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Cost-savingsteelsandtheirmanufacturingprocessesWANGGuo-dong,LIUXiang-hua,WUDi(TheStateKeyLaboratoryofRolling&Automation(NortheasternUniversity),Shenyang,110004,China)Abstract:Resources-conservingmanufacturingisbecominganimportanttendencyinmaterialsproduction.Cost-savingsteelsandtheirmanufacturingprocesseswereexplored,duringwhichtheviewpointinenergysavingandsources-savingtorealizecost-savingproductionwasdiscussed.Therewereaboutfouraspectsindetail:designandproductiontechnologyforcost-savingsteels,cost-savingproductionprocesses,cost-savingproductionlifecycleandenvironment-friendlyproduction.Keywords:Cost-savingsteels,Manufacturingprocess,Environment-friendlyproductionChinahasissuedthemedium-termandlong-termdevelopmentplanningcompendium,whichisaguidingdocumentforthedevelopmentofscienceandtechnology.Ithasbeenpointedoutthatmanufacturingprocessfornewgenerationsteelsneedstobedeveloped,andthreemajorfunctionsneedtoberealizedduringtheproduction,includingrawironandsteelsupplying,energyanddisposingwastetransferring.Torealizecost-savingmanufacturingprocessesofnewgenerationsteelswillpromotecontinuoussocio-economicdevelopmentofourcountry.1.Designingandmanufacturingprocessforcost-savingsteelsIronandsteelmaterialsarewidelyusedfortworeasons.Ontheonehand,theyareinexpensiveandinlargescaleproduction,ontheotherhand,theymaypossessdifferentstrengthsinalargerangebyapplyingsuitablecontrolledrollingandcontrolledcooling,ortheso-calledTMCP.Thechiefgoalofcontrolledrollingistocontrolthestateoftheaustenite,whilecontrolledcoolingistocontrolthephasetransformationofdeformedausteniteandtorefineferritegrain,orimprovethesteelperformancebycontrollingthephaseproportiontoformcomplexphasestructure.Intensivelyutilizingthecharacteristicsofphasetransformationinironandsteelmaterialsplaysanimportantroleintappingthematerialspotentialandrealizingcost-savingmanufacturing[1].1.1Developmentof400-500MPagradestripsNewgenerationironandsteelmaterialsaredevelopedtosavemoreresources.Thatistoaddnoneorlessalloying/microalloyingelementstoproducethesteelswithhighperformance.Forexample,thestrengthandtoughnessof200MPagradecarbonsteelcanreachthesamelevelof400MPasteelsbyimprovingandoptimizingprocessingparameters.Accordingtotheresearchonstaticrecrystallizationoflowcarbonsteel,deformedaustenitedoesnotrecrystallizewhentheinter-passtimeislessthan5safterhotdeformationatthedeformationtemperaturebetween850℃and900℃.Consideringthetime,controlledcoolingcarriedoutinthenon-recrystallizationzoneinseveralminutesafterdeformationisthekeytorefinethegrainsofC-MnandlowC-Mnsteels.Therefore,thecoolingafterrolling(includinglaminarcurrentcoolingdeviceofhighdensityandlargeflux,curlingatlowtemperature)playsanimportantroleinthedevelopmentofcost-savingstrip.Accordingtothethoughtsabove,byoptimizingrollingschedules,checkingtherollingload,loweringfinishingrollingtemperatureto800℃,increasingcoolingratetobehigherthan30℃/s,lowcarbonsteelscanpossessthesameover-allpropertiesas400MPagradesteels.Itsstructureanalysesindicatethattheincreasingofstrengthisduetonotonlygrainrefinement,butalsotheformationofbainite.Owningtothecombinedeffectofrefinementandtransformation,itreachestheneedofcustomerwiththeyieldingstrengthexceeding400MPa,thetensilestrengthexceeding540MPa,elongationpercentageexceeding27%.Expensivealloyingelementshavebeensavedtosubstitutemicroalloysteels,andcost-savingsteelmanufacturingprocessisrealized.1.2Theexploitationofcost-saving400－500MPagradewireWirerollingbelongstohigh-speedrollingprocess,thedeformationheatleadstohighertemperatureforthework-piece,thefinishingtemperaturecanreachto1000℃,solowtemperaturefinishingrollingcannotbeexecutedasinplaterolling.Inwirerolling,thetotalreductionishigh,rollingspeedishigh,directionofdeformationvariescontinuouslyandinter-passtimeisshort.Suchacontinuouslargedeformationispronetorealizestrainaccumulationandleadstohardeningtheaustenite.Inallusiontothefeatureofwirerolling,inordertorealizedeformationhardening,alargestraincontinuousaccumulationdeformationisusedinwirerolling;cross-waterquickcoolingbeginsimmediatelyafterrolling,andwaterspraycoolingisusedinordertogethighcoolingrateandnecessaryfinalcoolingtemperaturetolimitrecrystallizationofausteniteandkeepthehardeningstateofaustenite.Byfinishingcoolingatapropertemperatureandcontrollingphasetransformationprocess,thequenchingorganizationispreventedtooccur.Accordingtosuchatechnicalroute,byusingC0.22-0.25%－Si0.33-0.42%－Mn0.7-0.8%(massfraction)asmaterial,HRB400MPafine-grainedbarwireisproduced,thestableandlarge-scaleindustrialproductionhasbeenrealized(Fig.1)[3].Fig.1Routeofreductionwireproductiontechnology1.3Theexploitationofcost-saving400－500MPagradebarsScrewthreadsteelisasteelproductwiththelargestproductioninChina,andhasadrasticcompetingmarket.400MPagradehotstripfine-grainedbarHRBisusuallyaddeddefiniteamountofmicroalloyelementssuchasNb,V,andTionthebaseof20MnSi,whichhasincreasedthecostofproductionandconsumeplentyofmicroalloyelements.InordertouseHRB335(viz.20MNSi,IIgradesteelbar)asthebasicmaterial,theoverallstandardquantityIIIgrades