285ChallengesinFormingAdvancedHighStrengthSteelsE.Billur,M.S.andProf.Dr-IngT.AltanEngineeringResearchCenterforNetShapeManufacturing(ERC/NSM)www.ercnsm.orgAbstractAdvancedHighStrengthSteels(AHSS)offeradvantagesforweightreductionandincreaseincrashworthinessandsafety.However,thereareseveralissuestobeaddressedinformingAHSS.ThispaperdiscussesthechallengesencounteredinformingAHSSandsummarizessomeoftheresultsoftheR&Dconductedtoimprovetheapplicationofthesematerials.1IntroductionAdvancedHighStrengthSteels(AHSS)aremulti-phasesteelswhichcontainmartensite,bainiteand/orretainedaustenite/1/.Thismicrostructureenableshighyield(min.300MPa)andtensile(min.500MPa)strength/2/.AlthoughtheformabilityofAHSSisimprovedcomparedtoconventionalHSS,theyarestillmuchlessformablethanmildsteels.Fig.1depictshowthetotalelongation(i.e.,formability)decreaseswithincreasingstrength.ThispapermainlydiscussesDP(DualPhase)andTRIP(Transformation-InducedPlasticity)materials.Fig.1.TotalElongation(%EL)vs.UltimateTensileStrength(UTS)“BananaCurve”ofautomotivesteels/3/.286ChallengesinFormingAHSSBillurandAltanThereareseveralchallengesinformingAHSS.Thesearemainly,Duetomulti-phasestructureandcomplexmanufacturingprocesses:(1)determiningthematerialpropertieswithaccuracyrequiresnewtestingmethods,(2)batch-to-batchinconsistencyiscommon.Duetotheirhighstrengthandlowformability:(3)earlyfracturesareobservedinseveralformingoperations,requiringinvestigationoffracture,(4)largerpresscapacitiesarerequiredforformingorblanking,(5)toolswearoutquickly.Lubricants,toolmaterialsandcoatingsrequirecarefulselection,(6)largerspringback(leadingtodimensionalinaccuracy)isanimportantissuerequiringadditionaldevelopment.2MaterialProperties2.1FlowStressFlowstresscurvesareoftenfittoHollomon’sequationkn.Inthisequation,thestrainhardeningexponent(n)isalsousedasanindicationforuniformelongation.However,inAHSS,thestrainhardeningcharacteristicisnotconstant.Thisismainlybecauseofthemulti-phasemicr