Method Of Continuous Casting

Abstract

Method involves continuously but incrementally passing molten metal directly from a holding vessel progressively through an open-ended mold containing three consecutive zones. The first zone immediately adjacent the holding vessel conveys the molten metal to the second zone without significant solidification due to its low heat transfer capacity. A thin skin of metal forms progressively in the second zone due to its relatively high heat transfer capacity. This thin skin is then transferred as a segment into the third zone in which the molten metal solidifies sufficiently to form a self-sustaining rod.

Parent Case Text

This application is a continuation-in-part of the patent application Ser. No. 827,673 (now abandoned) filed on May 26, 1969 and assigned to the assignee of the present application.

Description

This invention relates to the continuous casting of round bars or ingots in a horizontally disposed mold, and more particularly to the continuous casting of round bars formed of relatively high melting point metals which are unsaturated in carbon, such as steel.

In the common practice of the continuous casting of steel, the mold apparatus is usually of the vertical type including a vertically positioned open-ended mold, a tundish positioned above the mold and spaced therefrom, and a teeming ladle positioned above the tundish. The molten metal is teemed by gravity into the tundish and thence directly into the mold. This arrangement offers the advantage that no molten metal is held in continuous contact with the mold wall inasmuch as the skin of solidified metal forms progressively at the metal mold interface and the rate of propagation of this skin is at least equal to the withdrawal rate of the casting from the bottom of the mold. This requires, of course, a mold material having good thermal conductivity and adequate cooling. In most current practice, the mold wall is made of a water cooled copper.

A further characteristic of this vertical arrangement is that the surface of the metal being poured into the mold is exposed so that a lubricating medium can be continuously added during the casting operation. Various lubricants such as rapeseed oil, mineral oil, and powdered graphite have been successfully used. Because a convex meniscus is developed at the point of contact of the molten metal with the mold wall, a lubricant may readily be distributed between the solidifying skin and the mold wall as the metal passes through the mold.

The vertical casting arrangement described above has achieved wide industrial application in casting steel billets and slabs of approximately eight square inches in cross-section and larger. However, for casting billets having a diameter of three inches or less, the teeming action becomes more difficult to control and the linear rate of extraction becomes high. In consequence, the surface quality and internal soundness of the casting is seriously impaired. As a result, under the present state of technology, the vertical casting method has not been successfully used commercially to cast steel bars two inches or less in diameter.

Vertical casting is well adapted to casting relatively large slabs and billets on a high volume continuous basis but requires very substantial vertical plant space which well suits the operation of metal producers such as steel mills. However, in view of persistent efforts by steel users to achieve greater efficiency and economy by the utilization of scrap metals resulting from their operation, there is a great need for small compact casting units for converting scrap steel into relatively small diameter useable rods of about two inches or less in diameter, which may be conveniently installed in existing plant facilities.

It is an object of this invention to provide a method for continuously casting by compact horizontal means ingots formed of relatively high temperature metals such as ferrous metals, nickel base alloys and cobalt base alloys having melting temperatures in excess of about 2,200.degree. F. It is a further object of this invention to provide a method for continuously casting steel ingots including ingots having a diameter of three inches or less which are not saturated in carbon, as for example, low carbon steel.

These and other objects are accomplished by the provision of a horizontally disposed open-ended mold associated with a molten metal holding vessel or furnace, which mold includes means providing a low heat transfer first zone immediately adjacent the holding vessel which is effective to contain and convey the molten metal therethrough without appreciable solidification and which is substantially chemically inert to the molten metal, means providing a relatively high heat transfer second zone adjacent the first zone which effects the initial solidification in the form of a thin skin of solidified metal progressively and coextensively, first at the interface of the first and second zones and progressively to the end of the second zone, and means providing a third zone adjacent the second zone wherein the molten metal is further solidified to form a self-sustaining rod which may be progressively withdrawn from the mold by mechanical means. The solidified rod is mechanically pulled from the mold continuously but intermittently in predetermined increments of length or segments and with predetermined time intervals between the increments of movement of the rod. Each increment corresponds in length to the aforesaid second or initial solidification zone so that with each incremental pull of the rod the thin solidified skin layer or segment formed in the second zone is advanced into the third zone thereby exposing the second zone to the advance of the molten metal from the first zone and the progressive solidification of a new skin layer or segment is formed in the second zone. The time interval or dwell time between the pulling intervals is sufficient to permit the forward end of the newly formed skin layer in the second zone to weld to the rod in the third zone, so that when the rod is again pulled, it will carry with it the newly formed segment into the third zone in a continuous rod solidification process. The method may be used to cast ingots of various diameters including ingots up to 5 inches or more.

Suitable apparatus for practicing the method of this invention is disclosed and claimed in the copending patent application Ser. No. 827,747 filed May 26, 1969, now abandoned.

Other objects and advantages of the invention will be apparent from the following description, reference being had to the drawings in which:

FIG. 1 is a cross-sectional view of a horizontal continuous casting apparatus;

FIG. 2 is an enlarged view of a portion of the mold shown in FIG. 1;

FIGS. 3 - 5 are fragmentary cross-sectional views of the mold at various stages of the casting process; and

FIG. 6 is a schematic view of the mold showing variable internal diameter dimensions.

Referring now to FIG. 1 of the drawings, the molding apparatus of this invention consists generally of a molten metal reservoir 10 shown as a fragment thereof and a horizontally disposed open-ended mold 12 mounted adjacent an opening 14 near the base of the reservoir. The reservoir is of conventional construction including an outer metal shell (not shown) having a lining 16 of a suitable refractory material for containing molten metal such as steel. The opening or channel 14 in the reservoir is formed in a frustoconical refractory body 18 cemented to the lining 16. The refractory reservoir may include heating means such as an induction heating coil or resistance heating element for maintaining the metal at a desired temperature.

Referring to FIG. 2, the mold 12 consists of three distinctly different portions with different heat transfer characteristics. The first portion immediately adjacent the reservoir includes a nozzle portion 20 preferably formed of boron nitride having relatively low heat transfer characteristics such that it will contain the molten metal therein without any appreciable solidification. The second portion 22 is positioned immediately adjacent the nozzle 20 and is formed of a material having relatively high heat transfer characteristics as, for example, a beryllium-copper alloy. The third portion 24 is disposed immediately adjacent the second portion 22 and is preferably provided with a graphite liner 26. The third portion preferably has somewhat lower heat transfer characteristics than the second portion 22 for reasons which will appear hereinafter.

An important feature of the mold structure resides in the shape of the nozzle 20 including the annular radially disposed shoulder 30 and the frustoconical axial surface 32 which mates with a corresponding frustoconical surface 42 on the second mold portion 22. Preferably, the angle of the frustoconical surfaces with the longitudinal axis of the mold is about five degrees for reasons to be hereinafter explained. The mold portion 22 receives a portion of the nozzle 20 with the frustoconical surface providing a snug fit and with the shoulder 30 engaging a radial surface 33 of the mold portion 22 to accurately locate the nozzle 20 with respect to the mold portion 22. An annular refractory ring 34 is in engagement with the nozzle 20 and is securely locked in place by a flanged ring 36 bolted to the mold housing 35. The aperture 37 through the ring 34 is preferably somewhat smaller than the opening 21 through the nozzle. The ring 34 is preferably made of zirconia because of the expensive nature of boron nitride. However, if desired, the nozzle 20 and the ring 34 may be both formed of boron nitride.

The second mold portion 22 as well as the third mold portion 24 are both provided with coolant passages 38. The second mold portion 22 is preferably formed of a beryllium-copper alloy because of its high heat transmission characteristics. As will be explained hereinafter, the molten metal contacts the surfaces of the second mold portion 22 only in a transient manner.

After the process of this invention has been started and is in continuous operation as hereinafter described, it is characterized basically by the molten metal passing from the reservoir 10 through three successive zones in the mold 12. The molten metal is conveyed from the reservoir 10 through the first zone without exposure to air whereby the buildup of oxide deposits in the region of zone one is substantially prevented. No significant solidification occurs due to a sufficiently low heat transfer capacity of the first zone. As the metal flows into the second zone, a thin skin layer of solidified metal is progressively formed along its length due to the high heat transfer capacity of the second zone portion of the mold. This skin layer is then advanced as a segment or increment into the third zone of the mold wherein the molten metal is further solidified to form a self-sustaining rod which is mechanically pulled out of the mold by suitable means such as the rollers 31 of FIG. 3. As the aforesaid skin layer is advanced from the second zone to the third zone, a second skin layer is formed in the second zone, which subsequently welds itself to the rod being solidified in the third zone. This second skin layer is advanced into the third zone as the rod is pulled incrementally whereby a continuous rod is formed in a continuous but incremental process.

The following detailed explanation will make the nature of the process more clear. The reservoir 10 is provided with a suitable quantity of molten metal such as steel so that its level extends substantially above the mold 12. The molten metal advances due to gravity into the mold through the ring 34 and the boron nitride nozzle 20 which constitutes the aforementioned first zone. Since boron nitride is a material of relatively low heat conductivity, and is not provided with any cooling means, the molten metal does not significantly solidify therein. The use of boron nitride for this purpose is also advantageous because the material has a high heat shock resistance; it is not wetted by the molten metal and it is relatively inert to the molten metal. Other materials with similar desirable properties may be used instead of boron nitride.

As soon as the molten metal enters the second zone, an initial circumferential annulus solidifies against the mold surface portion 22 at the interface 25 of the nozzle element 20 and the mold portion 22 as is shown in FIG. 2. This occurs because the mold portion 22 is formed of a material of relatively high heat conductivity and is cooled by means of suitable coolant, such as water, circulating in the coolant passages 38 to provide a high heat transfer capacity whereby a film or skin of metal 23, FIG. 3, solidifies on the surface of the mold 22 the instant contact is made. It is essential in the casting process of this invention that solidification begin immediately at the interface 25 of the nozzle 20 and the mold portion 22. As the molten metal advances into the second zone, a solidified skin layer 23 forms progressively on the surfaces of the mold portion 22 in the downstream direction. This progressive formation of the skin layer 23 occurs entirely within the mold 22 portion and coextensively with zone one.

The skin layer segment 23 is then advanced as a segment into the third zone of the mold wherein further solidification takes place to form the self-sustaining rod.

As the skin layer 23 begins to advance into the third zone, it must first release from the nozzle 20 at the interface 25 as shown in FIG. 4 to form a slight space 27 between the skin 23 and the nozzle shown in greatly exaggerated dimensions. This space is immediately filled with molten metal flowing from the first zone to initiate the formation of a new skin layer at the interface 25 of the nozzle and the mold portion 22 and to closely follow the advancing skin layer 23 and to progressively form the new skin layer 29 as shown in FIG. 5. After the layer 23 has reached its full increment of movement, it is permitted to remain stationary for a time sufficient to permit the new layer 29 to weld to the layer 23 as shown at 27 of FIG. 5. It is essential to the successful operation of the process that the skin layer 29 part cleanly from the nozzle 20 and that skin layer 23 remain stationary for a time sufficient to permit the new skin layer 29 to weld thereto. If either of these process steps are not performed properly, a break will occur in the successively formed skin layers causing molten metal to break out and to prevent proper rod solidification. The use of boron nitride for forming at least that portion of the nozzle adjacent the mold portion 22 is highly advantageous because the skin layer does not adhere to the boron nitride to thereby result in a clean release.

The above description of the process and apparatus is applicable to normal operational conditions and after the molding process has commenced. The process is commenced by inserting a suitable rod (not shown) into the exit end of the mold until it reaches approximately to the junction of the first and second zones. The initial molten metal flowing into the mold is permitted to flow against the rod end and to bond thereto. This bar is then pulled out incrementally as described above to establish the casting process.

The axial length of the skin layer or segment 23 has practical limitation and we have found that it should preferably be from 0.1 to 1.5 times the diameter of the rod being cast for bar diameters up to about 5 inches. If the incremental pull or stroke is shorter, casting rate is sacrificed and nozzle erosion is excessive. If the stroke is longer, shrinkage porosity of the casting will be excessive. By way of specific example, a bar about 11/2 inches in diameter is successfully cast with the segment 23 being about 1 inch in length.

As the skin layer 23 moves into zone three, a progressively greater radial thickness of the molten metal solidifies therein as the bar is advanced to eventually form a self-sustaining bar which is pulled mechanically from the zone three as shown in FIG. 3.

It will be observed from the above description that the molten metal contacts only the first zone of the mold portion to any substantial extent wherein it is not contaminated because of the inert character of the boron nitride. The molten metal contacts the primary solidification zone two portion of the mold for only an extremely transitory period of time since solidification occurs at virtually the instant the molten metal contacts the mold 22 portion. Since the initial solidification occurs in the metal portion of the mold, the carbon chemistry of the metal is not altered as would be the case if this portion of the mold were formed of graphite. When the metal has advanced into the third zone, the solidified layer is of substantial thickness and is relatively cool so that no significant graphite diffusion occurs in consequence of the graphite liner provided in the third zone of the mold. The use of the graphite liner is advantageous because it is relatively soft and self-lubricating and it permits the solidified bar to be readily drawn through even though minor imperfections may have occurred in the surface of the rod during solidification thereof. There is no need for fluid lubricants such as rapeseed oil which is commonly used in vertical continuous casting.

In accordance with this invention, round bar stock may be cast in sizes of from about one to three inches in diameter with a roundness variation of 21/2 percent or less, expressed in terms of the difference in major and minor diameters of the rod. Both the roundness and mean diameter variations are markedly less than the commercial limits for hot rolled bar.

In casting stock one and one-half inches in diameter, we have successfully used segment lengths of one inch and a cycle time of 0.25 seconds, the cycle being the sum of the time consumed in drawing the bar one segment as above described and the dwell time, i.e., the time the rod is permitted to remain at rest. A typical dwell time is 0.12 seconds.

Satisfactory casting results are obtained with a variation in the dwell time of from about 0.1 to about 0.36 seconds with the proportion of the dwell time to the cycle time being between about 33 to 65 percent and with the cycle time accordingly being about 0.15 to 1.1 seconds.

It will be observed from FIG. 2 that the zone one consists of more or less the refractory ring 34 and the nozzle 20. Zone two is generally defined by the mold portion 22 and zone three includes the balance of the mold. However, it should be recognized that the three defined zones are process concepts and are not necessarily coextensive with these mold portions. In particular, it should be noted that the zone two of the process is located entirely within the confines of the mold portion 22 extending from the interface 25 for the length of the segment 23 or the pull stroke. It is important that this segment solidifies initially entirely within the mold portion 22. Depending upon the length of the segment employed, it is to be expected that in a given mold design, the zone three will actually commence within the mold portion 22.

In practicing the process of this invention, it is preferable that the inside diameter of the mold vary in accordance with the progressive solidification of the rod so that the mold surfaces are in close contact with the solidifying and shrinking rod to enhance roundness of the rod and to effect optimum heat transfer between the mold and the solidifying rod. FIG. 6 is a diagrammatic representation showing a preferred design. The zone one, which includes the refractory ring 34 and the nozzle 20, is shown to be of constant diameter, although this is not necessary since the metal exists in this zone only in molten form. It has been found advantageous that the mold portion 22 have a gradually increasing diameter over its length in the direction of the outlet end of the mold. As shown in FIG. 6, a 5-minute taper with the longitudinal axis in the mold wall produces desired results in the case where the length of the mold portion 22 is about 1 inch. The reason for the zone two portion of the mold being tapered outwardly is that it appears to prevent molten metal breakouts through the solidified skin. The mold in the zone three portion is provided with a graphite liner and is gradually decreased in diameter in an amount of 41/2 minutes to the longitudinal axis over the first 3-inch portion. For casting a 1 17/16 inch diameter bar, this mold portion continues to decrease in diameter in increments of 2 to 4 inches by about 2/1000 of an inch, as shown in FIG. 6. The purpose of this taper is to compensate for the fact that the rod is undergoing substantial solidification as may be seen from inspection of FIG. 3. Then, for a final 26 inch interval, the diameter of the mold remains constant. The zone three portion of the mold tapers in accordance with the increased solidification and decreasing temperature to compensate for shrinkage. The effect is to maintain roundness and good heat transmission from the bar to the mold. In the last 26 inch portion of zone three, referred to above, the diameter is preferably maintained constant to slow down heat transfer from the bar to the mold. This is desirable to minimize the reheating of the bar surface and hence, cracking thereof after the bar has emerged from the mold and to reduce frictional resistance to the movement of the bar.

As above indicated, the method of this invention has particular utility in casting metals which have a relatively high melting temperature of about 2,200.degree.F. or more, and are unsaturated in carbon so that they cannot be cast or solidified in a graphite mold because of their tendency to absorb carbon by diffusion. Of particular importance in this class of metals are ferrous metals such as steel, and other ferrous metals typically containing up to about 2 percent carbon. Illustrative of metals which may be cast in accordance with this invention are SAE 4118 steel containing, by weight, 0.18 percent to 0.23 percent carbon, 0.7 to 0.9 percent manganese, 0.4 to 0.6 percent chromium, 0.08 to 0.15 percent molybdenum, 0.04 percent maximum, phosphorus, 0.04 percent maximum, sulphur, and the balance essentially iron; SAE 5160 steel containing, by weight, 0.55 to 0.65 percent carbon, 0.75 to 1.0 percent manganese, 0.2 to 0.9 percent chromium, 0.04 percent maximum, phosphorus, 0.04 percent maximum, sulphur, and the balance essentially iron; SAE 52100 steel containing, by weight, 0.95 to 1.1 percent carbon, 0.25 to 0.45 percent manganese, 1.3 to 1.6 percent chromium, 0.25 percent maximum, phosphorus, 0.25 percent maximum, sulphur, and the balance essentially iron. Ferrous metals such as cast iron having a carbon content greater than 2 percent may, of course, also be cast by the method of this invention. Nickel based alloys and cobalt based alloys containing predominant amounts of nickel or cobalt may also be successfully cast in accordance with the process of this invention.

Illustrative of a nickel based alloy of this type is Inconel 610 consisting of 68.5 percent nickel, 0.2 percent carbon, 1.0 percent manganese, 9 percent iron, 1.6 percent silicon, 0.5 percent copper, 15.5 percent chromium, columbium plus tantalum about 2 percent, and the balance essentially nickel; and Rene 41 consisting of about 18 to 20 percent chromium, 10 to 12 percent cobalt, 9 to 10.5 percent molybdenum, 5 percent iron, 0.09 to 0.12 percent carbon, 0.5 percent silicon, 0.1 percent manganese, 3 to 3.3 percent titanium, 1.4 to 1.6 percent aluminum, and the balance nickel. Illustrative of a cobalt based alloy which may be cast in accordance with the invention is Haynes 25, consisting of 0.05 to 0.15 percent carbon, 1.0 to 2 percent manganese, 19 to 21 percent chromium, 9 to 11 percent nickel, 14 to 16 percent tungsten, 3 percent iron, 1 percent silicon, and the balance essentially cobalt.

As described above, the metal solidification occurs in a metal mold portion of the zone two so that there is no carbon source for carbon diffusion. The skin layer 23 is well formed when it is transferred to the graphite lined zone three so that no appreciable carbon diffusion occurs during the casting process.

Although this invention has been described in terms of specific examples, it is to be understood that other forms of the invention may be readily adapted within the scope of the invention.

Claims

What is claimed is:

1. A method of continuously casting, horizontally, a continuous rod comprising the steps of

a. continuously introducing molten metal taken from the group consisting of ferrous metals, nickel based metals or cobalt based metals into the inlet end of the cavity of a stationary open-ended horizontally disposed continuous casting mold;

b. said mold including a first zone adjacent said inlet end having a relatively low heat transfer capacity, a non-lubricated second zone immediately adjacent said first zone having a relatively high heat transfer capacity, and a third zone adjacent said second zone terminating in an open outlet end;

c. advancing said molten metal into said first zone, the heat transfer characteristics of said first zone being operative to substantially prevent any metal solidification therein;

d. advancing said molten metal into said second zone, the high heat transfer characteristics of said second zone being operative to cause solidification of a thin layer of said metal at first immediately at the junction of said first and second zone and then progressively in the direction of said third zone whereby a solidified thin layer of said molten metal is formed coextensively of said second zone, the portion of said first zone immediately adjacent said second zone being formed of a material which is substantially inert to said molten metal and is non-adherent to said thin layer; and

e. advancing said rod continuously but in fixed predetermined increments at fixed predetermined time intervals, said increments being equal to the length of said second zone whereby said thin layer of said solidified metal formed in said second zone is advanced progressively into said third zone and the molten metal advancing from said first zone follows the advance of said thin layer to progressively fill said second zone immediately behind said advancing thin layer and to thereby progressively form a new thin solidified layer coextensively of said second zone cavity surface, said intervals being of sufficient duration to permit the forward axial end of said newly formed thin layer to weld to the solidified metal in said third zone.

2. A method of continuously casting, horizontally, a continuous rod comprising the steps of

a. continuously introducing molten metal taken from the group consisting of ferrous metals, nickel based metals or cobalt based metals into the inlet end of the cavity of a stationary open-ended horizontally disposed continuous casting mold;

b. said mold including a first zone adjacent said inlet end having a relatively low heat transfer capacity, a non-lubricated second zone immediately adjacent said first zone having a relatively high heat transfer capacity, the portion of said first zone immediately adjacent said second zone being formed of boron nitride, and a third zone adjacent said second zone terminating in an open outlet end;

c. advancing said molten metal into said first zone, the heat transfer characteristics of said first zone being operative to substantially prevent any metal solidification therein;

d. advancing said molten metal into said second zone, the high heat transfer characteristics of said second zone being operative to cause solidification of a thin layer of said metal at first immediately at the junction of said first and second zone and then progressively in the direction of said third zone whereby a thin layer of said molten metal is formed coextensively of said second zone; and

e. advancing said rod continuously but in fixed predetermined increments at fixed predetermined time intervals, said increments being equal to the length of said second zone whereby said thin layer of said solidified metal formed in said second zone is advanced progressively into said third zone and the molten metal advancing from said first zone follows the advance of said thin layer to progressively fill said second zone immediately behind said advancing thin layer and to thereby progressively form a new thin solidified layer coextensively of said second zone cavity surface, said intervals being of sufficient duration to permit the forward axial end of said newly formed thin layer to weld to the solidified metal in said third zone.

3. A method of continuously casting horizontally, a continuous rod comprising the steps of

a. continuously introducing molten metal taken from the group consisting of ferrous metals, nickel based metals or cobalt based metals into the inlet end of the cavity of a stationary open-ended horizontally disposed continuous casting mold;

b. said mold including a first zone adjacent said inlet end having a relatively low heat transfer capacity, a non-lubricated second zone immediately adjacent said first zone having a relatively high heat transfer capacity, and a third zone adjacent said second zone terminating in an open outlet end;

c. advancing said molten metal into said first zone, the heat transfer characteristics of said first zone being operative to substantially prevent any metal solidification therein;

d. advancing said molten metal into said second zone, the high heat transfer characteristics of said second zone being operative to cause solidification of a thin layer of said metal at first immediately at the junction of said first and second zone and then progressively in the direction of said third zone whereby a thin layer of said molten metal is formed coextensively of said second zone, the portion of said first zone immediately adjacent said second zone being formed of a material which is substantially inert to said molten metal and is non-adherent to said thin layer; and

e. advancing said rod continuously but in fixed increments of 0.1 to 1.5 times the diameter of the rod being cast at fixed predetermined time intervals, said increments being equal to the length of said second zone whereby said thin layer of said solidified metal formed in said second zone is advanced progressively into said third zone and the molten metal advancing from said first zone follows the advance of said thin layer to progressively fill said second zone immediately behind said advancing thin layer and to thereby progressively form a new thin solidified layer coextensively of said second zone cavity surface, said intervals being of sufficient duration to permit the forward axial end of said newly formed thin layer to weld to the solidified metal in said third zone.

4. A method of continuously casting, horizontally, a continuous rod comprising the steps of

a. continuously introducing molten metal taken from the group consisting of ferrous metals, nickel based metals or cobalt based metals into the inlet end of the cavity of a stationary open-ended horizontally disposed continuous casting mold;

b. said mold including a first zone adjacent said inlet end having a relatively low heat transfer capacity, a non-lubricated second zone immediately adjacent said first zone having a relatively high heat transfer capacity, and a third zone adjacent said second zone terminating in an open outlet end;

c. advancing said molten metal into said first zone, the heat transfer characteristics of said first zone being operative to substantially prevent any metal solidification therein;

d. advancing said molten metal into said second zone, the high heat transfer characteristics of said second zone being operative to cause solidification of a thin layer of said metal at first immediately at the junction of said first and second zone and then progressively in the direction of said third zone whereby a thin layer of said molten metal is formed coextensively of said second zone, the portion of said first zone immediately adjacent said second zone being formed of a material which is substantially inert to said molten metal and is non-adherent to said thin layer; and

e. advancing said rod continuously but in fixed increments of 0.1 to 1.5 times the diameter of the rod being cast at fixed cycle timely intervals of about 0.15 to 1.10 seconds, said increments being equal to the length of said second zone whereby said thin layer of said solidified metal formed in said second zone is advanced progressively into said third zone and the molten metal advancing from said first zone follows the advance of said thin layer to progressively fill said second zone immediately behind said advancing thin layer and to thereby progressively form a new thin solidified layer coextensively of said second zone cavity surface, said rod being at rest for a time of 33 to 65 percent of said cycle time interval to permit the forward axial end of said newly formed thin layer to weld to the solidified metal in said third zone.

5. The method of claim 4 wherein said metal is a ferrous metal containing less than 2 percent by weight carbon.

6. A method of continuously casting, horizontally, a continuous rod comprising the steps of

a. continuously introducing molten metal taken from the group consisting of ferrous metals having a carbon content up to about 2 percent by weight, nickel based alloys or cobalt based alloys into the inlet end of the cavity of a stationary open-ended horizontally disposed continuous casting mold;

b. said mold including a first zone adjacent said inlet end having a relatively low heat transfer capacity, a non-lubricated, non-graphitic second zone immediately adjacent said first zone having a relatively high heat transfer capacity, and a third zone adjacent said second zone terminating in an outlet end, the mold in said third zone having a progressively decreasing internal diameter for at least a portion thereof and having at least a surface layer formed of graphite;

c. advancing said molten metal into said first zone, the heat transfer characteristics of said first zone being operative to substantially prevent any metal solidification therein;

d. advancing said molten metal into said second zone, the heat transfer characteristics of said second zone being operative to cause the solidification of a thin layer of said metal initially immediately at the junction of said first and second zones and then progressively in the direction of said third zone whereby a thin solidified layer of said molten metal is formed coextensively of said second zone, the portion of said first zone immediately adjacent said second zone being formed of a material which is substantially inert to said molten metal and is non-adherent to said thin layer; and

e. advancing said rod continuously but in fixed predetermined increments at fixed predetermined time intervals, said increments being equal to the length of said second zone whereby said thin layer of said solidified metal formed in said second zone is incrementally advanced into said third zone and the molten metal advancing from said first zone follows the advance of said thin layer to progressively fill said second zone immediately behind said advancing thin layer and to thereby progressively form a new thin solidified layer coextensively of said second zone cavity surface, said intervals being of sufficient duration to permit the said forward end of said newly formed thin layer to weld to said solidified metal in said third zone, said solidifying and cooling metal in said third zone gradually shrinking in diameter as the metal solidifies and cools and the said progressively decreasing diameter of said mold in said third zone being adapted to snugly engage the solidifying rod as it passes through said third zone to maintain efficient heat transmission and roundness of the rod.