DD148736A5 - CONTINUOUS STEEL MOLDING PROCESS - Google Patents

Abstract

Cast steel product, in particular steel product produced by continuous casting, with an equal distribution of constituents and the associated production process. The object of the invention is to provide improved properties and cost-effective production compared to known products, while its object is to provide a continuous steel casting process and a steel product which ensures a rapid change in the orientation of the hardening steel, and a particularly uniform one Distribution of manganese, oxygen, sulfur and carbon is characterized. According to the invention this is achieved by the steps of the process: a) pouring molten metal b) cooling the mold c) stripping the strand d) cooling d. cast bar, and in stage e, stages a to d are controlled so as to produce an endless cast steel rod or steel strand having a lack of microsegregation and a particular uniform distribution of components and contaminants, measured in cross-sectional profile ( Fig.1).

Description

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Gas steel product and method for its production Field of application of the invention

The invention relates to a new cast steel product, in particular a continuous product produced by continuous casting with a uniform distribution of constituents and a process for its preparation.

Characteristic of the known technical solutions

A desirable fourth feature of steel in its as-cast state is known to be as uniform a distribution as possible of its components and impurities normally found in steel within the steel product. The term "component" is used here in the usual sense, i. h ,, under a "component" is a component of a chemical system or phase. or to understand a combination of phases that form a chemical system that occur in a characteristic configuration in a ligation microstructure, while "impurities" are to be understood as elements or compounds whose presence in a material or product is undesirable. The term components thus includes here the substances or materials combined into a chemical system to produce a special steel produced by casting.

However, the term components does not include the impurities or undesirable ones. Elements or compounds present in the cast metal. In any case, segregation or precipitation of the components in cast steel makes it suitable for subsequent processing, such as forging or hot forming or

1? 8 80- 877Γ> 7 lbs

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Rolling out into a rod and warping to a wire less suitable. As used herein, the term "segregation" or "excretion" is also used in the usual sense, ie. tu, the term "segregation" or "precipitate" is a term used with reference to the non-uniform distribution or concentration of components (or impurities) induced during the solidification of the metal. A concentration or accumulation of For example, impurities in various positions within the metal are referred to as segregation or precipitation in the literature. The segregation that occurs between the arms of dendrites is referred to as low segregation or microsegregation, therefore, the composition within a single crystal is variable can. Macrosegregation occurs around primary or secondary voids or cavities, such as voids and porons, as well as in similar districts or areas, and often appears in the form of protruding lines that have a clearly upright or hanging conical shape, which is evident when segmenting and etching barron or blocks »Segregationζoneη tend to occur in the middle areas of the product obtained by potting and normally within the part mainly occupied by equiaxed crystals. · Micro segregation can occasionally be overcome by tempering or freshness. whereas macroso-aggregation outlasts the subsequent heating and processing stages »So-called blowhole segregates occur around the so-called blowholes. In normal segregation in steel accumulates

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the components or constituents (solutes) in the iron (solvent) excreted from the solidifying liquid settle on the advancing solid-liquid contacting surface so that the lowest melting point components or ingredients concentrate in the final consolidating fractions, whereas this is reversed in reverse or inverse segregation, and the liquid with a high concentration of solute is trapped between the dendrites, causing a decrease in the concentration of solutes from the ingot or block surface towards the center. An inverse segregation then consists in a concentration of constituents or impurities to a higher degree near the outer surfaces (in comparison to the inside) of a billet or block, or casting,

There are known methods of casting steel in which steel products having a relatively high segregation degree of impurities and alloy constituents within the cast steel are obtained. Due to the high concentration of components and impurities in the steel, inverse or reverse segregation usually occurs. Such nonuniform distribution of impurities and / or components within the cast steel makes it desirable to reduce the total amount thereof within the steel so that subsequent processing of the cast steel does not result in unacceptable internal characteristics and surface characteristics in the product to be made of cast stainless steel , However, reducing the total amount of contaminants usually requires a costly extra

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Refining or refining the steel prior to casting, and is sometimes impractical or impractical from a commercial point of view, while occasionally the addition of special components or components (including alloying elements) is desired or necessary.

Among the impurities and alloying elements within the steel that tend to segregate in the case of prior art products are sulfur, oxygen, phosphorus, manganese, silicon, and carbon. "Segregation or precipitation of these elements is of great importance the products are lessor geoignot from a commercial point of view. "For example, significant segregation can induce uneven tensile or breaking strength within the steel, making it less suitable for further processing into wire." Excretion of gaseous contaminants may become too porous Bezirkon close to the surface of the molded product, which cause among other disadvantages, an insufficient surface quality of sheets. Reference is made in this connection to B. Ce Whitmoxo and J «Y /. Hlinka "Continuous Casting of Low-Carbon Steel Slabs by tho Hazelett Strip-Casting Process", Open Hearth Proceedings, 1969 ·

Severe microsegregation of manganese causes problems in many end-products made from ingots obtained by continuous casting due to the large influence on the Auatenite to pearlite / bainite-martensite transformations

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often obtained high strands of manganese in the core, which promotes the local formation of Martens it during casting, resulting in frequent breaks during the subsequent wire drawing process.

This problem has been known for a long time, but only a few publications have been found which communicate production data obtained in practice. A related study by Hans Van Vuuren of South African Iron and Steel Industrial Corporation, Ltd. * (a copy is on pages 306 to 334 of the "Steelmaking Proceedings" reference, Volume 61, Chicago Meeting, April 16-20, 1978, describe an attempt to control the microsegregation as well as the effects of the process in the case of a rod-shaped final product,

Van Vuuren concluded that the occurrence of central martensite can normally be avoided in some steel wire rods by limiting the total concentration of manganese to a maximum of 0.75%, phosphorus to a maximum of 0.020% and monitoring the cooling during the cooling stage following the rolling process. No milk segregation values are reported for the blocks made by continuous casting (it is assumed that ISCOE begins by continuously casting a 205 mm x 315 mm block on a Concast Bloom machine, but the bar end product was analyzed and found to be manganese -Microsegregation values are between 101.5 to 139.0 % of the baseline analysis, due to the pronounced thermal diffusion between the time of pouring and the time of pouring

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Weighing out, it is believed that the skeletal levels of the manganese in the cast block have been considerably greater than in the rod-shaped final product.

To date, among the known methods of the prior art that deal with the solution of problems due to segregation (ζ. Β "wire break), the repair (z _e as homogenization) of intermediates (ζ. _Β β rods or bars ) instead of the prevention of occurrence of segregation during the casting process "one reason for this is based entirely OFI ¹ QnSichtlieh that it is considerably more difficult to control the performed in the practice of continuous casting process.

In the known Barron or block casting processes, segregation occurs as the molten steel slowly solidifies, with the impurities entering the upper part of the ingots or blocks by gravity separation, in the case of processes leading to higher quality products lead, is occasionally occurring concentrated layer of impurities and / or solidification "lunkem in the upper part of an ingot or block removed by physical means, skinned or beveled _s before the cast rod is vseiterverarbeitet" vaults, for example, to the work "Bacent Developments in Machine Scarfing of Continuous Cast and Rolled Steel ", published in the journal" Iron and Steel Engineer ", January 1978, pages 68 to 71 and US Pat. No. 4,155,399" Col. 1, lines 61 to 68 "

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Further, there are known methods of continuously casting steel that have been developed to avoid machining a large number of ingots or blocks and the need to remove the topsheet. In the case of the most common and commercially most conventional method of continuous casting of steel by the Applicant, the molten metal is poured into a vertically disposed mold with an open end consisting of a highly conductive material, for example copper, in which circulates for cooling water. As the outer surface of the metal solidifies to form a skin or shell of solidified or solidified steel adjacent to the mold rim, the strand or strand of steel is slowly withdrawn from the bottom of the mold while molten metal is continuously poured into the upper portion of the mold. This type of process is sometimes referred to as the Junghans type or Junghans-Eossi type continuous casting system and has been successfully practiced. (See, for example, an earlier Junghans US Pat. No. 2,135,183) Case of certain applications, it will be necessary to remove a surface. Reference is made in this connection to US Pat. No. 4,155,399.

In the case of a Junghans type method, the mold may oscillate or oscillate vertically along a comparatively short path so that the mold moves with the strand during each downward oscillation, thereby increasing heat transfer during the periods of time; where no relative movement

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between the beach or the strand and the shape takes place. Such back and forth conditions or oscillations increase the potential for casting, but often cause undesirable vibrational or oscillatory sites or rings extending around the casting on its surface.

Normally, when the strands leave the mold, water streams are directed to the surface of the semi-solidified strands to complete their solidification. "In order to reduce the vertical height of the building housing the Junghans-type casting machine, it is known To use guide vias to divert the strand through an angle of approximately 90 ° over a radius of, for example, 12.20 m, and then redirect the strand so that ex "assumes a horizontal position for cutting or for subsequent processing To avoid twice deflecting the strand in this manner and to install a caster in a smaller building, curved shapes have been developed, in which case the cords emerge from the shapes in accordance with the desired curved path and then the cords in one Deflection or bending step to a horizontal orientation for cutting to be aligned at the end of production «,

A notable presentation of the traditional continuous steel casting process can be found in the December 1953 issue of Scientific American Magazine entitled "The Continuous Casting of Steel" by L ₀ V. Gallagher and B "S. Old, Volume 209 ,. 6, pages 74-88.

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Thus, in a prior art casting process using a vertical mold, which would normally require a five-story or higher-floor building, there would be no rapid change in the orientation of the solidifying steel and, in this process, the molten metal in the mold Center of the strand may temporarily remain in a horizontal position, as shown for example in US Patent 3,542,115. Contaminants thus have the opportunity to float upwardly during progressive solidification, and segregation generally occurs which may occasionally occur in a (long) cross-section of a prior art cast bar of size 10.16χ10.16 cm in the form of a segregation line that appears about 2.54 cm from the inner Badius of the strand out.

On a research scale, steel has also been cast continuously into relatively horizontal shapes, using a twin-belt caster that operates in principle similar to the earlier Hazelett Strip Casting Corp * machine of the type disclosed in U.S. Patent No. 2,640,235 Type (mentioned in the Whitmore and Hlinka Piblication) "These two authors stated that due to the influence of gravity and about 20 ° of the horizontal position of the steel strand during solidification in the case of these research experiments, the impurities within the steel tend to rise to form a substantial zone of segregated material near the surface of the cast material. These two authors stated that coupled with the surface an oxide attack state

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internal oxide segregation was found during macroetch testing of cross profiles. Although the oxide segregation is progressively variable, the profile was similar in the case of all slabs or slabs cast, and the authors concluded that it is apparent from these data that oxide segregation was strong enough to have poor sheet surface quality to cause "a number investigated possible solutions of the problem, ζ ', B _e a concentration in the elimination of the form-Beck slag, the use of stationary, water-cooled copper edge dams, the use of turned ~ dipped supply lines and the like" _o However, the authors noted that all these attempts to solve the problem were unsuccessful ,. It has been suggested that greater concentrations of segregating oxides in the solidifying plates or .Rohb ram at a time eingefan & ene, to which the upper skin was about 1.25 to 1.90 cm thick _e The authors concluded that a casting in at an angle of 20 ° to a metallurgical unacceptable sheet metal product made from either Al-killed or vacuum-treated steel, since no way could be found to remove these oxides, and because the inclusions in direction to the upper part of the cast block segregated _o the authors suggested to return to the procedure of the prior art, in which the mold (Junghans-type) is arranged in a vertical position as a way _s in order to overcome the segregation problem *

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It is also believed that the off-centered and segregated distribution of the components or components and impurities also leads to unpredictable changes in subsequent trials in further processing such as hot rolling of the material.

Object of the invention

The object of the invention is to provide a cast steel product and a process for its production, which has improved properties compared to the known products and can be produced more cheaply.

As rleg ung the Weeena of the invention

The invention is based on the object, a continuous Stahlgießverfahren with the process steps

(a) pouring molten metal into a traveling closed mold which is produced by means of at least one band which seals the mold over part of its length;

b) cooling the mold whereby the molten metal begins to solidify on the mold walls to form a skin of solid metal around a molten core

c) removing the at least partially solidified cast rod or strand from the outlet to the closed part of the mold and

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d) cooling the cast rod or strand by direct and / or indirect impact of the supplied from nozzles or showers coolant

to create a steel product which ensures a rapid change in the orientation of the hardening steel and is characterized by a particularly uniform distribution of manganese, oxygen, sulfur and carbon »

According to the invention, this object is achieved by controlling steps a to d in stage e such that an endless cast steel rod or steel strand is produced having a lack of micro-segregation and a particularly uniform predisposition of components and impurities measured in the cross-sectional profile , having",

Advantageously, the e-stage is controlled so as to obtain a maximum average sulfur content variation of less than about 0.004 % = 40 ppm as measured in cross-section.

In another embodiment, the step e indicates the average sulfur content calculated from arbitrary empirical data whose standard deviation is less than about 0.001 % .

Preferably, step e will receive a maximum variation in average oxygen content of less than about 0.002 % = 20 ppm, as measured in cross-sectional profile.

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Conveniently, the step θ is to provide a maximum variation in the average carbon content of less than 0.01 % = 100 ppm as measured in the cross-sectional profile.

It is particularly advantageous if, for stage e, there is provided generation of average carbon content calculated from arbitrary empirical data whose standard deviation is less than about 0.004%.

More advantageously, the e step produces a maximum variation in the average sulfur content of less than about 0.002 % s 20 ppm.

According to a further feature of the invention, the step e achieves a maximum variation of the manganese content of less than about 400% of the average manganese content,

Preferably, step a includes the use of a closed mold created by a peripheral recess in a rotating casting wheel and a band which seals the recess over part of its length.

Preferably, step a includes the use of a continuously advancing closed mold, which is produced by at least one endless moving surface in conjunction with other sealing surfaces to form a closed mold.

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The process according to the invention is characterized in that at step e the maximum variation in average oxygen content is less than about 10 ppm,

Preference Figure Q is an endless moving bath-type surface mold intended for continuous casting of steel bars or steel strands for commercial use, wherein the cast bar or strand is rotated over a radial arc of substantially more than about 90 ° during solidification, and wherein the Uniformity of the formation of concentrations of segragierten components and impurities is controlled to such a degree that a, from a commercial point of view, suitable steel rod or steel * strand is generated.

It is advantageous that the rotation of the casting wheel changes the orientation of the molten steel in the mold sufficiently rapidly to avoid a conspicuous flotation and segregation of impurities in the steel.

It is also according to the invention that at step e, the endless cast steel bar or steel strand for a given molten steel has a tensile strength which is at least 10 % greater than the tensile strength of a steel bar or steel strand cast from the same melt on a similar caster is _e

Advantageously, the arc is greater than about 180 °.

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The steel bar produced by the method of the invention is characterized in that the cross-sectional profile has a maximum average oxygen content variation of less than 25 ppm.

Preferably, the cross-sectional profile has an oxygen segregation standard deviation of less than about 0.001% a 10 ppm. "

In another embodiment, the cross-sectional profile has an oxygen segregation standard deviation of less than 0.0005% ss 5 ppm.

According to the invention, the transverse profile has a maximum average variation of manganese content of less than about 275% of the average manganese content.

Advantageously, the cross-sectional profile has a maximum average sulfur content variation of less than about 0.0Of%, the cross-sectional profile having a standard sulfur segregation control of less than about 0.0015 % .

In another feature, the cross-sectional profile has a maximum average carbon content variation of less than 0.01%, with a carbon segregation standard deviation of less than about 0.004 % .

A further embodiment provides that the tensile strength is at least 10 % qtqQq ^ and the elongation at least 10 % greater than the tensile strength or elongation of a steel

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Bar, which is cast from the same melt by means of a known foundry »

Preferably, the cross profile has a maximum average oxygen content variation of less than 0.0025 % -25 ppm, a maximum sulfur content variation of less than 0.004% = 40 ppm, and a maximum average carbon content variation of less than 0.01 % = 100 ppm on.

The invention enables the production of a cast steel rod or a cast steel rod which is characterized by a new lack of segregation of manganese, oxygen, sulfur and carbon as compared to a prior art rod or rod. The invention enables the Herstollung a cast steel bar or a cast steel rod _t that is or "the characterized by a particularly uniform distribution of manganese, oxygen, sulfur and carbon," A cast according to the method of the invention steel rod (or bar) has steel on which , a (long) cross-sectional profile is examined for macrosegregation, a maximum average oxygen content variation of less than about 20 ppm (0.0020%), and an acidulence segregation standard deviation of less than about 8 ppm (0.008 %) in the case of samples with also shows a maximum average deviation in sulfur content of less than about 0.03% (40 ppm) and a sulfur segregation standard deviation of less than about 0.001 % (10 ppm) in the case of a sample of about .05 % oxygen

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0.02 % sulfur and a maximum average carbon content deviation of less than about 0.01 % (100 ppm) and a carbon segregation standard deviation of less than about 0.004 % (4-0 ppm) in the case of a sample at about 0.185 % Carbon and improved tensile strength and elongation in the case of the molded product,

Correspondingly good results are to be expected in the case of Si, P, Cr and other alloying elements which are normally used in steelmaking. A microeggregation analysis was carried out for C, Mn, S, Cr and Si by means of an electron microsample. The results obtained gave a much lower microsegregation of manganese compared to samples obtained by the known Concast method. For example, batches of molten steel containing about 0.46 % carbon and about 0.98% manganese were potted both by the method described herein and by the well-known Concast method of the prior art. Samples of the cast bars were cut in the vertical direction, and small samples were taken from the same places, about half the distance from the edge toward the center. As a result, neither the best nor the worst districts were selected for comparison. The small samples were then used for an electron microscopic examination and analyzed for the purpose of determining the concentration of manganese along an arbitrary line of about 1800 microns.

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This process is well known and believed to be the easiest method of determining microsegregation in metals. The known method is based essentially on the bombardment of a specimen with a beam of high-energy electrons of small diameter, which causes the specimen to emit characteristic X-rays according to the concentration of the elements present. The X-rays then become analyzed by diffraction with a crystal to select one element at a time, its intensity being determined by means of a suitable detector. The concentrations of a particular element can be determined by comparing the relative intensities of the X-ray generated by an element present in the sample with a known standard. In order to achieve maximum accuracy, about 1/2 of a percent, the ratio can be corrected for the absorption and fluorescence of the emitted X-rays. "Alternatively, the average intensity level can be considered to be the base concentration produced by a normal chemical Analysis and that the deviations of the intensity directly represent deviations from the basic concentration

When this latter method is used to compare a number of samples, it has been found useful to assign a value to each candidate indicating the average intensity of the pronounced deviations and thus the average concentration deviation from the base level. This value may be the microsegregation value are expressed in terms of percent of the base tone zone,

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In the case of the present comparison, the base analysis of the examined sample gave about 0.98 % manganese. These results indicated that the steel bar produced by the prior art had a manganese microsegregation value expressed as a percentage of the base analysis of about 300%, whereas the manganese microsegregation value of the cast bar produced by the method of the present invention was less than 175%

An essential feature of the present invention is that the new product can be made using a known prior art casting apparatus using process methods that are within the experimental experience of those having ordinary experience in the art ,

The preferred method of carrying out the invention is to produce a moving domed shape by rotating a casting wheel with a peripheral recess on its central axis and moving a strip along its length in contact with the peripheral recess on the upper part of the casting wheel. Moving the belt and casting wheel in conjunction with about the lower part of the casting wheel and moving the belt from the casting wheel (creating a type of continuous surface-type moving mold), pouring molten steel into the curved or arcuate shape, cooling the mold below Inducing a solidification of the molten steel in the arched form, peeling off the cast. Bar or cast bar from the arched shape, usually additional cooling of the cast bar

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or the cast bar by application of an aftercooler after the poured material has exited the closed portion of the mold, and progressive alignment of the cast bar or cast bar as it travels away from the domed form. For example, reference is made to US Pat 3,623,535 and U.S. Patent 359,348.

The invention thus relates to the production of a cast steel product having improved properties such as the production of a new, continuous cast steel rod or a cast, continuous steel rod characterized by a lack of a normally usual degree of segregation or a reverse or inverse segregation of impurities or In-rod or Bar Ingredients The sputtered steel rod performs better than comparable prior art rods for subsequent further processing, for example, rod-to-wire and wire-to-wire or die-hot, z _e B forging. The process for continuously casting a steel product has improved internal properties.

Ausführungsbe ispiel

The invention will be explained in more detail below with reference to an exemplary embodiment. In the accompanying drawings:

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Fig. 1: a schematic representation of an example of a prior art plant suitable for producing a cast product according to the invention, having a casting machine with a rotatable casting wheel defined by a peripheral recess and an endless belt forming part of the Length of the recess to form a closed mold covered in this section;

Fig. 2 is a graph showing the sulfur distribution in a steel bar cast according to the method of the invention;

Fig. 3 is a graph showing the distribution of oxygen in a steel bar cast according to the method of the invention;

Fig. 4: is a diagram showing the distribution of oxygen in a steel bar cast according to the known Hazelett double belt method;

Fig. 5? a diagram illustrating the oxygen distribution in a steel bar, which was cast according to a further method of the prior art, d. h, the so-called Junghans-type method, and more specifically using a Concast machine of the type which is successful in practice;

Fig. 6; a diagram illustrating the carbon distribution in a steel rod cast according to the present invention;

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Fig. 7 is a graph comparing the tensile strength of a new cast steel product according to the invention with another cast steel product made by a prior art process;

Fig. 8 is a graph illustrating X-ray intensity monitoring due to micro-segregation of manganese in a steel bar cast according to the method of the invention;

Figure 9s is a graph depicting x-ray intensity monitoring due to microsegregation of manganese in a steel bar cast according to the prior art Concast method. "

The casting apparatus shown in FIG. 1 is one having a casting wheel 10 for producing a product of the invention. The apparatus is similar to the apparatus known from, for example, US Pat. No. 3,623,535. A casting wheel 10 defines a peripheral recess G within the wheel 10, which is covered over part of its surface by an endless flexible belt or belt 11 to form a closed mold M. The flexible band 11 is engaged with a part of the periphery of the casting wheel 10 by Trägerraalzen 12; 13; 14 * and moves with the casting wheel 10 as it rotates. "Near the belt support roll 12, where the closed mold M begins, molten steel is removed from a casting machine.

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head or funnel 16 introduced into the mold M through an opening I6a. According to a particularly advantageous embodiment of the invention, all outer surfaces of the casting wheel 10 and belt 11 are continuously cooled by spraying a cooling liquid, wherein the outer portion of the recess 6 and the belt 11 is cooled by cooling jets of spray nozzles, not shown, which are in headers or manifolds S2; S3; S4 ·, and wherein the inner portion of the peripheral recess 6 is cooled by irradiation with a cooling liquid from nozzles in the head piece S1. The cooling liquid ejected from each nozzle or the cooling liquids ejected from groups of nozzles along the inside of the peripheral recess has been individually controlled, so that the volume of the cooling liquid that is ejected can be changed, which in turn can change the speed at which the metal is cooled within the mold M. The supply of cooling liquid to the nozzles or groups of nozzles can also be controlled by controllable valves, thus enabling the spraying to be started and the supply of cooling liquid to be interrupted, as well as a change in the total volume of the cooling flow. For example, reference is made to the cooling arrangement described in US Pat. No. 3,279,000 ,

Beyond and above the belt support roller 14 is an extended turn or turn portion 18. This portion 18 serves to align the cast steel bar B which is withdrawn from the peripheral recess G of the casting wheel 10 after the rod B leaves the closed portion of the mold M. , The bending section 18 has

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a plurality of carrier guide rollers 19 which are mounted on a frame, not shown. Lateral, also not shown Führungsvjalzen can also be used in the bending section 18 to limit the cast steel bar B to an approximate vertical plane. Although the carrier guide rollers 19 may either be driven or may not be driven, it has been found to be advantageous that at least a portion of the carrier rollers 19 be driven to assist alignment of the cast bar B.

In a particularly advantageous embodiment of the invention, an aftercooler 21 is disposed above and adjacent to the belt-carrying roller 14 to direct a direct flow of cooling fluid onto the cast steel bar B exiting the domed mold M.

In operation of the system according to the method of the invention, the casting wheel 10 is set in motion in the counterclockwise direction, and molten steel is poured from the hopper 16 through the opening 16a into the closed mold M which is between the peripheral split G of the casting wheel 10 and the flexible band 11 is formed. Molten steel is thereby poured into the mold M in a controlled manner by a method known for the casting of ferrous and non-ferrous metals, at a rate such that the rotational movement of the casting wheel 10 causes the bar B to be in the shape M. away from the opening 16a, as fast as the molten steel flows through the opening 16a, to keep the surface of the basin of molten steel at a constant level at the

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Introductory office of Form M to hold. The exit end of the spout or orifice 16a is as close as possible to the entry port of the mold M to allow the molten steel to flow directly from the spout into the basin of molten metal in the mold M.

When the molten steel is fed around the casting wheel 10 within the mold M, cooling liquid is directed directly against the mold M from the nozzles in the device S1 and the nozzles of the other devices S2; S3; S4 and the amount of cooling liquid supplied to the belt 11 and the casting wheel 10 are set as desired to control the cooling rate of the molten metal.

The preferred embodiment of the invention has a state of very uniform cooling over and along the longitudinal axis of the cast bar B or cast bar. Dehydrated cooling and solidification of the molten metal at the surfaces of the casting wheel 10 and belt 11, thereby forming a skin or shell of solidified steel having an equiaxed grain structure, are initially performed is caused. Continuous extraction or removal of heat from the partially solidified rod B or the partially solidified rod causes solidification of the metal within the molten core progressively and uniformly (including a uniform manner at each point around the periphery) to produce a dendritic or substantially equiaxed structure, depending on the overheating of the steel from the shell

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or shell towards the center of the consolidated steel table B ·

Dor steel, which has entered the form M in the form of a molten metal in the upper portion of the casting wheel 10, moves in a downward direction about the lower portion of the casting wheel 10 and then in an upward motion until it reaches the closed portion of the mold M. passes near the belt support roller 14 passes through the Nachkühlstrahlen from the nozzles in connection with the device and reaches a guide roller 15 _{f in} front of the rod B is continued by the casting wheel 10.

According to a preferred embodiment of the invention, the temperature of the outer surface of the peripheral skin of the solidified steel as it emerges from the closed section of the mold M does not exceed a temperature of about 1370 ⁰ C (2500 ^° F), but the temperature does not at is less than about 1037 or 104-9 ⁰ C (190 or 2000 ⁰ F).

The bar leaving the casting wheel 10 has a shape corresponding to the curvature of the mold M, for which reason the bar B is progressively aligned by a progressive increase in the radius of the bar B as it moves through the extended bending section 18. The guide rolls 19 support the bar B thereby and guide it through the Umwoge- or Ausrichtabschnitt 18 above the casting wheel 10, wherein at least one pair of Fübrungsvjalzen 19 is preferably driven to pull the rod B over its length from the casting wheel 10 "The melted

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Core of the rod B is completely solidified by the time it has passed at least the last spray from the last nozzle on the device 21, to ensure that the rod B is fully solidified before it reaches a point on a level with the level of the pool of molten metal at the entrance to the mold M. As a result, the molten metal in the core of the rod B does not flow counter to the molding movement through the unconsolidated rod center creating a voids or pore in the center of the rod 3 B. The rod B is thereby also solid and metallurgical before entering the bend portion 18, and its temperature just before turning can also be adjusted by adjusting the volume of cooling fluid supplied by the device 21 to control the internal stresses of the rod B during alignment.

In the illustrated embodiment of the casting wheel 10, the mold M has an approximately trapezoidal shape with a small expansion in the inner portion of the peripheral recess G and a larger extension adjacent to the belt 11. This means that a steel bar B formed using a typical casting apparatus 10, has a maximum width of approximately 66.675 mm, a minimum width of 53.975 mm and a depth of 47.625 mm with an approximate radius of 0.635 cm connecting the smaller width to the two sides of the bar B. However, other bar sizes and bar shapes may also be cast if desired. For example, let

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according to the invention advantageously 12.19 cm -

Cast rods at a speed of approximately 13-411 m / min and approximately 2O, 57 cm ² rods approximately 10,668 m / min.

and about 20.57 cm ² bars at a speed of

It is believed that the new cast steel bars B of the present invention can be produced at a comparatively high linear velocity because the comparatively long length of the arcuate or curved mold M cooled by rapidly quenching cooling jets permits solidification despite the comparatively high rate of eotation of the casting wheel 10 , Furthermore, the relatively small radius of the casting wheel 10 causes the orientation of the molten steel to change rapidly as the bath 10 rotates, in contrast to the conventional continuous cast steel manufacturing processes heretofore practiced in which the hardening steel is horizontal or horizontal approximately horizontal orientation remains for a substantial period of time, so that impurities are allowed to float upwards during the process of solidification. It is believed that when a bar B having a comparatively small cross-section is cast according to the method of the present invention, the bar B is rapidly displaced by the refrigerant coming from the nozzles in connection with the devices S1; S2} S3; S4; 21 is rapidly solidified before significant segregation of constituents or contaminants can take place.

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The process of the present invention, wherein a relatively fast rotating casting wheel 10 having a relatively small diameter is sufficiently cooled to rapidly solidify contaminants before segregation and / or reverse segregation, thus produces the new cast steel product of the invention Properties that are substantially different from the properties of a cast steel made in prior art continuous casting or casting machines.

It is believed that the design or implementation of the wheel shape, the design or design of cooling water spray zones, and the comparison of the small cross-section of the cast rods enables a higher heat transfer compared to the previously known continuous cast steel manufacturing processes.

Some ideas of the high cooling rate or solidification result from the metallurgical sizes of the casting system. The metallurgical size is defined as the distance between the upper part of the liquid pulse in the mold and the point of complete solidification or solidification,

In the case of the process according to the invention, with a metallurgical size of about 4.57 m or less in the preparation of a 12.19 cm bar B at 10.67 to

13.41 m / min and in the case of a 20.57 cm bar B at a speed of 7.62 to 10.67 m / min worked »In the case of conventional continuous casting systems.

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Junghan3 type metallurgical sizes of about 15.24 m to 21.336 m are generally reported when casting ingots of a size of 10.16 χ 10.16 cm at a speed of 25 ^ to 305 cm / min. "Bs was found that in the case of the process according to the invention, the casting rods B produced according to the invention are completely solidified in about 25 to 30 seconds, it being understood that in the case of a rod of the Junghans type about 6 minutes are required until complete solidification.

It is believed that the high rate of cooling reduces the flow of liquid from higher concentrations of stripped material into the interdendritic channels and thereby reduces inverse segregation while the non-metallic impurities present in the liquid steel are nonuniformly distributed with the liquid freeze or freeze.

It is further believed that the rapid orientation change of the molten steel in moving wheel molds reduces the chances of segregation of contaminants in undesired positions within the cast rod. That is, to give an example, the cast rod is moved with its initially comparatively thin solidified shell or shell and a large centered counterclockwise center from opposite the manifold S2 (see Figure 1), at the manifolds S3; S4 and then 21 to a point where the solidified shell has become quite large relative to the molten center, which means that the cast

21 8 632

Bar B has moved over an arc of more than 90 °, and preferably more than 180 °, it is believed that such replacement of the casting body over the course of solidification tends to segregate the formation of large concentrations To eliminate constituents or components or impurities that would otherwise float into the upper part of the interior of the solidifying shell or shell, since essentially the "upper portion ^{11 of} the solidifying shell or shell will always change during the rotation of Hades".

Measurements were made to determine the degree of segregation of sulfur and oxygen contaminants and the degree of carbon segregation in new cast steel stakes made by the process of the present invention. To produce a segregation profile from the wheel side of cast bars to the strip side of the cast bars, three sets of samples were punched out from (long) cross sections of the cast bar, a sample from the center of the section, a 20 mm to the left of the center, and a 20 mm to the right of the center. The values obtained were then averaged to obtain an average profile for each bar. The results of such studies are shown in FIGS. 2, 3 and 6. It is assumed that in the case of the prior art "(long) cross sections" and even straight "cross sections" are used interchangeably if there is no likelihood of confusion with a short cross section (cf., ASTM Regulation E399-74-, Split-level orientation identification code, eg,),

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218632

Pig. Fig. 2 is a graph showing the average percent sulfur as a function of the location between the eave side and the bar (P mm) and the belt side of the bar (44 mm in this case), the steel having a composition of approximately 0; 45 wt, -% carbon, 0.02 wt .-% sulfur, 0.99 wt .-% manganese, 0.02 wt .-% phosphorus and 0.21 wt _# - had% silicon (sample no. 45). The maximum deviation in average sulfur content over the rod was 0.0013% (13 ppm) in the case of the measurements shown in Fig. 2, and the standard deviation was 0.000498%. This represents an unexpectedly high uniform distribution of sulfur without significant deleterious segregation. Examinations of other samples of the new product showed that maximum average sulfur deviations were 0.00114% to 0.004% (11.4 ppm to 40 ppm) and that sulfur standard deviations were 0.000483% to 0.00138 % in the case of specimens containing 0.01755% and 0.02993% sulfur, respectively, as shown below.

Average of 3 sulfur measurements in each indicated position in ppm

Sample No. = 26 41 43 45 48 .5 now = 170.3 308.0 234.3 226.7 316 15 mm = 180.7 310.6 233.0 240.0 328 25 mm = 174.3 271.0 223.7 235.0 316 35 now = 170.7 297.6 227.0 239.7 317 40 mm = 181.7 297.6 231.0 238.7 325 47 mm 311.0 238.7 -

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Average of 3 sulfur measurements in each indicated position in ppm

Duxch-

Cut s 175.5 299.3 231.2 236.0 320.4 Range s 11.4 40.0 11.7 13.0 12.0

Standard deviation a 4.83 13.8 4.88 4.93 5.08

In the graph shown in FIG. 3, the average oxygen content (ppm) is plotted as a function of the position between the wheel and the belt sides for the cast bar Nr. 45, as shown in FIG. The oxygen content was approximately 70 ppm (0.007 %) , and the maximum variation in average oxygen content over the rod as shown in Figure 3 was 5 ppia (0.0005%), and the standard deviation was 1.651 ppm. Again, this represents an unexpectedly favorable result, namely a very high degree of uniformity of beatane parts in the structure of the nGuen cast steel bar. It should also be noted that the center porosity which occasionally occurs in a steel rod made by continuous casting (even in the present invention) can contribute to the measured oxygen content in the particular layer in the rod. It is believed that such porosity does not represent proper segregation to those skilled in the art, and is generally cured during subsequent hot working.

The improved oxygen segregation properties which can be achieved according to the invention are shown by comparing FIG. 3 bits to FIGS. 4 and 5. In the case of the diagram illustrated in FIG

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of oxygen content versus position between the bottom and the top of the cast bar cast using a Hazelett strip casting machine of substantially horizontal shape. The diagram was taken from page 4-3, Fig. 6, a work by BC Whitmore and JW, Hlinka, Continuous Casting of Low-Carbon Steel Slabs by the Eezelett Strip-Casting Process, Open Hearth Proceedings, 1969 By ppm based conversion, Fig. 1 shows a maximum change or deviation of approximately ΪΟΟ ppm (,,%%) or more and a standard deviation of approximately 29.88 ppm Dieser, which is approximately 20 ° from the horizontal Hazelett experimentation method rod produced is thus a cast rod with a substantial oxygen segregation problem, even if the average oxygen content was relatively low, d _e h · was about 0,0C4% DSe worst segregation occurred while near the upper surface of the rod on , as can be seen from Fig. 4 and the Whitmore and Hlinka publications.

In Fig. 5, the oxygen content is shown in dependency of the position in the case of a cast steel bar made by using a continuous cast-type casting machine of the Concast type vertical, including a domed oscillating mold. The graph represents an average of five specimens taken from a (long) cross-sectional profile from the bottom to the top of the rod containing 0.46 wt% carbon, 0.94 wt% manganese, 0.021 wt% phosphorus, 0.016 wt% Sulfur and 0.22 wt .-% silicon. The maximum change, which is shown in FIG.

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is about 26.5 ppm and the standard deviation is 10.6 ppm. The average oxygen content is about 0.006 %, another sample with an average oxygen content of about 0.009 % showed a change of 29 ppm.

A bar cast according to the method of the invention further has an unexpectedly uniform carbon distribution, as shown in Fig. 6, which consists of a graph representing the average profile of the carbon content of such a cast bar (Sample No. 48). This particular rod had about 0.185% by weight of carbon, 0.59% by weight of manganese, 0.01% by weight of phosphorus, 0.032% by weight of sulfur, and 0.17% by weight of silicon. The points plotted in the graph of Fig. 6 are average values of three measurements for each position over the cast bar between bath and band sides, which was also the case with Figs. From Figure 6, there is a maximum average carbon content change across the bar of about 0.009% (90 ppm) and a standard deviation of 0.00305%. According to the invention, the molten steel is preferably produced from a chemical system containing carbon as a constituent in a concentration of about 0.04 wt .-% to 1.4 wt · _e - contains%. The maximum change in the case of specimens in this range with a degree of freedom (variance) in the case of inventive specimens is expected to be proportional.

It has been found that particularly advantageous results are achieved when the carbon content of the steel

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between about 0.05% by weight and 0.80% by weight.

Further measurements were made to determine the tensile strength of the new cast steel rod of the invention and to compare it to the tensile strength of a steel rod obtained by a conventional prior art casting method using a conventionally conventional casting Casting machine with a swinging or oscillating arcuate shape, wherein steel bars were cast from the same molten steel. The measurements were carried out with a loading or loading speed of 0.001 / sec. using a 2.54 cm Sxtensometer.

From Fig. 7, the tensile strength of a test piece of a rod cast according to the method of the invention of about 7522 to 7733 kg / cm ² compared to the strength of a prior art Concast rod of about 654-1 to 6611 kg / The composition of the steel in the case of this melt was 0.45% by weight of carbon, 0.97% by weight of manganese, 0.019% by weight of phosphorus, 0.017% by weight of sulfur and 0.21% by weight. silicon.

It is believed that an increase of about 10 to 15 % or more in the case of bars made in accordance with the present invention is consistent with the unusually uniform distribution of the ingredients or components and impurities found in the novel product of the present invention. In the case of these experiments it was further found that the new cast

56 934-23 21 8 632

Bars a greater percentage elongation and a larger one

Proportional limit in kg / cm than conventionally manufactured Concast rods · Reference is made to the following results:

Test sample Tensile strength in kg / cm ² % Elongation Proportional limit kg / cm ^ 4501 5019 5040 Weuer wand 1 2 3. 7522 7733 7592 10 13 16. 4340 4046 Rod according to the prior art 4 5 6611 6541 8 8

From Fig. 8, the intensity of the characteristic manganese X-rays along an arbitrary line of about 800 microns in length within a specimen of a steel bar cast according to the method of the present invention follows. It is found that the degree of intensity is relative is constant over the line marked 100 % and corresponding to a base concentration of 0.98% manganese and which also corresponds to an absolute value of about 11 units in the graphic scanning of the electron microprobe analyzer. There is only one noticeable fourth change, measured at about 173% of the baseline level, ie. equivalent to a local concentration of about 1.69% manganese ·

FIG. 9 shows the manganese X-ray intensity of a specimen cast according to the prior art Concast method. It should be noted that the intensity level has many peaks, which

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correspond to manganese. Holders were found to have an absolute value of approximately 12 units on the stripe card from the electron microprobe unit and used for the 100% line. The average value of the most important peaks is about 320 % of the baseline level, and the maximum change in manganese content observed was over 400%, as shown by the following values:

top 1 % Base level No. 2 396 % No. 3 22? % No. 4 292 % No. 5 404% No. 6 262 % No. 335%

It has been found that particularly advantageous results are achieved when the manganese content of the steel is about 0.30 to 1.20% by weight.

The invention has been described in detail with reference to preferred embodiments. It is understood that deviations and modifications can be made within the scope of the invention. For example, in the foregoing, only a few representative samples have been given of an unlimited number of steel compositions that can be cast by the process of the present invention. This means that according to the method of

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Steel bars and steel bars with concentrations other than those specified and components and impurities can be produced with the achievement of corresponding, proportionately improved results.

Claims (25)

- 40 -; 56 934 23 1. Continuous steel casting process with the following process steps: a) pouring molten metal into a traveling closed mold which is produced by means of at least one moving belt which seals the mold over part of its length; b) cooling the mold whereby the molten metal begins to solidify on the mold walls to produce a skin of solid metal around a molten core; c) removing the at least partially solidified cast rod or strand from the outlet to the closed part of the mold and d) cooling of the cast rod or strand by direct and / or indirect impact of the coolant supplied by nozzles or showers, characterized in that, in step β, steps a to d are controlled so as to produce an endless cast steel rod or steel strand having a lack of microsegregation and a particularly uniform distribution of components and contaminants as measured in cross-sectional profile. -41 - 56 93 ^ 23 2t 8 6 32 Method according to item 1, characterized in that the step e is controlled so as to obtain a maximum variation of the average sulfur content of less than about O ₁ OW% = 40 ppm as measured in the transverse profile, Method according to item 1, characterized in that step e comprises the average threshold calculated from arbitrary empirical data whose standard calibration is less than about 0.0015 % . 4. The method according to item 1 or 2, characterized in that the step e is a maximum variation of the average Säuerstoffgehaltes of less than about 0.002% = 20 ppm, measured in the cross-sectional profile, is obtained. 5. The method according to any one of the preceding items 1 to 4, characterized in that for the step e is a bringing about a maximum fluctuation of the average carbon content of less than 0.01 % = 100 ppm, measured in the cross-sectional profile, is provided. A method according to any one of items 1 to 4, characterized in that, for step e, there is provided generation of average carbon content calculated from arbitrary empirical data whose standard deviation is less than about 0.004%. - 42 - 56 934 23 2t8 632 A method according to any one of items 1 and 4 to 6, characterized in that step e produces a maximum variation in the average sulfur content of less than about 0.002 % = 20 ppm. 8. The method of item 1, characterized in that the step e reaches a maximum variation of the manganese content of less than about 400 % of the average manganese content. A method according to any of the preceding claims, characterized in that the step a includes the use of a closed mold created by a peripheral recess in a rotating casting wheel and a band which seals the recess over part of its length. A method according to any one of items 1 to 8, characterized in that step a includes the use of a continuously moving closed mold created by at least one endless moving surface in conjunction with other sealing surfaces to form a closed mold. 11. The method according to any one of items 1, 2 and 5 to 10, characterized in that at the level e, the maximum fluctuation in the average oxygen content is less than about 10 ppm. - 43 -. 56 934 23 218632 Method according to any of the preceding items 1 to 11, characterized in that an endless moving bath-belt-type surface mold is intended for continuous casting of steel bars or steel strands for commercial use, the cast bar or strand passing during solidification a radial arc of substantially more than about 90 °, and wherein the uniformity of the formation of concentrations of segregated constituents and impurities is controlled to such a degree as to produce a suitable steel rod or steel strand from a commercial point of view. Method according to any of the preceding items 1 to 12, characterized in that the rotation of the casting wheel changes the orientation of the molten steel in the mold sufficiently rapidly to avoid significant flotation and segregation of impurities in the steel. A method according to any of the preceding items 1 to 13, characterized in that at step e the endless cast steel bar or steel strand for a given molten steel has a tensile strength which is at least 10% greater than the tensile strength of a steel bar or steel strand cast from the same melt on a similar caster, Method according to item 12, characterized in that the arc is greater than about 180 °. - Ά - 56 934 23 2t 8 6 32 16. Steel rod, produced by continuous casting according to the points 1 to 15, characterized in that the cross-sectional profile has a maximum average variation of the oxygen content of less than 25 ppm. 17. Rod rod according to items 1 to 15 »characterized in that the cross-sectional profile has an oxygen segregation standard deviation of less than about 0.001 % ss 10 ppm. A steel rod according to items 1 to 15, characterized in that the cross-sectional profile has an oxygen segregation standard deviation of less than about 0.0005% = 5 ppm. 19. Steel bar according to items 1 to 15, characterized in that the transverse profile has a maximum average variation of the manganese content of less than about 275 % of the average manganese content. Steel rod according to items 16 to 19, characterized in that the cross-sectional profile has a maximum average variation of the sulfur content of less than about 0, OW % . 21 8 632 21. A steel bar according to items 16 to 19, characterized in that the cross-sectional profile has a sulfur segregation standard deviation of less than about 0.0015%. 19 - 45 -. 56 934-23 21 8 6 32 invention claim 22. Steel bar according to points 16 to 21, characterized in that the cross-sectional profile has a maximum average variation of the carbon content of less than 0.01 % , Steel rod according to items 16 to 21, characterized in that the transverse profile has a carbon segregation standard deviation of less than about 0.004 % . Steel rod according to any one of items 16 to 23, characterized in that the tensile strength is at least 10% greater and the elongation at least 10 % greater than the tensile strength or elongation of a steel rod made from the same melt by means of a known Foundry is poured. 25. Steel 3tab according to items 16 to 24, characterized in that the transverse profile has a maximum average fluctuation of the oxygen content of less than 0.0025 % = 25 ppm, a maximum variation of the sulfur content of less than 0.004 % s 40 ppm and a maximum average Fluctuation of carbon content of less than 0.01 % =: 100 ppm. Dazu.it_Seten drawings