RU2453610C2 - Slag mixture for treatment of liquid metal - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: slag mixture contains titanium ferrite production slag and chromium ferrite production slag as a material based on calcium oxide, as well as calcium and sodium carbonates, sodium hydroxide, aluminium oxide and ferrous oxides.

EFFECT: set of the above components of the slag mixture ensures removal of phosphorus from molten metal in the ladle when using it in a solid form.

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Description

The invention relates to metallurgy, and more particularly to processes for the refining processing of liquid metal in a ladle by slag-forming mixtures.

In the literature, methods are known for refining cast iron and steel and compositions of slag-forming mixtures intended for removing non-metallic inclusions, including phosphorus, from metal [1] (V. G. Voskoboinikov, V. A. Kudrin, A. M. Yakushev. General metallurgy Textbook for Universities. - 5th ed., Revised and enlarged. - M .: Metallurgy. - 2000. - P.292; P.324).

The main conditions for the effective removal of phosphorus from a liquid metal are the high basicity and oxidation of the slag, its low melting point, and the low metal processing temperature.

The high basicity of refining slag is usually achieved when a large amount of calcium oxide (CaO) is used in its composition. However, pure calcium oxide has a high melting point (about 2650 ° C). Therefore, in the compositions of refining slags, together with calcium oxide, various additives are used that lower its melting point.

Often in known methods for removing non-metallic inclusions, including phosphorus, from molten metal, pre-molten synthetic slags based on calcium oxide are used, which are mixed with the molten metal, and then the slag is separated from the metal. However, these operations are energy-consuming, time-consuming and lengthy to perform.

A known method of processing molten metal in a ladle for dephosphorization, according to which a pre-molten synthetic slag based on calcium oxide and aluminum oxide is used as a dephosphor, is mixed in the ladle with iron oxides and molten metal in another melting unit and then the slag is separated from metal [2] (RU 2139942, IPC С21С 7/076, publ. 07.28.1999).

Positive in the known method is that synthetic slag is used in conjunction with iron oxides, which are the source of oxygen necessary for dephosphorization.

However, this method has a disadvantage that reduces the efficiency of dephosphorization. Namely, the composition of synthetic slag recommended in the method, for example, according to option 1, containing 49 wt.% CaO and 45 wt.% Al ₂ O ₃ , even when mixed with a large amount of iron oxide has a high melting point and requires a large expenditure of energy for melting during the preliminary preparation of synthetic slag and during dephosphorization in the ladle.

More economical and simpler is the refining of liquid metal in a ladle with solid slag mixtures with a low melting point.

The closest in composition is the known slag mixture for processing molten metal in order to remove sulfur from the metal [3] (USSR author's certificate No. 704200, class C21C 7/00, published on March 15, 1981 in BI No. 10).

The known mixture as a source of calcium oxide contains lime and slag of ferrochrome production (ferrochrome slag in the form of compound 2CaOSiO ₂ ), as well as components to reduce the melting point of the slag in the form of fluorspar (CaF ₂ ) and sodium carbonate (Na ₂ CO ₃ ).

Positive in the known slag mixture is that the slag of the ferrochrome production used in the mixture contains, together with calcium oxide, a series of chemically related components that contribute to the acceleration of slag formation in the ladle when interacting with molten metal.

A disadvantage of the known mixture is that the specified composition of the slag mixture cannot be used to remove phosphorus from the molten metal, since it does not satisfy the conditions necessary for dephosphorization. Namely, the slag mixture does not have a sufficiently high basicity (about 2.5 units), insufficient fusibility, oxidation and does not provide the temperature reduction necessary for dephosphorization when mixed with metal.

The objective of the invention is to develop such a composition of a refining slag mixture based on ferrochrome slag (ferrochrome slag - FS), a material containing calcium oxide and sodium carbonate, which would ensure the removal of phosphorus from the molten metal directly in the ladle when the mixture is loaded in solid form.

The problem is solved in that the slag mixture for processing liquid metal, including slag of ferrochrome production (FS), a material based on calcium oxide and sodium carbonate (Na ₂ CO ₃ ), according to the invention as a material based on calcium oxide contains slag of ferrotitanium production (SHFT ) and additionally calcium carbonate (CaCO ₃ ), aluminum oxide (Al ₂ O ₃ ), sodium hydroxide (NaOH) and iron oxides (Fe _x O _y ) in the following ratios of components, wt.%:

Ferrochrome Slag   production 10-20 Ferrotitanium Slag   production (SHFT) 10-30 Sodium Carbonate (Na ₂ CO ₃ ) 3-10 Calcium Carbonate (CaCO ₃ ) 15-30 Alumina (Al ₂ O ₃ ) 13 Sodium Hydroxide (NaOH) 3-15 Iron oxides (Fe _x O _y ) 10-30

The indicated additional and well-known ratios of the components provide the formation of the following advantageous properties necessary for dephosphorization of a liquid metal: high basicity, oxidation, fusibility and cooling ability.

The technical effect when implementing the invention is to ensure metal dephosphorization directly in the ladle when using solid slag mixture, in which, together with ferrochrome production slag (FS) and sodium carbonate, ferrotitanium production slag (SHFT) and components are used as a material based on calcium oxide in the form of calcium carbonate, alumina, sodium hydroxide and iron oxides.

These components and their ratios provide a combination of the following advantageous properties of the slag mixture in the complex: basicity, oxidation, fusibility, and cooling ability high enough for metal dephosphorization.

The high basicity of the slag mixture is provided by the materials SHF, FS and calcium carbonate - CaCO ₃ .

ShFT (TU 0798-060-00186482-2006) contains calcium oxide (CaO) - an average of 25 wt.%; MgO - 5 wt.%; aluminum oxide (Al ₂ About ₃ ) - 45 wt.% and impurities - the rest.

FSh (TU 14-11-325-1997) contains calcium oxide CaO - 55 wt.%, MgO - 10 wt.%, SiO ₂ - 25 wt.%.

Calcium carbonate after decomposition when heated forms CaO - 56% by weight of calcium carbonate.

The selection of component ratios is based on calculations and laboratory test results.

The condition for the basicity of the slag mixture minimally necessary for dephosphorization (an indicator of the ratio of basic compounds to acidic (CaO + MgO) / SiO ₂ ) is 3 units. (see [1] p. 364). The calculation was carried out on the basis of the minimum content of basic compounds (CaO + MgO) in the materials and the maximum content of the acid compound - SiO ₂ . The sources of the main compounds (CaO + MgO) are SHF, FS and calcium carbonate. The source of the acid compound (SiO ₂ ) is FS.

The total minimum content of basic oxides (CaO + MgO) from FS, SHF and CaCO ₃ according to the minimum values of the content of materials in the composition of the slag mixture per 100 kg is 17.9 kg (from FS 6.5 kg; from SHFT 3.0; from carbonate calcium 8.4 kg). The source of the acidic compound SiO ₂ are FS. The maximum content of SiO ₂ in the slag mixture is 5 kg. At the indicated contents of the components, the basicity of the slag mixture is 3.6 units.

Thus, the composition of the slag mixture at the minimum values of the content of the components satisfies the basic condition for the removal of phosphorus from the metal.

Moreover, taking into account that other components in the slag mixture, for example sodium carbonate and sodium hydroxide, also contribute to the increase in basicity, its real values in the slag mixture will be significantly higher than the calculated ones.

At maximum ratios of the components in the compositions of the slag mixture, a basicity of 40 or more units can be achieved.

Thus, the proposed composition of the slag mixture satisfies the condition of dephosphorization of the metal in basicity.

An important criterion for the kinetics of the liquid metal dephosphorization process in the ladle is the fusibility of the slag mixture. The quick and easy melting of the slag mixture when interacting with heated metal poured into the ladle provides a deeper and faster removal of phosphorus into the slag. In the proposed slag mixture, the components are selected in accordance with this condition.

Compounds are most efficiently fusible: sodium carbonate, sodium hydroxide, iron oxides, and also aluminum oxide with its contents up to 8 wt.%. The source of alumina is impurities in SHF and FSh, as well as with the addition of kaolin, corundum or alumina to 1-3 wt.%

According to the results of tests on a Paulik-Erdei system high-temperature derivatograph, the slag mixture begins to melt within the given compositions already at a temperature of 880-890 ° C with a rapid transition to the active liquid state at temperatures from 1280 ° C and above. This is sufficient to ensure dephosphorization of the metal in the ladle even in the diffusion mode of the process.

Thus, the proposed composition of the slag mixture satisfies the condition for dephosphorization of the metal by fusibility.

The efficiency of dephosphorization is increased by mixing the slag mixture by any known method. To some extent, the mixing is ensured by the components of the slag mixture used in the form of carbonates, including CaCO ₃ , Na ₂ CO ₃ . When heated, these components decompose with the release of CO ₂ gas, which provides for "bubbling" in the volume of slag and at its border with the metal. In this case, diffusion processes in the slag and acceleration of metal dephosphorization are also enhanced.

It is known that the decomposition reactions of carbonate compounds are endothermic, therefore, in the process of their decomposition, heat is removed from slag and liquid metal. In this case, the slag mixture is cooled, especially intensively due to the decomposition of calcium carbonate in the microvolumes of the slag, at the locations of the particles of this material.

A uniform cooling in the slag volume provides an intensification of the metal dephosphorization process and the binding of phosphorus compounds in the slag.

The calculation showed that with a minimum content of carbonate compounds in the slag mixture and a minimum consumption of 1 ton of liquid metal of 0.6-0.8 wt.% Cooling in the slag volume occurs at 25-30 ° C, which helps to remove phosphorus from the metal.

The tests found that when using the proposed component slag mixture during processing in the ladle, the slag temperature decreases both due to heat removal for heating the slag mixture and due to the decomposition of calcium and sodium carbonates. Thus, the proposed composition of the slag mixture contributes to the cooling of the metal, the removal of phosphorus from it and the stable binding of its compounds in the slag.

The conditions for effective dephosphorization of a liquid metal — oxidation — are achieved by using a sufficient amount of iron oxides in the slag mixture, which are an oxygen source for the oxidation of phosphorus. Moreover, the formula of iron oxides in terms of oxygen content can be different, therefore, it is denoted by the general formula Fe _x O _y .

Tests of the slag mixture showed that the minimum content of iron oxides, for example, in the form of mill or forge scale, for a minimum dephosphorization of 10-15% and at a flow rate of 0.6 wt.% Per 1 ton of metal is 10 wt.%. The use of iron oxides in a slag mixture of more than 30 wt.% Is impractical due to excessive cooling of the metal due to the large heat extraction for heating heat-resistant scale and for economic reasons.

Check the slag mixture was carried out in laboratory conditions when processing liquid pig iron in order to reduce the amount of phosphorus in it.

Cast iron smelted in an induction furnace was poured into a 200 kg bucket and treated with a slag mixture of a 3-10 mm fraction. The temperature of cast iron in the ladle ranged from 1380 to 1410 ° C.

During the test, the flow rate of the slag-dephosphorator mixture was determined for the efficiency of phosphorus removal from pig iron.

Option 1. The slag mixture was loaded onto the bottom of the bucket and then cast iron was poured. After filling the bucket with metal, an exposure was made for 2-3 minutes and the metal was poured into molds. When testing, the consumption of slag mixture was changed: 0.6%, 1.0% and 1.2% based on 1 ton of metal.

Option 2. Slag mixture was loaded onto the metal when filling the bucket in 1/3 of its volume. The flow rate of the slag mixture was varied within the same limits.

Option 3. Slag mixture was loaded onto the metal after the bucket was completely filled. The flow rate of the slag mixture was varied within the same limits.

The results for the removal of phosphorus are shown in table 1.

Table 1 Test option Slag consumption,% Contents phosphorus in metal % dephosphorization Ref. After processing one 0.6 0.121 0,099 18.18 1,0 0.106 0,086 18.86 1,2 0.108 0,078 27.77 2 0.6 0.104 0,087 16.35 1,0 0.113 0,088 22.12 1,2 0.141 0.102 27.66 3 0.6 0.122 0.106 13.11 1,0 0.108 0,088 18.52 1,2 0.106 0,084 20.75

Table 1 shows that when the slag mixture is consumed even 0.6% per ton of metal, dephosphorization in various cases is on average 15%, which meets the production requirements.

To determine the limiting values of the components in the slag mixture, tests were carried out according to the composition options shown in table 2.

The basicity of the compositions of the slag mixture was determined by calculation.

The fusibility of the slag mixture was determined by measurements on a Paulik Erdei derivatograph by the intensive melting temperature.

The cooling ability of the slag mixture was determined by the value of the temperature decrease during the decomposition of carbonates after holding the melt for 1.5 minutes.

The oxidation of the slag mixture was determined by the value of the content of iron oxides in the compositions based on their use in the form of mill scale. Rolling mill scale for 98% contains iron oxides in the form of compounds with high oxidation Fe ₃ O ₄ and Fe ₂ About ₃ . When the scale is heated in a slag mixture in the presence of alkaline sodium and calcium compounds, iron oxide compounds are involved in the oxidation of phosphorus in the metal.

The test results are shown in table 2.

As can be seen in table 2, with a decrease in the content of SHFT and FS less than 10 wt.% And calcium carbonate less than 15 wt.%, The basicity of the slag mixture significantly decreases, although it remains higher than the basicity of the mixture according to the prototype. The basicity of the slag mixture decreases somewhat with an increase in the content of SHF and FS in the amount of more than 50 wt.%, Since the acid compound of silicon oxide (in FS) and the excess content of alumina (in SHF) begin to have a predominant effect on the basicity of SHF and FS materials. Therefore, the minimum content of SHFT and FS is taken to be 10 wt.% And calcium carbonate - 15 wt.%, And the maximum content for SHFT - 30 wt.%, For FS - 20 wt.% And for calcium carbonate - 30 wt. %

The value of the melting temperature of the slag mixture is influenced by sodium carbonate and sodium hydroxide, as well as at low alumina contents. As can be seen in table 2, when the content of sodium carbonate and sodium hydroxide is less than 3 wt.% Of each material, the melting temperature of the mixture 1360 ° C does not allow to effectively reduce the phosphorus content in the metal. With an increase in the content of sodium carbonate and sodium hydroxide, respectively, more than 10 and more than 15 wt.% Metal dephosphorization practically does not change. Therefore, the minimum contents of these components are taken: for sodium carbonate and sodium hydroxide, respectively, 3 wt.%, And for the maximum contents of 10 and 15 wt.%, Respectively.

The oxidation of the slag mixture is determined by the content of iron oxides. The calculations showed that the minimum sufficient oxidation of the slag mixture is achieved when the content of iron oxides is 10 wt.%. At lower values of iron oxide, the desulfurization ability of the slag mixture decreases (only about 8%). Therefore, the minimum content of iron oxides in the slag mixture is 10 wt.%. When the content of iron oxides in the slag mixture is more than 30 wt.% And calcium carbonate more than 30 wt.%, A slowdown in metal desulfurization is observed, ceteris paribus. Therefore, 30 wt.% Is taken as the maximum content of iron oxides in the slag mixture.

A production check of the slag mixture was carried out during the processing of blast furnace pig iron at the Serov Metallurgical Plant. At a dephosphorizer consumption of 0.8 wt.% And loading it onto the metal after the bucket is completely filled, phosphorus removal by 26.5% is obtained. This allows the company to transfer, according to GOST 805-95, the grade of pig iron from category "B" to a higher quality category "A" and to ensure the expansion of the supply of high-quality cast iron in mechanical engineering, to increase the profitability and economic benefits of production.

We also tested at the Kachkanar Metallist plant to remove phosphorus from 110G13 grade manganese steel. At a slag mixture consumption of 1% by weight of the metal, phosphorus removal in the ladle was obtained 10%. Specialists of the plant noted that the proposed slag mixture allows to simplify the process of dephosphorization of steel when transferring it to the ladle. Moreover, even such a decrease in phosphorus during the processing of alloy steel in the ladle can significantly increase the cold brittleness of parts, which is important when operating machines in the North.

We tested the slag mixture at the company Ural Diesel Plant LLC. The metal was smelted in an induction 5-ton furnace. Metal processing was carried out in a 5-ton ladle with a solid slag mixture at the rate of 1% per ton of metal. Treated removal of phosphorus from the metal 25% of the initial content, which fully satisfies the production of this enterprise.

Industrial applicability. It is most advisable to use the proposed slag mixture for dephosphorization of cast iron and steel in the conditions of machine-building enterprises and small metallurgy. The processing of cast iron by the proposed slag mixture can be carried out both in a ladle and in an induction furnace with a main lining.

When cast iron or steel is smelted in furnaces with an acid lining, phosphorus removal is difficult due to saturation of the slag from the lining with an acid component - SiO ₂ . Therefore, if necessary, it is advisable to dephosphorize the metal in a bucket, which usually has a neutral chamotte lining.

The removal of phosphorus can also be carried out in the smelting of ferroalloys.

At the Serov Ferroalloy Plant, a test was conducted to remove phosphorus in the ladle in the production of ferrosilicon chromium. At a slag mixture consumption of 1%, phosphorus removal by 10% was achieved.

Claims (1)

Slag mixture for processing liquid metal, including calcium oxide-based material, ferrochrome slag and sodium carbonate, characterized in that as calcium oxide-based material it contains ferrotitanium production slag, calcium carbonate, aluminum oxide, sodium hydroxide and iron oxides at the following ratios of the components of the mixture, wt.%:
ferrotitanium slag production 10-30 ferrochrome slag production 10-20 sodium carbonate 3-10 calcium carbonate 15-30 aluminium oxide 1-3 sodium hydroxide 3-15 iron oxides 10-30