RU2327745C2 - Method of rail steel production - Google Patents

Abstract

FIELD: metallurgy; production of rail steel.

SUBSTANCE: method includes steel smelting in an electric furnace without deacidification of metal and slag, then tapping of metal into a ladle with cutting off furnace slag. Metal is blasted in the ladle with nitrogen and argon. During tapping and blasting slag forming mixture and ferroalloys containing silicon and manganese are being added. Then steel micro alloying is performed with vanadium on a unit "furnace-ladle". Further steel is modified with ferroalloy, containing silicon, calcium and barium, where ratio of barium to calcium is 1.0-1.5, and their quantity in the ferroalloy contents is 150-300g/t of steel. Blasting of steel with argon is performed on the unit "furnace-ladle".

EFFECT: upgrading of malleable characteristics of rail steel.

2 cl, 1 tbl

Description

The invention relates to ferrous metallurgy, and in particular to a technology for the production of steel intended for the manufacture of rails.

It is known that the operational stability of railway rails depends on the physicomechanical properties of the metal and the nature of the contamination of their non-metallic inclusions.

A known method of deoxidation and modification of rail steel by ferrosilicon [1]. This method allows to obtain non-metallic inclusions of silicates of complex composition in rails, which are less harmful during their operation than lines of alumina during deoxidation of steel with aluminum. The disadvantage of this method is that its use leads to a decrease in the toughness of rails, which increases their tendency to brittle fracture, especially at low temperatures.

It is known that the microalloying of rail steel by vanadium to 0.15% with a content of 0.01-0.02% nitrogen in it leads to an increase in impact strength even at -60 ° C [2], however, the plastic properties of the metal are reduced.

The closest in technical essence and the achieved result to the claimed method is a method for the production of rail steel, including steel smelting in an electric furnace without metal and slag deoxidation, metal release into a ladle with furnace slag cut-off, nitrogen purging in the ladle with nitrogen and argon, an additive during production and blowing slag-forming mixture and ferroalloys containing silicon and manganese, and microalloying steel on a ladle furnace with vanadium [3]. The disadvantage of this method is that the melted steel has an insufficient level of ductility, which leads to the premature formation of contact-fatigue defects during the long-term operation of the rails.

The task is to create a method for the production of rail steel, providing an increase in the plastic properties of the rails while maintaining the required strength.

The problem is achieved in that in the proposed method for the production of rail steel, including steel smelting in an electric furnace without metal and slag deoxidation, metal discharge into a ladle with furnace slag cut-off, metal purging in a ladle with nitrogen and argon, an additive during the production and purging of a slag-forming mixture and ferroalloys containing silicon and manganese, and microalloying steel at the ladle furnace with vanadium, after microalloying steel at the ladle furnace with vanadium, it is modified with a ferroalloy containing silicon, cal tions, barium, wherein the ratio of barium to calcium is 1.0-1.5, and their amount in the composition of the ferroalloy - 150-300 g / t of steel. To ensure the necessary nitrogen content in the steel when it is purged with argon at the ladle furnace, vanadium is introduced in the form of nitrided ferrovanadium.

The essence of the proposed method is that the increase in the level of ductility of rails, in particular the values of elongation, relative narrowing and impact strength, is achieved by the simultaneous introduction of barium and calcium into the steel after microalloying it with vanadium. Under such conditions, a high effect of steel modification is ensured due to a change in the microstructure of the melt and its approximation to the equilibrium state. It is this sequence of introducing vanadium, calcium and barium that leads to a change in the crystallization conditions of steel, grinding of the cast structure and an increase in the plastic properties of the solid metal.

A comparison of the physicochemical characteristics of barium and calcium (atomic radius, structure of the electron shell, density, melting and evaporation temperatures, saturated vapor pressure) suggests that barium should manifest itself as a stronger modifier in steelmaking. At the same time, the equivalent mass consumption of barium for the bonding and removal of oxygen and sulfur from steel, as follows from the ratio of atomic masses of barium and calcium, is 3.4 times higher. The total amount of barium and calcium in the range of 150-300 g / t of steel introduced at the ladle furnace was established experimentally based on the results of industrial tests of the proposed method and determination of the physicomechanical properties of the rails obtained.

The lower limit on the amount of introduced barium and calcium is determined by the beginning of a noticeable manifestation of the effect of increasing the ductility of steel. The upper limit on the amount of introduced barium and calcium is due to restrictions on the regulation of the amount of formed calcium sulfides, which complicate the process of steel casting due to overgrowing of the pouring glass, and globular oxides that are not deformed during rolling and create a local stress state in the metal matrix near these inclusions.

Under the indicated limitations of the total amount of introduced barium and calcium, the ratio in the introduced barium to calcium ferroalloy should be observed in the range of 1.0-1.5. This is due to the fact that with a ratio of less than 1.0, the effect of increasing the ductility of the metal is not sufficiently manifested, and with a ratio of more than 1.5, the effect of a further increase in the ductility of rails is practically absent and the degree of desulfurization of steel is reduced.

The experimental melts were carried out in 100-ton electric arc furnace ESPC-2 with the main lining at the Novokuznetsk Metallurgical Plant. Rail steel was smelted without preliminary sedimentary and diffusion deoxidation in a furnace, released into a ladle with furnace slag cut-off, metal was purged with nitrogen and argon in the ladle, and a slag-forming mixture and part of the ferroalloys were introduced along the way. Another part of them was planted on a ladle furnace during argon purging. Vanadium in experimental swimming trunks purged with argon was introduced in the form of 50% ferrovanadium and nitrided ferrovanadium to provide the required nitrogen content. After the introduction of ferrovanadium, a wire filled with a ferroalloy filler containing 8.0% Ba and 7.8% Ca was introduced. The average total consumption of barium and calcium in the experimental melts was 272 g / t of steel. In comparative melts, a wire filled with FeSiCa filler was introduced based on the introduction of calcium on average 230 g / t of steel.

The average values of the mechanical properties, hardness and toughness of rails from steel smelted according to the proposed method and the prototype method currently used at OJSC NKMK are presented in the table.

The comparative average data given in the table for 10 experimental melts show that with the simultaneous introduction of barium and calcium into steel containing 0.07-0.15% vanadium, the effect of increasing the ductility of the metal, in particular, elongation and relative narrowing, as well as impact viscosity at + 20 ° С and -60 ° С.

The proposed method for the production of rail steel can be used for smelting steel intended for mass production of rails for various purposes in order to increase their ductility and operational stability.

Information sources

1. The method of deoxidation and alloying of rail steel. A.S. USSR No. 632736, cl. C21C 7/06.

2. Optimization of the chemical composition of steel and technology for the production of low-temperature reliability rails. Steel. 2005. No. 6, from 134-136.

3. A method of producing rail steel. RF patent №2254380, cl. 7 C21C 7/00.

Table Comparison of average values of mechanical properties, hardness and toughness of rails of experimental and comparative melts according to the results of acceptance tests Variant of microalloying and steel modification The vanadium content in steel,% Number of swimming trunks The average amount of input modifier, g / t σ _in , N / mm ² σ ₀₂ , N / mm ² δ,% ψ,% HB, PCG

Дж/см²

J / cm ² The proposed method 0.07-0.15 10 272 sa and wa 1280 920 13.25 37,20 369.0

Prototype method 2004 average 230 sa 1280 920 11.48 36.63 368.8

Claims (2)

1. A method for the production of rail steel, including smelting steel in an electric furnace without deoxidizing metal and slag, releasing metal into a ladle with furnace slag cut-off, purging metal in a ladle with nitrogen and argon, an additive during the production and purging of slag-forming mixture and ferroalloys containing silicon and manganese and microalloying the steel in the ladle furnace with vanadium, characterized in that after microalloying the steel in the ladle furnace with vanadium, it is modified with a ferroalloy containing silicon, calcium, barium, in which the barium ratio calcium is 1.0-1.5, and their amount in the composition of the ferroalloy 150-300 g / t of steel. 2. The method according to claim 1, characterized in that on the installation of the ladle furnace, the steel is purged with argon, while vanadium is introduced in the form of nitrided ferrovanadium to provide the necessary nitrogen content in the steel.