US3067473A - Producing superior quality ingot metal - Google Patents

Description

Dec. 11, 1962 R. K. HOPKINS PRODUCING SUPERIOR QUALITY INGOT METAL Original Filed Oct. 51, 1956 FIG.I.

4 Sheets-Sheet 1 ROBERT K. HOPKINS IN VEN TOR.

ATTORNEYS Dec. 11, 1962 R. K. HOPKINS 3,067,473

PRODUCING SUPERIOR QUALITY INGOT METAL Original Filed Oct. 51, 1956 4 Sheets-Sheet 2 in, mm 6% Dec. 11, 1962 R. K. HOPKINS 3,067,473

PRODUCING SUPERIOR QUALITY INGOT METAL Original Filed Oct. 31, 1956 4 Sheets-Sheet 3 R. K. HOPKINS 3,067,473

PRODUCING SUPERIOR QUALITY INGOT METAL 4 Sheets-Sheet 4 Dec. 11, 1962 Original Filed Oct. 31, 1956 ,4 ifamc/J ire 3,367,473 Patented Dec. 11, 1962 filice 3,667,473 PRQDUCING giJPlERIUR QUALITY TNGOT METAL Robert K. Hopkins, West New Brighton, Staten Island, N.Y., assignor, by mesne assignments, to Firth Sterling, Inc, a corporation of Pennsylvania Continuation of applications Ser. No. 619,457, Oct. 31,

1956 and Ser. No. 619,596, Oct. 31, 1956. This application Mar. 29, 1960, Ser. No. 18,353

2 Claims. (Cl. 22212) This invention relates to the production of consistently uniform high quality semi-finished alloy products and particularly, to the production of such products of analyses normally troublesome with regard to uniformity and quality.

This application is a continuation of my applications Nos. 619,596 and 619,457 of October 31, 1956, respectively, entitled Method for the Production of High Quality Metal From Low Quality Conventionally Produced Metal, and Method of Producing High Quality Ingot Metal by Electrical Fusion, both abandoned.

In making ingot metal, see US. Patent No. 2,191,474, I have employed a so-called I-melt procedure which involves feeding metered quantities of metal particles or pieces through a hollow or tubular electrode and fusing the electrode metal and the metal pieces in a cooled mold by employing the hollow electrode as a consumable electrode in arc fusing and melting the metal pieces under a slag. The purpose has been to fuse the constituents as supplied and to withdraw the heat from the mold at such a rate that metal of predetermined analysis is continuously solidified While a bath of molten metal is maintained of a sufficient depth to intermingle and alloy the constituents under the flux.

This produces products that are normally substantially homogenous in physical structure; the process has been particularly successful in producing ferrous alloys and steels of low and medium alloy content. With more precision of control, alloys of comparatively higher alloy contents, such as some of the molybdenum, chromium, vanadium, and tungsten containing tool steels, may also be produced in commercial quantities.

During recent years, there has been an increasing demand for so-called super-alloys for high strength high temperature service, such as those used for the turbine components of turbo-jet engines which include a high percentage of alloy ingredients, some of which are of a refractory nature and thus present melting, solidification and refining problems of special character. The production of such super-alloys is further complicated by the fact that practically perfect macro metal must be produced if rigid quality requirements are to be satisfied and as a result, material which was normally considered of sufiiciently high quality for tool steels, for example, may be rejected if it is to be used as a material for turbine components of a turbo-jet engine.

I have found that in producing these so-called superalloys, all heretofore employed methods of ingot production, even when precisely controlled, do not produce uniformly acceptable material and particularly, from the standpoint of the full elimination of macro metallic and non-metallic inclusions, segregation, carbon and refractory metal, carbo-nitride stringers, etc. The desideratum is a substantially uniform grain structure throughout the ingot from its central axis outwardly to its outer periphery as well as longitudinally of the ingot axis, and with a minimized requirement for removal of metal from the standpoint of top and bottom crop and peripheral areas before the ingot is suitable for usage in making forgings for high temperature high operating stress parts.

During recent years, metal alloys have been made employing my above-mentioned process, by electrical induction melting, by air arc melting, by are melting in an insert gas atmosphere, and by vacuum arc melting with and Without the use of a consumable electrode. Since certain refractory metals, such as titanium, zirconium, etc., are extremely sensitive to pick-up of contaminants, including atmospheric gases, the trend in recent years has been towards the use of consumable electrode vacuum melting procedure, on the basis that atmospheric contaminants will be prevented from contaminating the melt and that contaminants and particularly gaseous contaminants in the melt, may be withdrawn during the melting procedure. However, in order to properly control the arc, high currents and melt rates are required and will result in a relatively deep molten pool, with usual ingot segregation problems, and with precipitation hardening and defective areas, particularly along the axis of the ingot. Segregation and inclusions in high performance materials of all types of metals serve as focal points for fatigue and rupture failures.

The tendency in recent years in producing super-alloys has been to use iron or nickel base alloys that contain materials, such as titanium as hardening constituents, with and without aluminum, and these materials further aggravate the difliculties encountered in melting practice. In order to minimize engine weight in turbo design, both stresses and temperatures have been increased; on the other hand, turbine wheel failure in a jet engine must be avoided at all cost. Thus, the quality standards for the material used have become extremely rigid.

Although fairly good quality ingots have been produced, particularly by my above-mentioned process and by vacuum melting process, objectionable macro structures in the form of so-called dark or black spots or specks (possibly in the nature of undissolved metal or nonmetallic inclusions), freckles (which may be lower melting point alloys With a relatively high silicon content), phase changes, and nitride stringers, carbo nitride inclusions, etc., have been particularly troublesome. In a first melt, dark spots tend to extend somewhat randomly across the full section of the ingot. Those skilled in the art have endeavored to at least minimize so-called dark spots by remelting under a consumable vacuum process which tends to cause many of them to concentrate in a peripheral area about the ingot, such that by machining or turningoff about 20 to 33% of such areas of the ingot about its periphery, this concentrated area may be eliminated. However, freckles have a tendency to occur in the central areas of inert gas, vacuum and air melted ingots, whether or not a second melting is accomplished. Also, dual melting of this type still leaves random dark spots throughout the section of the ingot and does not fully eliminate non-metallic inclusions with particular reference to refractory metal nitrides or carbo nitrides.

it has been heretofore determined that a slower m'elting rate in a conventional consumable electrode process is advantageous in providing a more shallow pool but is disadvantageous in that it results in a poor peripheral surface about the ingot; on the other hand, a faster melting rate is advantageous in providing a better peripheral surface but is disadvantageous in that it results in central segregation of the ingot. If an attempt is made to reach a happy medium, both disadvantageous factors are present. By my slag or flux blanket melting method, I eliminate both factors in that a higher melt temperature is accomplished under inherently substantially quiescent melting, and a peripheral surface is inherently produced that is much improved over anything that could heretofore be attained, even employing a faster melting rate. On the other hand, using a conventional melting procedure, such as consumable electrode vacuum, air or inert gas melting, irrespective of whether it is a first or second melting, a so-called pineapple or corn cob type of peripheral surface is produced which has to be ground or turned off before the ingot can be employed in making a forging. This, of course, is extremely wasteful of the metal.

Those skilled in the art have felt that a slag method was not the proper approach in producing ingots of ultimate high quality and particularly from the standpoint of those containing higher alloys and refractory alloying materials. It was believed that the slag would contaminate the melt and that gases, such as hydrogen, nitrogen and the element carbon that produce non-metallic inclusions, could not be removed in this manner. Although a second melting by the consumable vacuum method appeared to be the only approach to obtain the ultimate in ingot quality, in departing from the thinking in this field, I have obtained surprisingly improved results and have been able to eliminate even gaseous impurities that appear as macro inclusions in ordinary melts. I have discovered that a slag is actually beneficial and not detrimental in a second stage consumable melt, and that it will enable the attainment of a final ingot of maximum quality with a minimum of cost where its metal is made available essentially by a previously-formed lower quality ingot employed as a dense body or solid consumable electrode.

I have discovered that a dual melting procedure employing, in its final melting stage, a continuous body of solid or dense, prefused or melted and cast ingot that contains alloy metal of substantially the final analysis, such as may be produced by a conventional procedure, and which is of relatively poor or low quality, could be used as a consumable electrode in a slag-melting final ingot-forming stage to produce an ultimate high quality ingot in which macro inclusions are fully eliminated, whether of a metallic or non-metallic nature, and without the necessity of extensive cutting-away of the ingot, particularly from the standpoint of its peripheral area. A slag blanket as herein employed and which is inherently ionized when used in my final stage process, has a highly beneficial effect from the standpoint of removing all macro black spots, freckles, metallic and non-metallic segregation and inclusions; it serves as a dampening agency and makes possible a relatively higher or superheated temperature operation at a relatively slower melting rate corresponding to the solidification rate of the conditioned molten metal; it makes possible the bringing of all the metal particles from the metal-supply electrode into a fully molten solution condition in the pool that is substantially quiescent (see FIGURE 1), and before they are cooled and solidified to form the ingot.

In this connection, I have found that, irrespective of whether a poor quality so-called scrap metal ingot is provided by the first melting stage, which in accordance with my procedure should contain substantially the full base metal and alloying content of the final ingot (subject to small corrective additions), and irrespective of whether or not the outer surface of the ingot is removed or ground off to remove concentrated black spots, etc., and irrespective of whether the preliminary ingot is produced by any conventional melting procedure, including air or inert gas melting, induction melting, vacuum melting, etc., that a second or final stage treatment in accordance with my invention will so condition the ingot that on remelting and resolidification, the ultimate in quality standards can be obtained, and particularly from the standpoint of ingots having higher alloying contents, including refractory metal contents.

In accordance with my procedure, I have been able to eliminate the inherent spattering of metal, such as in- 'volved in consumable air, inert gas and vacuum melting procedures, which forms a solidified collar about the top of the ingot. Further, I eliminate the necessity for fast or hard arc melting, and totally eliminate corn cob or pineapple peripheral surface effects. The so-called dark specks such. as heretofore encountered, particularly in the case of aluminum and titanium containing iron and nickel in a random manner through the section of the ingot.

Previous to my invention, it has been proposed'that the high quality standards be made flexible enough toprovidefor a certain maximum of such specks for a given area of alloy metal as supplied. However, my procedure has made it unnecessary to broaden specification require ments in this respect.

It has thus been an object of my invention to provide simple and inexpensive method for converting alloy ma-- terial whose quality is low by reason of non-metallic or metallic inclusions, phase changes, segregated areas andthe like, to a final ingot product of superior quality by a second or final stage consumable melting and solidification under a protective slag or flux blanket;

Another object of my invention has been to provide a method for producing alloy bodies of a substantially uniform quality that are acceptable for the severest service conditions and which contain relatively large proportions of alloying constituents and which may contain refractory metal alloying constituents;

Another object has been to provide a procedure which will eliminate the difiiculties inherent in prior art procedures and which, although departing from the thinking of those skilled in the art, will answer the problem presented from the standpoint of commercial production of super quality alloy metals of substantially uniform characteristics and of such a nature that an improved peripheral surface will be provided and only top and bottom crop has to be removed;

These and other objects of my invention will appear to those skilled in the art from the specification, the drawings and the claims.

In the drawings, FIGURE 1 is a front view, partially in section, illustrating apparatus suitable for carrying out the final, novel melting and solidification step of my procedure which may be employed in raising the quality of non-ferrous as well as ferrous alloys, and, irrespective of whether such alloys contain relatively small or relatively large proportions of alloy constituents, including refractory constituents;

FIGURE 2 is a macro etch plate of the top of a 9-inch square final billet forged from an ingot of an A-286 alloy produced by my dual melt process showing that segregation and subsurface nitrides are substantially eliminated;

FIGURE 3 is a macro etch plate of the bottom of the billet of FIGURE 2 illustrating the substantial uniformity of the structure;

FIGURE 4 represents longitudinal macro etch slices cut from transverse 9-inch square discs of billets forged from final ingot products; the first slice (on the left) is a section from the top of a vacuum consumable product or billet; the second slice from the left is a section from the same billet as the top slice after a recut of 4 inches; the third slice from the left is a section from my final dual melted product showing the absence of nitride stringers which have been circled in the first and second slices of the vacuum consumable product.

In accordance with my concept, an ingot of dense somewhat homogeneous alloy metal produced by my I melt (see my U.S. Patent No. 2,191,479) or any other conventional procedure is used as a solid consumable electrode and principal source of metal alloy for the final ingot product, and is remelted under an electrically ionized slag blanket. A relatively soft are results from the submerging of the arcing end of the solid metal-supplying electrode within the slag blanket and that ionizes the slag and produces a soft or relatively quiescent top melt-- ing action that eliminates the formation of a top collar by the inherent spattering of other processes, including air, inert gas or vacuum arc melting. Thus, a viscous slag serves as a dampening agency in the final stage which, as distinguished from inert gas or vacuum melting procedure, makes possible melting effectively at a relatively slow rate.

It has been determined that with an electric current discharge at 50 volts and of about 3,000 amperes, metal was produced at the rate of about 5 pounds per minute and that under these (relatively slow) conditions the best quality metal was obtained. It was found that when 6 pounds per minute is materially exceeded, it is difficult to maintain the required quality in the final metal; although variables such as electrode and mold diameters infiuence the rate, it is a slower rate for comparable diameters than used in consumable vacuum arc melting. The rate at which the mold is cooled is so controlled that the residence time is short enough to insure against undesired separation and/or segregation of the constituents of the alloy in the bath 28 during the phase change from the liquid bath 28 to the solid metal 29.

The slag is of a type such as set forth in my prior U.S. Patent No. 2,694,023 and a sufficient amount is used to provide a blanket of about three to six inches over the molten metal. The current discharge may be maintained in the neighborhood of about 50 volts with an amperage of about 1000 to about 2500 to 10,000 amperes or more. The depth of the slag may be adjusted to the size of the ingot being formed, the size of the consumable electrode being used and the particular alloy being melted. Since it is apparent that the depth of the slag governs the temperature of the metal in the pool, I prefer a greater depth of slag, the higher the melting point or refractory metal content of the alloy. By way of example, I have used a 6 inch blanket for an A286 alloy and a 1% inch blanket for a 16-25-6 alloy. Cooling water is supplied to the rr old Wall at a rate substantially equal to the fusing rate to cool and solidify the molten metal at substantially the rate of fusion thereof, and the molten metal bath beneath the slag may be maintained at a depth of about 5 to 6 inches. Under such conditions, the surface temperature of the slag or flux blanket is about 3500 F.

Cooling is employed along the full length of the mold so that solidified metal is cooled quickly down to a temperature well below the color range. One or more preliminarily produced ingots (electrodes) may be melted consecutively. Minor additions of constituents of the alloys may be made through the slag blanket to maintain a desired final analysis or to take care of analysis variations. Slag additions may also be made during the melting procedure.

The final ingot, as examined, shows a substantially uniform analysis throughout its length. The macro etch transverse sections of the ingot show a complete lack of ferritic inclusions without evidence of any macro segregation, of metallic or non-metallic inclusions or of sonic defects. Tensile and other tests indicate a lack of absorbed hydrogen. Macrographs of the drawings show the small grain character of the metal in its final, as cast, condition. No large dendritic structures are in evidence and the grains are substantially equiaxial with their axes hetrogeneously oriented. Hetrogeneously dispersed nodules of reaction products that may be present in the consumable electrode or preliminary ingot are completely eliminated in the final ingot. The relatively quiescent and complete melting of each increment of metal assures a full levitation off of non-metallics, gases and gaseous compounds.

It will be noted that the constituents of the base metal are fusible at moderate temperatures below about 3000 F. while those of the higher melting point metals, including the refractory metals, are fusible at higher temperatures in excess of 3000" F. and are thus ineffectively soluble in the base constituents at temperatures in the order of the melting points of the base constituents and any carbon present. Such refractory metals readily react with carbon and atmospheric components to form metallic compounds of extreme hardness and of melting points greatly in excess of 3000 F. in accordance with a phase of my procedure, the first melting zone or stage may be maintained at a temperature intermediate the above-mentioned moderate temperatures and the higher temperatures; the residence time of the constituents in the melting zone is sutlicient for a substantial completion of the reaction of the melting metals with carbon and atmospheric components, as well as for segregation of the reaction products. In this stage, constituents of the desired alloy to provide a metal of the desired analysis are supplied to a melting zone within which they are intermixed and fused at the intermediate temperature. The constituents used include base metal constituents fusible at moderate temperatures and others that are difficultly soluble in the base constituents at temperatures in the order of the temperatures of the base constituents. The residence time is less than required for complete solution of the diflicultly soluble constituents. In this way, I can produce a better initial quality of ingot for use as a consumable electrode in the final melting operation, although the inherent nature of my final melting operation is such that relatively poorer quality ingots may be employed, such as those produced by air melting, from scrap metal, etc.

In the second stage melting of my invention, the dense or solid consumable ingot electrode is positioned with its lower end beneath the surface of a protective blanket of slag in a cooled air or Water-jacketed mold. Electric current is discharged from the submerged end of the electrode to thus ionize the slag, generate heat and progressively fully melt cross-sectional increments of the electrode metal to form a molten metal pool across the full transverse extent of the mold cavity (see FIGURE 1). The current discharge is controlled to generate at least a sufficient quantity of heat, as retained by the slag blanket, to completely fuse, dissolve, intermingle, homogenize and refine all the metal entering the mold and to release, float or levitate out gases and non-metallics into the slag blanket, such that non-metallic compounds are retained by the slag blanket, including carbo-nitrides, and the relatively heavier metal forms a pool therebeneath and thereacross.

The rate of cooling of the mold is controlled to provide a metal pool of sufiicient temperature and size such that substantially each of the cross sectional increments resides therein for a sufficient time to completely fuse and intermingle with the remainder of the metal of the pool and at a rate to continuously solidify metal of the pool along its bottom at substantially the rate of metal supplied thereto from the electrode (see FIGURE 1). The slag blanket rapidly removes the non-metallic inclusions and other impurities from the pool and particularly, from the metal nodules or increments as they are progressively melted from the submerged end of the consumable electrode. This is inherent due to the high surface to niass ratio between the increments and the slag blanket through which they pass in their movement to the molten metal pool. The consumable electrode is in the form of a continuous body of dense somewhat homogeneous alloy metal of substantially the required analysis but of low or poorer quality, as produced by a prior combined fusing and casting operation involving the essential constituents of the alloy metal desired. As a result, the molten pool is made up substantially entirely of the material of the electrode or of metal that has been previously rough conditioned by fusion and solidification as a mass, as distinguished from powdered metal or metal pieces or particles which increase the temperature burden of the melting, tend to incompletely fuse in their movement from the electrode to the molten pool and which, in some ordinary melting processes, tend to sinter along outer areas of the ingot being formed rather than fuse. The molten or liquid metal beneath the slag is maintained at generally a super-heated condition, such that the metal refining, etc. can effectively proceed.

in accordance with my procedure, electrically-charged spam-re a metal increments, nodules or discrete portions are progressively arc-fused-ofi" the end of a previously-formed consumable electrode by discharging electric current therefrom and forming a molten pool from the incre- I thus progressively comexpcrienced in vacuum consumable melting. The re-' moval of nitride macro inclusions is directly contrary to What others skilled in the art felt could be accomplished with the use of a slag. the art were of the opinion that nitrogen could only merits Within the ingot mold. n pletely fuse or vaporize each metal increment of one be substantially removed as a gas and not through levitaof the electrode, while maintaining a slag blanket of a tion of its compounds during the melting operation. sufficient depth to exclude the atmosphere from the dis- The so-called dark specks and freckles which are so charge end of the electrode, the fused-off increments movtroublesome in other melting procedures are not in eviing therefrom, the are, and the molten metal pool. l dence in macrographs. Cuts for sonic deficiencies are no have found that under the controlled exemplary rates longer necessary. The protective slag egg shell provides of electric arc discharge fusion and of mold cooling at relatively smooth and void-free peripheral surface such herein set forth, gaseous and non-gaseous impurities are that the ingot can be forged into billets with a minimum removed from the energizedfused metal increments durof grinding and without machine turning. Further, coning their dispersed travel through the slag and before trary to the thinking of those skilled in the art, the slag they reach the molten metal bath. I thus obtain a maxiis not taken up by the melt, and the removal of a slight mum cleansing action by reason of the surface to mass top crop is sufficient for any residually retained slag. ratio of the completely fused metal increments to the That is, substantially 100% of the material of the final molten slag and before the increments reach the molten ingot can be passed on to working operations looking bath. The need for upward movement or levitation of to the production of a saleable product, as compared impurities from molten metal bath into the slag is thus to 80% or less for conventional operations. Rejections substantially reduced, although conditions are mainare substantially nil as to the end product, as compared tained conducive to such action. The pool of the molten to about for conventional procedures. The over metal bath is maintained by the fused increments being all result has been a cost saving of about 30% and a suintroduced and they are uniformly intermingled in the 25 perior final ingot product. 7 bath while it is being progressively cooled and solidified The following list of alloys is illustrative of those of from its bottom to form the ingot. The full quantity a type to which the invention is particularly applicable;

Typical Analyses Designation C Mn Si Cr Ni M0 Ti C0 Fe V Al W of metal going into and forming the ingot is, in elfect, A preliminary ingot or fused body, such as produced pro-conditioned by the slag during its movement there employing conventional procedures is, in accordance with through, so that macro-gaseous and non-gaseous conthe second stage procedure of my invention, used as an taminants are removed and do not enter the metal when impure consumable electrode, whereby it is subjected to the increments are combined and intermingled uniformly a remelting in a generally superheated condition and is in the molten bath. The use of a previously iusionre-solidified in such a manner as to greatly improve its formed dense or solid metal electrode body for supplya; quality. For this purpose the alloy metal maybe formed ing substantially the full quantity of the metal going into directly by electric fusion into ingots or such ingots as and being formed into the final ingot and of a molten Worked into dense bars of a section and length suitable slag in the manner outlined assures completely fused for use as a consumable electrode of the character remetal increments as the source of metal for the superior quircd for the efficient production of the ultimate alloy' quality final ingot. .50 product.

Thus, in accordance with my procedure, I employ an electrode which contains the basic constituents of the desired final alloy and effect a full solution and hemogenization of its metal content in slag blanketed pool in such a manner as to prevent the take-up of undesirable compounds in the ingot metal and produce a superior physical and metallur ical structure. t is apparent that, if desired, a vacuum or an inert gas may be maintained above the slag lanket of my second stage melt. It is of significance that a thin egg shell sleeve of slag is inherently formed along the outside wall or periphery of the ingot during the melting and solidification, such that the surface roughening effects of other melting procedures are eliminated, and such that peripheral removal of metal of the ingot is made unnecessary. This thin egg shell ser es as a protective coating during the forming of the final ingot.

An ingot produced in accordance with my invention has no macro surface and sub-surface nitride stringers and nitride segregation at the mid radius and center thereof. These result in sonic unsoundness and Zyglo rejections of an end product. The slag blanket serves not only as a protective covering during the final electrode melting, but also removes harmful nitride inclusions, rather than dispersing them through the ingot, as

The remelting and refining step may be conveniently carried out by apparatus shown diagrammatically in FlG URE 1. This electric fusion apparatus 10 includes elcc-' tric current supply and control arrangements of the character common in electric furnace and welding arts, and may be considered as housed in back of a panel 11. Extending from the panel 11 is a drive wheel 12 that is mounted on the shaft of an electrode feed motor which may be of a conventional type and which is controlled in accordance with the characteristics of the electric current discharge to feed the electrode at rates required to maintain arc discharge of pro-determined pie-established characteristics.

The drive wheel may, as shown, be a gear Wheel that engages a rack that is mounted on a rod 36 that is backed up by a pressure wheel 15. The rod 16 terminates in a head 17 to which the electrode 14 is attached. For convenience, the electrode is shown as attached to the head 17 by a series of tack or spot Welds l8 and extends into the mold 20 which is of a size to provide the final alloy body of the required section.

'Various conventional arrangements may be provided for cooling the mold However, I have shown an arrangement for illustrative purposes as including a jacket 21 which provides an annular space about the mold That is, those skilled in cavity for circulating water or another suitable cooling medium therethrough. As shown, the cooling medium enters through a lower inlet 22 and exits or exhausts through an upper outlet 23. This mold preferably has a copper liner and a steel jacket Which sits on a stool 24 and may be attached thereto by a convenient connecting means, not shown.

Current is, as shown, positively-directly conducted to the electrode 14 by a cable 25 that may be connected to a current supply in back of the panel 11; the other side of the current source may be connected to the mold 2-0 through cable 26. If desired, the other side may be grounded and the mold or stool also may be grounded. Cables 25 and 26 are connected to the electrode feed motor control circuit to energize the feed motor, as required, and maintain an electric discharge or are 13 of pre-determined characteristics from the end of the electrode 14 while it is submerged beneath a blanket of slag 27. The current discharged from the end of the electrode ionizes the slag 27 and is of sufficiently high amperage to assure a complete fusion of each increment or nodule of the metal thereof and the establishment of a liquid bath 28 at a sufiiciently high temperature to assure rapid intermingling of all of the constituents of the alloy together with a rapid movement therethrough and the floating out thereof of all undesired non-metallic content of the electrode. The cooling medium is circulated through the jacket at such a rate to provide for the production of solidified metal 29 at a rate substantially equal to the rate at which the electrode metal 14 is fused, while keeping the bath 28 at such volume and temperature that each increment of the metal electrode resides therein for a length of time required to insure complete intermingling and homogenization thereof with the metal in the pool.

The rate at which the mold is cooled is further so controlled that the residence time is short enough to insure against undesired separation or segregation of the com stituents of the alloy in the bath during the phase change from the liquid bath 28 to solid metal 29.

The proportion of the total constituents supplied to the electric discharge by the hollow electrode of the apparatus of my I-melt procedure is limited. Thus, the amount of heat that can be generated by the fusion of the hollow electrode is limited and is not sufiicient to invariably insure a complete fusion and homogenization of the alloy metal and particularly, of the loose metal pieces or particles; the metal particles are not completely fused during their movement through the slag, thus the inherent purifying action of the present invention is lacking. However, employing the second stage of FIGURE 1, the electrode 14 always approaches 100% of the total metal supplied to the electric current discharge. Since it will contain only a comparatively small amount of material of higher melting point or otherwise that has not been fully intermingled and fused with the remaining constituents, there is a surplus of heat produced, such that the pool 27 can be easily maintained of proper size and at a proper temperature for the production of metal of highest quality. The refusing and resolidification operation under a slag blanket not only insures complete fusing and intermixing of all of the components of the alloy, including refractory materials, but eliminates non-metallics, ceramics, gases and other materials that may be picked-up in the first ingot forming operation.

By way of example, I have melted two primary ingots 14, consecutively, to produce the final ingot 29, using a primary ingot of about 6 inches in diameter and about 24 inches in length to produce about a 20 inch length of final ingot in a 9 inch mold cavity; I have also melted a primary ingot of the same diameter but of 45 inches in length to produce a final ingot in the same diameter of mold. I have produced final ingot metal at rates of up to about to or more pounds per minute, based, of course, on a corresponding melting rate, as controlled by current amperage. A final ingot of about 360 pounds is representative. The remelting is accomplished under conditions that shield the allow from atmospheric contamination and, at the same time, further the release of gaseous elements and non-metallic elements out of the alloy. The molten metal is maintained in a pool of such size and at a temperature such that complete fusing, fluxing, refining, etc., of the metal can take place; the bath size is controlled by cooling and at a rate such that the pre-determined size and temperature are maintained. The operation is controlled so that the molten bath 2% which may be at a temperature of about 3000 degrees to 4000 degrees F. and of a depth of about 2 inches for a mold 20 of larger diameter, to 6 inches or more when the mold is of moderate or smaller diameter; for example, for a mold of 0 inches in diameter, a bath thickness in the order of 6 inches is satisfactory. I inherently attain a full surface to mass action between the fully arc-melted or vaporized increments of the metal-supplying electrode and the slag. As shown in FIGURE 1, the electrode is preferably of comparatively large diameter, for example, of from 1 to 10 inches in diameter, depending on the diameter of the alloy body 29 desired and on the amperage of the current supply. The discharge 13 is of sufficient amperage to assure the complete fusion of each increment of the metal thereof.

The macrographs of FIGURES 2 to 4, inclusive, were based upon the use of 9 inch billets forged from 15 inch diameter alloy ingots of A-286 alloy metal.

By utilizing a slag blanket, my final stage melting operation is accomplished in a quiescent manner (see FIG- URE l) with the absence of the turbulence and inherent spattering of other processes (such as air and vacuum melting), and the heat from the electric discharge and the cooling action of the molten metal pool is controlled to effect a substantially complete removal, movement or levitation of gases and non-metallic inclusions into the slag from the metal used in forming the molten pool (without inclusions by slag action) and enable a relatively slow but more efficient type of melting, such that macro segregation is avoided or segregation is substantially eliminated in the ingot being formed from the molten pool. An inherent feature of this controlled action and of the cooling of the solidified metal down below a color temperature range within the ingot mold before the ingot is removed is the formation of a thin protective egg shell of solidified slag along the periphery of the metal being solidified in the mold and which progressively advances in its formation upwardly along the mold as the ingot metal builds-up therein. The relatively quiescent type of slag-protected action and the formation of the solidified protective egg shell entirely eliminates the corn cob or pineapple roughened surface which is inherent in other melting procedures.

It will be noted that I exclude atmospheric gases from the molten metal, the end of the electrode from which electrically-energized metal particles are being fused-off and the arc, and thus prevent contamination of the final ingot by employing an electrically ionized slag blanket, by cooling such ingot below its color range and by forming the thin peripheral egg shell before the ingot is removed from the mold. Heretofore, even where a vacuum or air melted ingot was pre-conditioned as to its outer peripheral surface area to remove concentrated inclusions before being used as a consumable electrode in a second stage melting operation, macro freckles and dark spots throughout the cross sectional area of the ingot could not be eliminated. For the first time, I have been able to effectively accomplish this. Since an ingot produced by my so-called I-melt procedure showed inclusions, there was no reason to believe that the use of a slag blanket in a final stage controlled consumable melting, employing a dense consumable electrode body of poor or lower quality than that required in the final ingot and which body is of substantially the final analysis of the final ingot openers "to be formed, would make possible the results which are attained in accordance with my present invention.

invention that I have been able to employ a relatively slow but more elficient type of melting of a prefused or premelted and precast alloy metal solid electrode body,

such that a relatively shallow molten pool is produced, as compared to conventional consumable electrode inert gas or vacuum melting procedures. Thus, a slower and more efilcient type of progressive cooling and solidifying of the molten alloy pool, as maintained under a protective slag blanket, is made possible and without segrega tion, precipitation hardening, etc.

What I claim is:

1. A method of consumableelectrode-forming a cast alloyed metal ingot of superior quality within an ingot mold which comprises, providing a premelted and precast alloyed metal solid body of dense somewhat homogeneous metal of substantially the required analysis for the alloyed metal ingot to be produced; supplying energizing electric current from a current source to the ingot mold, positively-directly supplying energizing electric curent from the current source to and employing the precast alloyed metal solid body as a consumable electrode projecting endwise into the ingot mold, progressively arcf'using-off alloyed metal increments from the end of the electrode Within the ingot mold by discharging electric current therefrom, and forming and maintaining a molten :alloy metal pool from the alloyed metal increments within the ingot mold, all while ma ntaining the end of the electrode, the fused-off metal increments, and the molten alloy metal pool under a protective slag blanket; progressively-completely arc-fusing-ofl each alloyed metal incre- :ment of the alloyed metal body from the end of the electrode and moving the alloyed metal increments in a fully fused condition through the slag into the molten alloy metal pool; substantially solely maintaining the molten alloy metal pool from the fused alloyed metal increments of the solid body being introduced thereto through the slag and uniformly intermingling them in the molten alloy metal pool, While progressively slowly cooling and solidifying molten alloy metal from the bottom of the pool to form the ingot; effecting a conversion of all the metal introduced into the molten alloy metal pool into a molten condition before it is solidified, and controlling the electric arc discharge, the movement of the alloyed metal increments, and the slow cooling of the molten alloy metal of the pool to substantially completely remove impurities from the molten alloy metal of the pool before such metal is solidified to form the ingot.

2. A method of consumableelectrode-forming a cast alloyed metal ingot of superior quality, particularly from the standpoint of the absence of macro-metallic and non metallic inclusions and segregation within aningct mold which comprises, pre'rnelting and casting a longitudinal alloyed metal solid body of dense somewhat homogeneous metal of substantially the required analysis for and of lower quality than the ingot to be produced; applying electric current from a current source to the ingot mold, positively-directly applying electric curr nt from the current source to and employing the alloyed metal body as a consumable electrode projecting endwise into the ingot mold, progressively arc-fusing-ofl alloyed metal increments from the end of the electrode within the ingot mold by discharging electric current therefrom, and forming and maintaining a molten alloy metal pool from the alloyed metal increments within the ingot mold, all while maintaining the end of the electrode, the fused-off alloyed metal increments, and the molten alloy metal pool under a slag blanket of sufficient depth to shield them from atmospheric contamination; progressively completely fusing-olf each alloyed metal increment of the alloyed metal body from the end of the electrode and moving the alloyed metal increments in a fully fused condition through the slag while removing impurities from and refining the alloyed metal increments before they reach the molten alloy metal pool; maintaining the molten alloy metal pool substantially solely from the alloyed fused metal increments being introduced thereto and uniformly intermingling them therein, While progressively slowly cooling and solidifying molten alloy metal from the bot tom of the pool to form the ingot at substantially the rate that the fused-off alloyed metal increments are introduced thereto from the electrode, and controlling the electric arc discharge, the movement of the alloyed metal increments, and the slow cooling of the molten alloy metal of the pool to substantially completely remove impurities from the molten alloy metal of the pool before such metal is solidified to form the ingot.

References Cited in the file of this patent UNITED STATES PATENTS 2,191,479 Hopkins Feb. 27, 1940 2,541,764 Herres et a1 Feb. 13, 1951 2,631,344 Kennedy Mar. 17, 1953 2,880,483 Hanks et al. Apr. 7, 1959 OTHER REFERENCES Iron Age, pages l46148 relied upon, Aug. 6, 1953. Iron Age, pages 1 61l9 relied upon, Sept. 23, 1954.

Claims (1)

1. A METHOD OF CONSUMABLE-ELECTRODE-FORMING A CAST ALLOYED METAL INGOT OF SUPERIOR QUALITY WITHIN AN INGOT MOLD WHICH COMPRISES, PROVIDING A PREMELTED AND PRECAST ALLOYED METAL SOLID BODY OF DENSE SOMEWHAT HOMOGENEOUS METAL OF SUBSTANTIALLY THE REQUIRED ANALYSIS FOR THE ALLOYED METAL INGOT TO BE PRODUCED; SUPPLYING ENERGIZING ELECTRIC CURRENT FROM A CURRENT SOURCE TO THE INGOT MOLD, POSITIVELY-DIRECTLY SUPPLYING ENERGIZING ELECTRIC CURRENT FROM THE CURRENT SOURCE TO AND EMPLOYING THE PRECAST ALLOYED METAL SOLID BODY AS A CONSUMABLE ELECTRODE PROJECTING ENDWISE INTO THE INGOT MOLD, PROGRESSIVELY ARCFUSING-OFF ALLOYED METAL INCREMENTS FROM THE END OF THE ELECTRODE WITHIN THE INGOT MOLD BY DISCHARGING ELECTRIC CURRENT THEREFROM, AND FORMING AND MAINTAINING A MOLTEN ALLOY METAL POOL FROM THE ALLOYED METAL INCREMENTS WITHIN THE INGOT MOLD, ALL WHILE MAINTAINING THE END OF THE ELECTRODE, THE FUSED-OFF METAL INCREMENTS, AND THE MOLTEN ALLOY METAL POOL UNDER A PROTECTIVE SLAG BLANKET; PROGRESSIVELY COMPLETELY ARC-FUSING-OFF EACH ALLOYED METAL INCREMENT OF THE ALLOYED METAL BODY FROM THE END OF THE ELECTRODE AND MOVING THE ALLOYED METAL INCREMENTS IN FULLY FUSED CONDITION THROUGH THE SLAG INTO THE MOLTEN ALLOY METAL POOL; SUBSTANTIALLY SOLELY MAINTAINING THE MOLTEN ALLOY METAL POOL FROM THE FUSED ALLOYED METAL INCREMENTS OF THE SOLID BODY BEING INTRODUCED THERETO THROUGH THE SLAG AND UNIFORMLY INTERMINGLING THEM IN THE MOLTEN ALLOY

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