34-paper-Laser-based diagnostics for the steel ind

SECRETARIATUSE;Headershouldbeblank.SECRETARIATUSE;FootershouldbeblankLaser-baseddiagnosticsforthesteelindustryMONCHALINJean-Pierre,SABSABIMohamad,KRUGERSilvio,MOREAUAndré(IndustrialMaterialsInstitute,NationalResearchCouncilofCanada,75deMortagneBlvd,Boucherville,Quebec,J4B6Y4,Canada)Abstract:Thepropertiesandperformanceofsteelproductsdependessentiallyontheirchemicalcompositionandtheirmicrostructure(phasefraction,grainsize,texture…).Twolaser-basedtechnologiesthatarebeingdevelopedbytheIndustrialMaterialInstituteoftheNationalResearchCouncilofCanadapermiton-lineandin-processmeasurementofthesekeyparameters.First,weoutlineLaser-InducedBreakdownSpectroscopy(LIBS),whichisbasedontheproductionofaplasmabyahigh-powerpulsedlaserandtheanalysisoftheemittedlightwithaspectrometertofindouttheelementspresentinthematerial.Thistechnologywhichwecouldforeseebeingusedinladlemetallurgyhasbeendemonstratedsofarforrealtimedeterminationofcompositioningalvanizationbathsandisbeingcommercialized.Theothertechnologyislaser-ultrasonics,whichconsistsinthegenerationofultrasoundwithalaserandthedetectionoftheultrasonicwaveswithasecondlasercoupledtoanopticalinterferometer.Thistechnologyisnowusedformeasuringthewallthickness,eccentricityandaustenitegrainsizeofseamlesstubes.Ithasbeenlicensedandisnowcommerciallyavailable.Also,laser-ultrasonicshasmeasuredon-linetextureandthicknessofsteelstrips.WhencombinedwithaGleeblethermo-mechanicalsimulator,manyotherapplicationstosteelprocessinghavebeendemonstratedsuchasthemonitoringofgraingrowth,phasetransformationsandrecrystallization.ExamplesofsuccessfulmonitoringofmetallurgicaltransformationsincludeaustenitedecompositioninTRIPsteelsandrecrystallizationofIFsteels.Theseapplicationscouldultimatelybeimplementedon-lineforprocesscontrol.Keywords:LaserInducedBreakdownSpectroscopy,LaserInducedPlasmaSpectroscopy,chemicalcomposition,galvanization,laser-ultrasonics,laser-ultrasound,microstructure,grainsize,retainedaustenite,texture,on-linesensing1IntroductionProductivityinthesteelindustry,likeinmanyotherindustries,canbeimprovedbysensorsthatcanbeusedon-lineorduringprocessing.Suchsensorscanprovidekeyinformationallowingtofinetunetheprocessortorejectout-of-specificationsorflawedproducts.Sinceinthesteelindustry,mostoftheprocessesareatelevatedtemperatureorinvolvefastmovingproductsoroccurinaharshenvironment,sensingatdistancewithlasersisadvantageousandinsomecasestheonlyfeasibletechnique.Inthispaper,wearepresentingtwolaser-basedtechnologiesthatarebeingdevelopedbytheIndustrialMaterialInstituteoftheNationalResearchCouncilofCanada.Theyaredesignedforon-lineandin-processmeasurementofchemicalcomposition(LaserinducedBreakdownSpectroscopy)andforthedeterminationofthicknessandmicrostructuralproperties(Laser-Ultrasonics).Thesetechniqueshavebeendemonstratedinlaboratory,inon-linetrialsandforsomeapplicationshavebeencommerciallyavailableandusedinindustryforafewyears.SECRETARIATUSE;Headershouldbeblank.SECRETARIATUSE;Footershouldbeblank2LaserInducedBreakdownSpectroscopyLaser-inducedbreakdownspectroscopy(LIBS)isanall-opticaltechniqueforthecontinuouselementalanalysisofliquids,solids,andgasses[1].LIBSanalysisiscarriedoutbyfocusingahigh-powerpulsedlaserbeamonthematerial,therebyvaporizingandionizingasmallvolumeofthetarget(typically108106cm3)toproduceaplasma.Opticalemissionfromthisplasma,whichisrepresentativeoftheablatedmaterial,isanalyzedwithaspectrographtoobtainqualitativeandquantitativeinformationaboutitsatomiccomposition.Thetechniqueoperatesatadistance(onemeterandmore)andisthereforeverysuitableforon-lineandin-situanalysisinhostileenvironments,inparticularfortheanalysisofthecompositionofmoltenmetals.TheapproachthatweuseforperformingameasurementtrulyrepresentativeofthebulkofthemoltenmetalbathandnotfromitssurfacewherecontaminationoccursisdepictedinFigure1.Atubeorlanceisimmersedinthemoltenmetal.Inertgas(argon)isflowndownthetubeandproducesbubbles.Thelaserisfiredinsidethebubble,thusinsuringasurfacewithcompositiontrulyrepresentativeofthemelt.Thetechniquehasmanyindustrialapplicationstohydroandpyrometallurgyandhasbeenappliedinparticulartothemonitoringofthecompositionofthezincbathforhotdipgalvanizationofsteel[2].Forthispurpose,aspectralwindowcenteredon305nmthatincludesspectralemissionlinesfromzinc,aluminumandironischosen.ZincbathLaserhead+lightcollectionopticsGasinletLaserbeamPlasmaProbetubeBubblesZincbathLaserhead+lightcollectionopticsGasinletLaserbeamPlasmaProbetubeBubblesFigure1SchematicsoftheapproachusedforcompositionmeasurementbyLIBSinmoltenmetalsThetechniquewastestedon-siteduringthetransitionfromgalvannealingtogalvanizingbathcompositions.AsseeninFigure2,thecompositioninformationprovidedinrealtimebyLIBSagreesverywellwithlaboratorymeasurementsmadefromtimetotimefollowingbathsampling.LIBShasthedistinctadvantageofrespondingmorerapidlytoanychangeofcomposition,asshowninthefigurebythespikesinAlorFecompositionthatfollowtheintroductioninthebathofaningotwith4.5%Al.Theapplicationtogalvanizationhavingbeenverysuccessful,acommercialprototypeisbeingdevelopednowspecifi