RU2640108C1 - Method of producing tube steel - Google Patents

Abstract

FIELD: metallurgy.SUBSTANCE: invention relates to ferrous metallurgy, in particular, production of carbon and low-alloy tube grades of steel deoxidized by aluminium. The method includes melting a half-product in an arc steel-melting furnace, discharging the half-product into a steel-teeming ladle with a simultaneous addition of deoxidizing agents, and alloying and part of slag-forming materials, doping of metal by chemical composition and temperature, and final deoxidation and calcium modification in furnace-ladle plant, vacuum treatment with subsequent blowing of metal with argon and pouring metal in continuous casting machine. Tapping of metal melt into steel-teeming ladle is carried out at oxidation of not more than 800 ppm, metal modification is carried out containing not more than 0.004% of sulphur, calcium is introduced in the amount of 15-20 ppm, after final deoxidation of metal to aluminium content of 0.025-0.03% followed by vacuum treatment and blowing of metal with argon no more than 30 s after vacuum removal.EFFECT: improved quality of steel due to reduced content of non-metallic inclusions, reduced cost of steel due to reduced consumption of deoxidizing agents and modifiers.2 tbl, 3 dwg

Description

The invention relates to ferrous metallurgy, in particular to the production of continuously cast carbon and low alloy pipe grades of steel deoxidized by aluminum.

A known method of production of pipe steel, including the smelting of an intermediate in an electric arc furnace (hereinafter - chipboard), the release of an intermediate in a steel ladle with the simultaneous addition of deoxidizing agents, alloys and parts of slag-forming materials, bringing the metal in chemical composition and temperature, as well as the final deoxidation of metal with aluminum to 0.01% and calcium modification in the amount of 4-8 ppm in a vacuum degassing unit after at least 20 minutes of vacuum treatment (RF patent No. 2555304, C21C 5/52, C21C 7/00, published on July 10, 2015).

Significant disadvantages of this method is that:

- the invention can be applied only in the production of seamless hot-deformed oil and gas pipelines with increased resistance against local corrosion for fields of OJSC "SURGUTNEFTEGAS" according to TU 14-3R-91-2004 and ensures the purity of the metal by corrosion-active non-metallic inclusions (hereinafter - CANV). This type of inclusion is not regulated in the production of other types of pipe products;

- metal modification with calcium is carried out at the final stage of metal preparation for casting - after vacuum treatment. The negative side of this method is the limited time for removing non-metallic inclusions and the need for additional "soft" purge lasting 3-5 minutes. In this case, the interaction of the metal with atmospheric oxygen during the “soft” purge, under conditions of non-slag vacuum treatment, leads to the secondary oxidation of aluminum and calcium dissolved in the metal, which, in turn, leads to an increase in the contamination of the metal with oxide non-metallic inclusions and reduces the spillability of steel;

;- a low concentration of calcium in the metal of 4-8 ppm, due to the regulation of the CANV, provides satisfactory spillability only under the conditions of a limitation of 0.01% aluminum content in the metal within the limits of TU 14-3P-91-2004. The practice of producing steels with an aluminum content of more than 0.02% leads to the conclusion that it is necessary to maintain, for stable casting conditions, especially in large batches, significantly higher concentrations of calcium in the metal. Known concepts for ensuring high spillability of steel at

;

- the high purity of the metal in sulfur provided for by the method before modification (not more than 0.003%) is also of direct importance for the production of steels with a regulated value of CANV, but in the production of steel without these restrictions it is unnecessary for reasons of efficiency of the process.

The closest is the method of production of high carbon steel, followed by casting into a billet of small cross section (RF patent No. 2460807, C21C 7/00, B21D 11/00, publ. 09/10/2012), adopted as a prototype. To reduce contamination by non-metallic inclusions and increase the spillability of steel, the method involves the introduction of calcium-containing materials as a modifier, in terms of pure calcium, according to the following relationship:

Ca = 120 * (- 0.0002 * Ln (a [O]) + [Al] * (0.2 0.4)), kg / t of melt,

where a [O] is the activity of oxygen in the steel before the introduction of calcium-containing materials, ppm (100 ppm - used in the formula without dimension);

[Al] - the content of residual aluminum, wt. % (1 part per hundred - in the formula it is used without dimension);

120 - an empirical coefficient that takes into account the amount of metal per unit volume, kg;

- 0,0002 - correction factor, 1 / m ³ ;

(0.2 0.4) is an empirical coefficient taking into account the state of slag in the steel pouring ladle, m ³ / t.

A significant drawback of this method is the fact that the proposed algorithm for calculating the consumption of calcium-containing materials is developed empirically for steels with a background aluminum content in the metal of up to 50 ppm and for metal deoxidized by aluminum in the range of 0.025-0.030%, leads to an increased consumption of pure calcium, which will be 0.726 kg / t (Ca = 120 × (-0.0002 × Ln (2.2) + [0.027] × 0.23 = 0.726 kg / t), which is unacceptable, since subsequently it will lead to increased erosion of stoppers tundish when casting on a continuous casting machine (yes next - CCM) and a high specific consumption of silico-calcium wire.

Despite the fact that the method is aimed at improving the quality of steel by reducing the contamination of the metal with non-metallic inclusions, the issue of limiting the oxidation of the intermediate has not been considered. At the same time, it was found that the oxidation of liquid metal in a particleboard has a direct effect on the oxygen content [O] _total , which is in the workpiece in the form of oxide non-metallic inclusions (Fig. 1). Also, the issue of the limits of calcium and sulfur concentrations before evacuation and their influence on the level of metal contamination by non-metallic inclusions and casting conditions is not considered.

The technical problem to which the claimed invention is directed is to improve the castability on continuous casting machines of pipe grades of steel deoxidized by aluminum, by reducing the content of non-metallic inclusions.

To this end, we propose a method for the production of tube steel, deoxidized by aluminum, including the smelting of the intermediate in an arc steel furnace, the release of the melt into a steel ladle with the simultaneous addition of deoxidizing agents, alloys and parts of slag-forming materials, bringing the metal in chemical composition and temperature, as well as final deoxidation and modification to “ladle furnace” installation, vacuum treatment with subsequent metal purging with argon and metal casting on a continuous casting machine, I distinguish Since the semi-product is discharged into the ladle at an oxidation of not more than 800 ppm, calcium is added in an amount of 15-20 ppm to a metal containing not more than 0.004% sulfur to be modified after aluminum is deoxidized with aluminum to 0.025-0.03% followed by vacuum processing and purging of argon metal for more than 30 s after vacuum removal.

The declared limits are selected experimentally.

The invention is illustrated by drawings, where in FIG. 1 shows a graph of the dependence of the content of [O] _total in the preform on the oxidation of the intermediate in particleboard, in FIG. 2a shows a graph of the position of the stopper during casting a series of heats with a tightening of the metal wiring, FIG. 2b is a graph of the stopper position when casting a series of heats with corroding metal wiring, in FIG. 2c is a graph of the position of the stopper when casting a series of swimming trunks produced by the present method, in FIG. 3 - dependence of stop erosion rate on calcium content.

The limitation of the oxidation of the intermediate in the particleboard before the release of the smelting (not more than 800 ppm) is due to a decrease in the level of [O] _total not more than 10 ppm, which is a standard requirement for the quality of the cast metal. Studies have shown that increasing the oxidation of the intermediate by more than 800 ppm leads to an increase in the content of [O] _total in the continuously cast billet, which means an increase in metal contamination by nonmetallic inclusions - deoxidation products, which negatively affects the spillability of the metal and the quality of steel (Fig. 1) .

Studies have shown that a significant improvement in the spillability of pipe grades of steel, deoxidized by aluminum, at continuous casting machines, ceteris paribus, is associated with optimization of out-of-furnace treatment modes: deoxidation, desulfurization and modification of non-metallic inclusions. It is known that the modification of metal with silicocalcium at the end of out-of-furnace treatment at the ladle furnace ensures the formation of liquid globular oxysulfide inclusions based on aluminum and calcium, therefore, the necessary condition for eliminating the release of solid calcium sulfide is to limit the sulfur content in the metal to less than 0.004%. With a sulfur content of more than 0.004%, both single and complex CaS-based inclusions are formed. Inclusions of this type lead to tightening of the metal wiring during casting of metal at the continuous casting machine, which is confirmed by the analysis of metal spillability and stopper position graphs shown in FIG. 2a.

The mode of metal deoxidation at the stage of metal release from particleboard, as well as during out-of-furnace processing, must ensure that the aluminum content in the metal before modification is not less than 0.025%, which allows fulfilling the technical requirements for aluminum content in the marking analysis. The process of oxidation of aluminum occurring during metal deoxidation is accompanied by the formation of solid inclusions of alumina, which hinder the casting of steel due to the tightening of the wiring of the intermediate ladle. A necessary condition for the exclusion of this process is the modification of alumina with calcium, which occurs with strict observance of the content of aluminum and calcium in the metal. The excess of aluminum content of more than 0.03% before the introduction of calcium-containing materials into the metal is accompanied by the need to increase the consumption of calcium and, as a result, leads to erosion of refractories during casting with a closed stream.

Carrying out the operation of modifying the metal with calcium at the stage of out-of-furnace treatment before evacuation in an amount of up to 15-20 ppm ensures the transfer of Al ₂ O ₃ -based inclusions formed during metal deoxidation by aluminum into easily removable globular non-metallic inclusions of calcium aluminates, which are favorable from the point of view of metal spillability on continuous casting machines. Modification of the metal with calcium in an amount of less than 15 ppm is not sufficient to bind all inclusions based on Al ₂ O ₃ and leads to a tightening of the wiring of the intermediate ladle (Fig. 2a, Fig. 3). Modification of the metal with calcium in an amount of more than 20 ppm leads to the interaction of excess calcium oxide with the metalwork of the intermediate ladle, which is expressed in an increased erosion rate of stoppers of more than 2 mm / hour (Fig. 2b, Fig. 3).

The traditional technological technique aimed at increasing the purity of the metal by contamination with non-metallic inclusions is a “soft” blowing of the metal with inert gas for 3-10 minutes at the final stage of metal preparation - before the ladle is transferred to the continuous casting machine. It is also known that the “soft” purging of metal with argon after vacuum treatment leads to exposure of the metal mirror, re-oxidation of aluminum and calcium with the formation of oxide inclusions of a complex composition, which subsequently cause the wiring of the intermediate ladle to be tightened. Modification of metal with calcium in the early stages of out-of-furnace treatment at the ladle furnace allows to optimize the metal refining process by removing non-metallic inclusions when the metal is purged with an inert gas under vacuum. Limiting the contact of the metal with the oxidizing atmosphere after evacuation for no more than 30 s increases the purity of the metal due to contamination with non-metallic inclusions and the spillability of the metal in the continuous casting machine (Fig. 2c).

The inventive method was implemented in the production of pipe grades of steel, deoxidized with aluminum, more than 500 heats.

Smelting of the intermediate was carried out in DSP-135. The oxidation of the intermediate before the release of melting from particleboard did not exceed 800 ppm, the temperature - 1635-1655 ° C. When the intermediate product was produced from particleboard, the following were produced: metal deoxidation with granular aluminum in an amount of 1.6 kg / t; guidance of slag by the addition of aluminum-containing material and lime in an amount of 6 kg / t; the return of carbon-containing materials and ferroalloys to the lower limit of the grade composition.

The refinement of the metal by chemical composition and temperature was carried out on a ladle furnace. To ensure sulfur concentrations before calcium input of less than 0.004%, refining slag was induced by returning slag-forming materials in an amount of 10 kg / t. The final deoxidation of the metal was carried out with aluminum rod in an amount that ensures the aluminum content before modification in the range of 0.025-0.030%.

At the end of the metal processing, a silica-calcium wire with a SK30 filler was fed at the ladle-furnace plant based on the calculation of calcium content in the range of 0.0015-0.0020%, after which the steel casting ladle was transferred to a vacuum degassing unit.

The exposure time of the metal under high vacuum (less than 0.8 mbar) is 5-15 minutes with an argon consumption of 5-8 m ³ / h, depending on the requirements of regulatory documents on the gas content. To ensure the operability of the purge plugs, the ladle steel after removing the vacuum, the metal was purged with argon for 10-30 s at an argon flow rate of 2-3 m ³ / h. After that, the argon supply was stopped, the temperature of the metal was measured, and the bucket was transferred to a continuous casting machine.

Metal was cast on a 5-strand continuous casting machine of curvilinear type into molds with a cross section of ∅ 150, 156, 290, 360 mm. Casting was carried out in a closed stream using a protective tube and immersion glasses. The spillability of the metal was evaluated by changing the position of the caster stopper during casting. To determine the quality of the microstructure of the metal in the CCM line, templates were selected.

Contamination of metal by non-metallic inclusions was controlled in accordance with the methodology for evaluating a continuously cast billet (TU 14-1-5319-2012, Continuous Cast Billet Billet, Central Research Institute of Iron and Steel named after IP Bardin).

Table 1 presents the results indicating the level of contamination of the metal with non-metallic inclusions and the amount of mass-spilled metal that underwent out-of-furnace treatment according to the proposed method for the production of steel. Table 2 shows the data of swimming trunks produced with a deviation from the values declared in the method.

From the data presented it follows:

1. In the steel production using the technologies used (table 2), there is an increase in the level of metal contamination with non-metallic inclusions, a decrease in the batch production of a continuously cast billet due to the tightening / erosion of the intermediate ladle metal wiring and an increase in the costs of deoxidizers and modifiers.

2. The proposed method for the production of pipe steel (table 1) allows to improve the spillability of steel in continuous casting caster by reducing the content of non-metallic inclusions, to reduce the cost of smelting steel by reducing the consumption of deoxidizing agents and modifiers.

Claims (1)

A method for the production of tube steel, deoxidized by aluminum, including the smelting of a semi-product in an electric arc furnace, the release of molten metal into a steel pouring ladle with the simultaneous addition of deoxidizing agents, alloys and parts of slag-forming materials, bringing the metal in chemical composition and temperature, and final deoxidation and modification of the ladle furnace , vacuum treatment with subsequent purging of metal with argon and casting metal on a continuous casting machine, characterized in that the output in a tug pouring ladle of a molten metal is carried out at an oxidation of not more than 800 ppm, it is modified by adding calcium in an amount of 15-20 ppm to a metal containing not more than 0.004% sulfur, after the final deoxidation of the metal to an aluminum content of 0.025-0.03%, followed by vacuum treatment and blowing metal argon no more than 30 s after removal of the vacuum.

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