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MicrostructureofStainlessSteelSingle-CrystalElectronBeamWeldsS.A.DAVID,J.M.VITEK,M.RAPPAZ,andL.A.BOATNERPreviouslydevelopedtechniquesbytheauthorsforthemicrostructuralanalysisofwelds,thatincludedtheeffectsofboththegrowthcrystallographyandtheweldpoolshape,areappliedtoseveralcasesinvolvingthesingle-crystalelectronbeamweldingofanFe-15Ni-15Cralloy.Thisevaluationofweldmicrostructuresandassociateddendriticgrowthpatternsisbasedonathree-dimensional(3-D)geometricalanalysis.Thepresentstudyincludesexaminationoftheeffectsobservedinoverlapping,multipassautogenousweldsandbuttweldsoftwosinglecrystalswithdifferentorientations,aswellaseffectsduetovariationsintheweldingspeed.Weldpoolshapeswerefoundtochangesignificantlywithincreasingweldingspeed--becomingnarrowerincrosssectionbutmoreelongatedintheweldingdirection.Additionally,allelectronbeamweldsshowedevidenceofaplateauregioninthecenteroftheweldpool.Thepoolshapes,however,werefoundtobeindependentofthecrystallographicorientation.Therefore,itispossibletoextendthepoolshaperesultstocrystalsweldedinanyorientationandeventopolycrystals.Theover-lappingmultipassweldsshowedremarkablereproducibilityfrompasstopassandduplicatedthestructuralpatternsfoundinsingle-passwelds.Thesimilarityindendriticpatternswithineachpassindicatedthattheweldpoolshapeswereidenticalinallofthepasses.Themicro-structureofbuttweldsoftwosinglecrystalswithdifferentrelativeorientationsshowedare-markablerelationshiptothatassociatedwitheachindividualcrystallographicorientation,andthemicrostructurewas,ineffect,simplyacompositeoftwosingle-passmicrostructures.Ad-ditionalmicrostructuraldetailswerealsoexamined.Thetendencytowardbranchingofdendriteswasassociatedwiththetransitionfromonedendritegrowthorientationtoanother.Itwasalsofoundthatthenonpenetratingweldsexhibitedasmallprotrusionatthebottomoftheweld.Itissuggestedthatthemodelingofweldpoolshapescanbedirectlyevaluatedbycomparingthepredicteddendriticgrowthpatternsbasedonthemodeledshapeswiththeactualexperimentall
