SU1488110A1 - Method of producing steel ingots - Google Patents

Abstract

The invention relates to ferrous metallurgy, in particular, to the technology for producing large ingots from structural low- and medium-alloyed high-quality steels. The purpose of the invention is to improve the quality of ingots by reducing the zonal segregation along the height of the said ingots. The essence of the invention consists in portion casting of the mold, with the mass of each batch of metal being 0.2 ... 0.6 mass of the ingot, and the content of carbon and molybdenum in each batch of metal is kept equal to CI and MOI and determined from the following ratios: ΣCIMI / ΣMI = C, MO = (1.3-1.5) ΔСI, where N is the number of metal portions

MI is the mass of the first portion of the metal. The carbon content in the first portion of the metal is taken equal to 1.1-1.6 of the mean (brand) content of carbon in the ingot, and in the latter - 0.4-0.9, respectively, of the mean.

Description

The invention relates to ferrous metallurgy and can be used in the casting of large ingots for engineering products, such as energy and nuclear, mainly from structural low- and medium-alloyed high-quality steels.

The aim of the invention is to improve the quality of ingots by reducing the zonal segregation along the height of the said ingots.

The essence of the invention is that the pouring of the metal is

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are portions of a mass equal to 0.2-0.6 mass of the ingot, while the carbon content in the metal of the first slurry is maintained equal to 1.1-1.6 of the average carbon content of the ingot, in the metal of the last portion 0.4-0-0, 9 average, and in the metal intermediate portions - equal to the value of C, obtained from the ratio

ig

Z С m;

WITH,

where C is the carbon content of the talle of the i-th portion;

in me

m; - i-Pi mass of the metal portion, С - middle set (vintage)

carbon content in ingot metal

the content of molybdenum in each portion is set from the ratio 5M (, j (1.3-1.5) - / dCj. The change in the content of carbon and molybdenum in each pore is 191) and can be carried out by introducing carbon and molybdenum-containing materials into the tundish .

It is known that the liquation of manganese, chromium, nickel and vanadium in ingots weighing up to 500 tons is insignificant. The elimination of ingot height of such elements as sulfur, phosphorus and K (this can be significantly reduced, for example, by reducing their absolute content in steel when refining it. This cannot be done for carbon and molybdenum, since their average content should correspond to the grade composition become.

Changing the carbon content during casting is not sufficient to reduce the carbon and molybdenum segregation levels in ingot height due to the effect of redistribution of liquids in density in large volumes: large portions of metal with a lower carbon content will be located in the lower part of the ingot and contribute to strengthening as negative and positive carbon segregation.

It is possible to increase the uniformity of the ingot by stabilizing the density of the melt along its casting. In particular, for structural low and medium alloyed steels, this goal is achieved by changing the content of the heaviest element in the metal

m is molybdenum (the density of liquid molybdenum is 9.1 –10 kg / m); In portions of a metal with a higher carbon content, the concentration of molybdenum should be higher and vice versa.

Experimental studies allowed us to determine the effect of carbon and molybdenum on changes in the density of low- and medium-alloyed liquid steel (such as 15Х2НМФА, 25ХНЗМФА, 26ХНЗМФА, and others). In addition, studies have shown that in order to compensate for the change in density of liquid steel of the considered class with a change in its content

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20

25

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40

45

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In each metal portion, the content of molybdenum must be varied according to the following relationship: 4Mv (1.3-1.5) 4C. .

The proposed relationship is valid for the case when the carbon content in the liquid steel varies from 0.05% to 0.45%.

It is impractical to stabilize the density of the melt by any other element, but it is included in the composition of this steel grade, since this will cause the steel to become more expensive and its grade will change. Change is solid. It is possible, but not practical, to melt simultaneously with several elements, since the manufacturability of the production of large ingots sharply increases, starting from preparing the charge for smelting until the moment of each melting is strictly regulated for each element within narrow limits.

Thus, in order to reduce the level of carbon and molybdenum segregation along the ingot height, it is necessary to change the carbon content during casting, and the density of the liquid steel should be stabilized by a corresponding change in the content of molybdenum in steel. In the first portion of the metal, washed down into the mold, the carbon content should be 10-60 wt.% Higher than the content corresponding to the grade composition. An increase in the carbon content of less than 10 rel.% And a corresponding increase in the molybdenum content does not produce the desired results: an increase in the carbon content by more than 60 rel.% With a corresponding increase in the molybdenum content may lead to their increased content in the lower part of the ingot. beyond the brand composition.

The carbon content and the corresponding molybdenum content in the liquid steel in the casting process after pouring 20-60% of the mass of the ingot every 20-60% of its mass is reduced due to the fact that in the upper part of the ingot the positive liquation of these elements develops. Further, in each subsequent portion of the cast metal, the content of carbon and molybdenum is reduced, and the carbon content in the last portion of the metal is 90-40% of its average market content.

514881106

The mass of each batch of metal is determined by technological peculiarities of the mass of the ingot by the scheme of the metal set for the ingot with the composition of the metal, etc. (for example, for an ingot with a mass of 500 t - 20%, and for an ingot with a mass of 235 t - 60%).

The content of carbon and molybdenum in each portion of the metal can be varied both before the steel is cast during its refining, and directly in the tundish when steel is cast.

The method can be carried out by ig casting steel in air, in a protective atmosphere or in a vacuum.

Example. For ingot casting; weighing 360 tons of 25KhNMMA steel are used: sequential pouring of equal 20 portions of metal from one acidic open-hearth furnace (120 tons of steel) and two furnaces of the installation of the ACEA-SCF construction (120 tons each). The carbon content in the metal of each bucket was 0.31; 0.21 25 including head, out-of-furnace and 0.14% refinery; molybdenum 0.53 j 0.39 and 0.29% nosing and portion pouring of metal, respectively. The average mark content into the mold that distinguishes | - the elements are as follows: carbon so that, in order to increase ca. 0.22%, molybdenum 0, AO%. Investigations of ingots by decreasing zonal, carbon content in the first calcareous ° segregation along the heights mentioned | It was 40% higher than the average. ingots, the pouring of the metal is carried out - and in the latter - 40% lower than the average firing content. Ingot cast

and above, instead of manufacturing them in welded-forged design, as well as other critical products for power and nuclear engineering.

Thus, the introduction of a new technology makes it possible to increase the chemical homogeneity of ingots weighing 360 tons and to switch to the production of one-piece forged rotor blanks of TBV-1000/1500 generators instead of welded. In this way, the metal consumption is reduced, the costs of a whole range of technological operations are reduced (welding, mechanical processing, heat treatment, control) and a significant eco- nomic effect is achieved.

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Claims (1)

Formula of inventions The method of producing steel ingots mainly from structural low- and medium-alloyed steels; Yed portions of a mass equal to 0.2-0.6 including top-hatchery, out-of-furnace refining and portion-wise pouring of metal into a mold, distinguishing | - so that, in order to increase the quality of ingots by reducing the zonal segregation in height of the mentioned | ingots, metal casting carried out - and above, instead of manufacturing them in welded-forged design, as well as other critical products for power and nuclear engineering. Thus, the introduction of a new technology makes it possible to increase the chemical homogeneity of ingots weighing 360 tons and to switch to the production of one-piece forged rotor blanks of TBV-1000/1500 generators instead of welded. In this way, the metal consumption is reduced, the costs of a whole range of technological operations are reduced (welding, mechanical processing, heat treatment, control) and a significant eco- nomic effect is achieved. ( Formula of inventions The method of producing steel ingots mainly from structural low- and medium-alloyed steels; including the top head, the extra-furnace refining and portion pouring of metal into the mold, which, in order to improve the quality of the ingots by reducing the zone segregation in height of the said ingots, Yed portions of a mass equal to 0.2-0.6 in vacuum at a residual pressure of 0.5 mm. Hg A study of metal billets from an ingot weighing 360 tons of a rotor of a turbogenerator with a capacity of 1000 MW showed that the degree of maximum carbon segregation over the height of the ingot heat does not exceed 30%, and molybdenum 15%, which is significantly lower than for control ingots weighing 290-360 tons. The difference in the level of mechanical properties of metals in the lower part of the workpiece is insignificant. ; The use of the proposed method provides, in comparison with the known, the possibility of obtaining ferrule ingots from structural low- and medium-alloyed high-quality steels with high chemical homogeneity, allows to obtain stable properties of products and organize the production of solid forged ones. blanks, for example, 1000 MW turbogenerator rotor shafts the carbon in the first portion metal is kept at 1.1-1.6 times the average content of ingot carbon; in the last portion of the metal - 0.4-0.9 average, and in the metal, the ration portions is equal to the value C obtained from the ratio , ,- WITH, where C {. - carbon content in the metal of the i-th portion, t- - the mass of the metal of the i-th portion} С - average set (vintage) carbon content in ingot metal, and the molybdenum content in the metal portion is set from the ratio Lmo; (1.3-1.5) 4Cj, where Л1 .о, ЯС, are the deviations of the content of molybdenum and carbon in the i-th portion, respectively, from the average (branded) content.