US2942334A - Powdered ferrous metals and articles and methods of making the same - Google Patents

Description

' June as, 1960 2,942,334

R. E. BLUE POWDERED FERROUS METALS AND ARTICLES AND METHODS OF MAKING THE SAME 1 Filed Jan. 18. 1957 INVENTOR- gay 2;, ,ZZzle.

nited files This invention relates to improvements in particulate ferrous metals, more generally referred to as powdered iron, formaking sintered compacts and other articles or products; to products essentially comprising such particulate ferrous metals; and to methods of making said products and preparing said particulate metals for use therein. 7 t

In making porous articles or products by sintering a formed or compacted mass of powdered iron, itis normal to have some iron oxide present inthe mass. However, it is also found that such iron oxide when present on the surface area of the ferrous particles is detrimental in that it substantially inhibits sintering and the obtaining of a goodmetallurgical bond between adjacent particles of the mass during sintering. Such has been true for example Where the weight loss due to .oxides as determinedby MPA specification 2- 48- hydrogen loss method is in excess arm Certain iron particles for instance, low cost, low grade type iron particles for example those known commercially as mill scale or magnetiteand made by reducingdron oxide in a hydrogen atmosphere, inherently contain iron oxide at their center and at the surface areas thereof, These and other iron powders, such as electrolytic iron powders, also "obtain. such 'iron[ oxide on ,their surface ai 'eas by exposure, prior to briquetting and.especially du r-.

' ing storage, to oxidizing influences such as air, which produce completely oxidized areasontheparticles. A similar action occurs during the early stages of sintering. In many instances these areas extend over the greater part of the particles and exist as a heavy layer.

, Where these conditions heretofore existed, it has been atent l ice I have further discovered that if the ferrous particl are provided with such iron sulfide films or layers dur ing the making thereof or at an early period after their making, it is possible to obtain optimum coverage of the particles with the iron sulfide and preferably obtain a substantial envelopment of the particle with films of iron sulfide before a complete iron oxide layer is produced on the particles by exposure to air or other oxidizing influences. This layer of iron sulfide will thereafter protect the under surface of the particles during storage from oxidizing influences and during sintering up to the temperature at which coalescence occurs.

Accordingly, the principal object of this invention is to so treat particulate ferrous metals prior totheir use in the making of sintered articles to provide them with surface'portions or films of iron sulfide capable of having a scavenging actionon iron oxide during the sintering of compacted masses of such particles and effect a coalescence of the iron sulfide and iron oxide of adjacent particles to form particle boundaries of pure grain character and of iron oxysulfide to enhance the metallurgical bond between adjacent particles. v

Another object is to carry out the treatment set forth in the preceding object at the time the particulate ferrous materials are-formed, or shortly thereafter, whereby to inhibit the conversion of pure iron ofthe particle'sur faces to iron oxide and thereby inhibit formation of excessive surface iron-'oxide'on the particles. I 7

Another object is to provide particulate ferrous material as described in the preceding objects whichfwill provide in siutered. articles made therefrom many favorable characteristics including uniformly high physicalfound essential in order to obtain a satisfactory bonded the resultant products have usually had a lower ultimate strength and ductility than in cases where the oxide condition is not present and their lack of uniformity in duc- I tility and yield strength have caused rejections. Furthermore, they have left much to be desired by way of facilitating machining and coining.

' Among other reasons why sintered iron products have been desirable commercially has been the cost savings possible by combining powder metallurgy and finish machining. In some applications sintered parts made from low grade iron powders do not have machining characteristics which make this combination attractive. I I 'I'have discovered that some of the surfacev iron oxide of the iron particles presently considered detrimental, canbe advantageously employed to improve sintering, to obtain a better metallurgical bond between the particles, to improve the physical properties'of the resultant sintered product. I accomplish this by providing surface areas or films of iron sulfide on the particles which in sintering will have a scavenging effect upon the iron oxide at. the surfaces of the particles by forming a liquid phase therewith, i.e. coalescing with or absorbing this iron oxide of adjacent particles to producean iron oxysulfide properties, good ductility, easy 'machinability," anda yield strength which facilitates sizing and coining'operations andtheobtaining by the latter of ultimate strengths higher than those .n'ormally expected where the particles did not contain the advantageous iron sulfide in their surface portions. 1

A particular object isto treat particles'of low cost, low grade iron suchas mill scale, in a manner to'pro- 'vide on them surface areas ofiron sulfide whereby 'to inhibit the production on such particles of completely oxidized areas of: the underlying pure iron by oxidizing influences subsequent to theirinitial formation and during storage. 7

Another object is to provide particulate ferrous metals of the character of the preceding objects which lend themselves to briquetting without seizure with'the die and which may be sintered at relatively low temperatures at which the surface iron is most active in effecting bonding for instance 1300 to 1700 F.

A specific object of my invention is to provide individual particles of ferrous metal with surface films o-r layers of ferrous sulfide (FeS) capable of effecting a scavenging action on adjacent iron oxide surface portions of the particles during sintering of products made from such particles as a result of which the ferrous sulfide (FeS) surface portions coalesce and form a liquid phase with theiron oxide .(Fe O surface portions to produce to effect a reaction between the latter and the pure iron or slightly oxidized iron surface portions of'the'particles to form in situone or more films'or layers of ferrous'sulfide adapted to inhibit new or additionaloxidati'onof such iron surfaces of the particles during storage and to'serve as a scavenging and bond improving agent"dus ing sintering of a massof such particles.

ewsassa ings wherein:

apistonembodyingrmyinventiomrandl I indiizidualparticles- I I I appear from-the following deseriptionand from the draw- I g, I Figure 1; isanzelcvational view partly in section showing I II I Figure: 2. is IahighIy magnified view' typifying the in ternalr structure ofthe piston of Figure 1 as evident from a 'photomicrograph. I I I I I I I I I-ziii'a've discovered that-toobtainoptimum-1 distribution of the'ironsulfide in the particle mass 'andcoverage of' the individual particles to resist. further oxidizing effects during storageand :enhance-the'extent' of scavenging action I during: sintering, the ferrous particles should be treated i 1 i bysubjecting them at, 'roorn temperature-'on'wlziiletsuib ably heated to thevchemical action of .a sulphur bearing I .gaseouscomppsition, preferably hydrogen sulfide: (H S);

I tHeatingt the particles is. advantageous; to increase the 3 I I t intensity ofchemicalreaction; I ;Agitation:ofthetparticles I is helpful especially whenytreatinga thezparticlesatroomf I temperature Oncontactofithehydrogentsulfide gaswitlr the: individual particles, a-reactio n occursrwitlr the: pure or} slightly I oxidized-iron, surfaces of the particles to I i I produce, in situ one or more integral protective; and I $caveng ngfilmsoi' ferrous. sulfidendescribedi above-onthe a l The gaseous. treatment preferably carried out} im- I media-tely after. makingthe-particles.or ateantearly'period I I thereaftento obtaintmaximum conversionzof-ithe ironzsui' sinteringa;

accordance with the invention and successfully made into articleshavingtsatisfactory properties; Theferrous metal particles may also containsmalliamounts of alloying: constituents-such. ascarbon, silicon, nickel, etc; Thus the particlesmaybe those offreduced magnetite; low carbon steeh; low carbon atomized-iron, stainlessiron or steel. The particulate ferrousinaterialfmay be treated by the hydrogen sulfide in any suitable piece of equipment to effect the: formatio'nrofr ironv sulfide on the surface of the particles. Thus-for example, the particliesmay be placed as a loose mass on astray in'a. suitably heate'dretort-type furnacehaving a frontal opening into which hydrogensul fide gas may be introduced, filtered through the mass and be exhausted through another opening at the'back of the furnace; Suchretort maybe housed in a=-hood equipped with a blower to exhaust'the gas from the-furnace and the-furnace will be'provided with a suitable temperature control and recording equipment to maintain uniform temperatures. Moreover'thetray may 'be agitated by a suitable :vibrator; Satisfactory results are obtained when thwpowders are treated at a temperaturein' theirange of 3759' F1 to 325"F. for periodsranging from S'to 25. minutesandwhereby th e'sulphurcontent' of the treated particles by chemical analysisis in'the range of 0' 275% fo0.325"%. v

Thus mill scale iron powder-havingtthe.following-screen analysis:

7 7 Percent Retained on .100. mesh; 12.8" Retained'o'nr 150. mesh .2l. I Retained on 200-mesh 1821 I I Retained onr250tmesh; 6 32' Retained:on;'325"mesh; s 13.9

Passed thru 325 mesh 2s faceportions totiron-sulfidebefore new 'or'additiona'l iron I I I oxide-layers are:- formed onxthe: particle surfaces by en'- 3 ;posure toair or;otheroxidizinginfiuenceszln anyeventt' the; panielesshouldbe treated as zdescrilied 'prionto I the topof. a rotating*tower suitably heated and having] an I outletiattlie' basefrom whiehztoremove:theipowdetafter I I treatment. Hydrogen sulfide gas' will be fed" into the tower atwthe l-owcr end through a suitable inlet and'xex I hausted-at the top through asuitableoutlet therefor; I I The particles of particulate ferrous material treated I I asdescribedabove and having the deposit of-ironsulfid'e formed} insitu 'mayflthereafter" be advantageously com;- i I I I pasted, by: known means and conventional briquetting,

andhaving;achemicalanalysis as follows:- I I Carbon .03 I I Manganese .36 t I I Phosphorous I salesmen"- y I '.0;1 I S l c -t--- -t--t 1 00 :OXy'ge'm; j' 1.26

'I-ron remainder I when treated-as described in a retort furnace having-a 6" diameter opening and 14" long," for: a period of fifteen rate of.5.to 6 cu; ft. per hour to effect conversionof the iron. surface portions to iron-sulfide was capable of. handling-between6 to 10*lhs. of material for each v1 -5 minute II I period. A chemical analysis of this materialafter treatment showed a sulphur content-of between 0.275% to, 0.30%.

The: increasezin weight'of a 80 gram sample of the-treated: I I iron powder 'was',0;1 25-%'.' Based on-' a v mathematical I computation in which ,it' wasassumed that the: particles t I were spherical and perfectly homogeneous and wereyflG tt I I I indiametenthe deposit or coating. produced'on the particles was" estimated to'be" approximately .00001".

:The time and temperature treatment of otheri'particulatel I ferrou'stmaterials may readily'zhe determined" in accordance,

particles,the particulate ferrous material mayj beifed into pressures'of about 30,000t0 60,000 psi. depending upon thedensity' desired to form desired articles of commerce such as the pistons 'shown' inFigure land the compacts sintered inta suitable furnace, for example an electrically heated furnace having. means providing a controlled atmosphere thereinof the exothermic type.

-As previously described, I have discovered that the surface'iron sulfide deposit or formation on the particles has-a scavenginga'ction duringsintering of the compact causing-coalescence of the iron oxide and iron sulfideto form puregrain' boundaries between particles and boundaries comprising'iron oxysulfide to thus produce an .improved metallurgical bond between adjacent particles of thestructure.

This is evident in Figure 2 for example, where the scavenging eifect of the iron sulfide is apparent in the relatively clean1 grain boundaries illustrated at 4' and by the coalesced iron oxide and iron sulfide indicated at 5 in this figure; the areas of concentrated iron oxysulfide being indicated by' the stippling at 6 in this figure.

One of the advantages of the use of iron sulfide" bearing particles of iron produced as above is the substantial saving in required kilowatt power consumption of the sintering furnaceand in its maintenance cost. He'retofiore it was necessary for example to sinter high grade iron particles of electrolytically produced powder ata temperature of approximately 2050 F. By utilizing sucli iron particlesias treated in accordance with the present invention compacts thereof may be successfully sintered at temperatures in therange of 1300 F." to 1700 F;'best results being obtained in the" range 1550 F. to 1700' F. Th'ese same-low temperatures are likewise possible when employing other' iron' powders, even low grade mill scale iron powder"; I

Not only does the presence of .the' iron sulfide on the particles permit lower sintering temperatures and'iinprove Percent I particles prior to Qbriquetting and sintering; Moreo er,

the metallurgical bond but there isalso a pronounced increase in the degree of sintering that occurs at the lower s'intering temperatures than would be possible without the presence of the iron sulfide. This is only possible because of the scavenger effect or coalescence described above effected by the iron sulfide on the iron oxides which inhibit sintering. In addition to the foregoing the coalescence eifect of the sulfide on theoxides in absorbing the same reduces the yield strength of the product in the as sintered condition because the oxide is then no longer available to produce a precipitation hardening effect which normally exists in prior sintered iron masses in which the sulfide is not present. This reduced yield strength material with its excellent ductility makes it particularly suitable for coining and cold work- 4. As an articleoimanufactm'e a metal body .compris.

5. In a process of preparing particulateferrous metals for use in the making of sintered products the improvement which consists in heatingsaid particles to a temperature in the. order of about 275? -to 325 F., passing hydrogen sulfide gas through a loosemass of said ing by which techniques the yield strength for a given specific gravity may be greatly increased above those heretofore possible, and even doubled where such prop- Further increase in the ductility of the resultant sintered product of even in the case of electrolytic iron powder and certain other iron powders has been found 'posfsible by the addition of 0.5% to 1.5% by'weig-ht of ferric oxide in powdered form to the gas neat anen po additions of small amounts, for instance about 74% by weight of stearic acid to the prior to briquetting are desirable as a lubricant.

Although my invention has been illustrated in conjunction with a piston 3, it will be understood thatthe same is not limited to the making of such articles but can be employed in the making of other articles and in the making of various stock material from which articles are fabricated. Moreover, while the invention has been described utilizing hydrogen sulfide gas as the agent for treating the ferrous particles it will be understood that some of the desirable effects of the invention although to a markedly lesser extent and with less uniformity may be obtained by directly adding to the powdered mass and thoroughly mixing therewith, prior to briquetting, from 0.5 to 5% by weight of powdered metallic sulfides. Examples of suitable additives are cupric sulfide, cuprous sulfide, iron sulfide (FeS and FeS manganese sulfide, nickel sulfide, cuprous sulfide and nickel sulfide eutectic, cuprous sulfide and sodium sulfide eutectic, cuprous sulfide plus metallic copper, nickel sulfide plus metallic copper, iron sulfide plus iron oxide and nickel sulfide plus iron oxide.

I claim:

1 As a product of manufacture a mass of individual powdered metal particles for use in making sintered compacts, said particles comprising ferrous metal bodies hav ing integral chemically bonded surface films of ferrous sulfide and said particles having a sulfur content between 0.275% to 0.375% by Weight.

2. As a product of manufacture a mass of powdered metal particles for use in making sintered compacts, said particles comprising ferrous metal bodies having integral surfacings of ferrous sulfide comprising the reaction product of said ferrous bodies and sulfur bearing composition and said particles each having a sulfur content between 0.275% to 0.375% by weight.

3. As a product of manufacture a mass of powdered metal particles for use in making sintered compacts, said particles comprising ferrous metal bodies having integral surface portions of iron oxide and further integral surface portions of ferrous sulfide, said particles each having a sulfur content in the range of about 0.275% to 0.375% by weight.

particles and effecting contact of said gas with the surfaces of said particles wherebyv to form by chemical reaction; of said gas on the. ferrous surfaces of said particles an integral layerof iron sulfide and. producetreated particles having a sulfur content in the range of 0.275% to 0.325% b tg i I 6. The method of making articles from particulate fer- ,rous metals having completely oxidized surface portions comprisingiron oxide and having other surface portions comprising. substantially pure and slightly oxidized iron, comprising providing'a loose collection of said particles,

passing hydrogen sulfide gas through said mass ofipar ticles to effect contact thereof with said'substantially pure and slightly oxidized portions. of the surfacing of said particles whereby to produce by chemical action thereon integral films of iron sulfide, compacting .amassofIsaid treated. particles into a predetermined, form and heat treating said compact to effect a metallurgical bond". at adjacent surfaces'ofsaid particles, the iron sulfide films of said particles serving'during said. heat treatment to jefiectfa coalescence of the completely oxidized portions of said particle surfacing therewith into iron oxysul-fide and the formation of clear grain boundaries. I

7. The method of making articles from particulate r rous metals jhaving completely oxidized surface portions comprising iron oxideand having other surface portions comprising substantially pure and slightly oxidized iron, comprising heating a loose collection of said particles, passing hydrogen sulfide gasthrough said mass of particles to effect contact thereof with said substantially pure and slightly oxidized portions of the surfacing of said particles whereby to produce by chemical action thereon integral films of iron sulfide, compacting a massof said treated particles into a predetermined form and heat treating said compact at a temperature between about 1300 F. to 1700 F, to effect a metallurgical bond at adjacent surfaces of said particles, the iron sulfide films of said particles serving during said heat treatment to effect a coalescence of the completely oxidized portions of said particle surfacing therewith into iron oxysulfide and the formation of clear grain boundaries.

8. The method of making articles from particulate ferrous metals comprising subjecting said particles to the action of a hydrogen sulfide atmosphere until an integral film of iron sulfide has been formed on the particles by chemical reaction of said gas and the iron surfacing of said particles, adding between about /2% to l /2% by weight of powdered ferric iron oxide to said mass of particles and mixing therewith, compacting a mass of said mixed particles into predetermined form, and heat treating the compressed particle mass at a temperature between 1300 F. to 1700 F. to metallurgically bond together adjacent surfaces of said particles, the said iron sulfide of said particles acting in response to said heat treatment to effect a coalescence of the iron oxide present at the surfaces of said particles therewith.

9. In a process of preparing particulate ferrous metals for use in the making of sintered products, the improvement which consists in heating said particles to a temperature below about 325 F., and treating a loose mass of said particles with a sulphur containing composition "toefiect' contact of the latter with the surfaces 'of said particles-whereby to form an integral layer of iron=sulfide (Q11 atheferroussurfaces of the particles by chemical reaction of said-composition withsaid 'surfaces's'aid-particles having a sulfurcontent after treatmentof'between about "0.275 to 0.325% by weight.

"10. The method of -making articles :from particulate ferrous metals having completely oxidizedsurface-portions comprising-iron oxide and having other surface pordons comprising substantially pure and'slightly oxidized iron, comprisingproviding a-loosecollection ofsaid particles, passing'hydrogen sulfide'gas through sa'id=mass of particles to effect "contact-thereof with said substantial- =ly pure and'slightly oxidizedportions of'thesu'rfacin'g-o'f "said particles whereby to produce "by' chemical action thereon integral films of iron sulfide, compacting a mass of said treated particles into a-predetermine d form and heat treating said compact at "a temperature "between about l300 to 1700 to efiect a metallurgical bond at adjacentsurfaces of said particles, the iron sulfide films of 'said particles serving during said heat treatment to effecta coalescence of the completely oxidizedportions 'of said-particle surfacing therewith into ironoxysulfide 'and the formation of cleargrain boundaries.

I '11.'The process of making articles from particuiate ferrous metals comprising mixing ferrous particles having completely oxidized surface portionscompris'in'g iron :oxide-with O:% -to 5% 'by 'weight of powdered metallic sulfides, compacting a mass of said mixed particles into a predetermined form, and heat treating "the compressed 'particl'elmass at a temperature between about 130? F. to 1700 F. to metallurgically bond together adjacent surfaces of said particles with the sulfides acting in reproduce-by chemical'action thereon integral films 'of iron sulfide, mixing -with said particles 0.5% to 1.5% -by Weight of "ferric oxide, compacting amass of said mixed particles into a predetermined form and heat treating saidcornp-actat a temperature between about 1300 F. to 1700 F. 'to e'tfect a metallurgica1 bond at adjacent surfaces of said; particles, the iron sulfide films of said particles serving during said heat treatment to effect a coalescencethere'of with said ferric oxide intowiron oxysu'lfidetordmprov'ing the bond betweenthe particles and the formation of clear grain boundaries.

l3. Ina-process of-preparing particulate ferrousmetals Toruse in the making of sintered productsthe improvem'ent'which consists in'heating the particles at a temperature of "about 300 F. for a period of about fifteen minutes while'treatingtheparticles withghydrogen sulfide wherebyto'etfectconversion of the iron surface portions 'toiron sulfide, 'thesaid particles 'havinga sulfur content aftertreatmcnt of between 0.275% to 0.30% "by weight.

14. The method of making articles from particulate ferrous metals comprisingcompactinga mass of particles having completely oxidized surface portions comprising ironoxide and-having other surface portions comprising integral 'films of iron sulfide into a predetermined form and heat treating said compact at a temperature between 1300 F.1to 1700 F. toeifect'a metallurgical bond at adjacent surfaces of said particles, the iron sulfide'films of said particles serving during said 'heat treatment to effect a coalescence of the completely oxidized portions of said particle surfacing thcrewith'into iron oxysulfi'de andjthe formation of clear grain boundaries.

Conradson Jani 2;7, '1885 2,420,886 :Laifoon 'May 20, .1947

7 $791,561 -Beller May 7, 195-7 UNITED STATES PATENT OFFICE CERTIFICATE @F CORRECTION Patent No. 2,942,334 June 28, 1960 Roy E. Blue It is hereby certified that error appears in theprinted specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5, line 66 before "sulfur" insert a column 6, line 4, strike out "chemically bonded".

Signed and sealed this 31st day of January 1961.,

SEAL) Attest:

KARL H. AXLINE Attesting Oflicer ROBERT C. WATSON Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,942,334 June 28 1960 Roy E. Blue It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5, line 66 before "sulfur" insert a column 6, line 4, strike out "chemically bonded".

Signed and sealed this 31st day of January 1961a (SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents

Claims (1)

1. AS A PRODUCT OF MANUFACTURE A MASS OF INDIVIDUAL POWDERED METAL PARTICLES FOR USE IN MAKING SINTGERED COMPACTS, SAID PARTICLES COMPRISING FERROUS METAL BODIES HAVING INTEGRAL CHEMICALLY BONDED SURFACE FILMS OF FERROUS

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