65Mn弹簧钢在弯曲应力下的松弛行为

65Mn,,,,,(天津大学材料科学与工程学院,天津　300072):65Mn。,。TEM,,,。,,0.24eV0.64eV,,,,。:;;;:TG142.41;O377　　:A　　:0254-6051(2007)05-0090-05BendingStressRelaxationBehaviorof65MnSpringSteelLIJian-ming,ZHAONai-qin,LIQun-ying,DUXi-wen,SHIChun-sheng,WEIFang-rong(DepartmentofMaterialsScienceandEngineering,TianjinUniversity,Tianjin300072,China)Abstract:Thebendingstressrelaxationbehaviorofthequenched-tempered65Mnspringsteelwasinvestigatedbyaspe-ciallydesignedspringstressrelaxationmeasurementsystem.Thestressrelaxationcurveswerefittedusingthesecondor-derexponentialdecayfunctionanditshowedthatthecoefficientofdeterminationwaslarge.ThemicrostructuresofthespecimenswereexaminedusingTEM.Itcouldbeobservedthatthemicrostructureofthespecimenbeforestressrelaxa-tionwascomposedmainlyoftemperedmartensite.Akindofmicrobandstructurewasformedduringstressrelaxationandtangledandpiledupdislocationswerealsoobservedintherelaxedspecimen.Thestressrelaxationmechanismwasana-lyzedusingthermalactivationtheoryanditwasrevealedthattheapparentactivationenergyofthestressrelaxationprocessincreaseswithtimefrom0.24eVatthetransientrelaxationstagetoabout0.63eVatthesaturatedrelaxationstage.Thus,itcouldbeconcludedthatdislocationsslipduringthetransientstageandovercomecarbidebarriersincross-slippinginthesaturatedstage,thisresultsinfurtherincreaseofplasticstrain.Keywords:springsteel;stressrelaxation;microstructureevolution;dislocationmechanism:(1980—),,,,。:13920950152E-mail:[e-mail]:2007-01-19　　,,,。,,,[1]。,[2]。,。,,。Furr,,[3]。,,[1,4],,。,,。,。TEM(),[5],。,,90《》2007325,,。[5],,,。,,,,。,65Mn,,TEM,。1　试验材料及方法65Mn,0.5mm,1,L,b,h。L、b、h8mm、20mm、0.5mm。[6],(1),([6])。[7],P(:N)σ(:MPa)σ=6Lbh2P(1):850℃,9min,;400℃,30min,;。130℃、150℃、170℃、200℃。,0.6(835MPa),(1)87N。,。2,,,±0.5℃。,AIRS232/485,。0.1N,1/6s。TEM/,80μm,10μm。TEMPHILPSTECNAIG2F20,200kV。1　Fig.1　Designofthestressrelaxationspecimenandaschematicillustrationoftheloadingmode2　Fig.2　Schematicillustrationofthestressrelaxationmeasurementsystem2　试验结果与讨论2.1　3130℃、150℃、170℃、200℃。,[5],,,y=y0+A1exp(-t/t1)+A2exp(-t/t2),y,t,y0、A1、A2、t1、t2。Origin,1。1　Table1　Fittedcurvesofstressrelaxationdata/℃R2200809.54954+7.98441exp(-t/10.80604)+16.9602exp(-t/0.57597)0.97884170813.52584+13.04782exp(-t/0.46466)+9.3976exp(-t/5.89204)0.98524150810.4683+9.32301exp(-t/22.60307)+13.19205exp(-t/0.95668)0.97597130815.04961+7.24366exp(-t/17.00036)+10.77541exp(-t/1.0518)0.96981　　1,,91《》20073253　(a)(b)Fig.3　Stressrelaxationcurves(a)andthefittedcurves(b)。4,,,。,Ⅰ:;Ⅱ:(3)。,,,。。2.2　4a、b65MnTEM。4a,,,(4b)。4c150℃40h,,,,4c;4d,;,。4　TEM(a,b)　(c,d)150℃40hFig.4　TEMphotograghsoftherelaxationspecimensbeforeandafterthestressrelaxationtest(a,b)beforestressrelaxation　(c,d)relaxedat150℃for40h　　4a,,,,。[8],,、“”“”。,,,、92《》2007325,“”“”。“”“”,“”“”,“”“”,,[8],。,,,,。,,,4d。,,,4d,,。,,(4d),(4d),;,。4c,6550CrVA[5],。,,,。,,,,,,。,,4c。,。2.3　,Arrhenius[9-10],σ·=σ·0exp(-Qapp/kT)(2)σ0,,[10],Qapp,k(8.6×10-5eV/K),T,Qappσeff,Qapp=Q0-Vσeff(3)V,Q0σeff=0,σeffσσi,σeff=σ-σi(4)σi。(2)(σ·),ln(-σ·)=ln(-σ·0)-Qapp/kT(5),(1),(3b),,σ,5。,,Qappσ,5Qapp。5　Fig.5　Relaxationratewhenthestressisrelaxedtoacertainlevelatdifferenttemperatures5m,(5),Qapp=-km(6)k。(6),5。6σ,。6,,,,。,,Qapp,,;,;,93《》2007325Q0,,,(3),Qapp,,。,,,,[11]。,,,,[12],。6　Fig.6　Variationoftheapparentactivationenergywiththerelaxationoftheappliedstress3　结论(1)65Mn;;,。(2)TEM,,。。(3),(0.24～0.63eV),,。;,,,,。:[1]　YangZA,WangZ.Cycliccreepandcyclicdeformationofhigh-strengthspringsteelandtheevaluationofthesagEffect:PartIcyclicplasticdeformationbehavior[J].Metal.lTrans.A,2001,32A:1687-1698.[2]　Assefpour-DezfulyMandBrownriggA.Parametersaffectingsagresistanceinspringsteels[J].Metal.lTrans.A,1989,20A:1951-1959.[3]　WonJongNam,ChongSooLee,DeokYoungBan.Effectsofalloyadditionsandtemperingtemperatureonthesagresist-anceofSi-Crspringsteels[J].Mater.Sc.iEng.A,2000,289:8-17.[4]　,,[].[M].:,1994:234-239.[5]　.()[M].:,2002:33-170.[6]　,,,.[J].-,1999,35(1):15-17.[7]　,,.[M].:,1997:147-208.[8]　MughrabiH.Dislocationwallandcellstructuresandlong-rangeinternalstressesindeformedmetalcrystals[J].ActaMetal.l,1983,31(9):1367-1379.[9]　ChangYeolJeong,SooWooNam,JánosGinsztler.Activationprocessesofstressrelaxationduringholdtimein1Cr-Mo-Vsteel[J].Ma.tSc.iEng.A,1999,264:188-193.[10]　MauroJKobrinsky,CarlVThompson.ActivationvolumeforinelasticdeformationinpolycrystallineAgthinfilms[J].ActaMater.,2000,48:625-633.[11]　.[M].:,1988:40-42.[12]　WangYM,HamzaAV,MaE.Temperature-dependentstrainratesensitivityandactivationvolumeofnanocrystal-lineNi[J].ActaMater.,2006,54:2715-2726.:《(、)》《》、(12),200671。:、、、、;:、、、、、、(、、、、)。、、,,、、、。、、,4634。、、、,。:345。:010-82755375。94《》2007325