RU2573847C1 - Steelmaking at electric furnaces - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: claimed process comprises the loading of the charge including the scrap steel, metalised pellets, slag-forming materials and metallurgical briquettes of the metalling degree of 65-70% into the furnace. Metallurgical briquettes are made from iron-bearings wastes of the direct iron recovery process. Said briquettes are loaded on the furnace bottom layer-by-layer with the steel scrap. As the charge melts, the metalised pellets and slag-forming materials are fed.

EFFECT: higher efficiency of the furnace die to accelerated charge melting.

Description

The invention relates to ferrous metallurgy, in particular to methods of steel smelting in various steelmaking units, mainly in electric arc furnaces.

Known methods of steel smelting using a variety of materials in the charge, such as cast iron, steel scrap, metallized pellets, briquettes, etc. Technical and economic indicators of smelting are determined by the smelting technology, cost and composition of the metal charge used.

A known method of steelmaking using charge briquettes (RF patent No. 2213788, IPC C21C 5/00, publ. 10.10.2003) of the following composition,% mass .: oxidized iron-containing material 5-57, carburetor 20-30, binder 10-20, alloying additive 1-15, iron-carbon alloy 1-30, slag-forming material 1-10, plasticizer 1-10. Significant disadvantages of this smelting technology include the high content of harmful impurities in briquettes, which is undesirable in the smelting of high-quality steel grades.

A known method of steel smelting (RF patent No. 2180007, IPC C21C 5/52, C21C 5/04, publ. 02/27/2002) with the addition of iron-carbon briquettes (ZHUB) in the metal charge, containing, in wt%: 70 - iron oxides, 30 - carbon-containing substance and a binder - 5-10 in excess of 100% - in the form of a concentrate of soda ash and loam, generating a reducing gas medium (CO) when heated. As iron-containing materials, such briquettes use steel oxide, iron-containing metallurgical dust, iron ore, etc. The use of oxidized iron-containing materials in the charge requires an increase in the melting time to complete the processes of iron reduction, which leads to additional energy consumption.

Known charge briquette (RF patent No. 21505514, C21C 5/00, C22B 1/00, publ. 10.06.2000) for the production of high quality steel containing metallic iron, iron oxides, carbon and waste rock, in the following ratio, wt. %:

the ratio of carbon to oxygen of iron oxides is greater than or equal to 0.8. Briquettes are produced by hot briquetting with a metallization degree of 75-85%. The size of the briquettes, mm: 110 × 50 × 30 mm.

Steel is smelted in chipboard on a charge with a ratio of components: 35% of briquettes and 65% of scrap metal.

Significant disadvantages of this briquette are:

- high costs associated with the manufacture of this briquette, resulting in an increase in the cost of steel obtained;

- reduced strength of briquettes, leading to the formation of a large amount of fines during the transportation of briquettes, as a result of which the technical and economic indicators of smelting are worsened;

- high melting time due to the fact that the oxides in the material are not distributed over the volume of the material, but are located in the central part, which requires additional time for diffusion of the active oxygen of the oxide-containing alloy to the carbon of the iron-carbon alloy;

- a high concentration of carbon, increasing the duration of the heat due to the need to remove it for certain grades of steel.

A known method of steelmaking in an electric arc furnace using metallized pellets in the charge (prototype) (ed. Certificate of the USSR No. 1350179, IPC C21C 5/52, publ. 07.11.1987).

Steel is smelted on a batch consisting of steel scrap - 20-40%, metallized pellets, the proportion of which is 60-80% of the mass of smelting, coke and slag-forming materials. After releasing the previous melting, a part of the mixture of lime and limestone in the ratio 1: (0.1-1) is loaded into the electric arc furnace, steel scrap is piled up, the furnace is turned on, and during the penetration by the electrodes of the wells in the charge, the rest of the specified lime mixture is loaded through the opening in the arch and limestone with a total amount of 0.7-2% by weight of the smelting, as well as the required estimated amount of coke. After penetration by electrodes in the steel scrap of the wells, metallized pellets, lime and limestone are continuously loaded into the furnace in a ratio of 10: (0.5-1.2) :( 0.2-1.2).

The disadvantages of using a mixture of metallized pellets include the following:

- a high degree of metallization (90-98%) of the pellets determines their high cost, which increases the cost of steel smelted from them;

- in the case of the use of imported pellets, they must be passivated or briquetted to protect against fire and deterioration of technological properties;

- metallized pellets are dosed for melting in time, the feed rate of the pellets must be coordinated with the electric energy supplied to the furnace, which together with their high surface (pellet diameter 10-15 mm) leads to significant waste, i.e. to iron loss, environmental degradation;

- when the degree of metallization is more than 95%, the relative fraction of iron oxides in the material is small. In this case, iron oxides are completely reduced by carbon, as a result of which there is no transition to slag. The formation of slag low in iron oxide and lime impairs its refining properties in relation to the removal of phosphorus and sulfur;

- the lack of oxygen for carbon oxidation leads to a low intensity of boiling baths and an increased concentration of carbon in the metal by melting. To intensify the process, oxidizing agents are introduced.

These factors lead to an increase in the duration of the heat, as well as to an increase in energy consumption.

The present invention is directed to solving the technical problem of expanding the base of raw materials that could be used in steelmaking.

The desired technical results of the invention are: reducing the duration of the melting of metal filling, reducing the cost of smelting steel due to the involvement in the redistribution of waste from the process of direct reduction of iron and reduce the cost of the charge.

The specified technical result is achieved by the fact that according to the method of steel smelting, a metallurgical briquette with a metallization degree of 65-70%, made from iron-containing waste from the process of direct reduction of iron, is used as part of the charge. The proportion of briquettes is 10-15%, which allows to reduce the share of expensive metallized pellets and / or HBI with a metallization degree of 89-98%. The chemical composition of the briquettes,%: Fe _total. - 78-80; Fe _meth - 56-61; FeO - 21-30; SiO ₂ - 3.6-3.9; CaO - 1.5-1.6; S 0.05-0.06; P is 0.01. Sizes, mm: diameter 50; height 15. Briquettes do not contain impurities harmful to the metallurgical process in excess of the permissible level, and have sufficient strength for transportation and melting.

The composition of the metal charge includes steel scrap, metallized pellets and briquettes.

Scrap and briquettes are fed into the filling. The loading of steel scrap and briquettes on the bottom of the furnace is carried out in layers: scrap - briquettes - scrap - briquettes. The size of the briquettes is optimal to ensure the conditions for their uniform distribution in the volume of metal filling. With this briquette feeding method, the optimal stacking density is ensured, the charge is more uniform, the conditions of heat and mass transfer in the working space of the furnace are improved, which leads to a reduction in the duration of the melting period.

The increased content of oxygen in briquettes in the form of iron oxides (21-30%), contributes to their intense interaction with carbon briquettes. The resulting carbon monoxide ensures the maintenance throughout the melting of foamy slag, shielding arcs, good conditions for refining the metal, which also has a positive effect on the heat transfer conditions in the furnace and reduces the duration of the melting of the charge.

The supply of metallized pellets and slag-forming materials is carried out as the charge is melted.

When using a fraction of briquettes of less than 10% in the filling, a reduction in the duration of the melting period is not ensured, since there is not enough compaction of the charge, the oxidation of the carbon of the melt by oxygen of the oxides present in the briquette is not enough for foaming the slag and closing electric arcs. The economic effect of reducing the cost of the charge is negligible.

The use of a briquette fraction of more than 15% in the filling leads to an increase in the duration of the charge melting due to a decrease in its conductivity, the formation of a large amount of slag obtained by binding oxides of briquettes with calcium oxides, and also the time required to melt the required slag-forming additives.

The implementation of the method.

Steel 20 was smelted in an experimental laboratory setup with a crucible capacity of 0.003 tons and a transformer power of 23.7 kW. For experimental melting, the mixture used steel scrap, metallized pellets and briquettes with a metallization degree of 65-70%.

The chemical composition of the briquettes used,%, mass .: Fe _total. - 76; Fe _met. - 52.93; SiO ₂ - 3.73; FeO 21.44; CaO - 1.46; P is 0.011; C is 2.5; S 0.058. The degree of metallization is 69.6%.

The chemical composition of metallized pellets%, mass .: Fe _total. - 90.8; Fe _met. - 85.8; SiO ₂ - 3.54; CaO - 1.51; P is 0.011; C 2.07; S is 0.007. The degree of metallization is 94.5%. Carbon scrap according to GOST 2787-75 was used as scrap.

Three series of pilot melts were carried out with a different ratio of components in the charge. The mixture according to the first embodiment for the first series of heats did not contain briquettes. In the second series of heats, part of the metallized pellets was replaced with briquettes.

In the process of smelting, the charge heating rate was estimated by measuring the temperature with thermocouples, and the start and end times of the charge melting were recorded.

During the smelting of the first series of heats, scrap was fed to the furnace bottom and the pellets and slag-forming pellets were loaded as it was melted.

For the second and third series of experimental melts, scrap and briquettes were loaded onto the hearth in layers and pellets were loaded as the mixture melted.

The results of experimental swimming trunks showed:

- the use of briquettes in the composition of the mixture in the range of 8-12% for steelmaking is technologically possible;

- loading briquettes must be carried out on the hearth of the furnace together with steel scrap in layers;

- there is an increased foaming of the slag melt associated with the reaction of the interaction of iron oxides with carbon.

According to the results of experimental melts, it was found that the shortest time of the process of metal melting corresponds to a charge according to the second embodiment, with a briquette content of 8%, an increase in the proportion of briquettes in a charge in excess of 12% leads to an increase in the duration of melting.

According to tests, the proposed method provides:

- reduction in the duration of the melting of the mixture during melting using briquettes in the filling by 6.0-7.3%;

- reduction in the cost of metal by 50-70 rubles / ton of steel.

Claims (1)

The method of steelmaking in an electric furnace, including loading into the furnace a mixture containing steel scrap, metallized pellets and slag-forming materials, melting the mixture, finishing and metal production, characterized in that metallurgical briquettes with a metallization degree of 65-70% are loaded into the mixture, which They are made of iron-containing waste from the direct iron reduction process, while metallurgical briquettes are loaded onto the furnace hearth in layers with steel scrap, and metallized pellets and slag-forming m Materials are served as the charge is melted.