US2470790A - Manufacture of alloys - Google Patents

Description

May 24, 1949. T, PRlCE MANUFACTURE oF ALLoY's Filed April 24', 1945 ATTORN EY Patented May 24, 1949 UNITED STATES T GFFICE MANUFACTURE OF ALLOYS Application April 24, 1945, Serial No. 590,046

(Cl. 7S-176) 2 Claims.

This invention relates to the manufacture of readily-oxidizable refractory metals of group VI of the periodic table of the elements, and more particularly molybdenum, tungsten and mixtures thereof, alloyed with metal such as chromium to protect the product against oxidation when heated.

The principal object of my invention, generally considered, is to provide `alloys of molybdenum and/or tungsten containing suiiicient chromium,

whereby the readily-oxidizable refractory metal is protected when used at elevated temperatures in air or oxygen-containing atmospheres.

Another object of my invention is to provide chromium-molybdenum, chromium-tungsten and tertiary alloys, in which the chromium content is sufficiently high to prevent the other refractory metal or metals of group VI of the periodic table from oxidation at reasonably elevated temperatures, even though not enough to reduce the melting point of said other metal or metals more than a small amount.

A further object of my invention is to manu- `facture refractory alloys from metal of group VI of the periodic table, by making a balanced oxygen-carbon mixture of compounds of such metal in the metal proportions desired in the resulting product, heating in a protective atmosphere to drive oii the resulting carbon monoxide, and sintering to coherent form, said oxygen-carbon mixture being initially treated either in a powdered or pressed form, and followed by a pressing, if necessary, to the shape desired prior to sintering.

A still further object of my invention is to l lmanufacture molybdenum-chromium alloys by Other objects and advantages of the invenf tion will become apparent as the description proceeds.

Referring to the drawing:

Fig. 1 is a Vertical sectional view of a receptable for mixing the selected materials to produce a Lit) balanced oxygen-carbon mixture of compounds of the selected metal.

Fig. 2 shows the apparatus of Fig. l during a Subsequent stage in which the mixture is being dried, as by means of steam, while stirring.

Fig. 3 is a vertical longitudinal sectional view of an electrical reducing furnace in which the mixture is first heat-treated.

Fig. 4 is a vertical sectional View of a hydraulic press in which slugs of the mixture, reduced in the furnace of Fig. 3, are formed.

Fig. 5 is a vertical sectional view of a sintering furnace in which the slugs produced in the press of Fig. 4 are finally treated.

Diiiiculty is experienced in the manufacture of alloys, such as those adapted to resist oxidation at elevated temperatures, and involving a combination of a refractory metal, such as molybdenum, the oxide of which is readill reducible by hydrogen, and a metal such as chromium, the oxide of which is not readily reducible by hydrogen. Chromium is rather oxidized by hydrogen containing water vapor. If a mixture of the oxides of the two metals is heated in hydrogen, the molybdenum oxide is reduced leaving the chromium oxide mixed with the metallic molybdenum. In order to get chromium to alloy with molybdenum, the molybdenum has to be sintered at high temperature in hydrogen to effect some dissociation of the chromium oxide and absorption of the chromium so formed by the molybdenum,

The e'icient way to reduce chromic oxide to chromium is by carbon. However, if carbon is used to reduce molybdenum oxide, the result is molybdenum carbide or a considerable impregnation of molybdenum with carbon which is -dilicult to eliminate.

I will now describe the preparation of a. molybdenum-chromium alloy in proportions such that the melting point will be near that of molybdenum, that is, above about 90% of the melting point of molybdenum measured in degrees C. It will, however, be understood that a similar process is applicable to the manufacture of other metal alloys of group VI of the periodic table, whether alloys of molybdenum and chromium or not. That is, my process includes the manufacture of alloys of tungsten and chromium; and tungsten, molybdenum and chromium as well as molybdenum and chromium.

Referring to the drawing in detail, there is shown in Fig. l a receptacle I I in which is placed a desired quantity l2 of a mixture of powdered oxide of chromium and powdered carbide of molybdenum. The chromium oxide may be chromic oxide, CrzOa, or other oxide of that metal, and the molybdenumcarbide is that represented by the formula MOC. As an alternative, however, I may substitute chromium carbide for the oXi-de, or use no carbide, rather substituting an equivalent mixture of oxide and iinely-divided carbon, such as'lamp fblackfonpowdered x-coal, but the purer the better.

Upon this mixture is poured molybdenum oxide, such as the trioxide or dioxide, mixed with or suspended in water. During the addition of the suspension I3, the mixture is constantly stirred, as by means of arod `Hl, while the freceptacle is heated, preferably by means of .steam- I5. On account of drying with constant stirring, segregation of the liquid is avoided yanda mixture of oxides and carbides, or `oxides an'd carbon, uniformly commingled together is obtained. As a further alternative, Imay introduce the chromium as a -water-solub1e.-salt, such as chromous acetate, dissolved in water andmixed with the .oxide rand canbide fofmoly'bdenum, .lorwsaid `oxide `and finely-divided.canbon,-tofget not only the` desired oxygen-.carbon balancebut also the desired .metals r-atio.

'I may add.a.sma1l..proportion, that is `from about .01% to about l%,ase.a preferredrange, of -one or` more .of metals :of the..nickel-cobalt-iron group, that is, onetof'series .4, group VIII of the periodic table as intheiform of Aa soluble salt or .salts,along.with the chromium salt, to increase .the facility with-wlsiich` the molybdenum or tungsten and the chromium combine, thereby de- Icreasing the-necessary sintering temperature of y the alloy andgiving. it..ia..denser grain structure so that it :is-more:readilyprotected against oxidation.

Themixturevabove described, which may be in .accordance with thesleft Ahand side of the following equation, whemheat-treated to `el`ect a reaction between ethe components, theoretically .givestan lalloyof about l91% molybdenum and 9% chromium:

Ilo veffect Aa vreaction :in accordance With-the .above formula, f the i dry "well-mixed mass is then .placed inrsuitable :receptacles orboats |16, A.and passed throughaa reducingz'fumace l1. Such a furnace may-comprise ra suitably-insulated tube Iii of refractory material such as alumina, surrounded by' afcoil t9 of. molybdenum or tungsten through which electricity; isi 'passed to supply the heating power. Ther-atmosphere inthe furnace may be protective orreducing. It is `desirably .dry "hydrogen, i that ishydrogen preferably having a dew point of not higher than -609 C., a1- though other dry atmospheres may :be used. If desired, .the` furnace -may -be `of the type illustrated in Fig. 1 of the Hall etial.,lapplication, Ser. No. 579,080, -led February.21, 1945, now.,Patent No. 2,431,690, dated December. 2,.1947,'and owned-by theassignee of the presentapplication.

During this treatmentthefurnace need only .be operatedxat a rela-tively low temperature, but it must be-.one high Ienough-tov eiect a reaction between the Ioxide andcarbide, or` a, reduction oi the oxide by the..nely-divided carbon. Such temperatures are between about-800 and 1000o C., although higher temperatures may be employed if obtained gradually so.,as.not to appreciably sublime the molybdenum trioxide, if used, .beforereduction. vThe length of treatment may .be from one totWo hours or longer. .Atmospheres other than hydrogen may be used and produced by JIf it contains an undesirable excess of carbon or carbide, this may .be removed by mixing with a sufcientiamount of molybdenum oxide to provvide the necessary ,oxygen for removing the car- .bid-e as carbonvrnonoxide upon subsequent heating. Aslight excess of the oxide is not objectionable as it either reduces or vaporizes during the subsequent heat-treating process.

The powdered metal or mixture is then pressed into slugs or articles 2| of Aform desired, as in a die ..22 by means .of .a plunger .23 :operated .by a

hydraulic press ...215, f so that .sufficient f coherence of the particles is provided toallownfor. necessary handlingof the formed slugs.

The` pressed` slugs .or other articles .21, afterremoval from the die, are placed in =a sinteringturnace 25 which may be the same or like the'furnace il, except that. said slugsare there treated .in dry hydrogen, hydrogen-bearing` gas, `or=a.pr-0 tective gas such .as argon, helium torlnitrogen. Hydrogen is desirably .used if. it `is..desired to. eliminate residual carbon from the slugs, #aait combines therewith `to `.produce .hydrocarbons `which pass .off with .theiiowinggas .Howevenif 4the slugs produceda-re free from` carbon, one ofthe other gasesmentionedimay be :employed The temperatures of treatment .are in accorda-nce with conventional practice in fsntering such metal, the preferredtemperature Idependingcon whether it is mainlymolybdenum or tungsten.

As .analternatiua .thas-lugs may` besinteredfin accordance with the sintering Y.treatment ,for such chromium 1 alloys, ndescribed ,in .ther Ramage application, Ser.. No. .559,693, ^Jled .Qctober-21, 194.4,Y and owned bythe `assigneeof the. present application.

'Instead of the` foregoing, Imayuse the.- following equation which `would theoretically yieldtan alloy of about .9.8% chromium:

From the. foregoing equations and explanation, it `will be seen thatzthe 'expression.balanceid oxygen-carbon mixture, as used in this application, means thatfthelmixture whichis prepared has, prior to firing; .the` .proper ratiof Fbetweentlfie ingredients, softhat afterthe reactionlpro'duct, carbon' monoxide, has :been driven .oifonlysfmetal remains which is: freeyorsubstantially: free, from both carbon and 1 oxygen.

As `an alternative, alibal-ancedcarbide `and oxide mixture could `be pressed into .aislug andrslowiy heated,l as in` thefurnace :of "Fig. i5, in afhydrogen or otherV protective'atmospherafito `first drive :oi the carbon `monoxide produced during Vthe Areaction, Aand then sinterthe resultingsmetallfparticles to form la Acoherent alloy.

`Although the yforegoing. equations :have 4:been shown using molybdenum trioxide, other oxides ofl molybdenum .or mixtures thereof .couldtbesubstituted yand the .process .is suitable-fori theypro-` duction of other alloys or mixtures of refractory metals of group VI of.the.periodictable.

One of the big...advantagesof .-.thismethods` of Valloy formation is that .the ingredients .can..be

prepared in a pure form and mixed in the molecular proportion required to give the product desired, the carbide or carbon protecting material such as chromium, which is oxidizable by water vapor, and the oxide of which is not ordinarily reducible by hydrogen.

Although preferred embodiments of my invention have been disclosed, it will be understood that modications may be made within the spirit and scope of the appended claims.

I claim:

1. The method of manufacturing coherent chromium alloys of metals selected from the group consisting of molybdenum and tungsten, comprising making a mixture of a powdered oxide and a powdered carbide of the selected metal and a solution of a chromium compound in an amount suflcient to yield approximately 9% of chromium in the product and containing from about .01% to about 1% of at least one metal of series 4, group VIII, of the periodic table, in the form of a soluble salt, to facilitate combination of the chromium with the selected alloying metal, the proportions of the ingredients and the ratio between the carbide and the other ingredients being such that after the reaction product, carbon monoxide has been driven off during the operation of the method, the metal produced is substantially free from both carbon and oxygen, constantly stirring the mixture and heating to a temperature of about 100 C., thereby avoiding segregation of the liquid and obtaining a uniformly comming-led dry mixture, loading said well-mixed mass in suitable receptacles, Aand heating said loaded receptacles slowly in an atmosphere of dry hydrogen to a temperature between about 800 and 1000 C., continuing said treatment for from one to two hours, and cooling the reduced material.

2. The method as defined in claim 1, in which the chromium compound is the acetate.

TOWSON PRICE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,308,907 Keyes July 8, 1919 1,418,081 Laise May 30, 1922 1,665,636 Marden et al. Apr. 10, 1928 1,731,267 Rich Oct. 15, 1929 2,205,386y Balke June 25, 1940 2,242,759 Schlecht et al May 20, 1941

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