RU2660495C1 - Method of obtaining a hollow billet by electroslag remelting at a solid start - Google Patents

Abstract

FIELD: technological processes; metallurgy.

SUBSTANCE: invention relates to electrometallurgy, namely to obtaining a hollow billet by electroslag remelting using a start on a solid flux. Before the beginning of the process, a hollow preform is welded to the end of the consumable electrode to dilute the necessary amount of slag at the beginning of the melting, dielectric layer is applied to the surface of the tray, a seed is placed between which the consumable electrode with a hollow preform is set up with springs, fill them with an exothermic mixture to create a short circuit at the beginning of the process, after which a water-cooled crystallizer is installed on the pallet, in the working space of which, before the start, a calcined solid flux is fed, slag is carried out by passing a current of 2.2 kA through the consumable electrode, the solid flux is melted, then the current is reduced to 1.5 kA, rotate the consumable electrode and perform its vertical surfacing in a water-cooled mold with simultaneous feeding of the sewing mandrel through the hole in the pan.

EFFECT: invention allows to increase the profitability of formation of hollow blanks by electroslag remelting with the rotation of the electrode by simplifying the technological chain and eliminating additional equipment.

1 cl, 2 dwg, 1 tbl

Description

The present invention relates to the field of electrometallurgy, and in particular to special processes of electric melting.

A known method of obtaining a hollow billet by electroslag firmware (Electroslag remelting / Klyuev MM, Volkov S.E. - M .: Publishing House "Metallurgy", 1984, 208 S. S. 22).

As the closest analogue (prototype), a method for producing a hollow ingot by electroslag remelting with rotation of the electrode about its axis was selected (RU 2413016 C22B 9/18, publ. 02.27.2011).

In this method, the production of a hollow ingot (billet) by electroslag remelting involves vertical surfacing in a water-cooled mold of a consumable electrode with the simultaneous supply of a piercing mandrel through an opening in the pallet, while the consumable electrode placed in the liquid slag bath rotates around its axis throughout the remelting process at a speed that ensures the delivery of drops of electrode metal along a radial path to the periphery of the slag and liquid metal baths outside the sub-electrode zone.

The disadvantage of this method is its technical side, namely, the need to start using liquid flux, which entails the need for additional equipment in the form of flux-smelting furnaces, an increase in the stages of obtaining a hollow ingot by the method of electroslag remelting in such a complex technological chain, and a significant increase in the cost of production.

An object of the invention is to reduce the cost of production and increase profitability through the use of start on solid flux, which also leads to a simplification of the technological chain of the process of obtaining a hollow billet.

The technical problem is solved in that the method of producing a hollow billet by electroslag remelting on a solid start includes vertical cladding in a water-cooled mold with the simultaneous supply of a flashing mandrel through a hole in the pan and rotation of the consumable electrode, but before the start of the process, a hollow workpiece is welded onto the end of the electrode opposite solid slag and an exothermic mixture are poured into the crystallizer, wiring is carried out by passing a current of 2.2 kA through the electrode, melt flux, then the current is reduced to 1.5 kA, and the electrode is rotated.

Electroslag remelting of the consumable electrode on a solid start is carried out according to three modes corresponding to steel grades.

- Wiring (in our case, the current strength is 2.2 kA);

It serves as the initial mode and the beginning of remelting. At the time of wiring, the solid flux melts due to the current flowing through the electrode to the pallet. Since the melting point of the flux is lower than the melting point of the metal, the electrode remains in the solid state.

- The main mode of remelting (in our case, 1.5 kA);

Follows immediately after wiring. After the formation of a bath of liquid slag, they switch to a mode corresponding to the grade of steel (each grade of steel has its own standard regime that excludes the burning of alloying elements). It is the longest time mode.

- Shrinkage (in our case, excluded due to the small size and mass of the ingots);

Before the start of electroslag remelting, a hollow billet is welded to the end of the electrode opposite to the holder to enable a solid start. After preparing the unit for remelting, a solid flux is poured into the mold and wiring begins.

After melting the flux, the electrode begins to rotate around its axis with the required speed, as in the prototype method (RU 2413016 C22B 9/18, publ. 02.27.2011).

In FIG. 1 a), b), c) a flow chart of a method for producing a hollow billet by electroslag remelting with a rotating electrode on a solid start is presented, wherein: a) is the start of the process, the rotation speed of the electrode is ω = 0, after the flux is melted and a liquid bath is obtained - b) - the electrode is brought into rotation, with ω> 0 during the entire remelting process, after the remelting is completed - c) - again, the electrode speed is ω = 0;

In FIG. 2 illustrates the essence of the proposed method.

An example of a specific implementation of the method

Obtaining hollow ingots by electroslag remelting was carried out on a modernized A-550 unit (Fig. 2). For remelting (Fig. 2), an electrode (1) was used from steel grade 20X13 with a diameter of 40 mm, having a length of 1500 mm, the diameter of the remelted electrode plays an important role in choosing the rotation mode, since it directly affects the centrifugal force. The electrode was mounted on a movable carriage for electroslag remelting using a collet clamp. After fixing the remelted electrode, conductive brushes were pressed against it using springs to provide a larger contact surface. Remelting was carried out in a mold (2) with a diameter of 90 mm. Before starting the experiment, the contacting surfaces of the mold and the pan (3) were thoroughly cleaned. A hollow billet (9) was welded to the end of the electrode for dilution (wiring process) of the flux; it was also necessary to use a seed (6) to obtain liquid slag at the beginning of the electroslag remelting process. The role of seeds in the course of these experiments was performed by plates with a diameter of 40 mm and a height of 10 mm, made of the same steel grade as the remelted electrodes. Between the seed and the remelted electrode, springs (8) were installed from a wire with a diameter of 2 mm to create a short circuit at the beginning of the process. The diameter of the springs was 12 mm and the length was 10 mm. Over the entire height, this spring was covered with an exothermic mixture of С-2 (7), which allowed melt the required amount of slag at the beginning of melting. Composition of the mixture: 20 ... 30% PAM-3 or PAM-4 powder, the rest is ANF-6 flux. The chemical composition of PAM corresponds to GOST 5593-78. To exclude the effect of sticking of the electrode to the platform of the mold tray during the ignition process, previously in the place of future contact of the metal and the surface of the tray, a thin layer of alumina powder was applied (5), which is an insulator. A dielectric also laid under the pallet, the role of which was performed by an asbestos sheet, to exclude the occurrence of a short circuit between the pallet and the floor covering. After the preliminary preparation of the electrode, the water-cooled mold was mounted on the pallet so that its walls did not touch the electrode, in order to avoid their mutual closure and, as a result, burnout of the mold. Before starting, the ANF-6 flux (10), the chemical composition of which is presented in Table 1, was poured into the working space of the installed water-cooled crystallizer. 1. The flux granules were pre-sieved and had a fraction of not more than 3 mm, the flux was also preliminarily calcined for two hours at a temperature of 200 ° C to remove residual moisture from it.

Table 1 - Chemical composition of flux ANF-6,%

CaF2 Al2O3 CaO SiO2 FROM TiO2 Fe2O3 S P The basis 25 No more 31 8 2,5 0.10 0.05 0.5 0.05 0.02

The flux fell asleep immediately in full in the amount of 1.7 kg. After completing all the preliminary stages of the preparation of the electroslag remelting process, the installation was launched. The ignition, the course of melting and the piercing mandrel (4) were carried out in automatic mode. The control and adjustment of electroslag remelting was carried out using a touch panel containing all the information about the process. Making changes to the course of the remelting process using this control was possible in two ways:

- change in the lowering speed of the electrode,

- change in current strength;

Changes are required, since at start-up, a higher voltage is needed to create an arc and corresponding adjustment after its appearance. Characteristic signs of the appearance of an arc is a decrease in current strength. The choice of current is an important step in the preparation of ingots by the method of electroslag remelting and is selected depending on the chemical composition of the steel, since an increase in current increases the rate of remelting and productivity. However, in this case, the liquid metal bath becomes deeper, which in turn leads to a deterioration in the structure of the ingot. In this example of the method, the optimal current was selected for the given values of the remelted ingot and the mold, which was 2.2 kA during wiring, and 1.5 kA in the main remelting period. The melting period continued until the electrode was completely remelted and amounted to 30 minutes. After the remelting process was stopped, the carriage with the cinder of the electrode (1) (Fig. 2) was raised up to its original position to simplify the operation of extracting the obtained ingot from the mold. Before removing the obtained ingots, the slag was allowed to cool, the time of its complete solidification was 8 minutes. After solidification of the slag, the ingots were removed from the mold. The ingot obtained by remelting an electrode of steel grade 20X13 had a height of 225 mm, a diameter of 90 mm, and had a satisfactory surface quality.

To enable assessment of the suitability of the proposed method for the quality of the metal, one heat was carried out according to the technology of the prototype, i.e. on a liquid start without a weld.

After smelting from the bottom, middle and head parts of the ingots, samples were cut out to control the metal for the content of non-metallic inclusions in it. The ingots obtained by the proposed technology for contamination with non-metallic inclusions are not inferior to the prototype, and the technological chain for producing a hollow billet by electroslag remelting on a solid start with electrode rotation is significantly simplified and production costs are reduced.

The proposed method allows to obtain a hollow billet for the manufacture of critical parts, such as pipelines of nuclear and thermal power plants, oil and gas industry.

Claims (1)

A method of obtaining a hollow billet by electroslag remelting using a start on solid flux, which consists in the fact that before starting the process, a hollow billet is welded to the end of the consumable electrode to dilute the required amount of slag at the beginning of melting, a dielectric layer is applied to the surface of the pallet, a seed is placed between which and using a sacrificial electrode with a hollow billet, springs are installed, they are filled with an exothermic mixture to create a short circuit at the beginning of the process, and then onto the pallet a water-cooled crystallizer is installed, in the working space of which a calcined solid flux is fed before start-up, slag is wired when a current of 2.2 kA is passed through a consumable electrode, the solid flux is melted, then the current strength is reduced to 1.5 kA, the consumable electrode is rotated and its vertical surfacing in a water-cooled mold with the simultaneous supply of a stitching mandrel through an opening in the pallet.

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