium carbide source, when calcium carbide is used, most of the impurities are Ca○ as described above, but the influence of Ca0 on refining and the allowable limit value are not clear. When we actually analyze the slag after dephosphorization treatment, we find that in addition to calcium carbide, evolved calcium, metallic calcium, and reaction products, it contains several tens of percent or more of Ca○
is found. This Ca0 is generated when impurities in the flash and calcium carbide are oxidized during refining. Therefore, Ca as an impurity in the flux
0, it was considered that there was no need to significantly lower it than what is normally obtained. Furthermore, Ca0 has the latter half of the action of calcium fluoride mentioned above, that is, it has the effect of controlling the melting point and fluidity of slag, so it actively increases the amount of C in the flux.
It is even possible that the required amount of calcium fluoride can be reduced by increasing a○%. From the above points of view, when dephosphorization treatment of actual port hot springs was carried out using calcium carbide containing Ca○ with a normal composition and refined fluorite, the dephosphorization rate varied widely and The results showed that the average rate level was also low. The present invention takes advantage of the above circumstances and adds a flux containing calcium carbide and an alkali metal halide such as calcium fluoride as main components to a molten metal or alloy whose carbon content is less than the saturation solubility. This result was obtained by examining the influence of various conditions in order to particularly increase the dephosphorization rate and reduce the variation when refining the flux. This method is characterized by the following. Hereinafter, the configuration of the invention will be explained in detail.

The objects of smelting are high-chromium molten metals, such as ferrochrome and stainless steel, which contain several percent or more of components that are more easily oxidized than iron, and which are difficult to dephosphorize using normal oxidation refining methods. Prior to refining, these molten metals must be carbon unsaturated so that they can absorb the carbon from calcium carbide. Therefore, in the case of high carbon ferrochrome, an appropriate amount of carbon is removed by a method such as oxidation, and in the case of high chromium steel such as stainless steel, appropriate raw materials are melted and mixed, and if necessary, a portion is further removed. Perform decarburization. Furthermore, before adding the dephosphorizing flux, it is desirable to separate as much as possible the oxidizing slag coexisting with the molten metal.

For this purpose, it is desirable to carry out the technique using commonly used means and to be able to separate the slag mixed into the reaction vessel using, for example, a partition wall. The dephosphorizing flux is mainly composed of calcium carbide and an alkali metal halide such as calcium fluoride, and is a mixture of, for example, powdered calcium carbide and purified fluorite.

As shown in FIG. 1, the blending ratio of calcium carbide and calcium fluoride in the flux is preferably in the range of CaC2/CaF2 from 1.5 to 6.5 in order to obtain a stable and high dephosphorization rate. This upper limit is for metallic calcium and Ca
It depends on the amount of calcium fluoride required to stably present 3P2 in the slag. On the other hand, if the amount of calcium fluoride is too large, the amount of erosion of the refractory will increase when processing is carried out in a reaction vessel lined with a refractory as in the present invention.
Since metallic calcium is oxidized and consumed by oxides such as M mosquitoes and Si02 that enter the slag from the refractory, the dephosphorization rate decreases on the contrary.
The lower limit of . The optimum value of this CaC2/CaF2 ratio depends on the strength of the molten metal during the refining reaction, and the stronger the strength, the larger the value becomes. Calcium fluoride sources are expensive and have the effect of promoting corrosion of refractories, so by strengthening the molten metal rope, CaC2/C
Increasing the aF2 ratio is also advantageous in terms of cost.
For example, if gas is blown into the molten metal to form a strong molten metal, the optimum ratio of CaC2/CaF2 is 3 to 6. Next, it is necessary that Ca0 contained in the flux be 15% by weight or less.

This is based on the following experimental results. Figure 2 shows the dephosphorization test of Ayato using calcium carbide containing various levels of Ca○% (please refer to the examples for the implementation conditions), and the results of the dephosphorization test in flux. It is organized in relation to Ca0%. As mentioned above, most of the Ca○ component is composed of calcium carbide, but as is clear from Figure 2, Ca○ in the flux is 1.
When it exceeds 5% by weight, the dephosphorization rate decreases rapidly. Regarding the negative effects of Ca0 observed here, Si02, A
This cannot be explained by the mechanism of oxidation and consumption of metallic calcium as in 〆203, Mg○, etc., and this is a new finding obtained through experiments. The adverse effects of Ca○ are due to the following reasons.

Ca0 in 'a' calcium carbide reacts with water vapor in the atmosphere, and part of it becomes hydroxide (Ca(OH)2), increasing the amount of water brought into the refining reaction system.

As a result, when the flux comes into contact with the molten metal, it generates water vapor, which oxidizes and consumes the metallic calcium. Once the water is captured by the impurity Ca0 in calcium carbide, it cannot be removed by heating like in the case of quicklime (because calcium carbide is easily oxidized), so the amount of water brought into the refining reaction system is reduced. In order to make the impurity Ca, especially as calcium carbide,
This means that one with a low content of 0 must be used. If the equilibrium constant of the {b''1} formula is K, then
Equilibrium amount of metallic calcium (Ca) in slag is (Ca)=
K, (CaC2)/[C]2......'31. Therefore, if [C] is constant, (C
a) is proportional to the concentration of calcium carbide (CaC2) in the slag. Therefore, in order to increase the dephosphorization efficiency, it is desirable to increase the calcium carbide concentration as much as possible. However, when flux is added to the molten metal, it is inevitable that calcium carbide and metallic calcium will be oxidized to some extent due to the atmosphere, mixed slag, refractories, oxygen in the melt, etc. when it is carried out on an industrial scale.

For example, oxygen in the sun can be lowered by adding a deoxidizing agent such as A, but if flux is added without completely separating the deoxidized products, the deoxidized products become a source of slag oxidation. obtain. However, it is actually quite difficult to separate the deoxidized products without causing re-oxidation. Immediately after flux is added to the molten metal, the fresh flux with a large specific surface area is able to react with the molten metal without being affected by refractory corrosion, and this is the most important time for the reaction to proceed. The flux is easily oxidized by the molten metal, and this is the period. If the Ca% in the flux is not sufficiently low, when Ca0 produced by oxidation is also taken into account, [CaC2] becomes too low, making it difficult to proceed the reaction favorably. therefore,
Considering that oxidation occurs to some extent, it is desirable that the Ca% content in the flux be as low as possible in order to advantageously proceed with dephosphorization. In order to obtain such a stable high dephosphorization rate on an industrial scale, it is necessary to limit the amount of calcium oxide contained as an impurity in the flux to 15% by weight or less.

Therefore, in the present invention, it is necessary to use calcium carbide with lower Ca% than commercially available calcium carbide, and for this purpose, the atmosphere during grinding must be inert,
It is necessary to avoid excessive pulverization and to seal the pulverized carbide to prevent atmospheric reactions as much as possible. Various forms of contact between the molten metal and flux are possible as in the case of normal slag refining, but the slag of the present invention
Because the content is high and it tends to corrode refractories, it is necessary to devise ways to shorten the reaction time as much as possible.

For this purpose, it is necessary to strongly control the slag and metal, and it is desirable to use methods such as using the rope action when transferring the molten metal, or blowing gas into the molten metal. Next, regarding the atmospheric conditions within the reactor, it is necessary to prevent air from entering as much as possible in order to prevent the metallic calcium in the slag from being consumed by oxygen or nitrogen.

For this purpose, it is desirable to use a lid on the reaction vessel and supply an inert gas such as Ar or a reducing gas such as hydrocarbon into the reaction vessel. However, when carrying out the process on an industrial scale, it is difficult to make the inside of the reaction vessel completely non-oxidizing, and on the other hand, if it is made completely non-oxidizing, calcium vapor will not be oxidized and will be ejected from the reaction vessel, resulting in severe This creates an operational problem in that it produces a three-dimensional bright frame. Therefore, it is easier to carry out the work under conditions in which calcium vapor is oxidized to some extent within the reaction vessel. In this way reaction 2
In order to obtain a high dephosphorization rate under conditions where oxidation of calcium carbide and metallic calcium occurs in the reactor, it is necessary that the Ca content in the added flux be low. As described above, when refining molten metal using a flux containing calcium carbide and alkali metal halides as main components, by controlling the amount of calcium oxide contained as an impurity in the flux to 15% by weight or less, slag Conditions related to oxidation are relaxed, the process is easy to perform, and a high dephosphorization rate can be obtained.

Therefore, by carrying out the present invention, a stable dephosphorization effect can be obtained on an industrial scale. Note that the effects of refining other than dephosphorization, such as desulfurization and denitrification, are also improved. Example: 18%C-8%Ni-0.6%C- melted in an electric furnace
0.030%P-0.035%S crude molten stainless steel was transferred to a reaction vessel lined with chromaglen, and ~ was blown into the hot water and the following flux was added while stirring.
Allow the reaction to run for 0 minutes.

The flux is a mixture of calcium carbide with different Ca% as shown in Table 1 and fluorite made from clay, and the basic unit is 10%.
~30k9/t. Table 1 The test results are shown in Table 2 and Figures 1 and 2.

Table 2 Dephosphorization test results

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the weight ratio of CaC2 and CaF2 in flux and the dephosphorization rate, and FIG. 2 is a diagram showing the relationship between Ca○% in the flux and the dephosphorization rate. Figure 1 Figure 2

Claims (1)

[Claims] 1. When refining a molten metal or alloy whose carbon content is less than the saturation solubility by adding a flux containing calcium carbide and an alkaline earth metal halide as its main components, the flux is contained as an impurity in the flux. A method for dephosphorizing metals or alloys, the method comprising reducing calcium oxide to 15% by weight or less.