RU2258083C1 - Method of making rail steel - Google Patents

Abstract

FIELD: ferrous metallurgy; making rail steel.

SUBSTANCE: proposed method includes charging scrap and lime into electric steel-making furnace. After melting of scrap liquid cast iron is poured from above at power requirement of 180-300 kW·h/t and temperature of 1280-1400°C in the amount of 30-60% of mass of charge containing the following components, mass-%:C, 2.0-3.5; Si lesser than 0.01;P, lesser than 0.015 and S, lesser than 0.025. Carbon is oxidized by gaseous oxygen at temperature in furnace not higher than 1700°C. At tapping the steel, furnace slag is separated and molten metal in the amount of 10-15% of total mass is left in furnace. Slag-forming mixture containing lime and fluorspar at ratio of (0.8-1.2) : (0.2-0.5) at flow rate of steel of 10-17 kg/t is fed to ladle during tapping.

EFFECT: reduced melting time; reduced power requirements; enhanced assimilation of alloys and ferroalloys; reduced level of contamination of steel by non-metallic inclusions.

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Description

The invention relates to ferrous metallurgy, in particular to methods for smelting rail steel in electric furnaces.

A known method of smelting rail steel selected as a prototype is known, including filling scrap metal, cast iron and lime in an electric arc furnace, melting a metal charge, oxidizing carbon with gaseous oxygen, dephosphorizing by adding iron ore and lime, downloading oxidative slag through a working window threshold, deoxidizing steel and steel in the furnace, the subsequent release of steel under the furnace slag into the ladle, the additive in the ladle during the production of the mixture consisting of lime, fluorspar, silicocalcium and ferrovanadium, characterized by the fact that iron ore is additionally planted in the amount of 4-5% of the weight of the filling, lime is fed in the amount of 4-8% of the weight of the filling, the iron is planted in the form of molten iron, which is poured from above into the furnace after scrap metal is melted at a power consumption 220-320 kWh / t of scrap metal in an amount of 30-35% of the weight of the filling at a speed of 6-12 t / min, while gaseous oxygen is supplied at a rate of 15-30 nm ³ / t of steel, and the temperature in the furnace during carbon oxidation maintain no more than 1680 ° C, iron ore and lime for dephosphorization at planted with a flow rate of 70-120 kg / t of steel in the ratio, respectively (1-2) :( 2.5-3.5) followed by the discharge of oxidizing slag, and the flow rate of the mixture that is seated in the ladle during steel production is maintained within 18-27 kg / t of steel with a ratio of lime, fluorspar, silicocalcium and ferrovanadium (1-1.50) in it: (0.30-0.40) :( 0.50-0.65) :( 0.07-0 , 15) respectively [1].

Significant disadvantages of this method of smelting rail steel are:

- a significant duration of smelting due to the need to oxidize significant concentrations of silicon and phosphorus and the formation of slag to ensure high-quality dephosphorization of steel,

- high energy consumption and electrodes due to the increased melting time associated with a significant time for the recovery period in the furnace (deoxidation of metal and slag), as well as a decrease in the amount and time for the formation of furnace slag of the required chemical composition and fluidity for dephosphorization in furnaces and desulfurization in the release of metal from the furnace into the bucket,

- high "waste" of ferroalloys due to the increased oxidation of furnace slag and the addition of a significant amount of ferroalloys to the furnace,

- increased level of steel contamination by non-metallic inclusions due to high oxygen concentrations in steel and slag.

The desired technical results of the invention are: reducing the duration of the smelting, reducing the consumption of electrodes and electricity, increasing the absorption of alloying and ferroalloys, reducing the level of contamination of steel with non-metallic inclusions.

To this end, a method for smelting rail steel is proposed, including filling scrap metal and lime in an electric arc furnace, melting scrap metal, pouring molten iron, oxidizing carbon with gaseous oxygen, dephosphorizing by adding iron ore and lime, downloading oxidative slag through the threshold of the working window, and then releasing steel into ladle and additive in the ladle during the production of a slag-forming mixture consisting of lime and fluorspar, and pour cast iron in the amount of 30-60% by weight of the filling, with the content in it, wt.%: carbon 2.0-3.5, less than 0.01 silicon, less than 0.015 phosphorus, less than 0.025 sulfur, and cast iron is poured at a temperature of 1280-1400 ° C from above into the furnace after melting scrap metal at a power consumption 180-300 kW · h / t of scrap metal, the temperature in the furnace during carbon oxidation is maintained no more than 1700 ° С, steel is released into the ladle with furnace slag cut-off leaving 10-15% of the total mass of liquid metal in the furnace, fed to the ladle during steel production slag-forming mixture with a ratio of lime and fluorspar (0.8-1.2): (0.2-0.5) with a flow rate of 10-17 kg / t of steel.

The claimed limits are selected experimentally. The amount of liquid cast iron in the amount of 30-60% by weight of the filling is selected on the basis of obtaining the necessary carbon concentration in the steel; when using liquid cast iron less than 30% of the filling weight, the carbon concentration during melting will not allow enhanced degassing of the steel and removal of non-metallic inclusions, and the use of liquid cast iron in an amount of more than 60% by weight of the filling leads to an increased carbon concentration during melting and an increase in the duration of smelting due to the need to oxidize the "excess" carbon ali.

The concentration of carbon in liquid cast iron was chosen on the basis that, with a carbon content of less than 2.0%, due to slight overheating above the liquidus temperature and a short crystallization time, liquid iron can not be transported over long distances, and with an increase in carbon content of more than 3.5% melting time increases during the oxidation of "excess" concentration.

With an increase in silicon content of more than 0.01%, a significant amount of lime is necessary to neutralize SiO ₂ formed during oxidation, and therefore significant heat losses are observed and the consumption of electricity and electrodes increases.

Exceeding the declared concentrations of phosphorus and sulfur in the intermediate result in the need for intensive processes for dephosphorization and desulfurization of steel, which in turn leads to an increase in the duration of smelting and the associated consumption of electricity and electrodes.

Pouring at a temperature of 1280-1400 ° C provides the smallest speleobrazovanie (allocation of scaly graphite) and reduce the likelihood of a short circuit in electric furnaces. When the temperature drops below 1280 ° C, the intermediate crystallizes, and when the temperature rises above 1400 ° C, high overheating of the liquidus temperature leads to increased wear of the ladle lining and the likelihood of metal "leaving" the bucket.

Pouring liquid cast iron at an energy consumption of less than 180 kW · h / t leads to an increase in the duration of smelting and an increase in the total energy consumption for smelting due to the formation of a cast iron-steel conglomerate. Moreover, when the latter is melted, the water-cooled parts of the roof and panels are exposed to intense radiation, as well as the destruction of the refractory parts of the furnace, which leads to an increase in the overall level of contamination of steel with non-metallic inclusions. In the case of pouring molten iron at a flow rate of more than 300 kWh / t of scrap metal, the steel overheats and reoxidizes due to the intensive introduction of gaseous oxygen into the furnace, in connection with which conditions of unpredictable oxidation of carbon may arise with the subsequent release of slag and metal from the furnace. In this case, the carbon concentration in the furnace allows to reduce the claimed limits to 180-300 kW · h / t in comparison with the prototype 220-320 kW · h / t.

When the temperature in the furnace exceeds 1700 ° C during the oxidation of carbon, intensive lining erosion and steel contamination by non-metallic inclusions occur. The release of steel with a cutoff of furnace slag reduces the likelihood of steel contamination with non-metallic inclusions of exogenous type, while leaving 10-15% of the total mass of liquid metal in the furnace ensures a good cut-off. Exceeding the residue in the furnace by more than 15% reduces the technical and economic indicators of smelting, and reducing the residue by less than 10% does not provide a guaranteed cut-off of furnace slag.

The additive in the furnace of a slag-forming mixture consisting of lime and fluorspar in the ratio (0.8-1, 2): (0.2-0.5) and a flow rate of 10-17 kg / t of steel provides good desulfurization of steel and high refining ability from non-metallic inclusions.

The inventive method of smelting rail steel was implemented in the smelting of steel in electric arc furnace type DSP 100I7. The parameters and indicators of 12 experimental heats are given in Tables 1 and 2. Preparation of molten iron for smelting was carried out in 420 t open-hearth furnaces. In cast-iron ladles, delivery was made to the electric steel-smelting shop, where the E76F rail steel was smelted. The filling consisted of 40-70 tons of scrap metal and slag-forming materials. Liquid cast iron was poured from an iron ladle by means of a bridge crane with an open arch of the furnace after the melting of “wells” and partial precipitation of scrap metal in the furnace at an electric power consumption of 160-320 kWh / t. Immediately after casting the pig iron, slag was charged through the threshold of the furnace working window. Carbon oxidation was carried out by purging the steel in the furnace with gaseous oxygen through a water-cooled vault lance. For better dephosphorization, portions of iron ore and fluorspar were seated in the furnace. During the oxidation of carbon, the temperature in the furnace did not exceed 1700 ° С, and the temperature of the filled in intermediate varied in the range of 1280-1400 ° С. When the desired carbon, phosphorus and temperature contents were reached, melting was performed with cut-off of furnace slag. To completely misfire the furnace slag and reduce the likelihood of steel contamination by non-metallic inclusions, 10-15 tons of steel were left in the furnace.

When producing steel for better desulfurization, lime and fluorspar were planted in the bucket in the amount of 800-1200 and 200-500 kg, respectively, and with a flow rate of 10-17 kg / t of steel. The required ferroalloys were seated in the bucket upon release, which reduced the loss of ferroalloys.

When steel is smelted according to the claimed method, the melting time is reduced from 1 h 40 min to 1 h 10 min -1 h 30 min, electricity from 400-420 kW · h / t to 380-400 kW · h / t, electrodes from 3.9 kg / t to 3.5-3.6 kg / t, steel pollution by non-metallic inclusions is reduced (the index of total pollution by non-metallic inclusions is reduced by 0.2), carbon fumes of ferroalloys are reduced (manganese-containing by 5%, silicon-containing by 10-15%) .

Sources of information

1. RF patent No. 2197536, cl. C 21 C 5/52, 7/06.

Table 1
Parameters of experimental swimming trunks No. of swimming trunks steel grade The amount of intermediate, t Intermediate pouring temperature, ° С Power consumption before pouring the intermediate product, kW · h / t The temperature in the furnace during carbon oxidation, ° C Slag-forming mixture (lime and fluorspar) consumption, kg / t steel Ratio 1 E76F thirty 1280 160 1655 10 0.8-0.2 2 E76F 40 1300 180 1655 thirteen 0.8-0.5 3 E76F 40 1300 180 1680 12 0.8-0.4 4 E76F 40 1350 250 1690 14 0.9-0.5 5 E76F 45 1380 280 1670 thirteen 0.9-0.4 6 E76F 45 1360 300 1685 12 0.9-0.3 7 E76F fifty 1310 210 1700 12 1.0-0.2 8 E76F fifty 1320 270 1690 fifteen 1.0-0.5 nine E76F 55 1380 220 1690 16 1.1-0.5 10 E76F 60 1400 240 1670 14 1.2-0.2 eleven E76F 60 1290 300 1660 fifteen 1.2-0.3 12 E76F 65 1410 320 1700 17 1.2-0.5 prototype 30-35 not negotiated 220-320 1680 ° C - (1-1.5) :( 0.3-0.4)

table 2
Technological indicators No. of swimming trunks steel grade The degree of dephosphorization,% The degree of desulfurization,% Pollution index, point Total energy consumption, kW · h / t The total consumption of electrodes, kg / t The duration of the heat, h-mi 1 E76F 41 74 0.76 400 3.57 1-20 2 E76F 45 70 0.78 395 3,50 1-10 3 E76F 42 75 0.79 380 3,58 1-10 4 E76F 44 76 0.80 380 3,54 1-10 5 E76F 44 76 0.76 385 3,59 1-10 6 E76F 40 75 0.78 390 3.60 1-20 7 E76F 40 75 0.74 390 3,58 1-20 8 E76F 40 76 0.70 385 3,59 1-20 nine E76F 41 74 0.71 390 3,59 1-20 10 E76F 46 74 0.73 380 3.60 1-15 eleven E76F 44 73 0.75 385 3,54 1-20 12 E76F 45 75 0.81 380 3,55 1-30 prototype 30-40 70-74 0.8-1.0 400-420 3.9-4.5 1-20-1-40

Claims (1)

A method of smelting rail steel, including filling scrap metal and lime in an electric arc furnace, melting scrap metal, pouring molten iron, oxidizing carbon with gaseous oxygen, dephosphorizing by adding iron ore and lime, downloading oxidative slag through the threshold of the working window, and then releasing steel into the ladle and additive into the ladle during the production of a slag-forming mixture consisting of lime and fluorspar, characterized in that liquid cast iron is poured in an amount of 30-60% by weight of the filling with soda neighbors in it, wt.%: carbon 2.0 - 3.5, less than 0.01 silicon, less than 0.015 phosphorus, less than 0.025 sulfur, and cast iron is poured at a temperature of 1280 - 1400 ° C from above into the furnace after scrap metal is melted at an electric power consumption 180 - 300 kW · h / t of scrap metal, the temperature in the furnace during carbon oxidation is maintained no more than 1700 ° С, steel is released into the ladle with furnace slag cut-off with the remaining 10-15% of the total mass of liquid metal in the furnace, fed to the ladle during steel production slag-forming mixture with a ratio of lime and fluorspar in it (0.8 - 1.2): (0.2 - 0.5) with a flow rate of 10 - 17 kg / t of steel.