RU2247784C1 - Batch for steel smelting - Google Patents

Abstract

FIELD: non-iron metallurgy, in particular steel smelting in various melting furnace.

SUBSTANCE: claimed batch contains carbon-carbide-silicon material ,material comprising less than 15 % of silicium carbide and not less than 65 % of free carbon. Material, containing (mass %) said carbon-carbide-silicon material 30-60; carbon of high-temperature calcinations 25-40; and slag-making materials 7-13 is fed into batch in briquette form.

EFFECT: batch for steel smelting of improved quality due to decreased carburizer losses.

2 cl

Description

The invention relates to ferrous metallurgy, namely to the production of steel in smelting units of various types. The claimed invention can be used in steelmaking processes both ordinary and high alloy steel grades.

Known charge for steelmaking, containing cast iron as a carburizing material, scrap metal, slag-forming materials in the following ratio of components, wt.%:

cast iron 6-40

steel scrap 60-94

slag-forming 0.5-2.0

(technological instruction TI - 243 MM-01-98 for steel production in the open-hearth furnace of the Nizhnedneprovsky pipe rolling plant, OJSC; technological instruction DTI-48-CT-97 for steel production in arc furnaces of the Dnipropetrovsk switch plant, OJSC).

As a carburizing material, cast iron is introduced into the composition of the above charges to provide a carbon content in the metal bath after the charge is melted that is 0.3-0.5% higher than the lower limit of carbon concentration in a given steel grade. The specified carbon content in the metal after melting is necessary for a high-quality oxidation process. The boundary of the content of cast iron in the mixture is justified by the physicochemical and kinetic features of the passage of the melting process of the mixture in various melting units (electric arc furnace, open-hearth furnace, etc.).

The main disadvantage of the above composition is that expensive and scarce cast iron is used as the carburizing material;

the high content of sulfur and phosphorus as a carburizer in pig iron leads to an increase in energy and, consequently, material costs for their further removal from the melt;

reoxidation of the steel bath occurs during the melting process and the subsequent oxidation period.

The closest is the technical solution according to the patent of Ukraine No. 47979, IPC C 21 C 5/00, BI No. 7, 2002, in which the mixture for steelmaking contains: steel scrap, carburizing materials, slag-forming substances, and is used as carburizing material silicon carbon carbide material and carbon of high temperature calcination in the following ratio of components, wt.%:

silicon carbide material 0.4-1.1

high-temperature calcination carbon 0.6-1.9

slag-forming substances 1.5-2.0

steel scrap else

The disadvantage of the charge according to the prototype is that the carburizing materials are part of the charge in a finely divided form, which, in turn, leads to the loss of carburizing materials (up to 30%) due to the aerodynamic flows that occur in the melting units.

The technical problem solved in this invention is the qualitative improvement of the charge for steelmaking by reducing the loss of carburizing materials and, accordingly, reducing the cost of carburizing materials.

This technical problem is solved due to the fact that the batch for steelmaking contains steel scrap, carbon-silicon carbide material, high-temperature calcination carbon, slag-forming materials, while it contains carbon-silicon-silicon material - a material containing silicon carbide of less than 15% and free carbon of not less than 65%, while the material containing silicon carbide is less than 15% and free carbon is at least 65%, high-temperature calcination carbon and slag-forming materials are set into a briquette in the charge prefecture as the following ratio of the component, wt.%:

material containing silicon carbide less than 15%

and free carbon not less than 65% 30-60

high temperature calcination carbon 25-40

slag-forming materials 7-13

The technical result is achieved due to the fact that the content in the charge of additional components, such as carbon-silicon carbide material and high-temperature calcination carbon with a high sulfur content, in the ratios determined empirically and given above and mainly in briquetted form, improves the quality of finished steel and reduces loss of carburizing materials. It is also very important that the composition of the mixture according to the invention includes secondary materials of electrothermal production, which affects the reduction in the cost of steel and the improvement of the environmental situation.

As steel scrap, steel scrap is used in accordance with GOST 2787-75.

As the carbon-silicon carbide material, secondary material is used, which is used in the production of graphitized materials (for example, MU-1 grade). This material contains less than 15% silicon carbide and at least 65% free carbon. Silicon carbide present in the composition of the carbon-silicon carbide material during the melting of steel scrap interacts with liquid iron by the reaction:

SiC _tv + [Fe] → [Si] _Fe + [C] _Fe ,

with assimilation by molten metal of a steel bath of silicon and carbon.

The indicated feature of the interaction of SiC affects the mechanism and regulates the decarburization rate of the steel bath, blocks metal reoxidation during carbon oxidation.

The combination of carbon-containing materials with silicon carbide provides a sufficient carbonization process and a deoxidizing effect.

Additional management of metallurgical silicon carbide (STP 002222-162-99) is introduced to adjust the ratio SiC-C = 0.15-0.65, selected empirically, providing the maximum metallurgical effect of the briquette.

When the ratio SiC -: - C is less than 0.15, at the beginning of the oxidation period of smelting, increased oxidation of iron to FeO is observed. When the ratio SiC -: - With more than 0.65, carbon oxidation is blocked, which requires an additional consumption of oxidizing agents, leads to overheating of the steel bath, which negatively affects the furnace lining, and also prolongs the melting time.

The combination of carbon-containing materials with silicon carbide provides a sufficient carbonization process and a deoxidizing effect.

The limits of the content of components in the composition of the mixture are explained as follows.

Silicon carbon-carbide material (TUU 322-00196204.005-99) when the content of silicon-carbon carbide material (MU-1) in the briquette is less than 30% does not block the processes of steel bath oxidation. When the content of carbon-silicon carbide material (MU-1) in the briquette exceeds 60%, the concentration of silicon oxide in the slag increases, which leads to a decrease in the basicity of the slag and, as a consequence, a decrease in its desulfurizing and dephosphorizing properties.

High-temperature calcination carbon (graphite) (TUU 322-00196204.005-99) is a secondary material that is formed during the production of graphite electrodes (for example, PF-1 grade). When the content of this material in the briquette is less than 25%, the carburization of the steel bath is insufficient, and when the content of high temperature calcination in the briquette is more than 40%, the process of oxidizing the steel bath is not sufficiently blocked.

Slag-forming materials - binders - are the oxide system CaO-SiO ₂ -Al ₂ O ₃ , are characterized by hydration hardening and a relatively high melting point, which allows to produce briquettes of sufficiently high strength and fire resistance. The presence of free silica in the briquettes leads to its interaction with the CaO of a slag-forming material - a binder and a decrease in its melting temperature.

The gradual melting of slag-forming compounds, by the moment of formation of a metal melt, is accompanied by the interaction of free carbon and silicon carbide with liquid metal.

When the content of the slag-forming briquette — the binder — is less than 7 wt.%, The necessary briquette strength is not provided, and the briquette spills. When the content is more than 13 wt.%, The reaction rate of the briquettes with a metal melt decreases.

The proposed technical solution “The mixture for steelmaking” meets the criterion of “novelty”, as evidenced by the above list of differences with respect to the prototype selected by the applicant on the basis of a search for scientific, technical and patent sources of information.

The analysis of the known technical solutions showed that the claimed list of essential features was not found among the known solutions, which meets the criteria of the invention - inventive step.

The optimality of the percentage ratios of the components of the charge for steelmaking is confirmed by experimental smelting conducted in an electric arc furnace of OJSC “DZS” and in an open-hearth furnace in the conditions of OJSC “NTZ”. The analysis of the melts on the charge claimed by this invention showed that the absorption of carbon was 85 - 90%, while when using the charge according to the prototype, the absorption of carbon was 79-84%.

The use of the mixture in briquetted form allows to increase the degree of assimilation of carbon, reduce the loss of carburizing materials (up to 30% on some steel grades) and reduce the use of deoxidizers.

The proposed composition of the mixture using briquettes of the given composition can be easily reproduced and used in the production of ordinary and high alloy steel grades.

Thus, the technical solution meets the criterion of industrial applicability.

Claims (2)

1. A steel batch containing steel scrap, carbon-silicon carbide material, high-temperature calcination carbon, slag-forming materials, characterized in that it contains silicon carbide material less than 15% and free carbon not less than 65% as carbon-carbide material, while the material containing silicon carbide less than 15% and free carbon not less than 65%, high-temperature calcination carbon and slag-forming materials are set in the mixture in briquetted form in the following ratio and components, wt.%: Material containing silicon carbide less than 15% and free carbon not less than 65% 30-60 High temperature calcination carbon 25-40 Slag-forming materials 7-13 2. The mixture according to claim 1, characterized in that the briquettes additionally contain metallurgical silicon carbide to adjust the ratio SiC: C = 0.15: 0.65, selected empirically, providing the maximum metallurgical effect of the briquette.