RU2549024C1 - Consumable electrode for ingot melting by electroslag remelting process - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy and is intended for production by electroslag remelting process (ERP) of the ingots out of crack sensitive steel. The consumable electrode contains inventory head and melted part comprising top and bottom steel part with different composition. The top part is made out of tool crack sensitive steel. The bottom part is made out of low carbon unalloyed steel, and its weight is 35-50% of weight of the process cut of the ingot bottom.

EFFECT: during ERP of the consumable electrode the ingot out of tool crack sensitive steel is made with required composition without cracks and with less consumption of expensive tool steel.

1 dwg, 3 tbl

Description

The invention relates to the field of electrometallurgy and is intended for the production of ingots from crack-sensitive steel, for example, for mandrels of continuous tube rolling mills, by the method of electroslag remelting (ESR).

Known consumable electrode used in the implementation of the electroslag remelting method (US Pat. RU No. 2332471, IPC C22B 9/18 (2006.01), publ. 2008), the fused part of which is made of a homogeneous material corresponding to the material of the smelted ingot.

During the ESR of such a consumable electrode, when the bottom of the ingot is cooled, the temperature of the metal drops below the point of martensitic transformation, which leads to the formation of surface cracks during the smelting of ingots from tool crack-sensitive steel.

Closest to the claimed and adopted as a prototype is a consumable electrode used in the implementation of the method for producing layered ingots by electroslag remelting (US Pat. RU No. 2432406, IPC C22B 9/18 (2006.01), publ. 2011), the fused part of which consists from the upper and lower steel parts of different composition. The composition of the consumable electrode is controlled in length depending on the chemical composition of the ingot in height, and during the ESR, the heat flux directed from the slag bath through the crystallization front to the ingot body is modulated.

The use of such a consumable electrode allows you to get a layered ingot of the desired composition.

However, with an ESR of such a consumable electrode, it is impossible to obtain a high-quality ingot from tool crack-sensitive steel, for example, for mandrels of continuous tube rolling mills.

The objective of the invention is the creation of a consumable electrode for smelting a high-quality (without cracks and the required chemical composition) ingot from tool crack-sensitive steel, for example, for mandrels of tube rolling mills.

The problem is solved by improving the consumable electrode for smelting ingots by the ESR method, the fused part of which consists of upper and lower steel parts of different composition.

This improvement lies in the fact that the upper part of the alloyed part is made of tool crack-sensitive steel, and the lower part is made of low-carbon unalloyed steel and its mass is 35-50% of the mass of the technological trim of the bottom of the ingot.

This design of the consumable electrode allows the ESR to maintain a temperature above the point of martensitic transformation (300 ° C) in the crack-sensitive steel, and to prevent crack formation during cooling of the lower part during the ESR. Moreover, due to the fact that the mass of the part from low-carbon unalloyed steel is 35-50% of the mass of the technological trim of the bottom of the ingot, the required chemical composition is provided in the billet used for further processing remaining after the trim. When the mass of the part from low-carbon unalloyed steel is less than 35% of the mass of the technological cut-off, cracks are formed in the ingot due to a decrease in temperature below the point of martensitic transformation. When the mass of the part from low-carbon unalloyed steel is more than 50% of the mass of the technological trimming of the bottom of the ingot in the billet remaining after trimming used for further processing, the required chemical composition is not provided.

The invention is illustrated in the drawing, which shows the proposed consumable electrode.

The consumable electrode for smelting by the ESR method contains an inventory head 1 and a fusion part consisting of upper 2 and lower 3 steel parts of different composition. The upper part 2 is made of tool crack steel. In the above example, for part 2, we used spent mandrels of a tube rolling mill with a diameter of 167 mm in the form of a bundle of four mandrels made of steel "X35CrMoV05KU-UNI 2955-68 Std" (analogue to steel 4X5MFS GOST 5950-73). The lower part 3 is made of low-carbon unalloyed steel, which was used as a plate (rolled steel) from St3 steel, and its mass is 35-50% of the mass of the technological cut of the bottom of the ingot.

Smelting of the ingots was carried out on EShP U552M furnaces under ANF-35 flux, using 5 consumable electrodes with the mass of the lower part of low-carbon alloy steel St3, shown in table 1:

Table 1 No. of consumable electrode one 2 3 four 5 weight St3, kg 65 77 one hundred BY 122 % by weight of technological trimmings thirty 35 45 fifty 55

Under ESR, the lower part 3, consisting of low-carbon steel, was cooled, and temperature was higher than the point of martensitic transformation in instrumental crack-sensitive steel, which excluded the formation of cracks in the ESR process. Moreover, due to the fact that the mass of part 3 of low-carbon steel is 35-50% of the mass of the technological trim of the bottom of the ingot, the required chemical composition is provided in the billet remaining after trimming, which is used for further processing.

After the end of the ESR, after 3-8 minutes, the mold was removed from the ingots and kept on a pallet for 8-10 minutes, the slag skull was removed from the bottom of the ingot to a height of 150-250 mm and the temperature of the ingots was measured at points corresponding to 30%, 35%, 45 %, 50%, 55% of the mass of technological trimmings.

The average results of temperature measurements are shown in table 2:

table 2 No. of consumable electrode one 2 3 four 5 % by weight of technological trimmings thirty 35 45 fifty 55 ingot temperature, ° C 280 310 330 360 400

The melted ESR ingots were accumulated in a heated caisson at a temperature of 800-900 ° C, after which they were shipped to the forge shop under lined caps. Billets with a diameter of 400 mm were forged from the ingots, and from the bottom of the ingot, trimming was performed in accordance with the requirements of the technological process of the gross technology for the production of forgings from 600 mm ingots. Forged blanks were subjected to annealing and subsequent visual and magnetic particle inspection of the surface.

As can be seen from table 2, the ingot obtained by the ESR of the consumable electrode No. 1, at a point corresponding to 30% of the mass of the technological trimmings, has a temperature below the martensitic transformation point, which led to cracks 30-50 mm long from the lower end of the workpieces. In ingots obtained by ESR of consumable electrodes Nos. 2, 3, 4, and 5, at points corresponding to 35%, 45%, 50%, and 55% of the technological trimmings mass, the temperature is higher than the martensitic transformation point, and no cracks were found in the obtained workpiece from instrumental crack-sensitive steel, not in technological trimmings.

The chemical composition at the lower end of the workpieces obtained after removing the cutting edge, the average composition at the upper end of the workpieces and the composition of spent mandrels for part 2 of the consumable electrode are shown in table 3:

Table 3 Billet Chemical composition, % C Si Mn Mo Cr V S P waste mandrels 0.36 1.05 0.50 1.30 4.80 0.90 0.008 0.012 from ingot 1 at the lower end 0.36 0.98 0.51 1.29 4.80 0.91 0.007 0.013 from ingot 2 at the lower end 0.36 0.99 0.48 1.28 4.78 0.89 0.007 0.013 from ingot 3 at the lower end 0.35 0.95 0.43 1.26 4.75 0.88 0.008 0.013 from ingot 4 at the lower end 0.34 0.94 0.43 1.25 4.73 0.85 0.007 0.013 from ingot 5 at the lower end 0.34 0.93 0.43 1.25 4.65 0.85 0.006 0.015 average composition of ingots 1-5 at the upper end 0.36 0.88 0.49 1.29 4.81 0.89 0.005 0.013

As can be seen from table 3, the chemical composition of the lower part of the ingots obtained by the ESR of the inventive consumable electrode meets the requirements for the brand X35CrMoV05KU-UN1 2955-68 Std General specification NP0206 B ″ Production and control of mandrels for a tube mill ″.

Thus, the use of the proposed sacrificial electrode for smelting ingots by the ESR method allows one to obtain an ingot from tool crack-sensitive steel of the required chemical composition without cracks and to reduce the consumption of costly steel by reducing the proportion of expendable expensive tool steel in the technological cut from the bottom of the ingot by 35-50%. For example, when smelting ingots with a diameter of 600 mm and a mass of 4800 kg, the loss reduction will be 75-110 kg.

Claims (1)

Consumable electrode for smelting ingots from tool crack-sensitive steel by electroslag remelting method, characterized in that the upper fused part of the electrode is made of tool crack-sensitive steel and the lower part is made of low-carbon unalloyed steel, and the mass of the lower part is 35-50% of the mass of the technological cut of the bottom of the ingot.

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