US2191475A - Manufacture of metal articles - Google Patents

Description

MANUFACTURE 0F METAL ARTICLES Filed Jan. 27, 1938 INVENTQRv ROBERT K. HOPKINS Patented Feb. 27, 1940 UNITED. STATES PATENT ori-Ica N.

MANUFACTURE OF METAL ARTICLES Robert K."Hopkins., New York. N. Y., .assignor to M. W. Kellogg Co., New York, N. Y., a cor-v poration of Delaware Application January 27, 1938 Serial No. 187,104`

'2 claimt.v (ci. zz-zw include iron as a major constituent, from which worked articles such as plates, sheets, bars, tubes and the like are made, after being producedv in the furnace is cast into ingots. The ingots are then usually worked to form intermediate workpieces such as slabs and billets and these further workedto produce the final articles. The ingots as removed from the molds -show imperfections, particularly at and near the surface. These imperfections include folds, cracks, blow holes, porous areas, areas containing segregated impurities, and the like, and must be removed if acceptable articles are to be produced. The imperfections are usually removed as byl grinding, drilling, gas or arc cutting, and the like. In'the removal of the imperfections not only is the metal defining the imperfections removed but sufficient soundmetal is alsoremoved to form the surface voids produced with 'sufficiently gently sloped sides to prevent folding over of the metal at the edges of the voids during the subsequent working operations. Even with carbon steel and steels containing low percentages of alloying elements this operation represents a material proportion of the cost of the final articles. With alloy steels such as chrome steels, chrome nickel steels, tungsten steels, manganese steels and the like, of high alloying element content, which do not appreciably forge weld during working and as a consequehce, it is necessary to remove even minor imperfections such as pin holes and small cracks that in carbon steel are disregarded. These steels, furthermore, because of their crystallizing characteristics show more surface imperfections than carbon steel. The amount of vmetal removed from ingots of these steels is, in the average case, a substantial proportion of the total metal cast.

With carbon steel itis sometimes necessary to remove further metal because of imperfections developed during rolling; with the h igh alloy steels'it is always necessary to do this. In fact the metal body Vworked is gone over three or four times and the imperfections developed are generally so numerous that substantial proportions o'f the surface metal is removed during each going over. 4

It is an'object of this invention to provide a. simple and expedient method ofproducing ingots of ferrous lmetal and ferrous alloys that are substantially free fromv surface imperfections'and can be worked directly into nal articles.

It is also an object of this invention to provide a method for producing ingots and cast workpieces ofthe character mentioned fin which a worked shell of the metal is used as a mold and cast metal united to the mold'by electric energy discharge under ar blanket of protective flux.

It is a further object of this invention .to provide a method for producing ingots and cast metal bodies of s'pecial'analysis which cannot bc produced with the present'jcommercial practicaA The further objects and advantages` of the' invention will be better understood from the following description taken with the accompanying drawing, in which, `the single ligure illustrates schematically a mode of carrying the invention out in practice. y

The invention'is of general application and may be used in connection with a wide variety of metals whether ferrous or non-ferrous. The invention is particularly useful when appliedA to ferrous metals and especially lto those ferrous alloys known as high alloy steels, such as chrome steels, chrome-nickel steels, manganese steels, tungsten steels and the like that do not 'forge weld readilyand when cast into ingots, in accordancewith the usual presenty practice, develop a large grain structure and exhibit a surface of such poor character as to require an excessive removal of imperfections. l

The apparatus shown in the drawing includes an electric current supply and electrode feed device IIJ. Device I0 is similar to the usual welding head employed in electric arc welding and should include arrangements for supplyingelectric 'current fat controllable voltages and amper*- ages and means for feeding an electrode at rates automatically controlled to maintain'a discharge of predetermined characteristics. While device I0 is shown as feeding a single electrode II it is contemplated that device I0 feed a 4plurality of electrodes. When a plurality of electrodes are employed device I0 should be arranged to feed and to control their feed either individually or in groups. When a pluralitylof electrodes are'employed it is also contemplated to electricallyl connect pairs of them in parallel or seriesgf i f Device I0 feeds electrodev II into'moldt'llthat is supported on lmold stand I3. {DevicefIIl' and mold stand I3 may be so supported thatfrotation of one of them relativel to the other effeeted when desired. stand 13 is prefl'efrbiy mader of metal, such as cast iron, andincludes aplu rality of conduits I4 through which Vmay be' passed a cooling medium, as for'instance,waterQ'fQonduits I4 are preferably so arranged and lconnected that all or any portion of stand VI3 may be lcooled as desired; 'Mold I2 as shown, is of cylindrical formV but may be of 4any preferred form such as rectangular, polygonal etc. To the bottom of the `cylindncai wens of'meld I2 is welded a bottom plug no I5 The cylindrical walls and plug I5 are made of metal substantially of the same composition as the desired cast body or ingot. Since the walls of mold I2 form the outside surface metal of the iinal ingot it is necessary to employ metal that is free from imperfections and is of a high quality. For this reason the cylindrical walls are preferably made of worked metal. Thus, the cylindrical Walls may be made by shaping plate to the cylindrical form and welding the longitudinal edges together or they may be made from worked seamless cylinders. The cylindrical walls should be of a. sui'licient thickness to provide a tough. strong skin for the ingot during the working thereof. Depending on the size of the ngot and the reduction contemplated the cylindrical walls may range in thickness from one inch or less to six inches or more.

To form the ingot, molten metal is united to the mold I2 'under the iniluence of the discharge of electric current through a gap between electrode, or electrodes, Il and the metal of mold I2. Initially the discharge will take place between the sides or bottom of mold I2 and electrode II but as the operation progresses the discharge may also take place between the molten metal in mold I2 and electrode II. To effect the current discharge the electric current outlet of head III has one side connected to mold I2 by cable I6 and the other side connected by cable I 'I to contact device I8 through which electrode Il passes. Electrode, or electrodes, II are preferably located adjacent the walls of the mold I2 to assure fusion of a predetermined depth of the mold metal and an integral union, thereof with the molten ingot metal. This may be accomplished by employing a plurality of closely spaced electrodes disposed around the whole surface of the mold walls, or by using a small number of electrodes andv rotating either mold stand I3 or device III.

Molten metal for union with the metal of mold I2 may be supplied in various ways. Thus, it may be supplied entirely by the fusion oi' electrode, or electrodes, II of a composition to give molten metal of the required analysis. In such case.

` especially when high alloy steel ingots are to be made, a plurality of electrodes of different composition are employed and these electrodes chosen of such relative size and fed at such rates to produce a molten metal of the required analysis. Thus, if the ingot metal is to be a high chromium steel one of the electrodes may be of iron or steel and the other electrode may be of a chromium steel containing enough chromium to compensate for that lacking in the iron or steel electrode, also instead of using a chromium steel electrode, an electrode may be employed made up of ferro-chrome or this electrode may have a steel or iron lining illled with a ferro-chrome core.

The molten metal may also be supplied in part as cast metal and in part by the fusion of electrode, or electrodes, II. When cast metal is supplied it may be top poured or bottom poured. When top pouring is employed the molten metal may be poured from ladle 20 through conduit 2|, which is preferably of ceramic material, that extends either entirely or partly through flux blanket I9. When bottom pouring is employed the molten metal may be poured from ladle 22 through conduit 23, which likewise is preferably of ceramic material, that extends through the bottom of mold stand I3 and plug I5. Both the cast metal and the electrode may be of the same composition or they may be of such composition that together they will produce the required analysis. When supplying cast metal it is preferred to so locate and so move the electrode, or electrodes, II` that the electric discharge will fuse a depth of the exposed wall metal of mold I2 to assure an intermingling of these metals and the production of a unitary structure. In place of cast metal a solidiiled rod unconnected to the supply of electrical energy may be fed to the region of the electric current discharge to be fused thereby. When either of these last mentioned expedients are employed for supplying molten metal the cast or solid metal as well as the electrode, or electrodes, may be steel and the required alloy constituents supplied during the operation in the form of ferro-chrome, ferromanganese, etc., to the molten metal in the vicinity of the electric current discharge.

At present, I prefer, especially when forming ingots of high alloy steels, to employ a hollow electrode of one composition and supply the remainder of the required constituents through this hollow electrode, the rate of feed of the hollow electrode and rate of feed of the constituents supplied through it being controlled to produce the required analysis. Thus, in depositing chrome-steel, I prefer to employ a hollow electrode of iron or steel and supply the chromium as ferro-chrome through the hollow electrode at a rate controlled in accordance with the rate of feed of the hollow electrode so that the resulting molten metal will have the required analysis. I may use this expedient by itself, that is. employ one or more hollow electrodes, or I may use it in connection with a solid electrode or other source of metal. Thus, when depositing chrome-nickel steels I may employ an iron or steel hollow electrode as above stated, and pass the chromium therethrough as ferro-chrome and also feed a nickel electrode, which may or may not be connected to the source of electric current, at the proper rate to furnish the required nickel.

It will be apparent from the above that a wide variety of expensive alloys may be produced in the ingot form from comparatively inexpensive raw materials, and also that alloy ingots may be produced commercially of analyses not attainable by use of prior art practice. Thus, low carbon chrome nickel steels may be produced of such low carbon content that they are not appreciably subject to carbide precipitation, intergranular corrosion, etc., these steels having these desirable properties without containing columbium, titanium, etc. In producing ingots of such steels I employ commercial low carbon ferrochrome to supply the chrome and some of the iron required, commercial low carbon or carbon free nickel to supply the nickel, and commercial low carbon iron or mild steel to supply the remainder of the iron. Low carbon iron or mild steel is available with carbon content ranging from .03% to as little as .0l%; ferro-chrome may be obtained commercially that averagely contains 70% chromium, 0.06% carbon and the remainder substantially all iron. The iron or mild steel may be supplied as a hollow electrode and the ferro chrome passed through it to the current discharge; the nickel may also be passed through the hollow electrode or it may be passed in the form of a separate electrode. Alternatively the nickel may be the hollow electrode and the iron supplied as a separate electrode. With these materials 18 chrome 8 nickel steels may be produced with carbon contents of from .03 to .02%.

25 chrome 20 nickel steel and higher steels of this type will have somewhat lower carbon contents.

In order to assure a proper intermingling of the constituents of the molten metal and a proper refinement thereof in all of the variations of the novel method above set forth, the metal depositing operation is carried out beneath a protective blanket of flux I9.

The flux blanket I9 should preferably be such that it will not liberate deleterious gas either as to q'uantity or kind during the metal depositing operation and will not add substantial quantities of undesirable ingredients to or remove substantial quantities of desirable ingredients from the molten metal but will ux out impurities.` The flux, furthermore, should be such that it will readily free itself from the molten metal. A wide variety of fluxes may be used satisfactorily. Silicates in general, either simple silicates or mixtures thereof, or complex silicates or mixtures thereof are satisfactory iiuxes. Aluminates, titanates and similar compounds are likewise satisfactory and may also be used in connection with/silicates 'both simple and complex. Flux thinners such as feldspar may also be employed to obtain a flux of desired melting characteristics. The flux need not be composed of reacted materials but may be made up of their dried or calcined unreacted components. Thus, in the case of calcium silicates the flux may be made up of calcium oxide and silica. At present, silicates of the alkaline earth metals, manganese and aluminum, are preferred as uxes. The flux may be used in the solidified and comminuted condition or maybe passed into mold I2 in the molten condition from a convenient source of supply.

In carrying out the metal depositing operation. electrode, or electrodes, I I are fed until they approach the bottom of mold I2. An arc starter as, for instance, a ball of steel wool, a nail, a sliver of graphite and the like, is then interposed between the end of the electrode, or electrodes, and the metal of mold I2; The iiux blanket I9 is then placed in the mold I2. Flux blanket I9 should be deep enough to exclude the atmosphere from contact with the molten metal and to protect the electrical discharge therefrom. Flux blankets ranging in thickness from an inch to six inches or more will be satisfactory for the average purposes.

When the electric circuit is closed the arc starter will quickly be destroyed to provide a path for the passage of the electric current between the end of the electrode and themetalof mold I2. The heat generated by the electric discharge will fuse the metal of electrode II and metal of the mold into a molten pool. When metal either in the solid or molten condition is supplied to the mold separately of electrode II the heat generated by the discharge will incorporate it into the molten pool. By reason of the iiux blanket the heat is not rapidly dissipated so that thorough intermingling and refinement is assured.

Excessive penetration into the metal of mold I2 may be easily avoided by circulating a cooling medium through connected conduits I4. When casting ingots of metals that ordinarily crystallize with large grains the cooling of the mold may also of the molten metal and thus produce a liner grain structure. Cooling medium may be circulated at or below the level of the molten metal ing operations directly i in the molten condition,

be availed of to accelerate the cooling at a rate to cause the solidication of the metal in mold I2 to a predetermined distance below the level of molten metal in mold I2. By removing heat in the manner just stated it is possible to so ,carry on the operation that a minimum of molten metal will be present when mold I2 is completely lled. In this way pipes and other shrinkage defects may be avoided or greatly minimized.

In order to prevent pipes and similar shrinkage defects it is also possible to control the deposition of the molten metal so that at the end of the operation there is little molten metal present. This may be done by tapering off the rate of deposition of molten metal after the bulk of the i molten metal has been deposited so that in the iinal stages heat will be removed at agreater rate than that at which it is supplied. When this expedient is used water, or other cooling medium, may also be circulated through'conduits I4.

At the end of the operation and when the whole of the metal within mold I2 is solidied,

mold I2 is removed from stand I3. At this'V stage mold I2 is a solidied body of metal that includes an outer ring of high grade substantially flawless metal to which is integrally united a core of castmetal.

This body of metalmay be subjected to workwithout the necessity of removing imperfections from its outer surface. Furthermore, during the Working operations there is no need to handle the body with any special care as its worked tough outer skin will withstand the ordinary working operations without developing any serious imperfections.

I claim:

1. The method of manufacturing metal ingots which comprises forming a mold substantially free from surface defects with metal of the composition of the desired ingot, discharging electric current in said mold from the ends of a plurality of fusible electrodes of suflicient energy to fuse metal of said electrodes and metal of said mold into a common pool of molten metal, said electrodes all being made up of constituents of the desired ingot metal and at least one of said electrodes being of a composition different from the others, providing. a blanket of flux over said discharge and said molten metal, and fusing said electrodes at rat'es to give said pool substantially the same composition as the desired ingot metal.

2. The method of manufacturing alloy lngots Y positing molten alloy metal of substantially the same analysis y in the mold, the molten metal deposition being carried out in a manner to maintain the whole surface of the deposited metal and simultaneously with said deposition discharging current through one or more gaps beneath the surface of a protective blanket of flux on the surface of the molten metal to fuse a depth of the mold metal at the level of the molten metal throughout its vextent to unite .the metals into an integral body made up of a cast metal core within a worked metal shell of sufilcient thickness to protect the cast core during subsequent work deformation.

. ROBERT K. HOPKINS.

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