RU2299247C1 - Steel melting method in oxygen converter - Google Patents

Abstract

FIELD: ferrous metallurgy, namely processes for melting steel in oxygen converters.

SUBSTANCE: method comprises steps of loading to bath metallic scrap; pouring cast iron; blowing with oxygen; adding lime and slag forming material. After 85 -90% of oxygen is consumed for blowing, lime is added. Lime consumption is determined according to expression Q_cao = 0.0011 - Q_oxyg + 850,46 x N_blp - 1557,56 x N_cc - 17,97 where Q_oxyg - quantity of oxygen consumed before lime adding, m³/min; N_blp - nitrogen content in sample taken by means of apparatus for measuring parameters of melting during blowing process, %; N_cc - nitrogen content in sample taken according to converter charge,%; 0.0011, 850.46, 1557,56 and 17.97 - empiric coefficients.

EFFECT: enhanced strength of oxygen converter, possibility for providing desired content of nitrogen in metal.

1 ex

Description

The invention relates to ferrous metallurgy, in particular to methods for smelting steel in oxygen converters.

A known method of steel smelting in a converter, including filling scrap metal into a converter, casting iron, blowing metal with oxygen, an additive of lime and slag-forming material containing oxides of calcium, magnesium and iron. As a slag-forming material, a ferruginous lime-magnesia flux in the amount of 5-40 kg / t of suitable steel, made by sintering finely ground materials containing calcium, magnesium and iron oxides, is added to the converter, while 10-80% of the flux is added to the converter before filling oxygen supply, and the remaining amount of flux is introduced up to the 8th minute of the duration of the metal purge. The flux introduced into the converter contains, wt.%: Calcium oxide 45-60; magnesium oxide 26-35 and iron oxide 5-15 (see the description of the patent of the Russian Federation No. 2164952, IPC 7 C21C 5/28).

The disadvantages of this method include an increase in the saturation of the metal with nitrogen in the process of purging the metal, due to the deterioration of slag formation associated with an increase in the viscosity of the converter slag.

The closest analogue of the claimed invention is a method of steelmaking in an oxygen converter, including filling metal scrap in a bath, cast iron casting, oxygen blowing, lime additive, calcined dolomite and iron-calcined magnesia flux. Calcined dolomite and ferruginous lime-magnesia flux are added to the bath at a ratio of 0.1-9.0, while the total amount of introduced dolomite and flux is 10-45 kg / t of steel. Calcined dolomite is introduced into the bath during filling the charge and along the purge process until intensive decarburization begins, while the iron-calcined lime-magnesia flux is introduced at the same time, and also 1-3 minutes before the end of metal purging in the amount of 2.0-10.0 kg / t of steel. The content of magnesium oxides in the calcined dolomite and in the iron-lime-magnesia flux is the same value equal to 25-35% (see the description of the patent of the Russian Federation No. 2196181, IPC 7 C21C 5/28).

Signs of the closest analogue that coincide with the essential features of the claimed invention: metal scrap filling, cast iron casting, oxygen blowing and additive of lime and slag-forming material containing calcium, magnesium and iron oxides.

The known method does not provide the desired technical result for the following reasons.

Found in the known method, the technological method of using calcined dolomite and iron-lime-magnesia flux leads to the need to use additional consumables for their separate storage.

At the same time, the addition of a ferruginous lime-magnesia flux 1-3 minutes before the end of the purge without taking into account the nitrogen content in the metal leads to an overspending of the material, obtaining an MgO content higher than necessary, thickening the slag, reduces its refining ability, and makes it difficult to remove nitrogen from the metal.

In addition, the manufacture of ferruginous lime-magnesia flux requires the use of additional expensive equipment for wet grinding of flux components and firing it in an oxidizing atmosphere in rotary kilns.

The basis of the invention is the task of improving the method of steelmaking in a converter, in which at the minimum cost of slag-forming materials and increasing the resistance of the converter, the required nitrogen content in the finished steel is obtained.

The problem is solved in that in the method of steel smelting in a converter, which includes filling scrap metal in a bath, cast iron casting, oxygen blowing, lime and slag-forming material containing calcium, magnesium and iron oxides, the amount of oxygen consumed for blowing is determined before lime addition and the nitrogen content in the metal and after the consumption of 85-90% of oxygen is added lime with a flow rate determined from the expression

Q _Cao = 0.0011 × Q _acid + 850.46 × N _mzpp -1557.56 × N _pov -17.97,

where Q _Cao - lime consumption, t;

Q _acid - the amount of oxygen consumed, m ³ / min;

N _mzpp - nitrogen content before lime additive,%;

N _pov - the required nitrogen content in the metal,%;

0.0011; 850.46; 1557.56 and 17.97 are empirical coefficients.

The essence of the proposed technical solution consists in the addition of lime after spending 85-90% of oxygen on the purge, depending on the nitrogen content in the sample, selected by the machine for measuring the melting parameters along the purge before the lime additive. Additive of lime leads to an increase in the specific surface at the boundary of the metal - bubble WITH, improves metal deazotization.

Calculation of lime consumption depending on the nitrogen content allows to reduce the total consumption of slag-forming materials, slag viscosity, increase the resistance of the oxygen converter and obtain the required nitrogen content in the metal.

This method is illustrated by the following example.

65 tons of scrap metal, 35 tons of pig iron were poured for smelting and 319 tons of liquid iron of the following chemical composition were poured: 0.73% silicon, 0.16% manganese, 0.005% sulfur and 0.056% phosphorus. The temperature of cast iron was 1374 ° C. 4.1 tons of freshly burnt lime were delivered to the filling. At 16:33, the purge of the metal began. The purge intensity before the intermediate slag download was 1100 m ³ / min of oxygen. According to the consumption of 7463 m ^{3 of} oxygen at 16:40, an intermediate slag download was carried out lasting 4 minutes. At the beginning of the intermediate download, 1.6 tons of lime were planted in the converter bath.

After the end of the slag download at 16:44, the metal purge was continued with an intensity of 1098 m ³ / min. To direct the slag into the converter, 25 tons of lime (in portions of 2-4 tons) and 350 kg of aluminum flux were added during purging.

At 16:58, after consuming 19887 m ^{3 of} oxygen, the temperature of the bath was measured by a smelting measurement machine (MZPP) and a metal sample was taken. The temperature of the bath was 1615 ° C.

After obtaining the results of the nitrogen content in the metal sample (0.0051%), lime was given to the converter based on the expression:

Q _Cao = 0.0011 × 19887 + 850.46 × 0.0051-1557.56 × 0.0033-17.97 = 4.1 t

At 5:02 p.m. the purge is completed.

The total oxygen consumption for purging was 24602 m ³ , 34.8 tons of lime, 0.35 tons of aluminum flux.

After purging, the converter is pushed. The temperature of the bath on the dump was 1726 ° C.

At 17:08 the beginning of the production of swimming trunks. At the time of release, 0.7 tons of FMN70 were delivered to the steel pouring ladle; 1.2 tons of lime; 55 kg of pig aluminum and 60 kg of MGR. At 17:16, the release of the heat was over. The duration of the release was 7 minutes 34 seconds. The chemical composition of the metal obtained after the release of the heat is presented below,%:

C Mn S P Cr Ni Cu N Kosheva 0,041 0.11 0.009 0.005 0.01 0.01 0.02 0.0033

After sampling, the ladle with melting was transferred for further processing to the finishing units.

Claims (1)

A method of steelmaking in a converter, including filling scrap metal in a bath, cast iron casting, oxygen blowing, lime and slag-forming material additives containing calcium, magnesium and iron oxides, characterized in that before the lime additive the amount of oxygen consumed and the nitrogen content in metal and after the consumption of 85-90% oxygen, lime is added with a flow rate determined from the ratio Q _cao = 0.0011 · Q _acid. + 850.46 · N _mzpp -1557.56 · N _pov -17.97, where Q _cao - lime consumption, t; Q _acid - the amount of oxygen consumed, m ³ / min; N _mzpp - nitrogen content before lime additive,%; N _pov - the required nitrogen content in the metal,%; 0.0011; 850.46; 1557.56 and 17.97 are empirical coefficients.