RU2365631C1 - Method of refining of steel in ladle-furnace - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to ferrous metallurgy, namely to methods of secondary treatment of the rail steel in the ladle-furnace. The method involves electric heating of steel, gas blowing of the liquid steel through the porous bottom lances and steel treatment with slag. The electric heating of steel is performed with the rate of 0.07°C/min minimum under slag with basicity of 2.1-3.4 and initial content of ferric oxide 3% maximum, gas blowing of the liquid steel through the porous bottom lances is performed with both nitrogen and argon, and in the beginning nitrogen is blown with the flow rate of 0.08-0.25 m³/t of liquid steel and 5-40 m³/hr until the total amount of the nitrogen blown into the steel reaches 0.20 m³/t of liquid steel in which case agron blowing starts with the rate of 3-30 m³/hr.

EFFECT: reduced cost price of the manufactured steel, improved physical-mechanical properties of the steel, no nitrated ferroalloys are spent.

Description

The invention relates to ferrous metallurgy, in particular to methods for out-of-furnace treatment of rail steel on ladle furnace units.

A known method of refining rail steel in a ladle furnace, selected as a prototype, includes arc heating of metal, purging of the melt with argon and metal processing with slag, in which the arc heating of metal is carried out with an intensity of at least 40 kWh / t of liquid steel, metal is purged with argon through porous bottom tuyeres with a flow rate of 15-30 m ³ / t of molten steel for at least 40 minutes, while providing an FeO content in the slag of not more than 0.5% by slag oxidation by coke powder and crushed ferrosilicon with a flow rate of 0.5-1 each 5 kg / t liquid oh steel and steel deoxidation is conducted further based silicocalcium administration 250-300 g calcium per ton of molten steel, wherein silicocalcium sits in two equal portions after deoxidation of the slag and steel for 5-10 minutes to end of the processing [1].

Significant disadvantages of this method are:

- the high cost of smelted steel due to the use of argon as an inert gas;

- reduced level of physical and mechanical properties associated with a low level of nitrogen in steel and, accordingly, the possibility of the formation of vanadium carbonitrides, grinding steel grain and increasing the toughness and tensile strength of steel.

There is also known a method of producing rail steel, including smelting steel in the furnace, its release into the ladle, deoxidation and subsequent purging in the ladle with gaseous nitrogen through a slotted bottom refractory lance having a slit thickness of up to 0.1 mm for 15-30 minutes with a flow rate of 40- 65 nm ³ / h, at a pressure of (6-8) · 10 ⁵ Pa and a total nitrogen flow rate of 0.10-0.30 nm ³ / t of liquid steel [2].

Significant disadvantages of this method are

- low degree of assimilation of nitrogen during purging;

- unstable assimilation of nitrogen;

- the impossibility of a long nitrogen treatment due to significant heat losses and the lack of a source of additional heating of liquid steel during purging.

There are also known methods of increasing the toughness due to microalloying of rail steel with nitrogen, which lead to an increase in the number of carbonitrides and grain refinement, and due to the additional isolation of the nitride phase, to disperse hardening. Usually, nitrided vanadium-containing ferroalloys are used for this [3].

Significant disadvantages of these methods are:

- the high cost of nitrided ferroalloys;

- increase in smelting time due to the need to dissolve ferroalloys and, accordingly, increase the cost of smelted steel.

The desired technical results of the invention are to reduce the cost of smelting steel, increase the physico-mechanical properties of steel, reduce the consumption of nitrided ferroalloys.

To this end, a method is proposed for refining rail steel in a ladle furnace, including arc heating of metal, blowing the melt with inert gas through porous bottom tuyeres and treating the metal with slag, characterized in that the arc heating of metal is carried out with an intensity of at least 0.07 ° C / min under slag with a basicity of 2.1-3.4 and an initial FeO content of less than 3%, the metal is blown through porous bottom tuyeres in combination with nitrogen and argon, and in the initial period, nitrogen is purged with a flow rate of 0.08-0.25 m ³ / t liquid steel and intensive awn 5-40 m ³ / h, and when the total amount of injected nitrogen 0,20 m ³ / ton of molten steel is performed with argon purge intensity

3-30 m ³ / h.

The declared limits are selected experimentally.

The intensity of the arc heating is selected taking into account the fact that when the heating intensity is less than 0.07 ° C / min, the effect of arc heating on the saturation of the metal with nitrogen is negligible.

A nitrogen purge with a flow rate of 0.08-0.25 m ³ per tonne of molten steel provides a nitrogen content in the metal in the range of 0.008-0.020%. Moreover, with a decrease in flow rate of less than 0.08 m ³ / t, the processing time increases and, accordingly, costs increase, and with an increase in flow rate of more than 0.25 m ³ / t, nitrogen absorption by steel decreases during purging and heat losses increase.

A metal purge with nitrogen at a flow rate of 5-40 m ³ / h allows the metal to be homogenized by temperature and chemical composition. At a nitrogen flow rate of less than 5 m ³ / h, poor mixing was observed and, as a result, an uneven distribution of temperature and chemical composition over the height of the bucket, as well as incomplete removal of non-metallic inclusions. At a nitrogen flow rate of more than 40 m ³ / h, nitrogen absorption by steel decreases, and metal mirrors are exposed, followed by oxygen and hydrogen saturation of the steel, as well as the creation of conditions for increasing the content of non-metallic inclusions in steel.

The total consumption of nitrogen used to purge the metal was chosen based on the fact that when the gas flow rate is more than 20 m ³ for melting, it is possible to get a macrostructure defect under the spotted segregation defect, as well as a gas bubble.

Subsequent purging with argon with a flow rate of 3-30 m ³ / h allows the metal to be averaged over the chemical composition and temperature without reducing the nitrogen content in the steel. At a flow rate of less than 3 m ³ / h, the required mixing of the steel in the ladle is not ensured, which ensures uniform distribution of temperature and chemical composition along the height of the bucket, and with an increase in flow rate of more than 30 m ³ / h, the nitrogen concentration in the steel decreases.

The claimed method of refining rail steel in a ladle furnace was implemented in the smelting of rail steel grades NE76F and E76F. After melting and carrying out the oxidation period in an electric arc furnace, the smelting was produced with cut-off of furnace slag into a ladle. The steel refinement was carried out on a ladle furnace unit with a transformer of 16 MBA. Processing was carried out as follows. Arc metal heating was carried out with an intensity of 0.07 ° C / min, nitrogen was blown through porous bottom tuyeres with a flow rate of 0.08-0.25 m ³ / t of liquid steel with a total flow rate of up to 20 m ³ for melting, upon reaching which further processing was carried out with argon with an intensity of 3-30 m ³ / h.

The inventive method allows to reduce the cost of smelting steel by 45 rubles / t, to eliminate the consumption of nitrided ferroalloys, to increase the physical and mechanical properties of steel: yield strength by 5 N / mm ² , tensile strength by 4 N / mm ² , elongation and narrowing by 1 , 0%, impact strength of 5 J / cm ² .

Information sources

1. RF patent 2312902, cl. C21C 7/06.

2. RF patent 2161205, cl. C21C 7/100, 7/072.

3. V.V. Polyakov, A.V. Velikanov. The basics of rail technology. - M.: Metallurgy, 1990 .-- 416 p.

Claims (1)

The method of refining rail steel in a ladle furnace, including arc heating of metal, blowing the melt with gas through porous bottom tuyeres and treating metal with slag, characterized in that the arc heating of metal is carried out with an intensity of at least 0.07 ° C / min under slag with a basicity of 2 , 1-3,4 and an initial content of iron oxide of less than 3%, the metal is blown through porous bottom tuyeres in combination with nitrogen and argon, and in the initial period, nitrogen is purged with a flow rate of 0.08-0.25 m ³ / t of liquid steel and intensity of 5-40 m ³ / h and with d stizhenii total amount of injected nitrogen 0,20 m ³ / ton of molten steel is performed with argon purging with an intensity of 3-30 m ³ / h.