RU2113503C1 - Method for production of melting stock - Google Patents

Abstract

FIELD: ferrous metallurgy; may be used in production of melting stock and steel from melting stock. SUBSTANCE: method of melting stock production for steel making includes introduction of solid oxidizer (oxidized iron ore pellets) and liquid iron-carbon alloy (cast-iron) in molds of casting machines, their mixing, soaking, and pigs of melting stock are removed from mold at temperature of 700-750 C. Then pigs are heated to 950-1100 C and soaked at this temperature for 0.3-6.0 h. Pigs are cooled down to 700-750 C on casting machine due to their contact with mold surface. At temperature of 700-750 C pigs are sent to constant-temperature furnace and heated up to 950 C and soaked at this temperature from 0.3 to 4.5 h. Then pigs are heated up to 1100 C and soaked from 0.2 to 1.5 h. Pigs are soaked at specified temperature in weakly oxidizing or neutral atmosphere. EFFECT: higher efficiency. 5 cl, 1 tbl

Description

 The invention relates to ferrous metallurgy, in particular to the production of steel.

A known method of producing steel in an arc furnace, which uses a billet obtained by casting a cast iron machine by filling in mold molds of ore-coal pellets, followed by pouring them with pig iron, cooling the billet on a machine, followed by loading a cold billet into an arc steel furnace where the billet charge is heated by burning natural gas to 900-1150 ^o C and iron oxides of the pellets are reduced by 20-25% with carbon rolled into pellets. The amount of charge stock in the metal charge is 1-5 t / t scrap. The carbon content in the charge stock is 3.0-3.5% when using ore pellets, and when using ore-coal pellets will be much larger. It should be noted that the strengthening of ore-coal pellets is associated with significant difficulties, since the oxidative roasting of raw pellets is unsuitable for this. With a greater consumption of charge stock (3-5 t / t scrap), the carbon content in the bath of the chipboard for melting even when using ore pellets exceeds 1.2-1.3%, which leads to an increase in the duration of smelting, especially when smelting low- and medium-carbon grades of steel, reducing the productivity of the steelmaking unit, increasing energy consumption and, ultimately, to higher prices for steel. An increase in the content of pellets (iron oxides) in the charge stock over 25-30% leads to their precipitation (shedding) from the composition of the workpiece due to the insufficient quantity of cast iron in this case, which is no longer able to form a strong workpiece and bind the increased amount of pellets into a single mass , the pellets fall out of the composition of the workpiece, that is, it is impossible to increase the amount of iron oxides in the charge stock in excess of 20-25%.

The technical task of the present invention is such an organization of the production technology of the billet billet, in which the carbon contained in it is spent on the reduction of iron oxides of the pellets of the billet in the process of cooling the billet on a filling machine to 700-750 ^o C, further heating to 950-1100 ^o C and exposure at these temperatures. Such an organization of the production of a charge billet will make it possible to have a high degree of metallization of iron pellets in the billet and the required carbon content in the steelmaking bath for melting the metal charge. This, in turn, will make it possible to increase the charge of a billet stock in a steel mill up to 100% (depending on the steel grade smelted) and to have a predetermined carbon content in the metal bath by melting the metal charge by spending it on reducing iron oxides.

The technical result is achieved by a method of producing a charge billet for steelmaking on a casting iron casting machine, including introducing a solid oxidizing agent (oxidized iron ore pellets) and liquid iron-carbon alloy (cast iron) into the casting machine’s molds, mixing, holding, free cooling, and removing the ingot stocks from the molds with a temperature of 700-750 ^o C, characterized in that the ingot billet billets are then additionally heated to 950-1100 ^o C outside the steelmaking furnace and maintained at these temperatures for 0.3-6.0 hours

Until now, the ingots were cooled in the last 2/3 of the length of the filling machine by spraying water to a temperature of about 180-200 ^o C. If you do not do this, that is, do not water the ingots of the workpiece with water, but cool them in air, then that the heat capacity of the air is more than four times less than the heat capacity of the water, the temperature of the ingots when leaving the casting machine, which is established experimentally, will be about 700-750 ^o C. With this temperature, the ingot stocks are fed into a thermos furnace, where they are loaded before in the steelmaking furnace l heated to 950 ^o C and maintained at this temperature from 0.3 to 4.5 hours. The exposure time of the workpiece at the specified temperature depends on the required degree of metallization of iron oxides of the pellets of the workpiece and the residual carbon in it after exposure. With a shutter speed of less than 0.3 hours, studies have shown that the process of reducing iron oxides due to solid carbon preforms does not have time to develop to a significant degree and does not have practical value.

Exposure at a temperature of 950 ^o C for more than 4.5 hours also does not lead to a noticeable increase in the degree of reduction of iron oxides of the workpiece, since the process after exposure for 3.0-3.5 hours is already limited by the amount of thermal energy supplied to the reaction zone, and not aging time. To increase the rate of reduction of iron oxides, an additional supply of thermal energy to the reaction zone is required to a greater extent than increasing the exposure time.

After holding for a specified time at 950 ^o C, the ingots of the charge stock (if it is necessary to have a very low carbon content in the metal after melting) are heated to 1100 ^o C and held at this temperature for 0.2 to 1.5 hours. preforms at 1100 ^o C less than 0.2 h also gives nothing in terms of a marked increase in the degree of reduction of iron oxides.

During the exposure of the workpiece for 1.0-1.5 hours at a temperature of 1100 ^o C, the recovery process manages to complete as much as the carbon content in the workpiece allows. As experiments have shown, for 1.0-1.5 hours at the indicated temperature, the carbon of the billet remaining after soaking at 950 ^o C has almost completely consumed and the reduction of the iron oxides of the billet practically ceases. Moreover, the exposure of ingots at the indicated temperatures is carried out in a slightly oxidizing or, in extreme cases, in a neutral atmosphere. Creating a reducing atmosphere in the furnace, where the workpiece is held at a given temperature, will significantly increase the cost of the workpiece, as well as reduce the carbon burn rate in it. Therefore, the billet is aged in a slightly oxidizing or (in the smelting of high-carbon steel grades) in a neutral atmosphere. In this case, the carbon burn-out of the billet occurs almost exclusively due to the oxygen of the iron oxides of the billet and is determined by the temperature conditions and the exposure time, and only a small fraction of the carbon will react with the oxidizing agents in the furnace atmosphere. The furnace atmosphere is created by burning combustible gas (natural, coke oven, blast furnace gas or a mixture thereof), solid or liquid fuels with an excess air coefficient of 1.10-1.25.

An example of a specific implementation. Calcined oxidized iron ore pellets with ambient temperature are loaded into mold molds of a casting machine with a fill volume factor of 97 = 99% and filled with molten cast iron from an iron ladle with a temperature of 1300-1350 ^o C. In this case, cast iron fills the voids between the pellets and fastens them when solidifying into a single mass, having the form of mold molds. During continuous movement of the mold mold conveyor to the discharge end at a speed of 9-14 m / min, the ingot stock ingots are cooled in the room atmosphere through the mold mold walls and due to the contact of the open surface of the ingots with the environment.

Obtaining ingots of a charge stock with a temperature of 700-750 ^o C is dumped from the machine into a thermos furnace, where they are heated to 950 ^o C and kept at this temperature for 0.3 to 4.5 hours, then, if necessary, in the bath low carbon content ingots are heated to 950-1100 ^o C and incubated for 0.2 to 1.5 hours and then loaded at this temperature in a steel furnace.

The change in carbon content by melting a metal charge containing 40% of the charge stock, depending on the exposure time of the workpiece at 950 and 1100 ^o C shown in the table.

It is known that 3/4 of the energy [RZH, 1993, 1B286] spent on steel smelting is spent on heating the melt to the temperature of casting the metal into ingots and on technological operations (oxidation of impurities, removal of phosphorus and sulfur, alloying, etc.). Moreover, the energy consumed for steelmaking is of high quality (electricity). For example, for heating 1 ton of a billet to 1000 ^o C, it is necessary to spend (with 100% assimilation of thermal energy) 175000 kcal or 203 kW • h.

According to the invention, the preform is heated to 700-750 ^o C due to the heat of molten iron, which is usually irretrievably lost when casting it into ingots. Moreover, in order to cool pig iron pigs to ambient temperature, water and electricity are expended for its supply and spraying.

The preform is heated from 700-750 ^o C to 950-1100 ^o C by burning low-quality fuels, for example, coal near Moscow, blast furnace gas or a mixture of coke oven and blast furnace gas, which are waste products of metallurgical production. When loading a hot billet with a temperature of 950-1100 ^o C into the steelmaking unit, the energy savings when working at 100% of the billet in the charge will be at least 200 kW • h. per ton of steel.

Claims (5)

1. A method of producing a billet stock, comprising introducing a solid iron-containing oxidizing agent and a liquid iron-carbon alloy into the molds of a casting machine, mixing, holding, cooling, removing pigs from the molds, heating the pigs to a certain temperature and holding them at this temperature for at least 0, 3 hours, characterized in that the ingots are removed from the molds at a temperature of 700 - 750 ^o C, heated to 950 - 1100 ^o C and kept at this temperature for 0.3 to 6.0 hours 2. The method according to claim 1, characterized in that after reaching a temperature of 700 - 750 ^o C, the heating and soaking of the ingot is carried out stepwise to obtain the carbon content in it, ensuring its required content in the steelmaking bath by melting the metal charge, while at the first stage it heated from 700 - 750 ^o C to 950 ^o C and incubated for 0.3 to 4.5 hours, and in the second stage they are heated from 950 to 1100 ^o C and maintained at this temperature for 0.2 - 1.5 h 3. The method according to claim 1, characterized in that when heated to 950 - 1100 ^o C ingots are kept in an atmosphere of slightly oxidizing or neutral gas.  4. The method according to any one of claims 1 to 3, characterized in that the heating and aging of ingots is carried out in a thermos furnace.  5. The method according to claim 1, characterized in that the ingots are cooled by the method of contacting it with the surface of the mold.

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