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SteelSurfaces
ZAHNER’SARCHITECTURALMETALSSERIES
Zahner’sArchitecturalMetalsSeries offersin-depthcoverageofmetalsusedinarchitectureandart today.Metalsinarchitectureareselectedfortheirdurability,strength,andresistancetoweather.The metalscoveredinthisseriesareusedextensivelyinthebuiltenvironmentsthatmakeupourworld andarealsofindingappealandfascinationtotheartist.Theseheavilyillustratedguidesoffercomprehensivecoverageofhoweachmetalisusedincreatingsurfacesforbuildingexteriors,interiors, andartsculpture.Thisseriesprovidesarchitects,metalfabricatorsanddevelopers,designprofessionals,andstudentsinarchitectureanddesignprogramswithalogicalframeworkfortheselection anduseofmetallicbuildingmaterials.Forthcomingbooksin Zahner’sArchitecturalMetalsSeries willincludeCopper,Brass,andBronze;Steel;andZincsurfaces.
Titlesin Zahner’sArchitecturalMetalsSeries include:
StainlessSteelSurfaces:AGuidetoAlloys,Finishes,FabricationandMaintenanceinArchitecture andArt
AluminumSurfaces:AGuidetoAlloys,Finishes,FabricationandMaintenanceinArchitecture andArt
Copper,Brass,andBronzeSurfaces:AGuidetoAlloys,Finishes,FabricationandMaintenancein ArchitectureandArt
SteelSurfaces:AGuidetoAlloys,Finishes,FabricationandMaintenanceinArchitectureandArt
SteelSurfaces
inArchitectureandArt
L.WilliamZahner
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LibraryofCongressCataloging-in-PublicationData
Names:L.WilliamZahner,author.
Title:Steelsurfaces:aguidetoalloys,finishes,fabricationand maintenanceinarchitectureandart/L.WilliamZahner.
Description:Hoboken,NewJersey:Wiley,2021.|Series:Zahner’s architecturalmetalsseries|Includesindex.
Identifiers:LCCN2020021102(print)|LCCN2020021103(ebook)|ISBN 9781119541622(paperback;acid-freepaper)|ISBN9781119541554(adobe pdf)|ISBN9781119541646(epub)
Subjects:LCSH:Steel–Surfaces.|Steel–Finishing.|Architectural metal-work.|Artmetal-work.
Classification:LCCTS320.Z2852021(print)|LCCTS320(ebook)|DDC 672—dc23
LCrecordavailableathttps://lccn.loc.gov/2020021102
LCebookrecordavailableathttps://lccn.loc.gov/2020021103
CoverDesign:Wiley
CoverImage:©lior2/GettyImages
PrintedintheUnitedStatesofAmerica
10987654321
ThisbookisinhonorofDavidNorris.Afriendandmentor.
CHAPTER4Expectations117
CHAPTER5DesigningwiththeAvailableForms163
CHAPTER6WorkingwithSteels205
GalvanicCorrosionandGalvanicProtectionofSteels294
GalvanicCorrosionandtheRatioofAreas297 KeyConditionsNeededforGalvanicCorrosiontoOccur298 TransferCorrosion299 PittingCorrosion300 IntergranularCorrosion300 CreviceCorrosion300 LineCorrosion302
CHAPTER8MaintainingtheSteelSurface305 Introduction305 PaintedSteelSurfaces305 DevelopaMaintenanceStrategy308 MaintainingSteelsinDifferentEnvironments311 Vandalism334
APPENDIXATerms345
APPENDIXBComparativeAttributesofMetals349
APPENDIXCAlloyCrossReferences351
APPENDIXDAbrasivePreparationofSteels353
APPENDIXESpecificationInformation355
APPENDIXFAFewRelevantspecificationsfromtheASTMInternational–(NotaCompleteList)365
APPENDIXGHot-DippedGalvanizingSpecification367
Index369
Preface
“Knowyourownvalue.”
HankRearden ofReardenSteel
AtlasShrugged byAynRand
SteelwasoneofthefirstmetalsIbecameacquaintedwithearlyinmycareer.Itwasdifferentthan theshinycoppertheshophadstackedinaneatpileorthelightweightaluminumstoredinracks upofftheground.Steelwasheavy,thickerthanmostothersheetmetals,andoftenpossessedthe intricatespangleofzinccrystalsonthesurfacefromthehot-dipgalvanizingprocess.
Steelwastreatedrougher.Storedinopenstacks.Oftencoatedinalayerofslickoil.Ithada smelltoit—thesmellofmachinery,thesmellofindustry.Steellackedthecareandconcernthe othermetalsseemedtoberegarded.Itwasthemetalusedformakingpatterns,1 beforetheshapes wouldbecutincopper,aluminum,orsteel’sroyalcousin,stainlesssteel.Afterwhich,theywouldbe relegatedtothescrapbintoberecycled.Weusedtorecycleallthemetals,andonoccasionIwould takeamassiveloadofsteelscraptotherecyclingyard,onlytoreceivelessthan20dollars.Ithardly seemedworthit,butwewereacompanythathadworkedwithmetalsthroughthehardtimesof theDepression,andyouwastednothing.Everysteelpackagingbandwascollectedandrecycled.
ThefirstmajorprojectsIwasinvolvedwithoutofcollegehadsteelsidingpanelsforcladding thewallsoflargecoal-poweredelectricalgeneratingplantsthatdottedtheMissouriRiver.These heavypanelswereroll-formedfrom18-gaugecold-rolledsteelsheetmadebyINRYCO,shortforthe InlandRyersonCompany,aoncemassivelylargesteelproducerintheUnitedStates.InlandSteel Company,foundedin1893,wasoneofthelastintegratedsteelcompaniesthatturnedoreintosteel andintosemifabricatedwroughtmaterials.Itssubsidiary,InlandBuildingSystems,mergedwith RyersonandlaterbecameINRYCO,buteventuallyfelttheimpactofforeignsourcesofsteeland modernizationandefficienciesofthemini-mills.
Thesesteel-cladpowerplantshavestoodforover40years.Thepaintcoatingsusedonthesteel structureandonthesteelpanelsIworkedwithwasofveryhighqualityandtodayshowlittlesigns ofdeterioration—somefadingwithtimeandultravioletexposure,butgenerallythesurfacesarein excellentcondition.
1 Upuntiltheearly1980s,patternsweremadefrompaperblueprints.TherewerenoCAD–CAMfiles.Steelpatterns wouldbecuttoforlaterusetomakeelbowsorroofjacks.Thepatternswerehungfromhooksonthewall,andwhen similaritemsweremade,thepatternswouldbeusedonthelayoutbenches.Abitarchaicinlightofthetechnology oftoday.
Overtime,myexperiencemovedawayfromthemildcarbonsteelsofsidingandmetaldecking. Aluminumbecamethebasemetalforhigh-qualitypaintsystems.Stainlesssteel,copperalloys,and laterzincwerethemetalsfordesignofexposed,uncoatedsurfaces.
Buttherewasthisotherinterestingsteel,aparadoxofmetal.ItwascalledCorten.
Herewasthisstrangesteelthatyouwantedthesurfacetocorrode.Itwouldstaineverything belowitwhileitformedtheinitialrust,yetitwassupposedtolastaslongasthestainlesssteels.
Thecompanybuiltitsfirstmajorbuildingin1982,andthedesignerwantedanaturalappearance.HechoseCortensidingfortheplantportionandalcladaluminumfortheoffice.Thesiding wasroll-formedbyINRYCOasoneofthelastgaspsofsteelproduction,asINRYCOwastocloseits doorsin1986.Thearchitectdescribedhisdesignasthenewgrowingfromtheold–theoldbeing therustymetalsurfaceofCorten.Itisinterestingthatoverthelast40years,itistheCorten,the weatheringsteel,thathasembracedthefutureandstillappearssturdyandstrongwhilealuminum islookingfragileandantiquated.
Ihaveworkedwithweatheringsteel,thenameusedasoftenastheolderCorten—or COR-TEN®,astheinventorandtrademarkholder,USSteelcallsit.CORstandsforcorrosion resistanceandTENstandsfortensilestrength.Bothofthesecharacteristicsandmorearepossessed bythisamazingsteel.
Nearly25yearsagowerealizedthemajordrawback,fromanaestheticstandpoint,wasthetime ittookfortherealdeepcolortoappear.Peopledidnotwanttowaitandwatchastheirbuildingrusted andpaintedthesidewalksandstoneworkwitharedstain.Theideaofpreweatheringthistypeof steelseemedtobetheanswer.Manyanartistpushedthemetaltoachievethispreweatheringon theirsculptureusingacidsandwettingthesurface.Inadditiontobeinghazardoustoone’shealth andsafety,thisprocessisimpracticalforlargeprojects.
Afterabitoftestingandtrials,wecameupwithaprocesswenowcall Solanum, theLatin wordforeggplant.Thecolorofeggplantisadeeppurplebrown,similartowhatisachievedwhen weatheringsteelreachesitspointofsurfaceequilibrium. Solanum soundedfittingforametal,in tunewiththegreatSirHumphreyDavy,whonamedsuchmetalsaspotassium,sodium,and,of course,aluminum.
Theideawithpreweatheringistocontroltheoxidedevelopmentinanenvironmentspecifically controlledforthisspecialsteeltocorrodeslowlyandformthreerichformsofoxideonthesurface, similarto,butmuchquickerthan,thecolorthatformedafteryearsofexposure.Thestainingwould becontainedforthemostpartandcollectedinourplant.
Theweatheringsteelshavearichcolortonethatcomesacrossasamaterialoftheearth.Like brick,wood,orpatinacopper,weatheringsteelhasaverynatural,pleasingappearanceoncethe oxidationtakesroot.Manyoftheprojectsshowninthisbookdemonstratethenaturalcharacterof thisamazingsteel.
Thesteelswesometimesrefertoasmildsteelorcarbonsteelareubiquitousinoureveryday environment.Unliketheweatheringsteels,wedonotnoticethemuntiltheydobegintocorrode. Otherwise,theygoabouttheirbusinessofprotectingusaswedrivedowntheroad,orholdour buildingsupagainsttheforcesofgravityandwind.Oncetheystarttocorrode,theygetnoticedlike moldonbread.Thecarbonsteelswiththeirbeautifullyrugged,darkgray-bluecolorrequiresome
formofprotectiontoholdbackrustfromdeveloping.Itisthematerialofbattleshipsandtanks, armortobeabusedandtowithstandabuse,butalittlemoistureandtroublesetsin.
Moreandmoredesignersareseeingtheintrinsicbeautyofthecarbonsteels.Conquering,orat leastforestalling,theonsetofthefeelingofneglecttheconditionofrustcanportrayisparamount. Iron,themainelementinsteel,wantstojoinupwithoxygen–andironhasmorewaystojoinwith oxygenthanwecancountonbothhands.Thereare16oxideformsofiron.Youwanttokeepthe steelsurfacedry;wateristhecatalystforthiscouplingwithoxygen.
Conversioncoatingsslowdownthemarriagewithoxygenbyintroducingotherelementssuch asphosphates,sulfates,andcopperselenidecoatingsthatclingtotheironsurfaceandformabarrier ofdarkenedcolor.Atthesametime,thesecoatingscanofferauniqueappearancewhilemaintaining theintrinsicbeautyofsteel.
OfallthemetalsIhavewrittenabout,steelhasbeenoneofthemorechallenging.Fromanart andarchitectureperspective,steelhasplayedavaluablerole,butasabitplayer,itisaninexpensive alternative.Withnewtechniquesofpreweatheringthehigh-strength,low-alloy(HSLA)steels,this surfaceisbeingrecognizedasabeautiful,naturalmaterialbydesignersandartistsaroundtheworld. Thedarkening,bluing,andvariegatefinishonecanobtainfromthemildcarbonsteelsaddsan entirenewarrayofpossibilitiestothedesigncommunity.Easytoworkwith,weldable,andnow withappealingsurfacefinishing,steelisgivingnewvaluetothedesignerandartist.
L.WilliamZahner
SteelSurfaces
CHAPTER 1 Introduction
Theonlywaytoknowhowstrongyouareistokeeptestingyourlimits.
Jor–LtoSuperman,themanofSteel.
IRONANDSTEEL
Ironandsteelhavealonghistorywithmankind.
Thehistoryofcontemporarycivilizationisintermingledwiththeprowessofironandsteel.Steel isanalloyofironwithasmallamountofcarbon,usuallylessthan2%.Ironhasbeenusedthroughout civilizationtomakeusefultoolsandarmaments.Implementsmadefromironwereharderandcould holdanedgebetterthananyothersubstanceknownatthattime.Eventoday,hardnessandstrength arecomparedtoiron.
TheatomicsymbolforironisFe,whichisshortenedfromtheLatinwordforthemetal, ferrum, whichmeans“firmness.”Ironiselement26ontheperiodicchart.SeeFigure1.1.
Ironsitsbetweenmanganeseandcobaltandinthesamelinewithrutheniumandosmium,two verydenseelements.
IronisthefourthmostabundantelementfoundontheEarth’soutercrustbehindoxygen,silicon,andaluminum,whilethecoreoftheEarthissaidtobecomposedmostlyofiron.
Ironisoneofthefewsubstancesthatdemonstratemagnetism. Ferromagnetism isatermgiven todescribeaphenomenonofafewmaterialstoshowmagneticattraction.Ironischiefamongthese; nickelandcobaltaretwootherelementsthatexhibitthistrait.Ferromagnetismoccursintherare earthelementgadoliniumandafewothercompounds.Neodymium,rareearthmagnets,arealloys ofneodymium,iron,andboron.Theseexhibitastrongmagneticfield.
FIGURE1.1 Periodictableoftheelements.
VIIIA
Oneofironschiefores,magnetite,sometimescalledthe lodestone, wasknowntoearlymanas aspecialmaterialthat,whenattachedtoathread,alwaysalignedinagivendirection.Thiswasthe firstcompass,andtheterm lodestone means“leadingstone,”foritwouldpointtheway.
Thereisamysterysurroundingtheabilityofmagnetitetobecomemagnetic.Notallmagnetiteis magnetic,andtomakeitintoalodestonesomestrongmagneticfieldhastobeapplied.Itissuggested thatlightningstrikesnearoredepositscausedsomeofthemagnetitetobecomestronglymagnetized becausetheelectricalcurrentassociatedwithlightningpossessesastrongmagneticfieldandthis magnetizedthemagnetitenearby.
Artisticadaptionstoironimplementsinvolvedetchingthesurfaceofforgedironusing organicacidstoselectivelyremoveareasofmetal.Inlaysofsoftermetalssuchasbronze,copper, andevensilvercouldfurtherenhancetheironsurface.Thesesoftermetalscouldbehammered intogroovesinthemuchharderiron,keyingthemintothesurfacetocreatecontrastingartistic effects.Earlymanufacturingtechniquesanduseofironallowedthedevelopmentofartisticsurface treatmentsthatexpandedtheintricatedetailingalreadyunderwayonthesoftermetalsofbronze andcopper.
Ironisenigmatic.Withalliron’sstrengthandhardness,itisquicktogiveitup.Airandmoistureareallthatareneededtostripthisstrengthfromiron.Thosetwoelectronsintheoutershell anxiouslycombinewithoxygen,sulfur,oranynumberofotherelements(Figure1.3).Ironisnever foundpureinnature.Ironfindsthermodynamicequilibriumwhenitcombineswithoxygenand othersubstances.Withiron,unlikeothermetalssuchasaluminumandtitanium,whenitcombineswithoxygenandwaterispresent,itexpandsasitformsoxyhydroxide.So,asthesurfaceof ironoxidizes,ittakesupmorevolume,creatingcracksandallowingmoreironunderthesurfaceto beexposed.
FIGURE1.2 Bodycenteredcubicstructureofironcrystal.
FIGURE1.3 Theironatom.
IronElement26
IronisthefourthmostabundantelementonEarth’ssurface;6.3%ofEarth’scrustiscomposed ofiron.
Steelisanalloyofiron.Carbonisthemainalloyingelementintroducedintoirontocreate steel.Otherelementsareaddedinsmallamountstocreatespecificproperties.
Excellentductility,deepformingability,superiorhardness,machinable.Canbebothcold andhotworked.
Highfracturetoughness
Highelasticity–resiliencyundershockloading.Highvibrationresistance.
Hardedge.Canbesharpenedandholdanedge.
Nontoxic.
Poorcorrosionresistanceunlessalloyedwithspecificelementsorcoatedwithsacrificial metals.
Finishes:
Millfinishinmostapplications. Rarelypolishedormechanicallyfinished. Usuallycoated.
Organiccoatingsintheformofpolymersandresinsarecommoncoatings. Inorganiccoatingsintheformofglass,likeporcelains,arecommoncoatings.
Metalcoatingsbyhotdippingorbyelectroplatingarecommoncoatings.
Metaloxidesaltsarecommonblackeningtechniquesthatprovidebothappearanceandcorrosionresistance.
Oxyhydroxidelayersthatdeveloponparticularsteelalloyscalled weatheringsteels are commonsurfacesusedinartandarchitecture.
Artificialpatina
Darkappearance
Blacksandmottledgrays.Darkgreensanddarkredscanbeproduced onsteels.
Ironabsorbsandreflectsevenlyacrossthespectrumwithslightly moreontheshorterwavelengthsportionofthespectrum.Alloysalter thisreflection.Weatheringsteelshavegreateremissionaroundthe yellowwavelengthsandtheredendofthevisiblespectrum.
(continued)
(continued)
Reflectance
ofUltraviolet Verygood ofInfrared Poor.Copperabsorbsinfraredwavelengths.
Relativecost Low
Strengthening Coldworking,alloying,andtemperingaremethodsusedtoadjustthe strengthofsteels.
Recyclability Easilyrecycled.Highermeltingpointandcoatingsonthesteelmake thescrapvalueverylow.
Weldingandjoining Canbewelded,brazed,andsoldered.
Casting Steelisfrequentlycastusingallcastmethodologies.
Plating Commonlyelectroplatedwithzinc,nickel,andchrome.
Etchingandmilling Canbeetchedandchemicallymilled.
HISTORY
Ironartifacts,asoldas3500 BCE,havesurvivedtothisday.Nickelwasfoundmixedwithmanyof theseartifacts,indicatingthesourceofthemetalwasmeteoritescollectedfromthegroundrather thanmined. 1
Theearliestusesofironoccurredinvariousregionsaroundtheworld.Anatonia,India,Egypt, Greece,Babylon,Japan,China,andmuchofnorthernAfrica,whererichironoreconcentrations arestillminedtoday,weresomeofthefirstregionstocreateironimplementsforuseineveryday life,warfare,andart.
Ironusagefollowedthatofbronze,thelatterbeingeasiertorefineandcast.Additionally, copper-bearingmineralsweremoreeasilyidentifiableduetothecolorfulmineralforms.
Itwasmostlikelymankind’saggressiveandassertivebehaviorthatdrovetheearlygrowthand discoveryofworkingwithiron.Oncemankindfiguredouthowtocastandshapethismetal,it soonsupplantedcopperandthecopperalloy,bronze,asthematerialofwar.Thealchemistusedthe symbolofadiagonalarroworthesymbolforman–whichisalsothesymbolforMars,thegodof war.SeeFigure1.4.
TheHittitesaresaidtohavebeenoneofthefirstcivilizationstomineandworkthemetalby smeltingore.TheHittitecivilization,alsoreferredtoasthe KingdomofHatti, controlledtheregion aroundAnatoliabackin1700 BCE.TheywererivalstotheEgyptians.Theiruseofironpredates othercivilizations,andbecausetheywereoftenatwar,onecanonlypresupposetheadvantageof
1 Giauque,G.,‘Thehistoryofcarbonsteels’, TheBookofSteel,LavoisierPublishing,1997,p.4.
FIGURE1.4 Symbolofironusedbytheearlyalchemists.
thisharderandstrongermaterialpresentedtotheHittites.TheChalybeswereatribesubjecttothe Hittites.TheylivedalongtheshoresoftheBlackSea.Thistribeiscreditedwithbeingsomeofthe firsttoworkwithiron.
TherearesitesinAfricathatcouldbeevenolder;however,controversysurroundstheirexact date.Thus,iron,enteringtherealmofman,ismostoftenattributedtothecentralAsianregion. InIndia,wherecastingandworkingwithironwasarefinedart,excavationsintheMiddleGanga Valleyshowironworkingbeganasearlyas2800 BCE.TheMughalEmpireofthiserawasprolific intheexploitationofironandtheearlyunderstandingofcastingthismetal.Themetalworkersof theMughalperiodwereexpertsandweresomeofthefirsttoworkwiththelostwaxtechniqueof casting.Theywereknownforcastingnear-perfectironsphereswithnoseams.
Ithasbeenwellestablishedthatpeopleofthisregionexhibitedsignificantprowessintheproductionofironandlatersteelasearlyas300 BCE.Forthenext500years,high-qualitysteelwasbeing producedbythepeopleofthisregion.Theyusedamethodreferredtodayasthe crucibletechnique toproducethishigh-qualitysteel.ThesteelproducedwasofsuchgreatqualitythatKingPorusof Indiaoffered15kgofirontoAlexandertheGreatasagift.
Thecrucibletechniqueinvolvedheatinghigh-puritywroughtironmixedwithcharcoaland glass.Thesiliconintheglasswouldattachtoimpuritiesinthewroughtironandfloattothetop, whilesomeofthecarbonwouldbeabsorbedintotheirontocreatesteel.Thissteelwasknownby theArabsas fülåd, andinEuropeitwascalled wootz.
ThepeopleofthisregiontradedwiththeGreeksandRomans,aswellastheeasterncultures. Theexchangeofthescienceofmetallurgyslowlypercolatedoutofthisregiontootherpartsofthe knownworld.
TheknowledgeandabilitytotempersteelwaswellknowntothemetalworkersofancientIndia. Theywereknownformakingincredibleswordsandbladessuperiortoanythingatthetime.Even today,someoftheartofcreatingthesespecialbladeshasyettobeuncovered.
Onespecializedprocesswastheproductionofthe Damascussword,alsocalleddamascene. Damascene standsforthedecorativeprocessofproducingwavylinesinmetalbyinlayingother metalsorbyetchingthesurfaceofmetals.Figure1.5showswhatdamascenesteellookedlike.The Damascusswordwasmadefromsteelproducedthisway.
ThedamascenesteeltechniqueswerebelievedtobefirstdevelopedinIndia.Decorativeetching andmetalinlaymethodswereperfectedinIndiainthefirstmillennia BCE.RomanstradedwithIndia toobtainswordsandcutlerymadefromtheirspecializedironworks.
FIGURE1.5 DamasceneSteelThedamasceneswordtechniqueswerebelievedtobefirstdevelopedinIndia. DecorativeetchingandmetalinlaymethodswereperfectedinIndiainthefirstmillenniaBC.
Source: L.WilliamZahner
Thisearlysteelwasknownaswootzsteelforthecarboncontent.DevelopedinsouthernIndia aroundthesixthcentury BCE,wootzisasteelcreatedusingthisearlycruciblemeltingprocess. UsedinIndia,thenDamascusandtheregionaroundToledo,Spain,thisearlyprocessusedsand, glass,andothersubstancesasafluxtoaidinmeltingiron.Theresultingsteelwasofveryhighquality.Wootzishighincarbonandcontainedbandsofpearlite,martensite,andferrite.Tomakewootz, orewouldbecookedinsideasealedclaycrucibleoveracharcoalfire.Earlycruciblesteelwoulduse thehighwindsfromstormstoforceairintothecharcoalinordertoachievethenecessaryheat.
Littleremainsofearlyironarticlesduetothepropensityofironarticlestocorrodewhenexposed tomoistureandoxygen.Oncecorrosionwouldstart,itwasdifficulttostop.Theresimplywereno goodmeansofinhibitingironfromwantingtocombinewithoxygenandformironoxideorrust.
Mostcertainly,muchoftheearlyironwascollectedfrommeteorites.Thisfactcanbededuced fromthelanguageoftheregions.TheGreekwordforironis sideros, translatedtomean,“fromthe stars.”TheEgyptianwordforironis baaenepe, or“giftfromheaven.”Tomeltiron,however,requires ablastfurnacetoachievethetemperaturesneeded.
Eventually,itwasdeterminedthatifironwereheatedforlongperiodsoftimeinacrudefurnace, afurnacesetsothatairwouldrushthroughtheburningmassofcharcoalandore,aspongylumpof metalwouldform.Thismalleableironcouldbehammeredandflattened.Reheatingwouldsoften itor,ifleftforlongperiodsoftimeinhotcharcoal,theoutersurfacewouldhardenascarbonwas absorbed–processestodaycalled annealing and casehardening.
Castirontechniquesdevelopedoutofthecastingofbronzeworkashighertemperatureswere achievedascastingprocessesimproved.Withtheinclusionofsmallquantitiesofcarbon,say2–4%, themeltingpointofironisreduced.Manydiverseancientculturespracticedandimprovedtheart ofcastingmetals.TheChinesemadevarioussmallfarmingutensilsasfarbackas500 BCE,whilein Indiaexceptionalcastingtechniqueshadbeenindevelopmentcenturiesearlier.Indiantechniques wereacceptedandadoptedbythePersiansandtheRomansassuperiorsourcesofironproducts; bothcastandwroughtcouldbeproduced.
AnexampleoftheprowessoftheIndianmetallurgyistheIronPillarofDelhi.SeeFigure1.6. Thisamazingstructureis8mtallandweighs7tons.ItwascastduringtheChandraguptaIIreign sometimearoundthefourthcentury CE.Tothisday,this1600-year-old,high-purityironformshows littlesignsofcorrosion.
