US2610118A - Sintered iron bodies and processes therefor - Google Patents

Description

Patented Sept. 9, 1952 SINTERED IRON BODIES AND PROCESSES THEREFOR Joseph E. Drapeau,

Jr., Calumet City, Ill., and

James H. Smith and Richard J. Halsted, Hammond, Ind, assignors to The Glidden Company, Cleveland, Ohio, a corporation of Ohio N Drawing. Application June 17, 1948, Serial No. 33,658

Claims.

This invention relates to improvements in sintered bodies composed predominantly of copper-coated iron powders, and to processes associated therewith.

It is known that thestrength of sintered bodies composed of soft iron powders can be improved considerably by incorporating copper with the iron powder prior to sintering the body. The copper has been incorporated in the past either by admixing copper powder with the iron powder, or by applying a coating of copper to the iron powder by aqueous chemical displacement or electrolytic methods. In a co-pending application of Drapeau et al., Serial No. 33,656, filed June 17, 1948, a process is disclosed for applying a coating of copper to ferrous powders by means of a thermochemical reaction between the ferrous powder and cuprous oxide, cupric oxide or mixtures of these oxides in a protective atmosphere. We have now found, howeventhat the atmosphere employed during the thermal treatment of soft iron powders in effecting the reaction alters the powder in some manner so that the strength of sintered bodies made from the coated iron powder depends on and varies with the nature of that atmosphere. We have found especially that by employing a reducing or inert atmosphere during the thermal coating operation, andby subsequently sintering the coated powders in a neutral or reducing atmosphere with or without the concurrent presence of small amounts of fluxes and/ or metal-containing components, particularly high-strength sintered bodies may be obtained.

It accordingly is an object of this invention to provide a process for producing high-strength sintered bodies composed predominantly of iron powders, at least a major part of said iron powders having been coated with copper by a thermochemical reaction.

It is a further object to provide a process for producing high-strength sintered bodies from iron powders which have been thermally coated with copper, by sintering bodies of the coated powder in hydrogen, nitrogen, carbon monoxide and like neutral or reducing atmospheres, with or without the concurrent presence of small amounts of flux and/or metal-containing components.

These and other objects will be apparent from the following description of the invention.

As disclosed in the Drapeau et al. application identified above, iron powder may be coated with an adherent film of copper by mixing the iron powder intimately with finely-divided copper oxide and then heating the mixture for ashort time at temperatures between about 1000 F. and

1500 F; in a substantially non-oxidizing, neutral 2 or reducing atmosphere. The amount of copper so deposited on the iron may be varied at will by suitably proportioning the iron powder and finely-divided copper oxide, but when the copper coating is applied for the purpose of producing a coated molding powder which can be sintered into a strong body, the amount of copper ranges generally from about 4% to 330% by weight of the iron. During our investigations of the sintering'properties of iron powders coated with such quantities of copper, we have found that the iron powders which have been thermally coated in the manner described in the said 00- pending application of Drapeau et al., in a hydrogen, carbon monoxide, nitrogenorlike reducing or inert atmospheres produced much; stronger sintered bodies than otherwise-identical powders coated in an atmosphere such as'c'arbon dioxide. The following examples illustrate this effect. f

Examples 1 and-2 Eighty parts of minus 100 Il'lGSh'llOIl powder having a hydrogen loss less than about 1.5% were mixed intimately with .2 part of stearic acid and 20 parts of minus 7 micron copper oxide powder composed of about 60% cuprous oxide and 40 cupric oxide. The stearic acid was added to improve the uniformity with which the oxide coating distributed itself over the surfaces of the iron particles, and to avoid segregation of the mixture. Half of the mixture (designated Batch A) was then heated in a carbon dioxide atmosphere at 1200 F. for 15 minutes and'afterwards was cooled in carbon dioxide to room temperature. The other half of the mixture (designated Batch B) was heated in a hydrogen atmosphere at 1200 F. for '15 minutes and afterwards cooled in hydrogen to room temperature. Samples of both batches were then pressed at 40 tons per square inch into briquettes having the shape of rectangular bars 1%" long by /zf wide by about thick. The bars were then sintered ,,in hydrogen for hour at 2050 Fifand afterthe following results:

ward cooled in hydrogen. Thesinter ed bars were then tested for modulus or ruptura with Modulus of Rupture (lbs. per sq. in.)

Sample 1.-.. sintered bar made from iron powder 45, 000 coated with copper in carbon dioxide atmosphere (Batch A). 1 Sample 2.... Sintered bar made from iron powder 70, 000

coated with copper inhydrogen atmos pherc (Batch 13).

3 Similar results were obtained when nitrogen and carbon monoxide atmospheres were tested for comparison-with .a carbon dioxide atmosphere, in that .the nitrogen and carbon :monoxideatsintered in hydrogen at 2050 F. for hour and finally cooled to room temperature in hydrogen. Tests for modulus of rupture iwere rmade in the same manneras the tests in Examples 1 and 2.

Coating Operations 7 t v f, V Mtogulus .1 ar. s'o .0 up- Ex. "Iron i Furnace Additives turein Towder Parts of lbs. per Cu Oxide Atmns .Time sq. in.

phere (Hours) '70 T530 3112' 1% ZnO Borax. 97,000

70 30 CO2 d 39,000

90 10 CO1 M 55,000

" 80 "20 "Hz 'M' 75,000

so .20 ,.H2 ..7o,000

80 "20 Atl'lllos 65,000

100 0 None 13, 250

'Machine-proriucedcontrolled atmosphere, containing some free carbon monoxide and hydrogen, .together with carbOndiOXideandnitmgen.

oniospheres yield higher moduli of -rupture than is "obtained from a carbondioxide atmosphere.

--We havealso found that when hydrogen; nitrogen or carbon monoxide atmospheres, orl mixtures thereof are used in thetherma-L coating op- ;eration, the strength of the sintered rbodiesjmade krfroml'theicoated :iron powders may be even; Mr- ';.:.theri improved ,by eincorporating .i-in= the .coated gpowder prior to :sintering small amounts of alkaf lineifluxes and for materials containing low-.melting-point white metals. Among the alkaline fluxes which wvecontemplate-may be mentioned the alkali'metal carbonates, nitrates, and borates ('in -glass form) and. lime. Suchfluxeamay be us'ed'inamounts between about -'.*1 '%-and-2% by weig'ht of the coated powder. "The metal-containing .components which-may be incorporated I inthe coated powder either by themselves or in -'-'combination with the alkaline fluxes include zinc, brass; tin, bronze, cadmium, zinc oxide, tin" oxide an'd cadrriium'oxide. Such white-metal-contain- "-'-ing componen'ts'--maybe used in amounts equiva- "ler'irrin-metal content to between about /4-'%--and ---4'% by weigh't of the coated powders. The fol- "-1owing'examples illustrate the-effects'of-such adfditi'ons-of flux-and/on-metal component. In

theseexamplesminus40 mesh iron, powder 'hav- ""ing'=a"hydrogenlossdess than" about 1.5% was "coated with copper by mixing the iron-powder "with12%"stearicacid (by weight of "the copper .oxide) and the indicated "'percentage'ofmopper "oxide i('by-wei'ght:of the *iron powder) "I-he cop- I per oxide-which was used was .a .IIllXtllIG "composed "of about 60% "cuprous oxide and 40% i'f'cupricoxi'de, andwas 'of a fineness'such that 123111 particles were .smaller than about -7 microns.

Thecoatimg'of the iron powderswaseffectedv by heating the mixture of powdersfor 15minutes -(except where otherwise noted) at 1200 F. in

.-;.either a carbon dioxide, nitrogen or hydrogen atmosphere (as indicated below) and cooling to mom temperature in the same atmosphere. The

"copper-coated powder was vthenmixed .with the indicatedflux and/or indicatedmetal component in the amount indicated, after which the molding mixture was pressed at 40 tons per square inch intoa test bar ofthe'size'indicated in Examples 1 and 2. The pressed bars were then -.-It"--will beapparentifrom the :foregoingexam- ;plesithat the use of a hydrogen atmosphere in the. :thermal', coating operation is highly :benefiwcialzin gproducing. a'zcopper-coated; powder-which cicani be :Sintered: into a :strong'zsbody, .Wemave :':found, was prefiously; stated; that .otherastrong "reducing 'ratm'ospheres which :are .:;substantially tnon=icarburizingzzor :slightly-rcarburizingi have a similar 1 effect. .Carbon :monoxide' is .a. substanntiallyr*non#carburizing. atmosphere :under .the ;conditions .:of :time. and :temperature here emzployed as are mixtures of. hydrogenandicarbon 40 m'onoxide in all: proportions. .:&Z\tmospheres 'comiiposedtofi carbonmonoxide; hydrogen and nitro- "-:gen, .such .as those obtained from commercial ..contr'olledaatmosphere ,gas machines are also frsuita'ble.

i'lhe'. strengthfiof sintered bodies made in ac- ;:cordance with f' the foregoing principles can be rifurth'er improved by repressing and resinter-ing zztheibody. The repressing-and resintering I of bodies made Jfrom 'powders which 'have been coatedwith copperm a carbon -dioxide'atmosphere is particularlybeneficial; since by'this expedient such powders can be-manufactured-into sintered bodieswhich are strong-as bodies made J from powders which have been coated ina'jhy- 5:,dmgen, -nitrogen,--or carbon monoxide "atmos phere.

bondioxide atmosphere has on copper-coated iron powders, these effectsmaybeoffset'by'pressing-the-powdersat moderate pressures, sintering sot-he body in-the-customaryi atmospheres'then "repressing the sinteredrbody ata higher pressure -and resintering the repressed body. :Forexam- -p1e;-a-niron powderwhi'ch 'had' been coated with -about* 18%--of-- copper -in-a carbonnioxide' atmos- 5" phone; whempresse'd atj20"tons :per square inch and-sintered 'at' 2050 F; for /2 hour in hydrogen, developed a modulus of .rupture of 2 8;300 p. s. i. When acorresponding'sintered1b ar was repressed at 40"-tons, 'p;i s: i. and" Iesinteredat'I2050". F. for f /21101.11, it:develop.ed a modulus of. rupture of "l05j0.00*p."s. i. The strengths .of' sinteredbodies made from :iron powders which 'have'been coated with copper in a hydrogen atmosphere L may..'also "be increased appreciably by repressing. and. resinqgteringfallthough such...repressing anderesintering Thus whateverimpairing effects a car- 7 is seldom needed with such powders, since moduli of rupture of close to 100,000 lbs. or higher may be obtained from the first pressing and sintering thereof, as shown by Example 3.

We have found that copper-coated iron powders on which the copper coating was applied by chemical precipitation of copper from aqueous copper salt solutions do not respond materially to the additions of flux and/or metal-component prior to sintering, in producing increased strength in the sintered body. Likewise, electrolytic copper coatings on iron powders do not respond to the flux and/or metal-component additions.

We have also found that strong sintered bodies composed largely of iron powders may be made from mixtures of uncoated iron powders with the thermochemically coated iron powders, the latter being more than about 50% of the total mixture and carrying sufficient copper as a coating to provide between about 4% and 80% of copper by weight of the total iron powder in the mixture.

In this specification, the term iron powder refers to the briquettable powders composed almost entirely of iron and containing so little carbon that they are readily briquettable as contrasted with the hard powders, containing larger amounts of carbon or alloying elements which are unbriquettable at pressures below about 60 tons per square inch. The briquetting and sintering of such hard ferrous powders coated with copper is described and claimed in the copending application of Drapeau et al., Serial No. 52, filed June 17, 1948.

In summary, our invention broadly involves the steps of (a) providing a sinterable mass composed substantially completely of iron powders, at least a major part of the iron powders being thermochemically coated with copper, said iron powder mass being mixed or not, as desired, with from about 0.1% to 2% by weight of the coated powders of a fluxing material as described herein, and/or from about to 4% by weight of the coated powders of a white-metal-containing material as described herein; and (b sintering the so-provided sinterable mass with or without an intermediate or concurrent briquetting operation. In providing the coated powders of the sinterable mass, the thermochemical coating reaction is carried out by reacting the iron powder in intimate admixture with cuprous oxide or cupric oxide or mixtures thereof, to provide a copper coating weighing between about 4% and 30% of the weight of the iron powder. The reaction is efiected in a neutral atmosphere or in a hydrogen or other reducing atmosphere which may be carburizing or non-carburizing with respect to the iron powder, and the reaction temperature is between about 1000 F. and 1500" F., but is preferably between about 1100 F. and 1300 F. The thermochemical reaction mass is heated at the indicated temperatures for a sufiicient length of time to deposit the required weight of coating. This time may vary between about 3 minutes and 60 minutes but the actual amount of time required, whether within this range or more or less, may be determined readily by trial. The admixture of copper-coated iron powder with uncoated iron powder or with the flux and/ or white-metal-containing material may be effected by mixing any combination of the latter materials with the copper-coated powder, or alternatively the fluxes and/or white-metal components may be mixed with the thermochemical reaction mass of iron owder and copper oxide, any uncoated iron powders desired in the mass being added after the thermochemical coating has been formed. In making the admixture by either procedure, the fluxes and white-metal-containing materials which are used should preferably be very finely divided so that the resulting admixture will be very intimate. For example, pigment grade of zinc oxide is very suitable since its fineness promotes its thorough dispersion throughout the reaction mass. The use of about 0.1% to 1%, preferably about .2% of stearic acid or mineral oil by weight of the copper oxide not only aids the uniform dispersion of the copper oxide but similarly aids the dispersion of the fluxes and/or white metal oxides when these latter materials are incorporated in the thermochemical reaction mixture.

The sintering of the aforesaid provided sinterable mass is effected in a hydrogen, carbon monoxide or mixtures thereof at temperatures somewhat below, at or above the melting point of copper, and preferably at temperatures between about 2000 F. and 2200 F. Commercially useful strengths can be obtained by sintering at temperatures as low as about 1800 F. The duration of the sintering operation within the indicated range of temperatures depends on various factors such as the selected temperature, the size of the body being sintered, its density (whether briquetted or unbriquetted), the capacity of the sintering furnace, the rate of heating, etc. The optimum duration of heating can readily be determined by one skilled in the art.

However, a soaking period of about /g hour is generally required after the body has attained the desired temperature, even for small bodies heated in about 3 to 4 minutes to temperatures of 2200 F. The invention contemplates the cooling of the sintered body under non-oxidizing conditions, such as by cooling in the same atmosphere as used in the sintering furnace. However, any suitably non-oxidizing cooling treatment may be used whether it be a gaseous reducing or inert atmosphere, an oil cooling bath or otherwise.

Many modifications may be made in the practice of the invention as disclosed herein, and will be apparent to those skilled in the art. We contemplate as part of our invention all such modifications as fall within the scope of the following claims.

Having disclosed our invention, what we claim 1s:

1. The method of making sintered iron bodies of improved strength from thermochemicallycoated ir-on powders, said method comprising the steps of: providing a sinterable mass consisting essentially of an intimate mixture of (al iron powders, at least a major part of which powders carries a copper coating amounting to between about 4% and 30% of the total weight of the iron powders, said coating having been applied to the said major part of the iron powders by a thermochemical reaction between said. iron powder and finely-divided copper oxide at temperatures between about 1000 F. and 1500 F. in a non-oxidizing atmosphere, and (b) between about 0.1% and 2% by weight of the coppercoated iron powder of at least one powdered fluxing material selected from the group consisting of the alkali metal carbonates, the alkali metal nitrates, the alkali metal borates in glass form, and lime; sintering said sinterable mass in a --to=between..about4% and30*% about 1000 F; and I500 F. in a non-oxidizing atmosphere, and (12') between about 0.1% and 22% 'b'y'weightlof the copper-coated iron powder of at least-one-p owd'ered fluxing; material selected from the group consisting of the alkali metal carbonates, the alkali metal: nitrates, the alkali metal borat'es in glass form, and lime; briquetti'ng' said 'sint'erable mass; sintering' said :briquetted massin areducing atmosphere at temperatures between about 1800 F. and'2200 F;; and cooling said sin tered mass under non-oxidizing conditions.

3. The method as claimed in claim 2 wherein the fiuxi-ng material is powdered borax glass in an'amount of about /2%.

'4. The method as claimed in claim 2 wherein a reducing atmosphere is employed in said thermochemicalreaction.

5. A sinteredproduct asprod-uced by the methed claimed in claim 2'.

6i The-method as claimed in claim 2 wherein said sinterab-le mass also includes between about and 4% of metallic tin equivalent in finelydivided form; by weight of the copper-coated iron powder.

' 7 The method as claimed in claim 2 wherein said sinterable mass also includes between about 4% and 4% of metallic zinc equivalent in finelydivided form; by weight of the copper-coated ironpowder.

" vidd copper oxide at temperatures between 8-. The method as claimed in claim 2 wherein said sinterable mass also includes between'about and 4% of metallic cadmium equivalent in finely-divided ,form', by weight of the coppercoated iron powder.

9. The method of making sintered iron bodies of improved strength from thermochemieallycoated iron powders,'said method comprising-the steps of: providing a sinterable mass consisting essentially of an intimate admixture of (a) iron powders, at least-a major part of which powders carries a copper coating amounting; to between about 4% and 30% of the'totalweight of' the iron'powders, saidcoating having beenuapplied to the said major part of the iron powders by a, thermochemical reaction betweensaid iron powder and finely-divided copper oxide at temperatures between about 1000 F; and 1:500 F.-

in a non-oxidizing atmosphere, and (In) between about and 4% in metallic tin equivalent in finely-divided form, by weight of the coppercoa'ted iron powder; sintering said'sinterable mass in a reducing atmosphere at temperatures between about -1800 F. and 2200 F.; and cooling said sintered mass in a non-oxidizing atmosphere. I

10. A sinteredproduct as produced by the method claimed. in claim 9-.

JOSEPH E. DRAPEAU, JR. JAMES H. SMITH. RICHARD J-. HALSTED.

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

UNITED vSTATES PATENTS Date

Claims (1)

1. 9. THE METHOD OF MAKING SINTERED IRON BODIES OF IMPROVED STRENGTH FROM THERMOCHEMICALLYCOATED IRON POWDERS, SAID METHOD COMPRISING THE STEPS OF: PROVIDING A SINTERABLE MASS CONSISTING ESSENTIALLY OF AN INTIMATE ADMIXTURTE OF (A) IRON POWDERS, AT LEAST A MAJOR PART OF WHICH POWDERS CARRIES A COPPER COATING AMOUNTING TO BETWEEN ABOUT 4% AND 30% OF THE TOTAL WEIGHT OF THE IRON POWDERS, SAID COATING HAVING BEEN APPLIED TO THE SAID MAJOR PART OF THE IRON POWDERS BY A THERMOCHEMICAL REACTION BETWEEN SAID IRON POWDER AND FINELY-DIVIDED COPPER OXIDE AT TEMPERATURES BETWEEN ABOUT 1000* F. AND 1500* F. IN A NON-OXIDIZING ATMOSPHERE, AND (B) BETWEEN ABOUT 1/4% AND 4% IN METALLIC TIN EQUIVALENT IN FINELY-DIVIDED FORM, BY WEIGHT OF THE COPPERCOATED IRON POWDER; SINTERING SAID SINTERABLE MASS IN A REDUCING ATMOSPHERE AT TEMPERATURES BETWEEN ABOUT 1800* F. AND 2200* F.; AND COOLING SAID SINTERED MASS IN A NON-OXIDIZING ATMOSPHERE.