heat treatment steel

7/29/2019 Heat Treatment Steel

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UNITEDSTATESDEPA RTMENTOFCOMMERCE JohnT.Connor,SecretaryNATIONALBURE AUOFTANDARDS A .V.stin,Director

r

HeatTreatmentandPropertiesofIronandSteel

ThomasG .Digges,Samuel.Rosenberg,ndGlennW .Geil

DISTRIBUTION STATEMENT A Approved fo r Public ReleaseDistributionUnlimited

NationalBureauofStandardsMonograph8IssuedNovember,96 6

SupersedesCircular95ndMonograph8 ForaleyheuperintendentofDocuments, .S .overnmentPrintingOffice,Washington, .C .0402 rice5ents

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Contents

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1 .ntroduction g. 2.ropertiesofro n2.1.ransformationemperatures2.2.Mechanical roperties3 .lloysofro nndarbon3 . 1 .ron-carbon hasediagram3 .2Correlat ion of mechanical properties withmicrostructuresoflowlyooled.carbonteels4.ecomposit ionofaustenite4.1.sothermalransformationa.Topearliteb.Toainite 1 0. c.Tomartensite4.2.Continuousooling5.eatreatmentofteels5.1.Annealing 0a.ullannealing__0b.rocessannealing0c.pheroidizing05.2.ormalizing 05.3 . ardeninga .Effectofmass__1 5.4.Tempering5.5.Caseardening4a.Carburizing 4 n,b.yanidingc.arbonitriding6d.Nitriding Q 5.6.urfaceardening7 a .nductionhardening7 b.l ameardening7 5.7.pecialtreatments7 a.Austempering7 b.Martempering8 c.Coldtreatment8 d.Ausforming 8 6.ardenabil ity g7 .ea ttreatmentofcastirons07 . 1 .Relievinges idualtressesaging)07.2.Annealing 0a.Malleabil iz ing 27.3 .ormalizing,quenching,and tempering-27.4.pecialheatreatments2 1 2. Practicalonsiderations8 . 1 .urnacesan dsaltbathsa.rotective tmospheresb.emperature measurement an dcontrol8.2. uenchingmediand ccessories8.3 .elationofdesigntoheattreatmentNomenclature an d chemical composit ions ofsteels9.1.tructuralteels9.2.Toolteels9.3.tainlessan dheatresistingsteelsRecommendedheattreatments10 . 1 .tructuralteels10.2.oo lteels10 . 3 .tainlessndheatesistingteelsa.roup IHardenable chromiumsteelsmartensiticndag- netic)b.Group IINonhardenable chro-miumteelsferriticndma g -netic)c.Group IIINonhardenable chro-mium-nickelndhromium-nickel-manganese steels (aus-teniticndnonmagnet ic)Propertiesnd se softeels1 1 . 1 .tructuralteelsa .Plainarbontructuralteelsb.Alloystructuralteels11 .2 .oo lteels11 . 3 .tainlessnd ea tesistingteelsa.roup IHardenable chromiumsteelsmartensiticndag- netic)b.roup IINonhardenable chro-miumteelsferriticndmag-netic)c.roup IIINonhardenable chro-mium-nickelndhromium-nickel-manganeseteelsaus-steniticnd onmagnet ic)d.recipitation-hardenable stainlesssteels11.4. ickelmaragingsteelsSelectedeferencesLibraryofCongressatalogardo .6-61523


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HeatTreatmentndropertiesfronndteelThomas .Digges,1amuel.osenberg,1nd lennW .Geil

ThisMonographisarevisionof th epreviousNB SMonograph18.tspurposeis to rovidennderstanding fth e ea treatment fronndteels, rincipallyothoseunacquaintedwiththissubject.hebasicprinciplesinvolvedinth eheattreat-mentfhesematerialsreresentednimplifiedorm.eneralea treatment proceduresaregivenfo rannealing,normalizing,hardening,tempering,casehardening,surfaceardening,ndpecialreatmentsuc hsustempenng,usforming,mar-temperingndoldreatment.hemicalompositions,ea treatments,ndomepropertiesndusesar epresentedorstructuralteels,toolteels,tainlessan dheat-resistingteels,recipitation-hardenabletainlessteelsndickel-maragingteels.1 . Introduction

TheNationalBureauofStandardseceivesmanyequestsoreneralnformationon -cerningheheatreatment fro nndteelan dordirectionsndxplanationsfuch processes.hi sMonographhas beenpreparedto answersuchinquiriesandto giveinsimpli-fiedorm workingknowledge fhebasictheoreticalan dpracticalprinciplesinvolvedin th eeatreatmentfro nndteel.he effectsofvarioustreatmentsonthestructuresan dmechanicalproperties fhesematerialsareescribed.an yheoreticalspectsrediscussednlybrieflyoromittedentirely,ndinomenstances,echnicaldetailshavebeenneglectedorimplicity.hepresentMono-graphsupersedesCircular495,whichwaspub-lishedn950,ndMonograph81960) .Heattreatmentmaybedefinedasanopera- tionorcombinationofoperationsthatinvolvesth eheatingan dcoolingofasolidmetaloralloyforthepurpose fobtainingcertaindesirableconditionsorproperties.tisusuallydesiredto reserve,s earlysossible,heorm,dimensions,ndurfacefheieceeingtreated.Steelsan dcastironsareessentiallyalloysofironndarbon,modifiedbyhepresence f

otherlements.teelay eefinedsnalloyofironan dcarbonwithorwithoutotheralloyinglements)ontaininglesshanbout2.0ercentfarbon,sefullymalleablerforgeablesnitiallyast.as tro nmaybe definedasan alloyofironan dcarbonwithorwithouttherlloyinglements)ontaining morehan .0percentofarbon,not suallymalleable rorgeablesnitiallyast.orreasonsthatwillbeapparentlater,thedivid-in glinebetweensteelsan dcastironsistaken at .0percentofarbon,venthoughcertain specialteelsontainarboninxcess fthisamount.ndditionoarbon,ourtherelements renormallypresentinsteelsan din castrons.hesereanganese,ilicon,phosphorus,ndulfur.Steelsayeroadlylassifiedntowotypes,1 )carbonan d2 )lloy.arbonsteelsow eheirropertieshieflyohearbon.Theyrerequentlyalledtraightorplaincarbonsteels.lloysteelsarethosetowhichoneormorealloyingelementsareaddedin suf-ficientmountsomodifyertainproperties.Thepropertiesofcastironalsom aybemodi-fiedbyth epresenceofalloyingelementssuchirons arecalledalloycastirons.2 . Propertiesofron

Sincero nshe asic lement fteel,knowledge fsomeoftspropertiessapre-requisiteonnderstanding fheunda-mentalprinciplesunderlying theheattreatmentofsteels.2.1 . TransformationTemperatures

Ifamoltensampleofpureironwereallowedtocoolslowlyandth etemperatureoftheironweremeasuredategularntervals,ndeal- 1Retired.

izedequilibrium)ime-temperature plotofth e datawouldappearasshowninfigure1 .hediscontinuitiestemperaturerrests)nhiscurveareausedyhysicalhangesnheiron.Thefirstarrestat2,800Fmarksth etem-peratureatwhichtheironfreezes.he otherarrestsknownsransformationempera- turesorcriticalpoints)marktemperaturesatwhichertainnternalhangesak e lacen th eolidron.om efheseemperaturesare erymportantnheheatreatment fsteel.


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FIGURE. Idealizedcoolingcurvefor pureiron.Theatomsinal lsolidmetalsarearrangedinsomedefinitegeometricorcrystallographic)pattern.heatomsiniron,immediately afterfreezing,arearrangednwhatsermedhebody-centeredubicystem.nhisrystalstructuretheunitcellconsistsofaubewithanronatomateachoftheeightcornersandanotherinthecenterfig.2,a).achofthemanyndividualrainscrystals)fwhichtheolidmetalsomposedsbuiltupofaveryargenumberofheseunitells, llori-entedalikeinthesamegrain.hishigh-tem-peratureormofronsknownasdelta8)iron.At2,550FtheApoint),ronundergoes|anallotropicransformationfig.1);hats,* therrangementofheatomsnhecrystal;changes.heewrystaltructuresace-icenteredcubic,andtheunitcellagainconsists;

ofaubewithanronatomateachofhe;eightcorners,butwithanironatominthecen-jterofeachofthesixfacesinsteadofonein the,'centerofheubefig. ,b).hisorms; knownasgammay)ron.t1,670Fthe;A 3oint) ironndergoesnotherllotropic*!

FIGURE. Crystalstructureofiron.(a)Body-centeredcubic(alphaan ddeltaIron);b)Face-centeredcubic (gammaIron).transformationndevertsoheody-centeredubicsystemfig. ,a).hisstruc-ture,whichiscrystallographicallythesameasdeltaron,stableat llemperatures elow theA 3pointandsknownasalphaa)ron(fig.,A).hearrestat ,420Fknown astheA 2point)snotcausedbyanallotropicchange,hats,achangencrystaltructure.Itmarksheemperaturetwhichrone- comeserromagneticandshereforeermedthemagnetictransition.bovethistempera-tureironisnonmagnetic.Thesevarioustemperaturearrestsoncoolingarecausedbyevolutionsofheat.nheating,therrestsccurneverserderndrecausedybsorptionfeat.heriticalpointsmaybedetectedalsobysuddenchangesinotherphysicalproperties,ornstance,x- pansivityorelectricalconductivity.

2.2. MechanicalPropertiesIronselativelyoft,eak* ,nductile andannot eppreciablyhardenedbyheattreatment.tstensilestrengthat,room temper-

aturesabout40 , 000lb/in.2 ,tsyieldstrengthisabout20 , 000lb/in.2 ,anditsBrinellhardnessisabout80 .hemodulusofelasticityisabout29 , 000 , 000lb/in.2 .hestrengthandhardnesscanbencreased,withcorrespondingdecreaseinductility,bycoldworking.3 . AlloysofronandCarbon

Theropertiesfronreffected.verymarkedlyydditionsfarbon.thouldbeealizedhatndiscussingron-carbcn l- loys,weactuallyaredealingwithplaincarbonsteelsandcastirons.3.1 . Iron-CarbonPhaseDiagram

Theompleteron-carbonphaseorconsti-tutional)iagramepresentsheelationshipbetweentemperatures,compositions,andstruc-turesofal lphasesthatmaybeformedbyiron

andarbonnderonditionsfquilibrium(verylo wooling).portionfhisia -gramor lloysangingupo .7percent fcarbonseproducednigure;hepperlimitofcarbonncastronsusuallynotnexcessof5percent.helefthandboundaryoftheiagramepresentsureron,ndhe right-handboundaryepresentsheompoundironcarbide,Fe3C,commonlycalledcementite.* Ironrownsingle-crystalwhiskersmayexhibitastoundinglyhightrengths.

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6.7% C STEELSAS T IRONS

C ARB O N , BYWEIGHTFIGURE. Iron-carbonphasediagram.

Theeginningfreezingfheariousiron-carbonalloysisgivenbythecurveABCD,termedheiquidusurve.hendingffreezingsivenyheurveHJECF,termedheoliduscurve.hereezingpointofronsoweredbyheadditionofcarbon(upo4.3%)ndheesultant l loysreezeoveraangenemperaturensteadofataconstantemperatureasoeshepuremetaliron.healloycontaining4 .3percentofcar-bon,calledtheeutecticalloyofironandcemen-tite,freezesataconstanttemperatureasindi-catedyheoint.hisemperatures2,065F,considerablybelowthefreezingpointofpureiron.Carbonasnmportantffectponhetransformationemperaturescriticalpoints)ofiron.traisestheA 4temperatureandlow-erstheA 3.hiseffectontheA 3temperatureiserymportantnheeatreatmentfcarbonandalloystructuralsteels,whilethatontheA 4smportantnheheatreatmentofcertainighlloyteels,articularlyfhestainlesstypes.Itispossibleforsolidirontoabsorbordis- solvecarbon,theamountbeingdependentuponthecrystalstructureoftheronandhetem-

perature.hebody-centeredalphaordelta)ironcan dissolvebutlittlecarbon,whereastheface-centeredgamma)roncandissolveacon-siderablemount,hemaximumeingabout2 .0ercentat ,065Ffig.).hisolid solutionfarbonnammaronsermedaustenite.hesolidsolutionofcarbonindeltaironistermeddeltaferrite,andthesolidsolu-tionofcarbonnalpharonsermedalphaferrite,or,moresimply,ferrite.Theechanismfolidificationfron-carbon lloys,especiallyhosecontainingessthanabout0 .6percentofcarbon,israther com-plicatedandsofnomportancenheheattreatmentofcarbonsteelsandcastirons.tis sufficientonowhatallron-carbonlloyscontaininglessthan2 .0 percentofcarbonthatis ,steel)will,immediatelyorsoonaftersolidi- ficationiscomplete,consistofthesinglephaseaustenite.astironswillconsistoftwophasesimmediatelyafterolidificationausteniteandcementiteFe3C).ndersomeconditionsthiscementiteormedonoolingthroughthetem-peraturehorizontalECFwilldecomposepartlyorompletelyntoustenitendraphite(carbon).


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2000

1800

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1000

600

400-

Austenite2065"F___

5^670F &cj!AusteniteA.*?._" T__o\|420F A, ~_^ CementiteF 1 1 1 1 _ Peorlite with l1 1 1 Peorliteith Excess Ferrit

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i-Excessementite

111 1 1 1 1 1 0.2 0.6.8.0.2 CARBON.%

FIGURE. Phasediagram forcarbonsteels.1 .6

Thepartoftheiron-carbondiagramthatis concernedwithheheatreatmentofteelsreproducednanexpandedcalenigure .Regardlessofhecarboncontent,teelexistsasusteniteboveheineOSE.teelfcompositionS0 .80%ofcarbon)sdesignatedas"eutectoid"teel,ndhosewithowerorhighercarbonas"hypoeutectoid"andhyper-,eutectoid,"respectively.Aeutectoidteel,whenooledatverylow!ratesromtemperatureswithinheausteniticfield,undergoes ochangeuntilheempera-turehorizontalPSKseached.tthisem-peratureknownasheA !emperature),heausteniteransformsompletelyoanaggre-gateofferriteandcementitehavingatypicallamellartructurefig., nd).hisaggregatesnownsearlitendhextemperatures,herefore,requentlyeferredtoshepearlitepoint.inceheA xrans-formationnvolvesheransformationofus- tenitetopearlitewhichcontainscementiteFe3C),pureirondoesnotpossessanA xtrans-formationfig.).heoretically,ronmustbe lloyedwithaminimumof0.03percentofcarbonbeforethefirstminutetracesofpearlitecanbeformedoncoolingpointP,fig.4).fthesteelisheldatatemperature justbelowA 1 ((eitherduringcoolingorheating),thecarbideinhepearliteendsooalescentoglobulesorpheroids.hishenomenon,nownsspheroidization,willbediscussedsubsequently.Hypoeutectoidsteelslessthan0 .80%ofcar-bon),whenlowlyooledromemperatures

abovetheA 3,begintoprecipitateferritewhen theA 3in eGOSfig. )seached.sthetemperaturedropsfromtheA 3toA x,thepre- cipitationofferriteincreasesprogressivelyandthemountfheemainingustenitee-creasesprogressively,tscarboncontentbeingincreased.ttheA xtemperaturetheremain-ingusteniteeachesutectoidomposition(0 .80%ofcarbonpointS,ig .4)nd, po nfurtherooling,ransformsompletelyntopearlite.hemicrostructuresofslowlycooledhypoeutectoidsteelsthusconsistofmixturesofferritendearlitefig., nd).helowerthecarboncontent,thehigheristhetem-peratureatwhichferritebeginstoprecipitateandhereatershemountnheinalstructure.Hypereutectoid,teelsmorehan .80% fcarbon)whenslowlycooledfromtemperaturesaboveheA cm ,beginoprecipitatecementitewhentheA cmlineSEfig.4)sreached.sthetemperaturedropsfromtheA cmtoA x,theprecipitationfementitencreasesrogres-sivelyandheamountofheemainingus-tenitedecreasesprogressively,tscarbonon -tenteingepleted.the xemperaturetheremainingaustenitereacheseutectoidcom-position0.80%ofcarbon)nd,uponfurthercooling,ransformsompletelyntoearliteThemicrostructuresofslowlycooledhypereu-tectoidteelshusonsistfixturesfcementiteandpearlitefig.5,F).hehigherthecarboncontent,hehighersheemper-atureatwhichcementitebeginsoprecipitate

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A ,Ferrite(airon). A ll grainsar eof thesamecomposition. X 100 .B,0.25%carbon. Lightareasar eferritegrains. Darkareasare pearlite. X 1 0 0 .C,0.5%carbon. SameasBbuthighercarboncontentresultsinmorepearliteandlessferrite. X 100 .D,0.8%carbon. A llpearlite. X 100 .E,SameasD. Athighermagnificationthelamellarstructureof pearliteisreadilyobserved. X 500 .F, .3 %carbon. Pearliteplusexcesscementiteas network. X 100 .A lletchedwitheitherpicralor nital.andhereatershemountnheinalstructure.TheemperatureangebetweenheA ,andA 3pointssalledhecriticalorransforma-tionange.heoretically,heriticalointsinnyteelhouldccurtboutheametemperaturesoneitherheatingorcoolingveryslowly.ractically,however,theydonotsince theA ,andA ,points,affectedbutlightlyby theate fheating,areaffectedremendouslybytherateofcooling.apidratesofheatingraisethesepointsonlyslightly,butrapidatesofoolingowerhetemperaturesoftransfor-

mationconsiderably.odifferentiatebetweenthecriticalpoints nheatingandooling,hesmallettersc"forchauffage"romheFrench,eaningeating)ndr"for"refroidissement"romherench,meaningcooling)redded.heerminologyfhecriticalpointsthusbecomesA c 3,Ar3,Ac,,Aretc.heettere"sse doesignateheoccurrencefheointsnderonditionsfextremelyslowoolingonheassumptionhatthisrepresentsequilibriumconditions"e"orequilibrium);ornstance,hee3,e! ,ndAe([1 |.L


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3 . 2 . Correlation of echanicalropertiesWithMicrostructuresofSlowlyCooledCarbonSteelsSomeechanicalropertiesfearliteformeduringlowoolingf utectoid(0.80% fcarbon)teelare approximatelyas follows:Tensiles trength115,000b/in*.Yieldstrength60,000lb/in1 .Brindellhardnessnumber200.Theamountofpearlitepresentin slowlycooledhypoeutectoidsteelsainearfunction ofth ecarboncontent,varyingfrom no pearlite,whenoarbonsresentth e erylightamountofcarbonsolublein alphaironmay be neglected),oll earliteat .80 ercent fcarbon.he balanceofth estructureofhypo-eutectoidsteelsiscomposedofferrite,th eme -chanicalproperties fwhichweregivennaprecedingsection.inceth emechanicalprop-ertiesofaggregatesofferritean dpearliteare functionsofth erelativeamountsofthesetw o constituents,heechanicalropertiesfslowlycooledhypoeutectoidsteelsarealsolin-earunctions fhearbonontent, arying

betweenthoseofironatnocarbonto thoseofpearliteat0.80percentofcarbonfig.6).4 . Decomposit ionofAustenite

Inlloys fro nndarbon,ustenites^ioL noSlyatemperaturesbovehee x (1,330F).elowthistemperatureitdecom-posesntomixtures ferritendementite(ironcarbide).heen dproductorfinalstruc- tureisgreatlyinfluencedbyth etemperatureatwhichhetransformation ccurs,ndthisnturn,snfluencedyheatefooling,mceth emechanicalpropertiesmay be variedoverawiderange,depending on th e decomposi- tionproductsofth eparentaustenite,aknowl-edgeofho waustenitedecomposesan dth efac- torsnfluencingtsecessaryor learunderstandingofth eheatt reatmentofsteel,inerogressiveransformationfustenite underonditionsfquilibriumextremelyslowcooling)hasbeendescribed.ractically however,teelisnotcooledunderequilibriumconditions,an dconsequentlyth ecriticalpointsoncoolingalwaysoccuratlowertemperaturesthanindicatedmfigure 4.Ifamples fsteel,ayofeutectoidarboncontentorheake fimplicity, reooledfromboveheext raduallyncreasing rates, th eorrespondingArransformationcur!L -owerandoweremperaturesfig.7).histransformation isdistinguished from that ccurringunderxtremelylowates fcoolingAr,)yth edesignationAr\sth eraj.o,0?lmSofhisteelsncreased,n additionalransformationtermedtheAr"or

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FIOURE. Relationofmechanicalpropertiesandstructuretocarboncontentofslowlycoo ledcarbonsteels.

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AUSTENITE

PEARLITEPEARLITE

+ MARTENSITE MARTENSITEINCREASEDRATEOFCOOLING-

FIGURE.chematicllustrationhowingheffectofrateofoolingnheransformationemperaturesnde- compositionroductsfustenitefutectoidarbonsteel.L


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r M .)ppearstelativelyowemperatures(about4 30F).ftherateofcoolingisstillfurtherncreased,heAr'ransformationssuppressedntirelyndnlyheAr"rans-formationsevident.tshouldbenotedhattheemperatureoftheAr"snotaffectedbytherateofcooling,whereasthetemperatureoftheAr'maybedepressedoasowasabout1 ,050Finthisparticularsteel.Theproductof theAr'transformationisfine pearlite.sheemperaturefheAr'sgraduallyowered,heamellartructureftheresultingpearlitebecomescorrespondinglyfinerandthesteelbecomesharderandstronger.TheproductoftheAr"transformationismar-tensitefig.,,nd5 ,A),whichshehardestandmostbrittleofthetransformationproductsofausteniteandischaracterizedbyatypicalacicularstructure.ThephenomenonofheoccurrenceofboththeAr'andAr"ransformationssknownasthesplittransformation.heresultantmicro-structuresofteelsooledatuchatesastoundergoasplittransformationconsistofvary-ingmountsfineearlitendmartensite(fig. ,C).heactualamountsofthesetwoconstituentsarefunctionsoftheratesofcool-ing,theslowerratesresultinginmorepearliteandlessmartensite,andthefasterratesresult-inginmoremartensiteandlesspearlite.

4.1. IsothermalTransformation Theoursefransformationfustenitewhenthesteelisquenchedtoandheldatvari-ousconstantelevatedemperatureevelsiso-thermaltransformation)sconvenientlyshownby iagramnownshe-curvealsotermedheTTdiagramforime,emper-ature,andransformation).uchadiagramforeutectoidcarbonsteelshownnfigure8andhediscussionofhisigurewillbeon-finedtosteelofthisparticularcomposition.

a.oPearliteAustenitecontaining0.80percentofcarbon,cooled uicklyoandheldat , 300F,oesnotbegintodecomposetransform)untilafterabout5min,anddoesnotcompletelydecom-poseuntilafterabout5hrfig.8).hus,attemperaturesustbelowheAd,austenitesstableforaconsiderableengthoftime.heproductofhedecompositionofusteniteatthistemperatureiscoarsepearliteofrelativelylo wardness.fheustenitesuicklycooledoandheldataomewhatowerem-perature,ay , 200F,ecompositionbeginsinabout5se candiscompletedafterabout3 0 sec,heesultantearliteeinginerndharderhanhatormedt , 300F.tatemperatureofabout , 050F,heaustenitedecomposesextremelyrapidly,onlyabout1se celapsingbeforethetransformationstartsand5

os T IME ,SECONDSFIGURE. Isothermalransformationiagram (S-curve) fo reutectoidcarbon steel.

(Metals Handbook,1948 edit ion, page 08.) Thehardness of th e structures formedat th evarioustemperaturesis Rivenbyth escaleon th eright.se cbeforeitiscompleted.heresultantpear-litesextremelyfineandtshardnesssela-tivelyhigh.hisregionoftheS-curvewheredecompositionfusteniteoin eearliteproceedssorapidlyistermedthe"nose"ofthecurve.

b. ToBainiteIftheausteniteisooledunchangedtotem-peratureselowheosefhe-curve (1 ,050F),heimeortsecompositionbeginstoincreasefig.8).hefinalproductofdecompositionnowisnotpearlite,butanew acicularconstituentcalledbainitefig.5,E)possessingnusualoughnesswithardnessevengreaterthanthatofveryfinepearlite.Depending nheemperature,hen,aer- tainfinitentervaloftimesnecessarybeforeaustenitestartstotransformintoeitherpear-liteorbainite.dditionalimesnecessarybeforeheransformationsareompleted.c.oMartensite If theausteniteiscooledunchangedtoarel- ativelyowemperaturebelowabout4 30Ffortheeutectoidcarbonsteelunderconsidera-tion),artialransformationakeslacen-stantaneously;theproductoftransformationis martensite.usteniteransformsntomar-tensiteveremperatureangendheamounthatransformss unction fhetemperature.nlyminutemountsil lotransformatabout 3 0F;ractically ll ftheustenitewilleransformedtbout1 75F.heeginningfhisransforma-tionangesermedhemartensitestart)ndheendoftherangestermedheM tmartensitefinish).slongasthetem-peratureseldconstantwithinheM s M rrange,hatportionofheaustenitehatdoesnotransformnstantaneouslyomartensite

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remainsntransformedoronsiderablelengthfime,ventuallyransformingobainite.Inordinaryheattreatmentoftheplaincar-bonteels,ustenitedoesotransformnto bainite.ransformationoftheaustenitetakesplaceeitheraboveoratthenoseoftheS-curve,formingearlite,rnassinghroughheM s M frange,formingmartensiteorboth.tisvidenthatnrderorusteniteoetransformedentirelyntomartensite,tmustbeooledufficientlyapidlyohatheem -peratureofthesteelisloweredpastthenoseoftheS-curvenes simehansnecessaryortransformationotartthisemperature.Ifhissnotccomplished,artofheteeltransformsntoearliteathehighemper-atureAr'),ndheemainderransformsintomartensiteatheowemperatureAr"orM,Fftemperaturerange).hisexplainsthehenomenonfheplitransformationdescribedpreviously.4.2. ContinuousCooling

Figure9epresentsatheoreticalS-curveonwhicharesuperimposedfivetheoreticalcooling curves.urvesAoEepresentsuccessivelysloweratesofooling,aswouldbeobtained,forinstance,bycoolinginicedbrine,water,oil,air,andinthefurnace,respectively.ThesteelcooledaccordingtocurveEbeginstoransformattemperaturetandompletestransformationatt2;thefinalproductiscoarsepearlitewithelativelyowhardness.hen cooledccordingourve,ransformationbeginsat3andsompletedatt;heinalproductsin eearlitendtsardnesssgreaterthanthesteelcooledaccordingtocurveE.henooledaccordingtocurveC,rans-formationeginst ndsnlyartiallycompletewhenemperature6seached;heproductofthispartialransformationsveryfinepearlite.heemainderofheaustenitedoesnotdecomposeuntilheM ,emperatureiseached,whenteginsoransformomartensite,completinghisransformationatthe femperature.heinaltructuresthenamixtureoffinepearliteandmartensite(typicalfncompletelyhardenedteel-f-fre-quentlytermed"slackquenched"steel)withahigherardnesshanwasbtainedwithhesteelcooledaccordingtocurveD.herate ofcoolingepresentedyurve sustuffi-cienttontersectthenoseoftheS-curve,on- sequentlyonly aminuteamountof theaustenitedecomposesintofinepearliteattemperaturet7;theemainderfheustenitesnchangeduntilhemartensiteransformationangesreached.fheteelsooledtalightlyfasterate,ohatoransformationakesplaceathe oseofhe-curve,heteelscompletelyhardened. Thisparticularates

FIGURE.chematicdiagramllustratingheelatione- tweenheS-curve,continuousoolingurves,ndesult-ingmicrostructuresofeutectoidcarbonsteel.Microstructures:A,martensite;B,martensitewith traceof veryfine pearlitedark):C ,martensitean der yfinepearlite;D,(ineearlite;,coarsepearlite. Alletched with nital. X 500 .

termedhecriticaloolingateandsdefinedashelowestateatwhichheteelan ecooledandyetbecompletelyhardened.incethisateannoteirectlyetermined,heratendicatedycurveB,roducing nlyatraceofin epearlitefig. ,B),srequently8


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usedas th ecriticalcoolingrate. The hardness cST5"V*btained-ampleiJL\fe?rate'


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5.1. AnnealingAnnealingisaprocessinvolvingheatingandcooling,suallyappliedo roduceoftening.Thetermalsorefersto treatmentsintendedtoaltermechanicalrhysicalroperties,ro-duceadefinitemicrostructure,orremovegases.Thetemperatureoftheoperationandtherateofcoolingdependuponthematerialbeingan-nealedandthepurposeofthetreatment.

a. FoilAnnealingFullnnealings ofteningrocessnwhichasteelisheatedtoatemperatureabove theransformationangeA cs)nd,fterbeingheldforasufficienttimeatthistemper-ature,scooledslowlytoatemperaturebelowthetransformationangeArt).hesteelisordinarilyallowedtocoolslowlyinthefurnace,althoughitmayberemovedandcooledinsomemediumuchasmica,ime,orashes,hatn-suresaslowrateofcooling.Sinceheransformationemperaturesareaffectedbythecarboncontent,tsapparentthatthehighercarbonteelscanbeullyan-nealedatoweremperatureshanheowercarbonsteels.ntermsofthediagramshowninfigure4 ,teelsmustbeheatedtoabovethelineGOSK.hetemperatureangenormallyusedforfullannealingis25to50degFabove thisinethepperritical),shownnfigure1 1 .Themicrostructuresfheypoeutectoidsteel -> thatresultafterfullannealingarequitesimilartothoseshownfortheequilibriumcon-ditionsfig., nd).utectoidndhypereutectoidteelsrequentlypheroidizepartiallyorompletely nullannealingse elaterectionandig .2 ,D).b. ProcessAnnealing Processannealing,requentlytermedstress-reliefnnealing,ssuallyppliedoold-workedowcarbonteelsupoabout .25% ofarbon)ooftenheteelufficientlyoallowurtherold-working.heteelsusuallyheatedcloseto ,butbelow,theA citem-peraturefig.1).fheteelsnoto efurtherold-worked,utelieffnternalstressessdesired,aowerangeoftempera-ture il lufficeabout,000F).atefcoolingisimmaterial.Thisypeofannealwillauseecrystalliza-

tionandofteningofheold-workederritegrains,butusuallywillnotaffecttherelativelysmallamountsofcold-workedpearlite.ypi-calstructuresofcold-worked,process-annealed,andfullyannealedow-carbonteelareshowninfigure 2,A ,B,andC,espectively.

O < X 2 0 0.40 O) 0.80 UX > 1.20 1.40 1 . 6 0 C A R B O N%

FIQUBE 1 1 . Recommended temperatureangesor heattreating plain carbonsteels.c Spheroidizing

Spheroidizings rocessfheatingndcoolingsteelthatproducesaroundedorglobu-larformofcarbideinamatrixofferrite.tisusuallyccomplishedbyprolongedheatingatemperaturesust elowheA cjfig.11),butmaybefacilitatedbyalternatelyheatingto temperaturesustboveheA c!andooling tojustbelowtheArt.hefinalstep,however ,shouldconsistofholdingatatemperaturejustbelowhecriticalArx).herateofcooling ismmaterialfterlowlyoolingobout1 , 000F.Therateofspheroidizationisaffectedbytheinitialtructure.heinerheearlite,hemoreeadilypheroidizationsccomplished. Amartensitictructureserymenableo spheroidization.Thistreatmentisusuallyappliedto thehigh carbonteels0 .60%fcarbonandhigher).Theurposefhereatmentsomprove machinabilityandtsalso se doondition high-carbonteelorcold-drawingntowire.Aypicalmicrostructureofpheroidizedhigh carbonsteelsshownnfigure1 2,D.

5.2. Normalizing Normalizingisaprocessinwhichasteelis heatedoatemperatureboveheA c3ortheA cmfig. 1 )ndthencooledinstillair.hepurposeofhereatmentsoobliterateheeffectsofanypreviousheattreatmentinclud-ing the coarse-grained structure sometimes

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FIGURE2. Representativemicrostructuresofcarbonsteels.taffectedby this treatment. X100.T Vm>,ii.SiS.T.x:r#";'"tSr?r" V'?? V VS ! " " " "'w'" "" ' " " ? Breeliminated,an dther e r r i t egrainsa r e largerthanin(B). X I O O .' ferrite >foSspheroidlMd- Autne< r t x > n ispresent In thef o r m of spheroidsorslightlyelongatedparticles of cementitein a matriiof'f mJiifa3j5!SMl?i??eIi(Wci,fSn?rmJ 11"d 'J. 0FinM - l n .round(centerarea). Becauseof the rapidrateof air coolingsucha smallsection,the Ielativelylittlef r e eferriteisformed. X100I Ir e e f e r r i t e " 6XU""(E)* " " normaUiedin2M" ln-rund(centcrarea> - Theslowerrateof > " B : du etothe largersection results incoarserDearliteand moreAll etched inpicral.resultingromhighorgingemperatures)rcold-workingndonsureomogeneous austeniteneheatingorardeningorullannealing.heresultantstructuresarepearl-

iteorpearlitewithexcessferriteorcementite,dependinguponhecompositionofheteel.Theyaredifferentromhestructuresesult-ingafterannealingnhat,orteelsofhesamecarboncontentnhehypo-orhypereu-tectoidanges,heresessxcesserriteor

cementiteandthepearliteisfiner. Thesearetheresultsofthemorerapidcooling.Sinceheypeoftructure,and,herefore,themechanicalproperties,are ffectedbyheratefooling,onsiderableariationsmayoccurnormalizedteelsecausefiffer-encesnectionhicknessofthehapesbeingnormalized.heeffectofsectionthicknesson thetructuref ormalized.5-percent-carbonsteelshowninfigure2,EandF.

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5.3. Hardening Steelscanbehardenedby th esimpleexpedi-entofheating to abovetheAc 3transformation,holdingongnoughonsurehe ttainment ofuniformtemperatureandsolutionofcarboninheustenite,ndhenoolingapidly (quenching).ompletehardeningdependson coolingoapidlyfig.,AndB)hatth eaustenite,whichotherwisewoulddecomposeon coolingthroughtheArlfismaintainedtorela-

tivelylo wtemperatures.henthisisaccom-plished,th eaustenitetransformsto martensiteonoolingthroughtheM,M fange.apid coolingisnecessary only to th eextentoflower-ingth etemperatureofthesteeltowellbelowth e oseofhe -curve.nc ehis asbeenaccomplished,slowcoolingfrom thenon ,eitherin oilorin air ,isbeneficialinavoidingdistor-tionandcracking.pecialtreatments,such ast imeuenchingndartempering,ree- signedoringboutheseonditions.smartensiteisquitebrittle,teelsarelyusedinhes-quenchedondition,hats,withouttempering.Themaximum hardnessthatca nbeobtainedin completely hardenedlow-alloy andplaincar-bonstructuralsteelsdepends rimarilyonth ecarboncontent.herelationshipofma x imumhardnessoarbonontentshownn figure3 .o0_i_iU J J0ooITV> bJ |'30< X|0sXio

00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.60 0.90 1 . 0 0 C A R B O N , % FIGURE3. Relationfmaximumttainableardnessfquenchedsteelsocarboncontent.(Burns,Moore,andArcher,Trans.Am .So cMetals2 6 ,1 4(1938)).

a . EffectofMassPreviousdiscussionoftheformation ofmar-tensiteaseglectedhenfluencefmass.Itmustberealizedthatevenwithasampleof

relatively smalldimensions,th erateofabstrac-tionofheatsnotniform.ea ts lways abstractedfromheurfaceayersatafasterratethanromth enterior.na ivenool-ingmediumth ecoolingrateofbothth esurfaceandnteriordecreasesshedimensionsof

samplencreasendhe ossibility fxceedingth ecriticalcooling ratefig.9,B )becomeless.overcomehis,heteelayquenchedinamediumhavingaveryhighratofea tbstraction,uchsce drine,utevenso ,many steelshaveaphysica lrestrictiononhe ax imumiz emenableoomplethardeningregardlessofth equenchingmediumThemarkedffecthatmass asponhhardnessofquenchedteelm a ybellustrateby measuringth ehardnessdistributionofdifferentiz eoundsofth eam eteelquencheinth esamemedium.urvesshowingth edistributionofhardnessinaseriesofroundbarofdifferentsizesof0.5-percent-carbon steelarshownnigure4.heuenchingmediumusedasater;heuenchingemperaturwas , 530F.heateofooling ecreaseashe iametersofth ebarsncreased.nlth e%-in.ound ardenedompletelyhrougth ecrosssection,whereaswithth e4-in.rounth ecriticaloolingratewasnotattainedeveatthesurface.

5.4.emperingTemperingsometimesalledrawing)th e processofreheating hardenedmartensit icor normalized steelstosometemperaturebeloth eowerrit icalAd). Thea teofcoolin70

60

so

40c< X

3/4"Dl/2"0 \ l"0

r i1 ! IT n% L 3020202RADIUS, I N C H E S FIGURE4. Variationnhardnessndifferentsizeounof0.5-percent-carbon steelssuenchedrom,530"inwater.(Jomlny,Hardenablllty of alloysteels,Am.Soc.Metals,D .75,1939.)1 2


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r

\v.$>:. . :

>*. .*..

P^^^S^ii^

'mIGURE5. Microsiruduresandcorrespondinghardnessofheat-treatedhighcarbonteel.A ,As quenchedInbrine;martensite,RockwellChardness=67. X 5 00 .B,SameasAaftertemperingat400F;temperedmartensite,RockwellChardness=61. X 5 00 .C,Sameas(A )attcrtemperingat800F;temperedmartensite,RockwellChardness=45. X 5 00 .D, am easA )afteremperingat ,200F;emperedmartensite,RockwellChardness=25. X 5 00 .E,Quenchednea dat650F;bainite,ockwellChardncss=49. X 5 00 .F,Heat-treatedsteelshowingdecarburizedsurfacelayer(lightarea)hatdidnotrespondtohardening. X 100 .A ll etchedin1% nltal.ismmaterialexceptorometeelshataresusceptibleoemperrittleness.2A sheemperingemperaturesncreased,themartensitefig.5 ,A)fhardenedteelpasseshroughtagesofemperedmartensite(fig.5, and) andsraduallychanged

2Temperrittlenesssmanifesteds os sfoughnessob-servednlyympactestsfotchedars)fterlo woolingfromemperingemperaturesf. 100Forigher,rfterem-?e.r nKheemPeratureangeetweenpproximately50 nd1 . 1 00F.tsostronouncednlloyteelshatontainmanganeserhromiumndsuallyanereventedyapidquenchingromheemperingemperature.hepresenceofmolyb- denumseneficialnounteractingheendencyowardemperbrittleness.

into tructureonsistingfpheroidsfcementiten matrixferrite,ormerlytermedorbitefig.5,D).hesehangesareaccompaniedbyadecreasinghardnessandincreasingtoughness.heemperingtemper-aturedependsuponthedesiredpropertiesandthepurposeorwhichheteelso e sed.Ifconsiderablehardnesssnecessary,hetem-peringemperaturehouldeow;fonsid- erableoughnesssequired,heemperingtemperaturehouldeigh.heffectftemperingnheardnessfullyardenedcarbonteelsshownnigure6.

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40 0 60 0 80 0 1000TEMPERING TEMPERATURE , * F 1400

FISURE16.Effectoftemperingtemperatureon thehard-nessofcarbon steelsofdifferentarboncontent.Specimenswereem per edor hr.Bain,Functionsofthealloy-ingelementn tel,Am. oc .Metals,p.S8 ,US9.)Properemperingf ardenedteele-quiresertainmountfime.tnyselectedemperingemperature,hehardnessdropsapidlytirst,raduallyecreasingmorelowlysheimesrolonged.heeffectofimeatdifferentemperingemper-aturesupontheresultanthardnessofaeutec-toidcarbonsteelisshowninfigure7.horttemperingeriodsreenerallyndesirableandshouldbeavoided.oodpracticerequiresateast%hror,preferably, o hr)ttemperingtemperatureforanyhardenedsteel.Thenecessityfortemperingasteelpromptlyafterhardeningcannotbeoveremphasized.ffullyhardenedteelis l lowedtocooltoroomtemperatureduringhardeningthereisdangerthatheteelmaycrack.arbonteelsandmostofthelo w alloysteelsshouldbetemperedasoonasheyareoo lenoughoeelom-fortable1 0 0o40F)ohebarehands.Steelsshouldnotbetemperedbeforetheycooltohisemperatureangeecausenom esteelstheM ttemperatureisquitelo wandun-transformedustenitemaybepresent.artorllfhisesidualusteniteil lrans-formomartensite noolingromheem-peringtemperatureohatthefinalstructurewillconsistofbothtemperedanduntemperedmartensite.herittlentemperedmarten-

site,togetherwiththeinternalstressescausedbyitsformation,caneasilycausefailureoftheheat-treatedart.hentsossiblehatsuch onditionxists, econdemperingtreatmentdoubletempering)houldbegiventotemperthefreshmartensiteformedoncool-ingaftertheinitialtemperingtreatment.1 4

70

60

30 Id40

30

":; __400*F\

600* F - 800*F

^JO00*F .

10 SECOND 10 I*MMUTES 2 5HOURS 25

TM EX TTEMPERM6TEMPERATURE FIGURE7 .ffectfimetemperingemperaturen th eardnessf.8-percent~carbonteel.Logarithmictimescale.)(Bain.Function of the allojlnc elements I n steel,Am .S o n ,Mttalt,p.2 3 3 ,MM.)

Ifstructuralsteelsaretobeusedinthenor-malizedcondition,thenormalizingoperationis frequentlyollowedbyheatingoaempera-tureofabout1 ,200to ,300F.hepurpose ofthisreatment,whichs ls odesignatedastempering,rtress-reliefnnealing,sorelieventernaltressesesultingnoolingfromhenormalizingemperatureandom-provetheductility.

5.5. CaseHardening Casehardeningisaprocessofhardeningaferrousalloyso thatthesurfacelayerorcaseis madesubstantiallyharderthantheinteriororcore.hechemicalcompositionofthesurfacelayerisalteredduringthetreatmentbythead-ditionofcarbon,nitrogen,orboth.hemost

frequentlysedase-hardeningprocessesrecarburizing,yaniding,arbonitriding,ndnitriding.a. Carburizing

Carburizingisaprocessthatintroducescar-bonntoaoliderrous l loybyheatinghemetalncontactwithacarbonaceousmaterialtoatemperatureabovetheA c 3ofthesteelandholdingthatemperature.heepthfpenetrationofcarbonisdependentontemper-ature,imeatemperature,andheomposi-tionfhearburizinggent.s oughindication, carburizeddepthofabout .030to .050n.canbeobtainedn.about hrat1 ,700F,dependinguponthetypeofcarburiz-ingagent,whichmaybeasolid,liquid,orgas.Sincetheprimaryobjectofcarburizingistosecureahardcaseandarelativelysoft,toughcore,onlylow-carbonsteelsuptoamaximumof about0 .25%ofcarbon)itherwithorwith-outalloyingelementsnickel,chromium,man-


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SURFACEjFIGURE8. Structureofacarburizedsteel.

Thespecimenwa scooledslowlyfrom thecarburizingtemperature. Etchedwithnital. X75.ganese,olybdenum),reormallysed.Aftercarburizing,heteelwillhave high-carbonas eraduatingntoheow-carboncorefig.18).Avariety fheatreatmentsmay e se dsubsequentocarburizing,but llofhemn-volvequenchingthesteeltohardenthecarbur-izedsurfacelayer.hemostsimpletreatmentconsistsfuenchingheteelirectlyromthearburizingemperature;hisreatmenthardensboththecaseandcoreinsofarasthecoresapableofbeinghardened).nothersimplereatment,nderhapshenemostfrequentlyused,consistsofslowlycoolingfromthearburizingemperature,eheatingoaboveheA c3fhecaseabout425F)andquenching;thistreatmenthardensthecaseonly.moreomplexreatmentsodoublequenchfirstromboveheA c 3 fhecore(about 1,650 F forow-carbon steel) and

MO,fo r i-ovehec3fhecaseabouti ,4Z5);hisreatmentefinestheoreandhardenshease.heplaincarbonsteelsareamostalwaysquenchednwaterorbrine;heflutelsresuallyuenchednil.l- thoughemperingollowinghardeningofcar-burizedteelsometimesomitted, ow-tem-peratureemperingtreatmentatabout30 0Fisgoodpractice.Itsometimesesirableocarburize nly certainartsfheurface.hisaneaccomplishedyoveringheurfaceoeprotectedgainstarburizingwithom ema-terialhatreventsheassagefhear-burizingagent.hemostwidelyusedmethodisopperlatingfheurfacesoeprotectedeveralroprietaryolutionsrpastes,whicharequite ffectivenpreventingcarbunzation,are ls oavailable.Theommercialompoundsommonlyse dtorpacksolid)arburizingcontainmixturesofcarbonateusuallybariumcarbonate),oke (diluent),andhardwoodcharcoal,withoilar

ormolassessabinder.ixturesofcharredleather, one,andcharcoalarealso sed.Thecarburizingactionofheseompoundsisdiminishedduringuseandtisnecessarytoaddewaterialeforeheompoundsreused.dditionfneartfnusedothreeoiv eparts f se dompoundsom-monpractice.hepartso ecarburizedarepackednboxesorothersuitablecontainers)madeofheat-resistantlloys,lthougholled orcastteelmay e se dwhereongifeofthe oxsnotmportant.heidofthe oxshould eealedwithire la yoromeotherrefractoryohelppreventscape fhecar-burizinggasgeneratedatthecarburizingtem-perature.hedepthanduniformityofcaseis affectedbyhemethodofpackinganddesignofthecontainer.Liquidarburizingconsistsfas eharden-ingteelrronnoltenaltathshatcontainmixturesprincipally fcyanidespoi- sonous),hlorides,ndarbonates.hease prod"eHhyhismethodcontainsbothcarbonandnitrogen,butprincipallytheformer.he temperatures se dangeromabout ,550o1,650Forhigher,depending ponheom-positionsofthebathandhedesireddepth fcase.t1,650Facasedepthofabout0 .01 0 to.015n.anebtainedn r;bout0.020o.030n.anebtainedn r.Considerablydeeperasesaneobtainedathigheremperatureswithongereriodsftime.fterarburizing,heartsmustequenchedustasnolidcarburizing,butitsusualodothisdirectlyfromthemoltenbath.In llpresent-daycommercialgascarburiz-ing,wororeydrocarbonsrese dncombinationorupplyinghearbonohesteel.heydrocarbonsse dremethane,ethane,ropane,ndilapors.heteelpartsare lacednealedcontainershroughwhichthecarburizinggasesarecirculated;hetemperatures se darenheneighborhood f

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0.140

0.120

/

24 28 260C A R 8 U R I Z C N G TIME HOURSRelationfimendemperatureoarbonpenetrationingascarburizing.(MetalsHandbook,1 9 3 edition,p.1 0 4 1 . )

FIGURE9. 1,700F.verageexpectationordepthofcaseingas-carburizedsteelisillustratedinfig-ure9.ftercarburizing,thepartsmustbe quenchhardened.

b.yanidingAard,uperficialaseanebtainedrapidlynow-carbonteelsyyaniding.Thisprocessnvolveshentroductionofbothcarbonandnitrogenintothesurfacelayersoftheteel .teelsobecyanidednormallyareheatednamoltenbathofcyanide-carbonate-chloridealtsusuallycontaining 0o95%oisodium cyanide)andthenquenchedinbrine,water,ormineraloil;thetemperatureofoper-ationsenerallywithinheangef,550 to ,600F.hedepthofcaseisaunctionofime,emperature,andcompositionofhecyanidebath;heimeofmmersionsquiteshortsomparedwitharburizing,suallyvaryingfromabout1 5minto2hr.hemax-imumas eepthsarelymorehanbout0.020in .andtheaveragedepthisconsiderablyless.Steelsaneyanidedlsoyeatingothepropertemperatureanddippinginapow-deredcyanidemixtureorsprinklingthepow-der nheteel,ollowedbyquenching.hecasethusformedisextremelythin.Cyanidingsaltsareviolentpoisonsifallowedtoomencontactwithcratchesorwounds;

theyareatallypoisonousftakennternally.Fatallyoisonousumesrevolvedhencyanidesarebroughtntocontactwithcids.Cyanidingathshouldequippedwithhoodforventingthegasesevolvedduringheat-ingandheworkoomhouldbewellventi-16

lated.oltenyanidehouldevereer-mittedoomenontactwithodiumrorpotassiumnitratescommonlyusedforbathsforemperingashemixturesarexplosive.Furthermore,aresecessarynreparingasaltbathandtheworkpiecesshouldbecom-pletelydrybeforeplacingnhemoltenbath.Thedvicefaltmanufacturershouldeobtainedndollowednheperationndmaintenanceofsaltbaths.carbooitr iding Carbonitriding,ls oermedasyaniding,drycyaniding,andnitrocarburizing,isaproc-essorasehardeningateelpartnagas-carburizingatmospherethatcontainsammoniainontrolledercentages.arbonitridingsusedmainlyasa low-costsubstituteforcyanid-ingand,asincyaniding,both carbonandnitro-genreddedoheteel.herocessscarriednboveheA c xemperatureofhesteel,andispracticalupto1,700F.uench- inginoilissufficientlyfasttoattainmaximumsurfacehardness;thismoderaterateofcooling tendsominimizeistortion.heepthowhicharbonnditrogenenetratearieswithemperatureandime.hepenetrationofcarbonsapproximatelyheameashatobtainednasarburizingfig.9).d. Nitriding

Thenitridingprocessconsistsnubjectingmachinedandheat-treatedsteel,freefromsur-faceecarburization,ohectionfnitrogenousmedium,usuallyammoniagas,ataemperaturefbout5 0o,050F,wherebyaveryhardsurfaceisobtained.hesurface-hardeningffectsdu eoheabsorp-tionofnitrogenandsubsequentheattreatmentofthesteelisunnecessary.hetimerequirediselativelylong,normallybeing or2days.Thecase,evenafter2daysofnitriding,isgen-erallylessthan0 .020in.andthehighesthard-nessexistsnthesurfacelayersto adepthofonlyafewthousandthsofaninch.Liquidnitridingnitridinginamoltensaltbath,enerallyomposedf mixturefsodiumandpotassiumsalts)mploysthesame temperaturerangeasgasnitriding.Specialow-alloyteelshavebeendevelopedforitriding.heseteelsontainlementsthateadilyombinewithitrogenoormnitrides,hemostavorablebeingaluminum,chromium,ndanadium.olybdenumndnickelareusednthesesteelstoaddstrengthandtoughness.hecarboncontentusuallyis about .2 0o .5 0percent,lthoughnomesteels,wherehighcorehardnessisessential,itmaybeashighas1 .3percent.tainlesssteelsalsocanbenitrided.Becausenitridingsarriedoutataela-tivelyowemperature,tsadvantageouso y


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use uenchedandemperedteelashe as e material.hisgivesastrong,toughcorewithanntenselyardwear-resistingasemuchharder,ndeed,thancan beobtainedby quenchhardeningeithercarburizedoryanidedteel.Althoughwarpagesnota roblemduringnitriding,steelsincreaseslightlyinsizeduringthisreatment.l lowanceaneadeorthisgrowthnthefinishedarticle.rotectionagainstnitridingcan be effectedbytin,copper,orbronzeplating,orbytheapplicationofcer- tainpaints.5.6. SurfaceHardening

Itsrequentlydesirabletoharden nlythesurfaceofsteelswithoutalteringthechemicalcompositionofheurfaceayers.fateelcontainssufficientcarbonto respondto harden-ing,tspossibletohardenthesurfaceayersonlybyveryapidheatingforashortperiod,thusonditioningheurfaceorardeningbyquenching.a. Inductionardening

Innductionardening, igh-frequencycurrentsassedhroughaoi lurroundingthesteel,thesurfacelayersofwhichareheatedbylectro-magneticnduction.heeptho whichheheatedoneextendsdependsnhefrequencyofthecurrentthelowerfrequenciesgivingthegreaterdepths)andonthedurationofheeatingycle.heimeequiredoheatheurfaceayersobovehec3ssurprisinglybrief,frequentlybeingamatterofonly eweconds.electiveeatingandthereforehardening)sccomplished vuit-abledesignofthecoilsorinductorblocks.ttheendoftheheatingcycle,thesteelisusuallyquenchedywateretsassinghroughheinductoroils.recisemethodsorontroll-in gtheoperation,thatis ,rateofenergyinput,durationfheating,andateofooling,renecessary.hesefeaturesareincorporatedin inductionhardeningequipment,whichs su - allyntirelyutomaticnperation.igure20showsthehardenedlayerininductionhard-enedteel.b. FlameHardening

Flamehardeningisaprocessofheatingthesurfaceayersofteelboveheransforma-tionemperaturebymeansofahigh-tempera-tureflameandthenquenching.nthisprocess theaslamesmpingeirectlynheteelsurfaceo ehardened.heateofheatingisveryapid,althoughnotso fastaswithn-ductioneating.lainarbonteelsreusuallyquenchedbyawaterspray,whereastherateofoolingof lloyteelsmay evariedfromaapidwaterquencho lo wairool dependingnheomposition.

FIGURE20 .Macrographofinductionhardenedgearteeth.Originalize,-in. iameterOsborn).A nyypefhardenableteelan elamehardened.orestesults,hearbonon-tenthould eateast .3 5percent,he sualrangebeing0.40to 0.50percent.

5.7. SpecialTreatmentsa. Austempering

Austemperingisatradenameforapatentedheat-treating rocess.ssentially,tonsistsofheatingteeloboveheA c3ransformartiontemperatureandthenquenchingintoahotbathheldatatemperaturebelowthatatwhichfineearliteouldormtheosefheS-curve,ig.8),butabovetheM stemperature(fig.0 ).heproductfsothermalecom-positionofausteniteinthistemperatureregionisainite.hisonstituentombinesela- tivelyhightoughnessandhardness.typicalmicrostructureofaustemperedteelshown infigure1 5,E.Theaustemperingprocesshascertainimi- tationsthatmakeitimpracticableforusewithmanyteels.nrderossure niformstructureandenceniformroperties),tisessentialhattheentirecrossection fthesteel ecooledapidlyenoughsothateventhecenterscapesransformationtheoseftheS-curve.ncarbonsteelsthetimerequiredtotartransformationtheosefheS-curvesextremelyhort,ohat nlyela-tivelymallectionsabout%-in.maximumthickness)aneuccessfullyotuenched inaustemperingbaths.hetimerequiredortransformationofheaustenite f lloyteels

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toin eearlitessuallyonger,ndencelarger sectionsca nbesuccessful ly austempered(about n.maximum) .owever,heim erequiredorransformat ionoainitere-quentlybecomesnordinatelyongwithmany alloyteelsndhe rocessofustempering,therefore,seneral lympracticableforthesesteels.b. Martempering

Martemperingonsistsofheatingateelto aboveitsAcstransformation andthenquench-ingintoabathheldatatemperatureapprox i -matelyqualohatoftsM..heteelsmaintainednhehotbathuntiltsempera-turesssentiallyuniformndhensooledinair.Severe internal stressesdevelop in steelduring hardening.teelcontractsduringcoolingbutundergoes arkedxpansionhenheausteniteransformsomartensite.incequenchedteelustoolromheurfaceinward,arious ortionsransformat iffer-entimes.heteelshusubjectedovarietyofdifferentialexpansionsandcontrac-tions,esultinginconsiderableinternalstress.B yequalizingth eemperaturethroughoutth esectionbeforetransformation takes lace,and thenoolinglowlyhroughhe artensite(M,M f)ange ,th einternalstressesa recon-siderablyeduced.hissherimebjec-tiveofmartempering.Modifiedmartempering iffersromtand-ardartemperingnlynhathea th temperatureislower,rangingfromjustbelowth eM,pointtoabout200F .ithth efastercoolingattheselowerbathtemperatures,steels oflowerhardenabil itycanbehardenedtosuffi-cientepth.owever,reateristortionfsensitiveartssikelyit hheodified process.

c. ColdTreatment TheMftemperatureof many alloy steels isso lo wthatcompleteransformat ionofaustenite tomartensiteoes otccurnquenchingoroomtemperaturernoolingafteremper-ing.hisetainedustenitemaybepartial ly orompletelyransformedyoolingelowatmosphericemperaturesnduchreatmentisalledcoldreatment."heeneficialeffectsofol dreatment a ve otbeenullyexplored.tsnownhatheetainedausteniteofhighly alloyedteelssrequently difficultoransform.oolingtheseteelsolo wtemperaturestoth etemperatureofsolidCO*rve nower)mmediatelyfterhequenchssometimesffectivenransformingtheetainedustenite,butwithheoncomi-tantdangerofcracking.henth ecoldtreat-mentsppliedafterempering,heetained austenite is considerably more resistanto1 8

transformation. Ifcoldtreatmentisused,th esteelshouldalwaysbetemperedafterwards.Repeatedalternateheatingtoatemperatureslightlybelowthatusedintempering andcool-in gtoasubzerotemperatureinarefrigeratedicedbrine,arbondioxide,liquidair,rliquidnitrogensommonlyse dorransformingth eetainedustenitedimensionaltabiliza-t ion)ofsteelgages,especial lythoseof th eball-bearingtypecompositionAISI52100).d. Ausforming

Inhisrocess,medium-carbonlloyteelsa reirstustenitizedndhenooledapidlyto th etemperature rangeaboveM.in th e"bay"ofth eS-curve,betweenth epearl iteandbainitetransformation ands.hile eldat em -peraturewithinthisbayth esteelsa replastic-allydeformedandsubsequentlytransformedatloweremperaturesomartensiter ainite.Thesteelsa rethentempered.his"ausform-ing"rhot-working"echniquea seenemployedorovide igher ieldndensilestrengthvaluesthanthoseobtainableforthesesteelsyheormaluenchndempertreatments.6. Hardenability

Hardenabil itysheropertyhateter-mineshe epthnd istributionofhardnessinducedinsteelbyquenching.tisincreasedby increasingcarbonandbyth eadditionofallth ecommonalloyingelementsexceptcobalt),providedha theselementsreompletelydissolvednheustenitetuenchingem -peratures.heelementsmostfrequentlyusedforthispurposeare manganese ,chromium,andmolybdenum.ardenabilitys ls onhancedbyncreasedrainize'nd omogeneity ftheustenite.owever,oarse-grainedaustenitencreasesheendencyof teelo' Thegrainliehatnfluenceshardenabilityshatgrainizeoftheaustenitethatexistsatthequenchingtemperature.tis suallymeasurednderhemicroscopenermsfheumberofgrainsperquarencht magnificationf100.heom m onangeofgrainize umberssasollowsnotehatheargerhe um -ber,heinershegrainixe;.e..hem or egrainsherere ersquarench):

AmericanSocietyorTestingndMateria lsGrainizeno .

00. 5 1 .0 1 .5 2. 0 2.5 8. 0 8 .5 4. 0 4.55.05.5 6.06.57 .0

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G rainize7 .68.08. 59.09.5

10.010.511 . 020 .11 . 550.12.050 .12.500 .13 .000 .13 . 600 .14.000 .Grains/inaat X 1 0 0 _0. 5 .-28 ..-81 .-56 ..-62 ..-1 2. 72 4.J


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distortndrackuringeatreatment.Coarse-grainedteels ls oarees soughhanfine-grainedsteels.Acleardistinctionmustbedrawnbetweenthemaximumhardnessbtainablen teelanditshardenability.nstraightcarbonandlow-alloyteels,hemaximumardnesssfunctionfarbonontentnlyfig.3),whereasardenabilitysoncernedprimarilywiththedepthofhardening.Numerousmethodshavebeenproposedandusedfordeterminingthehardenabilityofsteel.Theselectionofamethoddependslargelyupon theinformationdesiredandtherangeinhard-enabilityofthesteels.For undamentaltudy,ardenabilitysoftenmeasuredintermsofthecriticalcoolingratefig. ,B),buthestandardend-quench(Jominy)estsidelyse dommercially.Inhend-quenchestabarofteel n.ndiameterby n.ong,previouslynormalizedandmachinedtoremovethedecarburizedsur-face,sheatedohehardeningemperaturefor3 0min.tisthenquicklytransferredtoafixturethatholdsthebarinaverticalpositionandajetofwaterundercontrolledconditionsimmediatelyisdirectedagainstthebottomendonly.heendofthebarshusooledveryquicklywhile rossectionsemoteromheendarecooledmoreslowly,therateofcoolingbeingependentponheistanceromhequenchedend.ftercoolingiscompleted,twodiametricallyoppositelatsabout4n-widearegroundthelengthofthebarandRockwellhardnessmeasurementsaremadeatntervalsofy16in .ononeorbothoftheflatsurfacesso prepared.herelationshipofhardnesstodis- tancefromthequenchedendisanindicationoftheardenability (fig.1).Theconditionsofheend-quenchesthavebeentandardizedandheatesofoolingatvariousdistancesromthequenchedendhavebeendeterminedandarehownattheopoffigure21 .tisthuspossibletocorrelatehard-nesswithoolingate,whichsaunctionofthedistanceromhewater-coolednd.hecoolingratesatvariouspositionsnthecross-sectionsofdifferentsizerounds,whenquenchedintillilandntillwater ls ohavebeendetermined.orrelationscanbemade,here-fore,betweenthehardnessobtainedatvariouspositions nhend-quenchbarandpositionsofequivalenthardnessofroundbarsquenchedintill ilorwaterassuminghatpointsofequalardnessaveheameoolingate).Figure22howsthisrelationshipbetweenthedistancesontheend-quenchedbarandvariouslocationsorquivalentardnessesnoundbarsquenchednstill il ;igure23howscor-respondingrelationsorbarsquenchedntillwater.Ifhehardenabilityend-quench)urveofateelsnown,tsossibleoscertain

COOLINGRATEA T1300'F,"F /SEC 31025 32 1 6 10.2 7 :0 4, 8 3.9 34 32 3JO 4901195 55 |2212.4 8.4 5. 6 4.3 3.6 3.3 31511 1 TIT I 1 1 1 1 C

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0 -LLL , I .,..1 1 1 -..!.__1_8 12 1 6 20 24 28 32 DISTANCEFROMQUENCHEDEN D 1/16 IN. 3 6 40 FIGURE1. Hardenabilityurvesorifferentteelsithth esamecarboncontent.

A,hallowardoning;B ,ntermediate ardening;C, ee p ardening.Th ecoolingratesshownIn thisfigurear eaccordingtoth eresultsofBoege-holdan dWeinman,N.D.B.C.ReportOSRDNo .3743,p. 42 (June1 ,IM4).4.0

//3.553.0M

SURFACE// 3'4// RADIUS//ta .< CD /' ,/CENTERu .2.0oa . /

' V//K ^1/2 A D I U S 5 '"u /0.51

4 6 8 10 1 2 14 16 1 8 20DISTANCE RO MWATERQUENCHEDEN D,1/16IN. 22 24

FIGURE22.elationbetweendistancesontheend-quenchbarandvariousocationsorequivalenthardnessorcoolingatesinoundbarsquenchednstilloil.(MetalsHandbook,94 8edition, .92.)

fromthiscurveandthecurvesgiveninfigures2 2and23whetherornotaselectedsizeroundmaderomthesteelwillhaveadesiredhard-nessttsurface,%adius,2adius,rcenter,whenuencheditherntillilrwater.onversely,heardnessaluessdeterminedatvariouspositionsinroundsafterquenchinginoilorwatercan beusedtoadvan-tagenapproximatinghedegreeofharden-abilityofateeluitableoreplacement fsimilarparts.Thestandardnd-quenchtestismostusefulforteelsfmoderateardenability,hats,theow-alloyteels.orhallowardeningsteels,uchasplaincarbon,amodificationofthistestthe -typebar)sused.1 9


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ill

4.03.5

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1 e20B 1 .5 < 5 |.o 05

/ S U R F A C E/J //2 /RADIUS

///CENTER/'//f2 4 6 8 10 1 2 14 16 S

DISTANCEFROMWATERQUENCHEDEND .1/16N. 20FIGURE3 .elationetween istancesnhend-quenchba rndariousocationsorquivalentardnessesrcoolingralesinroundbarsquenchedin stillwater.(MetalsHandbook,1 9 4 8 edition,p .4 M . )

7. HeatTreatmentofCastronsCastironsareofthreegeneralypes,gray,white,andnodular.hetermsgrayandwhiteareescriptivefheharacteristicppear-ancesoftheracturesandnodularsdescrip-tiveoftheshapeofthegraphiteparticles.Ingrayironalargeproportionofthecarbonispresentasgraphiticoruncombinedcarbonintheformofflakes.hesmallproportionofcarbonhatspresentasombinedcarbonorcementiteisintheformofpearlitejustasinasteel.epending nheamountofombinedcarbon,thematrixofcastironmaybesimilartoahypoeutectoidteelwithvaryingamountsofreeerritendraphitelakesispersedthroughoutfig.4 ,,,nd).fheamountofombinedcarbonsabout .8per-cent,thematrixwillbeentirelypearlitic;iftheamountisgreater,thematrixwillbesimilartoahypereutectoidsteel.Inwhiteironmost,fnotall,ofthecarbonisresentsementitefig.4 ,).hedividinglinebetweenwhiteandgraycastironisnotclearlydefinedandironpossessingchar-acteristicsofbotharecalledmottledcastiron.Whetheracastronwill egrayorwhitedependsontwofactorscompositionandateofooling.ertainelementsendopromotetheormationfgraphiticarbon;hemostimportantfhesereilicon,ickel,ndsulfur.therstendtopromotetheformationofombinedarbon;hemostmportantf

theserehromium, olybdenum,anadium,andmanganese.apidsolidificationandcool-ing,uchasesultromhinectionscastnsandorlargersectionscastagainstchills,pro-moteheormationfwhiteron.rono produced is frequently termed chilled iron.

Becauseofvariationsntheateofsolidifica- tionandcooling,castingsmaybewhiteatthesurfacelayers,mottledimmediatelybelow,andgrayintheinterior.Innodularcastiron,alsoknownas"ductileiron,"nodularraphiteron,"spheruliticiron,"and"spheroidalgraphiteiron,"thegra-phitesresentnheormfodulesrspheroidsfig.2 4 ,EandF)bestowingconsid- erableductilityohecastron.hese od- ulesformduringsolidificationdu etothetreat-mentofthemolteniron,justpriortocasting,withafewhundredthspercentusuallyof eithermagnesiumorcerium;thesulfurcontentmustbebelowabout0 .01 5percentforthetreatmentto e ffectivewithhese lements.odularironandgrayironhavethesametotalcarboncontent.hemechanicalpropertiesof nodularironcanbevariedbyalloying.Castronsmay egivenavarietyofheattreatments,dependingonthecompositionsanddesiredproperties.heprinciplesoftheheattreatmentsappliedocastronareimilartothosealreadydiscussedforsteels.

7.1.elievingResidualStressesAging)Theeatreatmenthatelievesesidualstressesiscommonlycalled"aging,""normaliz-ing,"or"mildannealing;"theterm"stressre -lieving"smoreaccuratelydescriptive.his treatmentcanbeaccomplishedbyheatingthecastirontobetween80 0and1 , 100F.,holdingattemperaturefrom3 0min.o hr,thetimedependingnheiz endemperature,ndcoolingslowlyinthefurnace.uchtreatmentwillcause nlyalightdecreasenhardness,verylittledecompositionofcementite,andonlyaslightchangeinthestrengthofthemetal.

7.2. Annealing Sometimes,tsdesirabletooftencastingsinordertofacilitatemachining.hetemper-atureangemostcommonlyusedforthispur-poses, 400o,500F,lthoughemper-aturesaslo was ,200o1 ,250Fhavebeenusedatisfactorily.ighly lloyedronsaresometimesannealedattemperaturesashighas1 ,800F.nllnnealing,arehouldetakenopreventoxidationofthecastingandcoolingshouldbeslow.Ineneral,ofteningormachinabilitysaccompaniedbyadecreasenstrengthandntheamountofcombinedcarbon,andbyanin -creaseingraphitecontent.ronsthatcontain

carbide-formingelementssuchashromium,molybdenum,anadium,ndmanganese)remoreesistantoofteningthanheordinarygrayronand,herefore,must eannealedatconsiderablyhighertemperatures.ompletelyannealedordinarygraycastironhasaBrinell20

I T


23/48

1 ^ - ^ " Y /^*

warn*?*y.*S a f e "

T4** . ..JT -A.;:\,V

FIGURE4. Microstructureofcastirons.A .,Orayiron. Thedarkflakesaregraphite. Unetched. X 1 0 0 .B, am esA ). Etchedwithicral. X 1 0 0 .C, am e as(B). Thematrixconsistsof pearlitewithasmallamountof freeferrite(white)andissimilartoahypoeutectoidsteel. Theappearanceof thegraphitelakessnotffectedyheetchant. X 500 .D, Whitei ron. Thewhiteneedlesarecementite;thedarkareasarepearlite;thedarkspheroidalareasare the eutectic(Ledeburlte). Etchedwithpicral.X 5 00 .E,Nodulariron. Thedarknodulesaregraphite;thewhitematrixisferrite. Etchedwithpicral. X 100 .F,earliticnodularron. Nodulargraphitedark)napearliticmatrix. Etchedwith icral. X 100 .G,Malleableiron. Thedarknodulesaregraphite;hewhitematrixisferrite. Etchedwith icral. X 100 .H,Pearliticmalleableiron. Nodulargraphitedark)n pearliticmatrix. Etchedwith icral. X 100 .

21


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/

hardnessf20o3 0 ,ndompletelyn-nealedalloyironsmayhaveaBrinellhardnessof30o80 ,depending nheomposition.Thematrixfodularronanemadecompletelyferriticbyheating at1 ,300Ffor1 to5hr,dependingoncomposition,sizeofcast-ing,andamount ofpearlitein theas-caststruc-ture;oolingromheannealingemperaturecanbeatanyconvenientate.fmassiveorprimaryarbidesreresentnhes-caststructure,theymaybeconvertedtospheroidalgraphitebyheatingat ,600o ,700For1o hr.lowlycoolingfromhistempera-turerangeto about1 ,275Fandholdingfrom3o hrwillconverthematrixoerrite.Nodularronwith erriticmatrixhashedesirableombinationfmaximummachin-ability,oughness,nductility.heard-nessferriticnodularronvarieswithhealloycontentromaowofabout 3 0Brinelltoahigh of about21 0Brinell.

a.MalleabilizingMalleabilizingalsotermedgraphitizing)saprocessofannealingwhitecastironinsuchawayhatheombinedcarbonswhollyorpartlytransformedographitenhenodular

formfig.4 ,GandH)nsteadofthelakyformthatexistsingraycastiron.henodu-larormfcarbonsalledemperorreecarbon.nsomeinstances,partofthecarbonislostinthemalleabilizingprocess.Whiteironthatistobemalleabilizedshouldcontain lltscarbonnheombinedorm.Anycarbonpresentasgraphiticcarbonandhencein theformofflakes)willnotbeaffectedbyhegraphitizingreatmentandsundesir-ablein thefinalstructure.Theemperaturessednalleabilizingusuallyangeromabout,500o,650F.Timeatemperaturesquiteong,requentlybeingasmuchastwotohreedays.oldingathisemperaturecauseshedecompositionofheementitentoustenitelusatherroundedformsofgraphite.ftheironisthencooledverylowlyhroughhecriticalange(lesshan0F/hr),heesultantstructurewillonsistferritelusemperarbon.Coolinglessslowlythroughthetransformationrange,orusinganironcontaininganalloyingelementthatetardsgraphitization,esultsnainalproductcontainingvariousamountsofpearlitelu serritewith,fourse,empercarbon.ronsaving earlitictructureplusemperarbonrenownsearliticmalleableironsfig. 4 ,H).smightbeex- pected,pearliticmalleableironsaresusceptibletoheattreatmentinthesamemannerassteels.

7.3. Normalizing,Quenching,ndTemperingWhenheatedoabovehecriticalempera-turelineSK,fig.3),castironconsistsofaus-

teniteplusexcesscementiteorgraphiteandtheaustenite.canbetransformedin thesameman-nerasin steel.lthoughironsthatarealmostcompletelyraphitictheommonoftrayirons)canbehardened,thisisnotcustomary.Suchronsmustbeheldatemperatureswellabovehecriticalorongperiodsofimenorderoassureheolutionofcarbonnheaustenite.Forptimumesults,heraphitelakesshouldbesmallanduniformlydistributedandthematrixhouldeearliticwithotoo muchfreeferritecombinedcarbonfromabout0.50 to0.80%).astingsshouldbeheateduni-formlyoheuenchingemperature,hich usuallyangesrom,500o ,600F.hequenchingmediumcommonlyusedisoil;waterisse do imitedxtentndomelloycastingsmaybequenchedinair.heironsquenched,generallyhasalowerstrengththanascast,butthestrengthsncreasedbytem- peringintherange of 350 to1 ,200F.often-ingproceedsuniformlyasthetemperingtem-peraturesncreasedbovebout50o1 ,200F.Apearliticmatrixcanbeproducedinnodu-larronsastryormalizing.he normalizingreatmentonsistsfeatingo 1 ,600o ,650F,holdingattemperatureforsolutionofcarbon,ollowedbycoolingnair.Themechanicalropertiesfheormalized ironsvarywithheomposition,ineness,andamountsofpearlite;heavyectionsareowerinhardnessandhighernductilitythanightsections.heBrinellhardnessnumbersrangefromabout200 to275.Martensiticrainitictructuresrero - ducedinnodularironbyquenchingfrom1,600 to,700Fnilrwater.heronssquenchedhavehighstrengthsbutlo wductility.However ,heductilityoftheas-quenchedroncanemateriallyncreasedstrengthndhardnessecreased)yemperingtbout1 , 000to ,300F.7.4. SpecialHeatTreatments

Subjecttothesamelimitationsassteels,castironsanelame-hardened,nduction-hard-ened,ustempered,martempered,rnitrided.8 . Practicalonsiderations

Satisfactoryeatreatmentfteelan diron)equiresfurnacesthathaveuniformcon-trolledemperatures,meansoraccuratetem-peraturemeasurement,andorprotectingthesurfaceofthematerialfromcalingordecar-burizing.roperuenchingquipmentsneededalso.

22


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8.1.urnacesan dSaltBathsTherearemanydifferenttypesandsizesoffurnacesse dnheatreatment.sa en- eralule,urnacesaredesignedooperatencertainpecificemperatureangesndt-tempteduseinotherrangesfrequentlyresultsinworkofinferiorquality.naddition,usingaurnacebeyondtsatedmaximumemper-aturehortenstsifendmayecessitate

costlyandime-consumingepairs.Fuel-firedurnacesgasor il )equireairforpropercombustionandanaircompressororlowersherefore ecessaryjwunctTheseurnacesareusuallyofthemuffletype,thatis ,hecombustionofthefueltakesplaceoutsideofandaroundhechambermwhichtheworkisplaced. Ifanopenmuffleisused,thefurnaceshouldbedesignedsoastopreventthedirectmpingementofflame nthework.Infurnacesheatedbyelectricitytheheatingelementsaregenerallyntheformofwireorribbon. Gooddesignrequiresincorporationofadditionalheatingelementsatlocationswheremaximumeatossmayexpected. Suchfurnacesommonlyoperateuptoamaximumtemperature of about 2 , 000 F. Furnacesoperating at temperaturesuptoabout2,500 Fusually employ resistor bars of sinteredcarbides.Furnacesntendedprimarilyoremperingmaybeheatedbygasorelectricityandarefrequentlyequippedwithafanforcirculatingthehotair.Saltathsrevailableorperatingteitheremperingorardeningemperatures.Dependingonthecompositionofthesaltbath,heatingcanbeonductedatemperaturesaslo was 25Foashighas , 450F.eadbathscanbeusedinthetemperaturerangeof65 0 to1 ,700F.he rate ofheatinginleadorsaltbathssmuchfasterthaninfurnaces.

a. ProtectiveAtmospheres Itsoftennecessaryordesirabletoprotectsteelorcastironfromsurfaceoxidationscal-ing)andlossofcarbonfromthesurfacelayers(decarburization,fig.1 5 ,F). Commercialfur-

naces,herefore,aregenerallyequippedwithsomemeansofatmospherecontrol. Thisusu-allysnheormofaburnerorburningcontrolledamountsofgasandairanddirectingtheroductsfombustionntoheurnacemuffle. Watervapor,aproductofhisom-bustion,sdetrimentalandmanyfurnacesareequippedwithameansfor eliminatingit. Forfurnacesnotequippedwithatmospherecontrol,aarietyfxternaltmosphereeneratorsareavailable. Thegasogeneratedspipedintothefurnaceandonegeneratormaysupplyseveralfurnaces. Ifnomethodofatmospherecontrolsavailable,om edegreeofprotection

maybesecuredbycoveringtheworkwithcastironboringsorchips.Sincetheworknsaltoreadbathssur-roundedyheiquideatingedium,heproblemofpreventingcalingordecarburiza-tionissimplified.Vacuumfurnacesalsoareusedforannealingsteels,speciallywhen righton-oxidized surfaceisaprimeconsideration.b.emperatureMeasurementndControl

Accuratetemperaturemeasurementisessen- tialogoodheattreating.heusualmethodisbymeansofhermocouples ;hemostom-monbase-metalouplesarecopper-Constantan(uptoabout70 0F),ron-Constantanuptoabout ,400F),andChromel-Alumelupo about, 200F).hemostommonoble- metaloupleswhichcanbeuseduptoabout2,800F)areplatinumcoupledwitheitherthealloy87percentplatinum13percentrhodiumorhe lloy 0percentplatinum10percentrhodium.heemperaturesuotedreorcontinuousoperation.Thelifeofthermocoupless ffectedbythemaximumtemperaturewhichmayfrequentlyexceedhosegivenabove)ndbythefurnaceatmosphere. Iron-Constantansmoreuitedforseneducingndhromel-Alumeln oxidizing atmospheres. Thermocouples areusuallyncasednmetallicreramicubesclosedatthehotendtoprotectthemfromthefurnace gases. A necessary adjunct is aninstrument,uchasamillivoltmeterorpoten-tiometer, for measuring the electromotiveforcegeneratedbyhehermocouple. Inheinterestofaccuratecontrol,thehotjunctionofthehermocouplehouldbeplacedas loseo theworkaspossible. Theuse ofanautomaticcontrollerisvaluableincontrollingthetemper-atureatthedesiredvalue.ifemperature-measuringequipmentsnotavailable,tecomesecessaryostimatetemperaturesbysomeothermeans.nnex-pensive,yetfairlyaccuratemethodinvolvestheuseofommercia lcrayons,ellets,orpaintsthatmeltatvariousemperatureswithinherange25o,600F.heeastccuratemethodoftemperatureestimationisbyobser-vationofthecolorofthehothearthofthefur-naceorofthework.heheatcolorsobserved areaffectedbymanyfactors,uchasthecon-ditionsofartificialornaturalight,hechar-acterofthescaleonthework,etc.Steeleginsoppearulledtbout

1 , 000F,andasthetemperatureincreasesthecolorchangesgraduallythroughvariousshades ofredto orange,toyellow,andfinallytowhite.Aoughapproximationofthecorrespondencebetweenolorandemperaturesndicatednfigure25 .23


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_f15002700-z- C 2600~z .~ m 14002500_Zi

2400^ 13002300~E Colorof

Hotody 2200~E 1200~ Whit2100-E

2000E1001900-E-I000Y,"0Wleoo E i1700- Orange- 9001600-E LightCherry 1800^- 8001400~E Fullherry1300E 7001200E Darkherry1100 600

loooE Da rked 00900

800^ _ _ 400700 -E TemperColors600-; ~:00 Blue

800i Purple Brown40 0-E 00 Straw300 200-Eoo100--

FIGURE5.emperaturehartndicatingonversionfCentrigradeoFahrenheitric eersa,oloremperaturescaleorardening-lemperalureange,ndempering-temperaturerange.

Itisalsopossibletosecuresomeideaofthetemperatureofhe ieceofacarbonorow -alloyteelnheowemperatureange se dfortemperingfromthecolorofthethinoxidefilmhatorms nhe leanedurfaceofhesteelwhenheatedinthisrange.heapproxi-matetemperature-colorrelationshipforatimeattemperatureofaboutone-halfhoursndi-catednheowerortionfhe .calenfigure25 .8.2. QuenchingMediaan dAccessoriesQuenchingolutionsact nlyhroughheirabilityooo lheteeLheyhavenobene-ficialchemicalactiononthequenchedsteelan dinhemselvesmpartonusualroperties.Mo stequirementsoruenchingmediaremetatisfactorilybywaterrqueousolu-tionsofnorganicaltsuchasablealt rcausticsoda,orbysometypeofoil.herateofcoolingisrelativelyrapidduringquenchinginrine,omewhatessapidnwater,ndslowinoil.Brineusuallysmadeofa -o 0-percensolutionfaltsodiumhloride)nwater

Inadditionotsgreateroolingpeed,brinehastheabilityto"throw"hescalefromsteeduringquenching.hecoolingabilityofbothwaterndrine,articularlywater,sonsiderablyaffectedbytheirtemperature.othshouldbekeptcold.wellbelow60F.fthevolumeofteelbeingquenchedendsoaistheemperatureofhebathappreciably,hquenchingbathshouldbecooledbyaddingicorbysomemeansofrefrigeration.Therearemanypeciallyprepared uenching il s nhemarket;heiroolingatesdnotvarywidely.straightmineral ilwitaSayboltviscosityofabout 00at00Fgenerally sed.nlikebrinendwater,hoilsavehereatestoolingelocitytslightlylevatedemperatureabout001 40Fbecauseofheirecreased iscositattheseemperatures.Whensteelisquenched,theliquidinimmedatecontactwiththehotsurfacevaporizes;thvaporeducesheatefeatbstractiomarkedly.igorousagitationofheteeltheuseofapressuresprayquenchisnecessatodislodgehesevaporfilmsandhuspermthedesiredrate ofcooling.Shallowhardeningteels,uchasplaincabonandcertainvarieties f lloyteels,havsuchahighcriticalcoolingratethattheymubequenchedinbrineorwatertoeffecthardeing.neneral,ntricatelyhapedectioshouldnotbemadeofshallowhardeningsteebecauseofthetendencyofthesesteelstowaandrackuringardening.uchtemshouldbemadeofdeeperhardeningsteelscpableofbeinghardenedbyquenchinginoilair.24


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Avariety fdifferenthapesndizes ftongsforhandlinghotsteelsisnecessary.tshouldberememberedthatcoolingofth eareacontactedyheongssetardedndhatsuchareasmay notharden,particularlyifth esteelbeingtreatedisveryshallowhardening.Smallpartsm ay be wiredtogetherorquenchedin baskets made ofwire mesh.Specialuenchingjigsan dfixturesar efre-quently sedooldteelsduringuenching in amanner to restraindistortion.Whenselectivehardening isdesired,portionsofth esteelmay be protectedbycoveringwith alundumcementorsomeotherinsulatingma- terial.electiveardeningayeccom-plishedlsoyhe se fwater r iletsdesigned todirectthequenching medium ontheareasoeardened.hislsosccom-plishedbythenductionndlame-hardening proceduresreviouslyescribed,articularlyon largeproduction jobs.

8.3.elationofDesignto HeatTreatmentInternalstrainsarisefrommanycauses,butth emosteriousarehosedevelopedduring

quenchingbyreasonofdifferentialcoolingan dfromth eincreaseinvolumethataccompaniesth e martensitictransformation.hesestressesare frequentlysufficienttodistortorcrackth e hardenedteel.inceemperaturegradientsarelargelyafunctionofthesizean dshapeofth epiecebeingquenched,th ebasicprincipleofgooddesignsoplanhapeshatwillkeepth etemperaturegradientthroughout apieceataminimumduringquenching.Becauseoftheabruptnessinthechangeofsection,someshapesareimpracticalto harden,withoutcrackingordistortion,byquenchingin water,butacertainlatitudeindesignisper-missiblewhen singan il-hardening r ir -hardeningteel.therhingseingqual,temperatureradientsreuchowernshapesquenchedinoilthaninwater,an darestilles snair.hu saertaindesignmay beperfectlysafeforonetypeofsteel,oron etypeofcoolant,an dunsafeforanother.Errorsindesignreachfartherthanmerelyaffectingtheinternalstrainsduringhardening.Asharpangleornotchservestogreatlycon-centratehetressespplieduringervice,an dthedesignofthepartmaybeentirelyre -sponsibleforconcentratingtheservicestressesat apointalreadyweakenedbyinternalstrainsproducedduringhardening.oncentrationofservicestressesfrequentlyparallelsconcentra-tionofheat-treatingstrainsan disfrequentlycausedan dcuredbyth eam ecombinationofcircumstances.Apartsproperlydesigned,ro matand-pointofheattreatment,ifth eentirepiececan beeatedndooledtpproximatelyhe samerateduringth eheat-treatingoperations.

Z3 o 3

FIGURE26. Examplesofgoodandbaddesigns fromland-?oint ofhardeningbyheattreatment(Palmer andLuerssen,Wsteelsimplified,p.392,1948).

A ,E nd view of an undercutt ingformtoolincorrectly designed.B ,T he sametoolbetterdesignedrom th e iewpointofheatreatment.Heavysectionshavebeenl ightenedbydrillingholes,hu sinsuringmoreuniform cooling.he filletat (a)minimizesdanger of cracking at th e sharpre-entrantngle.here illetisnot llowable,reatmentshownt(b)ishelpful.C,Crackingwilltendto occuratth esharprootsof th ekeyways. D,illetsat th eootsof th e eyw a yswilleduceheendencyowardcracking.he incorporation of th etw oaddit ional ey way s ,ve nhoughunnecessary inactualservice,helpsbalanceth esectionan davoidwarping.E, A blanking di ewithth ecenter ri bheavierthanth esurrounding areas.Thismaycausewarpingon quenching.F,Th esamedi ewithholesdrilled in th ecenterribto equalize th e amount of met a lthroughoutth edie,hu seliminatingwarpagedifficulties. Q,A stem pinionwithakeywayaboutone-half th ediameterof th estem.Thebase of th ekeyway is extremely sharp, an dth epiece is further weakenedbyaholedrilledthroughth ecenter of th estem nearth ekeyw a y .he baseofth e eyw a yshould efilletedan dholere-located.H,A dangerous designconsisting of athincollaradjoiningathick section.W henhardeningsuchpieces,hethinsectionoftenwarpsorcracksatth eJunctionwith th e hub.xtremely generous filletsan ddrilling holesthrough th ehu btol ightenitsmasswillbe elpful.J,W henhardening,th econcentrat ionof strainsatth eJunction of the two holesInth ecenterar eap ttocausefailure.uc hholesshouldbepluggedbeforehardening.K .Ablankingdi epoorlydesigned.rackwilloccurfrom ointofforkprongto setscrew hole.he posit ionof th esetscrewholeshouldbe changedto eliminate cracking.

25


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1 h

Perfectionnhisegards nattainablee- cause,evenm asphere,th esurfacecoolsmorerapidlythan th e interior.he designer should,however, t tempttohapepartsohathey willeatndoo lsniformlysossible.Th ereaterheemperatureifferencee- tweennywopointsn givenpartduring quenching,an dth ecloserthesetw opointsaretogether,th egreaterwillbe th einternalstrainand,therefore,th epoorerth edesign.Whenargean dsmallectionsareunavoid-able in thesamepiece,the thickpart frequentlyca nbeightenedydrillingholeshrought.Wherehangesnectionrencountered,angleshouldeillettedenerously.om eexamplesofpoorndooddesignarehowninfigure26.

9. NomenclaturendChemicalCompositionsofSteels9.1.tructuralSteels

Inorderto facilitate th ediscussionofsteels,someamiliarity ithheiromenclaturesdesirable.Anumericalindex,sponsoredby th eSocietyofutomotivengineersSAE )ndhe Americanro nndSteelnstituteAISI)susedodentifyth ehemicalompositionsofth etructuralteels.nhisystem, our-numeraleriess sedodesignateth eplaincarbonan dalloysteels;fivenumeralsareusedtodesignatecertaintypesofalloysteels.he firsttw odigitsndicateheypeofteel,he seconddigitlsogenerallybutnot lways)giveshepproximatemount fhemajoralloyinglementndheastwoorhree)K?ar?mtende toindicateth eapproximatemiddleofth ecarbonrange.owever,adevi-ationro mheule fndicatinghearbon rangeissometimesnecessary.Theeriesdesignationndypesareum -marizedasfollows: Serie*denotation

lOxx llxx ___.1 2 x x1 3 x x 2 3 x x 2 5 x x31xx33xx40xx41xx43xx44xx45xx46xx

26

Type*NonsulphurizedarbonteelsResulphurizedarbonteelsfreea-chining)Rephosphorizedndesulphurizedarbonsteelsfreemachining)Manganese.75% Nickel .50% Nickel.00% Nickel . 25%,chromium .65% Nickel3 . 5 0 % ,hromium .55% Molybdenum0.20or0.25% Ch0 ri2io 02 % 0r '95%' molybdenumNickel 1 . 80 % , chromium.5 0r 0.80%,molybdenum .25% Molybdenum .40% Molybdenum .52% Nickel. 80%,molybdenum .25%

4 7 x x ckel.05%,hromium . 45%,molybdnu m0.20or0.35% 48xxckel .50%,molybdenum .25% 60xxromium0.25,0.40or0.50% 50xxxarbon.00%,hromium .50% 5 1 x x romium0.80,0.90,0.95,or1.00% Blxxxarbon.00%,hromium.05% 52xxxarbon.00%,hromium.45% 6 1 x xromium .60, .8 0r .95%,anadium0 .12%,0.10%min.,or0.15%min.81xxckel 0.30%,hromium 0.40%, molybdenum. 12% 86xxckel 0 .55%, chromium 0.50%, molybdenum .20% 87xxckel 0.55%, chromium 0.05%, molybdenum .25% 88xxckel 0.55%,hromium 0.50%,olybdenum . 35% 92xxanganese 0 .85%, silicon 2.00%, chromium or0.35% 93ckel 3 .25%,hromium 1 .20%,olybdenum .12% 94xxckel 0.45%, chromium 0.40%, molybdenum. 12% 98xxckel 1 .00%,hromium 0.80%,olybdenum.25%

* Notncludednheurrentistoftandardteels.Listingsofth eAISItypenumbersan dchemicalompositionimits fhetandardtructuralsteelscompleteasofJanuary1966) rgivenin table1 .he SA Etypenumbersnoshowninth etable) re th esameasth eAISnumbers,exceptthatth elattermay be givenletterprefixondicatehemethod fmanufacture.heserefixesndheireaningareas follows:Bdenotesacidbessemercarbonsteel, enotesasicpe nearthrasielectricurnacearbonteels,Edenoteslectricurnacelloyteels.ew fth eAISsteelsarenotincludedinSA Elistings.Smalluantitiesfertainlementsrepresentinalloysteelsthatarenotspecifiedarequired.heselementsreonsideredincidentalan dmay be presentto themaximum

amountssollows:opper,.3 5ercentnickel, .2 5 ercent;hromium, .2 0 ercentmolybdenum,0.06percent.Theis t ftandardteelss lteredro mtimeotimetoccommodateteelsofprovenmeritan dto provideforchangesin th emetallurgicalndngineeringequirementsindustry.Manyofthealloystructuralsteelsaremanufacturedoeetertainpecifiedimitsnhardenabilitysdeterminedyhetandardend-quenchtest.uchsteels,table2,aredesignatedbyheetter"H"ollowingheAISnumber.hehemicalompositionimitsthesesteelshavebeenmodifiedsomewhatfromth eangesrimitspplicableoheam egradeswhenspecifiedbychemicalcompositiononly.heardenabilityfanH"teelguaranteedbythemanufacturertofallwithinaardenabilityan davingaximumndminimumlimitsasshown bytw olimiting hardenabilityurvesorhatparticularteel.

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29/48

TABLE. CompositionlimitsofstandardsteelsNONRESULPHURIZEDCARBONSTEELS

Designat ion Designation number Chemicalcomposit ionlimits,percent number Chemicalcompositon limits,percentAISI C Mn P(max) S ( max) AISI C Mn P(max) S ( max)

C00 6 0.06ma x 0.36ma x 0.040 0.050 C04 2 0.40/0.47 0.60/0.90 0.040 0.050C00 6 .08ma x 0.25/0.40 .040 .050 C04 3 .40/0.47 .70/1.00 .040 .050 C00 8 .10ma x .25/0.50 .040 .050 C04 4 .43/0.50 .30/0.60 .040 .050 C01 0 0.08/0.18 .30/0.60 .040 .060 C04 5 .43/0.50 .60/0.90 .040 .050 C01 1 .08/0.18 .60/0.90 .040 .050 C04 6 .43/0.50 .70/1.00 .040 .050 C01 2 .10/0.15 .30/0.60 .040 .050 C04 8 .44/0.62 1.10/1.40 .040 .050 C01 3 .11/0.16 .60/0.80 .040 .050 C04 9 .46/0.63 .60/0.90 .040 .050 C01 6 .13/0.18 .30/0.60 .040 .050 C05 0 .48/0.55 .60/0.90 .040 .050 C01 6 .18/0.18 .60/0.90 .040 .060 C05 1 .45/0.66 .86/1.15 .040 .050C01 7 .16/0.20 .30/0.60 .040 .050 C05 2 .47/0.66 1.20/1.50 .040 .050 C01 8 .16/0.20 .60/0.90 .040 .060 C05 3 .48/0.55 .70/1.00 .040 .050 C01 9 .16/0.20 .70/1.00 .040 .060 C05 6 .60/0.60 .60/0.90 .040 .050C02 0 .18/0.23 .30/0.60 .040 .050 C05 9 .56/0.65 .60/0.80 .040 .050 C02 1 .18/0.23 .60/0.90 .040 .050 C06 0 .66/0.65 .60/0.90 .040 .060C02 2 .18/0.28 .70/1.00 .040 .050 C06 1 .56/0.65 .76/1.05 .040 .060C02 8 .20/0.26 .30/0.60 .040 .050 C06 4 .60/0.70 .50/0.80 .040 .050 C02 4 .19/0.25 1.36/1.66 .040 .050 C06 5 .60/0.70 .60/0.90 .040 .050 C02 6 .22/0.28 0.30/0.60 .040 .060 C06 6 .60/0.70 .85/1.15 .040 .060 C02 6 .22/0.28 .60/0.90 .040 .050 C06 9 .65/0.75 .40/0.70 .040 .050 C02 7 .22/0.29 1.20/1.60 .040 .060 C07 0 .66/0.76 .60/0.90 .040 .050 C02 9 .26/0.31 0.60/0.90 .040 .050 C07 2 .66/0.76 1.00/1.30 .040 .050 C03 0 .28/0.34 .60/0.90 .040 .060 C07 4 .70/0.80 .50/0.80 .040 .060 C03 4 .32/0.38 .60/0.80 .040 .050 C07 5 .70/0.80 .40/0.70 .040 .050C03 6 .32/0.88 .60/0.90 .040 .050 C07 8 .72/0.86 .30/0.60 .040 .050 C08 6 .30/0.37 1.20/1.60 .040 .050 C08 0 .76/0.88 .60/0.90 .040 .050 C03 7 .32/0.38 0.70/1.00 .040 .050 C08 4 .80/0.93 .60/0.90 .040 .050 C03 8 .86/0.42 .60/0.90 .040 .060 C08 6 .80/0.98 .30/0.60 .040 .050 C08 9 .37/0.44 .70/1.00 .040 .050 C09 0 .86/0.98 .60/0.90 .040 .050C04 0 .37/0.44 .60/0.90 .040 .050 C09 6 .90/1.03 .30/0.50 .040 .050 C04 1 .36/0.44 1.85/1.65 .040 .050 1

RESULPHURIZEDC A R B O NSTEELSDesignation number Chemicalcomposit ionlimits,percent Designationnumber Chemicalcomposit ionlimits,percent

AISI C Mn P(max) S AISI C Mn P(max) SC1 08 C1 09 C1 1 0 C1 1 6C1 1 7 C1 1 8 C1 1 9C1 82

0.08/0.13.08/0.13.08/0.13.14/0.20.14/0.20.14/0.20.14/0.20.27/0.84

0.60/0.80.60/0.90.30/0.601.10/1.401.00/1.301.30/1.601.00/1.301.35/1.65

0.040.040.040.040.040.040 .040 .040

0.08/0.13.08/0.13.08/0.13.16/0.23.08/0.13.08/0.13.24/0.33.08/0.13

C1 3 7 C1 89 C1 40 C1 41 C1 44 C1 45 C1 46 C1 61

0.32/0.39.35/0.43.37/0.44.87/0.46.40/0.48.42/0.49.42/0.49.48/0.65

1.85/1.651.35/1.66.70/1.001.35/1.651.35/1.66.70/1.00.70/1.00.70/1.00

0.040.040 .040 .040 .040 .040 .040 .040

0.08/0.13.12/0.20.08/0.13.08/0.13.24/0.33.04/0.07.08/0.13.08/0.13

ACIDBESSEMERRESULPHURIZEDC A R B O NSTEELS REPHOSPHORIZEDANDRESULPHURIZEDCARBONTEELS Designationnumber Chemicalcomposit ionlimits,percent Designation number Chemicalcomposit ionlimits,percentAISI C Mn P S AISI C Mn P S

B1 1 1 B1 1 2 B1 1 3 0.13ma x .1 3ma x .13ma x 0.60/0.90.70/1.00.70/1.00 0.07/0.12.07/0.12.07/0.12 0.08/0.16.16/0.23.24/0.33 C21 1 C21 2 C21 3 C21 6JC2L 140.13ma x .18m ax .13m ax .09 ma x .15ma x

0.60/0.90.70/1.00.70/1.00.76/1.05.80/1.20

0.07/0.12.07/0.12.07/0.12.04/0.09.04/0.09

0.08/0.15.16/0.23.24/0.33.26/0.35.25/0.35tLead=0.16/0.36percent. Seeootnotesaten doftable.

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TABLE. Compositionlimitsof standardsteelsContinued OPENHEARTHANDELECTRICFURNACEA LLOYTEELS

Dodcnation number Chemicalcomposit ionlimits,percent AISI C Mn P(nutt) S(maz) Si Ni Cr Mo V

1 8 3 0 0.28/0.33.33/0.38.38/0.43.43/0.48.38/0.43.08/0.13.09/0.14.20/0.26.20/0.26.26/0.80.26/0.80.86/0.40.40/0.46.45/0.50.60/0.67.18/0.23.28/0.88.88/0.38.86/0.40.88/0.43.40/0.45.48/0.48.45/0.60.48/0.68.66/0.64.17/0.22.35/0.40.86/0.40.88/0.43.88/0.43.18/0.23.20/0.25.24/0.29.13/0.18.16/0.20.17/0.22.18/0.28.24/0.29.16/0.21.17/0.22.13/0.18.15/0.20.18/0.23.12/0.17.43/0.50.18/0.18.17/0.22.28/0.33.30/0.85.83/0.38.38/0.43.48/0.48.45/0.52.48/0.53.60/0.60.55/0.650.95/1.10.95/1.10.95/1.10.16/0.21.17/0.22.48/0.63.13/0.18.13/0.18.15/0.20.18/0.23.20/0.25.23/0.28.25/0.30.28/0.33.35/0.40.38/0.43.40/0.45.43/0.48.48/0.53.50/0.60.55/0.65

1.60/1.901.60/1.901.60/1.901.60/1.900.70/0.90.45/0.60.75/1.00.70/0.90.70/0.90.70/0.90.70/0.90.70/0.90.70/0.90.70/0.90.76/1.00.70/0.90.40/0.60.70/0.90.70/0.90.75/1.00.75/1.00.76/1.00.75/1.00.75/1.00.76/1.00.46/0.65.60/0.80.65/0.85.60/0.80.66/0.85.45/0.65.70/0.90.70/0.90.45/0.65.46/0.66.46/0.65.70/0.90.46/0.65.70/0.90.60/0.70.40/0.60.40/0.60.50/0.70.30/0.60.76/1.00.70/0.90.70/0.90.70/0.90.60/0.80.60/0.80.70/0.90.70/0.90.70/0.90.70/0.90.70/0.90.76/1.000.25/0.45.25/0.45.25/0.45.50/0.70.70/0.90.70/0.90.70/0.90.70/0.90.70/0.90.70/0.90.70/0.90.70/0.90.70/0.90.70/0.90.75/1.00.76/1.00.75/1.00.75/1.00.75/1.00.75/1.00.75/1.00

0.035. 0 36.035 . 0 36. 0 36.026.085.036.086.085.085 .085 . 0 35.085.085 .086. 0 35. 0 35. 0 35. 0 36.085 .085 .086 .085 .086 .085 .036 .025. 0 35 .025 . 0 35 .085 .086.035. 0 36. 0 35 . 0 35 . 0 35 . 0 35 . 0 35 . 0 36. 0 35 . 0 35 .035.036. 0 35. 0 36. 0 35. 0 36.036.035.035.035.035.035.0350.025-.025.025 .035.035. 0 35. 0 35. 0 35.035. 0 35.035. 0 35 . 0 35 .035.035. 0 35 . 0 35 . 0 35 .035 . 0 35.035

0.040.040.040.040 .040 .025.040.0400.085/0.060.040.035/0.060.040 .040.040.040.040 .040.040 .040.040.040.040.040.040 .040.040.040.026.040 .026.040 .040.040 .040.040 .040.040 .040.040.040.040.040.040.040 .040.040 .040.040.040.040.040 .040 .040 .040.040.040 0.040.025.025

.040 .040.040

.040

.040 .040 .040 .040 .040.040

.040.040 .040 .040.040.040 .040 .040

0.20/0.35.20/0.85.20/0.85.20/0.85.20/0.85.20/0.86.20/0.86.20/0.85.20/0.26.20/0.86.20/0.86.20/0.86.20/0.86.20/0.86.20/0.35.20/0.85.20/0.85.20/0.85.20/0.86.20/0.86.20/0.85.20/0.86.20/0.80.20/0.85.20/0.85.20/0.35.20/0.35.20/0.86.20/0.26.20/0.86.20/0.85.20/0.36.20/0.86.20/0.35.20/0.85.20/0.85.20/0.86.20/0.85.20/0.86.20/0.35.20/0.85.20/0.36.20/0.36.20/0.35.20/0.35.20/0.35.20/0.86.20/0.85.20/0.86.20/0.85.20/0.35.20/0.35.20/0.85.20/0.85.20/0.85.20/0.860.20/0.35.20/0.85.20/0.36.20/0.85.20/0.85.20/0.35.20/0.85.20/0.35.20/0.85.20/0.85.20/0.35.20/0.35.20/0.35.20/0.35.20/0.35.20/0.35.20/0.35.20/0.35.20/0.35.20/0.36.20/0.36

1 8 8 51 840 1 846 8140 1.10/1.40

8.26/8.750.66/0.751.40/1.763 1 0 401 2 0.16/0.25.20/0.30.20/0.80.20/0.30.20/0.80.20/0.80.20/0.30.20/0.30.20/0.30

.08/0.15.15/0.25.15/0.25.16/0.25.15/0.25.15/0.25.15/0.25.15/0.25.15/0.25.26/0.35.20/0.30.20/0.30.20/0.30.20/0.30.20/0.30.45/0.60.35/0.45.35/0.45.20/0.30.20/0.30.20/0.80.20/0.30.15/0.25.30/0.40.15/0.25.20/0.30.20/0.30.20/0.30

4023 40244027 4028 4087 40424047 4068 4 1 1 8 4 1 8 0 41 864 1 8 7 41 40 41 42 41 4641 47

1.65/2.001.65/2.001.65/2.001.65/2.001.66/2.00

0.40/0.60.80/1.10.80/1.10.80/1.10.80/1.10.80/1.10.80/1.10.80/1.10.80/1.10.70/0.90.40/0.60.70/0.90.70/0.90.70/0.90.70/0.90

:::::....::::

41 6041 61 4820 4337 E3 3 7 4340 E84 04 4 1 9

: : : : : : : : : : : : :4422 4427 461 6 1.65/2.001.66/2.001.66/2.001.66/2.00.70/1.00

.90/1.20.90/1.208.25/3.753.25/8.768.26/2.75

4617 46204621 4626 4 7 1 8 47204 8 1 64 8 1 7

.36/0.55.35/0.65 ::::::::::.:4820501 5 .30/0.40.20/0.35

.70/0.90.70/0.90

.80/1.10.75/1.00.80/1.06.70/0.90.70/0.90.85/1.16.70/0.90.70/0.90.70/0.900.40/0.60.90/1.161.30/1.60.60/0.70.70/0.90.80/1.10.30/0.60.40/0.60.40/0.60.40/0.60.40/0.60.40/0.60.40/0.60.40/0.60.40/0.60.40/0.60.40/0.60.40/0.60.40/0.60.40/0.60.40/0.60

6046 611561 206 1 3 061 826 1 3 561 4061 45 61 47 61 606165 6160

E01 00E1 1 0 0E21 00 6 1 1 8 6120 61 50

8 1 1 5861 6861 7 8620

0.20/0.40.40/0.70.40/0.70.40/0.70.40/0.70.40/0.70.40/0.70.40/0.70.40/0.70.40/0.70.40/0.70.40/0.70.40/0.70.40/0.70.40/0.70

0.08/0.15.15/0.25.15/0.25.15/0.25.16/0.25.15/0.25.15/0.25.15/0.25.15/0.25.15/0.25.15/0.25.15/0.25.15/0.25.15/0.25.15/0.25

0.10/0.1.1 0mi.1 5mi

8622 86258627 8630 8637 8640

- '86428645 8650 8655 8660

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TABU. Composition,limitof tandardsteelsContinuedOPENHEARTHANDELECTRICFURNACEA LLOYTEELS'-(continued)

Designat ionnumber Chemicalcompoeit ionlimit*,percentAISI C Mn P(nuut) S(msx) Si Ni Cr Mo V

8720* 8 7 8 68 7 4 08742 8822 9266

.18/0.23.88/0.88.88/0.43.40/0.46

.20/0.26

.60/0.60.66/0.66.66/0.66

.08/0.18

.38/0.48.48/0.68

.70/0.90.76/1.00.76/1.00.76/1.00

.76/1.00

.70/0.96.70/1.00.76/1.00

.46/0.66

.70/0.90.70/0.90

.036.036.036.036

.036

.086.086.086

.026

.086 .036

.040.040.040.040

.040

.040.040.040

.026

.040.040

.20/0.86.20/0.85.20/0.36.20/0.36

.20/0.861.80/2.201.80/2.201.80/2.20.20/0.86.20/0.86.20/0.36

.40/0.70.40/0.70.40/0.70.40/0.70

.40/0.70

.40/0.60.40/0.60.40/0.60.40/0.60

.40/0.60

.20/0.30.20/0.30.20/0.80.20/0.30

.80/0.40:::::::::::::

9260 9262 .25/0.401.00/1.40.70/0.90.70/0.90

E8 1 0 9840 9860

8.00/3.50.86/1.15.86/1.16

.08/0.16

.20/0.30.20/0.80 _._.BORONSTEELS

Then steel ca nbe expected toha0.0006percentminimum boroncontent.Designationnumber Chemicalcomposit ionl imit,percentAISI M n P(maz) 8(m a x) Ni Cr Mo

60B 4460B 4660B 6060B60 61B60 8 1 B 4 5 9 4 B 1 7 94BS0

0.48/0.48.48/0.50.48/0.63.56/0.66.56/0.65.48/0.48.15/0.20.28/0.33

0.76/1.00.76/1.00.76/1.00.76/1.00.76/1.00.76/1.00.76/1.00.76/1.00

0.035.036.086.086.086 .086.036.036

0.040.040.040.040.040.040.040.040

0.20/0.36.20/0.36.20/0.86.20/0.85.20/0.36.20/0.86.20/0.85.20/0.35

0.20/0.40.30/0.60.80/0.60

0.40/0.60.20/0.35.40/0.60.40/0.60.70/0.90.36/0.55.30/0.50.80/0.60

0.08/0.15.08/0.15.08/0.15

NITRIDINGSTEELDesignationnumber C hemica lcomposit ionlimits,percent AISI C M n P(max) S(m a x) Si Al Cr Mo V

0.88/0.48 0.50/0.70 0.036 0.040 0.20/0.40 0.95/1.30 1.40/1.80 0.30/0.40Standardsteel fo rwirerodson ly .Silicon: W h e niliconsequired,heollowing;rusesndimitsareom m only sed: Standardteel