CA1184792A - Continuous cast steel product having reduced microsegregation - Google Patents
Continuous cast steel product having reduced microsegregationInfo
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- CA1184792A CA1184792A CA000449719A CA449719A CA1184792A CA 1184792 A CA1184792 A CA 1184792A CA 000449719 A CA000449719 A CA 000449719A CA 449719 A CA449719 A CA 449719A CA 1184792 A CA1184792 A CA 1184792A
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Abstract
TITLE
CONTINUOUS CAST STEEL PRODUCT
HAVING REDUCED MICROSEGREGATION
INVENTORS
George Charles WARD
Thomas Noel WILSON; and Uday Kumar SINHA
ABSTRACT
An improved continuously cast steel bar having a more uniform distribution of constituents and impurities to thereby provide a better cast steel product for subsequent proces-sing. The novel continuously cast steel bar has, when measured in transverse cross-section, particularly low and consistent variations in average oxygen content, average carbon content, average sulfur content, and average manganese content while possessing a tensile strength in the as-cast condition that is approximately ten percent greater than as-cast steel bars cast from the same melt but using a commer-cially proven prior art process.
CONTINUOUS CAST STEEL PRODUCT
HAVING REDUCED MICROSEGREGATION
INVENTORS
George Charles WARD
Thomas Noel WILSON; and Uday Kumar SINHA
ABSTRACT
An improved continuously cast steel bar having a more uniform distribution of constituents and impurities to thereby provide a better cast steel product for subsequent proces-sing. The novel continuously cast steel bar has, when measured in transverse cross-section, particularly low and consistent variations in average oxygen content, average carbon content, average sulfur content, and average manganese content while possessing a tensile strength in the as-cast condition that is approximately ten percent greater than as-cast steel bars cast from the same melt but using a commer-cially proven prior art process.
Description
'79~
FIELD OF THE INVENTION
The present invention relates to a novel cast steel products, and particularly to a novel continuously cast steel product having a uniform distribution of constituents, and the method of producing said product.
BACKGRO~ND ART
A desirable property of steel in its as-cast condi-tion is a uniform distribution within the steel product of the con-stituents and impurities normally ~ound in steel. As used herein, what applicants believe to be the meaning of these terms is their standard meanings in the art, that is, "consti-tuent" means one of the ingredients which make up a chemical system or a phase or combination of phases which occur in a characteristic configura~ion in an alloy microstructure, while "impurities" means elements or compounds whose presence in any material is undesired. Constituents, as used herein, then, would include the materials combined into a chemical system to produce the particular type of steel being cast but would not include the impurities, or undesired elements or compounds present in the cast metal~ In any case, segregation of the components in -the cast steel makes it less suitable for subse-quent processing such as forging or rolling into rod and then drawing into wire. As used herein, the term "segregation"
also has wha-t applicants believe to be lts normal meaning in the art, that is, segregation is a term used in re~erence to the non-uniform distribution or concentration of constituents (or impurities) which arises during the solidification of the metal. A concentration or accumulation o~ impurities in various positions within the metal is, for example, referred to in the art as segregation. The segregation that occurs between the arms o~ dendrites is referred to as minor or microsegregaton and thus the composition may vary within a single crystel. Macrosegregation occurs around primary or secondary shrinkage cavities, such as pipa and in similar rl ~
~ 2 --regions, and is often revealed as marXed lines, having a pronounced erect or inverted cone shape, ~hich are made evi-dent whenthe ingots are sectioned and etched. Zones of segre-gation tend -to occur in the middle regions of the casting and usually within that part mainly occupied by equiaxed crystals. Microsegregation may sometimes be overcome by annealing, but macrosegregation persists through subsequent heating and working operations. So-called pipe segregates occur around the pipe cavi-ty. In normal segregation in steel, the constituents ~solute) in the iron (solvent) rejected from the freezing liquid accumulate at the advancing solid~liquid interface so that the constituents of lowest melting point concentrate in the last portions to solidify, but in inverse segregation this is reversed, for theliquid with high solute concentration becomes trapped in between the dendrites thereby causing a decrease in concentration of solutes from the ingot surface toward the center. Inverse segregation, then, is a concentration of constituents or impurities to a higher degree near the outer surfaces (as compared to the interior) of an ingot or casting.
Prior art methods of casting steel have provided cast steel products having a relatively high degree of segreyation oE isnpurities and allo~ing materials within the cast steel.
Because of the high level of constituents and impurities in steel, inverse segregation normally occurs. Such uneven dist-ribution of impurities and/or constituents withln the cast steel makes it desirable that the total amount of same within the steel be reduced so that subsequent processing o~ the cast steel does not result in unacceptable internal and surface characteristics in the product manufactured from the cast steel. A reduction in the total amount of impurities, how-ever, usually requires expensive additional refining of the steel prior to casting and is sometimes commercially unféa-sible or impractical altogether while sometimes the addition of particular constituents (including alloying elements) is desirable or necessary.
Among the impurities and alloying elements within the ~, steel likely to become segregated in prior art products are sulphur, oxygen, phosphorus, manganese, silicon and carbon.
Any significant segregation of same will make it less commer-cially useful. For example, significant segregation may cause non-uniformity of tensile strength within the steel and make it less suitable ~or subsequent drawing into wire. Segre-gation of gaseous impurities may result ~n areas of porosity near the top surface of the cast product, which, among othe drawbacks, causes inferior sheet surface quality. (See Whit-more, B.C. and ~linka, J.W., "Continuous Casting of Low-Carbon Steel Slabs by the Haselett Strip-Casting Process", Open _ Hearth Proceedings, 1969.) Severe microsegregation of manga-nese will cause problems in many end products made from the continuously cast billet due to its great effect on the auste-nite to pearlite/bainite/martensite transformations. For example continuously cast billets rolled into ~ire rod often have high concentrations of manganese in the core which will promote the local formation of martensite during cas-ting, thus causing frequent breakage during the subsequent wire drawing process.
This problem has long been known in the art bwt there have been ~ew publications found by the inventors which dis-close actual production data. ~ related ætudy by Hans Van Vuuren of the South AErican Iron and Steel Industrial Corpora-tion, L~d. (copy contained in pages 306 to 334 of Steelmaking Proceedlngs, Vol. 61, Chicago Meeting, April 16~20, 1978.) illustrates one approach to con-trolling microsegregation and its effects in a final rod product.
Van Vuuren concluded that central marter~ite could usually be avoided in some steel wire rod by limiting the total amount o~ manganese to 0.75~ maximum, phosphorus to 0.020~ maximum, and then controlling the cooling in the cooling line fiubsequent to the rolling process. There was no mention of the microsegregation values of the continuous cast blooms ~ISCOR is believed to start by continuously casting a 205 r~m x 315 mm bloom on a Concast Bloom Machine) but the final rod product was analyzed and showed manganese microse '~, '7~
gregation values ranging from 101.5~ to 139.0~ of the base analysis. Because of the extensive thermal diffusion between the time of casting and the time of rolling, it is believed that the microsegregation values of manganese in the cast bloom would have been much greater than in the final rod product.
Up until now the prior art methods o~ solving problems due to segregation (e.g., wire breakage) involved repairing (e.g. homogeni~ing) the intermediate products (e.g., rod) instead of avoiding the initial segregation during casting.
One reason for this is believed to be that it is much more difficult to control the commercial high volume continuous casting process.
In prior art ingot castin~ methods, segregation occurs as the molten steal slowly solidifies, the impurities being allowed to float by gravity separation to the top of the ingot. In higher quality applications, a resulting concentra-ted layer of impurities and/or solidification cavity at the top of the ingot sometimes had -to be physically removed (scalped or scarfed) before the cast steel could be further processed (see, for example, "recent Developments in Machine Scarfing of Continuous Cast and Rolled S-teel", Iron and Steel Engineer, January, 1978, pgs. 6~-71 and U.S. P~tent No.
__ 4,155,399, col. 1, lines ~1 6~.
~ ethods of continuous cas-ting of steel have been deve-loped to avoid the handling of a large number of ingots and the necessity of removing the top surface layer. In what the applicants consider to be the most material and most corr,mer-cially accepted prior art method of continuous casting of steel, molten metal is poured into an open ended vertically-disposed mold constructed of a highly conductive material such as copper, within which water is circulated for cooling pur-poses. As the periphery of the metal solidifies to form a shell of solidified steel adjacent to the mold wall, the strand of steel is slowly withdrawn ~rom the bottom of the mold while molten metal is conti.nuously poured into the top of the mold. This type of process is sometimes referred to as .~
3~
the Junghans-type or Junghans-Rossi-type of conti~uous casting system and has been successfully commercialized by Concast A.G. of Zurich, Switzerland and Koppers Co., Inc. of the United 5tates, for example. An early Junghans patent is U.S.
Patent No. 2,135,183 (U.S. Class 164-83). Even here, however, a surface may need to be scarfed for certain applications -see U.S. Patent No. 4,155,399 (U.S. Class 164-82).
In the Junghans-type process the mold may be vertically oscillated along a short path so that the mold moves with the strand during each downward oscillation to increase the heat trans~er during the times when there is no relative movement between the strand and the mold. Such oscillation increases the possible speed of casting but often creates undesirable oscillation marks or rings extending around the casting on the surface thereof.
As the strand leaves the mold, water sprays are normally directed onto the surface of the semi-solid strand to complete solidification thereof. In order to reduce the vertical height requirement of the building containing the Junghans-type casting machine, guide rollers have been utilized to bend the strand through an arc of approximately 90 about a radius of, for example, forty feet, and then to rebend the strand so that it extends horizontally ~or cutting or subsequent proces-sing. I'o avoid bending the strand twice in this fashion, and to be able to install the caster in a smaller building, curved molds have been developed so tha-t the strand emerges from the mold conforming to the desired curved path and then i5 straightened in one bending step to a horizontal orientaticn for cutting.
A very readable exposition of traditional continuous steel casting is provided in the December 1963 issue of Scientific _America magazine, "The Continuous Casting of Steel," by L. V. Gallagher and B.S. Old, Vol. 209, No. 6, pp.
74-88.
It will thus be seen that casting according to prior art vertical mold processes does not rapidly (it usually takes a 5 story building or more) change the orientation of the solidi-fying steel, and allows molten metal in the center of the strand to, at times, remain in a horizontal at-titude as shown in U.S. Patent No. 3,542,115 (U.S. Class 164-82) assigned to Concast Incorporated, for example. Thus, impurities have an opportunity to float upwardly during the progress of soli.difi-caction and in general, segregation occurs which sometimes may be observed in a (long) transverse section of a prior art ~
inch x 4 inch square bar as a line of segregation occurring about 1 inch in from the inner radius of the strand.
On a research basis, steel has also been continuously cast in relatively horizontal molds, this being performed on twin-belt casting machines similar in principle to the early Hazelett Strip-Casting Corp. machine as shown in U.S. Patent ~o. 2,640,235 (mentioned in the Whitmore and Hlinka publi-cation). These two authors reasoned that because of the influence of gravity and the approximately 20 from hori20ntal attitude of the steel strand during solidification in these research projects, the impurities within the steel tended to rise and form a substantial æone of segregated material near the top surface of the casting. These two authors state that coupled with the top-surface oxide pit condition was an inter~
nal oxide segregation noted in macroetch tests of transverse sections. Although the oxide segregation varied in deyree, the profile was simi.lar in all slabs cast and the authors con-cluded that from this data it was apparent that the oxide seg-regation was severe enough to cause inferior sheet surface quality. A number of possible solutions were tried, such as concentrating on the elimination of mold~pool slag, use of stationary, water-cooled copper edge-dams, use of submerged feed tubes, etc., but the authors admitted that all these attempts at a solution proved fruitless. It was reasoned that heavy concentrations of segregating oxides were trapped in the solidifying slab at the time when the top skin was between l/2 to 3/4 inch thick. The authors concluded that casting at a 20 angle resulted in a me-tallurgically unacceptable product for sheet application produced from either Al-killed or vacuum-treated steel because no way to remove these oxides was ~ound and the inclusions segregated -toward the upper part of the cast billet. They suggested going back to operating the mold in the prior art (Junghans-type) vertical position as a possibility ~or overcoming the segregation problem. It is believed by applicants that the of~-center and segregated dis-tribution of the constituents and impurities also caused unpredictable variations in subsequent attempts at processing such as hot-rolling of the material.
SUMl~ARY OF THE INVENTION
_ _ .
Generally described, the present invention provides an as-cast steel bar characterized by, when compared to the prior art, a novel lack of segregation of manganese, oxygen, sulphur and carbon. On the contrary, the present invention provides an as-cast steel bar characterized by a particularly uniform distribution of manganese, oxygen, sulphur and carbon. The cast steel bar of the invention comprises steel -that, ~hen viewed in (long) transverse cross-section for macrosegre-gation, displays a maximum average variation in oxygen content less than about 20 ppm (0.0020~) and an oxygen segregation 20 standard deviation less than about ~ ppm (0.0008%) on samples containing about 0.01% oxygen, a maximllm average variation in sulphur content less than about 0.004~ (40 ppm) and a sulphur segrega-tion s-tandard deviation less than aboui 0.001 (10 ppm) on a sample con-taining about 0.02% sulphur, and a maximum avsrage variation in carbon content less than about 0.01% (100 ppm) and a carbon segregation standard deviation o~
less than about 0.004% (40 ppm) on a sample containing about 0.185~ carbon, and an improved as-cast tensile strength and elongation. Similar good results are expec-~ed for Si, P. Cr and other alloying elements normally used in steel. Microseg-regation analysis has been carried out for C, Mn, S, Cr, and Si by el0ctron microprobe. The results indicate much less microsegregation of manganese compared to prior art Concast samples. For example, heats of molten steel, con~ainng about .46% carbon and about .98% manganese, were cast both by the method disclosed herein and by the wellknown prior ar~ Concast process. Sa~nples of the as-cast bars were sectioned transver-~, sely and small specimens were cut from equivalent locations about one-half the distance from the edge toward the center.
Thus neither the best nor the worst areas were selected for comparison. The small specimens were mounted for electron micro-probe examination and analyzed to determine the concent-ration of manganese along a random line, about 1800 microns long.
This procedure is generally well-known in the ar-t and is believed to be the easiest method for detecting microsegre-gation in metals. Basically the process involves bombardingthe specimen with a small diameter beam of high energy elec-trons which cause the specimen to give off characteristic x-rays corresponding to the concentration of the elements present. The x-rays are analyzed by diffracting them with a crystal (to select one element at a time) then measuring their intensity with any appropriate detector. Concentrations of a specific element may be determined by comparing the relative intensi-ties of the x-rays generated by the element in the specimen to a known standard. To obtain maximum accuracy, about one-half of one percent, the ratio should be corrected for absorption and flourescence of the emitted x-ra~s. Alter-nately, the average intensity level can be assumed to repre-sent -the base concentration obtained by a normal chemical analysis and then the variations in intensity directly repre-sent variations from the base concentra~ion.
When this latter procedure is used to compare a number of specimens, it is useful to assign one value to each speci-men which indicates the average intensity of the significant variations and thus the average variati.on in concentration from the base level. This value may be called the microsegre-gation value and is expressed as a percentage of the base con-centration.
In our comparison the base analysis of our sample was about 0.98~ manganese. The results indicated that the prior art as-cast steel bar has a manganese microsegregation value, expressed as a percentage of base analysis, of about 300~
while the manganese microsegregation value of the as-cast bar ~,~
~,,~
produced by the method of our invention was less than about 175~.
One important feature of the invention is ~hat our novel product can be made on a known, prior art casting machine using methods of operation within the experimental skills of those having ordinary skill in our art. Our preferred method of practicing our invention consists of forming a moving arcuate mold by rotating a castlng wheel, having a peripheral groove, on its central a~is and moving a band along its length into contact with the peripheral groove at the upper part of the casting wheel, moving the band and wheel in conjunction about the lower portion of the wheel, and moving the band away from the wheel (thusly forming one type of endless moving sur-face-type mold), pouring molten steel into the arcuate mold, cooling the mold to cause the molten steel to solidify in the arcuate mold, withdrawing the cast bar from the arcuate mold, normally additionally cooling the cast bar by the use of an after-cooler after the cast bar has exited the closed portion of the mold, and progressively straightening the cast bar as it moves away from the arcuate mold. See for example U.S.
Patent No. 3,623,535 (U.S. Class 164-87) and U.S. Patent ~o.
359,348 (U.S. Class 16~-263).
Thus, it is an vbject of the present invention to pro-vide an improved a~-cast steel product.
It is a further object of the inven-tion to provide a novel continuous cast steel ~ar characterized by a lack, to an unusual degree, of segregation or inverse segregation of impurities or constituents within the bar.
It is a further object of the invention to provide a cast steel bar more suitable than prior art bars for subse-quent processing such as rolling into rod and drawing into wire or hot-forming as by forging.
It is a further object of the invention to provide a method for continuously casting a steel produc~t having improved internal properties.
Other objects, features and advantages of -the present invention will become apparent upon reading the following r ,/ ~
specification when taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic diagram illustrating one example of prior art apparatus suitable to produce the cast steel product of the invention, the apparatus including a casting machine having a rotatable casting wheel defined by a peri-pheral groove therein and an endless band covering a portion of -the length of the groove so as -to form a closed mold over that portion.
Fig. 2 is a graph showing sulphur distribution in a steel bar cast according to our invention.
Fig. 3 is a graph showing oxygen distribution in a steel bar cast according to our invention.
Fig. 4 is a graph showing oxygen distribution in a steel bar cast according to the prior art Hazelett twin-belt process.
Fig. 5 is a graph showing oxygen distribution in a steel bar cast according to another prior art process, the Junghans-type procass, and in particular, a Concast machine o~ the commercially successful -type.
Fig. 6 is a graph showing carbon distribution in a steel bar cast acco~ding -to our invention.
Fig. 7 i9 a his-tograph com~aring -the tensile strength of the novel cast steel product of our inven-tion -to another cast steel produc-t produced by a prior art process.
Fig. ~ is a graph showing the x-ray in-tensity variation due to microsegregation o manganese in a steel bar cast according to our invention.
Fig. ~ is a graph showing the ~-ray intensity variation due to microsegregation of manganese in a steel bar cast according to the prior art Concast process.
DESCRIPTION OF THE PREFERRED E~BODI~ENT
Referring now in more detail to the drawing, in which like numerals of reference illustrate like parts throughout the several views, Fig. 1 shows a cas-ting wheel apparatus 10 or producing product o the present invention. This appara-.,r tus is similar to that disclosed in U.S. Patent l~O. 3,623,535 (U.S. Class 164-87) for example. A casting wheel lO defines a peripheraî groove G therein which is covered, for a portion of the periphery of the casting wheel, by an endless flexible band or belt 11 to form a closed mold M. The flexible band 11 is held against a portion of the periphery of the casting wheel b~ band support wheels 12, 13 and 14 and moves with the wheel 10 as it rotates. Near the band support wheel 12 where the closed mold M begins, molten steel is discharged from a pouring pot or tundish 16 into the mold M through a spout 16a. In our preferred embodiment, all exterior surfaces of the casting wheel and band are continuously cooled by a spray of coolant fluid, the outer portion of the groove and band being cooled by cooling sprays from nozzles (not shown) from headers or manifolds S2, S3, S4, and the inner portion of the peripheral groove G being cooled by sprays from the nozzles on header Sl. The spray of each nozzle (or groups of nozzles) along the inner side of the peripheral groove may be indivi-dually adjusted to vary the volume of cooling fluid sprayed therefrom, and thus vary the rate at which the me-tal within the mold M is cooled. A supply ot coolant fluid to the nozzles (or groups of nozzles) may likewise be controlled by adjustable valves to allow starting and stopping of the coolant ~low and to permit variation in the total volume of coolant flow. See, for example, the cooling arrangement suggestsd by Southwire Company's U.S. Patent No. 3,279,000 (U.S. Class 164-433).
An extended bending section 18 is positioned beyond and above the band support wheel 14. The bending section 18 serves as a means for straightening the cast steel bar B with-drawn from the peripheral groove of -the casting wheel 10 a~ter exiting the closed portion o~ mold M. The bending section 18 includes a plurality o~ support guide rolls 19 mounted on a frame (not shown). Side guide rolls (not shown) may also be utilized in the bending section 18 to confine the cast steel bar approximately to a vertical plane. Although the suppor-t guide rolls 19 may be either driven or non-driven, we Eind it ~,r is preferable that at least some of the support rolls 19 be driven to assist in the straightening of the cast bar.
In our preferred embodiment an after-cooling header 21 is located above and adjacent the band support wheel 14 -to appl~ a direct spray of coolant fluid onto the cast steel bar emerging from the arcuate mold M.
In the operation of the system according to the method of the invention, the casting wheel 10 is rotated in a counter-clockwise direction and molten steel is poured from the tundish 16 through the spout 16a into the closed mold formed between the peripheral groove G of the casting wheel and the flexible band 11. Molten steel is poured in a cont-rolled manner well ~nown in the ferrous and non-ferrous casting arts into the mold M at a rate so that the rotation of the casting wheel moves the steel in the mold M away from the spout 16a as fast as the molten steel flows through the spout to maintain the surface of the pool of molten steel at a cons-tant level at the entrance of the mold M. The exit end of the spout 16a is located as closely as possible to the entrance to the mold M to allow the molten steel to flow directly from the spout into -the pool of molten metal in the mold.
As the molten steel is carried around the casting wheel 10 within the mold ~, coolant fluid is directed against the mold from the nozzle~ in header Sl and the nozzles of the other headers S2, S3 and S4, and the amount of coolan-t applied to the band and casting wheel is adjusted as desired to cont-rol the rate of cooling of the molten metal. Our preferred embodiment has a condition of ver~ uniform cooling about and along the longitudinal axis of the cast bar, see for exam~le Southwire Company's U.S. Patent No. 3,279,000 to Cofer (U.S.
Class 164-433). Initial rapid cooling and solidification of the molten metal occurs at the surfaces of the casting wheel and band, causing the formation o~ a skin or shell of soliai-fied steel having an equiaxed grain structure. Continued extraction of heat from the partially solidified bar then causes solidification of the metal within the molten core in a progressive and uniform (including uniform at each point ~;
around the periphery) manner to form a dendri-tic or substantially equiaxed structure, depending upon the superheat of the steel, from the shell toward the center of a solid steel bar B.
The steel which entered the mold M as `molten metal at an upper portion of the casting wheel moves in a downward direc-tion about the lower portion of the casting wheel and then in an upward direction until it leaves the closed portion of the mold M near the band support wheel 14, passes through the after~coolant spray from the nozzles associated with the header 21 and reaches a guide wheel 15, whereupon it is guided away from the casting wheel. In our preferred embodiment, the temperature of the exterior surface of the peripheral skin of the solidified steel as it emerges ~rom the closed portion of the mold M does not exceed about 2500F. but is not less than about 1900 or 2000F. The cast bar leaving the casting wheel has a shape conforming to the curvature of the arcuate mold M
and therefore is progressively straightened by progressively increasing the radius of the bar B as the bar moves through the extended bending section 18. The guide rolls 19 support the bar and guide it th.rough its unbending or straightening path above the casting wheel 10, at least one pair of the guide wheels 19 preferably being driven to pull the bar B
along it~ length from the casting wheel 10. The molten core of the bar ~ is compl.etely solidified by the time it passes at least the last coolant spra~ from the last nozzle on header 21 to assure that the bar is completely solid before reaching a point which is on a level with the level o~ the pool of molten metal at the entrance to the mold M. I~usly, the molten metal in the core of the bar will not flow opposite to mold movement through the unsolidified bar center thereby creating a void in the center of the bar. The bar is thereby also solid and sound metalluryically before entering the bending section 18, and its temperature just prior to bending may also be adjusted by adjusting the volume of coolant supplied by the header 21 in order to control the internal stresses of the bar during straightening.
7~
In the embodiment of the casting wheel 10 disclosed herein, the mold M is approximately trapezoidal in shape with small dimension located at the inner portion of the peripheral groove and a large dimension located adjacent -the band 11.
Thus the steel bar cast by a typical casting machine 10 may be approximately 2-5/8 inches wide a-t its largest width, 2-1/8 inches wide at its smaller width and 1-7/8 inches deep, with an approximately 1/4 inch radius joining the smaller width with the two sides of the bar. Other bar sizes and shapes may be cast as desired. To date, for example, applicants have been successful in casting an approximately 4.8 square inch bar at a speed of appriximately ~4 feet per minute (528 inches per minute) and an appriximate 8.1 square inch bar at a speed of appriximately 35 feet per minute (420 inches per minute).
Applicants believe that the novel cast steel bar of the present invention may be produced at a relatively high linear speed because the relatively long leng-th of the arcuate mold M
cooled by quick chilling coolant sprays allows solidification to be achieved in spite oE the relatively high rotational velocities of -the cast.ing wheel 10. Fur-thermore, the rela-tively small radius of the cas-ting wheel 10 causes the orien-tation of the molten steel to change rapidly as the wheel rotates, in contrast to prior art commercially proven steel continuous casting techniques wherein the solidifying steel rernains in a horizontal or apprixima-tely horizontal orien-tation for a substantial period, allowing impurities to float upwardly during the process of solidification. Applicants believe that when casting a bar B with a relatiYely small cross-sectional area according to the present invention, the bar B may be quickly solidified by the coolant spray from the nozzles associated with headers Sl, S2, S3, S4 and 21 before any substantial segregation of constituents or impurities may occur. Thus, the method of the inven-tion whereby a relatively rapidly rotating casting wheel having a relatively small radius is cooled sufficiently to quick freeze impurities before segregation and/or inverse segregation can occur, produces the novel cast steel produc-t of our invention, having ' properties significantly different from cast steel produced in prior art continuous casting machines.
Applicants believe that the design of the wheel mold, cooling water spray ~ones, and the relatively smaller cross-section of the cast bar makes it possible to achieve a higher rate of heat transfer compared to the prior art continuous steel casting methods.
Some idea of the high rate of cooling or solidification can be obtalned from the metallurgical heigh-ts of the casting systems. The metallurgical height is defined as the distance between the top of the liquid pool in the mold to the point of complete solidification. In our method, we have worked with a metallurgical height of about 15 feet or less when manufac-turing a 4.8 sq. in. bar at 35 to 44 FPM (420 to 528 IPM) and for 8.1 sq. in. bar at 25 to 35 FPM (300-420 IPM). In the conventional continuous casting systems of the Junghans-type the metallurgical heights are generally reported to be about 50 to 70 feet for casting of 4" by 4" billets at a speed of 100 to 120 inches per minute (8.33 to 10.0 FPM). We have found that our cast bar becomes completely .solid in about 25 to 30 seconds whereas we understand it requires about 6 minutes for complete solidification of the Junghans-type bar.
We believe that our fast rate of cooling reduces the flow of liquid of higher solute concentration into the inter-dendri-tic channels and thereby reduces the invarse segregation while the non-metallic impurities present in the liquid steel freeze with the liquid with a random distribution.
~ e also believe that the quick orientation change of molten steel in the moving wheel mold reduces the chances of segregation of impurities at an undesired position within the cast bar. ~lat is, offering an example, as the cast bar with its initial relatively thin frozen shell and larye molten center moves counter clockwise from opposite approximately manifold S2 (see Fig. 1), past manifolds S3, S4, and then 21 to a point where -the frozen shell has become quite large with respect to the molten center, which means that the cast bar ~r 3~
has moved through an arc of more than 90 and preferably more than 180, applicants believe that such orientation change of the casting throughout the course of solidification tends to eliminate khe forma-tion of heavy concentrations of segregated constituents or impurities which would otherwise normally float to the upper portion of the interior of the solidif~ing shell, because, essentially, the "upper portion" of the soli-difying shell is always changing throughout the rotation of the wheel.
Measurements have been made to determine the degree of segregation of sulphur and oxygen impurities, and the degree of segregation of carbon, in novel cast steel bars that were cast according to the method disclosed. To establish a segre-gation profile from the wheel side of the cast bars to the band side of the cast bars, three sets of samples for analysis were punched from (long) transverse sections of the as-cast bar, one at the center of -the section, one 20 mm to the left of the center and one 20mm to the right of the center. The values obtained were then averaged to obtain an average pro-file for each bar. Such results are shown in Fiys. 2, 3 and 6. Applicants believe that those in the art use "(long) tran-sverse" and just "transverse" interchangeably if there is no likelihood of confusion with a short transverse sec-tion (see ASTM Designation E3~9-74, Crack Plane Orientation Identifi-cation Code, for example).
Fig. 2 is a graph of average percentage sulphur composi-tion vs. position between the wheel side of the bar (Omm) and the band side of the bar (44mm in -this case), the steel having a composition by weight of approximately 0.45% carbon, 0.02%
sulphur, 0.99~ manganese, 0.02% phosphorus and 0.21% silicon (Specimen ~45). The maximum variation in average sulphur con-tent across the bar was 0.0013~ (13 ppm), for the measurements shown in Fig. 2, and the standard deviation was 0.000~98%.
Applicants believe this represents an unexpectedly high uniform distribution of sulphur with no significant delete-rious segregation. Tests of other specimens o~ the novel product indicated maximum average sulphur content variations ./~
ranging from 0.00114~ (11.4 ppm to 40 pmm), and sulphur standard deviations varying from 0.000483~ to 0.00138% in samples having 0.01755% and 0~02993% sulphur, respectively, as shown below.
Average of 3 sulphur measurements at each position listed ln PPM
Specimen ~ = 26 41 43 45 48 5mm = 170.31308.0 234.3 226.7 316 15mm = 180.7310.6 233.0 240.0 328 10 25mm = 174.3271.0 223.7 235.0 316 35mm = 170.7297.6 227.0 239.7 317 40mm = 181.7297.6 231.0 238.7 325 47mm = -- 311.0 238.7 -- --Average = 175.5299.3 231.2 236.0 320.4 Range = 11.440.0 11.7 13.0 12.0 Std.
Deviation = 4.83 13.8 4.88 4.98 5.03 Fig. 3 is a graph of average oxygen content (in pmm) vs. position between wlleel and band sides for the same cast bar, #~5, measured in Fig. 2. I'he oxygen content was approximately 70 ppm (0.007~) and the maximum variation in average oxygen content across the bar, as shown in Fig. 3, was 5 ppm (0.0005~), and the standard deviation was 1.65L ppm.
I'his again represents an unexpectedly good result -- a very high degree of uniformi-ty of constituents in the structure of the novel cast steel bar. It should also be noted that center porosity, sometimes present in a continuously cast steel bar (even ours), may contribute to the measured oxygen content at that particular location in the bar. Applicants believe that such porosity does not represent true segregation to those in the art and is generally healed during subsequent hot proces-sing.
~''.'1 ....
The improved oxygen segregation properties oE the present invention may be seen by comparing Fig. 3 to Figs. 4 and 5. Fig. 4 is a graph of percentage of oxygen content vs~
position between the bottom and the top of a cast bar cast using a Hazelett Strip-Casting machine having a substantially horizontal mold. The graph is taken from page 43, Fig~ 6 of ~hitmore, B.C. and Hlinka, J~Wo ~ ~Continuous Casting of Low-carbon steel Slabs by the Hazelett Strip-Casting Process,"
Open Hearth Proceedings, 1969. Converting to a ppm basis, Fig. 4 shows a maximum variation of approximately 100 ppm t0-01%) or more and a standard deviation of approximately 29.8~ ppm. This approximately 20 from horizontal Haselett experimental mold process thus produced a cas-t bar with a significant oxygen ~egregation problem even when the average oxygen content was relatively low, about 0.004%. The worst segregation was located near the top surface of the bar as is evident from Fig. 4 herein and the Whitmore and Hlinka publi~
cation.
Fig. 5 is a graph of oxygen content vs. position for a cast steel bar produced by a Concast vertical mold csn-tinuous casting machine including an arcuate oscillating moLd. The graph represents an average of five samplings taken in (lony) transverse section from the bottom to the top of the bar, which had a cornposition by weight of 0.46% carbon, 0~94% man-ganese, 0.021% phosphorus, 0.016% sulphur and 0.22% silicon.
I'he maximum variation shown in Fig. 5 is approximately 2~.5 ppm, and the standard deviation is 10.6 ppm. The average oxy-gen content is about 0.006%. ~nother specimen, having an average oxygen content of about 0.00~%, showed a variation of 29 ppm.
~ cast bar produced according to the me-thod of the invention also has an unexpectedl~ uniform carbon distribu tion, as shown in Fig. ~ which is a graph showing an average profile of the carbon content of such a cast bar (Specimen #48). This particular bar had a composition by weight of approximately 0.185% carbon, 0.59% manganese, 0.01% phos-phorus, 0.032~ sulphur, and 0.17% silicon. The psints plotted ,.,,,~
,1' in Fig. 6 are averages of three measurements for each position across the cast bar between wheel and band sides, as was the case for Figs. 2 and 3. Fig. 6 shows a maximum average carbon content variation across the bar of approximately 0.009% (90 ppm), and a standard deviation of 0.00305%. In accordance with this invention, the steel melt is preferably prepared from a chemical system which has carbon present as one of the constituents in a range of appro~imately 0.04~ by weight to 1.4% by weight. The maximum variation for samples in this range at variance with our specimens are expected to be pro-portional. Applicants have found that particularly superior results are achieved when the carbon content of the steel is between about 0.06% and 0.80~ by weight.
Still further measurements have been made to determine the as-cast tensile strength of the novel cast steel bar of the invention, and to compare it to the as-cast tensile strength of a steel bar cast using a prior art commercially proven Concast machine including an oscillating, arcuate mold, both steel bars having been cast from the same steel melt.
The measurements were carried out at a strain rate of 0.001/
second using an one inch Extensometer. Fig. 7 is a hlstograph showing the tensile strength of a sample of the novel cast bar to be approximately 107 110 ksi (107,000-110,000 pounds per square inh) as compared to that of the prior art Concast bar which had a tensile strength of approximately 93-9~ ksi. '~he composition of the steel on this melt was 0.~5~ carbont 0.97%
manganese, 0.019% phosphorus, 0.017% sulphur, and 0.21% sili-con. Applicants believe that the approximate 10~-15~ or more increase in tensile strength o~ their novel product is consis-tent with the unusually uniform distribution of constituentsand impurities observed in the novel product, as described above. In these same tests it was also observed that the novel as-cast ~ar had a greater percent elongation and a greater proportional limit in ksi than the prior art Concast bar, see below:
Proportional Test Sample Tensile Strength % Elongation Limit NoveL 1 107 ksi 10 6403 ksi Bar 2 110 ksi 13 71.7 ksi 3 108 ksi 16 72.0 ksi .. _ . _ . . . ~
Prior 4 94 ksi 8 62.0 ksi Art Bar 5 93 ksi ~ 8 57.8 ksi Fig. 8 graphically shows the intensity o~ characteristic manganese x-rays, along a random line of about 1800 microns in length, within a specimen of steel bar cast by the present invention. It can be seen that the intensity level is rela-tively constant about -the line marked 100% which corresponded to the base concenkration of 0.98% manganese and which also corresponded to an absolute reading of approximately ll units on the graphical readout from the electron microprobe analyzer. l~here is only one significant variation which measures about 173% of the base leve; i.e., equivalent to a local concentration of about 1.69~ manganese.
Fig. 9 graphically shows the manganese x-ray intensity in a specimen cast by the prior art Concast process. It should be noted that the intensity level con~ains many peaks which correspond ~o small areas of segregated manganese.
Here, an absolute reading of approximately 12 units was observed on the strip chart readout from the electron micro-probe unit and used for the 100% line. The average value ofthe most significant peaks is about 320% of the base level and the maximum variation in manganese content observed was over 400%, see below:
Peak % of Base Level . _ ~1 3966
FIELD OF THE INVENTION
The present invention relates to a novel cast steel products, and particularly to a novel continuously cast steel product having a uniform distribution of constituents, and the method of producing said product.
BACKGRO~ND ART
A desirable property of steel in its as-cast condi-tion is a uniform distribution within the steel product of the con-stituents and impurities normally ~ound in steel. As used herein, what applicants believe to be the meaning of these terms is their standard meanings in the art, that is, "consti-tuent" means one of the ingredients which make up a chemical system or a phase or combination of phases which occur in a characteristic configura~ion in an alloy microstructure, while "impurities" means elements or compounds whose presence in any material is undesired. Constituents, as used herein, then, would include the materials combined into a chemical system to produce the particular type of steel being cast but would not include the impurities, or undesired elements or compounds present in the cast metal~ In any case, segregation of the components in -the cast steel makes it less suitable for subse-quent processing such as forging or rolling into rod and then drawing into wire. As used herein, the term "segregation"
also has wha-t applicants believe to be lts normal meaning in the art, that is, segregation is a term used in re~erence to the non-uniform distribution or concentration of constituents (or impurities) which arises during the solidification of the metal. A concentration or accumulation o~ impurities in various positions within the metal is, for example, referred to in the art as segregation. The segregation that occurs between the arms o~ dendrites is referred to as minor or microsegregaton and thus the composition may vary within a single crystel. Macrosegregation occurs around primary or secondary shrinkage cavities, such as pipa and in similar rl ~
~ 2 --regions, and is often revealed as marXed lines, having a pronounced erect or inverted cone shape, ~hich are made evi-dent whenthe ingots are sectioned and etched. Zones of segre-gation tend -to occur in the middle regions of the casting and usually within that part mainly occupied by equiaxed crystals. Microsegregation may sometimes be overcome by annealing, but macrosegregation persists through subsequent heating and working operations. So-called pipe segregates occur around the pipe cavi-ty. In normal segregation in steel, the constituents ~solute) in the iron (solvent) rejected from the freezing liquid accumulate at the advancing solid~liquid interface so that the constituents of lowest melting point concentrate in the last portions to solidify, but in inverse segregation this is reversed, for theliquid with high solute concentration becomes trapped in between the dendrites thereby causing a decrease in concentration of solutes from the ingot surface toward the center. Inverse segregation, then, is a concentration of constituents or impurities to a higher degree near the outer surfaces (as compared to the interior) of an ingot or casting.
Prior art methods of casting steel have provided cast steel products having a relatively high degree of segreyation oE isnpurities and allo~ing materials within the cast steel.
Because of the high level of constituents and impurities in steel, inverse segregation normally occurs. Such uneven dist-ribution of impurities and/or constituents withln the cast steel makes it desirable that the total amount of same within the steel be reduced so that subsequent processing o~ the cast steel does not result in unacceptable internal and surface characteristics in the product manufactured from the cast steel. A reduction in the total amount of impurities, how-ever, usually requires expensive additional refining of the steel prior to casting and is sometimes commercially unféa-sible or impractical altogether while sometimes the addition of particular constituents (including alloying elements) is desirable or necessary.
Among the impurities and alloying elements within the ~, steel likely to become segregated in prior art products are sulphur, oxygen, phosphorus, manganese, silicon and carbon.
Any significant segregation of same will make it less commer-cially useful. For example, significant segregation may cause non-uniformity of tensile strength within the steel and make it less suitable ~or subsequent drawing into wire. Segre-gation of gaseous impurities may result ~n areas of porosity near the top surface of the cast product, which, among othe drawbacks, causes inferior sheet surface quality. (See Whit-more, B.C. and ~linka, J.W., "Continuous Casting of Low-Carbon Steel Slabs by the Haselett Strip-Casting Process", Open _ Hearth Proceedings, 1969.) Severe microsegregation of manga-nese will cause problems in many end products made from the continuously cast billet due to its great effect on the auste-nite to pearlite/bainite/martensite transformations. For example continuously cast billets rolled into ~ire rod often have high concentrations of manganese in the core which will promote the local formation of martensite during cas-ting, thus causing frequent breakage during the subsequent wire drawing process.
This problem has long been known in the art bwt there have been ~ew publications found by the inventors which dis-close actual production data. ~ related ætudy by Hans Van Vuuren of the South AErican Iron and Steel Industrial Corpora-tion, L~d. (copy contained in pages 306 to 334 of Steelmaking Proceedlngs, Vol. 61, Chicago Meeting, April 16~20, 1978.) illustrates one approach to con-trolling microsegregation and its effects in a final rod product.
Van Vuuren concluded that central marter~ite could usually be avoided in some steel wire rod by limiting the total amount o~ manganese to 0.75~ maximum, phosphorus to 0.020~ maximum, and then controlling the cooling in the cooling line fiubsequent to the rolling process. There was no mention of the microsegregation values of the continuous cast blooms ~ISCOR is believed to start by continuously casting a 205 r~m x 315 mm bloom on a Concast Bloom Machine) but the final rod product was analyzed and showed manganese microse '~, '7~
gregation values ranging from 101.5~ to 139.0~ of the base analysis. Because of the extensive thermal diffusion between the time of casting and the time of rolling, it is believed that the microsegregation values of manganese in the cast bloom would have been much greater than in the final rod product.
Up until now the prior art methods o~ solving problems due to segregation (e.g., wire breakage) involved repairing (e.g. homogeni~ing) the intermediate products (e.g., rod) instead of avoiding the initial segregation during casting.
One reason for this is believed to be that it is much more difficult to control the commercial high volume continuous casting process.
In prior art ingot castin~ methods, segregation occurs as the molten steal slowly solidifies, the impurities being allowed to float by gravity separation to the top of the ingot. In higher quality applications, a resulting concentra-ted layer of impurities and/or solidification cavity at the top of the ingot sometimes had -to be physically removed (scalped or scarfed) before the cast steel could be further processed (see, for example, "recent Developments in Machine Scarfing of Continuous Cast and Rolled S-teel", Iron and Steel Engineer, January, 1978, pgs. 6~-71 and U.S. P~tent No.
__ 4,155,399, col. 1, lines ~1 6~.
~ ethods of continuous cas-ting of steel have been deve-loped to avoid the handling of a large number of ingots and the necessity of removing the top surface layer. In what the applicants consider to be the most material and most corr,mer-cially accepted prior art method of continuous casting of steel, molten metal is poured into an open ended vertically-disposed mold constructed of a highly conductive material such as copper, within which water is circulated for cooling pur-poses. As the periphery of the metal solidifies to form a shell of solidified steel adjacent to the mold wall, the strand of steel is slowly withdrawn ~rom the bottom of the mold while molten metal is conti.nuously poured into the top of the mold. This type of process is sometimes referred to as .~
3~
the Junghans-type or Junghans-Rossi-type of conti~uous casting system and has been successfully commercialized by Concast A.G. of Zurich, Switzerland and Koppers Co., Inc. of the United 5tates, for example. An early Junghans patent is U.S.
Patent No. 2,135,183 (U.S. Class 164-83). Even here, however, a surface may need to be scarfed for certain applications -see U.S. Patent No. 4,155,399 (U.S. Class 164-82).
In the Junghans-type process the mold may be vertically oscillated along a short path so that the mold moves with the strand during each downward oscillation to increase the heat trans~er during the times when there is no relative movement between the strand and the mold. Such oscillation increases the possible speed of casting but often creates undesirable oscillation marks or rings extending around the casting on the surface thereof.
As the strand leaves the mold, water sprays are normally directed onto the surface of the semi-solid strand to complete solidification thereof. In order to reduce the vertical height requirement of the building containing the Junghans-type casting machine, guide rollers have been utilized to bend the strand through an arc of approximately 90 about a radius of, for example, forty feet, and then to rebend the strand so that it extends horizontally ~or cutting or subsequent proces-sing. I'o avoid bending the strand twice in this fashion, and to be able to install the caster in a smaller building, curved molds have been developed so tha-t the strand emerges from the mold conforming to the desired curved path and then i5 straightened in one bending step to a horizontal orientaticn for cutting.
A very readable exposition of traditional continuous steel casting is provided in the December 1963 issue of Scientific _America magazine, "The Continuous Casting of Steel," by L. V. Gallagher and B.S. Old, Vol. 209, No. 6, pp.
74-88.
It will thus be seen that casting according to prior art vertical mold processes does not rapidly (it usually takes a 5 story building or more) change the orientation of the solidi-fying steel, and allows molten metal in the center of the strand to, at times, remain in a horizontal at-titude as shown in U.S. Patent No. 3,542,115 (U.S. Class 164-82) assigned to Concast Incorporated, for example. Thus, impurities have an opportunity to float upwardly during the progress of soli.difi-caction and in general, segregation occurs which sometimes may be observed in a (long) transverse section of a prior art ~
inch x 4 inch square bar as a line of segregation occurring about 1 inch in from the inner radius of the strand.
On a research basis, steel has also been continuously cast in relatively horizontal molds, this being performed on twin-belt casting machines similar in principle to the early Hazelett Strip-Casting Corp. machine as shown in U.S. Patent ~o. 2,640,235 (mentioned in the Whitmore and Hlinka publi-cation). These two authors reasoned that because of the influence of gravity and the approximately 20 from hori20ntal attitude of the steel strand during solidification in these research projects, the impurities within the steel tended to rise and form a substantial æone of segregated material near the top surface of the casting. These two authors state that coupled with the top-surface oxide pit condition was an inter~
nal oxide segregation noted in macroetch tests of transverse sections. Although the oxide segregation varied in deyree, the profile was simi.lar in all slabs cast and the authors con-cluded that from this data it was apparent that the oxide seg-regation was severe enough to cause inferior sheet surface quality. A number of possible solutions were tried, such as concentrating on the elimination of mold~pool slag, use of stationary, water-cooled copper edge-dams, use of submerged feed tubes, etc., but the authors admitted that all these attempts at a solution proved fruitless. It was reasoned that heavy concentrations of segregating oxides were trapped in the solidifying slab at the time when the top skin was between l/2 to 3/4 inch thick. The authors concluded that casting at a 20 angle resulted in a me-tallurgically unacceptable product for sheet application produced from either Al-killed or vacuum-treated steel because no way to remove these oxides was ~ound and the inclusions segregated -toward the upper part of the cast billet. They suggested going back to operating the mold in the prior art (Junghans-type) vertical position as a possibility ~or overcoming the segregation problem. It is believed by applicants that the of~-center and segregated dis-tribution of the constituents and impurities also caused unpredictable variations in subsequent attempts at processing such as hot-rolling of the material.
SUMl~ARY OF THE INVENTION
_ _ .
Generally described, the present invention provides an as-cast steel bar characterized by, when compared to the prior art, a novel lack of segregation of manganese, oxygen, sulphur and carbon. On the contrary, the present invention provides an as-cast steel bar characterized by a particularly uniform distribution of manganese, oxygen, sulphur and carbon. The cast steel bar of the invention comprises steel -that, ~hen viewed in (long) transverse cross-section for macrosegre-gation, displays a maximum average variation in oxygen content less than about 20 ppm (0.0020~) and an oxygen segregation 20 standard deviation less than about ~ ppm (0.0008%) on samples containing about 0.01% oxygen, a maximllm average variation in sulphur content less than about 0.004~ (40 ppm) and a sulphur segrega-tion s-tandard deviation less than aboui 0.001 (10 ppm) on a sample con-taining about 0.02% sulphur, and a maximum avsrage variation in carbon content less than about 0.01% (100 ppm) and a carbon segregation standard deviation o~
less than about 0.004% (40 ppm) on a sample containing about 0.185~ carbon, and an improved as-cast tensile strength and elongation. Similar good results are expec-~ed for Si, P. Cr and other alloying elements normally used in steel. Microseg-regation analysis has been carried out for C, Mn, S, Cr, and Si by el0ctron microprobe. The results indicate much less microsegregation of manganese compared to prior art Concast samples. For example, heats of molten steel, con~ainng about .46% carbon and about .98% manganese, were cast both by the method disclosed herein and by the wellknown prior ar~ Concast process. Sa~nples of the as-cast bars were sectioned transver-~, sely and small specimens were cut from equivalent locations about one-half the distance from the edge toward the center.
Thus neither the best nor the worst areas were selected for comparison. The small specimens were mounted for electron micro-probe examination and analyzed to determine the concent-ration of manganese along a random line, about 1800 microns long.
This procedure is generally well-known in the ar-t and is believed to be the easiest method for detecting microsegre-gation in metals. Basically the process involves bombardingthe specimen with a small diameter beam of high energy elec-trons which cause the specimen to give off characteristic x-rays corresponding to the concentration of the elements present. The x-rays are analyzed by diffracting them with a crystal (to select one element at a time) then measuring their intensity with any appropriate detector. Concentrations of a specific element may be determined by comparing the relative intensi-ties of the x-rays generated by the element in the specimen to a known standard. To obtain maximum accuracy, about one-half of one percent, the ratio should be corrected for absorption and flourescence of the emitted x-ra~s. Alter-nately, the average intensity level can be assumed to repre-sent -the base concentration obtained by a normal chemical analysis and then the variations in intensity directly repre-sent variations from the base concentra~ion.
When this latter procedure is used to compare a number of specimens, it is useful to assign one value to each speci-men which indicates the average intensity of the significant variations and thus the average variati.on in concentration from the base level. This value may be called the microsegre-gation value and is expressed as a percentage of the base con-centration.
In our comparison the base analysis of our sample was about 0.98~ manganese. The results indicated that the prior art as-cast steel bar has a manganese microsegregation value, expressed as a percentage of base analysis, of about 300~
while the manganese microsegregation value of the as-cast bar ~,~
~,,~
produced by the method of our invention was less than about 175~.
One important feature of the invention is ~hat our novel product can be made on a known, prior art casting machine using methods of operation within the experimental skills of those having ordinary skill in our art. Our preferred method of practicing our invention consists of forming a moving arcuate mold by rotating a castlng wheel, having a peripheral groove, on its central a~is and moving a band along its length into contact with the peripheral groove at the upper part of the casting wheel, moving the band and wheel in conjunction about the lower portion of the wheel, and moving the band away from the wheel (thusly forming one type of endless moving sur-face-type mold), pouring molten steel into the arcuate mold, cooling the mold to cause the molten steel to solidify in the arcuate mold, withdrawing the cast bar from the arcuate mold, normally additionally cooling the cast bar by the use of an after-cooler after the cast bar has exited the closed portion of the mold, and progressively straightening the cast bar as it moves away from the arcuate mold. See for example U.S.
Patent No. 3,623,535 (U.S. Class 164-87) and U.S. Patent ~o.
359,348 (U.S. Class 16~-263).
Thus, it is an vbject of the present invention to pro-vide an improved a~-cast steel product.
It is a further object of the inven-tion to provide a novel continuous cast steel ~ar characterized by a lack, to an unusual degree, of segregation or inverse segregation of impurities or constituents within the bar.
It is a further object of the invention to provide a cast steel bar more suitable than prior art bars for subse-quent processing such as rolling into rod and drawing into wire or hot-forming as by forging.
It is a further object of the invention to provide a method for continuously casting a steel produc~t having improved internal properties.
Other objects, features and advantages of -the present invention will become apparent upon reading the following r ,/ ~
specification when taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic diagram illustrating one example of prior art apparatus suitable to produce the cast steel product of the invention, the apparatus including a casting machine having a rotatable casting wheel defined by a peri-pheral groove therein and an endless band covering a portion of -the length of the groove so as -to form a closed mold over that portion.
Fig. 2 is a graph showing sulphur distribution in a steel bar cast according to our invention.
Fig. 3 is a graph showing oxygen distribution in a steel bar cast according to our invention.
Fig. 4 is a graph showing oxygen distribution in a steel bar cast according to the prior art Hazelett twin-belt process.
Fig. 5 is a graph showing oxygen distribution in a steel bar cast according to another prior art process, the Junghans-type procass, and in particular, a Concast machine o~ the commercially successful -type.
Fig. 6 is a graph showing carbon distribution in a steel bar cast acco~ding -to our invention.
Fig. 7 i9 a his-tograph com~aring -the tensile strength of the novel cast steel product of our inven-tion -to another cast steel produc-t produced by a prior art process.
Fig. ~ is a graph showing the x-ray in-tensity variation due to microsegregation o manganese in a steel bar cast according to our invention.
Fig. ~ is a graph showing the ~-ray intensity variation due to microsegregation of manganese in a steel bar cast according to the prior art Concast process.
DESCRIPTION OF THE PREFERRED E~BODI~ENT
Referring now in more detail to the drawing, in which like numerals of reference illustrate like parts throughout the several views, Fig. 1 shows a cas-ting wheel apparatus 10 or producing product o the present invention. This appara-.,r tus is similar to that disclosed in U.S. Patent l~O. 3,623,535 (U.S. Class 164-87) for example. A casting wheel lO defines a peripheraî groove G therein which is covered, for a portion of the periphery of the casting wheel, by an endless flexible band or belt 11 to form a closed mold M. The flexible band 11 is held against a portion of the periphery of the casting wheel b~ band support wheels 12, 13 and 14 and moves with the wheel 10 as it rotates. Near the band support wheel 12 where the closed mold M begins, molten steel is discharged from a pouring pot or tundish 16 into the mold M through a spout 16a. In our preferred embodiment, all exterior surfaces of the casting wheel and band are continuously cooled by a spray of coolant fluid, the outer portion of the groove and band being cooled by cooling sprays from nozzles (not shown) from headers or manifolds S2, S3, S4, and the inner portion of the peripheral groove G being cooled by sprays from the nozzles on header Sl. The spray of each nozzle (or groups of nozzles) along the inner side of the peripheral groove may be indivi-dually adjusted to vary the volume of cooling fluid sprayed therefrom, and thus vary the rate at which the me-tal within the mold M is cooled. A supply ot coolant fluid to the nozzles (or groups of nozzles) may likewise be controlled by adjustable valves to allow starting and stopping of the coolant ~low and to permit variation in the total volume of coolant flow. See, for example, the cooling arrangement suggestsd by Southwire Company's U.S. Patent No. 3,279,000 (U.S. Class 164-433).
An extended bending section 18 is positioned beyond and above the band support wheel 14. The bending section 18 serves as a means for straightening the cast steel bar B with-drawn from the peripheral groove of -the casting wheel 10 a~ter exiting the closed portion o~ mold M. The bending section 18 includes a plurality o~ support guide rolls 19 mounted on a frame (not shown). Side guide rolls (not shown) may also be utilized in the bending section 18 to confine the cast steel bar approximately to a vertical plane. Although the suppor-t guide rolls 19 may be either driven or non-driven, we Eind it ~,r is preferable that at least some of the support rolls 19 be driven to assist in the straightening of the cast bar.
In our preferred embodiment an after-cooling header 21 is located above and adjacent the band support wheel 14 -to appl~ a direct spray of coolant fluid onto the cast steel bar emerging from the arcuate mold M.
In the operation of the system according to the method of the invention, the casting wheel 10 is rotated in a counter-clockwise direction and molten steel is poured from the tundish 16 through the spout 16a into the closed mold formed between the peripheral groove G of the casting wheel and the flexible band 11. Molten steel is poured in a cont-rolled manner well ~nown in the ferrous and non-ferrous casting arts into the mold M at a rate so that the rotation of the casting wheel moves the steel in the mold M away from the spout 16a as fast as the molten steel flows through the spout to maintain the surface of the pool of molten steel at a cons-tant level at the entrance of the mold M. The exit end of the spout 16a is located as closely as possible to the entrance to the mold M to allow the molten steel to flow directly from the spout into -the pool of molten metal in the mold.
As the molten steel is carried around the casting wheel 10 within the mold ~, coolant fluid is directed against the mold from the nozzle~ in header Sl and the nozzles of the other headers S2, S3 and S4, and the amount of coolan-t applied to the band and casting wheel is adjusted as desired to cont-rol the rate of cooling of the molten metal. Our preferred embodiment has a condition of ver~ uniform cooling about and along the longitudinal axis of the cast bar, see for exam~le Southwire Company's U.S. Patent No. 3,279,000 to Cofer (U.S.
Class 164-433). Initial rapid cooling and solidification of the molten metal occurs at the surfaces of the casting wheel and band, causing the formation o~ a skin or shell of soliai-fied steel having an equiaxed grain structure. Continued extraction of heat from the partially solidified bar then causes solidification of the metal within the molten core in a progressive and uniform (including uniform at each point ~;
around the periphery) manner to form a dendri-tic or substantially equiaxed structure, depending upon the superheat of the steel, from the shell toward the center of a solid steel bar B.
The steel which entered the mold M as `molten metal at an upper portion of the casting wheel moves in a downward direc-tion about the lower portion of the casting wheel and then in an upward direction until it leaves the closed portion of the mold M near the band support wheel 14, passes through the after~coolant spray from the nozzles associated with the header 21 and reaches a guide wheel 15, whereupon it is guided away from the casting wheel. In our preferred embodiment, the temperature of the exterior surface of the peripheral skin of the solidified steel as it emerges ~rom the closed portion of the mold M does not exceed about 2500F. but is not less than about 1900 or 2000F. The cast bar leaving the casting wheel has a shape conforming to the curvature of the arcuate mold M
and therefore is progressively straightened by progressively increasing the radius of the bar B as the bar moves through the extended bending section 18. The guide rolls 19 support the bar and guide it th.rough its unbending or straightening path above the casting wheel 10, at least one pair of the guide wheels 19 preferably being driven to pull the bar B
along it~ length from the casting wheel 10. The molten core of the bar ~ is compl.etely solidified by the time it passes at least the last coolant spra~ from the last nozzle on header 21 to assure that the bar is completely solid before reaching a point which is on a level with the level o~ the pool of molten metal at the entrance to the mold M. I~usly, the molten metal in the core of the bar will not flow opposite to mold movement through the unsolidified bar center thereby creating a void in the center of the bar. The bar is thereby also solid and sound metalluryically before entering the bending section 18, and its temperature just prior to bending may also be adjusted by adjusting the volume of coolant supplied by the header 21 in order to control the internal stresses of the bar during straightening.
7~
In the embodiment of the casting wheel 10 disclosed herein, the mold M is approximately trapezoidal in shape with small dimension located at the inner portion of the peripheral groove and a large dimension located adjacent -the band 11.
Thus the steel bar cast by a typical casting machine 10 may be approximately 2-5/8 inches wide a-t its largest width, 2-1/8 inches wide at its smaller width and 1-7/8 inches deep, with an approximately 1/4 inch radius joining the smaller width with the two sides of the bar. Other bar sizes and shapes may be cast as desired. To date, for example, applicants have been successful in casting an approximately 4.8 square inch bar at a speed of appriximately ~4 feet per minute (528 inches per minute) and an appriximate 8.1 square inch bar at a speed of appriximately 35 feet per minute (420 inches per minute).
Applicants believe that the novel cast steel bar of the present invention may be produced at a relatively high linear speed because the relatively long leng-th of the arcuate mold M
cooled by quick chilling coolant sprays allows solidification to be achieved in spite oE the relatively high rotational velocities of -the cast.ing wheel 10. Fur-thermore, the rela-tively small radius of the cas-ting wheel 10 causes the orien-tation of the molten steel to change rapidly as the wheel rotates, in contrast to prior art commercially proven steel continuous casting techniques wherein the solidifying steel rernains in a horizontal or apprixima-tely horizontal orien-tation for a substantial period, allowing impurities to float upwardly during the process of solidification. Applicants believe that when casting a bar B with a relatiYely small cross-sectional area according to the present invention, the bar B may be quickly solidified by the coolant spray from the nozzles associated with headers Sl, S2, S3, S4 and 21 before any substantial segregation of constituents or impurities may occur. Thus, the method of the inven-tion whereby a relatively rapidly rotating casting wheel having a relatively small radius is cooled sufficiently to quick freeze impurities before segregation and/or inverse segregation can occur, produces the novel cast steel produc-t of our invention, having ' properties significantly different from cast steel produced in prior art continuous casting machines.
Applicants believe that the design of the wheel mold, cooling water spray ~ones, and the relatively smaller cross-section of the cast bar makes it possible to achieve a higher rate of heat transfer compared to the prior art continuous steel casting methods.
Some idea of the high rate of cooling or solidification can be obtalned from the metallurgical heigh-ts of the casting systems. The metallurgical height is defined as the distance between the top of the liquid pool in the mold to the point of complete solidification. In our method, we have worked with a metallurgical height of about 15 feet or less when manufac-turing a 4.8 sq. in. bar at 35 to 44 FPM (420 to 528 IPM) and for 8.1 sq. in. bar at 25 to 35 FPM (300-420 IPM). In the conventional continuous casting systems of the Junghans-type the metallurgical heights are generally reported to be about 50 to 70 feet for casting of 4" by 4" billets at a speed of 100 to 120 inches per minute (8.33 to 10.0 FPM). We have found that our cast bar becomes completely .solid in about 25 to 30 seconds whereas we understand it requires about 6 minutes for complete solidification of the Junghans-type bar.
We believe that our fast rate of cooling reduces the flow of liquid of higher solute concentration into the inter-dendri-tic channels and thereby reduces the invarse segregation while the non-metallic impurities present in the liquid steel freeze with the liquid with a random distribution.
~ e also believe that the quick orientation change of molten steel in the moving wheel mold reduces the chances of segregation of impurities at an undesired position within the cast bar. ~lat is, offering an example, as the cast bar with its initial relatively thin frozen shell and larye molten center moves counter clockwise from opposite approximately manifold S2 (see Fig. 1), past manifolds S3, S4, and then 21 to a point where -the frozen shell has become quite large with respect to the molten center, which means that the cast bar ~r 3~
has moved through an arc of more than 90 and preferably more than 180, applicants believe that such orientation change of the casting throughout the course of solidification tends to eliminate khe forma-tion of heavy concentrations of segregated constituents or impurities which would otherwise normally float to the upper portion of the interior of the solidif~ing shell, because, essentially, the "upper portion" of the soli-difying shell is always changing throughout the rotation of the wheel.
Measurements have been made to determine the degree of segregation of sulphur and oxygen impurities, and the degree of segregation of carbon, in novel cast steel bars that were cast according to the method disclosed. To establish a segre-gation profile from the wheel side of the cast bars to the band side of the cast bars, three sets of samples for analysis were punched from (long) transverse sections of the as-cast bar, one at the center of -the section, one 20 mm to the left of the center and one 20mm to the right of the center. The values obtained were then averaged to obtain an average pro-file for each bar. Such results are shown in Fiys. 2, 3 and 6. Applicants believe that those in the art use "(long) tran-sverse" and just "transverse" interchangeably if there is no likelihood of confusion with a short transverse sec-tion (see ASTM Designation E3~9-74, Crack Plane Orientation Identifi-cation Code, for example).
Fig. 2 is a graph of average percentage sulphur composi-tion vs. position between the wheel side of the bar (Omm) and the band side of the bar (44mm in -this case), the steel having a composition by weight of approximately 0.45% carbon, 0.02%
sulphur, 0.99~ manganese, 0.02% phosphorus and 0.21% silicon (Specimen ~45). The maximum variation in average sulphur con-tent across the bar was 0.0013~ (13 ppm), for the measurements shown in Fig. 2, and the standard deviation was 0.000~98%.
Applicants believe this represents an unexpectedly high uniform distribution of sulphur with no significant delete-rious segregation. Tests of other specimens o~ the novel product indicated maximum average sulphur content variations ./~
ranging from 0.00114~ (11.4 ppm to 40 pmm), and sulphur standard deviations varying from 0.000483~ to 0.00138% in samples having 0.01755% and 0~02993% sulphur, respectively, as shown below.
Average of 3 sulphur measurements at each position listed ln PPM
Specimen ~ = 26 41 43 45 48 5mm = 170.31308.0 234.3 226.7 316 15mm = 180.7310.6 233.0 240.0 328 10 25mm = 174.3271.0 223.7 235.0 316 35mm = 170.7297.6 227.0 239.7 317 40mm = 181.7297.6 231.0 238.7 325 47mm = -- 311.0 238.7 -- --Average = 175.5299.3 231.2 236.0 320.4 Range = 11.440.0 11.7 13.0 12.0 Std.
Deviation = 4.83 13.8 4.88 4.98 5.03 Fig. 3 is a graph of average oxygen content (in pmm) vs. position between wlleel and band sides for the same cast bar, #~5, measured in Fig. 2. I'he oxygen content was approximately 70 ppm (0.007~) and the maximum variation in average oxygen content across the bar, as shown in Fig. 3, was 5 ppm (0.0005~), and the standard deviation was 1.65L ppm.
I'his again represents an unexpectedly good result -- a very high degree of uniformi-ty of constituents in the structure of the novel cast steel bar. It should also be noted that center porosity, sometimes present in a continuously cast steel bar (even ours), may contribute to the measured oxygen content at that particular location in the bar. Applicants believe that such porosity does not represent true segregation to those in the art and is generally healed during subsequent hot proces-sing.
~''.'1 ....
The improved oxygen segregation properties oE the present invention may be seen by comparing Fig. 3 to Figs. 4 and 5. Fig. 4 is a graph of percentage of oxygen content vs~
position between the bottom and the top of a cast bar cast using a Hazelett Strip-Casting machine having a substantially horizontal mold. The graph is taken from page 43, Fig~ 6 of ~hitmore, B.C. and Hlinka, J~Wo ~ ~Continuous Casting of Low-carbon steel Slabs by the Hazelett Strip-Casting Process,"
Open Hearth Proceedings, 1969. Converting to a ppm basis, Fig. 4 shows a maximum variation of approximately 100 ppm t0-01%) or more and a standard deviation of approximately 29.8~ ppm. This approximately 20 from horizontal Haselett experimental mold process thus produced a cas-t bar with a significant oxygen ~egregation problem even when the average oxygen content was relatively low, about 0.004%. The worst segregation was located near the top surface of the bar as is evident from Fig. 4 herein and the Whitmore and Hlinka publi~
cation.
Fig. 5 is a graph of oxygen content vs. position for a cast steel bar produced by a Concast vertical mold csn-tinuous casting machine including an arcuate oscillating moLd. The graph represents an average of five samplings taken in (lony) transverse section from the bottom to the top of the bar, which had a cornposition by weight of 0.46% carbon, 0~94% man-ganese, 0.021% phosphorus, 0.016% sulphur and 0.22% silicon.
I'he maximum variation shown in Fig. 5 is approximately 2~.5 ppm, and the standard deviation is 10.6 ppm. The average oxy-gen content is about 0.006%. ~nother specimen, having an average oxygen content of about 0.00~%, showed a variation of 29 ppm.
~ cast bar produced according to the me-thod of the invention also has an unexpectedl~ uniform carbon distribu tion, as shown in Fig. ~ which is a graph showing an average profile of the carbon content of such a cast bar (Specimen #48). This particular bar had a composition by weight of approximately 0.185% carbon, 0.59% manganese, 0.01% phos-phorus, 0.032~ sulphur, and 0.17% silicon. The psints plotted ,.,,,~
,1' in Fig. 6 are averages of three measurements for each position across the cast bar between wheel and band sides, as was the case for Figs. 2 and 3. Fig. 6 shows a maximum average carbon content variation across the bar of approximately 0.009% (90 ppm), and a standard deviation of 0.00305%. In accordance with this invention, the steel melt is preferably prepared from a chemical system which has carbon present as one of the constituents in a range of appro~imately 0.04~ by weight to 1.4% by weight. The maximum variation for samples in this range at variance with our specimens are expected to be pro-portional. Applicants have found that particularly superior results are achieved when the carbon content of the steel is between about 0.06% and 0.80~ by weight.
Still further measurements have been made to determine the as-cast tensile strength of the novel cast steel bar of the invention, and to compare it to the as-cast tensile strength of a steel bar cast using a prior art commercially proven Concast machine including an oscillating, arcuate mold, both steel bars having been cast from the same steel melt.
The measurements were carried out at a strain rate of 0.001/
second using an one inch Extensometer. Fig. 7 is a hlstograph showing the tensile strength of a sample of the novel cast bar to be approximately 107 110 ksi (107,000-110,000 pounds per square inh) as compared to that of the prior art Concast bar which had a tensile strength of approximately 93-9~ ksi. '~he composition of the steel on this melt was 0.~5~ carbont 0.97%
manganese, 0.019% phosphorus, 0.017% sulphur, and 0.21% sili-con. Applicants believe that the approximate 10~-15~ or more increase in tensile strength o~ their novel product is consis-tent with the unusually uniform distribution of constituentsand impurities observed in the novel product, as described above. In these same tests it was also observed that the novel as-cast ~ar had a greater percent elongation and a greater proportional limit in ksi than the prior art Concast bar, see below:
Proportional Test Sample Tensile Strength % Elongation Limit NoveL 1 107 ksi 10 6403 ksi Bar 2 110 ksi 13 71.7 ksi 3 108 ksi 16 72.0 ksi .. _ . _ . . . ~
Prior 4 94 ksi 8 62.0 ksi Art Bar 5 93 ksi ~ 8 57.8 ksi Fig. 8 graphically shows the intensity o~ characteristic manganese x-rays, along a random line of about 1800 microns in length, within a specimen of steel bar cast by the present invention. It can be seen that the intensity level is rela-tively constant about -the line marked 100% which corresponded to the base concenkration of 0.98% manganese and which also corresponded to an absolute reading of approximately ll units on the graphical readout from the electron microprobe analyzer. l~here is only one significant variation which measures about 173% of the base leve; i.e., equivalent to a local concentration of about 1.69~ manganese.
Fig. 9 graphically shows the manganese x-ray intensity in a specimen cast by the prior art Concast process. It should be noted that the intensity level con~ains many peaks which correspond ~o small areas of segregated manganese.
Here, an absolute reading of approximately 12 units was observed on the strip chart readout from the electron micro-probe unit and used for the 100% line. The average value ofthe most significant peaks is about 320% of the base level and the maximum variation in manganese content observed was over 400%, see below:
Peak % of Base Level . _ ~1 3966
2 227~6
3 292%
4 404 6 335~
Applicants have found that particularly superior results are achieved when the manganese content of the steel is between about 0~30~ and 1.20~ by weight.
While this invention has been described in detail with particular reference to pre~erred embodiments thereof, it will be understood that variations and modifications can be effec-ted within the spirit and scope of the invention as described hereinbefore and as defined in the appended claims. For example, applicants have reported herein only a representative sampling of the infinite number of steel compositions which may be cast according to the present invention. For other compositions in which the concentrations of the constituents and impurities are at variance with the exact concentrations in the specimens analyzed, applicants expect propor-tionally improved results.
~,
Applicants have found that particularly superior results are achieved when the manganese content of the steel is between about 0~30~ and 1.20~ by weight.
While this invention has been described in detail with particular reference to pre~erred embodiments thereof, it will be understood that variations and modifications can be effec-ted within the spirit and scope of the invention as described hereinbefore and as defined in the appended claims. For example, applicants have reported herein only a representative sampling of the infinite number of steel compositions which may be cast according to the present invention. For other compositions in which the concentrations of the constituents and impurities are at variance with the exact concentrations in the specimens analyzed, applicants expect propor-tionally improved results.
~,
Claims (13)
1. A continuous cast steel bar comprising in transverse cross-section an oxygen segregation standard deviation less than about 10 ppm.
2. The continuous cast steel bar as claimed in claim 1, wherein the oxygen segregation standard deviation is less than about 5 ppm.
3. The continuous cast steel bar as claimed in claim 1 or 2, further comprising in transverse cross-section a maximum average variation in sulfur content less than about 0.004%.
4. The continuous cast steel bar as claimed in claim 1 or 2, further characterized as comprising in transverse cross-section a sulfur segregation standard deviation less than about 0.0015%.
5. The continuous cast steel bar as claimed in claim 1 or 2, further characterized as comprising in transverse cross-section a maximum average variation in carbon content less than about 0.01%.
6. The continuous cast steel bar as claimed in claim 1 or 2, further characterized as comprising in transverse cross-section a carbon segregation standard deviation of less than about 0.004%.
7. The continuous cast steel bar as claimed in claim 1 or 2, further characterized as having a tensile strength at least 10% greater and an elongation at least 10% greater than a steel bar cast on a Junqhans-type caster from the same melt.
8. The continuous cast steel bar as claimed in claim 1 or 2, further characterized as comprising in transverse cross-section a sulfur segregation standard deviation less than about 0.0015% and in transverse cross-section a maximum average variation in carbon content less than about 0.01%.
9. The continuous cast steel bar as claimed in claim 1 or 2, further characterized as comprising in transverse cross-section a sulfur segregation standard deviation less than about 0.0015% and in transverse cross-section a carbon segregation standard deviation of less than about 0.004%.
10. The continuous cast steel bar as claimed in claim 1 or 2, further characterized as comprising in transverse cross-section a maximum average variation in carbon content less than about 0.01% and in transverse cross-section a carbon segregation standard deviation of less than about 0.004%.
11. The continuous cast steel bar as claimed in claim 1 or 2, further characterized as comprising in transverse cross-section a sulfur segregation standard deviation less than about 0.0015% and in transverse cross-section a maximum average variation in carbon content less than about 0.01% and having a tensile strength at least 10% greater and an elongation at least 10% greater than a steel bar cast on a Junqhans-type caster from the same melt.
12. The continuous cast steel bar as claimed in claim 1 or 2, further characterized as comprising in transverse cross-section a sulfur segregation standard deviation less than about 0.0015% and in transverse cross-section a carbon segregation standard deviation of less than about 0.004% and having a tensile strength at least 10% greater and an elongation at least 10% greater than a steel bar cast on a Junqhans-type caster from the same melt.
13. The continuous cast steel bar as claimed in claim 1 or 2, further characterized as comprising in transverse cross-section a maximum average variation in carbon content less than about 0.01% and in transverse cross-section a carbon segregation standard deviation of less than about 0.004% and having a tensile strength at least 10% greater and an elongation at least 10% greater than a steel bar cast on a Junqhans-type caster from the same melt.
Applications Claiming Priority (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US614879A | 1979-01-24 | 1979-01-24 | |
| US006,148 | 1979-01-24 | ||
| US7055079A | 1979-08-29 | 1979-08-29 | |
| US070,550 | 1979-08-29 | ||
| CA000344279A CA1179473A (en) | 1979-01-24 | 1980-01-23 | Continuous cast steel product having reduced microsegregation |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000344279A Division CA1179473A (en) | 1979-01-24 | 1980-01-23 | Continuous cast steel product having reduced microsegregation |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1184792A true CA1184792A (en) | 1985-04-02 |
Family
ID=27166566
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000449720A Expired CA1188910A (en) | 1979-01-24 | 1984-03-15 | Continuous cast steel product having reduced microsegregation |
| CA000449719A Expired CA1184792A (en) | 1979-01-24 | 1984-03-15 | Continuous cast steel product having reduced microsegregation |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000449720A Expired CA1188910A (en) | 1979-01-24 | 1984-03-15 | Continuous cast steel product having reduced microsegregation |
Country Status (1)
| Country | Link |
|---|---|
| CA (2) | CA1188910A (en) |
-
1984
- 1984-03-15 CA CA000449720A patent/CA1188910A/en not_active Expired
- 1984-03-15 CA CA000449719A patent/CA1184792A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| CA1188910A (en) | 1985-06-18 |
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