US2087768A - Ferrous metal and method of making same - Google Patents

Description

July zo,-1931. .VD-.F.'FOBEsfE-m ="2,1)87J68y FERRoUs METAL AND METHOD oFMAKING 'SAME l original Filed Feb. 2v, 1933 e UNITEDSTATESKPATENTQFFIE Patented July'. 20, 1937 e i Y ...aos'mssw i v FERRoUs METALAND s Marnonorrm rim l 'v n. i my. i K,

l DuncanP. Forbes, Rockford, `andhEl'vvin-J. Mohr, deceased, late of Rockford,lll.; by Linf da Mohr, admnistratrlx.Milwaukegwis.,

assignors to `Gunite Foundries Corporation, f l' j Rockford, vIll., 'a corporationofV Illiluiiil` Continuation of application Serial No. v658,764, u e 1933. Thisapplication April 20, 193:6,Se`tllll N0. 754,508y r e February Z7,

1o claims. (c1. 414s-Lars) This invention relates tothe manufactureof yrolled products of graphitic irony andrwe have successfully made rolled sheets, platea and bars 'of such metal by the methods herein set forth.

l5 carbide),l which, under heat vtreatment,"can be decomposed withy a .resultant,precipitation of` graphite in the metal. AUnless otherwise jexpressly stated, the term cementite asfused throughout theSpCCiflcation and the appended:l claims is as that atfwhichl temper carbon` canbe' redis'soived ,5 By the term graphitic ironv we mean iron conintended to mean iron .carbide as a distinct Acrysf taining any form of precipitated free carbon. talline constituent formed upon solidication of v Broadly speaking, the invention, contemplates the metal and not cerrientiteformed at temperaproducts consisting of rolled graphitic iron wheretures below this point. ItI isiour belief `that those l .in the graphite is `distributed in the. matrix in skilled 1kin theartwill be lable ltor select. the -per'- the form of `elongated or fibrous clusters armissibleanalyses inthe light'of the disclosure 10 ranged in approximate parallelism. v n hereinafter made,and when considered with the l'Ihe products arenoveland commercially vuse-` specific examples'givevn. Whenthepr'oper white ful materials having among other properties adiron ingots havebeen prepared, as will presently `vantageous corrosion resistantfqualities. These bedescribedv andillustrated, they. are subjected 5 products maybe used for many vpurposes for `-to a heat treatment to yfacilitate the deformation 1.5: l whichv steel sheets, plates and-bars are ordinarily operations and to `prepare the metal for subseused and are preferable to steel for some purquent heat treatment. Thisinitial heattreatposes. .e ment may take any of three forms which are, A The present',` invention also vvcontemplates a in general, treatments for the purpose of decom- '20 novel method wherein white cast iron is sub ,posingrthe massive cementiteand precipitating .20H

l vv.iected to a heat treatmentuand subsequently graphite as so calledV ftemper carb on.inl the rolled into thegdesired shape -at elevated tem-v metal f y 'peratures The rolled metal may then be subi In the rstlan'd preferredform, the llngotsv are jectedto further heat treatment to impart thereheated upito above the graphitizing temperato desirable characteristics. o ture.y Withdronl of an analysis ordinarily'capable 25' In the drawing; t n Vof solidication vas white "iron and capable ofA Figurel is a showing 'of the. structure of the` graphitizationA without *unusualJ dimculty, thisN f. metal parallel to the direction` of rolling and temperature willllefaboveabout13509111, andperpendicular to the rolled surface `magnified 125 fOr the bestform of. graphite should be kept below f so diameters showing the elongated shape of the .t 1v5o r'.,-thoush 1t wm be'unde'rstood'that; with 3 graphite; .i :some metalof kspecialv analysis, graphitization Fig. 2 is a showing at about 500'diameters of might lie-brought about outside offthis temperathe structure of one form of the. product, .sl-iowturef4 range, as isk commonly knownyby jpeople ing the ferrite matrix resulting yfrom oneformv handling such materials.- Themetalis h'eld withof subsequent heat treatment;. y o in this graphitizingrange until decomposit'ionloi' 35 Fig.V 3 is a showing at about 500 diameters ofl vthe major part of `the cementite has occurred. the structure of a second form of. the product, Theremaining cementite, iLany, should'ot be showing 'the sorbite matrix resulting from a sec-- presentin sufllcient quantityf'fto'fcause difficulty ond form of subsequent heat treatment, and duringrolling. The metal 'isthen further-heated 40, 0 Fig. 4 is a'showingat about 500 diameters of lto a rolling temperature above ltlefcritical teml. n i

'a third formeof the product showing the spherperature, that is.v within' the rance at which the oidized cementite in a ferriteimatrix resulting metal isaustenitic' and preferably in thiresicn from a. third form of subsequent vheat treatment. oi":.1800 F. to 2100 F. atwhich temperature the Y y y y The rst step in the method consists inthe prometal is rolled, ashereinafter described, topro- 4" duction of suitable ingots of white castiron; v'I'he duce the I1e- 11`edShlil` 1 a f f Y ingots mayhave any convenient size or shape and By' critical temperature we mean the tempera- Y may be formed by pouring into metal molds,green ,ture separating th. ferritic lor pearlitlc and au'sor dry sand molds, or core sand, or anyffether. 1 tenitic phases, that is,'where 'ferrite or pearlitev i molds customary in foundry practice. ,'Ihevanaly.-l changes toaustenite andabove which then'ietal '50 sis of this iron will Vdependlargely uponthei will always be austenltic. This-temperature may subsequent treatment adopted andupon the ulti-l be between'1?`50` F.and 1500" F. depending upon mate product desired.. The ingotsf-'willfcontain Vvarious factors, principally the composition of the l f a certain proportion of massive cementite (iron metal. 'I'his temperaturewi's apparently 'the same .f j

: 2100 F., and holding'them atvthis temperature ized metal or without control, in which case' there may or may not be residue combined carbon, and at some subsequent time the ingots are reheated to the rolling temperature and rolled asin the y first form. It will be seen that this form differs from the first form in that the ingots are allowed to cool after' heat treatment and before rolling.

The practical results of these two forms will usually be substantially the same with the exy ception that the first formis more economical in' j* cases. where it isvpossible to have `continuous operation so thatthe ingots maybe rolled immediately afterwheat treatment.

.A third formof heat treatment consists in heating up thevingots directlyfto the `rolling temperature, that is, to atemperature above the critical temperature; that l is,` within the austenitic range at which thelmassive 'cementite breaks down and preferably to about 1800 to until the major ypart of the cementite has been decomposed and -then rolling-the ingots. The length of time the ingots need to be held at this ltemperature to accomplish thedecomposition of the cementite will vary Widely, say, from twenty .minutes to twenty-four hours, depending upon n conditions such as temperature, composition and size of the ingot, all of which will be understood by those skilled inthe art. 1' i The preliminary heat treating step confers upon the metal superior"ro1ling` characteristics.

and permits a reduction in. rolling time by inf creasing the amount of reduction possible at each pass through` the rolls .because of the greater plasticity of the heat treated metal. Furthermore, because of. this increased plasticity the metal can be 'rolled Witha given reduction until it has cooled to a lower temperature than would otherwise be the case and this permits it to be passed l through the rollsa greaterv number of times before reheating will be required, as subsequently described, thus reducing the amountof reheating.- rIfheV preliminary heat treatment also, be-

cause of the plasticity imparted to the metaLper- N mits-the rolling.` of more diflicult shapes.

In the last'above mentioned form of heat treatment the graphite isin amore dispersed form than/results from the. previous-two forms of heaty treatment and the metal vheat treated in `this `mannercwill notnormally vpermit as great'a degree of deformation during each pass-through' the rolls'. Thisv is doubtless because of the fact that thegraphite is not present in the most com` `pact form. However, :inpgeneralVthe lastA form of heat treatment normallygives fairly satisfactory rolling' characteristics* and .for many types method.` y

Our experience teaches usf that in general the rolling canv best.4 be carried out -attemperatures of vWork vwill be found to be the most economical above the criticaltemperature, that is, withinj 4 the austenitic range and preferably between ,about f `'1800 F., and the temperature at which a liquid phase begins to appear in the metal, the metal being more easily deformed above l800 F. and havingtherbest microstructure above the critical.

In general,- it seem'sthat theV best rolling temperature is' the highest temperature attainablev without the presence of a liquid phase. However. the temperature of the metal falls as the rolling operations proceed, and the rolling becomes more diflicult as the metal passes much below 1800 F. and approaches the critical temperature. One

"advantageofour method lies in the fact that because of prior heat treatment, the metal re' taivnsfalhi'ghdegree of its plasticity over a wider temperature range and may be passed and repassed through the rolls until a somewhat lower temperature is* reached without changing the degree of reduction.

` A feature of the invention lies in the manner of rolling. Any conventional rolling mechanism may beremployed butitwill be found that as rolling'nproceeds the operationbecomes inand the rapid decrease in plasticity with change in temperature, and we have discoveredl that if Hcreasingly' difllculti'v. 'I'his we' have found to be )due tothe rapid drop in temperature of the iron the`metal isreheated one or more 'times duringl rolling', the desired reduction in section may bespee'dily accomplished with a maximum degree VKofreduction., It isjtherefore, advisable tolocate the *heating vfurnace in such c proximity fto the rolling mechanism as to prevent excessive loss in temperature of the` metal ,between theheating 'I furnace'and the rolls.'

We have alsofdiscovered ,that wherethe prod- *u'ctis 'tobe used for .corrosion resistance purposes valuable improvement ,in such characteristics is' imparted by rolling the metal'infdirec- *i tions at right angles `to each other. I Inthis l, method the graphiteuisfrolled or 1 elonatedin/ two `directions so that'feach clusterv is spreadout into a-disc-like* for1n. As' the metal is'` reduced in'sectiong' thesediscs tendto overlap so that upon corrosion of the metal surface a greater proportion of the surface area vis coverecfiby graphite. It is .our beliefthat this increase in the proportion of the vmetal surface covered by graphite upon corrosion Vofthe surface'metal accounts for -thef improved lcorrosion resistance p'rcipertiesfoif metal rolledjin this manner.

4Another featureA of our: invention liefs in the treatmentl of the metal, subsequent, to the rolling step designed to 'render it utilizable commercial- `v`1y.""-'This phaseof the inventioncontemplates a metal 'in Vwhich the vceinentite is substantiallyr completely decomposed as it'comes from the rolls orl hotf` deformation' operations, `asl willv be the case withmetal which Khasbeenfheat treated in the manner previously described." p The subse-v quentv heat treatment` contemplates lvariousV `forms adapted'to producel a metal of commercially usablecharact'eristics and yinvolves the' heat vftreatmentjof the 'metal as ,it comes from the -rolling.operations,' the type `ofheat treatment depending upon' "the analysis of the4 metal and themicostructure desired. "I'hus'in order to produce a product of predetermined"physical characteristics, we 'control both the analysis of `thelmetal andthe heat treatmentimparted to `the rnetalsubsequent to the rolling operations, 1 tls'fheattreatment resultingin the production Y of--uniform products from rolled materials which would' `otherwise haver uncertain and erratic Vstructures.,y The subsequent heat treatment'v thus servestwo lpurposes, that. of. Y bringing the f parts of each rolled form and also thevarious rolled sired structuralcharacteristics tov the material.

In one formof this .subsequent heat treatv' Vment, we take a rolled metal having an analysis which would normally be suitable. for the production of malleable iron.. For most commercial purposes, this rolled metal will bestbeprepared in the manner previously set forthfrom ingots f of white iron capable of being graphitiz'ed and having a carbony content preferably. not 4less than about 1.5%, a percentageof carbon plus a percentage of silicon content vgreatery thanl about 2.9%, and a manganese'- content. which is twice the percentage of sulphur plus ,.10%jto .30%.y

It is l-rnown'by those familiarwith the art that the silicon can be replaced in equivalent Lproportions by other graphitizingagents.. `we heat this. rolled metal to atemperatureabove the, critical temperature, that is, the lowest temperature at which austinite is'forr'ned, and' cool it very slowly through the critical ternperaturc'e until the combined carbon hasbeen,completelyprecipitated, or else heat to a temperature within the critical range or to just below the critical temvperature and.hold'atthattemperature until the 'combined carbon has been decomposed to form graphite, in either case producing a material` having the graphite in anelongatedfform dispersed in a matrix of ferrite. The critical range may be defined as the temperaturey krange between the critical temperatures rof the'stable and meta-stable iron-carbon diagrams, respectively..

This range is variously estimated asfbeing from.

to 15 Fahrenheit. degrees. v

We have successfully executed the following procedure which is given by .way ofexample illustrative ofthe first formof subsequent heat,v

treatment. An ingot tras prepared of white. iron of 'the following analysis: Carbon 2.4%;Silicon phorus .16%. This ingot was preheated to 1700 'F.,and held at this temperature for 'twenty-four.

hours.` VIt was'then further heated to 1950 F.,

y' and rolled, using a' reductionvr of'a'pproximately` 20%V for ea'ch pass through the rolls..V When the temperature ofthe metal dropped below 1800 F., it was reheated to`1950 F., and rolling continued until the V desired size andthickness. ofsheet or bar was obtained, reheating asjfrequently as,

necessaryto keepjthe material aboveabcut 1800 F. After rolling was completed, .the material was placed in a heattreating furnace before excessive loss of temperature had 'occurred and was -he1d at about 135o F.,.for twentyhours. The

final product consisted of arolled graphitic iron wherein the graphite or temper carbon was in an v elongated form in a matrix o f ferrite. 'Ihe micrograph shown in.Fig. 2 `illicistrates the mate- `rial obtained.`f, A A secondrform of subsequent heat treatment involves heat treatment of a rolled metal wherein Avthe metal has a carboncontent preferably not less than about 1.5%; a percentage of carbonplus a percentage of silicon content: greater than vabout 2.9%; and a manganese content which is y 1 twice the 'percentage of sulphur plus .10% to .80%,` preferably twice thel percentage of sulphur Y 2,087,768 z forms to uniformity-'and that of imparting de- `v The following eirampleoutlinesa method in-v .volving y.the second form `of lsubsequent heat treatment. A.white iron ingotwas made of: the

followinganalysisLCarbon 2.40%; silicon .90%;

manganese .80% sulphur .07% and phosphorus .16%. I'he ingots were preheated to..1700 FL, and held at ,this Atemperature for twenty-four hours. T he temperature was then raised-to 1950-F.,. and the metal rolled as described inthe first eiaxnple. vAfter leaving the rolls, the metal was brought toa temperature of about 1500 F., and then cooled rapidly through `thecritical temperature .to room temperature Cooling in the open air usually provides a satisfactory rate of cooling. .The resultant materialgshowed a pear- Alitio matiix` containing elongated'. clusters of graphite ortemper carbon.. Fig. y3 illustrates the structure obtained as a result of this procedure.

A third form; of subsequent heat `treatment deals-with a rolled vmetal of an analysis wherein fthe carbon is `n otless thanabout 1.5 the percentage of ca'rbon, plus `thef percentage ofv silicon is greater than, about 2.9% and lthe manganese content is about twice thepercentage of Asulphur plus .10% to .80%, preferably twice the;perce'nt v.age of sulphur plus .30% to 80%. lIn this form, Y the rolled metal 'is heated to above `the-'critical temperature but not morefthanabou't 200JF.,

thereaboye, and.fisthen -cooled through the. critilcal temperature at agspeed such as to retain the combinedjcarbonfintlie matrix in thezform of pearlite'onsorbite, andis then fheld at or re-v heated to. the; spheroidizing range (about 1200 to 1300 F.) fora sufficienttimeto.spheroldizeV the pearlte or sorbite `toxthel desired degree.

We haye successfully used the following-method which is given as a concrete 'exa'.mvple off-aproa cedure utilizing the third form of subsequent heat treatment. A white ironingot ofthe composiV tionlfset forthl .underjthe second `example was made andheated '.to 1700 F., where; it was held for .twenty-four hours.' yThe metal was then .broughteto-a temperatureL of 1950?*SF., androlled in the manner set forth in the` firstiexample.

After e` rolling operation was complete, the material as cooled atthe-4 rate of-about 600.? per.

hour `through the critical temperature .(in vthis case about 1375 F.) and then held at `a temperaturefof about 1275" F., for twenty-four hours, whereupon it rwas cooled. to room temperature. This Ymetal had a matrix -of finely` spheroidized crystals, and elongated clustersl of graphite: were embedded in this matrix. Fig. 4 illustrates the structure thus obtained.

It will be seen that in.ou r processweuse'l as a starting point white iron. This enables usk to control' the structure of the vmetal throughout the various subsequent operations to produce the proper microstructure atv the proper time.'y Thus,

by. starting with white iron, weare enabled tor cementite, uniformlydistributed through ferrite so 4heat treat, the metal priorvtofthe rolling operations for thebest economy 'and sofasrto obmetal, '.that is, ,the structure in which the lmetal is the most plastic and in ,whichzfthe precipitated carbonyis most favorable. to such operations.

kLikewise-,through these steps, themetal emerges from 'the rolling operations in a structural condition mst favorable to subsequent heat treatment and to the production of, a desired product.

During the rolling operations, the metal cools to various indefinite andv variable temperatures` and is in many instances reheated and again cools during the additional rolling.4 DFurthertainga most favorable rolling structurenof the i tions whenL at different temperaturesd Various f parts of the same piece of metal may be sub' more', the various ingots will require diierent amounts of rolling and reach the desired reducjected to different conditions so that there may be a variation in the structure 4of each piece. As a result of all ofl` these variables; the physical Vproperties of the material 'or different pieces of the material as it emerges from the rolling'operation may not be uniform;` nevertheless, where there are no special requirements in the rolled metal the subsequent heat treatment' may in many instances be dispensedwithfand the metal' used directly as it comes from the rolls. In order to overcomethis lack 'of uniformity, we may subject the metal after rolling to a heat treatmentr for the purpose of imparting uniform characteristics to the product;v As another phase of the invention, we regulate the analysis of the white makes it commercially Afeasible to roll-such metal, but prepares the iron for the subsequent heat treatment.` Y

Newand novel products result' from the method above disclosed. These are briey of four types.

In .each type the graphite and otherinclusions are inthe form of elongatedior at'tned'deposits in substantially parallel relationship, such as clearly shown in Figure 1. One type of product consists of the metal as rolled without subse-k quent heat treatment; "in" a second form the matrix consists-of ferrite as illustrated in Fig. 2,

in athird form the matrix is pearlite or sorbite as illustrated in Fig. 3, and in a fourth form the or other shapes` of graphitic iron which includes matrix is`ofV spheroidized cementite uniformly distributed through ferrite'crystals' as shown inv Fig. 4.

Cast iron and metals containing graphite have long been well known fori-their corrosion resistance properties, particularly corrosion due to atmospheric exposure and'lunderground services.

For thisuse the metals vmust in many cases be thinin section; In theipast, metals Vfor this purpose have been non-ferrous metals or steel alloys which contain `substantial quantities of other metals, such as chromium, copper, nickel, etc.

These alloys are-relatively expensive. The dimculty has been that while iron containing graph ite has inthe past been available in the form ofl individually' cast plates, there is a limitation to the minimum section whichfcan be ycast of graphite'bearing iron. That is, in the past there has been no method of making graphite bearing iron in sheetsof suillcient size andthinness of section to permit the general use of such metals for corrosion resistance purposes or-for other purposes Vto which such metal in the sheet form might be adapted. Our method completely' obviates this difllculty and permits the rolling of lsuch metall in very thinsection and in relatively large sheetsl The method brings about the production of sheets of graphite bearing metal with almosty the same facility with which steel sheets are made, thus opening up a large `varietyof new materials for thesheet metal industry. 'I'he method also permits the production of graphite bearing metal in shapes and sizes which have heretofore not been obtainable.

A number of uses for the metals made in accordance with our method might be listed. The metal made in accordance with the rst example l'the like.

anceandcorrosion resistance are important, such, 1 for example, as in thelmanufacture of elevator buckets., Metalmadein accordance with the third example :possesses corrosion resistance as well as high strength andrductility, and is voi' particular value in the manufacture of such materials as ship plates, coal hoppers,,.tanks,. and

4We have dealt throughout this specication with'the composition' of the metal as this is concerned withfcertain well known constituents. lt'willl be'understood, however, that numerous otherelementsjmay be present in the metal or may be adcled thereto which will, or may, effect the method or theproduct, some benecially and some otherwise. 1 This-is a coritinuation of copending applicavtion of Duncan 5P. j Forbes and Erwin J. Mohr, Serial N og'Y 658,764,"f1ed February 27, 19331 While `we havethus described and illustrated specific embodiments-) of our invention, we are aware that numerous alterations and changes may be made v-withoutdeparting from the spirit -of the invention and the scope of the appended claims, in which Wnatis claimed is:

1. The-n thodof making rolled sheets, bars or other shapes of graphitic iron, comprising holdingfr graphitizable white iron ingots at a.l

, graphitizing temperatureuntil the majorpart of the massive cementitehasbeen decomposed, and thereafter rolling tli'eingots at altemperature at "whichfthe metal is austenitic.

`2.'Tlfiejmeth v d of makingrolled shee'ts, bars the steps offhat treating the ironto decompose the.' massive cementite, rollingy the iron tothe metalis austeniticgand heat treating the rolled iron in a manner dependentupon the chemical composition 'o f .the metal to produce any of a pluralityjof uniform tures of the metal."` f 3 The method of making `rolled sheets, bars or other shapes of graphitic' iron,- Acomprising predetermined microstrucv"bringingjjgraphitizable 'white iron; to a .rolling temperature' above that separating the `pearlite 4. The method rof making rolled sheets, plates orbars `of graphitic iron, ycomprising heating a wholly or partially graphitizedV white iron of an -analysis ywithin the following limitscarbon not less than about 1.5%, percentage of carbon plus percentage of silicon greater than about 2.9%,

` manganese equal to twice the; percentage 'of sul- `'desired'shape at a temperature at which the phur plus about .10 to .30%. to a rolling temperature above that'separating the pearlite and austeniteY phases, rollingjsaid iron substantially at said temperature, and thereafter holding the. rolledmetal at a temperature belowthe'stable` critical temperature until the `combined carbon has been substantiallycompletely precipitated as graphite.

5. The method ofmaking rolled sheets, plates Yor bars-of graphitic iron, comprising heating a combined carbon in the matrix in the form of pearlite.

6. The method of making rolled sheets, plates or bars of graphitic iron, comprising heating a wholly or partially graphitized White iron of an analysis within the following limits-carbon not less than 1.5%, percentage of carbon plus percentage of silicon greater than 2.9%, manganese equal to twice the percentage of sulphur plus .10% to .80%, to the rolling temperature, rolling said iron, cooling the iron from a point slightly above the critical range through the critical range at a speed such as to retain the combined carbon in the matrix in the form of pearlite and then holding the metal at a spheroidizing temperature to spheroidize the pearlite.

7. The method of making rolled sheetsplates or bars of graphtic iron which consists in producing ingots of White cast iron, heating said ingots to substantially decompose the cementite, causing said ingots to be brought to a high temperature above l800 F., but below the melting pointof the metal, and reducing saidl ingots to rolled formsof av desired size by rollingthe ingots first while at substantially said high temperature and then successively while the ingots are at a y temperature above about 1800 F., reheating of the ingots between successive rolling operations being resorted to if necessary to maintain the ingots at a temperature above about 1800 F., until so reduced. y .A y Y 8.- The making ofrolled` sheets, plates or bars by producing ingots of white cast iron, heat treating the ingots to substantially decompose the cementite, and reducing said ingots to the desired form by rolling, the ingots being maintained at a temperature above about-l800 F., during the rolling.

9. A metal product comprising rolled graphitic iron having a matrix of pearlite containing subi stantially uniformly distorted velongated deposits of free graphite uniformly. distributed therein in approximately'lparallel relation.

10. A metal product comprising rolled graphitic iron having a matrix yof spheroidizedr cementite uniformly distributed through ferrite crystals and f containing uniformly distributed elongated de' posits of free graphite arranged in approximately parallel relation. r v

DUNCAN P. FORBES.`

LINDA E. MOI-IR, Administratri of the Estate of Erwin J. Mohr,

Deceased.

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