NL8000463A - CONTINUALLY CAST STEEL PRODUCTION WITH REDUCED MICROSEGREGATION. - Google Patents

Description

-1- '80509 / BZ / CD

Applicant: Southwire Company of Carollton, U.S.A.

Title: Continuously cast steel product with reduced microsegregation.

The invention relates to a new cast steel product and in particular to a new continuously cast steel product with homogeneously distributed components and to a process for the manufacture of this product.

The good properties of cast steel include the homogeneous distribution of the constituents and the steel impurities commonly found in steel. In the description, these terms are used in their normal meanings, ie that one refers to one of the parts of the chemical system or a phase or a combination of phases, which occur in the normal composition of the alloy microstructure, while with impurities are designated elements or compounds, the presence of which is undesirable in any material. * Components therefore also include the materials added to the chemical system to obtain a specific type of casting steel, but not the impurities present in the cast metal or undesirable elements or connections. Segregation of the cast steel components make it less suitable for subsequent treatments, e.g. forging, rolling into bars and wire drawing. Segregation also has the meaning here of the non-homogeneous distribution or concentration of constituents (or impurities) that occurs during the solidification of the metal. For example, the concentration or accumulation of impurities at various locations within the metal is referred to as segregation. Segregation occurring between the points of dentrites are referred to as minor or microsegregation, allowing the composition to vary within a single crystal. Macro segregation arises around primary or secondary shrink cavities, such as pipes and the like, and is often visible in the form of clear lines with a pronounced upright or inverted cone shape, which become visible as the castings are cut and etched. Segregation zones tend to occur in the middle of the castings and usually in the portion mainly occupied by equimaxial crystals. Micro flniwun _ 2 _ segregation can sometimes disappear by annealing, but macro segregation persists during heating and processing. So-called pipe segregations occur around pipe cavities. In normal segregation in stasl, the constituents in the iron separated from the solidifying liquid form on the progressive interface between solid and liquid material, the constituents having the lowest melting point concentrating in the last solidifying portion, at reverse segregation in reverse, since the liquid with a high concentration of constituents is trapped between the dentrites, thereby decreasing the concentration of the components of the casting surface toward the center. Thus, in reverse segregation, the concentration of the constituents or impurities is more near the outer surface (compared to the interior) of a rolling block or casting. The steel cast in the known manner provides cast steel products with a relatively high segregation of impurities and alloy materials in the cast steel. Due to the high content of components and impurities, reverse segregation usually occurs in steel. Due to the non-homogeneous distribution of impurities and / or constituents in cast steel, it is necessary to reduce the total amount in order to prevent undesirable properties of the product made of cast steel during the machining of the cast steel and on the surface. However, the reduction of the total amount of impurities in most cases requires an expensive additional purification of the steel before casting which in some cases is commercially disadvantageous or completely impracticable, although the addition of certain components (including the alloying elements) is desirable or necessary .

Steel impurities and alloying elements which can segregate in the products made by known processes are sulfur, oxygen, phosphorus, manganese, silicon and carbon, with strong segregation making the product less attractive commercially. For example, strong segregation can cause uneven tensile strength in the steel, making it less suitable for wire drawing 55. Segregation of gaseous contaminants can lead to porous areas near the surface of the cast product, creating 8000463 t 4, in addition to other disadvantages, an inferior quality plate surface (Whitmore, BC and Hlinka, JW "Continuous Casting of Low-Carbon Steel Slabs by the Hazelett Strip -Casting Process "Open Hearth Proceedings, 1969). Strong microsegregation of manganese causes problems in many end products made of continuous cast steel, due to the large influence on the conversion of austenite into pearl / bainite / martensite. For example, continuous cast wire rod rolled rolled steel often contains a high manganese concentration in the curr, thereby promoting local martensite formation during casting and fractures often occurring during wire drawing.

Pit problem has been known for a long time but there are only a few publications that mention actual production data. A related investigation by Hans van Yuuren of the Soutl African Iron and Steel Industrial Corporation, ntd (copy 15 of which appears on pages 506-354 of Steelmaking Proceedings, vol 61,

Chicago Meeting, April 16-20, 1976), indicates an ability to control microsegregation and its effect on the resulting rod-shaped product.

Van Vuuren concludes that the centrally present martensite in some steel wire rods can in many cases be avoided by limiting the total amount of manganese to a maximum of 0.75 # and phosphorus to a maximum of 0.02 # and cooling it down. during the cooling period before rolling. No mention is made of the microsegregation in continuous cast loupes (ISC0H is assumed to start with continuous casting of a 205mm x 315mm loupe in a Concast Bloom Machine) but the resulting steel-shaped product appears to be a manganese upon analysis microsegregation from 101.5 # to 139 # according to the basic analysis. Due to the large heat spread between the time of casting and rolling 30, it is believed that the microsegregation of manganese in the cast loupe is much higher than in the final steel product.

However, the problems associated with segregation (e.g., wire breakage) have now been solved by repairing (e.g., homogenizing) the intermediates (e.g., rods) instead of counteracting segregation during casting. The reason for this is presumably that intervention in the extensive commercially acceptable process is much more difficult.

In the known methods of casting rolling blocks, segregation occurs when the molten steel slowly solidifies, with the impurities rising up in the rolling block due to the difference in gravity. For applications where high quality is required, the molded layer with concentrated impurities and / or voids at the top of the roll block may need to be cut or scraped before the cast steel can be further treated (see for example "Recent Developments in Machine Scarfing of 10 Continuous Cast and Rolled Steel, Iron and Steel Engineer, January 1978, pages 60-7I and U.S. Patent 4 * 155, 599, column 1, lines 61-68.

Methods of continuous casting of steel have been developed to thereby avoid handling large numbers of rolling blocks and removing the top layer. According to one of the best known most commercial methods of continuous casting of steel, molten steel is poured into a vertically arranged open-ended mold, which is made of a very highly conductive material, for example copper, in which cooling water circulates. While the outside of the metal solidifies to form a solid steel casing in contact with the wall of the mold, the rod-like steel is slowly removed from the bottom of the mold, while molten metal is continuously melted at the top of the mold cast. This method, sometimes referred to as Junghans or 23 Junghans-Rossi continuous casting system, has been favorably reported by Concast A.G. in Zurich,

Switzerland and goers Go. commercially useful in the United States. One of Junghans' first patents is U.S. Patent 2,135 * 183. But here too the surface has to be planed for certain applications, see for example the American oc-30 trooisehrift 4 * 155 * 599 *

In the Junghans process, the mold can be moved vertically back and forth for a short distance so that the mold moves with the rod during each downward movement, increasing the heat transfer during the instant that there is no mutual movement between the rod and mold . This up-and-down movement increases the casting speed but often causes unwanted marks or rings around the surface of the casting.

When leaving the vora, water is usually sprayed on the surface of the semi-solidified rod to complete the solidification. To calculate the vertical height of the building containing the 5 Junghans caster, the guide roller uses to bend the rod over an arc of approximately 90 ° with a radius of, for example, 12 meters and to straighten it again so that the rod is cut horizontally or can be treated further. In order to prevent the rod from being bent twice in this way and to be able to install the casting device in smaller buildings, curved shapes have been developed so that the rod emerges from the mold along a desired curved path and then in one go for cutting is bent in a horizontal direction.

A good description of the known continuous casting method for steel has appeared in the December 1963 issue of Scientific American Magazine, "The Gontinious Casting of Steel" by LVGallagher and BS Old.Band 209, no. 6, p. 74-88.

This shows that when casting according to the known methods in vertical forms, the solidifying steel does not change direction quickly (which usually requires a building with five floors or more), while the molten steel in the core of the rod takes some time remains horizontal as shown in U.S. Pat. No. 3,542,115. This gives the contaminants the opportunity to rise during solidification, generally resulting in segregation which can be observed as a segregation line in a (long) cross-section of a square rod of 10 x 10 cm cast in a known manner, which line about 2.5 cm from the internal radius of the bar.

Investigations have also continuously cast steel in nearly 30 horizontal shapes on double belt casting machines, basically corresponding to an older machine from Hazelett Strip-Casting Corp., as shown in U.S. Pat. No. 2,640,235 (cited in the publication of Whitmore and Hlinka). Both writers assumed that under the influence of the force of gravity and the angle of approximately 20 ° of the steel bar during the

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The solids become contaminants in the steel when these tests tend to rise and form a substantial zone of separated material near the surface of the casting. The authors state that in addition to the oxide holes in the top surface. macro-etch examination of cross-sectional internal oxidation segregation was observed. Although the degree of oxide segregation varied, the profile was the same in all cast plates, from which it was concluded that it clearly follows from this data that the oxidation segregation is strong enough to cause a plate surface of inferior quality. A number of possible solutions were tested, such as the elimination of slag in the molten metal intended for molding, the use of stationary water-cooled copper edge dams and of submerged feed tubes, etc., however admitting that all these attempts were unsuccessful. It is believed that when the top layer is between 1.25 and 1.9 cm thick, a strong concentration of segregated oxides is trapped in the solid plate. The conclusion was that the casting at an angle of 20 ° leads to metallurgically inadequate plate making products starting from nAl-Killed or vacuum-treated steel, as no possibility could be found to remove the oxides and inclusions near the top of the cast steel rolled, proposing to re-position the mold vertically according to the well-known Junghans principle as an opportunity to avoid the segregation problem The applicant considers that 29 the off-center segregation of the components and impurities also cause the unpredictable variations in the subsequent processing, e.g. hot rolling, of the material.

The present invention now provides cast steel bars, which, when compared to the known bars, not only lack the segregation of manganese, oxygen, sulfur and carbon, but are also characterized by a particularly homogeneous distribution of manganese, oxygen, sulfur and carbon. The cast steel rod according to the invention contains steel which has a (long) cross-section with a maximum average variation in the oxygen content of less than about 20 ppm (0.025 °) and a segregation 8000463 * <- 7 - standard deviation in macro-segregation research. of the oxygen segregation of less than about 8 ppm (0.00085 ») in samples containing about 0.01% oxygen; has a maximum mean variation in the sulfur content of less than about 0.004% (40 ppm) and a standard deviation of the sulfur segregation of less than about 0.0015¾ (10 ppm) in samples containing about 0.02% sulfur; and a maximum mean variation in the carbon content of less than about 0.01% (100 ppm) and a standard deviation of the carbon segregation of less than about 0.004% (40 ppm) in samples containing about 0.185% carbon; and improved post-casting tensile strength. The same good results can be expected with Si, P, Cr and other alloying elements commonly used in steel. * They have performed microsegregation analyzes for C, Mn, S, Cr and Si by electron microscope examination. The results indicate a much lower microsegregation of manganese (than in the known Concast samples. For example, they have molten steel with a content of about 0.46% carbon and about 0.98% manganese according to the method described here and according to the Known Concast Method Cast Monetars of the cast steel bars were cut transversely and small samples were cut from them in equivalent places about half the distance from the edge to the center, so they did not have the best for comparison neither the worst places selected .. The small samples were confirmed for the electronic examination and analyzed to determine the manganese concentration along an arbitrary line about 100 microns in length.

This well known method is believed to be the simplest way to demonstrate microsegregation in metals.

In principle, this method consists of bombarding the sample with an electron beam of small diameter and high energy, whereby the sample typically emits X-rays corresponding to the concentration of the elements present. The X-rays are analyzed by diffraction with a crystal (for each element separately), measuring the intensity with a suitable detector. They can determine the concentrations of an element by comparing the relative intensity of the X-rays emitted by the element into the sample with a known standard. To achieve a maximum 8000463 - Ö - male accuracy, approximately 0.5%, correction for absorption and fluorescence of the emitted X-rays must be corrected, in addition it can be assumed that the average intensity corresponds to the base-5 found according to normal chemical analysis. concentration, where variations in intensity directly reflect the deviations from the base concentration.

When using this method when comparing different samples, it is recommended to assign a specific value to each sample, which indicates the average intensity of the major variations and thus the mean deviations of the concentrations from the base level. This value can be called the microsegregation value and is expressed as a percentage of the base concentration.

In the present comparison, the basic analysis of the sample yields approximately Q.9% manganese. The results show that the known cast steel bar has a manganese microsegregation value expressed as a percentage of the basic analysis of about 300%, while the manganese microsegregation value of the bar cast by the method dex invention is less than about 175%.

An important feature of the present invention is that the new product can be manufactured on a known casting machine using methods that can be performed by those skilled in the art. According to a preferred embodiment of the present method, a moving arc-shaped mold is produced by a casting wheel, which is provided on the periphery with a slot-shaped recess for rotating a central axis, with a belt in the longitudinal direction in the top part of the casting wheel. comes into contact with the groove on the circumference, advancing tire and wheel in the lower portion of the wheel in contact with each other and removing the tire from the wheel (thus creating a socrt endlessly moving surface type mold), pour molten steel into the arc, the mold cools to solidify the molten steel into the arc, pull the cast rod out of the arc, in most cases, further cool the cast bar using an aftercooler, after the cast rod has left the closed target of the mold

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The cast rod gradually bends straight when removed from the arcuate mold (see, for example, U.S. Pat. Nos. 623,535 and 359,348).

The present invention therefore aims to provide an improved cast steel product.

Furthermore, the invention provides a new continuously cast steel bar characterized by the unprecedented lack of segregation or inverse segregation of impurities or components in the interior of the bar.

The invention further provides a cast steel bar which is better suited than the known bars to undergo operations such as rolling into bars, drawing into wire or hot forming by forging.

The invention further provides a method for continuously casting a steel product with improved internal properties.

The invention will now be further elucidated with reference to the drawing, in which Fig. 1 shows a schematic representation of a known device, which can be used for the production of the cast steel product according to the invention, consisting of a casting machine with a rotatable yeast wheel provided with a gouge-shaped circumferential recess and an endless belt covering part of the groove to form a closed mold; Fig. 2 is a graph showing the sulfur distribution in a steel bar cast according to the invention; Fig. 3 is a graph showing oxygen distribution in a steel bar cast according to the invention; FIG. 4 is a graph showing oxygen distribution in a steel bar cast in accordance with the known double cast steel; FIG. 5 is a graph showing the oxygen distribution in a steel bar cast by another known method, the Junghans method, in particular in a machine of the commercially successful Gone ast type; Fig. 6 is a graph showing the carbon distribution in a steel bar cast according to the present invention; Fig. 7 is a histograph comparing the tensile strength of the new cast steel product according to the invention with another cast steel product manufactured according to a known method; FIG. 8 is a graph showing variations in X-ray intensity in microsegregation of manganese cast in a steel bar according to the present invention; FIG. 9 is a graph showing the variations in X-ray intensity in microsegregation of manganese in a steel bar cast according to the known method of Concast.

In the drawings, like numerals in the different views indicate like parts. Fig. 1 shows a casting wheel apparatus 10 for the manufacture of the product according to the invention, which corresponds to, for example, the apparatus described in US patent 5,625,535. Casting wheel 10 is provided on the periphery with groove G which extends over part of the circumference of the casting wheel is covered by an endless flexible band 11, whereby closed mold M is formed. Flexible belt 11 is pressed against a portion of the circumference of the casting wheel by the belt supporting rollers 12, 13 and 14 and moves as wheel 10 is operated. Near belt supporting roller 12, where the closed casting mold M begins, molten steel flows from casting pot 16 through tube 16a into casting mold M. In the preferred embodiment, the outer surface of the casting wheel and the belt are continuously cooled by spraying with a coolant, the outside of the groove and belt being cooled by spraying from nozzles (not shown) into the manifolds S2, S3 »S4, and the inside of the circumferential groove G by spraying from the nozzles in manifold S1 is becoming. Spraying from the nozzles (or group of nozzles) onto the inner circumference groove can be individually adjusted for each nozzle to control the amount of coolant sprayed and thereby the rate of cooling of the metal in Form M. The supply of coolant to the nozzles (or groups of nozzles) 35 can also be controlled with adjustable shut-off valves, starting or stopping the 8000483 - 11_ ♦ f 'coolant flow and controlling the total amount of coolant (see for example the cooling described in U.S. Patent 5,279 * 000).

Above and behind the belt-supporting roller 14 is a long bending section 18, which serves to straighten the cast steel rod 3 drawn from the circumferential groove of casting 1 wheel 10 after it emerges from the closed portion of form M . Bending section 18 includes a plurality of bearing guide rollers 19 mounted on a frame (not shown). In order to keep the cast steel bar in an approximately vertical plane, laterally mounted guide rollers (not shown) can also be used in section 18. Although the bearing guide rollers 19 may or may not be driven, drive of at least some of the bearing rollers 19 is recommended to aid straightening of the cast bar.

In a preferred embodiment, an aftercooler 21 is placed above and in the vicinity of belt-supporting roller 14, which injects the cooling liquid directly onto the cast steel rod emerging from arcuate shape M.

When using the method according to the invention, casting wheel 10 is rotated in a counter-clockwise direction and molten steel from vessel 16 is passed through tube 16a in closed form M, which is located between the peripheral groove G of the casting wheel and flexible band 11, cast * The molten steel is poured into mold M at a rate known in the manner of casting iron or non-iron metal at such a rate that the revolution of the casting wheel turns the steel into mold M at the same rate of tube 16a carried away as molten steel flows through the tube, so that the molten steel at the beginning of form M remains at a constant level. The end of tube 16a is arranged as close as possible to the opening of mold M to allow the molten steel to flow directly from the tube into the molten metal bath in the mold.

While the molten steel is being fed around casting wheel 1) inside mold M, a cooling liquid is directed from the nozzles of liquid chamber S1 and the nozzles of the other liquid chambers S2, S3 8000465-12- and S4 to the mold, wherein the amount of liquid sprayed onto the belt and the casting wheel is adjusted to control the cooling of the molten metal. According to a preferred embodiment, cooling around the longitudinal axis of the cast rod is very uniform, as described, for example, in U.S. Pat. No. 3,279,0 ° 0. The initial rapid cooling and solidification of the molten metal on the surface of the casting wheel and belt, creating a skin or casing of solidified steel with a similarly aligned grain structure. Continued extraction of heat from the partially solidified rod results in the progressive and gradual solidification of the molten metal in the core to form a dentrite or similar structure which is dependent on the heat transfer from the steel from the jacket to the center of the fixed steel bar B.

13 The steel entering Form M as molten metal in the upper part of the casting wheel moves down the lower part of the casting wheel and then upwards until the closed part of Form M is exited near the belt-supporting roller H and passes through the after-cooling sprayed liquid from the nozzles is bonded to liquid chamber 21, and stretches guide roller 15, after which it is diverted from the casting wheel. In the preferred embodiment, the temperature of the outer surface of the skin of the solidified steel when emerging from the closed portion of mold M is no more than about 1370 ° C and no less than about 1038 or 140 ° C. The cast bar coming from the casting wheel has a shape corresponding to the curvature of arcuate shape M and therefore must be gradually straightened by gradually increasing the radius of bar B as it passes through the long bending section 18. The guide rollers 19 support and guide the rod through the straight-bending portion above casting wheel 10, preferably at least one pair of guide rollers 19 being driven to pull bar B off casting wheel 10. The molten core of rod B, when passing at least the last cooling jet from the last liquid nozzle, has become fully solid chamber 21 to ensure that the rod is completely solid before it reaches the point that same height: as the level of the molten metal at the entrance of mold M. In 8000463 - 15- this way, the molten metal in the core of the bar will not be in a direction opposite the direction of travel of the mold flow through the center of the bar that has not yet solidified, creating an empty cavity in the center of the bar. Thus, the bar is solid 5 and metallurgically in good condition for entering bending section 18, the temperature just prior to bending also being adjustable by controlling the volume of the coolant supplied through liquid chamber 21 to adjust the internal stresses in the bar during straightening.

In the embodiment of the casting wheel 10 described here, the shape of shape H is approximately that of a trapeze with the short side at the bottom of the circumferential groove and the long side at the side of tape 11.

Thus, the steel bar cast in caster 10 may have a maximum width of about 5 to 0.95 cm, a narrow side of 5 to 0.5 cm and a height of 2.5 to 2.2 cm at a radius of about 0.6 cm, which connects the short side to the two sides of the bar. If desired, rods with other dimensions can also be cast.

2

To date, bars of about 11 cm have been successfully cast at a speed of about 13.4 m / mm and a bar of about 2 20.5 cm at a speed of about 10.6 m / min.

It is believed that the new cast steel bar can be manufactured according to the invention at a relatively high linear speed, because due to the relatively long length of arcuate shape M, which is sprayed by rapidly cooling coolants, it solidifies despite the relatively high rotational speed of casting wheel 10 is possible.

Furthermore, due to the relatively small radius of casting wheel 10, the direction of the molten steel changes rapidly during the rotation of the wheel, in contrast to the known methods in which the solidifying steel is horizontal or approximately horizontal for quite a long time, so that the impurities while ascending. It is believed that when casting rod B of a relatively small cross section according to the present invention, the rod quickly solidifies through the coolant sprayed from the nozzles, connected to liquid chambers S1, S2, S3, S4 and 21 for ·· 8000 463-14 - that segregation of the constituents or impurities occurs. According to the method of the invention, in which a proportionally rotating cast wheel with a relatively small radius is sufficiently cooled, the impurities are quickly immobilized before the segregation and / or inverse segregation, so that the new cast steel product according to the invention is obtained. 8000463 -15- with properties that differ considerably from cast steel, which is manufactured in the known manner in a continuously operating casting machine.

It is believed that due to the shape of the molding wheel, the cooling water spray zones and the relatively smaller cross-section of the cast rod, it is possible to achieve better heat transfer compared to the known continuously operating steel casting methods.

The faster cooling or the faster solidification is evident from the metallurgical heights of the casting systems. The metallurgical height is the distance from the surface of the liquid mass in the mold to the point of solidification. According to the present method, metallurgical heights of about 4.5 meters or less are used in the manufacture of a 78.7 cm bar 3 at a speed of 10 to 13.4 per minute and 3 a bar of 132.8 cm and at 7.6 to 10.6 m per minute. In the prior art Junghans continuous casting systems, the metallurgical height is usually about 15.25 to 21.35 m when casting 10 by 10 cm of rolled steel at a speed of 2.5 to 3 m per minute. It has been found that the rod cast according to the invention is completely solid in about 20 to 30 seconds, while the Junghans type rod is believed to take about 6 minutes to fully solidify.

It is believed that the rapid cooling decreases the flow of liquid with a higher solids concentration in the inter-trietal channels, thereby reducing inverse segregation while the non-iron impurities become random at random distribution with the solidification of the liquid turn into.

Furthermore, it is believed that the rapid change in the location of the molten steel in the moving molding wheel reduces the likelihood of contaminant segregation at undesirable locations within 8000463 cast cast rod. For example, if the cast bar with its initially relatively thin solidified casing and large molten core conforms to the direction of rotation of timepieces approximately dividing S2 (see FIG. 1) along the 5 dividers S3, S4 and then 21 to a point advancing where the solidified casing has become quite thick relative to the molten core, the cast rod has described an arc of more than 90 °, preferably more than 180 °, assuming that at such a location change of casting during the solid 10, the formation of high concentrations of segregated constituents or impurities, which could rise within the solidified casing, is prevented as "the top" of the solidifying casing keeps changing during the wheel revolution.

The segregation of sulfur, oxygen and carbon impurities and the segregation of carbon in new cast steel bars prepared by the present method were measured.

To measure the segregation course from the wheel side to the tire side of the cast bars, three sample-20 groups of long transversely cut pieces of the cast bar were punched for analysis, one in the center, one 20 mm left and the other 20 mm to the right of the center. The values found were averaged to obtain an average gradient from each bar. The results are shown in Figures 2,3 and 6. The applicant contends that "long transversal" and "transversal" are used interchangeably by experts if there is no risk of confusion with a short transverse cross section (see ASTM Designation E399-74, for example Crack Plane Orientation Identification Code).

FIG. 2 is a graph of the average sulfur percentage at a location between the wheel side (0 mm) and the tire side of the bar, in this case 44 mm, of which the steel is about 0.45 wt.% Carbon, 8000455-17 0.02 wt. contains sulfur, 0.99 wt% manganese, 0.02 wt% phosphorus and 0.21 wt% silicon (Sample 45). The maximum deviation from the average sulfur content in the crossbar is 0.0013 $ (13 ppm) in the measurements shown in Fig. 2, the standard deviation being 0.000498 $. This represents an unforeseen very homogeneous distribution of sulfur sulfur without significant harmful segregation. Tests with other samples of the new product yield maximum deviations from average sulfur content of 0.00114 wt.% To 0.004 wt.% (11.4 ppm to 40 ppm) and deviations from the sulfur standard from $ 0.000483 to 0. 0.00138 $ in samples with $ 0.01755 and $ 0.02993 sulfur, respectively, as indicated in the following table.

Average of 3 sulfur measurements at the places indicated in ppm.

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Sample = 26 41 43 45 48 5mm = 170.3 308.0 234.3 226.7 316 15mm = 180.7 310.6 233.0 240.0 328 25mm = 174.3 271.0 223, 7 235.0 316 2o 35 mm = 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

Average = 175.5 299.3 231.2 236.0 320.4 25 Max, difference = 11.4 40.0 11.7 13.0 12.0

Standard deviation = 4.83 13.8 4.88 4.98 5.08 deviation

Fig. 3 is a graph showing the average oxygen content in ppm at different locations between wheel and tire side of the cast bar of FIG. 2. The oxygen content is approximately 70 ppm (0.007 $), while the maximum deviation from the mean oxygen content across the bar of Fig. 3 is 5 ppm (0.0005 $) 8000463 -18- at a standard deviation of 1.651 ppm. This is also an unforeseen good result with a very high homogeneity of the components in the structure of the new cast steel bar. It is pointed out here that the porosity in the core, which sometimes occurs in continuous cast and even in the present cast steel rod, may also be the cause of the oxygen content found in the rod in this place. It is believed that said porosity is not caused by actual segregation and usually disappears in the subsequent hot operation.

The improved properties of the oxygen segregation achieved according to the present invention can be seen from comparison of Fig. 3 with Figs. 4 and 5. Figs. 4 is a graph of percent oxygen content between the top and bottom of a bar cast in a substantially horizontal shape with a Hazelett Strip-Casting machine. The graph is on page

43, Fig. 6 of Whitmore, BC and Hlinka, JW, "Continuous Casting of Low-Carbon Steel Slabs at the Hazelett Strip-Casting Process", Open Hearth Proceedings, 1969. Converted to ppm, Fig. 4 shows a maximum deviation of approximately 100 ppm (0.01 $) or more and a standard deviation of about 29.88 ppm. Thus, Hazelett's experimental method with a shape at an angle of about 20 ° provides a cast rod with a large oxygen segregation problem, even at a relatively low average oxygen content of about 0.004%. The strongest segregation, as shown in Fig. 4 and the Whitmore and Hlinka publication, is close to the top surface of dg & taaf.

The graph of Fig. 5 shows the oxygen content at various locations in a cast steel bar, which is produced with a continuous casting concast machine with a vertical arcuate up and down moving mold. The graph represents the average of 5 samples in a long cross-sectional view from the bottom to the top of the bar, representing 0.46 wt. $ Carbon, 0.94 wt. $ 8000463 - Ί9 - manganese, 0.021 wt. # Phosphorus, Contains 0.016 wt% sulfur and 0.22 wt% silicon. The maximum deviation in Fig. 5 is about 26.5 ppm with a standard deviation of 10.6 ppm. The average oxygen content is about 0.006%. Another sample with the average oxygen content of about 0.009 # shows a deviation of 29 ppm.

Moreover, the rod cast according to the method of the present invention has an unforeseen homogeneous carbon distribution, as can be seen from the graph of Fig. 6, which shows the average variation of the carbon content in such a cast rod (sample 48). This rod contains about 0.185 wt% carbon, 0.59 wt% manganese, 0.01 wt% phosphorus, 0.032 wt% sulfur, and 0.17 wt% silicon. The in-_fig. 6 plotted points are the average of 3 observations at the indicated locations across the cast rod 15 between wheel and tire side as in figures 2 and 3. FIG. 6 shows a maximum deviation from the average carbon content across the bar of about 0.009 # (90 ppm) and a standard deviation of 0.00305 #. According to the invention, the steel melt is preferably prepared from a chemical system with a carbon content of about 0.04 wt.% To 1.4 wt.%. The maximum deviation for samples with the same values differ proportionally with the present samples. It has been found that particularly good results are obtained when the carbon content of the steel is between about 0.06 and 0.08% by weight.

Other tests relate to the tensile strength of the new cast steel bars according to the invention which were compared with the tensile strength of a steel bar cast with an Ooncast machine equipped with a reciprocating arcuate mold, whereby for both steel bars of the same steel melt, 30 was started. The tests were performed with an Extensometer (1 inch) at a strain rate of 0.001 / sec.

In Fig. 7, a histogram for a sample of the 8000463 -20 newly cast rod gives a tensile strength of about 107-110 ksi versus a tensile strength of the known Concast bar of about 93-94 ksi. The melt steel contains 0.45 wt% carbon, 0.97 wt% manganese, 0.019 wt% phosphorus, 0.017 wt% sulfur, and 0.21 wt% 5 silicon. It is believed that the increase of about 10 to 15% or more in the tensile strength of the new product results from the abnormally homogeneous distribution of the components and impurities in the new product described above. In the same tests, it has also been found that the new cast bar itself has a higher percent elongation and a higher proportional limit in ksi than the known Concast bar (see table).

Sample Tensile Tensile Elongation in% Proportional Limit New Bar 1 107 ksi 10 64.3 ksi 2: 110 ksi 13 71.7 ksi 15 3 103 ksi 16 72.0 ksi

Known rod 4 94 ksi 3 62.0 ksi 5 93 ksi 8 57.8 ksi

Fig. 8 is a graph showing the intensity of the characteristic X-rays of manganese, along an arbitrary line about 800 microns in length, in a sample of a steel bar cast according to the invention. It turns out that the intensity level is almost constant at the line indicated by $ 100 corresponding to the base concentration of $ 0.98 manganese as well as with an absolute reading of about 11 units on the graphical recording of the electron micro sample analyzer . There is only one major deviation of about $ 173 from the baseline, that is, equivalent to a local concentration of about $ 1.69 manganese.

Fig. 9 graphs the X-ray intensity of manganese in a sample cast by the Concast process. The 8000463 -21- appears that the intensity level shows a large number of peaks corresponding to small areas of segregated manganese.

In the strip chart record of the electron micro or sample unit, an absolute reading of about 12 units for the 100 $ line was observed.

The average value of the main peaks is approximately $ 320 from the base level while the maximum deviation from the manganese content is more than $ 400 (see table).

Peak $ from base level 1 396 $ 2 227 $ 3 292 $ 4 404 $ 5 262 $ 6 335 $

It has been found that particularly good results are obtained when the manganese content of the steel is about 0.3 to 1.2% by weight.

800046J

Claims (24)

1. Continuous casting method in which a) pour molten metal into a moving closed mold consisting of at least one moving belt sealing said mold over part of its total length, 5 b) cool the mold, whereby the molten metal is deposited on the walls of the mold becomes solid and forms a skin of solid metal around a molten core, c) withdraws the at least partially solidified rod from the exit of the closed part of the mold, and d) direct and / or indirectly cast the cast rod. spraying with a coolant cools, characterized in that according to the new method for continuous casting of steel, e) the steps a to d are reacted in such a way that a continuous cast in cross-section steel bar is produced without microsegregation and during measurement / a bee -15 without homogeneous distribution of constituents and impurities, A method according to claim 1, characterized in that step e yields a maximum deviation from the average sulfur content of less than about 0.004 $ (40 ppm) when measured in cross section. 3. A method according to claim 1, characterized in that when using step e the average sulfur content is calculated from arbitrary empirical data with a standard deviation of less than about 0.0015. 4. A method according to claim 1 or 7r, characterized in that step e provides a maximum deviation from the average oxygen content of less than about 0.002 ^ (20 ppm) when measured in cross section. 8000463 .23_ A method according to any of the preceding claims, characterized in that step e provides a maximum deviation from the average carbon content of less than about 0.01% (100 ppm) when measured in cross section. 6. Process according to claims 1 - 4T, characterized in that when using step e the average carbon content is calculated from arbitrary empirical data with a standard deviation of less than about 0.004. Method according to one or more of claims 1 and 4 to 6, 10, characterized in that step e produces a maximum deviation from the average sulfur content of less than about 20 ppm. A method according to claim 1, characterized in that step e provides a maximum deviation of the manganese content of less than about 400% from the average manganese content. 9. A method according to any one or more of the preceding claims, characterized in that in step a a closed mold is used, consisting of a groove in the circumference of a rotating casting wheel and a band which extends this groove over a part of the total length. Method according to one or more of claims 1 to 8, characterized in that in step a a continuously moving closed mold is used, consisting of at least one endlessly moving surface in communication with another sealing surface to form a closed mold. A method according to any one of claims 1, 2 and 5 to 10, characterized in that step e provides a maximum deviation from the average 8000463 - 24-1 oxygen content of less than about 10 ppm. 12. A method according to any one or more of the preceding claims, characterized in that a rad-belt-type endless moving surface mold is used for continuous casting of a steel bar for commercial purposes, in which the cast bar is fixed during solidification. are advanced through an arcuate angle of more than about 90 ° and the homogeneity of the concentrations of segregated components and impurities formed is controlled in such a way that a commercially available steel bar is obtained. Method according to one or more of the preceding claims, characterized in that the rotation of the casting wheel changes the position of the molten steel in the mold sufficiently quickly to prevent the possible rise and separation of impurities in the steel. 14. Method according to one or more of the preceding claims, characterized in that step e provides a continuously eaten steel rod starting from a random steel melt with a tensile strength that is at least 10% higher than the tensile strength of a Junghans casting device from the same melt-cast steel rod. 15. A method according to claim 12, characterized in that the arc is more than about 180 °. 16. Continuously cast steel bar with in cross section a maximum average oxygen content deviation of less than 25 approximately 25 ppm. 8000463 _ 25 - 17. Continuously cast steel bar with a cross-sectional acidity segregation standard deviation of less than about 10 ppm. 18. Continuously cast steel bar with an oxygen segregation cross-section standard deviation of less than about 5 ppm. 19. Continuously cast steel bar with a cross-sectional area of maximum mean manganese content of less than about $ 275 from the average manganese content. 20. Continuously cast steel bar according to claims 1-19, with in cross section a maximum mean sulfur content deviation of less than about 0.004%. Continuously cast steel bar according to claims 16-19, having a sulfur segregation standard deviation in cross section of less than about 0.0015 $. Continuously cast steel bar according to claims 16-21, 15 having in transverse cross-section a maximum average carbon content deviation of less than about 0.01 $. Continuously cast steel rod according to claims 16-21, with a transverse cross section carbon segregation standard deviation of less than about 0.004 $, Continuously cast steel bar according to one or more of claims 16-22, with a tensile strength at least 10 $ and a stretch at least 10 $ higher than that of a steel bar cast in a Junghans casting machine from the same melt. 8000463 -26 - 25. Continuously cast steel bar with a cross-sectional area with a maximum average oxygen content deviation of less than 25 ppm, a maximum sulfur content deviation of less than 40 ppm and a maximum average carbon content deviation of less than 100 ppm. 8000463