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Metals 2016,6, 218 X-raydiffraction andmicrostructural observation showed that aging alsopromotes a partial reversionofmartensite intoaustenite.Ashift tohigheragingtemperaturesandover-agingfurther increasedtheamountofγ-Fephase. Different aging temperatureswere selected to evaluate tensile performanceof thepeak-aged andover-agedsamplesasa functionof theamountof reversedaustenite. The results showedthat agingpromotesadramatic increase instrengthover theasbuilt condition,butalsoadropintensile ductility.Amongagedandover-agedsamples,nosystematic changeswere foundin tensileproperties asa functionofmeasuredaustenite. It is suggestedthat, asopposedto the trendexpected incorrespondingwroughtmaragingalloys, thesubmicrometric structure inheritedbytherapidsolidificationconditionbroughtbyselective laser meltingaresuchthatchanges in tensilestrengthandductilityaremainlygovernedbytheeffectsgiven bythestrengtheningprecipitates,whereas theconcurrentreversionof theγ-Fephaseseemstoplay aminorrole. Acknowledgments:Thefinancial supportofRegioneLombardia (BandoCreativitàLinea2,AddMe.Labproject) isacknowledged. Author Contributions: R.C. and J.N.L. performed the experiments. A.T. contributed to XRD analysis and discussionof results. R.C.andM.V.wrote thepaper.M.V.supervisedtheproject. Conflictsof Interest:Theauthorsdeclarenoconflictsof interest. References 1. Pardal, J.M.;Tavares,S.S.M.;Terra,V.F.;daSilva,M.R.;dosSantos,D.R.Modelingofprecipitationhardening duringtheagingandoveragingof18Ni-Co-Mo-Timaraging300steel. J.Alloy. Compd. 2015,393, 109–113. [CrossRef] 2. Sha,W.;Cerezo,A.;Smith,G.D.W.PhaseChemistryandPrecipitationReactions inMaragingSteels: Part I. IntroductionandStudyofCo-ContainingC-300Steel.Metall. Trans.A1993,24A, 1221–1232. [CrossRef] 3. Pardal, J.M.;Tavares,S.S.M.;Fonseca,M.P.C.;Abreu,H.F.G.;Silva, J.J.M.Studyof theaustenitequantification byX-raydiffraction in the18Ni-Co-Mo-Timaraging300steel. J.Mater. Sci. 2006,41, 2301–2307. [CrossRef] 4. Guo,Z.;Sha,W.;Li,D.Quantificationofphase transformationkineticsof18wt.%NiC250maragingsteel. Mater. Sci. Eng.A2004,373, 10–20. [CrossRef] 5. Tewari,R.;Mazumder,S.;Batra, I.S.;Dey,G.K.;Banerjee,S.Precipitation in18wt.%maragingsteelofgrade 350.ActaMater. 2000,48, 1187–1200. [CrossRef] 6. Jägle, E.A.; Choi, P.P.; van Humbeeck, J.; Raabe, D. Precipitation and austenite reversion behavior of amaragingsteelproducedbyselective lasermelting. J.Mater. Res. 2014,29, 2072–2079. [CrossRef] 7. Li,X.;Yin,Z.Revertedausteniteduringagingin18Ni (350)maragingsteel.Mater. Lett. 1995,24, 239–242. [CrossRef] 8. Viswanathan,U.K.;Dey,G.K.;Sethumadhavan,V.Effectsofaustenite reversionduringoverageingonthe mechanicalpropertiesof18Ni (350)maragingsteel.Mater. Sci. Eng.A2005,398, 367–372. [CrossRef] 9. Tavares, S.S.M.; Abreu, H.F.G.; Neto, J.M.; da Silva, M.R.; Popa, I. A thermomagnetic study of the martensite-austenite phase transition in the maraging 350 steel. J. Alloy. Compd. 2003, 358, 152–156. [CrossRef] 10. Kempen,K.;Yasa,E.;Thijs,L.;Kruth, J.-P.;vanHumbeeck, J.Microstructureandmechanicalpropertiesof SelectiveLaserMelted18Ni-300steel.Phys. Proc. 2011,12, 255–263. [CrossRef] 11. Casalino,G.; Campanelli, S.L.; Contuzzi,N.; Ludovico,A.D. Experimental investigation and statistical optimizationof theselective lasermeltingprocessofamaragingsteel.Opt. LaserTechnol. 2015,65, 151–158. [CrossRef] 12. Croccolo,D.;deAgostinis,M.;Fini, S.;Olmi,G.;Vranic,A.;Ciric-Kostic, S. Influenceof thebuildorientation on the fatigue strength of EOSmaraging steel produced by additivemetalmachine. Fat. Fract. Eng. Mater.Struct. 2016. [CrossRef] 13. Murr,L.E.;Martinez,E.;Amato,K.N.;Gaytan,S.M.;Hernandez, J.;Ramirez,D.A.;Shindo,P.W.;Medina,F.; Wicker,R.B.Fabricationofmetalandalloycomponentsbyadditivemanufacturing:Examplesof3Dmaterials science. J.Mater. Res. Technol. 2012,1, 42–54. [CrossRef] 85