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Æ 475Vol.47No.5 20115513—519ACTAMETALLURGICASINICAMay.2011pp.513–519 ∗ Mn (,100084) Mn(LCMB).,LCMB ,4602h,,6002h,, .,LCMB4602h, 725MPa,−40CharpyA146J,,−18 KV −48.EBSDTEM, . ,,,, TG146.2A0412−1961(2011)05−0513−07 EFFECTOFTEMPERINGTEMPERATUREONLOW TEMPERATUREIMPACTTOUGHNESSOFALOW CARBONMn–SERIESBAINITICSTEEL GAOGuhui,ZHANGHan,BAIBingzhe KeyLaboratoryofAdvancedMaterialsofMinistryofEducation,DepartmentofMaterialScienceandEngineering, TsinghuaUniversity,Beijing100084 Correspondent:BAIBingzhe,professor,Tel:(010)62772976,E-mail:bzbai@mail.tsinghua.edu.cn SupportedbyScienceandTechnologyProjectofBejing(No.D08050303450804) Manuscriptreceived2010–10–15,inrevisedform2010–12–21 ABSTRACTInordertoreducethecostofalloyingelements,lowcarbonMnseriesbainiticsteels havebeendeveloped.Theeffectoftemperingtemperatureonthemicrostructureandlowtemperature impacttoughnessofalowcarbonMn–seriessteelhasbeeninvestigatedinthepresentstudy.The asrolledsteelplatesampleswith30mmthicknessweretemperedfrom280to600for2h. Metallographicmicrostructureshowthatthemicrostructureoftheas–rolledsteelismostlybainite laths.Bainitelathsstarttomergeandbroadenaftertemperingat460,andquasi–polygonalferrite structurescouldberevealedaftertemperingat600.Comparedwiththeas–rolledsteel,after temperingat460,theyieldstrengthofthesteelchangesslightly,remaining725MPa,whilethe − Charpyabsorbedenergyat40increasesfrom38Jto146J,andtheductile–brittletransition − temperature(DBTT)decreasesfrom−18to48.TheEBSDandTEMresultsindicatethatthe improvementoflowtemperatureimpacttoughnessaftertemperingat460iscausedbytheincrease offractionofhighangleboundariesand