Field of the invention

The invention relates to ferrous metallurgy, namely to materials for processing of iron melts to remove oxygen, sulfur and purification from non-metallic inclusions (NI).

Background of the invention

Steadily increasing requirements for the quality of the final products of ferrous metallurgy cause the use of new methods and materials in technological processes. Meanwhile, reducing the level of harmful impurities in cast iron, steels and ferroalloys by traditional methods of melt refining results to a significant increase in the cost and duration of production processes.

In view of the existing problems, the current task is to use new materials and methods in ferrous metallurgy, which reliably and at low cost will ensure improved quality of the products obtained: steels, cast iron and ferroalloys.

Known are the materials which, when used as additives in metallurgical processes, make it possible, at low cost, to improve the quality of the processed metal, especially of iron melts, such as cast iron and steel.

One of such materials is a deoxidizer for steel (patent RU2638470), which is the closest technical solution to the claimed invention. The known deoxidizer is an alloy of calcium carbide (CaC2) with a low-melting flux system of CaO-AhOs and contains, in wt.%, calcium carbide (40-55% CaC2), calcium oxide (20-38% CaO), aluminum oxide (12-25% AI2O3) and impurity compounds in the amount of 3-10%, at a ratio of calcium oxide content to aluminum oxide content in the material in the range of 1-2.5.

The alloy in the known solution refers to a product formed from a number of starting raw materials by complete melting, chemical reactions, heating to the temperature of normal tapping from the furnace and subsequent crystallization (solidification) of the melt, wherein these materials may be of a metallic or non-metallic nature, and preferably contain one or more metals in free or bound form.

The material known from RU2638470 is intended for steel deoxidation and has a guaranteed melting point, i.e. the temperature at which the deoxidizer is completely in a liquid state, not higher than 1550°C, which at normal liquid steel processing temperatures ensures its melting in metallurgical melts and calcium carbide absorption by metal oxygen to form a liquid slag containing calcium and aluminum oxides.

The known material as a whole has proven to be effective in replacing aluminum, silicon and calcium carbide for steel deoxidation at different stages of production.

However, disadvantages consisting in that the minimum guaranteed melting point of such a material exceeds 1450°C, which inhibits the melting of the supplied material when interacting with iron melts and increases the required processing time have been revealed. In turn, with insufficient processing time, solid pieces of material float to the surface of the melts, which results to losses of calcium carbide for its combustion in the atmosphere, undesirable foaming of slag, and, in some cases, to uncontrolled carburization of metal.

As a result, the known material provides a degree of calcium carbide absorption (beneficial use), provided that the melt is sufficiently oxidized until a balance equilibrium with metal oxygen is reached, at the level of 85-88%, with the remainder being losses.

In addition, the material known from RU2638470 has proved to be unsuitable for processing cast iron due to the fact that its melting point is higher than the processing temperature of liquid iron.

In view of the existing problem with the material known from RU2638470, there is a need for improved material for processing of metal in the processes of ferrous metallurgy, including the removal of oxygen, sulfur and the purification from non-metallic inclusions, using which calcium and carbon absorption by the melt is maximum, including at its increased consumption, while the material has a lower guaranteed melting point, i.e. the temperature measured by conventional technical means, wherein the specified material is completely liquid and can be introduced into iron melts in a larger amount compared to the prototype, with no uncontrollable negative factors. Objectives of the invention and technical results achieved

The objective of the present invention is to create an improved material for processing of metal in the processes of ferrous metallurgy, including the removal of oxygen, sulfur and the purification from non-metallic inclusions, the guaranteed melting point of which is 1350-1450°C, owing to which a high degree of calcium and carbon absorption by the oxygen of the melt is achieved, which makes it possible to ensure, in particular:

- deoxidation of steel, with the possibility of more complete replacement of aluminum or other deoxidizers for processing of oxidized steel, with no undesirable carburization of the melt, which allows the proposed material to be used for a wide range of products, including for low-carbon steel grades;

- rapid formation of a highly basic liquid slag with high desulfurizing capacity, which facilitates the removal of sulfur from iron melts, reduces the processing time and costs (electricity, electrodes and materials);

- fluidity and high assimilative capacity allow the resulting slag to easily remove non-metallic inclusions of the melt, reducing both their total amount and, in particular, NI containing AI2O3, owing to which it is possible to reduce the cost of removing NI from the melt and ensure high quality of the resulting cast steel or iron products.

The material according to the invention is suitable for processing a wide range of iron melts, including cast irons.

Disclosure of the invention

The inventors conducted practical studies on the use of the material known from RU2638470, which showed the need to facilitate the supplied material melting to ensure easy calcium and carbon absorption by the oxygen of the melt, by reducing the melting point of the alloy in order to more fully realize its chemical and physical potential in the processing of iron melts.

It was found that the melting point of the alloy, based on the known from RU2638470 and related to the fused product of CaC2-CaO-AhO3 system, can be further reduced if the system contains a certain amount of silicon and magnesium oxides, while maintaining the required CaC2/CaO ratio in the alloy and changing the CaO/AhC ratio compared to the prototype. Preferably, the inventive alloy is a fused product of CaC2-CaO-AhO3-SiO2-MgO system with a controlled free carbon content and a stable ratio between the main components, which ensures its guaranteed melting point in the range of 1350-1450°C and efficient refining of not only steel, but also liquid iron.

According to the inventors, the guaranteed melting point is understood as the temperature range, above which the inventive alloy is completely in the liquid phase. This temperature can be determined by technical means for measuring temperature and controlling the liquid phase, for example, pyrometers and high -temperature image controls.

It is also worth noting that the inventive alloy refers to a product formed from a number of starting raw materials by chemical reactions during complete melting, heating to the temperature of normal tapping from the furnace and subsequent crystallization (solidification) of the melt, wherein these substances may be of a metallic or non-metallic nature, and preferably contain one or more metals in free or bound form.

Thus, according to the present invention and to the patent RU2638470, the alloy also refers to such alloys.

On the other hand, it is worth noting that when producing the alloy according to the present invention, the raw materials, undergoing chemical changes during complete melting and subsequent crystallization, form low-melting phases, which facilitate the alloy melting when the alloy is used and introduced into the metallurgical melt.

In term of micro structure, the inventive alloy is a fused product of CaC2- CaO- AhO3-SiO2-MgO system, which, at a certain ratio of its components, corresponds to a low- melting phase.

Preferably, the inventive alloy does not have a layered structure of the sample, which can be determined by visual inspection methods.

The essence of the present invention, created based on the studies conducted by the inventors, the revealed patterns and the inventive work performed, is as follows:

1. An alloy for processing iron melts in the processes of ferrous metallurgy, including at least the removal of oxygen, sulfur and the purification from non-metallic inclusions, containing in wt.%:

CaC ₂ - (25-55),

CaO - (15-40),

AI2O3 - (15-40),

SiO ₂ - (0.5-5), MgO - (0.5-5),

Free C - (0.5-2), unavoidable impurities not exceeding 4, with a CaO/AhCh ratio in the range of 0.75-1.5 and a CaC2/CaO ratio in the range of 0.6-3.6.

2. The alloy according to claim 1, being a product of CaC2-CaO-AhO3-SiO2-MgO system with a melting point in the range of 1350-1450°C.

3. The alloy according to claim 1, which is fusible at the temperatures of processing cast iron and steel with the formation of liquid slag.

4. The alloy according to claim 1, wherein unavoidable impurities include sulfide sulfur in an amount not exceeding 1%.

Sulfide sulfur is mainly present as calcium sulfide, with the presence of other sulfides not excluded.

In addition, unavoidable impurities in the alloy may be, but not limited to, oxides of iron, manganese, chromium or other metals, the amount of which is insufficient to materially affect the properties of the claimed alloy.

Also, according to the present invention, it is proposed:

5. The use of alloy (l)-(4) for desulfurization of liquid iron.

Desulfurization of liquid iron can be carried out both directly using the inventive alloy, and in proportions with magnesium to reduce the overall cost of processing.

Desulfurization can be carried out either by the use of a lumpy alloy, or by injection of powder mixtures or using a flux-cored wire.

In another aspect, the present invention relates to the use of the inventive alloy in the processing of liquid steels, in particular, its deoxidation, desulfurization and purification from non-metallic inclusions.

As in the processing of cast iron, the proposed alloy can be used both in the form of a lumpy alloy and in the form of powders, for example, blown into the melt or supplied in the core of the sheath wire.

More detailed explanations regarding the limitation of the content of the alloy components are given further.

The values of the component contents given below refer to mass fractions (percentage) calculated for the total weight of the alloy. All values given should be considered as including normal deviations due to the method of analysis or measurement selected.

The proportions of the individual components of the alloy can be determined using standard methods suitable for the analysis of refractory, ceramic or other non-metallic materials.

As suitable methods, it is worth noting, for example, GOST 1460-13, which was used by the inventors in the selection and analysis of samples of the proposed alloy.

The upper limit of CaC2 content in the inventive alloy is set to 55% or less. Exceeding the specified content of CaC2 results to a sharp increase in the melting point of the system and the impossibility of providing high degree of calcium and carbon absorption by oxygen of iron melts.

The lower limit of CaC2 content in the alloy is set to 25%. At levels below this limit, the alloy does not contain enough calcium carbide to provide efficient processing of iron melts. Thus, the lower limit of 25% is determined by practical expediency when used as a processing alloy and by the ratio between the cost relative to traditional slag-forming and deoxidizing materials and the quality of the resulting steel. Preferably, the content of calcium carbide is more than 30%, more preferably more than 35%.

The content of oxides (CaO-AhCh-SiCh-MgO), as well as the CaO/AhC ratio determine the fusibility conditions of the system as a whole within the specified temperatures (1350-1450°C).

The amount of SiCh in the inventive alloy is set to 0.5-5%. Above this amount, active formation of a silicate phase, in particular, aluminosilicates or calcium silicates begins, which makes it difficult to melt the low-melting binder phase of the alloy, results to an increase in the melting point as a whole, and also makes it difficult to obtain a highly basic liquid slag when processing iron melts with the proposed alloy. When the content of SiO2 is less than 0.5%, it is difficult to form a low-melting binder phase during solidification when producing the alloy according to the present invention, which results to an increase in the melting point of the alloy and reduces the efficiency of iron melts processing. Preferably, the amount of SiCh oxide is less than 3.0%.

The amount of MgO in the inventive alloy is set to 0.5-5%. Above the specified upper limit, conditions for the formation of spinels arise, which results to a sharp increase in the melting point of the low-melting binder phase and the inventive alloy as a whole. Reducing the magnesium oxide content to less than 0.5% is difficult due to the need to select purer raw materials for producing the alloy according to the present invention, which results to a sharp increase in production costs. On the other hand, the magnesium oxide content of 1.5-4.5% makes it possible to provide more advantageous conditions for the interaction of the lining of metallurgical units and liquid slags formed during the processing of iron melts with the inventive alloy. Thus, the preferred magnesium oxide content is in the range of 1.5- 4.5%.

The content of free carbon is due to the use of carbon-containing materials for the formation of calcium carbide in the inventive alloy production and is limited by the possibility to process low-carbon steel grades. Accordingly, when the content of free carbon is less than 0.5%, stable formation of calcium carbide is not ensured in the inventive alloy production. When the content of free carbon is above 2%, undesirable carburization of iron melts and foaming of slag occur when the iron melts are treated with the inventive alloy. Preferably, the upper limit of free carbon content is less than 1.5% .

The CaO/AhC ratio in the inventive alloy is set to 0.75-1.5. When the value of this ratio is less than 0.75 and above 1.5, the melting point of the low-melting binder phase in the inventive alloy increases significantly due to the formation of compounds of C2A and CA2 type, where CaO oxide is designated as C, and AI2O3 oxide is designated as A, thus, the CaO/AhC ratio in the alloy is set in the range of 0.75-1.5, preferably of 0.85-1.3.

The CaC2/CaO ratio is essential for determining the proportion of the low-melting binder phase in the alloy relative to the number of carbide grains. When the value of this ratio is less than 0.6, the content of calcium carbide in the alloy is insufficient for effective processing of iron melts.

If the CaC2/CaO ratio exceeds 3.6, sufficient bonding of the carbide due to the low- melting binder phase is not ensured, since its amount is relatively low, and the alloy does not have the properties claimed by this invention. Thus, the CaC2/CaO ratio in the inventive alloy is set in the range of 0.6-3.6, preferably of 1.2-3.

Unavoidable impurities in the inventive alloy are present in an amount not exceeding 4%.

Unavoidable impurities come from raw materials and/or from the production environments for obtaining an alloy according to the present invention in the form of a fused product. Unavoidable impurities do not significantly affect the properties of the inventive alloy when it is used for processing of iron melts. As unavoidable impurities, the alloy may contain, but not limited to, S, P, Fe2Os, TiCh, CnCh, MnO, V2O5, Moth and others.

It is advantageous if, among the unavoidable impurities, the amount of sulfide sulfur in the alloy does not exceed 1.0%. Then the alloy is particularly suitable for desulfurization of iron melts. It is worth noting that the sulfide sulfur is preferably present as calcium, iron and manganese sulfides, with the presence of other sulfides not excluded.

It is worth noting that Fe2Os and MnO oxides slow down the formation of the carbide phase, while TiO2, CnCh, V2O5 and MoOs can slightly increase the melting point of the low- melting binder phase. Proceeding from the above, the presence of these oxides is undesirable in the inventive alloy.

If unavoidable impurities are present at the level, these components do not have a negative effect when their total content is less than 4%. It is advantageous if the total content of unavoidable impurities is less than 1.5-2%.

Producing the alloy according to the present invention

The inventive alloy can be obtained in the form of a fused product, for example, in arc furnaces, from a proportioned charge, including lime, coke (anthracite), as well as additives containing AI2O3, SiCh, MgO. An example of a charge for producing the alloy is presented in table 1 below.

Table 1: Chemical composition of the charge, %

The approximate number of charge components to obtain 1 ton of the finished alloy is given in table 2.

Table 2: Charge per 1 ton of alloy, kg

The composition of the resulting product is given in table 3. Table 3: Chemical composition of the resulting alloy, %

The charge, according to table 2, was completely melted in an arc furnace with accompanying chemical reactions, tapping the melt into a flat mold at a temperature of 1750- 1850°C and air cooling.

After extracting the resulting alloy according to the present invention from the mold, it can be crushed to a fraction size specified by the consumer, followed by packaging in a sealed container for its further use in the processing of iron melts.

Embodiments of the invention

The alloy having the composition given in table 4 was obtained by mixing raw materials and melting in an electric furnace, followed by cooling in a mold.

For comparison, table 4 also shows the composition corresponding to the material known from RU2638470 (Comparative example).

To determine the guaranteed melting point, the alloy according to the present invention was placed in a high-temperature furnace, such as a resistance furnace, for heating in an inert gas, and heated in a furnace with visual control over the alloy melting degree.

The guaranteed melting point of the alloy was determined by pyrometric measurement of the temperature of the alloy in the furnace after its complete melting, being observed via high-temperature image controls. Temperature measurement results are also given in table 4.

Table 4

*the specified values in the material known from RU2638470 are not regulated, data are given only for the exemplary composition used in this comparison.

The measurements have shown that the melting point of the inventive alloy is in the range of 1350-1450°C.

The examples of the use of the alloy for the processing of iron melts in metallurgical processes are given further.

It is worth noting that the estimated average degree of the alloy absorption when introduced into iron melts was more than 92%, which significantly exceeds the level for the known material and confirms the fact that the inventive alloy has better fusibility compared to the prior art.

Example 1

The alloy according to table 4 was used to partially replace secondary aluminum (AB87) in the production of 08PS steel at the outlet of a 350-ton converter, followed by processing of the semi-finished product in a ladle furnace with casting at a continuous casting machine (CCM).

Average figures for melts according to basic technology (steel deoxidation with aluminum): metal oxidation at the output - 981 ppm; sulfur: at the output - 0.023%, upon arrival to the ladle furnace - 0.016%, in the CCM -0.010%; through consumption of aluminum in terms of secondary aluminum - 1307 kg per melt; (FeO+MnO) in ladle furnace slag - 1.1%.

For the consumption of Material 001 (according to table 4) in the amount of 525 kg per melt (1.5 kg/t), the following results were obtained: oxidation at the output - 985 ppm; sulfur: at the output - 0.022%, upon arrival to the ladle furnace - 0.016%, in the CCM - 0.009%; through consumption of aluminum at all technological sites in terms of secondary aluminum - 897 kg per melt; (FeO+MnO) in ladle furnace slag - 1.11%.

Savings of secondary aluminum - 410 kg per melt. To assess the efficiency of the inventive alloy, it is proposed to use the secondary aluminum replacement ratio, i.e. the amount of alloy (kg/kg Al) that has the same deoxidizing effect on the melt as kg of secondary aluminum. Thus, the lower the value of the said coefficient, the more efficient the alloy is. Since the process of steel deoxidation is more complex, in order to assess the efficiency of a new alloy, the balances for manganese, silicon, and other elements should be additionally accounted for.

The secondary aluminum replacement ratio for this example is 525/410=1.28.

For the consumption of Material 002 (according to table 4) in the amount of 360 kg per melt (1.03 kg/t), the following results were obtained: oxidation at the output - 979 ppm; sulfur: at the output - 0.021%, upon arrival to the ladle furnace - 0.014%, in the CCM - 0.007%; through consumption of aluminum in terms of secondary aluminum - 940 kg per melt; (FeO+MnO) in ladle furnace slag - 1.1%.

Savings of secondary aluminum - 367 kg per melt.

The secondary aluminum replacement ratio is 0.98.

For the consumption of Material 003 in the amount of 525 kg per melt (1.5 kg/t): oxidation at the output - 986 ppm; sulfur: at the output - 0.023%, upon arrival to the ladle furnace - 0.015%, in the CCM - 0.009%; through consumption of aluminum in terms of secondary aluminum - 830 kg per melt; (FeO+MnO) in ladle furnace slag - 0.9%.

Savings of secondary aluminum - 477 kg per melt.

The secondary aluminum replacement ratio is 1.1.

For the consumption of Material 004 in the amount of 800 kg per melt (2.3 kg/t): oxidation at the output - 980 ppm; sulfur: at the output - 0.023%, upon arrival to the ladle furnace - 0.016%, in the CCM - 0.010%; through consumption of aluminum at all technological sites in terms of secondary aluminum - 714 kg per melt; (FeO+MnO) in ladle furnace slag - 1.0%.

Savings of secondary aluminum - 593 kg per melt.

The secondary aluminum replacement ratio is 1.35. No carburization of the melt was observed with the consumption of the alloy according to the present invention up to 2.5 kg per ton with metal oxidation sufficient for complete absorption of CaC2.

No slag boiling at the end of melt discharge was observed, and calcium carbide was completely absorbed by metal oxygen during the metal discharge from the melting unit.

When using the inventive alloy, the secondary aluminum replacement ratio compared to RU2638470, with equal CaC2 contents, is lower by 15-20%.

Example 2

Material 005 according to table 4 was made in the form of a flux-cored wire with a diameter of 14 mm. Filling of 260 g/m, the fill factor of 59.23%.

Basic melting of 40KhN grade steel according to the scheme: EAF-25 - ladle furnace - vacuum degasser - CCM.

The main task of vacuum degassing was to reduce contamination with non-metallic inclusions.

The samples for basic melts on average had: before vacuuming, the total proportion of steel contamination with non-metallic inclusions was 0.0528%, after vacuuming it was 0.0291%.

A variant of experimental melts in a ladle furnace: after performing all operations for deoxidation of metal and slag, the injection of alloying components, with the arcs turned off, sample No.l was taken. 50 meters of wire with the inventive alloy were used; 2 minutes of soft argon purge without arcs, sample No.2 was taken.

Average results for samples with metal processing with a wire containing the inventive alloy:

Sample No.l (before processing) - 0.0494%

Sample No.2 (after processing) - 0.0094%

It is shown that the use of the inventive alloy is justified and effective for removing non-metallic inclusions in steel, while due to the presence of a low-melting flux component in the inventive alloy and to the additional effect of deoxidation of the iron melt with the release of CO, a better removal of non-metallic inclusions is achieved than during vacuum treatment.

Example 3

Material 006 according to table 4 was used mixed with magnesium in flux -cored wire in proportions (Mg 35%, the inventive product 65%). The wire was used for external iron desulphurization with equal results for sulfur with a 25-30% reduction in consumption against a base wire filled with a mixture of magnesium with flux (Mg 35%, flux 65%). As a result, 1 kg of Material 006 replaces 0.15- 0.20 kg of magnesium metal during the external iron desulfurization. If the price of magnesium exceeds the price of a Material 006 type product by more than 5 times, the use of a new alloy to remove sulfur from cast iron will be especially advantageous.

Example 4

For a series of melts, an analysis of the final rejection of metal upon delivery of finished rolled products was carried out by the factor - non-metallic inclusions for three groups of steel grades:

(1) - low carbon without silicon;

(2) - medium carbon with low silicon;

(3) - low carbon with medium silicon.

Basic melts were deoxidized according to conventional technology using silicon and aluminum.

The experimental melts used the inventive alloy, having the following range of chemical composition:

CaC2-45-48%;

CaO 20-27%,

AI2O320-27%,

SiO ₂ 1-2.5%,

MgO 0.5-2.0%,

Free C no more than 1.5, and with a CaO/AhC ratio in the range of 0.8-1.2.

The CaC2/Co ratio in the alloy was 1.6-2.2.

This material had a melting point in the range of 1350-1400°C.

The inventive alloy was fed as a replacement for secondary aluminum at the outlet from the converter to the ladle in a one-to-one ratio.

For steels of group (1), 1 kg of the inventive alloy per ton of steel was used, for steels of groups (2) and (3) - 1.5 kg/t.

Table 5 shows the results obtained for the rejection of rolled metal products due to non-metallic inclusions: Table 5

The results in table 5 show a significant refining (cleaning) effect relative to non- metallic inclusions when using the alloy according to the present invention when tapping metal from the furnace to the ladle.

Further, using the same alloy, the impact of the quantitative characteristics of the fed alloy on the rejection value was studied for an array of steel melts of group (2) - (grade St3). The results obtained are summarized in tables 6 and 7.

Table 6

Further, using the same alloy at its consumption of 1.5 kg/t, the impact of the CaO/AhC ratio on the rejection value was studied for an array of steel melts of group (2) - (grade St3). The results obtained are summarized in table 7.

Table 7

The results from tables 6 and 7 show that the higher the consumption of the inventive alloy, and the closer the CaO/AhC ratio is to the interval (0.8- 1.0), the higher the effect of reducing rejects due to non-metallic inclusions (NI).

The above examples confirm that the inventive alloy has been effectively used in the processing of iron melts, especially steel and cast iron, at least for the removal of oxygen and sulfur, and the purification from non-metallic inclusions, and has shown better processing results compared to known and traditional materials.

Those skilled in the art may propose other variants or modifications to the use, preparation and composition of the alloy according to the present invention, which in general should be considered as included within the scope of the present invention, determined by the invention claims.

For example, the alloy according to the present invention can be effectively used to replace other conventional deoxidizers and materials for processing of iron melts, such as cast iron, steel or ferroalloys. Examples of such conventional deoxidizers and materials for processing can be ferrosilicon, calcium carbide, silicon carbide, calcium metal and other materials.