SU1730174A1 - Method for charging open-hearth furnace with burden - Google Patents

Abstract

This invention relates to ferrous metallurgy, in particular to steel production in open-hearth furnaces using the scrap process. The aim of the invention is to reduce the duration of smelting, reduce the specific consumption of pig iron and stabilize the bath melting process on carbon. Loading solid pig iron is produced in two portions, with the first portion of pig iron in the amount of 65-75% of the calculated load on the slopes and the front line of the furnace after heating the fine steel scrap and slag-forming materials and at the same time, lightweight steel scrap is fed over the entire bottom of the furnace, and the second portion of pig iron is fed to coarse steel scrap at the end of the charge of metal charge, which is heated for 10–20 min. 1 tab. Csh / fe

Description

This invention relates to ferrous metallurgy, in particular to steel production in open-hearth furnaces using the scrap process.

There is a known method of charging the charge to the open-hearth furnace at the scrap process, which includes loading of fine steel scrap in the amount of 10-20% of the charge plummet to the hearth, then lime or lime in a continuous layer, the remaining part of the metal charge and, upstairs, pig iron.

The closest in technical essence to the claimed is the method of filling the charge in the open-hearth furnace during the scrap process, which includes loading onto the surface of the bottom of a small steel scrap, then a larger scrap, dispersing lime (lime) and, above, cast iron .

In the known method, due to the dispersed loading of lime (lime), the duration of the melting period is somewhat reduced. However, the productivity of the furnace remains relatively low. Another disadvantage of this method is the high and unstable carbon monoxide, as a result of which the smelting process and the smelting process are slowed down, the productivity of the unit decreases. In addition, the method is not sufficiently economical with regard to the use of iron.

The aim of the invention is to reduce the duration of melting, reducing the specificity of

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about

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cast iron consumption and stabilization of the molten bath process on carbon.

The goal is achieved by the fact that in the process of charging the mixture to an open-hearth furnace, including loading small steel scrap, slag-forming materials, heating them, supplying large steel scrap, heating loaded materials and subsequent supplying solid pig iron, loading solid pig iron to the furnace hearth, two solid pig iron is fed portions, with the first portion of pig iron in the amount of 65-75% of the calculated load on the slopes and the front line of the furnace after warming up the small steel scrap and slag-forming and at the same time Lightweight steel scrap is delivered over the entire area of the furnace hearth, and the second portion of pig iron is fed to large steel scrap at the end of the charge, which is heated for 10–20 minutes.

The period of filling and melting of the mixture at. The scrap process takes up to 3/4 of the total melting time, and therefore the furnace's performance depends on the rational loading method. The unstable melting of the bath in carbon, the so-called soft and hard melting, has a significant impact on the productivity of the open-hearth furnace. The cast iron should contribute only that amount of carbon, the oxidation of which would be sufficient for the normal conduct of the process.

The process of scrap melting proceeds under conditions of continuously raising the temperature of the bath from about 1300 to 1550 ° C and simultaneously reducing the carbon content in the melt from about 4.0 to 1.0%. The melting of solid scrap in a high-carbon iron melt is due to the saturation of its surface with carbon from a liquid metal (diffusion mode). When organizing the filling according to the proposed method, the cast iron, introduced at the beginning of smelting, has a lower melting point, forms local high carbon zones. The process of melting scrap in a high-carbon melt is facilitated due to the carburization of the surface layer and the associated significant decrease in the liquidus temperature, which promotes the melting of scrap pieces, and also accelerates the process of dissolution of the charge pieces that have not yet become liquid.

Loading most of the cast iron together with scrap in the initial period of filling on the slopes and along the front line of the furnace eliminates the penetration of the molten iron to the cold lower layers, since

In the case of cast iron, it is dispersed throughout the bath, increasing the surface area, which, as is well known, increases the overall melting rate.

The cast iron loaded onto the heated upper layer of the charge, having melted, also carbonizes the surface layer, failing to penetrate into the cold lower regions, much less reach the limestone. Oxidation

Silicon and the formation of silicates are accompanied by the release of heat, and the melting of the metal is accelerated.

When cast iron is charged at the beginning of the filling, there is noticeable oxidation of carbon in the period

5, melting does not occur due to the thermodynamic inhibition of the decarburization process, which is explained by the high concentration of silicon and manganese in the melt, which at the existing low

0 temperature greater affinity for oxygen. As a result, silicon and manganese do not allow the development of a decarburization process on such interfacial surfaces as metal lining, metal slag. Low

5, the temperature and the relatively high viscosity of the metal outside the reaction zone do not provide the necessary rate of supply of the carbon component to the reaction site, which leads to low total rates of carbon oxidation during the period of melting and stabilization of the molten bath over carbon.

The amount of pig iron in the initial period of the filling is determined by experienced swimming trunks.

5 Filling more than 75% of the pig iron from the calculated one leads to the formation of refractory local zones and prolonged melting, and less than 65% increases the proportion of iron after the end of the filling, which leads to increased carbon oxidation and unstable melting.

Warming up before filling the second batch of pig iron for less than 10 minutes does not ensure the compaction of the charge, which reduces its heat conduction and impairs the melting process, and for more than 20 minutes leads to a sharp overcooling of the upper layer of the molten charge, and then to boiling and soft melting.

0 Such an integrated approach to charging the charge to the open-hearth furnace during the scrap process improves the productivity of the unit, reduces the consumption of pig iron and fuel by reducing the periods of rolling and melting, as well as stabilizing the melting of the bath in carbon.

To confirm the optimality of the technological parameters of the proposed method, pilot smelting was carried out. The smelting campaign was controlled by the consumption of cast iron for smelting and the first part of the filling, the duration of the melting and the entire melting, the time of heating of the charge and the filling of the second part of the cast iron and the carbon content of melting. For comparison, conventional smelting was taken. The results of experimental and row heats are presented in the table.

Example. Steel smelting Art. 45 produced scrap process in a 45-ton open-hearth furnace by the proposed method.

After refueling the working space of the furnace, the loading of charge materials was started. On the hearth, 6 molds (5.7 tons) of small charge and 6 molds (5.9 tons) chips were evenly loaded. Then, in accordance with the technological instruction adopted at the enterprise, 5 tons (4.3 tons) of burnt lime are distributed evenly into all windows of the furnace. The load time of this portion is 26 minutes. They were heated for 12 minutes, since the charge materials were located above the threshold levels of the charging windows. Immediately after warming up, two molds (5.8 tons) of cast iron were loaded — one on the left slope from the outermost window and a friend — along the front line into the rightmost window, then along the axis of the furnace, 9 tons of small charge were loaded (7.4 tons) and two more cast iron tins (6.6 tonnes) —one on the right slope and one on the front line of the leftmost window; on the back line of the furnace wastes of own production were loaded (not measured lump blooms, (9.4 tons). After heating up for 7 minutes, the filling was finished with loading of small scrap (6.4 tons). Then they heated 16 minutes (controlled parameter) and loaded the second 5.2 t of pig iron on top

the entire charge. Technological parameters of this melting are presented in the table (example 3).

As can be seen from the table, the consumption of pig-iron bottoms cast by the proposed method, lower by 12-14%; at the consumption of hot metal of hot melts (example 7), at the level of experienced melts, a soft melting and casting of steel were obtained out of schedule; the duration of the experimental heats is reduced by 12-20%; Experimental melts are characterized by melting stability of carbon (carbon loss compared with the calculated carbon content is 20–25%).

Claims (1)

Claims of the Invention The method of charging the mixture to an open-hearth furnace, including loading of small steel scrap, slag-forming materials on the hearth of the furnace, their heating, feeding of large steel scrap; heating the loaded materials and the subsequent supply of solid pig iron, characterized in that, in order to reduce the duration of smelting, reduce the specific consumption of pig iron and stabilize the process of carbon melting of the bath, solid pig iron is loaded in two portions, while the first portion of pig iron in the amount of 65-75% of the calculated load on the slopes and the front line of the furnace after warming up the small steel scrap and slag-forming and at the same time serves over the entire area of the furnace bottom lightweight steel scrap, and the second portion of pig iron is fed to coarse steel scrap at the end of the charge, which is heated for 10–20 minutes.