RU2407606C1 - Procedure for production of continuous cast work piece of upgraded quality - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: procedure consists in steel melting, in refining, modifying, in casting into crystalliser and in introducing macro-coolers into crystalliser. The macro-coolers (Mc) correspond to melt band steel elements of 0.4 to 2.8 mm thickness. Simultaneously with macro-coolers modifiers (Mm) are introduced into the crystalliser. Summary amount of macro-coolers and modifiers is (Mm+Mc)=(0.0004÷0.009)Ms at ratio Mm:Mc≤(0.003÷0.7), where Ms - is weight of steel in the crystalliser.

EFFECT: increased dispersion of crystal structure of continuous cast work pieces, reduced degree of liquation of chemical elements both in axial zone and along whole cross section of work pieces.

9 cl, 7 dwg, 3 ex

Description

The invention relates to the field of metallurgy, in particular to methods for producing continuously cast billets of high quality, implemented through the use of accelerated cooling of steel in the mold.

Improving the quality of steel is directly related to the possibility of achieving a dispersed dendritic structure in continuously cast billets and a more uniform distribution of chemical elements throughout the billet cross section.

An important condition for the formation of dispersed structures of steels with improved properties is to reduce the degree of overheating of steels during their casting, where the degree of overheating is the difference between the temperature of the melt and its liquidus temperature. In the absence of overheating of the melt, oriented columnar dendritic structures are not formed in the preform, but crystals with different orientations are formed. The dispersion of the formed cast structure is largely inherited during the subsequent stages of processing cast billets into products.

In world practice, alloying and steel modification are the most common ways to improve the quality of cast metal, not only by increasing the dispersion of the structure over the entire cross section of continuously cast billets, especially their central zone, but also due to the strengthening of structural components. It was found that the most important condition for the formation of a dispersed cast structure is to reduce the overheating of steel located precisely in the mold. Reducing or completely removing overheating and increasing the rate of heat removal accelerate the crystallization process and, therefore, reduce the degree of segregation (chemical) heterogeneity and increase the dispersion of structures.

The solution to the problems of reducing the heterogeneity of the steel structure in continuously cast billets, due to the presence of steel overheating, is carried out by introducing micro- and macro-refrigerators, as well as modifying additives, into the melt. Moreover, these additives are introduced either into the scoop or directly into the mold (USSR patent No.SU 1813114 from 06/27/1991; US patent No.US 4440658 from 06/30/1981). The most characteristic drawback of these methods was the uncontrolled and incomplete degree of assimilation of the modifying components contained in the additives. This is especially true for materials with a large specific surface (granular and powder) with their inherent high content of oxide inclusions, the mismatch of the composition of the additives to the requirements for their melting temperatures. In addition, in some cases, additives containing aluminum are recommended, the oxides of which are dangerous for some classes of steels (in particular, transport steels), since aluminates significantly reduce the cyclic endurance of the metal.

US Pat. No. 4,440,658 dated June 30, 1981 sets forth a method for modifying steel with boron mixtures. Additives are mainly used in the form of granules (based on Fe) containing 0.25–3.0% B, 2.5–40% REM, 6–60% Ti; they are introduced into the crystallizer through a channel supplying steel from the ladle. In addition to boron, rare-earth metals and titanium, additives may contain Si; Ca; Mn, Zr. The ratio of the mass fractions of Ti to B in the additive material is in the range of 20: 1-60: 1, and the ratio of the mass fractions of titanium and rare earth metals to boron varies from 30: 1 to 90: 1. The result of the use of the invention is the formation of a finely dispersed, i.e., fine-grained metal structure that is formed even in a molten state. Final content of elements in cast steel: 0.0005-0.003% B; 0.005-0.035% Ti, 0.2-0.6% C, is subject to preliminary deoxidation of the steel with silicon. In this case, no more than 0.004% Al should be dissolved in the steel, and the silicon concentration should not exceed 0.35%.

The disadvantages of this method of steel modification is the inconsistent and low degree of assimilation of the modifying mixtures added to the mold and the formation of a large and variable volume of non-metallic inclusions.

Among the works in which microchillers introduced into the mold of a continuous steel casting plant are used to improve the structure, the article should be noted [M.Ardelean, E.Ardelean, A.Socalici, T.Heput, Experimental equipment for introducing microchillers into a tundish and crystallizer installations for continuous casting of steel, Annales of the Oradea University (ISSN 1583-0691), 2008, vol. 39 No. 3, ppl 190-1195]. In this work, we consider the industrial technology implemented in practice for the continuous casting of carbon steels with the introduction of a micro-refrigerator alloy into the melt. According to this publication, granules of the same chemical composition as the cast steel are introduced directly into the mold with a cross section of ~ 270 × 240 mm (or simultaneously into several molds according to the number of streams of the continuous casting plant). The micro-refrigerator alloy is introduced into the melt from above, pouring from special conveyors onto the melt mirror covered with a layer of slag.

The disadvantage of this method is the increase in the number of non-metallic inclusions in the material. The melt will freeze onto the oxidized surface of the cold alloy granules, fixing existing oxide films and preventing the granules from penetrating into the melt. Thus, there is a heterogeneity of steel along the length and cross section of the workpieces. Randomly spaced granules or wire segments with a metal layer frozen on them can contribute to the accumulation of such conglomerates near and inside metal-supplying channels and destabilize the rate of steel entry into the mold.

A known method of casting a metal having high ductility (patent EP 0605379 from 07/06/1994).

According to patent EP 0605379, the metal is poured through a hollow water-cooled adapter located between the tundish and the mold, while finely dispersed metallic material (micro-refrigerator alloy) is introduced into the interior of the hollow adapter. Fine metal material is supplied in the form of a suspension in an inert gas and has the lowest possible amount of oxygen. Fine material consists of a powder of the same metal as the metal being cast, and it is introduced at a rate less than or equal to 1% of the mass casting speed. Alternatively, the particulate powder introduced may be of a different metal than the cast metal, with the total feed rate varying from 0.5% to 10% of the casting speed. Preferably, powders with a particle size not exceeding 1000 microns are recommended. In the description of the patent EP 0605379 it is indicated that the removal of overheating of the melt due to the use of this invention can be 25-35 ° C. The technical result of the invention in this patent is to obtain a homogeneous finely dispersed structure, including in the axial zone of continuously cast billets. However, the above technology cannot be recommended for mass production of steel, as the required amount of powder material can reach 2 ~ 10% by weight of the cast steel, which is unacceptable for economic reasons.

There is also known a method of processing continuously cast steel [USSR copyright certificate SU 1774898 of 02.25.1991]. According to the invention SU 1774898, the forced removal of overheating of the melt is carried out at a rate of 5-10 ° C / min by adding lumpy waste of steel of the same chemical composition in an amount of 0.5-5.0 kg / ton, purged with argon with a flow rate of 3 ÷ 5 m ³ / min and counter flows introduce clad powder modifier and argon into the vertical metal channel of the sectional intermediate ladle with flow rates of 0.5–1.5 kg / ton and 1.15–1.30 m ³ / ton, respectively. The technical result of this invention is: improving the quality of steel, increasing the depth of refining, reducing structural macro- and microinhomogeneity, as well as reducing the consumption of alloying materials.

The disadvantage of this invention is the inability to effectively affect the structure of the crystallizing metal, because the additive cooling the melt materials is made far from the mold, in which the structure of continuously cast ingot begins to form.

A known method of continuous casting of billets of rectangular cross section [Ukrainian patent UA 4927 from 12.28.1994]. According to UA 4927, metal is fed into the crystallizer and a refrigerator is introduced into it in the form of a tape with a speed depending on the casting speed, characterized in that a steel tape with a liquidus temperature T _l ≤T _s - 5 is used as a refrigerator, and its input speed into the mold determined by the dependence:

V _B = K · S · (δ · l) ^-1 (T _p -T _c ) V _p

where K = 0,00044 is an empirical coefficient; S is the cross-sectional area of the slab, mm ² ; T _p - temperature cast steel; T _with - liquidus temperature of cast steel, degrees; δ and l are the thickness and width of the tape, respectively, mm; V _p - steel casting speed, m / min.

As a result, an improvement was achieved in the macrostructure of continuously cast billets (reduction in axial segregation, friability, etc.).

The disadvantage of the above method is the lack of modification of cast steel in the mold, which does not lead to the formation of additional crystallization centers in the melt and does not provide the formation of a more dispersed cast structure.

A known method of processing a metal melt during continuous casting of blanks [patent of Ukraine UA 40053 from 07.16.2001 g]. According to the description, the patented method includes feeding metal into a crystallizer of rectangular cross-section, imparting a necessary trajectory to the metal tape and introducing into the melt of refrigerators in the form of a metal tape at a certain angle relative to the vertical axis of the mold and its wide side, and electro-hydraulic shock pulses are introduced into the melt through the tape, which direct in the direction of movement of the tape. When tape macrochillers are introduced into the crystallizer according to the above method, the melting of the macrochairs is accelerated, which reduces the likelihood of freezing the material of the macrochiller into the crystallizing melt. The disadvantage of the above method is the lack of modification of cast steel in the mold, which does not lead to the formation of additional crystallization centers.

Closest to the claimed invention according to the achieved technical results is the USSR patent No. SU 1813114 of 06/27/1991, which served as a prototype.

In the description of the USSR patent No. SU 1813114 of 06/27/1991, a method for modifying the axial zone of a continuously cast billet is described. According to this invention, to reduce the segregation of elements in the axial zone of wide continuously cast slabs with a cross section of 300 × 1850 mm ^{2, a} metal macro-refrigerator in the form of a tape (or strip with a cross-section, for example, 1.5 × 1500 mm) made of an alloy is introduced into the continuous casting mold in the caster of the casting nozzle the following chemical composition: carbon 0.3-0.45 wt.%, silicon 0.2-0.45%, manganese 0.3-0.65%, titanium 0.01-0.04%, aluminum 0.2 -0.5%, the rest is iron. The technical result of the use of this invention is to reduce the level of segregation of elements in the axial zone of the workpieces, primarily for manganese and phosphorus, to the extent that exclude the formation of intermediate structures in the axial zone of the slab, which prevents microcracks and significantly reduces the rejection by ultrasonic inspection.

The disadvantages of this invention is the use by the authors of compositions characterized by a high content of aluminum and titanium, which is unacceptable for removing overheating of a large number of steel grades, since it leads to the formation of high-alumina non-metallic inclusions in the workpieces, which have a sharp negative effect on the metal resistance to fracture and endurance in cyclic loading, as well as leading to the appearance of a number of surface and bulk defects, reducing the service life of the products. In addition, the possibility of using the proposed method for casting carbon steels is limited by the formation of titanium carbides in them, leading to the manifestation of carbide inhomogeneity of cast billets. The use of the chemical compositions of the input materials declared in this prototype during the casting of high-carbon steels can lead to the freezing of tapes into cast melts with characteristic low liquidus temperatures, and their use at elevated steel casting temperatures eliminates the possibility of the required reduction in overheating and does not counteract the manifestation of the dendritic structure of the steel .

The main tasks to be solved by the present invention are directed, are to increase the dispersion of the crystalline structure of the metal, to reduce the degree of segregation of chemical elements both in the axial zone and throughout the cross section of the workpieces. One of the possible ways to solve these problems is to forcefully reduce the overheating of the steel entering the mold.

The need for the initial overheating of steel is due to heat loss at all stages of its movement from the melting unit to the crystallizer. The final overheating of the steel entering the mold is necessary and technologically due to the requirement to exclude emergency situations associated with its solidification in the supply channels. At the same time, the presence of overheating contributes to the emergence of fluctuations in the solidification rate, at which not only the dispersion of the structure, but also the composition of the hardening steel changes, resulting in the formation of segregation zones. That is, the degree of segregation depends on the linear velocity of the crystallization front V _k , its temperature T _k and the diffusion mobility D _{i of the} components that make up the steel. It is known that in steels carbon has the highest diffusion mobility. In the presence of modifying additives or carbide-forming elements, it forms refractory compounds in the diffusion layer, which are crystallization nuclei. The change in the dispersion of the structure of a crystallized metal depends on the number of nuclei arising per unit mass of the modifying components. It is known that a very large number of nucleus particles are formed when boron is added, since it is for him that the amount of decrease in free energy during the formation of one gram of refractory compounds is maximum (more than with other modifying components). Additives of boron significantly change the structure of steel with its contents of the order of 10 ^-3 %. Additives of modifying elements such as titanium, zirconium and vanadium are effective at contents exceeding hundredths of a percent.

The technical result - improving the quality of continuously cast billets and products made from it, due to the formation of dispersed cast structures and reduce the degree of segregation heterogeneity in continuously cast billets of predominantly high-carbon steels.

The claimed technical result is achieved in that in a method for producing a continuously cast billet, including steel smelting, refining, modifying, casting into a mold and introducing macro-refrigerators into it, according to the invention simultaneously with macro-refrigerators (MX) in the form of molten steel strip elements from 0.4 to Modifiers (Mm) are introduced into the crystallizer 2.8 mm, the total amount of which is (Mm + Mx) = (0.0004 ÷ 0.009) Ms with the ratio Mm: Mx ≤ (0.003 ÷ 0.7), where Mc is the mass of steel in crystallizer.

As macrochillers use steel elements with liquidus temperatures 5 ÷ 35 ° C lower than the liquidus temperature of cast steel. Modifiers are introduced in the form of tapes and / or plates with a thickness of 0.4 to 2.8 mm containing modifying elements, or in the form of powder mixtures in sealed tubular shells with a shell wall thickness of 0.15 to 0.8 mm. The tubular shell is made of stainless steel, the liquidus temperature of which does not exceed the liquidus temperature of the cast steel.

Macro-refrigerators and / or modifiers contain manganese and silicon in an amount exceeding up to 7 times their content in cast steel, which reduces the liquidus temperature, and also increases the degree of steel deoxidation and improves the conditions for removing non-metallic inclusions. Boron is introduced into the composition of macro-refrigerators and / or modifiers, while in tape macro-refrigerators and / or modifiers, its content ranges from 0.07 to 0.45% (by weight).

The composition of modifiers in the form of powder mixtures in sealed tubular shells introduce boron in an amount of from 1% to 15% (by weight). According to the invention, high carbon steel is poured with a carbon content of from 0.65% to 1.1% (by weight).

A decrease in the thickness of the tape macrochillers or modifiers introduced into the crystallizer is less than 0.4 mm leads to instability of the feed of the tape into the melt, and an increase in the thickness of the tapes above 2.8 mm causes a danger of freezing of the tapes into the continuously cast billet, which is associated with the dissolution rate of the tape material in the steel melt. When freezing, the complete melting of the introduced steel elements is not achieved, which negatively affects the chemical uniformity of the continuously cast billet and reduces its quality.

If the total number of macro-refrigerators (Mx) and modifiers (Mm) introduced into the mold is less than 0.0004 Ms, where Mc is the mass of steel entering the mold, then the efficiency of using macro-refrigerators and modifiers becomes low, which does not ensure the formation of a dispersed structure of continuously cast billets. If the total amount (Mx + Mm)> 0.009 Ms, then there is a danger of freezing of the tapes in the continuously cast billet, which is associated with supercooling of the molten steel being cast. If the number of modifiers introduced into the crystallizer is Mm <0.003 Mx, then the necessary concentration of additional crystallization centers is not provided in the melt and the dispersed cast structure is not achieved. If the number of modifiers Mm exceeds 0.7 Mx, there is a danger of a change in the chemical composition of the cast steel above the limits regulated by GOST; there is a danger of the appearance of zones with increased chemical inhomogeneity of the workpiece, and the efficiency of using macro-refrigerators is reduced, which leads to an increase in costs, because the cost of modifiers exceeds the cost of macro-refrigerators.

For macro-refrigerators introduced into the mold, steel with liquidus temperatures is 5 ÷ 35 ° C lower than the liquidus temperature of the cast steel. In the case of using macro-refrigerators with a melting temperature less than 5 ° C lower than the melting temperature of cast steel, the risk of freezing of the feed tape into a continuously cast billet increases, which is associated with a change in the chemical composition of steel from smelting to smelting (within the grade range). The use of macro-refrigerators with a melting point more than 35 ° C below the melting temperature of cast steel can lead to an undesirable change in the chemical composition of the steel, as well as to an inhomogeneous distribution of chemical elements, which will reduce the quality of the continuously cast billet.

If the content of manganese and silicon in the tape materials introduced into the mold exceeds 7 times their content in the cast steel, there is a risk of a change in the chemical composition of the cast steel or the appearance of a chemical inhomogeneity of the workpiece.

If the boron content in the material of the tapes exceeds 0.45% by weight, technological difficulties in the manufacture of tapes increase excessively, and a decrease in the boron content below 0.07% leads to an insufficient increase in its content in the cast steel and to the ineffectiveness of its use due to the fact that a dispersed cast billet structure will not be realized. The low boron content (less than 1%) in powder materials encapsulated in tubular shells also leads to an insufficient increase in its content in cast steel, and when boron content is above 15%, the sintering of powder mixtures, which are put into practice, are complicated.

An important point is that as the material of the tubular shells for sealing powder modifiers, it is preferable to use not ordinary carbon steel that is oxidized, but stainless steel, which serves the same purpose - reducing the number of non-metallic inclusions. However, the main reason why carbon stainless steel is preferred is its lower liquidus temperature. If a low-carbon steel or a shell of cast high-carbon steel is chosen as a shell, then, as noted, it can be frozen into crystallizing melt at high feed rates of the modifying material.

The invention is illustrated by graphs and photographs, in which Fig. 1 shows the thickness distribution of carbon in cross section of a continuously cast billet with a size of 300 × 360 mm for a comparative billet and for a pilot billet obtained in accordance with the method described in Example 1. Fig. 2 presents macrostructure of a transverse template of a continuously cast billet with a section of 300 × 360 mm obtained by comparative technology. Figure 3 shows the macrostructure of the transverse template of a continuously cast billet with a section of 300 × 360 mm obtained in accordance with the method described in Example 2. Figure 4 shows the macrostructure of the transverse rail template obtained by comparative technology. Figure 5 presents the macrostructure of the transverse rail template, obtained in accordance with the method described in Example 2. Figure 6 shows the carbon distribution in thickness in the cross section of a continuously cast billet 300 × 360 mm for a comparative billet and for the experimental billet obtained in accordance with with the method described in Example 2. FIG. 7 shows the thickness distribution of carbon in cross section of a continuously cast billet of 300 × 360 mm for a comparative billet and for a pilot billet obtained in accordance with with the method described in Example 3.

Examples of practical implementation of the proposed method

Example 1. In the converter shop of the Nizhny Tagil Metallurgical Combine smelted rail steel grade K76F chemical composition: C - 0.75 wt.%, Mn - 0.9 wt.%, Si - 0.36 wt.%, P - 0.01% , S - 0.011%, Cr - 0.02%, Ni - 0.05%, the rest - Fe and impurities. Melted steel liquidus temperature: Tlемой1465 ° С. When melting rail steel, a macro-refrigerator made of steel with a high silicon content (1.63 wt.%) And a boron-containing modifier sealed in stainless steel tubes were simultaneously introduced into the melt entering the crystallizer (having a temperature T = 1485 ± 1.5 ° C) powder mixture. Casting was carried out in a mold with a cross section of 300 × 360 mm. The casting speed was 0.46 m / min, which corresponded to the mass of the cast steel Ms = 390 kg per 1 minute. A macro-refrigerator tape with a cross section of 2.8 × 60 mm ² had the chemical composition: C — 0.44%, Mn — 2.0%; Si - 1.63%; Ni - 3.06%; Cu - 0.09%; Cr - 0.1%; the rest is Fe and impurities. The material of the macro-refrigerator had an increased (compared to cast steel) more than 2 times the manganese content and almost 5 times higher silicon content. The liquidus temperature of the tape material was T≅1457 ° С. The rate of introduction of the macro-refrigerator ribbon into the crystallizer was ν = 2.44 m / min, which corresponded to the mass of macro-refrigerators introduced into the crystallizer, Mx = 3.2 kg per 1 minute, while the ratio of Mx and Ms was Mx = 0.0082 Ms.

The rate of introduction of the tube with the modifying powder mixture was 0.13 m / min. The composition of the boron-containing modifying powder mixture: FeB - 46 wt.%, Fe ₂ B - 33%, FeSi - 3% and 18% carbonyl nickel. The powder mixture was sealed in a tubular shell made of 12X18H10 steel, which has a lower liquidus temperature than the liquidus temperature of the cast steel. The stainless tube had an inner diameter of f = 18.5 mm and a wall thickness of δ = 0.3 mm. The average packing density was 8.6 grams of powder mixture per 1 linear centimeter of the tube (0.86 g of boron was contained in 1 cm of the tube length). The total weight of one centimeter of the modifier (including the tubular casing) was 10.2 grams. To ensure a uniform flow of modifiers into the crystallizer, the powder mixture was sintered in a vacuum furnace after being filled into the tubes during continuous pumping by a foreline pump.

At a rate of introducing a tubular modifier into the mold ν = 0.13 m / min, the total mass of the introduced modifier was Mm = 132.5 grams per minute, which corresponded to Mm = 0.00033 Ms. The total number of materials introduced into the mold was (Mm + Mx) = 0.00853 Ms, while the quantitative ratio of macrochillers and modifiers introduced into the mold was Mm = 0.04 Mx.

After casting, transverse templates were cut off from continuously cast billets, on which the degree of segregation heterogeneity was studied. The segregation coefficient was calculated, defined as the ratio of the content of the element in the axial zone to the content of the element in the metal (calculated as the average content over the cross section of the template based on N = 24 or N = 44 measurements). It was found that the segregation coefficient of manganese and phosphorus in continuously cast billets obtained by the above technology is CL = 0.98 and CL = 0.92, respectively. According to the description of the invention SU 1813114, the achieved values of the segregation coefficients were Cl = 1.11-1.17 for manganese and Cl = 1.47-1.52 for phosphorus. Ideal is the distribution of chemical elements with CL = 1.0. Therefore, the CL values achieved in the above experiment are preferred over the CL values described in the prototype of the present invention.

Since the description of the invention SU 1813114 does not provide data on the structure of continuously cast billets obtained, a comparative analysis of the dispersion of the structure (as well as chemical heterogeneity) was carried out on the templates of continuously cast billets obtained both by the technology adopted by NTMK and the proposed method. According to the technology adopted by NTMK, neither macro-refrigerators nor modifiers were introduced into the CCM mold. A comparative analysis showed that the experimental blanks are distinguished by grinding dendritic structure. The central porosity is approximately the same in both cases - 2.0 points. The degree of segregation heterogeneity in the pilot blanks was lower than in the comparative blanks, as illustrated in FIG. 1, which shows the carbon distribution over the cross section of the transverse template of the continuously cast blank.

The mechanical properties of rails made from an experimental billet obtained by the above method were higher than the mechanical properties of rails obtained by comparative technology. With approximately the same values of σ _B = 1030-1040 N / mm ² , the plastic characteristics of the experimental samples are increased: elongation δ = 13% (in comparative samples δ = 11%); the impact strength also increased: a _K = 16-18 J / cm ² (versus a _K = 14-15 J / cm ² in comparative rail samples).

Example 2. In the converter shop of the Nizhny Tagil Metallurgical Combine smelted rail steel grade K76F chemical composition: C - 0.76 wt.%, Mn - 0.9 wt.%, Si - 0.36 wt.%, P - 0.01% , S - 0.011%, Cr - 0.02%, Ni - 0.05%, the rest - Fe and impurities. Melted steel liquidus temperature: Tlемой1464 ° С. Casting was carried out in a mold with a cross section of 300 × 360 mm. The casting speed was 0.44 m / min, which corresponded to the mass of the cast steel Ms≈370 kg per 1 minute. During the smelting process, a macrocooler made of an iron-nickel alloy (36% Ni, the rest Fe) in the form of a tape 2.2 mm thick (80 mm wide) and sealed in a 0.3 mm thick stainless steel tubular shell modifying boron-containing was simultaneously introduced into the caster of the continuous casting machine. composition mixture: FeB - 46 wt.%, Fe ₂ B - 33%, FeSi - 3% and 18% carbonyl nickel. The density of the packing of the powder mixture was 8.6 g / cm, which corresponds to 0.86 grams of boron in 1 cm of the tube. The total weight of one centimeter of the modifier (including the tubular casing) was 10.2 grams. To ensure a uniform flow of modifiers into the crystallizer, the powder mixture was sintered in a vacuum furnace after being filled into the tubes during continuous pumping by a foreline pump. The liquidus temperature of the macrochiller was T≅1455 ° С, and that of the modifier was ~ 1420 ° С. Both the macro-refrigerator and the modifier were introduced into the mold with the same speed ν = 0.13 m / min, which corresponded to the mass of the introduced macro-refrigerator Mx = 0.179 kg per 1 minute and the mass of the introduced modifier Mm = 0.132 kg per 1 minute. In this case, the amount of MX refrigerant introduced into the crystallizer satisfies the relation MX = 0.00048 MS, where MS is the mass of steel entering the mold. The amount of modifier Mm introduced into the mold satisfies the relation Mm = 0.00035 Ms. The mass of the modifier Mm and the mass of the macro refrigerator Mx were related by the ratio Mm ≈ 0.7 Mx, and their total number (Mm + Mx) was 0.00083 of Ms.

The introduction of a macro-refrigerator and a modifying mixture led to a significant increase in the uniformity of the distribution of chemical elements over the bloom section. It was found that the segregation coefficient of manganese and phosphorus in continuously cast billets obtained by the above technology is CL = 1.02 and CL = 1.11, respectively. According to the description of the invention SU 1813114, the achieved values of the segregation coefficients were Cl = 1.11-1.117 for manganese and Cl = 1.47-1.52 for phosphorus. Thus, the CL values achieved in the above experiment are preferred over the CL values described in the prototype of the present invention.

The macrostructures of continuously cast billets with a cross section of 300 × 360 mm (comparative and experimental) are shown in FIGS. 2 and 3. On the comparative blank (FIG. 2), macrostructure defects (axial segregation and friability) concentrated in the axial zone are clearly visible. As a result of the introduction of a macro-refrigerator and a tubular modifier, an improvement in the macrostructure (in particular, dispersal of axial segregation) was achieved, as can be seen in Figure 3.

From the above continuously cast billets were obtained railway rails (Fig.4-5). It is clearly seen that in the rails obtained from the experimental blanks (Figure 5), the dispersion of the structure is increased, the degree of concentrated axial segregation in the neck of the rail is reduced (marked by an arrow).

It was also established that the central porosity of the pilot cast billet corresponded to 1 point, axial segregation to 2 points, which is not only comparable with the indicated characteristics obtained in steelmaking according to the accepted technology, but surpasses them in central porosity. The degree of segregation heterogeneity in the pilot blanks was lower than in the comparative blanks, as illustrated in FIG. 6, which shows the distribution of carbon over the cross section of the transverse template of continuously cast blanks. A decrease in the degree of segregation heterogeneity in the experimental blanks was observed for other elements. The average boron content in the test pieces was 0.005%.

Example 3. In the converter shop of the Nizhny Tagil Metallurgical Combine smelted rail steel grade K76F chemical composition: C - 0.79 wt.%, Mn - 0.9 wt.%, Si - 0.36 wt.%, P - 0.01% , S - 0.011%, Cr - 0.02%, Ni - 0.05%, the rest - Fe and impurities. Melted steel liquidus temperature: Tlла1462 ° С. Casting was carried out in a mold with a cross section of 300 × 360 mm. The casting speed was 0.46 m / min, which corresponded to the mass of the cast steel Ms≈390 kg per 1 minute. During casting, the melt temperature was forcibly reduced in the continuous casting mold due to the simultaneous introduction of a macro-refrigerator tape with a cross section of 1.5 × 80 mm ² and a modifier tape with a cross section of 3.0 × 20 mm ² . The chemical composition of the modifier tape: C - 0.65%, Mn - 0.75%, Si - 0.38%, Cu - 0.015%, Ni - 0.045%, S - 0.013%, P - 0.034%, B - 0 , 4%, the rest is Fe and impurities. The liquidus temperature of the material of the modifier tape was T = 1443 ° C, which is approximately 30 ° C lower than the liquidus temperature of the cast steel. The chemical composition of the macro-refrigerator tape: C - 0.55 wt.%, Mn - 0.78%, Si - 0.51%, B - 0.4%, the rest - Fe and impurities. The liquidus temperature of the material of the macro-refrigerator tape was T = 1449 ° C, which is approximately 20 ° C lower than the liquidus temperature of the cast steel. The rate of insertion of the macro-refrigerator tape and the modifier tape was the same. Therefore, the modifier tape, which had an increased thickness, penetrated much deeper into the melt and contributed to the modification of the deep layers of the melt. The input speed of both tapes was 2.35 m / min, which corresponded to the number of input tape-macrochiller Mx = 2.2 kg per 1 minute and the number of input tape-modifier Mm = 1.1 kg per 1 minute. The total amount of materials introduced into the mold (Mx + Mm) = 3.3 kg per 1 minute, which was (Mx + Mm) = 0.085 Ms. In this case, the quantitative ratio between the mass of the modifier Mm and the mass of the macro-refrigerator Mx corresponded to Mm = 0.5 Mx.

After casting, transverse templates were cut off from the experimental continuously cast billets, on which the degree of segregation heterogeneity was studied. It was found that the segregation coefficient of manganese and phosphorus in continuously cast billets obtained by the above method is Kl = 1.06 and Kl = 1.37, respectively. According to the description of the invention SU 1813114, the achieved values of the segregation coefficients were Cl = 1.11-1.17 for manganese and Cl = 1.47-1.52 for phosphorus. Thus, the CL values achieved in the above experiment are preferred over the CL values described in the prototype of the present invention.

Studies have also shown that, despite the relatively low boron content in the experimental billets (up to 0.0018%), in the axial zone of the experimental continuously cast billets obtained by the above technology, an increased dispersion of structural components is observed, the macrostructure of the billet has become more uniform. The degree of segregation heterogeneity in the pilot blanks was lower than in the comparative blanks, as illustrated in Fig. 7, which shows the carbon distribution over the cross-section of the transverse template of continuously cast blanks.

Claims (9)

1. A method of producing a continuously cast billet, including steel smelting, refining, modification, casting into a crystallizer and the introduction of macro-refrigerators in it, characterized in that at the same time as macro-refrigerators (Mx) in the form of molten tape steel elements from 0.4 to 2.8 mm thick modifiers (Mm) are introduced into the mold, and the total number of macro-refrigerators and modifiers is (Mm + Mx) = (0.0004 ÷ 0.009) Ms with the ratio Mm: Mx ≤ (0.003-0.7), where Ms is the mass of steel in the mold . 2. The method according to claim 1, characterized in that the elements of steel with liquidus temperatures of 5-35 ° C lower than the liquidus temperature of the cast steel are used as macro-refrigerators. 3. The method according to claim 1, characterized in that the modifiers are introduced in the form of tapes and / or plates with a thickness of 0.4 to 2.8 mm. 4. The method according to claim 1, characterized in that the modifiers are introduced in the form of powder mixtures in sealed tubular shells with a wall thickness of the shell from 0.15 to 0.8 mm 5. The method according to claim 4, characterized in that the tubular shell is made of stainless steel, the liquidus temperature of which does not exceed the liquidus temperature of the cast steel. 6. The method according to claim 1 or 3, characterized in that the macro-refrigerators and / or modifiers contain manganese and silicon in an amount exceeding up to 7 times their content in cast steel. 7. The method according to claim 1 or 3, characterized in that boron is introduced into the composition of macro-refrigerators and / or modifiers, while in tape macro-refrigerators and / or modifiers, its content ranges from 0.07 to 0.45 wt.%. 8. The method according to claim 4 or 5, characterized in that the composition of the modifiers in the form of powder mixtures in sealed tubular shells introduce boron in an amount of from 1 to 15 wt.%. 9. The method according to claim 1, characterized in that smelted high carbon steel with a carbon content of from 0.65 to 1.1 wt.%.

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