CA1130981A - Continuous cast steel bar and the method to produce same - Google Patents
Continuous cast steel bar and the method to produce sameInfo
- Publication number
- CA1130981A CA1130981A CA317,970A CA317970A CA1130981A CA 1130981 A CA1130981 A CA 1130981A CA 317970 A CA317970 A CA 317970A CA 1130981 A CA1130981 A CA 1130981A
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- Canada
- Prior art keywords
- bar
- casting
- mold
- cast
- mould
- Prior art date
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/06—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars
- B22D11/0602—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars formed by a casting wheel and belt, e.g. Properzi-process
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/06—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Continuous Casting (AREA)
- Metal Rolling (AREA)
- Molds, Cores, And Manufacturing Methods Thereof (AREA)
Abstract
TITLE
AN IMPROVED CONTINUOUS CAST STEEL
BAR AND THE METHOD TO PRODUCE SAME
INVENTORS
George Charles WARD, Thomas Noell WILSON and Uday Kumor SINHA
ABSTRACT
A cast steel bar having improved qualities is produced by means of a continuous casting machine of the type having a rotating casting wheel with a peripheral.
groove which is closed along a portion of its length by a metal band moving along its length into engagement with the peripheral groove, then moving about the lower portion of the casting wheel, and then moving away from the casting wheel to form a moving arcuate mold. As molten steel is poured into the arcuate mold the casting wheel and band are cooled to solidify the steel while in the arcuate mold, and means are provided for progressively straightening the curved bar as the bar is withdrawn from the arcuate mold of the castin? machine.
AN IMPROVED CONTINUOUS CAST STEEL
BAR AND THE METHOD TO PRODUCE SAME
INVENTORS
George Charles WARD, Thomas Noell WILSON and Uday Kumor SINHA
ABSTRACT
A cast steel bar having improved qualities is produced by means of a continuous casting machine of the type having a rotating casting wheel with a peripheral.
groove which is closed along a portion of its length by a metal band moving along its length into engagement with the peripheral groove, then moving about the lower portion of the casting wheel, and then moving away from the casting wheel to form a moving arcuate mold. As molten steel is poured into the arcuate mold the casting wheel and band are cooled to solidify the steel while in the arcuate mold, and means are provided for progressively straightening the curved bar as the bar is withdrawn from the arcuate mold of the castin? machine.
Description
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BACKG~OUND OF T~IE INVENTION
__ This inverltion relates to continuous casting of steel and pertains more part:icularly to methods and apparatus for the production of continuous lengths of steel bars which have improved qualities.
In the usual methods for the continuous casting of metals such as steel, the molten metal is poured into an open ended vertical mold. The mold chills the periphery of the metal and solidifies a skin or shell on the mold wall to define a strand which is withdrawn continuously from the bottom of the mold while molten metal is poured continuously into the top of the mold. The rate of withdrawal of the cast metal from the mold is adjusted to equal the volume of molten metal poured into the mold. After issuing from the mold, the hot strand is cooled, for example, by water sprays directed on the semi-solid strand to Eorm a fully solidified strand. The cooliny appli~d to the strand after it issues from the mold is known in the art as secondary cooling and is sufficient to complete the solidification of the strand prior to any subsequent processing.
In most continuous casting installations, the axis of the mold is vertical and the strand issues vertically downwardly therefrom. After the strand is completely solidified, pieces of the desired lcngth are severed frorn the moving strand. Because it is necessary that the strand be completely solidified before cutting, casting speeds have been limited by vertical height considerations. That is, it has been necessary to limit casting speeds in order to permit complete solidification to take place within reasonable vertical dimensions between the mold and the cutting station. Otherwise, plant construction costs become excessive.
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BACKG~OUND OF T~IE INVENTION
__ This inverltion relates to continuous casting of steel and pertains more part:icularly to methods and apparatus for the production of continuous lengths of steel bars which have improved qualities.
In the usual methods for the continuous casting of metals such as steel, the molten metal is poured into an open ended vertical mold. The mold chills the periphery of the metal and solidifies a skin or shell on the mold wall to define a strand which is withdrawn continuously from the bottom of the mold while molten metal is poured continuously into the top of the mold. The rate of withdrawal of the cast metal from the mold is adjusted to equal the volume of molten metal poured into the mold. After issuing from the mold, the hot strand is cooled, for example, by water sprays directed on the semi-solid strand to Eorm a fully solidified strand. The cooliny appli~d to the strand after it issues from the mold is known in the art as secondary cooling and is sufficient to complete the solidification of the strand prior to any subsequent processing.
In most continuous casting installations, the axis of the mold is vertical and the strand issues vertically downwardly therefrom. After the strand is completely solidified, pieces of the desired lcngth are severed frorn the moving strand. Because it is necessary that the strand be completely solidified before cutting, casting speeds have been limited by vertical height considerations. That is, it has been necessary to limit casting speeds in order to permit complete solidification to take place within reasonable vertical dimensions between the mold and the cutting station. Otherwise, plant construction costs become excessive.
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In the casting of steel, thesc problems have been of particular concern because o~ the high temperature of the molten steel, and the long time required to completely solidify the strand. For example, in typical installations for the continuous casting of steel, a distance of seventy feet between the mold and the cutting station is not uncommon, and even this distance requires restriction of the casting speed to less than that which is theoretically possible.
In order to reduce the vertical height requirements, it has been proposed to cast the strand in a vertically disposed mold, then to cool the emerging strand in a vertically disposed secondary cooling zone in which the casting is supported by rollers. The strand is then bent toward the horizontal by pairs of pressure rollers. In such installations, the strand is bent throuyh an arc o~
approximately 90 so that the bent strand becomes tangent to the horizontal. At the tangent point, the strand is rebent and straightened by pairs of pressure rollers, and it is then transported horizonally to a cutting station. This permits some reduction of machine height, but has not provided a satisfactory solution of the problem because a bending arc of relatively long radius is required. Even with a large radius, there is still difficul-ty in bending and then rebending thc solidified casting without cracking or otherwise damaging the casting.
A further reduction of height and overall length of casting machines has been achieved by making the mold cavity curved so that the strand emerges from the mold in curved condition conforming to the curved path. Molds with curved cavities, however, have not been completely satisfactory. Mold cavities are customarily provided with
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In the casting of steel, thesc problems have been of particular concern because o~ the high temperature of the molten steel, and the long time required to completely solidify the strand. For example, in typical installations for the continuous casting of steel, a distance of seventy feet between the mold and the cutting station is not uncommon, and even this distance requires restriction of the casting speed to less than that which is theoretically possible.
In order to reduce the vertical height requirements, it has been proposed to cast the strand in a vertically disposed mold, then to cool the emerging strand in a vertically disposed secondary cooling zone in which the casting is supported by rollers. The strand is then bent toward the horizontal by pairs of pressure rollers. In such installations, the strand is bent throuyh an arc o~
approximately 90 so that the bent strand becomes tangent to the horizontal. At the tangent point, the strand is rebent and straightened by pairs of pressure rollers, and it is then transported horizonally to a cutting station. This permits some reduction of machine height, but has not provided a satisfactory solution of the problem because a bending arc of relatively long radius is required. Even with a large radius, there is still difficul-ty in bending and then rebending thc solidified casting without cracking or otherwise damaging the casting.
A further reduction of height and overall length of casting machines has been achieved by making the mold cavity curved so that the strand emerges from the mold in curved condition conforming to the curved path. Molds with curved cavities, however, have not been completely satisfactory. Mold cavities are customarily provided with
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liners of copper because of its good heat conducting properties. The curved copper mold liners have higher fabricating and maintenance costs than straight copper liners for straight mold cavities. In addition, proper aligning of a mold with a curved cavity is more difficult than properly aligning a mold with a straight cavity.
Mowever, the strand which emerges in straight condition from a straight mold cavity must then be bent into the curved path and this bending operation requires additional vertical space as compared with the vertical space requirement for machines having curved mold cavities. Thus, in known casting machines the benefit.s of conducting the strand along a curved path from thc mold warrant the continued usc of curved paths, but thcse beneEits have been diminished by the above-descrihed problems with the molds.
In addition to eEforts to reduce the vertical space required for continuous casting there has been a continuing effort to increase the casting speed. It is known that continuous relative motion between the casting and the mold impedes the transfer of heat from the solidifying casting to the mold wall and thus limits the casting rate. To date the most notable increase has been achieved by oscillating the mold along a short path in the casting direction as disclosed by Junghans in U.S. Patent No. 2,135,183. For casting steel, a usual amount of oscillation of the mold is about 1/10 to 1/30 the length of the mold, 1/16 to 2 inches, for example. In known constructions, molds having curved mold cavities are oscillated in an arc corresponding to the curvature of the path along which the strand is conducted from the mold. If, however, a mold having a straight cavity is used--to avoid the above-mentioned difficulty with curved mold .,,.j, ~3~)98~
passages--the strand must be conducted from the rnold in a straight vertical line for a sufficient distance to avoid rubbing of the lower edge of the mold against the portion of the casting at the inside of its arcuate path. But this involves increasing the vertical space required. In addition, tests have shown that at higher casting speeds a strand cast in a straight mold cavity and then bent to follow a curved path from the mold tends to develop internal defects and surface cracks.
A much more serious problem, common to both straight and curved mold cavities, is one which arises as a direct consequence of increased casting rate, namely, the problem of obtaining satisfactory surface characteristics.
A characteristic oE castings produced by an oscillating mold is the presence of oscillation marks or rings extendinc3 around the casting in the surface thercof.
Duc to friction bctwcerl the advancing cast bar and the oscillating mold surface, axial stresses are imposed on the thin solidifying metal shell. These alternating stresses can cause surface cracks or other defects at intervals along the length of the casting usually in the form of rings around the entire circumference of the strand. These rings are spaced at distances e~ual to the total advance of the casting between successive strokes of the mold. That is, if the total advance of the casting is two inches between the beginning of one retracting stroke of the mold and the beginning of the next succeeding retracting stroke, the rings will be found to be spaced at two inch intervals.
Further, the width of the rings, i.e., the distance lengthwise of the casting which these defects may be observed, varies depending on the conditions of the casting operation. With extreme care and operating at a low casting 9~
rate, the effects may be minilnized, but in general, the width of the rings is related to the time of the retracting stroke of the mold. That is, if the return stroke consumes one fourth of the time of a complete cycle~ the rings will be formed to cover at least one fourth of the surface of the cavity.
These rings are characterized by a roughened exterior surface, frequently with surface cracking, and frequently with evidence of "bleeding" i.e., the leaking of molten metal through a lesion in the formerly modified skin of the casting, with subsequent solidification of the leaking metal. The crystalline structure of the metal lying just under the rings is also irregular and disturbed.
In the case of non-ferrous metals, these effects have been undesirable, but not too scrious. In many cases, dcspite the surface imp~rfections the castinys could be rolled, extrudcd or otherwise processed without difficulty.
In other cases a light scalping or other surface conditioning operation was sufficient to remove all objectionable surface imperfections. In the case of steel, however, such surface imperfections cannot be tolerated, and it is not economically feasible to remove the imperfections by scalping. Moreover, the economical continuous casting of steel demands a far greater casting rate than is customary or desirable in casting non-ferrous metals, and it has been found that the increased casting rate magnifies the difficulty. Thus, in casting non-ferrous metals a casting rate of thirty to sixty inches per minute is usually ade~uate, and at these speeds, the suirface imperfections are tolerable in non-ferrous metals. In casting stee, on the other hand, casting rates as high as two hundred inches per minute have already been successfully achieved with the ~L~3~98~
Junghans process, but this success is tempered by the fact that at these speeds, the surface imperfections within the ring areas are often extremely bad. Between successive rings, the surface is usually good and the interior crystalline structure is acceptable.
From the theoretical point of view, thereforee, the ideal form of mold for continuous casting might be a curved one of greatly extencled length, but since this cannot exist in practice, other devices have been utilized.
Thus, it has been proposed to use endless supports such as revolving drums, wheels and the like, or endless moving bands or endless chains of mold sections which join together to form a mold at the start of the solidification process and separate at its conclusion to release the solidified metal. Sincc the surEaces of such movable supports CAn rc~main stationary with respect to the metal during the solidification process, favorable conditions are provided for the solidification of metal with good crystalline structure and smooth surface characteristics.
But while such methods offer some theoretical advantages, actual experience with them has been disappointing.
Constructional and operating difficulties have provided so many obstacles to practical successful operation that such methods have made little or no headway in actual commercial operation.
Therefore on balance, the use of oscillating molds with curved cavities has, up to the present, been considered the most satisfactory arrangement for reducing the height of the apparatus and for increasing the rate of casting, despite the problems with oscillating curved mold liners, described above.
Horizontal molds have been utilized heretofore for the continuous casting o~ aluminum and some other non-ferrous metals in machines in which the molten metal is introduced into a horizontal mold through a refractory feed spout which extends through the end wall of the mold. When casting aluminum, the feed spout is not wet by the molten aluminum and it remains clean as casting proceeds. ~lowever, when casting steel, and in partic~llar, where it is desired to use an oscillating mold, this type of horizontal mold with a refractory feed spout cannot be emp:Loyed. It has been found that steel wéts the spout and solidifies around the spout. The solidified steel tends to build up a false tube extending the length of the mold, resulting in a breakout of molten metal at the exit end of the mold.
In addition, it is known that the position and direction of th~ in1Owing st:ream of molten metal greatly a~ects the solidiication proccss and thereore the resulting product.
A horizontal casting mold usually necessitates a horizontal inflowing stream of molten metal which washes against metal which is already beginning to solidify on the mold wall. This causcs the solidifying metal to remelt, often resulting in blceding of molten metal to the outside of the casting. If the velocity of thc inflowing metal is high or is such to cause turbulence in the pool of molten metal, bubbles of gas and particles of oxides, slag, or dirt floating on the surface of the molten metal may be entrapped, causing holes and inclusions in the casting sometimes even resulting in gross porosity and "piping" in the casting. At the very least, a horizontally solidified bar exhibits internal variations across its section due to the effects of gravityO For example trapped gases ancl light particles tend to float upwards toward the topside of the ~ ~098~
bar. Thus the center of the bar may be sound but an area of porosity or of inclusions is located near one edge of the bar. This off-center distribution of defects is often more serious than center defects since it causes unpredictable variations in subsequent processing, e.g., hot-rolling into rod. Consequently, if it is desirable that the pool of molten metal be open or exposed at the top so that trapped gases and other impurities can avoid being trapped into the solidifying bar, or at least confined to the center where they are least harmful.
When a continuous casting of rectangular cross scction initially solidifi~s inside a typical horizontal mold, the larger top and bottom surfaces are necessarily exposed to morc rapid cooling. The resulting shrinkage eEfects cause these surfaces, especially the top, to pull away erom the walls of the mold before moving very far from the molten pool thus slowing the initially rapid cooling.
Since the several edges and surfaces do not all shrink uniformly, the cooling rates and therefore temperatures, stresses, and thickness of the frozen shell all differ from one surface to another. ~hese drawbacks become more pronounced at higher casting rates and as the casting continues to move through the mold, bright and dark areas appear on the billet as it issues from the mold. The bright areas often indicate high temperature locations where remelting of the once frozen shell can occur. Remelting occurs due to the transfer of heat from the still hot interior of the bar. At these points of weakness, the stresses in the frozen shell produce cracks which can cause breakouts or other surface defects.
Moreover, the unequal stresses have another undesirable consequence, namely that of causing a type of - _ 9 ~L~3~
geometrical distortion of the cast bar known as rhombic distortion which is a nuisance in subsequent processing of the casting.
SUMMARY OE' THE INVENTION
It is therefore an object of the invention to provide an improved method and apparatus for continuously casting steel.
It is another object of the invention to provide a novel continuous cast steel bar having improved qualities when compared to previous continuously cast steel bars.
More particularly, it is an object of this invention to provide a much faster method of continuously casting a steel bar which is suitable for directly rolling into wrought products.
Now in order to implement these and still further objects of the invention, which will become more readily apparent as the description proceeds, the method aspects of this development are manifested by casting steel into a mold formed by a peripheral groove in a rotating casting wheel and a band which seals a length of the groove.
In accordance with prevailing practice, the mold is preferably made of a metal of high thermal conductivity, such as copper alloy, and the mold is chilled by directly spraying coolant onto the mold or by circulating coolant, such as cold water, therethrough.
The mold groove may be of various shapes~ as desired, in transverse cross section, as for example, semi-circular, or approximately rectangular. However, it has been found advantageous to use a trape20idal cross-sectional shape having small (7 to 14) relief angles on the sides and having a width to depth ration of 1.5 to 1 or greater.
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In casting, the molten steel is cast into the mold and is uniformly chilled by withdrawal of heat throuyh the mold walls to form a thin peripheral skin of solidified metal surrolnding the molten metal within. The rate oE
withdrawal of heat is controlled with relation to the casting speed, by regulation of the rate of circulation of the mold coolant, or otherwise, so that the temperature of the exterior surface of the peripheral skin of solidified metal as it emerges from the mold does not exceed about 2500F. but is not less than about 2000~F.
The emerging strand is then conducted along a supporting passageway to a substantially horizontal cooling zone for final cooling.
The supporting passageway can be forrned by a series of members which have surfaces which enyage and support the strand. The members may have provisions for urging the bar along its path to the next process station.
The cast bar follows a path of progressively increasing radius until it becomes rectilinear.
Another important difference is that this invention provldes for controlling the heat-transfer rate in coordination with the solidification process. For example, since the molten metal is continually introduced into a relativcly large cold wheel structure, the wheel functions as a heat sink and the heat transfer rate is very high, causing rapid cooling which forms a relatively thick chilled layer in the cast product, while later the heat transfer rate is lower, allowing an orderly growth of the solidification front.
The resulting continuous length of cast bar has better surface and interior qualities than known prior art steel bars cast by prior art methods. For exarnple, the ~3~
surface is free from laps or seams normally associated with oscillation marks. In addition, due to the unique casting process, elongated casting mold and fast casting rate, the as-cast bar has a thinner oxide scale on the surface than prior art bars.
The invention therefore comtemplates a process of continuously casting steel, characterized by the steps of progressively casting molten steel in an arcuate mold into a bar having an arcuate shape along its length, progressively moving the arcuate bar along its length from the mold, and progressively straightening the bar as the bar is withdrawn from the mold.
BRIEF DESCRIPTION OF THE DRAWING
The invention will now bc explained in more detail with respect to the accornpanying drawings in which:
Figure 1 is a schematic cliagram illustrating one example of apparatus suitable to practice the invention, this apparatus comprising a casting machine having a rotatable casting wheel containing a peripheral groove and endless metallic band which seals a length of the groove;
Figures 2 - 11 are histographs of the properties of the novel cast steel product and of the properties of another cast steel product cast by a prior art process.
DETAILED DESCRIPTION
While these figures and the following detailed description disclose an embodiment of the invention, it will be understood that the present invention is not limited to the exact details disclosed herein since it may be embodied in other equivalent forms without departing from the inventive concepts.
Referring now in more detail to the drawing, in which like numerals of reference illustrate like parts 9~
throughout the several views, Figure 1, shows casting wheel 10 having a four foot radius and a groove in its periphery and an endless flexible band or belt 11 positioned against a portion of its periphery by band support wheels 12, 13 and 14. The band support wheel 12 is positioned near that point on the casting wheel 10 wherein molten steel is discharged by a pouri,g pot or tundish 16 into a mold M formed by the band 11 and a peripheral groove G around the casting wheel 10. The band support wheel 14 is positioned adjacent that point on the casting wheel 10 at which partially solidified metal is discharged from the casting wheel 10. The exterior surfaces of the casting wheel and band are continuously cooled by coolant fluid, as by the sprays of coolant fluid from the nozzles Sl at the inner portion oE the peripheral groove and the nozzles (not shown) extending from the headers S2, S3 and S4 ahout the outer portion of the peripheral groove. Each nozzle can be individually adjustable to vary thc volume of fluid sprayed therefrom, and the conduits which supply the coolant fluid to the nozzles are controlled by adjustable valves for the purpose of starting and stopping coolant flow and for varying the volume of coolant flow.
Positioned beyond and above the band support wheel 14 is an extended bending section 18 which serves as a means straightening the cast steel bar withdrawn from the casting wheel 10. The bending section 18 includes a plurality of support rolls 19 supported by a frame (not shown). An after cooling header 21 is located above and adjacent band support wheel 14 and applies a direct flow of coolant fluid to the cast bar emerging from the arcuate mold.
The support rolls 19 may either be driven or non-driven; however, it is anticipated that in most ~- - 13 circumstances at least some of the support rolls will be driven to assist in the straightening of the cast bar. Side guide rolls (not shown) also can be positioned on opposite sides of path P to retain the bar in its path.
In the operation of the system, the molten steel is poured from the rundish 16 through its downwardly projecting spout 16a into the peripheral groove G of the casting wh.el lO. The exit end of the spout 16a is located as closely adjacent the beginning of the arcuate mold as practical so as to allow the molten steel to flow directly from the nozzle exit into the pool of mol-ten steel in the arcuate mold. The flow of steel and the angular velocity of the casting wheel are regulated so that the steel being cast in the arcuate mold is moved away from the nozzle 16a as fast as the molten steel flows through the nozzle so as to main~in thc ~ureace o~ the pool of molten steel at a constant level at the cntrance o the arcuate mold. [n addition, the ~low control system for the conduits that direct coolant fluid to the nozzles Sl and the headers S2, S3 and S4 are also adjusted so as to apply the desired amount of coolant to the band and casting wheel, to thereby control the rate of cooling of the molten metal as it moves about the arcuate mold. The relatively large size of the casting wheel 10 causes the casting wheel to function as a heat sink in that the heat given up by the molten metal first flowing into the arcuate mold is dispersed into the relatively large casting wheel and the relatively large surface of the casting wheel is cooled by the coolant fluid applied from the nozzles of the system. As a result, a large amount of rapid cooling and solidification of the molten metal takes places at the surfaces of the casting wheel and bànd, and the continuous extraction of heat from ~309~
the partially cast bar by the casting whecl, band and coolant fluid continues to cause solidification of the molten metal in what is believed to be a progressive and uniform solidi~ication from the surface of the cast bar toward the center of the cast bar.
The band 11 moves into contact with the annular groove G of the casting wheel 10 as it moves off guide roll 12, so that the band makes contact with the casting wheel 10 at an upper portion of the casting wheel and then moves in a downward direction about the lower portion of the casting wheel, then in an upward direction until it reaches the guide wheel 15, whereupon it is guided away from the cas-ting wheel. The mold M formed by the peripheral groove G and the band 11 is an elongated arcuate mold that moves continuously with the rotation of the casting wheel 10, and the cast bar B formed in the arcuate mold M conforms to the ar¢~late shape of the mold until it is extracted from the mold. The radius of the bar B must be increased in order to extract the bar from the arcuate mold, and the bar is progressively straightened with a progressively increasing radius as the bar moves through the extended bending section 18 of the assembly. The rolls 19 guide the bar through its ~nbending or straightening path over the casting wheel 10, and preferably, at least one pair of the guide wheels 19 are driven so as to pull the bar B along its length from the casting wheel 10. The pulling forces applied to the bar as well as the leverage applied to the bar by the lower ones of the guide rolls 19 located beneath the bar B function to support and straighten the bar. Also, the continuous straightening of the bar as -the bar moves away from the casting wheel causes a substantial amount of internal stress in the bar. The amount of stress applied to the bar can be 1.~.3098~
increased or decreased by decreasing or increasing the temperature of the bar as the bar moves through the bending section 18 of the assembly. Moreover, by varying the amount of coolant applied by manifold 21 adjacent the exit of the bar from the casting wheel the temperature of the bar passing through the bending section 18 can be varied and controlled so as to adjust the internal stresses of the bar B during its travel through the bending section 18. As the bar first leaves the casting wheel the bar is more radically bent and the bar then progresses further on its path through the bending section 18 where it is less radically bent. The header 21 applies coolant fluid to the bar at its exit from the mold to assure that the bar is completely solid before the bar reaches the level of the pool of molten metal at nozzle 16a. This assures that the internal core of molten metal in the bar will not create a negative pressure and form a void in the bar. Also, the volume of coolant applied by header 21 can be adjusted to adjust the temperature of the solid bar being extracted from the mold, thereby controlling the internal stresses of the bar.
Because of the relatively long length of the arcuate casting mold formed by the band 11 and peripheral groove G of thc casting wheel 10, the casting wheel can be rotated at a relatively high angular velocity and still achieve the solidification of the molten metal as desired.
In the particular disclosed embodiment, the mold M is approximately trapezoidal shaped with a small dimension located at the inner portion of the peripheral groove and with a large dimension located adjacent the band 11. The bar cast by the casting machine in the example disclosed is approximately 2 5/8 inches wide at its larger width, 2 1/8 inch wide at its smaller width and 1 7/8 inches deep, with .,~
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an approximately 1/4 inch radius joining the smaller width with the two sides of the bar. Other bar sizes and shapcs can be cast as may be desired.
The relatively high rotational velocity of the casting wheel causes the bar B to exit from the casting wheel at a relatively high linear speed, so that the bar is advanced at a rapid rate on toward the next processing stage, such as to a rolling mill. The rapid movement of the bar together with the bar having been enc:Losed in a relatively long mold reduces the tendency of the surface of the bar to form scale.
Measurements have been made of the properties of a cast steel bar which was cast in a rotatable casting whcel of the type illustrated at 10 in E'igure 1. Thc prope~ties of this cast stcel bar were compared with thc properties of a cast bar fabricated from a concast~ continuous casting machine which includes an arcuate oscillating mold. The properties of the novel cast steel bar and of the prior art cast steel bar are compared in Figures 2-11. These figures are histographs of the properties of the two cast bars, with the prior art cast bar being indicated in each figure with the letters "PA".
Figures 2-8 are histographs of the novel cast steel bar and the prior art cast stcel bar when measured from long transverse sections of each bar. Figure 2 is a measure of the chilled layer thickness of the two bars, showing that the prior art bar had an average chilled layer thickness of approximately 0.2 millimeters while the novel cast bar had an average chilled layer thickness of more than 1.0 millimeters.
~ ~3~g81 : -Figure 3 indicates that the prior art cast steel bar had an average equiaxed grain size in the chill layer of approximately 0.4 millimeters while the novel cast steel bar had grain sizes of approximately .35 millimeters.
Figure 4 indicates that the prior art cast steel bar had an average columnar grain length of approximately 7.8 millimeters while the novel cast steel bar had an average columnar grain length of 3.0 millimeters.
Figure 5 indicates that the prior art cast steel bar had an average columnar grain width of approximately 1.0 millimeters while the novel cast steel bar had an average columnar grain width of approximately 0.67 millimeters.
Figure 6 indicates that the prior art cast steel bar had an average dendrite length of approxirnately 3.8 millimeters while th~ novel cast steel bar had an average ~endritc len~th of 2.3 millimeters.
Figure 7 indicates that the prior art cast steel bar had an average dendrite spacing of 0.1 millimeters while the novel cast steel bar had an average dendrite spacing of 0.18 millimeters.
Figure 8 illustrates that the prior art cast steel bar had an average secondary arm length of 0.05 millimeters while the novel cast steel bar had an average secondary arm length of 0.12 millimeters.
Figure 9 is a histograph of a measurement taken from a longitudinal section of the two cast bars, and indicates that the prior art cast steel bar has an average equiaxed grain size longitudinally of the bar of 1.08 millimeters while the novel cast steel bar has an averaye equiaxed grain size of 0.76 millimeters.
Figure 10 and 11 are histographs of measurements taken along a short transverse section of the two ~ars.
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f`igurc 10 illustratcs that the prior art cast steel bar had a columnar grain length of 3.8 millimeters while the novel cast steel bar had an average columnar grain length of 2.4 millimeters.
Figure 11 illustrates that the prior art cast steel bar had an average columnar grain width of 1.1 millimeters while the novel cast steel bar had an average columnar grain width of 0.8 millimeters.
It will be understood by those skilled in the art that many variations may be made in the embodiment chosen herein for the purpose of illustrating the present invention without departing from the scope thereof as defined by the appended claims.
liners of copper because of its good heat conducting properties. The curved copper mold liners have higher fabricating and maintenance costs than straight copper liners for straight mold cavities. In addition, proper aligning of a mold with a curved cavity is more difficult than properly aligning a mold with a straight cavity.
Mowever, the strand which emerges in straight condition from a straight mold cavity must then be bent into the curved path and this bending operation requires additional vertical space as compared with the vertical space requirement for machines having curved mold cavities. Thus, in known casting machines the benefit.s of conducting the strand along a curved path from thc mold warrant the continued usc of curved paths, but thcse beneEits have been diminished by the above-descrihed problems with the molds.
In addition to eEforts to reduce the vertical space required for continuous casting there has been a continuing effort to increase the casting speed. It is known that continuous relative motion between the casting and the mold impedes the transfer of heat from the solidifying casting to the mold wall and thus limits the casting rate. To date the most notable increase has been achieved by oscillating the mold along a short path in the casting direction as disclosed by Junghans in U.S. Patent No. 2,135,183. For casting steel, a usual amount of oscillation of the mold is about 1/10 to 1/30 the length of the mold, 1/16 to 2 inches, for example. In known constructions, molds having curved mold cavities are oscillated in an arc corresponding to the curvature of the path along which the strand is conducted from the mold. If, however, a mold having a straight cavity is used--to avoid the above-mentioned difficulty with curved mold .,,.j, ~3~)98~
passages--the strand must be conducted from the rnold in a straight vertical line for a sufficient distance to avoid rubbing of the lower edge of the mold against the portion of the casting at the inside of its arcuate path. But this involves increasing the vertical space required. In addition, tests have shown that at higher casting speeds a strand cast in a straight mold cavity and then bent to follow a curved path from the mold tends to develop internal defects and surface cracks.
A much more serious problem, common to both straight and curved mold cavities, is one which arises as a direct consequence of increased casting rate, namely, the problem of obtaining satisfactory surface characteristics.
A characteristic oE castings produced by an oscillating mold is the presence of oscillation marks or rings extendinc3 around the casting in the surface thercof.
Duc to friction bctwcerl the advancing cast bar and the oscillating mold surface, axial stresses are imposed on the thin solidifying metal shell. These alternating stresses can cause surface cracks or other defects at intervals along the length of the casting usually in the form of rings around the entire circumference of the strand. These rings are spaced at distances e~ual to the total advance of the casting between successive strokes of the mold. That is, if the total advance of the casting is two inches between the beginning of one retracting stroke of the mold and the beginning of the next succeeding retracting stroke, the rings will be found to be spaced at two inch intervals.
Further, the width of the rings, i.e., the distance lengthwise of the casting which these defects may be observed, varies depending on the conditions of the casting operation. With extreme care and operating at a low casting 9~
rate, the effects may be minilnized, but in general, the width of the rings is related to the time of the retracting stroke of the mold. That is, if the return stroke consumes one fourth of the time of a complete cycle~ the rings will be formed to cover at least one fourth of the surface of the cavity.
These rings are characterized by a roughened exterior surface, frequently with surface cracking, and frequently with evidence of "bleeding" i.e., the leaking of molten metal through a lesion in the formerly modified skin of the casting, with subsequent solidification of the leaking metal. The crystalline structure of the metal lying just under the rings is also irregular and disturbed.
In the case of non-ferrous metals, these effects have been undesirable, but not too scrious. In many cases, dcspite the surface imp~rfections the castinys could be rolled, extrudcd or otherwise processed without difficulty.
In other cases a light scalping or other surface conditioning operation was sufficient to remove all objectionable surface imperfections. In the case of steel, however, such surface imperfections cannot be tolerated, and it is not economically feasible to remove the imperfections by scalping. Moreover, the economical continuous casting of steel demands a far greater casting rate than is customary or desirable in casting non-ferrous metals, and it has been found that the increased casting rate magnifies the difficulty. Thus, in casting non-ferrous metals a casting rate of thirty to sixty inches per minute is usually ade~uate, and at these speeds, the suirface imperfections are tolerable in non-ferrous metals. In casting stee, on the other hand, casting rates as high as two hundred inches per minute have already been successfully achieved with the ~L~3~98~
Junghans process, but this success is tempered by the fact that at these speeds, the surface imperfections within the ring areas are often extremely bad. Between successive rings, the surface is usually good and the interior crystalline structure is acceptable.
From the theoretical point of view, thereforee, the ideal form of mold for continuous casting might be a curved one of greatly extencled length, but since this cannot exist in practice, other devices have been utilized.
Thus, it has been proposed to use endless supports such as revolving drums, wheels and the like, or endless moving bands or endless chains of mold sections which join together to form a mold at the start of the solidification process and separate at its conclusion to release the solidified metal. Sincc the surEaces of such movable supports CAn rc~main stationary with respect to the metal during the solidification process, favorable conditions are provided for the solidification of metal with good crystalline structure and smooth surface characteristics.
But while such methods offer some theoretical advantages, actual experience with them has been disappointing.
Constructional and operating difficulties have provided so many obstacles to practical successful operation that such methods have made little or no headway in actual commercial operation.
Therefore on balance, the use of oscillating molds with curved cavities has, up to the present, been considered the most satisfactory arrangement for reducing the height of the apparatus and for increasing the rate of casting, despite the problems with oscillating curved mold liners, described above.
Horizontal molds have been utilized heretofore for the continuous casting o~ aluminum and some other non-ferrous metals in machines in which the molten metal is introduced into a horizontal mold through a refractory feed spout which extends through the end wall of the mold. When casting aluminum, the feed spout is not wet by the molten aluminum and it remains clean as casting proceeds. ~lowever, when casting steel, and in partic~llar, where it is desired to use an oscillating mold, this type of horizontal mold with a refractory feed spout cannot be emp:Loyed. It has been found that steel wéts the spout and solidifies around the spout. The solidified steel tends to build up a false tube extending the length of the mold, resulting in a breakout of molten metal at the exit end of the mold.
In addition, it is known that the position and direction of th~ in1Owing st:ream of molten metal greatly a~ects the solidiication proccss and thereore the resulting product.
A horizontal casting mold usually necessitates a horizontal inflowing stream of molten metal which washes against metal which is already beginning to solidify on the mold wall. This causcs the solidifying metal to remelt, often resulting in blceding of molten metal to the outside of the casting. If the velocity of thc inflowing metal is high or is such to cause turbulence in the pool of molten metal, bubbles of gas and particles of oxides, slag, or dirt floating on the surface of the molten metal may be entrapped, causing holes and inclusions in the casting sometimes even resulting in gross porosity and "piping" in the casting. At the very least, a horizontally solidified bar exhibits internal variations across its section due to the effects of gravityO For example trapped gases ancl light particles tend to float upwards toward the topside of the ~ ~098~
bar. Thus the center of the bar may be sound but an area of porosity or of inclusions is located near one edge of the bar. This off-center distribution of defects is often more serious than center defects since it causes unpredictable variations in subsequent processing, e.g., hot-rolling into rod. Consequently, if it is desirable that the pool of molten metal be open or exposed at the top so that trapped gases and other impurities can avoid being trapped into the solidifying bar, or at least confined to the center where they are least harmful.
When a continuous casting of rectangular cross scction initially solidifi~s inside a typical horizontal mold, the larger top and bottom surfaces are necessarily exposed to morc rapid cooling. The resulting shrinkage eEfects cause these surfaces, especially the top, to pull away erom the walls of the mold before moving very far from the molten pool thus slowing the initially rapid cooling.
Since the several edges and surfaces do not all shrink uniformly, the cooling rates and therefore temperatures, stresses, and thickness of the frozen shell all differ from one surface to another. ~hese drawbacks become more pronounced at higher casting rates and as the casting continues to move through the mold, bright and dark areas appear on the billet as it issues from the mold. The bright areas often indicate high temperature locations where remelting of the once frozen shell can occur. Remelting occurs due to the transfer of heat from the still hot interior of the bar. At these points of weakness, the stresses in the frozen shell produce cracks which can cause breakouts or other surface defects.
Moreover, the unequal stresses have another undesirable consequence, namely that of causing a type of - _ 9 ~L~3~
geometrical distortion of the cast bar known as rhombic distortion which is a nuisance in subsequent processing of the casting.
SUMMARY OE' THE INVENTION
It is therefore an object of the invention to provide an improved method and apparatus for continuously casting steel.
It is another object of the invention to provide a novel continuous cast steel bar having improved qualities when compared to previous continuously cast steel bars.
More particularly, it is an object of this invention to provide a much faster method of continuously casting a steel bar which is suitable for directly rolling into wrought products.
Now in order to implement these and still further objects of the invention, which will become more readily apparent as the description proceeds, the method aspects of this development are manifested by casting steel into a mold formed by a peripheral groove in a rotating casting wheel and a band which seals a length of the groove.
In accordance with prevailing practice, the mold is preferably made of a metal of high thermal conductivity, such as copper alloy, and the mold is chilled by directly spraying coolant onto the mold or by circulating coolant, such as cold water, therethrough.
The mold groove may be of various shapes~ as desired, in transverse cross section, as for example, semi-circular, or approximately rectangular. However, it has been found advantageous to use a trape20idal cross-sectional shape having small (7 to 14) relief angles on the sides and having a width to depth ration of 1.5 to 1 or greater.
113~
In casting, the molten steel is cast into the mold and is uniformly chilled by withdrawal of heat throuyh the mold walls to form a thin peripheral skin of solidified metal surrolnding the molten metal within. The rate oE
withdrawal of heat is controlled with relation to the casting speed, by regulation of the rate of circulation of the mold coolant, or otherwise, so that the temperature of the exterior surface of the peripheral skin of solidified metal as it emerges from the mold does not exceed about 2500F. but is not less than about 2000~F.
The emerging strand is then conducted along a supporting passageway to a substantially horizontal cooling zone for final cooling.
The supporting passageway can be forrned by a series of members which have surfaces which enyage and support the strand. The members may have provisions for urging the bar along its path to the next process station.
The cast bar follows a path of progressively increasing radius until it becomes rectilinear.
Another important difference is that this invention provldes for controlling the heat-transfer rate in coordination with the solidification process. For example, since the molten metal is continually introduced into a relativcly large cold wheel structure, the wheel functions as a heat sink and the heat transfer rate is very high, causing rapid cooling which forms a relatively thick chilled layer in the cast product, while later the heat transfer rate is lower, allowing an orderly growth of the solidification front.
The resulting continuous length of cast bar has better surface and interior qualities than known prior art steel bars cast by prior art methods. For exarnple, the ~3~
surface is free from laps or seams normally associated with oscillation marks. In addition, due to the unique casting process, elongated casting mold and fast casting rate, the as-cast bar has a thinner oxide scale on the surface than prior art bars.
The invention therefore comtemplates a process of continuously casting steel, characterized by the steps of progressively casting molten steel in an arcuate mold into a bar having an arcuate shape along its length, progressively moving the arcuate bar along its length from the mold, and progressively straightening the bar as the bar is withdrawn from the mold.
BRIEF DESCRIPTION OF THE DRAWING
The invention will now bc explained in more detail with respect to the accornpanying drawings in which:
Figure 1 is a schematic cliagram illustrating one example of apparatus suitable to practice the invention, this apparatus comprising a casting machine having a rotatable casting wheel containing a peripheral groove and endless metallic band which seals a length of the groove;
Figures 2 - 11 are histographs of the properties of the novel cast steel product and of the properties of another cast steel product cast by a prior art process.
DETAILED DESCRIPTION
While these figures and the following detailed description disclose an embodiment of the invention, it will be understood that the present invention is not limited to the exact details disclosed herein since it may be embodied in other equivalent forms without departing from the inventive concepts.
Referring now in more detail to the drawing, in which like numerals of reference illustrate like parts 9~
throughout the several views, Figure 1, shows casting wheel 10 having a four foot radius and a groove in its periphery and an endless flexible band or belt 11 positioned against a portion of its periphery by band support wheels 12, 13 and 14. The band support wheel 12 is positioned near that point on the casting wheel 10 wherein molten steel is discharged by a pouri,g pot or tundish 16 into a mold M formed by the band 11 and a peripheral groove G around the casting wheel 10. The band support wheel 14 is positioned adjacent that point on the casting wheel 10 at which partially solidified metal is discharged from the casting wheel 10. The exterior surfaces of the casting wheel and band are continuously cooled by coolant fluid, as by the sprays of coolant fluid from the nozzles Sl at the inner portion oE the peripheral groove and the nozzles (not shown) extending from the headers S2, S3 and S4 ahout the outer portion of the peripheral groove. Each nozzle can be individually adjustable to vary thc volume of fluid sprayed therefrom, and the conduits which supply the coolant fluid to the nozzles are controlled by adjustable valves for the purpose of starting and stopping coolant flow and for varying the volume of coolant flow.
Positioned beyond and above the band support wheel 14 is an extended bending section 18 which serves as a means straightening the cast steel bar withdrawn from the casting wheel 10. The bending section 18 includes a plurality of support rolls 19 supported by a frame (not shown). An after cooling header 21 is located above and adjacent band support wheel 14 and applies a direct flow of coolant fluid to the cast bar emerging from the arcuate mold.
The support rolls 19 may either be driven or non-driven; however, it is anticipated that in most ~- - 13 circumstances at least some of the support rolls will be driven to assist in the straightening of the cast bar. Side guide rolls (not shown) also can be positioned on opposite sides of path P to retain the bar in its path.
In the operation of the system, the molten steel is poured from the rundish 16 through its downwardly projecting spout 16a into the peripheral groove G of the casting wh.el lO. The exit end of the spout 16a is located as closely adjacent the beginning of the arcuate mold as practical so as to allow the molten steel to flow directly from the nozzle exit into the pool of mol-ten steel in the arcuate mold. The flow of steel and the angular velocity of the casting wheel are regulated so that the steel being cast in the arcuate mold is moved away from the nozzle 16a as fast as the molten steel flows through the nozzle so as to main~in thc ~ureace o~ the pool of molten steel at a constant level at the cntrance o the arcuate mold. [n addition, the ~low control system for the conduits that direct coolant fluid to the nozzles Sl and the headers S2, S3 and S4 are also adjusted so as to apply the desired amount of coolant to the band and casting wheel, to thereby control the rate of cooling of the molten metal as it moves about the arcuate mold. The relatively large size of the casting wheel 10 causes the casting wheel to function as a heat sink in that the heat given up by the molten metal first flowing into the arcuate mold is dispersed into the relatively large casting wheel and the relatively large surface of the casting wheel is cooled by the coolant fluid applied from the nozzles of the system. As a result, a large amount of rapid cooling and solidification of the molten metal takes places at the surfaces of the casting wheel and bànd, and the continuous extraction of heat from ~309~
the partially cast bar by the casting whecl, band and coolant fluid continues to cause solidification of the molten metal in what is believed to be a progressive and uniform solidi~ication from the surface of the cast bar toward the center of the cast bar.
The band 11 moves into contact with the annular groove G of the casting wheel 10 as it moves off guide roll 12, so that the band makes contact with the casting wheel 10 at an upper portion of the casting wheel and then moves in a downward direction about the lower portion of the casting wheel, then in an upward direction until it reaches the guide wheel 15, whereupon it is guided away from the cas-ting wheel. The mold M formed by the peripheral groove G and the band 11 is an elongated arcuate mold that moves continuously with the rotation of the casting wheel 10, and the cast bar B formed in the arcuate mold M conforms to the ar¢~late shape of the mold until it is extracted from the mold. The radius of the bar B must be increased in order to extract the bar from the arcuate mold, and the bar is progressively straightened with a progressively increasing radius as the bar moves through the extended bending section 18 of the assembly. The rolls 19 guide the bar through its ~nbending or straightening path over the casting wheel 10, and preferably, at least one pair of the guide wheels 19 are driven so as to pull the bar B along its length from the casting wheel 10. The pulling forces applied to the bar as well as the leverage applied to the bar by the lower ones of the guide rolls 19 located beneath the bar B function to support and straighten the bar. Also, the continuous straightening of the bar as -the bar moves away from the casting wheel causes a substantial amount of internal stress in the bar. The amount of stress applied to the bar can be 1.~.3098~
increased or decreased by decreasing or increasing the temperature of the bar as the bar moves through the bending section 18 of the assembly. Moreover, by varying the amount of coolant applied by manifold 21 adjacent the exit of the bar from the casting wheel the temperature of the bar passing through the bending section 18 can be varied and controlled so as to adjust the internal stresses of the bar B during its travel through the bending section 18. As the bar first leaves the casting wheel the bar is more radically bent and the bar then progresses further on its path through the bending section 18 where it is less radically bent. The header 21 applies coolant fluid to the bar at its exit from the mold to assure that the bar is completely solid before the bar reaches the level of the pool of molten metal at nozzle 16a. This assures that the internal core of molten metal in the bar will not create a negative pressure and form a void in the bar. Also, the volume of coolant applied by header 21 can be adjusted to adjust the temperature of the solid bar being extracted from the mold, thereby controlling the internal stresses of the bar.
Because of the relatively long length of the arcuate casting mold formed by the band 11 and peripheral groove G of thc casting wheel 10, the casting wheel can be rotated at a relatively high angular velocity and still achieve the solidification of the molten metal as desired.
In the particular disclosed embodiment, the mold M is approximately trapezoidal shaped with a small dimension located at the inner portion of the peripheral groove and with a large dimension located adjacent the band 11. The bar cast by the casting machine in the example disclosed is approximately 2 5/8 inches wide at its larger width, 2 1/8 inch wide at its smaller width and 1 7/8 inches deep, with .,~
9~L3~913~
an approximately 1/4 inch radius joining the smaller width with the two sides of the bar. Other bar sizes and shapcs can be cast as may be desired.
The relatively high rotational velocity of the casting wheel causes the bar B to exit from the casting wheel at a relatively high linear speed, so that the bar is advanced at a rapid rate on toward the next processing stage, such as to a rolling mill. The rapid movement of the bar together with the bar having been enc:Losed in a relatively long mold reduces the tendency of the surface of the bar to form scale.
Measurements have been made of the properties of a cast steel bar which was cast in a rotatable casting whcel of the type illustrated at 10 in E'igure 1. Thc prope~ties of this cast stcel bar were compared with thc properties of a cast bar fabricated from a concast~ continuous casting machine which includes an arcuate oscillating mold. The properties of the novel cast steel bar and of the prior art cast steel bar are compared in Figures 2-11. These figures are histographs of the properties of the two cast bars, with the prior art cast bar being indicated in each figure with the letters "PA".
Figures 2-8 are histographs of the novel cast steel bar and the prior art cast stcel bar when measured from long transverse sections of each bar. Figure 2 is a measure of the chilled layer thickness of the two bars, showing that the prior art bar had an average chilled layer thickness of approximately 0.2 millimeters while the novel cast bar had an average chilled layer thickness of more than 1.0 millimeters.
~ ~3~g81 : -Figure 3 indicates that the prior art cast steel bar had an average equiaxed grain size in the chill layer of approximately 0.4 millimeters while the novel cast steel bar had grain sizes of approximately .35 millimeters.
Figure 4 indicates that the prior art cast steel bar had an average columnar grain length of approximately 7.8 millimeters while the novel cast steel bar had an average columnar grain length of 3.0 millimeters.
Figure 5 indicates that the prior art cast steel bar had an average columnar grain width of approximately 1.0 millimeters while the novel cast steel bar had an average columnar grain width of approximately 0.67 millimeters.
Figure 6 indicates that the prior art cast steel bar had an average dendrite length of approxirnately 3.8 millimeters while th~ novel cast steel bar had an average ~endritc len~th of 2.3 millimeters.
Figure 7 indicates that the prior art cast steel bar had an average dendrite spacing of 0.1 millimeters while the novel cast steel bar had an average dendrite spacing of 0.18 millimeters.
Figure 8 illustrates that the prior art cast steel bar had an average secondary arm length of 0.05 millimeters while the novel cast steel bar had an average secondary arm length of 0.12 millimeters.
Figure 9 is a histograph of a measurement taken from a longitudinal section of the two cast bars, and indicates that the prior art cast steel bar has an average equiaxed grain size longitudinally of the bar of 1.08 millimeters while the novel cast steel bar has an averaye equiaxed grain size of 0.76 millimeters.
Figure 10 and 11 are histographs of measurements taken along a short transverse section of the two ~ars.
~r ~3~
f`igurc 10 illustratcs that the prior art cast steel bar had a columnar grain length of 3.8 millimeters while the novel cast steel bar had an average columnar grain length of 2.4 millimeters.
Figure 11 illustrates that the prior art cast steel bar had an average columnar grain width of 1.1 millimeters while the novel cast steel bar had an average columnar grain width of 0.8 millimeters.
It will be understood by those skilled in the art that many variations may be made in the embodiment chosen herein for the purpose of illustrating the present invention without departing from the scope thereof as defined by the appended claims.
Claims (12)
1. A process for continuously casting a steel product comprising pouring molten steel into a mould formed in a continuous casting machine, continuously cooling the molten steel in the casting machine to form a continuous cast product, and continuously withdrawing the cast steel product from the the casting machine, characterised in that in order to improve the microstructure of the cast steel so that it has an average equiaxed grain size less than 0.8 mm when viewed in longitudinal section and an average columnar grain length less than 3.5 mm in short transverse section, the molten steel is at least partially solidified in a wheel-band type continuous casting machine having endless mould surfaces advancing with substantially no relative movement between the cast product and the mould surfaces, and the at least partially solidified cast bar is withdrawn from the mould at a temperature above approximately 1100°C
and at a rate greater than approximately 600 cm per minute and then further cooled by the impingement of coolant sprays thereon.
and at a rate greater than approximately 600 cm per minute and then further cooled by the impingement of coolant sprays thereon.
2. The process according to claim 1, in which the band and casting wheel are cooled with liquid.
3. The process according to claim 1, in which the mould has an approximately trapezoidal cross section.
4. The process according to claim 2, in which the mould has an approximately trapezoidal cross section.
5. The process according to claim 3 in which the mould has a width-to-depth ratio not less than 1.5:1.
6. The process according to claim 4 in which the mould has a width-to-depth ratio not less than 1.5:1.
7. The process according to claim 1, 2 or 3 in which the mould has a radius of approximately 120 cm.
8. The process according to claim 4, 5 or 6 in which the mould has a radius of approximately 120 cm.
9. A continually cast steel bar characterized to improve the microstructure of the east steel so that it has an average equiaxed grain size less than 0.8 mm when viewed in longitudinal section and an average columnar grain length less than 3.5 mm in short transverse section, having in cross section average dendrite lengths less than 2.5 millimetres and average dendrite spacing more than 0.1 millimetre.
10. The cast steel bar according to claim 9, having an average chilled layer thickness greater than 0.2 millimetre.
11. The cast steel bar according to claim 10, in which the averaged equiaxed grain size in the chilled layer is less than approximately 0.4 millimetre.
12. The cast steel bar as claimed in claim 9, 10 or 11, characterised in that it has substantially trapezoidal cross section.
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|---|---|---|---|
| US86047577A | 1977-12-14 | 1977-12-14 | |
| US860,475 | 1992-03-30 |
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| CA317,970A Expired CA1130981A (en) | 1977-12-14 | 1978-12-14 | Continuous cast steel bar and the method to produce same |
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| DE2903975A1 (en) * | 1979-02-02 | 1980-08-14 | Southwire Co | Steel slab continuously cast in a mould which moves continuously - and has an endless surface moving cooperatively with other surfaces to form the mould |
| JPS5741860A (en) * | 1980-08-21 | 1982-03-09 | Southwire Co | Improved continuous casting steel bar and its manufacture |
| JPS61138844U (en) * | 1985-02-19 | 1986-08-28 | ||
| JP4634559B2 (en) * | 2000-01-07 | 2011-02-16 | 株式会社ショーワ | Electric power steering device |
| CN102430727A (en) * | 2011-12-30 | 2012-05-02 | 襄阳博亚精工装备股份有限公司 | Open belting leather type wide-weight-belt casting device |
| CN102407303A (en) * | 2011-12-30 | 2012-04-11 | 襄阳博亚精工装备股份有限公司 | Opening belting leather type wide lead belt casting device |
| CN114354971B (en) * | 2022-01-14 | 2023-07-21 | 华北理工大学 | Continuous casting crystallizer molten steel flow velocity measurement equipment |
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| US359348A (en) * | 1887-03-15 | Mechanism for forming ingots | ||
| FR1412218A (en) * | 1963-10-24 | 1965-09-24 | Means for improving the mechanical characteristics of a bar or ingot produced by an apparatus comprising a continuous casting wheel | |
| FR1444598A (en) * | 1964-08-19 | 1966-07-01 | Southwire Co | Apparatus and method for preparing metal for rolling |
| FR90679E (en) * | 1965-08-05 | 1968-01-26 | Means for improving the mechanical characteristics of a bar or ingot produced by an apparatus comprising a continuous casting wheel | |
| US3623535A (en) * | 1969-05-02 | 1971-11-30 | Southwire Co | High-speed continuous casting method |
| US3785428A (en) * | 1972-03-02 | 1974-01-15 | Hazelett Strip Casting Corp | Wheel-belt continuous casting machine |
| US3818972A (en) * | 1972-10-05 | 1974-06-25 | Southwire Co | Cast bar draft angle |
| JPS5433151B2 (en) * | 1973-04-12 | 1979-10-18 | ||
| US4030537A (en) * | 1975-06-25 | 1977-06-21 | Southwire Company | Thin gauge casting wheel band |
| JPS5342140A (en) * | 1976-09-29 | 1978-04-17 | Hitachi Ltd | Device for removing water in continuous casting machine |
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1978
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1982
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| PL211755A1 (en) | 1979-08-27 |
| ES476014A1 (en) | 1979-06-16 |
| LU80657A1 (en) | 1979-04-13 |
| AU4246078A (en) | 1979-06-21 |
| KR830000064A (en) | 1983-03-25 |
| CS216925B2 (en) | 1982-12-31 |
| MX150623A (en) | 1984-06-12 |
| IT1106823B (en) | 1985-11-18 |
| BR7808221A (en) | 1979-08-14 |
| JPS5825850A (en) | 1983-02-16 |
| ZA787005B (en) | 1979-09-26 |
| JPS5825849A (en) | 1983-02-16 |
| IT7852302A0 (en) | 1978-12-14 |
| GB2010149A (en) | 1979-06-27 |
| NL7812179A (en) | 1979-06-18 |
| SE7812816L (en) | 1979-06-15 |
| FR2422461B1 (en) | 1983-09-30 |
| FR2422461A1 (en) | 1979-11-09 |
| BE872777A (en) | 1979-06-14 |
| SE450554B (en) | 1987-07-06 |
| JPS54151516A (en) | 1979-11-28 |
| IN150414B (en) | 1982-10-02 |
| DE2853868C2 (en) | 1985-07-18 |
| AU531775B2 (en) | 1983-09-08 |
| DD143221A5 (en) | 1980-08-13 |
| DE2853868A1 (en) | 1979-06-21 |
| GB2010149B (en) | 1982-05-19 |
| JPS625702B2 (en) | 1987-02-06 |
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