JournalofShanghaiUniversity(EnglishEdition),2005,9(5):455-457ArticleID:100726417(2005)0520455203AbstractofDoctoralDissertationComputerAidedAlloyDesignofHighPerformancePrehardenedMoldSteelforPlasticPh.D.Candidate:HEYan2lin(何燕霖)Advisor:Prof.LiLin(李麟)SchoolofMaterialsScienceandEngineering,ShanghaiUniversity,Shanghai200072,P.R.ChinaReceivedJun.15,2005ProjectsupportedbyKeyProjectofShanghaiMunicipalCommis2sionofScienceandTechnology(GrantNo.015211010)HEYan2lin,Ph.D.Candidate,E2mail:；LILin,Ph.D.,Prof.,E2mail:Keywordsprehardenedmoldsteelforplastic,Thermo2Calc&DICTRAsoftwarepackage,machinability,heattreatmenttechnology,freecuttingphase.Prehardenedmoldsteelforplasticistheprimaryformanufacturinghighqualityplasticmold.Withtherapiddevelopmentofmoldindustryinourcountry,thiskindofsteelexhibitsextensiveapplicationprospect.How2ever,becauseofpropertydeficienciesofdomesticpro2ducedsteel,importsteelsholdmajorpartofmarketshare1,2.Inordertochangethesituation,using“methodofacceleratedmaturationofmaterials”inthisarticle,thecompositionandtechnologyofprehard2enedmoldsteelforplasticareoptimizedanddesignedbyThermo2Calc&DICTRAthermodynamicsoftwarepackage3.Onthestrongbackgroundofindustrialap2plication,thepropertyofdomesticproducedsteeliseffectivelyimprovedatthepremiseofnoincrementalcost,whichreachestotheperformancelevelofthesamekindofhighqualitysteelintheworld,e.g.,ASSAB718steel.Inaddition,onthebasisofresearchresultsmentionedabove,thenewkindoffreemachin2abilitysteelwithhighperformanceandbetterapplica2tionisdeveloped.Withthecomparedandstudiedinthisarticle,itisshownthatthemechanicalpropertyatroomtempera2turebetweenimportprehardenedmoldsteelforplasticwithlargesectionanddomesticproducedsteelissimi2lar.CombinedwithmicroscopeandSEM&EDXanaly2ses,itisshownthatthecontentofoxideinclusionindomesticproducedsteelishigherandmainlycom2posedofaluminumoxide,butthenon2metallicinclu2sioninASSAB718steelismainlycomposedofsoftphasesulphideinclusionintheformofmanganesesul2phidewithaluminumoxideatthecore.Theflankwearamount,cuttingforceandthesurfaceroughnessofmachiningsamplesarecomprehensivelytestedbyturn2ingtestatlowcuttingspeedandpolishingtest,itisshownthatthemainperformancedifferencebetweendomesticproducedsteelandASSAB718steelisma2chinability.Becausethekeytoaffectmachinabilityofsteelisnon2metallicinclusion,machinabilityofsteelcanbeimprovedbythedeformationanddecreasingabrasioneffectofsulphideduringmachining4,5.Themachinabilityofdomesticproducedsteelismarkedlydecreasedbysevereabrasioneffectofaluminumoxidewithhighhardnessandhighmeltingpointonthecar2bidetool.Soitisthemainmeanstoimprovesteelsperformancethatremoveormodifytheoxideinclusioninsteel.SLAGdatabasebasedonGayemodelandthermody2namiccomputationsystembasedonCALPHADtech2niqueinThermo2Calc&DICTRAsoftwarepackagearepowerfultoolsforcomputationequilibriumrelationofmulticomponentandmultiphasesystemduringsteel2makingprocess6,7.Accordingtocomputationalre2sults,theprecipitationprocessanditsinfluencingfac2torsofnon2metallicinclusionarepredicted.Itisshownthattheirrationalcompositionratioisthemainfactortoresultinhighercontentofaluminumoxidein2clusionindomesticproducedsteelbytheestimationofinclusiontypeprecipitatedinsteel.Thenthecomposi2tionofthesteelisoptimized,itisshownthattheweightpercentofalloyelementscarbon,manganese,silicon,chromium,nickelandmolybdenumareattherangeof0.36-0.42wt%,1.35-1.45wt%,0.2-0.3wt%,1.8-2.0wt%,0.8-1.0wt%and0.2-0.4wt%respectively.Theexperimentalresultsshowthatthecontentofaluminumoxideinclusionismark2edlyreducedandmainlysubstitutedbyMnSwithmi2nusculealuminumoxideparticleatthecore,thema2chinabilityofdomesticproducedsteelaftercomposi2tionregulationismarkedlyimproved.Duetothecloserelationshipbetweenphasetrans2formationandheattreatmenttechnologyestablish2ment,themaintypeofcarbideinprehardenedmoldsteelforplasticisM7C3typebyTEManalysesandcomputedresults.ThentheeffectoftemperatureandalloycompositiononthedissolutionofM7C3typecar2bideinsteelissimulatedby“Cell”modelinDICTRAprogram8210.ItisshownthatgenerallythedissolutioncontentsofM7C3typecarbideareincreasedwithen2hancedheatingtemperatureandprolongedkeepingtemperaturetime,therelationshipbetweendissolutioncontentofM7C3typecarbideandtimeatthetempera2tureof1183K(910)isclosetothatatthetempera2tureof1203K(930),asshowninFig.1.Fig.1RelationshipbetweenM7C3carbidecontentandtimeunderdifferentKelvinstemperatureAlloyelementsCr、Mn、MoaffectthedissolutionofM7C3typecarbide,asshowninFig.2.Accordingtosimulatedresults,thesegregationofelementsinlargemoduleisbasicallyeliminatedbyhightemperatureho2mogenizingtreatmentbeforeforging,thatisdonebykeeping10hoursatthetemperatureof120010,thussurfaceroughnessofmachiningsteelsampleisimproved.Inaddition,thecrackingofmodulewithsmallthicknessresultingfromquenchingisavoidedby910normalizing,themicrostructureandpropertyofthesteelarenotbasicallyaffected.Fig.2RelationshipbetweenM7C3carbideamountandtimeinsteelswithdifferentcompositi2onsatthetemperatureof1183KTheperformanceofdomesticproducedsteelwithlargesectionaftercompositionregulationandhomoge2nizationtreatmentathightemperaturebeforeforging,includingmachinability,polishingpropertiesandanti2corrosionperformance,reachtothelevelofASSAB718steelanditcanbeproducedinmass.Itishelpfultoimprovethemachinabilityofsteelwithadditionoffreecuttingelementssuchassulphur,calcium,etc11,12.Butprecipitationofharmfulnon2metallicinclusion,suchascalciumaluminatesandcal2ciumsulphide,canbeavoidedonlybyregulationthecontent.TheeffectofelementsS,Cawithdifferentcontentsontheprecipitationofnon2metallicinclusioniscomputedbyThermo2Calcsoftwarepackage,itisshownthatperfectfreecuttingphasecanforminsteelatthepropercompositionrange,suchasglassyoxideinclusion2CaOAl2O3SiO2(thatisC2AS).Freema2chinabilityprehardenedmoldsteelforplasticwithmodifiedcompositionistentativelyproduced.Com2binedwithSEM&EDXanalyse,itisshownthatfreecuttingphaseC2AScanbeobtainedbyaddition20-40ppmcalciumand0.02wt%sulphur,butC2ASisnoteasytobeobtainedifthecontentofsulphurincreasedto0.04wt%,whichisagreewiththeprediction.Comparedwithcuttingatlowspeed,itisshownthatathighcuttingspeed,thedamageoftoolisheavyandtoollifeisshort,butthecuttingforcebecomessmallandthesurfaceroughnessofmachiningsurface654JournalofShanghaiUniversityisalsoimproved.Theexistenceofsoftphasesulphideresultsinbetterpropertiesofsteelatlowcuttingspeedcondition,butathighcuttingspeedcondition,onlytheglassyoxideC2ASistestifiedtoformprotectivelayeratthesurfaceoftool,thenthewearoftoolisef2fectivelyinhibitedandthemachinabilityofsteelisim2proved.Inaddition,thefreemachinabilityeffectofsulphidephasecanbeimprovedbyadditionofcalciumandbismuthbecauseofchangingsulphidesshapeandincreasingthestickstrength.Theductilityandisotro2pyofsteeldecreasedbecauseofthedeformationofsoftphasesulphide,butthemodifiedeffectofcalciumonMnScandecreasethedisadvantage.Withthecom2prehensiveassessmentofmechanicalpropertiesandmachinability,thecomplexadditionofS2Ca2Biwithsmallcontentisaaccessibleprojectformanufacturingfreemachiabilityprehardenedmoldsteelforplastic.References1GanYong,ChenZai2zhi,ZhaoXiao2cun.StatusofdiesteeldevelopmentinChinaandcountermeasureforthecomingnewcenturyA,ProceedingofanInternationalConferenceonToolsSteelforDiesandMoldsC.Shanghai,1998,42-49.2GehrickeB,SchruffI.Trendsinplasticmouldsteelap2plicationsA.Proceedingsofthe5thInternationalCon2ferenceonToolingC.Austria,1999,83-90.3AnderssonJ2O,HelanderT,HoglundL,etal.Thermo2Calc&DICTRA,computationaltoolsformaterialsscienceJ.CALPHAD,2002,26(2):273-312.4SubramanianSV,GekondeHO,ZhangX,etal.Inclu2sionengineeringofsteelsforhighspeedmachiningJ.CIMBulletin,1998,(4):107-114.5YaguchiH.EffectofMnSinclusionsizeonmachinabilityoflow2carbonleaded,resulfurizedfree2machiningsteelJ.J.AppliedMetalworking,1986,4(3):214-225.6SundmanB,JanssonB,AnderssonJ2O.TheThermo2CalcdatabasesystemJ.CALPHAD,1985,(9):153-190.7GayeH,GatellierC.Slagsandinclusions:controlinsec2ondarysteelmakingA,ProceedingsoftheThirdInter2nationalConferenceonCleanSteelOrganizedbytheIn2stituteofMetalsandtheHungarianMiningandMetal2lurgicalSociety,Hungary,1986,6:137-147.8BorgenstamA,En