US1892044A - Method of casting ingots - Google Patents

Description

Dec. 27, 1932. B. E. ELDRED ET Al.

METHOD OF CASTING INGOTS Filed April 9, 1951 INVENTORS ATTORNEY Patented Dec. 27, 1932 UNITED STATES PATENT oFFlc BYRON E. EDBED, OF NEW YORK, N. Y.; AND HOMER CLYDE SNOOK, OF SUMMIT, NEW JERSEY; SAID ELDRED ASSIGNOR TO SAIDVSNOOK METHOD OF CASTING INGOTS Applicationv led April 9,

Our present invention involves a solution of the many complicated problems involved in casting ingots of steel and has for its object the production of sound steel ingots suitable for rolling and mechanical working.

There are many kinds of steel and steel alloys having widely varying percentage of carbon as well as varying percentages of other ingredients, some beneficial and others detrimental, but our present invention does not particularly concern the composition or the methods of making the various kinds of steel. 'llVeassume that the steel will be made in accordance with the best known practices of the art and will be available. and ready for pouring; also that in thepractice of our method, the pouring ladles and methods, as Well as the molds and technique of assembling, lining, luting, etc., will be in accordance with approved practices in these branches of the art.

While our method will be of advantage in connection with any variety of steel, We have preferred to assume for purposes of our present disclosure that the steel is one of the conventional types containing less than 1/% of carbon and of good quality as concerns detri mental impurities.

In view of and to a large extent because of the unique qualities of steel, the art of casting 'has developed along what we find to be entirely improper lines, resulting in serious defects which it is an object of our invention to avoid.

For instance, in the prior art of casting steel ingots, it has been the usual practice to employ cast iron molds whereby the heat is extracted from the molten metal mainlyk by radial conduction, from the molten interior, outward through the side walls'of'the iron mold. This has been true for ingotsboth of the billet and slab types and regardless of whether cast horizontally, vertically or centrifugally. fOne of the defects, particularly .5 in the case of large ingots intended for roll 1931. Serial No. 528,762.

ing and mechanical working, is the formation of blow holes which may be formed either throughout the casting, or near vthe surface only. Other defects are piping and/or. adjacent segregation of constituents which should be uniformly distributed throughout the ingot. These defects are always serious, due to the waste that results from chopping oil` a substantial part of the top of each ingot, the top being the part where piping and segregation defects are more or less localized, even where the casting methods are in accordance with the best practices of the prior art.

As set forth in a prior patent to one of us, No. 1,217,581, it has long been recognized that sound castings of copper and other metals having similar qualitites of relatively low melting point and high heat conductivity, e could be made by a process'which comprises 65 basally and positively cooling'a body o f molten copper in a thermally "conductive mold While exposing the body of the mold to heat, such cooling and heating beingso performed as to cause the regular progress 4upward of 70 the solidiication of the molten metal; also that one method of utilizing the above basic principle is to place a body of such metal ina mold in a name-heated furnace until the metal melts and then positively cooling the bottom of such mold by placing it on awater cooled floor until the metal solidilies ,while still allowing the ame to heat the top of the -mold; also molten copper may be used instead of melting it in the mold. TheI patent AX A also specifies metals of the same class as including gold, which has practically the same lmelting point and cooling rate4 as copper; silver which has slightly lower 'meltingpoint and higher cooling rate; and aluminum which has a much lower melting point and high cooling rate. The principle is also applicable to zinc which has a much lower` melting point but lower cooling rate; alsoto magnesium.

having approximately the same melting point as aluminum and a cooling rate higher than that of zinc. v

We have long recognized that the patented method would be of advantage if it could be applied to making of steel ingots, but the totally different and wholly unique qualities of steel presented difficulties which have heretofore .seemed unsolvable.

One diiculty is that steel has a meltingI point of approximately 1530o C., as against 1080o for copper, or 660 for aluminum, or 650 for magnesium, or 420 for zinc.

On the other hand, the heat conductivity and resulting rate of cooling is far less for. steel. lVhile the conduction cooling rates vary somewhat with the temperature and while that of steel is less for those of greater carbon content, the relative cooling rates may be represented in a general way and not too in accurately as steel 1, copper 9, aluminum 5, zinc 2.6 and magnesium 3.7. Alloys such as aluminum-bronze are in the same general class as concerns having low melting points and high heat conductivity, as compared with hot, metal that has been pre-melted and poured into the mold. By our method, the steel is initially super-molten, that is, heated to a temperature las high or higher than that characteristic of what is known as rising steel and We utilize the thus vstored heat in the molten metal tomaintain complete liquidity as against all possible radial heat losses through the top and side walls of the mold, -such loss being prevented by heavily insulating the interior of the mold throughout its entire length. Complete liquidity of the contents of the mold being assured for a reasonable time, substantially all of the heat is withdrawn through a water cooled base of the mold. By such method, radial heat losses are made negligible and substantially all of the heat flow is Vdownwardparallel with the v axis of the' ingot.` Solidificaton begins at the bottom and progresses upward substantially at a horizontal plane, thus accomplishing with steel what has been previously accomplished for metals of lower melting point and higher heat conductivity, by the totallyV f different method described in said prior patent. To accomplish this with steelgives a result not found in the case of copper, namely, the super-molten metal source of heat affords high temperatures, maintaining complete iiuidity almost down to the `horizontal solidification surface, thereby minimizing the depth of the mushy or viscous layer, thereby practically eliminating all difficulty of escape of the gas or slag which is ejected from the solidifying surface.

The above and other features of oui' invention will be more evident'from the following description in connection withI the accompanying drawing, in which The. figure is a somewhat diagrammatic representation of a mold in which supermolten steel is being solidified in accordance with our present invention.

In this drawing the exterior shell 1 may be of cast iron formed with lifting lugs after the manner of the usual. mold, but it is provided with inturned anges 3 to support a refractory linin the interior surface of which constitutes t e mold. The refractoryl lining preferably comprises a layer of lire brick 4 laid with refractory cement 5. The inner sur- `face of the lire brick lining may constitute the mold but fire brick, though of most excel- `lent non-conducting qualities, are liable to contaminate the steel under certain conditions, and we prefer to employ athin inner lining 6,l which may consist df refractory chromite material which, though slightly more conducting, is likel to be more resistant as concerns contaminating the molten Y steel. It may be in the form of slabs secured by chromite cement, as shown; or the cement alone may be used. In either case, the entire lining is permitted to dry thoroughly before use. Also it may be initially' heated to very high temperature after the manner of refractory lined ladles into which molten steel is drawn for pouring. Moreover, if the steel happens to be of a quality or made u nder conditions where it is likely to be deficient in super heat, such pre-heating of the lining may immediately precede the pouring of the steel into the' mold.

The bottom o f the mold is formed by the massive'plate 7 supported by and preferably integral with the base 8. This base is preferably formed with a water chamberf9, directly below the plate 7, which chamber is kept cold by circulation of vwater or other cooling medium through pipes 10 and 11, supplied from any suitable source.

The mold is preferably providedrwith a hot top which may comprise a cast iron shell 12 filled with fire brick 13 and provided with a vent 14 for escape of gases during cooling. I

The brick may be of the same thickness as the wall lining brick 4 and the hot top may be dried and. may be heated to incandescence jus;1 prior to use, as in the case of the mold Wa SI lng must be taken as i the area would be nearly 50% The walls of the mold cavity preferably diverge toward the bottom. This facilitates strippin of the ingot and affords and may be speci cally designed with a view to progressively smaller cross-sections ofv molten metal from which the heat is to be drained downward through the base. For instance, if the diameters were top 10 greater at the base than at the top.

IVithin the mold, we have endeavored to show the solidifying operation, but such showpurely diagrammatic. The solidified steel A is indicated as having a vertical grain parallel with the lines of vertical heat flow and perpendicular to the horizontal surface ,B where the solidification is taking place. C isV intended' to indicate the thin transition zone where the steel is in the mushy or viscous transition state, and D-is intended to represent the great body of supermolten metal which contains heat enough to insure complete liquidity almost down to the surface of solidiication at B, thereby making the transition layer C very thin. E is intended to represent the slag on top of the molten steel.

In practice of the invention, the` supermolten steel is prepared and poured into the mold according to approved practice in the art, the mold being preheated or not as seems necessary or desirable in any particular case.

. A sheet of iron or steel may be placed on strong,

mold bottom 7 to prevent erosion,rif desired.

The water which is kept flowing through the water chamber 9, in cast iron base 8, extracts heat from the bottom 7 which in turn extracts heat rapidly from the bottom of the liquid steel. By extracting the heat from the liquid steel rapidly and from the lower end of the ingot only, a number of beneficial results are obtained in the resulting solidified metal, A. The solidification progresses in an upwardly shifting horizontal plane, and the crystal formation grows from the bottom upward with the major axes of the crystals vertical to said plane and parallel with the length. of the ingot, as diagrammatically indicated. The crystal axes are thus parallel with each other and parallel with the direction of extension of the metal when subsequently rolled. They are thus in the most favorable position to afford maximum ductility, density and strength for the rolled product.

Heretofore the'best and strongest metal has been found in the lower portions of ingot-s that have been cast in wallchill molds. In such case the lower portions of the ingot are solidified in basaltic colum'ns and are cleaner and stronger than the metal in the rest of the ingot. By our method, the steel is solidified rapidly upwards so that basaltic columns of equiaxed crystals, extend longitudiand base 12",.

nally throughout the ingot, instea confined to the bottom of the ingot.

This may be explained on thetheory that of being gases and slag dissolved in steel are rejected surface is substantially horizontal and such flow lines are vertically upward, while heat abstraction is vertically downward, the crystals grow vertically upward. Hence, the gas and slag are correlatively more free to "escape upward between such vertical crystals, instead of being trapped by horizontal crystals such as grow from the side walls of the mold when theingot is frozen`by side wall cooling processes heretofore employed. In this connection, it is to be noted that in the prior art, cooling of the steel, even when applied to the side walls progressively, from the' lower portions upward, has not been controlled by effective side wall insulation, and the result lhas been that side wallfreezing has progressed in advance of interior freezing, to growand the viscous zones to develop radially, instead of vertically-throughout a lage part of the ingot volume, .thereby causing entrapment of gas, piping, liquation, segregation and coarse crystallization. It is obvious that under such conditions a large part of the metal is being cooled all the time, and even though this may result in a shorter total time for the final cooling, the actual cooling time at anyone point is relatively long. The point is that the longer the cooling time of any givenv zone or layer independently of the total cooling time, the more voluminous will be the viscous zone, the coarser the`crystallization on freezing, the greater the segregation, the greater the liquation, and the greater the tendency to pipe formation. l

By our method, the body of liquid is initially super-molten and the complete side wall insulation keeps this liquid from cooling to mushy temperatures except as and where heat is conducted downward through the horizontal freezing surface. Under such conditions, by extracting the heat rapidly by water cooling at the lower end of theingot, while rendering side wall cooling practically negligible, we are able to reduce lthe size of the crystals and to prevent or minimize liquationand segregation, and to prevent the formation of pipes.

Naturally, the hotter themass of liquid thus causing the crystals steel when poured into the mold and the more rapidly the heat is extracted from the bottom of the ingot, the thinner will the viscous layer be-squeezed, so to speak, between the hot molten metal and the advancing surface o f the freezing, solid steel.

This viscous layer being thin, the fraction of the volume of the ingot in the viscousstate at any one time is small, and the time between liquid and solid state is small. Hence our method involves quick freezing and smaller crystals and such segregation and liquation as can take place is very small in amount becausethe'volume of viscous metal upon which crystals can feed is small and the time is short. i

Thus, by our method of orderly, localized, rapid heat extraction from the molten steel, we produce in the solidified ingot a crystalline structure that, in addition to being dense ductile and homogeneous, is made up of small-sized, equiaxed crystals. Consequently, our ingots require less mechanical worklng and rolling to yield the desired fine grainedfhomogeneous structure required in a strong and tough finished product.

It is understood that the steel to be cast by our process should be deoxidized and degasified 'before pouring as well as is practicable, considering the present state of the art. The. proper use of a suiiicient quantity of aluminum, ferro-silicon or other well known deoxiziders may be desirable.

While thevgreat, outstanding merit of our present invention, is its successful application to and solution of the unique problems of steel ingot casting, it will be evident that it is applicable to other metalsor alloys of far lower melting point and higher conductivity, as well as to those of high melting point and ofeither higher or lower conductivity than steel,

We claim: 1. In the art of casting an elongated steel ingot to be furtherv elongated by rolling or the like, a process which includes forming an elongated upright mold of insulating inaterial constituting the lining of an exterior cast iron ca`sing mold; charging said mold with liquid steel hot enough to insure initial super-molten .temperature for all of said liquid and for the top and side wallsof said insulating liner mold; cooling the lower end of the liquid so as to form a solid layer having la substantially horizontal top; and thereafter causing solidification to progress upward in a substantially horizontal plane by abstracting heat from the liquid downwardly and substantially uniformly throughout all parts of the pre-formed surface.

2. In the art of casting an elongated steel ingot to be further elongated by rolling or the like, a process whichincludesforming an elongated upright mold of insulating material constituting the lining of an exterior cast iron l casing mold; charging said mold with 1i uid steel hot enough to insure initial super-mo ten temperature for all of said liquid and for the top and side walls of said insulating liner.

zontal boundary between the solid and the.

liquid.

3. In the art of casting an elongated steel ingot to be further elongated by rolling cr the like, a process which includes forming an elongated upright mold of insulating material constituting the lining of an exterior cast iron casing mold; charging said mold with liquid steel hot enough to insure initial super-molten temperature for all of said liquid and for the top and side walls of said insulating liner mold; and chilling the steel by removing heat congelations from a narrow horizontal zone by downflow of the heat substantially uniformly through all of the top area of the preformed solidied material.

4.y In the art of casting an elongated steel f ingot to be further elongated by rolling or the like, a process which includes forming an elongated upright mold of insulating material constituting the lining of an exterior cast iron casing mold; charging said mold with liquid steel hot enough to insure initial super-molten temperaturefor all of said liquid and for the top and side walls of said insulating liner mold; and chilling the steel by removing heat congelations from a narrow horizontal zone by downiow of the heat substantially uniformly through all tof the top area of the preformed solidified material.

5. A method of casting ingots having a grain structure of the metal disposed approximately parallel with the direction in which the metal is to be elongated, which method includes charging the metal super-molten, heat insulating its interior, metal contacting surface to substantially prevent solidification by cooling at one end and also by cooling transversely of the desired direction of the grain, solidifying the other end by withdrawing heat from the liquid substantially uniformly over all the area of said other end, and thereafter similarly, uniformly and progressively withdrawing substantially all of the heat through the advancing pre-formed surface of the solid. A

6. A method of casting elongated ingots having a grain structure disposed approxi mately parallel with the axis of the ingot, which method includes charging the metal, super-molten, into an upright mold; heat insulating its interior, metal containing surface to substantially prevent solidication by cooling horizontally or through the top solidiying a horizontal layer Aat the bottom by withdrawing heat from the liquid down- 13o-" wardly and substantially uniformly through all portions of the area of said bottom; and

., lthereafter progressively solidiying the remaining liquid by withdrawing substantially all of the liquefying heat downwardly and substantially uniformly through all portions of the area of the advancing pre-formed surface of the solid.

Signed, at New York, in the county of New York and State of New York, this 8th day of April, A. D. 1931.

BYRON E. ELDRED.

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